SYNTHETIC SWELLING CLAY MINERALS

Description

[0001] The invention relates to new, synthetic swelling clay minerals, as well as to a process for the preparation of such clay minerals.

[0002] Clay minerals are solid substances, substantially made up of metal and oxygen atoms, whose crystal lattice has a layered structure. This layered structure consists of three repeating layers. Located centrally in this elementary three-layer structure is a layer of substantially trivalent or substantially divalent metal ions (cations). Examples of clay minerals with substantially trivalent ions are montmorillonite and beidellite; examples of clay minerals with substantially divalent ions are hectorite and saponite. The metal ions present in the central layer are octahedrally surrounded by oxygen and hydroxyl ions. In a clay mineral with trivalent ions, two of the three octahedron positions are occupied by metal ions. Accordingly, this is referred to as a di-octahedral clay mineral. In a clay mineral with divalent metal ions, all three octahedron positions are occupied by metal ions; this is referred to as a tri-octahedral clay mineral. On opposite sides of this layer of octahedrally surrounded metal ions occurs a layer of tetrahedrally surrounded ions. These tetrahedrally surrounded ions are generally silicon ions, while a part of the silicon can optionally be replaced by germanium. The unit of the tetrahedrally surrounded silicon ions is Si₂O₅(OH). In this connection it is noted that in the tetrahedron and octahedron layers the actual point where the charge is located cannot always be indicated equally clearly. The term 'ions' as used in this context accordingly relates to the situation where an atom, given a completely ionic structure, should possess an electrostatic charge corresponding with the oxidation state.

[0003] Essential to clay minerals is that a part of the cations present are substituted by ions of a lower valency. Thus it is possible to substitute a part of the trivalent or divalent metal ions in the octahedron layer by divalent and monovalent metal ions, respectively. With substantially trivalent metal ions, this substitution results in montmorillonite and with substantially divalent metal ions in hectorite. It is also possible to substitute the tetravalent silicon ions in the tetrahedron layers by trivalent aluminum ions. With a clay mineral with almost exclusively trivalent ions in the octahedron layer, the result is then a beidellite and with a clay mineral having almost exclusively divalent ions in the octahedron layer, the result is a saponite. Of course, substitution by an ion of lower valency leads to a deficiency of positive charge of the platelets. This deficiency of positive charge is compensated by including cations between the platelets. Generally, these cations are included in hydrated form, which leads to the swelling of the clay. The distances between the three-layer platelets is increased by the inclusion of the hydrated cations. This capacity to swell by incorporating hydrated cations is characteristic of clay minerals.

[0004] If no metal ions or silicon ions are substituted by ions of a lower valency, the platelets are not charged. The mineral then does not absorb any water into the interlayer and therefore does not swell. The mineral with exclusively aluminum in the octahedron layer and silicon in the tetrahedron layer is pyrophyllite and the mineral with exclusively magnesium in the octahedron layer and silicon in the tetrahedron layer is talc. The swelling clay minerals having a negative charge of from 0.2 to 0.6 per unit cell, -O₁₀(OH)₂, are known as smectites.

[0005] The cations in the interlayer of swollen clay minerals are strongly hydrated. As a result, these ions are mobile and can be readily exchanged. The exchange is carried out by suspending the clay mineral in a concentrated solution of the cation to be provided in the interlayer. The high concentration provides for a concentration gradient as a result of which the exchange proceeds. Upon completion of the exchange, the concentrated solution is removed by filtration or, preferably, by centrifugation and washing, whereafter, if necessary, the last metal ions not bound in the interlayer can be removed by dialysis.

[0006] The negative charge of the platelets can be compensated not only with hydrated cations, but also with (hydrated) hydrogen ions, H₃O⁺. In this case the clay can function as a solid acid, which leads to important catalytic applications. Suspending a clay mineral in a concentrated acid does not lead without more to the provision of hydrogen ions in the interlayer. In fact, it has been found that the acid reacts with the cations of the clay structure, so that these ions are removed from the clay structure. These cations eventually end up in interlayer positions.

[0007] If it is desired to provide Brønsted-acid groups in a hydrated clay mineral, in general hydrolysing metal ions are provided in the interlayer. As a result of the hydrolysis, hydrogen ions are formed. Upon reduction of the amount of water in the interlayer, for instance through thermal desorption, the acid strength increases. Due to the lesser amount of water, the residual water molecules are polarised more strongly by the metal ions. Upon complete removal of the water, however, the Brønsted-acid groups disappear. If it is desired to impart Brønsted-acid properties to clay minerals at elevated temperatures, (hydrated) ammonium ions can be provided in the interlayer. Upon heating, the water and the ammonia escape while a proton remains behind.

[0008] Natural clay minerals have long been used for the practice of catalytic reactions in liquid and in gaseous phase. In general, the catalytic activity of clay minerals is based on the presence of Brønsted- or Lewis-acid groups in the clay minerals. In the conventional acid-catalysed reactions in the liquid phase often sulfuric acid is used. This acid yields Brønsted-acid groups while, moreover, it can dehydrate in that it has strong water-binding properties, and can take up undesired higher molecular by-products. What results, however, are large amounts of polluted sulfuric acid, acid tar, for which it is difficult to find any use. Neutralisation of large amounts of sulfuric acid used as catalyst leads to ammonium sulfate, which can be disposed of as less high-grade fertilizer, which is useful only for a business which also produces and/or sells other kinds of fertilizer.

[0009] In syntheses where Lewis-acid catalysts are needed, such as the Friedel-Crafts synthesis, metal chlorides, such as aluminum chloride, are used as catalyst. Hydrolysis of the aluminum chloride upon completion of the reaction leads to large amounts of highly corrosive suspensions of aluminum hydroxide.

[0010] Accordingly, both the use of sulfuric acid and the use of Lewis-acid catalysts, such as aluminum chloride or zinc chloride, entail drawbacks. Therefore, there is a need for solid acid catalysts that are suitable for carrying out such acid-catalysed reactions. Accordingly, one of the objects of the invention is to provide such solid acid catalysts for carrying out reactions in the liquid and/or gaseous phase, which are catalysed by Brønsted- and/or Lewis-acids.

[0011] Of great importance in this connection is the degree of hydration of the clay minerals. If water-immiscible, liquid reactants are to be processed, the presence of water on the surface of clay minerals prevents the required intensive contact between the reactants and the clay surface. The water will preferentially wet the clay surface. In many liquid phase reactions, therefore, it will be necessary to priorly dehydrate the clay mineral to be used. This must take place without any substantial reduction of the accessible clay surface. Also, the reagents used will generally have to be dried to a far-reaching extent.

[0012] Another important problem with the use of solid catalysts in liquid phase reactions is the separation of the catalyst from the reaction mixture. Generally, this is effected by filtration or centrifugation. The known, mostly natural, clay minerals generally lead to a compressible filter cake. This makes it cumbersome to separate the clay mineral by filtration or centrifugation from the reaction products and unreacted reactants. One of the tasks of the invention is therefore to provide clay minerals in a form which is readily separable from the reaction products and unreacted reactants.

[0013] Another problem occurring in catalytic reactions in the presence of heterogeneous catalysts relates to the occurrence of transport impediments in the porous catalyst body. In the liquid phase diffusion coefficients are generally a factor 10⁴ lower than in the gaseous phase. As a result, soon transport impediments arise when high-porosity solid catalysts are used in liquid phase reactions. Especially in organo-chemical reactions transport impediments have a highly adverse effect on the selectivity. Thus, it will be desired, when alkylating benzene for instance, to minimize the amounts of di- or tri-substituted reaction products. This is possible only when reactants and reaction products are quickly transported through the solid catalyst. This requires a catalyst with short and wide pores. A third task of the invention is thus to provide clay minerals with short, wide pores which can be readily separated from a liquid phase.

