AU2001245713A1

AU2001245713A1 - Highly active fischer-tropsch synthesis using doped, thermally stable catalyst support

Info

Publication number: AU2001245713A1
Application number: AU2001245713A
Authority: AU
Inventors: Rachid Oukaci; Alan H. Singleton
Original assignee: Sasol Technology (UK) Ltd
Current assignee: Sasol Technology (UK) Ltd
Priority date: 2000-03-17
Filing date: 2001-03-14
Publication date: 2001-12-13
Anticipated expiration: 2021-03-14

Description

HIGHLY ACTIVE FISCHER-TROPSCH SYNTHESIS USING DOPED, THERMALLY STABLE CATALYST SUPPORT

BACKGROUND OF THE INVENTION

1. Technical Field:

This invention relates to alumina supported cobalt catalysts having an improved

stability and high activity for Fischer-Tropsch (F-T) synthesis conducted in a slurry bubble

column and other three-phase type reactors.

2. Background:

In Fischer-Tropsch processes, synthesis gases comprising carbon oxides and hydrogen

are reacted in the presence of Fischer-Tropsch catalysts to produce liquid hydrocarbons.

Fischer-Tropsch synthesis processes are most commonly conducted in fixed bed, gas-solid or

gas-entrained fluidized bed reaction systems, fixed bed reaction systems being the most

commonly used. It is recognized in the art, however, that slurry bubble column reactor

systems offer tremendous potential benefits over these commonly used Fischer-Tropsch

reaction systems.

As mentioned above, the synthesis gas, or "syngas," used in Fischer-Tropsch

processes is typically a mixture consisting primarily of hydrogen and carbon oxides. Syngas

is typically produced, for example, during coal gasification. Processes are also well known

for obtaining syngas from other hydrocarbons, including natural gas. U.S. Patent No.

4,423,265 to Chu et al. notes that the major processes for producing syngas depend either

upon the partial combustion of a hydrocarbon fuel with an oxygen-containing gas or the

reaction of the fuel with steam, or on a combination of these two reactions. U.S. Patent No.

5,324,335 to Benham et al., explains the two primary methods (i.e., steam reforming and

partial oxidation) for producing syngas from methane. The Encyclopedia of Chemical Technology, Second Edition, Nolume 10, pages 3553-433 (1966), Interscience Publishers,

New York, N.Y. and Third Edition, Nolume 11, pages 410-446 (1980), John Wiley and Sons,

New York, N.Y. is said by Chu et al. to contain an excellent summary of gas manufacture,

including the manufacture of synthesis gas.

It has long been recognized that syngas can be converted to liquid hydrocarbons by

the catalytic hydrogenation of carbon monoxide. The general chemistry of the Fischer-

Tropsch synthesis process is as follows:

(1) CO + 2H₂ → (-CH₂-)+H₂O

(2) 2CO+H₂ → (-CH₂-) + CO₂

The types and amounts of reaction products, i.e., the lengths of carbon chains, obtained via

Fischer-Tropsch synthesis vary dependent upon process kinetics and the catalyst selected.

Many attempts at providing active catalysts for selectively converting syngas to liquid

hydrocarbons have previously been disclosed. U.S. Patent No. 5,248,701 to Soled et al.,

presents an over- view of relevant prior art. The two most popular types of catalysts

heretofore used in Fischer-Tropsch synthesis have been iron-based catalysts and cobalt-based

catalysts. U.S. patent No. 5,324,335 to Benham et al. discusses the fact that iron-based

catalysts, due to their high water gas shift activity, favor the overall reaction shown in (2)

above, while cobalt-based catalysts tend to favor reaction scheme (1).

Recent advances have provided a number of catalysts active in Fischer-Tropsch

synthesis. Besides iron and cobalt, other Group NIII metals, particularly ruthenium, are

known Fischer-Tropsch catalysts. The current practice is to support such catalysts on porous,

inorganic refractory oxides. Particularly preferred supports include silica, alumina, silica- alumina, and titania. In addition, other refractory oxides selected from Groups III, IN, N, NI

and NIII may be used as catalyst supports.

The prevailing practice is to also add promoters to the supported catalyst. Promoters

can include ruthenium (when not used as the primary catalyst component), rhenium, hafnium,

cerium, and zirconium. Promoters are known to increase the activity of the catalyst,

sometimes rendering the catalyst three to four times as active as its unpromoted counterpart.

