EP1159243A1

EP1159243A1 - Method for carrying out the heterogeneously catalyzed gas phase oxidation of propane into acrolein and/or acrylic acid

Info

Publication number: EP1159243A1
Application number: EP00910721A
Authority: EP
Inventors: Harald Jachow; Andreas Tenten; Signe Unverricht; Heiko Arnold; Otto Machhammer; Susanne Haupt; Frank Rosowski
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1999-03-10
Filing date: 2000-02-28
Publication date: 2001-12-05
Also published as: CN1343189A; WO2000053555A1; BR0008824A; DE19910507A1; JP2002539099A

Abstract

The invention relates to a method for carrying out the heterogeneously catalyzed gas phase oxidation of propane into acrolein and/or acrylic acid in which the initial mixture of reaction gas is fed over a fixed-bed catalyst which is comprised of catalyst charges A, B arranged in two reaction zones A, B that are placed in a spatially successive manner, whereby the temperature of reaction zones A, B are kept at different temperatures.

Description

Process of heterogeneously catalyzed gas phase oxidation of propane to acrolein and / or acrylic acid

description

The present invention relates to a process of heterogeneously catalyzed gas phase oxidation of propane to acrolein and / or acrylic acid, in which a reaction gas starting mixture containing> 50 vol.% Propane,> 10 vol.% 0 and 0 to 40 vol Temperature leads over a fixed bed catalyst, which consists of two spatially successive reaction zones A, B arranged catalyst beds A, B, the active mass of the catalyst bed A located in reaction zone A at least one multimetal oxide of the general formula I

M ^ MOi-bM ^ Ox (I),

With

M ¹ = Co, Ni, Mg, Zn, Mn and / or Cu,

M ² =, V, Te, Nb, P, Cr, Fe, Sb, Ce, Sn and / or La, a = 0.5 to 1.5, b = 0 to 0, 5 and x = a number that is determined by the valency and frequency of the elements in I other than oxygen,

and the active composition of the catalyst bed B located in the reaction zone B is at least one multimetal oxide of the general formula II

Bi _a -Mθ _{b '} X ¹ c _' X ² d _' X ³ e _' X ⁴ _{f '} X ⁵ g _' X ⁶ _{h '} O _x - (II),

with χi = W, V and / or Te, χ2 = 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, AI, Ga, In, Si, Ge, Th and / or ü, 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,

and the reaction gas starting mixture flows through the catalyst beds A, B in the sequence “first A”, “then B”.

A method as described above is already proposed in DE-A 19807079 and in DE-A 19746210.

It is recommended in these documents that the reaction gas starting mixture at a temperature of 325 to 480 or 450 ° C, preferably at 350 to 420 ° C and particularly preferably at 350 to 400 ° C over the fixed bed catalyst consisting of the catalyst beds A, B. respectively. Furthermore, it is stated in the abovementioned documents that the catalyst beds A, B normally have identical temperatures.

However, a disadvantage of such a procedure is that the selectivity of the formation of the valuable product is unsatisfactory.

The object of the present invention was therefore to provide a process as described at the outset with improved selectivity in the formation of valuable products.

Accordingly, a process for the heterogeneously catalyzed gas-phase oxidation of propane to acrolein and / or acrylic acid, in which a> 50 Vol .-% of propane,> 10 vol .-% 0 ₂ and 0 to 40 Vol .-% inert gas-containing starting reaction gas mixture at elevated Temperature leads over a fixed bed catalyst, which consists of two spatially successive reaction zones A, B arranged catalyst beds A, B, the active mass of the catalyst bed A located in reaction zone A at least one multimetal oxide of the general formula I

M ^ MOi- _b M ^ O _x (I),

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 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 preferred

0, 01 to 0, 3 as well as x = a number determined by the valency and frequency of the

Oxygen different elements in I is determined

Bi _a -Mo _b .χ ¹ _c .χ ² _d -X ³ _e -χ4 _f , χ5, χ6 _h , _0χ , (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 Sn, preferably K and / or Na, X ⁶ = rare earth metal, Ti, Zr, Nb, Ta, Re, Ru, Rh, Ag, Au, AI,

