CO2 absorption rate in biphasic solvent of aminoethylethanolamine and diethylethanolamine

Abstract

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 (kg′) 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 (PCO2*) lower than 100 Pa, 25% AEEA/50% DEEA is homogeneous. The CO2 absorption rate, kg′, is as fast as 30% PZ (3 times faster than 30% MEA). When PCO2* 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 PCO2* and physical mass transfer coefficient. The kg′ 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 PCO2*. The slow kg′ 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.