Kinetics of the ReversibleReaction of CO2(aq) and HCO3–with Sarcosine Salt inAqueous Solution.

Aqueous sarcosine salts are fast carbon dioxide (CO2) absorbents suitable for use in postcombustion CO2capturein coal-fired power plants. We have developed a detailed reactionscheme including all the reactions in the sarcosine–CO2–water system. All unknown rate and equilibrium constantswere obtained by global data fitting. We investigated the temperature-dependentrate and equilibrium constants of the reaction between aqueous CO2and sarcosine using stopped-flow spectrophotometry, by followingthe pH changes over the wavelength range 400–700 nm via couplingto pH indicators. The corresponding rate and equilibrium constantsranged from 15.0 to 45.0 °C and were analyzed in terms of Arrhenius,Eyring, and van’t Hoff relationships. The rate constant forthe reaction between CO2and sarcosine to form the carbamateat 25.0 °C is 18.6(6) × 103M–1s–1, which is very high for an acyclic amine;its activation enthalpy is 59(1) kJ mol–1and theentropy is 33(4) J mol–1K–1.In addition, we investigated the slow reaction between bicarbonateand sarcosine using 1H nuclear magnetic resonance spectroscopyand report the corresponding rate and equilibrium constants at 25.0°C. This rate constant is 5.9 × 10–3M–1s–1. [ABSTRACT FROM AUTHOR]