WO2008129034A1

WO2008129034A1 - Hydrotalcite-like layered double hydroxide (ldh) composition and process of making same

Info

Publication number: WO2008129034A1
Application number: PCT/EP2008/054805
Authority: WO
Inventors: Olga Gonsiorova; Renee Van Yperen
Original assignee: Euro Support Catalyst Group Bv
Priority date: 2007-04-20
Filing date: 2008-04-21
Publication date: 2008-10-30

Abstract

The present invention pertains to a hydrotalcite-like Layered Double Hydroxide (LDH) comprising a divalent (M2+ ) and a trivalent (M3+) metal with interlayer hydroxyl ions as charge balancing anions, and wherein the composition in a compacted powder form, exhibits an PXRD pattern such that the ratio R of the sum of the intensities of the hydrotalcite reflections in the region of 8 to 28° 2Θ to the sum of the hydrotalcite reflections in the region of 25 to 55° 2Θ is at least 3, and the material is substantially free of nitrate, sulphate, and chloride. The present invention also pertains to a method for manufacturing this material, and to its use in various applications.

Description

The invention is directed to a novel Layered Double Hydroxide (LDH) or hydrotalcite-like anionic clay and its production and use in various applications.

Anionic clays or otherwise called Layered Double Hydroxide (LDH) represent a class of ionic lamellar materials with positive charged metal hydroxide sheets with the negative charge balance provided by the intercalated anions. These layered synthetic inorganic solids are related to the mineral classes of hydrotalcite-sjogrenite-pyroaurite. They are represented with the generic composition of:

[M²⁺ ₍,_x!M^3t _x(OH)₂]A" _ώ*mH₂O

wherein M²⁺ and M³⁺ can be divalent and trivalent metals occupying lattice positions in the brucite-like sheets and A^*v is an exchangeable anion located in the gallery between the layers along with water molecules. x is the ratio of M³⁺Z(M²⁺ + M³⁺). In Hydrotalcite, M²⁺ is Mg²⁺, and M³⁴ is Al³⁺. A"^' is CO.3^2"and typically x is ¹A, and m is Vi.

In these LDHs₅ the ordering of the hydroxide layers is similar to that of the brucite where Mgⁱ⁺ ions in the structure are octahedral Iy coordinated with six hydroxyl groups (OH^') and each of the octahedra share edges to form sheets.

In the brucite-like [Mg(OH)?, ] sheets, isomorphous substitutions of Mg²⁺ with trivalent cations (Al³⁺) takes place in the octahedral sites, thus producing a net positive charge which is neutralized by the negative charged anions. As more smaller cations than

Mg^2*, for example Al³⁺. substitute into the brucite-like lattice, the crystal lattice parameter

(a) is decreased, as well as the (c) crystal parameter.

In the prior art, references are made to these materials, interchangeably, as anionic clays, Layered Double Hydroxides (LDHs), mixed metal hydroxides, hydrotalcite and hydrotalcite-like materials.

A class of these Layered Double Hydroxides (LDHs) related to the mineral hydrotalcite is represented with composition of [Mg₆ AI₂C OH)₁₆] C O₃ • 4H₂O, or in a generic form

[M²VM³ⁱ ₂(OH)_!6] Aⁿ _2/n ^®4H₂G wherein M^ represents divalent cations, M^J* represents trivalent cations and A^" represents monovalent anions that are exchangeable with organic or inorganic anions.

The divalent M²⁺ cation can be selected from the groups of alkaline earth or transition metals or mixtures thereof. For example, one or more OfMg²⁺, Fe²⁺, Co²⁺. Cu^2f, 5 Ni , Zn , Ca , Sr , Ba , and Mn may he used.

The trivalent M³⁺ cation can be selected from the group of one or more of Al³⁺, Cr³⁺, Ga³⁺, La³⁺, Mn³⁺, Co³⁺, Ni³⁺, B³⁺, V³⁺, Ti³⁴, and In³\

The anion A can be selected from one or more from the group of inorganic and organic anions, such as F^", Cl^", T₅ ClO₄ ^", NO₃ ^", ClOj^", OH; CO₃ ^2", HVO₄ ²; SO₄ ^2", WO₄ ^2", ϊ O CrO,,^2", [Fe(CN)₆J⁴; [SiO(OH)₃]; MnO₄ ^", heteropolyacids such as (PMo₁₂O₄₀)³; (PWi₂O₄₀)^3", as well as polyoxometalates such as [WZn₃(H₂O)(ZnW₉O₃₄)J^12". Further, A can be an organic anion from an acid.

A variety of hydrotalcite and hydroialcite-like compositions can be prepared by different 15 M²⁺ M³⁺ A^n" combinations as well as by varying the M²V M³'^" metal ratio,

Upon heating the hydrotalcite at above 300°C, the interstitial water and carbonate anions leave the structure and the metal oxides are formed such as

₂(QFfy ®CQ₃®4H₂O -> Mg₆Al₂O₈(OH)₂ + CO₂ + 13H₂O

At high temperatures, the lattice hydroxy! groups condense and leave as water and the mixed metal oxide solid-solution/spinel is formed. Depending on the mole ratio Of M²⁺ to M³⁺ and calcination conditions (temperature, atmosphere, time), the spinel formation can be initiated at above 600⁰C. Further, the presence of other than Mg^2f and Al³⁺ cations 5 can alter the temperature of spinel formation.

It is the mixed metal oxide solid solution which is the active component for catalytic applications of the hydrotalcite precursor. For example, as Ziegler-Natta catalyst support, hydrogenation, polymerization, steam reforming, hydroprocessing, Fluid Cracking Catalyst (FCC), FCC-Additives, and so on. 0 Furthermore, hydrotalcite can be used in non-catalytic applications such as in medicines, as antacid, stabilizer, also as sorbents, in PVC stabilizers, in wastewater purifiers, halogen scavengers, ion exchangers, flame retardants, etc. The hydrotalciie compositions exhibit the so called "memory effect" when the hydrotalcite is calcined at temperatures above 400⁰C to 600⁰C, preferably about 500⁰C, to form the solid solution of the mixed metal oxides, and subsequently is rehydrated in water, usually at 65⁰C to 95⁰C for 6 to 18 hours and optionally with the aid of some sodium carbonate solution to reconstruct the original structure of the hydrotalciie as evidenced by the powder X-ray diffraction patterns (PXRD).

