WO2005113127A1

WO2005113127A1 - Method for the extended operation of a heterogeneous catalyzed gas phase partial oxidation of at least one organic compound

Info

Publication number: WO2005113127A1
Application number: PCT/EP2005/005334
Authority: WO
Inventors: Martin Dieterle; Gerhard Laqua; Klaus Joachim MÜLLER-ENGEL
Original assignee: Basf Aktiengesellschaft
Priority date: 2004-05-19
Filing date: 2005-05-17
Publication date: 2005-12-01
Also published as: BRPI0511156A; RU2006144830A; KR20070029748A; JP2007538034A; EP1750837A1; TW200611750A

Abstract

The invention relates to a method for the extended operation of a heterogeneous catalyzed gas phase partial oxidation of at least one organic compound on a catalyst bed during which, in order to prevent the deactivation the catalyst bed, the working pressure in the gas phase is increased during the operating period of the catalyst bed.

Description

Process for long-term operation of a heterogeneously catalyzed gas phase partial oxidation of at least one organic compound

description

The present invention relates to a process for the long-term operation of a heterogeneously catalyzed gas phase partial oxidation of at least one organic compound in at least one oxidation reactor, in which the reaction gas starting mixture containing at least one organic compound, molecular oxygen and at least one inert diluent gas is passed through at least one catalyst bed located at elevated temperature.

Complete oxidation of an organic compound with molecular oxygen is understood here to mean that the organic compound is reacted under the reactive action of molecular oxygen in such a way that the total carbon contained in the organic compound in oxides of carbon and that in the organic compound as a whole contained hydrogen is converted into oxides of hydrogen. All of the different reactions of an organic compound under the reactive action of molecular oxygen are summarized here as partial oxidations of an organic compound.

In particular, partial oxidations are to be understood here as reactions of organic compounds under the reactive action of molecular oxygen in which the organic compound to be partially oxidized contains at least one more oxygen atom after the reaction has ended than before the partial oxidation was carried out.

A diluent gas which is essentially inert under the conditions of the heterogeneously catalyzed gas phase partial oxidation is understood to be those diluent gases whose components under the conditions of the heterogeneously catalyzed gas phase partial oxidation - each component considered individually - to more than 95 mol%, preferably more than 99 mol% remain unchanged.

It is generally known that numerous basic chemicals can be produced by partial and heterogeneously catalyzed oxidation of a wide variety of organic compounds with molecular oxygen in the gas phase. Examples include the conversion of propylene to acrolein and / or acrylic acid (see, for example, DE-A 23 51 151), the conversion of tert-butanol, isobutene, isobutane, isobutyraldehyde or the methyl ether of tert. Butanol to methacrolein and / or methacrylic acid (see, for example, DE-A 2526 238, EP-A 92097, EP-A 58927, DE-A 41 32 263, DE-A 41 32 684 and DE-A 40 22 212), the conversion of acrolein to acrylic acid, the conversion of methacrolein to methacrylic acid (cf., for example, DE-A 25 26 238), the conversion of o-xylene, p-xylene or naphthalene to phthalic anhydride (cf. for example EP-A 522 871) or the corresponding acids and the conversion of butadiene to maleic anhydride (see, for example, DE-A 21 06 796 and DE-A 16 24 921), the conversion of n-butane to maleic anhydride (see, for example, GB-A 14 64 198 and GB 12 91 354), the conversion of indanes to, for example, anthraquinone (see, for example, DE-A 20 25 430), the reaction of ethylene to ethylene oxide or from propylene to propylene oxide (see, for example, DE-AS 12 54 137, DE-A 21 59 346, EP-A 372 972, WO 89/0710, DE-A 43 11 608 and Beyer, Textbook of Organic Chemistry, 17th edition (1973), Hirzel Verlag, Stuttgart, p. 261), the reaction of propylene and / or acrolein to acrylonitrile (see, for example, DE-A 23 51 151), the conversion of isobutene and / or methacrolein to methacrylonitrile (ie, the term partial oxidation in this document is also intended to mean partial ammoxidation, ie partial Include oxidation in the presence of ammonia), the oxidative dehydrogenation of hydrocarbons (see, for example, DE-A 23 51 151), the conversion of propane to acrylonitrile or to acr olein and / or acrylic acid (cf. eg DE-A 10 13 1297, EP-A 1090 684, EP-A 608 838, DE-A 10 04 6672, EP-A 529 853, WO 01/96270 and DE-A 10 02 8582), the reaction of iso -Butane to methacrolein and / or methacrylic acid, as well as the reactions of ethane to acetic acid, from ethylene to ethylene oxide, from benzene to phenol and from 1-butene or 2-butene to the corresponding butanediols etc.

The catalysts to be used are usually solids.

The catalysts used are particularly often oxide masses or noble metals (e.g. Ag). In addition to oxygen, the catalytically active oxide composition can only contain another element or more than another element (multi-element oxide compositions). Particularly often used as catalytically active oxide compositions are those which comprise more than one metallic, in particular transition metallic, element. In this case one speaks of multimetal oxide masses. Multielement oxide materials are usually not simple physical mixtures of oxides of the elemental constituents, but heterogeneous mixtures of complex poly compounds of these elements.

Mostly, heterogeneously catalyzed gas phase partial oxidations, in particular the aforementioned ones, are carried out at elevated temperature (generally a few hundred ° C., usually 100 to 600 ° C.).

Since most of the heterogeneously catalyzed gas phase partial oxidations are highly exothermic, they are expediently often carried out in a fluidized bed or in isothermal fixed bed reactors where they are located in a reaction space around which a heat exchange medium is passed for the purpose of indirect heat exchange (for example because of heat dissipation) the catalyst bed can be located as a fixed bed in the contact tubes of a tube bundle reactor, around which a salt melt is passed for heat dissipation). In principle, heterogeneously catalyzed gas phase partial oxidations can also be carried out on catalyst beds located in adiabatic reactors. It is known that the working pressure (absolute pressure) in heterogeneously catalyzed gas phase partial oxidations can be either below 1 bar, at 1 bar or above 1 bar. As a rule, it is 1 to 10 bar, usually 1 to 3 bar.

The target conversion takes place during the residence time of the reaction gas mixture in the catalyst feed through which it is passed.

Because of the generally exothermic character of most heterogeneously catalyzed gas phase partial oxidations of organic compounds with molecular oxygen, the reactants are usually diluted with a gas which is essentially inert under the conditions of the gas phase catalytic partial oxidation and which, with its thermal capacity, is able to absorb the heat of reaction released ,

One of the most common inert diluent gases used is molecular nitrogen, which is automatically used whenever air is used as the oxygen source for the heterogeneously catalyzed gas phase partial oxidation.

Another inert diluent gas that is widely used is water vapor because of its general availability. Both nitrogen and water vapor also advantageously form non-flammable inert diluent gases.

In many cases, cycle gas is also used as an inert diluent gas (see, for example, EP-A 1180508). Circular gas is the residual gas that is used after a single-stage or multi-stage (in the multi-stage heterogeneously catalyzed gas phase partial oxidation of organic compounds, the gas phase partial oxidation is not carried out in one, but in at least two reactors connected in series, in contrast to the single-stage heterogeneously catalyzed gas phase partial oxidation (which are carried out in a common Housing can merge seamlessly), with the addition of oxidizing agents between successive reactors if necessary; the multi-stage is used in particular when the partial oxidation takes place in successive steps; in these cases it is often advisable to apply both the catalyst and the other reaction conditions to the adapt the respective reaction step in an optimizing manner and carry out the reaction step in a separate reactor in a separate reaction stage; however, it can also be used if, for reasons of heat dissipation or for other reasons (cf. eg DE-A 19 90 2562) the turnover is smeared on several reactors connected in series; an example of a frequently two-stage Guided heterogeneously catalyzed gas phase partial oxidation is the partial oxidation of propylene to acrylic acid; in the first reaction stage the propylene is oxidized to acrolein and in the second reaction stage to acrolein to acrylic acid; in a corresponding manner, the methacrylic acid preparation, usually starting from isobutene, is often carried out in two stages; Both of the aforementioned partial oxidations can also be carried out in one stage (both steps in one reactor) if suitable catalyst feeds are used) heterogeneously catalyzed gas phase partial oxidation of at least one organic compound remains when the target product is more or less selectively selected from the product gas mixture (for example by absorption in a suitable solvent ) separated. As a rule, it consists predominantly of the inert diluent gases used for the partial oxidation as well as of water vapor usually formed as a by-product or added as a diluent gas in the partial oxidation and of carbon oxides formed by undesired complete oxidation. In some cases it still contains small amounts of oxygen (residual oxygen) not consumed in the partial oxidation and / or of unreacted organic starting compounds.

The water vapor formed as a by-product ensures in most cases that the partial oxidation proceeds without significant changes in the volume of the reaction gas mixture.

According to the above, in most heterogeneously catalyzed gas-phase partial oxidations of organic compounds, the inert diluent gas used is ≥ 90% by volume, often ≥ 95% by volume, of N ₂ , H ₂ O, and / or CO ₂ and thus essentially from non-flammable inert dilution gases.

The inert diluent gases which are used on the one hand help to absorb the heat of reaction and on the other hand ensure safe operation of the heterogeneously catalyzed gas phase partial oxidation of an organic compound by keeping the reaction gas mixture outside the explosion range. In the case of heterogeneously catalyzed gas phase partial oxidations of unsaturated organic compounds, saturated hydrocarbons, i.e. flammable gases, as inert diluent gases.

It is furthermore known that heterogeneously catalyzed gas phase partial oxidations of at least one organic compound on catalyst beds located in at least one oxidation reactor can be operated essentially continuously over long periods of time on one and the same catalyst beds. The reaction conditions can generally be kept essentially constant.

However, the catalyst bed loses quality over the course of the operating time. As a rule, the activity of the at least one catalyst betts. This is particularly disadvantageous because, as the operating time of the at least one catalyst bed increases, the educt conversion decreases under otherwise constant operating conditions, which reduces the possible space-time yield.

EP-A 990 636 and EP-A 11 06 598 attempt to take account of the above-mentioned development in the long-term operation of a heterogeneously catalyzed gas phase partial oxidation of at least one organic compound on one and the same catalyst bed in that the temperature of the catalyst bed over the course of the operating time is otherwise largely below constant operating conditions is gradually increased in order to essentially maintain the reactant conversion with a single passage of the reaction gas mixture through the at least one catalyst bed.

A disadvantage of the procedure recommended in EP-A 99 636 and in EP-A 11 06 598 is that its aging process generally accelerates with increasing temperature of the catalyst bed, which is why when the temperature of the catalyst bed is reached a maximum value the catalyst bed is usually completely replaced.

EP-A 614 872 and DE-A 10 35 0822 recommend delaying the need for complete replacement of the catalyst by regenerating the catalyst bed from time to time (for example from time to time a hot mixture of molecular oxygen and inert gas through the catalyst bed to lead). However, a disadvantage of this procedure is that it requires an interruption in production over a long period of time.

As a compromise solution, DE-A 10 23 2748 recommends that instead of completely replacing the catalyst bed, only a subset of the same should be replaced by a fresh catalyst feed.

A disadvantage of this proposal is that even with a partial change of the catalyst bed, considerable effort is involved.

It has also already been proposed as a solution to connect a more extensive catalyst bed I, which is comparatively complex in an isothermal reactor, and a smaller catalyst bed II, which is comparatively less complex in an adiabatic reactor, with the objective that the adiabatic reactor begins to help out there , where the isothermal reactor cannot generate the maximum turnover under its own power, so that the exchange of the catalyst bed in the isothermal reactor can be pulled out as long as possible. However, a disadvantage of this procedure is that it requires an increased number of reactors and thus an increased investment.

In view of the prior art described, the object of the present invention was to provide an improved process for the long-term operation of a heterogeneously catalyzed gas phase partial oxidation of at least one organic compound in at least one oxidation reactor and on at least one (one and the same) catalyst bed.

Accordingly, a process for the long-term operation of a heterogeneously catalyzed gas phase partial oxidation of at least one organic compound in at least one oxidation reactor, in which a starting mixture containing the at least one organic compound, molecular oxygen and at least one inert diluent gas is passed through at least one catalyst bed located at elevated temperature, found, which is characterized in that, in order to counteract the deactivation of the at least one catalyst bed, the working pressure in the gas phase, based on an identical loading of the at least one catalyst bed with reaction gas starting mixture in Nl / lh, is increased during the operating time of the catalyst bed.

Pressure increases that occur due to the fact that components contained in the reaction gas mixture separate out in the fixed catalyst bed over the course of the operating time are excluded.

Under the load on a catalyst bed catalyzing a reaction step with reaction gas (starting) mixture, the amount of reaction gas (starting) mixture in standard liters (= Nl; the volume in liters that the corresponding reaction gas (starting) mixture quantity under normal conditions, ie, at 25 ° C and 1 bar), which is passed through one liter of catalyst bed per hour. The load can also relate only to a component of the reaction gas (output) mixture. Then it is the amount of this component in Nl / l-h that is passed through one liter of the catalyst bed per hour.

The increase in the working pressure according to the invention in the gas phase can be achieved in a simple manner, for example, by placing a pressure regulator behind (ie downstream of the at least one oxidation reactor) the (outlet for the reaction gas mixture of) the at least one oxidation reactor containing the at least one catalyst bed ( attaches a device for regulating the working pressure in the at least one oxidation reactor). This can be, for example, a swirl regulator or, in a particularly simple manner, a throttle device, for example a throttle valve. Alternatively, for example, only partially permeable pinholes can be faded into the flow path of the reaction gas mixture, so that Pressure loss of the reaction gas mixture on its flow path and thereby automatically increasing the working pressure with the same load on the at least one catalyst bed with reaction gas starting mixture. Such a pinhole can have, for example, a plurality of through openings (in the simplest case, holes) which can be successively partially or completely closed.

The pressure regulator does not necessarily have to be installed immediately behind the relevant oxidation reactor. Rather, in order to implement the procedure according to the invention, it is sufficient if the pressure control device is introduced into the further flow path of the product gas mixture leaving the oxidation reactor in question and the pressure increase is propagated by backflow into the oxidation reactor. That is, the product gas mixture leaving the oxidation reactor is subsequently fed into the lower region of a column for absorption of the target product in a e.g. in the upper area of the column, the pressure regulator can also be located at the top of the absorption column. However, this variant will generally be less preferred, since column pressures are usually comparatively limited for safety reasons. The absorption behavior could also be adversely affected. The same applies to the case in which the product gas mixture is passed on to the lower region of a column for fractional condensation of the target product. As a rule, the aforementioned columns contain separating internals to enlarge the mass transfer interface.

When oxidation reactors are connected in series, a pressure control device can be installed behind each of the individual reactors in the sense of the invention.

The success of the procedure according to the invention is presumably due to the fact that the increase in pressure is accompanied by an increase in the residence time of the reactants on the catalyst surface. This increased residence time is then presumably sufficient to enable the target reaction again at reaction centers which have already been deactivated to a certain extent. In addition, the measure according to the invention is accompanied by increased partial pressures of the relevant reactants.

How high the increase in the working pressure in the process according to the invention is selected in the individual case depends both on the extent of the deactivation of the catalyst bed at the time of the increase in the working pressure and on the reaction system in detail. According to the invention, the increase in the working pressure (in this document, for reasons of standardization, always refers to the entry point of the reaction gas mixture into the catalyst bed, to which inert pre-fillings are added in this connection) will be at least 25 mbar or at least 50 mbar before that Catalyst bed is partially or completely replaced. In As a rule, the aforementioned increase in working pressure in the method according to the invention is 25 or 50 mbar to 3000 mbar, often 100 mbar to 2500 mbar, often 200 to 2000 mbar, often 300 to 1500 mbar, sometimes 400 to 1000 mbar and not infrequently 500 to 750 mbar be.

Advantageously according to the invention, the pressure increase according to the invention is carried out continuously and in accordance with the deactivation rate of the at least one catalyst bed (a measure of the activity is the temperature which is required to achieve the same starting material conversion, based on a single pass of the reaction gas mixture, with the same load on the catalyst bed and the same working pressure through the catalyst bed). But it can also be done in stages.

The maximum value of the increase in working pressure according to the invention is generally reached when a further decrease in the working pressure is accompanied by a significant reduction in the selectivity of the target product formation. The latter can e.g. then occur when the residence times of the reactants on the catalyst surface at the still fully active centers lead to increasing full combustion, which reduces the yield of the target product. However, such a reduction in selectivity can e.g. be accepted with approval if the demanded sales would otherwise only be achievable at temperatures that e.g. damage the catalyst and / or the reactor.

This influence on selectivity is normally also the reason why the heterogeneously catalyzed gas phase partial oxidation of at least one organic compound on the catalyst bed is not carried out from the start at the greatest possible working pressure. Finally, increased working pressures also result in increased reaction gas starting mixture compression costs. Another limitation for the pressure increase according to the invention can be the resulting difference between the highest and the lowest temperature in the catalyst bed, since in many partial oxidations this difference is frequently 100 100 ° C, preferably 80 80 ° C or 60 60 ° C or 40 40 ° C, or ≤ 20 ° C, or ≤ 10 ° C.

