WO2000056689A1

WO2000056689A1 - Method for producing an aromatic compound containing at least one hydroxyl group by catalytic oxidation using at least one peroxidic compound as an oxidizing agent on a catalyst

Info

Publication number: WO2000056689A1
Application number: PCT/EP2000/002162
Authority: WO
Inventors: Mark Duda; Gerhard HÖRPEL; Christian Hying; Adolf KÜHNLE
Original assignee: Creavis Gesellschaft Für Technologie Und Innovation Mbh
Priority date: 1999-03-20
Filing date: 2000-03-11
Publication date: 2000-09-28
Also published as: DE19912644A1

Abstract

The invention relates to a method for hydroxylating aromatics with peroxides using a catalyst and an inorganic membrane. The novel method improves conversions and selectivities for the hydroxylation of aromatics, especially benzene, with peroxides. By carrying out the inventive procedure using inorganic membranes, it is possible to achieve not only higher conversions and selectivities for the hydroxylation of benzene to phenol with hydrogen peroxide but also greater selectivity in relation to the peroxide. In addition, the unwanted decomposition of hydrogen peroxide to oxygen and water is reduced. The aromatic educt can also be oxidised with a higher ratio of peroxide to aromatic than was previously the case without losing selectivity. The inventive method can be used for oxidising benzene to phenol.

Description

Process for the preparation of an aromatic compound containing at least one hydroxyl group by catalytic oxidation with at least one peroxidic compound as an oxidizing agent on a catalyst

The invention relates to a process for producing an aromatic compound containing at least one hydroxyl group by catalytic oxidation using at least one peroxidic compound as an oxidizing agent on a catalyst

Hydroxyaromatics are valuable intermediates in the chemical industry. They serve as starting materials for a large number of other compounds. The most important compound from the group of hydroxyaromatics is phenol. Phenol is used for phenolic resins, caprolactam, bisphenol A, adipic acid, etc

The cumene process has become technically established for the production of phenols starting from benzene. Here, the cumene produced from benzene and propene is usually peroxidized and the oxidation product is then split into phenol and acetone

Furthermore, starting from toluene, the benzoic acid process is in use, whereby the benzoic acid produced from toluene can be decarboxylated to phenol. However, the decarboxylation step, ie the loss of an organically bound carbon, consumes any price advantage of toluene over benzene at this stage. The process is therefore only interesting if the target product is benzoic acid and free capacities are used for the production of phenol

Other processes, e.g. via chlorobenzene (chlorination or oxychlorination of benzene) or the sulfonation process (production of benzenesulfonic acid) have proven to be uneconomical. Reasons were unsatisfactory selectivity, corrosion problems and the occurrence of unwanted by-products

The cyclohexanol process (hydration of cyclohexene in the 1 stage) is also not economical. The process runs through too many stages to arrive at the target product phenol For this reason, the largest proportion of phenol is produced worldwide via the above-mentioned cumene route. However, since acetone is also produced here, the cost-effectiveness of this process depends on the market prices for phenol and acetone

In order to circumvent the dependence on the by-product acetone, many attempts focus on the selective oxidation of benzene or benzene derivatives to the corresponding hydroxyaromatics.All attempts to carry out these reactions failed, however, due to a lack of selectivity. The reaction with benzene with molecular oxygen always became aromatic Split the core, producing maleic acid or total oxidation occurred. The product range for benzene derivatives was even more diverse, since the functional groups were also non-selectively oxidized

It has been known for some years that the transition metal-containing silicalites or zeolites in conjunction with hydrogen peroxide have an activity with respect to the hydroxylation of aromatic compounds

There is a number of investigations in particular for the oxidation of phenols to the corresponding quinones. US Pat. No. 4,396,783 describes the oxidation of phenol to hydroquinone and pyrocatechol with hydrogen peroxide. Modified silicalites were used as catalysts at a reaction temperature of 80 to 120 ° C. Modifications were carried out the silicalite eg with metals such as titanium, vanadium, manganese, iron, cobalt, zinc, beryllium, chromium and rhodium. This document also mentions the possibility of oxidizing other substrates as well as substrates such as toluene, anisole, nitrobenzene and benzene yields of 50% are described with phenol or anisole. Poorer yields have been achieved with the other substrates or, as in the case of benzene, no examples have been given

