GB737085A - Improvements relating to the catalytic cracking of petroleum hydrocarbons - Google Patents

Abstract

<PICT:0737085/III/1> Sulphurous petroleum fractions boiling in the wax distillate boiling range are hydrofined by contacting the fraction in the presence of hydrogen and at a temperature of 780 DEG F. and a pressure of 1000 p.s.i.g. with a catalyst consisting of the combined oxides of cobalt and molybdenum deposited on alumina; the hydrofined fraction is then subjected to catalytic cracking. An alternative embodiment comprises subjecting to catalytic cracking a feedstock boiling in the wax distillate boiling range obtained from a hydrofined crude petroleum oil. A synthetic silica-alumina or silica-magnesia catalyst may be used in the cracking stage, or a natural cracking catalyst may be used. Wax distillate (B.R. 280-580 DEG C.) containing 1.7 per cent sulphur is passed through line 10 into heater 11, where it is heated to 750 DEG F. The oil is then mixed with recycle gas stream, containing hydrogen, leaving heater 12 via line 13 at 1100 DEG F. The combined oil/gas stream, which has a temperature of 800 DEG F., is passed through line 14 into chamber 15 which is filled with bauxite to remove vanadium and sodium from the oil. The oil/gas stream is then passed into reactor 16 which contains cobalt molybdate at 780 DEG F. The products from the reactor are passed to hot separator 18. The separated liquid (containing only 0.06 per cent sulphur) is taken via line 19 to the bottom of pipe 47 where it picks up hot regenerated silica-alumina catalyst from regenerator 24; the mixture then flows into reactor 21 where the catalyst is maintained as a fluidized bed at a temperature of 930 DEG F. Entrained catalyst is separated from the reaction products in cyclone 25; and the products are passed via line 26 to fractionating tower 27. Settled slurry from the base of tower 27 is returned to the reactor via lines 28 and 19. Decanted oil from the top of the settling section of the tower is withdrawn via line 29; and heavy and light gas oils are taken off as side streams via lines 30 and 31 respectively and steam strippers 32. Gas and gasoline are taken overhead to separator 34 from which gas and liquid streams are taken via lines 35 and 36 respectively to the gas recovery plant, some liquid also being returned to tower 27 as reflux. The yield of gasoline is 45 per cent. The vapours from hot separator 18 are passed via cooler 39 to cold separator 40 from which liquid is passed to tower 27. The gases from separator 40 are scrubbed in scrubber 43 with lean oil from the gas recovery plant. Hydrogen-enriched gas from scrubber 43 is recycled to reactor 16 via line 45; and the rich oil is returned to the gas recovery plant via line 46. Specifications 632,193 and 653,320 are referred to.