Fine-Tuning the CO₂ capture performance of novel CO₂-binding organic liquids by a combined experimental-molecular modeling approach

CO₂-binding organic liquids (CO₂BOLs) are currently being explored as next generation solvents for CO₂ capture. In this study, 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU)-based CO₂BOLs were selected to quantify the impact of molar ratio, chain length, and type of hydroxyl groups on CO₂ capture performance. The CO₂BOLs included formulations of DBU with hydroxy compounds such as butanol, hexanol, ethylene glycol methyl ether (EGME), and ethylene glycol ethyl ether (EGEE) at molar ratios of (1:2), (1:4) and (1:6). Experimental measurements provided their density, viscosity, vapor pressure, CO₂ solubility and heat of absorption. The study revealed that novel ether CO₂BOLs have 10–20 % higher CO₂ uptake capacity and 8 % lower heat of absorption than alkanols. Moreover, higher molar ratio of hydroxy compounds (i.e., alcohol/ether) decrease the viscosity by up to 35 %, while also decreasing the CO₂ solubility by 50 %, and increasing heat of absorption by 36 %. Quantum chemistry calculations showed minor effect of hydroxy compound on the reaction enthalpy; while slightly unfavorable for ethers, their higher spontaneity is key to their highest absorption capacity, compared to alkanols. The soft-statistical associating fluid theory (soft-SAFT) was utilized to model the properties of CO₂BOLs at different conditions and the chemisorption process using a physical aggregation model. Soft-SAFT enabled solvent evaluation based on diffusivity, CO₂ uptake and regeneration energy as key performance indicators. DBU:EGME (1:2) was found to be the best performing solvent amongst all examined CO₂BOLs with CO₂ capacity of 2.6 mol CO₂. kg⁻¹ solvent with viscosities below 4 cP and requiring 1.87 GJ per ton CO₂ for regeneration.