WO2008090105A2

WO2008090105A2 - Process for preparing a catalyst

Info

Publication number: WO2008090105A2
Application number: PCT/EP2008/050603
Authority: WO
Inventors: Abderrahmane Chettouf; Ronald Jan Dogterom; Carolus Matthias Anna Maria Mesters
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 2007-01-23
Filing date: 2008-01-21
Publication date: 2008-07-31
Also published as: WO2008090105A3

Abstract

A process for the preparation of a Fischer-Tropsch catalyst or catalyst precursor, comprising the steps of : (a) shaping a carrier material comprising titania; (b) calcining the shaped carrier; (c) impregnating the carrier with an excess volume of a melt of a cobalt nitrate salt; and (d) keeping the temperature of the resulting catalyst or catalyst precursor below 180 °C up to the moment the resulting catalyst or catalyst precursor is subjected to an activation step or used in a Fischer-Tropsch reaction.

Description

PROCESS FOR PREPARING A CATALYST

The present invention relates to a process for preparing a catalyst or catalyst precursor suitable for use in producing normally gaseous, normally liquid and optionally solid hydrocarbons from synthesis gas generally provided from a hydrocarbonaceous feed, for example a Fischer-Tropsch process. The invention further relates to the obtained catalyst or catalyst precursor and the use thereof in Fischer-Tropsch processes.

Many documents are known describing processes for the catalytic conversion of (gaseous) hydrocarbonaceous feedstocks, especially methane, natural gas and/or associated gas, into liquid products, especially methanol and liquid hydrocarbons, particularly paraffinic hydrocarbons. In this respect often reference is made to remote locations and/or off-shore locations, where direct use of the gas, e.g. through a pipeline or in the form of liquefied natural gas, is not always practical. This holds even more in the case of relatively small gas production rates and/or fields. Re-injection of gas will add to the costs of oil production, and may, in the case of associated gas, result in undesired effects on the crude oil production. Burning of associated gas has become an undesired option in view of depletion of hydrocarbon sources and air pollution. The Fischer-Tropsch process can be used as part of the conversion of hydrocarbonaceous feed stocks into liquid and/or solid hydrocarbons. Generally the feed stock (e.g. natural gas, associates gas and/or coal-bed methane, coal) is converted in a first step into a mixture of hydrogen and carbon monoxide (this mixture is often referred to as synthesis gas or syngas) . The synthesis gas is then fed into a reactor where it is converted in one or more steps over a suitable catalyst at elevated temperature and pressure into compounds ranging from methane to high molecular weight modules comprising up to 200 carbon atoms, or, under particular circumstances, even more, (and water) .

Catalysts used in the Fischer-Tropsch synthesis often comprise a carrier based support material and one or more metals from Group VIII of the Periodic Table, especially from the cobalt or iron groups, optionally in combination with one or more metal oxides and/or metals as promoters selected from zirconium, titanium, chromium, vanadium and manganese, especially manganese. Such catalysts are known in the art and have been described for example, in the specifications of WO 9700231A and US 4595703.

Catalysts can be prepared by obtaining a cobalt hydroxide, applying it to a carrier, and carefully oxidising the cobalt hydroxide to cobalt oxide. Before use, the cobalt oxide is normally reduced to metallic cobalt. Such a reduction step may be performed after placing the catalyst in the appropriate reactor.

One catalyst for Fischer-Tropsch reactions is cobalt on titania carrier material. In one method to prepare the catalyst, cobalt hydroxide (Co(OH)₂) is mixed with titania, and then formed, for example extruded. The obtained particles, for example extrudates, are then calcined.

Calcination is carried out at a temperature generally from 350 to 750⁰C, often a temperature in the range of from 450 to 550⁰C. The aim of the calcination treatment is to provide strength to the particles, to decompose volatile products and to convert organic and inorganic compounds to their respective oxides. During the calcination, the Co (OH) 2 is decomposed to form cobalt oxide (CoO), and further oxidised to Co₃O₄, being a mixture of Co^⁺ and Co-^⁺. Before being used in a Fischer- Tropsch reaction, the cobalt oxide (Co₃O₄) is reduced to metallic cobalt (Co) .

