WO2019011566A1

WO2019011566A1 - Selective hydrogenation method using a catalyst obtained by comulling comprising a specific support

Info

Publication number: WO2019011566A1
Application number: PCT/EP2018/065726
Authority: WO
Inventors: Malika Boualleg; Anne-Claire Dubreuil
Original assignee: IFP Energies Nouvelles
Priority date: 2017-07-13
Filing date: 2018-06-13
Publication date: 2019-01-17
Also published as: FR3068982A1

Abstract

A method for selective hydrogenating of polyunsaturated compounds containing at least 2 carbon atoms per molecule, contained in a hydrocarbon feedstock having a final boiling point less than or equal to 300°C in the presence of a catalyst comprising an oxide matrix having a calcined alumina content greater than or equal to 90% by weight with respect to the total weight of said matrix, and an active phase comprising nickel, said active phase being comulled within said largely calcined aluminised oxide matrix, the content of nickel being between 1 and 65% by weight of said element with respect to the total weight of the catalyst, the nickel particles having a diameter less than 15 nm, said catalyst having a median mesoporous diameter between 3 and 25 nm, a macroporous median diameter between 50 and 300 nm, a mesoporous volume measured by mercury porosimetry greater than or equal to 0.40 mL/g and a total porous volume measured by mercury porosimetry greater than or equal to 0.45 mL/g.

Description

SELECTIVE HYDROGENATION PROCESS USING A CATALYST OBTAINED BY COMALAXING COMPRISING A SPECIFIC SUPPORT

Technical area

The subject of the invention is a process for the selective hydrogenation of polyunsaturated compounds in a hydrocarbon feedstock, in particular in steam-cracked C2-C5 cuts and steam-cracking gasolines, in the presence of a nickel-based catalyst supported on a carrier. alumina having a very connected porosity, that is to say having a very large number of adjacent pores.

STATE OF THE ART The most active catalysts in hydrogenation reactions are conventionally based on noble metals such as palladium or platinum. These catalysts are used industrially in refining and in petrochemistry for the purification of certain petroleum fractions by hydrogenation, especially in selective hydrogenation reactions of polyunsaturated molecules such as diolefins, acetylenics or alkenylaromates. It is often proposed to substitute palladium for nickel, a less active metal than palladium, which is therefore necessary to have a larger quantity in the catalyst. Thus, nickel-based catalysts generally have a metal content of between 5 and 60 wt.% Nickel relative to the catalyst.

The speed of the hydrogenation reaction is governed by several criteria, such as the diffusion of the reagents on the surface of the catalyst (external diffusional limitations), the diffusion of the reagents in the porosity of the support towards the active sites (internal diffusion limitations) and the intrinsic properties of the active phase such as the size of the metal particles and the distribution of the active phase within the support.

With regard to the internal diffusion limitations, it is important that the porous distribution of the macropores and mesopores is adapted to the desired reaction in order to ensure the diffusion of the reagents in the porosity of the support towards the active sites as well as the diffusion of the formed products. outwards. The importance of a suitable porous distribution and in particular the presence of macropores in a selective hydrogenation reaction of a pyrolysis gasoline in the case of a palladium-based catalyst has for example been described by Z. Zhou, T. Zeng, Z. Cheng, W. Yuan, in AICHE Journal, 201 1, Vol. 57, No. 8, pages 2198-2206.

As regards the size of the metal particles, it is generally accepted that the catalyst is all the more active as the size of the metal particles is small. Moreover, he It is important to obtain a particle size distribution centered on the optimum value and a narrow distribution around this value.

The often important content of nickel in the hydrogenation catalysts requires particular synthetic routes.

The most conventional way of preparing these catalysts is the impregnation of the support with an aqueous solution of a nickel precursor, followed generally by drying and calcination. Before their use in hydrogenation reactions these catalysts are generally reduced in order to obtain the active phase which is in metallic form (that is to say in the state of zero valence). The nickel-based catalysts on alumina prepared by a single impregnation step generally make it possible to attain nickel contents of between 12 and 15% by weight of nickel, depending on the pore volume of the alumina used. When it is desired to prepare catalysts having a higher nickel content, several successive impregnations are often necessary to obtain the desired nickel content, followed by at least one drying step, then possibly a calcination step between each impregnation. . Thus, the document WO201 1/080515 describes a catalyst based on nickel on hydrogenation-active alumina, in particular aromatics, said catalyst having a nickel content greater than 35% by weight, and a large dispersion of nickel metal on the surface of a metal. alumina with very open porosity and high surface area. The catalyst is prepared by at least four successive impregnations. The preparation of nickel catalysts having a high nickel content by the impregnation route thus involves a sequence of numerous steps which increases the associated manufacturing costs.

Another route of preparation also used to obtain catalysts with a high nickel content is coprecipitation. The coprecipitation generally consists of a simultaneous casting in a batch reactor of both an aluminum salt (aluminum nitrate for example) and a nickel salt (nickel nitrate for example). Both salts precipitate simultaneously. Then calcination at high temperature is necessary to make the transition from alumina gel (boehmite for example) to alumina. By this preparation route, contents up to 70% by weight of nickel are reached. Catalysts prepared by coprecipitation are described, for example, in US 4,273,680, US Pat. No. 5,518,851 and US 2010/01 16717.

Finally, it is also known the preparation route by comalaxing. Comalaxing generally consists of a mixture of a nickel salt with an alumina gel such as boehmite, said mixture being subsequently shaped, generally by extrusion, then dried and calcined. US 5,478,791 discloses a nickel-on-alumina catalyst having a nickel content of 10 to 60 wt.% And a nickel particle size. between 15 and 60 nm, prepared by comalaxing a nickel compound with an alumina gel, followed by shaping, drying and reduction.

The Applicant has discovered that a catalyst prepared by comalaxing an active phase of nickel with an alumina resulting from the calcination of a particular alumina gel prepared according to the preparation process described below, makes it possible to obtain a catalyst which has a porous distribution and a size of nickel particles particularly suitable for selective hydrogenation reactions of polyunsaturated molecules such as diolefins, acetylenic and / or alkenylaromatic. The resulting porous distribution of the method of preparation by comalaxing a calcined aluminum oxide matrix obtained from a specific alumina gel, and in particular the presence of macropores, makes it possible to provide a porosity that is particularly suitable for promoting the diffusion of the reagents into the porous medium and then their reaction with the active phase. In fact, in addition to the reduction in the number of stages and therefore in the manufacturing cost, the advantage of a comalaxing compared to an impregnation is that it avoids any risk of reducing the pore volume, or even partial blockage of the porosity of the support during the deposition of the active phase and thus the appearance of internal diffusion limitations.

The catalyst used in the context of the selective hydrogenation process according to the invention has the particularity of being able to contain high amounts of active phase. Indeed, the fact of preparing the catalyst according to the invention by comalaxing makes it possible to strongly charge this catalyst in the active phase in a single pass.

It is important to emphasize that the catalyst used in the context of the selective hydrogenation process according to the invention differs structurally from a catalyst obtained by simply impregnating a metal precursor on the alumina support in which the alumina forms the support and the active phase is introduced into the pores of this support. Without wishing to be bound by any theory, it appears that the process for preparing the catalyst used in the selective hydrogenation process according to the invention by comalaxing a particular aluminous porous oxide with one or more nickel precursors of the active phase allows to obtain a composite in which the nickel particles and alumina are intimately mixed thus forming the structure of the catalyst with a porosity and an active phase content adapted to the desired reactions.

Objects of the invention The subject of the present invention is a process for the selective hydrogenation of polyunsaturated compounds containing at least 2 carbon atoms per molecule, such as diolefins and / or acetylenes and / or alkenyl aromatics, contained in a hydrocarbon feed having a point final boiling point less than or equal to 300 ° C., which process is carried out at a temperature of between 0 and 300 ° C., at a pressure of between 0.1 and 10 MPa, at a molar ratio of hydrogen / (polyunsaturated compounds to be hydrogenated) ) between 0.1 and 10 and at a hourly volume velocity of between 0.1 and 200 h ^-1 when the process is carried out in the liquid phase, or at a molar ratio of hydrogen / (polyunsaturated compounds to be hydrogenated) of between 0, 5 and 1000 and at an hourly space velocity between 100 and 40000 h ^-1 when the process is carried out in the gas phase, in the presence of a catalyst comprising an oxide matrix having a cullet alumina content it is greater than or equal to 90% by weight relative to the total weight of said matrix, and an active phase comprising nickel, said active phase being comalaxed within said predominantly calcined aluminum oxide matrix, the nickel content being between 1 and 65 % weight of said element relative to the total weight of the catalyst, said active phase not comprising a group VIB metal, the nickel particles having a diameter of less than 15 nm, said catalyst having a median mesoporous diameter of between 3 and 25 nm, a median macroporous diameter between 50 and 300 nm, a mesoporous volume measured by mercury porosimetry greater than or equal to 0.40 ml / g and a total pore volume measured by mercury porosimetry greater than or equal to 0.45 ml / g.

