NOVELTY - Preparation of biodiesel oil from soybean oil deodorizer distillate using double frequency pulse ultrasonic auxiliary reactor involves esterification of soybean oil deodorized distillate using sulfuric acid methyl ester catalyst, gradually cooling and removing plant sterol, and preesterification of soybean oil deodorizer distillate, ultrasonic reaction of distillate using double frequency pulse ultrasonic wave reactor, after the reaction, water washing, dehydrating, and distilling to obtain biodiesel oil.    USE - For preparation of biodiesel oil from soybean oil deodorizer distillate by using double frequency pulse ultrasonic auxiliary reactor (claimed).    ADVANTAGE - The double frequency pulse ultrasonic auxiliary reactor allows preparation of biodiesel oil from soybean oil deodorizer distillate; reduces the catalyst dosage, reduces the energy consumption and saves the time.    DETAILED DESCRIPTION - Preparation of biodiesel oil from soybean oil deodorizer distillate using double frequency pulse ultrasonic auxiliary reactor involves 1) esterification of soybean oil deodorizer distillate using sulfuric acid methyl ester catalyst, where the condition is as follows: methanol and fatty acid mol ratio of 12:1, the reaction time is 120 minutes, reaction temperature is 60 degrees C, mass concentration of 98% concentrated sulfuric acid is 1.0% total mass of oil (v/m), (2) after completion of the catalytic reaction, the reaction solution is placed in the dispenser, standing and layering, removing the lower layer, washing the upper layer with de-ionized water according to ratio of 1:1 until the washing water is neutral, obtaining soybean oil methyl ester after acid-catalyzed removal of smelly distillate; 3) gradually cooling the ester, removing plant phytosterin, where cooling temperature is 15 degrees C, 5 degrees C, and 5 degrees C, for 2 hours each, centrifuging at 5000 revolutions/minutes for 15 minutes; removing the plant sterol; adding anhydrous sodium sulfate to the soybean oil deodorized distillate, according to total weight of 25% for 2 hours to obtain pre-esterified soybean oil deodorizer distillate, (4) ultrasonic reaction of the distillate using double frequency pulse ultrasonic reactor, where the ultrasonic probe energy frequency is 20 kHz and 28 kHz, two opposite ultrasound probe is placed on both sides of reaction tank; two ultrasonic probes form an angle of 45 degrees and the liquid oil and methanol into boundary level, each probe only set power is 200W-600W, the ultrasonic working time is 2-6 seconds, intermittent for 1-3 seconds, total working time is 30-60 minutes, methanol and the triglyceride mol ratio is 6: 1-15, mass of sodium hydroxide (NaOH) for pre-esterification for soybean oil deodorizer distillate is 1.0-2.0%, initial temperature is 10-30 degrees C, the two ultrasonic wave generator (3), and the reaction mix liquid to a counter-current manner through circulation energy, collecting type ultrasonic probe, the flow speed is 100-200 ml/minutes, (5) dual-pulse ultrasound-assisted pre-esterification of soybean oil deodorizer distillate for production of biodiesel oil, when the reaction is finished, obtaining reaction liquid, standing and layering, using decompression distilling layer of un-reacted methanol, the upper layer using 50 degrees C deionized water according to 1: 1 for multi-washing until the washing liquid is neutral, the step obtained in the step (5) the crude biological diesel oil according to weight of 25% is taking in inner rectifying device, adding anhydrous sodium sulfate for 2 hours, obtaining crude biological diesel oil, (6), placing the crude biodiesel in a distillation apparatus having a vacuum degree of -0.01 MPa, and collecting fraction of 120-240 degrees C to give biodiesel.    DESCRIPTION OF DRAWING(S) - The figure shows a flow sketch map of the double frequency pulse ultrasonic device.    Reflux condenser (1)    Ultrasonic generator (2)    Ultrasonic wave generator (3)    Energy collecting type ultrasonic transducer (4)    Ultrasonic energy transducer (5)    Peristaltic pump (6, 7)    Reaction tank (8)    Storage tank (9)    Iron. (10)