WO2016192894A1 - Method for preparing a boehmite having specific crystallites - Google Patents

Method for preparing a boehmite having specific crystallites Download PDF

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Publication number
WO2016192894A1
WO2016192894A1 PCT/EP2016/058821 EP2016058821W WO2016192894A1 WO 2016192894 A1 WO2016192894 A1 WO 2016192894A1 EP 2016058821 W EP2016058821 W EP 2016058821W WO 2016192894 A1 WO2016192894 A1 WO 2016192894A1
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Prior art keywords
temperature
preparation process
alumina
precipitation
process according
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PCT/EP2016/058821
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French (fr)
Inventor
Malika Boualleg
Olivier LAFON
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IFP Energies Nouvelles
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Priority to DE112016002510.6T priority Critical patent/DE112016002510T5/en
Priority to CN201680032784.3A priority patent/CN107848825A/en
Publication of WO2016192894A1 publication Critical patent/WO2016192894A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/34—Preparation of aluminium hydroxide by precipitation from solutions containing aluminium salts
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/60—Compounds characterised by their crystallite size
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer

Definitions

  • the present invention relates to the preparation of alumina gels or boehmite gels.
  • the present invention relates to a new process for the precipitation preparation of an alumina gel having small crystallites.
  • Obtaining very small size boehmite particles results in a different surface reactivity (faces exposed in different proportions and with improved reactivity) than those of particles of larger sizes. This will consequently result in an active phase interaction with the surface of the different crystallites during the impregnation as well as an improved reactivity of the corresponding catalyst during the catalysis such as hydrotreatment or catalytic reforming, for example.
  • the preparation process according to the invention makes it possible to obtain alumina or boehmite gel composed of crystallites whose size, obtained by the Scherrer formula in X-ray diffraction according to the crystallographic directions [020] and [ 120] is respectively between 0.5 and 10 nm and between 0.5 and 15 nm and preferably respectively between 0.5 and 2 nm and between 0.5 and 3 nm and very preferably between 0.5 and 0.5 nm respectively. and 1, 5 and between 0.5 and 2.5.
  • U.S. Patent No. 4,676,928 discloses a method for producing a water-dispersible alumina comprising a step of forming an aqueous dispersion of alumina, a step of adding an acid to produce an acidic dispersion having a pH between 5 and 9, a maturation step at an elevated temperature of greater than 70 ° for a time sufficient to transform the alumina into a colloidal gel, then a drying step of said colloidal gel obtained.
  • US Pat. No. 6,589,908 describes, for example, a process for preparing a alumina in two stages of precipitation of alumina precursors under conditions of well-controlled temperature, pH and flow rates.
  • the first stage operates at a temperature between 25 and 60 °, a pH of between 3 and 10 and preferably at a pH between 3 and 4.5 and between 7.5 and 10.
  • the precursors are selected from aluminum nitrate, aluminum chloride in combination with sodium aluminate or sodium hydroxide in combination with an acidic aluminum salt.
  • the preferred precursor combination is aluminum sulphate with sodium aluminate.
  • This process makes it possible to obtain an alumina characterized by an absence of macropores, less than 5% of the total pore volume constituted by pores with a diameter greater than 35 nm, a high pore volume greater than 0.8 ml / g, and a bimodal pore distribution in which the two modes are separated by 1 to 20 nm and the primary porous mode being larger than the average pore diameter.
  • the size of the crystallites is not specified.
  • the patent application WO2004 / 052534 A1 also describes a process for the preparation of catalysts comprising a support prepared by co-precipitation preferably of aluminum sulphate with sodium aluminate, the gel obtained is then dried, extruded and calcined. . It is possible to add silica during or after co-precipitation.
  • the document describes a process for preparing an alumina gel in which an alkaline solution of sodium aluminate, sodium hydroxide or aluminum hydroxide is added to a reactor in the presence of water. .
  • An acid solution of aluminum sulphate or aluminum nitrate is added simultaneously.
  • the pH of the reaction medium is between 7 and 9 at the end of the addition of acid and that the temperature is maintained during the mixing between 60-75%, for a duration of between 30 minutes to 1 hour. h30.
  • the mixture is then subjected to mixing steps, extrusion, drying (200 ⁇ ) under air, heat treatment.
  • the adjustment of the formatting makes it possible to obtain the characteristics of the support.
  • the process makes it possible to obtain an alumina gel having a particular porous distribution but the size of the crystallites is not mentioned.
  • the alumina gel preparation by precipitation is also well known in the prior art.
  • US Pat. No. 7,790,652 describes the preparation by precipitation of an alumina support having a very specific porous distribution, which can be used as a catalyst support in a process for hydroconversion of heavy hydrocarbon feeds.
  • the alumina support is prepared in two precipitation steps according to a method comprising a first step of forming an alumina dispersion by mixing, in a controlled manner, a first aqueous alkaline solution and a first aqueous acidic solution, at least one of said acidic and basic solutions, or both comprising an aluminum compound.
  • the acidic and basic solutions are mixed in such proportions that the pH of the resulting dispersion is between 8 and 11.
  • the acidic and basic solutions are also mixed in quantities making it possible to obtain a dispersion containing the desired quantity of alumina, in particular, the first step makes it possible to obtain 25 to 35% by weight of alumina with respect to the total amount. of alumina formed at the end of the two precipitation steps.
  • the first stage operates at a temperature between 20 and 40 ⁇ .
  • the temperature of the slurry is raised to a temperature between 45 and 70 ⁇ , and then the heated slurry is then subjected to a second precipitation step by contacting said slurry with a second alkaline aqueous solution and a second acidic aqueous solution, at least one or both of the solutions comprising an aluminum compound.
  • the pH is adjusted between 8 and 10.5 by the proportions of the acid and basic solutions added and the remaining quantity of alumina to be formed in the second stage is provided by the amounts of the second acid and basic solutions added.
  • the second stage operates at a temperature between 20 and 40 ⁇ .
  • the alumina gel thus formed comprises at least 95% of boehmite.
  • the alumina gel is then filtered, washed and optionally dried according to the methods known to those skilled in the art, without prior curing step, to produce an alumina powder which is then shaped according to the known methods of the present invention. skilled in the art, and then calcined to produce the final alumina support.
  • the Applicant has thus discovered that a method for preparing an alumina gel in a single precipitation stage, said step consisting in the placing in solution of a precursor specific aluminum acid, aluminum chloride, followed by a pH adjustment using a specific basic precursor, sodium hydroxide, without a subsequent co-precipitation step, led to an alumina gel having crystallites of small size.
  • the preparation process according to the invention makes it possible to obtain alumina or boehmite gel composed of crystallites whose size, obtained by the Scherrer formula in X-ray diffraction according to the crystallographic directions [020] and [ 120] is respectively between 0.5 and 10 nm and between 0.5 and 15 nm and preferably respectively between 0.5 and 2 nm and between 0.5 and 3 nm and very preferably between 0.5 and 0.5 nm respectively. and 1, 5 and between 0.5 and 2.5.
  • X-ray diffraction on alumina or boehmite gels was performed using the conventional powder method using a diffractometer.
  • Scherrer's formula is a formula used in X-ray diffraction on powders or polycrystalline samples which connects the width at half height of the diffraction peaks to the size of the crystallites. It is described in detail in the reference: Appl. Cryst. (1978). 1 1, 102-1. Scherrer after sixty years: A survey and some new results in the determination of crystallite size, J. I. Langford and A. J. C. Wilson.
  • the invention relates to a process for the preparation of an alumina gel in a single precipitation step, said precipitation step consisting in the solution of the precursor acid aluminum aluminum chloride in water at a temperature between 10 and 90 °, so that the pH of the solution is between 0.5 and 5, for a period of between 2 and 60 minutes and then adjusting the pH to a pH between 7.5 and 9.5 by adding sodium hydroxide to the solution obtained with a basic precursor, to obtain a suspension at a temperature of between 5 and 35 ° and for a period of between 5 minutes and 5 hours.
  • An advantage of the present invention is to provide a preparation process for obtaining an alumina gel having a reduced crystallite size compared to the alumina gels prepared according to the prior art and in particular having crystallites of small size.
  • an advantage of the present invention is to provide a preparation process for obtaining a gel of alumina or boehmite composed of crystallites whose size, obtained by the Scherrer formula in X-ray diffraction according to the crystallographic directions [020] and [120] is respectively between 0.5 and 10 nm and between 0.5 and 15 nm and preferably respectively between 0.5 and 2 nm and between 0.5 and 3 nm and so very preferably between 0.5 and 1.5 respectively and between 0.5 and 2.5.
  • Another advantage of the present invention is to provide a process for the preparation of an alumina gel having a reduced crystallite size, simplified and inexpensive compared to the conventional alumina preparation methods of the prior art such as by for example, sol-gel type preparation processes, in that the process according to the invention comprises only a single precipitation step.
  • the process for preparing the alumina gel according to the invention comprises a single precipitation step.
