Avaliação de antioxidantes aplicados à produção de biodiesel

Abstract

This paper presents a study of the behavior and effectiveness of antioxidants additives for biodiesel from soybean oil. The most commonly used antioxidants are ofphenolic structure, thereby synthesizing, examining and comparing the antioxidant action for evaluating possible causes for a structure to be more effective when compared to another, brings forth necessary tools in the search for better performance antioxidant compounds. For use as an organic substrate, it was synthesized biodiesel from soybean oil, since this oil is from producing about 81 % of biodiesel produced in Brazil. Another factor for the use of soybean oil is that it has in its composition mainly oleic and linoleic acids, unsaturated acids highly susceptible to oxidation. The biodiesel was synthesized by the transesterification reaction with methyl alcohol, the molar ratio alcohol / oil of 1:6 and sodium hydroxide 0.5% (m / m). The biodiesel samples were doped with antioxidants (BHT and ionol), and biomass (hydrogenated cardanol and cardanol alkylated) at concentrations of 300, 600, 900, 1200, 1500, 2000, 3000 and 4000 mg.kg-1 and stored in an amber vial at a temperature of 22, ± 3 º C. All samples were analyzed in an accelerated oxidation test (Rancimat), at the beginning (immediately after the moment additives) and after 2, 4, 6, 9 and 12 months storage. During monitoring the observed variation via Rancimat induction time as a function of storage time of the samples. The thermal analyzes were performed with biodiesel from soybean oil, BHT, ionol, hydrogenated cardanol, cardanolalkylated, and biodiesel doped antioxidants at concentrations of 300, 900, 1500, 3000 and 4000 mg.kg-1 rate heating to 10 ° C / min in a nitrogen atmosphere with heating range of 30 º C - 600 º C.Through thermal analysis verified the behavior of the samples when exposed to elevated temperatures. The analysis by UV-vis were conducted in order to evaluate the process of autoxidation of the samples after12 months of storage. The experiments via rancimat revealed that the commercial antioxidants are better than those of biomass, and to the thermogravimetric experiments via UV-vis the finding that helped to optimize phenolic antioxidants should be added low molecular weight substituent at the ortho and para positions. Through the results via Rancimat software was developed to predict the time depending on the oxidative stability of the antioxidant used, this added amount, time of storage and, perform an economic analysis cost of use of each antioxidant.