EP3223941A1

EP3223941A1 - Method for preparing a fischer-tropsch catalyst with steam treatment

Info

Publication number: EP3223941A1
Application number: EP15781918.6A
Authority: EP
Inventors: Dominique DECOTTIGNIES; Antoine Fecant; Leonor DUARTE MENDES CATITA
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2014-11-26
Filing date: 2015-10-19
Publication date: 2017-10-04
Also published as: US20170304807A1; WO2016083020A1; FR3028770A1; FR3028770B1

Abstract

The invention relates to a method for preparing a catalyst comprising an active phase which comprises at least one group-VIIIB metal deposited on an oxide substrate; said method comprising the following steps: a) providing a substrate of oxides comprising alumina, silica, or a silica-alumina; b) impregnating the substrate of oxides of step a) with an aqueous or organic solution comprising at least one salt of a group-VIIIB metal selected among cobalt, nickel, ruthenium and iron, and then drying the obtained product at a temperature of 60°C to 200°C; c) treating the solid obtained in step b) with water vapour at a temperature of 110°C to 195°C for a duration of 30 minutes to 4 hours, in the presence of an air/steam mixture comprising 2% to 50% by volume of water in steam form.

Description

PROCESS FOR PREPARING A FISCHER-TROPSCH CATALYST WITH

STEAM TREATMENT

Technical field of the invention

The present invention relates to the field of Fischer-Tropsch synthesis processes and in particular to the preparation of a catalyst having an improved reducibility.

State of the art

The Fischer-Tropsch synthesis methods make it possible to obtain a wide range of hydrocarbon cuts from the CO + H ₂ mixture, commonly called synthesis gas. The global equation of the Fischer-Tropsch synthesis can be written in the following way:

n CO + (2n + 1) H ₂ → C _n H ₂ n ₊ 2 + n H ₂ 0

Fischer-Tropsch synthesis is at the heart of processes for converting natural gas, coal or biomass into fuels or intermediates for the chemical industry. These processes are called GTL ("Gas to Liquids" in the English terminology) in the case of the use of natural gas as the initial charge, CTL ("Coal to Liquids" in the English terminology) for coal, and BTL (Biomass to Liquids) for biomass.

In each of these cases, the initial charge is first gasified to synthesis gas, a mixture of carbon monoxide and dihydrogen. The synthesis gas is then mainly converted into paraffins by Fischer-Tropsch synthesis, and these paraffins can then be converted into fuels by a hydroisomerization-hydrocracking process. For example, transformation processes such as hydrocracking, dewaxing, and hydroisomerization of heavy cuts (C16 +) make it possible to produce different types of fuels in the range of middle distillates: diesel (180-370 ° C) and kerosene (cut 140-300 ° C). The lighter C5-C15 fractions can be distilled and used as solvents.

The Fischer-Tropsch synthesis reaction can be carried out in different types of reactors (fixed bed, mobile bed, or three-phase bed (gas, liquid, solid), for example of perfectly stirred autoclave type, or bubble column), and the products of the reaction. have the particular feature of being free of sulfur compounds, nitrogen or aromatic type.

In an implementation in a bubble column type reactor (or "slurry bubble column" according to the English terminology, or "slurry" in a simplified expression), the implementation of the catalyst is characterized by the fact that it it is divided into the state of very fine powder, typically of the order of a few tens of micrometers, this powder forming a suspension with the reaction medium.

The Fischer-Tropsch reaction is conventionally carried out between 1 and 4 MPa (10 and 40 bar), at temperatures traditionally between 200 ° C and 350 ° C. The reaction is generally exothermic, which requires particular attention to the implementation of the catalyst.

The catalysts used for Fischer-Tropsch synthesis are essentially cobalt or iron catalysts, although other metals may be used. Nevertheless, cobalt and iron offer a good performance / price compromise compared to other metals.

The conventional methods for preparing the supported metal catalysts used for the Fischer-Tropsch synthesis consist in depositing a metal salt or a metal-ligand coordination complex on the support, then in carrying out one or more heat treatment (s) carried out under air, followed by a reductive treatment carried out ex situ or in situ.

In order to improve the activity of the catalysts used for Fischer-Tropsch synthesis, numerous documents propose modifications of the impregnation and / or drying and / or calcination and / or activation (reduction) stages.

Furthermore, there are known documents disclosing processes for the preparation of catalysts used for Fischer-Tropsch synthesis in which processes are carried out a steam treatment step. In the article published in Topics in catalysis, 45 (1 - 4) 2007 by Borg et al., A treatment under an air / water vapor mixture (50% vol / 50% vol.) Of a precursor of previously dried catalyst is described. This document teaches that the concentration of water vapor during treatment does not affect the reducibility of cobalt. Patent Application WO201 1/027104 describes a process for preparing a Fischer-Tropsch catalyst based on cobalt formed having improved product selectivity C _5+, wherein a process step of oxidizing treatment is carried out under a gas mixture containing at least 2% water vapor. This step is carried out on a previously reduced catalyst precursor. A last step of activation under reducing gas is necessary to obtain the active catalyst in Fischer-Tropsch synthesis.

