Secondly, unlike H 2 /CH 4 or He/N 2 separations where the product is the weakly adsorbing component, in CO 2 /N 2 separation, we are interested in the strongly adsorbing component, CO 2 . The concentration of CO 2 will be higher in the membrane than that of N 2 , contributing to the flux, and this has been considered as the primary driver for separation.