WO2023001639A1

WO2023001639A1 - Method for preparing a catalyst from molten salts and a particular support

Info

Publication number: WO2023001639A1
Application number: PCT/EP2022/069488
Authority: WO
Inventors: Malika Boualleg; Laetitia Jothie
Original assignee: IFP Energies Nouvelles
Priority date: 2021-07-22
Filing date: 2022-07-12
Publication date: 2023-01-26
Also published as: FR3125438A1

Abstract

The invention relates to a method for preparing a catalyst comprising a nickel-based active phase and an alumina support, comprising the following steps: - shaping and performing a particular heat treatment of an alumina gel; - addition of an organic additive and a nickel metal salt at a temperature lower than the melting point of nickel in order to form a solid mixture; - heating of the solid mixture under stirring in order to obtain a catalyst precursor; - drying of the catalyst precursor at a temperature lower than 250°C; and - heat treatment of the catalyst precursor.

Description

METHOD FOR PREPARING A CATALYST FROM MOLTEN SALTS AND

OF A PARTICULAR SUPPORT

Technical area

The present invention relates to a process for the preparation of a catalyst intended particularly for the hydrogenation of unsaturated hydrocarbons, and more particularly, for the selective hydrogenation of polyunsaturated compounds or in the hydrogenation of aromatic compounds.

State of the art

Many synthesis processes are known from the prior art to optimize the content and accessibility of metals in catalysts. Among these methods, the use of molten salts as precursors of the active phase of a catalyst or of a capture mass is known from the literature.

For example, document US 5,036,032 discloses a method for preparing a supported catalyst based on cobalt by bringing a support into contact (of the order of a few tens of seconds) in a bath of molten salt of cobalt nitrate, followed by a step of drying and reduction without intermediate calcination. This method allows the preferential localization of the cobalt phase at the periphery of the support. Nevertheless, the method does not allow precise control of the amount of active phase (here cobalt) deposited due to the very short contact time and on the other hand the type of catalyst obtained is not suitable for implementation. in a reactor operating in the liquid phase with a catalyst in suspension (called a "slurry reactor" or "slurry" according to English terminology) due to the excessive loss of metal by attrition. Moreover, the absence of a calcination step is risky since the reaction between the reduction element and the nitrates in the solid is very exothermic. Finally, this method requires the manipulation of large quantities of cobalt nitrate (toxic) in liquid form and at temperature, with ratios of approximately 4 grams of active phase precursors for 1 gram of support. The catalysts obtained by this preparation route are used for the synthesis of Fischer-Tropsch hydrocarbons.

It is known to Chem. Mater., 1999, 11, p.1999-2007 to prepare mixed phosphates by a molten salt type route. The reaction mixture contains a metal precursor salt (in particular Ni(NC> ₃ )2 or CO(NÛ3)2), a source of phosphorus (NH4HPO4), and an alkali metal nitrate (Na or K). These preparations are carried out at high temperatures of the order of 400°C to 450°C. Mixed phosphate solids are obtained, for example Na3NI2(P2O7)PC>4, K2NL(PO4)2P2C>7 OR NagCo3(PC>4)5. These solids can find applications in ion exchange, high temperature ionic conduction or in catalysis. The document GB191308864 discloses a process for the synthesis of bulk catalysts based on nickel or cobalt for the production of hydrogen by steam reforming (“steam-reforming” according to the Anglo-Saxon terminology). These catalysts can be obtained by liquefaction of metal salts at moderate temperatures, then poured into a mold before heat treatment for calcination.

The publication by J. -Y. Tilquin entitled “Intercalation of CoC into graphite: Mixing method vs molten sait method” published in Carbon, 35(2), p. 299-306, 1997, proposes the use in the form of molten salt of a CoCh-NaCl mixture at high temperature (450-580°C) for the intercalation between sheets of graphite. These graphite intercalation compounds find applications in catalysis for oxygen reduction in polymer electrolyte fuel cells.

Document EP2921227 discloses a Fischer-Tropsch catalyst based on a group VIIIB metal deposited on an oxide support comprising alumina, silica, spinel and phosphorus as well as its method of manufacture. This process includes the preparation of the oxide support as well as the impregnation of this support with an aqueous solution of a metal precursor followed by drying and calcination. In the case of high metal contents, the impregnation/drying/calcination of the active phase in several stages is preferred.

Finally, document FR3104461 discloses a method for preparing a selective hydrogenation catalyst comprising an active phase of nickel and an alumina support, said support being brought into contact with at least one organic additive comprising oxygen and/ or nitrogen and with at least one nickel metal salt at a temperature below the melting point of said nickel metal salt. However, this document does not disclose the process for preparing the alumina or discuss a potential impact of the properties of the alumina used.

Objects of the invention

The present invention relates to a new method for preparing a catalyst exhibiting performance at least as good, or even better than the catalysts obtained according to preparation methods according to the prior art, while using a quantity of active phase based on nickel equal to or even less than that typically used in the state of the art.

The present invention relates to a process for the preparation of a catalyst comprising an active phase based on nickel and an alumina support, said active phase not comprising any metal from group VI B, said catalyst comprising a higher nickel element content or equal to 1% by weight and less than or equal to 50% by weight relative to the total weight of the catalyst, the size of the nickel particles in the catalyst, measured in oxide form, is less than 8 nm, said method comprising the following steps a) supplying an alumina gel; b) the alumina gel of step a) is shaped; c) the shaped alumina gel obtained at the end of step b) is subjected to a heat treatment comprising at least one hydrothermal treatment step in an autoclave in the presence of an acid solution, at a temperature between between 100°C and 800°C for a time of between 45 minutes and 150 minutes, and at least one calcining step, at a temperature of between 400°C and 1500°C, carried out after the hydrothermal treatment step, for obtaining an alumina support; d) the alumina support is brought into contact with at least one organic additive comprising oxygen and/or nitrogen, the molar ratio between the organic additive and the nickel being greater than 0.05 mol/mol ; e) the alumina support is brought into contact with at least one nickel metal salt, at a temperature below the melting point of said nickel metal salt, to form a solid mixture, the mass ratio between said metal salt and the alumina support being between 0.1 and 2.3, steps d) and e) being carried out either successively in this order, or simultaneously; f) the solid mixture obtained at the end of steps d) and e) is heated with stirring to a temperature between the melting point of said metal salt and 200° C., to obtain a catalyst precursor; g) the catalyst precursor is dried at the end of step f) at a temperature below 250° C. to obtain a dried catalyst precursor; h) a stage of heat treatment of the dried catalyst precursor obtained at the end of stage g) is carried out at a temperature of between 250° C. and 1000° C.

The Applicant has discovered, surprisingly, that it is possible to obtain a catalyst exhibiting performance at least as good, or even better, in terms of activity in the context of the reactions of selective hydrogenation of polyunsaturated compounds or of hydrogenation of aromatic compounds, as catalysts obtained according to processes known from the prior art, by applying a particular heat treatment (hydrothermal treatment) during the synthesis of the catalyst support from an alumina gel, said catalyst being obtained by introducing an organic additive and a nickel metal salt onto the particular alumina support to form a solid mixture, said solid mixture being heated with stirring, then dried and heat-treated without resorting to a final hydrothermal treatment. Without wishing to be bound by any theory, the preparation process comprising the addition of a specific organic additive and a nickel precursor (in the form of molten salts) on a particular alumina support having a surface reactivity very particular, and having undergone a hydrothermal treatment in the presence of an acid solution, allows an improved accessibility of nickel (less strong interaction with the support).

