High-severity fluidized catalytic cracking systems and processes having partial catalyst recycle

1. A method for operating a system having a first fluid catalytic cracking (FCC) unit and a second FCC unit for producing products from a hydrocarbon feed stream, the method comprising:

introducing the hydrocarbon feed stream to a feed separator;

separating the hydrocarbon feed stream into a lesser boiling point fraction and a greater boiling point fraction in the feed separator;

passing the greater boiling point fraction to the first FCC unit;

passing the lesser boiling point fraction to the second FCC unit, where the first FCC unit and the second FCC unit are downflow FCC units;

cracking at least a portion of the greater boiling point fraction in the first FCC unit in the presence of a first catalyst at a first cracking temperature of from 500° C. to 700° C. to produce a first cracking reaction product and a spent first catalyst;

cracking at least a portion of the lesser boiling point fraction in the second FCC unit in the presence of a second catalyst and at a second cracking temperature of from 500° C. to 700° C. to produce a second cracking reaction product and a spent second catalyst;

passing the at least a portion of the spent second catalyst to the first FCC unit where the first catalyst comprises the at least a portion of the spent second catalyst and a regenerated catalyst; and

controlling a catalytic activity of the first catalyst in the first FCC unit or the first cracking temperature in the first FCC unit by adjusting a weight ratio of the at least a portion of the spent second catalyst to the regenerated catalyst in the first catalyst;

where the cracking of the at least a portion of the greater boiling point fraction is in the presence of steam, the cracking of the at least a portion of the lesser boiling point fraction is in the presence of steam, or both.

2. The method of claim 1 , where the hydrocarbon feed stream comprises crude oil.

3. The method of claim 1 , where the first FCC unit and the second FCC unit are High-Severity Fluidized Catalytic Cracking (HSFCC) units.

4. The method of claim 3 , where a weight ratio of catalyst to hydrocarbon in the first FCC unit and the second FCC unit is greater than 5 and a residence time in the first FCC unit and the second FCC unit is less than 3 seconds.

5. The method of claim 1 , where the first cracking reaction product or the second cracking reaction product comprises one or more of ethylene, propene, butene, or pentene.

6. A method for operating a system having a first fluid catalytic cracking (FCC) unit and a second FCC unit for producing products from a hydrocarbon feed stream, the method comprising:

introducing the hydrocarbon feed stream to a feed separator;

separating the hydrocarbon feed stream into a lesser boiling point fraction and a greater boiling point fraction in the feed separator;

passing the greater boiling point fraction to the first FCC unit;

passing the lesser boiling point fraction to the second FCC unit, where the first FCC unit and the second FCC unit are downflow FCC units;

cracking at least a portion of the greater boiling point fraction in the first FCC unit in the presence of a first catalyst at a first cracking temperature of from 500° C. to 700° C. to produce a first cracking reaction product and a spent first catalyst;

cracking at least a portion of the lesser boiling point fraction in the second FCC unit in the presence of a second catalyst and at a second cracking temperature of from 500° C. to 700° C. to produce a second cracking reaction product and a spent second catalyst;

passing at least a portion of the spent first catalyst or the spent second catalyst to the first FCC unit;

mixing the at least a portion of the spent first catalyst or spent second catalyst, a regenerated catalyst, and the greater boiling point fraction in a mixing zone positioned upstream of a cracking reaction zone of the first FCC unit, where the first catalyst comprises the regenerated catalyst and the at least a portion of the spent first catalyst or spent second catalyst;

passing the at least a portion of the spent second catalyst to the first FCC unit where the first catalyst comprises the at least a portion of the spent second catalyst and the regenerated catalyst; and

controlling a catalytic activity of the first catalyst in the first FCC unit or the first cracking temperature in the first FCC unit by adjusting a weight ratio of the at least a portion of the spent second catalyst to the regenerated catalyst in the first catalyst,

where the cracking of the at least a portion of the greater boiling point fraction is in the presence of steam, the cracking of the at least a portion of the lesser boiling point fraction is in the presence of steam, or both.

