WO2005085390A1 - Cobalt catalyst for the synthesis of fischer-tropsch, catalyst support, processes for the preparation of support and catalyst and the use of the catalyst - Google Patents

Cobalt catalyst for the synthesis of fischer-tropsch, catalyst support, processes for the preparation of support and catalyst and the use of the catalyst Download PDF

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WO2005085390A1
WO2005085390A1 PCT/BR2005/000028 BR2005000028W WO2005085390A1 WO 2005085390 A1 WO2005085390 A1 WO 2005085390A1 BR 2005000028 W BR2005000028 W BR 2005000028W WO 2005085390 A1 WO2005085390 A1 WO 2005085390A1
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catalyst
cobalt
range
support
niobium
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PCT/BR2005/000028
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French (fr)
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Ana Carlota Belizário DOS SANTOS
Antônio Telhado PEREIRA
Eduardo Falabella Sousa-Aguiar
Jorge Luiz Moraes
Kensley Alves De Oliveira
Marcos De Freitas Sugaya
Martin Schmal
Robson De Souza Monteiro
Valéria Perfeito VICENTINI
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Companhia Brasileira De Metalurgia E Mineração
Oxiteno S.A. Indústria E Comércio
Petróleo Brasileiro S.A. - Petrobrás
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Publication of WO2005085390A1 publication Critical patent/WO2005085390A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/20—Vanadium, niobium or tantalum
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/84—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/847—Vanadium, niobium or tantalum or polonium
    • B01J23/8474—Niobium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G33/00—Compounds of niobium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G51/00—Compounds of cobalt
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G2/00—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon
    • C10G2/30—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen
    • C10G2/32—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen with the use of catalysts
    • C10G2/33—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen with the use of catalysts characterised by the catalyst used
    • C10G2/331—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen with the use of catalysts characterised by the catalyst used containing group VIII-metals
    • C10G2/332—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen with the use of catalysts characterised by the catalyst used containing group VIII-metals of the iron-group
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/74—Iron group metals
    • B01J23/75—Cobalt
    • B01J35/613—
    • B01J35/615—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/03—Precipitation; Co-precipitation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/16—Reducing
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
    • C01P2004/84—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases one phase coated with the other
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C01P2006/13—Surface area thermal stability thereof at high temperatures
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/14—Pore volume

Definitions

  • the invention relates to a cobalt catalyst supported on a high- surface area niobium pentoxide, the processes for making the support and the catalyst itself, the use of the support for making the catalyst and the use of the catalyst for the Fischer-Tropsch synthesis (FTS).
  • FTS Fischer-Tropsch synthesis
  • the Fischer-Tropsch synthesis consists of the chemical conversion of synthesis gas (CO and H 2 ) in a mixture of hydrocarbons, which composition depends upon the type of catalyst used and the reaction conditions. Typically, light hydrocarbons (Ci to C 4 ), linear or branched paraffin in the range of gasoline and diesel fuels (C 5 -C1 9 ), alpha-olefins, heavy waxes (C ⁇ 9 + ) and oxygenated compounds can be obtained.
  • the most employed catalysts comprise, as active metal, iron (Fe), cobalt (Co), ruthenium (Ru) and mixtures thereof, supported or not in metal oxides.
  • cobalt catalysts present the best performance in terms of productivity and selectivity to hydrocarbons of C5 composition. Liquid fuels, gasoline and diesel, are found in this fraction.
  • the preparation method the nature of cobalt precursor salts, the support, the cobalt content, the presence of promoters and pretreatment conditions for calcination, reduction and activation are important parameters to guarantee the performance of the catalytic material.
  • the most common supports for cobalt catalysts are silica (Si0 2 ) and alumina (A1 0 3 ).
  • Alternative supports such as titania (Ti0 2 ) are also used due to their capacity of forming intermetallic compounds with Lewis acid-base properties.
  • SMSI strong metal-support interaction
  • U.S. Samuel J. Tauster
  • Patent 4,149,998 who observed the suppression of chemisorption capacity of hydrogen (H 2 ) and carbon monoxide (CO) by Group VIIIB elements when supported in Ti0 2 , V 2 0 5 , Ce0 2 , Nb 2 0 5 , among others. As a result, the activity and selectivity of reactions that involve the adsorption-desorption of H 2 and CO were significantly altered.
  • the present invention takes advantage of SMSI properties of Nb 2 0 5 -supported cobalt catalyst by "using a high-surface area niobium pentoxide support to promote its activity ⁇ , selectivity and stability towards a higher fraction of hydrocarbons of C 5 + composition, very selective to diesel fuel fraction, with negligible formation of branched, unsaturated and oxygenated compounds.
  • the present invention describes the prep aration of a catalyst and its use in the Fischer-Tropsch synthesis.
  • the catalyst comprises cobalt supported on a high-surface area niobium pentoxide (Nb 2 0 5 ) in powdery form with a well- defined particle size distribution, pellets or extrudates. It is highly selective to C 5 + hydrocarbons, which composition is very rich in diesel (C 12 -C 19 ). In addition, the catalyst does not produce a significant amount of olefins and oxygenated compounds.
  • the catalyst in its oxide form is activated, prior to the utilization on FTS, through reduction of cobalt oxide to metal cobalt by exposing it to a reducing atmosphere comprising either hydrogen (H 2 ) or carbon monoxide (CO) at a suitable temperature that guarantees thorough cobalt oxide reduction.
  • the reduced catalyst may be or not passivated to further u_se on FTS without the need of another reduction.
  • the SMSI state is formed, indicated by the presence of non-stoichiorne ⁇ tric niobium oxides (NbO x ) in the interface Co-Nb 2 0 5 .
  • the extent of reduction of the niobium pentoxide is a function of the temperature.
  • the activated catalyst is then submitted to reaction conditions by introducing synthesis gas (CO and H 2 mixture) at a suitable time, temperature and pressure to higher activity and selectivity to Cs + hydrocarbons, specially in diesel fuel fraction, with minimal production of olefin and oxygenated compounds.
  • synthesis gas CO and H 2 mixture
  • One goal of the present invention is a cobalt catalyst for Fischer- Tropsch synthesis supported on a high-surface area niobium pentoxide with a content of metal cobalt in the final composition of the catalyst supported on niobium pentoxide in the range of 3 to 40 wt.%, preferentially in the range of 4 to 25 wt.% and more preferentially in the range of 5 to 15 wt.%.
  • the catalyst for FTS might be exposed to the action of a reducing gas comprising either hydrogen (H 2 ), carbon monoxide (CO) or mixtures thereof, the hydrogen being the preferential reducing gas, at a reduction temperature between 300 to 600°C, preferentially between 350 to 550°C and more preferentially between 400 to 500°C.
