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Adsorption: Journal of the International Adsorption Society (v.11, #1)

Molecular Modeling of Adsorption in Activated Carbon: Comparison of Monte Carlo Simulations with Experiment by Jin-Chen Liu; P. A. Monson (pp. 5-13).

We present Mont Carlo computer simulation results for a molecular model of fluids adsorbed in porous carbon materials. The model carbon used is based on the platelet model for carbon of Segarra and Glandt (1994). The model we use has a single basal plane per platelet and the structure is isotropic, disordered, with weak short-range correlations between the platelets. We have performed grand canonical Monte Carlo simulations of the adsorption isotherms for methane, ethane, and their mixtures in this model carbon. We find generally good agreement with experimental and the mixture results are quite accurately described by the ideal adsorbed solution theory. An exception to this is the behavior for the mixture at the highest pressures. In this case the experimental data show significant deviations from ideal adsorbed solution theory and the simulation results.

Keywords: activated carbon; platelet model; Monte Carlo simulation; methane; ethane

Preface by Orhan Talu; Sasidhar Gumma (pp. 15-15).

Empirical Multicomponent Equilibrium and Film-Pore Model for the Sorption of Copper, Cadmium and Zinc onto Bone Char by Chun-wai Cheung; Keith K. H. Choy; John F. Porter; Gordon Mckay (pp. 15-29).

The adsorption of three metal ions onto bone char has been studied in both equilibrium and kinetic systems. An empirical Langmuir-type equation has been proposed to correlate the experimental equilibrium data for multicomponent systems. The sorption equilibrium of three metal ions, namely, cadmium (II) ion, zinc (II) ion and copper (II) ion in the three binary and one ternary systems is well correlated by the Langmuir-type equation. For the batch kinetic studies, a multicomponent film-pore diffusion model was developed by incorporating this empirical Langmuir-type equation into a single component film-pore diffusion model and was used to correlate the multicomponent batch kinetic data. The multicomponent film-pore diffusion model shows some deviation from the experimental data for the sorption of cadmium ions in Cd-Cu, Cd-Zn and Cd-Cu-Zn systems. However, overall this model gives a good correlation of the experimental data for three binary and one ternary systems.

Keywords: film-pore diffusion; batch sorption; metal ions; bone char; multicomponent

Nanospace Molecular Science and Adsorption by Katsumi Kaneko; Tomonori Ohba; Takahiro Ohkubo; Shigenori Utsumi; Hironobu Kanoh; Masako Yudasaka; Sumio Iijima (pp. 21-28).

The relationships between the enhanced interaction potential and intensive confinement effect of slit-shaped and cylindrical nanospaces are shown. The structures of water molecules and aqueous ions confined in nanospaces of activated carbon fiber (ACF) and single wall carbon nanohorn (SWNH)s were studied by adsorption, in situ small angle X-ray scattering(SAXS), GCMC simulation, and EXAFS spectroscopy. Water molecules are associated with each other to form the clusters, being stabilized in the carbon nanospaces. This stabilization mechanism of water in carbon nanospaces were evidenced by the interaction potential calculation, GCMC simulation, and the density fluctuation analysis of in situ SAXS. The Ornstein-Zernike analysis of in situ SAXS profiles lead to the conclusion that the critical size of water clusters for predominant water adsorption in hydrophobic carbon nanospaces is about 0.5 nm corresponding to the octomer to decamer. The adsorption hysteresis of water adsorption isotherm of nanoporous carbon was interpreted by the cluster growth, which is confirmed by the density fluctuation analysis. The Rb and Br ions confined in the carbon nanospaces were examined by EXAFS spectroscopy. The remarkable decreases in the hydration number and the water-Rb ion distance of the solution confined in the nanospaces were observed. In particular, the hydration number of the Rb ion in the nanospaces of SWNH is less than 3, being much smaller than the hydration number (6) of the bulk solution. The electrical double layer structure in the nanospaces should be quite different from that in the bulk solution.

Keywords: adsorption; activated carbon fiber; single wall carbon nanohorn; nanoconfinement; water; nanosolution

Recent Progress in Molecular Modeling of Adsorption and Hysteresis in Mesoporous Materials by Peter A. Monson (pp. 29-35).

We review some recent progress in molecular modeling of the behavior of fluids confined in mesoporous materials. We address three issues. The first is the applicability of the grand canonical ensemble for studying adsorption and hysteresis in porous materials. Next we discuss models of complex pore structure and how these can be coarse grained using a lattice model. Then we consider the question of how hysteresis is related to a vapor-liquid phase transition for disordered mesoporous materials. In concluding we assess the prospects of developing a unified description of adsorption and hysteresis valid over the range of mesoporous materials.

Keywords: adsorption; hysteresis; mesoporous materials; molecular modeling; phase transitions

ZLC Response for Systems with Surface Resistance Control by Douglas Ruthven; Federico Brandani (pp. 31-34).

The forms of the ZLC response for surface resistance and internal diffusion control are compared and it is suggested that for linear or nearly linear systems, these two patterns of behavior can be distinguished experimentally by examining the ratio of slope to intercept of the ZLC response plotted in log-linear coordinates.

Keywords: ZLC; diffusion; surface resistance

Cooperative and Competitive Adsorption of Ethylene, Ethane, Nitrogen and Argon on Graphitized Carbon Black and in Slit Pores by D. D. Do; H. D. Do (pp. 35-50).

In this paper we investigate the mixture adsorption of ethylene, ethane, nitrogen and argon on graphitized thermal carbon black and in slit pores by means of the Grand Canonical Monte Carlo simulations. Pure component adsorption isotherms on graphitized thermal carbon black are first characterized with the GCMC method, and then mixture simulations are carried out over a wide range of pore width, temperature, pressure and composition to investigate the cooperative and competitive adsorption of all species in the mixture. Results of mixture simulations are compared with the experimental data of ethylene and ethane (Friederich and Mullins, 1972) on Sterling FTG-D5 (homogeneous carbon black having a BET surface area of 13 m²/g) at 298 K and a pressure range of 1.3–93 kPa. Because of the co-operative effect, the Henry constant determined by the traditional chromatography method is always greater than that obtained from the volumetric method.

Prediction of Adsorption of Nonideal Mixtures in Nanoporous Materials by Alan L. Myers (pp. 37-42).

The prediction of multicomponent adsorption equilibria from single-component adsorption experiments is a challenging and important problem. Predictions based upon the assumption of an ideal adsorbed solution (IAS) may give unacceptable errors, especially in the case of large differences in the size or the polarity of the adsorbate molecules. These differences in molecular properties generate differences in the chemical potential of the solid (ψ) that may be used to predict activity coefficients for nonideal adsorbed solutions (NIAS). The ψ plots for pure-gas isotherms identify ideal solutions and provide reliable predictions of mixture equilibria for nonideal adsorbed solutions.

Keywords: adsorption; nanopores; ideal; nonideal; mixtures

Prediction of Adsorption Equilibria from Physical Properties of the Pure Components by Gudrun Schürer; Wolfgang Peukert (pp. 43-47).

The prediction of adsorption energies equilibria is often based on mixed terms influenced by both the adsorptive and the adsorbent. Our aim is to predict adsorption equilibria by using physical properties of the pure components. Based on the concept of equivalent surface properties we introduce models using one or two mean parameters (Hamaker constant, mean partial charge) as well as a model which takes partial charge distributions into account. Density functional theory (DFT) calculations can be used to describe well defined and regular surfaces. However, the structure and topology of heterogeneous surfaces are generally unknown. Thus the combination of DFT-calculations with a continuum solvation model and experimental data allows the prediction of the adsorption equilibrium at infinite dilution. For activated carbon in the gas phase and in water the Henry’s law coefficients obtained by this method cover a range of 7 orders of magnitude. In order to gain a better understanding of the role of heterogeneities, DFT-calculations of model surfaces like functionalized coronenes or fullerenes were performed. A good qualitative agreement with the experimentally determined results was observed.

Keywords: adsorption equilibria prediction; activated carbon; Henry’s law coefficient; COSMO-RS

Exploiting Pore or Cavity Size and Shape in Separating Linear and Branched Hydrocarbons by Inverse Selectivity: Enthalpy, Entropy and Packing Effects by Joeri F. M. Denayer; Refik A. Ocakoglu; Kurt De Meyer; Gino V. Baron (pp. 49-53).

Different enthalpic, entropic and packing effects occurring in zeolites are reviewed which can be used to control elution order in the gas and liquid phase separation of linear and branched alkanes. Ordering effects in ZSM-5 can be used to separate long linear alkanes, even when only different by one carbon. Inverse selectivity occurs with stronger adsorption of the shorter chain, and azeotropes can be formed. Preferential adsorption of branched over linear alkanes (inverse selectivity) was for the first time experimentally determined for some mono- and multi-branched isomers in MCM-22 (rotational entropy effect) and at low coverage in SAPO-5 (enthalpy effect). These selectivity reversals identified both in gas and liquid phase can potentially be useful in more efficient hydrocarbon processes such as the production of clean gasoline with high octane number.

Keywords: hydrocarbon; inverse shape selectivity; energy; entropy; molecular packing

Kinetic Study of Erbium Ion Adsorption on Activated Charcoal from Aqueous Solutions by Riaz Qadeer (pp. 51-55).

The kinetics of the adsorption of erbium ions on activated charcoal from aqueous solutions has been studied in the temperature range of 10 to 40∘C. It was observed that the diffusion of erbium ions in to the pores of activated charcoal controls the kinetics of the adsorption process, and the values of intra-particle diffusion rate constant, k_d (g/g ⋅ min^1/2) were evaluated as 0.7 × 10⁻³ to 1.6 × 10⁻³ in the temperature range studied. Various thermodynamic parameters Δ H, Δ G and Δ S were also computed from values of the equilibrium constant K_C. The results showed that the adsorption of erbium ions on activated charcoal is an endothermic process.

Keywords: activated charcoal; erbium ions; adsorption; kinetics; aqueous solutions

Determination of Azeotropic Behavior in Adsorbed Mixtures by Flor R. Siperstein (pp. 55-59).

An analogy between vapor adsorbed equilibrium and vapor liquid equilibrium is made to determine the condition where azeotropes are observed, using a relationship between infinite dilution activity coefficients and pure component pressures in the reference state. The range of conditions where azeotropic behavior is expected in vapor-adsorbed equilibrium (VAE) was determined for the multisite Langmuir model for a mixture of two components with molecules of different size, and for CO₂-C₃H₈ on NaX using an empirical model (Siperstein and Myers, 2001), which has been shown to correlate accurately experimental data.

Keywords: azeotrope; mixture; thermodynamics

The Influence of Heat Pre-Treatment on the Sorption of Water Vapour on Bentonite by Pavel MokrejŠ; Arlette ZikÁnovÁ; David Hradil; Karel ŠTulÍk; VĚra PacÁkovÁ; Milan KoČiŘÍk; Mladen EiĆ (pp. 57-63).

Sorption isotherms of water vapour on bentonite from the Rokle locality of northwest Bohemia in the Czech Republic were measured and analysed after being treated with heat. Protracted sorption measurements were performed at 30∘C in the range of water vapour relative pressures between 0.12 and 0.94. Prior to sorption measurements, the bentonite samples were exposed to flowing dry nitrogen for 18 hours at 115, 220 and 300∘C. Compared to the sample heated at 115∘C, the bentonite samples that were treated at 220 and 300∘C exhibited a decrease in water vapour sorption capacity. This decrease in sorption capacity was accompanied by structural changes that were confirmed by X-ray diffraction analysis.

Keywords: adsorption; bentonite; montmorillonite; water vapour

Gas Adsorption Data Uncertainty and Propagation Analyses by Phillip Pendleton; Alexander Badalyan (pp. 61-66).

Experimental uncertainties inherent to manometric gas adsorption techniques are identified, analysed, calculated and discussed. Contributions of these uncertainties to the amount of nitrogen adsorbed and to the BET specific surface area of a carbon black standard were evaluated. Inaccurate liquid nitrogen level control affects the equilibrium pressure and hence the amount of gas adsorbed. The sources of greatest (controllable) uncertainty are liquid nitrogen level control, sample preparation conditions and sample mass measurement.

Keywords: adsorption; BET specific surface area; experimental uncertainty

Correlation of Adsorption Equilibrium Data for Water Vapor on F-200 Activated Alumina by Joshua D. Moore; Atanas Serbezov (pp. 65-75).

Single component adsorption equilibrium data for water vapor on commercially available activated alumina F-200 measured in a previous study (Serbezov, 2003) is correlated by two adsorption isotherm equations, both of which are based on the adsorption potential theory. The first equation is the well known Dubinin-Astakhov (D-A) equation. The second equation is obtained from a methodology proposed by Kotoh et al. (1993). It is referred to as a dual mechanism adsorption potential (DMAP) equation because it is a linear combination of two D-A terms with n = 1 where each term accounts for a specific mechanism of water retention. The D-A equation has two fitting parameters; the DMAP equation has three fitting parameters. The DMAP model provides a better fit for the adsorption data than the D-A model, while neither model describes the desorption data well. Analysis of the DMAP equation parameters shows that most of the water is retained by virtue of capillary condensation. In addition to fitting the experimental data, the heat of adsorption was calculated as function of the relative humidity and adsorbent loading. When capillary condensation is present, the heat of adsorption is only slightly higher than the latent heat of vaporization.

Keywords: activated alumina; water vapor; adsorption equilibrium models; adsorption potential theory; heat of adsorption

Chromatographic Detectors in Systems of Three Components by Mark J. Heslop; Geoffrey Mason; Bryan A. Buffham (pp. 67-72).

The chromatographic theory for the adsorption in binary systems has been well-established over the years. A binary mixture of known composition flows through a column packed with adsorbent. The system is then disturbed by adding a pulse of one of the pure components, and this causes a composition front to travel through the column. The retention time of this composition front is measured with a detector. This retention time can be related to the isotherm gradients of the two components. The situation is more complicated for a system of three components. In this case there are two composition fronts, and it is not easy to relate the retention times to the three isotherm gradients. In this preliminary investigation, we present a new theory to show how by using another composition detector, it is possible to evaluate the composition retention time for each component. We present some data for the ethane-ethylene-helium-13X zeolite system, and show that a simple detector based on the measurement of viscosity might be suitable.

Keywords: adsorption; chromatography; retention time; binary mixtures

Do the Differential Enthalpies of Adsorption Vary Between 77 K and 302 K? An Experimental Case Study of Argon and Nitrogen on Two Faujasite Type Zeolites by Philip L. Llewellyn; Guillaume Maurin; Thomas Poyet; Nathalie Dufau; Renaud Denoyel; Françoise Rouquerol (pp. 73-78).

Adsorption microcalorimetry of non-polar argon and quadrupolar nitrogen gases was carried out at 77 K and 302 K on two chemically different faujasite type zeolites (DAY and NaX). Considering absolute quantities adsorbed, the differential enthalpies of adsorption at zero coverage obtained with each system do not vary with temperature. Similarities in the differential enthalpies with increasing coverage are observed only if one considers non-specific adsorption phenomena either with a non-polar probe or on a non-polar surface. Where “specific” polar interactions occur for the nitrogen-NaX system, significant differences are observed. This experimental study is the first to compare microcalorimetric measurements of adsorption in such a wide range of temperature.

Keywords: microcalorimetry; nitrogen; argon; faujasite; differential enthalpy; adsorption isotherm

Estimation of Adsorption Capacity for Dissociating and Non Dissociating Aromatic Compounds on Activated Carbon with Different Models by Sirous Nouri; F. Haghseresht (pp. 77-86).

The process of adsorption of two dissociating and two non-dissociating aromatic compounds from dilute aqueous solutions on an untreated commercially available activated carbon (B.D.H.) was investigated systematically. All adsorption experiments were carried out in pH controlled aqueous solutions. The experimental isotherms were fitted into four different models (Langmuir homogenous Models, Langmuir binary Model, Langmuir-Freundlich single model and Langmuir-Freundlich double model). Variation of the model parameters with the solution pH was studied and used to gain further insight into the adsorption process. The relationship between the model parameters and the solution pH and pK_a was used to predict the adsorption capacity in molecular and ionic form of solutes in other solution.A relationship was sought to predict the effect of pH on the adsorption systems and for estimating the maximum adsorption capacity of carbon at any pH where the solute is ionized reasonably well.N₂ and CO₂ adsorption were used to characterize the carbon. X-ray Photoelectron Spectroscopy (XPS) measurement was used for surface elemental analysis of the activated carbon.

Keywords: activated carbon; adsorption; Langmuir homogenous models; Langmuir binary models; spectrophotometer

Simultaneous Determination of Multi-Component Isotherm Parameters from Single Sample of Liquid by Kohei Satoh; H. Ted Chang; Hideo Hattori; Kiyohiko Tajima; Eiji Furuya (pp. 79-83).

For the adsorption of multiple organic compounds using activated carbon in aqueous systems, several useful models have been developed to describe the equilibrium relationship. One of the easy-to-use models was developed by Suzuki et al. and the model was extended to determine equilibrium parameters for each component simultaneously. The determination procedure required liquid mixtures at various initial concentrations. The industrial sample, however, is normally controlled at constant concentration and hence the determination procedure mentioned above was limited to be applied. In this study, simultaneous determination procedure of multi-component isotherm parameters from single sample was discussed theoretically and experimentally. Then, it was found that Freundlich-type parameters for each component dissolved in water could be obtained from constant composition solutions based on Ideal Adsorbed Solution Theory.

Keywords: multi-component; IAS theory; Freundlich equation; parameter determination

The Confinement Factor: A Thermodynamic Parameter to Characterize Microporous Adsorbents by Joeri F. M. Denayer; Gino V. Baron (pp. 85-90).

Low coverage adsorption properties of n-alkanes were used to characterize microporous adsorbents. A confinement factor Z, defined as the ratio of the increase of adsorption entropy with carbon number over the increase of adsorption entropy with carbon number, correlates well with the pore size.

Keywords: zeolites; adsorption; enthalpy; entropy; confinement; pore size

Removal of Phenolic and Lignin Compounds from Bleached Kraft Mill Effluent by Fly Ash and Sepiolite by Mehmet Ugurlu; Ahmet Gurses; Mehmet Yalcin; Cetin Dogar (pp. 87-97).

This study aimed to remove phenolic and lignin compounds from paper mill industry (4500 m³/h) wastewaters, which is discharged to sea from a plant located in the western Turkey. As adsorbent, fly ash, raw sepiolite and heat-activated sepiolite were used. The effect of factors such as, particle size, temperature and pH on adsorption process was investigated. From kinetic studies, equilibrium time was found as 1 h for both. The kinetic data supports pseudo-second order model but shows very poor fit for pseudo-first order model. Intraparticle model also shows that there are two separate stages in sorption process, namely, external diffusion and pore diffusion. Adsorption isotherms for fly ash and activated sepiolite were obtained at two different temperatures. From experiments carried out at different pHs, it was observed that pH plays an important role in the adsorption process in removing of both lignin and phenolic compounds, providing both ionizating the compounds and modifying sorbent surfaces. It was also observed that heat-activated sepiolite is more effective than raw sepiolite and fly ash to remove these compounds. Adsorption of lignin and phenolic compounds increases with decreasing particle size. In addition, the efficiency of adsorption decreases with increasing adsorption temperature for both fly ash and untreated sepiolite.

Keywords: Bleached Kraft Mills Effluent; adsorption; sepiolite; fly ash; phenolic and lignin compounds

Menisci Interactions during Adsorption on Mesoporous Materials: Evaluation of Delayed and Advanced Adsorption by Salomon Cordero; Fernando Rojas; Isaac Kornhauser; Marcos Esparza (pp. 91-96).

Menisci interactions can strongly affect the development of adsorption processes in mesoporous materials. Phenomena such as delayed and advanced adsorption represent outright manifestations of these interactions then leading to deceptive determinations of the pore-size distribution. At present, a characterization study involving simulated porous networks with qualities similar to those owned by real materials and in which the above processes can occur is still lacking. A Monte Carlo procedure is used to evaluate the extent of delayed and advanced adsorption in porous structures of assorted morphologies. This treatment allows a clear detection of the types of mesoporous structures that can experience the incidence of delayed and advanced adsorption.

