Non-Aqueous Solvent Mixtures for CO₂ Capture: Choline Hydroxide-Based Deep Eutectic Solvents Absorbent Performance at Various Temperatures and Pressures

Carbon dioxide (CO₂) absorption in a non-aqueous solution is a potential technology for reducing greenhouse gas emissions. In this study, a non-aqueous solvent, sulfolane and dimethylsulfoxide (DMSO), was functionalized with a deep eutectic solvent (DES) consisting of choline hydroxide and polyamines diethylenetriamine (DETA) and triethylenetetramine (TETA). The non-aqueous absorbents’ CO₂ absorption ability was investigated in a high-pressure absorption reactor with a variable absorption temperature (303.15–333.15 K) and pressure (350–1400 kPa). The results showed that 2M ChOH:TETA−DMSO solution had the highest CO₂ loading capacity when compared with other screened solutions, such as 2M ChOH:TETA−Sulfolane, 2M ChOH:DETA−DMSO and 2M ChOH:DETA−Sulfolane. It was also found that the absorption capacity increased with increasing pressure and decreased with temperature. The highest CO₂ absorption by 2M ChOH:TETA−DMSO was observed at a partial pressure of 1400 kPa at 303.15 K 1.2507 mol CO₂/mol DES. The use of a non-aqueous solvent in the mixture showed a phase separation phenomenon after the CO₂ absorption reaction due to the formation of insoluble carbamate salt, which was identified through FTIR analysis. These findings suggest that the use of a DES polyamine mixed with a non-aqueous solvent could be a promising solution for CO₂ capture.