Patent ID: 8178716

Claim:
A multi-stage crystallization process comprising the steps of: feeding a solution of terephthalic acid or a slurry (raw slurry) containing terephthalic acid partially precipitated to a first crystallization vessel to precipitate the terephthalic acid therein; and feeding a slurry (crystallization slurry) containing the thus precipitated terephthalic acid sequentially to at least a second crystallization vessel, wherein a solvent contained in the crystallization slurry is water, and while continuously supplying water as a cleaning solvent to a delivery conduit connecting the former-stage crystallization vessel and the next latter-stage crystallization vessel to each other, the crystallization slurry is fed through the delivery conduit, and wherein the cleaning solvent is supplied to the delivery conduit at an angle of 30 to 60° relative to a direction of a flow of the crystallization slurry fed through the delivery conduit from an upstream side to a downstream side thereof by means of a cleaning nozzle, and a linear feed velocity of the cleaning solvent at a feed orifice of the cleaning nozzle is from 15 to 200 [m/s].