Prediction of Henry's law constants for CO2 and CH4 in levulinic acid via different Monte Carlo approaches

Abstract

Henry's law constants of CO₂ and CH₄ in levulinic acid are predicted at 313.15 K and 101.325 kPa. The Widom test particle insertion method (which is based on excess chemical potential computation) in the NPT ensemble via two different Monte Carlo approaches, viz., CBMC and CFCMC, is implemented. GEMC-NVT simulations are performed to calculate Henry's law constants from the slope of the line fitted to the plot of partial pressure of solute (CO₂ or CH₄) in the vapour phase versus the mole fraction of solute in liquid levulinic acid. Henry's law constants estimated via all three Monte Carlo methods and for both the solutes show good agreement within statistical uncertainties. The negative value of the Gibbs free energy of transfer (ΔG_trans) of CO₂ from the vapour to the solvent (levulinic acid) phase suggests a preference of CO₂ for liquid levulinic acid over the vapour phase. The solvation number computed from solute–solvent centre-of-mass radial distribution functions (RDFs) shows a higher value for CH₄ than CO₂, contrary to the trend in Henry's law constant. Therefore, the local environment around the solute molecule is investigated by computing the solute–solvent site–site intermolecular RDFs. The number integral calculated (up to the first minimum) from site–site intermolecular RDFs of the C(CO₂)–methyl group of levulinic acid (CH₃(1)) is more than that calculated from the CH₄–CH₃(1) RDF, confirming the higher solubility of CO₂ in levulinic acid than CH₄.