薄膜電荷量測與膜過濾電動現象分析

Measurements of membrane surface charge and analysis of the electrokinetic behavior in membrane filtration

江宜蓁(Yi-Chen Chiang)

指導教授 ： 莊清榮

中原大學/工學院/化學工程研究所/碩士(2003年)

https://doi.org/10.6840/cycu200300230

摘要

膜電荷是決定欲過濾物質與膜面相互作用之主要變數，對較緻密薄膜而言，膜電荷是控制膜結垢和分離選擇性的重要因子，由此可知，膜電荷的量測將有助於膜過濾時對膜材之選擇提供一重要的參考依據，但目前膜電荷量測的技術仍未成熟，如電雙層效應的修正及電極選擇等，這些均有待進一步探討。
本研究藉由平行膜面流線電位量測以決定不同材質薄膜膜面之界達電位，同時也比較不同電極材料所測得之膜面電位的差異，並說明操作條件如pH值及蛋白質吸附等對膜電性的影響，除此之外，亦理論探討膜面有濾餅附著時垂直膜面之電動現象。
結果顯示，PTFE薄膜界達電位隨著溶液pH值減小而降低，在所操作之pH=3.5~7.5範圍內薄膜皆帶負電荷，且膜面電位量測值受膜孔徑影響小，而PVDF薄膜電位隨pH而變化的趨勢與PTFE薄膜相似，在10-3M KCl電解質溶液下，該膜面等電點約為3.6。而白金與氧化銥兩電極所獲致的界達電位，兩者於定量上已甚接近，而銀/氯化銀電極所決定的電位較前兩者大，這可能與電極的過電壓有關。
PC薄膜經BSA溶液吸附後，因BSA之界達電位較薄膜低，導致吸附後薄膜電位之絕對值小於潔淨膜者，而較疏水之PTFE膜其蛋白質吸附量遠大PC膜，因此，潔淨膜與經蛋白質吸附後膜面之界達電位有較顯著的變化。
為分析以流線電位量測來判定過濾濾餅成長情形，本研究亦理論探討膜面有濾餅附著時垂直膜面電動現象，結果顯示，僅在濾餅與薄膜帶相同電性條件下，且濾餅及薄膜之厚度與界達電位乘積比值(L1ζ1/ L2ζ2 )大於某一特定值後，濾餅層所佔總體流線電位的比重高於90%時方可以整體流線電位的量測來判定濾餅成長。而若濾餅層與薄膜層兩者帶相異電性時，可能造成E1/Et的比值甚大於1或呈現負值，則無法以總體流線電位值的量測來判定濾餅生長情況。

關鍵字

流線電位 ； 薄膜 ； 界達電位

並列摘要

It has been recognized that the electric charge of membrane plays an important role in determining the performance of membrane separation, especially for the filtrations influenced significantly on the nature and magnitude of the interaction between the membrane and the charged particles in solutions, and for the electrofiltrations in which the filtration rate may be enhanced significantly by the electroosmostic flow induced through the membrane. For the reason, there is much interest in developing the method to determine the electric charge of membrane.
In this study, the streaming potential between two parallel membrane surfaces was measured to determine the zeta potential of PTFE and PVDF membranes under different pH and membrane pore size. The variation of zeta potential on membrane surface after absorbing protein was also investigated. The global electrokinetic phenomena through the cake-membrane combined in series, as in cake filtration, was analyzed theoretically and the contribution of cake layer to the global properties was discussed in term of the physiochemical properties of each layer.
Experiments results indicated that in the pH range from 3.5 to 7.5 used in the study the zeta potentials of PTFE membrane are negative and decrease with the increase of the pH value. However, the pore size only has a little effect on the determined zeta potential. It was also indicated that after absorbing BSA the fouled membranes were of lower zeta potential, especially for the more hydrophobic membrane formed with PTFE component.
A comparison of the zeta potentials of membrane determined using three different electrodes showed that the zeta potentials measured by platinum and IrO2 electrodes are very close, however the Ag/AgCl electrode gives the more large zeta potential.
Based on the electrokinetic model developed for the cake–membrane two layer in series, it can be seen that the application of streaming potential measurement to characterize the cake growth is feasible only under the conditions of larger ratio of L1ζ1/ L2ζ2 (cake layer/membrane layer) and both layer have the same potential polarity. The ratio between the streaming potential through the cake layer to the global streaming potential may vary vastly with the filtering time when the cake layer and membrane both have opposite polarity in zeta potential.

並列關鍵字

zeta potential ； streaming potential ； membrane

參考文獻

左煒憶,”以電滲透及流線電位決定薄膜之膜孔界達電位”, 碩士學位論文, 中原大學化工所,（2001）

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