  • the reduction time is no less than 6 hours, preferentially between 10 to 24 hrs and more preferentially between 14 and 20 hrs.
  • the cobalt catalyst in accordance with the invention is obtained from soluble precursors such as cobalt (II) nitrate [Co(N0 3 ) 2 .6H 2 0], cobalt (II) chloride (CoCl 2 .6H 2 0), cobalt (II) sulfate (CoS0 4 .xH 2 0), cobalt (II) hydroxide [Co(OH) 2 ] and cobalt (II) acetate [(CH 3 C0 2 ) 2 Co], the cobalt nitrate and chloride, and more preferred the cobalt nitrate, being preferred as soluble precursors.
  • cobalt (II) nitrate Co(N0 3 ) 2 .6H 2 0
  • cobalt (II) chloride CoCl 2 .6H 2 0
  • cobalt (II) sulfate CoS0 4 .xH 2 0
  • Another goal of the invention is the support for the catalyst for FTS, which consists of a high-surface area niobim pentoxide (Nb 2 0 5 ) with BET surface area in the range of 30 to 160 m 2 .g _1 , preferentially between 60 to 150 m 2 .g _1 and more preferentially between 80 to 100 m 2 .g _1 , and presenting as crystal structure the pseudo-hexagonal phase.
  • Nb 2 0 5 niobim pentoxide
  • a further goal of the invention is the process of preparation of the high-surface area niobium pentoxide as a catalyst support that involves the calcination of hydrated niobium oxide at temperatures between 200 to 800°C for a period of 2 to 4 hours. Preferentially the calcination is carried out between 300 to 700°C and more preferentially between 400 to 600°C.
  • Another process of preparation of the catalyst support of niobium pentoxide consists of the synthesis of niobium pentoxide from precipitation or sol-gel of either organic or inorganic niobium precursors such as niobium oxalate, pentachloride and alkoxides (methoxide, isopropoxide and butoxide).
  • the solvents employed in the preparation of the cobalt precursor solution are water, methanol, ethanol, propanol, isopropanol and acetone, preferentially water, methanol, ethanol and isopropanol and more preferentially water and ethanol.
  • the step of support impregnation can be done or selected among several techniques such as incipient wetness impregnation, wet impregnation and deposition-precipitation.
  • Another goal of this invention is the use of Nb 2 0 5 -supported cobalt catalyst for the Fischer-Tropsch synthesis to obtain hydrocarbons with carbon atoms equal or higher than 5 (five), the so-called C 5 + fraction, containing preferentially linear parafins in the fraction of diesel oil, with minimal formation of light hydrocarbons, olefins, aromatics and oxygenated compounds.
  • the selectivity to C 5 + hydrocarbons is superior to 70 wt.%, and the fraction in the diesel oil range (C ⁇ 2 -C ⁇ 8 ) is higher than 80 wt.%, the formation of light hydrocarbons (C0 2 , CH , C 2 -C 4 ), olefins, aromatics and oxygenated compounds are less than 10 wt.%.
  • the catalyst is active and selective to produce hydrocarbons through the reaction of a mixture of carbon monoxide (CO) and hydrogen (H 2 ) with a pre-defined H 2 /CO ratio, temperature, pressure and space velocity suitable to a more selective production of hydrocarbons with carbon atoms equal or higher than 5 (Cs + ).
  • the H 2 /CO volumetric ratio of the reaction is preferentially in the range of 1 to 3, more preferentially in the range of 1.5 to 2.5, and even more preferentially in the range of 1.8 to 2.2.
  • the reaction temperature varies from 200 to 300°C, preferentially from 200 to 250°C, and more preferentially from 210 to 240°C.
  • the reaction pressure varies from 405 to 5,000 kPa, preferentially from 1,500 to 4,000 kPa and more preferentially from 1,800 to 2,200 kPa.
  • the space velocity of the reaction is in the range of 100 to 6,000 h "1 , preferentially from 300 to 2,000 h "1 and more preferentially from 400 to 1,000 h "1 .
  • FIG. 1 X-ray diffraction of niobium pentoxide: as-prepared Nb 2 0 5 and calcined Nb 2 0 5 at 500°C.
  • FIG. 2 BET surface area of niobium pentoxide as function of calcination temperature.
  • FIG. 3 TPR profile of catalysts showing the formation of SMSI effect between particles of Co and support of Nb 2 0 5 .
  • FIG. 4 Distillation of Fischer-Tropsch hydrocarbon liquid fraction obtained according to one of the prepared catalysts.
  • the high-surface area support of niobium pentoxide can be obtained by the calcination of a hydrated niobium oxide (Nb 2 0 5 .nH 2 0), for instance, the commercial HY® niobia from CBMM (Companhia Brasileira de Metalurgia e Mineracao) with a water content in the range of 15 to 25 wt.%.
  • the support of niobium pentoxide can also be obtained by synthesis techniques such as precipitation and sol-gel from the use of either organic or inorganic niobium precursors.
  • the hydrated niobium oxide is an amorphous material as shown its X-ray diffraction pattern ( Figure 1) with a BET surface area around 160 m .gX
  • the thermal treatment of this material causes the loss of surface area as a function of calcination temperature as indicated in Figure 2. Above 500°C, the loss of surface area is significant, reaching values lower than 30 m 2 .g _1 .
  • the loss of surface area is attributed to water removal and the crystallization process of the amorphous material.
  • X-ray diffraction pattern of ttie calcined material at 500°C reveals a material with a low degree of crystalliza,tion, pseudo-hexagonal structure and lamellar morphology.
  • the surface area of Nb 2 0 5 which is a function of calcination temperature, is in the range of 30 to 1 1 9 1 160 m .g " , preferentially between 60 and 150 m .g " , and more preferentially around 80 to lOO rr ⁇ g "1 ,
  • the niobium pentoxide prepared by the calcination of a hydrated niobium oxide is impregnated by a solution of cobalt precursors.
  • the cobalt precursors used are cobalt (II) nitrate [Co(N0 3 ) 2 .6H 2 0], cobalt (II) chloride (CoCl 2 .6H 2 0), cobalt (II) sulfate (CoS0 4 .xH 2 0), cobalt (II) hydroxide [Co(OH) 2 ] and cobalt (II) acetate [(CH 3 C0 2 ) 2 Co], preferentially cobalt nitrate and cobalt chloride, and more preferentially cobalt nitrate.
  • the solvents employed in the preparation of the impregnating solution are water (H 2 0), methanol (CH 3 OH), ethanol (CH 3 CH 2 OH), propanol (CH 3 CH 2 CH 2 OH), isopropanol (CH 3 CHOHCH 3 ) and acetone (CH 3 COCH 3 ).