Advantageously, the catalyst comprises a macroporous volume of between 0.05 and 0.3 mIg.

Preferably, the nickel content is between 5 and 55% by weight relative to the total weight of the catalyst.

Advantageously, the catalyst comprises a mesoporous volume of between 0.45 and 0.65 ml / g.

Preferably, the catalyst comprises a median mesoporous diameter of between 4 and 23 nm.

Advantageously, the catalyst comprises a median macroporous diameter of between 80 and 250 nm.

Advantageously, the catalyst does not comprise micropores.

Preferably, the catalyst comprises an oxide matrix consisting of alumina.

Preferably, the catalyst used in the context of the hydrogenation process according to the invention is prepared by at least the following stages:

a) at least a first step of precipitating alumina, in an aqueous reaction medium, of at least one basic precursor chosen from sodium aluminate, potassium aluminate, aqueous ammonia, sodium hydroxide and potassium hydroxide and at least an acid precursor selected from aluminum sulphate, aluminum chloride, aluminum nitrate, sulfuric acid, hydrochloric acid, and nitric acid, wherein at least one of the basic precursors or acid comprises aluminum, the relative flow rate of the acidic and basic precursors is chosen so as to obtain a pH of the reaction medium of between 8.5 and 10.5 and the flow rate of the acidic and basic precursor (s) containing aluminum. is set so as to obtain a progress rate of said first step of between 40 and 100%, the feed rate being defined as the proportion of alumina formed in Al ₂ 0 ₃ equivalent during said first precipitation step relative to the total amount of alumina formed at the end of step c) of the preparation process, said first precipitation step operating at a temperature of between 10 and 50 ° C., and for a duration of between 2 minutes and 30 minutes ;

b) a step of heat treatment of the suspension heated to a temperature between 50 and 200 ° C for a period of between 30 minutes and 5 hours to obtain an alumina gel;

c) a filtration step of the suspension obtained at the end of the heat treatment step b), followed by at least one washing step of the gel obtained;

d) a step of drying the alumina gel obtained at the end of step c) to obtain a powder;

e) a step of heat treatment of the powder obtained at the end of step d) at a temperature of between 500 and 1000 ° C., with or without a flow of air containing up to 60% by volume of water, to obtain a calcined aluminous porous oxide;

f) a step of kneading the calcined aluminous porous oxide obtained in step e) with a solution comprising at least one nickel precursor to obtain a paste;

g) a step of shaping the paste obtained;

h) a step of drying the shaped dough at a temperature between 15 and 250 ° C to obtain a dried catalyst.

In an embodiment according to the invention, in which in the case where the advancement rate obtained at the end of the first precipitation step a) is less than 100%, said preparation method comprises a second precipitation step a ') after the first precipitation step a).

Advantageously, the sulfur content of the alumina gel obtained at the end of step b) is between 0.001% and 2% by weight relative to the total weight of the alumina gel, and the sodium content of said gel of alumina is between 0.001% and 2% by weight relative to the total weight of said alumina gel.

Preferably, at least one step i) of heat treatment of the dried catalyst obtained at the end of step h) is carried out at a temperature of between 250 and 1000 ° C., in the presence or absence of water. Advantageously, at least one reducing treatment step j) is carried out in the presence of a reducing gas after steps h) or i) so as to obtain a catalyst comprising nickel at least partially in metallic form.

In one embodiment according to the invention, the filler is chosen from a C2 steam cracking cut or a C2-C3 steam cracking cut, and in which the molar ratio (hydrogen) / (polyunsaturated compounds to be hydrogenated) is between 0.degree. , 5 and 1000, the temperature is between 0 and 300 ° C, the hourly volume velocity (VVH) is between 100 and 40000 h ^"1 , and the pressure is between 0.1 and 6.0 MPa.

In another embodiment according to the invention, the filler is chosen from steam cracking gasolines and in which the molar ratio (hydrogen) / (polyunsaturated compounds to be hydrogenated) is between 0.5 and 10, the temperature is between 0 and 200 ° C, the hourly volume velocity (VVH) is between 0.5 and 100 h ^"1 , and the pressure is between 0.3 and 8.0 MPa Detailed description of the invention

1. Definitions

"Macropores" means pores whose opening is greater than 50 nm.

By "mesopores" is meant pores whose opening is between 2 nm and 50 nm, limits included. By "micropores" is meant pores whose opening is less than 2 nm.

By total pore volume of the catalyst or the support used for the preparation of the catalyst according to the invention is meant the volume measured by mercury porosimeter intrusion according to the ASTM D4284-83 standard at a maximum pressure of 4000 bar (400 MPa), using a surface tension of 484 dyne / cm and a contact angle of 140 °. The anchoring angle was taken equal to 140 ° according to the recommendations of the book "Techniques of the engineer, treated analysis and characterization", pages 1050-1055, written by Jean Charpin and Bernard Rasneur.

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

The volume of macropores and mesopores is measured by mercury intrusion porosimetry according to 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 value at which mercury fills all the intergranular voids is fixed at 0.2 MPa, and it is considered that beyond this mercury enters the pores of the sample.

The macroporous volume of the catalyst or support used for the preparation of the catalyst according to the invention is defined as the cumulative volume of mercury introduced at a pressure of between 0.2 MPa and 30 MPa, corresponding to the volume contained in the pores of diameter apparent greater than 50 nm.

The mesoporous volume of the catalyst or support used for the preparation of the catalyst according to the invention is defined as the cumulative volume of mercury introduced at a pressure of between 30 MPa and 400 MPa, corresponding to the volume contained in the pores of apparent diameter included between 2 and 50 nm.

The micropore volume is measured by nitrogen porosimetry. The quantitative analysis of the microporosity is carried out using the "t" method (Lippens-De Boer method, 1965) which corresponds to a transformation of the starting adsorption isotherm as described in the book "Adsorption by powders and porous solids. Principles, methodology and applications "written by F. Rouquérol, J. Rouquérol and K. Sing, Academy Press, 1999.

The mesoporous median diameter is also defined as being the diameter such that all the pores, among all the pores constituting the mesoporous volume, of size less than this diameter constitute 50% of the total mesoporous volume determined by intrusion into the mercury porosimeter.

The macroporous median diameter is also defined as the diameter such that all the pores, among all the pores constituting the macroporous volume, of size less than this diameter constitute 50% of the total macroporous volume determined by intrusion into the mercury porosimeter. The specific surface of the catalyst or support used for the preparation of the catalyst according to the invention is understood to mean the BET specific surface area determined by nitrogen adsorption in accordance with ASTM D 3663-78 established from the BRUNAUER-EMMETT method. -TELLER described in the periodical "The Journal of American Society", 60, 309, (1938). In the following, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief DR Lide, 81 st edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUPAC classification. 2. Description

Selective hydrogenation process

The present invention 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 hydrocarbon feed having a final boiling point less than or equal to 300 ° C., which process is carried out at a temperature of between 0 and 300 ° C., at a pressure of between 0.1 and 10 MPa, at a molar ratio of hydrogen / (polyunsaturated compounds) to hydrogenate) between 0.1 and 10 and at a hourly space velocity of between 0.1 and 200 h ^-1 when the process is carried out in the liquid phase, or at a molar ratio of hydrogen / (polyunsaturated compounds to be hydrogenated) between 0.5 and 1000 and at a hourly space velocity between 100 and 40000 h ^-1 when the process is carried out in the gas phase, in the presence of a catalyst as described below in the desc said catalyst being prepared by a specific method of preparation as described below in the description.

Monounsaturated organic compounds such as, for example, ethylene and propylene, are at 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 spurious reactions in the polymerization units. It is therefore necessary to eliminate them before valuing these cuts. Selective hydrogenation is the main treatment developed to specifically remove undesired polyunsaturated compounds from these hydrocarbon feeds. It allows the conversion of the polyunsaturated compounds to the corresponding alkenes or aromatics, avoiding their total saturation and thus the formation of the corresponding alkanes or naphthenes. In the case of steam crackers used as filler, selective hydrogenation also allows to selectively hydrogenate alkenyl aromatics to aromatics by avoiding the hydrogenation of aromatic rings.

