DE19843329A1 - Preparation of methacrylic acid - Google Patents

Abstract

Preparation of methacrylic acid by the catalyzed gas phase-oxidation of methacrolein comprises using a multi-metal oxide composition. Preparation of methacrylic acid by the catalyzed gas phase-oxidation of methacrolein comprises using a multi-metal oxide composition of formula M<1>a-bM<2>bM<3>lM<4>12-cM<5>cOd.e(MoP2Of).g(SbOh).i(SOk).l(H2O).(I) M<1> = Na, K, Rb, Cs and/or NH4<+>; M<2> = Cu and/or Ag; M<3> = P; M<4> = Mo and/or W; M<5> = Nb, V and/or Ta; a = 2.7-3.3; b and c = 0-2; d = 0-0.6; g = 0-3; d, f, h and k = numbers dependent on the valency of O; i = 0-0.1; l = 0-03. An Independent claim is included for the composition.

Description

The present invention relates to a method for producing Methacrylic acid by heterogeneously catalyzed gas phase oxidation of methacrolein on a solid multimetal oxide mass as Kataly sator.

Methacrylic acid is an important intermediate, which ins especially in the form of its alkyl esters for the production of polymers saten is used. A known methacrylic acid derivative is e.g. B. the methyl ester of methacrylic acid. Currently the World annual production of methyl methacrylate about 1.5 million tons nen. The polymethacrylates are versatile raw materials in the plastics sector.

The commercial production of methacrylic acid takes place at which by heterogeneously catalyzed gas phase oxidation of meth acrolein on solid multimetal oxide masses as a catalyst. At The aforementioned multimetal oxide materials are usually to heteropoly compounds that differ from phosphoromolybdic acid deduce. In addition to molybdenum and phosphorus, they usually contain Metal elements such as copper, vanadium, arsenic, antimony, cesium as well Potassium (see e.g. DE-A 43 29 907, DE-A 26 10 249, EP-A 113 156, DE-A 19 638 249 or JP-A 7/185354). Implementation of the hetero Catalyzed gas phase oxidation usually takes place that a methacrolein, molecular oxygen as well as usually Gas mixture comprising inert diluent gases at increased Temperature over the catalytically active multimetal oxide mass is conducted, the on the surface of the multimetal oxide mass Conversion of methacrolein with oxygen to methacrylic acid follows.

A disadvantage of the aforementioned procedure is that the thermi cal stability of the known heteropoly compounds not fully can satisfy what the catalyst life at the hete roe-catalyzed gas phase oxidation of methacrolein to meth limited acrylic acid.

The object of the present invention was therefore a Process for the preparation of methacrylic acid by heterogeneous ka Talised gas phase oxidation of methacrolein on a solid  To provide multimetal oxide mass as a catalyst, which has an improved catalyst life.

Accordingly, a process for the preparation of methacrylic acid by heterogeneously catalyzed gas-phase oxidation of methacrolein on a solid multimetal oxide mass as a catalyst was found, which is characterized in that the catalytic active composition is one of the general formula I

M ¹ _from M ² _b M ³ ₁ M ⁴ _12-c M ⁵ _c O _d .e (MoP ₂ O _f ) .g (SbO _h ) .i (SO _k ) .l (H ₂ O) (I),

With
M ¹ = Na, K, Rb, Cs and / or NH ₄ ^⊕ , preferably Cs and / or NH ₄ ^⊕ ,
M ² = Cu and / or Ag, preferably Cu,
M ³ = P,
M ⁴ = Mo and / or W, preferably Mo,
M ⁵ = Nb, V and / or Ta, preferably V,
a = 2.7 to 3.3, preferably 2.85 to 3.15, particularly preferably 2.95 to 3.05 and very particularly preferably 3.0,
b = 0 to 2, preferably 0.3 to 1.0 and particularly preferably 0.5,
c = 0 to 2, preferably 0.5 to 1.5, particularly preferably 0.75 to 1.25 and very particularly preferably 0.9 to 1.1, in particular 1,
e = 0 to 0.6, preferably 0.1 to 0.4,
g = 0 to 3, preferably 0.5 to 2, particularly preferably 0.75 to 1.5 and very particularly preferably 0.9 to 1.1, in particular 1,
h, d, f, k = numbers which are determined by the valency and frequency of the elements in I other than oxygen,
i = 0 to 0.1 and
l = 0 to 30,
is used.

