阅读说明：本技术 多孔铝水合物 (Porous aluminium hydrate ) 是由 J·赫尔南德斯 O·拉切尔 于 2018-12-18 设计创作，主要内容包括：本发明涉及一种多孔铝水合物,涉及一种用于制备其的方法,并且涉及其作为中间体在制备氧化铝或基于铝、铈和锆的混合氧化物中的用途。本发明还涉及由该铝水合物获得的氧化铝。(The invention relates to a porous aluminum hydrate, to a method for producing the same, and to the use thereof as an intermediate for producing aluminum oxide or mixed oxides based on aluminum, cerium and zirconium. The invention also relates to alumina obtained from the aluminium hydrate.)

1. Boehmite-based aluminium hydrate optionally comprising at least one additional element chosen from the group formed by lanthanum, praseodymium or a mixture of these two elements, characterized in that, after calcination in air at a temperature of 900 ℃ for 2h, it has:

pore volume in the region of pores having a size of less than or equal to 20nm (from VP_20nm-N₂Represent) so that VP_20nm-N₂：

-greater than or equal to 10% × VPT-N₂More particularly greater than or equal to 15% × VPT-N₂Or even greater than or equal to 20% × VPT-N₂Or even greater than or equal to 30% × VPT-N₂；

-less than or equal to 60% × VPT-N₂；

Pore volume in the region of pores with a size between 40nm and 100nm (from VP)_40-100nm-N₂Represent) so that VP_40-100nm-N₂Greater than or equal to 20% × VPT-N₂More particularly greater than or equal to 25% × VPT-N₂Or even greater than or equal to 30% × VPT-N₂；

·VPT-N₂Represents the total pore volume of the aluminum hydrate after calcination at 900 ℃ for 2h in air;

these pore volumes are determined by nitrogen porosimetry techniques.

2. The aluminum hydrate of claim 1, wherein VPT-N₂Is between 0.65 and 1.20ml/g, more particularly between 0.70 and 1.15ml/g, or between 0.70 and 1.10 ml/g.

3. The aluminum hydrate according to any one of claims 1 and 2, characterized in that it is in the form of a mixture of boehmite and a phase which is not visible in X-ray diffraction, in particular an amorphous phase.

4. Aluminium hydrate according to one of the preceding claims, characterized in that the percentage of crystalline phases is less than or equal to 60%, more particularly less than or equal to 50%.

5. Aluminium hydrate according to one of the preceding claims, characterized in that the boehmite has an average size of crystallites of at most 6.0nm, or even at most 4.0nm, still more particularly at most 3.0 nm.

6. The aluminum hydrate of any of the preceding claims, having a mass of at least 130m after calcination in air at 900 ℃ for 2h²A/g, more particularly at least 150m²(BET) specific surface area in g.

7. The aluminum hydrate of any of the preceding claims, having a mass of at least 80m after first calcination at 940 ℃ for 2h in air and subsequently calcination at 1100 ℃ for 3h in air²A/g, more particularly at least 100m²(BET) specific surface area in g.

8. The aluminum hydrate of any of the preceding claims, comprising an additional element selected from the group formed by lanthanum, praseodymium or a mixture of these two elements, and characterized in that the aluminum hydrate has a thickness of at least 45m after calcination first at 940 ℃ for 2h in air and subsequently at 1200 ℃ for 5h in air²A/g, more particularly at least 50m²(BET) specific surface area in g.

9. An aluminum hydrate comprising residual sulfate, which can be in an amount less than or equal to 0.50% by weight, or less than or equal to 0.20% by weight.

10. An aluminum hydrate comprising residual sodium, the content of residual sodium can be less than or equal to 0.15% by weight, or less than or equal to 0.10% by weight.

11. Aluminium hydrate, according to one of the preceding claims, characterized in that the proportion of the additional element or the total proportion of the additional elements is between 0% and 15%, more particularly between 0% and 10%, still more particularly between 0% and 8%, or even between 2% and 8% by weight.

12. A process for preparing the aluminium hydrate as claimed in any one of claims 1 to 11, comprising the steps of:

(a) introducing into a stirred tank containing an aqueous nitric acid solution:

an aqueous solution (A) comprising aluminium sulphate, optionally one or more of the additional elements in the form of nitrates, and nitric acid;

sodium aluminate aqueous solution (B);

continuously introducing the aqueous solution (a) throughout step (a) and adjusting the introduction flow rate of the solution (B) so that the average pH of the reaction mixture is equal to a target value between 4.0 and 6.0, more particularly between 4.5 and 5.5;

(b) when the entire aqueous solution (a) has been introduced, the introduction of the aqueous solution (B) is continued until a target pH of between 8.0 and 10.5, preferably between 9.0 and 10.0, is reached;

(c) the reaction mixture was then filtered and the recovered solid was washed with water;

(d) the solid resulting from step (c) is then dried.

13. The method of claim 12, wherein the powder obtained at the end of step (d) is milled and/or sieved.

14. Use of an aluminium hydrate according to any one of claims 1 to 11 for the preparation of aluminium oxide.

15. A process for the preparation of alumina, which comprises calcining the aluminium hydrate as claimed in any one of claims 1 to 11 in air.

16. Use of an aluminium hydrate according to any one of claims 1 to 11 for the preparation of a mixed oxide based on aluminium, cerium, zirconium, lanthanum and optionally at least one Rare Earth Metal (REM) other than cerium and lanthanum.

