Hydrogen desulfurization method in the presence of a catalyst on a meso-macroporous support

Abstract

Disclosed is a method for hydrodesulfurization of a sulfur-containing olefinic gasoline fraction, comprising contacting the sulfur-containing olefinic gasoline fraction, hydrogen, and a catalyst, the catalyst comprising a Group VIB metal, a Group VIII metal, and a mesoporous and macroporous alumina support having a bimodal mesopore distribution, wherein the volume of the mesopores having a diameter of 2 nm or more and less than 18 nm represents between 10% and 30% by volume of the total pore volume of the support, the volume of the mesopores having a diameter of 18 nm or more and less than 50 nm represents between 30% and 50% by volume of the total pore volume of the support, and the volume of macropores having a diameter of 50 nm or more and less than 8000 nm represents between 30% and 50% by volume of the total pore volume of the support.

Description

[Technical Field]

[0001] The present invention relates to the field of hydrogenation treatment of gasoline fractions, particularly gasoline fractions obtained from fluidized bed catalytic cracking units. More specifically, the present invention relates to the use of catalysts in a method for hydrodesulfurization of sulfur-containing olefinic gasoline fractions, such as gasoline obtained from catalytic cracking, where it is desired to reduce the content of sulfur-containing compounds without hydrogenating olefins and aromatic compounds. [Background technology]

[0002] Petroleum refining and petrochemicals are now facing new constraints, as countries are gradually adopting stricter sulfur standards, the goal of which, for example in Europe and Japan, is to reduce the sulfur content in commercially available gasoline to 10 ppm by weight. The issue of reducing sulfur content is essentially focused on gasoline obtained by either catalytic cracking (FCC or fluid catalytic cracking) or non-catalytic cracking (coking, vis-breaking, steam cracking), which are the main precursors of sulfur in the gasoline pool.

[0003] A well-known solution to reduce sulfur content, as described by those skilled in the art, involves hydrotreating (or hydrodesulfurizing) hydrocarbon fractions (particularly catalytic cracking gasoline) in the presence of hydrogen and a heterogeneous catalyst. However, this method has a major drawback: if the catalyst used is not sufficiently selective, it causes a very significant decrease in octane number. This decrease in octane number is particularly related to the hydrogenation of olefins present in this type of gasoline, which occurs simultaneously with hydrodesulfurization. Therefore, unlike other hydrotreating methods, hydrodesulfurization of gasoline must be designed to address the dual antagonistic constraints of extreme hydrodesulfurization of gasoline and the limitation of hydrogenation of present unsaturated compounds.

[0004] One way to address these two problems is to use a hydrodesulfurization catalyst that is active in hydrodesulfurization and is also highly selective in hydrodesulfurization for the reaction of hydrogenating olefins.

[0005] Therefore, the prior art uses an active metal phase containing cobalt / molybdenum and high-temperature alumina (i.e., alumina calcined at temperatures above 800°C) as a base, and contains less than 50% by weight of gamma, eta, and chialumina, and is 40 to 200 m 2 Patent Document 1 is known to disclose a hydrogenodesulfurization catalyst comprising a carrier having a specific surface area between / g. The catalyst is obtained by dry impregnation with an aqueous solution containing cobalt, molybdenum, and at least one additive in the form of an organic compound.

[0006] Patent Document 2 describes a selective hydrogenodesulfurization catalyst comprising at least one support, at least one group VIII element, at least one group VIB element, and phosphorus, wherein the support essentially consists of at least one transition alumina, i.e., comprising at least 51% by weight of transition alumina, and the support is possibly 135m 2 It has a specific surface area of ​​less than / g.

[0007] Furthermore, prior art has shown that the pore distribution of the catalyst support, particularly the presence of multi-modal pores, can have a beneficial effect on catalytic performance.

[0008] Patent Document 3 describes an active phase based on cobalt and molybdenum, an alkali dopant, and 260 to 290 m 2 A method for hydrodesulfurizing catalytic cracking (FCC) gasoline in the presence of a catalyst comprising an alumina support having a specific surface area between / g, a total pore volume between 0.8 and 2.2 ml / g, and pores having diameters between 10 and 200 nm, wherein the volume of pores having diameters between 10 and 50 nm corresponds to between 10% and 50% of the total pore volume of the support, and the volume of pores having diameters between 50 and 200 nm corresponds to between 50% and 90% of the total pore volume of the support. The support used comprises mesopores and macropores with a unimodal distribution.

[0009] Document CN109420504 discloses a method for hydrodesulfurization of fluid catalytic cracking (FCC) gasoline in the presence of a catalyst comprising an active phase based on cobalt and molybdenum and an alumina support with mesopores and macropores, wherein the volume of pores having diameters between 60 and 200 nm corresponds to between 1% and 80% of the total pore volume of the support, and the volume of pores having diameters between 5 and 50 nm corresponds to between 20% and 70% of the total pore volume of the support. The support used contains mesopores with a unimodal distribution and macropores with a unimodal distribution.

[0010] Document US6,589,908 discloses a method for preparing a catalyst support that does not contain macropores, has a bimodal pore structure in the mesopores, and the two pore modes are separated by 1 - 20 nm.

[0011] Therefore, there is still a strong interest today among refiners in hydrodesulfurization catalysts, particularly those for hydrodesulfurization of gasoline fractions, that have improved catalyst performance from the perspective of catalyst activity and / or selectivity in hydrodesulfurization, and thus, once used, can produce low - sulfur gasoline without significantly reducing the octane number.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0013] In this regard, one of the objects of the present invention is to provide a method for hydrodesulfurizing sulfur-containing olefin gasoline fractions in the presence of a supported catalyst that has performance at least as good as, or even better than, known methods from the prior art in terms of activity and selectivity. [Means for solving the problem]

[0014] The present invention relates to a method for hydrodesulfurizing a sulfur-containing olefin-based gasoline fraction, comprising contacting the sulfur-containing olefin-based gasoline fraction with hydrogen and a catalyst, wherein the hydrodesulfurizing method is performed at a temperature between 200°C and 400°C, a total pressure between 1 and 3 MPa, and a space velocity per hour defined as the flow rate of the volume of raw materials relative to the volume of catalyst between 1 and 10 h⁻¹. -1 The experiment is conducted between the following intervals, and the volume ratio of the hydrogen / gasoline fraction is between 100 and 600 Nl / l, and the catalyst comprises at least one group VIB metal, at least one group VIII metal, and a macroporous and mesoporous alumina support having a bimodal distribution of mesopores. The volume of the mesopores having diameters of 2 nm or more and less than 18 nm corresponds to between 10% and 30% by volume of the total pore volume of the carrier. The volume of the mesopores having a diameter of 18 nm or more and less than 50 nm corresponds to between 30% and 50% by volume of the total pore volume of the carrier. The volume of macropores having diameters of 50 nm or more and less than 8000 nm corresponds to between 30% and 50% by volume of the total pore volume of the carrier.

