Amino Acids as Carbon Capture Solvents: Chemical Kinetics and Mechanism of the Glycine + CO2 Reaction

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• 作者：Dongfang Guo ; Hendy Thee ; Chun Y. Tan ; Jian Chen ; Weiyang Fei ; Sandra Kentish ; Geoffrey W. Stevens ; Gabriel da Silva
• 刊名：Energy & Fuels
• 出版年：2013
• 出版时间：July 18, 2013
• 年：2013
• 卷：27
• 期：7
• 页码：3898-3904
• 全文大小：326K
• 年卷期：v.27,no.7(July 18, 2013)
• ISSN：1520-5029

文摘

Amino acids are potential solvents for carbon dioxide separation processes, but the kinetics and mechanism of amino acid鈥揅O₂ reactions are not well-described. In this paper, we present a study of the reaction of glycine with CO₂ in aqueous media using stopped-flow ultraviolet/visible spectrophotometry as well as gas/liquid absorption into a wetted-wall column. With the combination of these two techniques, we have observed the direct reaction of dissolved CO₂ with glycine under dilute, idealized conditions, as well as the reactive absorption of gaseous CO₂ into alkaline glycinate solvents under industrially relevant temperatures and concentrations. From stopped-flow experiments between 25 and 40 掳C, we find that the glycine anion NH₂CH₂CO₂^{鈥?/sup> reacts with CO_2(aq) with k (M鈥? s鈥?) = 1.24 脳 1012 exp[鈭?459/T (K)], with an activation energy of 45.4 卤 2.2 kJ mol鈥?. Rate constants derived from wetted-wall column measurements between 50 and 60 掳C are in good agreement with an extrapolation of this Arrhenius expression. Stopped-flow studies at low pH also identify a much slower reaction between neutral glycine and CO₂, with k (M鈥? s鈥?) = 8.18 脳 1012 exp[鈭?624/T (K)] and activation energy of 71.7 卤 9.6 kJ mol鈥?. Similar results are observed for the related amino acid alanine, where rate constants for the respective neutral and base forms are 1.02 卤 0.40 and 6250 卤 540 M鈥? s鈥? at 25 掳C (versus 2.08 卤 0.18 and 13鈥?00 卤 750 M鈥? s鈥? for glycine). This work has implications for the operation of carbon capture systems with amino acid solvents and also provides insight into how functional groups affect amine reactivity toward CO₂.}