Isothermal Vapor–Liquid Equilibrium Data for a Binary System of (−)-α-Pinene + (−)-Limonene and a Quaternary System of (−)-α-Pinene + (−)-Limonene + Water + Ethephon at 313.2, 323.2, and 333.2 K

For the isolation and purification of (−)-α-pinene and (−)-limonene from pine resin tapping by spraying ethephon solution on the cutting surface of pine tree, vapor–liquid equilibrium data for (−)-α-pinene and (−)-limonene with ethephon are indispensable. In this work, the isothermal vapor–liquid equilibria of binary system (−)-α-pinene + (−)-limonene and quaternary system (−)-α-pinene + (−)-limonene + water + ethephon were determined using headspace gas chromatography. The thermodynamic consistency of the experimental data was tested by the Van Ness point test and Redlich-Kister area test. The universal quasi-chemical (UNIQUAC) and nonrandom two-liquid (NRTL) models were applied to correlate the experimental data, and the absolute mean deviation of the vapor phase mole fraction and the relative mean deviation of the total system pressure were calculated. The results showed that the UNIQUAC model correlated the system more accurately than the NRTL model. The relative volatility of (−)-α-pinene to (−)-limonene was promoted by adding ethephon solution. In addition, the binding energies of (−)-α-pinene + water + ethephon and (−)-limonene + water + ethephon were calculated by DFT. The results showed that the intermolecular interaction between ethephon solutions with (−)-limonene was greater than that with (−)-α-pinene.