Influência de metais de transição no processo oxidativo do biodiesel de soja

Abstract

The biodiesel stability can be affected by the presence of transition metals, introduced during the processing, transport and storage of the biodiesel. The presence of Fe3+, Cr3+, Mn2+, Cu2+ and Co2+ ions decreased the stability of ethylic soybean biodiesel as measured by Rancimat, PetroOxy and P-DSC methods. The kinetic model obtained by the P-DSC isothermal mode (ASTM E 2070-08) showed better results when evaluated by methods based on the determination of the activation energy of the maximum oxidation heat flow curve. Synthetic antioxidants (TBHQ, BHA and BHT) showed low thermal resistance at 110 oC when compared to natural antioxidants (α-tocopherol, caffeic acid, ferulic acid and gallic acid), volatilizing during first hours of analysis. The caffeic acid showed a higher efficiency than BHT and TBHQ when evaluated in the biodiesel containing metals, requiring smaller amounts (500 mg.L-1) to increase the induction period over 6 h, according to EN 14214. The high efficiency of caffeic acid is associated with its ability to stabilize the phenol radical by resonance and by metal chelation.