WO2001076734A1

WO2001076734A1 - Process for preparing fischer-tropsch catalyst

Info

Publication number: WO2001076734A1
Application number: PCT/US2000/010457
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

Abstract

Disclosed herein is a process for preparing a Fischer-Tropsch catalyst. The process comprises the steps of: a) impregnating a particulate carrier with an alpha-hydroxy carboxylic acid; b) impregnating the acid impregnated carrier with and active metal selected from cobalt, iron, manganese, and nickel; c) 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. In

preparation of a Fischer-Tropsch catalyst, a particulate carrier is typically

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

nickel. 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 alpha-hydroxy carboxylic acid; impregnating the acid impregnated carrier

with an active metal, preferably selected from cobalt, iron, manganese, nickel

and mixtures thereof; 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 substantially

uniform distribution 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, the substantially uniform distribution of active

metal 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.

Suitable alpha-hydroxy carboxylic acids include citric, glycolic,

malic, glyceric, and tartaric acids. Citric acid is most preferred. The particulate

carrier can be impregnated with the acid by using a solution having the acid

dissolved in a suitable solvent, preferably water. According to an incipient

wetness technique, the particulate carrier can be sprayed with the solution while

agitating the particulate carrier with an inclined rotary apparatus, as was used in

the subsequently described examples. Alternatively, slurry impregnation could

be employed. The acid impregnated caπier is then dried, preferably in air, at a

temperature of at least about 80°C for a time of about 0.5-4 hours. When citric

acid is used, the drying temperature is preferably about 100-275°C. The acid

present in the acid impregnated carrier is preferably in the range of about 2-20

wt.%, as based on the weight of the particulate carrier.

The acid impregnated and dried carrier can be impregnated with

the active metal by using a solution with a suitable active metal compound

dissolved in a solvent, preferably water. The impregnation techniques

described above could be employed. Suitable active metal compounds soluble

in water include halides, nitrates, sulfates, acetates, and thiocyanates of the

active metal. The most prefened active metal is cobalt, and cobalt(II) nitrate hexahydrate is a preferred cobalt compound. Optionally, the particulate carrier

can also be impregnated with a promoter metal. 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 I A or IIA of the periodic table of the elements.

Preferred promoters are selected from platinum, rhodium, ruthenium, and

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

typically carried out by using a promoter metal containing compound.

Preferably the promoter metal compound is soluble in the above mentioned

solution containing the active metal compound. Suitable compounds include

halides, nitrates, sulfates, acetates and thiocyanates of the promoter metal. The

thus impregnated carrier is preferably dried in flowing air at a temperature of

about 60-150°C for a time of about 0.1-4 hours. The dried, impregnated earner

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.

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 specific 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

50.0 g of a particulate alumina carrier (obtained from Condea

Chemie, Hamburg, Germany, under the designation "Puralox SCCa") was

placed in a beaker, and the beaker was positioned on an inclined rotary

apparatus. A citric acid solution was prepared by dissolving 5.0 g citric acid in

25 ml of distilled water. The citric acid solution was sprayed on the alumina

while the beaker was rotated by the inclined rotary apparatus. The resulting

acid impregnated alumina was dried at 250°C for 2 hours in an oven. The acid

impregnated alumina was then removed from the oven and allowed to cool.

A cobalt and platinum containing solution was prepared by

dissolving 27.8 g of cobalt(II) nitrate hexahydrate in 13 ml of distilled water,

and then adding 1.4 g of tetraammine platinum nitrate solution (containing 2.0 wt.% platinum). A beaker containing the acid impregnated alumina was rotated

by the inclined rotary apparatus while the cobalt-platinum solution was sprayed

on the alumina with an ultrasonic atomizing nozzle. The alumina, as now

impregnated with cobalt and platinum, was loaded into a 2 inch diameter quartz

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

temperature at 3°C/min to 80°C, and then held at such temperature for 2 hours

while flowing air through the tube at 80 cc/min. The temperature was ramped

at 3°C/min to 240°C, and then held at this temperature for 2 hours while

flowing air through the tube at 300 cc/min. After cooling, the impregnated

alumina was further impregnated with cobalt and platinum and then heated a

second time using the same procedure as described above, with the exception

that 28.4 g of cobalt(II) nitrate hexahydrate and 12 ml of distilled water were

used in preparing the cobalt-platinum solution. A third impregnation and

heating procedure, identical to the second, was performed to result 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 2.63

