非均相離子交換膜之製備及其電透析效能之評估

Preparation of Heterogeneous Ion Exchange Membranes and Evaluation of Their Electrodialysis Performance

江得榮(Te-Jung Chiang)

指導教授 ： 王大銘

國立臺灣大學/工學院/化學工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.10604

摘要

目前台灣的工業用水仍有過半比率來自於企業自行取水的方式，由於對於低鹽度鹹水而言，逆滲透處理成本過高且水回收率較低，不符合工業用水的需求與經濟效益，而電透析技術對於大部分水中污染物的分離效果幾乎可達與逆滲透相同的水準，且離子交換膜的壽命與操作容忍度皆優於逆滲透膜，因此發展電透析製水的技術已逐漸受到業界的重視。目前市售的離子交換膜依然有均相膜價格較高與非均相膜電阻過大的缺點，因此發展出成本低且具低電阻的離子交換膜是目前的重要課題。
本研究使用聚氯乙烯(PVC)做為黏結劑，以四氫夫喃(THF)做為溶劑，混入市售的陽離子交換樹脂Amberjet 1200H或陰離子交換樹脂Amberjet 4200Cl，再利用乾濕兩步驟綜合製程來製備非均相陰陽離子交換膜。為了改善非均相離子交換膜電阻過高、導電度不足的缺陷，本研究嘗試改變製膜配方的比例與製程中的溶劑揮發時間，並於自製陰離子交換膜中改變添加氯化十六烷基三甲基銨(CTAC)分子的比例。
實驗發現樹脂顆粒大小改變時，對於薄膜含水量與離子交換容量雖然沒有明顯影響，卻在導電度方面則有明顯效應，樹脂顆粒變小可將整體薄膜導電度提升至2倍甚至3倍以上。當樹脂比例增加時，薄膜的含水量、離子交換容量與導電度都會隨之提升；改變CTAC的比例時，則發現添加CTAC首先會使薄膜導電度、水含量與離子交換容量同時急遽下降，直到持續增加至2wt%後才開始有所回升，但整體仍略低於添加前的數值。若改變製程中的溶劑揮發時間，則可發現隨著溶劑揮發時間增加，薄膜表面與內部的孔洞與孔隙度會逐漸減少，使得整體薄膜呈現較為緻密的結構，同時導電度也逐漸降低，兩者間是否有直接關係仍須探討。
最後本研究使用自製的非均相膜進行電透析程序操作去除氯化鈉溶液中的離子以製備純水。選用樹脂比例70wt%、攪拌時間8天(平均粒徑約5μm)、揮發時間15分鐘的自製非均相陰陽膜與市售商業均相陰陽膜進行電透析實際操作比較。操作條件為進料濃度約3wt%、固定電壓10V、流速1L/min、室溫下操作4小時。結果顯示自製非均相膜在電透析操作前期有較快的除鹽速度，120分鐘時即達到了99%的除鹽率，淡水導電度降至0.336mS/cm，已達到工業用水甚至自來水的標準，到操作後期則以商業均相膜的整體去鹽率略高0.63%，自製非均相膜與商業均相膜之整體除鹽率皆可達99%以上。經由調整配方與製程變數，自製的非均相離子交換膜可提升導電度進而加快電透析操作的除鹽製水速度，並成功將鹽份幾乎移除。

關鍵字

電透析 ； 非均相離子交換膜 ； 聚氯乙烯 ； 樹脂顆粒大小 ； 氯化十六烷基三甲基銨 ； 揮發時間

並列摘要

For industry in Taiwan, there is still over half of industrial water is obtained voluntarily. Because of the higher expense and lower water recovery of Reverse Osmosis (RO) technique, this treatment wouldn’t becost-effective for the demands of industry. Gradually, they put emphasis on the Electrodialysis(ED) technique, which has longer operating life, higher tolerance and that also almost hasthe same ability to remove pollutants in water. Nowadays, the commercial ion exchange membranes still have drawbacks in their high price of homogeneous membranes and low conductivity of heterogeneous ones. There’s no doubt that research and development of improved ion exchange membranes is an important issue.
We used the polyvinylchloride (PVC) as binder, which can dissolve in tetrahydrofuran (THF), then blended the grinded resin into the solution. The pattern of commercial cation exchange resin is Amberjet 1200H, and for anion exchange resin is Amberjet 4200Cl. Subsequently, we used the dry-wet two-step process to prepare our heterogeneous membranes. In order to improve the low conductivity of our membranes, we try to change the weight ratio of resin in solid, the particle size of resin, the solvent evaporation time of process and the weight ratio of cetyltrimethylammonium chloride (CTAC) in anion exchange membranes.
By experiment,when we tried to change resin particle size,we found that it didn’t make any difference to the water content and ion exchange capacity of membranes.However, the membrane conductivity changed intensely with the resin particle size.As the size of resin became smaller, the membrane conductivity can even increase by 2 to 3-folds. Furthermore, we also found that the water content, ion exchange capacity and conductivity of home-made membranes increased as the weight ratio of resin increased. As we increased the weight ratio of CTAC, the conductivity and water content of membranes decreased intensely until the ratio exceed 2wt%. The conductivity, water content and ion exchange capacity started to increase when the CTAC was added more than 2wt%, these results, however, were still lower than that before adding CTAC.If we change the evaporation time of solvent, we can found that as the evaporation time became longer, the cavities and the gap between PVC and resins gradually became smaller. The longer evaporation time, the denser membrane structure, and therefore decreased the conductivity of membranes.
At last, we applied home-made heterogeneous ion exchange membranes to electrodialysis in order to remove the ion in sodium chloride solution and product pure water. We chose the membranes that were made by blending 70wt% resin, stirred 8 days (mean diameter was about 5μm), evaporation time were 15 minutes to compare the efficiency of electrodialysis with commercial homogeneous ones. These experiments were conducted under fixed voltage 10V, flow rate 1L/min, input concentration was about 3wt% for 4 hours under room temperaturefixed. Results revealed that home-made membranes had faster desalting rate in the early stage of operation, up to 99% after operated 120 minutes; furthermore, the conductivity of diluate decrease to 0.366mS/cm, which reached the criteria of industrial water and running water. However, in the later stage, the rejection of commercial membranes showed 0.63% higher than home-made membranes. The rejection of home-made heterogeneous membranes and commercial homogeneous ones can both reach over 99%. By adjusting recipe and factors of preparation process, we successfully increased the conductivity of home-made ion exchange membranes, and therefore increase the speed of removing ions and water production; almost all the ions in solution were removed.

並列關鍵字

electrodialysis ； heterogeneous ion exchange membrane ； polyvinylchloride ； particle size of resin ； cetyltrimethylammonium chloride ； evaporation time

參考文獻

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