DE102006054214A1 - Exothermic heterogeneously catalyzed partial gas phase oxidation of a starting compound e.g. propylene to a target compound e.g. acrylic acid, comprises oxidizing a gas mixture containing e.g. the starting compound and molecular oxygen - Google Patents

Abstract

Conducting an exothermic heterogeneously catalyzed partial gas phase oxidation of an organic starting compound to an organic target compound in two different operating conditions I and II, comprises oxidizing a reaction gas starting mixture containing the organic starting compound, molecular oxygen and at least an inert dilution gas, through a solid bed catalyst present in the tube of a tube bundle reactor to produce a product mixture containing the organic target compound. Conducting an exothermic heterogeneously catalyzed partial gas phase oxidation of an organic starting compound to an organic target compound in two different operating conditions I and II, comprises oxidizing a reaction gas starting mixture containing the organic starting compound, molecular oxygen and at least an inert dilution gas, through a solid bed catalyst present in the tube of a tube bundle reactor to produce a product mixture containing the organic target compound; where: the tubes are surrounded by spaces for adjusting the reaction temperature; at least a fluid thermal carrier is passed in with an inlet temperature (Ti) and passed out with an outlet temperature (To) through the tubes; the outlet temperature is greater than the inlet temperature; the solid bed catalyst is charged with a load (L1) having the organic starting compound in an operating condition I at an inlet temperature (Ti1) and is charged with a load (L2) having the organic starting compound in the operating condition II at an inlet temperature (Ti2); the load (L2) is greater than the load (L1) and the inlet temperature (Ti2) is greater than (Ti1); the inlet temperature (Ti1) is elevated to the inlet temperature (Ti2) during the change of operating condition I to the operating condition II and subsequently the loading of the solid bed catalyst with the organic starting compound increases the (L1) value to the (L2) value.

Description

The present invention relates to a process for operating an exothermic heterogeneously catalyzed partial gas phase oxidation of an organic starting compound to an organic target compound in mutually different operating states I and II, comprising reacting a starting gas mixture containing the organic starting compound, molecular oxygen and at least one inert diluent gas to obtain a organic target compound-containing product gas mixture passes through an in-the tubes of a tube bundle reactor, fixed catalyst bed as well as in the fixed catalyst bed containing tubes of the surrounding tube bundle reactor chamber to the reaction temperature setting in located in the tubes fixed catalyst bed, at least a fluid heat carrier having an entry temperature ^T in and with a outlet temperature T ^out> T ^again leads out of this, while the fixed catalyst bed in operation ^{A a a>} T _I ^a load I at an inlet temperature T _I with a load L ^I of the organic starting compound and in the operating state II at an inlet temperature T _II with an L ^II of the organic starting compound with the proviso L ^II> L ^I and T _II.

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 them different reactions of an organic compound be under reactive action of molecular oxygen here summarized as partial oxidations of an organic compound.

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

When under the conditions of the heterogeneously catalyzed partial Gas phase oxidation Substantially inert diluent gas become such diluent gases understood, their constituents under the conditions of heterogeneous catalyzed gas phase partial oxidation - each component considered separately - more as unchanged from 95 mol%, preferably more than 99 mol% stay.

Under the loading of a reaction step catalyzing a catalyst fixed bed with reaction gas mixture, the amount of reaction gas mixture in Normlitern (= Nl, the volume in liters, the corresponding reaction gas mixture amount under normal conditions, i.e. at 0 ° C and 1 atm), the fixed catalyst bed, based on the volume of its bed, i.e., on his bulk volume (pure inert material sections are not included), fed per hour becomes (→ unit = Nl / lh). The load can only on a part of the reaction gas mixture (for example, the organic starting compound of the partial oxidation). Then it is the volume amount of this ingredient (e.g., the organic Starting compound of the partial oxidation), which is the fixed catalyst bed, based on the volume of its bed, is fed per hour (In the case of the organic starting compound of the partial oxidation the load in this document is also referred to as L).

It is generally known that numerous basic chemicals (organic target compounds, target products) can be generated by partial and heterogeneously catalyzed oxidation of various organic starting compounds with molecular oxygen in the gas phase in the fixed catalyst bed. By way of example (all of them are suitable for the process according to the invention), the reaction of propylene to acrolein and / or acrylic acid (cf., for example, US Pat DE-A 23 51 151 ), the reaction of tert-butanol, isobutene, isobutane, isobutyraldehyde or the methyl ether of tert-butanol to methacrolein and / or methacrylic acid (cf., for example DE-A 25 26 238 . EP-A 92097 . EP-A 58927 . 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 (cf., for example DE-A 25 26 238 ), the reaction of o-xylene, p-xylene or naphthalene to phthalic anhydride (cf., for example EP-A 522 871 ) or the corresponding acids and the reaction of butadiene to maleic anhydride (cf., for example DE-A 21 06 796 and DE-A 16 24 921 ), the reaction of n-butane to maleic anhydride (cf., for example GB-A 14 64 198 and GB-A 12 91 354 ), the conversion of indanes to eg anthraquinone (cf., eg DE-A 20 25 430 ), the reaction of ethylene to ethylene oxide or of propylene to propylene oxide (cf., for example DE-AS 12 54 137 . DE-A 21 59 346 . EP-A 372 972 . WO 89/07101 . DE-A 43 11 608 and Beyer, Textbook of Organic Chemistry, 17th Edition (1973), Hirzel Verlag, Stuttgart, p. 261 ), the reaction of propylene and / or acrolein to acrylonitrile (cf., for example DE-A 23 51 151 ), the conversion of isobutene and / or methacrolein to methacrylonitrile (ie, the term partial oxidation in this document is also intended to include partial ammoxidation, ie partial oxidation in the presence of ammonia), oxidative dehydrogenation of hydrocarbons (cf., for example, US Pat DE-A 23 51 151 ), the reaction of propane to acrylonitrile or to acrolein and / or acrylic acid (cf., for example DE-A 101 31 297 . EP-A 1090 684 . EP-A 608 838 . DE-A 100 46 672 . EP-A 529 853 . WO 01/96270 and DE-A 100 28 582 ), the reaction of iso-butane to methacrolein and / or methacrylic acid, and the reactions of ethane to acetic acid, of ethylene to ethylene oxide, of benzene to phenol and of 1-butene or 2-butene to the corresponding butanediols etc ..

the Fixed catalyst bed has the task of causing the desired Gas phase partial oxidation over the complete Oxidation preferably proceeds. The chemical reaction takes place when the reaction gas mixture the Fixed bed flows through while the residence time of the reaction gas mixture in selbigem.

at the solid state catalysts to be used they are common around oxide masses or precious metals (e.g., Ag). The catalytically active Oxide compound can be just another element besides oxygen contain more than one other element (multielement oxide masses). Especially common 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 These are not simple physical mixtures of oxides of the elementary constituents, but heterogeneous mixtures of complex Poly compounds of these elements.

In practice, the abovementioned catalytically active solids are generally shaped into very different geometries (rings, solid cylinders, spheres, etc.). The molding (to the molding) can be carried out so that the catalytically active composition is formed as such (for example in extruders or tableting), so that the result is a so-called solid catalyst, or in that the active composition is applied to a preformed support ( see eg WO 2004/009525 and WO 2005/113127 ).

Examples of catalysts which are suitable for heterogeneously catalyzed gas phase partial oxidations according to the invention in the fixed catalyst bed of at least one organic starting compound can be found, for example, in US Pat DE-A 100 46 957 , in the EP-A 1097745 , in the DE-A 44 31 957 , in the DE-A 100 46 928 , in the DE-A 199 10 506 , in the DE-A 196 22 331 , in the DE-A 101 21 592 , in the EP-A 700714 , in the DE-A 199 10 508 , in the EP-A 415347 , in the EP-A 471853 and in the EP-A 700893 ,

Most of time be heterogeneously catalyzed gas phase partial oxidation, in particular mentioned at the beginning of this document, at elevated reaction temperatures (usually a few hundred ° C, usually 100 to 600 ° C) carried out.

Of the Working pressure (absolute pressure) in heterogeneously catalyzed gas phase partial oxidations may be below 1 atm, at 1 atm, or above 1 atm. Usually is he 1 to 10 atm, usually 1 to 3 atm.

by virtue of normally pronounced exothermic character of heterogeneously catalyzed gas phase partial oxidations organic compounds containing molecular oxygen, the Reaction partner usually with one under the conditions of gas-phase catalytic Partial oxidation diluted in essentially inert gas, the with its heat capacity released 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.

One other commonly used inert diluent gas is because of its general availability Steam. Both nitrogen and water vapor also form advantageously non-combustible inert diluent gases.

Frequently, cycle gas is also used as inert diluent gas (cf., for example, US Pat EP-A 1180508 ) or diluted exclusively with recycle gas. As recycle gas, the residual gas is referred to, the after a one-stage or multi-stage (in the multi-stage heterogeneously catalyzed gas phase partial oxidation of organic compounds, the gas phase partial oxidation, in contrast to the single-stage heterogeneously catalyzed gas phase partial oxidation not in one, but in at least two reactors connected in series are performed (which can seamlessly merge into one another in a common housing (eg the "single reactor") and then form separate reaction zones where oxidants are added between successive reactors, and the multistage is used in particular when the partial oxidation takes place in successive steps In these cases, it is often expedient to optimally adapt both the catalyst and the other reaction conditions to the particular reaction step, and the reaction step in a separate reactor (or in a separate (own) reaction zone of a reactor), in a separate reaction stage However, it can also be used if, for reasons of heat dissipation or for other reasons (cf. DE-A 199 02 562 ) the sales is smeared on several successive reactors; an example of a frequently carried out in two stages heterogeneously catalyzed gas phase partial oxidation is the partial oxidation of propylene to acrylic acid; in the first reaction stage, the propylene is oxidized to acrolein, and in the second reaction stage, the acrolein is oxidized to acrylic acid; In a corresponding manner, methacrylic acid production, usually starting from isobutene, is also frequently carried out in two stages; both aforementioned partial oxidations can also be carried out in one stage (both steps in one and the same fixed catalyst bed superimposed in a reactor) using heterogeneously catalyzed gas phase partial oxidation of at least one organic compound, if the target product is more or less selectively selected from the product gas mixture (eg by absorption in a suitable solvent) has separated. As a rule, it consists predominantly of the inert diluent gases used for the partial oxidation and of water vapor which is usually formed by-product or added as diluent gas in the partial oxidation and carbon oxides formed by undesired complete oxidation. In some cases, it still contains small amounts of oxygen not consumed in the partial oxidation (residual oxygen) and / or of unreacted organic starting compounds.

Of the As a by-product formed steam ensures in most cases that the partial oxidation without significant volume changes of the reaction gas mixture runs.

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 .-%, often at ≥ 95 vol .-% of N _2, H ₂ O and / or CO ₂ and thus in essentially non-combustible inert diluent gases.

The co-used inert diluent gases On the one hand, they help to absorb and ensure the heat of reaction on the other hand, safe operation of the heterogeneously catalyzed Gas phase partial oxidation of an organic compound by the reaction gas mixture outside of the explosion area. In heterogeneously catalyzed gas-phase partial oxidations unsaturated organic compounds can often also saturated Hydrocarbons, i. flammable gases, as inert diluent gases be used. The concomitant use of inert diluent gases with elevated specific molar heat is advantageous.

As a result of a variety of possible parallel and / or subsequent reactions, the measures of co-use of catalysts and inert diluent gas are usually not sufficient to thermally adequately control the gas phase partial oxidation with a view to selective conversion of the partially oxidized organic starting compound to the desired target product. Rather, it is necessary for the most selective possible implementation of a heterogeneously catalyzed gas phase partial oxidation in the fixed catalyst bed to additionally guide the course of the reaction temperature in the fixed catalyst bed by further measures. These additional measures usually also have an advantageous effect on the service life of the fixed catalyst bed. Namely, it is well known that one can operate a heterogeneously catalyzed gas phase partial oxidation of an organic starting compound in the fixed catalyst bed substantially continuously over extended periods of time (the service life) on the same fixed catalyst bed, wherein the reaction conditions can be maintained substantially constant if the occurrence is too high Temperatures in the catalyst fixed bed largely temperatures in the fixed catalyst bed is largely avoided (see, eg DE-A 103 51 269 ).

