Process for producing a Fischer-Tropsch synthesis catalyst

Abstract

The present invention relates to a process for conveniently preparing a supported cobalt-containing Fischer-Tropsch synthesis catalyst having improved activity and selectivity for C.sub.5+ hydrocarbons. 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: i) a cobalt-containing compound and ii) acetic acid, or a manganese salt of acetic acid, in a single impregnation step to form an impregnated support material; and (b) drying and calcining the impregnated support material; wherein the support material impregnated in step (a) has not previously been modified with a source of metal other than cobalt; and wherein when the cobalt-containing compound is cobalt hydroxide, a manganese salt of acetic acid is not used in step (a) of the process.

Claims

1. A process for preparing a supported cobalt-containing Fischer-Tropsch synthesis catalyst, said process comprising the steps of: (a) impregnating a support material, wherein the support material is in the form of a powder or granulate, with: i) a cobalt-containing compound and ii) acetic acid, or a manganese salt of acetic acid, in a single impregnation step to form an impregnated support material then extruding the impregnated support material to form an extrudate; and then (b) drying and calcining the extrudate to provide the supported cobalt-containing Fischer Tropsch synthesis catalyst; wherein the support material impregnated in step (a) comprises a material selected from the group consisting of silica, alumina, silica/alumina, ceria, gallia, zirconia, titania, magnesia, zinc oxide, and mixtures thereof, and has not previously been modified with a source of metal other than cobalt; wherein when the cobalt containing-compound is cobalt hydroxide, a manganese salt of acetic acid is not used in step (a) of the process, and wherein the supported cobalt-containing Fischer Tropsch synthesis catalyst comprises cobalt oxide crystallites below 10 nm in particle size.

2. A process according to claim 1, 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.

3. A process according to claim 1, wherein the support material is impregnated with a solution or suspension comprising i) the cobalt-containing compound and ii) acetic acid or a manganese salt of acetic acid.

4. A process according to claim 3, wherein the solution or suspension is an aqueous solution or suspension.

5. A process according to claim 1, wherein the cobalt-containing compound is the nitrate, acetate, hydroxide or acetylacetonate of cobalt.

6. A process according to claim 1, wherein the support material is impregnated with acetic acid in step (a) in an amount from 0.1 to 5 wt. %, based on the dry weight of the impregnated support material; or wherein the support material is impregnated with a manganese salt of acetic acid in step (a) in an amount from 0.1 to 5 wt. %.

7. A process according to claim 1, wherein impregnation step (a) affords a synthesis catalyst containing from 5 wt. % to 20 wt. % of cobalt, on an elemental basis, based on the total weight of the supported synthesis catalyst.

8. A process according to claim 1, wherein the support material impregnated in step (a) comprises alumina, silica/alumina, zirconia, titania, or zinc oxide.

9. 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.

10. A process according to claim 9, wherein the one or more promoters, dispersion aids and/or binders, or precursors thereof, is/are introduced during impregnation step (a).

11. A process according to claim 9, 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.

12. A process according to claim 11, 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.

13. A process according to claim 1, wherein calcining in step (b) is conducted at a temperature of at least 250° C.

14. 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.

15. 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, wherein the titania support material is in the form of a powder or granulate, with: i) a cobalt-containing compound and ii) acetic acid, or a manganese salt of acetic acid, in a single impregnation step to form an impregnated support material, then extruding the impregnated support material to form an extrudate; and then (b) drying and calcining the extrudate; wherein the titania support material impregnated in step (a) has not previously been modified with a source of metal other than cobalt; wherein when the cobalt containing-compound is cobalt hydroxide, a manganese salt of acetic acid is not used in step (a) of the process; and wherein the supported cobalt-containing Fischer Tropsch synthesis catalyst comprises cobalt oxide crystallites below 10 nm in particle size.

16. A process according to claim 15, wherein the cobalt-containing compound is the nitrate, acetate, hydroxide or acetylacetonate of cobalt.