  • the preferred solvents are water, methanol, ethanol and isopropanol, and the more preferred solvents are water and ethanol.
  • the amount of cobalt precursor added to the impregnating solution is a function of the desirable final content of metal cobalt in the composition of the catalyst.
  • the metal cobalt content varies from 3 to 40 wt.%, preferentially between 4 and 25 wt.%, and more preferentially between 5 and 15 wt.%.
  • the catalyst preparation techniques employed are selected among many known in the art such as wet impregnation, incipient wetness impregnation and deposition-precipitation, preferentially wet impregnation and incipient wetness impregnation, and more preferentially the incipient wetness impregnation.
  • the volume of the impregnating solution must have the same pore volume of niobium pentoxide.
  • Nb 2 ⁇ 5 pore volume is done by water titration, in which a known amount of the support, for instance, 100 g, suffers gradual dropping up to a point the powdery support becomes a mud-like cake. The amount of water added before reaching the mud-like cake point is the solution volume corresponding to the pore volume of the support. This volume is the impregnating volume used to prepare the cobalt (II) nitrate solution. The addition of the impregnating solution of cobalt precursor is continuously done and the support is strongly stirred up to guarantee the total penetration of the solution into the pore volume of the support. After the impregnation, the support is dried at temperature in the range of 100 to 250°C for a period of 18 to 24 hours.
  • the impregnated support is calcined for the decomposition of cobalt (II) nitrate precursor, resulting m the formation of cobalt oxide (Co 3 0 4 ) dispersed on Nb 2 0 5 surface.
  • the calcination temperature used is in the range of 300 to 600°C, preferentially b etween 350 and 550°C, and more preferentially between 400 and 500°C.
  • the heating rate, during the calcination step, is an important variable, since very fast rate s may cause the creation of hot spots during the cobalt nitrate decomposition leading to the agglomeration of the metal particles.
  • the agglomeration is undesirable due to the loss of metallic area, and as consequence the density of catalytic sites available for reaction significantly decreases.
  • the heating rate is less than 10°C.min "1 , preferentially between 1 and 5°C.min "1 , and more preferentially between 1 and 2°C.min "1 .
  • the calcination time is no less than 4 hours, preferentially between 4 and 12 hours, and more preferentially between 4 and 6 hours.
  • the Nb 2 0 5 -supported cobalt catalyst is loaded to a Fischer-Tropsch synthesis reactor, where it is activated befoxe submitted to reaction mixture.
  • the catalyst activation consists of the transformation of cobalt oxide into metallic cobalt by the action of a reducing gas at suitable temperature and reduction time to guarantee the complete reduction.
  • the reducing gas used is hydrogen (H 2 ), carbon monoxide (CO) or mixtures thereof, but the most preferred is hydrogen. Therefore, the calcined catalyst is exposed to a hydrogen flux with a space velocity between 500 and 2,000 h "1 , preferentially between 700 and 1,500 h "1 , and more preferentially between 800 and 1,200 h "1 .
  • the reduction temperature is in the range of 300 to 600°C, preferentially between 350 and 550°C, and more preferentially between 400 and 500°C.
  • the reduction time should no less than 6 hours, being preferred between 10 and 24 hours and more preferred between 14 and 20 hours.
  • the activation process of catalyst in hydrogen is also known as hydrogenation or reduction of the catalyst.
  • the activation, reduction or hydrogenation of cobalt catalyst is the same transformation process of cobalt oxides into metallic cobalt, which is the phase that contains the active sites for FTS.
  • the importance of catalyst activation goes beyond the preparation of catalytic sites of metallic character for FTS.
  • the reduction is also responsible for the formation of the SMSI effect between Co and Nb 2 0 5 , which in the present invention is the essential factor to promote the activity and selectivity of the cobalt catalyst supported on niobium pentoxide.
  • the temperature- programmed reduction (TPR) of the 5 wt.% Co supported on Nb 2 0 5 ( Figure 3) 94- shows that the hydrogen uptake for the complete reduction of Co species at temperatures between 370°C and 480°C is much higher than the stoichiometry.
  • the hydrogen uptake excess is assigned to the partial reduction of Nb 2 0 5 to non-stoichiometric niobium oxides (NbO x ).
  • NbO x non-stoichiometric niobium oxides
  • These non-stoichiometric oxides are formed in the interface Co-Nb 2 0 5 , and depending upon the extent of the SMSI effect, they can partially recover the metal cobalt surface or give origin to new adsorption sites, which results in the modification of the adsorption/desorption properties of cobalt related to H 2 and CO molecules.
  • the activated or reduced catalyst, loaded to a catalytic reactor for FTS, is exposed to the reaction mixture of H 2 and CO at a volumetric H 2 /CO ratio between 1 and 3, preferentially between 1.5 and 2.5, and more preferentially between 1.8 and 2.2.
  • the space velocity measured as the function of the catalyst weight (WHSV: weight hourly space velocity), is in the range of 100 to 6,000 h "1 , preferentially between 300 and 2,000 h "1 , and more preferentially between 400 and 1,000 h "1 .
  • the reaction temperature varies from 200 to 300°C, preferentially between 200 and 250°C, and more preferentially in the range of 210 to 240°C.
  • the reaction pressure is in the range of 400 to 5,000 kPa, preferentially between 1,000 to 4,000 kPa and more preferentially between 1,800 and 2,200 kPa.
  • the catalyst activity measured by the carbon monoxide conversion, and selectivity to the desirable products are function of reaction temperature and time. At low temperatures, CO conversion is lower than 40% with minimal formation ( ⁇ 5 wt.%) of carbon dioxide (C0 2 ) and methane (CH 4 ). The majority of the products are C 5 + hydrocarbons in weight amounts higher than 80 wt.%. At high temperatures, CO conversion remarkably increases reaching levels higher than 90%). However, the selectivity to light products (C0 2 , CH 4 , C 2 -C 4 ) significantly increases. Regarding the reaction time, the level of activity is low during the first hours of reaction and CO conversion gradually increases up to the steady state regime. At long periods of reaction, it is observed the formation of heavy paraffin compounds, which are hydrocarbons with carbon atoms equal or higher than 19 (Ci 9 + fraction), mainly heavy waxes.
  • the cobalt catalyst supported on niobium pentoxide is highly selective to C 5 + linear paraffin with minimal formation of light products (C0 2 , CH 4 , C 2 -C 4 ), olefins, aromatics and oxygenated compounds. Moreover, the amount of hydrocarbons in the diesel oil fraction (C ⁇ 2 -C ⁇ 8 ) is very high.
