Study on Vapor–Liquid Equilibrium of CaCl₂ Solutions with Ionic Liquids: Modeling and Molecular Interaction Analysis

CaCl2 is a typical inorganic salt with a hygroscopic aqueous solution and a low eutectic point, and it has excellent snow-melting ability at low temperatures. The VLE of aqueous solutions of CaCl2 with three ionic liquids ([AOEMIM][BF4], [HOEMIM][BF4], and [EMIM][BF4]) over the pressure range of 6.3–99.8 kPa was investigated. The NRTL model was used for correlation fitting to the VLE data. The total average interaction and hydrogen bonding energies were investigated using the COSMOthermX 2021 software, and the interactions were further elucidated by analyzing the absorption peaks using FTIR. The results showed that the hydrogen bonding interaction energy of water molecules decreased with increasing ionic liquid concentration, resulting in increased volatility of water molecules and higher vapor pressure in high-concentration ionic liquid solutions. The order of the effects of the three ionic liquids on decreasing the hydrogen bonding interaction energy of water molecules was [AOEMIM][BF4] > [HOEMIM][BF4] > [EMIM][BF4].