Both β-caryophyllene and longifolene are natural sesquiterpenes, and their hydrogenation products demonstrate significant potential as high-energy-density (HED) fuels. However, the purity of hydrogenated products is a key factor affecting the fuel performance. Thus, it is necessary to investigate the thermodynamic properties of hydrogenated sesquiterpene systems to separate fuel components from hydrogenation mixtures. Herein, β-caryophyllane and longifolane were obtained via hydrogenation. Subsequently, their saturated vapor pressures within the temperature range of 353.2–403.2 K were first determined via thermogravimetric analysis (TGA). Moreover, the vapor–liquid equilibrium (VLE) data for the fuel systems were determined via headspace gas chromatography (HS-GC) and correlated using Wilson, NRTL, and UNIQUAC activity coefficient models. Azeotropic points were identified in three systems, and all three models exhibited satisfactory correlations, among which the Wilson model demonstrated the best fitting performance. Additionally, the excess Gibbs energy was calculated using the Wilson model to investigate the nonideality of different systems. Furthermore, the binding energies of the binary and ternary mixtures were computed at the M06–2X-D3/def2-TZVP level based on density functional theory (DFT). And the computational results further elucidated the separation observed in the VLE data across different systems.
Wei et al. (Mon,) studied this question.