Thermochemical data of the oleic acid esterification reaction: A quantum mechanics approach

Abstract

Biodiesel is an important renewable fuel that can be obtained from low cost oils once the esterification reaction of free fatty acids is carried out as a pretreatment. Scarcity of reliable thermochemical properties motivated the use of computational calculations to accurately predict these data for biodiesel compounds. The purpose of this study is to calculate thermochemical data of oleic acid esterification reactions with methanol, ethanol and propanol at several temperatures using the B3LYP hybrid functional with the standard 6-311+G(d,p) basis set. Calculated values of enthalpy of formation were corrected by applying a linear regression correction specifically developed for fatty acids and esters in order to decrease systematic errors related to the negligence of high order electron correlation energies in the B3LYP functional. Results showed that, although the esterification reactions are favoured by the temperature increase, these reactions are not spontaneous within the considered temperature range (from 273.15 to 373.15K), which indicates that additional energy is necessary to accomplish them. Methanol is the most reactive alcohol due its higher partial charge values and chemical equilibrium constants. All these values can be useful to supply missing experimental data in the literature and to better understand the thermodynamics of the oleic acid esterification reaction for biodiesel production purpose.