DE19753817A1 - Production of acrolein and acrylic acid by catalytic oxidation of propane - Google Patents

Abstract

Heterogeneous, catalytic, gas-phase oxidation of propane to acrolein and/or acrylic acid comprises passing a mixture of propane, oxygen and optionally an inert gas, at 300-500 deg C, over a two-part fixed-bed catalyst, each part containing different, specific mixed metal oxide phases. The catalyst in the first bed (A) has the formula M<1>a Mo1-bM<2>b Ox (I) M<1> = cobalt, nickel, magnesium, manganese and/or copper; M<2> = wolfram, vanadium, tellurium, niobium, phosphorus, chromium, iron, antimony, cerium, tin and/or lanthanum; a = 0.5-1.5; b = 0-0.5; x = a number required to satisfy the valencies of the other components and the catalyst in the second bed (B) has formula Bia,Mob, X<1>c, X<2>d, X<3>e, X<4>f, X<5>g, X<6>h, Ox, (II) X<1> = wolfram, vanadium and/or tellurium; X<2> = alkaline earth metal, cobalt, nickel, zinc, manganese, copper, cadmium, tin and/or mercury; X<3> = iron, chromium and/or cerium; X<4> = phosphorus, arsenic, antimony and/or boron; X<5> = alkali metal, thallium and/or tin; X<6> = rare earth metal, titanium, zirconium, niobium, tantalum, rhenium, ruthenium, rhodium, silver, gold, aluminum, gallium, indium, silicon, germanium, thorium and/or uranium; a' = 0.01-8; b' = 0.1-30; c', d' and e' = 0-20; f' = 0-6; g' = 0-4; h' = 0-15 The starting mixture of reactants contains at least 5 volume % propane, at least 15 volume % oxygen and 0-35 volume % inert gas and it passes through layer A first, then through B.

Description

The present invention relates to a heterogeneous kata process lysed gas phase oxidation of propane to acrolein and / or Acrylic acid, which is made from propane, molecular oxygen and optionally inert gas existing reaction gas outlet mix at a temperature of 300 to 500 ° C over a feast bed catalyst leads.

Acrolein and acrylic acid are important intermediates that for example in the context of the production of active ingredients and Find polymers.

The process currently used mainly for large-scale African production of acrolein and / or acrylic acid forms the Gas phase catalytic oxidation of propene (e.g. EP-A 575 897), the propene predominantly as a by-product of the ethylene position is generated by steam cracking from Naphta.

Since the other areas of application of propene, e.g. B. The Her position of polypropylene, it would expand further and further advantageous over a large-scale, competitive capable, process for the production of acrolein and / or acrylic acid, whose raw material base is not propene but that e.g. B. naturally occurring in large quantities as a natural gas component Is propane.

EP-A 117146 proposes acrylic acid from propane by making propane in a first stage heterogeneous catalytic dehydrogenation with the exclusion of moles kular oxygen in a product stream containing propylene transferred and this for the oxidation of the propene contained therein by means of molecular oxygen to acrolein and / or acrylic acid in subsequent oxidation stages using suitable oxidation data conductors.

The disadvantage of this procedure is that it is necessary Way requires several reaction stages, the individual Reak tion stages realized under different reaction conditions need to be light.

Furthermore, the above-mentioned procedure is from Nach part, than that for the non-oxidative dehydrogenation of propane required catalyst due to carbon deposits relatively quickly  must be deactivated and regenerated. Because the dehydration product mixture also contains hydrogen, the CN-A 110532 doubts furthermore the possibility of a direct forwarding of the Dehydrogenation product mixture in a subsequent oxidation stage.

CN-A 1105352 and Y. Moro-oka in Proceedings of the 10th International Congress on Catalysis, July 19-24, 1992, Bu Budapest, Hungary, 1993, Elsevier Science Publishers B.V., S. 1982 to 1986, recommend propane first in a homogeneous to partially convert oxidative dehydration into propene and this without prior separation in subsequent heterogeneous catalysis oxidation levels in acrolein and / or acrylic acid respectively. The disadvantage of this procedure is that one partly also in the context of a homogeneous oxidative dehydrogenation of Propane goes hand in hand with propene carbon formation and that also Selectivity of product formation (acrolein and / or acrylic acid) not to be satisfied with such a procedure can In CN-A 1105352, this is due to homogeneous oxidative dehydration achieved selectivity in propene formation in the exemplary embodiments only ≦ 40% by volume and also Moro-oka is related to selectivities of acrolein formation restricted to converted propane of 64 mol%.

