Method for preparing biodiesel
Chemical production and a serious problem: the cost of the production process using alkaline catalyst for raw materials must be such as crude oil, crude rapeseed oil and soybean oil, raw material costs accounted for 75% of the total cost. Therefore the use of cheap raw materials and improve the conversion to reduce the cost of biodiesel is the key to practical, so the United States has begun through the genetic engineering method of high oil content of the plant (see "project microalgae" method), Japan uses industrial waste oil and waste frying oil, Europe is rich in oil is not suitable for planting food crops crops on the land. In order to solve the above problems, people began to study the synthesis of biodiesel by biological enzyme method, that is, the esterification of fatty acid methyl ester and ethyl ester was carried out by using animal oil and low carbon alcohol. Enzymatic synthesis of biodiesel has the advantages of mild condition, low alcohol consumption and no pollution emission. In 2001, the immobilized Rhizopus oryzae cells were used in the production of biodiesel, the conversion rate was about 80%, and the microbial cells could be used continuously for 430 hours.
But the chemical synthesis of biodiesel has the following disadvantages: high reaction temperature and complicated process; excessive use of methanol in the reaction process, the subsequent process must have the corresponding alcohol recovery device, the complicated process and high energy consumption; oil in the raw water and free fatty acids will seriously affect the biodiesel yield and product quality; purification the complex, difficult to esterification product recovery; byproducts of the reaction is difficult to remove, but also produce large amounts of wastewater using alkali catalyst and alkali (acid) solution is easy to cause two pollution emissions on the environment.