Abstract
This paper proposes to examine the effect of temperature on the oxidation behavior of biodiesel. Soybean biodiesel was oxidized at different temperatures (room temperature, 60, and 110 °C), and the increase in primary and secondary oxidation products was determined based on the peroxide and anisidine values, respectively, during the induction period (IP). The results indicated that the evolution of hydroperoxides followed zero-order reaction kinetics during the IP at all temperatures, and their rate of formation was exponentially affected by temperature. It was also deduced that temperature influenced the ratio between primary and secondary oxidation products formation, which decreased as the temperature increased. Additionally, it was possible to predict the oxidation behavior of the soybean biodiesel at room temperature by an exponential model fitted to the IP values at different temperatures (70, 80, 90, 100, and 110 °C) using the Rancimat apparatus.
Highlights
Interest in new energy sources, especially for partially replacing fossil fuel, has drawn attention to biodiesel research (Nigam and Sing, 2011)
The sample does not meet the specifications for oxidative stability, it is recognized that most of the biodiesels produced from polyunsaturated vegetable oils present low oxidative stability when no antioxidants have been added (Dantas et al, 2011; Jain and Sharma, 2011; Maia et al, 2011)
Increasing the temperature to 60 °C and 110 °C accelerated the oxidation rate 45- and 855-fold, respectively, relative to the ambient conditions. These results indicate that temperature has an exponential influence on the oxidation rate of the soybean biodiesel
Summary
Interest in new energy sources, especially for partially replacing fossil fuel, has drawn attention to biodiesel research (Nigam and Sing, 2011). Hydroperoxides are quite unstable and form secondary oxidation products in the advanced stages of oxidation These secondary products can originate from rearrangements in monomeric products (keto, hydroxy, and epoxy functional groups), from decomposition into lower-mass products (aldehydes, alcohols and hydrocarbons), or from polymerization (dimers and oligomers) (Frankel, 1984; Knothe, 2007). In this stage of the oxidation process, biodiesel does not fulfill the main quality specifications (Lacoste and Lagardere, 2003) and is not suitable for use. Hydroperoxides can attack elastomers, acid products formed from hydroperoxide cleavage cause the corrosion of metal systems, and gums and sediments of high-molecular mass can clog injection pumps and filters (Fazal et al, 2010; Monyem and Van Gerpen, 2001; Sorate and Bhale, 2013)
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