Finally, patent application WO2008 / 122636 describes a method for preparing a Fischer-Tropsch catalyst, including a treatment step under steam or under liquid water. This steam treatment is carried out using a gas containing at least 80% of water vapor or with liquid water, on a solid containing a metallic phase homogeneously distributed, predominantly in the form of divalent oxide or divalent hydroxide.

The Applicant has surprisingly discovered that pretreatment with water vapor carried out under specific operating conditions makes it possible to prepare catalysts having an improved reducibility, measured by reduction in programmed temperature RTP (or TPR for "programmed temperature reduction"). according to the English terminology, which makes it possible to improve their catalytic performances in a Fischer-Tropsch type process According to the invention, the steam treatment (called "steaming" according to the English terminology) is carried out on a catalyst precursor previously dried.

The Fischer-Tropsch process is then carried out in the presence of a catalyst having an improved reducibility, that is to say that the temperature necessary for the reduction of the catalyst is lower than the temperature necessary for the reduction of the catalysts of the prior art. Indeed, the catalyst used in the Fischer-Tropsch synthesis process according to the invention has a decrease in the interaction between a Group VIIIB metal and the support relative to the catalysts of the prior art, which allows an increase in the 'activity.

Objects of the invention

The invention relates to a process for preparing a catalyst comprising an active phase comprising at least one Group VIIIB metal selected from cobalt, nickel, ruthenium and iron deposited on an oxide support; which method comprises the following steps:

a) providing an oxide support comprising alumina, silica, or a silica-alumina; b) the oxide support of step a) is impregnated with an aqueous or organic solution comprising at least one group VIIIB metal salt selected from cobalt, nickel, ruthenium and iron, and then the product is dried; obtained at a temperature between 60 and 200 ° C;

c) a steam treatment of the solid obtained in step b) is carried out at a temperature between 1 10 and 195 ° C, for a period of between 30 minutes and 4 hours, in the presence of an air mixture steam comprising between 2 and 50% by volume of water in vapor form.

According to one variant, the thermal treatment under steam is carried out at a temperature of between 1 and 190 ° C., preferably between 1 and 180 ° C., for a period ranging from 30 minutes to 4 hours and with a air / steam mixture comprising between 20 and 50% by volume of water in vapor form.

According to a first variant of the process according to the invention, step a ') is carried out between step a) and b) of said process in which the oxide support provided in step a) is impregnated with an aqueous solution or organic phase of a phosphorus precursor, then a drying step is carried out at a temperature of between 60 ° C. and 200 ° C., followed by a step of calcination of the solid obtained at a temperature of between 200 ° C. and 1 ° C. 100 ° C.

According to another variant of the process according to the invention, a step a ") in which said support comprising alumina, silica, or silica-alumina, optionally phosphorus, with an aqueous or organic solution comprising at least one metal salt M or M 'selected from the group consisting of magnesium (Mg), copper (Cu), cobalt (Co), nickel (Ni), tin (Sn), zinc (Zn), lithium (Li), calcium (Ca), cesium (Cs), sodium (Na), potassium (K), iron (Fe) and manganese (Mn), and then dried and calcined at a temperature between 700 and 1200 ° C, so as to obtain a simple spinel MAI ₂ 0 ₄ or mixed M _X M ' ₍₁ _X) AI ₂ 0 ₄ partial or not, where M and M 'are distinct metals and where x is between 0 and 1, the values 0 and 1 being themselves excluded.

According to another variant of the process according to the invention, the steps a ') and a ") are carried out simultaneously in order to introduce the phosphorus and the metal M or M' in a single step onto said oxide support provided to the step a).

Advantageously, the metal content M or M 'is between 1 and 20% by weight relative to the total mass of the final support.

According to a variant, a calcination step d) is carried out at a temperature of between 320 ° C. and 460 ° C.

According to one variant, a reducing treatment step is carried out after step c) of treatment under steam and / or step d) of calcination, at a temperature of between 200 ° C. and 600 ° C.

Advantageously, the group VIIIB metal content of the active phase of said catalyst is between 0.5 and 60% by weight relative to the weight of said catalyst.

Advantageously, the phosphorus content of the oxide support is between 0.1% by weight and 10% by weight relative to the weight of said support.

Advantageously, the active phase of said catalyst comprising at least one Group VIIIB metal is cobalt.

Advantageously, the specific surface of the oxide support is between 50 m ² / g and 500 m ² / g, and wherein the pore volume of said mercury porosimetric oxide support is from 0.2 ml / g to 2.0 ml / g.

Advantageously, the oxide support is a silica-alumina support.

According to one variant, the step of impregnating b) of the support with the active phase comprises at least one step b ') of deposition of at least one dopant chosen from a noble metal of groups VI IB or VIIIB, an alkaline element (Group IA element) or an alkaline earth element (element of the MA group) or an element of the NIA group, alone or in mixture, on said oxide support.

Advantageously, the size of the catalyst particles is between 10 and 500 microns.