The hydrocarbon feedstock 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 comprises 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 filler is selected from the group consisting of a C2 steam cracking cut, a C2-C3 steam cracking cut, a steam cracking C3 cut, a steam cracking C4 cut, a steam cracking C5 cut and a still called steam cracking gasoline. pyrolysis gasoline or C5 + cut.

The steam cracking section C2, advantageously used for carrying out 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 steam cracking sections, between 0.1 and 1% by weight of C 3 compounds may also be present.

The C3 steam-cracking cut, advantageously used for carrying out 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 C 2 compounds and C 4 compounds may also be present.

A C2 - C3 cut can also be advantageously used for the implementation of 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 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 steam-cracking cut, 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% by weight 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 steam-cracking cut, 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 and 34% by weight of pentadienes.

The steam cracking gasoline or pyrolysis gasoline, advantageously used for carrying out the selective hydrogenation process according to the invention, corresponds to a hydrocarbon fraction whose boiling point is generally between 0 and 300 ° C., preferably between 10 and 250 ° C. The polyunsaturated hydrocarbons to be hydrogenated present in said steam cracking gasoline are, in particular, diolefinic compounds (butadiene, isoprene, cyclopentadiene, etc.), styrenic compounds (styrene, alpha-methylstyrene, etc.) and indene compounds (indene). ). Steam cracking 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 of 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 sulfur, preferably from 0 to 500 ppm by weight of sulfur.

Preferably, the polyunsaturated hydrocarbon feedstock treated according to the selective hydrogenation process according to the invention is a C2 steam cracking cut, or a C2-C3 steam cracking cut, or a steam cracking gasoline.

The selective hydrogenation process according to the invention aims at eliminating said polyunsaturated hydrocarbons present in said feedstock 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 feedstock is a C3 cut, the selective hydrogenation process aims to selectively hydrogenate propadiene and methylacetylene. In the case of a C4 cut, it is intended to remove butadiene, vinylacetylene (VAC) and butyne, in the case of a C5 cut, it is intended to eliminate pentadienes. When said feed is a steam cracking 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 to mono-olefins and that the styrenic and indene compounds are partially hydrogenated to corresponding aromatic compounds by avoiding the hydrogenation of aromatic rings.

The technological implementation of the selective hydrogenation process is for example carried out by injection, in ascending or descending current, of the hydrocarbon feedstock. polyunsaturates and hydrogen in at least one fixed bed reactor. Said reactor may be of the isothermal or adiabatic type. An adiabatic reactor is preferred. The polyunsaturated hydrocarbon feedstock may advantageously be diluted by one or more reinjections of the effluent, coming from said reactor where the selective hydrogenation reaction occurs, 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 may also be advantageously carried out by implanting at least one of said supported catalyst in a reactive distillation column or in reactor-exchangers or in a slurry-type reactor. . The flow of hydrogen can be introduced at the same time as the feedstock to be hydrogenated and / or at one or more different points of the reactor.

The selective hydrogenation of the steam-cracking cuts C2, C2-C3, C3, C4, C5 and C5 + 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 phase gaseous for C2 and C2-C3 cuts. A reaction in the liquid phase makes it possible to lower the energy cost and to increase the catalyst cycle time.

In general, the selective hydrogenation of a hydrocarbon feed containing polyunsaturated compounds containing at least 2 carbon atoms per molecule and having a final boiling point of less than or equal to 300 ° C. temperature between 0 and 300 ° C, at a pressure of between 0.1 and 10 MPa, at a molar ratio of hydrogen / (polyunsaturated compounds to be hydrogenated) of between 0.1 and 10 and at an hourly space velocity VVH (defined as the ratio of the volume flow rate of charge to the volume of the catalyst) of between 0.1 and 200 h ^-1 for a process carried out in the liquid phase, or at a molar ratio of hydrogen / (polyunsaturated compounds to be hydrogenated) of between 0.5 and 1000 and at a hourly volume velocity VVH between 100 and 40000 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 cracking gasoline containing polyunsaturated compounds, the molar ratio (hydrogen) / (polyunsaturated compounds to be hydrogenated) is generally understood. 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 and 200 ° C, preferably between 20 and 200 ° C and even more preferably between 30 and 180 ° C, the hourly volume velocity (VVH) is generally between 0.5 and 100 h ^"1 , preferably between 1 and 50 h ^{" 1} and the pressure is generally between 0.3 and 8.0 MPa, preferably between 1.0 and 7.0 MPa and even more preferably between 1.5 and 4.0 MPa. More preferably, a selective hydrogenation process is carried out in which the feedstock is a steam cracking gasoline comprising polyunsaturated compounds, the molar ratio of hydrogen / (polyunsaturated compounds to be hydrogenated) is between 0.7 and 5.0, the temperature is between 20 and 200 ° C, the hourly volume velocity (VVH) is generally between 1 and 50 h ^-1 and the pressure is between 1.0 and 7.0 MPa.

Even more preferentially, a selective hydrogenation process is carried out in which the feedstock is a steam cracking gasoline comprising polyunsaturated compounds, the molar ratio of hydrogen / (polyunsaturated compounds to be hydrogenated) is between 1.0 and 2.0, the temperature is between 30 and 180 ° C, the hourly volume velocity (VVH) is generally between 1 and 50 h ^"1 and the pressure is between 1, 5 and 4.0 MPa.

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

In another embodiment according to the invention, when a selective hydrogenation process is carried out in which the feedstock is a steam-cracking cross-section C2 and / or a C2-C3 steam-cracking cross-section 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 and 300 ° C, preferably between 15 and 280 ° C, the speed Hourly volume volume (VVH) is generally between 100 and 40000 h ^-1 , preferably between 500 and 30000 h ^-1 and the pressure is generally between 0.1 and 6.0 MPa, preferably between 0.2 and 5, 0 MPa.

Catalyst characteristics

The catalyst according to the invention is in the form of a composite comprising an oxide matrix having a calcined alumina content greater than or equal to 90% by weight relative to the total weight of said matrix, in which is distributed the active phase comprising nickel. The characteristics of the gel which has led to obtaining the alumina contained in said oxide matrix, as well as the textural properties obtained with the active phase, give the catalyst its specific properties.

More particularly, said catalyst comprises an oxide matrix having a calcined alumina content greater than or equal to 90% by weight relative to the total weight of said matrix, and an active phase comprising nickel, said active phase being comalaxed within said oxide matrix , the nickel content being between 1 and 65% by weight of said element relative to the total weight of the catalyst, said active phase not comprising any Group VIB metal, the nickel particles having a diameter of less than 15 nm, said catalyst having a mesoporous median diameter of between 3 and 25 nm, a median macroporous diameter of between 50 and 300 nm, a mesoporous volume measured by mercury porosimetry greater than or equal to 0.40 ml / g and a total pore volume measured by mercury porosimetry greater than or equal to 0.45 ml / g.

The nickel content is between 1 and 65% by weight of said element relative to the total weight of the catalyst, preferably between 5 and 55% by weight, preferably between 8 and 40% by weight, more preferably between 10 and 35% by weight. % weight, and particularly preferably between 12 and 30% by weight. The Ni content is measured by X-ray fluorescence.

The size of the nickel particles in the catalyst according to the invention is less than 15 nm, preferably of between 1.5 and 12 nm, and preferably of between 2 and 10 nm. The term "size of the nickel particles" is understood to mean 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 at the angle 2theta = 43 ° (i.e. in the crystallographic direction [200] ]) using Scherrer's relationship. This method, used in X-ray diffraction on powders or polycrystalline samples which connects the half-height width of the diffraction peaks to the particle size, is described in detail in the reference: Appl. Cryst. (1978), 11, 102-1. "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 active phase of the catalyst does not include a Group VIB metal. It does not include molybdenum or tungsten.

Without wishing to be bound by any theory, it seems that the catalyst used in the context of the selective hydrogenation process according to the invention has a good compromise between a high pore volume, a high macroporous volume, a small size of nickel particles permitting and to have hydrogenation performance in terms of activity at least as good as known catalysts of the state of the art.

The catalyst further comprises an oxide matrix having a calcined alumina content greater than or equal to 90% by weight relative to the total weight of said matrix, optionally supplemented with silica and / or phosphorus to a total content of at most 10 % equivalent weight Si0 ₂ and / or P ₂ 0 ₅ , preferably less than 5% by weight, and very preferably less than 2% by weight relative to the total weight of said matrix. Silica and / or phosphorus can be introduced by any technique known to those skilled in the art, during the synthesis of the alumina gel or during the comalaxing. Even more preferably, the oxide matrix consists of alumina.

