Process for oxidative desulfurization with integrated sulfone decomposition

Abstract

The process provided herein is concerned with disposal of oxidized sulfur compounds formed by oxidative desulfurization. The process uses solid base catalyst pretreated with a base and eliminates the need to separate the sulfones from the hydrocarbon streams and recover the hydrocarbons.

Claims

1. A process for reducing the concentration of oxidized sulfur compounds from a mixture of liquid hydrocarbons and the oxidized sulfur compounds, the process comprising: a. contacting the mixture of hydrocarbons and oxidized sulfur compounds with a solid base catalyst composition in the presence of a caustic solution, the solid base catalyst composition comprising separate components or a mixture of zinc oxide, aluminum oxide, zinc aluminates, layered double hydroxides, and magnesium/aluminum layered double hydroxide, the contacting occurring under conditions effective to promote catalytic decomposition of a portion of the oxidized sulfur compounds into SO.sub.x compounds; b. removing SO.sub.x compounds from the hydrocarbon mixture; and c. recovering a hydrocarbon product having a reduced concentration of oxidized sulfur compounds.

2. The process as in claim 1, wherein the solid base catalyst composition includes a layered double hydroxide of the general formula (I)
ZnAl.sub.2O.sub.4.x(ZnO).y(Al.sub.2O.sub.3)(I) wherein x and y are independently between 0 and 2, and wherein the total proportion of ZnAl.sub.2O.sub.4 in the formula (I) is at least 10 percent by weight.

3. The process as in claim 2, wherein the layered double hydroxide comprises 100% by weight of the solid base catalyst composition.

4. The process as in claim 2, wherein the layered double hydroxide comprises at least 50% by weight of the solid base catalyst composition.

5. The process as in claim 2, wherein the layered double hydroxide comprises at least 1% by weight of the solid base catalyst composition.

6. The process as in claim 1, wherein the solid base catalyst is a porous material in the form of powder, extrudates or spheres.

7. The process as in claim 1, wherein the solid base catalyst has a surface area in the range of from 10 m.sup.2/g to 600 m.sup.2/g.

8. The process as in claim 1, wherein the solid base catalyst has a surface area in the range of from 50 m.sup.2/g to 600 m.sup.2/g.

9. The process as in claim 1, wherein the solid base catalyst has a pore volume in the range of from 0.1 cm.sup.3/g to 0.5 cm.sup.3/g.

10. The process as in claim 1, wherein the solid base catalyst has a pore volume in the range of from 0.3 cm.sup.3/g to 0.5 cm.sup.3/g.

11. The process as in claim 1, wherein the solid base catalyst has a pore distribution of 0.001 microns to 0.1 microns.

12. The process of claim 1, the mixture of hydrocarbons and oxidized sulfur compounds being contacted at a temperature in the range of from 200 C. to 600 C.

13. The process of claim 1, the mixture of hydrocarbons and oxidized sulfur compounds being contacted at a temperature in the range of from 300 C. to 400 C.

14. The process of claim 1, the mixture of hydrocarbons and oxidized sulfur compounds being contacted at a temperature in the range of from 300 C. to 350 C.

15. The process of claim 1, the mixture of hydrocarbons and oxidized sulfur compounds being contacted with the solid base catalyst in the presence of a caustic solution, wherein the base is dissolved in the mixture of hydrocarbons and oxidized sulfur compounds.

16. The process of claim 15, wherein the amount of the caustic solution is in the range of from 0.05 to 30 percent by weight based on the total quantity of solid base catalyst.

17. The process of claim 1, the mixture of hydrocarbons and oxidized sulfur compounds being contacted at a liquid hourly space velocity in the range of from about 0.1 h.sup.1 to about 10 h.sup.1.

18. The process of claim 1, the mixture of hydrocarbons and oxidized sulfur compounds being contacted at a liquid hourly space velocity in the range of from about 0.1 h.sup.1 to about 4 h.sup.1.

19. The process of claim 1, the mixture of hydrocarbons and oxidized sulfur compounds being contacted at a liquid hourly space velocity in the range of from about 0.5 h.sup.1 to about 2 h.sup.1.

