FR3132646A1 - CATALYST COMPRISING AN ACTIVE PHASE OF PALLADIUM AND COPPER - Google Patents

Abstract

Catalyst comprising an active phase consisting of palladium and copper and a porous alumina support, in which the palladium content is between 0.02% and 0.2% by weight of palladium element relative to the total weight of the catalyst , the copper content is between 0.1% and 15% by weight of copper element relative to the total weight of the catalyst, at least 80% by weight of the palladium is distributed in a crust at the periphery of said support, the thickness of said crust being between 20 and 300 µm, characterized in that:- the copper is distributed homogeneously through the porous support;- the mass ratio between the copper and the palladium is between 20 and 1000 weight/weight;- said porous alumina support comprises a specific surface of between 55 and 150 m²/g.

Description

CATALYST COMPRISING AN ACTIVE PHASE OF PALLADIUM AND COPPER

The present invention relates to a supported metal catalyst based on palladium and copper intended particularly for the hydrogenation of unsaturated hydrocarbons, and more particularly, for the selective hydrogenation of polyunsaturated compounds or the hydrogenation of aromatics.

State of the art

Monounsaturated organic compounds, such as ethylene and propylene, are the source of the manufacturing of polymers, plastics and other value-added chemicals. These compounds are obtained from natural gas, naphtha or diesel 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+ gasoline fraction (gasolines containing hydrocarbon compounds having 5 or more carbon atoms), in particular styrenic or indenic compounds . These polyunsaturated compounds are very reactive and lead to parasitic reactions in the polymerization units. It is therefore necessary to eliminate them before valorizing these cuts.

Selective hydrogenation is the primary 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.

Selective hydrogenation catalysts are generally based on metals from group VIII of the periodic table, preferably palladium or nickel. The metal is in the form of metallic particles deposited on a support. The metal content, the size of the metal particles and the distribution of the active phase in the support are among the criteria which have an importance on the activity and selectivity of the catalysts.

The macroscopic distribution of metal particles in the support constitutes an important criterion, mainly in the context of rapid and consecutive reactions such as selective hydrogenations. It is generally desirable that these elements be located in a crust at the periphery of the support in order to avoid intragranular material transfer problems which could lead to activity defects and a loss of selectivity. Such catalysts are also called "eggshell" catalysts according to Anglo-Saxon terminology.

Such catalysts are widely known in the case of palladium-based selective hydrogenation catalysts. Indeed, thanks to the low palladium content (generally less than 1% by weight (1% by weight) of palladium relative to the catalyst) and suitable preparation processes, a thin crust of palladium at the periphery of the support grains can be obtained (FR2922784, US2010/217052).

Palladium-based catalysts are widely used in selective hydrogenation reactions of light C2-C4 cuts. Typically, the palladium is distributed in a crust on the periphery of the catalyst (egg-shell catalyst according to Anglo-Saxon terminology). Recent years have seen the appearance of bimetallic catalysts which allow a notable gain in activity, but especially in selectivity in the hydrogenation of acetylenes and diolefins. Typically, the element added to palladium is silver or gold.

Document US2006/025302 discloses a catalyst for the selective hydrogenation of acetylene and diolefins, comprising palladium, with a content of between 0.01 and 0.1% by weight relative to the total weight of the catalyst, and a metal from group IB, preferably silver, with a content of between 0.005 and 0.6% by weight relative to the total weight of the catalyst. The palladium is distributed in such a way that 90% of the palladium introduced into the catalyst is included in a crust of less than 250 μm. The support used has a specific surface area of between 2 and 20 m²/g.

Surprisingly, the Applicant has developed a new catalyst consisting of an active phase comprising copper and a low palladium content, and an alumina support comprising a determined specific surface area, the palladium being distributed in a crust around the periphery of the support. alumina and the copper being distributed homogeneously throughout the section of the catalyst support. Such a catalyst makes it possible to significantly improve the activity of the catalyst in selective hydrogenation reactions of polyunsaturated compounds, while using a quantity of palladium phase lower than that typically used in the state of the art.

Objects of the invention

The present invention relates to a catalyst comprising an active phase consisting of palladium and copper and a porous alumina support, in which the palladium content is between 0.02% and 0.2% by weight of palladium element relative to to the total weight of the catalyst, the copper content is between 0.1% and 15% by weight of copper element relative to the total weight of the catalyst, at least 80% by weight of the palladium is distributed in a crust at the periphery of said support , the thickness of said crust being between 20 and 300 µm, characterized in that:

- the copper is distributed homogeneously across the porous support;

- the mass ratio between copper and palladium is between 20 and 1000 weight/weight;

- said porous alumina support has a specific surface area of between 55 and 150 m²/g.

According to one or more embodiments, the mass ratio between copper and palladium is between 50 and 500 weight/weight.

According to one or more embodiments, the copper content is between 0.5 and 13% by weight of copper element relative to the total weight of the catalyst.

According to one or more embodiments, the palladium content is between 0.03 and 0.1% by weight of palladium element relative to the total weight of the catalyst.

According to one or more embodiments, said porous support comprises a specific surface area of between 60 and 140 m²/g.

According to one or more embodiments, said porous support is in the form of an extrusion comprising four lobes.

According to one or more embodiments, said porous support is in the form of a ball.

Another object according to the invention relates to a process for preparing a catalyst according to the invention comprising the following steps:

a) an aqueous solution comprising at least one palladium precursor salt is impregnated onto the porous support;

b) the impregnated support obtained at the end of step a) is matured in the wet state for 0.5 hour to 40 hours to obtain a catalyst precursor;

c) the catalyst precursor obtained at the end of step b) is dried at a temperature below 250°C to obtain a dried catalyst precursor;

d) an aqueous solution comprising at least one copper precursor salt is impregnated on the dried catalyst precursor obtained in step c);

e) the catalyst precursor obtained at the end of step d) is dried at a temperature below 250°C to obtain a dried catalyst;

f) the dried catalyst obtained in step e) is calcined at a temperature between 250°C and 900°C.

According to one or more embodiments, in which in step a), the palladium precursor is selected from the group consisting of sodium chloropalladate, palladium nitrate and palladium sulfate.