  • Said precipitation step consists in dissolving a specific aluminum acid precursor, aluminum chloride AICI 3 , in water at a temperature of between 10 and 90 ⁇ , preferably between 10 and 80 ⁇ , of preferred way between 10 and 75 ⁇ and more preferably between 15 and 70 ° C.
  • the pH of the solution obtained is between 0.5 and 5, preferably between 1 and 4, preferably between 1, 5 and 3, 5.
  • the solution is left stirring for a period of between 2 and 60 minutes, and preferably 5 to 30 minutes and preferably between 5 and 10 minutes.
  • the pH of the suspension obtained is then adjusted to a pH called the end-of-precipitation pH of between 7.5 and 9.5, preferably between 7.5 and 9 and, preferably, between 7.7 and 8.8 per liter.
  • a specific basic precursor sodium hydroxide NaOH at a temperature of between 5 and 35 °, preferably between 10 and 30 ° and preferably between 10 and 25 ° and for a duration of between 5 minutes and 5 hours preferably between 10 minutes and 5 hours, preferably between 15 minutes and 2 hours.
  • the precipitation is carried out in the absence of organic additive.
  • the precipitation of the alumina gel is carried out with stirring.
  • the method according to the invention does not comprise an additional precipitation step and does not comprise a subsequent co-precipitation step by contacting, in aqueous reaction medium, at least one basic precursor and at least one acidic precursor, at least one of the basic or acidic precursors comprising aluminum.
  • alumina gel having a reduced crystallite size compared with the alumina gels prepared according to the prior art and in particular a gel of alumina or boehmite composed of crystallites whose size, obtained by the Scherrer formula in X-ray diffraction according to the crystallographic directions [020] and [120] is respectively between 0.5 and 10 nm and between 0, 5 and 15 nm and preferably respectively between 0.5 to 2 nm and between 0.5 to 3 nm and very preferably respectively between 0.5 and 1, 5 and between 0.5 and 2.5.
  • the process for preparing the alumina gel according to the invention also comprises a filtration step of the suspension obtained at the end of the precipitation step.
  • Said filtration step is carried out according to the methods known to those skilled in the art.
  • Said filtration step is advantageously followed by at least one washing step, with an aqueous solution, preferably with water and preferably from one to three washing steps, with a quantity of water equal to the amount of water. precipitate filtered.
  • the alumina gel obtained at the end of the precipitation step, followed by a possible filtration step and at least one optional washing step, is then advantageously dried in a drying step of the optionally filtered suspension. obtained at the end of the precipitation step to obtain a powder, said drying step being advantageously carried out by drying at a temperature greater than or equal to 120 ° C. or by spray drying or by any other drying technique known to man of career.
  • said drying step e may advantageously be carried out in a closed and ventilated oven.
  • said drying step operates at a temperature between 120 and 300 ⁇ , very preferably at a temperature between 150 and 250 ⁇ C.
  • the cake obtained at the end of the second precipitation step, followed by a filtration step is resuspended.
  • Said suspension is then sprayed in fine droplets, in a vertical cylindrical chamber in contact with a stream of hot air to evaporate the water according to the principle well known to those skilled in the art.
  • the powder obtained is driven by the heat flow to a cyclone or a bag filter that will separate the air from the powder.
  • the atomization is carried out according to the operating protocol described in the publication Asep Bayu Dani Nandiyanto, Kikuo Okuyama, Advanced Powder Technology, 22, 1 -19, 201 1.
  • the powder obtained at the end of the drying step can then advantageously be shaped to obtain a green material.
  • raw material is meant the material shaped and having not undergone any heat treatment steps.
  • said shaping step can be carried out by kneading-extrusion, by granulation, by the technique of oil drop (dewatering or coagulation of drop in French), by pelletization.
  • said shaping step is carried out by kneading - extrusion.
  • the obtained green material obtained in shape can optionally then undergo a heat treatment step at a temperature of between 500 and 1000 °, for a duration advantageously between 2 and 10 h, in the presence or absence of a flow of air containing up to at 60% water volume.
  • a heat treatment step at a temperature of between 500 and 1000 °, for a duration advantageously between 2 and 10 h, in the presence or absence of a flow of air containing up to at 60% water volume.
  • said heat treatment is carried out in the presence of an air flow containing water.
  • said heat treatment step performed at a temperature between 540 ⁇ C to 850 ⁇ C.
  • said heat treatment step operates for a duration of between 2 h and 10 h.
  • Said heat treatment step allows the transition from boehmite to the final alumina.
  • the heat treatment step may optionally be preceded by drying at a temperature of between 50 ° and 120 °, according to all techniques known to those skilled in the art.
  • the process according to the invention makes it possible to obtain an alumina gel, optionally in the form of a powder, having a reduced crystallite size compared to the alumina gels prepared according to the prior art.
  • the alumina gel or the boehmite obtained in powder form according to the invention is composed of crystallites whose size, obtained by the Scherrer formula in X-ray diffraction according to the crystallographic directions [020] and [120] is respectively between 0.5 and 10 nm and between 0.5 and 15 nm and preferably respectively between 0.5 and 2 nm and between 0.5 and 3 nm and very preferably between 0.5 and 1 respectively. , 5 and between 0.5 and 2.5.
  • the present invention also relates to the alumina gel that can be obtained by the preparation process according to the invention.
  • a commercial powder of a Pural SB3 alumina gel is prepared according to a sol-gel route by hydrolysis-polycondensation of an aluminum alkoxide.
  • Example 2 (comparative):
  • the synthesis of an alumina gel is carried out according to a non-compliant preparation process in that the process for preparing the gel according to Example 2 is carried out in a 7 l reactor and a final suspension of 5 l in two. precipitation steps with precursors not in accordance with the invention.
  • the amount of water added to the reactor is 3868 ml.
  • the final concentration of alumina is 30g / l.
  • the agitation is 350 rpm throughout the synthesis.
  • the temperature of the reaction medium is maintained at 30 °.
  • a suspension containing a precipitate of alumina is obtained.
  • the flow rate of the aluminum sulphate precursors Al 2 (SO 4 ) and aluminum aluminate NaAlO 4 introduced in the first precipitation step are respectively 19.6 ml. / min and 23.3 ml / min.
  • the suspension obtained is then subjected to a temperature rise of from 30 to 57 ⁇ C.
  • a second step of co-precipitation of the suspension obtained is then carried out by adding aluminum sulphate Al 2 (S0 4) at a concentration of 102 g / l of Al 2 0 3 and sodium aluminate at a concentration NaAIOO 155 g / L in Al 2 O 3 .
  • a solution of aluminum sulphate Al 2 (SO 4 ) is therefore added continuously to the heated suspension obtained at the end of the first precipitation step for 30 minutes at a flow rate of 12.8 ml / min.
  • sodium aluminate NaAlOO in a weight ratio base / acid 1.68 of way to adjust the pH to a value of 8.7.
  • the temperature of the reaction medium in the second stage is maintained at 57 ⁇ C.
  • a suspension containing a precipitate of alumina is obtained.
  • the flow rate of the aluminum sulphate precursors Al 2 (SO 4 ) and sodium aluminate NaAlOO containing aluminum introduced in the second precipitation stage are respectively 12.8 ml. / min and 14.1 ml / min.
  • the suspension thus obtained does not undergo a ripening step.
  • the suspension obtained is then filtered by water displacement on a sintered Buchner-type tool and the alumina gel obtained is washed 3 times with 5 liters of distilled water at 70 ⁇ C.
  • the filtration time and washing is 4 h.
  • An alumina gel is prepared according to a synthetic process not in accordance with the invention, in that the pH of the end of precipitation of the alumina gel is carried out at a pH greater than 9.5.
  • a solution containing 326 ml of deionized water and 135.6 g of aluminum chloride hexahydrate (AlCl 3) is prepared at a temperature of 25 ⁇ C, so as to obtain a solut ion having a pH of 0.5, for a period of 5 minutes.
  • An alumina gel is prepared according to a synthetic process not according to the invention, in that the pH adjustment is carried out at a temperature of 40 °.
  • a solution containing 326 ml of deionized water and 135.6 g of aluminum chloride hexahydrate (AlCl 3 ) is prepared at a temperature of 25 ° C, so as to obtain a solution. having a pH of 0.5, for a period of 5 minutes.
  • EXAMPLE 5 (According to the Invention) An alumina gel is prepared according to a synthesis method according to the invention.
  • a solution containing 326 ml of deionized water and 135.6 g of aluminum chloride hexahydrate (AlCl 3 ) is prepared at a temperature of 25 °, so as to obtain a solution having a pH of 0.5 for a period of 5 minutes.
  • a sample of the precipitate obtained is taken from the reaction medium.
  • the DRX (FIG. 3) of the precipitate shows that the precipitate obtained in Example 5 is indeed a boehmite precipitate.
  • the boehmite precipitate obtained in Example 5 is poorly crystallized.
