Method for industrially preparing O-hydroxypropyl chitosan

The invention discloses a method for industrially preparing O-hydroxypropyl chitosan. The method comprises the following steps: 1. proportionally mixing alkali and water, and stirring to completely dissolve caustic soda flakes; 2, after the alkali liquor is cooled to 30 DEG C or below, slowly adding the alkali liquor into chitosan, putting the materials into a tank mixer, uniformly stirring, standing to fully swell the chitosan, and filling a double-layer inner film bag with the chitosan; 3, putting the bagged chitosan wet materialinto a refrigeration house to be frozen; and 4, unfreezing thefrozen material, carrying out filter pressing to remove excess alkali liquor, then putting the material into a reaction kettle, adding isopropanol with the mass 5-10 times that of chitosan, carrying out vacuum pumping into the reaction kettle, and carrying out soaking so as to enable chitosan to be fully swollen. According to the method, the reaction design is more reasonable, the cost is greatlyreduced, industrial large-