| Biodiesel is a sort of bioenergy, which is green, renewable and environmental friendly. It has become a research hotspot around the world for it could alleviate the crisis brought by the depletion of petroleum resources and environmental pollution. Compared with the traditional chemical method, the synthesize technology of biodiesel by lipase has many advantages such as mild conditions, simple process, low consumption of energy and environmental friendly. However, it is difficult for the development and industrialization of biodiesel produce by lipase method due to low yield, long time, high cost. In order to increase the yield, shorten the reaction time, reduce costs, transesterification of rapeseeds oil catalyzed by Lipozyme TL IM for biodiesel production were studied in this paper. Main results were described as follows:1. A gas chromatography(GC)method for the determination of fatty acid methyl esters composition and its quantity using Agilent 6890 with DB-1701 capillary.2. The effect of enzyme load, substrate ratio, reaction time, reaction temperature, shaking speed and organic solvent on the yield of fatty acid methyl ester (FAME) were studied by single factor method in single batch experiments. The optimal conditions were 50% enzyme based on oil weight, methanol/oil molar ratio 3:1, shaking speed 150rpm, temperature 50℃, added water 5% based on enzyme load, reacting for 12h. Under these conditions, the FAME yield was 92.3±5.12% after 9.75g rapeseed oil and 3mol methanol were added into 5mL hexane initially.3. The effect of pretreament of lipase by immersing, post-treatment by washing with solvents, the reaction temperature and the way of adding methanol on the stability of Lipozyme TL IM in multi-batches experiments were investigated. The pretreated Lipozyme TL IM was used to catalyse methnolysis at 40℃reacting 24h as one batch. One molar equivalent of methanol was added at reacton time of 0,8,16h at each batch. Acetone was used to remove glycerol at 8,16,24h and the lipase was reused for the next step or batch. The residual activity of lipase was still about 85% after being continuously reacting for 10 batches.4. The Box-Behnken design was used to optimize the conditions for ultrasonic pretreatment of Lipozyme TL IM and the evaluation index is the yield of FAME at 8h. The results suggested that the predicted value of the FAME yield at 8h was 72.29%. The experimental value was 71.30% under the optimal ultrasonic conditions of total time 30min, ultrasonic working time 6s, ultrasonic power 90W. The methanolysis reaction conditions were 50% enzyme based on oil weight, shaking speed 150rpm, reaction temperature 50℃, and adding 9.75g rapeseed oil and 3mol methanol into 5mL hexane initially.5. The nonlinear model fitting was done on the initial rate of enzymatic reaction after ultrasonic pretreatment by the least square method. The results showed that the methanol/oil molar ratio became 1:1 at the optimal initial rate after ultrasonic pretreatment compared with methanol/oil molar ratio 3:1 without ultrasonic pretreatment. The FAME yield at 15h could attain 91.34% when the methanol was added stepwise at 0, 5, 10h. The residual activity of Lipozyme TL IM of ultrasonic pretreatment was 80% after 5-batch reaction by the three-time addition method of methanol.6. The reaction conditions of biodiesel preparation from rapeseeds oil catalyzed by pretreated Lipozyme TL IM by ultrasound were optimized by Plackett-Burman design, CCD design and the response surface methodology. The optimal conditions were 19.79% Lipozyme TL IM based on oil weight, methanol/oil molar ratio 3:1, temperature 48℃, total time 13.26h. The predicted value of the FAME yield could attain 93.28%. The experimental value was 92.08%, which confirm the correlation between the predicted and experimental values and the model was wakable and reasonable in the studied range. |
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