Kinetics of absorption of carbon dioxide in aqueous piperazine solutions

In the present work the absorption of carbon dioxide into aqueous piperazine (PZ) solutions has been studied in a stirred cell, at low to moderate temperatures, piperazine concentrations ranging from 0.6 to 1.5 kmol m- 3, and carbon dioxide pressures up to 500 mbar, respectively. The obtained experimental results were interpreted using the DeCoursey equation [DeCoursey, W., 1974. Absorption with chemical reaction: development of a new relation for the Danckwerts model. Chemical Engineering Science 29, 1867-1872] to extract the kinetics of the main reaction, 2 PZ + CO2 → PZCOO- + PZH+, which was assumed to be first order in both CO2 and PZ. The second-order kinetic rate constant was found to be 70 m3 mol- 1 s- 1 at a temperature of 298.15 K, with an activation temperature of 4.1 × 103 K. Also, the absorption rate of CO2 into partially protonated piperazine solutions was experimentally investigated to identify the kinetics of the reaction 2 PZH+ + CO2 → H+ PZCOO- + PZH22 +. The results were interpreted using the Hogendoorn approach [Hogendoorn, J., Vas Bhat, R., Kuipers, J., Van Swaaij, W., Versteeg, G., 1997. Approximation for the enhancement factor applicable to reversible reactions of finite rate in chemically loaded solutions. Chemical Engineering Science 52, 4547-4559], which uses the explicit DeCoursey equation with an infinite enhancement factor which is corrected for reversibility. Also, this reaction was assumed to be first order in both reactants and the second-order rate constant for this reaction was found to be (0.28 ± 0.10) m3 mol- 1 s- 1 at 298.15 K.