EP1761334A1

EP1761334A1 - Multi-layer catalyst for producing phthalic anhydride

Info

Publication number: EP1761334A1
Application number: EP05750896A
Authority: EP
Inventors: Christian GÜCKEL; Markus Niedermeier; Marvin Estenfelder
Original assignee: Sued Chemie AG
Current assignee: Sued Chemie AG
Priority date: 2004-05-29
Filing date: 2005-05-22
Publication date: 2007-03-14
Also published as: DE102004026472A1; WO2005115616A1; CN101166572A; CN101166572B; US20080064593A1; US7718561B2

Abstract

The invention relates to a catalyst for producing phthalic anhydride by the gas phase oxidation of o-xylol and/or naphthalene, said catalyst containing at least three catalyst layers with different compositions, which are designated in order, starting from the gas inlet side to the gas outlet side, as the first, second and third catalyst layers. Said catalyst layers respectively contain an active material containing Ti02 and the active material content reduces from the first catalyst layer facing the gas inlet side to the third catalyst layer facing the gas outlet side, with the proviso that (a) the first catalyst layer comprises an active material content of between approximately 7 and 12 wt. %, (b) the second catalyst layer comprises an active material content ranging between 6 and 11 wt. %, the active material content of the second catalyst layer being less than or equal to the active material content of the first catalyst layer and (c) the third catalyst layer comprises an active material content ranging between 5 and 10 wt. %, the active material content of the third catalyst layer being less than or equal to the active material content of the second catalyst layer. The invention also relates to a preferred method for producing a catalyst of this type and to the preferred use of the inventive titanium dioxide.

Description

20th May 2005

4465 -X- 23. 349

MULTI-LAYER CATALYST FOR PRODUCING PHTHALSAUREANHYDRID

DESCRIPTION

The invention relates to a multilayer catalyst, i.e. a catalyst with three or more different layers (layers) for the production of phthalic anhydride (PSA) by gas phase oxidation of o-xylene and / or naphthalene, the active composition content decreasing from the first catalyst layer lying towards the gas inlet side to the catalyst layer lying towards the gas outlet side.

The large-scale production of phthalic anhydride is achieved by the catalytic gas phase oxidation of o-xylene and / or naphthalene. For this purpose, a catalyst suitable for the reaction is filled into a reactor, preferably a so-called tube bundle reactor, in which a multiplicity of tubes are arranged in parallel, and from above or below with a mixture of the hydrocarbon (s) and an oxygen-containing gas , for example air, flows through. by virtue of Due to the strong heat build-up of such oxidation reactions, it is necessary to rinse the reaction tube with a heat transfer medium in order to avoid so-called hot spots ("hot spots") and thus to dissipate the resulting amount of heat. This energy can be used to produce steam. A molten salt, and here preferably a eutectic mixture of NaN0 ₂ and KN0 _{3, is} generally used as the heat transfer medium.

Likewise, to suppress the unwanted hot spots, a structured catalyst can be filled into the reaction tube, which can result in, for example, two or three catalyst layers composed of differently composed catalysts. Such systems are already known as such from EP 1 082 317 B1 or EP 1 084 115 B1.

The layered arrangement of the catalysts also has the purpose of reducing the content of undesired by-products, i.e. To keep compounds in a possible reaction mechanism of o-xylene to phthalic anhydride before the actual product of value in the raw PSA as low as possible. These undesirable by-products mainly include the compounds o-tolylaldehyde and phthalide. The further oxidation of these compounds to phthalic anhydride also increases the selectivity with regard to of the actual value product.

In addition to the underoxidation products mentioned above, overoxidation products also occur in the reaction. These include maleic anhydride, citraconic anhydride, benzoic acid and the carbon oxides. A targeted suppression of the formation of these undesired by-products in favor of the valuable product leads to a further increase in the productivity and economy of the catalyst.

From EP 1 084 115 it is known: a process for the preparation of phthalic anhydride by catalytic gas phase oxides dation of xylene and / or naphthalene with a molecular oxygen-containing gas in a fixed bed at elevated temperature and by means of at least three shell catalysts arranged in layers one above the other, on the core of which a layer of catalytically active metal oxides is applied from carrier material, characterized in that the catalyst activity of layer to the layer increases from the gas inlet side to the gas outlet side, the activity of the catalysts of the individual layers being adjusted so that the least active catalyst has a lower active mass content and, if appropriate, additionally more alkali metal, selected from the group consisting of potassium, rubidium and cesium, has as doping as the catalyst of the next layer and the subsequent still more active catalyst has the same amount of active material and even less alkali metal as doping or a larger amount of active material and possibly less alkali metal ll as doping as the catalyst of the second layer, with the proviso that

a) the least active catalyst on non-porous support material has 5 to 9% by weight, based on the total catalyst, of active composition containing 3 to 8% by weight of V ₂ 0 ₅ ,

0 to 3.5 wt% Sb ₂ 0 ₃ , 0 to 0.3 wt% P, 0.1 to 0.5 wt% alkali (calculated as alkali metal) and the remainder Ti0 ₂ in ana- tasform with a BET surface area of 18 to 22 m ² / g,

b) the next more active catalyst with otherwise the same composition as catalyst (a) has a 1 to 5% by weight (absolute) higher active mass content and the alkali content is 0 to 0.25% by weight (absolute) lower and

c) the most active catalyst with otherwise the same composition as (a) a 1 to 5% by weight (absolute) higher active has a mass content than for (a) and the alkali content is 0.15 to 0.4% by weight (absolute) less than for (a).

A disadvantage of the catalysts according to the invention specified there is that, despite the use of such structured catalysts, very high proportions of the undesired by-product phthalide are still present in the crude PSA. It is clear to the person skilled in the art that the two products can only be separated by distillation if the actual product of value is lost. Furthermore, the PSA yields can still be improved.

There is therefore a constant need for improved multilayer (multilayer) catalysts for the production of phthalic anhydride.

The object of the present invention was therefore to provide an improved catalyst for the preparation of phthalic anhydride by gas phase oxidation of o-xylene and / or naphthalene, which avoids the disadvantages of the prior art and in particular enables high selectivity and activity even after a long operating time.

