Patent ID: 8288586

Claim:
A method for separating and refining 2,6-naphthalene dicarboxylic acid from crude 2,6-naphthalene dicarboxylic acid having a purity of 98.0Ëœ99.5%, comprising the steps of: (a) mixing crude 2,6-naphthalene dicarboxylic acid and water to prepare slurry; (b) dissolving the mixed slurry; (c) performing crystallization to grow the dissolved mixture into crystals through multiple-step crystallization using a plurality of crystallization units; (d) washing the crystals obtained; (e) performing solid-liquid separation to separate 2,6-naphthalene dicarboxylic acid and water after washing; and (f) drying 2,6-naphthalene dicarboxylic acid; wherein: the plurality of crystallization units linked in series is four crystallization units, and the temperature and pressure thereof are set at 260-280Â° C. and 60-85 kg/cm 2 , respectively, in a first crystallization unit, at 240-260Â° C. and 40-65 kg/cm 2 in a second, 220-240Â° C. and 30-45 kg/cm 2 in a third and 200-220Â° C. and 20-35 kg/cm 2 in a fourth; the plurality of crystallization units linked in series is two crystallization units, and the temperature and pressure thereof are set at 250-260Â° C. and 60-75 kg/cm 2 , respectively, in a first crystallization unit and at 200-240Â° C. and 25-45 kg/cm 2 , respectively, in a second; or the plurality of crystallization units linked in series is three crystallization units, and the temperature and pressure thereof are set at 260-280Â° C. and 60-85 kg/cm 2 , respectively, in a first crystallization unit, at 240-260Â° C. and 40-65 kg/cm 2 in a second and at 200-220Â° C. and 20-35 kg/cm 2 in a third.