One advantage of a preparation method in which a cobalt compound is mixed with the carrier material before forming or shaping the material is that the cobalt is loaded throughout the carrier material.

However, the required calcination step naturally involves some cost both in terms of the process and equipment. There is also possibly uncontrolled cracking and tension in the catalyst particles which is undesired. There is the further problem of formation of unwanted compounds such as cobalt titanate . All these factors limit the range and types of compounds that can be used in catalyst formation, as well as reducing the activity of the catalyst formed. Another method to prepare a cobalt catalyst suitable for Fischer-Tropsch is to impregnate a carrier with a cobalt compound. Several factors determine the distribution profile of the cobalt in the carrier after impregnation. For example, the carrier material, the carrier shape, and the cobalt compound have an influence on the distribution of the cobalt. Normally egg-shell catalysts are obtained.

US 5,036,032 relates to a method of preparing a supported cobalt catalyst particle which comprises contacting a carrier particle with a molten cobalt salt only for a very short (seconds) period sufficient to impregnate the salt on the carrier to a depth of less than 200 micron, followed by drying and reducing the cobalt. Catalyst particles where only minimum penetration of cobalt into the carrier is achievable, are also known as 'egg-shell ' catalysts. US 5,036,032 shows that calcination after impregnation may be omitted for cobalt/silica catalysts prepared by this process, but there is little loading of cobalt catalyst into the carrier. It is considered in US 5,036,032 that diffusion limitations are almost completely eliminated by deliberately concentrating cobalt only in the outer surface of silica carrier particles.

Loading of the catalyst throughout a silica carrier is also mentioned in US 5,036,032, but only by way of comparison with egg-shell loading, and only by using an aqueous solution of cobalt, the water from which must then be removed by a separate drying process. Moreover, the water reduces the possible cobalt loading through its own presence.

In US 5,981,608 a preparation method is described with which a cobalt on titania catalyst suitable for Fischer-Tropsch can be prepared. In one embodiment titania is impregnated with a solution of a cobalt salt and a solution of a manganese salt, followed by a drying step and a calcination step. As mentioned above, calcination naturally involves several disadvantages with regard to costs and catalyst properties. The preparation method of US 5,981,608 has been illustrated by preparing 30-80 MESH catalyst particles. A specific preparation method using shaped particles, for example extrudates, whereby the catalytically active metal is loaded throughout the carrier is not mentioned nor discussed in US 5,981,608.

WO 98/25870 discloses a preparation method for cobalt on titania catalysts suitable for Fischer-Tropsch. In one embodiment titania is impregnated with a mixture of molten cobalt nitrate and manganese nitrate salts, whereby the volume of the impregnation solution is substantially the same as the pore volume of the carrier. The preparation method of WO 98/25870 has been illustrated by impregnating titania powder (P25 ex Degussa) . A specific preparation method using shaped particles, for example extrudates, whereby the catalytically active metal is loaded throughout the carrier is not mentioned nor discussed in WO 98/25870.

It is one object of the present invention to improve the process for preparing a cobalt comprising Fischer- Tropsch catalyst.

Thus, according to one aspect of the present invention, there is provided a process for the preparation of a Fischer-Tropsch catalyst or catalyst precursor, comprising the steps of:

(a) shaping a carrier material comprising titania, the titania preferably being <5 wt% brookite and >20 wt% anatase;

(b) calcining the carrier material of step (a) to provide a material with a pore volume ("X");

(c) impregnating the calcined carrier material of step (b) with an excess volume (> 1.1 X) of a melt of a cobalt nitrate salt at a temperature below 180 ⁰C; and

(d) keeping the temperature of the resulting catalyst or catalyst precursor below 180 ⁰C, preferably below

150 ⁰C, up to the moment the resulting catalyst or catalyst precursor is subjected to an activation step or used in a Fischer-Tropsch reaction.

