Cobalt catalysts and precursors therefor

Abstract

A cobalt catalyst precursor is described comprising cobalt oxide crystallites disposed within pores of a titania support, wherein the cobalt oxide crystallites have an average size as determined by XRD in the range 6 to 18 nm, and the titania support is a spherical titania support with a particle size in the range 100 to 1000 m, wherein the catalyst precursor has a pore volume of 0.2 to 0.6 cm.sup.3/g and an average pore diameter in the range 30 to 60 nm, and wherein the catalyst precursor has a ratio of the average cobalt oxide crystallite size to the average pore diameter in the range 0.1:1 to 0.6:1. The catalyst precursor may be reduced to provide catalysts suitable for use in Fisher-Tropsch reactions.

Claims

1. A cobalt catalyst precursor comprising cobalt oxide crystallites disposed within pores of a titania support, wherein the catalyst precursor has a cobalt content in the range 5 to 25% by weight, expressed as Co, the cobalt oxide crystallites have an average size as determined by XRD in the range 6 to 18 nm, and the titania support is a spherical titania support with a particle size in the range 100 to 1000 m, wherein the catalyst precursor has a pore volume of 0.2 to 0.6 cm.sup.3/g and an average pore diameter in the range 30 to 60 nm, and wherein the catalyst precursor has a ratio of the average cobalt oxide crystallite size to the average pore diameter in the range 0.1:1 to 0.6:1.

2. The cobalt catalyst precursor according to claim 1 wherein the cobalt oxide crystallites have an average size in the range 7-16 nm.

3. The cobalt catalyst precursor according to claim 1 wherein the particle size of the catalyst precursor is in the range 300-800 m.

4. The cobalt catalyst precursor according to claim 1 wherein the volume-median diameter, D[v,0.5], of the catalyst precursor is in the range 300-500 m.

5. The cobalt catalyst precursor according to claim 1 wherein the sulphur content of the catalyst precursor is <30 ppmw, the alkali metal content of the catalyst precursor is <50 ppmw, and the chloride content of the catalyst precursor is <1500 ppmw.

6. The cobalt catalyst precursor according to claim 1 wherein the titania support used is an anatase-containing support, in which the anatase is present in an amount >50% by weight of the support.

7. The cobalt catalyst precursor according to claim 1 wherein the pore volume of the catalyst precursor is in the range 0.3 to 0.5 cm.sup.3/g, and the average pore diameter is in the range 40-50 nm.

8. The cobalt catalyst precursor according to claim 1 further comprising one or more additives selected from compounds of molybdenum (Mo), barium (Ba), silver (Ag), copper (Cu), nickel (Ni), iron (Fe), vanadium (V), tin (Sn), gallium (Ga), manganese (Mn), zirconium (Zr), lanthanum (La), cerium (Ce), chromium (Cr) magnesium (Mg), zinc (Zn), aluminium (Al), thorium (Th), tungsten (W) or silicon (Si), wherein the amount of additive metal is between 1 and 25% by weight on the catalyst precursor.

9. The cobalt catalyst precursor according to claim 1 further comprising one or more promoters selected from rhodium (Rh), iridium (Ir), ruthenium (Ru), rhenium (Re), platinum (Pt) and palladium (Pd), wherein the amount of promoter metal is between 0.01 and 1.00% by weight on the catalyst precursor.

10. A method for preparing the cobalt catalyst precursor according to claim 1 by impregnating a spherical titania support with a cobalt nitrate solution and drying and calcining the impregnated titania support to form cobalt oxide crystallites within the pores of the titania support.

11. The method according to claim 10 wherein the impregnation is performed with a heated cobalt nitrate solution at a temperature above 50 C.

12. The method according to claim 10 wherein the volume of the cobalt nitrate solution used is equal to or less than the total pore volume of the titania support.

