MXPA00003076A - Method of heterogeneous catalyzed vapor-phase oxidation of propane to acrolein and/or acrylic acid - Google Patents

Abstract

The invention relates to a method of heterogeneous catalyzed vapor-phase oxidation in which a reaction gas initial mixture comprised of propane, molecular oxygen and optionally of inert gas is conducted over a fixed-bed catalyst at a temperature ranging from 300 to 500°C.

Description

OXIDATION OF PROPANE TO ACROLEIN AND / OR ACRYLIC ACID IN GASEOUS PHASE, HETEROGÉNEAMENTE CATALIZADA The present invention relates to a process for the gas phase oxidation, heterogeneously catalyzed, from propane to acrolein and / or acrylic acid, in which an initial mixture of reaction gases composed of propane, molecular oxygen and, if desired, Inert gas passes from 300 to 500 ° C on a fixed bed catalyst. Acrolein and acrylic acid are important intermediates that are used, for example / to produce active compounds and polymers. At present, by far the most widely used process for the industrial preparation of acrolein and / or acrylic acid is catalytic gas phase oxidation of propene (e.g., EP-A 575 897), with propene being mainly produced as a byproduct of ethylene production by fractionation of naphtha vapor. Since the other areas of application for propene, for example, the production of polypropylene, continues to expand, it would be advantageous to have a competitive process, of industrial use to prepare acrolein and / or acrylic acid that uses as nonpropene raw material but propane that , for example, is present in large quantities in its natural state as a constituent of natural gas.

EP-A 117146 proposes the preparation of acrylic acid from propane by converting propane into a product stream containing propylene by means of heterogeneous catalytic dehydrogenation in the absence of molecular oxygen in a first stage and, in subsequent oxidation stages, passing this current of product together with molecular oxygen on suitable oxidation catalysts to oxidize the propene present therein to acrolein and / or acrylic acid. A disadvantage of this method is that it necessarily requires a plurality of reaction steps, with individual reaction steps having been carried out under different reaction conditions. Furthermore, the aforementioned process has the disadvantage that the catalyst necessary for the non-oxidative dehydrogenation of propane is deactivated relatively quickly as a result of carbon deposits and has to be regenerated. Since the mixture of the dehydrogenation product also contains hydrogen, CN-A 1105352 mentions doubts about the possibility of passing the mixture of the dehydrogenation product directly in a subsequent oxidation step. CN-A 1105352 and Y. Moro-oka in Procedure of the Tenth International Congress on Catalysts, from July 19 to 24, 1992, Budapest, Hungary, 1993, Elsevier Science, Publishers BV pages 1982 to 1986, recommend first converting partially propane in propene in a homogeneous oxidative dehydrogenation and converting this propene, without separating it in advance, into acrolein and / or acrylic acid in heterogeneously catalyzed, subsequent oxidation stages. The disadvantages of this process are, on the one hand, that carbon is also formed in a homogeneous oxidative dehydrogenation of propane to propene and, on the other hand, that the selectivity of the formation of the desired product (acrolein and / or acrylic acid) does not it is satisfactory in such a procedure. Thus, in the examples in CN-A 1105352, the selectivity of the propene formation obtained by homogeneous oxidative dehydrogenation is only < 40% by volume and Moro-oJca is also limited to the 64% mol acrolein formation selectivities, based on the propane that reacts. It has also been proposed that a heterogeneously catalyzed oxidative dehydrogenation of propane (which is not necessarily accompanied by the formation of carbon) is coupled with a subsequent heterogeneously catalyzed oxidation of propene thus produced to obtain acrolein and / or acrylic acid (e.g. ACS National, Chicago, dated 20-24 of 1995 or WO 97/36849. However, no further details are provided regarding the type and form of the coupling (in general, both reaction steps require reaction conditions that can not be reconciled). CN-A 1105352 still strongly advises against coupling, given that, at reasonable propane conversions, the selectivities that can be obtained from the formation of propene in a heterogeneously catalyzed oxidative dehydrogenation does not exceed those of homogeneous