Method for producing silica-alumina having high acidity

Abstract

The present invention describes a method for preparing an amorphous silica-alumina-based material having incorporated therein, by means of precipitation, at least one acid solution and / or suspension of an aluminium source together with colloidal alumino-silicate particles having the structure of zeolite and conferring on the final material improved acidity relative to silica-alumina of the prior art, thereby providing a catalyst or a catalyst support that can be used in hydroconversion reactions.

Description

[0001] PROCESS FOR PRODUCING SILICA ALUMINA HAVING HIGH ACIDITY

[0002] Field of invention

[0003] USY (Ultra Stable Y) faujasite zeolites are commonly used as catalysts in refining and petrochemical processes. They have a pore size of 0.74 nm, which allows the conversion of relatively large molecules. However, the crystal size of faujasite zeolites is generally quite large (of the order of 500 nm or more), which leads to diffusion limitations in the conversion of heavy feedstocks, such as vacuum distillates or polyolefins (polyethylene, polypropylene, etc.). One approach to overcome this problem is to reduce the crystal size.

[0004] To avoid diffusion limitations, silica-alumina can also be used as a catalyst for the conversion of heavy charges (or very crowded molecules). However, the acidity of a silica-alumina is much lower than the acidity of a zeolite.

[0005] Sang et al., Materials Letters 2006, 60, 1131 describe a protocol for the synthesis of faujasite zeolite NaY (i.e., containing Na + as an extra-framework cation) which allows the crystal size to be reduced to < 400 nm. The gains in catalysis were not evaluated in this article.

[0006] US Patent 10,370,256 describes the preparation of faujasite Y zeolites with a crystal size less than 100 nm. The NaY nanocrystals obtained by this method have good crystallinity, but to transform them into USY catalyst it is necessary to apply ultra-stabilization protocols, which increase the Si / Al ratio of the structure and simultaneously convert it into the acid form. These protocols have been optimized for larger faujasites. However, nanocrystals are more fragile and known ultra-stabilization processes can lead to the destruction of the crystalline structure of the nanocrystals.

[0007] Another approach is to prepare so-called embryonic zeolites, that is, the synthesis of aluminosilicate is stopped after the germination stage, but before the formation of zeolite crystals detectable by DRX.

[0008] Preparation protocols are described in the publications of Haw et al., New J Chem 2016, 40, 4307 and Akouche et al., Chem. Mater. 2020, 32, 2123. Synthesis mixtures containing a large amount of organic structuring agent or OSDA (Organic Structure Directing Agent) and highly diluted are used. This produces a so-called "clear" or colloidal solution, which contains colloidal-sized aluminosilicate particles. The syntheses are carried out at room temperature or with an additional maturation step at 90°C. In no case is a precipitate formed. To recover the so-called embryonic zeolites, the authors use a freeze-drying step. However, freeze-drying is very expensive and time-consuming, so this method cannot be used on an industrial scale.

[0009] After freeze-drying, the embryonic zeolites are calcined to remove the organic structuring agent. Calcination directly results in an acidic aluminosilicate which, unlike NaY nanocrystals, does not require additional ultra-stabilization steps.

[0010] Patent WO2015 / 001004 and the publication by Haw et al., ACS Catalysis 2018, 8, 8199 describe a way to bypass the freeze-drying step. The clear solution containing so-called embryonic zeolites is impregnated onto a silica-alumina support. However, the pore volume of silica-alumina limits the impregnation volume and the concentration of embryonic zeolites in the very dilute clear solution is low. Therefore, this method does not allow a significant amount of embryonic zeolite to be deposited on the support.

[0011] Today, there is therefore no viable method for preparing acid catalysts comprising colloidal-sized aluminosilicate zeolite particles, known as embryonic, i.e. characterized by an absence of long-range organization, and not giving rise to X-ray diffraction lines.

[0012] An alternative to the use of nanometric zeolites are aluminosilicates (silica-aluminas) without long-scale structural organization. The prior art offers numerous examples of silica-alumina preparation. Examples include US 6,872,685 or FR 2,819,430. However, the acidity of silica-aluminas is generally well below that of zeolites. Known silica-aluminas are therefore not suitable as catalysts for reactions requiring high activity.

[0013] In the context of the present invention, the term "colloidal solution" means a clear and homogeneous solution which contains particles and preferably aluminosilicate particles according to the invention, of colloidal size which are not precipitated and not visible under a microscope, i.e. less than 800 nm, preferably less than 600 nm, preferably less than 500 nm and more preferably less than 400 nm.

[0014] ADVANTAGES OF THE METHOD ACCORDING TO THE INVENTION

[0015] The applicant has demonstrated that it is possible to obtain an acidic material and preferably an acidic catalyst support based on silica-alumina and also a catalyst comprising said acidic support, from a clear solution of so-called embryonic zeolites having a basic pH, by precipitation of said clear solution and of a solution and / or of a suspension) containing a salt, an oxide or an aluminium hydroxide, said precipitation step being carried out at a specific pH and in particular at a pH between 2 and 10. The process according to the invention therefore makes it possible to obtain an amorphous silica-alumina having an increased acidity compared to the silica-aluminas known in the state of the art.

[0016] An advantage of the present invention is to provide a process for preparing a silica-alumina having improved acidity compared to the silica-aluminas of the prior art, allowing its use as a catalyst support in conversion processes involving reactions requiring high activity.

[0017] Another advantage of the present invention is to provide a process for preparing a silica-alumina having improved acidity compared to the silica-aluminas of the prior art according to a preparation process which is simple and inexpensive to implement and easily extrapolated to an industrial scale.