  • An alumina gel is prepared according to a synthesis process according to the invention. 1 / boehmite precipitation AIOOH
  • a solution containing 326 ml of deionized water and 135.6 g of aluminum chloride hexahydrate (AlCl 3 ) is prepared at a temperature of 25% to obtain a solution. having a pH of 0.5, for a period of 5 minutes. Then, with magnetic stirring, 67.5 g of sodium hydroxide (NaOH) are added for 30 minutes to adjust the pH. The pH reached at the end of the synthesis is 8.5. The temperature is maintained at 20 ° throughout the duration of the step. This cake is suspended in a 3 L beaker with 320 mL of water.
  • a sample of the precipitate obtained is taken from the reaction medium.
  • the DRX (FIG. 4) of the precipitate shows that the precipitate obtained in example 6 is indeed a boehmite precipitate.
  • the boehmite precipitate obtained in Example 6 is poorly crystalline.

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  • Organic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
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  • Inorganic Chemistry (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
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Abstract

The invention relates to a method for preparing an alumina gel in a single precipitation step, said precipitation step consisting of dissolving the acid precursor of aluminium, aluminium chloride, in water, at a temperature of between 10 and 90 °C, such that the pH of the solution is between 0.5 and 5, for a period of between 2 and 60 minutes, then adjusting the pH to a pH of between 7.5 and 9.5 by adding a basic precursor, sodium hydroxide, to the obtained solution in order to obtain a suspension, at a temperature between 5 and 35 °C, and for a period of between 5 minutes and 5 hours.

Description

PROCEDE DE PREPARATION D'UNE BOEHMITE PRESENTANT  PROCESS FOR PREPARING A BOEHMITE PRESENTING
DES CRISTALLITES PARTICULIERES  SPECIAL CRYSTALLITES
Domaine technique Technical area
La présente invention se rapporte à la préparation de gels d'alumine ou gels de boehmite. En particulier, la présente invention se rapporte à un nouveau procédé de préparation par précipitation d'un gel d'alumine présentant des cristallites de faible taille. L'obtention de particules de boehmite de très petites tailles a pour conséquence une réactivité de surface différentes (faces exposées en proportion différentes et de réactivité améliorée) de celles de particules de tailles supérieures. Ceci aura pour en conséquence un interaction phase active avec la surface des cristallites différentes lors de l'imprégnation ainsi qu'un réactivité améliorée du catalyseur correspondant lors de la catalyse tel que l'hydrotraitement ou le reformage catalytique par exemple... The present invention relates to the preparation of alumina gels or boehmite gels. In particular, the present invention relates to a new process for the precipitation preparation of an alumina gel having small crystallites. Obtaining very small size boehmite particles results in a different surface reactivity (faces exposed in different proportions and with improved reactivity) than those of particles of larger sizes. This will consequently result in an active phase interaction with the surface of the different crystallites during the impregnation as well as an improved reactivity of the corresponding catalyst during the catalysis such as hydrotreatment or catalytic reforming, for example.
En particulier, le procédé de préparation selon l'invention permet l'obtention de gel d'alumine ou de boehmite composée de cristallites dont la taille, obtenue par la formule de Scherrer en diffraction des rayons X selon les directions cristallographiques [020] et [120] est respectivement comprise entre 0,5 et 10 nm et entre 0,5 et 15 nm et de préférence respectivement comprise entre 0,5 à 2 nm et entre 0,5 à 3 nm et de manière très préférée respectivement entre 0,5 et 1 ,5 et entre 0,5 et 2,5. In particular, the preparation process according to the invention makes it possible to obtain alumina or boehmite gel composed of crystallites whose size, obtained by the Scherrer formula in X-ray diffraction according to the crystallographic directions [020] and [ 120] is respectively between 0.5 and 10 nm and between 0.5 and 15 nm and preferably respectively between 0.5 and 2 nm and between 0.5 and 3 nm and very preferably between 0.5 and 0.5 nm respectively. and 1, 5 and between 0.5 and 2.5.
Art antérieur Plusieurs protocoles opératoires connus dans l'art antérieur conduisent à des gels d'alumine. Plusieurs brevets décrivent notamment un procédé de préparation dit "sol-gel". PRIOR ART Several operating protocols known in the prior art lead to alumina gels. Several patents describe in particular a preparation process called "sol-gel".
Le brevet US 4 676 928 décrit un procédé de production d'une alumine dispersible dans l'eau comprenant une étape de formation d'une dispersion aqueuse d'alumine, une étape d'ajout d'un acide pour produire une dispersion acide ayant un pH compris entre 5 et 9, une étape de maturation à une température élevée supérieure à 70^ pendant une durée suffisante pour transformer l'alumine en gel colloïdal, puis une étape de séchage dudit gel colloïdal obtenu. U.S. Patent No. 4,676,928 discloses a method for producing a water-dispersible alumina comprising a step of forming an aqueous dispersion of alumina, a step of adding an acid to produce an acidic dispersion having a pH between 5 and 9, a maturation step at an elevated temperature of greater than 70 ° for a time sufficient to transform the alumina into a colloidal gel, then a drying step of said colloidal gel obtained.
Des procédés de préparation de gels d'alumine par co-précipitation sont également connus de l'art antérieur. Ainsi le brevet US 6 589 908 décrit par exemple un procédé de préparation d'une alumine en deux étapes de précipitation de précurseurs d'alumine dans des conditions de température, pH et débits bien contrôlées. La première étape opère à une température comprise entre 25 et 60Ό, un pH compris entre 3 et 10 et de préféren ce à un pH compris entre 3 et 4,5 et entre 7,5 et 10. Methods for preparing alumina gels by co-precipitation are also known from the prior art. Thus, US Pat. No. 6,589,908 describes, for example, a process for preparing a alumina in two stages of precipitation of alumina precursors under conditions of well-controlled temperature, pH and flow rates. The first stage operates at a temperature between 25 and 60 °, a pH of between 3 and 10 and preferably at a pH between 3 and 4.5 and between 7.5 and 10.
Les précurseurs sont choisis parmi le nitrate d'aluminium, le chlorure d'aluminium en combinaison avec l'aluminate de sodium ou l'hydroxyde de sodium en combinaison avec un sel d'aluminium acide. La combinaison de précurseurs préférée est le sulfate d'aluminium avec l'aluminate de sodium. La suspension est ensuite chauffée jusqu'à une température comprise entre 50 et 90^. Des réactifs sont de nou veau ajoutés à la suspension, qui est ensuite lavée, séchée, mise en forme et calcinée pour former un support de catalyseur. Ce procédé permet l'obtention d'une alumine caractérisée par une absence de macropores, moins de 5 % du volume poreux total constitué par les pores de diamètre supérieur à 35 nm, un haut volume poreux supérieur à 0,8 ml/g, et une distribution de pores bimodale dans laquelle les deux modes sont séparés par 1 à 20 nm et le mode poreux primaire étant plus grand que le diamètre moyen poreux. La taille des cristallites n'est pas précisée. The precursors are selected from aluminum nitrate, aluminum chloride in combination with sodium aluminate or sodium hydroxide in combination with an acidic aluminum salt. The preferred precursor combination is aluminum sulphate with sodium aluminate. The suspension is then heated to a temperature of between 50 and 90%. Reagents are added to the slurry, which is then washed, dried, shaped and calcined to form a catalyst support. This process makes it possible to obtain an alumina characterized by an absence of macropores, less than 5% of the total pore volume constituted by pores with a diameter greater than 35 nm, a high pore volume greater than 0.8 ml / g, and a bimodal pore distribution in which the two modes are separated by 1 to 20 nm and the primary porous mode being larger than the average pore diameter. The size of the crystallites is not specified.
La demande de brevet WO2004/052534 A1 décrit par ailleurs un procédé de préparation de catalyseurs comprenant un support préparé par co-précipitation de préférence de sulfate d'aluminium avec de l'aluminate de sodium, le gel obtenu est ensuite séché, extrudé et calciné. Il est possible d'ajouter de la silice durant ou après la co-précipitation. The patent application WO2004 / 052534 A1 also describes a process for the preparation of catalysts comprising a support prepared by co-precipitation preferably of aluminum sulphate with sodium aluminate, the gel obtained is then dried, extruded and calcined. . It is possible to add silica during or after co-precipitation.
