METHOD FOR PRODUCING BETA-COBALT MOLYBDENUM OXIDE CATALYST HAVING ENHANCED SELECTIVITY FOR THE PRODUCTION OF C3-C4 ALCOHOLS AND CATALYST OBTAINED THEREBY

Abstract

Methods for producing cobalt/molybdenum catalysts having enhanced selectivity for the production of C.sub.3-C.sub.4 alcohols. The catalyst production methods allow for the selective production of beta-phase catalysts over alpha-phase catalysts. The catalyst is a calcined composition comprising: -CoxMoyOz, wherein x ranges from 0.5 to 2.0, y ranges from 0.5 to 2.0, and z ranges from 3.5 to 4.5, wherein said calcined composition is essentially free of catalytically-active amounts of beta-molybdenum carbide (-Mo2 C), and wherein said calcined composition is essentially free of catalyst-promoting amounts of an alkaline metal promoter or alkaline earth metal promoter.

Claims

1. A calcined composition comprising: -Co.sub.xMo.sub.yO.sub.z, wherein x ranges from 0.5 to 2.0, y ranges from 0.5 to 2.0, and z ranges from 3.5 to 4.5, wherein said calcined composition is essentially free of catalytically-active amounts of beta-molybdenum carbide (-Mo.sub.2C), and wherein said calcined composition is essentially free of catalyst-promoting amounts of an alkaline metal promoter or alkaline earth metal promoter.

2. The calcined composition of claim 1, wherein the composition exhibits a synthesis gas conversion of at least 10%.

3. The calcined composition of claim 1, wherein the composition exhibits a cumulative C.sub.3-C.sub.4 alcohols selectivity of at least 35%.

4. A process for conversion of a synthesis gas stream into a product stream comprising C.sub.3-C.sub.4 alcohols, said process comprising: exposing said synthesis gas stream to a calcined composition under conditions suitable to convert at least 10% of the synthesis gas stream with at least 35% selectivity for C.sub.3-C.sub.4 alcohols, wherein said calcined composition comprises -Co.sub.xMo.sub.yO.sub.z, with x ranging from 0.5 to 2.0, y ranging from 0.5 to 2.0, and z ranging from 3.5 to 4.5, wherein said calcined composition is essentially free of catalytically-active amounts of beta-molybdenum carbide (-Mo.sub.2C), and wherein said calcined composition is essentially free of catalyst-promoting amounts of an alkaline metal promoter or alkaline earth metal promoter.

5. The process of claim 4, wherein suitable conditions comprise a reaction pressure ranging from 50 to 100 bar.

6. The process of claim 4, wherein suitable reaction conditions comprise a reaction temperature ranging from 150 to 450 C.

7. The process of claim 4, wherein suitable reaction conditions comprise a synthesis gas CO:H.sub.2 ratio ranging from 0.8:1 to 1.2:1.

8. A method for making a -phase catalyst capable of producing C.sub.3-C.sub.4 alcohols from a synthesis gas stream with at least 25% conversion and at least 50% selectivity, the method comprising: a) preparing a solution comprising a cobalt salt and a molybdenum salt and collecting a precipitate from the solution; b) drying the precipitate to give a dried precipitate comprising one or more hydrates of cobalt molybdenum oxide; c) pelleting the dried precipitate to produce pellets; and d) calcining the pellets to generate the -phase catalyst, wherein the pellets are not subjected to mechanical deformation subsequent to calcination.

9. The method of claim 8, wherein the cobalt salt is cobalt acetate.

10. The method of claim 8, wherein the molybdenum salt is ammonium heptamolybdate.

11. The method of claim 8, wherein the solution comprising a cobalt salt and a molybdenum salt comprises a binary solvent.

12. The method of claim 11, wherein the binary solvent comprises preferably from 10 to 30% ethanol and from 70 to 90% water, vol:vol.

13. The method of claim 8, wherein the precipitate is dried at a temperature ranging from 70 to 150 C.

14. The method of claim 8, wherein the precipitate is dried for a period of time ranging from 2 to 6 hours.

15. The method of claim 8, wherein the pellets are calcined at a temperature ranging from 300 to 700 C.

16. The method of claim 8, wherein the pellets are calcined for a period of time ranging from 2 to 6 hours.

17. The calcined composition of claim 2, wherein the composition exhibits a cumulative C.sub.3-C.sub.4 alcohols selectivity of at least 35%.

