Thermal behaviors of soy biodiesel

Biodiesel is a prospective and promising fuel for diesel engines. However, some aspects need improvement, to develop into an ideal fuel, such as flow properties at low temperatures and storage stability at high temperatures with exposure to the air. Thermal analysis is an efficient tool for measuring properties, such as crystallization temperature, and thermal and oxidative stabilities. In this study, the thermal behaviors of biodiesel at low and high temperatures were investigated by using thermogravimetric analyzer, differential scanning calorimetry, pressurized differential scanning calorimetry (PDSC), and sorption analyzer (SA). The soy biodiesel was obtained through a transesterification reaction with a homogeneous catalyst. The constituents of the soy biodiesel as determined by gas chromatography show that methyl esters content was 99 % and of these 84 % were unsaturated fatty acids. TG results illustrate that the total weight loss of the biodiesel was 99 % below 300 °C under nitrogen flow, indicating a high purity biodiesel. The onset decomposition temperature and the peak temperatrue of the soy biodiesel were 193 and 225 °C, respectively, implying the biodiesel has good thermal stability. PDSC results show that the oxidation onset temperature of the soy biodiesel was 152 °C, and the oxidative induction time was 24 min. DSC results demonstrate that the onset crystallization temperature of the soy biodiesel was 1.0 °C. The SA results point out that with increasing temperature and humidity, the soy biodiesel absorbed more water, and in which humidity was the dominant factor. The water absorption and desorption of the soy biodiesel is a non-reversible process. The preferable storage conditions for soy biodiesel occur when humidity is less than 30 % and the temperature is less than 30 °C. In summary, thermal analysis is a faster alternative for thermal behavior studies as compared with conventional standard methods.