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Adsorption: Journal of the International Adsorption Society (v.13, #3-4)

Foreword by Marco Mazzotti (pp. 171-172).

(in the middle of the first row of the FOA9 photo, between Minoru Miyahara and Giorgio Carta), an Italian citizen born in 1960, married to Mietta, with two children, has been professor of process engineering at ETH Zurich, Switzerland since May 1997. He holds a Laurea (M.S., 1984) and a Ph.D. (1993), both in Chemical Engineering from the Politecnico di Milano, Italy. Before joining ETH Zurich, he had worked for IBM Italy (1985–1987) and Montefluos (1988–1990), and had been assistant professor at the Politecnico di Milano (1994–1997). His research activity deals with adsorption based separations and chromatography, and with crystallization and precipitation processes. The application areas of interest are the purification of biopharmaceuticals and carbon dioxide capture and storage systems. Twelve PhD students have graduated with him and thirteen are currently advised by him. His refereed publications include more than 130 journal articles, 20 papers in books and 6 book chapters. He was a coordinating lead author of the Intergovernmental Panel on Climate Change Special Report on Carbon Dioxide Capture and Storage (2005). He is an active member of the AIChE, of the Working Party on Crystallization of the EFCE, and of the IAS, of which he is the current Vice-President (2007-10).

Water adsorption with hysteresis effect onto microporous activated carbon fabrics by Patrick D. Sullivan; Brenton R. Stone; Zaher Hashisho; Mark J. Rood (pp. 173-189).

Understanding the adsorption of water vapor onto activated carbons is important for designing processes to remove dilute contaminants from humid gas streams, such as providing protection against chemical warfare agents (CWAs), or against toxic industrial compounds (TICs) used in a terrorist chemical attack. Water vapor isotherms for Calgon BPL granular activated carbon (GAC), military ASZM-TEDA GAC, electrospun activated carbon nanofibers (ACnF), Calgon Zorflex^™ activated carbon cloth, and Novoloid-based activated carbon fiber cloth (ACFC) are presented. Of particular interest are the ACFC isotherms, which exhibit an unusually high degree of hydrophobicity. The ACFC isotherms also show a correlation between water vapor adsorption hysteresis and the level of activation. Water vapor isotherm models from the literature are compared.

Keywords: Activated Carbon Fiber Cloth (ACFC); Water vapor adsorption; Hysteresis; Isotherm models

Freezing of Lennard-Jones fluid in cylindrical nanopores under tensile conditions by Hideki Kanda; Minoru Miyahara (pp. 191-195).

We have shown the Lennard-Jones (LJ) phase diagram for a slit-shaped nanopore by molecular simulations and thermodynamically predicted the results with no adjustable parameter. With this success, LJ phase diagrams are predictable. In this study, the freezing of an LJ CH₄ capillary condensate under a tensile condition in a nonstructural carbon nanopore with a cylindrical geometry was examined using molecular dynamics (MD) simulation. We employ a unit cell in contact with a bulk vapor phase, which is useful for the determination of the bulk vapor pressure in equilibrium with the molecules in a pore. The MD simulation results show liquid-solid (amorphous) phase transitions with a variation in the bulk vapor pressure. The frozen particles are arranged in concentric circular regions along the wall similar to those reported by Maddox and Gubbins. The freezing points are determined from the variations in density, enthalpy, arrangement, and structural functions. The obtained liquid-solid coexistence points are found to exhibit a significant dependence of the freezing point on the equilibrium bulk vapor pressure, forming an extraordinarily skewed curve on the p-T diagram, in contrast to the bulk phase coexistence that is represented by an almost vertical line. The origin of the significant dependence is considered to be the Laplace effect on the capillary condensate similar to the case with a slit-shaped pore. A simple model, which the authors earlier presented for slit-shaped nanopores, successfully predicted the p-T relation of the freezing point for cylindrical nanopores as well.

Keywords: Solidification; Thermodynamic model; Molecular dynamics simulation

Supercritical fluids in mesopores—new insight using NMR by Muslim Dvoyashkin; Rustem Valiullin; Jörg Kärger (pp. 197-200).

