DE102008054760A1 - Heterogeneous catalyst for the Fischer-Tropsch synthesis and a process for its preparation - Google Patents

Abstract

The present invention relates to a catalyst for the Fischer-Tropsch synthesis on a catalyst support of SiO, whose shaped body consists of highly pure fumed silica, which was prepared without the addition of binders and the catalyst as active component one or more elements from the group comprising iron , Cobalt, nickel and ruthenium.

Description

The The invention relates to a catalyst for the Fischer-Tropsch synthesis based on cobalt as an active component extruded on binder-free and thus highly pure and at the same time high surface area Carrier moldings and a process for the preparation this catalyst.

In the process known as Fischer-Tropsch synthesis, mixtures of carbon monoxide and hydrogen, commonly known as synthesis gas, on a heterogeneous catalyst at elevated temperature and pressure to a mixture of lower gaseous and higher liquid hydrocarbons consisting of alkanes, alkenes and alkanols according to the formulas nCO + (2n + 1) H ₂ → C _n H _{2n + 2} + nH ₂ O (alkanes) nCO + (2n) H ₂ → C _n H ₂ n + nH ₂ O (alkenes) nCO + (2n) H ₂ → CnH _{2n + 1} OH + (n - 1) H ₂ O (alkanols) implemented.

Of the increasing demand for oil and the simultaneous shortage its worldwide supplies and the resulting growing importance of alternative and sustainable as possible Fuels for internal combustion engines provide for great interest in the Fischer-Tropsch synthesis as attractive Process for the representation of high quality energy sources.

Next the desired long-chain, liquid hydrocarbons also always unwanted short-chain gaseous fall Hydrocarbons as components of the complex mixture, in particular Methane to about 10 mol% of the total resulting reaction product. This is particularly unfavorable because that is the implementation most of the synthesis gas currently used from natural gas (methane) is obtained.

For industrial processes catalysts are therefore in the center of interest, which have high chain activities in addition to high activities to reduce methane selectivity, since maximizing the yield of components of the wax fraction (C ₁₈₊ ) during subsequent hydrocracking the efficiency over the entire process chain can be significantly increased.

The catalytic properties of the catalysts used governed by the active metal, the promoters and the preparation conditions, but also about the used carrier material determined.

Catalysts for the Fischer-Tropsch synthesis often contain iron or cobalt as active components together with one or more promoters on an inert support material such as Al ₂ O ₃ , SiO ₂ , TiO ₂ with high specific surface area.

The Catalysts can be made via several production routes to be obtained. Common for the preparation of Fischer-Tropsch catalysts are, for example, as precipitation and methods known as impregnation, wherein the impregnation is preferred because it usually faster and is more cost-effective and reproducible results supplies.

to Representation of support materials for catalysts The Fischer-Tropsch synthesis are also different methods known.

EP-0428223 describes a process in which carrier tablets are obtained for use as Fischer-Tropsch catalysts by grinding dispersions consisting of silica and a soluble zirconium compound, surfactants and other additives in an electrolyte solution and subsequent extrusion.

Out EP-0510771 a similar method is known, in which case also the catalytically active component, preferably cobalt, is added to the dispersion before the extrusion of the shaped bodies and this is ground in a pug mill.

In EP-0110449 describes a process for the preparation of catalysts for the Fischer-Tropsch synthesis, in which the carrier materials of silicon dioxide sequentially impregnated first with a titanium or zirconium compound and impregnated after calcination with a compound of the catalytically active cobalt and then calcined and reduced.

US 4717702 describes a process in which Fischer-Tropsch synthesis based on high purity, high surface area, low acidity, high purity alumina after modification with thorium oxide or other lanthanide or actinide oxide is prepared by impregnation with non-aqueous solvents and thereby high Metal dispersions are achieved. However, it is disadvantageous that only comparatively low conversions are achieved with the catalysts described, even at high cobalt loadings of up to 47% by weight, and significant amounts of undesirable methane are also formed at industrially relevant H2 / CO ratios.

adversely In all known methods is that the support materials or the catalysts prepared therefrom on the basis of their Properties, such as low specific surface area or impurities contained in the Fischer-Tropsch synthesis in terms of their activity and selectivity to the desired long-chain hydrocarbons, limited are.

It Therefore, the task was a highly active and at the same time the representation of long-chain hydrocarbons selective catalyst for the Fischer-Tropsch synthesis based on carrier moldings to develop from silicon dioxide.

Surprisingly has been found to be highly active and selective catalysts for the Fischer-Tropsch synthesis based on binder-free extruded and thus highly pure molded body of fumed silica can be obtained due to their manufacturing process high specific surface areas and a narrow pore radius distribution in the meso and macropores area.

