Prediction of Melting Point Temperatures and Enthalpies of Fusion for Pure Wax Esters Using a Group Contribution Model

This contribution presents an approach for modeling the enthalpy of fusion (Δhf) and melting point temperature (TSL) for pure wax esters (WEs). Predicting these properties is valuable because experimental data and the availability of sample materials are scarce. Saturated WEs are long-chain aliphatic molecules that vary in the total carbon number (CN) and the position of the ester bond within the molecule (ΔCN). A review of existing experimental data on WEs (WAXS/SAXS, DSC) reveals systematics comparable to those of other aliphatic molecules. However, at equal CN, the data vary according to the variable ΔCN. Existing approaches for modeling the pure properties of WEs do not sufficiently address these features. Analogous to triacylglycerols (TAGs), a linear correlation between enthalpy and entropy of fusion is found, irrespective of CN or ΔCN. Due to this limitation and the similarity in molecular makeup, a new model based on an approach for TAGs presented by Seilert and Flöter (2021) was developed. Based on the properties of WEs, the model is simplified, and WE-specific parameters are defined. This approach includes the essential structural parameters of WEs, CN and ΔCN, and yields thermodynamically consistent results across a broad CN spectrum.