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

Phase change absorbents based on amine chemical absorption for CO capture exhibit energy-saving potential, but generally suffer from difficulties in CO 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 CO regeneration. In this investigation, N-aminoethylpiperazine (AEP)/sulfolane/HO 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 CO products in different alcohol solutions. The results demonstrated that these ion pair products reached the maximum solvation-free energy (ΔE) 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 C 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 (CHOCOO), which enhanced the regeneration reactivity. In addition, the decomposition paths of different CO products were simulated visually, and every reaction's activation energy (ΔE) was calculated. Remarkably, the ΔE for the decomposition of CHOCOO (9.465 kJ/mol) was lower than that of the AEPCOO (26.163 kJ/mol), implying that CO 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 CO, which had excellent energy-saving potential.