Process for preparation of a supported cobalt-containing Fishcer-Tropsch synthesis

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 following steps of: (a) impregnating a support powder or granulate with a cobalt-containing compound; (b) calcining the impregnated support powder or granulate and extruding to form an extrudate; or extruding the impregnated support powder or granulate to form an extrudate and calcining the extrudate; and (c) impregnating the calcined product with a cobalt-containing compound; or forming a powder or granulate of the calcined product, impregnating with a cobalt-containing compound and extruding to form an extrudate.

Claims

1. A process for preparing a titania supported cobalt-containing Fischer-Tropsch synthesis catalyst, said process comprising: (a) impregnating a titania support powder or granulate with a cobalt-containing compound; (b) calcining the impregnated titania support powder or granulate and extruding the calcined impregnated titania support powder or granulate to form an extrudate; or extruding the impregnated titania support powder or granulate to form an extrudate and calcining the extrudate; and (c) impregnating the calcined product with a cobalt-containing compound; or forming a powder or granulate of the calcined product, and impregnating the powder or granulate of the calcined product with a cobalt-containing compound and extruding to form an extrudate, wherein: the catalyst contains cobalt in an amount of up to 30 wt. % on an elemental basis; and the titania support powder or granulate is at least 95 wt. % titania and comprises no alumina or silica.

2. A process according claim 1, wherein the process includes at least one step of forming a powder or granulate of the calcined product, impregnating with a cobalt-containing compound and extruding to form an extrudate.

3. A process according to claim 1, wherein any one or more steps of impregnating a support powder or granulate with a cobalt-containing compound is followed by an intervening step of calcination of the impregnated support powder or granulate prior to extruding to form an extrudate.

4. A process according to claim 1, wherein the process further comprises calcining the impregnated support material or extrudate obtained in step (c).

5. A process according to claim 1, wherein calcining steps are conducted at a temperature of from 150° C. to 700° C.

6. A process according to claim 1, wherein each impregnation that is performed during the process adds up to 10 wt. % cobalt, on an elemental basis.

7. A process according to claim 1, wherein prior to any extrusion, the powdered or granulated support material is mulled with the cobalt-containing compound.

8. A process according to claim 1, wherein any forming a powder or granulate comprises crushing, milling or grinding, or a combination thereof.

9. A process according to claim 1, wherein the powder or granulate formed during any step of forming a powder or granulate has a median particle size diameter (d50) of less than 50 μm.

10. A process according to claim 1, wherein the cobalt-containing Fischer-Tropsch synthesis catalyst obtained comprises one or more promoters, dispersion aids, strength aids, binders, or a combination thereof.

11. A process according to claim 10, wherein the one or more promoters, dispersion aids, binders or a combination thereof are introduced during one or more of the impregnation steps.

12. A process according to claim 10, wherein the one or more promoters is 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.

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

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 according to claim 1, wherein the supported cobalt-containing Fischer-Tropsch synthesis catalyst contains cobalt, on an elemental basis, in the range of 15 wt % to 35 wt %.

16. A process according to claim 1, wherein the supported cobalt-containing Fischer-Tropsch synthesis catalyst contains cobalt, on an elemental basis, in the range of 18 wt % to 30 wt %.

17. A process according to claim 1, wherein the supported cobalt-containing Fischer-Tropsch synthesis catalyst contains cobalt, on an elemental basis, in the range of up to 25 wt %.

18. A process according to claim 1, wherein the supported cobalt-containing Fischer-Tropsch synthesis catalyst contains 20 wt % Co, and a single particle crush strength in the range of 24.9 N to 39.6 N.

19. A process according to claim 1, wherein step (b) comprises calcining the impregnated titania support powder or granulate and extruding the calcined impregnated titania support powder or granulate to form an extrudate.

20. A process according to claim 1, wherein step (b) comprises extruding the impregnated titania support powder or granulate to form an extrudate and calcining the extrudate.

