WO2017186405A1

WO2017186405A1 - Cobalt catalyst comprising a support with a mixed oxide phase containing cobalt and/or nickel, prepared using oxalic acid or oxalate

Info

Publication number: WO2017186405A1
Application number: PCT/EP2017/056559
Authority: WO
Inventors: Antoine Fecant; Sylvie Maury; Adrien Berliet
Original assignee: IFP Energies Nouvelles
Priority date: 2016-04-29
Filing date: 2017-03-20
Publication date: 2017-11-02
Also published as: FR3050663A1

Abstract

The invention relates to a catalyst containing an active cobalt phase deposited on a support comprising alumina, silica or silica-alumina, said support having a mixed oxide phase containing cobalt and/or nickel, wherein the catalyst is prepared by adding at least oxalic acid or oxalate. The invention also relates to the use thereof in the field of Fischer-Tropsch processes.

Description

COBALT CATALYST BASED ON A SUPPORT COMPRISING A MIXED OXIDE PHASE CONTAINING COBALT AND / OR NICKEL PREPARED BY THE USE OF OXALIC ACID OR OXALATE

The invention relates to a catalyst containing an active phase of cobalt, deposited on a support comprising alumina, silica or silica-alumina, said support containing a mixed oxide phase containing cobalt and / or nickel said catalyst has been prepared by introducing at least one organic compound selected from oxalic acid or an oxalate compound. The invention also relates to its method of preparation and its use in the field of Fischer-Tropsch synthesis methods.

The present invention relates to the field of Fischer-Tropsch synthesis processes which make it possible to obtain a broad range of hydrocarbon cuts from the CO + H ₂ mixture, commonly called synthesis gas or syngas. The simplified stoichiometric equation (limited in the equation below to the formation of alkanes) of the Fischer-Tropsch synthesis is written:

n CO + (2n + 1) H ₂ -> C _n H _{2n +} 2 + n H ₂ O

The catalysts used in Fischer-Tropsch synthesis are most often supported catalysts based on alumina, silica or silica-alumina or combinations of these supports, the active phase consisting mainly of iron (Fe) or cobalt ( Co) optionally doped with a noble metal such as Pt, Rh or Ru.

The addition of an organic compound on Fischer-Tropsch catalysts to improve their activity has been recommended by those skilled in the art.

Many documents describe the use of different ranges of organic compounds as additives, such as organic compounds containing nitrogen and / or organic compounds containing oxygen. In particular, patents US 5,856,260 and US 5,856,261 respectively teach the introduction, during the preparation of the catalyst, of polyols of general formula CnH _{2n + 2} O _x with n an integer of between 2 and about 6, and x an integer between 2 and 1 1 or sugars of mono- or disaccharide type, sucrose being particularly preferred.

Other documents teach the use of polyethers (WO2014 / 092278 and WO2015 / 183061), glyoxylic acid (WO2015 / 183059), unsaturated dicarboxylic acids (US201 1/0028575) or multifunctional carboxylic acids of formula HOOC- (CRR ¹ ) _n -COOH with n> 1 in the preparation of Fischer-Tropsch catalysts (WO98 / 47618).

WO2012 / 013866 discloses the use of a cyclic oligosaccharide, especially cyclodextrin, as additive of a Fischer-Tropsch catalyst. This document also describes the use of a silica-alumina support optionally containing a spinel.

However, none of the additive literature discloses a cobalt catalyst prepared using an oxalic acid or oxalate compound deposited on a support containing a mixed oxide phase containing cobalt and / or nickel.

Whatever the compounds chosen, the modifications induced do not always make it possible to increase sufficiently the performances of the catalyst in order to make the process profitable. In addition, it is often very complicated to proceed with their industrial deployment as the methods are complex to implement. Therefore, it is essential for catalyst manufacturers to find new catalysts and preparation processes for improved performance Fischer-Tropsch synthesis.

summary

The subject of the invention is a catalyst containing an active phase of cobalt, deposited on a support comprising alumina, silica or silica-alumina, said support containing a mixed oxide phase containing cobalt and / or nickel, said catalyst being prepared by a process comprising at least: a) a step of contacting a support comprising alumina, silica or silica-alumina with at least one solution containing at least one precursor of cobalt and / or nickel, then dried and calcined at a temperature between 700 and 1200 ° C, so as to obtain an oxide phase mixture containing cobalt and / or nickel in the support, then b) a step of contacting said support containing said mixed oxide phase with at least one solution containing at least one cobalt precursor, c) a step contacting said support containing said mixed oxide phase with at least one organic compound comprising at least oxalic acid or an oxalate, steps b) and c) being carried out separately, in any order, d) and then performs a drying step at a temperature below 200 ° C. The Applicant has indeed found that the use of an organic compound comprising at least oxalic acid or an oxalate as an organic additive during the preparation of a catalyst containing an active phase of cobalt deposited on a support comprising alumina, silica or silica-alumina, said support also containing a mixed oxide phase containing cobalt and / or nickel provided a catalyst for Fischer-Tropsch synthesis showing catalytic performance improved.

In fact, the catalyst according to the invention shows increased activity and selectivity, as well as improved stability (loss of selectivity and limited activity over time) compared to catalysts containing a mixed oxide phase containing cobalt and / or nickel in their support but prepared without additivation or with respect to the additive catalysts having no mixed oxide phase containing cobalt and / or nickel in the support. The use of such an organic compound during the preparation of a cobalt-based catalyst containing a support containing a mixed oxide phase containing cobalt and / or nickel appears to have a synergistic effect on activity, selectivity and stability in a Fischer-Tropsch process.

Without being bound by any theory, it has been discovered that such a catalyst has a substantially greater cobalt dispersion than that exhibited by catalysts prepared in the absence of such an organic compound. This results in the presence of a greater number of active sites for the catalysts prepared in the presence of at least one organic compound containing at least oxalic acid or an oxalate, even if this compound of oxalic acid or oxalate is at least partially subsequently removed by drying and possibly calcination.

