丁聚醣和羧甲基纖維素鈉聚電解質複合膜在滲透蒸發分離異丙醇與水混合物之應用

On the separation of IPA / water by pervaporation using polyelectrolyte complex membranes

蕭勝陽(Sheng-Yang Hsiao)

指導教授 ： 孫一明

元智大學/工程學院/化學工程與材料科學學系/碩士(2004年)

摘要

本研究利用幾丁聚醣(chitosan, CS)與羧甲基纖維鈉(carboxymethyl cellulose sodium, CMC)形成聚電解質複合膜(polyelectrolyte complex membrane)，應用於滲透蒸發分離異丙醇與水混合溶液。薄膜製備原理是利用聚陽離子型高分子(polycation)的CS與聚陰離子型高分子(polyanion)的CMC，藉著amine group和carboxy group間庫倫靜電交互作用力而產生離子鍵結，形成聚電解質複合膜。研究中利用兩種方式製備薄膜，一種是使用刮刀在玻璃板上成出CS基材薄膜，之後在基材膜上成出CMC膜，形成膜厚20±2 μm的聚電解質複合膜﹔其次是利用培養皿成膜法，製備出厚度較厚之聚電解質複合膜。研究中利用了SEM來觀察聚電解質複合膜表面與截面形態，藉AFM觀察表面粗糙度變化，藉FTIR光譜鑑定CS膜材改質後官能基的變化，使用XPS來觀測表面元素組成，以及觀察各種膜材表面接觸角的差異。
滲透蒸發結果發現，當加入甲基纖維素鈉後的複合膜不論在通量與滲透水濃度都比純幾丁聚醣膜高，且隨著加入的羧甲基纖維素鈉的濃度越高，滲透通量與滲透水濃度都有顯著提高。CSCMC-4膜在溫度70℃，進料濃度為70 wt% IPA時，滲透通量可達1970 (g / m2 × h)，而滲透水濃度可以維持在98 wt% 以上，隨著進料IPA濃度越高，膜材膨潤性也就降低，進而減少滲透通量，但可提高滲透水濃度，而溫度升高增加了氣體分子動能，讓高分子鏈變的更柔軟，因此隨著操作溫度增加，滲透通量也隨著增加，但是滲透水濃度會有稍微下降的趨勢。由Arrhenius關係圖可算出IPA的活化能的是水的3.3倍以上，可證明聚電解質複合膜在滲透蒸發實驗上是選擇水的。由於複合膜材整體還是以CS材料為主，所以膜材並沒有因為形成聚電解質複合膜而增加長時間的穩定度。
研究中發現CS膜的機械性質雖明顯比CMC好，但CS膜加入CMC後，膜材的強度、硬度與韌度都比改質前更佳。由於複合膜的改質只在薄膜表面，所以複合膜主體還是以CS膜為主，因此在TGA的實驗結果上，並沒有因為離子交聯而明顯提高熱穩定度。

關鍵字

幾丁聚醣 ； 羧甲基纖維鈉 ； 聚電解質複合膜 ； 滲透蒸發

並列摘要

In this study, polyelectrolyte complex membranes were prepared by chitosan (CS) and carboxymethyl cellulose sodium (CMC) for the separation of isopropyl alcohol and water by pervaporation. Dense chitosan membranes were prepared on glass plates by solvent casting methods. After drying at room temperature, carboxymethyl cellulose sodium solution was cast on the top of the chitosan membranes. The thickness of polyelectrolyte complex membranes was 20±2μm. The polyelectrolyte complex reaction took place by electrostatic interaction, and the ionic crosslinking between the polycation (chitosan) and the polyanion (carboxylmethyl cellulose) was found. The ionic crosslinking was confirmed and characterized by SEM, AFM, FTIR-ATR/microscope, XPS, and contact angle measurement.
The performance of the polyelectrolye complex membranes in pervaporation was evaluated. The total permeate flux and water concentration in permeate through a CS-CMC complex membrane were better than that through a pure chitosan membrane. The total flux and water concentration in permeate increased as the concentration of CMC used to prepare the membranes increased. In addition, the total flux increased with temperature, and the water concentration in permeate decreased with temperature. The increase of total flux with temperature was resulted from the increase of the kinetic energies of the polymer chains and the penetrating molecules. The activation energy of pervaporation for IPA was about 3.3 times of that for water. It indicates that the polyelectrolyte complex membranes favor water permeation in the pervaporation process.
The mechanical properties of a chitosan membrane are obviously better than those of a CMC membrane. However, the Young’s modulus, tensile strength and elongation at break of the CMC modification polyelectrolyte complex membranes were better than those of a pure chitosan membrane. The thermal decomposition behaviors of the polyelectrolyte complex membranes were similar to that of a pure chitosan membrane in a TGA study indicated that the main body of the complex membrane was still composed of chitosan.

並列關鍵字

chitosan ； carboxymethyl cellulose sodium ； polyelectrolyte complex membrane ； pervaporation

參考文獻

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