Patent ID: 7029571

Claim:
A multi stage selective catalytic cracking process, for producing high yield of middle distillate products having carbon atoms in the range of about C 8 to C 24 from heavy hydrocarbon feed stocks in the absence of added hydrogen, said process comprising the steps of: i) contacting preheated feed stock with a mixed catalyst in a first riser reactor under catalytic cracking conditions including catalyst to oil ratio of about 2 to 8, WHSV of about 150–350 hr −1 , contact period of about 1 to 8 seconds and top temperature in the range of about 400° C. to 500° C., to obtain first cracked hydrocarbon products; ii) separating the first cracked hydrocarbon products from the first riser reactor into a first fraction comprising hydrocarbons with boiling points less than or equal to about 370° C. and a second fraction comprising hydrocarbons with boiling points greater than or equal to about 370° C., comprising unconverted hydrocarbons; iii) cracking the second fraction from the first riser reactor comprising hydrocarbons having boiling points greater than or equal to about 370° C., in the presence of regenerated catalyst, in a second riser reactor operating under catalytic cracking conditions including WHSV of about 75–275 hr −1 , catalyst to oil ratio of about 4–12 and riser top temperature of about 425–525° C. to obtain second cracked hydrocarbon products; iv) separating the catalytically cracked products from the second riser reactor along with the cracked products comprising hydrocarbons having boiling points less than or equal to about 370° C., from the first riser reactor to yield cracked products comprising dry gas, LPG, gasoline, middle distillates, heavy cycle oil and slurry oil; and v) recycling substantially the entire heavy cycle oil comprising hydrocarbons having boiling points in the range of about 370° C. to 450° C. and at least part of the slurry oil having boiling points greater than or equal to 450° C., into the second riser reactor at a vertically displaced position lower than the position of introduction of the main feed, comprising bottom unconverted hydrocarbon fraction having boiling points greater than or equal to about 370° C., from the first riser reactor to obtain middle distillate products comprising hydrocarbons having carbon atoms in the range of C 8 –C 24 in a proportion of about 50 to 65 wt % of the feed stock.