17. A process for preparing mixed oxides based on aluminum, cerium, zirconium, lanthanum and optionally at least one rare earth metal other than cerium and lanthanum (REM), which comprises calcining in air a solid precipitate obtained from a dispersion of an aluminum hydrate as claimed in one of claims 1 to 11 and an aqueous solution comprising the salts of the elements Ce, Zr, La, if appropriate, and REM, if appropriate.

18. A process for the preparation of a mixed oxide based on aluminum, cerium, zirconium, lanthanum and optionally at least one Rare Earth Metal (REM) other than cerium and lanthanum, comprising the following steps:

(i) adding an alkaline aqueous solution to the dispersion formed from the aluminum hydrate as claimed in one of claims 1 to 11 and the aqueous solution S, comprising salts of cerium, zirconium, lanthanum, if appropriate, and the rare earth metal other than cerium and lanthanum, if appropriate, in order to precipitate salts of the constituent elements of the solution S;

(ii) (ii) optionally washing the solid obtained at the end of step (i);

(iii) calcining the solid obtained at the end of step (i) or (ii) in air at a temperature between 700 ℃ and 1200 ℃.

19. A process for the preparation of a mixed oxide based on aluminum, cerium, zirconium, lanthanum and optionally at least one Rare Earth Metal (REM) other than cerium and lanthanum, comprising the following steps:

(i) adding an aqueous solution S to a dispersion formed from an aluminum hydrate as claimed in one of claims 1 to 11 and an aqueous alkaline solution, in order to precipitate a salt of the element of the solution S, the solution S comprising salts of cerium, zirconium, lanthanum, if appropriate, and of the rare earth metal other than cerium and lanthanum, if appropriate;

(ii) (iii) optionally washing the solid obtained at the end of step (ii);

(iii) calcining the solid obtained at the end of step (i) or (ii) in air at a temperature between 700 ℃ and 1200 ℃.

20. A process for the preparation of a mixed oxide based on aluminum, cerium, zirconium, lanthanum and optionally at least one Rare Earth Metal (REM) other than cerium and lanthanum, comprising the following steps:

(i) adding to an alkaline aqueous solution a dispersion formed from the aluminium hydrate as claimed in one of claims 1 to 11 and an aqueous solution S comprising salts of cerium, zirconium, lanthanum, if appropriate, and the rare earth metal other than cerium and lanthanum, if appropriate, in order to precipitate a salt of the solution S;

(ii) (iii) optionally washing the solid obtained at the end of step (ii);

(iii) calcining the solid obtained at the end of step (i) or (ii) in air at a temperature between 700 ℃ and 1200 ℃.

21. The method of one of claims 18 to 20, comprising between steps (ii) and (iii) or (iii) and (iv) a step during which the solid is subjected to heating at a temperature between 70 ℃ and 150 ℃.

22. The method of any of claims 17 to 21, wherein the mixed oxide comprises hafnium.

23. The process according to claim 22, wherein the proportion of hafnium, expressed as oxide equivalents relative to the total weight of the mixed oxide, is less than or equal to 2.0%.

24. A dispersion of an aluminium hydrate as claimed in any one of claims 1 to 11 in an aqueous solution, in particular an acidic aqueous solution, comprising salts of cerium, zirconium, lanthanum, and optionally rare earth metals other than cerium and lanthanum.

25. A dispersion of the aluminium hydrate according to any one of claims 1 to 11 in an aqueous alkaline solution, in particular in an aqueous ammonia solution.

Technical Field

The invention relates to a porous aluminum hydrate, to a method for producing the same, and to the use thereof as an intermediate for producing aluminum oxide or mixed oxides based on aluminum, cerium, zirconium, lanthanum and optionally at least one Rare Earth Metal (REM) other than cerium and lanthanum. The invention also relates to alumina obtained from the aluminium hydrate.

Technical problem

Aluminum hydrates are used to prepare catalysts or catalyst supports. The preparation typically involves shaping the aluminum hydrate and then calcining it to convert it to alumina. The characteristics of the aluminium hydrate influence the characteristics of the alumina obtained and therefore the application characteristics of the catalyst and of the catalyst support. In the case of preparing alumina having a high specific surface area, the aluminum hydrate is usually boehmite.

Mixed oxides based on aluminium, cerium and/or zirconium can be obtained by a process in which aluminium is provided in the form of aluminium hydrate. The aluminum hydrates have to be highly dispersible in the reaction mixture of these processes in order to obtain mixed oxides having good properties, in particular a high heat resistance.

The applicant has developed a specific aluminium hydrate aimed at solving this technical problem.

Background

WO 2006/119549 and WO 2013007242 describe processes for preparing mixed oxides based on aluminum, cerium and zirconium, wherein the aluminum source is a solid compound based on aluminum.

EP 1098848 describes a different boehmite.

Drawings

Figure 1 shows the cumulative pore volume obtained by nitrogen porosimetry for the aluminum hydrates of examples 1 and 3.

Figure 2 shows the pore distribution obtained by nitrogen porosimetry of the aluminum hydrates of examples 1 and 3. The entries in this figure represent the derivative (dV/dlogD) as a function of D (V: pore volume; D: pore size).

Figure 3 shows the X-ray diffraction of the aluminium hydrate of example 1 and of the reference (product corresponding to example B1 of application US 2013/017947). The peaks of boehmite from the document JCPDS 00-021-.

