EP2321045A2

EP2321045A2 - Catalyst for the catalytic gas phase oxidation of aromatic hydrocarbons to form aldehydes, carboxylic acids and/or carboxylic acid anhydrides, in particular phthalic acid anhydride, and method for producing said type of catalyst

Info

Publication number: EP2321045A2
Application number: EP09777410A
Authority: EP
Inventors: Josef Breimair
Original assignee: Breimair Josef
Current assignee: Stesatec GmbH
Priority date: 2008-08-29
Filing date: 2009-07-24
Publication date: 2011-05-18
Also published as: CN102196859A; CN102196859B; TWI518079B; BRPI0913160A2; BRPI0913160B1; TW201012805A; WO2010022830A3; WO2010022830A2; KR101706790B1; KR20110050694A; DE102008044890A1; DE102008044890B4

Abstract

The invention relates to a catalyst for catalytic gas phase oxidation of aromatic hydrocarbons to form aldehydes, carboxylic acids and/or carboxylic acid hydrides, in particular phthalic acid anhydride. The active mass comprises vanadium oxide, preferably vanadium pentoxide, titanium dioxide, preferably in the anatas-modification, and at least one silver mixing element oxide with defined elements, preferably vanadium and/or molybdenum and/or tungsten and/or niobium and/or antimony, and/or a vanadium mixing element oxide with defined elements, preferably bismuth and/or molybdenum and/or tungsten and/or antimony and/or niobium. When producing the catalyst, in particular during the production of a catalyst suspension or a powder mixture necessary for coating a carrier, at least one silver and/or vanadium mixing element oxide and/or at least one precursor compound, in particular at least one multi-core precursor compound, of at least one silver and/or vanadium mixing element oxide is used as a raw material source.

Description

description

Catalyst for the catalytic gas-phase oxidation of aromatic

Hydrocarbons to aldehydes, carboxylic acids and / or

Carboxylic anhydrides, especially to phthalic anhydride, and

Process for the preparation of such a catalyst

The catalytic gas phase oxidation of aromatic hydrocarbons such as benzene, xylene, naphthalene, toluene or durene in fixed-bed reactors, preferably tube-bundle reactors, has long been known and described many times in the literature. For example, benzoic acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid and pyromellitic anhydride are prepared in this way.

For this purpose, in general, a mixture of a molecular oxygen-containing gas, for example air, and the hydrocarbon to be oxidized, for example o-xylene or naphthalene, passed through a plurality of arranged in a reactor tubes in which a bed of at least one catalyst is located ,

To control the temperature or to dissipate the heat generated during the exothermic reaction, the tubes filled with catalyst are surrounded by a heat transfer medium, for example a molten salt.

Despite such a temperature control, localized maximum temperatures ("hot spots") can occur in the catalyst bed, which can lead to undesirable effects, such as the total oxidation of the starting material or the formation of by-products which are difficult to separate, up to a limited throughput of starting material.

In order to avoid such hot spots one has gone over in practice, catalysts with different activity and chemical composition layer by layer in the reaction tubes to arrange in layers, which according to the prior art usually the catalyst has the lowest activity in the region of the largest temperature maximum and the catalyst layers following in the direction of gas exit have an increased activity.

In this case, so-called coated catalysts have proven useful, which generally consist of an inert, non-porous carrier material, on which at least one thin layer of the catalytically active material is applied in the form of a dish.

For the catalytic properties of the catalysts in question, the composition of the catalytically active material plays a crucial role.

For the production of phthalic anhydride from o-xylene and / or naphthalene by oxidation in the gas phase with molecular oxygen-containing gases on a fixed bed catalyst, a large number of catalysts have been proposed in the past.

According to the prior art, virtually all industrial phthalic anhydride catalysts contain in their catalytically active composition the compounds titanium dioxide in the anatase modification and vanadium pentoxide and other components or promoters in mostly small amounts to improve the activity, the conversion, the yield, the selectivity and the long-term stability of the catalysts in question.

Such additives are, for example, cesium, antimony, phosphorus, boron, molybdenum, tungsten, tin, bismuth, silver, niobium, iron, potassium, rubidium, chromium and calcium.

There is therefore an attempt by a targeted doping with different substances to further increase the performance and stability of the PSA catalysts. This means that, over time, more and more complicated catalyst formulations and combinations of different catalysts are being developed to solve these problems.

Increasingly, so-called "multilayer" catalysts are used, which differ in activity and selectivity due to their different composition of active material Catalyst bed several, different catalysts sequentially arranged in layers to perform different tasks depending on the location in the catalyst bed. This is essentially the requirement to control the exothermic reaction at high throughputs of starting material, while high selectivity and stability of the catalyst, safely.

EP A 21 325 describes catalysts for the preparation of phthalic anhydride whose active material comprises 60 to 99% by weight of titanium dioxide, 1 to 40% by weight of vanadium pentoxide and, based on the total amount of TiO ₂ and V ₂ O ₅ up to 2% by weight Phosphorus and up to 1, 5 weight% rubidium and / or cesium, wherein the catalytically active material is applied in two layers on the support. The inner layer contains 0 to 2.0% by weight of phosphorus and no rubidium and / or cesium, and the outer layer contains 0 to 0.20% by weight of phosphorus and 0.02 to 1.5% by weight of rubidium and / or cesium , The catalytically active composition of these catalysts may contain, in addition to the constituents mentioned, further substances, for example up to 10% by weight of an oxide of the metals molybdenum, tungsten, niobium, tin, silicon, antimony, hafnium. As inert carrier material steatite is used.

EP A 286448 describes a process for the preparation of phthalic anhydride, in which two different catalysts are used with similar content of titanium dioxide and vanadium pentoxide. They differ essentially in that one catalyst additionally contains 2 to 5% by weight of a cesium compound, in particular cesium sulfate, but no phosphorus, tin, antimony, bismuth, tungsten or molybdenum compounds, and the second catalyst additionally contains 0, 1 to 3.0% by weight of a phosphorus, tin, antimony, bismuth, tungsten or molybdenum compound.

US 4,864,036 relates to a catalyst for the production of phthalic anhydride, which is prepared in several steps. Here, in the first step, a

Compound of a metal of the 6th subgroup, preferably a molybdenum or

Tungsten compound on titanium dioxide in the anatase modification and then calcined. Thereafter, in a second step, the calcined

Added a vanadium compound precursor and this precursor calcined again. GB 1140264 relates to an oxidation catalyst for aromatic and non-aromatic hydrocarbons to carboxylic acids, which consists of an inert, nonporous support and a 0.02 to 2 mm thick layer of active material, which in turn from 1 to 15% V ₂ O ₅ and 85 to 99 % Titanium dioxide, wherein the vanadium content of the total catalyst is in the range of 0.05 to 3%. It describes a catalyst in which the active material in addition to titanium dioxide and vanadium pentoxide additionally contains 0.1 to 3% by weight of at least one metal oxide from the group of silver, iron, cobalt, nickel, chromium, molybdenum or tungsten.

EP 0 447 267 describes a catalyst for the preparation of phthalic anhydride which comprises as catalytically active composition: (A) 1 to 20% by weight of V ₂ O ₅ and 99 to 80% by weight of a titanium dioxide in the anatase modification with a BET Surface of 10 to 60nτ7g and (B), based on 100 parts by weight of this mixture (A), 0.05 to 1, 2 parts by weight of at least one element from the group K, Cs, Rb and Tl as oxide and 0.05 to 2 parts by weight Silver, calculated as silver oxide.

EP 0522 871 B1 relates to a catalyst which, in addition to titanium dioxide and vanadium pentoxide, also contains 0.01 to 1% by weight of niobium as niobium pentoxide, 0.05 to 2% by weight of at least one element selected from potassium, cesium, rubidium or thallium as oxide, 0.2 to 1.2% by weight of phosphorus as P2O5, and 0.55 to 5.5% by weight of antimony oxide and 0.05 to 2% by weight of silver as Ag2O, using a pentavalent antimony compound as the source of the antimony becomes.

CN1108996 relates to a catalyst with two layers based on titanium dioxide / 2O5 which additionally contains at least one rare earth compound and at least one oxide of the elements antimony, phosphorus, zinc and silver, wherein the layer closer to the gas inlet additionally contains at least one alkali metal compound

Silver-vanadium oxide compounds with an atomic ratio Ag: V <1 are known as silver bronzes. The use of silver vanadium bronzes as the oxidation catalyst is well known in the literature.

DE 198 51 786 A1 describes a multimetal oxide of the general formula Ag ₃ . _b M _b V ₂ O _x ^* c H ₂ O, where a has a value of 0.3 to 1, 9, M selects a metal from the group Li, Na, K, Rb ₁ Cs Tl, Mg, Ca, Sr, Ba, Cu, Zn, Cd, Pb, Cr, Au, Al, Fe, Co, Ni and / or Mo and b is a value from 0 to 0.5, with equal to or greater than 0.1. The use of the relevant multimetal oxides as precursor compounds for the preparation of precatalysts and catalysts for the gas phase oxidation of aromatic hydrocarbons is described.