In the prior art we find examples where metal salts, acids, bases, etc., have been included in the rehydrating solution of the calcined hydrotalcite in order to introduce such metal cations or anions into the reconstructed hydrotalcite structure. Hydrotalcite and hydrotal cite-like anionic clays which have been calcined above

700⁰C and mostly above 800⁰C which have formed some spinel, show poor rehydration and reconstruction properties, and at higher temperatures the memory effect is lost. In the temperature region of 800⁰C to 900⁰C, and depending on the calcination conditions, usually mixtures of MgO and MgAl₂O₄ spinel are formed. Synthetic hydrotalcites and hydrotalcϊte-like materials have been prepared by co- precipitation methods, using soluble salts of magnesium such as Mg(NOa)₂ ⁸OH₂O and aluminium salts such as Al(Nθ₃)₃ ^β9H₂O (aided with the addition of NaOH, Na₂CO₃, urea, etc.).

Usually, these salts are added simultaneously to the reaction vessel while the ρil is kept constant by the addition of NaOH. The precipitation is followed by aging at temperatures below K)O⁰C, mostly at 65 to 85°C for up to two days or more, or aged in autoclave hydrothermally at temperatures above 100⁰C for a few hours to several days, followed by extensive washing to remove unwanted salts.

A substantial amount of this prior art is described in an extensive review article by

F. Cavani, et al: Hydrotalcite-type Anionic Clays: Preparation, Properties and Applications. Catalysis Today. 1991, J_l, Elsevier Science Publishers, Amsterdam. Additional information regarding preparation of hydrotalcite-type materials by the co- precipitation methods can be found in U.S. Patents: 3,796,792; 3,879,525; 4,351,814 by Miyata. et al., and 4,458,026 by Reichle, also, W.T. Reichle, et. al. Journal of Catalysis 101, 352-359 (1986), T. Solo, et al, Reactivity of Solids, 2, 253-260 (1986). Precipitation processes produce good quality anionic clays; however, such processes have certain major disadvantages. First, the cost of aluminium and magnesium salts is higher than other useable solid magnesium and aluminium bearing materials.

The precipitation process requires additional chemicals such as sodium hydroxide, sodium carbonate, ammonium hydroxide, urea, etc., which further increases the cost of production.

The filtration and washing process steps are difficult due to the small particles of the anionic clay which make filtration and washing a slow process. Further, these processes are not environmenially friendly as they require disposal of the nitrates, chlorides, and sulphates in the washings which require special disposal.

The aging process is very long and this decreases the through-put capacity of the plant.

Usually, the precipitation takes place using very dilute solutions, so the final concentration of the solids in the slurry is quite low. Thus, the low concentration of solids in the slurry requires large plant equipment to obtain a cost-effective production rate, which, in turn, requires larger capital investment for the large volume equipment.

Besides the precipitation routes, there are other routes known to the prior art, to produce anionic clays, which involve at least one of the reactants to be a water insoluble component bearing Mg or AL For example, U.S. patents 4,656,156 and 4,904,457 describe the preparation of hydrotalcite using an activated alumina prepared by the flash calcination of gibbsite (alumina trihydrate) and an activated magnesium oxide. Further, aluminum in the form of hydroxides in crystalline or semi-crystalline forms, such as boehmϊtes and pseudoboehmites, has been used as a source of aluminum for producing hydrotalcite and hydrotalcite-types of anionic clays. In conjunction with this type of alumina, magnesium oxide, magnesium hydroxide (brucite), and magnesium hydroxy carbonate have been used as sources of magnesium.

For example, U.S. Patent 6,800,578 describes a process using boehmite alumina which is first treated with an acid and then neutralized by the addition of a base such as sodium or ammonium hydroxide in a slurry form, to which a magnesium source is subsequently added and the slurry then aged at temperatures in the range of 55⁰C to 250⁰C. The magnesium source can be derived from MgO, MgCO₃, Mg₃(OHCO₃J₂, Mg(NOs)₂, Mg(acetate)2, Mg(OH)₂, etc. This process, like the precipitation process, has the disadvantage that it requires filtrations and washings to remove the salts (such as NaNO₃, NH₄NO₃. NaCl, (NHu)₂SO₄, etc., formed by the neutralization of the acid-treated boehniite with a strong base.

U.S. Patent 6,541,409 describes a process in which pseudoboehmite types of alumina are used as sources of aluminium, which are reacted with magnesium oxide (MgO) in water slurry and aged at temperatures in the range of 65°C to 85°C for 18 to 48 hours. The preparation conditions and the quality of the products are not suitable and consistent to be able to produce a high quality hydrotalcite-type anionic clay without being contaminated and diluted with substantial quantities of unreacted magnesia and pseudoboehmite alumina. These products are, in essence, mixtures of anionic clays and unreacted magnesium and aluminium sources, which make the products inferior in quality as compared to those produced by the precipitation processes.

U.S. Patent 6,171,991 describes a process for producing an anionic clay composition, using a gibbsite as the source of aluminium and MgO as the source of magnesium. The process conditions are such that only a part of the gibbsite and magnesium oxide were converted to hydrotalciie, as shown in examples 7 to 10, indicating the products were mixtures. Therefore, this process is not suitable to produce pure anionic clays from gibbsite and magnesium oxide.

When hydrotalcite-type anionic clays are prepared in the absence of carbonate anions or in CO₂ -free atmosphere, the intercalated anion in the hydrotalcite structure may be predominantly hydroxy 1 anions, and the crystal structure of this anionic clay is that of a hydrotalcite-like clay, otherwise referred to as meixnerite-like anionic clays.

Historically, S, Koritnig was first to identify the analog of hydrotalcite containing hydroxyl ions as the negative charge balancing anions which was named meixnerite with a composition of Mg₆Al₂C OH)₁₈* 4H₂O, based on the natural mineral. S. Koritnig and P. Susse. TMPM Tschermaks Min. Petr. Mitt. 22, 79-87 (1975)

Based on Koritnig 's crystal lographic data, subsequently the J.C.P.D.S. - DATABASE was published. Record 38-478, ICDD.

