Amorphous Teflons AF as organophilic pervaporation materials: Separation of mixtures of chloromethanes

Pervaporation of binary mixtures (CH2Cl2–CHCl3, CHCl3–CCl4, CH2Cl2–CCl4) through two amorphous copolymers of 2,2-bis-trifluoromethyl-4,5-difluoro-1,3-dioxole and tetrafluoroethylene was studied at different temperatures, feed composition, and downstream pressure. It was shown that the copolymer with the larger content of the dioxole comonomer and having the greater free volume (AF 2400) is more permeable, whereas selectivity of separation of the two copolymers are similar for some regimes. The dependence of permeation rate and selectivity on the process parameters of the AF copolymers indicated that mobility selectivity prevails for pervaporation of the mixtures studied through these membrane materials. The deviation coefficients used for analysis of mixed permeation indicated strong interactions of the components in pervaporation of binary mixtures. Pervaporation separation index (PSI), which depends on permeability and selectivity of pervaporation, was used to characterize the performance of the process. It was shown that PSI increases for higher contents of the components enriched in the permeate and at higher temperatures.