Finally, WO 2005/092496 A1 describes a catalyst for the preparation of aldehydes, carboxylic acids and / or carboxylic anhydrides whose active composition comprises a phase A and a phase B in the form of three-dimensionally extended delimited regions, the phase A being a silver vanadium oxide bronze and Phase B is a mixed element oxide phase based on titania and vanadium pentoxide. The molar ratio of Ag: V in phase A is 0.15 to 0.95.

The above-described, known in the prior art catalysts with different composition of the active material either reach unsatisfactory selectivities, yields or activities or have too short a lifetime or their industrial production is associated with a huge effort or cost.

There is therefore a continuing need for catalysts with further improved selectivity and yield combined with high raw material throughput and long service life, which can be produced industrially in an acceptable cost-benefit ratio.

The present invention is therefore based on the object to develop an improved catalyst for the gas phase oxidation of aromatic hydrocarbons to aldehydes, carboxylic acids and / or carboxylic anhydrides, in particular to phthalic anhydride, which results in high raw material throughput improved selectivity and long service life. Next, the technical and economic costs for the large-scale production of the catalyst should be kept as low as possible.

This object is achieved with the features of claim 1. Preferred embodiments are the subject of the dependent claims, the disclosure content of which is expressly included in this description. According to claim 1, a catalyst for the catalytic gas phase oxidation of aromatic hydrocarbons to aldehydes, carboxylic acids and / or carboxylic anhydrides, in particular to phthalic anhydride, claimed in which the active composition vanadium oxide, preferably vanadium pentoxide, titanium dioxide, preferably in the anatase modification, and at least one Mixed element oxide of silver with defined elements, preferably vanadium and / or molybdenum and / or tungsten and / or niobium and / or antimony, and / or a mixed element oxide of vanadium with defined elements, preferably bismuth and / or molybdenum and / or tungsten and / or Antimony and / or niobium. In the preparation of the catalyst, in particular in the preparation of a catalyst suspension or a powder mixture required for the coating of a carrier, at least one mixed element oxide of silver and / or vanadium and / or at least one precursor compound, in particular at least one polynuclear precursor compound, at least one Mischelementoxides of Silver and / or vanadium used as a source of raw materials.

It has surprisingly been found that the use of mixed element oxides, preferably of mixed metal oxides, of silver with, for example, vanadium, molybdenum, tungsten, niobium and / or antimony, and / or the use of mixed element oxides, preferably of mixed metal oxides, of vanadium with, for example, bismuth, Molybdenum, tungsten, niobium and / or antimony, or their precursor compounds as a raw material source in the preparation of the catalyst suspension or in the preparation of a powder mixture used for the coating process and / or as part of the active material of the catalysts in addition to the components titanium dioxide and vanadium oxide, a significant increase in the selectivity pulls.

The reason for this is not clear, but it seems likely that the interaction of the silver with the other catalytically active components such as the titanium dioxide / anadium oxide monolayer is much more effective and therefore the actual promoter action of the silver (the suppression of total oxidation of the organic Raw material to carbon oxides) comes to fruition.

In the art, the use of silver as a constituent of the active material has been described many times. Here were used as raw material source of silver for the production the catalyst suspension used in addition to silver oxide and corresponding salts such as silver nitrate, silver sulfate, silver halides, silver sulfide, silver phosphate, silver salts of organic acids, silver hydroxide, ammonium salts of silver and amine complexes of silver. Most of these sources are mononuclear converted into silver oxide upon heating of the catalyst in the reactor and are thus present in the active mass as silver oxide, while, for example, silver phosphates and silver halides are present in the active mass unchanged and are not converted to silver oxide during the thermal treatment.

An essential aspect of the catalysts according to the invention is that conventional catalysts which contain at least titanium dioxide and vanadium oxide in the active composition contain as additional dopants mixed element oxides of silver with vanadium and / or other defined elements and / or mixed element oxides of vanadium with other defined elements at least one mixed element oxide of silver and / or vanadium and / or a corresponding precursor compound is added to at least one of these mixing element compounds in the preparation of the catalyst suspension or in the preparation of a powder mixture used for the coating of the carrier.

The invention also expressly also relates to a process for the preparation of the catalysts according to the invention just described, comprising preparing a catalyst suspension or a mixture of the various components containing at least titanium dioxide in the anatase modification and a vanadium compound and at least one mixed element oxide of the silver and / or Vanadiums with defined elements or a corresponding precursor compound contains at least one of these mixed element oxides as a raw material source.

All components are advantageously mixed together in an aqueous medium and then applied by a spray process (preferably fluidized bed or drum method) on a ceramic support. The Mischelementoxidphase of silver and / or vanadium or their Mischelementoxid precursor compounds are advantageously added directly to the catalyst suspension with the main constituents of titanium dioxide and vanadium oxide and other promoters and are generally not spatially δ separate phases to a phase consisting of titanium dioxide and vanadium oxide before. Thus, all constituents of the catalyst suspension form a uniform phase which, in addition to the components titanium dioxide and vanadium oxide, also contains the relevant mixed element oxides and optionally further components.

However, systems are also conceivable in which successively different layers of different chemical composition are applied to the inert support and wherein at least one layer contains at least one mixed element oxide of silver and / or vanadium with defined elements. In this case, the individual coating layers of a catalyst according to the invention may also consist of a combination of compositions according to the invention and not of the invention.

Likewise, the respective mixed element oxides may also be used alone or in combination with other compounds in one or more coating layers which do not contain titanium dioxide and / or vanadium oxide in the active composition.

According to the invention, catalysts or precursors for the production and preparation of catalysts for the gas phase partial oxidation of aromatic hydrocarbons can thus be realized with a gas containing molar oxygen, which are composed of an inert, non-porous support material and one or more layers (s) applied thereon, wherein at least one of these layers contains 0.01 to 15% by weight, based on the total weight of these layers, of one or more of the above-mentioned mixed element oxides or their precursor compounds.

In addition, a concrete process procedure for the production of carboxylic acids and / or carboxylic anhydrides by the partial oxidation of aromatic hydrocarbons in the gas phase with a molecular oxygen-containing gas at elevated temperature on a catalyst whose active mass is applied shell-shaped on an inert carrier claimed that characterized in that a shell catalyst whose catalytically active composition, based on their total weight, 0.01 to 15% by weight of a Mischelementoxids of silver with vanadium and / or a Mischelementoxids of silver with other defined elements and / or 0.01 to 10% by weight of a mixed element oxide of vanadium with bismuth and / or a Mixed element oxide of vanadium with other defined elements and simultaneously titanium dioxide in the anatase modification and a vanadium compound (preferably V2O5), wherein the mixed element oxide compound (s) or their precursor compound (s) already for the preparation of the catalyst suspension and / or the powder mixture, from which the active composition is formed after coating the support by thermal treatment is or will be used.

Here, at least one non-inventive coated catalyst, the vanadium oxide in its active material as essential constituents, in particular

Vanadium pentoxide, and titanium dioxide, especially in the anatase modification, but none of the below-mentioned mixed element oxides or their

Contains precursor compounds in the oxidation of aromatic

Hydrocarbons to carboxylic acids and / or carboxylic anhydrides or absent and be used in a combined bed (that is, in a single or multi-layered mixture) together with one or more of the inventive catalysts described above.

For this purpose, the gaseous stream is preferably passed over a bed of at least two layers of catalysts, wherein the catalyst located closer to the gas inlet contains a catalyst according to the invention and the bed of the downstream catalyst contains at least one catalyst whose catalytically active material comprises vanadium oxide and a titanium dioxide in the Anatase modification contains, but no mixed element oxide of the silver with elements such as vanadium, molybdenum, tungsten, niobium, antimony and / or no mixed element oxide of vanadium with elements such as bismuth, molybdenum, tungsten, niobium, antimony.

However, catalyst beds consisting of at least two layers may also be used, all catalyst layers containing catalysts according to the invention. In this case, the catalysts used according to the invention can differ by the type and amount of the respective mixed element oxides in the active composition,

Preferably, at least one part, particularly preferably all catalyst layers used in the catalyst bed, including the catalysts according to the invention having a catalytically active composition comprising 1 to 40% by weight of vanadium oxide (calculated as V ₂ O ₅ ), 50 to 99% by weight of titanium dioxide (calculated as TiO ₂ ), up to 1% by weight of an alkali metal compound (preferably a cesium compound, calculated as alkali metal), up to 1.5% by weight of a phosphorus compound (calculated as P) and up to 10% by weight of an antimony compound (calculated as Sb ₂ O ₃ ).

According to a particularly advantageous embodiment, the catalysts according to the invention preferably contain 0.01 to 15% by weight of at least one mixed element oxide of silver with at least one element from the group vanadium, niobium, tantalum, titanium, zirconium, chromium, molybdenum, tungsten, cerium, lanthanum, Aluminum, boron, manganese, iron, cobalt, nickel, copper, zinc, gold, cadmium, tin, lead, bismuth, antimony, arsenic, hafnium, rhenium, ruthenium, rhodium and palladium, and / or preferably 0.01 to 10 weight % of at least one mixed element oxide of vanadium with at least one of bismuth, antimony, niobium, tantalum, titanium, zirconium, chromium, molybdenum, tungsten, cerium, lanthanum, aluminum, boron, manganese, iron, cobalt, nickel, copper, Zinc, gold, cadmium, tin, lead, arsenic, hafnium, rhenium, ruthenium, rhodium and palladium.