oxidative dehydrogenation. Topics in Catalysis 3 (1996), page 265-275, reports the heterogeneously catalyzed oxidative dehydrogenation of propane to propene on cobalt molybdate and magnesium molybdate. A disadvantage of the aforementioned reference method is that, supposedly to ensure a satisfactory selectivity of the propene formation, it is carried out at a high dilution, that is, the initial mixture of reaction gases composed of propane and molecular oxygen also contains up to 75% by volume of inert nitrogen (inert gas). Such a high proportion of inert gas does not favor coupling with a subsequent propene oxidation, since it reduces the space-time yields of acrolein and / or acrylic acid that can be obtained in a single step. Furthermore, such a nitrogen ratio hinders the recirculation of unreacted propane and / or propene after having separated acrolein and / or acrylic acid, if this is attempted after the oxidation of propene. Journal of Catalysis 167 (1997), 550-559 in the same way reports the heterogeneously catalyzed oxidative dehydrogenation of propane to propene or molybdates [sic]. A disadvantage of the method in this reference is that it also recommends the use of an initial mixture of reaction gases whose molecular nitrogen ratio is 70% by volume. In addition, the aforementioned reference proposes a dehydrogenation temperature of 560 ° C. Such a high dehydrogenation temperature also does not suggest coupling for the oxidation of heterogeneously catalyzed propene, downstream, since it damages the ultimetal oxide compositions which are commonly used for an oxidative conversion of propene to acrolein and / or acrylic acid. Journal of Catalysis 167 (1997), 560-569 in the same way recommends a dehydrogenation temperature of 560 ° C for a heterogeneously catalyzed oxidative dehydrogenation. In the same way, DE-A 19530454 recommends temperatures above 500 ° C for a heterogeneously catalyzed oxydative dehydrogenation of propane to obtain propene. In addition, the literature reports experiments on a heterogeneously catalyzed direct oxidation of propane to acrolein and / or acrylic acid (eg, Proceedings, 210 ACS National Assembly, Chicago, 20-24 August 1994, FR-A 2693384 and the Third World Congress on Oxidation Catalysts, RK Grasselli, ST Oya a, AM Gaffney and JE Lyons (editors), 1997 Elsevier Science BV, pages 375-382), although in these studies, likewise, the reported selectivity of acrolein formation and / or acrylic acid and / or the reported yield of acrolein and / or acrylic acid in a single step are not satisfactory. EP-B 608838 in the same way refers to the heterogeneously catalyzed direct oxidation of propane to acrylic acid. However, a disadvantage of the method described in EP-B 608838 is that the selectivities of acrylic acid formation reported as examples herein can not be reproduced. Thus, our attempts to repeat the work provides a fleeting selectivity for the formation of acrylic acid. In contrast, acrolein formation was found when these examples were repeated, but the selectivity for acrolein formation was only 30 mol%. An object of the present invention is to provide a process for the gas-phase, heterogeneously catalyzed oxidation of propane to acrolein, and / or acrylic acid, in which an initial mixture of reaction gases passes from 300 to 500 ° C on a catalyst fixed bed, whose process does not have the disadvantages of the methods described and / or recommended in the prior art. We have found that this goal is achieved by a process for the gas phase oxidation, heterogeneously catalyzed from propane to acrolein and / or acrylic acid, in which an initial mixture of reaction gases containing propane, molecular oxygen, and if desired, inert is passed from 300 to 500 ° C on a fixed bed catalyst containing two catalytic beds A and B arranged in the space in succession, with the proviso that the active composition of bed A is at least one multi-valent oxygen of the Formula I: M1a Mox-b M2b 0K where M = Co, Ni, Mg, Zn, and / or Cu, preferably Co, Ni, and / or Mg, particularly preferably Co and / or Ni, M "* W, V, Te, Nb, P, Cr , Fe, Sb, Ce, Sn and / or La, preferably Sn, W, P, Sb and / or Cr, particularly preferably W, and / or Sb, 0.5-1.5, preferably 0.7-1.2, particularly preferably 0.9-1.0, b = 0-0.5, preferably> 0-0.5 and, particularly preferably 0.01-0.3, and x = a number that is determined by the valence and amount of the different oxygen elements in I, and the active composition of the B bed is at least one multimetal oxide of the formula II.

