Impact of the porous support disc of a gas permeation cell on the estimation of the membrane transport properties

Abstract

The rapid development of polymeric membranes for gas separation requires an accurate and suitable method for promptly assessing their performance. The time-lag method is one of the most commonly used methods to estimate the permeation parameters (permeability, diffusivity, and solubility) of single gases in membranes. However, a membrane is not evaluated in isolation; it is placed in a permeation cell, which may impact the determination of these parameters. This paper explores the effect of using a porous support disc on estimating the membrane permeation parameters. The impact of a porous disc supporting an ideal membrane was assessed by solving Fick's second law of diffusion. Results clearly show that the membrane thickness, along with the pore size and the porosity of the porous disc, may significantly influence the estimation of the diffusivity and permeability of the membrane using the time-lag method. Interestingly, the observed effect was not dependent on the intrinsic diffusivity of the membrane. The relative diffusivity and relative permeability are strictly a function of the porosity of the porous disc and the ratio of the pore diameter to the membrane thickness. Results can be used to correct the impact of the porous plate and recover the intrinsic membrane properties.