The working pressures at the start of the process according to the invention will often be 1.2 to 2 bar. By contrast, when the catalyst bed is replaced, the working pressure, according to the invention, will typically be up to 3 bar.

Basically, the process according to the invention is suitable for all heterogeneously catalyzed gas phase partial oxidations specifically mentioned at the beginning of this document. These include in particular the heterogeneously catalyzed gas phase partial oxidation of propane to acrylic acid described in the documents WO 01/96270, DE-A 10316465, DE-A 10245585, DE-A 10246119. The aforementioned writings are to be regarded as an integral part of this writing. However, the procedure according to the invention is particularly suitable for the heterogeneously catalyzed fixed bed gas phase partial oxidation of propene to acrolein and / or acrylic acid, which is preferably carried out in one step in the tube bundle reactor, and for the first and second stage of a heterogeneously catalyzed fixed bed gas phase partial oxidation of propene to acrolein in tube bundle reactors or from acrolein to acrylic acid, as described, for example, in EP-A 700 893, EP-A 700 714, DE-A 19 91 0508, DE-A 19 91 9596, DE-A 10351269, DE-A 10350812, DE - A 10350822, EP-A 11 59 247, DE-A 10 31 3208, DE-A 102004021764, DE-A 19 94 8248, EP-A 990 636. EP-A 11 06 598, DE-A 30 02 8289 and DE-A 10232482 are described.

The process according to the invention is suitable for a heterogeneously catalyzed gas phase fixed bed partial oxidation of propene to acrolein, in particular when catalysts are used whose active composition is a multi-element oxide which contains the elements molybdenum and / or tungsten and at least one of the elements bismuth, tellurium, Contains antimony, tin and copper or is a multmetallic oxide containing the elements Mo, Bi and Fe. Multimetal oxide compositions of the aforementioned type which are particularly suitable according to the invention are Mo, Bi and Fe and are, in particular, the multimetal oxide compositions disclosed in DE-A 10 34 4149 and DE-A 10 34 4264. These are in particular the multimetal oxide active compositions of the general formula I in DE-A 19 95 5176, the multimetal oxide active compositions of the general formula I of DE-A 19 94 8523, the multimetal oxide active compositions of the general formulas I, II and III in DE-A 10 10 1695 , the multimetal oxide active compositions of the general formulas I, II and III of DE-A 19 94 8248 and the multimetal oxide active compositions of general formulas I, II and III of DE-A 19 95 5168 and the multimetal oxide active compositions mentioned in EP-A 700 714.

It is also suitable to use the process according to the invention if, for the at least one fixed catalyst bed to be used according to the invention in the case of the partial oxidation of propene to acrolein, the multimetal oxide catalysts containing Mo, Bi and Fe, which are described in the documents DE-A 10 04 6957, DE -A 10 06 3162, DE- C 33 38 380, DE-A 19 90 2562, EP-A 15 565, DE-C 23 80 765, EP-A 807 465, EP-A 279 374, DE-A 33 00 044, EP-A 575 897, US-A 4 438 217, DE-A 19 85 5913, WO 98/24746, DE-A 19 74 6210 (those of the general formula II), JP-

A 91/294 239, EP-A 293 224 and EP-A 700 714 are used. This applies in particular to the exemplary embodiments in these documents, among which those of EP-A 15565, EP-A 575 897, DE-A 19 74 6210 and DE-A 19 85 5913 are particularly preferred. Particularly noteworthy in this context are a catalyst according to Example 1c from EP-A 15 565 and a catalyst to be produced in a corresponding manner, the active composition of which, however, has the composition Mθι ₂ Ni ₆ , ₅ Zn ₂ Fe ₂ Bi ₁ Po _ι oo ₆₅ Ko , o ₆ θx • 10 SiO ₂ . Furthermore are to emphasize the example with the current No. 3 from DE-A 19855913 (stoichiometry: Mθi ₂ Co ₇ Fe ₃ Bi ₀ , ₆ Ko _, o ₈ Siι, ₆ θx) as a hollow cylinder full catalyst of geometry

5 mm x 3 mm x 2 mm or 5 mm x 2 mm x 2 mm (in each case outer diameter x height x inner diameter) and the multimetal oxide II full catalyst according to Example 1 of DE-A 19 74 6210. Furthermore, the multimetal oxide catalysts would be the

To name US-A 4438217. The latter applies in particular if it has a hollow cylinder geometry of the dimensions 5.5 mm × 3 mm × 3.5 mm, or 5 mm × 2 mm × 2 mm, or 5 mm × 3 mm × 2 mm, or 6 mm x 3 mm x 3 mm, or 7 mm x 3 mm x 4 mm

(each outer diameter x height x inner diameter). The multimetal oxide catalysts and geometries of the are also suitable in the sense of the invention

DE-A 10 10 1695 and WO 02/062737.

Further, the Example 1 of DE-A 10046957 (stoichiometry: [Bi ₂ W ₂ O ₉ x 2WO _3] o, ₅ •

as a hollow cylinder (ring) fully catalytic converter with a geometry of 5 mm x 3 mm x 2 mm or 5 mm x 2 mm x 2 mm (in each case outer diameter x length x inner diameter), and shell catalysts 1, 2 and 3 from DE-A 10063162 (stoichiometry:

however, applied as ring-shaped shell catalysts of appropriate shell thickness and on carrier rings of the geometry 5 mm x 3 mm x 1.5 mm or 7 mm x 3 mm x 1.5 mm (in each case outer diameter x length x inner diameter), well suited in the sense according to the invention.

A large number of multimetal oxide active compositions which are particularly suitable for the catalysts of propene partial oxidation to acrolein in the sense according to the invention can be obtained using the general formula I,

Mo ₁₂ Bi _a F _eb X ¹ _c X ² _d X ³ eX ⁴ (I),

in which the variables have the following meaning:

X ¹ = nickel and / or cobalt,

X ² = thallium, an alkali metal and / or an alkaline earth metal,

X ³ = zinc, phosphorus, arsenic, boron, antimony, tin, cerium, lead and / or tungsten,

X ⁴ = silicon, aluminum, titanium and / or zirconium,

a = 0.5 to 5, b = 0.01 to 5, preferably 2 to 4, c = 0 to 10, preferably 3 to 10, d = 0 to 2, preferably 0.02 to 2, e = 0 to 8 , preferably 0 to 5, f = 0 to 10 and n = a number which is determined by the valency and frequency of the elements in I other than oxygen, subsumed.

They are available in a manner known per se (see, for example, DE-A 4023239) and are usually shaped into spheres, rings or cylinders in bulk or else 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 I can be prepared in a simple manner by producing an intimate, preferably finely divided, dry mixture of suitable elemental constituents according to their stoichiometry 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 materials I are those compounds which are already oxides and / or those compounds which can be converted into oxides by heating, at least in the presence of oxygen.

In addition to the oxides, such starting compounds are, above all, 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 CHO ₂ , CH ₃ COOH, NH ₄ CH ₃ CO ₂ and / or ammonium oxalate, which can decompose and / or decompose into gaseous escaping compounds at the latest 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 compositions I can take place in dry or in wet form. If it is carried out in dry form, the starting compounds are expediently used as finely divided powders and, after mixing and, if appropriate, compaction, are subjected to the calcination. However, the intimate mixing is preferably carried out in wet form. Usually, the starting compounds are mixed together in the form of an aqueous solution and / or suspension. Particularly intimate dry mixtures are obtained in the mixing process described if only sources of the elementary constituents present in dissolved form are used. Water is preferably used as the solvent. The aqueous mass obtained is then dried, the drying process preferably being carried out by spraying. drying of the aqueous mixture with exit temperatures from the spray tower of 100 to 150 ° C.

The multimetal oxide active compositions of the general formula I are usually used in the fixed catalyst bed not in powder form but in the form of specific catalyst geometries, it being possible for the shaping to take place before or after the final calculation. For example, full catalysts can be produced from the powder form of the active composition or its uncalcined and / or partially calcined precursor composition by compressing it to the desired catalyst geometry (e.g. by tableting, extruding or extruding). Graphite or stearic acid can be added as lubricants and / or molding aids and reinforcing agents such as microfibers made of glass, asbestos, silicon carbide or potassium titanate. Suitable unsupported catalyst geometries are e.g. Solid cylinder or hollow cylinder with an outer diameter and a length of 2 to 10 mm. In the case of the hollow cylinders, a wall thickness of 1 to 3 mm is appropriate. Of course, the full catalyst can also have a spherical geometry, the spherical diameter being 2 to 10 mm.

A particularly favorable hollow cylinder geometry is 5 mm x 3 mm x 2 mm (outer diameter x length x 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 usually carried out in a suitable rotatable container, as is e.g. is known from DE-A 2909671, EP-A 293859 or from EP-A 714700. For coating the support bodies, the powder mass to be applied is expediently moistened and, after application, e.g. using hot air, dried again. 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. Alternatively, the powder mass to be applied can also be applied directly from its suspension or solution (e.g. in water) to the carrier body.

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 in the first reaction stage. The carrier bodies can have a regular or irregular shape, with regularly shaped carrier bodies with clearly The surface roughness, for example balls or hollow cylinders, are preferred. It is suitable to use essentially non-porous, rough-surface, spherical supports made of steatite (for example steatite C220 from CeramTec), 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 (for example 8 mm) and the outside diameter of 4 to 10 mm (for example 6 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 x 3 mm x 4 mm or 5 mm x 3 mm x 2 mm (outer diameter x length x inner diameter) are particularly suitable as carrier bodies. The fineness of the catalytically active oxide compositions 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 which are particularly suitable for the catalysts of the fixed catalyst bed of a propene partial oxidation to acrolein in the sense of the invention are also compositions of the general formula II, [Y ¹ ..Y ^a _b .O _J ,] p [Y ³ _c .Y _tf Y ^5. -Y ^β fYVY ² h-0] _q (II),

in which the variables have the following meaning:

Y ¹ = only bismuth or bismuth and at least one of the elements tellurium, antimony, tin and copper,

Y ² = molybdenum or molybdenum and tungsten,

Y ³ = an alkali metal, thallium and / or samarium,

Y ⁴ = an alkaline earth metal, nickel, cobalt, copper, manganese, zinc, tin, cadmium and / or mercury, Y ⁵ = iron or iron and at least one of the elements chromium and cerium,

Y ⁶ = phosphorus, arsenic, boron and / or antimony,

Y ⁷ = a rare earth metal, titanium, zirconium, niobium, tantalum, rhenium, ruthenium, rhodium, silver, gold, aluminum, gallium, indium, silicon, germanium, lead, thorium and / or uranium,

a '= 0.01 to 8, b' = 0.1 to 30, c '= 0 to 4, d' = 0 to 20, e '> 0 to 20, f = 0 to 6, g' = 0 to 15 h '= 8 to 16, x' = numbers determined by the valency and frequency of elements other than oxygen in II and p, q = numbers whose ratio p / q is 0.1 to 10,

containing three-dimensionally extended areas of the chemical composition Y ¹ _a Y ² _b O _X ', which are separated from their local surroundings due to their composition which is different from their local surroundings, the size of which (longest direct connecting section 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 masses II are those in which Y ^{1 is} only bismuth.

Of these, those which have the general formula III,

[Z ² ₁₂ Z ³ _c .Z ⁴ _d .Fe _e -Z ⁵ rZ ⁶ _g -Z ⁷ _h -O _y .] _Q. (III)

in which the variants have the following meaning:

Z ² = molybdenum or molybdenum and tungsten,

Z ³ = nickel and / or cobalt,

Z ⁴ = thallium, an alkali metal and / or an alkaline earth metal, Z ⁵ = phosphorus, arsenic, boron, antimony, tin, cerium and / or lead,

Z ⁶ = silicon, aluminum, titanium and / or zirconium,

Z ⁷ = copper, silver and / or gold,

a "= 0.1 to 1, b" = 0.2 to 2, c "= 3 to 10, d" = 0.02 to 2, e "= 0.01 to 5, preferably 0.1 to 3, f = 0 to 5, g "= 0 to 10, h" = 0 to 1, x ", y" = numbers determined by the valency and frequency of the element in III other than oxygen, p ", q" = Numbers whose ratio p'Yq "is 0.1 to 5, preferably 0.5 to 2,

correspond, those masses III being particularly preferred in which

Z ² _b "= (tungsten) t," and Z ² ₁₂ = (molybdenum) ^. 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 Υ ² _b O _x ] p ([Bi _a »Z ² " O _X "] p") of the multimetal oxide compositions II (multimetal oxide compositions III) which are suitable according to the invention in the multimetal oxide compositions II (multimetal oxide compositions III) which are suitable according to the invention in the form of three-dimensionally extended regions of the chemical composition which are differentiated from their local environment on account of their chemical composition and their local environment chemical composition Y ¹ _a Y _b O _x - [Bi _a »Z ² b-Oχ") are present, the largest diameter of which is in the range 1 nm to 100 μm.

With regard to the shape, what has been said about the multimetal oxide mass I catalysts applies to multimetal oxide mass II catalysts.

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

In the sense of the invention, the multimetal oxides known for this type of reaction and containing the elements Mo and V are suitable as active mass for catalysts of at least one fixed catalyst bed suitable for the partial oxidation of acrolein to acrylic acid.

Such Mo and V-containing multimetal oxide active compositions can be described, for example, in US Pat. No. 3,775,474, US Pat. No. 3,954,555, US Pat. No. 3,893,951 and US Pat. No. 4,339,355, or EP-A 614872 or EP-A 1041062 or WO 03/055835 or WO 03/057653 can be found.

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

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

A large number of these multimetal oxide active compositions containing the elements Mo and V can be obtained using the general formula IV,

Mo ₁₂ V _a X ¹ _b X ² _c X ³ _d X ⁴ _e X ⁵ , X ⁶ „O _n (IV), in which the variables have the following meaning:

X ¹ = W, Nb, Ta, Cr and / or Ce,

X ² = Cu, Ni, Co, Fe, Mn and / or Zn, X ³ = Sb and / or Bi,

X ⁴ = one or more alkali metals,

X ⁵ = one or more alkaline earth metals,

X ⁶ = Si, Al, Ti and / or Zr, a = 1 to 6, b = 0.2 to 4, c = 0.5 to 18, d = 0 to 40, e = 0 to 2, f = 0 to 4, g = 0 to 40 and n = a number which is determined by the valency and frequency of the elements other than oxygen in IV,

subsumed.

Preferred embodiments within the active multimetal oxides IV in the sense of the invention are those which are covered by the following meanings of the variables of the general formula IV:

X ¹ = W, Nb, and / or Cr,

X ² = Cu, Ni, Co, and / or Fe,

X ³ = Sb,

X ⁴ = Na and / or K,

X ⁵ = Ca, Sr and / or Ba, X ⁶ = Si, Al, and / or Ti, a = 1.5 to 5, b = 0.5 to 2, c = 0.5 to 3, d = 0 to 2, e = 0 to 0.2, f = 0 to 1 and n = a number which is determined by the valency and frequency of the elements in IV other than oxygen.

However, very particularly preferred multimetal oxides IV in the sense of the invention are those of the general formula V Mo ₁₂ V _a Υ ¹ _b .Y ² _c .Y ⁵ _f Y ⁶ _g O _n (V),

With

Y ¹ = W and / or Nb,

Y ² = Cu and / or Ni,

Y ⁵ = Ca and / or Sr,

Y ⁶ - Si and / or Al, a "= 2 to 4, b '= I to 1, 5, c' = 1 to 3, f = 0 to 0.5 g '= 0 to 8 and n' = one Number that is determined by the valency and frequency of the elements in V other than oxygen.

Multimetal oxide active compositions (IV) are known per se, e.g. available in DE-A 43 35 973 or in EP-A 714 700. Particularly suitable as Mo and V-containing multimetal oxide active compositions in the sense of the invention for the partial oxidation of acrolein to acrylic acid, but also the multimetal oxide active compositions of DE-A 10 261 186.

In principle, such Mo and V-containing multimetal oxide active compositions, in particular those of the general formula IV, can be prepared in a simple manner by producing an intimate, preferably finely divided, dry mixture of suitable stoichiometry from suitable sources of their elemental constituents and this at temperatures of Calcined at 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 mentioned reducing gases by themselves) are carried out. 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.

The intimate mixing of the starting compounds for the production of multimetal oxide compositions IV can be carried out in dry or in wet form. If it is carried out in dry form, the starting compounds are expediently in the form of finely divided powders used and subjected to calcination after mixing and optionally compressing. However, the intimate mixing is preferably carried out in wet form.

Usually, the starting compounds are mixed with one another in the form of an aqueous solution and / or suspension. Particularly intimate dry mixtures are obtained in the mixing process described if only sources of the elementary constituents present in dissolved form are used. Water is preferably used as the solvent. The aqueous mass obtained is then dried, the drying process preferably being carried out by spray drying the aqueous mixture at exit temperatures of 100 to 150 ° C.