Bia, M? B, X ^, X2d X3e, X4f XSg, X6h, Ox, (II), where X = W, V and / or Te, preferably and / or VX = 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 = Fe, Cr, and / or Ce, preferably Fe, and / or Cr, X4 »P, As, Sb, and / or B, preferably P and / or Sb, X = alkali metal, TI, and / or Sn, preferably K and / or Na, X = rare earths, 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 '= 0.01-8, preferably 0.3-4 and, particularly preferably 0.5-2, b '= 0.1-30, preferably 0.5 to 15 and, particularly preferably 10-13, c' = 0-20, preferably 0.1 to 10 and particularly preferably 0.5-3, d ' = 0-20, preferably 2-15 and particularly preferably 3-10, e '= 0-20, preferably 0.5-10 and particularly preferably 1-7, f = 0-6, preferably 0-1, g '= o-4, preferably 0.01-1, h' = 0-15, preferably 1-15, x '= a number that is determined by the valence and amount of the different elements of oxygen in II, where the initial mixture of the reaction gases contains = 50% by volume of propane, > 15% by volume of Q 2 and from 0 to 35% by volume of inert gas and flows through the catalytic beds A and B in the first order A, then B. The preferred multimetal oxides I are, therefore, those of Formula 1" [Co, Ni a. /or. Mgja M? _ B [Sn, W, P, Sb a. /or. Cr] b Ox (IA) where at 0.5-1.5, preferably 0.7-1.2, particularly preferably 0.9-1.0, b = 0-0.5, preferably > 0-0.5 and particularly preferably 0.01-0.3, and x = is a number that is determined by the valence and amount of the different oxygen elements in I '. Particularly preferred multimetal oxides I are those of the formula I ".

[Co, a. / o. Ni] to MOi-b [W, Sn a. / o. Sb] b Ox (I 'where a, b and x are as defined above.) Preferred multimetal oxides II are those of formula II', BiafM0b'Wc < [Co, Nia. / o. Zn] d 'Fee' [Pa. / o. Sb] f • [Ka. / o .Na] g »X tlO? ' (II ') where X in the stoichiometric coefficients are as defined for formula II. Particularly preferred multimetal oxides II 'are those in which X, 6 Si, Zr, Al, Nb, Ag and / or Ti, among which preference is given in turn to those in which Xd = Si- is also advantageous that e 'is 0.5-10, particularly when X = Si. The foregoing applies particularly when the metal oxide compositions II 'are prepared as described in EP-B 575897. Particularly advantageous pairs of catalyst bed pairs a, b, are combinations I', II 'and I ", II'. This applies particularly when X = Si and e '= 0.5-10 In the process of the present invention, the initial mixture of the reaction gases advantageously passes over a fixed bed catalyst consisting of catalyst beds A and B at a temperature from 325 to 480 or 450 ° C, preferably from 350 to 420 ° C and, particularly preferably from 350 to 400 ° C.Catalyst beds A, B usually have identical temperatures, if the catalyst bed pair A , B used is a combination I ', II' or I ", II ', the reaction temperature in both beds is conveniently from 350 to 420 ° C, often from 350 to 400 ° C. In addition, the initial mixture of the reaction gases advantageously contains = 30% by volume, preferably <; 20% by volume and particularly preferably < 10% or < 5% by volume of inert gas. Of course, the initial mixture of the reaction gases may also not contain inert gas. In the present context, the inert gases are gases that react up to an amount of < 5% mole passing through the fixed bed catalyst that is used according to the present invention. The possible inert gases are, for example, H20, CO2, CO, N2 and / or noble gases. In addition, the initial mixture of the reaction gases conveniently contains > 60% in volume > 70% by volume or = 80% by volume of prspane. The propane content of the initial mixture of reaction gases used according to the invention is, in general, = 85% by volume, often = 83 or < 82 or < 81 or = 80% by volume. The amount of molecular oxygen present in the initial mixture of the reaction gases may be up to 35% by volume in the process of the present invention. This is conveniently at least 20% by volume or at least 25% by volume. The initial mixtures of the reaction gases that are useful according to the present invention contain > 65% by volume and = 85% by volume of propane plus = 15% by volume and = 35% by volume of molecular oxygen. According to the invention, it is convenient (with respect to selectivity and conversion) that the molar ratio of propane to molecular oxygen in the initial mixture of the reaction gases is < 5: 1, preferably = 4.75: 1, better = 4.5; 1 and particularly preferably = 4: 1. As a rule, the aforementioned relationship will be = 1: 1 or > 2: 1, In principle, the active compositions I that are useful in accordance with the present invention can be easily prepared by forming a dry, intimate, preferably finely divided mixture of suitable sources of their elemental constituents having a composition corresponding to their stoichiometry and calcining this mixture at a temperature from 450 to 1000 ° C. The calcination can be carried out under inert gas or in an oxidizing atmosphere such as air (the mixture of inert gas and oxygen) and still in a reducing