Carbon Dioxide Solubility in Phosphonium-Based Deep Eutectic Solvents: An Experimental and Molecular Dynamics Study

Considering the great potential of deep eutectic solvents (DESs) for CO₂ capture, this work studies the CO₂ solubility in DESs by combining experimental measurement and molecular dynamics (MD) simulation. First, four phosphonium-based DESs are prepared in the laboratory, involving two types of hydrogen bond acceptors (HBAs), namely, tetrabutylphosphonium bromide and allyltriphenylphosphonium bromide, and two types of hydrogen bond donors (HBDs), namely, phenol and diethylene glycol. The CO₂ solubility in the obtained DESs is measured under 313.15–333.15 K and pressure below 2000 kPa and compared with those of previously reported DESs and ionic liquids. Second, MD simulations are performed to study the microscopic behaviors of the involved DESs and mixtures. Through the analyses of radial distribution functions, spatial distribution functions, and intermolecular interaction energy, the eutectic formation and CO₂ absorption mechanisms as well as the effect of HBA/HBD type and molar ratio are interpreted.