HIGH METALS CONTENT HYDROLYSIS CATALYST FOR USE IN THE CATALYTIC REDUCTION OF SULFUR CONTAINED IN A GAS STREAM, AND A METHOD OF MAKING AND USING SUCH COMPOSITION

Abstract

Disclosed is a composition useful in the hydrolysis of sulfur compounds that are contained in a gas stream. The composition comprises a calcined co-mulled mixture of psuedoboehmite, a cobalt compound, and a molybdenum compound such that the composition comprises gamma-alumina, at least 7.5 wt. % molybdenum, and at least 2.75 wt. % cobalt. The composition is made by forming into an agglomerate a co-mulled mixture pseudoboehmite, a cobalt component, and a molybdenum component followed by drying and calcining the agglomerate to provide a catalyst composition comprising gamma-alumina, at least 7.5 wt. % molybdenum, and at least 2.75 wt. % cobalt.

Claims

1. A catalyst composition useful in the catalytic reduction of sulfur compounds contained in a gas stream, wherein said catalyst composition comprises: a formed agglomerate of a comulled mixture, comprising pseudoboehmite, a cobalt compound and a molybdenum compound, wherein said formed agglomerate has been calcined to provide said catalyst composition, comprising gamma-alumina, at least 7.5 wt. % molybdenum; and at least 2.75 wt. % cobalt, wherein each wt. % is based on the total weight of said catalyst composition and the metal as an oxide regardless of its actual form.

2. A catalyst composition as recited in claim 1, wherein said catalyst composition has a bimodal pore structure such that less than 6 percent of the total pore volume of said catalyst composition is contained within pores having a pore diameter greater than 10,000 Å.

3. A catalyst composition as recited in claim 2, wherein said bimodal pore structure of said catalyst composition is further characterized such that greater than 15% and less than 60% of the total pore volume of said catalyst composition is contained within pores having a pore diameter in the range of from 50 Å to 150 Å.

4. A catalyst composition as recited in claim 3, wherein said bimodal pore structure of said catalyst composition is further characterized such that greater than 10% and less than 50% of the total pore volume of said catalyst composition is contained within pores having a pore diameter in the range of from 1000 Å to 10,000 Å.

5. A catalyst composition as recited in claim 4, wherein said bimodal pore structure of said catalyst composition is further characterized such that less than 15% of the total pore volume of said catalyst composition is contained within pores having a pore diameter in the range of from 150 Å to 1000 Å.

6. A catalyst composition as recited in claim 5, wherein said catalyst composition is further characterized such that the ratio of the total pore volume contained within its pores having a diameter of greater than 10,000 Å to the total pore volume contained within its pores having a diameter of greater than 1,000 Å is less than 0.6.

7. A catalyst composition as recited in claim , wherein said catalyst composition comprises from 7.75 to 15 wt. % molybdenum and from 2.85 wt. % to 6 wt. % cobalt.

8. A catalyst composition as recited in claim 7, wherein said bimodal pore structure of said catalyst composition is such that greater than 20% and less than 50% of the total pore volume of said catalyst composition is contained within pores having a pore diameter in the range of from 50 Å to 150 Å; less than 13% of the total pore volume of said catalyst composition is contained within pores having a pore diameter in the range of from 150 Å to 1000 Å; greater than 12% and less than 45% of the total pore volume of said catalyst composition is contained within pores having a pore diameter in the range of from 1000 Å to 10,000 Å; and less than 6 percent of the total pore volume of said catalyst composition is contained within pores having a pore diameter greater than 10,000 Å.

9. A hydrolysis process, comprising: introducing a gas stream, comprising a sulfur compound or carbon monoxide, or both, into a reactor that defines a reaction zone containing a catalyst composition and operated at suitable reaction conditions; and contacting said gas stream with said catalyst composition, wherein said catalyst composition comprises a formed agglomerate of a comulled mixture, comprising pseudobohemite, a cobalt compound and a molybdenum compound, wherein said comulled mixture has been calcined to provide said catalyst composition, comprising gamma-alumina, at least 7.5 wt. % molybdenum; and at least 2.75 wt. % cobalt, wherein each wt. % is based on the total weight of said catalyst composition and the metal as an oxide regardless of its actual form.

10. A process as recited in claim 9, wherein said sulfur compound is present in said gas stream at a sulfur compound concentration in the range of from 0.01 volume % to 2 volume %, and wherein said sulfur compound is selected from the group of compounds consisting of carbonyl sulfide (COS), carbon disulfide (CS.sub.2), sulfur dioxide (SO.sub.2), and elemental sulfur (S.sub.x).

11. A process as recited in claim 10, wherein said suitable reduction reaction conditions include an inlet temperature to said reactor that is in the range of from 115.degree. C. to 300.degree. C.

