Fluidized catalytic cracking of paraffinic naphtha in a downflow reactor
A process for producing a product stream consisting primarily of the lower olefins ethylene, propylene and butylenes, and of gasoline is provided. The process includes cracking a mixture of paraffinic naphtha feedstream and regenerated catalyst in a downflow reactor. The reaction product stream is separated from the spent catalyst and subsequently fractionated into individual product streams, while the spent catalyst is regenerated and recycled.
1. A method of enhancing the conversion of a major proportion of a paraffinic naphtha feedstream into lighter hydrocarbon reaction products that include a high proportion of the lower olefins comprising ethylene, propylene and butylenes, and gasoline, the method comprising:
a. introducing a feedstream containing a minimum of 40% by weight of paraffinic naphtha boiling in the range of from 30° C. (86° F.) to 200° C. (392° F.) and containing less than 10% by weight of olefin components, or a feedstream containing a minimum of 60% by weight of combined paraffinic naphtha and naphthenic compounds and containing less than 10% by weight of olefin components into the top of a downflow reactor and mixing it with catalyst;
b. operating the downflow reactor with a residence time of 0.1 seconds to 5 seconds of the mixture of the feedstream and catalyst in a reaction zone at an operating temperature in the range of 480° C. (896° F.) to 700° C. (1292° F.) and with a catalyst-to-feedstream ratio in the range of from 25:1 to 80:1 by weight to produce a reaction product stream that includes the lower olefins comprising ethylene, propylene and butylenes, and gasoline;
c. separating the reaction product stream produced in the downflow reactor from spent catalyst in a stripper zone downstream of the reaction zone;
d. recovering the reaction product stream from the stripper zone;
e. passing spent catalyst from the stripper zone to a regeneration vessel for regeneration with a supplemental source of heat to increase the temperature in the regeneration vessel thereby producing a regenerated catalyst, the regeneration vessel receiving spent catalyst only from the downflow reactor; and
f. recycling the regenerated catalyst to the top of the downflow reactor.
2. The method of claim 1 , wherein the paraffinic naphtha feedstream is subjected to preheating to a temperature in the range of from 150° C. (302° F.) to 315° C. (599° F.) prior to its introduction into the reaction zone.
3. The method of claim 2 in which the feedstream is preheated in a heat exchanger or a furnace.
4. The method of claim 1 , wherein the residence time in the reaction zone is in the range of from 0.2 seconds to 2 seconds.
5. The method of claim 1 in which the downflow reactor is operated continuously.
6. The method of claim 1 in which the reaction product stream is separated from the spent catalyst in a cyclonic separation apparatus.
7. The method of claim 1 , further comprising applying a quenching fluid to the reaction product stream and the catalyst at a location downstream of the reaction zone.
8. The method of claim 1 , further comprising stripping the spent catalyst downstream of the reaction zone with steam.
9. The method of claim 1 , wherein the regeneration vessel includes a catalyst lift riser into which heated combustion air is passed to support combustion and provide lift.
10. The method of claim 9 in which the regeneration vessel includes a dense phase bed to which additional heated combustion air is added.
11. The method of claim 1 in which the quantity of coke formed on the spent catalyst is insufficient to raise the temperature of the regenerated catalyst exiting the regeneration vessel to the operating temperature range; and the method further comprises adding a liquid fuel to the catalyst in the stripper zone.
12. The method of claim 10 in which the regeneration vessel includes a dense phase bed, and the method further comprises introducing a liquid fuel and/or fuel gas as the supplemental heat source into the dense phase bed and burning the fuel to thereby raise the temperature of the regenerated catalyst.
13. A method of enhancing the conversion of a major proportion of a paraffinic naphtha feedstream into lighter hydrocarbon reaction products that include a high proportion of the lower olefins comprising ethylene, propylene and butylenes, and gasoline, the method comprising:
a. introducing a first feedstream containing a minimum of 40% by weight of paraffinic naphtha boiling in the range of from 30° C. (86° F.) to 200° C. (392° F.) and containing less than 10% by weight of olefin components, or a first feedstream containing a minimum of 60% by weight of combined paraffinic naphtha and naphthenic compounds and containing less than 10% by weight of olefin components into the top of a downflow reactor and mixing it with catalyst;
b. operating the downflow reactor with a residence time of 0.1 seconds to 5 seconds of the mixture of the feedstream and catalyst in a first reaction zone at an operating temperature in the range of 480° C. (896° F.) to 700° C. (292° F.) and with a catalyst-to-feedstream ratio in the range of from 25:1 to 80:1 by weight to produce a first reaction product stream that includes the lower olefins comprising ethylene, propylene and butylenes, and gasoline;
c. separating the first reaction product stream produced in the downflow reactor from spent catalyst in a first stripper zone downstream of the first reaction zone;
d. recovering the first reaction product stream from the first stripper zone;
e. directing a second feedstream comprising at least a portion of the gasoline contained in the first reaction product stream into an ancillary downflow reactor;
f. operating the ancillary downflow reactor with a residence time of 0.1 seconds to 5 seconds of the mixture of the second feedstream and catalyst in a second reaction zone at an operating temperature in the range of 480° C. (896° F.) to 700° C. (1292° F.) and with a catalyst-to-feedstream ratio in the range of from 25:1 to 80:1 by weight to produce a second reaction product stream that includes the lower olefins comprising ethylene, propylene and butylenes, and gasoline
g. separating the second reaction product stream produced in the ancillary downflow reactor from spent catalyst in a second stripper zone downstream of the second reaction zone;
h. passing spent catalyst from the first and second stripper zones to a regeneration vessel for regeneration with a supplemental source of heat to increase the temperature in the regeneration vessel thereby producing a regenerated catalyst, the regeneration vessel receiving spent catalyst from the first and second stripper zones; and
i. recycling the regenerated catalyst to the top of the downflow reactor and the top of the ancillary reactor.
14. The method of claim 13 , wherein the residence time in the first reaction zone or the second reaction zone is in the range of from 0.2 seconds to 2 seconds.
15. The method of claim 14 in which the first feedstream to the downflow reactor or the second feedstream to the ancillary downflow reactor is preheated in a heat exchanger or a furnace.
16. The method of claim 13 in which the downflow reactor or the ancillary downflow reactor is operated continuously.
17. The method of claim 13 in which the first reaction product stream or the second reaction product stream is separated from the spent catalyst in a cyclonic separation apparatus.
18. The method of claim 13 , further comprising applying a quenching fluid to the first reaction product stream and its catalyst at a location downstream of the first reaction zone or to the second reaction product stream and its catalyst at a location downstream of the second reaction zone.
19. The method of claim 13 , further comprising stripping the spent catalyst downstream of the first reaction zone or the second reaction zone with steam.
20. The method of claim 13 , wherein the regeneration vessel includes a catalyst lift riser into which heated combustion air is passed to support combustion and provide lift.
21. The method of claim 20 in which the regeneration vessel includes a dense phase bed to which additional heated combustion air is added.
22. The method of claim 13 in which the quantity of coke formed on the spent catalyst is insufficient to raise the temperature of the regenerated catalyst exiting the regeneration vessel to the operating temperature range, and the method further comprises adding a liquid fuel to the catalyst in the stripper zone.
23. The method of claim 21 in which the regeneration vessel includes a dense phase bed, and the method further comprises introducing a liquid fuel and/or fuel gas as the supplemental heat source into the dense phase bed and burning the liquid fuel and/or fuel gas to thereby raise the temperature of the regenerated catalyst.