Alcohol regulated phase change absorbent for efficient carbon dioxide capture: Mechanism and energy consumption

Phase change absorbents based on amine chemical absorption for CO₂ capture exhibit energy-saving potential, but generally suffer from difficulties in CO₂ regeneration. Alcohol, characterized as a protic reagent with a low dielectric constant, can provide free protons to the rich phase of the absorbent, thereby facilitating CO₂ regeneration. In this investigation, N-aminoethylpiperazine (AEP)/sulfolane/H₂O was employed as the liquid-liquid phase change absorbent, with alcohol serving as the regulator. First, appropriate ion pair models were constructed to simulate the solvent effect of the CO₂ products in different alcohol solutions. The results demonstrated that these ion pair products reached the maximum solvation-free energy (ΔE_solvation) in the rich phase containing ethanol (EtOH). Desorption experiment results validated that the inclusion of EtOH led to a maximum regeneration rate of 0.00763 mol/min, thus confirming EtOH's suitability as the preferred regulator. Quantum chemical calculations and ¹³C NMR characterization were performed, revealing that the addition of EtOH resulted in the partial conversion of AEP-carbamate (AEPCOO^-) into a new product known as ethyl carbonate (C₂H₅OCOO^-), which enhanced the regeneration reactivity. In addition, the decomposition paths of different CO₂ products were simulated visually, and every reaction's activation energy (ΔE_act) was calculated. Remarkably, the ΔE_act for the decomposition of C₂H₅OCOO^- (9.465 kJ/mol) was lower than that of the AEPCOO^- (26.163 kJ/mol), implying that CO₂ was more likely to be released. Finally, the regeneration energy consumption of the alcohol-regulated absorbent was estimated to be only 1.92 GJ/ton CO₂, which had excellent energy-saving potential.