The present application relates to the technical field of preparation of
quercetin, and discloses a method for preparing
quercetin by using
troxerutin waste liquid
powder, which comprises the following steps: step S1, dissolving the
troxerutin waste liquid
powder in a protonic acid or a Lewis acid, heating and refluxing until the reaction is complete; and step S2, reducing to normal temperature, filtering, washing the
filter cake with deionized water until neutral, and
drying to obtain
quercetin. In the technical solution, the acid is used as a catalyst, the
sugar molecules are hydrolyzed while the hydroxyethyl groups are removed, all the
rutin substitutes in the waste liquid
powder are converted into quercetin, the
hydrolysis of two molecules of
sugar on the
rutin molecules and the removal of the hydroxyethyl groups are completed at the same time in one step, the
process time is effectively shortened, the production cost is reduced, and good
economic benefits are achieved.