The method for preparing the catalyst according to the invention leads to a catalyst having a nickel particle size of less than 8 nm, conferring a significant intrinsic activity of the nickel active phase. Furthermore, the method for preparing the catalyst used in the context of the present invention allows, without addition of solvent and therefore in a very limited number of steps and above all less than the conventional preparation method (i.e. by impregnation), the Obtaining a catalyst whose catalytic performances are at least as good or even superior to conventional catalysts.

According to one or more embodiments, the melting point of said metal salt is between 20°C and 150°C.

According to one or more embodiments, the molar ratio between said organic additive introduced in step d) and the nickel element introduced in step e) is between 0.1 and 5.0 mol/mol.

According to one or more embodiments, steps d) and e) are carried out simultaneously.

According to one or more embodiments, the organic additive is chosen from aldehydes containing 1 to 14 carbon atoms per molecule, ketones or polyketones containing 3 to 18 carbon atoms per molecule, ethers and esters containing 2 to 14 carbon atoms per molecule, alcohols or polyalcohols containing 1 to 14 carbon atoms per molecule and carboxylic acids or polycarboxylic acids containing 1 to 14 carbon atoms per molecule, or a combination of the different functional groups above

According to one or more embodiments, said organic additive is chosen from formic acid, formaldehyde, acetic acid, citric acid, oxalic acid, glycolic acid, malonic acid, levulinic acid, ethanol, methanol, ethyl formate, methyl formate, paraldehyde, acetaldehyde, gamma-valerolactone acid, glucose and sorbitol. According to one or more embodiments, the organic additive is chosen from citric acid, formic acid, glycolic acid, levulinic acid and oxalic acid.

According to one or more embodiments, step f) is carried out by means of a drum operating at a speed of between 4 and 70 revolutions per minute.

According to one or more embodiments, in step e) the mass ratio between said metal salt and the alumina support is between 0.2 and 2.

According to one or more embodiments, in step c) the duration of the hydrothermal treatment is carried out between 1 hour and 2 hours.

According to one or more embodiments, the alumina obtained at the end of step c) comprises a specific surface of between 10 m ² /g and 250 m ² /g.

According to one or more embodiments, the size of the nickel particles in the catalyst, measured in oxide form, is between 2 nm and 4 nm.

Detailed description of the invention Definitions

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 D.R. Lide, 81st 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.

By the specific surface of the catalyst or of the support used for the preparation of the catalyst according to the invention is meant the specific surface B.E.T. determined by nitrogen adsorption in accordance with standard ASTM D 3663-78 based on the BRUNAUER-EMMETT-TELLER method described in the periodical "The Journal of American Society", 60, 309, (1938).

In this application, the term "include" is synonymous with (means the same as) "include" and "contain", and is inclusive or open ended and does not exclude other unrecited material. It is understood that the term “include” includes the exclusive and closed term “consist”.

By total pore volume of the catalyst or of the support used for the preparation of the catalyst according to the invention is meant the volume measured by intrusion with a mercury porosimeter according to the ASTM D4284-83 at a maximum pressure of 4000 bar (400 MPa), using a surface tension of 484 dyne/cm and a contact angle of 140°. The wetting angle was taken as equal to 140° by following the recommendations of the work “Engineering techniques, treatise on analysis and characterization”, pages 1050-1055, written by Jean Charpin and Bernard Rasneur.

In order to obtain better precision, the value of the total pore volume corresponds to the value of the total pore volume measured by intrusion with a mercury porosimeter measured on the sample minus the value of the total pore volume measured by intrusion with a mercury porosimeter measured on the same sample for a pressure corresponding to 30 psi (about 0.2 MPa).

The term “size of the nickel particles” means the diameter of the crystallites of nickel in oxide form. The diameter of nickel crystallites in oxide form is determined by X-ray diffraction, from the width of the diffraction line located at the angle 2theta=43° (i.e. along the crystallographic direction [200 ]) using the Scherrer relation. This method, used in X-ray diffraction on powders or polycrystalline samples which links the width at mid-height of the diffraction peaks to the size of the particles, is described in detail in the reference: Appl. Crystal. (1978), 11, 102-113 "Scherrer after sixty years: A survey and some new results in the determination of crystallite size", J. I. Langford and A. J. C. Wilson.

The nickel content is measured by X-ray fluorescence.

Preparation process

The steps of the catalyst preparation process are described in detail below.

Step a)

The catalyst according to the invention comprises an alumina support which is obtained from an alumina gel (or alumina gel) which essentially comprises a precursor of the aluminum oxy(hydroxide) type (AIO(OH)) - also called Boehmite.

According to the invention, the alumina gel (or otherwise called boehmite gel) is synthesized by precipitation of basic and/or acidic solutions of aluminum salts induced by a change in pH or any other method known to those skilled in the art. (P. Euzen, P. Raybaud, X. Krokidis, H. Toulhoat, JL Le Loarer, JP Jolivet, C. Froidefond, Alumina, in Handbook of Porous Solids, Eds F. Schüth, KSW Sing, J. Weitkamp, Wley- VCH, Weinheim, Germany, 2002, pp. 1591-1677). Generally the precipitation reaction is carried out at a temperature between 5°C and 80°C and at a pH between 6 and 10. Preferably the temperature is between 35°C and 70°C and the pH is between 6 and 10.

According to one embodiment, the alumina gel is obtained by bringing an aqueous solution of an acid aluminum salt into contact with a basic solution. For example, the acid aluminum salt is chosen from the group consisting of aluminum sulphate, aluminum nitrate and aluminum chloride, and preferably, said acid salt is aluminum sulphate. The basic solution is preferably chosen from sodium hydroxide or potassium hydroxide. Alternatively, an alkaline solution of aluminum salts which may be chosen from the group consisting of sodium aluminate and potassium aluminate can be brought into contact with an acid solution. In a highly preferred variant, the gel is obtained by bringing a solution of sodium aluminate into contact with nitric acid. The sodium aluminate solution advantageously has a concentration of between 10 ⁵ and 1CH mol.L · ¹ and preferably this concentration is between 10 ⁴ and 10 ² mol.L ¹ . According to another embodiment, the alumina gel is obtained by bringing an aqueous solution of acid aluminum salts into contact with an alkaline solution of aluminum salts.

Step b) Shaping the alumina gel

The alumina gel can advantageously be shaped by any technique known to those skilled in the art. The shaping can be carried out, for example, by kneading-extrusion, by pelleting, by the drop coagulation method (“oil-drop” according to Anglo-Saxon terminology), by granulation on a turntable or by any other well-suited method. known to those skilled in the art. The catalysts according to the invention can optionally be manufactured and used in the form of extrudates, tablets, beads. The advantageous shaping method according to the invention is extrusion and the preferred extrudate shapes are cylindrical, twisted cylindrical or multilobed (2, 3, 4 or 5 lobes for example).

In a particular embodiment, the alumina gel obtained at the end of step a) is subjected to a kneading step, preferably in an acid medium. The acid used may for example be nitric acid. This step is carried out by means of known tools such as Z-arm mixers, wheel mixers, single or twin continuous screws allowing the transformation of the gel into a product having the consistency of a paste. According to an advantageous embodiment, one or more compounds called "pore-forming agents" are added to the mixing medium. These compounds have the property of being degraded by heating and thus creating porosity in the support. For example, it is possible to use as pore-forming compounds wood flour, charcoal, tars, materials plastics. The paste thus obtained after mixing is passed through an extrusion die. Generally, the extrudates have a diameter of between 0.5 mm and 10 mm, preferably between 0.8 mm and 3.2 mm and very preferably between 1.0 mm and 2.5 mm and a length of between 0.5 mm and 20mm. These extrudates can be cylindrical, multi-lobed (for example tri-lobed or quadri-lobed).

