PROCESS FOR PRODUCING A FISCHER-TROPSCH SYNTHESIS CATALYST AND FISCHER-TROPSCH START-UP PROCESS

Abstract

The present invention relates to a process for producing a Fischer-Tropsch synthesis catalyst wherein from 15 to 40 mol. % of the cobalt thereon is in the form of cobalt oxide. The present invention also relates to a start-up process for a reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst, wherein from 15 to 40 mol. % of the cobalt thereon is in the form of cobalt oxide and the reduced-and-passivated catalyst is activated by contacting the catalyst with a syngas stream.

Claims

1. A process for producing a reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst, the process comprising the following steps: (a) contacting a cobalt-containing Fischer-Tropsch catalyst with a reducing gas under conditions suitable to produce a reduced cobalt-containing Fischer-Tropsch catalyst; (b) under a non-oxidising atmosphere, adjusting the temperature of the reduced cobalt-containing Fischer-Tropsch catalyst to a temperature in the range of from 0° C. to 200° C.; (c) contacting the reduced cobalt-containing Fischer-Tropsch catalyst with an oxygen-containing gas stream comprising from 0.1% v/v to 5% v/v oxygen with the balance being an inert gas, at a temperature in the range of from 0° C. to 200° C., in order to produce a reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst; wherein, in step (c), the amount of oxygen in the oxygen-containing gas stream, and the temperature, are selected and maintained to produce a reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst wherein from 15 to 40 mol. % of the cobalt thereon is in the form of cobalt oxide.

2. A process according to claim 1, wherein from 20 to 38 mol. % of the cobalt on the reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst is in the form of cobalt oxide.

3. A process according to claim 1, wherein the contacting step (c) comprises contacting the reduced cobalt-containing Fischer-Tropsch catalyst with the oxygen containing stream at a temperature of from 5° C. to 150° C.

4. A process according to claim 1, wherein the oxygen containing stream comprises from 0.2% v/v to 2.5% v/v oxygen.

5. A process according to claim 1, wherein the oxygen containing stream is contacted with the reduced cobalt-containing Fischer-Tropsch catalyst continuously in a fixed bed reactor.

6. A process according to claim 5, wherein the oxygen containing stream is contacted with the reduced cobalt-containing Fischer-Tropsch catalyst at a GHSV of from 1000 to 30000 h.sup.−1.

7. A process according to claim 1, wherein the contacting step is conducted at a pressure of from 1 bar absolute to 31 bar absolute.

8. A process according to claim 1, wherein the amount of oxygen in the oxygen-containing gas stream, and the temperature, are selected by the steps of: (i) performing steps (a) to (c) of the method for a Fischer-Tropsch catalyst having a given composition and under a given set of process conditions at a first temperature and using an oxygen-containing gas stream having a first oxygen content to produce a test catalyst; (ii) determining the proportion of cobalt on the test catalyst that is in the form of cobalt oxide by performing temperature programmed reduction of the test catalyst; (iii) if the proportion of cobalt on the test catalyst that is in the form of cobalt oxide is outside the range of from 15 to 40 mol. %, repeating steps (i) and (ii) at a second temperature, different to the first temperature, and/or a second oxygen content, different to the first oxygen content.

9. A process according to claim 1, wherein the reduced cobalt-containing Fischer-Tropsch catalyst is a supported catalyst.

10. A process according to claim 9, wherein the reduced cobalt-containing Fischer-Tropsch catalyst is supported on a support material selected from the list consisting of silica, alumina, silica/alumina, ceria, titania, gallia, zirconia, magnesia, zinc oxide and mixtures thereof.

11. A process according to claim 1, wherein the reduced cobalt-containing Fischer-Tropsch catalyst comprises one or more promoters, preferably selected from the list consisting of ruthenium, palladium, platinum, rhodium, rhenium, manganese, chromium, nickel, iron, molybdenum, boron, tungsten, zirconium, gallium, thorium, lanthanum, cerium and mixtures thereof.

12. A process according to claim 1, wherein the reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst is stored under a dry atmosphere, preferably under an inert atmosphere; and/or wherein the reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst is coated with wax or hydrocarbons.

13. A process according to claim 12, wherein in part (a) the cobalt-containing Fischer-Tropsch catalyst is reduced by contacting the catalyst with a flow of hydrogen at a temperature of from 200° C. to 600° C.

14. A reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst produced by the process of claim 1.

15. A start-up process for a Fischer-Tropsch catalyst, the start-up process comprising the steps of: (a) providing a reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst, wherein from 15 to 40 mol. % of the cobalt on the catalyst is in the form of cobalt oxide; (b) contacting the catalyst from step (a) with a syngas gas stream under conditions suitable to activate the catalyst for Fischer-Tropsch synthesis; (c) optionally adjusting the temperature to the desired reaction temperature for performing Fischer-Tropsch synthesis with the activated catalyst from step (b).

