Thermodynamics of Carbon Capture Through Reversible Ionic Liquids

We have developed a novel class of reversible ionic liquids (RevIL) that offer numerous advantages over ethanolamine solvents for CO₂ capture applications. These novel RevIL are silylamine based compounds capable of dual mode of CO₂ capture through chemisorption (reaction of amine with CO₂ to form ammonium-carbamate ion pair) and physisorption (solubility of CO₂ in the ion pair.) The latter is particularly significant in the natural gas sweetening application. Subsequently, modest elevation in temperature reverses the reaction to regenerate the silylamine and CO₂ which can then be sent for sequestration. There are several key thermodynamic properties of the RevIL that have a significant impact on the economics of the carbon capture process. In this talk, we will discuss both theoretical and experimental approaches to determining these properties.

Thermodynamics of these systems is summed up by the following quantities of interest:

1.  The reaction equilibrium constant K for the amine CO₂ reaction, which determines the extent of reaction.

2.  Solubility of CO₂ in ionic liquid (Henry’s Law Constant) and the associated enthalpy ( DH_solution ).

3.  The heat required to raise the ionic liquid to the regeneration temperature: Q = mC_pDT. This quantity in turn depends on (a) the mass m and hence the absorption capacity, (b) the heat capacity, C_p, and (c) the regeneration temperature T_reg (DT = T_reg - T_capture).

4.  The enthalpy of reaction DH_rxn, which dictates the amount of heat required to regenerate the silylamine

For determining the first two properties (equilibrium constant and solubility), we have used in situ FTIR spectroscopy, while DSC/TGA is our primary tool for analyzing the latter two. We have also used COSMO-RS to supplement our experimental results. Based on these theoretical and experimental techniques, we will present a structure-property relationship based approach to finding a silylamine solvent with optimum set of thermodynamic properties. We will also make comparisons with non-silyl compounds to demonstrate the superiority of our compounds in CO₂ capture applications.