POLYURETHANE MEMBRANES FROM POLYETHER AND POLYESTER DIOLS FOR GAS FRACTIONATION

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 prepolymer 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-degrees-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-degrees-C (> T(g)). 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-T(g), 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.