AN EXPERIMENTAL-STUDY OF COMBINED GAS-PHASE AND SURFACE-DIFFUSION IN POROUS-GLASS

The diffusion of inert and adsorbable gases and binary gas mixtures th rough porous glass has been studied experimentally. A modified Wicke-K allenbach cell consisting of two gas compartments separated by a tubul ar mesoporous membrane was used. The scope of this paper is to quantif y the contributions of gas phase and surface diffusion. Adopting the d usty gas model (DGM) for the description of gas phase mass transfer an d a generalized Stefan-Maxwell (GSM) theory to quantify surface diffus ion a combined transport model has been applied. The DGM was found to be well suited for the description of transport through the pores, Sur face diffusion of adsorbable gases was analyzed experimentally for dif ferent loadings. The obtained Fickian surface diffusivities were found to be strongly concentration dependent. Multicomponent surface diffus ion is mainly affected by adsorption equilibrium. Reliable predictions require an accurate knowledge of the competitive adsorption isotherms . (C) 1998 Elsevier Science B.V.