According to one or more embodiments, in which the copper precursor is chosen from copper acetate, copper acetylacetonate, copper nitrate, copper sulfate, copper chloride, copper bromide, copper iodide or copper fluoride.

According to one or more embodiments, in which a step g) of hydrothermal treatment in air of the calcined catalyst obtained in the step is further carried out, comprising between 150 and 5000 grams of water per kg of air, at a temperature between 500°C and 900°C.

Another object according to the invention relates to a process for preparing a catalyst according to the invention comprising the following steps:

a1) a colloidal suspension of palladium oxide or palladium hydroxide is impregnated in the aqueous phase by mixing an aqueous solution (I) comprising at least one hydroxide selected from the group consisting of alkali hydroxides and hydroxides alkaline earth metal and an aqueous solution (II) comprising at least one palladium precursor on the porous support;

b1) the impregnated porous support obtained in step a1) is subjected to maturation in order to obtain a catalyst precursor;

c1) the catalyst precursor obtained in step b1) is dried at a temperature below 250°C;

d1) a colloidal suspension of copper oxide or copper hydroxide in the aqueous phase is impregnated on the dried catalyst precursor obtained at the end of step c1) by mixing an aqueous solution (III) comprising at at least one hydroxide selected from the group consisting of alkali hydroxides and alkaline earth hydroxides and an aqueous solution (IV) comprising at least one copper precursor;

e1) the catalyst precursor obtained in step d1) is dried at a temperature below 250°C;

f1) the dried catalyst obtained in step e1) is calcined at a temperature between 250°C and 900°C.

According to one or more embodiments, said palladium precursor salt is chosen from palladium chloride, palladium nitrate and palladium sulfate.

Another object according to the invention relates to a process for the selective hydrogenation of polyunsaturated compounds containing at least 2 carbon atoms per molecule contained in a hydrocarbon feed having a final boiling point less than or equal to 300°C, which process being carried out at a temperature between 0 and 300°C, at a pressure between 0.1 and 10 MPa, at a hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio between 0.1 and 10 and at an hourly volume rate between 0.1 and 200 h ^-1 when the process is carried out in the liquid phase, or at a hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio of between 0.5 and 1000 and at an hourly volume rate between 100 and 40,000 h ^-1 when the process is carried out in the gas phase, in the presence of a catalyst according to the invention.

According to one or more embodiments, the hydrocarbon feed is a steam cracking gasoline.

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 IB according to the CAS classification corresponds to the metals of column 11 according to the new IUPAC classification.

The BET specific surface area is measured by nitrogen physisorption. The BET specific surface area is measured by nitrogen physisorption according to standard ASTM D3663-03 as described in Rouquerol F.; Rouquerol J.; Singh K. “Adsorption by Powders & Porous Solids: Principle, methodology and applications”, Academic Press, 1999.

The total pore volume is measured by mercury porosimetry according to standard ASTM D4284-92 with a wetting angle of 140°, for example using an Autopore® III model device from the Microméritics® brand.

The palladium and copper contents are measured by X-ray fluorescence.

Palladium crust thickness: In order to analyze the distribution of the metallic phase on the support, a crust thickness is measured by Castaing microprobe (or microanalysis by electron microprobe). The device used is a CAMECA XS100, equipped with four monochromator crystals allowing the simultaneous analysis of four elements. The Castaing microprobe analysis technique consists of the detection of X-ray radiation emitted by a solid after excitation of its elements by a high-energy electron beam. For the purposes of this characterization, the catalyst grains are coated in epoxy resin pads. These pads are polished until they reach the cut to the diameter of the balls or extruded then metallized by carbon deposition in a metal evaporator. The electronic probe is scanned along the diameter of five balls or extrusions to obtain the average distribution profile of the constituent elements of the solids. This method, well known to those skilled in the art, is defined in the publication by L. Sorbier et al. “ Measurement of palladium crust thickness on catalyst by EPMA” Materials Science and Engineering 32 (2012). It makes it possible to establish the distribution profile of a given element, here palladium, within the grain. Furthermore, the palladium concentration is defined for each measurement and therefore for each analysis step. The density of palladium within the grain is therefore defined as the concentration of palladium per mm ³ .

Definition of the R coefficient

The distribution profiles of the elements within the catalyst grains are obtained by Castaing microprobe. At least 30 analysis points are carried out along the diameter of the ball or the extrusion at the rate of around ten points on the crust of an active element (here gold) and around ten points in the center of the grain. The distribution profile c(x) is thus obtained for x ∈ [ -r ;+r ] with c the local concentration of the element, r the radius of the ball or the extrusion and x the position of the point d analysis along the diameter of the grain relative to the center of this grain.

The distribution of the elements is characterized by a dimensionless coefficient R weighting the local concentration by an increasing weight as a function of the position on the diameter. By definition :

Thus an element whose concentration is uniform (that is to say an element distributed homogeneously throughout the section of the support) has a coefficient R equal to 1, an element deposited in a dome (concentration at the core greater than the concentration at the edges of the support) has a coefficient greater than 1 and an element distributed in the crust (concentration at the edges greater than the concentration at the heart of the support) presents a coefficient less than 1. Analysis by Castaing microprobe gives the values of the concentrations in a finite number of values of x, R is thus evaluated numerically by integration methods well known to those skilled in the art. Preferably, R is determined by the trapezoid method. The distribution of copper is defined as homogeneous when the distribution coefficient R defined above is between 0.8 and 1.2.

Catalyst

The invention relates to a catalyst comprising an active phase consisting of palladium and copper, and a porous alumina support, in which the palladium content is between 0.02% and 0.2% by weight of palladium element per relative to the total weight of the catalyst, the copper content is between 0.1% and 15% by weight of copper element relative to the total weight of the catalyst, at least 80% by weight of the palladium is distributed in a crust at the periphery of said support, the thickness of said crust being between 20 and 300 µm, characterized in that:

- the copper is distributed homogeneously across the porous support;

- the mass ratio between copper and palladium is between 20 and 1000 weight/weight;

- said porous alumina support has a specific surface area of between 55 and 150 m²/g.

