Study Of New Preparation Method And Pervaporation Performance Of Polyelectrolyte Composite Membranes

Ethanol is not only an important industrial material, but also an important regenerated energy. Distillation is of the mainly conventional ethanol purification methods, its disadvantages are high engrgy consumption, great installation cost and poor economic performance. Moreover, it is difficult to obtain the highly concentrated ethanol by distillation method. Pervaporation is a new membrane separation technique to separate liquid mixture. Pervaporation shows obvious advantages to purify ethanol. In this paper, composite membranes were prepared by casting and self-assembly methods using Chitosan (CS) and Polyacrylic sodium (PAAs) as the raw materials. The pervaporation performances of the prepared composite membranes were study for ethanol-water mixture separation. The experiment results were shown as follows.Frist, CS/PAN and PAAs/PAN composite menbranes were prepared by casting the CS and PAAs solutions on polyacrylonitrile (PAN) ultrafiltration membrane respectively. The effect of operation conditions of membrane pervaporation, for example, feed temperature and feed compositions were discussed. The results showed that the pervaporation performance of the PAAs/PAN composite membrane was not good for separating the 95wt% ethanol/water mixture, the separation factor (a) is only 23. The pervaporation performance of CS/PAN composite membrane is better. Increasing of the feed temperature results in the increase of both flux and water permeation content. The decrease of ethanol concentration in the feed results the same tendency. Besides, the CS/PAN composite membrane was more distinctively affected by feed temperature, while the PAAs/PAN composite membrane was more remarkablely affected by feed concentration.Second, two layers polyelectrolyte PAAs-CS/PAN and CS-PAAs/PAN composite membranes were prepared by casting the different polyelectrolyte solution on PAN membrane twice. The results showed that the CS-PAAs/PAN composite menbranes pervporation performance was better than that of the PAAs-CS/PAN. Compared with that of the corresponding one layer ployelectrolyte membranes, the separation factor were enhanced, but the flux were decreased, especially for the CS-PAAs/PAN composite menbrane. For 95% ethanol aqueous solution, its separation factor was 904.6 and flux was 316 g/m~2h respectively when the feed temperature was 60℃. We also found that the inside polyelectrolyte layer was more important to flux. Either feed temperature increase or ethanol concentration decrease results both the flux and water permeate content increase. Moreover, the flux of CS-PAAs/PAN composite menbrane is more depended on the feed composite.Finally, CS/PAAs-PAN and PAAs/CS-PAN composite membranes were prepared by means of electrostatic self-assembly of polyelectrolytes on PAAs/PAN and CS/PAN membranes. The result showed that the separation performance of the prepared PAAs/CS-PAN membrane was enhanced greatly. The pervaporation results for 95wt% ethonol aqueous solution were as follows: the permeate flux=747.9 g/m~2h, a=942. Increasing pervaporation operation temperature and decreasing the feed ethonol concentration all resulted in the increase of the pervaporation flux. After successively operated 7 day, the pervaporation performance of PAAs/CS-PAN membrane kept normal.