It has also been proposed to heterogeneously catalyze oxidative dehydrogenation of propane (this is not necessary maneuverably carbon formation) with a subsequent one heterogeneously catalyzed oxidation of the propene thus produced To couple acrolein and / acrylic acid (e.g. 210th ACS National Meeting, Chicago, August 20-24, 1995 or WO 97/36849). Closer Information about the type of coupling (usually require both reaction steps to be incompatible However, reaction conditions) were not made. The CN-A 1105352 even strongly advises against such a coupling since the achievable with reasonable propane sales Selectivities of propene formation in a heterogeneous kata did not lysed oxidative dehydration over those homogeneous oxidative dehydration.

In Topics in Catalysis 3 (1996) on pages 265 to 275 about the heterogeneously catalyzed oxidative dehydrogenation of propane Propene reported on cobalt and magnesium molybdenum data. Disadvantageous of the procedure of the aforementioned reference is that, probably to ensure satisfactory selectivity propene formation is carried out in high dilution, d. H., that the reaction containing propane and molecular oxygen starting gas mixture to 75 vol .-% from molecular nitrogen (Inert gas) exists. Such a high proportion of inert gas cannot  to stimulate coupling with a subsequent propene oxidation, it reduces the acroles that can be achieved in a single pass in and / or acrylic acid space-time yields. It also complicates such nitrogen content following propene oxidation possibly intended return of unconverted Propane and / or propene after acrolein and / or acrylic acid separation.

In Journal of Catalysis 167, 550-559 (1997) is also about the heterogeneously catalyzed oxidative dehydrogenation of propane Propene reported on molybdate. A disadvantage of the procedure this reference is that they also use a Reaction gas starting mixture recommends the proportion of moles molecular nitrogen is 70% by volume. Also calls for the aforementioned Reference a dehydration temperature of 560 ° C. Such a high one Dehydration temperature is also unable to be coupled with a subsequent heterogeneously catalyzed propene oxidation, since they lead to an oxidative propene conversion to acrolein and / or Acrylic acid usually used multimetal oxide active mass damage.

Journal of Catalysis 167, 560-569 (1997) also a dehydrogenation temperature of 560 ° C for a heterogeneously catalyzed oxidative dehydration recommended. In a similar way DE-A 19530454 also recommends temperatures above 500 ° C Temperatures for a heterogeneously catalyzed oxidative Dehydration from propane to propene.

Furthermore, the literature on experiments is heterogeneous catalyzed direct oxidation of propane to acrolein and / or Acrylic acid reports (e.g. conference proceedings, 210th ACS National Meeting, Chicago, August 20-24, 1995, FR-A 2693384 and 3rd World Congress on Oxidation Catalysis, R.K. Grasselli, S.T. Oyama, A.M. Gaffney and J.E. Ijyons (Editors), 1997 Elsevier Science B.V., pp. 375-382), but is also capable of this work either the reported selectivity of the acrolein and / or Acrylic acid formation and / or the reported yield of acro Linseed and / or acrylic acid not satisfactory in a single pass.

EP-B 608838 also relates to the heterogeneously catalyzed Direct oxidation of propane to acrylic acid. Disadvantage of the However, EP-B 608838 is exemplary in that document did not report selectivities of acrylic acid formation are workable. So this rework resulted in a vanishing selectivity of acrylic acid formation. Instead was in the reworking of these examples acrolein formation  found, however, the selectivity of acrolein formation ≦ 30 mol% was.

The object of the present invention was therefore a Process of heterogeneously catalyzed gas phase oxidation of Propane to acrolein and / or acrylic acid, where one is made from Propane, molecular oxygen and possibly inert gas existing reaction gas starting mixture at a temperature of 300 to 500 ° C leads over a fixed bed catalyst available to provide that described the disadvantages of the prior art level and / or recommended procedures.

