DE10246119A1 - Heterogeneously catalyzed gas-phase partial oxidation of acrolein to acrylic acid, used to produce polymers for adhesives, involves using active multimetal oxide material containing e.g. molybdenum and vanadium - Google Patents

Abstract

A heterogeneously catalyzed gas-phase partial oxidation of acrolein to acrylic acid over a catalytically active multimetal oxide material which contains the elements molybdenum and vanadium, tellurium or antimony, and elements consisting of niobium, tantalum, tungsten or titanium, whose X-ray diffraction pattern has no reflections with the peak position 2 theta = 50 +/- 0.30 but has reflections whose peaks are at specified diffraction angles. Heterogeneously catalyzed gas-phase partial oxidation of acrolein to acrylic acid over a catalytically active multimetal oxide material which contains the elements molybdenum and vanadium, tellurium or antimony, and elements consisting of niobium, tantalum, tungsten or titanium, whose X-ray diffraction pattern has no reflections with the peak position 2 theta = 50 +/- 0.30 but has reflections h, i and k whose peaks are at the diffraction angles (2 theta) 22.2 +/- 0.5 degrees (h), 27.3 +/- 0.50 (i) and 28.2 +/- 0.50 (k). The reflection (h ) is the one with the strongest intensity within the X-ray diffraction pattern and having a full width at half height of not more than 0.50; the intensity (Pi) of the reflection (i) and the intensity (Pk) of the reflection (k) fulfill the relationship that R is 0.65-0.85, where R is the intensity ratio defined by the formula R = Pi/(Pi + Pk); and the full width at half height of the reflection (i) and of the reflection (k) is in each case at most 10. The catalytically active multimetal oxide material is of formula (I). Mo1VaM1bM2cM3dOn (I). M1 = element(s) from the group consisting of Te and Sb; M2 = element(s) from the group consisting of Nb, Ti, W, Ta and Ce; M3 = element(s) consisting of Pb, Ni, Co, Bi, Pd, Ag, Pt, Cu, Au, Ga, Zn, Sn, In, Re, Ir, Sm, Sc, Y, Pr, Nd or Tb; a = 0.01-1; b = 0-1; c = 0-1; d = 0-0.5; n = number that is determined by the valency and frequency of the elements other than oxygen in formula (I).

Description

• a) in einem ersten Schritt Roh-Propan im Beisein und/oder unter Ausschluss von Sauerstoff einer homogenen und/oder einer heterogen katalysierten Dehydrierung und/oder Oxidehydrierung unterwirft, wobei ein Propan und Propylen enthaltendes Gasgemisch 1 erzeugt wird, und
• b) aus im ersten Schritt gebildetem Gasgemisch 1 von den darin enthaltenen, von Propan und Propylen verschiedenen, Bestandteilen gegebenenfalls eine Teilmenge abtrennt und/oder in andere Verbindungen wandelt, wobei aus dem Gasgemisch 1 jeweils ein Propan und Propylen sowie auch von Sauerstoff, Propan und Propylen verschiedene Verbindungen enthaltendes Gasgemisch 1' erzeugt wird, und in wenigstens einem weiteren Schritt
• c) Gasgemisch 1 und/oder Gasgemisch 1' als Bestandteil eines Gasgemisches 2 einer heterogen katalysierten Gasphasen-Partialoxidation und/oder partiellen Gasphasen-Ammoxidation von im Gasgemisch 1 und/oder Gasgemisch 1' enthaltenem Propylen unterwirft.

The present invention relates to a process for producing at least one partial oxidation and / or ammoxidation product of propylene, in which

• a) subjecting crude propane in the presence and / or in the absence of oxygen to a homogeneous and / or heterogeneously catalyzed dehydrogenation and / or oxydehydrogenation, a gas mixture containing propane and propylene being generated, and
• b) from the gas mixture 1 formed in the first step from the constituents contained therein, different from propane and propylene, if appropriate, a partial amount is separated and / or converted into other compounds, in each case one propane and propylene and also of oxygen, propane and Gas mixture 1 'containing propylene is generated, and in at least one further step
• c) gas mixture 1 and / or gas mixture 1 'as part of a gas mixture 2 is subjected to a heterogeneously catalyzed gas phase partial oxidation and / or partial gas phase ammoxidation of propylene contained in gas mixture 1 and / or gas mixture 1'.

Raw propane is said in this document a gas containing propane can be understood, in addition to propane and optionally propylene, at least one, often at least two or three and often at least four or five of propane and propylene contains various chemical compounds. The latter is the case when such chemical compounds are chromatographically, e.g. can be detected by gas chromatography, in raw propane.

In this document, oxydehydrogenation of propane is to be understood as meaning a dehydrogenation which is forced by the presence of oxygen and in which no free hydrogen is formed or is detectable as an intermediate. In contrast to conventional dehydrogenation, which is endothermic, the heat of the oxydehydrogenation is exothermic. The oxydehydrogenation of propane can be both homogeneous (ie without the presence of, for example, a solid catalyst; cf. US-A 3 798 283 ) and heterogeneously catalyzed (e.g. on solid catalysts; cf. DE-A 2058054 and DE-A 19530494 ) be performed.

The same applies essentially to conventional dehydrogenation, in which the dehydrogenation step takes place without the active participation of oxygen (cf. e.g. EP-A 731 077 and WO 01/96270). This means that the primary by-product is hydrogen and not water as in the case of oxide dehydrogenation.

A complete oxidation of propylene is understood in this document to mean that the total carbon contained in propylene is converted into oxides of carbon (CO, CO ₂ ). All of these different reactions of propylene under the reactive action of molecular oxygen are subsumed in this document with the term partial oxidation. The additional reactive action of ammonia characterizes the. Ammoxidation.

The preferred in this document partial oxidation and / or ammoxidation products of propylene are acrolein, acrylic acid, Propylene oxide and acrylonitrile.

Partial oxidation and / or ammoxidation products of propylene are important intermediates, e.g. for the production of polymers.

The implementation of such partial oxidations and / or ammoxidations (by controlled in a manner known per se The reaction can be selected by selecting the ammonia content in the reaction gas mixture essentially exclusively as partial oxidation, or exclusively as partial ammoxidation, or as an overlay both reactions are designed) is known per se. It deals are heterogeneously catalyzed gas phase reactions on solid, usually oxidic, catalysts.

They are cited as an example DE-A 2 351 151 (Example for the conversion of propylene to acrolein and / or acrylic acid and from propylene to acrylonitrile) and the EP-A 372 972 (Example for the conversion of propylene to propylene oxide).

Molecular oxygen is normally used as the oxidizing agent, which can be added to the reaction gas mixture, for example in pure form or in a mixture with gases which are essentially inert with respect to the partial oxidation / ammoxidation (for example as air). Frequently, the reactants in the reaction gas mixture are also for reasons of heat dissipation and for reasons of safe reaction by at least one inert gas (for example N ₂ , H ₂ O, CO, CO ₂ , saturated, for example C ₁ -C ₅ hydrocarbons (for example in accordance with DE-A 1924431 and EP-A 293224 ), He and / or Ar etc.) diluted. The DE-AS 2251364 recommends using butane as an inert diluent gas. The ammoxidation differs, as already mentioned, by an additional presence of ammonia.

In contrast to laboratory and pilot plant trials, the starting propylene is usually not a chemically pure, but a raw propylene that contains impurities, but which has a comparatively high purity (for example "polymer grade" or "chemical grade"; cf. DE-A 10131297 ).

Obtaining comparatively pure crude propylene in this way is relatively complex and costly. It usually starts from crude paraffinic hydrocarbons and usually includes at least one purification stage in which unreacted paraffinic hydrocarbons are separated from formed propylene by means of physical processes (cf. e.g. DE-A 3 521 458 )). Usually, the at least one purification step also includes a separation of olefins other than propylene and other by-products other than propylene, including the secondary components already contained in the crude paraffinic hydrocarbon.

The aforementioned partitions are usually investment-intensive and due to the similarity of olefinic / paraffinic hydrocarbons very energy intensive. They are therefore usually only used in conjunction with refinery crackers and steam crackers and only pay off because the vast majority of the so obtained Raw propylene for subsequent polymerizations (e.g. production of polypropylene) on the one hand in large Quantities needed (keyword: "economy of scale ") and thereby on the other hand a high added value experiences.

The one of these crude propylenes Partial oxidations and / or amoxidations flowing part is of minor importance Meaning and running as an auxiliary supply stream, so what is generated in this way Raw propylene also for Partial oxidations and / or amoxidations are still acceptable Commodity price.

This raw material price could be noticeably lower only if at least on a part of the mentioned separations or their total amount waived could be.

As a solution to the problem EP-B 938463 before in a first step, for example, partially dehydrogenating crude propane heterogeneously catalyzed in the presence of oxygen, producing a first gas mixture containing propylene and propane which, as such, ie without intermediate treatment, is part of a second gas mixture of a heterogeneously catalyzed gas phase Partial oxidation of propylene contained in the first gas mixture to acrolein and / or acrylic acid is subjected.

The question arises as to the purity of the crude propane to be used EP-B 938463 in column 3, lines 40 et seq. from: "The purity of the starting material alkane is not particularly limited". "Further, the starting material alkane may be a mixture of various alkanes. Typically the feed will comprise at least 30 mole percent, preferably at least 50 mole percent and more perferably at least 80 mole percent propane. The source of the alkane, eg propane feed, for use in the process of the present invention is not critical. "

It also teaches EP-B 938463 in column 3, lines 17ff: "Hence, after recovery of the acrolein, the noncondensed gases containing propane may be recycled without significant, additional purification steps."

The teaching of EP-A 117146 corresponds essentially to the EP-B 938463 , apart from the fact that the EP-A 117146 recommends carrying out the heterogeneously catalyzed dehydrogenation of propylene in the absence of oxygen.

Furthermore, the EP-A 117146 on page 11, lines 14ff regarding the aforementioned recycling stream: "Since the light and heavy hydrocarbon by - products, such as methane, ethane, ethylene, butane, and butenes boil at temperatures significantly different from those of acrolein or the C ₃ hydrocarbons, they may be separated by distillation. Alternatevely, streams containing the by - products in concentrated amounts may be purged. " She also sees the possibility of such a purge flow of recycled gas EP-B 938463 in column 11, line 10.

The need for separation the aforementioned secondary components prior to the partial oxidation and / or -ammoxidation do not see either font.

The teaching of WO 01/96270 follows that in the EP-B 938463 and to those in the EP-A 117 146 given teaching. On page 4, line 10ff, she explains: "It goes without saying that the feed gas mixture of oxidation level B can, in addition to the components already mentioned, other components such as CO, CO ₂ , H ₂ O, noble gases such as He and / or Ar in addition to the components already mentioned , Hydrogen, methane, ethylene, butanes, butenes, butynes, pentanes, propyne, allenes and / or acrolein. " Furthermore, WO 01/96270 on page 15, lines 26ff teaches about the crude propane to be used for the dehydrogenation step: "According to the invention, it is essential that the propane used in stage A need not be pure propane. Rather, the propane used can be up to 50% Vol .-% of other gases such as ethane, methane, ethylene, butanes, butenes, propyne, acetylene, H ₂ S, SO ₂ , pentanes, etc. contain. "

WO 01/96270 also recommends that from the first gas mixture formed in the dehydrogenation step and containing propane and propylene at least a partial amount of the hydrogen contained in the first gas mixture and, if necessary, others in the course of this separation for the partial oxidation of the propylene contained therein, if appropriate, essentially separate all of the constituents other than propane and propylene, and in the EP-B 731077 A quantitative separation of all constituents other than propane, propylene and possibly molecular oxygen from such a first gas mixture is even considered to be particularly preferred prior to its further use, but on the one hand each separation process to be used in this regard reduces the economy of the overall process and On the other hand, some of the methods recommended in the aforementioned documents prove to be unsuitable for such a quantitative separation. The latter applies, for example, to the absorption / desorption process recommended in WO 01/96270 on page 16 below, which on closer examination proved to be unsuitable for separating, for example, C ₄ hydrocarbons from C ₃ hydrocarbons.

The need to change raw materials from raw propylene to raw propane after the dehydrogenation and / or oxydehydrogenation step or in advance this step to separate certain secondary components in order to at least one oxidation and / or ammoxidation step in addition the formation of the desired target product The cited state sees the reduction of the formation of by-products of technology not. Although he is concerned with the raw material change changing By-product formation deliberately (according to WO 01/96270 e.g. the presence of propane in the partial oxidation increases formation on propionaldehyde and / or propionic acid; the advantage of not separating of the propane from the propylene formed in the dehydrogenation, however rated higher), sees it, however, as not being particularly critical as one Pre-separation is usually more complex than the separation of Target product and by-product. This also against the background that in any case, a target product separation of by-products formed carried out must become.

Obviously, this view is shared by those who like that EP-A 1192987 or the DE-A 10122027 , or the EP-A 608838 , or the EP-A 529853 , or the DE-A 10051419 , or the DE-A 10119933 recommend performing the process defined at the beginning of this document in a single reaction zone (usually it is carried out in at least two reaction zones) on a catalyst feed whose active oxide mass is at least one multimetal oxide which contains the elements Mo, V and Te and / or Sb. The basis of this procedure is that the relevant active oxide mass on the one hand both the oxydehydrogenation of propane to propylene (cf. e.g. EP-B 938463 , Column 4, line 37ff) and on the other hand is also able to catalyze the partial oxidation and / or amoxidation of propylene. Of course, in such a procedure, the gas mixture 1 is used as such for the subsequent at least one partial oxidation and / or ammoxidation step.

Nevertheless, the EP-A 1192987 on page 9, line 26ff: "Similarly, there is no limitation on the source of the alkane. It may be purchased, per se, or in admixture with an alkene and / or other impurities. Furthermore, the alkane, regardless of source, and the alkene, regardless of source, may be blended as desired. " The teaches in complete correspondence DE-A 10122027 on page 3, lines 35/36: "The propane to be used for the process according to the invention is not particularly demanding in terms of its purity."

A disadvantage of the above recommendations The state of the art is that they do not question which in inexpensive Raw propane components or ingredients already contained formed from such components in the course of the first step and then chemical compounds contained in the first gas mixture (not in the normally used raw propylenes or are only contained in traces, so their negative effects have so far remained unnoticed) the subsequent heterogeneously catalyzed partial oxidation and / or -ammoxidation act as catalyst poisons by their activity and / or selectivity with regard to the desired partial oxidation and / or amoxidation of propylene.

As a result of thorough and careful investigations, it has now been found that C ₄ -hydrocarbons (chemical compounds which consist of four carbon atoms and hydrogen) in general and among these in particular the group of olefinic representatives (butene-1, trans-butene-2, cis-butene-2 and isobutene) and among these in particular the butene-1 form such catalyst poisons. However, the saturated representatives (n-butane and isobutane) and the other unsaturated representatives also have a disadvantageous effect.

Especially C ₄ -hydrocarbons (e.g. n-butane, isobutane, trans-butene-2, cis-butene-2, isobutene, butadiene 1.3, butadiene 1,2, 1-butyne and / or 2-butyne ), however, form ubiquitous companions of propane and are therefore usually contained in significant quantities in inexpensive raw propanes. This statement applies to a very particular extent to the saturated C ₄ -hydrocarbons, from which, however, under the conditions of partial dehydrogenation and / or oxydehydrogenation of propane, the olefinic C ₄ -hydrocarbons, in particular the particularly troublesome butene-1, be formed.

The object of the present invention therefore consisted, in contrast to the procedures of the state the technology as a process described in the introduction to manufacture of at least one partial oxidation and / or ammoxidation product of propylene to provide, which takes into account the aforementioned circumstances.

• a) in einem ersten Schritt Roh-Propan im Beisein und/oder unter Ausschluss von Sauerstoff einer homogenen und/oder heterogen katalysierten Dehydrierung und/oder Oxidehydrierung unterwirft, wobei ein Propan und Propylen enthaltendes Gasgemisch 1 erhalten wird, und
• b) aus im ersten Schritt gebildetem Gasgemisch 1, von den darin enthaltenen, von Propan und Propylen verschiedenen, Bestandteilen gegebenenfalls eine Teilmenge abtrennt und/oder in andere Verbindungen wandelt, wobei aus dem Gasgemisch 1 jeweils ein Propan und Propylen sowie auch von Sauerstoff, Propan und Propylen verschiedene Verbindungen enthaltendes Gasgemisch 1' erzeugt wird, und in wenigstens einem weiteren Schritt
• c) Gasgemisch 1 und/oder Gasgemisch 1' als Bestandteil eines Gasgemisches 2 einer heterogen katalysierten Gasphasen-Partialoxidation und/oder partiellen Gasphasen-Ammoxidation von im Gasgemisch 1 und/oder Gasgemisch 1' enthaltenem Propylen unterwirft,

gefunden,
das dadurch gekennzeichnet ist,
dass der Gesamtgehalt des Gasgemisches 2 an C₄-Kohlenwasserstoffen ≤ 3 Vol-% beträgt.Accordingly, a process for the preparation of at least one partial oxidation and / or ammoxidation product of propylene, in which

• a) subjecting crude propane in the presence and / or with the exclusion of oxygen to a homogeneous and / or heterogeneously catalyzed dehydrogenation and / or oxydehydrogenation, a gas mixture 1 containing propane and propylene being obtained, and
• b) from the gas mixture 1 formed in the first step, from the constituents contained therein, different from propane and propylene, if appropriate, a partial amount is separated off and / or converted into other compounds, in each case one propane and propylene and also of oxygen, propane from the gas mixture 1 and propylene-containing gas mixture 1 'is generated, and in at least one further step
• c) subjecting gas mixture 1 and / or gas mixture 1 'as part of a gas mixture 2 to heterogeneously catalyzed gas phase partial oxidation and / or partial gas phase ammoxidation of propylene contained in gas mixture 1 and / or gas mixture 1',

found,
which is characterized by
that the total content of the gas mixture 2 in C ₄ hydrocarbons is ≤ 3% by volume.

According to the invention, the total content of the gas mixture 2 in C ₄ hydrocarbons is preferably ≤ 2.5% by volume, better ≤ 2.0% by volume, even better ≤ 1.5% by volume, or ≤ 1.0% by volume. -%, or ≤ 0.50 vol .-% and very particularly preferably ≤ 0.30 vol .-%, or ≤ 0.10 vol .-%.

In the case of gas mixtures 2 which no longer contain any C ₄ hydrocarbons, their negative effect of course no longer occurs. In the context of an overall economic analysis, however, it may be justifiable to accept a certain reducing effect of the C ₄ hydrocarbons in gas mixture 2, and their total content in gas mixture 2 at values of ≥ 0.05% by volume, or ≥ 0.07 Vol .-%, or ≥ 0.09 vol .-%, or ≥ 0.1 vol .-% or in extreme cases ≥ 0.2 vol .-%.

According to the invention, at the same time as the aforementioned total contents of C ₄ hydrocarbons, the content of butene-1 in the gas mixture 2 is 1 1% by volume, or 0 0.9% by volume, or 0,7 0.75% by volume, or ≤ 0.6 vol.%, Or ≤0.5 vol.%, Or ≤ 0.4 vol.%, Particularly preferably ≤ 0.3 vol.%, Very particularly preferably ≤. 2 vol. % and even better ≤ 0.1% by volume or ≤ 0.05% by volume, or ≤ 0.03% by volume or ≤ 0.01% by volume. In the case of gas mixtures 2 which no longer contain any butene-1, its negative effect of course no longer appears at all. However, in the context of a general economic assessment, it may be justifiable to accept a certain reducing effect of butene-1 in gas mixture 2 and its content in gas mixture 2 at values of ≥ 0.001% by volume, or ≥ 0.003% by volume, or ≥ 0.006% by volume, or in extreme cases ≥ 0.009% by volume.

• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 3 Vol.-% und Gesamtgehalt an Butenen ≤ 1 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 2,5 Vol.-% und Gesamtgehalt an Butenen ≤ 1 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 2,0 Vol.-% und Gesamtgehalt an Butenen ≤ 1 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 1,5 Vol.-% und Gesamtgehalt an Butenen ≤ 1 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 1,0 Vol.-% und Gesamtgehalt an Butenen ≤ 0,75 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 1,0 Vol.-% und Gesamtgehalt an Butenen ≤ 0,50 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 0,5 Vol.-% und Gesamtgehalt an Butenen ≤ 0,30 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 0,3 Vol.-% und Gesamtgehalt an Butenen ≤ 0,1 Vol.-%; usw.

