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  Single and multicomponent adsorption equilibria on micro- and mesoporous glass membranes

Markovic, A., Schlünder, E.-U., & Seidel-Morgenstern, A. (2008). Single and multicomponent adsorption equilibria on micro- and mesoporous glass membranes. Talk presented at Jahrestreffen der ProcessNet-Fachausschüsse Adsorption und Fluidverfahrenstechnik. Bingen, Germany. 2008-03-13 - 2008-03-14.

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Markovic, A.1, Author              
Schlünder, E.-U.2, Author
Seidel-Morgenstern, A.1, 3, Author              
Affiliations:
1Physical and Chemical Foundations of Process Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Max Planck Society, ou_1738150              
2University Karlsruhe, D76128 Karlsruhe, Germany Otto-von-Guericke University, D39106 Magdeburg, Germany, ou_persistent22              
3Otto-von-Guericke-Universität Magdeburg, External Organizations, ou_1738156              

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 Abstract: Porous glass membranes attract increasingly attention for gas separation processes and as chemosensors [1,2]. This interest is due to the good thermal stability, chemical resistance and high selectivity. The description of the transport through these materials needs systematic investigation of equilibrium and non-equilibrium properties. The main objective of this paper is to examine adsorption properties of different gases on micro- and mesoporous glass membranes. Four thin, flat membranes in a range of pore sizes between 1.4 nm and 4.2 nm (1.4 nm; 2.3 nm; 3.1 nm; 4.2 nm) were selected for the investigation [1]. The membranes were characterized by large BET specific surface areas, as determined by standard nitrogen adsorption techniques (Table 1). The specific surface areas decrease with increasing pore diameter. Adsorption isotherms of Ar, N2, CO2 and C3H8 as pure gases and as binary mixtures were determined experimentally as a function of temperature using the well-known volumetric method. The membranes were characterized in a temperature range from 20°C to 80°C and at pressures up to 2.5 bar. The applied self-made sorption apparatus consisted of two chambers (V1 and V2) separated by a valve. At the beginning of the experiment the whole equipment was evacuated, and then the chamber V1 (adsorption chamber, where glass membranes were placed) was closed, while the storage chamber V2 was filled with a gas mixture of a certain composition at a certain pressure. Then, the chambers V1 and V2 were connected. After reaching equilibrium the common pressure was measured. The start and final composition of the mixtures were measured by a gas chromatographic method with thermal conductivity detector. There are many different types of adsorption isotherm models available to describe adsorption equilibria. The most often used adsorption models including only single component information were applied first to quantify the observations made. The single component isotherms were described with Langmuir and Freundlich isotherms. Measured adsorption amounts of different gases on each of the membrane were in consistency with determined BET surface areas (the adsorbed amounts of gases are decreasing with decreasing BET surface areas). But, with strongly decreasing surface area from 271 m2/g for 3.1 nm to 143 m2/g for 4.2 nm the adsorption affinity of components changed. In order to describe binary mixture, simple extensions of the single isotherm models were used i.e. the conventional competitive Langmuir and Freundlich equation based on the ideal adsorbed solution theory (IAS) [3]. Since the observed partial loadings of C3H8 in mixture with CO2 were found to be larger in comparison with the amount of single gas C3H8 adsorption, these two simple isotherm models failed to represent the observed degree of competition. Several more sophisticated competitive isotherm models which need additional mixture parameters were applied i.e., two modified multi-Langmuir equations based on: (a) statistical thermodynamics and (b) vacancy solution theory and a modified multi-Freundlich IAS model correcting spreading pressure uncertainties [4]. The results obtained with the isotherm models will be presented. [1] Enke D., F. Janowski, W. Schwieger, “Porous glasses in the 21st century-a short review”, Microporous and mesoporous materials 60 (2003) 19-30. [2] Bhandarkar M., A. B. Shelekin, A.G. Dixon and Y. H. Ma, “Adsorption, permeation and diffusion of gases in microporous glass membranes. I. Adsorption of gases on microporous glass membranes”, Journal of Membrane Science 75 (1992) 221-231. [3] Seidel A. and D. Gelbin, “On applying the Ideal Adsorbed Solution Theory to Multicomponent Adsorption Equiliria of Dissolved Organic Components on Activated Carbon”, Chem. Eng. Sci. 43 (1988), 79-89. [4] Rezničkova Čermakova J., A. Marković, P. Uchytil, A. Seidel-Morgenstern: “Single Component and Competitive Adsorption of Propane, Carbon Dioxide and Butane on Vycor glass”, Chem. Eng. Sci. (2007), accepted, available online.

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Language(s): eng - English
 Dates: 2008
 Publication Status: Not specified
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 Identifiers: eDoc: 339775
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Title: Jahrestreffen der ProcessNet-Fachausschüsse Adsorption und Fluidverfahrenstechnik
Place of Event: Bingen, Germany
Start-/End Date: 2008-03-13 - 2008-03-14

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