Kinetics of the reversible reaction of CO2(aq) with taurate in aqueous solution

Taurate has potential as an absorbent for CO2 capture and is also an effective rate promoter in aqueous NH3‐based absorbents. However, the detailed mechanism involved in the reaction of CO2(aq) with taurate in aqueous solution is not available and the reaction rate and equilibrium constants for some reactions in the mechanism have not yet been determined. This limits our understanding of the role of taurate in the capture process using an NH3/taurate mixture and hinders rigorous rate‐based process simulation. In this work, we studied the reaction of taurate with CO2 in aqueous solution with added acid‐base indicators at 288.0, 298.0, 308.0, and 318.0 K. Stopped‐flow spectrophotometry was used to record absorbance of the solutions, which reflects pH changes via colored acid‐base indicators as a function of time and over the wavelength range from 400.0–700.0 nm. Through global analysis of the kinetic data from the stopped flow reactor, we determined the temperature dependence of the rate and equilibrium constants using a detailed reaction scheme including all reactions in the taurate–CO2–H2O system. We then used stopped‐flow spectrophotometry to investigate the effect of taurate on the reaction of CO2 in the mixed taurate−NH3−CO2−H2O system at 298.0 K. The mechanism for the reaction of the taurate and NH3 mixture with CO2(aq) was found to be a simple combination of two individual systems. Taurate in the mixture can significantly enhance the CO2 absorption rate and NH3 can work as a proton sink making more taurate available for CO2 and the potential reduction of NH3 loss. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.