Kinetics, Thermodynamics, and Mechanism of a Novel Biphasic Solvent for CO₂ Capture from Flue Gas

The main issue related to the deployment of the amine-based absorption process for CO₂ capture from flue gas is its intensive energy penalty. Therefore, this study screened a novel biphasic solvent, comprising a primary amine e.g., triethylenetetramine (TETA) and a tertiary amine e.g., N,N-dimethylcyclohexylamine (DMCA), to reduce the energy consumption. The TETA-DMCA blend exhibited high cyclic capacity of CO₂ absorption, favorable phase separation behavior, and low regeneration heat. Kinetic analysis showed that the gas- and liquid-side mass transfer resistances were comparable in the lean solution of TETA-DMCA at 40 °C, whereas the liquid-side mass transfer resistance became dominant in the rich solution. The rate of CO₂ absorption into TETA-DMCA (4 M, 1:3) solution was comparable to 5 M benchmark monoethanolamine (MEA) solution. Based on a preliminary estimation, the regeneration heat with TETA-DMCA could be reduced by approximately 40% compared with that of MEA. ¹³C NMR analysis revealed that the CO₂ absorption into TETA-DMCA was initiated by the reaction between CO₂ and TETA via the zwitterion mechanism, and DMCA served as a CO₂ sinker to regenerate TETA, resulting in the transfer of DMCA from the upper to lower phase. The proposed TETA-DMCA solvent may be a suitable candidate for CO₂ capture.