Hydrocracking of heavy hydrocarbon oils with heavy hydrocarbon recycle

A process for hydrocracking a heavy hydrocarbon oil feedstock, a substantial portion of which boils above 524.degree. C., which comprises:

• (a) passing a slurry feed of (1) fresh heavy hydrocarbon oil feedstock and a heavy hydrocarbon recycle and (2) from about 0.01-4% by weight (based on fresh feedstock) of iron sulphate additive particles having sizes less than 45 .mu.m with at least 50% by weight of the particles having sizes less than 10 .mu.m, upwardly through a confined vertical hydrocracking zone, said hydrocracking zone being maintained at a temperature between about 350.degree. and 600.degree. C., a pressure of at least 3.5 MPa and a space velocity of up to 4 volumes of fresh .hydrocarbon oil per hour per volume of hydrocracking zone capacity,
• (b) removing from the top of said hydrocracking zone a mixed effluent containing a gaseous phase comprising hydrogen and vaporous hydrocarbons and a liquid phase comprising heavy hydrocarbons,
• (c) passing said mixed effluent into a hot separator vessel,
• (d) withdrawing from the top of the separator a gaseous stream comprising hydrogen and vaporous hydrocarbons,
• (e) withdrawing from the bottom of the separator a liquid heavy hydrocarbon stream comprising heavy hydrocarbons and particles of the iron sulphate additive converted mainly to an iron sulphide phase,
• (f) fractionating the separated liquid heavy hydrocarbon stream to obtain a heavy oil which boils above 450.degree. C., said heavy oil containing said additive particles, and
• (g) recycling said fractionated heavy oil containing said additive particles to and mixing with the hydrocracking zone feed slurry in an amount up to 40% by weight of the combined feed slurry.