THEORY OF GAS-DIFFUSION AND PERMEATION IN INORGANIC MOLECULAR-SIEVE MEMBRANES

Theoretical models of gas diffusion and permeation in microporous mole cular-sieve membranes are presented The effect of the adsorbed diffusa nt on the total transmembrane flow is insignificant for permanent gase s. For highly adsorbable gases the effect of the adsorbed molecules on the total transmembrane flux may be high at low temperatures. The act ivation energy of diffusion increases when the kinetic diameter of the diffusant increases. The activation energy of gas diffusion compares well with the values calculated based on the Lennard-Jones potential. Maximum possible permeability coefficients calculated for He in the mo lecular-sieve membranes do not exceed similar to 30,000 Barrer at room temperature. The experimentally observed value for Ne permeability is similar to 1,000 Barrer (T=30 degrees C) because of the high tortuosi ty (tau approximate to 25) and low porosity (theta=0.22) of the membra ne porous structure.