Accordingly, a process of heterogeneously catalyzed gas phase oxidation of propane to acrolein and / or acrylic acid, in which a reaction gas starting mixture consisting of propane, molecular oxygen and optionally inert gas at a temperature of 300 to 500 ° C over a fixed bed catalyst, was found is characterized in that the fixed bed catalyst consists of two spatially successively arranged catalyst beds A, B, with the proviso that the active composition of the bed A at least one multimetal oxide of the general formula I.

M _a ¹ Mo _1-b M _b ² O _x

With
M ¹ = Co, Ni, Mg, Zn, Mn and / or Cu, preferably Co, Ni and / or Mg, particularly preferably Co and / or Ni,
M ² = W, V, Te, Nb, P, Cr, Fe, Sb, Ce, Sn and / or La, preferably as Sn, W, P, Sb and / or Cr, particularly preferably W, Sn and / or Sb ,
a = 0.5 to 1.5, preferably 0.7 to 1.2, particularly preferably 0.9 to 1.0,
b = 0 to 0.5, preferably <0 to 0.5 and particularly preferably 0.01 to 0.3 and
x = a number which is determined by the valency and frequency of the elements in I other than oxygen,
and the active mass of the bed B is at least one multimetal oxide of the general formula II

Bi _{a '} Mo _b' X ¹ _{c '} X ² _d' X ³ _{e '} X ⁴ _f' X ⁵ _{g '} X ⁶ _h' O _{x '} (II),

With
X ¹ = W, V and / or Te, preferably W and / or V
X ² = alkaline earth metal, Co, Ni, Zn, Mn, Cu, Cd, Sn and / or Hg, preferably Co, Ni, Zn and / or Cu, particularly preferably Co, Ni and / or Zn,
X ³ = Fe, Cr and / or Ce, preferably Fe and / or Cr,
X ⁴ = P, As, Sb and / or B, preferably P and / or Sb,
X ⁵ = alkali metal, Tl and / or Sm, preferably K and / or Na,
X ⁶ = rare earth metal, Ti, Zr, Nb, Ta, Re, Ru, Rh, Ag, Au, Al, Ga, In, Si, Ge, Th and / or U, preferably Si, Zr, Al, Ag, Nb and / or Ti,
a '= 0.01 to 8, preferably 0.3 to 4 and particularly preferably 0.5 to 2,
b '= 0.1 to 30, preferably 0.5 to 15 and particularly preferably 10 to 13,
c '= 0 to 20, preferably 0.1 to 10 and particularly preferably 0.5 to 3,
d '= 0 to 20, preferably 2 to 15 and particularly preferably 3 to 10,
e '= 0 to 20, preferably 0.5 to 10 and particularly preferably 1 to 7,
f '= 0 to 6, preferably 0 to 1,
g '= 0 to 4, preferably 0.01 to 1,
h '= 0 to 15, preferably 1 to 15 and
X '= a number which is determined by the valency and frequency of the elements in II other than oxygen,
and where the reaction gas starting mixture consists of ≧ 50% by volume of propane, ≧ 15% by volume of O ₂ and 0 to 35% by volume of inert gas and the catalyst beds A, B flow through A, then B, in the sequence.

Preferred multimetal oxides I are therefore those of the general formula I '

[Co, Ni u./o. Mg] _a Mo _1-b [Sn, W, P, Sb u./o. Cr] _b O _x (I '),

With
a = 0.5 to 1.5, preferably 0.7 to 1.2, particularly preferably 0.9 to 1.0,
b = 0 to 0.5, preferably <0 to 0.5 and particularly preferably 0.01 to 0.3 and
x is a number which is determined by the valency and frequency of the elements I 'other than oxygen.

Particularly preferred multimetal oxides I are those of the general formula I ''

[Co u./o. Ni] _a Mo _1-b [W, Sn u./o. Sb] _b O _x (I ''),

with the above meanings for a, b and x.

Preferred multimetal oxides II are those of the general formula II '

Bi _{a '} Mo _b' W _{c '} [Co, Ni u./o. Zn] _{d '} Fe _e' [P u./o. Sb] _{f '} [K u./o. Na] _{g '} X ⁶ _h' O _{X '} (II')

where x ⁶ and the stoichiometric coefficients have the meaning according to the general formula II.

Particularly preferred multimetal oxides II 'are those with X ⁶ = Si, Zr, Al, Nb, Ag and / or. Ti, among which those with X ⁶ = Si are preferred.

