Recovery of para-xylene from solutions containing the xylene isomers

Claim 1

A PROCESS OF CRYSTALLIZING PARA-XYLENE FROM A CRUDE XYLENES MIXTURE CONTAINING AT LEAST 10% OF PARA-XYLENE AND SUBSTANTIAL QUANTITIES OF ORTHO-AND META-XYLENE, ETHYLBENZENE AND NON-AROMATICS WHICH COMPRISES CIRCULATING COLD XYLENES LIQUOR BETWEEN A REFRIGERATED COOLING ZONE AND A CRYSTALLIZING VESSEL HAVING AN UPPERMOST ZONE FROM WHICH MOTHER LIQUOR IS DECANTED, AN INTERMEDIATE ZONE FROM WHICH THE CIRCULATING LIQUOR IS WITHDRAWN AND A LOWERMOST ZONE FROM WHICH A CRYSTAL SLURRY IS WITHDRAWN, PRECOOLING THE CRUDE XYLENES CHARGE MIXTURE, ADMIXING THE PRECOOLED CHARGE MIXTURE WITH THE CIRCULATING COLD XYLENES LIQUOR AT A RATE PROVIDING A RATE RATIO OF COLD XYLENES LIQUOR 50 TO 150 TIMES THE RATE OF CHARGE INPUT: COOLING THE RESULTING MIXTURE WITHOUT SUBSTANTIAL CRYSTALLIZATION TO A TEMPERATURE WHICH IS JUST ABOVE THE SPONTANEOUS CRYSTALLIZATION TEMPERATURE OF THE FIRST CRYSTALLIZABLE COMPONENT OTHER THAN PARA-XYLENE AND BETWEEN -120*F. TO -130*F., CRYSTALLIZING PARA-XYLENE FROM SAID COOLED MIXTURE IN THE CRYSTALLIZING VESSEL, DECANTING MOTHER LIQUOR FROM THE UPPERMOST ZONE OF THE CRYSTALLIZING VESSEL BRINGING COOL MOTHER LIQUOR INTO INDIRECT CONTACT WITH WARM COMPRESSED REFRIGERANT IN THE REFRIGERATION ZONE, PASSING MOTHER LIQUOR FROM THE REFRIGERATION ZONE INTO INDIRECT CONTACT WITH FRESHLY INTRODUCED CRUDE ZYLENES MIXTURE AND EFFECTING SAID PRECOOLING OF THE CRUDE XYLENES MIXTURE TO A TEMPERATURE NOT BELOW ABOUT -80* F., AND WITHDRAWING A PARA-XYLENE RICH SLURRY FROM THE LOWERMOST ZONE OF THE CRYSTALLIZING VESSEL.