Hydrogen separation from carbon dioxide using [EMIm]-based ionic liquid solvents

Given the high CO₂ content typically present in waste-derived hydrogen streams, this study investigates the solubility behavior of CO₂ and H₂ in imidazolium-based ionic liquids ([EMIm][HSO₄], [EMIm][Cl], and [EMIm][TFSI]) and polyethylene glycol (PEG 200) under ambient conditions. Among the tested systems, [EMIm][HSO₄] exhibited the highest CO₂ solubility (0.0553 mol/mol), attributed to strong hydrogen bonding and electrostatic interactions between CO₂ and the [HSO₄]⁻ anion. Density functional theory (DFT) analysis further confirmed that [HSO₄]⁻ forms the most stable interaction with CO₂, promoting partial cation–anion separation and enhancing CO₂ binding. The addition of PEG 200 improved CO₂ solubility to 0.0671 mol/mol by reducing viscosity and facilitating diffusion, while maintaining solvent stability. Conversely, H₂ solubility remained minimal across all systems, with the lowest value observed in [EMIm][TFSI] (7.59 × 10⁻3 mol/mol), confirming excellent CO₂/H₂ selectivity. These findings highlight that the combination of [EMIm]-based ILs and PEG offers a tunable, low-volatility solvent system with enhanced CO₂ absorption capacity, suitable for applications in CO₂ capture and hydrogen purification.