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Biodiesel is a kind of cleansing reproducible energy sources, which is harmless to the environment. Nowadays, the global fuel deficiency and environmental degradation are becoming more and more serious, nations of the world has been attaching importance to the study of the development of biodiesel. One of the factors which restrict the development of biodiesel is the high price of raw materials, so, finding a kind of cheap raw materials is also an important researching direction. In this paper, cheap and easily obtained waste oil is used to produce biodiesel. Waste oil not only pollutes the environment, but also does harm to the health of people. So, using of waste oil as a raw material can receive many advantages.In this paper, waste oil was used as a raw material, two-step reaction which was pre-esterification and transesterification was used to produce biodiesel. We reduced the condensation point of biodiesel on the side, and optimized the production process. The main findings were as follows:(1)In the experiments, a variety of acid catalysts phosphotungstic acid, citric acid, oxalic acid,98% concentrated sulfuric acid were investigated under the same condition, which was molar ratio of methyl to oil 6:1, reaction time 1h, the quantity of catalystis is 2% of the oil, reaction temperature 60℃. So the right catalysts were chosen, and the pre-esterification conversion process with the chosen acid catalysts was optimized using the method of single factor experiments.A.Phosphotungstic acid:the optimized conditions:molar ratio of methyl to oil is 6:1, reaction time is 2h, the quantity of catalystis is 2% of the oil, reaction temperature is 62℃;B.98% concentrated sulfuric acid:the optimized conditions:molar ratio of methyl to oil is 7:1, reaction time is 60min, reaction temperature is 62℃, the quantity of catalystis is 2% of the oil;By investigating the acid value of the product, the appropriate pre-esterification acid catalyst(concentrated sulfuric acid) was chosen. The minimum acid value can reach 1.8mgKOH/g, fully met the requirements of the transesterification.(2)In the transesterification step, the optimized process of washing biodiesel by the distilled water was obtained:the volume ratio of distilled water to oil 2:1,washing temperature 80℃, washing time 15s, after three times washing, the saponifiable matter in biodiesel can be controlled below 1% of the quantity of biodiesel.The single-factor experiments and orthogonal experiments method were used, meanwhile, the range analysis was used to explore the order of the effects of the various factors on the yield of biodiesel, that is molar ratio of methyl to oil> reaction temperature> reaction time> the quantity of catalysti. The optimized production process obtained:molar ratio of methyl to oil 6:1, reaction temperature 62℃, reaction time 30min,the quantity of catalysti 1% of the oil, under these conditions, the biodiesel production rate can reach 94.97%. And the relation of the product yield, acid value and heating value was found. The higher the product yield is, the lower the acid value will be, and the higher the heating value will be. Finally, the biodiesel ingredient was detected by gas chromatography method.(3) In order to reduce the condensation point of biodiesel, a certain amount of ethanol, propanol, isopropanol were separately mixed in methanol in the producing process in the paper. The results showed that, the method of mixing ethanol is better than others; only using mixed alcohol in the esterification reaction can not reduce biodiesel condensation point, but will increase condensation point of biodiesel; only using mixed alcohol in transesterification stage is better, and with ethanol addition level of 20%, the condensation point of biodiesel can reach-8℃.
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