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Adsorption: Journal of the International Adsorption Society (v.5, #4)
Monte Carlo Simulations of Adsorbed Solutions in Heterogeneous Porous Materials by T. Vuong; P.A. Monson (pp. 295-304).
We present results of a Monte Carlo simulation study of binary mixtures of ethane and methane in silica gel. The molecular model treats the adsorbent as a matrix of silica microspheres. The adsorption isotherms, adsorption selectivities and isosteric heats of adsorption have been determined for these systems. The results are compared with predictions from the ideal adsorbed solution (IAS) theory and with experiment. The heats of adsorption are accurately described by the IAS theory. The adsorption isotherms are accurately described by the IAS theory at low bulk pressure but the IAS theory overpredicts the density at high bulk pressure. This latter effect is opposite to that observed in bulk mixtures of this type where nonidealities generally lead to a density increase on mixing. The pressure dependence of the selectivity does not exhibit a maximum at low pressure. We discuss this effect in terms of the adsorbent microstructure.
Keywords: mixture adsorption; molecular simulation; silica gel; Monte Carlo simulation
Microstructural Analysis of the Effects of Poly(ethylene glycol) on an Acid Catalyzed Sol-Gel Derived Ceramic Material by P. Ågren; P. Pendleton; J.B. Rosenholm (pp. 305-312).
Ceramic materials have been derived from an acid catalyzed sol-gel process. The addition of different molecular weights and concentrations of polyethylene glycol (PEG) to the sol mixture modifies the phase behaviour of the sol-gel process. The resulting gel is burned at 973 K to make porous ceramic materials. Nitrogen adsorption-desorption isotherms are used to assess the effects of PEG on the internal structure of the burned ceramic material. These isotherms indicate an extensive pore network exists consisting of micropores and mesopores. In the micropore region of the isotherms, the αS-plot analysis reveals changes in specific primary micropore volumes, specific total pore volumes, specific external surface areas and specific SPE surface area when PEG is added in the sol-gel process. The average pore width and the overall mesopore size distribution curves shift to higher pore size values and ranges on addition of PEG to the sol-gel mixture. The presence of PEG during the sol-gel process leads to an apparent narrowing of the micropore size distribution. The results of this work clearly indicate that the molecular weight and the concentration of a polymer, such as PEG, influences the eventual internal structure of a ceramic after burning.
Keywords: silica; synthesis techniques; characterisation of structure; pore condensation
Adsorption and Thermogravimetric Methods for Monitoring Surface and Structural Changes in Ordered Mesoporous Silicas Induced by their Chemical Modification by M. Jaroniec; C.P. Jaroniec; M. Kruk; R. Ryoo (pp. 313-317).
The current work demonstrates that the standard adsorption analysis has a limited applicability for characterization of chemically modified porous silicas. Since low-pressure nitrogen adsorption isotherms are sensitive to the surface changes caused by chemical modification of silicas, these isotherms were successfully used to evaluate their surface heterogeneity during different stages of modification. The surface analysis was accomplished by using adsorption energy distributions and high-resolution comparative plots.
Keywords: MCM-41; bonding of organosilanes; surface analysis; adsorption energy distribution; pore structure analysis
On the Azeotropic Behaviour of Adsorption Systems by D.D. Do; H.D. Do (pp. 319-329).
This paper addresses the azeotropic behaviour of adsorption occurring on a heterogeneous solid, which is composed of patches of different adsorption energies. One of the adsorbates is excluded from adsorption onto one or more patches. If such species is the weaker adsorbing species, then the azeotropic behaviour does not occur. On the other hand, if that species is the stronger adsorbing species then the azeotropic phenomenon might occur. The occurrence of the azeotropic depends on the relative affinities of all species and the total pressure must be greater than a threshold pressure. We shall illustrate this theory with two systems exhibiting azeotropic behaviour: isobutane/ethylene/13X and propane/carbon dioxide/mordenite.
Keywords: azeotropic; heterogeneous solid; equilibrium
Adsorption Equilibrium of Binary Mixtures in Zeolites and State of Adsorbed Phase by Eugene A. Ustinov; Leonid E. Klyuev (pp. 331-343).
The criterion of ideal behavior of a mixture of a few molecules within a separate zeolite cavity is formulated on the basis of the statistical thermodynamics. The criterion determines the dependence of the Helmholtz free energy, internal energy, and entropy of a molecular aggregate on the ratio of the number of molecules of components 1 and 2. The similarity between this criterion and the criterion of ideal behavior for bulk solutions is shown. Expressions of excess thermodynamic functions of the molecular mixture in a cavity are obtained. The negative magnitude of these excess functions is proposed to be due to rearrangement of molecules under influence of energetic heterogeneity. The calculation procedure of the excess functions has been demonstrated for the system CO2-C2 H6-zeolite NaX, the information of both isotherms and isosteric adsorption heats being used simultaneously. The approach offered allows the state of adsorbed mixture in a separate cavity to be analyzed from pure-component and multicomponent experimental data.
