訂製非均相陰離子及陽離子交換膜於薄膜電容去離子技術應用之研析

Abstract

薄膜電容去離子技術 (Membrane capacitive deionization, MCDI)是一種節約 能源、對環境友善的脫鹽技術，本技術適用於半鹽水淡化與再生水利用的處理， 以期日後能作為淡水資源短缺的解方之一。離子交換膜 (Ion-exchangemembrane, IEM)是 MCDI 系統中的組成關鍵，利用其對離子的選擇性可提高本技術的電荷 效率及脫鹽量表現。以市面上可取得的商業用均相 IEM 為例，其雖具備良好電 化學特性，但價格高昂且機械強度較低，在長期操作下容易破裂、降低 IEM 之 使用壽命，導致整體系統的成本增加。反觀非均相 IEM，雖然其電化學特性表現 略低於均相 IEM，但其生產成本較低且機械強度良好。同時，近幾年針對非均相 IEM 的研究數量逐漸增加，藉由改善 IEM 製備流程以延長其使用壽命和降低操 作成本。此外，過去的相關研究缺乏針對薄膜電容去離子系統應用而研發的非均 相離子交換膜。因此，本研究將探討所製備的非均相 IEM 之薄膜特性並探討其 應用於 MCDI 系統之潛力。 本研究利用調整離子交換樹脂及聚合物的比例製成鑄膜液，塗布成膜以製備 非均相的陰離子(Anion-exchange membrane, AEM)和陽離子交換膜(Cation- exchange membrane, CEM)，並分析製備之非均相 IEM 特性並應用於 MCDI 系統， 進行半鹽水溶液之脫鹽實驗，探討出適合應用於 MCDI 的 IEM 之製膜配方。結 果顯示，樹脂含量為 50 wt.% 的非均相 AEM 及 CEM 在薄膜特性分析中，具有 適宜之含水量 (20-35%)、離子交換能力(約1.65meq/g)及離子傳輸量(Cl-:23.91mg; Na+: 11.32 mg)。在電化學特性、薄膜強度及電吸附試驗穩定性的評比中，樹脂含 量為 50 wt.% 的非均相 AEM 及 CEM 擁有較好的綜合表現。同時，應用於 MCDI 系統中的非均相 AEM 及 CEM 亦成功促進系統整體的電吸附表現，並具有與商 業用均相 IEM 相似之電吸附效能指標。綜合上述，本研究成果研發出可與商業 用均相 IEM 匹敵之非均相 IEM 的最適配方，且具有應用於 MCDI 技術的潛力。

As an energy-saving and environmentally friendly desalination technology, membrane capacitive deionization (MCDI) has been developed for brackish water treatment to supply fresh water. Ion exchange membranes are key components of the MCDI system, enhancing the charge efficiency and salt adsorption capacity of CDI. Taking the commercial homogeneous IEM as an example, it exhibits good electrochemical properties but the high manufacturing cost and weak mechanical strength make it easily broken and decreases its lifetime, further leading to an increase in capital cost. From several past studies, fabricating heterogeneous IEM has become an effective strategy to lower the production cost and enhance membrane mechanical strength with structural polymer. However, heterogeneous IEM involves resin with functional groups and binder as structural former so leading to discontinuous functional groups distribution in the internal membrane, which results in poor electrochemical properties. In addition, past research lacks the development of heterogeneous IEM applied to MCDI systems. In this research, both heterogeneous AEMs and CEMs are fabricated with resin contents of 30, 50, and 70 wt.% to investigate the optimized resin content for the MCDI system. The results revealed that both heterogeneous AEM and CEM with 50 wt.% resin content struck a good balance between electrochemical property and membrane strength. The fabricated heterogeneous IEMs with 50 wt.% resin content were chosen to compete with commercial homogeneous IEMs. In the MCDI system, the fabricated heterogeneous IEMs (A50/C50) exhibited MDC of 10.41 mg/g, Em of 0.03 kWh/mole, and ! > 99%. The commercial homogeneous IEMs (ASE/CSE) applied to MCDI exhibited MDC of 9.23 mg/g, Em of 0.03 kWh/mole, and ! > 99%. It was found that the fabricated heterogeneous IEMs are competitive with the commercial homogeneous ones of the MCDI system. The results provide a suitable resin content to fabricate heterogeneous IEMs, further showing the great potential of fabricated heterogeneous IEMs in MCDI for future development.