Characterizing the Potential of Phosphonium-Based Ionic Liquids for CO₂ Capture via Multiscale Modeling

Efforts to reduce atmospheric CO₂ levels focus on minimizing fossil fuel consumption, integrating renewable energy systems, and implementing CO₂ capture, storage, and utilization. While carbon removal from atmosphere technologies shows promising, industrial efforts prioritize point-source capture for sustainability. A key challenge in solvent design is screening candidates and defining selection criteria. Robust models are needed to characterize their thermophysical behavior for CO₂ capture. This study adopts a multiscale approach to investigate the CO₂ gas absorption in phosphonium-based ionic liquids (ILs) with eight anions. The trihexyltetradecylphosphonium cation [P_666,14]⁺ was paired with various anions due to their known CO₂ absorption capacity. New molecular models are developed using the soft-SAFT equation, leveraging existing coarse-grain models, analyzing molecule charge distribution through Turbomole-COSMO software for new ILs, and approximating association parameters via density functional theory calculations. Once the models are validated against experimental data, soft-SAFT is used predictively to evaluate the thermophysical properties of these ILs in a wide range of conditions. The analysis encompasses estimations of key process indicators, including the cyclic working capacity, enthalpy of desorption, and CO₂ diffusion coefficient, ultimately proposing the [P_666,14]-[Ac] and [P_666,14]-[bis-(2,4,4-TMPP)] ILs as the most promising solvents. This study validates soft-SAFT as a reliable screening tool for CO₂ capture solvents and process modeling.