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

Oxygen various elements in II is determined

is, and wherein the reaction gas starting mixture flows through the catalyst beds A, B in the sequence "first A", "then B", found, which is characterized in that the temperature of the reaction zone A is 380 to 480 ° C and the temperature of the Reaction zone B is on the one hand> 300 ° C and on the other hand is at least 20 ° C below the temperature of reaction zone A. The temperature of a reaction zone is understood here to mean the temperature of the catalyst bed in the reaction zone when the process is carried out in the absence of a chemical reaction. If this temperature is not constant within the reaction zone, 5 the term temperature of a reaction zone here means the number average of the temperature of the catalyst bed along the reaction zone. The temperature of reaction zone A in the process according to the invention is preferably 400 to 450 ° C. Furthermore, the temperature of reaction zone B is preferably at least 10 40 ° C. below the temperature of reaction zone A. Advantageously, the temperature of reaction zone B is 320 to 380 ° C. and particularly preferably 330 to 370 ° C.

Multimetal oxides I which are preferred according to the invention are therefore 15 of the general formula I '

[Co, Ni u./o. Mg] _a MOI _b TSN, W, P, Sb u./o. Cr] _b O _x (I '),

with 20 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 25 oxygen.

Multimetal oxides I which are particularly preferred according to the invention are those of the general formula I "

30 [Co u./o. Νi] _a Mθ _! - _b [W, Sn u./o. Sb] _ O _x (I ")

with the above meanings for a, b and x.

In general, according to the invention, such multimetal oxides I, I '35 and I "are advantageous as active compositions, their average pore diameters <0.09 μm and> 0.01 μm and their specific surface area

> 10 m ² / g. The aforementioned average pore diameter is particularly preferably> 0.02 μm and <0.06 μm. In addition, such multimetal oxide materials I

40 I 'and I "as active compositions, their average pore diameter

Is> 0.025 μm and <0.040 μm.

Furthermore, it is advantageous according to the invention if the aforementioned multimetal oxide compositions at the aforementioned average pore diameters 45 simultaneously have a specific surface area of __ 15 m ² / g or of __ 25 m ² / g. As a rule, the said specific The surface area of the multimetal oxide compositions according to the invention is <50 m ² / g.

In this document, the specific surface area 0 means the specific surface area determined according to DIN 66133 by means of the mercury intrusion method (measuring range: 1 μm to 3 nm pore diameter).

The mean pore diameter is defined in this document as four times the ratio of the total pore volume to the specific surface area 0 determined according to the aforementioned mercury intrusion method.

Multimetal oxides II preferred according to the invention are those of the general formula II '

Bi _{a '} Mθb _' W _{C '} [Co, Ni u./o. Zn] _d <Fe _{e '} [P u. / o. Sb] _£ - [Ku./o. Na] _g <X ⁶ 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.

It is also expedient if e '= 0.5 to 10, which is particularly true when X ⁶ = Si. The above applies especially when the multimetal oxide masses II 'are produced in accordance with EP-B 575897.

The combinations I ', II' and I ", II 'are particularly advantageous catalyst bed pairs A, B. This applies especially when X ⁶ = Si and e' = 0.5 to 10.

The reaction gas starting mixture to be used for the process according to the invention 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%.

The reaction gas starting mixture furthermore advantageously contains

> 60 vol% or> 70 vol% or> 80 vol% propane. The propane content of the reactant to be used according to the invention is generally ongas starting mixture at 90 vol.% or <85 vol.%, often at <83 or <82 or <81 or <80 vol.%. The content of molecular oxygen in the reaction gas starting mixture can be up to 35% by volume in the process according to the invention. It is advantageously at least 15% by volume or 20% by volume or at least 25% by volume. Reaction gas starting mixtures which are favorable according to the invention contain> 65% by volume and <90% by volume of propane and

> 10 vol% and <35 vol% molecular oxygen. According to the invention (in terms of selectivity and conversion) is advantageous if the molar ratio of propane to molecular oxygen in the reaction gas starting mixture is <8: 1, preferably <5: 1 or 4.75: 1, better <4.5: 1 and particularly preferably <4: 1. As a rule, the aforementioned ratio will be> 1: 1 or 2: 1. Normally, the reaction gas starting mixture contains essentially no further components apart from the components mentioned.