The palladium content in the catalyst is between 0.02% and 0.2% by weight of palladium element relative to the total weight of the catalyst, preferably between 0.03% and 0.1% by weight, and even more preferably between 0.04% and 0.08% by weight.

The copper content in the catalyst is between 0.1% and 15% by weight of copper element relative to the total weight of the catalyst, preferably between 0.5% and 13% by weight, and even more preferably between 0. 8% and 11% by weight.

According to an essential characteristic of the invention, the mass ratio between copper and palladium is between 20 and 100 weight/weight, preferably between 50 and 500 weight/weight, and more preferably between 70 and 300 weight/weight, and even more particularly between 80 and 200 weight/weight.

Advantageously, at least 80% by weight of the palladium is distributed in a crust at the periphery of the porous support, the thickness of said crust being between 20 and 300 µm, preferably between 25 and 280 µm, more preferably between 30 and 250 µm , and even more preferably between 30 and 200 µm.

According to the invention, the copper is distributed homogeneously in the porous support. Advantageously, the copper is distributed homogeneously in the porous support with a distribution coefficient R, measured by Castaing microprobe, of between 0.8 and 1.2, preferably between 0.85 and 1.1, and more preferably between 0.9 and 1.1.

The average particle size (in size) of palladium is advantageously between 0.5 to 10 nm, preferably between 1 and 6 nm. The average size of the crystallites is deduced from the measurements of metallic dispersion of the particles (D), by applying the dispersion-particle size relationships known to those skilled in the art and described in “Physico-chemical analysis of industrial catalysts, Chapter I, Editions Technip, Paris 2001.

The specific surface area of the catalyst is between 55 m²/g and 150 m²/g, preferably between 60 m²/g and 140 m²/g, even more preferably between 65 m²/g and 135 m²/g, and more preferably between 65 m²/g and 130 m²/g.

The total pore volume (VPT) of the catalyst is advantageously between 0.1 and 1.5 cm ³ /g, preferably between 0.2 and 1.4 cm ³ /g, and even more preferably between 0.25 and 1.3 cm ³ /g.

Support

The porous support according to the invention is alumina, that is to say that the support comprises at least 95%, preferably at least 98%, and particularly preferably at least 99% by weight of alumina per in relation to the weight of the support. 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 IIA, IIIB, IVB, IIB, IIIA, IVA according to the CAS classification, preferably silica, titanium dioxide, zirconium dioxide, zinc oxide, magnesium oxide and calcium oxide, or even alkali metals, preferably lithium, sodium or potassium, and/or alkaline earth metals, preferably magnesium, calcium, strontium or barium or even sulfur.

The specific surface area of the porous support is between 55 m²/g and 150 m²/g, preferably between 60 m²/g and 140 m²/g, even more preferably between 65 m²/g and 135 m²/g, and more preferably between 65 m²/g and 130 m²/g.

The total pore volume (VPT) of the porous support is advantageously between 0.1 and 1.5 cm ³ /g, preferably between 0.2 and 1.4 cm ³ /g, and even more preferably between 0. 25 and 1.3 cm ³ /g.

Advantageously, the porous support is in the form of beads or in the form of a quadrilobe-shaped extrusion. When the support is in the form of balls, the diameter of the balls is generally between 1 mm and 10 mm, preferably between 2 and 8 mm, and even more preferably between 2 and 6 mm. When the support is in the form of a quadrilobe type extrusion, the length of the extrusion is generally between 2 and 10 mm, preferably between 2 and 8 mm, and more preferably between 3 and 6 mm. When the support is in the form of a quadrilobe type extrudate, the extrudates have a 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 length between 0.5 and 2.0 mm.

Preparation of the catalyst

The deposition of the active phase of palladium and copper on the support can be carried out using all the techniques known to those skilled in the art.

Preferably, the palladium solution is deposited by dry impregnation method or by colloidal method.

Dry impregnation

In one embodiment according to the invention, the palladium and copper solutions are deposited by dry impregnation method. According to the invention, the palladium solution and the copper solution are impregnated separately on the support and in a very particular order. The aqueous solution containing the precursor of the active phase of palladium is first impregnated on the support before impregnating the aqueous solution containing the precursor of the active phase of copper.

More particularly, the process for preparing the catalyst comprises the following steps:

a) an aqueous solution comprising at least one palladium precursor salt is impregnated onto the porous support;

b) the impregnated support obtained at the end of step a) is matured in the wet state for 0.5 hour to 40 hours to obtain a catalyst precursor;

c) the catalyst precursor obtained at the end of step b) is dried at a temperature below 250°C to obtain a dried catalyst precursor;

d) an aqueous solution comprising at least one copper precursor salt is impregnated on the dried catalyst precursor obtained in step c);

e) the catalyst precursor obtained at the end of step d) is dried at a temperature below 250°C to obtain a dried catalyst;

f) the dried catalyst obtained in step e) is calcined at a temperature between 250°C and 900°C;

g) optionally, a hydrothermal treatment is carried out in air, comprising between 150 and 5000 grams of water per kg of air, at a temperature between 500°C and 900°C;

h) optionally, a reducing treatment is carried out by contact with a reducing gas.

The different stages are explained in detail below.

a) Impregnation of the support

During step a), an aqueous solution is prepared comprising at least one palladium precursor salt. The palladium precursor salt is preferably selected from sodium chloropalladate, palladium nitrate and palladium sulfate.

The deposition of palladium on the porous support is carried out by dry impregnation of the aqueous solution comprising at least one palladium precursor salt on the porous support, the volume of said aqueous solution generally being between 0.9 and 1.1 times the porous volume of the support.

b) maturation of the impregnated support

After impregnation, the impregnated support is matured in the wet state for 0.5 hour to 40 hours, preferably for 1 to 30 hours. Longer durations are not excluded, but do not necessarily bring improvement.

c) drying

The catalyst precursor is dried in order to eliminate all or part of the water introduced during impregnation at a temperature below 250°C, preferably between 70°C and 200°C. The drying time is preferably between 0.5 h and 20 h. Longer durations are not excluded, but do not necessarily bring improvement.

