Method for cleanly preparing acylchitosan

The invention provides a method for preparing acyl chitosan with clean process, which comprises using carboxylation cation and chloride ion to form an ion water solution or using an amino acid ion water solution as reaction medium, preparing the ion liquid into 0.5-20% water solution at a normal temperature and a normal pressure, adding chitose, adding chitose, ortho-phthalic anhydride, succinic anhydride, maleic anhydride or itaconic anhydride with an amount of 2-3 powered of chitose repeated units to react for 6-15h, filtering, drying until constant weight to obtain white or light yellow powder as the target product acyl chitosan, recovering the reacted mother liquid, steaming out alcohol, while the left ion solution can be repeatedly used. The invention overcomes the defects of prior acyl chitosan production art as easily volatilized solvent, serious pollution and hard recovery, to provide a homogeneous-phase and environment-friendly technique for the production of acyl chitosan.