Screening Novel Aqueous Amine Solvents for Carbon Capture: Integrating Speciation Effects for Viscosity Prediction

Solvent-based chemical absorption is the most widely adopted carbon capture technology. Typically, CO2 is absorbed into an aqueous amine solution resulting in zwitterionic chemical reactions and the formation of carbamate (R′RNHCOO−), bicarbonate (HCO3−), and protonated amine (R′RNH2+) species. Given the importance of the solvent viscosity in process design, the ability to accurately predict the viscosity of aqueous amine/CO2 systems using computational tools, such as molecular dynamics (MD) simulation, would be very beneficial. Since classical MD force fields do not allow for chemical reactions, previous work has typically ignored chemical speciation; however, the viscosity of the system is strongly influenced by the presence of the amine-CO2 reaction products. Although speciation can be determined experimentally, it is not feasible to study all of the amines that could be used in carbon capture processes. To address this issue, we employ the SAFT-γ Mie equation of state to implicitly model the amine-CO2 reactions and determine the reaction products. Simulations using the predicted extent of speciation, demonstrate that incorporation of reaction products enables the simulations to accurately capture the viscosity trends as a function of CO2 loading across the systems studied. Building on this methodology, screening of amine-based solvents to identify candidates with high CO₂ solubility and low viscosity is performed. Candidate molecules were generated using Grouper, a graph-based molecular design tool, and subject to structural feasibility and water miscibility checks before viscosity calculations were performed. The workflow developed provides a strong foundation for accurate solvent screening, ensuring that the influence of reaction products is captured in transport property predictions.