According to one variant, the mixed oxide phase content in the support is between 0.1 and 50% by weight relative to the weight of the support.

According to one variant, the mixed oxide phase comprises an aluminate of formula CoAl ₂ O ₄ or NiAl ₂ O ₄ in the case of a support based on alumina or silica-alumina.

According to one variant, the mixed oxide phase comprises a silicate of formula Co ₂ SiO ₄ or Ni ₂ SiO ₄ in the case of a support based on silica or silica-alumina. According to one variant, the silica content of said support is between 0.5% by weight and 30% by weight relative to the weight of the support before the formation of the mixed oxide phase when the support is a silica-alumina.

According to one variant, the molar ratio of oxalic acid or oxalate introduced during step c) relative to the cobalt element introduced in step b) is between 0.01 and 4.0 mol / mol.

According to one variant, the content of cobalt element introduced during step b) as active phase is between 2 and 40% by weight expressed as metallic cobalt element relative to the total weight of the catalyst.

Alternatively, the catalyst further comprises a member selected from VIIIB, IA, IB, MA, MB, NIA, IIIB and VA.

Alternatively, the catalyst further contains an organic compound other than oxalic acid or oxalate, said organic compound containing oxygen and / or nitrogen. According to this variant, the organic compound is chosen from a compound comprising one or more chemical functions chosen from a carboxylic function, alcohol, ether, aldehyde, ketone, ester, carbonate, amine, nitrile, imide, oxime, urea and amide.

According to a variant, after the drying step d), a calcination step e) is carried out at a temperature of between 200 and 550 ° C. under an inert atmosphere or under an atmosphere containing oxygen.

According to one variant, the catalyst obtained in the drying step d) or obtained in the calcining step e) is reduced to a temperature of between 200 ° C. and 500 ° C.

The invention also relates to the use of the catalyst according to the invention in a Fischer-Tropsch synthesis process in which the catalyst according to the invention is brought into contact with a feedstock comprising synthesis gas at a total pressure of between 0.degree. 1 and 15 MPa, at a temperature of between 150 and 350 ° C., and at an hourly space velocity of between 100 and 20000 volumes of synthesis gas per volume of catalyst and per hour with a H ₂ / CO molar ratio of synthesis between 0.5 and 4.

In the following, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief DR Lide, 81 ^st edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUPAC classification.

The textural and structural properties of the support and the catalyst described below are determined by the characterization methods known to those skilled in the art. The total pore volume and the porous distribution are determined in the present invention by nitrogen porosimetry as described in the book "Adsorption by powders and porous solids. Principles, methodology and applications "written by F. Rouquérol, J. Rouquérol and K. Sing, Academy Press, 1999.

Specific surface area is defined as the BET specific surface area (S _B AND in m ² / g) determined by nitrogen adsorption according to ASTM D 3663-78. established from the method BRUNAUER-EMMETT-TELLER described in the periodical "The Journal of American Society, 1938, 60, 309.

Detailed description of the invention

The catalyst according to the invention is a catalyst containing an active phase of cobalt, deposited on a support comprising alumina, silica or silica-alumina, said support containing a mixed oxide phase containing cobalt and / or or nickel, said catalyst being prepared by a process comprising at least: a) a step of contacting a support comprising alumina, silica or silica-alumina with at least one solution containing at least a precursor of cobalt and / or nickel, and then dried and calcined at a temperature between 700 and 1200 ° C, so as to obtain a mixed oxide phase containing cobalt and / or nickel in the support, then performs b) a step of contacting said support containing said mixed oxide phase with at least one solution containing at least one cobalt precursor, c) a step of contacting said support containing said mixed oxide phase with least one organic compound at least oxalic acid or an oxalate, steps b) and c) being carried out separately, in any order, d) then a drying step is carried out at a temperature below 200 ° C.

The various steps of the process leading to the catalyst according to the invention will be detailed subsequently: Step a) Formation of the mixed oxide phase containing cobalt and / or nickel

The objective of step a) is the formation of a mixed oxide phase containing cobalt and / or nickel in a support comprising alumina, silica or silica-alumina by setting contacting a solution containing at least one cobalt and / or nickel precursor, followed by drying and calcining at a high temperature.

It is known that the presence of a mixed oxide phase containing cobalt and / or nickel in a support of the alumina, silica or silica-alumina type makes it possible to improve the resistance to the phenomenon of chemical and mechanical degradation in a process. Fischer-Tropsch, and thus stabilize the support.

The formation of the mixed oxide phase in the support, often called the stabilization stage of the support, can be carried out by any method known to those skilled in the art. It is generally carried out by introducing cobalt and / or nickel in the form of a salt precursor, for example of the nitrate type, onto the initial support containing alumina, silica or silica-alumina. By calcination at a very high temperature, the mixed oxide phase containing cobalt and / or nickel is formed and stabilizes the entire support. The cobalt and / or nickel contained in the mixed oxide phase is not reducible during the final activation of the Fischer-Tropsch catalyst (reduction). The cobalt and / or nickel contained in the mixed oxide phase does not therefore constitute the active phase of the catalyst.

According to step a), a step is performed to bring a support comprising alumina, silica or silica-alumina into contact with at least one solution containing at least one precursor of cobalt and / or nickel. and then dried and calcined at a temperature between 700 and 1200 ° C, so as to obtain a mixed oxide phase containing cobalt and / or nickel in the support.

More particularly, the step a) of contacting can be carried out by impregnation, preferably dry, of a support comprising alumina, silica or silica-alumina, preformed or in powder form, with least one solution aqueous solution containing the precursor cobalt and / or nickel, followed by drying and calcination at a temperature between 700 and 1200 ° C.

