Preparation Of Hollow Fiber Pervaporation Membrane For Methanol / Dimethyl Carbonate Separation

Polyvinyl alcohol（PVA）- chitosan（CS） mixtures were used as coating solution. Tetraethyl orthosilicate（TEOS）, acid treatment MWCNTs and other ways treated MWCNTs were used as inorganic phase to added to the coating solution.To get hollow fiber membrane which can be used at pervaperation area, the dip-coating method had been applied. The membrane was prepared for separation methanol（Me OH） / dimethyl carbonate（DMC） mixture. The content of this work mainly divided into three aspects as follows:Firstly, TEOS was dissolved in water to hydrolysis. Then added it into PVA-CS coating solution, the polyacrylonitrile（PAN） was treated as base membrane and coated the selective layer by dip-coating method. Then PVA-CS-SiO₂/PAN hollow fiber pervaporation membrane was applied to separate Me OH/DMC mixture. From scanning electron microscopy（FESEM）, it can be seen that the morphology of prevapration membrane was complete. The cohesion of base membrane and selective layer was favorable. No obvious defects were found. The requirements of pervaporation experiments next could be fulfill totally. The composite membranes were characterized by XRD spectra. It can be learned crystallinity of polymer has a certain decreases when adding inorganic phase. The pervaporation performance of PVA-CS-SiO₂/PAN hollow fiber membrane had improved to some extent. As for the influence of some kinds of experiment condition for pervaporation performance, the coating solution ratio of polymers and coating solution concentration etc. were studied: when the ratio of polymer in coating solution was 70:30, pervaporation performance of the membrane was relatively good. The selective layer was moderate when the concentration of coating solution was 2%. At this concentration, the value of permeation flux and selectivity factor was superior. The membrane structure was relatively complete when coating times was twice. It also can be seen that the pevaporation performance was outstanding when the addition of inorganic phase content of TEOS was 10%. The feed concentration and temperature had also been studied to find out the influence for pervaporation performance. The results showed that when the feed temperature from 30 ℃ increased to 60 ℃ gradually, the permeation flux increased but the selective factor decreased. It’s worth to mention that the best performance emerged when the feed temperature at 40 ℃; When Me OH concentration in the feed solution from 10% increased to 70%, the flux increased gradually while the selective factor decreased.Secondly, the acid treatment of MWCNTs which used as inorganic phase was added in coating solution to study pervaporation properties of hollow fiber membrane. It can be found out that on the surface of MWCNTs appeared –COOH groups successfully through infrared spectrum diagram. The hydrophilic and dispersion of MWCNTs increased effectively because of this groups appeared. Through the XRD patterns of composite membranes the crystallinity of polymers reduced when adding COOH-MWCNTs to coating solution. When concentration of COOH-MWCNTs was 2% in coating solution the pervaporation performance of prepared membrane was much better. It also can be found how heat treatment temperature influenced the pervaporation performance of membrane. When the heat treatment temperature increased the permeation flux decreased meanwhile the selective factor increased. In the end, changes of pervaporation performance had similar trends with the first chapter with the condition changed in feed temperature and concentration.Finally, COOH-MWCNTs were processed by in situ polymerization and ionic cross-linking ways. By infrared spectrum diagram and Zata potential it can be found the PAA groups and PEI groups was grafted on the surface of MWCNTs successfully. There was evident the dispersion of MWCNTs in solution effectively enhanced. Compared to the experimental results of the previous two chapters, the separation performance of this membrane was much poor. It is more suitable to use this further treatment COOH-MWCNTs in some others membrane separation field because of the excellent hydrophilicity and dispersion they are performed.