Preferably, the alumina present in said matrix is a transition alumina such as gamma, delta, theta, chi, rho or eta alumina, alone or as a mixture. More preferably, the alumina is a gamma, delta or theta transition alumina, alone or as a mixture.

Said catalyst containing a co-ordinated active phase is generally presented in all the forms known to those skilled in the art, for example in the form of beads (generally having a diameter of between 1 and 8 mm), extrudates, tablets, hollow cylinders . Preferably, it consists of extrudates of diameter generally 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 of average length. between 0.5 and 20 mm. The term "mean diameter" of the extrudates means the average diameter of the circle circumscribed in the cross-section of these extrusions. The catalyst may advantageously be in the form of cylindrical, multilobed, trilobed or quadrilobed 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.

The catalyst has a total pore volume of at least 0.45 ml / g, preferably at least 0.48 ml / g, and preferably between 0.50 and 0.95 ml / g.

The catalyst advantageously has a macroporous volume of between 0.05 and 0.3 ml / g, preferably between 0.05 and 0.25 ml / g. The mesoporous volume of the catalyst is at least 0.40 ml / g, preferably at least 0.45 ml / g, and particularly preferably between 0.45 ml / g and 0.65 ml / g. .

The median mesoporous diameter is between 3 nm and 25 nm, and preferably between 4 and 23 nm, and particularly preferably between 6 and 20 nm.

The catalyst has a macroporous median diameter of between 50 and 300 nm, preferably between 80 and 250 nm, even more preferably between 90 and 200 nm.

The catalyst has a BET surface area of at least 3 m ² / g, preferably at least 15 m ² / g, preferably between 20 and 300 m ² / g, and even more preferably between 30 and 300 m ² / g. and 250 m ² / g.

Preferably, the catalyst has a low microporosity, very preferably it has no microporosity. Process for preparing the catalyst

The catalyst used in the context of the selective hydrogenation process according to the invention is prepared from a specific alumina gel. The particular porous distribution observed in the catalyst is in particular due to the process of preparation from the specific alumina gel.

The catalyst used in the context of the selective hydrogenation process according to the present invention is advantageously prepared according to the preparation process comprising at least the following stages:

a) at least a first step of precipitating alumina, in an aqueous reaction medium, of at least one basic precursor chosen from sodium aluminate, potassium aluminate, aqueous ammonia, sodium hydroxide and potassium hydroxide and at least one acidic precursor selected from aluminum sulphate, aluminum chloride, aluminum nitrate, sulfuric acid, hydrochloric acid, and nitric acid, wherein at least one of the basic or acid precursors comprises aluminum, the relative flow rate of the acidic and basic precursors is chosen so as to obtain a pH of the reaction medium of between 8.5 and 10.5 and the flow rate of the aluminum-containing acidic and basic precursors are adjusted to obtain a forwarding rate of said first step of between 40 and 100%, the feed rate being defined as the proportion of alumina formed in Al ₂ equivalent 0 ₃ during said first precipitate step itation relative to the total amount of alumina formed at the end of step c) of the preparation process, said first precipitation step operating at a temperature of between 10 and 50 ° C, and for a period of time between 2 minutes and 30 minutes;

g) a step of shaping the dough obtained in step f); h) a step of drying the shaped dough obtained in step g) at a temperature between 15 and 250 ° C to obtain a dried catalyst;

i) optionally, a step of heat treatment of the dried catalyst obtained in step h) at a temperature between 250 and 1000 ° C in the presence or absence of water.

In general terms, the term "advancement rate" of the nth precipitation stage means the percentage of alumina formed in Al ₂ 0 ₃ equivalent in said nth stage, relative to the total quantity of alumina formed. at the end of all the precipitation steps and more generally after the steps of preparation of the alumina gel. In the case where the progress rate of said precipitation step a) is 100%, said precipitation step a) generally makes it possible to obtain an alumina suspension having an Al ₂ O ₃ concentration of between 20 and 20%. and 100 g / L, preferably between 20 and 80 g / L, more preferably between 20 and 50 g / L. Step a) precipitation

The mixture in the aqueous reaction medium of at least one basic precursor and at least one acidic precursor requires either that at least the basic precursor or the acidic precursor comprises aluminum, or that the two precursors basic and acidic include aluminum.

Basic precursors comprising aluminum are sodium aluminate and potassium aluminate. The preferred basic precursor is sodium aluminate.

Acidic precursors comprising aluminum are aluminum sulphate, aluminum chloride and aluminum nitrate. The preferred acidic precursor is aluminum sulphate. Preferably, the aqueous reaction medium is water.

Preferably, said step a) operates with stirring.

Preferably, said step a) is carried out in the absence of organic additive.

The acidic and basic precursors, whether they contain aluminum or not, are mixed, preferably in solution, in the aqueous reaction medium, in such proportions that the pH of the resulting suspension is between 8.5 and 10. 5.

According to the invention, it is the relative flow rate of the acidic and basic precursors that they contain aluminum or not, which is chosen so as to obtain a pH of the reaction medium of between 8.5 and 10.5. In the preferred case where the basic and acidic precursors are respectively sodium aluminate and aluminum sulphate, the mass ratio of said basic precursor to said acidic precursor is advantageously between 1.6 and 2.05.

For the other basic and acid precursors, whether they contain aluminum or not, the base / acid mass ratios are established by a curve of neutralization of the base by the acid. Such a curve is easily obtained by the skilled person.

Preferably, said precipitation step a) is carried out at a pH of between 8.5 and 10 and very preferably between 8.7 and 9.9. The acidic and basic precursors are also mixed in amounts to obtain a suspension containing the desired amount of alumina, depending on the final concentration of alumina to be achieved. In particular, said step a) makes it possible to obtain 40 to 100% by weight of alumina with respect to the total amount of alumina formed at the end of the precipitation stage (s) and more generally at the end of the steps of preparing the alumina gel and preferably at the end of step c) of the preparation process.

According to the invention, it is the flow rate of the acidic and basic precursor (s) containing aluminum which is adjusted so as to obtain a forwarding rate of the first stage of between 40 and 100%. Preferably, the rate of progress of said precipitation step a) is between 40 and 99%, preferably between 45 and 90% and preferably between 50 to 85%. In the case where the advancement rate obtained at the end of step a) of precipitation is less than 100%, a second precipitation step is necessary so as to increase the amount of alumina formed. In this case, the advancement rate being defined as the proportion of alumina formed in Al ₂ 0 ₃ equivalent during said step a) of precipitation with respect to the total amount of alumina formed at the end of the two stages precipitation of the preparation process according to the invention or more generally at the end of step c) of the process for preparing alumina.

Thus, depending on the alumina concentration targeted at the end of the precipitation step (s), preferably between 20 and 100 g / l, the quantities of aluminum that must be provided by the acid and / or basic precursors are calculated and the flow rate of the precursors is adjusted according to the concentration of said added aluminum precursors, the amount of water added to the reaction medium and the rate of progress required for the precipitation step or steps. The flow rates of the acidic and / or basic precursor (s) containing aluminum depend on the size of the reactor used and thus on the amount of water added to the reaction medium. Preferably, said precipitation step a) is carried out at a temperature between

10 and 45 ° C, preferably between 15 and 45 ° C, more preferably between 20 and 45 ° C and very preferably between 20 and 40 ° C.

It is important that said precipitation step a) operates at a low temperature. In the case where said preparation process according to the invention comprises two precipitation stages, the precipitation step a) is advantageously carried out at a temperature below the temperature of the second precipitation stage.

Preferably, said precipitation step a) is carried out for a period of between 5 and 20 minutes, and preferably of 5 to 15 minutes.

Step b) heat treatment

According to the invention, said preparation process comprises a step b) of heat treatment of the suspension obtained at the end of the precipitation step a), said heat treatment step operating at a temperature of between 50 and 200 ° C for a period of between 30 minutes and 5 hours to obtain the alumina gel. Preferably, said heat treatment step b) is a ripening step.

Preferably, said heat treatment step b) operates at a temperature of between 65 and 150 ° C., preferably between 65 and 130 ° C., preferably between 70 and 110 ° C., very preferably between 70 and 95 ° C. ° C.

Preferably, said heat treatment step b) is carried out for a duration of between 40 minutes and 5 hours, preferably between 40 minutes and 3 hours, and preferably between 45 minutes and 2 hours.