The multi-metal oxide active materials containing Mo and V, in particular those of the general formula IV, can be used for the partial oxidation of acrolein to acrylic acid according to the invention, both in powder form and in the form of certain catalyst geometries, the shaping being able to take place before or after the final calcination. For example, full catalysts can be produced from the powder form of the active composition or its uncalcined precursor composition by compression to the desired catalyst geometry (e.g. by tableting, extrusion or extrusion), where appropriate auxiliaries such as e.g. Graphite or stearic acid can be added as a lubricant and / or molding aid and reinforcing agent such as microfibers made of glass, asbestos, silicon carbide or potassium titanate. Suitable unsupported catalyst geometries are e.g. Solid cylinder or hollow cylinder with an outer diameter and a length of 2 to 10 mm. In the case of hollow cylinders, a wall thickness of 1 to 3 mm is advisable. Of course, the full catalyst can also have a spherical geometry, the spherical diameter being 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 usually carried out in a suitable rotatable container, as is e.g. is known from DE-A 2909671, EP-A 293859 or from EP-A 714700.

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 mass 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. It is suitable to use essentially non-porous, rough-surface, spherical supports made of steatite, the diameter of which is 1 to 10 mm (for example 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 suitable as support bodies according to the invention, the wall thickness is moreover usually 1 to 4 mm. Annular support bodies to be used preferably according to the invention have a length of 3 to 6 mm, an outer diameter of 4 to 8 mm and a wall thickness of 1 to 2 mm. Particularly suitable according to the invention are rings with a geometry of 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter) as support bodies. The fineness of the catalytically active oxide compositions 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 containing Mo and V, to be used in the sense of the invention for an acrolein partial oxidation to acrylic acid, are also compositions of the general formula VI,

[D] _p [E] _q (VI),

in which the variables have the following meaning:

D = Mo ₁₂ V _a .Z ¹ _b .Z ² _c .Z ³ _d .Z ⁴ _e "Z ⁵ _r Z ⁶ _g -O _x -,

E = Z ⁷ ₁₂ Cu _h .H _r O _v .,

Z ¹ = W, Nb, Ta, Cr and / or Ce, z ² = Cu, Ni, Co, Fe, Mn and / or Zn, z ³ = Sb and / or Bi, z ⁴ = Li, Na, K, Rb, Cs and / or H z ⁵ = Mg, Ca, Sr and / or Ba, z ⁶ = Si, Al, Ti and / or Zr, z ⁷ = Mo, W, V, Nb and / or Ta,

a "= 1 to 8, b" = 0.2 to 5, c "= 0 to 23, d" = 0 to 50, e "= 0 to 2, f = 0 to 5, g "= 0 to 50, h" = 4 to 30, i "= 0 to 20 and x", y "= numbers which are determined by the valency and frequency of the elements other than oxygen in VI 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 _κ .H _r O (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 ₁₂ V _a .ZVZ ² _c .Z ³ _d .Z ⁴ _e .Z ⁵ _f Z ⁶ _g . (D),

contains (starting mass 2), incorporated in the desired ratio p: q, 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 those multimetal oxide active materials VI in which the preformed solid starting material 1 is incorporated into an aqueous starting material 2 at a temperature <70 ° C. A detailed description of the production of multimetal oxide III Ill catalysts contains e.g. EP-A 668104, DE-A 19736105 and DE-A 19528646.

With regard to the shape, the statements made with regard to the multimetal oxide active compositions IV catalysts apply with regard to multimetal oxide active compositions VI catalysts.

Other multimetal oxide active compositions containing Mo and V which are favorable in the sense described are also multielement oxide active compositions of the general formula VII,

in which the variables have the following meaning:

A = Mo ₁₂ V _a X ¹ _b X ² _c X ³ _d X _e X ⁵ _f X ⁶ _g O _x , B = X CU _h HiOy, C = X ^ Sb _j H _k Oz, X ¹ = W, Nb, Ta, Cr and / or Ce, preferably W, Nb and / or Cr,

X ² = Cu, Ni, Co, Fe, Mn and / or Zn, preferably Cu, Ni, Co and / or Fe,

X ³ = Sb and / or Bi, preferably Sb,

X ⁴ = Li, Na, K, Rb, Cs and / or H. preferably Na and / or K, X ⁵ = Mg, Ca, Sr and / or Ba, preferably Ca, Sr and / or Ba,

X ⁶ = Si, Al, Ti and / or Zr, preferably Si, Al and / or Ti,

X ⁷ = Mo, W, V, Nb and / or Ta, preferably Mo and / or W,

X ⁸ = Cu, Ni, Zn, Co, Fe, Cd, Mn, Mg, Ca, Sr and / or Ba, preferably Cu and / or Zn, particularly preferably Cu,

a = 1 to 8, preferably 2 to 6, b = 0.2 to 5, preferably 0.5 to 2.5 c = 0 to 23, preferably 0 to 4, d = 0 to 50, preferably 0 to 3, e = 0 to 2, preferably 0 to 0.3, f = 0 to 5, preferably 0 to 2, g = 0 to 50, preferably 0 to 20, h = 0.3 to 2.5, preferably 0.5 to 2 , particularly preferably 0.75 to 1.5, i = 0 to 2, preferably 0 to 1, j = 0.1 to 50, preferably 0.2 to 20, particularly preferably 0.2 to 5, k = 0 to 50 , preferably 0 to 20, particularly preferably 0 to 12, x, y, z = numbers which are determined by the valency and frequency of the elements in A, B, C other than oxygen, p, q = positive numbers r = 0 or a positive number, preferably a positive number, the ratio p / (q + r) = 20: 1 to 1:20, preferably 5: 1 to 1:14 and particularly preferably 2: 1 to 1: 8 and, for the If r is a positive number, the ratio q / r = 20: 1 to 1:20, preferably 4: 1 to 1: 4, particularly preferably 2: 1 to 1: 2 and very particularly is preferably 1: 1,

which the portion [A] p in the form of three-dimensionally extended areas (phases) A of the chemical composition

A: Mo ₁₂ VaX ¹ _b X ² _c X ³ _d X ⁴ eX ⁵ _f X ⁶ gO _x ,

the proportion [B] _q in the form of three-dimensionally extended areas (phases) B of the chemical composition

B: X CU _h HiOy and

the proportion [C] _r in the form of three-dimensionally extended areas (phases) C of the chemical composition

included, the areas A, B and optionally C being distributed relative to one another as in a mixture of finely divided A, finely divided B and optionally finely divided C, and all variables within the predetermined ranges being selected with the proviso that the molar fraction of the element Mo in the total amount of all elements of the multielement oxide active composition VII other than oxygen is 20 mol% to 80 mol%, the molar ratio of Mo contained in the catalytically active multielement oxide composition VII to V, Mo contained in the catalytically active multielemethylene oxide composition VII / V, 15: 1 to 1: 1, the corresponding molar ratio Mo / Cu 30: 1 to 1: 3 and the corresponding molar ratio Mo / (total amount of W and Nb) is 80: 1 to 1: 4.

Preferred multielement oxide active materials VII in the sense of the invention are those whose regions A have a composition in the subsequent stoichiometric grid of the general formula VIII,

Mo ₁₂ V _a X Λ ¹ _b X v2% X γ5 ^ö _f Xv6 ⁶ _g O _x (VIII),

With

X ¹ zz W and / or Nb,

X ² = Cu and / or Ni,

X ⁵ = Ca and / or Sr,

X ⁶ = Si and / or Al, a = 2 to 6, b = 1 to 2, c = 1 to 3, f = 0 to 0.75, g = 0 to 10, and

X ⁼ a number which is determined by the valency and frequency of the elements other than oxygen in (VIII).

The term “phase” used in connection with the multielement oxide active materials VIII means three-dimensionally extended regions whose chemical composition is different from that of their surroundings. The phases are not necessarily homogeneous by X-ray diffraction. Phase A generally forms a continuous phase in which particles of the Phase B and optionally C are dispersed.

The finely divided phases B and optionally C advantageously consist of particles whose size diameter, ie the longest, go through the center of gravity of the particles. de connecting distance of two points on the surface of the particles is up to 300 μm, preferably 0.1 to 200 μm, particularly preferably 0.5 to 50 μm and very particularly preferably 1 to 30 μm. Particles with a size of 10 to 80 μm or 75 to 125 μm are also suitable.

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

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

The basic principle of the production of intimate dry mixtures, which lead to multielement oxidative compositions of the general formula VII when subjected to thermal treatment, is to use at least one multielement oxide composition B (X / CU _h HOy) as starting mass 1 and optionally one or more multielement oxide compositions C (X ^ Sb _j H _k Oz) as the starting mass 2, either separately from one another or associated with one another in a finely divided form, and then the starting masses 1 and optionally 2 with a mixture, the swelling of the elementary constituents of the multielement oxide mass A Mo ₁₂ V _a X _b ¹ X _c ² X _d ³ X _e ⁴ X _f ⁵ X _g ⁶ O _x (A),

in a composition corresponding to stoichiometry A, in intimate contact in the desired quantitative ratio (according to general formula VII) and optionally drying the resulting intimate mixture.

The intimate contact of the constituents of the starting materials 1 and optionally 2 with the mixture containing the sources of the elemental constituents of the multimetal oxide composition A (starting material 3) can be carried out either dry or wet. In the latter case, it is only necessary to ensure that the preformed phases (crystallites) B and possibly C do not go into solution. The latter is guaranteed in aqueous medium at pH values that do not deviate too much from 7 and that are usually guaranteed at not too high temperatures. If the intimate contact takes place wet, the final drying step is normally normally to the intimate dry mixture to be thermally treated according to the invention (for example by spray drying). Such a dry mass is automatically obtained during dry mixing. Of course, the finely pre-formed phases B and optionally C can also be converted into a plastically deformable mixture which is the source of the elementary constituents of the multimetal oxide mass A can be incorporated, as recommended by DE-A 10046928. Of course, the intimate contact of the constituents of starting materials 1 and optionally 2 with the sources of multielement oxide material A (starting material 3) can also be carried out as described in DE-A 19815281.

The thermal treatment to obtain the active composition and the shaping can be carried out as described for the multimetal oxide active compositions IV to VI.

In general, multimetal oxide active compositions IV to VN catalysts can advantageously be produced in accordance with the teaching of DE-A 10 325 487 or DE-A 10 325 488.

The reaction stage (and the use of the procedure according to the invention in the same) from propene to acrolein can be carried out in a simple manner and in terms of application technology using the catalysts described for the corresponding fixed catalyst bed in a tube bundle reactor charged with the fixed bed catalysts, as described e.g. in EP-A 700 714 or DE-A 4 431 949 or WO 03/057653, or WO 03/055835, or WO 03/059857, or WO 03/076373.

This means that the fixed catalyst bed is in the simplest way in the uniformly charged metal tubes of a tube bundle reactor and a tempering medium (single-zone mode), usually a molten salt, is passed around the metal tubes. Salt melt (temperature control medium) and reaction gas mixture can be carried out in simple cocurrent or countercurrent. However, the temperature control medium (the salt melt) can also be passed through the reactor, viewed in a meandering manner, around the tube bundle, so that, viewed over the entire reactor, there is a cocurrent or countercurrent to the direction of flow of the reaction gas mixture. The volume flow of the temperature control medium (heat exchange medium) is usually dimensioned such that the temperature rise (due to the exothermic nature of the reaction) of the heat exchange medium from the entry point into the reactor to the exit point from the reactor 0 to 10 ° C, often 2 to 8 ° C , is often 3 to 6 ° C. The inlet temperature of the heat exchange medium in the tube bundle reactor is usually 250 to 450 ° C, often 300 to 400 ° C or 300 to 380 ° C. The associated reaction temperatures then also move in these temperature ranges. Fluid heat transfer media are particularly suitable as heat exchange medium. The use of melts of salts such as potassium nitrate, potassium nitrite, sodium nitrite and / or sodium nitrate, or of low-melting metals such as sodium, mercury and alloys of various metals is particularly favorable. Ionic liquids can also be used.

The reaction gas starting mixture is advantageously fed to the feed with fixed bed catalyst preheated to the desired reaction temperature. Especially in the case of the desired high (e.g. ≥ 130 Nl / lh, or ≥ 140 Nl / lh, or ≥ 150 Nl / lh, or ≥ 160 Nl / lh, but usually ≤ 600 Nl / lh, often ≤ 350 Nl / lh) The propene partial oxidation process is advantageously carried out in a two- or multi-zone tube bundle reactor (loads in the single-zone tube bundle reactor are also possible, however). A preferred variant of a two-zone tube bundle reactor which can be used according to the invention for this purpose is disclosed in DE-C 2830765. But also those in DE-C 2513405, US-A 3147084, DE-A 2201528, EP-A 383224 and DE-A 2903582 disclosed two-zone tube bundle reactors are suitable. EP-A 1106598 also gives a description of the process.

In other words, the at least one fixed catalyst bed to be used according to the invention is then located in the uniformly charged metal tubes of a tube bundle reactor, and two temperature-regulating media, generally molten salts, which are essentially spatially separated from one another, are guided around the metal tubes. The pipe section over which the respective salt bath extends represents a reaction zone.

Preferably flows around e.g. a salt bath A is the section of the tubes (reaction zone A) in which the oxidative conversion of the propene (in a single pass) takes place until a conversion value in the range from 40 to 80 mol% is reached, and a salt bath B flows around the section of the tubes (the reaction zone B), in which the oxidative subsequent conversion of the propene (in a single pass) until a conversion value of at least as a rule is reached

93 mol% takes place (if necessary, reaction zones A, B can be followed by further reaction zones which are kept at individual temperatures).

In principle, the salt bath can be conducted within the respective temperature zone as in the single-zone mode. The inlet temperature of salt bath B is normally at least 5 to 10 ° C. above the temperature of salt bath A. Otherwise, the inlet temperatures can be in the temperature range recommended for the single-zone procedure for the inlet temperature.

Otherwise, the two-zone high-load procedure of propene partial oxidation to acrolein e.g. as in DE-A 10 30 8836, EP-A 11 06 598, or as in WO 01/36364, or DE-A 19 92 7624, or DE-A 19 94 8523, DE-A 10 31 3210, DE-A 10 31 3213 or as described in DE-A 19 94 8248.

In general, the process according to the invention is suitable for propene partial oxidation to acrolein for propene loads on the fixed catalyst bed of 70 70 Nl / lh, or ≥ 70 Nl / lh, ≥ 90 Nl / lh, ≥ 110 Nl / lh, ≥ 130 Nl / lh, ≥ 140 Nl / lh, ≥ 160 Nl / lh, ≥ 180 Nl / lh, ≥ 240 Nl / lh, ≥ 300 Nl / lh, but usually ≤ 600 Nl / lh. The load is based on the volume of the fixed catalyst bed only if necessary, also used sections which consist exclusively of inert material (as is generally the case in this document, unless explicitly stated otherwise).

In order to prepare the fixed catalyst bed for a partial oxidation of propene to acrolein according to the invention, only shaped catalyst bodies having the corresponding multimetal oxide active composition or largely homogeneous mixtures of multimetal oxide active catalyst compositions and no multimetal oxide active composition which are essentially inert propylene oxide which are essentially heterogeneously catalyzed in partial propylene oxide oxidation and can be used in the process according to the invention behaving (consisting of inert material), shaped bodies (thinning molded bodies) can be used. In principle, all those materials which are also suitable as support materials for “propene-to-acroline” shell catalysts are suitable as materials for such inert shaped bodies. Examples of such materials are porous or non-porous aluminum oxides, silicon dioxide, thorium dioxide, zirconium dioxide, silicon carbide, silicates such as Magnesium or aluminum silicate or the already mentioned steatite (eg steatite C-220 from CeramTec).

In principle, the geometry of such inert shaped dilution bodies can be as desired. That means, for example, spheres, polygons, solid cylinders or rings. It is preferred to choose those inert diluent shaped bodies whose geometry corresponds to that of the first-stage shaped catalyst bodies to be diluted with them.

As a rule, it is advantageous if the chemical composition of the active composition used does not change via the fixed catalyst bed for the propene partial oxidation to acrolein described. That is, the active composition used for a single shaped catalyst body can be a mixture of different, e.g. the elements Mo and / or W and at least one of the elements containing Bi, Fe, Sb, Sn and Cu are multimetal oxides, but the same mixture is then advantageously used for all shaped catalyst bodies of the fixed catalyst bed.

Preferably, in the case of propene partial oxidation to acrolein, the volume-specific activity (i.e. the activity normalized to the unit of volume) within the fixed catalyst bed increases continuously, abruptly or stepwise in the direction of flow of the reaction gas starting mixture.

The volume-specific activity can be reduced, for example, in a simple manner by homogeneously diluting a basic amount of uniformly produced shaped catalyst bodies with shaped dilution bodies. The higher the proportion of is selected, the lower the active mass or catalyst activity contained in a certain volume of the fixed bed.

