Patent ID: 6565653
Filing Date: 2003-05-20
Classification: C07C,C30B,Y02P

Abstract:
A process for the production of paraxylene from a paraxylene-containing feedstream comprising C8 aromatic hydrocarbons and having a paraxylene concentration of at least about 60 weight percent, the process comprising:a) crystallizing said feedstream in a first crystallizer at a temperature of about 10Â° F. to about 55Â° F.; b) recovering an effluent comprising paraxylene crystals in a mother liquor; c) separating the paraxylene crystals from the mother liquor in a first separation unit, washing the paraxylene crystals with liquid paraxylene, completely melting the paraxylene crystals, and collecting the liquid paraxylene product; d) transferring at least a portion of filtrate from the first separation unit to a second crystallizer, which is operated at a temperature lower than that of the first crystallizer, crystallizing the filtrate, and recovering an effluent comprising paraxylene crystals in a mother liquor; e) separating the paraxylene crystals from the mother liquor in a second separation unit and sending the paraxylene crystals to a slurry apparatus; f) transferring at least a portion of filtrate from the second separation unit to a third crystallizer, which is operated at a temperature lower than that of the second crystallizer, crystallizing the filtrate, and recovering an effluent comprising paraxylene crystals in a mother liquor; g) separating the paraxylene crystals from the mother liquor in a third separation unit and sending the paraxylene crystals to the slurry apparatus; h) contacting the paraxylene crystals in the slurry apparatus with paraxylene-containing liquid to form a slurry mixture having a temperature higher than that of the lowest temperature crystallizer; i) separating the slurry mixture in a fourth separation unit to produce a filtrate and a crystalline paraxylene product, washing the paraxylene crystals with liquid paraxylene, completely melting the paraxylene crystals, and collecting the liquid paraxylene product; j) recycling at least a portion of filtrate from the fourth separation unit to the second crystallizer; and k) recycling at least another portion of filtrate selected from the group consisting of filtrate from the first separation unit, filtrate from the fourth separation unit, and filtrate from the first and fourth separation units to the slurry apparatus.