Optimization of alkaline transesterification of rice bran oil for biodiesel production using response surface methodology.

BACKGROUND: Response surface methodology (RSM), based on central composite rotatable design (CCRD), was used to optimize four transesterification reaction variables: methanol-to-oil molar ratio (3:1–12:1), catalyst (NaOCH3) concentration (0.5–1.25 wt% in relation to oil mass), reaction temperature (45–65 °C) and reaction time (30–90 min) at two levels (24 experimental design) to produce rice bran oil methyl esters (RBOME). RESULTS: The molar ratio of methanol to oil and reaction temperatures were the most significant (P < 0.01) factors affecting the yield of RBOME. A linear relationship was found between the observed and predicted values (R2 = 0.9520). Using multiple regression analysis a quadratic polynomial equation was established for methyl ester yield. The quadratic term of catalyst concentration showed a significant (P < 0.01) effect on esters yield. The interaction terms of methanol to oil molar ratio and catalyst concentration with reaction time exhibited a positive effect on the methyl esters yield (P < 0.05). The optimum reaction conditions for transesterification of rice bran oil were 7.5:1 methanol-to-oil ratio, 0.88% catalyst concentration, 55 °C reaction temperature and 60 min reaction time, resulting in a RBOME yield of 83.3%. Gas chromatographic analysis of RBOME produced in the present experiment revealed linoleic, oleic, palmitic and stearic acids to be the major fatty acid methyl esters (FAMEs). CONCLUSION: RSM was found to be a suitable technique for optimizing transesterification of rice bran oil. Fuel properties of RBOME as measured according to accepted methods were found to satisfy almost all prescribed ASTM (D 6751) and EN 14214 specifications. Copyright © 2009 Society of Chemical Industry