Disclosure of Invention

The invention relates to a boehmite-based aluminium hydrate optionally comprising at least one additional element selected from the group formed by lanthanum, praseodymium or a mixture of these two elements, characterized in that, after calcination in air at a temperature of 900 ℃ for 2h, it has:

pore volume in the region of pores having a size of less than or equal to 20nm (from VP_20nm-N₂Represent) so that VP_20nm-N₂：

-greater than or equal to 10% × VPT-N₂More particularly greater than or equal to 15% × VPT-N₂Or even greater than or equal to 20% × VPT-N₂Or even greater than or equal to 30% × VPT-N₂；

-less than or equal to 60% × VPT-N₂；

Pore volume in the region of pores with a size between 40nm and 100nm (from VP)_40-100nm-N₂Represent) so that VP_40-100nm-N₂Greater than or equal to 20% × VPT-N₂More particularly greater than or equal to 25% × VPT-N₂Or even greater than or equal to 30% × VPT-N₂；

·VPT-N₂Represents the total pore volume of the aluminum hydrate after calcination at 900 ℃ for 2h in air;

these pore volumes are determined by nitrogen porosimetry techniques.

The invention also relates to a process for obtaining this aluminium hydrate, comprising the steps of:

(a) introducing into a stirred tank containing an aqueous nitric acid solution:

an aqueous solution (A) comprising aluminium sulphate, optionally one or more of the additional elements in the form of nitrates, and nitric acid;

sodium aluminate aqueous solution (B);

continuously introducing the aqueous solution (a) throughout step (a) and adjusting the introduction flow rate of the solution (B) so that the average pH of the reaction mixture is equal to a target value between 4.0 and 6.0, more particularly between 4.5 and 5.5;

(b) when the entire aqueous solution (a) has been introduced, the introduction of the aqueous solution (B) is continued until a target pH of between 8.0 and 10.5, preferably between 9.0 and 10.0, is reached;

(c) the reaction mixture was then filtered and the recovered solid was washed with water;

(d) the solid resulting from step (c) is then dried.

The invention also relates to the use of the hydrate for producing aluminum oxide and to the use of the aluminum hydrate for producing mixed oxides based on aluminum, cerium, zirconium, lanthanum and optionally at least one Rare Earth Metal (REM) other than cerium and lanthanum.

Detailed Description

The present invention relates to an aluminium hydrate based on boehmite having a specific pore size (described below). The term "boehmite" is expressed in european nomenclature and is known as gamma hydroxy oxide (gamma-AlOOH). In the present application, the term "boehmite" denotes various aluminium hydrates having a specific crystalline form, which are known to the person skilled in the art. Thus, boehmite can be characterized by X-ray diffraction. The term "boehmite" also covers "pseudoboehmite", which according to some authors is only similar to a particular kind of boehmite and has only a broadening of the characteristic peaks of boehmite (broadaging).

Boehmite is identified by X-ray diffraction of its characteristic peaks. These are given in the document JCPDS 00-021-. It will be noted that the vertex of the peak (020) may be between 13.0 ° and 15.0 °, in particular depending on:

-crystallinity of boehmite;

-the crystallite size of boehmite.

Reference may be made to Journal of Colloidal and Interface Science [ Journal of Colloidal and interfacial Science ],2002,253,308-314 or J.Mater.chem. [ Journal of Material chemistry ],1999,9,549-553 which states that for a certain number of boehmites, the position of the peaks varies depending on the number of layers in the crystal or the size of the crystallites. This apex may more particularly be between 13.5 ° and 14.5 °, or between 13.5 ° and 14.485 °.

The aluminium hydrate may optionally comprise at least one additional element selected from the group formed by lanthanum, praseodymium or a mixture of these two elements. Thus, the aluminum hydrate may comprise La or Pr or La + Pr. The proportion of this element or the total proportion of these elements may be between 0% and 15% by weight, more particularly between 0% and 10% by weight, still more particularly between 0% and 8%. This proportion may be between 2% and 8%. This ratio is given in terms of the weight of the element or elements expressed in oxide form, relative to the total weight of the elements Al, La and/or Pr (which are also expressed in oxide form). To calculate this ratio, lanthanum oxide was considered to be in La₂O₃Form (Pr) of praseodymium oxide₆O₁₁Form (a), and the alumina is in Al₂O₃Form (a). Thus, the aluminum hydrate containing lanthanum in a proportion of 7% is such that it contains La equivalent to 7%₂O₃And Al corresponding to 93%₂O₃. The proportion of one or more additional elements can be determined by: the aluminium hydrate is calcined in air in order to convert it into aluminium oxide and one or more oxides of the additional element(s), the product thus calcined is then etched, for example with a concentrated nitric acid solution, in order to dissolve its elements in the solution, which can then be analysed by techniques known to those skilled in the art, such as for example ICP.

The boehmite contained in the aluminium hydrate may have an average size of crystallites of at most 6.0nm, or even at most 4.0nm, still more particularly at most 3.0 nm. The average size of these crystallites is determined by X-ray diffraction techniques and corresponds to the size of the coherent domain calculated from the full width at half maximum (020) of the line.

To calculate the size of these crystallites, the Debye-Scherrer (Debye-Scherrer) model is used, which is used in a known manner on powders in X-ray diffraction and which enables the size of these crystallites to be determined from the full width at half maximum of the diffraction peak. For more information, reference may be made to appl.crystal. [ applied crystallography ],1978,11,102- "Scherrer after texture year: a surveyy and new stresses in the determination of texture size, j.i. langford and a.j.c. wilson [ six decades shlef: survey to determine crystallite size and some new results ] ". The formula used is as follows:

t: crystallite size

k: shape factor equal to 0.9

λ (lambda): the wavelength of the incident beam (λ 1.5406 angstrom)

H: full width at half maximum of diffraction line

s: the width due to instrument optical defects, depending on the instrument used and the 2 θ (theta) angle;

θ: bragg angle (Bragg angle)

The aluminium hydrates of the present invention may be in the form of a mixture of boehmites (identifiable as described above by X-ray diffraction techniques) and in the form of phases which are not visible in X-ray diffraction, in particular amorphous phases.