16. The process of claim 15, wherein step (b) is performed at a temperature of less than 350° C.

17. The process of claim 15, wherein the syngas stream in step (b) comprises hydrogen and carbon monoxide in a H.sub.2:CO ratio of from about 1:1 to about 3:1.

18. The process of claim 15, wherein less than 10 mol. % of the cobalt on the activated catalyst from step (b) is in the form of cobalt oxide.

19. The process of claim 15, wherein in step (b) the syngas stream is contacted with the catalyst at a GHSV of from 500 to 10000 h.sup.−1.

20. The process of claim 15, wherein in step (b) the syngas stream is contacted with the catalyst at a pressure of from atmospheric pressure to 51 bar absolute.

21. The process of claim 15, wherein in step (c) the temperature is adjusted to a temperature of from 100° C. to 400° C.; or wherein in step (c) the temperature is maintained at a temperature used in step (b).

22. The process of claim 15, wherein from 20 to 38 mol. % of the cobalt on the reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst is in the form of cobalt oxide.

23. The process of claim 15, wherein the reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst in step (a) is a supported catalyst.

24. The process of claim 15, wherein the reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst in step (a) is produced by the process: (i) contacting a cobalt-containing Fischer-Tropsch catalyst with a reducing gas under conditions suitable to produce a reduced cobalt-containing Fischer-Tropsch catalyst; (ii) under a non-oxidising atmosphere, adjusting the temperature of the reduced cobalt-containing Fischer-Tropsch catalyst to a temperature in the range of from 0° C. to 200° C.; (iii) contacting the reduced cobalt-containing Fischer-Tropsch catalyst with an oxygen-containing gas stream comprising from 0.1% v/v to 5% v/v oxygen with the balance being an inert gas, at a temperature in the range of from 0° C. to 200° C., in order to produce a reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst; wherein, in step (iii), the amount of oxygen in the oxygen-containing gas stream, and the temperature, are selected and maintained to produce a reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst wherein from 15 to 40 mol. % of the cobalt thereon is in the form of cobalt oxide.

25. The process of claim 15, wherein the reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst provided in step (a) is produced in a different location to where the start-up process is performed.

26. The process according to claim 25, wherein the reduced-and-passivated cobalt-containing Fischer-Tropsch catalyst is stored under a dry or inert atmosphere during transportation.

27. (canceled)

Description

[0112] The present invention will now be described by reference to the following non-limiting examples and the accompanying Figures, in which:

[0113] FIG. 1 shows schematically an arrangement of four catalyst beds connected in series for reducing the catalyst.

[0114] FIG. 2 shows a schematically an arrangement of four catalyst beds connected in parallel for performing Fischer-Tropsch synthesis.

EXAMPLES

[0115] Catalyst Synthesis and Passivation

[0116] The initial catalyst material was prepared by impregnation of a P25 titania support with a solution containing cobalt nitrate hexahydrate and manganese acetate tetrahydrate to give a catalyst material comprising 10 wt. % cobalt and 1 wt. % manganese on the support. The support material was shaped and impregnated with the active components, then dried and calcined.

[0117] A series of catalysts were passivated according to Table 1 below. The catalysts were prepared using the above catalyst material by first contacting 10 g of catalyst in a fixed bed tubular reactor with a 100% hydrogen stream at 300° C. and at atmospheric pressure for 15 hours to reduce the cobalt on the catalyst material, followed by adjustment to the specified temperature. The catalysts were then contacted with an oxygen-containing gas stream at a GHSV of 2000 h.sup.−1 and at atmospheric pressure for 2 hours. The temperature of the catalysts was monitored by a thermocouple in the catalyst bed.

[0118] The catalyst samples were then analysed by temperature programmed reduction (TPR) to determine the proportion of cobalt oxide that was present in the catalyst samples. The TPR test was conducted on an approximately 50 mg catalyst sample using a Micromeritics 2920 AutoChem II analyser combined with an integrated thermal conductivity detector (TCD) and Cirrius 2 quadrupole mass spectrometer. The sample was loaded into a quartz glass U-tube and dried under flowing argon, heating from room temperature to 110° C. at 5° C./min and holding the temperature for 15 mins. Samples were then cooled to room temperature under argon. TPR analysis was carried out using 4% v/v hydrogen in argon (30 ml/min), and heating from room temperature to 550° C. at a rate of 5° C./min.

TABLE-US-00001 TABLE 1 Temperature O.sub.2 content Exotherm Co oxide (° C.) (%) peak (° C.) (%) Example 1 30 0.5 45 30 Example 2 30 1.0 73 31 Example 3 60 0.25 84 37 Example 4 90 0.25 120  41 (comparative) Example 5* 90 <0.25 — 31 *= Example 5 catalyst was a 10 g catalyst bed arranged downstream of and in series with the catalyst in Example 4, resulting in a stream having an oxygen content of less than 0.25% to the downstream catalyst

[0119] As can be seen in Table 1, temperature and oxygen content of the oxygen-containing stream may be varied to vary the proportion of cobalt oxide on the reduced-and-passivated catalyst.

