GB642325A - Improvements relating to the catalytic cracking of heavy hydrocarbons - Google Patents

Abstract

<PICT:0642325/III/1> Hydrocarbon oils boiling above the gas oil range are cracked catalytically at a relatively high space velocity to give a high yield of gas oil which is withdrawn from the system; and the cracked residue boiling above the gas oil range is passed, at a relatively low space velocity, through a second catalytic cracking stage where a high yield of good quality gasoline is obtained. The gas oil separated after the first stage may be used as Diesel fuel. An Iranian wax distillate is cracked, in the presence of steam, in reactor 11 which contains a synthetic silica-alumina catalyst at 900 DEG F., the space velocity being 10.3 expressed as weight of oil per hour per unit weight of catalyst, and the reactor-outlet gauge-pressure being 10 lbs. per square inch. The products are passed to fractionator 13 where gasoline and higher hydrocarbons are withdrawn overhead, and gas oil of Diesel index 20 is taken off through line 15. The residue boiling above the gas oil range is separated as bottoms through line 16, and passed (diluted with steam) at a space velocity of 0.81 through catalytic reactor 20 where the same temperature and pressure are maintained as in reactor 11. The products are passed to fractionator 22 from which gasoline and higher hydrocarbons are withdrawn overhead, and gas oil of Diesel index 7 is withdrawn through line 24. The gasoline head fractions from fractionators 13 and 22 may either be stabilized separately, in fractionators 17 and 27, to give gasoline with octane numbers 77 and 81 respectively. Or the two fractions may be united via line 25 and stabilized in fractionator 17 to give a single product of octane number 79. Fluidized catalyst may be used in both reactors, the second reactor being operated with bottom catalyst draw-off, while the first is preferably operated by the upflow method in order to deal conveniently with the high linear velocities.