Regarding the nomenclature of the meixnerite subsequently D. L. Bish (Bull. Mineral 103, 170-175 (1980)), suggested that, in view of the analog structure being the same of hydrotalcite and meixnerite, a more proper name for tills anionic clay will be hydroxy hydroialcite instead of meixnerite. Bish further showed the high ion exchange affinity of the hydroxy hydrotalcite to absorb CO₂ or carbonate ions from a solution and hence replace the hydroxy] anions with carbonate anions, which leads to the conversion of the Hydroxy hydrotalcite to carbonate hydrotalciie having the composition of [Mg₈Al₂(OH)₁₆]CO₃^H₂O

G. Mascolo and O. Marino were able to synthesize the analog of the natural mineral (meixnerite) or hydroxy hydrotalcite.

In their process they used MgO and an alumina gel dispersed in distilled CG₂ -free water and reacted in sealed teflon containers at 8O⁰C in a CO₂ -free atmosphere. (Mineralogical Magazine, March 1980, 43, pp 619-621)

Further, synthetic meixnerite or hydroxy hydrotalcite was also produced by L, Pausch (Clays and Clay Minerals Vol. 34, 1986, 507-510) using γ-alumina. MgO reacted hydrothermally at temperatures in the range of 100⁰C to 350⁰C under a CO₂-free atmosphere and autogenous pressures. A new process of introducing anions into LDH or into hydrotalcite or hydrotalcite-like structures, was demonstrated by W. Jones, et. al., comprising calcining a regular synthetically produced carbonate-hydrotalcite and rehydrating it in a CO₂-free atmosphere in a solution containing the anion of interest. (J. Chem Soc, Chem. Commnn. 1989).

Further, E. Dirnotakis and T. Pinnavaia, produced hydroxy hydrotalcite (meixnerite) using the same procedures as W. Jones, by calcining (at 500⁰C for 3 hours) a synthetically produced Carbonate Hydrotalcite (Hydrotalcite) in CO₂ -free atmosphere and rehydrating, the mixed metal oxide solid solution, in a distilled water free of CO_?, and CO₃ ^2" at 25°C for 16 hours (Inorganic Chemistry, Comm. Vol. 29, Number 13, June 27, 1990) using this process they were able to produce pure hydroxy hydrotal cites (raeixnerites).

Patented related technology first appeared in U.S. Patent 5,112,784 of M. Atkins, W. Jones and M. Chibwe wherein catalytically active materials where produced by calcining an anionic Double Hydroxide clay; rehydrating the resulting material in water free of dissolved ions; and calcining the rehydrated material. Accordingly, meixnerite or hydroxy hydrotalcϊtes were produced by this process.

U.S. Patent 5,514,361 describes a process of preparing a meixnerite-type material from flash calcined gibbsite (a transition, activated or rehydratable alumina) and magnesium oxide. The preparation was done at boiling temperatures (98°C) and hydrothermally at 150⁰C. As shown in the examples of this patent, the two reactants, the magnesium oxide and the flash calcined gibbsite (Alcoa's CP-2 grade) were stirred in water and the temperatures raised, either to 98⁰C or to 15O⁰C and kept at these temperatures for several hours,

US patent 5,728,363 and 5,645,810 and 5,750,453 were also directed to the production of meixnerite type of materials by reacting magnesium oxide and transition alumina (an activated or rehydratable alumina) in aqueous suspension.

Based on the analysis of the products of these examples, using PXRD, it is shown that the examples contained some alumina, magnesia or both which did not react. The lack of complete reaction of the alumina and magnesia resulted in contaminated products. The meixnerite component in these products had an PXRD pattern characteristic of meixnerite known to the prior art.

F. Prinεtto εt al. (Study of relevant properties influencing die catalytic activity of Layered Double Hydroxides in the Meixnerite- like form, Studies in Surface Science and Catalysis 130, A. Corma, F,V, MeIo, S. Mendioroz and L.G. Fierro (Eds), 2000, Elsεvier Science B. V.) describes the preparation of well-crystallised LDHs containing Mg²⁺ or Ni²⁺ and AV or Ga^J" by copreeipitation or sol-gel method. In these methods, the resulting material will contain substantial amounts of soluble salts resulting from the precipitation, e.g., nitrate salts or chloride salts. While ion exchange or washing will remove substantial amounts of these anions, the final products will still contain some of these compounds, which, in some embodiments, may turn out to be detrimental. Further, for economic reasons the necessity of ion exchange steps and washing steps is considered disadvantageous. This process involves first making the LDH from expensive raw material salts, requiring filtration and washing, and subsequently calcination and rehydration in a C€Vfree environment, which is an energy intensive and non-economical multi-step process,

SUMMARY OF THE INVENTION

In this invention, unexpectedly, it was discovered that by using a new synthesis process a new form of meixnerite is synthesized having a different distribution of intensities for the reflections in the powder X-ray diffraction pattern, from the distribution of intensities of the same reflections known in the prior art. This new type of meixnerite may be produced in pure form, without being contaminated with unreacted ingredients such as alumina and magnesia or bi -products such as brucite. In addition, unwanted ions introduced during co-precipitation, e.g. Na⁺ from sodium hydroxide, NO₃ ^" from magnesium nitrate, SQ₄ ^" from magnesium sulphate, Cl^" from magnesium chloride or from the equivalent aluminium salts are absent. The main intercalated charge balancing ions of the material as synthesised are hydroxy! anions. The material according to the invention is, therefore, substantially free of nitrate, sulphate, and chloride. Within the context of the present specification, the wording "substantially free of "substantially" means that these components may the present in amounts the presence of which cannot realistically be avoided in commercial scale production. More in particular, the composition contains less than 3 wt.%, in particular less than 2 wt.%, even more in particular less that 1 wt%, still more in particular less than 0.5 wt.% of nitrate, sulphate, and chloride.

Even more in particular, the composition of the present invention is substantially free of anions other than hydroxides and carbonates. More specifically, the composition contains less than 3 wt.%, in particular less than 2 wt.%, even more in particular less that 1 wt%, still more in particular less than 0.5 wt.% of anions other than hydroxides and carbonates.

