Supported cobalt-containing fischer-tropsch catalyst, process for preparing the same and uses thereof

Abstract

The present invention relates to a process for preparing a cobalt-containing Fischer-Tropsch synthesis catalyst with good physical properties and high cobalt loading. In one aspect, the present invention provides a process for preparing a supported cobalt-containing Fischer-Tropsch synthesis catalyst, said process comprising the steps of: (a) impregnating a support material with cobalt haydroxide nitrate, or a hydrate thereof, of formula (I) below to form an impregnated support material, [Co(OH).sub.x(NO.sub.3).sub.(2-x).yH.sub.2O] (I) where: 0<x<2 0≤y≤6 (b) drying and calcining the impregnated support material.

Claims

1. A process for preparing a titania supported cobalt-containing Fischer-Tropsch synthesis catalyst, said process comprising the steps of: (a) impregnating a titania support material with cobalt hydroxide nitrate, or a hydrate thereof, of formula (I) below to form an impregnated support material,
[Co(OH).sub.x(NO.sub.3).sub.(2-x).yH.sub.2O]  (I) where: 0<x<2 0≤y≤6 (b) drying and calcining the impregnated support material.

2. A process for preparing a supported cobalt containing Fischer-Tropsch synthesis catalyst, said process comprising the steps of: (i) impregnating a support material with cobalt hydroxide nitrate, or a hydrate thereof, of formula (I) below to form an impregnated support material,
[Co(OH).sub.x(NO.sub.3).sub.(2-x).yH.sub.2O]  (I) where: 0<x<2, and 0≤y≤6; (ii) forming shaped particles from the impregnated support material; and (iii) drying and calcining the shaped particles.

3. A process according to claim 1, wherein x is at most 1.5.

4. A process according to claim 2, wherein in step (ii), the shaped particles are formed by extrusion.

5. A process according to claim 1, wherein the support material is in the form of a powder or granulate and impregnation step (a) forms an impregnated support powder or granulate and calcination in step (b) forms a calcined powder or granulate, the process further comprising extruding the calcined powder or granulate to form an extrudate.

6. A process according to claim 5, wherein the support material is in the form of a powder having a median particle size diameter (d50) of less than 50 μm; or wherein the support material is in the form of a granulate having a median particle size diameter (d50) of from 300 to 600 μm.

7. A process according claim 1, wherein the average pore radius of the support material prior to impregnation is in the range of from 10 to 500 Å.

8. A process according to claim 1, wherein the support material is in the form of an extrudate and impregnation step (a) forms an impregnated extrudate prior to step (b).

9. A process according to claim 1, wherein the support material has not previously been impregnated with a cobalt-containing compound and the impregnation step of the process is the only step in which cobalt-containing compound is introduced to the support material prior to calcination.

10. A process according to claim 1, wherein impregnation step affords a synthesis catalyst containing greater than or equal to 10 wt. % of cobalt, on an elemental basis, based on the total weight of the supported synthesis catalyst.

11. A process according to claim 1, wherein the support material is impregnated with an aqueous solution or suspension of cobalt hydroxide nitrate.

12. A process according to claim 1, wherein the support material comprises a material selected from any of silica, alumina, silica-alumina, ceria, gallia, zirconia, titania, magnesia, zinc oxide, and mixtures thereof.

13. A process according to claim 12, wherein the support material is a titania and selected from titanium dioxide anatase, titanium dioxide rutile, titanium dioxide brookite and combinations thereof.

14. A process according to claim 1, wherein the cobalt-containing Fischer-Tropsch synthesis catalyst obtained comprises one or more promoters, dispersion aids, strength aids and/or binders, optionally further comprising wherein the one or more promoters, dispersion aids, strength aids and/or binders, or precursors thereof, is/are introduced during impregnation step.

15. A process according to claim 14, wherein the cobalt-containing Fischer-Tropsch synthesis catalyst obtained comprises one or more promoters selected from the group consisting of ruthenium, palladium, platinum, rhodium, rhenium, manganese, chromium, nickel, iron, molybdenum, tungsten, zirconium, gallium, thorium, lanthanum, cerium and mixtures thereof.

16. A process according to claim 15, wherein the one or more promoters are present in the cobalt-containing Fischer-Tropsch synthesis catalyst obtained in an amount from 0.1 wt. % to 3 wt. %, on an elemental basis, based on the total weight of the supported synthesis catalyst.