Plus précisément, le document décrit un procédé de préparation d'un gel d'alumine dans lequel une solution alcaline d'aluminate de sodium, d'hydroxyde de sodium ou d'hydroxyde d'aluminium est ajoutée dans un réacteur en présence d'eau. Une solution acide de sulfate d'aluminium ou de nitrate d'aluminium est ajoutée simultanément. Il est préférable que le pH du milieu réactionnel soit compris entre 7 et 9 à la fin de l'ajout d'acide et que la température soit maintenue pendant le mélange entre 60-75^, pe ndant une durée comprise entre 30 min à 1 h30. Le mélange est ensuite soumis à des étapes de malaxage, extrusion, séchage (200Ό) sous air, traitement thermique. L'ajustemen t de la mise en forme permet d'obtenir les caractéristiques du support. Le procédé permet d'obtenir une gel d'alumine présentant une distribution poreuse particulière mais la taille des cristallites n'est pas mentionnée. La préparation de gel d'alumine par précipitation est également bien connue dans l'art antérieur. More specifically, the document describes a process for preparing an alumina gel in which an alkaline solution of sodium aluminate, sodium hydroxide or aluminum hydroxide is added to a reactor in the presence of water. . An acid solution of aluminum sulphate or aluminum nitrate is added simultaneously. It is preferable that the pH of the reaction medium is between 7 and 9 at the end of the addition of acid and that the temperature is maintained during the mixing between 60-75%, for a duration of between 30 minutes to 1 hour. h30. The mixture is then subjected to mixing steps, extrusion, drying (200Ό) under air, heat treatment. The adjustment of the formatting makes it possible to obtain the characteristics of the support. The process makes it possible to obtain an alumina gel having a particular porous distribution but the size of the crystallites is not mentioned. The alumina gel preparation by precipitation is also well known in the prior art.
En particulier, le brevet US 7 790 652 décrit la préparation par précipitation d'un support alumine présentant une distribution poreuse bien spécifique, pouvant être utilisé comme support de catalyseur dans un procédé d'hydroconversion de charges hydrocarbonées lourdes. In particular, US Pat. No. 7,790,652 describes the preparation by precipitation of an alumina support having a very specific porous distribution, which can be used as a catalyst support in a process for hydroconversion of heavy hydrocarbon feeds.
Le support alumine est préparé en deux étape de précipitation selon une méthode comprenant une première étape de formation d'une dispersion d'alumine par le mélange, de manière contrôlée, d'une première solution aqueuse alcaline et d'une première solution aqueuse acide, au moins une desdites solutions acide et basiques, ou les deux comprenant un composé aluminique. Les solutions acide et basique sont mélangées dans des proportions telles que le pH de la dispersion résultante est compris entre 8 et 1 1 . Les solutions acide et basique sont également mélangées dans des quantités permettant d'obtenir une dispersion contenant la quantité désirée d'alumine, en particulier, la première étape permet l'obtention de 25 à 35% poids d'alumine par rapport à la quantité totale d'alumine formée à l'issue des deux étapes de précipitation. La première étape opère à une température comprise entre 20 et 40Ό. Quand la qua ntité d'alumine désirée est formée, la température de la suspension est augmentée à une température comprise entre 45 et 70Ό, puis la suspension chauffée est ensuite soumise à une deuxième étape de précipitation par mise en contact de ladite suspension avec une seconde solution aqueuse alcaline et une seconde solution aqueuse acide, au moins l'une des deux solutions ou les deux comprenant un composé aluminique. De même, le pH est réglé entre 8 et 10,5 par les proportions des solutions acide et basique ajoutées et la quantité restante d'alumine à former dans la deuxième étape est apportée par les quantités des deuxièmes solutions acide et basique ajoutées. La deuxième étape opère à une température comprise entre 20 et 40Ό. Le gel d'alumine ainsi formé comprend au moins 95% de boehmite. Le gel d'alumine est ensuite filtré, lavé et éventuellement séché selon les méthodes connues de l'homme du métier, sans étape de mûrissement préalable, pour produire une poudre d'alumine qui est ensuite mise en forme selon les méthodes connues de l'homme du métier, puis calciné pour produire le support alumine final. The alumina support is prepared in two precipitation steps according to a method comprising a first step of forming an alumina dispersion by mixing, in a controlled manner, a first aqueous alkaline solution and a first aqueous acidic solution, at least one of said acidic and basic solutions, or both comprising an aluminum compound. The acidic and basic solutions are mixed in such proportions that the pH of the resulting dispersion is between 8 and 11. The acidic and basic solutions are also mixed in quantities making it possible to obtain a dispersion containing the desired quantity of alumina, in particular, the first step makes it possible to obtain 25 to 35% by weight of alumina with respect to the total amount. of alumina formed at the end of the two precipitation steps. The first stage operates at a temperature between 20 and 40Ό. When the desired alumina qua nity is formed, the temperature of the slurry is raised to a temperature between 45 and 70Ό, and then the heated slurry is then subjected to a second precipitation step by contacting said slurry with a second alkaline aqueous solution and a second acidic aqueous solution, at least one or both of the solutions comprising an aluminum compound. Similarly, the pH is adjusted between 8 and 10.5 by the proportions of the acid and basic solutions added and the remaining quantity of alumina to be formed in the second stage is provided by the amounts of the second acid and basic solutions added. The second stage operates at a temperature between 20 and 40Ό. The alumina gel thus formed comprises at least 95% of boehmite. The alumina gel is then filtered, washed and optionally dried according to the methods known to those skilled in the art, without prior curing step, to produce an alumina powder which is then shaped according to the known methods of the present invention. skilled in the art, and then calcined to produce the final alumina support.
La demanderesse a ainsi découvert qu'un procédé de préparation d'un gel d'alumine en seule étape de précipitation, ladite étape consistant en la mise en solution d'un précurseur acide d'aluminium spécifique, le chlorure d'aluminium, suivie d'un ajustement du pH au moyen d'un précurseur basique spécifique, l'hydroxyde de sodium, sans étape de co- précipitation ultérieure, conduisait à un gel d'alumine présentant des cristallites de faible taille. En particulier, le procédé de préparation selon l'invention permet l'obtention de gel d'alumine ou de boehmite composée de cristallites dont la taille, obtenue par la formule de Scherrer en diffraction des rayons X selon les directions cristallographiques [020] et [120] est respectivement comprise entre 0,5 et 10 nm et entre 0,5 et 15 nm et de préférence respectivement comprise entre 0,5 à 2 nm et entre 0,5 à 3 nm et de manière très préférée respectivement entre 0,5 et 1 ,5 et entre 0,5 et 2,5. The Applicant has thus discovered that a method for preparing an alumina gel in a single precipitation stage, said step consisting in the placing in solution of a precursor specific aluminum acid, aluminum chloride, followed by a pH adjustment using a specific basic precursor, sodium hydroxide, without a subsequent co-precipitation step, led to an alumina gel having crystallites of small size. In particular, the preparation process according to the invention makes it possible to obtain alumina or boehmite gel composed of crystallites whose size, obtained by the Scherrer formula in X-ray diffraction according to the crystallographic directions [020] and [ 120] is respectively between 0.5 and 10 nm and between 0.5 and 15 nm and preferably respectively between 0.5 and 2 nm and between 0.5 and 3 nm and very preferably between 0.5 and 0.5 nm respectively. and 1, 5 and between 0.5 and 2.5.
La diffraction des rayons X sur les gels d'alumine ou boehmites a été effectuée en utilisant la méthode classique des poudres au moyen d'un diffractomètre. X-ray diffraction on alumina or boehmite gels was performed using the conventional powder method using a diffractometer.
La formule de Scherrer est une formule utilisée en diffraction des rayons X sur des poudres ou échantillons polycristallins qui relie la largeur à mi-hauteur des pics de diffraction à la taille des cristallites. Elle est décrite en détail dans la référence : Appl. Cryst. (1978). 1 1 , 102-1 13 Scherrer after sixty years: A survey and some new results in the détermination of crystallite size, J. I. Langford and A. J. C. Wilson. Scherrer's formula is a formula used in X-ray diffraction on powders or polycrystalline samples which connects the width at half height of the diffraction peaks to the size of the crystallites. It is described in detail in the reference: Appl. Cryst. (1978). 1 1, 102-1. Scherrer after sixty years: A survey and some new results in the determination of crystallite size, J. I. Langford and A. J. C. Wilson.
Résumé et intérêt de l'invention Summary and interest of the invention
L'invention concerne un procédé de préparation d'un gel alumine en une seule étape de précipitation, ladite étape de précipitation consistant en la mise en solution du précurseur acide d'aluminium chlorure d'aluminium dans l'eau, à une température comprise entre 10 et 90Ό, de sorte que le pH de la solution soit corn pris entre 0,5 et 5, pendant une durée comprise entre 2 et 60 minutes puis en l'ajustement du pH à un pH compris entre 7,5 et 9,5 par ajout dans la solution obtenue d'un précurseur basique, l'hydroxyde de sodium, pour obtenir une suspension, à une température comprise entre 5 et 35Ό, et pendant une durée comprise entre 5 minutes et 5 heures. The invention relates to a process for the preparation of an alumina gel in a single precipitation step, said precipitation step consisting in the solution of the precursor acid aluminum aluminum chloride in water at a temperature between 10 and 90 °, so that the pH of the solution is between 0.5 and 5, for a period of between 2 and 60 minutes and then adjusting the pH to a pH between 7.5 and 9.5 by adding sodium hydroxide to the solution obtained with a basic precursor, to obtain a suspension at a temperature of between 5 and 35 ° and for a period of between 5 minutes and 5 hours.
