二氧化碳直接合成碳酸甘油酯技術評估：製程、經濟、生命週期與安全性分析

Abstract

碳酸甘油酯（glycerol carbonate, GC）之合成若能經由二氧化碳（carbon dioxide, CO₂）與甘油（glycerol, GLY）直接轉化而成，將可視為一項能將兩種廢棄原料轉化為具高附加價值之化學產品的創新技術。儘管已有相當多實驗研究投入於此領域，其製程設計的技術可行性仍有待深入評估。為解決此問題，本研究提出兩種直接轉化路徑以生產GC：製程一（Scheme 1）為光熱催化轉化；製程二（Scheme 2）則採用熱催化轉化並添加化學脫水劑2-氰基吡啶（2-cyanopyridine, 2-CP）以提升反應轉化率。兩種製程皆設計對應之嚴謹分離策略。接著，本研究對兩製程進行製程優化，並與其他GC生產途徑（如間接轉化及以反應精餾為基礎之酯交換法）進行經濟性、環境影響與安全性之比較分析。 整體而言，技術經濟評估 (techno-economic analysis, TEA) 指出，在現行技術條件下，兩種直接轉化方案尚未具備經濟可行性，其最低銷售價格（minimun selling price, MSP）分別為Scheme 1之每公斤8.15美元與Scheme 2之每公斤15.76美元。然而，若能降低反應器所產生之資本成本，並透過2-CP的再生使用或其水合副產物2-吡啶甲醯胺（2-picolinamide, 2-PA）之銷售回收成本，兩製程之MSP能有潛力地分別降至每公斤1.57美元與1.38美元。 根據搖籃到大門（cradle-to-gate）之生命週期評估（life cycle assessment, LCA）結果顯示，兩種直接轉化製程的永續性皆低於間接路徑；假如能提升Scheme 1之轉化率，其整體永續表現有機會與間接製程相當。此外，兩製程之固有安全指數（inherent safety index, ISI）皆相對較低，為未來深入開發該類製程提供安全性佐證。綜上所述，本研究點出了直接轉化途徑之應用潛力與所面臨之挑戰，並有助於後續製程開發與研究方向之規劃。

The synthesis of glycerol carbonate (GC) through the direct conversion of carbon dioxide (CO2) and glycerol (GLY) represents a novel methodology that repurposes two waste materials into a commercially valuable product. Despite extensive experimental investigations, the technological feasibility of this process remains inadequately explored. To tackle this issue, the current study presents two distinct processes for the production of GC via the direct conversion route. Scheme 1 features photothermal catalytic conversion, while Scheme 2 employs thermal catalytic conversion with the addition of a chemical dehydrant (2-cyanopyridine, 2-CP) to enhance reaction efficiency. Rigorous separation strategies have been proposed for both schemes. Subsequently, both processes were optimized and compared against alternative GC production pathways (i.e., indirect conversion and reactive-distillation-based transesterification) with respect to economic, environmental, and safety considerations. Overall, the techno-economic analysis (TEA) reveals a lack of economic feasibility based on current technologies, reporting a minimum selling price (MSP) of $8.15 per kg for Scheme 1 and $15.76 per kg for Scheme 2. However, these values can be improved to $1.57 per kg for Scheme 1 and $1.38 per kg for Scheme 2, provided that the capital cost of the reactor is reduced and the expense of 2-CP can be offset through either regeneration or the sale of the hydration product, 2-picolinamide (2-PA). A cradle-to-gate life cycle assessment (LCA) indicates that both Schemes 1 and 2 exhibit lower sustainability compared to the indirect pathway. Nevertheless, should the yield of the product in Scheme 1 be improved, the overall sustainability could potentially align with that of the indirect process. Finally, both direct conversion schemes demonstrate lower values for the inherent safety index (ISI). This, in turn, provides supportive evidence for the further development of this pathway. In summary, this study highlights the potential benefits and obstacles associated with this conversion pathway. It may serve as a significant reference for future research aimed at process development.