Keywords: delayed adsorption; advanced adsorption; Monte Carlo simulation; porous networks

Heterogeneity of Adsorption Energy of Water, Methanol and Diethyl Ether on Activated Carbons by Vladimir Gun’Ko (pp. 97-102).

Three samples of activated carbon of wood origin with various amounts of surface functional groups and different porous structure were used as adsorbents of water, methanol, and diethyl ether. Then the isotherms at three different temperatures were used to calculate distributions of adsorption potential, free energy of adsorption and adsorption energy. The results showed that the strength of interactions depends on both the porosity of the sample and its surface chemistry. The effect of surface chemistry is the most important in the case of water and the least important in the case of diethyl ether. The high-energy centers are related to adsorption in narrow pores containing functional groups. For molecules consisting of hydrocarbon moiety and oxygen containing groups (methanol and diethyl ether) the surface chemistry plays a role at low surface coverage.

Keywords: adsorption energy; activated carbon; surface heterogeneity

The Structure of Water Monolayers on a Hydroxylated Chromium Oxide Surface by Shigeharu Kittaka; Hiroyuki Sugiyama; Hiroshi Sumi; Shuichi Takahara (pp. 103-107).

We have investigated the structure of monolayer water molecules on a hydroxylated (001) plane of Cr₂O₃ using GCMC simulations. The water molecules are adsorbed commensurately in the center of three surface hydroxyl groups by directing the proton of a water hydroxyl group towards the solid surface. Another type of water is adsorbed by bridging anchored water molecules, whereby, a two-dimensional (2D) condensed layer is formed. It was ascertained that 2D condensed monolayer water is not in a crystalline state below the 2D critical temperature (319 K), but is composed of many hexagonally linked rings. Above the 2D critical temperature, the hexagonal alignment of water changes to form a one-dimensional linked water structure.

Keywords: adsorption; chromium oxide; 2D water; supercritical water; GCMC

Adsorption and Coadsorption of 2-methylpentane and 2,2-dimethylbutane in a ZSM-5 Zeolite by Jean Pierre Bellat; Edith Lemaire; Jean Marc Simon; Guy Weber; Anne-Claire Dubreuil (pp. 109-114).

In this paper we present the major results of a thermodynamic and structural study of the adsorption of 2-methylpentane (2MP) and 2,2-dimethylbutane (22DMB) on a ZSM-5 zeolite under isothermal and isobaric conditions. A thermodynamically inconsistent behavior is observed with 22DMB at constant pressure: the adsorbed amount increases as the temperature of the zeolite increases from 343 to 443 K. We suspect that this particular phenomenon is the result to the monoclinic/orthorhombic phase transition undergone by the zeolite. This flexibility of the zeolite framework seems to have a significant effect on the separation of both isomers by selective adsorption. Coadsorption experiments show that the ZSM-5 zeolite has a poor selectivity for 2MP with respect to 22DMB when the structure is orthorhombic whereas it is very selective in the monoclinic structure. However the selectivity decreases sharply as the filling increases. The presence of 22DMB molecules located at the intersections of the channels probably obstructs the adsorption of 2MP.

Keywords: coadsorption; ZSM-5; 2-methylpentane; 2,2-dimethylbutane; phase transition

The Physics of Capillary Condensation in Disordered Mesoporous Materials: A Unifying Theoretical Description by Francois Detcheverry; Edouard Kierlik; Martin Luc Rosinberg; Gilles Tarjus (pp. 115-119).

We present a unifying theoretical approach of capillary condensation in disordered mesoporous materials. It provides a comprehensive picture of this phenomenon that accounts for processes occuring on all length scales and clarifies the relation between hysteretic and equilibrium behavior. The shape of the hysteresis loop is shown to depend on the presence or absence of out-of-equilibrium phase transitions, whose nature differs on adsorption and on desorption.

Keywords: capillary condensation; hysteresis; disordered solids

A New Method for the Determination of Low Coverage Adsorption Heats for Zeolite-VOC Systems by Joelle Nokerman; Xavier Canet; Guy De Weireld; Marc Frere (pp. 121-125).

In this paper, we present a new experimental technique and a mathematical procedure for the calculation of the isosteric heats of adsorption of VOC-zeolite systems. This procedure provides a continuous isosteric heat curve over a large coverage ratio range including the low-coverage area. Results are given for a toluene-NaY system at 423 K. The validity of the method is discussed by comparison with other methods.

Keywords: adsorption; dynamic flowing method; isosteric heat of adsorption; low coverage ratios

Chromatographic Retention Times Using Mixture Pulses of Different Compositions by Mark J. Heslop; David J. Richardson; Paul A. Russell; Geoffrey Mason; Bryan A. Buffham (pp. 127-131).

This work is concerned with how gas chromatographic (GC) retention times are determined for adsorption measurements. The standard way is to add a pulse (slug) of one of the pure gases using either an injection valve or a syringe. A chromatographic detector is used to determine the time taken for the pulse to travel through the column. The whole procedure is then repeated using a pulse of the other pure gas. Experience from other workers would suggest that the two retention times are not the same. We take a novel approach. We add pulses of the same size but of different composition. That is, we use mixture pulses. Our investigation involves the ethane-helium-13X zeolite system at 50 ∘C and we consider only one main (carrier) flow. Our results show that there is a linear variation between the composition of the pulse and the retention time. Indeed, it is not sufficient to simply add the retention times for the two pulses and take the average. The standard GC detector is based on thermal conductivity measurements (TCD). In a novel development, we also show how a detector based on the measurement of viscosity can be used to determine these retention times.

Keywords: adsorption; chromatography; retention time; binary mixtures

Capillary Phenomena in the Framework of the Two-Dimensional Density Functional Theory by Eugene A. Ustinov; Duong D. Do (pp. 133-138).

We present results of application of the density functional theory (DFT) to adsorption and desorption in finite and infinite cylindrical pores accounting for the density distribution in radial and axial directions. Capillary condensation via formation of bridges is considered using canonical and grand canonical versions of the 2D DFT. The potential barrier of nucleation is determined as a function of the bulk pressure and the pore diameter. In the framework of the conventional assumptions on intermolecular interactions both 1D and 2D DFT versions lead to the same results and confirm the classical scenario of condensation and evaporation: the condensation occurs at the vapor-like spinodal point, and the evaporation corresponds to the equilibrium transition pressure. The analysis of experimental data on argon and nitrogen adsorption on MCM-41 samples seems to not completely corroborate this scenario, with adsorption branch being better described by the equilibrium pressure – diameter dependence. This points to the necessity of the further development of basic representations on the hysteresis phenomena.

Keywords: adsorption; cylindrical pore; density functional theory; capillary condensation; nucleation

Confined Water in Mesoporous MCM-41 and Nanoporous AlPO₄-5: Structure and Dynamics by Nicole Floquet; Jean Paul Coulomb; Nathalie Dufau; Gilles Andre; Remi Kahn (pp. 139-144).

Confined water presents unusual properties in comparison with other sorbate species. First of all, the sorption isotherm is of type III, even in the microporous confinement range (Ø < 20 Å). Whatever the pore diameter, water sorption phenomenon looks like the so-called capillary condensation phase transition. Our results clearly valid such an expected behaviour in the mesoporous confinement range (20 Å < Ø < 40 Å). The water confined phase is a liquid phase characterized by a short range order and a high translational molecular mobility. The confinement induces a strong displacement towards the low temperature of the water confined liquid solidification T_sol. (for instance, T_sol. = 230 K for D₂O confined liquid in MCM-41 (Ø = 24 Å). We have determined the structure of the water confined solid phase observed below T_sol.. It looks like those of the cubic ice structure affected by strong quasi-isotropic finite size effects induced by the confinement. Such a quasi-(1d) solid appears as a polycrystalline column rather than a single crystalline nanofiber. Concerning water confinement in the microporous range (as for example, AlPO₄-5 zeolite (Ø = 7.3 Å)), our results are more surprising. Type III sorption isotherm is the signature of a crystallization phenomenon at room temperature (T = 300 K). The confined water crystallizes in two helices that are commensurate with the AlPO₄-5 micropore structure. The confined ice has a density of 1.2 g⋅ cm^{− 3}.

Keywords: confinement; water; MCM-41; AlPO₄-5; neutron scattering

Comparison of AgNO₃/Clay and AgNO₃/ALSG Sorbent for Ethylene Separation by Soon-Haeng Cho; Jong-Ho Park; Sang-Sup Han; Jong-Nam Kim (pp. 145-149).

Two π -complexation adsorbents, AgNO₃/clay and AgNO₃/ALSG, were prepared by dispersing AgNO₃ on clay and aluminosilica substrate, respectively. Incipient wetness method was used in preparing the adsorbents. Adsorption capacities of AgNO₃/ALSG and AgNO₃/clay for ethylene at 25 ^oC and 1 atm were 1.81 mmol/g and 1.26 mmol/g, respectively. Binary adsorption measurement shows that the selectivity of AgNO₃/ALSG for ethylene at total pressure of 900 mmHg and 25^oC was twice as high as that of AgNO₃/clay in the composition range of C₂ gas mixture of practical importance. The performance of AgNO₃/ALSG has been compared with that of AgNO₃/clay by simulating a 3-bed VSA process. The simulation revealed that the recovery with AgNO₃/ALSG was higher by 4% at the purity of 99.9% than that with the AgNO₃/clay.

Keywords: silver nitrate; adsorption; π-complexation; ethylene; pressure swing adsorption

CO₂ and N₂ Adsorption on the Acid (HCl, HNO₃, H₂SO₄ and H₃PO₄) Treated Zeolites by Asli Ertan; Fehime Çakicioğlu-ÖZKAN (pp. 151-156).

CO₂ and N₂ adsorption on the acid treated natural and synthetic zeolites at 5^∘C and 25^∘C was studied. The system heterogeneity was higher for CO₂ than N₂ adsorption and decreased with acid treatment.

Keywords: adsorption; acid treatment; natural zeolites; heterogeneity

Adsorption Behavior of Dioxin Model Compounds on Activated Carbon in Supercritical Carbon Dioxide by Motonobu Goto; Mitsuru Sasaki; Shiho Kawahara; Tsutomu Hirose (pp. 157-161).

Removal of toxic substances such as dioxins and PCBs in the environmental matrices such as fly ash and soil is becoming important. We have been developing combined process of extraction with supercritical carbon dioxide, concentration by adsorption, and then destruction by supercritical water oxidation as a national project (NEDO/Energy Conservation Center). In the extraction—adsorption process, dioxins contained in solid samples can be transferred and concentrated into adsorbent. Then, the adsorbent containing dioxins is completely destructed by supercritical water oxidation. For supercritical CO₂ extraction and supercritical water oxidation, efficiencies of more than 99% were achieved. In this work, we studied the adsorption of model compounds of dioxins onto activated carbon in supercritical carbon dioxide to obtain the design data for the process. The adsorption behavior of dioxins model compounds was measured by impulse or step response technique in supercritical CO₂ in the pressure range of 10–40 MPa at 323 K. As the model compounds, we used benzene, monochlorobenzene, dichlorobenzene, biphenyl, and anthracene to evaluate the effect molecular weight and the presence of chlorine in the molecule. By using the step response technique, we obtained the amount adsorbed on activated carbon. Adsorption decreased as molecular weight increased, but was not affected by pressure. The adsorbed amount was not significantly influenced by the pressure. This result suggests that these components can be effectively adsorbed on activated carbon in supercritical CO₂. We have also measured impulse response to evaluate the adsorption equilibrium constant. Analysis based on the molecular shape and the size is applied to evaluate the adsorption behavior.

Keywords: dioxin; supercritical carbon dioxide; step response; impulse response

Influence of Organics on Structure of Water Adsorbed on Activated Carbons by Vladimir M. Gun’Ko; Vladimir V. Turov; Roman Leboda; Jadwiga Skubiszewska-Zięba; Magdalena D. Tsapko; Dorota Palijczuk (pp. 163-168).

Influence of organics on the properties of water adsorbed on carbon and silica gel adsorbents was studied by ¹H NMR spectroscopy, thermal gravimetry, breakthrough dynamics, and quantum chemistry methods. Te behavior of interfacial water depends strongly on the properties of organic solvents, which can remove a major (nonpolar solvents) or minor (polar solvents) portion of water from narrow pores to larger ones of carbon adsorbents. The opposite effect is observed on the interaction of water/organics with silica gel.

Keywords: activated carbon; silica gel; adsorption; water-organic mixture¹H NMR; TG; breakthrough

Structural Study of CHCl₃ Molecular Assemblies in Micropores Using X-ray Techniques by Taku Iiyama; Yoshie Kobayashi; Atsushi Matsumoto; Yoshitaka Nakahigashi; Sumio Ozeki (pp. 169-172).

The X-ray diffraction from CHCl₃ molecules adsorbed in slit-shaped micropores of activated carbon fibers were measured at 298 K. The pore effect on structure of molecular assemblies in the graphitic micropores was examined. The peak positions due to the first nearest neighbor CHCl₃ in the electron radial distribution function of adsorbed phase agreed with those of bulk liquid, although their peak intensities were different. In narrow pores (pore width w = 1.1 nm), the peak intensities due to the first nearest molecule are stronger than the bulk liquid, because a peak due to the correlation between carbon walls and CHCl₃ molecules was overlapped. In the wider pores of ACF W10 (w = 1.3 nm) having high CHCl₃ removal efficiency from tap water, the intensity of the peak of r = 0.4 nm is the strongest. It suggests that CHCl₃ molecules in the 1.3 nm micropores should be orientated for a Cl atom to meet with a carbon atom in wall surfaces. These results demonstrate that the structure of a polar molecule such as CHCl₃ will sensitively be subject to micropore effects.

Keywords: CHCl₃(chloroform); microporous carbon; XRD; radial distribution function; dipole

Adsorption of N₂, O₂, and Ar in Potassium Chabazite by Ranjeet Kaur Singh; Paul Webley (pp. 173-177).

Chabazite with Si/Al of 2.4 ratio was synthesized and exchanged with cations viz. K⁺, Li⁺ and Ca^{2 +}. N₂, O₂ and Ar adsorption isotherms were measured in the pressure range 0–1000 torr and temperatures viz. 0, 30 and 50 ∘C. K-CHA showed better O₂/Ar selectivity than Ca-CHA although adsorption capacity was larger for Ca-CHA. Zero loading isosteric heat of adsorption values for K-CHA, were considerably lower than Ca-CHA which reflect diminished charge density of the K cation. The high O₂/Ar selectivity is possibly due to partial pore blockage as a result of the large potassium cation located near the 8-member ring leading to the 20-hedron cage. The O₂/Ar selectivity may be exploited to produce high purity oxygen (> 99%) from a two stage PSA system employing K-CHA in the second stage.

Keywords: K-CHA; Li-CHA; Ca-CHA; adsorption

A Complete Set of Experimental Devices for the Determination of the Gas Separation Capacity of Adsorbents by Riad Khoder Agha; Guy De Weireld; Marc Frère (pp. 179-182).

In this work, we present a complete experimental procedure which aims at measuring adsorption isotherms, selectivity curves and kinetics of air compounds on porous media in broad ranges of pressure and temperature. The experimental set-up and the experimental procedures are presented as well as a complete report on treatments of the rough experimental results to obtain the adsorption isotherms, selectivity and kinetics curves. Results are provided for nitrogen/LiLSX and oxygen/LiLSX systems (adsorption isotherms curves at 278 and 303 K in the pressure range 0–400 kPa), for a binary mixture nitrogen/oxygen/LiLSX system at 303 K and 400 kPa (selectivity curves). Kinetics curves are presented for nitrogen/LiLSX and oxygen/LiLSX systems at 303 K and 400 kPa.

Keywords: adsorption; zeolite; isotherm; selectivity; kinetics

Adsorption Equilibrium of Light Mercaptans on Faujasites by Guy Weber; Jean-Pierre Bellat; Frederic Benoit; Christian Paulin; Sophie Limborg-Noetinger; Michel Thomas (pp. 183-188).

Both thermogravimetry and manometry coupled to calorimetry techniques were used to determine the adsorption equilibrium of ethyl mercaptan in pure and extruded NaX zeolites. Sorption isotherms were investigated from 298 to 373 K, and over a large range of pressure from 10^{− 4} to 100 hPa. Adsorption heats were measured at 298 K. Reversible adsorption-desorption isotherms are type I shaped and characterize a very high adsorption affinity of NaX zeolites for ethyl mercaptan. The sulfur compound entirely probes NaX zeolite α-cages at micropore saturation. The presence of the mineral binder for the extruded zeolite does not affect the adsorption phenomenon. Adsorption data were well fitted using the Polanyi-Dubinin model. Calorimetric and isosteric heats do not change very much with loading, indicating that NaX zeolite is energetically homogeneous for the adsorption of ethyl mercaptan. Additional information concerning state of adsorbed phase were obtained from isosteric molar entropy curves. Therefore, the NaX faujasite appeared as a powerful potential candidate for industrial desulfurization of natural gas by adsorption process.

Keywords: adsorption; zeolite; ethyl mercaptan; thermogravimetry; calorimetry

Evaluation of Experimental Methods for the Study of Liquid-Phase Adsorption of Alkane/Alkene Mixtures on Y Zeolites by Inge Daems; Philibert Leflaive; Alain Méthivier; Joeri F. M. Denayer; Gino V. Baron (pp. 189-194).

Liquid phase adsorption of alkane/alkene mixtures on NaY was studied using different methods. It was shown that the presence of traces of water in the feed, has a tremendous influence on subsequent measurements during continuous flow through experiments. The hydrophilic character of the adsorbent combined with the inevitable presence of water inside the mobile phase made the application of the pulse chromatographic technique impossible. The influence of water became neglectable in an optimized batch technique allowing to determine binary adsorption isotherms of alkane/alkene mixtures in the low alkene concentration range (0–15wt%). 1-octene was shown to adsorb more selective from decane and dodecane than from its mixture with hexane or heptane on NaY. This unexpected selectivity effect was attributed to molecular packing in the supercages of NaY.

Keywords: liquid; adsorption; faujasites; alkane; alkene

Adsorption and Desorption Isotherms at Ambient Temperature Obtained by Ellipsometric Porosimetry to Probe Micropores in Ordered Mesoporous Silica Films by Alexis Bourgeois; Aline Brunet-bruneau; Serge Fisson; Josette Rivory; Muriel Matheron; Thierry Gacoin; Jean-pierre Boilot (pp. 195-199).

Ellipsometric Porosimetry is a non destructive technique well adapted to the measurement of isotherms of porous thin films. We present results obtained on ordered mesoporous silica films prepared by surfactant templating methods. Although the applications of such films require knowledge of mesoporous network, the micropores, which remain uncontrolled during the film elaboration, could play a main role in the film properties and then need to be characterized. We take advantage of the ability of our experiment to perform isotherms with different organic adsorptives of different sizes (branched or linear molecules) in order to probe micropores in these ordered mesoporous silica films.

Keywords: adsorption; microporous; mesoporous; silica; ellipsometry

Integrating Gas Sorption with Mercury Porosimetry by Sean P. Rigby; Matthew J. Watt-Smith; Robin S. Fletcher (pp. 201-206).

Previous work has shown that it is possible to use intergrated nitrogen sorption and mercury porosimetry experiments to determine the distribution of average pore length with pore diameter for mesoporous solids. In this work, the previous data analysis method has been generalised such that it is also suitable for application to samples with higher levels of mercury entrapment than before. This generalisation of the theory has facilitated the ability to use a series of progressively larger mercury scanning loops, in integrated gas sorption and porosimetry experiments, to potentially determine the full pore length distribution for pores of a given diameter, and the distribution of pore co-ordination number. The new analysis has been applied to a silica catalyst support.

Keywords: network percolation; pore length distribution

A Study on Adsorption Equilibrium for Oxygen and Nitrogen into Carbon Nanotubes by Byeong Ho Kim; Bok Reon Kim; Yang Gon Seo (pp. 207-212).

In this work, it was investigated adsorption equilibria of pure oxygen and nitrogen in carbonaceous materials such as an activated carbon (AC), single-walled nanotubes (SWNTs), and Multi-walled nanotubes (MWNTs). The microporous structure of AC was a slit-shaped pore while carbon nanotubes (CNTs) were cylindrical structure. This different pore structure and pore size distribution may be led to difference in selectivity of oxygen to nitrogen. The adsorption capacity of oxygen and nitrogen was in the order AC > SWNTs > MWNTs, while the selectivity of oxygen to nitrogen was SWNTs > MWNTs > AC.