Catalytically active multimetal oxide compositions of the general formula I are z. B. obtainable in that one from sources of their elementa ren constituents as intimate as possible, preferably fine Partial, dry mix produces and this at temperatures calcined from 150 to 450 ° C for several hours.  

As sources of the constituents of the multimetal oxide materials general formula I come quite generally oxides or such Compounds considered by heating in the presence of Oxygen can be converted into oxides (see, for example, DE-A 44 05 058).

In addition to the oxides, the main starting compounds are therefore Halides, nitrates, formates, oxalates, acetates, carbonates or Hydroxides into consideration. Possible output connections of Mo, V and W are their molybdates, vanadates and tungstates, respectively from these derived acids (examples include ammonium called heptamolybdate and ammonium metavanadate). Regarding the Elements Sb come as an element source alongside Valentinit and Senar montit also include simple salts of Sb such as antimony nitrate. The intimate mixing of the starting compounds can be done in drier or in wet form. It is done in dry form, who which the starting compounds expediently as finely divided Powder used and z. B. after mixing to catalyst bodies desired geometry (e.g. tableted), which is then the Be subjected to calcination. The calcination can also before forming. The intimate vermi is preferred but in wet form. Usually the output connections in the form of a solution and / or suspension mixed together. After the mixing process is complete, the fluid mass dried and after drying (before or after For mung) calcined. Drying is preferably carried out by spraying drying (starting temperature usually: 100 to 150 ° C). The The resulting powder is often too hot for direct shaping fine, which is why it is often either by means of a solid compact tion and subsequent grinding to a defined particle size coarsened or with the addition of a liquid, more common white water, processed into a plasticine and as such ge molded and then calcined according to the invention. Does that happen in Some mixing in wet form can also increase temperature be turned. Furthermore, the loosening and / or suspending of with an addition of acids or bases.

Expediently, the kata Lytically active multimetal oxide masses I as full catalysts used, d. that is, as such a catalyst body that excludes Lich consist of the mass of the invention. Thereby form hollow cylinders with an outer diameter and a length of 2 to 10 mm and a wall thickness of 1 to 3 mm a cheap Kataly sator geometry.

An aqueous mixture of the starting components can be used for production of the catalytic active material as an additional aid in quantities from 1 to 20% by weight, based on the calcined catalyst  mass, organic compounds such as nitrogen-containing cycli cal connections, e.g. B. pyridine, but also carboxylic acids or Al contains alcohol. Drying from wet, usually watery, Mixing usually takes place at 60 to 180 ° C. To form the Catalyst mass or its non-calcined precursor mass can be known methods such as tableting, extruding or extrusion, lubricants such as Gra phite or stearic acid as well as molding aids and reinforcing agents such as microfibers made of glass, asbestos, silicon carbide or potassium Titanate can be added.

The compositions of the invention can also in the form of Trä ger or shell catalysts, d. that is, on a preformed, in essential inert, material applied for the production of Use methacrylic acid by gas phase oxidation of methacrolein be det, the application to the substantially inert Material z. B. in the form of the aqueous starting solution or Suspen sion, combined with subsequent drying and calcination or in combination as an already calcined pulverized mass can be done with a binder. An application to the carrier ger before the final calcination is preferably carried out according to EP-B 293 859.

Of course, the ak tive multimetal oxide masses I also in powder form Catalysts are used.

Incidentally, the catalytic gas phase oxidation according to the invention of methacrolein to methacrylic acid is carried out using the multimetal oxide to be used according to the invention as catalysts in a manner known per se, inter alia, in DE-A 40 22 212, shown. The same applies to the separation of methacrylic acid from the product gas stream. The oxidation medium molecular oxygen can, for. B. in the form of air, but also in pure form. Because of the high heat of reaction, the reactants are preferably diluted with inert gas such as He, N ₂ , CO ₂ , lower saturated hydrocarbons and / or with water vapor.