atmosphere (for example, the mixture of inert gas, oxygen and NH3, CO and / or H2). The calcination time can be from a few minutes to a few hours and usually decreases with increasing temperatures. Suitable sources of elementary constituents of the compositions I of active multimetal oxides are those compounds which are already oxides and / or compounds which can be converted into oxides by heating, at least in the presence of oxygen. Furthermore, of the oxides, suitable starting compounds are, in particular, halides, nitrates, formations, oxalates, citrates, acetates, carbonates, amine complexes, ammonium salts and / or hydroxides (compounds such as NH4OH, (NH) 2C? 3, NH4NO3, NH4CHO2, CH3COOH, NH4CH3CO2 and / or ammonium oxalate, which dissociate and / or can be decomposed at least during the subsequent calcination to form compounds that are all released in gaseous form, can also be incorporated into the mixture intimate dry). Intimate mixing of the starting compounds to produce multimetal oxide compositions I can be carried out in dry or wet form. If carried out in dry form, the initial compounds are conveniently used as finely divided powders and are subjected to calcination after mixing and, if desired, compaction. However, intimate mixing preferably takes place in a moist form. In this case, the initial compounds are usually mixed together in the form of a solution and / or aqueous suspension. The particularly intimate dry mixtures are obtained in the described mixing process if all the sources of the elementary constituents used are present in dissolved form. The solvent used is preferably water. The resulting aqueous composition is subsequently dried, preferably by performing the spray-drying process of the aqueous mixture at discharge temperatures from 100 to 150 ° C. The particularly suitable initial compounds of Mo, V, W, and Nb are its oxo compounds (molybdates, vanadates, tungstates and niobatos) of the acids derived from these. This applies in particular to the corresponding ammonium compounds (ammonium molybdate, ammonium vanadate, ammonium tungstate). In the process of the present invention, the multimetal oxide compositions I can be used in powder form or after molding to give particular catalyst geometries; the molding or forming can be done before or after the subsequent calcination. For example, unsupported catalysts can be produced from the powder form of the active composition and its precursor composition not calcined by compaction to obtain the desired catalyst geometry (for example, by rattling or extrusion). If desired, auxiliaries such as graphite or stearic acid as lubricants and / or molding aids and reinforcing materials such as glass microfibers, asbestos, silicon carbide or potassium titanate can be used. The geometries of the unsupported catalyst are, for example, solid cylinders or hollow cylinders having an external diameter and a length from 2 to 10 mm. In the case of hollow cylinders, the wall thickness from 1 to 3 mm is advantageous. Of course, unsupported catalysts may also have a spherical geometry, in which case the diameter of the sphere may be from 2 to 10 mm. Of course, the formation of the pulverulent active composition or its pulverulent but not yet calcined precursor composition can also be obtained by the application of inert, preformed catalyst supports. The coating of the bodies of the support for producing the coated catalysts is generally carried out in a suitable rotary vessel, as is known for example from DE-A 2909671 or EP-A 293859. In order to coat the support bodies, it is advantageous to moisten the composition in powder to be applied and dry it again after application, for example, by means of hot air. The thickness of the layer of the powder composition applied to the support body is advantageously selected to be in the range of 50 to 500 μ, preferably in the range of 150 to 250 μ. The support materials which can be used in this case are aluminum oxides, silicon dioxide, thorium dioxide, zirconium dioxide, silicon carbide or silicates such as porous or non-porous magnesium silicate or aluminum silicate, customary. The support bodies can have regular or irregular shapes, giving preference to the bodies of the support having a regular shape and a different surface roughness, for example, spheres or hollow cylinders. The spherical, essentially non-porous steatite supports having a rough surface and a diameter from 1 to 8 mm, preferably from 4 to 5 mm, are useful. With respect to the preparation of the metal oxide compositions II, what has been said is applied for the multimetal oxide compositions I. However, the calcination temperature which is generally used is from 350 to 650 ° C. The mutimetallic oxide compositions II, particularly preferred are the multimetal oxide compositions I described in EP-B 575897, particularly their preferred variants. In these, the mutimetallic oxides are first preformed from portions of the elementary constituents and used as source of elements in the course of the preparation.

