PROCESS FOR PRODUCING Mg-CONTAINING NON-Al ANIONIC CLAY

ES 2 211 596 T3

DESCRIPTION

Procedure to obtain anionic clays without Mg that contain Al.

Background of the invention

This invention relates to the preparation of Mg-free anionic clays containing Al. Anionic clays have a crystalline structure consisting of positively charged layers built with specific combinations of metal hydroxides, among which are anions and water molecules. Hydrotalcite is an example of a naturally occurring anionic clay, in which carbonate is the predominant anion present. Meixnerite is an anionic clay in which OH^- it is the predominant anion present.

In hydrotalcite-like anionic clays, the brucite-like main layers are formed by octahedra alternating with interlayers, in which water molecules and anions, more particularly carbonate ions, are distributed. The interlayers contain anions such as NO3^- , OH, Cl^-, Br^-, I^-, SO4^2-, SiO3^2-, CrO4^2-, BO3^2-, MnO4^-, HgaO3^2- , HVO4^2- , ClO4 ^- , BO₃^2- , stacking anions such as V10 O28 ^-6 and MO7O24^6- , monocarboxylates such as acetate, dicarboxylates such as oxalate, alkyl sulfonates such as lauryl sulfonate.

It should be noted that a variety of terms are used to describe the material referred to in this patent as anionic clay. Similar to hydrotalcite and double-layered hydroxide are interchangeable expressions for those skilled in the art. In this patent application, we refer to the materials as anionic clays, encompassing within such term hydrotalcite-like materials and double-layered hydroxides.

The most commonly described anionic clays are the Mg-Al anionic clays. In the prior art, the emphasis is generally placed on this type of anionic clays, whereas anionic clays without Mg, which contain Al, are only mentioned in passing, even though the chemistry of their preparation and their properties may be very different and unpredictable. Anionic Mg-Al clays are suitable for many applications in the fields of absorbents and catalysts, but Mg-free anionic clays that contain Al have specific applications in these fields.

The preparation of anionic clays has been described in many prior art publications.

Two important reviews on anionic clays chemistry have been published, summarizing the available synthesis methods for the synthesis of anionic clays, F. Cavan et al "Hydrotalcitetype anionic clays: Preparation, Properties and Applications" Catalysis Today, 11 ( 1991) Elsevier Science Publishers BV Amsterdam.

JP Besse and others "Anionic clays: trends in pillaring chemistry, its synthesis and microporus solids" (1992), 2, 108, editors: MI Ocelli, HE Robson, Van Nostrand Reinhold, NY

These reviews basically describe two types of anionic clay preparation. The most conventional method is the co-precipitation (in Besse's review, this method is called the salt-base method) of a soluble divalent metal salt and a soluble trivalent metal salt, optionally followed by hydrothermal treatment or aging, to increase the crystal size. The second method is the salt-oxide method, in which a divalent metal oxide is reacted at atmospheric pressure with a soluble trivalent metal salt, followed by aging at atmospheric pressure. This method has only been described for the use of ZnO and CuO in combination with soluble trivalent metal salts.

For working with anionic clays, the reference of the following articles is provided:

Helv. Chim. Acta, 25, 106-137 and 555-569 (1942)

J. Am. Ceram. Soc., 42, n ° 3, 121 (1959)

Chemistry Letters (Japan), 843 (1973)

Clays and Clay Minerals, 23, 369 (1975)

Clays and Clay Minerals, 28, 50 (1980)

Clays and Clay Minerals, 34, 507 (1996)

Materials Chemistry and Physiscs, 14, 569 (1986)

In addition, there is an extensive body of patent literature on the use of anionic clays and the procedures for their preparation.

European Patent Application 0536879 describes a method for introducing pH-dependent anions into clay. Clay is prepared by adding a solution of Al (NO3) 3 and Mg (NO3) 2 to a basic solution containing borate anions. The product is then filtered, washed repeatedly with water, and dried overnight. Additionally, Zn / Mg mixtures are used.