In the case of a methacrolein, preference is given to: oxygen: water vapor: inert gas ratio of 1: (1 to 3): (2 to 20): (3 to 30), particularly preferably from 1: (1 to 3): (3 to 10): (7 to 18) worked. The methacrolein used can ver have been obtained in various ways, e.g. B. by gas phases oxidation of isobutylene or precursors of isobutylene such as tert-butanol, methyl ether of tert-butanol or acetic acid ester of tert-butanol. Methacrolein is used with advantage  by condensation of propanol with formaldehyde in the presence of secondary amines and acids in the liquid phase according to those in the DE-PS 875 114 or described in DE-AS 2 855 514 is available.

The gas phase oxidation according to the invention can be carried out in vortexes Layer reactors as well as in fixed bed reactors. It is preferably carried out in tube bundle reactors, in whose tubes the catalyst mass, preferably in the form of zylin drisch shaped particles, is firmly arranged. The reaction tem temperature is usually 250 to 350 ° C, the reaction pressure is usually in the range of 1 to 3 bar and the total room load is preferably 800 to 1800 Nl / l / h. Under In these conditions, the methacrolein conversion is simple Reactor passage usually at 50 to 80 mol%. Preferably the mentioned boundary conditions within the framework of the mentioned Ra sters coordinated so that with a single pass through the reactor a methacrolein conversion of 60 to 70 mol% re results.

In the gas phase oxidation according to the invention is usually not pure methacrylic acid, but a product mixture, from which the methacrylic acid must subsequently be separated. This can be done in a manner known per se, e.g. B. by the Reaction gases after indirect and / or direct cooling at tem temperatures of 40 to 80 ° C washes with water, an aqueous Methacrylic acid solution is obtained from which the methacrylic acid usually by extraction with an organic solution medium removed and separated from the same by distillation becomes.

The calcination of the dry precursor mass to the active composition to be used according to the invention can be carried out under inert gas (e.g. N ₂ , noble gas), under a mixture of inert gas and oxygen (e.g. air), but also under a mixture of O ₂ and reducing Gases such as hydrocarbons, methacrolein or ammonia occur. It is preferably calcined in an atmosphere which has the character of oxidizing. Favorable calcination conditions can be found e.g. B. in DE-A 19 638 249.

The active compositions I obtained after the calcination are suitable especially as catalysts with improved service life Gas-phase catalytic oxidative production of methacrylic acid from methacrolein.  

In addition to the gas phase catalytic oxidation of methacrolein However, methacrylic acid can also be used in active masses I gas phase catalytic oxidation and ammoxidation of other ge saturated, unsaturated and aromatic hydrocarbons, Catalyze alcohols, aldehydes and amines.

The gas phase catalytic oxidation of other alkanes, alkanols, alkenes containing 3 to 6 carbon atoms and alkenols (e.g. propylene, acrolein, tert-butanol, methyl ether of tert-butanol, acetic acid ester of tert-butanol, iso-butane or iso-butyraldehyde to olefinically unsaturated aldehydes and / or carboxylic acids, and the corresponding nitriles (ammon oxidation, especially from propene to acrylonitrile and isobutene or tert-butanol to methacrylonitrile). Particularly highlighted be the production of acrylic acid, acrolein and methacrolein, and the oxidation of n-butane to maleic anhydride and the like few from butadiene to furan. But they are also suitable for oxida tive dehydration of organic compounds.

Examples A) Production of active materials Comparative Example 1

593.7 g (NH ₄ ) ₆ Mo ₇ O ₂₄ .4H ₂ O were dissolved in 725 ml of water, which was warmed to 35 ° C. 20.7 g of NH ₄ VO _{3 were} added to the resulting solution and the mixture was heated to 40.degree. While maintaining the 40 ° C an 80 ° C solution of 57.5 g of CsNO ₃ in 100 ml of water was then added dropwise within 3 min. While maintaining the 40 ° C further 38.04 g of a 76 wt .-% aqueous H ₃ PO ₄ solution were added all at once. The resulting aqueous suspension was heated to 95 ° C. with constant stirring. While maintaining the 95 ° C 61.1 g of an aqueous copper nitrate solution (15.5 wt .-% Cu) were added all at once. The aqueous suspension was then evaporated and the solid catalyst precursor mass obtained was tabletted, and the resulting tablets were then broken down into split (average size diameter (longest connecting line passing through the center of gravity of two points on the surface) = approx. 0.3 mm). The solid split (250 g per batch) was calcined in a circulating air oven (internal volume = 40 l), through which 500 Nl / h of air (which always had the calcination temperature) flowed through, the calcination temperature initially being from 25 ° C. to 4 ° C / h was increased to 270 ° C (when the calcination temperatures 180 ° C and 220 ° C reached the heating was interrupted and these temperatures were maintained for 30 min). After reaching the calcination temperature of 270 ° C, this was also maintained for 30 min. Finally, the calcination temperature was increased to 385 ° C at a rate of 2 ° C / h and this calcination temperature was maintained for 3 h.