13. The method according to claim 10 wherein the impregnated support is dried at a temperature in the range 50-150 C.

14. The method according to claim 10 wherein the calcination is performed at a temperature in the range 200-350 C.

15. The method according to claim 10 wherein the calcination is performed in a fluidized bed reactor.

16. A catalyst comprising elemental cobalt crystallites formed by the reduction of the cobalt oxide crystallites in the cobalt catalyst precursor according to claim 1 with a reducing gas stream.

17. The catalyst according to claim 16 wherein the catalyst is subjected to a passivation treatment or encapsulated in a hydrocarbon wax.

18. A process to produce hydrocarbons from a synthesis gas comprising hydrogen and carbon monoxide using a catalyst according to claim 16 in a Fischer-Tropsch reactor.

19. The process according to claim 18 wherein the Fischer-Tropsch reactor is a microchannel reactor, a multi-tubular Fischer-Tropsch reactor, a slurry-phase reactor, a slurry bubble-column reactor, a loop reactor or a fluidised bed reactor.

20. The process according to claim 18 wherein the catalyst comprises said combination of the cobalt catalyst precursor or the catalyst comprising elemental cobalt crystallites formed by the reduction of the cobalt oxide crystallites in the cobalt catalyst precursor with a reducing gas stream and the Fischer-Tropsch reactor is a multi-tubular Fischer-Tropsch reactor.

21. A combination of the cobalt catalyst precursor or the catalyst comprising elemental cobalt crystallites formed by the reduction of the cobalt oxide crystallites in the cobalt catalyst precursor with a reducing gas stream according to claim 1, disposed within a catalyst carrier suitable for use in a reaction tube of a Fischer-Tropsch reactor.

22. The combination according to claim 21 wherein the catalyst carrier comprises an annular container suitable for holding the catalyst precursor or catalyst in place, said container having a perforated inner container wall defining an inner channel, a perforated outer container wall, a top surface closing the annular container and a bottom surface closing the annular container; and a surface closing the bottom of said inner channel formed by the inner container wall of the annular container.

23. The cobalt catalyst precursor according to claim 1 wherein the cobalt oxide crystallites have an average size in the range 8-12 nm.

24. The cobalt catalyst precursor according to claim 1 wherein the cobalt content of the catalyst precursor is in the range 8 to 16% by weight, expressed as Co.

25. A cobalt catalyst precursor comprising cobalt oxide crystallites disposed within pores of an anatase-containing titania support, in which the anatase is present in an amount >50% by weight of the support, wherein the cobalt oxide crystallites have an average size as determined by XRD in the range 6 to 18 nm, and the titania support is a spherical titania support with a particle size in the range 100 to 1000 m, wherein the catalyst precursor has a pore volume of 0.2 to 0.6 cm.sup.3/g and an average pore diameter in the range 30 to 60 nm, and wherein the catalyst precursor has a ratio of the average cobalt oxide crystallite size to the average pore diameter in the range 0.1:1 to 0.6:1.

Description

EXAMPLE 1

Catalyst Precursor Preparation on 312 m Titania Spheres

(1) a) 20% w/w Co, 0.2% w/w Ru.

(2) (i) 346.4 g of cobalt nitrate hexahydrate crystals (19.80% w/w Co) and 5.4 g of ruthenium nitrosyl nitrate solution (12.54% w/w Ru) were placed in a glass beaker and heated on a hotplate to 80 C. The hot solution was added to 500.05 g of 312 m D50 titania spheres (>85% w/w anatase by XRD) in a preheated Z-blade mixer. The temperature of the titania was 65 C. and the mixer walls were 69 C. before addition of solution. The solution was poured into the mixing titania spheres over approximately 4 minutes. After solution addition, mixing was continued for 2 minutes. 842.0 g of impregnated material was discharged and placed in 7 stainless steel trays. This material was then dried for 3 hours at 110 C. and calcined at 280 C. for 2 hours. 599.9 g of calcined material was produced.

