Production Of Biodiesel

As the increase of the demand for and the decrease of the storage of the fossil fuel, biodiesel has been paid increasing attention as one of the alternative fuels. Presently, biodiesel is mainly produced by transesterification of vegetable oils or animal fats with alcohol using NaOH or KOH as a catalyst. Although this is a mature technology, there are some shortcomings including emulsion formation during the reaction, which results in the difficulty in separation the products, and wastewater produced from the washing of the products to remove the base catalyst. The recently developed supercritical transesterification can overcome the above shortcomings. However, it must be operated at high temperature and pressure.We proposed a method for the production of biodiesel, by which the transesterification was carried out at subcritical condition of methanol with cheap and volatile organic bases added in the reaction system. In the way, high temperature and pressure of the supercritical condition can be avoided and the catalysts can be easily recovered, as well as the high yield of the product can be maintained. Following this idea, large numbers of experiments had been conducted using the transesterification of triavetin and methanol as a model reaction, at the aid of a series of organic amines. The research results indicated that four kinds of organic bases, i.e., triethanolamine, isopropylamine, tert-butylamine and triethylamine, exhibited good catalytic activity for the model reaction under subcritical condition. The purpose of this thesis is to examine the reaction properties of the transesterification of vegetable oils and methanol by using the above four kinds of organic amines under subcritical condition.First, two kinds of raw materials, i.e., rapeseed oil and soybean oil, were used and various factors were investigated. It is found that the yield of fatty acid methyl ester increases with the increase of the filling level of the reactor, the increase of the methanol to oil ratio, the increase of the temperature at the temperature range of 60 ~ 230 ℃, the decrease in the water content in the material, and the increase of the catalyst content. The optimum reaction condition is as follows: 100% of the filling level of the reactor, areaction temperature of 230 °C, the methanol to oil mole ratio of 14:1, the water content of less than 0.5%, and the catalyst content of 6.0wt%. under such circumstance, the yield of methyl esters is 84.8%, 95.8%> 98.5%^U 80.2%, respectively, when triethanolamine, isopropylamine, tert-butylamine and triethylamine are used as the catalyst with a reaction time of 6 h, using the rapeseed oil as the raw material.In order to get good solubility between methanol and oil, two kinds of solvents, n-hexane and fatty acid methyl ester, were used and the effect of the solvent on the yield of the product was examined. It is found that, when triethanolamine, tert-butylamine and triethylamine are respectively used as the catalyst and the rapeseed oil to hexane volume ratio is 10:1, with 100% of the filling level of the reactor, a reaction temperature of 230 °C, the methanol to oil mole ratio of 14:1, the water content of less than 0.5%, the catalyst content of 3.0wt%, and a reaction time of 4 h, the yields of methyl ester increase from 45.8%, 70.1% and 45.8% to 46.2%, 94.0% and 96.0%, respectively. When the rapeseed oil to methyl ester volume ratio is 15:1 with the same reaction conditions as above, the yields of fatty acid methyl ester increase to 46.3%, 86.1%, and 71.1%. Therefore, higher yield of fatty acid methyl ester can be obtained when hexane is used as the solvent than methyl ester.When soybean oil is used as the raw material, the yield of fatty acid methyl ester is always 5-15% lower than that when rapeseed oil is used, with triethanolamine, isopropylamine and triethylamine are used as the catalyst, respectively. When isopropylamine is used as the catalyst, the yields of the product are close no matter what kind of oil is used as the raw material. On the other hand, some experiments were also carried out in a continuous tubular reactor. The results obtained at the same reaction conditions as those in the batch reactor are very close and the difference of the yields of the methyl ester is within about 5%.