Supercritical fluids are an essential constitute of modern chemical industry. However, their optimal use in processes involving porous solids is rather limited due to our poor knowledge about their transport properties under confinements. By using the non-invasive pulsed field gradient NMR method, we directly assessed molecular diffusivities of n-pentane in mesopores at sub- and supercritical temperatures. The obtained results ultimately point out that criticality in pores occurs at lower temperatures than in the bulk liquid surrounding the porous solid. The data on molecular diffusivities and pore density may be self-consistently quantified using simple gas-kinetic arguments.

Keywords: Supercritical state; Mesopores; Diffusion; NMR

Adsorption of fission products on stainless steel and zirconium by Réka Répánszki; Zsolt Kerner; Gabor Nagy (pp. 201-207).

Contamination of the structural materials of nuclear reactors is a crucial question in view of radiation protection, especially, if due to some leakage, uranium and its fission products appear in the cooling water. Since it is rather difficult to obtain in situ experimental data on the actual amount of adsorbed radioactive species, the surface contamination may be quantified by measuring bulk activity concentrations of the cooling water and by calculating the amount of adsorbed material on the surfaces by using a partition coefficient. To do this, the knowledge of an appropriate adsorption isotherm is needed. Thus, our paper presents results, based on electrochemical measurements, about the extent and effect of the adsorption of certain fission products—caesium and iodide—in their ionic forms on the surface of some alloys used in the nuclear industry. Our findings allow the conclusion that the adsorption of these ions can be described by a Langmuir-type isotherm, where the saturation values correspond to surface monolayers.

Keywords: Electrochemical quartz crystal microbalance; Fission products

CO₂ diffusivity in LiY and NaY faujasite systems: a combination of molecular dynamics simulations and quasi-elastic neutron scattering experiments by David Plant; Herve Jobic; Philip Llewellyn; Guillaume Maurin (pp. 209-214).

Quasi-elastic Neutron Scattering combined with Molecular Dynamics simulations have been carried out to gain further insight into the CO₂ dynamics in LiY and NaY Faujasites. In both materials, it was pointed out that the transport diffusivity (D_T) increases with the loading whereas the self diffusivity (D_S) decreases. In addition, it was shown that LiY exhibits a significant slower CO₂ self diffusivity process due to a strong interaction between the Li⁺ cation and the adsorbate molecules at the initial stage of diffusion. This result is consistent with higher simulated activation energy in this cation exchanged faujasite form. By contrast, the transport diffusivity is revealed to be slightly faster in LiY than in NaY.

Keywords: CO₂ ; LiY; NaY; Self and transport diffusivities; Quasi elastic neutron scattering; Molecular dynamics

The options of interference microscopy to explore the significance of intracrystalline diffusion and surface permeation for overall mass transfer on nanoporous materials by L. Heinke; P. Kortunov; D. Tzoulaki; J. Kärger (pp. 215-223).

After a short introduction into interference microscopy and its potentials in monitoring transient concentration profiles in nanoporous materials, we concentrate on the special options of an analysis of these profiles close to the crystal surfaces. We shall in particular introduce a novel route of correlating the overall uptake, at a certain instant of time, with the current boundary concentration. In this way, the significance of surface resistances to overall molecular uptake may be most vividly demonstrated. Considering a large variety of nanoporous host-guest systems, including methanol in zeolites ferrierite, methanol in MOF Manganese(II)-formate and methanol in SAPO STA-7, quite different patterns of surface resistivities may be observed. A generalized analysis is complicated by the fact that both the diffusivities and the surface permeabilities are found to notably depend on the actual concentration. As a consequence, for one and the same system and over identical pressure steps, the relative contributions of diffusion and surface permeation to the overall process may be quite different for desorption and adsorption.

Keywords: Diffusion; Surface resistance; Interference microscopy

Diffusion of aromatic hydrocarbons in silicalite/HZSM-5 by Douglas M. Ruthven (pp. 225-230).

