Absorption of CO2 in aqueous diglycolamine

Absorption of CO2 into aqueous DGA (Diglycolamine) was performed at 25-60 degrees C in a wetted-wall column. The absorption data were analyzed using a rigorous model based on eddy diffusivity theory and approximations assuming pseudo-first-order (PFO) and interface pseudo-first-order (IPFO) reactions. The PFO is a good approximation for CO2 absorption into DGA at a CO2 loading of less than 0.2 mol/mol DGA. At CO2 loadings greater than 0.4, instantaneous reactions are approached. The IPFO model matches the rigorous model very well. The second-order rate constant in 65 wt % DGA at 25 degrees C for the reaction with CO2 is four times larger than previously published values, but 25 wt % DGA yields a rate constant which is in good agreement with literature values. This finding Suggests that the second-order rate constant is probably a function of DGA concentration. The second-order rate constant in 65 wt % DGA increases by a factor of 5 from 0 to 0.4 mol CO2/mol DGA. Experiments with 65 wt % DGA + glycolic acid and 65 wt % DGA + potassium formate at 25 degrees C and 40 degrees C showed similar trends. The rate constant increases a factor of 2 to three in these solutions, suggesting that the rate constant is a function of ionic strength.