Un avantage de la présente invention est de fournir un procédé de préparation permettant l'obtention d'un gel d'alumine présentant une taille de cristallites réduite par rapport aux gels d'alumine préparés selon l'art antérieur et en particulier présentant des cristallites de faible taille. En particulier, un avantage de la présente invention est de fournir un procédé de préparation permettant l'obtention d'un gel d'alumine ou de boehmite composée de cristallites dont la taille, obtenue par la formule de Scherrer en diffraction des rayons X selon les directions cristallographiques [020] et [120] est respectivement comprise entre 0,5 et 10 nm et entre 0,5 et 15 nm et de préférence respectivement comprise entre 0,5 à 2 nm et entre 0,5 à 3 nm et de manière très préférée respectivement entre 0,5 et 1 ,5 et entre 0,5 et 2,5. An advantage of the present invention is to provide a preparation process for obtaining an alumina gel having a reduced crystallite size compared to the alumina gels prepared according to the prior art and in particular having crystallites of small size. In particular, an advantage of the present invention is to provide a preparation process for obtaining a gel of alumina or boehmite composed of crystallites whose size, obtained by the Scherrer formula in X-ray diffraction according to the crystallographic directions [020] and [120] is respectively between 0.5 and 10 nm and between 0.5 and 15 nm and preferably respectively between 0.5 and 2 nm and between 0.5 and 3 nm and so very preferably between 0.5 and 1.5 respectively and between 0.5 and 2.5.
Un autre avantage de la présente invention est de fournir un procédé de préparation d'un gel d'alumine présentant une taille de cristallites réduite, simplifié et peu coûteux par rapport aux procédés de préparation d'alumine classique de l'art antérieur tel que par exemple les procédés de préparation de type sol-gel, en ce que le procédé selon l'invention ne comprenant qu'une seule étape de précipitation. Another advantage of the present invention is to provide a process for the preparation of an alumina gel having a reduced crystallite size, simplified and inexpensive compared to the conventional alumina preparation methods of the prior art such as by for example, sol-gel type preparation processes, in that the process according to the invention comprises only a single precipitation step.
Description de l'invention Description of the invention
Conformément à l'invention, le procédé de préparation du gel alumine selon l'invention comprend une seule étape de précipitation. Ladite étape de précipitation consiste en la mise en solution d'un précurseur acide d'aluminium spécifique, le chlorure d'aluminium AICI3, dans l'eau, à une température comprise entre 10 et 90Ό, de préférence entre 10 e t 80Ό, de manière préférée entre 10 et 75Ό et de manière plus préférée entre 15 et 70° C. Le pH de la solution obtenue est compris entre 0,5 et 5, de préférence entre 1 et 4, de manière préférée entre 1 ,5 et 3,5. La solution est laissée sous agitation pendant une durée comprise entre 2 et 60 minutes, et de préférence de 5 à 30 minutes et de manière préférée entre 5 et 10 minutes. According to the invention, the process for preparing the alumina gel according to the invention comprises a single precipitation step. Said precipitation step consists in dissolving a specific aluminum acid precursor, aluminum chloride AICI 3 , in water at a temperature of between 10 and 90Ό, preferably between 10 and 80Ό, of preferred way between 10 and 75Ό and more preferably between 15 and 70 ° C. The pH of the solution obtained is between 0.5 and 5, preferably between 1 and 4, preferably between 1, 5 and 3, 5. The solution is left stirring for a period of between 2 and 60 minutes, and preferably 5 to 30 minutes and preferably between 5 and 10 minutes.
Le pH de la suspension obtenue est ensuite ajusté à un pH appelé pH de fin de précipitation compris entre 7,5 et 9,5, de préférence entre 7,5 et 9 et de manière préférée entre 7,7 et 8,8 par l'ajout d'un précurseur basique spécifique, l'hydroxyde de sodium NaOH à une température comprise entre 5 et 35Ό, de préférence entre 10 et 30Ό et de manière préférée entre 10 et 25Ό et pendant une durée comp rise entre 5 minutes et 5 heures, de préférence entre 10 minutes et 5 heures, de manière préférée entre 15 minutes et 2 heures. The pH of the suspension obtained is then adjusted to a pH called the end-of-precipitation pH of between 7.5 and 9.5, preferably between 7.5 and 9 and, preferably, between 7.7 and 8.8 per liter. addition of a specific basic precursor, sodium hydroxide NaOH at a temperature of between 5 and 35 °, preferably between 10 and 30 ° and preferably between 10 and 25 ° and for a duration of between 5 minutes and 5 hours preferably between 10 minutes and 5 hours, preferably between 15 minutes and 2 hours.
L'ajout de NaOH permet de précipiter la boehmite et d'obtenir une suspension. The addition of NaOH makes it possible to precipitate the boehmite and to obtain a suspension.
De préférence, la précipitation est réalisée en l'absence d'additif organique. De préférence la précipitation du gel d'alumine est opérée sous agitation. Preferably, the precipitation is carried out in the absence of organic additive. Preferably, the precipitation of the alumina gel is carried out with stirring.
De préférence, le procédé selon l'invention ne comprend pas d'étape supplémentaire de précipitation et ne comprend pas d'étape de co-précipitation ultérieure par mise en contact, en milieu réactionnel aqueux, d'au moins un précurseur basique et d'au moins un précurseur acide, au moins un des précurseurs basique ou acide comprenant de l'aluminium. Preferably, the method according to the invention does not comprise an additional precipitation step and does not comprise a subsequent co-precipitation step by contacting, in aqueous reaction medium, at least one basic precursor and at least one acidic precursor, at least one of the basic or acidic precursors comprising aluminum.
Le choix des précurseurs spécifiques associés aux conditions de températures et de pH sélectionnées permettent l'obtention d'un gel d'alumine présentant une taille de cristallites réduite par rapport aux gels d'alumine préparés selon l'art antérieur et en particulier d'un gel d'alumine ou de boehmite composée de cristallites dont la taille, obtenue par la formule de Scherrer en diffraction des rayons X selon les directions cristallographiques [020] et [120] est respectivement comprise entre 0,5 et 10 nm et entre 0,5 et 15 nm et de préférence respectivement comprise entre 0,5 à 2 nm et entre 0,5 à 3 nm et de manière très préférée respectivement entre 0,5 et 1 ,5 et entre 0,5 et 2,5. The choice of specific precursors associated with the selected temperature and pH conditions makes it possible to obtain an alumina gel having a reduced crystallite size compared with the alumina gels prepared according to the prior art and in particular a gel of alumina or boehmite composed of crystallites whose size, obtained by the Scherrer formula in X-ray diffraction according to the crystallographic directions [020] and [120] is respectively between 0.5 and 10 nm and between 0, 5 and 15 nm and preferably respectively between 0.5 to 2 nm and between 0.5 to 3 nm and very preferably respectively between 0.5 and 1, 5 and between 0.5 and 2.5.
De préférence, le procédé de préparation du gel d'alumine selon l'invention comprend également une étape de filtration de la suspension obtenue à l'issue de l'étape de précipitation. Preferably, the process for preparing the alumina gel according to the invention also comprises a filtration step of the suspension obtained at the end of the precipitation step.
Ladite étape de filtration est réalisée selon les méthodes connues de l'homme du métier. Said filtration step is carried out according to the methods known to those skilled in the art.
Ladite étape de filtration est avantageusement suivie d'au moins une étape de lavage, avec une solution aqueuse, de préférence à l'eau et de préférence d'une à trois étapes de lavage, avec une quantité d'eau égale à la quantité de précipité filtré. Said filtration step is advantageously followed by at least one washing step, with an aqueous solution, preferably with water and preferably from one to three washing steps, with a quantity of water equal to the amount of water. precipitate filtered.
Le gel d'alumine obtenu à l'issue de l'étape de précipitation, suivie d'une éventuelle étape de filtration et d'au moins une éventuelle étape de lavage, est ensuite avantageusement séché dans une étape de séchage de la suspension éventuellement filtrée obtenue à l'issue de l'étape de précipitation pour obtenir une poudre, ladite étape de séchage étant mise en œuvre avantageusement par séchage à une température supérieure ou égale à 120Ό ou par atomisation ou par toute autre technique de séchage connue de l'homme du métier. The alumina gel obtained at the end of the precipitation step, followed by a possible filtration step and at least one optional washing step, is then advantageously dried in a drying step of the optionally filtered suspension. obtained at the end of the precipitation step to obtain a powder, said drying step being advantageously carried out by drying at a temperature greater than or equal to 120 ° C. or by spray drying or by any other drying technique known to man of career.
Dans le cas où ladite étape de séchage est mise en œuvre par séchage à une température supérieure ou égale à 120Ό, ladite étape de séchag e peut avantageusement être réalisée en étuve fermée et ventilée. De préférence ladite étape de séchage opère à une température comprise entre 120 et 300Ό, de manière très préférée à une température comprise entre 150 et 250<C. In the case where said drying step is carried out by drying at a temperature greater than or equal to 120 °, said drying step e may advantageously be carried out in a closed and ventilated oven. Preferably, said drying step operates at a temperature between 120 and 300Ό, very preferably at a temperature between 150 and 250 <C.
