A new method based on binary mixture concept for prediction of ionic liquids critical properties using molecular dynamics simulation

All substances exhibit complex behavior near their critical points, where even slight variations in temperature and pressure can lead to significant changes in density, heat capacity, and compressibility. This rapid variation results in a loss of surface energy and maximizes the compressibility and heat capacity of fluids at the critical point. This study employed molecular dynamics (MD) simulations based on the binary mixture concept to predict the critical properties of ionic liquids (ILs) that are difficult to measure experimentally. Initially, to validate this method, we investigated the variations in heat capacity and density of pure water, pure ethanol, and their mixture across different temperatures and pressures, specifically at phase transition, critical, and supercritical points. Then, the changes in these properties were studied for [C₄mim][BF₄] IL to predict its critical points. The results for pure water, pure ethanol, and water-ethanol mixture were compared with the experimental data. The simulation of [C₄mim][BF₄] revealed that its behavior near critical points resembles that of a binary mixture with three critical points, where the middle point represents the mixture's critical point. The predicted critical temperature and pressure for [C₄mim][BF₄] were 1400 ± 10 K and 11 ± 0.5 bar, respectively.