Detailed description of the invention

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

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 mercury porosimetry (see Rouquerol F. Rouquerol J. Singh K. "Adsorption by Powders & Porous Solids: Principle, methodology and applications", Academy Press, 1999). More particularly, the total pore volume is measured by mercury porosimetry according to the ASTM D4284-92 standard with a wetting angle of 140 °, for example by means of an Autopore III ™ model apparatus of the Micromeritics ™ brand. The specific surface is determined in the present invention by the B.E.T method, described in the same reference work as mercury porosimetry, and more particularly according to ASTM D3663-03.

Process for preparing the catalyst

The preparation of the catalyst used in the Fischer-Tropsch process according to the invention can be carried out by several variants. The preparation of the catalyst generally comprises, in a first step, the preparation of the oxide support comprising alumina, silica or a silica-alumina, optionally at least one spinel and possibly phosphorus, and then, in a second step, introduction of the active phase.

The process for preparing the catalyst used in the Fischer-Tropsch process according to the invention comprises the following steps:

a) providing an oxide support comprising alumina, silica, or a silica-alumina;

b) the oxide support of step a) is impregnated with an aqueous or organic solution comprising at least one group VIIIB metal salt chosen from cobalt, nickel, ruthenium and iron, preferably cobalt, then the product obtained is dried at a temperature between 60 and 200 ° C;

c) the product obtained in step b) is treated under steam at a temperature of between 10 and 195 ° C, preferably between 1 and 190 ° C, and even more preferably between 1 and 10 and 180 ° C, for a period of 30 minutes to 4 hours and with an air / vapor mixture, said mixture comprising between 2 and 50% by volume of water in vapor form, preferably between 20 and 50% by volume of water in vapor form.

More particularly, according to step a), there is provided a support comprising alumina, silica or a silica-alumina. When the support is a silica-alumina, the SiO ₂ silica content can vary from 0.5% by weight to 30% by weight, preferably from 1% by weight to 30% by weight, and even more preferably by 1%, 5 to 20% by weight relative to the weight of the support. Preferably, a silica-alumina support is provided. Such a support can be purchased or manufactured, for example by atomizing an alumina precursor in the presence of a compound comprising silicon. The support comprising alumina and silica may be provided by any means known to those skilled in the art, for example by impregnation of an organosilyl compound of TEOS (tetraethylorthosilicate) type on an alumina. In this case, this impregnation, followed by drying and calcination, is preliminary to step a) described above.

In a particular embodiment of the process according to the invention, a step a ') is carried out between step a) and b) of the process according to the invention in which the oxide support provided in step a) is impregnated. ) by an aqueous or organic solution of a phosphorus precursor, followed by a step of drying and calcination of the solid obtained. The impregnation step a ') is advantageously carried out by at least one solution containing at least one phosphorus precursor. In particular, step a ') may advantageously be carried out by dry impregnation, by excess impregnation, or again by deposition - precipitation according to methods well known to those skilled in the art. Preferably, said impregnation step is carried out by dry impregnation, preferably at room temperature. Said impregnation step comprises contacting said support with at least one solution containing at least one phosphorus precursor, whose volume is equal to the pore volume of said support to be impregnated. This solution contains the phosphorus precursor at the concentration desired to obtain the desired phosphorus content on the final support, preferably between 0.1% by weight and 10% by weight, preferably between 0.3% by weight and 5% by weight. and particularly preferably between 0.5 and 3% by weight relative to the weight of the support.

The phosphorus precursor used may be any phosphorus precursor known to those skilled in the art. It is advantageous to use phosphoric acid and its phosphate derivatives, phosphorous acid and its phosphonate derivatives, phosphinic acid and its phosphinate derivatives, phosphonic acid and its phosphonate derivatives, pyrophosphoric acid and its phosphate derivatives, and diphosphorus pentoxide, phosphines, phosphites, phosphinites, or phosphonites. Preferably, the phosphoric acid in aqueous solution is used.

After impregnation of the phosphorus precursor, the solid obtained is then dried and calcined. 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 48 hours. The calcination is advantageously carried out at a temperature of between 200 ° C. and 1100 ° C., preferably for a period ranging from 1 hour to 24 hours, and preferably from 2 hours to 8 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.

All the drying and calcination steps described in the present description can be carried out by any technique known to those skilled in the art: fixed bed, fluidized bed, oven, muffle furnace, rotary kiln.

In yet another particular embodiment of the process according to the invention, and more particularly when the support comprises alumina, is carried out between step a) or a ') and b) a step a ") in which one impregnates, preferably dry, the support with an aqueous or organic solution comprising at least one metal salt M or M 'selected from the group consisting of magnesium (Mg), copper (Cu), cobalt (Co), nickel (Ni), tin (Sn), zinc (Zn), lithium (Li), calcium (Ca), cesium (Cs), sodium (Na), potassium (K), iron (Fe) and manganese (Mn), preferably cobalt, nickel, magnesium, calcium and zinc and very preferably cobalt and nickel, and particularly preferably cobalt, then a drying step and a calcination step, so as to obtain a simple spinel MAI ₂ 0 ₄ or mixed M _X M _(1. _X) Al ₂ 04 partial or not, where M and M 'are different metals and where x is between 0 and 1, the values 0 and 1 themselves being excluded.

