Mass transfer and kinetics of carbon dioxide absorption into loaded aqueous monoethanolamine solutions

Abstract

The kinetics of the reaction between carbon dioxide and aqueous solutions of 1 and 5molL−1 monoethanolamine (MEA) pre-loaded with CO2 were investigated over the temperature range 298 to 343K and for CO2 loadings from 0 to 0.4mol CO2/mol MEA in a wetted wall column reactor (WWC) and a string of discs contactor (SDC). A total of 227 new data points are provided for loaded solutions including all underlying data necessary for other researchers to develop own models. Comparisons are made between recent literature data and this study and they are found to be consistent with each other. Three different kinetic models, a simplified soft model, a concentration-based model and an activity-based model were developed and validated against the experimental data and by a penetration type mass transfer model in order to analyze the absorption rate and understand the reaction process. Results show good agreement between the models at low loadings and kinetic parameters are provided for all models. Above a loading of 0.3mol CO2/mol MEA it is recommended to use the activity based model as systematic deviations occurred in the soft and concentration based models. The effect of depletion of free amine at the gas–liquid interface on the kinetic and mass transfer calculations was investigated and it was found insignificant at high amine concentrations, low CO2 loadings, low CO2 driving forces and temperatures. However, the effect does become significant when either reducing the amine concentration or increasing the CO2 driving force, CO2 loading or temperature. Furthermore, there is an upper limit for the CO2 driving force for each amine concentration below which the chemical reaction can be assumed to be in the pseudo 1st order regime.