Process for isomerizing normal paraffins

Claim 1

IN THE HYDROISOMERIZATION PROCESS WHICH COMPRISES CONTACTING WITH A PLATINUM-ALUMINA CATALYST A HYDROCARBON FRACTION REACTOR FEED COMPRISING AT LEAST 90 VOLUME PERCENT OF AT LEAST ONE ALIPHATIC PARAFFIN HAVING FROM 4 TO 6 CARBON ATOMS IN ADMIXTURE WITH HYDROGEN IN A CONCENTRATION CORRESPONDING TO A MOL FRACTION OF HYDROCARBON GREATER THAN 0.5 BUT LESS THAN THE MOL FRACTION HYDROCARBON CORRESPONDING TO RAPID CATALYST AGING, AT A CHARGE LIQUID HOURLY SPACE VELOCITY OF AT LEAST 5 VOLUMES OF HYDROCARBON PER VOLUME OF CATALYST PER HOUR, A TEMPERATURE FROM 600 TO 1000* F. AND A PRESSURE FROM 300 TO 600 P.S.I.G., WHILE ADDING TO THE REACTOR FEED AN ALKYL HALIDE THAT VAPORIZES UNDER THE PROCESS CONDITIONS, AND RECOVERING FROM THE REACTION ZONE AN EFFLUENT STREAM ENRICHED IN BRANCHED CHAIN PARAFFINS, THE IMPROVEMENT WHICH COMPRISES RESTORING THE CATALYST ACTIVITY FOLLOWING A RAPID DECLINE IN THE BRANCHED CHAIN PARAFFIN CONTENT OF THE PRODUCT BY CHARGING SAID HYDROCARBON FRACTION TO THE REACTION ZONE SUBSTANTIALLY FREE OF HALOGEN UNTIL THE CATALYST ACTIVITY REACHES A SUBSTANTIALLY CONSTANT LEVEL, AND THEREAFTER RESUMING THE ADDITION OF SAID ALKYL HALIDE TO THE HYDROCARBON FEED IN A CONCENTRATION FROM 10 TO 50 PARTS OF HALOGEN PER MILLION PARTS OF HYDROCARBON.