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

to the center of the particle. Platinum was not measured. Table 1 provides data

for ten particles (where "P" stands for "Particle"). This data clearly shows the effectiveness of the inventive process in achieving substantially uniform

distribution of cobalt in the particles.

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H - B. Example II

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 the beaker was positioned on an inclined rotary apparatus. A

citric acid solution was prepared by dissolving 5.0 g citric acid in 25 ml of

distilled water. The citric acid solution was sprayed on the alumina while the

beaker was rotated by the inclined rotary apparatus. The resulting acid

impregnated alumina was dried at 250°C for 2 hours in an oven. The acid

impregnated alumina was then removed from the oven and allowed to cool.

A cobalt and platinum containing solution was prepared by

and then adding 1.4 g of terra ammine platinum nitrate solution (containing 2.0

wt.% platinum). A beaker containing the acid impregnated alumina was rotated

by the inclined rotary apparatus while the cobalt-platinum solution was sprayed

on the alumina with an ultrasonic atomizing nozzle. The alumina, as now

impregnated with cobalt and platinum, was loaded into a 2 inch diameter quartz

tube. The temperature of the tube and its contents was ramped from ambient temperature at 3°C/min to 80°C, and then held at such temperature for 2 hours

while flowing air through the tube at 80 cc/min. The temperature was ramped

at 3°C/min to 240°C, and then held at this temperature for 2 hours while

flowing air through the tube at 300 cc/min. After cooling, the impregnated

alumina was further impregnated with cobalt and platinum and then heated a

second time using the same procedure as described above, with the exception

that 28.4 g of cobalt(II) nitrate hexahydrate and 12 ml of distilled water were

used in preparing the cobalt-platinum solution. A third impregnation and

heating procedure, identical to the second, was performed to result in the

finished catalyst (Catalyst B).

Scanning Electron Microprobe analysis was performed on

particles of the catalyst. The weight percentage of cobalt was measured in 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. Table 2 provides data

for ten particles (where "P" stands for "Particle"). This data clearly shows the

effectiveness of the inventive process in achieving substantially uniform

distribution of cobalt in the particles. TABLE 2

Cobalt (wt.%)

P 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0

1 12.1 11.8 13.5 12.9 8.9 11.1 13.1

2 15.6 15.1 12.3 13.2 13.1 13.7 14.3 13.3 13.5

3 9.4 10.1 10.7 9.1 9.3 12.8

4 15.1 13.2 12.0 10.9 9.9 12.4 12.6 10.6 12.7

5 14.5 9.6 9.5 11.0 9.4 7.7 8.1 9.7 11.3

6 13.1 13.8 16.1 13.0 13.3 18.1 13.5

7 19.9 9.9 21.4 19.7 19.8 19.2 11.2 7.1 7.0 9.1

8 18.7 20.2 14.9 18.7 13.8 9.8 19.4 18.3 14.1

9 8.8 10.2 10.2 8.7 8.8 9.2 9.9 9.0 9.3

10 11.6 10.0 9.9 16.6 15.8 11.0 13.0 12.1 14.0 8.3

C. Control I

A Catalyst was prepared in accordance with the process described

in US 5,733,839. 50 g of Puralox SCCa Alumina was added to a solution of

40.0 g of Co(N0₃)₂6H₂0 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 1, min. The resultant calcined sample was re-slurried in a solution that was

made up by dissolving 35.0 g Co(N0₃)₂6H₂0 and 53 mg Pt(NH₃)₄(N0₃)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 C).