Diffusion of benzene and the xylene isomers in silicalite/HZSM-5 has been studied by a wide range of different experimental techniques. The available data are reviewed in an attempt to draw general conclusions concerning the intracrystalline diffusion process. The results for benzene are remarkably consistent, and the conformity between transport and tracer diffusion and between single crystal membrane and ZLC and frequency response data suggests that diffusion is essentially isotropic with no significant difference between the self and “corrected” transport diffusivity. The situation is more complex for p-xylene which shows clear evidence of non-isotropic behavior and a significant difference between tracer and transport diffusivities.

Effective intraparticle diffusion coefficients of CoCl₂ in mesoporous functionalized silica adsorbents by Tanja Djekic (pp. 231-237).

The scope of this work is to determine the effective intraparticle diffusion coefficient of CoCl₂ over mesoporous functionalized silica. Silica is selected as a carrier of the functionalized groups for its rigid structure which excludes troublesome swelling, often found in polymeric adsorbents. 2-(2-pyridyl)ethyl-functionalized silica is selected as a promising affinity adsorbent for the reversible adsorption of CoCl₂. The adsorption kinetics is investigated with the Zero Length Column (ZLC) method. Initially, experiments were performed at different flow rates to eliminate the effect of external mass transfer. The effect of pore size (60 Å and 90 Å), particle size (40⋅10⁻⁶ m–1000⋅10⁻⁶ m) and initial CoCl₂ concentration (1 mol/m³–2.0 mol/m³) on the mass transfer was investigated. A model was developed to determine the pore diffusion coefficient of CoCl₂ by fitting the experimental data to the model. The pore diffusion coefficients determined for two different pore sizes of silica are D p(60 Å) =1.95⋅10⁻¹⁰ [m²/s] and D p(90 Å) =5.8⋅10⁻¹⁰ [m²/s]. The particle size and the initial CoCl₂ concentration do not have an influence on the value of diffusion coefficient. However, particle size has an influence on the diffusion time constant. In comparison with polymer adsorbents, silica based adsorbents have higher values of diffusion coefficients, as well as a more uniform and stable pore structure.

Keywords: Effective intraparticle diffusion coefficients; Mesoporous silica; ZLC method

Diffusion processes in mesoporous adsorbents probed by NMR by Rustem Valiullin; Muslim Dvoyashkin (pp. 239-245).

In this contribution, we review the results of our experimental studies on diffusion of guest molecules in mesoporous solids using pulsed field gradient (PFG) NMR technique. Having unique potentials to non-invasively probe the microscopic diffusion processes in pores, this method may provide quintessential information on the character of molecular propagation for different pore morphologies and fluid phase state. In particular, different modes of molecular diffusion in partially filled pores may be separately probed and the overall diffusion process could be analyzed taking account of the details of the inter-phase coexistence. In addition to the dynamic properties, some information concerning the distribution of guest molecules within the porous matrix may also be obtained.

Keywords: Diffusion; Mesoporous materials; NMR; Inter-phase equilibrium; Fluid distribution

Preparation of MCM-41 silica using the cationic surfactant blend by Arnošt Zukal; Helena Šiklová; Jiří Čejka; Matthias Thommes (pp. 247-256).

A series of samples of MCM-41 silica was synthesized using surfactant blends of 1-alkyl-3-methylimidazolium and alkyltrimethylammonium salts or blends of two different 1-alkyl-3-methylimidazolium salts (alkyl denotes octyl or hexadecyl) as structure-directing agents. The precipitation of solid particles from a homogeneous water solution of sodium metasilicate and surfactant blend was achieved by lowering the pH due to the hydrolysis of ethyl acetate added. The molecular sieves were characterized by scanning as well as transmission electron microscopy, X-ray powder diffraction, and nitrogen adsorption using a proper nonlocal density functional theory approach for calculations of the textural parameters. All the prepared silicas were of MCM-41-type; they differ in the integral breadth of the pore size distribution curve and the presence of secondary mesopores. The best quality MCM-41 silica of spherical particle morphology was synthesized by using of optimized blend of hexadecyltrimethylammonium bromide and 1-methyl-3-octylimidazolium chloride. The results obtained showed that spherical particles are composed of domains of perfectly ordered hexagonal porous structure. Some samples prepared by using 1-alkyl-3-methylimidazolium salts featured a narrow pore size distribution. However, they contained a small volume of secondary mesopores.