[0018] Subject of the invention

[0019] More specifically, the present invention relates to a process for preparing a material comprising a silica alumina, said process comprising at least the following steps and preferably consisting of: a) a step of mixing in an aqueous medium, optionally mixed with an alcohol R2OH chosen from ethanol, propanol, isopropanol and butanol, at least one source of silicon in the form of oxide SiO2, at least one source of aluminum in the form of oxide AI2O3, an organic compound in the form of hydroxide RiOH or halide RiX, with X being chosen from the elements Cl, Br and I, and optionally at least one source of an alkali metal M, with M being chosen from lithium, potassium, sodium, alone or as a mixture, the reaction mixture having the following molar composition: x1 Ri : x2 M2O : y AI2O3 : 1 SiC>2 : z H2O : a R2OH with x1 = 0.1 to 0.6, x2 = 0 to 0.1, y = 0.002 to 0.02, z = 10 to 50 and a = 0 to 4, and R1 being a quaternary ammonium cation,of general formula RaRbRcRdN+ in which Ra, Rb, Rc and Rd are chosen from methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclopentyl, cyclohexyl and adamantyl groups, and R2 being chosen from ethyl, propyl, isopropyl and butyl groups, with stirring, until a colloidal solution comprising zeolite seeds is obtained, b) a step of heat treatment of the colloidal solution obtained at the end of step a), said step b) being carried out at a temperature of between 60 and 120°C, preferably between 70 and 100°C, and for a duration of between 1 hour and 24 hours and preferably between 4 and 16 hours. c) a step of precipitation of the colloidal solution obtained at the end of step b) with a solution and / or a suspension of at least one source of aluminum chosen from aluminum salts and an aluminum oxide or hydroxide, alone or as a mixture,said solution and / or suspension being acidic and having a pH between 1 and 5, so that said precipitation step c) is carried out at a pH between 2 and 10 and preferably between 2 and 9), d) a step of filtration or centrifugation of the silica-alumina precipitate obtained at the end of step c), followed by a step of drying said precipitate to obtain a silica-alumina powder.,

[0020] The present invention therefore lies in the preparation of a material based on amorphous silica-alumina in which colloidal particles of aluminosilicate having the zeolite structure have been incorporated by precipitation under specific conditions with at least one source of aluminum, giving said final material an improved acidity compared to the silica-alumina of the prior art.

[0021] An advantage of the present invention is to provide a method for preparing a material comprising a silica-alumina directly using the colloidal solution comprising the seeds of zeolites or so-called embryonic zeolites, without requiring a step of separating said embryonic zeolites from the colloidal solution beforehand.

[0022] Detailed description of the invention

[0023] Preparation of colloidal solution of zeolite seeds or embryonic zeolites

[0024] Step a)

[0025] According to the invention, said method comprises a step a) of mixing in an aqueous medium, optionally in a mixture with an alcohol R2OH chosen from ethanol, propanol, isopropanol and butanol, at least one source of silicon in the form of oxide SiO2, at least one source of aluminum in the form of oxide AI2Os, an organic compound in the form of hydroxide RiOH or halide RiX, with X being chosen from the elements Cl, Br and I, and optionally at least one source of an alkali metal M, with M being chosen from lithium, potassium, sodium, alone or as a mixture, the reaction mixture having the following molar composition: xi RiOH: x2M2O: y AI2Os: 1 SiO2: z H2O: a R2OH with x1 = 0.1 to 0.6, preferably from 0.2 to 0.5 x2 = 0 to 0.1, of preferably from 0 to 0.05 y = 0.002 to 0.02, preferably from 0.05 to 0.02 z = 10 to 50, preferably from 10 to 25 a = 0 to 4 and R1 being a quaternary ammonium cation, of general formula R a RbR c RdN +in which Ra, Rb, Rc and Rd are chosen from methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclopentyl, cyclohexyl and adamantyl groups, and R2 being chosen from ethyl, propyl, isopropyl and butyl groups, with stirring, until a colloidal solution is obtained comprising zeolite seeds or so-called embryonic zeolites.

[0026] The silicon source is preferably comprised among powdered silica, silicic acid, colloidal silica, dissolved silica and tetraethoxysilane (TEOS), alone or as a mixture. Among the powdered silicas, precipitated silicas may be used, in particular those obtained by precipitation from an alkali metal silicate solution, fumed silicas, for example "CAB-O-SIL" and silica gels. Colloidal silicas having different particle sizes may be used, for example with an average equivalent diameter of between 10 and 15 nm or between 40 and 50 nm, such as those marketed under registered trademarks such as "LUDOX". Preferably, the silicon source is tetraethoxysilane (TEOS).

[0027] In the preferred embodiment where the silicon source is tetraethoxysilane (TEOS), the tetraethoxysilane (TEOS) decomposes in the reaction mixture of step a) into an alcohol R2OH, where R2OH is ethanol.

[0028] The aluminum source is preferably aluminum hydroxide or an aluminum salt, selected from aluminum chloride, nitrate, and sulfate, sodium aluminate, aluminum alkoxide, or alumina itself, preferably in hydrated or hydratable form, such as, for example, colloidal alumina, pseudoboehmite, gamma alumina, or alpha or beta trihydrate. Mixtures of the above-mentioned sources may also be used.

[0029] According to the invention, R1 is a quaternary ammonium cation, in the form of hydroxide R1 OH or halide RiX (X = Cl, Br, I), Ri having the general formula R a RbR c RdN + in which R a, Rb, Rc and Rd are selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclopentyl, cyclohexyl and adamantyl groups. Preferably, R1 is tetrapropylammonium. Cyclic quaternary ammoniums are also within the scope.