Description

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

(2) FIG. 1: Graphical representation of applied temperature in a Fischer-Tropsch synthesis reaction against time of catalyst exposure to a feed stream (“hours on stream”-HOS);

(3) FIG. 2: Graphical representation of methane selectivity (%) in a Fischer-Tropsch synthesis reaction against time of catalyst exposure to a feed stream (“hours on stream”-HOS);

(4) FIG. 3: Graphical representation of C.sub.5+ selectivity (%) in a Fischer-Tropsch synthesis reaction against time of catalyst exposure to a feed stream (“hours on stream”-HOS);

(5) FIG. 4: Microscope image of a plain titania extrudate surface;

(6) FIG. 5: Microscope image of a catalyst surface for a supported catalyst comprising a cobalt loading of 10 wt. % prepared by a single impregnation of a support powder followed by a single extrusion (not in accordance with the present invention);

(7) FIG. 6: Microscope image of catalyst surface for a supported catalyst comprising a cobalt loading of 20 wt. % prepared by a single impregnation of a support powder with a solid solution followed by a single extrusion (not in accordance with the present invention); and

(8) FIG. 7: Microscope image of catalyst surface for a supported catalyst comprising a cobalt loading of 20 wt. % prepared by a double impregnation, double extrusion with intervening calcination (in accordance with an embodiment of the present invention).

(9) FIG. 8: Microscope image of a plain titania trilobe extrudate surface;

(10) FIG. 9: Microscope image of a catalyst surface for a supported trilobe shaped catalyst comprising a cobalt loading of 10 wt. % prepared by a single impregnation of a support powder followed by a single extrusion (not in accordance with the present invention);

(11) FIG. 10: Microscope image of catalyst surface for a supported trilobe shaped catalyst comprising a cobalt loading of 20 wt. % prepared by a single impregnation of a support powder with a solid solution followed by a single extrusion (not in accordance with the present invention); and

(12) FIG. 11: Microscope image of catalyst surface for a supported trilobe shaped catalyst comprising a cobalt loading of 20 wt. % prepared by a double impregnation, double extrusion with intervening calcination (in accordance with an embodiment of the present invention).

EXAMPLES

(13) General Experimental Procedure for Catalyst Extrudate Preparation (Double Impregnation-Double Extrusion)

(14) Stage 1—First Impregnation-Extrusion:

(15) Cobalt nitrate hexahydrate mentioned below was obtained from Alfa Aesar ACS 98-102% (code 36418) and the titania used was P25 aeroxide from Evonik. The 1.6 mm trilobe dies mentioned were made by JMP industries.

(16) Deionised water was added to an amount of cobalt nitrate hexahydrate. The mixture was heated to about 40° C. or less and stirred to totally dissolve the cobalt nitrate. (For a 10 wt. % cobalt loading, 550 g of cobalt nitrate hexahydrate may be used per 1000 g of titanium dioxide.) The resulting impregnating solution was then added to an amount of titanium dioxide powder, before the resulting mixture was hand mixed to a form a light paste. The paste was then added to a Simpson Muller before being mulled for 5 minutes to yield a clay-like pink paste. The paste was subsequently added to a Bonnet Extruder before the paste was extruded onto steel pans with a maximum extrudate depth of 5 cm. The extrudate was then transferred to a box furnace and dried and calcined following a temperature program of: 60° C.-1 hr; 120° C.-4 hr; 200° C.-2 hr, cool to 60° C. and hold in a box furnace (ramp rates at 2° C./min).

(17) Stage 2—Second Impregnation-Extrusion:

(18) An amount of the dried and calcined extrudate from Stage 1 was added to a muller and mulled for 45 minutes to produce a powder of particle size of d50<15 μm. The mass of titania in the powder was calculated and the amount of cobalt nitrate needed for an additional 10 wt. % loading was determined. The determined amount of cobalt nitrate hexahydrate was totally dissolved in deionised water with gentle heating (<40° C.) and stirring. The resulting impregnating solution was added to the mulled powder in the muller before the mixture was mulled for 5 to 10 minutes to produce a black paste. The paste was subsequently transferred to the Bonnet extruder and extruded using a 1.6 mm trilobe die onto a tray with a maximum extrudate depth of 5 cm. The extrudate was then transferred to a box furnace for drying and calcination, following a temperature program of: 60° C.-5 hr; 120° C.-5 hr; 300° C.-2 hr; cool to 60° C. and hold (ramp rates at 2° C./min).

(19) The cobalt impregnating solutions used in either impregnation steps may additionally contain promoters, dispersion aids, strength aids and or binders. Stage 2 may be repeated to reach higher loadings while also maintaining strength and morphology. Each impregnation typically loads 7-10% cobalt.