Furthermore, it is advantageous if e 'is 0.5 to 10, which is particularly true when X ⁶ = Si.

The above applies especially when the multimetal oxide materials II 'are produced in accordance with EP-B 575897.

Combinations I ', II' and I '', II 'are particularly advantageous catalyst bed pairs A, B. This is especially true when X ⁶ = Si and e '= 0.5 to 10.

This is advantageous in the method according to the invention Reaction gas starting mixture at a temperature of 325 to 480 or 450 ° C, preferably at 350 to 420 ° C and particularly preferred at 350 to 400 ° C above that from catalyst beds A, B existing fixed bed catalyst. Usually point the catalyst beds A, B have identical temperatures.

If the catalyst bed pair A, B used by a combination I ', II' or I '', II ', the reaction is temperature in both fillings with advantage 350 to 420, often 350 to 400 ° C.

Furthermore, the reaction gas starting mixture advantageously comprises ≦ 30% by volume, preferably ≦ 20% by volume and particularly preferably ≦ 10% by volume or ≦ 5% by volume of inert gas. Of course, the reaction gas starting mixture can also comprise no inert gas. Inert gas is understood here to mean those gases whose conversion when passing through the fixed bed catalyst to be used according to the invention is ≦ 5 mol%. As an inert gas z. B. H ₂ O, CO ₂ , CO, N ₂ and / or noble gases.

The reaction gas starting mixture furthermore advantageously contains ≧ 60% by volume, or ≧ 70% by volume, or ≧ 80% by volume of propane. As a general rule is the propane content of the one to be used according to the invention Reaction gas starting mixture at ≦ 85 vol .-%, often at ≦ 83 or ≦ 82 or ≦ 81 or ≦ 80 vol .-%. The content of the reaction gas starting mixture of molecular oxygen can in the invention according to methods up to 35 vol .-%. It lies with advantage at least 20% by volume or at least 25% by volume. Favorable reaction gas starting mixtures according to the invention ≧ 65 vol .-% and ≦ 85 vol .-% propane as well as ≧ 15 vol .-% and ≦ 35 vol .-% molecular oxygen. According to the invention advantageous (with regard on selectivity and conversion) when the molar ratio of Propane to molecular oxygen in the initial reaction mixture <5: 1, preferably ≦ 4.75: 1, better ≦ 4.5: 1 and particularly preferred ≦ 4: 1. As a rule, the aforementioned ratio ≧ 1: 1 or ≧ 2: 1.

In principle, active compositions I which are suitable according to the invention can be prepared in a simple manner by producing an innermost, preferably finely divided, stoichiometrically composed dry mixture of suitable sources of their elemental constituents, and calcining them at temperatures of 450 to 1000 ° C. The calcination can be carried out both under inert gas and under an oxidative atmosphere such as e.g. B. air (mixture of inert gas and oxygen) and also under a reducing atmosphere (z. B. mixture of inert gas, oxygen and NH ₃ , CO and / or H ₂ ). The calcination time can be a few minutes to a few hours and usually decreases with temperature. Suitable sources for the elementary constituents of the multimetal oxide active compositions 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 in particular halides, nitrates, formates, oxalates, citrates, acetates, carbonates, amine complex salts, ammonium salts and / or hydroxides (compounds such as NH ₄ OH, (NH ₄ ) ₂ CO ₃ , NH ₄ NO _3, NH ₄ CHO ₂ , CH ₃ COOH, NH ₄ CH ₃ CO ₂ and / or ammonium oxalate, which can decompose and / or decompose to form completely gaseous 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 masses I can take place in dry or in wet form. If it is done in dry form, the starting compounds are expediently used as finely divided powders and, after mixing and, if appropriate, compressing, 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 described dry process if it is assumed that the elemental constituents are present in dissolved form. 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. Particularly suitable starting compounds of Mo, V, W and Nb are their oxo compounds (molybdates, vanadates, tungstates and niobates) and the acids derived from them. This applies in particular to the corresponding ammonium compounds (ammonium molybdate, ammonium vanadate, ammonium volframate).