Remarkably, the present invention has found that after the impregnation step (c), the resulting catalyst or catalyst precursor does not need to be calcined as a separate step to achieve the required catalytic activity for use in a reactor. That is, the process of the present invention does not include a separate calcining or calcination step between the impregnation step and the activation or use of the obtained catalyst or catalyst precursor. With calcination is meant heating to a temperature above 350 ⁰C, generally from 350 to 750⁰C, often a temperature in the range of from 450 to 550⁰C, in an oxygen-containing atmosphere, for example air. Hence, with a process according to the present invention a cobalt on titania catalyst can be prepared with sufficient strength and good activity, without titania being subjected to calcination in the presence of a cobalt compound. Any uncontrolled cracking and tension in the impregnated calcined carrier material can be avoided. Additionally, the problem of formation of unwanted compounds such as cobalt titanate can be avoided.

It has been found that activation of the catalyst or catalyst precursor is just as efficient to remove any

(crystalline) water, to decompose volatile decomposition products, and to convert organic and inorganic compounds to their required form, as a separate calcination step following impregnation. In step (a) the carrier material is shaped. The term

'shaped' relates to a process wherein particles are formed from a powder, each of particles having a particular shape. Suitable processes are pelletizing, (wheel) pressing and extrusion. Water or another liquid may be added to the titania before shaping.

The volume of shaped particles is suitably between 1 and 250 mm^, preferably between 2 and 100 mm^, more preferably between 4 and 50 mm^, especially in the case that an extrusion process is used.

The shaped carrier material particles preferably have a particle size of at least 1 mm. Particles having a particle size of at least 1 mm are defined as particles having a longest internal straight length of at least 1 mm. The particle size of a carrier, catalyst or catalyst precursor prepared according to the present invention preferably is at least 1 mm, more preferably at least 1.5 mm, even more preferably at least 2 mm.

In step (b) the shaped carrier material of step (a), is calcined. In other words, the shaped carrier particle (s) is/are calcined in step (b) . After calcination the carrier material has a certain pore volume; this pore volume is referred to as "X".

The pore volume of the carrier after calcination preferably is at least 0.10 ml/g, more preferably between 0.20 and 1.5 ml/g, even more preferably between 0.25 and 1.0 ml/g. In step (c) the calcined carrier material of step (b) is impregnated with a melt of a cobalt nitrate salt. The volume of the impregnation material is significantly larger than the pore volume of the carrier. The volume of the impregnation material is more than 1.1 times the pore volume of the carrier (> 1.1 X), more preferably more than 1.2 times (>1.2 X), even more preferably more than 1.4 times the pore volume of the carrier (>1.4 X) .

Examples of suitable cobalt nitrate salts are Co (NO₃) ₂ and (Co (NO₃) ₂.6H₂O . The molten salt is preferably used in the absence of water. Up to 10 wt% water, calculated on the weight of solid salt, can be tolerated. Preferably less than 5 wt% of water is present in the melt. When cobalt nitrate hydrate is used, the amount of additional water that can be tolerated is lower than for Co (NO₃) ₂.

The catalyst or catalyst precursor provided by the present invention is intended to have a distribution of the catalytically active element throughout the catalyst precursor particles which is even or evenmost. That is, to have a variation in the concentration of catalytically active element of less than 50%, preferably <40%, <30%, <20% and even <10%, from the surface to the centre. In a preferred embodiment, the difference between the concentration of catalytically active element at or just below the surface of the particle and the concentration of catalytically active element in the centre of the particle is less than 50%, preferably <40%, <30%, <20% and even <10%, calculated on the concentration of catalytically active element at or just below the surface of the particle. In a preferred embodiment, the difference between the concentration of catalytically active element at or just below the surface of the particle and the average concentration of catalytically active element is less than 50%, preferably <40%, <30%, <20% and even <10%, calculated on the average concentration of catalytically active element in the particle . The homogeneous distribution of the catalytically active element throughout the carrier material is achieved in the present invention by any suitable impregnation process or method, as long as an excess volume of a melt of a cobalt nitrate salt is used. A preferred impregnation method is vacuum impregnation.

Use of an excess of catalyst material during impregnation ensures that there is filling of all the pores of the carrier material, especially with the application of a vacuum.