Contemporary cobalt catalysts are typically prepared by impregnating the support

with the catalytic material. As described in U.S. Patent No. 5,252,613 to Chang et al., a

typical catalyst preparation may involve impregnation, by incipient wetness or other known

techniques, of, for example, a cobalt nitrate salt onto a titania, silica or alumina support,

optionally followed or preceded by impregnation with a promoter material. Excess liquid is

then removed and the catalyst precursor is dried. Following drying, or as a continuation

thereof, the catalyst is calcined to convert the salt or compound to its corresponding oxide(s).

The oxide is then reduced by treatment with hydrogen, or a hydrogen-containing gas, for a

period of time sufficient to substantially reduce the oxide to the elemental or catalytic form of

the metal. U.S. Patent No. 5,498,638 to Long points to U.S. Patent Nos. 4,673,993,

4,717,702, 4,477,595, 4,663,305, 4,822,824, 5,036,032, 5,140,050, and 5,292,705 as

disclosing well known catalyst preparation techniques.

As also mentioned above, Fischer-Tropsch synthesis has heretofore been conducted

primarily in fixed bed reactors, gas-solid reactors, and gas-entrained fluidized bed reactors,

fixed bed reactors being the most utilized. U.S. Patent No. 4,670,472 to Dyer et al. provides a

bibliography of several references describing these systems. The entire disclosure of U.S.

Patent No. 4,670,472 is incorporated herein by reference. In contrast to these other hydrocarbon synthesis systems, slurry bubble column

reactors are "three phase" (i.e., solid, liquid, and gas/vapor) reaction systems involving the

introduction of a fluidizing gas into a reactor containing catalyst particles slurried in a

hydrocarbon liquid. The catalyst particles are slurried in the liquid hydrocarbons within a

reactor chamber, typically a tall column. Syngas is then introduced at the bottom of the

column through a distributor plate, which produces small gas bubbles. The gas bubbles

migrate up and through the column, causing beneficial agitation and turbulence, while

reacting in the presence of the catalyst to produce liquid and gaseous hydrocarbon products.

Gaseous products are captured at the top of the SBCR, while liquid products are recovered

through a filter which separates the liquid hydrocarbons from the catalyst fines. U.S. Patent

Nos. 4,684,756, 4,788,222, 5,157,054, 5,348,982, and 5,527,473 reference this type of system

and provide citations to pertinent patent and literature art. The entire disclosure of each of

these patents is incorporated herein by reference.

It is recognized that conducting Fischer-Tropsch synthesis using a SBCR system

could provide significant advantages. As noted by Rice et al. in U.S. Patent No. 4,788,222,

the potential benefits of a slurry process over a fixed bed process include better control of the

exothermic heat produced by the Fischer-Tropsch reactions, as well as better maintenance of

catalyst activity by allowing continuous recycling, recovery and rejuvenation procedures to

be implemented. U.S. Patent Nos. 5,157,054, 5,348,982, and 5,527,473 also discuss

advantages of the SBCR process.

Normal operation of F-T synthesis leads to the buildup of carbonaceous deposits on a

cobalt catalyst resulting in catalyst deactivation with time-on-stream, the amount of this

major source of deactivation being related to the reaction conditions used. In general, cobalt catalysts may be regenerated by calcination at relatively high temperatures (burning off the

carbon residues) followed by reduction. However, the successive exposure of these catalysts

to high temperatures may result in a slow decrease of the support surface area followed by

encapsulation of cobalt particles and the formation of harder to reduce or totally non¬

reducible cobalt-metal compounds. All these changes are associated with a decrease of the

cobalt surface area accessible to reactants which results in a slow loss of activity after each

regeneration cycle.

Alumina, one of the common oxides used as a support for cobalt-based F-T catalysts,

is well known to be sensitive to the pretreatment temperatures and the amount of time it is

subjected to high temperatures. The crystalline form of the alumina most commonly used as

catalyst support is γ-alumina. It is generally obtained by dehydration of aluminum hydroxide

(boehmite) by heating under suitable conditions (typically, 300-650 °C). Further heating,

either during the pretreatment step, during the use of the catalyst or during catalyst

regeneration may result in a slow and continuous loss of surface area and a slow conversion

of the alumina from its γ-alumina phase to other forms (δ-alumina then θ-alumina) which

have much lower surface areas. Finally, especially at very high temperatures, a collapse of

the structure resulting in the formation of a dense, highly stable, low surface area α-alumina

can occur.

It has been suggested by Condea/Nista and by R. Gaugin, M. Graulier, and D. Papee,

"Thermally Stable Carriers," Advances in Chemistry Series. Vol. 143, p. 147 (1975) that the

thermal stability of some γ-aluminas materials can be enhanced by incorporating into the

alumina small amounts of divalent ions, such as calcium, magnesium, or barium or rare earth

oxides such as lanthana. These are believed to occupy tetrahedral voids in the spinel and retard the diffusion of Al³⁺ cations. However, the effects of such support additives on the

activities and other characteristics of any catalysts formed therefrom are unknown. The

activities and selectivities of Fischer-Tropsch catalysts, for example, are known to be extremely sensitive to changes in catalyst or support compositions.

