Flow of adsorbable gases and vapours in a microporous medium, I. Single sorbates

Abstract

Adsorption and flow measurements have been made in a microporous membrane of a consolidated, high specific area, gas-sorbing carbon. The gases and vapours studied were SO$_2$, CO$_2$, N$_2$, A, and He, over a range of temperatures and pressures. Steady-state permeation rates have shown that in the membrane used, for the vapours SO$_2$ and CO$_2$, and for N$_2$ and A at liquid oxygen and nitrogen temperatures, flow is dominated by the flux of the adsorbed film. Even for nitrogen at 190 $^\circ$K adsorbed flow is considerably larger than gas-phase flow. From the results surface diffusion coefficients have been evaluated which are characteristic functions of the amount adsorbed. The properties of these diffusion coefficients have been considered in relation to the pore structure and the coverage of the surface by adsorbate. Attention has been given to the transient state time-lags. Using the method of Frisch (1957), it has not proved possible to represent these time lags in terms of the steady-state diffusion coefficients, thus emphasizing the distinction between transient and steady-state diffusion in heterogeneous media.