Improving the regeneration of CO2-binding organic liquids with a polarity change

Abstract

This paper describes a solvent regeneration method unique to CO2-binding organic liquids (CO2BOLs) and other switchable ionic liquids: utilizing changes in polarity to shift the free energy of the system. The degree of CO2 loading in CO2BOLs is known to control the polarity of the solvent; conversely, polarity can be exploited as a means to control CO2 loading. In this process, a chemically inert nonpolar “antisolvent” (AS) such as hexadecane (C16) is added to aid in de-complexing CO2 from a CO2-rich CO2BOL. The addition of this polarity assist reduces the temperature required for regeneration of our most recent CO2BOL, 1-((1,3-dimethylimidazolidin-2-ylidene)amino)propan-2-ol by as much as 73 °C. The lower regeneration temperatures realized with this polarity change allow reduced solvent attrition and thermal degradation. Furthermore, the polarity assist shows considerable promise for reducing the regeneration energy of CO2BOL solvents, and separation of the CO2BOL from the AS is as simple as a cooling the mixture to promote phase separation. Based on vapor–liquid and liquid–liquid equilibrium measurements of a candidate CO2BOL with CO2, with and without an AS, we present the evidence and impacts of a polarity change on a CO2BOL. Equilibrium thermodynamic models and analysis of the system were constructed using Aspen Plus®, and forecasts of preliminary process configurations and feasibility are also presented. Lastly, projections of solvent performance for removing CO2 from a subcritical coal-fired power plant (total net power and parasitic load) are presented with and without this polarity assist and compared to the U.S. Department of Energy's Case 10 monoethanolamine baseline.