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Schlagwörter:
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Zusammenfassung:
Flat sheet homogeneous CA membranes of different thicknesses and different acetyl contents (43.1, 39.1, 32.0 wt.-%) were cast from solutions of Bayer Cellit T-900 and K-700 as well as Eastman Kodak CA E-320 in mixtures of dioxan with dimethylacetamide (9:1 by volume), in pure methyl glycol acetate, and in mixtures of methyl glycol with either dimethylformamide or dimethylacetamide (9:1 by volume). The permeabilities (Pg), diffusion coefficients (Dg), and solubilities (Sg) of the membranes for He, N2, CH4, and CO2 were then determined as functions of pressure (0.1 atm to 100 atm) and temperature (20°C up to 80°C) by use of time-lag measurements. In the presence of pin-holes the permeabilities increased linearly with increasing mean pressure whereas imperfection-free membranes exhibited both pressure-independent and slightly pressure-dependent permeabilities, diffusivities, and solubilities. The sorption isotherms of He, N2, and CH4 obeyed either Henry's law or the dual-sorption model relationship whereas the sorption isotherm of CO2 followed Henry's law only up to pressures of p′ ⋍ 18 atm and increased nonlinearly with increasing p′ at pressures beyond p′ − 18 atm. The temperature dependence of Pg, Dg, and Sg, measured at some reference pressure, yielded activation energies of permeation, Ep, and diffusion, ED, as well as enthalpies of sorption, ΔHS.