[0030] Preferably, no alkali metal M is added with M being chosen from lithium, potassium, sodium, alone or as a mixture, in the reaction mixture of step a).

[0031] In one embodiment according to the invention, a source of alkali metal M with M preferably being sodium Na may be provided by the aluminum source in the case where said aluminum source is sodium aluminate (NaAlC^). The provision of said sodium source Na may also advantageously be supplemented by an addition of aluminum hydroxide NaOH.

[0032] According to the invention, step a) of mixing is carried out with stirring until a colloidal solution containing zeolite seeds or so-called embryonic zeolites is obtained. Colloidal solution is understood to mean a clear and homogeneous solution which contains particles of colloidal size, that is to say less than 500 nm, preferably less than 400 nm, more preferably less than 300 nm and more preferably less than 200 nm.

[0033] In the context of the present invention, said particles are aluminosilicate particles and in particular zeolite seeds or so-called embryonic zeolites characterized by an absence of long-distance organization, and not giving rise to X-ray diffraction lines).

[0034] Preferably, mixing step a) is carried out at a temperature between room temperature and 80°C, preferably between room temperature and 60°C and for a period of 0.5 to 8 h, preferably 1 to 6 h.

[0035] At the end of step a), the colloidal solution obtained is subjected to a heat treatment step b).

[0036] Step b)

[0037] In accordance with the invention, the method according to the invention comprises a step b) of heat treatment of the colloidal solution obtained at the end of step a), said step b) being carried out at a temperature between 50 and 120°C, preferably between 60 and 100°C, for a period between 1 and 48 h, preferably between 2 and 24 h.

[0038] At the end of heat treatment step b), the colloidal solution advantageously still has a clear appearance, i.e. there is no formation of precipitate and no particles visible under an optical microscope.

[0039] The pH of the colloidal solution obtained at the end of step b) is basic, preferably between 9 and 14, and more preferably between 10 and 13.

[0040] The concentration of silica SiO2 in the colloidal solution is preferably between 3 and 15% by mass.

[0041] An X-ray diffractogram analysis makes it possible to highlight the absence of long-range structural organization of so-called embryonic zeolites within the colloidal solution obtained at the end of step b). To carry out the analysis, part of the colloidal solution is freeze-dried to obtain a powder of aluminosilicate particles.

[0042] The X-ray diffractogram of the obtained particle powder is essentially amorphous, i.e. it does not show diffraction lines attributable to a structural type of zeolite. These particles are called embryonic zeolites, i.e., the synthesis of the aluminosilicate material is stopped by the implementation of specific operating conditions in steps a) and b) after the germination step, but before the formation of zeolite crystals detectable by XRD.

[0043] The 27AI NMR analysis of the solid shows that the aluminum in the solid is overwhelmingly tetra-coordinated, that is, the percentage of the AIIV signal between 40 and 70 ppm represents at least 70% of the total signal, preferably at least 80% of the total signal.

[0044] Step c)

[0045] According to the invention, the method comprises a step c) of precipitation of the colloidal solution obtained at the end of step b) with a solution and / or a suspension of at least one source of aluminum chosen from aluminum salts and an aluminum oxide or hydroxide, alone or as a mixture, said solution and / or suspension being acidic and having a pH of between 1 and 5, so that said precipitation step c) is carried out at a pH of between 2 and 10 and preferably between 2 and 9).

[0046] According to the invention, the source of aluminum is chosen from aluminum salts and an aluminum oxide or hydroxide, alone or as a mixture.

[0047] Preferably, the aluminum salts are chosen from aluminum sulfate and nitrate.

[0048] Preferably, the aluminum oxides or hydroxides are chosen from boehmites or (pseudo)-boehmites. Commercial boehmites, such as Pural, Catapal or Versai, or boehmites obtained by precipitation methods known to those skilled in the art, may be used. It is preferable for the boehmite to have a high specific surface area, preferably greater than 150 m2 / g, preferably greater than 200 m2 / g, and a high dispersibility. The dispersibility index of the boehmite used is preferably greater than 50%.

[0049] The use of pseudo-boehmite allows the textural properties of precipitated silica-alumina to be oriented, particularly in terms of pore volume and pore size. To induce precipitation of the colloidal solution, it must be mixed with at least one acid solution to lower the pH to a value between 2 and 10 and preferably between 2 and 9.

[0050] In a first embodiment, the colloidal solution obtained at the end of step b) is precipitated with an acid solution containing an aluminum salt, preferably aluminum sulfate or nitrate. The concentration of AI2O3 in said aluminum salt solution is advantageously between 1 and 15% by mass. The quantity of the acid solution containing an aluminum salt is adjusted in order to obtain a mass content of SiC>2 in the precipitate of less than 70%, preferably between 20 and 50%. Preferably, the pH of the acid solution containing an aluminum salt is between 1 and 5.

[0051] The precipitation step can advantageously be carried out by the simultaneous addition of the colloidal solution and the acid solution containing an aluminum salt to a foot of water, for example by a pump or a burette. The foot of water advantageously represents less than one third of the final total volume.

[0052] In a second embodiment, the colloidal solution is precipitated by mixing with an acid solution containing a suspension of pseudo-boehmite in water. If the boehmite suspension is peptized by adding an acid, its pH is low enough to cause precipitation. Otherwise, a simultaneous addition of an aqueous solution of an acid chosen from nitric acid, sulfuric acid and acetic acid alone or as a mixture, can advantageously be carried out to adjust the pH of said acid solution to a pH between 1 and 5.