After it has been shaped, the support is optionally dried before undergoing the hydrothermal treatment according to step c) of the process. For example, the drying is carried out at a temperature between 50°C and 200°C. The dried support is optionally calcined before undergoing the hydrothermal treatment according to step c) of the process. For example, calcination is carried out at a temperature between 200°C and 1000°C, in the presence or not of an air flow containing up to 150 of water per kilogram of dry air.

Step c) Hydrothermal treatment of the alumina gel

The support obtained at the end of step b) then undergoes a heat treatment step which makes it possible to give it physical properties corresponding to the application envisaged.

The term “hydrothermal treatment” designates a treatment by passing through an autoclave in the presence of water at a temperature above ambient temperature.

During this hydrothermal treatment, the shaped alumina can be treated in different ways. Thus, the alumina can be impregnated with an acid solution, prior to its passage through the autoclave, the hydrothermal treatment of the alumina being able to be carried out either in the vapor phase or in the liquid phase, this vapor or liquid phase of the autoclave may or may not be acidic. This impregnation, before the hydrothermal treatment, can be carried out dry or by immersing the alumina in an acidic aqueous solution. By dry impregnation is meant bringing the alumina into contact with a volume of solution less than or equal to the total pore volume of the treated alumina. Preferably, the impregnation is carried out dry.

It is also possible to treat the shaped support without prior impregnation with an acid solution, the acidity being in this case provided by the aqueous liquid of the autoclave.

The acid aqueous solution comprises at least one acid compound making it possible to dissolve at least part of the alumina of the shaped support. The term "acid compound allowing to dissolve at least a part of the alumina of the support" means any acid compound which, brought into contact with the alumina support, carries out the dissolving of at least a part of the aluminum ions . The acid should preferably dissolve at least 0.5% by weight alumina from the alumina carrier.

Preferably, this acid is chosen from strong acids such as nitric acid, hydrochloric acid, perchloric acid, sulfuric acid or a weak acid used at a concentration such that its aqueous solution has a pH lower than 4, such as acetic acid, or a mixture of these acids.

According to a preferred mode, the hydrothermal treatment is carried out in the presence of nitric acid and acetic acid taken alone or in a mixture. The autoclave is preferably a rotating basket autoclave such as that defined in patent application EP-A-0387 109.

The hydrothermal treatment can also be carried out under saturated vapor pressure or under a partial water vapor pressure at least equal to 70% of the saturated vapor pressure corresponding to the treatment temperature.

Preferably the hydrothermal treatment is carried out at a temperature between 100°C and 800°C, preferably between 200°C and 700°C.

According to an essential aspect of the preparation process according to the invention, the hydrothermal treatment is carried out for a period of between 45 minutes and 150 minutes, preferably between 1 hour and 2 hours.

A duration of less than 45 minutes does not enable the "Oswald ripening phenomenon" to be implemented (phenomenon of re-dissolution of small alumina particles and increase of larger ones) and therefore renders hydrothermal treatment ineffective. The support thus obtained does not have adequate physico-chemical properties (Lewis and Bronsted acidity of surface -OH).

A treatment time of more than 150 minutes, however, leads to excessive Oswald ripening, and therefore to excessive aggregation of elementary alumina crystallites.

Preferably, the calcination step which takes place after the hydrothermal treatment by passage in an autoclave takes place at a temperature generally between 400° C. and 1500° C., preferably between 800° C. and 1300° C., generally for 1 hour. and 5 hours, in air, the water content of which is generally between 0 and 700 g of water per kilogram of dry air.

At the end of step c), the alumina obtained has the specific textural properties as described below.

Step d) Addition of the organic additive

According to step d) of the process for preparing the catalyst, the support is brought into contact with at least at least one organic additive comprising oxygen and/or nitrogen, preferably chosen from aldehydes containing from 1 to 14 carbon atoms per molecule (preferably from 2 to 12), ketones or polyketones containing from 3 to 18 (preferably from 3 to 12) carbon atoms per molecule, ethers or esters containing from 2 to 14 (from preferably from 3 to 12) carbon atoms per molecule, the alcohols or polyalcohols containing from 1 to 14 (preferably from 2 to 12) carbon atoms per molecule and the carboxylic acids or polycarboxylic acids containing from 1 to 14 (preferably from 1 to 12) carbon atoms per molecule. The organic additive can be composed of a combination of the various functional groups mentioned above.

Preferably, the organic additive is chosen from formic acid HCOOH, formaldehyde CH ₂ 0, acetic acid CH ₃ COOH, citric acid, oxalic acid, glycolic acid (HOOC-CH ₂ - OH), malonic acid (HOOC-CH ₂ -COOH), levulinic acid (CH ₃ CCH ₂ CH ₂ CO ₂ H), ethanol, methanol, ethyl formate HCOOC ₂ H ₅ , HCOOCH ₃ methyl formate, paraldehyde (CH ₃ -CHO) ₃ , acetaldehyde C ₂ H ₄ O, gamma-valerolactone acid (C ₅ H ₈ O ₂ ), glucose and sorbitol.

Particularly preferably, the organic additive is chosen from citric acid, formic acid, glycolic acid, levulinic acid and oxalic acid.

In one embodiment according to the invention, said step d) is carried out by bringing the support into contact with at least one organic additive in the form of a powder.

In another embodiment according to the invention, said step d) is carried out by bringing the support into contact with at least one organic additive in the form of a powder dissolved in a minimum amount of water. The term “minimum quantity of water” means the quantity of water allowing the at least partial dissolution of said organic additive in water. This minimum quantity of water cannot be assimilated to a solvent. In this case, and, when the step of introducing the additive is carried out separately from the introduction of the precursor of the active phase of the catalyst (i.e. steps d) and e) are carried out separately) each step of setting contact of the support with the organic additive is advantageously followed by drying at a temperature below 250°C, preferably between 15°C and 240°C, more preferably between 30°C and 220°C.

The bringing into contact according to step d) is generally carried out at a temperature between 0° C. and 70° C., preferably between 10° C. and 60° C., and in a particularly preferred manner at ambient temperature.

According to step d), the bringing into contact of said porous support and of the organic additive can be done by any method known to those skilled in the art. Preferably, convective mixers, drum mixers or static mixers can be used. Step d) is advantageously carried out for a period of between 5 minutes to 5 hours depending on the type of mixer used, preferably between 10 minutes and 4 hours. According to the invention, the molar ratio between the organic additive and the nickel is greater than 0.05 mol/mol, preferably between 0.1 and 5 mol/mol, more preferably between 0.12 and 3 mol/ mol, and even more preferably between 0.15 and 2.5 mol/mol.

Step e) Addition of the nickel-based active phase

According to step e), the alumina support is brought into contact with at least one nickel metal salt, at a temperature below the melting point of the metal salt, for a period advantageously between 5 minutes to 5 hours, to form a solid mixture, the mass ratio between said metal salt and the alumina support being between 0.1 and 2.3, preferably between 0.2 and 2.

Preferably, the melting point of said metal salt is between 20°C and 150°C. Preferably the metal salt is hydrated. Preferably, the metal salt is hexahydrated nickel nitrate (Ni(NC>3) _2.6H ₂ O, T fusion=56.7° C.).

According to step e), the contacting of said porous oxide support and the nickel metal salt can be done by any method known to those skilled in the art. Preferably, convective mixers, drum mixers or static mixers can be used. Step e) is advantageously carried out for a period of between 5 minutes to 5 hours depending on the type of mixer used, preferably between 10 minutes and 4 hours.

Implementation of steps d) and e)

According to the invention:

- steps d) and e) are carried out successively in this order, or

- Steps d) and e) are carried out simultaneously.

In a preferred embodiment, step d) is carried out before step e) is carried out.