Keywords: Mesoporous molecular sieves; Synthesis and characterization; Nitrogen adsorption isotherms

Synthesis and adsorption investigations of zeolites MCM-22 and MCM-49 modified by alkali metal cations by Justyna Pawlesa; Arnošt Zukal; Jiří Čejka (pp. 257-265).

Ion exchange was made on MCM-22 and MCM-49 zeolites with different Si/Al molar ratios, with Li⁺, Na⁺, K⁺, and Cs⁺ ions and the study of the influence of alkali metal cations on CO₂ adsorption properties was performed. The degree of ion-exchange decreased for larger cations (Cs⁺) apparently due to steric hindrances. The exchange with different cations led to a decrease in the surface area and the micropore volume. Our study shows that the adsorption capacity of the tested zeolites depends significantly on the nature and the concentration of the charge-compensating cations. The highest CO₂ adsorption capacity was obtained on the MWW zeolites with the lowest Si/Al molar ratio and the Li⁺ or K⁺ cations.

Keywords: MCM-22 zeolite; MCM-49 zeolite; Alkali metal cation exchange; N₂ and CO₂ adsorption

Novel zeolite composites and consequences for rapid sorption processes by Alfons Brandt; Martin Bülow; Anna Deryło-Marczewska; Jacek Goworek; Jens Schmeißer; Wolfgang Schöps; Baldur Unger (pp. 267-279).

Novel sorbents for rapid dynamic sorption processes based on the concept of sorption-active shell/sorption-inert core composite granules are presented. Tailoring such composites to a technical sorption process is exemplified by NaX and LiLSX zeolites as sorption-active components. Composite granules are characterized by various techniques specifically by oxygen-VPSA pilot-scale tests and liquid-phase sorption experiments. The composite sorbents exhibit excellent potential for efficiency enhancement of existing processes by lowering investment and operating costs.

Keywords: Gas-phase and liquid-phase sorption; Oxygen VPSA; Mixtures of non-electrolytes; Cu²⁺-ion kinetics; Zeolites NaX and LiLSX; Zeolite-sorbent shapes; Composites; Sorption-inert cores; Granulation

Synthesis of SBA-15/carbon composite with an ink-bottle-like pore structure by a novel pulse CVD technique by Chun He; Frank L. Y. Lam; Xijun Hu (pp. 281-290).

A novel and easy post modification method, pulse chemical vapor deposition (pulse CVD), was developed to tailor the pore-opening of SBA-15 while largely keeping its surface area and pore volume. By using acetylene as carbon precursor and nitrogen as carrier gas, the pore-mouth of SBA-15 was effectively reduced from 8.1 nm to 5.1 nm within 5 min while maintaining the pore body at 8.1 nm. This ink-bottle-structured SBA-15/carbon composite only losses 12% BET specific surface area and 16% total pore volume, respectively. The SBA-15/carbon composite is highly hexagonally ordered and has similar particle morphology as the original SBA-15. The effect of three pore modification factors—the number of cycles of pulse CVD, the ratio of acetylene/nitrogen and the feeding time of carbon precursor, on the final pore structure of the SBA-15/carbon composite is also studied.

Keywords: SBA-15; Pulse CVD; Ink-bottle-like pore

Effect of preparative conditions on the surface characteristics of mixed zirconium and titanium oxides by Adham R. Ramadan; Nahed Yacoub; Sofi Bahgat; Jehane Ragai (pp. 291-297).