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 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 numeral is used to refer to the same or similar elements, in which:

(2) FIG. 1 is a schematic diagram of an integrated desulfurization system and process of disposal of oxidized sulfur compounds formed by oxidative desulfurization; and

(3) FIG. 2 is a schematic diagram of another integrated desulfurization system and process of disposal of oxidized sulfur compounds formed by oxidative desulfurization.

DETAILED DESCRIPTION OF THE INVENTION

(4) A process is provided for reducing the concentration of oxidized sulfur compounds from a mixture of liquid hydrocarbons and oxidized sulfur compounds. For instance, such a mixture is commonly produced by oxidative desulfurization of liquid hydrocarbons.

(5) In one embodiment, the mixture of hydrocarbons and oxidized sulfur compounds are contacted with an effective amount of layered double hydroxide solid catalyst in the presence of a caustic solution.

(6) In another embodiment, the mixture of hydrocarbons and oxidized sulfur compounds is contacted with an effective amount of layered double hydroxide solid catalyst pretreated with a caustic solution.

(7) In both embodiments, the contacting of the mixture of hydrocarbons and oxidized sulfur compounds with the solid catalyst occurs under conditions effective to promote catalytic decomposition of a portion of the oxidized sulfur compounds into SO.sub.x which is subsequently removed. The resulting hydrocarbon product stream has a reduced concentration of oxidized sulfur compounds, and advantageously, the yield of the total liquid hydrocarbon stream is maximized by not removing the entire oxidized sulfur compounds.

(8) While not wishing to be bound by theory, the reaction mechanism at the catalyst for pretreatment or co-treatment shown in Equation [1] is expected:
Al.sub.2O.sub.3+2NaOH.fwdarw.2NaAlO.sub.2+H.sub.2O[1]

(9) The caustic changes the alumina into sodium aluminate, which is the basic material as shown below. Sodium aluminate is the active species. The concentration is stoicmetric. Sufficient quantities are added to the solid catalyst for conversion.

(10) FIG. 1 shows an apparatus 20 for carrying out oxidative desulfurization and sulfone decomposition. Apparatus 20 includes an oxidative desulfurization zone 22 and a sulfone decomposition zone 32. Oxidative desulfurization zone 22 includes a feed inlet 24, an oxidizing agent inlet 26, an oxidizing catalyst inlet 28 and an oxidized effluent outlet 30. Sulfone decomposition zone 32 includes an inlet 34 in fluid communication with oxidized effluent outlet 30, a liquid caustic stream inlet 36, a gas outlet 38 and a desulfurized oil outlet 40.

(11) A hydrocarbon stream is introduced via inlet 24 of the oxidative desulfurization zone 22 and into contact with an oxidizing agent via inlet 26 and an oxidizing catalyst via inlet 28 to oxidize sulfur compounds contained in the hydrocarbon feedstock. The oxidized effluent of oxidative desulfurization zone 22 containing oxidized sulfur compounds and hydrocarbons is discharged via outlet 30 and conveyed to inlet 34 of the sulfone decomposition zone 32 and into contact with an effective amount of solid catalyst and a liquid caustic solution that is introduced to the sulfone decomposition zone 32 via inlet 36. The contacting of the oxidized effluent with solid catalyst and liquid caustic solution occurs under conditions effective to promote catalytic decomposition of a portion of the oxidized sulfur compounds into SO.sub.x which is subsequently removed via outlet 38. The hydrocarbon product stream discharged via outlet 40 has a reduced concentration of oxidized sulfur compounds. The sulfur concentration may be as low as 10 ppmw for distillate fuels, in certain embodiments less than 1 percent by weight (W %) for fuels oil, and in further embodiments less than 0.1 W %.

(12) FIG. 2 shows another apparatus 120 for carrying out oxidative desulfurization and sulfone decomposition. Apparatus 120 includes an oxidative desulfurization zone 122 and a sulfone decomposition zone 132. Oxidative desulfurization zone 122 includes a feed inlet 124, an oxidizing agent inlet 126, an oxidizing catalyst inlet 128 and an oxidized effluent outlet 130. Sulfone decomposition zone 132 includes an inlet 134 in fluid communication with oxidized effluent outlet 130, an optional liquid caustic stream inlet 136, a gas outlet 138 and a desulfurized oil outlet 140.

