PROCESS FOR PRODUCING SPHEROIDAL ALUMINA PARTICLES

Abstract

The present invention relates to a method for manufacturing spheroidal alumina particles comprising the following steps: a) preparing a suspension comprising water, an acid and at least one boehmite powder having X-ray diffraction lines [020] and [120] whose line intensity ratio [020] / [120] is between 0.7 and 1; b) preparing an emulsion comprising a pore-forming agent, a surfactant and water; c) mixing the suspension of step a) and the emulsion of step b); d) shaping the spheroidal particles by drop coagulation from the mixture of step c); e) drying the particles obtained in step d); f) calcining the particles obtained in step e).

Description

Scope of the invention: The invention relates to a method for manufacturing spheroidal alumina particles. The invention also relates to spheroidal alumina particles obtained according to the method of the invention. Finally, the invention relates to catalysts comprising such particles as a support and the use of such catalysts in catalytic hydrocarbon processing. Prior art: Spheroidal alumina particles used as a porous catalytic support are well known to those skilled in the art. For example, US patent 2,422,499 describes a process for manufacturing such particles using the so-called "oil-drip" process. The principle of this technique consists of preparing an aqueous alumina sol and dripping the alumina sol, in fine droplets, through a nozzle into a column comprising an upper, water-immiscible phase and a lower aqueous phase. The shaping of the particles then occurs during passage through the water-immiscible phase and subsequent coagulation in the aqueous phase. Once collected, the particles are washed, dried, and calcined. Among the parameters to control during the synthesis of such spheroidal particles, density and pore volume are particularly important because they affect the final use of these particles. It is known from document FR 1 503 495 that to lower the particle density, it is possible to add porogenic agents to the alumina sol. During particle formation, these porogenic agents, which are subsequently removed during the calcination step, create macroporosity within the particle. This macroporosity increases the pore volume and thus decreases the particle density. However, this macroporosity has a negative impact on the mechanical strength of low-density supports. Mechanical strength (in particular, crushing and attrition resistance) is a crucial parameter to consider for the intended application of alumina particles in catalysis. Indeed, during their implementation, e.g.In a moving bed reactor, alumina particles are subjected to shocks and friction that can lead to the formation of fines which may clog equipment or filters and also contribute to the loss of some of the catalyst loaded in the catalytic reactor. Therefore, it is important to be able to manufacture alumina particles that exhibit two opposing characteristics: low density and good mechanical strength. Summary of the invention: One objective of the invention is thus to provide a method for manufacturing spheroidal alumina particles with low density (e.g., packed density around 0.5 g / mL to 0.6 g / mL) and sufficient mechanical strength for use in catalytic reactors.According to the invention, the process for manufacturing spheroidal alumina particles comprises the following steps: a) preparation of a suspension comprising water, an acid and at least one boehmite powder having X diffraction lines

