Purification of paraxylene

Claim 1

A PROCESS FOR SEPARATING PARAXYLENE OF OVER 90% BY WEIGHT PURITY FROM A FEED STOCK CONSITING OF A LIQUID MIXTURE OF AROMATIC HYDROCARBONS INCLUDING PARAXYLENE IN THE RANGE FROM ABOUT 15 TO 25% VOLUME, THE OTHER ISOMERIC XYLENES INCLUDING ORTHOXYLENE AND ETHYL BENZENE AND CONTAINING NO MORE THAN A SMALL AMOUNT OF OTHER AROMATIC MATERIAL, WHICH COMPRISES THE STEPS OF CHILLING SAID MIXTURE AND HOLDING IT AT A TEMPERATURE BELOW THE CRYSTALLIZATION TEMPERATURE OF PARAXYLENE AND JUST ABOVE THE EUTECTIC POINT OF PARAXYLENE WITH THE MOST EASILY PRECIPITATED COMPONENT WITHIN THE RANGE OF -90* AND -110*F. FOR AT LEAST 30 MINUTES TO FROM A FIRST SLURRY OF PARAXYLENE CRYSTALS IN A MOTHER LIQUOR WITH SAID CRYSTALS HAVING A NEEDLE-LIKE SHAPE WITH A TYPICAL CRYSTAL SIZE OF 10 X 100 MICRONS WHEN VIEWED IN A MICROSCOPE, SEPARATION CRYSTALS FROM SAID FIRST SLURRY TO FORM A FIRST CAKE HAVING A TOTAL PARAXYLENE CONTENT WITHIN THE RANGE OF 65 TO 85% BY WEIGHT, MELTING SAID FIRST CAKE TO FORM A MELT, CHILLING SAID MELT AND HOLDING IT AT A TEMPERATURE BELOW THE CRYSTALLIZATION POINT OF PARAXYLENE WITHIN THE RANGE OF -20* AND 20*F. FOR AT LEAST 30 MINUTES TO FORM A SECOND SLURRY OF PARAXYLENE CRYSTALS IN MOTHER LIQUOR, SAID PARAXYLENE CRYSTALS HAVING A PLATE-LIKE RECTANGULAR SHAPE WITH A TYPICAL CRYSTAL SIZE OF 90 X 270 MICRONS WHEN VIEWED IN A MICROSCOPE, SUBJECTING SLURRY COMPRISING SAID CRYSTALS IN MOTHER LIQUOR TO A SEPARATION STEP TO FORM A SECOND CAKE CONTAINING PARAXYLENE HAVING A PURITY IN EXCESS OF 90% BY WEIGHT RECOVERING SAID CAKE.