DE102005017050A1 - Preparing organic target compound by heterogeneously catalyzed gas phase partial oxidation of organic precursor compound with molecular oxygen in two oxidation reactor lines operated in parallel and removal of compound from gas stream - Google Patents

Abstract

Preparing at least one organic target compound (I) by heterogeneously catalyzed gas phase partial oxidation of at least one organic precursor compound with molecular oxygen in at least two oxidation reactor systems comprising catalyst charges and are operated in parallel to obtain at least two product gas streams (II) each comprising (I) and each stemming from one of the at least two oxidation reactor systems and subsequent removal of (I) from (II) to obtain at least one crude target product stream, where the process comprises before, during and/or after the removal, mixing together (II). Preparing at least one organic target compound (I) by heterogeneously catalyzed gas phase partial oxidation of at least one organic precursor compound with molecular oxygen in at least two oxidation reactor systems comprising catalyst charges and are operated in parallel to obtain at least two product gas streams (II) each comprising (I) and each stemming from one of the at least two oxidation reactor systems and subsequent removal of (I) from (II) to obtain at least one crude target product stream, where the process comprises before the removal, mixing together (II); or in the course of the removal, mixing together at least two of any target product-comprising subsequent streams obtained on the route from (II) to the at least one crude target product stream; and/or after the removal from (II), mixing together any crude target product streams obtained in the course of the removal, to form a mixture stream, where at least one of the catalyst charges of the at least two oxidation reactor systems operated in parallel, over which the target compounds comprised in the mixture stream were formed, comprises at least one portion of catalyst over which the heterogeneously catalyzed gas phase partial oxidation has already been carried out longer than over all portions of catalyst of the at least one other catalyst charge. An independent claim is included for an apparatus comprising two oxidation reactor systems which are charged with catalysts that are suitable for the preparation of (I) by heterogeneously catalyzed partial oxidation of an organic precursor compound and at whose outlet is disposed in each case a line for the removal of the product gas stream comprising (I) from the particular oxidation reactor system, which lines are combined with increasing distance from the two oxidation reactor systems to give a product gas line which leads to an apparatus in which the product gas stream can be condensed partly or fully, where the catalyst charge of one of the two oxidation reactor systems comprises at least one portion of catalyst over which more target product has already been generated than over the portions of catalyst of the catalyst charge of the other oxidation reactor system.

Description

• a) heterogen katalysierte Gasphasen-Partialoxidation wenigstens einer organischen Vorläuferverbindung mit molekularem Sauerstoff in wenigstens zwei parallel betriebenen, Katalysatorbeschickungen enthaltenden, Oxidationsreaktorsystemen unter Erhalt von wenigstens zwei die Zielverbindung jeweils enthaltenden und jeweils auf eines der wenigstens zwei Oxidationsreaktorsysteme zurückgehenden Produktgasströmen und
• b) anschließende Abtrennung der wenigstens einen Zielverbindung aus den wenigstens zwei Produktgasströmen unter Erzeugung von wenigstens einem Roh-Zielproduktstrom, bei dem man
• c) vor der Abtrennung wenigstens zwei der wenigstens zwei Produktgasströme, oder im Verlauf der Abtrennung wenigstens zwei der auf dem Weg von den wenigstens zwei Produktgasgemischströmen zu dem wenigstens einen Roh-Zielproduktstrom gegebenenfalls erzeugten Zielprodukt enthaltenden Folgeströme und/oder nach der Abtrennung aus den wenigstens zwei Produktgasströmen im Verlauf der Abtrennung gegebenenfalls erzeugte Roh-Zielproduktströme miteinander zu einem Gemischstrom vermischt.

The present invention relates to a process for preparing at least one organic target compound by

• a) heterogeneously catalyzed gas phase partial oxidation of at least one organic precursor compound with molecular oxygen in at least two parallel, catalyst feed containing oxidation reactor systems to obtain at least two target compound containing respectively and each on one of the at least two oxidation reactor systems going back product gas streams and
• b) subsequent separation of the at least one target compound from the at least two product gas streams to produce at least one crude target product stream, wherein
• c) prior to separation, at least two of the at least two product gas streams, or in the course of the separation at least two of the at least two of the at least two product gas mixture streams to the at least one raw target product stream optionally generated target product containing subsequent streams and / or after the separation of the at least two Product gas streams in the course of the separation optionally produced raw target product streams mixed together to form a mixture stream.

Under a complete Oxidation of an organic compound with molecular oxygen It is understood here that the organic compound is reactive Exposure to molecular oxygen is converted so that the total carbon contained in the organic compound Oxides of carbon and in total in the organic compound contained hydrogen is converted into oxides of hydrogen.

All of which various reactions of an organic compound under Reactive action of molecular oxygen is referred to herein as Partial oxidation of an organic compound summarized.

that is, the term of partial oxidation is intended in this document in particular also include partial ammoxidations characterized thereby are that partial oxidative reaction of the organic compound in the presence of ammonia.

in the in particular, such reactions are intended here under partial oxidations organic compounds under the reactive action of molecular Oxygen be understood in which the partially oxidized organic compound (the organic precursor compound) after completion Reaction contains at least one oxygen atom more chemically bound than before implementation the partial oxidation.

It is well known to be characterized by partial and heterogeneously catalyzed Oxidation of various organic precursor compounds with molecular Oxygen in the gas phase numerous basic chemicals are generated can. Examples include the reaction of tert-butanol, iso-butene, Iso-butane, iso-butyraldehyde or the methyl ether of tert-butanol to methacrolein and / or methacrylic acid (see for example DE-A 25 26 238, EP-A 092 097, EP-A 058 927, DE-A 41 32 263, DE-A 41 32 684 and DE-A 40 22 212), the conversion of acrolein to acrylic acid, the conversion of methacrolein to methacrylic acid (See, for example, DE-A 25 26 238), the reaction of o-xylene and / or naphthalene to phthalic anhydride (see, for example, EP-A 522 871), from m-xylene to isophthalic acid, from p-xyxlol to terephthalic acid or dimethyl terephthalate and the reaction of butadiene to maleic anhydride (See, for example, DE-A 21 06 796 and DE-A 16 24 921), the implementation of n-butane to maleic anhydride (See, for example, GB-A 1 464 198 and GB 1 291 354), the aforementioned reactions to obtain the corresponding anhydrides acids, the reaction of propylene to acrolein and / or acrylic acid (See, for example, DE-A 23 51 151), the conversion of indanes to e.g. anthraquinone (See, for example, DE-A 20 25 430), the reaction of ethylene to ethylene oxide or from propylene to propylene oxide (see, for example, DE-AS 12 54 137, DE-A 21 59 346, EP-A 372 972, WO 89/0710, DE-A 43 11 608 and Beyer, textbook of Organic Chemistry, 17th Edition (1973), Hirzel Verlag, Stuttgart, Page 261), the reaction of propylene and / or acrolein to acrylonitrile (see, for example, DE-A 23 51 151), the reaction of isobutene and / or Methacrolein to methacrylonitrile, the oxidative dehydrogenation of Hydrocarbons (see, for example, DE-A 23 51 151), the reaction of Propane to acrylonitrile, or to acrolein and / or to acrylic acid (see. e.g. DE-A 101 31 297, EP-A 1 090 684, EP-A 608 838, DE-A 100 46 672, EP-A 529 853, WO 01/96270 and DE-A 100 28 582), as well as the reactions from ethane to acetic acid, from benzene to phenol and from 1-butene or 2-butene to the corresponding ones Butanediols etc.

A disadvantage of the processes of heterogeneously catalyzed gas phase partial oxidation of organic Vor Runner compounds is that the resulting product gases contain the target organic compound not in pure form but as part of a mixture which usually additionally contains by-products, unreacted reactants and inert diluent gases (as being substantially inert under the conditions of a heterogeneously catalyzed gas phase partial oxidation Behavioral diluent gas are understood in this document as such diluent gases whose constituents under the conditions of heterogeneously catalyzed Gasphasenpartialoxi dation - each component considered by itself - to more than 95 mol%, preferably retained to more than 99 mol% chemically unchanged).

Out This product gas (mixtures) must be separated from the target compound become. As a rule, the organic target compound is used for this purpose the product gas (gaseous Product mixture) first (possibly after previous direct and / or indirect Cooling) in suitable devices in the condensed (liquid and / or fixed) phase. This overpass can e.g. through complete or by partial condensation of the product gas. In a preferred embodiment it is carried out by fractional condensation (e.g., in a separating effective Internals containing column; see. e.g. DE-A 103 32 758 and therein cited prior art).

alternative can the overpass in the condensed phase can also take place by the target compound from the previously possibly cooled product gas mixture) in an absorption device (e.g., in a separable fixture containing absorption column) a suitable liquid absorbent (see, for example, DE-A 103 36 386, US-A 2004/0242826 and US Pat the prior art cited in these references). It also exists the possibility, the organic target compound from the product gas mixture) by adsorption on solid adsorption materials or by freezing in the Condensed phase to convert.

Either contains the condensed phase already has the target compound (the target product) in the for the further use of the target product desired purity (then forms the condensed phase already contains the targeted crude target product stream; the prefix "raw" should be expressed bring the raw target product stream alongside the desired one Target connection usually additional at least one other than the target product component contains in analytically detectable amounts), or it is a higher purity of the crude target product stream desired. In the latter case, the condensed phase forms only one Following stream, from which the desired Raw target product stream in a conventional manner by using more downstream (consecutive) separation process is obtained. Such further separation processes are usually connected in series Extraction and / or rectification separation process. Possibly can these in advance of their application or in between by low boiler stripping be supplemented (Low-boiling components are understood to mean secondary components, their boiling point under normal conditions (25 ° C, 1 atm) below the corresponding Boiling point of the target compound). In addition, the aforementioned separation processes supported by intermediary crystallative separation processes. Also can Such crystallative separation processes are the sole further purification processes of form condensed phase. The one of a cleaning stage (cleaning device) to the next Cleaning stage (cleaning device) promoted target product containing Material flow forms a subsequent stream in the sense of this document. In general contains the from a previous follow-on stream in a further purification step (Cleaning device) subsequent subsequent stream generated the target compound in increased Purity. Another feature of the preparation of organic target compounds via heterogeneous catalyzed gas phase partial oxidation of organic precursor compounds with molecular oxygen is that in the heterogeneous catalysed gas phase partial oxidations to be used catalysts normally around solids is.

Especially often If the catalysts used are oxide materials or precious metals (e.g., Ag). The catalytically active oxide mass besides oxygen, only one other element or more can be used contain another element (multielement oxide masses). Especially often are used as catalytically active oxide materials such as more than one metallic, especially transition metallic, element include. In this case one speaks of Multimetalloxidmassen. Usually Multielementoxidmassen are not simple physical mixtures of oxides of elementary constituents, but heterogeneous mixtures of complex poly compounds of these elements.

Further be heterogeneously catalyzed gas phase partial oxidation, in particular the above, at elevated Temperature (usually several hundred ° C, usually 100 to 600 ° C) performed.

Since most of the heterogeneously catalyzed gas phase partial oxidations are highly exothermic, it is expediently carried out for reasons of heat removal in a fluidized bed or in (usually isothermal) Fixed bed reactors where they are located in a reaction space around which a heat exchange medium for the purpose of indirect heat exchange is passed (eg, the catalyst bed can be as a fixed bed in the contact tubes of a tube reactor to which a molten salt is passed for heat removal).

Heterogeneous catalyzed gas phase partial oxidations can in principle but also be carried out on catalyst beds located in adiabatic reactors.

It is known that the working pressure (absolute pressure) at heterogeneous catalyzed gas phase partial oxidations below 1 bar 1 bar or over 1 bar can lie. As a rule, it is 1 to 10 bar, usually 1 up to 3 bar.

The Reacting the at least one organic precursor compound to the target compound (the goal conversion) takes place during the residence time of the reaction gas mixture in the catalyst feed, through which it is conducted.

by virtue of of the usually pronounced exothermic character of most heterogeneously catalyzed gas phase partial oxidations organic precursor compounds with molecular oxygen, the reactants become common with one under the conditions of gas-phase catalytic Partial oxidation diluted in essentially inert gas, the with its heat capacity liberated heat of reaction to absorb.

One the most common co-used inert diluent gases is molecular nitrogen, which is always used automatically comes when as an oxygen source for the heterogeneously catalyzed Gas phase partial oxidation air is used.

Another widely used inert diluent gas is water vapor due to its general availability. In many cases, recycle gas is also used as inert diluent gas (cf., for example, EP-A 1 180 508). According to the foregoing, there is thus at most heterogeneously catalyzed gas phase partial oxidations of organic compounds, the inert diluent gas used to ≥90 vol .-%, frequently to ≥95 vol .-% of N _2, H ₂ O and / or CO _2. On the one hand, the inert diluent gases used help to absorb the heat of reaction and, on the other hand, ensure safe operation of the heterogeneously catalyzed gas phase partial oxidation of an organic compound by keeping the reaction gas mixture outside the explosion range. In heterogeneously catalyzed gas phase partial oxidations of unsaturated organic compounds, saturated hydrocarbons, ie combustible gases, are frequently used as inert diluent gases.

frequently does not become the heterogeneously catalyzed gas phase partial oxidation in one, but in two or more cascaded Reactors performed (which in a common housing too seamlessly merge can). Both such series connections of oxidation reactors as well as individual for reactors used in this document are to be subsumed under the term "oxidation reactor system". In the same way, both a single device, a single Apparatus for separating the at least one target compound from the product gas mixture) of the partial oxidation used for itself is, as well as the series connection of such Abtrennapparate (Separators) referred to in this document as Abtrennsystem become. Neither the term oxidation reactor system nor the term Separation system includes parallel operation.

Usually now forms a series connection of an oxidation reactor system (a reactor line) and a separation system (a reprocessing line) a production system (a production line) for manufacturing organic target compounds by heterogeneously catalyzed gas phase partial oxidation at least one organic precursor compound with molecular Oxygen. In the oxidation reactor system, the at least one organic precursor compound, molecular oxygen and at least one inert diluent gas containing reaction gas starting mixture by at least one at increased Temperature fixed catalyst fixed bed out and in the separation system the target compound from the product gas mixture) of the partial oxidation separated as crude target product stream. If the separation system consists of several successive disconnecting devices (separating devices), thus, the product gas mixture) of the partial oxidation forms that of the first Separating device of the separation system supplied material flow. The last one Separating device of the separation system is constituting stream the raw target product stream and within the separation system of form upstream streams fed to downstream separators, as already stated, in this document "secondary streams".

One from more than one reactor existing oxidation reactor system used especially when the partial oxidation in successive Steps takes place. In these cases it is common appropriate, both the catalyst as well as the other reaction conditions at the adapt optimizing reaction step, and the respective Reaction step in a separate reactor zone or in its own Reactor to perform. Typically, such a multi-stage oxidation reactor system will become z. B. used in the partial oxidation of propylene to acrylic acid. In the first reaction zone (in the first reactor, in the first reaction stage) the propylene becomes acrolein, and in the second reaction zone (in the second reactor, in the second reaction stage) the acrolein to acrylic acid oxidized. In a similar way, as a rule, the methacrylic acid production, mostly starting from iso-butene, in two series Reaction zones (in two reactors connected in series) performed.

Of course you can in an oxidation reactor system, the reaction gas mixture between cooled two consecutive oxidation reactors and / or with molecular oxygen (e.g., by air addition) and / or inert gas added become. Both aforementioned partial oxidation can also in so-called Single reactor systems carried out where the two are using different catalysts fed successive reaction zones in a single, then usually two temperature zones having, reactor housed are. Both aforementioned partial oxidation can, when using suitable Catalysts but also in a single, only one temperature zone having carried out reactor become.

A Series connection of multiple oxidation reactors is often but also applied for reasons the heat dissipation or for other reasons (see DE-A 199 02 562) the conversion to several cascaded Blur reactors. Typically, heterogeneously catalyzed Gas-phase partial oxidations in tube bundle reactors carried out, as they are e.g. in the German application DE-A 10 2004 025 445 are executed.

The Separation system for by heterogeneously catalyzed partial oxidation of propane and / or Propylene produced acrylic acid typically consists of a series connection of Direct cooling, Absorption, stripping, rectifications) and optionally crystallizations) (See, for example, DE-A 103 36 386 and US-A 2004/0242826).

While it structurally relatively simple, separation apparatuses for large production capacities to disposal to put, push Oxidation reactors here earlier on borders. This is touching causal therefore, that heterogeneously catalyzed gas-phase partial oxidations usually pronounced exothermic. this leads to to the fact that with increasing production size of a single reactor the Task of adequate heat dissipation becomes unmanageable.