In US 4,410,501, Taramasso et al describe the preparation of the titanium silicalite TS-1. The ratio of titanium to silicon was 0 0005 to 0 04. GB 2 116 974 then presented the use of these silicalites for the oxidation of phenol to diphenols

Studies on the hydroxylation of benzene with H ₂ O ₂ using various zeolites and molecular sieves were carried out by Thangaraj et al in J. Applied Catalysis 1990, 57, Ll- L3 described It was shown that the catalytic activity based on the reaction of HO ₂ with benzene to give hydroxylated aromatics in the order TS-1>Fe-TS-1>Al-TS-1>Fe-ZSM-5> Al-ZSM -5 decrease In contrast, the order with regard to the selectivity of phenol is exactly the opposite. In other words, TS-1 is the most active catalyst for utilizing the oxidation potential of hydrogen peroxide, but this oxidation has the lowest phenol selectivity at the same time.This is because phenol can be oxidized very easily under the reaction conditions shown

Further work, such as document US 5 233 097, showed no breakthrough in the field of direct oxidation of benzene to phenol in the liquid phase, so that no technically relevant solution to this chemical problem can be identified to date. The promising results from Pinnavaia et al ( Natur e 1994, 368, 321) proved to be too high with regard to the phenol yield, since there was an error in the product analysis (Chem. Commun. 1996, 979)

In addition to zeolites and molecular sieves, other catalysts such as amorphous microporous mixed metal oxides are also suitable. The production of these amorphous, microporous mixed metal oxides is described in DE 195 06 843, where it is mentioned that the compounds are suitable for all types of catalysis, such as isomerization reactions, hydrogenation reactions, selective and unselective oxidation reactions with atmospheric oxygen , Hydrogen peroxide or organic peroxides, alkylation reactions, disproportionation reactions, alcohol formation from olefins, coupling reactions, substitution reactions, cycloaddition or cycloreversion reactions, ether formation, alcohol cracking and hydrocracking, Fischer-Tropsch synthesis of alcohols or hydrocarbons and many others can possibly be used in the reaction of However, benzene with hydrogen peroxide using a vanadium-containing amorphous microporous mixed metal oxide was only satisfied with a low conversion of 2.6% Selectivity achieved with phenol Again, the problem of further oxidation of the desired phenol product was not solved

It was therefore an object of the present invention to provide a process for preparing at least one aromatic compound containing a hydroxyl group by catalytic oxidation using a peroxidic compound as the oxidizing agent, which leads to higher conversions and higher selectivity in the hydroxylation of aromatics, in particular in the hydroxylation of benzene

Surprisingly, it was found that a process for the preparation of an aromatic compound containing at least one hydroxyl group by catalytic oxidation with a peroxidic compound as an oxidizing agent on an inorganic membrane leads to higher conversions and selectivities in the hydroxylation of aromatic compounds

The present invention therefore relates to a process for producing an aromatic compound containing at least one hydroxyl group by catalytic oxidation using at least one peroxidic compound as an oxidizing agent on a catalyst, characterized in that the oxidation is carried out using an inorganic membrane

The process according to the invention has the advantage that the oxidation of the aromatic starting material can also be carried out at a higher peroxide / aromatic ratio than has hitherto been the case without loss of selectivity. In this way, a higher conversion of aromatic used Connection reached The hydroxylated aromatic compound passes through the membrane after the oxidation and is transported away from the catalyst. As a result, the hydroxylated aromatic compound is only exposed to a small part to further oxidation processes. For this reason, the selectivity of the process according to the invention is greater than in the case of conventional processes

Furthermore, the process according to the invention has the advantage that the undesired decomposition of the peroxidic compounds, such as the decomposition of hydrogen peroxide to oxygen and water, takes place to a lesser extent than in conventional processes. As a result, less peroxidic compound is required, so that the process according to the invention can be operated more economically

The inventive method for producing at least one, at least one An aromatic compound having a hydroxyl group by catalytic oxidation with a peroxidic compound on a porous compound is described below by way of example, but is not restricted thereto