Step f) Heating the solid mixture with stirring

According to step f), the mixture obtained at the end of steps d) and e) is heated with stirring to a temperature between the melting point of the metal salt and 200° C., and advantageously under atmospheric pressure. Preferably, the temperature is between 50°C and 100°C.

Advantageously, step f) is carried out for a period of between 5 minutes and 12 hours, preferably between 5 minutes and 4 hours. According to step f), the mechanical homogenization of the mixture can be done by any method known to those skilled in the art. Preferably, convective mixers, drum mixers or static mixers can be used. Even more preferentially, step f) is carried out by means of a drum mixer whose speed of rotation is between 4 and 70 revolutions/minute, preferably between 10 and 60 revolutions/minute. Indeed, if the rotation of the drum is too high, the active phase of the catalyst will not be distributed in a crust around the periphery of the support, but will be distributed homogeneously throughout the support, which is not desirable.

Step g) Drying of the catalyst precursor

Stage g) of drying the catalyst precursor obtained at the end of stage f) is carried out at a temperature below 250° C., preferably between 15° C. and 180° C., more preferably between 30° C. C and 160° C., even more preferably between 50° C. and 150° C., and even more preferably between 70° C. and 140° C., typically for a period of between 10 minutes and 24 hours. Longer durations are not excluded, but do not necessarily bring improvement. The drying temperature in step g) is generally higher than the heating temperature in step f). Preferably, the drying temperature of step g) is at least 10°C higher than the heating temperature of step f).

The drying step can be carried out by any technique known to those skilled in the art. It is advantageously carried out under an inert atmosphere or under an atmosphere containing oxygen or under a mixture of inert gas and oxygen. It is advantageously carried out at atmospheric pressure or at reduced pressure. Preferably, this step is carried out at atmospheric pressure and in the presence of air or nitrogen.

Step h) Heat treatment of the dried catalyst

The dried catalyst precursor undergoes an additional heat treatment step, before step i) optional reduction, at a temperature between 250 ° C and 1000 ° C and preferably between 250 ° C and 750 ° C, typically for a duration between 15 minutes and 10 hours, under an inert atmosphere or under an atmosphere containing oxygen, in the presence of water or not. Longer treatment times are not excluded, but do not bring necessary improvement.

The term “heat treatment” is understood to mean the temperature treatment respectively without the presence or in the presence of water. In the latter case, contact with water vapor can take place at atmospheric pressure or at autogenous pressure. Several cycles combined without presence or with the presence of water can be made. After this or these treatment(s), the catalyst precursor comprises nickel in the oxide form, that is to say in the NiO form.

In the event of the presence of water, the water content is preferably between 150 and 900 grams per kilogram of dry air, and even more preferably between 250 and 650 grams per kilogram of dry air.

Step i) Reduction with a reducing gas (optional step)

Prior to the use of the catalyst in the catalytic reactor and the implementation of a hydrogenation process, at least one stage of reducing treatment is advantageously carried out i) in the presence of a reducing gas after stage e) of so as to obtain a catalyst comprising nickel at least partially in metallic form.

This treatment makes it possible to activate said catalyst and to form metallic particles, in particular nickel in the zero valent state. Said reducing treatment can be carried out in-situ or ex-situ, that is to say after or before loading the catalyst into the hydrogenation reactor.

The reducing gas is preferably hydrogen. The hydrogen can be used pure or in a mixture (for example a hydrogen/nitrogen, or hydrogen/argon, or hydrogen/methane mixture). In the case where the hydrogen is used as a mixture, all the proportions are possible.

Said reducing treatment is carried out at a temperature comprised between 120°C and 500°C, preferably between 150°C and 450°C. When the catalyst does not undergo passivation, or undergoes a reducing treatment before passivation, the reducing treatment is carried out at a temperature between 180° C. and 500° C., preferably between 200° C. and 450° C., and even more preferably between 350°C and 450°C. When the catalyst has previously undergone passivation, the reducing treatment is generally carried out at a temperature of between 120°C and 350°C, preferably between 150°C and 350°C.

The duration of the reducing treatment is generally between 2 hours and 40 hours, preferably between 3 hours and 30 hours. The rise in temperature up to the desired reduction temperature is generally slow, for example fixed between 0.1° C./min and 10° C./min, preferably between 0.3° C./min and 7° C./min .

The hydrogen flow rate, expressed in L/hour/gram of catalyst, is between 0.01 and 100 L/hour/gram of catalyst, preferably between 0.05 and 10 L/hour/gram of catalyst, even more preferably between 0.1 and 5 L/hour/gram of catalyst. Catalyst

The catalyst obtained by the preparation process according to the invention comprises an active phase based on nickel, and an alumina support.

The nickel content in said catalyst is advantageously between 1 and 50% by weight relative to the total weight of the catalyst, more preferably between 2 and 40% by weight and even more preferably between 3 and 35% by weight and even more preferably 5 and 25% weight relative to the total weight of the catalyst. “% wt” values are based on the elemental form of nickel.

The specific surface of the catalyst is generally between 10 m ² /g and 200 m ² /g, preferably between 25 m ² /g and 110 m ² /g, more preferably between 40 m ² /g and 100 m ² /g.

The total pore volume of the catalyst is generally between 0.1 ml/g and 1 ml/g, preferably between 0.2 ml/g and 0.8 ml/g, and particularly preferably between 0.3 ml/g and 0.7 ml/g.

The size of the nickel particles, measured in oxide form, in the catalyst is less than 8 nm, preferably less than 7 nm, more preferably less than 6 nm, preferably less than 5 nm, and even more preferably between 2 and 4 nm. The active phase of the catalyst does not comprise any metal from group VI B. In particular, it does not comprise molybdenum or tungsten.

Said catalyst (and the support used for the preparation of the catalyst) is in the form of grains advantageously having a diameter of between 0.5 and 10 mm. The grains can have any shape known to those skilled in the art, for example the shape of beads (preferably having a diameter of between 1 and 8 mm), extrudates, tablets, hollow cylinders. Preferably, the catalyst (and the support used for the preparation of the catalyst) are in the form of extrudates with a diameter of between 0.5 and 10 mm, preferably between 0.8 and 3.2 mm and very preferably between 1.0 and 2.5 mm and length between 0.5 and 20 mm. The term “diameter” of the extrudates is understood to mean the diameter of the circle circumscribed to the cross section of these extrudates. The catalyst can advantageously be presented in the form of cylindrical, multi-lobed, tri-lobed or quadri-lobed extrudates. Preferably, its shape will be trilobed or quadrilobed. The shape of the lobes can be adjusted according to all known methods of the prior art.

Support

The characteristics of the alumina, mentioned in this section, correspond to the characteristics of the alumina before the addition of the organic additive (step d) and/or addition of the active phase of nickel (step e), ie the alumina support obtained at the end of step c) of the process for preparing the catalyst according to the invention.

According to the invention, the support is an alumina, that is to say that the support comprises at least 95%, preferably at least 98%, and in a particularly preferred manner at least 99% by weight of alumina relative to the weight of the medium. Alumina generally has a crystallographic structure of the delta, gamma or theta alumina type, alone or in a mixture.

According to the invention, the alumina support may comprise impurities such as metal oxides of groups MA, INB, IVB, NB, NIA, IVA according to the CAS classification, preferably silica, titanium dioxide, zirconium dioxide, zinc oxide, magnesium oxide and calcium oxide, or alternatively alkali metals, preferably lithium, sodium or potassium, and/or alkaline earth metals, preferably magnesium, calcium, strontium or barium or sulfur.

Advantageously, the sulfur content of the alumina support is between 0.001% and 2% by weight relative to the total weight of the alumina support, and the sodium content of said alumina support is between 0.001% and 2% by weight. relative to the total weight of said alumina gel.