The content of mixed element oxides of silver with defined elements, in particular with, for example, vanadium and / or tungsten and / or molybdenum and / or niobium and / or antimony, in the active mass of catalysts in a preferred embodiment is in a range of 0.01 to 15% by weight, in a further preferred embodiment in a range of 0.01 to 10% by weight and in a particularly preferred embodiment in a range of 0.01 to 5% by weight. The content of mixed element oxides of vanadium with defined elements (except silver, see previous details regarding a mixed element oxide of silver with vanadium), in particular with, for example, tungsten and / or molybdenum and / or niobium and / or antimony, is in the active mass of catalysts in a preferred embodiment in a range of 0.01 to 10% by weight and in a particularly preferred embodiment in a range of 0.01 to 5% by weight.

In a preferred embodiment, a catalyst according to the invention is used in a first catalyst layer located closest to the gas inlet, which is also the location with the highest hot spot. In the direction of gas outlet at least one further catalyst layer is connected, which generally has a higher activity than the first catalyst layer and which is generally a catalyst according to the prior art. The catalyst according to the invention in this case contains at least one mixed element oxide of silver, preferably silver vanadate, and preferably a mixed element oxide of vanadium, preferably bismuth vanadate.

It has also proved to be advantageous if in a multilayer catalyst system with at least one of the hot spot catalyst layer in the direction

Gas inlet upstream layer, at least one of the catalyst layers of

Gas inlet up to and including the location with the highest hot spot containing a catalyst according to the invention and for subsequent layers conventional, prior art catalysts are used and / or catalysts of the invention are used with a reduced content of the claimed mixed element oxides in the active material.

In another particularly preferred embodiment, at least one of the catalyst layers located in front of the highest hotspot layer contains a mixed element oxide of silver, preferably a mixed element oxide of silver with molybdenum and / or tungsten, and more preferably a mixed element oxide of silver with vanadium the layer with the highest hot spot and the layers downstream therefrom do not contain mixed element oxide of the silver. The layer with the highest hot spot advantageously contains a mixed element oxide of the vanadium with bismuth. The catalyst layers following in the direction of the gas outlet of the hot spot catalyst layer preferably correspond to the prior art and generally do not contain catalysts according to the invention.

In a particularly preferred embodiment of the catalyst, the compounds AgVOß and / or Ag ₂ MoO ₄ and / or Ag ₂ WO ₄ and / or BiVO _{4 are used} in the preparation of the catalyst suspension and / or are contained in the active material of the catalysts.

It is important to choose the content of the mixed element oxides acting as "promoters" neither too small nor too large

Mischelementoxiden of silver too small, comes the selectivity-enhancing effect not fully bear, while too much content of Mischelementoxiden of silver increased activity is observed, which leads to a reduced selectivity due to increased total oxidation to CO and CO ₂ .

Furthermore, it is advantageous to use the catalysts according to the invention in particular in the catalyst layers located closer to the gas inlet up to and including the position with the highest hot spot, since otherwise the full selectivity-increasing effect can no longer be achieved since a substantial part of the raw material has already been converted.

Too high a content of mixed element oxides of bismuth also has a negative effect on the selectivity of the catalyst and at the same time it can lead to an increased formation of by-products which cause a poorer color stability of the desired product phthalic anhydride. On the other hand, too low a proportion of mixed element oxides of bismuth leads to no significant increase in the selectivity.

By combining at least two, but particularly advantageous, of several catalyst layers in one bed, of which at least one catalyst layer contains a catalyst according to the invention, a significantly higher overall yield can be achieved than with the sole use of multilayer catalyst systems with catalysts not according to the invention is.

In this case, according to the state of the art, in many cases the catalyst activity gradually increases from the first catalyst layer used at the gas inlet to the last layer closest to the Gaustritt. The activity adjustment can be carried out by various methods familiar to the person skilled in the art. For example, an increase in the catalyst activity in the layers from the gas inlet to the gas outlet by a gradual reduction of the alkali metal content in the active mass, an increase in the average BET surface area of the titanium dioxide used or an increase in the active material content of the total weight of the catalyst. A combination of different activity-setting measures can also be used. The catalysts according to the invention advantageously comprise in the active composition at least one kind of titanium dioxide in the anatase modification, at least one compound of vanadium (preferably V2O5), at least one mixed element oxide of silver and / or vanadium and optionally a compound of the antimony, a compound of an alkali element and / or a phosphorus compound.

The total content of titanium dioxide is 50 to 99% by weight in the active composition of the catalysts according to the invention and particularly preferably 80 to 99% by weight.

In this case, only one kind of titanium dioxide in the anatase modification with defined physical properties or else a mixture of several titanium dioxides with different physical properties can be used to prepare the catalyst suspension and / or the active material of the catalysts.

The average BET surface area of the titanium dioxide of the catalysts according to the invention in the case of one or more titanium dioxide grades is advantageously 10-60 m ² / g and particularly advantageously 12-30 m ² / g, while the BET surface area of the individual grades is in the range of 3 to 300 m ² / g.

The average BET surface area of the titanium dioxide used is calculated from the amount and BET surface area of the individual types used. At least one type of titanium dioxide whose mean particle size is in the range from 0.3 to 0.8 μm is preferably used.

The content of vanadium oxide in the active composition (calculated as V2O5) is in a preferred range of 1 to 40% by weight and in a particularly preferred embodiment in a range of 1 to 20% by weight.

For the preparation of the catalysts according to the invention, the raw material sources vanadium pentoxide and / or vanadium oxalate are advantageously used. In principle, however, other vanadium compounds are also suitable, such as, for example, ammonium metavanadate, polyvanadic acid, inter alia, or a mixture of various sources. As a rule, these precursor compounds or raw material sources of vanadium are converted into vanadium pentoxide in the thermal treatment of the catalyst or during heating of the catalyst in the reactor in the presence of molecular oxygen, so that the vanadium is present essentially in the pentavalent oxidation state in the active composition.

Depending on the position of the particular catalyst according to the invention in the catalyst bed, the active materials of these catalysts, in addition to titanium dioxide, vanadium oxide, one or more mixed element oxides of silver and / or vanadium and additionally one or more elements from the group of alkali metals.

These are usually added as salts (for example, sulfates, carbonates, nitrates, phosphates) of the catalyst suspension and are converted in the heating of the catalyst to the corresponding oxides or are in the active material (after the thermal treatment of the catalyst) before unchanged ,

Alkali metal compounds are used to control activity while improving the selectivity of the catalysts.

In a preferred embodiment, the alkali metal content in the active composition is in a range of 0 to 1.0% by weight, and more preferably in a range of 0 to 0.6% by weight. Particularly advantageously, a soluble cesium compound such as cesium sulfate is used to prepare the catalyst suspension.

The catalysts of the invention advantageously contain, in particular in the active mass of the hot spot catalyst layer, also an antimony compound as part of the active material for improving the thermal stability. The content of antimony in the active composition is advantageously in a range of 0 to 10% by weight (calculated as Sb 2 O 3), and more preferably in a range of 0 to 5% by weight, depending on the position of the catalyst in the entire catalyst bed and depending on the thermal load of the respective catalyst in the respective position. As starting materials for the preparation of the catalyst suspension or of a powder mixture of the catalysts according to the invention required for coating the support, it is possible to use various antimony compounds, for example antimony salts or antimony oxides, in various oxidation states.

In a preferred embodiment of the catalyst according to the invention, antimony III oxide is used in the preparation of the catalyst suspension.

Likewise, the catalysts according to the invention may contain a phosphorus compound in the catalytically active composition or it may be added a phosphorus compound as a raw material source in the preparation of the catalyst suspension or a powder mixture used for the coating of the carrier. In a particularly advantageous embodiment of the catalysts according to the invention, the phosphorus content of the active composition is in a range from 0 to 1.5% by weight (calculated as P).

Particularly advantageous increases in catalyst systems with multiple layers with one or more inventive and / or one or more non-inventive catalysts in a bed of phosphorus content from the gas inlet to the gas outlet. The raw material source for the catalysts according to the invention is preferably ammonium dihydrogen phosphate.

Furthermore, a large number of further compounds which reduce or increase the activity as promoters and / or have an influence on the selectivity of the catalyst can be present in small amounts in the active compositions of the catalysts according to the invention.

It has been described in the literature that to control the activity or to mitigate or avoid so-called "hot spots" (hot spots) in the art, it has been necessary to use multilayer catalysts which, in layers, in particular with a plurality of superimposed catalyst layers, in the catalyst bed, are arranged, wherein in the prior art usually the least active catalyst is closest to the gas inlet and the activity increases from layer to layer in the direction of gas outlet. The catalysts of the individual layers have different chemical compositions, which in turn cause different activities and selectivities.

For the invention, it is sufficient if, in the case of a multilayer catalyst system, at least one layer contains a catalyst according to the invention which contains at least one of the relevant mixed element oxides.