In principle, suitable multimetal oxides I as active compositions to be used according to the invention can be prepared in a simple manner by generating an intimate, preferably finely divided, dry mixture of suitable stoichiometry from suitable sources of their elemental constituents, and this at temperatures of 450 to 1000, preferably 450 to 700, frequently 450 to 600 or 550 to 570 ° C calcined.

The calcination can take place both under inert gas and under an oxidative atmosphere, such as air or mixtures of inert gas and oxygen, and also under a reducing atmosphere, for example under mixtures of inert gas, oxygen and NH ₃ , CO and / or H ₂ . The calcination time can range from a few minutes to a few hours and usually decreases with increasing calcination temperature. The calcination can be carried out in a simple manner by placing the active mass precursor in a rotating container, heating the container to the calcination temperature and letting the corresponding gas mixture flow through it. A rotating tube furnace or a rotating round quartz flask can be considered as a rotating container. The preparation of the active material precursor is, for example possible by one of THE APPROPRIATE sources of the elemental constituents of the desired Mul - timetalloxids produces an aqueous solution and spray dried, the spray outlet temperatures expedient 100 ^• amounted to 150 ° C.

Halides, nitrates, formates, oxalates, citrates, acetates, carbonates, ammonium complexes, and ammonium compounds are the main sources for the elemental constituents of the multimetal oxy-active compounds (I). Salts and / or hydroxides into consideration (compounds such as NH0H, (NH) ₂ C0 ₃ , NH ₄ N0 ₃ , NHCH0 ₂ , CH ₃ COOH, NHCH ₃ C0 ₂ and / or ammonium oxalate, which become completely gaseous at the latest during the later galvanizing escaping compounds disintegrate and / or decompose can also be incorporated into the precursor to be calcined). The intimate mixing of the starting compounds for the production of multimetal oxide 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 are subjected to calcination after mixing and, if appropriate, compaction. 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 when only sources of the elementary constituents in dissolved form are used. Water is preferably used as the solvent. The aqueous mass obtained is then dried. Particularly suitable starting compounds for Mo, V, W and Nb are their oxo compounds (molybdates, vanatates, tungstates and niobates) and the acids derived from them. This applies in particular to the corresponding ammonium compounds (ammonium molybdate, ammonium vanadate, ammonium wolf ramate).

The multimetal oxide materials I can be used for the process 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, solid 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 the hollow cylinder, a wall thickness of 1 to 3 mm is appropriate. The full catalyst can of course also have a spherical geometry, the spherical diameter being 2 to 10 mm.

Of course, the shape of the powdery active composition or its powdery, not yet calcined,

Precursor mass can also be made by application to preformed inert catalyst supports. The coating of the carrier body for Production of the shell catalysts is generally carried out in a suitable rotatable container, as is known, for example, from DE-A 2909671 or from EP-A 293859. For coating the support bodies, the powder mass to be applied can expediently be 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 50 to 700 μm, preferably in the range from 150 to 500 μm. Of course, the layer thickness can also be 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, with regularly shaped carrier bodies with a clearly formed surface roughness, e.g. Balls or hollow cylinders are preferred. It is suitable to use essentially non-porous, rough-surface, spherical supports made of steatite, the diameter of which is 1 to 8 mm, preferably 3 to 5 mm.

With regard to the production of the multimetal oxide compositions II, what has been said for the multimetal oxide compositions I applies. However, the calcination temperature used is usually 350 to 650 ° C. Particularly preferred multimetal oxide compositions II are the multimetal oxide compositions I disclosed in EP-B 575897, in particular their preferred embodiment variants. They are characterized in that multimetal oxides are initially formed from subsets of the elementary constituents and are used as an element source in the further course of production.