A volume-specific activity which increases at least once in the flow direction of the reaction gas mixture over the fixed catalyst bed can thus be easily e.g. adjust by starting the bed with a high proportion of inert dilution moldings based on a type of catalyst moldings, and then reduce this proportion of dilution moldings in the flow direction either continuously or at least once or several times abruptly (e.g. step-shaped). An increase in volume-specific activity is also e.g. This is possible by increasing the thickness of the active mass layer applied to the support while the geometry and type of active mass of a shaped shell catalyst body remain the same, or increasing the proportion of shaped catalyst bodies with a higher proportion of active mass weight in a mixture of shell catalysts with the same geometry but with a different proportion by weight of the active mass. Alternatively, you can also dilute the active materials yourself by using e.g. into the dry mixture to be calcined from starting compounds, inert, diluent materials such as burned silicon dioxide are incorporated. Different amounts of diluting material automatically lead to different activities. The more diluting material is added, the lower the resulting activity will be. Analog effects can also be e.g. achieve by changing the mixing ratio in a corresponding manner in mixtures of unsupported catalysts and shell catalysts (with identical active mass). Of course, the variants described can also be used in combination.

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

Before and / or after the sections of the fixed catalyst bed of a propene partial oxidation according to the invention to acrolein which contain active substance, there can only be beds consisting of inert material (for example only dilution moldings). These beds can also be brought to the temperature of the fixed catalyst bed. The shaped diluent bodies used for the inert bed can have the same geometry as the shaped catalyst bodies used for the sections of the fixed catalyst bed having the active composition. The geometry of the shaped diluent bodies used for the inert bed can also be different from the aforementioned geometry of the shaped catalyst bodies (for example spherical instead of annular). The shaped bodies used for such inert beds often have the ring-shaped geometry 7 mm x 7 mm x 4 mm (outside diameter x length x inside diameter) or the spherical geometry with the diameter d = 4-5 mm.

In the process according to the invention, the section of the fixed catalyst bed for active propene partial oxidation to acrolein in the flow direction of the reaction gas mixture is often structured as follows.

First of all over a length of 10 to 60%, preferably 10 to 50%, particularly preferably 20 to 40% and very particularly preferably 25 to 35% (ie, for example over a length of 0.70 to 1.50 m, preferably 0. 90 to 1, 20 m), each of the total length of the portion of the fixed bed catalyst bed having active composition, a homogeneous mixture or two (with decreasing dilution) successive homogeneous mixtures of shaped catalyst bodies and shaped dilution bodies (both of which preferably have essentially the same geometry), the Weight fraction of the shaped diluent bodies (the mass densities of shaped catalyst bodies and of thinned shaped bodies generally differ only slightly) normally 5 to 40% by weight, preferably 10 to 40% by weight or 20 to 40% by weight and particularly preferably 25 to 35 % By weight. This first zone is then advantageously either up to the end of the section of the fixed catalyst bed having active composition (ie, for example over a length of 2.00 to 3.00 m, preferably 2.50 to 3.00 m) either a bed of the shaped catalyst bodies diluted only to a lesser extent (than in the first zone), or, very particularly preferably, a single bed of the same shaped catalyst bodies which were also used in the first zone.

The above applies in particular when full catalyst rings or coated catalyst rings are used as shaped catalyst bodies in the fixed catalyst bed (in particular those which are mentioned as preferred in this document). Within the framework of the structuring mentioned above, both the shaped catalyst bodies or their carrier rings and the shaped dilution bodies in the process according to the invention essentially have the ring geometry 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter).

The above also applies if, instead of inert shaped diluent moldings, shaped catalyst moldings are used whose active mass fraction is 2 to 15% by weight points lower than the active mass fraction of the shell catalyst shaped bodies at the end of the fixed catalyst bed.

A pure bed of inert material, the length of which, based on the total length of the fixed catalyst bed, is expediently 1 or 5 to 20%, tion of the reaction gas mixture usually a fixed catalyst bed. It is normally used as a heating zone for the reaction gas mixture.

The contact tubes in the tube bundle reactors for the stage of the partial oxidation of propene to acrolein are usually made from ferritic steel and typically have a wall thickness of 1 to 3 mm. Their inside diameter is usually (uniformly) 20 to 30 mm, often 21 to 26 mm. Appropriately from an application point of view, the number of contact tubes accommodated in the tube bundle container is at least 5000, preferably at least 10,000. The number of contact tubes accommodated in the reaction vessel is often 15,000 to 30,000. Tube bundle reactors with a number of contact tubes above 40,000 are rather the exception for this reaction stage , The contact tubes are normally arranged homogeneously distributed within the container, the distribution being expediently chosen such that the distance between the central inner axes from the closest contact tubes (the so-called contact tube division) is 35 to 45 mm (cf., for example, EP-B 468290 ).

The reaction stage (and the procedure according to the invention in the same) can be carried out from acrolein to acrylic acid using the catalysts described as suitable for the fixed catalyst bed of this reaction in the simplest manner and in terms of application technology, in a tube bundle reactor charged with the fixed bed catalysts, as described eg in EP-A 700 893 or DE-A 4 431 949 or WO 03/057653, or WO 03/055835, or WO 03/059857, or WO 03/076373.

That is, in the simplest way, the fixed catalyst bed to be used is located in the uniformly charged metal tubes of a tube bundle reactor, and a temperature control medium (single-zone mode of operation), usually a molten salt, is passed around the metal tubes. Salt melt (temperature control medium) and reaction gas mixture can be carried out in simple cocurrent or countercurrent. The temperature control medium (the molten salt) can also be passed through the reactor, viewed in a meandering manner, around the tube bundle, so that, viewed over the entire reactor, there is only a cocurrent or countercurrent to the direction of flow of the reaction gas mixture. The volume flow of the temperature control medium (heat exchange medium) is usually dimensioned such that the temperature rise (due to the exothermic nature of the reaction) of the heat exchange medium from the point of entry into the reactor to the point of exit from the reactor is 0 to 10 ° C., often 2 to 8 ° C, often 3 to 6 ° C. The inlet temperature of the heat exchange medium in the tube bundle reactor (in this document corresponds to the temperature of the fixed catalyst bed) is generally 220 to 350 ° C, often 245 to 285 ° C or 245 to 265 ° C. Fluid heat transfer media are particularly suitable as heat exchange medium. The use of melts of salts such as potassium nitrate, potassium nitrite, sodium nitrite and / or is particularly favorable Sodium nitrate, or of low melting metals such as sodium, mercury as well

Alloys of various metals. Ionic liquids can also be used.

The reaction gas starting mixture is advantageously fed to the feed with fixed bed catalyst preheated to the desired reaction temperature.

In particular in the case of desired high (for example ≥ 130 Nl / lh, or 140 140 Nl / lh, but usually 350 350 Nl / lh, or 600 600 Nl / lh) loads on the fixed catalyst bed with acrolein, the process according to the invention is carried out Acrolein partial oxidatone to acrylic acid is expedient in a two- or multi-zone tube bundle reactor (however, it can also be carried out in a single-zone tube bundle reactor). A preferred variant of a two-zone tube bundle reactor which can be used according to the invention for this purpose is disclosed in DE-C 2830765. But also those in DE-C 2513405, US-A 3147084, DE-A 2201528, EP-A 383224 and DE-A 2903582 disclosed two-zone tube bundle reactors are suitable.

In other words, the at least one fixed catalyst bed to be used according to the invention is in a simple manner in the uniformly charged metal tubes of a tube bundle reactor, and two temperature-regulating media which are essentially spatially separated from one another, usually molten salts, are passed around the metal tubes. The pipe section over which the respective salt bath extends represents a temperature or reaction zone.

Preferably flows around e.g. a salt bath C is the section of the tube (the reaction zone C) in which the oxidative conversion of acrolein (in a single pass) takes place until a conversion value in the range of 55 to 85 mol% is reached, and a salt bath D flows around the section of the tubes (the reaction zone D) in which the oxidative subsequent conversion of acrolein (in a single pass) takes place until a conversion value of at least 90 mol% is usually reached (if necessary, further reaction zones can follow the reaction zones C, D) which are kept at individual temperatures).

In principle, the salt bath can be conducted within the respective temperature zone as in the single-zone mode. The inlet temperature of the salt bath D is normally at least 5 to 10 ° C above the temperature of the salt bath C. Otherwise, the inlet temperatures can be in the temperature range recommended for the single-zone procedure for the inlet temperature.

Otherwise, the two-zone high-load procedure of partial acrolein oxidation to acrylic acid can be carried out, for example, as described in DE-A 19 948523, EP-A 11 06 598 or as described in DE-A 19 94 8248. The method according to the invention is therefore suitable for acrolein loads on the fixed catalyst bed of 70 70 Nl / lh, or 70 70 Nl / lh, 90 90 Nl / lh, 110 110 Nl / lh, 130 130 Nl / lh, 180 180 Nl / lh, ≥ 240 Nl / lh, ≥ 300 Nl / lh, but usually ≤ 600 Nl / lh. The load is based on the volume of the fixed catalyst bed exclusively, if necessary, also used sections which consist exclusively of inert material.

To prepare the at least one fixed catalyst bed for a partial oxidation of acrolein to acrylic acid according to the invention, only the corresponding shaped multimetal oxide active substance or also largely homogeneous mixtures of shaped multimetal oxide active substance and no multimetal oxide active substance, which are essentially inert gas oxidation with respect to the heterogeneously catalyzed partial oxidation (essentially Inert material existing), moldings (dilution moldings) are used. Suitable materials for such inert moldings are in principle all those which are also suitable as support materials for "acrolein-to-acrylic acid shell catalysts" which are suitable according to the invention. Examples of such materials are porous or non-porous aluminum oxides, silicon dioxide, thorium dioxide, zirconium dioxide, Silicon carbide, silicates such as magnesium or aluminum silicate or the already mentioned steatite (eg steatite C-220 from CeramTec) can be considered.

In principle, the geometry of such inert shaped dilution bodies can be as desired. That means, for example, spheres, polygons, solid cylinders or rings. According to the invention, preference will be given to choosing the inert shaped diluent whose geometry corresponds to that of the shaped catalyst body to be diluted with them.

As a rule, in the context of a partial oxidation of acrolein to acrylic acid according to the invention, it is advantageous if the chemical composition of the active composition used does not change via the fixed catalyst bed. In other words, the active composition used for a single shaped catalyst body can be a mixture of different multimetal oxides containing the elements Mo and V, but it is then advantageous to use the same mixture for all shaped catalyst bodies of the fixed catalyst bed.

Preferably, for a partial oxidation of acrolein to acrylic acid according to the invention, the volume-specific (i.e., the normalized to the unit of volume) activity within the fixed catalyst bed increases continuously, abruptly or stepwise in the direction of flow of the reaction gas mixture.

A volume-specific activity that increases at least once in the direction of flow of the reaction gas mixture over the fixed catalyst bed can thus be easily achieved for a method of partial acrolein oxidation to acrylic acid, e.g. adjust by starting the bed with a high proportion of inert dilution moldings based on a type of catalyst moldings, and then reduce this proportion of dilution moldings in the flow direction either continuously or at least once or several times abruptly (e.g. stepwise). An increase in volume-specific activity is also e.g. This is possible by increasing the thickness of the active mass layer applied to the support with the geometry and type of active mass of a shell catalyst body remaining the same, or increasing the proportion of shaped catalyst bodies with a higher active mass weight fraction in a mixture of shell catalysts with the same geometry but with a different proportion by weight of the active mass. Alternatively, you can also dilute the active materials yourself by using e.g. into the dry mixture to be calcined from starting compounds, inert, diluent materials such as burned silicon dioxide are incorporated. Different additions of thinning material automatically lead to different activities. The more diluting material is added, the lower the resulting activity will be. Analog effects can also be e.g. by changing the mixture ratio in a corresponding manner in mixtures of unsupported catalysts and shell catalysts (with identical active mass). Of course, the variants described can also be used in combination.

Of course, mixtures of catalysts with chemically different active composition and, as a result of this different composition, different activity can also be used for the fixed catalyst bed of an inventive acrolein oxidation to acrylic acid. These mixtures can in turn be diluted with inert diluents.

Prior to and / or after the sections of the fixed catalyst bed having the active composition, there can only be beds consisting of inert material (for example, only dilution moldings). These can also be brought to the temperature of the fixed catalyst bed. The shaped diluent bodies used for the inert bed can have the same geometry as the shaped catalyst bodies used for the sections of the fixed catalyst bed having the active composition. The geometry of the shaped diluent bodies used for the inert bed can also be different from the aforementioned geometry of the shaped catalyst bodies (for example spherical instead of annular). The shaped bodies used for such inert beds often have the ring-shaped geometry 7 mm x 7 mm x 4 mm (outside diameter x length x inside diameter) or the spherical geometry with the diameter d = 4-5 mm.

In a method according to the invention of partial acrolein oxidation to acrylic acid of the active composition, the section of the fixed catalyst bed in the flow direction of the reaction gas mixture is often structured as follows.

First of all over a length of 10 to 60%, preferably 10 to 50%, particularly preferably 20 to 40% and very particularly preferably 25 to 35% (ie, for example over a length of 0.70 to 1.50 m, preferably 0, 90 to 1.20 m), each of the total length of the portion of the fixed bed catalyst bed having active composition, a homogeneous mixture or two (with decreasing dilution) successive homogeneous mixtures of shaped catalyst bodies and shaped dilution bodies (both of which preferably have essentially the same geometry), the proportion by weight the dilution molded body (the mass densities of shaped catalyst bodies and of diluted molded bodies generally differ only slightly) is normally 10 to 50% by weight, preferably 20 to 45% by weight and particularly preferably 25 to 35% by weight. This first zone is then advantageously either up to the end of the section of the fixed catalyst bed having active composition (ie, for example over a length of 2.00 to 3.00 m, preferably 2.50 to 3.00 m) either a bed of the shaped catalyst bodies diluted only to a lesser extent (than in the first (or in the first two) zones), or, very particularly preferably, a bed of the same shaped catalyst bodies, which is also in the first (or the first two) zone have been used.

The above applies in particular when shell catalyst rings or shell catalyst balls are used as shaped catalyst bodies in the fixed catalyst bed (in particular those which are mentioned in this document as preferred for acrolein partial oxidation to acrylic acid). Within the framework of the aforementioned structuring, both the shaped catalyst bodies or their carrier rings and the shaped diluent bodies in a process according to the invention for partial acrolein oxidation to acrylic acid essentially have the ring geometry 7 mm × 3 mm × 4 mm (outer diameter × length × inner diameter).

The above also applies if, instead of inert shaped diluent moldings, shaped catalyst catalyst bodies are used whose active mass fraction is 2 to 15% by weight points lower than the active mass fraction of the shell catalyst shaped bodies at the end of the fixed catalyst bed. A pure bed of inert material, the length of which is expediently 5 to 20%, based on the total length of the fixed catalyst bed, generally initiates the fixed catalyst bed for the acrolein partial oxidation in the direction of flow of the reaction gas mixture. It is normally used as a heating zone for the reaction gas mixture.

For the acrolein partial oxidation according to the invention, the contact tubes in the tube bundle reactors are usually made of ferritic steel and typically have a wall thickness of 1 to 3 mm. Their inside diameter is usually (uniformly) 20 to 30 mm, often 21 to 26 mm. Appropriately from an application point of view, the number of contact tubes accommodated in the tube bundle container is at least 5000, preferably at least 10,000. The number of contact tubes accommodated in the reaction vessel is frequently 15,000 to 30,000. Tube bundle reactors with a number of contact tubes above 40,000 are rather the exception for acrolein partial oxidation , The contact tubes are normally arranged homogeneously distributed within the container, the distribution being expediently chosen such that the distance between the central inner axes from the closest contact tubes (the so-called contact tube division) is 35 to 45 mm (cf., for example, EP-B 468290 ).

As already described, both the propene and the acrolein partial oxidation can be carried out in single-zone or in two-zone tube bundle reactors in the process according to the invention. If the two reaction stages are connected in series, only the first reaction stage can be carried out in a single-zone tube bundle reactor and the second reaction stage in a two-zone tube bundle reactor (or vice versa). The product gas mixture of the first reaction stage is fed directly to the second reaction stage, if appropriate after supplementing with inert gas or with molecular oxygen, or with inert gas and molecular oxygen and, if appropriate, after direct and / or indirect intermediate cooling.

An intercooler can be located between the tube bundle reactors of the first and second reaction stages, which can optionally contain inert beds.

Of course, for the process according to the invention of a two-stage partial oxidation of propene to acrylic acid, the fixed catalyst bed of the propene partial oxidation and the fixed catalyst bed of the acrolein partial oxidation can also be spatially successively accommodated in a single, multi-contact tubular tube bundle reactor, which also has, for example, two temperature zones, as described, for example, in WO 03/059857. describe EP-A 911313 and EP-A 990636. In this case, one speaks of a single-reactor two-stage process. A temperature zone extends in the Usually over a fixed catalyst bed. There can also be an inert bed between the two fixed catalyst beds, which may be in a third temperature zone and is heated separately. The contact tubes can be continuous or interrupted by the inert bed.

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

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

If propene loads on the fixed catalyst bed of the “propene-to-acrolein reaction stage” exceed 250 Nl / lh, however, the use of inert diluent gases such as propane, ethane, methane, butane, pentane, CO ₂ , CO, water vapor and / or or noble gases are recommended. Of course, these gases can also be used with lower propene loads.