This object is achieved by the catalyst according to claim 1. Preferred embodiments are specified in the subclaims.

It has surprisingly been found that particularly advantageous catalysts can be produced if the catalyst is composed of at least three different layers, the active composition content decreasing from the first catalyst layer located towards the gas inlet side to the catalyst layer located towards the gas outlet side. It has been found to be essential that the first catalyst layer has an active mass content between approximately 7 and 12% by weight, In particular between approximately 8 and 11% by weight, the second catalyst zone has an active composition content between approximately 6 and 11% by weight, in particular between approximately 7 and 10% by weight, and the third catalyst zone has an active composition content between about 5 and 10% by weight, in particular between about 6 and 9% by weight.

The terms first, second and third catalyst layer are used in connection with the present invention as follows: the first catalyst layer is the catalyst layer located towards the gas inlet side. Towards the gas outlet side, the catalyst according to the invention also contains two further catalyst layers, which are referred to as second and third catalyst layers. The third catalyst zone is closer to the gas outlet side than the second catalyst zone.

According to a particularly preferred embodiment according to the invention, the catalyst according to the invention has three catalyst layers. Then the third catalyst layer is on the gas outlet side. However, the presence of additional catalyst layers downstream of the first catalyst layer is not excluded. For example, according to an embodiment of the invention, the third catalyst zone, as defined herein, can be followed by a fourth catalyst zone (with an identical or even lower active mass content than the third catalyst zone).

According to the invention, the active composition content can decrease between the first and the second catalyst zone and / or between the second and the third catalyst zone.

According to a particularly preferred embodiment according to the invention, the active mass content decreases between the second and the third catalyst layer. It is understood that from the active mass content never increases in the sequence of the catalyst layers from the gas inlet side to the gas outlet side, but at most remains the same.

It is assumed, without the invention being restricted to the correctness of this assumption, that, due to the different layer thicknesses of the catalytically active mass in the individual layers associated with the different active mass contents, particularly preferably the decreasing layer thicknesses of the catalytically active mass from the first to the third Layer on the one hand the reaction of o-xylene to PSA in the first and optionally second layer is influenced, and furthermore in the third layer with the even thinner layer of active mass the remaining underoxidation products such as phthalide to PSA , but not PSA to the so-called overoxidation products, such as CO _{x are} oxidized. As a result, the maximum productivity in the oxidation of o-xylene to PSA is achieved over the entire structured pack with a minimal proportion of the so-called undesired by-products.

According to a preferred embodiment of the invention, the BET surface area increases from the first catalyst layer located towards the gas inlet side to the third catalyst layer located towards the gas outlet side. This allows surprisingly good catalyst performance to be achieved. Preferred ranges for the BET surface area are 15 to 25 m ² / g for the first catalyst zone, 15 to 25 m ² / g for the second catalyst zone and 25 to 45 m / g for the third catalyst zone.

In general, it is preferred according to the invention that the BET surface area of the first catalyst zone is less than the BET surface area of the third catalyst zone. Particularly advantageous catalysts are also obtained if the BET Surface of the first and second catalyst zone are the same, while the BET surface area of the third catalyst zone is larger. If more than three catalyst layers are present, it is also advantageous according to a preferred embodiment of the invention that the BET surface area of the last catalyst layer located towards the gas outlet side is larger than the BET surface area of the catalyst layers closer to the gas inlet side. According to a further embodiment, the BET surface area of all the catalyst layers can be the same except for the last catalyst layer located on the gas outlet side.

According to a preferred embodiment of the invention, the catalyst activity to the gas inlet side is lower than the catalyst activity to the gas outlet side.

It has also been found, surprisingly, that the multilayer or multilayer catalysts according to the invention with decreasing active composition content can be used particularly advantageously for the production of phthalic anhydride if the individual catalyst layers are present in a certain length ratio to one another.

Thus, according to a particularly preferred embodiment of the invention the first, toward the gas inlet side catalyst layer a ^• Length fraction, based on the total length of the catalyst bed of at least 40%, especially at least 45%, more preferably at least 50%. It is particularly preferred that the proportion of the first catalyst zone in the total length of the catalyst bed is between 40 and 70%, in particular between 40 and 55%, particularly preferably between 40 and 52%.

The second layer preferably takes up about 10 to 40%, in particular about 10 to 30% of the total length of the catalyst bed on. Furthermore, it has surprisingly been found that a ratio of the length of the third catalyst zone to the length of the second catalyst zone is between about 1 and 2, in particular between 1.2 to 1.7, particularly preferably between 1.3 and 1.6, particularly good results with regard to provides the economy as well as the efficiency of raw material use and productivity of the catalyst.

It has been shown that the above selection of the length proportions of the individual catalyst layers, in particular in conjunction with the decreasing active compound contents as defined above, enables the hot spot to be positioned particularly advantageously, in particular in the first layer, and good temperature control to avoid excessive hot Spot temperatures are made possible even when the catalytic converter is operating for a long time. This improves the yield, in particular based on the life of the catalyst. It is assumed, without the invention being restricted to this assumption, that due to the above layer length ratio of the individual catalyst layers to one another, practically complete conversion of the o-xylene used takes place within the second catalyst layer and thus in the third catalyst layer with those described above Advantages of the so-called "product polishing", ie the cleaning of the reaction gas from undesired by-products by oxidation to the actual valuable product. It is also known to the person skilled in the art that such catalysts deactivate in the area of the hot spot (generally in the first position) after a certain runtime. This deactivation leads to a shift of the reaction into the second, more active position, which leads to very high hot spot temperatures and the associated problems with regard to selectivity and plant safety. Due to the layer ratios selected in the catalyst according to the invention, there is a maximum residence time _ _

which has at least about 30 angstroms. It was found that such Ti0 ₂ primary crystallites with the above (minimum) size enable the production of particularly advantageous catalysts. The primary crystal size is preferably below 80 angstroms, in particular below 50 angstroms. The above primary crystallite size apparently enables, without the invention being restricted to this assumption, the formation of a not too compact, but rather open-pored structure of the titanium dioxide in the catalyst. A method for determining the primary crystallite size is given in the method section below.