17. A process according to claim 15, wherein the titania support material is impregnated with acetic acid in step (a) in an amount from 0.1 to 5 wt. %, based on the dry weight of the impregnated support material; or wherein the titania support material is impregnated with a manganese salt of acetic acid in step (a) in an amount from 0.1 to 5 wt. %.

18. A process according to claim 15, wherein impregnation step (a) affords a synthesis catalyst containing from 5 wt. % to 20 wt. % of cobalt, on an elemental basis, based on the total weight of the supported synthesis catalyst.

19. A process according to claim 15, wherein calcining in step (b) is conducted at a temperature of at least 250° C.

20. A process according to claim 15, further comprising reducing the cobalt-containing Fischer-Tropsch synthesis catalyst obtained to form a reduced Fischer-Tropsch synthesis catalyst.

21. A process according to claim 15, wherein the titania support material is impregnated with a manganese salt of acetic acid.

Description

EXAMPLE 1

(1) Catalyst Preparation—with a Manganese Salt of Acetic Acid

(2) 55.6 g Co(NO.sub.3).sub.2.6H.sub.2O and varying amounts of Mn(OAc).sub.2 (see Table 1) were mixed in a solution with a small amount of water. This mixture was then added slowly to 100 g P25 TiO.sub.2 powder and mixed to obtain a homogeneous mixture. Co(NO.sub.3).sub.2.6H.sub.2O was used in an amount so as to give 10 wt. % elemental Co on TiO.sub.2. The resultant paste/dough was extruded to form extrudate pellets and then dried and calcined at 300° C.

(3) TABLE-US-00001 TABLE 1 Mn loading 1 wt. % 1.5 wt. % 2 wt. % 3 wt. % 5 wt. % 10 wt. % Mass of 5.4 g 8.1 g 10.8 g 16.2 g 27.0 g 54.0 g Mn(OAc).sub.2

EXAMPLE 2

(4) Catalyst Preparation—with Acetic Acid

(5) 14.82 g Co(NO.sub.3).sub.2.6H.sub.2O and varying amounts of acetic acid (see Table 2) were mixed in a solution with a small amount of water. This mixture was then added slowly to 27 g P25 TiO.sub.2 powder and mixed to obtain a homogeneous mixture. Co(NO.sub.3).sub.2.6H.sub.2O was used in an amount so as to give 10 wt. % elemental Co on TiO.sub.2. The resultant paste/dough was extruded to form extrudate pellets and then dried and calcined at 300° C.

(6) TABLE-US-00002 TABLE 2 AcOH loading 0.5 wt. % 1 wt. % 2 wt. % 3 wt. % Mass of AcOH 0.656 g 1.310 g 2.620 g 3.930 g

COMPARATIVE EXAMPLE 1

(7) Catalyst Preparation—without Acetic Acid or Manganese Acetate

(8) 14.8 g Co(NO.sub.3).sub.2.6H.sub.2O was mixed in a solution with a small amount of water. This mixture was then added slowly to 27 g P25 TiO.sub.2 powder and mixed to obtain a homogeneous mixture. Co(NO.sub.3).sub.2.6H.sub.2O was used in an amount so as to give 10 wt. % elemental Co on TiO.sub.2. The resultant paste/dough was extruded to form extrudate pellets and then dried and calcined at 300° C.

COMPARATIVE EXAMPLE 2

(9) Catalyst Preparation—without Acetic Acid or Manganese Acetate

(10) 14.82 g Co(NO.sub.3).sub.2.6H.sub.2O and 0.98 g Mn(NO.sub.3).sub.2 were mixed in a solution with a small amount of water. This mixture was then added slowly to 27 g P25 TiO.sub.2 powder and mixed to obtain a homogeneous mixture. Co(NO.sub.3).sub.2.6H.sub.2O was used in an amount so as to give 10 wt. % elemental Co on TiO.sub.2. The resultant paste/dough was extruded to form extrudate pellets and then dried and calcined at 300° C.