[020] and

[120] having a ratio of line intensities

[020] /

[120] between 0.7 and 1; b) preparation of an emulsion comprising at least one pore-forming agent, a surfactant and water; c) mixing of the suspension from step a) and the emulsion from step b); d) shaping of the spheroidal particles by droplet coagulation from the mixture from step c); e) drying of the particles obtained in step d); f) calcination of the particles obtained in step e). 25 The applicant has indeed surprisingly found that it is possible to form low-density particles with mechanical resistance at least equivalent to the dense alumina support (e.g.(packed filling density around 0.6 g / mL to 0.7 g / mL), while limiting the amount of porogen used in the process, provided that at least a portion of the boehmite powder used has a crystallographic structure as defined above. Thus, thanks to the process according to the invention, it is possible to limit the formation of macroporosity, which leads to a decrease in mechanical strength, and conversely, to promote the formation of mesoporosity, which provides the porosity useful for using the material as a catalyst support. Furthermore, by limiting the amount of porogen used, the process according to the invention offers an additional economic advantage, particularly by reducing the costs of raw materials and the processing of volatile organic compounds released during the calcination step from the decomposition of the porogen.According to an alternative embodiment of the invention, the acidic suspension of boehmite powder and the emulsion are prepared in a single step a') by mixing the constituents, either simultaneously or in successive steps. Preferably, the aqueous suspension further comprises a charge of alumina or an alumina precursor. This charge may be selected from the group consisting of hydrargillite, bayerite, amorphous gels, and so-called transition aluminas comprising at least one rho, chi, eta, gamma, kappa, theta, delta, and alpha phase. The alumina charge may be in the form of powder or alumina particles obtained by grinding and sieving shaped alumina bodies; these particles, after grinding, have a median diameter of less than 50 µm, preferably less than 30 µm, and even more preferably less than 20 µm.The term "median diameter" refers to D50, i.e., the diameter of an equivalent sphere such that 50% of the particles, by volume, have a larger diameter and 50% have a smaller diameter. The porogen that is particularly suitable for the process is a petroleum fraction with a boiling point between 220 and 350°C and which will be degraded during the calcination step. According to one embodiment, so-called "promoting" elements are also incorporated during the formation of said particles. To this end, a soluble salt of one or more elements chosen from groups IIIA, IVA, VA and the lanthanides of the periodic table of elements is added to the aqueous suspension of boehmite powder. Preferably, the particle shaping step comprises the following steps: a) transferring the suspension into a draining pot equipped with nozzles whose orifices are calibrated to form droplets; b) draining the suspension by gravity into a column containing an organic phase at the top and a basic aqueous phase at the bottom so as to collect the spheroidal particles at the bottom of the basic aqueous phase. The drying step of the spheroidal particles according to the process of the invention is carried out at a temperature between 60 and 150°C, for example, for 0.5 to 20 hours. The calcination step of the spheroidal particles is carried out at a temperature between 450 and 900 [deg.]C, preferably between 550 and 800 [deg.]C for 0.5 to 12 hours, preferably between 1 and 8 hours, even more preferably between 1 and 5 hours. Thus, after calcination, it is possible to form spheroidal particles generally having an average diameter between 1.2 and 3 mm, a specific surface area BET between 150 and 300 m2 / g, and an average grain-by-grain crushing value (EGG) of at least 2.5 daN, preferably at least 3.0 daN. The EGG value is obtained via a standardized test (ASTM D4179-01) which consists of subjecting a material in the form of a millimeter-sized object, such as a ball in the case of the present invention, to a compressive force that causes it to break. This test is therefore a measure of the tensile strength of the material.The analysis is repeated on a number of individual solids and typically on a number of solids between 10 and 200. The average of the measured lateral fracture forces constitutes the average EGG which is expressed in the case of spheroidal particles in units of force (N). Spheroidal particles after calcination generally exhibit: - a nitrogen adsorption isotherm volume (which we will call Vmeso), representative of the mesoporous volume (pore diameter between 2 and 50 nm), which is between 0.65 and 0.85 mL / g and - a pore volume with a diameter less than 7 pm (which we designate as Vmeso+macro), measured by mercury porosimetry, which is between 0.65 and 0.85 mL / g and for which the ratio Q = [(Vmeso+macro Vmeso) (Vmeso+macro)] *100 is less than 2 5 10%, preferably less than 8%, even more preferably less than 5%.Thus, in the context of the present invention, the term "mesoporous volume" refers to the volume constituted by pores with a diameter between 2 and 50 nm, while the term "macroporous volume" refers to the volume occupied by pores with a diameter between 50 nm and 7 pm. The measurement of the nitrogen adsorption isotherm is performed according to ASTM D3663-03. The pore volume, referred to as Vmeso, is taken as the volume of nitrogen measured during the adsorption step and corresponding to a relative pressure P / Ps (measurement pressure divided by saturated vapor pressure) equal to 0.99. As for the measurement of pore volume by mercury porosimetry, it is performed according to ASTM D4284-03. After calcination, the spheroidal particles according to the invention generally exhibit a packed filling density (PHD) of between 0.5 and 0.6 g / ml. The PHD measurement consists of introducing the beads into a test tube of predetermined volume and then, by vibration, compacting them until a constant volume is obtained. The apparent density of the compacted product is calculated by comparing the introduced mass with the volume occupied after compaction. The invention also relates to spheroidal alumina particles obtainable by the process according to the invention. The invention further relates to a catalyst comprising at least one or more metals selected from Group VIII of the periodic table, deposited on a support formed by spheroidal alumina particles according to the present invention.The catalyst according to the invention may optionally also include at least one promoter selected from groups IIIA, IVA, and VA of the periodic table. These promoting elements are present in the catalyst, after calcination, at a content generally ranging from 0.01 to 2 wt% of the catalyst. The catalyst according to the invention may also preferably include a halogenated compound selected from the group consisting of fluorine, chlorine, bromine, and iodine. The content of the halogenated compound is generally between 0.1 and 8 wt%, preferably between 0.2 and 5 wt% of the catalyst after calcination. As an example, a catalyst useful as a reforming catalyst for petroleum fractions may comprise platinum, tin (optionally other metals), and chlorine, deposited on a spheroidal alumina support obtained according to the process of the present invention. These catalysts are also useful in catalytic reforming reactions or in the production of aromatics by contacting said catalyst with a hydrocarbon feedstock. Catalytic reforming processes make it possible to increase the octane rating of gasoline fractions obtained from crude oil distillation and / or other refining processes such as, for example, catalytic cracking or thermal cracking. Finally, these catalysts can find applications in steam reforming, cracking, hydrocracking, hydrogenation, dehydrogenation, and dehydrocyclization of hydrocarbons or other organic compounds. Detailed description of particular embodiments The method for preparing the spheroidal alumina particles according to the invention thus comprises the following main steps: a) the preparation of a suspension comprising water, an acid, and at least one boehmite powder exhibiting X-ray diffraction lines