The aforementioned limit values apply simultaneously with the previously mentioned total contents of C ₄ hydrocarbons in the process according to the invention preferably not only for the amount of butene-1 contained in the gas mixture 2, but, independently of one another, also for any other possible representative within the butenes (ie, for trans-butene-2, for cis-butene-2 and for isobutene), and very particularly preferably at the same time also for the total amount of butenes in the gas mixture 2. That is, gas mixtures 2 suitable according to the invention are, for example, those for which applies:

• - total content of C ₄ hydrocarbons ≤ 3% by volume and total content of butenes ≤ 1% by volume; or
• - total content of C ₄ hydrocarbons ≤ 2.5% by volume and total content of butenes ≤ 1% by volume; or
• - total content of C ₄ hydrocarbons ≤ 2.0% by volume and total content of butenes ≤ 1% by volume; or
• - total content of C ₄ hydrocarbons ≤ 1.5% by volume and total content of butenes ≤ 1% by volume; or
• - total content of C ₄ hydrocarbons ≤ 1.0% by volume and total content of butenes ≤ 0.75% by volume; or
• - total content of C ₄ hydrocarbons ≤ 1.0% by volume and total content of butenes ≤ 0.50% by volume; or
• - total content of C ₄ hydrocarbons ≤ 0.5% by volume and total content of butenes ≤ 0.30% by volume; or
• - total content of C ₄ hydrocarbons ≤ 0.3% by volume and total content of butenes ≤ 0.1% by volume; etc.

To comply with the aforementioned limit values offers the inventive method essentially two ways of which either only one or both can be used.

On the one hand, it can be assumed that there is a crude propane which either no longer contains any C ₄ hydrocarbons, or which only contains C ₄ hydrocarbons in such quantities that the limits to be observed according to the invention for the total C ₄ hydrocarbons , Total butenes and butene-1 in the gas mixture 2 are met. Which content of which of the possible C ₄ hydrocarbons in the crude propane is still compatible with the process according to the invention depends, inter alia, on the specific boundary conditions used for the first step of the process and can be adapted by the person skilled in the art to these specific boundary conditions, can be determined in a few preliminary tests.

Any necessary removal of C ₄ hydrocarbons from commercially available crude propane can be carried out in a manner known per se, for example by rectification. Of course, all other separation processes such as adsorption / desorption (eg pressure swing adsorption), extraction and / or absorption / desorption can also be considered.

In addition and / or alternatively, the gas mixture 1 can be used in advance for its Wei ter-use as a gas mixture 1 'C ₄ -hydrocarbons in general and butene-1 or butenes in particular separated until the limits to be observed according to the invention are reached or undershot. This measure is appropriate, for example, if the disruptive C ₄ -hydrocarbons, for example from propane, are only formed in the course of the oxide dehydrogenation or dehydrogenation step, for example by disproportionation and / or metathesis. The probability of this is increased, inter alia, if for the first step of the method according to the invention (in the case of catalytic dehydrogenation) the partial gas cycle mode of operation of the DE-A 10211275 is applied. For example, the separation methods used in the DE-A 10131297 described combination of absorption and desorption or stripping (preferably as pressure absorption), pressure swing adsorption, rectificative and / or extractive methods can be used. In the case of stripping, it must be ensured that no C ₄ hydrocarbons are introduced via the stripping gas used.

If this (e.g. from the product gas mixture a catalytic dehydrogenation absorptively) in the absorbent Propane and propene contained in enriched form are stripped free of air, can be one of the process constellations according to the invention are present, in which the gas mixture generated by the free stripping 1 'with skillful Selection of the amount of stripping gas directly for the partial gas phase partial oxidation and / or the partial gas phase ammoxidation can be used and thus is identical to the gas mixture 2. Usually this one Case the content of other than propane, propene and oxygen Components in the gas mixture 1 '35 up to 55 vol .-%. In the case of the manufacture according to the invention of acrolein and / or acrylic acid such a procedure is preferred.

Of course, within the scope of the separations from C ₄ hydrocarbons mentioned, a separation of other constituents other than propane and propylene can also go hand in hand. Of course, partial amounts of propane and / or propylene can also be separated off.

Appropriately according to the invention, the separation processes mentioned will be aimed specifically at separating off the C ₄ -hydrocarbons in order to limit the total separation effort required and thus the reduction in economy.

That usually a gas mixture 1 'in the method according to the invention still at least ≥ 0.1% by volume, frequently ≥ 0.2% by volume, or ≥ 0.3 Vol .-% or ≥ 0.4 Vol .-%, or ≥ 0.5 Vol .-%, often ≥ 0.6 Vol .-%, or ≥ 0.8 Vol .-% or ≥ 1 Vol .-%, often ≥ 2 Vol .-%, or ≥ 3 Vol .-% or ≥ 5 Vol .-%, quite common ≥ 10 vol .-%, or ≥ 15 Vol .-% or ≥ 20 Vol .-%, or ≥ 25 Vol .-%, or ≥ 30 Vol .-%, or ≥ 35 Vol .-% of other than propane and propylene and oxygen Ingredients included.

As a rule, the proportion of Propane and propylene as well as oxygen various components in the gas mixture 1 'at method according to the invention however ≤ 80 Vol .-%, or ≤ 70 Vol .-%, or ≤ 60 vol .-%, or ≤ 50 Vol .-%, or ≤ 40 % By volume.

As already mentioned, it is advantageous according to the invention if the separations mentioned so far are carried out in such a way that the gas mixture 2 not only has the total contents of C ₄ -hydrocarbons which are suitable according to the invention but at the same time has a butene-1 content which is ≤ 1% by volume. %, or ≤ 0.9% by volume, etc.

That is, the objectives of the procedure according to the invention are achieved in particular if at least one limit according to the invention set for the total content of C ₄ hydrocarbons and at the same time one limit set for the butene-1 content in this document is met for the gas mixture 2.

• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 3 Vol-% und Gehalt an Buten-1 ≤ 1 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 2 Vol-% und Gehalt an Buten-1 ≤ 1 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 3 Vol-% und Gehalt an Buten-1 ≤ 0,5 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 2 Vol-% und Gehalt an Buten-1 ≤ 0,5 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 3 Vol-% und Gehalt an Buten-1 ≤ 0,75 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 2 Vol-% und Gehalt an Buten-1 ≤ 0,75 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 3 Vol-% und Gehalt an Buten-1 ≤ 0,4 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 2 Vol-% und Gehalt an Buten-1 ≤ 0,4 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 1 Vol-% und Gehalt an Buten-1 ≤ 0,4 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 3 Vol-% und Gehalt an Buten-1 ≤ 0,3 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 2 Vol-% und Gehalt an Buten-1 ≤ 0,3 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 1 Vol-% und Gehalt an Buten-1 ≤ 0,3 Vol.-%; usw..

In other words, gas mixtures 2 which are suitable according to the invention are, for example, those for which it is simultaneously fulfilled

• - total content of C ₄ hydrocarbons ≤ 3% by volume and content of butene-1 ≤ 1% by volume; or
• - total content of C ₄ hydrocarbons ≤ 2% by volume and content of butene-1 ≤ 1% by volume; or
• - total content of C ₄ hydrocarbons ≤ 3% by volume and butene-1 content ≤ 0.5% by volume; or
• - total content of C ₄ hydrocarbons ≤ 2% by volume and content of butene-1 ≤ 0.5% by volume; or
• - total content of C ₄ hydrocarbons ≤ 3% by volume and content of butene-1 ≤ 0.75% by volume; or
• - total content of C ₄ hydrocarbons ≤ 2% by volume and butene-1 content ≤ 0.75% by volume; or
• - total content of C ₄ hydrocarbons ≤ 3% by volume and content of butene-1 ≤ 0.4% by volume; or
• - total content of C ₄ hydrocarbons ≤ 2% by volume and content of butene-1 ≤ 0.4% by volume; or
• - total content of C ₄ hydrocarbons ≤ 1% by volume and content of butene-1 ≤ 0.4% by volume; or
• - total content of C ₄ hydrocarbons ≤ 3% by volume and content of butene-1 ≤ 0.3% by volume; or
• - total content of C ₄ hydrocarbons ≤ 2% by volume and content of butene-1 ≤ 0.3% by volume; or
• - total content of C ₄ hydrocarbons ≤ 1% by volume and butene-1 content ≤ 0.3% by volume; etc..

Are particularly favorable for the method according to the invention Gas mixtures 2, for which at the same time additionally at least one limit for the total salary set in this document of butenes in gas mixture 2 fulfilled is.

• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 3 Vol-% und Gesamtgehalt an Butenen ≤ 1 Vol.-% und Gehalt an Buten-1 ≤ 1 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 3 Vol-% und Gesamtgehalt an Butenen ≤ 1 Vol.-% und Gehalt an Buten-1 ≤ 0,75 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 3 Vol-% und Gesamtgehalt an Butenen ≤ 1 Vol.-% und Gehalt an Buten-1 ≤ 0,5 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 3 Vol-% und Gesamtgehalt an Butenen ≤ 1 Vol.-% und Gehalt an Buten-1 ≤ 0,3 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 3 Vol-% und Gesamtgehalt an Butenen ≤ 0,75 Vol.-% und Gehalt an Buten-1 ≤ 0,5 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 3 Vol-% und Gesamtgehalt an Butenen ≤ 0,5 Vol.-% und Gehalt an Buten-1 ≤ 0,5 Vol.-%; oder
• – Gesamtgehalt an C₄-Kohlenwasserstoffen ≤ 2 Vol-% und Gesamtgehalt an Butenen ≤ 0,5 Vol.-% und Gehalt an Buten-1 ≤ 0,5 Vol.-%; usw..

In other words, gas mixtures 2 which are suitable according to the invention are, in particular, those for which is simultaneously fulfilled

• - Total content of C ₄ hydrocarbons ≤ 3% by volume and total content of butenes ≤ 1% by volume and content of butene-1 ≤ 1% by volume; or
• - total content of C ₄ hydrocarbons ≤ 3% by volume and total content of butenes ≤ 1% by volume and content of butene-1 ≤ 0.75% by volume; or
• - total content of C ₄ hydrocarbons ≤ 3% by volume and total content of butenes ≤ 1% by volume and content of butene-1 ≤ 0.5% by volume; or
• - Total content of C ₄ hydrocarbons ≤ 3% by volume and total content of butenes ≤ 1% by volume and content of butene-1 ≤ 0.3% by volume; or
• - total content of C ₄ -hydrocarbons ≤ 3% by volume and total content of butenes ≤ 0.75% by volume and content of butene-1 ≤ 0.5% by volume; or
• - total content of C ₄ hydrocarbons ≤ 3% by volume and total content of butenes ≤ 0.5% by volume and content of butene-1 ≤ 0.5% by volume; or
• - total content of C ₄ hydrocarbons ≤ 2% by volume and total content of butenes ≤ 0.5% by volume and content of butene-1 ≤ 0.5% by volume; etc..

Processes in which not only the aforementioned combinations of total content of C ₄ hydrocarbons and total content of butenes and, if appropriate, butene-1 content in gas mixture 2 are fulfilled are particularly favorable, but at the same time a gas mixture 1 'is used which is at least still ≥ 0.1 vol%, or ≥ 0.2 vol%, or ≥ 0.3 vol%, or ≥ 0.4 vol%, or ≥ 0.5 vol%, or ≥ 0.6 vol%, or ≥ 0.8 vol%, or ≥ 1 vol%, or ≥ 2 vol%, or ≥ 3 vol%, or ≥ 5 vol% , or ≥ 10 vol .-%, or ≥ 15 vol .-%, or ≥ 20 vol .-%, or ≥ 25 vol .-%, or ≥ 30 vol .-%, (but mostly ≤ 80 vol .-% , or ≤ 70 vol .-%, or ≤ 60 vol .-%, or ≤ 50 vol .-%) of components other than propane and propylene and oxygen.

The studies performed in the context of this invention also revealed that it for the inventive method in the sense of avoiding unwanted full combustion Propylene for partial oxidation and / or amoxidation in general Cheap is when the propane content in the gas mixture 2 is a comparatively limited is. Preferred according to the invention is the propane content in the gas mixture 2 ≤ 60 vol .-%, or ≤ 50 Vol .-%. Very cheap are propane contents in the gas mixture 2 from 20 to 40% by volume, e.g. approximately 30 vol%.

If one disregards an ammonia content that may also be used for the production of nitrile (ie does not take it into account in the reference basis for the volume%), gas mixtures 2 which are suitable for the process according to the invention are generally those which on the one hand relate to the limits according to the invention their total C ₄ hydrocarbon content, preferably additionally 1-butene and particularly preferably additionally total butene, and on the other hand have the following contents:
7 to 15 vol% O ₂
5 to 10% by volume of propylene,
15 to 40 vol .-% propane, often 25 to 35 vol .-%,
25 to 60 vol .-% nitrogen, often 40 to 60 vol .-%,
1 to 5 vol .-% sum of CO, CO ₂ and H ₂ O and
0 to 5% by volume of other ingredients.

The above statement is particularly true then when the gas mixture 2 for a heterogeneously catalyzed partial oxidation of the gas mixture 2 contained propylene used for the production of acrolein and / or acrylic acid becomes.

Moreover, for all heterogeneously catalyzed partial oxidations and / or amoxidations of propylene encompassed by the process according to the invention, gas mixtures 2 are particularly suitable which, if an NH ₃ content which may be present are again not taken into account for nitrile formation (also in the reference basis) , are in the following composition grid:
H ₂ O ≤ 60 vol .-%, mostly ≤ 20 vol .-%, usually 0 to 5 vol .-%;
N ₂ ≤ 80 vol .-%, mostly ≤ 70 vol .-%, usually 40 to 60 vol .-%;
O ₂ up to 20 vol .-%, usually 2 to 20 vol .-%, usually 5 to 15 vol .-%;
CO ≤ 2 vol .-%, mostly ≤ 1 vol .-%, usually 0 to 0.5 vol .-%;
CO ₂ ≤ 5 vol .-%, mostly ≤ 3 vol .-%, usually 0 to 2 vol .-%;
Ethane ≤ 10 vol .-%, mostly ≤ 5 vol .-%, usually 0 to 2 vol .-%;
Ethylene ≤ 5 vol .-%, mostly ≤ 2 vol .-%, usually 0 to 0.5 vol .-%;
Methane ≤ 5 vol .-%, mostly ≤ 2 vol .-%, usually 0 to 0.2 vol .-%;
Propane> 0, ≤ 50 vol .-%, mostly 10 to 50 vol .-%, usually 20 to 40 vol .-%;
Cyclopropane ≤ 0.1 vol .-%, mostly ≤ 0.05 vol .-%, usually 0 to 150 vol.ppm;
Propane ≤ 0.1 vol .-%, mostly ≤ 0.05 vol .-%, usually 0 to 150 vol.ppm;
Propadiene ≤ 0.1 vol .-%, mostly ≤ 0.05 vol .-%, usually 0 to 150 vol.ppm;
Propylene> 0, ≤ 30% by volume, mostly ≥ 2, ≤ 20% by volume, usually 5 to 10% by volume;
H ₂ ≤ 30 vol .-%, mostly ≤ 20 vol .-%, usually 0 to 10 vol .-%;
isobutane ≤ 3% by volume, preferably ≤ 2% by volume, frequently 0.1 to 1% by volume;
n-butane ≤ 3% by volume, preferably ≤ 2% by volume, frequently 0.1 to 1% by volume;
trans-butene-2 ≤ 1% by volume, preferably ≤ 0.5% by volume, frequently ≥ 0.003% by volume, ≤ 0.1% by volume;
cis-butene-2 ≤ 1% by volume, preferably ≤ 0.5% by volume, frequently ≥ 0.003% by volume, ≤ 0.1% by volume;
Butene-1 ≤ 1% by volume, preferably ≤ 0.5% by volume, often ≥ 0.003% by volume, ≤ 0.1% by volume;
isobutene ≤ 1% by volume, preferably ≤ 0.5% by volume, frequently> 0.003% by volume, ≤ 0.1% by volume;
Butadiene 1.3 ≤ 1% by volume, preferably ≤ 0.5% by volume, frequently ≥ 0.003% by volume, ≤ 0.1% by volume;
Butadiene 1.2 ≤ 1% by volume, preferably ≤ 0.5% by volume, often> 0 to 0.1% by volume;
1-butyne ≤ 0.5% by volume, preferably ≤ 0.3% by volume, often 0 to 0.1% by volume; and
2-butyne ≤ 0.5% by volume, preferably ≤ 0.3% by volume, often 0 to 0.1% by volume.

Gas mixtures 2 which are suitable according to the invention are also those which not only meet the aforementioned specifications, but also the following specifications:
other unsaturated C ₄ hydrocarbons in total ≤ 0.5% by volume, preferably ≤ 0.3% by volume, often 0 to 0.1% by volume;
C ₅ hydrocarbons in total ≤ 0.1 vol .-%, mostly ≤ 0.05 vol .-%, usually 0 to 300 vol. Ppm;
C ₆ to C ₈ hydrocarbons in total ≤ 200 vol.ppm, mostly ≤ 150 vol.ppm, usually 0 to 30 vol.ppm;
Acetone ≤ 100 vol.ppm;
C ₁ to C ₄ alcohols ≤ 100 vol.ppm;
C ₂ to C ₄ aldehydes ≤ 100 vol.ppm;
Acetylene ≤ 10 vol.ppm;
Total compounds containing carbonyl groups (calculated as Ni (CO) ₄ ) ≤ 100 vol.ppm;
ionic chlorine ≤ 1 mg / kg, usually 0 to 0.2 mg / kg;
Total compounds containing Cl and expressed as Cl ≤ 1 mg / kg, usually 0 to 0.2 mg / kg;
Compounds containing F in total and expressed as F ≤ 1 mg / kg, usually 0 to 0.2 mg / kg; and
Compounds containing S in total and expressed as S ≤ 10 mg / kg, often 0 to 1 mg / kg, usually 0 to 0.1 mg / kg;
with the proviso that in all of the aforementioned cases the total content of all C ₄ hydrocarbons is ≤ 3% by volume (particularly preferably ≤ 2% by volume and very particularly preferably ≤ 1% by volume) and particularly preferably at the same time the total content of butenes ≤ 1% by volume (preferably ≤ 0.75% by volume and particularly preferably ≤ 0.5% by volume).

Unspecified connections (Components) are preferred in the gas mixtures 2 according to the invention not included, i.e. undetectable.

Such gas mixtures 2 are generally also obtainable in the context of the process according to the invention, in particular when using the separation processes mentioned for converting gas mixtures 1 into gas mixtures 1 'according to the invention, if crude propanes are used in the first step, the C ₄ hydrocarbons, eg up to 6% by volume (e.g. 0.1% by volume or 0.5% by volume to 6% by volume), especially if they meet the following specification:
Propane content ≥ 90% by volume, mostly ≥ 93% by volume, usually ≥ 95% by volume;
Content of propane and propylene ≤ 99.75 vol .-%, or ≤ 99.5 vol .-%, mostly ≤ 99 vol .-% or ≤ 98 vol .-%, usually ≤ 97 vol .-%;
Total content of C ₄ hydrocarbons ≤ 6% by volume, mostly ≤ 5% by volume, generally ≤ 4% by volume; but often ≥ 0.5% by volume, or ≥ 1% by volume, sometimes ≥ 2% by volume, or sometimes ≥ 3% by volume;
Butene-1 content ≤ 0.5% by volume, mostly ≤ 0.3% by volume, usually ≤ 0.1% by volume; often but ≥ 5 vol.ppm, sometimes ≥ 10 vol.ppm, or sometimes ≥ 20 vol.ppm;
Total butenes content ≤ 0.5% by volume, usually ≤ 0.3% by volume, usually ≤ 0.1% by volume; often however ≥ 10 vol.ppm, sometimes ≥ 20 vol.ppm, or partly ≥ 30 vol.ppm;
Ethane content ≤ 10% by volume, usually ≤ 5% by volume, usually 0 to 2% by volume;
Ethylene content ≤ 5% by volume, mostly ≤ 2% by volume, usually 0 to 0.5% by volume;
Methane content ≤ 5% by volume, mostly ≤ 2% by volume, usually 0 to 0.2% by volume;
Cyclopropane content ≤ 0.1% by volume;
Content of propylene ≤ 10% by volume, mostly ≤ 5% by volume, usually ≤ 2% by volume;
Total content of C ₃ hydrocarbons other than propane and propylene ≤ 0.3% by volume;
Total content of C ₅ hydrocarbons ≤ 0.3% by volume; and
Total content of C ₆ to C ₈ hydrocarbons ≤ 600 vol.ppm.