The cobalt is brought into contact with the support via any soluble cobalt precursor in the aqueous phase. Preferably, the cobalt precursor is introduced in aqueous solution, preferably in the form of nitrate, carbonate, acetate, chloride, complexes formed with acetylacetonates, or any other soluble inorganic derivative in aqueous solution, which is brought into contact with said support. The cobalt precursor advantageously used is cobalt nitrate or cobalt acetate.

The nickel is brought into contact with the support via any soluble nickel precursor in the aqueous phase. Preferably, said nickel precursor is introduced in aqueous solution, for example in the form of nitrate, carbonate, acetate, chloride, hydroxide, hydroxycarbonate, complexes formed with acetylacetonates, or any other soluble inorganic derivative in aqueous solution, which is brought into contact with said support. The nickel precursor advantageously used is nickel nitrate, nickel chloride, nickel acetate or nickel hydroxycarbonate.

The total content of cobalt and / or nickel at the end of step a) is advantageously between 1 and 20% by weight and preferably between 2 and 10% by weight relative to the weight of the final support.

The drying is advantageously carried out at a temperature of between 60 ° C. and 200 ° C., preferably for a period ranging from 30 minutes to three hours.

The calcination is carried out at a temperature of between 700 and 1200 ° C., preferably between 850 and 1200 ° C., and preferably between 850 and 900 ° C., generally for a period of between one hour and 24 hours, and preferably between 2 hours and 5 hours. The calcination is generally carried out under an oxidizing atmosphere, for example under air, or under oxygen-depleted air; it can also be carried out at least partly under nitrogen. It makes it possible to transform cobalt and / or nickel precursors and alumina and / or silica in the mixed oxide phase containing cobalt and / or nickel. According to one variant, the calcination can also be carried out in two stages, said calcination is advantageously carried out at a temperature of between 300 ° C. and 600 ° C. under air for a period of between half an hour and three hours, and then at a temperature of between 700 ° C and 1200 ° C, preferably between 850 and 1200 ° C and preferably between 850 and 900 ° C, generally for a period of between one hour and 24 hours, and preferably between 2 hours and 5 hours.

The support comprises alumina, silica or silica-alumina.

When the support comprises alumina, it contains more than 50% by weight of alumina relative to the weight of the support before the formation of the mixed oxide phase and, preferably, it contains only alumina. The alumina may be present in a crystallographic form of gamma alumina, delta, theta or alpha type, taken alone or as a mixture.

In another preferred case, the support comprises silica. In this case, it contains more than 50% by weight of silica relative to the weight of the support before the formation of the mixed oxide phase and, preferably, it contains only silica. Silicon sources are well known to those skilled in the art.

In another preferred case, the support comprises a silica-alumina. By a support comprising a silica-alumina is meant a support in which the silicon and the aluminum is in the form of agglomerates of silica or alumina respectively, of amorphous aluminosilicate or any other mixed phase containing silicon and aluminum. aluminum, it being understood that the support is not mesostructured. Preferably, the alumina and the silica are present in the form of a mixture of oxides SiO ₂ -Al ₂ O ₃ . The silica content in the silica-alumina support ranges from 0.5% by weight to 30% by weight, preferably from 1% by weight to 25% by weight, and even more preferably from 1.5 to 20% by weight relative to the weight of the support before the formation of the mixed oxide phase.

According to a preferred variant, the support consists of alumina, silica or silica-alumina, and particularly preferably the support consists of silica-alumina. The support also contains a mixed oxide phase containing cobalt and / or nickel. Mixed oxide phase containing cobalt and / or nickel is understood to mean a phase in which cobalt and / or nickel cations are combined with the oxide O ^{2 -} ions of the alumina and / or silica support thus a mixed phase containing aluminates and / or silicates containing cobalt and / or nickel The mixed oxide phase may be in amorphous form or in crystallized form.

When the support is based on alumina, the mixed oxide phase can comprise an aluminate of formula CoAl ₂ O ₄ or NiAl ₂ O ₄ , in amorphous or crystallized form, for example in spinel form.

When the support is based on silica, the mixed oxide phase may comprise a silicate of formula Co ₂ SiO ₄ or Ni ₂ SiO ₄ (cobalt- or nickelorthosilicate), in amorphous or crystallized form.

When the support is based on silica-alumina, the mixed oxide phase may comprise an aluminate of formula CoAl ₂ O ₄ or NiAl ₂ O ₄ in amorphous or crystallized form, for example in spinel form, and / or a silicate of formula Co ₂ SiO ₄ or Ni ₂ SiO ₄ , in amorphous or crystalline form.

Generally, the content of the mixed oxide phase in the support is between 0.1 and 50% by weight relative to the weight of the support, preferably between 0.5 and 30% by weight, and more preferably between 1 and 20% weight

The presence of mixed oxide phase in the catalyst according to the invention is measured by programmed temperature reduction RTP (or TPR for "temperature programmed reduction" according to the English terminology) such as for example described in OH & Gas Science and Technology, Rev. IFP, Vol. 64 (2009), No. 1, pp. 11-12. According to this technique, the catalyst is heated under a stream of a reducing agent, for example under a flow of dihydrogen. The measurement of dihydrogen consumed as a function of temperature gives quantitative information on the reducibility of the species present. The presence of a mixed oxide phase in the catalyst is thus manifested by a consumption of dihydrogen at a temperature above about 800 ° C. The support may have a morphology in the form of beads, extrudates (for example of trilobed or quadrilobic form) or pellets, especially when said catalyst is used in a reactor operating in fixed bed, or have a morphology in the form of variable particle size powder, especially when said catalyst is implemented in a bubble column type reactor (or "slurry bubble column" according to the English termination). The size of the catalyst grains may be between a few microns and a few hundred microns. For an implementation in "slurry" reactor, the particle size of the catalyst is preferably between 10 microns and 500 microns, preferably between 10 microns and 300 microns, very preferably between 20 and 200 microns, and so even more preferred between 30 and 160 microns.

