Method for preparing diisopropanolamine

The invention relates to a method of manufacturing diisopropanolamine. Liquid ammonia and water are mixed to form ammonia water which is fully mixed with propylene oxide; the mixed solution is preheated until the temperature reach 140 to 145 DEG C and then is delivered into a reactor for reacting, the temperature is controlled within 148 to 155 DEG C when in reacting, the pressure is controlled within 16.0 to 18.0MPa, the inputting molar ratio of the ammonia and the propylene oxide is controlled within 5 to 8, and the reaction is fully performed for 1.5 to 3 hours; the mixture products obtained in the reaction are separated to obtain isopropanolamine products, diisopropanolamine products and triisopropanolamine products through flash evaporation and rectification in a stepwise way. In thediisopropanolamine products which are manufactured by adopting the method, the component of 1, 1 -nitrousalkyl-dipropyl-2-alcohol accounts for more than 99 percent (hereinafter referred to as mass percent), and the isomeride thereof is less than 1 percent. In addition, the cost of the production operation in the method is less, the production cost is low, the product quality is high, and the high-end requirement of products such as synthetic medicine, farm insecticide, etc. is satisfied.