A melt also allows increased loading throughout the carrier material compared with using an aqueous solution. Indeed, the impregnation of step (c) of the present invention is preferably carried out in the absence of water. A melt allows direct ingression of the catalytically active element into the carrier material without other extraneous compounds or substances which have to subsequently be removed by the same diffusion channels .

Preferably, the impregnation is carried out over a time period of greater than 10 minutes greater, more preferably greater than 15 minutes, even more preferably greater than 45 minutes, or longer. The impregnation time period should be long enough to fill of all the pores of the carrier material. The time required for the impregnation is related to the temperature of the melt of a cobalt nitrate salt. Also the temperature of the carrier material has an influence on the impregnation process. The time required for the impregnation is also related to the impregnation method. When a vacuum is applied, the impregnation period may be shorter as compared to impregnation without a vacuum. One advantage of the preparation method of the present invention is that there is a reduction in the amount, which can be measured in wt%, of cobalt required for use in a Fischer-Tropsch reactor. For example, it is conventional to consider that about 20wt% of the catalytically active element is required. Cobalt on titania catalysts prepared by mixing and shaping (e.g. extruding) normally comprise about 20wt% of the catalytically active element. Also cobalt on titania catalysts prepared by impregnating titania carrier material normally comprise about 20wt% of the catalytically active element. The present invention allows the catalyst material to impregnate the carrier material much more deeply and evenly, so that in tests, only 11 wt% of cobalt has been required to effect the same or similar catalytic activity in a Fischer-Tropsch reactor. This is a near 50% reduction in the requirement of the expensive cobalt. In step (c), the calcined carrier material is impregnated with a cobalt nitrate salt which is liquid at the time of impregnation, generally having a viscosity of <100,000 cps . Such salts may be solid at ambient temperature. Impregnation is performed at a temperature below 180 ⁰C. Preferably impregnation is performed at a temperature above ambient, such as above 50⁰C, possibly up to 150⁰C, with an intermediate range of between 70⁰C and 100⁰C.

Preferably the melt of the cobalt nitrate salt which is impregnated into the calcined carrier material has a temperature above ambient, such as above 50⁰C, possibly up to 150⁰C, with an intermediate range of between 70⁰C and 100⁰C. Even more preferably, both the melt of the cobalt nitrate salt and the calcined carrier material has a temperature above ambient, such as above 50⁰C, possibly up to 150⁰C, with an intermediate range of between 70⁰C and 100⁰C during impregnation.

By way of example, cobalt nitrate is a solid at ambient temperature, but melts at about 56⁰C, such that it is then impregnatable into the carrier material. Any crystalline water in nitrate salts generally remains partly conjugated at such relatively low temperatures . A further advantage of the present invention is that the possible occurrence of unwanted reactions or conversions during the hitherto normal calcination step, such as forming cobalt titanate, can be avoided, or reduced, or minimised.

Preferably >50 wt% of the cobalt is maintained at a 2+ valence in the catalyst or catalyst precursor prior to activation or use in a reactor. This can be achieved by refraining from any processing of the catalyst or catalyst precursor which would alter the 2+ valence of the >50 wt% of the cobalt.

Preferably, >50%, >60%, >70%, >80%, >90% or even >95% of the cobalt is maintained in its 2+ valance prior to activation or use of the catalyst or catalyst precursor. Another advantage of the present invention is the reduction of the amount of hydrogen required to reduce the catalytically active element from its supplied form into its elemental form. For example, cobalt in its nitrate form used in forming the catalyst or catalyst precursor of the present invention, has a 2+ valance which is maintained by the process of the present invention, as opposed to the 2+/3+ valance of C03O4 formed by calcination of a cobalt compound on titania.

Thus, less hydrogen is needed to reduce the cobalt to its elemental form, further providing saving and economical benefit of the present invention.

The catalyst material is generally 'supported' on the carrier material. The titania carrier material is preferably porous. Particular preferred examples of the titania carrier material are based on one or more forms of titania, such as anatase, rutile, brookite, amorphous titania, or a mixture of one or more thereof. More preferably the titania carrier material is titania with

<5 wt% brookite and >20 wt% anatase.