[0053] Precipitation step c) is advantageously carried out at a temperature between 50 and 100°C, preferably between 60 and 90°C. Precipitation step c) is advantageously carried out for at least the time necessary to mix the two solutions.

[0054] The duration of precipitation step c) may advantageously be extended for a period of between 30 min and 6 h, at the initial temperature or at a higher temperature but always in the temperature range of between 50 and 100°C, preferably between 60 and 90°C.

[0055] During precipitation, the pH stabilizes at a value between 2 and 10, and preferably between 2 and 9. A third basic solution containing ammonia may advantageously be added during precipitation step c) so as to adjust and control the pH at a value less than or equal to 9.

[0056] Said step c) of precipitation of the colloidal solution having a basic pH with an acidic solution having a pH between 1 and 5 and comprising at least one source of aluminum chosen from aluminum salts and an aluminum oxide or hydroxide, alone or in a mixture, makes it possible to incorporate the colloidal particles of alumino-silicate of the colloidal solution into an amorphous silica-alumina of strong acidity.

[0057] Step d)

[0058] According to the invention, the method comprises a step d) of filtration and centrifugation of the silica-alumina precipitate obtained at the end of step c), followed by a step of drying said precipitate to obtain a silica-alumina powder.

[0059] The precipitate is separated from the solution by filtration or centrifugation. It is then advantageously washed with water, then dried at a temperature between 80 and 150°C and for a period of between 30 min and 24 h and preferably between 1 h and 6 h.

[0060] Preferably, the drying is carried out according to techniques known to those skilled in the art and preferably in an oven or in a muffle furnace.

[0061] In the case where drying is carried out in a study, it is carried out at a temperature between 60 and 150°C and preferably between 80 and 130°C and for a duration between 1 and 48 hours and preferably between 2 and 24 hours.

[0062] The silica-alumina powder obtained at the end of step d) may optionally be calcined at a temperature between 450°C and 800°C, under a flow of gas. At least part of the calcination must advantageously be carried out under an oxidizing atmosphere, in order to burn the organic molecules used in the preparation of the colloidal solution. The calcination may advantageously be carried out in two stages, with a first stage under a flow of inert gas chosen from nitrogen, argon and helium in order to partially decompose the organic molecules, followed by a second stage under an oxidizing atmosphere and preferably under air or under a controlled mixture of oxygen and nitrogen in order to oxidize the organic residues to CO2.

[0063] It is preferable to limit the water vapor content of the calcination atmosphere to a value below 20% by volume, preferably below 10% by volume. Preferably, the calcination step is carried out in the absence of water vapor.

[0064] The silica-alumina powders obtained at the end of step d) have a mass content of silica SiO2 of less than 70% by weight, preferably between 20 and 55% by weight relative to the total mass of said powders, the remainder to 100% being alumina AI2O3.

[0065] The silica-alumina powders obtained at the end of step d) also have a specific surface area of ​​between 100 and 500 m2 / g, preferably between 200 and 400 m2 / g, a pore volume of between 0.15 and 1 ml / g, preferably between 0.2 and 0.8 ml / g and a Bronsted acidity of between 75 and 300 pmol / g, preferably between 100 and 200 pmol / g.

[0066] Step e) optional

[0067] The silica-alumina powder obtained at the end of step d) of the process according to the invention and optionally calcined can advantageously be shaped in the presence or absence of binder according to the various methods known to those skilled in the art to obtain a material comprising shaped silica-alumina.

[0068] Preferably, said shaping step e) is carried out by kneading extrusion, by pelletizing, by the oil-drop coagulation method, by granulation on a rotating plate and preferably by kneading extrusion to obtain a material comprising shaped silica alumina and preferably an extrudate.

[0069] In the case where a binder is used in the shaping step of the silica-alumina powder, the preferred binder is pseudo-boehmite. In this case, the mass fraction of binder used in shaping step d) is between 3 and 35% by mass, preferably between 5 and 25% by mass.

[0070] After shaping, the shaped material comprising silica alumina and preferably an extrudate may advantageously undergo again at least one step of heat treatment, drying and calcination. The preferred drying and calcination conditions are the same as those described in step d).

[0071] In a preferred embodiment, the co-precipitated silica-alumina-comprising materials which have not undergone a calcination step in step d) may advantageously be calcined after shaping.

[0072] Preferably, the shaped material comprising silica alumina and obtained at the end of steps a) to e) of the process according to the invention is in the form of irregular and non-spherical beads, extrudates, pellets or agglomerates whose specific shape may result from a crushing step and preferably in the form of extrudates.

[0073] Preferably, the shaped material comprising silica alumina and obtained at the end of steps a) to e) of the process is used as a catalyst or as a catalyst support. The shape taken by the support comprising said material is preferably that of extrudates whose diameter is between 0.8 and 3 mm, preferably between 1.2 and 2.6 mm. The geometry of the extrudates can be cylindrical, trilobal, quadrilobal or any other advantageous shape depending on the desired application.

[0074] Step f) optional

[0075] The material comprising silica-alumina in which the colloidal aluminosilicate particles have been incorporated by precipitation, prepared according to steps a) to d) and preferably according to steps a) to e) of the process according to the invention and optionally dried and / or calcined, can advantageously be used as a catalyst or catalyst support for numerous acid catalysis reactions (isomerization, cracking, oligomerization, etc.), in particular for hydrocracking / hydroisomerization.