Drying is generally carried out under combustion air of a hydrocarbon, preferably methane, or under heated air comprising between 0 and 80 grams of water per kilogram of combustion air, an oxygen level of between 5% and 25% volume and a carbon dioxide level of between 0% and 10% volume.

d) Impregnation of the support

During step d), an aqueous solution is prepared comprising at least one copper precursor salt. The copper precursor salt is preferably selected from copper acetate, copper acetylacetonate, copper nitrate, copper sulfate, copper chloride, copper bromide, copper iodide or fluoride of copper.

The deposition of copper on the catalyst precursor obtained at the end of step c) is carried out by dry impregnation of the aqueous solution comprising at least one copper precursor salt on the catalyst precursor obtained at the end of step c). step c), the volume of said aqueous solution generally being between 0.9 and 1.1 times the pore volume of the support. The concentration of copper in solution is supplied so that the mass ratio between copper and palladium is between 20 and 1000 w/w, preferably between 50 and 500 w/w, and more preferably between 70 and 300 wt. /weight, and even more particularly between 80 and 200 weight/weight.

e) drying

The catalyst precursor obtained at the end of step d) is dried in order to eliminate all or part of the water introduced during impregnation at a temperature below 250°C, preferably between 70°C. C and 200°C. The drying time is preferably between 0.5 h and 20 h. Longer durations are not excluded, but do not necessarily bring improvement.

Drying is generally carried out under combustion air of a hydrocarbon, preferably methane, or under heated air comprising between 0 and 80 grams of water per kilogram of combustion air, an oxygen level of between 5% and 25% volume and a carbon dioxide level of between 0% and 10% volume.

f) calcination of the dried catalyst obtained in step e)

After drying, the dried catalyst obtained at the end of step e) is calcined in air, preferably combustion air, and more preferably methane combustion air, comprising between 40 and 80 grams of water per kg of air, an oxygen level of between 5% and 15% volume and a CO ₂ level of between 4% and 10% volume. The calcination temperature is generally between 250°C and 900°C, preferably between approximately 300°C and approximately 700°C. The calcination time is generally between 0.5 h and 5 h. The hourly volumetric speed (VVH) is generally between 150 and 3000, preferably between 300 and 1500 liters of combustion air per hour and per liter of catalyst.

g) hydrothermal treatment of the calcined catalyst obtained in step f) (optional)

After calcination step f), the catalyst can undergo a hydrothermal treatment under air, preferably under combustion air, comprising between 150 and 5000 grams of water per kg of air, preferably between 300 and 4500, and again more preferably between 500 and 4000 grams of water per kg of air.

The temperature of the hydrothermal treatment is between 500°C and 900°C, preferably between 600°C and 700°C.

The duration of the hydrothermal treatment is generally between 0.5 and 5 hours.

h) reduction (optional step)

The catalyst is generally reduced. This step is preferably carried out in the presence of a reducing gas, either in situ , that is to say in the reactor where the catalytic transformation is carried out, or ex situ . Preferably, this step is carried out at a temperature between 80°C and 180°C, even more preferably between 100°C and 160°C.

The reduction is carried out in the presence of a reducing gas comprising between 25 vol% and 100 vol% of dihydrogen, preferably 100 vol% of dihydrogen. The dihydrogen is optionally supplemented by an inert gas for reduction, preferably argon, dinitrogen or methane.

The reduction generally includes a temperature rise phase then a plateau.

The duration of the reduction stage is generally between 1 and 10 hours, preferably between 2 and 8 hours.

The Volumetric Hourly Speed (V.V.H) is generally between 150 and 3000, preferably between 300 and 1500 liters of reducing gas per hour and per liter of catalyst.

Colloidal impregnation

In another embodiment according to the invention, the solutions of palladium and copper are deposited by colloidal method. According to the invention, the palladium suspension and the copper suspension are impregnated separately on the support and in a very particular order. The suspension containing the precursor of the active phase of palladium is first impregnated on the support before impregnating the suspension containing the precursor of the active phase of copper.

More particularly, the process for preparing the catalyst comprises the following steps:

a1) a colloidal suspension of palladium oxide or palladium hydroxide is impregnated in the aqueous phase by mixing an aqueous solution (I) comprising at least one hydroxide selected from the group consisting of alkali hydroxides and hydroxides alkaline earth metal and an aqueous solution (II) comprising at least one palladium precursor on the porous support;

b1) the impregnated porous support obtained in step a1) is subjected to maturation in order to obtain a catalyst precursor;

c1) the catalyst precursor obtained in step b1) is dried at a temperature below 250°C;

d1) a colloidal suspension of copper oxide or copper hydroxide in the aqueous phase is impregnated on the dried catalyst precursor obtained at the end of step c1) by mixing an aqueous solution (III) comprising at at least one hydroxide selected from the group consisting of alkali hydroxides and alkaline earth hydroxides and an aqueous solution (IV) comprising at least one copper precursor;

e1) the catalyst precursor obtained in step d1) is dried at a temperature below 250°C;

f1) the dried catalyst obtained in step e1) is calcined at a temperature between 250°C and 900°C;

g1) optionally, a hydrothermal treatment of the calcined catalyst obtained in step f1) is carried out at a temperature between 500°C and 900°C, in air, comprising between 150 and 5000 grams of water per kg of air;

h1) optionally, a reducing treatment is carried out by contact with a reducing gas.

The different stages are explained in detail below.

a1) Impregnation of a colloidal suspension of palladium oxide or palladium hydroxide in aqueous phase

The colloidal suspension is generally obtained by hydrolysis of the palladium cation in an aqueous medium, which leads to the formation of palladium oxide or hydroxide particles in suspension.

The aqueous solution of alkali hydroxide or alkaline earth hydroxide is generally selected from the group consisting of aqueous solutions of sodium hydroxide, aqueous solutions of magnesium hydroxide. Preferably, preferably the aqueous solution is an aqueous solution of sodium hydroxide.

The palladium precursor salt is generally selected from the group consisting of palladium chloride, palladium nitrate and palladium sulfate. Very preferably, the palladium precursor salt is palladium nitrate.