[0015] The applicant has discovered, surprisingly, that the catalytic performance of the method can be improved in terms of catalytic activity and selectivity by using a catalyst based on at least one group VIB metal and at least one group VIII metal on a mesoporous and macroporous support having bimodal mesopores with a high mesopore volume coupled to a given macropore volume. This improves the conversion rate of the raw materials under the same operating conditions as those used in the prior art. Specifically, without being bound by any scientific theory, the use of such a catalyst in the gasoline hydrodesulfurization method improves the internal diffusion of reactants and products due to the presence of a group of mesopores of different sizes. Furthermore, the combination of macropores is particularly recommended when the raw materials to be treated contain a large amount of reactive olefins (unsaturated compounds), especially in the case of gasoline containing diolefins, which can cause gum formation and, in the absence of macropores, clog the catalyst pores. Optimizing the pore range of the catalyst is a critical factor in the performance of the gasoline hydrodesulfurization method.

[0016] According to one or more embodiments, the carrier is 50 to 210 m 2 It has a specific surface area between / g. According to one or more embodiments, the carrier has a total pore volume between 0.7 and 1.3 ml / g.

[0017] According to one or more embodiments, the volume of the mesopores having diameters of 2 nm or more and less than 18 nm corresponds to between 15% and 25% by volume of the total pore volume of the carrier.

[0018] According to one or more embodiments, the volume of the mesopores having a diameter of 18 nm or more and less than 50 nm corresponds to between 35% and 45% by volume of the total pore volume of the carrier.

[0019] According to one or more embodiments, the volume of the macropores having diameters of 50 nm or more and less than 8000 nm corresponds to between 35% and 50% by volume of the total pore volume of the carrier.

[0020] According to one or more embodiments, the content of metals from Group VIb in the catalyst, expressed in the form of oxides, is between 1% by weight and 30% by weight relative to the total weight of the catalyst.

[0021] According to one or more embodiments, the content of the group VIII metal in the catalyst, expressed in the form of an oxide, is between 0.5% by weight and 10% by weight relative to the total weight of the catalyst.

[0022] According to one or more embodiments, the Group VIII metal is cobalt.

[0023] According to one or more embodiments, the group VIB metal is molybdenum.

[0024] According to one or more embodiments, the catalyst further contains phosphorus, expressed in the form of P2O5, and the phosphorus content is between 0.1% by weight and 10% by weight relative to the total weight of the catalyst.

[0025] According to one or more embodiments, the pore distribution of the mesopores having diameters of 2 nm or more and less than 18 nm is concentrated in the range of values ​​between 10.5 and 14.5 nm. According to one or more embodiments, the pore distribution of the mesopores having diameters of 18 nm or more and less than 50 nm is concentrated in the range of values ​​between 22 and 28 nm.

[0026] According to one or more embodiments, the gasoline is catalytic cracking gasoline.

[0027] According to one or more embodiments, the carrier is in the form of beads having a diameter between 2 and 4 mm.

[0028] According to one or more embodiments, the bead-shaped carrier is obtained by the following steps: s1) In order to obtain alumina powder, a step is taken to dehydrate aluminum hydroxide or aluminum oxyhydroxide for a time of 0.1 to 5 seconds, preferably 0.1 to 4 seconds, at a temperature between 400°C and 1200°C, preferably between 600°C and 900°C. s2) A step of forming the alumina powder obtained in step s1) into the form of beads, s3) A step of heat-treating the alumina beads obtained in step s2) at a temperature of 200°C or higher. s4) A step of hydrothermal treatment in which the alumina beads obtained at the end of step s3) are impregnated with water or an aqueous solution and then left in an autoclave at a temperature between 100°C and 300°C, Step s5) A step of firing the alumina beads obtained at the end of step s4) at a temperature between 500°C and 820°C. [Modes for carrying out the invention]

[0029] 1.Definition In the following, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, edited by DR. Lide, published by CRC Press, 81st edition, 2000-2001). For example, Group VIII according to the CAS classification corresponds to the metals in columns 8, 9, and 10 according to the new IUPAC classification.

[0030] The BET specific surface area was measured by nitrogen physicoadsorption in accordance with standard ASTM D3663-03, a method described in the study “Adsorption by Powders & Porous Solids: Principles, Methodology and Applications”, Academic Press, 1999, by Rouquerol F., Rouquerol J., and Singh K.

[0031] In this explanation, according to IUPAC convention, "micropores" are understood to mean pores with a diameter of less than 2 nm, or 0.002 μm; "mesopores" are understood to mean pores with a diameter greater than 2 nm, or 0.002 μm, and less than 50 nm, or 0.05 μm; and "macropores" are understood to mean pores with a diameter of 50 nm, or 0.05 μm or more.

[0032] In the following description of the present invention, the "total pore volume" of the alumina or catalyst is measured by mercury porosimetry at a maximum pressure of 4000 bar (400 MPa), a surface tension of 484 dynes / cm, and a contact angle of 140°, in accordance with the standard ASTM D4284-83. The wetting angle was set to 140° in accordance with the recommendation of the publication "Techniques de l'ingenieur, traiteanalyse et caracterisation" [Techniques of the Engineer, Analysis and Characterization Treatise], pages 1050-5, written by Jean Charpin and Bernard Rasneur.

[0033] For better accuracy, the total pore volume values ​​in ml / g given in the following text correspond to the total mercury volume in ml / g measured in the sample (total pore volume measured by mercury intrusion porosimetry) minus the mercury volume in ml / g measured in the same sample at a pressure corresponding to 30 psi (approximately 0.2 MPa).

[0034] The volumes of macropores and mesopores are measured by mercury intrusion porosimetry in accordance with standard ASTM D4284-83, using a maximum pressure of 4000 bar (400 MPa), a surface tension of 484 dynes / cm, and a contact angle of 140°.