  • Example 1 - The preparation of 5 wt.%Co/Nb 2 0 5 catalyst
  • niobium pentoxide 100 g was calcined in aerated muffle (50 ml.min "1 of dry air) at temperature of 550°C for 2 hours with the heating rate of 2°C.min "1 . After calcination, the niobium pentoxide presented a pore volume of 0.30 rnl.g "1 .
  • aqueous solution of a cobalt precursor was prepared dissolving 24.7 g of cobalt (II) nitrate [Co(N0 3 ) 2 .6H 2 0] in 30 ml of distillated water. This solution was gradually added to the niobium pentoxide support, which was continuously stirred up to allow better distribution and complete penetration into the pore volume of the same. Following the impregnation, the catalyst was dried in aerated muffle at 120°C for 18 hours. The dry sample was then calcined in aerated muffle (50 ml.min "1 of dry air) at temperature of 400°C for 2 hours with a heating rate of 2°C.min "1 . The calcined catalyst has a 5 wt.% of cobalt supported on niobium pentoxide in its oxide form.
  • Example 1 60 g of the catalyst prepared in the Example 1 was loaded to a fixed- bed reactor that comprises of stainless steel tube of 25.4 mm of diameter and 1 m of height. The catalyst was placed in the central part of the reactor and electrical resistance heated the catalyst region. The catalyst was then activated or reduced by passing through it pure hydrogen (1,000 ml.min "1 ) at 500°C for 16 hours at atmospheric pressure. The heating rate during the activation was of 2°C.min "1 and the space velocity around 1,000 h "1 . After activation, the temperature of the catalytic bed was then reduced under hydrogen flow to the desirable reaction temperature.
  • the hydrogen flow was then adjusted to 3,900 ml.min "1 and carbon monoxide (CO) was introduced into the reactor at 1,950 ml.min "1 that results in a H 2 /CO volumetric ratio of 2.
  • the space velocity, initially set at 6,000 h was gradually reduced up to 600 h "1 .
  • the reactor pressure was controlled to be between 20 to 30 kPa. Table 1 shows the selectivity and product distribution for CO conversion of 30% and reaction temperature of 240°C.
  • Table 1 and Table 2 show that the use of a high-surface area niobium pentoxide as a support for cobalt catalyst in Fischer-Tropsch improved the selectivity to C 5 + hydrocarbons. This fraction is richer in saturated carbon, mainly linear paraffins.

Abstract

The present invention is related to a cobalt catalyst supported on high-surface area niobium pentoxide for Fischer-Tropsch synthesis, the support of this catalyst which is a niobium pentoxide (Nb2O5) with a BET surface area in the range of 30 to 160 m2.g-1, the process for the preparation of the high-surface area support of niobium pentoxide by calcination of a hydrated niobium oxide or by synthesis from either organic or inorganic niobium precursors, a process for the preparation of said catalyst, and the use of the catalyst for the Fischer-Tropsch synthesis to obtain hydrocarbons with carbon atoms equal or higher than five containing specially linear paraffins in the diesel fuel range, and without a significant formation of light hydrocarbons, olefins, aromatics and oxygenated compounds.

Description

"COBALT CATALYST FOR THE SYNTHESIS OF FISCHER- TROPSCH, CATALYST SUPPORT, PROCESSES FOR THE PREPARATION OF SUPPORT AND CATALYST AND THE USE OF THE CATALYST"
FIELD OF THE INVENTION
The invention relates to a cobalt catalyst supported on a high- surface area niobium pentoxide, the processes for making the support and the catalyst itself, the use of the support for making the catalyst and the use of the catalyst for the Fischer-Tropsch synthesis (FTS).
PRIOR ART The Fischer-Tropsch synthesis (FTS) consists of the chemical conversion of synthesis gas (CO and H2) in a mixture of hydrocarbons, which composition depends upon the type of catalyst used and the reaction conditions. Typically, light hydrocarbons (Ci to C4), linear or branched paraffin in the range of gasoline and diesel fuels (C5-C19), alpha-olefins, heavy waxes (Cι9 +) and oxygenated compounds can be obtained. The most employed catalysts comprise, as active metal, iron (Fe), cobalt (Co), ruthenium (Ru) and mixtures thereof, supported or not in metal oxides.
According to the article "Design, Synthesis, and Use of Cobalt- based Fischer-Tropsch Synthesis Catalysts" (Enrique Iglesia, Applied Catalysis
ArGeneral, volume 161, pages 59-78, 1997), cobalt catalysts present the best performance in terms of productivity and selectivity to hydrocarbons of C5 composition. Liquid fuels, gasoline and diesel, are found in this fraction. During the preparation of a cobalt-based catalyst, the preparation method, the nature of cobalt precursor salts, the support, the cobalt content, the presence of promoters and pretreatment conditions for calcination, reduction and activation are important parameters to guarantee the performance of the catalytic material.
In order to obtain an optimum metallic dispersion the important variables in the preparation of cobalt catalyst should be controlled and correlated. Optimum cobalt dispersions are in the range of 0.10 to 0.15, and though higher dispersion is intuitively desirable, it leads to rapid deactivation during reaction, which cancels off any productivity gain (Enrique Iglesia, Natural Gas Conversion IV, Studies in Surface Science and Catalysis 107, pages 153-162, 1997). Recent attempts to increase the catalyst efficiency and resistance to deactivation are focused on loading great amounts, 15 to 50 -weight percent, of cobalt on metal oxide supports (PCT International WO 01/87840), but keeping the optimum dispersion ofθ.lθ to θ.15.
Higher contents of cobalt are inconvenient due to the cost of the catalyst, since cobalt is expensive. Several factors are associated with the catalyst deactivation, and the most critical is the loss of cobalt specific superficial area, due to sintering, to strong support interaction with the formation of inactive compounds and to coke deposition. Another issue related to catalyst deactivation is the fonnation of considerable amounts of water in FTS, which may change the physical properties of the support such as specific area and crystal structure.
The most common supports for cobalt catalysts are silica (Si02) and alumina (A1 03). Alternative supports such as titania (Ti02) are also used due to their capacity of forming intermetallic compounds with Lewis acid-base properties. In typical conditions for the metallic catalysts activation, where reducing atmosphere is employed, these supports are partially reduced, and non- stoichiometric oxides are formed, which interact with the metallic particles of the catalyst thus affecting their adsorption properties. This phenomenon is known as strong metal-support interaction (SMSI), according to Samuel J. Tauster (U.S. Patent 4,149,998), who observed the suppression of chemisorption capacity of hydrogen (H2) and carbon monoxide (CO) by Group VIIIB elements when supported in Ti02, V205, Ce02, Nb205, among others. As a result, the activity and selectivity of reactions that involve the adsorption-desorption of H2 and CO were significantly altered.