12. A process as recited in claim 11, wherein said reduced concentration of sulfur compound in said treated gas is less than 75 ppmv.

13. A method of making a catalyst composition useful in the catalytic reduction of sulfur compounds or carbon monoxide, or both, contained in a gas stream, wherein said method comprises: mixing pseudoboehmite, a cobalt component and a molybdenum component to form a comulled mixture; forming said comulled mixture into a formed agglomerate; and drying and calcining said formed agglomerate to provide said catalyst composition, comprising gamma-alumina, at least 7.5 wt. % molybdenum; and at least 2.75 wt. % cobalt, wherein each wt. % is based on the total weight of said catalyst composition and the metal as an oxide regardless of its actual form.

14. A method as recited in claim 13, wherein said mixing step includes comulling with said pseudoboehmite a first aqueous solution of said cobalt component and a second aqueous solution of said molybdenum component.

15. A method as recited in claim 14, wherein prior to mixing said first aqueous solution and said second aqueous solution with said pseudoboehmite in said mixing step, said pseudoboehmite in powder form is mixed with water and nitric acid to form a plastic mixture having a loss on ignition in the range of from 40% to 80%, and, thereafter, said plastic mixture, said first aqueous solution and said second aqueous solution are comulled to thereby form said comulled mixture.

16. A method as recited in claim 15, wherein said first aqueous solution comprises cobalt nitrate dissolved in water and said second aqueous solution comprises ammonium dimolybdate dissolved in water.

Description

EXAMPLE I

[0063] This Example I illustrates the preparation of the inventive catalyst composition and of the comparison catalyst.

[0064] Inventive Catalyst Composition

[0065] An embodiment of the inventive catalyst composition was prepared by mulling a wide pore alumina powder, which comprised primarily psuedoboehmite, with nitric acid, and water in such proportions as to provide a plastic mixture, e.g., an extrudable mixture, having a water content such that its loss on ignition is around 61%. An aqueous cobalt solution, including cobalt, was prepared by dissolving cobalt nitrate in water and an aqueous molybdenum solution, including molybdenum, was prepared by dissolving ammonium dimolybdate in water with 30% hydrogen peroxide. The two metal solutions were added to the mulling mixture and, after mixing for a period of time, a small percentage of ammonium hydroxide was mixed with the mulling mixture. The resulting mixture was then extruded through 3.2 mm trilobe extrusion dies, and the extrudates were dried and calcined. The finished catalyst composition included alumina that was predominately in the gamma form, 9.4 wt. % molybdenum, and 3.6 wt. % cobalt. The wt. % of the metals is based on the total weight of the finished catalyst with the metals in the oxide form.

Comparison Catalyst Composition A

[0066] Comparison Catalyst Composition A was prepared in a similar manner as was the inventive catalyst with the exception that the concentrations of the metals were substantially lower than those of the inventive catalyst composition. The finished comparison catalyst composition A contained 7.2 wt. % molybdenum and 2.5 wt. % cobalt.

Comparison Catalyst Composition B

[0067] An impregnation solution was prepared by mixing aqueous ammonia, ammonium di-molybdate and cobalt hydroxide in amounts such as to target in the finished catalyst 8.5 wt. % molybdenum (on an elemental basis) and 3.3 wt. % cobalt (on an elemental basis). This mixture was heated to 45° C. and an amount of monoethanolamine (MEA) of from 1.2 to 1.5 moles MEA per mole cobalt was added to the mixture. The mixture was stirred while maintaining the temperature until the metal salts were digested. The solution was then cooled to approximately 30° C. and topped-off with water so as to provide a total volume of solution that approximated the pore volume of the alumina spheres which were to be impregnated with the solution. Alumina spheres or beads having a nominal diameter of 4 mm were impregnated with the solution and aged for two hours with occasional mixing to prevent agglomeration. The impregnated alumina spheres were dried in a convection oven at a temperature of 125° C. for one hour. The dried spheres were calcined in a muffle furnace at a temperature of 538° C. for one hour.

EXAMPLE II

[0068] This Example II illustrates the use of the catalysts described in Example I in the hydrolysis of a gas stream containing a concentration of at least one sulfur compound and presents performance data for the catalysts.

[0069] The catalysts of Example I were performance tested using a tail gas pilot unit reactor equipped with a tube furnace used to control the reactor temperature. In preparation for the activity testing, each respective catalyst was sulfided by introducing into the reactor 3 hours at 300° C. and a 467 GHSV a feed comprising H.sub.2S and H.sub.2. A synthetic tail gas that included H.sub.2S, SO.sub.2, COS, CS.sub.2, S, H.sub.2, CO, N.sub.2, and steam, and having the typical composition as shown in Table 2, was then charged to the tail gas reactor, operated at various reactor temperatures, at a rate so as to provide a 2052 nGHSV (normal gas hourly space velocity, 3 psi unit pressure).

