Transport of single gases and of binary gas mixtures in a microporous carbon membrane

Abstract

A study has been made of steady-state flow of the single species He, H₂, D₂, N₂ and NH₃, and of the binary mixtures H₂+ N₂, He + NH₃, H₂+ NH₃ and N₂+ NH₃ through a microporous membrane of high area compressed carbon powder. For the weakly sorbed species (He, H₂, D₂, N₂) the permeability, K, was independent of pressure and hence of amount sorbed and isotherm curvature. With the strongly sorbed ammonia K increased with pressure and, at lower temperatures, reached a maximum and then rapidly declined. Experiments with mixtures of ammonia and a weakly sorbed gas showed that blockage of gas phase flow by the sorbed ammonia could be severe. Under appropriate conditions this resulted in extremely high fractionation factors approaching those expected for an ideal semipermeable membrane. Ammonia permeated rapidly but the weakly sorbed gases were retained on the high pressure side of the membrane.