CO₂ sorption in triethyl(butyl)phosphonium 2-cyanopyrrolide ionic liquid via first principles simulations

Predicting gas-liquid solubility using traditional force field based approaches is not reliable in cases where gas molecules can chemically complex with the liquid phase. Using electronic structure calculations to calculate system energy on-the-fly can overcome this deficiency albeit at a higher computational cost. Here, we use first-principles simulations to predict the solubility of CO₂ in triethyl(butyl)phosphonium 2-cyanopyrrolide ionic liquid (IL). We utilize Gibbs ensemble Monte Carlo (GEMC) simulations to predict solubility, and employ ab-initio molecular dynamics (AIMD) to study dynamics and structural properties. Solubility prediction from GEMC simulations is in good agreement with the experimental data. Analyzing complexation states of CO₂ molecules reveals that approximately 30% of CO₂ molecules are chemically bonded with the anion component of the IL. The combined distribution function analysis shows that upon reaction, the O–C–O angle of the CO₂-anion complex varies from 132 to 134 °. Despite these structural changes, plots of mean square displacement (MSD) show minimal difference between the dynamics of neat and IL with dissolved CO₂. The vibrational spectra obtained from AIMD simulations match reasonably well for pure and mixed IL as compared to the experimental data.