TABLE-US-00002 TABLE 2 Typical Feed Composition Component Mole % H.sub.2 2 CO.sub.2 7 H.sub.2S 0.8 CO 1 COS 0.025 SO.sub.2 0.4 CH.sub.3SH 0 CS.sub.2 0.025 CH.sub.4 0 H.sub.2O 26 S 0 N.sub.2 62.75

[0070] The composition of the reactor effluent for each of the reactor temperature conditions was analyzed using gas chromatography. The results from the testing are presented in the following Tables 3-6, which are further illustrated by the bar charts of FIG. 1 and FIG. 2.

TABLE-US-00003 TABLE 3 Unconverted COS in the Reactor Effluent Uncoverted Uncoverted Unconverted Reactor COS - COS - COS - Isothermal Inventive Comparison Comparison Improvement Temp Catalyst Catalyst A Catalyst B vs. Catalyst B (° C.) (ppmv) (ppmv) (ppmv) (%) 260 12 11 20 40 240 14 30 34 59 220 44 284 147 70 200 154 281 144 −7

TABLE-US-00004 TABLE 4 Unconverted CO in the Reactor Effluent Uncoverted Uncoverted Unconverted Reactor CO - COS - CO - Isothermal Inventive Comparison Comparison Improvement Temp Catalyst Catalyst A Catalyst B vs. Catalyst B (° C.) (wt %) (wt %) (wt %) (%) 260 0.018 0.041 0.030 38 240 0.023 0.072 0.045 50 220 0.037 0.405 0.139 74 200 0.302 0.563 0.257 −17

TABLE-US-00005 TABLE 5 K-Values for COS Hydrolysis Reaction Reactor RVA Isothermal Inventive Comparison Comparison Improvement Temp Catalyst Catalyst A Catalyst B vs. Catalyst A (° C.) (k-value) (k-value) (k-value) (%) 260 2.8 3.0 2.3 −7 240 2.4 1.9 1.6 26 220 1.2 0 0.4 ∞ 200 0.4 0 0.4 ∞

TABLE-US-00006 TABLE 6 K-Values for CO Water Gas Shift Reaction Reactor RVA Isothermal Inventive Comparison Comparison Improvement Temp Catalyst Catalyst A Catalyst B vs. Catalyst A (° C.) (k-value) (k-value) (k-value) (%) 260 3.4 3.2 28 240 2.7 2.4 42 220 1.6 0.8 188 200 1.1 0.5 100

[0071] The data presented in the above Tables show that the inventive catalyst exhibits enhanced catalytic performance over the comparative low-metals, co-mulled catalyst composition and the comparative impregnated catalyst composition.

[0072] It is demonstrated that the reaction rate constant provided by the inventive catalyst for the carbonyl sulfide hydrolysis reaction at the lower temperatures in comparison to that of Catalyst A is significantly higher and that this rate constant at the higher reaction temperature is relatively unchanged. In a comparison to Catalyst B, the COS hydrolysis reaction rate constant provided by the inventive catalyst is significantly higher at all reaction temperatures with the exception of the very low temperature of 200° C., at which temperature, the rate constants provided by the two catalysts are substantially equivalent.

[0073] As a result of the higher COS hydrolysis reaction rate constant provided by the inventive catalyst, a much reduced concentration of unconverted carbonyl sulfide is yielded with the treated gas stream as compared to that which results with the comparison catalysts. This reduced concentration of unconverted carbonyl sulfide results with the use of the inventive catalyst even at the lower or reduced reaction temperatures.

[0074] FIG. 1 shows the data presented in Table 3 in the form of a bar chart, and it helps illustrate the enhanced performance characteristics of the inventive catalyst when compared to the low-metals, co-mulled catalyst composition (Catalyst A) and the impregnated catalyst (Catalyst B).

[0075] The inventive catalyst composition also exhibits improved reaction performance for the carbon monoxide water-gas shift equilibrium reaction when compared to the performance of the comparison catalysts. The reaction rate constant provided by the inventive catalyst is significantly improved for all temperatures when compared with that provided by Catalyst A. And, when the rate constant is compared against Catalyst B, the inventive catalyst provides for a greater reaction rate constant at all temperatures except the very lowest of the temperature at which the rate constants are closely equivalent.

[0076] The higher water-gas rate constant provides for a much reduced concentration of unconverted carbon monoxide that is yielded with the treated gas stream as compared to that which results with the comparison catalyst. The higher rate constant allows for the operation of the reactor at low reaction temperatures.

[0077] FIG. 2 shows the data presented in Table 4 in the form of a bar chart, and it helps illustrate the enhanced performance characteristics of the inventive catalyst when compared to the low-metals, co-mulled catalyst composition and the impregnated catalyst.