[0014] In summary, clay minerals for use as liquid phase catalysts should satisfy the following, partly contradictory, requirements:

• (i) a far-reaching dehydration must be possible without a substantial reduction of the active surface accessible to reactants,
• (ii) ready separation of the liquid phase in which the reaction has been carried out,
• (iii) excellent transport properties, that is, the presence of wide, short pores; short pores require small catalyst bodies, which renders the separation from the liquid phase more difficult again.

[0015] In the gaseous phase clay minerals were used especially for catalytically cracking petroleum fractions. By the end of the thirties, natural clays were used on a large scale in the catalytic cracking of petroleum fractions. Soon, however, clay minerals were replaced by amorphous aluminum oxide-silicon dioxide catalysts, which were found to satisfy better the requirements of the technical implementation of the cracking process. By spray-drying, on the basis of amorphous aluminum oxide-silicon dioxide, wear-resistant bodies of dimensions of from 50 to 200 µm could be easily produced. These bodies are simple to transport in a gas stream from the regeneration zone to the cracking zone.

[0016] Subsequently, in the sixties, cracking catalysts based on zeolites were developed, which exhibited a higher activity and selectivity. From natural clays, bodies of the required dimensions can be prepared which contain only zeolite crystallites. In general, however, small zeolite crystallites (approximately 1 µm or less) are included in amorphous aluminum oxide-silicon dioxide, which functions as binder. The limited dimensions of the pores in zeolites have as a consequence that heavier fractions can no longer be cracked with zeolites.

[0017] The elementary platelets of current, natural clay minerals'are relatively large, > 1 to 30 µm, while mostly a large number of platelets, viz. more than 20 to 50 elementary platelets, are stacked into packages. As a result, upon dehydration, which renders the interlayer inaccessible, the catalytically active surface is relatively small. Is has now been found that the accessible surface of dehydrated clay minerals can be markedly enlarged by 'pillaring' the clay mineral. In that case, by metal ion-exchange hydrated oligomers or polymers of inter alia aluminum, zirconium, titanium and/or chromium are provided between the clay layers. Upon dehydration, a metal oxide 'pillar' is left. After dehydration, the distance between the clay layers varies from 0.6 to 1.6 nm. It is endeavored to realise even greater distances between the clay layers by arranging greater pillars. This is to make it possible to process heavier petroleum fractions.

[0018] Especially around 1980, much research was done on the pillars of clay minerals, as appears from the number of patent applications filed and the number of patents granted. An example is U.S. Patent 4,176,090, which discloses pillared clay materials that are useful as catalysts and sorbents. According to this patent specification, an aqueous suspension of a natural clay mineral, such as calcium bentonite or beidellite, is prepared and the suspension is mixed with a solution of polymeric metal (hydr)oxide particles. The positively charged polymeric complexes exchange with the cations originally present in the clay. Then the clay is separated from the aqueous solution, the material is dried, and finally calcination is carried out at a temperature of about 200 to 700°C. While initially the interlayer is completely filled with water, in which the originally present cations or the polymeric complexes occur, after drying and calcination only the oxide of the polymeric complex is present. The greater part of the interlayer is now accessible to gas molecules since the elementary clay layers are kept separate by the oxide formed from the polymeric complex. As appears from the examples included in the patent specification, half an hour is sufficient to complete the exchange in the aqueous suspension. It should be noted here that in the examples relatively small clay particles are used, viz. less than about 2 µm. This appears from Example 3 of the above U.S. Patent 4,176,090; in fact, it is communicated that the separation of the clay particles from the aqueous phase poses problems. For this reason, in that example a flocculating agent is used. For this purpose, inter alia a sodium silicate solution can be used.

[0019] Mentioned as pillaring agents are positively charged hydroxy complexes of aluminum, zirconium, and/or titanium. In one of these examples, a mixed hydroxy complex of magnesium and aluminum is prepared. In most examples of the above U.S. Patent 4,176,090 pillaring is carried out with polymers based on hydrated aluminum oxide. It is possible to prepare discrete complexes with thirteen aluminum ions, the so-called Al₁₃ complex. However, it is difficult to obtain this complex in pure form; nearly always a considerable part of the aluminum is present in the system in a different form, while the strongly diluted solutions of Al₁₃ generally necessitate large volumes of water. For the preparation of pillared clay minerals on a technical scale, this is a disadvantage.

[0020] The distance of the elementary platelets in the clay structure, which is easy to determine by X-ray diffraction, is 0.7 to 1.0 nm after pillaring and after calcination. The BET surface varies from 150 to 600 m² per gram and the pore volume from 0.1 to 0.6 ml per gram. Further, it is found that more than 50% of the surface and in many cases even more than 75% of the surface is present in pores of a size less than 3 nm. This means that the elementary platelets of the clay structure are stacked to a considerable extent. If the elementary platelets were arranged relatively arbitrarily, as in a house of cards, a much larger fraction of the surface should occur in much wider pores.

[0021] U.S. Patent 4,216,188 relates to the preparation of pillared clay minerals from bentonite (montmorillonite). Here, polymeric hydroxy complexes of aluminum and chromium are mentioned as reagents for obtaining the pillars. The process of this patent distinguishes over that of U.S. Patent 4,176,090 in that now the colloidal suspension of the starting clay mineral is prepared more carefully. The clay mineral is suspended in water and by treatment with NaCl the interlayer ions originally present are exchanged for sodium. Then the suspension is washed thoroughly and the last residues of NaCl are removed by dialyses. By centrifugation, the particles of less than 2 µm are then separated. Next, the suspended clay particles are reacted with the polymeric aluminum or chromium complex, with the concentration of the chromium complex in particular being very low. After a thermal treatment at 150 to 450°C a BET surface of 160 to 240 m² per gram is obtained. This patent mentions a distance between the elementary platelets of about 0.9 nm.

[0022] U.S. Patent 4,248,739 describes a method wherein the pillars are provided using positively charged hydroxy complexes having a molecular weight of from 2000 to 20,000. However, the properties of the calcined pillared clay minerals are not significantly different from those mentioned in US-A 4,176,090. The methods for the preparation of pillared clay minerals mentioned in US-A 4,271,043 are not essentially different, either. Although the specification mentions that the thermal stability of the pillared clay minerals is high.

[0023] If form-selective catalytic reactions are to be carried out, a catalyst of narrowly defined pore dimensions is required. Zeolites satisfy this requirement exellently. However, a problem is that the transport in zeolites often proceeds poorly. Thus it has been demonstrated that molecules cannot pass each other in the pores of zeolites. Pillaring clay minerals also leads to pores of sharply limited dimensions, so that such materials can be suitable heterogeneous catalysts for such reactions. One condition, however, is that the materials can be prepared on a technical scale in a well reproducible manner.

[0024] Now, the preparation of suitable pillaring agents, such as the polymeric hydroxy complexes on a technical scale is difficult. In general, there are only a few businesses that produce suitable solutions of these complexes. In addition, in most cases the fraction of the aluminum that is present as Al₁₃ is not large. As a consequence, very large volumes have to be employed to produce large amounts of pillared clay minerals, which in general is technically very difficult. Accordingly, one of the objects of the invention is to provide processes for the production of suitable pillaring agents on an industrial scale. Since the provision of the hydrated pillars in the clay mineral does not pose any problems technically, provided the clay particles are not too large, the production of the hydrated pillars on a technical scale seems to be the chief problem.