The specific surface of the support containing the mixed oxide phase is generally between 50 m ² / g and 500 m ² / g, preferably between 100 m ² / g and 300 m ² / g, more preferably between 150 m ² / g and 250 ² / g. The pore volume of said support is generally between 0.3 ml / g and 1.2 ml / g, and preferably between 0.4 ml / g and 1 ml / g.

Thus, after said step a), said support comprising alumina, silica or silica-alumina further comprises a mixed oxide phase containing cobalt and / or nickel.

Step b) and c): Introduction of the active phase and the oxalic acid or oxalate compound

After the formation of the mixed oxide phase, the following steps are carried out in the preparation of the catalyst according to the invention: b) a step of contacting said support containing said mixed oxide phase with at least one solution containing at least one at least one cobalt precursor, c) a step of contacting said support containing said mixed oxide phase with at least one organic compound comprising at least one acid oxalate or an oxalate, steps b) and c) being performed separately, in any order.

Step b) bringing said support into contact with at least one solution containing at least one cobalt precursor can be carried out by any method that is well known to a person skilled in the art. Said step b) is preferably carried out by impregnation of the support with at least one solution containing at least one cobalt precursor. In particular, said step b) can be carried out by dry impregnation, by excess impregnation, or by precipitation-deposition (as described in US Pat. Nos. 5,874,381 and 6,534,436) according to methods that are well known in the art. 'Man of the trade. Preferably, said step b) is carried out by dry impregnation, which consists in bringing the catalyst support into contact with a solution containing at least one cobalt precursor whose volume is equal to the pore volume of the support to be impregnated. This solution contains the cobalt precursor at the desired concentration.

The cobalt is brought into contact with said support via any soluble cobalt precursor in the aqueous phase or in the organic phase. When introduced in organic solution, said cobalt precursor is, for example, cobalt acetate. Preferably, said cobalt precursor is introduced in aqueous solution, for example in the form of nitrate, carbonate, acetate, chloride, complexes formed with acetylacetonates, or any other soluble inorganic derivative in aqueous solution, which is brought into contact with said support. Cobalt precursor is advantageously cobalt nitrate or cobalt acetate.

The content of cobalt element is between 2 and 40% by weight, preferably between 5 and 30% by weight, and more preferably between 10 and 25% by weight expressed as cobalt metal element relative to the total weight of the catalyst.

The catalyst may advantageously furthermore comprise at least one element chosen from a group VI 11B, IA, IB, MA, MB, NIA, MB and / or VA.

The possible elements of the group VI 11 B that are preferred are platinum, ruthenium and rhodium. The preferred group IA elements are sodium and potassium. The Preferred group IB elements are silver and gold. The preferred MA group elements are manganese and calcium. The element of the preferred MB group is zinc. Preferred NIA group elements are boron and indium. Preferred group IIIB elements are lanthanum and cerium. The preferred VA group element is phosphorus.

The optional element content of groups VI 11B, IA, IB, MA, MB, NIA, IIIB and / or VA is between 50 ppm and 20% by weight, preferably between 100 ppm and 15% by weight, and more preferred between 100 ppm and 10% weight expressed as element relative to the total weight of the catalyst.

According to one variant, when the catalyst contains one or more additional elements of the groups VIIIB, IA, IB, MA, MB, NIA, IIIB and / or VA, this or these elements may be either initially present on the support before the preparation of the catalyst, is introduced at any time of the preparation and by any method known to those skilled in the art.

The contacting of the organic compound employed for the implementation of said step c) with said support is carried out by impregnation, in particular by dry impregnation or excess impregnation, preferably by dry impregnation. Said organic compound is preferably impregnated on said support after solubilization in aqueous solution.

Said organic compound comprises at least oxalic acid or an oxalate. In the case where an oxalate is chosen, its counterion will preferably be potassium, lithium or sodium.

The molar ratio of oxalic acid or oxalate introduced during stage c) with respect to the cobalt element introduced in stage b) is between 0.01 and 4.0 mol / mol, preferably between 0.05 and 1.0.

The catalyst according to the invention may comprise, in addition to oxalic acid or oxalate, another organic compound or a group of organic compounds known for their role as additives. The function of the additives is to increase the activity catalytic compared to non-additive catalysts. More particularly, the catalyst according to the invention may further comprise one or more organic compounds containing oxygen and / or nitrogen.

Generally, the organic compound is selected from a compound having one or more chemical functions selected from a carboxylic function, alcohol, ether, aldehyde, ketone, ester, carbonate, nitrile, imide, oxime, urea and amide function.

The oxygen-containing organic compound may be one or more selected from compounds having one or more chemical functions selected from a carboxylic, alcohol, ether, aldehyde, ketone, ester or carbonate function. For example, the organic oxygen-containing compound may be one or more selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol (with a molecular weight between 200 and 1500 g mol), propylene glycol, 2-butoxyethanol, 2- (2-butoxyethoxy) ethanol, 2- (2-methoxyethoxy) ethanol, triethylene glycol dimethyl ether, glycerol, acetophenone, 2,4-pentanedione, pentanone, acetic acid, maleic acid, malic acid, malonic acid, malic acid, oxalic acid, gluconic acid, tartaric acid, citric acid, succinic acid, γ-ketovaleric acid, γ-valerolactone, 4-hydroxyvaleric acid, 2-pentenoic acid, 3-pentenoic acid, 4-pentenoic acid, C1-C4 dialkyl succinate, methyl acetoacetate, a lactone, dibenzofuran, a crown ether, orthophthalic acid, glucose and opylène.