The process according to the invention is carried out in a manner which is expedient in terms of application technology in a two-zone tube bundle reactor. DE-C 2830765 discloses a preferred variant of a two-zone tube bundle reactor which can be used according to the invention. However, the two-zone tube bundle reactors disclosed in DE-C 2513405, US-A 3147084, DE-A 2201528 and DE-A 2903582 are also suitable for carrying out the according to the invention

Process suitable. In other words, the fixed bed catalyst to be used according to the invention is in the simplest way in the metal tubes of a tube bundle reactor and two temperature media, generally salt melts, which are essentially spatially separated from one another, are guided around the metal tubes. According to the invention, the tube section over which the respective salt bath extends represents a reaction zone. That is, in the simplest way each reaction tube of the tube bundle reactor contains the two catalyst beds A, B to be used according to the invention (for example, directly or separated by an inert layer) arranged in succession and a salt bath A flows around the section of the tubes in which the catalyst bed A is located and a salt bath B flows around the Section of the tubes in which the catalyst bed B is located.

The two salt baths can in relative to the flow direction of the reaction gas mixture flowing through the reaction tubes

Direct current or countercurrent through the space surrounding the reaction tubes. Of course, according to the invention, a cocurrent flow can also be used in reaction zone A and a counterflow (or vice versa) in reaction zone B.

Of course, in all of the above-mentioned constellations, a transverse flow can be superimposed on the parallel flow of the molten salt relative to the reaction tubes, so that the individual reaction zone is as described in EP-A 700714 or in EP-A 700893 Corresponds to the tube bundle reactor and, overall, a longitudinal section through the contact tube bundle results in a meandering flow profile of the heat exchange medium.

The reaction gas starting mixture is advantageously fed to the catalyst feed preheated to the reaction temperature. In such tube bundle reactors, the contact tubes are usually made of ferritic steel and typically have a wall thickness of 1 to 3 mm. Their inner diameter is usually 20 to 30 mm, often 22 to 26 mm. Appropriately from an application point of view, the number of contact tubes accommodated in the tube bundle container is at least 5,000, preferably at least 10,000. The number of contact tubes accommodated in the reaction container is often

15,000 to 30,000. Tube bundle reactors with a number of contact tubes above 40,000 are rather the exception. 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. e.g. EP-B 468290).

Fluid temperature media are particularly suitable as the 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 and alloys of various metals.

As a rule, in all of the above-mentioned constellations of current flow in the two-zone tube bundle reactor, the flow rate within the two required heat exchange medium circuits is selected such that the temperature of the heat exchange medium increases from 0 to 15 ° C. from the entry point into the reaction zone to the exit point from the reaction zone. That is, the aforementioned ΔT can be 1 to 10 ° C or 2 to 8 ° C or 3 to 6 ° C according to the invention.

According to the invention, the entry temperature of the heat exchange medium into reaction zone A is normally 380 to 480 ° C., frequently 400 to 450 ° C.

According to the invention, the entry temperature of the heat exchange medium into reaction zone B is normally on the one hand> 300 ° C. and on the other hand is normally at least 20 ° C. below the entry temperature of the heat exchange medium entering reaction zone A. According to the invention, the entry temperature of the heat exchange medium into reaction zone B is preferably at least 40 ° C. below the entry temperature of the heat exchange medium entering reaction zone A. According to the invention, the entry temperature of the heat exchange medium into reaction zone B is advantageously from 320 to 380 ° C. and particularly preferably from 330 to 370 ° C.

Of course, in the process according to the invention, the two reaction zones A, B can also be implemented in spatially separated tube bundle reactors. If necessary, an intercooler (which can be filled with inert material) can be installed between the two reaction zones. It goes without saying that the two reaction zones A, B can also be designed as a fluidized bed.

The working pressure in the process according to the invention is generally> 0.5 bar. As a rule, the reaction pressure will not exceed 100 bar, ie 0.5 to 100 bar. The reaction pressure is expediently 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. Often the upper limit of 10 bar or 20 bar is not exceeded. In many cases the reaction pressure will be 3 to 4 bar. Of course, the reaction pressure can also be 1 bar (the above statements regarding the reaction pressure apply in general to the process according to the invention).