18. The method of claim 9, wherein the precipitate is dried for a period of time ranging from 2 to 6 hours.

19. The method of claim 9, wherein the pellets are calcined at a temperature ranging from 300 to 700 C.

20. The method of claim 9, wherein the pellets are calcined for a period of time ranging from 2 to 6 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0021] FIG. 1 is graph depicting CO conversion and product selectivity profile for batch 1 of powdered -CoMoO.sub.4.

[0022] FIG. 2 is graph depicting CO conversion and product selectivity profile for batch 2 of powdered -CoMoO.sub.4.

[0023] FIG. 3 is a graph depicting CO conversion and product selectivity profile for -CoMoO.sub.4 in powdered form.

[0024] FIG. 4 is a graph depicting CO conversion and product selectivity profile for -CoMoO.sub.4 in pellet form.

[0025] FIG. 5 is a graph depicting CO conversion and product selectivity profile for batch 1 of -CoMoO.sub.4 in pellet form.

[0026] FIG. 6 is a graph depicting CO conversion and product selectivity profile for batch 2 of -CoMoO.sub.4 in pellet form.

[0027] FIG. 7 is a graph depicting CO conversion and product selectivity profile for batch 3 of -CoMoO.sub.4 in pellet form.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Cobalt/molybdenum oxide catalysts of the formula CoMoO.sub.4 can exist in - or -crystal forms. Although the two forms may have similar stoichiometries, their distinct crystal structures play a role in their respective catalytic activities. A method has been discovered for the preparation of a cobalt/molybdenum catalyst that maintains a -phase crystal structure during work-up and processing. The -phase catalyst exhibits improved syngas conversion and butanol selectivity.

[0029] Through investigating cobalt/molybdenum catalyst activities, the inventor has discovered that conventional catalyst processing, specifically, post-calcination grinding or pelletization, induces the phase change of -CoMoO.sub.4 to -CoMoO.sub.4. Without wishing to be bound by theory, it is believed that the energy transmitted to the calcined catalyst by grinding or pelletization enables the conversion of -crystallites to -crystallites. The two crystal forms can be visually differentiated by their colors; -CoMoO.sub.4 is purple, whereas -CoMoO.sub.4 is green. More importantly, the two crystal forms can be experimentally distinguished by their distinct catalytic activities.

[0030] The inventor has developed a strategy that preserves the improved-activity -phase before reduction in situ. Preparing catalyst powder or pellets before calcination (when the catalyst is in the hydrated form of -CoMoO.sub.4) ensures the catalyst remains in the -form and provides high selectivity towards C.sub.3-C.sub.4 alcohols at a conversion of approximately 30%. In a further aspect, the alcohols produced by this process can be dehydrated into the corresponding olefins. Dehydration can be performed at a temperature above alcohol boiling points in the presence of an acid-type catalyst, e.g., cesium-doped silicotungstic acid supported on alumina.

[0031] In some aspects, the disclosure provides a calcined composition comprising -Co.sub.xMo.sub.yO.sub.z, wherein x ranges from 0.5 to 2.0, y ranges from 0.5 to 2.0, and z ranges from 3.5 to 4.5. In some aspects, the calcined composition is essentially free of catalytically-active amounts of beta-molybdenum carbide (-Mo.sub.2C). In some embodiments, the calcined composition is essentially free of catalyst-promoting amounts of an alkaline metal promoter or alkaline earth metal promoter.

[0032] In some aspects, the composition exhibits a synthesis gas conversion of at least 10%, under suitable reaction conditions. In preferred aspects, the composition exhibits a synthesis gas conversion of at least 25% under suitable reaction conditions. In some embodiments, the composition exhibits a cumulative C.sub.3-C.sub.4 alcohol selectivity of at least 35% under suitable reaction conditions. In preferred aspects, the composition exhibits a cumulative C.sub.3-C.sub.4 alcohol selectivity of at least 50% under suitable reaction conditions. In some embodiments, suitable reaction conditions include a reactor pressure ranging from 50 to 100 bar, preferably from 60 to 90 bar, more preferably from 70 to 80 bar. In some aspects, suitable reaction conditions include a reactor temperature ranging from 150 to 450 C., preferably from 200 to 400 C., more preferably from 250 to 350 C. In some embodiments, suitable reaction conditions include a synthesis gas CO:H.sub.2 ratio ranging from 0.8:1 to 1.2:1, preferably 1:1. An inert gas, such as nitrogen, may be provided with the synthesis gas in an amount ranging from 1 to 20%, based on the total amount of CO and H.sub.2. In some embodiments, the calcined composition comprises -Co.sub.xMo.sub.yO.sub.z, where x ranges from 0.9 to 1.1, y ranges from 0.9 to 1.1, and z ranges from 3.9 to 4.1.