Raw propanes which are suitable according to the invention are also those which not only meet the abovementioned specifications, but also the following specifications:
Total content of oxygen-containing organic compounds ≤ 300 vol.ppm;
Acetylene content ≤ 30 vol.ppm;
Inogenous chlorine content ≤ 1 mg / kg;
Total content of Cl containing compounds and expressed as Cl ≤ 1 mg / kg;
Total content of compounds containing F and expressed as F ≤ 1 mg / kg;
Total content of S-containing compounds and expressed as S ≤ 10 mg / kg (in the case of catalytic dehydrogenations, it may be expedient if the reaction gas mixture, based on the propane contained therein, 1 to 1000 ppm by volume, preferably 1 to 100 ppm by volume, contains sulfur-containing compounds (e.g. H ₂ S and / or dimethyl sulfide), since on the one hand they passivate steel components (of the reactor) such as Ni, Cr and Fe (which reduces unwanted cracking of the propane) and on the other hand they can activate the catalysts used ( see "Catalytic dehydrogenation of lower alkanes, Resasco, Daniel E .; Haller, Gary L., University of Oklahoma, USA, Catalysis (1994), 11, 379-411");
with the proviso that the total content of C ₄ hydrocarbons is preferably ≤ 3% by volume, or ≤ 2.5% by volume, or ≤ 2% by volume and particularly preferably at the same time the total content of butenes is ≤ 0.1% by volume .-%.

The specifications defined under the stipulation of raw propane are suitable for the inventive method usually when the gas mixture 1 as such as a component of a gas mixture 2 of a heterogeneously catalyzed gas phase partial oxidation and / or a partial gas phase ammoxidation in the gas mixture 1 contained propylene is subjected. It has an advantageous effect from that in the first step of the method according to the invention a limited one Oxidehydrogenation and / or dehydrogenation conversion overall is favorable according to the invention. As a rule, this turnover lies with every single one included saturated Hydrocarbon, at values ≥ 5 mol%, but ≤ 30 mol%, often ≤ 25 mol% and often ≤ 20 mol%.

The crude propanes specified above and suitable for the process according to the invention normally contain at least 0.25% by volume, or at least 0.5% by volume, or at least 1% by volume, often at least 1.5% by volume. % or at least 2% by volume and often at least 2.5% by volume or at least 3% by volume of constituents other than propane and propylene (but <10% by volume, usually ≤ 7% by volume and in usually ≤ 5 vol .-% of these components). These foreign contents usually also apply to other crude propanes suitable for the process according to the invention, for example those which are free from C ₄ hydrocarbons. However, these can also contain up to 6% by volume of C ₄ hydrocarbons (for example 0.1 or 0.5% by volume to 6% by volume). In addition and at the same time, they can contain up to 0.5 vol.% Of butenes (for example 5 vol.ppm to 0.5 vol.%). Furthermore, they can also simultaneously contain up to 0.5% by volume of butene-1 (for example 5% by volume to 0.5% by volume).

Crude propanes which are particularly suitable according to the invention are also those which not only meet the abovementioned specifications but also the following specifications:
Ag ≤ 1 µg / kg;
Al ≤ 10 μg / kg;
As ≤ 1 μg / kg;
Au ≤ 1 μg / kg;
Ba ≤ 1 μg / kg;
Be ≤ 1 μg / kg;
Bi ≤ 1 μg / kg;
Ca ≤ 2 µg / kg;
Cd ≤ 1 µg / kg;
Co ≤ 1 µg / kg;
Cr ≤ 1 µg / kg;
Cu ≤ 1 μg / kg;
Fe ≤ 10 μg / kg;
Ga ≤ 1 µg / kg;
Ge ≤ 1 μg / kg;
Hg ≤ 1 µg / kg;
In ≤ 1 μg / kg;
Ir ≤ 1 μg / kg;
K ≤ 1 μg / kg;
Li ≤ 1 µg / kg;
Mg ≤ 1 µg / kg;
Mn ≤ 1 µg / kg;
Mo ≤ 1 μg / kg;
Na ≤ 1 µg / kg;
Nb ≤ 1 μg / kg;
Ni ≤ 1 µg / kg;
Pb ≤ 1 μg / kg;
Pd ≤ 1 µg / kg;
Pt ≤ 1 µg / kg;
Rh ≤ 1 µg / kg;
Sb ≤ 1 μg / kg;
Sn ≤ 1 µg / kg;
Sr ≤ 1 µg / kg;
Ta ≤ 1 μg / kg;
Ti ≤ 1 µg / kg;
Tl ≤ 1 μg / kg;
V ≤ 1 μg / kg;
Zn ≤ 1 µg / kg; and
Zr ≤ 1 μg / kg.

Crude propanes which are particularly suitable according to the invention are those which not only simultaneously meet the abovementioned specifications, but also the following specifications at the same time.
Mass density at 20 ° C = 500 ± 2.0 kg / m ³ ;
Vapor pressure at 20 ° C = 7.6 ± 0.2 bar;
Water ≤ 10 mg / kg;
Evaporation residue ≤ 2 mg / kg.

Obtain the specified specifications refer to determinations using gas chromatography and atomic absorption spectroscopy. The evaporation residue refers to gravi metric determination. It usually exists from high-boiling hydrocarbons (e.g. green oil).

Components not specified are preferred in the invention suitable raw propanes preferably not included, i.e. undetectable.

The is of particular importance Procedure according to the invention when it is applied in a circular mode.

In this case, the desired target product is separated from the product gas mixture of the gas phase partial oxidation and / or amoxidation by one of the known separation processes, and at least unreacted propane contained in this product gas mixture, as a rule together with unreacted propylene contained therein, is oxidized - And / or dehydrogenation step and / or recycled into the gas phase partial oxidation and / or amoxidation. This recycling (recirculation) of the propane and propylene usually takes place as part of the residual gas remaining after the target product has been separated off without the same being subjected to intermediate treatment, or if it is subjected to intermediate treatment (e.g. removal of CO, CO ₂ , H ₂ and / or O ₂ contained therein before repatriation), this intermediate treatment is only carried out with limited effort. That is, even if the raw propane used contains only small amounts of C ₄ hydrocarbons such as n-butane, isobutane, butene-1 or other butenes (e.g. total content of C ₄ hydrocarbons> 0.01 vol.% , possibly up to 6 vol.%), these can level up in the gas mixture 2 in the context of a cycle gas procedure and exceed the limit values according to the invention, unless special measures are taken. These measures can consist, for example, of the residual gas remaining after the target product being separated, the C ₄ hydrocarbons being rectificative and / or by absorption / desorption and / or stripping and / or by adsorption / desorption and / or by condensation and / or by membrane processes are separated and only then the remaining gas containing propane and propylene is circulated.

The EP-A 938463 such a separation step was not considered necessary, although it recommends using the gas mixture 1 as such for the partial oxidation and using crude propanes of essentially any purity for the first step.

As an alternative to a recycle gas procedure, the residual gases mentioned can also be used for other purposes in order to avoid undesirable levels of C ₄ hydrocarbons. For example, they can be burned together with the propane and propylene contained therein for the purposes of electricity generation and / or for the production of synthesis gas and the like. be used.

Otherwise, the method according to the invention like the various basic variants described in the prior art carried out become.

That is, in the simplest variant, all steps of the process according to the invention are carried out in a single reaction zone and on a catalyst feed located in the same, as described, for example, in the documents EP-A 608838 . EP-A 529853 . DE-A 19835247 . EP-A 895809 . JP-A 7-232071 . JP-A 11-169716 . EP-A 1192987 . JP-A 10-57813 . JP-A 2000-37623 . JP-A 10-36311 , WO 00/29105, EP-A 767164 . DE-A 10029338 . JP-A 8-57319 . JP-A 10-28862 . JP-A 11-43314 . JP-A 11-574719 , WO 00/29106, JP-A 10-330343 . JP-A 11-285637 . JP-A 310539 . JP-A 11-42434 . JP-A 11-343261 . JP-A 3423262 , WO 99/03825, JP-A 7-53448 . JP-A 2000-51693 . JP-A 11-263745 . DE-A 10046672 . DE-A 10118814 . DE-A 10119933 . JP-A 2000/143244 . EP-A 318295 . EP-A 603836 . DE-A 19832033 . DE-A 19836359 . EP-A 962253 . DE-A 10119933 . DE-A 10051419 . DE-A 10046672 . DE-A 10033121 . DE-A 101 459 58 . DE-A 10122027 . EP-A 1193240 and the literature cited in these writings is taught.

The active composition of the catalyst feed to be used is essentially multimetal oxide compositions which contain the elements Mo, V, at least one of the two elements Te and Sb, and at least one of the elements from the group comprising Nb, Ta, W, Ti, Al, Zr, Cr, Mn, Ga, Fe, Ru, Co, Rh, Ni, Pd, Pt, La, Bi, B, Ce, Sn, Zn, Si, Na, Li, K, Mg, Ag, Au and In included in combination.

The combination preferably contains the last element group the elements Nb, Ta, W and / or Ti and the element Nb is particularly preferred.

The relevant multimetal oxide active compositions preferably contain the aforementioned combination of elements in stoichiometry I. Mo ₁ V _b M ¹ _c M ² _d (I), With
M ¹ = Te and / or Sb,
M ² = at least one of the elements from the group include Nb, Ta, W, Ti, Al, Zr, Cr, Mn, Ga, Fe, Ru, Co, Rh, Ni, Pd, Pt, La, Bi, Ce, Sn , Zn, Si, Na, Li, K, Mg, Ag, Au and In,
b = 0.01 to 1,
c => 0 to 1, and
d => 0 to 1.

According to the invention, M ¹ = Te and M ² = Nb, Ta, W and / or Ti are preferred. M ² = Nb is preferred.

The stoichiometric coefficient b is with advantage 0.1 to 0.6. The corresponding amount is Preferred area for the stoichiometric Coefficients c from 0.01 to 1 or from 0.05 to 0.4 and favorable values for d 0.01 to 1 or 0.1 to 0.6.

According to the invention is particularly cheap it when the stoichiometric Coefficients b, c and d simultaneously in the aforementioned preferred ranges lie.

The above applies in particular then when the active mass of the catalyst feed with respect their elements other than oxygen from a foregoing Element combination exists.

These are then in particular the multimetal oxide active materials of general stoichiometry II Mo ₁ V _b M ^l _c M ² _d O _n (II), where the variables have the meaning given with respect to stoichiometry I and n = a number which is determined by the valency and frequency of the elements other than oxygen in (II).

Furthermore, the single-zone procedure for the inventive method preferably such multimetal oxide active materials are used, on the one hand either contain one of the aforementioned combinations of elements, or in terms of the elements other than oxygen, consisting of it and at the same time an X-ray diffractogram which shows diffraction reflexes h and i, their vertices at the diffraction angles (2⦵) 22.2 ± 0.5 ° (h) and 27.3 ± 0.5 ° (i) (all in this document related to an X-ray diffractogram Specifications relate to using Cu-Kα radiation as x-rays generated X-ray diffractogram (Siemens diffractometer Theta-Theta D-5000, tube voltage: 40 kV, tube current : 40mA, aperture diaphragm V20 (variable), anti-scatter diaphragm V20 (variable), Sekundärmonochromatorblende (0.1 mm), detector aperture (0.6 mm), measuring interval (2⦵): 0.02 °, measuring time each Step: 2.4s, detector: scintillation counter tube).

The half-width of these diffraction reflections can be very small or very pronounced.

Are particularly preferred for the method according to the invention those of the aforementioned multimetal oxide active materials, their X-ray diffractogram additionally has a diffraction reflex k for the diffraction reflexes h and i, the apex of which is 28.2 ± 0.5 ° (k).

Of the latter, each is preferred according to the invention, in which the diffraction reflex h is the most intense within the X-ray diffractogram, and has a half-value width of at most 0.5 °, and those in which the half-value width of the diffraction reflex i and the diffraction reflex k are very particularly preferred is simultaneously ≤ 1 ° and the intensity P _{k of} the diffraction reflex k and the intensity P _{i of} the diffraction reflex i have the relationship 0.2 ≤ R ≤ 0.85, better 0.3 ≤ R ≤ 0.85, preferably 0.4 ≤ R 0,8 0.85, particularly preferably 0.65 R R 0,8 0.85, even more preferably 0.67 R R 0,7 0.75 and very particularly preferably R = 0.70 to 0.75 or R = 0.72 fulfill in the R that by the formula R = P i / (P i + P k ) is defined intensity ratio. The aforementioned X-ray diffractograms preferably have no diffraction reflection, the maximum of which is 2⦵ = 50 ± 0.3 °.

In this document, the definition of the intensity of a diffraction reflex in the X-ray diffractogram relates to that in the DE-A 19835247 , the DE-A 10122027 , as well as in the DE-A 10051419 and DE-A 10046672 laid down definition. The same applies to the definition of the full width at half maximum.

In addition to the diffraction reflections h, i and k, the abovementioned X-ray diffractograms of multimetal oxide active materials which can be used advantageously according to the invention also contain further diffraction reflections whose apex points lie at the following diffraction angles (2 ():
9.0 ± 0.4 ° (l)
6.7 ± 0.4 ° (o) and
7.9 ± 0.4 ° (p).

Cheap it is also when the X-ray diffractogram additionally contains a diffraction reflex, whose apex is at the diffraction angle (2⦵) = 45.2 ± 0.4 ° (q).

Frequently contains the X-ray diffractogram also the reflections 29.2 ± 0.4 ° (m) and 35.4 ± 0.4 ° (n).

It is also advantageous if the element combinations defined in the formulas I and II are present as pure i-phase. If the catalytically active oxide mass also contains the k phase, its X-ray diffractogram contains, in addition to the above-mentioned, other diffraction reflections, the apex of which lies at the following diffraction angles (2 ⦵): 36.2 ± 0.4 ° (m) and 50 ± 0, 4 ° (the terms i- and k-phase are used in this document as in the DE-A 10122027 and DE-A 10119933 fixed used).

If the intensity 100 is assigned to the diffraction reflex h, it is advantageous according to the invention if the diffraction reflexes i, l, m, n, o, p, q have the following intensities in the same intensity scale: i: 5 to 95, often 5 to 80, sometimes 10 to 60; l: 1 to 30; m: 1 to 40; n: 1 to 40; O: 1 to 30; p: 1 to 30 and q: 5 to 60.

Contains the X-ray diffractogram of the aforementioned additional Diffraction reflections, the full width at half maximum is usually ≤ 1 °.

The specific surface area of multimetal oxide active compositions of the general formula II to be used according to the invention or of multimetal oxide active compositions which contain element combinations of the general formula I is in many cases 1 to 30 m ² / g (BET surface area, nitrogen), especially if their X-ray diffraction pattern is as described is.

The preparation of the multimetal oxide active compositions described can be found in connection with the prior art cited. These include in particular DE-A 10122027 , the DE-A 10119933 . DE-A 10033121 , the EP-A 1192987 , the DE-A 10029338 , the JP-A 2000-143244 , the EP-A 962253 , the EP-A 895809 , the DE-A 19835247 , WO 00/29105, WO 00/29106, the EP-A 529853 and the EP-A 608838 (Spray drying is to be used as the drying method in all of the execution examples of the latter two documents, e.g. with an inlet temperature of 300 to 350 ° C and an outlet temperature of 100 to 150 ° C; countercurrent or cocurrent).

The multimetal oxidative compositions described can be shaped as such (ie in powder form) or into suitable geometries (cf. for example the shell catalysts of the DE-A 10051419 as well as the geometric variants of the DE-A 10122027 ) are used for the single-zone design of the method according to the invention. They are particularly suitable for the production of acrolein and / or acrylic acid and for the production of acrylonitrile.

The basis for the single-zone mode of operation is that the catalysts to be used all steps of the process according to the invention are able to catalyze.

You can both in a fixed catalyst bed or be carried out in a fluidized bed or moving bed (moving bed). Corresponding process descriptions can be found in the writings the state of the art. If the method according to the invention is e.g. for the production of acrylic acid carried out in the single-zone mode as a fixed bed reaction the implementation in an expedient manner in a tube bundle reactor, whose catalyst tubes are loaded with the catalyst. To the contact tubes is usually a heat transfer medium Liquid, usually performed a molten salt. Alternatively, a Thermoplate reactor are used, the catalyst feed as a flat arrangement between cooling plates located.

The reaction gas mixture is viewed in the catalyst tubes via the reactor either in cocurrent or in countercurrent to the salt bath. The salt bath itself can perform a pure parallel flow relative to the contact tubes. Of course, this can also be superimposed on a cross flow. Overall, the salt bath around the catalyst tubes can also perform a meandering flow, which, viewed only via the reactor, is conducted in cocurrent or in countercurrent to the reaction gas mixture. Tube bundle reactors suitable for the process according to the invention, for example, disclose the documents EP-A 700714 and EP-A 700893 ,

The different possible Compositions of the reaction gas starting mixture for the single-zone variant of the method according to the invention can the status cited in connection with this process variant be taken from the technology.

For the production of acrylic acid, the composition of the reaction gas starting mixture typically ranges within the following framework (molar ratios):
Propane: Oxygen: H ₂ O: Other ingredients (especially inert diluent gases) = 1: (0.1–10): (> 0–50): (> 0-50).

The aforementioned ratio is preferably 1: (0.5-5) :( 1-30) :( 1-30).

The abovementioned ranges apply in particular when molecular nitrogen is predominantly used as the other constituents. The reaction temperature is typically 250 to 550 ° C (the conditions for ammoxidation are comparable, apart from the fact that the reaction gas mixture additionally comprises ammonia (cf. e.g. EP-A 929853 ).

The load on a fixed bed catalyst feed with propane in the single-zone variant of the method according to the invention e.g. 10 to 500 Nl / 1 (fixed bed) · h. The load with reaction gas starting mixture is often in the range from 100 to 10000 Nl / lh, often in the range 500 to 5000 Nl / l · h.

The target product, for example acrylic acid, can be obtained from the resulting product gas mixture in a manner known per se, for example in DE-A 10122027 described, be separated. In other words, the acrylic acid contained can be taken up from the product gas mixture, for example by absorption with a high-boiling inert hydrophobic organic solvent (for example a mixture of diphenyl ether and diphenyl, which may also contain additives such as dimethyl phthalate). The resulting mixture of absorbent and acrylic acid can then be worked up in a manner known per se by rectification, extraction and / or crystallization to give pure acrylic acid. Alternatively, the basic separation of acrylic acid from the product gas mixture can also be carried out by fractional condensation, as is the case, for example, in DE-A 10053086 . DE-A 19627847 . DE-A 19740253 . DE-A 19740252 . DE-A 19606877 and DE-A 19740253 is described. The resulting acrylic acid condensate can then be further purified, for example by fractional crystallization (for example suspension crystallization and / or layer crystallization).

That which remains with the basic separation of acrylic acid Contains residual gas mixture in particular unreacted propane and possibly unreacted Propylene.

Depending on the content of this residual gas mixture of butene-1, total butenes and total C ₄ hydrocarbons and the oxygen source used (whether pure oxygen, an oxygen-containing inert gas or air), the residual gas mixture can be recycled as such. If necessary, it will also be divided into two parts of identical composition and only recycle one part and purify the other part (e.g. its combustion or other use (e.g. supply synthesis gas)). The latter could of course also be done with the total amount of the residual gas mixture.

With increased proportions of the C ₄ components undesirable according to the invention and / or increased proportions of other undesirable components in the residual gas mixture, the propane and, if appropriate, propene contained in the residual gas mixture can be separated off, for example by fractional pressure rectification (the separation factor can be selected accordingly) and then returned to the process according to the invention and be combined with the crude propane and other constituents of the reaction gas starting mixture. From the point of view of the invention, however, it may be sufficient to bring the residual gas into contact with an hydrophobic organic solvent which preferably absorbs C ₃ hydrocarbons in an extraction device (for example by passing it through). Subsequent desorption and / or stripping with air (which would be required anyway as an oxygen source) can release the absorbed propane and, if appropriate, propene again and return it to the process according to the invention. Of course, the acrylic acid could also according to the DE-A 10059122 described procedure can be separated from the product mixture. The multimetal oxide active compositions recommended for the single-zone procedure can of course also be used in the process according to the invention in a form diluted with finely divided, for example colloidal, materials such as silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide and niobium oxide.

The dilution mass ratio can be up to 9 (thinner): 1 (active mass). Ie, possible dilution mass ratios are, for example, 6 (thinner): 1 (active mass) and 3 (thinner): 1 (active mass). The diluents can be incorporated according to the DE-A 10122027 take place before or after the calcination. Of course, other catalyst systems such as those used, for example, can also be used for the single-zone procedure according to the invention JP-A 3-170445 describes.

If the process according to the invention is implemented in a reaction zone, one of the cases exists in which the gas mixture 1 and the gas mixture 2 are identical. The method according to the invention is used in particular when the content limits for C ₄ hydrocarbons according to the invention are exceeded in the product gas mixture of the method according to the invention.

According to the invention, the process according to the invention is preferably carried out in more than one reaction zone, such as, for example, the EP-A 938463 , the EP-A 117146 , the DE-A 3313573 , the GB-A 2118939 , the US-A 3161670 , WO 01/96270, the EP-A 731077 , the DE-A 19837520 , the DE-A 19837517 , the DE-A 19837519 , the DE-A 19837518 , the DE-A 19837520 , the DE-A 10131297 and the DE-A 10211275 describe.