The nitrogen-containing organic compound may be one or more of compounds having one or more chemical functions selected from an amino or nitrile function. By way of example, the nitrogen-containing organic compound may be one or more selected from the group consisting of ethylenediamine, diethylenetriamine, hexamethylenediamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, acetonitrile octylamine, guanidine or carbazole. The organic compound containing oxygen and nitrogen may be one or more chosen from compounds comprising one or more chemical functional groups chosen from a carboxylic acid, alcohol, ether, aldehyde, ketone, ester, carbonate or nitrile function. , imide, amide, urea or oxime. By way of example, the organic compound containing oxygen and nitrogen may be one or more selected from the group consisting of 1,2-cyclohexanediaminetetraacetic acid, monoethanolamine (MEA), N methylpyrrolidone, dimethylformamide, ethylenediaminetetraacetic acid (EDTA), alanine, glycine, nitrilotriacetic acid (NTA), N- (2-hydroxyethyl) ethylenediamine-N, N ', N'-triacetic acid ( HEDTA), diethylenetriaminepentaacetic acid (DTPA), tetramethylurea, glutamic acid, dimethylglyoxime, bicine or tricine, or a lactam.

The total molar ratio of organic compound (s) containing oxygen and / or nitrogen other than the organic compound comprising at least oxalic acid or an oxalate relative to the cobalt element introduced at step b) is between 0.01 to 2 mol / mol, preferably between 0.1 to 2 mol / mol, preferably between 0.2 and 1.5 mol / mol, calculated on the basis of components introduced into the impregnating solution (s).

When the catalyst additionally contains an organic compound other than oxalic acid or an oxalate, this organic compound may be either initially present on the support before the preparation of the catalyst, or is incorporated into the catalyst at any point in the preparation and by any method known to those skilled in the art.

Implementation of steps b) and c)

The process for preparing the catalyst according to the invention, in particular steps b) and c) comprises several modes of implementation. They are distinguished in particular by the moment of the introduction of the organic compound which can be carried out either before the impregnation of cobalt of the active phase (pre-impregnation), or after the impregnation of cobalt of the active phase (post-impregnation). The introduction of cobalt precursor and oxalic acid or oxalate can not be carried out simultaneously as it would precipitate cobalt oxalate.

A first mode of implementation consists in performing said step b) prior to said step c) (post-impregnation). According to said second embodiment, one or more steps b) of contacting at least cobalt present in the active phase of the catalyst precedes (s) said step c).

A second mode of implementation consists in performing said step c) prior to said step b) (pre-impregnation). Advantageously, said step c) is followed by several steps b).

A drying step is advantageously carried out between the two impregnation steps. The intermediate drying step is carried out at a temperature below 200 ° C, advantageously between 50 and 180 ° C, preferably between 70 and 150 ° C, very preferably between 75 and 130 ° C and optionally a period of maturation was observed between the impregnation step and the intermediate drying step.

Advantageously, after each impregnation step, whether it is a step of impregnating the cobalt or the organic compound, the impregnated support is allowed to mature. The maturation allows the impregnating solution to disperse homogeneously within the support.

Any maturation step described in the present invention is advantageously carried out at atmospheric pressure, in an atmosphere saturated with water and at a temperature of between 17 ° C. and 50 ° C., and preferably at ambient temperature. Generally a ripening time of between ten minutes and forty-eight hours and preferably between thirty minutes and five hours, is sufficient. Longer durations are not excluded, but do not necessarily improve.

Any impregnation solution described in the present invention may comprise any polar solvent known to those skilled in the art. Said polar solvent used is advantageously chosen from the group formed by methanol, ethanol, water, phenol, cyclohexanol, alone or as a mixture. Said polar solvent can also be advantageously chosen from the group formed by propylene carbonate, DMSO (dimethylsulfoxide), N-methylpyrrolidone (NMP) or sulfolane, alone or as a mixture. Preferably, a polar protic solvent is used. A list of the usual polar solvents and their dielectric constant can be found in the book "Solvents and Solvent Effects in Organic Chemistry" (Reichardt, Wiley-VCH, 3rd edition, 2003, pages 472-474). The solvent used is water or ethanol, and particularly preferably the solvent is water. In one possible embodiment, the solvent may be absent in the impregnating solution.

When carrying out several impregnation steps, each impregnation step is preferably followed by an intermediate drying step at a temperature below 200 ° C., advantageously between 50 and 180 ° C., preferably between 70 and 150 ° C. ° C, very preferably between 75 and 130 ° C and optionally a period of maturation was observed between the impregnation step and the intermediate drying step.

Step d) drying

According to the drying step d) of the implementation for the preparation of the catalyst, prepared according to at least one embodiment described above, the drying is carried out at a temperature below 200 ° C, advantageously included between 50 and 180 ° C, preferably between 70 and 150 ° C, very preferably between 75 and 130 ° C. The drying step is preferably carried out for a period of between 1 and 4 hours, preferably under an inert atmosphere or under an atmosphere containing oxygen.

The drying step may be performed by any technique known to those skilled in the art. It is advantageously carried out at atmospheric pressure or under reduced pressure. Preferably, this step is carried out at atmospheric pressure. It is advantageously carried out in crossed bed using air or any other hot gas. Preferably, when the drying is carried out in a fixed bed, the gas used is either air or an inert gas such as argon or nitrogen. Very preferably, the drying is carried out in a bed traversed in the presence of nitrogen and / or air. Preferably, the drying step has a short duration of between 5 minutes and 4 hours, preferably between 30 minutes and 4 hours and very preferably between 1 hour and 3 hours.

According to a first variant, the drying is carried out so as to preferably retain at least 30% of the oxalic acid or oxalate compound introduced during an impregnation step, preferably this amount is greater than 50% and even more preferably , greater than 70%, calculated on the basis of the carbon remaining on the catalyst. When an organic compound containing oxygen and / or nitrogen other than oxalic acid or an oxalate is present, the drying step is carried out so as to preferably retain at least 30%, preferably minus 50%, and very preferably at least 70% of the amount introduced calculated on the basis of the carbon remaining on the catalyst.

At the end of the drying step d), a dried catalyst is then obtained, which will be subjected to an activation step for its subsequent implementation in Fischer-Tropsch synthesis.

