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Abstract:
Flat sheet, homogeneous CA membranes of different thicknesses (10.1 μm, 89 μm, and 157 μm) were cast from solutions of Bayer Cellit T-900 in a mixture of dioxan and dimethyl acetamide (9:1 by weight). The permeabilities (Pg), diffusion coefficients (Dg), and solubilities (Sg) of He, N2, and CO2 through the CA membranes were measured as functions of pressure (1 atm to 100 atm) and temperature (20°C up to 80°C) using time-lag measurements. Imperfection-free membranes exhibited pressure-independent permeabilities, diffusivities and solubilities for He and N2 at pressures up to 30 atm, with a slight change of the gas permeability with pressure at pressures of 30 atm to 100 atm. On the other hand, the permeability increased linearly with increasing mean pressure if the membrane contained pin-holes. The sorption of He, N2, and CO2 follows Renry's law over the entire pressure range. However, the sorption capability of the membranes for CO2 increased discontinuously at p′ ⋍ 22 atm. Two different Henry's law constants were thus obtained for the two different pressure ranges. The temperature dependence of Pg, Dg, and Sg, measured at p′ = 20 atm, gave activation energies of permeation, EP, and diffusion, ED, and enthalpies of dissolution, ΔHS.