Keywords: zeolite; equilibrium theory; multicomponent system; gases phase; adsorbed solution; excess functions
Sorption of C6 Alkanes in Aluminophosphate Molecular Sieve, AlPO4-5 by B.L. Newalkar; R.V. Jasra; V. Kamath; S.G.T. Bhat (pp. 345-357).
Sorption of C6 alkanes viz.,n-hexane, 2-methylpentane, 2,2-dimethyl butane, 2,3-dimethyl butane, cyclohexane and methyl cyclopentane in AlPO4-5 is studied and sorption capacity and thermodynamic parameters (ΔH0, ΔH, ΔG, ΔS and Sa) at various sorption coverage for these sorbates have been estimated. The initial heat of sorption (ΔH0) is found to increase with the degree of branching in the alkane chain. The sorbate-sorbate interactions are found to be more prominent during the sorption of doubly branched alkanes and cyclic alkanes and a higher sorption capacity has been observed for cyclic alkanes. Based on the results obtained, a packing model has been proposed for various C6 alkanes inside the AlPO4-5 channel.
Keywords: AlPO4-5; C6 alkanes sorption; sorption energetics
Binary Adsorption of Phenol and m-Cresol Mixtures onto a Polymeric Adsorbent by Agostinho Garcia; Licinio Ferreira; Anabela Leitão; AlÍrio Rodrigues (pp. 359-368).
Adsorption processes are gaining interest as methods of purifying industrial effluents. Most industries discharge effluents containing several components. The adsorption of phenol and m-cresol mixtures from aqueous solutions onto a macroporous polymeric adsorbent, Duolite ES-861, was investigated experimentally in a fixed-bed adsorber for different flowrates, feed concentrations and bed initial conditions (clean or pre-saturated).The experimental results are presented in this work, where the major objective is placed on the modelling of these fixed bed adsorption experiments using an extended Langmuir isotherm equation for two components, based on single component equilibrium data obtained for phenol and m-cresol.The model presented in this paper takes into account axial dispersion of the liquid phase, film diffusion and intraparticle mass transfer and successfully simulates the adsorption behaviour of the phenol and m-cresol mixtures.
Keywords: binary adsorption; polymeric adsorbents; fixed bed adsorption
Sorption and Diffusion of SF6 in Silicalite Crystals by Heather macdougall; Douglas M. Ruthven; Stefano Brandani (pp. 369-372).
Kinetic and equilibrium data for sorption of SF6 in silicalite have been determined by the ZLC method. The equilibrium constants and adsorption energy are comparable with the values reported previously for SF6-NaX. Intracrystalline diffusion is relatively rapid with diffusivities of order 10−7– 10−8 cm2·s−1 at temperatures in the range 30–90°C. The implications for the use of SF6 as a probe molecule for assessing the integrity of silicalite membranes are considered.
New Approximate Model for Nonlinear Adsorption and Concentration Dependent Surface Diffusion in a Single Particle by Gerardine G. Botte; Ruyu Zhang; James A. Ritter (pp. 373-380).
A new approximate model for nonlinear adsorption (Langmuir model) and concentration dependent surface diffusion (HIO model) in a single particle was derived, based on a parabolic concentration profile assumption for the summation of the gas and adsorbed phases. The surface diffusivity was approximated with the adsorbed phase concentration evaluated at the surface of the particle, as the average of the adsorbed phase concentration, and as the average of the first two approximations. Overall, the approximate model based on the average of the first two approximations compared the best with the exact solution for a wide variety of systems and conditions.
Keywords: langmuir isotherm; parabolic profile; pore diffusion; concentration dependent surface diffusion; HIO
Effect of pH on Adsorption of Cephalosporin C by A Nonionic Polymeric Sorbent by Jae Wook Lee; Hee Moon (pp. 381-390).
Adsorption of cephalosporin C in a column charged with a nonionic polymeric sorbent, SP850, was studied at various pH values to assess the effect of pH on the dynamic behavior in column adsorbers. Since cephalosporin C is amphoteric, the fractions of each ionic form were calculated from the pK values at a given solution pH. Single-species isotherm parameters for each ionic form were simultaneously extracted from all sets of adsorption equilibrium data measured at several pH values. The mutual interaction between different ionic forms on SP850 was described by a competitive adsorption, namely the ideal adsorbed solution theory (IAST). This treatment made it possible to simulate the dynamic behavior of cephalosporin C at low pH values properly by a dynamic model which was incorporated with the mutual competitive adsorption.
Keywords: adsorption of cephalosporin C; polymeric sorbent; effect of pH; column operation
Chromatographic Processing Scheme for Continuous Harvesting of rec-Prourokinase from Serum Free Medium Cell Cultures by Donald A. Ross; Alexander H. Chu; Thomas J. Nikolai; Jon M. Ryan; Donald G. Schaefer; Andrew R. Schmidt (pp. 391-398).