EXAMPLE 3

(11) Catalyst Preparation—Mn Nitrate and Acetic Acid

(12) The procedure of Comparative Example 2 was followed, except with the addition of 0.656 g acetic acid alongside Co(NO.sub.3).sub.2.6H.sub.2O and Mn(NO.sub.3).sub.2.

COMPARATIVE EXAMPLE 3

(13) Catalyst Preparation—with Manganese Acetate (Sequential Impregnation)

(14) 5.93 g Co(NO.sub.3).sub.2.6H.sub.2O was mixed in a solution with a small amount of water. This mixture was then added slowly to 10.7 g P25 TiO.sub.2 powder and mixed to obtain a homogeneous mixture. Co(NO.sub.3).sub.2.6H.sub.2O was used in an amount so as to give 10 wt. % elemental Co on TiO.sub.2. The resultant paste/dough was extruded to form extrudate pellets and then dried and calcined at 300° C. The resultant Co/TiO.sub.2 catalyst was impregnated with 0.54 g Mn(OAc).sub.2 so as to give 1 wt. % Mn on the TiO.sub.2 then dried and calcined to give a sequentially impregnated CoMn/TiO.sub.2 catalyst.

EXAMPLE 4

(15) Effect of Mn(OAc).sub.2 and Acetic Acid on Co.sub.3O.sub.4 Particle Size

(16) Catalysts prepared by the above procedures were analysed by X-ray diffraction to obtain a measurement of the average size of Co.sub.3O.sub.4 crystallites on the TiO.sub.2 support.

(17) Table 3 shows crystallite size for catalysts prepared by the methods of Examples 1 to 3 and Comparative Examples 1 to 3.

(18) TABLE-US-00003 TABLE 3 Catalyst - Co.sub.3O.sub.4 average Example 10 wt. % Co on TiO.sub.2 prepared with: size (nm) E1 1 wt. % Mn (Mn(OAc).sub.2) 8.1 1.5 wt. % Mn (Mn(OAc).sub.2) 5.7 2 wt. % Mn (Mn(OAc).sub.2) 4.9 3 wt. % Mn (Mn(OAc).sub.2) 3.4 5 wt. % Mn (Mn(OAc).sub.2) 2.3 10 wt. % Mn (Mn(OAc).sub.2) 2.8 E2 0.5 wt. % Acetic acid 8.9 1 wt. % Acetic acid 7.3 2 wt. % Acetic acid 8.3 3 wt. % Acetic acid 8.4 CE1 n/a 10.7 CE2 1 wt. % Mn (Mn(NO.sub.3).sub.2) 12.1 E3 1 wt. % Mn (Mn(NO.sub.3).sub.2) + AcOH 7.8 CE3 1 wt. % Mn (Mn(OAc).sub.2) (sequential 20.9 impregnation)

(19) The results in Table 3 show that the size of Co.sub.3O.sub.4 crystallites can be controlled by the addition of acetic acid, or the manganese salt thereof, during preparation of the catalyst. While addition of Mn acetate achieves an optimal crystallite size (˜8 nm) at 1% loading and decreasing size with increasing Mn acetate loading, acetic acid addition was found to give optimal crystallite sizes of around 8 nm when any amount above 0.5% loading was used.

(20) Both acetic acid and Mn acetate addition showed an improvement over Comparative Example 1 where only cobalt nitrate was used without any acetic acid or manganese acetate. Comparative Example 2 shows that the use of Mn nitrate in place of acetate does not give the same advantageous reduction in crystallite size. However, Example 3 shows clearly that by adding acetic acid to the Mn nitrate and cobalt, a crystallite size of around 8 nm is obtained.

(21) Comparative Example 3 shows that the benefits of the present invention cannot be obtained by subsequently impregnating with Mn acetate a dried and calcined Co/TiO.sub.2 catalyst, followed by further drying and calcining.