The metal M or M 'is brought into contact with the support via any aqueous metal soluble precursor. Preferably, the precursor of the group VIIIB metal is introduced in aqueous solution, preferably in the form of nitrate, carbonate, acetate, chloride, oxalate, complexes formed by a polyacid or an acid-alcohol and its salts, complexes formed with acetylacetonates, or any other soluble inorganic derivative in aqueous solution, which is brought into contact with said support. In the preferred case where the metal M is cobalt, the cobalt precursor advantageously used is cobalt nitrate, cobalt oxalate or cobalt acetate. The metal content M or M 'is advantageously between 1 and 20% by weight and preferably between 2 and 10% by weight relative to the total mass 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 48 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 the precursors M and M 'and alumina into a spinel type structure (aluminate of M and M').

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.

Thus, at the end of said step a "), said support further comprises a simple MAI ₂ 0 ₄ or mixed M _x M ' _(1-x) Al ₂ O ₄ partial or non-partial spinel, in which the metals M and M 'are in the form of aluminates The catalyst preparation comprising a support comprising phosphorus and / or spinel makes it possible to improve the hydrothermal and mechanical resistance catalyst in a Fischer-Tropsch process. The metal or metals M and M 'when they are in spinel form are not reducible under the usual conditions of reduction and are not part of the active phase

According to another variant of the preparation of the catalyst according to the invention, the steps a ') and a ") are carried out simultaneously in order to introduce the phosphorus and the metal M or M' in a single step onto the support. alumina, silica, phosphorus and a spinel in the support gives the final catalyst much better hydrothermal resistance and attrition resistance than the state of the art catalysts containing only one, two or three of these four components.

According to yet another variant of the preparation of the catalyst, precursors of silica, metal M or M 'and phosphorus are simultaneously introduced into the support comprising alumina.

In another variant embodiment, the support is prepared by co-precipitation of an aqueous solution containing the elements Al, Si, P, M or M ', for example in the nitrate form for aluminum and M or M', and acid or salt of acid for phosphorus and silicon, with an aqueous solution of carbonate or hydrogencarbonate, followed by washing, drying and calcination.

It is also possible to prepare the support by sol-gel process, or by complexation of an aqueous solution containing the elements M or M ', Al, Si and P with at least one alpha-alcohol acid added at a rate of 0, 5 to 2 moles of acid per mole of elements M or M ', Al, Si and P, followed by drying under vacuum leading to the production of a homogeneous vitreous substance, followed by calcination.

The specific surface of the oxide support comprising alumina, silica, or a silica-alumina, optionally comprising at least one spinel as described above and optionally phosphorus, 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 1 10 m ² / g and 250m ² / g. The pore volume of said support is generally between 0.2 ml / g and 2.0 ml / g, and preferably between 0.4 ml / g and 1.5 ml / g.

The oxide support comprising alumina, silica, or a silica-alumina, optionally comprising at least one spinel as described above and optionally phosphorus, may further comprise a single oxide selected from oxide titanium (TiO 2), ceria (CeO 2) and zirconia (ZrO 2), alone or in admixture. The support on which said active phase is deposited 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 a fixed bed, or have a morphology in the form of powder of variable particle size, especially when said catalyst is used in a bubble column type reactor.

According to step b), the impregnation of the support resulting from step a), and optionally from step a ') and / or from step a ") is carried out by at least one solution containing at least one precursor of a group VIIIB metal chosen from cobalt, nickel, ruthenium and iron, preferably the group VIIIB metal is cobalt, in particular said step may advantageously be carried out by dry impregnation with impregnation in excess, or by deposition - precipitation according to methods that are well known to those skilled in the art Preferably, said impregnation step is carried out by dry impregnation, preferably at ambient temperature. contacting said oxide support with at least one solution containing at least one precursor of said group VIIIB metal, the volume of which is equal to the pore volume of said support to be impregnated, This solution contains the precursor metal Group VIIIB metal (s) at the desired concentration in order to obtain the desired metal content on the final catalyst, advantageously a metal content of between 0.5 and 60% by weight, and preferably between 5 and 30% by weight relative to the weight of the catalyst.

The metal or metals of group VIIIB are brought into contact with the support via any soluble metal precursor in aqueous phase or in organic phase. When introduced in organic solution, the group VIIIB metal precursor is preferably the oxalate or the acetate of said group VIIIB metal. Preferably, the precursor of the group VIIIB metal is introduced in aqueous solution, preferably in the form of nitrate, carbonate, acetate, chloride, oxalate, complexes formed by a polyacid or an acid-alcohol and its salts, complexes formed with acetylacetonates, or any other soluble inorganic derivative in aqueous solution, which is brought into contact with said support. In the preferred case where the group VIIIB metal is cobalt, the cobalt precursor advantageously used is cobalt nitrate, cobalt oxalate or cobalt acetate. Most preferably, the precursor used is cobalt nitrate.