From Process Economics Program Report No. 6C, Acrylic Acids and Acrylic Esters, SRI International, Menlo Park California 94025 (1987), pages 1 to 40 is therefore known to operate in parallel for the production of acrylic acid two reactor lines, each of which consists of a series connection of a one-stage reactor (propylene → acrolein) and a two-stage reactor (acrolein → acrylic acid). This is also referred to as parallel operation of two tandem reactor arrangements. The product gas leaving the respective tandem reactor arrangement is then mixed with the product gas leaving the parallel operated tandem reactor system to form a mixture stream and this mixture stream is subsequently conducted to separate the acrylic acid into only one separation line (workup line) common to the two reactor lines. The above operation also recommends 6 WO 01/96271 and DE-A 199 02 562 it is referred to as a classic parallel circuit and again exemplified. The above-mentioned SRI report was also part of the public opposition proceedings against the patents EP-B 700 714 and EP-B 700 893 and in US-A 2004/0242826 the opponent attempts to regain the patent for the classic parallel connection.

adversely at the classic parallel circuit, where the catalyst feeds both reactor lines both in parallel commissioned as well subsequently operated in parallel, however, is that both the target product selectivity as well as by-product selectivity in both reactor lines over their Develop operating time synchronously.

Typically, such operating times of catalyst feeds for heterogeneously catalyzed gas phase partial oxidations, depending on the catalyst system and partial oxidation, will be several months to several years. A target and by-product selectivity of classically parallel partial oxidation catalyst feeds that develop synchronously over such operating periods is disadvantageous in that both the target product selectivity and the by-product selectivities of the catalyst feeds generally do not remain constant over the stated operating times. Rather, in many cases, target product selectivity decreases over time and by-product selectivity increases. However, cases are also known in which the target product selectivity increases over the operating time of the catalyst feed and the by-product selectivity decreases. The above also applies if, as recommended in EP-A 990 636 and EP-A 1 106 598, the aging of the catalyst bed is counteracted by the fact that the operating temperature of the catalyst bed remains constant during the operating time of the catalyst bed under otherwise largely constant operating conditions is gradually increased (which usually causes an acceleration of the aging process at the same time) and / or if, as recommended in EP-A 614 872 and in DE-A 103 50 822, the catalyst charge is regenerated from time to time. Both the partial catalyst change recommended in DE-A 102 32 748 and the variation of the working pressure recommended in the German application DE-A 10 2004 025 445 can not remedy the above-mentioned problem of the change in selectivity.

A in such a way over the However, operating time associated with selectivity change forms one Burden for the above the time required performance the separation road. Is the by-product selectivity small, It can be kept low in order to complete the separation task satisfactory way to solve. Is the by-product selectivity large, the Abtrennstrasse must be elaborately designed to the then more difficult separation task satisfactory to solve.

varies the by - product selectivity over the Operating time, the design of the separation line must be classic Parallel operation therefore at the highest while orient the by-product selectivity achieved over the entire operating time, around during the total operating time (until changing the catalyst charge) the raw target product to produce with the required purity. That is, the design the separation road must with highest Effort made. The latter is economically burdening. The task of the present invention has therefore been e.g. in it, as at the beginning described method for producing at least one organic Target compound by heterogeneously catalyzed gas-phase partial oxidation at least one organic precursor compound with molecular Oxygen available to provide, which is less expensive economically.

• a) heterogen katalysierte Gasphasen-Partialoxidation wenigstens einer organischen Vorläuferverbindung mit molekularem Sauerstoff in wenigstens zwei parallel betriebenen, Katalysatorbeschickungen enthaltenden, Oxidationsreaktorsystemen unter Erhalt von wenigstens zwei die Zielverbindung jeweils enthaltenden und jeweils auf eines der wenigstens zwei Oxidationsreaktorsysteme zurückgehenden Produktgas(gemisch)strömen und
• b) anschließende Abtrennung der wenigstens einen Zielverbindung aus den wenigstens zwei Produktgas(gemisch)strömen unter Erzeugung von wenigstens einem Roh-Zielproduktstrom, bei dem man
• c) vor der Abtrennung wenigstens zwei der wenigstens zwei Produktgas(gemisch)ströme, oder im Verlauf der Abtrennung wenigstens zwei der auf dem Weg von den wenigstens zwei Produktgas(gemisch)strömen zu dem wenigstens einen Roh-Zielproduktstrom gegebenenfalls erzeugten Zielprodukt enthaltenden Folgeströme und/oder nach der Abtrennung aus den wenigstens zwei Produktgas(gemisch)strömen im Verlauf der Abtrennung gegebenenfalls erzeugte Roh-Zielproduktströme zu einem Gemischsstrom miteinander vermischt, gefunden, das dadurch gekennzeichnet ist, dass wenigstens eine der Katalysatorbeschickungen der wenigstens zwei parallel betriebenen Oxidationsreaktorsysteme eine Katalysatorteilmenge (bezogen auf die Katalysatorbeschickung vorzugsweise wenigstens 20 Gew.-%, bzw. wenigsten 40 Gew.-%, besser wenigstens 60 Gew.-%, noch besser wenigstens 80 Gew.-% und am besten wenigstens die Gesamtmenge der Katalysatorbeschickung) enthält, an der die heterogen katalysierte Gasphasen-Partialoxidation bereits länger durchgeführt wird, als an allen Katalysatorteilmengen der wenigstens einer anderen Katalysatorbeschickung.

Accordingly, a process for producing at least one organic target compound has been accomplished

• a) heterogeneously catalyzed gas phase partial oxidation of at least one organic precursor compound with molecular oxygen in at least two parallel, catalyst feeds containing Oxidationsreaktorsystemen to obtain at least two the target compound each containing and each on one of the at least two oxidation reactor systems going back product mixture (mixture) and
• b) subsequent separation of the at least one target compound from the at least two product gas (mixture) streams to produce at least one crude target product stream in which
• c) before the separation at least two of the at least two product gas (mixture) streams, or in the course of the separation at least two of the at least two product gas (mixture) flow to the at least one raw target product stream optionally generated target product containing subsequent streams and / or or after the separation from the at least two product gas (mixture) in the course of separation optionally generated raw target product streams mixed together to form a mixture stream found, which is characterized in that at least one of the catalyst feeds the at least two parallel operated oxidation reactor systems a partial amount of catalyst (relative preferably at least 20% by weight, or at least 40% by weight, more preferably at least 60% by weight, more preferably at least 80% by weight and most preferably at least the total amount of catalyst charge) to which the catalyst feed contains heterogeneously catalyzed gas-phase partial oxidation is performed longer than at all catalyst portions of the at least one other catalyst charge.

As a rule, the number of oxidation reactor systems operated in parallel in the process according to the invention in the process according to the invention (that is, the oxidation reactor systems in which the target compounds present in the mixture stream were formed) is two. This number can also be three, four, five or more. Furthermore, the oxidation reactor systems operated in parallel in accordance with the invention in the process according to the invention will preferably be of identical reactor design. That is, they are preferably for the same production capacity of target product and this in the same way and Way designed. In the case of tube bundle reactors this means that their contact tubes are usually of the same nature and substantially the same number. The same applies to the applied principle of heat dissipation.

Basically, the in the method according to the invention in accordance with the invention but also operated from each other in parallel oxidation reactor systems to be different. This is true in the case of tube bundle reactors e.g. both in terms of of different contact tube properties (e.g., length, wall thickness, Inner diameter, length, Material) and with respect to each different number of contact tubes. Also can the invention in parallel operated oxidation reactor systems of completely different types be. As a rule, the feed gas mixture of the invention is parallel be operated identical oxidation reactor systems. That is, both the composition of the feed gas mixture as well as the loads the catalyst feeds in the oxidation reactor systems with Feed gas mixture is normally parallel in accordance with the invention be operated equal oxidation reactor systems.

that is, one can e.g. first a total stream of the at least one organic precursor compound produce starting reaction gas mixture and this then via a Distribution system the at least two parallel operated oxidation reactor systems (e.g., those for partial oxidation of acrylic acid).

While you are in the above variant in natural Only one air compressor (which also the possibly needed secondary air is removed) and only a cycle gas compressor (according to the invention preferred only one recycle gas remains in the target product separation) for the at least two oxidation reactor systems operated in parallel (Preferred are radial compressors according to DE-A 10353014, wherein the compression of the circulating gas and the air in two separate compressors, the be driven by two separate motors, or in two compressors, which are powered by a motor, or in a single with a compressor driven by a motor), it is expedient according to the invention, too then only one air compressor (which also takes the secondary air that may be needed and apply only one cycle gas compressor if the starting reaction gas mixture for each the at least two oxidation reactor systems operated in parallel spatial is mixed separately. In that case you will be the condensed one Gases e.g. keep in lines, from same the respective static Add mixer and there with organic under appropriate pressure precursor bond to the respective starting reaction gas mixture for the respective oxidation reactor system mix.

Of the Entry of the individual gases into the line supplied to the static mixer is doing in a useful manner often chosen so that the formation of explosive mixtures is avoided (in the case a partial oxidation of propylene to e.g. Acrolein and / or acrylic acid could do this Entry sequence in an appropriate manner e.g. first Circle gas and / or water vapor, then (raw) propene and then air). The individually produced reaction gas starting mixture is then the each associated with him oxidation reactor system of at least fed to two parallel operated oxidation reactor systems.

Under the loading of a catalyst bed catalyzing a reaction step with reaction gas (exit) mixture is in this document the Quantity of reaction gas (outlet) mixture in standard liters (= Nl; Volume in liters, which is the corresponding reaction gas (outlet) mixed amount under normal conditions, i.e. at 25 ° C and 1 bar), which is passed through one liter of catalyst bed per hour. The load can only on one part of the reaction gas (exit) mixture be related. Then it is the amount of this ingredient in Nl / l · h that per hour through one liter of the catalyst bed. Pure inert material cuts do not become a catalyst bed expected.

The same applies to the working pressure and the working temperature in the invention in parallel operated oxidation reactor systems. Of course, the aforementioned parameters (composition of the feed gas mixture (with the same precursor compound and the same target product), loading of the catalyst feeds with organic precursor compound or reaction gas mixture, working temperature, working pressure) but also individually or in groups of different from each other. By type (that is, in their chemical and physical nature) the catalyst charge in the invention is parallel often be identical to operating oxidation reactor systems (apart from the differences due to different operating times). The invention in parallel operated oxidation reactor systems can also be used with catalysts be loaded of different types.

Substantially according to the invention is that at least one of the relevant catalyst feeds (These are the catalyst feeds to those in the mixture stream the target compounds have been formed) of the at least two parallel according to the invention operated oxidation reactor systems at least a partial amount of catalyst contains at the heterogeneously catalyzed gas phase partial oxidation already over a longer period carried out is, as at all catalyst portions of at least one other Catalyst charge.

This inventive feature is in a simple manner e.g. This can be realized by first of all at least two oxidation reactor systems, e.g. an identical load with catalyst, in parallel with e.g. identical feed gas mixture and under identical other reaction conditions in operation takes and over longer Time is running. falls the selectivity target product formation with increasing service life due to aging the catalyst charge (e.g., to a level appropriate for target product separation in terms of the desired Purity of the crude target product would be prohibitive), one can the operation of the invention e.g. in a simple way achieve that only in one of the at least two oxidation reactor systems operated in parallel a partial catalyst change e.g. according to DE-A 102 32 748 performs. After that the parallel operation can be continued in accordance with the invention. The target product separation is only burdened with by-product mixing selectivity and can continue to produce the desired raw product To produce purity.

On that way the lifetime of that catalyst feed, at the no Catalyst part change was made, without additional expense significantly extend. Of course you can instead only a subset of a catalyst charge to replace with fresh catalyst, also the total of these Replace catalyst feed with fresh catalyst and subsequently Continue according to the invention.

According to the invention advantageous one will see the product gas (mixture) flows of at least two in accordance with the invention parallel operated oxidation reactor systems prior to their entry into the first device of the target product separation to a mixture stream unite. Of course may target product separation in the process of the invention but first also in e.g. corresponding manner as the at least two parallel operated oxidation reactor systems to be executed in parallel. This may be advantageous if the target product separation consists of several series-connected separators, only one of which is particularly investment-intensive or to others Way is critical. It may now be useful according to the invention, the target product separation to the particularly costly (critical) Abtrennapparat to execute in parallel, and then the corresponding target product containing subsequent streams then to combine to a mixture stream to this mixture then stream only still to supply a critical separator. Behind this separator becomes the parallel version if necessary continuing Target product separation preferably reversed in a corresponding manner be.

on the other hand may target product separation in the process of the invention but also until the raw target product streams accumulate in parallel accomplished be. In this case, according to the invention, crude target product streams are normally obtained, have the different impurity levels. During one from both the pollution specification required by the market if necessary, it fulfills the other raw target product stream may not be. If one blends both raw target product streams, can a crude target product stream can be obtained in its total amount is in accordance with specifications.

Become three oxidation reactor systems operated in accordance with the invention in parallel, can e.g. instead of the product gas (mixed) streams from all three systems to unify and work up the resulting mixture, too only two of the three product gas (mixed) streams combined and mixed be worked up. The processing of the third product gas stream can be done separately and then the two accruing Crude target product streams to be mixed u.s.w ..

However, a different operating time of the catalyst feeds of at least two oxidation reactor systems operated in parallel can also be adjusted (eg also by appropriate time-delayed startup of the fresh catalyst feeds) by operating the catalyst feeds continuously or during a scheduled period of time at different temperatures and / or different loads with precursor compound , That is, the invention relevant measure of the service life of a catalyst feed is only in the case of identical operating conditions and identical catalyst feed type the time in the chronometric sense. Otherwise it is the target product quantity already produced at the catalyst feed. The more target product has already been produced on the catalyst feed, the greater its perceived age. In the case of a multi-level, over at least one Intermediate extending, heterogeneously catalyzed gas phase partial oxidation is considered as a measure of the service life of the catalyst charge, on which the intermediate formation takes place, in a corresponding manner, the total amount of this feed already produced intermediate amount.

in the This would be the case of a two-stage production of acrylic acid from propylene for the Catalyst charge of the first reaction stage e.g. the total acrolein already formed on this catalyst feed.

in the Case of a two-stage production of methacrylic acid iso-butene would be this for the catalyst feed of the first reaction stage e.g. the total amount of methacrolein already formed on this catalyst feed. For the Catalyst feeds of the second reaction stage would be the corresponding one Measure of the operating length the at the respective catalyst feed already formed amount of acrylic acid or methacrylic acid.

that is, from the procedure according to the invention makes in the case of in at least two parallel operated oxidation reactor systems conducted multistage heterogeneously catalyzed gas-phase partial oxidation even the one already in use, after a certain period of use only in a single oxidation state of the relevant oxidation reactor system at least a portion of the catalyst charge (preferably at least 20% by weight, more preferably at least 40% by weight, more preferably at least 60 wt .-%, or at least 80 wt .-% and most preferably 100 wt .-% based on the catalyst charge) replaced by fresh catalyst and subsequently continued according to the invention. in the Case of a two-stage production of acrylic acid from propylene can this Partial or full catalyst change, e.g. only in the reaction stage "propylene → acrolein" in one of the relevant carried out at least two parallel oxidation reactor systems become. Naturally But he can also in both reaction stages in one of the relevant carried out at least two parallel oxidation reactor systems become. But according to the invention is also conceivable that the partial and Vollkatalysatorwechsel in the one of the relevant at least two parallel operated oxidation reactor systems only in the first reaction stage and in the other of the relevant at least two oxidation reactor systems operated in parallel only in the second reaction stage.

Does that grow? selectivity the target product formation with increasing service life of the catalyst feed and decreases with increasing operating time only their activity can be proceeded in a similar manner.

So you can see the relevant at least two parallel operated oxidation reactor systems each with fresh catalyst feeds initially for some Operate time under identical conditions and the mixture flow the at least two product gas streams in a single separation system respectively. The latter can be designed so that it is based on the initially high selectivity the by-product formation first a crude target product stream with comparatively low purity generated. For example, this crude target product stream may be a crude acrylic acid, used only for the preparation of alkyl esters (for example butyl, Methyl, ethyl or 2-ethylhexyl ester) is reusable. Leading subsequently in the sense of the invention a partial or Vollkatalysatorwechsel, is in the further Course of the operation of the invention a mean target product selectivity in the mixture of the relevant at least two product gas streams obtained in the same separation system to a crude target product stream with comparatively elevated Purity leads. For example, this crude target product stream may then be a "pure" acrylic acid, for the production of superabsorbent polyacrylic acids or their sodium salts are suitable.

Of course you can you too first produced less specification-compliant raw acrylic acid in one huge Store tank and with subsequent, the desired specification over-fulfilling raw acrylic acid to one specification-compliant raw acrylic acid total Mix.

from inventive method but it is also used when the relevant at least two parallel oxidation reactor systems with catalyst feeds are fed, one of which is the target connection with over the Operating time of increasing selectivity and the other the target compound with more than the service life of decreasing selectivity forms. That way are in the at least two catalyst feeds already after a short time chronometical operating time different target product quantities has been formed and thus in the sense of the invention "different" operating lives of achieved both catalyst feeds.

