TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The mixture of triglyceride and free fatty acid is crude palm oil, crude sunflower oil, crude rapeseed oil, crude Jatropha oil, crude soybean oil, circulating cooking oil, edible and non-edible animal grease, or palm oil fatty acid. The mass ratio of oil/grease, water, and solvent 1:0.1-0.3:0.2-0.5. The solvent is heptane or hexane. The contacting step of oil/grease, solvent, and water is conducted at 40-120, preferably 90-110 degrees C for 10-60, preferably 15-20 minutes. Dicarboxylic acid is added into water, such as citric acid or tartaric acid at 0.1-0.5 mass% (based on the mass of oil/grease). The reaction temperature in the fluidized bed is kept at 64-150 degrees C; and the minimum reaction pressure corresponds to the steam pressure of methanol under the selected reaction temperature. The water dissolved in excessive methanol in the reaction mixture taken from the fluidized bed reactor reacts with calcium oxide to obtain calcium hydroxide, where calcium oxide is taken as the catalyst for follow-up ester exchange reaction. After the reaction of reaction mixture and calcium oxide, they are supplied into ester exchange reactor by piston flow. The reactor comprises two pipes (where outer pipe provides heating medium: steam or hot oil to keep the selected reaction temperature). The length of the reactor corresponds to the total volume, so that the retention time is 30-60, preferably 45 minutes. When the total volume flow enters the reactor, the reaction temperature is kept at 65-130, preferably 75-90 degrees C. The diameter of the inner pipe is selected, so that Reynolds number is greater than 10000 to ensure enough vortex along the length of the reactor, where two pipes are changed to single pipe with smaller diameter at every 1/10 place of the length of the reactor, so that the speed of the reaction mixture in the pipe with reduced section is 2-3.2 m/s, and the length of the pipe with reduced section is 50 times the diameter of the reduced section.