As such an additional measure, an exothermic heterogeneously catalyzed gas phase partial oxidation is normally carried out in a shell-and-tube reactor. The fixed catalyst bed is located in the tubes (reaction tubes or catalyst tubes) of the tube bundle reactor and the reaction gas mixture is passed through the thus charged reaction tubes. By surrounding the reaction tubes in the tube bundle reactor space (ambient space) for targeted removal of the heat of reaction at least one fluid (liquid and / or gaseous) heat transfer medium (usually a molten salt, or a flüssi ges metal, or a boiling liquid, or a hot gas phase). He is screwing in at an inlet temperature T ^into the surrounding space and led out at an outlet temperature T ^from out of the surrounding space, where T ^{is a} true ^off> T (see. Eg EP-A 700 714 and EP-A 700 893 ). Basically, the surrounding space may also be segmented by corresponding partition walls and through each of the surrounding space segments a substantially separate (the partition walls may be permeable, and communicating the separately supplied heat carriers enable small extent) fluid heat carriers are guided, for the T ^off> T ^a met is. Such a shell-and-tube reactor type is referred to as a multi-zone tube bundle reactor or also simply shortened as a multizone reactor (cf., for example, US Pat DE-A 199 27 624 . DE-A 199 48 523 . WO 00/53557 . DE-A 199 48 248 . WO 00/53558 . WO 2004/085365 . WO 2004/085363 . WO 2004/085367 . WO 2004/085369 . WO 2004/085370 . WO 2004/085362 . EP-A 1 159 247 . EP-A 1 159 246 . EP-A 1 159 248 . EP-A 1,106,598 . WO 2005/021149 . US-A 2005/0049435 . WO 2004/007064 . WO 05/063673 . WO 05/063674 . DE-A 10 2004 025 445 , the European Application No. 06100535.1 and the literature cited in these references) and an individual ambient space segment is referred to as the temperature zone of the tube bundle reactor.

Frequently becomes now an exothermic heterogeneously catalyzed partial gas phase oxidation an organic starting compound to an organic target compound via a longer Period (several days or weeks) under substantially stable Operated operating conditions (the gas phase oxidation is located in a substantially stationary Operating state).

That is, in an operating condition I, a reaction gas input mixture containing the organic starting compound, molecular oxygen and at least one inert diluent gas is substantially retained over time and with substantially constant loading of the fixed catalyst bed in the reaction tubes (the reaction tubes are normally all as possible) uniformly filled) out to a load L ^I of the organic starting compound by an in-the tubes of a tube bundle reactor, fixed catalyst bed, in the surrounding space at least one fluid heat carrier having a substantially stable inlet temperature T ^{_I, a} in and with an essentially stable outlet temperature T _I ^{is led out} of this again. The selected operating conditions are in this case primarily adapted to the space-time yield of organic target compound demanded by the production plant in the production period concerned and to the operating age of the fixed catalyst bed (deactivation of the fixed catalyst bed associated with a longer operating life can be achieved, for example, by measures such as increasing the working pressure ( see eg DE-A 10 2004 025 445 ) And / or be counteracted by T _I ^(cf.. DE-A 103 51 269 ).

In many cases However, the market demand for an organic target connection is not a stable size, but fluctuates over longer Periods.

For example, it can skyrocket. Instead of responding to such an increased market demand with an additional production plant, it can also be responded to by increasing the space-time yield of target product in existing production facilities. This is possible, for example, by leaving the operating state I, and changing to an operating state II, which is characterized both by a higher value L ^II (> L ^I ) for the loading of the fixed catalyst bed with the organic starting compound, and by a higher inlet temperature T _II ^(a> T _I) a fluid heat-carrier is characterized in the surrounding space of the at least ^one. The increase in the inlet temperature T ^{a of} the fluid heat carrier pursues the purpose of reacting at reduced by the load increase Reaktandenverweilzeit in the fixed catalyst bed the same molar proportion of the organic starting compound and thereby increase the space-time yield of target product.

The EP-A 1 695 954 now teaches to make the change from the operating state I to the operating state II so that ^a first of the load L is increased while maintaining the value T _I for the inlet temperature of the fluid heat-carrier ^I to the value L ^II and only subsequently the temperature T _I ^a in small steps to the temperature T _II ^{one is} increased. As an advantage of this procedure makes the EP-A 1 695 954 asserted that the increase in the so-called hot spot temperature of the fixed catalyst bed associated with the change of the operating state passes through the lowest possible maximum value when carrying out the change.

In this case, the highest temperature occurring in the flow direction of the reaction gas mixture in the fixed catalyst bed within a temperature zone is referred to as hotspot temperature T ^max . This highest temperature of the fixed catalyst bed is ^a in the respective temperature zone above the respective temperature zone for each corresponding value for T. T ^max is essentially identical to the highest reaction temperature value occurring in the corresponding temperature. The difference between T ^max and T ^a is referred to as the hotspot expansion of the respective temperature zone.

A disadvantage of the in the EP-A 1 695 954 However, the proposed procedure is that after the increase of L ^I to L ^II to the time, ^{a a a} has the T when changing from T _I to T _II reached for T _II ^{is a} required value, the value for T ^a the increased value L ^II for the loading of the fixed catalyst bed with the organic starting compound. That is, during the passage of the reaction gas input mixture through the fixed catalyst bed, an increased proportion of the organic starting compound is not converted to the desired target product. After separation of the target product from the product gas mixture thus remains a residual gas with an increased proportion of the organic starting compound. Since the residual gas can at most be partially recycled as recycle gas in the partial oxidation (otherwise the inert gas content of the reaction gas input mixture steadily levels up) and otherwise normally disposed of (eg burned), results along in the EP-A 1695954 recommended procedure, a significant loss of value product. Moreover, if the starting organic compound is a compound which is prone to undesired spontaneous radical polymerization, as in the case of acrolein (eg its partial oxidation to acrylic acid), unreacted acrolein may be present in the course of the acrolein partial oxidation Target product (eg acrylic acid) separation to a considerable extent lead to unwanted polymer formation and make an interruption of the target product separation required to rid the separator used for this purpose (eg column) of undesirable polymer.

The It is an object of the present invention to provide a process to change the operating state of an exothermic heterogeneously catalyzed partial gas phase oxidation of an organic starting compound to disposal to provide that the disadvantages of the prior art recommended procedure, if any, to a lesser extent having.

Accordingly, there is provided a process for operating an exothermic heterogeneously catalyzed partial gas phase oxidation of an organic starting compound to an organic target compound in mutually different operating conditions I and II, comprising reacting a reaction gas input mixture containing the organic starting compound, molecular oxygen and at least one inert diluent gas to obtain the organic target compound -containing product gas mixture passes through an in-the tubes of a tube bundle reactor, fixed catalyst bed as well as in the fixed catalyst bed containing tubes of the surrounding tube bundle reactor chamber to the reaction temperature setting in located in the tubes fixed catalyst bed, at least a fluid heat carrier with a inlet temperature T ^a in and at an outlet temperature T ^from> T again brought out ^one of this, while the fixed catalyst bed in operating state I with an immersion rode temperature T _I ^{a a} a load L ^II of the organic starting compound with the proviso L ^II> L ^I and T _II ^a> T _I ^a loaded with a load L ^I of the organic starting compound and in the operating state II at an inlet temperature T _II, found which is characterized in that one when changing the operating state I to the operating state II, first, the inlet temperature T _I to ^the value T ^_II, and then increases the load on the fixed catalyst bed with the organic starting compound from the value of L ^I to the value L ^II.

According to the invention advantageously is _I to perform ^a change from T to T _II ^is as a succession of small temperature increase steps. After performing a temperature raising step, the new operating conditions are first each time (typically over an operating period of at least 5 minutes, or at least 10 minutes, ie 5 minutes to 360 minutes, often over an operating period of 10 minutes to 240 minutes and many times over operation period of 15 minutes, retained to 120 minutes, or from 20 minutes to 60 minutes) before the next temperature increase step T ^a is reacted on. The lower the individual temperature increase step is selected in each case, the more moderate is the concomitant change in the hotspot temperature. An application point, a temperature increase step by T amounts to not less than ^a 0.1 ° C. Normally, a temperature increase step for T is ^one but not more than 10 ° C, usually not more than 5 ° C and be in application terms, particularly advantageously no more than 2 ° C. Typical temperature increase steps for ^a T amount therefore 0.2 ° C, or 0.3 ° C, or 0.4 ° C, or 0.5 ° C, or 0.6 ° C, or 0.7 ° C, or 0 , 8 ° C, or 0.9 ° C, or 1 ° C. Of course, a temperature increase step for T can be ^an even 1.5 ° C. In application terms, conveniently a temperature increase step by T is ^a 0.1 to 1 ° C, preferably 0.2 to 0.8 ° C, particularly preferably from 0.3 to 0.7 ° C, and most preferably from 0.4 to 0 6 ° C.

In a completely corresponding manner, the increase in the loading of the fixed catalyst bed with the organic starting compound from the value L ^I to the value L ^{II will} advantageously be carried out according to the invention as a succession of small load-increasing steps. After performing a stress increasing step, the new operating conditions are first each time for some time (typically over an operating period of at least 5 minutes, or at least 10 minutes, ie, for example, 5 minutes to 360 Minutes, often over an operating period of 10 minutes to 240 minutes, and often over an operating period of 15 minutes to 120 minutes, or from 20 minutes to 60 minutes) before the next stress increasing step on the loading of the fixed catalyst bed is reacted with the starting organic compound. The lower the individual load increase step is selected, the more moderate the concomitant change in the hot spot temperature. Relative to the value of L ^I , a load increase step expediently amounts to not less than 1% in terms of application technology. Normally, a load increasing step will be related in a similar manner but not more than 50%, usually not more than 40%, suitably not more than 30% in terms of application, and most suitably not more than 20%. Typical load increasing steps as described above are therefore 5%, or 10%, or 15%, or 20%, or 25%, or 30%, or 35%, or 40%, or 45%, or 50%. In a practical manner, a load increasing step relating to the load of the fixed catalyst bed with the organic starting compound becomes 1% to 50%, or 2% to 45%, or 5% to 40%, or 10% to 35%, or 15% to 30%, or 20% to 30%, or 25% to 30%.

Very particularly advantageously according to the invention, in order to increase the space-time yield of the desired target compound in order to satisfy increased market demand, the procedure according to the invention will be repeated several times in succession. That is, starting from the operating state I (hereinafter referred to as the initial operating state I) is first often increased T _I ^a for only a temperature increasing step (for example, 0.1 to 10 ° C, preferably 0.1 to 2 ° C or up to 1 ° C to 0.5 ° C). As a result, while a new entrance temperature T _II results in ^a. Then, under the new operating conditions, the process is run for some time (eg 5 minutes to 360 minutes, or 10 minutes to 240 minutes, or 15 minutes to 120 minutes, preferably 10 minutes to 60 minutes). Subsequently increasing the loading of the fixed catalyst bed with the organic starting compound from the value of L ^I to the value L ^II of the new entry temperature T _II ^{is a} corresponding substantially (usually so that the conversion of the organic starting compound largely to that in the so resulting operating state II in the previous Operating state I is the same).

Then One operates the procedure under the new operating conditions some Time (e.g., 5 minutes to 360 minutes, or 10 minutes to 240 minutes, or 15 minutes to 120 minutes, preferably 10 minutes to 60 minutes).

Of the then assumed operating state II forms the new output operating state I, from which proceeding proceeding in the same way as from the original one Operating state I, etc. After such multiple successive Application of the procedure according to the invention finally becomes reached a final operating state II, which the increased market demand according to the desired target product to satisfy. It is from the original operating condition I starting a path to the final operating state II, in which the accompanying change the hotspot temperature one in a very special way Extent is moderate. All the more so, the less also with this procedure the single temperature increase step each chosen becomes.

