Long storage stability of biodiesel made from rapeseed and used frying oil

The degree of physical and chemical deterioration of biodiesel produced from rapeseed and used frying oil was studied under different storage conditions. These produced drastic effects when the fuel was exposed to daylight and air. However, there were no significant differences between undistilled biodiesel made from fresh rapeseed oil and used frying oil. The viscosity and neutralization numbers rose during storage owing to the formation of dimers and polymers and to hydrolytic cleavage of methyl esters into fatty acids. However, even for samples studied under different storage conditions for over 150 d the specified limits for viscosity and neutralization numbers had not been reached. In European biodiesel specifications there will be a mandatory limit for oxidative stability, because it may be a crucial parameter for injection pump performance. The value for the induction period of the distilled product was very low. The induction period values for the undistilled samples decreased very rapidly during storage, especially with exposure to light and air.