Second stage a ') of precipitation (optional)

According to a preferred embodiment, in the case where the advancement rate obtained at the end of the precipitation step a) is less than 100%, the said preparation method preferably comprises a second precipitation step a '. ) after the first precipitation step.

Said second precipitation step makes it possible to increase the proportion of alumina produced.

Said second precipitation step a ') is advantageously carried out between said first precipitation step a) and the heat treatment step b). In the case where a second precipitation step is carried out, a heating step of the suspension obtained at the end of the precipitation step a) is advantageously carried out between the two precipitation steps a) and ). Preferably, said step of heating the suspension obtained at the end of step a), carried out between said step a) and the second precipitation step a ') operates at a temperature of between 20 and 90 ° C. preferably between 45 and 80 ° C, preferably between 50 and 70 ° C. Preferably, said heating step is carried out for a period of between 7 and 45 minutes and preferably between 7 and 35 minutes.

Said heating step is advantageously carried out according to all the heating methods known to those skilled in the art. According to said preferred embodiment, said preparation method comprises a second step of precipitating the suspension obtained at the end of the heating step, said second step operating by adding to said suspension at least one basic precursor chosen from sodium aluminate, potassium aluminate, ammonia, sodium hydroxide and potassium hydroxide and at least one acidic precursor selected from aluminum sulphate, aluminum chloride, aluminum nitrate, sulfuric acid, hydrochloric acid, and nitric acid, wherein at least one of the basic precursors or acid comprises aluminum, the relative flow rate of the acidic and basic precursors is selected from in order to obtain a pH of the reaction medium of between 8.5 and 10.5 and the flow rate of the aluminum-containing acidic and basic precursor (s) is adjusted so as to obtain a progress rate of the second stage of between 0.degree. e t 60%, the advancement rate being defined as the proportion of alumina formed in Al ₂ 0 ₃ equivalent during said second precipitation step relative to the total amount of alumina formed at the end of the two stages of precipitation, more generally after the steps of preparation of the alumina gel and preferably at the end of step c) of the preparation process according to the invention, said step operating at a temperature of between 20 and 90 ° C, and for a period between 2 minutes and 50 minutes.

As in the first precipitation step a), the addition to the heated suspension of at least one basic precursor and at least one acidic precursor requires either that at least the basic precursor or the acidic precursor comprises aluminum, that the two basic precursors and acid include aluminum. Basic precursors comprising aluminum are sodium aluminate and potassium aluminate. The preferred basic precursor is sodium aluminate.

Acidic precursors comprising aluminum are aluminum sulphate, aluminum chloride and aluminum nitrate. The preferred acidic precursor is aluminum sulphate. Preferably, said second precipitation step operates with stirring.

Preferably, said second step is carried out in the absence of organic additive.

As in step a) of precipitation, it is the relative flow rate of the acidic and basic precursors that they contain aluminum or not, which is chosen so as to obtain a pH of the reaction medium of between 8, 5 and 10.5.

In the preferred case where the basic and acidic precursors are respectively sodium aluminate and aluminum sulphate, the mass ratio of said basic precursor to said acidic precursor is advantageously between 1.6 and 2.05.

Preferably, said second precipitation step is carried out at a pH of between 8.5 and 10 and preferably between 8.7 and 9.9.

The acidic and basic precursors are also mixed in amounts to obtain a suspension containing the desired amount of alumina, depending on the final concentration of alumina to be achieved. In particular, said second precipitation step makes it possible to obtain 0 to 60% by weight of alumina in Al ₂ 0 ₃ equivalent relative to the total amount of alumina formed at the end of the two precipitation stages.

Just as in step a) of precipitation, it is the flow rate of the acidic and basic precursor (s) containing aluminum which is adjusted so as to obtain a progress rate of the second stage of between 0 and 60.degree. %, the advancement rate being defined as the proportion of alumina formed during said second precipitation step relative to the total amount of alumina formed at the end of the two precipitation steps of the preparation process. Preferably, the rate of progress of said second precipitation step a ') is between 10 and 55% and preferably between 15 and 55%, the degree of progress being defined as the proportion of alumina formed during said second precipitation step relative to the total amount of alumina formed at the end of the two precipitation steps of the process for the preparation of alumina.

Thus, depending on the alumina concentration targeted at the end of the precipitation step (s), preferably between 20 and 100 g / l, the quantities of aluminum that must be provided by the acid and / or basic precursors are calculated and the flow rate of the precursors is adjusted according to the concentration of said added aluminum precursors, the amount of water added to the reaction medium and the rate of progress required for each of the precipitation steps.

As in step a) of precipitation, the flow rates of the acid-containing precursor (s) and / or base (s) containing aluminum depending on the size of the reactor used and thus the amount of water added to the reaction medium. For example, if one works in a reactor of 3 I and 1 1 alumina suspension of Al ₂ O ₃ final concentration of 50 g / 1 is targeted, the target rate of advancement is 50% Al ₂ 0 ₃ equivalent for the first precipitation stage. Thus, 50% of the total alumina must be provided during step a) of precipitation. The precursors of aluminas are sodium aluminate at a concentration of 155 g / l in Al ₂ O ₃ and aluminum sulphate at a concentration of 102 g / l in Al ₂ O _3. The precipitation pH of the first step is set at 9.5 and second at 9. The amount of water added to the reactor is 622 ml.

For the first step a) of precipitation operating at 30 ° C and for 8 minutes, the flow rate of aluminum sulfate should be 10.5 ml / min and the sodium aluminate flow rate is 13.2 ml / min . The weight ratio of sodium aluminate to aluminum sulfate is therefore 1.91. For the second precipitation stage, operating at 70 ° C., for 30 minutes, the aluminum sulfate flow rate should be 2.9 ml / min and the sodium aluminate flow rate is 3.5 ml / min. The weight ratio of sodium aluminate to aluminum sulfate is therefore 1.84.

Preferably, the second precipitation step is carried out at a temperature between 20 and 90 ° C, preferably between 45 and 80 ° C and very preferably between 50 and 70 ° C.

Preferably, the second precipitation step is carried out for a period of between 5 and 45 minutes, and preferably of 7 to 40 minutes. The second precipitation step generally makes it possible to obtain an alumina suspension having an Al ₂ O ₃ concentration of between 20 and 100 g / l, preferably between 20 and 80 g / l, preferably between 20 and 50 g / l. In the case where said second precipitation step is carried out, said preparation process also advantageously comprises a second step of heating the suspension obtained at the end of said second precipitation step at a temperature of between 50 and 95 ° C. and preferably between 60 and 90 ° C.

Preferably, said second heating step is carried out for a period of between 7 and 45 minutes.

Said second heating step is advantageously carried out according to all the heating methods known to those skilled in the art.

Said second heating step makes it possible to increase the temperature of the reaction medium before subjecting the suspension obtained in step b) of heat treatment.

Step c) Filtration

According to the invention, the process for preparing the catalyst used in the context of the selective hydrogenation process according to the invention also comprises a step c) of filtering the suspension obtained at the end of step b) of treatment thermal, followed by at least one washing step of the gel obtained. Said filtration step is carried out according to the methods known to those skilled in the art.

The filterability of the suspension obtained at the end of step a) of precipitation or of both precipitation steps a) and a ') is improved by the presence of said final b) heat treatment step of the suspension obtained, said a heat treatment step promoting the productivity of the preparation process and an extrapolation of the process at the industrial level.

Said filtration step is advantageously followed by at least one washing step with water and preferably from one to three washing steps, with a quantity of water equal to the amount of filtered precipitate.

The sequence of steps a) b) and c) and optionally of the second step a ') precipitation, and the second heating step, allows to obtain a specific alumina gel having a higher dispersibility index at 70%, a crystallite size of between 1 and 35 nm and a sulfur content of between 0.001% and 2% by weight and a sodium content of between 0.001% and 2% by weight, the weight percentages being expressed by relative to the total mass of alumina gel.

The alumina gel thus obtained, also called boehmite, has a dispersibility index between 70 and 100%, preferably between 80 and 100%, very preferably between 85 and 100% and even more preferably between 90 and 100%. and 100%. Preferably, the alumina gel thus obtained has a crystallite size of between 2 and 35 nm.

Preferably, the alumina gel thus obtained comprises a sulfur content of between 0.001 and 1% by weight, preferably between 0.001 and 0.40% by weight, very preferably between 0.003 and 0.33% by weight, and more preferably between 0.005 and 0.25% by weight. The sulfur content is measured by X-ray fluorescence.