Dans le cas où ladite étape de séchage est mise en œuvre par atomisation, le gâteau obtenu à l'issue de l'étape de deuxième précipitation, suivie d'une étape de filtration, est remis en suspension. Ladite suspension est ensuite pulvérisée en fines gouttelettes, dans une enceinte cylindrique verticale au contact d'un courant d'air chaud afin d'évaporer l'eau selon le principe bien connu de l'homme du métier. La poudre obtenue est entraînée par le flux de chaleur jusqu'à un cyclone ou un filtre à manche qui vont séparer l'air de la poudre. In the case where said drying step is carried out by atomization, the cake obtained at the end of the second precipitation step, followed by a filtration step, is resuspended. Said suspension is then sprayed in fine droplets, in a vertical cylindrical chamber in contact with a stream of hot air to evaporate the water according to the principle well known to those skilled in the art. The powder obtained is driven by the heat flow to a cyclone or a bag filter that will separate the air from the powder.
De préférence, dans le cas où ladite étape de séchage est mise en œuvre par atomisation, l'atomisation est réalisée selon le protocole opératoire décrit dans la publication Asep Bayu Dani Nandiyanto, Kikuo Okuyama, Advanced Powder Technology, 22, 1 -19, 201 1 . Preferably, in the case where said drying step is carried out by atomization, the atomization is carried out according to the operating protocol described in the publication Asep Bayu Dani Nandiyanto, Kikuo Okuyama, Advanced Powder Technology, 22, 1 -19, 201 1.
La poudre obtenue à l'issue de l'étape de séchage peut ensuite avantageusement être mise en forme pour obtenir un matériau cru. The powder obtained at the end of the drying step can then advantageously be shaped to obtain a green material.
On entend par matériau cru, le matériau mis en forme et n'ayant pas subi d'étapes de traitement thermique. By raw material is meant the material shaped and having not undergone any heat treatment steps.
De préférence, ladite étape de mise en forme peut être réalisée par malaxage-extrusion, par granulation, par la technique de l'oil drop (égouttage ou coagulation de goutte en français), par pastillage. Preferably, said shaping step can be carried out by kneading-extrusion, by granulation, by the technique of oil drop (dewatering or coagulation of drop in French), by pelletization.
De manière très préférée, ladite étape de mise en forme est réalisée par malaxage - extrusion. In a very preferred manner, said shaping step is carried out by kneading - extrusion.
Le matériau cru obtenu mis en forme peut éventuellement subir ensuite une étape de traitement thermique à une température comprise entre 500 et 1000Ό, pendant une durée avantageusement comprise entre 2 et 10 h, en présence ou non d'un flux d'air contenant jusqu'à 60% volume d'eau. De préférence, ledit traitement thermique est effectué en présence d'un flux d'air contenant de l'eau. The obtained green material obtained in shape can optionally then undergo a heat treatment step at a temperature of between 500 and 1000 °, for a duration advantageously between 2 and 10 h, in the presence or absence of a flow of air containing up to at 60% water volume. Preferably, said heat treatment is carried out in the presence of an air flow containing water.
De préférence, ladite étape de traitement thermique opère à une température comprise entre 540<C et 850<C. De préférence, ladite étape de traitement thermique opère pendant une durée comprise entre 2h et 10h. Preferably, said heat treatment step performed at a temperature between 540 <C to 850 <C. Preferably, said heat treatment step operates for a duration of between 2 h and 10 h.
Ladite étape de traitement thermique permet la transition de la boehmite vers l'alumine finale. L'étape de traitement thermique peut éventuellement être précédée d'un séchage à une température comprise entre 50Ό et 120Ό, selon tou te technique connue de l'homme du métier. Said heat treatment step allows the transition from boehmite to the final alumina. The heat treatment step may optionally be preceded by drying at a temperature of between 50 ° and 120 °, according to all techniques known to those skilled in the art.
Le procédé selon l'invention permet l'obtention d'un gel d'alumine, éventuellement sous forme de poudre, présentant une taille de cristallites réduite par rapport aux gels d'alumine préparés selon l'art antérieur. The process according to the invention makes it possible to obtain an alumina gel, optionally in the form of a powder, having a reduced crystallite size compared to the alumina gels prepared according to the prior art.
En particulier, le gel d'alumine ou la boehmite obtenue sous forme de poudre selon l'invention est composée de cristallites dont la taille, obtenue par la formule de Scherrer en diffraction des rayons X selon les directions cristallographiques [020] et [120] est respectivement comprise entre 0,5 et 10 nm et entre 0,5 et 15 nm et de préférence respectivement comprise entre 0,5 à 2 nm et entre 0,5 à 3 nm et de manière très préférée respectivement entre 0,5 et 1 ,5 et entre 0,5 et 2,5. In particular, the alumina gel or the boehmite obtained in powder form according to the invention is composed of crystallites whose size, obtained by the Scherrer formula in X-ray diffraction according to the crystallographic directions [020] and [120] is respectively between 0.5 and 10 nm and between 0.5 and 15 nm and preferably respectively between 0.5 and 2 nm and between 0.5 and 3 nm and very preferably between 0.5 and 1 respectively. , 5 and between 0.5 and 2.5.
La présente invention concerne également le gel d'alumine susceptible d'être obtenu par le procédé de préparation selon l'invention. The present invention also relates to the alumina gel that can be obtained by the preparation process according to the invention.
L'invention est illustrée par les exemples suivants qui ne présentent, en aucun cas, un caractère limitatif. The invention is illustrated by the following examples, which in no way present a limiting character.
Exemples : Examples:
Exemple 1 : (comparatif) : Example 1: (comparative)
Une poudre commerciale d'un gel d'alumine Pural SB3 est préparée selon une voie sol-gel par hydrolyse-polycondensation d'un alcoxyde d'aluminium. La taille des cristallites de la boehmite obtenue est mesurée selon la méthode de Sherrer Taille selon [020] = 3,1 ± 0,2 (nm) ; Taille selon [120] =4,7 ± 0,3 (nm). Exemple 2 (comparatif) : A commercial powder of a Pural SB3 alumina gel is prepared according to a sol-gel route by hydrolysis-polycondensation of an aluminum alkoxide. The size of the crystallites of the boehmite obtained is measured according to the method of Sherrer Size according to [020] = 3.1 ± 0.2 (nm); Size according to [120] = 4.7 ± 0.3 (nm). Example 2 (comparative):
On réalise la synthèse d'un gel d'alumine selon un procédé de préparation non-conforme en ce que le procédé de préparation du gel selon l'exemple 2 est réalisée dans un réacteur de 7 I et une suspension finale de 5 I en deux étapes de précipitation avec des précurseurs non conformes à l'invention. The synthesis of an alumina gel is carried out according to a non-compliant preparation process in that the process for preparing the gel according to Example 2 is carried out in a 7 l reactor and a final suspension of 5 l in two. precipitation steps with precursors not in accordance with the invention.
La quantité d'eau ajoutée dans le réacteur est de 3868 ml. The amount of water added to the reactor is 3868 ml.
La concentration finale en alumine visée est de 30g/l. The final concentration of alumina is 30g / l.
Une première étape de co-précipitation de sulfate d'aluminium AI2(S04) et d'aluminate de sodium NaAIOO est réalisée à 30Ό et pH=9,3 pendant une durée de 8 minutes. Les concentrations des précurseurs d'aluminium utilisées sont les suivantes : AI2(S04)= à 102g/l en Al203 et NaAIOO à 155g/l en Al203. L'agitation est de 350 rpm tout au long de la synthèse. A first step of co-precipitation of aluminum sulphate Al 2 (SO 4 ) and of sodium aluminate NaAlOO is carried out at 30 ° and pH = 9.3 for a period of 8 minutes. The concentrations of aluminum precursors used are as follows: AI 2 (SO 4 ) = 102 g / l in Al 2 O 3 and NaAlOO at 155 g / l in Al 2 O 3 . The agitation is 350 rpm throughout the synthesis.
Une solution de sulfate d'aluminium AI2(S04) est ajoutée en continu pendant 8 minutes à un débit de 19,6 ml/min à une solution d'aluminate de sodium NaAIOO selon un ratio massique base/acide = 1 ,80 de manière à ajuster le pH à une valeur de 9,3. La température du milieu réactionnel est maintenu à 30Ό. A solution of aluminum sulphate Al 2 (SO 4 ) is added continuously for 8 minutes at a flow rate of 19.6 ml / min to a solution of sodium aluminate NaAlOO in a mass ratio base / acid = 1.80 in order to adjust the pH to a value of 9.3. The temperature of the reaction medium is maintained at 30 °.
Une suspension contenant un précipité d'alumine est obtenue. A suspension containing a precipitate of alumina is obtained.
