以自組裝技術製備聚電解質/聚丙烯腈中空纖維滲透蒸發薄膜

Preparation of polyelectrolyte/polyacrylonitrile hollow fiber pervaporation membrane by self-assembly technique

許駿佑(Chun-Yu Hsu)

指導教授 ： 洪維松 ； 蔡惠安

中原大學/工學院/化學工程研究所/碩士(2012年)

https://doi.org/10.6840/cycu201200572

摘要

本研究中，利用濕式紡絲法(Wet spinning process)紡製具有非對稱結構之聚丙烯腈（Polyacrylonitrile, PAN）中空纖維膜，並進行自組裝(self-assembly)製備聚電解質/聚丙烯腈複合中空纖維膜。探討在不同PAN水解處理時間、聚電解質濃度、結構型態等條件對組裝之聚電解質/聚丙烯腈複合中空纖維膜進行滲透蒸發分離效能之影響。
實驗中，將紡製之PAN中空纖維膜置於NaOH水溶液中進行水解反應(mPAN)。結果發現，透過水解雖能有效提升PAN中空纖維膜外表面之親水性，卻也造成了孔洞緻密化而導致透過通量下降。
為了提升滲透蒸發分離效能，本研究利用mPAN中空纖維膜表面-COOH帶有負電之特性，結合自組裝技術，將mPAN中空纖維膜外表面自組裝上一層BPEI之陽離子聚電解質，成功製備出polycation/mPAN中空纖維膜。將其進行90 wt.%乙醇水溶液滲透蒸發分離時，以水解時間為20分鐘之mPAN中空纖維膜進行自組裝，製備之polycation/mPAN中空纖維膜能達到最佳之分離效能，其透過端水濃度與透過通量分別為77.5 wt.%與510 g/m2h。遠優於僅進行水解而未自組裝之mPAN中空纖維膜(其透過端水濃度及透過通量分別為19.2wt.%與1448 g/m2h)。
由於本研究中採用之BPEI為一弱電解質，而聚電解質溶液之pH值經常影響著自組裝效果，故在研究中亦改變了不同的BPEI溶液之pH值。研究發現，不改變任何BPEI聚電解質pH值時，具有最佳組裝效果。這可能由於此pH值下，BPEI分子能獲得最佳的伸展型態，而當聚電解質高分子溶液之pH值改變時，可能會影響其分子鏈的捲曲型態進而影響組裝效果。
另外，研究中亦選用親水性較高之聚丙烯酸(PAA)陰離子聚電解質於polycation/mPAN中空纖維膜上再進行組裝，製備出聚電解質/聚丙烯腈(polyanion/polycation/mPAN)中空纖維膜。由於PAA陰離子聚電解質其親水特性，能有效提高所製備之聚電解質/聚丙烯腈中空纖維膜之親水性，進而提升其滲透蒸發分離效能。將其應用在90 wt.%乙醇水溶液滲透蒸發分離時，具有233 g/m2h之透過通量以及99 wt.%的透過端水濃度，其選擇性達1637。
研究中同時利用polyanion/polycation/mPAN中空纖維膜探討包括進料溫度、進料濃度、透過端壓力以及不同碳數之進料醇類等滲透蒸發操作參數對醇類水溶液之分離效能影響。研究結果顯示，在55OC操作溫度下，仍擁有98.5 wt.%之透過端水濃度以及348 g/m2h透過通量。在透過端壓力的變化方面，隨著透過端壓力上升除了造成透過通量下降外，其透過端水濃度依然保持在99 wt.%以上。另外，polyanion/polycation/mPAN中空纖維膜之滲透蒸發透過通量會隨著進料乙醇濃度降低而增加，透過端水濃度則皆保持在99.9 wt.%以上。同時隨著進料醇類碳數增加，透過端水濃度上升，透過通量則略為下降。

關鍵字

自組裝技術 ； 聚電解質 ； 滲透蒸發 ； 中空纖維膜

並列摘要

In this study, polyelectrolyte/polyacrylonitrile (PAN) composition hollow fiber membranes were prepared by self-assembling polyelectrolyte polymer onto the outer surface of wet-spun asymmetric PAN hollow fiber membranes. The effect of PAN hollow fiber membranes hydrolysis time, polyelectrolyte solution concentration, structure and morphology on pervaporation performances of 90 wt.% aqueous ethanol solution through polyelectrolyte/PAN hollow fiber membranes were investigated.
The PAN hollow fiber membranes were hydrolyzed by immersing the as-spun PAN hollow fiber membranes into aqueous NaOH solution (mPAN). The results show that after hydrolyzed, the hydrophilic of mPAN hollow fiber membranes could be enhanced and the outer surface was become denser, resulted in the decrease of permeation flux.
To investigate the effects pH value of a weak polyelectrolyte solution on self-assembly results, this study used a weak polyelectrolyte polyethyleneimmine, BPEI. The initial pH value of BPEI polyelectrolyte solution led to the best self-assembly result. This might be due to the best elongation of the BPEI chain, but the polyelectrolyte chain elongation changed with different pH values of the polyelectrolyte solution, and it influenced the self-assembly results.
To enhance the pervaporation performances, polycation/mPAN hollow fiber membranes were fabricated by self-assembling the BPEI cation polyelectrolyte layer onto the outer surface of mPAN hollow fiber membranes with negative charge properties of -COOH. An optimal pervaporation performances of 90 wt.% aqueous ethanol solution at 25OC through polycation/mPAN hollow fiber membranes with 20min hydrolysis reaction time can be gotten, the permeation flux and water concentration in permeate were 510 g/m2h and 77.5 wt.%, respectively. These results were excellent than self-assemble free mPAN hollow fiber membranes (the permeation flux and water concentration in permeate of self-assemble free mPAN hollow fiber membranes were 1448 g/m2h and 19.2 wt.%, respectively.).
Moreover, the hydrophilic polyacrylic acid (PAA) anion polyelectrolyte was also used as the second layer of polyelectrolyte assembled layer to assemble onto the outer surface of polycation/mPAN hollow fiber membranes to form the polyanion/polycation/mPAN composite hollow fiber membranes. The pervaporation performances could be enhanced resulted from the hydrophilic property of polyanion/polycation/mPAN composite hollow fiber membrane. The permeation flux and water concentration in permeate for 90 wt.% aqueous ethanol solution at 25OC through polyanion (0.25 wt.% PAA) /polycation (0.1 wt.% BPEI )/mPAN composite hollow fiber membranes were 233 g/m2h and 99 wt.%, respectively with the separation factor of 1637.
Furthermore, the effect of pervaporation conditions such as: feed concentration, feed temperature, downstream pressure and carbon number of feed alcohol on the pervaporation performances through polyanion/polycation/mPAN composite hollow fiber membranes were also investigated. The separation performances of 98.5 wt.% water concentration in permeate and 348 g/m2h permeation flux could be gotten with 55OC operation temperature. The permeation flux decreased and water concentration in permeate kept 99 wt.% as increasing the downstream pressure. In addition, the permeation flux increased while water concentration kept above 99.9 wt.% as decreasing the feed ethanol concentration. As for the carbon number of feed alcohol, the water concentration in permeate increased while permeation flux decreased slight as increasing the carbon number of feed alcohol.

並列關鍵字

self-assembly technique ； polyelectrolyte ； pervaporation ； hollow fiber membrane

參考文獻

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