(7f) Reversible Ionic Liquids for CO2 Capture: A Thermodynamic Study

We have developed reversible ionic liquids (RevILs) for CO₂ capture that are capable of dual mode absorption: chemical and physical. Chemical absorption takes place when the silylamine-based solvents chemically react with CO₂ forming an ammonium-carbamate ion pair (RevIL). Physical absorption is then observed due to the solubility of CO₂ in the RevIL.  The chemically and physically absorbed CO₂ may be released by heating the CO₂-swollen RevIL to temperatures below 100°C.

CO₂ capture with reversible ionic liquids is governed by the thermodynamics of the process. The reaction equilibrium constant, K, of the silylamine and CO₂ dictates the extent of reaction at capture conditions and reversal temperatures. The additional CO₂ that is captured through physical absorption is determined by the solubility of the CO₂ in the RevIL (Henry’s constant). During regeneration (release of CO₂) the RevIL is heated to the reversal temperature. The energy required to complete the reversal is structure-specific and depends on the heat capacity of the RevIL, the regeneration temperature and the enthalpy of reaction. 

We have identified structural changes that may be made to the RevIL to increase CO₂ capture capacity and reduce the energy required for reversal.