The resulting catalytic active mass had the following stoichiometry: Cs ₁ Cu _0.5 P ₁ Mo _11.4 V _0.6 O _x .

example 1

572.9 g (NH ₄ ) ₆ Mo ₇ O ₂₄ .4H ₂ O were dissolved in 625 ml of water, which was warmed to 35 ° C. 34.5 g of NH ₄ VO _{3 were} added to the resulting solution and the mixture was heated to 40.degree. While maintaining the 40 ° C an 80 ° C solution of 115 g of CsNO ₃ in 300 ml of water was then added dropwise within 6 min. While maintaining the 40 ° C further 38.04 g of a 76 wt .-% aqueous H ₃ PO ₄ solution were added all at once. The resulting aqueous suspension was heated to 95 ° C. with constant stirring. While maintaining the 95 ° C 61.1 g of an aqueous copper nitrate solution (15.5 wt .-% Cu) were added all at once. The aqueous suspension was then evaporated and the solid catalyst precursor mass obtained was tabletted and the resulting tablets were then broken up into split (average size diameter = approx. 0.3 mm). The solid split (250 g per batch) was calcined in a circulating air oven (internal volume = 40 l), through which 500 Nl / h of air (which always had the calcination temperature) was calcined, the calcination temperature initially being 25 ° C was increased to 270 ° C at 4 ° C / h (when the calcination temperatures 180 ° C and 220 ° C were reached, the heating was interrupted and these temperatures were maintained for 30 min). After reaching the calcination temperature of 270 ° C, this was also maintained for 30 min. Finally, the calcination temperature was increased at a rate of 2 ° C / h to 400 ° C and this calcination temperature was maintained for 2 h.

The resulting catalytic active mass had the following stoichiometry: Cs ₂ Cu _0.5 P ₁ Mo ₁₁ V _1.0 O _x .

Example 2

As in Example 1, but the amount of CsNO _{3 used} was not 115 g but 147.8 g. The resulting catalytic active mass had the following stoichiometry: Cs _2.5 Cu _0.5 P ₁ Mo ₁₁ V _1.0 O _x .

Example 3

158.3 g of MoO ₃ and 9.2 g of V ₂ O ₅ (purity: 98.8% by weight) were added in succession to 6 l of water with constant stirring. Then 576 ml of a 1.7 wt .-% aqueous phosphoric acid were added dropwise within 25 min and the resulting aqueous mixture was heated to 90 ° C. This temperature was maintained for 9 hours with stirring. Then it was cooled to 25 ° C. Then a solution of 48.9 g of Cs ₂ CO ₃ in 551 ml of water was added dropwise within 35 min and the resulting mixture was evaporated. The resulting solid was dried at 105 ° C for 14 h and then left in the air at 25 ° C after 24 h. The catalyst precursor composition was then tabletted and the tablets obtained were broken again (number-average split size diameter = approx. 0.3 mm). The split material was then calcined at 350 ° C. for 5 hours in a circulating air oven through which air flowed, as in Example 1. The heating to 350 ° C. had a rate of 5 ° C./h.

The resulting catalytic active mass had the following stoichioms: Cs ₃ P ₁ Mo ₁₁ V _1.0 O _x .

Comparative Example 2

As in Example 3, but the Cs ₂ CO ₃ solution consisted of 65.2 g of Cs ₂ CO ₃ in 735 ml of water. The resulting catalytic active mass had the following stoichiometry: Cs ₄ P ₁ Mo ₁₁ V _1.0 O _x .

B) Investigations of the service life of the active materials produced in A)

A reaction tube was placed in the measuring chamber of a diffractometer (Microreactor) made of stainless steel, which has a height of 16 mm and had an inner diameter of 20 mm and at the end of a stainless steel carrier network has been completed. To the Trä 4 g of active substance were applied to the network and by lightly press the catalyst bed at the microreactor inlet smoothed tet. The active material layer was at the entrance of the reaction tube accessible to the x-rays.

