The bio-diesel is a clean energy with environmental friendly and sustainable development feature. At present, most of bio-diesel is made up of pure vegetable oil, so that the unit price is too high to have market competitiveness. There are many low price oils which can be used to produce bio-diesel and reduce the production cost of bio-diesel domestically. But most of these low price oils contain lots of free fatty acid, the conventional alkaline process can not be used to produce bio-diesel, and the pre-treatment is needed to be done to reduce it to certain value. The acid catalytic process is another way to produce bio-diesel, which has the advantage of fast reaction rate and high conversion ratio for the esterification of methyl group in free fatty acid. So, this study mainly uses pre-esterification reaction to reduce the content of free fatty acid in waste cooking oil, so as to meet the quality condition required for the post production of bio-diesel by alkaline process, and raise total yield of bio-diesel.
