Oxidative stability and storage behavior of fatty acid methyl esters derived from used palm oil

Fatty acid alkyl esters, especially FAME, are the most commonly used liquid biofuel. Because biofuels are expected to be important alternative renewable energy sources in the near future, more studies on their stability against oxidation need to be addressed. Biofuel derived from vegetable oils is well researched, currently with more attention focused on the reuse of waste oil sources than on pure vegetable oil for such production. A method to convert used palm oil, i.e., used frying oil, and residual oil of spent bleaching earths (SPE) to their respective methyl esters has been established by the Malaysian Palm Oil Board. These methyl esters can be used as diesel substitute. However, the methyl esters obtained from used frying oil have a low induction period (3.42 h). In Europe, any methyl esters must have an induction period of at least 6 h in Rancimat stability to be usable as biodiesel, as required by European Biodiesel Standard (EN 14214). To meet this requirement, the used frying oil methyl esters (UFOME) obtained can be treated with different types of antioxidants, either synthetic or natural, at different treatment levels, such as vitamin E, 3-ert-butyl-4-hydroxyanisole (BHA), 2,6-di-tert-butyl-4-methyl-phenol (BHT), 2,5-di-tert-butyl hydroquinone (TBHQ), and n-propyl gallate (PG), to investigate their oxidative stability and storage behavior. The order of increasing antioxidant effectiveness with respect to the oxidative stability of UFOME is: vitamin E