紡絲參數對熱處理PAN中空纖維膜結構型態與滲透蒸發效能之影響

Effect of spinning condition on membrane morphology and pervaporation performance of heat-treatment PAN hollow fiber membranes

李世偉(Shi-Wei Li)

中原大學/工學院/化學工程研究所/碩士(2011年)

https://doi.org/10.6840/cycu201100656

摘要

本研究是以乾/濕式紡絲方式(Dry-wet spinning process)製備非對稱性聚丙烯腈中空纖維膜(Asymmetric PAN hollow fiber membranes)，探討紡絲條件(包括高分子溶液濃度、氣距長度、芯液組成)以及紡絲後之熱處理溫度與時間等對薄膜結構型態與乙醇水溶液滲透蒸發分離效能之影響。

研究結果顯示，隨著高分子溶液濃度的上升，纖維膜純水透過量會隨之下降，但滲透蒸發透過量卻隨之上升，原因在增加高分子濃度，可使膜材碳化時形成較多之環狀結構，增加碳化時膜材之剛性，將造成分子鏈之柔曲度與擾動能力下降，而此剛硬結構生成，將使得進料溶液較易通過薄膜，因而使滲透蒸發透過量會隨之上升。

將PAN中空纖維膜經12小時不同溫度熱處理後發現，隨熱處理溫度增加中空纖維膜結構趨於緻密化。在210℃溫度下熱處理PAN高分子會有除氫與環化反應產生，致使膜材擁有較佳透過效能。而在此溫度下改變熱處理時間發現，隨著熱處理時間增加，有兩種效應競爭，因此PAN中空纖維膜滲透蒸發之透過量有先上升後下降的趨勢。綜合上述最適熱處理條件為210℃溫度下熱處理12小時。

另外研究中欲製備一單層連通的巨型孔洞，降低膜材阻力，以利整體透過效能提昇，研究中將分別由控制芯液組成與氣距，探討對於製備一單層連通的巨型孔洞之影響；研究結果顯示控制芯液組成並無法提昇透過量，而在改變氣距部份則是在30cm擁有最佳透過效能，並利用新穎的可變單一能量慢速正電子束測試儀(variable monoenergy slow positron beam , VMSPB)，探討改變紡絲參數對於所紡製之中空纖維膜自由體積尺寸、分佈、多層結構及化學組成變化，進而了解自由體積與分離效能之間的關聯性。

關鍵字

滲透蒸發 ； 熱處理 ； 中空纖維膜 ； 聚丙烯睛

並列摘要

In this study, stabilized polyacrylonitrile(PAN) hollow fiber membranes were fabricated by heat-treating dry/wet spun asymmetric PAN hollow fiber membrane. The effects of spinning conditions(such as Dope solution concentration, air gap, bore liquid composition)as well as heat-treatment process(temperature and time)on the morphology of PAN hollow fiber membrane and pervaporation performances of 90 wt.% aqueous ethanol solution through hollow fiber membrane were investigated.

The results showed that the pure water flux decreased but the permeation rate increased while water concentration in permeate constant with increasing PAN content in the dope for the heat-treated PAN hollow fiber membranes. These phenomena might be due to with increasing PAN content in the dope the dehydrogenation and cyclization reaction have occurred during the heat-treatment process will be increased.

The SEMs observation depicts that the morphology of heat-treated PAN hollow fiber membranes were denser with increasing the heat-treatment temperature. As the heat treatment temperature is 210 ℃, dehydrogenation and cyclization reaction of the PAN molecular occurred during the heat-treatment process. So the pervaporation performances increased. And then constant the heat treatment temperature is 210 ℃and change the heat treatment time, the pervaporation performances decreased and then increased. These phenomena might be due to two effect control.The results can find the best heat-treatment process condition is 210 ℃、12hr.

In the study, want to control membrane structure of macrovoids were passed through the entire cross section of PAN hollow fiber membrane to decreased the resistance , so changing the spinning condition of bore liquid composition and air gap. The results show that change bore liquid composition can not increase the pervaporation performances, but when change the air gap to 30 cm can get the best pervaporation performances.And then the hollow fiber membrane free volume size and distribution and variation in the multilayer structure were probed using a variable monoenergy slow positron beam (VMSPB) to understand the relationship between the membrane separation performance and free volume.

並列關鍵字

polyacrylonitrile ； heat-treatment ； pervaporation ； hollow fiber membrane

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