Determination of the rate of absorption for CO2 absorption systems

In order to properly design an absorption tower for CO2 capture knowledge on the absorption rate of CO2 is required. Several methods can be used to determine the absorption rate, such as a wetted wall column (WWC), stirred absorption cell or a string of discs setup. The aim of this work was to determine the absorption flux of CO2 into different amine solutions using anew method. Two absorption systems were investigated, namely aqueous solutions of monoethanolamine (MEA) and solutions of 2-amino-2-methyl-1-propanol (AMP) in the organic solvent N-methyl-2-pyrrolidone (NMP). Aqueous solutions of MEA have been widely researched and are considered benchmark amine solutions for CO2 capture whereas solutions of AMP in NMP are novel absorption systems that have been reported as promising alternatives for CO2 capture, based on its ability to be regenerated at lower temperatures.A new method for determining the rate of absorption was developed and evaluated. Experiments were performed using the true heat-flow reaction calorimeter CPA202, developed by ChemiSens AB, and the rate of pressure decrease in the reactor was measured during absorption of a known quantity of CO2. The absorption flux of CO2 could then be calculated from the experimental data obtained during the experiments. Different amineconcentrations for the aqueous MEA were investigated, 1.5, 5 and 7 m, as well as for solutions of AMP in NMP, 1.5 and 5 m. The experiments were carried out at 25°C. Duplicate experiments were performed for each amine concentration.The results of the study show that the absorption flux decreases linearly as the CO2-loading increases for aqueous solutions of MEA. The absorption flux was lower for the 1.5 m MEA solution than for the solutions of 5 and 7 m MEA, for which similar values were determined. The results obtained thus indicate that there may be a threshold concentration, most likely between 1.5 and 5 m MEA, above which the overall absorption flux does not significantlyincrease as a result of an increased amine concentration. The absorption flux determined for solutions of AMP in NMP was considerably higher than those determined for aqueous solutions of MEA and was very similar for both the 1.5 m and the 5 m AMP in NMP solutions. There was no clear indication of the absorption flux decreasing with CO2-loading for the solutions of AMP in NMP, as observed for the aqueous solutions of MEA. However, the determined absorption flux for the solutions of AMP in NMP were more scattered and therepeatability for these experiments was in general lower than for the experiments on aqueous MEA.The same experiments will be performed using a WWC. These results will be compared with those obtained with the new method developed in this study, in order to evaluate if the new method gives reliable absorption fluxes and can be used in order to quickly assess the absorption rate of new CO2 absorption systems