CO₂ absorption rate in biphasic solvent of aminoethylethanolamine and diethylethanolamine

Amine scrubbing is currently the most promising technology for CO₂ capture from gas turbine and coal-fired flue gas. It is hindered by high regeneration energy and high capital cost. Biphasic solvent of 25% aminoethylethanolamine (AEEA)/50% diethylethanolamine (DEEA) could be a potential solution as it may achieve significant reduction in regeneration energy. A fast CO₂ absorption rate is preferred to reduce the capital cost of the absorber. In this work, the CO₂ absorption rate (k_g′) of the biphasic solvent was measured in a wetted wall column at 40 °C and at the loading conditions in the absorber. At CO₂ equilibrium partial pressure (P_CO2*) lower than 100 Pa, 25% AEEA/50% DEEA is homogeneous. The CO₂ absorption rate, k_g′, is as fast as 30% PZ (3 times faster than 30% MEA). When P_CO2* is greater than 100 Pa, 25% AEEA/50% DEEA forms aqueous and organic phases after CO₂ absorption. It was first found that the organic phase of 25% AEEA/50% DEEA absorbs CO₂ 2–7 times faster than the aqueous phase because of greater physical CO₂ solubility at the same P_CO2* and physical mass transfer coefficient. The k_g′ of the organic phase is much faster than 30% MEA and 25% AEEA at lean and rich loading and even greater than 30% PZ at lean loading. The instantaneous reaction mechanism fits the kinetics of CO₂ absorption in the organic phase at low P_CO2*. The slow k_g′ of the aqueous phase results from greater viscosity which significantly reduces the physical mass transfer coefficient. The CO₂ capacity of the aqueous phase is 2.9 times, 1.8 times, and 5.3 times greater than that of 30% MEA, 30% PZ, and the organic phase, respectively.