[0035] The value at which mercury fills all intergranular voids is set at 0.2 MPa; above this value, mercury is thought to penetrate into the pores of the sample.

[0036] The macropore volume of a catalyst is defined as the cumulative volume of mercury introduced at pressures between 0.2 MPa and 30 MPa, and corresponds to the volume contained within pores with an apparent diameter greater than 50 nm.

[0037] The mesopore volume of a catalyst is defined as the cumulative volume of mercury introduced at a pressure between 30 MPa and 400 MPa, corresponding to the volume contained within pores with an apparent diameter between 2 and 50 nm.

[0038] When the incremental pore volume measured by mercury porosimetry is plotted as a function of pore diameter, the pore mode corresponds to the inflection point of the represented function.

[0039] The metallic elements (Group VIII and Group VIB metals) and phosphorus content are measured by X-ray fluorescence. 2. Explanation catalyst The catalyst used in the hydrogenodesulfurization method according to the present invention comprises at least one group VIB metal, at least one group VIII metal, and optionally an active phase containing phosphorus, preferably an active phase consisting of these.

[0040] The group VIB metal present in the active phase of the catalyst is preferably selected from molybdenum and tungsten, with molybdenum being more preferred. The group VIII metal present in the active phase of the catalyst is preferably selected from cobalt, nickel, and mixtures of these two elements, with cobalt being more preferred.

[0041] The total content of Group VIII metals is expressed in the form of oxides of Group VIII metals and is generally between 0.5% to 10% by weight, preferably between 1% to 10% by weight, preferably between 1% to 7% by weight, most preferably between 1% to 6% by weight, and even more preferably between 1.5% to 5% by weight, relative to the total weight of the catalyst. If the metal is cobalt or nickel, the metal content is expressed as CoO or NiO, respectively.

[0042] The content of group VIB metals is expressed in the form of an oxide of the group VIB metal and is generally between 1% to 30% by weight, preferably between 3% to 20% by weight, preferably between 5% to 18% by weight, and most preferably between 7% to 14% by weight, relative to the total weight of the catalyst. When the metal is molybdenum or tungsten, the metal content is expressed as MoO3 or WO3, respectively.

[0043] The phosphorus content, when present in the catalyst, is between 0.1% to 10% by weight, preferably between 0.5% to 5% by weight, and more preferably between 1% to 3% by weight, based on the weight of P2O5 relative to the total weight of the catalyst.

[0044] Catalysts are generally 50 to 200 m 2 Between / g, preferably 60 to 170m 2 Between / g, preferably 70 to 130m 2 It has a specific surface area between / g.

[0045] The pore volume of the catalyst is generally between 0.5 ml / g and 1.3 ml / g, preferably between 0.6 ml / g and 1.1 ml / g. Alumina carrier The alumina support catalyst used in the hydrogenodesulfurization method according to the present invention is a macroporous and mesoporous alumina support containing a bimodal distribution of mesopores: The volume of mesopores having a diameter of 2 nm or more and less than 18 nm corresponds to between 10% and 30% by volume of the total pore volume of the carrier. The volume of mesopores having a diameter of 18 nm or more and less than 50 nm corresponds to between 30% and 50% by volume of the total pore volume of the carrier. The volume of macropores having diameters of 50 nm or more and less than 8000 nm corresponds to between 30% and 50% by volume of the total pore volume of the carrier.

[0046] Preferably, the volume of the mesopores of the carrier having a diameter of 2 nm or more and less than 18 nm corresponds to between 15% by volume and 25% by volume of the total pore volume of the carrier.

[0047] Preferably, the volume of the mesopores of the carrier having a diameter of 18 nm or more and less than 50 nm corresponds to between 35% by volume and 45% by volume of the total pore volume of the carrier.

[0048] Preferably, the volume of the macropores of the carrier having a diameter of 50 nm or more and less than 8000 nm corresponds to between 35% by volume and 50% by volume of the total pore volume of the carrier.

[0049] In one embodiment according to the present invention, the pore distribution of the mesopores having a diameter of 2 nm or more and less than 18 nm is centered around a range of values between 10.5 and 14.5 nm, preferably between 12 and 13 nm.

[0050] In one embodiment according to the present invention, the pore distribution of the mesopores having a diameter of 18 nm or more and less than 50 nm is centered around a range of values between 22 and 28 nm, preferably between 23 and 二十七nm.

[0051] The carrier generally has a specific surface area between 50 and 210 m 2 / g, preferably between 70 and 180 m 2 / g, even more preferably between 70 and 160 m 2 / g.

[0052] The pore volume of the carrier is generally between 0.7 ml / g and 1.3 ml / g, preferably between 0.8 ml / g and 1.2 ml / g.

[0053] Advantageously, the carrier is in the form of beads having a diameter between 0.8 and 10 mm, preferably between 1 and 5 mm, more preferably between 2 and 4 mm. Method for preparing a support The alumina carrier of the catalyst used in the context of the hydrodesulfurization method according to the present invention is produced by any method known to those skilled in the art.

[0054] According to a preferred embodiment, the alumina carrier used in the present invention is in the form of beads. According to this preferred embodiment, the preparation of the carrier includes the following steps: s1) In order to obtain alumina powder, a step is taken to dehydrate aluminum hydroxide or aluminum oxyhydroxide for a time of 0.1 to 5 seconds, preferably 0.1 to 4 seconds, at a temperature between 400°C and 1200°C, preferably between 600°C and 900°C. s2) A step of forming the alumina powder obtained in step s1) into the form of beads, s3) A step of heat-treating the beads obtained in step s2) at a temperature of 200°C or higher. s4) A step of hydrothermally treating the alumina beads obtained at the end of step s3) by impregnating them with water or an aqueous solution, preferably an acidic aqueous solution, and then leaving them in an autoclave at a temperature between 100°C and 300°C, preferably between 150°C and 250°C. s5) A process of firing the alumina beads obtained at the end of step s4) at a temperature between 500°C and 820°C.

[0055] Processes s1) to s5) are described in detail below.

[0056] Process s1) In step s1), aluminum hydroxide or aluminum oxyhydroxide is dehydrated for a period of 0.1 to 5 seconds, preferably 0.1 to 4 seconds, at a temperature between 400°C and 1200°C, preferably 600°C to 900°C, to obtain alumina powder. The aluminum hydroxide can be selected from hydrargillite, gibbsite, or bayerite. The aluminum oxyhydroxide can be selected from boehmite or diaspore.