Keywords: adsorption; air separation; carbon nanotubes; kinetic separation

Determination of the Henry Constant for Zeolite-VOC Systems Using Massic and Chromatographic Adsorption Data by Xavier Canet; Joëlle Nokerman; Marc Frère (pp. 213-216).

Both the inverse gas chromatographic method and the dynamic gravimetric-calorimetric method were tested in order to determine the Henry constant for toluene on a Na-faujasite type zeolite. We used the pulse technique for the chromatographic method and a system generating low concentration of VOC in a helium flow for the gravimetric technique. The experimental determinations of the Henry constants for toluene were achieved in two different temperature ranges (from 363 to 548 K for gravimetry and from 548 to 673 K for chromatography). The results presented in this paper show the complementarity of two different techniques for the Henry constants determination. The Henry constants obtained with the two techniques at 548 K differ from 8%.

Keywords: adsorption; chromatography; gravimetry; VOC; zeolites; Henry constant

Adsorption and Separation Characteristics of Herbicides onto Activated Carbon by Tae-Young Kim; Seung-Jai Kim; Sung-Yong Cho (pp. 217-221).

Adsorption and desorption characteristics of the herbicides (CPA, 2,4-D and 2,4-DNP) in aqueous solution for a GAC, F-400, were studied at pH 3.5, 7.0 and 10.0. Adsorption equilibrium capacities of the herbicides onto GAC increased with decreasing pH of the solution. An adsorption model based on the linear driving force approximation (LDFA) was used for simulating the adsorption behavior of the herbicides in a fixed bed adsorber. Ninety percent desorption of 2,4-D can be obtained using distilled water.

Keywords: adsorption; desorption; herbicides; activated carbon

Adsorption Properties of Nitrogen, Carbon Dioxide and Nitrogen Dioxide onto Mesoporous Chromium Silicate by Masahiro Katoh; Tahei Tomida; Manabu Shinkawa; Hironori Aihara (pp. 223-226).

The adsorption properties of nitrogen, carbon dioxide and nitrogen dioxide onto mesoporous chromium silicates (Cr-FSM-16) were studied by spectroscopic analyses. The Cr-oxide moieties are highly dispersed in the framework of FSM-16. The UV-vis spectra of the Cr-FSM-16 exhibit three distinct absorption bands, which can be assigned to charge transfer from O^{2 −} to Cr^{6 +} of the tetrahedrally coordinated Cr-oxides moieties. The results of initial heat of adsorption of CO₂ indicated the interaction between Cr^{6 +} = O^{2 −} in Cr-FSM-16 and CO₂ was weak. The decomposition of NO₂ by FSM-16 or Cr-FSM-16 was caused by Si = OH site or Cr^{6 +} = O^{2 −} site, respectively. The co-adsorption models for NO₂ and CO₂ onto Cr-FSM-16 or FSM-16 were proposed in the end.

Keywords: adsorption; mesoporous chromium silicate; carbon dioxide; nitrogen dioxide

High Precision Volumetric Gas Adsorption Apparatus by Kazuyuki Nakai; Joji Sonoda; Haruo Iegami; Hiromitsu Naono (pp. 227-230).

We have developed a new volumetric gas adsorption apparatus into which the dead volume measurement cell (dVd cell) is incorporated (cf. Fig. 1). The dVd cell measures continuously the change of dead volume during adsorption measurement. The dead volume at every step of adsorption measurement is used in calculation of adsorbed amount of nitrogen gas. Introduction of the dVd cell makes the level-control system of liquid nitrogen unnecessary, and enables the adsorption error due to the minute fluctuation of liquid–nitrogen level small. The sensitivity and reproducibility of our new adsorption apparatus have been examined using some certified materials (cf. Fig. 4).

Keywords: volumetric method; continuous dead volume measurement; high reproducibility; surface area

On the Chromatographic Measurement of Equilibrium Isotherms Using Large Concentration Steps by Stefano Brandani (pp. 231-235).

The measurement of equilibrium isotherms from the dynamic response of an adsorption column subject to a large pulse or step change in inlet concentration requires the simultaneous measurement of concentration and flowrate. Based on the observation that for a single sorbate-carrier system the concentration and velocity transients are coupled, a procedure to estimate the true column outlet carrier flowrate from the measured concentration signal is derived, which is consistent with an overall mass balance of the carrier gas. The proposed approach has been validated using experimental breakthrough curves for CO₂ on UOP HiSIV 3000 pellets for integral step changes up to 75% in CO₂ concentration.

Keywords: adsorption equilibrium; breakthrough experiment; integral steps

Experimental and Theoretical Analysis for the CO₂ Adsorption on Hydrotalcite by Josél Soares; Gustavo L. Casarin; Humberto J. José; Regina De F. P. M. Moreira; Alírio E. Rodrigues (pp. 237-241).

The reduction of emission of carbon dioxide from flue gases can be achieved using post-combustion technologies, such as the adsorption using efficient solid sorbents. In this work, the adsorption of CO₂ on hydrotalcite was studied using dynamical and static methods. The breakthrough curves were obtained at different flow gas and total pressure 1.0 bar, using CO₂ diluted in helium at 29^∘C. The experimental data showed that the Freundlich model was more suitable to describe the adsorption equilibrium, and the constants of Freundlich (k = 5.5×10^{− 4} and n = 0.23), are typical for favorable isotherm. The linear driving force model was suitable to describe the breakthrough curves.

Keywords: breakthrough curves; CO₂hydrotalcite; isotherm; greenhouse gases

Adsorption of Nonylphenol Ethoxylates in the Presence of Competing Natural Organic Matter by Akira Yuasa; Fusheng Li; Eun-Jeong Cheong; Yoshihiko Matsui (pp. 243-248).

Three NPEO mixtures containing NPEO compounds having attached EO numbers in the ranges of 1–6, 2–12 and 4–19 were subjected to batch activated carbon adsorption experiments in solutions with and without the presence of competing natural organic matter (NOM) existent extensively in drinking water sources. The liquid phase composition of the NPEO mixtures, described in the ratios (C_i/C_T) of the equilibrium concentrations of individual compounds (C_i) to the total mixture (C_T), did not change after adsorption at varied carbon dosages, no matter if NOM was present or not. However, their adsorption capacity was significantly reduced with the adsorption of NOM due to site competition and pore blockage. The adversary impact was found to be greatly dependent upon the initial presence levels of NPEO and NOM as well as the NOM sources.

Keywords: adsorption; nonylphenol ethoxylate; natural organic matter; activated carbon; isotherm

Study of Multicomponent Gas Adsorption into MSC5A by Chromatograph by Kazuyuki Chihara; Yosuke Kaneko; Takuya Terakado; Hisashi Mizuochi (pp. 249-253).

Perturbation chromatography with multi component gas carrier and non-equilibrium thermodynamics liner law was applied for discussion of the interference effect and the displacement effect on mass transfer in multi component gas adsorption. Moment analysis method and stop & go simulation method were utilized to obtain each mass transfer parameters of adsorbate gases. Dependency of micropore diffusion on amount adsorbed and correlation of micropore diffusion with chemical potential driving force for microporous adsorbent were confirmed. Cross effect in micropore diffusion was found.

Keywords: chromatograph; stop & go simulation; multi component gas

Multicomponent Equilibrium Studies for the Adsorption of Basic Dyes from Solution on Lignite by Keith K. H. Choy; Stephen J. Allen; Gordon Mckay (pp. 255-259).

The ability of lignite or brown coal to adsorb basic dyes in single and multicomponent systems is analysed using IAST. The single component isotherms were correlated well using the Langmuir (L) and Freundlich (F) isotherms and the same isotherms, as L-L, F-F, L-F and F-L were used to model the binary dye-lignite isotherms. A sensitivity analysis was carried out on the Langmuir constants in the IAST.

Keywords: isotherm; adsorption; lignite; basic dyes; multicomponent

Thermodynamic Properties of Ar Film on ZnO Metal Oxide Powders Measured by Adsorption Isotherms by Jae Y. Kim; In C. Chang; Ik J. Lee; Byung I. Choi; Hyun S. Nham (pp. 261-264).

Adsorption and thermodynamic properties of Ar on ZnO powder were studied using a newly built gas adsorption isotherm apparatus, which has good temperature stability within 0.01 K in a wide rage (20–300 K) and good pressure accuracy with a resolution better than 10^{− 5} in 100 torr. Two distinct Ar atomic layers were measured. A specific surface area of the ZnO particle was also obtained from calculations of a molecular area of Ar on the surface of the adsorbents, and found to be approximately 100 m²/g. The thermodynamic results including the 2-dimensional compressibility indicate the surface melting occurs near 77 K.

Keywords: adsorption; ZnO; Ar

Diffusion-Controlled Hysteresis by Peter I. Ravikovitch; Alexander V. Neimark (pp. 265-270).

A new model of time-dependent sorption-desorption hysteresis is presented. This type of hysteresis is not related to transitions between metastable adsorption states, which are a common cause of capillary condensation hysteresis in mesoporous materials. We show that time-dependent hysteresis is a consequence of slow kinetics and failure to reach equilibrium at given experimental conditions. The model of diffusion-controlled hysteresis (DCH) we developed is capable of predicting time-dependent experimental data. It allows one to estimate the characteristic diffusion. We show that DCH model time and the equilibrium sorption isotherms from non-equilibrium sorption/desorption measurements. The DCH model has been tested using experimental CO₂ isotherms on polymeric and carbonaceous materials.

Keywords: sorption; hysteresis; equilibrium; kinetics; diffusion

Probing the Origins of Linear Free Energy Relationships with Molecular Theory and Simulation by David M. Ford (pp. 271-277).

Linear free energy relationships (also known as entropy-energy compensation) are seen in a range of physical processes, including adsorption and diffusion. The most interesting compensation effects presumably arise from geometric and energetic effects at the molecular level, but their origins are not well understood. We utilize molecular modeling of simple adsorbate-adsorbent systems to discover these origins in a semi-quantitative way. Sets of calculations were constructed to represent certain experimental processes, e.g. adsorption of a homologous series of molecules, for which linear free energy relationships might be expected. We find that the general correlation between energy and entropy is often much more complex than a simple linear relationship, although a linear approximation might be sufficient across limited ranges.

Keywords: linear free energy relationship; entropy-enthalpy compensation; molecular simulation; adsorption

Adsorption of Water and Aromatics in Faujasite Zeolites: A Molecular Simulation Study by Christèle Beauvais; Anne Boutin; Alain H. Fuchs (pp. 279-282).

We report a molecular simulation study of the equilibrium adsorption of water and aromatics in zeolite faujasite NaY. The Monte Carlo simulation methodology used in this work allows the nonframework cations to redistribute upon adsorption of fluids. We indeed observe a cation redistribution in model NaY upon water adsorption. The same phenomenon is observed in presence of adsorbed xylene molecules in the framework. A very small amount of water (some 5% weight) leads to the observed cation redistribution. The consequence of this is a change by a factor of 4 in the adsorption selectivity of NaY in favor of p-xylene, when a mixture of m and p-xylene are exposed to the zeolite sample.

Keywords: adsorption; separation; zeolites; molecular simulation; water

Adsorption in Controlled-Pore Glasses: Comparison of Molecular Simulations with a Mean-Field Lattice Gas Model by Lev D. Gelb; Rafael Salazar (pp. 283-288).

We consider the possible quantitative application of a lattice-gas model approach to the calculation of adsorption isotherms. In order to validate such application, we use the lattice-gas approach to solve for the adsorption and desorption isotherms in model controlled-pore glasses that have previously been the subject of an extensive series of Grand Canonical Monte Carlo simulations. We find that the lattice-gas model augmented with longer-ranged interactions provides a quite good account of adsorption in some of these systems for appropriate choice of several system parameters, but that the quality of agreement depends on the pore size of the material.

Keywords: molecular simulation; statistical mechanics; capillary condensation

Temperature Effect on Adsorption/Desorption Isotherms for a Simple Fluid Confined within Various Nanopores by Benoît Coasne; Keith E. Gubbins; Roland J.-M. Pellenq (pp. 289-294).

We report a Grand Canonical Monte Carlo study of the temperature dependence of adsorption/desorption hysteresis for porous matrices having different morphologies and topologies. We aim at gaining some insights on the concept of critical hysteresis temperature, T_cc, defined as the temperature at which the hysteresis loop disappears. Simulated T_cc for cylindrical, ellipsoidal, and constricted pores follow the experimental scaling law established for MCM-41 silica materials. In contrast, T_cc for Vycor samples with a largest pore size ~2.5 nm and 5.0 nm obey a different relationship, in qualitative agreement with experiments.

Keywords: capillary condensation; Monte-Carlo simulation; nanoporous material; hysteresis

Sublimation Phenomena in Slit Nanopores: Lennard-Jones Phase Diagram by Hideki Kanda; Minoru Miyahara; Ko Higashitani (pp. 295-299).

Sublimation phenomena of Lennard-Jones fluids in slit-shaped nanopores were examined. Vapor-phase pressure at which a solid phase forms in a pore at a constant temperature is determined by the authors’ molecular dynamics technique. The obtained phase-boundary pressure is remarkably lower than that of the bulk phase. A simple model of the sublimation is presented, which successfully predicts the molecular dynamics results with no adjustable parameter. Thus, a whole Lennard-Jones phase diagram in slit-shaped nanopores can now be predicted.

Keywords: vapor-solid equilibria; nanopore; phase transition; Lennard-Jones; molecular simulation

Freezing of Mixtures Confined in a Slit Nanopore by Benoit Coasne (pp. 301-306).

We report a Grand Canonical Monte Carlo study of the freezing/melting of Lennard-Jones A/B mixtures confined in a slit pore (H = 1.44 nm). The fluid/fluid interactions are chosen to model A = Ar and B = Kr. Fluid/wall interaction parameters are chosen so that the ratio of the wall/fluid to the fluid/fluid interactions for Kr and Ar is larger and smaller than 1, respectively. We find that the phase diagram of the confined mixture is of the same type than that for the bulk. The freezing temperature of confined mixtures rich in Kr is larger than the bulk. In contrast, we observe a decrease of the freezing temperature for mixtures rich in Ar. The confined crystal has a hexagonal structure (triangular symmetry), except for pure Ar where a square structure is observed.

Keywords: freezing; mixture; molecular simulation; confinement; solid–liquid phase diagram

Impact of Potential Models on Adsorption of Linear Molecules on Carbon Black by D. D. DO; H. D. DO (pp. 307-312).

In this paper, we investigate the effects of potential models on the description of equilibria of linear molecules (ethylene and ethane) adsorption on graphitized thermal carbon black. GCMC simulation is used as a tool to give adsorption isotherms, isosteric heat of adsorption and the microscopic configurations of these molecules. At the heart of the GCMC are the potential models, describing fluid-fluid interaction and solid-fluid interaction. Here we studied the two potential models recently proposed in the literature, the UA-TraPPE and AUA4. Their impact in the description of adsorption behavior of pure components will be discussed. Mixtures of these components with nitrogen and argon are also studied. Nitrogen is modeled a two-site plus discrete charges while argon as a spherical particle. GCMC simulation is also used for generating simulation mixture isotherms. It is found that co-operation between species occurs when the surface is fractionally covered while competition is important when surface is fully loaded.

Keywords: adsorption; Monte Carlo; ethylene; ethane; graphitized thermal carbon black

Gas Permeation Through Zeolite Single Crystal Membranes by M. Göktug Ahunbay; J. Richard Elliott Jr.; Orhan Talu (pp. 313-318).

Diffusion of methane and argon mixtures through single crystal membranes is studied using the Dual-Control Volume-Grand Canonical Molecular Dynamics method. This study focuses on understanding the impact of crystal structure on surface resistance and membrane performance by comparing diffusion through silicalite, mordenite, AlPO₄-5 and ZSM-12. Results showed that the contribution of surface resistance on membrane selectivity varies with the structure of the zeolite framework. Surface resistance is larger and longer range in silicalite, with an overall trend of silicalite > ZSM-12 > mordenite > AlPO₄-5. This difference is attributed primarily to the smaller diameter of the silicalite pores, but the one-dimensional pore systems also seem to focus the translational momentum such that the surface resistance is smaller and shorter range.

Keywords: gas diffusion; selectivity; molecular simulation; mass-transfer resistance; surface barrier

Molecular Simulation of Gas Separation by Equilibrium-Based Adsorption Processes by José P. B. Mota; Isabel A. A. C. Esteves; Rui C. R. Rodrigues; Nuno F. C. Formiga (pp. 319-324).

A new molecular simulation method is proposed to solve the governing equations of a multicompo-nent, isothermal batch adsorber under equilibrium-controlled conditions. The technique is formulated in the Gibbs ensemble, but is more appropriately viewed as a hybrid of a molecular simulation and continuum modelling. Our approach employs a basic idea behind the Gibbs-Duhem Integration and pseudo-ensemble Monte Carlo methods: a macroscopic model is established based on the differential material balances to the adsorption unit and a series of molecular simulations is conducted that integrate along the path described by the model. If an analytical equation of state for the fluid phase is known, the simulation procedure acquires many characteristics of a Monte Carlo simulation conducted in the grand canonical ensemble. The usefulness of the technique is demonstrated through application to a gas separation problem encompassing the major steps of practical value to batch adsorption processes.

Keywords: molecular simulation; adsorption processes; GEMC; GCMC; hybrid modelling

Molecular Modeling of Mercury Porosimetry by F. Porcheron; P. A. Monson; M. Thommes (pp. 325-329).

We present a molecular thermodynamic approach to model mercury porosimetry. A lattice model is used to describe the intrusion/extrusion of mercury into different pore structures. The non-wetting nature of mercury is modeled by setting the wall-fluid interaction of the lattice model to repulsive values. We perform Mean-Field Density Functional Theory calculations on a mesoporous Vycor glass for different temperatures. The shape of the intrusion/extrusion curves is in good agreement with experimental observations. Visualizations of the liquid distribution in the Vycor glass reveal a fragmentation of mercury along the extrusion curve. The calculations performed on ink-bottle pore show that this fragmentation is caused by the snap-off of mercury from the necks leading to a droplet of mercury entrapped into the bottle part of the pore. This phenomenon is likely to play a role in the mechanism of mercury entrapment frequently observed during experiments.

Keywords: mercury porosimetry; lattice model; Vycor

Adsorption of Non Polar and Quadrupolar Gases in Siliceous Faujasite: Molecular Simulations and Experiments by Guillaume Maurin; Robert Bell; Bogdan Kuchta; Thomas Poyet; Philip Llewellyn (pp. 331-336).

The adsorption of non polar (argon, methane) and quadrupolar (carbon dioxide, nitrogen) gases on siliceous Faujasite at ambient temperature and high pressure conditions up to 50 bar, is investigated both experimentally and theoretically by combining Microcalorimetry and Grand Canonical Monte Carlo techniques. The aim of this present work is to evaluate the adsorption isotherms as well as the evolution of the differential enthalpies of adsorption as a function of coverage, for each of the gases under study, and to compare directly results of simulations with our own experimental data. To this purpose, the choice of reliable interatomic potentials required to describe both the adsorbate/framework and adsorbate/adsorbate interactions is crucial. This work is thus based on new transferable pair potential models for methane and carbon dioxide, recently developed by one of the authors using quantum mechanical methods. Finally, we propose a simplified model which can relate the differential enthalpy of adsorption at low coverage to the polarisability of the gases.

Keywords: microcalorimetry; GCMC simulations; Faujasite; differential enthalpy of adsorption; isotherm of adsorption

The Effect of Pore Connectivity on Water Adsorption Isotherms in Non-Activated Graphitic Nanopores by Alberto Striolo; Keith E. Gubbins; Ariel A. Chialvo; Peter T. Cummings (pp. 337-341).

The adsorption of water in graphitic carbons is usually simulated via a weighted average of the adsorption isotherms simulated in carbon-slit pore of different widths. By following this procedure, details about pore morphology and pore connectivity may be overlooked. Towards a better match between virtual and real experiments, we present simulated adsorption isotherms for SPC/E model water in porous carbons composed by interconnected carbon-slit pores. The pores are separated from each other by one graphene layer. Imperfections (lack of carbon atoms) in the graphene layers result in interconnections between pores. The grand canonical Monte Carlo algorithm is used here to simulate water adsorption. Our results show that while the qualitative features obtained in the simulation of independent slit-shaped pores are reproduced when interconnected pores are considered, the adsorption isotherms rise more gradually and the adsorption/desorption hysteresis loops are narrower in the latter case.

