Hours on stream

Claim 1

IN A HYDROCRACKING PROCESS WHEREIN FUELS, INCLUDING NAPHTHAS AND MIDDLE DISTILLATES, ARE PRODUCED BY CONTACTING A FRESH HYDROCARBON FEED SELECTED FROM THE GROUP CONSISTING OF HYDROCARBON DISTILLATES AND HYDROCARBON RESIDUA BOILING ABOVE ABOUT 350*F. CONTAINING MATERIALS BOILING ABOVE ABOUT 900*F. IN A HYDROCRACKING ZONE WITHOUT PRIOR MULTIPLE STEP HYDROGENATION, IN THE PRESENCE OF AT LEAST 1000 S.C.F. OF HYDROGEN PER BARREL OF SAID FEED, WITH A CATALYST COMPRISING A HYDROGENATING-DEHYDROGENATING COMPONENT DISPOSED ON A SUPPORT AT A TEMPERATURE OF ABOUT FROM 400* TO 900*F., A PRESSURE OF AT LEAST 500 P.S.I.G. AND AN LHSV OF ABOUT FROM 0.1 TO 15, AND BY WITHDRAWING FROM SAID ZONE AT LEAST ONE NORMALLY GASEOUS FRACTION, AT LEAST ONE LIQUID PRODUCT FRACTION, AND AT LEAST ONE RECYCLE FRACTION CONTAINING MATERIALS BOILING ABOVE ABOUT 900*F., THE IMPROVEMENT WHICH COMPRISES, PRIOR TO RETURN OF SAID RECYCLE FRACTION TO SAID HYDROCRACKING ZONE, HYDROGENATING THE POLYNUCLEAR AROMATICS THEREIN AT LEAST DOWN SUBSTANTIALLY TO STRUCTURES CONTAINING NOT MORE THAN ONE AROMATIC RING IN THE CONDENSED RING STRUCTURE, TO AN EXTENT THAT THE COMPOUNDS REMAINING THEREIN THAT HAVE AT LEAST TWO FUSED AROMATIC RINGS ARE REDUCED AT LEAST DOWN TO 5 VOLUMES PERCENT OF SAID MATERIALS BOILING ABOVE ABOUT 900*F.