La concentration finale en alumine visée étant de 30g/l, le débit des précurseurs sulfate d'aluminium AI2(S04) et aluminate de sodium NaAIOO contenant de l'aluminium introduit dans la première étape de précipitation sont respectivement de 19,6 ml/min et de 23,3 ml/min. As the final concentration of alumina is 30 g / l, the flow rate of the aluminum sulphate precursors Al 2 (SO 4 ) and aluminum aluminate NaAlO 4 introduced in the first precipitation step are respectively 19.6 ml. / min and 23.3 ml / min.
La suspension obtenue est ensuite soumise à une montée en température de 30 à 57<C. The suspension obtained is then subjected to a temperature rise of from 30 to 57 <C.
Une deuxième étape de co-précipitation de la suspension obtenue est ensuite réalisée par ajout de sulfate d'aluminium AI2(S04) à une concentration de 102 g/l en Al203 et d'aluminate de sodium NaAIOO à une concentration de 155 g/L en Al203. Une solution de sulfate d'aluminium AI2(S04) est donc ajoutée en continu à la suspension chauffée obtenue à l'issue de la première étape de précipitation pendant 30 minutes à un débit de 12,8 ml/min à une solution d'aluminate de sodium NaAIOO selon un ratio massique base/acide = 1 ,68 de manière à ajuster le pH à une valeur de 8,7. La température du milieu réactionnel dans la deuxième étape est maintenu à 57<C. A second step of co-precipitation of the suspension obtained is then carried out by adding aluminum sulphate Al 2 (S0 4) at a concentration of 102 g / l of Al 2 0 3 and sodium aluminate at a concentration NaAIOO 155 g / L in Al 2 O 3 . A solution of aluminum sulphate Al 2 (SO 4 ) is therefore added continuously to the heated suspension obtained at the end of the first precipitation step for 30 minutes at a flow rate of 12.8 ml / min. sodium aluminate NaAlOO in a weight ratio base / acid = 1.68 of way to adjust the pH to a value of 8.7. The temperature of the reaction medium in the second stage is maintained at 57 <C.
Une suspension contenant un précipité d'alumine est obtenue. A suspension containing a precipitate of alumina is obtained.
La concentration finale en alumine visée étant de 30g/l, le débit des précurseurs sulfate d'aluminium AI2(S04) et aluminate de sodium NaAIOO contenant de l'aluminium introduit dans la deuxième étape de précipitations sont respectivement de 12,8 ml/min et 14,1 ml/min. As the final concentration of alumina is 30 g / l, the flow rate of the aluminum sulphate precursors Al 2 (SO 4 ) and sodium aluminate NaAlOO containing aluminum introduced in the second precipitation stage are respectively 12.8 ml. / min and 14.1 ml / min.
La suspension ainsi obtenue ne subit pas d'étape de mûrissement. The suspension thus obtained does not undergo a ripening step.
La suspension obtenue est ensuite filtrée par déplacement d'eau sur un outil type Buchner fritté et le gel d'alumine obtenu est lavé 3 fois avec 5 I d'eau distillée à 70<C. Le temps de filtration et de lavage est de 4 h. The suspension obtained is then filtered by water displacement on a sintered Buchner-type tool and the alumina gel obtained is washed 3 times with 5 liters of distilled water at 70 <C. The filtration time and washing is 4 h.
La taille des cristallites de la boehmite obtenue est mesurée selon la méthode de Sherrer : Taille selon [020] = 2,9 ± 0,2 (nm) ; Taille selon [120] =4,1 ± 0,3 (nm) The crystallite size of the boehmite obtained is measured according to the Sherrer method: Size according to [020] = 2.9 ± 0.2 (nm); Size according to [120] = 4.1 ± 0.3 (nm)
Exemple 3 : (comparatif) : Example 3 (Comparative):
On prépare un gel d'alumine selon un procédé de synthèse non conforme à l'invention, en ce que le pH de fin de précipitation du gel d'alumine est réalisée à un pH supérieur à 9,5. An alumina gel is prepared according to a synthetic process not in accordance with the invention, in that the pH of the end of precipitation of the alumina gel is carried out at a pH greater than 9.5.
1/ précipitation de boehmite AIOOH 1 / boehmite precipitation AIOOH
Dans un bêcher refroidit par un bain de glace, une solution contenant 326 ml d'eau permutée et 135,6 g de chlorure d'aluminium hexahydraté (AICI3) est préparée à une température de 25<C, de manière à obtenir une solut ion ayant un pH de 0,5, pendant une durée de 5 minutes. In a beaker cooled with an ice bath, a solution containing 326 ml of deionized water and 135.6 g of aluminum chloride hexahydrate (AlCl 3) is prepared at a temperature of 25 <C, so as to obtain a solut ion having a pH of 0.5, for a period of 5 minutes.
Ensuite sous agitation magnétique, 67,5 g d'hydroxyde de sodium (NaOH) sont ajoutés pendant 30 minutes de manière à ajuster le pH. Le pH atteint en fin de synthèse est de 10. La température est maintenue à 20<C pendant toute I e durée de l'étape. Ce gâteau est mis en suspension dans un bêcher de 3 L avec 320 mL d'eau. Un échantillon du précipité obtenu est prélevé du milieu réactionnel. La DRX (figure 1 ) du précipité montre que le précipité obtenu dans l'exemple 3 est bien un précipité de boehmite. La taille des cristallites de la boehmite obtenue est mesurée selon la méthode de Sherrer : Taille selon [020] = 2,1 ± 0,2 (nm) ; Taille selon [120] =2,8 ± 0,3 (nm) Then, with magnetic stirring, 67.5 g of sodium hydroxide (NaOH) are added for 30 minutes to adjust the pH. The pH reaches the end of synthesis was 10. The temperature was maintained at 20 <C for all I e duration of step. This cake is suspended in a 3 L beaker with 320 mL of water. A sample of the precipitate obtained is taken from the reaction medium. The DRX (FIG. 1) of the precipitate shows that the precipitate obtained in example 3 is indeed a boehmite precipitate. The crystallite size of the boehmite obtained is measured according to the Sherrer method: Size according to [020] = 2.1 ± 0.2 (nm); Size according to [120] = 2.8 ± 0.3 (nm)
Exemple 4 : (comparatif) : Example 4: (comparative)
On prépare un gel d'alumine selon un procédé de synthèse non conforme à l'invention, en ce que l'ajustement du pH est réalisée à une température de 40Ό. An alumina gel is prepared according to a synthetic process not according to the invention, in that the pH adjustment is carried out at a temperature of 40 °.
1/ précipitation de boehmite AIOOH 1 / boehmite precipitation AIOOH
Dans un bêcher refroidit par un bain de glace, une solution contenant 326 ml d'eau permutée et 135,6 g de chlorure d'aluminium hexahydraté (AICI3) est préparée à une température de 25Ό C, de manière à obtenir une sol ution ayant un pH de 0,5, pendant une durée de 5 minutes. In a beaker cooled by an ice bath, a solution containing 326 ml of deionized water and 135.6 g of aluminum chloride hexahydrate (AlCl 3 ) is prepared at a temperature of 25 ° C, so as to obtain a solution. having a pH of 0.5, for a period of 5 minutes.
Ensuite sous agitation magnétique, 67,5 g d'hydroxyde de sodium (NaOH) sont ajoutés pendant 30 minutes de manière à ajuster le pH. Le pH atteint en fin de synthèse est de 8. La température est maintenue à 40Ό pendant toute le d urée de l'étape. Ce gâteau est mis en suspension dans un bêcher de 3 L avec 320 mL d'eau. Un échantillon du précipité obtenu est prélevé du milieu réactionnel. La DRX (figure 2) du précipité montre que le précipité obtenu dans l'exemple 4 est bien un précipité de boehmite. Then, with magnetic stirring, 67.5 g of sodium hydroxide (NaOH) are added for 30 minutes to adjust the pH. The pH reached at the end of the synthesis is 8. The temperature is maintained at 40 ° throughout the duration of the stage. This cake is suspended in a 3 L beaker with 320 mL of water. A sample of the precipitate obtained is taken from the reaction medium. The DRX (FIG. 2) of the precipitate shows that the precipitate obtained in example 4 is indeed a boehmite precipitate.
La taille des cristallistes de la boehmite obtenue est mesurée selon la méthode de Sherrer : Taille selon [020] = 1 ,9 ± 0,3 (nm) ; Taille selon [120] =2,6 ± 0,2 (nm). The size of the crystallists of the boehmite obtained is measured according to the method of Sherrer: Size according to [020] = 1, 9 ± 0.3 (nm); Size according to [120] = 2.6 ± 0.2 (nm).
Exemple 5 : (selon l'invention) : On prépare un gel d'alumine selon un procédé de synthèse conforme à l'invention. EXAMPLE 5 (According to the Invention) An alumina gel is prepared according to a synthesis method according to the invention.
1/ précipitation de boehmite AIOOH 1 / boehmite precipitation AIOOH
Dans un bêcher refroidit par un bain de glace, une solution contenant 326 ml d'eau permutée et 135,6 g de chlorure d'aluminium hexahydraté (AICI3) est préparée à une température de 25Ό, de manière à obtenir une solut ion ayant un pH de 0,5, pendant une durée de 5 minutes. In a beaker cooled by an ice bath, a solution containing 326 ml of deionized water and 135.6 g of aluminum chloride hexahydrate (AlCl 3 ) is prepared at a temperature of 25 °, so as to obtain a solution having a pH of 0.5 for a period of 5 minutes.