In US Patent 3,796,792 to Miyata et al, entitled "Composite Metal Hydroxides", a range of materials is prepared in which a wide range of cations are incorporated, including Sc, La, Th, In, etc. . In the examples given, solutions of divalent and trivalent cations are prepared and mixed with a base to cause their precipitation. The resulting products are filtered, washed with water and dried at 80 ° C. Example 1 refers to Mg and Sb and Example 3 to Mg and Bi. Other examples are given, and in each case they are used to prepare solutions prior to precipitation of the anionic clay at high pH.

A large number of preparation examples are also provided in US Patent 3,879,523 to Miyata, entitled "Composite Metal Hydroxides". The underlying chemistry, however, is again based on the co-precipitation of soluble salts, followed by washing and drying. It is important to emphasize that washing is a necessary part of such preparations, because a basic environment needs to be created for the co-precipitation of metal ions in a basic solution, and this is provided by NaOH / Na2CO3 solutions. Residual sodium, for example, can have a significant deleterious effect on the subsequent performance of the product as a catalyst or oxide support.

Very similar procedures are again described in US Patent 3,879,525 (Miyata).

In US Patent 4,351,814 to Miyata et al., A method for preparing fibrous hydrotalcites is described. Such materials differ in structure from normal plate-like morphology. The synthesis again includes soluble salts. For example, an aqueous solution of a mixture of MgCl2 and CaCl2 is prepared and suitably aged. From this, a needle-like product Mg2 (OH) 3 Cl.4H2O precipitates. A separate solution of sodium aluminate is then reacted in an autoclave with the solid Mg2 (OH) 3Cl.4H2O, and the product is filtered again, washed with water and dried.

In US Patent 4,458,026 to Reichle, at

ES 2 211 596 T3 which describes heat-treated anionic clays as catalysts for aldol condensation reactions, again use is made of solutions of aluminum and magnesium nitrate salts. Said solutions are added to a second solution of NaOH and Na2 CO3. After precipitation, the suspension is filtered and washed twice with distilled water before drying at 125 ° C.

In US Patent 4,656,156 to Misra, the preparation of a new absorbent based on the mixture of alumina and hydrotalcite is described. Hydrotalcite is prepared by reacting activated MgO (prepared by activating a magnesium compound such as magnesium carbonate or magnesium hydroxide) with aqueous solutions containing aluminate, carbonate and hydroxyl ions. As an example, the solution is prepared with NaOH, Na2CO3 and Al2O3. In particular, the synthesis includes the use of industrial Bayer liquor as a source of Al. The resulting products are washed and filtered before drying at 105 ° C.

In US Patent 4,904,457 to Misra, a method for producing hydrotalcites in high yield is described by reacting activated magnesia with an aqueous solution containing aluminate, carbonate and hydroxyl ions.

The methodology is repeated in US Patent 4,656,156.

In US Patent 5,507,980 to Kelkar et al., A process for preparing novel catalysts, catalyst supports, and absorbents, comprising hydrotalcite-like synthetic binders, is described. The synthesis of the typical hydrotalcite in leaf form includes reacting pseudoboehmite to which acetic acid has been added, to peptize the pseudo-boehmite. This is then mixed with magnesia. More importantly, the patent abstract clearly states that the invention utilizes organic monocarboxylic acids such as formic, propionic and isobutyric acid. In this patent, conventional approaches to preparing hydrotalcites are presented.

In US Patent 6,539,861, a process for preparing a catalyst for the production of synthesis gas, based on hydrotalcites, is described.

The preparation method is based, again, on the co-precipitation of soluble salts by mixing with a base, for example, by adding a solution of RhCl3, Mg (NO3) 2 and Al (NO3) 3 to a Na2CO3 and NaOH solution.

Also, in US Patent 5,399,537 to Bhattacharyya, on the preparation of hydrotalcite-based nickel-containing catalysts, use is made of the co-precipitation of soluble salts of magnesium and aluminum.