[0076] Hydroisomerization refers to the transformation of paraffins into paraffins with a higher degree of branching. Hydrocracking refers to the transformation of hydrocarbons with a carbon number of n into hydrocarbons with a carbon number m < n-2. This is bifunctional catalysis, i.e., the acid catalyst, silica-alumina, is associated with a metallic function. The metallic function is either a noble metal with a high hydrogenation activity, such as Ni, Pt, Pd, etc., or a sulfide of a transition metal from group VI (Mo, W), promoted by Ni or Co. A catalyst can advantageously be prepared from the material comprising silica-alumina prepared according to steps a) to e) of the process according to the invention and optionally dried and / or calcined.

[0077] The method according to the invention may advantageously comprise a step f) of deposition on said material comprising silica-alumina prepared according to steps a) to e) of the method according to the invention and optionally dried and / or calcined of at least one metal from group VIII and / or at least one metal from group VIB of the periodic table of elements and / or a doping element chosen from boron and preferably phosphorus and optionally at least one organic additive to obtain a catalyst.

[0078] In the case where an organic additive is deposited, its deposition is followed by a drying step without calcination. In the case where no organic additive has been deposited, the deposition of the metals is followed by a drying step and possibly a calcination step.

[0079] The metal(s) from group VIII and / or at least one metal from group VIB may advantageously be introduced in one or more stages and preferably by dry or excess impregnation.

[0080] The group VIB metal present in the active phase of the catalyst is preferably chosen from molybdenum and tungsten. The group VIII metal present in the active phase of the catalyst is preferably chosen from cobalt, nickel and the mixture of these two elements. The active phase of the catalyst is preferably chosen from the group formed by the combination of the elements nickel-molybdenum, cobalt-molybdenum, nickel-tungsten, nickel-molybdenum-tungsten and nickel-cobalt-molybdenum, and very preferably the active phase consists of nickel and molybdenum, nickel and tungsten or a nickel-molybdenum-tungsten combination.

[0081] The content of group VIII metal in the catalyst is less than 20% by weight, preferably between 0.03 and 15% by weight, very preferably between 0.5 and 10% by weight, and even more preferably between 1 and 8% by weight expressed as group VIII metal oxide relative to the total weight of the catalyst.

[0082] The Group VIB metal content in the catalyst is between 1 and 50% by weight, preferably between 5 and 40% by weight, and more preferably between 10 and 35% by weight and even more preferably between 15 and 30% by weight expressed as Group VIB metal oxide relative to the total weight of the catalyst. The Group VIII metal to Group VIB metal molar ratio of the catalyst is generally less than 1, preferably between 0.01 and 0.75, and very preferably between 0.10 and 0.60 and even more preferably between 0.20 and 0.50.

[0083] Optionally, the catalyst may also have a phosphorus content generally less than 15% by weight, preferably between 0.1 and 10% by weight, very preferably between 0.1 and 8% by weight, and even more preferably between 0.2 and 6% by weight of P2O5 relative to the total weight of fresh catalyst.

[0084] Furthermore, in the case where the catalyst comprises phosphorus, the phosphorus / (group VIB metal) molar ratio is generally between 0.02 and 1, preferably between 0.04 and 0.8, and very preferably between 0.1 and 0.75.

[0085] Hydroisomerization and hydrocracking are carried out under H2 pressure, at a total pressure between 0.5 and 18 MPa, with an H2 / hydrocarbon ratio between x and y NL H2 / L hydrocarbon.The feedstock is advantageously chosen from LCO (Light Cycle Oil, light gas oils from a catalytic cracking unit), atmospheric distillates, vacuum distillates such as, for example, gas oils from the direct distillation of crude oil or from conversion units such as FCC, coker or visbreaking, feedstocks from units for extracting aromatics from lubricating oil bases or from solvent dewaxing of lubricating oil bases, distillates from desulfurization or hydroconversion processes in a fixed bed or in a bubbling bed of RAT (atmospheric residues) and / or RSV (vacuum residues) and / or deasphalted oils, and deasphalted oils, paraffins from the Fischer-Tropsch process, or any mixture of the feedstocks mentioned above.Examples include feedstocks from renewable sources (such as vegetable oils, animal fats, hydrothermal conversion oil or lignocellulosic biomass pyrolysis oil) as well as plastic pyrolysis oils, as well as any mixture of these feedstocks with each other or with the previously mentioned hydrocarbon feedstocks. The above list is not exhaustive.

[0086] Characterization techniques

[0087] The mass contents are expressed as the oxide content relative to the dry mass, i.e. corrected for loss on ignition.

[0088] The specific surface area of ​​the materials is measured by the adsorption of N2 at 77 K, via the BET method, as defined by ASTM D 3663-78. The micropore volume is determined by the t-plot method. The external surface area is obtained by the slope of the t-plot. The total pore volume is deduced from the amount of N2 adsorbed at p / pO = 0.99.

[0089] 27AI NMR spectra of solids are measured with hydrated solids (in equilibrium with saturated water vapor). The magic angle spinning method is used, with a rotation frequency of 12 Hz. The spectra are measured in a magnetic field of 9.4 T. The combination of a high field with a high rotation frequency minimizes the probability of not detecting all aluminum. The peak shift is expressed relative to AI(NO3)3.

[0090] Dispersion index measurement: 10 g of solid (dry mass) are mixed with 90 ml of nitric acid solution (HNO3). The HNO3 / AI2O3 ratio is 10% by mass. The solution is stirred for 5 min at 13000 rpm and centrifuged for 10 min at 6000 rpm. The fraction of solid remaining in the supernatant is determined via the refractive index of the suspension. It corresponds to the dispersibility index.