Furthermore, the loading is advantageously chosen so that the residence time of the reaction gas mixture over the two catalyst beds is 0.5 to 20 seconds, preferably 1 to 10 seconds, particularly preferably 1 to 4 seconds and often 3 seconds.

According to the invention, the ratio of the bulk volumes of the two catalyst beds A, B is advantageously 1:10 to 10: 1, preferably 1: 5 to 5: 1 and particularly preferably 1: 2 to 2: 1, often 1: 1.

Propane and / or propene and / or inert gas contained in the product mixture of the process according to the invention can be separated off and recycled into the gas phase oxidation according to the invention. Furthermore, the process according to the invention can be followed by a further heterogeneously catalyzed oxidation stage, as are known for the heterogeneously catalyzed gas phase oxidation of acrolein to acrylic acid (for example from EP-A 700893), into which the product mixture of the process according to the invention, optionally with the addition of further molecular oxygen. Subsequently, unreacted propane, propene and / or acrolein and / or inert gas can again be separated off and recycled into the gas phase oxidation. Air as well as air depleted in nitrogen or pure oxygen are generally considered as oxygen sources for the process according to the invention.

The acrolein and / or the 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%. However, normally no propane conversions> 20 mol% are achieved. The method according to the invention is particularly suitable for continuous implementation. If necessary, additional molecular oxygen can be injected at the level of the catalyst bed B. Otherwise, turnover, selectivity and retention time, unless otherwise stated, are defined in this document as follows: Mole number of propane converted

Turnover of propane (mol%) ^: x 100 mol number of propane used

Mole number of propane converted to

Selectivity S of acrolein and / or acrolein and / or acrylic acid x 100 acrylic acid formation (mol%) mole number of converted propane

10

Empty volume of the reactor filled with catalyst (1)

Dwell time (sec.) = X3600

15 enforced amount of reaction gas starting mixture (1)

Examples

Example I

20th

A) Production of a multimetal oxide mass I

876.9 g of ammonium heptamolybdate (81.5% by weight of MoO ₃ ) were dissolved in 3.6 kg of water at 45 ° C. and the resulting solution

25 2245.2 g of aqueous cobalt nitrate solution (based on the solution, 12.4% by weight of Co) were added. The resulting clear red solution was spray-dried in a spray dryer from Niro at an inlet temperature of 340 ° C. and an outlet temperature of 105 ° C. (A / S Niro Atomizer transportable minor system). 1.43 kg

30 of the NHN0 ₃ -containing spray powder obtained were decomposed as follows in a muffle furnace through which air flows (60 1 internal volume, air throughput 500 1 / h):

First, the heating was carried out at a heating rate of 75 ° C./h from room temperature 35 (25 ° C.) to 175 ° C. The temperature was then maintained at 175 ° C. for 1 h and then the temperature was increased from 175 ° C. to 185 ° C. at a heating rate of 40 ° C./h. This temperature was then maintained for 3 hours. The temperature was then increased to 40,300 ° C. at a heating rate of 38 ° C./h and maintained for 2 h.

The precursor mass obtained in this way was admixed with 3% by weight of graphite, based on its weight, and processed into fully catalytic converter cylinders of geometry 5 mm × 3 mm (outside diameter × height) with a side pressure resistance of 90.7 N (pressing pressure: 8600 N; Rotary tableting machine, Hörn company, type RP / 16H). 580 g of these full-cylinder tablets were calcined in an air-flowed muffle furnace (60 l internal volume, air flow 500 l / h) as follows:

With a heating rate of 87.5 ° C / h the mixture was first heated from room temperature (25 ° C) to 550 ° C. This temperature was then maintained for 6 hours. The lateral compressive strength of the calcined multimetal oxide full cylinders was 105.9 N. They were comminuted and, as a catalytically active multimetal oxide mass I of stoichiometry Cθo _{/ 95} MoO _x, the grain fraction with a grain size diameter of 0.6 to 1.2 mm was separated off by sieving. The average diameter of the pores of the active composition was 30 nm and the specific surface area was 13.2 m ² / g.