Keywords: SPC/E water; carbon-slit pores; grand canonical Monte Carlo simulations

Nitrogen Adsorption on Divalent Cation Substituted X-Faujasites: Microcalorimetry and Monte Carlo Simulation by Guillaume Maurin; Philip L. Llewellyn; Thomas Poyet; Renaud Denoyel (pp. 343-347).

Isotherms, differential enthalpies of adsorption and Henry’s constants were obtained for nitrogen at 300 K on CaX, BaX, SrX and MnX faujasite systems. The experimental data are compared with those obtained by Monte Carlo simulations based on newly derived force fields for describing the interactions between the extra-framework cations and the adsorbates. It is the first time that such good qualitative agreement is reported between experiment and simulation for a series of divalent cations.

Keywords: Microcalorimetry; Monte Carlo simulations; X-faujasite; divalent cations; nitrogen

Effect of Confinement on Chemical Reactions by Erik E. Santiso; Aaron M. George; Malgorzata Sliwinska-bartkowiak; Marco Buongiorno Nardelli; Keith E. Gubbins (pp. 349-354).

Molecular simulation studies of chemical equilibrium for several reactions in pores of slit-like and cylindrical geometry have shown a significant effect of the confinement on the equilibrium compositions, with differences of several orders of magnitude with respect to the bulk fluid phase in some cases. As a first step towards the calculation of rate constants in confinement, we have studied the reaction mechanisms for several reactions involving small organic molecules in slit-like pores. We show results for the rotational isomerization of 1,3-butadiene and the unimolecular decomposition of formaldehyde obtained using plane wave pseudopotential density functional theory (DFT). These examples show the influence that confinement can have through both geometrical constraints and fluid-wall interactions.

Keywords: chemical reactions; confinement; porous carbon; density functional theory

Effects of Activation on the Structure and Adsorption Properties of a Nanoporous Carbon Using Molecular Simulation by Surendra K. Jain; Jorge P. Pikunic; Roland J.-M. Pellenq; Keith E. Gubbins (pp. 355-360).

We present a study on the effects of activation on a saccharose-based carbon using molecular simulation. A constrained Reverse Monte Carlo method is used to build molecular models that match the experimental structure factors of both activated and unactivated carbon, using appropriate constraints for bond angle and coordination number to describe the three body correlation. The semi-coke sample, that is named CS1000, is obtained by pyrolyzing pure saccharose at 1000^∘C under nitrogen flow. An activated form of this carbon, CS1000a, was obtained by heating CS1000 in an atmosphere of CO₂ for 20 hours. We built molecular models for CS1000 and CS1000a and also simulated the TEM images of the model. We perform GCMC simulation of a Lennard-Jones model of Argon on the resulting models to obtain the adsorption isotherms. We then study the difference in the morphology of CS1000 and CS1000a that lead to different adsorption properties in carbon upon activation.

Keywords: Reverse Monte Carlo; molecular simulation; activation; adsorption

Monte Carlo Investigations of the Water Adsorption Behavior in MFI Type Zeolites for different Si/Al Ratios with Regard to Heat Storage Applications by Stefan K. Henninger; Ferdinand P. Schmidt; Tomas Nunez; Hans-Martin Henning (pp. 361-366).

Adsorption processes are turning more and more important for heat transformation applications like thermally driven heat pumps and cooling cycles as well as heat storage. Standard adsorption materials have not been developed for these purposes. New materials are necessary in order to improve the adsorption characteristics for these applications. Molecular simulations are seen as a promising tool to investigate the influence of molecular structure on the adsorption characteristics and thus to provide means for future improvements of such materials for application in heat transformation.Here, Molecular simulations of adsorption isotherms are performed using the Sorption module within Cerius² from Accelrys Inc. Existing Force-Fields are examined for their use in Grand Canonical Monte Carlo Simulation (GCMC) of water adsorption in zeolites. The augmented Consistent Valence Force-Field (CVFF-aug) is currently the best available force-field for use with non-polerizable water models like SPC in zeolite frameworks as reported by Hill and Sauer (1994a). Hence, this force field is used to compare simulated adsorption isotherms with experimental data obtained at Fraunhofer ISE for different types of zeolites.The significance of the Al/Si ratio is investigated with regard to a material optimization for the use in heat transformation applications.Furthermore the role of the extra-framework cations is evaluated as different ions are placed inside the zeolite structure. In the first instance the SPC (Berendsen et al., 1981) water model is used in the simulation.

Keywords: adsorption; monte carlo simulation; water; MFI

Influence of Strength of Atom-Wall Interactions on Adsorption Mechanism by Bogdan Kuchta; Lucyna Firlej; Guillaume Maurin (pp. 367-372).

The influence of the atom-wall interaction on adsorption in 4 nm cylindrical pores has been studied using Grand Canonical Monte Carlo simulations. A model with smooth ideal walls has been used to remove the influence of heterogeneous structures. It has been found that the layering transition pressures strongly depend on the atom-wall interaction. The interaction also defines the number of layers adsorbed below the capillary condensation pressure. It has been observed that the stability of adsorbed layers is modulated by the strength of the atom-wall interaction.

Keywords: adsorption mechanism; nanopores; Monte Carlo simulations; atom-wall interaction

Molecular Dynamics Studies of Two Particles in a Rectangular Box: Hard-Sphere and Square-Well Interactions by Soong-Hyuck Suh; Jae-Wook Lee; Hee Moon; James M. D. Macelroy (pp. 373-378).

Molecular dynamics simulations have been carried out for the simple few-body systems of two particles confined within a 2-dimensional rectangular box. The two different sets of interaction potentials between the colliding particles were employed in these studies: hard-sphere and square-well interactions. Wall pressures, the wall/particle and the particle/particle collision frequencies, and the position autocorrelation functions were computed to examine the thermodynamic, structural and time-dependent properties of such systems. Detailed dynamic effects are discussed to describe configurational particle trajectories including fast/slow relaxation processes observed in the position autocorrelation functions.

Keywords: molecular dynamics simulation; finite few-body system; hard-sphere; square-well

Adsorption of Various Hydrocarbons in Siliceous Zeolites: A Molecular Simulation Study by Pierre Pascual; Hélène Kirsch; Anne Boutin; Jean-Louis Paillaud; Michel Soulard; Bernard Tavitian; Delphine Faye; Alain H. Fuchs (pp. 379-382).

The adsorption of linear, branched and cyclic alkanes in several siliceous zeolites is reinvestigated using a recently developed forcefield based on the anisotropic united atom (AUA) potential scheme with no further readjustment. The simulation model is shown to be reasonably well transferable from on guest-host system to another, enabling thus to predict adsorption equilibria in systems for which experimental data are scarce.

Keywords: adsorption; zeolites; molecular simulation; hydrocarbons

Infrared Spectroscopic Study of Ethylene Adsorbed on Silicalite: Experiments and Molecular Dynamics Simulation by Veronique Bernardet; Armelle Decrette; Jean-Marc Simon; Odile Bertrand; Guy Weber; Ean-Pierre Bellat (pp. 383-389).

The present paper deals with a fundamental infrared (IR) study of the interaction of a gas on a microporous adsorbent at room temperature. Both in situ FTIR spectroscopy and molecular dynamics simulation were carried out to investigate the adsorption process of ethylene on a siliceous ZSM-5 zeolite at 300 K. Orthorhombic aggregates of 18 unit cells of silicalite and molecules of ethylene were simulated using a full atomic model. At a first step, FTIR spectra of the zeolite and the adsorptive were computed separately and compared with experimental spectra. At the second step, spectra of zeolite and ethylene adsorbed were calculated at different loadings and analyzed in shape, location and area, with regard to experimental results. Simulated and experimental data were in good agreement and characterized a continuous adsorption process.

Keywords: adsorption; ethylene; infrared spectroscopy; silicalite; molecular dynamics simulation

Effect of Confinement on Freezing of CCl₄ in Cylindrical Pores by Malgorzata Sliwinska-Bartkowiak; Francisco R. Hung; Erik E. Santiso; Benoit Coasne; Grazyna Dudziak; Flor R. Siperstein; Keith E. Gubbins (pp. 391-396).

We report experimental and molecular simulation results on the freezing and melting of fluids confined within cylindrical pores. Dielectric relaxation spectroscopy was used to determine the experimental melting points of carbon tetrachloride confined within multi-walled carbon nanotubes. Molecular simulations in the grand canonical ensemble and free energy calculations were performed for the same system to determine the structure and thermodynamic stability of the confined phases, as well as the temperatures and the order of the phase transitions. Both simulations and experiments show evidence of a rich phase behavior in confinement, with a number of inhomogeneous phases that are stable over extended temperature ranges. Multiple transition temperatures both above and below the bulk melting point were obtained from experiments and simulations, with good agreement between both series of results.

Keywords: confinement; solid-fluid transitions; molecular simulation; dielectric relaxation; carbon nanotubes

Simulated Water Adsorption Isotherms in Hydrophilic and Hydrophobic Cylindrical Nanopores by Alberto Striolo; Pavanandan K. Naicker; Ariel A. Chialvo; Peter T. Cummings; Keith E. Gubbins (pp. 397-401).

Grand canonical Monte Carlo simulations are performed to study the adsorption of water in single-walled carbon nanotubes (SWCNs). At room temperature the resulting adsorption isotherms in (10:10) and wider SWCNs are characterized by negligible amount of water uptake at low pressures, sudden and complete pore filling once a threshold pressure is reached, and wide adsorption/desorption hysteresis loops. The width of these loops decreases as pore diameter narrows. Adsorption/desorption hysteresis loops are not observed for water adsorption in (6:6) SWCNs. When the nanotubes are doped with small amounts of oxygenated sites it is possible to obtain adsorption isotherms in which the water uptake increases gradually as the pressure increases. Simulated X-ray diffraction patterns for confined water are also reported.

Keywords: SPC/E water; grand canonical Monte Carlo simulations; Debye-functional analysis; XRD pattern

Diffusivities of n-Alkanes in 5A Zeolite Measured by Neutron Spin Echo, Pulsed-Field Gradient NMR, and Zero Length Column Techniques by Hervé Jobic; Jörg Kärger; Cordula Krause; Stefano Brandani; A. Gunadi; A. Methivier; G. Ehlers; B. Farago; W. Haeussler; Douglas M. Ruthven (pp. 403-407).

Diffusion of linear alkanes in 5A zeolite crystals has been studied by several different experimental techniques. In the range C₃–C₈ the diffusivity decreases regularly with carbon number (with a corresponding increase in activation energy) and there is good agreement between ZLC values and the data provided by the “microscopic” techniques (PFG NMR and Quasi-Elastic Neutron Scattering). At higher carbon numbers the agreement between the different techniques is less satisfactory, partly because of uncertainty in the thermodynamic correction factors. The microscopic techniques both show that the monotonic decrease in diffusivity does not continue beyond C₈. The self-diffusivities determined by PFG NMR remain essentially constant with some indication of a weak maximum at C₁₀ while the transport diffusivities measured by the neutron spin-echo technique (NSE) show a clear maximum at C₁₂, reminiscent of the so-called “window effect” (Gorring, 1973).

Keywords: 5A zeolite; alkanes; ZLC; PFG NMR; neutron scattering; diffusion

New Developments in Flow-Through Apparatus for Measurement of Adsorption Mass-Transfer Rates by Frequency Response Method by Yu Wang; M. Douglas Levan (pp. 409-414).

A new flow-through frequency response method based on a sinusoidal modulation of pressure is developed to measure gas adsorption equilibria and kinetics simultaneously. The transfer phenomena of pure N₂ and O₂ gases in carbon molecular sieve are investigated for different pressures and particle sizes by this method. Also, this apparatus has been extended to measure data for mixtures at different compositions at atmospheric pressure and room temperature. This is the first application of the flow FR system for a mixture. A negative cross-term diffusivity is reported. It shows that for co-diffusion, the fast diffusing molecule O₂ is decelerated by the slow diffusing molecule N₂, and the slower moving molecule N₂ is sped up by the faster moving O₂. The main-term diffusivities agree with the pure component diffusivities.

Keywords: frequency response; mass transfer; adsorption rates; carbon molecular sieve

Adsorption Dynamics of Air on Zeolite 13X and CMS Beds for Separation and Purification by Jeong-Geun Jee; Sang-Jin Lee; Heung-Man Moon; Chang-Ha Lee (pp. 415-420).

The adsorption dynamics of N₂, O₂, and Ar in kinetic separation bed with CMS and equilibrium separation bed with zeolite 13X were investigated by using dried air as a feed. In the CMS bed initially saturated with He, Ar was the first breakthrough component showing a small roll-up and N₂ followed at a very close interval. Then, the breakthrough of O₂ occurred with a broad roll-up due to its fast diffusion rate and the relatively slow diffusion rate of N₂. In the zeolite 13X bed initially saturated with O₂, the breakthrough of Ar first occurred with roll-up owing to the strong adsorption of N₂, then the breakthrough of N₂ followed after a very short interval. Based upon these results, the cyclic adsorption dynamics of the zeolite 13X VSA for air bulk separation and CMS PSA for oxygen purification were studied. The five-step two-bed O₂ VSA with zeolite 13X produced O₂ of over 90% purity with high recovery. The MTZ variation of N₂ during the adsorption and vacuum steps was described in detail. In the case of the six-step two-bed PSA process for O₂ purification, O₂ of 99.8+% purity could be produced from the binary mixture (O₂/Ar—95:5 vol.%). The dynamic adsorption behaviors were investigated by using a concentration-dependent rate model incorporated with mass, energy, and momentum balances. The model reasonably predicted the adsorption dynamics at the equilibrium and kinetic separation beds.

Keywords: separation and purification; adsorption dynamics; zeolite 13X; CMS; air

Diffusion Characterization of a Novel Mesoporous Zeolitic Material by Vinh-Thang Hoang; Qinglin Huang; Amir Malekian; Mladen Eić; Trong-On Do; Serge Kaliaguine (pp. 421-426).

The last several years have seen a dramatic increase in the synthesis of new nanoporous materials. The promising ones include mesoporous molecular sieves (MMS) which are being developed as inorganic systems with 20–300 Å in pore dimensions, and having a narrow pore-size distribution. More recently significant efforts have been made to obtain MMS materials with enhanced hydrothermal stability and acidity. UL-zeolites belong to this class of materials in which zeolites are in the form of nano-particles, and are inter-grown in one-dimensional mesoporous structure being used as a matrix, e.g., SBA-15. UL-silicalite is one of the typical representatives of the UL-zeolites. These composite zeolitic materials possess a unique bi-porous structure consisting of micro- and mesopores. The main objective of this study is to characterize UL-silicalite with respect to its transport (diffusive) property and correlate this property with its structure using the zero length column (ZLC) method. n-Heptane, toluene and o-xylene were chosen as probe molecules with different kinetic diameters. Results reveal that the transport process of these probe molecules in UL-silicalite seems to be governed by combined surface/mesopore diffusion in which interconnecting micropores can also make a contribution to the overall transport process. The one-dimensional mesopore structure has strong influence on the overall transport rate. The obtained effective diffusivities of the probe molecules in UL-silicalite were found to be over one order of magnitude higher than in pure silicalite crystals, which were used as reference samples.

Keywords: diffusion; adsorption; micro-mesoporous materials; UL-silicalite; silicalite; ZLC method

Knudsen Diffusion and Viscous Flow Dusty-Gas Coefficients for Pelletised Zeolites from Kinetic Uptake Experiments by Richard S. Todd; Paul A. Webley; Roger D. Whitley; Matthew J. Labuda (pp. 427-432).

A simple volumetric uptake apparatus was used to determine uptake data of N₂ on a sample of LiLSX zeolite for two different particle sizes, two temperatures, and a variety of different dosing pressure levels. Using a mass and energy conservation model for the dosing and sample volumes and the Dusty Gas Model + viscous flow for the mass transfer description at the pellet level, the Knudsen and viscous flow structural parameters were derived. Our analysis gave structural coefficients C_K = 0.0827 ± 0.018 and C_v = 0.0608 ± 0.026 which gave good agreement across all of the experimental runs conducted for both particle sizes and all pressure ranges. From these, tortuosity coefficients for Knudsen and viscous flow were derived and gave τ_K = ε P_,macro/C_K = 3.7 ± 0.8 and τ_v = ε P_,macro/C_v = 5.1 ± 2.2 respectively. These are in good agreement with reported values. The apparatus and procedure is not very sensitive to the viscous flow coefficient but is sensitive to the Knudsen coefficient. All other parameters of the model were measured or determined by calibration experiments. This study suggests that the apparatus may be useful for determination of some of the fundamental structural coefficients employed in the Dusty Gas Model.

Keywords: kinetics; gas; diffusion; uptake; mass; transfer

A Simplified Model for Acoustic Measurement of Diffusion in Microporous Solids by Massimiliano Nori; Stefano Brandani (pp. 433-436).

An analytical model for sound propagation between two layers of a microporous material is presented in order to investigate the application of acoustic techniques for measuring adsorption and diffusion in microporous materials. The attenuation coefficient for the system CO₂—Silicalite crystals is analysed in the range of pressure [2 Torr-3 bar] at T = 304.55 K, and indicates the potential feasibility of a novel experimental technique.

Keywords: microporous diffusion; sound propagation; modelling

Adsorption Dynamics of Water Vapor on Activated Carbon by Jae-Wook Lee; Do-Young Choi; Dong-Heui Kwak; Heung-Joe Jung; Wang-Geun Shim; Hee Moon (pp. 437-441).

The effect of relative humidity on the adsorption of trichloroethylene (TCE) as a representative VOC, was investigated under the practical relative humidity (RH) range of 40–80%. Adsorption equilibria of water and TCE vapors were measured at 293.15, 303.15, and 313.15 K using gravimetric technique. Dubinin-Astakov (DA) and Sips isotherms correlated the measured adsorption data well over the whole pressure range. To investigate the effect of competitive adsorption between water and TCE vapors on hydrophobic activated carbon, adsorption and desorption breakthrough curves were conducted under various humidity conditions in a fixed-bed column. It was found that, under the experimental conditions studied, water vapor in the TCE stream had little effect on the adsorption capacity of TCE up to 80% RH.

Keywords: adsorption; desorption; trichloroethylene; humidity; activated carbon

Adsorbate Transport in Nanopores by Suresh K. Bhatia; Owen G. Jepps; David Nicholson (pp. 443-447).

We present a tractable theory of transport of simple fluids in cylindrical nanopores, considering trajectories of molecules between diffuse wall collisions at low-density, and including viscous flow contributions at higher densities. The model is validated through molecular dynamics simulations of supercritical methane transport, over a wide range of conditions. We find excellent agreement between model and simulation at low to medium densities. However, at high densities the model tends to over-predict the transport behaviour, due to a large decrease in surface slip that is not well represented by the model. It is also seen that the concept of activated diffusion, commonly associated with diffusion in small pores, is fundamentally invalid for smooth pores.

Keywords: transport phenomena; diffusion; nanopores; statistical mechanics; slip flow

Adsorption and Diffusion of N₂ and O₂ in LiLSX Studied by Neutron Scattering Techniques by Herve Jobic; Helmut Schober; Pluton Pullumbi (pp. 449-454).

The vibrational frequencies and diffusivities of N₂ and O₂ adsorbed in LiLSX have been studied by neutron scattering. Experiments were performed with the single components at 260 K, at various loadings. The stretching frequency of N₂ in interaction with Li cations, as observed by inelastic neutron scattering, is compared with quantum chemical calculations. The transport diffusivities of N₂ and O₂ are derived from quasi-elastic neutron scattering, O₂ diffusing faster than N₂. The Darken approximation is found to be inexact, the corrected diffusivities of O₂ and N₂ decreasing with increasing loading.

Keywords: diffusion; nitrogen; oxygen; LiLSX; neutron scattering

Internal Transport Resistances and their Influence on Diffusion in Zeolites as Traced by Microscopic Measuring Techniques by Christian Chmelik; Pavel Kortunov; Sergey Vasenkov; Jörg Kärger (pp. 455-460).