The multimetal oxide masses I can for the inventive Ver drive both in powder form and to certain catalyst geometries shaped are used, the shaping before or after the final calcination. At for example, from the powder form of the active material or its uncalcined precursor mass by compression to the desired Catalyst geometry (e.g. by tableting, extruding or Extrusion) full catalysts are produced, wherein optionally aids such. B. graphite or steric acid as Lubricants and / or molding aids and reinforcing agents such as Microfibers made of glass, asbestos, silicon carbide or potassium titanium can be added. Suitable all-catalyst geometries are e.g. B. solid cylinder or hollow cylinder with an outer diameter and a length of 2 to 10 mm. In the case of the hollow cylinder a wall thickness of 1 to 3 mm is appropriate. Of course the unsupported catalyst can also have spherical geometry, wherein the ball diameter can be 2 to 10 mm.

Of course, the shape of the powder Active composition or its powdery, not yet calcined, Precursor mass also by applying to preformed inert Catalyst carrier take place. The coating of the carrier body for Manufacture of the shell catalysts is usually in one suitable rotatable container executed, as z. B. from the DE-A 2909671 or EP-A 293859 is known. More appropriate way can be used to coat the carrier body Powder mass moistened and after application, e.g. B. means  hot air to be dried again. The layer thickness of the powder mass applied to the carrier body is expedient in the range from 50 to 500 μm, preferably in the range from 150 to 250 μm lying, chosen.

Usual porous or non-porous can be used as carrier materials Aluminum oxides, silicon dioxide, thorium dioxide, zirconium dioxide, Silicon carbide or silicates such as magnesium or aluminum silicate be used. The carrier bodies can be regular or irregular be shaped like a gel, with regularly shaped carrier bodies with clearly formed surface roughness, e.g. B. balls or Hollow cylinders are preferred. The use of essentially non-porous, rough, spherical Carriers made of steatite, the diameter of 1 to 8 mm, preferred 4 to 5 mm.

This applies to the production of multimetal oxide materials II for the multimetal oxide masses I said. However, that is Calcination temperature usually used 350 to 650 ° C. Particularly preferred multimetal oxide compositions II are those in the EP-B 575897 disclosed multimetal oxide compositions I, in particular their preferred versions. This makes you charak terized that initially from subsets of the elementary constants tuenten multimetal oxides pre-formed and further position history can be used as an element source.

The through takes place in an expedient manner in terms of application technology implementation of the method according to the invention in tube bundle reactors as they e.g. B. in EP-A 700893 and in EP-A 700714 ben are. Located in the metal pipes (usually made of stainless steel) is the fixed bed catalyst to be used according to the invention and a tempering medium is usually around the metal pipes a molten salt. That is, in the simplest way each reaction tube, the two to be used according to the invention Catalyst beds A, B in immediate succession arranged. The ratio of the bulk volumes of the two Catalyst beds A, B are advantageous according to the invention 1:10 to 10: 1, preferably 1: 5 to 5: 1 and particularly preferred 1: 2 to 2: 1, often 1: 1. The reaction pressure is generally mean ≧ 0.5 bar. As a rule, the reaction pressure becomes 100 bar do not exceed d. H. ≧ 0.5 to 100 bar. Appropriately reaction pressure is often <1 to 50 or <1 to 20 bar. The reaction pressure is preferably ≧ 1.25 or ≧ 1.5 or ≧ 1.75 or ≧ 2 bar. The upper limit of 10 or 20 bar is often used not exceeded. Of course, the reaction pressure also be 1 bar (the above statements regarding the reac tion pressure apply entirely to the inventive method  As a general rule). Furthermore, the load is advantageously chosen so that the residence time of the reaction gas mixture over the two Catalyst beds A, B 0.5 to 20 sec, preferably 1 to 10 sec, particularly preferably 1 to 4 sec and often 3 sec. Contained in the product mixture of the process according to the invention Propane and / or propene can be separated and used in the invention appropriate gas phase oxidation are recycled. Furthermore, can another heterogeneous kata to the method according to the invention Connect lysed oxidation stage, as for the heterogeneous Catalyzed gas phase oxidation of acrolein to acrylic acid are known, in which the product mixture of the Ver driving, possibly with the addition of further molecular Oxygen, is transferred. After that, again unreacted propane, propene and / or acrolein separated and be returned to the gas phase oxidations.

