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 softstatistical 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.