[020] and

[120] whose intensity ratio is between 0.7 and 1.; the preparation of an emulsion comprising a porogen, water and a surfactant; c) mixing the suspension with the emulsion; b) line

[020] /

[120] is less an agent d) shaping the beads by droplet coagulation from the mixture from step c); e) drying the particles coagulated in step d); f) calcining the particles obtained in step e). The emulsion is prepared by mixing the porogen, the surfactant and water under agitation. The pore-forming agent content, expressed as the ratio of the mass of pore-forming agent to the total mass of water involved in the emulsion and suspension, is between 0.2 and 30%, preferably between 0.5 and 20%, and even more preferably between 0.5 and 10%. The pore-forming agent is a product that is not completely miscible in water, is eliminable by combustion, and is liquid at room temperature. It may be selected from fats, mineral oils and waxes, oils, hydrocarbons, and petroleum fractions. For example, the pore-forming agent is a paraffinic fraction having 10 to 14 carbon atoms, composed of normal and isoparaffins, and having a boiling point between 220 and 350°C. The most suitable surfactants are non-ionic or ionic surfactants, for example cationic surfactants, alone or in mixtures. Non-ionic surfactants are preferred.The proportion of surfactant present in the emulsion is defined as the ratio of the mass of surfactant to the mass of porogen. This ratio is between 1 and 25% by weight, preferably between 1 and 15%, and most preferably between 3 and 10%. The amount of water in the emulsion represents 5 to 20% by weight of the total amount of water in the mixture (Boehmite suspension and emulsion). The emulsion is prepared at a temperature between 15 and 60°C, preferably between 20 and 40°C. The suspension is prepared by vigorously stirring an acidic aqueous solution to which one or more types of boehmite powder have been added. However, according to the invention, at least one boehmite powder exhibits an X-ray diffraction pattern with

[020] and

[120] diffraction lines and a

[020] /

[120] line intensity ratio between 0.7 and 1. If several boehmite powders are used, the proportion of boehmite exhibiting

