Patent ID: 7102029

Claim:
A crystallization process including the steps of feeding a terephthalic acid solution or a slurry solution in which a part of the terephthalic acid is precipitated to a crystallization vessel, precipitating the terephthalic acid in the crystallization vessel, generating a slurry containing crystals and solvent, and discharging the slurry, and comprising the further steps of: (i) introducing the slurry discharged from the crystallization vessel to a hydrocyclone, in a tangential direction of the hydrocyclone, (ii) returning all amount of the concentrated slurry flowing out as a downward swirling flow from a lower part of the hydrocyclone directly to the crystallization vessel, and (iii) discharging the slurry overflowing from an upper part of the hydrocyclone, wherein the concentration of crystals in said slurry overflowing from said upper part of said hydrocyclone is 5% or less.