Flash Point Behavior of Multicomponent Terpene Mixtures: An Experimental and Modeling Study

The flash point (FP) is a critical property for assessing fire and explosion hazards of flammable liquids. However, reliable FP data for terpene-rich mixtures are scarce, despite their relevance as the major constituents of commercial essential oils. This work provides a comprehensive investigation of the FP behavior of four naturally abundant monoterpenoids— p -cymene, linalool, carvacrol, and eugenol—and their binary and ternary mixtures. Experimental measurements were performed using the ASTM D6450 closed-cup procedure, revealing a quasi-linear relationship between the FP and the normal boiling point for the pure compounds. The mixtures, however, exhibited complex structure-property relationships, where specific intermolecular interactions play a key role in the FP behavior. To complement the experimental studies, the predictive capabilities of the Liaw-UNIFAC and COSMO-RS models were benchmarked against the ideal approach for the mixtures. COSMO-RS provided the best overall representation, with a global RMSE of 0.9 K. The Liaw-UNIFAC (global RMSE = 2.9 K) outperformed the ideal approach (RMSE = 3.6 K) in six of the ten mixtures studied, highlighting that its performance is highly system-dependent. This work delivers crucial experimental data and validates a modeling framework for assessing the FP of multicomponent monoterpene mixtures, providing valuable insights for process safety and fire risk assessment in the EO industry.