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Adsorption: Journal of the International Adsorption Society (v.6, #3)


Multicomponent Equilibrium Adsorption on Heterogeneous Adsorbents by Eugene A. Ustinov (pp. 195-204).
A generalized method for prediction of multicomponent adsorption is suggested based on representing that adsorbent volume as energetically inhomogeneous. The method depends on extending the Polanyi potential theory to mixture adsorption. The main feature of the method is that, at constant partial pressure and temperature the composition of an adsorbed phase is not uniform over its volume. Results of applying this theory to non-porous adsorbents have been considered. The prediction ability of the theory is confirmed for the strongly non-ideal system acetone–chloroform–graphitized carbon black. It was shown that the departure from ideal behavior of adsorbed phase is quite close to that for the liquid mixture. Another system considered was oxygen–nitrogen–anatase at 78 K. Although this mixture is ideal, it has been found that there is significant variation in composition over the adsorbed layer due to the difference in the interactions of the quadrupolar N2 molecule and nonpolar O2 molecule with the anatase surface.

Keywords: activated carbon; adsorbent surface; equilibrium theory; mixture adsorption; gases phase; adsorbed solution


Oxygen Selectivity on Na-A Type Zeolite at Low Temperature by Jun Izumi; Motoyuki Suzuji (pp. 205-212).
Na-A type zeolite (Na-A) shows favorable selectivity for nitrogen in an oxygen-nitrogen bi-component system at room temperature and also it is known that oxygen selectivity is dominated by differences in adsorption rates. In this study, the oxygen adsorption behavior of Na-A pellets at low temperature was evaluated. When temperature decreased, oxygen selectivity was enhanced as a result of the difference in adsorption rates. It was also strongly suggested that the oxygen equilibrium adsorbed amount of Na-A pellets was larger than that of nitrogen below 213 K. Na-A pellets are expected to be a good oxygen adsorbent for oxygen-nitrogen separation from air by pressure swing adsorption (PSA).

Keywords: Na-A type zeolite; Na-A pellets; oxygen selectivity; low temperature; rate selective adsorbent; pressure swing adsorption


Adsorption Isotherm Studies on Titanium Carbide Powders by M.-A. Lee; S.E. Weber; D. Wittmer; R. Koc; N. Dolan; A.D. Migone (pp. 213-218).
We have used adsorption isotherms to perform a comparative study of the substrate quality of five groups of titanium carbide powder, manufactured following different procedures. The isotherms were measured in an automated setup at 77.3 K using methane and argon as the adsorbates. We determined the specific surface area of each of the powders studied. We also determined whether or not there was evidence of steps (indicative of layer-by-layer adsorption) in each set of adsorption data. The isothermal compressibilities of the adsorbed films were determined from the data measured for each sample. Adsorption measurements were also conducted to determine the effect that heating the powders under vacuum had on the resulting substrate quality.

Keywords: adsorption isotherms; titanium carbide


Adsorption of Pesticides onto Granular Activated Carbon: Determination of Surface Diffusivities Using Simple Batch Experiments by S. Baup; C. Jaffre; D. Wolbert; A. Laplanche (pp. 219-228).
The Homogeneous Surface Diffusion Model (HSDM) has been successfully used to predict the adsorption kinetics for several chemicals inside batch adsorber vessels. In addition to the adsorption equilibrium, this model is based on external mass transfer and surface diffusion. This paper presents the determination of the surface diffusion coefficient (D s) using a differential column batch reactor (DCBR). The adsorption kinetics for three pesticides onto granular activated carbon have been established experimentally. Their corresponding three diffusion coefficients were determined by fitting the computer simulations to the experimental concentration-time data. The results show that this original apparatus increases by an order of magnitude the range of reachable diffusion coefficient compared to perfectly mixed contactors. Moreover the computed D s values are more accurate because of the better assessment of the external mass transfer coefficient (k f) for fixed beds.

Keywords: liquid adsorption; differential column batch reactor; granular activated carbon; homogeneous surface diffusion model; pesticides; surface diffusivity


Criticism on Jäntti's Three Point Method on Curtailing Gas Adsorption Measurements by Carel H. Massen; Johannes A. Poulis; Erich Robens (pp. 229-232).
Jäntti introduced a method to reduce the time required for the stepwise measurement of adsorption isotherms (Jäntti et al., Progress in Vacuum Microbalance Techniques, Vol. 1, Heyden, London, pp. 345–353, 1972). After a pressure change he measured the adsorbed mass three times and calculated its equilibrium value for the new pressure. In the present paper we discuss the applicability of this method in a broader scope (without starting from a single combination of gas and solid adsorbent) and also discuss the influence of measurement inaccuracies. It is shown that the method can serve as an early warning system, which decides whether an improvement of the adsorption model is necessary.