The process according to the invention is based on the generally known process for the catalytic oxidation of aromatics. According to the invention, the production of at least one aromatic compound containing at least one hydroxyl group is carried out by catalytic oxidation with at least one peroxidic compound as an oxidizing agent on at least one catalyst, the oxidation using at least one Membrane, preferably an inorganic membrane and very particularly preferably an inorganic polar membrane, is preferably carried out. The membrane preferably separates the reaction space into an educt side or reaction side and a product side. The catalyst is made available in the reaction space on the educt side. This can simply be poured into the reaction space or in the reaction chamber on a suitable holder, such as a metal network. The catalyst is preferably in the immediate vicinity of the membrane arranged on the reactant side in the reaction space The catalyst is very particularly preferably applied to the reaction side of the membrane

The oxidation reaction can be carried out both in the liquid phase and in the gas phase. The reaction is preferably carried out in the liquid phase. The reaction in the gas phase allows faster reaction and separation processes, but safety problems can occur with the peroxidic compounds used as oxidizing agents The liquid phase is preferably carried out at temperatures below the boiling point of all the starting materials, products and solvents involved. However, it can also be advantageous to set the temperature so that the product and starting material can exist in different aggregate states in order to facilitate separation of the products or starting materials, or to make it difficult to mix products and starting materials

If the reaction is carried out in the gas phase, the temperature is preferably set from 100 ° C. to 500 ° C. If the reaction is carried out in the liquid phase, the amount is set reaction temperature preferably from 0 ° C to 300 ° C, particularly preferably from 20 ° C to 80 ° C

When carrying out the reaction in the gas phase, it can be advantageous to provide a pressure difference between the reaction side and the product side of the reaction space. The pressure ratios are preferably set so that a higher pressure is present on the reaction side than on the educt side. The ratio of the Prints from reaction to product side from 10 to 1 to 1.1 to 1 This means that a negative pressure can also be set on the product side. When carrying out the reaction in the gas phase, it can also be advantageous to use a carrier to carry out the starting materials or products - and / or inert gas to mix For example, nitrogen or noble gases can be used as inert gases

When carrying out the process according to the invention in the liquid phase, it may be advantageous to mix the starting materials or products with a solvent. Polar systems, such as, for example, acetone, acetonitrile and alcohols of all types, can be used as the solvent liquid phase, it can be advantageous to have different on the reaction side and the product side in the reaction chamber

Setting the pressure ratios The pressure ratios are preferably set so that a higher pressure is present on the reaction side than on the product side

The at least one aromatic compound to be oxidized and the oxidizing agent are fed in gaseous and / or in liquid form, on the reaction or educt side into the reaction space. The unreacted part of the aromatic compound and the

Oxidizing agents are withdrawn again from the reaction space. It may be advantageous to circulate the aromatic compound and the mixture containing the oxidizing agent so that the unreacted starting materials are again fed into the reaction space

Preferably, exactly as much oxidizing agent and aromatic compound to be oxidized are metered into the circuit as are withdrawn from the circuit by reaction and / or passage through the membrane

The mixture of product, oxidizing agent and secondary product formed in the reduction of the oxidizing agent on the product side in the reaction chamber can be suctioned off. It can be advantageous to use a solvent or an inert gas on the product side of the To drive the reaction chamber in a circle The solvent or the inert gas have the purpose of absorbing the product that has passed through the membrane or the oxidizing agent or the secondary product of the oxidizing agent. The mixture of solvent or inert gas and product, oxidizing agent and / or that is used in the reduction of the oxidizing agent resulting product passed through a device which separates the product and / or the oxidizing agent or the resulting product resulting from the reduction of the oxidizing agent from the solvent or the inert gas from this mixture.This device can, for example, be connected from distillation columns connected in series or, in the case of gaseous products There are cold traps. The solvent or the inert gas thus prepared can be returned to the reaction space on the product side, but in principle the method according to the invention can also be used without the use of solvent and / or inert gas be led

All membranes which are stable at the temperatures mentioned and which are neither attacked nor changed by the starting materials involved in the reaction or by the products formed in the reaction are preferably used as membranes. Inorganic membranes are preferably used, and polar inorganic membranes are very particularly preferably used the membranes used have a maximum thickness of 200 μm and / or a pore size of up to a maximum of 100 nm. The membranes are particularly preferably membranes that are flexible. Such membranes are obtainable, for example, via the sol-gel process The production of such membranes is described, for example, in the documents WO 9600198 or PCT / EP98 / 05939