In the case of a multistage heterogeneously catalyzed gas phase partial oxidation according to the invention According to the invention, it is advantageous for at least one organic precursor compound to already combine the product gas streams of the relevant at least two first reaction stages operated in parallel into a mixture stream (as is already practiced in the classic parallel arrangement of DE-A 199 02 562) and with this, if appropriate by inert gas and / or molecular oxygen supplements that feed and operate at least two subsequent reaction stages in parallel.

Basically suitable the process of the invention for all At the beginning of this document specifically listed heterogeneously catalyzed Gas phase partial oxidations. This includes in particular the in the documents WO 01/96270, DE-A 103 16 465, DE-A 102 45 585 and DE-A 102 46 119 heterogeneously catalyzed example described Gas phase partial oxidation of propane to acrylic acid. The aforementioned publications should as well as the US-A 2004/0242826 and DE-A 103 36 386 as an integral part of this document. in principle the procedure according to the invention is suitable also for carried out in the catalyst fluidized bed heterogeneously catalyzed Partial oxidations.

According to the invention advantageous you can the heterogeneous invention catalyzed gas phase partial oxidation of at least one organic precursor compound with molecular oxygen also in at least two parallel operated Tube reactors perform according to the invention of the one over the Reactor viewed in cocurrent to the reaction gas mixture and the others over considered the reactor operated in countercurrent to the reaction gas mixture becomes. The latter leads usually accelerated aging of the catalyst charge, if apart from the directional approach under otherwise identical Conditions is operated.

According to the invention advantageous should in the inventive method at least one of the relevant catalyst feeds of at least two parallel oxidation reactor systems at least one Catalyst subset (in the case of a multi-stage partial oxidation e.g. the total catalyst amount of the first and / or the second Reaction stage, or subsets of catalyst feeds the first and / or second reaction stage) containing the heterogeneous catalyzed gas partial oxidation already at least 30 calendar days, preferably at least 60 calendar days or at least 90 calendar days, and more preferably at least 120 or at least 150 calendar days, and most preferably at least 180 calendar days or at least 210 or 240 calendar days longer as at all catalyst portions of the other catalyst feed.

Inventive method but are also those in which the aforementioned operating time difference at least 270, or at least 300, or at least 330, or at least 360, or at least 400, or at least 450, or at least 500, or at least 550, or at least 600, or at least 700, or at least 800, or at least 900, or at least 1000 days, or at least 2000 days, or at least 3000 days or more. As a general rule he will not be more than three years or 1000 days, usually not more be two years or 750 days.

Expressed in total at this total amount of catalyst already produced more total amount of target product or intermediate product of the aforementioned operating time difference least 10 ⁶ kg, or at least 2 x 10 ⁶ kg, or at least 3 x 10 ⁶ kg, or at least 4 x 10 ⁶ kg, or at least 5 x 10 ⁶ kg, or at least 6 x 10 ⁶ kg, or at least 7 x 10 ⁶ kg, or at least 8 x 10 ⁶ kg, or at least 9 x 10 ⁶ kg, or at least 10 ⁷ kg, or at least 1.5 · 10 ⁷ kg, or at least 2 · 10 ⁷ kg, or at least 3 · or 4 · 10 ⁷ kg, or at least 5 · 10 ⁷ kg, or at least 6 · 10 ⁷ kg, or at least 7.10 ⁷ kg, or at least 8 · 10 ⁷ kg, or at least 10 ⁸ kg, or at least 2 x 10 ⁸ kg, or at least 3 x 10 ⁸ kg, or at least 4 x 10 ⁸ kg. Normally, the aforementioned operating time difference will not be more than 10 ⁹ kg, usually not more than 0.5 × 10 ⁹ kg, and often not more than 10 ⁸ kg.

According to the invention of importance is that already minor changes the selectivity the by-product formation the extraction of specification-compliant Raw product significantly more difficult. A typical example is the propionic acid as a by-product of acrylic acid. To sell on the market to be, should be acrylic acid not more than e.g. 800 ppm by weight of propionic acid (depending on the intended use) contain. Similar Limit values apply in the case of acrylic acid, e.g. for formaldehyde and acetic acid as By-product impurities. In many cases, the selectivity of target product formation changes in heterogeneously catalyzed gas-phase partial oxidations within the first three months after commissioning the catalyst feed by at least 0.1 or 0.2 mol%, or by at least 0.3 or 0.5 mol%, or at least 1 mol% or at least 1.5 mol%, or by at least 2 mol%, in some cases even by at least 3 or at least 4 or at least 7 mol%. The overall selectivity of minor component formation changes usually in the same period accordingly many times also at least 0.1 to 7 mol% and more.

Accordingly, in inventive method the difference of the relevant at least two parallel operated Catalyst feeds in the selectivity of target product formation (e.g. Acrylic acid formation) e.g. up to 7 mol% or more (e.g., 0.1, or 0.2, or 0.3 to 7 mol%) and the difference in the overall eletkivität of Ne benkomponentenbildung also up to 7 mol% or more (e.g., 0.1, or 0.2, or 0.3 to 7 mol%).

In However, the procedure according to the invention is particularly suitable for the preferably in the Tube reactor single stage heterogeneously catalyzed fixed bed gas phase partial oxidation of propene to acrolein and / or acrylic acid and for the first and second stage of a two-stage heterogeneous in tube bundle reactors catalyzed fixed bed gas phase partial oxidation of propene via acrolein Acrylic acid, as they are e.g. in EP-A 700 893, EP-A 700 714, DE-A 199 10 508, DE-A 199 10 506, DE-A 103 51 269, DE-A 103 50 812, DE-A 103 50 822, EP-A 11 59 247, DE-A 103 13 208, DE-A 10 2004 021 764, DE-A 199 48 248, EP-A 990 636, EP-A 11 06 598, DE-A 30 02 829 and DE-A 102 32 482 are described.

The inventive method is suitable for a heterogeneously catalyzed gas phase fixed bed partial oxidation of Propene to acrolein especially when as catalysts such used, the active mass of a multielement oxide, the Elements molybdenum and / or tungsten and at least one of the elements bismuth, tellurium, Contains antimony, tin and copper or a multimetal oxide containing the elements Mo, Bi and Fe is. Particularly according to the invention suitable Mo, Bi and Fe-containing multimetal oxide of the aforementioned Species are mainly those in DE-A 10 34 4149 and in DE-A 10 34 4264 disclosed Mo, Bi and Fe containing multimetal oxide. These are in particular also the multimetal oxide active compounds of the general Formula I in DE-A 19 95 5176, the Multimetalloxidaktivmassen the general formula I of DE-A 19 94 8523, the Multimetalloxidaktivmassen of the general formulas I, II and III of DE-A 10 10 1695, the multimetal oxide active compositions the general formulas I, II and III of DE-A 19 94 8248 and the Multimetal oxide active compounds of the general formulas I, II and III DE-A 19 95 5168 and mentioned in EP-A 700 714 Multimetalloxidaktivmassen.

Furthermore, an application of the method according to the invention, if for the invention to be used at least two fixed catalyst beds in the case of the partial oxidation of propene to acrolein the Mo, Bi and Fe containing multimetal oxide, which in the DE-A 10 04 6957, DE-A 10 06 3162, DE-C 33 38 380, DE-A 19 90 2562, EP-A 15 565, DE-C 23 80 765, EP-A 807 465, EP-A 279 374, DE-A 33 00 044, EP-A 575 897, US Pat. No. 4,438,217, DE-A 19 85 5913, WO 98/24746, DE-A 19 74 6210 (those of the general formula II), JP-A 91/294 239, EP-A 293 224 and EP-A 700 714 are used. This applies in particular to the exemplary embodiments in these documents, among which those of EP-A 15565, EP-A 575 897, DE-A 19 74 6210 and DE-A 19 85 5913 are particularly preferred. Of particular note in this context are a catalyst according to Example 1c from EP-A 15 565 and a catalyst to be prepared in a corresponding manner, the active composition but the composition Mo ₁₂ Ni _6.5 Zn ₂ Fe ₂ Bi ₁ P _0.0065 K _{0, 06} Ox · 10 SiO ₂ . Further mention should be made of the example with the serial number 3 from DE-A 19855913 (stoichiometry: Mo ₁₂ Co ₇ Fe ₃ Bi _0.6 K _0.08 Si _1.6 Ox) as a hollow cylinder full catalyst of the geometry 5 mm × 3 mm × 2 mm or 5 mm × 2 mm × 2 mm (outer diameter × height × inner diameter) and the multimetal oxide II - full catalyst according to Example 1 of DE-A 19 74 6210. Further, the multimetal oxide catalysts of US-A 4438217 should be mentioned , The latter applies in particular if this is a hollow cylinder geometry of the dimensions 5.5 mm × 3 mm × 3.5 mm, or 5 mm × 2 mm × 2 mm, or 5 mm × 3 mm × 2 mm, or 6 mm × 3 mm × 3 mm, or 7 mm × 3 mm × 4 mm (outer diameter × height × inner diameter). Likewise suitable in the context of the invention are the multimetal oxide catalysts and geometries of DE-A 10 10 1695 or WO 02/062737.

Furthermore, the example 1 from DE-A 10046957 (stoichiometry: [Bi ₂ W ₂ O ₉ × 2WO ₃ ] _0.5 × [Mo ₁₂ Co _5.6 Fe _2.94 Si _1.59 K _0.08 O _x ] ₁ ) as a hollow cylinder (ring) full catalyst of the geometry 5 mm × 3 mm × 2 mm or 5 mm × 2 mm × 2 mm (each outer diameter × length × inner diameter), and the shell catalysts 1, 2 and 3 from the DE A 10063162 (stoichiometry: Mo ₁₂ Bi _1.0 Fe ₃ Co ₇ Si _1.6 K _0.08 ), but as annular shell catalysts of appropriate shell thickness and on carrier rings of geometry 5 mm × 3 mm × 1.5 mm or 7 mm × 3 mm × 1.5 mm (each outer diameter × length × inner diameter) applied, well suited in the sense of the invention.

A large number of multimetal oxide active compositions which are particularly suitable for the catalysts of a propene partial oxidation to acrolein in the context of the invention can be obtained under the general formula 1 Mo ₁₂ Bi _a Fe _b X ¹ _c X ² _d X ³ _e X ⁴ _f O _n (I) in which the variables have the following meaning:
X ¹ = nickel and / or cobalt,
X ² = thallium, an alkali metal and / or an alkaline earth metal,
X ³ = zinc, phosphorus, arsenic, boron, antimony, tin, cerium, lead and / or tungsten,
X ⁴ = silicon, aluminum, titanium and / or zirconium,
a = 0.5 to 5,
b = 0.01 to 5, preferably 2 to 4,
c = 0 to 10, preferably 3 to 10,
d = 0 to 2, preferably 0.02 to 2,
e = 0 to 8, preferably 0 to 5,
f = 0 to 10 and
n = a number which is determined by the valence and frequency of the elements other than oxygen in I,
subsume.

she are available in a manner known per se (see, for example, DE-A 4023239) and are customary in substance to spheres, rings or cylinders shaped or in Shape of shell catalysts, i.e. coated with the active composition preformed, inert support bodies used. Of course can you but also be used in powder form as catalysts.

In principle, active compounds of the general formula I can be prepared in a simple manner by producing a very intimate, preferably finely divided, stoichiometrically composed, dry mixture of suitable sources of their elemental constituents and this calcined at temperatures of 350 to 650 ° C. The calcination can be carried out both under inert gas and under an oxidative atmosphere such as air (mixture of inert gas and oxygen) and under a reducing atmosphere (eg mixture of inert gas, NH ₃ , CO and / or H ₂ ). The calcination time can be several minutes to several hours and usually decreases with temperature. Suitable sources of the elemental constituents of the multimetal oxide active compounds I are those compounds which are already oxides and / or those compounds which can be converted into oxides by heating, at least in the presence of oxygen.

In addition to the oxides, suitable starting compounds in particular are halides, nitrates, formates, oxalates, citrates, acetates, carbonates, amine complexes, ammonium salts and / or hydroxides (compounds such as NH ₄ OH, (NH ₄ ) ₂ CO ₃ , NH ₄ NO ₃ , NH ₄ CHO ₂ , CH ₃ COOH, NH ₄ CH ₃ CO ₂ and / or ammonium oxalate, which can disintegrate and / or decompose into gaseous compounds at the latest during later calcination, can be additionally incorporated into the intimate dry mixture) ,

The intimately mixing the starting compounds to produce multimetal oxide active compositions I can be done in dry or wet form. Is it done in dry form, so the starting compounds are suitably used as finely divided powder and after mixing and optionally Compacting subjected to calcination. Preferably, this is done intimate mixing but in wet form. Usually, the Starting compounds in the form of an aqueous solution and / or suspension with each other mixed. Particularly intimate dry mixtures are described Mixing method then obtained, if only from in dissolved form present sources of elementary constituents. As a solvent Water is preferably used. Subsequently, the resulting aqueous mass dried, the drying process preferably by spray drying the aqueous Mixture with outlet temperatures from the spray tower of 100 to 150 ° C takes place.

Usually become the Multimetalloxidaktivmassen of the general formula I im Fixed catalyst bed not in powder form but to certain catalyst geometries molded, the shaping before or after the final calcination can be done. For example, you can from the powder form of the active composition or its uncalcined and / or partially calcined precursor by compacting to the desired Catalyst geometry (e.g., by tableting, extruding, or Extrusion) Vollkatalysatoren be prepared, where appropriate Aids such as e.g. Graphite or stearic acid as a lubricant and / or Molding aids and reinforcing agents such as glass microfibers, asbestos, silicon carbide or potassium titanate can be added. Suitable unsupported catalyst geometries are e.g. Solid cylinder or Hollow cylinder with an outer diameter and a length from 2 to 10 mm. In the case of the hollow cylinder is a wall thickness of 1 to 3 mm appropriate. Of course you can the full catalyst also have spherical geometry, wherein the ball diameter 2 to 10 mm can be.

A especially cheap Hollow cylinder geometry is 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter), especially in the case of full catalysts.

Of course you can the shape of the powdered Active mass or its powdery, yet non-calcined and / or partially calcined, precursor material also by application carried out on preformed inert catalyst support. The coating the carrier body to Preparation of the coated catalysts is usually in one suitable rotatable container executed as it is e.g. from DE-A 2909671, EP-A 293859 or from EP-A 714700 is known. Conveniently, is used to coat the carrier body moistened and applied after application, e.g. by means of hotter Air, dried again. The layer thickness of the applied to the carrier body Powder mass is expediently in the range 10 to 1000 μm, preferably in the range 50 to 500 microns and more preferably in the range 150 to 250 microns, selected. alternative The powder to be applied also directly from their suspension or solution out (e.g., in water) onto the substrates.

When support materials can usual porous or nonporous Aluminas, silica, thoria, zirconia, silicon carbide or silicates such as magnesium or aluminum silicate are used. They are behaving the method of the invention in the first reaction stage underlying target reaction in the Usually substantially inert. The carrier bodies can be shaped regularly or irregularly being regularly shaped Carrier body with clearly designed surface roughness, e.g. Spheres or hollow cylinders are preferred. Suitable is the Use of substantially non-porous, surface rough, spherical carriers Steatite (e.g., Steatite C220 from CeramTec), whose diameter 1 to 8 mm, preferably 4 to 5 mm. It is also suitable the use of cylinders as carrier bodies whose length is 2 to 10 mm (e.g., 8 mm) and its outer diameter 4 to 10 mm (e.g., 6 mm). In the case of suitable according to the invention Rings as a carrier body lies the wall thickness also usually at 1 to 4 mm. According to the invention preferred to be used annular Own carrier body a length from 2 to 6 mm, an outer diameter from 4 to 8 mm and a wall thickness of 1 to 2 mm. Suitable according to the invention are above all rings of geometry 7 mm × 3 mm × 4 mm or 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter) as a carrier body. The Fineness of the surface of the carrier body to be applied catalytically active oxide masses will of course be of the desired shell thickness adapted (see EP-A 714 700).

