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

Authors: 
Cantu, D. C., Pacific Northwest National Laboratory
Malhotra, D., Pacific Northwest National Laboratory
Koech, P. K., Pacific Northwest National Laboratory
Heldebrant, D. J., Pacific Northwest National Laboratory
Rousseau, R., Pacific Northwest National Laboratory
Glezakou, V. A., Pacific Northwest National Laboratory

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.