Desulfurization of hydrocarbon feed using gaseous oxidant

Abstract

An apparatus and process for desulfurization of hydrocarbon feeds is disclosed in which pure nitrous oxide, or a mixture of nitrous oxide and oxygen or air, is used as a gaseous oxidant. Organosulfur compounds are converted to their corresponding oxides sulfones and/or sulfoxides in an oxidation reactor, and oxides are subsequently removed from the oxidation reactor effluent to recover a reduced sulfur-content hydrocarbon product.

Claims

1. A process for reducing the content of organosulfur compounds in a liquid hydrocarbon feedstream comprising: contacting the feedstream with an oxidation catalyst and an oxidant consisting essentially of nitrous oxide at a temperature of at least 150 C. and in an oxidant-to-feedstream molar ratio of 10:1 to 1:1 to produce oxidized organosulfur compounds; and removing at least a majority of the oxidized organosulfur compounds from the treated feedstream.

2. A process for reducing the content of organosulfur compounds in a liquid hydrocarbon feedstream comprising: contacting the feedstream with an oxidation catalyst and an oxidant consisting essentially of nitrous oxide and a source of gaseous oxygen at a temperature of at least 150 C. and in an oxidant-to-feedstream volumetric ratio of 10:1 to 1:1 to produce oxidized organosulfur compounds; and removing at least a majority of the oxidized organosulfur compounds from the treated feedstream.

3. A process for reducing the content of organosulfur compounds in a liquid hydrocarbon feedstream comprising: forming a nitrous oxide oxidant by reaction of ammonia and oxygen; contacting the feedstream with an oxidation catalyst and an oxidant consisting essentially of the formed nitrous oxide oxidant, or consisting essentially of nitrous oxide and a source of gaseous oxygen, at a temperature of at least 150 C. and in an oxidant-to-feedstream volumetric ratio of 10:1 to 1:1 to produce oxidized organosulfur compounds; and removing at least a majority of the oxidized organosulfur compounds from the treated feedstream.

4. The process of claim 3, wherein forming the nitrous oxide oxidant occurs in situ within a vessel in which oxidation reaction with the feedstream occurs.

5. The process of claim 3, wherein forming the nitrous oxide oxidant occurs upstream of a vessel in which oxidation reaction with the feedstream occurs.

6. The process as in claim 1, wherein removing at least a majority of the oxidized organosulfur compounds comprises extracting oxidized sulfur compounds with a polar solvent to produce a solvent-rich extract containing organosulfur sulfur compounds and a solvent-lean raffinate containing hydrocarbons having a reduced content of organosulfur compounds.

7. The process as in claim 6, further comprising flashing the solvent-rich extract to recover the polar solvent and discharge the oxidized organosulfur compounds.

8. The process as in claim 6, further comprising stripping solvent from the solvent-lean raffinate and recovering hydrocarbons having a reduced organosulfur content.

9. The process as in claim 8, further comprising contacting the recovered hydrocarbons with adsorbent material.

10. The process as in claim 2, wherein removing at least a majority of the oxidized organosulfur compounds comprises extracting oxidized sulfur compounds with a polar solvent to produce a solvent-rich extract containing organosulfur sulfur compounds and a solvent-lean raffinate containing hydrocarbons having a reduced content of organosulfur compounds.

11. The process as in claim 10, further comprising flashing the solvent-rich extract to recover the polar solvent and discharge the oxidized organosulfur compounds.

12. The process as in claim 10, further comprising stripping solvent from the solvent-lean raffinate and recovering hydrocarbons having a reduced organosulfur content.

13. The process as in claim 12, further comprising contacting the recovered hydrocarbons with adsorbent material.

14. The process as in claim 3, wherein removing at least a majority of the oxidized organosulfur compounds comprises extracting oxidized sulfur compounds with a polar solvent to produce a solvent-rich extract containing organosulfur sulfur compounds and a solvent-lean raffinate containing hydrocarbons having a reduced content of organosulfur compounds.

