Avaliação da estabilidade oxidativa do biodiesel de óleo de cártamo (Carthamus tinctorius L.) utilizando antioxidantes sintéticos e naturais

Abstract

Biodiesel is a renewable and non toxic fuel, resulting from the transesterification reaction from vegetable oils. In 2019, 68% of the biodiesel offered in Brazil was produced from soy oil, however, problems such as irregular rainfall and temperatures, common in Brazil, impact soy crops, being responsible for low yields, directly affecting the economy. In this context, safflower oil has been developed in the northeastern semi arid region, due to its characteristic of resistance to climatic adversities, especially droughts, since its roots are deep and adapt to high temperatures. However, as the disadvantage of safflower biodiesel is its low oxidative stability, it is necessary to use antioxidants, allowing its long term storage. Thus, the objective of this work was to study the biodiesel production process from safflower oil on a laboratory scale, to characterize it by means of physical chemical parameters (acidity index, density and viscosity), ¹HNMR, esters content by gas chromatography, and in particular, to evaluate their oxidative stability when added the synthetic antioxidants: BHT and DMP 30 and the natural antioxidants produced from the cashew nut shell: natural CNSL, technical CNSL. To obtain biodiesel, a two step transesterification reaction was carried out, and then the samples were doped with possible antioxidant potentials, to verify the oxidative stability of the samples using the Rancimat method and the UV Vis technique. Thus, it is concluded that safflower biodiesel,despite meeting the requirements for density, viscosity and acidity index , still needs the addition of antioxidants to stay within the limit of oxidative stability established by the ANP. In the structural characterization, nuclear magnetic resonance showed a conversion of 95.5%, while gas chromatography showed a conversion of 97.78%. DMP 30 was the antioxidant that achieved the greatest improvement in oxidative stability, surpassing the commercially available antioxidant, BHT. The natural antioxidants, however, did not present signif icant changes in the concentrations studied. It was also shown that with the use of the UV Vis technique it was possible to distinguish the oxidation bands of the oxidized samples from the non oxidized one, since the greater the oxidative stability by the Rancimat method, the smaller the absorbance peak. Therefore, the UV Vis absorption technique can be applied to quantitatively monitor the oxidative degradation of biodiesel in a fast and practical way.