Estudo da estabilidade termo-oxidativa de biodiesel por Rancimat, PetroOXY e Termogravimetria

Abstract

One of the main concerns of using biodiesel is with thermal and oxidative susceptibility when in contact with air during storage and when subjected to high temperatures under engine operating conditions. This susceptibility iscorrelated to the presence of fatty esters with multiple sites of unsaturations on its chemical composition, that are particularly pronetothermal and oxidative degradation.The transesterification yields of jatropha, soybean, radish and tungoils were 90,09%, 90,12%, 90,08% and 63,96% and the conversion rates of triglycerides to methyl esters, determined by proton nuclear magnetic resonance spectroscopy (1H NMR), were 97.89%, 89.29%, 93.77% and 96.17%. The gaschromatographycoupledtomassspectrometry (GC/MS) analysis of the samples confirm the predominance of unsaturated esters. The Rancimat and PetroOXY methods, employed to evaluate the oxidative stability of biodiesel, have a linear correlation (R2=0,93697) and show a direct relationship with the unsaturation content of the samples. It was obtained the following order of oxidative stability: tung biodiesel < radish biodiesel < soybean biodiesel < jatropha biodiesel. The thermogravimetric analysis of the samples shows the best quality of biodiesel as fuel when compared to their feedstocks. The aging of biodiesel samples under oxidizing atmosphere at high temperatures shows changes in thermal behavior. The thermogravimetric kinetic study, under nitrogen atmosphere, shows a direct relationshipbetween the activation energy (Ea) and the thermal decomposition and/or volatilization onset temperature. The lifetime results, from these kinetic studies, provide the following order of thermal stability: jatropha biodiesel < radish biodiesel < soybean biodiesel < tung biodiesel. The thermal stability order has no direct correlation with the oxidative stability order, determined by Rancimat and PetroOXY methods