The invention provides a method for utilizing
waste oil to produce bio-diesel, which regards waste animal and
vegetable oil as raw materials, in the producing process, no water-washing is needed, and the method consists of the following steps, first, pretreatment, degumming and
dewatering the
waste oil, second, pre-esterification, heating the
raw material after pretreatment, and stirring the material with methyl
alcohol and acid catalyst for reaction, third, alcoholysis, adding methyl
alcohol and organic alkali catalyst into the material after pre-esterification for heating reaction, fourth, glaciation, bio-diesel being got after separation. The method degums the
waste oil so as to eliminate the influence of gummy matter towards following steps and assure the stability of the process,
saponification is avoided, which can cause waste products in block, and the products can reach the main index of 0<model> diesel, the
cold filter plugging point is lower than 0 DEG C, the close
flash point is more than 65 DEG C, the conversion rate (
utilization rate) after pretreatment can reach more than 90 percent, no water-washing is needed so as not to produce a great amount of industrial
wastewater to pollute the environment and the
post treatment of products is rather convenient.