According to a further preferred embodiment, Ti0 _{2 is} used which has a bulk density of less than 1.0 g / ml, in particular less than 0.8 g / ml, particularly preferably less than about 0.6 g / ml. Most preferred are TiO ₂ materials with a bulk density of no more than about 0.55 g / ml. A method for determining the bulk density is given in the method section below. It has thus been found that the use of a titanium dioxide with a bulk density as defined above enables the production of particularly powerful catalysts. It is assumed, without the invention being restricted to this, that the bulk density here is a measure of a particularly favorable structure of the TiO ₂ surface provided in the catalyst, the reaction structures and feed spaces, which are particularly favorable due to the loose, not too compact structure, being and discharge routes for the reactants or reaction products are provided.

Without the invention being restricted to the accuracy of this theoretical assumption, it is believed that the use of the titanium dioxide with the properties described herein in a catalyst is particularly advantageous. - -

of the hot spot in the first layer with the known advantages, while at the same time the length of the second and third layers according to the invention ensures a minimum proportion of undesired by-products with a maximum yield of the actual product of value.

It has also been found that the layer length ratios defined herein also apply to other multi-layer catalysts, i.e. which do not have the decrease in the active mass fraction according to the invention shows advantages. In addition to the catalysts for the production of phthalic anhydride (PSA) by gas phase oxidation of o-xylene and / or naphthalene, this also generally applies to other multilayer catalysts for the gas phase oxidation of hydrocarbons.

The temperature management in the gas phase oxidation of o-xylene to phthalic anhydride is well known to the person skilled in the art from the prior art, reference being made, for example, to DE 100 40 827 A1.

According to a further preferred embodiment, the active composition (catalytically active composition) of the catalyst according to the invention contains titanium dioxide with a specific BET surface area and a specific pore radius distribution. It was surprisingly found that when using a titanium dioxide in which at least 25%, in particular at least about 40%, particularly preferably at least about 50%, most preferably at least about 60% of the total pore volume is found in pores with a radius between 60 and 400 nm are formed, particularly advantageous catalysts can be produced.

According to a further preferred embodiment, TiO _{2 is} used which has a primary crystallite size (primary particle size) of more than about 22 angstroms, preferably more than about 25 angstroms, more preferably at least 27 angstroms, in particular partial reaction spaces for the desired reactions, especially in the pore structure, can be achieved. At the same time, when using the Ti0 ₂ matrix according to the invention, advantageous feed routes for the starting materials to the reactive centers on the surface of the Ti0 ₂ matrix and discharge routes for the reaction products are provided.

In general, when using the catalyst according to the invention for the production of phthalic anhydride, a mixture of a gas containing molecular oxygen, for example air, and the starting material to be oxidized (in particular o-xylene and / or naphthalene) is passed through a fixed bed reactor, in particular a tube bundle reactor, which can consist of a plurality of tubes arranged in parallel. In each case there is a bed of at least one catalyst in the reactor tubes. The advantages of a bed of several (different) catalyst layers have already been discussed above.

When using the catalysts according to the invention for the production of phthalic anhydride by gas phase oxidation of o-xylene and / or naphthalene, it was surprisingly found that very good PSA yields with very low proportions of phthalide are achieved with the catalysts according to the invention.

According to a preferred embodiment of the invention, the Ti0 _{2 used has} a BET surface area of at least 15, preferably between 15 and 60 m ² / g, in particular between about 15 and 45 m ² / g and particularly preferably between 15 and 30 m ² / g , It is further preferred that up to 80%, preferably up to 75%, in particular up to 70% of the total pore volume of the TiO _{2 is formed} by pores with a radius between 60 and 400 nm. Unless stated otherwise, the pore volumes or proportions specified here are determined by means of mercury porosimetry (in accordance with DIN 66133). In the present description, the specification of the total pore volume relates in each case to the total pore volume between 7500 and 3.7 nm pore radius size measured by means of mercury porosimetry.

Pores with a radius of more than 400 nm are preferably less than about 30%, in particular less than about 22%, particularly preferably less than 20% of the total pore volume of the TiO _{2 used} .

It is further preferred that about 50 to 75%, in particular about 50 to 70%, particularly preferably 50 to 65% of the total pore volume of the TiO ₂ by pores with a radius of 60 to 400 nm, and preferably about 15 to 25% of the total Pore volume are formed by pores with a radius of more than 400 nm.

With regard to the smaller pore radii, it is preferred that less than 30%, in particular less than 20%, of the total pore volume of the TiO _{2 are formed} by pores with a radius of 3.7 to 60 nm. A particularly preferred range for this pore size is about 10 to 30% of the total pore volume, in particular 12 to 20%.

According to a further preferred embodiment, the Ti0 _{2 used has} the following particle size distribution: the D ₁₀ value is preferably 0.5 μm or less; the D ₅₀ value (ie the value at which half of the particles have a larger or smaller particle diameter) is preferably 1.5 μm or less; the D ₉₀ value is preferably 4 μm or less. The D ₉₀ value of the TiO ₂ used is preferably between about 0.5 and .20 microns, in particular between about 1 and 10 microns, particularly preferably between about 2 and 5 microns.

In electron micrographs, the TiO ₂ used according to the invention preferably has an open-pore, sponge-like structure. The primary crystallites are preferably more than 30%, in particular more than 50%, preferably open-pore agglomerates. It is assumed, without the invention being restricted to this assumption, that this special structure of the TiO _{2 used} , which is reflected in the pore radius distribution, creates particularly favorable reaction conditions for the gas phase oxidation.

Depending on the intended use of the catalyst according to the invention, in addition to the Ti0 ₂ used according to the invention, the components familiar and customary to the person skilled in the art can be contained in the active composition of the catalyst. The shape of the catalyst or its homogeneous or heterogeneous structure is also in principle not restricted in the sense of the present invention and can include any embodiment which is familiar to the person skilled in the art and appears suitable for the respective field of application.

So-called coated catalysts have proven particularly useful for the production of phthalic anhydride. Here, “a carrier that is inert under the reaction conditions, for example made of quartz (Si0 ₂ ), porcelain, magnesium oxide, tin dioxide, silicon carbide, rutile, alumina (Al ₂ 0 ₃ ), aluminum silicate, magnesium silicate (steatite), zirconium silicate or cerium silicate, or from mixtures of the above materials used. The carrier can have the shape of rings, balls, shells or hollow cylinders, for example. The catalytically active material is applied to it in relatively thin layers (shells). It can also have two or more layers the same or differently composed catalytically active mass are applied.