EXAMPLE 5

(22) General Procedure for Fischer-Tropsch Reactions

(23) 10 ml of catalyst was charged into a microreactor and reduced under a H.sub.2 stream (15 h, 300° C., 100% H.sub.2, 0.1 MPa). The gaseous supply was switched to a mixture of hydrogen and carbon monoxide (H.sub.2/CO=1.8) comprising 18% nitrogen and the pressure maintained at 4.3 MPa. The temperature was raised to 195° C. and maintained throughout the Fischer-Tropsch reaction.

EXAMPLE 6

(24) Effect of Mn(OAc).sub.2 and Acetic Acid on Fischer-Tropsch Reactions

(25) Catalysts prepared according to Example 1, using 9.88 g Co(NO.sub.3).sub.2.6H.sub.2O, 21.4 g P25 TiO.sub.2 powder and varying amounts of Mn(OAc).sub.2 (0.09 g-0.1 wt. % Mn; 0.22 g-0.25 wt. % Mn; 0.45 g-0.5 wt. % Mn; 0.89 g-1 wt. % Mn; 1.79 g-2 wt. % Mn), were used in Fischer-Tropsch synthesis according to Example 5. The results are shown in Table 4.

(26) CO conversion, CH.sub.4 selectivity, C.sub.5+ selectivity, and C.sub.5+ productivity data were compiled and results for the above Examples are provided in Table 4 below. Exit gasses were sampled by on-line mass spectrometry and analysed. The C.sub.5+ selectivity is determined by difference from the C.sub.1-C.sub.4 components in the gas phase. The CH.sub.4 selectivity is determined by difference from the C.sub.2+ components in the gas phase. The productivity of the catalyst is defined as the weight in grams of products formed over the catalyst per litre of packed catalyst volume per hour of reaction time. Values for CO conversion, CH.sub.4 selectivity, C.sub.5+ selectivity, and productivity are average values obtained at steady state.

(27) TABLE-US-00004 TABLE 4 Catalyst - 10 wt. % Co on CH.sub.4 C.sub.5+ TiO2 prepared GHSV CO conv. CH.sub.4 sel. C.sub.5+ sel. prod. prod. C.sub.5+/CH.sub.4 with: (h.sup.−1) (%) (%) (%) (g/h/l) (g/h/l) prod. 0.1 wt. % Mn 690 34.7 16.2 75.4 9.2 42.9 4.66 0.25 wt. % Mn 697 42.7 14.6 78.2 10.3 55.1 5.35 0.5 wt. % Mn 725 50.8 13.6 79.9 11.6 68.3 5.89 1% wt. Mn 682 56.3 12.2 81.3 11.1 74.0 6.67 2% wt. Mn 691 54.1 12.0 78.4 10.3 68.1 6.61

(28) The results in Table 4 show that, at constant temperature and pressure, the activity of the CoMn/TiO.sub.2 catalyst increases with increasing loading of Mn acetate, achieving a maximum at 1 wt. % Mn acetate, which corresponds to the loading shown to give a Co.sub.3O.sub.4 crystallite size of around 8 nm. Crucially, increased loadings of Mn acetate also give an increasing C.sub.5+/CH.sub.4 productivity ratio, again reaching a maximum at 1 wt. % Mn acetate loading.

(29) In addition, Table 5 below shows the effect of the rate on CO conversion per gram of catalyst for Mn acetate impregnated simultaneously (as in Example 1), Mn acetate impregnated sequentially (as in Comparative Example 3) and without Mn acetate (as in Comparative Example 1). Rate is defined as mmol of CO converted per hour, per gram of catalyst.

(30) The results in Table 5 further demonstrate that the benefits of the present invention cannot be obtained by sequential impregnation.

(31) TABLE-US-00005 TABLE 5 Loading GHSV Rate (wt. %) Impregnation (h.sup.−1) (mmol/h/g) 0% N/A 1550 3.2 1 wt. % Mn Simultaneous 1500 5.0 (with cobalt) 1 wt. % Mn Sequential 710 3.8 (after cobalt)