SUMMARY OF THE INVENTION

The invention unexpectedly and surprisingly provides highly stable and highly active

alumina supported cobalt catalysts for use in Fischer-Tropsch synthesis processes.

In another aspect, the inventive method comprises the step of reacting a synthesis gas

in a slurry bubble column reactor system in the presence of a catalyst comprising a γ-alumina

support, wherein the γ-alumina support includes an amount of lanthana or barium oxide

effective for increasing the thermal stability of the catalyst.

Further objects, features, and advantages of the present invention will be apparent

upon examining the accompanying drawings and upon reading the following detailed

description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 provides a graph comparing the thermal stability of lanthanum- and barium-

doped aluminas to the thermal stability of a more common non-doped alumina.

Figure 2 provides a graph comparing the Fischer-Tropsch synthesis performances in a

slurry bubble column reactor of promoted cobalt catalysts supported on non-doped,

lanthanum-doped and barium-doped aluminas.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Catalyst Compositions The present invention provides supported cobalt catalysts which are well suited for

use in Fischer-Tropsch synthesis processes. These catalysts are particularly well suited for

use in three-phase reactor processes. Examples of general catalyst compositions provided by

the present invention include: (a) cobalt, without any promoter, preferably supported on

doped γ-alumina ; (b) cobalt, with one or more noble metal promoters, preferably supported

on doped γ-alumina; (c) cobalt, promoted with both a noble metal promoter and one or more

selectivity promoters (preferably an alkali or rare earth oxide), preferably supported on doped

γ-alumina; and (d) cobalt, promoted with one or more selectivity promoters and without a

noble metal promoter, preferably supported on doped γ-alumina. Examples of typical

promoters include, but are not limited to, noble metals such as ruthenium, metal oxides such

as oxides of zirconium, lanthanum, or potassium, and other oxides of elements from Groups

IA, IIA, IVB, VB, and VIB.

Preferred catalyst compositions comprise (per 100 parts by weight of support): from

about 10 to about 70 pbw cobalt; from about 0.1 to about 8 pbw ruthenium (when present);

from about 0.1 to about 8 pbw potassium (when present); and from about 0.5 to about 8 pbw

lanthana (when present). The catalyst can also include other promoter materials. We have

discovered that, to obtain a particularly desirable combination of selectivity and activity,

particularly in reaction systems such as slurry bubble column reactors, the catalysts will most

preferably comprise (per 100 parts by weight of support): from about 15 to about 55 pbw

(more preferably from about 20 to about 45 pbw) cobalt; from about 0.2 to about 1.5 pbw

ruthenium (when present); from about 0.2 to about 1.0 pbw potassium (when present); and

from about 0.5 to about 5.0 pbw (most preferably from about 0.9 to about 2.5 pbw) lanthana

(when present). The Catalyst Support

The catalyst support employed in the present invention is preferably a lanthanum or a

barium doped γ-alumina support having: a low level of impurities, especially sulfur

(preferably less than 100 ppm sulfur); a spheroidal shape; an average particle size in the range

of from about 10 to about 150 μm (most preferably from about 20 to about 80 microns); a

BET surface area, after calcination, in the range of from about 200 to about 260 m²/g; and a

porosity in the range of from about 0.4 to about 1.0 cm³/g.

The alumina support is preferably produced from relatively high purity, synthetic

boehmite. As discussed hereinbelow, the boehmite can be formed from aluminum alkoxide

of the type obtained in the manufacture of synthetic fatty alcohols. Alternatively, suitable,

high purity boehmite materials can be formed from aluminum alkoxide produced by

alcohol/aluminum metal reaction processes.

The aluminum alkoxide is preferably hydrolyzed to produce high purity, synthetic,

monohydrate alumina. Next, this material is preferably spray-dried to yield highly porous,

spherical boehmite particles of relatively high surface area. The particulate boehmite material

is preferably then sieved to remove fines and large particles so that a desired particle size

range is obtained (most preferably from about 20 to about 80 microns). The sieved material

is calcined to convert the boehmite particles to a γ-alumina support material having the

desired surface area and porosity. The boehmite material will preferably be calcined at a

temperature of at least 350°C (more preferably from about 400°C to about 700°C and most

preferably about 500 °C) for a period of from about 3 to about 24 hours (more preferably from

about 5 to about 16 hours and most preferably about 10 hours). The desired calcination temperature is preferably reached by slowly heating the system at a rate of about 0.5-

2.0°C/minute.