The specific surface of the alumina is generally between 10 m ² /g and 250 m ² /g, preferably between 30 m ² /g and 200 m ² /g, more preferably between 50 m ² /g and 150 m ² /g.

The pore volume of the alumina is generally between 0.1 ml/g and 1.2 ml/g, preferably between 0.3 ml/g and 0.9 ml/g, and very preferably between 0.5ml/g and 0.9ml/g.

Selective hydrogenation process

The present invention also relates to a process for the selective hydrogenation of polyunsaturated compounds containing at least 2 carbon atoms per molecule, such as diolefins and/or acetylenics and/or alkenylaromatics, also called styrenics, contained in a charge of hydrocarbons having a final boiling point less than or equal to 300°C, which process is carried out at a temperature between 0 and 300°C, at a pressure between 0.1 MPa and 10 MPa, at a hydrogen molar ratio /(polyunsaturated compounds to be hydrogenated) of between 0.1 and 10 and at an hourly volume rate of between 0.1 and 200 lr ¹ when the process is carried out in the liquid phase, or at a molar ratio hydrogen/(polyunsaturated compounds to be hydrogenated ) between 0.5 and 1000 and at an hourly volume rate between 100 h ^-1 and 40000 h ^-1 when the process is carried out in the gas phase, in the presence of a catalyst obtained by the preparation process as described below before in the description. Monounsaturated organic compounds such as ethylene and propylene, for example, are the source of the manufacture of polymers, plastics and other value-added chemicals. These compounds are obtained from natural gas, naphtha or gas oil which have been treated by steam cracking or catalytic cracking processes. These processes are operated at high temperature and produce, in addition to the desired monounsaturated compounds, polyunsaturated organic compounds such as acetylene, propadiene and methylacetylene (or propyne), 1-2-butadiene and 1-3 -butadiene, vinylacetylene and ethylacetylene, and other polyunsaturated compounds whose boiling point corresponds to the C5+ cut (hydrocarbon compounds having at least 5 carbon atoms), in particular diolefinic or styrenic or indenic compounds. These polyunsaturated compounds are very reactive and lead to side reactions in the polymerization units. It is therefore necessary to eliminate them before recovering these cuts.

Selective hydrogenation is the main treatment developed to specifically remove unwanted polyunsaturated compounds from these hydrocarbon feedstocks. It allows the conversion of polyunsaturated compounds to the corresponding alkenes or aromatics while avoiding their total saturation and therefore the formation of the corresponding alkanes or naphthenes. In the case of steam cracked gasolines used as feed, selective hydrogenation also makes it possible to selectively hydrogenate alkenylaromatics into aromatics by avoiding the hydrogenation of aromatic rings.

The hydrocarbon feed treated in the selective hydrogenation process has a final boiling point less than or equal to 300°C and contains at least 2 carbon atoms per molecule and includes at least one polyunsaturated compound. The term “polyunsaturated compounds” means compounds comprising at least one acetylenic function and/or at least one diene function and/or at least one alkenylaromatic function.

More particularly, the feedstock is selected from the group consisting of a C2 steam cracking cut, a C2-C3 steam cracking cut, a C3 steam cracking cut, a C4 steam cracking cut, a C5 steam cracking cut and a steam cracking gasoline also called pyrolysis gasoline or C5+ cut.

The C2 cut from steam cracking, advantageously used for the implementation of the selective hydrogenation process according to the invention, has for example the following composition: between 40 and 95% by weight of ethylene, of the order of 0.1 to 5% by weight of acetylene, the remainder being essentially ethane and methane. In certain C2 cuts from steam cracking, between 0.1 and 1% by weight of C3 compounds may also be present. The C3 steam cracking cut, advantageously used for the implementation of the selective hydrogenation process according to the invention, has for example the following average composition: of the order of 90% by weight of propylene, of the order of 1 to 8% by weight of propadiene and methylacetylene, the remainder being essentially propane. In some C3 cuts, between 0.1 and 2% by weight of C2 compounds and C4 compounds may also be present.

A C2-C3 cut can also be advantageously used for implementing the selective hydrogenation process according to the invention. It has for example the following composition: of the order of 0.1 to 5% by weight of acetylene, of the order of 0.1 to 3% by weight of propadiene and methylacetylene, of the order of 30% by weight of ethylene, of the order of 5% by weight of propylene, the remainder being essentially methane, ethane and propane. This filler may also contain between 0.1 and 2% by weight of C4 compounds.

The C4 cut from steam cracking, advantageously used for the implementation of the selective hydrogenation process according to the invention, has for example the following average mass composition: 1% weight of butane, 46.5% weight of butene, 51% weight of butadiene, 1.3% by weight of vinylacetylene and 0.2% by weight of butyne. In some C4 cuts, between 0.1 and 2% by weight of C3 compounds and C5 compounds may also be present.

The C5 cut from steam cracking, advantageously used for carrying out the selective hydrogenation process according to the invention, has for example the following composition: 21% by weight of pentanes, 45% by weight of pentenes, 34% by weight of pentadienes.

The steam cracking gasoline or pyrolysis gasoline, advantageously used for the implementation of the selective hydrogenation process according to the invention, corresponds to a hydrocarbon cut whose boiling point is generally between 0 and 300° C., from preferably between 10°C and 250°C. The polyunsaturated hydrocarbons to be hydrogenated present in said steam cracked gasoline are in particular diolefinic compounds (butadiene, isoprene, cyclopentadiene, etc.), styrenic compounds (styrene, alpha-methylstyrene, etc.) and indene compounds (indene, etc.). ). Steam cracked gasoline generally comprises the C5-C12 cut with traces of C3, C4, C13, C14, C15 (for example between 0.1 and 3% by weight for each of these cuts). For example, a charge formed from pyrolysis gasoline generally has the following composition: 5 to 30% by weight of saturated compounds (paraffins and naphthenes), 40 to 80% by weight of aromatic compounds, 5 to 20% by weight of mono-olefins, 5 to 40% by weight of diolefins, 1 to 20% by weight of alkenylaromatic compounds, all the compounds forming 100%. It also contains from 0 to 1000 ppm by weight of sulphur, preferably from 0 to 500 ppm by weight of sulphur. Preferably, the charge of polyunsaturated hydrocarbons treated in accordance with the selective hydrogenation process according to the invention is a C2 cut from steam cracking, or a C2-C3 cut from steam cracking, or a gasoline from steam cracking.

The selective hydrogenation process according to the invention aims to eliminate said polyunsaturated hydrocarbons present in said charge to be hydrogenated without hydrogenating the monounsaturated hydrocarbons. For example, when said feed is a C2 cut, the selective hydrogenation process aims to selectively hydrogenate acetylene. When said feed is a C3 cut, the selective hydrogenation process aims to selectively hydrogenate propadiene and methylacetylene. In the case of a C4 cut, the aim is to eliminate the butadiene, vinylacetylene (VAC) and the butyne, in the case of a C5 cut, the aim is to eliminate the pentadienes. When said feed is a steam cracked gasoline, the selective hydrogenation process aims to selectively hydrogenate said polyunsaturated hydrocarbons present in said feed to be treated so that the diolefinic compounds are partially hydrogenated into mono-olefins and the styrenic and indenic compounds are partially hydrogenated to the corresponding aromatic compounds avoiding the hydrogenation of the aromatic rings.