In particular, the first layer, which is closest to the gas inlet and which is also the location with the highest hot spot, preferably contains a catalyst according to the invention. In particular, it is advantageous if all the layers in the

Catalyst bed, starting from the gas inlet up to and including the location with the highest hot spot catalysts according to the invention. The salary and the

The nature of the mixed element oxides of, for example, silver can vary in the various layers concerned. It is advantageous, also the other compositions of the active material according to their position in the

Adjust catalyst bed.

In a preferred embodiment, in particular the layer with the highest local temperature maximum contains a mixed element oxide of the silver and / or a mixed element oxide of the bismuth with vanadium.

In particular, the use of a combination of the mixed element oxides of AgVO3 and BiVO4 in the position with the highest hot spot have proven to be selective in the catalysts of the invention.

It has surprisingly been found that it is particularly advantageous if at least one of the active masses of the catalyst layers, which are located upstream in the direction of gas inlet before the location with the highest hot spot, reduced compared to the situation with the highest hot spot content of antimony contained in the active mass.

In a further advantageous embodiment of a catalyst with several

Layers in one or more beds, contains at least one catalyst layer which is located upstream of the hot spot catalyst layer, at least one Mixed element oxide of the silver with the specified elements, particularly advantageously with vanadium and / or molybdenum and / or tungsten.

In a particular embodiment of the catalysts according to the invention, at least one of the layers from the gas inlet to the layer with the highest hot spot contains a mixed element oxide of the silver, in particular a mixed element oxide of silver with vanadium and / or molybdenum and / or tungsten, while the layer with the highest hot Spot preferably contains a mixed element oxide of vanadium, in particular a mixed element oxide of vanadium with bismuth.

In a further particularly preferred embodiment, all layers from the gas inlet to the layer with the highest hot spot contain a mixed element oxide of silver and only the layer with the highest hot spot contains an additional mixed element oxide of vanadium with bismuth.

Particularly advantageous is the use of polynuclear mixed element oxides or their precursor compounds as a source in the preparation of the catalyst suspension or a powder mixture used for the coating of the support material.

In addition, mixed element oxides of silver can also be used to prepare the catalyst suspension and / or the active material which have a smaller or greater atomic ratio to the silver than is present in the case of AgVO 3. Depending on the atomic ratio of the elements in the respective mixed element oxide, the amount of mixed element oxide and / or precursor compounds in the catalyst suspension or powder coating mixture must be adjusted to provide an optimum level of silver in the active mass of the finished catalyst to obtain.

It is advantageous if the described Mischelementoxidphase or its precursor compound is already formed before it is added to the catalyst suspension or the powder mixture used for the coating of the carrier. However, it is also possible to add one or more corresponding precursor compounds to the catalyst suspension or to the powder mixture, which are then converted to the corresponding mixed-element oxides during the thermal treatment of the catalyst. As already described above, mixed element oxides of silver present with other elements and / or their precursor compounds can be used not only in the integer molar ratio as raw material source in the production of the catalyst suspension or in the active composition of the inventive catalysts, but also two- or polynuclear mixed element oxides of Silver with a large atomic deficit or excess silver. Depending on the general formula of the mixed element oxides or their silver constituent, the content of the relevant mixed element oxide in the catalyst suspension and / or the active composition must then be increased or decreased.

The two or more nuclear mixed element oxides of silver are represented by the general formula

Ag _x M _y N _z O _n (Formula I)

described according to claim 11:

In the mixed metal oxide of the formula I, x more preferably has a value of 0.1 to 5, the value of the variable y is preferably 0 to 0.3.

Particularly preferred are mixed metal oxides of the following general formula:

Ag _x N ₂ O _n

wherein

Ag = silver x = a value of 0.1 to 5

N = an element of the group vanadium, molybdenum, tungsten, niobium, antimony z = 1 n = a number which is determined by the valence and frequency of the elements other than oxygen in the formula I,

It is possible in principle and expressly included in the invention that one or more of them are also used in the preparation of the catalyst suspension

Precursor compounds of the respective mixed element oxides and / or their Starting compounds are used and the catalysts of the invention with the relevant Mischelementoxiden be formed only in the reactor by calcination at elevated temperature or during the heating of the catalyst in the reactor.

In a preferred embodiment of the catalyst, in particular the use of the mixed element oxides AgVO3, Ag2MoO4, Ag2WO4 and / or mixed element oxides of these elements with other atomic ratios leads to an improvement of the catalysts

It has now been found that the addition of mixed element oxides of silver, preferably with, for example, vanadium, tungsten and molybdenum, to the catalyst suspension instead of "mononuclear" silver compounds results in a considerable improvement in the selectivity compared to catalysts which do not have silver in the active material and / or in which silver as the oxide (AgO or Ag2O) or as a salt (nitrate, phosphate, sulfate, chloride, ammonium salt, salt of an organic acid) or as a hydroxide or as an amine complex of the catalyst suspension is added or in It is believed that silver in the form of a mixed element oxide or compound element compound may participate more intensely in the catalytic process than in the form of a salt or a mononuclear oxide.

By way of example, but not limitation, mention should be made at this point of the compound AgVO3 as a constituent of the catalysts according to the invention, which is used as an additive in the preparation of the catalyst suspension or the active composition, wherein the active composition at least still titanium dioxide in the anatase modification and a vanadium compound contains. The catalyst according to the invention preferably also comprises at least one compound of an element of the first main group. Depending on the position of the catalyst according to the invention in the catalyst bed, the catalyst according to the invention also contains an antimony compound, in particular Sb 2 O 3 in the active composition and optionally a phosphorus compound

It has surprisingly been found that with multilayer catalysts it is of particular advantage with regard to increasing the selectivity, at least one

Mixed element oxide of silver with vanadium and / or tungsten and / or molybdenum or to use their precursor compounds in the preparation of the catalyst, wherein the catalyst according to the invention is advantageously used in one or more catalyst layers from the gas inlet up to and including the layer with the highest hotspot.

In a particularly preferred embodiment, one or more or all of said catalyst layers from gas entrance to and including the highest hot spot layer has a mixed element oxide of silver with vanadium and / or tungsten and / or molybdenum of from 0.01% to 15% by weight, in particular from 0.01 to 10.0% by weight and more preferably from 0.01 to 5% by weight in the active composition.

In a particular embodiment of the catalyst according to the invention, the silver vanadium mixed element oxides are compounds having a molar ratio of Ag: V of 1: 1, in particular the mixed element oxide AgVO3. This is not a so-called silver vanadium bronze in which the atomic ratio of Ag: V is by definition less than 1: 1.

It has also been found that the use of mixed element oxides of vanadium with bismuth, molybdenum, tungsten, antimony, arsenic, lead, tin, zinc, copper, nickel, cobalt, iron, manganese, chromium, niobium, zirconium, titanium, gold, rhenium, Lantha, cerium, tantalum, rhenium as a source of raw material in the catalyst preparation and / or as an ingredient of the active mass causes an improvement in the selectivity.

In particular, the use of bismuth vanadate as a source of raw material in the preparation of the catalyst suspension or as part of the active composition has led to an improvement in the selectivity. It is advantageous if the catalysts of the invention contain BiVO4 as a constituent of the active material, in particular in one or more layers from the gas inlet up to and including the layer with the highest hotspot.

The catalysts of the invention can in addition to titanium dioxide and

Vanadium oxide simultaneously at least one mixed element oxide of the silver with one or more of said elements and at least one mixed element oxide of the

Vanadiums containing one or more of the said elements. In a In a particularly preferred embodiment, silver vanadate and bismuth vanadate are used to prepare the catalyst suspension of the catalysts according to the invention and / or are present side by side in the active mass of the catalysts.

Depending on the position of the catalysts according to the invention in the catalyst bed, the catalysts according to the invention additionally contain at least one alkali metal compound, preferably a cesium compound, an antimony compound, preferably antimony I-1 oxide and optionally a phosphorus compound.

It can not only be used in integer atomic ratio Mischelementoxide of vanadium with other elements or their precursor compounds as a source of raw material in the preparation of the catalyst suspension or present in the active material of the catalysts of the invention, but also two or more nuclear mixed element oxides of vanadium with a large atomic Deficit or excess of vanadium. Depending on the general formula of the mixed element oxides or their vanadium content, the content of the relevant mixed element oxide in the catalyst suspension and / or the active mass must then be increased or decreased.

The two or more nuclear mixed element oxides of vanadium are described by the following general formula according to claim 12:

M ₃ N _b V _c O _d (formula II)

For the catalysts according to the invention, it is advantageous to use so-called coated catalysts in which the catalytically active composition is cup-shaped in one or more layers to a support material which is generally inert under the reaction conditions, such as porcelain, magnesium oxide, tin dioxide, silicon carbide, cersilicate, magnesium silicate (steatite), zirconium silicate , Alumina, quartz, or mixtures of these carrier materials is applied. In particular, carrier materials made of steatite or silicon carbide have proven successful in the art. To prepare such coated catalysts, an aqueous solution and / or an organic solvent-containing solution or suspension (referred to herein as "catalyst suspension") of the active composition components and / or their precursor compounds is generally applied to the support material in the fluidized bed process (DE-A 2106796) at elevated temperature. The coating of the inert, non-porous carrier material with the active ingredient components or their precursor compounds as a suspension or powder mixture can likewise be carried out in a heated coating drum at elevated temperatures.

