鹽水濃度與組成對直接接觸式薄膜蒸餾膜結垢之影響

Effects of saline concentration and composition on membrane fouling in direct contact membrane distillation

韓知融(Chih-Jung Han)

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(2009年)

https://doi.org/10.6846/TKU.2009.00516

摘要

本研究採用Toyo公司之聚四氟乙烯(PTFE)薄膜以及GE osmonics公司之聚偏二氟乙烯(PVDF)薄膜，進行直接接觸式薄膜蒸餾，實驗操作分為薄膜通量測試及薄膜結垢測試。薄膜通量測試研究中為在不同氯化鈉水溶液濃度(4.5 wt%、10 wt%)與薄膜材料(PTFE薄膜、PVDF薄膜)下，探討操作參數(進料溫度、進料流率)對滲透通量及鹽阻隔之影響，並比較實驗透過率與理論預測透過率值之差異；薄膜結垢測試研究中固定溫度差及進料流率，進行24小時蒸餾操作，探討不同進料溶液組成下之透過率及溶質阻隔率，另量測實驗前後純水滲透通量之變化，並利用場發射槍掃描式電子顯微鏡、能量散佈X光分析儀及接觸角量測儀觀察薄膜結垢現象。
薄膜通量測試結果顯示，增加進料流量可以減緩濃度極化及溫度極化現象，進而提升滲透通量，在PTFE薄膜中所提升之滲透通量非常些微；而PVDF薄膜之滲透通量提昇則較明顯；增加進料溫度可以有效提升蒸氣通過薄膜孔洞之驅動力，而PTFE薄膜以及PVDF薄膜之滲透通量皆有明顯之提升情形，但使用PVDF薄膜時，滲透液之導電度值會隨著增大進料流量、進料溫度以及進料濃度有上升趨勢，造成使用PVDF薄膜操作中滲透通量液之含鹽量升高，而不符合實驗操作之期待。實驗隨操作進料濃度及進料流量變化之趨勢與理論模擬結果相似，但實驗值大於模擬理論值。
薄膜結垢測試之結果發現NaCl濃度及0.05 wt% BSA溶質對PTFE薄膜之實驗前後純水滲透通量並無明顯之下降，而CaSO4、MgSO4或MgCl2等溶質對降低薄膜純水滲透通量之影響較明顯。由場發射槍掃描式電子顯微鏡觀察得知，鹽之結晶只出現在薄膜表面上，且隨著NaCl濃度上升及種類的增加，結晶附著在薄膜表面的數目也會上升。接觸角量測儀之測量結果可顯示出當溶液加入0.05 wt% BSA溶質時，對PTFE薄膜之疏水性有較明顯之下降。

關鍵字

直接接觸式薄膜蒸餾 ； 結垢現象 ； 溫度極化 ； 濃度極化

並列摘要

In this study, polymeric membranes were employed in a direct contact membrane distillation system to investigate the effects of solution concentrations, solution compositions and membrane properties on distillation flux. The experimental results and theoretical fluxes were discussed under various as feed flow rate and feed temperature. For the tests of membrane fouling, operations under different concentrations of NaCl solution and multiple saline compounds were conducted for flux and solute rejection. The FESEM, EDAX and contact angle instrument were also applied for the observation of membrane fouling.
The experimental results show that the flux increases with the increase of feed volume flow rate or feed temperature. However, the solute rejection by the PVDF membrane decreases at the high feed flow rate and feed temperature. The theoretical predicted fluxes agree with the experimental results in the same trend but having under estimation.
Membrane fouling tests show that the pure water permeability of PTFE membrane varied unapparently after the experiments using NaCl solutions or 0.05 wt% BSA solution, while the pure water permeability decreased significantly after the experiments using CaSO4, MgSO4, MgCl2 or their mixture compound solutions. From the observation of FESEM, the crystal of salt exited on the surface of PTFE membrane and its amount increased with the increase of NaCl. From the measurements of contact angle, it concentration the degree of hydrophobicity for PTFE membrane decreased apparently while 0.05 wt% BSA added to feed solution.

並列關鍵字

Direct contact membrane distillation ； Fouling ； Temperature polarization ； Concentration polarization

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