For a convenient distinction of this new hydroxy hydrotalcite or meixnerite, Layered Double Hydroxide, from the known types in the prior art, in this invention the peak heights are taken to represent the intensities, and are used for measuring the ratio (R) of the sum of the intensities of the hydrotalcite reflections in the region of 8 to 28° 2Θ to the sum of the hydrotalcite reflections in the region of 25 to 55 ° 2Θ (PXRD determined in reflection geometry on a flat plate sample using Cu Ka radiation (λ is 1,5418A)), wherein R is at least 3, in particular at least 4, more in particular more than 5, still more in particular more than 6. In one embodiment, the region of 8 to 28° 2Θ may be further specified to the region of 10 to 25° 2Θ. In another embodiment, the region of 25 to 55° 2Θ may be further specified to the region of 28 to 55° 2Θ, or to the region of 25 to 50° 2Θ, It is noted that these further specifications of the 8-28° 2Θ and the 25-55° 2Θ region also apply to other embodiments of the present invention, whether or not this is explicitly indicated. Whether or not such further specifications are appropriate will depend on the exact location of the hydrotalcite-reflections in the PXRD pattern. This can easily be determined by the skilled person for a pattern at hand.

More in particular, the major crystallographic characteristics specific to this new type of meixnerite, which are different from the XRPD of the well known in prior art synthetic meixnerite, are represented by the high intensities of the <003>, <006> reflections, in the region of 8 to 28° 2Θ, as compared to the very low intensities of the <012>, <015>, <018> reflections in the region of 25 to 55° 2Θ. Again, in one embodiment, the region of 8 to 28° 2Θ may be further specified to the region of 10 io 25° 2Θ and the region of 25 to 55° 2Θ may be further specified to the region of 28 to 55° 2Θ, or to the region of 25 to 50° 2Θ.

The present invention is accordingly characterized by a composition of a hydrotalcite-like Layered Doubled Hydroxide (LDH) comprising divalent M²⁺ and trivalent M ⁺ metals and having hydroxyl ions as the major charge balancing anions and having an X-ray powder diffraction pattern wherein the ratio (R) of the sum of the relative intensities of the X-ray reflections (IQ_UL and W) is such that:

R - ∑(/ < 001 >)/ Σ(I < hkt >) is at least 3, preferably at least 4, more preferably more than 5 and more preferably more than 6 wherein, L =^■ 1 , 2, 3 ...infinity, I = 0. 1 , 2, 3, 4 ...infinity: h = 0, 1, 2, 3, 4 ...infinity, and k = 0, 1 , 2, 3, 4 ...to infinity, wherein h, and k are not 0 simultaneously. For more information on the assignment of the intensities in the XRD spectrum, reference is made to S.P. Newman et al. (Synthesis of the 3R2 polytype of a hydrotalcite-Hke mineral, J. Mater. Chem., 2002, 12, 153-155).

Another embodiment involves a composition of 3R₁ type hydrotalcite-like Layered Double Hydroxide (LDH) comprising divalent (M²⁺) and trivalent (M^3u) metals and having hydroxyl ions as charge balancing anions, and having an X-ray powder diffraction pattern wherein the ratio (R) of the sum of the relative intensities of the X-ray reflections (IQ_UL and is such that: i? = ∑(/ < GGZ > /Σ(/ < ,

is at least 3, preferably at least 4, more preferably more than 5 and more preferably more than 6. wherein L = 3 and 6, h = 0, k = 1, and I = 2, 5, and 8. Figure 2a of Newman cited above illustrates the intended peaks. In this figure, the R values is estimated to be 1.4 to 1.5.

Still another embodiment involves a composition of 3R₂ type hydrotalcite-like Layered Double Hydroxide (LDH) comprising divalent (M^2"") and trivalent (M³⁺) metals and having hydroxyl ions as charge balancing anions, and having an X-ray powder diffraction pattern wherein the ratio (R) of the sum of the relative intensities of the X-ray reflections (IQ_OI. and Ihu) is such that:

^' < 0QL > /Σ(I < hkf

is at least 3, preferably at least 4 preferably more than 5 and more preferably more than 6 wherein L = 3 and 6, h = 1, k = 0, and € = 1, 4 and 7,

For comparison purposes for a typical, pure carbonate hydrotalcite. prepared by the well known methods using precipitation processes, the ratio (R) is about 1.5. Other carbonate hydrotalcites and hydrotalcite-like materials known in the prior art prepared by reacting aluminium oxides or aluminium hydroxides with magnesium oxides exhibit a ratio (R) in the range of 1.4 to 1.8.

Hydroxy hydrotalcites or meixnerites prepared by Dimotakis and Pinnavaia as well by W. Jones et, al.₃ exhibit a ratio (R) of about 1.5 to 2.

1 he material of the present invention also differs from the material described in the following publications: "'1 he Effect of Synthetic Conditions on Tailoring the Size of Hydrotalcite particles" by Jae-Min Oh, et al, Solid State Ionics 151 (2002), 285-291 ; '"Crystallization of Synthetic Hydrotalcite under Hydrothermal Conditions." Frantisck Kovanda, et al. Applied Clay Science 28 (2005) 101-109; "Increasing the Basicity and Catalytic Activity of Hydrotalcites by Different Synthesis Procedures" MJ. Climent, et al, J. of Catalysis 225 (2004), 316-326. In these publications different compositions of carbonate hydrotalciles were synthesized through co~ρreeipitation, thermally and hydrothermally, which also exhibit ratios (R) above 2 or 3 which compositions of said hydrotalcitc-like materials contain mostly carbonate/nitrate ions as a negative charge balancing anions, and are thus distinguished from the present invention.

Figure 1 illustrates the difference in PXRD spectrum between a material according to the invention and a commercial hydrotalcite material, obtainable from Reheis. The commercial material has an R value of 1.4, while the material according to the invention has an R value of 17.

