Gas separation properties in cyclic olefin copolymer membrane studied by positron annihilation, sorption, and gas permeation

In this article, the gas transport and sorption properties of a series of cyclic olefin copolymer (COC, Topas®) membranes containing 40–66 mol% norbornene were investigated. The permeability, diffusion, and sorption coefficients of He, N2, O2, and CO2 in a COC membrane were determined at 35 °C and pressures in the range of (2.0265–10.1325) × 105 Pa (2–10 atm). Compared with the smallest norbornene content membrane (Copoly40), the highest norbornene content membrane (Copoly66) markedly improved the oxygen permeability. The improved gas separation properties appear to be associated with free volume of the membranes. Free volume data were determined by means of positron annihilation lifetime spectroscopy (PALS). Furthermore, the penetrant solubility, characterized by isotherm sorption analysis, correlated strongly with the free volume and penetrant condensability. The results presented and discussed in this work suggest that the COC copolymer can be used as membrane material for the separation of O2/N2 at moderate pressure (<10.1325) × 105 Pa (<10 atm)), additionally, it exhibits an adequate thermal, mechanical, and gas separation properties balance.