Interference microscopy (IFM) and FTIR microscopy (IRM) are applied to study intracrystalline concentration profiles in SAPO-5, CrAPO-5 and ZSM-5 zeolite crystals. By using both techniques, the high spatial resolution of interference microscopy is complemented by the ability of FTIR spectroscopy to pinpoint adsorbates by their characteristic IR bands. In this way the experimental results are shown to unveil a number of remarkable deviations in the real structure of zeolite crystals from their textbook patterns. The influence of structural defects on the equilibrium concentration profiles as well as on sorption dynamics of guest molecules is investigated. Owing to the ability to gain direct insight into the influence of surface defects and intracrystalline defects on molecular uptake, the applied techniques give more accurate information on the molecular transport in zeolite crystals than the classical uptake methods.

Keywords: zeolite; diffusion; concentration profiles; defects; interference microscopy

Predictions of H₂S Breakthrough Capacity of Activated Carbons at Low Concentrations of Hydrogen Sulfide by Andrey A. Bagreev; Wayne Kuang; Teresa J. Bandosz (pp. 461-466).

In this study a combined approach based on known theoretical solution of a dynamic model, where the parameters of the model are determined from the experimental data at high concentration of an adsorbate is used. The breakthrough time for the required conditions is calculated from the extrapolation of the experimental data fitted by the theoretical equation derived from the model. Parameters of the model used, e.i. kinetics coefficient and the capacity of an adsorbent are found by fitting theoretical and experimental breakthrough curves obtained for high concentrations of H₂S. The results are compared to those collected in “real life” long term tests of coconut shell based activated carbons at North River Water Pollution Control Plant in New York City.

Keywords: adsorption; activated carbon; dynamics; hydrogen sulfide

Micropore Adsorption Dynamics in Synthetic Hard Carbons by Gudrun Reichenauer (pp. 467-471).

The kinetics of the adsorption of CO₂ at 296 K in the micropores of sol-gel derived, monolithic carbons indicates two different types of micropores. While the micropore volume as well as the micropore width of both species turns out to be very similar, their accessibility is significantly different. To study the adsorption kinetics in more detail a set of sol-gel derived hard carbons was prepared with average macropore sizes ranging from about 50 nm to 5 micron at a total porosity of about 85%. To characterize the morphology of the samples small-angle X-ray scattering and N₂ sorption at 77 K were applied. Evaluation of the structural characteristics and the adsorption kinetics of the carbons investigated reveals that the two different types of micropores are homogeneously spread throughout the carbon backbone. The adsorption kinetics in the readily accessible type of micropores is dominated by the gas phase transport through the macropores combined with transport along the inner surface. In contrast, the access to the second category of micropores is highly restricted even at 296 K; this is reflected in equilibration times of about 500 s. The characteristics of the slow adsorption component is almost independent of the macroscopic size and the morphology of the specimen, suggesting that the slow kinetics is controlled by the local accessibility of the micropores. Surprisingly, the equilibrium data of the two adsorption components as a function of the relative pressure reveal that the micropores that are only slowly filled are actually characterized by a lower (Dubinin-Raduskevich) energy and thus a larger micropore width than the ones that are readily filled. This can be interpreted in terms of micropores with a very narrow entrance (restricted diffusion) or a widening of the micropores due to swelling of the carbon upon CO₂ adsorption.

Keywords: adsorption; micropores; restricted diffusion; kinetics; carbon

Dynamics of Carbon Dioxide Breakthrough in a Carbon Monolith Over a Wide Concentration Range by Hyungwoong Ahn; Stefano Brandani (pp. 473-477).

Monoliths, and structured column packings in general, offer the advantage of allowing increased throughput and reduced pressure drops. The performance of a monolith is commonly based on models of an equivalent characteristic channel representative of the system. The HETP or the dispersion of a breakthrough curve are indicative of the separation efficiency of an adsorption column, and what is typically observed is that the experimental results are below expectation. We present a detailed model that we have developed recently, which takes into account the distribution of the size of the monolith channels, the distribution of the wall thicknesses as well as the number of monolith sections in the column. In this contribution, the mathematical model is extended to include nonlinear isotherms and a procedure to determine the equilibrium parameters from a modified moment equation is applied to characterise the system CO₂ on a carbon based monolith. Model predictions, based on independently measured kinetic parameters, are shown to provide an excellent match to the experimental results over a wide range of gas phase concentrations.

Keywords: monolith; carbon dioxide; breakthrough; HETP

Neutron Scattering Study on Dynamics of Water Molecules Confined in MCM-41 by Shuichi Takahara; Shigeharu Kittaka; Toshinori Mori; Yasushige Kuroda; Toshio Yamaguchi; Marie-Claire Bellissent-Funel (pp. 479-483).

Quasi-elastic neutron scattering (QENS) spectra of water-filled MCM-41 samples having different pore sizes (pore diameters: 2.14 and 2.84 nm) were measured over the temperature range 200–298 K and analyzed by a model in which contributions of translational and rotational diffusions of water molecules are expressed by a linear combination of Lorentzian functions (Teixeira et al., 1985). The results indicated that the translational diffusion is decelerated by confinement and that the deceleration increases with a decrease in pore size. QENS spectra of water-filled MCM-41 samples having the same pore sizes (pore diameter: 3.36 nm) but a different amount of the hydroxyl groups (0.7 and 2.6 OH’s/nm²) were also measured over the temperature range 220–298 K. It was found that the vibrational amplitude of water molecules in MCM-41 increases with increasing amount of the surface hydroxyls, which implies that the hydrogen-bond network of confined water is distorted by interaction with the surface hydroxyls.

Keywords: confined water; MCM-41; surface hydroxyls; quasi-elastic neutron scattering; diffusion coefficient

Diffusion of Particles Adsorbed on a Reconstructive Surface by Nataliya A. Tarasenko; Alexander A. Tarasenko; Lubomir Jastrabik (pp. 485-489).

The influence of surface reconstruction on diffusion of particles, adsorbed on the surface, is investigated in the framework of symmetrical four-position model. The analytical expressions for the free energy and chemical and jump diffusion coefficients are obtained assuming the lateral interaction between the particles is negligibly small. The coverage dependencies of the tracer, jump and chemical diffusion coefficients are calculated using the expressions and MC simulations. The results demonstrate clearly a drastic change of the behavior of all diffusion coefficients on the reconstructed surface.

Keywords: lattice gas; surface reconstruction; surface diffusion; phase transitions

2D Automaton Simulation of Bubble Growth by Solute Diffusion in Correlated Porous Media by Carlos Felipe; Raúl H. López; Ana M. Vidales; Armando Domínguez (pp. 491-496).

Simulations of bubble growth in porous media were carried out via a 2D numerical automaton built under a set of hypotheses derived from experimental observations at pore scale. Various types of 2D numerical networks (320× 320 sites and corresponding bonds) were used as models of porous media to study the consequences of the spatial correlation length, ξ_BB, existing among the porous network void entities with respect to the growth of a gas cluster by solute diffusion occurring therein. The studied range was ξ_BB∊ [0.86± 0.12, 10.63± 0.12], in lattice units. The results obtained show that bubble development is truly affected by ξ_BB. The growth law exponent β changes as: β = 4.95 − 0.53 ξ_BB+ 0.04 ξ _BB², while the fractal dimension of the gas cluster body, D_f, varies as: D_f = 1.31 + 0.04ξ_BB.

Keywords: automaton simulation; bubble growth; diffusion; porous media; spatial correlation

Application of Nonlinear Frequency Response to Adsorption Systems with Complex Kinetic Mechanisms by Menka Petkovska (pp. 497-502).

The paper is a contribution to formation of a library of sets of frequency response functions of different orders, for complex kinetic mechanisms typical for adsorption on bidispersed sorbents. The first and second order frequency response functions have been derived starting from a general model, taking into account macro-pore diffusion, micro-pore diffusion, adsorption/desorption kinetics at the micropore mouth and film mass transfer at the particle surface. Simplified models, which neglect one or more mass transfer resistances, were also considered. The frequency response functions were derived for isothermal case, constant diffusion coefficients and planar geometry. The first and second order functions were simulated for the general and for some special cases. Based on these simulation results, some characteristic patterns of the amplitude and phase functions, corresponding to different cases, have been recognized. These patterns can serve as a basis for model and mechanism identification.

Keywords: nonlinear frequency response; adsorption kinetics; complex mechanisms; bidispersed sorbents

Column Dynamics of Benzene Vapor Adsorption on MCM-48 by Wang Geun Shim; Do Young Choi; Seung Phil Choi; Jae-Wook Lee; Hee Moon (pp. 503-507).

Adsorption equilibrium and column dynamics of benzene vapors on various pelletized MCM-48 were examined. The adsorption equilibrium data was measured by gravimetric method. Adsorption equilibria of benzene on pelletized MCM-48 showed a type IV isotherm. In addition, the proposed hybrid isotherm equations described the adsorption data satisfactorily. The adsorbed amount greatly decreased and gradually the structural characteristics of MCM-48 were lost with increasing pelletizing pressure. It was also shown that fixed bed mathematical model with hybrid isotherm simulates the unusual behavior of adsorption breakthrough curves.

Keywords: adsorption; benzene; fixed bed; hybrid isotherm; MCM-48

Influence of Gas-Solid Heat Transfer on Rapid PSA by Shivaji Sircar (pp. 509-513).

A simple analytical model of a Differential Pressure Swing Adsorption (DPSA) process on a single adsorbent particle was used to evaluate the effects of gas-solid heat transfer resistance on the cyclic working capacity of the particle. The commonly used assumption of instantaneous thermal equilibrium between the gas and the adsorbent inside an adsorber may not be valid when the gas flow rates are low, the adsorption kinetics is relatively fast, and the PSA cycle times are small.

Keywords: pressure swing adsorption; heat transfer; efficiency

Compact Pressure Swing Adsorption Processes-Impact and Potential of New-Type Adsorbent-Polymer Monoliths by Andreas B. Gorbach; Matthias Stegmaier; Gerhart Eigenberger; Jochen Hammer; Hans-Gerhard Fritz (pp. 515-520).

The approach considered in this work is based upon the development of novel monolithic adsorbent-polymer materials, featuring low pressure drop and high mechanical stability. The potential is evaluated by comparison with commercial adsorbent pellets used in randomly packed beds. The adsorption of water vapor on a Zeolite 4A-Polyamide compound is considered as example case. Proper models for adsorption equilibrium and kinetics have been fit to measured data and implemented into a detailed PSA process model. This model has been validated by comparison with an experimental setup of a single column rapid PSA unit (RPSA). The productivity of the RPSA process has been analyzed for defined purity and recovery specifications and compared to a conventional design based on adsorbent pellets. The study shows that the novel adsorbent monoliths largely eliminate the kinetic and pressure drop limitations faced in conventional compact design, resulting in a substantial enhancement of productivity.

Keywords: RPSA; adsorbent; monolith; polymer

Integrated Recovery and Recycling of Homogeneous Catalysts by Reverse Flow Adsorption: Selection of Suitable Adsorbents by Jeroen Dunnewijk; Hans Bosch; André B. De Haan (pp. 521-526).

A promising concept for the recovery of homogeneous catalysts is Reverse Flow Adsorption. In actual homogeneous catalyzed processes, a homogeneous transition-metal catalyst is at equilibrium with its free transition-metal center and ligands. Therefore, to apply Reverse Flow Adsorption, a combination of two adsorbents has to be used to reversibly adsorb: the transition-metal center and its ligands. The transition-metal center can be adsorbed by a suitable ligand immobilized onto a solid carrier, while the ligand is adsorbed by an immobilized transition-metal. Two groups of potential adsorbents were selected by the Hard and Soft Acid and Base (HSAB) theory for the adsorption of Co(II) and PPh₃: (1) phosphor (polymer bound PPh₃), sulfur (polymer bound methylsufanylmethyl) and chloride (polymer bound benzylchloride) functionalized adsorbents and (2) metal (Ag⁺, Co^{2 +} and Na⁺) functionalized Amberlyst 15. The CoCl₂ adsorption decreased, as predicted by the HSAB theory, according to: P > S > Cl. Metal functionalized adsorbents adsorbed the PPh₃ with capacities decreasing as predicted by the HSAB theory: Ag⁺ > Co^{2 +} > Na⁺. All adsorption interactions proved to be reversible.

Keywords: reverse flow adsorption; process intensification; recovery; recycling; homogeneous catalysts

Applications of Pressure Swing Adsorption Technology by Christian Voss (pp. 527-529).

Pressure Swing Adsorption (PSA) technology represents an important separation process for gases. In addition to typical integration of PSA units in the plant structures (e.g. combination of steam reformer and H₂-PSA) more complex combinations are possible to optimise the overall process performance. The PSA process itself is strongly influenced by certain process parameters like tail gas pressure, number of pressure equalisation steps etc. PSA units can handle growing throughputs meanwhile they are getting specifically smaller. Sophisticated control systems enhance the performance, flexibility and automation.

Keywords: adsorption; PSA; TSA; hydrogen

New Pressure Swing Adsorption Cycles for Carbon Dioxide Sequestration by Steven P. Reynolds; Armin D. Ebner; James A. Ritter (pp. 531-536).

A rigorous pressure swing adsorption (PSA) process simulator was used to study a new, high temperature PSA cycle, based on the use of a K-promoted HTlc adsorbent and a simple, 4-step, Skarstrom-type, vacuum swing cycle designed to process a typical stack gas effluent at 575 K containing (in vol%) 15% CO₂, 75% N₂ and 10% H₂O. The effects of the purge-to-feed ratio (γ), cycle step time (t_s) (with all four steps of equal time), and pressure ratio (π _T) on the process performance was studied in terms of the CO₂ recovery (R) and enrichment (E) at a constant throughput θ of 14.4 L STP/hr/ kg. R increased with increasing γ and π_T and decreasing t_s, while E increased with increasing t_s and π _T and decreasing γ. The highest E of 3.9 was obtained at R = 87% and π_T = 12, whereas at R = 100% the highest E of 2.6 was obtained at π_T = 12. These results are very encouraging and show the potential of a high temperature PSA cycle for CO₂ capture.

Keywords: pressure swing adsorption; hydrotalcite; carbon dioxide; sequestration; mathematical modeling

Carbon Monoliths: A Comparison with Granular Materials by Barry Crittenden; Andrew Patton; Christophe Jouin; Semali Perera; Steve Tennison; Juan Angel Botas Echevarria (pp. 537-541).

An activated carbon monolith synthesized from a phenolic resin precursor provides capacity and kinetic properties which compare most favourably with the same mass of its granular counterpart. Experimental data have been obtained using a dynamic, flow apparatus. The comparative performances are readily explained by an analysis of internal and external mass transfer coefficients. The effect of axial dispersion is neglected. Internal mass transfer coefficients are based on the linear driving force assumption, being approximated for the monolith by a geometric transformation from the square channel to a hollow cylinder impervious to mass at its outer radius. The monolith is predicted to have a pressure drop which is less than 6% of that of its equivalent granular system.

Keywords: monoliths; activated carbon; volatile organic compounds; linear driving force

Experimental Evaluation of a Multi-Tubular Adsorber Operating with Activated Carbon-Methanol by Antonio Pralon F. Leite; Marcelo Bezerra Grilo; Rodrigo Ronelli D. Andrade; Francisco A. Belo; Francis Meunier (pp. 543-548).

It is the purpose of this work to present an experimental analysis of the thermodynamic cycles in a multi-tubular adsorber of a solar-powered icemaker that uses activated carbon-methanol pair. The experimental cycles were obtained from tests made under different meteorological conditions—mainly the conditions pertaining to cloud cover degree. The system was tested in a Brazilian region close to the Equator (7^∘8′S, 34^∘50′WG) during the period October-December 2003. On a typical clear sky day, the regenerating temperature reached 94^∘C, the condensed methanol mass amounted to 3 kg, and the machine produced 6 kg of ice/m² day at −3.3^∘C, with a net solar coefficient of performance (COP_s) of 0.085. These results were compared to those obtained from a similar prototype that utilizes the same adsorptive pair and an usual flat adsorber, tested in Tunisia (35^∘45′N, 10^∘45′WG).

Keywords: activated carbon; methanol; solar refrigeration

Layered Pressure Swing Adsorption for Methane Recovery from CH₄/CO₂/N₂ Streams by Simone Cavenati; Carlos A. Grande; Alrio E. Rodrigues (pp. 549-554).

In this paper we discuss the performance of Layered PSA (Layered Pressure Swing Adsorption) for methane/carbon dioxide/nitrogen separation for methane upgrading from contaminated natural gas. A four-step PSA cycle was defined using extrudates of zeolite 13X (selective for carbon dioxide) and CMS 3 K (nitrogen selective) in a layered packed bed. Ternary breakthrough curves are reported as well as PSA experiments using a stream composition of 70% CH₄–20% CO₂–10% N₂. Purity of methane of 92% with no carbon dioxide contamination and 43.5% recovery was obtained.

Keywords: kinetic separation; natural gas; Layered Pressure Swing Adsorption

Development of Energy Balances for Fixed-Bed Adsorption Processes: Thermodynamic Paths, Heat Capacities and Isosteric Heats by Krista S. Walton; M. Douglas Levan (pp. 555-559).

This paper provides a simplified treatment of the method of Walton and LeVan (2003) for the development of energy balances for bidisperse particles in fixed-bed adsorption using thermodynamic paths. When adsorbed-phase enthalpy is properly defined, terms involving reference states cancel out of the energy balance, and only gas-phase heat capacities appear in the equation. Calculations show that adsorbed-phase heat capacities may deviate significantly from gas-phase heat capacities when the isosteric heat has a relatively small temperature dependency. Thus, special attention should be given to the path used to derive the energy balance to avoid inconsistencies in heat capacity definitions.

Keywords: energy balance; thermodynamic path; heat capacity; isosteric heat

Dual Reflux PSA Process Applied to VOC Recovery as Liquid Condensate by Reiko Wakasugi; Akio Kodama; Motonobu Goto; Tsutomu Hirose (pp. 561-566).

A new pressure swing adsorption process was proposed for treatment of low-VOC-concentration air streams. Feed gas is supplied to the high pressure column at some intermediate position to divide it into an enriching and a stripping sections. A part of air stream leaving the high pressure column is returned to the low pressure column as stripping reflux while air stream leaving the low pressure column is returned totally to the high pressure column as enriching reflux. With this dual reflux policy, VOC vapor can be enriched in the enriching section up to a concentration high enough to be condensed in liquid state as well as VOC free air is produced in the stripping section. High efficiency of the dual reflux PSA was confirmed experimentally in a lab-scale unit with a model system of ethanol-activated carbon for various parameters such as half cycle time, feed rate, feed inlet position etc. The optimum feed inlet position was found experimentally and its behavior was interpreted based on an analytical simulation by short cycle time approximation.

Keywords: pressure swing adsorption; volatile organic compounds; dual reflux PSA

Solvent Recovery by PSA, an Experimental and a Simulation Study by Kazuyuki Chihara; Hajime Minaki; Tadahiro Aiko; Takashi Kaneko; Shiren Oda (pp. 567-572).

Solvent recovery by pressure swing adsorption (PSA) with resin adsorbent or high silica zeolite was tried and was related with characteristics of each adsorbent, i.e., the adsorption isotherms and the rates of adsorption and desorption. CH₂Cl₂ vapor was chosen as adsorbate. The performance by each adsorbent, shown in terms of the yield against purity of the product gas, was discussed. The high silica zeolite gave better performance than the resin adsorbent in a small-scale experiment, as expected from their isotherms (Chihara et al., 2004). Computer calculations were carried out to simulate the experimental results using the Stop-Go method to show the calculated results coincide well with experimental results. The method is useful to predict the performance of a solvent recovery system operated by PSA. The performance of Dual Reflux PSA which is the new type of PSA method (Wakasugi et al., 2002) was also simulated by this method.

Keywords: PSA; solvent recovery; Stop-Go method

Automatic Control of Simulated Moving Beds—Experimental Verification by Gültekin Erdem; Stefanie Abel; Mohammad Amanullah; Manfred Morari; Marco Mazzotti; Massimo Morbidelli (pp. 573-577).