7. The method of claim 6 where the hydrocarbon feed stream comprises crude oil.

8. The method of claim 6 further comprising regenerating a non-recycled portion of the spent first catalyst and a non-recycled portion of the spent second catalyst in a regeneration zone to produce the regenerated catalyst.

9. The method of claim 6 comprising passing the at least a portion of the spent first catalyst to the first FCC unit where the first catalyst comprises the at least a portion of the spent first catalyst and the regenerated catalyst.

10. The method of claim 9 where the first catalyst comprises a weight ratio of the at least a portion of the spent first catalyst to the regenerated catalyst of from 1:99 to 99:1.

11. The method of claim 9 further comprising controlling a catalytic activity of the first catalyst in the first FCC unit or the first cracking temperature in the first FCC unit by adjusting a weight ratio of the at least a portion of the spent first catalyst to the regenerated catalyst in the first catalyst.

12. The method of claim 6 where the first catalyst comprises a weight ratio of the at least a portion of the spent second catalyst to the regenerated catalyst of from 1:99 to 99:1.

13. The method of claim 6 where the first cracking reaction product or the second cracking reaction product comprises one or more of ethylene, propene, butene, or pentene.

14. A method for producing olefins, the method comprising:

separating a hydrocarbon material into a lesser boiling point fraction and a greater boiling point fraction;

cracking at least a portion of the greater boiling point fraction in the presence of a first catalyst in a first FCC unit at a first cracking temperature of from 500° C. to 700° C. to produce a first cracking reaction product and a spent first catalyst;

cracking at least a portion of the lesser boiling point fraction in the presence of a second catalyst in a second FCC unit at a second cracking temperature of from 500° C. to 700° C. to produce a second cracking reaction product and a spent second catalyst;

separating at least a portion of the first cracking reaction product from the spent first catalyst;

separating at least a portion of the second cracking reaction product from the spent second catalyst;

mixing at least a portion of the spent first catalyst or at least a portion of the spent second catalyst, a regenerated catalyst, and the greater boiling point fraction or the lesser boiling point fraction, where the first catalyst comprises at least a portion of the spent first catalyst or at least a portion of the spent second catalyst and the regenerated catalyst, wherein the second catalyst comprises at least a portion of the spent first catalyst or at least a portion of the spent second catalyst and the regenerated catalyst;

passing the at least a portion of the spent second catalyst to the first FCC unit where the first catalyst comprises the at least a portion of the spent second catalyst and the regenerated catalyst;

controlling a catalytic activity of the first catalyst in the first FCC unit or the first cracking temperature in the first FCC unit by adjusting a weight ratio of the at least a portion of the spent second catalyst to the regenerated catalyst in the first catalyst; and

recovering the first cracking reaction product and the second cracking reaction product,

where the cracking of the at least a portion of the greater boiling point fraction is in the presence of steam, the cracking of the at least a portion of the lesser boiling point fraction is in the presence of steam, or both.

15. The method of claim 14 , comprising mixing at least a portion of the spent first catalyst, the regenerated catalyst, and the greater boiling point fraction before cracking the at least a portion of the greater boiling point fraction, wherein the first catalyst comprises the at least a portion of the spent first catalyst and the regenerated catalyst.

16. The method of claim 14 , comprising mixing at least a portion of the spent first catalyst, the regenerated catalyst, and the lesser boiling point fraction before cracking the at least a portion of the lesser boiling point fraction, wherein the second catalyst comprises the at least a portion of the spent first catalyst and the regenerated catalyst.

17. The method of claim 14 , comprising mixing at least a portion of the spent second catalyst, the regenerated catalyst, and the greater boiling point fraction before cracking the at least a portion of the greater boiling point fraction, wherein the first catalyst comprises the at least a portion of the spent second catalyst and the regenerated catalyst.

18. The method of claim 14 , comprising mixing at least a portion of the spent second catalyst, the regenerated catalyst, and the lesser boiling point fraction before cracking the at least a portion of the lesser boiling point fraction, wherein the second catalyst comprises the at least a portion of the spent second catalyst and the regenerated catalyst.