The technological implementation of the selective hydrogenation process is for example carried out by injection, in ascending or descending current, of the charge of polyunsaturated hydrocarbons and hydrogen into at least one fixed-bed reactor. Said reactor can be of the isothermal type or of the adiabatic type. An adiabatic reactor is preferred. The charge of polyunsaturated hydrocarbons can advantageously be diluted by one or more re-injections) of the effluent, from said reactor where the selective hydrogenation reaction takes place, at various points of the reactor, located between the inlet and the outlet of the reactor in order to limit the temperature gradient in the reactor. The technological implementation of the selective hydrogenation process according to the invention can also be advantageously carried out by the implantation of at least said supported catalyst in a reactive distillation column or in reactors-exchangers or in a reactor of the slurry type. . The hydrogen flow can be introduced at the same time as the charge to be hydrogenated and/or at one or more different points of the reactor.

The selective hydrogenation of the C2, C2-C3, C3, C4, C5 and C5+ cuts from steam cracking can be carried out in the gaseous phase or in the liquid phase, preferably in the liquid phase for the C3, C4, C5 and C5+ cuts and in the carbonated for C2 and C2-C3 cuts. A reaction in the liquid phase makes it possible to lower the energy cost and to increase the cycle time of the catalyst. In general, the selective hydrogenation of a hydrocarbon charge containing polyunsaturated compounds containing at least 2 carbon atoms per molecule and having a final boiling point less than or equal to 300°C is carried out at a temperature between 0°C and 300°C, at a pressure between 0.1 MPa and 10 MPa, at a hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio between 0.1 and 10 and at an hourly volume rate (defined as the ratio of the volume flow rate of charge to the volume of the catalyst) of between 0.1 h ¹ and 200 h ^-1 for a process carried out in the liquid phase, or at a molar hydrogen/(polyunsaturated compounds to be hydrogenated) ratio comprised between 0.5 and 1000 and at an hourly volume rate of between 100 and 40,000 h ^-1 for a process carried out in the gas phase.

In one embodiment according to the invention, when a selective hydrogenation process is carried out in which the feedstock is a steam cracked gasoline comprising polyunsaturated compounds, the molar ratio (hydrogen)/(polyunsaturated compounds to be hydrogenated) is generally comprised between 0.5 and 10, preferably between 0.7 and 5.0 and even more preferably between 1.0 and 2.0, the temperature is between 0°C and 200°C, preferably between 20°C C and 200°C and even more preferably between 30°C and 180°C, the hourly volume velocity (VVH) is generally between 0.5 h ¹ and 100 h ¹ , preferably between 1 and 50 h ^-1 and the pressure is generally between 0.3 MPa and 8.0 MPa, preferably between 1.0 MPa and 7.0 MPa and even more preferably between 1.5 MPa and 4.0 MPa.

More preferably, a selective hydrogenation process is carried out in which the feedstock is a steam cracked gasoline comprising polyunsaturated compounds, the hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio is between 0.7 and 5.0, the temperature is between 20° C. and 200° C., the hourly volume velocity (VVH) is generally between 1 h ¹ and 50 h ^-1 and the pressure is between 1.0 MPa and 7.0 MPa.

Even more preferably, a selective hydrogenation process is carried out in which the feedstock is a steam cracked gasoline comprising polyunsaturated compounds, the hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio is between 1.0 and 2.0, the temperature is between 30° C. and 180° C., the hourly volume velocity (VVH) is generally between 1 h ^-1 and 50 h ^-1 and the pressure is between 1.5 MPa and 4.0 MPa. The hydrogen flow rate is adjusted in order to have a sufficient quantity of it to theoretically hydrogenate all of the polyunsaturated compounds and to maintain an excess of hydrogen at the reactor outlet.

In another embodiment according to the invention, when a selective hydrogenation process is carried out in which the feed is a C2 cut from steam cracking and/or a C2-C3 cut from steam cracking comprising polyunsaturated compounds, the molar ratio ( hydrogen)/(polyunsaturated compounds to be hydrogenated) is generally between 0.5 and 1000, preferably between 0.7 and 800, the temperature is between 0°C and 300°C, preferably between 15°C and 280° C, the hourly volume velocity (VVH) is generally between 100 h ¹ and 40,000 h ¹ , preferably between 500 h ^-1 and 30,000 h ^-1 and the pressure is generally between 0.1 MPa and 6.0 MPa, preferably between 0.2 MPa and 5.0 MPa.

Aromatics hydrogenation process

The present invention also relates to a process for the hydrogenation of at least one aromatic or polyaromatic compound contained in a charge of hydrocarbons having a final boiling point less than or equal to 650° C., generally between 20° C. and 650° C. °C, and preferably between 20°C and 450°C. Said hydrocarbon charge containing at least one aromatic or polyaromatic compound can be chosen from the following petroleum or petrochemical fractions: reformate from catalytic reforming, kerosene, light gas oil, heavy gas oil, cracking distillates, such as FCC recycle oil, coker diesel, hydrocracking distillates.

The content of aromatic or polyaromatic compounds contained in the hydrocarbon charge treated in the hydrogenation process according to the invention is generally between 0.1% and 80% by weight, preferably between 1% and 50% by weight, and most preferably between 2% and 35% by weight, the percentage being based on the total weight of the hydrocarbon charge. The aromatic compounds present in said hydrocarbon charge are, for example, benzene or alkylaromatics such as toluene, ethylbenzene, γ-xylene, m-xylene, or p-xylene, or alternatively aromatics having several aromatic rings (polyaromatics) such as naphthalene.

The sulfur or chlorine content of the charge is generally less than 5000 ppm by weight of sulfur or chlorine, preferably less than 100 ppm by weight, and in a particularly preferred manner less than 10 ppm by weight. The technological implementation of the process for the hydrogenation of aromatic or polyaromatic compounds is for example carried out by injection, in ascending or descending current, of the hydrocarbon charge and hydrogen into at least one fixed-bed reactor. Said reactor can be of the isothermal type or of the adiabatic type. An adiabatic reactor is preferred. The hydrocarbon charge can advantageously be diluted by one or more re-injection(s) of the effluent, from said reactor where the hydrogenation reaction of the aromatics takes place, at various points of the reactor, located between the inlet and the outlet of the reactor in order to limit the temperature gradient in the reactor. The technological implementation of the process for the hydrogenation of aromatics according to the invention can also be advantageously carried out by the implantation of at least said supported catalyst in a reactive distillation column or in reactors-exchangers or in a reactor of the slurries. The hydrogen flow can be introduced at the same time as the charge to be hydrogenated and/or at one or more different points of the reactor.

The hydrogenation of the aromatic or polyaromatic compounds can be carried out in the gas phase or in the liquid phase, preferably in the liquid phase. In general, the hydrogenation of aromatic or polyaromatic compounds is carried out at a temperature of between 30° C. and 350° C., preferably between 50° C. and 325° C., at a pressure of between 0.1 MPa and 20 MPa, preferably between 0.5 MPa and 10 MPa, at a hydrogen/(aromatic compounds to be hydrogenated) molar ratio between 0.1 and 10 and at an hourly volume rate of between 0.05 h ¹ and 50 h ¹ , preferably between 0.1 h ^-1 and 10 h ^-1 of a hydrocarbon charge containing aromatic or polyaromatic compounds and having a final boiling point less than or equal to 650°C, generally between 20°C and 650°C, and preferably between 20°C and 450°C.

The hydrogen flow is adjusted in order to have a sufficient quantity of it to theoretically hydrogenate all the aromatic compounds and to maintain an excess of hydrogen at the reactor outlet.

The conversion of the aromatic or polyaromatic compounds is generally greater than 20% by mole, preferably greater than 40% by mole, more preferably greater than 80% by mole, and in a particularly preferred manner greater than 90% by mole of the aromatic compounds or polyaromatics contained in the hydrocarbon charge. The conversion is calculated by dividing the difference between the total moles of the aromatic or polyaromatic compounds in the hydrocarbon feed and in the product by the total moles of the aromatic or polyaromatic compounds in the hydrocarbon feed.