More than one reaction zone means primarily that at least one step of the method according to the invention is carried out under conditions which can be selected at least partially independently of those of the at least one other step within the method according to the invention NEN, or, however, only secondarily, that reaction conditions that are at least partially independent of one another are achieved within the same step along the directional path (the latter is the case, for example, when so-called multi-zone procedures (with temperature zones that can be set independently) are used for one step, like it for example DE-A 19948241 , the DE-A 19927624 , the DE-A 19910508 , the DE-A 19910506 and the DE-A 19948248 describe). That is, if the method according to the invention comprises, for example, two steps, a different catalyst or a different catalyst feed could be used for the first step than for the second step. Or one could proceed in such a way that when using identical catalysts or catalyst feeds for both steps, the reaction temperatures for the two steps can be selected and adjusted independently of one another. Of course, both can also be applied in superimposed form.

The advantage of multi-zone operation is because that they basically have an improved adaptation of the reaction conditions to the requirements of the individual steps of the method according to the invention enable.

This advantage is heterogeneous catalyzed gas phase partial oxidation of propylene to acrylic acid with molecular oxygen well known.

It runs along the reaction coordinate basically in two lengthways the reaction coordinate of successive steps, of which the first leads to acrolein and the second leads from acrolein to acrylic acid.

This reaction sequence opens in in a manner known per se the possibility the partial oxidation according to the invention of the propylene contained in the gas mixture 2 in two in a row arranged to perform oxidation zones, being in each of the two Oxidation zones of the oxidic catalyst to be used in optimizing Adapted way can be (this adjustment option also allows the partial oxidation of propylene at the level of acrolein to stop and isolate the acrolein). So for the first one Oxidation zone (propylene → acrolein) usually a catalyst based on the element combination Mo-Bi-Fe containing multimetal oxides preferred, while for the second Oxidation zone (acrolein → acrylic acid) normally Catalysts based on the multimetal oxides containing the element combination Mo-V are preferred (e.g. also those in this document for the single-zone mode of operation were recommended). In principle can but these two reaction steps in a single reaction zone and be carried out on a single catalyst.

In general, you will be in the inventive method in an expedient manner perform the first step in a separate reaction zone.

In the case of an oxydehydrogenation of the Propane can be used as a homogeneous and / or heterogeneously catalyzed oxide hydrogenation from propane to propylene with molecular oxygen, in the gas phase carried out become. Air, purer, can be used as the source of molecular oxygen molecular oxygen or enriched in molecular oxygen Air can be used.

If the reaction zone is designed as a homogeneous oxide dehydrogenation, this can in principle be carried out as described, for example, in the documents US-A 3,798,283 . CN-A 1 105 352 , Applied Catalysis, 70 (2) 1991, pp. 175-187, Catalysis Today 13, 1992, pp. 673-678 and in the application DE-A 19 622 331 is described. A suitable source of oxygen is air. The temperature of the homogeneous oxide dehydrogenation is expediently chosen to be in the range from 300 to 700 ° C., preferably in the range from 400 to 600 ° C., particularly preferably in the range from 400 to 500 ° C. The working pressure can be 0.5 to 100 bar, in particular 1 to 10 bar. The residence time is usually 0.1 or 0.5 to 20 seconds, preferably 0.1 or 0.5 to 5 seconds.

For example, a Tube furnace or a tube bundle reactor can be used, such as a counterflow tube furnace with flue gas as a heat transfer medium or a tube bundle reactor with molten salt as a heat transfer medium. The Propane to oxygen ratio in the starting mixture preferably 0.5: 1 to 40: 1, in particular between 1: 1 to 6: 1, stronger preferably between 2: 1 to 5: 1. The starting mixture can also contain other preferably inert (among inert constituents in this document in general, such constituents are preferably understood which are less than 5 mol% in the relevant reaction step, preferably less than 3 mol% and particularly preferably less convert as 1 mol%; they particularly preferred to sit down at all not around), components such as water, carbon dioxide, carbon monoxide, Nitrogen, noble gases, other hydrocarbons (e.g. in raw propane contain minor components), and / or propylene etc., which are also recycled (cycle gas) components can.

If the propane dehydrogenation is designed as a heterogeneously catalyzed oxide dehydrogenation, this can in principle be carried out as described, for example in the publications US-A 4 788 371 . CN-A 1073893 , Catalysis Letters 23 (1994), 103-106, W. Zhang, Gaodeng Xuexiao Huaxue Xuebao, 14 (1993) 566, Z. Huang, Shiyou Huagong, 21 (1992) 592, WO 97/36849, DE-A 197 53 817 . US-A 3 862 256 . US-A 3 887 631 . DE-A 195 30 454 . US-A 4,341,664 , J. of Catalysis 167, 560-569 (1997), J. of Catalysis 167, 550-559 (1997), Topics in Catalysis 3 (1996) 265-275, US-A 5 086 032 , Catalysis Letters 10 (1991), 181-192, Ind. Eng. Chem. Res. 1996, 35, 14-18, US-A 4,255,284 , Applied Catalysis A: General, 100 (1993), 111-130, J. of Catalysis 148, 56-67 (1994), V. Cortés Corberán and S. Vic Bellón (Ed.), New Developments in Selective Oxidation II, 1994, Elsevier Science BV, pp. 305-313, 3 ^rd World Congress on Oxidation Catalysis, RK Grasselli , ST Oyama, AM Gaffney and JE Lyons (Ed.), 1997, Elsevier Science BV, pp. 375ff or in DE-A 19837520 . DE-A 19837517 . DE-A 19837519 and DE-A 19837518 , Air can also be used as an oxygen source. Often, however, the oxygen source has at least 90 mol% of molecular oxygen, and often at least 95 mol% of oxygen.

The catalysts suitable for the heterogeneously catalyzed oxide hydrogenation are not subject to any particular restrictions. All oxydehydrogenation catalysts which are known to the person skilled in the art and are capable of oxidizing propane to propylene are suitable. In particular, all of the oxydehydrogenation catalysts mentioned in the abovementioned documents can be used. Suitable catalysts are, for example, oxydehydrogenation catalysts which comprise MoVNb oxides or vanadyl pyrophosphate, optionally with a promoter. An example of a cheap oxide dehydrogenation catalyst is a catalyst, as was also recommended for the single-zone procedure, which contains a mixed metal oxide with Mo, V, Te, O and X as essential constituents, where X is at least one element selected from niobium, tantalum, Tungsten, titanium, aluminum, zirconium, chrome, manganese, gallium, iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, antimony, bismuth, boron, indium, silicon, lanthanum, sodium, lithium, potassium, magnesium, silver, Gold and cerium (see also EP-A 938463 and EP-A 167109 ). Further particularly suitable oxide dehydrogenation catalysts are the multimetal oxide compositions or catalysts A or DE-A-197 53 817 and the catalysts of the DE-A 19838312 , the multimetal oxide compositions or catalysts A mentioned as preferred in the first-mentioned document being very particularly favorable. This means that, in particular, multimetal oxide compositions of the general formula III come as active compositions M ¹ _a Mo _{1 – b} M ² _b O _x (III), in which
M ¹ = Co, Ni, Mg, Zn, Mn and / or Cu,
M ₂ = W, V, Te, Nb, P, Cr, Fe, Sb, Ce, Sn and / or La,
a = 0.5-1.5
b = 0-0.5
such as
x = a number which is determined by the valency and frequency of the elements other than oxygen in (III),
into consideration.

In principle, suitable active materials can be used (III) can be produced in a simple manner by one of suitable sources of their elementary constituents as possible intimate, preferably finely divided, composed according to their stoichiometry, Generated dry mixture and this calcined at temperatures from 450 to 1000 ° C. As sources for the elementary constituents of the multimetal oxide active materials (III) such connections come into consideration which are already are oxides and / or those compounds which are produced by heating, at least in the presence of oxygen, can be converted into oxides. All of these are halides, nitrates, formates, Oxalates, citrates, acetates, carbonates, amine complex salts, ammonium salts and / or hydroxides. The intimate mixing of the starting compounds for the production of the multimetal oxide masses (III) can be in dry Form, for example as a fine powder or in wet form, for example with water as a solvent, respectively. The multimetal oxide materials (III) can be in powder form as well can also be shaped into certain catalyst geometries, used, the shaping taking place before or after the final calcination can. It can Full catalysts are used. The shaping of a powdery active material or precursor mass but can also be carried out by application to preformed inert catalyst supports. As carrier materials usual, porous or non-porous Aluminum oxides, silicon dioxide, thorium dioxide, zirconium dioxide, silicon carbide or silicates are used, the carrier bodies being shaped regularly or irregularly could be.

For the heterogeneously catalyzed oxydehydrogenation of propane, the reaction temperature is preferably in the range from 200 to 600 ° C., in particular in the range from 250 to 500 ° C., more preferably in the range from 350 to 440 ° C. The working pressure is preferably in the range from 0.5 to 10 bar, in particular from 1 to 10 bar, more preferably from 1 to 5 bar. Working pressures above 1 bar, for example from 1.5 to 10 bar, have proven to be particularly advantageous. As a rule, the heterogeneously catalyzed oxydehydrogenation of the propane takes place on a fixed catalyst bed. The latter is expediently heaped up in the tubes of a shell-and-tube reactor, as is the case, for example, in EP-A-0 700 893 and in the EP-A-0 700 714 as well as the literature cited in these publications. The average residence time of the reaction gas mixture in the catalyst bed is advantageously 0.5 to 20 seconds. The ratio of propane to oxygen varies appropriately with the desired conversion and the selectivity of the catalyst it is in the range of 0.5: 1 to 40: 1, especially 1: 1 to 6: 1, more preferably 2: 1 to 5: 1. As a rule, the propylene selectivity decreases with increasing propane conversion. The propane to propylene reaction is therefore preferably carried out in such a way that relatively low conversions with propane are achieved with high selectivities to propylene. The conversion of propane is particularly preferably in the range from 5 to 40 mol%, frequently in the range from 10 to 30 mol%. Here, the term "propane conversion" means the proportion of propane supplied (sum of propane contained in the crude propane and possibly recycled cycle gas which is converted in a single pass). Typically, the selectivity of propylene formation is 50 to 98 mol%, more preferably 80 to 98 mol%, the term "selectivity" referring to the moles of propylene that are generated per mole of propane converted, expressed as a molar percentage.

This usually includes in oxidative propane dehydrogenation Starting mixture used 5 to 95 mol% propane (based on 100 mol% starting mixture). In addition to propane and oxygen, the starting mixture for the heterogeneously catalyzed oxydehydrogenation, in particular inert components such as carbon dioxide, carbon monoxide, nitrogen, Noble gases, other hydrocarbons, e.g. contained in the raw propane Incidental ingredients, and / or propylene include. The heterogeneous oxide hydrogenation can also be in the presence of diluents, such as Water vapor become.

Any reactor sequence can to carry out homogeneous oxide hydrogenation or heterogeneously catalyzed oxide hydrogenation of propane can be used, which is known to those skilled in the art. For example Oxydehydrogenation can be carried out in a single reactor or in one Cascade of two or more reactors, between which if necessary Oxygen introduced is carried out become. There is also the possibility the homogeneous and the heterogeneously catalyzed oxide hydrogenation with one another combined to practice.

This can be a possible component Product mixture of a propane oxydehydrogenation according to the Examples include the following components: propylene, propane, carbon dioxide, Carbon monoxide, water, nitrogen, oxygen, ethane, ethene, methane, Acrolein, acrylic acid, Ethylene oxide, butane (e.g. n-butane or isobutane), acetic acid, formaldehyde, formic acid, propylene oxide and butenes (e.g. butene-1). Typically, a contains the propane oxydehydrogenation according to the invention Product mixture obtained: 5 to 10 mol% of propylene, 0.1 to 2 mol% Carbon monoxide, 1 to 3 mol% carbon dioxide, 4 to 10 mol% water, 0 to 1 mol% nitrogen, 0.1 to 0.5 mol% acrolein, 0 to 1 mol% Acrylic acid, 0.05 to 0.2 mol% of acetic acid, 0.01 to 0.05 mol% formaldehyde, 1 to 5 mol% oxygen, 0.1 to 1.0 mol% of other components mentioned above, and essentially the remainder Propane, each based on 100 mol% product mixture.

In general, the propane dehydrogenation in the first reaction zone can also be used as a heterogeneously catalyzed propane dehydrogenation with extensive exclusion of oxygen as in the DE-A 3313573 , in WO 01/96270, the DE-A 10131297 or the DE-A 10211275 described or carried out as follows.

Since the heterogeneously catalyzed dehydrogenation reaction takes place with an increase in volume, the conversion can be increased by lowering the partial pressure of the products. This can be achieved in a simple manner, for example by dehydrogenation under reduced pressure and / or by admixing essentially inert diluent gases, such as water vapor, which is normally an inert gas for the dehydrogenation reaction. A further advantage of dilution with water vapor is generally reduced coking of the catalyst used, since the water vapor reacts with coke formed according to the principle of coal gasification. In addition, water vapor can also be used as the dilution gas in the subsequent at least one oxidation and / or ammoxidation zone (in this document also referred to as a short name at least one partial zone). However, steam can also be partially or completely separated from the dehydrogenation product mixture in a simple manner (for example by condensation), which opens up the possibility of increasing the proportion of the diluent gas N ₂ in the at least one partial zone when the modified product mixture obtainable in this way is used further , Further diluents suitable for heterogeneously catalyzed propane dehydrogenation are, for example, CO, methane, ethane, CO ₂ , nitrogen and noble gases such as He, Ne and Ar. All of the diluents mentioned can be used either individually or in the form of a wide variety of mixtures. It is advantageous that the diluents mentioned are generally also suitable diluents in the at least one partial zone. In general, as already stated, diluents which behave inertly (that is to say less than 5 mol%, preferably less than 3 mol% and even better less than 1 mol%) in the respective reaction zone are preferred. In principle, all dehydrogenation catalysts known in the prior art are suitable for the heterogeneously catalyzed propane dehydrogenation. They can be roughly divided into two groups. Namely in those which are oxidic in nature (for example chromium oxide and / or aluminum oxide) and in those which consist of at least one, generally comparatively noble, metal (for example platinum) deposited on a generally oxidic carrier.

Among other things, all dehydrogenation catalysts described in WO 01/96270, the EP-A 731077 , the DE-A 10211275 , the DE-A 10131297 , WO 99/46039, the US-A 4 788 371 , the EP-A-0 705 136 , WO 99/29420, the US-A 4,220,091 , the US-A 5 430 220 , the US-A 5 877 369 , the EP-A-0 117 146 , the DE-A 199 37 196 , the DE-A 199 37 105 as well as the DE-A 199 37 107 be recommended. In the be can both the catalyst according to Example 1, Example 2, Example 3, and Example 4 of the DE-A 199 37 107 be used.

These are dehydrogenation catalysts, the 10 to 99.9% by weight of zirconium dioxide, 0 to 60% by weight of aluminum oxide, Silicon dioxide and / or titanium dioxide and 0.1 to 10 wt .-% at least an element of the first or second main group, an element the third subgroup, an element of the eighth subgroup of the Periodic table of the elements containing lanthanum and / or tin with the proviso that the sum of the weight percent is 100% by weight.

To carry out the heterogeneously catalyzed In principle, propane dehydrogenation all come in the prior art known reactor types and process variants into consideration. descriptions such process variants include, for example, all of the Dehydrogenation catalysts cited prior art documents.

A comparatively comprehensive description of dehydrogenation processes suitable according to the invention also contains "Catalytica® ^® Studies Division, Oxidative Dehydrogenation and Alternative Dehydrogenation Processes, Study Number 4192 OD, 1993, 430 Ferguson Drive, Mountain View, California, 94043-5272 USA.

Characteristic of the partial Heterogeneously catalyzed dehydrogenation of propane is endothermic runs. This means, the for the setting of the required reaction temperature required heat (energy) must either the reaction gas starting mixture beforehand and / or in the course of the heterogeneous catalyzed dehydrogenation fed become.

It is also particularly heterogeneous catalyzed dehydrogenation of propane due to the high reaction temperatures required typical that in small quantities high-boiling high molecular weight organic Compounds, right down to carbon, are formed that are on the catalyst surface separate and thereby deactivate it. To this disadvantageous Minimizing side effects can lead to heterogeneously catalyzed Dehydration with increased Temperature above the catalyst surface Propane-containing reaction gas to be mixed with water vapor. Precipitated carbon becomes under the given conditions partially or completely eliminated according to the principle of coal gasification.

Another way, deposited carbon compounds to eliminate is to remove the dehydrogenation catalyst from time at the time of increased To flow through temperature with an oxygen-containing gas and to burn off the deposited carbon. An extensive one suppression The formation of carbon deposits is also possible because one catalyzes the heterogeneous propane to be dehydrogenated before it with increased Temperature above the dehydrogenation catalyst is passed, molecular hydrogen.

Of course there is also the possibility the heterogeneously catalyzed to dehydrogenated propane steam and add molecular hydrogen in a mixture. An addition of molecular Hydrogen for the heterogeneously catalyzed dehydrogenation of propane also reduces the unwanted Formation of all (propadiene), propyne and acetylene as by-products.

A suitable reactor form for the heterogeneous Catalyzed propane dehydrogenation is the fixed-bed tube or Tube reactor. This means, the dehydrogenation catalyst is in or in a bundle of Reaction tubes as a fixed bed. The reaction tubes are thereby heated that in the space surrounding the reaction tubes a gas to Example a hydrocarbon like methane is burned. Is cheap it, this direct form of contact tube heating only at first about 20 to 30% of the fixed bed apply and the remaining bed length by the under the Radiation released radiant heat to the required reaction temperature warm. In this way there is an approximation isothermal reaction control reachable. Suitable inner tube diameters are about 10 up to 15 cm. A typical dehydrogenation tube bundle reactor comprises 300 to 1000 reaction tubes. The temperature inside the reaction tube moves range from 300 to 700 ° C, preferably in the range from 400 to 700 ° C. The reaction gas starting mixture is advantageous fed to the tubular reactor preheated to the reaction temperature. It is possible, that the product gas mixture the reaction tube with a 50 to 100 ° C lower Temperature leaves. This The initial temperature can also be higher or at the same level. In the context of the above procedure, the use of oxidic dehydrogenation catalysts based on chromium and / or aluminum oxide appropriate. Frequently no diluent gas use, but from essentially the only raw propane go out as the starting reaction gas. The dehydrogenation catalyst too is usually undiluted applied.

On an industrial scale, you can do several (e.g. three) of such tube bundle reactors operate in parallel. You can if necessary according to the invention two of these reactors are in dehydration mode while in a catalyst is regenerated in a third reactor, without the operation in the at least one partial zone suffering.

Such a procedure is useful, for example, in the BASF-Linde propane dehydrogenation process known in the literature. According to the invention, however, it is important that the use of egg Such a tube bundle reactor is sufficient.

Such a procedure can also be used in the so-called "steam active reforming (STAR) process", which was developed by Phillips Petroleum Co. (cf. for example US-A 4,902,849 . US-A 4,996,387 and US-A 5 389 342 ). Platinum on zinc (magnesium) spinel containing promoters is advantageously used as the dehydrogenation catalyst in the STAR process (see for example US-A 5 073 662 ). In contrast to the BASF-Linde propane dehydrogenation process, the propane to be dehydrated is diluted with water vapor in the STAR process. A molar ratio of water vapor to propane in the range from 4 to 6 is typical. The reactor outlet pressure is frequently 3 to 8 atm and the reaction temperature is expediently chosen to be 480 to 620 ° C. Typical catalyst loads with the total reaction gas mixture are 0.5 to 10 h ^-1 (LHSV).

The heterogeneously catalyzed propane dehydrogenation can also be designed in a walking bed. For example, that Catalyst moving bed housed in a radial flow reactor his. In the same, the catalyst slowly moves upwards down while the reaction gas mixture flows radially. This procedure will used for example in the so-called UOP-Oleflex dehydrogenation process. Since the reactors are operated practically adiabatically in this process, it is appropriate to have several To operate reactors connected in series as a cascade (in typically up to four). This allows differences that are too high the temperatures of the reaction gas mixture at the reactor inlet and Avoid at the reactor outlet (works in adiabatic mode the reaction gas starting mixture as a heat transfer medium, from its heat content the drop in reaction temperature is dependent) and still appealing total sales achieve.

When the catalyst bed has left the moving bed reactor, it is fed to the regeneration and then reused. A spherical dehydrogenation catalyst which essentially consists of platinum on a spherical alumina support can be used as the dehydrogenation catalyst for this process. In the UOP variant, hydrogen is added to the propane to be dehydrogenated in order to avoid premature catalyst aging. The working pressure is typically 2 to 5 atm. The hydrogen to propane ratio (the molar) is expediently 0.1 to 1. The reaction temperatures are preferably 550 to 650 ° C. and the contact time of the catalyst with the reaction gas mixture is selected to be about 2 to 6 h ⁻¹ .

In the fixed bed process described The catalyst geometry can also be spherical, but also cylindrical (hollow or full) or otherwise geometrically designed.