[0025] Purifying natural clays is cumbersome. In general, the clay must be suspended and the impurities allowed to settle. Then the clay must be separated from the suspension, which is technically problematic. This appeared hereinabove in the discussion of US-A 4,176,090, which publication mentioned that much leakage of clay particles through the filter occurred. In addition, there is the problem that important clay minerals do not occur in nature or do so to an insufficient extent. One of the major problems in the use of natural clay minerals for catalytic purposes is moreover that although these materials may be very cheap, the properties are very difficult to control.

[0026] The synthesis of clay minerals according to the current state of the art is technically difficult. Customarily, a protracted (a few weeks) hydrothermal treatment is used at relatively high temperatures and pressures, under agitation of the aqueous suspension. In general, only a few grams or even only some tens of milligrams of a clay mineral can be synthesized simultaneously. The application of this technology on a large (industrial) scale is very difficult, if not impossible. As a result, synthetic clay minerals are costly. An example of such a synthesis, in this case of hectorite, is given in US-A 3,666,407. Because hectorite has especially interesting rheological properties and does not occur much in nature, the synthesis of this mineral is of interest. This preparation starts from natural talc, which contains magnesium, oxygen and silicon and which occurs amply in nature in pure form. This material, after being crushed and mixed with lithium carbonate, is heated at 760 to 980°C for approximately 1 hour. After cooling, water glass and soda are added and for 8 to 16 hours the mixture thus obtained is treated hydrothermally, i.e. at high temperature and high pressure, under agitation of the preparation. It is clear that this is a relatively costly preparative procedure.

[0027] This also applies to the method for the preparation of synthetic clay minerals discussed in US-A 3,671,190. In this patent it is observed that the preparative procedures thus far known have only been carried out on a laboratory scale and often yield only milligrams of the desired clay mineral which moreover is often polluted with quarts. In the method of US-A 3,671,190, magnesium and silicon are coprecipitated by mixing water glass with a solution of a magnesium salt. The suspension thus obtained is then treated hydrothermally. To that end, the mixture is maintained under pressure at 250°C for about 4 hours with stirring. It is difficult to control the degree of crystallization and hence the dimensions of the crystallites.

[0028] Owing to the poorly controllable properties of natural clay minerals and the high price of synthetic clay minerals, the use of clay minerals for catalytic purposes has remained quite limited. Although the patent literature around 1980 evidenced much research effort in the field of the catalysis of (pillared) clay minerals, the technical application thereof has remained very slight.

[0029] Surprisingly, it has now been found that the above-mentioned tasks can be fulfilled by making use of a structure of clay minerals of which the dimensions of clay platelets are controllably variable from 1 µm to 0.05 µm, the stacking of elementary platelets can be controlled from on average one to three platelets to a number of approximately twenty platelets, while the ratio of different metal ions in the octahedron layer and/or tetrahedron layer is adjustable.

[0030] Accordingly, the invention therefore relates in a first embodiment to a structure of clay minerals as defined defined in claim 1.

[0031] The deficiency of positive charge is compensated by protons and/or cations which are present between the platelets. According to the invention, it is essential that at least a part of the octahedrally and/or the tetrahedrally surrounded ions have been replaced by other ions of lower valency. In a first embodiment, the trivalent ions in the octahedron layer can be replaced by divalent ions. If the octahedron layer is made up of divalent ions, a part thereof can be replaced by lithium ions.

[0032] In a second embodiment, the silicon (germanium) in the tetrahedron layer can be replaced by trivalent ions. It is also possible to have a replacement in the octahedron layer as well as in the tetrahedron layer. In the case where a clay mineral is synthetized with an octahedron layer based on divalent ions and with a substitution of trivalent ions in the tetrahedron layer, a slight substitution of trivalent ions may also occur in the octahedron layer. However, the net charge of the elementary platelets will always be negative, i.e. there is a deficiency of positive charge in the platelets.

[0033] In this connection, it is observed that the term 'replacement' or 'substitution' is employed in the meaning that a change has occurred relative to the ideal structure. After all, typically, in practice both components (ions of higher and lower valency) will simultaneously be presented during the preparation of the clay minerals.

[0034] In the octahedron layer, aluminum, chromium, iron (III), cobalt(III), manganese (III), gallium, vanadium, molybdenum, tungsten, indium, rhodium and/or scandium are preferably present as trivalent ions.

[0035] As divalent ions, magnesium, zinc, nickel, cobalt(II), iron(II), manganese(II), and/or berillium are preferably present in the octahedron layer. This may be the component of the higher valency as well as the component of the lower valency.

[0036] In the tetrahedron layer, silicon and/or germanium is present as tetravalent component and preferably aluminum, boron, gallium, chromium, iron(III), cobalt(III) and/or manganese(III) are present as trivalent component.

[0037] A part of the hydroxyl groups present in the platelets can partly be replaced by fluorine.

[0038] For processing heavier petroleum fractions, catalysts having pores of at least 6 nm are preferably used. For the time being, this seems hard to achieve by means of the pillaring of clay materials. For this reason, a following objective of the invention is to provide clay minerals having, in a dehydrated state, a large and properly accessible surface. Efforts are directed to having the active surface present in wide pores of a dimension of at least 6 nm. One of the objectives of the invention is the preparation of clay minerals in such a manner that the elementary platelets are hardly mutually stacked, but form a house of cards, as it were. Such a house of cards-stucture is characterized by the presence of wide pores having a pore size of at least 6 nm, determined by means of nitrogen sorption at 77K, as described by S.J. Gregg & K.S.W. Sing in 'Adsorption, Surface Area and Porisity, Academic Press London, New York (1967) and/or in K.S.W. Sing, 'Characterization of CAtalysts' (J.M. Thomas and R.M. Lambert eds), pp. 11-29, John Wiley & Sons, Chichester (1980).

[0039] Such a structure has the property that hardly any (001) or no reflections occur in the X-ray diffraction pattern, which indicates that hardly any stacking is present. In addition, this appears from the fact that the larger part of the accessible surface area, more in particular more than 150 m²/g, occurs in pores wider than 6 nm.

[0040] The preparation of the synthetic clay minerals according to the invention proves to be surprisingly simple. In the widest sense, one may argue that the components required for the synthesis, oxides of silicon (germanium) for the tetrahedron layer and the tri/di/monovalent ions for the octahedron layer, are presented in aqueous medium, are brought to the desired pH (3-9, preferably 5-9) and are then maintained for some time at a temperature of 60-350°C, with the pH being maintained within the desired range. The reaction time strongly depends on temperature, and hence on pressure, with higher temperatures enabling shorter reaction times. In practice, reaction times to the order of 5-25 hours are found at the lower temperatures, 60-125°C, whereas at temperatures in the range of 150°C and higher, reaction times to the order of some minutes to approximately 2.5 hours may suffice. The reaction time partly determines the dimensions of the clay minerals.

[0041] Such a process can be carried out in a number of manners, depending on the nature of the components and the desired result. Preferably, chlorides of the metals involved are not worked with, as they lead to a reaction into clay minerals that is hardly perceptible, if at all.

[0042] In accordance with a first variant, the starting products for the preparation are mixed as a solution and the pH is adjusted to the range where the preparation is to take place. During the following heating operation, the pH is kept substantially constant, for instance through hydrolysis of urea, injection of a neutralizing agent below the surface of the well-stirred liquid, or with electrochemical means.