For the catalysts of the fixed catalyst bed of a Propenpartialoxidation to acrolein in the context of the invention particularly suitable Multimetalloxidaktivmassen are also compounds of general formula II, [Y ¹ _{a '} Y ² _b' O _{x '} ] _p [Y ³ _c' Y ⁴ _{d '} Y ⁵ _e' Y ⁶ _{f '} Y ⁷ _g' Y ² _{h '} O _y' (II) in which the variables have the following meaning:
Y ¹ = only bismuth or bismuth and at least one of the elements tellurium, antimony, tin and copper,
Y ² = molybdenum or molybdenum and tungsten,
Y ³ = an alkali metal, thallium and / or samarium,
Y ⁴ = an alkaline earth metal, nickel, cobalt, copper, manganese, zinc, tin, cadmium and / or mercury,
Y ⁵ = iron or iron and at least one of the elements chromium and cerium,
Y ⁶ = phosphorus, arsenic, boron and / or antimony,
Y ⁷ = a rare earth metal, titanium, zirconium, niobium, tantalum, rhenium, ruthenium, rhodium, silver, gold, aluminum, gallium, indium, silicon, germanium, lead, thorium and / or uranium,
a '= 0.01 to 8,
b '= 0.1 to 30,
c '= 0 to 4,
d '= 0 to 20,
e '> 0 to 20,
f '= 0 to 6,
g '= 0 to 15,
h '= 8 to 16,
x ', y' = numbers which are determined by the valence and frequency of the elements other than oxygen in II and
p, q = numbers whose ratio p / q is 0.1 to 10,
comprising three-dimensionally extended areas of the chemical composition Y ¹ _{a '} Y ² _b' O _{x '} defined by their local environment on the basis of their composition different from their local environment, whose maximum diameter (longest direct line passing through the centroid of the area) range of two points on the surface (interface) of the area) 1 nm to 100 μm, often 10 nm to 500 nm or 1 micron to 50 or 25 microns, is.

Particularly advantageous multimetal II are those in which Y ¹ is only bismuth.

Among these, in turn, those are preferred which are of the general formula III, [Bi _{a ''} Z ² _{b ''} O _{x ''} ] _{p ''} [Z ² ₁₂ Z ³ _{c ''} Z ⁴ _{d ''} Fe _{e ''} Z ⁵ _{f ''} Z ⁶ _{g ''} Z ⁷ _{h ''} O _y'' ] _q'' (III), in which the variants have the following meaning:
Z ² = molybdenum or molybdenum and tungsten,
Z ³ = nickel and / or cobalt,
Z ⁴ = thallium, an alkali metal and / or an alkaline earth metal,
Z ⁵ = phosphorus, arsenic, boron, antimony, tin, cerium and / or lead,
Z ⁶ = silicon, aluminum, titanium and / or zirconium,
Z ⁷ = copper, silver and / or gold,
a '' = 0.1 to 1,
b '' = 0.2 to 2,
c '' = 3 to 10,
d "= 0.02 to 2,
e "= 0.01 to 5, preferably 0.1 to 3,
f '= 0 to 5,
g '' = 0 to 10,
h '' = 0 to 1,
x '', y '' = numbers determined by the valency and frequency of the element other than oxygen in III,
p ", q" = numbers whose ratio p "/ q" is 0.1 to 5, preferably 0.5 to 2,
with those masses III being particularly preferred in which Z ² _{b "} = (tungsten) _b" and Z ² ₁₂ = (molybdenum) ₁₂ .

Furthermore, it is advantageous if at least 25 mol% (preferably at least 50 mol% and particularly preferably at least 100 mol%) of the total fraction [Y ¹ _{a '} Y ² _b' O _{x '} ] _p ([Bi _a'' Z ² _{b "} O _x" ] _{p "} ) of the multimetal oxide compositions II (multimetal oxide compositions III) which are suitable according to the invention in the multimetal oxide compositions II (multimetal oxide compositions III) which are suitable according to the invention in the form of three-dimensionally extended chemical substances which are different from their local environment because of their local environment Composition of demarcated, areas of chemical composition Y ¹ _{a '} Y ² _b' O _{x '} [Bi _a'' Z ² _b'' O _x'' ) are present, the largest diameter in the range 1 nm to 100 microns.

Regarding the shaping applies with respect Multimetal oxide II catalysts in the case of the multimetal oxide materials I catalysts said.

The Preparation of multimetal oxide compositions II-active compositions is e.g. in EP-A 575897 and in DE-A 19855913, DE-A 10344149 and DE-A 10344264 described.

When Active mass for Catalysts of at least one for the partial oxidation of acrolein to acrylic acid suitable catalyst fixed bed are suitable in the sense of the invention the for This type of reaction known multimetal oxides containing the elements Mo and V included.

Such For example, Mo and V-containing multimetal oxide active compositions may be used US-A 3775474, US-A 3954855, US-A 3893951 and US-A 4339355 or EP-A 614872 or EP-A 1041062 or WO 03/055835 or WO 03/057653 are taken.

Especially The multimetal oxide active compounds of DE-A 10 32 5487 are also suitable and DE-A 10 325 488.

Further are suitable for the partial oxidation of acrolein to acrylic acid in the sense of the invention in a special way, the multimetal oxide compositions of EP-A 427508, the DE-A 29 09 671, DE-C 31 51 805, DE-AS 26 26 887, DE-A 43 02 991, EP-A 700 893, EP-A 714 700 and DE-A 19 73 6105 as active masses for the fixed bed catalysts. Particularly preferred in this context the exemplary embodiments EP-A 714 700 and DE-A 19 73 6105.

A multiplicity of these multimetal oxide active compounds comprising the elements Mo and V can be classified under the general formula IV Mo ₁₂ V _a X ¹ _b X ² _c X ³ _d X ⁴ _e X ⁵ _f X ⁶ _g O _n (IV) in which the variables have the following meaning:
X ¹ = W, Nb, Ta, Cr and / or Ce,
X ² = Cu, Ni, Co, Fe, Mn and / or Zn,
X ³ = Sb and / or Bi,
X ⁴ = one or more alkali metals,
X ⁵ = one or more alkaline earth metals,
X ⁶ = Si, Al, Ti and / or Zr,
a = 1 to 6,
b = 0.2 to 4,
c = 0.5 to 18,
d = 0 to 40,
e = 0 to 2,
f = 0 to 4,
g = 0 to 40 and
n = a number determined by the valence and frequency of the elements other than oxygen in IV,
subsume.

Preferred embodiments within the active multimetal oxides IV in the context of the invention are those which are covered by the following meanings of the variables of general formula IV:
X ¹ = W, Nb, and / or Cr,
X ² = Cu, Ni, Co, and / or Fe,
X ³ = Sb,
X ⁴ = Na and / or K,
X ⁵ = Ca, Sr and / or Ba,
X ⁶ = Si, Al, and / or Ti,
a = 1.5 to 5,
b = 0.5 to 2,
c = 0.5 to 3,
d = 0 to 2,
e = 0 to 0.2,
f = 0 to 1 and
n = a number determined by the valence and frequency of the elements other than oxygen in IV.

Very particularly preferred multimetal oxides IV, however, in the context of the invention are those of the general formula V Mo ₁₂ V _{a '} Y ¹ _b' Y ² _{c '} Y ⁵ _f' Y ⁶ _{g '} O _n (V) With
Y ¹ = W and / or Nb,
Y ² = Cu and / or Ni,
Y ⁵ = Ca and / or Sr,
Y ⁶ = Si and / or Al,
a '= 2 to 4,
b '= 1 to 1.5,
c '= 1 to 3,
f '= 0 to 0.5
g '= 0 to 8 and
n '= a number which is determined by the valence and frequency of the elements other than oxygen in V.

Multimetal oxide active compositions (IV) are obtainable in a manner known per se, for example as disclosed in DE-A 43 35 973 or in EP-A 714 700. Particularly suitable as Mo and V containing Multimetalloxidak tivmassen in the inventive sense for the partial oxidation of acrolein to acrylic acid but also the Multimetalloxidaktivmassen of DE-A 10 261 186.

In principle, such Mo and V containing Multimetalloxidaktivmassen, in particular those of the general formula IV, can be prepared in a simple manner by suitable sources of their elemental constituents an intimate, preferably finely divided, their stoichiometry correspondingly assembled, dry mixture and this at temperatures of Calcined 350 to 600 ° C. The calcination can be carried out both under inert gas and under an oxidative atmosphere such as air (mixture of inert gas and oxygen) and under reducing atmosphere (eg mixtures of inert gas and reducing gases such as H ₂ , NH ₃ , CO, methane and / or acrolein or The calcination period can be from a few minutes to a few hours and usually decreases with temperature. Suitable sources of the elemental constituents of the multimetal oxide active compositions IV are those compounds which are already oxides and / or those compounds which can be converted into oxides by heating, at least in the presence of oxygen.

The intimate mixing of the starting compounds for the preparation of multimetal oxide materials IV can be done in dry or wet form. Is it done in dry form, so the starting compounds are suitably used as finely divided powder and after mixing and optionally Compacting subjected to calcination. Preferably, this is done intimate mixing but in wet form.

Usually be the starting compounds in the form of an aqueous solution and / or suspension mixed together. Especially intimate dry mixtures are then obtained in the described mixing method, if only from in dissolved Form present sources of elementary constituents becomes. As a solvent Water is preferably used. Subsequently, the resulting aqueous mass dried, the drying process preferably by spray drying the aqueous Mixture with outlet temperatures of 100 to 150 ° C takes place.

The Mo and V containing Multimetalloxidaktivmassen, especially those the general formula IV, can for the inventive method a partial oxidation of acrolein to acrylic acid both in powder form as can also be used shaped to specific catalyst geometries, wherein the shaping takes place before or after the final calcination can. For example, you can from the powder form of the active composition or its uncalcined precursor composition by compacting to the desired Catalyst geometry (e.g., by tableting, extruding, or Extrusion) Vollkatalysatoren be prepared, where appropriate Aids such as e.g. Graphite or stearic acid as a lubricant and / or Molding aids and reinforcing agents such as glass microfibers, asbestos, silicon carbide or potassium titanate can be added. suitable Full catalyst geometries are e.g. Solid cylinder or hollow cylinder with an outer diameter and a length from 2 to 10 mm. In the case of the hollow cylinder is a wall thickness of 1 to 3 mm appropriate. Of course you can the full catalyst also have spherical geometry, wherein the ball diameter 2 to 10 mm can be.

Of course you can the shape of the powdered Active mass or its powdery, yet uncalcined, precursor material also be carried out by applying to preformed inert catalyst support. The coating of the carrier body for Preparation of the coated catalysts is usually in a suitable rotatable container executed as it is e.g. from DE-A 2909671, EP-A 293859 or from EP-A 714700 is known.

Conveniently, is used to coat the carrier body moistened and applied after application, e.g. by means of hotter Air, dried again. The layer thickness of the applied to the carrier body Powder mass is expediently in the range 10 to 1000 μm, preferably in the range 50 to 500 microns and more preferably in the range 150 to 250 microns, selected.

As carrier materials, it is possible to use customary porous or non-porous aluminum oxides, silicon dioxide, thorium dioxide, zirconium dioxide, silicon carbide or silicates, such as magnesium silicate or aluminum silicate. The carrier bodies may be regularly or irregularly shaped, with regularly shaped carrier bodies having a clearly formed surface roughness, for example spheres or hollow cylinders, being preferred. Suitable is the use of substantially nonporous, surface roughness, spherical steatite supports whose diameter is 1 to 10 mm (eg 8 mm), preferably 4 to 5 mm. However, it is also suitable to use cylinders as support bodies whose length is 2 to 10 mm and whose outer diameter is 4 to 10 mm. In the case of inventively suitable rings as a carrier body, the wall thickness is beyond usually at 1 to 4 mm. According to preferred invention to be used annular carrier body have a length of 3 to 6 mm, an outer diameter of 4 to 8 mm and a wall thickness of 1 to 2 mm. Particularly suitable according to the invention are also rings of geometry 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter) as the carrier body. The fineness of the catalytically active oxide masses to be applied to the surface of the carrier body is, of course, adapted to the desired shell thickness (cf EP-A 714 700).

Favorable Mo and V-containing multimetal oxide active compositions to be used in the sense of the invention for acrolein partial oxidation to acrylic acid are furthermore compounds of the general formula VI, [D] _p [E] _q (VI), in which the variables have the following meaning:
D = Mo ₁₂ V _{a "} Z ¹ _b" Z ² _{c "} Z ³ _d" Z ⁴ _{e "} Z ⁵ _f" Z ⁶ _{g "} O _x"' ,
E = Z ⁷ ₁₂ Cu _{h "} H _i" O _{y "} ,
Z ¹ = W, Nb, Ta, Cr and / or Ce,
Z ² = Cu, Ni, Co, Fe, Mn and / or Zn,
Z ³ = Sb and / or Bi,
Z ⁴ = Li, Na, K, Rb, Cs and / or H
Z ⁵ = Mg, Ca, Sr and / or Ba,
Z ⁶ = Si, Al, Ti and / or Zr,
Z ⁷ = Mo, W, V, Nb and / or Ta,
a '' = 1 to 8,
b '' = 0.2 to 5,
c '' = 0 to 23,
d '' = 0 to 50,
e '' = 0 to 2,
f '' = 0 to 5,
g '' = 0 to 50,
h '' = 4 to 30,
i '' = 0 to 20 and
x '', y '' = numbers which are determined by the valence and frequency of the element different from oxygen in VI and
p, q = numbers other than zero whose ratio p / q is 160: 1 to 1: 1 and which are obtainable by using a multimetal oxide composition E, Z ⁷ ₁₂ Cu _{h "} H _i" O _{y "} (E), in finely divided form vorbildet (starting material 1) and then the preformed solid starting material 1 in an aqueous solution, an aqueous suspension or in a finely divided dry mixture of sources of elements Mo, V, Z ¹ , Z ² , Z ³ , Z ⁴ , Z ⁵ , Z ⁶ , which the aforementioned elements in the stoichiometry D, Mo ₁₂ V _{a "} Z ¹ _b" Z ² _{c "} Z ³ _d" Z ⁴ _{e "} Z ⁵ _f" Z ⁶ _{g "} (D) contains (starting material 2), in the desired ratio p: q incorporated, which optionally dried resulting aqueous mixture, and the dry precursor material thus calcined prior to or after drying to the desired catalyst geometry at temperatures of 250 to 600 ° C.

Prefers are those Multimetalloxidaktivmassen VI, in which the incorporation the preformed solid starting material 1 into an aqueous starting material 2 takes place at a temperature <70 ° C. A detailed description of the preparation of multimetal oxide compositions III catalysts contain e.g. EP-A 668104, DE-A 19736105 and DE-A 19528646.

Regarding the shaping applies with respect Multimetal oxide active bulk VI catalysts that in the multimetal oxide IV catalysts said.

Other multimetal oxide active compositions which are advantageous in the described sense and which contain Mo and V are furthermore multielement oxide active compounds of the general formula VII, [A] _p [B] _q [C] _r (VII) in which the variables have the following meaning:
A = Mo ₁₂ V _a X ¹ _b X ² _c X ³ _d X ⁴ _e X ⁵ _f X ⁶ _g O _x ,
B = X ₁ ⁷ Cu _h H _i O _y ,
C = X ₁ ⁸ Sb _j H _k O _z ,
X ¹ = W, Nb, Ta, Cr and / or Ce, preferably W, Nb and / or Cr,
X ² = Cu, Ni, Co, Fe, Mn and / or Zn, preferably Cu, Ni, Co and / or Fe,
X ³ = Sb and / or Bi, preferably Sb,
X ⁴ = Li, Na, K, Rb, Cs and / or H. preferably Na and / or K,
X ⁵ = Mg, Ca, Sr and / or Ba, preferably Ca, Sr and / or Ba,
X ⁶ = Si, Al, Ti and / or Zr, preferably Si, Al and / or Ti,
X ⁷ = Mo, W, V, Nb and / or Ta, preferably Mo and / or W,
X ⁸ = Cu, Ni, Zn, Co, Fe, Cd, Mn, Mg, Ca, Sr and / or Ba, preferably Cu and / or Zn, particularly preferably Cu,
a = 1 to 8, preferably 2 to 6,
b = 0.2 to 5, preferably 0.5 to 2.5
c = 0 to 23, preferably 0 to 4,
d = 0 to 50, preferably 0 to 3,
e = 0 to 2, preferably 0 to 0.3,
f = 0 to 5, preferably 0 to 2,
g = 0 to 50, preferably 0 to 20,
h = 0.3 to 2.5, preferably 0.5 to 2, particularly preferably 0.75 to 1.5,
i = 0 to 2, preferably 0 to 1,
j = 0.1 to 50, preferably 0.2 to 20, particularly preferably 0.2 to 5,
k = 0 to 50, preferably 0 to 20, particularly preferably 0 to 12,
x, y, z = numbers determined by the valency and frequency of the elements other than oxygen in A, B, C
p, q = positive numbers
r = 0 or a positive number, preferably a positive number, wherein the ratio p / (q + r) = 20: 1 to 1:20, preferably 5: 1 to 1:14 and more preferably 2: 1 to 1: 8 and, in the case where r is a positive number, the ratio q / r = 20: 1 to 1:20, preferably 4: 1 to 1: 4, more preferably 2: 1 to 1: 2, and most preferably 1 : 1, which is the proportion [A] _p in the form of three-dimensionally extended regions (phases) A of the chemical composition
A: Mo ₁₂ V _a X ¹ _b X ² _c X ³ _d X ⁴ _e X ⁵ _f X ⁶ _g O _x , the proportion [B] _q in the form of three-dimensionally extended regions (phases) B of the chemical composition
B: X ₁ ⁷ Cu _h H _i O _y and the proportion [C] _r in the form of three-dimensionally extended regions (phases) C of the chemical composition
C: X ₁ ⁸ Sb _j H _k O _z
contain, wherein the areas A, B and optionally C relative to each other as in a mixture of finely divided A, finely divided B and optionally finely divided C are distributed, and wherein all variables are to be selected within the given ranges with the proviso that the molar fraction of the element Mo is the total amount of all non-oxygen elements of the multielement oxide active composition VII 20-mol% to 80 mol%, the molar ratio of Mo contained in the catalytically active multielement oxide composition VII to V contained in the catalytically active Multielementoxidmasse VII, Mo / V, 15th Is 1 to 1: 1, the corresponding molar ratio Mo / Cu is 30: 1 to 1: 3, and the corresponding molar ratio Mo / (total amount of W and Nb) is 80: 1 to 1: 4.