With regard to the other components of the catalytically active composition of the catalyst according to the invention (in addition to TiO ₂ ), reference can in principle be made to the compositions or components described in the relevant prior art and familiar to the person skilled in the art. These are mainly catalyst systems that contain oxides of vanadium in addition to titanium oxide (s). Such catalysts are described, for example, in EP 0 964 744 B1, the disclosure of which in this regard is hereby expressly incorporated into the description by reference.

In particular, a number of promoters for increasing the productivity of the catalysts are described in the prior art, which can also be used in the catalyst according to the invention. These include the alkali and alkaline earth metals, thallium, antimony, phosphorus, iron, niobium, cobalt, molybdenum, silver, tungsten, tin, lead and / or bismuth and mixtures of two or more of the above components. For example, DE 21 59 441 A describes a catalyst which, in addition to titanium dioxide of the anatase modification, consists of 1 to 30% by weight of vanadium pentoxide and zirconium dioxide. The activity and selectivity of the catalysts can be influenced via the individual promoters, in particular by lowering or increasing the activity. The promoters which increase the selectivity include, for example, the alkali metal oxides, whereas oxidic phosphorus compounds, in particular phosphorus pentoxide, increase the activity of the catalyst at the expense of the selectivity.

Numerous suitable processes for producing the catalysts according to the invention have been described in the prior art, so that a detailed description is essential here is not required. For the preparation of coated catalysts, reference can be made, for example, to the process described in DE-A-16 42 938 or DE-A 17 69 998, in which a solution or suspension of the components of the catalytically active composition comprising an aqueous and / or an organic solvent and / or their precursor compounds (often referred to as "mash") are sprayed onto the support material in a heated coating drum at elevated temperature until the desired content of catalytically active composition, based on the total catalyst weight, has been reached. According to DE 21 06 796, the application (coating) of the catalytically active composition to the inert support can also be carried out in fluidized coaters.

So-called coated catalysts are preferably produced by applying a thin layer of 50 to 500 μm of the active components on an inert support (e.g. US 2,035,606). Balls or hollow cylinders have proven particularly suitable as carriers. These moldings result in a high packing density with low pressure loss and reduce the risk of formation of packing errors when filling the catalyst into the reaction tubes.

The molten and sintered moldings must be heat-resistant within the temperature range of the reaction taking place. As stated above, silicon carbide, steatite, quartz, porcelain, SiO ₂ , Al ₂ O ₃ or alumina are suitable.

The advantage of coating carrier bodies in the fluidized bed is the high uniformity of the layer thickness, which plays a decisive role in the catalytic performance of the catalyst. A particularly uniform coating is obtained by spraying on a suspension or solution of the active components the heated carrier at 80 to 200 ° C. in a fluidized bed, for example according to DE 12 80 756, DE 198 28 583 or DE 197 09 589. In contrast to the coating in coating drums, hollow cylinders can also be used as carriers in the fluidized bed processes mentioned evenly coat the inside of the hollow cylinder. Among the above-mentioned fluidized bed processes, the process according to DE 197 09 589 is particularly advantageous, since the predominantly horizontal, circular movement of the supports, in addition to a uniform coating, also results in low abrasion of apparatus parts.

For the coating process, the aqueous solution or suspension of the active components and an organic binder, preferably a copolymer of vinyl acetate / vinyl laurate, vinyl acetate / ethylene or styrene / acrylate, is sprayed onto the heated, fluidized carrier via one or more nozzles. It is particularly favorable to apply the spray liquid at the location of the highest product speed, as a result of which the spray material can be distributed evenly in the bed. The spraying process is continued until either the suspension has been used up or the required amount of active components has been applied to the support.

According to a particularly preferred embodiment of the invention, the catalytically active composition of the catalyst according to the invention is applied in a fluidized bed or fluidized bed with the aid of suitable binders, so that a coated catalyst is produced. Suitable binders include organic binders familiar to the person skilled in the art, preferably copolymers, advantageously in the form of an aqueous dispersion, of vinyl acetate / vinyl laurate, vinyl acetate / acrylate, styrene / acrylate, vinyl acetate / maleate and vinyl acetate / ethylene. An organic polymeric or copolymeric adhesive, in particular a vinyl acetate-copolymer adhesive, is particularly preferred as the binder used. The binder used is added to the catalytically active composition in customary amounts, for example about 10 to 20% by weight, based on the solids content of the catalytically active composition. For example, reference can be made to EP 744 214. Insofar as the catalytically active composition is applied at elevated temperatures of approximately 150 ° C., it is possible, as is known from the prior art, to apply it to the support even without organic binders. Usable coating temperatures when using the above-mentioned binders are, for example, between about 50 and 450 ° C. according to DE 21 06 796. The binders used burn out within a short time when the catalyst is heated when the filled reactor is started up. The binders primarily serve to increase the adhesion of the catalytically active composition to the support and to reduce abrasion during transport and filling of the catalyst.

Further possible processes for the preparation of coated catalysts for the catalytic gas phase oxidation of aromatic hydrocarbons to carboxylic acids and / or carboxylic acid anhydrides have been described, for example, in WO 98/00778 and EP-A 714 700. Thereafter, a powder is first produced from a solution and / or a suspension of the catalytically active metal oxides and / or their precursor compounds, if appropriate in the presence of auxiliaries for catalyst production, which is then used for catalyst production on the support, if appropriate after conditioning and if appropriate, after the heat treatment to produce the catalytically active metal oxides, applied in the form of a shell and the support coated in this way is subjected to a heat treatment to produce the catalytically active metal oxides or a treatment to remove volatile constituents. Suitable conditions for carrying out a process for the preparation of phthalic anhydride from o-xylene and / or naphthalene are likewise familiar to the person skilled in the art from the prior art. In particular, reference is made to the summary presentation in K. Towae, W. Enke, R. Jäckh, N. Bhargana "Phtalic Acid and Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry Vol. A. 20, 1992, 181, which is hereby incorporated by reference , For example, the boundary conditions known from the above literature reference of WO-A 98/37967 or WO 99/61433 can be selected for the steady-state operating state of the oxidation.