The process of the present invention is advantageously carried out in multitubular reactors as described, for example, in EP-A 700893 and EP-A 700714. The fixed-bed catalyst used in accordance with the present invention is located in metallic tubes. (in general stainless steel) and a heat transfer medium, usually a salt melt, passes around the metal tubes. In the simplest case, the two catalyst beds A and B to be used, according to the invention, are arranged in direct succession in each reaction tube. The ratio of the bed volumes of the two catalyst beds A and B is, according to the present invention, conveniently from 1:10 to 10: 1, preferably from 1: 5 to 5: 1 and particularly preferably from 1 : 2 to 2: 1, often 1: 1. The reaction pressure is generally > 0.5 bar In general, the reaction pressure will not exceed 100 bar, that is, it will be from = 0.5 to 100 bar. It is often advantageous if the reaction pressure is from > 1 to 50 bar or from > 1 to 20 bar. The reaction pressure of preference is > 1.25 or = 1.5 bar or = 1.75 or = 2 bar. It is common that the upper limit of 10 or 20 bar is not exceeded in this case. Of course, the reaction pressure can also be 1 bar (the above statements with respect to the reaction pressure is very generally applied to the process of the present invention). In addition, the space velocity is advantageously selected so that the residence time of the reaction gas mixture on the two catalyst beds A and B is from 0.5 to 20 seconds, preferably from 1 to 10 seconds, particularly preferably from 1 to 4 seconds and, frequently, 3 seconds. The propane and / or propene present in the product mixture of the process of the present invention can be separated and returned to the gaseous phase oxidation according to the present invention. In addition, the process of the present invention can be followed by another oxidation step heterogeneously catalyzed as is known for the heterogeneously catalyzed gas phase oxidation of acrolein to acrylic acid, in which the product mixture of the process of the present invention, if it is desired, with the addition of more molecular oxygen, it is transported [sic]. At the end of this, the propane, propene and / or acrolein that do not react can again be separated and returned to the oxidation in the gas phase. The acrolein and / or acrylic acid formed can be separated from the gas mixtures of product in a manner known per se. In general, the conversion of propane obtained using the process of the present invention is = 5 mol% or > 7.5% mol. However, propane conversions from > 20% mol. The process of the present invention is particularly suitable for continuous operation. If necessary, it is possible to inject additional molecular oxygen at the level of the catalyst bed B. The conversion, selectivity and residence time referred to in this document are, unless otherwise indicated, defined as follows: Number of propane moles that react Propane conversion (% mol) = x 100 Number of moles of propane fed Selectivity S of No. of moles of propane converted to crolein and / or acrylic acid formation of Acrolein ~ x 100 No. of moles of propane that react and / or acrylic acid (% mol) free volume of the reactor (1) in the area where the catalyst is located 10 Time of stay = amount of initial mixture of reaction gases passing x 3600 (sec) Examples Example 1 a) Preparation of a multimetal oxide composition I. 292. 4 g of ammonium heptamolybdate (81.5) by weight of M0O3) were dissolved at 80 ° C in 1.2 kg of water and the resulting solution was mixed with 742.4 g of aqueous solution of cobalt nitrate (12.5% by weight of Co, based on the solution). The formed solution was evaporated with stirring in a water bath at 100 ° C until a paste-like mass was formed. This was subsequently dried for 16 hours at 110 ° C in a drying oven and then calcined in an air stream in a muffle furnace (internal volume 60 1, air performance: 500 1 / h as follows: the temperature was first increased from room temperature (25 ° C) to 300 ° c at a heating rate of 120 ° C / h. The temperature of 300 ° C was subsequently maintained for 3 hours and the calcination temperature was then increased from 300 to 550 ° C at a heating rate of 125 ° C / h. This temperature was maintained afterwards for 6 hours. The resulting multimetal oxide was crushed and the particle size fraction having a particle diameter from 0.6 to 1.2 mm was sieved off as the catalytically active metal oxide I composition of M? C? O? 9sOx stoichiometry. b) Preparation of a multi-metal oxide composition ID 1. Preparation of an initial composition 50 kg of a solution of Bi (3 3) 3 in acidic nitric acid (11% by weight of Bi, 6.4% by weight of HNO3 in each case based on the solution) was mixed with 13.7 kg of ammonium paratungstate (89% by weight of O3) and stirred for one hour at 50 ° C. The suspension obtained was spray-dried and calcined for 2 hours at 750 ° C. The resulting blended, calcined, preformed oxide was milled and the particle size fraction of l μ = d = 5 μ (d = particle diameter) was separated. This fraction of particle size was subsequently mixed with 1% of its weight of finely divided SiO2 (number average particle diameter: 28 nm). 