The invention relates to a catalyst for the Fischer-Tropsch synthesis on a catalyst support of SiO ₂ , characterized in that the shaped body consists of highly pure fumed silica, which was prepared without the addition of binders and the catalyst as the active component one or more elements of the group comprising iron, cobalt, nickel and ruthenium.

The as starting material for the preparation of the carrier tablets used high-purity fumed silica, for example by combustion of a resulting in the presentation of ultrapure silicon Mixture of tri- and tetrachlorosilane obtained in a blast gas flame become. The fumed silica is made by grinding or simple coagulation dispersed in water and avoiding contamination by additives such as binders, rheology improvers or pore-forming agent as well as by other entry of impurities how to extrude abrasion to moldings.

Production methods for high purity fumed silica moldings are made WO-08/071610 and WO-08/071612 known. The preparation of these publications should be part of this application (incorporated by reference).

WO-08/071610 describes processes for the production of high-purity carrier bodies from SiO ₂ by grinding and dispersion without binders or other additives.

WO-08/071612 describes a process for the production of moldings, in which the metal oxide is predispersed in water and then finely dispersed and this dispersion is subjected to a change in the pH and then shaping and subsequent drying takes place.

The Carrier molding of the invention Catalysts can be used, for example, as pellets, rings, spheres, Wheels, armchairs, honeycombs or any other for catalysts common embodiment. Especially suitable for the catalyst according to the invention are cylindrical extrudates such as pellets or rings.

By the subsequent thermal treatment of the green body can properties of catalyst supports such as For example, pore structure and mechanical stability be targeted. In a particularly preferred embodiment of the method come moldings with defined pore structure with a very narrow monomodal pore radius distribution in the range between 5 and 30 nm, preferably between 10 and 20 nm, which have less than 1% micropores and are characterized by a high Proportion of mesopores in the total pore volume of over 75%, preferably over 90%.

When come active component for the Fischer-Tropsch synthesis one or more of the metals of the group iron, cobalt, nickel and ruthenium used, particularly preferably cobalt. Cobalt as Active component is characterized by high chain growth probabilities and the lack of activity in the water gas shift reaction out.

By the very high purity of the invention used Catalyst support can also be the catalyst very targeted dope with different promoters. As dopants, for example ruthenium, Rhenium, chromium and iron for use. Particularly preferred Ruthenium as a promoter.

Due to the high purity, the support material can also be very selectively modified by further metal oxides such as ZrO ₂ , La ₂ O ₃ , CeO ₂ , TiO ₂ , HfO ₂ , ThO ₂ . In a particular embodiment of the method, the carrier tablets are modified with 0.1 and 25 wt .-% ZrO ₂ . Preferred is a modification between 2 and 20 wt .-% ZrO ₂ and more preferably between 5 and 15 wt .-% ZrO ₂ .

The Application of the components described may be common Methods of preparing heterogeneous catalysts, For example, under impregnation, Auffällung, Ligand exchange known method. In a particularly preferred Embodiment, the preparation of the catalyst by impregnation of the support materials with Solutions of compounds of active metals and others Components of the catalyst.

Possible Solvents for impregnation are Water and organic solvents such as Methanol, ethanol, propanol, acetone, diethyl ether, tetrahydrofuran, Acetonitrile and dimethylformamide. Especially preferred for the process is the use of water for application of the components.

The Amount of solution is usually larger or equal to the pore volume of the carrier moldings to be impregnated.

In a further embodiment of the catalyst Precursors of the active metal and the promoters already in the manufacturing process added to the support materials and subjected to this with the shaping. This procedure is particularly advantageous because the application larger amounts of active component in conventional Impregnation sequentially done in several steps got to. In the case of the catalyst shown here, the required amounts of the precursor of the active metal in a single Manufacturing step are added, which is the preparation of the catalyst much easier.

The Catalyst precursors are prepared prior to the Fischer-Tropsch synthesis subjected to a defined pretreatment. This is how the precursors become common for 1 to 10 hours at temperatures between 250 and 500 ° C in an inert or oxidizing atmosphere calcined and then a reduction for 1 to 10 hours at temperatures between 250 and 500 ° C subjected to reductive atmosphere.

Of the catalyst according to the invention can be used as a fixed bed catalyst or used as a suspension catalyst. Is preferred However, the implementation of the Fischer-Tropsch synthesis with this catalyst in a fixed bed.

The Reactions with the catalyst according to the invention are at temperatures between 100 and 300 ° C, preferably at 180 to 240 ° C and at pressures of 0 to 50 bar, preferably carried out at 15 to 30 bar. The molar ratios from hydrogen to carbon monoxide are between 1.0 and 3.0, preferably between 1.8 and 2.5.

In The following examples are intended to illustrate the present invention in more detail be explained.

