Mechanism of permeation through molecular-sieve carbon membrane. Part 1.—The effect of adsorption and the dependence on pressure

Abstract

The permeation in narrow-pore molecular-sieve carbon membranes (MSCM) is governed by adsorption and activated transport and proceeds exclusively through the ultramicropores. Contribution from the solution–desolution mechanism is unlikely. The dependence of permeabilities on pressure and extent of pore opening has been studied. On the basis of adsorption isotherms the relation between adsorption and permeation is established. It is maintained that the slope of the adsorption isotherm of the penetrant determines the concentration gradient responsible for the flow through the membrane. For weakly adsorbing gases, permeability is independent of pressure, as corresponding to a free molecule in the pore system or to a linear adsorption isotherm. For adsorbing gases permeability decreases with pressure, owing to the decrease in the slope of the type I adsorption isotherm.