The amount of cobalt present in the catalyst or catalyst precursor may range from 1 to 100 parts by weight per 100 parts by weight of carrier material, preferably from 10 to 50 parts by weight per 100 parts by weight of carrier material.

The catalyst or catalyst precursor may also include one or more further components, either added with the carrier material, or with the catalytically active compound. These include promoters and/or co-catalysts.

Suitable co-catalysts include one or more metals such as iron, nickel, or one or more noble metals from Group

VIII of the Periodic Table of Elements. Preferred noble metals are platinum, palladium, rhodium, ruthenium, iridium and osmium. Such co-catalysts are usually present in small amounts.

References to "Groups" and the Periodic Table as used herein relate to the previous IUPAC version of the Periodic Table of Elements such as that described in the

68th Edition of the Handbook of Chemistry and Physics

(CPC Press) .

One or more metals or metal oxides may be present as promoters, more particularly one or more d-metals or d- metal oxides. Suitable metal oxide promoters may be selected from Groups HA, 11 IB, IVB, VB, VIB, VIIB and

VIIIB of the Periodic Table of Elements, or the actinides and lanthanides. In particular, oxides of magnesium, calcium, strontium, barium, scandium, yttrium, lanthanum, cerium, titanium, zirconium, hafnium, thorium, uranium, vanadium, chromium and manganese are most suitable promoters . Suitable metal promoters may be selected from Groups VIIB or VIII of the Periodic Table of Elements. Manganese, iron, rhenium and Group VIII noble metals are particularly suitable, and are preferably provided in the form of a salt.

The promoter (s) and or co-catalyst ( s ) may be added to the carrier material in a similar manner to the addition of the catalytically active compound, and/or together with the catalytically active compound, and/or as part of the catalytically active compound itself. For example, where it is desired to include manganese in the catalyst or catalyst precursor, the manganese can be added as a salt.

In one embodiment, the carrier material can be impregnated with a melt of a manganese salt, for example manganese nitrate, and with a melt of a cobalt nitrate salt in separate steps.

In another embodiment, the manganese salt such as manganese nitrate could be admixed or combined with the cobalt salt in any suitable process, such as being mulled together. A manganese salt, for example manganese nitrate, can be made part of the melt of the cobalt nitrate by heating a mixture or combination of these materials to form the melt. The titania carrier material can be impregnated with such a melt.

The amount of promoter present in the catalyst is suitably in the range of from 0.01 to 100 pbw, preferably 0.1 to 40, more preferably 1 to 20 pbw, per 100 pbw of carrier material. Any promoter (s) are typically present in an amount of from 0.1 to 60 parts by weight per 100 parts by weight of any carrier material used. It will however be appreciated that the optimum amount of promoter (s) may vary for the respective elements which act as promoter (s). If the catalyst comprises cobalt as the catalytically active element and manganese and/or vanadium as promoter, the cobalt: (manganese + vanadium) atomic ratio is advantageously at least between 5:1 and 30:1.

In one embodiment of the present invention, the catalyst comprises the promoter (s) and/or co-catalyst ( s ) having a concentration in the Group VIII metal (s) in the range 1-10 atom% (based on cobalt), preferably 3-7 atom%, and more preferably 4-6 atom% .

A most suitable final catalyst comprises cobalt as the catalytically active element and zirconium as a promoter. Another most suitable catalyst comprises cobalt as the catalytically active element and manganese and/or vanadium as a promoter.

General methods of preparing catalyst materials and forming catalyst mixtures and precursors are known in the art, see for example US 4409131, US 5783607, US 5502019, WO 0176734, CA 1166655, US 5863856 and US 5783604. These include preparation by co-precipitation and impregnation. Such processes could also include freezing, sudden temperature changing, etc. Control of the component ratio in the solid solution can be provided by parameters such as residence time, temperature control, concentration of each component, etc.

The carrier material is shaped in step (a) . The shaping can be provided by many methods known in the art, for example by pelleting. In one embodiment of the present invention, the shaping of the carrier material is carried out by extrusion. In another embodiment of the present invention, the carrier material could be formed or shaped by gluing or pressing small carrier material particles, like micro-spheres and platelets, into shapes like trilobes .

