WO2001076735A1

WO2001076735A1 - Process for preparing fischer-tropsch catalyst

Info

Publication number: WO2001076735A1
Application number: PCT/US2000/010520
Authority: WO
Inventors: Gyanesh P. Khare
Original assignee: Phillips Petroleum Company
Priority date: 2000-04-07
Filing date: 2000-04-18
Publication date: 2001-10-18
Also published as: AU2000246479A1

Abstract

Disclosed herein is a process for preparing a Fischer-Tropsch catalyst. The process comprises the steps of: impregnating a particulate carrier with an active metal selected from cobalt, iron, manganese, and nickel by mixing the particulate carrier with a particulate active metal compound at a temperature approximately at or above the melting point of the active metal compound but below the temperature at which such compound decomposes; and then calcining the thus impregnated carrier to produce the catalyst.

Description

PROCESS FOR PREPARING FISCHER-TROPSCH CATALYST

BACKGROUND OF THE INVENTION

This invention relates to Fischer-Tropsch catalysts, and more

particularly to a process for preparing a Fischer-Tropsch catalyst.

Synthesis gas (typically a mixture of carbon monoxide and

hydrogen) can be converted into hydrocarbons in the presence of a Fischer-

Tropsch catalyst under suitable pressure and temperature conditions. The

Fischer-Tropsch catalyst is typically comprised of a particulate carrier

impregnated with an active metal, particularly cobalt, iron, manganese, or

nickel. In preparing such a catalyst, impregnation is commonly carried out by

using a compound of the active metal in aqueous solution. SUMMARY OF THE INVENTION

The invention provides a novel process for preparing a Fischer-

Tropsch catalyst comprising the steps of: impregnating a particulate carrier with

an active metal selected from cobalt, iron, manganese, nickel and mixtures

thereof by mixing the particulate carrier with a particulate compound of

containing said active metal at a temperature approximately at or above the

melting point of the active metal compound but below the temperature at which

such compound decomposes; and then calcining the thus impregnated carrier to

produce the catalyst.

As demonstrated in the subsequent examples, the process of the

invention produces a Fischer-Tropsch catalyst in which there is substantial

penetration of the active metal in the carrier particles. As compared to a more

typical profile in which the active metal is concentrated on the outer surfaces of

the carrier particles, active metal penetration as achieved by the inventive

process will generally enhance selectivity and/or activity, and will also

minimize attrition or loss of active metal from the carrier particles and

consequent contamination of the hydrocarbon product. DETAILED DESCRIPTION OF THE INVENTION

Now describing preferred details of the inventive process, the

particulate carrier can be an oxide of silicon, aluminum, titanium, zinc,

zirconium, or magnesium; zeolites; or a mixture thereof. Alumina is most

preferred.

The active metal compound preferably has an active metal

selected from cobalt, iron, manganese, nickel and mixtures thereof. Suitable

active metal compounds include halides, nitrates, sulfates, acetates and

thiocyanates of the active metal. The active metal compound preferably has a

melting point in the range of about 25-400°C, most preferably about 25-100°C.

Falling within the latter most preferred range are, for example, cobalt(II)

bromide hexahydrate, cobalt(II) chlorate hexahydrate, cobalt(II) nitrate

hexahydrate, cobalt(II) acetate, dicobalt octacarbonyl, cobalt palmitate,

cobalt(II) sulfate heptahydrate, iron(III) chloride hexahydrate, iron(II) nitrate

hexahydrate, iron(II) sulfate heptahydrate, nickel(II) nitrate hexahydrate,

nickel(II) sulfate heptahydrate, nickel(II) sulfate hexahydrate, manganese(II)

chloride tetrahydrate, and manganese(II) nitrate tetrahydrate. The most

preferred active metal is cobalt, and the most preferred cobalt compound is

cobalt(II) nitrate hexahydrate. Any suitable means can be used to mix the particulate carrier and

the particulate active metal compound. The inclined rotary apparatus used in a

subsequent example has been found to be an effective mixing means. As

indicated previously, the mixing is carried out at a temperature approximately

at or above the melting point of the active metal compound but below the

temperature at which such compound decomposes. By way of example, the

mixing temperature for cobalt(II) nitrate hexahydrate is preferably in the range

of about 55-170°C, most preferably about 60-130°C. The required time for

mixing is typically less than 1 hour, most typically about 15-30 minutes. By

such procedure, the particulate carrier is impregnated with the active metal

compound.

