. Predição das propriedades termodinâmicas do biodiesel e diesel comum, suas blendas e efeitos de aditivos via teoria do funcional da densidade e ensemble canônico.

Abstract

In this study, we analyzed the thermodynamic properties of soy biodiesel, the most widely used biodiesel source among the world's largest consumers, and rapeseed biodiesel, a source with significant employment in the European Union and biodiesel additives. Also, the study of ordinary diesel was carried out to simulate the situations in which this fuel is in mixtures with different concentrations of biodiesel blends. The objective of this work is to study the thermodynamic properties of the fuels mentioned. Based, where possible, on experimental results to validate the expansion of theoretical results and point out the most appropriate methodology for this type of approach. To this end, computational simulations were carried out with theoretical support in the Density Functional Theory combined with the canonical ensemble model. The functional used in the simulations was type B3LYP with bases 6-31 + (d) and 6-311 + g (d), in addition to the composite method CBS-QB3. The calculated enthalpy values are higher in the biofuels in relation to diesel and the same happened with Entropy. When we analyze the change of Gibbs Free Energy, the largest variations were noted for biofuels. The coefficient of adiabatic expansion revealed lower degrees of freedom until 400 K temperature in both types of biodiesel, from that point all fuels have the same behavior for this property. The lowest relative error was found with the B3LYP/6-311 +g(d) method, with a value of 0.15% for the combustion of ordinary diesel. In relation to biofuels, the same method provided 0.48% relative error in the combustion of rapeseed biodiesel as the best result. Regarding the effects of temperature on these fuels, the results showed that both types of biodiesel are less susceptible to heating than ordinary diesel at all calculated points, always requiring more energy to raise their temperature. The results in the additives showed that the antioxidant pyrogallol that most interferes in the biodiesel properties.