[0091] The Bronsted acidity of solids is evaluated by adsorption of lutidine (2,6-dimethylpyridine), followed by infrared (IR) spectroscopy. A pellet of the solid is prepared and inserted into a cell with IR-transparent windows. It is then treated at 450°C for 10 h under vacuum to dehydrate the solid. Afterwards, it is cooled to 150°C and a low vapor pressure of lutidine (of the order of 1 mbar) is introduced into the cell for 10 min. The cell is evacuated at the same temperature for 2 h. The Bronsted acidity is evaluated by the intensity of the band at 1620 cm-1 , applying an extinction coefficient of 5.3 cm 2 / pmol (Gora-Marek et al., J. Phys. Chem. C 2014, 1 18, 23).

[0092] To evaluate the catalytic activity of the silica-aluminas of the invention, two reactions were chosen: the isomerization of meta-xylene and the hydrocracking of a vacuum distillate.

[0093] For the isomerization of m-xylene (mX), silica-alumina is pelletized and crushed to obtain grains between 200 and 500 pm. Approximately 300 mg are then loaded into a capillary reactor. The dead volume in the reactor is filled with Zirblast. The catalysts are first dehydrated under N2 flow at a temperature of 450°C for 2 h, before adjusting the temperature to 325°C. A flow rate of 0.x ml / h m-xylene is injected, diluted in N2 (molar ratio N2 / m-xylene = 8.25). The pressure is maintained at 5 bar. The effluents are analyzed by GC. The m-xylene conversion is calculated by

[0094] X(mX) = 100% - %mX %mX: chromatographic mass percentage of mX taking into account its response coefficient.

[0095] The activity (mol mX / (hgcat)) is calculated by

[0096] • Qmx: mass flow rate of metaxylene reactor inlet in g / h;

[0097] • Mmx: molar mass of metaxylene in g / mol;

[0098] • meat: mass of catalyst loaded into the reactor in g;

[0099] The catalysts deactivate strongly during the reaction; for comparison, the activity stabilized after 10 hours under load is used.

[0100] The examples illustrate the invention without limiting its scope.

[0101] EXAMPLES

[0102] The hydrocracking performance of a feedstock comprising a vacuum distillate fraction is evaluated using a unit comprising an isothermal fixed-bed reactor in downflow configuration. The tests are carried out with bifunctional catalysts, where a sulfide of a group VI metal has been deposited on the silica-alumina extrudates. The sulfide formation takes place in situ in the reactor, via the treatment of a compound of a group VI metal and a compound of Ni or Co, deposited on the silica-alumina extrudates, with a sulfur compound.

[0103] This sulfurization step is carried out using a straight-run diesel fuel with an additive of 4% by weight of dimethyl disulfide (DMDS) and 2% by weight of aniline. The sulfurization is carried out at a WH of 2 h-1 (WH = Hourly Volume Velocity), an H2 / charge volume ratio of 1000 NL / L, a total pressure of 14 MPa and a temperature of 350°C for 6 hours.

[0104] Then we switch to the vacuum distillate feed (VDF). The VDF has been previously hydrotreated. After this hydrotreatment step, the VDF has the properties shown in Table 1 below. In order to simulate the partial pressures of hydrogen sulfide and ammonia generated by the hydrotreatment step of the process, the test feed is supplemented with dimethyl disulfide (DMDS) and aniline respectively so as to obtain 15300 ppm by weight of sulfur and 1400 ppm by weight of nitrogen in the final additive feed. Table 1 Characteristics of the hydrotreated feed

[0105] The hydrocracking test is carried out under the following conditions: WH of 1.5 h-1, H2 / load volume ratio of 1000 NL / L, total pressure of 14 MPa. The reactor temperature is adjusted to target a net conversion of the 370°C+ fraction of approximately 60-85% after 150 hours under load. To do this, two temperatures T1 and T2 are applied successively.

[0106] The net conversion is calculated by the equation

[0107] Xnette = 1 - x370- / x370-charge x370- = mass fraction of the effluent having a boiling point lower than 370°C x370-charge= mass fraction of the charge having a boiling point lower than 370°C

[0108] Assuming pseudo-first-order kinetics, a hydrocracking kinetic constant can be calculated: k = WH * ln(1 / (1 -Xnet) To correct activity notes, introduced by differences in extrudate density, this kinetic constant can be normalized by the support density to obtain a mass kinetic constant (instead of volume): km = k / DRT

[0109] DRT = Packed Fill Density of the Catalyst Support

[0110] The examples below illustrate the invention without limiting its scope.

[0111] Non-compliant example 1: preparation of a silica-alumina according to the prior art A silica-alumina was prepared according to example 3 of patent FR 2,846,574: A suspension of boehmite is mixed with a solution of silicic acid freshly prepared by exchange on decationizing resin. The proportions of boehmite and silicic acid are adjusted so as to reach a final composition of 65% AI2O3 and 35% SiO2. The suspension is filtered and the cake is dried to obtain an extrudable paste. Boehmite is added to adjust the composition to 70% AI2O3 - 30% SiO2. The paste is kneaded for approximately 30 minutes and extruded through a trilobed die with a diameter of 2.5 mm. The extrudates are dried at 150°C, then calcined, then calcined at 750°C in the presence of water vapor. Table 1 Characteristics of the reference support (example 1)

[0112] Example 2 conforms: preparation of a silica-alumina by precipitation of a colloidal solution with an acidic solution of an aluminum salt at acid pH a) steps a) and b) according to the invention: Preparation of the colloidal solution 34.67g TEOS, 38.79g of distilled water, 1.11g of aluminum sulfate, then 30.45g of a 40% mass TPAOH (tetrapropylammonium hydroxide) solution are introduced into a polypropylene bottle. Stirring is ensured by a magnetic bar. The reaction takes place at room temperature. The hydrolysis time is set at 6 hours. A colloidal solution is obtained, which is placed in an oven at 90°C for 16 or 24 hours. After the oven treatment, part of the colloidal solution obtained is dried by lyophilization to analyze the products obtained and the other part undergoes the following steps of the process according to the invention.Freeze-drying is a very gentle drying method that does not cause any changes in the structure or texture of the solid. The characterizations of the solid obtained are therefore representative of the colloidal particles in the colloidal solution.