The LajOj or BaO dopant will preferably be present in the γ-alumina support in an

amount in the range of from about 1% to about 5 % of La^ or BaO based on the total

weight of the support. The dopant will more preferably be present in the support in an

amount in the range of 2 to 3% by weight and will most preferably be present in an amount of

about 3% by weight. The dopant can be added at substantially any time but will most

preferably be added prior to crystallization of the boehmite.

As is well known to those skilled in the art, one of the ways of producing synthetic

boehmite materials utilizes aluminum alkoxides recovered as byproducts of certain processes

(e.g., the Ziegler Process) for manufacturing synthetic fatty alcohols. The Ziegler Process

comprises the steps of: (1) reacting high purity alumina powder with ethylene and hydrogen

to produce aluminum triethyl; (2) polymerizing ethylene by contacting it with the aluminum

triethyl, thus resulting in the formation aluminum alkyls; (3) oxidizing the aluminum alkyls

with air to produce aluminum alkoxides; and (4) hydrolizing the aluminum alkoxides to

produce alcohols and an alumina byproduct.

In another process, aluminum alkoxide is formed by reacting an alcohol with a highly

pure aluminum powder. The aluminum alkoxide is then hydrolyzed to produce an alcohol,

which is recycled for use in the alkoxide formation step, and alumina. For purposes of the

present invention, any desired amount of dopant, whether lanthanum and/or barium, can be

included in the alumina product by, for example, adding a corresponding dopant alkoxide to,

and co-hydrolyzing the dopant alkoxide with, the aluminum alkoxide formed in the first step

of this process. For comparison purposes, examples of commercially-supplied boehmite materials

suitable for forming non-doped γ-alumina supports otherwise of the type employed in the

present invention include the CATAPAL and PURAL aluminas supplied by Condea/Nista.

These materials may contain up to 2000 ppm of titanium by weight, depending on the process

used for their manufacture. The commercial materials of this type, which can be effective for

making highly active F-T cobalt-based catalysts, do not always provide adequate thermal

stability and may limit the number of reaction-regeneration cycles allowable during the

overall life of these catalysts.

Figure 1, reproduced from data obtained by Condea/Nista, shows the reported effect

of lanthanum and barium doping on the thermal stability of aluminas. The doped aluminas

contain about 3% by weight of lanthana and barium oxide, respectively. These results show

that the surface area of the conventional (non-doped) alumina Pural SB decreases

significantly when it is heated above 1000 °C for several hours. However, the doped

aluminas did not undergo such a drastic decrease in surface area when subjected to the same

heat treatment. Thus, the lanthana and barium oxide played a major role in improving the

stabilities of these bare aluminas even at temperatures where the aluminas are expected to be

converted to a phase having a surface area of only a few m /g. Although F-T catalysts

using these aluminas will not be subjected to such high temperatures, repeated regenerations

even at much lower temperatures of the order of 300-500 °C may, eventually, also

significantly decrease the surface areas of conventional, non-doped alumina supports.

Catalyst Preparation

The catalytic components of the preferred catalysts are preferably added to the support

by totally aqueous impregnation using appropriate aqueous solution compositions and volumes to achieve incipient wetness of the support material with the desired metal

loading(s). Promoted catalysts are most preferably prepared by totally aqueous co-

impregnation. Examples of typical promoters include: noble metals; metal oxides such as

oxides of Zr, La, K; and other oxides of elements from Groups IA, IIA, IVB, VB, and VIB.

In accordance with the present invention, the totally aqueous impregnation of cobalt

onto the support, with or without one or more desired promoters, is preferably accomplished

by the steps of: (a) calcining the alumina support in the manner described above; (b)

impregnating the support with an aqueous solution of cobalt nitrate, or of cobalt nitrate and

one or more promoter compounds (preferably one or more promoter-nitrates [e.g., ruthenium

(III) nitrosyl nitrate] and/or promoter-chlorides [e.g., ruthenium III chloride], most preferably

promoter- nitrates) using a sufficient quantity of the solution to achieve incipient wetness

with a desired loading of cobalt and of any desired promoter(s); (c) drying the resulting

catalyst precursor for about 5-24 hours at approximately 80-130°C, with moderate mixing, to

remove solvent water and obtain a dried catalyst; and (d) calcining the dried catalyst in air or

nitrogen by slowly raising the temperature of the system at a rate of about 0.5-2.0°C per

minute to approximately 250-400°C and then holding for at least 2 hours to obtain the oxide

form of the catalyst. Multiple impregnation/co-impregnation steps (b) can be used when

higher cobalt loadings are desired.