The working pressure in the gas phase partial oxidation of propene to acrolein according to the invention (in particular at the beginning of the operating life of a fixed catalyst bed) can be both below normal pressure (e.g. up to 0.5 bar) and above normal pressure. Typically, the working pressure in the gas phase partial oxidation of the propene will be from 1 to 5 bar, often 1 to 3 bar.

The reaction pressure in the propene partial oxidation to acrolein according to the invention will normally not exceed 100 bar. It is essential according to the invention, however, that the working pressure is increased during the operating period of the at least one fixed catalyst bed for the partial oxidation of propene to acrolein, based on an identical load thereof with reaction gas starting mixture 1 in Nl / lh, in order to counteract the deactivation of the at least one fixed catalyst bed. The extent of the pressure increase can be designed as described in the general part of this document. Of course, the procedure (s) according to the invention can generally be carried out using the methods described in EP-A 990 636, EP-A 11 06 598, EP-A 614 872, DE-A 10 35 0822, DE-A 10 23 2748 and DE- A 10351269 procedures recommended for extending the service life of a catalyst bed can also be used in combination. This enables catalyst bed service lives of several years to be achieved. The molar ratio of O ₂ : propene in the reaction gas starting mixture 1 for the propene partial oxidation to acrolein, which is led through the corresponding fixed catalyst bed in the process according to the invention, will normally be ≥ 1 (essentially irrespective of whether an acrolein partial oxidation stage follows to acrylic acid). This ratio will usually be at values ≤ 3. Often the molar ratio of O ₂ : propene in the aforementioned feed gas mixture will advantageously be 1 to 2 or 1 to 1.5. In many cases, the process of propene partial oxidation to acrolein with a propene present in the reaction gas starting mixture 1 will be: oxygen: inert gas (including water vapor) - volume ratio (NI) of 1: (1 to 3): (3 to 30), preferably 1: (1 , 5 to 2.3): Execute (10 to 15).

The propene content in the reaction gas starting mixture 1 can e.g. with values of 4 to 20% by volume, often 5 or 7 to 15% by volume or 6 or 8 to 12% by volume or 5 to 8% by volume (in each case based on the total volume).

A typical composition of the reaction gas starting mixture 1 (regardless of the load chosen and regardless of whether an acrolein partial oxidation step to acrylic acid follows) may contain the following components:

6 to 6.5 vol.% Propene, 3 to 3.5 vol.% H ₂ O, 0.3 to 0.5 vol.% CO, 0.8 to 1.2 vol.% CO ₂ , 0.025 to 0.04 vol.% Acrolein, 10.4 to 10.7 vol.% O ₂ and as a residual amount ad 100% molecular nitrogen, or: 5.4 vol.% Propene, 10.5 vol.% Oxygen, 1.2 vol.% CO _x , 80.5 vol.% N ₂ and 2.4 vol.% H ₂ O.

The reaction gas starting mixture 1 for the propene partial oxidation to acrolein can also be composed according to the invention as follows:

6 to 15% by volume of propene, 4 to 30% by volume (often 6 to 15% by volume) of water, ≥ 0 to 10% by volume (preferably ≥ 0 to 5% by volume) of propene , Water, oxygen and nitrogen various constituents, so much molecular oxygen that the molar ratio of tenem molecular oxygen to contain molecular propene 1, 5 to 2.5 and as a residual amount up to 100 vol .-% total amount of molecular nitrogen.

Another possible reaction gas starting mixture 1 composition for propene partial oxidation to acrolein can contain according to the invention:

6.0 vol.% Propene, 60 vol.% Air and 34 vol.% H ₂ O.

Alternatively, reaction gas starting mixtures 1 of the composition according to Example 1 of EP-A 990 636, or according to Example 2 of EP-A 990 636, or according to Example 3 of EP-A 1 106 598, or according to Example 26 of EP-A 1 106 598, or according to Example 53 of EP-A 1 106 598 for the “propene-to-acrolene reaction stage”.

Further reaction gas starting mixtures 1 suitable according to the invention for the “propene-to-acrolein reaction stage” can lie in the following compositional grid:

7 to 11% by volume of propene, 6 to 12% by volume of water, ≥ 0 to 5% by volume of constituents other than propene, water, oxygen and nitrogen, so much molecular oxygen that the molar ratio of oxygen contained also contained molecular propene is 1.4 to 2.2, and as a residual amount up to 100 vol .-% total amount of molecular nitrogen.

As propene to be used in the reaction gas starting mixture 1, especially polymer-grade propene and chemical-grade propene are suitable, as is the case, for example, with DE-A 10232748 describes.

At this point it should also be mentioned that, regardless of whether an "acrolein-to-acrylic acid reaction stage" follows, part of the feed gas mixture of the "propene-to-acrolein reaction stage" can be so-called cycle gas. As already described, this is gas which remains after the product has been separated off from the product gas mixture of this reaction stage in the workup which usually follows the last reaction stage (acrolein or acrylic acid separation) and as a rule partly as a largely inert diluent gas for charging the propene and / or the optionally subsequent acrolein reaction stage is recycled.

Air is normally used as the oxygen source.

The loading of the fixed catalyst bed (only pure inert sections) with reaction gas starting mixture 1 will typically be 1000 to 10000 Nl / lh, mostly 1000 to 5000 Nl / lh, often 1500 to 4000 Nl / lh in the process according to the invention (regardless of whether a “ Acrolein-to-acrylic acid reaction stage "connects).

If the propene partial oxidation to acrolein is followed by an acrolein partial oxidation, the product gas mixture is optionally fed to the propene reaction stage of the acrolein reaction stage after intermediate cooling. The oxygen required in the acrolein reaction stage can already be added in excess to the reaction gas starting mixture 1 for the propene reaction stage and can thus be part of the product gas mixture of the propene reaction stage. In this case, the product gas mixture of the propene reaction stage, which may be intercooled, can be the feed gas mixture of the acrolein reaction stage. However, the oxygen required for the second oxidation step from acrolein to acrylic acid can only be partially or completely added to the product gas mixture of the propene reaction stage even before it enters the acrolein reaction stage, e.g. in the form of air. This addition may involve direct cooling of the product gas mixture of the acrolein reaction stage.

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

Often, however, the inert diluent gas in the feed gas for the acrolein reaction stage is 5 to 25 or 20% by weight H ₂ O (can be formed and / or optionally added in a preceding propene reaction stage) and 70 up to 90 vol .-% consist of N ₂ .

If the fixed catalyst bed for the partial oxidation of acrolein to acrylic acid is above 250 Nl / lh, the use of inert diluent gases such as propane, ethane, methane, butane, pentane, CO ₂ , steam and / or noble gases is recommended for the process according to the invention. Of course, However, these gases can also be used at lower acrolein loads.

The working pressure in the gas phase partial oxidation of the acrolein to acrylic acid according to the invention (in particular at the beginning of the operating life of a fixed catalyst bed) can be both below normal pressure (e.g. up to 0.5 bar) and above normal pressure. Typically, the working pressure in the gas phase partial oxidation of acrolein will be from 1 to 5 bar, often 1 to 3 bar.

The reaction pressure in the partial acrolein oxidation according to the invention will normally not exceed 100 bar. It is essential according to the invention, however, that the working pressure is increased during the operating period of the at least one fixed catalyst bed for the partial oxidation of acrolein to acrylic acid, based on an identical load thereof with reaction gas starting mixture 2 in Nl / lh, in order to counteract the deactivation of the at least one fixed catalyst bed , The extent of the pressure increase can be designed as described in the general part of this document. Of course, the procedure (s) according to the invention can generally also be carried out using the methods described in EP-A 990 636, EP-A 11 06 598, EP-A 614 872, DE-A 10 35 0822, DE-A 10 23 2748 and DE -A 10351269 can be used in combination to extend the life of a catalyst bed. This enables catalyst bed service lives of several years to be achieved.

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

The acrolein content in the feed gas mixture for the acrolein reaction stage can be, for example (regardless of whether a propene reaction stage precedes or not) at values of 3 or 6 to 15 vol.%, Often at 4 or 6 to 10 vol.% Or 5 to 8% by volume (each based on the total volume). The loading of the fixed catalyst bed (here only pure inert sections) with feed gas mixture (reaction gas starting mixture 2) is carried out in an “acrolein-to-acrylic acid process” according to the invention in a typical manner as for the “propene-to-acrolein Reaction step "1000 to 10000 Nl / lh, mostly 1000 to 5000 Nl / lh, often 1500 to 4000 Nl / lh.

When carrying out the process according to the invention, a fresh fixed catalyst bed for the partial oxidation of propene to acrolein after its formation will normally be operated (ie regardless of whether there is a partial oxidation of the acrolein formed to acrylic acid) in such a way that after the composition has been determined of the reaction gas starting mixture 1 and determining the load on the fixed catalyst bed for the propene partial oxidation with reaction gas starting mixture 1, the temperature of the fixed catalyst bed (or the entry temperature of the temperature control medium into the temperature control zone of the tube bundle reactor) is set such that the conversion U ^{Pro of} the propene with one pass of the reaction gas mixture 1 through the Fixed catalyst bed is at least 93 mol%. If inexpensive catalysts are used, values for U ^Pro ≥ 94 mol%, or ≥ 95 mol%, or ≥ 96 mol%, or ≥ 97 mol% and often even more are also possible.

If the heterogeneously catalyzed partial oxidation of propene to acrolein is carried out continuously, the composition of the reaction gas starting mixture 1 and the load on the corresponding fixed catalyst bed with reaction gas starting mixture 1 will be maintained essentially constant (if necessary, the loading will be adjusted to the fluctuating market demand). A drop in the activity of the fixed catalyst bed over time under these production conditions will normally initially be countered by increasing the temperature of the fixed catalyst bed (the temperature of the temperature of the temperature control medium entering the temperature zone of the tube bundle reactor) from time to time (the flow rate of the temperature control medium normally becomes essentially also maintained), the propene conversion in one pass of the reaction gas mixture in the desired target corridor (ie, with U ^Pr0 ≥ 93 mol%, or ≥ 94 mol%, or ≥ 95 mol%, or ≥ 96 mol .-%, or ≥ 97 mol .-%) to keep. However, such a procedure alone entails the disadvantages described at the beginning of this document.

It is therefore advantageous to proceed in such a way that the gas phase partial oxidation is interrupted from time to time according to the invention in order, at a temperature of the fixed catalyst bed of 250 to 550 ° C., as described in DE-A 10351269, from molecular oxygen, inert gas and, if appropriate To conduct water vapor existing gas mixture G through the fixed catalyst bed. Subsequently, the partial oxidation of the propene is continued with the process conditions being largely retained (the propene loading on the fixed catalyst bed is preferably restored slowly) and the temperature of the fixed catalyst bed is adjusted so that the propene conversion reaches the desired target value. As a rule, for the same conversion, this temperature value will be at a somewhat lower value than the temperature which the fixed catalyst bed had before the interruption of the partial oxidation and the treatment according to the invention with the gas mixture G. Starting from this temperature value of the fixed catalyst bed, the partial oxidation is continued while largely maintaining the other conditions, and the decrease in the activity of the fixed catalyst bed over time is expediently counteracted by increasing the temperature of the fixed catalyst bed from time to time. Within a subsequent calendar year, for example, the partial oxidation is expediently interrupted at least once in accordance with the invention in order to pass the gas mixture G through the fixed catalyst bed in the manner according to the invention. Thereafter, the partial oxidation according to the invention is advantageously resumed as described, etc. However, with the temperature of the catalyst bed increasing over the operating period of the catalyst bed, the measure according to the invention of increasing the working pressure will be incorporated in an appropriate manner. This can be done in steps or uniformly.

Correspondingly, when the process according to the invention is carried out, a fresh fixed catalyst bed for the partial oxidation of acrolein to acrylic acid after its formation will normally be operated in such a way that after determining the operation of this reaction stage and the composition of the reaction gas starting mixture 2 and determining the load on the corresponding catalyst solid bed with reaction gas starting mixture 2 adjusts the temperature of the fixed catalyst bed (or the entry temperature of the temperature control ^medium into the temperature control ^zone of the tube bundle ^reactor ) such that the conversion U ^acr of acrolein is at least 90 mol% when the reaction ^{gas starting} mixture 2 passes through the ^{fixed catalyst bed} once. When using inexpensive catalysts, values for U ^Acr are also ≥ 92 mol%, or ≥ 94 mol%, or ≥ 96 mol%, or ≥ 98 mol%, and often even ≥ 99 mol% and more possible.

If the heterogeneously catalyzed partial oxidation of acrolein to acrylic acid is carried out continuously, the composition of the reaction gas starting mixture 2 and the loading of the corresponding fixed catalyst bed with reaction gas starting mixture 2 will be maintained essentially constant (if necessary, the loading will be adapted to the fluctuating market demand). A drop in the activity of the fixed catalyst bed over time under these production conditions will normally be countered by increasing the temperature of the fixed catalyst bed (the temperature of the temperature of the temperature control medium entering the temperature zone of the shell-and-tube reactor) from time to time (the flow rate of the temperature control medium normally becomes essentially the same) maintained), the acrolein conversion with a single passage of the feed gas mixture in the desired target corridor (ie, at values of ≥ 90 mol%, or ≥ 92 mol%, or ≥ 94 mol%, or ≥ 96 mol .-%, or ≥ 98 mol .-%, or ≥ 99 mol .-%) to keep. However, such a procedure alone entails the disadvantages described at the beginning of this document. It is therefore advantageous to proceed in such a way that, for example, before the temperature increase of the fixed catalyst bed is permanently ≥ 10 ° C or ≥ 8 ° C (based on the previously set temperature of the same fixed catalyst bed), the gas phase partial oxidation is interrupted at least once, at a temperature of the fixed catalyst bed from 200 to 450 ° C (in a two-stage partial oxidation of propene to acrylic acid via the fixed catalyst bed of propene oxidation to acrolein) leading the gas mixture G through the fixed catalyst bed of the partial oxidation of acrolein to acrylic acid. The partial oxidation is then continued while the process conditions are largely maintained (the restoration of the acrolein load on the corresponding fixed catalyst bed is preferably slow, for example as described in DE-A 10337788) and the temperature of the fixed catalyst bed is adjusted so that the acrolein conversion reaches the desired target value , As a rule, for the same conversion, this temperature value will be at a somewhat lower value than the temperature which the fixed catalyst bed had before the interruption of the partial oxidation and the treatment with the gas mixture G. Starting from this temperature value of the fixed catalyst bed, the partial oxidation of acrolein is continued while largely maintaining the other conditions, and the decrease in the activity of the fixed catalyst bed over time is expediently counteracted by increasing the temperature of the fixed catalyst bed from time to time. For example, before the temperature increase of the fixed catalyst bed is permanently ≥ 10 ° C or ≥ 8 ° C, the partial oxidation according to the invention is again interrupted at least once in order to pass the gas mixture G (possibly leading over the fixed catalyst bed of a propene reaction stage) through the fixed catalyst bed of the acrolein partial oxidation of acrolein lead to acrylic acid. Thereafter, the partial oxidation according to the invention is advantageously resumed, as described, etc. However, as the temperature of the catalyst bed increases over the operating period of the catalyst bed, the measure according to the invention of increasing the working pressure will be incorporated in an appropriate manner. This can be done in steps or uniformly. In the case of a two-stage partial oxidation of propene to acrylic acid according to the invention, for example, behind each of the two reaction stages and additionally at the top of a subsequent absorption or fractional condensation column, the conversion of the acrylic acid from the gaseous product gas mixture of the partial oxidation into the lower part into the condensed phase tracked, a pressure control device may be attached.

However, in the case of such a two-stage reaction procedure, a pressure control device downstream (preferably directly at the outlet of the product gas mixture) of the second reaction stage, in which the partial oxidation of the acroleins to acrylic acid takes place, is often sufficient. It is surprising that if the fixed catalyst bed is partially deactivated over longer operating times, the measure of increasing the working pressures requires the catalyst bed to be reactivated. It is also surprising that if this pressure increase is carried out with a sense of proportion, there is no significant reduction in the selectivity of the target product formation.

The process according to the invention thus enables on the one hand longer service lives of the catalyst beds, in particular fixed catalyst beds, in the reactor systems before they have to be partially or completely replaced. On the other hand, the reactant conversions achieved integrally over time are also increased.

The process according to the invention is particularly advantageous if, in the case of a propene partial oxidation to acrolein (in the case of an acrolein partial oxidation to acrylic acid), the fixed catalyst bed is loaded with propene (with acrolein) of 110 110 Nl / lh or 120 120 Nl / lh, or ≥ 130 Nl / lh is operated (under high educt loading, catalysts usually deactivate faster). In the case of a two-stage partial oxidation of propene to acrylic acid connected in series, the loading of the fixed catalyst bed for the acrolein partial oxidation with acrolein can in each case be up to 20 Nl / l-h below the propene loading of the fixed catalyst bed for the propene partial oxidation.