These membranes have in common that an inorganic material is placed on a support in the sol-gel process. The inorganic material can contain at least one compound of at least one metal, semimetal or mixed metal with at least one element of the 3 to 7 main group of the periodic table or at least one The compounds of the metals, semimetals or mixed metals can have at least elements of the subgroup elements and the 3 to 5 main group or at least elements of the subgroup elements or the 3 to 5 main group, these compounds preferably having a particle size of 0.001 to 25 μm the inorganic component at least one compound of an element of the 3 to 8 subgroup or at least one element of the 3 to 5 main group with at least one of the elements Te, Se, S, O, Sb, As, P, N, Ge, Si, C, Ga, AI or B or at least one connection of an element from the 3 to 8 subgroup and at least one element from the 3 to 5 main group with at least one of the elements Te, Se, S, O, Sb, As, P, N, Ge, Si, C, Ga, Al or B or a mixture of these compounds. The inorganic component particularly preferably has at least one compound of at least one of the elements Sc, Y, Ti, Zr, V, Nb, Cr, Mo, W, Mn, Fe, Co, B, AI, Ga, In, Tl, Si, Ge, Sn, Pb, Sb or Bi with at least one of the elements Te, Se, S, O, Sb, As, P, N, C, Si, Ge or Ga, such as B TiO ₂ , Al ₂ O ₃ , SiO ₂ , ZrO ₂ , Y ₂ O ₃ , BC, SiC, Fe ₃ O ₄ , SiN, SiP, nitrides, sulfates, phosphides, silicides, spinels or yttrium aluminum garnet, or one of these elements itself on the inorganic component also aluminosilicates, aluminum phosphates, zeolites or partially exchanged zeolites, such as ZSM-5, Na-ZSM-5 or Fe-ZSM-5 or amorphous microporous mixed metal oxides, which can contain up to 20% non-hydrolyzable organic compounds, such as vanadium oxide Silicon oxide glass or aluminum oxide-silicon oxide-methyl silicon-sesquioxide glasses

The carrier of the inorganic membrane can be, for example, a grid, a fleece, a knitted fabric or a perforated plate. The material requirement to be met by the carrier is in principle a resistance to the chemicals claimed, in particular a dimensional stability at the claimed reaction temperatures. This means that it also, for example made of suitable inorganic materials which do not conduct electricity or only conduct it to a limited extent. However, the carrier is frequently metallic in nature, all metals and semimetals of the periodic table, except from the 1 and 2 main group, and all types of metal alloys being preferred If iron, zinc, copper, aluminum or titanium or metal alloys are used, which contain at least 50% by weight of these metals, support materials based on at least 80% by weight of iron or copper are very preferred. By applying electrical current to them from metals or semimetals Existing supports can also be influenced, for example, by flow and cleaning processes of membranes. In addition, the membrane or catalyst layers applied thereon can be specifically heated by the application of electrical current Suitable catalysts according to the invention are, for example, transition metal-containing zeolites and molecular sieves. In general, zeolites are crystalline aluminum silicalites which have a highly ordered structure. This three-dimensional network consists of AlO ₄ and SiO ₄ tetrahedra. The ratio of Si and Al atoms to oxygen is 1 2 The incorporation of Aluminum entails the inclusion of cations. These can be alkali or hydrogen ions, but also transition metal cations

Zeolites are divided into different groups according to the size of their cavities and pores, such as, for example, zeolites of the types A, L, X or Y. For the process according to the invention, one or more other elements can be built into the lattice instead of aluminum and silicon It is possible to make aluminum by B, Ga, Fe, Cr, V, As, Sb, Bi, Be or a mixture of at least two of these elements or silicon by a tetravalent element such as Ge, Ti, Zr, Hf or a mixture To replace at least two of these elements. Examples of the production of, for example, titanium-containing zeolites are described in US Pat. No. 5,233,097

Silicalites also have a three-dimensional network, but this is only formed by SiO ₄ tetrahedra.So the titanium silicalite TS-1 has the same crystal structure as the zeolite ZSM-5. Titanium silicalites can be produced from a homogeneous reaction mixture consisting of a silicon compound, a titanium-containing component, one Tetraalkylammonium compound and water in a hydrothermal synthesis in an autoclave