According to another variant, at the end of step d) of drying, a calcination step e) is carried out at a temperature of between 200 ° C. and 550 ° C., preferably between 250 ° C. and 500 ° C. under an inert atmosphere (nitrogen for example) or an atmosphere containing oxygen (air for example). The duration of this heat treatment is generally between 0.5 hours and 16 hours, preferably between 1 hour and 5 hours. After this treatment, the cobalt of the active phase is thus in oxide form and the catalyst contains no more or very little organic compound introduced during its synthesis. However, the introduction of the organic compound during its preparation has made it possible to increase the dispersion of the active phase, thus leading to a more active, more selective and more stable catalyst. Activation (Reduction)

Prior to its use in the catalytic reactor and the implementation of the Fischer-Tropsch process according to the invention, the dried catalyst obtained in step d) or the calcined catalyst obtained in step e) advantageously undergoes a reducing treatment, for example with hydrogen, pure or diluted, at high temperature. This treatment activates said catalyst and form metal cobalt particles in the zero state valent. The temperature of this reducing treatment is preferably between 200 and 500 ° C and its duration is between 2 and 20 hours.

This reducing treatment is carried out either in situ (in the same reactor as that where the Fischer-Tropsch reaction is carried out according to the process of the invention), or ex situ before being loaded into the reactor.

Fischer-Tropsch process

Finally, another object of the invention is the use of the catalyst according to the invention in a Fischer-Tropsch synthesis process.

The Fischer-Tropsch process according to the invention leads to the production of essentially linear and saturated hydrocarbons C5 + (having at least 5 carbon atoms per molecule). The hydrocarbons produced by the process of the invention are thus essentially paraffinic hydrocarbons, the fraction having the highest boiling points can be converted with a high yield of middle distillates (gasoil and kerosene cuts) by a process of hydroconversion such as hydrocracking and / or catalytic hydroisomerization (s). The charge used for the implementation of the process of the invention comprises synthesis gas. The synthesis gas is a mixture comprising in particular carbon monoxide and hydrogen having H ₂ / CO molar ratios that can vary in a ratio of 0.5 to 4 depending on the process by which it was obtained. The molar ratio H ₂ / CO of the synthesis gas is generally close to 3 when the synthesis gas is obtained from the process of steam reforming hydrocarbons or alcohol. The molar ratio H ₂ / CO of the synthesis gas is in the range of 1.5 to 2 when the synthesis gas is obtained from a partial oxidation process. The H ₂ / CO molar ratio of the synthesis gas is generally close to 2.5 when it is obtained from a thermal reforming process. The H ₂ / CO molar ratio of the synthesis gas is generally close to 1 when it is obtained from a CO ₂ gasification and reforming process.

The catalyst used in the hydrocarbon synthesis process according to the invention can be implemented in different types of reactors, for example in a fixed bed, in a moving bed, in a bubbling bed or in a three-phase fluidized bed. The implementation of the catalyst in suspension in a three-phase fluidized reactor, preferably of the bubble column type, is preferred. In this preferred implementation of the catalyst, said catalyst is divided into a state of very fine powder, particularly of the order of a few tens of microns, this powder forming a suspension with the reaction medium. This technology is also known by the terminology of "slurry" process by the skilled person.

The hydrocarbon synthesis process according to the invention is carried out under a total pressure of between 0.1 and 15 MPa, preferably between 0.5 and 10 MPa, at a temperature of between 150 and 350 ° C., preferably between 180 and 270 ° C. The hourly volume velocity is advantageously between 100 and 20000 volumes of synthesis gas per volume of catalyst per hour (100 to 20000 h ^-1 ) and preferably between 400 and 10,000 volumes of synthesis gas per volume of catalyst and per hour (400 to 10000 hr ^-1 ).

The following examples demonstrate the performance gains on the catalysts according to the invention.

Examples

Example 1 (Comparative) Catalyst A of Formula Co / Al ₂ O ₃

A catalyst A comprising cobalt deposited on an alumina support is prepared by dry impregnation of an aqueous solution of cobalt nitrate so as to deposit in two successive stages of the order of 10% by weight of Co on a gamma alumina powder (PURALOX® SCCa 5/170, SASOL) with a mean particle size equal to 80 μηπ, a surface area of 1 65 m ² / g and a pore volume measured by nitrogen adsorption isotherm of 0.4 ml /boy Wut.

After a first dry impregnation, the solid is dried in a bed passed through at 120 ° C. for 3 hours in air and then calcined at 400 ° C. for 4 hours in a bed traversed under a stream of air. The intermediate catalyst contains about 6% by weight of Co. It is subjected to a second dry impregnation step using a solution of cobalt nitrate. The solid obtained is dried in a bed passed through at 120 ° C. for 3 hours in air and then calcined at 400 ° C. for 4 hours in a bed traversed under a stream of air. The final catalyst A which contains 10.5% by weight of Co (in the form of oxide Co ₃ O ₄ ) is obtained.

Example 2 (Comparative): Catalyst B of the formula Co / Al ₂ 0 ₃ ₂ .Si0

A catalyst B comprising cobalt deposited on a silica-alumina support is prepared by dry impregnation of an aqueous solution of cobalt nitrate so as to deposit in one step approximately 10% by weight of Co on a silica-alumina initially containing 5 % weight of SiO ₂ and having a specific surface area of 180 m ² / g and a pore volume of 0.8 ml / g.

