Study On Pervaporation Separation Of Dimethyl Carbonate/methanol Binary Mixtures With Menbranes

Regenerated perfluoro-ion-exchange membranes (PFIEM) in chlor-alkali industry,polymer membrane of poly (vinyl alcohol)-perfluorslulfonic acid/poly (acrylonitrile)(PVA-PFSA/PAN) hollow fiber composite membranes and organic/inorganic hybridmembranes of poly (vinyl alcohol)-perfluorslulfonic acid-tetraethyl orthosilicate/poly (acrylonitrile)(PVA-PFSA-TEOS/PAN) hollow fiber composite membranes wereprepared and used for the pervaporation separation of dimethyl carbonate/methanol (DMC/MeOH) binary mixtures.Firstly, PFIEM was regenerated with HCl as regenerating regents, andregenerated membranes were prepared after treatment of ultrasonic wave. Theenergy-dispersive spectrum (EDS) demonstrates that the impurities on the surfacesof waste PFIEMs can be effectively cleared by the regeneration process. The degreeof swelling, sorption, and pervaporation properties of the regenerated PFIEMs withdifferent counter ions were investigated. The results indicate that the counter ions ofPFIEMs conspicuously influence the degree of swelling, sorption, and pervaporationproperties for DMC/MeOH mixtures. The degree of swelling and solubility selectivityboth decreases with the alkali metal counter ions in the sequence: Li+> Na+> K+> Cs+.The degree of swelling increases with MeOH concentration increasing in feed liquid.The per-vaporation measurements illustrate that the permeation flux decreases andthe separation factor increases with the rising in ion radius of counter ions. Theincrease of feed concentration (MeOH) and feed temperature is advantageous toimprove permeation flux while at the cost of separation factor decreasing.Secondly, using isoproranol（IPA）and water as solvents, the regenerated PFIEMas raw material, the particles of PFSA were prepared under high temperature andhigh pressure. Using poly(vinyl alcohol)(PVA) and perfluorslulfonic acid (PFSA) ascoating materials, poly(acrylonitrile)(PAN) hollow fiber ultrafiltration membrane as substrate, PVA-PFSA/PAN composite membranes were fabricated by dip-coatingmethod. The fabricated composite membranes were used to the separation ofdimethyl carbonate (DMC)/methanol (MeOH) binary mixtures by pervaporationprocess. SEM images verify that the coated layer is well combined with substrate andthe thickness nearly linearly increases with the coating solution concentration. Theseparation factor increases but at cost of the decline of permeation flux when theconcentration of the coating solution or its PVA mass fraction increase. Thepermeation flux increases and separation factor slightly increases with the feedtemperature increasing at30-60℃. The increase of feed MeOH concentration leadsto an improvement of permeation flux and a decline of separation factor.Lastly, tetraethyl orthosilicate（TEOS）was added in the PVA-PFSA coatingsolutions, and PVA-PFSA-TEOS/PAN hollow fiber composite membranes wereprepared by dip-coating method and used for the separation of dimethyl carbonate/methanol (DMC/MeOH) binary mixtures by pervaporation process. SEM imagesverify that the coated layer is well combined with substrate, and the coated layer isdense and smooth. FTIR spectra and XRD patterns verify that heat treatmenttemperature and TEOS content have different effects on membrane performance.The pervaporation experiments results showed that separation factor increased withthe increasing of heat treatment temperature，while the flux decreased. When feedMeOH concentration increased, flux increased from102g?m-2?h-1to1086g?m-2?h-1, but the separation decreased from15.8to5.7.