The impregnation of said active phase of step b) can be carried out in one or more impregnation steps. In the case of high metal contents, two-step or even three-step impregnation is preferred. Between each impregnation stage, it is preferred to carry out at least one additional drying step, optionally followed by a treatment step under steam under the conditions described above, and / or optionally a calcination step under the conditions described below. .

Said step of impregnation b) of the support with the active phase, may also advantageously comprise at least one step b ') of depositing at least one dopant selected from a noble metal of groups VI IB or VIIIB, an alkaline element (element of group IA) or an alkaline earth element (element of the MA group) or an element of the NIA group, alone or as a mixture, on said oxide support. The impregnation step b) of the support with the active phase and step b ') of the deposition of at least one dopant can be carried out concomitantly or sequentially. Deposition of the dopant on the support may advantageously be carried out by any method known to those skilled in the art, preferably by impregnation of said oxide support with at least one solution containing at least one precursor of said dopant, and preferably by impregnation with dry or by excess impregnation. This solution contains at least one precursor of said dopant at the desired concentration in order to obtain the desired dopant content on the final catalyst, advantageously a dopant content of between 20 ppm and 1% by weight, and preferably between 0.01 and 0.5. % by weight based on the weight of the catalyst. Subsequently, the catalyst containing the dopant is dried, then treated with steam and optionally calcined under the same conditions as those described in the drying and calcination steps during the impregnation of the active phase. The impregnation of the active phase and the dopant can also be carried out by a single solution (co-impregnation).

The catalyst precursor thus obtained is then dried. 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 48 hours. For the purposes of the present invention, drying is understood to mean any drying carried out under a dry gas atmosphere, i.e. under a gaseous atmosphere without the addition of water. This can be done using any type of gas or dry gas mixture with respect to the various constituents of said catalyst. By way of example, mention may be made of nitrogen, argon, helium, xenon and air.

According to step c), the catalyst precursor obtained in step b) undergoes a thermal treatment under steam. More particularly, the thermal treatment under water vapor is advantageously carried out at a temperature of between 10 and 195 ° C, preferably between 1 and 190 ° C, and preferably between 1 and 180 ° C, for a period ranging from 30 minutes to 4 hours and with an air / steam mixture comprising between 2 and 50% by volume of water in vapor form, preferably between 20 and 50% by volume of water in vapor form. The flow rate of air / vapor mixture is between 0.1 and 20 L / h / g, preferably between 0.2 and 5 L / h / g. Step c) of thermal treatment under steam is a technique known to those skilled in the art. The thermal treatment under steam can be achieved by means of a vaporizer. The Applicant has found that the catalyst reducibility is significantly improved when the temperature of the steam heat treatment and the duration of the treatment are within the ranges of values specified above. After step c) of the process according to the invention, the product obtained may optionally be calcined according to a step d). The calcination is advantageously carried out at a temperature of between 320 ° C. and 460 ° C., preferably between 350 ° C. and 440 ° C. and preferably between 360 ° and 420 ° C. It is preferably carried out for a period of between 15 min and 15 h and preferably between 30 min and 12 h and even more preferably between 1 h and 6 h. The calcination is generally carried out under a dry oxidizing atmosphere, ie under an atmosphere without the addition of water, for example under air, or under oxygen-depleted air; it can also be carried out at least partly under nitrogen.

Prior to its use in the Fischer-Tropsch synthesis reaction, the catalyst is generally subjected to a reducing treatment, for example in pure or dilute hydrogen, at high temperature, for activating the catalyst and forming metal particles in the zero state. are worth (in metallic form). This treatment can be carried out in situ (in the same reactor as that where the Fischer-Tropsch synthesis is performed), or ex situ before being loaded into the reactor. The temperature of this reducing treatment is preferably between 200 ° C. and 600 ° C. and its duration is generally between 2 and 20 hours.

Fischer-Tropsch process

The Fischer-Tropsch process allows the production of essentially linear and saturated hydrocarbons C5 ⁺ . According to the invention, the term "substantially linear and saturated hydrocarbons C5 ^+" is intended to mean hydrocarbons whose proportion of hydrocarbon compounds having at least 5 carbon atoms per molecule represents at least 50% by weight, preferably at least 80% by weight. of all the hydrocarbons formed, the total content of olefinic compounds present among said hydrocarbon compounds having at least 5 carbon atoms per molecule being less than 15% by weight. The hydrocarbons produced by the process of the invention are thus essentially paraffinic hydrocarbons, whose fraction having the highest boiling points can be converted with a high yield of middle distillates (gasoil and kerosene cuts) by a catalytic hydroconversion process such as hydrocracking and / or hydroisomerization.