(13) A hydrocarbon stream is introduced via inlet 124 of the oxidative desulfurization zone 122 and into contact with an oxidizing agent via inlet 126 and an oxidizing catalyst via inlet 128 to oxidize sulfur compounds contained in the hydrocarbon feedstock. The oxidized effluent of oxidative desulfurization zone 122 containing oxidized sulfur compounds and hydrocarbons is discharged via outlet 130 and conveyed to inlet 134 of the sulfone decomposition zone 132 and into contact with an effective amount of pretreated solid catalyst. In certain embodiments, additional caustic solution can be introduced via optional inlet 136 (or mixed with feed via inlet 134) on a continuous or intermittent basis to maintain the caustic level of the pretreated solid catalyst composition. The contacting of the oxidized effluent with pretreated solid catalyst occurs under conditions effective to promote catalytic decomposition of a portion of the oxidized sulfur compounds into SO.sub.x which is subsequently removed via outlet 138. The hydrocarbon product stream discharged via outlet 140 has a reduced concentration of oxidized sulfur compounds. The sulfur concentration may be as low as 10 ppmw for distillate fuels, in certain embodiments less than 1 W % for fuels oil, and in further embodiments less than 0.1 W %.

(14) While it is expected that a substantial portion of the SO.sub.x compounds produced by catalytic decomposition of the oxidized sulfur compounds will be SO.sub.2, in certain reaction conditions, other SO.sub.x compounds will be produced.

(15) The hydrocarbon stream that is subjected to oxidative desulfurization can be naturally occurring fossil fuels such as crude oil, shale oils, coal liquids, intermediate refinery products or their distillation fractions such as naphtha, gas oil, vacuum gas oil or vacuum residue or combination thereof. A suitable feedstock is characterized by a boiling point in the range of about 36 C. to about 1500 C., in certain embodiments in the range of about 80 C. to about 560 C., and in further embodiments in the range of about 180 C. to about 400 C., although one of ordinary skill in the art will appreciated that certain other hydrocarbon streams can benefit from the practice of the system and method of the present invention.

(16) The hydrocarbon feedstream subjected to oxidation in oxidative desulfurization zone can also be an effluent from a hydrodesulfurization zone. In such case, the oxidized effluent from the oxidative desulfurization zone can be fractioned to remove the portion not containing oxidation products, e.g., a fraction boiling below about 320 C. to about 360 C., thereby reducing the requisite flow capacity of the sulfone decomposition zone.

(17) In general, the operating conditions for the oxidative desulfurization zone include a reaction pressure in the range of from about 1 bar to about 30 bars, in certain embodiments about 1 bar to about 10 bars, in further embodiments about 1 bar to about 3 bars; a reaction temperature in the range of from about 20 C. to about 350 C., in certain embodiments about 20 C. to about 150 C., in further embodiments about 45 C. to about 80 C.; a liquid hourly space velocity in the range of from about 0.1 h.sup.1 to about 10 h.sup.1, in certain embodiments about 0.5 h.sup.1 to about 4 h.sup.1, in further embodiments about 1 h.sup.1 to about 2 h.sup.1; and a molar ratio of oxidizing agent-to-sulfur in the range of from about 1:1 to about 100:1, in certain embodiments about 1:1 to about 30:1, and in further embodiments about 1:1 to about 4:1.

(18) In general, the operating conditions for the sulfone decomposition zone include a catalytic decomposition temperature in the range of from about 200 C. to about 600 C., in certain embodiments about 300 C. to about 400 C., in further embodiments about 300 C. to about 350 C.; a catalytic decomposition pressure in the range of from about 1 bar to about 30 bars, in certain embodiments about 1 bar to about 10 bars, in further embodiments about 1 bar to about 3 bars; and a liquid hourly space velocity in the range of from about 0.1 h.sup.1 to about 10 h.sup.1, in certain embodiments about 0.1 h.sup.1 to about 4 h.sup.1, in further embodiments about 0.5 h.sup.1 to about 2 h.sup.1.

(19) In certain embodiments, the pressure in the sulfone decomposition zone is maintained by the hydrocarbon pressure alone, without additional overhead or blanketing gas. The sulfone decomposition zone can be in the form of a fixed, moving, fluidized, ebullated or swing bed system, with a fixed bed catalyst system being preferred in certain embodiments.