The aluminum hydrate may have a crystalline phase (boehmite) percentage of less than or equal to 60%, more particularly less than or equal to 50%. This percentage may be between 40% and 55%, or between 45% and 50%. This percentage is determined in a manner known to those skilled in the art. This percentage can be determined using the following formula: the percent crystallinity is the intensity of the peak (120)/the intensity of the peak (120) of the reference x 100, where the intensity of the peak (120) of the aluminum hydrate and the intensity of the peak (120) of the reference are compared. The reference used in the present application is a product corresponding to example B1 of application US 2013/017947. The measured intensity corresponds to the surface area of the peak (120) above the baseline. These intensities are determined on a diffraction pattern relative to a baseline taken within an angular range of 2 theta between 5.0 deg. and 90.0 deg.. The baseline is automatically determined using software for analyzing the diffractogram data.

The aluminum hydrate has a specific porosity. Thus, after calcination in air at 900 ℃ for 2 hours, the aluminium hydrate has a pore volume (from VP) in the region of pores having a size of less than or equal to 20nm_20nm-N₂Represent) so that VP_20nm-N₂Greater than or equal to 20% × VPT-N₂More particularly greater than or equal to 25% × VPT-N₂Or even greater than or equal to 30% × VPT-N₂. In addition, VP_20nm-N₂Less than or equal to 60 percent × VPT-N₂。

Furthermore, after calcination in air at 900 ℃ for 2 hours, the aluminium hydrate has a pore volume (from VP) in the region of pores having a size between 40nm and 100nm_40-100nm-N₂Represent) so that VP_40-100nm-N₂Greater than or equal to 15% × VPT-N₂More particularly greater than or equal to 20% × VPT-N₂Or even greater than or equal to 25% × VPT-N₂Or even greater than or equal to 30% × VPT-N₂. In addition, VP_40-100nm-N₂Can be less than or equal to 65% × VPT-N₂。

The aluminium hydrate of the invention may have a total pore volume (VPT-N) of between 0.65 and 1.20ml/g, more particularly between 0.70 and 1.15ml/g, or between 0.70 and 1.10ml/g, after calcination in air at 900 ℃ for 2 hours₂). It will be noted that the pore volume thus measured is mainly formed by pores whose diameter is less than or equal to 100 nm.

The aluminium hydrate may have a thickness of at least 200m²A/g, more particularly at least 250m²Specific surface area in g. The specific surface area can be between 200 and 400m²Between/g. The specific surface area is understood to mean the BET specific surface area obtained by nitrogen adsorption. The specific surface area is as conventionally understood by those skilled in the art. The surface area is based on Bruna's Brunauer-Emmett-Teller) method (BET method) determined by adsorption of nitrogen on the powder. This method is described in ASTM D3663-03 (re-approval in 2015). This method is also described in "The Journal of The American chemical society [ Journal of The American chemical society]60,309(1938) ".

The pore volumes given in this application were determined by nitrogen porosimetry techniques. For porosity or specific surface area measurements, samples are pretreated at high temperature and/or under vacuum in order to eliminate surface volatile species (such as, for example, H)₂O, etc.). For example, heating at 200 ℃ for 2 hours may be applied to the sample.

Further, the aluminum hydrate may have at least 130m after calcination at 900 ℃ for 2 hours in air²A/g, more particularly at least 150m²(BET) specific surface area in g. The specific surface area can be between 130 and 220m²Between/g.

After calcination at 940 ℃ for 2 hours in air, followed by calcination at 1100 ℃ for 3 hours in air, the aluminum hydrate may have a thickness of at least 80m²A/g, more particularly at least 100m²(BET) specific surface area in g. The specific surface area can be between 80 and 120m²Between/g.

When the aluminum hydrate contains at least one additional element as described above, the aluminum hydrate will be able to have high heat resistance. Thus, after calcination at 940 ℃ for 2 hours in air, followed by calcination at 1200 ℃ for 5 hours in air, the aluminum hydrate may have a thickness of at least 45m²A/g, more particularly at least 50m²(BET) specific surface area in g. The specific surface area can be between 45 and 75m²Between/g.

In the present application, the expression "aluminium hydrate has" for characterizing it after calcination in air at a temperature x ℃ for y hours, even if the measured characteristic (specific surface area or pore volume) is that of the product resulting from the calcination of the aluminium hydrate.

The aluminum hydrate may contain residual sulfate. The content of residual sulfate may be less than or equal to 0.50% by weight, or less than or equal to 0.20% by weight. The sulfate content may be greater than or equal to 50 ppm. This content is expressed as sulphate in relation to the elementWeight of the weight of oxides of Al and optionally one or more additional elements. Thus, a residual sulphate content of 0.5% corresponds to 0.5g of SO₄Oxide (Al) 100g₂O₃、Pr₆O₁₁、La₂O₃). Methods for determining the sulfate content within this concentration range are known to those skilled in the art. For example, microanalysis techniques can be used. Accordingly, a model Horiba EMIA 320-V2 microanalysis device may be used.