Titanium silicalites, which preferably have a pore diameter of 0J to 0.8 nm, particularly preferably 0.4 to 0.7 nm and very particularly preferably a pore diameter of 0.5 to 0.6 nm, are used as catalysts Production of titanium silicalites, tetraethyl orthosilicate and tetraethyl orthotitanate can be used as silicon or titanium source. These processes are described in US Pat. No. 4,410,501 (1983). Furthermore, titanium silicalites made from mixed pyrogenic silicon dioxide / titanium dioxide can be formed by gel formation with aqueous tetrapropylammonium hydroxide at 25 ° C. subsequent crystallization at 175 ° C and subsequent washing and calcining at 550 ° C. Amorphous microporous mixed metal oxides can also be used as catalysts for the process according to the invention. The production of these amorphous, microporous mixed metal oxides is described in DE 195 06 843

These amorphous, microporous mixed metal oxides consist of 50 to 100% by weight of oxides of elements from the 3 main group, the 4 main group, the 3 sub-group or from the 4 sub-group of the periodic table, including the lanthanoids and actinides

The mixed metal oxide matrix preferably consists of at least two of the compounds from the group SiO ₂ , TiO ₂ , Al ₂ O ₃ , vanadium oxide, zirconium oxide, cerium oxide, spinel, mullite, silicon carbide, silicon nitrite and titanium nitrite

The mixed metal matrix can also contain at least 50% by weight of one of the compounds of the elements titanium, silicon, aluminum, zirconium or cerium and up to 50% by weight of one or more metal oxides in an atomic distribution from the group of the metals molybdenum, tin, zinc, vanadium, Manganese, iron, cobalt, nickel, arsenic, lead, antimony, bismuth, ruthenium, rhenium, chromium, tungsten, niobium, hafnium, lanthanum, cerium, gadolinium, gallium, indium, thallium, silver, copper, lithium, potassium, sodium, Contain beryllium, magnesium, calcium, strontium and barium

This mixed metal matrix can additionally contain up to 10% by weight of one of the metals platinum,

Rhodium, iridium, osmium, silver, gold, copper, nickel, palladium and cobalt in highly dispersed form in a metallic or oxidized state

The amorphous, microporous mixed metal oxides can be obtained by acidic or fluoride-catalyzed linear polymerization or polycondensation of hydrolyzable, soluble compounds of the above-mentioned metals and oxides pH range used in the sol-gel process. This is followed by mild drying and slow calcination, the end of the calcination temperature being 120 to 800 ° C The production of non-polar or hydrophobic amorphous, microporous mixed metal oxides is described, for example, in DE 195 45 042. The polarity of the inner and outer surfaces of amorphous, microporous mixed metal oxides can be adjusted, for example, by alkyl or aryloxysilanes having non-hydrolyzable R or R type alkyl or aryl groups - Si (OR) ₃ , where OR can be an alkyl or aryl group bonded via the oxygen, can be copolycondensed with the other components of the sol-gel process. The metal oxide reacted with this non-hydrolyzable group comes from the above-mentioned list of metals The ligand used for the starting compound, i.e. the soluble metal compound, is preferably halides, alkoxides, oxyalkoxides, carboxylates, oxalates, nitrates, sulfates, sulfonates, acetylacetonates, glycolates or aminoalkoxylates. The base material is SiO ₂ , Al ₂ O ₃ , TiO ₂ or ZrO _2nd

All catalysts which can be used for the process according to the invention have a pore size of at most 10 nm, preferably an average pore size of 0.1 to 1.0 nm, determined according to Horvath and Kawazoe (J Chem Eng Jpn 16 (1983) 470 ff)

The total surface area of the catalysts in the dried state is preferably above 50 m ² / g, particularly preferably from 50 to 5,000 m ² / g and very particularly preferably from 75 to 1,500 m ² / g, in each case determined by the BET method according to WF Maier et al Tetrahedron 51 (1995) 3787 ff