After dry impregnation, the solid is dried in a bed passed through at 120 ° C. for 3 hours in air and then calcined at 400 ° C. for 4 hours in a traversed bed. The final catalyst B which contains 9.9% by weight of Co (in the form of oxide Co ₃ O ₄ ) is obtained. Example 3 (Comparative) A catalyst C of the formula Co / C0AI ₂ O4-Al ₂ O ₃ .S1O2

A catalyst C comprising cobalt deposited on a support, based on a mixed oxide phase (in the form of spinel) included in a silica-alumina, is prepared by dry impregnation of an aqueous solution of cobalt nitrate of to deposit in one step about 10% weight of cobalt on the support. The spinel present in the support of the catalyst C is a simple spinel formed of cobalt aluminate, which is included in a silica-alumina containing 5% by weight of SiO ₂ , and having a specific surface area of 180 m ² / g and a volume of porous 0.8 ml / g. The spinel preparation included in the silica-alumina is performed by dry impregnation of an aqueous solution of cobalt nitrate so as to introduce 5% by weight of Co in said silica-alumina. After drying at 120 ° C for 3 hours, the solid is calcined at 850 ° C for 4 hours in air. The support of the catalyst denoted C is formed of 5% by weight of cobalt in the form of cobalt aluminate (ie 15% by weight of spinel) in the silica-alumina.

The active phase based on cobalt is then deposited on said support in one step, by dry impregnation, according to a protocol identical to that described for the preparation of catalyst B. The drying and calcination steps are also performed under the same conditions The concentration of cobalt in the cobalt nitrate solution, used for the successive impregnations, is chosen to obtain the catalyst C with the desired final Co content.

The final catalyst C has a total cobalt content of 15.7% by weight (the content of Co present in the spinel phase being included) and a cobalt content in the form of Co ₃ 0 ₄ oxide of 10.7% by weight.

Example 4 (Comparative) Catalyst D of formula Co / C0AI ₂ O4-Al ₂ O ₃ .S1O ₂ containing citric acid.

A catalyst D comprising cobalt and citric acid deposited on a support, based on a spinel included in a silica-alumina, is prepared by dry impregnation of an aqueous solution of cobalt nitrate and citric acid. so as to deposit about 10% by weight of cobalt on the support.

The active phase based on cobalt is deposited on the support C of Example 3 in one step, by dry impregnation of a solution containing cobalt nitrate and citric acid (Sigma Aldrich®,> 99%) in a molar ratio citric acid: Co of 0.5. After the dry impregnation, the solid is matured in a saturated water atmosphere for 9 hours at room temperature, then is dried in a bed passed through at 120 ° C. for 3 hours in air and then treated under nitrogen at 400 ° C. for 4 hours in crossed bed. The final catalyst D has a total cobalt content of 14.1% by weight (the content of Co present in the spinel phase being included) and a cobalt content in the form of Co ₃ 0 ₄ oxide of 9.1% by weight.

Example 5 (Comparative) Catalyst E of formula Co / C0AI ₂ O4-Al ₂ O ₃ .S1O2 containing citric acid.

A catalyst E comprising cobalt and citric acid deposited on a support, based on a spinel included in a silica-alumina, is prepared by dry impregnation with an aqueous solution of cobalt nitrate, followed by aqueous solution of citric acid so as to deposit about 10% by weight of cobalt on the support.

The active phase based on cobalt is deposited on the support C of Example 3 in one step, by dry impregnation of a solution containing cobalt nitrate. After the dry impregnation, the solid undergoes drying in a crossed bed. at 120 ° C for 3 hours in air. In a second step, the citric acid is deposited on the above solid in one step, by dry impregnation of a solution containing citric acid (Sigma Aldrich®,> 99%) at a concentration which makes it possible to reach a molar ratio on the final catalyst citric acid: Co 0.5. After the dry impregnation, the solid is matured in a saturated water atmosphere for 9 hours at room temperature, then is dried in a bed passed through at 120 ° C. for 3 hours in air and then treated under nitrogen at 400 ° C. for 4 hours in crossed bed.

The final catalyst E has a total cobalt content of 14.0% by weight (the content of Co present in the spinel phase being included) and a cobalt content in the form of Co ₃ 0 ₄ oxide of 9.0% by weight. Example 6 (according to the invention) Catalyst F of formula Co / CoAl ₂ O ₄ - Al ₂ O ₃ SiO ₂ containing oxalic acid.

A catalyst F comprising cobalt and oxalic acid deposited on a support, based on a spinel included in a silica-alumina, is prepared by dry impregnation of an aqueous solution of cobalt nitrate, then an aqueous solution of oxalic acid so as to deposit about 10% by weight of cobalt on the support.

The active phase based on cobalt is deposited on the support C of Example 3 in one step, by dry impregnation of a solution containing cobalt nitrate. After the dry impregnation, the solid undergoes drying in a crossed bed. at 120 ° C for 3 hours in air.

In a second step, the oxalic acid is deposited on the above solid in one step, by dry impregnation of a solution containing oxalic acid (Sigma Aldrich®,> 99%) at a concentration which makes it possible to attain molar ratio on the final catalyst oxalic acid: Co of 0.5. After the dry impregnation, the solid is matured in a saturated water atmosphere for 9 hours at room temperature, then it is dried in a bed passed through at 120 ° C. for 3 hours in air and then treated under nitrogen at 400 ° C. for 4 hours. in bed crossed. The final catalyst F has a total cobalt content of 14.5% by weight (the content of Co present in the spinel phase being included) and a cobalt content in the form of Co ₃ 0 ₄ oxide of 9.5% by weight.

Example 7 (Invention): Catalyst G of formula Co / IBOC ₄ ₂ 0 - AI ₂ 0 ₃ ₂ .Si0 containing oxalic acid. A catalyst G comprising cobalt and oxalic acid deposited on a support, based on a spinel included in a silica-alumina, is prepared by dry impregnation of an aqueous solution of oxalic acid, followed by aqueous solution of cobalt nitrate so as to deposit in one step about 10% by weight of cobalt on the support. The oxalic acid is deposited on the support C of Example 3 in one step, by dry impregnation of a solution containing oxalic acid (Sigma Aldrich®,> 99%) at a concentration which makes it possible to attain molar ratio on the oxalic acid final catalyst: Co of 0.5. After the dry impregnation, the solid undergoes drying in a bed passed through at 120 ° C. for 3 hours in air.