[0033] In some embodiments, a process for the conversion of a synthesis gas stream into a product stream comprising C.sub.3-C.sub.4 alcohols is provided. The method comprises exposing a synthesis gas stream to a calcined composition under conditions suitable to convert at least 10% of the synthesis gas stream with at least 35% selectivity for C.sub.3-C.sub.4 alcohols, wherein said calcined composition comprises -Co.sub.xMo.sub.yO.sub.z, with x ranging from 0.5 to 2.0, y ranging from 0.5 to 2.0, and z ranging from 3.5 to 4.5. In some aspects, the calcined composition is essentially free of catalytically-active amounts of beta-molybdenum carbide (-Mo.sub.2C). In additional aspects, the calcined composition is essentially free of catalyst-promoting amounts of an alkaline metal promoter or alkaline earth metal promoter. In some embodiments, the calcined composition comprises -Co.sub.xMo.sub.yO.sub.z, where x ranges from 0.9 to 1.1, y ranges from 0.9 to 1.1, and z ranges from 3.9 to 4.1.

[0034] In some aspects, the process for the conversion of a synthesis gas stream into a product stream comprising C.sub.3-C.sub.4 alcohols comprises a reactor pressure ranging from 50 to 100 bar, preferably from 60 to 90 bar, more preferably from 70 to 80 bar. In some embodiments, the process for the conversion of a synthesis gas stream into a product stream comprising C.sub.3-C.sub.4 alcohols comprises a reactor temperature ranging from 150 to 450 C., preferably from 200 to 400 C., more preferably from 250 to 350 C. In some embodiments, the process for the conversion of a synthesis gas stream into a product stream comprising C.sub.3-C.sub.4 alcohols a synthesis gas CO:H.sub.2 ratio ranging from 0.8:1 to 1.2:1, preferably 1:1. An inert gas, such as nitrogen, may be provided with the synthesis gas in an amount ranging from 1 to 20%, based on the total amount of CO and H.sub.2.

[0035] In further embodiments, a method for making a -phase catalyst capable of producing C.sub.3-C.sub.4 alcohols from a synthesis gas stream with at least 25% conversion and at least 50% selectivity is provided. In some aspects, the method comprises the steps of preparing a solution comprising a cobalt salt and a molybdenum salt and collecting a precipitate from the solution; drying the precipitate to give a dried precipitate comprising one or more hydrates of cobalt molybdenum oxide; pelleting the dried precipitate to produce pellets; and calcining the pellets to generate the -phase catalyst. In specific aspects, the pellets are not subjected to mechanical deformation subsequent to calcination. In a preferred embodiment, the cobalt salt is cobalt acetate and the molybdenum salt is ammonium heptamolybdate. In some embodiments, the solution comprises a binary solvent, preferably ethanol and water, more preferably from 10 to 30% ethanol and from 70 to 90% water, even more preferably 20% ethanol and 80% water, vol:vol. In some embodiments, the precipitate is dried at a temperature ranging from 70 to 150 C., preferably from 90 to 130 C., more preferably from 100 to 120 C. In some aspects, the precipitate is dried for a period of time ranging from 4 to 8 hours, preferably from 5 to 7 hours. In some embodiments, the pellets are calcined at a temperature ranging from 300 to 700 C., preferably from 400 to 600 C., more preferably from 450 to 550 C. In some aspects, the pellets are calcined for a period of time ranging from 2 to 6 hours, preferably from 3 to 5 hours, more preferably from 2.5 to 3.5 hours. In some aspects, the pellets are calcined under an ambient air environment. Ambient air is defined as atmospheric air present at the calcination unit. In further embodiments, the pellets are calcined under oxygen, nitrogen, helium, or a combination thereof.

EXAMPLES

[0036] As part of the disclosure of the present invention, specific examples are included below. The examples are for illustrative purposes only and are not intended to limit the invention. Those of ordinary skill in the art will readily recognize parameters that can be changed or modified to yield essentially the same results.

