Abstract: Potential problems associated with the formation of polynuclear aromatic compounds during hydrocracking of residual oils are eliminated by operating at high conversion rates with a high hydrogen concentration followed by a unique separation method. The feed to the final product recovery column is preferably highly vaporized before or within the column. All of the net bottoms stream of the product recovery column, which is equal to less than 5 vol. percent of the feed, is withdrawn from the process. Only PNA free distillate is recycled.

Abstract: High boiling hydrocarbons are upgraded to products including low aromatic content kerosene or jet fuel in a dual reaction zone process. Feeds such as gas oils are fed to a hydrocracking reactor, with the effluent separated into vapor and liquid fractions. The vapor fraction is partially condensed to yield a liquid comprising kerosene/diesel boiling range hydrocarbons which is charged to a hydrogenation reactor. Liquid recovered from both reactors goes to a common fractionator. Vapor remaining after the partial condensation goes to the hydrogenation zone product separator to recover recycle hydrogen.

Abstract: Potential problems associated with the formation of polynuclear aromatic compounds during hydrocracking of residual oils are eliminated by operating at high conversion rates with a high hydrogen concentration followed by a unique separation method. The feed to the final product recovery column is highly vaporized. All of the net bottoms stream of the product recovery column, which is equal to less than 5 vol. percent of the feed, is withdrawn from the process. Only PNA free distillate is recycled.

Abstract: Problems associated with the formation of polycyclic aromatic compounds within hydrocracking reaction zones are reduced by a feed pretreating sequence which comprises first contacting the feed with a metal-free alumina to produce polycyclic compounds or their precursors followed by their removal by contacting the feed with a bed of adsorbent such as charcoal. The feed pretreatment steps are operated at an elevated temperature but at a very reduced pressure and preferably substantially free of hydrogen.

Abstract: A multiple single-stage process for the conversion of heavy hydrocarbonaceous charge stock into a lower boiling distillate hydrocarbon product. Fresh charge stock and hydrogen are introduced into a first catalytic reaction zone for substantially 100% conversion of the feed. Hydrocracked product effluent from the first hydrocracking reaction zone which comprises a predetermined distillate fraction is passed with an accucracked effluent from a second catalytic hydrocracking or accucracking reaction zone into a separation zone and separated into various hydrocarbon streams including a light hydrocarbon stream comprising the distillate product, a middle hydrocarbon stream and a heavy hydrocarbon stream. The middle hydrocarbon stream comprising said distillate fraction and hydrogen is introduced into the second catalytic hydrocracking or accucracking reaction zone for conversion into a lower boiling accucracked effluent stream comprising the distillate hydrocarbons boiling in the distillate product range.