If the active metal compound is a hydrate and loses water of

hydration during impregnation, the impregnated carrier is preferably dried in

flowing air at a temperature of about 60- 120°C for a time of about 0.1-4 hours.

The impregnated carrier is then calcined at a suitable temperature, typically in

the range of about 200-800°C. Calcination is preferably carried out in a

flowing air environment for a time of about 0.5-8 hours.

Optionally, the particulate carrier can be impregnated with a

promoter metal to enhance the catalytic activity or to modify its selectivity.

Useful promoter metals are potassium, chromium, magnesium, zirconium, ruthenium, thorium, hafnium cerium, rhenium, uranium, vanadium, titanium,

manganese, nickel, molybdenum, wolfram, lanthanum, palladium,

praseodymium, neodymium or other elements from groups IA or IIA of the

periodic table of the elements. Preferred promoters are selected from platinum,

rhodium, ruthenium, and palladium. Platinum is most preferred. Any suitable

means can be used to impregnate the particulate carrier with the promoter

metal. Impregnation of the particulate carrier with the promoter metals is

typically carried out by using a promoter metal containing compound. Suitable

compounds include halides, nitrates, sulfates, acetates and thiocyanates of the

promoter metal. Preferably the metal promoter containing compound will be

soluble in water. According to an incipient wetness technique, the particulate

carrier can be sprayed with an impregnation solution, having a suitable

promoter metal compound dissolved in water or other solvent, while agitating

the particulate carrier with the above-mentioned inclined rotary apparatus.

Alternatively, slurry impregnation could be employed. The particulate carrier,

as now impregnated with a promoter metal as well as the active metal, is again

dried and calcined, substantially as described above.

The active metal in the finished catalyst can be, by way of

example, in the range of about 1-30 wt.%. The promoter metal in the catalyst

can be in the range of about 0.01-5 wt.%. Weight percentages are based upon the total weight of the catalyst. If desired, the particulate carrier could also be

impregnated with a carrier stabilizer such as barium or lanthanum.

All steps of the inventive process can be conveniently carried out

at atmospheric pressure; as was the case in the inventive examples which are

described below to further illustrate the invention. These examples should not

be construed to limit the invention in any manner.

EXAMPLES

A. Example I

A particulate alumina carrier (obtained from Condea Chemie,

Hamburg, Germany, under the designation "Pural SCF") was first heated in a

muffle furnace at 750°C for 16 hours. After cooling, a sample was analyzed

and found to have a surface area of 148 m²/g. 50.0 g of the alumina was placed

in a beaker and heated in an oven to 121°C (250°F). The beaker was then

placed on an inclined rotary apparatus. While such apparatus rotated the

beaker, 67.5 g of powdered (250-325 mesh) cobalt(II) nitrate hexahydrate was

gradually sprinkled into the beaker to thereby mix with the alumina. The

beaker contents were kept hot by using a hot air gun. This procedure was

continued until there was a uniform coating of the cobalt compound on the

alumina particles. Alumina impregnated with the cobalt compound results. The thus impregnated alumina was loaded into a 2 inch diameter

quartz tube. After starting a flow of air through the tube at 80 cc/min, the

temperature of the tube and its contents was ramped from ambient temperature

to 80°C at 3°C/min. The temperature was held at 80°C for 2 hours. After

cooling to ambient temperature, air flow was reset at 300 cc/min. The

temperature was ramped to 240°C at 3°C/min, and held at 240°C for 2 hours.

The cobalt impregnated alumina was allowed to cool, and then transferred from

the quartz tube to a beaker.

1.4 g of terra ammine platinum nitrate solution (containing 2.0

wt.% platinum) was diluted in 20.0 ml of distilled water to produce an aqueous

solution. While rotating the beaker with the inclined rotary apparatus, an

ultrasonic atomizer was used to spray the aqueous solution onto the cobalt

impregnated alumina particles. The alumina, as now impregnated with

platinum as well as cobalt, was heated in flowing air at 100°C for 2 hours and

then at 240°C for 2 hours in a manner substantially similar to that described

above, thereby resulting in the finished catalyst (Catalyst A).