[0113] In both cases (i.e., after 16 or 24 h at 90°C), X-ray diffractograms indicate that the solids are amorphous. The textural properties are shown in Table 2.

[0114] Table 2. Textural properties of embryonic zeolites step c): precipitation of the colloidal solution with an acidic solution of an aluminum salt at acidic pH

[0115] In a 250mL jacketed reactor heated to 70°C, 40 mL of water base is introduced. The colloidal solution from Example 1 (pH=12.53) and an 8% aluminum sulfate acid solution (i.e. 102 g / L of AI2(SO4)3), at pH=2.8, are gradually injected using peristaltic pumps. The base and acid are introduced at a volume ratio of 1:1 or 1:2. The mixture is mechanically stirred using a Teflon blade. The pH is regularly monitored during the addition of the solutions. It stabilizes at a value close to 2.5.

[0116] In all cases, precipitation is immediate and observable upon addition of the acidic aluminum and the colloidal solution of so-called embryonic zeolites. Once both solutions have been introduced into the reactor, heating and stirring are maintained for 30 to 60 minutes to allow the sample to mature and promote crystallization. The reactor is then emptied and the samples are recovered and washed three times with distilled water by centrifugation. The centrifugation cycles last 2 minutes at 6000 rpm. The solid thus isolated is then dried in an oven at 120°C for 16 hours. It is ground before being calcined according to the following protocol: 2 hours at 200°C then 2 hours at 600°C.

[0117] The products are labeled Cx:ymt, where x:y is the ratio of the volumes of the colloidal solution and the A^SC h solution, m I eripening time after precipitation (in minutes), and t the baking time of the colloidal zeolite solution (in hours).

[0118] XRD indicates that all products are essentially amorphous, except for a few weak lines attributable to A^SC h- Textural properties are compiled in Table 3.

[0119] Table 3 Properties of silica-aluminas obtained by precipitation at acid pH

[0120] The Bronsted acidity of the solids was evaluated by lutidine adsorption. The results are also compiled in Table 3. It can be seen that the acidity of the solids obtained by precipitation of the colloidal solution is significantly higher than that of the reference solid.

[0121] Example 3: preparation of a silica-alumina by precipitation of a colloidal solution with an acid solution of an aluminum salt at basic pH

[0122] Precipitation is carried out as in Example 2, but the water base is replaced by 50 g of 25% ammonia. As the pH drops rapidly when the solutions are added, it was necessary to gradually add ammonia (a total of 50 ml additional volume) to maintain a basic pH range between 2 and 9. The product is labeled CBx:ymt, where x:y is the ratio of the volumes of the clear solution and the AI2(SO4)3 solution, m the ripening time after precipitation (in minutes), and t the drying time of the colloidal zeolite solution (in hours). Table 4. Properties of silica-aluminas obtained by precipitation at basic pH

[0123] THE

[0124] Table 4 shows the textural properties of the precipitate obtained in basic medium. The pore volume of silica-alumina is significantly higher under these precipitation conditions, which may be advantageous for certain catalysis applications.

[0125] Example 4: preparation of a silica-alumina by precipitation of a colloidal solution with an acidic boehmite solution

[0126] In a jacketed reactor heated to 70°C, 80 mL of water, 1 1.3 g of Pural SB3 boehmite and 3.9 g of HNO3 at 68% by mass are introduced. The initial pH of the boehmite suspension is 1.6. 65 mL of the clear solution from Example 1 are gradually injected with peristaltic pumps, after 18 h in the oven (pH = 12.5) and 175 mL of a nitric acid solution, at pH = 1 or 2, in order to control the pH. The addition of the solutions is spread over a period of 30 minutes. Afterwards, the mixture is stirred for another 1 h at 70°C. The final pH is 2.7 or 7.6, if the pH of the nitric acid solution is 1 or 2, respectively.

[0127] The reactor is then drained and the samples are collected and washed three times with distilled water by centrifugation. Centrifugation cycles last 2 minutes at 6000 rpm.

[0128] The solid thus isolated is then dried in an oven at 90°C for 16 hours. It is ground before being calcined according to the following protocol: 2 hours at 200°C then 4 hours at 500°C. Table 5 Properties of silica-aluminas obtained by precipitation on boehmite

[0129] Example 5: Shaping of precipitated solids

[0130] Shaping is carried out in a planetary mixer. 25% of dry mass 5 of a highly dispersible boehmite (dispersibility index > 60%) is added to the coprecipitation products of Example 4 (uncalcined), as well as the quantity of water necessary to form a paste. The mixture is then extruded on a 2 mm trilobal die and dried at 80°C for 16 h.

[0131] The extrudates are divided in two to compare two heat treatment protocols.

[0132] 10 The extrudates are calcined in an air flow containing 6% volume H2O at 600°C for 2 h.