Preferably, the alumina gel thus obtained comprises a sodium content of between 0.001 and 1% by weight, preferably between 0.001 and 0.15% by weight, very preferably between 0.0015 and 0.10% by weight, and 0.002 and 0.040% by weight. The sodium content is measured by Inductively Coupled Plasma Spectrometry (ICP).

In particular, the alumina gel or the boehmite in powder form according to the invention is composed of crystallites whose size, obtained by the Scherrer formula in X-ray diffraction according to the crystallographic directions [020] and [120] are respectively between 1 and 20 nm and between 1 and 35 nm.

Preferably, the alumina gel according to the invention has a crystallite size in the crystallographic direction [020] of between 1 to 15 nm and a crystallite size in the crystallographic direction [120] of between 1 to 35 nm. X-ray diffraction on alumina or boehmite gels was performed using the conventional powder method using a diffractometer.

Scherrer's formula is a formula used in X-ray diffraction on powders or polycrystalline samples which connects the width at half height of the diffraction peaks to the size of the crystallites. It is described in detail in the reference: Appl. Cryst. (1978). 1 1, 102-1. Scherrer after sixty years: A survey and some new results in the determination of crystallite size, J. I. Langford and A. J. C. Wilson.

Step d) drying

According to the invention, the alumina gel obtained at the end of the filtration step c) is dried in a drying step d) to obtain a powder.

Said drying step is advantageously carried out at a temperature of between 20 and 250 ° C., preferably between 50 and 200 ° C., for a duration of between 1 day and 3 weeks, preferably between 2 hours and 1 week, and still more more preferably between 5 hours and 48 hours. This drying step is advantageously carried out by any technique known to those skilled in the art. Step e) Heat treatment

According to the invention, the powder obtained at the end of step d) of drying then undergoes a step e) of heat treatment at a temperature of between 500 and 1000 ° C., for a duration advantageously between 2 and 10 hours, with or without a flow of air containing up to 60% by volume of water, to obtain a calcined aluminum porous oxide.

Said heat treatment can be carried out in the presence of a flow of air containing up to 60% by volume of water, also called hydrothermal heat treatment. The term "heat treatment or hydrothermal" means the temperature treatment respectively without presence or in the presence of water. In the latter case, the contact with the water vapor can take place at atmospheric pressure or autogenous pressure. Several combined cycles of thermal or hydrothermal treatments can be carried out. The temperature of said treatments is between 500 and 1000 ° C, preferably between 540 and 850 ° C. In 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.

Said heat treatment step e) allows the transition from boehmite to calcined aluminous porous oxide. The alumina has a crystallographic structure of the type transition alumina gamma, delta, theta, chi, rho or eta, alone or in mixture. More preferably, the alumina is a gamma, delta or theta transition alumina, alone or as a mixture. The existence of the different crystallographic structures is related to the conditions of implementation of the heat treatment step e).

Step f) Comalaxaqe

In this step, the calcined aluminous porous oxide obtained in step e) is kneaded with a solution comprising at least one nickel precursor to obtain a paste.

The active phase is provided by one or more solutions containing at least nickel. The said solution (s) may be aqueous or consist of an organic solvent or a mixture of water and at least one organic solvent ( for example ethanol or toluene). Preferably, the solution is aqueous. The pH of this solution may be modified by the possible addition of an acid. According to another preferred variant, the aqueous solution may contain ammonia or ammonium ions NH ₄ ⁺ . Preferably, said nickel precursor is introduced in aqueous solution, for example in the form of nitrate, carbonate, acetate, chloride, hydroxide, hydroxycarbonate, 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 calcined aluminous porous oxide. Preferably, nickel precursor nickel nitrate, nickel chloride, nickel acetate or nickel hydroxycarbonate is advantageously used. Very preferably, the nickel precursor is nickel nitrate or nickel hydroxycarbonate.

According to another preferred variant, said nickel precursor is introduced into an ammoniacal solution by introducing a nickel salt, for example nickel hydroxide or nickel carbonate, into an ammoniacal solution or into an ammonium carbonate or ammonium carbonate solution. ammonium hydrogen carbonate.

The quantities of the nickel precursor (s) introduced into the solution are chosen such that the total nickel content is between 1 and 65% by weight of said element relative to the total weight of the catalyst, preferably between 5 and 55% by weight. preferably between 8 and 40% by weight, more preferably between 10 and 35% by weight, and particularly preferably between 12 and 30% by weight. The nickel contents are generally adapted to the intended hydrogenation reaction as described above in the section of the catalyst description.

Any other additional element may be introduced into the mixing tank during the comalaxing step or in the solution containing the metal salt or salts of the precursors of the active phase.

When it is desired to introduce silica into the matrix, a silicic precursor solution or emulsion may be introduced.

When it is desired to introduce phosphorus into the matrix, a solution of phosphoric acid may be introduced.

Comalaxing is advantageously carried out in a kneader, for example a "Brabender" kneader, well known to those skilled in the art. The calcined alumina powder obtained in step e). Then the solution comprising at least one nickel precursor, and optionally deionized water is added to the syringe or with any other means for a period of a few minutes, typically about 2 minutes at a given kneading speed. After obtaining a paste, kneading can be continued for a few minutes, for example about 15 minutes at 50 rpm. The solution comprising at least one nickel precursor can also be added in several times during this comalaxing phase.

Step g) Formatting

The paste obtained at the end of the comalaxing step f) is then shaped according to any technique known to those skilled in the art, for example extrusion forming methods, pelletizing, by the method of the drop of oil (dripping) or by granulation at the turntable.

Preferably, the paste is shaped by extrusion in the form of extrudates of diameter generally between 0.5 and 10 mm, preferably 0.8 and 3.2 mm, and very preferably between 1, 0 and 2 , 5 mm. This may advantageously be in the form of cylindrical, trilobed or quadrilobed extrudates. Preferably its shape will be trilobed or quadrilobed.

Very preferably, said step f) of comalaxing and said step g) shaping are combined in a single kneading-extruding step. In this case, the paste obtained after the mixing can be introduced into a piston extruder through a die having the desired diameter, typically between 0.5 and 10 mm.

Step h) Drying the shaped dough

According to the invention, the shaped dough undergoes drying h) at a temperature between 15 and 250 ° C, preferably between 15 and 240 ° C, more preferably between 30 and 220 ° C, even more preferably between 50 and 200 ° C, and even more preferably between 70 and 180 ° C, for a period of time typically between 10 minutes and 24 hours. Longer durations are not excluded, but do not necessarily improve.

The drying step may be performed 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 under reduced pressure. Preferably, this step is carried out at atmospheric pressure and in the presence of air or nitrogen.

Step i) Heat treatment of the dried catalyst (optional)

The catalyst thus dried can then undergo a complementary heat treatment or hydrothermal step i) at a temperature between 250 and 1000 ° C and preferably between 250 and 750 ° C, for a period of typically 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 require improvement. Several combined cycles of thermal or hydrothermal treatments can be performed. After this or these treatment (s), the catalyst precursor comprises nickel in oxide form, that is to say in NiO form. In the case where water is added, the contact with the water vapor can take place at atmospheric pressure or autogenous pressure. 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)

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

This treatment makes it possible to activate the said catalyst and to form metal particles, in particular nickel in the zero state. Said reducing treatment can be carried out in situ or ex situ, that is to say after or before the catalyst is loaded into the hydrogenation reactor. Said step j) of reducing treatment can be implemented on the catalyst which has or has not been subjected to the passivation step k), described below.

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

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

The duration of the reducing treatment is generally between 2 and 40 hours, preferably between 3 and 30 hours. The rise in temperature to the desired reduction temperature is generally slow, for example set between 0.1 and 10 ° C / min, preferably between 0.3 and 7 ° C / min. The flow rate of hydrogen, expressed in L / hour / g of catalyst, is between 0.01 and 100 L / hour / g of catalyst, preferably between 0.05 and 10 L / hour / g of catalyst, moreover more preferably between 0.1 and 5 L / hour / gram of catalyst.

