Kinetic study of the reaction of diethanolamine with carbon dioxide in aqueous and mixed solvent systems - application to acid gas cleaning

The observed pseudo first-order reaction rate constants, k(o), for the overall reaction between CO2 and diethanolamine (DEA) in aqueous, aqueous ethylene glycol (AQ-EG), aqueous diethylene glycol (AQ-DEG) and aqueous polyethylene glycol 200 (AQ-PEG) systems using the stopped flow technique at 298-313 K have been determined. The rate constants of involved reactions have been calculated according to the zwitterion mechanism. Good parity has been observed between the experimentally determined and calculated k(o) values. Partial substitution of water by the diols is found to effect the k(o) values, the reaction order with respect to the amine and the determined rate constants of the involved reactions. Under the conditions studied, the fastest reaction kinetics were observed in the AQ-EG system at low amine concentrations, while at high [DEA] the reaction in water was found to be the fastest. Changes in the intermolecular attractive forces cause changes in the zwitterion formation rate (k(2) values) and affect the ease with which the amine can access the formed zwitterion for deprotonation (k(A) values). Differences in steric factor cause the changes in the extent of zwitterion deprotonation by the diol (k(D) values). Changes in the ease with which water molecules can access the zwitterion as well as the presence of ether groups in the diols result in changes in the extent of zwitterion deprotonation by water (k(W) values). (C) 2004 Elsevier B.V. All rights reserved.