15. The process as in claim 14, further comprising flashing the solvent-rich extract to recover the polar solvent and discharge the oxidized organosulfur compounds.

16. The process as in claim 14, further comprising stripping solvent from the solvent-lean raffinate and recovering hydrocarbons having a reduced organosulfur content.

17. The process as in claim 16, further comprising contacting the recovered hydrocarbons with adsorbent material.

18. The process of claim 1, wherein the oxidation catalyst is a heterogeneous catalyst.

19. The process of claim 18, wherein the heterogeneous catalyst includes a metal from Group IVB to Group VIIIB of the Periodic Table.

20. The process of claim 18, wherein the heterogeneous oxidation catalyst includes a metal selected from the group consisting of Ti, V, Mn, Co, Fe, Cr and Mo.

21. The process of claim 20, wherein the heterogeneous oxidation catalyst includes a support material selected from the group consisting of alumina, silica-alumina, silica, titania, natural zeolites, synthetic zeolites, and combinations comprising one or more of alumina, silica-alumina, silica, titania, natural zeolites, synthetic zeolites.

22. The process of claim 1, wherein the contacting step occurs at reaction conditions including an operating pressure of about 1 bar to about 90 bars.

23. The process of claim 1, wherein the contacting step occurs at reaction conditions including an operating pressure of about 10 bars to about 50 bars.

24. The process of claim 2, wherein the oxidation catalyst is a heterogeneous catalyst.

25. The process of claim 24, wherein the heterogeneous catalyst includes a metal from Group IVB to Group VIIIB of the Periodic Table.

26. The process of claim 24, wherein the heterogeneous oxidation catalyst includes a metal selected from the group consisting of Ti, V, Mn, Co, Fe, Cr and Mo.

27. The process of claim 26, wherein the heterogeneous oxidation catalyst includes a support material selected from the group consisting of alumina, silica-alumina, silica, titania, natural zeolites, synthetic zeolites, and combinations comprising one or more of alumina, silica-alumina, silica, titania, natural zeolites, synthetic zeolites.

28. The process of claim 2, wherein the contacting step occurs at reaction conditions including an operating pressure of about 1 bar to about 90 bars.

29. The process of claim 2, wherein the contacting step occurs at reaction conditions including an operating pressure of about 10 bars to about 50 bars.

30. The process of claim 3, wherein the oxidation catalyst is a heterogeneous catalyst.

31. The process of claim 30, wherein the heterogeneous oxidation catalyst includes a metal from Group IVB to Group VIIIB of the Periodic Table.

32. The process of claim 30, wherein the heterogeneous oxidation catalyst includes a metal selected from the group consisting of Ti, V, Mn, Co, Fe, Cr and Mo.

33. The process of claim 32, wherein the heterogeneous oxidation catalyst includes a support material selected from the group consisting of alumina, silica-alumina, silica, titania, natural zeolites, synthetic zeolites, and combinations comprising one or more of alumina, silica-alumina, silica, titania, natural zeolites, synthetic zeolites.

34. The process of claim 3, wherein the contacting step occurs at reaction conditions including an operating pressure of about 1 bar to about 90 bars.

35. The process of claim 3, wherein the contacting step occurs at reaction conditions including an operating pressure of about 10 bars to about 50 bars.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing summary, as well as the following detailed description of preferred embodiments of the invention will be best understood when read in conjunction with the attached drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and apparatus shown. In the drawings the same numerals are used to refer to the same or similar elements, in which:

(2) FIG. 1 is a schematic diagram of a desulfurization system and process of the present invention that includes gas-phase oxidative desulfurization; and

(3) FIG. 2 is a schematic diagram of a separation apparatus for removing oxidized organosulfur compounds from an oxidized feedstock.

