The characterization of CO2 permeation in a CMSM derived from polyimide

Abstract

Abstract Carbon molecular sieve membrane (CMSM) is prepared from Kapton polyimide. The CMSM presents strong molecular sieving effect for gas molecules with different dimensions. CO 2 sorption and permeation experiments were performed on the CMSM over a wide pressure range (up to 40 atm). The permeation time lag and steady state permeation flux were employed to characterize the concentration dependence of the diffusion coefficient of the adsorbate. A new functional form is proposed for the concentration dependence of the surface diffusivity [ D μ ( C )/ D μ 0 =1/(1− θ ) n , where θ is the ratio of surface coverage and n ≥1] to cope with the experimental observations. With the sorption–diffusion mechanism, both transient time lag and steady state flux indicates that the surface diffusivity of CO 2 takes a concentration dependence much stronger than that described by the traditional HIO model, [i.e. D μ ( C )/ D μ 0 =1/(1− θ )]. The reason for this abnormality is discussed.