In Situ Nuclear Magnetic Resonance Mechanistic Studies of Carbon Dioxide Reactions with Liquid Amines in Mixed Base Systems: The Interplay of Lewis and Br酶nsted Basicities

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• 作者：Pavel V. Kortunov ; Lisa Saunders Baugh ; Michael Siskin ; David C. Calabro
• 刊名：Energy & Fuels
• 出版年：2015
• 出版时间：September 17, 2015
• 年：2015
• 卷：29
• 期：9
• 页码：5967-5989
• 全文大小：1486K
• ISSN：1520-5029

文摘

A new approach to non-aqueous CO₂鈥揳mine carbon capture has been elucidated on the basis of the utilization of a combination of a nucleophilic amine CO₂ sorbent (Lewis base) with a second, non-nucleophilic Br酶nsted base, a 鈥渕ixed base鈥?system. The nucleophilic amines, typically alkanolamines, e.g., ethanolamine, react directly with CO₂ in the gas stream, while the typically stronger nitrogenous Br酶nsted non-nucleophilic proton-acceptor base, e.g., a guanidine, then forms a more stabilized mixed carbamate reaction product. The proper choice of these bases allows for tailoring absorbent structure and properties and reaction conditions (T and P) to specific applications. Significant increases in absorption capacity are achieved because CO₂ capture ratios greater than 1:1 on a molar basis (CO₂ per amine group) can be obtained, resulting also in enhanced cyclic regeneration efficiency. In non-aqueous solutions, primary amines are carboxylated by reaction with one or two CO₂ molecules, forming either mono- or di-N-carboxylated products. These carbamic acids, unstable in aqueous media, are then stabilized as guanidinium carboxylates. A total of 2 mol of CO₂ per mol of a primary alkanolamine is thereby captured. In addition, under non-aqueous conditions, the hydroxyl group of alkanolamine reacts with CO₂ (O-carbonation) to form an alkylcarbonic acid that is subsequently stabilized by forming the corresponding alkylbicarbonate salt on reaction with a guanidinine. Each hydroxyl group thereby also absorbs up to 1 mol of CO₂. Thereby, enhanced capacity is achieved at both basic N and OH sites of monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), etc. These products may be decomposed by thermal treatment or CO₂ partial pressure decrease to liberate CO₂ and regenerate the liquid sorbent suitable for reuse in carbon capture operations.