Since during spraying of the catalyst suspension with the active composition components contained therein and / or their precursor compounds in the coating drum or during coating of the inert carrier material in a fluidized bed, in some cases high losses occur due to nebulisation of the catalyst suspension and / or due to partial abrasion of the already coated carriers to the catalyst suspension organic binder, 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 u. a, wherein usually binder amounts of 10-20% by weight, based on the solids content of the catalyst suspension are used. With the addition of one of said binders, the coating temperature is advantageously in a range of 50-450 ⁰ C. The binder used decomposed after filling the catalyst in the reactor usually when the reactor is heated to operating temperature or at the latest when commissioning the catalyst and completely removed from the catalyst.

The remaining on the inert support material as a thin shell catalytically active components are referred to as active mass. The components of the active material may be partially derived from the components used in the catalyst suspension

Raw material sources or precursor compounds differ because some of them are chemically converted by the heat treatment of the catalyst and are usually converted into the corresponding metal oxides. It has now surprisingly been found that the performance of the catalysts depends not only on the composition and amount of the active material (after heating or annealing present catalytically active compounds) of the catalysts, but used in the catalyst suspension or for the coating of the carrier Powder mixed raw material sources have a significant influence on the selectivity, activity and service life of the catalysts.

The invention also relates to a process for the preparation of aldehydes, carboxylic acids and / or carboxylic acid anhydrides comprising contacting a gaseous stream containing an aromatic hydrocarbon and a gas containing molecular oxygen at an elevated temperature with a catalyst as defined above.

The mixed element oxides used as raw material source for the catalyst suspension can be prepared in various ways and be added to the catalyst suspension as an isolated compound or directly as a reaction mixture. Likewise, corresponding precursor compounds of the mixed metal oxides can be added to the catalyst suspension. These are advantageously polynuclear mixed element compounds or Mischmetalloxidverbindungen, which generally have a different crystal structure than the corresponding present in the active composition thermally treated Mischelementoxide and also may contain water of crystallization.

In many cases, the reaction of a solution of a metal compound with a suspension of a metal oxide at elevated temperatures in an aqueous or nonaqueous solvent is also advantageously suitable for the preparation of the mixed element oxides and / or their precursor compounds used in the catalysts according to the invention. Thus, for example, a silver vanadium oxide used for the catalysts according to the invention can advantageously be prepared by reacting silver nitrate in aqueous solution at elevated temperatures with vanadium pentoxide in the corresponding desired atomic ratios. The resulting reaction mixture with the mixed metal compound contained therein can be added directly to the catalyst suspension or the corresponding mixed metal compound but also previously isolated and optionally thermally treated.

In addition to water, polar organic solvents such as polyols, polyethers or amines can also be used as solvents. The reaction of a metal oxide or a plurality of metal oxides (such as vanadium pentoxide and molybdenum trioxide) with a silver compound and optionally another compound (such as

Example, a phosphorus compound) may be generally carried out at room temperature or elevated temperature. Preferably, the reaction is carried out at temperatures of 50 to 100 ⁰ C and takes depending on the used

Starting materials and reaction conditions 20 minutes to 5 days.

The mixed metal compound thus formed can be isolated from the reaction mixture and optionally stored until further use or as a suspension solution of the catalyst suspension, which still contains at least titanium dioxide and a vanadium compound added. The mixed metal compound obtained and isolated by the reaction may also be subjected to thermal treatment at elevated temperatures prior to addition to the catalyst suspension to effect rearrangement of the crystal structure and removal of water of crystallization.

In the case of a prior isolation of the mixed metal compound, this can be done by filtering off the suspension and drying of the resulting solid, wherein the drying can be carried out by various methods. Advantageously, the drying of the mixed metal suspension is carried out by spray drying or freeze drying.

Alternatively to the reaction in solution, however, the mixed metal compounds may also be produced by fusing together, for example, such that various finely mixed metal oxide powders are reacted in a solid state reaction at elevated temperatures of 400 to 800 ^° C.

The components of the catalyst suspension are generally in the form of

Oxides and / or in the form of compounds, for example salts, which convert to oxides upon heating in the presence of oxygen. However, metal salts such as phosphates or halides of the Catalyst suspension are added, which are unchanged in the active material of the catalyst after a thermal treatment.

The preparation of the catalysts according to the invention is generally carried out via a precursor of the finished catalyst, which can be stored as such. This is an inert ceramic support on which the raw materials used in the catalyst suspension are applied by means of a spraying process and are advantageously fixed using an organic binder.

The active catalyst is usually formed by thermal treatment of this precursor or already during the heating of the catalyst in the reactor. In this case, the metal compounds used are usually converted into the corresponding metal oxides. For example, vanadium oxalate is decomposed and converted to V ₂ O ₅ . Also, other compounds contained in the catalyst suspension can be converted to their oxidic compounds upon heating of the catalyst. Thus it can be assumed that the ammonium dihydrogen phosphate is converted to P ₂ O ₅ and is present as such in the active composition. In the case that hydrous mixed metal oxides are prepared and used as a raw material source in the preparation of the catalyst suspension, it is generally assumed that they lose the water of crystallization during the thermal treatment of the catalyst and possibly change its crystal structure.

The conversion of the raw material sources used in the catalyst suspension is preferably carried out at temperatures of 200 to 500 ⁰ C and more preferably in the range of 300 to 500 ⁰ C.

The shape of the inert carrier material is not critically important for the performance of the catalysts of the invention, however, in the prior art, in particular spheres or rings have proven to be advantageous moldings.

The layer thickness of the active composition or the sum of the layer thicknesses of the shells which contain the active composition is generally 20-400 μm and varies depending on the position of the catalyst according to the invention in the catalyst bed. It has further been found, surprisingly, that a spatial separation of the various components of the catalyst suspension from the mixed metal oxides used is generally not necessary in order to obtain improved catalysts. All components used in the catalyst suspension are generally mixed or mixed with the corresponding mixed element oxides and the uniformly mixed suspension is applied to the inert support. However, catalysts are also conceivable in which variously composed catalyst suspensions are applied successively to the inert ceramic support, wherein at least one layer contains a catalyst according to the invention and thus an inventive improved catalyst is formed.

In addition, improved catalysts are conceivable in which a non-inventive catalyst suspension containing at least titanium dioxide, a vanadium compound and advantageously also an alkali metal compound, first isolated and optionally thermally treated and then the resulting powder is generally mixed again with a powder (advantageous in Water) previously obtained from a catalyst suspension consisting of at least titanium dioxide, a vanadium compound and at least one mixed metal oxide or its precursor compound. This new catalyst suspension can be applied as a layer alone to an inert ceramic support or else used in combination with other coating layers according to the invention and / or not according to the invention.

The catalysts of the invention are generally used for the partial gas phase oxidation of aromatic hydrocarbons to aldehydes, carboxylic acids and / or carboxylic anhydrides. These catalysts are particularly suitable for the gas phase oxidation of o-xylene and / or naphthalene to phthalic anhydride with a molecular oxygen-containing gas.

As already mentioned, the catalysts according to the invention can be used for this purpose in a catalyst bed alone or in combination with other, differently active catalysts, for example catalysts of the prior art (vanadium pentoxide / anatase base without Mischmetalloxidkomponente). Here, the different catalysts according to the invention and not according to the invention are generally used in separate catalyst beds, which are arranged in at least one catalyst bed. Overall, the use of the catalysts according to the invention in the catalyst layers closest to the gas inlet up to the position with the highest hot spot is advantageous.

Although the use of the catalysts according to the invention in the catalyst layers following the location with the highest hot spot and closer to the gas outlet closer to the gas outlet also has a positive effect, but already a much lower positive effect in terms of selectivity as the use of the catalysts of the invention the closer to the gas inlet catalyst layers. The novel catalysts and / or their precursor catalysts according to the invention are introduced into the reaction tubes of a reactor in layers. The various layers may in this case consist of catalysts according to the invention and not according to the invention.

It is also conceivable to use in one layer a bed of a mixture of at least one catalyst according to the invention and at least one catalyst not according to the invention and to use this bed alone or in combination with further catalyst layers of inventive and / or non-inventive catalysts.

The reaction tubes are in this case thermostated from the outside, which is generally done by means of a salt melt, which flows around the pipes.

When the reactor is heated with the reaction tubes newly filled with catalyst and / or during the subsequent thermal treatment of the catalyst, the actually active catalyst is formed from the precursor of the catalyst by burning out the organic binder and generally using the respective raw material sources used in the catalyst suspension convert the corresponding oxidic compounds. In addition, depending on the nature of the mixed metal compounds, their chemical composition and / or their crystalline structure may also change. About such a thermally treated catalyst bed consisting of at least one catalyst according to the invention, the reaction gas at temperatures of 250-550 ° C, especially at 330 to 500 ⁰ C and at a Überduck of generally 0.1 to 2.5 bar, preferably 0.3 to 1, 5 bar passed, the space velocity is generally 1000 to 5000 h (-1).

