Models for predicting the surface tension of biodiesel and methyl esters

Biodiesel is obtained from vegetable oils or animal fats, and it is emerging as an attractive alternative to petroleum diesel. The surface tension of biodiesel has been little studied, although it plays an important role in the atomization process. In this work, models of group contribution, corresponding state, and empirics were tested to predict the surface tension of methyl esters, whereas two mixing rules were used to estimate the surface tension of biodiesel as a function of its chemical composition and temperature. A statistical analysis (by means of the relative error (D), standard deviation (SD), correlation coefficient (R-2), analysis of variance (ANOVA), and parity plots) was applied to evaluate the predictive capability of models. The empirical correlation developed to estimate the surface tension of fatty acid methyl esters (FAMEs) closely reproduces the experimental data, with an average absolute deviation (AAD) of 0.93%. This model highlights the dependence between the surface tension with its molecular weight and temperature. On the other hand, the simple mixing rule on mass fraction basis offers the best prediction for the biodiesel surface tension (AAD=2.88%). (C) 2014 Elsevier Ltd. All rights reserved.