Λs indicated above the materials according to the invention have an R value of at least 3, in particular at least 4, still more in particular more than 5, still more in particular more than 6, In some embodiments, R values of at least 8 may be obtained, or even at least 10. Sometimes values of at least 12. or at least 14 mav be obtained. As indicated above, due to the absence of anions such as nitrate, sulphate, chloride the present composition principally contains interlayer hydroxy! principally ions as charge balancing anions. More in particular, the hydroxyl groups make up at least at least 20%, preferably more than 40% and more preferably more than 60% , still more preferably more than 80% of the total intercalated anion concentration, with the balance being carbonate anions. In the material as synthesized, it is preferred for the charge-balancing anions to consists for at least 90% of OH^', the balance being CO₃ ^"", more in particular at least 95% of OH^", the balance being CO₃ ^2". Still more in particular, in the as synthesised material the intercalated anions substantially consists of OH^", wherein the wording "substantially consists of" means that minor amounts of other components the presence of which cannot realistically be avoided in commercial scale production may still be present.

In the material as synthesised, it is preferred for the charge-balancing anions to consists for at least 90% of OH^", the balance being CO₃ ^2", more in particular at least 95% of OH^", the balance being CO₃ ^2". Still more in particular, in the as synthesised material the intercalated anions substantially consists of OH^", wherein the wording "substantially consists of means that minor amounts of other components the presence of which cannot realistically be avoided in commercial scale production may still be present. As will be explained in more detail below, it is one of the features of the present invention that during synthesis the contact Of CO₂ from the air with the reaction medium should be minimized. As the material is exposed to carbon dioxide in the air, the amount Of CO₃ ^2" will increase, until a balance value obtained.

In one of its embodiments, the material of the present invention meets the formula

[M%M^s+ ₂ (OH)₁₆] AV ®4H₂O

wherein M^÷/' represents a divalent cation, M³⁺ represents a trivalent cation and A^n" represents an anion, wherein M²⁺ is selected from the groups of alkaline earth and transition metals, and mixtures thereof, M³⁺ is selected from Al³⁺, Cr³⁺, Ga³⁺, La³⁺, Mn³⁺, Co^{' +}, Ni^''^", B^{' +}, V^{" +}, Tr⁺, In³⁺, and mixtures thereof, and wherein A"^" is selected from OH^" and mixtures of OH^" with CO₃ ^2". In one embodiment M²⁺ is selected from one or more Of Mg²⁺, Fe²⁺, Co²⁺, Cu²⁺, Ni²⁺, Zn²⁺, Ca²⁺, Sr²⁺, Ba^{2 i"}, and MnT . In a preferred embodiment. M²⁺Is Mg²". In a preferred embodiment, M^{3 ;} is Al^3"1".

Thus, in a preferred embodiment, the material of the present invention meets the formula

Mg_δAl₂A%_/n ^®4H₂O

wherein A^n" is selected from OH^" and mixtures of OH^" with CO₃ ^2". More in particular, and this also goes for the more general formula above, in the material as synthesised, the A^n" consists for at least 90% of OH^", the balance being CO₃ ^2", more in particular at least 95% of OH^", the balance being CO₃ ^2". Still more in particular, in the as synthesised material A^n" substantially consists of OH^", wherein the wording '"substantially consists of means that minor amounts of other components the presence of which cannot realistically be avoided in commercial scale production may still be present. As the material is exposed to carbon dioxide in the air, the amount OfCO₃ ^2" will increase, until a balance value obtained.

The material according to the invention is characterised in that it consists of thicker sheets in the [001] direction thicker than materia! which is synthesised in other ways, e.g., by precipitation from salt solutions. More in particular, the platelets are thicker than those obtained conventionally. This can be seen, e.g., by microscopical evaluation of the samples. Additionally, in the material of the present invention, the crystallite size in the [001] direction as derived from the full width at half maximum of the reflections via the Seherrer formula is greater than 200A . more preferable greater than 250A and even more preferably greater than 30OA. For more information on this manner of calculating crystallite sizes, reference is made to Kovanda et al. (F. Kovanda et al., Crystallization of synthetic hydrotalcite under hydrothermal conditions, Applied Clay Science 28 (2005) 101-109). where this method is described for a different type of material. The composition according to the invention is preferably substantially free from uπreaeted starting material sources. It is, however, possible to add, e.g., aluminium trihydrate to the final composition, as will be elucidated below.

A PANaiytical® X-ray diffractomεter with Ni filter Cu radiation was used. (Model number PW3040/60 X' Pert PRO®). The X-ray tube was a PANaiytical® PW3373/00 Cu LFF tube operating at 4OkV and 4OmA.

Samples were gently ground using a pestie and mortar to break up any large agglomerated masses. The powder sample is pressed into the ground area of a glass flat plate sample holder using a microscope slide, (depth of ground area is approximately

0.5mm) so that the powder sample surface was compacted, smooth, flat and flush with the sample holder surface. The sample holder was inserted into a sample stage (model PW3071/60 Bracket®; sample not spun and measured Bragg-Brentano geometry),.

A PANaiytical scanning RTMS (Real Time Multiple Strip ) X'Celerator® detector was used with an active length of 9mm covering ca 2.127 ° 2-theta. Samples were typically analysed between 2 and 80 ° 2-theta with a Step Size of 0.01675, Time per step of 50 seconds and total scan time of 30 minutes.

As indicated above, the materials prepared according to this invention exhibit a preferred particle orientation when placed in a compacted flat-bed sample holder for the XRD measurements that produced the XRD patterns characterizing the new hydroxy hydrotalcite or new meixnerite described in this invention.

When some samples are placed in a capillary sample holder the differences in the ratios (R) are smaller than the differences in ratios (R) observed when the samples of the invention are placed in flat-bed compacted PXRD sample holders. Typical X-ray-diffraction patterns of the hydroxy hydrotalcite or meixnerite anionic clays produced by this invention are characterized by reflections with d (spacings) in A at 7.52, 3.79, 2.56, 2.28, 1.93, 1.52 and 1.49.

The position of the 003, d (7.52), reflection varies somewhat e.g., with the conditions of preparation, reactant materials, and the water content. Typical values range between 7.4 and 7.6. It is well within the scope of the skilled person to determine the exact d (spacings) for the various peaks on a case by case basis. The new meixnerite-type anionic clay of this invention is preferably produced by homogenizing in a water slurry a solid divalent metal source and a solid trivalent metal source, of which one at least is water insoluble, and with pH higher than 11 and at temperatures in the range of 6O⁰C to 100⁰C, or hydrothermally under autogenous pressures at a temperature above 100⁰C, the reaction being carried out in the absence of salts of nitrate, sulphate, or chloride, and under such conditions that the contact between the reaction medium and carbon dioxide from the air is minimised. In a preferred embodiment, the material according to the invention is synthesised in the absence of substantial amounts of carbon dioxide and carbonate ions. Still more in particular, the reaction is carried out in the absence of salts other than oxides or hydroxides.