The reaction gas supplied to the catalyst is generally produced by mixing a molecular oxygen-containing gas, preferably air, which may contain, besides oxygen, still suitable reaction moderators and or diluents such as steam, nitrogen and / or carbon dioxide, with the aromatic hydrocarbon to be oxidized the molecular oxygen-containing gas is generally 1 to 100% by volume and more preferably 10 to 30% by volume oxygen, 0 to 30% by volume steam, preferably 0 to 20% by volume water vapor and 0 to 50% by volume. -%, preferably 0 to 1 vol .-% carbon dioxide, the rest may contain nitrogen. To form the reaction gas, the gas containing molecular oxygen is generally mixed at 20 to 200 g per Nm ^3, and more preferably at 60 to 120 g per Nm ^{3 of} the aromatic hydrocarbon to be oxidized.

In a preferred embodiment of the process for the partial oxidation of aromatic hydrocarbons to aldehydes, carboxylic acids and / or carboxylic anhydrides, which proves to be particularly advantageous for the oxidation of o-xylene and / or napthhalin to phthalic anhydride, the aromatic hydrocarbon is first on a bed of the catalyst of the invention only partially converted to a reaction mixture of starting material, intermediates and end product and this mixture reacted with at least one further catalyst, which may also be according to the invention or may be a catalyst according to the prior art.

However, the reaction can also be carried out with more than one reactor, wherein each reactor can be thermostated individually at different reaction temperatures and contains at least one catalyst bed with at least one catalyst layer. It suffices for the process according to the invention in this case if at least one of these reactors has a layer with a catalyst according to the invention. For the preparation of phthalic anhydride from o-xylene, the partially reacted reaction gas after passing through one or more catalyst layers with catalyst according to the invention in addition to the desired product phthalic anhydride also contains a substantial amount of unreacted o-xyloxy and intermediates such as o-tolualdehyde and o-toluic acid and phthalide.

Subsequently, the product mixture is passed without further separation over at least one further catalyst layer, which differs in terms of their chemical composition and activity of the catalyst according to the invention to ensure complete conversion of the raw material or the oxidation of the suboxidation to phthalic anhydride.

Furthermore, a separation of the unreacted o-xylene after passing through the

Catalyst bed with the catalyst according to the invention conceivable before the reaction gas is fed to one or more further catalyst beds.

However, such a variant is technically feasible only with relatively great effort.

It is therefore preferred that the reaction mixture successively passes through several catalyst layers without separation of starting materials or intermediates, wherein at least one of these catalyst layers, preferably the position (s) closer to the gas inlet, contains a bed of a catalyst according to the invention.

In general, the catalyst according to the invention is used together with at least one further or several catalyst layers, wherein at least one of the catalyst layers from the gas inlet up to and including the layer with the highest hot spot located catalyst layers according to the invention

Catalyst generally contains from 1 to 40% by weight of vanadium pentoxide, calculated as V2O5, 50 to 99% by weight of titanium dioxide, calculated as TiO2, up to 1% by weight of an alkali metal compound, calculated as alkali metal

Cesium, up to 1.5% by weight of a phosphorus compound, calculated as P, up to

10% by weight of an antimony compound, calculated as Sb 2 O 3 and up to 15

Weight% of at least one Mischelementoxids of silver with at least one of the previously described elements and / or up to 10% by weight of a Mischelementoxides of vanadium with at least one of the elements previously described. The catalysts used in combination generally used in layers which are closer to the gas outlet and follow the position with the highest hot spot, are based mostly on non-inventive catalysts based on titanium dioxide / V205, but contain no mixed element oxides of silver and / or vanadium. However, it is also possible to use exclusively catalysts according to the invention in all layers. In this case, the catalysts generally differ in the type and amount of mixed metal oxides present in the active composition.

The catalysts of the prior art used in combination with the catalysts of the invention generally have a titanium dioxide content of 60-99% by weight, a vanadium oxide content of 1 to 40% by weight, an alkali metal content up to 1% by weight, a phosphorus content of up to 1.5% by weight and an antimony content of up to 10% by weight.

Unaffected by the above-described compositions, the active materials of the catalysts according to the invention and / or not according to the invention may contain small amounts of further oxidic compounds for activity and selectivity control.

Examples

Preparation of the Catalysts The various components of the catalyst suspension are added successively as solutions and / or as a powder in deionized water, and the resulting suspension is advantageously stirred for at least 12 hours. Titanium dioxide in the anatase modification, V2O5 or vanadyl oxalate, cesium sulfate, ammonium dihydrogen phosphate, antimony trioxide, bismuth vanadate and silver vanadate, silver molybdate, silver tungstate and / or other mixed metal oxides of silver and vanadium are advantageously used as raw material sources for the components contained in the catalyst according to the invention.

Subsequently, an organic binder in the form of an aqueous dispersion of a vinyl acetate copolymer is added to the aqueous catalyst suspension and the total of about 20 to 25% suspension is stirred for a further 30 minutes. Thereafter, an appropriate amount of the aqueous suspension, which contains the active ingredients and / or their precursor compounds and the organic binder, spray applied to the inert support (steatite rings with 7x7x4 mm or 8x6x5 mm dimension) until a certain amount of the adhesive-containing Suspension is applied to the rings, so that results after calcination, the active mass given in the examples.

The proportion of active material (proportion of catalytically active substances without binder) in each case refers to the proportion of the catalytically active composition in the total weight of the catalyst, including the support in the respective catalyst layer, determined after calcining at 400 ^° C. for 4 h.

The stated content of phosphorus refers to the amount of a phosphorus compound added in the catalyst suspension preparation. It is known to those skilled in the art that the actual content of phosphorus in the active mass may vary depending on how heavily the TiO 2 used is contaminated with phosphorus compounds.

oxidation reaction

In a tubular reactor with a reaction tube made of iron with an inner diameter of 25 mm and a length of 3.7 m, which is bathed by a salt bath, the relevant multilayer catalyst system is filled, wherein in the examples described in each case the R1 layer next to the gas inlet and the R4 layer or the R5 layer is closest to the gas outlet.

In the reaction tube was centrally arranged a thermowell of 2mm with built-in tension element for temperature measurement. 4 Nm ^{3 of} air at a loading of about 30 to 70 g-xylene / Nm ³ air were passed through the reaction tube hourly from top to bottom at a salt bath temperature of 340-380 ⁰ C.

To determine the catalytic performance data, the reaction gas leaving the reaction tube is passed through an oil-cooled condenser, in particular by the fact that most of the phthalic anhydride formed is only completely separated off and by-products such as benzoic acid, maleic anhydride and phthalide are only partially precipitated. The separated in the condensers raw PSA is using hot oil melted, collected, weighed and then determined the content of phthalic anhydride by GC analysis.

The raw PSA yield given in the examples is calculated as follows:

Crude PSA yield (% by weight) = (amount of raw PSA (g) x purity of crude PSA (%)) / (feed of o-xylene (g) x purity of o-xylene (%))

Despite the deduction of the by-products contained therein, the yield of solid PSA thus determined is referred to as the crude PSA yield, since the pure PSA is generally a product obtained after the thermal pretreatment and distillative work-up. This is also familiar to the person skilled in the art.

Since the conversion of o-xylene in each case is almost 100%, the raw yield thus determined corresponds directly to the selectivity of the catalyst system.

Example 1 (Comparative Example): Catalyst System A (4 layers)

This catalyst system is a multi-layer system with four different layers. The individual beds of this comparative catalyst contain no mixed element oxide of the silver.

At a loading of 50 to 65 g of o-xylene per Nm ^{3 of} air and a total air flow of 4.0 Nm ³ per hour and 344 to 347 ° C SBT the catalyst system A described in Example 1 was tested.

In this case, an average raw PSA yield (based on 100% o-xylene purity) after the break-in of 113.4% by weight was achieved and the phthalide content in the raw PSA was 0.01% by weight.

Example 2 (Inventive): Catalyst System B (4 layers)

At a loading of 58 to 63 g of o-xylene per Nm ^{3 of} air and a total air flow of 4.0 Nm ³ per hour and 346 to 352 ° C SBT the catalyst system B described in Example 2 was tested. In this case, an average raw PSA yield (based on 100% o-xylene purity) was achieved after the run-in phase of 114.0% by weight and the phthalide content in the crude PSA was 0.06% by weight.

Example 3 (according to the invention): Catalyst system C (4 layers)

At a loading of 58 to 65 g of o-xylene per Nm ^{3 of} air and a total air flow of 4.0 Nm ³ per hour and 346 to 347 ° C SBT the catalyst system C described in Example 3 was tested. In this case, an average raw PSA yield (based on 100% o-xylene purity) was achieved after the run-in phase of 115.3% by weight and the phthalide content in the crude PSA was 0.04% by weight.