Typically, the aqueous solution comprising at least one precursor salt of palladium [also called here solution (II)] is supplied to suitable equipment, then the aqueous solution comprising at least one alkaline or alkaline earth hydroxide [also called here solution (I)]. Alternatively, solutions (I) and (II) can be poured simultaneously into the apparatus. Preferably, the aqueous solution (II) then the aqueous solution (I) is poured into the apparatus.

The colloidal suspension generally remains in the apparatus for a residence time of between 0 and 20 hours.

The concentrations of the solution (I) and (II) are generally chosen in order to obtain a pH of the colloidal suspension between 1.0 and 3.5. Thus, the pH of the colloidal suspension can be modified during this residence time by adding quantities of acid or base compatible with the stability of the colloidal suspension.

In general, the preparation temperature is between 5°C and 40°C and preferably between 15°C and 35°C.

The palladium concentration is preferably between 5 and 150 millimoles per liter (mmol/L), more preferably between 8 and 80 millimoles per liter.

Once the colloidal suspension has been prepared, said suspension is impregnated onto the porous support.

The colloidal suspension is preferably poured onto said support. Preferably, the volume of the colloidal suspension impregnated on the support is between 0.9 and 1.1 times the pore volume of the support.

b1) maturation of the impregnated support during step a1) for a period of between 0.5 and 40 hours

After impregnation, the impregnated support can be matured in the wet state for 0.5 hour to 40 hours, preferably for 1 hour to 30 hours. Longer durations are not excluded, but do not necessarily bring improvement.

c1) drying of the catalyst precursor obtained in step b1)

The catalyst precursor is dried in order to eliminate all or part of the water introduced during impregnation at a temperature below 250°C, preferably between 70°C and 200°C. The drying time is generally between 0.5 h and 20 h. Longer durations are not excluded, but do not necessarily bring improvement.

Drying is generally carried out under combustion air of a hydrocarbon, preferably methane, or under heated air comprising between 0 and 80 grams of water per kilogram of combustion air, an oxygen level of between 5% and 25% volume and a carbon dioxide level of between 0% and 10% volume.

d1) Impregnation of a colloidal suspension of palladium oxide or palladium hydroxide in aqueous phase

According to step d1), the dried catalyst precursor obtained at the end of step c1) is impregnated with a colloidal suspension of copper oxide or copper hydroxide in an aqueous phase by mixing an aqueous solution. (III) comprising at least one hydroxide selected from the group consisting of alkali hydroxides and alkaline earth hydroxides and an aqueous solution (IV) comprising at least one copper precursor.

This step can be carried out under the same operating conditions as step a1).

The copper precursor salt is generally selected from the group consisting of copper acetate, copper acetylacetonate, copper nitrate, copper sulfate, copper chloride, copper bromide, copper iodide or copper fluoride. Very preferably, the copper precursor salt is copper nitrate.

The concentration of copper in solution is supplied so that the mass ratio between copper and palladium is between 20 and 1000 w/w, preferably between 50 and 500 w/w, and more preferably between 70 and 300 wt. /weight, and even more particularly between 80 and 200 weight/weight.

e1) drying of the catalyst precursor obtained in step d1)

The catalyst precursor obtained at the end of step d1) is dried in order to eliminate all or part of the water introduced during impregnation at a temperature below 250°C, preferably between 70°C. C and 200°C. The drying time is generally between 0.5 h and 20 h. Longer durations are not excluded, but do not necessarily bring improvement.

Drying is generally carried out under combustion air of a hydrocarbon, preferably methane, or under heated air comprising between 0 and 80 grams of water per kilogram of combustion air, an oxygen level of between 5% and 25% volume and a carbon dioxide level of between 0% and 10% volume.

f1) calcination of the dried catalyst obtained in step e1)

After drying, the catalyst is calcined in air, preferably combustion air, and more preferably methane combustion air, comprising between 40 and 80 grams of water per kg of air, an oxygen level of between 5% and 15% volume and a CO ₂ level of between 4% and 10% volume. The calcination temperature is generally between 250°C and 900°C, preferably between approximately 300°C and approximately 500°C. The calcination time is generally between 0.5 h and 5 h. The hourly volumetric speed (VVH) is generally between 150 and 3000, preferably between 300 and 1500 liters of combustion air per hour and per liter of catalyst.

g1) hydrothermal treatment of the calcined catalyst obtained in step f1)

After step f1) of calcination, the catalyst can undergo a hydrothermal treatment under air, preferably under combustion air, comprising between 150 and 5000 grams of water per kg of air, preferably between 300 and 4500, and again more preferably between 500 and 4000 grams of water per kg of air.

The temperature of the hydrothermal treatment is between 500°C and 900°C, preferably between 600°C and 700°C.

The duration of the hydrothermal treatment is generally between 0.5 and 5 hours.

h1) reduction (optional step)

The catalyst is generally reduced. This step is preferably carried out in the presence of a reducing gas, either in-situ, that is to say in the reactor where the catalytic transformation is carried out, or ex-situ. Preferably, this step is carried out at a temperature between 80°C and 180°C, even more preferably between 100°C and 160°C.

The reduction is carried out in the presence of a reducing gas comprising between

25 vol% and 100 vol% hydrogen, preferably 100 vol% hydrogen. The hydrogen is optionally supplemented by an inert gas for reduction, preferably argon, nitrogen or methane.

The reduction generally includes a temperature rise phase then a plateau.

The duration of the reduction stage is generally between 1 and 10 hours, preferably between 2 and 8 hours.

The Volumetric Hourly Speed (V.V.H) is generally between 150 and 3000, preferably between 300 and 1500 liters of reducing gas per hour and per liter of catalyst.

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 being carried out at a temperature between 0 and 300°C, at a pressure between 0.1 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 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 an hourly volume speed between 100 and 40,000 h ^-1 when the process is carried out in the gas phase, in the presence of a catalyst according to the invention as described above in the description.

Monounsaturated organic compounds, such as ethylene and propylene, are the source of the manufacturing of polymers, plastics and other value-added chemicals. These compounds are obtained from natural gas, naphtha or diesel 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 parasitic reactions in the polymerization units. It is therefore necessary to eliminate them before valorizing these cuts.