DETAILED DESCRIPTION OF THE INVENTION

(4) The present invention comprehends an oxidative desulfurization process to produce hydrocarbon fuels with a reduced content of organosulfur compounds. The process includes the following steps:

(5) a. contacting a hydrocarbon feedstock containing organosulfur compounds with a gaseous oxidizing agent consisting essentially of pure nitrous oxide (N.sub.2O) or N.sub.2O in combination with oxygen, and a heterogeneous or homogeneous oxidation catalyst, in an oxidation reaction zone to convert the organosulfur compounds into oxidized sulfur-containing compounds; and

(6) b. removing oxidized sulfur-containing compounds in a separation zone by oxidation product removal processes and apparatus that include extraction, distillation, adsorption, or combined processes comprising one or more of extraction, distillation and adsorption.

(7) The hydrocarbon feedstock to be desulfurized according to the present invention can be one or a combination of a variety of feedstocks, including but not limited to whole crude oil; fractional distillates boiling in the range of about 36 C. to about 370 C.; residues boiling above 370 C.; hydrocarbons from intermediate refinery processing units such as coking gas oils, FCC cycle oils, or deasphalted oils; bitumens from tar sands and/or its cracked products; or coal liquids. In certain embodiments, diesel feedstocks are used, as they are relatively easy to handle at mild conditions, and the targeted sulfur molecules such as di-methyl-dibenzothiophene and its derivatives are reactive at oxidation conditions. Their electron structures enable them to react at these mild conditions.

(8) Referring now to FIG. 1, an oxidative desulfurization apparatus 10 according to the present invention is schematically illustrated. Apparatus 10 includes an oxidative desulfurization reaction zone 12 and a separation zone 14. A hydrocarbon stream 16 and a gaseous oxidant stream 18 are introduced to the oxidative desulfurization reaction zone 12 operating at mild operating conditions. As used herein, mild operating conditions include: operating pressures of from about 1 bar to about 90 bars, in certain embodiments about 10 bars to about 50 bars, and in further embodiments about 10 bars to about 30 bars; and temperatures of from about 100 C. to about 400 C., in certain embodiments about 100 C. to about 350 C., and in further embodiments about 150 C. to about 300 C.

(9) In certain embodiments the gaseous oxidizing agent is supplied in gaseous form, and can be:

(10) a. essentially pure nitrous oxide; or

(11) b. a mixture consisting essentially of nitrous oxide and a source of gaseous oxygen, having a nitrous oxide molar concentration ranging from about 1% to about 99%, in certain embodiments about 10% to about 50% and in further embodiments about 20% to about 30%.

(12) In additional embodiments, the gaseous oxidant can be formed in a separate vessel (not shown) upstream of the oxidative desulfurization reaction zone 12, or in situ in the oxidative desulfurization reaction zone 12, e.g. by reaction of ammonia and oxygen.

(13) The oxidation catalyst can be selected from one or more heterogeneous or homogeneous catalysts having metals from Group IVB to Group VIIIB of the Periodic Table, including those selected from of Ti, V, Mn, Co, Fe, Cr and Mo. In certain embodiments, suitable homogeneous catalysts include molybdenum naphthanate, sodium tungstate, molybdenum hexacarbonyl, tungsten hexacarbonyl, and vanadium pentaoxide. In certain embodiments, suitable heterogeneous catalysts include Ti, V, Mn, Co, Fe, Cr and Mo or combination thereof deposited on a support such alumina, silica-alumina, silica, natural zeolites, synthetic zeolites, or combinations comprising one or more of the above supports.

(14) The feedstock, the gaseous oxidizing agent and the oxidation catalyst are maintained in contact for a period of time that is sufficient to complete the oxidation reactions, generally about 1 to about 120 minutes, in certain embodiments about 15 to about 60 minutes and in further embodiments about 30 minutes to about 60 minutes. The reaction conditions of the oxidative desulfurization zone 12 include: an operating pressure of about 1 bar to about 90 bars, in certain embodiments about 10 bars to about 50 bars and in further embodiments at about 10 bars to about 30 bars; and an operating temperature of about 100 C. to about 400 C., in certain embodiments about 150 C. to about 350 C. and in further embodiments about 150 C. to about 300 C.