According to a particular variant of the process according to the invention, a process is carried out for the hydrogenation of benzene from a hydrocarbon charge, such as the reformate from a unit catalytic reforming. The benzene content in said hydrocarbon charge is generally between 0.1 and 40% by weight, preferably between 0.5 and 35% by weight, and particularly preferably between 2 and 30% by weight, the percentage by weight being based on the total weight of the hydrocarbon charge.

The sulfur or chlorine content of the charge is generally less than 10 ppm by weight of sulfur or chlorine respectively, and preferably less than 2 ppm by weight.

The hydrogenation of the benzene contained in the hydrocarbon charge can be carried out in the gaseous phase or in the liquid phase, preferably in the liquid phase. When it is carried out in the liquid phase, a solvent may be present, such as cyclohexane, heptane, octane. In general, the hydrogenation of benzene is carried out at a temperature between 30° C. and 250° C., preferably between 50° C. and 200° C., and more preferably between 80° C. and 180° C. C, at a pressure between 0.1 MPa and 10 MPa, preferably between 0.5 MPa and 4 MPa, at a hydrogen/(benzene) molar ratio between 0.1 and 10 and at an hourly volume rate between 0 .05 h ¹ and 50 h ¹ , preferably between 0.5 h ^-1 and 10 h ¹ .

The conversion of benzene is generally greater than 50 mol%, preferably greater than 80 mol%, more preferably greater than 90 mol% and particularly preferably greater than 98 mol%.

The invention will now be illustrated via the examples below which are in no way limiting.

Examples

Example 1: Preparation of alumina AL-1

An alumina gel is synthesized via a mixture of sodium aluminate and aluminum sulphate. The precipitation reaction takes place at a temperature of 60° C., at a pH of 9, for 60 min and with stirring at 200 rpm.

The gel thus obtained undergoes mixing on a Z-arm mixer to provide the paste. Extrusion is carried out by passing the paste through a die fitted with 1.6 mm diameter orifices in the shape of trilobes. The extrudates thus obtained are dried at 150° C. and then calcined at 450° C. in dry air.

The extrudate undergoes a hydrothermal treatment at 200°C in the presence of an aqueous solution of acetic and nitric acid at 6.5% by weight for 90 minutes in an autoclave, then is calcined in dry air at 1000°C for 2 hours in tubular reactor. Alumina AL-1 is obtained. Example 1bis: Preparation of alumina AL-2

The extrudate then undergoes a calcining step in dry air at 650°C for 2 hours in a tubular reactor. Alumina AL-2 is obtained.

Example 1ter: Preparation of alumina AL-3

The extrudate undergoes a hydrothermal treatment at 200°C in the presence of an aqueous solution of acetic and nitric acid at 6.5% by weight for 180 minutes (3 hours) in an autoclave, then is calcined in dry air at 1000°C for 2 hours in a tubular reactor. Alumina AL-3 is obtained.

Example 2: Preparation of an aqueous solution of Ni precursors

The aqueous solution of Ni precursors (solution S) used for the preparation of catalyst E is prepared by dissolving 43.5 grams (g) of nickel nitrate (N1NO ₃ , supplier Strem Chemicals®) in a volume of 13 mL of distilled water. The solution S is obtained, the Ni concentration of which is 350 g of Ni per liter of solution.

Example 3 (compliant) alumina AL-1 + citric acid + Ni molten salt

10 g of AL-1 alumina support are brought into contact with 1.18 g of citric acid dissolved in 5.4 g of water. The solid thus obtained is then dried in an oven for 2 hours at 60°C then 12 hours at 120°C.

Then, the support is brought into contact with 9.47 g of hexahydrated nickel nitrate in a drum rotating at a speed of 40 to 50 revolutions per minute and at a temperature of 62° C. for 15 minutes. The molar ratio by weight between citric acid and nickel is 0.2. The nickel content aimed at in this stage is 22% by weight of Ni relative to the weight of the final catalyst. The solid thus obtained is then dried in an oven overnight at 120° C., then calcined under an air flow of 1 L/h/g of catalyst at 450° C. for 2 hours.

Catalyst A containing 22% by weight of the element nickel relative to the total weight of the catalyst is obtained. The characteristics of catalyst A thus obtained are reported in Table 1 below.

Example 4 (non-compliant): alumina AL-2 + citric acid + molten salt Ni

10 g of AL-2 alumina support are brought into contact with 1.18 g of citric acid dissolved in 5.4 g of water. The solid thus obtained is then dried in an oven for 2 hours at 60°C then 12 hours at 120°C.

Then, the support is brought into contact with 9.47 g of hexahydrated nickel nitrate in a drum rotating at a speed of 40 to 50 revolutions per minute and at a temperature of 62° C. for 15 minutes. The molar ratio by weight between citric acid and nickel is 0.2.

The nickel content targeted in this step is 22% by weight of Ni relative to the weight of the final catalyst. The solid thus obtained is then dried in an oven overnight at 120°C, then calcined under an air flow of 1 L/h/g of catalyst at 450°C for 2 hours.

Catalyst B containing 15% by weight of the element nickel relative to the total weight of the catalyst is obtained. The characteristics of catalyst B thus obtained are reported in Table 1 below.

Example 5 (non-compliant): alumina AL-3 + citric acid + molten salt Ni

10 g of AL-3 alumina support are brought into contact with 1.18 g of citric acid dissolved in 5.4 g of water. The solid thus obtained is then dried in an oven for 2 hours at 60°C then 12 hours at 120°C.

Catalyst C containing 15% by weight of the element nickel relative to the total weight of the catalyst is obtained. The characteristics of catalyst C thus obtained are reported in Table 1 below. Example 6 (non-compliant): alumina AL-1 + citric acid + Ni molten salt + final hydrothermal treatment

Catalyst D containing 22% by weight of the element nickel relative to the total weight of the catalyst is obtained.

At the end of the impregnation of the aqueous solution containing formic acid, the catalyst precursor undergoes a heat treatment at 150° C. for 2 hours under a flow of air containing 50 grams of water per kilogram of air. dry with a flow rate of 1 L/h/g of catalyst, then for 1 hour at 120° C. under a flow of dry air.

The characteristics of catalyst D thus obtained are reported in Table 1 below.

Example 7 (non-compliant): alumina AL-1 + citric acid + Ni solution (example 2)

The solid obtained is then dry impregnated with the solution S described in Example 2 in a drum rotating at a speed of 40 to 50 revolutions per minute and at a temperature of 62° C. for 15 minutes. The citric acid to Ni molar ratio is 0.2.

The Ni content aimed at in this step is 15% by weight of Ni relative to the weight of the final catalyst. The solid thus obtained is then dried in an oven overnight at 120°C, then calcined under an air flow of 1 L/h/g of catalyst at 450°C for 2 hours.

Catalyst E containing 15% by weight of the element nickel relative to the total weight of the catalyst is obtained. The characteristics of catalyst E thus obtained are reported in Table 1 below. In a dry impregnation it is not possible to obtain 22% weight of Ni (limited nickel nitrate solubility). Example 8 (non-compliant): alumina AL-1+ molten salt

10 g of AL-1 alumina support is brought into contact with 9.47 g of hexahydrated nickel nitrate in a drum rotating at a speed of 40 to 50 revolutions per minute and at a temperature of 62° C. for 15 minutes . The nickel content targeted in this step is 22% by weight of Ni relative to the weight of the final catalyst. The solid thus obtained is then dried in an oven overnight at 120°C, then calcined under an air flow of 1 L/h/g of catalyst at 450°C for 2 hours.

