The paper presents the results on modelling high pressure phase behaviour of the systems consisting of refrigerant, trifluoromethane (R23) and 1-phenylpropane. There were used cubic equations of state (GEOS, SRK and PR) coupled with van der Waals mixing rules in a semi-predictive approach (SPA). Based on the experimental VLE isothermal data in the range 300–330 K, binary interaction parameters (BIPs) were optimized, through regression of bubble pressure type. Unique sets of interaction parameters were estimated for each EoS, and used in the SPA to calculate the critical, subcritical and supercritical behaviour of the system. The SPA calculations are comparatively discussed with the available experimental data in the temperature range (250–400) K and pressures up to 12 MPa. The calculations of critical line and of vapour-liquid, liquid-liquid, vapour-liquid-liquid phase equilibria, and of critical endpoints indicate a good modelling capacity of the tested EoSs and an accurate representation of the complex critical and subcritical behaviour of the investigated system.

Monte Carlo simulations are used to calculate the solubility of natural gas components in ionic liquids (ILs) and Selexol, which is a mixture of poly(ethylene glycol) dimethyl ethers. The solubility of the pure gases carbon dioxide (CO₂), methane (CH₄), ethane (C₂H₆), and sulfur dioxide (SO₂) in the ILs 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C_nmim][Tf₂N], n = 4, 6), 1-ethyl-3-methylimidazolium diethylphosphate ([emim][dep]), and Selexol (CH₃O[CH₂CH₂O]_nCH₃, n = 4, 6) have been computed at 313.15 K and several pressures. The gas solubility trend observed in the experiments and simulations is: SO₂ > CO₂ > C₂H₆ > CH₄. Overall, the Monte Carlo simulation results are in quantitative agreement with existing experimental data. Molecular simulation is an excellent tool to predict gas solubilities in solvents and may be used as a screening tool to navigate through the large number of theoretically possible ILs.

Computing bubble-points of multicomponent mixtures using Monte Carlo simulations is a non-trivial task. A new method is used to compute gas compositions from a known temperature, bubble-point pressure, and liquid composition. Monte Carlo simulations are used to calculate the bubble-points of carbon dioxide (CO₂) and methane (CH₄) mixtures in the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [bmim][Tf₂N] and 1-ethyl-3-methylimidazolium diethylphosphate [emim][dep]. The Continuous Fractional Component Monte Carlo (CFCMC) method in the osmotic ensemble has been used to compute the solubility of CO₂/CH₄ gas mixtures at different temperatures (T), pressures (P), and gas compositions (y_i). The effect of T, P, and y_i on the real CO₂/CH₄ selectivity (i.e., the selectivity of CO₂ in the presence of CH₄) is investigated. The real selectivity will differ from the ideal selectivity, which is defined as the ratio of the Henry's constants, if the solubility of CO₂ is influenced by the presence of CH₄. The computed real selectivities are compared with the experimentally obtained real and ideal selectivities. The real CO₂/CH₄ selectivity decreases with increasing temperature and pressure, while the gas phase composition has a minor effect. The real selectivity is approximately identical to the ideal selectivity for relatively low pressures and low solute concentrations in the liquid phase. The real selectivity deviates from the ideal selectivity as the solute concentration in the liquid phase increases.