The novel catalysts for the Fischer-Tropsch synthesis were subsequently compared with identically prepared catalysts based on two alternative support materials (comparative support 1 and comparative support 2). invention. carrier Comparison carrier 1 Comparison carrier 2 SSA_BET, m ² / g 234 130 234 SSA_Hg, m ² / g 250 137 74 d50, nm 15 20 48 Proportion 10-20 nm 79% 31% 20% contamination Na, ppm <10 1100 2100 Ca, ppm <10 430 120 Al, ppm <10 5800 1200 Ni, ppm <1 2.7 1.5 Fe, ppm <1 1300 107 Ti, ppm <1 1900 170 Sum, ppm 7 10530 3750

definitions:

• - SSA_BET specific surface by physisorption to BET
• - SSA_Hg specific surface by mercury porosimetry
• - d50 mean pore diameter by porosimetry
• - Impurities by elemental analysis

1 shows the pore radius distribution of the carrier shaped bodies according to the invention and the two comparative carriers. The catalyst of the invention shows a much narrower pore radius distribution. Also, the significant difference between the specific surface area of Comparative Support 2 from BET nitrogen adsorption and from Mercury Porosimetry indicates a high level of micropores in this material.

Example 1: Fischer-Tropsch synthesis with 20% Co-Ru / SiO 2

at the preparation of the catalyst according to the invention was a carrier mold made of highly pure pyrogenic Silica, made without the addition of binders, with an aqueous solution of cobalt nitrate and Ruthenium nitrosyl nitrate impregnated and dried. cobalt serves as an active component and ruthenium as a promoter. The The catalyst precursor obtained was initially 4 hours Calcined at 400 ° C in air and then slowly heated to 400 ° C under hydrogen and for reduced another 4 hours. The catalyst contained 20% by weight Cobalt and 0.27 wt .-% ruthenium.

The catalyst was investigated with synthesis gas with a constant molar ratio of H ₂ to CO of 2.0 and at temperatures between 200 and 220 ° C and a reaction pressure of 20 bar and a GHSV of 2200 NL (gas) per L (catalyst) and hour. Results: Temperature, ° C 200 ° C 205 ° C 210 ° C 220 ° C Sales CO 16.6% 21.7% 29.5% 54.0% Selectivity C13 + 52.2% 59.2% 52.0% 56.6% Selectivity C5-C12 26.5% 22.6% 26.6% 24.4% Selectivity CH4 8.7% 7.6% 8.9% 8.3%

Comparative Example 1

The procedure was analogous to Example 1, but the comparative carrier 1 was used as a carrier molding. Temperature, ° C 200 ° C 205 ° C 210 ° C 220 ° C Sales CO 18.6% 24.3% 23.6% 57.6% Selectivity C13 + 51.2% 55.4% 48.2% 34.4% Selectivity C5-C12 26.9% 24.6% 28.4% 36.2% Selectivity CH4 9.6% 8.8% 10.3% 13.3%

Of the catalyst of the invention and the catalyst on the basis of the comparison carrier 1 have the same Reaction conditions similar sales. The Chain growth probability in the invention Catalyst remains even with higher sales, respectively temperatures, constant while these at the Catalyst based on the comparative carrier 1, however decreases significantly.

Comparative Example 2:

The procedure was analogous to Example 1, but the support carrier 2 was used as a carrier molding. Temperature, ° C 200 ° C 205 ° C 210 ° C 220 ° C Sales CO 6.2% 8.0% 10.1% 19.9% Selectivity C13 + 37.0% 39.6% 33.4% 34.7% Selectivity C5-C12 37.9% 33.8% 34.1% 34.0% Selectivity CH4 17.1% 16.2% 17.5% 16.5%

Of the Catalyst based on the comparative carrier 2 shows in Contrary to the catalyst according to the invention under the same reaction conditions significantly lower sales and worse selectivities.

Example 2: Fischer-Tropsch synthesis with 30% Co-Ru / SiO 2

at the preparation of the catalyst according to the invention was a carrier mold made of highly pure pyrogenic Silica, made without the addition of binders, with an aqueous solution of cobalt nitrate and Ruthenium nitrosyl nitrate impregnated and dried. cobalt serves as an active component and ruthenium as a promoter. The The catalyst precursor obtained was initially 4 hours Calcined at 400 ° C in air and then slowly heated to 400 ° C under hydrogen and for reduced another 4 hours. The catalyst contained 30% by weight Cobalt and 0.41% by weight of ruthenium.