[0043] However, for achieving a rapid and proper preparation, it is preferred to homogeneously increase the pH of a solution of the metal ions to be incorporated into the octahedron layer in the presence of solid silicon dioxide. For this, an acid solution of the components is started from, which is for instance obtained by mixing water glass and aluminate with each other, acidifying it and adding a solution of a nickel salt thereto. The pH should be kept low enough for the nickel not to precipitate. Then, the pH is increased homogeneously, for instance through hydrolysis of urea, injection of a neutralizing agent below the surface of the vigorously stirred liquid, or with electrochemical means.

[0044] It is also possible to start from a suspension of finely divided silicon dioxide or silica gel in a solution of the metal ions to be incorporated into the octahedron layer. The metals are then preferably precipitated by increasing the pH homogeneously. It is also possible to carry out this process in the presence of a thin layer of silicon oxide provided on a solid surface, for instance on the walls of the channels of a monolith or on the surface of a stirrer. At an increasing pH of the liquid, the metal ions react with the silicon dioxide to form silicate structures. For this preparation no high pressures are required; it is possible to operate under atmospheric pressure, while scaling up of the process is extremely simple, because a homogeneous solution of the metal ions to be incorporated is worked from.

[0045] Surprisingly, it has been found that in the presence of two different metal ions, these metal ions are incorporated into the octahedron layer side by side. The typical swelling clay structure is brought about by the presence of divalent and trivalent ions side by side in the octahedron layer.

[0046] The temperature at which the pH is homogeneously increased influences the dimensions of the clay platelets formed. At higher temperatures, larger clay platelets are formed. In accordance with the invention, the dimensions of the elementary clay platelets are hence set by selecting the temperature and the time of the preparation at the proper values. Generally, the temperature will be set between approximately 40 and 200°C. Of course, at temperatures above approximately 100°C it is necessary to operate under pressure. A skilled person is able to determine the proper temperature and time through simple routine tests.

[0047] The stacking of the elementary clay platelets, i.e. the number of elementary three-layer systems, is determined by the ionic strength of the solution from which the precipitation takes place. At a higher ionic strength, which can be achieved through the addition of, for instance, sodium nitrate, the elementaire clay platelets are stacked more. Without limiting the scope of the invention, it is assumed that reduction of the thickness of the electrostatic double layer around the clay platelets by the higher ionic strength decreases the mutual repulsion of the clay platelets. In accordance with the invention, the stacking of the elementary clay platelets is therefore controlled by setting the ionic strength of the solution wherein the reaction resulting in the clay minerals is carried out.

[0048] In accordance with a preferred embodiment of the invention, synthetic clay minerals are prepared at a low ionic strength of the solution. This may for instance by achieved by increasing the pH through the hydrolysis of urea. During the hydrolysis of urea, carbon dioxide escapes from the suspension, while the dissociation of ammonia is limited and ammonia escapes at higher pH levels. For this reason, ammonia can also be injected below the surface of the suspension. In these cases, a synthetic clay mineral results wherein the orientation of the elementary platelets is analogous with a house of cards. Hence, the stacking of the platelets is slight. In that case, a synthetic clay mineral is obtained having a high surface area present in wide pores. In particular, a clay having a surface area of at least 150 m2 per gram mainly present in pores of at least 6 nm belongs to the invention.

[0049] This requires operating at a high ionic strength of the solution. If one wishes to increase the pH value of the suspension homogeneously, according to the invention, the disproportionation of sodium nitrite can advantageously be used. Sodium nitrite reacts according to

        3NaNO₂ + H₂O = NaNO₃ + 2NO + 2NaOH

[0050] The pH value of the suspension rises because of the release of sodium hydroxide. Of course, the reaction should be caused to proceed in the absence of oxygen (air) to prevent oxidation of the NO. After oxidation to NO₂, it reacts to form nitric acid and NO, as a result of which the pH decreases. Because no reactants escape in a gaseous form, the ionic strength in this case remains high, so that the elementary clay platelets are stacked to a large extent. Also, through injection of sodium hydroxide or other alkaline solutions below the surface of the suspension, the pH value can be increased homogeneously. However, in that case, it is more difficult to prevent inhomogeneities in the suspension on an industrial scale.

[0051] Further, incorporation of substantially zinc ions into the octahedron layer has proved to result in much larger elementary platelets than incorporation of substantially magnesium ions. The dimension of the elementary platelets of clay minerals having substantially zinc ions in the octahedron layer is approximately 0.1-0.2 µm, whereas the corresponding dimension in the case of substantially magnesium ions in the octahedron layer is only 0.02 µm. Surprisingly, it has now appeared that in the presence of zinc ions and magnesium ions in the solution, both being present in the solution as divalent ions, these ions are incorporated into the octahedron layer side by side. The dimensions of the elementary clay platelets vary continuously with the zinc/magnesium ratio set, contrary to expectation, viz. the formation of a mixture of two clays, one on the basis of zinc and the other on the basis of magnesium. In acordance with the invention, the dimensions of the elementary clay layers are set within wider limits by setting the zinc/magnesium ratio.

[0052] The process of precipitating metal ions from homogeneous solution by increasing the pH of the solution in the presence of a suspended carrier material has priorly been proposed for the provision of a catalytically active precursor uniformly distributed over the surface of the carrier. This process is known as deposition precipitation. The procedure for providing catalytically active precursors on the surface of carriers suspended in the solution is described at length in US-A 4,113,658 and in J.W. Geus 'Production and Thermal Pretreatment of Supported Catalysts' in 'Preparation of Catalysts III Scientific Bases for the Preparation of Heterogeneous Catalysts' (G. Poncelet, P. Grange and P.A. Jacobs eds.) pp. 1-33 Elsevier Amsterdam (1983). It was found that during deposition precipitation of in particular divalent metal ions, such as nickel and cobalt, reaction of suspended silicon dioxide occurs to form a hydrosilicate, a structure analogous with the structure of talc of garnierite. However, such structures do not exhibit any acid properties. This is caused by the fact that only divalent metal ions occur in the octahedron layer and only silicon ions occur in the tetrahedron layer, as a consequence of which the clay platelets do not have a negative charge.

[0053] The absence of acid properties of the above-mentioned structures with only nickel ions in the octahedron layer is known in literature. As a measure for the acid properties of the catalyst, the activity of the solid substance for cumene cracking is used. Granquist (W.T. Granquist, US Patent 3,852,405, 1974) determined the activity of nickel garnierite, the equivalent of talc with nickel ions instead of magnesium ions, for the cracking of cumene. See also Harold E. Swift in 'Advanced Materials in Catalysis' (James J. Burton and Robert L. Garten eds.) pp. 209-233 Academic Press New York (1977). He observed that no cumene was converted. The activity can therefore not be measured. On the other hand, a montmorillonite with nickel ions and aluminum ions exhibited under the same conditions a conversion of 84-100%. The montmorillonite was synthetically prepared under hydrothermal conditions. In view of these publications, it is surprising that during precipitation from homogeneous solution by increasing the pH in the presence of suspended silicon dioxide under atmospheric pressure at temperatures below 100°C, clay minerals are obtained with two metal ions from the aqueuos solution being incorporated into the structure side by side.

[0054] In general, substitution of silicon by aluminum in the tetrahedron layer results in stronger acid sites than substitution of metal ions of lower valency in the octahedron layer. The negative charge is then present closer to the surface of the clay platelets. Surprisingly, it has now been found that aluminum ions can be incorporated in an excellently controllable manner into the tetrahedron layer, where they replace silicon ions. In accordance with the invention, this can be effected by treating silicon dioxide with a basic aluminate solution, by setting, through acidification, the pH at such a level that the metal ions to be incorporated into the octahedron layer are still solluble, adding these metal ions, and then increasing the pH of the solution (homogeneously). In accordance with a preferred embodiment of this process according to the invention, a solution of water glass is started from to which a basic aluminate solution has been added. Then, this solution is acidified whereby the pH is reduced to a level at which the metal ions to be incorporated into the octahedron layer are soluble. After that, the pH of the liquid is increased homogeneously to create the desired clay mineral in insoluble form. Al MAS-NMR measurements show that a fraction of maximally 15 at% of the silicon ions can thus be replaced by aluminum ions. The aluminum is hardly incorporated, if at all, into the octahedron positions or at sites between the clay layers.