What is important is the proximity to the membrane used for separation purposes.This membrane is intended to prevent the transition of the aromatic starting materials to the product side of the reaction space.As the membrane is preferably a polar inorganic membrane, this is replaced by the hydroxylated compounds which, due to the presence of at least one hydroxyl group, itself polar, such as phenol, are easier to penetrate. The non-polar aromatic starting materials, such as benzene, are retained by the membrane and remain predominantly on the educt side of the reaction space. The peroxidic compounds, such as hydrogen peroxide, can also pass through the membrane that educts and products mix and possibly react with each other The membrane should preferably be located in close proximity to the catalyst. This can be achieved, for example, by attaching the membrane in the reaction space directly over the catalyst poured out in the reaction space Side facing the starting material, the catalyst can be dispensed with if the particle size of the catalyst allows it to be unable to penetrate the membrane. In this case, the catalyst can move freely on the reaction side A higher surface area can often result in more favorable Raun time yields. Which embodiment of the method according to the invention is ultimately used is a question of the membrane used, the work-up possibilities and the required space / time yield. One possibility for producing such a catalytic converter The active membrane is described, for example, in PCT / EP98 / 05938. In this method, a catalytically active layer can be applied to a membrane as described above. This can be done, for example, by having at least one catalytic compound, for example one of the compounds described above , or a mixture of catalytically active and inactive compounds is applied to the membrane and solidified by the sol-gel method. The solidifying can be achieved, for example, by calcining the applied layer. By using a membrane with an applied catalytic layer, the Proportion of subsequent reactions, for example further oxidative reactions which destroy the desired product, were avoided since the product migrates through the membrane to the product side of the reaction chamber after the reaction, for example also due to the pressure difference between the starting material and the product side of the reaction chamber no catalysis on this side of the reaction space Ator is present, the product no longer reacts with the oxidizing agent. In this way, the yield of the product can be increased by using the process according to the invention Increasing sales and reducing the non-productive decomposition of the oxidizing agent In addition to hydrogen peroxide and other inorganic peroxides that form H ₂ O ₂ in situ, organic peroxides such as benzoyl peroxide, tert-butyl hydroperoxide or peracetic acid can of course also be used as the oxidizing agent this method can also be coupled with a process for the in situ production of peroxides Both educlear aromatic compounds such as benzene, phenol, toluene, anisole and polynuclear aromatics such as naphthalene or anthracene can be used as starting materials in the process according to the invention, in particular benzene is used as an aromatic compound Process aromatic compounds which have at least one hydroxyl group, such as, for example, phenol, hydroquinone, naphthol, hydroxyanisole or pyrocatechol, are produced. The process according to the invention is particularly suitable for the production of phenol

Fig. 1 shows an example of an embodiment of the process according to the invention, without this being limited thereto. A tubular reactor is divided into a reaction space and a product side by a membrane to which a catalyst layer is applied.The reaction space is the part of the reactor facing the catalyst layer Reaction chamber flows a mixture of benzene and hydrogen peroxide Due to the lower pressure on the product side of the reactor, part of the benzene reacts with the hydrogen peroxide in the catalyst layer to form phenol, which together with excess hydrogen peroxide passes through the membrane and reaches the product side of the reactor

The process according to the invention is described in the following examples, but is not restricted to it

Example 1J: Catalyst made of amorphous, microporous mixed metal oxide (hydrophobic, contains Ti)

0.133 ml of tetraisopropoxytitanium, 8 ml of tetraethoxysilane, 1.8 ml of methyltriethoxysilane and 7.9 ml of ethanol were successively dissolved in one another, and 1.98 ml of 8N hydrochloric acid were added with stirring. After gel formation and hardening of the gel, it was applied under protective gas Heated to 65 ° C with a heating rate of 0.2 ° C / min, held at 65 ° C for 3 hours, heated to 250 ° C with a heating rate of 0.2 ° C / min and calcined for a further 3 hours at this temperature. The product shows a monomodal pore distribution

BET 540 m ² / g Pore diameter 0.70 nm

Example 1.2: Catalyst made of amorphous, microporous mixed metal oxide (hydrophobized, contains V)

0.66 g of vanadylacetonate, 9 ml of tetraethoxysilane, 2 ml of methyltriethoxysilane and 9 ml of ethanol were successively dissolved in one another and 2.25 ml of 8N hydrochloric acid were added with stirring. After gel formation and hardening of the gel, the latter was brought to 65 ° under protective gas C heated at a heating rate of 0.2 ° C / min, held at 65 ° C for 3 hours, heated to 250 ° C at a heating rate of 0.2 ° C / min and calcined at this temperature for a further 3 hours. The product showed a monomodal pore distribution BET 420 m ² / g pore diameter 0.71 nm