In US Patent 5,591,418 to Bhattacharyya, a catalyst is prepared for removing sulfur oxides or nitrogen oxides from a gaseous mixture, by calcining an anionic clay, said anionic clay having been prepared by co -precipitation of a solution of Mg (NO3) 2, Al (NO3) 3 and Ce (NO3) 3. The product is again filtered and washed repeatedly with deionized water.

In US Patent 5,114,898 / WO 9110505 to Pinnavala et al., Double layer hydroxide absorbents are described for the removal of sulfur oxides from combustion waste gases, said double layer hydroxide being prepared by reacting a solution of nitrates or chlorides of Al and Mg, with a solution of NaOH and Na2CO3. In the

US Patent 5,079,203 / WO 9118670 describes double chain hydroxides interspersed with polyoxo-anions, in which the precursor clay was prepared by co-precipitation techniques.

In US Patent 5,578,286, in the name of Alcoa, a process for the preparation of meixnerite is described. Said meixnerite can be contacted with a dicarboxylate or polycarboxylate anion to form a hydrotalcite-like material.

In US Patents 4,946,581 and 4,952,382 to van Broekhoven, the co-precipitation of soluble salts such as Mg (NO3) 2 and Al (NO3) 3 with, or without the incorporation of salts of rare earths, for the preparation of anionic clays as catalyst components and additives. A variety of di and trivalent anions and cations are described.

US Patent 5,518,704 describes the preparation of a nickel-Al hydrotalcite prepared from peptized pseudoboehmite and nickel hydroxide.

As indicated in the description of the prior art provided above, there are many applications for anionic clays.

These include but are not limited to: catalysts, absorbents, drilling muds, catalyst carriers and vehicles, extenders and applications in the medical field. In particular van Broekhoven has described its use in SOx depletion chemistry.

Due to the wide variety of large-scale commercial applications of these materials, new processes using inexpensive alternative raw materials are needed to provide a more economical and environmentally compatible process for preparing anionic clays. In particular, from the prior art previously described, it can be concluded that the preparation process can be improved in the following ways: the use of a cheaper source of reactants, procedures for a simpler handling of the reactants, in such a way that no washing or filtration is necessary, eliminating the filtration problems associated with these fine particulate materials, avoiding alkali metals (which can be particularly disadvantageous for some catalytic applications): Furthermore, in the drying or calcination processes of the anionic clay prepared by the above techniques, gaseous emissions of nitrogen oxides, halogens, sulfur oxides, etc., occur, which cause environmental pollution problems.

Summary of the invention

Our invention includes processes for producing Al-containing Mg-free anionic clays, using relatively inexpensive starting materials, in a simple process, including reaction mixtures with or without stirring in water, optionally under hydrothermal conditions. Such procedures can be performed with standard laboratory or industrial equipment. More specifically, no washing or filtration is necessary, and a wide range of M (II) / Al (III) ratios is possible in the reaction product.

This invention includes the use of a source of aluminum and a source of divalent metal in sus3

ES 2 211 596 T3 aqueous pensions, which are reacted, optionally under hydrothermal conditions, and the reaction mixture results in the direct formation of a Mg-free anionic clay containing Al. The powder X-ray diffraction pattern (PXRD ), suggests that the product is comparable to anionic clays prepared by other standard methods. The physical and chemical properties of the product are also comparable to those of anionic clays prepared by other conventional methods. The overall process of this invention is very flexible, allowing a wide variety of anionic clay compositions and anionic clay-like materials, including for example the preparation of carbonate, hydroxide and other anions in an economical and environmentally friendly manner. . The process can be carried out as a one-step process, continuously or in batches.