The aluminum hydrate may contain residual sodium. The content of residual sodium may be less than or equal to 0.15% by weight, or less than or equal to 0.10% by weight. The sodium content may be greater than or equal to 50 ppm. The content is expressed as Na₂The weight of O relative to the weight of the oxides of the element Al and optionally one or more additional elements. Thus, a residual sodium content of 0.15% corresponds to 0.15g of Na₂O/100g oxide (Al)₂O₃、Pr₆O₁₁、La₂O₃). Methods for determining sodium content within this concentration range are known to those skilled in the art. For example, plasma emission spectroscopy techniques can be used.

The aluminium hydrate of the invention is obtained by a process comprising the steps of:

(a) introducing into a stirred tank containing an aqueous nitric acid solution:

an aqueous solution (A) comprising aluminium sulphate, optionally one or more of the additional elements in the form of nitrates, and nitric acid;

sodium aluminate aqueous solution (B);

continuously introducing the aqueous solution (a) throughout step (a) and adjusting the introduction flow rate of the solution (B) so that the average pH of the reaction mixture is equal to a target value between 4.0 and 6.0, more particularly between 4.5 and 5.5;

(b) when the entire aqueous solution (a) has been introduced, the introduction of the aqueous solution (B) is continued until a target pH of between 8.0 and 10.5, preferably between 9.0 and 10.0, is reached;

(c) the reaction mixture was then filtered and the recovered solid was washed with water;

(d) the solid resulting from step (c) is then dried to give the hydrate of the invention.

The aqueous solution (a) is obtained from aluminium sulphate and nitric acid. The aqueous solution (a) may also comprise one or more additional elements in the form of nitrates. The alumina concentration of the aqueous solution (a) may be equivalent to between 1% and 5% by weight.

The aqueous solution (B) is obtained from sodium aluminate. It preferably has no precipitated alumina. The sodium aluminate preferably has a Na of greater than or equal to 1.2, for example between 1.20 and 1.40₂O/Al₂O₃A ratio.

The aqueous solution (a) is continuously introduced into the stirred tank throughout step (a). The duration of the introduction of the aqueous solution (a) may be between 10min and 2 h. The aqueous solution (B) is introduced simultaneously with the aqueous solution (a) at a flow rate adjusted so that the average pH of the reaction mixture is equal to the target value. The target value is between 4.0 and 6.0, more particularly between 4.5 and 5.5. "average pH" is understood to mean the arithmetic mean of the pH values recorded continuously during step (a). Since the flow rate of the aqueous solution (B) is regulated, it is possible that it is zero at some point, that is to say only the aqueous solution (A) is introduced into the stirred tank.

During step (B), when the entire aqueous solution (a) has been introduced into the reactor at the end of step (a), the introduction of the aqueous solution (B) is continued until a target pH of between 8.0 and 10.5, preferably between 9.0 and 10.0, is reached. The duration of step (b) may be variable. This duration may be between 5min and 2 hours.

The temperature of the aqueous nitric acid solution initially present in the tank may be between 50 ℃ and 80 ℃. The temperature of the reaction mixture during step (a) may also be between 50 ℃ and 80 ℃. The temperature of the reaction mixture during step (b) may also be between 50 ℃ and 80 ℃.

During step (c), the reaction mixture (in slurry form) is filtered. The solids recovered on the filter can be washed with water. Hot water having a temperature of at least 50 ℃ may be used.

During step (d), the solid resulting from step (c) is dried using any drying technique known to those skilled in the art. Spray drying can be effectively utilized. The aluminum hydrate is in the form of a dry powder.

The powder may optionally be milled and/or sieved in order to obtain a powder with a fixed particle size. The milled or unground aluminium hydrate may be in the form of a powder having a mean diameter d50 (median) of between 1.0 and 40.0 μm, more particularly between 3.0 and 30.0 μm, d50 being determined by laser diffraction on a volume distribution.

The aluminum hydrate of the present invention can be used for preparing alumina. The alumina is obtained by calcining aluminum hydrate in air. The invention also relates to a process for obtaining alumina by calcining the aluminium hydrate of the invention. The calcination temperature is at least 500 ℃. It may be between 500 ℃ and 1100 ℃. The duration of the calcination may be between 30 minutes and 10 hours.

The alumina of the present invention has the same porosity characteristics as aluminum hydrate. The alumina may have a thickness of at least 80m after calcination in air at 1100 ℃ for 3 hours²A/g, more particularly at least 100m²Specific surface area in g. The specific surface area can be between 80 and 120m²Between/g. When the alumina contains at least one additional element as described above, the alumina will be able to have high heat resistance. Thus, the alumina may have a thickness of at least 45m after calcination at 1200 ℃ for 5 hours in air²A/g, more particularly at least 50m²Specific surface area in g. The specific surface area can be between 45 and 75m²Between/g.

The alumina of the present invention can be advantageously used as a catalyst support. The alumina can be used in particular as a support for at least one noble metal for pollution control catalysis of motor vehicles. In the case of so-called "three-way" catalysis for gasoline vehicles, alumina containing at least one additional element will advantageously be able to be used due to its thermal stability at high temperatures, typically above 1100 ℃. The porous alumina obtained according to the present invention will advantageously be used under conditions in which a high flow rate of gas is passed through the catalyst. Alumina can also be used in pollution control applications for engines operating under combustion conditions (diesel or gasoline). In the case of diesel vehicles, which are generally subjected to low thermal stresses, it will be possible to use pure alumina with or without additional elements.

The aluminium hydrates of the present invention can also be used for the preparation of mixed oxides based on aluminium, cerium, zirconium, lanthanum and optionally at least one Rare Earth Metal (REM) other than cerium and lanthanum. REM may for example be selected from yttrium, neodymium or praseodymium.