[0057] Preferably, step s1) is carried out using hydral dilite.

[0058] Generally, step s1) is carried out in the presence of a high-temperature gas flow, such as dry air or humid air, which allows for the rapid removal and incorporation of evaporated water.

[0059] Generally, activated alumina powder obtained after dehydration of aluminum hydroxide or aluminum oxyhydroxide is pulverized to a particle size of 10 to 200 μm.

[0060] Generally, the activated alumina powder obtained after dehydration of aluminum hydroxide or aluminum oxyhydroxide is washed with water or an acidic aqueous solution. When the washing step is carried out using an acidic aqueous solution, any inorganic or organic acid can be used; preferably, for inorganic acids, nitric acid, hydrochloric acid, perchloric acid, or sulfuric acid; and for organic acids, carboxylic acids (formic acid, acetic acid, or malonic acid), sulfonic acids (para-toluenesulfonic acid), or sulfuric acid esters (lauryl sulfate) can be used. Process s2) In step s2), the alumina powder obtained at the end of step s1) is molded.

[0061] The alumina powder is molded to produce beads, a process called granulation, which is generally carried out using rotary technology such as a rotary granulator or rotary drum. This type of process makes it possible to obtain beads with controlled diameter and pore distribution, which are generally created during the agglomeration process.

[0062] Pores can be created by various means, such as selecting the particle size distribution of alumina powder or agglomerating several alumina powders having different particle size distributions. Another method involves mixing the alumina powder with one or more compounds known as pore-forming compounds, which disappear upon heating and consequently create pores in the beads, either before or during the agglomeration step. Possible pore-forming compounds used include wood flour, charcoal, activated carbon, carbon black, sulfur, tar, plastics, or plastic emulsions, such as polyvinyl chloride, polyvinyl alcohol, and naphthalene. The amount of pore-forming compound added ranges from 500 to 1100 kg / m³. 3 During this period, the preferred range is 700 to 950 kg / m³. 3 The desired volume for obtaining beads having a compaction density between 0.8 and 10 mm, preferably between 1 and 5 mm, and more preferably between 2 and 4 mm, is determined by the compaction density between 0.8 and 10 mm, and the diameter between 1 and 5 mm, and more preferably between 2 and 4 mm. The resulting beads can be selected by screening according to the desired particle size. Process s3) In accordance with step s3), the heat treatment of the alumina powder formed into beads at the end of step s2) is generally carried out for 1 to 24 hours, preferably 1 to 6 hours, at a temperature of 200°C or higher, preferably between 200°C and 1200°C, preferably between 300°C and 900°C, and very preferably between 400°C and 750°C. The beads obtained in this intermediate step are 50 to 420 m 2 Between / g, preferably 60 to 350m 2 Between / g, and even more preferably between 80 and 300m 2 It has a specific surface area between / g. Process s4) In accordance with step s4), the alumina beads obtained at the end of step s3) are impregnated with water or an aqueous solution, preferably an acidic aqueous solution, and then subjected to hydrothermal treatment by being kept in an autoclave at a temperature between 100°C and 300°C, preferably between 150°C and 250°C.

[0063] Hydrothermal treatment is generally carried out at a temperature of 100°C to 300°C, preferably 150°C to 250°C, for a time longer than 45 minutes, preferably 1 to 24 hours, and very preferably 1.5 to 12 hours. Hydrothermal treatment is generally carried out using an acidic aqueous solution containing one or more inorganic and / or organic acids, preferably nitric acid, hydrochloric acid, perchloric acid, sulfuric acid, and a weak acid whose solution has a pH of less than 4, such as acetic acid or formic acid. Generally, the acidic aqueous solution also contains one or more compounds that can release anions capable of binding with aluminum ions, preferably nitrate ions (e.g., aluminum nitrate), chlorine, sulfuric acid, perchloric acid, chloroacetic acid, trichloroacetic acid, bromoacetic acid or dibromoacetic acid ions, and anions of the general formula R-COO, such as formic acid and acetic acid. Process s5) In accordance with step s5), the alumina beads obtained at the end of step s4) are generally fired at a temperature between 500°C and 820°C, preferably between 550°C and 750°C, for a period of 1 to 24 hours, preferably between 1 to 6 hours. The alumina beads obtained at the end of this step are 50 to 210 m 2 Between / g, preferably 70 to 180m 2 Between / g, and even more preferably between 70 and 160m 2 It has a specific surface area between / g. Method for preparing a catalyst The catalyst used in the hydrogenodesulfurization method according to the present invention can be prepared by any technique known to those skilled in the art, particularly by impregnation of Group VIII and Group VIB elements, and optionally phosphorus, on a selected carrier.

[0064] According to the first embodiment, the components of metals from Group VIB, metals from Group VIII, and phosphorus are deposited on the carrier by one or more co-impregnation steps, i.e., the components of metals from Group VIB, metals from Group VIII, and phosphorus are introduced into the carrier simultaneously. The co-impregnation step(s) are preferably carried out by dry impregnation or by over-impregnation of solution. If the first embodiment includes the implementation of several co-impregnation steps, each co-impregnation step is preferably followed by an intermediate drying step at a temperature generally below 200°C, preferably between 50 and 180°C, more preferably between 60 and 150°C, and most preferably between 75 and 140°C.

[0065] According to a preferred embodiment of co-impregnation, the impregnation solution is preferably an aqueous solution. Preferably, the aqueous impregnation solution, if it contains cobalt, molybdenum, and phosphorus, is prepared under pH conditions that promote the formation of heteropolyanions in the solution. For example, the pH of such an aqueous solution is between 1 and 5.

[0066] According to the second embodiment, the catalyst precursor is prepared by sequentially depositing components of a group VIB metal, a group VIII metal, and optionally phosphorus on the support in any order. Deposition can be carried out by dry impregnation, over-impregnation, or deposition / precipitation according to methods well known to those skilled in the art. In this second embodiment, the deposition of the group VIB and group VIII metal components, and optionally phosphorus, can be carried out by several impregnations having an intermediate drying step between two sequential impregnations at a temperature generally below 200°C, preferably between 50°C and 180°C, more preferably between 60°C and 150°C, and very preferably between 75°C and 140°C.

[0067] Regardless of the deposition method of the metal and phosphorus used, the solvent involved in the composition of the impregnation solution, such as water or an organic solvent (e.g., alcohol), is selected to dissolve the metal precursor in the active phase.

