Abstract: An integrated hydrotreating/hydrocracking process employs two hydrotreating catalysts of different relative activities in sequence to provide improved products. A more active second catalyst is employed after the first hydrotreating catalyst. The jet fuel fraction recovered from the effluent of the downstream hydrocracking reaction zone has a reduced aromatic hydrocarbon content compared to the prior art.

Abstract: The safety, convenience and environmental acceptability of starting a two-stage hydrocracking process unit is increased by employing aqueous ammonia as a selective catalyst poison. The aqueous ammonia is injected into the recycle gas system of the hydrocracking process. The invention eliminates the possibility of forming a large airborne cloud of ammonia gas upon an accidental release of the ammonia stream as is possible with the injection of anhydrous ammonia. The invention also stabilizes the operation of the unit through the use of a maintenance injection rate sufficient to maintain an inlet ammonia content above about 40 ppm.