The difference between L ^I and L ^II can in principle vary widely in the method according to the invention. In many cases, however, the ratio V of L ^II to L ^{I will} be ≤ 2.

that is, V can e.g. > 1 and ≤ 2, or ≥ 1.05 and ≤ 1.90, or ≥ 1.10 and ≤ 1.80, or ≥ 1.20 and ≤ 1.60, or ≥ 1.25 and ≤ 1.50, or ≥ 1.30 and ≤ 1.40.

In a simple manner according to the invention required increase in the load L ⁱ to L ^II can be effected by that at a substantially constant composition of the reaction gas input mixture, the loading of the fixed catalyst bed with reaction gas input mixture (in a corresponding manner, that is, in the same ratio L ^II / L ^I ) is increased. Alternatively, the increase of the load L ^I according to the invention to the value L ^{II can} also be achieved by increasing the proportion of the organic starting compound in the reaction gas input mixture in a corresponding manner while maintaining the catalyst fixed bed substantially constant with reaction gas input mixture. In such a procedure, one will normally also increase the proportion of molecular oxygen in the reaction gas input mixture in a corresponding manner, so that the molar ratio R of organic starting compound to molecular oxygen in the reaction gas input mixture of the operating state II is substantially equal to that in the reaction gas input mixture of the operating state I (in this In the case, the proportion of inert gas in the reaction gas input mixture decreases during the transition from operating state I to operating state II). It is expedient according to the invention to increase the proportion of the molecular oxygen and to increase the proportion of the organic starting compound in the reaction gas input mixture synchronously (ie, in the essential at the same time). Of course, the two aforementioned methods for increasing L ^{I can} also be used in combination. Normally, the value for R in the reaction gas input mixture of the operating state I during the transition to operating state II will then be substantially retained.

that is, often will one proceed in such a way that the cycle gas flow (the cycle gas quantity / time) for the Reaction gas mixture input current keeps substantially constant and the Feed stream of the organic source compound and the oxygen source (usually) air) for increases the reaction gas mixture input stream.

These it is the process of the invention to the second reaction stage of a two-stage heterogeneously catalyzed Partial oxidation, is the target product of the first reaction stage usually the organic starting compound for the second Reaction stage (see, e.g., the two-stage heterogeneously catalyzed partial Gas phase oxidation of propylene to acrylic acid; that in the first reaction stage from the organic starting compound propylene formed acrolein forms the organic starting compound for those in the second reaction stage formed acrylic acid).

The fed to the second reaction stage Reaction gas input mixture is regularly that, previously possibly cooled, Product gas mixture of the first reaction stage, optionally supplemented with molecular Oxygen and / or inert gas.

If one then carries out each of the two reaction stages in a tube bundle reactor (eg each in one (eg such as in 1 of the EP-A 1 695 954 shown) of two series-connected tube bundle reactors or each in at least one temperature zone of a multi-zone tube reactor (a so-called "single reactors") so one will apply the inventive method synchronously to both the first and the second reaction stage.

That is, the process of the present invention also includes a process for operating a two-stage exothermic heterogeneously catalyzed partial gas phase oxidation of a first organic starting compound to an organic end-target compound in mutually different operating conditions I and II comprising obtaining the first organic starting compound, molecular oxygen and at least one inert diluent gas to obtain a first product gas mixture containing an organic target intermediate through a first fixed catalyst bed in the tubes of a tube bundle reactor, and in the space surrounding the first fixed catalyst tube of this tube bundle reactor for adjusting the reaction temperature in the first fixed catalyst bed at least a first fluid heat carrier with an inlet temperature T ^{1, one} in and with an outlet temperature T ^{1, from>} T ^{1, a} wied he leads out of this and the first, optionally optionally cooled and optionally with molecular oxygen, or optionally with inert gas, or optionally with molecular oxygen and inert gas as secondary gas additive (secondary gas addition) supplemented product gas mixture as molecular oxygen, at least one inert diluent gas and the organic intermediate target compound as second reaction gas input mixture containing second organic starting compound to give the organic end target compound containing second product gas mixture through a located in the tubes of a tube reactor second, different from the first fixed catalyst bed catalyst fixed bed leads and in the surrounding the second fixed catalyst tube of this tube bundle reactor surrounding space for adjusting the reaction temperature the second fixed catalyst bed at least a second fluid heat carrier with an inlet temperature T ^{2, a} hinei n and with an outlet temperature T ^{2, from} > T ^{2, one} again leads out of this and while in operation I the first fixed catalyst bed at an inlet temperature T _I ^{1, one} with a load L ^{1, I of} the first organic starting compound and the second fixed catalyst bed at an inlet temperature T _I ^{2, one} with a load L ^{2, I of} the second organic starting compound and in operation II, the first fixed catalyst bed at an inlet temperature T _II ^{1, one} with a load L ^{1, II of} the first organic starting compound and the second fixed catalyst bed an inlet temperature T _II ^{2, one} with a load L ^{2, II of} the second organic starting compound with the proviso L ^{1, II} > L ^{1, I} , T _II ^{1, a} > T _I ^{1, a} , L ^{2, II} > L ^{2 , I} and T _II ^{2, a} > T _I ^{2, a} loaded, which is characterized in that when changing from the operating state I to the operating state II first the inlet temperature T _I ^{1, one} to the value T _II ^1, and the inlet temperature T _I ^{2, one} to the value T _II ^2, and then the load of the first fixed catalyst bed with the first organic starting compound of value L ^{1, I} to the value L ^{1, II} and as a consequence of the latter measure above, and optionally additionally modified Secondary gas addition increases the load of the second fixed catalyst bed of value L ^{2, I} to the value L ^{2, II} .

The The above is especially true when it comes to the two-stage exothermic heterogeneously catalyzed partial gas phase oxidation to the two-stage exothermic heterogeneously catalyzed partial gas phase oxidation from propylene to acrylic acid or an exothermic, two-stage heterogeneously catalyzed partial oxidation of iso-butene too methacrylic acid is. In the former case, the first organic starting compound Propylene, the intermediate target compound (the second organic starting compound) Acrolein and the final target compound acrylic acid.

In principle, in the case of the two-stage partial oxidation described above, the increase in the inlet temperature T _I ^{1, one} to the value T _II ^1, and the increase of the inlet temperature T _I ^{2, one} to the value T _II ^{2, will be performed} substantially synchronously (simultaneously) ,

However, in order to avoid increased levels of unreacted target intermediate (on unreacted target intermediate) in the second product gas mixture of the two-stage heterogeneously catalyzed exothermic gas phase partial oxidation, it is advantageous to lag behind the increase in T _I ^1, which is always slightly behind the increase in T _I ² (the second reaction stage is in fact always prepared for this by the increase of T _I ^{1, a} slightly increased formation rate of intermediate target compound in the first reaction stage, even if the first catalyst fixed bed initially remains at constant load with the first organic starting compound). In principle, however, the present invention also encompasses such procedures in the case of two-stage heterogeneously catalyzed exothermic gas phase partial oxidations in which, in the context of a change from an operating state I to an operating state II, the increase in the inlet temperatures T _I ^1, T ² and T _II ² is carried out in such ^a way that the increase of T _I ^{2, one of} the increase of T _I ^{1, one} time always lagging behind.

Advantageously in accordance with the invention, in a two-stage procedure, the change from T _I ^{1, one} to T _II ^{1, one} and the change from T _I ^{2, one} to T _II ^2, in the same way as in the single-stage procedure, preferably as a succession of Perform small temperature increase steps.

that is, after essentially synchronous in both reaction stages execution a temperature raising step the new operating conditions are first each time (typically over a Operating period of at least 5 minutes, or at least 10 minutes, i.e. e.g. 5 minutes to 360 minutes, often over an operating period of 15 minutes to 120 minutes, or from 20 minutes to 60 minutes) maintain before the next, for both Reaction stages to be performed substantially synchronously, Temperature increment concerning the respective inlet temperature of the respective fluid Implemented heat carrier becomes. The lower the individual temperature increase step is chosen in each case, the more moderate fall the changes associated therewith in both temperature zones the respective hot spot temperature out.

An application point, a temperature increase step for the respective T amounts ^also in a two-step procedure to not less than 0.1 ° C. Normally, however, such a temperature raising step will not be more than 10 ° C, usually not more than 5 ° C, and in a particularly advantageous manner from an application point of view, not more than 2 ° C. Typical temperature increase steps for the respective T ^a be therefore 0.2 ° C, or 0.3 ° C, or 0.4 ° C, or 0.5 ° C, or 0.6 ° C, or 0.7 ° C, or 0.8 ° C, or 0.9 ° C, or 1 ° C. Of course, a temperature increasing step for each T may be also ^a 1.5 ° C. In a technically advantageous manner, a temperature increase step for T _I ^{1, a} or T _I ^{2, a} 0.1 to 1 ° C, preferably 0.2 to 0.8 ° C, most preferably 0.3 to 0.7 ° C and most preferably 0.4 to 0.6 ° C.

In a completely corresponding manner, in a two-stage procedure, the loading of the first fixed catalyst bed with the first organic starting compound from the value L ^{1, I} to the value L ^{1, II will} advantageously be carried out according to the invention as a succession of small load-increasing steps. After performing a stress increasing step, the new operating conditions are first each time (typically over an operating period of at least 5 minutes, or at least 10 minutes, ie 5 minutes to 360 minutes, often over an operating period of 10 minutes to 240 minutes and many times over a Operating period of 15 minutes to 120 minutes, or from 20 minutes to 60 minutes) before the next stress increasing step on the load of the first fixed catalyst bed is reacted with the first organic starting compound. The lower the individual load increase step is selected in each case, the more moderate is the associated change in the associated hot spot temperature. Relative to the value of L ^{1, I} , a load-increasing step expediently amounts to not less than 1% in terms of application technology. Normally, a load increase step is related in a similar manner but not more than 50%, usually not more than 40%, in terms of application, suitably not more than 30% and particularly expediently not more than 20%.

typical, as previously referred to, load increasing steps is therefore 5%, or 10%, or 15%, or 20%, or 25%, or 30%, or 35%, or 40%, or 45%, or 50%. In application technology favorable way is a load increasing step related to the above-mentioned Loading of the first fixed catalyst bed with the first organic Starting compound 1% to 50%, or 2% to 45%, or 5% to 40%, or 10% to 35%, or 15% to 30%, or 20% to 30%, or 25% to 30% be.

The increase in the load L ^{1, I} to the value L ^{1, II to} be carried out according to the invention in a two-stage heterogeneously catalyzed exothermic partial oxidation of a first organic starting compound as described above can be carried out in a simple manner by using the first composition of a substantially constant composition organic starting compound containing reaction gas input mixture, the load of the first fixed catalyst bed with reaction gas input mixture in a corresponding manner (ie, in the same ratio as L ^{1, II} / L ^{1, I} ) is increased.

Alternatively, the increase in the load L ^{1, I} to the value L ^{1, II} but also be carried out by the proportion of the first organic starting compound in the reaction gas input mixture at substantially constant loading of the first fixed catalyst bed with the first organic starting compound reaction gas input mixture increased in a corresponding manner. In such a procedure, one will normally also increase the proportion of molecular oxygen in the first reaction gas input mixture containing the first organic starting compound in a corresponding manner, so that the molar ratio R of the first organic starting compound to molecular oxygen in the first reaction gas input mixture of the operating state II is substantially the same as in the first Reaction gas input mixture of the operating state I is (in this case, the inert gas decreases in the first reaction gas input mixture in the transition from operating state I to operating state II). It is expedient according to the invention to increase the proportion of molecular oxygen and increase the proportion of the first organic starting compound in the first reaction gas input mixture synchronously (ie, essentially simultaneously).