Simulated moving bed (SMB) chromatography has become the state of the art technology applied for the complex separation tasks in the pharmaceutical and fine chemical industry. Nevertheless, operation of SMB units at their optimal operating conditions is still an issue challenging SMB practitioners due to absence of proper process control schemes. We have developed a feedback control scheme that integrates the on-line optimization and control of SMB units. A significant feature of the developed SMB control concept is that only a minimum of system information has to be provided, i.e., the average packing characteristics of the SMB columns and the linear adsorption isotherm, regardless of the type of isotherm characterizing the mixture to be separated. Therefore a detailed characterization of the columns and the separation system is no longer required. This paper demonstrates the experimental implementation of this control concept and presents results referring to two different experimental runs.

Keywords: simulated moving bed chromatography; RMPC; optimization; control

Thermally Assisted Simulated Moving Bed Systems by Jeung Kun Kim; Nadia Abunasser; Phillip C. Wankat; Andrew Stawarz; Yoon-Mo Koo (pp. 579-584).

The principles of simulated moving bed (SMB) and thermal swing adsorption (TSA) are combined to develop a traveling wave mode, thermally assisted SMB. The four-zone, thermal SMB and the corresponding one-column, thermal Analog to the SMB are studied for separating binary systems with linear isotherms. Design parameters and operating conditions are determined using the local equilibrium theory and detailed simulations are done with the commercially available chromatography/SMB software package Aspen Chromatography v12.1. Simulations were performed for the separation of toluene/xylene with silica gel as the adsorbent and n-heptane as the desorbent. The SMB and Analog are operated with a heat exchanger heating or cooling the fluid before it enters each adiabatic column. The advantage of the traveling wave mode compared to the direct mode of heat transfer is since heat transfer rates are not limiting, the SMB and Analog systems can be scaled up easily.

Keywords: adsorption; SMB; TSA

Electrothermal Desorption in an Annular—Radial Flow—ACFC Adsorber—Mathematical Modeling by Menka Petkovska; Danijela Antov; Patrick Sullivan (pp. 585-590).

A mathematical model of an annular, radial-flow adsorber with the possibility of electroresistive heating of the adsorbent bed has been postulated. The model consists of a set of coupled nonlinear PDEs, ODEs and algebraic equations (material and energy balances for the gas and solid in the adsorbent bed and for the gas in the inlet and in the outlet tube, plus equilibrium relation, criterial equations etc.). The model was solved numerically, using the method of orthogonal collocation for space discretization. It can be used for simulation of adsorption, desorption and TSA processes (cyclic adsorption-desorption). The simulation was used for investigation of the influence of the main process parameters and optimization of the TSA process.

Keywords: electrothermal desorption; radial-flow adsorber; mathematical modeling; optimization; ACFC; TSA

Coupling Chromatography and Crystallization for Efficient Separations of Isomers by Knut Gedicke; Wolfgang Beckmann; Andreas Brandt; Dragomir Sapoundjiev; Heike Lorenz; Uwe Budde; Andreas Seidel-Morgenstern (pp. 591-596).

Within the pharmaceutical industry and in biotechnology there is an increasing need for selective and efficient separation technologies to isolate and purify value-added products. A hybrid process approach combining chromatography and fractional crystallization is studied below. The work presented is concerned with the application and evaluation of this concept in order to isolate a certain pharmaceutical intermediate from a binary mixture. A comparison with performing the same separation exclusively in a single chromatographic process is given also.

Keywords: chromatography; simulated moving bed process; crystallization; hybrid processes

An Energy Flow Analysis of a Solar Desiccant Cooling Equipped with a Honeycomb Adsorber by Akio Kodama; Masashi Ohkura; Tsutomu Hirose; Motonobu Goto; Hiroshi Okan (pp. 597-602).

A solar assisted adsorptive desiccant cooling process has been experimentally tested. This study aimed to investigate an actual performance of the cooling process with a typical configuration (one desiccant wheel, one sensible heat exchanger and two water spray evaporative coolers) driven with solar heated water. The performance was examined in terms of COP_s (thermal coefficient of performance based on solar irradiation), Temperature decrease (temperature difference between outside air and supply air) and cooling effect CE (= enthalpy difference between outside air and supply air) at various operating conditions of regeneration temperature, air condition of ambient air and solar irradiation. Stable irradiation at a clear sky gave the desiccant cooling process a higher dehumidifying performance. Temperature decrease and COP_s in this condition were 10^∘C and 0.41, respectively. Unstable irradiation at somewhat cloudy made the system lower dehumidifying performance. However, decrease of the cooling performance was comparably small due to buffering effect by thermal storage in the circulating water. At higher humidity condition, the amount of dehumidified water became higher than that dehumidified at low humidity condition due to increasing relative humidity of outside air or effective adsorption capacity of the desiccant rotor. However, resulting temperature decrease in this condition was just 6.9^∘C. This behavior is mainly due to humidity increase and simultaneous temperature rise in the dehumidified air. In this situation, an effective evaporation in the following water spray evaporative cooler did not occur.

Keywords: desiccant cooling; dehumidification; adsorbent rotor; solar heat; honeycomb adsorbent

Performance of a Multipass Honeycomb Adsorber Regenerated by a Direct Hot Water Heating by Akio Kodama; Naoki Watanabe; Tsutomu Hirose; Motonobu Goto; Hiroshi Okano (pp. 603-608).

A multi-pass honeycomb rotary adsorber has been proposed to achieve a low temperature heat driven desiccant cooling process. This multi-pass honeycomb rotary adsorber has a sandwich arrangement of honeycomb shaped adsorbent blocks and aluminum passages. In the regeneration step, hot water flows in the passages heating the honeycomb adsorbent. Simultaneously, outside air is co-currently supplied to the adsorbent layer to discharge the desorbed water vapor. On the other hand, adsorption heat caused in the adsorption step can be removed by cool air which is counter-currently passing through inside of the passages to keep the sufficient adsorption capacity/rate. The vaporization heat of water remaining in the passages also accelerates the cooling of the adsorbent rotor. Dehumidifying performance of the above mentioned adsorber has been investigated under various operating conditions, which are air velocity of each sector, temperature of hot water and so on. It was confirmed that the adsorber could be regenerated by direct hot water heating and removal of adsorption heat generated in the adsorption step achieved the semi-isothermal dehumidification. It was also found that lower temperature heat around 50^∘C was still effective in regeneration of the adsorbent rotor although the same temperature air was needed to discharge the desorbed water vapor. At the moment, detailed investigations including the influence of heat transfer between honeycomb rotor and aluminum passage are being carried out to improve the dehumidifying performance.

Keywords: desiccant cooling; dehumidification; adsorption; heat of adsorption

Extended Short Cycle Time Analysis of Pressure Swing Adsorption with Nonlinear Adsorption Isotherm by Takuya Nakamura; Akio Kodama; Motonobu Goto; Tsutomu Hirose (pp. 609-614).

A set of differential equations of material balance for a twin column, two-step PSA (Pressure Swing Adsorption) was expanded into a power series of small value of half cycle time t_c. The effect of finite value of cycle time on the time average product concentration CA₁ started with the second order term and was interpreted by an additional resistance of mass transfer due to the difference in adsorbed amount between adsorption and desorption steps. Finally the column height L or NTU(N_A = K_A amL/u) required to obtain a given concentration of product gas CA₁ was given by the following closed form equation for both linear and nonlinear isotherms $$igg{{frac{1}{N_A} + frac{u_A}{u_D}frac{1}{N_D} + frac{1}{ u _Delta}} igg}^{- 1} = int_{C_{A1}}^{_ 1} {frac{dC_A}{G(C_A) - G(C_D)},}quad hbox{with}quad C_D = frac{p_D}{p_A}C_{A1} + frac{u_D}{u_A}(C_A - C_{A1})$$ in which parameters Ka, L, m, p and u are overall volumetric mass transfer coefficient, column length, adsorption coefficient, pressure and superficial gas velocity, respectively. Subscript A and D refer to adsorption and desorption steps. The function G(C) is a dimensionless adsorption isotherm and the term 1/ν_Δ is the above mentioned additional mass transfer resistance proportional to square of t_c. The performance prediction by the equation agreed well with more rigorous numerical solutions over a wide range of cycle time by introducing the additional resistance 1/ν_Δ. The concentration swing Δ CA₁, i.e. concentration difference during a half cycle time, was also discussed in a frame of the same concept.

Keywords: adsorption; pressure swing adsorption; short cycle time approximation; analytical solution

Simulation and Optimization of a Pressure Swing Adsorption System: Recovering Hydrogen from Methane by Seth P. Knaebel; Daeho Ko; Lorenz T. Biegler (pp. 615-620).

Recent developments in the fuel cell industry have yielded an increase in expected demand for a pure hydrogen source; one attractive method for meeting this demand involves separating hydrogen from a hydrogen-methane mixture using pressure swing adsorption (PSA). In designing PSA systems, the selection of the adsorbent and operational flowsheet are the most important and limiting decisions; beyond this, implementing systematic methods to find optimal operating conditions and bed parameters is essential. These decision variables include flowrates, bed pressures, step times and bed dimensions. This research examines this PSA system via dynamic simulation and optimization; the primary purpose of the optimization is to maximize the recovery of the key components while meeting both the hydrogen purity and cyclic steady state requirements. In this study, the process model is formulated for this separation using gPROMS. The model discretizes the spatial domain, and binary variables are used to adjust the boundary conditions for the bed as the system runs through the four-step PSA cycle. Two alternative PSA cycles are simulated, optimized and compared to assess the best performance for this PSA separation.

Keywords: PSA; process simulation; process optimization

Propylene Recovery from Propylene/Propane/Nitrogen Mixture by PSA Process by Sang-Sup Han; Jong-Ho Park; Jong-Nam Kim; Soon-Haeng Cho (pp. 621-624).

This study is on the process performance (purity, recovery and productivity) of a four-bed bench-scale PSA unit [1000 mm (L) × 25 mm (ID) × 4 beds], with which is applied to enrich propylene from propylene/propane/nitrogen gas mixture (35 mol% propylene, 15 mol% propane, 50 mol% nitrogen). Adsorbent, i.e. AgNO₃ impregnated on silica substrate, was prepared and loaded in the above PSA unit. The unit was operated at the pressure of 25–870 mmHg and at the temperature of 10–70^∘C. By a four-bed PSA process at 50^∘C, the propylene product purity and recovery were 91.9 mol% (7.0 mol% propane, 1.1 mol% nitrogen) and 86.5%, respectively. More than 99% of nitrogen was removed from the feed. The propylene productivity by the process was 0.89 mol/(kg ⋅ hr).

Keywords: adsorption; propylene; polypropylene process off-gas; π-complexation; pressure swing adsorption

Improved Purge Step in Pressure Swing Adsorption for CO Purification by Hideki Miyajima; Akio Kodama; Motonobu Goto; Tsutomu Hirose (pp. 625-630).

Supported Cu⁺ on activated carbon carrier was used to enhance the CO selectivity and thus to produce high concentration CO gas in a single stage CO-PSA which simulated a commercial 4-beds system operating in six steps (equalization, blow down, purge, desorption, repressurization and adsorption). Since the adsorbent adsorbed CO by chemisorption very strongly, we decided that a system should be high-pressure adsorption (500 kPa) and vacuum-desorption (9 kPa). In the conventional cycle operation, the total amount of purge gas has great influence on CO recovery because this system uses a part of product CO as purge gas. We focus our discussion on the effect of purge step and propose a new CO-PSA system using the Variable Purge gas Concentration Method (VPCM for short). The VPCM method was found to be able to reduce the product CO amount consumed for purge and thus to improve CO yield without any product purity reduction.

Keywords: adsorption; pressure swing adsorption; carbon monoxide; purification

Experimental Study on a Process Design for Adsorption Desiccant Cooling Driven with a Low-Temperature Heat by Kosuke Ando; Akio Kodama; Tsutomu Hirose; Motonobu Goto; Hiroshi Okano (pp. 631-636).

Among the desiccant cooling process, 2-rotor process consisting of a honeycomb rotor dehumidifier and a sensible heat exchanger is the mainstream of the cooling processes which are practically applied to supermarket, hospital and so on. Most of them are driven with a higher regeneration temperature around 100–140^∘C obtained from gas-engine heat pump or micro gas turbine generator. However, dehumidifying performance of this typical configuration driven with a low temperature heat is not sufficient for cooling at higher ambient humidity. In this study, 4-rotor desiccant cooling process equipped with a double stage dehumidification was proposed and investigated experimentally. In this process, regeneration temperature around 70^∘C could produce a sufficient dehumidifying performance at high ambient humidity. Furthermore, the cascade use of hot water inside the cooling cycle was applied and confirmed somewhat lower cooling performance than that operated with parallel supply of hot water. Against this result, COP_r of the former was much higher than that of the latter. Effect of water spray evaporative cooling at the inlet of regeneration air stream on the process performance was also investigated. This evaporative cooling was expected to cause humidity increase in regeneration air reducing the dehumidifying performance of the honeycomb absorber, while the evaporative cooling plays an important role to produce a lower temperature in supply air. Experimental results showed that the amount of dehumidified water at the process without water spray evaporative cooler was actually larger than that of process with water spray evaporative cooler. This behavior was due to increase of humidity or relative humidity in the regeneration air as expected. However, temperature of supply air produced by the process with evaporator was rather lower than that of the other, resulting higher COP value. It was concluded that the evaporative cooler effectively worked at higher regeneration temperature and lower ambient humidity.

Keywords: desiccant cooling; dehumidification; adsorption; evaporative cooling

Adsorption on Kureha Activated Carbon: Isotherms and Kinetics by Weidong Zhu; Freek Kapteijn; Johan C. Groen; Jacob A. Moulijn (pp. 637-641).

Adsorption equilibria and kinetics of butane isomers in Kureha activated carbon were investigated using a volumetric method and the tapered element oscillating microbalance (TEOM). The isotherm data measured by the TEOM technique are in good agreement with those determined by the volumetric method. The Tóth model appropriately describes the equilibrium data. The model used to describe the desorption profiles determined with the TEOM is based on the overall transport kinetics controlled by both micropore diffusion and mass transfer across the gas film around the adsorbent particles. The conventional Darken relation fails to capture the concentration-dependent diffusion in Kureha carbon. Alternatively, the structural model proposed by Do (1996) well describes this stronger concentration-dependent micropore diffusion.

Keywords: activated carbon; TEOM; Tóth isotherm; micropore diffusion; modelling

Modeling of Organically Functionalized Mesoporous Silicas for the Design of Adsorbents by Chrisitan Schumacher; Nigel A. Seaton (pp. 643-648).

In order to obtain atomic-level models for hybrid inorganic-organic adsorbents that are based on ordered mesoporous silicas, molecular simulation methods have been developed which follow the reaction path of the synthesis of the silica material in a kinetic Monte Carlo Simulation. Organic surface groups such as phenyl or aminopropyl are introduced by replacing surface hydroxyl groups. The adsorption in these models is simulated by Grand Canonical Monte Carlo simulation. The experimental and simulated adsorption isotherms of ethane and carbon dioxide on MCM-41-based hybrid adsorbents agree well. In combination, these methods enable the computer-aided design of hybrid inorganic-organic adsorbents.

Keywords: mesoporous silica; MCM-41; functional groups; adsorption; molecular simulation

Adsorptivity Control and Microcalorimetric Characterization of Silanized Ordered Porous Silica by Akihiko Matsumoto; Takahiro Kogawa; Kazuo Tsutsumi (pp. 649-652).

Microporous silica (PS) with an ordered pore array of two-dimensional hexagonal symmetry was successfully prepared by regulated hydrolysis and co-condensation of tetramethoxysilane in decyltrimethylammonium bromide solution. The porous silica, PS, was silanized by 2-(3,4 epoxycyclohexyl) ethyltriethoxysilane to control hydrophilicity of the surface (PS-echx). The pore size of PS-echx was 0.8 nm, which is intermediate size between those of microporous aluminosilicate zeolites and conventional mesoporous silica, MCM-41 and MCM-48. PCS-echx exhibited significant water adsorptivity at low relative pressure region (P/P₀ = 0.2), and low differential heats (44 and 50 kJ/mol, for the first and the second adsorption runs, respectively).

Keywords: adsorption; heat of adsorption; mesopore; micropore; silica; water

Characterization of Worm-Like Micro- and Mesoporous Silicas by Small-Angle Scattering and High-Resolution Adsorption Porosimetry by Bernd Smarsly; Matthias Thommes; Peter I. Ravikovitch; Alexander V. Neimark (pp. 653-655).

Mesoporous silica with worm-like pores of 9–10 nm in size were studied by small-angle neutron scattering (SANS) and high-resolution porosimetry, using nitrogen at 77 K and argon at 87 K. The pore sizes determined from SANS are in excellent agreement with those obtained from a recently developed non-local density functional theory (NLDFT) approach. Furthermore, the additional micropores in the mesopore walls could be quantified by SANS and physisorption, and again good agreement between both methods was observed. Our results clearly demonstrate that the NLDFT approach allows an accurate determination of the pore size distribution of materials which contain both narrow micropores and mesopores larger than 10 nm.

Keywords: SANS; nitrogen sorption; mesoporous silica

Investigation of Structural and Adsorptive Characteristics of Various Carbons by S. V. Mikhalovsky; V. M. Gun’Ko; V. V. Turov; R. Leboda; W. R. Betz (pp. 657-662).

Structural and adsorption properties of carbon sieves, activated carbons and graphitized carbon blacks were studied using adsorption of nitrogen, water, and high molecular organics. Several types of pore models were used to study the pore size distributions (PSD) of the adsorbents. The interfacial behavior of water adsorbed in the presence of organics depends on both the surface chemistry of an adsorbent, its structure and the characteristics of organics. A smaller size (1–10 μm) of particles of microporous Carboxen 1010 than that of Carboxen 1003 (150–200 μm) provides initially faster adsorption of lipopolysaccharide (LPS) molecules by the first carbon. However, the LPS adsorption on micro/meso/macroporous Carboxen 1003 becomes greater with time since this carbon has broad pores appropriate in size for the adsorption of large biopolymer molecules in contrast to Carboxen 1010, which adsorbs LPS mainly on the outer surface of the particles.

Keywords: carbon adsorbents; structural and adsorption characteristics; interfacial water; polymer adsorption

Preparation of Carbon Molecular Sieves by Pyrolytic Carbon Deposition by Carlota Gómez De Salazar; Antonio Sepúlveda-Escribano; Francisco Rodríguez-Reinoso (pp. 663-667).

The effect of different preparation parameters (pyrolysis temperature, process time, benzene concentration and residence time) on the properties of carbon molecular sieves obtained by pyrolytic carbon deposition from benzene on a microporous activated carbon, has been studied. For a fixed process time of 2 h, the increase of the pyrolysis temperature from 525 to 700^∘C produced a strong increase of the CO₂/CH₄ selectivity, reaching a maximum value of 13 for pyrolysis at 700^∘C. Selectivity also increased with process time (up to 5 h, with the pyrolysis temperature fixed at 650 and 675^∘C), yielding values as high as 28. The obtained results have allowed to find the optimal preparation parameters for the preparation of CMS with high selectivity.

Keywords: carbon molecular sieves; carbon deposition; adsorption; separation

Production and Characterization of Carbonaceous Adsorbents from Biomass Wastes by Aqueous Phase Carbonization by Kazuhiro Mochidzuki; Nobuaki Sato; Akiyoshi Sakoda (pp. 669-673).

This paper deals with a method to produce carbonaceous adsorbents from biomass using a technique of aqueous phase carbonization (hydrothermal carbonization). A series of laboratory-scale tests to produce carbonaceous materials from existing biomass such as Japanese cedar, which is a typical construction material in Japan, were conducted. The biomass feedstock was subjected to (1) hydrothermal carbonization at 350^∘C, followed by (2) hydrothermal oxidation at 350^∘C with the existence of hydrogen peroxide and (3) short-tome heat treatment at 950^∘C in a closed crucible with no water. Thus-obtained carbonaceous materials were found to have mesoporous structures with ca. 350 m²/g of specific surface area and the adsorption capacity for phenol could reach to around three-quarters of that of a commercial activated carbon.

Keywords: adsorption; biomass; mesoporous adsorbent

Reversible Adsorption/Desorption of Target Molecules with Novel Temperature-Sensitive Heteropolymer Gels by Yoshio Nakano; Maki Saito; Yoshitsugu Hirokawa (pp. 675-678).