The acrolein and / or acrylic acid formed can be separated off from the product gas mixtures in a manner known per se. As a rule, the propane conversion achieved with the process according to the invention is ≧ 5 mol% or ≧ 7.5 mol%. Usually, however, no propane conversions ≧ 20 mol% are achieved. The method according to the invention is particularly suitable for a continuous implementation. If necessary, additional molecular oxygen can be injected at the level of the catalyst bed B. Incidentally, in this document turnover, selectivity and residence time, unless otherwise stated, are defined as follows:

Examples a) Production of a multimetal oxide mass I

292.4 g of ammonium heptamolybdate (81.5% by weight of MoO ₃ ) were dissolved in 1.2 kg of water at 80 ° C., and 742.4 g of aqueous cobalt nitrate solution (based on the solution, 12.5% by weight) were added to the resulting solution. % Co) added. The resulting solution was evaporated with stirring on a water bath at 100 ° C. until a pasty mass had formed. This was dried in a drying cabinet at 110 ° C for 16 h and then calcined in an air-flow muffle furnace (60 l internal volume, air flow rate 500 l / h) as follows: First, at a heating rate of 120 ° C / h from room temperature (25 ° C) heated to 300 ° C. The temperature was then maintained at 300 ° C. for 3 hours and then the calcination temperature was increased from 300 to 550 ° C. at a heating rate of 125 ° C./h. This temperature was then maintained for 6 hours. The multimetal oxide thus obtained was comminuted and the core fraction with a grain size diameter of 0.6 to 1.2 mm was separated by sieving as catalytically active multimetal oxide mass I of stoichiometry Mo ₁ Co _0.95 O _x .

b) Production of a multimetal oxide mass II 1. Production of a starting mass

50 kg of a solution of Bi (NO ₃ ) ₃ in aqueous nitric acid (11% by weight Bi, 6.4% by weight HNO ₃ , based in each case on the solution) was mixed with 13.7 kg ammonium paratungstate (89% by weight). % WO ₃ ) was added and the mixture was stirred at 50 ° C. for 1 h. The suspension obtained was spray dried and calcined at 750 ° C. for 2 hours. The pre-formed calcined mixed oxide thus obtained was ground and the particle size fraction 1 μm ≦ d ≦ 5 μm (d = particle size diameter) was classified. The grain fraction was then mixed with 1% of its weight of finely divided (number-average size 28 nm) SiO ₂ .

2. Production of a starting mass 2

48.9 kg of Fe (NO ₃ ) _{3 were} dissolved in 104.6 kg of Co nitrate solution (12.5% by weight of Co based on the solution). The resulting solution was added to a solution of 85.5 kg of ammonium heptamolybdate (81.5% by weight of MoO ₃ ) in 240 l of water. The resulting mixture was mixed with 7.8 kg of an aqueous mixture containing 20% by weight of colloidal SiO ₂ and 377 g of an aqueous solution containing 48% by weight of KOH. The mixture was then stirred for 3 hours and the resulting aqueous suspension was spray-dried to give starting material 2.

3. Production of the multimetal oxide II

The starting mass 1 was compared with the starting mass 2 for a multimetal oxide II of stoichiometry

Mo ₁₂ W ₂ Bi ₁ Co _5.5 Fe ₃ Si _1.6 K _0.08 O _{x '}

required quantity mixed and to hollow cylinders with 3 mm Length, 5 mm outer diameter and 1.5 mm wall thickness and pressed then calcined as follows. The calcination took place in Air flowing through the muffle furnace (60 l internal volume, 1 l / h air per gram of catalyst precursor mass). With a heating rate of 180 ° C / h was first from room temperature (25 ° C) to 190 ° C heated. This temperature was maintained for 1 h and then increased to 220 ° C with a heating rate of 60 ° C / h. The 220 ° C were again maintained for 2 h before using a Heating rate increased from 60 ° C / h to 260 ° C. The 260 ° C were then maintain for 1 h. After that was first cooled to room temperature and thus the decomposition phase in essentially completed. Then with a heating rate of Heated to 180 ° C / h at 465 ° C and this calcination temperature during Maintain for 4 hours.