If so desired, the slurry is subsequently aged at temperatures below K)O⁰C or elevated temperatures hydrothermally under autogenous pressures.

The materials of the present invention, characterized by the specific PXRD pattern as defined by the ratio R, show advantageous properties in terms of particle size, dispersability. high porosity, binding properties and attridon resistance. This makes the material extremely suitable for use as catalysts, catalyst support, adsorbants and polymer additives.

The material may be used as such after production, filtration and drying. It is also possible to spray dry the material or to extrude it in the presence of an additional binder In one embodiment of the present invention the solid divalent metal source and the solid trivalent metal source are dispersed in water at a pH of over 11 having a temperature of between 60 and 100⁰C, preferably between 65 and 95 °C and more preferred between 85 and 95^QC. This is in contrast with conventional synthesis methods where the metal sources are brought into water at room temperature, after which the mixture is heated to reaction temperature, In one embodiment, the solid divalent metal source is added to water having the specified temperature, followed by addition of the trivalent metal source. Sn another embodiment, the solid trivalent metal source is added to water having the specified temperature, followed by addition of the divalent metal source.

In one embodiment, the reaction is carried out under such conditions that the atmosphere above the slurry consists primarily of water vapour (steam). This was found to lead to a product with better properties. Further the slurry is preferably at least partially heated by steam injection. The dispersion is mixed vigorously. Subsequently the dispersion may be aged for a suitable period of time, such as between 1 and 10 hours, preferably between 2 and 10 hours, at a temperature in the same range of between 60 and 100⁰C, preferably between 65 and 95°C and more preferred between 85 and 95⁰C, Again, this aging step is preferably carried out under such conditions that the contact between the reaction medium and carbon dioxide from the air is minimized.

Depending on the use of the LDH the dispersion may be used as such in further processing. As an alternative the LDH may be filtered and spray dried, or extruded.

It is possible to contact (impregnate) hydrotalcite-like material after formation with other metals, such as metal salts and other metal compounds, including transition and/or noble metals. This may either be done directly after formation or in any further stage, such as after (re)calcinalion, rehydration, drying, etc. To increase the physical properties of the resulting solid material it may be desired to decrease the pH of the reaction medium before shaping, ε.g, to a value of about 10, e.g., using acetic acid.

The meixnerite type layered double hydroxide of the present invention can advantageously be prepared using a solid magnesium source and a solid aluminium source. While the present invention will be described referring in particular to magnesium as the divalent metal ion and aluminium as the trivalent metal ion. ii should be understood that other divalent and trivalent metal ions are also envisaged within the scope of the present invention, as are combinations of magnesium with one or more other divalent metal ions and aluminium with one or more other trivalent metal ions. In one embodiment of the present invention, aluminium oxide or hydroxide is used as solid aluminium source. More in particular, the solid aluminium source is selected from the group consisting of aluminium hydroxide, boehmite, pseudoboehmite, gibbsitε, gel alumina, calcined aluminium hydroxide, and mixtures thereof.

In prior art there is much literature and many patents wherein the terms, "activated/active alumina" is interchangeably used with the term ""transition" alumina. Both of these terms refer to the same material, Briefly, when aluminum hydroxides such as boehmites, gibbsite, hydrous gel alumina are calcined, they transform to "transition'^" or '"activated/active" forms of alumina. Depending on the severity of calcination (i.e., temperature, time, atmosphere and particle size of the starting alumina source) different 18

types of transition forms of alumina are formed which have different PXRD patterns, physical, and chemical properties. Another characteristic property of these transition forms of alumina is that during the process of calcination, dehydration and dehydroxylation takes place, thus the produced transition forms contain minimal or no hydroxyl groups and water. Further, when gibbsite is "flash calcined," the transition/activated form of aluminum oxide formed shows a very broad PXRD pattern, and, when contacted with water under thermal or hydrothermal conditions, it reacts with the water and this oxide form of transition alumina forms hydroxyl groups. Under the appropriate hydration conditions (i.e., temperature, time, pH, etc), this kind of transition form can be reconverted to a crystalline or semi-crystalline type of boehmite or gibbsite. Due to this property, these kinds of transition aluminum oxides sometimes are referred to in the prior art, as rehydratable aluminium oxides. Commercial examples of these "transition/activated," or "rehydratable oxide alumina" are the Alcoa's CP 1, 2, 3 and 7 and used grades and described in patents US 4,579, 839, and 4,120,942. For the purpose of the present invention, we define transition (activated) alumina as products formed by calcining or flash calcining aluminum hydroxides (ATH, boehmites. gel alumina) sufficiently that their original crystalline structure (based on PXRD) has substantially disappeared, and/or that the associated hydroxyl groups have been dεhydroxylated. This definition is consistent with the teachings of prior art and established scientific nomenclature.

Further, the activated, transition and rehydratable forms of alumina are, in essence, aluminum oxides since which have been produced by the calcination treatments and are essentially dehydrated and dehydroxylated, and have different XRD patents and different physical and chemical properties from their precursor alumina hydroxides. A clear distinction in this patent application is made between aluminum oxides and aluminum hydroxides.

Therefore, for the purpose of this patent application: the terms activated/active alumina oxides are equivalent and refer to the same materials as the term "transition" alumina oxides or simply "aluminum metal oxides" or "metal oxides." The term "rehydratable alumina oxides" is one kind of the activated/active alumina oxides which exhibits the property, that when contacted with water reforms hydroxyl groups and may be transformed to aluminum hydroxides such as gibbsite, boehmite, bayerite, etc. L7

In one embodiment of die present invention, the solid magnesium source is selected from magnesium oxide, magnesium hydroxide, calcined forms of magnesium carbonate or magnesium hydroxy! carbonate. In a preferred embodiment of the present invention, the solid magnesium source is selected from magnesium oxide and magnesium hydroxide.