2. Preparation of the initial composition 2 48.9 kg of Fe (N03) 3 were dissolved in 104.6 kg of cobalt 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 M0O3) in 240 1 of water. The resulting mixture was mixed with 7.8 kg of an aqueous mixture containing 20% of its weight of colloidal SIO2, and with 377 g of an aqueous solution containing 48% by weight of KOH. This mixture was subsequently stirred for 3 hours and the resulting aqueous suspension was spray-dried to obtain the initial composition 23. Preparation of the multimetal oxide II The initial composition I was mixed with the initial composition 2 in the amount necessary for a multimetal oxide II of the stoichiometry M012 2Bi1C05.5Fe3Si1.6Ko.88Ox, compressed to form hollow cylinders having a length of 3 m, an outer diameter of 5 mm and a wall thickness of 1. 5 mm and subsequently calcined as follows. The calcination was carried out in an air stream in a muffle furnace (internal volume 60 1, 1 1 / h of air per gram of the catalyst precursor composition). The temperature first increased from room temperature (25 ° C) to 190 ° C at a heating rate of 180 ° C / h. This temperature was maintained for 1 hour and then increased to 220 ° C at a heating rate of 60 ° C / h. Again it was maintained at 220 ° C for 2 hours before increasing to 260 ° C at a heating rate of 60 ° C / h.

Subsequently, 260 ° C was maintained for one hour. The mixture was then first cooled to room temperature, practically concluding the decomposition phase, and then heated to 465 ° C at a heating rate of 180 ° C / h and this calcination temperature was maintained for 4 hours. 200 g of the resulting active composition were ground and the particle size fraction of 0.6 to 1.2 mm was sieved as the active multimetal oxide composition II. c) Catalytic oxidation in gaseous phase of prspane A reaction tube (steel V2A, 2.5 cm wall thickness, 8.5 mm internal diameter, with electric heating) having a length of 1.4 m was loaded, from the bottom upwards on a catalyst base (7 cm in length) first at a length of 13 cm with quartz granules (average numerical particle diameter of 1 to 2 mm) and subsequently to a length of 42.5 cm with the active multimetal oxide II composition and then to a length of 42.5 cm with the composition of active metal oxide I, before the charge was complete to a length of 13 cm with quartz granules (number average particle diameter from 1 to 2 mm). The reaction tube loaded as already described was heated to 430 ° C throughout and then supplied, from the top down, with 56 1 / h normal of an initial mixture of reaction gases consisting of 80% by volume of propane and 20% in oxygen volume. In a single step, a product gas mixture having the following characteristics was obtained: Propane conversion: 10% mol Acrolein formation selectivity: 59% mol Acrylic acid formation selectivity: 14% mol Propene formation selectivity: 3% mol Example 2 a) Preparation of a multimetal oxide composition I. The preparation of the multimetal oxide composition I was carried out as in Example la), but the final calcination temperature was 560 ° C instead of 550 ° C. b) Preparation of a multimetal oxide composition II) Preparation of the multimetal oxide composition II was performed as in Example Ib. c) Catalytic oxidation in gas phase of propane A reaction tube (steel V2A, 2.5 cm wall thickness, 8.5 mm internal diameter, heated by electricity) having a length of 1.4 m was loaded, from the bottom towards up on a catalyst base (7 cm long) first to a length of 18 cm with quartz granules (number average particle diameter from 1 to 2 mm) and subsequently to a length of 42.5 cm with the multimetal oxide composition active II and then to a length of 42.5 cm with the active multimetal oxide composition II, before the loading was completed to a length of 30 cm with quartz granules (number average particle diameter from 1 to 2 mm) . The loaded reaction tube as described above was heated to 415 ° C throughout and then supplied from top to bottom with 56 1 / h of an initial mixture of reaction gases consisting of 80% by volume of propane and 20% by volume of oxygen. The pressure at the inlet of the reaction tube was 1.68 bar (absolute). The pressure drop along the reaction tube was 0.27 bar. In a single step, a mixture of the product gas having the following characteristics was obtained: Propane conversion: 11.5% mol Selectivity of acrolein formation: 66% mol Acrylic acid formation selectivity: 10% mol Propane formation selectivity: 2% mol Example 3 a) Preparation of a multimetal oxide composition I 877. 2 g of ammonium heptamolybdate (81.5% by weight of M0O3) were dissolved at 45 ° C in 3.6 kg of water and the resulting solution was mixed with 2227.2 g of aqueous solution of cobalt nitrate (12.5% by weight of Co based on the solution). The resulting red, clear solution was spray-dried in a Niro spray drier (Niro Atomizer transportable Minor A / S) at an intake temperature of 330-340 ° C and a discharge temperature of 110 ° C. 450 g of the spray-dried powder obtained were kneaded (1 liter sigma blade kneader from Werner & Pfleiderer) with 75 ml of HO for 40 minutes and drying at 110 ° C for 16 hours in a convection drying oven.