Step k) Passivation (optional)

Prior to its implementation in the catalytic reactor, the catalyst according to the invention may optionally undergo a passivation step (step k) with a sulfur or oxygenated compound or with CO ₂ before or after the reducing treatment step j) . This passivation step may be performed ex situ or in situ. The passivation step is carried out by the implementation of methods known to those skilled in the art. The sulfur passivation step makes it possible to improve the selectivity of the catalysts and to avoid thermal runaways when starting new catalysts ("run away" according to the English terminology). Passivation generally consists in irreversibly poisoning with the sulfur compound the most virulent active sites of the nickel which exist on the new catalyst and thus in attenuating the activity of the catalyst in favor of its selectivity. The passivation step is carried out by the implementation of methods known to those skilled in the art and in particular, for example by the implementation of one of the methods described in patent documents EP0466567, US5153163, FR2676184, WO2004 / 098774, EP0707890. The sulfur compound is for example chosen from the following compounds: thiophene, thiophane, alkylmonosulfides such as dimethylsulfide, diethylsulfide, dipropylsulphide and propylmethylsulphide or an organic disulfide of formula HO-R SSR ₂ -OH such as di-thio-di-ethanol of formula HO-C ₂ H4-H4 SSC _2-OH (often called DEODS). The sulfur content is generally between 0.1 and 2% by weight of said element relative to the mass of the catalyst.

The passivation step with an oxygenated compound or with CO ₂ is generally carried out after a reducing treatment beforehand at elevated temperature, generally between 350 and 500 ° C., and makes it possible to preserve the metallic phase of the catalyst in the presence of air. . A second reducing treatment at a lower temperature, generally between 120 and 350 ° C., is then generally carried out. The oxygenated compound is generally air or any other stream containing oxygen.

The invention is illustrated by the following examples. Examples

Example 1 Preparation of an aqueous solution of Ni precursors

The aqueous solution of Ni precursors (solution S) used for the preparation of catalysts A, B, and C is prepared by dissolving 46.1 g of nickel nitrate (NiNO ₃ , supplier Strem Chemicals®) in a volume of 13 ml. distilled water. Solution S is obtained whose NiO concentration is 20.1% by weight (relative to the mass of the solution).

EXAMPLE 2 Preparation of the Comalaxed Catalyst A (in Accordance with the Process According to the Invention)

Catalyst A is prepared by the comalaxing of alumina A1 and solution S of Ni precursors.

Step a): In a first step, the synthesis of alumina A1 in a 7L reactor and a final suspension of 5L in 3 steps, two precipitation steps followed by a ripening step are carried out.

The final alumina concentration is 45g / L. The amount of water added to the reactor is 3267 mL. The agitation is 350 revolutions per minute (rpm) throughout the synthesis.

A first step of co-precipitation in water, aluminum sulphate Al ₂ (SO ₄ ) and sodium aluminate NaAlOO is carried out at 30 ° C. and pH = 9.5 for a period of 8 minutes. The concentrations of the aluminum precursors used are as follows: AI ₂ (SO ₄ ) at 102 g / L in Al ₂ O ₃ and NaAlOO at 155 g / L in Al ₂ O ₃ .

A solution of aluminum sulphate Al ₂ (SO ₄ ) is added continuously for 8 minutes at a flow rate of 69.6 ml / min to a solution of sodium aluminate NaAlOO at a flow rate of 84.5 ml / min. a base / acid mass ratio = 1.84 so as to adjust the pH to a value of 9.5. The temperature of the reaction medium is maintained at 30 ° C.

A suspension containing a precipitate of alumina is obtained.

The final alumina concentration targeted at 45 g / l, the flow rates of aluminum sulphate precursors Al ₂ (SO ₄ ) and sodium aluminate NaAlOo introduced in the first precipitation step are respectively 69.6 ml / min and 84, 5 mL / min.

These flow rates of aluminum-containing acidic and basic precursors make it possible to obtain at the end of the first precipitation step an advancement rate of 72%.

The suspension obtained is then subjected to a temperature rise of 30 to 65 ° C. in 15 minutes. A second step of co-precipitation of the suspension obtained is then carried out by adding aluminum sulphate Al ₂ (S0 ₄₎ at a concentration of 102 g / L of Al ₂ 0 ₃ and NaAIOO sodium aluminate at a concentration from 155g / L to Al ₂ 0 ₃ . A solution of aluminum sulphate Al ₂ (SO ₄ ) is therefore added continuously to the heated suspension obtained at the end of the first precipitation step for 30 minutes at a flow rate of 7.2 ml / min. sodium aluminate NaAlOO in a mass ratio base / acid = 1.86 so as to adjust the pH to a value of 9. The temperature of the reaction medium in the second step is maintained at 65 ° C.

A suspension containing a precipitate of alumina is obtained.

As the final concentration of alumina is 45 g / L, the flow rates of aluminum sulphate precursors Al ₂ (SO ₄ ) and NaAlOO sodium aluminate introduced into the second precipitation stage are respectively 7.2 ml / min and 8 ml. 8 mL / min.

These flow rates of acid and basic precursors containing aluminum make it possible to obtain at the end of the second precipitation stage a progress rate of 28%.

The resulting suspension is then subjected to a temperature rise of 65 to 90 ° C.

Step b): The slurry then undergoes a heat treatment step in which it is held at 90 ° C for 60 minutes. Step c): The suspension obtained is then filtered by displacement of water on a sintered Buchner type tool and the alumina gel obtained is washed 3 times with 5 L of distilled water.

The characteristics of the alumina gel thus obtained are summarized in Table 1 below. TABLE 1 Characteristics of the Alumina Gel Obtained in Example 2

A gel having a dispersibility index of 100% is thus obtained.

Step d): The alumina gel obtained is then dried in an oven for 16 hours at 200 ° C. Step e): The powder obtained at the end of the drying step is then calcined at 750 ° C. for 2 hours to obtain the transition from boehmite to alumina. Alumina A1 is then obtained.

Catalyst A is then prepared from alumina A1 and solution S of Ni precursors, prepared above, according to the following four steps:

Step f) Comalaxing: A "Brabender" mixer is used with a bowl of 80 mL and a mixing speed of 30 rpm. Alumina powder A1 is placed in the tank of the kneader. Then solution S of Ni precursors is added to the syringe for about 2 minutes at 15 rpm. After obtaining a paste, the kneading is maintained for 15 minutes at 50 rpm.

Step g) Extrusion: The paste thus obtained is introduced into a piston extruder and is extruded through a 2.1 mm diameter die at 50 mm / min.

Step h) Drying: The extrudates thus obtained are then dried in an oven at 80 ° C. for 16 hours. A dried catalyst is obtained.

Step i) Heat treatment: The dried catalyst is then calcined in a tubular furnace, under a flow of air of 1 L / h / g of catalyst, at 450 ° C for 2 hours (ramp temperature rise of 5 ° C / min). The calcined catalyst A is then obtained.

The characteristics of the calcined catalyst A thus obtained are reported in Table 3 below. Example 3 Preparation of the Comalaxed Catalyst B from Boehmite (Not in Accordance with the Process According to the Invention)

Catalyst B is prepared by comalaxing boehmite (non-calcined alumina gel) and solution S of Ni precursors.

The boehmite synthesis is carried out in a laboratory reactor of 5L capacity following the first five steps, steps a) to d), of Example 2 described above.

The operating conditions of the five steps a) to d) are strictly identical to those described in Example 2 above. At the end of step d), a boehmite powder B1 is obtained. This boehmite powder B1 is then mixed with the solution S of Ni precursors (described in Example 1). No calcination occurs between step d) and the step of comalaxing.

Catalyst B is then prepared according to the four steps f) to i) described in Example 2. The operating conditions are strictly identical, with the exception of the following two points:

in step f) of comalaxing, the boehmite powder B1 is mixed with the solution S of precursors of Ni;

in calcination step i), the calcination is carried out at 750 ° C. so as to convert the boehmite into alumina. This calcination at high temperature gave rise to refractory phases of nickel aluminate type.

The characteristics of the calcined catalyst B thus obtained are reported in Table 2 below.

Compared to the catalyst A, the macroporous volume is higher, the mesoporous volume and the mesoporous median diameter are much smaller. Catalyst B also has microporosity, unlike catalyst A. Catalyst B also has NiO crystallites much larger than those of Catalyst A.

EXAMPLE 4 Preparation of the Comalaxed Catalyst C from an Alumina (Not in Accordance with the Process According to the Invention)

Catalyst C is prepared by comalaxing a C1 alumina and solution S of Ni precursors.

The synthesis of C1 alumina is carried out in a 5L reactor in six stages, named below a) to e). The concentration of the precursor acid and basic aluminum is: aluminum sulphate Al ₂ (S0 ₄₎ 3 to 102 g / L of Al ₂ 0 ₃ and NaAIOO sodium aluminate in 155 g / L of Al ₂ 0 _{3 .} It is sought to obtain a final alumina concentration of 45 g / L in the slurry obtained after the second step c) precipitation.