Catalyst F containing 22% by weight of the element nickel relative to the total weight of the catalyst is obtained. The characteristics of catalyst F thus obtained are reported in Table 1 below.

Table 1

Example 9: Catalytic tests: performances in selective hydrogenation of a mixture containing styrene and isoprene (AHYDI)

Catalysts A to F described in the examples above are tested against the selective hydrogenation reaction of a mixture containing styrene and isoprene.

The composition of the charge to be selectively hydrogenated is as follows: 8% by weight styrene (Sigma Aldrich® supplier, purity 99%), 8% by weight isoprene (Sigma Aldrich® supplier, purity 99%), 84% by weight n-heptane (solvent ) (VWR® supplier, purity > 99% chromanorm HPLC). This feed also contains very low sulfur compounds: 10 ppm wt of sulfur introduced in the form of pentanethiol (Fluka® supplier, purity > 97%) and 100 ppm wt of sulfur introduced in the form of thiophene (Merck® supplier, purity 99 %). This composition corresponds to the initial composition of the reaction mixture. This mixture of model molecules is representative of a pyrolysis gasoline.

The selective hydrogenation reaction is carried out in a 500 mL stainless steel autoclave, fitted with a mechanical stirrer with magnetic drive and capable of operate under a maximum pressure of 100 bar (10 MPa) and temperatures between 5°C and 200°C.

Prior to its introduction into the autoclave, a quantity of 3 ml_ of catalyst is reduced ex situ under a flow of hydrogen of 1 L/h/g of catalyst, at 400°C for 16 hours (temperature rise ramp of 1° C./min), then it is transferred to the autoclave, in the absence of air. After adding 214 ml_ of n-heptane (VWR® supplier, purity > 99% chromanorm HPLC), the autoclave is closed, purged, then pressurized under 35 bar (3.5 MPa) of hydrogen, and brought to the temperature of the test equal to 30°C. At time t=0, approximately 30 g of a mixture containing styrene, isoprene, n-heptane, pentanethiol and thiophene are introduced into the autoclave. The reaction mixture then has the composition described above and stirring is started at 1600 rpm. The pressure is kept constant at 35 bar (3.5 MPa) in the autoclave using a reservoir bottle located upstream of the reactor.

The progress of the reaction is monitored by taking samples from the reaction medium at regular time intervals: the styrene is hydrogenated to ethylbenzene, without hydrogenation of the aromatic ring, and the isoprene is hydrogenated to methyl-butenes. If the reaction is prolonged longer than necessary, the methyl-butenes are in turn hydrogenated to isopentane. Hydrogen consumption is also monitored over time by the decrease in pressure in a reservoir bottle located upstream of the reactor. The catalytic activity is expressed in moles of H ₂ consumed per minute and per gram of Ni.

The catalytic activities measured for catalysts A to F are reported in Table 2 below. They are related to the catalytic activity (AHYDI) measured for catalyst F.

Table 2

Catalyst A obtained by the process according to the invention has both a high Ni content and is of small size, which leads to a very high selective hydrogenation activity. The use of an alumina different from that according to the invention does not make it possible to obtain high Ni content on the final catalyst (catalyst B) which therefore leads to lower catalytic performance. A dry impregnation on the support (catalyst E) also does not make it possible to obtain a catalyst with better performance in selective hydrogenation than that of catalyst A. In addition, too long a hydrothermal treatment of the alumina (3 hours) does not make it possible to obtain the adequate physico-chemical and textural properties. Thus, catalyst C does not have an optimum Ni content for the same quantity of molten salts used at the start. Catalyst D has a larger particle size than desired due to the heat treatment after impregnation. The performance of this catalyst is therefore very much behind compared to catalyst A prepared by the process according to the invention. Dry impregnation does not make it possible to obtain a Ni content above 15% by weight, which explains the shrinking performance of catalyst E. For catalyst F, citric acid was not added, which which leads to a very low activity due to the size of the nickel particles of 14 nm.

Claims

1. Process for the preparation of a catalyst comprising an active phase based on nickel and an alumina support, said active phase not comprising any group VI B metal, said catalyst comprising a nickel element content greater than or equal to 1 % by weight and less than or equal to 50% by weight relative to the total weight of the catalyst, the size of the nickel particles in the catalyst, measured in oxide form, is less than 8 nm, said method comprising the following steps: a) supplies an alumina gel; b) the alumina gel of step a) is shaped; c) the shaped alumina gel obtained at the end of step b) is subjected to a heat treatment comprising at least one hydrothermal treatment step in an autoclave in the presence of an acid solution, at a temperature between between 100°C and 800°C for a time of between 45 minutes and 150 minutes, and at least one calcining step, at a temperature of between 400°C and 1500°C, carried out after the hydrothermal treatment step, for obtaining an alumina support; d) the alumina support is brought into contact with at least one organic additive comprising oxygen and/or nitrogen, the molar ratio between the organic additive and the nickel being greater than 0.05 mol/mol ; e) the alumina support is brought into contact with at least one nickel metal salt, at a temperature below the melting point of said nickel metal salt, to form a solid mixture, the mass ratio between said metal salt and the alumina support being between 0.1 and 2.3, steps d) and e) being carried out either successively in this order, or simultaneously; f) the solid mixture obtained at the end of steps d) and e) is heated with stirring to a temperature between the melting point of said metal salt and 200° C., to obtain a catalyst precursor; g) the catalyst precursor is dried at the end of step f) at a temperature below 250° C. to obtain a dried catalyst precursor; h) a step of heat treatment of the dried catalyst precursor obtained at the end of step g) is carried out at a temperature of between 250°C and 1000°C.

2. Process according to claim 1, in which the melting temperature of said metal salt is between 20°C and 150°C.

3. Method according to one of claims 1 or 2, wherein the molar ratio between said organic additive introduced in step d) and the nickel element introduced in step e) is between 0.1 and 5, 0 mol/mol.

4. Method according to any one of claims 1 to 3, in which steps d) and e) are carried out simultaneously.

5. Process according to any one of claims 1 to 4, in which the organic additive is chosen from aldehydes containing 1 to 14 carbon atoms per molecule, ketones or polyketones containing 3 to 18 carbon atoms per molecule, ethers and esters containing 2 to 14 carbon atoms per molecule, alcohols or polyalcohols containing 1 to 14 carbon atoms per molecule and carboxylic acids or polycarboxylic acids containing 1 to 14 carbon atoms per molecule, or a combination of the different groups functional above

6. Method according to any one of claims 1 to 5, wherein said organic additive is chosen from formic acid, formaldehyde, acetic acid, citric acid, oxalic acid, glycolic acid, malonic acid, levulinic acid, ethanol, methanol, ethyl formate, methyl formate, paraldehyde, acetaldehyde, gamma-valerolactone acid, glucose and sorbitol.

7. Process according to claim 6, in which the organic additive is chosen from citric acid, formic acid, glycolic acid, levulinic acid and oxalic acid.

8. Method according to any one of claims 1 to 7, in which step f) is carried out by means of a drum operating at a speed of between 4 and 70 revolutions per minute.

9. Method according to any one of claims 1 to 8, wherein in step e) the mass ratio between said metal salt and the alumina support is between 0.2 and 2.

10. Method according to any one of claims 1 to 9, wherein in step c) the duration of the hydrothermal treatment is carried out between 1 hour and 2 hours.

11. Process according to any one of claims 1 to 10, in which the alumina obtained at the end of step c) comprises a specific surface of between 10 m ² /g and 250 m ² /g.

12. Process according to any one of claims 1 to 11, in which the size of the nickel particles in the catalyst, measured in oxide form, is between 2 nm and 4 nm.