Example 1.3: Catalyst Ti-ZSM-5

100 g of ZSM-5 (containing ammonium) were placed in 400 ml of H ₂ O. At a temperature of 70 ° C., 41.22 g (NFL ^ TiFe were added and the mixture was then heated to 95 ° C. for 24 hours. This was followed by filtration and subsequent rinsing with water In order to obtain an exchange of protons for potassium ions, the zeolite was treated several times in a KCl solution under reflux

Example 1.4: Catalyst titanium silicalite

A commercially available titanium silicalite TS-1 from Degussa AG was used

Example 2.1: Suspension 1

120 g of titanium tetraisopropylate were stirred with 140 g of deionized ice with vigorous stirring until the resulting precipitate was finely divided. After addition of 100 g of 25% hydrochloric acid, the mixture was stirred until the phase became clear, 280 g of α-aluminum oxide of the type CT3000SG from Alcoa, Ludwigshafen, added and stirred for several days until the aggregates dissolved. This suspension was then used Example 2.2: Suspension 2

80 g of titanium tetraisopropylate were hydrolyzed with 20 g of water and the resulting precipitate was peptized with 120 g of nitric acid (25%). This solution was stirred until clear and after adding 40 g of titanium dioxide from Degussa (P25) the agglomerates were dissolved stirred, the suspension was then used

Example 2.3: Suspension 3

20 g of titanium tetraisopropylate were hydrolyzed with 15 g of water and the resulting precipitate was peptized with 30 g of nitric acid (25% strength). After the precipitate had been completely dissolved, the catalyst from Example 11 was stirred until the agglomerates had completely dissolved and this suspension was used

Example 2.4: Suspension 4

20 g of titanium tetraisopropylate were hydrolyzed with 15 g of water and the resulting precipitate was peptized with 30 g of nitric acid (25% strength). After the precipitate had been completely dissolved, the catalyst from Example 12 was stirred until the agglomerates had completely dissolved and this suspension was used

Example 2.5: Suspension 5

20 g of titanium tetraisopropylate were hydrolyzed with 15 g of water and the resulting precipitate was peptized with 30 g of nitric acid (25% strength). After the precipitate had been completely dissolved, the catalyst from Example 13 was stirred until the agglomerates had completely dissolved and this suspension was used

Example 2.6: Suspension 6

20 g of titanium tetraisopropylate were hydrolyzed with 15 g of water and the resulting precipitate was peptized with 30 g of nitric acid (25%). After the After the addition of the catalyst from Example 1.4, the precipitate was stirred until the agglomerates had completely dissolved and this suspension was used.

Example 3.1: Membrane 1

A stainless steel wire mesh with a mesh size of 90 μm was coated with suspension 1 in a thickness of 120 μm and then immediately solidified at a temperature of 400 ° C. within 10 seconds. The resulting basic membrane body had an average pore size of approx. 100 nm with a thickness of 80 μm.

The suspension from Example 2J was spread onto the base body in a thickness of approximately 20 μm and also solidified at 400 ° C. within 10 seconds. This membrane now has a fine cover layer of approx. 5 μm thickness with a pore size of 10 nm.

Example 3.2: Membrane 2

The side with the finer pores of a membrane produced as in Example 3J was subsequently provided with a third layer. This was produced from a suspension produced as in Example 2J, by applying the suspension to the side with the finer pores with an application height of 50 μm and solidifying at 400 ° C. within 10 seconds. In this way, a catalytically active hydrophilic membrane was obtained.

Example 3.3: Membrane 3

The side with the finer pores of a membrane produced as in Example 3J was subsequently provided with a third layer. This was produced from a suspension prepared as in Example 2.4, by applying the suspension to the side with the finer pores with an application height of 50 μm and solidifying at 400 ° C. within 10 seconds. In this way, a catalytically active hydrophilic membrane was obtained.

