Oxidative stability and cold flow behavior of palm, sacha-inchi, jatropha and castor oil biodiesel blends

Abstract

Oxidative stability and cold-filter plugging points (CFPP) of blends of biodiesel from palm, sacha-inchi, jatropha and castor oils were evaluated. Blends were made as a strategy to obtain a biodiesel with a better performance. These properties of biodiesel depend on the type of methyl-ester constituents and they are generally opposed, i.e., a biodiesel with good oxidative stability exhibits bad CFPP. Biodiesel was produced through KOH-catalyzed methanolysis of the oils. Binary blends of biodiesel from castor-jatropha, palm-castor and palm-sacha inchi were made, in proportions of 25:75, 50:50 and 75:25. The oxidative stability was evaluated following the standard EN 14112. CFPP of pure biodiesels and binary blends were evaluated according to ASTM D6371. An induction time greater than 6 hours and a CFPP below 0°C were set as quality criteria. Among the pure biodiesels, only castor oil biodiesel achieved this quality because its induction time and CFPP were 31h and −7°C, respectively. The best biodiesel blend was made of 75% jatropha and 25% castor. This blend achieved an induction time of 7.56h and a CFPP of −12°C. However, this blend has a viscosity higher than the required by international standards. The oxidative stability (induction time) and the CFPP were correlated with the structural indices APE (allylic position equivalent), BAPE (bis-allylic position equivalent), SME (saturated methyl esters content), MUME (mono-unsaturated methyl esters content) and PUME (poly-unsaturated methyl esters content); it was found that BAPE and PUME correlate with IT, while CFPP does not correlate with any of these indices.