[0120] Fischer-Tropsch Synthesis

Example 6 (Comparative)

[0121] 1.5 ml of a calcined catalyst, not passivated according to the above procedure, was charged into a microreactor and reduced under a Hz stream (15 h, 300° C., 100% Hz, 1 bar absolute, GHSV of 5000 h.sup.−1). After cooling, the gas stream over the catalyst was switched to a mixture of syngas (H.sub.2/CO=1.8) and 60% nitrogen and the pressure maintained at 43 bar absolute. The temperature was ramped at 10° C./hour from 130° C. until approximately 60% CO conversion was reached (about 215° C.).

Example 7

[0122] The procedure of Example 6 was followed, except passivated catalysts according to Examples 1 and 5 were used and no reduction under hydrogen was carried out before contacting the catalyst with the syngas stream and ramping the temperature at 10° C./hour from 130° C. to approximately 215° C.

[0123] Table 2 shows the results of the Fischer-Tropsch synthesis at steady state after around 400 to 450 hours on stream for the catalysts of Examples 1 and 5, and Example 6.

TABLE-US-00002 TABLE 2 Applied CO CH.sub.4 C.sub.5+ Temperature Conversion selectivity selectivity Catalyst (° C.) (%) (%) (%) Example 6 215 60.7 5.5 88.0 (comparative) Example 1 216 60.5 5.3 88.0 Example 5 215 62.5 6.2 87.6

[0124] As can be seen in Table 2, the reduced and passivated catalysts activated under the syngas stream used in the Fischer-Tropsch reaction surprisingly show comparable activity to a catalyst reduced with hydrogen in situ.

[0125] A further Fischer-Tropsch reaction was also conducted using a further catalyst passivated according to the above procedure which had a cobalt oxide content of 39%. The catalyst was found to be active for Fischer-Tropsch synthesis, but to show comparatively less activity than the catalysts of Examples 1 and 5 above.

[0126] Catalyst Bed Uniformity Test

[0127] An arrangement of four connected catalyst beds was used to test catalyst bed uniformity for a calcined cobalt-containing catalyst and a reduced-and-passivated catalyst according to the present disclosure (a calcined catalyst reduced under 50% H.sub.2/N.sub.2, GHSV 8000 hr.sup.−1, atmospheric pressure, 300 C; then passivated under 1% O.sub.2/N.sub.2 at <30° C.). Three tests were performed as shown in Table 3 below, according to the below general procedure. One test was performed using a calcined catalyst activated under 100% H.sub.2 (Example 8), a further test using a calcined catalyst activated under 50% H.sub.2/N.sub.2 (Example 9), and a final test using the reduced and passivated catalyst activated under 50% H.sub.2/N.sub.2 (Example 10).

[0128] Catalyst Activation

[0129] The catalyst was loaded into four fixed beds connected in series as shown in FIG. 1. To reduce the cobalt on the catalysts, a hydrogen containing stream (either 100% H.sub.2 or 50% H.sub.2/N.sub.2) was passed over the catalyst beds from catalyst bed 1 through beds 2 to 4 (GHSV 8000 h.sup.−1, 1 bar absolute, 300° C.).

[0130] Fischer-Tropsch Synthesis

[0131] After performing the above activation and cooling the catalyst beds, a mixture of syngas (H.sub.2/CO=1.8) in 51% nitrogen was fed to the catalyst beds separately in parallel as shown in FIG. 2 (GHSV 8795 h.sup.−1, 31 bar absolute). In this way, it was possible to analyse the activity of each of the catalyst beds tin relation to its relative position during activation. The temperature was ramped to 215° C. and the CO conversion at steady state at 215° C. was recorded for each of the four catalyst beds and is shown in Table 3 below. The temperature at each catalyst bed that was required to reach matching conversion was also measured, and is shown in Table 3 below.

TABLE-US-00003 TABLE 3 CO conversion (%)/Catalyst bed Activation 1 2 3 4 Example 8 100% H.sub.2 38.0 30.5 25.6 27.3 Example 9 50% H.sub.2/N.sub.2 38.3 29.8 26.6 25.1 Example 10 50% H.sub.2/N.sub.2 37.2 38.1 39.7 35.9 Reactor temperature to reach matching conversion (° C.)/Catalyst bed 1 2 3 4 Example 8 100% H.sub.2 215 219 222 221 Example 9 50% H.sub.2/N.sub.2 219 224 227 228 Example 10 50% H.sub.2/N.sub.2 217 217 216 218

[0132] As can be seen from Table 3, where a catalyst that is reduced-and-passivated according to the present disclosure is used (Example 10), the activity across the four catalyst beds is more uniform than where a calcined catalyst is used. By analogy, a reactor using a single catalyst bed may also be expected to show the same trend of improved catalyst bed uniformity from the upstream end of the bed to the downstream end.

[0133] Without wishing to be bound by any particular theory, it is believed that by using a reduced-and-passivated catalyst in accordance with the present disclosure, the effect of water generated during the activation of the catalyst on the downstream end of the catalyst bed is minimised compared to conventional catalyst reduction.