Example 4 (Inventive): Catalyst System D (4 layers)

At a loading of 57 to 69 g of o-xylene per Nm ^{3 of} air and a total air flow of 4.0 Nm ³ per hour and 346 to 348 ° C SBT the catalyst system D described in Example 4 was tested. In this case, an average raw PSA yield (based on 100% o-xylene purity) was achieved after the run-in phase of 113.9% by weight, and the phthalide content in the crude PSA averaged 0.02% by weight.

Example 5 (according to the invention): Catalyst system E (4 layers)

At a loading of 52 to 62 g of o-xylene per Nm ^{3 of} air and a total air flow of 4.0 Nm ³ per hour and 347 to 348 ⁰ C SBT the catalyst system E described in Example 5 was tested. In this case, an average raw PSA yield (based on 100% o-xylene purity) was achieved after the run-in of 114.2% by weight and the phthalide content in the crude PSA was on average 0.01% by weight.

Example 6 (Comparative Example): Catalyst System F (5 layers)

At a loading of 58 to 61 o-xylene per Nm ^{3 of} air and a total amount of air of 4 Nm ³ per hour and 350 to 354 ° C SBT, the catalyst system F described in Example 6 was tested. In this case, an average raw PSA yield (based on 100% o-xylene purity) of 113.1% by weight was achieved after the run-in phase and the phthalide content in the crude PSA was 0.01% by weight.

Example 6 (Inventive): Catalyst System G (5 layers)

At a loading of 58 to 75 g of o-xylene per Nm ^{3 of} air and a total amount of air of 4 Nm ³ per hour and 348 to 350 ⁰ C SBT the catalyst system G described in Example 6 was tested. An average raw PSA yield (based on 100% o-xylene purity) of 114.8% by weight after the run-in phase was achieved and the phthalide content in the crude PSA was 0.03% by weight.

Table I:

Performance data of the catalysts of the invention

From the comparison of Examples 2 to 5 and Comparative Example 1, it can be seen that the use of mixed element oxides of silver as a source of raw material to produce a catalyst suspension for a catalyst in the first catalyst layer closest to the gas inlet results in a marked increase in selectivity.

It can be seen from the comparison of Example 7 with Comparative Example 6 that the use of silver vanadate in the active mass of the hot spot catalyst layer results in an improvement in the selectivity even when used in at least one of the catalyst layers following the first catalyst layer.

Claims

claims

1. Catalyst for the catalytic gas-phase oxidation of aromatic hydrocarbons to aldehydes, carboxylic acids and / or carboxylic acid anhydrides, in particular to phthalic anhydride,

wherein the active composition is vanadium oxide, preferably vanadium pentoxide,

Titanium dioxide, preferably in the anatase modification, and at least one mixed element oxide of the silver with defined elements, preferably vanadium and / or molybdenum and / or tungsten and / or niobium and / or antimony, and / or a mixed element oxide of the vanadium with defined elements, preferably Bismuth and / or molybdenum and / or tungsten and / or antimony and / or niobium, and

at least one mixed element oxide of silver and / or vanadium and / or at least one precursor compound, in particular at least one polynuclear precursor compound, at least one mixed element oxide of the catalyst in the preparation of the catalyst, in particular in the preparation of a catalyst suspension or a powder mixture required for the coating of a carrier Silver and / or vanadium is used as a source of raw materials.

2. A catalyst according to claim 1, characterized in that the active composition comprises 0.01 to 15% by weight, preferably 0.01 to 10% by weight, most preferably 0.01 to 5% by weight, of a Mischelementoxides of silver.

3. Catalyst according to claim 1 or 2, characterized in that the at least one mixed element oxide of silver, a mixed element oxide with at least one further element from the group of vanadium, molybdenum, tungsten, niobium, tantalum, chromium, titanium, manganese, iron, cobalt, Nickel, copper, zinc, cadmium, gold, tin, zirconium, antimony, arsenic, cerium, lanthanum, bismuth, hafnium, lead, boron, aluminum, ruthenium, rhenium, palladium, rhodium.

4. Catalyst according to one of claims 1 to 3, characterized in that the active composition comprises 0.01 to 10% by weight, preferably 0.01 to 5% by weight, of a Mischelementoxides of vanadium.

5. Catalyst according to one of claims 1 to 4, characterized in that the at least one mixed element oxide of vanadium a Mischelementoxid with at least one further element from the group of bismuth, antimony, molybdenum, tungsten, chromium, lanthanum, cerium, iron, manganese, Niobium, tantalum, rhenium, cobalt, nickel, copper, zinc, gold, cadmium, lead, tin, boron, titanium, zirconium, hafnium, aluminum, arsenic, ruthenium, rhodium,

Palladium is.

6. A catalyst according to any one of claims 1 to 5, characterized in that the vanadium oxide content of the active composition 1 to 40% by weight, calculated as V ₂ O ₅ , and the titanium dioxide content of the active material 50 to 99

Weight%, calculated as TiO ₂ , is.

7. Catalyst according to one of claims 1 to 6, characterized in that the active composition 0 to 10% by weight of an antimony compound, calculated as Sb ₂ θ ₃ , and / or 0 to 1% by weight of a compound of at least one element of the Group of lithium, sodium, potassium, rubidium, cesium, each calculated as alkali metal, and / or 0 to 1, 5% by weight of a phosphorus compound, calculated as P comprises.

8. Catalyst according to one of claims 1 to 7, characterized in that the active material AgVO _ß and / or Ag ₂ MoO ₄ and / or Ag ₂ WO ₄ and / or BiVO ₄ has.

9. A catalyst according to claim 8, characterized in that a predetermined amount of AgVO _ß and / or Ag ₂ MoO ₄ and / or Ag ₂ WO ₄ and / or

BiVO ₄ and / or at least one precursor compound of these compounds is used in the preparation of the catalyst as a source of raw material.

10. A catalyst according to any one of claims 1 to 9, characterized in that used as a source of raw material in the preparation of the catalyst

Mixed element oxides and / or mixed element oxide precursor compounds of Mischelementoxides or the mixed element oxides of silver and / or vanadium are isolated before use as a source of raw material in the catalyst production during their preparation from the reaction mixture or the reaction mixture in question is used directly as a source of raw material in the catalyst production.

A catalyst according to any one of claims 1 to 10, characterized in that the mixed element oxide of silver has the following formula (I) below:

Ag _x My N _z O _n (formula I) with

Ag = silver x = 0.01 to 100, in particular 0.1 to 10,

M = an element selected from the group Li, Na, K, Rb, Cs, P, Mg, Ca,

Sr, Ba, Tl, y = 0 to 1

N = at least one element selected from the group V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Cu, Au, Zn, Cd, Sn, Pb, B , Al, Bi, Sb, As, Ti, Zr, Hf, Ce, La z = 1

O = oxygen n = a number which is determined by the valence and frequency of the elements other than oxygen in the formula I,

12. Catalyst according to one of claims 1 to 11, characterized in that the mixed element oxide of vanadium has the following formula (II):

M _a N _b V _c O _d (formula II) with M = at least one element selected from the group consisting of Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Cu, Au, Zn, Cd, Sn ₁ Pb, B, Al , Bi, Sb, As, Ti, Zr, Hf, Ce, La a = 0.01 to 100

N = at least one element selected from the group Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Tl, Pb = O to 1,

V = vanadium c = 1

O = oxygen d = a number determined by the valency and frequency of the elements other than oxygen in formula II.

13. A catalyst according to any one of claims 1 to 12, characterized in that is used as the vanadium source for the preparation of the catalyst V ₂ O ₅ and / or vanadium oxalate and / or V ₆ O ^ and / or NH ₄ VO ₃ and / or polyvanadic acid, wherein at least a portion of the vanadium is present in the active composition after the thermal treatment of the catalyst as vanadium pentoxide.

14. A catalyst according to any one of claims 1 to 13, characterized in that for the preparation of the catalyst at least one kind of titanium dioxide is used in the anatase modification and as such is present in the active composition, wherein the average BET surface area, calculated from quantity and surface ratios of the individual varieties, the total titanium dioxide between 10 to 60 m ² / g.

15. A catalyst according to claim 14, characterized in that in the active composition, a mixture of a plurality of different titanium dioxide varieties is used in the anatase modification, wherein at least one titanium dioxide variety in the anatase modification has an average particle size of 0.3 microns to 0.8 microns and a BET surface area of 13 to 60 m ² / g and wherein at least Another type of titanium dioxide in the anatase modification has a BET surface area of 2 to 15 m ² / g.

16. Catalyst according to one of claims 1 to 15, characterized in that for the preparation of a catalyst suspension or one for the

Coating of a carrier required powder mixture used antimony compound and / or present in the active material of the catalyst antimony compound is an antimony-l oxide and / or antimony V-oxide.