[020] and

[120] X-ray diffraction lines and a

[020] /

[120] line intensity ratio between 0.7 and 1 is at least 10% by weight relative to the total quantity of boehmite powder. During the preparation of the boehmite suspension, it is possible to add a charge of alumina or an alumina precursor.The amount of filler used, expressed as a percentage by weight of A12O3, is less than or equal to 30% by weight of the total weight of A12O3 equivalent in the suspension. Optionally, the suspension may include a salt of one or more elements selected from groups IIIA, IVA, VA, and lanthanides, which act as a promoter. These elements will be incorporated into the final spheroidal particles after drying and calcination. The proportion of the metallic salt(s) is calculated so that the mass content of elements from groups IA, IIA, IIIA, IVA, VA, or lanthanides in the final product, after calcination, is between 0.01 and 2% by weight, preferably between 0.05 and 1% by weight. The acid content of the suspension is such that the ratio of the mass of said acid to the dry mass of the boehmite source(s) and the feedstock (if present in the suspension) is between 0.5 and 20%, preferably between 1 and 15%.As an example, the acidic aqueous solution is a solution of a strong mineral acid, such as HNO3 or H2SO4. The proportion of water in the suspension is calculated so that the ratio of the dry mass (corresponding to the mass of boehmite powder plus, if applicable, the filler, expressed as A12O3 equivalent) to the total mass of water in the mixture (emulsion + suspension) is between 10 and 50%, preferably between 15 and 40%. After mixing the suspension and the emulsion, the resulting solution is stirred until its viscosity reaches between 200 and 700 MPa·s, preferably between 250 and 400 MPa·s. At this point, the solution has the appropriate rheological properties for draining through the nozzles of the draining container. A particularly suitable method for shaping is droplet coagulation. This method involves passing the mixture (alumina suspension + emulsion) through a drip tray equipped with nozzles of calibrated orifice size to form droplets. The drip tray is placed at the top of a column containing an upper organic phase and a lower phase consisting of a basic aqueous phase. The organic phase is chosen so that its density is slightly lower than that of water. Spherical shaping occurs as the droplet passes through the organic phase, while gelation (or coagulation) takes place in the aqueous phase. Additives such as surfactants or phase-transfer agents can be added to the aqueous phase to facilitate the passage across the interface and the coagulation of particles in the basic aqueous phase. In the context of this invention, the immiscible organic phase can be selected from fats, mineral oils and waxes, oils, hydrocarbons, and petroleum fractions. Preferably, the organic phase is a paraffinic fraction having 10 to 14 carbon atoms, composed of normal and isoparaffins, and exhibiting a boiling point between 220 and 350°C. The basic aqueous phase is, for example, a solution of ammonia, ammonium carbonate, or amines. Preferably, the basic aqueous phase is an ammonia solution. After the formation of the spheroidal particles, the beads are collected and separated from the aqueous phase using a sieve.It is also possible to subject the particles thus formed to one or more maturation stages, as taught in EP 001 023. The beads are dried at a temperature between 60 and 150°C, under dry or humid air, generally for between 0.5 and 20 hours. The drying protocol may optionally include one or more temperature plateaus. It may also require variable humidity levels during drying, preferably between 40 and 1000 g of water per kg of dry air, and even more preferably between 100 and 1000 g of water per kg of dry air. The beads are then calcined at a temperature between 450 and 900°C, preferably between 550 and 800°C. The calcination usually lasts one to several hours, preferably between 0.5 and 12 hours, preferably between 1 and 8 hours, and even more preferably between 1 and 5 hours.This calcination step may include one or more temperature steps. Examples: X-ray diffraction of the boehmites in the examples shown below was performed using the classical powder diffraction method with a Brüker D5005 diffractometer (CuKa1+2 = 0.15418 nm) equipped with a curved graphite back monochromator and a scintillation detector. Solid analyses were recorded in Debye-Scherrer mode from 3 to 80° (20) with a step size of 0.02° for 8 seconds. Viscosity was measured using a cone-plate rheometer at a shear rate of 100 s⁻¹. Example 1 (comparative) The support for Example 1 is prepared using Pural SB3 type boehmite, commercially available from Sasol, whose X-ray diffraction pattern shows a line intensity ratio

[020] /

[120] of 0.66. A suspension containing 20% ​​mineral matter (expressed as % Al₂O₃) is prepared by mixing an alumina feed (y) with a volume median diameter D₅₀ = 50 µm and Pural SB3 boehmite powder in an acidified aqueous solution containing 3.6 wt% HNO₃ / Al₂O₃. The solid fraction of Al₂O₃ is provided at 88 wt% by the boehmite and 12 wt% by the alumina feed (y). This suspension also contains a pore-forming agent and a surfactant necessary for the formation of an emulsion. The porogen is an organic phase comprising a mixture of paraffins containing between 10 and 12 carbon atoms, with a boiling point of approximately 290°C and a density of 0.75 g / cm³. The surfactant is Galoryl, a commercial emulsifying agent.These compounds are introduced in the following proportions: 3% mass fraction of porogen / water = 9.4% and 6% mass fraction of surfactant / porogen = 6%. The system is stirred at 600 rpm until a suspension with suitable rheological properties is obtained for draining (viscosity 250 MPa). The draining column is loaded with an ammonia solution at a concentration of 28 g / L and an organic solution consisting of the same petroleum fraction used as the porogen in the emulsion preparation (organic phase in the upper layer). The suspension is drained through calibrated nozzles. The beads are collected at the bottom of the column and placed in a ventilated oven at 120°C under humid air containing 200 g of water per kg of dry air for 12 hours. They are then calcined under dry air at 650°C for 3 hours. The resulting beads have a diameter of 1.9 mm.Example 2 (according to the invention) Boehmite was synthesized by alkalinizing a 0.1 mo11-1 aluminum nitrate solution with a 1 mei:1 sodium hydroxide solution at room temperature and a controlled pH of around 10. The suspension was then matured for one week in an oven at 95°C without stirring. The pH of the suspension after maturation changed; the final pH was 11.5. The solid was recovered by filtration and then washed in a volume of water approximately equal to the initial volume, and then dried under a stream of air at room temperature. The boehmite powder exhibited an X-ray diffraction pattern with a ratio of the