The catalyst was reacted with synthesis gas with a constant molar ratio of H ₂ to CO of 2.0 with a proportion of 10% by volume of nitrogen as internal standard and at temperatures between 200 and 240 ° C. and a reaction pressure of 20 bar and a GHSV of 1200 NL (cf. gas) per L (catalyst) and hour. Results: Temperature, ° C 200 ° C 220 ° C 240 ° C Sales CO 28.5% 55.0% 76.6% Selectivity CH4 12.8% 11.4% 14.9%

Comparative Example 3

The procedure was analogous to Example 2, but the comparative carrier 1 was used as a carrier molding. Temperature, ° C 200 ° C 220 ° C 240 ° C Sales CO 9.5% 40.3% 66.0% Selectivity CH4 19.0% 13.1% 18.0%

As From the table it can be seen that the catalyst has on the Comparison carrier 1 with respect to the invention Catalyst from Example 2 under the same reaction conditions both lower activities as well as higher selectivity to undesirable methane.

Example 3: Fischer-Tropsch synthesis with 20% Co-Ru / SiO 2 -ZrO 2

at the preparation of the catalyst according to the invention was a carrier mold made of highly pure pyrogenic Silica, made without the addition of binders, first with a solution of zirconium propoxide impregnated in propanol, dried and for 2 Calcined hours at 300 ° C under air. The so modified Carrier molding contained 10 wt .-% zirconium oxide. This was in the next step with an aqueous Solution of cobalt nitrate and Rutheniumnitrosylnitrat impregnated and dried. Cobalt serves as the active component and ruthenium as a promoter. The resulting catalyst precursor was only 4 hours Calcined at 400 ° C in air and then slowly heated to 400 ° C under hydrogen and for reduced another 4 hours. The catalyst contained 20% by weight Cobalt and 0.27 wt .-% ruthenium.

The catalyst was reacted with synthesis gas with a constant molar ratio of H ₂ to CO of 2.0 with a proportion of 10% by volume of nitrogen as internal standard and at temperatures between 200 and 240 ° C. and a reaction pressure of 20 bar and a GHSV of 1200 NL (cf. gas) per L (catalyst) and hour. Results: Temperature, ° C 200 ° C 220 ° C 240 ° C Sales CO 40.8% 61.2% 79.1% Selectivity CH4 8.0% 11.0% 14.8%

As can be seen from the table, the activity of the catalyst according to the invention by the doping be significantly increased again with zirconium.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 0428223 [0010]
• - EP 0510771 [0011]
• - EP 0110449 [0012]
• US 4717702 [0013]
• WO 08/071610 [0019, 0020]
• WO 08/071612 [0019, 0021]

Claims (13)

Catalyst for the Fischer-Tropsch synthesis on a catalyst support of SiO ₂ , characterized in that the shaped body consists of highly pure fumed silica which was prepared without the addition of binders and the catalyst as active component one or more elements from the group comprising iron, Contains cobalt, nickel and ruthenium. Catalyst according to claim 1, characterized in that that the active component is cobalt. Catalyst according to Claims 1 to 2, characterized that the catalyst with one or more of the elements from the Group ruthenium, rhenium, chromium and iron is doped. Catalyst according to claim 1 to 3, characterized in that the catalyst support is modified by one or more metal oxides from the group containing ZrO ₂ , La ₂ O ₃ , CeO ₂ , TiO ₂ , HfO ₂ , ThO ₂ . Catalyst according to Claims 1 to 4, characterized the catalyst support has a defined pore structure with a monomodal pore radius distribution in the range between 5 and 30 nm. Catalyst according to claim 5, characterized in that the catalyst support has less than 1% micropores and the proportion of mesopores in the total pore volume 75%. Catalyst according to Claims 1 to 6, characterized that the shaped catalyst bodies take the form of pellets, rings, Own balls, wheels, armchairs or honeycombs. Catalyst according to Claims 1 to 7, characterized that the application of the catalytic mass to the substrates by impregnation with solutions of compounds the active metals and the other components of the catalyst takes place. Catalyst according to claim 8, characterized in that that the impregnation by means of aqueous solutions or solutions with organic solvents. Catalyst according to Claims 1 to 9, characterized that the precursors of the active metal and the promoters already in the Manufacturing process of the carrier materials are added. Catalyst according to claims 1 to 10, characterized in that that this as a fixed-bed catalyst or as a suspension catalyst is used. Catalyst according to Claims 1 to 11, characterized that the catalyst precursors for 1 to 10 hours at Temperatures between 250 and 500 ° C in inert or oxidizing Atmosphere calcined and then a reduction for 1 to 10 hours at temperatures between 250 and 500 ° C in a reductive atmosphere were subjected. Catalyst according to claims 1 to 12, characterized in that that the catalytic reaction at temperatures between 100 and 300 ° C and at pressures of 0 to 50 bar and at a molar ratio of hydrogen to carbon monoxide between 1.0 and 3.0.