(3) (ii) 594.3 g of the calcined material from step (i) was placed in the preheated Z-blade mixer. 286.7 g of cobalt nitrate hexahydrate crystals and 4.6 g of ruthenium nitrosyl nitrate were placed in a glass beaker and heated on a hotplate up to 80 C. The temperature of the material was 64 C. and the mixer walls were 68 C. before addition of solution. The solution was poured into the mixing material over approximately three minutes. After solution addition mixing was continued for 2 minutes. 876.2 g of impregnated material was discharged and placed in 7 stainless steel trays. This material was then dried for 3 hours at 110 C. and calcined at 280 C. for 2 hours. 671.8 g of calcined material was produced.

(4) FT Catalyst Precursor Characterization

(5) D50=311 m

(6) BET SA=39 m.sup.2/g

(7) Co SA=8 m.sup.2/g

(8) Hg intrusion volume=0.23 cm.sup.3/g

(9) Hg average pore diameter=36 nm

(10) Hg median pore diameter=42 nm

(11) Co.sub.3O.sub.4 crystallite size (XRD)=13.5 nm

(12) Co content (ICP)=18.4% w/w

(13) Ru content (ICP)=0.15% w/w

(14) Ratio of the average cobalt oxide particle size to the average pore diameter of the catalyst precursor=13.5:36=0.38:1

(15) b) 11% w/w Co, 1% w/w Mn.

(16) 320.6 g of cobalt nitrate hexahydrate crystals (19.80% w/w Co) and 12.0 g of demineralised water were placed in a glass beaker and heated on a hotplate. 39.14 g of manganese nitrate solution (15.4% w/w Mn) was added at 60 C. and the mixture heated further until reaching 70 C. The hot solution was added to 500.05 g of 312 m D50 titania spheres (>85% w/w anatase by XRD) in a preheated Z-blade mixer. The temperature of the titania was 64 C. and the mixer walls were 68 C. before addition of solution. The solution was poured into the mixing titania spheres over approximately three minutes. After solution addition mixing was continued for 2 minutes. 852.2 g of impregnated material was discharged and placed in 7 stainless steel trays. This material was then dried for 3 hours at 100 C. and calcined at 250 C. for 2 hours. 596.7 g of calcined material was produced.

(17) FT Catalyst Precursor Characterization

(18) D50=310 m

(19) BET SA=44 m.sup.2/g

(20) Co SA=6 m.sup.2/g

(21) Hg intrusion volume=0.28 cm.sup.3/g

(22) Hg average pore diameter=37 nm

(23) Hg median pore diameter=45 nm

(24) Co.sub.3O.sub.4 crystallite size (XRD)=13.0 nm

(25) Co content (ICP)=10.4% w/w (oxide)

(26) Mn content (ICP)=0.96% w/w (oxide)

(27) Ratio of the average cobalt oxide particle size to the average pore diameter of the catalyst precursor=13:37=0.35:1.

EXAMPLE 2

Catalyst Precursor Preparation on 413 m Titania Spheres

(28) a) 11% w/w Co, 1% w/w Mn,

(29) The method of Example 1(b) was repeated using 413 m D50 titania spheres.

(30) FT Catalyst Precursor Characterization

(31) D50=412 m

(32) BET SA=43 m.sup.2/g

(33) Co SA=5 m.sup.2/g

(34) Hg intrusion volume=0.29 cm.sup.3/g

(35) Hg average pore diameter=43 nm

(36) Hg median pore diameter=43 nm

(37) Co.sub.3O.sub.4 crystallite size (XRD)=14.8 nm

(38) Co content (ICP)=10.6% w/w (oxide)

(39) Mn content (ICP)=1.03% w/w (oxide)

(40) Ratio of the average cobalt oxide particle size to the average pore diameter of the catalyst precursor=14.8:43=0.34:1.

EXAMPLE 3

Comparative Example: Catalyst Preparation on 309 m Alumina Spheres

(41) a) 20% w/w Co, 0.2% w/w Ru.