As one example, a particularly preferred ruthenium-promoted cobalt catalyst is

prepared according to the following procedure. First, the support, preferably a lanthanum or

barium doped γ-alumina, is calcined at from about 400 °C to about 700°C, preferably about

500 °C, for about 10 hours. The calcined support is then impregnated with an aqueous

solution containing both cobalt nitrate [Co(NO₃)₂ - 6H₂O] and ruthenium (III) nitrosyl nitrate [Ru(NO)(NO₃)₃ - xH₂O] using an appropriate quantity to achieve incipient wetness with the

desired loadings of cobalt and ruthenium. The resulting catalyst precursor is then dried for 5

hours at 115°C with moderate stirring in order to remove the solvent water. The dried

catalyst is then calcined in air by raising its temperature at a rate of l°C/min to 300°C and holding for at least 2 hours.

Catalyst Activation

To provide optimum performance, it is presently preferred that the catalyst be

activated/reduced in a hydrogen-containing gas by slowly increasing the temperature of the

catalyst, preferably at a rate of about 0.5-2.0°C/minute, to approximately 250-400°C

(preferably about 350°C) and holding at the desired temperature for at least 2 hours. After

reduction, the catalyst is preferably cooled in flowing nitrogen.

The reducing gas preferably comprises from about 1% to 100% by volume hydrogen,

with the remainder (if any) being an inert gas, typically nitrogen. The reducing gas is

preferably delivered at a rate of about 2-4 (preferably about 3) liters per hour per gram of

catalyst. The reduction procedure is preferably conducted in a fluidized bed reactor. The

reduction procedure is most preferably conducted at conditions (i.e., temperature, flow rate,

hydrogen concentration, etc.) effective to ensure that a very low water vapor partial pressure

is maintained during the procedure.

The Fischer-Tropsch Reaction Process

The catalysts prepared and activated in accordance with the present invention can be

employed in generally any Fischer-Tropsch synthesis process. For slurry bubble column and

other three-phase reaction systems, the catalyst will preferably be slurried in a Fischer-

Tropsch wax or in a synthetic fluid (e.g., a C₃₀ to C₅₀ range isoparaffin polyalphaolefin such as that available from Chevron under the name S YNFLUID) having properties similar to

those of Fischer-Tropsch wax. The catalyst slurry will preferably have a catalyst

concentration in the range of from about 5% to about 40% by weight based on the total

weight of the slurry.

The synthesis gas feed used in the reaction process will preferably have a CO:H₂

volume ratio of from about 0.5 to about 3.0 and will preferably have an inert gas (i.e.,

nitrogen, argon, or other inert gas) concentration in the range of from 0 to about 60% by

volume based on the total volume of the feed. The inert gas is preferably nitrogen.

Prior to initiating the reaction process, the activated catalyst will most preferably be

maintained in an inert atmosphere. Before adding the catalyst thereto, the slurry fluid will

preferably be purged with nitrogen or other inert gas to remove any dissolved oxygen. The

slurry composition will also preferably be transferred to the reaction system under an inert

atmosphere.

A particularly preferred SBCR reaction procedure comprises the steps of: (a) filling

the SBCR, under an inert atmosphere, with the activated catalyst slurry; (b) heating and

pressurizing the SBCR, under an inert atmosphere, to the desired pretreatment conditions

(preferably a temperature in the range of from about 220°C to about 250°C and a pressure in

the range of from about 50 to about 500 psig) ; (c) replacing the inert gas with hydrogen and

holding the system at these conditions for from about 2 to about 20 hours; (d) purging the

system with inert gas and lowering the reaction system temperature, if necessary, to a point at

least about 10°C below the desired reaction temperature; (e) carefully replacing the inert gas

with the desired synthesis gas; and (f) heating and pressurizing the reaction system, as

necessary, to a desired operating temperature, preferably in the range of from about 190°C to about 300°C, and a desired operating pressure, preferably in the range of from about 50 to about 900 psig.

EXAMPLES

The following examples describe the preparation of various catalysts and the results

obtained from testing these catalysts for conversion of synthesis gas into hydrocarbons.

Before being tested, each catalysts was reduced in a pure hydrogen gas by slowly increasing

the temperature of the catalyst, at a rate of about 1.0 °C/minute, to about 350°C and holding

at this temperature for 10 hours. The hydrogen was delivered at a rate of about 3 liters per

hour per gram of catalyst. After reduction, the catalyst was cooled in flowing nitrogen.

