P-dichlorobenzene separating purification method

The invention provides a high-purity, high-yield, low-energy-consumption and pollution-free p-dichlorobenzene separating purification method which mainly includes the dissolving precipitation and fractional crystallization steps, wherein the dissolving precipitation is as follows: putting a p-dichlorobenzene mixture in an ethanol solution, then adding distilled water, controlling the temperature at 5 to 8 DEG C, and standing to obtain p-dichlorobenzene with the purity of 80-88%; the p-dichlorobenzene with the purity of 80-88% is refined by fractional crystallization to obtain the p-dichlorobenzene with the purity of more than 90%, and the fractional crystallization is two-stage and six-fraction crystallization. The composite separating purification method uses the ethanol as a main solvent and water as a precipitation agent, and is low in solvent cost, free of pollution, mild in process conditions, and convenient in operation; in each step of the fractional crystallization process, a DCS (distributed control system) system is used to realize the continuous production, material sublimation and loss can be reduced, handling capacity and product quality can be further improved, and the method has obvious economic benefits.