SSS-VBTA gel was synthesized with sodium styrene sulfate (SSS) and vinylbenzyl trimethylammonium chloride (VBTA). The SSS-VBTA gel was found to show the thermo-reversible changes in its volume and properties, that is, shrunken and hydrophobic state at around room temperature while swollen and hydrophilic state at above room temperature. It was revealed that the SSS-VBTA gel concentrated trace amounts of Bisphenol-A present in very dilute aqueous solutions at around room temperature and released the concentrated Bisphenol-A above room temperature.

Keywords: adsorption; temperature-sensitive; gel; reversible

Growth Mode of Hydrogen in Mesoporous MCM-41. Adsorption and Neutron Scattering Coupled Studies by Nicole Floquet; Jean Paul Coulomb; Philippe Llewellyn; Gilles Andre; Remi Kahn (pp. 679-684).

X-ray or neutron diffractograms of calcined MCM-41 samples are strongly modified during the sorption phenomenon. Intensity of the main (100) peak (I₁₀₀) could undergo a non monotonous behaviour. At the sorption beginning I₁₀₀ increases and I₁₀₀ strongly decreases in the medium and high loading regimes. These observed intensity modifications in the diffractograms are closely related to the MCM-41 sample and to the filling mechanisms of its porosity. Actually each synthesis produces MCM-41 sample with its own silica wall and porosity. Several MCM-41 structural models and adsorption filling modes were attempted to fit all the diffractograms recorded during the D₂ adsorption in a MCM-41 (Ø = 25 Å) sample at T = 16.4 K. Our data agree with a MCM-41 having low density silica walls (20% voids) that is rarely reported. Consequently, the D₂ adsorption mechanism is proved to be more defined: at the low relative adsorption pressure D₂ fills the wall voids and forms a layer on the rough wall surface. Then at the relative pressure of the capillary step, D₂ fills the whole free MCM-41 mesopores. Even the solid capillary phase does not grow layer by layer on the inner pore walls but is growing up along the pore axis.

Keywords: MCM-41; porous structure; neutron diffraction; hydrogen sorption; filling modes

Adsorption Characterization of Ordered Mesoporous Silicas with Mercury-Specific Immobilized Ligands by Oksana Olkhovyk; Mietek Jaroniec (pp. 685-690).

Nitrogen adsorption was employed to study the surface properties of organically modified ordered mesoporous silicas (OMS) of different structures as potential adsorbents for environmental applications. MCM41, MCM48, and SBA15 materials were functionalized via post-synthesis, one-pot synthesis and template-displacement synthesis with organic ligands containing mono- or multiple binding sites for heavy metal ions adsorption. Nitrogen adsorption isotherms at 77 K were used to evaluate the specific surface area, pore volume, pore size and pore accessibility of OMS after surface modification. It is shown that the adsorption and structural properties of OMS can be tailored by introducing multifunctional ligands of desired affinity towards mercury ions.

Keywords: adsorption; mercury removal; ordered mesoporous organosilica; surface modification

Polydisperse Adsorption Characteristics of Aqueous Organic Matrices in Water and Wastewater Sources by Fusheng Li; Akira Yuasa; Yoshihiko Matsui; Eun-Jeong Cheong (pp. 691-696).

Batch adsorption isotherms of fourteen dissolved organic matrices (DOMs) from river water, ground water, wastewater and commercial sources were measured using lumped quality indices of DOC and UV260, and analyzed using a distributed fictive component method. By accounting for the heterogeneity of DOM constituents with a log-normal distribution of Freundlich K, the adsorption equilibrium of each DOM was characterized by searching for only three parameters. Indicating strong adsorbability dependency upon the sources and types of DOMs, the distribution ranges of the Freundlich K differed markedly. Compared to a river water DOM that had a K range in 10.8–190 (mg/g)/(mg/l)^1/n, a commercial humic acid was found most heterogeneous: K varied in 0.01–1494.3 (mg/g)/(mg/l)^1/n. In addition, based upon chromatographic results measured using a HPSEC system for all DOMs before and after adsorption, preferential adsorption of small molecular weight constituents was revealed for commercial humic acids; for aquatic organic matrices, however, such a trend was not found.

Keywords: NOM; humic matter; adsorption; molecular weight distribution; isotherm

Cellulose Based Adsorbent Materials for the Dehydration of Ethanol Using Thermal Swing Adsorption by Tracy J. Benson; Clifford E. George (pp. 697-701).

In this study, a thermal swing adsorption (TSA) column was used to evaluate the effectiveness of three ligno-cellulose based adsorbents on the removal of water from ethanol/water mixtures of 90, 95, and 97 wt% ethanol. The three adsorbents studied were bleached wood pulp, oak sawdust, and kenaf core. A glass adsorption column with an inside diameter of 2.54 cm was used to generate breakthrough curves to determine the effectiveness of the adsorbents and to allow comparability with starch based adsorbents that are currently used within the ethanol industry. Experimental results indicate that water is preferentially adsorbed allowing for complete dehydration of ethanol. Also, an evaluation has been made of the mass transport properties for the diffusion of water molecules into the porous matrices of the adsorbents as well as the length and velocity of the mass transfer zone.

Keywords: adsorption; ethanol; water; ligno-cellulosics; dehydration

Structural and Energetic Characteristics of Silicas Modified by Organosilicon Compounds by V. M. Gun’ko; V. I. Zarko; D. J. Sheeran; S. M. Augustine; J. P. Blitz (pp. 703-708).

Structural and adsorptive characteristics of unmodified and modified silica gels Davisil 633 and 643, and fumed silica Cab—O—Sil HS-5, were analyzed on the basis of nitrogen adsorption isotherms. The properties of aqueous suspensions of the initial and modified fumed silicas were also studied. Deviation of the pore shape from simple models, cylindrical pores for silica gels and gaps between spherical particles for fumed silica, increases for modified silicas.

Keywords: silica; modification; adsorption; pore shape; aqueous suspension

Selenium and Carbon Nanostructures in the Pores of AlPO₄-5 by Thomas Roussel; Christophe Bichara; Roland J.-M. Pellenq (pp. 709-714).

A Tight Binding Grand Canonical Monte Carlo (TB-GCMC) simulation of the adsorption of selenium and carbon in ALPO₄-5 zeolite is presented. We show that the structure of confined Se varies from a stretched chain to a piling of Se₅ rings, with intermediate structures combining chains and rings, while that for carbon reveals the mechanism for producing ultra small nanotubes. In the case of selenium, the ring structures are favored at low temperature and high pressures while chains are stable at higher temperatures and lower pressures. The diversity of carbon bonding allows to form chains, in-chain loops that transform into aromatic clusters and eventually tubes. These results are in qualitative agreement with recent experimental results.

Keywords: adsorption; Grand Canonical Monte-Carlo simulation; selenium nanostructures; carbon nanotubes

Influence of Presence of Inert Impregnant (NaCl) on Adsorptive Characteristics of Activated Carbon by Stefan Zietek; Andrzej Swiatkowski; Radoslaw Szmigielski; Dorota Palijczuk; Jadwiga Skubiszewska-Zieba (pp. 715-718).

Influence of presence of inert impregnant (NaCl) on adsorptive properties of activated carbon was studied by breakthrough dynamics, and nitrogen adsorption. It was noticed that contribution of inert impregnant (NaCl) had fundamental influence on volume of micro-, mesopores and breakthrough times.

Keywords: activated carbon; adsorption; breakthrough

Adsorption and Desorption Characteristics of Maltooligosaccharide for the Surface Treated Activated Carbons by Jung-Wook Yoo; Tae-Young Kim; Sung-Yong Cho; Seon-Gyun Rho; Seung-Jai Kim (pp. 719-723).

The adsorption and desorption characteristics of maltooligosaccharide for raw and surface treated activated carbons were studied experimentally. The TLC imaging densitometry method was used in determining the sugar concentration in the maltooligosaccharide. Adsorption amount of larger molecules, such as maltopentaose and maltoheptaose on F400 were greater than those of smaller molecules. On the other hand, Adsorption amount of smaller molecules, such as maltose and maltotriose on SLS103 were greater than those of larger molecules. Acid treatment of the GAC increases the carboxyl group, but did not affect much on the adsorption rate of saccharides. Heat treatment decreases the adsorption time of F400 due to substantial surface area increase. For the desorption of the adsorbed saccharides with ethanol, the amount of ethanol in the solution was more important than the concentration.

Keywords: activated carbon; adsorption; desorption; maltooligosaccharide; thin-layer chromatography (TLC)

Synthesis and Adsorption Characteristics of Nanoporous Graphite-Derived Carbon-Silica Composites by Zheng-Ming Wang; Miki Yamagishi; Yinghao Chu; Takahiro Hirotsu; Hirofumi Kanoh (pp. 725-730).

A novel nanoporous C/SiO₂ composite was synthesized using graphite precursor by a soft chemical method and its adsorption properties were characterized by nonane, water, and nitrogen adsorption. It was found that only one part of micropores can strongly confine nonane molecules, indicating a wide micropore size distribution. Water adsorption leads to disappearance of one part of micropores, possibly due to closing of pores by dissociative adsorption of water on defective sites. Fractal analysis of the original and the differential nitrogen adsorption isotherms indicate that micropores have a rougher surface and mesopore a flatter surface, suggesting that micropores are surrounded by silica particles and mesopores involve the flat carbon layers.

Keywords: nanoporous; C/SiO₂ composite; adsorption

Mercury Ion Recovery Using Natural and Crosslinked Chitosan Membranes by Rodrigo S. Vieira; Marisa M. Beppu (pp. 731-736).

The adsorption and desorption of Hg(II) ions onto natural and crosslinked chitosan membranes were investigated. Batch adsorption experiments were carried out as function of pH, concentration of Hg(II) ions, type of crosslinking (glutaraldehyde (GLA) or epichlorohydrin (ECH)) and desorbent solution (NaCl (1M) or EDTA (10⁻⁴ M)). Isotherm studies indicated that Hg(II) ions can be effectively removed by chitosan membranes, mainly by the glutaraldehyde-crosslinked chitosan, at pH = 6.0, and can be easily removed by elution with NaCl (1M) solution.

Keywords: adsorption; desorption; chitosan; crosslinking; mercury

Comparison of Adsorption Properties of Polymer-Templated Mesoporous Silicas with Incorporated Niobium by Izabela Nowak; Mietek Jaroniec; Maria Ziolek (pp. 737-743).

Two types of Nb-containing mesoporous materials were studied: (i) NbSBA-15 with 2D-hexagonal structure and (ii) NbFDU-1 with cage-like structure. The elucidation of the pore connectivity and the pore blockage on the basis of nitrogen and argon desorption isotherms combined with FTIR and H₂-TPR studies is presented for niobium-containing materials. Moreover, the surface properties are studied by FTIR with NO, while the catalytic activity is examined by sulfide and cyclohexene oxidation with hydrogen peroxide.

Keywords: adsorption; catalysis; niobium; polymer-templating synthesis

Adsorption Monitoring of Hydrothermal and Thermal Stability of Polymer-Templated Mesoporous Materials by Ewa B. Celer; Michal Kruk; Mietek Jaroniec (pp. 745-750).

The thermal and hydrothermal stability of FDU-1 silica with ordered, large (~10 nm), cage-like mesopores was studied using nitrogen and argon adsorption at −196^∘C. It was confirmed that FDU-1 silica retains uniform mesoporosity even after heating for 5 hours at 950–1000^∘C. Although typical FDU-1 silicas and other polymeric-templated silicas with large cage-like mesopores tend to be significantly microporous, the FDU-1 sample calcined at 1000^∘C appeared to be essentially free from microporosity, as can be inferred from the relation between its surface area, pore volume and pore diameter. This result suggests that high-temperature calcination can be used to synthesize model mesoporous adsorbents with large cage-like (spherical) mesopores. Evidence of the concomitant decrease in the pore diameter and the pore entrance size with an increase in the calcination temperature is presented. The structural stability of FDU-1 during heating in water at 100^∘C for 2, 4, and 8 days is additionally demonstrated.

Keywords: argon adsorption; ordered mesoporous silica; pore size distribution; thermal stability

Studies on Selective Adsorbents for Oxo-Anions. NO₃⁻ Adsorptive Properties of Ni-Fe Layered Double Hydroxide in Seawater by Satoko Tezuka; Ramesh Chitrakar; Akinari Sonoda; Kenta Ooi; Tahei Tomida (pp. 751-755).

We report the selective adsorptive properties for NO₃⁻ in seawater of Ni-Fe layered double hydroxide (LDH (Ni-Fe)), containing Ni and Fe metal atoms in each layer. LDH (Ni-Fe) with Cl⁻ in the interlayers was synthesized by co-precipitation at constant pH. It showed a higher distribution coefficient (K_d) for NO₃⁻ than for other anions (HPO₄^{2 −}, SO₄^{2 −} etc.). NO₃⁻ adsorption on LDH (Ni-Fe) was also studied batchwise using NO₃⁻ enriched seawater (NO₃⁻ concentration: 40 μ mol/dm³). The NO₃⁻ uptake attained equilibrium after the adsorption for 4 h. The adsorption isotherm followed Freundlich’s equation. The NO₃⁻ uptake reached 0.33 mmol/g when LDH (Ni-Fe) (0.10 g) was added to NO₃⁻ enriched seawater (1 dm³), corresponding to the removal of 83% NO₃⁻ from seawater. The pH dependence of NO₃⁻ adsorption showed a maximum NO₃⁻ uptake at around pH 8 with low Ni dissolution (less than 0.6%). This adsorbent is therefore promising for the selective removal of NO₃⁻ from seawater for the benefit of the environment.

Keywords: selective adsorption; nitrate ion; layered double hydroxide; seawater; environment

Adsorptive Properties of Biobased Adsorbents by Leszek Czepirski; Ewa Komorowska-Czepirska; Joanna Szymońska (pp. 757-761).

Water and methanol vapor adsorption isotherms for native and modified potato starch were investigated. For obtaining the best fit for the experimental data several models based on the BET approach was evaluated. The hypothesis that water is adsorbed on the starch granules at the primary and secondary adsorption sites as well as a concept considering the adsorbent fractality were also tested. It was found, that the equilibrium adsorption points in the examined range of relative humidity (0.03–0.90) were most accurately predicted by using a three-parameter model, proposed by Kats and Kutarov (1998). For methanol a good representation of experimental data was obtained using model proposed by Talu and Meunier (1996).

Keywords: bio-based adsorbents; water and alcohols adsorption; BET model; fractal dimension

Preparation and Characterization of Nanoporous Ceria Containing Heteroatoms, With and Without a Matrix by Charis R. Theocharis; Georgia Kyriacou; Maria Christophidou (pp. 763-767).

We have been interested in the synthesis and study of porous ceria, because of its importance in several catalytic applications, and notably in automobile exhaust catalysts. The mesoporosity of these solids is susceptible to changes in synthesis conditions such as pH and concentration of the cerium and other cations precursors used. The use of organic matrices to control pore production during synthesis, was also investigated. In this contribution we present results from the synthesis of mixed Mn(III/IV) cerium (IV) oxide precipitated from aqueous solution. The interest presented by these samples was that they had higher BET surface area as well as pore volume than the pristine ceria. The samples were studied using nitrogen adsorption, X-ray diffraction, diffuse reflectance FTIR (DRIFTS) and TGA.

Keywords: adsorption; ceria; template; manganese (III); FTIR spectroscopy

Preparation of Active Carbons for Adsorption Cooling System by Bronislaw Buczek; Eliza Klimowska; Elzbieta Vogt (pp. 769-773).

Among the gas–solid adsorption processes the active carbon methanol adsorption seems to be interesting for use in thermodynamic systems such as heat pumps and cooling systems. The porous structure of active carbon modified by successive removal of external layers from a particle surface as produced by abrasion in spouted bed, next by demineralization and oxidation was evaluated on the basis of nitrogen adsorption data and those for methanol. The aim of this study was to test the improvement of texture and nature of surface of active carbon for adsorption refrigeration system.

Keywords: adsorption; refrigeration; active carbon-methanol pair

Propane/Propene Separation by SBA-15 and π-Complexated Ag-SBA-15 by Carlos A. Grande; Norberto Firpo; Elena Basaldella; Alírio E. Rodrigues (pp. 775-780).

Synthesis, characterization and adsorption properties of propane/propylene on mesoporous SBA-15 are reported. This material was also used as high surface area material for silver deposition to enhance propylene adsorption improving selectivity towards the olefin. Two different silver loadings were tested: Ag/SiO₂ = 0.5 and Ag/SiO₂ = 1.0. With the lower silver content, better selectivity and amount adsorbed was obtained. Preliminary studies were done for the use of this adsorbent in Vacuum-Pressure Swing Adsorption (VSA-PSA) units. With a four-step cycle comprising feed, pressurization, rinse and blowdown recovery of 97% propylene with chemical grade purity (91%) was obtained and also fuel grade HD-5 propane at high pressure. If higher propylene purity is required, a five-step cycle has to be used (pressurization, feed, rinse, co-current depressurization to intermediate pressure and counter-current blowdown). In this case, purity of 99% was obtained with 63% recovery.

Keywords: SBA-15; π-complexation; propylene; adsorption; Pressure Swing Adsorption

Removal of Adsorbed Organic Impurities from Surface of Spent Catalysts Pd/Activated Carbons by Lidia Dabek; Andrzej Swiatkowski; Jerzy Dziaduszek (pp. 781-785).

Influence of method and conditions of spent Pd/AC catalyst regeneration on its catalytic activity was studied. It has been stated that supercritical fluid extraction (CO₂) followed by heating in hydrogen atmosphere is an effective method of that catalyst regeneration. The results of FTIR and XPS investigations indicate that regeneration of a spent Pd/AC catalyst, irrespective of the reaction in which it has been used, should be based on the complete removal of by-products and cleaning the catalyst surface as well as on restoring the original form of the palladium. Proposed in this paper procedure i.e. SFE (CO₂) and heating in H₂ fulfils both above mentioned conditions.

Keywords: Pd/activated carbon catalyst; spent catalyst; regeneration

Evaluation of Polytetrafluoroethylene Surfaces by Nitrogen Physisorption and the Effects of Alkali Etching by E. Loren Fuller Jr. (pp. 787-792).

Polytetrafluoroethylene (PTFE, Teflon^™) is well known as a highly stable material with a very low energy surface. Nitrogen physical adsorption on this material aids in an overall paradigm development for vapor sorption on solid surfaces. Extreme measures are needed to generate porous PTFE. Some examples are presented for the amount, population and energy of these surfaces and pores.

Keywords: Teflon; physical adsorption; monolayer; multilayer; shielding; micropores; ASP methodology

Production and Characterization of Adsorbent Materials from an Industrial Waste by S. Rio; C. Faur-Brasquet; L. Le Coq; P. Le Cloirec (pp. 793-798).

Preparation of activated carbon is carried out from an abundant and very cheap waste by-product from wastewater treatment plant: sewage sludge. The first step of preparation consists in a carbonization process under a 10 mL min^{− 1} nitrogen flow, at 600∘C during 1 hour. The second step is a physical activation, performed with carbon dioxide. The experimental conditions of the activation were optimized using experimental design methodology. Three factors were studied: activation temperature (from 700 to 900∘C), activation duration (from 30 to 120 min) and CO₂ flow rate (from 0.7 to 2.9 L min^{− 1}). The porous carbonaceous materials were characterized in terms of physico-chemical and structural properties (specific surface area, pore volumes, surface pH, surface functional groups) and adsorption properties in aqueous and gaseous phase, these characteristics constituting the responses of the experimental design. A surface response methodology enabled to define optimum values for the 3 factors (at 900∘C during 30 min for a CO₂ flow rate of 2.9 L min^{− 1}) which involve an adsorbent with a specific surface area of 260 m² g^{− 1} and a pore size distribution comprising meso and micropores. Adsorption capacities of organic pollutants (phenol, dyes, VOC) are proportional to the specific surface area, apart from copper adsorption capacities (up to 80 mg g^{− 1}) due to an ion-exchange mechanism with Ca^{2 +} ions present in the raw material. In order to decrease the high ash content in the produced material (51 wt.%) and thus to improve the pore development, carbonized sludge were washed with an acid (HCl, 3 M) at room temperature before the activation step. This oxidation pre-treatment allowed to reach a 410 m² g^{− 1} specific surface area with an ash content of 26.4 wt.%.

