Thermodynamic selection of effective additives to improve the cloud point of biodiesel fuels

Abstract

We assessed a simple thermodynamic model, with the aim of identifying biodiesel fuel cloud point (CP) improving additives, by predicting the CP values of fatty acid methyl esters with additives. The results showed that the molar mass of the additive has a significant effect in terms of improving the CP; the melting point and fusion enthalpy of the additive, however, produce lesser effects. On the basis of these results, we selected the additives tert-butyl alcohol, 2-butanol, cineol, 2-decanol, 2-decanone and oleyl alcohol, and examined their effects on the CP of a model biodiesel fuel (a methyl oleate and methyl palmitate mixture). The same trials were carried out using fatty acid methyl ester mixtures derived from commercial cooking oils. As predicted, the selected test additives decreased the sample CP values, with the optimum reduction obtained when using 10wt.% of the additive. The results demonstrate that additives capable of improving the CP can be readily screened using a simple thermodynamic model.