A comparative structural study of cracking catalyst, porous glass, and carbon plugs by surface and volume flow of gases

Abstract

Transient and steady states of volume and surface flow of gases and vapours in microporous media require for their description four different diffusion coefficients, namely, a surface and a gas-phase coefficient for transient and a surface and gas-phase coefficient for steady flow. The distinction between steady and transient flow arises in part because of the role of blind pores. Similarly, two different porosities $\epsilon $ and $\epsilon _{s}$ and two different surface areas A and A$_{s}$ govern transient and steady-state flow respectively. By comparing the two gas-phase and the two surface diffusion coefficients with gas-phase and surface diffusion coefficients in a smooth cylindrical capillary having $\epsilon $/A equal to that for the porous medium, four structure factors can be defined, in terms of which the pore properties of microporous media can be discussed. Data are presented for sorption, transient flow (time lag) and steady flow of He, Ne, A and N$_{2}$ in compressed alumina-silica catalyst plugs. These, and previously obtained data for Vycor porous glass (Barrer & Barrie 1952) and Carbolac carbon plugs (Barrer & Strachan 1955) have been analyzed according to the above procedure, and pore properties compared. In this way it was possible to obtain information regarding pore structure which could not have been derived by other methods.