Detailed description of the invention

This invention includes the preparation of Mg-free anionic clay, which contains Mg. In particular, it describes a process for the preparation of an anionic clay in which a suspension is provided containing an aluminum source and a divalent metal source, which are thermally or hydrothermally reacted, to obtain an anionic clay without Mg, which contains Al, the aluminum source being aluminum trihydrate or its heat-treated form, and the divalent metal source not being a magnesium source.

It has been observed that anionic clays without Mg containing Al are obtained directly from the reaction according to the invention. This is in contrast to the co-precipitation method, in which soluble salts are first precipitated, then filtered and washed to remove unwanted ions, and then hydrothermally aged or not. By the process according to the present invention, the presence of unwanted ions in the product can be avoided, as will be explained later. The source of aluminum is aluminum trihydrate or its heat-treated form. This source of alumina is much cheaper than the usual aluminum sources, such as aluminum salts or peptized boehmites. From this compound no other ions appear in the anionic clay apart from hydroxide, which is one of the normal building blocks of anionic clays. If a compound with non-hazardous ions, such as nitrate or acetate, is chosen as the source of the divalent metal, washing and filtration of the reaction product can be avoided together. In fact, it has been found that the reaction also takes place when hydroxides, oxides, hydroxycarbonates or carbonates are used as the source of divalent metal, in combination with aluminum trihydrate or its heat-treated form, in which case no washing or washing has to be done. filtration.

As the process described in this patent does not require washing of the product or filtration, there is no filtering waste or gaseous emissions (for example from acid decomposition), which makes the process particularly environmentally friendly, and more suitable for increasingly imposed environmental restrictions on business operations. The product can be directly spray dried to form microspheres, or it can be extruded, pelleted, or shaped into pellets, resulting in shaped bodies.

Anionic clays prepared with this method exhibit well-known properties and characteristics (e.g. chemical analysis, X-ray powder diffraction pattern, FTIR, thermal decomposition characteristics, specific surface area, pore volume, and pore size distribution). , generally associated with anionic clays prepared by the usual and previously described methods.

The anionic clay according to the invention has a layered structure corresponding to the general formula

[M (II) m²+ Aimi). (() II). 2 · | Χ,.^Ζ BH2O

Where m and n have a value such that m / n = 1 to 10, preferably 1 to 6, and b has a value in the range of 0 to 10, generally a value of 2 to 6, and frequently a value of about 4 X can be CO3^2-, OH^- or any other anion normally present in the interlayers of anionic clays. It is more preferred that m / n has a value of 2 to 4, more particularly a value close to 3. Trivalent metal source

In addition to aluminum trihydrate or its heat-treated form, which is the main source of trivalent metal, other sources of trivalent metal such as Al-containing compounds can be added.³⁺, Mn³⁺, Faith³⁺, Co³⁺, Neither³⁺, Cr³⁺, Ga³⁺, B³⁺, trivalent rare earth metal cations, such as La³⁺ and Ce³⁺ or mixtures of said compounds. Oxides, hydroxides and carbonates of these metals are preferably used, but nitrate chlorides, sulfates and phosphates can also be used.

Divalent metal font

Suitable sources of divalent metals are compounds containing Ca²⁺, Zn²⁺, Mn²⁺, Co²⁺, Mo²⁺, Neither²⁺, Faith²⁺, Mr²⁺, Ba²⁺, Cu²⁺, and mixtures of said compounds. Oxides, hydroxides and carbonates of these metals are preferably used, but nitrates, chlorides, sulfates and phosphates can also be used. Terms

As mentioned above, the reaction is carried out under thermal or hydrothermal conditions. In the context of this description, hydrothermal means in the presence of water at a temperature greater than 100 ° C, with increased pressure. Thermal means at a temperature between room temperature and 100 ° C. Preferably the reaction is carried out in water in an autoclave at a temperature higher than 100 ° C, that is to say under autogenous pressure.

It is possible to purge the suspension with nitrogen or inert gas, if an anionic clay with predominantly hydroxide anions is desired, but in general this is not necessary. Thus, the reaction can be carried out in the presence of CO2. Said CO2 can be the CO2 normally present in air, or it can be added to the reaction, for example, using a source of divalent or trivalent metal carbonate.