For this purpose, the catalysts are first filled into the reaction tubes of the reactor, which are thermostatted from the outside to the reaction temperature, for example by means of molten salts. The reaction gas at temperatures of generally 300 to 450 ° C., preferably 320 to 420 ° C., and particularly preferably from 340 to 400 ° C. and at an excess pressure of generally 0.1 to 2.5, preferably from 0.3 to 1.5 bar with a space velocity of generally 750 to 5000 h ^"1 .

The reaction gas supplied to the catalyst is generally produced by mixing a gas containing molecular oxygen, which in addition to oxygen may also contain suitable reaction moderators and / or diluents such as steam, carbon dioxide and / or nitrogen, with the aromatic hydrocarbon to be oxidized, this being the molecular oxygen-containing gas in general 1 to 100, preferably 2 to 50 and particularly preferably 10 to 30 mol% of oxygen, 0 to 30, preferably 0 to 10 mol% of water vapor and 0 to 50, preferably 0 to 1 mol% of carbon dioxide , Balance nitrogen. To generate the reaction gas, the gas containing the molecular oxygen is generally mean with 30 to 150 g of Nm ³ gas of the aromatic hydrocarbon to be oxidized.

According to a particularly preferred embodiment of the invention, the catalyst of the invention has an active composition content of between about 7 and 12% by weight, preferably between 8 and 10% by weight, the active composition (catalytically active composition) between 5 and 15% by weight of V ₂ 0 ₅ , 0 to 4 wt .- Sb ₂ 0 ₃ , 0.2 to 0.75 wt .-% Cs, 0 to 3 wt .-% Nb ₂ 0 ₅ and the rest of Ti0 ₂ contains. Such a catalyst according to the invention can advantageously be used, for example, in the case of a two-layer or multi-layer catalyst as the first catalyst layer located towards the gas inlet side.

According to a particularly preferred embodiment of the invention, the BET surface area of the catalyst is between 15 and about 25 m ² / g. It is further preferred that such a first catalyst layer has a length fraction of approximately 40 to 60% of the total length of all the catalyst layers present (total length of the catalyst bed present).

According to a further preferred embodiment according to the invention, the catalyst according to the invention has an active composition content of about 6 to 11% by weight, in particular 7 to 9% by weight, the active composition 5 to 15% by weight of V ₂ O ₅ , 0 to 4 wt .-% Sb ₂ 0 ₃ , 0.05 to 0.3 wt .-% Cs, 0 to 2 wt .-% Nb ₂ 0 ₅ and the rest contains Ti0 ₂ . Such a catalyst according to the invention can, for example, advantageously be used as a second catalyst zone, ie downstream of the first catalyst zone (see above), which is located towards the gas inlet side. It is preferred that the catalyst has a BET surface area between about 15 and 25 m ² / g. It is further preferred that this second layer occupies a length fraction of approximately 10 to 30% of the total length of all the catalyst layers present. According to a further embodiment according to the invention, the catalyst according to the invention has an active composition content between approximately 5 and 10% by weight, in particular between 6 and 8% by weight, the active composition (catalytically active composition) 5 to 15% by weight V ₂ O ₅ , 0 to 4 wt .-% Sb ₂ 0 ₃ , 0 to 0.1 wt .-% Cs, 0 to 1 wt .-% Nb0 ₅ and the rest Ti0 ₂ contains. Such a catalyst according to the invention can, for example, advantageously be used as a third catalyst layer arranged downstream of the second catalyst layer described above. A BET surface area of the catalyst / which is somewhat higher than that of the layers closer to the gas inlet side is preferred, in particular in the range between about 25 to about 45 m ² / g. It is further preferred that such a third catalyst layer occupies a length fraction of approximately 10 to 50% of the total length of all existing catalyst layers.

It is further preferred according to the invention that when the catalyst according to the invention is used in a multi-layer catalyst bed, the content of alkali metals in the catalyst layers drops from the gas inlet side to the gas outlet side.

In principle, another titanium dioxide with a different specification than that described above, ie a different BET surface area, porosimetry and / or particle size distribution, can also be used in the catalyst according to the invention. According to the invention, however, it is particularly preferred that at least 50%, in particular at least 75%, particularly preferably the entire Ti0 _{2 used has} a BET surface area and porosimetry as defined herein, and preferably also has the particle size distribution described. Mixtures of different Ti0 ₂ materials can also be used.

It has also been found that, according to a preferred embodiment, catalysts according to the invention which have no phosphorus in the catalytically active composition, in interaction with the invented Ti0 ₂ used according to the invention enable particularly good activities with very high selectivity at the same time. It is further preferred that at least 0.05% by weight of the catalytically active composition is formed by at least one alkali metal, calculated as the alkali metal (s). Cesium is particularly preferred as the alkali metal.

In addition, according to the results of the inventors, in one embodiment it is preferred that the catalyst according to the invention contains niobium in an amount of 0.01 to 2% by weight, in particular 0.5 to 1% by weight, of the catalytically active composition.

The catalysts according to the invention are heat-treated or calcined (conditioned) in a conventional manner before use. It has proven to be advantageous if the catalyst is calcined for at least 24 hours at at least 390 ° C., in particular between 24 and 72 hours at> 400 ° C., in a gas containing 0 ₂ , in particular in air. The temperature should preferably not exceed 500 ° C, in particular 470 ° C. In principle, however, other calcination conditions which appear to be suitable for the person skilled in the art are also not excluded.

According to a further aspect, the present invention relates to a method for producing a catalyst according to one of the preceding claims, comprising the following steps: a. Providing a catalytically active mass as defined herein, b. Providing an inert carrier, in particular an inert shaped carrier body; c. Applying the catalytically active composition to the inert support, in particular in a fluidized bed or a fluidized bed. According to a further aspect, the invention also relates to a process for the preparation of phthalic anhydride by gas phase oxidation of o-xylene and / or naphthalene, a three-layer or multilayer catalyst as defined in the present description being used.