In a second step, the active phase based on cobalt is deposited on the previous solid in one step, by dry impregnation of a solution containing cobalt nitrate. After the dry impregnation, the solid is matured in a saturated water atmosphere for 9 hours at room temperature, then is dried in a bed passed through at 120 ° C. for 3 hours in air and then treated under nitrogen at 400 ° C. for 4 hours in crossed bed.

The final catalyst G has a total cobalt content of 14.2% by weight (the content of Co present in the spinel phase being included) and a cobalt content in the form of Co ₃ 0 ₄ oxide of 9.2% by weight.

Example 8 (Invention): Catalyst H of the formula Co / IBOC ₄ ₂ 0 - AI ₂ 0 ₃ ₂ .Si0 containing oxalic acid.

Catalyst H is prepared in a manner similar to catalyst F, except that it is not subjected to thermal treatment under nitrogen at 400 ° C. at the end of preparation.

Example 9 (according to the invention) Catalyst I of formula Co / CoAl ₂ O ₄ - Al ₂ O ₃ SiO ₂ containing oxalic acid.

Catalyst I is prepared in a manner similar to catalyst F, except that the heat treatment at the end of the preparation at 400 ° C. for 4 hours is carried out under air rather than under nitrogen.

Example 10 Catalytic Performance of Catalysts A to I in Fischer-Tropsch Reaction

Catalysts A, B, C, D, E, F, G, H and I, before being tested in Fischer-Tropsch synthesis, are reduced in situ under a flow of pure hydrogen at 400 ° C. for 16 hours. . The Fischer-Tropsch synthesis reaction is carried out in a continuous bed-type tubular reactor operating continuously. Each of the catalysts is in the form of a powder with a diameter of between 40 and 150 microns.

The test conditions are as follows:

Temperature = 21 6 ° C

· Total pressure = 2MPa

Hourly volume velocity (VVH) = 4100 NL / h ^"1 / kg _C ataiyzer

H ₂ / CO molar ratio = 2/1

The results, expressed in terms of activity (CO conversion in%), selectivity (percentage by mass of hydrocarbons in C ₈ ⁺ on all the products formed) and stability (loss in production of C ₈ ⁺ hydrocarbons in point of selectivity per hour), are shown in Table 1.

Table 1: Catalyst performance of each catalyst The results in Table 1 demonstrate that the catalysts according to the invention are more active, more selective and more stable than the catalysts known from the prior art.

Claims

1) Catalyst containing an active phase of cobalt, deposited on a support comprising alumina, silica or silica-alumina, said support containing a mixed oxide phase containing cobalt and / or nickel, said catalyst being prepared by a process comprising at least: a) a step of contacting a support comprising alumina, silica or silica-alumina with at least one solution containing at least one cobalt precursor and / or nickel, and then dried and calcined at a temperature between 700 and 1200 ° C, so as to obtain a mixed oxide phase containing cobalt and / or nickel in the support, then b) a step of contacting said support containing said mixed oxide phase with at least one solution containing at least one cobalt precursor, c) a step of contacting said support containing said mixed oxide phase with at least oxalic acid or an oxalate, steps b) and c) being performed separately, in any order, d) and then performs a drying step at a temperature below 200 ° C.

2) Catalyst according to claim 1, wherein the content of mixed oxide phase in the support is between 0.1 and 50% by weight relative to the weight of the support.

3) Catalyst according to one of claims 1 or 2, wherein the mixed oxide phase comprises an aluminate of formula CoAI ₂ O ₄ or NiAl ₂ O ₄ in the case of a support based on alumina or silica -alumina.

4) Catalyst according to one of claims 1 or 2, wherein the mixed oxide phase comprises a silicate of formula Co ₂ SiO ₄ or Ni ₂ SiO ₄ in the case of a support based on silica or silica-alumina.

5) Catalyst according to one of claims 1 to 4, wherein the silica content of said support is between 0.5% weight to 30% by weight relative to the weight of the support before the formation of the mixed oxide phase when the support is a silica-alumina.

6) Catalyst according to one of claims 1 to 5, wherein the molar ratio oxalic acid or oxalate introduced in step c) relative to the cobalt element introduced in step b) is between 0, 01 and 4.0 mol / mol.

7) Catalyst according to one of claims 1 to 6, wherein the content of cobalt element introduced in step b) as active phase is between 2 and 40% weight expressed as cobalt metal element relative to the weight total catalyst.

8. Catalyst according to one of claims 1 to 7, wherein the catalyst further comprises a member selected from VIIIB, IA, IB, MA, MB, NIA, IIIB and VA.

9) Catalyst according to one of claims 1 to 8, wherein the catalyst further contains an organic compound other than oxalic acid or oxalate, said organic compound containing oxygen and / or nitrogen.

10) The catalyst according to claim 9, wherein the organic compound is chosen from a compound comprising one or more chemical functional groups chosen from a carboxylic function, alcohol, ether, aldehyde, ketone, ester, carbonate, amine, nitrile, imide, oxime, urea and amide.

1 1) Catalyst according to one of claims 1 to 10, wherein after the drying step d), a calcination step e) is carried out at a temperature of between 200 and 550 ° C under an inert atmosphere or under an atmosphere containing oxygen. 12) Catalyst according to one of claims 1 to 1 1, wherein reducing the catalyst obtained in the drying step d) or obtained in the calcining step e) at a temperature between 200 ° C and 500 ° vs.

13) Fischer-Tropsch hydrocarbon synthesis process in which the catalyst according to any one of claims 1 to 12 is contacted with a feedstock comprising synthesis gas at a total pressure of between 0.1 and 15 MPa, at a temperature between 150 and 350 ° C, and at a volume hourly velocity of between 100 and 20000 volumes of synthesis gas per volume of catalyst and per hour with a H ₂ / CO molar ratio of the synthesis gas between 0.5 and 4.