17. A catalyst according to any one of claims 1 to 16, characterized in that the catalyst consists of at least three layers, wherein the antimony content of at least one of the hot spot catalyst layer in the direction of gas inlet layer is reduced by 20 to 100% compared to the antimony content of the hot spot catalyst layer ,

18. A catalyst according to any one of claims 1 to 17, characterized in that the active material of the catalyst after tempering of the catalyst at 400 ⁰ C over a defined, preferably several, in particular in about 4 hours lasting period has the following composition:

Vanadium oxide: 1-40% by weight (calculated as V ₂ O ₅ ) Titanium dioxide: 50-99% by weight (calculated as TiO ₂ )

AgxMyNzOn: 0.01-15% by weight (calculated as AgxMyNzOn) MaNbVcOd: 0 -10% by weight (calculated as MaNbVcOd)

Alkali metal: 0-1, 0% by weight (calculated as alkali metal)

Antimony oxide: 0-10% by weight (calculated as Sb ₂ Os) phosphorus: 0-1, 5% by weight (calculated as P)

19. A catalyst according to claim 18, characterized in that the active material of the catalyst after tempering of the catalyst at 400 ⁰ C over a defined, preferably several, in particular in about 4 hours lasting period has the following composition:

Vanadium oxide 1-20% by weight (calculated as V ₂ O ₅ )

Titanium dioxide: 80-99% by weight (calculated as TiO ₂ ) Silver vanadate: 0-5% by weight (calculated as AgVO ₃ )

Silver tungstate: 0-5% by weight (calculated as Ag ₂ WO ₄ )

Silver molybdate: 0-5% by weight (calculated as Ag ₂ MoO ₄ )

Bismuth vanadate: 0-3% by weight (calculated as BiVO ₄ ) cesium: 0-1% by weight (calculated as Cs)

Antimony oxide: 0-5% by weight (calculated as Sb ₂ O ₃ )

Phosphorus: 0-1, 5% by weight (calculated as P)

wherein at least one mixed element oxide of the silver and / or bismuth vanadate is part of the active material of the catalyst.

20. A catalyst according to any one of claims 1 to 19, characterized in that the active material of the catalyst after the heat treatment of the catalyst at least 400 ⁰ C and a period of at least 4 h, a proportion of 2 to 25% by weight of the total weight of the catalyst is.

21. A catalyst according to any one of claims 1 to 20, characterized in that the layer thickness of the active material on an inert support material is 20 to 400 microns and the catalytically active composition is applied to an inert, non-porous support, wherein it is preferably carrier steatite, in particular steatite rings.

22. A catalyst according to any one of claims 1 to 21, characterized in that at least two different layers are cup-shaped applied to a preferably inert carrier, wherein at least one of the layers contains titanium dioxide, vanadium oxide and a mixed element oxide of silver and / or vanadium

23. A catalyst according to any one of claims 1 to 22, characterized in that at least two different layers are cup-shaped applied to a preferably ceramic support, wherein at least one layer at least titanium dioxide and vanadium oxide and at least one further layer at least one silver and / or Vandadium Containing mixed element oxide with or without additional titanium dioxide and vanadium oxide.

24. Catalyst according to one of claims 1 to 23, characterized in that in at least one catalyst layer from the gas inlet to the layer with the highest hot spot, a shell catalyst is used whose active material is a mixed element oxide of the silver of claim 11 and / or a mixed element oxide of Vanadium according to claim 12 and in which catalyst as a raw material source for the preparation of the catalyst, a Mischelementoxid of silver and / or vanadium and / or a precursor compound of a Mischelementoxids of silver and / or vanadium was used, and in which catalyst in at least one catalyst layer of the situation with the highest hot spot to the position at the gas outlet a shell catalyst for the oxidation of aromatic hydrocarbons is used, which contains in its active material as essential constituents vanadium pentoxide and titanium dioxide.

25. A catalyst according to any one of claims 1 to 24, characterized in that the binder for producing at least one catalyst layer is an organic polymer or copolymer, in particular a vinyl acetate copolymer, which is used in particular in the form of an aqueous dispersion.

26. A catalyst according to any one of claims 1 to 25, characterized in that the catalytically active composition, based on their total weight, 0.01 to 15% by weight of a Mischelementoxids of silver with vanadium and in which the ratio Ag: V of greater 0.95 (> 0.95): 1 to 10: 1.

27 precursor for a catalyst, in particular for a catalyst according to one of claims 1 to 26, characterized by an inert, non-porous support material and one or more shell-like layers applied thereto, wherein at least one layer at least one precursor compound of a mixed element oxide of the general formula I according to

Claim 11, or the formula II according to claim 12, containing titanium dioxide and a vanadium compound, and wherein this precursor compound is converted in the thermal treatment of the precursor of the catalyst in a mixed element oxide of silver or vanadium.

28, precursor for a catalyst, in particular for a catalyst according to one of claims 1 to 26, characterized in that at least two different layers are cup-shaped applied to a preferably ceramic support, wherein at least one layer at least titanium dioxide and a vanadium compound and at least one further

Layer containing at least one precursor compound of a Mischelementoxids with or without additional titanium dioxide and with or without an additional vanadium compound, and wherein this precursor compound is converted in the thermal treatment of the catalyst in a mixed element oxide of silver or vanadium.

29. A process for preparing a catalyst according to any one of claims 1 to 26, characterized in that a powder or a suspension, in particular an aqueous suspension containing at least titanium dioxide, a vanadium compound and at least one mixing element compound of

Silver and / or vanadium and / or at least one precursor compound of a mixed element compound of silver and / or vanadium, is prepared and applied to an inert support.

30. A process for preparing a precursor of a Mischelementoxids or a Mischelementoxids according to claim 1 1, characterized in that in a liquid, preferably water, suspended metal oxide N, preferably vanadium pentoxide and / or molybdenum trioxide and / or tungsten trioxide, and / or a dissolved metal compound N , preferably ammonium metavanadate, with a suspension or solution, preferably an aqueous solution, a silver compound and optionally a solution or suspension of an oxide of a metal compound M is heated and the reaction product is isolated and used as a raw material source for a catalyst.

31. The method according to claim 30, characterized in that the resulting reaction mixture or the isolated reaction product for

Preparation of catalysts or for the preparation of precursors of

Catalysts for the gas phase oxidation of aromatic hydrocarbons is used.

32. A process for preparing a precursor of a Mischelementoxids or a Mischelementoxids according to claim 12, characterized in that in a liquid, preferably water, a suspended and / or dissolved vanadium compound, preferably vanadium pentoxide and / or ammonium vanadate and / or vanadium (IV, V) oxide, with a solution or a suspension, preferably an aqueous solution, a salt or an oxide of a metal compound M, preferably bismuth and / or molybdenum and / or tungsten and / or niobium and / or antimony and optionally a solution of a salt or a suspension an oxide of a metal N, is heated and the reaction product isolated or as a reaction mixture as

Raw material source is used for a catalyst.

33. The method according to claim 32, characterized in that the isolated reaction product and / or the resulting reaction mixture for the preparation of catalysts or for the preparation of precursors of

Catalysts for the gas phase oxidation of aromatic hydrocarbons is used.

34. A process for preparing a Mischelementoxids according to claim 11, characterized in that at least one metal oxide N, preferably

Vanadium pentoxide and / or molybdenum trioxide and / or tungsten trioxide, and / or at least one metal salt N with an oxide or a salt of silver, preferably AgO and / or Ag ₂ O and optionally an oxide or a salt of a metal M, in dry form or in Solution is mixed and the mixture if necessary after prior drying then at

Temperatures of 200 to 900 ⁰ C over a defined period of time is heated and the reaction product is used as a raw material source for a catalyst.

35. The method according to claim 34, characterized in that the

Reaction product or the resulting reaction mixture for the preparation of catalysts or for the preparation of precursors of catalysts for the gas phase oxidation of aromatic hydrocarbons is used.

36. A method for producing a Mischelementoxids according to claim 12, characterized in that at least one salt or an oxide of vanadium, preferably vanadium pentoxide and / or ammonium vanadate and / or vanadium (IV ₁ V) oxide, with at least one oxide and / or a salt a metal M, preferably bismuth oxide, and optionally an oxide or a salt of a metal N, in dry form or mixed in solution and the mixture optionally after prior drying then heated at temperatures of 200 to 900 ⁰ C over a defined period of time and the reaction product is used as a raw material source for a catalyst for the gas phase oxidation of aromatic hydrocarbons.

37. A process for the preparation of aldehydes, carboxylic acids and / or carboxylic anhydrides by partial oxidation of aromatic hydrocarbons at elevated temperature on a catalyst, the catalytically active material is applied to an inert, non-porous support, characterized in that a shell catalyst whose catalytically active material 0.01 to 15% by weight, based on their total weight, of a mixed element oxide of silver with vanadium and / or molybdenum and / or tungsten and / or niobium and / or antimony and / or 0.01 to 10% by weight of a mixed element oxide of Vanadium with bismuth and / or molybdenum and / or niobium and / or antimony and simultaneously titanium dioxide and a vanadium compound, preferably V ₂ O ₅ , wherein the mixed element oxide compound (s) or their precursor compound (s) in the preparation of the catalyst suspension and or the powder mixture is used for the later active mass, in the presence or absence at least ns a werteren shell catalyst containing in its active material as essential constituents vanadium pentoxide and titanium dioxide in the anatase modification used.

38. A process for preparing a catalyst according to any one of claims 1 to 26, characterized in that the catalytically active material or the compounds contained in the catalyst suspension or in the powder mixture is applied in a fluidized bed or preferably in a fluidized bed to the inert carrier or become.