In a preferred embodiment, a liquid is added to the carrier material before or during its shaping, such as an extrusion aid. The liquid may be any of suitable liquids known in the art, for example: water; ammonia, alcohols, such as methanol, ethanol and propanol; ketones, such as acetone; aldehydes, such as propanol and aromatic solvents, such as toluene, and mixtures of the aforesaid liquids. A most convenient and preferred liquid is water.

The liquid may include viscosity improvers such as a polyvinylalcohol .

After shaping, the carrier material, optionally including further components, is strengthened by calcination thereof in a manner known in the art. Titania is preferably calcined at a temperature between 350 and 700 ⁰C, more preferably between 400 and 650 ⁰C, more preferably between 450 and 600 ⁰C.

The catalytically active component is then added to the carrier material using any impregnation process or impregnation method of several that are known in the art in the preparation of supported catalysts and catalyst precursors .

After the impregnation of the cobalt nitrate salt into the titania carrier material, there may be a drying step for a period of time in order to remove any (crystal) water or similar volatile material. The drying step is not equivalent to a calcination step. That is, any drying step after the impregnation step and prior to the activation or use of the catalyst or catalyst precursor is below 180⁰C. Any drying step preferably is in the range 100-180⁰C, more preferably in the range 120- 150⁰C. Activation of a catalyst or catalyst precursor of the present invention can be carried out in any known manner and under conventional conditions. For example, the catalyst or catalyst precursor may be activated by contacting the catalyst with hydrogen or a hydrogen- containing gas, typically at temperatures of about 200° to 350⁰C. As discussed above, it is possible to activate the catalyst or catalyst precursor of the present invention with less hydrogen or hydrogen-containing gas than is required for Cθ3C>4-comprising catalysts or catalyst precursors.

The activation of a catalyst or catalyst precursor of the present invention leads to decomposition of the cobalt nitrate and/or reduction of the cobalt to its metal form, and the present invention extends to the resulting activated catalyst.

A catalyst or catalyst precursor provided by the present invention is particularly, but not exclusively, useful for a hydrocarbon synthesis process such as a Fischer-Tropsch reaction.

A steady state catalytic hydrocarbon synthesis process may be performed under conventional synthesis conditions known in the art. Typically, the catalytic conversion may be effected at a temperature in the range of from 100 to 600⁰C, preferably from 150 to 350⁰C, more preferably from 180 to 270⁰C. Typical total pressures for the catalytic conversion process are in the range of from 1 to 200 bar absolute, more preferably from 10 to 70 bar absolute. In the catalytic conversion process mainly C5 hydrocarbons are formed, based on the total weight of hydrocarbonaceous products formed, (at least 70 wt%, preferably 90 wt%) . According to a second aspect of the present invention, there is provided a process for producing normally gaseous, normally liquid and optionally normally solid hydrocarbons from synthesis gas which comprises the steps of :

(i) providing the synthesis gas; and (ii) catalytically converting the synthesis gas of step (i) at an elevated temperature and pressure to obtain the normally gaseous, normally liquid and optionally normally solid hydrocarbons; wherein the catalyst for step (ii) is formed by a process herein described.

The present invention also provides a process further comprising: (iϋ) catalytically hydrocracking higher boiling range paraffinic hydrocarbons produced in step(ii), as well as hydrocarbons whenever provided by a process as described herein.

The present invention also provides use of a catalyst as defined herein in a process for producing normally gaseous, normally liquid and optionally normally solid hydrocarbons from synthesis gas which comprises the steps of:

(i) providing the synthesis gas; and (ii) catalytically converting the synthesis gas of step (i) at an elevated temperature and pressure to obtain the normally gaseous, normally liquid and optionally normally solid hydrocarbons .