(15) The catalyst-to-feedstock ratio for homogeneous catalyst systems is generally about 0.01 W % to about 10 W %, in certain embodiments about 0.01 W % to about 5 W %, and in further embodiments about 0.01 W % to about 1 W %. For heterogeneous catalyst systems, the liquid hourly space velocity over the catalyst volume is about 0.1 h-1 to about 8.0 h-1, in certain embodiments about 0.5 h-1 to about 4.0 h-1, and in further embodiments about 1 h-1 to about 2.0 h-1.

(16) The molar feed ratio of gaseous oxidizing agent to sulfur is generally about 10 to about 1, in certain embodiments about 5 to about 1, and in further embodiments about 2 to about 1.

(17) In the oxidative desulfurization zone 12, at least a substantial portion of the sulfur-containing compounds are converted to oxidized sulfur-containing compounds, i.e. sulfones and sulfoxides, and discharged as an oxidized hydrocarbon stream 20.

(18) Stream 20 from the oxidative desulfurization zone 12 is passed to the separation zone 14 to remove the oxidized sulfur-containing compounds as discharge stream 22. In certain preferred embodiments, a hydrocarbon stream 24 is obtained that contains an ultra-low level of sulfur, i.e., less than 15 ppmw. For instance, the oxide content, e.g., sulfones and/or sulfoxides, can be reduced by solvent extraction using polar solvents and adsorption using solid adsorbents.

(19) Stream 22 from the separation zone 14 is passed to sulfones and sulfoxides handling unit (not shown) to recover hydrocarbons free of sulfur, for example, by cracking reactions, thereby increasing the total hydrocarbon product yield. Alternatively, stream 22 can be passed to other refining processes such as coking or solvent deasphalting.

(20) Referring to FIG. 2, the oxidized hydrocarbon stream 20 is introduced generally to the separation zone 14. In particular hydrocarbon stream 20 is passed to a vessel 26 to remove catalyst (if a homogeneous catalyst system is used) and/or water as discharge stream 28 and separate a hydrocarbon mixture stream 30. The hydrocarbon stream 30 is introduced into one end of a counter-current extractor 32, and a solvent stream 34 is introduced into the opposite end. Oxidized sulfur-containing compounds are extracted from the hydrocarbon stream with the solvent as solvent-rich extract stream 38. The solvent stream 34 can include a selective solvent such as methanol, acetonitrile, any polar solvent having a Hildebrandt value of at least 19, and combinations comprising at least one of the foregoing solvents. Acetonitrile and methanol are preferred solvents for the extraction due to their polarity, volatility, and low cost. The efficiency of the separation between the sulfones and/or sulfoxides can be optimized by selecting solvents having desirable properties including, but not limited to boiling point, freezing point, viscosity, and surface tension. The raffinate 36 is introduced into an adsorption column 40 where it is contacted with an adsorbent material such as an alumina adsorbent to produce the finished hydrocarbon product stream 24 that has an ultra-low level of sulfur, which is recovered. The solvent-rich extract 38 from the extractor 32 is introduced into the distillation column 42 for solvent recovery via the overhead recycle stream 44. Stream 22 includes oxidized sulfur-containing compounds, i.e., sulfones and/or sulfoxides.

(21) The present invention offers distinct advantages when compared to conventional processes for desulfurization of hydrocarbon fuel. For example, in certain conventional approaches to oxidative desulfurization, aqueous solutions of oxidant are used to convert organosulfur compounds to their corresponding sulfoxides and/or sulfones, requiring subsequent steps to remove excess oxidant and water from oil. This can be increasingly difficult if the mixture contains water-oil emulsions. However, in the present invention, by using gaseous oxidant, the aqueous content from aqueous oxidants is avoided, thereby minimizing these handling problems.

(22) The method and system of the present invention have been described above and in the attached drawings; however, modifications will be apparent to those of ordinary skill in the art and the scope of protection for the invention is to be defined by the claims that follow.