The material of the invention has the advantage that it can be calcined under conventional condition as indicated above, while retaining the memory of the original, which means that after rehydrating, it still possesses a ratio R within the range of the invention. When extrudatεs are rehydrated again to get the original meixnerite material back the strength may be improved. It is also possible to rehydratε in the presence of carbonate ions, resulting in hydrotalcite. Rehydration can take place under suitable conditions of temperature, in water, such as ambient or elevated temperature, either hydrothermally or under autogenous conditions, If a material according to the invention is to be produced, such rehydration should occur in a substantially CO₂-free atmosphere. Another possibility is to convert the meixnerite type of material to other LDH's by exchanging the anion by other suitable anions, for example during rehydrating.

Depending on the intended use, the layers of the LDH can be pillared with organic, inorganic or mixtures of pillaring ions.

The material may be used as such, as a shaped body further optionally comprising a organic or inorganic binder, preferably aluminium trihydrate (ATH), more preferred gibbsite. In a preferred embodiment of this invention aluminium trihydrate (ATHj is applied as a low cost effective binder for the preparation of extrudates or other forms of shaped bodies. Such shaped bodies are obtained by combining the material of the present invention with a binder or matrix (if used), and subjecting the material to a shaping step, e.g., an extrusion step, pelletising step, beading step, or any other shaping step known in the art.

In one embodiment, the aging step is carried out after the formation of shaped bodies. It is also possible to age the material partially in the slurry, shape it, and subject the shaped bodies to a further aging step.

In one embodiment, shaped anionic clay according to the invention is calcined, rehydrated, and again calcined, wherein if so desired at any point in time the material may or may not be subjected to a shaping step. In one embodiment of the present invention the material as formed, or the calcined form thereof, comprises a composite containing a M²⁺ZM³⁺ spinel.

The material can also have the form of a matrix, comprising an organic, inorganic or combined organic-inorganic matrix material, and the composition of the present invention.

The matrix material is preferably selected from polymer, resin, paint, boεhmite, pseudoboelimiie, gibbsite, amorphous alumina, calcined forms of or mixtures thereof, anionic or catiomc clay, synthetic or natural zeolite. The clay material of the present invention may be present in a suspension using water or other solvents, optionally with the aid of an organic additive, such as surfactant, dispersing agent, and so on. It is also possible to apply the material to the surface of a preformed body, for example as a washcoat on a structured material (monolith).

The materials of the invention, and the calcined forms thereof, can advantageously be used in various applications in the chemical industry, including the use as catalyst, catalyst support and as additives in various applications, such as paper, polymers, and

Specific examples of these uses are as refining catalyst or support in JFCC₅ HPC, HT, hydro-cracking, reforming, Steam-Reforming, Watergas shift, Zϊegler-Natta, GTL, CTL, Fischer-Tropsch, SCOT, Glaus, estherification, etherifi cation, Aldol-condensation, and/or the production of fine chemicals, including oleo-chemicals, olefins, alcohols and fragrances.

The materia! of the invention can also suitably be used as polymer additive in PA⁷C₅ polyester packaging (PET), other thermoplastics, for example to impart flame retardant properties.

In the paper industry it can be used as an additive for paper, board or carton, for example as acid scavenger, flame retardant or adsorbent.

An other use is in building materials, as additive for cellulose building materials.

Further uses are - in polymers (as flame retardant, alone or in combination with ATH₅ coated or impregnated onto ATH)₅ as adsorbent for acids, halogens, or gases such as NO_x or SO_x, in waste water treatment, as additive (excipient, crystallization aid) in pharmaceuticals in (enhanced) oil recovery of heavy oils, crudes, oil or tar sands, shale oil, and the like, as additive in biomass conversion, - in carbon dioxide sequestration, and in

Radio-active metal scavenging (e.g. Fe).

The invention is further elucidated on the basis of the following, non-limiting, examples.

Example 1

In a vigorously stirred reactor containing 100 liters of water at a temperature of 85°C was added boehmite alumina (e.g., Versal 700) that was mixed for about thirty minutes.

Subsequently magnesium oxide (Zolitho 40) was rapidly added and the resulting slurry yielding a pH greater than 12 was further vigorously stirred while heated at about 95⁰C for another thirty minutes. The reactor is a closed vessel and the final volume of slurry is such that the tank is essentially full to minimize the open head space above the slurry, so that there is a continuous purge of steam escaping through the small opening in the lid on the tank. This steam purge minimizes the introduction of air/carbon dioxide into the slurry during this mixing phase, which is referred to as nucleation.

The resulting slurry is piped to a second closed tank in such a manner as to minimize the introduction of air/carbon dioxide. This slurry is further aged at 95°C for six hours. Again the steam purge minimizes the introduction of air/carbon dioxide into the slurry during this crystallization phase.

The PIiXD spectrum of this material is given in Figure 1. The material has an R- value of 17.

.E.xamEl.?..2

The slurry from Example 1 is spray dried into the form of microspheres with an average particle size of 80 to 100 microns and an LOl(IOOO⁰C) of about 40%. Ex_amρle_3__

To the resulting slurry from Example 1. sufficient acetic acid is added to lower the pH to about 10. This slurry was spray dried into the form of microspheres with an average particle size of 80 to 100 microns and an LOI(I OOO⁰C) of about 40%, The addition of acetic acid results in a material with improved physical properties, such as an improved average bulk density and improved attrition properties,

Example 4

To the resulting slurry from Example 1, sufficient aluminum trihydrate (ATH) was added such that weight percentage (dry basis) was 20% based of the overall weight of the product. To this suspension was added sufficient acetic acid to lower the pH to 10 , The resulting slurry was spray dried into the form of microspheres with an average particle size of 80 to 100 microns and an LOI(IOOO⁰C) of about 40%,

Example s,

The spray dried product from Example 4 was calcined at 600⁰C for one hour followed by rehydration in aluminium sulfate solution (equivalent to 6% A12O3 on the final product) at 90⁰C for one hour, The slurry is filtered and dried at 100⁰C. This calcinations/rehydration process improves the mechanical strength of the microspheres.