Preferably, the feedstock used for carrying out the process of the invention consists of the synthesis gas, which is a mixture of carbon monoxide and hydrogen of H ₂ / CO molar ratios that can vary between 0, 5 and 4 depending on the manufacturing process from which it is derived. 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 synthesis gas is of the order 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 an autothermal reforming process. The H ₂ / CO molar ratio of the synthesis gas is generally close to 1 when it is obtained from a gasification and C0 ₂ hydrocarbon reforming process (called dry reforming). The Fischer-Tropsch 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 Fischer-Tropsch process according to the invention can be carried out in a perfectly stirred autoclave type reactor, bubbling bed, bubble column, fixed bed or moving bed. Preferably, it is carried out in a bubble column reactor.

As a result, the grain size of the catalyst used in the Fischer-Tropsch process may be between a few microns and 2 millimeters. Typically, for a three-phase reactor "slurry" (bubble column), the catalyst is finely divided and is in the form of particles. The size of the catalyst particles will be between 10 and 500 micrometers (μηι), preferably between 10 and 300 μηι and very preferably between 20 and 150 μηι, and even more preferably between 20 and 120 μηι. To illustrate the invention and to enable the person skilled in the art to perform it, we present below various embodiments of the process for the preparation of a catalyst used for Fischer-Tropsch synthesis; however this can not limit the scope of the invention.

Example 1 Preparation of catalysts A to C (comparative) and catalysts D to F (according to the invention) Catalyst A (non-compliant): Catalyst 13% Co on silica-alumina stabilized with 5% Co in aluminate form ( spinel) without water vapor treatment

A catalyst A is prepared by dry impregnation of an aqueous solution of cobalt nitrate on a silica-alumina (Siralox®, supplied by Sasol) powder (average particle size = 90 μηι) of 170 m ² / g. After drying for 12 hours in an oven at 120 ° C., the solid is calcined for 4 hours at 800 ° C. under a stream of air in a crossed-bed reactor. This calcination at high temperature makes it possible to form a Co aluminate spinel phase (5% by weight of cobalt). On this support stabilized with cobalt in the form of spinel, impregnated with a solution of cobalt nitrate. The solid obtained is then dried in an oven for 12 h at 80 ° C, and then calcined in air in a fixed bed tubular reactor at 420 ° C for 2 hours. The final catalyst which contains 13.7% by weight of cobalt (the content of Co present in the spinel phase being included) and a theoretical maximum reducible cobalt content of 8.7% by weight are obtained under the reduction conditions described above. above. The reducible cobalt content has the active phase and is obtained by programmed temperature reduction RTP (or TPR for "programmed temperature reduction" according to the English terminology).

Catalyst B (non-compliant): Catalyst 13% Co on silica-alumina stabilized with 5% Co in aluminate form (spinel) with treatment under steam at 400 ° C. for 2 hours

A catalyst B is prepared by dry impregnation of an aqueous solution of cobalt nitrate on a silica-alumina (Siralox®, supplied by Sasol) powder (average particle size = 90 μηι) of 170 m ² / g. After drying for 12 hours in an oven at 120 ° C., the solid is calcined for 4 hours at 800 ° C. under a stream of air in a crossed-bed reactor. This calcination at high temperature makes it possible to form a Co aluminate spinel phase (5% by weight of cobalt). On this support stabilized with cobalt in the form of spinel, impregnated with a solution of cobalt nitrate. The solid obtained is then dried in an oven for 12 h at 80 ° C. It is then treated at 400 ° C. for 2 hours in a tubular reactor under a stream of gas at 1.5 L / h / g containing 50% by volume of water and 50% by volume of air. We get the final catalyst which contains 13.8% by weight of cobalt (the content of Co present in the spinel phase being included) and a theoretical maximum reducible cobalt content of 8.8% by weight.

Catalyst C (non-compliant): Catalyst 13% Co on silica-alumina stabilized with 5% Co in aluminate form (spinel) with treatment under water vapor at 190 ° C. for 10 hours

A catalyst C is prepared by dry impregnation of an aqueous solution of cobalt nitrate on a silica-alumina (Siralox®, supplied by Sasol) powder (average particle size = 90 μηι) of 170 m ² / g. After drying for 12 hours in an oven at 120 ° C., the solid is calcined for 4 hours at 800 ° C. under a stream of air in a crossed-bed reactor. This calcination at high temperature makes it possible to form a Co aluminate spinel phase (5% by weight of cobalt). On this support stabilized with cobalt in the form of spinel, impregnated with a solution of cobalt nitrate. The solid obtained is then dried in an oven for 12 h at 80 ° C. It is then treated at 190 ° C. for 10 hours in a tubular reactor under a flow of gas at 1.1 L / hr / g containing 50% by volume of water and 50% by volume of air. The final catalyst which contains 13.5% by weight of cobalt (the content of Co present in the spinel phase being included) and a theoretical maximum reducible cobalt content of 8.5% by weight are obtained.