Since the Fischer-Tropsch synthesis deals with the conversion of synthesis gas, basically a mixture of H2 and CO, it is expected that the use of supports presenting SMSI properties may change the catalytic performance of supported cobalt. According to Soares et al. ("Effect of Preparation Method on
5%Co/Nb205 in Fischer-Tropsch Synthesis" Catalysis Today 16 (1993) 361-
370) and Frydman et al. ("High Selectivity of Diesel Fraction in Fisc er- Tropsch Synthesis with Co/Nb205" Studies in Surface Science and Catalysis, vol. 75, p. 2797-2800, 1993), the use of niobium pentoxide as support for cobalt catalyst improved the selectivity to long chain hydrocarbons, especially in diesel fraction (Cι3-Cι8). Due to the existence of a strong interaction of cobalt with
Nb205, different Co species in the interface Cox-NbOy would be responsible for the higher selectivity to diesel (31 to 41 wt.%). However, the amount of olefins, branched and oxygenated compounds were superior to 30 wt.%. In order to maximize the selectivity to hydrocarbons on diesel fraction and minimize the formation of olefins and oxygenated compounds would be interesting to promote the support interaction with cobalt particles in a controllable manner. At the light of those concerns, the present invention takes advantage of SMSI properties of Nb205-supported cobalt catalyst by "using a high-surface area niobium pentoxide support to promote its activity^, selectivity and stability towards a higher fraction of hydrocarbons of C5 + composition, very selective to diesel fuel fraction, with negligible formation of branched, unsaturated and oxygenated compounds.
SUMMARY OF THE INVENTION
The present invention describes the prep aration of a catalyst and its use in the Fischer-Tropsch synthesis. The catalyst comprises cobalt supported on a high-surface area niobium pentoxide (Nb205) in powdery form with a well- defined particle size distribution, pellets or extrudates. It is highly selective to C5 + hydrocarbons, which composition is very rich in diesel (C12-C19). In addition, the catalyst does not produce a significant amount of olefins and oxygenated compounds.
The catalyst in its oxide form is activated, prior to the utilization on FTS, through reduction of cobalt oxide to metal cobalt by exposing it to a reducing atmosphere comprising either hydrogen (H2) or carbon monoxide (CO) at a suitable temperature that guarantees thorough cobalt oxide reduction. The reduced catalyst may be or not passivated to further u_se on FTS without the need of another reduction. During the activation of the catalyst, the SMSI state is formed, indicated by the presence of non-stoichiorne~tric niobium oxides (NbOx) in the interface Co-Nb205. The extent of reduction of the niobium pentoxide is a function of the temperature. The activated catalyst is then submitted to reaction conditions by introducing synthesis gas (CO and H2 mixture) at a suitable time, temperature and pressure to higher activity and selectivity to Cs+ hydrocarbons, specially in diesel fuel fraction, with minimal production of olefin and oxygenated compounds.
One goal of the present invention is a cobalt catalyst for Fischer- Tropsch synthesis supported on a high-surface area niobium pentoxide with a content of metal cobalt in the final composition of the catalyst supported on niobium pentoxide in the range of 3 to 40 wt.%, preferentially in the range of 4 to 25 wt.% and more preferentially in the range of 5 to 15 wt.%.
The catalyst for FTS, according to this invention, might be exposed to the action of a reducing gas comprising either hydrogen (H2), carbon monoxide (CO) or mixtures thereof, the hydrogen being the preferential reducing gas, at a reduction temperature between 300 to 600°C, preferentially between 350 to 550°C and more preferentially between 400 to 500°C. The reduction time is no less than 6 hours, preferentially between 10 to 24 hrs and more preferentially between 14 and 20 hrs.
The cobalt catalyst in accordance with the invention is obtained from soluble precursors such as cobalt (II) nitrate [Co(N03)2.6H20], cobalt (II) chloride (CoCl2.6H20), cobalt (II) sulfate (CoS04.xH20), cobalt (II) hydroxide [Co(OH)2] and cobalt (II) acetate [(CH3C02)2Co], the cobalt nitrate and chloride, and more preferred the cobalt nitrate, being preferred as soluble precursors.
Another goal of the invention is the support for the catalyst for FTS, which consists of a high-surface area niobim pentoxide (Nb205) with BET surface area in the range of 30 to 160 m2.g_1, preferentially between 60 to 150 m2.g_1 and more preferentially between 80 to 100 m2.g_1, and presenting as crystal structure the pseudo-hexagonal phase.
A further goal of the invention is the process of preparation of the high-surface area niobium pentoxide as a catalyst support that involves the calcination of hydrated niobium oxide at temperatures between 200 to 800°C for a period of 2 to 4 hours. Preferentially the calcination is carried out between 300 to 700°C and more preferentially between 400 to 600°C. Another process of preparation of the catalyst support of niobium pentoxide consists of the synthesis of niobium pentoxide from precipitation or sol-gel of either organic or inorganic niobium precursors such as niobium oxalate, pentachloride and alkoxides (methoxide, isopropoxide and butoxide). The solvents employed in the preparation of the cobalt precursor solution are water, methanol, ethanol, propanol, isopropanol and acetone, preferentially water, methanol, ethanol and isopropanol and more preferentially water and ethanol. The step of support impregnation can be done or selected among several techniques such as incipient wetness impregnation, wet impregnation and deposition-precipitation. Another goal of this invention is the use of Nb205-supported cobalt catalyst for the Fischer-Tropsch synthesis to obtain hydrocarbons with carbon atoms equal or higher than 5 (five), the so-called C5 + fraction, containing preferentially linear parafins in the fraction of diesel oil, with minimal formation of light hydrocarbons, olefins, aromatics and oxygenated compounds. The selectivity to C5 + hydrocarbons is superior to 70 wt.%, and the fraction in the diesel oil range (Cι2-Cι8) is higher than 80 wt.%, the formation of light hydrocarbons (C02, CH , C2-C4), olefins, aromatics and oxygenated compounds are less than 10 wt.%.
The catalyst is active and selective to produce hydrocarbons through the reaction of a mixture of carbon monoxide (CO) and hydrogen (H2) with a pre-defined H2/CO ratio, temperature, pressure and space velocity suitable to a more selective production of hydrocarbons with carbon atoms equal or higher than 5 (Cs+).
The H2/CO volumetric ratio of the reaction is preferentially in the range of 1 to 3, more preferentially in the range of 1.5 to 2.5, and even more preferentially in the range of 1.8 to 2.2.