The surface characteristics of mixed zirconium and titanium oxides prepared from different starting materials are investigated. One mode of preparation entailed the use of zirconium sulfate and titanium oxysulfate as starting materials and ammonium hydroxide as precipitating agent. The produced oxides were washed to different extents to obtain samples with different sulfate content. A second preparative mode used zirconium oxychloride and titanous chloride as starting materials also with ammonium hydroxide as precipitating agent. The oxidation of the titanous to the titanic form for these oxides was carried out by means of oxygen gas. Resulting samples were heat treated at 400 °C and 600 °C, and textural characteristics determined from the adsorption of N₂ at 77 K, complemented by infrared and thermal studies. The samples precipitated from the oxychloride and chloride salts of zirconium and titanium, as well as those precipitated from the sulfate and oxysulfate salts and washed free of the sulfate ions displayed quite similar textural characteristics. The unheated samples and those heat-treated at 400 °C were mesoporous, with some microporosity, and relatively large surface areas in the order of 200–300 m²/g. Heat treatment to 600 °C led to a relative decrease in surface area, in the order of 100 m²/g, and to the disappearance of microporosity. The mixed zirconium and titanium oxides with a sulfate content of ≈17% displayed significantly lower surface areas, smaller than 10 m²/g, with a prevalence of micro and mesoporosity. Infrared and thermal studies indicated the presence of differently bounded sulfato groups, which seem to have a blocking effect on the pores, resulting in the observed smaller surface areas.

Keywords: Mixed oxides; Titanium oxide; Zirconium oxide; Surface area; Porosity

Preparation and structure characterization of carbons prepared from resorcinol-formaldehyde resin by CO₂ activation by M. A. Elsayed; P. J. Hall; M. J. Heslop (pp. 299-306).

In this work, carbon xerogels with a high pore volume and surface area (up to 2.58 cm³/g and 3200 m²/g respectively) have been synthesized using the sol-gel polycondensation of resorcinol (R) with formaldehyde (F) in a basic medium of monoethanolamine (MEA), followed by drying and pyrolysis. This medium (MEA) has not been used in previous investigations. The effect of activation with CO₂ on the pore size distribution and the chemical functional groups has been investigated using N₂ (77 K) adsorption, FTIR and elemental analysis techniques. A series of experiments has been conducted to investigate the effect of activation time and activation temperature. Activation of the samples was carried out at 850, 900 and 980 °C for times ranging from one to three hours. Within the range of activation conditions, an increase in activation time at 850 °C results in a continuous steady rise of the BET surface area and total pore volume. However, at the two higher temperatures, the surface area shows a maximum when plotted against activation time. FT-IR results show that the use of MEA as a catalyst leads to the formation of nitrogen functional groups in the surface of the resin.

Keywords: Activated carbon; Xerogels; CO₂ activation

Pore accessibility of N₂ and Ar in disordered nanoporous solids: theory and experiment by T. X. Nguyen; S. K. Bhatia (pp. 307-314).

Recently (Nguyen and Bhatia, J. Phys. Chem. C 111:2212–2222, 2007) we have proposed a new algorithm utilising cluster analysis principles to determine pore network accessibility of a disordered material. The algorithm was applied to determine pore accessibility of the reconstructed molecular structure of a saccharose char, obtained in our recent work using hybrid reverse Monte Carlo simulation (Nguyen et al., Mol. Simul. 32:567–577, 2006). The method also identifies kinetically closed pores not accessed by adsorbate molecules at low temperature, when their low kinetic energy cannot overcome the potential barrier at the mouths of pores that can otherwise accommodate them. In the current work, the results are validated by transition state theory calculations for N₂ and Ar adsorption, showing that N₂ can equilibrate in narrow micropores at practical time scales at 300 K, but not at 77 K. Large differences between time scales for micropore entry and exit are predicted at low temperature for N₂, the latter being smaller by over three orders of magnitude. For N₂ at 77 K the time constant for pore entry exceeds 3 hr., while for exit it is 134 days. At 300 K these values are smaller than 1 μs, indicating good accessibility at this temperature. These results are verified by molecular dynamics simulations, which reveal that while N₂ molecules enter and leave all pores frequently at 300 K, entry and exit events for apparently inaccessible pores are absent at 77 K. For Ar at 87 K better accessibility is evident for the saccharose char compared to N₂ at 77 K. This finding is now experimentally shown in this work by comparison of pore size distributions obtained from experimental nitrogen adsorption isotherms of nitrogen and argon at 77 K and 87 K.