Catalyst D (compliant): Catalyst 13% Co on silica-alumina stabilized with 5% Co in aluminate form (spinel) with treatment under steam at 190 ° C. for 1 hour

A catalyst D is prepared by dry impregnation of an aqueous solution of cobalt nitrate on a silica-alumina (Siralox®, supplied by Sasol) powder (average particle size = 90 μηι) of 170 m ² / g. After drying for 12 hours in an oven at 120 ° C., the solid is calcined for 4 hours at 800 ° C. under a stream of air in a crossed-bed reactor. This calcination at high temperature makes it possible to form a Co aluminate spinel phase (5% by weight of cobalt). On this support stabilized with cobalt in the form of spinel, impregnated with a solution of cobalt nitrate. The solid obtained is then dried in an oven for 12 h at 80 ° C. It is then treated at 190 ° C. for 1 hour in a tubular reactor under a flow of gas of 1 L / hr / g containing 50% by volume of water and 50% by volume of air. The final catalyst is obtained which contains 13.7% by weight of cobalt (the content of Co present in the spinel phase being included) and a theoretical maximum reducible cobalt content of 8.7% by weight. Catalyst E (compliant): Catalyst 13% Co on silica-alumina stabilized with 5% Co in aluminate form (spinel) with treatment under water vapor at 180 ° C. for 2 hours

A catalyst E is prepared by dry impregnation of an aqueous solution of cobalt nitrate on a silica-alumina (Siralox®, supplied by Sasol) powder (average particle size = 90 μηι) of 170 m ² / g. After drying for 12 hours in an oven at 120 ° C., the solid is calcined for 4 hours at 800 ° C. under a stream of air in a crossed-bed reactor. This calcination at high temperature makes it possible to form a Co aluminate spinel phase (5% by weight of cobalt). On this support stabilized with cobalt in the form of spinel, impregnated with a solution of cobalt nitrate. The solid obtained is then dried in an oven for 12 h at 80 ° C. It is then treated at 180 ° C. for 2 hours in a tubular reactor under a flow of gas of 1 L / hr / g containing 50% by volume of water and 50% by volume of air. The final catalyst is obtained which contains 13.4% by weight of cobalt (the content of Co present in the spinel phase being included) and a theoretical maximum reducible cobalt content of 8.4% by weight.

Catalyst F (compliant): Catalyst 8% Co on silica-alumina with treatment under steam at 180 ° C for 2 hours

Catalyst F is prepared by dry impregnation of a solution of cobalt nitrate. The solid obtained is then dried in an oven for 12 h at 80 ° C. It is then treated at 180 ° C. for 2 hours in a tubular reactor under a flow of gas of 1 L / hr / g containing 50% by volume of water and 50% by volume of air. The final catalyst which contains 8.1% by weight of theoretically reducible cobalt is obtained.

Example 2 Comparison of the Reduction Rates of Catalysts A to F

The reduction ratio (TR) of a catalyst is defined as the percentage of cobalt reduced after the catalyst reduction step. The reduction ratio (TR) corresponds to the ratio between the reduced amount of cobalt (Q1) and the theoretically reducible amount of cobalt present on the catalyst (Q2), ie TR (%) = (Q1 / Q2) × 100.

The measurement of the amount of reducible cobalt Q2 on these oxide catalysts is carried out by performing a programmed temperature reduction RTP (or TPR for "programmed temperature reduction" according to the English terminology). RTP is known to those skilled in the art and is for example described in the journal "OU & Gas Science and Technology", Rev. IFP, Vol. 64 (2009), No. 1, pp. 1 1 -12. RTP consists of treating a sample of 500 mg of catalyst under a gas flow rate of 58 Nml / min, the volume composition of which is 5% H ₂ diluted in helium with a temperature ramp of 5 ° C / min. between 25 and 800 ° C and to measure the total amount of hydrogen consumed (V1), which is proportional to the amount of reducible cobalt. The final catalysts A to F are then reduced in a tubular furnace under a stream of pure hydrogen at 400 ° C. for 16 hours with a VVH of 2 Nl / h / g. They are then discharged in air: a fraction of the reduced cobalt is re-oxidized in contact with the air, the reduced catalysts are thus passivated. The measurement of the amount of cobalt reduced Q1 is performed by performing a RTP on these reduced passivated catalysts. RTP consists of treating a sample of 500 mg of catalyst under a gas flow rate of 58 Nml / min, the volume composition of which is 5% H ₂ diluted in helium with a temperature ramp of 5 ° C / min. between 25 and 800 ° C and to measure:

the quantity of hydrogen (V 2) consumed between 25 and 400 ° C., proportional to the quantity of passivated cobalt; and

- the amount of hydrogen (V3) consumed between 400 and 800 ° C, related to the reduction of the unreduced cobalt fraction, proportional to the amount of unreduced cobalt, in the form of CoO.

The reduction rate TR (in%) is calculated by the following mathematical formula (1):

The reduction rates of solids A to F were measured according to the protocol previously described and are given in Table 1.