For the slurry bubble column reactor tests, the reduction procedure was conducted in a

fluidized bed reactor. After cooling to ambient temperature, the catalyst was weighed,

slurried in Synfluid and transferred to the SBCR under an inert atmosphere. All the F-T

reaction tests in the SBCR were carried out at 230 °C, 450 psig, 900 sl/hr syngas containing

60%) nitrogen and having a H₂/CO ratio of 2, using 15-25 g of reduced catalyst. The catalysts

comparison was based on results obtained after 24 hours of time-on-stream

The following catalysts were prepared in the same manner and with the same loading

of cobalt and ruthenium, but different alumina supports.

CATALYST 1: ( Ru-promoted cobalt F-T catalyst on CATAPAL B alumina with 20

wt% cobalt and 0.5 wt% ruthenium)

Preparation Procedure: Catapal B alumina from CondeaNista in the boehmite form was calcined at 500°C for

10 hrs to convert it to γ-alumina. It was then presieved to 400-170 mesh (or particle

size range greater than 38 microns and lower than 88 microns).

The γ-alumina was impregnated with an aqueous solution of cobalt nitrate

[Co(ΝO₃)₂6H₂O] and ruthenium (III) nitrosylnitrate [Ru(NO)(NO₃)₃ xH₂O] using an

appropriate quantity for incipient wetness (ca. 1.2 ml/g) with the desired loading of

Co. The catalyst precursor was then dried in air at 115°C for 5 hours and calcined in

air at 300°C for 2 hours (heating rate of ca. l°C/min to 300°C).

Reduction Procedure before Reaction:

The catalyst was reduced in a pure hydrogen flow of 3000 cc/g/hr by heating at

l°C/min to 350°C and holding for 10 hrs.

Each of the following catalysts 2-5 were prepared in the same manner as catalyst 1.

The specific supports employed in catalysts 2-5 were as follows:

CATALYST 2: PURAL SB support supplied by Condea/Vista. The PURAL SB was

produced by Condea/Vista in a manner similar to CATAPAL B, but at a different

plant using a blending process.

CATALYST 3: The support, PURAL SB 1, was also supplied by Condea/Vista and

was identical to PURAL SB except that the PURAL SB1 support did not contain

titanium. CATALYST 4: The support, PURALOX DP/L3, was also supplied by Condea/Vista

and was identical to PURAL SB except that the PURALOX DP/L3 support was

doped with 2.8% by weight of lanthanum oxide (La₂O₃) and precalcined by the

manufacturer at conditions similar to those used for Catalysts 1-3 in order to obtain a

comparable surface area (200-250 m /g).

CATALYST 5: The support, PURALOX DP/B3, was also supplied by Condea/Vista

and was identical to PURAL SB except that the PURALOX DP/B3 support was

doped with 2.7% by weight of barium oxide (BaO) and precalcined by the

comparable surface area (200-250 m²/g).

The particular CATAPAL B support material employed in Catalyst 1 was determined

to contain an amount of titania "impurity" of about 1000 ppm by weight (expressed as ppm by

weight of titanium) which was incidentally added, as part of the Ziegler Process, prior to the

crystallization of the boehmite. The BET surface area of the CATAPAL B alumina calcined

at 500 °C for 10 hours was 221 m²/g. In contrast, the particular PURAL SB support material

employed in Catalyst 2 had been formed by a blending process and was found to contain only

about 500 ppm of titanium. The BET surface area of the PURAL SB alumina calcined at 500

°C for 10 hours was 204 m²/g. The particular γ-alumina support, PURAL SB1, employed in

Catalyst 3 was specially produced for us by Condea/Vista. The PURAL SB1 was identical to

PURAL SB except that special efforts were made to prevent the addition of titanium. An

elemental analysis showed that the PURAL SB1 support contained only 7 ppm of titanium. The BET surface area of the PURAL SB1 alumina calcined at 500 °C for 10 hours was 209

m²/g.

The particular γ-alumina support, PURALOX DP/L3, employed in Catalyst 4 was

specially produced for us by Condea/Vista. The PURALOX DP/L3 was identical to PURAL

SB except that the PURALOX DP/L3 support was doped with lanthanum and precalcined by

the manufacturer at conditions similar to those used for Catalysts 1-3 in order to obtained a

comparable surface area. An elemental analysis showed that the PURALOX DP/L3 support

contained only 2.8% by weight of lanthanum oxide (La₂O₃) and 1865 ppm by weight of

titanium oxide (TiO₂). Its BET surface area was 201 m²/g.

