GB786358A - Processes for the catalytic cracking of hydrocarbon oils - Google Patents

Abstract

In a two-stage process of cracking a hydrocarbon oil with finely-divided catalyst wherein a fraction, boiling above the gasoline range, of the hydrocarbon products from the 1st cracking zone is cracked in the 2nd cracking zone which is maintained at a lower temperature than the 1st zone, hot freshly-regenerated catalyst is supplied to the 1st zone, the catalyst is separted from the hydrocarbon products formed in the <FORM:0786358/III/1> 1st zone, at least 20 per cent of this once-used catalyst is passed directly to a stripping zone, the remaining part of the once-used catalyst is employed as catalyst in the 2nd cracking zone, the twice-used catalyst separated from the products of 2nd zone is passed to the aforementioned stripping zone, and the stripped catalyst is passed to the regenerator. The process affords efficient stripping of the spent catalyst. A distillate of B.R. 218-538 DEG C. obtained by vacuum-flashing a straight-run residue is passed through line 1 into cracking zone A wherein it is contacted with hot freshlyregenerated silica-alumina catalyst at about 1120 DEG F. supplied through line 18, the catalyst/oil ratio being 12. A temperature of 1020 DEG F. and a pressure of 2.5 atm. are maintained in zone A, and a conversion of 48 per cent is obtained. The total vapour products, free from catalyst, are passed to fractionator 3, and gasoline (+ gas) is separated overhead. The higher boiling oil removed from the base of the fractionator is passed to cracking zone B wherein it is contactd with about 59 per cent by weight of the catalyst withdrawn from zone A via line 6. A temperature of 910 DEG F. and a pressure of 2.2 atm. are maintained in zone B; and a conversion of 28 per cent (based on the fresh feed to the plant) is obtained therein. The total product vapours from zone B are passed to fractionator 8, from which gasoline (+ gas) is taken-off overhead while catalytically-cracked gas oil is withdrawn from the base. This gas oil may be recycled to either zone A or zone B. The spent catalyst from zone B is passed by line 11 to stripping zone C; and the remaining part of the once-used catalyst from zone A is also passed to zone C via line 14. Steam is introduced into zone C through line 12; and a temperature of 955 DEG F. is maintained therein. The hydrocarbons stripped off the mixed catalyst are withdrawn through line 13. The stripped catalyst is regenerated in zone D, air being supplied through line 16; and the regenerated catalyst is then recycled to cracking zone A by line 18. Specification 784,546 is referred to.