According to a further aspect, the present invention finally also relates to the use of a catalyst as defined herein for the production of phthalic anhydride by gas phase oxidation of o-xylene and / or naphthalene.

METHODS

The following methods are used to determine the parameters of the catalysts according to the invention:

1. BET surface:

The determination is made according to the BET method in accordance with DIN 66131; A publication of the BET method can also be found in J. Am. Chem. Soc. 60, 309 (1938).

2. Pore radius distribution:

The pore radius distribution and the pore volume of the Ti0 ₂ used were determined by means of mercury porosimetry in accordance with DIN 66133; maximum pressure: 2,000 bar, Porosimeter 4000 (Porotec, DE), according to the manufacturer.

3. Primary crystallite sizes:

The primary crystallite sizes were determined by means of powder X-ray diffractometry. The analysis was carried out using a device from Bruker, DE: type BRUKER AXS - D4 Endeavor. The X-ray diffractograms obtained were recorded with the software package "DiffracPlus D4 Measurement" in accordance with the manufacturer's instructions and the half-value width - -

The 100% reflex was evaluated with the software "DiffracPlus Evaluation" according to the Debey-Scherrer formula according to the manufacturer's instructions in order to determine the primary crystallite size.

4. Particle sizes:

The particle sizes were determined using the laser diffraction method with a Fritsch Particle Sizer Analyzer 22 Economy (from Fritsch, DE) according to the manufacturer's instructions, also with regard to sample pretreatment: the sample is homogenized in deionized water without the addition of auxiliaries and 5 minutes with ultrasound treated.

5. Bulk density:

The bulk density was determined on the basis of the TiO ₂ used to prepare the catalyst (dried at 150 ° C. in vacuo, uncalcined). The values obtained from three determinations were averaged.

The bulk density was determined by pouring 100 g of the TiO ₂ material into a 1,000 ml can and shaking for about 30 seconds (if necessary, several parallel batches).

A measuring cylinder (capacity exactly 100ml) is weighed empty to 10 mg. The powder funnel is then attached to the opening of the cylinder using a stand and clamp. After starting the stopwatch, the measuring cylinder is filled with the Ti0 ₂ material within 15 seconds. With the spatula, filling material is continuously refilled, so that the measuring cylinder is always slightly protruding. After 2 minutes, the excess is wiped off with a spatula, making sure that no pressing forces compress the material in the cylinder. The filled measuring cylinder is brushed off and weighed.

The bulk density is given in g / ml. _ _-

The BET surface area, the pore radius distribution or the pore volume and the particle size distribution were determined with respect to the titanium dioxide in each case on the uncalcined material dried at 150 ° C. in vacuo.

The information in the present description relating to the BET surfaces of the catalysts or catalyst layers also relates to the BET surfaces of the TiO ₂ material used in each case (dried in vacuo at 150 ° C., uncalcined, see above).

In general, the BET surface area of the catalyst is determined by the BET surface area of the Ti0 ₂ used, the BET surface area being changed to a certain extent by the addition of further catalytically active components. This is familiar to the person skilled in the art.

The proportion of active mass (proportion of the catalytically active mass, without binder) relates in each case to the proportion (in% by weight) of the catalytically active mass to the total weight of the catalyst, including the support in the respective catalyst zone, measured after conditioning over 4 hours at 400 ° C. ,

The invention will now be explained in more detail with reference to the following, non-limiting examples:

EXAMPLES

Example 1: Preparation of Catalyst A

To prepare catalyst A with an active mass fraction of 8% by weight and the composition of 7.5% by weight of vanadium pentoxide, 3.2% by weight of antimony trioxide, 0.40% by weight of cesium (calculated net as cesium), 0.2% by weight of phosphorus (calculated as phosphorus) and the rest of titanium dioxide were 2600 g of steatite body in the form of hollow cylinder size 8 x 6.5 mm with a suspension of 17.9 g in a so-called fluidized bed coater Vanadium pentoxide, 7.6 g antimony trioxide, 1.3 g cesium sulfate, 1.9 g ammonium dihydrogen phosphate, 211.1 g titanium dioxide with a BET surface area of 21 m ² / g, 130.5 g binder from a 50% Dispersion of water and vinyl acetate / ethylene copolymer (Vinnapas ^" EP 65 W, Wacker) and 2000 g of water coated at a temperature of 70 ° C. The active composition was applied in the form of thin layers.

Example 2: Preparation of Catalyst B

For the preparation of the catalyst B with an active mass fraction of 8% by weight and the composition of 7.5% by weight of vanadium pentoxide, 3.2% by weight of antimony trioxide, 0.20. % By weight of cesium (calculated as cesium), 0.2% by weight of phosphorus (calculated as phosphorus) and the rest of titanium dioxide were combined in a so-called fluidized bed coater with 2200 g of steatite bodies in the form of hollow cylinders measuring 8 × 6 × 5 mm a suspension of 15.4 g vanadium pentoxide, 6.6 g antimony trioxide, 0.5 g cesium carbonate, 1.5 g ammonium dihydrogen phosphate, 182.9 g titanium dioxide with a BET surface area of 21 m ² / g, 110.7 g Binder coated from a 50% dispersion of water and vinyl acetate / ethylene copolymer (Vinnapas EP 65 W, Wacker) and 2000 g of water at a temperature of 70 ° C. The active mass was applied in the form of thin layers.

Example 3: Preparation of Catalyst C.

For the preparation of the catalyst C with an active mass fraction of 8% by weight and the composition of 7.5% by weight of vanadium Pentoxide, 3.2% by weight of antimony trioxide, 0.2% by weight of phosphorus (calculated as phosphorus) and the rest of titanium dioxide were mixed with 2200 g of steatite bodies in the form of hollow cylinders of size 8 × 6 × 5 mm in a so-called fluidized bed coater a suspension of 13.35 g vanadium pentoxide, 5.7 g antimony trioxide, 1.34 g ammonium dihydrogen phosphate, 158.65 g titanium dioxide with a BET surface area of 21 m ² / g, 109.4 g binder from a 50% dispersion of water and vinyl acetate / ethylene copolymer (Vinnapas ^" EP 65 W, Wacker) and 2000 g of water at a temperature of 70 ° C. The active composition was applied in the form of thin layers.