Multielement oxide active compositions VII which are preferred in the context of the invention are those whose regions A have a composition in the following stoichiometric raster of general formula VIII, Mo ₁₂ V _a X ¹ _b X ² _c X ⁵ _f X ⁶ _g O _x (VIII) With
X ¹ = W and / or Nb,
X ² = Cu and / or Ni,
X ⁵ = Ca and / or Sr,
X ⁶ = Si and / or Al,
a = 2 to 6,
b = 1 to 2,
c = 1 to 3,
f = 0 to 0.75,
g = 0 to 10, and
x = a number determined by the valence and frequency of the elements other than oxygen in (VIII).

Of the used in connection with the multielement oxide active materials VIII Term "phase" means three-dimensional extensive areas whose chemical composition is different from theirs Environment is different. The phases are not necessarily radiographically homogeneous. As a rule, phase A forms a continuous phase, in the particle of phase B and optionally C are dispersed.

The finely divided phases B and optionally C are advantageously from particles whose maximum diameter, that is, the longest through the center of gravity of the particle going link of two on the surface the particles located points up to 300 microns, preferably 0.1 to 200 microns, especially preferably 0.5 to 50 microns and most preferably 1 to 30 microns. But they are also suitable Particles with a largest diameter from 10 to 80 μm or 75 to 125 μm.

in principle can the phases A, B and optionally C in the multielement oxide active compositions VII amorphous and / or crystalline.

The the multielement oxide active compounds of the general formula VII lying and then for conversion into active compositions thermally treated intimate dry mixtures can e.g. be obtained as described in the documents WO 02/24327, DE-A 4405514, DE-A 4440891, DE-A 19528646, DE-A 19740493, EP-A 756894, DE-A 19815280, DE-A 19815278, EP-A 774297, DE-A 19815281, EP-A 668104 and DE-A 19736105.

The basic principle of the preparation of intimate dry mixtures, which lead to thermal treatment Multielementoxidaktivmassen the general formula VII, is at least one Multielementoxidmasse B (X ₁ ⁷ Cu _h H _i O _y ) as starting material 1 and optionally one or more Multielementoxidmassen C (X ₁ ⁸ Sb _j H _k O _z ) as starting material 2 either separately or in association with each other in finely divided form and then the starting materials 1 and optionally 2 with a mixture, the sources of elemental constituents of the Multielementoxidmasse A. Mo ₁₂ V _a X _b ¹ X _c ² X _f ⁵ X _g ⁶ O _x (A) contains in a composition corresponding to the stoichiometry A, in intimate contact in the desired ratio (according to the general formula VII) and to dry the resulting intimate mixture optionally.

The intimately bringing into contact the constituents of the starting materials 1 and optionally 2 with the sources of elemental constituents the mixture containing multimetal oxide composition A (starting material 3) can be done both dry and wet. In the latter case must just be careful that the preformed phases (Crystallites) B and optionally C do not go into solution. In watery Medium is the latter at pH values that do not deviate too much from 7 and usually guaranteed at not too high temperatures. If the intimate contact gets wet, it usually ends for the invention thermally dry intimate mixture to be treated (e.g., by spray-drying). As part of a dry mixing falls such a dry mass automatically. Of course you can the finely preformed phases B and optionally C also into a plastically deformable mixture, which is the source of the elementary Constituents of the multimetal oxide A contains incorporated, as it recommends DE-A 10046928. Of course, the intimate contact bring the constituents of the starting masses 1 and optionally 2 with the sources of the multielement oxide composition A (starting material 3) also be carried out as described in DE-A 19815281.

The thermal treatment to obtain the active composition and shaping can be described as in the case of the multimetal oxide active compounds IV to VI respectively.

All generally can Multimetal oxide active masses IV to VII catalysts with advantage according to the teaching DE-A 103 25 487 and DE-A 103 25 488 are produced.

The execution of a reaction stage (within a Oxidationsreaktorstrasse the process of the invention) from propene to acrolein, you can with the catalysts described suitable for the corresponding catalyst fixed bed in the simplest manner and in terms of application in a useful The shell-fed catalysts fed to the fixed-bed catalysts, as described, for example, in EP-A 700 714 or DE-A 4 431 949 or WO 03/057653, or WO 03/055835, or WO 03/059857, or WO 03 / 076373, realize.

that is, in the simplest way is the fixed catalyst bed in the uniformly charged metal tubes of a tube bundle reactor and around the metal tubes is a tempering medium (one-zone operation), usually a Molten salt, guided. Salt melt (temperature control) and reaction gas mixture can thereby be performed in simple DC or countercurrent. The temperature control medium (the molten salt) can also be considered via the reactor meandering around the tube bundles guided so that just over the whole reactor considered a DC or countercurrent to flow direction consists of the reaction gas mixture. The volume flow of the temperature control medium (Heat exchange medium) is usually so measured that the temperature rise (due to the exothermic the reaction) of the heat exchange medium from the entry point into the reactor to the exit point the reactor 0 to 10 ° C, often 2 to 8 ° C, often 3 to 6 ° C is. The inlet temperature of the heat exchange medium in the tube bundle reactor is usually 250 to 450 ° C, often 300 to 400 ° C or 300 to 380 ° C. In these temperature ranges, the associated reaction temperatures also move therein. As a heat exchange medium In particular, fluid temperature control media are suitable. Is particularly favorable the use of melts of salts such as potassium nitrate, potassium nitrite, Sodium nitrite and / or sodium nitrate, or of low-melting Metals such as sodium, mercury and alloys of various kinds Metals. But also ionic liquids are usable.

Conveniently, the reaction gas starting mixture becomes the feed with fixed bed catalyst to the desired Reaction temperature preheated fed.

Advantageous the completion of the reaction gas starting mixture takes place during inventive method before and after, the at least two are operated in parallel Oxidation reactor systems via a corresponding distribution system simultaneously with this reaction gas starting mixture fed.

Especially in the case of intended high (eg ≥ 130 Nl / lh, or ≥ 140 Nl / lh, or ≥ 150 Nl / l · h, or ≥ 160 Nl / l · h, but usually ≤ 600 Nl / l · h, often ≤ 350 Nl / l · h) loads the fixed catalyst bed with propene is carried out a Propenial oxidation to acrolein expediently in a two- or Mehrzonenrohrbündelreaktor (an execution in the single tube bundle reactor is also possible). A preferred variant of a for this purpose can be used according to the invention Two-zone tube bundle reactor DE-C 2830765. But also in DE-C 251340, the US-A 3147084, DE-A 2201528, EP-A 383224 and DE-A 2903582 disclosed two-zone tube bundle reactors are suitable. A description of the method is also given in EP-A 1106598.

that is, in a simple way, the present invention is at least a catalyst fixed bed to be used then in the uniform charged metal tubes of a tube bundle reactor and around the metal tubes be two mutually substantially spatially separated tempering, usually salt melts, led. The pipe section, over the respective salt bath extends, represents a reaction zone.

Preferably flows around e.g. a salt bath A that portion of the tubes (the reaction zone A), in which the oxidative conversion of the propene (the simple Passage) until a turnover value in the range of 40 to 80 mol.% And a salt bath B flows around the section of the tubes (the reaction zone B), in which the oxidative terminal reaction propens (in a single pass) until a sales value is reached of usually at least 93 mol.% completes (if necessary, can to the reaction zones A, B connect further reaction zones, the kept at individual temperatures).

Within the respective temperature zone, the salt bath in principle as in the one-zone mode become. The inlet temperature of the salt bath B is normally at least 5 to 10 ° C above the temperature of the salt bath A. Otherwise, the inlet temperatures im for the single-zone recommended temperature range for the inlet temperature lie.

Otherwise can be the two-zone high-load mode of propene partial oxidation to acrolein e.g. as in DE-A 10 30 8836, EP-A 11 06 598, or as in WO 01/36364, or DE-A 19 92 7624, or DE-A 19 94 8523, DE-A 103 13 210, DE-A 103 13 213 or as in DE-A 199 48 248 described.

As a general rule the method according to the invention is suitable as part of a propene partial oxidation to acrolein for propene loads of the fixed catalyst bed of ≤ 70 Nl / lh, or ≥ 70 Nl / lh, ≥ 90 Nl / lh, ≥ 110 Nl / lh, ≥ 130 Nl / lh, ≥ 140 Nl / lh, ≥ 160 Nl / lh, 180 Nl / lh, ≥ 240 Nl / lh, ≥ 300 Nl / lh, but normally ≤ 600 Nl / l · h. there the load on the volume of the fixed catalyst bed is exclusively optional Mitverwendeter sections which consist exclusively of inert material (as generally in this document, unless explicitly stated) something else is said).

According to the invention advantageous are the loads of the relevant at least two operated in parallel Oxidation reactor systems selected identically.

to Preparation of the fixed catalyst bed for a partial oxidation according to the invention from propene to acrolein in the method according to the invention only the corresponding Multimetalloxidaktivmasse having shaped catalyst body or also have largely homogeneous mixtures of multimetal oxide active material Catalyst bodies and no multimetal oxide active material, are heterogeneous with respect to catalyzed partial gas phase oxidation of propene to acrolein essentially inert (consisting of inert material), moldings (Dilution molding) used become. As materials for such inert shaped bodies In principle, all those who come to mind as well support material for "propene-to-acrolein" shell catalysts suitable. As such materials, e.g. porous or nonporous aluminas, Silica, thoria, zirconia, silicon carbide, silicates such as magnesium or aluminum silicate or the already mentioned steatite (e.g., Steatite C-220 from CeramTec).

The Geometry of such inert diluent bodies can in principle be arbitrary. That is, for example, spheres, Polygons, solid cylinders or rings. Preference is given as inert diluent bodies such choose, whose geometry corresponds to that of the first-stage catalyst moldings to be diluted with them.

In usually it is cheap if look for the described propene partial oxidation to acrolein the chemical Composition of the active composition used over the fixed catalyst bed not changed. That is, for a single shaped catalyst body Although the active composition used may be a mixture of different, e.g. the elements Mo and / or W and at least one of the elements Bi, Fe, Sb, Sn and Cu containing, multimetal oxides, for all catalyst bodies of the Catalyst fixed bed but then advantageously the same mixture used.

According to the invention advantageous have the relevant at least two oxidation reactor systems operated in parallel with catalyst in an identical manner fed Oxidationsreaktorstrassen on.

Prefers in propene partial oxidation to acrolein normally takes the volume-specific (i.e., normalized to the unit of volume) activity within the fixed catalyst bed in the flow direction of the reaction gas starting mixture continuous, abrupt or stepped.

The volume-specific activity can be e.g. be easily reduced by that one a basic amount of uniformly prepared catalyst bodies with Dilution moldings homogeneous diluted. The higher the proportion of dilution molded bodies is selected the lower it is in a given volume of the packed bed contained active mass or catalyst activity.

A volume-specific activity which increases at least once in the flow direction of the reaction gas mixture over the catalyst fixed bed can thus be adjusted in a simple manner, for example, by starting the bed with a high proportion of inert diluent bodies based on one type of shaped catalyst bodies, and then this proportion of diluent bodies in the flow direction either continuously or at least once or several times abruptly (eg stepped) reduced. However, an increase in the volume-specific activity is also possible, for example, by increasing the thickness of the active mass layer applied to the carrier while maintaining the geometry and the active mass of a shell catalyst molded body or by increasing the proportion of shaped catalyst bodies in a mixture of shell catalysts having the same geometry but with different weight proportions of the active mass increases with higher active weight percentage. Alternatively, it is also possible to dilute the active compounds themselves by incorporating inert diluent materials, such as highly burned silicon dioxide, into the dry mixture of starting compounds which is to be calcined during the production of the active material. Different addition amounts of diluting material automatically lead to different activities. The more diluting material is added, the lower will be the resulting activity. Analogue We kung can also be achieved, for example, by changing the mixing ratio in mixtures of unsupported catalysts and of coated catalysts (with identical active material) in a corresponding manner. Needless to say, the variants described can also be used in combination.

Of course, for the fixed catalyst bed a propene partial oxidation according to the invention to acrolein but also mixtures of catalysts with chemical different composition of active ingredients and as a result of this different composition of different activity used become. These mixtures can in turn diluted with inert diluents.

advance and / or subsequent to the active mass having sections the fixed catalyst bed of a propene partial oxidation according to the invention to acrolein exclusively of inert material (e.g., only shaped diluents) packings These can be also be brought to the temperature of the catalyst fixed bed. It can the for the inert bed used diluent tablets the Same geometry as the active mass having sections having the catalyst fixed bed used catalyst bodies. The geometry of for the inert bed used dilution molding can but also different from the aforementioned geometry of the shaped catalyst body (e.g., spherical rather than annular).

Often point the for such inert fillings used moldings the ring-shaped Geometry 7 mm × 7 mm × 4 mm (outer diameter × length × inner diameter) or the spherical one Geometry with the diameter d = 4-5 mm.

frequently is in the process of the invention the active mass portion of the fixed catalyst bed for propene partial oxidation to acrolein in the flow direction of the reaction gas mixture is structured as follows (preferred according to the invention) in all of the at least two oxidation reactor systems operated in parallel in accordance with the invention and in the same way).

First up a length from 10 to 60%, preferably 10 to 50%, more preferably 20 to 40% and most preferably 25 to 35% (i.e., e.g. length of 0.70 to 1.50 m, preferably 0.90 to 1.20 m), in each case the total length of the Active mass having portion of the fixed bed catalyst bed, a homogeneous mixture or two (with decreasing dilution) on each other The following homogeneous mixtures of shaped catalyst bodies and dilution molded bodies (where both preferably have substantially the same geometry), wherein the weight fraction of the diluent shaped bodies (the mass densities of Catalyst bodies and differ from diluent shaped bodies usually only slightly) usually 5 to 40 wt .-%, preferably 10 to 40 wt .-% or 20 to 40 wt .-% and particularly preferably 25 to 35 wt .-% is. In connection This first zone is then often beneficial to the end the length the active mass portion of the fixed catalyst bed (i.e., on a length, for example from 2.00 to 3.00 m, preferably 2.50 to 3.00 m) either one only to a lesser extent (than in the first zone) diluted bed of the Catalyst bodies, or, most preferably, a sole fill of the same Catalyst bodies, which have also been used in the first zone.

The The above applies in particular when in the fixed catalyst bed as a shaped catalyst body Vollkatalysatorringe or shell catalyst rings (especially those which are preferred in this document). With advantage in the context of the aforementioned structuring both the catalyst molding or their carrier rings as well as the dilution molded bodies in inventive method essentially the ring geometry 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter) on.

The The above also applies if, instead of inert dilution molded bodies, coated catalyst tablets are used whose active mass fraction is lower by 2 to 15% by weight is, as the active material content of the shell catalyst moldings on End of the fixed catalyst bed.

A pure inert material fill, their length, based on the total length of the fixed catalyst bed, expediently 1 or 5 to 20%, conducts in the direction of flow of the reaction gas mixture, as a rule, the fixed catalyst bed. It is normally used as a heating zone for the reaction gas mixture.

Usually, the catalyst tubes in the shell-and-tube reactors for the partial oxidation stage of propene to acrolein are made of ferritic steel and typically have a wall thickness of 1 to 3 mm. Their inner diameter is usually (uniformly) 20 to 30 mm, often 21 to 26 mm. To whom The number of contact tubes accommodated in the tube bundle container expediently amounts to at least 5,000, preferably to at least 10,000. Frequently, the number of contact tubes accommodated in the reaction container is 15,000 to 30,000. Tube bundle reactors with a number of contact tubes above 40000 form the exception for this reaction stage , Within the container, the contact tubes are normally distributed homogeneously, the distribution is suitably chosen so that the distance between the central inner axes of closest contact tubes (the so-called contact tube pitch) is 35 to 45 mm (see, eg EP-B 468290).