[0068] For example, among the sources of molybdenum oxides and hydroxides, molybdic acid and its salts, in particular ammonium salts, such as ammonium molybdate or ammonium heptamolybdate, phosphomolybdic acid (H3PMo 12 O 40 ) and its salts, optionally silicomolybdic acid (H4SiMo 12 O 40 ) and its salts can be used. The source of molybdenum can also be any heteropoly compound of the Keggin, cavity Keggin, substituted Keggin, Dawson, Anderson, or Strandberg type, for example. Preferably, molybdenum trioxide, as well as heteropoly compounds of the Keggin, cavity Keggin, substituted Keggin, and Strandberg type, are used.

[0069] The tungsten precursors that can be used are also well known to those skilled in the art. For example, among the oxides and hydroxides of tungsten, tungstic acid and its salts, in particular ammonium salts, such as ammonium tungstate or ammonium metatungstate, phosphotungstic acid and its salts, and optionally silicotungstic acid (H4SiW) 12 O 40 ) and its salts can be used. The source of tungsten can also be any heteropoly compound of the Keggin, cavity Keggin, substituted Keggin, or Dawson type, for example. Preferably, oxides and ammonium salts, such as ammonium metatungstate or Keggin, cavity Keggin, or substituted Keggin type heteropolyanions are used.

[0070] The cobalt precursors that can be used are preferably selected from, for example, oxides, hydroxides, hydroxycarbonates, carbonates, and nitrates. Preferably, cobalt hydroxide and cobalt carbonate are used.

[0071] The nickel precursors that can be used are preferably selected from, for example, oxides, hydroxides, hydroxycarbonates, carbonates, and nitrates. Preferably, nickel hydroxide and nickel hydroxycarbonate are used.

[0072] Phosphorus can preferably be introduced into the catalyst in various ways at various steps in its preparation. It can be introduced during the molding of the alumina support, or preferably after this molding. Preferably, it can be introduced alone or as a mixture with at least one of the Group VIB and Group VIII metals. Phosphorus is preferably introduced completely or partially onto the molded alumina support as a mixture with the Group VIB and Group VIII metal precursors by dry impregnation of the alumina support using a solution containing the metal precursor and the phosphorus precursor. A preferred source of phosphorus is orthophosphate H3PO4, but its salts and esters, such as ammonium phosphate or mixtures thereof, are also suitable. Phosphorus can also be introduced simultaneously with, for example, a Group VIB element in the form of a heteropolyanion of the form of Keggin, void Keggin, substituted Keggin, or Strandberg type.

[0073] After the step(s) of contacting the group VIII, group VIb metals and phosphorus with the support are completed, the catalyst precursor is subjected to a dry step carried out by any technique known to those skilled in the art. Preferably, this step is carried out under atmospheric pressure or under reduced pressure. Preferably, this step is carried out under atmospheric pressure. This step is carried out at a temperature of less than 200°C, preferably between 50°C and 180°C, preferably between 60°C and 150°C, and most preferably between 75°C and 140°C.

[0074] The dry process is preferably carried out on a traversed bed using hot air or any other hot gas. Preferably, when drying is carried out on a traversed bed, the gas used is either air or an inert gas, such as argon or nitrogen. Most preferably, drying is carried out on a traversed bed in the presence of air.

[0075] Preferably, this drying process is sustained for 30 minutes to 24 hours, preferably for 1 to 12 hours.

[0076] At the end of the drying process, a dried catalyst is obtained, which can be used as a hydrogenation catalyst after the activation process (sulfidation process).

[0077] In an alternative embodiment, the dried catalyst can then be subjected to a calcination step, for example, at a temperature of 200°C or higher under air. Calcination is generally carried out at a temperature of 600°C or lower, preferably between 200°C and 600°C, and particularly preferably between 250°C and 500°C. The calcination time is generally between 0.5 hours and 16 hours, preferably between 1 hour and 5 hours. Calcination is generally carried out under air. Calcination makes it possible to convert the precursors of Group VIB and Group VIII metals into oxides.

[0078] Before use as a hydrogenation catalyst, it is preferable to subject the dried, or optionally calcined, catalyst to a sulfidation step (activation step). This activation step is preferably carried out in a sulfo-reducing atmosphere in the presence of hydrogen and hydrogen sulfide, by a method well known to those skilled in the art. Hydrogen sulfide can be used directly or generated by a sulfidating agent (e.g., dimethyl disulfide). Method for hydrodesulfurization of gasoline The hydrogenation treatment method consists of contacting a sulfur-containing olefin gasoline fraction with the catalyst and hydrogen described above under the following conditions: • The temperature is between 200°C and 400°C, preferably between 230°C and 330°C. • The total pressure is between 1 and 3 MPa, preferably between 1.5 and 2.5 MPa. • The space velocity per hour (HSV), defined as the flow rate of the raw material volume relative to the catalyst volume, is between 1 and 10 h. -1 Preferably 2 to 6 hours -1 During, The volume ratio of hydrogen / gasoline raw materials is between 100 and 600 Nl / l, preferably between 200 and 400 Nl / l.

[0079] Therefore, the method according to the present invention makes it possible to process any type of sulfur-containing olefin gasoline fraction, such as fractions obtained from coking, bisque breaking, steam cracking, or catalytic cracking (FCC, fluid catalytic cracking) units. This gasoline can optionally consist mostly of gasoline derived from other production methods, such as atmospheric distillation (gasoline obtained from direct distillation (or straight-run gasoline)) or conversion methods (coking or steam cracking gasoline). The raw material preferably consists of a gasoline fraction obtained from a catalytic cracking unit.

[0080] The raw material is preferably a gasoline fraction containing sulfur-containing compounds and olefins, and having a boiling point between 30°C and less than 250°C, preferably between 35°C and 240°C, and in a preferred embodiment between 40°C and 220°C.

[0081] The sulfur content of gasoline fractions produced by catalytic cracking (FCC) depends on the sulfur content of the raw materials processed by the FCC, whether or not the FCC raw materials are pretreated, and the endpoint of the fraction. Generally, the sulfur content of the entire gasoline fraction, especially that derived from FCC, is greater than 100 ppm by weight, and in most cases greater than 500 ppm by weight. For gasoline whose endpoint is above 200°C, the sulfur content is often greater than 1,000 ppm by weight, and in some cases can even reach 4,000 to 5,000 ppm by weight.