Example 6

The slurry from Example 1 was filtered on a pressure filter without washing. To the resulting filtercake were added 1 to 10% aluminum trihydrate (ATH) and 5% citric acid, both based on the dry weight of the final product. This mixture was further mixed in a kneader-type mixer to produce a uniform "paste" that was processed in a standard extruder to produce 3 mm diameter extrudates . The resulting extrudates were then dried at 150⁰C for twelve hours in a stationary dryer and calcined at 600°C in a muffle furnace.

Example 7

The spray dried product from Example 4 was calcined at 600⁰C for one hour followed by rehydration in zinc sulfate solution (equivalent to 6% zinc oxide on the final product) at 9O⁰C for one hour. The slurry is filtered and dried at 100⁰C. This calcinations/rehydration process improves the mechanical strength of the microspheres.

Claims

1. Hydrotalcite-like Layered Double Hydroxide (LDH) comprising a divalent (M²⁺) and a trivalent (M^3*) metal with interlayer hydroxyl ions as charge balancing anions, and wherein the composition in a compacted powder form, exhibits a preferred crystallite orientation such that the ratio R of the sum of the intensities of the hydrotalcite reflections in the region of 8 to 28° 2Θ to the sura of the hydrotalcite reflections in the region of 25 to 55° 2Θ is at least 3, and the materia! is substantially free of nitrate, sulphate, and chloride.

2. Hydrotalcite-like Layered Double Hydroxide according to claim 1, wherein the ratio (R) of the sum of the intensities of the hydrotalcite reflections in the region of 8 to 28° 2Θ to the sum of the hydrotalcite reflections in the region of 25 to 55° 2Θ is at least 4, in particular more than 5, still more in particular more than 6.

3. Hydrotalcite-like Layered Double Hydroxide according to claim 1 or 2 wherein the ratio R of the sum of the intensities of the hydrotalcite reflections in the region of 8 to 28° 2Θ to the sum of the hydrotalcite reflections in the region of 25 to 55° 2Θ corresponds to the ratio R of the sum of the X-ray intensities of the <GOL> reflections over the sum of the intensities of the <hk€> reflections is at least 3, preferably more than 5, and more preferably greater than 6, wherein L = I₅ 2, 3 , , .infinity, i = 0, 1, 2, 3, 4 ...infinity; h = 0, 1 , 2, 3, 4 ...infinity, and k = 0, 1 , 2, 3, 4 ...to infinity, wherein h, and k are not 0 simultaneously, and wherein the <00L> reflections are determined in the region of 8 to 28° 2Θ and the <hkf > reflections are determined in the region of 25 to 55° 2Θ.

4. Hydrotalcite-like Layered Double Hydroxide according to any one of the preceding claims, which is substantially free of anions other than hydroxides and carbonates.

5. Hydrotalcite-like Layered Double Hydroxide according to any one of the preceding claims composition according to claim 1, wherein the intercalated Hydroxyl ion concentration is at least 20%, preferably more than 40% and most preferably more than 60% of the total intercalated anion concentration, still more preferably more than 80% of the total intercalated anion concentration, with the balance preferably being carbonate anions.

6. Hydrotalcite-like Layered Double Hydroxide according to any one of the preceding claims, wherein the divalent ion (M²⁺) is magnesium and the trivalent ion (M³⁺) metal is aluminium.

7. Method for manufacturing a Hydrotalcite-like Layered Double Hydroxide according to any one of the preceding claims, comprising the steps of homogenizing in a water slurry a solid divalent metal source and a solid trivalent metal source, of which one at least is water insoluble, and with pH higher than 11 and at temperatures in the range of 60°C to 100⁰C, or hydrothemially under autogeneous pressures at a temperature above 100⁰C, the reaction being carried out in the absence of salts of nitrate, sulphate, or chloride, wherein the process is carried out in such a manner that the contact between carbon dioxide from the air and the reaction medium is minimized,

8. Method according to claim 7, wherein the reaction is carried out in die absence of anions other than carbonates, oxides, of hydroxides.

9. Method according to claim 8, wherein the reaction is carried out in the absence of anions other than oxides or hydroxides.

10. Method according to any one of claims 7-9, wherein the slum' is subsequently aged at temperatures below 100⁰C or elevated temperatures hydrothermally under autogeneous pressures.

11. Method according to any one of claims 7-10, wherein the solid divalent metal source and the solid trivalent metal source are dispersed in water at a pH of over 11 having a temperature of between 60 and 100⁰C, preferably between 65 and 95°C and more preferred between 85 and 95⁰C.

12. Method according to any one of claims 7-11, wherein the reaction is carried out under such conditions that the atmosphere above the slurry consists primarily of water vapour (steam).

13. Method according to any one of claims 7-12, wherein the solid trivalent metal source is selected from aluminium oxide, aluminium hydroxide, or mixtures thereof, more in particular from aluminium oxide or hydroxide selected from the group consisting of aluminium hydroxide, boehmite, bayerite, pseudoboehmite, gibbsite, gel alumina, calcined aluminium hydroxide, and mixtures thereof.

14, Method according to any one of claims 7-13, wherein the solid divalent metal source is selected from magnesium oxide, magnesium hydroxide or calcined forms of magnesium carbonate or magnesium hydroxyl carbonate, in particular the solid magnesium source is selected from magnesium oxide, magnesium hydroxide, and mixtures thereof.

15. Shaped body comprising the hydrotalcite-like Layered Double Hydroxide according to any one of the claims 1 -6 and optionally a binder.

16. Method for manufacturing the shaped body according to claim 15. comprising the steps of combining the material of the present invention with a binder or matrix, if used, and subjecting the material to a shaping step.

17. Use of a composition according to claim 1-6 or 15, or the calcined form thereof as additive and/or sorbent for cellulose materials, resin, paint, pharmaceuticals and polymeric materials, anionic or cationic clays, synthetic or natural zeolites, in chemical industry as additive, sorbent, precursor, catalyst and/or catalyst support,

18. Use according to claim 17, as sorbent and/or refining catalyst or support in_. FCC, HPC, HT, hydro-cracking, reforming, Steam-Reforming, Watergas shift, Ziegler-

Natta, GTL, CTL, Fischer-Tropsch. SCOT, Claus, estherification, etherification, Aldol- condensation, and/or the production of fine chemicals, including oleo-chemicals, olefins, alcohols and fragrances.