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Biodiesel is perfect for substituting petroleum diesel, which is a typical "green energy". The characteristics of biodiesel is low content of sulfur and aroma hydrocarbon, high content of oxygen, high cetane value and flash point, less hazardous exhaust gas. The degree of commercial production is lower. Its main reason is the producing cost is too high. About 75% percent cost comes from feedstocks, therefore there is an important significance to have cheap resources as materials to produce biodiesel.In this study, Waste Cooking oil(WCO) were used to produce biodiesels by two-steps. After Methanol and conc.H2SO4 esterification, and then the oil produce biodiesels by transesterification with methanol under NaOH as catalyst. The optimal conditions of two-steps to produce biodiesel were studied. The results were stated as follows. Under conc. H2SO4 as catalyst, the WCO and methanol esterification was:the mole ratio of methanol to oil was 4:1,3% w/w catalyst of conc H2SO4 to WCO,60℃reaction temperature,80 min reaction time and 250 r/min stirring speed. The optimal reaction condition of producing of biodiesel by transesterification with the lower acid value esterified WCO was:the mole ratio of methanol to oil was 6:1,1.5% w/w catalyst of NaOH to WCO,60℃reaction temperature, 40min reaction time and 250 r/min stirring speed.The color of biodiesel is deep dark, which has an influence on quality. The study research the technic of removing color from biodiesel. Firstly, the impact trend, including dose of hydrogen peroxide, dose of activated bleaching earth, reaction time and temperature, catched through the single fact experience. And then design the experience to improve the reacting condition. The results showed that the optimum conditions were:m(hydrogen peroxide):m(biodiesel) dose of hydrogen peroxide (30%) was 3mL(3%v/w), dose of activated bleaching earth was 5g (5%w/w), mixing time 30min, temperature 70℃.The production analysis showed that the characteristics of the product were closer to diesel, which made them a good substitute for diesel fuel.
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