As a further process variant for the heterogeneous catalyzed propane dehydrogenation is described by Proceedings De Witt, Petrochem. Review, Houston, Texas, 1992 a, N1 the possibility a heterogeneously catalyzed propane dehydrogenation in a fluidized bed, where the propane is not diluted becomes.

According to the invention, e.g. two fluid beds operated side by side, one of which is without negative Effects on the overall process temporarily in the state of regeneration can be located. Chromium oxide on aluminum oxide is used as the active substance for use. The working pressure is typically 1 to 2 atm and the dehydration temperature is usually 550 to 600 ° C. The one for dehydration required heat is introduced into the reaction system in that the dehydrogenation catalyst the reaction temperature is preheated. The above dehydration mode is also known in the literature as the Snamprogetti-Yarsintez process.

Alternatively to those described above Procedures can be heterogeneously catalyzed propane dehydrogenation with extensive exclusion of oxygen even after one from ABB Lummus Crest developed procedures can be realized (see Proceedings De Witt, Petrochem. Review, Houston, Texas, 1992, P1).

The heterogeneous described so far catalyzed dehydrogenation of propane under extensive Is oxygen exclusion common that they have in propane sales from ≥ 30 mol% (usually ≤ 60 mol%) are operated (based on a single reaction zone passage). An advantage according to the invention it is sufficient to have a propane conversion of ≥ 5 mol% to ≤ 30 mol% or ≤ 25 mol%. This means, the heterogeneously catalyzed propane dehydrogenation can also be used for propane conversions of 10 to 20 mol% operated (the sales refer to one-off Reaction zone pass). This is moving among other things, that the remaining amount of unconverted Propane in the subsequent at least one partial zone essentially as an inert diluent gas acts and later largely lossless in the dehydrogenation zone and / or in the least a partial zone can be returned can.

For the realization of the aforementioned propane conversions, it is favorable to carry out the heterogeneously catalyzed propane dehydrogenation at a working pressure of 0.3 to 3 atm. It is also advantageous to dilute the propane to be dehydrogenated heterogeneously catalytically with water vapor. On the one hand, the heat capacity of the water makes it possible to compensate for part of the effect of the endothermic energy of the dehydrogenation, and on the other hand, dilution with water vapor reduces the educt and product partial pressure, which has a favorable effect on the equilibrium position of the dehydrogenation. Furthermore, the use of water vapor, as already mentioned, has an advantageous effect on the service life of dehydrogenation catalysts containing noble metal. If necessary Molecular hydrogen can also be added as a further component. The molar ratio of molecular hydrogen to propane is generally 5. 5. The molar ratio of water vapor to propane can accordingly be 0 0 to 30 with a comparatively low propane conversion, advantageously 0.1 to 2 and advantageously 0.5 to 1. It has also proven to be favorable for a procedure with a low propane conversion that only a comparatively low amount of heat is consumed when the reaction gas is passed once and that comparatively low reaction temperatures are sufficient to achieve conversion with a single pass of the reactor.

It can therefore be useful propane dehydrogenation with comparatively low propane conversion (quasi) adiabatic. This means, the reaction gas starting mixture is generally initially based on a temperature of 500 to 700 ° C (or from 550 to 650 ° C) heat (for example by directly firing the surrounding area Wall). Normally there will be a single adiabatic passage through a catalyst bed may be sufficient to achieve the desired To achieve sales, the reaction gas mixture by about 30 ° C to 200 ° C (depending on Conversion and dilution) cooling down becomes. A presence of water vapor as a heat carrier is also evident under the The aspect of an adiabatic driving style is noticeably noticeable. The lower reaction temperature allows longer service life of the used Catalyst bed.

In principle, the heterogeneously catalyzed Propane dehydration with comparatively low propane conversion, whether adiabatic or isothermal, both in a fixed bed reactor as well as in a moving bed or fluidized bed reactor.

It is noteworthy in the method according to the invention for their implementation, especially in adiabatic operation single shaft furnace reactor as a fixed bed reactor sufficient is flowed through axially and / or radially by the reaction gas mixture.

In the simplest case it is doing so by a single closed reaction volume, for example a container, whose inner diameter 0.1 to 10 m, possibly also 0.5 to 5 m is and in which the fixed catalyst bed on a support device (for example a grating) is applied. The one with a catalyst charged reaction volume that insulates in adiabatic operation is with the hot, Propane-containing, reaction gas flows axially. The catalyst geometry can be both spherical as well as circular or strand-like his. Because in this case the reaction volume is very economical Apparatus that can be realized are all catalyst geometries that have a particularly low pressure drop, to be preferred. These are primarily catalyst geometries that result in a large void volume to lead or have a structured structure, such as monoliths or Honeycombs. To realize a radial flow of the propane containing The reactor can, for example, contain two reaction gases in a jacket, there are concentric cylindrical grids and the catalyst bed be arranged in the annular gap. In the adiabatic case, the metal shell might be again thermally insulated.

As a catalyst feed for a heterogeneously catalyzed propane dehydrogenation with a comparatively low propane conversion in a single pass are particularly suitable in the DE-A 199 37 107 disclosed, especially all exemplified disclosed catalysts.

After a longer period of operation, the aforementioned catalysts can be regenerated in a simple manner, for example, by first diluting air with nitrogen and / or water vapor (preferably) at an inlet temperature of 300 to 600 ° C, often at 400 to 550 ° C the catalyst bed conducts. The catalyst load with regeneration gas can be, for example, from 50 to 10,000 h ⁻¹ and the oxygen content of the regeneration gas can be 0.5 to 20% by volume.

In subsequent further regeneration stages, air can be used as the regeneration gas under otherwise identical regeneration conditions. Appropriately from an application point of view, it is advisable to purge the catalyst with inert gas (for example N ₂ ) before it is regenerated.

Afterwards it is usually recommended still with pure molecular hydrogen or with inert gas (preferably water vapor) diluted molecular hydrogen (the hydrogen content should be ≥ 1 vol .-% to regenerate) in the otherwise identical condition grid.

The heterogeneously catalyzed propane dehydrogenation with comparatively low propane conversion (≤ 30 mol%) can in all cases be operated under the same catalyst loads (both for the reaction gas as a whole and for the propane contained in it) as the variants with high propane conversion (> 30 mol -%). This exposure to reaction gas can be, for example, 100 to 10,000 h ^-1 , frequently 300 to 5000 h ^-1 , that is to say in many cases approximately 500 to 3000 h ^-1 .

In a particularly elegant way the heterogeneously catalyzed propane dehydrogenation with comparative Realize low propane conversion in a tray reactor.

This contains more spatially in succession as a catalyst bed catalyzing the dehydrogenation. The number of catalyst beds can 1 to 20, suitably 2 to 8, but also 3 to 6. The catalyst beds are preferred arranged radially or axially one behind the other. application point becomes appropriate used in such a tray reactor of the fixed catalyst bed type.

In the simplest case, the fixed catalyst beds are in a shaft furnace reactor axially or in the annular gaps from centric arranged in cylindrical grids. It is however also possible the annular gaps one above the other in segments arrange and the gas after radial passage in a segment in the next about that- or lead segment below.

The reaction gas mixture is expediently on its way from one catalyst bed to the next catalyst bed, to Example by transfer with hot Gases or heated heat exchangers by passing through with hot Fuel gases heated pipes, in the tray reactor of an intermediate heating subjected.

If the tray reactor is operated adiabatically, it is necessary for the desired propane conversions (≤ 30 mol%), especially when using the DE-A 199 37 107 described catalysts, in particular of the exemplary embodiments, sufficient to preheat the reaction gas mixture to a temperature of 450 to 550 ° C. in the dehydrogenation reactor and to keep it within this temperature range within the tray reactor. This means that the entire propane dehydrogenation can be carried out at extremely low temperatures, which has proven particularly favorable for the service life of the fixed catalyst beds between two regenerations.

It is even more clever to carry out the intermediate heating described above in a direct way (autothermal driving style). To this end, molecular oxygen is added to the reaction gas mixture either already before flowing through the first catalyst bed and / or between the subsequent catalyst beds to a limited extent. Depending on the dehydrogenation catalyst used, a limited combustion of the hydrocarbons contained in the reaction gas mixture, possibly carbon or coal-like compounds already deposited on the catalyst surface and / or of hydrogen formed in the course of the heterogeneously catalyzed propane dehydrogenation and / or added to the reaction gas mixture is brought about (it can also be useful in terms of application technology) be to insert in the tray reactor catalyst beds which are charged with a catalyst which specifically (selectively) catalyzes the combustion of hydrogen (and / or hydrocarbon) (such catalysts come, for example, from the documents US-A 4 788 371 . US-A 4 886 928 . US-A 5 430 209 . US-A 5 530 171 . US-A 5 527 979 and US-A 5 563 314 into consideration; for example, such catalyst beds can be accommodated in the tray reactor in an alternating manner to the beds containing dehydrogenation catalyst). The heat of reaction released thereby enables, in a quasi-autothermal manner, an almost isothermal mode of operation of the heterogeneously catalyzed propane dehydrogenation. With increasing selected residence time of the reaction gas in the catalyst bed, propane dehydrogenation is possible with decreasing or essentially constant temperature, which enables particularly long standing times between two regenerations.

As a rule, an oxygen feed as described above should be carried out so that the oxygen content of the reaction gas mixture, based on the amount of propane and propylene contained therein, is 0.5 to 30% by volume. Both pure molecular oxygen or with inert gas, for example CO, CO ₂ , N ₂ , noble gases, diluted oxygen, but in particular also air, can be considered as the oxygen source. The resulting combustion gases usually have an additional dilution effect and thus promote heterogeneously catalyzed propane dehydrogenation.

The isothermal of the heterogeneously catalyzed Propane dehydrogenation can further improve that in the tray reactor in the spaces between closed the catalyst beds, but advantageously not necessarily before their filling evacuated, internals (for example tubular), attaches. such Built-in can can also be placed in the respective catalyst bed. These internals contain suitable solids or liquids above one evaporate or melt at a certain temperature while consuming heat and condense again where this temperature falls below and warmth release.

One way of heating the reaction gas starting mixture for the heterogeneously catalyzed propane dehydrogenation to the required reaction temperature is also to burn part of the propane and / or H ₂ contained therein by means of molecular oxygen (for example on suitable specific-action combustion catalysts, for example by simple means Transfer and / or pass through) and by means of the heat of combustion thus released to bring about the heating to the desired reaction temperature. The resulting combustion products, such as CO ₂ , H ₂ O and the N ₂ which may accompany the molecular oxygen required for the combustion, advantageously form inert diluent gases.

• – einer Reaktionszone ein das zu dehydrierende Propan enthaltendes Reaktionsgas kontinuierlich zugeführt wird,
• – das Reaktionsgas in der Reaktionszone über wenigstens ein Katalysatorfestbett geführt wird, an welchem durch katalytische Dehydrierung molekularer Wasserstoff und wenigstens partiell Propylen gebildet werden,
• – dem Reaktionsgas vor und/oder nach Eintritt in die Reaktionszone wenigstens ein molekularen Sauerstoff enthaltendes Gas zugesetzt wird,
• – der molekulare Sauerstoff in der Reaktionszone im Reaktionsgas enthaltenen molekularen Wasserstoff teilweise zu Wasserdampf oxidiert und
• – der Reaktionszone ein Produktgas entnommen wird, das molekularen Wasserstoff, Wasserdampf, Propylen und Propan enthält,

das dadurch gekennzeichnet ist, daß das der Reaktionszone entnommene Produktgas in zwei Teilmengen identischer Zusammensetzung aufgeteilt und eine der beiden Teilmengen als Kreisgas in die Dehydrierreaktionszone zurückgeführt und die andere Teilmenge erfindungsgemäß als Gasgemisch 1 weiterverwendet wird.The aforementioned hydrogen combustion can be particularly elegant as in the DE-A 10211275 realize described. That is, in a process of continuous heterogeneously catalyzed partial dehydrogenation of propane in the gas phase, in which

• A reaction gas containing the reaction gas to be dehydrogenated is fed continuously,
• The reaction gas is passed in the reaction zone over at least one fixed catalyst bed, on which molecular hydrogen and at least partially propylene are formed by catalytic dehydrogenation,
• At least one gas containing molecular oxygen is added to the reaction gas before and / or after entering the reaction zone,
• - The molecular oxygen in the reaction gas contained in the reaction gas partially oxidized to water vapor and
• A product gas which contains molecular hydrogen, water vapor, propylene and propane is withdrawn from the reaction zone,

which is characterized in that the product gas withdrawn from the reaction zone is divided into two portions of identical composition and one of the two portions is recycled as circulating gas into the dehydrogenation reaction zone and the other portion is used according to the invention as gas mixture 1.

This process variant is to be preferred in particular if, in addition to crude propane, the propane and optionally propylene-containing cycle gas (which may optionally be subjected to a secondary component separation (for example C ₄ -hydrocarbons such as butene-1) is added to the dehydrogenation zone as a further propane source was) leads. This is especially true when the cycle gas is the only oxygen source for hydrogen combustion in this process variant.

In the process according to the invention, the product gas mixture formed in the course of the heterogeneously catalyzed propane dehydrogenation generally contains propane, propene, molecular hydrogen, N ₂ , H ₂ O, methane, ethane, ethylene, butene-1, other butenes and other C ₄ hydrocarbons (n -Butane, isobutane, butadiene etc.), CO and CO ₂ . It will usually be at a pressure of 0.3 to 10 atm and often have a temperature of 400 to 500 ° C, in favorable cases 450 to 500 ° C.

While the EP-A 117 146 , the DE-A 3 313 573 and the US-A 3 161 670 recommend that the product gas mixture (gas mixture 1) formed in the heterogeneously catalyzed propane dehydrogenation be used as such to feed the at least one partial zone, it is usually expedient according to the invention from the product gas mixture (the gas mixture 1) of the oxydehydrogenation and / or dehydrogenation prior to its further use for feeding the at least one partial zone, at least part of the C ₄ hydrocarbons (eg n-butane, isobutane, butene-1, other butenes, butadienes, etc.) contained therein. If the gas mixture 1 contains hydrogen, the aforementioned separation can be accompanied by at least a partial separation of the hydrogen or such a hydrogen separation can be carried out in advance.

The latter can e.g. done by that the gas mixture 1, if necessary after having previously in it an indirect heat exchanger chilled has (expediently is the heat extracted to heat one for the inventive method required feed gas used) about a membrane, usually designed as a tube, which conducts only for is permeable to molecular hydrogen. The one so separated Molecular hydrogen can be partially heterogeneous if necessary catalyzed dehydrogenation of propane or other recycling supplied become. For example, it can be burned in fuel cells.

Alternatively, partial or complete hydrogen separation can also be carried out by partial condensation, adsorption and / or rectification (preferably under pressure). The partial or full separation of the molecular hydrogen from the product gas mixture (gas mixture 1) can also be carried out in the process according to the invention by selective (eg heterogeneously catalyzed) combustion of the same with molecular oxygen. The water of reaction which forms can either be partially or completely separated off or left in the gas mixture, since it can act as an inert diluent gas in the at least one partial zone. Suitable catalysts in this regard, for example, disclose the US-A 4 788 371 . US-A 4 886 928 . US-A 5 430 209 . US-A 5 5530171 . US-A 5 527979 and US-A 5 563314 ,

The selective combustion of the molecular hydrogen can also take place virtually in situ during the heterogeneously catalyzed dehydrogenation, for example by oxidation using a reducible metal oxide additionally added to the dehydrogenation catalyst, such as, for example, the EP-A 832056 describes.

According to the invention, at least 10 mol%, or at least 25 mol%, often at least 35 mol%, or at least 50 mol%, often at least 75 mol%, and often the total amount of the molecular mass formed in the heterogeneously catalyzed dehydrogenation are expedient Pre-separate and / or co-separate hydrogen before the remaining product gas mixture (gas mixture 1 ') is used to feed the at least one partial ozone. If necessary, any water which may be present can also be separated off from the gas mixture 1 before it is further processed in the at least one partial zone (for example condensation). Of course, if necessary, other components of the product gas mixture (gas mixture 1) other than propane and propylene can also be separated off as part of the separation of molecular hydrogen and / or C ₄ hydrocarbons such as butene-1 etc.

A simple possibility for this consists, for example, of the gas mixture 1, which is preferably cooled (preferably to temperatures of 10 to 70 ° C.), for example at a pressure of 0.1 to 50 atm and a temperature from 0 to 100 ° C, with a (preferably high-boiling) organic solvent (preferably a hydrophobic), in which propane and propylene are preferably absorbed, in contact (for example by simple passage). Subsequent desorption, rectification and / or stripping with a gas which is inert with respect to the at least one partial zone and / or is required as a reactant in this reaction zone (for example air), the propane and propylene in the mixture are recovered in purified form and for feeding the at least one Partial zone used (as already mentioned, in the case of stripping with air, the gas mixture 1 ′ produced in this way can be identical to the gas mixture 2, ie as such can be used directly to feed the at least one partial oxidation). The exhaust gas of the absorption, which may contain molecular hydrogen, can again be subjected to membrane separation, for example, and then, if necessary, the separated hydrogen can also be used for the heterogeneously catalyzed propane dehydrogenation.

However, the C ₃ -hydrocarbons / C ₄ -hydrocarbons separation factor in the above separation process is comparatively limited and is often not sufficient for the needs according to the invention.

As an alternative to the separation step described via absorption is for the purposes of the invention therefore often pressure swing adsorption or pressure rectification is preferred.

Basically all absorbents which are able to absorb propane and propylene are suitable as absorbents for the above-described absorptive separation. The absorbent is preferably an organic solvent, which is preferably hydrophobic and / or high-boiling. This solvent advantageously has a boiling point (at a normal pressure of 1 atm) of at least 120 ° C., preferably at least 180 ° C., preferably from 200 to 350 ° C., in particular from 250 to 300 ° C., more preferably from 260 to 290 ° C. The flash point (at a normal pressure of 1 atm) is expediently above 110 ° C. In general, relatively non-polar organic solvents are suitable as absorbents, such as, for example, aliphatic hydrocarbons, which preferably do not contain an outwardly acting polar group, but also aromatic hydrocarbons. In general, it is desirable for the absorbent to have a boiling point that is as high as possible while at the same time having a high solubility for propane and propylene. Examples of absorbents are aliphatic hydrocarbons, for example C ₈ -C ₂₀ -alkanes or alkenes, or aromatic hydrocarbons, for example middle oil fractions from paraffin distillation or ethers with bulky (sterically demanding) groups on the O atom, or mixtures thereof, where this a polar solvent, such as that in the DE-A 43 08 087 1,2-dimethylphthalate disclosed may be added. Also suitable are esters of benzoic acid and phthalic acid with straight-chain alkanols containing 1 to 8 carbon atoms, such as n-butyl benzoate, methyl benzoate, ethyl benzoate, dimethyl phthalate, diethyl phthalate, and so-called heat transfer oils, such as diphenyl, diphenyl ether and chlorides and mixtures thereof, and mixtures and triarylalkenes, for example 4-methyl-4'-benzyldiphenylmethane and its isomers 2-methyl-2'-benzyldiphenylmethane, 2-methyl-4'-benzyldiphenylmethane and 4-methyl-2'-benzyldiphenylmethane and mixtures of such isomers. A suitable absorbent is a solvent mixture of diphenyl and diphenyl ether, preferably in the azeotropic composition, in particular from about 25 wt .-% diphenyl (biphenyl) and about 75 wt .-% of diphenyl ether, for example the commercially available Diphyl ^® (for example, from Bayer Corporation related). This solvent mixture often contains a solvent such as dimethyl phthalate in an amount of 0.1 to 25% by weight, based on the total solvent mixture. Particularly suitable absorbents are also octanes, nonanes, decanes, undecanes, dodecanes, tridecanes, tetradecanes, pentadecanes, hexadecanes, heptadecanes and octadecanes, with tetradecanes in particular having proven to be particularly suitable. It is favorable if the absorbent used on the one hand meets the boiling point mentioned above, but on the other hand has a not too high molecular weight. The molecular weight of the absorbent is advantageously ≤ 300 g / mol. The in. Are also suitable DE-A 33 13 573 described paraffin oils with 8 to 6 carbon atoms. Examples of suitable commercial products are products sold by Haltermann, such as Halpasole i, such as Halpasol 250/340 i and Halpasol 250/275 i, and printing ink oils under the names PKWF and Printosol. Aromatic free commercial products, for example those of the PKWFaf type, are preferred.