B) Production of a multimetal oxide mass II

1. Production of a starting mass 1

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

The spray drying took place in a counter-rotating spray tower at a gas inlet temperature of 300 ά: 10 ° C and a gas outlet temperature of 100 zh 10 ° C. The spray powder obtained was then calcined at a temperature in the range from 780 to 810 ° C. (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 W0 ₃ (monoclinic) and Bi ₂ W ₂ 0 ₉ are desired, the presence of γ-Bi ₂ W0 ₆ (Russelite) is undesirable. If the compound γ-Bi ₂ W0 ₆ can therefore still be detected after the calcination using a reflection in the powder X-ray diffractogram at a reflection angle of 2 © ⁼ 28.4 ° (CuK radiation), the preparation must be repeated and the calcination temperature within the specified temperature range until the reflex disappears. The preformed calcined mixed oxide thus obtained was ground so that the X ₅₀ value (see FIG. Ullmann's Encyclopedia of Industrial Chemistry, 6 ^th Edition (1998), Electronic Release, Chapter 3.1.4 or DIN 66141) was the resulting particle size 5 .mu.m . The millbase was then finely ground with 1% by weight (based on the millbase). Partial Si0 ₂ (vibrating weight 150 g / 1; X ₅₀ value of the Si0 ₂ particles was 10 μm, the BET surface area was 100 m ² / g).

2. Production of a starting mass 2

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

A solution B was prepared by entering 116.25 kg of an aqueous iron nitrate solution (14.2% by weight of Fe) at 60 ° C. in 262.9 kg of an aqueous cobalt nitrate solution (12.4% by weight of Co). Solution B was then pumped continuously into solution A over a period of 30 minutes while maintaining the 60 ° C. The mixture was then stirred at 60 ° C for 15 minutes. Then the resulting aqueous mixture was 19.16 kg of a silica gel (46.80% by weight Si0 ₂ , density: 1.36 to 1.42 g / ml, pH 8.5 to 9.5, alkali content max. 0, 5% by weight) 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: 400zh 10 ° C, gas outlet temperature: 140 ± 5 ° C). The resulting spray powder had a loss on ignition of approximately 30% by weight (3 hours at 600 ° C.).

3. Production of the multimetal oxide active composition II

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

[B i ₂ W ₂ 0 ₉ ^• 2W0 ₃ ] ₀ , ₅ [Mθi ₂ Cθ _{5 5} Fe ₂ , ₉ S iι _{/ 59} Ko, _{θ 8} θ _x ] _l

required amount homogeneously mixed. Based on the aforementioned total mass, an additional 1.5% by weight of finely divided graphite (sieve analysis: min. 50% by weight <24 μm, max. 10% by weight> 24 μm and <48 μm, max. 5% by weight) was used. -%> 48 μm, BET surface area: 6 to 13 m ² / g) homogeneously mixed. The resulting dry mixture was pressed into hollow cylinders with a length of 3 mm, an outer diameter of 5 mm and a wall thickness of 1.5 mm and then thermally treated as follows.

Muffle furnace with air flowing through it (60 l internal volume, 1 l / h air per gram of active mass precursor mass) was first heated from room temperature (25 ° C) to 190 ° C at a heating rate of 180 ° C / h. This temperature was maintained for 1 h and then increased to 210 ° C with a heating rate of 60 ° C / h. The 210 ° C was again maintained for 1 h before it was increased to 230 ° C at a heating rate of 60 ° C / h. This temperature was also maintained for 1 hour before it was increased again to 265 ° C. 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.

200 g of the resulting active mass were comminuted and the grain fraction 0.6 to 1.2 mm was screened out as multimetal oxide active mass II.