Of course, the two aforementioned methods for increasing L ^{1, I can} also be used in combination. Of course, even then the value for R in the first reaction gas input mixture of the operating state I during the transition to operating state II will normally be maintained substantially.

Alternatively, with an increase of L ^{1, I can} also proceed so that the residual oxygen content in the first product gas mixture (in the product gas mixture of the first reaction stage) in the operating conditions I, II is kept stable (eg to a value in the range of 1 to 9 vol. -%). Any resulting sales reductions (due to an increasing R) can be intercepted by a corresponding increase of T _II ^1.a.

that is, often will one proceed in such a way that the cycle gas flow (the cycle gas quantity / time) for the Reaction gas mixture input current keeps substantially constant and the Feed stream of the first organic starting compound and the oxygen source (usually air) for increases the first reaction gas mixture input stream.

If no additional molecular oxygen and / or inert gas is added to the first product gas mixture of a two-stage heterogeneously catalyzed exothermic partial oxidation to be carried out as second reaction gas input mixture (no secondary gas added), as described, for example, in an embodiment of the two-stage partial oxidation in the "single reactor" (cf. eg 4 of the EP-A 1 695 954 ) is necessarily the case, with an increase of L ^{1, I} to L ^{1, II} normally automatically accompanied by the corresponding increase of L ^{2, I} to L ^{2, II} . The oxygen demand in the second reaction stage is already taken into account by a corresponding oxygen content in the first reaction gas input mixture. If secondary gas is added to the first product gas mixture between the two reaction stages, this normally takes place in such a way that increasing L ^{1, I} to L ^{1, II is accompanied by} the desired increase (the corresponding raising step) from L ^{2, I} to L ^{2, II} and at the same time the molar ratio R of second organic starting compound to molecular oxygen in the second reaction gas input mixture of the operating state II is substantially equal to that in the second reaction gas input mixture of the operating state I.

Very particular according to the invention it is advantageous to increase the space-time yield at the desired Final target link to meet increased market demand in one to be carried out as described two-stage exothermic heterogeneously catalyzed partial oxidation Proceed in such a way that the procedure according to the invention is repeated several times consecutively.

Alternatively, a secondary oxygen feed (eg as secondary air) can also be carried out so that the residual oxygen content in the product gas mixture of the second reaction stage is kept stable in the operating states I, II (eg at a value in the range from 1 to 4% by volume). Any resulting sales reductions (as a result of an increasing R) can be offset by a corresponding increase in T _II ^{2, a} .

That is, starting from the operating state I (hereinafter referred to as original operating state I) is first increased T _I ^{1, a} and T _I ^2, as described by only one temperature raising step (eg 0.1 to 10 ° C, preferably 0.2 to 5 ° C, more preferably 0.3 to 2 ° C, most preferably 0.4 to 1.5 ° C and in many cases 0.5 to 1 ° C). As a result, this results in the new inlet temperatures T _II ^{1, a} and T _II ^{2, a} . Then, under the new operating conditions, the process is run for some time (eg, over a period of at least 5 minutes, or at least 10 minutes, ie, 5 minutes to 360 minutes, often over an operating period of 10 minutes to 240 minutes, and often over an operating period of 15) Minutes to 120 minutes, or from 20 minutes to 60 minutes). Subsequently, the loading of the first fixed catalyst bed with the first organic starting compound of value L ^{1, I} to the value L ^{1, II} , which corresponds to the new inlet temperature T _II ^{1, one} substantially (usually so that the conversion of the first organic starting compound in the resulting operating state II is largely equal to that in the previous operating state I). As a consequence of this measure, as well as an optionally additionally modified secondary gas addition, is usually an increase (an increasing step) of the load of the second catalyst fixed bed with the second organic starting compound of value L ^{2, I} to the value L ^{2, II} associated with the new entry temperature T _II ^{2, one} substantially corresponds (usually so that the conversion of the second organic starting compound in the resulting operating state II largely corresponds to that in the previous operating state I). Then, under the new operating conditions, the process is run for some time (eg, over a period of at least 5 minutes, or at least 10 minutes, ie, 5 minutes to 360 minutes, often over an operating period of 10 minutes to 240 minutes, and often over an operating period of 15) Minutes to 120 minutes, or from 20 minutes to 60 minutes). The then assumed operating state II forms the new initial operating state I, from which proceeding proceeded in the same way as from the original operating state I etc. After such multiple successive application of the procedure according to the invention for two-stage heterogeneously catalyzed exothermic gas phase partial oxidation finally a final operating state II is achieved which is able to satisfy the increased market demand for the desired target product.

there is from the original one Operating state I, proceeding to the end operating state II, in which the associated change in the respective hot spot temperature one in very particular Extent is moderate. All the more so, the less also with this procedure the single temperature increase step each chosen becomes.

The difference between L ^{1, I} and L ^{1, II} may in principle vary widely in the described two-stage procedure. In many cases, however, the ratio V1 of L ^{1, II} to L ^{1, I will} be ≦ 2.

That is, V1 may be, for example,> 1 and ≦ 2, or ≥ 1.05 and ≦ 1.90, or ≥ 1.10 and ≦ 1.80, or ≥ 1.20 and ≦ 1.60, or ≥ 1.25 and ≤ 1.50, or ≥ 1.30 and ≤ 1.40. The same applies to the ratio V2 of L ^{2, II} to L ^{2, I.}

Of course, the method according to the invention can, however, not only be used for the purpose of adaptation to changed market situations. Rather, the procedure according to the invention can also be advantageously used when commissioning a production plant. As a rule, there is introduced a roughly suitable inlet temperature T _I ^* for the envisaged space-time yield of target product, the amount of which, however, is usually still a few ° C (usually not more than 15 ° C and usually not more than 10 ° C) below the members of the proposed space-time yield of target product load L ^I of the predetermined in its activity fixed catalyst bed with the organic starting compound belonging inlet temperature T _I ^a is (there is a restart after the regeneration of the the fixed catalyst bed T _I ^{a *} in each case, below the last value of T for ^a preliminary (the execution of the regeneration, for example, according to DE-A 103 51 269 ) lie.

Then the catalyst fixed bed is loaded with reaction gas input mixture. The chosen one Load L of the fixed catalyst bed with the organic starting compound is about 60% of that value, which is taken as a rated load than T _I ^{a *} duly considered. Now, with a substantially constant composition of the reaction gas input mixture (preferably as in the DE-A 103 37 788 described) increases the load of the fixed catalyst bed with the organic starting compound as described step by step until, based on the single pass of the reaction gas input mixture through the fixed catalyst bed, the conversion of the starting organic compound reaches its nominal conversion associated with the targeted space-time yield.

T _I is then ^a and ^I L is increased as far as in the inventive manner, until the space-time yield achieved their intended nominal value starting from this operating state I. In the case of a two-stage exothermic heterogeneously catalyzed gas phase partial oxidation, the procedure is completely analogous.

The values for L ^I and L ^II can extend over a wide range in the process according to the invention (depending on the heterogeneously catalyzed exothermic gas phase partial oxidation carried out in particular). That is, L ^I , L ^II may be 5 or 100 to 5,000 Nl / l · hr, or 20 or 150 to 4,000 Nl / l · h, or 50 or 200 to 2,000 Nl / l · h, and 250 to 1,000, respectively Nl / l · h.

For a successful application of the inventive procedure, it is not essential but advantageous if the on single pass of the respective reaction gas inlet mixture through the fixed catalyst bed turnover U ^A (in mol% based on the contained in the reaction gas input mixture molar amount of the organic starting compound) of the in the reaction gas input mixture contained organic starting compound in the operating conditions I (U ^{A, I} ) and II (U ^{A, II} ) is substantially the same. According to the invention, the difference between U ^{A, II} and U ^{A, I is} less than 5, better still less than 3, even better less than 1, particularly favorably less than 0.5 and most preferably less than 0.1 mol% points ,

The process according to the invention is advantageous according to the invention both when U ^{A, I} and U ^{A, II} ≥ 50 mol%, or ≥ 75 mol%, or ≥ 90 mol%, or ≥ 95 mol% or ≥ 98 mol -%, or ≥ 99 mol%, or ≥ 99.5 mol%, or ≥ 99.9 mol%.

These it can be carried out according to the invention heterogeneously catalyzed partial exothermic gas phase oxidation to the heterogeneously catalyzed partial gas phase oxidation of propylene to acrolein and / or acrylic acid (as a stand-alone Process or as the first reaction stage in a two-stage Partial oxidation of propylene to acrylic acid (first reaction step: Propylene → acrolein), it is advantageous according to the invention when the propylene content in the product gas mixture both in the operating state I and in operating state II the value 10,000 ppm by weight, preferably Does not exceed 6000 ppm by weight and more preferably 4000 or 2000 ppm by weight. It is even better if in the method according to the invention the respective the aforementioned propylene content in the product gas mixture not only in the operating conditions I and II, but also in all transitional states during transition from operating state I to operating state II is not exceeded becomes.

These it can be carried out according to the invention heterogeneously catalyzed partial exothermic gas phase oxidation to the heterogeneously catalyzed partial gas phase oxidation of acrolein to acrylic acid (as a stand-alone Process or as a second reaction stage in a two-stage Partial oxidation of propylene to acrylic acid (second reaction stage: Acrolein → acrylic acid) it is advantageous according to the invention when the acrolein content in the product gas mixture both in the operating state I and in operating state II the value 1500 ppm by weight, preferably 600 ppm by weight and particularly preferably does not exceed 350 ppm by weight. Even better it, if in the method according to the invention the respective aforementioned acrolein content in the product gas mixture not only in the operating states I and II, but also in all transitional states during transition from operating state I to operating state II is not exceeded becomes.

The inventive method is suitable for a heterogeneously catalyzed exothermic gas phase Festbettpartialoxidation of propylene to acrolein, especially when used as catalysts whose active composition is a multielement oxide containing the elements molybdenum and / or tungsten and at least one of the elements bismuth, tellurium, antimony, tin and copper or is a multi-metal oxide containing the elements Mo, Bi and Fe. Particularly suitable according to the invention Mo, Bi and Fe-containing multimetal oxide materials of the aforementioned type are especially in the DE-A 103 44 149 and in the DE-A 103 44 264 disclosed Mo, Bi and Fe containing multimetal oxide compositions. These are in particular the multimetal oxide of the general formula I in the DE-A 199 55 176 , the multimetal oxide of the general formula I of the DE-A 199 48 523 , the multimetal oxide of the general formulas I, II and III of the DE-A 101 01 695 , the multimetal oxide active compounds of the general formulas I, II and III of DE-A 199 48 248 and the multimetal oxide active compounds of the general formulas I, II and III of the DE-A 199 55 168 as well as in the EP-A 700 714 called Multimetalloxidaktivmassen.

Furthermore, an application of the method according to the invention is suitable, if in the case of partial oxidation of propylene to acrolein for the catalyst fixed bed to be used according to the invention, the Mo, Bi and Fe-containing multimetal oxide catalysts described in the publications DE-A 100 46 957 . DE-A 100 63 162 . DE-C 33 38 380 . DE-A 199 02 562 . EP-A 015 565 . DE-C 23 80 765 . EP-A 807 465 . EP-A 279 374 . DE-A 33 00 044 . EP-A 575 897 . US-A 4,438,217 . DE-A 198 55 913 . WO 98/24746 . DE-A 197 46 210 (those of general formula II), JP-A 91/294 239 . EP-A 293 224 and EP-A 700 714 be disclosed. This is especially true for the exemplary embodiments in these documents, among which those of EP-A 015 565 , of the EP-A 575 897 , of the DE-A 197 46 210 and the DE-A 198 55 913 particularly preferred. Particularly noteworthy in this context are a catalyst according to Example 1c of the EP-A 015 565 and a catalyst to be prepared in a corresponding manner, but whose active composition has the composition Mo ₁₂ Ni _6.5 Zn ₂ Fe ₂ Bi ₁ P _0.0065 K _0.06 Ox · 10SiO ₂ . Also to be highlighted are the example with the running No. 3 from the DE-A 198 55 913 (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 × internal diameter) and the multimetal oxide II - Vollkatalysator according to Example 1 of DE-A 197 46 210 , Furthermore, the multimetal oxide catalysts would be the US-A 4,438,217 to call. 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 101 01 695 respectively. WO 02/062737 , Particularly suitable for the propylene to acrolein partial oxidation also in the DE-A 10 2005 037 678 for these Parti aloxidation (reaction stage) recommended Multimetalloxidmassen, in particular those of the comparative examples and the embodiments of this document (the indicated there specific surface areas of the active masses are numerically correct, but the dimension must instead of cm ² / g correctly m ² / g read).

