| Biodiesel is a renewable biomass fuel, which is green, low energy consumption and environmental friendly. As an alternative fuel for diesel engine, biodiesel gained an important position regarding to the oil crisis and environmental concerns in the recent years. Compared with the traditional mechanical stirring, ultrasonically assisted transesterification has many advantages such as shorter reaction time, simple process, low consumption of methanol and energy. Preparation of biodiesel through transesterification of Jatropha curcas L. oil with methanol under ultrasonic irradiation was investigated.GC/MS analysis showed that the major compositions of fatty acid in the oil are oleic acid, linoleic acid, palmitic acid and stearic acid with content of 38.3%, 36.2%, 14.8% and 7.3% respectively. Spectrophotometry and HPLC were used to identify glycerol yield and methyl ester yield respectively during transesterification.A low acid value of raw material is required in alkali-catalyzed transesterification reaction. Methanol extraction and ultrasonically assisted pre-esterification were applied to pre-treat Jatropha curcas L. crude oil in order to reduce the free fatty acid content. Orthogonal experiments were done to optimize the conditions of methanol extraction as follows: 0.8 v/v methanol-to-oil ratio, 5-min extraction time at temperature of 30℃for 4 times. Comparing to the traditional acid-catalyzed esterification, methanol extraction is a more simple, higher efficiency and no acid wastewater producing process. Based on the results of ultrasonically assisted pre-esterification, a 90W power, 40kHz frequency, 90-min reaction time, 18% methanol and 1.2% catalyst provided optimum conditions of pre-treatment process for the oil with a 20mgKOH/g initial acid value. An over 98% of pre-esterification conversion was gained under this condition.Several homogeneous base catalysts were used during the ultrasonically driven transesterification of Jatropha curcas L. oil. It was found that KOH and NaOH were more activity than Na2CO3 and K2CO3 with an over 98% of glycerol yield and methyl ester yield after 40-min reaction time. Furthermore, glycerol yield was less than methyl ester yield for the same catalyst, and their difference reduced with increasing reaction time.Various solid base catalysts were developed by impregnation method, in which KOH/NaX was chosen as the target catalyst. Best preparation conditions were obtained with NaX zeolite loaded with 10% KOH, followed by heating at 393K for 3h. When the transesterification reaction was carried out at room temperature (303K) for 5h, with 90W ultrasonic power, 59kHz ultrasonic frequency, 8:1 molar ratio of methanol to oil and 2wt.% catalyst amount, the conversion of oil was more than 90%.Kinetic equations were obtained by linear regression of experimental data. The study of kinetics illustrated that the model for ultrasonically assisted pre-esterification under the optimum conditions was (1)/[(1)0.5(1)]20 2020=0 ?++?? A eA k?αtβeAk?αteAk?αt. While for the best conditions of solid base-catalyzed transesterification, it was ? r A =0. 006672CA0.8843 under ultrasonic irradiation, with comparison to ? rA =0. 002866CA0.4094 under stirring, which indicated that ultrasound can greatly enhance pre-esterification than stirring.
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