The particular γ-alumina support, PURALOX DP/B3, employed in Catalyst 5 was

also specially produced for us by Condea/Vista. The PURALOX DP/B3 was identical to

PURALOX DP/L3 except that the PURALOX DP/B3 support was doped with barium and

precalcined by the manufacturer at conditions similar to those used for Catalysts 1-3 in order

to obtained a comparable surface area. An elemental analysis showed that the PURALOX

DP/B3 support contained only 2.7% by weight of barium oxide (BaO) and 40 ppm by weight

of titanium oxide (TiO₂). Its BET surface area was 226 m²/g.

Catalysts 1-5 were tested in a slurry bubble column reactor. Table 1 and Figure 2

show the activities (expressed in g-HC/kg-cat/hr) exhibited by each catalyst after its first 24

hours of use. A comparison of catalysts 1-3 illustrates the detrimental effect of titania on the

activities of ruthenium promoted cobalt-on-alumina catalysts. As the amount of titania in the

support increased, the activity of the catalyst declined from about 1400 for Catalyst 3, to

about 1322 for Catalyst 2, and to about 1195 for Catalyst 1. However, doping the alumina with lanthanum is believed to have reversed the effect

of titanium. Catalyst 4 contained about the same amount of titanium as Catalyst 1, but its

activity was, within experimental error, as high as those of Catalysts 3 and 4 which contained

lower amounts of titanium.

The Catalyst 5 support contained almost no titanium, but was doped with about 3 %

barium oxide. The activity of this BaO doped catalyst was, within experimental error, almost

identical to that of Catalyst 4.

In addition to these desirable and surprising results, a comparison of the selectivities

of the five catalysts (see Table 1), shows that the doping of the alumina had no effect on

catalyst selectivity. Within experimental error, the selectivities of the five catalysts for

methane and C₅+ would be considered identical.

Thus, lanthanum or barium doping of the alumina support unexpectedly and

surprisingly provides not only a higher stability for the catalyst but also a higher activity for

Fischer-Tropsch synthesis, without any negative effect on the selectivity.

TABLE 1

EFFECT OF SUPPORT DOPANTS - SBCR SUMMARY DATA (FIRST 24 HOUR AVERAGE)

Thus, the present invention is well adapted to carry out the objects and attain the ends and

advantages mentioned above, as well as those inherent therein. While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification.

Claims

WHAT IS CLAIMED IS:

1. A catalyst comprising:

a γ-alumina support including a dopant selected from the group consisting of a lanthanum dopant, a barium dopant, and combinations thereof and an amount of cobalt, on said γ-alumina support, effective for hydrocarbon synthesis in a slurry bubble column-type reaction system, wherein said dopant is present in said γ-alumina support in an amount effective for increasing the thermal stability of said catalyst for use in said slurry bubble

column-type reaction system without reducing the activity of said catalyst for said hydrocarbon synthesis.

2. The catalyst of claim 1 wherein said amount of said dopant present in said support is in the range of from about 1% to about 5% by weight based on the total weight of said γ-alumina

support.

3. The catalyst of claim 1 wherein said amount of said dopant present in said support is in the range of from about 2% to about 3% by weight based on the total weight of said γ-alumina

support.

4. The catalyst of claim 1 wherein said amount of said dopant present in said support is

about 3% by weight based on the total weight of said γ-alumina support.

5. The catalyst of claim 1 wherein said γ-alumina support is produced from aluminum alkoxide using spray-drying and calcination processes effective such that said γ-alumina support has a spheroidal shape, a BET surface area in the range of from about 200 to about 260 m²/g, and a porosity in the range of from about 0.4 to about 1.0 cmVg.

6. The catalyst of claim 1 wherein said dopant is incorporated in said γ-alumina support by adding a dopant alkoxide to, and co-hydrolyzing said dopant alkoxide with, said aluminum alkoxide.

7. The catalyst of claim 1 wherein said dopant is barium oxide.

8. The catalyst of claim 1 wherein said dopant is lanthanum oxide.

9. The catalyst of claim 1 wherein said dopant is present in said γ-alumina support in an amount effective for increasing the activity of said catalyst for said hydrocarbon synthesis in said

slurry bubble column-type reaction system.

10. The catalyst of claim 1 wherein said cobalt is added to said support by totally aqueous impregnation.

11. The catalyst of claim 1 further comprising at least one promoter.

12. The catalyst of claim 11 wherein said cobalt and said promoter are added to said support by totally aqueous co-impregnation.

