Kinetics and mechanism study of homogeneous reaction of CO2 and blends of diethanolamine and monoethanolamine using the stopped-flow technique

The stopped-flow technique was applied on the measurement of the kinetics of carbon dioxide (CO2) absorption into aqueous blends of monoethanolamine (MEA) and diethanolamine (DEA) over the temperature range of 293-313 K. The investigation of blended MEA + DEA with various molar ratios of DEA to MEA revealed that the reaction mechanism between CO2 and blended absorbents could be different at different ratio of DEA to MEA. Consequently, the kinetic data obtained in this work was split into two groups with respect to the different molar ratios of DEA to MEA in order to study the different mechanisms. In group A, the concentration of MEA was in the range of 5-15 mol/m3 and the concentration of DEA was low (varied between 5 and 15 mol/m3), while in group B, the DEA concentration was high (varied between 140 and 240 mol/m3) and the concentration of MEA remained in the range of 5-15 mol/m3. Modified models based on the termolecular mechanism were developed for each group and used to interpret the experimental kinetic data. Results showed that the models could explain the data well with an AAD of 4.71% for group A at low concentration of DEA and 3.33% for group B at high concentration of DEA. It is interesting to point out that DEA barely reacts with CO2 at low molar ratios (i.e. group A) whereas at high DEA concentration (i.e. group B), both MEA and DEA reacted with CO2.