[020] /

[120] line intensities of 0.79.The support for Example 2 is prepared using the boehmite thus synthesized. A suspension containing 20% ​​mineral matter (expressed as % Al₂O₃) is prepared by mixing an alumina charge y with a volume median diameter D₅₀ = 50 µm and the boehmite powder in an acidified aqueous solution containing 10% wt. The solid fraction of Al₂O₃ is provided at 88 wt. by the boehmite and at 12 wt. This suspension also contains a porogen and a surfactant. The porogen is an organic phase comprising a mixture of paraffins containing between 10 and 12 carbon atoms with a boiling point of approximately 290°C and a density of 0.75 g / cm³. The surfactant is Galoryl. These compounds are introduced in the following proportions: mass fraction of porogen / water = 1.6% and mass fraction of surfactant / porogen = 6%.The system is agitated at 600 rpm until a suspension with rheological properties suitable for draining is obtained (viscosity 250 MPa). The draining column is loaded with an ammonia solution at a concentration of 28 g / L and an organic solution consisting of the same petroleum fraction used as a pore-forming agent in the emulsion preparation. The suspension is drained through calibrated nozzles. The beads are collected at the bottom of the column and placed in a ventilated oven at 120°C under humid air containing 200 g of water per kg of dry air for 12 hours. They are then calcined under dry air at 650°C for 3 hours. The resulting beads have a diameter of 1.9 mm. Example 3 (according to the invention) A boehmite was synthesized by alkalinizing a 0.1 mol / L aluminum nitrate solution with a 1 mol / L sodium hydroxide solution at room temperature and a controlled pH of around 10. The suspension was then matured for one week in an oven at 95°C without stirring. The pH of the suspension after maturation changed; the final pH was 11.5. The solid was recovered by filtration and then washed in a volume of water approximately equal to the initial volume. The solid was resuspended in water and autoclaved at 150°C for 4 hours. The suspension was centrifuged and then dried under a stream of air at room temperature.The support for Example 3 is prepared using the synthesized boehmite, whose X-ray diffraction pattern shows a line intensity ratio