Example 4: Preparation of Catalyst D.

For the preparation of the catalyst D with an active mass fraction of 9% by weight and the composition of 7.5% by weight of vanadium pentoxide, 3.2% by weight of antimony trioxide, 0.40% by weight of cesium (calculated as cesium), 0.2% by weight of phosphorus (calculated as phosphorus) and the remainder of titanium dioxide were mixed in a so-called fluidized bed coater with 2000 g of steatite body in the form of hollow cylinders of size 8 × 6 × 5 mm with a suspension of 17.0 g of vanadium pentoxide, 7. 0 g of antimony trioxide, 1.1 g of cesium sulfate, 1.65 g of ammonium dihydrogen phosphate, 194.9 g of titanium dioxide with a BET surface area of 21 m ² / g, 102.1 g of binder from a 50% dispersion of water and Vinyl acetate / ethylene copolymer (Vinnapas ^" EP 65 W, Wacker) and 2000 g of water coated at a temperature of 70 ° C. The active composition was applied in the form of thin layers.

Example 5: Preparation of Catalyst E.

For the preparation of the catalyst E with an active mass fraction of 8% by weight and the composition of 7.5% by weight of vanadium Pentoxide, 3.2% by weight of antimony trioxide, 0.20% by weight of cesium (calculated as cesium), 0.2% by weight of phosphorus (calculated as phosphorus) and the rest of titanium dioxide were 2000 g in a so-called fluidized bed coater Steatite body in the form of hollow cylinders measuring 8 x 6 x 5 mm with a suspension of 15.1 g vanadium pentoxide, 6.3 g antimony trioxide, 0.53 g cesium sulfate, 1.47 g ammonium dihydrogen phosphate, 173.7 g titanium dioxide with one BET surface area of 21 m ² / g, 101 g of binder from a 50% dispersion of water and vinyl acetate / ethylene copolymer (Vinnapas ^" EP 65 W, Wacker) and 2000 g of water coated at a temperature of 70 ° C. The active mass was applied in the form of thin layers.

Example 6: Preparation of Catalyst F

For the preparation of the catalyst F with an active mass fraction of 8% by weight and the composition of 7.5% by weight of vanadium pentoxide, 3.2% by weight of antimony trioxide, 0.2% by weight of phosphorus (calculated as phosphorus) and The rest of the titanium dioxide was in a so-called fluidized bed coater 2000 g steatite body in the form of hollow cylinders 8 x 6 x 5 mm in size with a suspension of 15.1 g vanadium pentoxide, 6.25 g antimony trioxide, 1.47 g ammonium dihydrogen phosphate, 174, 11 g of titanium dioxide with a BET surface area of 27 m ² / g, 101 g of binder from a 50% dispersion of water and vinyl acetate / ethylene copolymer (Vinnapas ^" EP 65 W, from Wacker) and 2000 g of water at a temperature of 70 ° C. The active composition was applied in the form of thin layers.

Example 7: Preparation of Catalyst G.

For the preparation of the catalyst G with an active mass fraction of 8% by weight and the composition of 7.5% by weight of vanadium Pentoxide, 3.2% by weight of antimony trioxide, 0.2% by weight of phosphorus (calculated as phosphorus) and the remainder of titanium dioxide were exactly as described in Example 6 above. Catalyst F proceeded, but using titanium dioxide with a BET surface area of 21 m ² / g.

Example 8: Catalytic performance data in the oxidation of o-xylene to phthalic anhydride (comparative example 1)

100 cm of catalyst C, 60 cm of catalyst B and 130 cm of catalyst A are filled in succession into a 450 cm long reaction tube. The reaction tube is in a molten salt melt, which can be heated to temperatures up to 450 ° C. In the catalyst bed there is a 3 mm protective tube with a built-in thermocouple, which can be used to display the catalyst temperature across the entire catalyst combination. To determine the catalytic performance data, this catalyst combination is passed in the sequence ABC from 0 to a maximum of 70 g / Nm ³ o-xylene (purity 99.9%) at 3.6 Nm ³ air / h and the reaction gas after the reaction tube emerges condenser through which all organic components of the reaction gas, apart from carbon monoxide and carbon dioxide, separate. The separated crude product is melted using superheated steam, collected and then weighed.

The raw yield is determined as follows.

Max. Raw PSA yield [wt. -%]

Balanced amount of raw PSA [g] x 100 / feed o-xylene [g] x purity o-xylene [% / 100]

The results of the test run are shown in Table 1. Example 9: Catalytic performance data in the oxidation of o-xylene to phthalic anhydride (Example 1 according to the invention)

90 cm of catalyst F, 60 cm of catalyst E and 140 cm of catalyst D are filled in succession into a 450 cm long reaction tube. Otherwise, proceed as described in Example 8. The results of the test run are shown in Table 1.

Example 10: Catalytic performance data in the oxidation of o-xylene to phthalic anhydride (comparative example 2)

130 cm of catalyst C, 60 cm of catalyst B and 100 cm of catalyst A are filled in succession into a 450 cm long reaction tube. Otherwise, proceed as described in Example 8. The results of the test run are shown in Table 1.

Example 11: Catalytic performance data in the oxidation of o-xylene to phthalic anhydride (Example 2 according to the invention)

90 cm of catalyst G, 60 cm of catalyst E and 140 cm of catalyst D are filled in succession into a 450 cm long reaction tube. Otherwise, proceed as described in Example 8. The results of the test run are shown in Table 1. Table 1

As can be seen from Table 1, the catalysts according to the invention according to Examples 9 and 11 show the highest PSA yield and the highest PSA quality. The hot spot is advantageously positioned in the first catalytic converter position. Example 9 according to the invention, in which the BET surface area increases from the first to the third catalyst zone (here: in the third catalyst zone is higher than in the first and second catalyst zone), is even better in terms of PSA quality than Example 11 according to the invention , in which the BET surface area does not increase from the first to the third catalyst zone.

