Kinetics of the Reversible Reaction of CO2(aq) and HCO3- with Sarcosine Salt in Aqueous Solution

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 degrees C and were analyzed in terms of Arrhenius, Eyring and van't Hoff relationships. The rate constant for the reaction between CO, and sarcosine to form the carbamate at 25.0 degrees C is 18.6(6) X 10(3) 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 H-1 nuclear magnetic resonance spectroscopy and report the corresponding rate and equilibrium constants at 25.0 degrees C. This rate constant is 5.9 X 10(-3) M-1 s(-1).