| Biodiesel is gaining more and more attention as an alternative fuel due to the depleting fossil fuel resources.All kinds of raw material such as herbaceous,woody,aquatic oil plants,animal fat and waste frying oil are made biodiesel.This liquid fuel produce less smoke and particles,have higher cetane number,produce lower carbon monoxide and hydrocarbon emissions,are renewable,biodegradable and non-toxic as compared to petroleum diesel.It is produced by transesterification in which,oil is reacted with a methanol in presence of alkali as a catalyst.In methanolysis system,a low dissolving rate of the oil in the methanol causes the important of the yield of transesterification is the mixing between the two immiscible layers,development slowing.Because triglycerides and alcohols are not totally miscible,the transesterification can occur only in the interfacial region and it is a very slow process.By adding cosolvent or ultrasonic to effect formation of the single phase,the transesterification is rapid and proceeds essentially to completion.In this thesis,by homogeneous transesterification the vegetable oil was transformed to the substitute fuel-biodiesel,which is composed of the following parts:①Ternary phase solubility comprising vegetable oils,methanol and several solvent are obtained at ordinary temperature and 60℃.The higher temperature of the ternary system could reduce the quantity of cosolvent,which is needed to achieve single phase. Ethanol,ether,tetrahydrofuran and 1,2-epoxypropane are chosen,which will continue experment.It is produced by transesterification in which,vegetable oil is reacted with a methanol and vary solvent in presence of alkali as a catalyst.The result showed that the conversion,which with ethanol as cosolvent was 21.0%higher then blank,and much better than others.The best molar ratios of methanol and ethanol is 3:1.②Transesterification was carried out with mixtures of methanol/ethanol and using NaOH as a catalyst.The results indicate that mixtures of alcohol increased the rate of transeserification reaction.Through the single factor experiments and the Box-Benhnken design experiment,the best optimum conditions of preparation of Biodidesl are:the reaction temperature is 48.2℃,the catalyst amount is 0.59%,and the reaction time is 25.4min.On this conditions,the conversion of Biodiesel reached 99.3%.③A batch ultrasonic enhanced equipment was designed and the effects of ultrasonic energy on the base-catalyst transesterification of vegetable oil with mixed methanol/ethanol system to prepare biodiesel were investigated.It was found that with the help of low frequency ultrasonic the reaction time was much shorter than that of conventional mechanical agitation.The conversion at frequency of 28kHz was 0.34%～7.55%higher than frequency of 45kHz.The results are in agreement with power of ultrasonic at 80W,90W and 100W.Under this frequency of 28kHz and power of 80W, the reaction conversion achieved almost 100%in 5minutes at the water bath temperature 48.2℃.④Study on reaction mechanism,fatty acid composition and product's performance of transesterification of biodiesel,the product's performance evaluation index accord with GB/T 20828-2007.The optimal process of mixed methanol/ethanol system to apply to multiple oils and catalyst,the effect is clear,and some important results was obtain. This results are good for development of homogeneous transesterification of biodiesel technology.
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