Keywords: Gas phase adsorption; Molecular modeling; Pore accessibility; Transition state theory

The effect of molecular imprinting on the pore size distribution of polymers by Mohammad Al Kobaisi; Margaret Tate; Colin Rix; Timur S. Jakubov; David E. Mainwaring (pp. 315-321).

Molecular imprinting techniques are becoming an increasingly important domain of porous polymers generally, to achieve molecule specific recognition through morphology or stereochemistry of cavities. Imprinting is sought to increase both selectivity and sensitivity where the polymer may be present as particulate, membrane or thin film forms. Here, we detail mechanisms involved in the formation, stability and adsorption of binding sites, through the influence of polymerisation conditions and templates on the porosity of highly crosslinked molecularly imprinted polymers (MIPs). Environmental control represents an important area for porous polymers, here we focus on two template fungicides, iprodione and pyrimethanil, for ethylene glycol dimethacrylate (EGDMA) based polymers. In general, control of the pre-polymerisation interactions were able to vary the surface areas of polymers from 40–60 m² g⁻¹ to 300–436 m² g⁻¹ while pore sizes fell into distributions (a) close to the micropore region at ∼3.8 nm, (b) in the 10 to 20 nm mesopore region and (c) in the 20 to 50 nm mesopore region. The importance of intermolecular interactions and aggregation in the pre-polymerisation solution to the Brunauer, Emmett, Teller (BET) surface areas and pore size distribution of final polymers has been demonstrated by systematic variation of chemical functionality. These effects confirm recent molecular dynamic simulation studies of MIP formation and cavity stability.

Keywords: Biochemical, energy and environmental applications; Fundamentals of adsorption; Liquid phase adsorption

Polymer-templated organosilicas with hexagonally ordered mesopores: the effect of organosilane addition at different synthesis stages by Rafal M. Grudzien; Bogna E. Grabicka; Ryan Felix; Mietek Jaroniec (pp. 323-329).

Two series of ordered mesoporous organosilica (OMO) SBA-15 materials with surface and bridging groups were fabricated by varying the organic precursor addition at different synthesis stages. The consequence of the delayed introduction of organic precursor on the structural and adsorption properties of the resulting OMOs was investigated. The OMOs studied were synthesized via co-condensation of tetraethyl orthosilicate (TEOS) and ureidopropyltrimethoxysilane (UPS) as well as TEOS and bis(triethoxysilylpropyl) disulfide (BTDS) in the presence of poly(ethylene oxide)-poly(propylene oxide)- poly(ethylene oxide) triblock copolymer Pluronic P123 (EO₂₀PO₇₀EO₂₀). The aforementioned OMOs were characterized by nitrogen adsorption-desorption isotherms at −196 °C and powder X-ray diffraction (XRD). Nitrogen adsorption isotherms were used to estimate the pore volume, mesopore diameter and the BET specific surface area, whereas the XRD data provided information about structural ordering and unit cell of the samples studied.

Keywords: Channel-like mesostructures; Ordered mesoporous organosilicas; Nitrogen adsorption; SBA-15; Ureidopropyl surface group; Bis(propyl)disulfide bridging group

Fixed bed adsorption of benzothiophene over zeolites with faujasite structure by J. L. Sotelo; M. A. Uguina; V. I. Águeda (pp. 331-339).

This work addresses the adsorption of benzothiophene (BT), as a model heterocyclic and aromatic sulphur compound present in road fuels, over agglomerated zeolites with faujasite structure. Several adsorbents based on zeolites with FAU structure have been prepared with different Si/Al molar ratios and exchange cations and then agglomerated. The influence of the zeolite basicity has been studied, both in equilibrium and dynamic liquid phase adsorption experiments. Basicity of the adsorbent increased as the Si/Al molar ratio and the electronegativity of the exchange cation decreased. In equilibrium experiments, the affinity towards the adsorbent increased as the Si/Al molar ratio decreased, showing the highest affinity for exchanged low silica X zeolites with medium basicity (A-KLSX-02). Dynamic experiments showed that the less zeolite basicity, the higher fractional bed utilization and adsorption capacity at breakthrough time. Besides, zeolites with high basicity did not reach the equilibrium capacity due to the low diffusivity of BT into the micropores. Thermogravimetric analyses of the spent adsorbents showed a stronger BT adsorption onto the more basic zeolites. As main conclusion, adsorbents with medium basicity could present the best performance in fuel desulphurization due to their high affinity with sulphur compounds, although diffusion problems should be taken into account.