Claims

Catalyst for the production of phthalic anhydride by gas phase oxidation of o-xylene and / or naphthalene, comprising a first catalyst layer located closer to the gas inlet side, a second catalyst layer closer to the gas outlet side and a third catalyst layer even closer to or on the gas outlet side, wherein the catalyst layers are composed differently and each have an active composition containing Ti0 ₂ , and wherein the active composition content decreases from the first catalyst layer to the third catalyst layer, with the proviso that

a) the first catalyst zone has an active mass content of between approximately 7 and 12% by weight,

b) the second catalyst layer has an active mass content in the range between 6 and 11% by weight, the active mass content of the second catalyst layer being less than or equal to the active mass content of the first catalyst layer, and

c) the third catalyst layer has an active mass content in the range between 5 and 10% by weight, the active mass content of the third catalyst layer being less than or equal to the active mass content of the second catalyst layer.

2. Catalyst according to claim 1, characterized in that the first catalyst zone has an active mass content between about 8 and 11 wt .-%.

3. Catalyst according to one of the preceding claims, characterized in that the second catalyst zone has an active composition content between about 7 and 10 wt .-%.

4. Catalyst according to one of the preceding claims, characterized in that the third catalyst zone has an active mass content between about 6 and 9 wt .-%.

5. Catalyst according to one of the preceding claims, characterized in that the catalyst activity of the catalyst layer towards the gas inlet side is lower than the catalyst activity of the catalyst layer towards the gas outlet side.

6. Catalyst according to one of the preceding claims, characterized in that the BET surface area of the first catalyst zone is less than the BET surface area of the third catalyst zone.

7. Catalyst according to one of the preceding claims, characterized in that the BET surface area of the first and the second catalyst zone are the same, whereas the BET surface area of the third catalyst zone is larger.

8. Catalyst according to one of the preceding claims, characterized in that the BET surface area of the first and second catalyst zone in each case between about 15 and 25 m ² / g, and the BET surface area of the third catalyst zone is between about 25 and 45 m ² / g.

9. Catalyst according to one of the preceding claims, characterized in that the first catalyst layer located towards the gas inlet side has a length fraction, based on the total length of the catalyst bed, of at least 40%, in particular at least 45%, particularly preferably at least 50%.

10. Catalyst according to one of the preceding claims, characterized in that the proportion of the first catalyst layer in the total length of the catalyst bed is between 40 and 70%, in particular between 40 and 55%, particularly preferably between 40 and 52%.

11. Catalyst according to one of the preceding claims, characterized in that the proportion of the second catalyst layer in the total length of the catalyst bed is between approximately 10 and 40%, in particular between approximately 10 and 30%.

12. Catalyst according to one of the preceding claims, characterized in that the ratio of the length of the third catalyst zone to the length of the second catalyst zone is between approximately 1 and 2, in particular between 1.2 and 1.7, particularly preferably between 1.3 and 1, 6, lies.

13. Catalyst according to one of the preceding claims, characterized in that at least about 40%, in particular at least about 50%, particularly preferably at least 60% of the total pore volume of the Ti0 _{2 used} by Po- with a radius between 60 and 400 nm.

14. Catalyst according to one of the preceding claims, characterized in that up to 75%, in particular up to 70% of the total pore volume of the Ti0 _{2 used are formed} by pores with a radius between 60 and 400 nm.

15. Catalyst according to one of the preceding claims, characterized in that the catalytically active composition is applied in a fluidized or fluidized bed.

16. Catalyst according to one of the preceding claims, characterized in that less than about 30%, in particular less than 22% of the total pore volume of the Ti0 _{2 used are formed} by pores with a radius of more than 400 nm.

17. Catalyst according to one of the preceding claims, characterized in that about 17 to 27% of the total pore volume of the Ti0 _{2 used are formed} by pores with a radius of more than 400 nm.

18. Catalyst according to one of the preceding claims, characterized in that about 50 to 75%, in particular about 50 to 70%, particularly preferably 50 to 65% of the total pore volume of the Ti0 _{2 used is formed} by pores with a radius of 60 to 400 nm become.

19. Catalyst according to one of the preceding claims, characterized in that less than 30%, in particular less than 20% of the total pore volume of the Ti0 _{2 used are formed} by pores with a radius of 3.7 to 60 nm.

20. Catalyst according to one of the preceding claims, characterized in that about 10 to 30% of the total pore volume of the Ti0 _{2 used are formed} by pores with a radius of 3.7 to 60 nm.

21. Catalyst according to one of the preceding claims, characterized in that the D ₉₀ value of the Ti0 _{2 used is} between approximately 0.5 and 20 μm, in particular between approximately 1 and 10 μm, particularly preferably between approximately 2 and 5 μm.

22. Catalyst according to one of the preceding claims, characterized in that less than 10%, in particular less than 5% of the total pore volume of the Ti0 ₂ used are present through micropores with a pore radius of less than 3.7 nm.

23. Catalyst according to one of the preceding claims, characterized in that 8% by weight or more of the catalytically active composition, in particular between approximately 8 and 15% by weight of vanadium, calculated as vanadium pentoxide, is present.

24. Catalyst according to one of the preceding claims, characterized in that at least 0.05% by weight of the catalytically active composition is formed from at least one alkali metal, calculated as the alkali metal (s).

25. Catalyst according to one of the preceding claims, characterized in that an organic polymer or copolymer, in particular a vinyl acetate copolymer, is used as the adhesive for the catalytically active composition.

26. Catalyst according to one of the preceding claims, characterized in that the catalyst is calcined or at least 24 hours at> 390 ° C, preferably between 24 and 72 hours at> 400 ° C, in a gas containing 0 ₂ , in particular in air is conditioned.

27. Catalyst according to one of the preceding claims, characterized in that niobium is present in an amount of 0.1 to 2% by weight, in particular 0.5 to 1% by weight, of the catalytically active composition.

28. Catalyst according to one of the preceding claims, characterized in that only one Ti0 ₂ source is used, the total Ti0 ₂ used having the BET surface area or pore radius distribution defined in one or more of the preceding claims.

29. Catalyst according to one of the preceding claims, characterized in that no phosphorus is contained in the active mass.

30. A process for the preparation of phthalic anhydride by gas phase oxidation of o-xylene and / or naphthalene, a three- or multi-layer catalyst according to one or more of the preceding claims being used.

1. Use of a catalyst according to one of the preceding claims for the production of phthalic anhydride by gas phase oxidation of o-xylene and / or naphthalene.