Vapor–Liquid Equilibrium of Monoterpene-Sesquiterpene System Containing Resin Acid

The phase equilibrium relationships of resin systems are indispensable for resin tapping, distillation, and investigating the release of terpenes in biogenic volatile organic compounds (BVOCs). Herein, we obtained the vapor–liquid equilibrium (VLE) data of monoterpene-sesquiterpene systems that contain resin acid by a headspace gas chromatography (HS-GC). There is no azeotropic behavior between terpenes, and abietic acid was found to inhibit the volatilization and separation of terpenes. Furthermore, the saturated vapor pressure of the systems almost triples when the experimental temperature increases from 313.15 to 333.15 K, which may exacerbate terpene emissions in ecosystems. Additionally, the thermodynamic consistency of the VLE values was confirmed by van Ness test, and the experimental data were correlated using NRTL, UNIQUAC, and Wilson activity coefficient models, while the Conductor-like Screening Model for Real Solvents (COSMO-RS) model was utilized for predictions. All of the data satisfy thermodynamic consistency, and the correlation results and prediction results demonstrate good adherence of the activity coefficient models to experimental values and the positive capacity of COSMO-RS in predicting the VLE relationship for the pine resin systems, respectively.