Keywords: Benzothiophene; LSX zeolites; Basicity; Agglomeration; Desulphurization; Adsorption; Fixed bed

A complete experimental approach for synthesis gas separation studies using static gravimetric and column breakthrough experiments by Youssef Belmabkhout; Gerhard Pirngruber; Elsa Jolimaitre; Alain Methivier (pp. 341-349).

In this work a combination of static gravimetric and inverse chromatographic techniques is used to study the adsorption and separation of the main synthesis gas components, i.e. CO₂, CO, CH₄ and H₂. The single component adsorption isotherms of CO₂, CO, CH₄ and H₂ on faujasite NaX were measured from 303 K to 473 K and over a large range of pressures (from 0 to 1200 kPa). Breakthrough curves of CO₂ and CO and their mixtures were determined at 323 K and 373 K and 100 kPa as an illustrative example. A nice agreement was noticed between the two above-mentioned techniques for single component adsorption. Binary mixture dynamics measurements were compared to the predictions of ideal adsorption solution theory (IAST) via the previously cited single component adsorption data.

Keywords: Adsorption; Co-adsorption; CO₂ ; CO; CH₄ ; H₂ ; Gravimetry; Inverse gas chromatography; Zeolite; NaX; Synthesis gas; Isosteric heat

High resolution adsorption isotherms of N₂ and Ar for nonporous silicas and MFI zeolites by Kazuyuki Nakai; Joji Sonoda; Masayuki Yoshida; Masako Hakuman; Hiromitsu Naono (pp. 351-356).

The high resolution adsorption isotherms of N₂ (77.4 K) and Ar (87.3 K) have been measured for two nonporous silicas with different silanol contents (3.3 and 0.35 OH/nm²) and for two MFI zeolite with different Al contents (Si/Al=12.5 and 500). Silanol groups and Al sites (acid sites) gives the significant effect on the N₂ isotherms at submonolayer, but the Ar isotherms are independent of silanols and Al sites. The Ar isotherms, therefore, are preferable in calculation of microporosity of zeolites. The N₂ and Ar isotherms for MFI zeolite (Si/Al=500) have been measured at temperatures of 77–94 K, from which the differential adsorption energies of N₂ and Ar are calculated. The interaction of N₂ with channel surface of MFI zeolite is greater than that of Ar in the range of α s=0.1–0.7. The hystereses are detected for the N₂ isotherm in p/p ^o=0.1–0.3 at 77.4 K and for the Ar isotherm in p/p ^o=3×10⁻⁴–2×10⁻³ at 87.3 K. However, it is difficult to explain the hysteresis phenomenon using differential adsorption energy.

Keywords: MFI zeolite; ZSM-5; Silicalite; Adsorption isotherms of N₂ and Ar; Differential adsorption energy

Multiphysics modeling of electric-swing adsorption system with in-vessel condensation by Menka Petkovska; Danijela Antov-Bozalo; Ana Markovic; Patrick Sullivan (pp. 357-372).

Mathematical modeling of an Electric-Swing Adsorption (ESA) system (adsorption cycle with electrothermal desorption step, performed by direct heating of the adsorbent particles by passing electric current through them), with annular, radial-flow, cartridge-type fixed-bed and in-vessel condensation, is performed by using Comsol Multiphysics™ software. Three multiphysics models are built, in order to describe three stages of a compete ESA cycle: adsorption, electrothermal desorption before the start of condensation and electrothermal desorption with in-vessel condensation. In order to describe the complete ESA cycle the models for the three stages are integrated, by using a combination of Comsol Multiphysics™ and Matlab™. The models were successfully used for simulation of separate stages of the process and of the complete ESA cycles, as well as for investigation of the influences of the main operational parameters on the process performance.