Example 1

-CoMo Powder Preparation

[0037] Separate solutions (each in 100 ml of a binary solvent; 80% H.sub.2O, 20% EtOH) of cobalt acetate (12.45 g) and ammonium heptamolybdate (8.45 g) were heated to 65 C. to dissolve the salts. The molybdenum solution was heated at 65 C. while stirring, and the cobalt solution was added dropwise using a separatory funnel. The combined solution was aged for 2 h. The solution was then filtered without washing and the dark purple precipitate was dried in an oven (110 C.) for 6 h. The dried catalyst precursor was ground to a powder then calcined (500 C., static air, 10 C./min heating rate, 4 h). The purple color was maintained after calcination. The calcined catalyst (6 ml volume comprising 3 ml catalyst and 3 ml SiC) was then reduced in situ (16 h, H.sub.2, 50 ml/min, 350 C., 1 C. min.sup.1). Two batches, batch 1 (B1) and batch 2 (B2) were than tested to asses reproducibility.

Example 2

-CoMoO.SUB.4 .Powder and Pellet Preparation

[0038] Separate solutions (each in 100 ml of a binary solvent; 80% H.sub.2O, 20% EtOH) of cobalt acetate (12.45 g) and ammonium heptamolybdate (8.45 g) were heated to 65 C. to dissolve the salts. The molybdenum solution was heated at 65 C. while stirring, and the cobalt solution was added dropwise using a separatory funnel. The combined solution was aged for 2 h. The solution was then filtered without washing and the dark purple precipitate was dried in an oven (110 C.) for 6 h. The dried catalyst precursor was ground to a powder then calcined (500 C., static air, 10 C./min, 4 h). The powder was then ground. Post-calcination grinding induced a phase change from -CoMoO.sub.4 (purple) to -CoMoO.sub.4 (green). The color and phase change were observed before loading the green -CoMoO.sub.4 into the reactor. An in situ pre-reduction H.sub.2 step was performed before syngas testing. Both powder and pellets (made at 10 tons pressure) were used.

Example 3

-CoMo Pellet Preparation

[0039] In order to confirm that the catalyst prepared in Example 1 is stable in pelleted form and does not change phase upon pelleting, a pelleted version of the Example 1 catalyst (Example 3) was prepared. After preparing the Example 1 catalyst powder described above, the powder was then pelleted (10 ton pressure) then calcined (500 C., static air, 10 C./min, 4 h) to give the final stable pelleted -CoMoO.sub.4 catalyst. Preparing the catalyst pellets before calcination (when catalyst exists as hydrated form of the -CoMoO.sub.4) ensured that the catalyst remained in the -form.

Catalyst Activity/Selectivity Evaluation

[0040] The catalysts produced in Examples 1-3 were evaluated for the activity and selectivity, as well as short- and long-term stabilities. Prior to activity measurement, all of the catalysts were subjected to a reductive activation procedure (H.sub.2, 100 ml/min, 350 C., 1 C./min, 16 h). Catalyst evaluation was carried out in a high-throughput, fixed-bed flow reactor setup housed in temperature-controlled system fitted with regulators to maintain pressure during reactions. The products of the reactions were analyzed through online GC analysis. The evaluation was carried out under the following conditions unless otherwise indicated: 75 bar, 300 C., 1 C./min, 48 h stabilization, 100 ml/min, 50% SiC mix. The mass balances of the reactions were calculated to be 955%.

Results and Discussion

[0041] Catalyst testing results are depicted in FIGS. 1-7. FIGS. 1-2 provide results for two catalyst batches prepared in powder form without pelleting, i.e., the -phase. Cumulative selectivity towards C.sub.3-C.sub.4 alcohols was in the range of 50-60%, with approximately 30% conversion.

[0042] When the catalyst is pelleted/ground post-calcination, the product distribution changes, with methane, methanol, and other hydrocarbons observed as major products (FIGS. 3-4). The distinct product distribution was attributed to the -CoMoO.sub.4 phase, which was green in color. The results demonstrate that the -phase catalyst is vastly superior for the production of C.sub.3-C.sub.4 alcohols.

[0043] In order to make the catalyst industrially applicable, robust catalytic material must be produced that will endure the harsh conditions provided by fixed bed reactor setups. This goal was achieved by pelleting the catalyst before calcination (in hydrated form). The catalyst (Example 3) was purple in color and successfully retained the -CoMoO.sub.4 phase. The results were examined for three batches (FIGS. 5-7). When -CoMoO.sub.4 was pelleted before calcination, it retained high selectivity for C.sub.3-C.sub.4 alcohols. Cumulative selectivity towards C.sub.3-C.sub.4 alcohols was in the range of 50-60%, however, butanol selectivity was higher for -pellets (Example 3, FIGS. 5-7) than for -powders (Example 1, FIGS. 1-2). Syngas conversion for -pellets and -powders was similar, with conversion amounts at approximately 30%.

