以電場輔助法製備聚電解質複合膜並探討製膜參數對其滲透蒸發效能的影響

Abstract

本研究使用聚丙烯腈當作基材，並利用電場增強法製備多層聚電解質複合膜。實驗結果發現，以NaOH預處理PAN基材薄膜，可以提高基材薄膜與聚電解質溶液之間的親和性，也會使基材薄膜表面較緻密，可提升選擇性，但透過量降低。 多層聚電解質複合膜的滲透效能會受到所使用聚電解質溶液PH值的影響。其中，PEI聚電解溶液的PH值會影響PAN基材薄膜-COOH官能基與PEI聚電解質-NH2官能基離子化的程度，PAA聚電解溶液的PH值則會影響PEI聚電解質層-NH2官能基與PAA聚電解質-COOH官能基離子化的程度。藉由選擇適當PH值的PEI與PAA聚電解質溶液製備聚電解質複合膜，其複合膜會有較高密度的離子交聯密度，且對於滲透蒸發分離異丙醇溶液有較好的選擇性。其中，利用PH值等於8的PEI聚電解質溶液與PH值等於6的PAA聚電解質溶液所製備的(PEI/PAA)聚電解質複合膜，對於滲透蒸發分離50°C, 90wt%的isopropanol/water，其透過量為1123 (g/m2hr)且其透過端水濃度為98.2wt%。 此外，於聚電解質複合膜製備過程中所加入電場的方向與所施加的電壓均會對其滲透蒸發效能有所影響。相較於利用正向電場所製備之聚電解質複合膜，利用反向電場所製備之聚電解質複合膜有較高的透過量與較低的透過端水濃度。隨著反向電場的電壓逐漸增加，聚電解質複合膜的透過端水濃度將逐漸降低且透過量逐漸增加。

In this study, multilayered polyelectrolyte complex membranes (PECMs) were formed on top of the polyacrylonitrile (PAN) substrate membrane by using the electric-field enhance method. It was found that the treatment of NaOH on the polyacrylonitrile substrate membrane could improve the affinity between the polyelectrolyte solution and the substrate membrane. It also makes the substrate denser, causing higher selectivity but lower flux. The pervaporation performance of the multilayered polyelectrolyte complex membranes is influenced by the PH value of the polyelectrolyte solution. The ionization degree of the –COOH functional group of the PAN substrate membrane and the ionization degree of the -NH2 functional group of the PEI polyelectrolyte are influenced by the PH value of the PEI polyelectrolyte solution. The ionization degree of the –COOH functional group of the PAA polyelectrolyte and the ionization degree of the -NH2 functional group of the PEI layer are influenced by the PH value of the PAA polyelectrolyte solution. Prepared by using adequate PH value of PEI and PAA polyelectrolyte solution, the polyelectrolyte complex membrane will have higher ionic cross-linking density and higher selectivity of the pervaporation of the isopropanol aqueous solution. With suitable conditions which the PH value of PEI polyelectrolyte solution is 8 and the PH value of PAA polyelectrolyte solution is 6, polyelectrolyte composite membranes with on PEI/PAA bilayer exhibited a flux of 1123 (g/m2hr) and a permeate water concentration of 98.2 wt % for the dehydration of 90 wt % of isopropanol aqueous solution at 50°C. In addition, it was found that the pervaporation performance of the polyelectrolyte complex membrane depends on the direction of the electric field and applied voltage during the fabrication process. Compared to the polyelectrolyte complex membrane prepared in positive electric field, the polyelectrolyte complex membranes prepared in negative electric field have higher flux and lower permeate water concentration. With the increasing applied voltage of the negative electric field, flux of the polyelectrolyte complex membrane increases and the permeate water concentration of the polyelectrolyte complex membrane decreases.