Table 1: Reduction rate (%) The catalysts D to F according to the invention all have higher reduction levels than the catalysts not in accordance with the invention A, B, and C. Example 3 Catalyst Performances in the Fischer-Tropsch Process of Catalyst B to F

Catalysts B to F, before being successively tested in conversion of the synthesis gas, are reduced ex situ under a stream of pure hydrogen at 400 ° C. for 16 hours with a VVH of 2 Nl / h / g in a tubular reactor . Once the catalyst is reduced, it is discharged under an argon atmosphere and coated in Sasolwax ^® to be stored protected from the air before testing. The Fischer-Tropsch synthesis reaction is carried out in a slurry-type reactor operating continuously and operating with a concentration of 10% (vol) of catalyst in the slurry phase.

Each of the catalysts is in the form of a powder with a diameter of between 30 and 170 μπι.

The test conditions are as follows: temperature = 230 ° C; total pressure = 2 MPa; molar ratio H ₂ / CO = 2

The conversion of CO is maintained between 45 and 50% throughout the duration of the test.

The test conditions are adjusted so as to be iso-conversion of CO and this whatever the activity of the catalyst.

The results, in terms of activity, were calculated for catalysts B to F relative to catalyst B as reference and are shown in Table 1.

The results in Table 2 show the catalytic performances of the catalysts B to F in terms of activity. It appears that the catalysts D, E and F according to the invention show significant gains in activity relative to the comparative catalysts B and C.

Table 2: Catalytic Performance

Claims

A process for preparing a catalyst comprising an active phase comprising at least one Group VI 11B metal selected from cobalt, nickel, ruthenium and iron deposited on an oxide support; which process comprises the following steps: a) providing an oxide support comprising alumina, silica, or a silica-alumina;

b) the oxide support of step a) is impregnated with an aqueous or organic solution comprising at least one metal salt of group VI 11 B selected from cobalt, nickel, ruthenium and iron, and then dried the product obtained at a temperature between 60 and 200 ° C;

Process according to Claim 1, characterized in that the heat treatment under steam is carried out at a temperature of between 1 10 and 190 ° C for a period ranging from 30 minutes to 4 hours and with an air / vapor mixture comprising between 20 and 50% by volume of water in vapor form.

Process according to claims 1 or 2, characterized in that between step a) and b) of said process is carried out a step a ') in which the oxide support provided in step a) is impregnated with a solution aqueous or organic phosphorus precursor, then one proceeds to a drying step at a temperature between 60 ° C and 200 ° C, and then proceeds to a step of calcination of the solid obtained at a temperature between 200 ° C and 1100 ° C.

Process according to any one of claims 1 to 3, characterized in that after step a) or a ') and b) a step a ") is carried out in which said support comprising alumina is impregnated, silica, or a silica-alumina, optionally phosphorus, with an aqueous or organic solution comprising at least one metal salt M or M 'selected from the group consisting of magnesium (Mg), copper (Cu), cobalt (Co), nickel (Ni), tin (Sn), zinc (Zn), lithium (Li), calcium (Ca), cesium (Cs), sodium (Na), potassium (K), iron (Fe) and manganese (Mn), and then dried and calcined at a temperature between 700 and 1200 ° C., so as to obtain a simple MAI ₂ 0 ₄ or mixed spinel M _X M ' ₍₁ _X) Al ₂ O ₄ partial or not, where M and M' are distinct metals and where x is between 0 and 1, the values 0 and 1 being themselves excluded.

5. Process according to claim 4, characterized in that steps a ') and a ") are simultaneously carried out in order to introduce the phosphorus and the metal M or M' in a single step onto said oxide support provided to step a).

6. Method according to claim 4 or 5, characterized in that the metal content M or M 'is between 1 and 20% by weight relative to the total mass of the final support.

7. Method according to any one of claims 1 to 6, characterized in that a step d) calcination is carried out at a temperature between 320 ° C and

460 ° C.

8. Process according to any one of claims 1 to 7, characterized in that a reducing treatment step is carried out after step c) of treatment under steam and / or step d) of calcination, at a temperature of between 200 ° C and 600 ° C. 9. A method according to any one of claims 1 to 8, wherein the group VII IB metal content of the active phase of said catalyst is between 0.5 and 60% by weight relative to the weight of said catalyst.

10. Process according to any one of claims 3 to 9, wherein the phosphorus content of the oxide support is between 0.1% by weight and 10% by weight relative to the weight of said support.

1 1. Process according to any one of claims 1 to 10, wherein the active phase of said catalyst comprising at least one Group VII IB metal is cobalt.

12. A process according to any one of claims 1 to 11, wherein the specific surface of the oxide support is between 50 m ² / g and 500 m ² / g, and wherein the pore volume of said support of oxides measured by mercury porosimetry is between 0.2 ml / g and 2.0 ml / g.

13. Process according to any one of claims 1 to 12, wherein the oxide support is a silica-alumina support.

14. Process according to any one of Claims 1 to 13, characterized in that the impregnation step b) of the support with the active phase comprises at least one step b ') of deposition of at least one chosen dopant. among a noble metal groups VIIB or VIIIB, an alkaline member (Group IA element) or an alkaline earth element (MA group element) or an NIA group element, alone or in mixture, on said oxide support.

The method of any one of claims 1 to 14, wherein the size of the catalyst particles is between 10 and 500 micrometers.