Selective hydrogenation is the primary 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 cracking gasolines used as feedstock, selective hydrogenation also makes it possible to selectively hydrogenate the alkenyl aromatics into aromatics while avoiding the hydrogenation of the aromatic nuclei.

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 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 alkenyl aromatic function.

More particularly, the feed used is a steam cracking gasoline also called pyrolysis gasoline or C5+ cut.

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 temperature is generally between 0 and 300 ° C, of 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, etc.). ). Steam cracked gasoline generally includes 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 alkenyl aromatic compounds, all of 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.

The technological implementation of the selective hydrogenation process is for example carried out by injection, in ascending or descending current, of the polyunsaturated hydrocarbon feed 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 polyunsaturated hydrocarbon feed can advantageously be diluted by one or more re-injection(s) 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 reactor outlet 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 slurry type reactor . The hydrogen flow can be introduced at the same time as the feed to be hydrogenated and/or at one or more different points in the reactor.

In one embodiment according to the invention, when carrying out a selective hydrogenation process in which the feedstock is a steam cracking gasoline comprising 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 hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio 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 preferably, a selective hydrogenation process is carried out in which the feedstock is a steam cracking 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 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 have a sufficient quantity to theoretically hydrogenate all the polyunsaturated compounds and to maintain an excess of hydrogen at the reactor outlet.

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

Examples

Example 1: Dry impregnation of palladium alone 0.3% by weight (non-compliant)

An aqueous solution of palladium nitrate is prepared at 25°C by dilution of 78.6 mg palladium nitrate of Pd(NO ₃ ).2H ₂ O (MERK®, CAS 32916-07-7) dissolved in 8.9 g demineralized water.

This solution is then impregnated (by the dry impregnation method) on 10 grams of an alumina whose S _BET is 70 m²/g. This alumina is in the form of quadrilobed extrudates with an average diameter of 1.6 mm.

A maturation stage of the impregnated support before drying lasting 20 hours is carried out under air in a confined and humid environment.

The catalyst A obtained is dried for 2 hours in air at 120°C, then is calcined for 2 hours at 650°C under a flow of combustion air with a V.V.H. of 3000 liters of combustion air per liter of catalyst per hour. Combustion air contains approximately 60 g of water per kg of dry air.

The final Pd content of catalyst A is 0.3% by weight of palladium element relative to the total weight of the catalyst. The characterization of catalyst A by Castaing microprobe shows that 80% of the Pd is distributed over a crust approximately 222 µm thick.

Example 2: Impregnations of Cu and Pd in a Cu/Pd mass ratio < 20 (non-compliant)

An aqueous solution of palladium nitrate is prepared at 25°C by dilution of 78.6 mg palladium nitrate of Pd(NO ₃ ).2H ₂ O (MERK®, CAS 32916-07-7) dissolved in 8.9 g demineralized water.

This solution is then impregnated (by the dry impregnation method) on 10 grams of an alumina whose S _BET is 70 m²/g. This alumina is in the form of quadrilobed extrudates with an average diameter of 1.6 mm.

A maturation stage of the impregnated support before drying lasting 20 hours is carried out under air in a confined and humid environment. The solid obtained is dried in air for 2 hours at 120°C.

1.92 g of Cu(NO ₃ ).3H ₂ O (Merk® CAS 10031-43-3) dissolved in 8.3 g of water are then dry impregnated on Pd/Al ₂ O ₃ .

The catalyst B obtained is dried under air for 2 hours at 120°C, then is calcined for 2 hours at 650°C under a flow of combustion air with a V.V.H. of 3000 liters of combustion air per liter of catalyst per hour. Combustion air contains approximately 60 g of water per kg of dry air.

Catalyst B comprises a palladium element content of 0.3% by weight and a copper element content of 5% by weight. The characterization of catalyst B by Castaing microprobe shows that 80% of the Pd is distributed over a crust approximately 222 µm thick. The copper distribution coefficient is 1, the copper distribution is homogeneous in the grain.

Example 3: Quatrefoil support (compliant)

An aqueous solution of palladium nitrate is prepared at 25°C by dilution of 13.1 mg palladium nitrate of Pd(NO ₃ ).2H ₂ O (MERK®, CAS 32916-07-7) dissolved in 8.9 g of demineralized water.

This solution is then impregnated (by the dry impregnation method) on 10 grams of an alumina whose S _BET is 70 m²/g. This alumina is in the form of quadrilobed extrudates with an average diameter of 1.6 mm.

A maturation step of the impregnated support before drying lasting 20 hours is carried out under air in a confined and humid environment. The solid obtained is dried in air for 2 h at 120°C.

1.92 g of Cu(NO ₃ ).3H ₂ O (Merk® CAS 10031-43-3) dissolved in 8.3 g of water are then dry impregnated on Pd/Al2O3.

The catalyst C obtained is dried under air for 2 hours at 120°C, then is calcined for 2 hours at 650°C under a flow of combustion air with a V.V.H. of 3000 liters of combustion air per liter of catalyst per hour. Combustion air contains approximately 60 g of water per kg of dry air.

Catalyst C comprises a palladium element content of 0.05% by weight and a copper element content of 5% by weight. The characterization of catalyst C by Castaing microprobe shows that 80% of the Pd is distributed over a crust approximately 50 µm thick. The copper distribution coefficient is 1, the copper distribution is homogeneous in the grain.

Example 4: Ball support (compliant)

An aqueous solution of palladium nitrate is prepared at 25°C by dilution of 13.1 mg palladium nitrate Pd(NO ₃ ).2H ₂ O (MERK®, CAS 32916-07-7) dissolved in 8.9 g of 'demineralized water.

This solution is then impregnated (by the dry impregnation method) on 10 grams of an alumina whose S _BET is 70 m²/g. This alumina is in the form of beads with a grain size centered on 3 mm in diameter.

A maturation stage of the impregnated support before drying lasting 20 hours is carried out under air in a confined and humid environment. The solid obtained is dried in air for 2 h at 120°C.

1.92 g of Cu(NO ₃ ).3H ₂ O (Merk® CAS 10031-43-3) dissolved in 8.3 g of water are then dry impregnated on Pd/Al2O3.

