PNNL

Abstract

This paper describes an unusual solvent regeneration method unique to 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 could be exploited as a means to control CO2 loading. In this process, a chemically inert non-polar “antisolvent” is added to aid in de-complexing CO2 from a CO2-rich CO2BOL. The addition of this polarity assist reduces temperatures required for regeneration of CO2BOLs by as much as 76 °C. The lower regeneration temperatures realized with this polarity change allow for reduced solvent attrition and thermal degradation. Furthermore, the polarity assist shows considerable promise for reducing regeneration energy of CO2BOL solvents, and separation of the CO2BOL from the antisolvent is as simple as cooling the mixture below the upper critical solution temperature. Vapour-liquid equilibrium and liquid-liquid equilibrium measurements of a candidate CO2BOL with CO2 with and without an antisolvent were completed. From this data, we present the evidence and impacts of a polarity change on a CO2BOL. Thermodynamic models and analysis of the system were constructed using ASPEN Plus, and forecasts preliminary process configurations and feasibility are also presented. Lastly, projections of solvent performance for removing CO2 from a sub-critical coal fired power plant (total net power and parasitic load) are presented with and without this polarity assist and compared to DOE’s Case 10 MEA baseline.