The execution the reaction stage from acrolein to acrylic acid, you can with the fixed catalyst for the bed This reaction also described as suitable catalysts in the simplest way and in terms of application appropriate in one with the fixed bed catalysts fed tube bundle reactor, as it e.g. in EP-A 700 893 or DE-A 4 431 949 or WO 03/057653, or WO 03/055835, or WO 03/059857, or WO 03/076373 described, perform.

that is, in the simplest way is the fixed catalyst bed to be used in the uniformly charged metal tubes of a tube bundle reactor and around the metal tubes is a tempering (single zone), usually a molten salt, ge leads. Molten salt (tempering medium) and reaction gas mixture can be guided in a simple DC or countercurrent. The temperature control medium (the molten salt) can also be considered via the reactor meandering around the tube bundles guided so that just over the whole reactor considered a DC or countercurrent to flow direction consists of the reaction gas mixture. The volume flow of the temperature control medium (Heat exchange medium) is usually so measured that the temperature rise (due to the exothermic the reaction) of the heat exchange medium from the entry point into the reactor to the exit point the reactor 0 to 10 ° C, often 2 to 8 ° C, often 3 to 6 ° C is. The inlet temperature of the heat exchange medium in the tube bundle reactor (In this document, it corresponds to the temperature of the fixed catalyst bed) is usually 220 to 350 ° C, often 245 to 285 ° C or 245 to 265 ° C. As a heat exchange medium In particular, fluid temperature control media are suitable. Is particularly favorable the use of melts of salts such as potassium nitrate, potassium nitrite, Sodium nitrite and / or sodium nitrate, or of low-melting Metals such as sodium, mercury and alloys of various kinds Metals. But also ionic liquids are usable.

Conveniently, the reaction gas starting mixture becomes the feed with fixed bed catalyst to the desired Reaction temperature preheated fed.

Especially in the case of intended high (e.g., ≥ 130 Nl / l · hr, or ≥ 140 Nl / l · hr, but usually ≤ 350 Nl / l · hr, or ≤ 600 Nl / l · hr) stresses the catalyst fixed bed with acrolein carried out the implementation of the method according to the invention an acrolein partial oxidation to acrylic acid useful in a two or more zone tube bundle reactor (an execution in the single tube bundle reactor is also possible). A preferred variant of a for this purpose can be used according to the invention Two-zone tube bundle reactor DE-C 2830765. But also in DE-C 2513405, the US-A 3147084, DE-A 2201528, EP-A 383224 and DE-A 2903582 disclosed two-zone tube bundle reactors are suitable.

that is, in a simple way is the invention to be used at least one fixed catalyst bed in the uniformly charged Metal pipes of a tube bundle reactor and around the metal tubes are two substantially spatially separated from each other Tempering, usually salt melts, led. The pipe section, over the the respective salt bath extends, represents a temperature or reaction zone.

Preferably flows around e.g. a salt bath C that portion of the tubes (the reaction zone C), in which the oxidative conversion of acrolein (at easy passage) until reaching a sales value in the range from 55 to 85 mol.% and a salt bath D flows around the section the tubes (the Rekationszone D), in which the oxidative terminal conversion of acrolein (in single pass) until reaching one Sales value of usually at least 90 mol.% Completes (at Need can connect to the reaction zones C, D further reaction zones, the kept at individual temperatures).

Within the respective temperature zone, the salt bath in principle as in the one-zone mode become. The inlet temperature of the salt bath D is normally at least 5 to 10 ° C above the temperature of the salt bath C. Otherwise, the inlet temperatures im for the single-zone recommended temperature range for the inlet temperature lie.

Otherwise may be the two-zone high-load mode of acrolein partial oxidation to acrylic acid e.g. as in DE-A 19 94 8523, EP-A 11 06 598 or as in DE-A 19 94 8248 be described described.

The inventive method is thus suitable for Acrolein loadings of the fixed catalyst bed of ≦ 70 Nl / l · h, or ≦ 70 Nl / l · h, ≥ 90 Nl / l · h, ≥ 110 Nl / l · h, ≥ 130 Nl / l · h, 180 Nl / lh, ≥ 240 Nl / lh, ≥ 300 Nl / lh, but normally ≤ 600 Nl / lh. there the load on the volume of the fixed catalyst bed is exclusively optional Mitverwendeter sections which consist exclusively of inert material based.

to Preparation of the at least one fixed catalyst bed can be used for a partial oxidation according to the invention from acrolein to acrylic acid only the corresponding Multimetalloxidaktivmasse having shaped catalyst body or also largely homogeneous mixtures of multimetal oxide active material comprising catalyst moldings and no multimetal oxide active material, with respect to heterogeneously catalyzed partial gas phase oxidation substantially inert behaving (consisting of inert material), moldings (dilution molding) used become. As materials for such inert shaped bodies In principle, all those who come to mind as well support material suitable for the invention "acrolein-to-acrylic acid-coated catalysts." As such Materials come e.g. porous or nonporous Aluminas, silica, thoria, zirconia, silicon carbide, Silicates such as magnesium or aluminum silicate or the already mentioned steatite (e.g., Steatite C-220 from CeramTec).

The Geometry of such inert diluent bodies can in principle be arbitrary. That is, for example, spheres, Polygons, solid cylinders or rings. According to the invention preferred Will be as inert diluent such choose, whose geometry corresponds to that of the catalyst molding to be diluted with them.

In It is usually within the scope of a partial oxidation of acrolein according to the invention cheap to acrylic acid, though the chemical composition of the active material used on the Fixed catalyst bed not changed. That is, for a single shaped catalyst body Although used active composition may be a mixture of different the Elements Mo and V containing multimetal be, for all catalyst bodies of However, catalyst fixed bed is then advantageously the same mixture to use.

Prefers takes for a partial oxidation according to the invention from acrolein to acrylic acid usually the volume specific (i.e., the unit normalized volume) activity within the fixed catalyst bed in the flow direction of the reaction gas mixture continuous, abrupt or stepped.

The volume-specific activity can be e.g. be easily reduced by that one a basic amount of uniformly prepared catalyst bodies with Dilution moldings homogeneous diluted. The higher the proportion of dilution molded bodies is selected the lower it is in a given volume of the packed bed contained active mass or catalyst activity.

A in the flow direction of the reaction gas mixture the fixed catalyst bed at least once increasing volume specific activity let yourself for a inventive method the Acroleinpartialoxidation to acrylic acid thus in a simple manner e.g. Adjust by filling the bed with a high proportion relative to inert shaped diluent bodies begins on a variety of shaped catalyst bodies, and then this Proportion of diluent bodies in flow direction either continuously or at least once or several times abruptly (e.g., stepped) reduced. However, an increase in volume-specific activity is also e.g. thereby possible that one with constant geometry and Aktivmassenart a Shaped coated catalyst body the thickness of the on the support applied active mass layer increased or in a mixture of Shell catalysts with the same geometry but with different Weight fraction of the active composition, the proportion of shaped catalyst bodies with higher Active mass fraction increases. Alternatively you can also the Dilute the active masses yourself, by making e.g. in the to be calcined Dry mixture of starting compounds inert diluent acting Materials such as burned-in silica incorporated. different Additional amounts of diluting lead active material automatically to different activities. The more diluting Material is added, the lower will be the resulting activity. Analogous effect leaves also e.g. achieved by mixing in mixtures of solid catalysts and of shell catalysts (with identical active material) in a corresponding Way the mixing ratio changed. Needless to say, the variants described can also be combined apply.

Of course, for the fixed catalyst bed of Acroleinpartialoxidation invention Acrylic acid but also mixtures of catalysts with chemically different active composition and be used as a result of this different composition of different activity. These mixtures can in turn be diluted with inert diluents.

advance and / or subsequent to the active mass having sections of the fixed catalyst bed exclusively of inert material (e.g., only shaped diluents) packings are located. these can also be brought to the temperature of the catalyst fixed bed. It can the for the inert bed used diluent tablets the Same geometry as the active mass having sections having the catalyst fixed bed used catalyst bodies. The Geometry of for the inert bed used dilution molding can but also different from the aforementioned geometry of the shaped catalyst body (e.g., spherical rather than annular).

Often point the for such inert fillings used moldings the ring-shaped Geometry 7 mm × 7 mm × 4 mm (outer diameter × length × inner diameter) or the spherical one Geometry with the diameter d = 4-5 mm.

frequently is in a method according to the invention the Acroleinpartialoxidation to acrylic acid having the active composition Section of the fixed catalyst bed in the flow direction of the reaction gas mixture structured as follows (preferred according to the invention in all of at least two operated in parallel according to the invention Oxidation reactor systems and this in the same way).

First up a length from 10 to 60%, preferably 10 to 50%, more preferably 20 to 40% and most preferably 25 to 35% (i.e., e.g. length of 0.70 to 1.50 m, preferably 0.90 to 1.20 m), in each case the total length of the Active mass having portion of the fixed bed catalyst bed, a homogeneous mixture or two (with decreasing dilution) on each other The following homogeneous mixtures of shaped catalyst bodies and dilution molded bodies (where both preferably have substantially the same geometry), wherein the weight fraction of the diluent shaped bodies (the mass densities of Catalyst bodies and differ from diluent shaped bodies usually only slightly) usually 10 to 50 wt .-%, preferably 20 to 45 wt .-% and particularly preferably 25 to 35 wt .-% is. Following this first Zone is then frequent advantageous to the end of the length the active mass portion of the fixed catalyst bed (i.e., on a length, for example from 2.00 to 3.00 m, preferably 2.50 to 3.00 m) either one only to a lesser extent (than in the first (or first two) Dilute zone) fill the shaped catalyst body, or, most preferably, a sole fill of the same Catalyst bodies, which have also been used in the first (or first two) zone are.

The The above applies in particular when in the fixed catalyst bed coated catalyst rings as shaped catalyst bodies or coated catalyst spheres (especially those the in this writing for an acrolein partial oxidation to acrylic acid are preferred). Advantageously, in the context of the aforementioned structuring both the shaped catalyst bodies or their carrier rings as well as the diluent molding a method according to the invention the acrolein partial oxidation to acrylic acid substantially the ring geometry 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter) on.

The The above also applies if, instead of inert dilution molded bodies, coated catalyst tablets are used whose active mass fraction is lower by 2 to 15% by weight is, as the active material content of the shell catalyst moldings on End of the fixed catalyst bed.

A pure inert material fill, their length, based on the total length of the fixed catalyst bed, expediently 5 to 20%, conducts in the direction of flow of the reaction gas mixture usually the fixed catalyst bed for the Acroleinpartialoxidation one. It is normally used as a heating zone for the reaction gas mixture.

Usually, for the acrolein partial oxidation according to the invention, the contact tubes in the tube bundle reactors are made of ferritic steel and typically have a wall thickness of 1 to 3 mm. Their inner diameter is usually (uniformly) 20 to 30 mm, often 21 to 26 mm. The number of contact tubes accommodated in the tube bundle container is expediently at least 5000, preferably at least 10000. Often, the number of contact tubes accommodated in the reaction container is 15,000 to 30,000. Tube bundle reactors having a number of contact tubes above 40000 tend to be the exception for acrolein partial oxidation , Inside the container the contact tubes are normally distributed homogeneously, the distribution is suitably chosen so that the distance between the central inner axes of closest contact tubes (the so-called contact tube division) is 35 to 45 mm (see, eg, EP-B 468290).

As already described, can in the method according to the invention both propene and acrolein partial oxidation in mononuclear or in two-zone tubular reactors carried out become. If you switch the two reaction stages one behind the other, but can also only the first reaction stage in a single zone tube reactor and the second reaction stage in a two-zone tubular reactor (or vice versa) performed become. The product gas mixture of the first reaction stage (preferably after mixing over all parallel operated oxidation reactor systems) is thereby, optionally after supplementation with inert gas, or with molecular oxygen, or with inert gas and molecular oxygen and optionally after direct and / or indirect intercooling, fed directly to the second reaction stage.

Between the tube bundle reactors the first and the second reaction stage may be an intercooler, the optionally inert bedding may contain.

Needless to say, can for the inventive method a two-stage partial oxidation of propene to acrylic acid the Fixed catalyst bed of propene partial oxidation and the fixed catalyst bed the acroleinpartialoxidation also spatially sequentially in a single, also e.g. having two temperature zones or more, Multiple catalyst tube bundle reactor be accommodated, as e.g. WO 03/059857, EP-A 911313 and EP-A 990636. One speaks in this case of a single-reactor two-stage process. One or two temperature zones usually extend over a fixed catalyst bed. Between the two fixed catalyst beds may additionally a inert bed optionally located in a third temperature zone is and is tempered separately. The contact tubes can thereby be executed continuously or interrupted by the inert bed.

The for the Feed gas mixture of the "propene-to-acrolein reaction stage" (the reaction gas starting mixture 1) to be used inert gas can be independent of that for the fixed catalyst bed selected propene load (and independent of whether an "acrolein-to-acrylic acid reaction stage" follows) to, for example, ≥ 20% by volume, or to ≥ 30 Vol .-%, or to ≥ 40 Vol .-%, or to ≥ 50 Vol .-%, or to ≥ 60 Vol .-%, or to ≥ 70 Vol .-%, or to ≥ 80 Vol .-%, or to ≥ 90 Vol .-%, or to ≥ 95 Vol .-% consist of molecular nitrogen.

However, the inert diluent gas can also consist of, for example, 2 to 35 or 20% by weight of H ₂ O and 65 to 98% by volume of N ₂ .

For propene charges of the fixed catalyst bed of the "propene-to-acrolein reaction stage" above 250 Nl / l · h for the inventive method, however, the concomitant use of inert diluent gases such as propane, ethane, methane, butane, pentane, CO ₂ , CO, water vapor and / or noble gases are recommended, but of course these gases can also be used at lower propene loads to dampen the formation of hot spots.

Of the Working pressure can in the gas phase partial oxidation according to the invention of the prop to acrolein (especially at the beginning of the period of use fixed catalyst bed) both below normal pressure (e.g. up to 0.5 bar) as well as above atmospheric pressure. typically, becomes the working pressure in the gas phase partial oxidation of the propene at values from 1 to 5 bar, often 1 to 3 bar.

Usually the reaction pressure in the propene partial oxidation according to the invention do not exceed acrolein 100 bar. Of course can the procedure according to the invention the propene partial oxidation in general with the in the EP-A 990 636, EP-A 11 06 598, EP-A 614 872, DE-A 10 35 822, DE-A 10 23 2748, DE-A 10351269 and in the German application DE-A 10 2004 025 445 for service life extension a catalyst bed recommended procedures also in combination be applied. It is so catalyst bed life of several Reachable years.

The molar ratio of O ₂ : propene in the starting reaction gas mixture 1 for the propene partial oxidation to acrolein, which is passed through the corresponding fixed catalyst bed in the process according to the invention, is usually ≥ 1 (essentially regardless of whether a Acroleinpartialoxidationsstufe follows to acrylic acid). Usually, this ratio will be at values ≤3. Frequently, the molar ratio of O ₂ : propene in the aforementioned charge gas mixture will advantageously be 1 to 2 or 1.4 to 2. In many cases, the process of propene partial oxidation to acrolein with one in the reaction gas starting mixture 1 propene present: oxygen: inert gas (including water vapor) - volume ratio (Nl) of 1: (1 to 3): (3 to 30), preferably 1: (1.5 to 2.3): (10 to 15 ) To run.

Of the Propene content in the starting reaction gas mixture 1 may be e.g. at Values of 4 to 20 vol.%, Often at 5 or 7 to 15 vol.% or 6 or 8 to 12 vol.% or 5 to 8 vol .-% are (in each case based on the total volume).

A typical composition of starting reaction gas mixture 1 (irrespective of the load chosen and whether an acrolein partial oxidation step follows acrylic acid) may include the following components:
6 to 6.5% by volume of propene,
From 3 to 3.5% by volume of H ₂ O,
0.3 to 0.5% by volume of CO,
0.8 to 1.2% by volume of CO ₂ ,
0.01 to 0.04 vol.% Acrolein,
10.4 to 10.7% by volume of O ₂ and
as residual amount ad 100% molecular nitrogen,
or: 5.4% by volume of propene,
10.5 vol.% Oxygen,
1.2 vol.% CO _x ,
80.5% by volume of N ₂ and
2.4% by volume H ₂ O.

The reaction gas starting mixture 1 may according to the invention for the propene partial oxidation to acrolein but also be composed as follows:
6 to 15% by volume of propene,
From 4 to 30 vol.% (Often 6 to 15 vol.%) Of water,
≥ 0 to 10% by volume (preferably ≥ 0 to 5% by volume) of constituents other than propene, water, oxygen and nitrogen, so much molecular oxygen that the molar ratio of molecular oxygen contained to the molecular propene present is 1.5 is up to 2.5 and as a residual amount up to 100 vol .-% total amount of molecular nitrogen.