The catalyst D obtained is dried for 2 hours in air at 120°C, then is calcined for 2 hours at 650°C under a flow of combustion air with a V.V.H. of 3000 liters of combustion air per liter of catalyst per hour. Combustion air contains approximately 60 g of water per kg of dry air.

Catalyst D comprises a palladium element content of 0.05% by weight and a copper element content of 5% by weight. The characterization of catalyst D by Castaing microprobe shows that 80% of the Pd is distributed over a crust approximately 70 µm thick. The copper distribution coefficient is 1, the copper distribution is homogeneous in the grain.

Example 5: Impregnations of Pd and Cu in a Cu/Pd ratio = 1 (non-compliant)

An aqueous solution of palladium nitrate is prepared at 25°C by dilution of 13.1 mg palladium nitrate of Pd(NO ₃ ).2H ₂ O (MERK®, CAS 32916-07-7 dissolved in 8.9 g of 'demineralized water.

This solution is then impregnated (by the dry impregnation method) on 10 grams of an alumina whose S _BET is 70 m²/g. This alumina is in the form of quadrilobed extrudates with an average diameter of 1.6 mm.

A maturation stage of the impregnated support before drying lasting 20 hours is carried out under air in a confined and humid environment. The solid obtained is dried in air for 2 h at 120°C.

19.2 mg of Cu(NO ₃ ).3H ₂ O (Merk® CAS 10031-43-3) dissolved in 8.3 g of water are then dry impregnated on Pd/Al2O3.

The catalyst E obtained is dried for 2 hours in air at 120°C, then is calcined for 2 hours at 650°C under a flow of combustion air with a V.V.H. of 3000 liters of combustion air per liter of catalyst per hour. Combustion air contains approximately 60 g of water per kg of dry air.

Catalyst E comprises a palladium element content of 0.05% by weight and a copper element content of 0.05% by weight. The characterization of catalyst E by Castaing microprobe shows that 80% of the Pd is distributed over a crust approximately 20 µm thick. The copper distribution coefficient is 0.4, the copper is crusted with a crust thickness of 80 µm.

Example 6: Support with specific surface area too low outside the claimed range (non-compliant)

An aqueous solution of palladium nitrate is prepared at 25°C by dilution of 13.1 mg palladium nitrate of Pd(NO ₃ ).2H ₂ O (MERK®, CAS 32916-07-7) dissolved in 8.9 g of demineralized water.

This solution is then impregnated (by the dry impregnation method) on 10 grams of an alumina whose S _BET is 30 m²/g. This alumina is in the form of quadrilobed extrudates with an average diameter of 1.6 mm.

A maturation step of the impregnated support before drying lasting 20 hours is carried out under air in a confined and humid environment. The solid obtained is dried in air for 2 h at 120°C.

1.92 g of Cu(NO ₃ ).3H ₂ O (Merk® CAS 10031-43-3) dissolved in 8.3 g of water are then dry impregnated on Pd/Al2O3.

The catalyst F obtained is dried under air for 2 hours at 120°C, then is calcined for 2 hours at 650°C under a flow of combustion air with a V.V.H. of 3000 liters of combustion air per liter of catalyst per hour. Combustion air contains approximately 60 g of water per kg of dry air.

Catalyst F comprises a palladium element content of 0.05% by weight and a copper element content of 5% by weight. The characterization of catalyst E by Castaing microprobe shows that 80% of the Pd is distributed over a crust approximately 300 µm thick. The copper distribution coefficient is 1, the copper distribution is homogeneous in the grain.

Example 7: Support with specific surface area too high outside the claimed range (non-compliant)

An aqueous solution of palladium nitrate is prepared at 25°C by dilution of 13.1 mg palladium nitrate of Pd(NO ₃ ).2H ₂ O (MERK®, CAS 32916-07-7) dissolved in 8.9 g of demineralized water.

This solution is then impregnated (by the dry impregnation method) on 10 grams of an alumina whose S _BET is 270 m²/g. This alumina is in the form of quadrilobed extrudates with an average diameter of 1.6 mm.

A maturation step of the impregnated support before drying lasting 20 hours is carried out under air in a confined and humid environment. The solid obtained is dried in air for 2 h at 120°C.

1.92 g of Cu(NO ₃ ).3H ₂ O (Merk® CAS 10031-43-3) dissolved in 8.3 g of water are then dry impregnated on Pd/Al2O3.

The catalyst G obtained is dried under air for 2 hours at 120°C, then is calcined for 2 hours at 650°C under a flow of combustion air with a V.V.H. of 3000 liters of combustion air per liter of catalyst per hour. Combustion air contains approximately 60 g of water per kg of dry air.

Catalyst G comprises a palladium element content of 0.05% by weight and a copper element content of 5% by weight. The characterization of catalyst G by Castaing microprobe shows that 80% of the Pd is distributed over a crust approximately 20 µm thick. The copper distribution coefficient is 0.9, the copper distribution is homogeneous in the grain.

Example 8: Catalytic tests: performance in selective hydrogenation of a mixture containing styrene and isoprene

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

The composition of the feed to be selectively hydrogenated is as follows: 8% by weight styrene (supplier Sigma Aldrich®, purity 99%), 8% by weight isoprene (supplier Sigma Aldrich®, purity 99%), 84% by weight n-heptane (solvent ) (VWR® supplier, purity > 99% HPLC chromanorm). This charge also contains very low levels of sulfur compounds: 10 ppm by weight of sulfur introduced in the form of pentanethiol (supplier Fluka®, purity > 97%) and 100 ppm by 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 essence.

The selective hydrogenation reaction is carried out in a 500 mL stainless steel autoclave, equipped with mechanical stirring with magnetic drive and capable of operating 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 reducedex situunder 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 into the autoclave, protected 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 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 of the reaction medium at regular time intervals: styrene is hydrogenated to ethylbenzene, without hydrogenation of the aromatic ring, and isoprene is hydrogenated to methyl-butenes. If the reaction is continued longer than necessary, the methyl-butenes are in turn hydrogenated to isopentane. Hydrogen consumption is also monitored over time by the reduction 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 G are reported in Table 1 below. They are related to the catalytic activity per gram of catalyst (A _HYDcata ) and per gram of Pd (A _HYDPd ) measured for catalyst B.

