Method of contribution of groups to estimate thermodynamic properties of components of biodiesel formation in liquid phase

An additive group contribution method extended from the Joback and Reid method for the liquid phase was developed in order to predict enthalpies of formation and absolute entropies in the standard state. The method uses the alkanes as reference chemical substances. In the case of enthalpy of formation, the methodology was tested for 50 chemicals related to the formation reactions of biodiesel and for absolute entropy it was tested for 15 compounds. The results were compared with data from the literature. The relative deviations found in the enthalpy estimates were lower than 6% and in the predicted entropy they were lower than 3%. The method was accurate to estimate the properties for triacylglycerides, such as glycerol triacetate and glycerol trioleate (triolein). Additionally, to develop the method, two equations were derived and used to supplement gaps found in the literature regarding the absolute entropies of the gaseous and liquid phase, both in its standard state. The contribution of this work is the development of a method using the group contributions to estimate the thermodynamic properties of reactions in the liquid phase, important to the formation of biodiesel. (C) 2011 Elsevier B.V. All rights reserved.