(20) Catalyst Reduction

(21) Catalyst extrudates were loaded into a fixed bed testing reactor with or without stacked dilution. Bed dilutions were used to control exotherms on the catalyst, where necessary. The catalyst extrudates were reductively activated using the following procedure:

(22) Drying: N.sub.2 was passed over the catalyst bed while the temperature was ramped from room temperature to 120° C., which temperature was held for 15 mins.

(23) Reductive Activation: a mixture of 50/50% v/v H.sub.2/N.sub.2 was passed over the catalyst bed and the temperature was raised from 120° C. to the activation temperature, which temperature was held for 15 hours before cooling to 90° C.

(24) Syngas: at 90° C. the H.sub.2/N.sub.2 mixture was replaced by a syngas mixture and the temperature was ramped incrementally from T=90° C. to T=170° C.

(25) Fischer-Tropsch Synthesis Reactions

(26) Each catalyst was run for a sufficient period to obtain steady state conditions and temperature adjusted to provide a particular level of CO conversion (typically between about 60 and 65%). Exit gasses were sampled by on-line GC and analysed for gaseous products. The He was used as an internal standard, the C.sup.5+ productivity is determined by difference from the C.sub.1 to C.sub.4 components in the gas phase. The productivity of the catalyst is defined as the weight in grams of products containing 5 carbon atoms or more, formed over the catalyst per litre of packed catalyst volume per hour of reaction time.

(27) Tables 1 to 5 below and FIGS. 1 to 3 appended hereto show the results of Fischer-Tropsch synthesis reactions conducted in accordance with the above general procedure with reduced catalysts obtained in accordance with the above activation procedure. Several catalysts with different cobalt (10, 20 or 30 wt. %) and promoter loadings (0% or 1%) were tested.

(28) Table 6 below shows the results of bulk crush strength testing for synthesis catalysts with 20 wt. % cobalt loading and including promoter (lwt. %) prepared in accordance with the present invention with intervening and final calcinations at 300° C. or 500° C. Results are also provided for synthesis catalysts with cobalt loadings of 20 wt. %, and also including 1% total promoter, prepared from a single impregnation with a solid solution of cobalt-containing compound and including a final calcination at 300° C. or 550° C. Single particle crush strength was determined in accordance with ASTM method No. D6175-03.

(29) Reduced catalysts having cobalt loadings of 10 wt. % are derived from extrudates prepared following a single impregnation and a single extrusion (not in accordance with the present invention). Reduced catalysts having cobalt loadings of 20 wt. % were obtained from extrudates prepared in accordance with the process of the present invention comprising a double impregnation/double extrusion with intervening calcination and powder forming steps. Reduced catalysts having cobalt loadings of 30 wt. % were obtained from extrudates prepared in accordance with the process of the present invention comprising a triple impregnation/triple extrusion process with two intervening calcination and powder forming steps.

(30) In Tables 1 to 5, CO conversion is defined as moles of CO used/moles of CO fed×100 and carbon selectivity as moles of CO attributed to a particular product/moles of CO converted×100.

(31) FIGS. 1 to 3 appended hereto illustrate the surprising effects of the catalyst preparation process of the present invention through a comparison of higher loaded reduced catalysts (20 and 30 wt. % cobalt) derived from catalysts prepared in accordance with the present invention and lower loaded reduced catalyst (10 wt. % cobalt) and higher loaded reduced catalyst (20 wt. % cobalt) derived from a catalyst which is not prepared in accordance with the present invention.

(32) FIG. 1 shows the applied temperature used for achieving comparable levels of CO conversion (approximately 60-65%) for the higher loaded reduced catalysts (20 and 30 wt. % cobalt) obtained in accordance with the present invention and lower loaded reduced catalyst (10 wt. % cobalt) which was not obtained in accordance with the present invention. FIG. 1 demonstrates that, for a similar level of CO conversion achieved with each catalyst, the applied temperatures are significantly lower for the reduced catalysts obtained from catalysts prepared in accordance with the present invention which contain high loadings of cobalt (20 and 30 wt. %). As depicted in FIG. 1, the applied temperatures for the higher loaded catalysts are approximately 10° C. lower than for the 10 wt. % cobalt catalyst. The results in Table 1 also demonstrate that a comparable level of CO conversion is obtainable at lower applied temperature for a higher loaded 20 wt. % cobalt catalyst versus a lower loaded 10 wt. % cobalt catalyst.

