AÇÃO DE ANTIOXIDANTES NATURAIS NA ESTABILIDADE OXIDATIVA DO BIODIESEL

Abstract

Soybean biodiesel has low oxidative stability due to its chemical composition leading to a degradation by photo-oxidation. Therefore, the stability to oxidation is a parameter of great importance regarding biodiesel quality control. The control of oxidation in vegetable oils and biodiesel is carried out by using antioxidants which, in some cases, are synthetic. The use of synthetic antioxidants may cause harmful effects to humans; for this reason, the use of natural substances is a possible alternative to be studied for the substitution of oxidation-inhibitor synthetic products. The objective of this paper is to test environmentally appropriate alternative antioxidants for soybean biodiesel oxidative stability. Soybean biodiesel was obtained through homogeneous alkaline catalysis with methanol, characterized through tests of ester content, specific mass, color and visual aspect, hydrogenionic potential (pH), acidity index, moisture content, flash point, and oxidative stability, which was established from Rancimat measurements. We also conducted a kinetic study on biodiesel degradation regarding the absence or presence of antioxidant. The antioxidants tested were Vitamin E, Vitamin D, Tannin, Caffeine, and Citric Acid. For the comparison of the results, we employed the synthetic antioxidant Butylhydroxytoluene (BHT). The samples containing tannin and BHT presented the most satisfactory antioxidant characteristics in relation to the remaining natural antioxidants. The values of induction time above 8h demanded for biodiesel commercialization were obtained, according to the Agência Nacional do Petróleo (ANP – National Petroleum Agency).