The reaction temperature varies from 200 to 300°C, preferentially from 200 to 250°C, and more preferentially from 210 to 240°C. The reaction pressure varies from 405 to 5,000 kPa, preferentially from 1,500 to 4,000 kPa and more preferentially from 1,800 to 2,200 kPa. The space velocity of the reaction is in the range of 100 to 6,000 h"1, preferentially from 300 to 2,000 h"1 and more preferentially from 400 to 1,000 h"1. BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 - X-ray diffraction of niobium pentoxide: as-prepared Nb205 and calcined Nb205 at 500°C. FIG. 2 - BET surface area of niobium pentoxide as function of calcination temperature.
FIG. 3 - TPR profile of catalysts showing the formation of SMSI effect between particles of Co and support of Nb205.
FIG. 4 - Distillation of Fischer-Tropsch hydrocarbon liquid fraction obtained according to one of the prepared catalysts.
DETAILED DESCRIPTION OF THE INVENTION
The high-surface area support of niobium pentoxide can be obtained by the calcination of a hydrated niobium oxide (Nb205.nH20), for instance, the commercial HY® niobia from CBMM (Companhia Brasileira de Metalurgia e Mineracao) with a water content in the range of 15 to 25 wt.%. The support of niobium pentoxide can also be obtained by synthesis techniques such as precipitation and sol-gel from the use of either organic or inorganic niobium precursors. The hydrated niobium oxide is an amorphous material as shown its X-ray diffraction pattern (Figure 1) with a BET surface area around 160 m .gX The thermal treatment of this material causes the loss of surface area as a function of calcination temperature as indicated in Figure 2. Above 500°C, the loss of surface area is significant, reaching values lower than 30 m2.g_1. The loss of surface area is attributed to water removal and the crystallization process of the amorphous material. X-ray diffraction pattern of ttie calcined material at 500°C reveals a material with a low degree of crystalliza,tion, pseudo-hexagonal structure and lamellar morphology. The hydrated niobium oxide used in the preparation of the niobium pentoxide, employed as support for cobalt catalyst, was calcined at temperatures in the range of 200 to 800°C, preferentially between 300 and 700°C, and more preferentially at temperatures between 400 and 600°C. The surface area of Nb205, which is a function of calcination temperature, is in the range of 30 to 1 1 9 1 160 m .g" , preferentially between 60 and 150 m .g" , and more preferentially around 80 to lOO rrΛg"1,
Several preparation techniques for supporte d metal catalysts can be used to disperse the cobalt particles on the surface of niobium pentoxide. The most common techniques, which involve the use of solutions of cobalt precursors, are incipient wetness impregnation, wet irαtpregnation, deposition- precipitation, anchoring and ion exchange.
The niobium pentoxide prepared by the calcination of a hydrated niobium oxide is impregnated by a solution of cobalt precursors. The cobalt precursors used are cobalt (II) nitrate [Co(N03)2.6H20], cobalt (II) chloride (CoCl2.6H20), cobalt (II) sulfate (CoS04.xH20), cobalt (II) hydroxide [Co(OH)2] and cobalt (II) acetate [(CH3C02)2Co], preferentially cobalt nitrate and cobalt chloride, and more preferentially cobalt nitrate. The solvents employed in the preparation of the impregnating solution are water (H20), methanol (CH3OH), ethanol (CH3CH2OH), propanol (CH3CH2CH2OH), isopropanol (CH3CHOHCH3) and acetone (CH3COCH3). The preferred solvents are water, methanol, ethanol and isopropanol, and the more preferred solvents are water and ethanol. The amount of cobalt precursor added to the impregnating solution is a function of the desirable final content of metal cobalt in the composition of the catalyst. The metal cobalt content varies from 3 to 40 wt.%, preferentially between 4 and 25 wt.%, and more preferentially between 5 and 15 wt.%. The catalyst preparation techniques employed are selected among many known in the art such as wet impregnation, incipient wetness impregnation and deposition-precipitation, preferentially wet impregnation and incipient wetness impregnation, and more preferentially the incipient wetness impregnation. For the incipient wetness impregnation, the volume of the impregnating solution must have the same pore volume of niobium pentoxide. The determination of Nb2θ5 pore volume is done by water titration, in which a known amount of the support, for instance, 100 g, suffers gradual dropping up to a point the powdery support becomes a mud-like cake. The amount of water added before reaching the mud-like cake point is the solution volume corresponding to the pore volume of the support. This volume is the impregnating volume used to prepare the cobalt (II) nitrate solution. The addition of the impregnating solution of cobalt precursor is continuously done and the support is strongly stirred up to guarantee the total penetration of the solution into the pore volume of the support. After the impregnation, the support is dried at temperature in the range of 100 to 250°C for a period of 18 to 24 hours. After drying, the impregnated support is calcined for the decomposition of cobalt (II) nitrate precursor, resulting m the formation of cobalt oxide (Co304) dispersed on Nb205 surface. The calcination temperature used is in the range of 300 to 600°C, preferentially b etween 350 and 550°C, and more preferentially between 400 and 500°C. The heating rate, during the calcination step, is an important variable, since very fast rate s may cause the creation of hot spots during the cobalt nitrate decomposition leading to the agglomeration of the metal particles. The agglomeration is undesirable due to the loss of metallic area, and as consequence the density of catalytic sites available for reaction significantly decreases. In order to avoid agglomeration of metallic particles during calcination, the heating rate is less than 10°C.min"1, preferentially between 1 and 5°C.min"1, and more preferentially between 1 and 2°C.min"1. In order to guarantee the total decomposition of cobalt nitrate, the calcination time is no less than 4 hours, preferentially between 4 and 12 hours, and more preferentially between 4 and 6 hours.
After calcination the Nb205-supported cobalt catalyst is loaded to a Fischer-Tropsch synthesis reactor, where it is activated befoxe submitted to reaction mixture. The catalyst activation consists of the transformation of cobalt oxide into metallic cobalt by the action of a reducing gas at suitable temperature and reduction time to guarantee the complete reduction. The reducing gas used is hydrogen (H2), carbon monoxide (CO) or mixtures thereof, but the most preferred is hydrogen. Therefore, the calcined catalyst is exposed to a hydrogen flux with a space velocity between 500 and 2,000 h"1, preferentially between 700 and 1,500 h"1, and more preferentially between 800 and 1,200 h"1. The reduction temperature is in the range of 300 to 600°C, preferentially between 350 and 550°C, and more preferentially between 400 and 500°C. The reduction time should no less than 6 hours, being preferred between 10 and 24 hours and more preferred between 14 and 20 hours. The activation process of catalyst in hydrogen is also known as hydrogenation or reduction of the catalyst. Hence, the activation, reduction or hydrogenation of cobalt catalyst is the same transformation process of cobalt oxides into metallic cobalt, which is the phase that contains the active sites for FTS.