[0055] As observed hereinabove, it is an object of the invention to prepare synthetic clay minerals which can effectively and easily be separated from a liquid phase and which are characterized by the presence of short and wide pores. It is known that it is possible to provide a highly porous, continuous layer of silicon dioxide on solid substrates so as to be firmly bound. This process is described in International patent application WO-A 92/13637. In this process, a solution of silicone rubber, for instance in ethyl acetate, is started from, and a thin layer of that solution is provided on the desired solid substrate. In this connection, one may think of the walls of the channels of a monolith or of the surface of a stirrer, whereupon, through calcination, a homogeneous, continuous (i.e. practically crack-free) layer of silicon oxide is formed. Surprisingly, it has been found that the above-mentioned reaction in which from homogeneous solution, metal ions, including aluminate ions, react with suspended silicon dioxide, can also be carried out with the finely divided silicon dioxide provided on the solid surface. This process according to the invention results in clay platelets. which are firmly connected to the solid surface. In accordance with a preferred embodiment of the process according to the invention, synthetic clay layers are provided on suitable solid surfaces in the above manner. Such clay layers, firmly bound to solid surfaces and having a controllable chemical composition and structure, also form part of the invention. In accordance with a preferred embodiment according to the invention, the clay layers are provided on the surface of the walls of the channels of monoliths, which are either made of ceramics or of metal, or on the surface area of stirrers.

[0056] This process enables providing relatively thin clay layers having wide pores on suitable solid substrates. The thickness of the clay layer determines the length of the pores, which is of great significance for the transport of reactants and reaction products in the clay structure. The thickness of the clay layer is 1-10 µm, preferably 1-5 µm, and more preferably 2-3 µm. Because of the stong bond to the solid surface, separation from the liquid is in this case no problem whatsoever. As the layer is thin, the pores are short, as a result of which no transport impediments occur, the less so because the pores of the clay layers thus provided are relatively wide. This is essential for the application of synthetic clay minerals for liquid phase reactions.

[0057] In accordance with another embodiment of the invention, elementary three-layer platelets of clay minerals according to the invention are provided on active carbon. Preferably, this takes place on carbon bodies having dimensions greater than 1µm. By carrying out the synthesis of the clay minerals in a suspension of the active carbon, such products are obtained. Preferably, filamentary carbon is used, for instance obtained through the growth of carbon on small metal particles. Such carbon filaments have great strength and occur as balls having dimensions of approximately 3 pm. The accessible surface area of the filaments is approximately 200 m²/g, which surface area is present in very wide pores. The clay minerals provided on the carbon have small dimensions, so that transport impediments do not occur, while a rapid and complete separation of the liquid phase is possible all the same.

[0058] The chemical reaction carried out is a reaction selected from the group of hydrocarbon cracking, isomerization, polymerization and hydration of olefins, the alkylation of aromatics and the dehydration of alcohols.

Preparation of Si/Al gel with Si/Al ratio of 5.67:

Example 1:

[0059] In a 250 ml beaker 100 ml demineralized water was added to 40.00 g water glass (approximately 27 wt.% SiO₂) and stirred vigorously.

[0060] An aluminate solution was prepared in another beaker (100 ml) by dissolving 11.90 g Al(NO₃)₃9H₂O in 80 ml 2M NaOH solution.

[0061] Then, with very vigorous stirring, the aluminate solution was poured into the water glass solution, whereupon a white gel was formed rather rapidly. This gel was XRD-amorphous and all Al was tetrahedrally coordinated (²⁷Al MAS NMR)

Synthesis of Mg saponite from gel

[0062] In a precipitation vessel, as described by van Dillen et al (A.J. van Dillen, J.W. Geus, L.A.M. Hermans, J. van der Meyden, Proc. 6th Int. Conf. on Cat., 11 (5) 1977), the gel as prepared above was suspended in 1.0 l demineralized water with vigorous stirring and brought to 90°C.

[0063] Then, 40.67 g Mg(NO₃)₂6H₂O and 0.6M urea (36.04 g) were dissolved in 500 ml demineralized water, whereupon it was introduced into the precipitation vessel. The temperature was 90°C; with continous stirring.

[0064] The first clay platelets were formed within some hours. After a reaction time of 20 hours, most of the gel had reacted to form small clay platelets of a length of 15-25 nm. A stacking was hardly (2 layers) present, if at all. The d(001) was absent at XRD measurements. The BET surface was 600-700 m²/g with a pore volume of approximately 0.3 ml/g. Effects of administration of an amount of urea/lye

Synthesis Zn saponite

[0065] The synthesis of Zn saponite can be performed in exactly the same manner as the Mg saponite synthesis mentioned in Example 1.

Example 2: Extra addition NaOH (comparative)

[0066] In a precipitation vessel as described in Example 1, the gel as prepared in Example 1 was suspended in 1.0 1 demineralized water with vigorous stirring and brought to 90°C.

[0067] Then, 40.67 g Mg(NO₃)₂6H₂O and 0.6M urea (36.04 g) were dissolved in 500 ml demineralized water, whereupon it was introduced into the precipitation vessel. The temperature was 90°C; with continuous stirring.

[0068] To the reaction mixture, NaOH was added until pH 8 was reached, whereupon the synthesis was started.

[0069] The first clay platelets were formed within some hours. After synthesis for 24 hours, a pH of 8.30 was reached, increasing only to 8.36 after a reaction period of 48 hours.

[0070] The stacking of the clay platelets, visible with TEM and XRD ((d(001)) was very great after a synthesis of 24 hours.

Example 3: (comparative)

[0071] An experiment was conducted similar to the process according to Example 1, the difference being that the amount of urea was doubled. After a synthesis of 24 hours, the pH was 7.73 (starting pH = 5.50).

[0072] The stacking of the clay platelets was again very great, yet slightly less intense than in the case of Example 2.

Example 4: (comparative)

[0073] This reaction is comparable with Example 1, but now only half the amount of urea as applied in Example 1 was used. After a synthesis of 24 hours, the end pH was 7.05 (starting pH = 5.25).

Example 5 :

[0074] This reaction is comparable with that of Example 4, but no urea was now added to the reaction mixture. After a synthesis of 24 hours, the end pH was 4.70 (starting pH = 5.54).

[0075] Now, hardly any stacking was perceptible anymore with TEM. XRD no longer showed any stacking: the d(001) was absent.

Example 6, Friedel-Crafts alkylation of benzene with propene to form cumenes

[0076] A saponite with Zn on the octahedron layer was prepared in the manner as described in Example 1. For this Zn saponite, the Si/Al ratio was 39.

[0077] After synthesis, the interlayer ions (Na⁺) at this clay were exchanged for Al³⁺, for application in the catalytic reaction.

[0078] After exchange, the clay was dried overnight at 120°C, whereupon a sieve fraction of from 0.1 to 0.4 mm was made. Next, 1.0 g saponite was dried under dry nitrogen for 3 hours at 120°C and suspended in 444.2 g dry benzene (Janssen Chimica, 99.5% G.C.), without having been in contact with the air.

