Association effect on the density, viscosity and excess properties of fatty acid ester + alcohol mixtures: Experiment and modeling

The mixtures of fatty acid ester + alcohol are promising substitution fuels in engines. Due to their strong self- and cross-hydrogen bonds, the properties of these kinds of mixtures may show different characteristics from the fossil fuels composed of non-associating substances. In this work, the association effects on density and viscosity of fatty acid ester + alcohol are investigated from both experimental and theoretical aspects. The ethyl laurate + ethanol mixtures with 9 M fraction compositions are chosen, and the two properties are measured using a capillary viscometer system at temperatures from 313 K to 343 K and pressures up to 15 MPa. The positive excess volume and viscosity deviation of the mixtures are obtained, and the former is negligible compared to the experimental uncertainty. The Cubic-Plus-Association equation of state (CPA EoS) and the friction theory model are used to model the mixtures of ethyl laurate + ethanol. The relations of their self- and cross-associations to density, viscosity, and two excess properties (excess volume and viscosity deviation) are summarized. Different saturated fatty acid ester + 1-alcohol mixtures are also modeled with the CPA EoS. The variation characteristics of their viscosity deviations are analyzed and explained by their different association strength and the mole number of associated molecules.