Polyurethane membranes from polyether and polyester diols for gas fractionation

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Abstract
Polyurethane prepolymers were prepared in ethylacetate from TDI and poly(oxypropilene)glicols) (PE‐PU) or poly(tetramethyleneglycoladipate)diols (PES‐PU) of different molecular weights (M). Homogeneous membranes were prepared by spreading the pre‐polymer solution added with a three, four or pentafunctional crosslinking agent, in the presence of stannous octoate as a catalyst. On increasing M, the PUs Tg decreases regularly in the range +30 to −47°C. PU's are amorphous with the exception of PES‐PU obtained from highest M polyester diols. Permeability P, diffusivity D, solubility coefficient S of N2, O2, CO2, CH4, CO were measured at T=35°C (>Tg).P, D, S do not depend on the crosslinker functionality, but mainly on M. P and D in PE‐PU are linear function of T‐Tg while in PES‐PU the function is not linear. Gas solubility fulfills in general the regular solution theory. P, D, S of water vapor is also given. Permeability decreases in the order H2O>CO2 > O2 > CH4 > CO > N2. Some practical application based on particular selectivities is suggested.

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