[0044] It is evident from the data provided herein that the -CoMoO.sub.4 provides higher selectivity towards C.sub.3-C.sub.4 alcohols, whereas -CoMoO.sub.4 catalyst produces more methanol and CO.sub.2. Upon further extending the process to dehydration, metal doped heteropoly acids like silicotungstic acid doped with cesium supported on alumina or silica may be used to produce propylene and butylene in high yields.

[0045] In the context of the present invention, embodiments 1-16 are described. Embodiment 1 is a calcined composition. The composition includes -Co.sub.xMo.sub.yO.sub.z, wherein x ranges from 0.5 to 2.0, y ranges from 0.5 to 2.0, and z ranges from 3.5 to 4.5, wherein said calcined composition is essentially free of catalytically-active amounts of beta-molybdenum carbide (-Mo.sub.2C), and wherein said calcined composition is essentially free of catalyst-promoting amounts of an alkaline metal promoter or alkaline earth metal promoter. Embodiment 2 is the calcined composition of embodiment 1, wherein the composition exhibits a synthesis gas conversion of at least 10%. Embodiment 3 is the calcined composition of either of embodiments 1 or 2, wherein the composition exhibits a cumulative C.sub.3-C.sub.4 alcohols selectivity of at least 35%.

[0046] Embodiment 4 is a process for conversion of a synthesis gas stream into a product stream containing C.sub.3-C.sub.4 alcohols. The process includes exposing said synthesis gas stream to a calcined composition under conditions suitable to convert at least 10% of the synthesis gas stream with at least 35% selectivity for C.sub.3-C.sub.4 alcohols, wherein said calcined composition includes -Co.sub.xMo.sub.yO.sub.z, with x ranging from 0.5 to 2.0, y ranging from 0.5 to 2.0, and z ranging from 3.5 to 4.5, wherein said calcined composition is essentially free of catalytically-active amounts of beta-molybdenum carbide (-Mo2C), and wherein said calcined composition is essentially free of catalyst-promoting amounts of an alkaline metal promoter or alkaline earth metal promoter. Embodiment 5 is the process of embodiment 4, wherein suitable conditions comprise a reaction pressure ranging from 50 to 100 bar. Embodiment 6 is the process of either of embodiments 4 or 5, wherein suitable reaction conditions comprise a reaction temperature ranging from 150 to 450 C. Embodiment 7 is the process of any of embodiments 4 to 6, wherein suitable reaction conditions comprise a synthesis gas CO:H.sub.2 ratio ranging from 0.8:1 to 1.2:1.

[0047] Embodiment 8 is a method for making a -phase catalyst capable of producing C.sub.3-C.sub.4 alcohols from a synthesis gas stream with at least 25% conversion and at least 50% selectivity. The method includes a) preparing a solution comprising a cobalt salt and a molybdenum salt and collecting a precipitate from the solution; b) drying the precipitate to give a dried precipitate comprising one or more hydrates of cobalt molybdenum oxide; c) pelleting the dried precipitate to produce pellets; and d) calcining the pellets to generate the 3-phase catalyst, wherein the pellets are not subjected to mechanical deformation subsequent to calcination. Embodiment 9 is the method of embodiment 8, wherein the cobalt salt is cobalt acetate. Embodiment 10 is the method of either of embodiments 8 or 9, wherein the molybdenum salt is ammonium heptamolybdate. Embodiment 11 is the method of any of embodiments 8 to 10, wherein the solution containing a cobalt salt and a molybdenum salt includes a binary solvent. Embodiment 12 is the method of embodiment 11, wherein the binary solvent includes preferably from 10 to 30% ethanol and from 70 to 90% water, vol:vol. Embodiment 13 is the method of any of embodiments 8 to 12, wherein the precipitate is dried at a temperature ranging from 70 to 150 C. Embodiment 14 is the method of any of embodiments 8 to 13, wherein the precipitate is dried for a period of time ranging from 2 to 6 hours. Embodiment 15 is the method of any of embodiments 8 to 14, wherein the pellets are calcined at a temperature ranging from 300 to 700 C. Embodiment 16 is the method of any of embodiments 8 to 15, wherein the pellets are calcined for a period of time ranging from 2 to 6 hours.

[0048] Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.