Fischer-Tropsch synthesis is preferably carried out at a temperature in the range from 125 to 350⁰C, more preferably 175 to 275°C, most preferably 180⁰C to 260⁰C. The pressure preferably ranges from 5 to 150 bar abs . , more preferably from 5 to 80 bar abs. Preferably, a Fischer-Tropsch catalyst is used which yields substantial quantities of paraffins, more preferably substantially unbranched paraffins. A part may boil above the boiling point range of the so-called middle distillates, to normally solid hydrocarbons. A most suitable catalyst for this purpose is a cobalt- containing Fischer-Tropsch catalyst. The term "middle distillates", as used herein, is a reference to hydrocarbon mixtures of which the boiling point range corresponds substantially to that of kerosene and gas oil fractions obtained in a conventional atmospheric distillation of crude mineral oil. The boiling point range of middle distillates generally lies within the range of about 150 to about 360⁰C. The higher boiling range paraffinic hydrocarbons if present, may be isolated and subjected to a catalytic hydrocracking step, which is known per se in the art, to yield the desired middle distillates. The catalytic hydrocracking is carried out by contacting the paraffinic hydrocarbons at elevated temperature and pressure and in the presence of hydrogen with a catalyst containing one or more metals having hydrogenation activity, and supported on a carrier. Suitable hydrocracking catalysts include catalysts comprising metals selected from Groups VIB and VIII of the Periodic Table of Elements.

Preferably, the hydrocracking catalysts contain one or more noble metals from Group VIII. Preferred noble metals are platinum, palladium, rhodium, ruthenium, iridium, and osmium. Most preferred catalysts for use in the hydrocracking stage are those comprising platinum.

The amount of catalytically active metal present in the hydrocracking catalyst may vary within wide limits and is typically in the range of from about 0.05 to about 5 parts by weight per 100 parts by weight of the carrier material. Suitable conditions for the catalytic hydrocracking are known in the art. Typically, the hydrocracking is effected at a temperature in the range of from about 175 to 400⁰C. Typical hydrogen partial pressures applied in the hydrocracking process are in the range of from 10 to 250 bar.

The process may be operated in a single pass mode ("once through") or in a recycle mode. Slurry bed reactors, ebullating bed reactors and fixed bed reactors may be used, the fixed bed reactor being the preferred option .

The product of the hydrocarbon synthesis and consequent hydrocracking suitably comprises mainly normally liquid hydrocarbons, beside water and normally gaseous hydrocarbons. By selecting the catalyst and the process conditions in such a way that especially normally liquid hydrocarbons are obtained, the product obtained ("syncrude") may transported in the liquid form or be mixed with any stream of crude oil without creating any problems as to solidification and or crystallization of the mixture. It is observed in this respect that the production of heavy hydrocarbons, comprising large amounts of solid wax, are less suitable for mixing with crude oil while transport in the liquid form has to be done at elevated temperatures, which is less desired.

The process as just described may be combined with all possible embodiments as described in this specification . Any percentage mentioned in this description is calculated on total weight or volume of the composition, unless indicated differently. When not mentioned, percentages are considered to be weight percentages. Pressures are indicated in bar absolute, unless indicated differently .

Experimental

Comparative Example A mixture was prepared containing 2200 g commercially available titania powder (P25 ex. Degussa) , 1000 g of prepared CoMn(OH)₂ co-precipitate (atomic ratio of Mn/Co is 0.05), 300 g water and several extrusion aids. The mixture was kneaded for 18 minutes and shaped using a Bonnot extruder. The extrudates were dried for 16 hours at 120 ⁰C and calcined for 2 hours at 550 ⁰C. The obtained catalyst (precursor) contained 20 wt% cobalt and

1 wt% of manganese.

Example 1 3192 g commercially available titania powder (P25 ex.

Degussa) was mixed with 981.3 g H2O and several extrusion aids. The mixture was kneaded for a period of 46 minutes and shaped using a Bonnot extruder. The extrudates were dried for 16 hours at 120⁰C and calcined for 2 hours at 500⁰C. The resulting extrudates possessed a pore volume of 0.31 ml/g. Example 2

The titania extrudates of Example 1 were impregnated with Co (NO3 ) 2 • 6H2O and Mn (NO3 ) 2 • 4H2O . Before impregnation the cobalt nitrate and manganese nitrate were molten by heating these materials at 8O⁰C for 1 hour. The impregnation method used was vacuum soak impregnation.

