Pervaporation Of Binary Mixtures Research Articles

PVC–activated carbon based matrices: A promising combination for pervaporation membranes useful for aromatic–alkane separations

The separation of aromatic–aliphatic liquid mixtures is difficult perform in a satisfactory technico-economic manner by conventional methods, such as extractive distillation, azeotropic distillation, or liquid–liquid extraction. The separation by pervaporation (PV) of liquid toluene–heptane mixtures, selected as a model mixture, was performed with several dense membranes based on poly(vinylchloride) (PVC) as the starting material. Aiming to improve the performances of pure PVC films, i.e. high selectivity and very low flux, composite membranes were prepared by incorporating different percentages of activated carbon introduced as selective sorbent fillers for toluene. In this study, we report the results obtained with composite PVC membranes containing up to 40wt% Maxsorb SPD30. The transport properties of these membranes were characterized by measurements of isothermal sorption and by pervaporation of binary mixtures. It was found that the performances of certain composite membranes were significantly increased compared with pure PVC membranes. Under the same experimental conditions, the pervaporation toluene flux was seven times higher, whereas the toluene selectivity was only slightly decreased (the permeate enrichment decreased from 89 to 83wt% at 74°C). Thus, the combination PVC with activated carbon appears to be a promising method to obtain effective PV membranes for aromatic–alkane separations.

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

Pervaporation of binary mixtures (CH 2Cl 2–CHCl 3, CHCl 3–CCl 4, CH 2Cl 2–CCl 4) 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.