D. Control II

A particulate alumina earner (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.

90 g 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 D).

E. 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 stining. 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 as solvent.

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

the temperature was 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 stining speed was maintained at 1200 rpm during all tests,

which was sufficient to minimize mass transfer effects between the gas and

slurry phases. The outlet 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 every day. 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 3.

TABLE 3

ϋatalyst Catalyst A Catalyst Catalyst C Catalyst D

Day 1 run

CO conversion (%) 68.96 31.67 31.33 25.49

Selectivity to HC 68.78 95.17 95.63 94.70

Selectivity to C0₂ 31.22 4.83 4.37 5.30

Day 2 run

CO conversion (%) 39.94 17.02 30.84 32.37

Selectivity to HC 92.69 94.98 96.40 96.56

Selectivity to C0₂ 7.31 5.10 3.60 3.44

Day 3 run

CO conversion (%) 39.91 18.01 28.00 22.69

Selectivity to HC 96.26 97.55 96.86 99.19

Selectivity to C0₂ 3.74 2.45 3.14 0.81

TABLE 3 (Cont.)

Catalyst Catalyst A Catalyst B¹ Catalyst C Catalyst D

Product Olefin to Olefin to Olefin to Olefin to distribution paraffin paraffin paraffin paraffin

(wt%) ratio ratio ratio ratio

Cl 8.85 12.04 9.45 10.25

C2-C4 9.82 0.85 10.46 0.83 10.28 1.51 10.47 1.20

C5-C11 29.30 0.42 24.24 0.39 23.64 0.72 27.59 0.56

C12-C18 23.02 0.01 21.41 0.01 22.95 0.02 20.97 0.02

C19+ 29.01 31.85 33.70 30.72

Co 3.1 1.4 13.3 1.9

Content²

(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 3 indicate that the inventive method of

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

selectivity, conversion and product distribution. Also, the inventive catalyst

shows a favorable attrition as shown by the Co content. Additionally, Table 3

indicates better olefin to paraffin ratios than the control methods.

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 alpha-hydroxy

carboxylic acid to produce an acid impregnated carrier;

impregnating the acid impregnated carrier with an active metal to

produce a metal impregnated earner; and

calcining the metal impregnated carrier to produce the catalyst.

2. A process according to claim 1 wherein the alpha-hydroxy

carboxylic acid is chosen from citric, glycolic, malic, glyceric, tartaric acids and

mixtures thereof.

3. A process according to claim 2 wherein the alpha-hydroxy

carboxylic acid is citric acid.

4. A process according to claim 1 wherein the acid impregnated

carrier is impregnated with the active metal by exposing the acid impregnated

ca ier to a solution of an active metal compound.

5. A process according to claim 4 wherein the active metal

compound is a halide, nitrate, sulfate, acetate or thiocyanate of the active metal

or a mixture thereof.

6. A process according to claim 5 wherein the active metal is

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

7. A process according to claim 6 wherein the active metal is

cobalt.

8. A process according to claim 1 further comprising

impregnating the acid impregnated canier with a promoter.

9. A process according to claim 8 wherein the promoter is

selected from platinum, rhodium and palladium.

10. A process according to claim 9 wherein the promoter is

platinum.

11. A process for preparing a Fischer-Tropsch catalyst

comprising the steps of:

impregnating a particulate canier with citric acid to produce an

acid impregnated canier;

impregnating the acid impregnated canier with a promoter and

with cobalt by exposing the acid impregnated carrier to a solution of a cobalt

compound selected from halides, nitrates, sulfates, acetates and thiocyanates of

cobalt and mixtures thereof; and

calcining the thus fonned cobalt impregnated carrier to produce

the catalyst.

12. A process according to claim 11 wherein the promoter is

selected from platinum, rhodium and palladium.

13. A process according to claim 12 wherein the promoter is

platinum.