Keywords: sorption; gravimetry; extrapolation method; curtailed measurement


Performance of a Two-Bed Pressure Swing Adsorption Process with Incomplete Pressure Equalization by Heung-Soo Shin; Dong-Ho Kim; Kee-Kahb Koo; Tae-Soo Lee (pp. 233-240).
Incomplete pressure equalization (PE) is practiced in a commercial oxygen concentrator for medical use by adopting simultaneous PE and feed-pressurization for pressurizing an adsorption bed. In such a cycle configuration, extent of equalization during PE affects process performance. In order to assess the effect, performance of pressure swing adsorption (PSA) process with incomplete PE was determined by both simulations and experiments. In simulations, an equilibrium model was used with the assumptions of multicomponent Langmuir isotherms, isothermal operation, and no pressure drop through a bed. The required parameters for simulations were measured in separate experiments. PSA experiments were performed for a two-bed cycle with PE. Two kinds of pressurization, feed and product, were examined. Effects of purge amount and extent of equalization on process performance were assessed in view of productivity and light-component recovery. From the obtained results performance contours were constructed. 95 oxygen mole percent production from air with zeolite 13× was considered as a case study. In both pressurizations, an optimal specific purge and an extent of equalization for the productivity and recovery were observed, but with a different level of equalization. For a maximum productivity feed-pressurization favored incomplete PE, while a maximum recovery occurred at complete PE for both pressurizations. The simulations depicted well existence of optimum conditions, though they showed quantitative disagreement with experiments.

Keywords: PSA; pressure equalization; extent of equalization; simulation; experiment


A Grand Canonical Monte-Carlo Simulation Study of Xenon Adsorption in a Vycor-like Porous Matrix by R.J.-M. Pellenq; S. Rodts; V. Pasquier; A. Delville; P. Levitz (pp. 241-249).
We have performed atomistic Grand Canonical Monte-Carlo (GCMC) simulations of adsorption of xenon in a Vycor-like matrix at 195 K. The disordered mesoporous network is obtained by applying a numerical 3D off-lattice reconstruction procedure to a simulation box originally containing silicon and oxygen atoms of a non-porous silica solid. In order to reduce the computational cost, we have applied a homothetic decrease of the simulation box dimensions which preserves the morphology and the topology of the pore network (the average pore dimension is then around 30 Å). The surface chemistry is obtained in a realistic fashion by saturating all dangling bonds with hydrogen atoms. Small angle scattering spectra calculated on different numerical samples have evidenced a departure from Porod's law due to surface roughness. The simulated isotherms calculated on such disordered connected porous networks, show the capillary condensation phenomenon. The shape of the adsorption curves differs from that obtained for simple pore geometries. The analysis of the adsorbed quantity distribution indicates partial molecular-film formation depending on the local surface curvature and roughness.

Keywords: silical glasses; CPG; Vycor; adsorption; capillary condensation; molecular simulation; Monte-Carlo; SANS; SAXS; fractals; surface roughness; Porod's law; Gurvitch rule; hysteresis loop


Adsorption Characteristics in Zeolite Nano-Pore Evaluated by use of Nitrogen Monoxide as a Probe Adsorbate by Akihiko Matsumoto; Masakazu Sano; Nobuyuki Nishimiya; Kazuo Tsutsumi (pp. 251-257).
Adsorption isotherms of nitrogen monoxide (NO) and in situ EPR spectra of adsorbed NO on mordenite zeolites (MOR) of different cation types (HM, NaM and CaM) are measured at different temperatures to elucidate the effect of the strong adsorption promoted by the enhancement of potential field in micropore of MOR (micropore filling) as well as the electrostatic interaction in MOR on NO adsorption. The NO molecules adsorb irreversibly and fill up the micropore of MOR at 201 K, above the critical temperature of NO, regardless of the kind of cation species. The NO adsorption takes place even at 273 K. In the adsorption at 273 K, the strength of electrostatic field formed by cation sites affects the adsorptivity and the order of saturation amount of adsorption (V s) corresponds to that of the electrostatic field strength. EPR results show that NO molecules strongly interact with cation sites in MOR and disproponation reaction of NO take place on CaM.

Keywords: adsorption; EPR; mordenite; MOR; NO; zeolite


The Adsorption of CHClF2 on NaY5.6 Zeolite by Mitsuhiro Yoshikawa; Toshihisa Yoshida; Mitsumasa Ishiwata; Toshio Hasegawa; Sentaro Ozawa (pp. 259-267).
The adsorption of CHClF2 on NaY5.6 zeolite has been studied by measuring the H and F NMR of the adsorbed CHClF2, focusing in particular on the measurements of the chemical shift and longitudinal relaxation time, as well as the adsorption isotherm measurements. It is possible to determine the coordination structure of the CHClF2 adsorbed on NaY5.6 zeolite by measuring the adsorption amount dependence of the chemical shift. In addition, the motional activity of the adsorbed molecules in the super cage of the zeolite is discussed on the basis of observed longitudinal relaxation times for various adsorption amounts.

Keywords: adsorption; zeolite; chlorodifluoromethane; adsorption structure; H and F NMR; chemicalshift; relaxation time; adsorbate mobility
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