[0079] Hereafter, this benzene/saponite mixture was introduced into a 1 liter stainless steel autoclave, whereupon 35.3 g propene (HoekLoos) was added.

[0080] The total catalyst concentration was 0.2 wt.%. With continuous stirring, the autoclave was brought to a temperature of 160°C, at which the Friedel-Crafts alkylation of benzene with propene started. The pressure in the autoclave was 10.9 bar.

[0081] After 15 minutes reacting a sample was tapped and analysed by a gas chromatograph (GC Carlo Erba Instruments HRGC 5300, capillary column CP-Sil-CB).

[0082] Results after 15 minutes: Conversion: 87% with a selectivity to cumene of 74%. By-products were: Di- and Tri-isopropyl benzene.

Example 7, Friedel-Crafts alkylation of benzene with tetradecene to form phenyl tetradecene

[0083] A saponite with Zn on the octahedron layer was prepared in the manner as described in Example 1. The Si/Al ratio for this Zn saponite was 39.

[0084] After synthesis, the interlayer ions (Na⁺) at this clay were exchanged for Al³⁺, for use in the catalytic reaction.

[0085] After exchange, the clay was dried overnight at 120°C, whereupon a sieve fraction of from 0.1 to 0.4 mm was made. Next, 5.0 g saponite was dried under dry nitrogen for 3 hours at 120°C and put in 441.8 g dry benzene (Janssen Chimica, 99.5% G.C.), without having been in contact with the air. Hereafter, this benzene/saponite mixture was introduced into a 1 liter stainless steel autoclave, whereupon 137.1 g trans-7-tetradecene (Janssen Chimica, 92%) was added.

[0086] The total catalyst concentration was 0.8 wt.%. With continuous stirring, the autoclave was brought to a temperature of 180°C, at which the reaction started. The pressure in the autoclave was 8.5 bar.

[0087] After 15 minutes reacting, a sample was tapped and analysed by a gas chromatograph (GC Carlo Erba Instruments HRGC 5300, capillary column CP-Sil-CB).

[0088] Results after 15 minutes: Conversion: 62% with a selectivity to phenyltetradecene of 67%.

Example 8, Friedel-Crafts alkylation of benzene with benzyl chloride to form diphenylmethane

[0089] A saponite with Mg in the octahedron layer was prepared in the manner as described in Example 1. The Si/Al ratio for this Mg saponite was 5.7.

[0090] After synthesis, the interlayer ions (Na⁺) at this clay were not exchanged.

[0091] After synthesis, the clay was dried overnight at 120°C, whereupon a sieve fraction of from 0.1 to 0.4 mm was made.

[0092] Next, 2.0 g saponite was dried under dry nitrogen for 3 hours at 350°C and put into 61.5 g dry benzene (Janssen Chimica, 99.5% G.C.), without having been in contact with the air.

[0093] Hereafter, this benzene/saponite mixture was introduced into a round-bottom flask, whereupon 7.7 g benzyl chloride (Janssen Chimica, 99.5% G.C.) was added.

[0094] The total catalyst concentration was 2.9 wt.%. With continuous stirring, the round-bottom flask was brought to a temperature of 84°C, at which the reaction started (reflux temperature).

[0095] After 1 hour reacting, a sample was tapped and analysed by a gas chromatograph (GC Carlo Erba Instruments HRGC 5300, capillary column CP-Sil-CB).

[0096] Results after 1 hour: Conversion: 42% with a selectivity to diphenylmethane of 98%.

Claims

1. Synthetic swelling clay minerals made up of a structure of elementary three-layer platelets consisting of a central layer of octahedrally oxygen-surrounded metal ions (octahedron layer), said layer being surrounded by two tetrahedrally surrounded, silicon atom-containing layers (tetrahedron layers), said elementary platelets being hardly mutually stacked, wherein the dimensions of the clay platelets vary from 0.01 µm to 1 µm, the number of the stacked elementary three-layer platelets varies from one platelet to twenty platelets, while in the octahedron layer at most 30 at.% of the metal ions has been replaced by ions of a lower valency and in the tetrahedron layers at most 15 at.% of the silicon ions has been replaced by ions of a lower valency, such a replacement having taken place in at least one of said layers and said layers having a deficiency of positive charge because of the replacement, and wherein hardly any or no (001) reflections occur in the X-ray diffraction pattern, said structure having pores with a pore size of at least 6 nm.

2. Clay minerals according to claim 1, characterized in that in the octahedron layer, magnesium, zinc, nickel, cobalt(II), iron(II), manganese (II), and/or beryllium are present as divalent ions.

3. Clay minerals according to claim 1 or 2, characterized in that in the octahedron layer, lithium is present as monovalent ions.

4. Clay minerals according to claims 1-3, characterized in that in the tetrahedron layer, silicon and/or germanium are present as tetravalent component and aluminum, boron, gallium, chromium, iron(III), cobalt(III) and/or manganese(III) are present as trivalent component.

5. Clay minerals according to any one of claims 1-4, characterized in that zinc and magnesium are incorporated into the octahedron layer, while the dimensions of the platelets are set by the choice of the magnesium and zinc ratio.

6. Clay minerals according to claims 1-5, characterized in that a part of the hydroxyl groups present in the platelets has been replaced by fluorine.

7. Clay minerals according to claims 1-6, characterized in that a surface area of at least 150 m² per gram is present in pores of at least 6 nm.

8. A process for the preparation of clay minerals according to claims 1-7, characterized in that the pH of an aqueous liquid containing the components of the clay to be prepared is brought to a value of 3-9 and the temperature of the liquid is brought to a value of from 60 to 350°C and maintained at said value for the time required for the reaction, said time not. exceeding 25 hours, the pH being maintained at a value within said range.

9. A process according to claim 8, characterized in that a solution of water glass and aluminate is started from, and said solution is brought, through acidification, to a pH where the metal ions to be incorporated into the clay structure are still soluble, and the pH of the thus obtained suspension is then increased homogeneously.

10. A process according to claim 8 or 9, characterized in that the dimensions of the elementary clay platelets are set by setting the temperature at which the pH is homogeneously increased between approximately 40 and 200°C.

11. A process according to claims 8-10, characterized in that the stacking of the elementary clay platelets is controlled by setting the ionic strength of the solution wherein the reaction leading to the clay minerals is carried out.

12. A process according to claims 8-11, characterized in that clay minerals having a high surface present in pores of great dimensions are obtained by carrying out the reaction leading to the clay minerals at a low ionic strength of the solution.

13. A process according to claims 8-12, characterized in that the elementary platelets are stacked to a high degree by setting the ionic strength of the solution from which the clay minerals are formed at a high value.

14. A process according to claims 8-13, characterized in that the pH of the solution is increased homogeneously through the disproportionation of sodium nitrite in the absence of oxygen.

15. A process according to claims 8-14, characterized in that the dimensions of the elementary clay layers are controlled within wide limits by setting the zinc/magnesium ratio.

16. A process according to claims 8-15, characterized by substituting in the tetrahedron layer a controllable amount of silicon ions by aluminum ions through the addition of a basic aluminate solution to a suspension of silicon dioxide, then, through acidification, setting the pH at such a level that the metal ions to be incorporated into the octahedron layer are still soluble, then adding said metal ions, and then increasing the pH of the suspension homogeneously.

17. A process according to claims 8-16 for providing clay layers on a solid surface, characterized in that a high-porous layer of silicon dioxide which is strongly bonded to said surface is converted into clay minerals.

18. Solid surfaces covered with a clay layer, obtained by the use of the process according to claim 17 and having a thickness of from 1 to 10 µm, preferably having a thickness of from 1 to 5 µm, and more preferably having a thickness of from 2 to 3 µm.