The importance of catalyst activation goes beyond the preparation of catalytic sites of metallic character for FTS. The reduction is also responsible for the formation of the SMSI effect between Co and Nb205, which in the present invention is the essential factor to promote the activity and selectivity of the cobalt catalyst supported on niobium pentoxide. The temperature- programmed reduction (TPR) of the 5 wt.% Co supported on Nb205 (Figure 3) 94- shows that the hydrogen uptake for the complete reduction of Co species at temperatures between 370°C and 480°C is much higher than the stoichiometry. Therefore, the hydrogen uptake excess is assigned to the partial reduction of Nb205 to non-stoichiometric niobium oxides (NbOx). These non-stoichiometric oxides are formed in the interface Co-Nb205, and depending upon the extent of the SMSI effect, they can partially recover the metal cobalt surface or give origin to new adsorption sites, which results in the modification of the adsorption/desorption properties of cobalt related to H2 and CO molecules. The activated or reduced catalyst, loaded to a catalytic reactor for FTS, is exposed to the reaction mixture of H2 and CO at a volumetric H2/CO ratio between 1 and 3, preferentially between 1.5 and 2.5, and more preferentially between 1.8 and 2.2. The space velocity, measured as the function of the catalyst weight (WHSV: weight hourly space velocity), is in the range of 100 to 6,000 h"1, preferentially between 300 and 2,000 h"1, and more preferentially between 400 and 1,000 h"1. The reaction temperature varies from 200 to 300°C, preferentially between 200 and 250°C, and more preferentially in the range of 210 to 240°C. The reaction pressure is in the range of 400 to 5,000 kPa, preferentially between 1,000 to 4,000 kPa and more preferentially between 1,800 and 2,200 kPa.
The catalyst activity, measured by the carbon monoxide conversion, and selectivity to the desirable products are function of reaction temperature and time. At low temperatures, CO conversion is lower than 40% with minimal formation (< 5 wt.%) of carbon dioxide (C02) and methane (CH4). The majority of the products are C5 + hydrocarbons in weight amounts higher than 80 wt.%. At high temperatures, CO conversion remarkably increases reaching levels higher than 90%). However, the selectivity to light products (C02, CH4, C2-C4) significantly increases. Regarding the reaction time, the level of activity is low during the first hours of reaction and CO conversion gradually increases up to the steady state regime. At long periods of reaction, it is observed the formation of heavy paraffin compounds, which are hydrocarbons with carbon atoms equal or higher than 19 (Ci9 + fraction), mainly heavy waxes.
The cobalt catalyst supported on niobium pentoxide is highly selective to C5 + linear paraffin with minimal formation of light products (C02, CH4, C2-C4), olefins, aromatics and oxygenated compounds. Moreover, the amount of hydrocarbons in the diesel oil fraction (Cι2-Cι8) is very high. Example 1 - The preparation of 5 wt.%Co/Nb205 catalyst
100 g of hydrated niobium pentoxide (HY® niobia from CBMM - Companhia Brasileira de Metalurgia e Mineracao) was calcined in aerated muffle (50 ml.min"1 of dry air) at temperature of 550°C for 2 hours with the heating rate of 2°C.min"1. After calcination, the niobium pentoxide presented a pore volume of 0.30 rnl.g"1. An aqueous solution of a cobalt precursor was prepared dissolving 24.7 g of cobalt (II) nitrate [Co(N03)2.6H20] in 30 ml of distillated water. This solution was gradually added to the niobium pentoxide support, which was continuously stirred up to allow better distribution and complete penetration into the pore volume of the same. Following the impregnation, the catalyst was dried in aerated muffle at 120°C for 18 hours. The dry sample was then calcined in aerated muffle (50 ml.min"1 of dry air) at temperature of 400°C for 2 hours with a heating rate of 2°C.min"1. The calcined catalyst has a 5 wt.% of cobalt supported on niobium pentoxide in its oxide form.
Example 2 - Fischer-Tropsch Synthesis
60 g of the catalyst prepared in the Example 1 was loaded to a fixed- bed reactor that comprises of stainless steel tube of 25.4 mm of diameter and 1 m of height. The catalyst was placed in the central part of the reactor and electrical resistance heated the catalyst region. The catalyst was then activated or reduced by passing through it pure hydrogen (1,000 ml.min"1) at 500°C for 16 hours at atmospheric pressure. The heating rate during the activation was of 2°C.min"1 and the space velocity around 1,000 h"1. After activation, the temperature of the catalytic bed was then reduced under hydrogen flow to the desirable reaction temperature. The hydrogen flow was then adjusted to 3,900 ml.min"1 and carbon monoxide (CO) was introduced into the reactor at 1,950 ml.min"1 that results in a H2/CO volumetric ratio of 2. The space velocity, initially set at 6,000 h was gradually reduced up to 600 h"1. The reactor pressure was controlled to be between 20 to 30 kPa. Table 1 shows the selectivity and product distribution for CO conversion of 30% and reaction temperature of 240°C.
Table 1 Selectivity (%) - Selectivity (%) - Selectivity (%) Reaction products dry basis wet basis - dry basis [1] H20 - 41.36 co2 6.70 3.93
Figure imgf000016_0001
c2 3.19 1.87 c3 5.06 2.96 c4 3.51 2.06 c5 + 81.19 47.61 60.1 Others(*} _ _ 39.4 Total 100 100
[1] R. R. Soares, A. Frydman and M. Schmal, Catalysis Today 16 (1993) 361-370 (*) branched hydrocarbons and oxygenates Table 2, magnetic resonance analysis of carbon and hydrogen, shows that the liquid fraction (C5 + hydrocarbons) posses a high degree of saturation and the presence of olefin, aromatic and oxygenated compounds are minimal.
Table 2
Figure imgf000017_0001
Table 1 and Table 2 show that the use of a high-surface area niobium pentoxide as a support for cobalt catalyst in Fischer-Tropsch improved the selectivity to C5 + hydrocarbons. This fraction is richer in saturated carbon, mainly linear paraffins.

Claims

1. A C5 +-selective Fischer-Tropsch catalyst wherein the catalyst is cobalt supported on a high surface area niobium pentoxide (Nb205) support, hereinafter defined as a support with surface area equal or higher than 30 m2/g.
2. A catalyst according to claim 1 wherein the metal cobalt content in the final composition of the catalyst is in the range of 3 to 40 wt.%.