200 g of the resulting active mass were crushed and the Grain fraction 0.6 to 1.2 mm as multimetal oxide active material II sifted out.

c) Gas phase catalytic oxidation of propane

A reaction tube (V2A steel; 2.5 cm wall thickness; 8.5 mm inside diameter; electrically heated) the length of 1.4 m was from below up on a contact chair (7 cm long) first on a Length of 13 cm with quartz chips (number-average size diameter 1 to 2 mm) and then over a length of 42.5 cm with the Multimetal oxide active material II and then on a Length of 42.5 cm loaded with the multimetal oxide active material I, before loading with a length of 13 cm with quartz chips (number average size diameter 1 to 2 mm) completed has been.

The reaction tube charged as above was on his entire length heated to 430 ° C and then with 56 Nl / h Reaction gas starting mixture of 80 vol% propane and 20 vol% Charged with oxygen.  

In a single pass, a product gas mixture was obtained which had the following characteristics:
Propane conversion: 10 mol%
Selectivity of acrolein formation: 59 mol%
Selectivity of acrylic acid formation: 14 mol%
Selectivity of propene formation: 3 mol%.

Claims (11)

1. The process of heterogeneously catalyzed gas phase oxidation of propane to acrolein and / or acrylic acid, in which a reaction gas starting mixture consisting of propane, molecular oxygen and optionally inert gas is conducted at a temperature of 300 to 500 ° C. over a fixed bed catalyst, characterized in that the fixed bed catalyst consists of two spatially successively arranged catalyst beds A, B, with the proviso that the active mass of the bed A at least one multimetal oxide of the general formula I
M _a ¹ Mo _1-b M _b ² O _x (I),
With
M ¹ = Co, Ni, Mg, Zn, Mn and / or Cu,
M ² = W, V, Te, Nb, P, Cr, Fe, Sb, Ce, Sn and / or La,
a = 0.5 to 1.5,
b = 0 to 0.5
x = a number which is determined by the valency and frequency of the elements in I other than oxygen,
and the active mass of the bed B at least one multi metal oxide of the general formula II
Bi _{a '} Mo _b' X ¹ _{c '} X ² _d' X ³ _{e '} X ⁴ _f' X ⁵ _{g '} X ⁶ _h' O _{x '} (II),
With
X ¹ = W, V and / or Te,
X ² = alkaline earth metal, Co, Ni, Zn, Mn, Cu, Cd, Sn and / or Hg,
X ³ = Fe, Cr and / or Ce,
X ⁴ = P, As, Sb and / or B,
X ⁵ = alkali metal, Tl and / or Sn,
X ⁶ = rare earth metal, Ti, Zr, Nb, Ta, Re, Ru, Rh, Ag, Au, Al, Ga, In, Si, Ge, Th and / or U,
a '= 0.01 to 8,
b '= 0.1 to 30,
c '= 0 to 20,
d '= 0 to 20,
e '= 0 to 20,
f '= 0 to 6,
g '= 0 to 4,
h '= 0 to 15,
x '= a number which is determined by the valency and frequency of the elements in II other than oxygen,
is, and the reaction gas starting mixture consists of ≧ 50 vol .-% propane, ≧ 15 vol .-% O ₂ and 0 to 35 vol .-% inert gas and flows through the catalyst beds A, B in the sequence first A, then B. 2. The method according to claim 1, characterized in that the Temperature is 325 to 450 ° C. 3. The method according to claim 1, characterized in that the Temperature is 350 to 420 ° C. 4. The method according to any one of claims 1 to 3, characterized indicates that the reaction gas starting mixture ≧ 60 vol .-% Contains propane. 5. The method according to any one of claims 1 to 3, characterized indicates that the reaction gas starting mixture ≧ 70 vol .-% Contains propane. 6. The method according to any one of claims 1 to 5, characterized in that the reaction gas starting mixture contains ≧ 20 vol .-% O ₂ . 7. The method according to any one of claims 1 to 6, characterized records that it is carried out continuously. 8. The method according to any one of claims 1 to 7, characterized records that the molar ratio of propane to molecular Oxygen in the reaction gas starting mixture is <5. 9. The method according to any one of claims 1 to 8, characterized records that the ratio of the bulk volumes of the two Catalyst beds A, B is 1: 5 to 5: 1. 10. The method according to any one of claims 1 to 9, characterized records that the reaction pressure is <1 bar.