The absorption is not subject to any particular restrictions. All methods and conditions common to those skilled in the art can be used. The gas mixture is preferably brought into contact with the absorbent at a pressure of 1 to 50 bar, preferably 2 to 20 bar, more preferably 5 to 10 bar, and a temperature of 0 to 100 ° C., in particular 30 to 50 ° C. , The absorption can be carried out both in columns and in quenching apparatus. You can work in cocurrent or in countercurrent. Suitable absorption columns are, for example tray columns (having bubble and / or sieve trays), columns with structured packings (for example, sheet metal packings with a specific surface area of 100 to 1000, or up to 750 m ² / m ^3, for example Mellapak ^® 250 Y) and Packed columns (for example filled with Raschig packings). However, trickle and spray towers, graphite block absorbers, surface absorbers such as thick-film and thin-film absorbers as well as plate washers, Cross-type washers and rotary washers are used. In addition, it can be advantageous to have the absorption take place in a bubble column with and without internals.

The separation of propane and propylene of the absorbent can be by stripping, flash evaporation (Flashing) and / or distillation.

The propane and propylene are preferably separated from the absorbent by stripping and / or desorption. The desorption can be carried out in the usual way via a change in pressure and / or temperature, preferably at a pressure of 0.1 to 10 bar, in particular 1 to 5 bar, more preferably 1 to 3 bar, and a temperature of 0 to 200 ° C, in particular 20 to 100 ° C, more preferably 30 to 70 ° C, particularly preferably 40 to 60 ° C. A gas suitable for stripping is, for example, water vapor, but oxygen / nitrogen mixtures, for example air, are particularly preferred. When using air or oxygen / nitrogen mixtures in which the oxygen content is above 10% by volume, it may make sense to add a gas before or during the stripping process that reduces the explosion area. Gases with a specific heat capacity ≥ 29 J / molK at 20 ° C, such as methane, ethane, propane, propene, benzene, methanol, ethanol, as well as ammonia, carbon dioxide, and water are particularly suitable for this. According to the invention, however, C ₄ hydrocarbons are to be avoided as such additives. Bubble columns with and without internals are also particularly suitable for stripping.

The separation of propane and propylene of the absorbent can also be distilled or Rectification takes place, the columns familiar to the person skilled in the art with packs, packing or appropriate internals can be used. Preferred conditions a pressure of 0.01 during distillation or rectification up to 5 bar, in particular 0.1 to 4 bar, more preferably 1 to 3 bar, and a temperature (in the sump) of 50 to 300 ° C, especially 150 to 250 ° C.

A gas mixture 1 'obtained by stripping from the absorbent can be fed to a further process step before it is used to feed the at least one partial zone, for example to reduce the losses of stripped absorbent (e.g. separation in demisters and / or depth filters) and the at least one To protect the partial zone from absorbent at the same time or to further improve the separation effect between C ₃ - / C ₄ hydrocarbons. Such a separation of the absorbent can be carried out according to all process steps known to the person skilled in the art. A preferred embodiment of such a separation within the scope of the method according to the invention is, for example, quenching the output stream from the stripping device with water. In this case, the absorbent is washed out of this loaded output stream with water and the output stream is simultaneously loaded with water. This washing or quenching can be carried out, for example, at the top of a desorption column above a liquid collecting tray by spraying water against one another or in a separate apparatus.

To support the separation effect can Quench room the quench surface magnifying internals be installed as the expert of rectifications, absorptions and desorption are known.

In this respect, water is a preferred one Detergent as there is in the subsequent at least one partial zone usually doesn't bother. After the water has been absorbed with propane and Has washed out the propylene laden output stream, the water / absorbent mixture phase separation and the treated output stream as a gas mixture 1 'of the partial zone are fed.

Both the C ₃ -free stripped absorbent and the absorbent recovered in the phase separation can be reused for the purpose of absorption.

The gas mixture 1 and / or the gas mixture 1 ′ generated from the same can now be used in a manner known per se in at least one further reaction zone for feeding a heterogeneously catalyzed gas phase oxidation and / or ammoxidation of propylene to acrolein and / or acrylic acid and / or acrylonitrile with a Feed gas mixture 2 are used. Pure molecular oxygen, air, oxygen-enriched air or any other mixture of oxygen and inert gas can be added as the oxidizing agent. If the partial oxidation involves the conversion of propylene to propylene oxide, it can, for example, as in the EP-A 372972 described procedure.

If it is a partial ammoxidation to acrylonitrile, for example according to the DE-A 2351151 be moved. In the case of a partial oxidation of propylene to acrolein and / or acrylic acid, the composition of the gas mixture 2 will be used in the process according to the invention using the gas mixture 1 and / or 1 '(mixtures of the two can also be used, ie one part is separated from one not change) so that it meets the following molar ratios:
Propane: propene: N ₂ : O ₂ : H ₂ O: other = 0.5 to 20: 1: 0.1 to 40: 0.1 to 10: 0 to 20: 0 to 1.

The above are advantageous molar ratios according to the invention = 2 to 10: 1: 0.5 to 20: 0.5 to 5: 0.01 to 10: 0 to 1.

It is also favorable if the aforementioned molar ratios according to the invention = 3 to 6: 1: 1 to 10: 1 to 3: 0.1 to 2: 0 to 0.5.

As already mentioned, the heterogeneously catalyzed runs Gas-phase partial oxidation from propylene to acrylic acid with molecular oxygen in two along the reaction coordinate successive steps, the first of which is to acrolein and the second leads from acrolein to acrylic acid.

This reaction sequence in two times successive steps opened in a manner known per se the possibility, the at least one partial zone of the method according to the invention in this case in two oxidation zones arranged one behind the other perform, the oxidic to be used in each of the two oxidation zones Catalyst can be adjusted in an optimizing manner. So for the first oxidation zone (Propylene → acrolein) usually a catalyst based on the element combination Mo-Bi-Fe containing multimetal oxides preferred, while for the second oxidation zone (Acrolein → acrylic acid) usually Catalysts based on the Mo-V combination of elements Multimetal oxides are preferred.

Corresponding multimetal oxide catalysts for the two oxidation zones have been described many times before and are well known to the person skilled in the art. For example, the EP-A 253 409 on page 5 for corresponding US patents.

Cheap catalysts for the two oxidation zones also reveal that DE-A 4 431 957 and the DE-A 4431949 , This applies in particular to those of the general formula I in the two aforementioned documents.

For the first step of the partial oxidation, which catalyzed heterogeneously Gas phase partial oxidation of propylene to acrolein, come as already said, in principle all Mo, Bi and Fe containing multimetal oxide materials into consideration.

These are in particular the multimetal oxide active compositions of the general formula I DE-A 19955176 , the multimetal oxide active compositions of the general formula I DE-A 19948523 , the multimetal oxide active compositions of the general formula I DE-A 19948523 , the multimetal oxide active compositions of the general formulas I, II and III of DE-A 10101695 , the multimetal oxide active compositions of the general formulas I, II and III of DE-A 19948248 and the multimetal oxide active compositions of the general formulas I, II and III of DE-A 19955168 as well as those in the EP-A 700714 called multimetal oxide active materials.

Also suitable for this Oxidation step the Mo, Bi and Fe containing multimetal oxide catalysts the in the scriptures DE-A 10046957 . DE-A 10063162 . DE-C 3338380 . DE-A 19902562 . EP-A 15565 . DE-C 2380765 . EP-A 807465 . EP-A 279374 . DE-A 3300044 . EP-A 575897 . US-A 4438217 . DE-A 19855913 , WO 98/24746, DE-A 19746210  (those of the general Formula II), JP-A 91/294239 . EP-A 293224  and EP-A 700714  disclosed become. This applies in particular to the exemplary embodiments in these writings, among which those of EP-A 15565 , the EP-A 575897 , the DE-A 19746210  and the DE-A 19855913  especially to be favoured. Of particular note in this context a catalyst according to the example 1c from the EP-A 15565  such as a catalyst to be produced in a corresponding manner, its active composition however the composition Mo₁₂Ni_6.5 Zn₂Fe₂Bi₁P_0.0065K_0.06O_x· 10SiO₂ having. It should also be emphasized that Example with the running number 3 from the DE-A 19855913  (Stoichiometry: Mo₁₂Co₇Fe₃Bi_0.6K_0.08Si_1.6 O_x) as hollow cylinder full catalyst of geometry 5 mm × 3 mm × 2 mm (outer diameter × height × inner diameter) as well as the multimetal oxide II full catalyst according to example 1 of DE-A 19746210 , Furthermore would be the multimetal oxide catalysts of the US-A 4438217  to call. The latter applies in particular then if this hollow cylinder has a geometry of 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 (each outer diameter × height × inner diameter) exhibit.

A large number of the multimetal oxide active compositions suitable for the step from propylene to acrolein can be obtained using the general formula IV Mo ₁₂ Bi _a Fe _b X 1 / cX 2 / dX 3 / eX 4 / fO _n (IV), 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 determined by the valency and frequency of elements other than oxygen in IV is true
subsumed.

They are available in a manner known per se (see, for example, the DE-A 4023239 ) and are usually formed into spheres, rings or cylinders in bulk or also in the form of coated catalysts, ie, preformed, inert support bodies coated with the active composition. Of course, they can also be used in powder form as catalysts.

In principle, active compositions of the general formula IV can be prepared in a simple manner by generating an intimate, preferably finely divided, dry mixture of suitable stoichiometry from suitable sources of their elemental constituents and calcining them at temperatures of 350 to 650 ° C. The calcination can take place both under inert gas and under an oxidative atmosphere such as air (mixture of inert gas and oxygen) and also under a reducing atmosphere (eg mixture of inert gas, NH ₃ , CO and / or H ₂ ). The calcination time can range from a few minutes to a few hours and usually decreases with temperature. Suitable sources for the elementary 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.

In addition to the oxides, such starting compounds are in particular 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 later decompose and / or decompose into compounds escaping in gaseous form during later calcination, can also be incorporated into the intimate dry mixture) ,

The intimate mixing of the starting compounds for the production of multimetal oxide active materials IV can be in dry or done in wet form. If it is done in a dry form, it will be the starting compounds expediently used as a finely divided powder and after mixing and optionally compacting subjected to calcination. The intimate mixing is preferably carried out however in wet form. Usually the starting compounds are in the form of an aqueous solution and / or Suspension mixed together. Particularly intimate dry mixes are obtained in the described mixing process if only from in dissolved Form of available sources of the elementary constituents becomes. As a solvent water is preferred. Then the aqueous mass obtained dried, the drying process preferably by spray drying the aqueous mixture with Outlet temperatures of 100 to 150 ° C takes place.

The multimetal oxide active materials of general formula IV can for the Step "Propylene → Acrolein" both in powder form as well as shaped to certain catalyst geometries be, the shape before or after the final calcination can be done. For example from the powder form of the active composition or its uncalcined and / or partially calcined precursor mass by compression to the desired one Catalyst geometry (e.g. by tableting, extruding or Extrusion) full catalysts are prepared, where appropriate Tools such as Graphite or stearic acid as a lubricant and / or Molding aids and reinforcing agents such as microfibers made of glass, 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, the wall thickness is 1 to 3 mm appropriate. Of course you can the full catalyst also have spherical geometry, the spherical diameter Can be 2 to 10 mm.

A particularly favorable 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 powdery active composition or its powdery, not yet and / or partially calcined, precursor composition can also be shaped by application to preformed inert catalyst supports. The coating of the support bodies for the production of the coated catalysts is generally carried out in a suitable rotatable container, such as that from the DE-A 2909671 , the EP-A 293859 or from the EP-A 714700 is known. To coat the carrier bodies, the powder mass to be applied is expediently moistened and dried again after application, for example by means of hot air. The layer thickness of the powder composition applied to the carrier body is expediently selected in the range from 10 to 1000 μm, preferably in the range from 50 to 500 μm and particularly preferably in the range from 150 to 250 μm.

Conventional porous or non-porous aluminum oxides, silicon dioxide, thorium dioxide, zirconium dioxide, silicon carbide or silicates such as magnesium or aluminum silicate can be used as carrier materials. As a rule, they are essentially inert with respect to the target reaction underlying the process according to the invention. The carrier bodies can have a regular or irregular shape, preference being given to regularly shaped carrier bodies with a clearly formed surface roughness, for example balls or hollow cylinders. It is suitable to use essentially non-porous, rough-surface, spherical supports made of steatite, the diameter of which is 1 to 8 mm, preferably 4 to 5 mm. Suitable but is also the use of cylinders as a support body, the length of which is 2 to 10 mm and the outside diameter is 4 to 10 mm. In the case of rings suitable as support bodies according to the invention, the wall thickness is moreover usually 1 to 4 mm. Annular support bodies to be preferably used according to the invention 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. According to the invention, rings of geometry 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter) are particularly suitable as carrier bodies. The fineness of the catalytically active oxide materials to be applied to the surface of the carrier body is of course adapted to the desired shell thickness (cf. EP-A 714 700 ).

Multimetal oxide active compositions to be used for the step from propylene to acrolein are also compositions of the general formula V [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 (V), in which the variables have the following meaning:
Y ¹ = only bismuth or bismuth and at least one of the elements tellurium, antimony, tin and copper,
Y ² = molybdenum or molybdenum and tungsten,
Y ² = an alkali metal, thallium and / or samarium,
Y ² = 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 valency and frequency of the elements in V other than oxygen 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 , which are different from their local surroundings due to their composition which differs from their local surroundings, and whose maximum diameter (longest connecting distance through the center of gravity of the area of two on the surface (interface ) of the range of points) is 1 nm to 100 μm, often 10 nm to 500 nm or 1 μm to 50 or 25 μm.

Particularly advantageous multimetal oxide compositions V according to the invention are those in which Y ^{1 is} only bismuth.

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

It is also advantageous if at least 25 mol% (preferably at least 50 mol% and particularly preferably at least 100 mol%) of the total fraction [Y ¹ _a , Y ² _b , O _x ,] _p ([Bi _{a ''} Z ² _b'' O _x'' ] _p'' ) of the multimetal oxide compositions V (multimetal oxide compositions VI) which are suitable according to the invention in the multimetal oxide compositions V (multimetal oxide compositions VI) which are suitable according to the invention in the form of three-dimensionally expanded form, from their local environment because of their different from their local environment chemical composition of limited areas of the chemical composition Y ¹ _a , Y ² _b , O _x , [Bi _{a ''} Z ² _{b ''} O _{x ''} ], the size of which is in the range from 1 nm to 100 μm.

Regarding the shape applies in terms of Multimetal oxide masses V-catalysts that with the multimetal oxide masses IV catalysts said.

The production of multimetal oxide compositions V-active compositions is for example in the EP-A 575897 as well as in the DE-A 19855913 described.

The inert ones recommended above support materials come among others also as inert materials for dilution and / or delimitation of the corresponding fixed catalyst beds, or as their protective and / or the pre-fill heating the gas mixture into consideration.

At this point it should be mentioned that everyone Catalysts and multimetal oxide materials required for the step from propylene were recommended as suitable for acrolein, in principle also for the Partial ammoxidation of propylene to acrylonitrile are suitable.

For the second step, the heterogeneously catalyzed gas phase partial oxidation of acrolein to acrylic acid, all Mo and V-containing multimetal oxide materials can in principle be considered as active materials, for example those of DE-A 10046928 ,

Many of them, for example those of DE-A 19815281 , can be under the general formula VII Mo _l2 V _a X ¹ _b X ² _c X ³ _d X ⁴ _e X ⁵ _f X ⁶ _g O _n (VII), 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 which is determined by the valency and frequency of the elements other than oxygen in VII,
subsumed.

Preferred embodiments according to the invention within the active multimetal oxides VII are those which are covered by the following meanings of the variables of the general formula VII:
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 which is determined by the valency and frequency of the elements other than oxygen in VII.

According to the invention, particularly preferred multimetal oxides VII are those of the general formula VIII Mo ₁₂ V _{a '} Y ¹ _b' Y ² _{c '} Y ⁵ _f' Y ⁶ _{q '} O _n' (VIII) 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 determined by the valency and frequency of elements other than oxygen in VIII.

The multimetal oxide active materials (VII) which are suitable according to the invention are known per se, for example in DE-A 4335973 or in the EP-A 714700 disclosed, way available.

In principle, multimetal oxide active compositions suitable for the “acrolein acrylic acid” step, in particular those of the general formula VII, can be prepared in a simple manner by generating an intimate, preferably finely divided, dry mixture composed of suitable stoichiometry from suitable sources of their elemental constituents and this calcined at temperatures from 350 to 600 ° C. The calcination can take place both under inert gas and under an oxidative atmosphere such as air (mixture of inert gas and oxygen) and also under a reducing atmosphere (eg mixtures of inert gas and reducing gases such as H ₂ , NH ₃ , CO, methane and / or acrolein or the reducing gases mentioned per se.) The calcination time can be from a few minutes to a few hours and usually decreases with temperature. As sources for the elemental constituents of the multimetal oxide active materials VII compounds which are already oxides and / or those compounds which can be converted into oxides by heating, at least in the presence of oxygen, are suitable.

The intimate mixing of the starting compounds for the production of multimetal oxide materials VII can in dry or done in wet form. If it is done in a dry form, it will be the starting compounds expediently used as a fine powder and after mixing and optionally Compacting subjected to calcination. This is preferably done intimate mixing, however, in wet form.

Usually the starting compounds are in the form of an aqueous solution and / or suspension mixed together. Particularly intimate dry mixtures are used in the described mixing process obtained when exclusively from in dissolved Form of available sources of the elementary constituents becomes. As a solvent water is preferred. Then the aqueous mass obtained dried, the drying process preferably by spray drying the aqueous mixture with outlet temperatures of 100 to 150 ° C.

The resulting multimetal oxide masses in particular those of the general formula VII, can be used for both acrolein oxidation molded in powder form as well as certain catalyst geometries are used, the shaping before or after the final calcination can be done. For example, from the powder form of the active composition or its uncalcined precursor composition by compression to the desired one Catalyst geometry (e.g. by tableting, extruding or Extrusion) full catalysts are prepared, where appropriate Tools such as Graphite or stearic acid as a lubricant and / or Molding aids and reinforcing agents such as microfibers made of glass, 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, the wall thickness is 1 to 3 mm appropriate. Of course you can the full catalyst also have spherical geometry, the spherical diameter Can be 2 to 10 mm.

Of course, the powdery active composition or its powdery, not yet calcined, precursor composition can also be shaped by application to preformed inert catalyst supports. The coating of the support bodies for the production of the coated catalysts is generally carried out in a suitable rotatable container, such as that from the DE-A 2909671 , the EP-A 293859 or from the EP-A 714700 is known.

The powder mass to be applied is expediently used to coat the carrier bodies moist and dried again after application, e.g. using hot air. The layer thickness of the powder composition applied to the carrier body is expediently selected in the range from 10 to 1000 μm, preferably in the range from 50 to 500 μm and particularly preferably in the range from 150 to 250 μm.

Conventional porous or non-porous aluminum oxides, silicon dioxide, thorium dioxide, zirconium dioxide, silicon carbide or silicates such as magnesium or aluminum silicate can be used as carrier materials. The carrier bodies can have a regular or irregular shape, preference being given to regularly shaped carrier bodies with a clearly formed surface roughness, for example balls or hollow cylinders with a split layer. It is suitable to use essentially non-porous, rough-surface, spherical supports made of steatite, the diameter of which is 1 to 8 mm, preferably 4 to 5 mm. However, it is also suitable to use cylinders as carrier bodies, the length of which is 2 to 10 mm and the outside diameter is 4 to 10 mm. In the case of rings as support bodies, the wall thickness is also usually 1 to 4 mm. Annular support bodies to be used preferably 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. Rings of geometry 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter) are particularly suitable as carrier bodies. The fineness of the catalytically active oxide materials to be applied to the surface of the carrier body is of course adapted to the desired shell thickness (cf. EP-A 714 700 ).

Favorable multimetal oxide active compositions to be used for the “acrolein acrylic acid” step are also compositions of the general formula IX, [D] _p [E] _q (IX), in which the variables have the following meaning:
D = Mo ₁₂ V _{a ''} Z ¹ _b Z ² _{c ''} Z ³ _{d ''} Z ⁴ _{f ''} Z ⁵ _{g ''} Z ⁶ _{g ''} O _{x ''} ,
E: = Z ⁷ ₁₂ Cu _{h ''} H _{i ''} O _'' ,
Z ¹ = W, Nb, Ta, Cr and / or Ce,
Z ² = Cu, Ni, Co, Fe, Mn and / or Zn,
Z ³ = Sb and / or Bi,
Z ⁴ = Li, Na, K, Rb, Cs and / or H
Z ⁵ = Mg, Ca, Sr and / or Ba,
Z ⁶ = Si, Al, Ti and / or Zr,
Z ⁷ = Mo, W, V, Nb and / or Ta, preferably Mo and / or W.
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 determined by the valency and frequency of the element other than oxygen in IX and
p, q = non-zero numbers whose ratio p / q is 160: 1 to 1: 1,
and which are obtainable by using a multimetal oxide mass E Z ⁷ ₁₂ Cu _{h ''} H _{i ''} O _{y ''} (E), separately in finely divided form (starting mass 1) and then the preformed solid starting mass 1 in an aqueous solution, an aqueous suspension or in a finely divided dry mixture of sources of the elements Mo, V, Z ¹ , Z ² , Z ³ , Z ⁴ , Z ⁵ , Z ⁶ , which the aforementioned elements in the stoichiometry D Mo _l2 V _{a ''} Z ¹ _{b ''} Z ² _{c ''} Z ³ _{d ''} Z ⁴ _{e ''} Z ⁵ _f '' Z ⁶ _{g ''} (D) contains (starting mass 2), incorporated in the desired p: q ratio, the resulting aqueous mixture dries, and the resulting dry precursor is calcined before or after drying to the desired catalyst geometry at temperatures of 250 to 600 ° C.