Furthermore, Example 1 from the DE-A 100 46 957 (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 (in each case outside diameter × length × inside diameter), as well as the shell catalysts 1, 2 and 3 from the DE-A 100 63 162 (Stoichiometry: Mo ₁₂ Bi _1.0 Fe ₃ Co ₇ Si _1.6 K _0.08 ), but as shell-shaped coated catalysts of corresponding shell thickness and on support 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 multiplicity of multimetal oxide active materials which are particularly suitable for the catalysts of a propylene partial oxidation to acrolein in the context of the invention can be found under the general formula I 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,
subsumed.

They are available in a manner known per se (see, for example, US Pat DE-A 40 23 239 ) and are usually molded in bulk to spheres, rings or cylinders or in the form of coated catalysts, ie, coated with the active material preformed inert carrier bodies used. Of course, they can 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, the shaping of the pulverulent active composition or its pulverulent, not yet and / or partially calcined, precursor composition can also be effected by application to preformed inert catalyst supports. The coating of the carrier body for the preparation of the coated catalysts is usually carried out in a suitable rotatable container, as for example from the DE-A 29 09 671 , of the EP-A 293 859 or from the EP-A 714 700 is known. Appropriately, the applied powder mass is moistened for coating the carrier body and after application, for example by means of hot air, dried again. The layer thickness of the powder mass applied to the carrier body is expediently chosen to be in the range 10 to 1000 μm, preferably in the range 50 to 500 μm and particularly preferably in the range 150 to 250 μm. Alternatively, the powder mass to be applied can also be applied directly from its suspension or solution (for example in water) to the carrier body.

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. They generally behave essentially inert with respect to the target reaction subject to the process of the invention in the first reaction stage. 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. The use of essentially is suitable nonporous, surface roughened, spherical steatite supports (eg Steatite C220 from CeramTec), whose diameter is 1 to 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 (eg 8 mm) and whose outside diameter is 4 to 10 mm (eg 6 mm). In addition, in the case of rings suitable as a carrier according to the invention, the wall thickness is usually from 1 to 4 mm. According to preferred invention to be used annular carrier body have a length of 2 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 or 5 mm × 3 mm × 2 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 support body is of course adapted to the desired shell thickness (cf. EP-A 714 700 ).

For the catalysts of the fixed catalyst bed of a Propylenpartialoxidation 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' ] _q (II) in which the variables have the following meaning:
Y ¹ = only bismuth or bismuth and at least one of tellurium, antimony, tin and copper,
Y ² = molybdenum, or tungsten, 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,
containing three-dimensionally extended areas of the chemical composition Y ¹ _{a '} Y ² _b' O _{x '} , delimited from their local environment due to their different composition from their local environment, whose largest diameter (longest passing through the center of gravity of the area direct connection of two on the surface (Interface) of the region of points) 1 nm to 100 microns, 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 tungsten, 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 present invention suitable Multimetalloxidmassen II (Multimetalloxidmassen III) in the present invention suitable Multimetalloxidmassen II (Multimetalloxidmassen III) in the form of three-dimensionally extended, different from their local environment because of their local environment chemical composition of demarcated, areas of the chemical composition Y ¹ _{a '} Y ² _b' O _{x '} [Bi _a'' Z ² _b'' O _x'' ) are present whose largest diameter is 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 II active compounds is eg in the EP-A 575 897 as well as in the DE-A 198 55 913 , of the DE-A 103 44 149 and the DE-A 103 44 264 described.

When Active mass for Catalysts for a 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 Mo and V-containing Multimetalloxidaktivmassen can, for example, the US-A 3,775,474 , of the US-A 3,954,855 , of the US-A 3,893,951 and the US-A 4,339,355 or the EP-A 614 872 respectively. EP-A 1 041 062 or the WO 03/055835 respectively. WO 03/057653 be removed.

In particular, the multimetal oxide active compositions are also suitable DE-A 103 25 487 as well as the DE-A 103 25 488 ,

Further suitable for the partial oxidation of acrolein to acrylic acid in the sense of the invention in a special way the multimetal oxide of the EP-A 427 508 , of the DE-A 29 09 671 , of the DE-C 31 51 805 , of the DE-AS 26 26 887 , of the DE-A 43 02 991 , of the EP-A 700 893 , of the EP-A 714 700 and the DE-A 197 36 105 as active materials for the fixed bed catalysts. Particularly preferred in this context are the exemplary embodiments of EP-A 714 700 as well as the DE-A 197 36 105 ,

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,
subsumed.

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 materials (IV) are known per se, for example in US Pat DE-A 43 35 973 or in the EP-A 714 700 revealed manner available. In particular, multimetal oxide active compositions which contain Mo and V in the sense according to the invention for the partial oxidation of acrolein to acrylic acid but also the multimetal oxide active compounds are also suitable DE-A 102 61 186 ,

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) as well as under reducing atmosphere (eg mixtures of inert gas and reducing gases such as H ₂ , NH ₃ , CO, methane and / or acrolein or the said reducing gases acting on their own) are carried out. 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 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 carried out in dry or in wet form. If it takes place in dry form, the starting compounds are expediently used as finely divided powders and after mixing and optionally Ver Densities of calcination subjected. Preferably, however, the intimate mixing takes place 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, the shaping of the powdered active composition or its powdery, not yet calcined precursor composition can also be effected by application to preformed inert catalyst supports. The coating of the carrier body for the preparation of the coated catalysts is usually carried out in a suitable rotatable container, as for example from the DE-A 29 09 671 , of the EP-A 293 859 or from the EP-A 714 700 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 addition, in the case of rings suitable as a carrier according to the invention, the wall thickness is usually from 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 support 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, Zn, Ni, Co, Fe, Mn and / or,
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.

Preference is given to those Multimetalloxidaktivmassen VI, in which the incorporation of the preformed solid starting material 1 in an aqueous starting material 2 at a temperature <70 ° C. A detailed description of the preparation of multimetal oxide III catalysts include the EP-A 668 104 , the DE-A 197 36 105 and the DE-A 195 28 646 ,

Regarding the shaping applies with respect Multimetal oxide active bulk VI catalysts that in the multimetal oxide VI 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,
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,
the proportion [A] p in the form of three-dimensionally extended regions (phases) A of the chemical composition
A: Mo ₁₂ VaX 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 areas (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 material VII 20 mol% to 80 mol%, the molar ratio of Mo contained in the catalytically active multielement oxide VII to V contained in the catalytically active multielement oxide VII, Mo / V, Is 15: 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 VII 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 intimate dry mixtures on which the multielement oxide active compositions of the general formula VII are based and then to be thermally treated for conversion into active masses can be obtained, for example, as described in the publications WO 02/24327 . DE-A 44 05 514 . DE-A 44 40 891 . DE-A 195 28 646 . DE-A 197 40 493 . EP-A 756 894 . DE-A 198 15 280 . DE-A 198 15 278 . EP-A 774 297 . DE-A 198 15 281 . EP-A 668 104 and DE-A 197 36 105 is described.

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 _d ³ X _e ⁴ 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 intimate contact of the constituents of the starting materials 1 and optionally 2 with the mixture containing the sources of the elemental constituents of the multimetal oxide composition A (starting material 3) can take place both dry and wet. In the latter case, care must only be taken that the preformed phases (crystallites) B and, if appropriate, C do not dissolve. In aqueous medium, the latter is usually ensured at pH values which do not deviate too much from 7 and at temperatures which are not too high. If the intimate contact is made wet, it is finally dried (for example by spray drying) to give the intimate dry mixture which is to be thermally treated according to the invention. In the context of dry mixing, such a dry mass accumulates automatically. Of course, the finely divided preformed phases B and optionally C can also be incorporated into a plastically deformable mixture which contains the sources of the elemental constituents of the multimetal oxide composition A, as is the case of DE-A 100 46 928 recommends. Of course, the intimate contact of the components of the starting materials 1 and, if appropriate, 2 with the sources of the multielement oxide composition A (starting material 3) can also be carried out in the same way as the DE-A 198 15 281 describes.

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.

Quite generally, multimetal oxide active compositions IV to VII catalysts can advantageously be used according to the teaching of US Pat DE-A 103 25 487 respectively. DE-A 103 25 488 getting produced.

The execution of a suitable for the process according to the invention heterogeneously catalyzed partial exothermic gas phase oxidation can be implemented with the appropriate for the corresponding catalyst fixed bed catalysts in the simplest and most appropriate application technology in a charged with the fixed catalyst bed, having only one temperature zone, tube bundle reactor, as he eg in of the EP-A 700 893 , of the EP-A 700 714 , or the DE-A 44 31 949 , or the WO 03/057653 , or the WO 03/055853 , or the WO 03/059857 , or the WO 03/076373 , or the EP-A 1 695 954 ( 1 ) and the prior art cited in these references.

That is, in the simplest way is the fixed catalyst bed in the preferably uniformly charged (metal) tubes of a tube bundle reactor and through the space surrounding the reaction tubes, a fluid heat carrier (a tempering, usually a molten salt) out. The fluid heat carrier (the temperature control medium, for example the molten salt) and the reaction gas mixture can be conducted in a simple direct or countercurrent flow. However, the fluid heat carrier (the temperature control medium, for example the molten salt) can also be guided meandering around the tube bundles, so that viewed only over the entire reactor a DC or countercurrent to the flow direction of the reaction gas mixture consists (see. EP-A 700 893 and EP-A 1 695 954 ). Regardless of the detailed current flow of the fluid heat carrier (the tempering medium, for example, the molten salt), the volume flow of the same is usually so dimensioned that the temperature increase (due to the exothermic reaction) of the fluid Heat transfer medium (of the temperature; for example, the salt melt) from the surrounding the reaction tubes space (, ie T ^off - T ^a) from the entry point in the space surrounding the reaction tubes space to the outlet point from 0 to 10 ° C, frequently from 2 to 8 ° C, often 3 to 6 ° C is. The inlet temperature of the fluid heat carrier in the space surrounding the contact tubes (T ^a) is generally from 250 to 450 ° C, frequently from 300 to 400 ° C or 300 ° to 380 ° C.

The reaction temperature within the reaction tubes also moves predominantly in the aforementioned temperature frame. Long stretches of the contact tube, the reaction temperature ^is (the temperature of the fixed catalyst bed) ≥ T. The maximum reaction temperature along the contact tube, T ^max (the temperature of the so-called hot spot), can be up to 70 ° C or more above T ^a . The difference T ^max - T ^one is referred to as the hotspot expansion .DELTA.T ^H.

As a rule, one tries to avoid a ΔT ^H ≥ 80 ° C. Usually, ΔT is ^H ≦ 70 ° C, often 20 to 70 ° C, and preferably ΔT ^{H is} small. That is, normally the fixed catalyst bed, the reaction gas input mixture, the load of the catalyst fixed bed with reaction gas input mixture and the removal of the heat of reaction by means of the fluid heat carrier are designed so that the aforementioned values for ΔT ^{H are} achieved in the desired space-time yields of target product.

Furthermore, the catalyst selection for the fixed catalyst bed and its possible dilution with inert material in the fixed catalyst bed normally takes place (cf. EP-A 990 636 and EP-A 1,106,598 ) So that the freshly charged catalyst fixed bed in the predetermined washed by the heat-transfer reaction tube .DELTA.T ^H when increase of T ^a to + 1 ° C usually ≤ 9 ° C, preferably ≤ 7 ° C, or ≤ 5 ° C, or ≤ 3 ° C is.

