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Amino acids are potential solvents for carbon dioxide separation processes, but the kinetics and mechanism of amino acid−CO 2 reactions are not well-described. In this paper, we present a study of the reaction of glycine with CO 2 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 CO 2 with glycine under dilute, idealized conditions, as well as the reactive absorption of gaseous CO 2 into alkaline glycinate solvents under industrially relevant temperatures and concentrations. From stopped-flow experiments between 25 and 40 °C, we find that the glycine anion NH 2 CH 2 CO 2 − reacts with CO 2(aq) with k (M −1 s −1 ) = 1.24 × 10 12 exp[−5459/T (K)], with an activation energy of 45.4 ± 2.2 kJ mol −1 . Rate constants derived from wetted-wall column measurements between 50 and 60 °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 CO 2 , with k (M −1 s −1 ) = 8.18 × 10 12 exp[−8624/T (K)] and activation energy of 71.7 ± 9.6 kJ mol −1 . Similar results are observed for the related amino acid alanine, where rate constants for the respective neutral and base forms are 1.02 ± 0.40 and 6250 ± 540 M −1 s −1 at 25 °C (versus 2.08 ± 0.18 and 13 900 ± 750 M −1 s −1 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 CO 2 .

The hydration of CO(2) plays a critical role in carbon capture and geoengineering technologies currently under development to mitigate anthropogenic global warming and in environmental processes such as ocean acidification. Here we reveal that borate catalyzes the conversion of CO(2) to HCO(3)(-) via the same fundamental mechanism as the enzyme carbonic anhydrase, which is responsible for CO(2) hydration in the human body. In this mechanism the tetrahydroxyborate ion, B(OH)(4)(-), is the active form of boron that undergoes direct reaction with CO(2). In addition to being able to accelerate CO(2) hydration in alkaline solvents used for carbon capture, we hypothesize that this mechanism controls CO(2) uptake by certain saline bodies of water, such as Mono Lake (California), where previously inexplicable influx rates of inorganic carbon have created unique chemistry. The new understanding of CO(2) hydration provided here should lead to improved models for the carbon cycle in highly saline bodies of water and to advances in carbon capture and geoengineering technology.

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