Preferred are the multimetal oxide compositions IX, in which the preformed solid starting composition 1 is incorporated into an aqueous starting composition 2 at a temperature ≤ 70 ° C. A detailed description of the production of multimetal oxide VI catalysts contain, for example, the EP-A 668104 , the DE-A 19736105 , the DE-A 10046928 , the DE-A 19740493 and the DE-A 19528646 ,

Regarding the shape applies in terms of Multimetal oxide materials IX catalysts that with the multimetal oxide materials VII catalysts said.

Multimetal oxide catalysts which are outstandingly suitable for the step "acrolein → acrylic acid" are also those of DE-A 19815281 , in particular with multimetal oxide active compositions of the general formula I of this document.

Be beneficial for the step from propylene to acrolein full catalyst rings and for the step from Acrolein to acrylic acid Cup catalyst rings used.

The implementation of the first step of the partial oxidation, from propylene to acrolein, can be carried out with the catalysts described, for example in a single-zone multi-contact tube fixed-bed reactor, as is the case with DE-A 4431957 describes.

Oxygen is used as the oxidizing agent. If N _{2 is} chosen as the inert diluent gas, the use of air as an oxygen source proves to be particularly advantageous.

Usually a propylene : Oxygen: indifferent gases (including water vapor) volume (Nl) ratio from 1: (1.0 to 3.0) :( 5 to 25), preferably 1: (1.7 to 2.3) :( 10 to 15) worked. The reaction pressure is usually in the range of 1 to 3 bar and the total space load is preferably 1500 to 4000 Nl / (l.h). The propylene load is typically 90 to 200 Nl / (1 x h).

The single-zone multi-contact tube fixed bed reactor with the feed gas mixture is preferably flowed from above. A salt melt, preferably consisting of 60% by weight of potassium nitrate (KNO ₃ ) and 40% by weight of sodium nitrite (NaNO ₂ ), or of 53% by weight of potassium nitrate (KNO ₃ ), 40% by weight, is expediently used as the heat exchange medium. Sodium nitrite (NaNO ₂ ) and 7% by weight sodium nitrate (NaNO ₃ ).

about can look at the reactor Salt melt and reaction gas mixture both in cocurrent and led in countercurrent become. The molten salt itself is preferably guided in a meandering shape around the contact tubes.

If you flow the contact tubes from downwards, it is advisable to move the contact tubes downwards to be loaded as follows (for the inflow from bottom to top, the loading sequence is convenient vice versa):

• - first on a length from 40 to 60% of the contact tube length either only catalyst, or a mixture of catalyst and inert material, the latter, based on the mixture, a weight fraction of up to accounts for 20% by weight (Section C);
• - on it subsequently on one length from 20 to 40% of the total pipe length either only catalyst, or a mixture of catalyst and inert material, the latter, based on the mixture, a proportion by weight accounts for up to 40% by weight (Section B); and
• - finally a length from 10 to 20% of the total pipe length a fill from inert material (section A), which is preferably chosen so that you have one if possible low pressure loss.

Section C is preferably undiluted.

The aforementioned feed variant is particularly expedient if the catalysts according to Example 1 of the DE-A 10046957 or according to Example 3 of DE-A 10046957 and rings of steatite with the geometry 7 mm × 7 mm × 4 mm (outer diameter × height × inner diameter) are used as the inert material. This applies to the salt bath temperature in the DE-A 4431957 Said.

The implementation of the first step of the partial oxidation, from propylene to acrolein, can also be carried out with the catalysts described, for example in a two-zone multi-contact tube fixed-bed reactor, as is the case with DE-A 19910506 describes. In both cases described above, the propene conversion achieved in a single pass is normally ≥ 90 mol% or ≥ 95 mol%. The second step of the partial oxidation, from acrolein to acrylic acid, can be carried out using the catalysts described, for example in a single-zone multi-contact tube fixed-bed reactor, as is the case with DE-A 4431949 describes. As a rule, the product mixture of the propylene oxidation to acrolein is passed as such (if appropriate after intermediate cooling of the same), ie, without separation of secondary components, into the acrolein oxidation to acrylic acid.

The one for the second step of the partial oxidation needed Oxygen is preferably added as air and usually Product gas mixture of the propylene oxidation added immediately.

Usually the feed gas mixture of such acrolein oxidation is then composed as follows: Acrolein: oxygen: water vapor: inert gas volume ratio (Nl) from 1: (1 to 3) :( 0 to 20) :( 3 to 30), preferably from 1: (1 to 3) :( 0.5 to 10) :( 7 to 18).

The reaction pressure is in the Usually 1 to 3 bar and the total space load is preferably at 1000 to 3800 Nl / (l · h). The acrolein load is typically 80 to 190 Nl / (1 x h).

The single-zone multi-contact tube fixed bed reactor with the feed gas mixture is preferably also flowed from above. A salt melt is also expediently used as the heat exchange medium in the second stage, preferably from 60% by weight potassium nitrate (KNO ₃ ) and 40% by weight sodium nitrite (NaNO ₂ ) or from 53% by weight potassium nitrate (KNO ₃ ), 40% by weight sodium nitrite (NaNO ₂ ) and 7% by weight sodium consisting of nitrate (NaNO ₃ ). When viewed through the reactor, the molten salt and reaction gas mixture can be conducted both in cocurrent and in countercurrent. The molten salt itself is preferably fed into the contact tubes in a meandering shape.

If you flow the contact tubes from downwards, it is advisable to move the contact tubes downwards to be loaded as follows:

• - first on a length from 50 to 70% of the contact tube length either only catalyst or a mixture of catalyst and inert material, the latter, based on the mixture, a weight fraction of accounts for up to 20% by weight (Section C);
• - on it subsequently on one length from 20 to 40% of the total pipe length either only catalyst, or a mixture of catalyst and inert material, the latter, based on the mixture, a proportion by weight accounts for up to 40% by weight (Section B); and
• - finally a length from 5 to 20% of the total pipe length a fill from inert material (section A), which is preferably chosen so that you have one if possible low pressure loss.

Section C is preferably undiluted.

For an inflow of the contact tubes from the bottom up, the contact tube loading in expediently vice versa.

The aforementioned charging variant is particularly expedient if the catalysts used are those according to Production Example 5 DE-A 10046928 or according to DE-A 19815281 and rings made of steatite with the geometry 7 mm × 7 mm × 4 mm or 7 mm × 7 mm × 3 mm (in each case outer diameter × height × inner diameter) are used as the inert material. This applies to the salt bath temperature in the DE-A 44 319 49 Said. It is usually chosen so that the acrolein conversion achieved in a single pass is normally ≥ 90 mol% or ≥ 95 mol%.

The implementation of the second step of the partial oxidation, from acrolein to acrylic acid, can also be carried out with the catalysts described, for example in a two-zone multi-contact tube fixed-bed reactor, as is the case with DE-19910508 describes. The above applies to acrolein conversion. Even if this second step is carried out in a two-zone multi-contact tube fixed-bed reactor, the product gas mixture of one directed to the first step of the partial oxidation (if necessary after intermediate cooling of the same) is expediently used to generate the feed gas mixture (as described above). The oxygen required for the second step of the partial oxidation is preferably added as air and in the second case is added directly to the product gas mixture of the first step of the partial oxidation.

With a two-stage driving style with immediate reuse of the product gas mixture of the first Partial oxidation step to feed the second step partial oxidation, you will usually have two single-zone multi-contact tube fixed-bed reactors or connect two two-zone multi-contact tube fixed bed reactors in series. A mixed series connection (single zone / two zones or vice versa) is also possible.

An intercooler can be located between the reactors, which can optionally contain inert beds which can perform a filter function. The salt bath temperature of multi-contact tube reactors for the first step of the partial oxidation of propylene to acrylic acid is usually 300 to 400 ° C. The salt bath temperature of multi-contact tube reactors for the second step of the partial oxidation of propylene to acrylic acid, the partial oxidation of acrolein to acrylic acid, is usually 200 to 350 ° C. In addition, the heat exchange means (preferably molten salts) are normally passed through the relevant multi-contact tube fixed bed reactors in such quantities that the difference between their inlet and outlet temperatures is generally ≤ 5 ° C. As already mentioned, both steps of the partial oxidation of propylene to acrylic acid can also be carried out as in the DE-A 10121592 described are carried out in a reactor on a feed.

It should also be mentioned that part the feed gas mixture (gas mixture 2) for the first step (“propylene → acrolein”) from the partial oxidation coming cycle gas can be.

This is gas that after separation of the target product (acrolein and / or acrylic acid separation) remains of the product gas mixture of the partial oxidation and as inert diluent gas into the feed for the first and / or optionally second step of the partial oxidation can be recycled from propylene to acrolein and / or acrylic acid.

Such propane and cycle gas optionally containing propylene, however, into the feed of the first step of the method according to the invention.

It should also be mentioned that a partial oxidation and / or amoxidation according to the invention can be carried out in such a way that a reaction gas mixture which does not contain oxygen is first passed over the catalyst feed via the catalyst feed. In this case, the oxygen required for the partial oxidation is made available as lattice oxygen. In a subsequent regeneration step with an oxygen-containing gas (eg air, oxygen-enriched air or oxygen) de-enriched air), the catalyst bed is regenerated in order to be subsequently available again for an oxygen-free reaction gas mixture, etc.

In summary, a tube bundle reactor again forms within which the catalyst feed along the individual contact tubes changes accordingly upon completion of the first reaction step (propylene partial oxidations suitable as reaction zone B according to the invention are taught, for example, by EP-A 911313 , the EP-A 979813 , the EP-A 990636 and the DE-A 2830765 ) the simplest implementation of two oxidation zones for the two steps of partial oxidation of propylene to acrylic acid. If necessary, the catalyst tubes are interrupted by an inert bed.

However, the two oxidation zones are preferably implemented in the form of two tube bundle systems connected in series. These can be located in a reactor, the transition from one tube bundle to the other tube bundle being formed by a bed of inert material which is not accommodated in the contact tube (expediently can be walked on). While the contact tubes are generally washed around by a heat transfer medium, the heat transfer medium does not reach an inert bed as described above. The two contact tube bundles are therefore advantageously accommodated in spatially separate reactors. As a rule, an intercooler is located between the two tube bundle reactors in order to reduce any acrolein afterburning in the product gas mixture which leaves the first oxidation zone. Instead of tube bundle reactors, plate heat exchanger reactors with salt and / or evaporative cooling, such as those used, can also be used DE-A 19 929 487 and the DE-A 19 952 964 describe, be used.

The reaction temperature in the first oxidation zone is usually 300 to 450 ° C, preferably 320 to 390 ° C. The reaction temperature in the second oxidation zone is usually 200 to 300 ° C, often 220 to 290 ° C. The reaction pressure in both oxidation zones is expediently 0.5 to 5, advantageously 1 to 3 atm. The loading (Nl / l · h) of the Oxidationska talysatoren with reaction gas in both oxidation zones is often 1500 to 2500 h ^-1 or up to 4000 h ^-1 . The contamination with Popylen can be 100 to 200 and more Nl / l · h.

In principle, the two oxidation zones in the method according to the invention can be designed as it is, for example, in the DE-A 19 837 517 , the DE-A 19 910 506 , the DE-A 19 910 508 as well as the DE-A 19 837 519 is described. Usually, the external temperature control in the two oxidation zones, optionally in multi-zone reactor systems, is adapted in a manner known per se to the special reaction gas mixture composition and catalyst feed.

The one required for the invention at least one partial zone as the total oxidizing agent required molecular Oxygen can be added to the feed gas mixture of at least one Partial zone in its total amount can be added in advance. Of course you can but also, e.g. in the production of acrylic acid, after the first partial zone supplemented with oxygen become. The latter is preferred in the production of acrylic acid.

Preferably, the first Oxidation zone (propylene → acrolein) a molar ratio of propylene : molecular oxygen from 1: 1 to 3, often 1: 1.5 to 2. Similar numerical values are suitable for the molar ratio Acrolein: molecular oxygen in the second oxidation zone (1st : 0.5 to 1.5 would be preferred) for the partial oxidation of acrolein to acrylic acid.

It works in both oxidation zones thereby an excess of molecular Oxygen is usually beneficial to the kinetics of gas phase oxidation out. In contrast to the circumstances in the to be used according to the invention Dehydration becomes the thermodynamic conditions in the at least one partial oxidation by the molar reactant ratio essentially unaffected because the heterogeneously catalyzed gas phase partial oxidation of propylene to acrylic acid is subject to kinetic control. In principle, e.g. in the first oxidation zone also propylene compared to molecular oxygen in a molar excess. In this Fall comes to excess propylene in fact the role of a diluent gas to.

In principle, the heterogeneously catalyzed However, gas phase partial oxidation of propylene to acrylic acid also can be implemented in a single oxidation zone. In this case both reaction steps in an oxidation reactor with one Catalyst is charged, the implementation of both reaction steps is able to catalyze. Of course, the catalyst feed can also longitudinally within the oxidation zone change the reaction coordinate continuously or abruptly. Of course you can in one embodiment of the to be used according to the invention at least one partial oxidation in the form of two series-connected Oxidation zones from which leaving the first oxidation zone Product gas mixture contained in the same, in the first oxidation zone As a by-product, carbon oxide and water vapor if required partially or before being transferred to the second oxidation zone Completely be separated. According to the invention, preference is given to a procedure choose, that does not need such a separation.

As a source of the molecular oxygen required in the at least one partial oxidation and / or amoxidation, that of the gas mixture 1 or 1 'before it is used to feed the partial zone is admixed, both pure molecular oxygen and molecular oxygen diluted with inert gas such as CO ₂ , CO, noble gases, N ₂ and / or saturated hydrocarbons.

In an expedient way you will at least to cover a partial need for molecular oxygen as air Use an oxygen source.

By adding cold air too hot Gas mixture 1 or 1 'can in the context of the method according to the invention cooling down directly of the gas mixture 1 or 1 'causes become.

In the case of a production of acrolein and / or acrylic acid, the product gas mixture leaving the partial zone to be used according to the invention is generally essentially composed of the target product acrolein or acrylic acid or its mixture with acrolein, unreacted molecular oxygen, propane, unreacted propylene, molecular nitrogen, Steam formed as a by-product and / or used as a diluent gas, as a by-product and / or carbon oxides used as a diluent gas, as well as small amounts of other lower aldehydes, lower alkane carboxylic acids (e.g. acetic acid, formic acid and propionic acid) as well as maleic anhydride, benzaldehyde, aromatic carboxylic acids and aromatic carboxylic acids (e.g. carboxylic acids and aromatic carboxylic acids) Phthalic anhydride and benzoic acid), optionally other hydrocarbons, such as C ₄ hydrocarbons (eg butene-1 and possibly other butenes), and other inert diluent gases.

The target product can be separated from the product gas mixture in a manner known per se (for example by partial condensation of acrylic acid or by absorption of acrylic acid in water or in a high-boiling hydrophobic organic solvent or by absorption of acrolein in water or in aqueous solutions of lower carboxylic acids and subsequent workup the absorbate; alternatively, the product gas mixture can also be fractionally condensed; see e.g. EP-A 117146 . DE-A 4308087 . DE-A 4335172 . DE-A 4436243 . DE-A 19 924 532 such as DE-A 19 924 533 ). Acrylic acid separation can also be carried out as in the EP-A 982287 , the EP-A 982289 , the DE-A 19924532 , the DE-A 10115277 , the DE-A 19606877 , the DE-A 19740252 , the DE-A 19627847 , the DE-A 10053086 and the EP-A 982288 be made.

Unreacted propylene and / or Acrolein are also optionally separated and in the Partial zone returned.

Preferably, as in 7 separated from WO / 0196271. Otherwise, the essential constituents of acrylic gas and acrolein, which are different from the residual gas remaining after the target product has been separated off, can be separated as required and / or with the propane as recycle gas (recycle stream) into the feed of the first one, depending on the requirement, the crude propane and the dehydrogenation / oxydehydrogenation catalyst used Step of the method according to the invention are returned. Of course, the unreacted propane in a mixture with the unreacted propylene can also be recycled into this feed (as a recycle stream). When the process according to the invention is carried out continuously, propane is converted continuously to acrylic acid and / or acrolein.

The separation of propane and propylene from the residual gas remaining after the target product has been separated off (it usually contains O ₂ , CO, CO ₂ , H ₂ O, N ₂ , noble gases and other lower aldehydes, lower alkane carboxylic acids (e.g. acetic acid, formic acid and propionic acid) and maleic anhydride, benzaldehyde, aromatic carboxylic acids and aromatic carboxylic anhydrides (e.g. phthalic anhydride and benzoic acid) and hydrocarbons, e.g. C ₄ -hydrocarbons (e.g. butene-1 and possibly other butenes)) can, as already described, by absorption with subsequent desorption and / or stripping (as well as absorbent reuse) in a high-boiling hydrophobic organic solvent. Further separation options are adsorption, rectification, membrane processes and partial condensation. The separation processes mentioned are preferably carried out at elevated pressure.

When using dehydrogenation catalysts which are sensitive to oxygen or oxygen-containing compounds, these oxygenates will be separated from the cycle gas before recycling cycle gas into the feed of the first step of the process according to the invention. Such oxygen separation can also be useful in order to avoid total oxidation of the propane in the dehydrogenation stage. The dehydrogenation catalysts of the DE-A 19 937 107 are not sensitive to oxygenates (especially those according to Examples 1 to 4 of DE-A).

Another separation option offers, as also mentioned above, fractional distillation. Preferably becomes a fractional pressure distillation at low temperatures carried out. The pressure to be applied can e.g. 10 to 100 bar. As rectification columns can packed columns, Tray columns or packing columns are used. As bottom columns are suitable with dual-flow floors, bell bottoms or Valve trays. The reflux ratio can e.g. 1 to 10. Other separation options are e.g. Pressure extraction, Pressure swing adsorption, pressure washing, partial condensation and pressure extraction.

Of course, according to the invention, for example, if after the first step of the process according to the invention a separation of secondary components (for example C ₄ -hydrocarbons (for example n-butane, isobutane, butene-1 and possibly other butenes)) is integrated or the disruptive C4 hydrocarbons do not level off (for example if they are burned in the partial zone on suitable catalysts), and also the total amount of residual gas (as a recycle stream) is fed back into the feed of the first step of the process according to the invention. In this case, the outlet for gas components other than propane, propylene and molecular oxygen can be located exclusively between the gas mixture 1 and the gas mixture 1 '.

Of course, another outlet can be set up after the target product has been separated. If the recycle gas recirculated to a propane dehydrogenation contains carbon monoxide, it can be catalytically burned to CO ₂ before fresh crude propane is added. The heat of reaction released can be used to heat up to the dehydrogenation temperature.

A catalytic afterburning of CO contained in the residual gas to CO ₂ can also be recommended if the carbon oxides are to be separated from the residual gas before it is recycled as cycle gas in propane dehydrogenation and / or oxydehydrogenation, since CO ₂ can be separated off comparatively easily (e.g. by washing with a basic liquid). Such a catalytic CO afterburning can also be carried out in the dehydrogenation zone, for example on the dehydrogenation catalysts described above (for example those of the DE-A 19937107 , in particular those from Ex. 1 to 4 of this DE-A).

Of course, this can also be done be that one part of the residual gas unchanged returns to the propane dehydrogenation and / or oxydehydrogenation and only separates propane and propylene in the mixture from the remaining part and also in propane dehydrogenation and / or oxide dehydrogenation and / or in the at least one partial zone. United in the latter case one expediently the remaining part of the residual gas with the gas mixture 1 or gas mixture 1 '.

As part of a fractional distillation of the residual gas, a dividing line can be placed, for example, in such a way that essentially all those constituents are separated off in the lifting section of the rectification column and can be drawn off at the top of the column whose boiling point is lower than the boiling point of propylene. These components will primarily be the carbon oxides CO and CO ₂ as well as unreacted oxygen and ethylene as well as methane and N ₂ . For example, heavier-boiling C ₄ hydrocarbons can be separated off in the sump.

If a heterogeneously catalyzed oxydehydrogenation of the propane is used as the first step of the process according to the invention, secondary component separations can also be carried out whenever in the documents DE-A 19837520 . DE-A 19837517 . DE-A 19837519 and DE-A 19837518 Separations from molecular nitrogen are made.

