Kinetics of the Reversible Reaction of CO2(aq) and HCO3– with Sarcosine Salt in Aqueous Solution
journal contributionposted on 25.10.2012, 00:00 by Qunyang Xiang, Mengxiang Fang, Hai Yu, Marcel Maeder
Aqueous sarcosine salts are fast carbon dioxide (CO2) absorbents suitable for use in postcombustion CO2 capture in coal-fired power plants. We have developed a detailed reaction scheme including all the reactions in the sarcosine–CO2–water system. All unknown rate and equilibrium constants were obtained by global data fitting. We investigated the temperature-dependent rate and equilibrium constants of the reaction between aqueous CO2 and sarcosine using stopped-flow spectrophotometry, by following the pH changes over the wavelength range 400–700 nm via coupling to pH indicators. The corresponding rate and equilibrium constants ranged from 15.0 to 45.0 °C and were analyzed in terms of Arrhenius, Eyring, and van’t Hoff relationships. The rate constant for the reaction between CO2 and sarcosine to form the carbamate at 25.0 °C is 18.6(6) × 103 M–1 s–1, which is very high for an acyclic amine; its activation enthalpy is 59(1) kJ mol–1 and the entropy is 33(4) J mol–1 K–1. In addition, we investigated the slow reaction between bicarbonate and sarcosine using 1H nuclear magnetic resonance spectroscopy and report the corresponding rate and equilibrium constants at 25.0 °C. This rate constant is 5.9 × 10–3 M–1 s–1.