(1) 25 kg of maleic anhydride waste residue added to 200 liters of tap water, heated to 85 C to make the waste residue dissolved, filtration to remove insoluble matter, add 0.5 kg of thiourea, hydrochloric acid to adjust the pH of the system to 3, heated reflux for 2.5 hours, cooling precipitation of crystals, and filtration of 17.6 kg of solid.
(2) the above obtained 17.6 kg of solid with 180 kg of tap water heated to 90 C to dissolve, add 2 kg of activated carbon heated reflux 1 hour decolorization, while hot filtration and removal of impurities, the filtrate pH with ammonia to 10, to the filtrate to add 44 grams of Escherichia coli, the reaction for 5 hours with 10 wt% hydrochloric acid solution to adjust the pH to 6, cooled dialysis of the crystals, filtration to get 15.7 kg of solid.
(3) Soak 15.7 kg of solid obtained above with 157 kg of ethanol at 20C for 5 hours, filter to obtain 5.8 kg of crystals, and bake the obtained crystals at 80C for 8 hours to obtain 4.9 kg of product, which is asparagine, and the HPLC content is 97.4%.