聚偏二氟乙烯中空纖維膜應用於薄膜蒸餾之研究

A study on performance of PVDF hollow fiber in membrane distillation

林智偉(Jhih-Wei Lin)

指導教授 ： 鄭東文

淡江大學/工學院/化學工程與材料工程學系碩士班/碩士(2014年)

https://doi.org/10.6846/TKU.2014.01211

摘要

本研究以實驗室合成之聚偏二氟乙烯(poly(vinylidene fluoride), PVDF)中空纖維膜組裝之模組進行真空式薄膜蒸餾(vacuum membrane distillation)及直接接觸式薄膜蒸餾(direct contact membrane distillation)實驗，進料溶液為3.5 wt%之鹽水溶液，操作參數為進料溫度(50~70 oC)及進料速率(0.1~0.4 L/min)，真空式薄膜蒸餾其真空度為持在8 kPa，直接接觸式薄膜蒸餾之冷水側溫度為17.5 oC及進料速率0.4 L/min。
製備中空纖維膜的條件為改變沉澱槽之組成，其中共五種條件分別為純水相及10、20、40、60 wt%磷酸三乙酯(TEP)水溶液，藉由硬性沉澱槽換成軟性沉澱槽的方式來改善中空纖維膜表面皮層結構。從SEM解析得知隨著磷酸三乙酯(TEP)在沉澱槽的比例增加薄膜表面皮層結構不易形成，且大孔洞數變多。
真空式及直接接觸式薄膜蒸餾操作中，提高進料溫度能明顯增加滲透通量，但極化現象也較嚴重，此外薄膜於真空式薄膜蒸餾會有fouling現象，造成氯化鈉顆粒析出於殼測薄膜表面，此種現象會造成薄膜之有效面積減少，降低純水通量。增加進料流率對於滲透通量之提升較不顯著，但對於高溫進料操作之溫度極化現象具有較明顯改善效果。
其結果顯示隨著沉澱槽TEP wt%的比例增加，所製成的薄膜在直接接觸式薄膜蒸餾有較高的通量，但在真空式薄膜蒸餾中較不明顯。孔洞較大的薄膜對於進料溫度及速率的增加在通量的提升效果高於小孔洞之薄膜。此外短模組在真空及直接接觸式薄膜蒸餾操作中的滲透通量都明顯高於長模組。

關鍵字

聚偏二氟乙烯 ； 中空纖維薄膜 ； 真空式薄膜蒸餾 ； 直接接觸式薄膜蒸餾

並列摘要

In this study, laboratory made poly(vinylidene fluoride), PVDF, hollow fiber membranes were used in vacuum and direct contact membrane distillation of saline solution. The feed solution was 3.5 wt% NaCl solution, the operating parameters included feed temperature (50 ~ 60 oC), feed rate (0.1 ~ 0.4 L / min), the vacuum pressure in the permeate side was controlled at 8 kPa for vacuum membrane distillation, and cooling water controlled at 17.5 oC with rate 0.4 L / min for direct contact membrane distillation.
The hollow fiber membranes were prepared by varying the composition of the coagulation bath. There were five conditions, which water phase、10、20、40、60 wt% triethylphosphate (TEP) solution. The outer skin of the hollow fiber membrane was improved by changed the bath from hard coagulation (water bath) to soft coagulation. Analysis the structure by SEM morphology, which membrane have large pore size in the outer surface by increasing the weight percent of TEP in coagulant bath.
In the vacuum and direct contact membrane distillation experiment, raising the temperature of the feed can significantly increase the flux, but the polarization phenomena become more serious. In addition, the membrane surface will have fouling phenomenon that NaCl was separated out to the shell side membrane surface in vacuum membrane distillation. This situation will cause decrease the effective area of the membrane and reduce the flux. Increasing feed flow rate has a finite effect on increasing the flux, but the temperature polarization phenomenon can be reduced by the feed flow rate as higher feed temperature.
The experimental results showed the higher flux performance on direct contact membrane distillation which prepared by higher weigh percent of TEP coagulation bath solution but not obviously in the vacuum membrane distillation. The large pore size membrane flux which increased by higher inlet temperature more obvious then the small one. Furthermore, the short module have higher flux then long module in the same inlet condition.

並列關鍵字

poly(vinylidene fluoride) ； hollow fiber membrane ； vacuum membrane distillation ； direct contact membrane distillation

參考文獻

40.陳勝昌，以非溶劑誘導相轉移法製備多孔型薄膜，淡江大學化學工程與材料工程碩士論文(2013)

1.Altena, F. W, Smolders, C. A., “Calculation of liquid-liquid phase separation in a ternary system of a polymer in a mixture of solvent and a nonsolvent”, Macromolecules, 15, 1491(1982)

2.Boom, R. M. and BoomgaardT.V., Smolders, C. A., “Mass transfer and thermodynamics during immersion precipitation for two-polymer system: Evaluation with the system PES-PVP-NMP-water”, Journal of membrane science, 90, 231 (1994)

3.Bonyadi, S., Chung, T. S., “Flux enhancement in membrane distillation by fabrication of dual layer hydrophilic-hydrophobic hollow fiber membrane”, Journal of Membrane Science, 306, 134-146, (2007)

4.Bonyadi, S., Chung, T. S., “ Highly porous and macrovoid-free PVDF hollow fiber membrane for membrane distillation by solvent-dope solution co-extrusion approach”,Journal of Membrane Science, 331, 66-74, (2009)