Systematic study of the effect of the co-solvent on the performance of amine-based solvents for CO2 capture

Absorption and separation by aqueous amines is seen today as a mature technology for CO2 capture at large scale. However, it still suffers from some drawbacks, especially the high energy required for the regeneration of the solvent. In this sense, water-free and water-lean solvents are attractive alternatives to replace them due to their potential in reducing this regeneration energy; however, systematic studies on the effect of the co-solvent on the required thermodynamic properties to optimize the separation process are still missing. In this work, we use the polar soft-SAFT equation of state for modeling CO2 chemisorption in a range of aqueous, water-free, and water-lean solvents, formulated using glycol co-solvents. In addition to accurately capturing the CO2 solubility in these solvents, the model allows to isolate the effect of a given organic diluent, and its ratio with water, on CO2 solubility, degree of speciation, and enthalpy of absorption. We find that ethylene glycol is a promising cosolvent, as the reduction in CO2 solubility is minimized, while exhibiting the largest decrease in enthalpy of absorption than other water-lean and water-free solvents, irrespective of the employed amine. This is the first study in which the effect of the co-solvent has been systematically evaluated at post-combustion capture conditions, helping in the rational design of novel solvents for CO2 capture.