Everything The above applies in particular with respect to all in this document as possible indicated Eduktumsätze (based on a single pass of the reaction gas mixture through the fixed catalyst bed).

When fluid heat transfer proves a 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 as appropriate for application. But also ionic liquids are usable.

Conveniently, the reaction gas input mixture of the catalyst fixed bed in substantially T ^a preheated supplied (this measure is minimized, inter alia, radial temperature gradients within the fluid heat-carrier through a cross section of the tube bundle reactor in the region of the inlet of the reaction gas input mixture in the tube bundle reactor).

In particular, in the case of desired elevated (eg ≥ 110 Nl / l · h, or ≥ 130 Nl / l · h, or ≥ 140 Nl / l · h, or ≥ 150 Nl / l · h, or ≥ 160 Nl / l · h, but generally ≦ 600 Nl / l · h, frequently ≦ 350 Nl / l · h) loading of the fixed catalyst bed with propylene (but also within the range of propylene loadings of the fixed catalyst bed of ≥ 60 Nl / l · h and <110 Nl / l · h), the propylene partial oxidation process to give acrolein and / or acrylic acid is advantageously carried out in a two-zone or multi-zone tube bundle reactor (a feedthrough in a single-zone tube reactor is also possible). A preferred variant of a two-zone tube bundle reactor which can be used according to the invention for this purpose is disclosed in US Pat DE-C 28 30 765 , But also in the DE-C 25 13 405 , of the US-A 3,147,084 , of the DE-A 22 01 528 , of the EP-A 383 224 and the DE-A 29 03 582 disclosed two-zone tube bundle reactors are suitable. Multizone variants are also used in the EP-A 1 106 598 , of the WO 2004/085362 , of the WO 2004/085370 and the WO 2004/085363 described.

that is, in a simple manner, the fixed catalyst bed is then in preferably uniformly charged (metal) tubes of a tube bundle reactor and around the reaction tubes two (or more) of each other (e.g. by means of partitions, through the holes of the reaction tubes are passed) essentially spatially separate fluid heat carrier (in usually molten salts) out.

Of the Pipe section (the ambient space segment) over which the respective Heat transfer medium (the respective salt bath), represents a temperature zone.

For example, a salt bath A preferably flows around the (longitudinal) section A of the tubes (the temperature zone A) in which the oxidative conversion of the propylene (in single pass) until a conversion value U _A in the range of 15 to 85 mol% is reached a salt bath B flows around the (longitudinal) section B of the tubes (the temperature zone B), in which the oxidative connection conversion of propylene (in single pass) until a conversion value U _B of generally at least 90 mol% (preferably ≥92 mol%, or ≥94 mol%, or ≥96 mol%) is reached (if required can connect to the temperature zones A, B further temperature zones, which are kept at individual temperatures).

Within the respective temperature zone, the particular salt bath can in principle be conducted as in the one-zone operation (in particular relative to the reaction gas mixture). That is, the salt bath A is at the temperature T on ^{, A} in the temperature zone A in and out with the temperature T ^{out, A} again, where T ^{out, A} > T in ^{, A} applies. In a corresponding manner, the salt bath B with the temperature T in ^{, B} in the temperature zone B in and out with the temperature T ^{out, B} , where T ^{out, B} > T in ^{, B} applies (it should be noted that the Terms salt bath A and salt bath B in this document are always representative of a fluid heat carrier A and a fluid heat carrier B, so that the respective disclosure also includes the wording that arises because "salt bath A" by "a fluid heat carrier A "and" salt bath B "is replaced by" a fluid heat carrier B ").

The fluid heat carrier (the temperature control medium, usually a molten salt) A (B) and the reaction gas mixture can be conducted within the temperature zone A (B) both in simple DC and in simple countercurrent. However, the fluid heat carrier (the tempering medium, for example the molten salt) A (B) can also be guided meandering around the tube bundle section A (B), so that viewed only over the entire tube bundle section A (B) a direct or countercurrent to the flow direction of the reaction gas mixture consists. Regardless of the detailed current flow of the fluid heat carrier (the tempering medium, for example, the molten salt) A (B) is the volume flow of the same usually dimensioned so that the temperature increase (due to the exothermic reaction) of the fluid heat carrier (the tempering, eg the molten salt ) A (B) from the point of entry in the space surrounding the tube bundle section A (B) to the exit point from the space surrounding the tube bundle section A (B) (ie, T ^{out, A} - T in ^{, A} (T ^{out, B} - T ^{a, B} )) 0 to 10 ° C, often 2 to 8 ° C, often 3 to 6 ° C.

The maximum reaction temperature (the temperature of the so-called respective hot spot) along the contact tube section A, T ^maxA (of the contact tube section B, T ^maxB ) may be up to 70 ° C or more above T ^{a, A} (T in ^{, B} ). The difference T ^maxA - T in ^{, A} (T ^maxB - T in ^{, B} ) is referred to as the hotspot extension ΔT ^{H, A} (ΔT ^{H, B} ).

According to the teachings of the prior art, the general process conditions are generally selected so that T ^{max A} - T ^{max B} ≥ 0 ° C and ≤ 80 ° C when freshly charged ^{fixed catalyst bed} (see, eg WO 2004/085362 . WO 2004/085370 . WO 2004/085363 and in the European Application No. 06 100 535 ).

At low Eduktbelastungen of fresh fixed catalyst bed which is often advantageously with T ^{a, B} - T ^{A, A} given <0 ° C, while with increasing Eduktbelastung the fresh fixed catalyst bed, the above condition often advantageously with T ^{a, B} - ^A T ^{, A} ≥ 0 ° C is given.

Furthermore, the catalyst selection for the fixed catalyst bed and its possible dilution with inert material in the fixed catalyst bed normally takes place (cf. EP-A 990 636 and EP-A 1,106,598 ) so that the freshly charged fixed catalyst bed in the given heat carrier-purged reaction tube section .DELTA.T ^{H, A} (.DELTA.T ^{H, B} ) with increasing T in ^{, A} (T in ^{, B} ) by + 1 ° C normally ≤ 9 ° C, preferably ≤ 8 ° C, more preferably ≦ 7 ° C, or ≤ 5 ° C, or ≤ 3 ° C is.

The inlet temperature of the respective fluid heat carrier in the space surrounding the respective contact tube section (T in ^{, A} or T in ^{, B} ) is generally 250 to 450 ° C., frequently 300 to 400 ° C. or 300 to 380 ° C.

To counteract the deactivation of the fixed catalyst bed in long-term operation, it is preferable as in the European Application No. 06 100 535 as well as the DE-A 10 2004 025 445 described procedure. In general, U _A = 15 to 85 mol% and U _B ≥ 90 mol% are generally retained during long-term operation.

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 metals also proves useful as a fluid heat carrier in a multizone operation. But also ionic liquids can be used. Application-wise appropriate In a multi-zone mode of operation, the same type of heat transfer medium will be used for the different temperature zones.

In principle, in a two-state propylene partial oxidation according to the invention to give acrolein and / or acrylic acid in operating state II, both T _II ^{, A} > T _{I in} ^{, A} and T _{II in} ^{, B} > T _{I in} ^{, B can be} fulfilled. As a rule, during the transition from an operating state I with a propylene loading of the fixed catalyst bed L ^I to an operating state II with a propylene load of the fixed catalyst bed L ^II > L ^I in the two-zone tubular reactor described, it will be advantageous to use both the T ₁ ^{and A} propellant charge prior to increasing the propylene load of the fixed catalyst bed on T _II ^{, A} and T _{I on} ^{, B} on T _{II on} ^{, B} increase (in terms of application, it is appropriate to proceed in such a way that T _{II is} ^{one, A} - T _{I on} ^{, A is} approximately equal to T _II ^{, B} - T _I ^{, B is} selected).

However, it is also possible to proceed in such a way that during the transition from operating state I to operating state II only T _{I on} ^{, A} on T _{II on} ^{, A} increases, and T _{I on} ^{, B} essentially remain (= T _{II on} ^{, B} ) or only T _{I in} ^{, B} on T _II ^{, B} increased, and T _{I on} ^{, A} substantially retained (= T _{II on} ^{, A} ). According to the invention, however, in all three possible cases, one proceeds in such a way that T ^maxA -T ^maxB ≥ 0 ° C. and ^≦ 80 ° C. is fulfilled (in particular on the fresh ^{fixed catalyst bed} ) both in operating state I and in operating state II. That is, both in operating state I and in operating state II, T ^maxA - T ^maxB may advantageously (and independently of each other) ≥ 1 ° C and ≤ 70 ° C, or ≥ 2 ° C and ≤ 60 ° C, or ≥ 3 ° C and ≤ 50 ° C, or ≥ 4 ° C and ≤ 40 ° C, or ≥ 5 ° C and ≤ 30 ° C, or ≥ 5 ° C and ≤ 25 ° C, or ≥ 5 ° C and ≤ 20 ° C or ≤ 15 ° C, or ≥ 0 ° C and ≤ 5 ° C. It is favorable according to the invention that when T ^maxA -T ^maxB in operating state I lies in a specific one of the aforementioned temperature difference intervals, T ^maxA -T ^maxB also lies in operating state II in this temperature difference interval.

In principle, in the operating state IT ^maxA -T ^maxB (T _I ^maxA -T _I ^maxB ) but also ≥ 0 ° C and ≤ 80 ° C and in operating state II (T _II ^maxA -T _II ^maxB ) <0 ° C (eg up to -20 ° C, or down to -10 ° C, or down to -5 ° C).

Is the transition from mode I to mode II both T _I ^{A, A} and T _I ^{A, B} increased (to T _II ^{a, A} or T _II ^{A, B),} these two temperature increases, both substantially the same time as (in synchronization can ) as well as with a time delay. In the case of a time-delayed increase, it is advantageous in terms of application technology to first increase T _I ^{, A} to T _II ^{, A} and then T _I ^{to B} on T _II to increase ^B (but in principle it is also possible to reverse the procedure).

All In general, one will in the context of the procedure according to the invention to be used catalysts and other process conditions Appropriately appropriate in terms of application technology so that the selectivity the target product formation, based on the single pass of the reaction gas mixture through the fixed catalyst bed, ≥ 80 mol%, or ≥ 90 mol%, in many cases even ≥ 92 mol%, or ≥ 94 mol%, or ≥ 96 mol% is.

Farther is the radial temperature gradient of the respective heat carrier within a temperature zone of a tube bundle reactor to be operated according to the invention preferably low designed. As a rule, this radial temperature gradient in the application technology practice 0.01 to 5 ° C, often 0.1 to 2 ° C.

The contact tubes of tube bundle reactors to be used according to the invention are usually made of ferritic steel and typically have a wall thickness of 1 to 3 mm. Their inner diameter is usually 20 to 30 mm, often 21 to 26 mm. Their length is in particular in the case of a partial oxidation of propylene according to the invention to acrolein or of acrolein to acrylic acid 3 to 4, often 3.5 m. Suitably in terms of application, the number of catalyst tubes accommodated in the tube bundle container (in particular in the case of the two aforementioned partial oxidations) amounts to at least 5000, preferably to at least 10000. Frequently the number of catalyst tubes accommodated in the reaction container is 15,000 to 30,000 or up to 40000. Tube bundle reactors with one above 50000 lying number of contact tubes are rather the exception. Within the container, the contact tubes are normally distributed homogeneously (preferably 6 equidistant adjacent tubes per contact tube), 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 , EP-A 468 290 ).