In the mixed oxides, the above-mentioned elements Al, Ce, La, REM and Zr are generally present in the form of oxides. Thus, a mixed oxide may be defined as a mixture of oxides. However, it is not excluded that these elements can be present at least partially in the form of hydroxides or oxyhydroxides. The proportions of these elements can be determined using customary analytical techniques in the laboratory, in particular plasma torches and X-ray fluorescence.

Examples of such mixed oxides may for instance comprise the above elements in the following proportions, expressed in weight of oxide:

between 20% and 60% aluminium;

between 15% and 35% cerium;

between 1% and 10% lanthanum;

between 0% and 10% of rare earth metals other than cerium and lanthanum, with the proviso that: if the mixed oxide contains more than one rare earth metal other than cerium and lanthanum, this proportion applies to each of these rare earth metals, and the sum of the proportions of these rare earth metals is still less than 15%;

between 15% and 50% zirconium.

The mixed oxide may also comprise hafnium, the proportion of which may be less than or equal to 2.0% expressed in oxide equivalents relative to the total weight of the mixed oxide. These proportions are given in weight of oxide equivalents relative to the total weight of the mixed oxide. Unless otherwise indicated, these proportions are given by weight of oxides. For these calculations, the cerium oxide is considered to be in the form of a cerium oxide and other rare earthsThe oxide of the metal is in REM₂O₃Form (REM stands for rare earth metal) of (iii) other than praseodymium (in Pr)₆O₁₁A formal representation of). Zirconium oxide and hafnium oxide at ZrO₂And HfO₂In the form of (1). Aluminum with Al₂O₃The form exists.

The process for obtaining the mixed oxide comprises calcining in air a solid precipitate obtained from a dispersion of aluminium hydrate and a solution comprising salts of the elements Ce, Zr, La (if appropriate) and REM (if appropriate).

One particular process (P1) for preparing mixed oxides of the elements Al, Ce, Zr, La and optionally REM may for example comprise the following steps:

(i) adding an alkaline aqueous solution to a dispersion formed of an aluminum hydrate and an aqueous solution S containing salts of cerium, zirconium, lanthanum (if appropriate) and rare earth metals other than cerium and lanthanum (if appropriate), so as to precipitate salts of the constituent elements of the solution S;

(ii) (ii) optionally washing the solid obtained at the end of step (i);

(iii) calcining the solid obtained at the end of step (i) or (ii) in air at a temperature between 700 ℃ and 1200 ℃.

One particular process (P2) for preparing mixed oxides of the elements Al, Ce, Zr, La and optionally REM may comprise the following steps:

(i) adding an aqueous solution S to a dispersion formed from an aluminium hydrate and an aqueous alkaline solution, in order to precipitate a salt of an element of the solution S, the solution S comprising salts of cerium, zirconium, lanthanum (if appropriate) and rare earth metals (if appropriate) other than cerium and lanthanum;

(ii) (iii) optionally washing the solid obtained at the end of step (ii);

(iii) calcining the solid obtained at the end of step (i) or (ii) in air at a temperature between 700 ℃ and 1200 ℃.

One particular process (P3) for preparing mixed oxides of the elements Al, Ce, Zr, La and optionally REM may comprise the following steps:

(i) adding to an alkaline aqueous solution a dispersion formed of aluminium hydrate and an aqueous solution S comprising salts of cerium, zirconium, lanthanum (if appropriate) and rare earth metals other than cerium and lanthanum (if appropriate), in order to precipitate a salt of the solution S;

(ii) (iii) optionally washing the solid obtained at the end of step (ii);

(iii) calcining the solid obtained at the end of step (i) or (ii) in air at a temperature between 700 ℃ and 1200 ℃.

Step (i) in which the aqueous solution is contacted with the dispersion is carried out under stirring. Furthermore, in this step, the term "adding" may more particularly denote an operation in which an aqueous solution is introduced into the dispersion or a dispersion is introduced into an aqueous solution, respectively, in particular as a vessel base (vessel heel).

Between steps (ii) and (iii) or (iii) and (iv), an intermediate step may be provided during which the solid is subjected to heating at a temperature between 70 ℃ and 150 ℃. This heating is preferably carried out on solids dispersed in water.

The salts of the elements Ce, Zr, La and REM may be selected from the group formed by nitrates, chlorides and acetates. It will be noted that in the case where REM represents lanthanum and/or praseodymium, these elements may be provided in whole or in part by aluminium hydrate. The aqueous alkaline solution may be, for example, an aqueous ammonia solution. Examples of such processes for preparing mixed oxides are given in US 9289751, and also in applications WO 13007272 and WO 14201094.

The aluminium hydrate enables a homogeneous dispersion to be obtained. This makes it possible to obtain a mixed oxide having good characteristics, particularly heat resistance. Thus, the mixed oxide may have a thickness of more than 30m after calcination at 1100 ℃ for 5h in air²BET specific surface area in g.

The invention also relates to a dispersion of an aluminium hydrate in an aqueous solution, in particular in an acidic aqueous solution, comprising salts of cerium, zirconium, lanthanum and optionally rare earth metals other than cerium and lanthanum. The invention also relates to a dispersion of aluminium hydrate in an aqueous alkaline solution, in particular in an aqueous ammonia solution.

Examples of the invention

For porosity or specific surface area measurements, the samples were pretreated at 200 ℃ for 2H in order to eliminate surface volatile species (such as for example H)₂O, etc.).

