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.