17. A process according to claim 1, wherein the calcining is conducted at a temperature of at least 250° C.

18. A process according to claim 1, further comprising reducing the cobalt-containing Fischer-Tropsch synthesis catalyst obtained to form a reduced Fischer-Tropsch synthesis catalyst.

19. A process for preparing cobalt hydroxide nitrate, or a hydrate thereof, of formula (I):
[Co(OH).sub.x(NO.sub.3).sub.(2-x).yH.sub.2O]  (I) where: 0<x<2, and 0≤y≤6; said process comprising the step of reacting cobalt hydroxide with cobalt nitrate.

20. A process according to claim 19, wherein cobalt nitrate is in the form of cobalt nitrate hexahydrate.

21. A process according to claim 19, wherein cobalt hydroxide is reacted with cobalt nitrate in solution.

22. A process according to claim 19, wherein cobalt hydroxide and cobalt nitrate are reacted in the presence of nitric acid.

23. A process according to claim 19, wherein the molar ratio of cobalt nitrate to cobalt hydroxide is from 1:1 to 5:1.

24. The process according to claim 1, wherein no Co(OH).sub.2 is observed after drying as measured by powder x-ray diffraction.

25. The process according to claim 1, wherein the cobalt hydroxide nitrate, or a hydrate thereof, is prepared by reacting cobalt hydroxide with cobalt nitrate.

26. The process according to claim 25, wherein the reacting is performed for at least 10 minutes prior to impregnation.

27. The process according to claim 1, wherein the impregnating of the titania support material with cobalt hydroxide nitrate or hydrate thereof comprises providing a purple solution of cobalt hydroxide nitrate or a hydrate thereof; then contacting the purple solution with the titania support to impregnate it.

28. The process according to claim 1, wherein the providing the purple solution of cobalt hydroxide nitrate or the hydrate thereof comprises reacting cobalt hydroxide with cobalt nitrate in aqueous solution for at least ten minutes, before the contacting of the purple solution with the titania support.

Description

(1) The present invention will now be illustrated by way of the following examples and with reference to the following FIGURE:

(2) FIG. 1: PXRD pattern (top) and phase identification results (bottom) of an extrudate prepared by the process of the invention.

EXAMPLES

Example 1—Preparation of Cobalt Hydroxide Nitrate from Cobalt Hydroxide and Cobalt Nitrate

(3) A predetermined amount of deionized water was weighed, the desired amount of cobalt nitrate hexahydrate (Co(NO.sub.3).sub.2.6H.sub.2O) was added and the solids dissolved under vigorous stirring at 60° C. Cobalt hydroxide (Co(OH).sub.2) was added to the solution in an amount so as to achieve a molar ratio of Co(OH).sub.2:Co(NO.sub.3).sub.2.6H.sub.2O of 1:3. The solution was maintained at a temperature of 60° C. with agitation for 60 min, upon which the colour of the solution changed from scarlet red to purple.

Example 2—Preparation of Cobalt Hydroxide Nitrate from Cobalt Hydroxide, Cobalt Nitrate, and Nitric Acid

(4) A predetermined amount of deionized water was weighed and the desired amount of nitric acid was added in a glass reactor associated with a heater and adjustable agitation system. Cobalt hydroxide (Co(OH).sub.2) was added to the solution in an amount so as to achieve a molar ratio of HNO.sub.3:Co(OH).sub.2 of 1:2 and the solids dissolved under vigorous agitation. Cobalt nitrate hexahydrate (Co(NO.sub.3).sub.2.6H.sub.2O) was then added to the solution so as to achieve a molar ratio of Co(NO.sub.3).sub.2.6H.sub.2O:Co(OH).sub.2 of 1:1. The resulting solution was heated to 60° C. and maintained at 60° C. with agitation for 60 min, upon which the colour of the solution changed from scarlet red to purple.