Said aqueous suspension can be obtained by combining suspensions of starting materials, or adding sources of divalent metals to a suspension of source of trivalent metal or vice versa. The product does not need to be washed or filtered as unwanted ions (eg sodium, ammonium, chloride, sulfate), which are often found when using other preparation methods, are absent from the product. If desired, you can add a clay

ES 2 211 596 T3 preformed to the reaction mixture. Said preformed clay can be anionic clay recycled from the reaction mixture, or anionic clay prepared separately by the process according to the invention or any other process.

Due to its simplicity, this procedure can be carried out continuously, mixing a first suspension containing boehmite, and a second suspension containing a source of divalent metal, and passing the mixed suspension through a reactor vessel, which it can be operated under hydrothermal conditions. Said first and second suspensions can be subjected to treatment prior to mixing of the suspensions. Said pre-treatment can include acid treatment, base treatment, thermal and / or hydrothermal treatment, all optionally in the presence of seeds, and combinations thereof.

As previously mentioned, if desired, acids and bases may be added to the suspension, for example to control pH, before or during the reaction, or to the individual reactants before combining them into the suspension. The acids and bases of choice are formic acid, acetic acid, nitric acid, and ammonium hydroxide, because these types of acids and bases do not introduce unwanted ions into the reaction mixture.

The most preferred combinations of divalent metal sources and Al sources are Al-Zn, and AlCu, because these combinations result in Al-containing magnesium-free anionic clays, with specific applications in the field of catalysts.

If desired, the anionic clay prepared by the process according to the invention can be ion exchanged. With ion exchange, the charge balance anions in the interlayers are replaced with other anions. These other anions are commonly present in anionic clays, and include stacking anions such as V10O28^6- , Mo7O24^6-. Said ion exchange can be carried out before drying, or after the anionic clay has formed in the suspension.

The process of the invention provides wide flexibility to prepare products with a wide range of M (II): Al (III) ratios. The relationship

M (II): Al (III) can range from 0.1 to 10, preferably from 1 to 6, more preferably from 2 to 4, and especially preferred around 3.

For some applications it is desirable to have additives present, both metals and non-metals, such as rare earth metals, Si, P, B, group VI, group VIII, alkaline earth metals (for example Ca and Ba) and / or metals. transition (eg Mn, Fe, Co, Ti, Zr, Cu, Ni, Zn, Mo, Sn). These metals can easily be deposited on the anionic clay. They can also be added to the divalent metal source or trivalent metal source, or to the suspension, during the preparation of the anionic clay.

The present invention is illustrated by the following examples, which are not to be construed as limiting in any way.

Examples

Example 1

A suspension of Cp was provided^®alumina (flash-calcined alumina) and zinc nitrate, with a Zn / Al ratio = 2.3. The suspension was aged at 65 ° C for 18 hours. The product was dried at 90 ° C. X-ray diffraction showed the characteristic reflections of anionic clay at 7.52 and 3.76 A. Example 2

A suspension of gibbsite and zinc oxide was provided, with a Zn / Al ratio = 2.3. The suspension was aged at 90 ° C for 18 hours. The product was dried at 90 ° C.

Example 3

A solution of copper nitrate was introduced into a suspension containing Cp alumina, with a Cu / Al molar ratio of around 2. The temperature was raised to 160 ° C in an autoclave, and the suspension was treated for 1 hour. The product was filtered, washed and dried at 120 ° C. XRD analysis indicated that the product was a Cu-Al-LDH.

Example 4

Example 3 was repeated except that the Cp alumina was replaced by gibbsite. The product, according to XRD, was a Cu-Al-LDH.

Example 5

Example 4 was repeated except that the copper nitrate was replaced by ferrous nitrate. according to XRD, the product was Fe-Al-LDH.