Reaction Kinetics of Carbon Dioxide (CO2) Absorption in Sodium Salts of Taurine and Proline Using a Stopped-Flow Technique

Abstract

The pseudo–first-order reaction rate constants (k0, s−1) for the reaction of carbon dioxide in aqueous solutions of sodium taurate (NaTau) and sodium prolinate (NaPr) were measured using a stopped-flow technique at a temperature range of 298–313 K. The solutions concentration varied from 5 to 50 mol m−3 and from 4 to 12 mol m−3 for NaTau and NaPr, respectively. Comparing the k0 values, aqueous NaPr was found to react very fast with CO2 as compared with the industrial standard aqueous monoethanolamine (MEA) and aqueous sodium taurate (NaTau) was found to react slower than aqueous MEA at the concentration range considered in this work. For the studied amino acid salts, the order of the reactions was found to be unity with respect to the amino acid salt concentration. Proposed reaction mechanisms such as termolecular and zwitterion reaction mechanisms for the reaction of CO2 with aqueous solutions were used for calculating the second-order reaction rate constants (k2, m3 mol−1 s−1). The formation of zwitterion during the reaction with CO2 was found to be the rate-determining step, and the deprotonation of zwitterion was instantaneous compared to the reverse reaction of zwitterion to form an amino acid salt. The contribution of water was established to be significant for the deprotonation of zwitterion. Comparing the pseudo–first-order reaction rate constants (k0, s−1) of various amino acid salts with CO2, NaPr was found to be the faster reacting amino acid salt. The activation energy for NaTau was found to be 48.1 kJ mol−1 and that of the NaPr was found to be 12 kJ mol−1. The Arrhenius expressions for the reaction between CO2 and the studied amino acid salts are