Keywords: activated carbon production; carbonization; physical activation; experimental design; adsorption

Amorphous MnO₂ –TiO₂ Composites as Sorbents for Sr²⁺ and UO₂²⁺ by Oksana I. Pendelyuk; Tetyana V. Lisnycha; Volodymyr V. Strelko; Sviatoslav A. Kirillov (pp. 799-804).

Hydrous, amorphous MnO₂–TiO₂ composites demonstrating high affinity towards strontium and uranium at pH = 7 are obtained by means of template synthesis. The best distribution coefficients, as found using model solutions (K_d^Sr = 55000 mL/g and K_d^U = 40000 mL/g) and Chernobyl shelter water (K_d^Sr = 3800 mL/g), are gained for the samples containing equimolar amounts of manganese dioxide and titania precipitated using K⁺ as template cation.

Keywords: adsorption; strontium; manganese oxide; titanium oxide

Polymeric Adsorbent for Radium Removal from Groundwater by Shuguang Deng (pp. 805-809).

Radium removal from groundwater by adsorption on polymeric adsorbent represents the latest application of adsorption process in water treatment. A three-month pilot study was carried out in the customer site to collect process performance data on Dowex RSC (radium selective complexer) for a large scale plant design. It was observed from the pilot test that the RSC resin has exceptionally high adsorption capacity for radium, no radium breakthrough from 38″ RSC bed during the entire pilot test; however the adsorbent mass transfer zone extended with the progress of pilot test. The increasing mass transfer zone was probably caused by the changing adsorbent properties. This interesting phenomenon presents a very tough challenge to both adsorption process design and simulation. Another very unique aspect of this process is that the adsorbent with the exceptionally high adsorption capacity may not be suitable for this process due to radiation safety concern and waste disposal limit.

Keywords: polymeric; adsorbent; radium; water treatment; complexation; MTZ

On the Reversibility of Hydrogen Storage in Novel Complex Hydrides by Jun Wang; Armin D. Ebner; James A. Ritter (pp. 811-816).

A comparison of the hydrogen release and uptake (cycling) capability of Ti-doped NaAlH₄, LiAlH₄ and Mg(AlH₄)₂ as a function of Ti dopant concentration, temperature, pressure, and cycle number is reported. Temperature programmed desorption revealed hydrogen release capacities of around 3 wt% at 140^∘C, 3 wt% at 100^∘C and 6 wt% at 150^∘C, respectively for the Ti doped Na, Li and Mg alanates. In the same order, release capacities of 0.5, 2.0 and 1.5 wt% were obtained in 150, 6 and 150 min during constant temperature desorption at 90^∘C. Although all three alanates exhibit striking characteristics that make them potential hydrogen storage materials, it remains that only Ti-doped NaAlH₄ exhibits around 3 wt% reversibility under reasonable conditions.

Keywords: titanium chloride; hydrogen storage; sodium alanate; lithium alanate; magnesium alanate

¹⁴CO and ¹²CO Separation on Na-X Using Pressure Swing Adsorption at Low Temperatures by Jun Izumi; Akinori Yasutake; Shigeki Kobayashi; Akira Shikichi; Atushi Kinugasa; Osamu Kohanawa; Minoru Okumura; Tomio Kanda; Yoshiaki Izumoji; Moriyuki Saigusa; Daiichirou Oguri; Takashi Inoue; Shiny A Oumori (pp. 817-821).

Economical ¹⁴CO separation is very important to provide the means of removal and fixation of the radio-acitve carbon (carbon-14) in atomic power industry.¹³C has been separated from ¹³C/¹²C CO or ¹³C/¹²C CH₄ by cryogenic process conventionally. However, since the separation factor is not so large, the separation cost is very expensive and thus the industrial application of ¹³C is very limited. Meanwhile, there is no report on the separation of ¹⁴C from ¹⁴C/¹²C until now. The authors found that there was a great difference on the adsorption equilibrium coefficient between ¹⁴CO and ¹²CO when they are adsorbed on low SiO₂/Al₂O₃ ratio Na-X type zeolite (Na-X) at low temperatures.

Keywords: Na-X type zeolite¹⁴CO selectivity; low temperature; equilibrium adsorbent; pressure swing adsorption

The Influence of Microporosity on the Hydrogen Storage Capacity of Ordered Mesoporous Carbons by Roger Gadiou; Nathalie Texier-Mandoki; Thierry Piquero; Seif-Eddine Saadallah; Julien Parmentier; Joël Patarin; Patrick David; Cathie Vix-Guterl (pp. 823-827).

The adsorption of hydrogen on nanostructured carbons prepared by templating of mesoporous silicas has been studied at 77 K and between 0.1 and 1 MPa. The maximum capacity was obtained with a carbon synthetized by a sucrose liquid infiltration process in MCM-48 silica. It was observed that the hydrogen weight percentage which can be adsorbed on a carbon can be correlated to its microporous volume determined by CO₂ adsorption and Dubinin-Radushkevich equation.

Keywords: adsorption; hydrogen; ordered mesoporous carbons

Fundamental Mechanism of Combined Sorption of Highly and Weakly Soluble Volatile Organic Compounds into Aqueous Slurries of Activated Carbon by Angelique Dubray; Jacques Vanderschuren (pp. 829-834).

The sorption of two hydrophilic and two hydrophobic airborne VOC into aqueous slurries containing up to 50 kg activated carbon/m³ was carried out in a cables scrubber to determine the effect of adsorbent particles. A reduction and an enhancement of the VOC uptake rate were observed respectively for the hydrophilic and the hydrophobic compounds. A model based on the penetration theory and taking account of the adsorption equilibrium and L-S mass transfer kinetics was developed to interpret the experimental findings.

Keywords: combined absorption and adsorption; VOC; activated carbon; aqueous slurries

Adsorbed Phase Ozonation of Water-Dissolved Organic Pollutants Using High-Silica Zeolites by Hirotaka Fujita; Kenji Shiraishi; Takao Fujii; Akiyoshi Sakoda; Jun Izumi (pp. 835-839).

This paper deals with a novel adsorbed phase ozonation process that enhances the reaction rate between ozone and organic pollutants, especially focusing on their reaction kinetics on ZSM-5s. In this study, we elucidated that adsorptive concentrations in ozone and organic chemical were dominant factors for the increases in reaction rate, and developed a novel method for predicting the reaction rates between ozone and organic chemical on ZSM-5s.

Keywords: ozone; adsorption; ZSM-5; reaction; micropore

SMB Operation for Three-Fraction Separations: Purification of Plasmid DNA by Galatea Paredes; Marco Mazzotti; Joachim Stadler; Stefan Makart; Massimo Morbidelli (pp. 841-845).

The Simulated Moving Bed technology is extended to incorporate a cleaning in place step, and it is then applied by exploiting size exclusion chromatography to purify plasmid DNA. Experimental performances are discussed in the light of our theoretical understanding of the SMB behavior.

Keywords: simulated moving bed; plasmid DNA; size exclusion chromatography; cleaning in place

Simulated Moving Bed Technology in the Reactive Process of Glucose Isomerization by Eduardo A. Borges Da Silva; Antonio A. Ulson De Souza; Selene Guelli U. De Souza; Alírio E. Rodrigues (pp. 847-851).

The glucose isomerization process coupled with adsorption using simulated moving bed technology to obtain high/higher fructose syrups (HFS) are discussed. The mathematical modeling of this process, based on the equivalence between True Moving Bed Reactor (TMBR) and Simulated Moving Bed Reactor (SMBR) is presented. Reaction and adsorption parameters are determined experimentally. A new configuration of the SMBR is proposed which allows the production of fructose-rich product (90% in purity).

Keywords: simulated moving bed reactor; glucose isomerization; SMBR configuration

VOC Adsorption in Circulating Gas Fluidized Bed by Wenli Song; Danieal Tondeur; Lingai Luo; Jinghai Li (pp. 853-858).

The purpose of the work is to show that CFB adsorption process is technically feasible to obtain an interesting pollution abatement, and to set the bases of a process design. Experimental results are presented, obtained with toluene being adsorbed from an air stream on polymeric adsorbent in a batch operation circulating fluidized bed. This results in a breakthrough behavior at the top of the riser, analogous to a fixed-bed experiment. The existence of breakthrough curves that are astonishingly sharp in spite of the strong mixing of the solid phase implies that efficient toluene abatement can be achieved. The breakthrough curves can be used to predict the behavior of the process in a continuous mode where the adsorbent would be partially regenerated, and which would lead to an less than total toluene abatement. The shape of the breakthrough curves clearly depends on the operating parameters, in particular the gas flow rate and the solids circulation rate. The EMMS model was adapted and implemented to describe the flow pattern of gas and solid. The model predicts the relative volume fractions of these phases, the volume fractions inside each, the superficial velocities of gas and solid in each phase, and the average cluster size. From this description, an estimation of the apparent gas/solid mass transfer coefficients may be done, and their dependence on operating conditions investigated.

Keywords: adsorption; circulating fluidized bed; volatile organic compounds

Interactions of Natural Aminated Polymers with Different Species of Arsenic at Low Concentrations: Application in Water Treatment by Claire Gerente; Gordon McKay; Yves Andres; Pierre Le Cloirec (pp. 859-863).

In the present work, the interactions between the amine functionnal groups present in chitosan, a natural polysaccharide and different species of inorganic arsenic are studied. Depending of the N-deacetylation rate, chitosan provides amine functions that could be protonated and shows interesting affinities to adsorb oxyanions of arsenic in solution. Two species, arsenate (AsV) and arsenite (AsIII), have been tested at pH 5, and commercial chitosan and chitin were used. Kinetics have been carried out at two initial concentrations (50 and 500 μ g/L) and different temperatures fixed between 4 to 40^∘C. The results have shown the reaction is very fast, and consequently, the equilibrium times are short (30 min in the best case). Experimental data are well fitted with a first order kinetic model. In a second part, isotherms have been performed with an As concentration range of 10 to 500 μ g/L and 0.5 g/L of biosorbent. Maximum adsorption capacities, deduced from the Langmuir model, range between 260 μ g/g at 40^∘C and 730 μ g/g at 4^∘C. Finally the fixation mechanism could be described by an ion exchange reaction between the protonated amine moities of the chitosan and the arsenate anion in solution.

Keywords: arsenate; chitosan; sorption; traces; water treatment

Adsorption and Photocatalytic Decomposition of Volatile Organic Compounds on Photocatalyst of TiO₂—Silica Beads by Tahei Tomida; Naoyuki Okada; Masahiro Katoh; Shigekazu Katoh (pp. 865-869).

Photocatalyst of TiO₂ coated on silica beads was prepared, and the adsorption isotherms and kinetics of photocatalytic decomposition of acetone and acetaldehyde on the photocatalyst were studied at room temperature (ca. 298 K). Adsorption isotherms of both acetone and acetaldehyde conformed to the Langmuir isotherm. FTIR spectra of the gas phase showed that these volatile organic compounds were mainly oxidized to CO₂ and H₂O. The time courses of concentration change due to photocatalytic decomposition under UV-irradiation were well represented by a proposed model by using the values of Langmuir parameters and the kinetic parameters determined.

Keywords: adsorption; acetone; acetaldehyde; photocatalyst; decomposition

Two Dimensional Model for the Design of Metal Hydride Hydrogen Storage Systems by Sarang A. Gadre; Armin D. Ebner; James A. Ritter (pp. 871-876).

A 2-D mathematical description of a metal hydride hydrogen storage vessel was developed. This 2-D model was calibrated against experimental discharge data obtained from a commercially viable system containing Lm_1.06Ni_4.96Al_0.04 metal hydride. The model was capable of predicting the performance of the vessel for both the discharge and charge processes over a wide range of conditions. This model should thus be very useful for the design and development of the next generation of metal hydride hydrogen storage systems.

Keywords: hydrogen storage; metal hydride; mathematical modeling

Improvement of Hydrogen Storage Capacity for Active Carbon by Bronislaw Buczek; Leszek Czepirski; Janusz Zietkiewicz (pp. 877-880).

The porous structure of activated carbon modified by successive removal of external layers from a granule surface as produced by abrasion in a spouted bed was investigated. Procedure used for activated carbon modification is the way to minimization voids and macropores without decreasing the volume of adsorbing pores. The concept of hydrogen adsorption storage in modified samples was analysed. The amount of hydrogen that can be stored in an adsorption system depends on the hydrogen volumetric uptake and densimetric characteristics. The results show that the cryoadsorption technique could provide a viable method for hydrogen storage.

Keywords: adsorption; activated carbon; hydrogen storage

Adsorbent Selection by Functional Group Interaction Screening for Peptide Recovery by Renze Wijntje; Hans Bosch; Andre B. De Haan; Paul Bussmann (pp. 881-886).

In order to selectively adsorb small peptides from complex aqueous feeds, selective adsorbents are required. The goal is to first find adsorbents with capacity for triglycine, as triglycine contains all groups common to small peptides. Selectivity studies will follow. Adsorbent selection was based on the interactions available to the triglycine groups and four types of interaction seemed theoretically suitable to provide adsorption of triglycine. These interaction types are hydrogen bonding, electrostatic interaction, π interaction and metal complex formation. This resulted in testing 16 different adsorbent functional groups for adsorption of triglycine under different solution conditions (triglycine only, with 0.2 M NaCl and at pH 8.2). Adsorbents using electrostatic interaction, such as zeolites, anion and cation exchangers, exhibit the strongest interaction, although in the presence of NaCl the distribution coefficient of triglycine is significantly lowered. The adsorbents, when loaded in the H⁺ form, interacting electrostatically with the peptide amino group show the highest selectivity. Regarding π interaction, several aromatic adsorbents show a weak interaction with triglycine, with low distribution coefficients. Transition metal complex adsorbents (copper(II) and vanadium(IV)oxide) show a weak interaction, limited by pH, or are stripped from the immobilizing ligand by triglycine. The hydrogen bonding adsorbents show no measurable adsorption of triglycine.

Keywords: peptide; separation; adsorption; interaction; triglycine

Salicylic Acid Adsorption onto Sephabeads SP206 in View of its Purification by Thermal Parametric Pumping by Marta Otero; Miriam Zabkova; Alirio Rodrigues (pp. 887-892).

Parametric pumping is a cyclic process that allows purification of industrial wastewaters without spending chemicals for regeneration and therefore avoiding a new pollution problem. The applicability of this technology to the purification of salicylic acid in liquid phase has been studied, salicylic acid being a phenolic compound with a high production in a world scale which is mainly linked to aspirin manufacture. The aim is to get at the same time a purified and a concentrated stream of salicylic acid, which allows recycling for the industrial process so contributing to achieve the concept of a zero-pollutant plant. Different operating conditions were accomplished in an automated pilot plant and experimental results were compared to those simulated by a previously developed package (Davesac et al., 2000). A satisfactory agreement is obtained with the linear driving force and axial dispersion model.

Keywords: parametric pumping; purification; salicylic acid

Separation of Tröger’s Base Enantiomers Through a Combination of Simulated Moving Bed Chromatography and Crystallization by Mohammad Amanullah; Stefanie Abel; Marco Mazzotti (pp. 893-897).

This paper studies the coupling of simulated moving bed (SMB) chromatography with crystallization for the separation of Tröger’s base enantiomers. SMB is used to achieve a certain level of enrichment and then evaporative crystallization of the extract and raffinate streams leads to the final product with the specified purity. The optimization of the combined process is based on thermodynamic data about adsorption isotherms of the two enantiomers in ethanol on microcrystalline cellulose triacetate (CTA) and about solubility of the two enantiomers in ethanol. The results, obtained using a genetic algorithm, prove that there is an optimal value of the purity achieved in the SMB that maximizes the productivity of the combined process.

Keywords: simulated moving bed; crystallization; hybrid process; Tröger’s base

Development of a New Effective Biogas Adsorption Storage Technology by Shuji Himeno; Toshiya Komatsu; Shoichi Fujita (pp. 899-904).

In this study, we report a new effective sludge-digestion gas (biogas) adsorption storage technology. The experimental data of the pure and binary adsorption equilibrium of methane and carbon dioxide, which are the main components of the biogas, on five types of activated carbons at a temperature range of 273–333 K and pressures up to 6 MPa, were measured. Pure isotherms were fitted with the Toth and extended Toth models. Binary equilibrium was predicted using the Ideal Adsorbed Solution Theory (IAST) based on the extended Toth model with the experimental data being predicted as well. The differential enthalpy of the pure and binary adsorption was calculated, and storage densities of the binary gases, methane and carbon dioxide, considering the increased activated carbon temperature, were estimated using the adiabat and isobar of mixed gases in the biogas composition.

Keywords: adsorption storage; activated carbon; biogas

Automatic Filtering and Reodorization of Adsorbed Natural Gas Storage Systems by Isabel A. A. C. Esteves; Marta S. Lopes; Pedro M. Nunes; Mário F. Eusébio; José P. B. Mota (pp. 905-910).

The presence of high molecular weight hydrocarbons and sulphur-based odorants in natural gas has a negative impact on the storage of this fuel using adsorption technology. The reason for this is the deterioration of the adsorbent capacity on extended cyclic operation. Although a good adsorbent is key to the success of ANG, its potential will be limited if it is not integrated into a well-designed system which compensates for the weakness inherent in the adsorption process, deleterious poisoning and heat effects. Although there appears to be a consensus on the use of a especially tailored carbon-based filter or guard-bed to prevent the contamination of the storage tank, this system has not yet been studied or evaluated in real depth. In this work, it is demonstrated for the fist time that it is indeed possible to filter and reodorize the delivered natural gas using a properly operated carbon-based filter.

Keywords: natural gas; adsorption storage; activated carbon; guard bed

Methane Adsorption Storage Using Microporous Carbons Obtained from Coconut Shells by Moisés Bastos-Neto; A. Eurico B. Torres; Diana C. S. Azevedo; Célio L. Cavalcante Jr. (pp. 911-915).

This paper presents an experimental and theoretical study of the adsorption equilibria of methane on activated carbon, focusing on the accurate determination of the absolute adsorbed mass from raw gravimetric measurements performed at high pressures (above 0.1 MPa). Two carbon samples were selected for these studies: a commercial sample (SRD-21) and a sample prepared in laboratory from coconut shells (CAQF-30). A gravimetric set up was used to measure the adsorption properties. Methane isotherms were obtained in the pressure range of 1 to 70 bar and under temperatures from 10 to 80^∘C. Equilibrium experimental data were evaluated with the aid of three approaches labeled as D, DD and DDA, the latter being proposed for the first time in this paper. The DDA approach provided consistent and physically meaningful results for the adsorbed phase density. The adsorption isotherm that was obtained following the DDA approach matched those obtained following an approach published in the literature. The results indicate that the CAQF-30 sample, despite being prepared from carbonaceous wastes, presents competitive values for the methane adsorption parameters when compared to the commercial sample.

Keywords: gas storage; carbon; adsorption; gravimetric measurements; buoyancy

Selective Adsorption of a Substance Derived from Saccharides onto Synthetic Resin Particles by Hideo Hattori; Kiyohiko Tajima; H. Ted Chang; Takashi Murayama; Eiji Furuya (pp. 917-920).

Most, if not all, of the chemicals and chemical products are made using crude oils as the feedstock. However, this feedstock is decreasing and the utilization of it is causing global climate change. An alternative feedstock must be developed to alleviate these problems. Saccharides (sugars) meet these requirements partly because many useful intermediates and products can be obtained in the presence of an acid. In the case when D-fructose reacts with concentrate hydrochloric acid, 5-hydroxymethyl-furfural (HMF) is formed as the primary product. HMF is well known as one of many useful chemicals from biomass. However, it reacts further to form a HMF dimmer, and it also decomposes to smaller molecules such as levulinic acid. This kind of complex reaction is difficult to control through process variables including temperature, time, pressure, and solvent, in order to obtain selectively a specific product. In this study, a method of direct reaction control using adsorption in the same vessel. The results show that HMF dimmer can be selectively adsorbed onto synthetic resin particles. The results are almost the same as those obtained from a phenolics-carbonaceous adsorbent system.

Keywords: saccharides; decomposition; synthetic resin; adsorption; HMF dimmer

Author Index (pp. 921-925).

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Adsorption: Journal of the International Adsorption Society (v.11, #1)

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Adsorption: Journal of the International Adsorption Society (v.11, #1)