Permeation of oxygen, argon and nitrogen through polymer membranes

Abstract

In order to screen polymer materials suitable for the separation of O 2/Ar mixtures, gas permeability coefficients of O 2, Ar and N 2 through a total of 19 polymers were measured at 25°C and atmospheric pressure. Diffusion coefficients and solubility coefficients were calculated from time-lag data. The gas permeabilities and diffusivities in all polymers tested are in the order of O 2>Ar>N 2, while the gas solubilities are in the order of Ar>O 2>N 2. Higher permselectivities are observed in glassy polymers than in rubbery polymers. Permeability ratios, which denote the ideal separation factors, for O 2/Ar in glassy polymers are strongly affected by the contribution of the diffusivity ratios. The absolute diffusivities and the diffusivity ratios are correlated rather well using the free volume theory of polymers which employs the group contribution method based on the chemical structure of polymers. Slight deviations from the expected values are discussed by introducing a factor of polymer chain fluctuation speed. Poly (2,6-dimethyl-1,4-phenylene oxide) and tetramethyl bisphenol-A polycarbonate exhibit a relatively high permeability of O 2 and a high permeability ratio of O 2/Ar. Temperature and pressure dependencies of gas permeabilities are examined with these two polymers.