Scanning Electron Microprobe analysis was performed on

particles of the catalyst. The weight percentage of cobalt was measured at 2.0

micron increments, starting at the edge (0.0) and ending at an increment close

to the center of the particle. Platinum was not measured. The following table provides data for nine particles (where "P" stands for "Particle"). This data

clearly shows the effectiveness of the inventive process in achieving cobalt

penetration in the particles.

Cobalt (wt.%)

P 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0

1 18.7 18.9 15.4 21.6 12.6 14.7

2 0.5 2.7 15.7 10.0 8.7 5.7

3 0.2 0.5 20.4 12.7 5.3 4.0 6.7 8.2 12.0

4 1.5 2.3 14.2 4.0 0.8 1.7 4.9 5 12.1 19.1 6.3 1.3 2.1 4.5 11.7 9.7 7.9

6 10.1 4.5 3.7 0.8 1.1 0.9 1.1 0.9 0.9

7 10.5 5.4 4.5 3.5 6.8 11.3 8.4 6 6..22 6 6..55 4.6 3.1 2.3

8 10.6 12.2 14.2 15.2 15.3 13.5

9 28.7 11.7 10.0 4.5 0.8 1.7 0.8 1.2 0.3 0.3 0.2

B. Control I

A Catalyst was prepared in accordance with the process described

in US 5,733,83 . 50 g of alumina carrier (obtained from Condea Chemie,

Hamburg, Germany, under the designation "Puralox SCCa") was added to a

solution of 40.0 g of Co(NO₃)₂6H₂O dissolved in 50 ml distilled water. The

resultant slurry was treated for 2.5 hours at 75°C and 3.4 kPa in a rotary

evaporator to impregnate the alumina carrier and to dry the impregnated carrier. The dried impregnated carrier was calcined at 230°C for 2 hours in an air flow

of 1.5 l„/min. The resultant calcined sample was re-slurried in a solution that

was made up by dissolving 35.0 g Co(NO₃)₂6H₂O and 53 mg Pt(NH₃)₄(NO₃)₂

in 50 ml of distilled water. This slurry was again vacuum treated for 2.5 hours

at 75°C and 3.4 kPa until free flowing in rotary evaporator. The dried

impregnated carrier was calcined at 230°C for 2 hours in an air flow of 1.5

1,/min to produce the finished catalyst (Catalyst B).

C. Control II

A particulate alumina carrier (obtained from Condea Chemie,

Hamburg, Germany, under the designation "Puralox SCCa") was first heated in

a muffle furnace at 120°C for 4 hours. After cooling, 50.0g of the alumina was

placed in a beaker. An aqueous solution was prepared containing 70g of water,

75 g Co(N03)2.6H20, and 0.68 g of a platinum chloride (10 wt.%) solution

(containing from 3.6 to 4.0 wt.% platinum). 90g of this solution was added to

the beaker containing the alumina and stirred at room temperature for 1 hour.

The mixture was next heated on a hot plate to dryness while stirring. The

resulting material was further dried overnight in air at a temperature of 120°C

followed by calcining at a temperature of 350°C for 3 hours. After cooling to

room temperature the resulting material was further impregnated with the remaining solution (55.68g) using the same procedure to produce the finished

catalyst (Catalyst C).

D. Catalyst Test Procedure

The reactor used in this catalyst test was a 300 cc stirred tank

reactor (purchased from Autoclave Engineers). For each catalyst tested, 10

grams of catalyst were loaded into the reactor and reduced with pure hydrogen

at 300°C, atmospheric pressure and 100 cc/min of hydrogen for approximately

6 hours with slow stirring. After the hydrogen reduction, the catalyst was

cooled to room temperature in hydrogen atmospheric environment. After

cooling, approximately 90 g of octadecane were injected into the reactor. Then

the system was pressurized to 300 psig with a mixture of CO and H₂ and the

temperature increased to 220°C for reaction. The feed gas (CO and H₂) flow

rate and feed ratio were controlled using two calibrated mass flow controllers.

The stirring speed was maintained at 1200 rpm during all tests, which was

sufficient to minimize mass transfer effects between the gas and slurry phases.