If the process according to the invention is combined with the procedure for the intermediate regeneration of the catalyst bed, it is possible to run the catalyst bed continuously at a predetermined conversion in long-term operation below a set maximum temperature.

The acrylic acid can be separated from the product gas mixture and the associated recycle gas formation can be carried out as described in WO 97/48669.

In general, freshly charged fixed catalyst beds for propene or acrolein partial oxidation to acrolein or acrylic acid will be designed in such a way that, as described in EP-A 990 636 and EP-A 11 06 598, both the formation of hot spots and their temperature sensitivity are as low as possible ,

In conclusion, it should be noted that for all gas phase partial oxidations mentioned and discussed in this document, the increase in the working pressure according to the invention after 2000, or after 4000, or after 7000, or after 9000, or after 12000, or after 15000, or after 18000, or after 21000, or after 24000, or after 27000, or after 30000 or more operating hours of the at least one catalyst bed. Intermediate regenerations are included. In a two-stage propene partial oxidation of propene to acrylic acid, it has proven to be advantageous to use fresh catalyst beds with an entry pressure in the propene reaction stage from 1.4 to 1.9 bar to start reaction operation and to increase this inlet pressure over the operating period to 2.5 to 3.0 bar.

It should also be noted that in order to carry out the process according to the invention, normally at least one air compressor is required to compress the air which is usually used as an oxygen source (for example a radial compressor according to DE-A 10259023 and DE-A 10353014) in order to bring the reaction gas starting mixture to the required working pressure bring. For reasons of economy, the air compressors to be used are normally designed for heterogeneously catalyzed partial gas phase oxidations so that they can run through a working pressure range of up to 0.5 bar at most when the catalyst bed is loaded with a reaction gas starting mixture. In contrast, to implement the procedure according to the invention, air compressors (for example the radial compressors mentioned) for the reaction gas mixture are advantageous, which are designed such that they have a working pressure range of> 0.5 to 4 bar, frequently 0.6 to, for a given load on the catalyst bed with reaction gas starting mixture 3.5 bar, often 0.7 to 3 bar and often 0.8 to 2.5 bar or 1 to 2 bar (ie, the maximum working pressure possible by means of the compressor can be up to 4 bar above the minimum working pressure) , The above applies in particular if the loading of the catalyst bed with reaction gas starting mixture is ≥ 1500 Nl / l-h, or ≥ 2000 Nl / l-h, or ≥ 2500 Nl / l-h, or ≥ 3000 Nl / l-h, or ≥ 4000 Nl / l-h. As a rule, the aforementioned load in the method according to the invention is at values of 5000 5000 Nl / l-h. Optionally, other components (e.g. recycle gas) of the reaction gas starting mixture can be brought to working pressure in the air compressor. However, reactants such as propene and propane are usually stored as a liquid and, as a rule, are vaporized from the same immediately at working pressure. Circular gas is sometimes compressed separately.

Examples and comparative examples

A) Preparation of a catalyst K _{p to be used} in the propene partial oxidation to acrolein

Production of an annular full catalyst with the following stoichiometry of the active multimetal oxide:

[Bi ₂ W ₂ O ₉ • 2WO ₃ ] o, ₅ [Mo ₁₂ Cθ ₅ , ₅ Fe ₂ , 9 Si ₁ , ₅ gKo, o ₆ θ _x ] ₁ .

1. Production of a starting mass 1

At 25 ° C., 775 kg of an aqueous bismuth nitrate solution (11.2% by weight of Bi, free nitric acid 3% to 5% by weight; mass density: 1.22 to 1.27 g / ml) were used portions of 209.3 kg of tungstic acid (72.94% by weight W) were stirred in. The resulting aqueous mixture was then stirred at 25 ° C. for a further 2 h and then spray-dried.

The spray drying was carried out in a rotary disc spray tower in countercurrent at a gas inlet temperature of 300 ± 10 ° C and a gas outlet temperature of 100 ± 10 ° C. The spray powder obtained (particle size essentially uniform 30 μm), which had an ignition loss of 12% by weight (3 hours at 600 ° C. in air), was then mixed with 16.8% by weight (based on the powder) Water pasted in a kneader and extruded into strands with a diameter of 6 mm using an extruder (torque: ≤ 50 Nm). These were cut into 6 cm sections on a 3-zone belt dryer with a residence time of 120 min at temperatures of 90-95 ° C. (zone 1) and 125 ° C. (zone 2) and 125 ° C. (zone 3) Air dried and then thermally treated at a temperature in the range from 780 to 810 ° C. (calcined; in a rotary kiln through which air flows (1.54 m ³ internal volume, 200 Nm ³ air / h)). It is essential for the exact setting of the calcination temperature that it has to be based on the desired phase composition of the calcination product. The phases WO ₃ (monoclinic) and Bi ₂ W ₂ O ₉ are desired, and the presence of γ-Bi ₂ WO ₆ (russellite) is undesirable. If the compound v- Bi ₂ WO ₆ can therefore still be detected after a calcination using a reflection in the powder X-ray diffractogram at a reflection angle of 2Θ = 28.4 ° (CuKa radiation), the preparation must be repeated and the calcination temperature within the specified temperature range or the dwell time at constant calcination temperature until the disappearance of the reflex is reached. The preformed calcium ned mixed oxide thus obtained was milled so that the X ^ value (see. Ullmann's Encyclopedia of Industrial Chemistry, 6 ^th Edition (1998) Electronic Release, Section 3.1.4 or DIN 66141) of the resulting particle size was 5 mm , The ground material was then treated with 1 wt .-% (based on the material to be ground) of finely divided SiO ₂ from Degussa type Si pernat ^® (bulk density 150 g / l;. Microns X ₅₀ value of the _Σ SiO particles 10 which BET surface area was 100 m ² / g) mixed.

2. Production of a starting mass 2

A solution A was prepared by dissolving 213 kg of ammonium heptamolybdate tetrahydrate (81.5% by weight of MoO ₃ ) at 60 ° C. with stirring in 600 l of water and the resulting solution while maintaining the 60 ° C. and stirring at 0.97 kg a 20 ° C aqueous potassium hydroxide solution (46.8 wt .-% KOH).

A solution B was prepared by at 116 ° C. in 262.9 kg of an aqueous Co (II) balt nitrate solution (12.4% by weight Co) 116.25 kg of an aqueous iron (III) nitrate solution (14 , 2% by weight of Fe). Subsequently, while maintaining the 60 ° C., the solution B was continuously in the presented solution over a period of 30 minutes A pumped. The mixture was then stirred at 60 ° C for 15 minutes. Then 19.16 kg of a silica gel from Dupont of the Ludox type (46.80% by weight SiO ₂ , density: 1.36 to 1.42 g / ml, pH 8.5 to 9) were added to the resulting aqueous mixture. 5, alkali content max. 0.5% by weight) added and then stirred for a further 15 minutes at 60 ° C.

Subsequently, spray drying was carried out in counter-current in a turntable spray tower (gas inlet temperature: 400 ± 10 ° C, gas outlet temperature: 140 ± 5 ° C). The resulting spray powder had an ignition loss of approximately 30% by weight (3 hours at 600 ° C. in air) and an essentially uniform grain size of 30 μm.

Production of the multimetal oxide active material

The starting mass 1 was compared with the starting mass 2 in the stoichiometry for a multimetal oxide active mass

[Bi ₂ W ₂ O ₉ ^' 2Wθ ₃ ] o. _5- Mo ₁₂ Cθ ₅ , 5Fe ₂ .9 ₄ Si ₁ , ₅₉ Ko, o ₈ θ _x ] ι

required quantities homogeneously mixed in a mixer with cutter heads. Based on the aforementioned total mass, an additional 1% by weight of fine-particle graphite from Timcal AG (San Antonio, US), of the TIMREX P44 type (sieve analysis: min. 50 wt.% <24 μm, max. 10 wt .-% ≥ 24 μm and ≤ 48 μm, max. 5% by weight> 48 μm, BET surface area: 6 to 13 m ² / g) homogeneously mixed. The resulting mixture was then run in a compactor (Hosokawa Bepex GmbH, D-74211 Leingarten) of the compactor type K200 / 100 with concave, corrugated smooth rollers (gap width: 2.8 mm, screen width: 1.0 mm, screen size undersize: 400 μm, nominal press force: 60 kN, screw speed: 65 to 70 revolutions per minute). The resulting compact had a hardness of 10 N and an essentially uniform grain size of 400 μm to 1 mm.

The compact was then mixed with, based on its weight, a further 2% by weight of the same graphite and then in a Kilian rotary machine (tableting machine) of the R x 73 type, from Kilian, D-50735 Cologne, under a nitrogen atmosphere to form annular full catalyst precursor shaped bodies the geometry (outer diameter x length x inner diameter) 5 mm x 3 mm x 2 mm with a lateral compressive strength of 19 N ± 3 N.

In this document, side compressive strength is understood to mean the compressive strength when the annular fully shaped catalyst precursor body is compressed perpendicular to the cylinder surface (i.e., parallel to the surface of the ring opening).

All side compressive strengths of this document relate to a determination by means of a material testing machine from Zwick GmbH & Co. (D-89079 Ulm) des Type Z 2.5 / TS1S. This material testing machine is designed for quasi-static loads with rapid, ^' stationary, swelling or changing course. It is suitable for tensile, compression and bending tests. The installed KAF-TC force transducer from AST (D-01307 Dresden) with the production number 03-2038 was calibrated in accordance with DIN EN ISO 7500-1 and could be used for the measuring range 1-500N (relative measurement uncertainty: + 0, 2%).

The measurements were carried out with the following parameters:

Preload: 0.5 N.

Preload speed: 10 mm / min. Test speed: 1.6 mm / min.

The upper punch was first lowered slowly until just before the cylindrical surface of the annular full catalyst precursor molded body. Then the upper punch was stopped in order to then be lowered at the significantly slower test speed with minimal pre-force required for further lowering.

The preload at which the shaped catalyst precursor body shows cracking is the lateral compressive strength (SDF).

For the final thermal treatment, 1000 g each of the shaped catalyst precursor body were initially in a muffle furnace through which air flows (60 l internal volume, 1 l / h air per gram shaped catalyst precursor body), initially with a heating rate of 180 ° C./h from room temperature (25 ° C.) heated to 190 ° C. This temperature was maintained for 1 h and then increased to 210 ° C at a heating rate of 60 ° C / h. The 210 ° C was again maintained for 1 h before being increased to 230 ° C at a heating rate of 60 ° C / h. This temperature was also maintained for 1 h before it was increased to 265 ° C, again at a heating rate of 60 ° C / h. The 265 ° C was then also maintained for 1 h. Thereafter, the mixture was first cooled to room temperature, essentially completing the decomposition phase. The mixture was then heated to 465 ° C. at a heating rate of 180 ° C./h and this calcination temperature was maintained for 4 hours.

In this way, annular unsupported catalysts K _{p were} obtained from the annular unsupported shaped catalyst precursors.

The specific surface area O, the total pore volume V, the pore diameter d ^max which makes the greatest contribution to the total pore volume, and the percentage of those pore diameters in the total pore volume whose diameters are> 0.1 and ≤ 1 μm, were K _P for the annular unsupported catalysts obtained as follows: O = 7.6 cm ² / g. V = 0.27 cm ³ / g. d ^max [μm] = 0.6. \ \ -% = 79.

In addition, the ratio R of apparent mass density to true mass density p (as defined in EP-A 1340538) was 0.66. In large quantities, the same annular catalyst was advantageously treated by thermal treatment as in Example 1 of DE-A 10046957 (the bed height in the decomposition (chambers 1 to 4) was 44 mm with a residence time per chamber of 1.46 h and in the calcination (chambers 5 to 8) it advantageously amounted to 130 mm with a residence time of 4.67 h) produced using a belt calciner; the chambers had a base area (with a uniform chamber length of 1.40 m) of 1.29 m ² (decomposition) and 1.40 m ² (calcination) and were flowed through from below through the coarse-mesh belt of 75 Nm ³ / h of supply air which were sucked in by means of rotating fans. Within the chambers, the time and place deviation of the temperature from the setpoint was always ≤ 2 ° C. Otherwise the procedure was as described in Example 1 of DE-A 10 04 6957.

B) Preparation of a catalyst K _A (shell catalyst) to be used in the acrolein partial oxidation to acrylic acid with the stoichiometry Mθi ₂ V ₃ Wι, ₂ Cu ₂ , ₄ O _{x of} the active composition

1. General description of the rotary kiln used for the calcination

A schematic representation of the rotary kiln is shown in FIG. 1 attached to this document. The following reference numbers refer to this FIG. 1.

The central element of the rotary kiln is the rotary tube (1). It is 4000 mm long and has an inside diameter of 700 mm. It is made of stainless steel 1.4893 and has a wall thickness of 10 mm.

On the inner wall of the rotary kiln, lances are attached, which have a height of 5 cm and a length of 23.5 cm. They primarily serve the purpose of lifting the material to be treated thermally in the rotary kiln and thereby mixing it.

At one and the same height of the rotary kiln, four lifting lances (one quadruple) are attached equidistantly around the circumference (each 90 ° apart). Along the

There are eight such quadruples in the rotary kiln (each 23.5 cm apart). The stroke lances of two neighboring quadruples are circumferentially puts. There are no lances at the beginning and end of the rotary kiln (first and last 23.5 cm).

The rotary tube rotates freely in a cuboid (2) which has four electrically heated (resistance heating) heating zones, which each follow the same length in the length of the rotary tube, each of which encloses the circumference of the rotary tube furnace. Each of the heating zones can heat the corresponding rotary tube section to temperatures between room temperature and 850 ° C. The maximum heating output of each heating zone is 30 kW. The distance between the electrical heating zone and the outer surface of the rotary tube is approximately 10 cm. At the beginning and at the end the rotary tube protrudes approx. 30 cm from the cuboid.

The speed of rotation can be variably set between 0 and 3 revolutions per minute. The rotary tube can be turned left as well as right. When turning to the right, the material remains in the rotary tube, when turning to the left, the material is conveyed from the entry (3) to the discharge (4). The angle of inclination of the rotary tube to the horizontal can be variably set between 0 ° and 2 °. In discontinuous operation, it is actually 0 °. In continuous operation, the lowest point of the rotary tube is at the material discharge. The rotary tube can be rapidly cooled by switching off the electrical heating zones and switching on a fan (5). This sucks in ambient air through holes (6) in the lower floor of the cuboid and conveys it through three flaps (7) in the lid with a variably adjustable opening.

The material input is checked via a rotary valve (mass control). As already mentioned, the material discharge is controlled via the direction of rotation of the rotary tube.

With discontinuous operation of the rotary tube, a material quantity of 250 to 500 kg can be thermally treated. It is usually only in the heated part of the rotary tube.

From a lance (8) lying on the central axis of the rotary tube, a total of three thermocouples (9) lead vertically into the material at intervals of 800 mm. They enable the temperature of the material to be determined. In this document, the temperature of the material is understood to mean the arithmetic mean of the three thermocouple temperatures. Within the material in the rotating tube, the maximum deviation of two measured temperatures is expediently less than 30 ° C., preferably less than 20 ° C., particularly preferably less than 10 ° C. and very particularly preferably less than 5 or 3 ° C. Gas streams can be passed through the rotary tube, by means of which the calcining atmosphere or generally the atmosphere of the thermal treatment of the material can be adjusted.

The heater (10) offers the possibility of heating the gas flow into the rotary tube to the desired temperature in advance of its entry into the rotary tube (e.g. to the temperature desired for the material in the rotary tube). The maximum output of the heater is 1 x 50 kW + 1 x 30 kW. In principle, the heater (10) can e.g. act as an indirect heat exchanger. Such a heater can in principle also be used as a cooler. As a rule, however, it is an electric heater in which the gas flow is conducted over metal wires heated by current (expediently a CSN instantaneous heater, type 97D / 80 from C. Schniewindt KG, 58805 Neuerade - DE).

In principle, the rotary tube device provides the possibility of partially or completely circulating the gas flow guided through the rotary tube. The circular line required for this is movably connected to the rotary tube at the rotary tube inlet and at the rotary tube outlet via ball bearings or via graphite press seals. These compounds are flushed with inert gas (e.g. nitrogen) (sealing gas). The two flushing streams (11) supplement the gas stream passed through the rotary tube at the inlet into the rotary tube and at the outlet from the rotary tube. The rotary tube expediently tapers at its beginning and at its end and protrudes into the tube of the circular line that leads in and out.

A cyclone (12) is located behind the outlet of the gas stream guided through the rotary tube, for separating solid particles entrained in the gas stream (the centrifugal separator separates solid particles suspended in the gas phase by the interaction of centrifugal and gravity forces; the centrifugal force of the gas stream rotating as a spiral vortex accelerates the sedimentation of the suspended particles).

The circulating gas flow (24) (the gas circulation) is conveyed by means of a circulating gas compressor (13) (fan) which draws in in the direction of the cyclone and presses in the other direction. Immediately behind the cycle gas compressor, the gas pressure is usually above one atmosphere. There is a behind the cycle gas compressor

Circulating gas outlet (circulating gas can be discharged via a control valve (14)). A cover located behind the outlet (cross-sectional taper by a factor of 3, pressure reducer) (15) facilitates the outlet.

