The concentration dependent permeation properties of binary CO2 gas mixtures through carbon molecular sieve membrane

This paper deals with the permeation properties of binary gas mixtures (CO2/He, CO2/H2) through a carbon molecular sieve membrane (CMSM). The permeation properties of binary gas mixtures were determined via an improved time lag technique, and the permeation flux of an individual component was determined by selectively capturing the CO2 in the permeate stream via a cold trap filled with liquid N2. The 'true' permeation properties (i. e., permeability and perm-selectivity) of the CMSM were found to deviate significantly from the 'ideal' values based on pure gas permeation, displaying a strong dependency on the composition of the feed gas mixtures. At certain concentration ranges, there was even a 'reverse' selectivity observed. This concentration-dependent selectivity was analyzed and modelled via the Maxwell-Stefan Equation, which highlighted the importance of competitive adsorption and competitive diffusion of different permeant components in the porous network of the membrane. Such concentration dependencies of permeabilities may post a challenge for certain gas separations but also represent an opportunity if properly and accurately exploited for certain membrane separation applications.

Automated summary

This paper investigates the permeation properties of binary gas mixtures through a carbon molecular sieve membrane and finds a significant correlation between the permeation properties and gas composition. The study also reveals that the 'true' permeation properties of the membrane deviate from 'ideal' values and exhibit concentration-dependent selectivity. This dependence can be modeled and analyzed using the Maxwell-Stefan Equation.