(20) The oxidizing agent for use during oxidative desulfurization is selected from liquid hydrogen peroxide and organic peroxides selected from the group consisting of alkyl or aryl hydroperoxides and dialkyl and diaryl peroxides, wherein the alkyl and aryl groups of the respective dialkyl and diaryl peroxides are the same or different. An effective quantity of oxidizing agent is used, which varies with the selected compound(s). For instance, a molar ratio of hydrogen peroxide-to-sulfur is typically at least 4:1 to effectively oxidize organosulfur compounds into their respective oxidized sulfur compounds. In certain embodiment, the quantity of oxidizing agent is selected so that the respective oxidized sulfur compounds are primarily sulfones. Gaseous oxidants, such as air, oxygen, or nitrous oxide may be used. The oxidation catalysts may be homogeneous transition metal catalysts, active species of Mo(VI), W(VI), V(V), Ti(IV), or a combination thereof possessing high Lewis acidity with weak oxidation potential.

(21) The solid catalyst for the sulfone decomposition zone may comprise separate components or a mixture of zinc oxide, aluminum oxide, zinc aluminates, layered double hydroxides such as hydrotalcite, and magnesium/aluminum layered double hydroxide. For example, such a catalyst may be a layered double hydroxide of the general formula ZnAl.sub.2O.sub.4.x(ZnO).y(Al.sub.2O.sub.3), wherein x and y are independently between 0 and 2, and wherein the total proportion of ZnAl.sub.2O.sub.4 in the formula is at least 10 percent by weight. Suitable catalysts are porous material in the form of powder, extrudates or balls. The surface area of solid catalyst is in the range of from about 10 m.sup.2/g to 600 m.sup.2/g, in certain embodiments about 50 m.sup.2/g to about 600 m.sup.2/g. The pore volume of solid catalyst is in the range of from about 0.1 cm.sup.3/g to about 0.5 cm.sup.3/g, in certain embodiments about 0.3 cm.sup.3/g to about 0.5 cm.sup.3/g. The pore distribution of solid catalyst is between 0.001 microns and 0.1 microns.

(22) The effective proportion of layered double hydroxide comprises at least 10 percent by weight of the total composition, in certain embodiments at least 50 percent by weight of the total composition, in further embodiments at least 100 percent by weight of the total composition.

(23) In embodiments in which the solid catalyst is pretreated, suitable liquid caustic solutions include sodium hydroxide or potassium hydroxide. The catalyst can be prepared in-situ or ex-situ. In in-situ preparation, the -alumina solid catalyst is loaded to a reactor which is heated to 320 C. at 1 bar pressure. The liquid caustic solution is passed to the catalyst bed at liquid hourly space velocity in the range of from 0.5 h.sup.1 to 2 h.sup.1 for 3 hours. In ex-situ preparation, the -alumina solid catalyst is prepared in a batch vessel which is heated to 320 C. at 1 bar pressure. The liquid caustic solution is added to the batch vessel in the concentration range of from 0.05 W % to 30 W %. The mixture is stirred for 3 hours.

(24) Accordingly, a system and process is described herein which is capable of efficiently and cost-effectively reducing the organosulfur content of hydrocarbon fuels. Deep desulfurization of hydrocarbon fuels according to the present invention effectively optimizes use of integrated apparatus and processes, combining oxidative desulfurization and sulfur decomposition using solid base catalyst. Using the apparatus and process of the present invention, refiners can adjust existing hydrodesulfurization equipment and run such equipment under mild operating conditions. The use of solid base catalyst eliminates the need to separate the sulfones from the hydrocarbon streams and recover the hydrocarbons. Accordingly hydrocarbon fuels can be economically desulfurized to an ultra-low level.

(25) The present process offers distinct advantages when compared to conventional processes for disposal of oxidized sulfur compounds. For example, in certain conventional approaches, the oxidized sulfur compounds were treated with caustic solution, requiring separation of the sulfones from hydrocarbon streams by extraction and/or adsorption and recover the hydrocarbons. Furthermore, the high operating costs that can negatively impact certain desired fuel characteristics are avoided using the process and apparatus of the present invention.

(26) 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.