電場奈米過濾特性之研究

A Study on Performances of Electro-Nanofiltration

溫家瑋(Chia-Wei Wen)

指導教授 ： 莊清榮

中原大學/工學院/化學工程學系/碩士(2008年)

https://doi.org/10.6840/cycu200900222

摘要

電場奈米過濾為在一般奈米過濾操作中，於薄膜兩端外加直流電場。進料液中離子受電場之作用產生離子遷移，同時膜內誘發電滲透導致破壞溶液本身電中性平衡，同時促進濾速提升。
本研究首先於未施加電場時過濾NaCl與Na2SO4等鹽類溶液，分析DK及NF-270等商業膜之篩析作用及道南效應對分離效能之影響，由結果得知DK膜之分離效能稍優於NF-270，分析其原因，DK膜之孔徑較大，對於離子的篩析作用較小，但DK膜之分離效能卻較佳，故為DK膜於操作之溶液下有較大ΔEDon導致。利用Linearized Transport模式預估阻擋率，發現估算值與實驗值定性有相同之趨勢，但定量上之相對誤差在13~28%之範圍，分析造成估算之誤差，因分離效能主要由選擇層之帶電荷量多寡所影響，但基於實驗上的限制，僅能量測濾膜整體之淨電荷密度，而導致誤差產生。
之後，於垂直膜面兩端施加一直流電場，分析離子於電場作用下之效能表現，探討進料組成、電場強度及離子濃度等操作條件對分離效能之影響。實驗結果顯示，在電場奈米過濾中，於3 bar及750 V/m條件下，34%濾速來自電滲透作用，即表示總濾速深受電滲透所影響，而隨著電場強度下降及壓差增加，電滲透之流速所佔之比例亦隨之降低。此外，於電場作用下，Na+離子通量大幅提高，主因為Na+離子受電場之電荷作用力影響而往濾液端遷移，並伴隨電滲透現象使濾速增加而導致，另一方面，陰離子因受反濾液方向之電場作用力，則維持較高之阻擋率，使得帶不同電性離子之阻擋率有明顯的差距，產生有選擇性分離的現象。最後，利用離子通量半經驗式，描述於電場作用下離子通量的變化，其結果與實驗值甚為接近(相對誤差15%以內)，且符合離子通量之變化趨勢。

關鍵字

奈米過濾 ； 電場 ； 空間孔道位阻模式 ； 道南效應

並列摘要

Electro-nanofiltration is a process by imposing an electric field on the traditional nanofiltration. The occurrence of ion migration would upset the electroneutrality of solution and meanwhile the electroomosis induced through membrane generally increases filtration flux. So far, most studies in applying electric field to enhance membrane filtration refer to electro-microfiltration or electro-ultrafiltration, only a few attentions paid to electro-nanofiltration. The main objective of this study was to investigate the effect of electric field on the nanofiltration performance. In addition, the effects of membrane charge density and membrane pore size on nanofiltration was also investigated by relating the sieving effect and Donnan potential to salt rejection.
Two commercial nanofiltraion membranes, DK and NF-270, were used for the experiments with NaCl and Na2SO4 solutions. Experiment results indicated that although the DK membrane has a larger pore size than NF-270 membrane, the former has a slightly better ability to salt rejection due to the membrane has a higher bulk charge density. A theoretical relationship based on the Linearized transport model was used to predict the salt rejection. It was indicated that the predicted values is 13~28% less than the experimental results. One of the reasons for such a discrepancy may be due to the commercial membrane used are composites in which the net charge density in the skin layer can not determined from the measured global (bulk) charge density.
Experimental results of electro-nanofiltration showed that under the lower ΔP as 3 bar and higher electric field strength as 750 V/m, nearly 34% filtration flux is contributed by electroosmotic flux of the membrane used in the study. The ionic flux of Na+ from NaCl and Na2SO4 solutions was increased substantially under the addition of electric field into the process. This is caused by the ionic mobility of cation in the direction toward the permeate side. On the other hand, there was only a slightly higher rejection of anions by the application of electric field. In addition, a semi-empirical relation was used to predict the ionic flux under electric field. The results showed that only a relative difference less than 15% was observed between the predicted ionic flux and the experimental values. Based on the results, it can be concluded that the electro-nanofiltration process has a good potential for ion fractionation.

並列關鍵字

Donnan effect ； Electric field ； SHP model ； Nanofiltration

參考文獻

顧聲茹，“膜電荷對奈米過濾效能影響之探討”，私立中原大學化學工程研究所，碩士學位論文 (2007)。

康嘉梅，”薄膜界達電位與膜內淨電荷密度之量測”，私立中原大學化學工程研究所，碩士學位論文 (2006)。

Anselme, C., Mandra, V., Baudin, I., Jacangelo, J. C. and Mallevialle, J., “Optimum Use of Membrane Processes in Drinking Water treatment,” 19th IWA Congress, Budapest, Hungary (1993)

Born, M., “Volumen and hydratationswarme der Ionen,” Z. Phys. Chem., 1, 45–56 (1920)

Bandini, S., “Modelling the mechanism of charge formation in NF membranes : Theory and application,” Journal of Membrane Science, 264, 75–86 (2005)