C) Gas phase catalytic oxidation of propane

A reaction tube (V2A steel; 2.5 cm wall thickness; 8.5 mm inner diameter; electrically heatable in sections) with a length of 1.4 m is placed from bottom to top on a contact chair initially over a length of 48.7 cm with quartz chips (number-average large diameter 1 to 2 mm) and then loaded with the multimetal oxide active composition II over a length of 21.3 cm and then with the multimetal oxide active composition I over a length of 21.3 cm before the loading over a length of 48.7 cm with Quartz grit (number-average large diameter 1 to 2 mm) is completed (the quartz grit is essentially inert and serves, for example, to heat the reaction gas starting mixture to the reaction temperature). The reaction tube charged as above is charged with a reaction gas starting mixture having a pressure of 2.7 bar and consisting of 80 vol.% Propane and 20% vol.% Oxygen from top to bottom. The dwell time is set to 1.8 s. The pressure loss across the reaction tube is 0.2 bar.

In two experiments (i), (ii), the temperature of the reaction tube is set as follows by means of hollow cylindrical, electrically heated aluminum blocks in contact with the reaction tube:

(i): over the entire contact tube 404 ° C;

(ii): in the direction of flow on a reaction tube length of 70 cm first 405 ° C, then up to the contact tube end 365 ° C; In a single pass, product gas mixtures are obtained which have the following characteristics (analysis using gas chromatography):

Case (i): propane conversion: 9.1 mol%

Selectivity of acrolein formation: 60 mol% selectivity of acrylic acid formation: 11 mol% total = 71 mol% selectivity of propene formation: 5.5 mol%

Case (ii): Propatt conversion: 9.0 mol%

Selectivity of acrolein formation: 67 mol% selectivity of acrylic acid formation: 8.9 mol% total = 75.9 mol% selectivity of propene formation: 3J mol%

A comparison of the design variants (i), (ii) shows the superiority of the procedure according to the invention with regard to the formation of valuable products.

Example II

A) Production of the multimetal oxide masks I and II

The same multimetal oxide masses I and II were used as in example I.

B) Gas phase catalytic oxidation of propane

A reaction tube (V2A steel; 2.5 cm wall thickness; 8.5 mm inner diameter; electrically heatable in sections) with a length of 1.4 m was first built from bottom to top on a contact chair over a length of 35 cm with quartz chips (number-average large diameter 1 to 2 mm) and then over a length of 21.3 cm with the multimetal oxide active material II and then afterwards over a length of 19 cm with quartz chips (number-average large diameter 1 to 2 mm) and then over a length of 21.3 cm charged with the multimetal oxide active material I before the loading was completed over a length of 43.4 cm with quartz chips (number-average large diameter 1 to 2 mm) (the quartz chips are essentially inert and serve, for example, to heat the reaction gas starting mixture to the reaction temperature ). The reaction tube charged as above was charged with a reaction gas starting mixture having a pressure of 2.7 bar and consisting of 80 vol.% Propane and 20% vol.% Oxygen from top to bottom. The dwell time was on 1.8 s set. The pressure drop across the reaction tube was 0.2 bar.

The temperature of the reaction tube was set as follows by means of hollow cylindrical, electrically heated aluminum blocks in contact with the reaction tube:

in the direction of flow on a reaction tube length of 70 cm first 405 ° C, then up to the contact tube end 365 ° C.

^• In a single pass, product gas mixtures were obtained which had the following characteristics (analysis using gas chromatography):

Propane conversion: 8.7 mol%%.

Selectivity of acrolein formation: 69 mol% r _

Selectivity of acrylic acid formation: 8.5 mol% total - 77.5 mol- / _ selectivity of propene formation: 2.5 mol%

Claims

claims

1. Process of heterogeneously catalyzed gas phase oxidation of propane to acrolein and / or acrylic acid, in which a reaction gas starting mixture containing> 50 vol.% Propane,> 10 vol.% 0 ₂ and 0 to 40 vol.% Inert gas at elevated temperature leads over a fixed bed catalyst which consists of catalyst beds A, B arranged in two spatially successive reaction zones A, B, the active composition of the catalyst bed A located in reaction zone A at least one multimetal oxide of the general formula I

M ^l _a Mθι _-b M ² _b 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 and x = a number, which is determined by the valency and frequency of the elements in I other than oxygen,

Bi _{a '} Mθb _' X ¹ c'X ² d _' X ³ e _' X ⁴ _{f '} X ⁵ g _' X ⁶ _{h '} 0 _: 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, TI and / or Sn,

X ⁶ = rare earth metal, Ti, Zr, Nb, Ta, Re, Ru, Rh, Ag, Au, AI, 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,

and the reaction gas starting mixture flows through the catalyst beds A, B in the sequence “first A”, “then B”, characterized in that

that the temperature of reaction zone A is 380 to 480 ° C and the temperature of reaction zone B is on the one hand> 300 ° C and on the other hand is at least 20 ° C below the temperature of reaction zone A.