[0133] Table 6 Characteristics of extrudates prepared from the silica-aluminas of the invention

[0134] Example 6: Activity in isomerization of m-xylene

[0135] 15 Table 8 illustrates the activity of the silica-aluminas of the invention with a silica-alumina of the prior art according to example 1. It shows a very significant gain in activity, thanks to the incorporation of embryonic zeolites.

[0136] Table 8 Activity in conversion of meta-xylene at 325°C Example 7: Preparation of hydrocracking catalysts

[0137] The extrudates of Example 5 were used for the preparation of hydrocracking catalysts, by dry impregnation of the extrudates with an aqueous solution containing tungsten and nickel salts. The tungsten salt is ammonium metatungstate (NH4)6H2W12O40*4H2O and the nickel salt is nickel nitrate Ni(NO3)2*6H2O. The quantities of Ni and W are chosen to achieve a WO3 content of 27% by weight and a Ni / W molar ratio = 0.4. After maturation at room temperature in a water-saturated atmosphere for 10 hours, the impregnated extrudates are dried at 120°C for 18 hours in a ventilated oven and then calcined at 500°C for 2 hours under air flow.

[0138] The reference silica-alumina support was impregnated and calcined in the same way.

[0139] Example 8: Hydrocracking Test

[0140] The catalysts of Example 7 were evaluated in a hydrocracking test, as described in the methods section. The table above compares the mass kinetic constants km of the different catalysts (from the supports of Example 5 or the reference support from Example 1).

[0141] Table 9 Hydrocracking activity

[0142] The results illustrate the gain in activity provided by supports based on embryonic zeolites.

[0143] At the same conversion level, the yield of middle distillate, the distillation fraction between 150 and 370°C, is identical for all catalysts of the

[0144] Table 9.

Claims

CLAIMS 1. Process for the preparation of a material comprising a silica-alumina, said process comprising at least the following steps and preferably consisting of: a) a step of mixing in an aqueous medium, optionally in a mixture with an alcohol R2OH chosen from ethanol, propanol, isopropanol and butanol, at least one source of silicon in the form of oxide SiO2, at least one source of aluminium in the form of oxide AI2O3, an organic compound in the form of hydroxide RiOH or halide RiX, with X being chosen from the elements Cl, Br and I, and optionally at least one source of an alkali metal M, with M being chosen from lithium, potassium, sodium, alone or as a mixture, the reaction mixture having the following molar composition: x1 Ri: x2 M2O: y AI2Os: 1 SiO2: z H2O: a R2OH with x1 = 0.1 to 0.6, x2 = 0 at 0.1, y = 0.002 to 0.02, z = 10 to 50 and a = 0 to 4, and R1 being a quaternary ammonium cation, of general formula RaRbRcRdN+ in which Ra, Rb,Rc and Rd are chosen from methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclopentyl, cyclohexyl and adamantyl groups, and R2 being chosen from ethyl, propyl, isopropyl and butyl groups, with stirring, until a colloidal solution comprising zeolite seeds is obtained, b) a step of heat treatment of the colloidal solution obtained at the end of step a), said step b) being carried out at a temperature of between 60 and 120°C, preferably between 70 and 100°C, and for a duration of between 1 hour and 24 hours and preferably between 4 and 16 hours. c) a step of precipitation of the colloidal solution obtained at the end of step b) with a solution and / or a suspension of at least one source of aluminum chosen from aluminum salts and an aluminum oxide or hydroxide, alone or as a mixture, said solution and / or suspension being acidic and having a pH between 1 and 5,so that said precipitation step c) is carried out at a pH of between 2 and 10 and preferably between 2 and 9), d) a step of filtration or centrifugation of the silica-alumina precipitate obtained at the end of step c), followed by a step of drying said precipitate to obtain a silica-alumina powder.

2. Process according to claim 1 in which the source of aluminum used in step a) is aluminum hydroxide or an aluminum salt, chosen from aluminum chloride, nitrate, and sulfate, a sodium aluminate, an aluminum alkoxide, or alumina itself, preferably in hydrated or hydratable form, such as for example colloidal alumina, pseudoboehmite, gamma alumina or alpha or beta trihydrate.

3. Method according to one of claims 1 or 2 in which the pH of the colloidal solution obtained at the end of step b) is basic, preferably between 9 and 14, and preferably between 10 and 13.

4. Process according to one of claims 1 to 3 in which the aluminum salts used in step c) are chosen from aluminum sulfate and nitrate.

5. Method according to one of claims 1 to 4 in which the aluminum oxides or hydroxides used in step c) are chosen from boehmites or (pseudo)-boehmites.

6. Method according to one of claims 1 to 5 in which step c) of precipitation is carried out at a temperature between 50 and 100°C, preferably between 60 and 90°C.

7. Method according to one of claims 1 to 6 in which a third basic solution containing ammonia is added during step c) of precipitation so as to adjust and control the pH to a value less than or equal to 9.

8. Method according to one of claims 1 to 7 in which the silica-alumina powder obtained at the end of step d) is calcined at a temperature between 450°C and 800°C, under a flow of gas.

9. Method according to one of claims 1 to 8 in which the silica alumina powder obtained at the end of step d) and optionally calcined is shaped in a step e) in the presence or absence of binder and preferably by extrusion mixing.

10. Method according to one of claims 1 to 10 in which the method comprises a step f) of deposition on said material comprising silica-alumina prepared according to steps a) to e) and optionally dried and / or calcined at least one metal from group VIII and / or at least one metal from group VIB of the periodic table of elements and / or a doping element chosen from boron, phosphorus and silicon and preferably phosphorus and optionally at least one organic additive to obtain a catalyst.

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