The dried powder was then calcined in a quartz flask, round bottom, rotary (15 revolutions / minute) through which air flowed (internal volume: 2 1, air yield: 250 1 / h constant) as follows (heating in a tilting oven): First the temperature was raised from room temperature (25 ° C) to 225 ° C at a heating rate of 180 ° C / h. The temperature of 225 ° C was subsequently maintained for 0.5 hours and the calcination temperature was then increased from 225 ° C to 300 ° C at a heating rate of 60 ° C / h. This temperature was subsequently maintained for 3 hours. The calcination temperature was then increased from 300 to 550 ° C at a heating rate of 125 ° C / h. Subsequently, this temperature was maintained for 6 hours. The multimetal oxide thus obtained was crushed and the particle size fraction having a particle diameter from 0.6 to 1.2 mm was sieved off as the catalytic active multimetal oxide I composition of stereochemistry MOICOQ.9SOX. b) Preparation of a multimetal oxide composition II) The preparation of the multimetal oxide composition II was carried out as in Example Ib). c) Catalytic oxidation in the gas phase of propane A reaction tube (steel V2A, 2.5 cm wall thickness, 8.5 mm internal diameter); with electric heating) having a length of 1.4 was loaded, from the bottom up on a catalyst base (7 cm in length) first up to a length of 18 cm with quartz granules (average numerical particle diameter of 1 to 2 mm) and subsequently to a length of 42.5 cm with the active multimetal oxide composition II, and then to a length of 42.5 cm with the active multimetal oxide composition I, before which the charge was complete to a length of 30 cm with quartz granules (average numerical particle diameter from 1 to 2 mm). The reaction tube loaded as already described was heated to 390 ° C over the entire length and then supplied, from top to bottom, with 84 1 / h normal of an initial mixture of the reaction gas consisting of 80% by volume of propane and 20% in oxygen volume. The pressure at the inlet of the reaction tube was 2.7 bar (absolute). The pressure drop along the reaction tube was 0.35 bar. In a single step, a mixture of the product gas having the following characteristics was obtained: Propane conversion: 9.0 mol% Acrolein formation selectivity: 69 mol% Acrylic acid formation selectivity: 10 mol%, Propane formation selectivity: 1 mol% Example 4 a) Preparation of a multimetal oxide composition I. 9 * 29.3 g of ammonium heptanomolybdate [sic] (81.5% by weight of M0O3) were dissolved at 45 ° C in 1.5 kg of water. 80.8 g of ammonium paratungstate (89.04 wt% of WO3) were dissolved separately at 95-98 ° C in 1.5 kg of water and then cooled to 45 ° C. The two solutions were combined at 45 ° C and mixed with an aqueous solution of cobalt nitrate (12.5% by weight of Co based on the solution) which was similarly at 45 ° C. The resulting red, clear solution was spray-dried in a Niro spray dryer (A / S Niro Atomizer transportable Minor) at an intake temperature of 320 ° C and an outlet temperature of 110 ° C. The 450 g of the spray-dried powder obtained were kneaded (1 liter sigma blade kneader from Werner & Pfleiderer) with 85 ml of H2O for 40 minutes and drying at 110 ° C for 16 hours in a convection drying oven. The dried composition was subsequently calcined in an air stream in a muffle furnace (internal volume: 60 1, air yield: 500 1 / h constant) as follows. First the temperature was raised from room temperature (25 ° C) to 300 ° C at a heating rate of 120 ° C / h. The temperature of 300 ° C was subsequently maintained for 3 hours and the calcination temperature was then increased from 300 ° C to 567 ° C at a heating rate of 125 ° C / h. This temperature was subsequently maintained for 6 hours. The multimetal oxide thus obtained was crushed and the particle size fraction having a particle diameter of 0.6 to 1.2 mm was sieved off as the catalytically active multimetal oxide I composition of stoichiometry b) Preparation of a multimetal oxide composition II) The preparation of the multimetal oxide composition II was carried out as in Example Ib). c) Catalytic