Xylene isomerization with hydrogenation

Claim 1

A PROCESS FOR RECOVERING A DESIRED XYLENE ISOMER FROM A (MIXTURE OF XYLENE ISOMERS) XYLENE-CONTAINING C8 AROMATIC HYDROCARBON FRACTION HAVING LESS THAN THE EQUILIBRIUM CONTENT OF THE DESIRED ISOMER WHICH COMPRISES CONTACTING SAID (XYLENE MIXTURE) HYDROCARBON FRACTION IN VAPOR PHASE AND HYDROGEN IN A CONVERSION ZONE WITH A HYDROGENATION-DEHYDROGENATION CATALYST COMPRISING PLATINUM ON A SUPPORT SELECTED FROM THE GROUP CONSISTING OF CLAY, ALUMINA, AND SILICA-ALUMINA AT A SPACE VELOCITY IN THE RANGE FROM 0.1 TO 10 V./V./HR., MAINTAINING THE CONVERSION ZONE (UNDER CONDITIONS OF TEMPERATURE, PRESSURE AND HYDROGEN PARTIAL PRESSURE THAT PERMIT THE EXISTENCE OF A MINOR AMOUNT OF NAPHTHENE IN EQUILIBRIUM WITH THE XYLENES) AT A PARTIAL PRESSURE OF HYDROGEN IN THE RANGE FROM ABOUT 20 TO 100 ATMOSPHERES AND AT A TEMPERATURE IN THE RANGE FROM ABOUT 400 TO ABOUT 800*F. IN A FIRST PORTION OF THE PROCESS AND A TEMPERATURE ABOVE 800*F. AND UP TO ABOUT 1200*F. IN A SUBSEQUENT PORTION OF THE PROCESS, WHEREBY HYDROGENATION OF XYLENES OCCURS IN SAID FIRST PORTION AND FORMATION OF A SUBSTANTIALLY EQUILIBRIUM MIXTURE OF XYLENES OCCURS IN SAID SECOND PORTION, AND SEPARATING THE DESIRED XYLENE ISOMER FROM THE RESULTING REACTION PRODUCT.