Continuous perfusion cell culture, using albumin containing medium, offers the potential advantages of higher recombinant Prourokinase (r-ProUK) yields, higher initial product purity and increased throughput compared to batch culture technology using medium supplemented with fetal bovine serum. We have characterized the production of r-ProUK in medium supplemented with a lipid rich bovine serum albumin (Albumax) in a perfusion system. The results of these studies showed that it was necessary to modify the r-ProUK batch recovery scheme to process r-ProUK from a perfusion system. To accommodate large volumes of perfusate harvested over a ten to fourteen day production cycle, cation exchange and hydrophobic interaction chromatography (HIC) resins were identified that had increased product binding capacity, better flow characteristics and wider pH ranges which allowed caustic cleaning. The mobile phase composition, pH and ionic strength were modified to improve r-ProUK yields from the identified resins, and procedures were developed to eliminate r-ProUK degradation products. Strategies were defined for processing continuous harvest, which contained four to seven times the amount of r-ProUK of batch harvests.
Keywords: perfusion cell culture; hydrophobic interaction chromatography; cation exchange chromatography
Liquid Phase Separation of Polar Hydrocarbons from Light Aromatics Using Zeolites by Anand G. Palkhiwala; Yi-Hsiung Lin; Daniel D. Perlmutter; David H. Olson (pp. 399-407).
The liquid phase removal of low concentrations of polar compounds (acetonitrile, acrylonitrile and dioxane) from toluene by adsorption on zeolites reveals very high selectivity factors. Kinetic selectivity factors as high as 16,100 are observed. The selection of the zeolites (MFI, MWW and FAU type) allowed the study of the effects of varying aluminum content, the presence and absence of acidic centers and varying pore volumes. To assess the relative effectiveness of each adsorbent, both equilibrium and continuous flow, pseudo equilibrium, breakthrough experiments were conducted. The continuous flow experiments were carried out at 25 and 75°C. The zeolites H-ZSM-5, H-MCM-22 and Na-X are highly effective in removing the polar compounds from toluene to a concentration level down to less than 20 ppm (detection limit). The results obtained with the equilibrium batch experiments are confirmed by the continuous flow breakthrough experiments.
Keywords: zeolites; polar compounds; adsorption; adsorption isotherms; equilibrium; liquid phase; breakthrough curves; acetonitrile; acrylonitrile; dioxane; ZSM-5; MCM-22; Na-X
Competitive Sorption of Copper and Nickel Ions from Aqueous Solution Using Peat by Y.S. HO; G. McKay (pp. 409-417).
Bicomponent aqueous solutions of copper and nickel ions have been used to investigate the sorption of metal ions onto peat. Peat, a low cost sorbent, has shown a high capacity for the sorption of single component metal ions attributed to extensive carboxylic acids within its structure. Copper and nickel ions were selected as typical metals in the effluents of electroplating industries. The effects of competitive sorption in batch systems were studied at various metal ion concentrations. In this study the Butler and Ockrent model was modified using a coefficient, η. Two models were developed based on the interaction coefficient η. The first model incorporates a constant fixed η factor for each metal ion into the Butler-Ockrent equation. The second model incorporates a variable η factor into the Butler-Ockrent equation; this interaction factor varies as a function of sorbent surface coverage. Predicted equilibrium data are found to be in excellent agreement with experimental values using both modified models for various mole ratios of copper and nickel ions in competitive sorption.
Keywords: competitive sorption; copper; nickel; peat; isotherm
Backfill Cycle of a Layered Bed H2 PSA Process by Hyungwoong Ahn; Chang-Ha Lee; Bongkook Seo; Jaeyoung Yang; Kihwang Baek (pp. 419-433).
The backfill cycle of two-bed PSA process using activated carbon beds, zeolite 5A beds, and layered beds was studied experimentally and theoretically to recover high purity H2 from coke oven gas. In a layered bed PSA, a comparison was made between two PSA processes with/without a backfill step before the feed pressurization step. Since the backfill step made the adsorption bed rich in H2 and this led to a rather steep concentration wave front at the feed pressurization step, incorporating a backfill step resulted in an increase in product purity with a decrease in recovery. Each step of the single-adsorbent and layered bed PSA processes with a backfill step was simulated with a dynamic model incorporating mass, energy, and momentum balances. The model agreed well with the experimental results in predicting the product H2 purity and recovery, thus giving a basic understanding of the bed dynamics of a backfill cycle. While the concentration and temperature profiles of a layered bed in each step showed characteristic behavior of each adsorbent in each layer, the product purity of a layered bed was not between the limits of two single-adsorbent bed processes. The concentration profiles predicted by simulation showed that CO and N2 played an important role in obtaining high H2 purity.
Keywords: backfill step; single-adsorbent bed; layered bed; coke oven gas; H2 PSA