oxidation in gas phase of propane A reaction tube (steel V2A, 2.5 cm wall thickness, 8.5 mm internal diameter, with electric heating) having a length of 1.4 m was loaded, from the bottom upwards on a catalyst base (7 cm in length), first at a length of 18 cm with quartz granules (average numerical particle diameter of 1 to 2 mm) and subsequently to a length of 45.5 cm with the active multimetal oxide composition II and then to a length of 42.5 cm with the active multimetal oxide composition I before the charge was completed to a length of 30 cm with quartz granules (number average particle diameter from 1 to 2 mm). The reaction tube loaded as already described was heated to 395 ° C over its entire length and then supplied, from the top down, with 98 1 / h normal of an initial mixture of reaction gases consisting of 80% in volume of propane and 20% in volume of oxygen. The pressure at the inlet of the reaction tube was 2.69 bar (absolute). The pressure drop along the reaction tube was 0.36 bar. In a single step, a product gas mixture having the following characteristics was obtained: Propane conversion: 8.2% mol Acrolein formation selectivity: 67% mol Acrylic acid formation selectivity: 11% mol. Selectivity of propane formation: 1% mol

Claims (9)

2. A process for the gas phase, heterogeneously catalyzed oxidation of propane to acrolein and / or acrylic acid, in which an initial mixture of reaction gases composed of propane, molecular oxygen, and if desired, inert is passed to a temperature of 300 to 500 ° C on a fixed bed catalyst comprising two catalytic beds A and B spatially arranged in succession, with the proviso that the active composition of the bed A is at least one multimetal oxide of the formula I:
3. MXa Moi- M b 0, where M = Co, Ni, Mg, Zn, and / or Cu, M = W, V, Te, Nb, P, Cr, Fe, Sb, Ce, Sn and / or La, a = 0.5-1.5, b = 0-0.5, x = a number that is determined by the valence and amount of the different oxygen elements in I, and the active composition of the B bed is at least one multimetal oxide of the formula II.
4. Ri 3. / Mni XJ Y¿ x ~? } * x5 ~. Qx, (in where X1 = W, V and / or Te, X = alkaline earth metal, Co, Ni, Zn, Mn, Cu, Cd, Sn and / or Hg, X3 = Fe, Cr, and / or Ce, X4 = P, As, Sb, and / or B, X = alkali metal, TI, and / or Sn, X = rare earth metal, Ti, Zr, Nb, Ta, Re, Ru, Rh,
5. Ag, Au, Al, Ga, In, Si, Ge, Th, and / or U, a '= 0.01-8, b' = 0.1-30, c '= 0-20, d' = 0-20 , e '- 0-20, f = 0-6, g' = 0-4, hr = 0-15, x '= a number that is determined by the valence and quantity of the different elements of oxygen in
6. II, where the initial mixture of the reaction gases contains = 50% by volume of propane, = 15% by volume of O2 and from 0 to 35% by volume of inert gas and flows through catalyst beds A and B in the first order A, then B. 2. The process as mentioned in claim 1, wherein the temperature is from 325 to 450 ° C. 3. The process as recited in claim 1, wherein the temperature is from 350 to 420 ° C. 4. The process as recited in any of claims 1 to 3, wherein the initial mixture of the reaction gases comprises > 60% by volume of propane. 5. The process as recited in any of claims 1 to 3, wherein the initial mixture of the reaction gases comprises > 70% by volume of propane. 6. The process as recited in any of claims 1 to 5, wherein the initial mixture of the reaction gases contains = 20 volume% O2.
7. 7. The process as mentioned in any of claims 1 to 6, which is carried out continuously. The process as recited in any of claims 1 to 7, wherein the molar ratio of propane to molecular oxygen in the initial mixture of the reaction gases is < 5. The process as recited in any of claims 1 to 8, wherein the ratio of the bed volumes of the two catalyst beds A, B is from 1: 5 to 5: 1. The process as mentioned in any of claims 1 to 9, wherein the reaction pressure is > 1 bar r tttn t r- T- An In a? Process for oxidation in fat > and already, catalyzed heterogeneously, an initial mixture of reaction gases composed of propane, molecular oxygen and, if desired, inert gas is passed at a temperature from 300 to 500 ° C on a fixed bed catalyst.