PERMEATION TIME-LAG WITH NONLINEAR ADSORPTION AND SURFACE-DIFFUSION

Time lag permeation experiments have been traditionally conducted with weakly adsorbing species or at low upstream concentrations, in order to simplify the asymptotic solution of the mass balance equations. In this paper, the solution is obtained for the case of non-linear adsorp tion according to the Freundlich and Langmuir isotherms and concentrat ion dependent surface diffusion described by the model proposed by Yan g et al. (1973, A.I.Ch.E. J. 19, 1052). This asymptotic solution is co mpared to the one obtained for the D-R isotherm with the concentration dependence of the surface diffusion coefficient represented by the gr adient in chemical potential. The solutions are applied to the permeat ion data of Ash et al. (1963, 1973, Proc. R. Soc. A275 and A271, 1 and 255). The parameters and relations obtained are compared to those pre viously obtained from experiment with good agreement. (C) 1997 Elsevie r Science Ltd.