Superior Kinetics and High-Pressure Absorption Performance of Aqueous Ionic Liquid-Amine Hybrid Solvents for Co2 Capture

Abstract

Ionic liquids (ILs) and amines are both recognized for their CO2 absorption capacities, but their combination in hybrid solvents can potentially improve the overall absorption efficiency. High-pressure studies are crucial for understanding how these solvents perform under conditions that mimic industrial processes. The current study investigates the high-pressure CO2 absorption and diffusion kinetics of aqueous hybrid solvents composed of 1-butyl-3-methylimmidazolium acetate ([BMIM][AC]), N-methyl diethanolamine (MDEA), and piperazine (PZ), referred to as ionic liquid-amine hybrid (ILAH) solvents. Design of Experiments (DOE) tool was employed to identify optimal conditions for high-pressure CO2 absorption by systematically varying factors such as pressure, temperature, and IL concentration. Experiments were carried out to evaluate CO2 intake capacity, CO2 capture efficiency, and overall rate constant of the ILAH solvents. CO2 solubility was measured across a partial pressure range of 2-50 bar at three temperatures (303.15, 313.15, and 333.15 K).. The results demonstrated that CO2 absorption capacity increased with higher CO2 partial pressure but decreased with rising temperature. A unique trend was observed, with CO2 loading capacity peaking at 10 wt.% [BMIM][AC] and declining at higher concentrations, indicating an equilibrium state at 10 wt.%. Notably, the highest CO2 loading capacity of 2.182 mol CO2/mol ILAH was achieved at 10 wt.% [BMIM][AC] and 50 bar pressure. The addition of 3 wt.% PZ to the aqueous IL-MDEA mixture significantly enhanced CO2 capture efficiency and the overall rate constant. The findings provide valuable insights for optimizing solvent formulations, contributing to the development of more efficient, stable, and scalable carbon capture technologies.

Keywords: CO2 absorption, CO2 capture efficiency, diffusion kinetics, Ionic liquid-amines, hybrid solvents