13. The catalyst of claim 11 wherein said promoter is a ruthenium promoter.

14. A method of Fischer-Tropsch hydrocarbon synthesis comprising the step of reacting a

synthesis gas in a Fischer-Tropsch reaction system in the presence of a catalyst comprising:

a γ-alumina support having an internal structure comprising γ-alumina and a controlled

amount of a dopant selected from the group consisting of a lanthanum dopant, a barium dopant, and combinations thereof and

an amount of cobalt, on said γ-alumina support, effective for said Fischer-Tropsch hydrocarbon synthesis in said Fischer-Tropsch reaction system,

wherein said controlled amount of said dopant is an amount effective for increasing the thermal stability of said catalyst for use in said Fischer-Tropsch reaction system without reducing the activity of said catalyst for said Fischer-Tropsch hydrocarbon

synthesis.

15. The method of claim 14 wherein said controlled amount of said dopant present in said internal structure of said γ-alumina support is in the range of from about 1% to about 5% by weight based on the total weight of said γ-alumina support.

16. The method of claim 14 wherein said controlled amount of said dopant present in said internal structure of said γ-alumina support is in the range of from about 2% to about 3% by

weight based on the total weight of said γ-alumina support.

17. The method of claim 14 wherein said controlled amount of said dopant present in said

internal structure of said γ-alumina support is about 3.0% by weight based on the total weight of said γ-alumina support.

18. The method of claim 14 wherein said γ-alumina support having said controlled amount

of said dopant in said internal structure thereof is produced from aluminum alkoxide using spray- drying and calcination processes effective such that said γ-alumina support has a spheroidal shape, a BET surface area in the range of from about 200 to about 260 m²/g, and a porosity in the

range of from about 0.4 to about 1.0 c Vg.

19. The method of claim 14 wherein said γ-alumina support is produced from aluminum

alkoxide and said controlled amount of said dopant is incorporated in said internal structure of said γ-alumina support by adding a dopant alkoxide to, and co-hydrolyzing said dopant alkoxide

with, said aluminum alkoxide.

20. The method of claim 14 wherein said dopant is barium oxide.

21. The method of claim 14 wherein said dopant is lanthanum oxide.

22. The method of claim 14 wherein said dopant is present in said γ-alumina support in an amount effective for increasing the activity of said catalyst for said hydrocarbon synthesis in said slurry bubble column-type reaction system.

23. The method of claim 14 wherein said cobalt is added to said support by totally aqueous impregnation.

24. The method of claim 14 wherein said catalyst further comprises at least one promoter.

25. The method of claim 24 wherein said cobalt and said promoter are added to said support

by totally aqueous co-impregnation.

26. The method of claim 24 wherein said promoter is a ruthenium promoter.

27. The method of claim 14 wherein: said γ-alumina support is produced from synthetic boehmite and said controlled amount of said dopant is added to said γ-alumina support prior to the

crystallization of said synthetic boehmite.

28. A method of Fischer-Tropsch hydrocarbon synthesis comprising the step of reacting a

a γ-alumina support; an amount of cobalt, supported on said γ-alumina support, effective for said Fischer-

Tropsch hydrocarbon synthesis in said Fischer-Tropsch reaction system; and at least one promoter on said γ-alumina support with said cobalt, said γ-alumina support having an internal structure comprising γ-alumina, at least 500 ppm of titania, expressed as elemental titanium and based on the total weight of

the γ-alumina support, and a controlled amount of a dopant selected from the group consisting of a lanthanum dopant, a barium dopant, and combinations

thereof and wherein said controlled amount of said dopant is an amount effective for increasing both the activity and the thermal stability of said catalyst for said Fischer-Tropsch hydrocarbon synthesis in said Fischer-Tropsch reaction system.

29. The method of claim 28 wherein said one promoter is ruthenium.

30. The method of claim 28 wherein said controlled amount of said dopant present in said internal structure of said γ-alumina support is in the range of from about 1% to about 5% by

weight based on the total weight of said γ-alumina support.

31. The method of claim 28 wherein said controlled amount of said dopant present in said internal structure of said γ-alumina support is in the range of from about 2% to about 3% by

weight based on the total weight of said γ-alumina support.

32. The method of claim 28 wherein said γ-alumina support is produced from aluminum alkoxide which is hydrolyzed to produce an alumina product and wherein said dopant is

incorporated in said γ-alumina support by adding a dopant alkoxide to, and co-hydrolyzing said

dopant alkoxide with, said aluminum alkoxide in an amount effective to yield said controlled amount of said dopant in said internal structure of said γ-alumina support.

33. The method of claim 28 wherein:

said γ-alumina support is produced from synthetic boehmite and

said controlled amount of said dopant is added to said γ-alumina support prior to

crystalizing said synthetic boehmite.