Catalyst Pd content (%wt) Cu content (%wt) Cu/Pd (wt/wt) Support S _BET Support
(m²/g) Crust thickness Pd (µm) R _Cu A _HYDcata (%) A _HYDPd (%) A (non-compliant) 0.3 - - extruded 70 222 - 80 80 B (non-compliant) 0.3 5 16.7 extruded 70 222 1 100 100 C (compliant) 0.05 5 100 extruded 70 50 1 100 400 D (compliant) 0.05 5 100 marbles 70 70 1 100 360 E (non-compliant) 0.05 0.05 1 extruded 70 20 0.4 20 20 F (non-compliant) 0.05 5 100 extruded 30 m²/g 300 1 80 150 G (non-compliant) 0.05 5 100 extruded 270 m²/g 20 0.9 100 150

Table 1: Comparison of the performances of catalysts A to G in selective hydrogenation of a mixture containing styrene and isoprene per gram of catalyst (A _HYDcata ) and per gram of Pd (A _HYDPd )

This clearly shows the improved performance of catalysts C and D according to the invention, compared to non-compliant catalysts A, B, E, F and G. This is explained by a synergistic effect between the choice of the active phase consisting of copper and palladium (in a very specific mass ratio) and the specific surface area of the support used. All of these characteristics make it possible to drastically reduce the palladium content while maintaining better activity than the same catalyst without copper but with six times more palladium (catalyst A).

Claims (15)

Catalyst comprising an active phase consisting of palladium and copper and a porous alumina support, in which the palladium content is between 0.02% and 0.2% by weight of palladium element relative to the total weight of the catalyst , the copper content is between 0.1% and 15% by weight of copper element relative to the total weight of the catalyst, at least 80% by weight of the palladium is distributed in a crust at the periphery of said support, the thickness of said crust being between 20 and 300 µm, characterized in that:
- the copper is distributed homogeneously across the porous support;
- the mass ratio between copper and palladium is between 20 and 1000 weight/weight;
- said porous alumina support comprises a specific surface area of between 55 and 150 m²/g. Catalyst according to claim 1, characterized in that the mass ratio between copper and palladium is between 50 and 500 weight/weight. Catalyst according to one of claims 1 or 2, characterized in that the copper content is between 0.5 and 13% by weight of copper element relative to the total weight of the catalyst. Catalyst according to any one of claims 1 to 3, characterized in that the palladium content is between 0.03 and 0.1% by weight of palladium element relative to the total weight of the catalyst. Catalyst according to any one of claims 1 to 4, characterized in that said porous support comprises a specific surface area of between 60 and 140 m²/g. Catalyst according to any one of claims 1 to 5, characterized in that said porous support is in the form of an extrusion comprising four lobes. Catalyst according to any one of claims 1 to 5, characterized in that said porous support is in the form of a ball. Process for preparing a catalyst according to any one of claims 1 to 7 comprising the following steps:
a) an aqueous solution comprising at least one palladium precursor salt is impregnated onto the porous support;
b) the impregnated support obtained at the end of step a) is matured in the wet state for 0.5 hour to 40 hours to obtain a catalyst precursor;
c) the catalyst precursor obtained at the end of step b) is dried at a temperature below 250°C to obtain a dried catalyst precursor;
d) an aqueous solution comprising at least one copper precursor salt is impregnated on the dried catalyst precursor obtained in step c);
e) the catalyst precursor obtained at the end of step d) is dried at a temperature below 250°C to obtain a dried catalyst;
f) the dried catalyst obtained in step e) is calcined at a temperature between 250°C and 900°C. Preparation process according to claim 8, wherein in step a), the palladium precursor is selected from the group consisting of sodium chloropalladate, palladium nitrate and palladium sulfate. Preparation process according to one of claims 8 or 9, in which the copper precursor is chosen from copper acetate, copper acetylacetonate, copper nitrate, copper sulfate, copper chloride, copper bromide, copper iodide or copper fluoride. Process according to any one of claims 9 or 10, in which a step g) of hydrothermal treatment in air of the calcined catalyst obtained in the step is further carried out, comprising between 150 and 5000 grams of water per kg of air , at a temperature between 500°C and 900°C. Process for preparing a catalyst according to any one of claims 1 to 7 comprising the following steps:
a1) a colloidal suspension of palladium oxide or palladium hydroxide is impregnated in the aqueous phase by mixing an aqueous solution (I) comprising at least one hydroxide selected from the group consisting of alkali hydroxides and hydroxides alkaline earth metal and an aqueous solution (II) comprising at least one palladium precursor on the porous support;
b1) the impregnated porous support obtained in step a1) is subjected to maturation in order to obtain a catalyst precursor;
c1) the catalyst precursor obtained in step b1) is dried at a temperature below 250°C;
d1) a colloidal suspension of copper oxide or copper hydroxide in the aqueous phase is impregnated on the dried catalyst precursor obtained at the end of step c1) by mixing an aqueous solution (III) comprising at at least one hydroxide selected from the group consisting of alkali hydroxides and alkaline earth hydroxides and an aqueous solution (IV) comprising at least one copper precursor;
e1) the catalyst precursor obtained in step d1) is dried at a temperature below 250°C;
f1) the dried catalyst obtained in step e1) is calcined at a temperature between 250°C and 900°C. A method according to claim 12, wherein said palladium precursor salt is chosen from palladium chloride, palladium nitrate and palladium sulfate. Process for the selective hydrogenation of polyunsaturated compounds containing at least 2 carbon atoms per molecule contained in a hydrocarbon feed having a final boiling point less than or equal to 300°C, which process being carried out at a temperature between 0 and 300°C, at a pressure of between 0.1 and 10 MPa, at a hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio of between 0.1 and 10 and at an hourly volume rate of between 0.1 and 200 h ^{- 1} when the process is carried out in the liquid phase, or at a hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio of between 0.5 and 1000 and at an hourly volume rate between 100 and 40,000 h ^-1 when the process is carried out in phase gaseous, in the presence of a catalyst according to any one of claims 1 to 7. Process according to claim 14, characterized in that the hydrocarbon feedstock is a steam cracking gasoline.