2. The method according to claim 1, characterized in that the temperature of the reaction zone B at least 40 ° C below the

Temperature of reaction zone A is.

3. The method according to claim 1 or claim 2, characterized in that the temperature of the reaction zone B is 320 to 380 ° C.

4. The method according to any one of claims 1 to 3, characterized in that the reaction gas starting mixture contains> 60 vol .-% propane.

5. The method according to any one of claims 1 to 4, characterized in that the reaction gas starting mixture contains> 20 vol .-% 0 ₂ .

6. The method according to any one of claims 1 to 5, characterized in that M ¹ = Co and / or Ni, M ² = W, Sn and / or Sb, a = 0.9 to 1.0 and b = 0.01 up to 0.3.

7. The method according to any one of claims 1 to 6, characterized in that X ¹ = W and / or V, X ² = Co, Ni and / or Zn, X ³ =

Fe and / or Cr, X ⁴ = P and / or Sb, X ⁵ = K and / or Na, X ⁶ = Si, Zr, Al, Ag, Nb and / or Ti, a '= 0.5 to 2 and b '= 0.1 to 30, C = 0.5 to 3, d' = 3 to 10, e '= 1 to 7, f = 0 to 1, g' = 0.01 to 1 and h '= 1 to 15.

8. The method according to any one of claims 1 to 6, characterized in that the at least one multimetal oxide I is such a ^' ches of the general formula I "

[Co u./o. V i] _a MOI _b [W, Sn u. / o. Sb] _b O _x (I "),

With a = 0.5 to 1.5, b = 0 to 0.5 and x = a number which is determined by the valency and frequency of the elements other than oxygen in I "5.

9. The method according to claim 8, characterized in that the at least one multimetal oxide II is one of the general formula II '10th

Bi _{a '} Mθ _' W _c - [Co, Ni u./o. Zn] _d -Fe _{e '} [P u./o. Sb] _f - [Ku./o. Na] _g -X ⁶ _' O _x <

(II '),

15 with

X ⁶ = rare earth metal, Ti, Zr, Nb, Ta, Ru, Rn, Rh, Ag, Au,

Al, Ga, In, Si, Ge, Th and / or U, a '= 0.01 to 8, b' = 0.1 to 30, 20 C = 0 to 20, d '= 0 to 20, e' = 0 to 20, f '= 0 to 6, g' = 0 to 4, 25 h '= 0 to 15 and x' = a number which is determined by the valency and frequency of the elements other than oxygen in II ', is.

30 10. The method according to any one of claims 1 to 9, characterized in that it is carried out continuously.

11. The method according to any one of claims 1 to 10, characterized in that the molar ratio of propane to molecular

35 oxygen in the reaction gas starting mixture 8 is 8.

12. The method according to any one of claims 1 to 11, characterized in that the ratio of the bulk volumes of the two catalyst beds A, B is 1: 5 to 5: 1.

40

13. The method according to any one of claims 1 to 12, characterized in that the reaction pressure is> 1 bar.

14. The method according to any one of claims 1 to 13, characterized 45 characterized in that it is carried out in a two-zone tube bundle reactor, the reaction tubes contain the catalyst beds A, B arranged in succession and in the a salt bath A flows around the reaction tube sections in which the catalyst bed A is located and a salt bath B flows around the reaction tube sections in which the catalyst bed B is located.

15. The method according to claim 14, characterized in that the salt baths A and B viewed over the respective reaction zone have a meandering flow course of the heat exchange medium.