In particular, in the case of desired elevated (eg ≥ 100 Nl / l · h, or ≥ 120 Nl / l · h, or ≥ 130 Nl / l · h, or ≥ 140 Nl / l · h, or ≥ 150 Nl / l · h, or ≥ 160 Nl / l · h, but usually ≤ 175 Nl / l · h, or ≤ 200 Nl / l · h, or ≤ 300 Nl / l · h, or normally ≤ 600 Nl / l · h) loads of the fixed catalyst bed with acrolein (but also quite in the range of acrolein loadings of the fixed catalyst bed of ≥ 50 Nl / l · h and ≤ 100 Nl / l · h) takes place the implementation of the Acroleinpartialoxidationsverfahrens to acrylic acid in a manner similar to the Propylenpartialoxidation appropriate in the two- or Mehrzonenrohrbündelreaktor (a implementation in Einzonenrohrbündelreaktor is also possible). A preferred variant of a two-zone tube bundle reactor which can be used according to the invention for this purpose is disclosed in US Pat DE-C 28 30 765 , But also in the DE-C 25 13 405 , of the US-A 3,147,084 , of the DE-A 22 01 528 , of the EP-A 383 224 and the DE-A 29 03 582 disclosed two-zone tube bundle reactors are suitable. Multizone variants are also used in the EP-A 1,106,598 , of the WO 2004/085362 , of the WO 2004/085370 and the WO 2004/085363 described.

that is, in a simple manner, the fixed catalyst bed is then in the preferably uniformly coated (metal) tubes of a Tube reactor and around the reaction tubes two (or more) of each other (e.g. by means of partitions, through the holes of the reaction tubes are passed) essentially spatially separate fluid heat carrier (in usually molten salts) out.

Of the Pipe section (the ambient space segment) over which the respective Heat transfer medium (the respective salt bath), represents a temperature zone.

For example, a salt bath C preferably flows around the (longitudinal) section C of the tubes (the temperature zone C) in which the oxidative conversion of the acrolein (in a single pass) takes place until a conversion value U _C in the range from 15 to 89 mol% is reached a salt bath D flows around the (longitudinal) section D of the tubes (the temperature zone D), in which the oxidative terminal conversion of acrolein (in single pass) until a conversion value U _D of usually at least 90 mol% (preferably ≥ 92 mol%, or ≥94 mol%, or ≥96 mol%, or ≥98 mol% and often even ≥99 mol% and more) (if necessary, more can be added to the temperature zones C, D) Connect temperature zones that are kept at individual temperatures).

Within the respective temperature zone, the respective salt bath (the respective fluid heat carrier) can be conducted as in the one-zone operation (in particular relative to the reaction gas mixture). That is to say, the salt bath C is introduced at the temperature T in ^{, C} into the temperature zone C and out at the temperature T ^{out, C} , where T ^{out, C} > T in ^{, C} holds. In a corresponding manner, the salt bath D is at the temperature T in ^{, D} in the temperature zone D in and out with the temperature zone T ^{out, D} again, where T ^{out, D} > T on ^{, D} applies (also at this point should be noted again, that the terms salt bath C or salt bath D in this document are always representative of a fluid heat carrier C or a fluid heat carrier D, so that the respective disclosure also includes the wording that results from the fact that "salt bath C" by "a fluid Heat carrier C "and" salt bath D "is replaced by" a fluid heat carrier D ").

The fluid heat carrier (the tempering medium, usually a molten salt) C (D) and the reaction gas mixture can be performed within the temperature zone C (D) in both simple DC and in the simple countercurrent. The fluid heat carrier (the tempering medium, for example the molten salt) C (D) can also be meandering around the tube bundle section C (D), so that viewed only over the entire tube bundle section C (D) a DC or countercurrent to the flow direction of the reaction gas mixture consists. Regardless of the detailed current flow of the fluid heat carrier (the tempering medium, for example, the molten salt) C (D), the volume flow of the same is usually so dimensioned that the temperature increase (due to the exothermicity of the reaction) of the fluid heat carrier (the tempering, eg the molten salt ) C (D) from the entry point in the space surrounding the tube bundle section C (D) to the exit point from the space surrounding the tube bundle section C (D) (ie, T ^{out, C} - T in ^{, C} (T ^{out, D} - T ^{a, D} )) 0 to 10 ° C, often 2 to 8 ° C, often 3 to 6 ° C.

The maximum reaction temperature (the temperature of the so-called respective hot spot) along the contact tube section C, T ^maxC (of the contact tube section D, T ^maxD , can be up to 70 ° C or more above T in ^{, C} (T in ^{, D} ).

The difference T ^maxC - T in ^{, C} (T ^{max D} - T in ^{, D} ) is referred to as the hotspot extension ΔT ^{H, C} (ΔT ^{H, D} ).

According to the teachings of the prior art, the general process conditions are usually chosen so that T ^{max C} - T ^{max D} ≥ 0 ° C and ≤ 80 ° C for freshly charged ^{fixed catalyst bed} (see, eg WO 2004/085362 . WO 2004/085370 . WO 2004/085363 and in the European Application No. 06 100 535 ).

At lower educt loadings of the fresh fixed catalyst bed, this is often advantageously given as T in ^{, D} - T in ^{, C} <0 ° C., while with increasing educt load of the fresh fixed catalyst bed the above condition is often advantageously given as T in ^{, D} - T in ^{, C} ≥ 0.

Furthermore, the catalyst selection for the fixed catalyst bed and its possible dilution with inert material in the fixed catalyst bed normally takes place (cf. EP-A 990 636 and EP-A 1,106,598 ) so that the freshly charged fixed catalyst bed in the given heat carrier-purged reaction tube section .DELTA.T ^{H, C} (.DELTA.T ^{H, D} ) with increasing T in ^{, C} (T in ^{, D} ) by + 1 ° C normally ≤ 9 ° C, preferably ≤ 8 ° C, more preferably ≦ 7 ° C, or ≤ 5 ° C or ≤ 3 ° C.

The inlet ^{temperature of} the respective fluid heat carrier in the space surrounding the respective contact tube section (T in ^{, C} or T in ^{, D} ) is generally 230 to 340 ° C., frequently 250 to 320 ° C. or 260 to 300 ° C.

To counteract the deactivation of the fixed catalyst bed in long-term operation, it is preferable as in the European Application No. 06 100 535 as well as the DE-A 10 2004 025 445 described procedure. In general, U _C = 15 to 85 mol% and U _D ≥ 90 mol% are generally retained in long-term operation. With respect to the eligible fluid heat transfer, what has been said in multizone propylene partial oxidation applies.

In principle, both T _II ^{a, C>} T _I ^{A, C} and T _II ^{a, D>} T _I ^{A, D} can also be met in an inventive two-zone acrolein partial oxidation to acrylic acid in the operating state II. As a rule, during the transition from an operating state I with an acrolein loading of the fixed catalyst bed L ^I to an operating state II with an acrolein loading of the fixed catalyst bed L ^II > L ^I in the described two-zone tube bundle reactor, suitably from the point of view of increasing the acrolein loading of the fixed catalyst bed both T _{I in} ^{, C} on T _II ^{, C} and T _{I on} ^{, D} on T _{II on} ^{, D} increase (in terms of application, it is advisable to proceed in such a way that T _{II is} ^{one, C} - T _{I is} ^{one, C is} approximately equal to T _II ^{, D} - T _{I on} ^{, D is} selected).

But it can also be done so that when transitioning from operating state I to operating state II only T _{I on} ^{, C} on T _{II on} ^{, C} increases, and T _{I on} ^{, D} substantially retained (= T _{II on} ^{, D} ) or only T _{I on} ^{, D} on T _{II on} ^{, D} increases, and T _{I on} ^{, C} essentially retained (= T _{II on} ^{, C} ). According to the invention, however, in all three possible cases, the procedure is such that T ^maxC -T ^maxD ≥ 0 ° C. and ^≦ 80 ° C. is fulfilled (in particular on the fresh ^{fixed catalyst bed} ) both in operating state I and in operating state II. That is, both in operating state I and in operating state II, T ^maxC - T ^maxD may advantageously (and independently of each other) ≥ 1 ° C and ≤ 70 ° C, or ≥ 2 ° C and ≤ 60 ° C, or ≥ 3 ° C and ≤ 50 ° C, or ≥ 4 ° C and ≤ 40 ° C, or ≥ 5 ° C and ≤ 30 ° C, or ≥ 5 ° C and ≤ 25 ° C, or ≥ 5 ° C and ≤ 20 ° C or ≤ 15 ° C, or ≥ 0 ° C and ≤ 5 ° C.

It is favorable according to the invention that when T ^{maxC -T maxD} in operating state I lies in a specific one of the aforementioned temperature difference ^intervals , T ^{maxC -T maxD} also lies in operating state II in this temperature difference interval.

In principle, in the operating state IT ^maxC - T ^maxD (T _I ^maxC - T _I ^maxD ) but also ≥ 0 ° C and ≤ 80 ° C and in operating state II (T _II ^maxC - T _II ^maxD ) <0 ° C (eg up to -20 ° C, or down to -10 ° C, or down to -5 ° C).

If, during the transition from operating state I to operating state II, both T _{I in} ^{, C} and T _{I in} ^{, D} increase (to T _{II in} ^{, C} or T in _II ^{, D} ), then these two temperature increases can occur both substantially simultaneously ) as well as with a time delay. In the case of a time-delayed increase, it is advantageous in terms of application technology to initially increase T _I ^{, C} to T _II ^{, C} and then T _I to increase ^D to T _II ^{, D} (in principle, however, the procedure can also be reversed).

Whether in the process according to the invention an increase of L ^I to L ^{II is} realized by increasing the load of the fixed catalyst bed with reaction gas input mixture with substantially constant Reaktionsgaseingangsgemischzusammensetzung and / or by increasing the proportion of organic starting compound in the reaction gas input mixture, also depends on the design of the separation-effective internals from separating column, in which the product gas mixture is passed to separate the target product. That is, the application of L ^I to L ^{II is} preferably the application of possible increase so that the load of the separation column with product gas mixture remains in the range in which the separation efficiency of the separation column is optimal. This is usually the case if, to increase L ^{I, it is} primarily the reactant content in the reaction gas input mixture that is increased.

Quite generally, when carrying out the process according to the invention, it is expediently desirable in terms of application technology to determine the compositions of the reaction gas mixture both in operating state I as well as in operating state II, as well as in all states during the transition from operating state I to operating state II to be designed so that they are outside the explosive range, as shown in the WO 2004/007405 is recommended.

Suitable reaction gas input mixtures according to the invention for a propylene partial oxidation to acrolein and / or acrylic acid are, for example, those which contain 5 to 15 (preferably 7 to 11)% by volume propylene, 4 to 20 (preferably 6 to 12)% by volume Water, ≥ 0 to 10 (preferably ≥ 0 to 5)% by volume constituents of propylene, water, molecular oxygen and molecular nitrogen, so much molecular oxygen that the molar ratio of molecular oxygen contained to propylene to be contained is 1.5 to 2.5 (preferably 1.6 to 2.2), and the remaining amount is up to 100 volume% of total molecular nitrogen.

Especially at high propylene loadings of the catalyst fixed bed is the concomitant use of inert diluent gases with high specific heat recommended.

For example may be a reaction gas input mixture for a heterogeneously catalyzed partial propylene oxidation to acrolein and / or acrylic acid bis to 70 vol .-% propane.

For example, such propylene partial oxidation reaction gas input mixtures may be included 5 to 11% by volume propylene, 2 to 12 vol.% Water, > 0 to 10% by volume Propane, ≥ 0 to 5 vol.% Propylene, Propane, Water, Molecular Oxygen and Molecular Nitrogen Different Ingredients, so much molecular oxygen that the molar ratio of molecular oxygen contained to the propylene to be contained is 1 to 3 and the remaining amount is up to 100% by volume of total molecular nitrogen; or 5 to 9 vol.% propylene, 8 to 18% by volume molecular oxygen, 6 to 35 vol.% Propane, and 32 to 72 vol.% molecular nitrogen, or 4 to 25 vol.% propylene, 6 to 70 vol.% Propane, 5 to 60 vol.% H ₂ O, 8 to 65 vol.% O ₂ , and 0.3 to 20 vol.% H ₂ .

