利用氧化還原介導雙極膜電透析系統同步碳捕捉及脫鹽之研析

Abstract

因應全球氣候變遷與淡水資源短缺問題，碳捕捉與脫鹽的整合技術逐漸受到重視。海洋作為最大的碳匯與水資源儲存場所，因富含溶解性無機碳(Dissolved Inorganic Carbon, DIC)，展現出碳捕捉與脫鹽應用的潛力。電化學方法因能源效率高、藥劑消耗少、操作彈性並與再生能源相容性高而成為重要研究方向。雙極膜電透析(Bipolar Membrane Electrodialysis, BMED)是一種先進的電化學薄膜分離技術，可透過雙極膜(Bipolar Membrane, BPM)中間層的水解反應(Water Dissociation, WD)產生酸與鹼，並結合離子交換膜(Ion Exchange Membrane, IEM)排列達到多樣化的功能。然而傳統BMED系統仍存在能耗較高的問題，限制了其大規模應用。 本研究開發一新穎的氧化還原介導雙極膜電透析系統(Redox-Mediated Bipolar Membrane Electrodialysis, RM-BMED)，該系統在電極室中循環可逆氧化還原電解質(K₃/K₄[Fe(CN)₆])，藉由較低的氧化還原電位與較快的電子傳遞速率，降低操作電壓，並達到同步碳捕捉與脫鹽的應用目標。在操作過程中，BPM產生的鹼性環境可將DIC轉化為碳酸根離子，與海水中的鈣離子反應形成碳酸鈣沉澱，同時藉由IEMs的選擇性離子傳輸進行脫鹽。 本研究系統性探討不同操作條件(電解液組成、施加電壓與進料濃度)對產鹼與脫鹽性能的影響。實驗結果顯示，RM-BMED系統相較於傳統BMED可以在低2.5 V的操作電壓下，達到相同的電流密度，顯示氧化還原電解質能有效提升電荷傳遞效率。進一步評估參數之影響，發現提高施加電壓有助於促進水解反應與離子遷移，並於1.0 V達到最佳的效能。當進流濃度增加，脫鹽的電流效率因電阻降低而提升；但產鹼的電流效率則可能因共離子洩漏與水傳輸現象下降。為進一步驗證RM-BMED系統在海水碳捕捉與脫鹽的應用潛力，本研究以合成海水進行實驗。結果顯示，透過控制流量可將鹼室pH維持於9.6–10，使DIC經由碳酸鈣沉澱反應去除，DIC去除率達62 ± 2%，脫鹽率為11 ± 1%，碳捕捉能耗為845 ± 59 kJ/mol DIC (2.35 ± 0.16 kWh/kg CaCO₃)。而系統產生的酸化海水亦能有效用於薄膜清洗，無需外加化學藥劑。整體結果顯示，RM-BMED系統具備同步碳捕捉與脫鹽的技術潛力，為因應氣候變遷與水資源短缺挑戰提供了一具前瞻性策略。

In response to the global climate change and freshwater scarcity, integrated technologies for carbon capture and desalination have gained attention. As the largest natural reservoir of both carbon and water, seawater can be utilized for the integrated processes of carbon capture and desalination, due to its high dissolved inorganic carbon (DIC) content. Electrochemical methods have emerged as a key research direction due to their renewable energy compatibility, high energy efficiency, low chemical consumption, and operational flexibility. Bipolar membrane electrodialysis (BMED) is an advanced electrochemical membrane separation technology that generates acid and alkali through water dissociation (WD) at the bipolar membrane (BPM) interface, combined with ion exchange membranes (IEMs) to achieve diverse functionalities. However, the high energy consumption of conventional BMED systems remains a major limitation for their large-scale deployment. This study develops a novel redox-mediated BMED (RM-BMED) system that circulates reversible redox electrolytes (K₃/K₄[Fe(CN)₆]) in the electrode chambers. Through lower redox potential and faster electron transfer rates, this system reduces operating voltage and simultaneously achieves carbon capture and desalination. During operation, the alkaline environment generated by BPM converts DIC into carbonate ions, which react with calcium ions in seawater to form calcium carbonate precipitates, while selective ion transport through IEMs enables desalination. The study systematically investigates the effects of various operating conditions (electrolyte composition, applied voltage, and feed concentration) on the performance of alkalization and desalination. Results demonstrate that RM-BMED achieves the same current density at 2.5 V lower operating voltage compared to conventional BMED, indicating effective improvement of charge transfer efficiency by the redox electrolyte. Further evaluation showed that increasing voltage promotes WD and ion migration, with optimal performance of alkalization and desalination achieved at 1.0 V. As feed concentration increases, system resistance decreases, improving performance of desalination; however, co-ion leakage and water transport lead to a decline in the performance of alkalization. To further demonstrate the RM-BMED system's potential for seawater carbon capture and desalination, experiments were conducted using synthetic seawater. Results show that controlling flow rate maintains pH at 9.6-10 in the alkali chamber, enabling DIC removal through calcium carbonate precipitation with 62 ± 2% DIC removal efficiency, 11 ± 1% salt removal efficiency, and carbon capture energy consumption of 845 ± 59 kJ/mol DIC (2.35 ± 0.16 kWh/kg CaCO₃). The system-generated acidified seawater can also effectively clean membrane components without additional chemical reagents. Overall results demonstrate the technical potential of RM-BMED for simultaneous carbon capture and desalination, offering a promising strategy to the challenges of climate change and water scarcity.