(33) FIGS. 2 and 3 demonstrate the effects of higher cobalt loading in the Fischer-Tropsch synthesis catalyst, together with lower applied temperatures, on methane and C.sub.5+ selectivity respectively. FIG. 2 demonstrates that by increasing the cobalt loading in the catalysts by means of the process of the present invention, thus allowing the use of lower applied temperatures, methane selectivity is lowered. In contrast, FIG. 3 demonstrates that by increasing the cobalt loading in the catalysts by means of the process of the present invention, thus allowing the use of lower applied temperatures, C.sub.5+ selectivity is desirably increased.

(34) Table 2 below illustrates the advantage of an unpromoted catalyst having a higher loading of for instance 20 wt. % cobalt versus a lower loaded conventional promoted 10 wt. % cobalt catalyst. The results of table 2 show that C.sub.5+ selectivity is 2% higher for the unpromoted 20 wt. % cobalt catalyst and, notably, the LPG selectivity is 1.5% lower, in comparison with the 10 wt. % cobalt catalyst with 1% manganese promoter.

(35) Table 6 shows that bulk crush strength is far superior for the synthesis catalysts prepared in accordance with the present invention compared with those having the same cobalt loading and total promoter loading but which are prepared with only a single impregnation with a solid solution of cobalt-containing compound. This is a result of the poor morphology which results from overloading a support with cobalt-containing compound and extruding, thereby forming large pores in the support. Following calcination, the large pores are no longer as well filled by the cobalt oxide, which is of smaller volume than the cobalt-containing compound used for impregnation, and a bubbled structure results. This is well illustrated in FIGS. 4 to 11 which show, by means of microscope images of the surface of supported catalysts, the results of overloading a support material and extruding.

(36) FIGS. 4 and 8 show microscope images of plain titania extrudate surfaces having good morphology with no evidence of any bubbles present. FIGS. 5 and 9 show microscope images of catalyst surfaces for supported catalysts comprising a cobalt loading of 10 wt. % prepared by a single impregnation of a support powder with a fully dissolved solution of cobalt-containing compound followed by a single extrusion step (not in accordance with the present invention). The 10 wt. % loaded catalysts display good morphologies with no evidence of any bubbles present. In contrast, FIGS. 6 and 10 show microscope images of catalyst surfaces for supported catalysts comprising cobalt loadings of 20 wt. % prepared by a single impregnation of a support powder with a solid solution followed by a single extrusion (not in accordance with the present invention). FIGS. 6 and 10 show poor morphologies in the extrudates with evidence of severe bubble formation. FIGS. 7 and 11 show microscope images of catalyst surfaces for supported catalysts comprising cobalt loadings of 20 wt. % prepared by a double impregnation with a fully dissolved solution of cobalt-containing compound and double extrusion with intervening calcination and powder forming steps (in accordance with an embodiment of the present invention). Despite the high cobalt loadings on the extrudates, FIGS. 7 and 11 show that good morphology is retained, with no evidence of bubbling.

(37) It is clear that a bubbled structure results from overloading a support and its pore structure. The process of the present invention is capable of affording higher cobalt loadings in an extruded Fisher-Tropsh catalyst whilst maintaining good morphology and high bulk crush strength, which has hitherto not been possible.

(38) TOS=Time On Stream (h)

(39) Conv=CO conversion (%)

(40) CH.sub.4═CH.sub.4 Selectivity (%)

(41) LPG=LPG Selectivity (%)

(42) C.sub.5+S═C.sub.5+ Selectivity (%)

(43) C.sub.5+P═C.sub.5+ Productivity (g/L.Math.h)

(44) T=Catalyst Bed Temperature (° C.)