Example 3—Preparation of Catalyst Extrudates

(5) An appropriate quantity of titania powder (Evonik Aeroxide P25) was weighed so as to achieve a weight ratio of elemental cobalt (Co) present in the solution prepared in either Example 1 or 2 to titania to achieve a weight percentage of cobalt in the final extrudate of 20 wt. %. The solution prepared in either Example 1 or 2 was slowly added to the titania with stirring so as to reduce the volume of the powder. The mixture was then transferred to a mechanical mixer (Vinci mixer or Simpson Muller) and kneaded into extrudable paste. The wetness of the paste was adjusted with water as needed so as to form an extrudable paste. The mixture was then extruded into green extrudates with the desired geometry. The extrudates were dried and calcined using the following profile: 60° C. for 5 h, 120° C. for 5 h, 300° C. for 2 h; ramp rate in between is 2.0° C./min.

(6) FIG. 1 shows the PXRD pattern of the extrudates dried at 120° C. The lines attributed to cobalt hydroxide nitrate hydrate are clearly discernible, as are various titanium oxides (anatase and rutile) and cobalt nitrate hydrate. The cobalt hydroxide (Co(OH).sub.2) used in the synthesis is not observed, suggesting the complete conversion of this compound.

Example 4—Use of Catalyst Extrudates in a Fischer-Tropsch Synthesis Process

(7) The cobalt species in the catalyst extrudates were fully reduced to cobalt metal using hydrogen before the reaction. The products in gas phase were analysed using an on-line GC equipped with a FID. The liquid products were collected in cryogenic containers and analysed off line. The operation conditions and results of the reaction are listed as follows: Space velocity: 1250 h.sup.−1 Reaction pressure: 42 barg H.sub.2/CO molar ratio: 1.8 Time on stream: 600 h Average reaction temperature: 192° C. Average conversion of CO: 64.29% Average selectivity of CO to C.sub.5+ hydrocarbons: 86.76% Average selectivity of CO to methane: 7.02%

Comparative Example 1—Preparation of Catalyst Extrudates Using Conventional Cobalt

(8) nitrate hexahydrate as the cobalt source A predetermined amount of cobalt nitrate hexahydrate (Co(NO.sub.3).sub.2.6H.sub.2O) was weighed and dissolved in a minimum amount water to form a clear solution at room temperature. To this solution was added a predetermined amount of titania powder (Evonik Aeroxide P25). The mixture was then transferred to a mechanical mixer (Vinci mixer or Simpson Muller) and kneaded into a paste. The wetness of the paste was adjusted with water as needed so as to form an extrudable paste. The mixture was then extruded into green extrudates with the desired geometry. The extrudates were dried and calcined using the following profile: 60° C. for 5 h, 120° C. for 5 h, 300° C. for 2 h; ramp rate in between is 2.0° C./min. The resultant catalyst had 10 wt. % of Co metal, which represents the maximum Co loading achieved by conventional methods.

Comparative Example 2—Use of Conventional Catalyst Extrudates in a Fischer-Tropsch Synthesis Process

(9) The cobalt species in the catalyst extrudates were fully reduced to cobalt metal using hydrogen before the reaction. The products in gas phase were analysed using an on-line GC equipped with a FID. The liquid products were collected in cryogenic containers and analysed off-line. The operation conditions and results of the reaction are listed as follows: Space velocity: 1250 h.sup.−1 Reaction pressure: 42 barg H.sub.2/CO molar ratio: 1.8 Time on stream: 600 h Average reaction temperature: 199.5° C. Average conversion of CO: 63.52% Average selectivity of CO to C.sub.5+ hydrocarbons: 84.13% Average selectivity of CO to methane: 8.33%

(10) A Fischer-Tropsch catalyst was not prepared using Co(OH).sub.2 because of its poor solubility in water.

(11) The above results demonstrate the usefulness of the catalyst according to the present invention in the Fischer-Tropsch process. Comparing the performance data of the catalyst with 10 wt % Co loading formed using conventional methods (Comparative Example 2) and the catalyst with 20 wt. % Co loading prepared according to the present invention (Example 4), it is clear that the catalyst prepared in the current invention is superior. Example 4 shows an average CO conversion of 64.29% at 192° C., whereas the catalyst made in Comparative Example 2 only reaches a CO conversion of 63.52% at 199.5° C. The decreased reaction temperature required in Example 4 when compared to Comparative Example 2 results in lower methane selectivity (7.02% vs. 8.33%) and higher C.sub.5+ hydrocarbon selectivity (86.76% vs. 84.13%), which is highly desirable in a Fischer-Tropsch process.