以流線電位法分析薄膜過濾程序之結垢

Membrane Fouling Analysis Using Streaming potential Method

陳志文(Zhi-Wen Chen)

指導教授 ： 莊清榮

中原大學/工學院/化學工程研究所/碩士(2009年)

https://doi.org/10.6840/CYCU.2009.00841

摘要

在薄膜過濾程序中所形成之膜結垢，會造成濾速嚴重衰減及選擇穿透性下降，而在密閉過濾系統中，以往僅能由濾速之衰減幅度判定膜結垢阻力，但膜結垢變化是連續的，如何於過濾程序中即時監控膜結垢程度是主要探討之課題。
目前欲藉由電動量測監控膜結垢已有數位學者提出，本研究以電動現象之量測，探討薄膜表面有濾餅附著及膜孔內有結垢發生時之垂直膜面流線電位與膜結垢之關係，並理論分析過濾過程中，其電動現象與濾餅成長及膜孔內結垢程度之關係。
結果指出，當濾餅過濾之操作條件為粒子電性較低之pH值，由於濾餅形成速度較快，可降低較小粒子進入膜材內部之機率，避免膜材阻塞，因此過濾初期，低pH值操作條件之通量衰減幅度較低。
當溶液pH值調整至接近粒子等電點進行過濾時，濾餅對整體流線電位之影響較小，整體之流線電位會隨著濾餅厚度增加，造成膜材之透膜壓差下降，而使流線電位呈現不斷遞減趨勢。提高粒子帶電性時，當過濾初期開始有濾餅附著時，流線電位會隨著濾餅層厚度增加而大幅度遞增或遞減，等濾餅層堆積至一定厚度時，流線電位變化幅度下降，並趨近於一定值，以理論進行解析時也有相同趨勢，但定量上則略有差異，其適用之範圍為濾餅厚度小於0.8 mm。
此外過濾時之粒子電性大小會影響膜內結垢程度，接近等電點之粒子容易吸附於膜孔壁上，並造成通量大幅下降，當提高pH值使粒子電性上升時，粒子較不易吸附於孔壁上，因此通量衰減幅度較低。在接近粒子等電點時進行過濾，所得之膜材阻力變化幅度較大，其後隨著pH值上升膜材阻力變化幅度漸小；而MCE膜材為網狀交錯結構，所補捉到之粒子數量大於直通狀PC膜材，因此所捕捉到之粒子量較多，MCE膜材過濾所造成之膜阻變化量較大。’
以垂直膜面流線電位偵測膜孔中結垢情形，所得到的流線電位變化和膜材與粒子的帶電性有關，當粒子帶電性與膜材相比之下較偏向負值，不論膜材與粒子電性帶負電性或正電性，過濾時之流線電位變化將呈現遞減趨勢，若粒子電性與膜膜材電性相比之下偏向正值，流線電位變化會有遞增趨勢。另外在膜孔過濾時，低pH值容易形成濾餅，使整體流線電位便會受到較大影響而與理論產生不同之趨勢，除此之外，高濃度過濾時所得之流線電位變化與理論差異較大，故此法僅適用於濃度極低之稀薄溶液。
以垂直膜面流線電位法分析膜結垢時，不論是膜面結垢或膜孔中結垢，所得到的流線電位變化大小，會受膜材與粒子所帶電性的差距影響，若膜材與粒子電性接近，則所得的流線電位變化極小，不易觀測。

關鍵字

流線電位 ； 薄膜結垢

並列摘要

Membrane fouling is a important factors that limiting the application of membrane filtration. Membrane fouling usually lead to a decrease tendency of filtration rate and sometime also leads an decrease tendency rejection of targeted component in selective separation. In a closed filtration chamber, the degree of fouling is generally determined based on the decline of the permeate flux. Since the rate of fouling is time dependent, how to on-line monitoring the fouling is very important for membrane processes.

Several studies have applied the electrokinetic method to characterize membrane fouling. The aim of this study is use electrokinetic method to analysis the relationship between streaming potential and membrane fouling. Theoretical models to relate the streaming potential to the degree of fouling and filtration rate in the membrane filtration process are developed and compared with the experimental data.

　　The result of constant pressure cake filtration is the growth rate of cake is more fast, when the zeta potential of particle is closed isoelectric point. The cake is reduce probability of the smaller particle into membrane pore. That will avoid obstruct on membrane pore. The decline of flux on low pH value condition is smaller at initial filtration.

　　When the pH value adjusted to isoelectric point of particle. The effect of cake on total streaming potential is smaller. Total streaming potential value will increase with thickness of cake increase. That lead to transmembrane pressure decrease and let streaming potential show a continuously decrease tendency. When rise the zeta potential of particle and cake start growth at initial filtration, streaming potential show a decrease or increase tendency with thickness of cake increase. When the thickness of cake growth to 0.8 mm, the range for change of streaming potential is reduce and trend to a value. Theoretical prediction under the conditions is obtain same result. But there are some difference exist between theoretical prediction and experiment in quantitative analysis. The limit of use streaming potential method to analysis thickness of cake is thickness of cake under 0.8 mm.

When we use streaming potential method to detect degree of fouling in membrane pore. The change of streaming potential is related to zeta potential of membrane and particle. If the zeta potential of particle is tend to negative value then membrane, the change of streaming potential is tend to decrease no matter the zeta potential of membrane and particle is negative positive value. The cake easy to produce on membrane surface when the pH value is lower and high concentration under membrane pore filtration. That will effect tendency of streaming potential lead to make some difference between experiment and theoretical. The streaming potential method is suitable for use diluted solution filtration.

As we use streaming potential method to detect membrane cake fouling or membrane pore fouling. The difference of zeta potential between membrane and particle will effect the value of streaming potential. If the zeta potential of membrane is closed to the zeta potential particle, the change of streaming potential will very smaller that is difficulty observe.

並列關鍵字

Streaming potential ； Membrane Fouling

參考文獻

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