The pressure behind the rotary tube outlet can be regulated via the control valve. This is done in conjunction with a pressure sensor (16), which is located behind the rotary tube outlet, the exhaust gas compressor (17) (fan), which is connected to the control valve. straightens the suction, the cycle gas compressor (13) and the fresh gas supply. Relative to the external pressure, the pressure (directly) behind the rotary tube outlet can be set, for example, up to +1, 0 mbar above and, for example, up to -1, 2 mbar below. That is, the pressure of the gas stream flowing through the rotary tube can be below the ambient pressure of the rotary tube when it leaves the rotary tube.

If the intention is not to circulate the gas flow through the rotary tube at least in part, the connection between the cyclone (12) and the cycle gas compressor (13) is closed according to the three-way valve principle (26) and the gas flow is passed directly into the exhaust gas purification device (23) guided. The connection to the exhaust gas cleaning device located behind the cycle gas compressor is also closed in this case according to the three-way valve principle. If the gas flow consists essentially of air, in this case it is sucked in (27) via the cycle gas compressor (13). The connection to the cyclone is closed according to the three-way valve principle. In this case, the gas stream is preferably drawn through the rotary tube, so that the internal pressure of the rotary tube is less than the ambient pressure.

With continuous operation of the rotary kiln device, the pressure behind the rotary tube outlet is advantageously set to be -0.2 mbar below the external pressure. In the case of discontinuous operation of the rotary tube device, the pressure behind the rotary tube outlet is advantageously set to be -0.8 mbar below the external pressure. The slight negative pressure serves the purpose of avoiding contamination of the ambient air with gas mixture from the rotary kiln.

There are sensors (18) between the cycle gas compressor and the cyclone which, for example, determine the ammonia content and the oxygen content in the cycle gas. The ammonia sensor preferably works according to an optical measuring principle (the absorption of light of a certain wavelength correlates proportionally to the ammonia content of the gas) and is expediently a device from Perkin & Eimer of the type MCS 100. The oxygen sensor is based on the paramagnetic properties of oxygen and is expedient an Oximat from Siemens of the type Oxymat MAT SF 7MB1010-2CA01-1AA1-Z.

Gases such as air, nitrogen, ammonia or other gases can be metered in between the orifice (15) and the heater (10) to the actually recirculated gas fraction (19). A base load of nitrogen is often added (20). With a separate nitrogen / air splitter (21) you can react to the measured value of the oxygen sensor.

The discharged cycle gas portion (22) (exhaust gas) often contains not completely harmless gases such as NO _x , acetic acid, NH ₃ , etc.), which is why these are normally separated off in an exhaust gas cleaning device (23). For this purpose, the exhaust gas is generally first passed through a scrubbing column (is essentially a column free of internals, which contains a packing which separates it before it leaves; the exhaust gas and aqueous spray mist are conducted in cocurrent and in countercurrent (2 spray nozzles with opposite spray directions) ,

Coming from the scrubbing column, the exhaust gas is led into a device which contains a fine dust filter (usually a bundle of hose filters), from the interior of which the penetrated exhaust gas is led away. Then it is finally burned in a muffle.

Using a sensor (28) from KURZ Instruments, Inc., Montery (USA) of the Model 455 Jr type, the amount of gas flow that is different from the sealing gas and is supplied to the rotary tube is measured and regulated (measuring principle: thermal convective mass flow measurement using a equal temperature anemometer).

In continuous operation, material and gas phase are passed through the rotary kiln in counterflow.

In connection with this example, nitrogen always means nitrogen with a purity> 99% by volume.

2. Production of a precursor mass for the purpose of producing a multielement oxide mass with the stoichiometry Mo ^ VsW ^ Cu _∑ ^ Ox

16.3 kg of copper (II) acetate hydrate (content: 40.0% by weight of CuO) were dissolved in 274 l of water at a temperature of 25 ° C. with stirring. A clear solution 1 was obtained.

Spatially separated from this, 614 l of water were heated to 40 ° C. and 73 kg of ammonium heptamolybdate tetrahydrate (81.5% by weight of MoO ₃ ) were stirred in while maintaining the 40 ° C. The mixture was then heated to 90 ° C. in the course of 30 minutes and, while maintaining this temperature, 11.3 kg of ammonium metavanadate and 10.7 kg of ammonium paratungstate heptahydrate (88.9% by weight of WO ₃ ) were stirred in successively and in the order mentioned. A clear solution 2 was obtained.

Solution 2 was cooled to 80 ° C. and then solution 1 was stirred into solution 2. The resulting mixture was mixed with 130 l of a 25% by weight aqueous NH ₃ solution which had a temperature of 25 ° C. With stirring, a clear solution was formed which briefly had a temperature of 65 ° C. and a pH of 8.5. A further 20 l of water at a temperature of 25 ° C. were added to this. The temperature of the resulting solution then rose again to 80 ° C. and this was then sprayed with a spray dryer from Niro-Atomizer (Copenhagen) of type S- 50-N / R spray dried (gas inlet temperature: 350 ° C, gas outlet temperature:

110 ° C). The spray powder had a particle diameter of 2 to 50 μm.

60 kg of the spray powder obtained in this way were kneaded by AMK (Aachener

Mixing and kneading machines factory) of type VM 160 (Sigma blades) dosed and kneaded with the addition of 5.5 I acetic acid (= 100% by weight, glacial acetic acid) and 5.2 I water

(Speed of the screw: 20 rpm). After a kneading time of 4 to 5 minutes, a further 6.5 l of water were added and the kneading process was continued until 30 minutes had passed (kneading temperature approx. 40 to 50 ° C.). Then the kneaded material was placed in a

Extruder emptied and by means of the extruder (Bonnot Company (Ohio), type: G 103-10 / D7A-572K (6 "extruder W packer) to strands (length: 1-10 cm; diameter

6 mm) shaped. The strands were dried on the belt dryer for 1 hour at a temperature of 120 ° C. (material temperature). The dried strands formed the precursor mass to be thermally treated.

3. Production of the catalytic active mass by thermal treatment of the precursor mass (calcination of the precursor mass) in a rotary kiln device

The thermal treatment was carried out in the rotary tube furnace according to FIG. 1 described under “B) 1.” and under the following conditions: the thermal treatment was carried out discontinuously with a material quantity of 300 kg, which, as in “B) 2.” had been produced; the angle of inclination of the rotary tube to the horizontal was * 0 °; the rotating tube rotated clockwise at 1.5 revolutions / min; During the entire thermal treatment, a gas flow of 205 Nm ³ / h was passed through the rotary tube, which (after displacement of the air originally contained) was composed as follows and supplemented by a further 25 Nm ³ / h barrier gas nitrogen at its outlet from the rotary tube has been:

80 Nm ³ / h composed of base load nitrogen (20) and gases released in the rotary tube, 25 Nm ³ / h barrier gas nitrogen (11), 30 Nm ³ / h air (splitter (21)); and 70 Nm ³ / h recirculated cycle gas (19).

The sealing gas nitrogen was supplied at a temperature of 25 ° C. The mixture of the other gas streams coming from the heater was fed into the rotary tube at the temperature that the material had in the rotary tube. The material temperature was heated from 25 ° C to 300 ° C essentially linearly within 10 h; the material temperature was then heated essentially linearly to 360 ° C. in the course of 2 h; subsequently the material temperature was reduced substantially linearly to 350 ^° C. within 7 hours; the material temperature was then increased substantially linearly to 420 ° C. in the course of 2 h and this material temperature was held for 30 min; Then the 30 Nm ³ / h of air were replaced in the gas flow through the rotary tube by a corresponding increase in the base load nitrogen (which ended the process of the actual thermal treatment), the heating of the rotary tube was switched off and the material was switched on by the rapid cooling of the rotary tube cooled by sucking in ambient air within 2 h to a temperature below 100 ° C and finally to ambient temperature; the gas stream was fed to the rotary tube at a temperature of 25 ° C;

- During the entire thermal treatment, the pressure (immediately) behind the rotary tube outlet of the gas stream was 0.2 mbar below the external pressure.

The oxygen content of the gas atmosphere in the rotary kiln was 2.99 vol.% In all phases of the thermal treatment. Arithmetically averaged over the total duration of the reductive thermal treatment, the ammonia concentration in the gas atmosphere in the rotary kiln was 4% by volume.

2 shows the amount of ammonia released from the precursor mass as a function of the material temperature in ° C. as a percentage of the total amount of ammonia released from the precursor mass in the overall course of the thermal treatment.

3 shows the ammonia concentration of the atmosphere in vol.% In which the thermal treatment was carried out as a function of the material temperature in ° C. during the thermal treatment.

Fig. 4 shows, depending on the material temperature, the molar amounts of molecular oxygen and ammonia, which were fed into the rotary tube per kg of precursor mass and hour via the thermal treatment with the gas stream. 4. Shape of the multimetal oxide active material

The catalytically active material obtained under “B) 3.” was ground using a Biplex cross-flow classifier mill (BQ 500) (from Hosokawa-Alpine Augsburg) to form a finely divided powder, of which 50% of the powder particles were a sieve with a mesh size of 1 to 10 μm happened and its proportion of particles with a longest expansion above 50 μm was less than 1%.

The shape was now as follows:

70 kg ring-shaped carrier body (7.1 mm outer diameter, 3.2 mm length, 4.0 mm inner diameter; steatite of the type C220 from CeramTec with a surface roughness R _z of 45 μm and a total pore volume based on the volume of the carrier body ≤ 1 Vol .-%; see DE-A 2135620) were filled into a coating pan (inclination angle 90 °; Hicoater from Lödige, DE) with an internal volume of 200 l. The coating pan was then set in rotation at 16 rpm. 3.8 to 4.2 liters of an aqueous solution of 75% by weight of water and 25% by weight of glycerol were sprayed onto the support bodies in the course of 25 minutes via a nozzle. At the same time, 18.1 kg of the ground multimetal oxide active composition (the specific surface area of which was 13.8 m ² / g) were metered in continuously via a shaking channel outside the spray cone of the atomizing nozzle. During the coating, the powder supplied was completely absorbed onto the surface of the carrier body, and no agglomeration of the finely divided oxidic active material was observed. After completion of the addition of active material powder and water was stirred at a rotational speed of 2 rev / min for 40 min (alternatively 15 to 60 min) 100 ° C (alternatively, 80 to 120 ^C C) hot air (about 400 m ³ / h) in the coating pan blown. Annular shell catalysts K _{A were} obtained, the proportion of active oxide mass, based on the total mass, of 20% by weight. The shell thickness, viewed both over the surface of a carrier body and over the surface of various carrier bodies, was 170 ± 50 μm.

FIG. 5 also shows the pore distribution of the ground active mass powder before it is shaped. The pore diameter is plotted in μm on the abscissa (logarithmic scale).

The logarithm of the differential contribution in ml / g of the respective pore diameter to the total pore volume is plotted on the right ordinate (curve O). The maximum shows the pore diameter with the largest contribution to the total pore volume. The integral over the individual contributions of the individual pore diameters to the total pore volume is plotted on the left ordinate in ml / g (curve ty) The end point is the total pore volume (all information in this document on determinations of total pore volumes and of diameter distributions to them Unless otherwise stated, total pore volumes relate to determinations using the mercury porosimetry method using the Auto Pore 9220 device from Micromeritics GmbH, 4040 Neuss, DE (bandwidth 30 A to 0.3 mm); All information in this document on determinations of specific surfaces or micropore volumes refer to determinations according to DIN 66131 (determination of the specific surface of solids by gas adsorption (N ₂ ) according to Brunauer-Emmet-Teller (BET))).

FIG. 6 shows the individual contributions of the individual pore diameters (abscissa, in angstroms, logarithmic scale) in the micropore range to the total pore volume for the active mass powder in ml / g (ordinate) before it is shaped.

FIG. 7 shows the same as FIG. 5, but for multimetal oxide active composition subsequently detached from the annular coated catalyst K _A by mechanical scraping (its specific surface area was 12.9 m ² / g).

FIG. 8 shows the same as FIG. 6, but for the multimetal oxide active composition subsequently detached from the annular coated catalyst by mechanical scraping.

C) Carrying out a two-stage partial oxidation of propene to acrylic acid (on an industrial scale)

Description of the general process conditions in the propene reaction stage (propene → acrolein)

Heat exchange medium used: molten salt, consisting of 60% by weight of potassium nitrate and 40% by weight of sodium nitrite.

Contact tube material: ferritic steel.

Dimensions of the contact tubes: 3200 mm length; 25 mm inner diameter; 30 mm outer diameter (wall thickness: 2.5 mm).

Number of contact tubes in the tube bundle: 25500.

Reactor: cylindrical vessel with a diameter of 6800 mm; ring-shaped tube bundle with a free central space.

Central free space diameter: 1000 mm. Distance of the outermost contact tubes to the tank wall: 150 mm. homogeneous ne contact tube distribution in the tube bundle (6 equidistant neighboring tubes per contact tube).

Contact tube pitch: 38 mm.

The ends of the contact tubes were sealed in contact tube bottoms with a thickness of 125 mm and each of their openings opened into a hood connected to the container at the upper and lower ends. A baffle plate was located between the upper hood and the upper contact tube base, against which the supplied reaction gas mixture flowed and was then redirected to the contact tubes.

Feeding the heat exchange medium to the tube bundle:

The tube bundle was divided into 4 equidistant (each 730 mm) longitudinal sections (zones) by three deflection disks (thickness 10 mm each) successively attached along the same along the contact tube sheets.

The bottom and the top deflection plate had ring geometry, the inner ring diameter being 1000 mm and the outer ring diameter extending sealingly up to the container wall. The contact tubes were not attached in a sealing manner to the deflection disks. Rather, a gap width of <0.5 mm was left in such a way that the cross-flow velocity of the molten salt was as constant as possible within a zone.

The middle baffle was circular and extended to the outermost contact tubes of the tube bundle.

The circulation of the molten salt was accomplished by two salt pumps, each of which supplied one half of the tube bundle.

The pumps pressed the molten salt into an annular channel around the bottom of the reactor jacket, which distributed the molten salt over the circumference of the vessel. The salt melt reached the tube bundle in the lowest longitudinal section through windows in the reactor jacket. The molten salt then flowed from outside to inside, from inside to outside in accordance with the specification of the baffle plates, from outside to inside, from inside to outside,

essentially meandering, viewed from above, from bottom to top. Through the windows in the uppermost longitudinal section around the circumference of the vessel, the molten salt collected in an upper ring channel around the reactor jacket and, after cooling to the original inlet temperature, was pressed back into the lower ring channel by the pumps.

The composition of the reaction gas starting mixture 1 (mixture of air, chemical grade propylene and cycle gas) was in the following pattern over the operating time:

5 to 7 vol.% Propene (chemical grade), 10 to 14 vol.% Oxygen, 1 to 2 vol.% CO _x , 1 to 3 vol.% H ₂ O, and at least 80 vol.% N ₂ .

Reactor feed: The molten salt and reaction gas mixture were passed through the reactor in countercurrent. The molten salt entered at the bottom, the reaction gas mixture at the top. The inlet temperature of the molten salt was 337 ° C at the beginning. The initial temperature of the molten salt was 339 ° C. The pumping capacity was 6200 m ³ molten salt / h. The reaction gas starting mixture was fed to the reactor at a temperature of 300 ° C.

Propen load of the fixed catalyst bed for propene partial oxidation: 100 to 120 Nl / l-h

Contact tube loading with fixed catalyst bed for propene partial oxidation (from top to bottom): Zone A: 50 cm pre-filling of steatite rings with a geometry of 7 mm x 7 mm x 4 mm (outer diameter x length x inner diameter) Zone B: 100 cm catalyst feed with a homogeneous mixture of 35% by weight of steatite rings of geometry 5 mm x 3 mm x 2 mm (outer diameter x length x inner diameter) and 65% by weight of that produced in A) annular full catalyst Kp).

Zone C: 170 cm catalyst feed with the annular (5 mm x 3 mm x 2 mm = outer diameter x length x inner diameter) produced in A) full catalyst Kp.

The thermotubes (their number was 10, which were evenly distributed in the central area of the tube bundle) were designed and loaded as follows: (they were used to determine the hot point temperature (maximum temperature along a thermotube) to control the inlet temperature of the molten salt; it is an arithmetic mean of independent measurements in the 10 thermotubes)

Each of the 10 thermotubes had a central thermowell with 40 temperature measuring points (that is, each thermotube contained 40 thermocouples, which were integrated into a thermowell with different lengths and thus formed a multithermocouple, with which the temperature could be determined simultaneously within the thermotube at different heights ).

At least 13 and at most 30 of the 40 temperature measuring points each were in the area of the first meter of the active section of the fixed catalyst bed (in the direction of flow of the reaction gas mixture).

The inside diameter of a thermotube was 27 mm. The wall thickness and the pipe material were the same as for the working pipes.

The outer diameter of the thermal sleeve was 4 mm.

