Evaluation of novel aqueous piperazine-based physical-chemical solutions as biphasic solvents for CO2 capture: Initial absorption rate, equilibrium solubility, phase separation and desorption rate

Abstract

Novel aqueous piperazine-based physical–chemical solutions were proposed as promising liquid–liquid biphasic solvents for energy-efficient CO2 capture in order to enhance the absorption and desorption performance. Various phase-change systems including Piperazine (PZ), 1-(2-aminoethyl) piperazine (AEP), methyldiethanolamine (MDEA), sulfolane, 1-propanol and water with different concentration ratios were investigated comprehensively in terms of initial absorption rate, equilibrium solubility, phase splitting and desorption rate in the present work. Experimental results indicated that with the aid of organic solvents, PZ and AEP were proved to be promising candidates to accelerate the initial absorption and desorption rates, as well as enhance the CO2 absorption capacity due to their excellent reaction kinetics. The tunable phase separation property could be achieved by varying the concentration ratios of amine/organic solvent. After achieving equilibrium, the two liquid–liquid phases would not return back to one homogeneous liquid phase. Among these biphasic solvents, aqueous 2.5 M PZ + 2.5 M sulfolane with a large CO2 loading 0.85 mol CO2/mol amine at the phase change point was the optimal choice owing to good phase separation and great absorption and desorption properties. Compared to aqueous 2.5 M PZ single solvent, it demonstrated a 16% higher initial absorption rate, 9% larger CO2 absorption capacity and double desorption rate. This research provided a potential alternative absorbent for CO2 capture.