NOVEL POLYMERIC MEMBRANES FOR SEPARATION OF HYDROCARBONS

The search for polymeric materials capable of separating lower paraffins from the corresponding olefins revealed that polyphenyleneoxide (PPO) and some PPO-based copolymers possess rather high selectivity and permeability in separation of the gaseous mixtures containing methane and ethane, ethylene and ethane, or propene and propane (selectivities alpha(CH4/C2H6) is-approximately-equal-to 12, alpha(C2H4/C2H6) is-approximately-equal-to 4-5 at 20-30-degrees-C, and alpha(C3H6/C3H8 is-approximately-equal-to 25-70 at 50-degrees-C were obtained). Solubilities of these hydrocarbons in PPO and its copolymers were measured, and were found to change in the sequence CH4 < C2H4 is-approximately-equal-to C2H6 < C3H6 is-approximately-equal-to C3H8. Effective diffusion coefficients were evaluated from the permeability and solubility data. The conclusion is reached that considerable differences in permeabilities of lower alkanes and the corresponding alkenes are caused by the higher diffusivity of the latter, whereas the solubilities of alkanes and alkenes are practically the same. The highest diffusion coefficients and the lowest solubility coefficients are observed for methane.