[020] /

[120] of 0.93. A suspension containing 25% mineral matter (expressed as % Al₂O₃) is prepared by mixing an alumina charge y with a volume median diameter D₅₀ = 50 pm and the boehmite powder in an acidified aqueous solution containing 15% wt. The solid fraction of Al₂O₃ is provided at 88 wt% by the boehmite and 12 wt% by the alumina charge y. This suspension also contains a porogen and a surfactant. The porogen agent is an organic phase comprising a mixture of paraffins containing between 10 and 12 carbon atoms, with a boiling point of approximately 290°C and a density of 0.75 g / cm³. The surfactant is Galoryl.These compounds are introduced in the following proportions: 1.4% mass fraction of porogen / water and 6% mass fraction of surfactant / porogen. The system is stirred at 600 rpm until a suspension with suitable rheological properties is obtained for draining (viscosity 30-250 MPa). Shaping is carried out according to Example 1. The beads are collected from the bottom of the column and placed in a ventilated oven at 120°C under humid air containing 200 g of water per kg of dry air for 12 hours. They are then calcined under dry air at 600°C for 3 hours. The resulting beads have a diameter of 1.9 mm. 35 Example 4 (according to the invention) A boehmite synthesized by alkalinization of a 0.1 molrl aluminium nitrate solution with a 1 mol.L-1 sodium hydroxide solution at room temperature and controlled pH around 10. The suspension is then matured for one week in an oven at 95[deg.]C without agitation.The pH of the suspension changes after maturation; the final pH is 11.5. The solid is recovered by filtration and then washed in a volume of water approximately equal to the initial volume. The solid is resuspended in water and autoclaved at 180°C for 24 hours. The suspension is centrifuged and then dried under a stream of air at room temperature. The boehmite powder exhibits an X-ray diffraction pattern with a ratio of the [O2O] / [O2O] line intensities of 0.91. The support for Example 4 is prepared using the synthesized boehmite. A suspension containing 25% mineral matter (expressed as % Al2O3) is prepared by mixing the boehmite powder in an acidified aqueous solution containing 18% wt. HNO3 / Al2O3. This suspension also contains a pore-forming agent and a surfactant. The pore-forming agent is an organic phase comprising a mixture of paraffins containing between 10 and 12 carbon atoms, with a boiling point of approximately 290°C and a density of 0.75 g / cm³. The surfactant is Galoryl. These compounds are introduced in the following proportions: pore-forming agent / water mass fraction = 1.1% and surfactant / pore-forming agent mass fraction = 6%. The system is agitated at 600 rpm until a suspension with suitable rheological properties is obtained for draining (viscosity 250 MPa). Shaping is carried out according to Example 1. The beads are collected from the bottom of the column and placed in a ventilated oven at 120°C under humid air containing 200 g of water per kg of dry air for 12 hours. They are then calcined under dry air at 550°C for 3 hours. The resulting beads have a diameter of 1.9 mm.Example 5 (according to the invention) The support of Example 5 is prepared using a boehmite source comprising 30 wt% of Pural SB3 and 70 wt% of boehmite synthesized according to Example 2. A suspension containing 20% ​​mineral matter (expressed as % of Al2O3) is prepared by mixing an alumina charge y having a volume median diameter D50=50pm and the boehmite source in an acidified aqueous solution containing 12 wt% of HNO3 / Al2O3. The solid fraction of Al₂O₃ is supplied at 88% by weight from the boehmite source and 12% by the alumina feedstock. This suspension also contains a pore-forming agent and a surfactant. The pore-forming agent is an organic phase comprising a mixture of paraffins containing between 10 and 12 carbon atoms, with a boiling point of approximately 290°C and a density of 0.75 g / cm³. The surfactant is galoryl. These compounds are introduced in the following proportions: pore-forming agent / water mass fraction = 3% and surfactant / pore-forming agent mass fraction = 6%. The system is agitated at 600 rpm until a suspension with rheological properties suitable for draining is obtained (viscosity 250 MPa). Shaping is carried out according to example 1. The beads are collected at the bottom of the column and placed in a ventilated oven at 120°C under humid air containing 200 g of water per kg of dry air for 12 h. They are then calcined under dry air at 650°C.]C for 3 hours. The resulting beads have a diameter of 1.9 mm. Example 6 (according to the invention) The support of Example 6 is prepared using the boehmite synthesized in Example 2. A suspension containing 30% mineral matter (expressed as % Al₂O₃) is prepared by mixing an alumina feedstock y having a volume median diameter D₅₀ = 15 pm and the boehmite powder of Example 2 in an acidified aqueous solution containing 20 wt% HNO₃ / Al₂O₃. The solid fraction of Al₂O₃ is provided at 80 wt% by the boehmite and 20 wt% by the alumina feedstock y. This suspension further contains a porogen and a surfactant. The porogen is an organic phase comprising a mixture of paraffins containing between 10 and 12 carbon atoms, with a boiling point of approximately 290°C and a density of 0.75 g / cm³. The surfactant is Galoryl. These compounds are introduced in the following proportions: mass fraction of porogen / water = 1.6% and mass fraction of surfactant / porogen = 6%. The system is agitated at 600 rpm until a suspension with suitable rheological properties is obtained for draining (viscosity 250 MPa). Shaping is carried out according to Example 1. The beads are collected from the bottom of the column and placed in a ventilated oven at 120°C under humid air containing 200 g of water per kg of dry air for 12 hours. They are then calcined under dry air at 650°C for 3 hours. The resulting beads have a diameter of 1.9 mm. Example 7 (according to the invention) The support of Example 7 is prepared using the boehmite synthesized in Example 2. A suspension containing 15% mineral matter (expressed as % of A12O3) is prepared by mixing an alumina charge having a volume median diameter D50 = 15 pm and the boehmite of Example 2 in an acidified aqueous solution containing 7% mass of HNO3 / A12O3. A sufficient quantity of SnCl2 was incorporated into this suspension to obtain a support having a weight percentage of Sn (promoting agent) of 0.3% after calcination. The solid fraction of A12O3 is comprised of boehmite (88% by weight) and alumina (12% by weight). This suspension also contains a pore-forming agent and a surfactant. The pore-forming agent is an organic phase consisting of a mixture of paraffins containing between 10 and 12 carbon atoms, with a boiling point of approximately 290°C and a density of 0.75 g / cm³. The surfactant is galoryl. These compounds are introduced in the following proportions: pore-forming agent / water mass fraction = 1.6% and surfactant / pore-forming agent mass fraction = 6%. The system is agitated at 600 rpm until a suspension with rheological properties suitable for draining is obtained (viscosity 250 MPa). The shaping is carried out according to example 1. The beads are collected at the bottom of the column and placed in a ventilated oven at 120°C under humid air containing 200 g of water per kg of dry air for 12 h. They are then calcined under dry air at 650°C.]C for 3 hours. The resulting beads have a diameter of 1.9 mm. 2 5 Example 8 (according to the invention) The support of Example 8 is prepared using the boehmite synthesized in Example 2. A suspension containing 17% mineral matter (expressed as % of A12O3) is prepared by mixing an alumina charge having a median diameter in volume D50 = 10 µm and the boehmite of Example 2 in an acidified aqueous solution containing 6% mass of HNO3 / A12O3. Sufficient quantities of SnCl2 and In(NO3)3 were incorporated into this suspension to obtain a support with weight percentages of Sn and In of 0.3% and 0.2% respectively, after calcination. 