The exit gas from the reactor passed through a high-pressure trap (same

pressure as the reaction), then to a low-pressure ice trap (atmospheric pressure)

to collect the liquid products. The outlet gas was sent to an on-line gas chromatograph for compositional analysis. A wet test meter was used to

measure the flow rate of the outlet gas. The tests were conducted for three

days. The liquid product was measured and analyzed everyday. At the end of

the run, the mixture of catalyst, octadecane and wax product accumulated in the

reactor was discharged from the reactor. The catalyst was separated by hot

filtration through a Whatmans 42 filter paper. The wax mixture was analyzed

by gas chromatography. The final product distribution was determined by

combining gas phase, liquid product from the two condensers, and product in

the octadecane solvent. The results for each catalyst are shown in Table I.

TABLE I

Catalyst Catalyst A Catalyst B¹ Catalyst C

Day 1 run

CO conversion (%) 25.08 31.33 25.49 Selectivity to HC 96.87 95.63 94.70 Selectivity to CO₂ 3.13 4.37 5.30

Day 2 run

CO conversion (%) 25.13 30.84 32.37 Selectivity to HC 97.95 96.40 96.56 Selectivity to C0₂ 2.05 3.60 3.44

Day 3 run

CO conversion (%) 19.88 28.00 22.69 Selectivity to HC 97.61 96.86 99.19 Selectivity to C0₂ 2.39 3.14 0.81

TABLE I (Cont.)

Catalyst Catalyst A Catalyst B¹ Catalyst C

Product Olefϊn to Olefin to Olefin to distribution paraffin paraffin paraffin

(wt%) ratio ratio ratio

Cl 9.47 9.45 10.25

C2-C4 8.75 0.86 10.28 1.51 10.47 1.20

C5-C11 20.90 0.30 23.64 0.72 ^' 27.59 0.56

C12-C18 19.65 0.01 22.95 0.02 20.97 0.02

C19+ 41.23 33.70 30.72

Co Content² 4.0 13.3 1.9

(ppm)

¹ The data for Catalyst B is an average of two runs except for the Co content where only one of the two runs was analyzed for Co content.

Cobalt content of the wax product and solvent measured using x-ray fluorescence.

The results from Table I indicate that the inventive method of

producing a Fischer-Tropsch catalyst results in a catalyst with favorable

selectivity, conversion and product distribution. The low Co content for

Catalyst A illustrates that the catalyst has a low attrition even using calcining

temperatures that are relatively low. (Note Catalyst A used a calcining

temperature of 240°C and Catalyst C used a calcining temperature of 350°C).

Additionally, experiments with other catalyst preparation methods have

indicated that Puralox SCCa alumina may result in better carbon monoxide

conversion and a more attrition-resistant catalyst than Pural SCF alumina.

Accordingly, it is believed that a catalyst made in accordance with the inventive

process and using Puralox SCCa alumina would result in an better catalyst than

Catalyst A.

Obviously, many modifications and variations of the present

invention are possible in light of the above teachings. It is, therefore, to be

understood that the invention may be practiced otherwise than as specifically

described.

Claims

THAT WHICH IS CLAIMED IS:

1. A process for preparing a Fischer-Tropsch catalyst

comprising the steps of:

impregnating a particulate carrier with an active metal by mixing

the particulate carrier with a compound containing the active metal at a

temperature approximately at or above the melting point of the compound but

below the temperature at which such compound decomposes to produce an

impregnated carrier.

2. A process according to claim 1 wherein after impregnation

with the active metal, the impregnated carrier is calcined.

3. A process according to claim 1 wherein the active metal is

selected from cobalt, iron, manganese, nickel and mixtures thereof.

4. A process according to claim 3 wherein the active metal is

cobalt.

5. A process according to claim 1 further comprising

impregnating the impregnated carrier with a promoter.

6. A process according to claim 5 wherein said promoter is

selected from platinum, rhodium and palladium.

7. A process according to claim 6 wherein the promoter is

platinum.

8. A process according to claim 1 where in the compound is a

particulate compound.

9. A process for preparing a Fischer-Tropsch catalyst

comprising the steps of:

impregnating a particulate carrier with cobalt by mixing the

particulate carrier with a particulate cobalt compound at a temperature

approximately at or above the melting point of the compound but below the

temperature at which such compound decomposes to produce an impregnated

carrier;

calcining the impregnated carrier to produce a calcined

impregnated carrier; and

impregnating the calcined impregnated carrier with a platinum

compound to produce the catalyst.