(45) GHSV=Gas Hourly Space Velocity (h.sup.−1) (gas volumes converted to standard temperature and pressure)

(46) TABLE-US-00001 TABLE 1 Catalyst TOS Conv CH.sub.4 LPG C.sub.5+S C.sub.5+P T GHSV P H.sub.2: loading (h) (%) (%) (%) (%) (%) (° C.) (h.sup.−1) (MPa) CO *10% Co 128 60.8 11.8 7.5 80.6 118 202 1339 3 1.8 *20% Co 125 59.0 13.3 9.3 77.4 110 209 1339 3 1.8  20% Co 128 60.0 8.2 5.0 86.7 124 188 1339 3 1.8 *Not of the invention—single impregnation

(47) TABLE-US-00002 TABLE 2 Catalyst TOS Conv CH.sub.4 LPG C.sub.5+S C.sub.5+P T GHSV P H.sub.2: loading (h) (%) (%) (%) (%) (%) (° C.) (h.sup.−1) (MPa) CO  30% Co 135 62.6 9.1 4.9 86.1 125 193 1250 3 1.8  20% Co 183 64.2 10.5 4.8 84.7 126 198 1250 3 1.8 *10% Co, 1% Mn 183 64.4 11.1 6.3 82.7 120 203 1250 3 1.8  20% Co, 1% Mn 124 66.6 9.0 5.4 85.6 129 197 1250 3 1.8 *Not of the invention—single impregnation

(48) TABLE-US-00003 TABLE 3 Catalyst TOS Conv CH.sub.4 LPG C.sub.5+S C.sub.5+P T GHSV P H.sub.2: loading (h) (%) (%) (%) (%) (%) (° C.) (h.sup.−1) (MPa) CO  30% Co 294 63.4 8.0 5.5 86.4 128 193 1250 4.2 1.8  20% Co 308 63.8 8.0 4.8 87.1 128 194 1250 4.2 1.8 *10% Co, 1% Mn 304 65.4 9.3 6.8 83.9 124 203 1250 4.2 1.8  20% Co, 1% Mn 220 65.8 7.4 6.0 86.5 130 196 1250 4.2 1.8 *Not of the invention—single impregnation

(49) TABLE-US-00004 TABLE 4 Catalyst TOS Conv CH.sub.4 LPG C.sub.5+S C.sub.5+P T GHSV P H.sub.2: loading (h) (%) (%) (%) (%) (%) (° C.) (h.sup.−1) (MPa) CO *10% Co, 1% Mn 198 64.1 10.7 5.8 83.4 123 197 1250 3 1.8 *10% Co, 0% Mn 198 65.3 19.3 10.3 70.5 106 218 1250 3 1.8  20% Co, 1% Mn 197 62.5 8.9 4.5 86.7 124 189 1250 3 1.8  30% Co, 1% Mn 196 62.6 8.1 4.5 87.3 127 181 1250 3 1.8  30% Co, 0% Mn 197 62.4 8.6 4.2 87.0 126 182 1250 3 1.8 *Not of the invention—single impregnation

(50) TABLE-US-00005 TABLE 5 Catalyst TOS Conv CH.sub.4 LPG C.sub.5+S C.sub.5+P T GHSV P H.sub.2: loading (h) (%) (%) (%) (%) (%) (° C.) (h.sup.−1) (MPa) CO *10% Co, 1% Mn 350 63.6 8.6 7.2 84.3 122 197 1250 4.2 1.8 *10% Co, 0% Mn 270 65.6 12.9 6.2 81.0 122 205 1250 4.2 1.8  20% Co, 1% Mn 270 63.2 7.5 5.2 87.2 127 188 1250 4.2 1.8  30% Co, 1% Mn 270 62.8 7.3 5.5 87.2 126 181 1250 4.2 1.8  20% Co, 0% Mn 350 63.0 9.3 4.9 85.8 128 190 1250 4.2 1.8  30% Co, 0% Mn 350 63.6 7.8 5.8 87.3 130 184 1250 4.2 1.8 *Not of the invention—single impregnation

(51) TABLE-US-00006 TABLE 6 Single Particle Crush Strength, Code Catalyst Description N (lbf) C1312159  20% Co, 1% Mn—(300° C. calcination, 24.9 (5.60) double impregnation-double extrusion) C1211619  20% Co, 1% Mn—(500° C. calcination, 39.6 (8.90) double impregnation-double extrusion) C1108801 *20% Co, 0.5% Mn, 0.5% V—(300° C. 6.05 (1.36) calcination, single impregnation-single extrusion) C1211380 *20% Co, 0.5% Mn, 0.5% V—(550° C. 10.7 (2.41) calcination, single impregnation-single extrusion) *Not of the invention—single impregnation

(52) The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.”

(53) Every document cited herein, including any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

(54) While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope and spirit of this invention.