Reaction kinetics of CO2 in aqueous ethylenediamine, ethyl ethanolamine, and diethyl monoethanolamine solutions in the temperature range of 298-313 K, using the stopped-flow technique

The observed pseudo-first-order rate constants (k(0)) for the reactions between CO2 and ethylenediamine (EDA), ethyl ethanolamine (EEA), and diethyl monoethanolamine (DEMEA) have been studied using the stopped-flow technique in an aqueous solution at 298, 303, 308, and 313 K. The amine concentrations ranged from 26.2 mol/m(3) to 67.6 mol/m(3) for EDA, 28.2 mol/m(3) to 81.9 mol/m(3) for EEA, and 196.5 mol/m(3) to 997.4 mol/m(3) for DEMEA. The zwitterion mechanism was used to correlate the experimentally obtained rate constants. Both the zwitterion formation step and the proton removal step had a significant role for the primary and secondary amines (EDA and EEA). The reaction rate of CO2 in an aqueous EDA solution was observed to be much faster than that in aqueous MEA solution. The rate in aqueous EEA was much faster than in aqueous DEA, under the conditions studied. Finally, the reaction rate constant of CO2 in an aqueous tertiary amine (DEMEA) solution was observed to be much faster than that in methyl diethanolamine (MDEA). Only the zwitterion formation step had a significant role in the overall reaction. The base catalysis of the CO2 hydration mechanism could explain the reaction between CO2 and the tertiary amine. Therefore, the three selected amines are considered to be of interest to the gas sweetening industry.