The specific surface area was automatically determined using a Tristar II 3020 device from mcmamericack (Micromeritics) following the instructions recommended by the manufacturer.

The pore size measurement was determined in an automated manner using Tristar II 3020 from mcmmerrilicak, inc, from which the pore volume was derived. The barrett, georgena and herond (Barett, Joyner and Halenda) (BJH) method with the Harkins-ru law (Harkins-Jura law) was used. Analysis of the results was performed on the desorption curve.

X-ray diffraction analysis was obtained using a copper source (CuK α 1, λ 1.5406 a). An X 'Pert Pro goniometer from panagical, equipped with a copper source, a rotator sample holder, and an X' Celerator 1D detector with an angular width of 2.122 ° was used. The device was equipped with a nickel filter and programmable slits on the front to illuminate a constant square surface area with a side length of 10 mm.

Example 1: aluminium hydrate according to the invention with 6.2% lanthanum (93.8% Al)₂O₃-6.2％La₂O₃) Preparation of

In a stirred tank, solution (a) was prepared by introducing: 34.7kg deionized water, 10.95kg aluminum sulfate solution (with alumina (Al)₂O₃) 8.31% concentration by weight), 1.43kg of lanthanum nitrate solution (having a concentration by La)₂O₃26.9% concentration by weight), and 4.97kg of 68% nitric acid solution by weight. The solution (B) is a sodium aluminate solution having a concentration based on alumina (Al)₂O₃) 24.9% by weight.

71kg of deionized water were introduced into a stirred reactor (250 rpm; stirrer with four blades inclined at 45 ℃). The reactor was then heated until a temperature of 65 ℃ was reached. This temperature is maintained throughout the reaction. A 69% nitric acid solution was introduced into the stirred reactor until a pH of 3 was reached.

In step (a), the solution (a) and the solution (B) are simultaneously introduced into the stirred reactor through an introduction tube near the stirrer. Solution (A) was introduced at a flow rate of 1.05 kg/min. Solution (B) was introduced at a flow rate such that a pH of 5 was reached within 3 minutes.

The flow rate of solution (A) was kept constant at 1.05kg/min and the flow rate of solution (B) was adjusted so as to maintain the pH at a value of 5.1 for 46 minutes.

In step (B), the introduction of solution (a) was stopped and the addition of solution (B) was continued until a pH of 10 was reached within 15 minutes.

In step (c), the reaction slurry is then poured onto a vacuum filter. At the end of the filtration, the filter cake was washed with deionized water at 60 ℃. The filter cake has a titanium oxide (Al)₂O₃-La₂O₃) A solids content of 11% by weight. The filter cake was then redispersed in deionized water to obtain a concentration close to that of the pro-oxide (Al)₂O₃-La₂O₃) 8% by weight of (c).

In step (d), the suspension is atomized to obtain a dry lanthanum-doped aluminum hydrate powder. The loss on ignition of the powder is obtained by weight loss after calcination at 950 ℃ -2 hours. The loss on ignition was 31.2% by weight. The aluminum hydrate powder contained Al in an amount equivalent to 64.5% by weight₂O₃And 4.2% by weight of La₂O₃. The powder has a particle size of 344m²BET surface area in g.

Example 2: has a composition of 93.8% Al₂O₃-6.2％La₂O₃Preparation of alumina

The powder of example 1 was calcined in air at 940 ℃ for 2 hours to obtain a lanthanum-doped alumina powder. The temperature was increased at a rate of 2.5 deg.C/min.

Example 3: aluminum hydrate with 6.2% La (93.8% Al)₂O₃-6.2％La₂O₃) Preparation of

In a stirred tank, solution (a) was prepared by introducing: 34.7kg deionizationWater, 10.95kg of aluminum sulfate solution (with alumina (Al)₂O₃) 8.31% concentration by weight), 1.43kg of lanthanum nitrate solution (having a concentration by La)₂O₃26.9% concentration by weight), and 4.96kg of 68% nitric acid solution. Solution (B) was a sodium aluminate solution at a concentration of 24.9% by weight of alumina.

71kg of deionized water were introduced into a stirred reactor (250 rpm; stirrer with four blades inclined at 45 ℃). The reactor was then heated until a temperature of 65 ℃ was reached. This temperature is maintained throughout the reaction. A 69% nitric acid solution was introduced into the stirred reactor until a pH of 3 was reached.

In step (a), the solution (a) and the solution (B) are simultaneously introduced into the stirred reactor through an introduction tube near the stirrer. Solution (A) was introduced at a flow rate of 1.05 kg/min. Solution (B) was introduced at a flow rate such that a pH of 4.4 was achieved in 3 minutes. The flow rate of solution (A) was kept constant at 1.05kg/min and the flow rate of solution (B) was adjusted so as to maintain the pH at a value of 4.4 for 46 minutes.

In step (B), the introduction of solution (a) was stopped and the addition of solution (B) was continued until a pH of 10 was reached within 15 minutes.

In step (c), the reaction slurry is then poured onto a vacuum filter. At the end of the filtration, the filter cake was washed with deionized water at 60 ℃. The filter cake has a titanium oxide (Al)₂O₃-La₂O₃) 13% solids content by weight. The filter cake was then redispersed in deionized water to obtain a concentration close to that of the pro-oxide (Al)₂O₃-La₂O₃) 8% by weight of (c).

In step (d), the suspension is atomized to obtain a lanthanum-doped aluminum hydrate powder. The loss on ignition of the powder is obtained by weight loss after calcination at 950 ℃ -2 hours. The loss on ignition was 38.5% by weight. The aluminum hydrate powder contained Al in an amount equivalent to 57.8% by weight₂O₃And 3.8% by weight of La₂O₃. The powder has a particle size of 259m²BET surface area in g.