Steps a) to e) are described below:

a) a first precipitation of aluminum sulphate Al ₂ (SO ₄ ) ₃ and sodium aluminate NaAlO 4 is carried out in 8 minutes at 40 ° C., pH = 9.1 and with a progress rate of 20 %.

The rate of progress corresponds to the proportion of alumina formed during the first step;

b) a temperature rise of 40 ° C to 60 ° C is carried out in 20 to 30 minutes; a ') a second precipitation of aluminum sulphate Al ₂ (SO ₄ ) ₃ and sodium aluminate NaAlOO was carried out for 30 minutes at 60 ° C., pH = 9.1 and with a progress rate of 80 %. The rate of progress corresponds to the proportion of alumina formed during the second precipitation step.

The characteristics of the alumina gel thus obtained are summarized in Table 2 below.

TABLE 2 Characteristics of the Alumina Gel for the Preparation of the Support C1

A gel having a dispersibility index of 60% is thus obtained. c) the suspension obtained at the end of step a ') is filtered by displacement on a sintered Buchner tool P4, followed by three successive washes with 5L of distilled water;

d) the alumina gel is dried for 16 hours at 200 ° C .;

e) air calcination of the powder obtained at the end of step d) is carried out at 750 ° C. for 2 hours. C1 alumina is obtained.

Catalyst C is then prepared by comalaxing alumina C1 and solution S of precursors of Ni described in Example 1 according to the four steps f) to i) described in Example 2. The operating conditions are strictly identical . At the end of step i), the calcined catalyst C is then obtained.

The characteristics of the calcined catalyst C thus obtained are reported in Table 3 below. This catalyst has a macroporous volume much higher than that of catalyst A and a mesoporous volume and mesoporous average diameter much lower than those of catalyst A. It also has NiO crystallites larger in size than those of catalyst A . Table 3: Properties of catalysts A, B and C

EXAMPLE 5 Evaluation of the Catalytic Properties of Catalysts A, B and C in Selective Hydrogenation of a Mixture Containing Styrene and Isoprene

The catalysts A, B, and C described in the above examples are tested for the selective hydrogenation reaction of a mixture containing styrene and isoprene.

The composition of the feedstock to be selectively hydrogenated is as follows: 8% styrene weight (Sigma Aldrich® supplier, 99% purity), 8% isoprene weight (Sigma Aldrich® supplier, 99% purity), 84% weight n-heptane (solvent ) (VWR® supplier, purity> 99% chromanorm HPLC). This feed also contains very low sulfur compounds: 10 ppm weight of sulfur introduced in the form of pentanethiol (supplier Fluka®, purity> 97%) and 100 ppm weight of sulfur introduced in the form of thiophene (supplier Merck®, purity 99 %). This composition corresponds to the initial composition of the reaction mixture. This mixture of model molecules is representative of a pyrolysis species. The selective hydrogenation reaction is carried out in a 500 ml autoclave made of stainless steel, equipped with magnetic stirring mechanical stirring and capable of operating at a maximum pressure of 100 bar (10 MPa) and temperatures of between 5 ° C. and 5 ° C. 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, protected from the air. After addition of 214 mL of n-heptane (supplier VWR®, purity> 99% chromanorm HPLC), the autoclave is closed, purged, then pressurized under 35 bar (3.5 MPa) of hydrogen, and brought to temperature. test equal to 30 ° C. At time t = 0, about 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 of 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 pressure decrease 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, B, and C are reported in Table 3 below. They are related to the catalytic activity measured for the catalyst

Table 3: Comparison of the performances in selective hydrogenation of a mixture containing styrene and isoprene (A _H YD)

Catalyst Conform? AHYD (%)

A Yes 100

B No 32

C No 67 This shows the improved performance of the selective hydrogenation process in the presence of catalyst A and in particular the impact of its specific textural properties. The preparation by alumina comalaxation makes it possible to obtain smaller NiO crystallites and thus improved catalytic performance (comparison with catalyst C). On the contrary, the preparation by comalaxing of boehmite (catalyst B) leads to a very significant decrease in catalytic performance due to the presence of large crystallites of NiO and refractory phases (nickel aluminate type) formed during the calcination at high temperature. temperature.

Claims

1. Process for the selective hydrogenation of polyunsaturated compounds containing at least 2 carbon atoms per molecule, such as diolefins and / or acetylenes and / or alkenyl aromatics, contained in a hydrocarbon feed having a lower or equal final boiling point at 300 ° C., which process is carried out at a temperature of between 0 and 300 ° C., at a pressure of between 0.1 and 10 MPa, at a molar ratio of hydrogen / (polyunsaturated compounds to be hydrogenated) of between 0.1 and 10 and at a hourly space velocity of between 0.1 and 200 h ^-1 when the process is carried out in the liquid phase, or at a molar ratio of hydrogen / (polyunsaturated compounds to be hydrogenated) of between 0.5 and 1000 and at a rate of hourly volume between 100 and

40000 h ^-1 when the process is carried out in the gaseous phase, in the presence of a catalyst comprising an oxide matrix having a calcined alumina content greater than or equal to 90% by weight relative to the total weight of said matrix, and an active phase comprising nickel, said active phase being comalaxed within said calcined predominantly aluminum oxide matrix, the nickel content being between 1 and

65% by weight of said element relative to the total weight of the catalyst, said active phase not comprising a group VIB metal, the nickel particles having a diameter of less than 15 nm, said catalyst having a median mesoporous diameter of between 3 and 25 nm a macroporous median diameter between 50 and 300 nm, a mesoporous volume measured by mercury porosimetry greater than or equal to 0.40 ml / g and a total pore volume measured by mercury porosimetry greater than or equal to 0.45 ml / g. .

2. The process according to claim 1, wherein the catalyst comprises a macroporous volume of between 0.05 and 0.3 ml / g.

3. Method according to claims 1 or 2, wherein the nickel content is between 5 and 55% by weight relative to the total weight of the catalyst.

4. Process according to any one of claims 1 to 3, wherein the catalyst comprises a mesoporous volume of between 0.45 and 0.65 ml / g.

5. Process according to any one of claims 1 to 4, wherein the catalyst comprises a median mesoporous diameter of between 4 and 23 nm. 6. Process according to any one of claims 1 to 5, wherein the catalyst comprises a median macroporous diameter of between 80 and 250 nm. Process according to any one of claims 1 to 6, wherein the catalyst does not comprise micropores.

The process of any one of claims 1 to 7, wherein the catalyst comprises an oxide matrix consisting of alumina.

Process according to any one of claims 1 to 8, wherein said catalyst is prepared by at least the following steps:

g) a step of shaping the paste obtained; h) a step of drying the shaped dough at a temperature between 15 and 250 ° C to obtain a dried catalyst.

10. The method of claim 9, wherein in the case where the advancement rate obtained at the end of the first step a) precipitation is less than 100%, said preparation process comprises a second precipitation step a ' ) after the first precipitation step a).

1 1. Process according to claims 9 or 10, in which the sulfur content of the alumina gel obtained after step b) is between 0.001% and 2% by weight relative to the total weight of the alumina gel, and the sodium content of said alumina gel is between 0.001% and 2% by weight relative to the total weight of said alumina gel.

12. Method according to any one of claims 9 to 11, wherein performs at least one step i) of heat treatment of the dried catalyst obtained at the end of step h) at a temperature between 250 and 1000 ° C, with or without water.

Process according to any one of claims 9 to 12, wherein at least one reducing treatment step j) is carried out in the presence of a reducing gas after steps h) or i) so as to obtain a catalyst comprising nickel at least partly in metallic form.

14. Process according to any one of Claims 1 to 13, characterized in that the filler is chosen from a C2 steam cracking cut or a C2-C3 steam cracking cut, and in which the molar ratio (hydrogen) / (compounds polyunsaturates to be hydrogenated) is between 0.5 and 1000, the temperature is between 0 and 300 ° C, the hourly volume velocity (VVH) is between 100 and 40000 h ^"1 , and the pressure is between 0.1 and 6.0 MPa.

15. Process according to any one of Claims 1 to 13, characterized in that the filler is chosen from steam cracking gasolines and in which the molar ratio (hydrogen) / (polyunsaturated compounds to be hydrogenated) is between 0.5 and 10, the temperature is between 0 and 200 ° C, the hourly volume velocity (VVH) is between 0.5 and 100 h ^"1 , and the pressure is between 0.3 and 8.0 MPa.