Another possible starting reaction gas mixture 1 composition may contain, according to the invention, for the propene partial oxidation to acrolein:
6.0% by volume of propene,
60 vol .-% air and
34% by volume H ₂ O.

alternative can also reaction gas starting mixtures 1 of the composition according to Example 1 of EP-A 990 636, or according to Example 2 of EP-A 990 636, or according to Example 3 of EP-A 1 106 598, or according to Example 26 of EP-A 1 106 598, or according to Example 53 of EP-A 1 106 598 for the "propene-to-acrolein Reaction stage "used become.

Further reaction gas starting mixtures 1 suitable for the "propene to acrolein reaction stage" according to the invention may be in the following composition grid:
7 to 11% by volume of propene,
6 to 12% by volume of water,
0 to 5% by volume of constituents other than propene, water, oxygen and nitrogen,
so much molecular oxygen that the molar ratio of oxygen contained to molecular propene to be contained is 1.4 to 2.2, and
as a residual amount up to 100 vol .-% total amount of molecular nitrogen.

Suitable propylene to be used in the starting reaction gas mixture 1 are, in particular, polymer-grade propene and chemical grade propene, as described, for example, in DE-A 10232748. In accordance with the invention advantageously as a propene source for a heterogeneously catalyzed propene gas phase partial oxidation with molecular oxygen to acrolein and / or acrylic acid (or ammoxidation to acrylonitrile) in at least two parallel oxidation reactor systems but also a heterogeneously catalyzed dehydrogenation and / or oxydehydrogenation of Propane propene act, as for example the writings DE-A 102 45 585, WO 03/076370, DE-A 103 16 039, DE-A 33 13 573, US 3,161,670 , WO 01/96270, WO 01/96271 and WO 03/011804. In an advantageous manner, this is the partially oxidized Propen accompanied by propane.

Preferably operates a dehydrogenation reactor at least two according to the invention in parallel operated oxidation reactor systems with propene.

The reaction gas starting mixture 1 is then preferably in the following composition grid:
7 to 15 vol.% O ₂ ,
5 to 10% by volume of propylene,
10 or 15 to 40% by volume of propane,
From 25 to 60% by volume of nitrogen,
1 to 5 vol .-% sum of CO, CO ₂ and H ₂ O and
0 to 5% by volume of other ingredients,
any ammonia present is disregarded.

At this point should be mentioned that, independently of whether an "acrolein-to-acrylic acid reaction step" follows Part of the feed gas mixture of the "propene-to-acrolein reaction stage" so-called recycle gas can be. These are, as already described, to Gas, after the target product separation from the product gas in the Oxidation reactor system according to the invention following separation system (for acrolein and / or acrylic acid) remains and usually in part as a largely inert diluent gas for charging the propene and / or optionally subsequent acrolein reaction stage is returned.

When Oxygen source is normally used air.

The Loading of the fixed catalyst bed (exclusively pure inert sections) with reaction gas starting mixture 1 is in particular in a method according to the invention for the preparation of acrolein and / or acrylic acid from propene in typical Way 1000 to 10000 Nl / l · h, usually 1000 to 5000 Nl / l · h, often 1500 up to 4000 Nl / l · h be.

Closes the propene partial oxidation to acrolein an acrolein partial oxidation on, so if necessary, after the intercooling the Product gas mixture of the propene reaction stage of the acrolein reaction stage fed. According to the invention advantageous in advance, the product gas streams of the at least two propene partial oxidations mixed into acrolein. The oxygen required in the acrolein reaction step can already be considered a surplus the starting reaction gas mixture 1 for the propene reaction stage be added and thus part of the product gas mixture of Propene reaction stage. In this case, this may, if necessary intercooled, Product gas mixture of the propene reaction stage directly the feed gas mixture the acrolein reaction step. The one for the second oxidation step from acrolein to acrylic acid needed However, oxygen can be the product gas mixture of the propene reaction stage even before it enters the acrolein reaction stage only partially or completely be added, e.g. in the form of air. With this addition can while a direct cooling be connected to the product gas mixture of the acrolein reaction stage.

Already resulting from the above-mentioned context, the in the feed gas mixture for an acrolein reaction stage (the reaction gas starting mixture 2) contained inert gas (regardless, whether a propene-type reaction precedes) to e.g. ≥ 20 vol.%, or to ≥ 30 Vol .-%, or to ≥ 40 Vol .-%, or to ≥ 50 Vol .-%, or to ≥ 60 Vol .-%, or to ≥ 70 Vol .-%, or to ≥ 80 Vol .-%, or to ≥ 90 Vol .-%, or to ≥ 95 Vol .-% consist of molecular nitrogen.

Often, however, the inert diluent gas in the feed gas for the acrolein reaction step becomes 5 to 25 or 20 wt% of H ₂ O (eg, may be formed in a preceding propene reaction step and / or optionally added) and 70 to 90 Vol .-% consist of N ₂ .

In acrolein loadings of the fixed catalyst bed for the partial oxidation of acrolein to acrylic acid above 250 Nl / l · h, however, the concomitant use of inert diluent gases such as propane, ethane, methane, butane, pentane, CO ₂ , water vapor and / or noble gases is recommended for the inventive method , Of course, these gases can also be used even at lower Acroleinbelastungen.

The working pressure may in the gas phase partial oxidation of the acrolein according to the invention to acrylic acid (especially at the beginning of the service life of a catalyst fixed bed) both below normal pressure (eg up to 0.5 bar) and above normal pressure. Typically, the working pressure in the gas phase partial oxidation of the acrolein will be at values of 1 to 5 bar, often 1 to 3 bar.

Usually the reaction pressure in the acrolein partial oxidation according to the invention Do not exceed 100 bar. Of course can the procedure according to the invention in general also with those in EP-A 990 636, EP-A 11 06 598, EP-A 614 872, DE-A 10 35 0822, DE-A 10 23 2748, DE-A 10351269 and in the German application DE-A 10 2004 025 445 for service life extension a catalyst bed recommended procedures in combination be applied. It is so catalyst bed life of several Reachable years.

The molar ratio of O ₂ : acrolein in the feed gas mixture for an acrolein reaction step, which is passed through the corresponding fixed catalyst bed in the process according to the invention, is usually ≥ 1 (regardless of whether or not a propene reaction stage precedes). Usually, this ratio will be at values ≤3. Frequently, the molar ratio of O ₂ : acrolein in the aforementioned feed gas mixture will be 1 to 2 or 1 to 1.5 according to the invention. In many cases, the process according to the invention is carried out using acrolein present in reaction gas starting mixture 2 (feed gas mixture for the acrolein reaction stage): oxygen: water vapor: inert gas volume ratio (Nl) of 1: (1 to 3) :( 0 to 20) :( 3 to 30), preferably from 1: (1 to 3): (0.5 to 10): (7 to 20).

Of the Acrolein content in the feed gas mixture for the acrolein reaction step can e.g. (independently of, whether a propene reaction stage precedes or not) in values from 3 or 6 to 15 vol.%, often at 4 or 6 to 10 vol.% Or 5 to 8 vol.% (In each case based on the total volume). The load of the fixed catalyst bed (here exclusively purer Inertabschnitte) with feed gas mixture (reaction gas starting mixture 2) is typically used in an "acrolein-to-acrylic acid process" according to the invention as for the "propene to acrolein reaction stage" 1000 to 10000 Nl / l · h, usually 1000 to 5000 Nl / lh, often 1500 up to 4000 Nl / l · h be.

When carrying out the process according to the invention, fresh fixed catalyst beds for the partial oxidation of propene to acrolein will normally be operated in such a way that, after determining the composition of the reaction gas starting mixture 1 and determining the load of the fixed catalyst beds for propene partial oxidation with starting reaction gas mixture 1, the temperature of the fixed catalyst beds (or the Inlet temperature of the temperature control medium in the temperature control zone of the tube bundle reactor) adjusted so that the conversion U ^{Pro of} the propene is at least 93 mol .-% with a single passage of the reaction gas mixture 1 through the fixed catalyst beds. When using favorable catalysts, values are also possible for U ^Pro ≥ 94 mol%, or ≥ 95 mol%, or ≥ 96 mol%, or ≥ 97 mol%, and often even more.

If the heterogeneously catalyzed partial oxidation of propene to acrolein is carried out continuously, the composition of the reaction gas starting mixture 1 and the load of the corresponding fixed catalyst beds with starting reaction gas mixture 1 are maintained substantially constant (the load is adapted to the fluctuating market demand, if necessary). A decrease in the activity of the fixed catalyst beds over time is normally initially counteracted under these production conditions by increasing the temperature of the fixed catalyst beds (the inlet temperature of the temperature control medium into the temperature zone of the tube bundle reactors) from time to time (the flow rate of the temperature control medium normally becomes substantially also maintained) to the propene conversion with a single pass of the reaction gas mixture in the desired target range (ie, at U ^Pro ≥ 93 mol .-%, or ≥ 94 mol .-%, or ≥ 95 mol .-%, or ≥ 96 mol .-%, or ≥ 97 mol .-%) to keep.

Advantageously, it will continue to proceed so that the gas phase partial oxidation according to the invention interrupts from time to time to at a temperature of the fixed catalyst bed of 250 to 550 ° C, as described in DE-A 10351269, from molecular oxygen, inert gas and optionally water vapor existing Pass gas mixture G through the fixed catalyst bed. Subsequently, the partial oxidation of the propene is continued while substantially maintaining the process conditions (the propene loading of the fixed catalyst beds is preferably restored slowly) and the temperature of the fixed catalyst beds is adjusted so that the propene conversion reaches the desired target value. In general, this temperature value for the same conversion will be at a somewhat lower value than the temperature which the fixed catalyst bed had before the interruption of the partial oxidation and the treatment with the gas mixture G. Starting from this temperature value of the fixed catalyst beds, the partial oxidation is continued while substantially maintaining the other conditions, and in doing so counteracting the decline in the activity of the fixed catalyst beds over time, in a suitable manner, by increasing the time increases the temperature of the fixed catalyst beds to time. Within, for example, a subsequent calendar year, the partial oxidation according to the invention expediently again interrupted at least once to lead the gas mixture G through the fixed catalyst beds. Thereafter, the partial oxidation is resumed as described and so on. If the target product selectivity achieved no longer satisfies, one will carry out a partial or full catalyst change as described in, for example, one of the at least two relevant oxidation reactor lines and then continue the process according to the invention.

In a similar manner, when carrying out the process according to the invention, fresh fixed catalyst beds for the partial oxidation of acrolein to acrylic acid will normally be operated in such a way that the temperature is determined after determining the operation of this reaction stage and the composition of the reaction gas starting mixture 2 and determining the loading of the corresponding fixed catalyst beds with reaction gas starting mixture 2 the ^{fixed catalyst beds} (or the inlet temperature of the temperature control in the temperature of the tube bundle reactors) adjusted so that the conversion U ^{Acr of} the acrolein is at least 90 mol .-% with a single pass of the ^{starting reaction gas} mixture 2 through the ^{fixed catalyst beds} . When using favorable catalysts, values for U ^Acr 92 mol .-%, or 94 mol .-%, or ≥ 96 mol .-%, or ≥ 98 mol .-%, and often even ≥ 99 mol .-% and more is possible.

at continuous exercise the heterogeneously catalyzed partial oxidation of acrolein to acrylic acid the composition of the starting reaction gas mixture 2 and the Load of the corresponding fixed catalyst beds with reaction gas starting mixture 2 maintained substantially constant (possibly the Burden adjusted to the fluctuating market demand). a Fall of activity the fixed catalyst beds over Time usually gets under these production conditions counteract that from time to time the temperature the fixed catalyst beds (the inlet temperature of the temperature in the temperature zone of the tube bundle reactor) elevated (the flow rate the tempering medium is normally also substantially retained) to reduce the acrolein turnover in a single pass of the Feed gas mixture in the desired target corridor (i.e., at Values of ≥ 90 mol .-%, or ≥ 92 mol .-%, or ≥ 94 mol .-%, or ≥ 96 mol%, or ≥ 98 mol .-%, or ≥ 99 mol .-%,).

Advantageous one will continue to proceed such that one, e.g. before the made temperature increase the fixed catalyst beds are permanently ≥ 10 ° C or ≥ 8 ° C (based on the previously set temperature the same fixed catalyst bed), the gas phase partial oxidation interrupts at least once to a temperature of the fixed catalyst beds from 200 to 450 ° C (in a two-stage partial oxidation of propene to acrylic acid over the Fixed catalyst beds of propene oxidation leading to acrolein) Gas mixture G through the fixed catalyst bed of the partial oxidation from acrolein to acrylic acid respectively. Subsequently the partial oxidation is achieved while largely maintaining the process conditions continued (the restoration of acrolein load of the corresponding Fixed catalyst bed is preferably carried out slowly, e.g. as in DE-A 10337788) and the temperature of the fixed catalyst beds adjusted so that the Acroleinumsatz the desired target value reached. In general, this temperature value for the same sales at a slightly lower value than the temperature, the the fixed catalyst bed before the interruption of the partial oxidation and the treatment with the gas mixture G had.

From Starting from this temperature value of the fixed catalyst bed, the Partial oxidation of acrolein, largely retaining the other conditions and thereby the decrease in the activity of the fixed catalyst beds on the Time in an appropriate manner counteracted by the fact that from time to time the Increases the temperature of the fixed catalyst beds. For example, before the conducted temperature increase the fixed catalyst bed is permanently ≥ 10 ° C or ≥ 8 ° C, the partial oxidation becomes again interrupted to the gas mixture G (optionally on the Fixed catalyst bed of a propene reaction stage leading) by the fixed catalyst bed of the acrolein partial oxidation of acrolein to acrylic acid respectively. Thereafter, the partial oxidation is resumed as described etc .. Does not satisfy the achieved target product selectivity more, as described e.g. in one of the at least two relevant oxidation roads a partial or Vollkatalysatorwechsel carry out and subsequently Continue according to the invention.

As a general rule should be an acrolein to acrylic acid heterogeneously catalyzed partial oxidation are operated so that the oxygen content in the resulting product gas still 1.5 to 3.5% by volume.

The separation of the acrylic acid is preferably carried out according to the invention from the mixture of product gas streams. This separation of acrylic acid and the generally accompanying cycle gas formation can be carried out, for example, as in the publications WO 97/48669, US-A 2004/0242826, WO 01/96271 and US Pat US 6,410,785 described in a Zielproduktabtrennstrasse.

There the separation efficiency of separation columns normally with increasing Number of theoretical plates increases, it is e.g. possible, over longer operating times with smaller (i.e., a lower number of theoretical plates having) and thus more cost-effective Separation columns the desired To achieve purity of the raw target product.

Become n (≥2) oxidation reactor systems in accordance with the invention operated so that the mixture stream target compounds from all n-oxidation reactor systems contains it is inventively favorable if the age of the n catalyst feeds of the n oxidation reactor systems on the time axis are so staggered that the operating age difference essentially between successive points on the time axis is the same size and no two points on top of each other.

• a) die heterogen katalysierte Gasphasen-Partialoxidation wenigstens einer organischen Vorläuferverbindung mit molekularem Sauerstoff in zwei parallel betriebenen, Katalysatorbeschickungen enthaltenden, Oxidationsreaktorsystemen unter Erhalt von zwei die Zielverbindung jeweils enthaltenden Produktgasströmen, von denen jeweils einer auf eines der beiden Oxidationsreaktorsysteme zurückgeht und
• b) anschließende Abtrennung der wenigstens einen Zielverbindung aus den zwei Produktgasströmen unter Erzeugung von einem Roh-Zielproduktstrom, bei dem man,
• c) vor der Abtrennung die zwei Produktgasströme, oder im Verlauf der Abtrennung zwei auf dem Weg von den zwei Produktgasströmen zu dem einen Roh-Zielproduktstrom gegebenenfalls erzeugte Zielprodukt enthaltende Folgeströme und/oder nach der Abtrennung aus den zwei Produktgasströmen im Verlauf der Abtrennung erzeugte Roh-Zielproduktströme miteinander zu einem Gemischstrom vermischt, dadurch gekennzeichnet, dass eine der beiden Katalysatorbeschickungen der zwei parallel betriebenen Oxidationsreaktorsysteme wenigstens eine Katalysatorteilmenge enthält, an der die heterogen katalysierte Gasphasen-Partialoxidation bereits länger durchgeführt wird, als an allen Katalysatorteilmengen der anderen Katalysatorbeschickung.

In a somewhat different manner, the present invention provides a process for preparing at least one organic target compound, which comprises:

• a) the heterogeneously catalyzed gas phase partial oxidation of at least one organic precursor compound with molecular oxygen in two parallel, catalyst feed containing oxidation reactor systems to obtain two target product compound respectively containing product gas streams, each of which goes back to one of the two oxidation reactor systems and
• b) subsequently separating the at least one target compound from the two product gas streams to produce a crude target product stream comprising:
• c) before the separation, the two product gas streams, or in the course of the separation two subsequent streams containing on the way from the two product gas streams to the raw target product stream optionally generated target streams and / or after separation from the two product gas streams generated in the course of the separation raw. Target product streams mixed together to form a mixture stream, characterized in that one of the two catalyst feeds of the two parallel oxidation reactor systems containing at least one catalyst portion at which the heterogeneously catalyzed gas phase partial oxidation is carried out for longer than at all catalyst portions of the other catalyst feed.