19. Monoliths and stirring bodies according to claim 18, whose surfaces are covered with the clay layer.

20. A process for carrying out a chemical reaction in the presence of a heterogeneous catalyst, said reaction being catalyzed by a Lewis acid or a Brønsted acid, with a clay mineral according to any one of claims 1-7 being used as catalyst.

21. A process according to claim 20, the reaction being selected from the group of hydrocarbon cracking, isomerization, polymerization and hydration of olefins, the alkylation of aromatics and the dehydration of alcohols.

22. A process according to claim 20 or 21 the reaction being selected from the group consisting of Friedel-Crafts reactions and (hydro)cracking reactions.

Ansprüche

1. Synthetische quellfähige Tonmineralien mit einer Struktur aus elementaren dreischichtigen Plättchen, die aus einer zentralen Schicht von oktaedrisch von Sauerstoff umgebenen Metallionen (Oktaederschicht) bestehen, wobei diese Schicht von zwei Schichten umgeben ist, die tetraedrisch umgebene Siliciumatome enthalten (Tetraederschichten), wobei die elementaren Plättchen kaum aufeinandergestapelt sind, wobei die Abmessungen der Tonplättchen von 0,01 µm bis 1 µm variieren, die Zahl der aufeinandergestapelten elementaren dreischichtigen Plättchen von einem Plättchen bis zwanzig Plättchen variiert, während in der Oktaederschicht höchstens 30 Atomprozent der Metallionen durch Ionen einer niedrigeren Wertigkeit ersetzt sind und in den Tetraederschichten höchstens 15 Atomprozent der Siliciumionen durch Ionen einer niedrigeren Wertigkeit ersetzt sind, wobei ein solcher Ersatz wenigstens in einer dieser Schichten stattgefunden hat und die Schichten aufgrund des Ersatzes einen Unterschuss an positiver Ladung haben, wobei im Röntgenbeugungsmuster kaum oder gar keine (001)-Reflexe auftreten, wobei die Struktur Poren mit einer Porengröße von wenigstens 6 nm aufweist.

2. Tonmineralien gemäß Anspruch 1, dadurch gekennzeichnet, dass in der Oktaederschicht Magnesium, Zink, Nickel, Cobalt(II), Eisen(II), Mangan (II) und/oder Beryllium als zweiwertige Ionen vorhanden sind.

3. Tonmineralien gemäß Anspruch 1 oder 2, dadurch gekennzeichnet, dass in der Oktaederschicht Lithium als einwertiges Ion vorhanden ist.

4. Tonmineralien gemäß den Ansprüchen 1-3, dadurch gekennzeichnet, dass in der Tetraederschicht Silicium und/oder Germanium als vierwertige Komponente vorhanden sind und Aluminium, Bor, Gallium, Chrom, Eisen (III), Cobalt(III) und/oder Mangan(III) als dreiwertige Komponente vorhanden sind.

5. Tonmineralien gemäß einem der Ansprüche 1-4, dadurch gekennzeichnet, dass Zink und Magnesium in die Oktaederschicht eingebaut sind, während die Abmessungen der Plättchen durch die Wahl des Magnesium- und Zinkverhältnisses eingestellt werden.

6. Tonmineralien gemäß den Ansprüchen 1-5, dadurch gekennzeichnet, dass ein Teil der in den Plättchen vorhandenen Hydroxylgruppen durch Fluor ersetzt wurde.

7. Tonmineralien gemäß den Ansprüchen 1-6, dadurch gekennzeichnet, dass eine spezifische Oberfläche von wenigstens 150 m²/g in Poren von wenigstens 6 nm vorhanden ist.

8. Verfahren zur Herstellung von Tonmineralien gemäß den Ansprüchen 1-7, dadurch gekennzeichnet, dass der pH-Wert einer wässrigen Flüssigkeit, die die Komponenten des herzustellenden Tons enthält, auf einen Wert von 3-9 gebracht wird und die Temperatur der Flüssigkeit auf einen Wert von 60 bis 350 °C gebracht wird und während der für die Reaktion erforderlichen Zeit auf diesem Wert gehalten wird, wobei diese Zeit 25 Stunden nicht überschreitet, wobei der pH-Wert auf einem Wert innerhalb des genannten Bereichs gehalten wird.

9. Verfahren gemäß Anspruch 8, dadurch gekennzeichnet, dass von einer Lösung von Wasserglas und Aluminat ausgegangen Wird und diese Lösung durch Ansäuern auf einen pH-Wert gebracht wird, bei dem die in die Tonstruktur einzubauenden Metallionen noch löslich sind, und der pH-Wert der so erhaltenen Suspension dann homogen erhöht wird.

10. Verfahren gemäß Anspruch 8 oder 9, dadurch gekennzeichnet, dass die Abmessungen der elementaren Tonplättchen eingestellt werden, indem man die Temperatur, bei der der pH-Wert homogen erhöht wird, zwischen ungefähr 40 und 200 °C einstellt.

11. Verfahren gemäß den Ansprüchen 8-10, dadurch gekennzeichnet, dass die Stapelung der elementaren Tonplättchen gesteuert wird, indem man die Ionenstärke der Lösung einstellt, in der die Reaktion durchgeführt wird, die zu den Tonmineralien führt.

12. Verfahren gemäß den Ansprüchen 8-11, dadurch gekennzeichnet, dass Tonmineralien mit einer hohen Oberfläche, die sich in Poren mit großen Abmessungen befindet, erhalten werden, indem man die Reaktion, die zu den Tonmineralien führt, bei einer niedrigen Ionenstärke der Lösung durchführt.

13. Verfahren gemäß den Ansprüchen 8-12, dadurch gekennzeichnet, dass die elementaren Plättchen in hohem Maße gestapelt werden, indem man die Ionenstärke der Lösung, aus der die Tonmineralien gebildet werden, auf einen hohen Wert einstellt.

14. Verfahren gemäß den Ansprüchen 8-13, dadurch gekennzeichnet, dass der pH-Wert der Lösung durch die Disproportionierung von Natriumnitrit in Abwesenheit von Sauerstoff homogen erhöht wird.

15. Verfahren gemäß den Ansprüchen 8-14, dadurch gekennzeichnet, dass die Abmessungen der elementaren Tonschichten innerhalb weiter Grenzen gesteuert werden, indem man das Verhältnis von Zink zu Magnesium einstellt.

16. Verfahren gemäß den Ansprüchen 8-15, dadurch gekennzeichnet, dass man durch die Zugabe einer basischen Aluminatlösung zu einer Suspension von Siliciumdioxid eine steuerbare Menge von Siliciumionen in der Tetraederschicht durch Aluminiumionen ersetzt, dann durch Ansäuern den pH-Wert auf einen solchen Wert einstellt, dass die in die Oktaederschicht einzubauenden Metallionen noch löslich sind, dann die Metallionen hinzufügt und dann den pH-Wert der Suspension homogen erhöht.

17. Verfahren gemäß den Ansprüchen 8-16 zum Bereitstellen von Tonschichten auf einer festen Oberfläche, dadurch gekennzeichnet, dass eine hochporöse Schicht von Siliciumdioxid, die fest an die Oberfläche gebunden ist, in Tonmineralien umgewandelt wird.

18. Feste Oberflächen, die mit einer Tonschicht bedeckt sind und durch die Verwendung des Verfahrens gemäß Anspruch 17 erhalten werden und eine Dicke von 1 bis 10 um aufweisen, vorzugsweise eine Dicke von 1 bis 5 µm aufweisen und besonders bevorzugt eine Dicke von 2 bis 3 µm aufweisen.

