Thermodynamic properties of formation estimated to biodiesel esters using Gaussian quantum chemistry software and group contribution method of Constantinou and Gani

Abstract

A lot of recent research has focused on the study of biocatalysts and nanocatalysts to improve biodiesel production. However, knowledge of the thermodynamic properties of the reaction components is necessary. In this work, the enthalpy of formation and Gibbs free energy of formation for methyl to pentyl esters were calculated using the Gaussian quantum chemistry software (model B3LYP/6-31G(d, p)) and the group contribution method of Constantinou and Gani (MCG). The values obtained by both methodologies present certain differences in relation to the values in the literature. Thus, three correction parameters, which were based on the number of atoms of 26 different molecules, were estimated by minimizing the error function and later used to extrapolate the results to larger molecules of interest. After the use of the correction parameters, the mean deviation between the experimental and calculated values by Gaussian was 0.723% for enthalpy and 1.087% for Gibbs, whereas for MCG, it was 1.324 and 2.540%, respectively. As the methodology proved to be efficient, the thermodynamic properties of the formation of 23 esters that compose the biodiesel were estimated. These properties are of great importance, mainly for the calculation of chemical equilibrium and reaction data in the development of new catalysts.