Ensuite sous agitation magnétique, 67,5 g d'hydroxyde de sodium (NaOH) sont ajoutés pendant 30 minutes de manière à ajuster le pH. Le pH atteint en fin de synthèse est de 8. La température est maintenue à 20^ pendant toute le d urée de l'étape de précipitation. Ce gâteau est mis en suspension dans un bêcher de 3 L avec 320 ml_ d'eau. Then, with magnetic stirring, 67.5 g of sodium hydroxide (NaOH) are added for 30 minutes to adjust the pH. The pH reached at the end of the synthesis is 8. The The temperature is maintained at 20 ° throughout the duration of the precipitation step. This cake is suspended in a 3 L beaker with 320 ml of water.
Un échantillon du précipité obtenu est prélevé du milieu réactionnel. La DRX (figure 3) du précipité montre que le précipité obtenu dans l'exemple 5 est bien un précipité de boehmite. Le précipité de boehmite obtenu dans l'exemple 5 est peu cristallisé. A sample of the precipitate obtained is taken from the reaction medium. The DRX (FIG. 3) of the precipitate shows that the precipitate obtained in Example 5 is indeed a boehmite precipitate. The boehmite precipitate obtained in Example 5 is poorly crystallized.
La taille des cristallites de la boehmite obtenue est mesurée selon la méthode de Sherrer : Taille selon [020] = 0,6 ± 0,1 (nm) ; Taille selon [120] =1 ,4 ± 0,1 (nm). The crystallite size of the boehmite obtained is measured according to the Sherrer method: Size according to [020] = 0.6 ± 0.1 (nm); Size according to [120] = 1, 4 ± 0.1 (nm).
Exemple 6 : (selon l'invention) : Example 6: (according to the invention)
On prépare un gel d'alumine selon un procédé de synthèse conforme à l'invention. 1/ précipitation de boehmite AIOOH An alumina gel is prepared according to a synthesis process according to the invention. 1 / boehmite precipitation AIOOH
Dans un bêcher refroidit par un bain de glace, une solution contenant 326 ml d'eau permutée et 135,6 g de chlorure d'aluminium hexahydraté (AICI3) est préparée à une température comprise de 25^, de manière à obtenir une solution ayant un pH de 0,5, pendant une durée de 5 minutes. Ensuite sous agitation magnétique, 67,5 g d'hydroxyde de sodium (NaOH) sont ajoutés pendant 30 minutes de manière à ajuster le pH. Le pH atteint en fin de synthèse est de 8.5. La température est maintenue à 20^ pendant toute I e durée de l'étape. Ce gâteau est mis en suspension dans un bêcher de 3 L avec 320 mL d'eau. In a beaker cooled by an ice bath, a solution containing 326 ml of deionized water and 135.6 g of aluminum chloride hexahydrate (AlCl 3 ) is prepared at a temperature of 25% to obtain a solution. having a pH of 0.5, for a period of 5 minutes. Then, with magnetic stirring, 67.5 g of sodium hydroxide (NaOH) are added for 30 minutes to adjust the pH. The pH reached at the end of the synthesis is 8.5. The temperature is maintained at 20 ° throughout the duration of the step. This cake is suspended in a 3 L beaker with 320 mL of water.
Un échantillon du précipité obtenu est prélevé du milieu réactionnel. La DRX (figure 4) du précipité montre que le précipité obtenu dans l'exemple 6 est bien un précipité de boehmite. Le précipité de boehmite obtenu dans l'exemple 6 est peu cristallisé. A sample of the precipitate obtained is taken from the reaction medium. The DRX (FIG. 4) of the precipitate shows that the precipitate obtained in example 6 is indeed a boehmite precipitate. The boehmite precipitate obtained in Example 6 is poorly crystalline.
La taille des cristallites de la boehmite obtenue est mesurée selon la méthode de Sherrer Taille selon [020] = 0,9 ± 0,1 (nm) ; Taille selon [120] =1 ,6 ± 0,2 (nm). The size of the crystallites of the boehmite obtained is measured according to the method of Sherrer Size according to [020] = 0.9 ± 0.1 (nm); Size according to [120] = 1, 6 ± 0.2 (nm).

Claims

REVENDICATIONS
1 . Procédé de préparation d'un gel alumine en une seule étape de précipitation, ladite étape de précipitation consistant en la mise en solution du précurseur acide d'aluminium chlorure d'aluminium dans l'eau, à une température comprise entre 10 et 90Ό, de sorte que le pH de la solution soit compris entre 0,5 et 5, pendant une durée comprise entre 2 et 60 minutes puis en l'ajustement du pH à un pH compris entre 7,5 et 9,5 par ajout dans la solution obtenue d'un précurseur basique, l'hydroxyde de sodium, pour obtenir une suspension, à une température comprise entre 5 et 35^, et pendant une durée comprise entre 5 minutes et 5 heures. 1. A process for the preparation of an alumina gel in a single precipitation step, said precipitation step consisting in the solution of the precursor acid aluminum aluminum chloride in water, at a temperature of between 10 and 90Ό, of so that the pH of the solution is between 0.5 and 5, for a period of between 2 and 60 minutes and then adjusting the pH to a pH between 7.5 and 9.5 by adding to the solution obtained of a basic precursor, sodium hydroxide, to obtain a suspension, at a temperature of between 5 and 35, and for a period of between 5 minutes and 5 hours.
2. Procédé de préparation selon la revendication 1 dans lequel la mise en solution du précurseur acide d'aluminium le chlorure d'aluminium AICI3, dans l'eau, est réalisée à une température comprise entre 10 et 75 Ό. 2. Preparation process according to claim 1 wherein the solution of the aluminum acid precursor aluminum chloride AICI 3 , in water, is carried out at a temperature between 10 and 75 Ό.
3. Procédé de préparation selon l'une des revendications 1 ou 2 dans lequel le pH de la solution de chlorure d'aluminium AICI3, dans l'eau, est compris entre 1 et 4. 3. Preparation process according to one of claims 1 or 2 wherein the pH of the solution of aluminum chloride AICI 3 , in water, is between 1 and 4.
4. Procédé de préparation selon l'une des revendications 1 à 3 dans lequel l'ajustement du pH est réalisé à une température comprise entre 10 et 30^. 4. Preparation process according to one of claims 1 to 3 wherein the adjustment of the pH is carried out at a temperature between 10 and 30 ^.
5. Procédé de préparation selon la revendication 4 dans lequel l'ajustement du pH est réalisé à une température comprise entre 10 et 25Ό . 5. Preparation process according to claim 4 wherein the adjustment of the pH is carried out at a temperature between 10 and 25Ό.
6. Procédé de préparation selon l'une des revendications 1 à 5 dans lequel l'ajustement du pH est réalisé à un pH compris entre 7,7 et 8,8. 6. Preparation process according to one of claims 1 to 5 wherein the adjustment of the pH is carried out at a pH between 7.7 and 8.8.
7. Procédé de préparation selon l'une des revendications 1 à 6 dans lequel le procédé selon l'invention ne comprend pas d'étape supplémentaire de précipitation. 7. Preparation process according to one of claims 1 to 6 wherein the method according to the invention does not include an additional step of precipitation.
8. Procédé de préparation selon l'une des revendications 1 à 7 dans lequel le procédé de préparation comprend également une étape de filtration de la suspension obtenue à l'issue de l'étape de précipitation. 8. Preparation process according to one of claims 1 to 7 wherein the preparation process also comprises a filtration step of the suspension obtained at the end of the precipitation step.
9. Procédé de préparation selon l'une des revendications 1 à 8 dans lequel le procédé de préparation comprend également une étape de séchage de la suspension éventuellement filtrée obtenue à l'issue de l'étape de précipitation pour obtenir une poudre, ladite étape de séchage étant mise en œuvre par séchage à une température supérieure ou égale à 120Ό ou par atomisation. 9. Preparation process according to one of claims 1 to 8 wherein the preparation process also comprises a step of drying the optionally filtered suspension obtained at the end of the precipitation step to obtain a powder, said step of drying being carried out by drying at a temperature greater than or equal to 120 ° C. or by atomization.
10. Procédé de préparation selon la revendication 9 dans lequel le procédé de préparation comprend également une étape de mise en forme de la poudre obtenue. 10. Preparation process according to claim 9 wherein the preparation process also comprises a shaping step of the powder obtained.
1 1 . Procédé de préparation selon la revendication 10 dans lequel l'étape de mise en forme est réalisée par extrusion. 1 1. Preparation process according to claim 10 wherein the forming step is carried out by extrusion.
PCT/EP2016/058821 2015-06-05 2016-04-21 Method for preparing a boehmite having specific crystallites WO2016192894A1 (en)

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