19. Monolithe und Rührkörper gemäß Anspruch 18, deren Oberflächen mit der Tonschicht bedeckt sind.

20. Verfahren zur Durchführung einer chemischen Reaktion in Gegenwart eines heterogenen Katalysators, wobei die Reaktion durch eine Lewis-Säure oder eine Brønsted-Säure katalysiert wird, wobei ein Tonmineral gemäß einem der Ansprüche 1-7 als Katalysator verwendet wird.

21. Verfahren gemäß Anspruch 20, wobei die Reaktion aus der Gruppe ausgewählt ist, die aus Kohlenwasserstoff-Cracken, Isomerisierung, Polymerisation und Hydratisierung von Olefinen, der Alkylierung von Aromaten und der Dehydratisierung von Alkoholen besteht.

22. Verfahren gemäß Anspruch 20 oder 21, wobei die Reaktion aus der Gruppe ausgewählt ist, die aus Friedel-Crafts-Reaktionen und (Hydro)-crack-Reaktionen besteht.

Revendications

1. Minéraux argileux gonflants synthétiques constitués par une structure de plaquettes élémentaires à trois couches consistant en une couche centrale d'ions métalliques entourés par de l'oxygène de manière octaédrique (couche octaédrique), ladite couche étant entourée par deux couches contenant des atomes de silicium entourées de manière tétraédrique (couches tétraédriques), lesdites plaquettes élémentaires étant à peine empilées mutuellement, où les dimensions des plaquettes d'argile varient de 0,01 µm à 1 µm, le nombre de plaquettes élémentaires à trois couches empilées varie d'une plaquette à vingt plaquettes, tandis que, dans la couche octaédrique, au plus 30 % atomiques des ions métalliques ont été remplacés par des ions d'une valence inférieure et, dans les couches tétraédriques, au plus 15 % atomiques des ions silicium ont été remplacés par des ions d'une valence inférieure, un tel remplacement ayant eu lieu dans au moins l'une desdites couches, et lesdites couches ayant un déficit de charge positive du fait du remplacement, et où il se produit à peine une réflexion (001) ou pas de réflexion (001) dans le diagramme de diffraction des rayons X, ladite structure ayant des pores d'une taille de pores d'au moins 6 nm.

2. Minéraux argileux selon la revendication 1, caractérisés en ce que, dans la couche octaédrique, du magnésium, du zinc, du nickel, du cobalt (II), du fer (II), du manganèse (II) et/ou du béryllium sont présents sous forme d'ions divalents.

3. Minéraux argileux selon la revendication 1 ou 2, caractérisés en ce que, dans la couche octaédrique, du lithium est présent sous forme d'ions monovalents.

4. Minéraux argileux selon les revendications 1 à 3, caractérisés en ce que, dans la couche tétraédrique, du silicium et/ou du germanium sont présents sous forme de composant tétravalent et de l'aluminium, du bore, du gallium, du chrome, du fer (III), du cobalt (III) et/ou du manganèse (III) sont présents sous forme de composant trivalent.

5. Minéraux argileux selon l'une quelconque des revendications 1 à 4, caractérisés en ce que du zinc et du magnésium sont incorporés dans la couche octaédrique, tandis que les dimensions des plaquettes sont fixées par le choix du rapport du magnésium et du zinc.

6. Minéraux argileux selon les revendications 1 à 5, caractérisés en ce qu'une partie des groupes hydroxyle présents dans les plaquettes ont été remplacés par du fluor.

7. Minéraux argileux selon les revendications 1 à 6, caractérisés en ce qu'une surface spécifique d'au moins 150 m²/g est présente dans les pores d'au moins 6 nm.

8. Procédé de préparation de minéraux argileux selon les revendications 1 à 7, caractérisé en ce que le pH d'un liquide aqueux contenant les composants de l'argile à préparer est amené à une valeur de 3-9 et la température du liquide est amenée à une valeur de 60 à 350°C et maintenue à ladite valeur pendant la durée nécessaire pour la réaction, ladite durée ne dépassant pas 25 h, le pH étant maintenu à une valeur située dans ledit domaine.

9. Procédé selon la revendication 8, caractérisé en ce que l'on part d'une solution de verre soluble et d'aluminate, et ladite solution est amenée, par acidification, à un pH où les ions métalliques à incorporer dans la structure de l'argile sont encore solubles, et le pH de la suspension ainsi obtenue est ensuite augmenté de manière homogène.

10. Procédé selon la revendication 8 ou 9, caractérisé en ce que les dimensions des plaquettes élémentaires d'argile sont fixées par fixation de la température à laquelle le pH est augmenté de manière homogène entre approximativement 40 et 200°C.

11. Procédé selon les revendications 8 à 10, caractérisé en ce que l'empilement des plaquettes élémentaires d'argile est contrôlé par fixation de la force ionique de la solution dans laquelle la réaction conduisant aux minéraux argileux est conduite.

12. Procédé selon les revendications 8 à 11, caractérisé en ce que des minéraux argileux ayant une grande surface présente dans des pores de grandes dimensions sont obtenus en conduisant la réaction conduisant aux minéraux argileux à une faible force ionique de la solution.

13. Procédé selon les revendications 8 à 12, caractérisé en ce que les plaquettes élémentaires sont empilées à un haut degré par fixation à une valeur élevée de la force ionique de la solution à partir de laquelle les minéraux argileux sont formés.

14. Procédé selon les revendications 8 à 13, caractérisé en ce que le pH de la solution est augmenté de manière homogène par dismutation du nitrite de sodium en l'absence d'oxygène.

15. Procédé selon les revendications 8 à 14, caractérisé en ce que les dimensions des couches élémentaires d'argile sont contrôlées dans de larges limites par fixation du rapport zinc/magnésium.

16. Procédé selon les revendications 8 à 15, caractérisé par la substitution dans la couche tétraédrique d'une quantité contrôlable d'ions silicium par des ions aluminium par addition d'une solution d'aluminate basique à une suspension de dioxyde de silicium puis, par acidification, fixation du pH à un niveau tel que les ions métalliques à incorporer dans la couche octaédrique sont encore solubles, puis addition desdits ions métalliques, puis augmentation du pH de la suspension de manière homogène.

17. Procédé selon les revendications 8 à 16 pour produire des couches d'argile sur une surface solide, caractérisé en ce qu'une couche très poreuse de dioxyde de silicium qui est fortement liée à ladite surface est convertie en minéraux argileux.

18. Surfaces solides recouvertes d'une couche d'argile, obtenues par l'utilisation du procédé selon la revendication 17 et ayant une épaisseur de 1 à 10 µm, de préférence ayant une épaisseur de 1 à 5 µm, et de préférence encore ayant une épaisseur de 2 à 3 µm.

19. Monolithes et corps d'agitation selon la revendication 18 dont les surfaces sont recouvertes de la couche d'argile.

20. Procédé pour conduire une réaction chimique en présence d'un catalyseur hétérogène, ladite réaction étant catalysée par un acide de Lewis ou un acide de Bronsted, un minéral argileux selon l'une quelconque des revendications 1 à 7 étant utilisé comme catalyseur.

21. Procédé selon la revendication 20, la réaction étant choisie dans le groupe du craquage d'hydrocarbures, de l'isomérisation, de la polymérisation et de l'hydratation d'oléfines, de l'alkylation de produits aromatiques et de la déshydratation d'alcools.

22. Procédé selon la revendication 20 ou 21, la réaction étant choisie dans le groupe consistant en les réactions de Friedel-Crafts et les réactions d'(hydro)craquage.

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