3. A catalyst according to claim 2 wherein the metal cobalt content in the final composition of the catalyst is in the range of 4 to 25 wt.%.
4. A catalyst according to claim 3 wherein the metal cobalt content in the final composition of the catalyst is in the range of 5 to 15 wt.%.
5. A catalyst according to claim 1 wherein the catalyst is reduced through the action of a reducing gas such as hydrogen (H2), carbon monoxide (CO) or mixtures thereof.
6. A catalyst according to claim 1 wherein the reduction temperature is in the range of 300 to 600°C.
7. A catalyst according to claim 6 wherein the reduction temperature is in the range of 350 to 550°C; 8. A catalyst according to claim 7 wherein the reduction temperature is in the range of400 to 500°C. 9. A catalyst according to claim 1 wherein the reduction time is no less than 6 hours. 10. A catalyst according to claim 9 wherein the reduction time is in the range of 10 to 24 hours.
1 l.A catalyst according to claim 10 wherein the reduction time is in the range of 14 to 20 hours. 12. A catalyst according to claim 1 wherein the cobalt is obtained from one of those soluble precursors such as cobalt (II) nitrate [Co(N03)2.6H20], cobalt (II) chloride (CoCl2.6H20), cobalt (II) sulfate (CoS04.xH20), cobalt (II) hydroxide [Co(OH)2] and cobalt (II) acetate [(CH3C02)2Co].
13. A support for a Fischer-Tropsch cobalt catalyst wherein the support consists of high surface area niobium pentoxide (Nb205) with BET surface area in the range of 30 to 160 m2.g_1. 14. A support according to claim 13 wherein the BET surface area is in the range of 60 to 150 m .g"1.
15. A support according to claim 14 wherein the BET surface area is in the range
Figure imgf000019_0001
16. A support according to claim 15 wherein the predominant crystal structure is pseudo-hexagonal. 17. A process for the preparation of a high-surface area catalyst support of niobium pentoxide wherein it consists of calcination of a hydrated niobium oxide at a given period of time. 18. A process according to claim 17 wherein the calcination temperature is in the range of 200 to 800°C for a period of 2 to 4 hours. 19. A process according to claim 17 wherein the calcination temperature is in the range of 300 to 700°C for a period of 2 to 4 hours. 20. A process according to claim 17 wherein the calcination temperature is in the range of 400 to 600°C for a period of 2 to 4 hours. 2 l.A process for the preparation of a high-surface area catalyst support of niobium pentoxide wherein it is synthesized from either organic or inorganic niobium precursors.
22. A process according to claim 21 wherein the niobium pentoxide is synthesized by precipitation or sol-gel sythesis of niobium precursors. 23. A process according to claim 21 wherein the niobium pentoxide is synthesized by precipitation of niobium precursors. 24. A process according to claim 21 wherein the niobium precursors are the niobium oxalate, niobium pentachloride and niobium alkoxides such as methoxide, ethoxide, isopropoxide and butoxide. 25. A process for catalyst preparation for Fischer-Tropsch synthesis wherein cobalt precursors are dissolved in either inorganic or organic solvents to allow cobalt to be introduced onto catalyst support surface.
26.A process according to claim 25 wherein the solvents are water, methanol, ethanol, propanol, isopropanol or acetone. 27. A process according to claim 26 wherein the solvents are water, methanol, ethanol or isopropanol. 28. A process according to claim 27 wherein the solvents are water or ethanol. 29.A process according to claim 25 wherein the method to introduce cobalt on catalyst surface is selected among incipient wetness impregnation, wet impregnation and deposition-precipitation of the cobalt precursor solution. 30.An use of a cobalt catalyst supported on a high-surface area niobium pentoxide for Fischer-Tropsch synthesis wherein the catalyst is highly selective to hydrocarbons with carbon atoms equal or higher than 5 (C5 fraction) containing preferentially linear paraffin in the diesel oil range with minimal formation of light hydrocarbon, olefin, aromatic and oxygenated compounds. 31. An use according to claim 30 wherein the selectivity to hydrocarbons in trie C5 + fraction is higher than 70 wt.%.
32.An use according to claim 31 wherein hydrocarbons in the Cs+ fraction comprise liquid fuels in the fraction of diesel oil
Figure imgf000021_0001
higher than 80 wt.%. 33. An use according to claim 30 wherein the formation of light hydrocarbons (C02, CH4, C2-C4), olefins, aromatics and oxygenated compounds are lower than 10 wt.%. 34.An use according to claim 30 wherein the catalyst highly selectivity is obtained through the adjustment of H2/CO volumetric ratio, temperature, pressure and space velocity. 35.An use according to claim 34 wherein the H2/CO volumetric ratio is in the range of 1 to 3. 36.An use according to claim 35 wherein the H2/CO volumetric ratio is in the range of 1.5 to 2.5. 37. An use according to claim 36 wherein the H2/CO volumetric ratio is in the range of 1.8 to 2.2.
38. An use according to claim 30 wherein the reaction temperature varies from 200 to 300°C. 39.An use according to claim 38 wherein the reaction temperature varies from 200 to 250°C. 40. An use according to claim 39 wherein the reaction temperature varies from 210 to 240°C. 41. An use according to claim 30 wherein the reaction pressure varies from 400 to 5,000 kPa. 42. An use according to claim 41 wherein the reaction pressure varies from 1,000 to 4,000 kPa.
43. An use according to claim 42 wherein the reaction pressure varies from 1,800 to 2,200 kPa. 44.An use according to claim 30 wherein the reaction space velocity is in the range of 100 to 6,000 h"1. 45. An use according to claim 44 wherein the reaction space velocity is in the range of 300 to 2,000 h"1. 46. An use according to claim 45 wherein the reaction space velocity is in the range of 400 to 1,000 h"1.
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EP2008714A1 (en) * 2007-06-19 2008-12-31 BASF Catalysts LLC Process for the preparation of a cobalt-zinc oxide Fischer-Tropsch catalyst
CN101628237B (en) * 2008-07-16 2011-05-11 中国科学院大连化学物理研究所 Egg-shell catalyst for preparing heavy hydrocarbon from synthesis gas, and preparation method and application thereof
CN115739139A (en) * 2021-09-03 2023-03-07 中国石油化工股份有限公司 Niobium-based carrier and preparation method thereof, niobium-based supported catalyst and preparation method thereof, and monocyclic aromatic hydrocarbon production method
CN115501878A (en) * 2022-09-29 2022-12-23 中国科学院青岛生物能源与过程研究所 Method for synthesizing niobium-cobalt catalyst by in-situ centrifugation and application

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