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Adsorption: Journal of the International Adsorption Society (v.6, #4)
Comparison of Experimental Techniques for Measuring Isosteric Heat of Adsorption by Dongmin Shen; Martin Bülow; Flor Siperstein; Maximilian Engelhard; Alan L. Myers (pp. 275-286).
Experimental measurements of heats of adsorption published in the literature are often in disagreement; differences of 10–20% are common. The three most widely used experimental methods are: (1) differentiation of adsorption isotherms at constant loading; (2) measurement of adsorption isosteres; (3) calorimetry. Results from these methods were compared for the systems nitrogen on CaA, oxygen on CaA, and carbon dioxide on NaX. Although the same materials and similar degassing procedures were used for all experiments, calorimetric heats are about 2 kJ/mol higher than the heats from isoteric measurements. Additional experiments are needed to bring these methods into exact agreement.
Keywords: sorption heats; calorimetry; isosteric technique; zeolites; gases
The Rectangular Isotherm Model for Adsorption Kinetics by Douglas M. Ruthven (pp. 287-291).
The transient uptake response of an adsorbent particle, subjected to a step change in surface concentration, is considered. It is shown that, when the isotherm is highly favorable, the theoretical curves derived for a Langmuirian system reduce asymptotically to the much simpler form for a rectangular isotherm. The simple rectangular model provides a useful approximation even when the form of the actual isotherm is quite far from the rectangular limit.
Keywords: diffusion; shrinking core; rectangular isotherm
A Novel Solution Method for Interpreting Binary Adsorption Isotherms from Concentration Pulse Chromatography Data by P.J.E. Harlick; F.H. Tezel (pp. 293-309).
Adsorption separation of carbon dioxide from nitrogen (N2, which represents air) was investigated by using H-ZSM-5 as the adsorbent with SiO2/Al2O3 ratios of 30 and 280. Pure and binary isotherms at 40°C have been determined experimentally using concentration pulse chromatography.Presently available methods for determining binary isotherms from concentration pulse chromatography data have been reviewed and shown incapable of interpreting this particular binary system. A novel solution method is presented and shown to be superior to the other methods.The binary isotherms for the CO2-N2 system show an increase in CO2 selectivity with increase in surface heterogeneity. The optimal separation factor for H-ZSM-5-30 was found to be 215 at 0.7% CO2 in the feed, whereas, H-ZSM-5-280 has an optimal separation factor of 48 at 2.7% CO2 in the feed.
Keywords: binary adsorption; concentration pulse method; adsorption of CO2 ; adsorption of N2 ; ZSM-5; separation of CO2 and N2
Single and Mixed Gas Adsorption Equilibria of Carbon Dioxide/Methane on Activated Carbon by Rick Van Der Vaart; Cindy Huiskes; Hans Bosch; Tom Reith (pp. 311-323).
Single gas adsorption isotherms of methane and carbon dioxide on micro-porous Norit RB1 activated carbon were determined in a gravimetric analyser in the temperature range of 292 to 349 K and pressures to 0.8 Mpa. Furthermore binary isotherms of carbon dioxide and methane mixtures were determined at 292 K and pressures up to 0.65 MPa. Adsorbed phase compositions were determined from the gravimetric data by the rigorous thermodynamic method of Van Ness.These experimental binary equilibrium data were compared with equilibrium data calculated by the Ideal Adsorbed Solution (IAS) model. Only moderate agreement could be obtained.Finally, activity coefficients, accounting for the non-ideality of the adsorbate mixture, were calculated from the experimental data. The Wilson equation, derived for bulk solutions, was fitted on these activity data and the Wilson interaction parameters were determined. The Wilson equation proved to correlate the experimental data reasonably. However, the Wilson interaction parameters are not only completely different from those found for bulk solutions, but also the physical interpretation of these parameter values is completely lacking.It is concluded that new solution models should be developed encompassing both non-ideal solution behaviour and surface heterogeneity.
Keywords: gas adsorption; activated carbon; theory; experimental data; activity coefficient; spreading pressure
Thermodynamics of Copper Adsorption-Desorption by Ca-Kaolinite by M. Doula; A. Ioannou; A. Dimirkou (pp. 325-335).
The temperature effect on Cu adsorption and desorption on kaolinite has been investigated at four temperatures (8°C, 25°C, 30°C and 40°C). The clay sample was saturated with Ca. Copper was sorbed from solutions containing eleven Cu concentrations between 0.0010 and 0.0211 M, equilibrated for 2 days. Cu adsorption decreased, but desorption increased with increasing temperature, indicating that adsorption is an exothermic process while desorption is endothermic. These conclusions are confirmed by the values of ΔH 0 estimated for adsorption and desorption.The initial copper concentration is a significant factor influencing mainly the adsorption process, which is spontaneous (ΔG 0 < 0) only for low initial Cu concentrations. The desorption process is spontaneous for all Cu concentrations. ΔS 0 values have also been calculated. Experimental adsorption data were successfully fitted to the Freundlich isotherm and to the Gouy-Chapman model in order to express the process quantitatively.
Keywords: copper; ca-koalinite; adsorption; desorption; thermodynamics
Dynamic Adsorption of Vapours by Activated Carbons and by Polymer-Derived Adsorbents: 1. Adsorption at 0% R.H. by F. Karpowicz; J. Hearn; M.C. Wilkinson (pp. 337-347).
The uptakes of volatile organic compounds from a nitrogen carrier gas at 0% R.H. onto packed beds of adsorbents have been measured by monitoring the effluent vapour concentration profile as a function of time. The profiles have been quantitatively fitted by a modified Bohart-Adams equation which was then integrated to yield the adsorbent capacities. Traditional activated carbons, carbonised macroreticular resins and a macroreticular polymer were used in the study. Performance in the dynamic tests has been related to the pore volume characteristics and surface areas determined from nitrogen adsorption isotherms. Whilst the extent of micropore filling basically increased as the sorbate boiling point increased and increased capacities reflected increased micropore volumes, these trends were interrupted by size exclusion and specific polar interaction effects.
Keywords: adsorbents; processes and applications
Static and Kinetic Studies on the Adsorption Behavior of Sulfadiazene by A.K. Bajpai; M. Rajpoot; D.D. Mishra (pp. 349-357).
To investigate the nature of interactive forces between sulfadiazene molecules and alumina surface the experiments were performed for the adsorption of sulfadiazene (SD) from its aqueous sulution onto the alumina surfaces at 25 ± 0.2°C and the influence of factors such as increasing concentration of SD (4.0–20.0 × 10−3 mol cm−3), the time required for adsorption equilibrium, pH (2.0–12.0) and temperature (5–45°C) of the adsorption medium, the presence of ions like Cl−, SO2− 4 and PO3− 4 (0.01–0.30 M) and organic solvents (5% v/v) were observed on the course of adsorption of SD. Various adsorption and kinetic parameters such as adsorption coefficient, the rate constants for adsorption and desorption were also evaluated. The results of the above cited studies facilitated to formulate the mechanisms of interaction between SD and alumina surfaces. From application view point the present work may be a potential tool for an effective chromatographic separation of sulfa drugs from industrial effluents.
Keywords: sulfadiazene; adsorption; kinetics
Publications on Adsorption Science and Technology by S. Sircar (pp. 359-365).
A key word search of Chemical Abstracts Registry and Derwent Patent Index on various topics of Adsorption Science and Technology between 1970–2000 reveals an immense volume of patents and publications in this area. A detailed breakdown of this search is provided.
Keywords: literature; patent; adsorption science and technology; bibliography