Claims
- 1. A hydrodesulfurization process for the production of low-boiling range, low-sulfur product streams from a petroleum residuum feedstock having a metals content more than 50 p.p.m. and having a sulfur content in excess of 2.0 weight percent where the residuum is passed upwardly through a first reaction zone and through a second reaction zone in succession under isothermal conditions in the presence of hydrogen and under hydrodesulfurization conditions, wherein the temperature in each reaction zone ranges from 650.degree. F. to 850.degree. F.; the pressure in each reaction zone ranges from 1000 to 3500 psia; wherein hydrogen gas is admitted to the first reaction zone in amount of 2000 to 10,000 SCFB and wherein the petroleum residuum is passed through the first reaction zone at a LHSV of 0.16 to 3.0 hr.sup.-1 ; both of the said zones containing a particulate alumina-supported catalyst which is placed in ebullation in the liquid phase environment by the upflow of said residuum and hydrogen and the internal recycle of reactor liquid products, the improvement which comprises:
- (a) in the final reaction zone introducing a fresh, particulate, high activity alumina-supported hydrotreating catalyst containing one or more metals of hydrotreating activity selected from the group consisting of cobalt, molybdenum, tungsten, phosphorus, nickel and vanadium,
- (b) withdrawing spent catalyst from the final reaction zone, said spent catalyst being partially deactivated by metals deposited thereon in the final reaction zone,
- (c) reactivating the spent catalyst by
- (A) stripping process oil from the spent catalyst by washing with a hydrocarbon solvent and drying the washed catalyst thus obtaining free-flowing spent catalyst,
- (B) contacting the free-flowing spent alumina-supported catalyst with steam at a temperature of 1000.degree. to about 1250.degree. F. in a steam treating zone,
- (C) recovering a reactivated alumina supported catalyst from the steam treating zone,
- (d) passing the entire effluent from the first reaction zone to the subsequent final reaction zone;
- (e) passing the reactivated catalyst from the final reaction zone to the first reaction zone,
- (f) withdrawing from the final reaction zone a liquid hydrocarbon stream which can be fractionated to recover the unconverted residuum stream with a boiling range of greater than or equal to 1000.degree. F. and a sulfur content of about 2-3 weight percent which is suitable for blending to a low sulfur fuel oil product.
- 2. The process of claim 1 wherein in step (a) the amount of fresh catalyst introduced to the second reaction zone is about 0.025-0.5 pounds per barrel of residuum introduced into the first reaction zone and in step (b) the amount of spent catalyst withdrawn from the final reaction zone is an amount equal to the amount of fresh catalyst introduced in step (a).
- 3. The process of claim 1 wherein the said hydrotreating catalyst introduced into the final reaction zone contains molybdenum and nickel.
- 4. The process of claim 1 wherein in step (B) the steam temperature ranges from about 1150.degree. to about 1250.degree. F.
- 5. The process of claim 1 wherein in step (B) the spent catalyst is contacted with steam for a period of about 2 to about 5 hours.
- 6. The process of claim 1 wherein before passing the said recovered reactivated catalyst from the final reaction zone to the first reaction zone the said reactivated catalyst is regenerated by contacting the said reactivated catalyst with an oxygen-containing gas at a temperature of about 700.degree. to about 900.degree. F. to remove carbon deposits thereby providing a regenerated catalyst.
- 7. The process of claim 6 wherein prior to regeneration the said regenerated catalyst is treated at a temperature of from 60.degree.-250.degree. F. for at least about 5 minutes with an aqueous solution consisting of sulfuric acid and an ammonium ion whereby the metal contaminants are converted to their respective sulfate compounds and the said metal contaminants removed from the catalyst and afterwards washing the treated catalyst to remove the aqueous solution.
- 8. The process of claim 1 wherein in step (A) the spent catalyst is stripped of process oil by washing with a hydrocarbon solvent selected from the group consisting of toluene, naphtha and mixtures thereof.
- 9. The process of claim 1 wherein in step (A) the spent catalyst is dried at a temperature of less than 250.degree. F. in air or air diluted with nitrogen.
- 10. The process of claim 1 wherein in step (A) the spent catalyst is dried at ambient temperature under vacuum conditions.
- 11. The process of claim 8 wherein in step (A) the spent catalyst is stripped of process oil by washing with toluene at a temperature of about 230.degree. and then dried in air at a temperature of about 250.degree. F.
- 12. The process of claim 1 wherein step (B) the free-flowing spent catalyst prior to being contacted with steam in the steam treating zone is heated to the steaming temperature with flowing nitrogen.
- 13. The process of claim 1 wherein in step (B) the free-flowing spent catalyst prior to being contacted with steam in the steam treating zone is heated to about 1000.degree. to about 1250.degree. F. with flowing nitrogen.
- 14. The process of claim 1 wherein in step (B) the said alumina-supported catalyst is contacted in the steam treating zone with steam diluted with up to 50% nitrogen.
- 15. The process of claim 1 wherein the sulfur content of the residuum feedstock is about 2 to 5 weight percent.
- 16. The process of claim 1 wherein the sulfur content of the residuum feedstock is about 4 to about 5 weight percent.
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of application Ser. No. 08/075,946, filed Jun. 14, 1993, now abandoned. Ser. No. 08/075,946 is a division of application Ser. No. 07/702,480, now U.S. Pat. 5,254,513.
US Referenced Citations (7)
Divisions (1)
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Number |
Date |
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Parent |
702480 |
May 1991 |
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Continuation in Parts (1)
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75946 |
Jun 1993 |
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