In detail : a suction erlenmeyer flask was loaded with 30 g of the titania extrudates of Example 1 and equipped with a separation funnel, containing 76 g of

Co(N0₃)2.6H₂0 and 4.12 g Mn (NO₃ ) ₂.4H₂O . Subsequently, this impregnation equipment was heated to 8O⁰C and maintained for 1 hour. Thereupon, vacuum was applied on the suction Erlenmeyer flask. After 15 minutes the impregnation liquid was introduced to the titania carrier particles by opening the valve of the separation funnel. In order to fill the pores of the extrudates completely with liquid, the amount of liquid was added in excess. The extrudates were contacted with the impregnation liquid for 15 minutes, at 80⁰C. The impregnated titania carrier particles were separated from the liquid by means of filtration and were subsequently dried in air at 100⁰C.

The obtained catalyst (precursor) particles contained 11.4 w% cobalt and 0.7 w% of manganese, having a relative ratio of these metals of "10" at their surface to "8.6" at their centres, i.e. the variation in the concentration of catalytically active element of only 14%. Example 3

3635 g commercially available titania powder (P25 ex. Degussa) was mixed with 1288 g H2O and several extrusion aids. The mixture was kneaded for a period of 120 minutes and shaped using a Bonnot extruder. The extrudates were dried for 2 hours at 120⁰C and calcined for 2 hours at

600⁰C. The resulting extrudates possessed a pore volume of 0.29 ml/g.

Example 4 20 g of the titania extrudates of Example 3 were impregnated with 51 g Co (NO3 ) 2 • 6H2O and 2.44 g

Mn (NO3 ) 2 ■ 4H2O by vacuum soak impregnation. The same procedure as described in Example 2 was followed. The impregnation temperature was 90⁰C. The obtained catalyst (precursor) contained 10.2 w% cobalt and 0.58w% of manganese . Example 5

The catalyst (precursors) of Examples 2 and 4 were were activated by means of reduction in hydrogen. Subsequently, the catalysts were used in Fischer-Tropsch synthesis processes, under test conditions. The catalysts were contacted with syngas, said syngas having a hydrogen to carbon monoxide ratio of 1.1, at different temperatures. The results are presented in Table 1.

Table 1

When compared to the catalysts of the Comparative Example, the catalysts of Examples 2 and 4 (prepared according to the present invention) provide a good STY activity and a good C5+ selectivity at different operating temperatures and pressures. This is surprising as the catalysts of Examples 2 and 4 were prepared with half the amount of cobalt, and were only dried in air and not calcined after impregnation.

Claims

C L A I M S

1. A process for the preparation of a Fischer-Tropsch catalyst or catalyst precursor, comprising the steps of:

2. A process as claimed in claim 1, characterized in that the cobalt nitrate salt is impregnated into the carrier material under vacuum.

3. A process as claimed in claim 1 or 2, characterized in that the impregnation in step (c) is performed at a temperature between 50 and 150⁰C.

4. A process as claimed in any one of the preceding claims, characterized in that the impregnation in step (c) is carried out over at least 10 minutes, preferably at least 15 minutes.

5. A process as claimed in any of the preceding claims, characterized in that during the impregnation in step (c) the cobalt nitrate melt comprises less than 5 wt% water, calculated on the weight of solid salt .

6. A process as claimed in any of the preceding claims characterized in that the calcined carrier material is impregnated with the cobalt nitrate salt and with manganese nitrate.

7. A catalyst prepared by a process according to any one of claims 1 to 6.

8. A process for producing normally gaseous, normally liquid and optionally normally solid hydrocarbons from synthesis gas which comprises the steps of: (i) providing the synthesis gas; and

(ii) catalytically converting the synthesis gas of step (i) at an elevated temperature and pressure to obtain the normally gaseous, normally liquid and optionally normally solid hydrocarbons; wherein the catalyst is a catalyst according to claim 7.

9. Hydrocarbons obtained by a process according to claim 8.

10. Use of a catalyst as defined in claim 7 in a process for producing normally gaseous, normally liquid and optionally normally solid hydrocarbons from synthesis gas which comprises the steps of: