(125e) Molecular Modeling of Non-Aqueous CO2 Capture Solvents

Guanidium-based carbon dioxide binding organic liquids (CO₂BOLs) are strong non-nucleophilic bases well suited for binding CO₂ to their aliphatic alcohol group. They become ionic upon reaction with CO₂ and revert to their non-ionic form by thermal removal of CO₂. Post-combustion capture of carbon dioxide can be performed with solvents that exhibit high CO₂ binding capacities, are non-volatile at operating conditions, and have low viscosity. CO₂BOLs meet the first two requirements, but their high viscosities in their CO₂-bound state render them costly for industrial applications. CO₂BOLs are still very attractive candidates for CO₂ capture because they require no additional solvents and are liquid at post-combustion temperature and pressure conditions, reducing thermal regeneration cost. In this work, candidate CO₂BOL molecules are studied, in collaboration with experiment, toward the design of low-viscosity CO₂BOL compounds. Ab initio electronic structure calculations were performed for accurate molecular properties including charges, as well as to obtain CO₂ adsorption energies. To simulate CO₂BOLs mixtures in their liquid state, classical molecular dynamics were used at varying carbon loadings. Viscosities were then calculated using Green-Kubo relations. We have found that the hydrogen-bonding network in the liquid state, both intra-molecular and between different molecules plays a key role in determining and tuning viscosities. Based on this, a reduced model was developed that predicts the CO₂BOL viscosity given a few molecular structural parameters and CO₂ loading. With the reduced model, a high number (100+) of candidate CO₂BOLs is screened. A list of promising candidate molecules is in the process of being synthesized and their viscosities experimentally measured.