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Keywords:

  • kinetics;
  • CO2;
  • 2-((2-aminoethyl)amino) ethanol;
  • stopped-flow;
  • aqueous;
  • non-aqueous;
  • zwitterion

Abstract

Observed pseudo-first-order rate constants (ko) for the reaction between CO2 and 2-((2-aminoethyl) amino) ethanol (AEEA) were measured using the stopped-flow technique in an aqueous system at 298, 303, 308 and 313 K, and in non-aqueous systems of methanol and ethanol at 293, 298, 303 and 308 K. Alkanolamine concentrations ranged from 9.93 to 80.29 mol m−3 for the aqueous system, 29.99–88.3 mol m−3 for methanol and 44.17–99.28 mol m−3 for ethanol. Experimentally obtained rate constants were correlated with two mechanisms. For both the aqueous- and non-aqueous-AEEA systems, the zwitterion mechanism with a fast deprotonation step correlated the data well as assessed by the reported statistical analysis. As expected, the reaction rate of CO2 in the aqueous-AEEA system was found to be much faster than in methanol or ethanol. Compared to other promising amines and diamines studied using the stopped-flow apparatus, the pseudo-first-order reaction rate constants were found to obey the following order: PZ (cyclic-diamine) > EDA (diamine) > AEEA (diamine) > 3-AP (primary amine) > MEA (primary amine) > EEA (primary amine) > MO (cyclic-amine). The reaction rate constant of CO2 in aqueous-AEEA was double that in aqueous-MEA, and the difference increased with an increase in concentration. All reaction orders were practically unity. With a higher capacity for carbon dioxide and a higher reaction rate, AEEA could have been a good substitute to MEA if not for its high thermal degradation. AEEA kinetic behaviour is still of interest as a degradation product of MEA. © 2012 Canadian Society for Chemical Engineering