Examples

Heterogeneously catalyzed gas phase partial oxidation of propylene in two fixed bed reactors connected in series by means of various gas mixtures containing propylene and propane 2

A) Description of the general process conditions

1. First fixed bed reactor for the Partial oxidation of propylene to acrolein

• Heat exchange medium used:  Molten salt, consisting of 53% by weight potassium nitrate, 40% by weight of sodium nitrite and 7% by weight sodium nitrate.
• Dimension of the contact tube: 4200 mm total length, 26 mm inside diameter, 30 mm outer diameter, 2 mm wall thickness.
• Reactor: Consists of a double-walled cylinder made of stainless steel (cylindrical guide tube, surrounded by a cylindrical outer container). The wall thicknesses were 2 to 5 mm everywhere. The inner diameter of the outer cylinder was 168 mm. The inside diameter of the guide tube was approx. 60 mm. The double-walled cylinder was closed off at the top and bottom by a lid and base. The contact tube was accommodated in the cylindrical container in such a way that it was led out (sealed) at the upper and lower ends of the same through the cover and bottom by 250 mm in each case. The heat exchange medium was enclosed in the cylindrical container. In order to achieve as uniform a thermal boundary condition as possible over the entire length of the contact tube in the cylindrical container (3700 mm) To ensure conditions on the outer wall of the contact tube, the heat exchange medium was circulated by bubbling nitrogen into the cylindrical container. Using the rising nitrogen, the heat exchange medium in the cylindrical guide tube was conveyed from bottom to top, in order to then flow down again in the space between the cylindrical guide tube and the cylindrical outer container (circulation of the same quality can also be achieved by pumping around (e.g. propeller pumps)). The temperature of the heat exchange medium could be regulated to the desired level by an electrical heater applied to the outer jacket. Otherwise there was air cooling.
• Reactor feed: viewed through the reactor, the molten salt and reaction gas mixture (the respective gas mixture 2) were conducted in countercurrent. The reaction gas mixture entered the top of the reactor. It was conducted into the reaction tube at a temperature of 250 ° C. The salt melt entered at ^the bottom and top with a temperature T ^out of the cylindrical guide tube in the cylindrical guide tube having a temperature T. The difference between T ^and T ^of was about 2 ° C. T ^average = (T ^a + T ^out) / 2.
• Contact tube loading (from top to bottom): Section A: 50 cm long pre-fill of steatite rings of geometry 7 mm × 7 mm × 4 mm (outer diameter × length × inner diameter). Section B: 100 cm length of contact tube feed with a homogeneous mixture of 30% by weight of steatite rings of geometry 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter) and 70% by weight of full catalyst from section C. Section C: 170 cm length of catalyst feed with annular (5 mm × 3 mm × 2 mm = outer diameter × length × inner diameter) full catalyst according to Example 1 of the DE-A 10046957 , Section D: 50 cm length of refill from steatite rings of geometry 7 mm × 7 mm × 4 mm (outer diameter × length × inner diameter).
• Loading of the reactor with reaction gas starting mixture: in all cases 3860 g / h of gas mixture 2.
• Propylene loading of the catalyst feed: 100 NLiter / l · h.

2. Description of the intermediate cooling and Intermediate oxygen feeding

The one leaving the first fixed bed reactor Product gas mixture was used for intermediate cooling (indirectly by means of air) through a connecting pipe (length = 400 mm, inner diameter = 26 mm, wall thickness = 2 mm, material = Stainless steel), that on a length centered of 200 mm, with an inert bed State balls with a diameter of 6 mm are loaded and immediately on the contract tube of the first fixed bed reactor was flanged.

The gas mixture occurred in all cases a temperature of more than 310 ° C into the connecting pipe and left it at a temperature of about 140 ° C. Subsequently were compressed to the gas mixture as an oxygen source 290 NLiter / h Air mixed in.

The resulting feed gas mixture was the fixed bed reactor for the step with a temperature of 220 ° C. the partial oxidation of acrolein to acrylic acid.

3. Second fixed bed reactor for the Partial oxidation of acrolein to acrylic acid

A fixed bed reactor was used the one with that for the first step was identical. Melting salt and reaction gas mixture were about viewed the reactor in cocurrent. The molten salt came below, the reaction gas mixture also.

The contact tube loading (from bottom to top) was:
Section A: 20 cm long pre-fill of steatite rings of geometry 7 mm × 7 mm × 4 mm (outer diameter × length × inner diameter).
Section B: 100 cm length of catalyst feed with a heterogeneous mixture of 30% by weight of steatite rings of geometry 7 mm × 3 mm × 4 mm (outside diameter × length × inside diameter) and 70% by weight coated catalyst from section C.
Section C: 200 cm length of catalyst feed with annular (7 mm × 3 mm × 4 mm = outside diameter × length × inside diameter) coated catalyst according to production example 5 of the DE-A 10046928 ,
Section D: 50 cm length of refill from steatite rings of geometry 7 mm × 7 mm × 4 mm (outer diameter × length × inner diameter).

The second reactor was in all make with nominally approx.

4240 g / h of feed gas mixture loaded. T ^medium is as defined for the first fixed bed reactor.

In all of the following examples the propylene conversion in the first reactor was 97.7 mol% and the Acrolein conversion in the second reactor set to 99.3 mol%.

The T ^means required as a function of the composition of the gas mixture 2 and the yields A ^AA (mol%) of acrylic acid and selectivities of carbon oxide formation S ^COx achieved based on propylene converted via both reactors (mol%) have the following values in the individual examples.

B) Example 1

The composition of the gas mixture 2 was: 6.18 vol.% propylene, 33.1% by volume Propane, 12.3% by volume Oxygen, 0.15 vol .-% CO _x , 46.7% by volume N ₂ , and 1.63 vol.% H ₂ O.
A ^AA = 86.1 mol% T ^medium 1st reactor = 316 ° C.
S ^COx = ^9.2 mol% T ^medium 2nd reactor = 274 ° C.

C) Example 2

The composition of the gas mixture 2 was: 6.04 vol .-% propylene, 42.3 vol% Propane, 10.4 vol .-% Oxygen, 0.15 vol .-% CO _x , 39.5% by volume N ₂ , and 1.60 vol.% H ₂ O.
A ^AA = 85.2 mol% T ^medium 1st reactor = 322 ° C.
S ^COx = 9.9 mol% T ^medium 2nd reactor = 278 ° C.

D) Example 3

The composition of the gas mixture 2 was: 0.20 vol% Ethan, 6.14 vol .-% propylene, 33.0 vol% Propane, 12.2 vol% Oxygen, 0.16 vol .-% CO _x , 46.6 vol .-% N ₂ , and 1.65 vol .-% H ₂ O.
A ^AA = 86.1 mol% T ^medium 1st reactor = 316 ° C.
S ^COx = 9.2 mol% T ^medium 2nd reactor = 274 ° C.

E) Example 4

The composition of the gas mixture 2 was: 0.22 vol% ethylene, 6.13 vol .-% propylene, 33.0 vol% Propane, 12.2 vol% Oxygen, 0.16 vol .-% CO _x , 46.6 vol .-% N ₂ , and 1.64 vol .-% H ₂ O.
A ^AA = 86.1 mol% T ^medium 1st reactor = 316 ° C.
S ^COx = 9.2 mol% T ^medium 2nd reactor = 274 ° C.

F) Example 5

The composition of the gas mixture 2 was: 0.20 vol% n-butane, 6.14 vol .-% propylene, 33.0 vol% Propane, 12.2 vol% Oxygen, 0.16 vol .-% CO _x , 46.6 vol .-% N ₂ , and 1.65 vol .-% H ₂ O.
A ^AA = 85.2 mol% T ^medium 1st reactor = 316.5 ° C.
S ^COx = ^9.9 mol% T ^medium 2nd reactor = 274 ° C.

G) Example 6 The composition of the gas mixture 2 was: 2.02 vol .-% n-butane, 5.98 vol.% propylene, 32.4% by volume Propane, 12.0 vol .-% Oxygen, 0.16 vol .-% CO _x , 45.8% by volume N ₂ , and 1.64 vol .-% H ₂ O.

The desired propylene conversion was not more through an increase of T means within the scope of the catalyst compatibility.

H) Example 7

The composition of the gas mixture 2 was: 0.05 vol .-% Butene-1, 6.16 vol .-% propylene, 33.0 vol% Propane, 12.3% by volume Oxygen, 0.16 vol .-% CO _x , 46.7% by volume N ₂ , and 1.70 vol.% H ₂ O.
A ^AA = 85.1 mol% T ^medium 1st reactor = 318 ° C.
S ^COx = 10 mol% T ^medium 2nd reactor = 281 ° C.

I) Example 8

The composition of the gas mixture 2 was: 0.09 vol% Butene-1, 6.16 vol .-% propylene, 32.9% by volume Propane, 12.3 vol% Oxygen, 0.15 vol .-% CO _x , 46.8 vol% N ₂ , and 1.68 vol.% H ₂ O.
A ^AA = 85.0 mol% T ^medium 1st reactor = 320 ° C.
S ^COx = ^10.2 mol% T ^medium 2nd reactor = 287 ° C.

J) Example 9

The composition of the gas mixture 2 was: 0.20 vol% Butene-1, 6.19 vol.% propylene, 32.7 vol% Propane, 12.3% by volume Oxygen, 0.18 vol% CO _x , 46.7% by volume N ₂ , and 1.71 vol .-% H ₂ O.

The desired propylene conversion could no longer be maintained by increasing T ^medium within the scope of the catalyst compatibility.

Claims (48)

Process for the preparation of at least one partial oxidation and / or ammoxidation product of propylene, in which a) in a first step crude propane in the presence and / or with the exclusion of oxygen of a homogeneous and / or a heterogeneously catalyzed dehydrogenation and / or oxide hydrogenation subjects, whereby a gas mixture 1 containing propane and propylene is obtained, and b) from the gas mixture 1 formed in the first step, from the components contained therein, different from propane and propylene, if necessary, a partial amount is separated and / or converted into other compounds, whereby from a gas mixture 1 'is generated for each gas mixture 1 and a gas mixture 1' containing compounds other than oxygen, propane and propylene, and in at least one further step c) gas mixture 1 and / or gas mixture 1 'as part of a gas mixture 2 of a heterogeneously catalyzed gas phase -Partialoxidation and / or partial gas phase ammoxidation of subject to propylene contained in gas mixture 1 and / or gas mixture 1 ', characterized in that the total content of C ₄ hydrocarbons in the gas mixture 2 is ≤ 3% by volume. Process according to Claim 1, characterized in that the total content of C ₄ hydrocarbons in the gas mixture 2 is ≤ 2.5% by volume. Process according to Claim 1, characterized in that the total content of C ₄ hydrocarbons in the gas mixture 2 is ≤ 2.0% by volume. A method according to claim 1, characterized in that the total content of the gas mixture 2 of C ₄ hydrocarbons is ≤ 1.5 vol .-%. Process according to Claim 1, characterized in that the total content of C ₄ hydrocarbons in the gas mixture 2 is ≤ 1.0% by volume. Process according to Claim 1, characterized in that the total content of C ₄ hydrocarbons in the gas mixture 2 is ≤ 0.5% by volume. A method according to claim 1, characterized in that the total content of the gas mixture 2 C4 hydrocarbons is ≤ 0.3 vol .-%. Process according to Claim 1, characterized in that the total content of C ₄ hydrocarbons in the gas mixture 2 is ≤ 0.1% by volume. Method according to one of claims 1 to 8, characterized in that that this Gas mixture 1 '≥ 0.1 vol .-% on components other than propane and propylene and oxygen contains. Method according to one of claims 1 to 8, characterized in that that this Gas mixture 1 '≥ 0.2 vol% on components other than propane and propylene and oxygen contains. Method according to one of claims 1 to 8, characterized in that that this Gas mixture 1 '≥ 0.3 vol% on components other than propane and propylene and oxygen contains. Method according to one of claims 1 to 8, characterized in that that this Gas mixture 1 '≥ 0.5 vol .-% on components other than propane and propylene and oxygen contains. Method according to one of claims 1 to 8, characterized in that that this Gas mixture 1 '≥ 1 vol .-% on components other than propane and propylene and oxygen contains. Method according to one of claims 1 to 8, characterized in that that this Gas mixture 1 '≥ 3% by volume on components other than propane and propylene and oxygen contains. Method according to one of claims 1 to 8, characterized in that that this Gas mixture 1 '≥ 5 vol .-% on components other than propane and propylene and oxygen contains. Method according to one of claims 1 to 8, characterized in that that this Gas mixture 1 '≥ 10 vol .-% on components other than propane and propylene and oxygen contains. Method according to one of claims 1 to 8, characterized in that that this Gas mixture 1 '≥ 30 vol .-% on components other than propane and propylene and oxygen contains. Method according to one of claims 1 to 17, characterized in that that this Gas mixture 2 contains up to 60 vol .-% of propane. Method according to one of claims 1 to 17, characterized in that that this Gas mixture 2 contains up to 50 vol .-% of propane. Method according to one of claims 1 to 17, characterized in that that this Gas mixture 2 contains 20 to 40 vol .-% propane. Method according to one of claims 1 to 17, characterized in that the gas mixture 2 has the following contents, 7 to 15 vol% O ₂ 5 to 10 vol% propylene, 15 to 40 vol% Propane, 25 to 60 vol% Nitrogen, 1 to 5 vol% Sum of CO, CO ₂ and H ₂ O and 0 to 5 vol% other ingredients, ammonia, if any, is disregarded. Method according to one of claims 1 to 17, characterized in that the gas mixture 2 has the following contents, H ₂ O ≤ 60 vol .-%, N ₂ ≤ 80 vol .-%, O ₂ ≤ 20 vol .-%, CO ≤ 2 vol .-%, CO ₂ ≤ 5 vol.%, Ethane ≤ 10 vol.%, Ethylene ≤ 5 vol.%, Methane ≤ 5 vol.%, Propane> O, ≥ 50 vol.%, Cyclopropane ≤ 0.1 vol .-%, propyne ≤ 0.1 vol.%, Propadiene ≤ 0.1 vol.%, Propylene> O, ≤ 30 vol.%, H ₂ ≤ 30 vol.%, Isobutane ≤ 3 vol .-%, n-butane ≤ 3% by volume, trans-butene-2 ≤ 1% by volume, cis-butene-2 ≤ 1% by volume, butene-1 ≤ 1% by volume, iso- Butene ≤ 1% by volume, butadiene 1.3 ≤ 1% by volume, butadiene 1.2 ≤ 1% by volume, 1-butyne ≤ 0.5% by volume and 2-butyne ≤ 0.5% by volume .-%, whereby ammonia which may be present is not taken into account. Method according to one of claims 1 to 22, characterized in that that this Raw propane ≥ 0.25 vol% contains components other than propane and propylene. Method according to one of claims 1 to 22, characterized in that that this Crude propane ≥ 1% by volume contains components other than propane and propylene. Method according to one of claims 1 to 22, characterized in that that this Crude propane ≥ 2 vol% contains components other than propane and propylene. Method according to one of claims 1 to 22, characterized in that that this Crude propane ≥ 3% by volume contains components other than propane and propylene. Method according to one of claims 1 to 26, characterized in that that this Raw propane contains up to 6 vol .-% of C4 hydrocarbons. Process according to one of claims 1 to 26, characterized in that the crude propane contains 0.1 to 6% by volume of C ₄ hydrocarbons. Process according to one of claims 1 to 28, characterized in that the crude propane meets the following specification: content of propane ≥ 90% by volume, total content of propane and propylene ≤ 99% by volume, total content of C ₄ hydrocarbons ≤ 6 vol%, butene-1 content ≤ 0.5 vol%, total butenes content ≤ 0.5 vol%, ethane content ≤ 10 vol%, ethylene content ≤ 5 vol. -%, content of methane ≤ 5% by volume, content of cyclopropane ≤ 0.1% by volume, content of propylene ≤ 10% by volume, total content of C ₃ hydrocarbons other than propane and propylene ≤ 0.3 Vol .-%, total content of C ₅ hydrocarbons ≤ 0.3 vol .-%, and total content of C _{6 to} C ₈ hydrocarbons ≤ 600 vol.ppm. Method according to one of claims 1 to 29, characterized in that that the Propane conversion in the first step ≥ 5 mol% to ≤ 30 mol% is. Method according to one of claims 1 to 30, characterized in that from the product separates the gas mixture of the gas phase partial oxidation and / or partial gas phase ammoxidation from the at least one partial oxidation and / or ammoxidation product of propylene and at least unreacted propane contained in this product gas mixture in the first step and / or into the gas phase partial oxidation and / or partial gas phase ammoxidation. Method according to one of claims 1 to 31, characterized in that that the inventive method is carried out in a reaction zone on a catalyst feed, whose active mass is at least one multimetal oxide mass which Elements Mo, V, at least one of the two elements Te and Sb, and at least one of the elements from the group comprising Nb, Ta, W, Ti, Al, Zr, Cr, Mn, Ga, Fe, Ru, Co, Rh, Ni, Pd, Pt, La, Bi, B, Contains Ce, Sn, Zn, Si, Na, Li, K, Mg, Ag, Au and In in combination. Process according to Claim 32, characterized in that the active composition is at least one multimetal oxide composition which has the element stoichiometry I Mo ₁ V _a M _b M 1 / cM 2 / d (I), with M ¹ = Te and / or Sb, M ² = at least one of the elements from the group comprising Nb, Ta, W, Ti, Al, Zr, Cr, Mn, Ga, Fe, Ru, Co, Rh, Ni, Pd , Pt, La, Bi, Ce, Sn, Zn, Si, Na, Li, K, Mg, Ag, Au and In, b = 0.01 to 1, c => 0 to 1 and d => 0 to 1 contains. A method according to claim 33, characterized in that M ¹ = Te and M ² = Nb, Ta, W and / or Ti. A method according to claim 33 or 34, characterized in that M ² = Nb. Method according to one of claims 32 to 35, characterized in that that this X-ray diffraction an X-ray diffractogram of the at least one multimetal oxide active material which shows diffraction reflexes h and i, their apex positions at 22.2 ± 0.5 ° (h) and 27.3 ± 0.5 ° (i). A method according to claim 36, characterized in that this X-ray diffraction additionally has a diffraction reflex k, the apex of which is 28.2 ± 0.5 °. A method according to claim 36 or 37, characterized in that the Diffraction reflex h within the X-ray diffractogram is the most intense and a maximum width at half maximum 0.5 °. Method according to Claim 38, characterized in that the half-value width of the diffraction reflex i and the diffraction reflex k is additionally <1 ° at the same time, and the intensity P _{k of} the diffraction reflex k and the intensity Pi of the diffraction reflex i have the relationship 0.20 <R <0, 85, in the R that by the formula R = P i / (P i + P k ) is defined intensity ratio. Method according to claims 32 to 39, characterized in that that this X-ray diffraction the at least one multimetal oxide active material has no diffraction reflex has, whose maximum at 2⦵ = 50 ± 0.3 °. Method according to one of claims 1 to 31, characterized in that that the first step is carried out in a separate reaction zone. A method according to claim 41, characterized in that the the first step is heterogeneously catalyzed dehydrogenation. A method according to claim 41 or 42, characterized in that 1 of the constituents contained therein, other than propane and propylene, are separated off in a portion which comprises at least one C ₄ hydrocarbon. Method according to one of claims 41 to 43, characterized in that that in the heterogeneously catalyzed gas phase partial oxidation and / or partial gas phase ammoxidation, a catalyst is also used, whose active mass contains the elements Mo, Bi and Fe. Process according to one of claims 41 to 44, characterized in that a catalyst is used in the heterogeneously catalyzed gas phase partial oxidation and / or partial gas phase ammoxidation, the active composition of which is a multimetal oxide of the general formula IV Mo ₁₂ Bi _a Fe _b X 1 / cX 2 / dX 3 / eX 4 / fO _n (IV), 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 to 5, b = 0.01 to 5, c = 0 to 10, d = 0 to 2, e = 0 to 8, f = 0 to 10 and n = a number which is determined by the valency and frequency of the elements other than oxygen in (IV). Method according to one of claims 41 to 45, characterized in that that in a heterogeneously catalyzed gas phase partial oxidation is used, whose active composition contains the elements Mo and V. Method according to one of claims 41 to 46, characterized in that a catalyst is used in the heterogeneously catalyzed gas phase partial oxidation, the active composition of which is a multimetal oxide of the general formula VII Mo ₁₂ v _a X 1 / bX 2 / cX 3 / d 3X 4 / e 4X 5 / f 5X 6 / g 6O _n (VII), 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 which is determined by the valency and frequency of the elements in VII other than oxygen. Method according to one of claims 1 to 47, characterized in that that this at least one partial oxidation and / or ammoxidation product of propylene comprising at least one compound from the group Propylene oxide, acrolein, acrylic acid and is acrylonitrile.