Mass transport in porous materials under combined gradients of composition and pressure

An expression is derived for the analysis of gas‐phase mass transport in porous media in the presence of gradients in pressure and mole fraction. The behavior of porous media is contrasted with that of capillary tubes. A continuous‐flow diffusion and permeation apparatus was employed for studies of mass transport in a fritted glass diaphragm. Measurements were obtained at varying levels of pressure and cover both isobaric binary diffusion and the permeation of pure gases and gas mixtures. These experimental results and previous data obtained by Hewitt and Sharratt and by Mason, et al. bear out the form of the equation and successfully provide independent checks of the three constants necessary to characterize a given porous medium.