Example 4: has a composition of 93.8％Al₂O₃-6.2％La₂O₃Preparation of alumina

The powder of example 3 was then calcined in air at 940 ℃ for 2 hours to obtain a lanthanum-doped alumina powder. The temperature was increased at a rate of 2.5 deg.C/min.

The characteristics of the atomized powder and the calcined powder are reported in tables I and II.

Example 5: preparation of the aluminum hydrate of example 1 with composition Al₂O₃(30％)-ZrO₂(35％)-CeO₂(27％)-La₂O₃(4％)-Y₂O₃(4%) (by weight%) use in mixed oxides

By introducing 357g of water, 114g of zirconyl nitrate solution ([ ZrO ] O) into a tank stirred by means of a stirrer (with four blades inclined at 45 DEG)₂]260 g/l; density 1.406), 56g Ce^IIINitrate solution ([ CeO ]₂]496 g/l; density 1.714), 4.4g lanthanum nitrate solution ([ La)₂O₃]472 g/l; density 1.711 and 16g yttrium nitrate solution ([ Y ]₂O₃]208.5 g/l; density 1.392) to prepare a solution based on the precursor nitrate.

Next, 2.3g of 69% by weight of nitric acid was added to the obtained solution to obtain a precursor solution. To this solution, while still stirring, a solution containing an amount equivalent to 64.5% by weight of alumina (18g of Al) was added by means of a spatula₂O₃) And 4.2% by weight of La₂O₃(1.17g) 28g of the aluminum hydrate of example 1. The mixture was stirred until a precursor mixture in the form of a homogeneous dispersion was obtained. Next, 5.3g of a 9.8mol/l aqueous hydrogen peroxide solution was added. The precursor mixture was kept under stirring.

The precursor mixture was introduced within 60min into a reactor stirred by a stirrer (575rpm) with four blades inclined at 45 °, which reactor contained 500ml of a 2mol/l aqueous ammonia solution at ambient temperature.

At the end of the addition of the precursor mixture, the mixture was heated to a temperature of 95 ℃ and maintained at this temperature for 30 min. The mixture was then cooled to a temperature below 40 ℃.12 g of lauric acid was added to this cooled mixture while stirring at 650 rpm. This stirring was maintained for 30 min.

The mixture was filtered under vacuum and the filter cake was washed with 720g of aqueous ammonia solution pH 9. The obtained wet cake is then introduced into a muffle furnace. The temperature of the furnace was increased at a rate of 4 ℃/min until 950 ℃ was reached; this temperature was then maintained for 4 h. At the end of this calcination in air, a mixed oxide is obtained. The recovered mixed oxide was then ground using a mortar.

Specific surface area of mixed oxide after calcination in air for 4 h:

950℃：82m²/g

1000℃：68m²/g

1100℃：40m²/g

example 6: preparation of the aluminum hydrate of example 2 with composition Al₂O₃(30％)-ZrO₂(35％)-CeO₂(27％)-La₂O₃(4％)-Y₂O₃(4%) (by weight%) use in mixed oxides

By introducing 357g of water, 114g of zirconyl nitrate solution ([ ZrO ] O) into a tank stirred by means of a stirrer (with four blades inclined at 45 DEG)₂]260 g/l; density 1.406), 56g Ce^IIINitrate solution ([ CeO ]₂]496 g/l; density 1.714), 4.4g lanthanum nitrate solution ([ La)₂O₃]472 g/l; density 1.711 and 16g yttrium nitrate solution ([ Y ]₂O₃]208.5 g/l; density 1.392) to prepare a solution based on the precursor nitrate.

Next, 2.3g of 69% by weight of nitric acid was added to the obtained solution, so as to obtain a precursor solution. To this solution, while still stirring, a solution containing an amount equivalent to 57.8% by weight of alumina (18 gAl) was added by means of a spatula₂O₃) And 3.8% by weight of La₂O₃(1.18g) of 31.1g of the aluminum hydrate of example 3. The mixture was stirred until a precursor mixture in the form of a homogeneous dispersion was obtained. Next, 5.3g of a 9.8mol/l aqueous hydrogen peroxide solution was added. The precursor mixture was kept under stirring.

500ml of a 2mol/l aqueous ammonia solution are introduced into a stirred reactor (600 rpm; stirrer with four blades inclined at 45 ℃). The precursor mixture was introduced into the stirred reactor within 60 min. The process is carried out at ambient temperature. At the end of the addition of the precursor mixture, the reaction medium is heated to a temperature of 95 ℃ and maintained at this temperature for 30 min. The reaction medium is then cooled to a temperature below 40 ℃.12 g of lauric acid was added to this cooled mixture while stirring at 500 rpm. This stirring was maintained for 30 min.

The reaction medium is filtered under vacuum and the filter cake is then washed with 1l of aqueous ammonia (pH 9). The obtained wet cake is then introduced into a muffle furnace. The temperature of the furnace was raised to 950 ℃ at a rate of 4 ℃/min; this temperature was maintained for 4 h. At the end of this calcination in air, a mixed oxide is obtained. The recovered mixed oxide was then ground using a mortar.

Specific surface area of mixed oxide after calcination in air for 4 h:

950℃：79m²/g

1000℃：66m²/g

1100℃：41m²/g

table II: characteristics of alumina (aluminum hydrate powder calcined in air at 940-2 h)