Keywords: Multiphysics modeling; Electric-Swing Adsorption (ESA); Electrothermal desorption; In-vessel condensation

Separation of carbon dioxide/methane mixtures by adsorption on a basic resin by José A. Delgado; María A. Uguina; José L. Sotelo; Beatriz Ruíz; Marcio Rosário (pp. 373-383).

In this work, the separation of carbon dioxide/methane mixtures by PSA using a basic resin (Amberlite IRA-900) has been studied. Adsorption equilibrium and kinetics of carbon dioxide and methane on a fixed-bed of this adsorbent have been measured, and a binary adsorption equilibrium isotherm has been obtained. The adsorbent deactivation with the number of adsorption-desorption cycles, and its regeneration, have also been analysed. A model based on the LDF approximation has been used to describe the experimental breakthrough curves. The applicability of the basic resin to the separation of carbon dioxide/methane mixtures has been studied in an experimental PSA setup using a single bed. The validity of the model used in the fixed-bed study for simulating a PSA system has been checked by comparing the simulated and the experimental performance of the proposed PSA cycle.

Keywords: Carbon dioxide; Methane; Basic resin; Amberlite IRA-900; Adsorption; Fixed-bed; PSA

Reversible chemisorption of carbon dioxide: simultaneous production of fuel-cell grade H₂ and compressed CO₂ from synthesis gas by K. B. Lee; M. G. Beaver; H. S. Caram; S. Sircar (pp. 385-397).

One vision of clean energy for the future is to produce hydrogen from coal in an ultra-clean plant. The conventional route consists of reacting the coal gasification product (after removal of trace impurities) with steam in a water gas shift (WGS) reactor to convert CO to CO₂ and H₂, followed by purification of the effluent gas in a pressure swing adsorption (PSA) unit to produce a high purity hydrogen product. PSA processes can also be designed to produce a CO₂ by-product at ambient pressure. This work proposes a novel concept called “Thermal Swing Sorption Enhanced Reaction (TSSER)” which simultaneously carries out the WGS reaction and the removal of CO₂ from the reaction zone by using a CO₂ chemisorbent in a single unit operation. The concept directly produces a fuel-cell grade H₂ and compressed CO₂ as a by-product gas. Removal of CO₂ from the reaction zone circumvents the equilibrium limitations of the reversible WGS reaction and enhances its forward rate of reaction. Recently measured sorption-desorption characteristics of two novel, reversible CO₂ chemisorbents (K₂CO₃ promoted hydrotalcite and Na₂O promoted alumina) are reviewed and the simulated performance of the proposed TSSER concept using the promoted hydrotalcite as the chemisorbent is reported.

Keywords: Thermal swing sorption enhanced reaction; Chemisorption; Hydrogen; Carbon dioxide; Promoted hydrotalcite; Promoted alumina

Evaluation of adsorbent materials for heat pump and thermal energy storage applications in open systems by A. Hauer (pp. 399-405).

The evaluation of solid adsorbents in open sorption systems for heating, cooling and thermal energy storage (TES) applications is crucial for the ecological and economical performance of these systems. An appropriate adsorbent has to reach the temperature limit given by the heating/cooling system of the consumer. It has to provide high energy efficiency and a high energy density for storage applications. A method for an easy evaluation of different adsorbents for a specific application has been developed. The method is based on the adsorption equilibrium of the adsorbent and water vapor. The crucial property for the discussed field of applications is the differential heat of adsorption. Criteria for the evaluation of the adsorbent are the breakthrough curves (responsible for the dynamics of the process), the possible temperature lift (or the dehumidification) of the air, the thermal COP and the storage capacity.

Keywords: Water vapor adsorption; Open sorption systems; Zeolite; Thermal energy storage; Desiccant cooling

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Adsorption: Journal of the International Adsorption Society (v.13, #3-4)

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Adsorption: Journal of the International Adsorption Society (v.13, #3-4)