The effect of Cr3+, Co2+, Fe2+ and Fe3+ ions on the oxidative stability and kinetics of biodiesel oxidation reaction with and without the addition of rosemary extract

Resumo

Since biodiesel has unsaturated esters in its composition, it is susceptible to oxidation reaction. Studies have shown that small traces of transition metals are able to promote biodiesel oxidation. Biodiesel samples containing Cr³⁺, Co²⁺, Fe²⁺ and Fe³⁺ ions, in the presence and absence of rosemary extract, were submitted to the Rancimat test at 110 ºC to verify the biodiesel oxidative stability against the catalytic action of these ions. The results were compared with control samples without and with rosemary extract. The control without extract presented induction period of 8.29 hours and the control with extract 11.42 hours. Regarding the catalytic effect of metal ions on biodiesel, in the absence of extract the sample containing Fe³⁺ showed induction period at 0.25 hours, indicating total degradation of the biofuel. For the samples containing the other cations, in the absence of the extract the catalytic effect followed the order Fe²⁺>Cr³⁺>Co²⁺. In the presence of extract the order presented was Fe³⁺>Fe²⁺>Co²⁺>Cr³⁺