Of course you can in the method according to the invention more than one organic target compound can be generated simultaneously. An example for is the propane partial oxidation, in which acrolein and acrylic acid in the Usually be formed simultaneously. Similarly, acrylic acid and Acrylonitrile in a partial oxidation of propene and / or propane are then formed simultaneously when the ammonia content of the reaction gas mixture correspondingly substoichiometric chosen becomes. Alternatively, one can also start from a reaction gas mixture, more than one precursor compound contains. Finally It should be noted that the principle of the procedure according to the invention analogous to catalyzed esterifications or other catalyzed Reactions can be applied. It is also essential according to the invention that a minor component outlet always forms the specification-compliant target connection.

Examples and Comparative Examples (Two-stage heterogeneously catalyzed gas-phase partial oxidation of Propene to acrylic acid)

A) General experimental setup

I. Reactors for the first reaction step from propene to acrolein

One Reactor consisted of a double-walled cylinder made of stainless steel (cylindrical guide tube, surrounded from a cylindrical outer container). The Wall thicknesses were everywhere 2 to 5 mm.

Of the Inner diameter of the outer cylinder was 91 mm. The inner diameter of the guide tube was about 60 mm.

Above and below was the double-walled cylinder through a lid, respectively Floor completed.

The contact tube (400 cm total length, 26 mm inner diameter, 30 mm outer diameter, 2 mm wall thickness, stainless steel) was guided by the cylindrical guide tube in the cylindrical container housed so that at the upper or lower end thereof (sealed) by the lid or Ground respectively just stood out. The heat exchange medium (molten salt consisting of 53% by weight of potassium nitrate, 40% by weight of sodium nitrite and 7% by weight of sodium nitrate) was in the cylindrical container with compound in the guide tube. In order to ensure as uniform as possible thermal boundary conditions on the outer wall of the contact tube over the entire contact tube length (400 cm), the heat exchange medium by means of a propeller pump for the purpose of its tempering first by the cylindrical container and then for the purpose of tempering the contact tube through the space between the guide tube and Contact tube pumped. It was then returned to the cylindrical container.

By an applied on the outer shell of the cylindrical container electrical heating, the temperature of the heat exchange medium could be regulated to the desired level. Otherwise, there was air cooling. Reactor charge: Considered over the first-stage reactor, molten salt and the starting reaction gas mixture 1 were conducted in cocurrent. The reaction gas starting mixture 1 entered from below into the contact tube. It was fed into the contact tube at a temperature of 165 ° C. The molten salt also entered from below with a temperature T in ^a cylindrical guide tube and above with a temperature T ^out of the cylindrical guide tube, which was up to 2 ° C above T ^a . The inlet temperature T ^was always dimensioned (about 320 ° C), that in all cases, a propene conversion of 97.5 ± 0.1 mol% for a single pass of the reaction gas mixture returned through the contact tube. Contact tube charge: (from bottom to top) Section A: 90 cm length Prefill of steatite balls of 4-5 mm diameter. Section B: 100 cm length of catalyst feed with a homogeneous mixture of 30 wt% steatite rings of geometry 5 mm x 3 mm x 2 mm (outside diameter x length x inside diameter) and 70 wt% of full catalyst from section C. Section C: 200 cm length catalyst charge with annular (5 mm × 3 mm × 2 mm = outer diameter × length × inner diameter) unsupported catalyst according to Example 1 of DE-A 10046957 (stoichiometry: [Bi ₂ W ₂ O ₉ × 2WO ₃ ] O _{, 5} [Mo ₁₂ Co _5.5 Fe _2.94 Si _1.59 K _0.08 O _x ] ₁ ). Section D: 10 cm length of bedding out of steatite rings of geometry 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter)

Two reactors as described above were operated in parallel.

II. Intercooling and possibly oxygen intermediate feed (air as secondary gas)

The the two first-stage reactors were leaving product gas streams for the purpose of intercooling (indirectly by means of air) together through a connecting tube (40 cm length, 26 mm inner diameter, 30 mm outer diameter, 2 mm wall thickness, stainless steel, wrapped with 1 cm of insulating material), which has a length of 20 cm centered, with an inert bed out Steatite rings of geometry 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter) loaded and Y-shaped was flanged directly to the first stage contact tubes.

The Mixture of the product gas streams occurred in all cases with a temperature of more than 320 ° C in the connecting pipe and left it with one above 200 ° C and below 270 ° C located temperature.

At the End of the connecting tube could the cooled mixture of the product gas streams depending on Needed on the pressure of the mixture flow compressed air metered become. The resulting reaction gas mixture 2 became the same Shares directly into the two parallel second stage contact tubes guided, at which the above-mentioned connecting pipe with its other End also Y-shaped was flanged.

III. Reactors for the second Reaction stage of acrolein to acrylic acid

Contact tube fixed bed reactors were used, which were identical to those for the first reaction stage. Salt melt and reaction gas mixture were also conducted in direct current over the individual reactor. The molten salt entered the bottom of the guide tube, the reaction gas starting mixture 2 also. The inlet temperature ^T of the molten salt was always set to (about 26.3 ° C), that in all cases an acrolein conversion of 99.3 ± 0.1 mol% for a single pass of the reaction gas mixture returned. T ^from the molten salt was up to 2 ° C above T ^a .

The Contact tube feed (from bottom to top) was:

Section A: 70 cm in length
Fillet of steatite rings of geometry 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter).

Section B: 100 cm in length
Catalyst feed with a homogeneous mixture of 30 wt% steatite rings of geometry 7 mm x 3 mm x 4 mm (outside diameter x length x inside diameter) and 70 wt% shell catalyst from section C.

Section C: 200 cm in length
Catalyst charge with annular (7 mm × 3 mm × 4 mm = outer diameter × length × inner diameter) coated catalyst according to Preparation Example 5 of DE-A 100 46 928 (stoichiometry: Mo ₁₂ V ₃ W _1.2 Cu _2.4 O _x ).

Section D: 30 cm in length
Bedding of steatite balls of 4-5 mm diameter.

IV. Separation of acrylic acid the mixture of product gas streams the second reaction stage

The two product gas streams coming from the second reaction stages together and the resulting product gas stream by means of water, the 350 gew.ppm Hydroquinone (HQ) as a polymerization inhibitor contained (temperature = 4 ° C) in a Venturi separator (similar in construction to the Venturi tubes and accelerate the gas mixture at the narrowest point of the Venturi tube, simultaneously inject the cooling water and mix intensively in the high pressure losses resulting turbulent Flow field; downstream Separators separate the liquid phase from) a direct cooling subjected and the resulting mixture to a liquid phase fed. About one heat exchangers became the deposited aqueous Phase returned to the venturi separator (360 l / h). Excess aqueous phase was continuously dissipated.

Of the to a temperature of 30 ° C cooled Mixture gas stream was passed from below into an absorption column, the 11 bell bottoms in equidistant Arrangement contained (ground clearance: 54 mm, bottom diameter: 12 mm) and the countercurrent of 1.10 kg / h by HQ stabilized water exposed as an absorbent (at the top of the column at a temperature from 2 ° C given up). The column sump was hourly 1.7 kg of about 40 wt .-% aqueous acrylic acid taken. The tail gas leaving the absorption column at the top was supplied as needed to the combustion and / or as recycle gas to Formation of the reaction gas starting mixture 1 used (via a Compressor returned to the first stage reactors).

B) Depending from the catalyst feeds and the composition of the starting reaction gas mixtures achieved results

Comparative Example 1

Both First stage reactors and both second stage reactors were fresh Catalysts fed.

The composition of the reaction mixture starting gas fed to both first-stage reactors was:
5.3% by volume of propene,
2.4% by volume of water,
0.7% by volume of propene, water, oxygen and nitrogen, various constituents,
molecular oxygen in an amount that the molar ratio of contained molecular oxygen to propene contained was 1.52, and
as residual amount up to 100% by volume of molecular nitrogen.

The propene load of the two first-stage contact tube charges was 110 Nl / lh. Fresh oxygen source was air. Per vol .-% Frischpropen the starting reaction gas mixture contained 8 vol .-% cycle gas. Secondary air was metered into the mixture of the product gas streams of the first reaction stages. Their amount was calculated so that the ratio of secondary air / fresh Propen (each in Nl) was 1.45. This resulted in a residual oxygen content of 3.0% by volume in the product gas of the second reaction stage. The pilot plant was operated continuously over 28 weeks. The selectivity of the target product formation (acrylic acid) S ^{AA achieved} as a function of the operating time (in weeks) and the by-product selectivities for acetic acid (S ^HAc ) and formaldehyde (S ^F ), depending on the operating time, in each case in mol% based on reacted propene , shows the following Table 1 (always based on the output of the second reaction stage). Likewise, Table 1 shows the molar ratio V of acrylic acid to acetic acid in the aqueous absorbate. Table 1

The further separation of the aqueous, Absorbate containing the target product must be designed for a ratio of V = 43.4.

example 1

First, Comparative Example 1 was repeated. After the repetition of Comparative Example 1 had produced 2200 kg of acrylic acid without interruption, the operation was interrupted and replaced only the catalyst feed of one of the two Oxidationsreaktorstrassen in both stages by a corresponding, but fresh catalyst charge. Then proceed as described in Comparative Example 1 weiterver. The results obtained after the interruption as a function of the operating time (weeks) are shown in Table 2. Table 2

The further separation of the aqueous, Absorbate containing the target product need only for a ratio V = 52.4 designed.

Comparative Example 2

Comparative example 1 was repeated (however, the dilution in section B of the second reaction step was chosen to be 40% by weight), but the composition of the feed mixture for the first reaction steps was chosen as follows:
7.3% by volume of propene,
10% by volume of water,
0.7% by volume of propene, water, oxygen and nitrogen, various constituents,
molecular oxygen in an amount that the molar ratio of contained molecular oxygen to propene contained was 1.73, and
as residual amount up to 100% by volume of molecular nitrogen.

Secondary air was not dosed. Per vol .-% Frischpropen contained the reaction gas starting mixture 3.5 vol .-% cycle gas.

Table 3 shows the results depending on the operating time (in weeks). Table 3

The further separation of the aqueous, Absorbate containing the target product must be designed for a ratio of V = 38.5.

Example 2

First, Comparative Example 2 was repeated. After the repetition of Comparative Example 2 had produced 2200 kg of acrylic acid without interruption, the operation was interrupted and only the catalyst charge of one of the two Oxidationsreaktorstrassen in both stages by a corresponding, but replaced fresh catalyst feed. Then, the procedure was continued as described in Comparative Example 3. The result obtained after the interruption as a function of the operating time (weeks) is shown in Table 4. Table 4

The further separation of the aqueous, Absorbate containing the target product need only for a ratio V = 42.3.

A Device according to claim 22 is suitable for implementation the method according to the invention.

method according to claim 14 to 20 form e.g. the basis for an application of the procedure according to the invention.

Claims (22)

A process for the preparation of at least one organic target compound by a) heterogeneously catalyzed gas phase partial oxidation of at least one organic precursor compound with molecular oxygen in at least two oxidation reactor systems containing catalyst feeds operated in parallel to yield at least two target compounds each containing one each of the at least two oxidation reactor systems Product gas streams; and b) subsequently separating the at least one target compound from the at least two product gas streams to produce at least one crude target product stream comprising c) at least two of the at least two product gas streams before separation, or at least two in the course of separation from the at least two product gas streams to the at least one raw target product stream optionally produced target product containing subsequent streams and / or after separation from the we at least two product gas streams in the course of the separation optionally produced raw target product streams mixed together to form a mixture stream, characterized in that at least one of the catalyst feeds of the at least two parallel operated oxidation reactor systems on which the target compounds contained in the mixture stream containing at least one catalyst portion contains the heterogeneously catalyzed gas phase partial oxidation has been carried out for longer than at all catalyst portions of the at least one other catalyst feed. Method according to claim 1, characterized in that that the at least one of the catalyst feeds of at least two parallel oxidation reactor systems in which the contained in the mixture stream target compounds were formed, at least contains a catalyst subset, at the heterogeneously catalyzed gas phase partial oxidation already at least 30 calendar days longer carried out is, as at all catalyst portions of at least one other Catalyst charge. Method according to claim 1 or 2, characterized that the heterogeneously catalyzed gas-phase partial oxidation in two parallel operated oxidation reactor systems and the separation the target compound made from the mixture flow of the two product streams becomes. Process according to one of claims 1 to 3, characterized in that the at least one organic precursor compound comprises propylene, isobutene, ethylene, ethane, propane, isobutane, acrolein, methacrolein, Butadiene, o-, m-, p-xylene and / or naphthalene. Method according to one of claims 1 to 4, characterized that the heterogeneously catalyzed gas phase partial oxidation the two-stage heterogeneously catalyzed partial oxidation of propene to acrylic acid. Method according to one of claims 1 to 4, characterized that the heterogeneously catalyzed gas phase partial oxidation the single-stage heterogeneously catalyzed partial oxidation of propane to acrylic acid. Method according to one of claims 1 to 4, characterized that the heterogeneously catalyzed gas phase partial oxidation the two-stage heterogeneously catalyzed partial oxidation of isobutene to methacrylic acid. Method according to one of claims 1 to 7, characterized that the at least two parallel operated Oxidationsraktorsysteme consist of two parallel operated tandem tube bundle reactor arrangements. Method according to claim 5, characterized in that that the catalysts of the first reaction stages Mo, Bi and Fe have containing multimetal oxide. Method according to one of claims 5 or 9, characterized in that the catalysts of the second reaction stage contain Mo and V. Multimetal oxide materials are. Method according to one of claims 1 to 10, characterized in that the separation of the at least one target compound from the at least two product gas streams includes a fractional condensation. Method according to one of claims 1 to 10, characterized in that the separation of the at least one target compound from the at least two product gas streams includes absorption. Method according to one of claims 1 to 10, characterized in that the separation of the at least one target compound from the at least two product gas streams a rectification, or a crystallization, or both. Process for the preparation of at least one organic Target compound by heterogeneously catalyzed gas-phase partial oxidation at least one organic precursor compound with molecular Oxygen in at least two parallel catalyst feeds containing oxidation reactor systems to obtain at least two each containing the target compound and each on one the at least two oxidation reactor systems receding product gas streams, characterized marked that one first a total stream of the at least one organic precursor compound produced starting reaction gas mixture and this then via a Distribution system the at least two parallel operated oxidation reactor systems with the proviso supplies, that at least one of the catalyst feeds of at least two parallel oxidation reactor systems at least one Contains catalyst subset, at the heterogeneously catalyzed gas phase partial oxidation already longer is carried out, as at all catalyst portions of at least one other Catalyst charge. Method according to claim 14, characterized in that that the at least one of the catalyst feeds of at least two parallel oxidation reactor systems at least one Contains catalyst subset, at the heterogeneously catalyzed gas phase partial oxidation already at least 30 calendar days longer carried out is, as at all catalyst portions of at least one other Catalyst charge. Method according to claim 14 or 15, characterized that the at least one organic precursor compound is propylene, isobutene, Ethylene, ethane, propane, iso-butane, acrolein, methacrolein, butadiene, o-, m-, p-xylene and / or naphthalene. Method according to one of claims 14 to 16, characterized that the heterogeneously catalyzed gas phase partial oxidation the two-stage heterogeneously catalyzed partial oxidation of propene to acrylic acid. Method according to one of claims 14 to 16, characterized that the heterogeneously catalyzed gas phase partial oxidation the single-stage heterogeneously catalyzed partial oxidation of propane to acrylic acid. Method according to one of claims 14 to 18, characterized that the at least two parallel operated oxidation reactor systems consist of two parallel operated tandem tube bundle reactor arrangements. Method according to claim 17, characterized in that in that the catalysts of the first reaction stage contain Mo, Bi and Fe Multimetal oxide materials and the catalysts of the second reaction stage Mo and V containing multimetal oxide materials. Method according to claim 5 or 17, characterized that the propene, the at least two parallel oxidation reactor systems from a heterogeneously catalyzed reaction carried out in a dehydrogenation reactor Dehydration and / or oxydehydrogenation of propane is fed to propene. Apparatus comprising two oxidation reactor systems, which are charged with catalysts that are used to produce a organic target compound by heterogeneously catalyzed partial oxidation an organic precursor compound are suitable and at the output in each case a line for the removal of the target compound containing product gas stream from the respective Oxidation reactor system is located with increasing distance from the two oxidation reactor systems to a product gas line together which leads to a device in which the product gas stream partially or completely can be condensed, characterized in that the catalyst charge one of the two oxidation reactor systems at least one partial catalyst fraction contains where more target product has already been produced than at the partial catalyst levels the catalyst feed of the other oxidation reactor system.