Example 3.4: Membrane 4 The side with the finer pores of a membrane produced as in Example 3 1 was subsequently provided with a third layer. This was made from a suspension produced as in Example 2 5, by applying the suspension to the side with the finer pores with an application height of 50 μm and solidification within 10 seconds at 400 ° C. In this way, a catalytically active hydrophilic membrane was obtained

Example 3.5: Membrane 5

The side with the finer pores of a membrane produced as in Example 3 1 was subsequently provided with a third layer. This was made from a suspension produced as in Example 2 6, by applying the suspension to the side with the finer pores with an application height of 50 μm and solidification within 10 seconds at 400 ° C. In this way, a catalytically active hydrophilic membrane was obtained

Example 4.1: Reaction of benzene with hydrogen peroxide without membrane (comparative example)

A tubular reactor with an inner diameter of 8 mm is divided in the middle with a network body which contains the catalyst from Example 1 1. The mesh size of the network is below the particle size of the catalyst. The reaction space is heated to 60 ° C. The temperature is controlled via a thermocouple A benzene / H ₂ O ₂ mixture in acetonitrile flows through the reaction chamber, the concentration of benzene and hydrogen peroxide being 1 mol / 1. The analysis of the product composition is carried out using a GC / MS system. The experiment was carried out using the catalysts the examples 1.2, 1 3 and 1 4 repeated

Example 4.2: Reaction of benzene with hydrogen peroxide using the process according to the invention

A tubular reactor with an inner diameter of 8 mm was divided in the middle with a membrane with a catalyst layer prepared as in Example 32. The reaction space was heated to 60 ° C. The temperature was checked via a thermocouple Als a benzene / H ₂ O mixture in acetonitrile was used, the concentration of benzene and hydrogen peroxide being 1 mol / 1. The pressure on the educt side was about 2 bar. On the product side, acetonitrile is guided past the membrane. Here the pressure was 1 bar. The product composition was analyzed using a GC / MS system. The experiment was repeated with the membranes from Examples 3J, 3.4 and 3.5.

The test results are recorded in Table 1. It can be clearly seen that the benzene conversion, the selectivity based on phenol and the selectivity based on the hydrogen peroxide when using a membrane according to the invention is significantly higher than in the experiments without using a membrane according to the invention. In addition to the different effectiveness of the catalysts, an average increase of 1% can be found in the use of a membrane in the conversion of benzene. With the catalyst from Example 1.4, a selectivity which is 5% higher, based on benzene, can be determined when using the membrane according to the invention.

Table 1

Claims

Claims:

1. A process for the preparation of an aromatic compound containing at least one hydroxyl group by catalytic oxidation with at least one peroxidic compound as an oxidizing agent on a catalyst, characterized in that the oxidation is carried out using an inorganic membrane.

2. The method according to claim 1, characterized in that porous compounds with a pore size of up to a maximum of 10 nm are used as the catalyst.

3. The method according to claim 2, characterized in that at least one compound from the group of the zeolites, the amorphous mixed metal oxides or the silicalites or a mixture of compounds of this group is used as the porous compound.

4. The method according to at least one of claims 1 to 3, characterized in that an inorganic membrane is used which is flexible.

5. The method according to at least one of claims 1 to 4, characterized in that an inorganic membrane is used which has a pore size of up to a maximum of 100 nm.

6. The method according to at least one of claims 1 to 5, characterized in that an inorganic membrane is used which has a thickness of at most 200 microns. Method according to at least one of claims 1 to 6, characterized in that an inorganic membrane is used which is polar

Process according to at least one of Claims 1 to 7, characterized in that benzene is used as the aromatic compound

Method according to at least one of claims 1 to 8, characterized in that hydrogen peroxide is used as the peroxidic compound

Method according to at least one of claims 1 to 9, characterized in that the ratio of aromatic starting material to peroxide is between 0J to 10

Method according to at least one of claims 1 to 10, characterized in that the product produced by oxidation is passed through the inorganic membrane after the reaction

Method according to at least one of claims 1 to 11, characterized in that the oxidation is carried out at a temperature of 0 ° C to 500 ° C

Method according to at least one of claims 1 to 12, characterized in that the oxidation is carried out in the gas phase

Method according to at least one of claims 1 to 13, characterized in that the oxidation is carried out in the liquid phase

5. The method according to at least one of claims 1 to 14, characterized in that an inorganic membrane is used, to which at least one catalyst has been applied on one side of the membrane.