Optimization of in-situ Biodiesel Production from Raw Castor Oil-Bean Seed

Optimization of in-situ biodiesel production from raw castor oil-bean seed was carried out from raw castor bean oil seed (37.9% oil content) by alkaline catalyzed in-situ trans-esterification with Sodium hydroxide as catalyst and ethanol as the solvent in a laboratory batch processor. Response surface methodology and central composite experimental design was applied to evaluate effects of reaction time (30 -120 min), alcohol/seed weight ratio (0.5 – 2.0), Catalyst amount (0.3 – 1.5%) and reaction temperature (40 – 70OC). Catalyst amount, reaction temperature and time all had significant main effects (p < 0.05) while Alcohol-seed ratio had only slight effects on yield of castor biodiesel as a main effect but was significantly involved in interactions with other factors. A modified statistical model comprised of all significant factors and interactions (p < 0.05) obtained by multiple regressions predicted that the highest yield of castor ethyl-ester was 99.5% of expressible oil at the following optimized reaction values; alcohol/seed weight ratio of 0.5, a catalyst./seed weight ratio of 1.31, reaction temperature of 60.33oC, and reaction time of 81.7minutes. A Taguchi L9(3^4) optimization experimental design used to confirm the modified model at optimum point and two other points within experimental region produced yield that was significantly comparable to model predictions at 95% confidence level using a paired t-test. Measured properties of the castor ethyl-ester such as viscosity(5.78mm2/s), pour point (-21.5 oC), flash point (177.12 oC), calorific value (47.76MJ/kg), acid value (0.34 mg KOH/g) and cetane number (48.73) were within the ASTM standard D6751-02 but specific gravity. Keywords: Castor oil-bean seed, biodiesel, in-situ trans-esterification, response surface methodology, optimization, Castor ethyl-este