3 5 The solid fraction of Al2O3 is provided at 90% wt% by boehmite and at 10% by the alumina charge y. This suspension also contains a porogenic agent and a surfactant.The pore-forming agent is an organic phase comprising a mixture of paraffins containing between 10 and 12 carbon atoms, with a boiling point of approximately 290°C and a density of 0.75 g / cm³. The surfactant is Galoryl. These compounds are introduced in the following proportions: pore-forming agent / water mass fraction = 1.6% and surfactant / pore-forming mass fraction = 6%. The system is stirred at 600 rpm until a suspension with suitable rheological properties is obtained for draining (viscosity 250 MPa). The shaping is carried out according to Example 1. The beads are collected from the bottom of the column and placed in a ventilated oven at 120°C under humid air containing 200 g of water per kg of dry air for 12 hours. They are then calcined under dry air at 650°C for 3 hours. The resulting beads have a diameter of 1.9 mm.Example 9 (according to the invention) The support of Example 9 is prepared using the boehmite synthesized in Example 2. A suspension containing 30% mineral matter (expressed as % Al₂O₃) is prepared by mixing an alumina feedstock y having a volume median diameter D₅₀ = 10 µm and the boehmite of Example 2 in an acidified solution containing 7 wt% HNO₃ / Al₂O₃. Sufficient quantities of SnCl₂ and Ce(NO₃)₃ have been incorporated into this suspension to obtain a support with a weight percentage of Sn and Ce (promoting agents) of 0.3% and 0.05% respectively after calcination. The solid fraction of Al₂O₃ is provided at 80 wt% by the boehmite and 20 wt% by the alumina feedstock y. This suspension also contains a porogen and a surfactant. The porogen agent is an organic phase comprising a mixture of paraffins containing between 10 and 12 carbon atoms with a boiling point of approximately 290°C and a density of 0.75 g / cm3.The surfactant is Galoryl. These compounds are introduced in the following proportions: mass fraction of porogen / water = 1.6% and mass fraction of surfactant / porogen = 6%. The system is agitated at 600 rpm until a suspension with suitable rheological properties is obtained for draining (viscosity 250 MPa). Shaping is carried out according to Example 1. The beads are collected from the bottom of the column and placed in a ventilated oven at 120°C under humid air containing 200 g of water per kg of dry air for 12 hours. They are then calcined under dry air at 650°C for 3 hours. The resulting beads have a diameter of 1.9 mm. Example 10 (according to the invention) The support of Example 10 is prepared using the boehmite synthesized in Example 2. A suspension containing 20% ​​mineral matter (expressed as % Al₂O₃) is prepared by mixing an alumina feedstock y having a volume median diameter D₅₀ = 10pₙ and the boehmite of Example 2 in an acidified aqueous solution containing 3.5 wt% HNO₃ / Al₂O₃. Sufficient quantities of SnCl₂ and H₃PO₃ have been incorporated into this suspension to obtain a support with Sn and P wt%s of 0.3% and 0.4%, respectively, after calcination. The solid fraction of Al₂O₃ is provided at 80 wt% by the boehmite and at 20 wt% by the alumina feedstock y. This suspension also contains a porogen and a surfactant. The porogen agent is an organic phase comprising a mixture of paraffins containing between 10 and 12 carbon atoms with a boiling point of approximately 290°C and a density of 0.75 g / cm3.The surfactant is Galoryl. These compounds are introduced in the following proportions: mass fraction of porogen / water = 1.6% and mass fraction of surfactant / porogen = 6%. The system is stirred at 600 rpm until a suspension with rheological properties suitable for draining is obtained (viscosity 20-250 MPa). Shaping is carried out according to Example 1. The beads are collected from the bottom of the column and placed in a ventilated oven at 120°C under humid air containing 200 g of water per kg of dry air for 12 hours. They are then calcined under dry air at 650°C for 3 hours. The resulting beads have a diameter of 1.9 mm. The particles obtained from the above examples were analyzed using various techniques. In particular, their specific surface area BE was measured.T, the EGG (grain-by-grain crushing) value according to ASTM D4179-88a, and finally, their N2 adsorption isotherm volume and their mercury adsorption volume were determined. Nitrogen adsorption isotherms and mercury porosimetry were performed according to standards D3663-03 and D4284-03, respectively, cited in the patent. The nitrogen adsorption isotherm was performed on a Micromeritics ASAP 2420 instrument, and the mercury intrusion on a Micromeritics Autopore 9500 instrument. The results of the measurements mentioned above are summarized in Table 1. Table 1 Example VV Ratio Q = EGG (daN) Surface Density meso meso+macro (ml / g) '' BET in (ml / g) uvmeso+macro - Vmeso) '' (m2ig) filling / (Vmeso+macro)] *100 packed (g / mL) 1 (comparative) 0.64 0.74 14.2 2.2 207 0.55 2 (according to the invention) 0.69 0.71 2.8 4.0 191 0.59 3 (according to the invention) 0.72 0.73 1.4 4.5 187 0.56 4 (according to the invention) 0.75 0.77 2.6 5.6 185 0.54 0.68 0.72 5.5 3.9 195 0.58 the invention) 6 (according to 0.69 0.71 2.8 4.5 193 0.59 the invention) 7 (according to 0.69 0.71 2.8 5.0 190 0.60 the invention) 8 (according to 0.70 0.72 2.8 5.3 192 0.59 the invention) 9 (according to 0.69 0.71 2.8 4.9 192 0.58 the invention) (according to 0.69 0.70 1.4 4.9 190 0.59 the invention) 5 The spheroidal alumina particles according to the invention therefore exhibit improved crush resistance. Thus the value of EGG is at least 3.9 daN (example 5) and even reaches 5.6 daN (example 4) compared to 2.2 daN for the comparative example.This improvement can be explained by a relative decrease in the volume of the macroporous pores. Indeed, the macroporous volume represents approximately 10–14% of the total pore volume for the comparative example, while for the examples according to the invention, this percentage varies between 1.4 and 5.5%. Furthermore, an increase in the packed density is observed. Finally, it should be noted that these technical effects were obtained by reducing the amount of pore-forming agent used during particle synthesis.

