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Gas Transport through amine-modified porous glass membranes


Stoltenberg,  D.
Physical and Chemical Foundations of Process Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Max Planck Society;

Seidel-Morgenstern,  A.
Physical and Chemical Foundations of Process Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Max Planck Society;
Otto-von-Guericke-Universität Magdeburg, External Organizations;

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Stoltenberg, D., & Seidel-Morgenstern, A. (2009). Gas Transport through amine-modified porous glass membranes. Talk presented at NAMS 2009 - 19th Annual Meeting of the North American Membrane Society. Charleston, USA. 2009-06-20 - 2009-06-24.

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Due to the threat of global warming caused by carbon dioxide accumulation in the atmosphere, the separation of carbon dioxide from other gases attracted much attention in the recent literature. Because of large surface areas and the possibility to modify the surface functionality, porous silica is regarded as a potential material class to contribute to solve this problem. Amino-functionalized porous silica was already used in various studies for carbon dioxide sequestration by adsorption as well as membrane separation [1, 2]. In this study, mesoporous glass membranes [3] were modified with intend to enhance the CO2 permselectivity. Controlled pore glass was chosen due to the adjustable pore size and the known adsorption potential for carbon dioxide and propane [4]. The prepared glass membranes were characterised by a narrow pore size distribution, an average pore diameter of 5 nm and inner surface areas of approx. 140 m²/g, measured by low temperature nitrogen adsorption. Approved surface grafting methods were used to functionalize the membrane surface. Various aminopropyl-trialkoxysilanes were grafted onto the membrane surface by reaction in toluene. Several substitutions of the amino-function were used to modify the basicity and steric hindrance of the amino-group in order to adjust the strength of carbon dioxide adsorption. Different concentrations of trialkoxysilanes were used to adjust the thicknesses of the grafted layers and therefore the surface concentrations of the amines. Adsorption isotherms of carbon dioxide were investigated at different temperatures using a volumetric method. The amino-modification led to an increased adsorption of carbon dioxide especially at elevated temperatures due to the formation of carbamate species. Single gas permeation was conducted using the gases carbon dioxide, propane and nitrogen by a modified Wicke-Kallenbach-cell [4]. Since carbon dioxide and propane have the same molecular weight, observed selectivities can be ascribed exclusively to the different interactions with the surface of the membrane. Higher surface concentrations of the adsorbable gases can result in increased surface diffusion. This effect can be exploited to generate separation performances beyond the Knudsen selectivity. Problems arise if the adsorbed species loose their mobility on the adsorbent's surface. Too strong adsorption suppresses the surface diffusion and reduces observed selectivities to Knudsen ratio. Literature [1] Knowles G. P., Graham J. V., Delaney S. W., Chaffee A. L., Fuel Proc. Tech. 86 (2005) 1435. [2] McCool B. A., DeSisto W. J., Ads. Funct. Mater. 15 (2005) 1635. [3] Enke D., Janowski F., Schwieger W., Microporous Mesoporous Mat. 60 (1-3) (2003) 19. [4] Markovic A., Stoltenberg D., Enke D., Schlünder E.-U., Seidel-Morgenstern A., J. Membrane Sci., submitted