[0082] Furthermore, the gasoline obtained from the catalytic cracking (FCC) unit contains, on average, 0.5% to 5% by weight of diolefins, 20% to 50% by weight of olefins, and 10% to 0.5% by weight of sulfur, and generally contains less than 300 ppm of mercaptans. The mercaptans are generally concentrated in the light fraction of gasoline, more specifically in the fraction with a boiling point below 120°C.

[0083] It should be noted that sulfur-containing compounds present in gasoline may also include heterocyclic sulfur-containing compounds, such as thiophenes, alkylthiophenes, or benzothiophenes. Unlike mercaptans, these heterocyclic compounds cannot be removed by extraction. These sulfur-containing compounds are removed by hydrogenation, which results in a change to hydrocarbons and H2S.

[0084] Preferably, the gasoline processed by the method according to the present invention is heavy gasoline (or HCN from heavy cracked naphtha) obtained from a distillation step aimed at separating the broadcut (or FRCN from full-range cracked naphtha) of gasoline obtained from a cracking method into light gasoline (LCN from light cracked naphtha) and heavy gasoline (HCN). The cut points for the light and heavy gasoline are determined to limit the sulfur content of the light gasoline and, preferably, to allow it to be used in a gasoline pool without additional post-treatment. The broadcut FRCN is preferably subjected to a selective hydrogenation step before the distillation step. [Examples]

[0085] [Examples]

[0086] Catalyst A (according to the present invention) The support S1 for catalyst A is obtained by dehydrating hydral dilite (Emplura®, Merck®) to obtain alumina powder. The temperature is set to 800°C, and the contact time between the material to be dehydrated and the dry air stream is 1 second. The obtained alumina powder is pulverized to a particle size between 10 and 200 μm, and then washed three times with distilled water equal to twice the volume of powder used. The alumina powder is then formed using a disc pelletizer (GRELBEX P30) with a conical cylindrical pan at a 30° angle and a rotation speed of 40 rpm in the presence of carbon black (N990 Thermax®) to obtain beads with a diameter mostly between 2 and 4 mm after screening for solids. The amount of carbon black is 800 kg / m³. 3 The beads are adjusted to obtain the compacted powder filling density of the target object. 2 The beads are subjected to heat treatment in air at 720°C to achieve a specific surface area of ​​ / g. Next, the beads are subjected to hydrothermal treatment by impregnation of the pore volume using an aqueous solution of nitric acid (0.1N, Merck). The hydrothermal treatment is carried out in a rotary basket autoclave at a temperature of 200°C for 6.5 hours. The resulting beads are then subjected to a final calcination treatment in air at 650°C for 2 hours. The carrier S1 is 141m 2 It has a specific surface area of ​​0.97 ml / g, a total pore volume of 0.97 ml / g, and the following pore distribution as determined by mercury porosimetry: • The volume of mesopores with a diameter of 2 nm or more and less than 18 nm, where the center of the pore distribution is 13 nm, is 0.15 ml / g, which corresponds to 15% of the total pore volume. • The volume of mesopores with a diameter of 18 nm or more and less than 50 nm, and with a pore distribution center of 26 nm, is 0.43 ml / g, which corresponds to 44% of the total pore volume. The volume of macropores with diameters of 50 nm or more and less than 8000 nm is 0.39 ml / g, which corresponds to 40% of the total pore volume.

[0087] The carrier S1 has a water absorption capacity of 0.95 ml / g. The impregnation solution is prepared by heating 1.15 g of molybdenum oxide (MoO3 > 99.5%, Merck), 0.28 g of cobalt hydroxide (95% Co(OH)2, Merck), and 0.26 g of phosphoric acid (85 wt% H3PO4, in water, Merck) in 9.3 ml of distilled water at 90°C for 3 hours. 10 g of the carrier is dry-impregnated and aged in a moisture-saturated atmosphere for 12 hours, after which the solid is dried at 120°C for 12 hours. The solid is then calcined in air at 450°C for 2 hours. The resulting catalyst A contains 1.9 wt% CoO, 10 wt% MoO3, and 1.4 wt% P2O5 relative to the total weight of the catalyst. Catalyst A has a total pore volume of 0.88 ml / g and 118 m 2 It has a specific surface area of ​​ / g. [Examples]

[0088] Catalyst B (according to the present invention) Catalyst B is prepared by dissolving 1.35 g of ammonium heptamolybdate ((NH4)6Mo7O) in 9.4 ml of distilled water. 24 Catalyst B is obtained by dry impregnation of an alumina support S1 with an aqueous solution prepared from 4H2O (99.98%, Merck) and 1.38 g of cobalt nitrate (Co(NO3)2·6H2O, 98%, Merck). 10 g of the support is dry impregnated and aged for 12 hours in a moisture-saturated atmosphere, after which the solid is dried at 120°C for 12 hours. Subsequently, the solid is calcined at 450°C under air for 2 hours. The resulting catalyst B contains 3.1% by weight of CoO and 9.6% by weight of MoO3 based on the total weight of the catalyst. Catalyst B has a total pore volume of 0.89 ml / g and a pore size of 124 m 2 It has a specific surface area of ​​ / g. [Examples]

[0089] Catalyst C (not according to the present invention (mesoporous catalyst with high macroporous and monomodal properties)) The catalyst C support S2 is obtained by dehydrating hydral dilite (Emplura®, Merck) to obtain activated alumina powder. The temperature is set to 800°C, and the contact time between the material to be dehydrated and the dry air stream is 1 second. The obtained activated alumina powder is pulverized to a particle size between 10 and 200 μm, and then washed three times with distilled water equal to twice the volume of the powder used. The activated alumina powder mostly has a diameter between 2 and 4 mm and weighs 780 kg / m³. 3 The compacted powder is formed using a disc pelletizer (GRELBEX P30) with a conical cylindrical pan at a 30° angle and a rotation speed of 40 rpm to obtain beads (after screening for solids) having a compacted powder filling density. The amount of carbon black is 800 kg / m³. 3 The beads are adjusted to obtain the compacted powder filling density of the target object. 2 The beads are subjected to heat treatment in air at 700°C to achieve a specific surface area of ​​ / g. Next, the beads are subjected to hydrothermal treatment by impregnating them with an aqueous solution of nitric acid (0.1N, Merck) to increase their pore volume. The hydrothermal treatment is carried out in a rotary basket autoclave at a temperature of 200°C for 6.5 hours. The resulting beads are then subjected to a final calcination treatment in air at 950°C for 2 hours. The carrier S2 is 71m 2 It has a specific surface area of ​​0.56 ml / g, a total pore volume of 0.56 ml / g, and the following pore distribution as determined by mercury porosimetry: • Mesopores with diameters of 10 nm or more and less than 50 nm, where the center of the pore distribution is 20 nm, have a volume of 0.35 ml / g, which corresponds to 63% of the total pore volume. The volume of macropores with diameters of 50 nm or more and less than 8000 nm is 0.21 ml / g, which corresponds to 38% of the total pore volume.