Claims

CLAIMS 1. Spheroidal alumina particles comprising a nitrogen adsorption isotherm volume, called VméS01 representative of the mesoporous volume, which is between 0.65 and 0.85 mL / g and a pore volume with a diameter of less than 7 pm, called Vmeso+macrO! measured by mercury porosimetry, which is between 0.65 and 0.85 mL / g and for which the ratio Q ~ [(Vmeso+m3cro - Vmé3O) / (Vmeso*macro)] is less than 10%, said particles comprising an average diameter of between 1.2 and 3 mm, a BET specific surface area of ​​between 150 and 300 m2 / g and a packed filling density value of between 0.5 and 0.6 g / m2.

2. Spheroidal alumina particles according to claim 1, in which the average grain-by-grain crushing value is at least 2.5 daN.

3. Catalyst comprising a support formed from particles according to claim 1 to 2 and one or more metals chosen from group VIII.

4. Catalyst according to claim 3, further comprising one or more elements selected from groups IIIA, IVA, VA and the lanthanides.

5. Catalyst according to one of claims 3 or 4 further comprising an element chosen from the group consisting of fluorine, chlorine, bromine and iodine.

6. Catalyst according to claim 5, comprising platinum, tin and chlorine.

7. Use of a catalyst according to one of claims 1 to 6 for carrying out transformation reactions chosen from catalytic reforming, steam reforming, cracking, hydrocracking, hydrogenation, dehydrogenation, dehydrocyclization of hydrocarbons or other organic compounds.