The thermal tubes were filled as follows: A thermal tube was filled with the annular unsupported catalyst K _p produced in A). In addition, the ring was made into the thermotube Fully catalytic converter K _p filled catalyst split of the longest dimension 2 to 3 mm.

The catalyst split was homogeneously distributed over the entire active section of the fixed catalyst bed of the respective thermal tube in such a way that the pressure loss of the reaction gas mixture when it passed through the thermal tube corresponded to that when the reaction gas mixture was passed through a working tube (based on the active section of the fixed catalyst bed (ie, the Except for inert sections (5 to 20% by weight of catalyst split was required in the thermotube). At the same time, the respective total filling level of active and inert sections in the working and thermotubes was dimensioned the same and the ratio of the total amount of active mass contained in the tube to the heat transfer area of the tube for working and thermotubes was set to essentially the same value.

II. Description of intermediate cooling

The product gas mixture leaving the propene reaction stage with a temperature essentially corresponding to the molten salt outlet temperature was passed through a single-zone tube bundle heat exchanger made of ferritic steel cooled with a molten salt of 60% by weight of potassium nitrate and 40% by weight of sodium nitrite, for the purpose of intermediate cooling. which was flanged directly to the reactor. The distance from the lower tube sheet of the reactor to the upper tube sheet of the cooler was 10 cm. The molten salt and the product gas mixture were passed through the heat exchanger in countercurrent. The salt bath itself flowed in a meandering manner around the cooling tubes through which the product gas mixture was passed, as in the first-stage, single-zone, multi-contact tube, fixed-bed reactor. The length of the cooling pipes was 1.65 m, their inner diameter was 2.6 cm and their wall thickness was 2.5 mm. The number of cooling pipes was 8,000. The diameter of the heat exchanger was 7.2 m.

They were evenly distributed over the cross-section with uniform pipe division.

Spirals made of stainless steel were introduced into the entrance of the cooling pipes (in the direction of flow), the cross-section of which almost corresponded to that of the cooling pipes. Their length was 700 mm to 1000 mm (alternatively, the cooling tubes can be filled with large inert material rings). They served to improve the heat transfer.

The product gas mixture left the intercooler at a temperature of 250 ° C. Subsequently, compressed air, which had a temperature of 140 ° C., was admixed in an amount of about 6700 Nm ³ / h, so that the one described below Composition of the feed gas mixture for the acrolein reaction stage resulted.

The resulting feed gas mixture (reaction gas starting mixture 2) was fed to the single-zone multi-contact tube fixed-bed reactor of the acrolein reaction stage at a temperature of 220 ° C.

III. Description of the general process conditions in the acrolein reaction stage (acrolein → acrylic acid)

A single-zone multi-contact tube fixed bed reactor was used which was identical to that of the first stage.

The composition of the feed gas mixture (reaction gas starting mixture 2) was in the following pattern over the operating time:

4 to 6% by volume of acrolein,

5 to 8% by volume of O ₂ , 1, 2 to 2.5% by volume of CO _x , 6 to 10% by volume of H ₂ O and at least 75% by volume of N ₂ .

Reactor feed: molten salt and feed gas mixture were passed through the reactor in countercurrent. The molten salt entered at the bottom, the feed gas mixture at the top.

The inlet temperature of the molten salt was approximately 263 ° C. at the beginning (after the formation of the fixed catalyst bed for the acrolein partial oxidation). The associated outlet temperature of the molten salt was initially around 265 ° C.

The pumping capacity was 6200 m ³ molten salt / h.

The reaction gas starting mixture was fed to the reactor at a temperature of 240 ° C. Acrolein load of the fixed catalyst bed for partial acrolein oxidation: 90 to 110 Nl / lh

The catalyst tube feed with fixed catalyst bed for the acrolein partial oxidation (from top to bottom) was: Zone A: 20 cm spillage of steatite rings of geometry 7 mm x 7 mm x 4 mm (outer diameter x length x inner diameter).

Zone B: 100 cm catalyst feed with a homogeneous mixture of 30% by weight of steatite rings of geometry 7 mm x 3 mm x 4 mm (outer diameter x length x inner diameter) and 70% by weight of the ring-shaped (approx. 7 mm x 3 mm x 4 mm) in B) produced shell catalyst K _A.

Zone C: 200 cm catalyst charge with the annular (about 7 mm x 3 mm x 4 mm) in B) produced coated catalyst K _A.

The thermal tubes (their number was 10, which were evenly distributed in the central area of the tube bundle) were designed and loaded as follows:

(They were used to determine the hot point temperature (maximum temperature along a thermal tube) to control the inlet temperature of the molten salt; it is an arithmetic mean value from independent measurements in the 10 thermal tubes)

At least 13 and at most 30 of the 40 temperature measuring points were located in the area of the first meter of the active section of the fixed catalyst bed (in the flow direction of the reaction gas mixture). The inside diameter of a thermotube was 27 mm. The wall thickness and the pipe material were the same as for the working pipes.

The outer diameter of the thermal sleeve was 4 mm.

The thermal tubes were filled as follows:

A thermotube was filled with the annular coated catalyst K _A produced in B). In addition, spherical shell catalyst was added to the thermal tube (same active mass as the ring-shaped shell catalyst, the diameter of the Steatit C220 (CeramTec) carrier balls was 2-3 mm; the active mass fraction was 20% by weight, the production was carried out as for the ring-shaped shell catalyst K _A described, but the binder was a corresponding amount of water).

The spherical coated catalyst was charged homogeneously over the entire active section of the fixed catalyst bed of the respective thermal tube in such a way that the pressure loss of the reaction gas mixture when it passed through the thermal tube corresponded to that when it passed through a working tube (based on the active section of the Fixed catalyst bed (ie excluding the inert sections) in the thermotube required 5 to 20% by weight of spherical coated catalyst). At the same time, the respective total filling level of active and inert sections in the working and thermotubes was dimensioned the same and the ratio of the total amount of active mass contained in the tube to the heat transfer area of the tube for working and thermotubes was set to the same value.

III. Long-term operation (results)

The fixed catalyst bed of the tube bundle reactor for the propene partial oxidation to acrolein had been freshly fed 1.5 years before the catalyst bed of the tube bundle reactor for the acrolein partial oxidation to acrylic acid.

The sales target for the propene to be converted in a single passage of the reaction gas starting mixture 1 through the fixed catalyst bed of the propene oxidation stage was set at 97.5 mol%.

This conversion value could be maintained over time by gradually increasing the inlet temperature of the molten salt into the reactor of the propene reaction stage. The sales target for the acrolein to be converted in a single passage of the reaction gas starting mixture 2 through the fixed catalyst bed of the acrolein reaction stage was set at 99.3 mol%.

By gradually increasing the inlet temperature of the molten salt into the reactor of the acrolein reaction stage, this conversion value could be maintained over time if the process was carried out continuously.

The partial oxidation was interrupted about once per calendar month (the increase in the molten salt inlet temperature into the reactor of the acrolein reaction stage until the monthly interruption was always ≥ 0.3 ° C and ≤ 4 ° C; in the case of the reactor for the propene reaction stage the approximately monthly increase values were ≥ 0.5 ° C), the inlet temperature of the molten salt last used in the respective reaction stage and in the intercooler was maintained and a gas mixture G of 6% by volume G was used for a period of time t _G from 24 h to 48 h O ₂ and 95 vol .-% N with a loading of the fixed catalyst bed of the propene reaction stage of 30 Nl / lh through the entire reaction system. The partial oxidation was then continued and the entry temperature of the molten salt into the respective reaction stage was adjusted so that the sales target of the respective reaction stage was further achieved.

After more than two years of operation of the reaction system, as described above (calculated from a fresh charge of the propene reaction stage), the operating conditions and results after a passage of the gas mixture G through the reaction system and subsequent partial oxidation continuation after the 13th day of operation were as follows (d = Operating days after continuing the partial oxidation; SV = loading of the propene reaction stage with propene in Nl / lh; U ^Pro = propene conversion in mol% based on one pass; U ^Acr = acrolein conversion in mol% based on one pass; A ^M = on single pass and propene reacted yield of acrylic acid in mol%; A ^co = one pass and propene reacted related undesirable secondary yield of carbon oxides in mol%; T ¹ = salt bath inlet temperature in the propene reaction stage in ^C C; T ² = salt bath inlet temperature in the acrolein reaction stage in ° C; P ¹ = working pressure uck at the entrance to the propene reaction stage in mbar; P ² = working pressure at the entrance to the acrolein reaction stage in mbar):

(= Comparative example)

After the 20th day of operation, gas mixture G was again passed through the reaction system as described and the partial oxidation was then continued as described, with the difference that a pinhole was installed behind the outlet of the tube bundle reactor for the partial oxidation of acrolein to acrylic acid for the purpose of increasing the working pressure has been. The diameter of the pinhole was 1.23 m. It contained 37 equally distributed holes, the diameter of which was 9 cm. After the 13th day of operation (calculated from the continuation of the partial oxidation), the operating conditions and results were as follows:

(= Example) The comparison of the values for T ¹ shows in the example under the increased working pressure P ¹ with the same propene conversion a significantly lower salt bath inlet temperature in the reactor of the propene reaction stage, without this being accompanied by a significant increase in the CO _{x by-} product formation. In the acrolein reaction level, the activity-increasing effect of increasing the working pressure is also clearly recognizable. However, since the catalyst bed of the acrolein reaction stage was put into operation 1.5 years after the catalyst bed of the propene reaction stage, the deactivation of the catalyst bed of the acrolein stage has not progressed so far, which is why the effect of increasing the working pressure is not yet so pronounced. D) Performing a two-stage partial oxidation of propene to acrylic acid (on a laboratory scale)

I. Description of the experimental setup for the two reaction stages

Propene reaction stage

A reaction tube (V2A steel; 30 mm outer diameter, 2 mm wall thickness, 26 mm inner diameter, centered a thermo sleeve (to accommodate a thermocouple) with an outer diameter of 4 mm, length: 320 cm) was loaded from top to bottom as follows:

Section 1: 50 cm length steatite rings of geometry 7 mm x 7 mm x 4 mm (outer diameter x length x inner diameter) as a pre-fill.

Section 2: 100 cm length of catalyst feed with a homogeneous mixture of steat rings with a geometry of 5 mm x 3 mm x 2 mm (outer diameter x length x inner diameter) and 70% by weight of an annular full catalyst K _p (as in A) ).

Section 3: 170 cm length of catalyst feed with exclusively circular full catalyst K _p according to Section 2.

The reaction tube was thermostatted in countercurrent using a nitrogen-saturated salt bath (53% by weight of potassium nitrate, 40% by weight of sodium nitrite and 7% by weight of sodium nitrate).

Acrolein reaction stage

Section 1: 20 cm long pre-fill from steatite rings of geometry 7 mm x 7 mm x 4 mm (outer diameter x length x inner diameter). Section 2: 100 cm length of catalyst feed with a homogeneous mixture of 30% by weight of steatite rings of geometry 7 mm x 3 mm x 4 mm (outside diameter x length x inside diameter) and 70% by weight of the ring-shaped coated catalyst K _A ( as produced in B)).

Section 3: 200 cm length of catalyst feed with only an annular cup catalyst K _A according to Section 2.

The reaction tube was thermostatted in countercurrent using a nitrogen-saturated salt bath (53% by weight potassium nitrate, 40% by weight sodium nitrite and 7% by weight sodium nitrate).

Between the two reaction stages there was an intermediate cooler filled with inert material, through which the product gas mixture of the first reaction stage was passed and cooled to a temperature of 250 ° C. by indirect cooling.

The first reaction stage (propene → acrolein) was continuously charged with a reaction gas starting mixture of the following composition:

5.5 to 5.7% by volume of propene (polymer grade), 3 to 3.2% by volume of H ₂ O, 1 to 2% by volume of CO _x ,

0.01 to 0.02% by volume of acrolein,

10.4 to 10.6% by volume of O ₂ and a residual amount of 100% by volume of molecular nitrogen.

The loading of the catalyst feed with propene was chosen to be 130 Nl / lh. The salt bath temperature of the first reaction stage was T ¹ (° C). The salt bath temperature of the second reaction stage (acrolein → acrylic acid) was T ² (° C). So much compressed air, which had a temperature of 140 ° C., was metered into the product gas mixture leaving the intercooler at a temperature of 250 ° C. that a reaction gas starting mixture was fed to the second reaction stage, in which the ratio of molecular oxygen to acrolein (ratio of Vol .-% shares), 3 was. A throttling device was located behind the exit of the second reaction stage, which made it possible to regulate the working pressure.

Depending on the working pressure (the pressure is given in bar immediately before the first reaction stage), T ¹ and T ^{2 were} each set so that that the propene conversion was 97.5 mol% and the acrolein conversion was 99.3 mol% (in each case based on a single passage of the reaction gas mixture through the reaction system).

Depending on the working pressure, the following results of the table were obtained. The results refer to a reaction operation following a preceding uninterrupted operating time of 100 h at a working pressure of 1.1 bar and the same sales.

The temperatures T ^1max or T ^2ma are the maximum reaction temperatures in ° C prevailing in the respective reaction stage. ΔP ¹ and ΔP ² are the pressure losses in bar in the respective reaction stage.

table

US Provisional Patent Application No. 60 / 572,124, filed on May 19, 2004, is incorporated into the present application by reference. In view of the above teachings, numerous changes and deviations from the present invention are possible. It is therefore believed that the invention, within the scope of the appended claims, may be practiced otherwise than as specifically described herein.

Claims

claims

1. A process for the long-term operation of a heterogeneously catalyzed gas phase partial oxidation of at least one organic compound in at least one oxidation reactor, in which a reaction gas starting mixture containing the at least one organic compound, molecular oxygen and at least one inert diluent gas is passed through at least one catalyst bed located at elevated temperature characterized in that, in order to counteract the deactivation of the at least one catalyst bed, the working pressure in the gas phase, based on an identical loading of the at least one catalyst bed with reaction gas starting mixture in Nl / lh, is increased during the operating time of the catalyst bed.

2. The method according to claim 1, characterized in that the at least one organic compound is at least one compound from the group comprising propylene, acrolein, 1-butene, 2-butene, ethane, benzene, m-xylene, p -Xylene, isobutene, isobutane, tert-butanol, isobutyraldehyde, methyl ether of tert-butanol, o-xylene, naphthalene, butadiene, ethylene, propylene, propane or methacrolein.

3. The method according to claim 1 or 2, characterized in that the at least one oxidation reactor is a tube bundle reactor and the catalyst bed is a fixed catalyst bed.

4. The method according to any one of claims 1 to 3, characterized in that the heterogeneously catalyzed gas phase partial oxidation is the two-stage partial oxidation of propene to acrylic acid.

5. The method according to any one of claims 1 to 4, characterized in that the increase in the working pressure is at least 25 mbar.

6. The method according to any one of claims 1 to 5, characterized in that the increase in the working pressure is 50 to 3000 mbar.

7. The method according to any one of claims 1 to 6, characterized in that the increase in the working pressure is carried out continuously and in accordance with the deactivation rate of the at least one catalyst bed.

8. The method according to any one of claims 1 to 7, characterized in that the increase in the working pressure is carried out in stages.

8 drawings

9. The method according to any one of claims 1 to 8, characterized in that the at least one organic compound propylene and the active mass of the catalysts of the at least one catalyst bed and the elements molybdenum and / or tungsten and at least one of the elements bismuth, tellurium, antimony , Multi-element oxide containing tin and copper.

10. The method according to any one of claims 1 to 8, characterized in that the at least one organic compound acrolein and the active composition of the catalysts of the at least one catalyst bed is a multi-element oxide containing the elements Mo and V.

11. The method according to any one of claims 1 to 10, characterized in that a pressure control device is attached behind the outlet of the at least one oxidation reactor.

12. The method according to claim 11, characterized in that the pressure control device is a throttle valve, or a swirl regulator or a pinhole.

13. Device comprising at least one oxidation reactor and at least one device located behind the outlet of the at least one oxidation reactor for regulating the working pressure in the at least one oxidation reactor.

14. Device comprising at least one oxidation reactor, at least one column downstream of the oxidation reactor with internals which have a separating action and one device downstream of the oxidation reactor for regulating the working pressure in the at least one oxidation reactor.

15. The device according to claim 14, the oxidation reactor of which contains a catalyst bed and which additionally comprises an air compressor which is designed such that it can pass through a working pressure range of> 0.5 to 4 bar under a given load on the catalyst bed in the oxidation reactor with reaction gas starting mixture ,

16. The device according to one of claims 13 to 15, wherein the at least one oxidation reactor is a tube bundle reactor.

17. The device according to one of claims 13 to 16, wherein the device for regulating the working pressure is a pinhole.

18. The method according to any one of claims 1 to 12, characterized in that it is carried out in a device comprising an air compressor, so is designed so that it can run through a working pressure range of> 0.5 to 4 bar at a given load on the catalyst bed in the oxidation reactor with reaction gas starting mixture.

19. The apparatus according to claim 15, characterized in that the given load with reaction gas starting mixture is ≥ 1500 Nl / l-h.

20. The method according to claim 18, characterized in that the given load with reaction gas starting mixture is ≥ 1500 Nl / l-h.