Sonication assisted transesterification of Jatropha oil for the production of biodiesel: a kinetic study

Fossil-based fuels are main sources for atmospheric pollution and global warming. Biodiesel is the most attractive alternative fuel to the fast depletion of fossil oil. Jatropha oil is renewable non edible oil with high percentage of free fatty acids (FFAs). It generally forms soap in the presence of alkali catalyst during the production of biodiesel. In order to overcome this problem, we attempted to produce biodiesel through two-step transesterification. In the first step 1 wt % sulfuric acid (H2SO4) in oil was used for transesterification of Jatropha oil at 60°C in the mixture of one part of acid free oil with six parts of methanol. The first step was carried out to reduce the FFAs content to a minimal value. In the second step Sodium Hydroxide (NaOH) catalyzed esterification was carried out at 60°C to convert FFA free Jatropha oil to biodiesel. Sonication at 20 KHz was used in both the steps. Sonication could help achieving intensive mixing of the reaction mixture during transesterification process. The conversion of biodiesel was estimated through hydrogen nuclear magnetic resonance. We could achieve in the first step 99% reduction of FFA followed by 92% conversion of resultant Jatropha oil to biodiesel in 45 min. The reaction rate constants k for transesterification were estimated at different temperatures and the rate equation was derived. We conclude that the two step transesterification is likely to be a most promising environment friendly method to convert Jatropha to biodiesel.