For a heterogeneously catalyzed acrolein partial oxidation according to the invention to acrylic acid, suitable reaction gas input mixtures are, for example, those which contain: 4.5 to 8 vol.% acrolein, 2.25 to 9% by volume molecular oxygen, 0 to 35 vol.% Propane, 32 to 72 vol.% molecular nitrogen, and 5 to 30% by volume Steam; or 3 to 25 vol.% acrolein, 5 to 65 vol.% molecular oxygen, 6 to 70 vol.% Propane, 0 to 20 vol.% molecular hydrogen, and 8 to 65 vol.% Steam.

Finally it should be noted that an application point, first T _II ^{is a} T ^a is reduced to the transition from one operating state to an operating state II I _I and subsequently L is reduced to L ^{I II.} Advantageously, the aforementioned reductions are carried out in the same way as the elevations according to the invention as a succession of small redemption steps.

In principle, the redemption of L to L ^{II I} can also substantially simultaneously with the withdrawal of ^a T _{II I} on T ^a take place (preferably but even in this case, as a succession of small steps). The load reductions can be carried out in a similar manner as described in this document for the load increases, but with the difference that the size that is increased in the load increase, is lowered at a load reduction in a corresponding manner.

In a two-stage exothermic heterogeneously catalyzed partial gas phase oxidation, the transition from an operating state II to an operating state I in terms of application will suitably initially T _{II on} ^{, 1} on T _{I on} ^{, 1} and then T _{II on} ^{, 2} on T _{I on} ^{, 2} decrease. In the case of a two-zone mode of operation, the transition from an operating state II to an operating state I will normally be the last to lower the heat-carrier inlet temperature, which was first raised in the case of the reverse operating state change.

example

A process of heterogeneously catalyzed partial gas phase oxidation of propylene to acrolein in a one-zone multi-contact fixed bed reactor Description of the general process conditions in operating condition I Used heat exchange agent: Molten salt consisting of 60% by weight Potassium nitrate and 40 wt .-% sodium nitrite. Material of the contact tubes: ferritic steel. Dimensions of the contact tubes: 3200 mm in length; 25 mm inside diameter; 30 mm outside diameter (Wall thickness: 2.5 mm). Number of contact tubes in the tube bundle: 25,500th Reactor: Cylindrical container with a diameter of 6800 mm; annularly arranged tube bundle with a free central space. Diameter of the central free space: 1000 mm. Distance of the outermost contact tubes to the vessel wall: 150 mm. Homogeneous contact tube distribution in the tube bundle (6 equidistant neighboring tubes per contact tube). Contact tube pitch: 38 mm. The contact tubes were sealed at their ends in contact tube plates of thickness 125 mm and ended with their openings in one at the top and bottom of the container connected to the hood. Supply of the heat exchange medium to the tube bundle: The tube bundle was divided into four equidistant (each 730 mm) longitudinal sections (zones) by three deflecting disks (thickness each 10 mm) placed successively between the contact tube plates along the same.

The lowermost and the top deflection pulley had ring geometry, wherein the ring inner diameter was 1000 mm and the ring outside diameter down to the container wall sealingly extended. The contact tubes were at the deflection pulleys not sealed. Rather, a gap width <0.5 mm had Leave column such that the cross-flow velocity of the molten salt within a zone as possible was constant.

The middle deflector was circular and extended to to the furthest outside lying contact tubes of the tube bundle.

The circle guide The salt melt was accomplished by two salt pumps, from each supplied a tube bundle half-length.

• – von außen nach innen,
• – von innen nach außen,
• – von außen nach innen,
• – von innen nach außen,

im wesentlichen mäanderförmig, über den Behälter betrachtet, von unten nach oben. Durch im obersten Längsabschnitt um den Behälterumfang angebrachte Fenster sammelte sich die Salzschmelze in einem oberen um den Reaktormantel angebrachten Ringkanal und wurde nach Abkühlung auf die ursprüngliche Eintrittstemperatur durch die Pumpen wieder in den unteren Ringkanal gedrückt.The pumps forced the molten salt into a ring channel mounted around the bottom of the reactor, which distributed the molten salt over the circumference of the container. Through the window located in the reactor shell, the molten salt reached the bottom longitudinal section of the tube bundle. The molten salt then flowed following the specification of the baffles in the sequence

• - from the outside to the inside,
• - from the inside to the outside,
• - from the outside to the inside,
• - from the inside to the outside,

essentially meandering, viewed over the container, from bottom to top. By in the top The molten salt was collected in a longitudinal section around the container circumference in an upper ring channel mounted around the reactor jacket and, after cooling to the original inlet temperature, was forced back into the lower annular channel by the pumps.

Composition of the reaction gas input mixture (mixture of air, polymer grade propylene and cycle gas): 5.4% by volume propylene, 10.5 vol.% Oxygen, 1.2% by volume CO _x , 81.3% by volume N ₂ , 1.6% by volume H ₂ O. Reactor charge: Salt melt and reaction gas mixture were over viewed in countercurrent to the reactor. The salt melt entered the bottom, the reaction gas mixture above. The inlet temperature of the molten salt was 337 ° C. The exit temperature of the molten salt was 339 ° C. The pumping power was 6200 m ³ molten salt / h. The reaction gas input mixture was added to the reactor supplied at a temperature of 170 ° C. Load with reaction gas input mixture: 68845 Nm ³ / h. Propylene load of Catalyst charge: 110 Nl / lh. Contact tube charge (from top to bottom): Zone A: 50 cm Precast of steatite rings of geometry 7 mm × 7 mm × 4 mm (outer diameter × length × inner diameter knife). Zone B: 100 cm Catalyst feed with a homogeneous mixture from 30 wt .-% of steatite rings of geometry 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter knife) and 70% by weight of full catalyst from zone C. Zone C: 170 cm Catalyst feed with annular (5 mm × 3 mm × 2 mm = outer diameter × length × inner diameter) Full catalyst according to Example 1 of DE-A 100 46 957 ,

Based on the single passage of the reaction gas input mixture by the fixed catalyst bed was the propylene conversion at 96.4 mol% a selectivity the acrolein formation of 85.7 mol%.

T ^max , determined as an average over six thermoreaction tubes provided with multi-thermocouples, was 398 ° C.

Description of the general process conditions in operating condition II

However, as in operating condition I, the loading of the fixed catalyst bed with propylene was 120 Nl / l-hr and the inlet temperature of the molten salt was 342 ° C, with the composition of the reaction gas input mixture remaining the same. T ^max was 403 ° C. Propylene conversion and selectivity of acrolein formation were as in operating state I.

The transition from operating state I to operating state II was as a series completed by successive steps. At first was the inlet temperature of the molten salt with identical propylene loading around 0.5 ° C elevated. Then these operating conditions were maintained for one hour before the propylene load at stable held inlet temperature of the molten salt by so much elevated was until the propylene conversion was again 96.4 mol%. Then were maintain the operating conditions for another 1 h before the inlet temperature the molten salt was again increased by 0.5 ° C at the new propylene load u.s.w ..

The highest ^Tmax value during the transition from operating state I to operating state II was 403 ° C.

Of the Propylene conversion never dropped below 96.4 mol%.

Comparative example

Increased during the transition from operating state I to operating state II with initially constant inlet temperature of the molten salt of 337 ° C, the load of the fixed catalyst bed with propylene of 110 Nl / l · h to 120 Nl / l · h (with constant composition of the reaction gas input mixture) and only then the inlet temperature of the molten salt of 337 ° C to 342 ° C (in 0.5 ° C steps, each increase in temperature before the subsequent increase in temperature over 1 h was held), was the so carried out transition from operating state I to II operating state continuous T ^max value 404 ° C. The propylene conversion temporarily dropped below 96.4 mol%.

Claims (5)

A method for operating an exothermic heterogeneously catalyzed partial gas phase oxidation of an organic starting compound to an organic target compound in mutually different operating states I and II, comprising reacting a starting gas mixture containing the organic starting compound, molecular oxygen and at least one inert diluent gas to obtain a product gas mixture containing the organic target compound an in-the tubes of a tube bundle reactor, fixed catalyst bed leads as well as in the area surrounding the fixed catalyst bed containing tubes of the tube bundle reactor chamber to the reaction temperature setting in located in the tubes fixed catalyst bed, at least a fluid heat carrier having an entry temperature ^T in and at an outlet temperature T ^off> T ^one again leads out of this, and thereby the fixed catalyst bed in the operating state I at an inlet temperature T _I ^{a an} L ^I and T _II ^a> T _I ^a loaded with a load L ^I of the organic starting compound and in the operating state II at an inlet temperature T _II with an L ^II of the organic starting compound with the proviso L ^II>, characterized in that when changing the operating state I to the operating state II, first, the inlet temperature T _I then increased to ^the value T ^_II, and the loading of the fixed catalyst bed with the organic starting compound from the value ^I L to the value L ^II. A method according to claim 1, characterized in that the ratio L ^II to L ^I > 1 and ≤ 2. Method according to claim 1 or 2, characterized the organic starting compound is propylene, acrolein, tert-butanol, iso-butane, iso-butene, iso-butyraldehyde, the methyl ether of tert-butanol, methacrolein, o-xylene, p-xylene, naphthalene, butadiene, n-butane, ethylene, indane, Benzene, 1-butene, 2-butene and / or ethane. A method for operating a two-stage exothermic heterogeneously catalyzed partial gas phase oxidation of a first organic starting compound to an organic end target compound in mutually different operating conditions I and II, comprising first organic starting gas mixture containing the first organic starting compound, molecular oxygen and at least one inert diluent gas Target intermediate compound containing first product gas mixture through a located in the tubes of a tube reactor first fixed catalyst bed, as well as in the first catalyst fixed bed containing tubes this tube bundle surrounding space for adjusting the Re reaction temperature in the first fixed catalyst bed at least a first fluid heat carrier with an inlet temperature T ^{1, a} into and out with an outlet temperature T ^{1, from} > T ^{1, a} back leads out of this and the first, previously gegeb optionally cooled and optionally supplemented with molecular oxygen and inert gas as secondary gas additive product gas mixture as molecular oxygen, at least one inert diluent gas and the organic intermediate target compound as a second organic Aus The second reaction gas input mixture containing the starting compound containing a second product gas mixture contained in the tubes of a tube bundle reactor, second, different from the first fixed catalyst bed, fixed catalyst bed and in the surrounding the second fixed catalyst tube of this tube bundle reactor surrounding space for adjusting the reaction temperature in the second Fixed catalyst bed at least a second fluid heat carrier with an inlet temperature T ^{2, one} into and out with an outlet temperature T ^2, > T ^{2, a} back out of this and while in operation I the first fixed catalyst bed at an inlet temperature T _I ^{1, one} with a Last L ^{1, I of} the first organic starting compound and the second fixed catalyst bed at an inlet temperature T _I ^{2, one} with a load L ^{2, I of} the second organic starting compound and in operating state II the first e Fixed catalyst bed at an inlet temperature T _II ^{1, one} with a load L ^{1, II of} the first organic starting compound and the second fixed catalyst bed at an inlet temperature T _II ^{2, one} with a load L ^{2, II of} the second organic starting compound with the proviso L ^{1, II} > L ^{1, I} , T _II ^{1, a} > T _I ^{1, a} , L ^{2, II} > L ^{2, I} and T _II ^{2, a} > T _I ^{2, a} loaded, characterized in that when changing from Operating state I in the operating state II first, the inlet temperature T _I ^{1, one} on the value T _II ^1, and the inlet temperature T _I ^{2, one} to the value T _II ^2, and then the load of the first fixed catalyst bed with the first organic starting compound from the value L ^{1, I} to the value L ^{1, II} and as a consequence of the last-mentioned above measure and an optionally additionally modified secondary gas addition, the load of the second fixed catalyst bed of value L ^{2, I increased} to the value L ^{2, II} . Method according to claim 4, characterized in that the organic starting compound is propylene, the intermediate target compound Acrolein and the ultimate target compound is acrylic acid.