[0090] The carrier S2 has a water absorption capacity of 0.54 ml / g. The impregnation solution is prepared by heating 1.15 g of molybdenum oxide (MoO3 > 99.5%, Merck), 0.28 g of cobalt hydroxide (95% Co(OH)2, Merck), and 0.26 g of phosphoric acid (85 wt% H3PO4, in water, Merck) in 5.2 ml of distilled water at 90°C for 3 hours. 10 g of the carrier is dry-impregnated and aged in a moisture-saturated atmosphere for 12 hours, after which the solid is dried at 120°C for 12 hours. The solid is then calcined in air at 450°C for 2 hours. The resulting catalyst C contains 1.9 wt% CoO, 10 wt% MoO3, and 1.4 wt% P2O5 relative to the total weight of the catalyst. Catalyst C has a total pore volume of 0.47 ml / g and a pore size of 62 m 2 It has a specific surface area of ​​ / g. [Examples]

[0091] Catalyst D (macroporous catalyst) not according to the present invention A commercially available carrier S3 (SA52124, UniSpheres® NorPro) in the form of beads with a diameter between 2 and 4 mm is provided. Carrier S3 is 8 m 2 It has a specific surface area of ​​0.33 ml / g, a total pore volume of 0.33 ml / g, and the following pore distribution determined by mercury porosimetry: The volume of macropores with diameters of 50 nm or more and less than 8000 nm is 0.33 ml / g, which corresponds to 100% of the total pore volume.

[0092] The carrier S3 has a water absorption capacity of 0.37 ml / g. The impregnation solution is prepared by heating 1.15 g of molybdenum oxide (MoO3 > 99.5%, Merck), 0.28 g of cobalt hydroxide (95% Co(OH)2, Merck), and 0.26 g of phosphoric acid (85% H3PO4, in water, Merck) in 3.5 ml of distilled water at 90°C for 3 hours. 10 g of the carrier is dry-impregnated and aged in a moisture-saturated atmosphere for 12 hours, after which the solid is dried at 120°C for 12 hours. After the completion of the two impregnation steps, the solid is calcined in air at 450°C for 2 hours. The resulting catalyst D contains 1.9 wt% CoO, 10 wt% MoO3, and 1.4 wt% P2O5 relative to the total weight of the catalyst. Catalyst D has a total pore volume of 0.21 ml / g and 5 m 2 It has a specific surface area of ​​ / g. [Examples]

[0093] Catalyst E (monomodal mesoporous catalyst) not according to the present invention The commercially available carrier S4 (SA 6578, NorPro) is supplied in the form of a 5mm diameter extruded product. Carrier S4 is 175m 2 It has a specific surface area of ​​0.82 ml / g, a total pore volume of 0.82 ml / g, and the following pore distribution determined by mercury porosimetry: The volume of mesopores with a diameter between 2 nm and 20 nm, and whose pore distribution center is 13 nm, is 0.82 ml / g, which corresponds to 100% of the total pore volume.

[0094] The support S4 has a water absorption capacity of 0.81 ml / g. The impregnation solution is prepared by heating 1.15 g of molybdenum oxide (MoO3 > 99.5%, Merck), 0.28 g of cobalt hydroxide (95% Co(OH)2, Merck), and 0.26 g of phosphoric acid (85 wt% H3PO4, in water, Merck) in 7.9 ml of distilled water at 90°C for 3 hours. 10 g of the support is dry-impregnated and aged in a moisture-saturated atmosphere for 12 hours, after which the solid is dried at 120°C for 12 hours. The solid is then calcined in air at 450°C for 2 hours. The resulting catalyst E contains 1.9 wt% CoO, 10 wt% MoO3, and 1.4 wt% P2O5 relative to the total weight of the catalyst. Catalyst E has a total pore volume of 0.74 ml / g and 136 m 2 It has a specific surface area of ​​ / g. [Examples]

[0095] Catalyst F not according to the present invention (mesoporous catalyst with low macroporous and monomodal properties) The commercially available carrier S5 (SA 6176, NorPro) is supplied in the form of an extruded product with a diameter of 1.6 mm. Carrier S5 is 250 m 2 It has a specific surface area of ​​1.05 ml / g, a total pore volume of 1.05 ml / g, and the following pore distribution determined by mercury porosimetry: • Mesopores with a diameter of 2 nm or more and 20 nm or less, where the center of the pore distribution is 7 nm, account for 65% of the total pore volume, which is 0.68 ml / g. The volume of macropores with diameters of 50 nm or more and less than 8000 nm is 0.37 ml / g, which corresponds to 35% of the total pore volume.

[0096] The carrier S5 has a water absorption capacity of 1.02 ml / g. The impregnation solution is prepared by heating 1.15 g of molybdenum oxide (MoO3 > 99.5%, Merck), 0.28 g of cobalt hydroxide (95% Co(OH)2, Merck), and 0.26 g of phosphoric acid (85 wt% H3PO4, in water, Merck) in 10.0 ml of distilled water at 90°C for 3 hours. 10 g of the carrier is dry-impregnated and aged in a moisture-saturated atmosphere for 12 hours, after which the solid is dried at 120°C for 12 hours. The solid is then calcined in air at 450°C for 2 hours. The resulting catalyst F contains 1.9 wt% CoO, 10 wt% MoO3, and 1.4 wt% P2O5 relative to the total weight of the catalyst. Catalyst F has a total pore volume of 0.87 ml / g and a density of 211 m 2 It has a specific surface area of ​​ / g. [Examples]

[0097] Performance evaluation of catalysts used in hydrodesulfurization reactors In this embodiment, the performance of catalysts A to F is evaluated in the hydrodesulfurization of catalytically cracked gasoline.

