Preparation And Pervaporation Behavior Of CA/EVA Blends And PHPVAc And Their Membranes For Seperating Organic Solvent Mixtures

The application of pervaporation in organic mixture separation is of energy-saving and environment-protecting significance. In this paper, pervaporation of two kinds of organic mixtures is investigated: one is using cellulose acetate/ethylene-co-ethylene acetate (CA/EVA) blend membrane for methanol(MeOH) removal from MTBE (methyl t-butyl ether); the other is using partly hydrolyzed poly(vinyl acetate)(PHPVAc) membrane for benzene removal from benzene/cyclohexane(50v/50v) mixture. Furthermore, the relationship between pervaporation performance(PVAP) and its dilute solution property of both materials has been studied.CA/EVA blends are successfully dissolved in selective casting solvents, which includes dioxane(DIO)/l,2-dichloroethane(DCE), DIO/cyclohexane(CYH) and DIO/chloroform(CF), by separate-step method. The compatibility of CA/EVA blends in different solvent mixtures is investigated by viscometry. It was found that CA is compatible with EVA in DIO/DCE solvent mixture and DIO/CF solvent mixture, and is uncompatible in DIO/CYH solvent mixture, which is due to the different conformation of EVA chain in DCE and CYH. The CA/EVA blend membranes, cast from DIO/DCE solvent mixture and DIO/CYH solvent mixture, was used to separate MeOH/MTBE mixture with 5(wt)% MeOH. Results reveal that CA/EVA blend membrane can get higher methanol flux(JMeOH) than CA membrane. Moreover, JMeOH of CA/EVA blend membrane cast in DIO/DCE solvent mixture is higher than that cast in DIO/CYH solvent mixture, which is also due to the the different conformation of EVA in DCE and CYH.PHPVAc, by alcoholysis from PVAc, and its membrane are charactered by Infrared spectral analysis, chemical titration, viscometer, DSC and contact angle machine. The PVAP of PHPVAc membrane were investigated by changing some factors such as degree of hydrolization(DH) of PHPVAc, solvent composition of casting solvent mixtures, feed temperature and feed composition. The results are as followed. First, the benzene flux(JBEN) of PHPVAc membrane from DIO/H2O solvent mixture and its Huggins constant Kh obey the rule Jben Kh. Second, the membrane with extendedchain of PHPVAc in the good casting solvent is preferred for larger α , that is to say the PHPVAc membrane with higher intrinsic viscosity [ η ] in the the selective solvent mixtures can obtain higher α . Third, the PHPVAc chain shrunk is disadvantage to gain high α for the PHPVAc membrane, especially the case of shrinking the hydrophilic segments with hydroxyl groups.