The Preparation And Separation Performance Of Poly(Vinyl Alcohol) Pervaporation Membranes Crosslinked By Initiation Reaction

Pervaporation is a new type of membrane separation technology, which has beenwidely used in the dehydration of organic solvent. poly(vinyl alcohol)(PVA) is ahydrophilic polymer material and has been widely used in preparing pervaporationmembrane because of its low price, easy accessibility and excellent water permeability.However, It is necessary to modify PVA before using it as separation membranebecause of its excessive swelling. Crosslinking is a effective modified method andusually use the hydroxyl to make crosslinking reaction, but it will decrease thehydrophily of the membrane and cause low selectivity and permeability of membranefor water. This paper, we explored a new crosslinking method of not using hydroxyl tomake crosslinking reaction, the hydrophily of the membrane did not decrease. Theconclusions can be listed as followings:(1) First, We would select the appropriate crosslinking initiator and cross-linker.Crosslinking initiator included ammonium ceric nitrate, ammonium persulfate(APS),azodiisobutyronitrile, benzoyl peroxide and UV-light; the cross-linker wereN’N-methylene double acrylamide, divinyl benzene and isocyanuric acid. Theresearch showed that ammonium persulfate could improve the swelling performanceof the membranes obviously, the swelling degree decreased from310%to20%, alsoN’N-methylene double acrylamide was a effective cross-linker.(2) Second, The composite membrane of PVA/polyacrylonitrile (PAN) wasprepared by crosslinking reaction of PVA and APS. The cross-linked membraneswere characterized with scanning electron microscopy and wide-angle X-raydiffraction. The swelling degree, gel fraction and thermal properties of the PVAmembranes were determined, the film thickness, basement membrane, temperatureand vacuum degree of downstream were also investigated. The results showed that theswelling of PVA in the solution were inhibited, the crystalline region of PVAdecreased and thermal stability increased. The cross-linked PVA membranecontaining1.5wt%APS exhibited best performance, the permeation flux was319.8g/m2·h and the separation factor was3781.8. With increasing the membranethickness, the permeation flux decreased while separation factor increased, the besttime for hydrolyzing of the membrane is1.5h. When increasing the temperature, theflux increased, while the separation factor decreased. In addition, with increasing thevacuum degree of downstream, the flux increased quickly while the selectivitydecreased slightly.(3) At last, The PVA/APS-MBA cross-linked membrane was prepared withcross-linker. The cross-linked membranes were characterized with infraredspectrometer, the swelling degree and gel fraction of the membranes were measured.The results showed that cross-linker could promote the crosslinking reaction, with increasing the cross-linker content, the gel fraction increased and the swelling degreedecreased. The cross-linked membranes were used to separating95wt%ethanolaqueous solution, isopropanol aqueous solution and n-butyl alcohol aqueous solution,all the performance were good. The membrane still existed high separation factorwhen it run48h continuously, only the flux of the membrane decreased slightly.We set up a new preparation method of PVA membranes crosslinked by reactivehydrogen. The membranes had good water resistance and maintained highhydrophilicity and high flux.