[0098] A representative model feedstock for catalytic cracking (FCC) gasoline containing 10% by weight of 2,3-dimethylbuta-2-ene and 0.33% by weight of 3-methylthiophene (i.e., 1000 ppm by weight of sulfur in the feedstock) is used to evaluate the catalytic performance of various catalysts. The solvent used is heptane.

[0099] The hydrogenosulfurization (HDS) reaction was carried out in a fixed transverse-bed reactor at a total pressure of 1.5 MPa and 210°C in the presence of 4 ml of catalyst, with HSV = 6h -1 The reaction is carried out using (HSV = flow rate of raw material volume / catalyst volume) and an H2 / raw material volume ratio of 300 Nl / l. Prior to the HDS reaction, the catalyst is sulfurized in situ at 350°C for 2 hours under a hydrogen gas stream containing 15 mol% H2S at atmospheric pressure.

[0100] Each catalyst is placed in succession in the reactor. Samples are taken at different time intervals and analyzed by gas chromatography to observe the disappearance of reactants and the formation of products.

[0101] The catalytic performance of a catalyst is evaluated from the viewpoints of catalytic activity and selectivity. Hydrodesulfurization (HDS) activity is standardized by the amount of catalyst introduced and expressed from the rate constant (kHDS) of the HDS reaction of 3-methylthiophene, assuming a first-order kinetic theory for sulfur compounds. Olefin hydrogenation (HydO) activity is standardized by the amount of catalyst introduced and expressed from the rate constant of the hydrogenation reaction of 2,3-dimethylbuta-2-ene, assuming a first-order kinetic theory for olefins.

[0102] Catalyst selectivity is expressed by the standardized ratio of the rate constant kHDS / kHydO. The kHDS / kHydO ratio increases as catalyst selectivity increases. The obtained value is standardized by adopting catalyst A as the baseline (relative HDS activity and relative selectivity equal to 100). Therefore, the performance criteria are relative HDS activity and relative selectivity.

[0103] [Table 1]

[0104] Therefore, it is clear that the catalyst according to the present invention has better performance in terms of activity and selectivity, and thus clearly demonstrates the importance of the pore range of the catalyst support for performance in gasoline hydrodesulfurization methods. This improvement in catalyst selectivity is particularly suitable for hydrodesulfurization methods of gasoline containing olefins, in order to limit the loss of octane due to the hydrogenation of olefins as much as possible.

Claims

1. A method for hydrodesulfurizing a sulfur-containing olefin-based gasoline fraction, comprising contacting the sulfur-containing olefin-based gasoline fraction with hydrogen and a catalyst, wherein the hydrodesulfurizing method is performed at a temperature between 200°C and 400°C, a total pressure between 1 and 3 MPa, and a space velocity per hour defined as the flow rate of the raw material volume relative to the volume of the catalyst volume between 1 and 10 h⁻¹. －１ The experiment is conducted between [times] and with a hydrogen / gasoline fraction volume ratio between 100 and 600 Nl / l, and the catalyst comprises at least one group VIB metal, at least one group VIII metal, and a mesoporous and macroporous alumina support having a bimodal distribution of mesopores. - The volume of the mesopores having a diameter of 2 nm or more and less than 18 nm corresponds to between 10% and 30% by volume of the total pore volume of the carrier. - The volume of the mesopores having a diameter of 18 nm or more and less than 50 nm corresponds to between 30% and 50% by volume of the total pore volume of the carrier. A method wherein the volume of macropores having a diameter of 50 nm or more and less than 8000 nm corresponds to between 30% and 50% by volume of the total pore volume of the carrier.

2. The carrier is 50 to 210 m 2 The method according to claim 1, having a specific surface area between / g.

3. The method according to either claim 1 or 2, wherein the carrier has a total pore volume between 0.7 and 1.3 ml / g.

4. The method according to any one of claims 1 to 3, wherein the volume of the mesopores having a diameter of 2 nm or more and less than 18 nm corresponds to between 15% and 25% by volume of the total pore volume of the carrier.

5. The method according to any one of claims 1 to 4, wherein the volume of the mesopores having a diameter of 18 nm or more and less than 50 nm corresponds to between 35% and 45% by volume of the total pore volume of the carrier.

6. The method according to any one of claims 1 to 5, wherein the volume of the macropores having a diameter of 50 nm or more and less than 8000 nm corresponds to between 35% and 50% by volume of the total pore volume of the carrier.

7. The method according to any one of claims 1 to 6, wherein the content of a group VIB metal in the catalyst, represented in the form of an oxide, is between 1% by weight and 30% by weight relative to the total weight of the catalyst.

8. The method according to any one of claims 1 to 7, wherein the content of the group VIII metal in the catalyst, represented in the form of an oxide, is between 0.5% by weight and 10% by weight relative to the total weight of the catalyst.

9. The method according to any one of claims 1 to 8, wherein the group VIII metal is cobalt.

10. The method according to any one of claims 1 to 9, wherein the VIB group metal is molybdenum.

11. The catalyst further contains phosphorus, P ２ O ５ The method according to any one of claims 1 to 10, wherein the phosphorus content is between 0.1% by weight and 10% by weight relative to the total weight of the catalyst, represented in the form of .

12. The method according to any one of claims 1 to 11, wherein the pore distribution of the mesopores having a diameter of 2 nm or more and less than 18 nm is centered in a range of values ​​between 10.5 and 14.5 nm.

13. The method according to any one of claims 1 to 12, wherein the pore distribution of the mesopores having a diameter of 18 nm or more and less than 50 nm is centered in a range of values ​​between 22 and 28 nm.

14. The method according to any one of claims 1 to 13, wherein the gasoline is catalytic cracking gasoline.

15. The method according to any one of claims 1 to 14, wherein the carrier is in the form of beads having a diameter between 2 and 4 mm.

16. The carrier undergoes the following process: s1) In order to obtain alumina powder, a step of dehydrating aluminum hydroxide or aluminum oxyhydroxide at a temperature between 400°C and 1200°C for a time between 0.1 seconds and 5 seconds, s2) A step of forming the alumina powder obtained in step s1) into the form of beads, s3) A step of heat-treating the alumina beads obtained in step s2) at a temperature of 200°C or higher, s4) A step of hydrothermal treatment in which the alumina beads obtained at the end of step s3) are impregnated with water or an aqueous solution, and then left in an autoclave at a temperature between 100°C and 300°C, s5) A step of firing the alumina beads obtained at the end of step s4) at a temperature between 500°C and 820°C. The method according to claim 15, obtained by...

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