Study of the methyl crambe (Crambe abyssinica Hochst) and soybean biodiesel oxidative stability

The quality of the biodiesel is of most importance for the success in the marketing of this fuel. Among the qualitative parameters there is the kinematic viscosity that can be affected due to the degradation of biofuel. Such degradation occurs on account of the weather changing and also because of some catalytic agents. Because of that the stability to oxidation was denominated as a factor which relates the resistance level of the product to the different oxidizing agents. The present work aimed to study the oxidative stability of the biodiesel produced of the crambe and the soybean vegetal oil. The techniques of infrared spectroscopy, refractive index and kinematic viscosity were used to monitor the level of oxidation of the biodiesels. The biodiesels were submitted to a thermal stress in an incubator, at 130 °C for a final period of 22 h of study, and were contaminated with iron and bronze filings. The viscometric studies showed that the crambe biodiesel is more stable than the soybean biodiesel at the end of their exposure to the thermal stress, as well as that the addition of 5% and 10% of crambe biodiesel lowers the viscometric alteration in about 43.9% regarding the pure soybean biodiesel. By observing the index of refraction it was verified that the alteration in the soybean biodiesel contaminated with bronze was enhanced when compared to the pure biodiesel and the biodiesel contaminated with iron. As for the pure crambe biodiesel and the biodiesel contaminated with iron, the alteration in the index of refraction is minimum, it is only significant for the biodiesel contaminated with bronze, but lower, however than the one observed for the soybean/bronze biodiesel.

► We obtained biodiesel from crambe and soybean oil.
► Pure and contaminated (bronze and iron filings) biodiesels were submitted to thermal stress in an incubator.
► Some parameters were used for monitoring the biodiesels oxidation level.
► The raw-material affected the biodiesel stability for thermal stress and metal contamination.