Tail-selective hydrocracking of heavy gas oil in diesel production

Hydrocracking of straight run heavy atmospheric gas oil (HAGO) was carried out in a batch high pressure autoclave and fixed-bed high pressure minipilot at 50-55 atm. and temperatures 350-390 degrees C with Ni-Mo-Al catalysts containing zeolite HY, H-ZSM-5 and mixtures of those zeolites. Addition of zeolite H-ZSM-5 to the Ni-Mo-Al-HY catalyst increased its activity significantly beyond corresponding increase of HY zeolite loading. It reduced the 90 and 95% boiling points (BP) of diesel fraction by 17-30 degrees C and pour point (PP) by about 12-20 degrees C depending on zeolite H-ZSM-5 loading and testing conditions. The overall conversion of HAGO with the hi-zeolite catalyst was not additive yielding lower gasoline yields compared to the sum of the yields obtained with mono-zeolite catalysts. Based on GC-MS analysis of the HAGO, tail fractions those effects were attributed to increased conversion of the least reactive paraffins as a result of H-ZSM-5 zeolite addition.