(42) 12.5 Kg of alumina spheres (-Al2O3) were placed in an RT80 mixer and the water-bath turned on at 80 C. This was left overnight to heat up. 15.9 Kg of cobalt nitrate hexahydrate crystals (19.80% w/w Co), 240 g of ruthenium nitrosyl nitrate (13.0% w/w Ru) and 1210.0 g of demineralised water were heated in stainless steel beakers on a hot plate until the cobalt nitrate crystals had melted. The solution was then transferred to a preheated spray pot. The hot solution was sprayed onto the alumina spheres at 54 C. The solution was then sprayed in over 20 minutes. After solution addition, the mixing was continued for 1 minute 30 seconds before discharging the material into a drum. 28.865 Kg of material was discharged. This was placed in stainless steel trays, which were placed in ovens and dried at 110 C. for 3 hours. The dried material was split into four batches. Each of the four batches was re-dried at 110 C. for 30 minutes then calcined at 280 C. for 2 hours.

(43) Comparative FT Catalyst Precursor Characterization

(44) D50=305 m

(45) BET SA=153 m.sup.2/g

(46) Co SA=12 m.sup.2/g (425 C. reduction)

(47) Hg intrusion volume=0.45 cm.sup.3/g

(48) Hg average pore diameter=14 nm

(49) Hg median pore diameter=13 nm

(50) Co.sub.3O.sub.4 crystallite size (XRD)=15.5 nm

(51) Co content (ICP)=18.4% w/w (oxide)

(52) Ru content (ICP)=0.13% w/w (oxide)

(53) Ratio of the average cobalt oxide particle size to the mean pore diameter of the catalyst precursor=15.5:14=1.11:1.

EXAMPLE 4

Catalyst Testing

(54) The tests were performed using 0.5 g of the catalyst precursors diluted with 2.00 g SiC placed in a laboratory reactor tube with an internal diameter of 4 mm. After in situ reduction at 300 C. (ramp 1 C./min) in pure hydrogen for 7 hours using a flow rate of 60 ml/min, the temperature was then reduced to 150 C. and the gas is switched to syngas (H.sub.2:CO=2:1), and the reactors pressurized to 20 barg using a flow rate of 110 ml/min. After 6 hours, the temperature was increased (1 C./min) to 210 C. and left overnight for about 16 hours. The flow rates were then reduced first to 50 ml/min, then to the required flow rate to achieve 50% syngas conversion and data collection continued for the duration of the test (about 160 hours). Inlet gases were metered into the reactor using mass flow controllers. Gaseous, liquid and solid hydrocarbon products and the aqueous phase were analyzed by gas chromatography to achieve a mass balance from which CO conversion and selectivity were calculated. Alpha was calculated from the slope of a plot of log(Wn/n) as a function of n, for which the gradient is log(), where Wn is the weight fraction of hydrocarbon with carbon number n, and is the chain growth probability. This expression was derived from the Anderson Schulz-Flory distribution, Wn=n.sup.n-1(1).sup.2. Typically, C.sub.20-C.sub.40 was the range of carbon numbers used to calculate alpha. The results were as follows;

(55) TABLE-US-00002 Example 1(a) Comparative Catalyst of Example 1(b) Example 2(a) Example 3(a) Example 1(a) 11% w/w Co, 11% w/w Co, 20% Co Ru Parameter 20% Co Ru 1% w/w Mn 1% w/w Mn on alumina CO conversion (%) 40 48 47 37 Selectivity to CH.sub.4 (%) 9.26 4.9 5.2 10.6 Selectivity to CO.sub.2 (%) 0.00 0.00 0.00 0.00 Selectivity to C.sub.2-C.sub.4 (%) 1.48 1.26 1.55 2.27 Selectivity to C.sub.5+ (%) 89.3 93.9 93.3 87.2 GHSV (hr.sup.1) 8216 4676 4475 8784 Alpha 0.92 0.92 0.92 0.89

(56) Comparing Example 1(a) with Example 3(a), the results demonstrate that the titania sphere supported catalyst precursor according to the present invention produced a catalyst with an enhanced activity and selectivity to higher hydrocarbons compared with the same metal and promoter levels on a corresponding spherical alumina support. Example 2(a) demonstrates the improved performance of a Mn-promoted cobalt catalyst on the titania sphere support, compared to Example 1(a).