7 Nl / h of a reaction gas mixture of the following composition were passed through the reaction tube:
5 vol% methacrolein
9 vol.% Oxygen
16 vol .-% water vapor and
70 vol .-% molecular nitrogen.

The reaction gas mixture was always at the temperature of the active mass preheated.

The active composition was first heated to 290 ° C and then at water temperature maintained until after about 10 h, based on the one pass of the reaction gas mixture, one stationary State (after the formation time of the active composition) in relation on methacrolein conversion and selectivity of methacrylic acid formation had set. The stationary methacrolein turnover was in all Cases at 40-60%.

Then the temperature of the reaction tube was successively increased in 10 ° C. steps and kept at this temperature for 10 h after each step. At a specific temperature for the respective active mass (the decomposition temperature), X-ray diffraction reflections of orthorhombic MoO ₃ occurred in the X-ray diffraction diagram (Cu _Kα1 radiation; characteristic MoO ₃ lines occurred, according to the JCPDS-ICDD index card 35-609 from 1996 2θ = 12.76 °, 23.33 ° and 27.34 ° on). The occurrence of these X-ray diffraction lines was accompanied by a deactivation of the active material, which was evident from a decrease in methacrolein conversion by about half. A long service life correlates with a high decomposition temperature and a short service life correlates with a low decomposition temperature. The table shows the decomposition temperatures observed as a function of the active mass used.

table

Claims (19)

1. Process for the preparation of methacrylic acid by heterogeneously catalyzed gas phase oxidation of methacrolein on a fe most multimetal oxide mass as a catalyst, characterized in that the multimetal oxide mass is one of the general formula I
M ¹ _from M ² _b M ³ ₁ M ⁴ _12-c M ⁵ _c O _d .e (MoP ₂ O _f ) .g (SbO _h ) .i (SO _k ) .l (H ₂ O) (I),
With
M ¹ = Na, K, Rb, Cs and / or NH ₄ ^⊕ ,
M ² = Cu and / or Ag,
M ³ = P,
M ⁴ = Mo and / or W,
M ⁵ = Nb, V and / or Ta,
a = 2.7 to 3.3,
b = 0 to 2,
c = 0 to 2,
e = 0 to 0.6,
g = 0 to 3,
h, d, f, k = numbers which are determined by the valency and frequency of the elements in I other than oxygen,
i = 0 to 0.1 and
l = 0 to 30,
is. 2. The method according to claim 1, characterized in that the multimetal oxide mass is one of the general formula I with M ¹ = Cs and / or NH ₄ ^⊕ . 3. The method according to claim 1 or 2, characterized in that the multimetal oxide mass is one of the general formula I with M ² = Cu. 4. The method according to claim 1 or 2, characterized in that the multimetal oxide mass is one of the general formula I with M ² = Ag. 5. The method according to any one of claims 1 to 4, characterized in that the multimetal oxide mass is one of the general formula I with M ⁴ = Mo. 6. The method according to any one of claims 1 to 5, characterized in that the multimetal oxide mass is one of the general formula I with M ⁵ = V. 7. The method according to any one of claims 1 to 6, characterized records that the multimetal oxide mass is one of the general my formula I with a = 2.95 to 3.05. 8. The method according to any one of claims 1 to 7, characterized records that the multimetal oxide mass is one of the general my formula I with b = 0.3 to 1.0. 9. The method according to any one of claims 1 to 8, characterized records that the multimetal oxide mass is one of the general my formula I with c = 0.9 to 1.1. 10. The method according to any one of claims 1 to 9, characterized records that the multimetal oxide mass is one of the general my formula I with e = 0.1 to 0.4. 11. The method according to any one of claims 1 to 10, characterized records that the multimetal oxide mass is one of the general my formula I with g = 0.75 to 1.5. 12. The method according to any one of claims 1 to 11, characterized records that it is at a temperature of 250 to 350 ° C. is carried out. 13. Multimetal oxide compositions of the general formula I
M ¹ _from M ² _b M ³ ₁ M ⁴ _12-c M ⁵ _c O _d .e (MoP ₂ O _f ) .g (SbO _h ) .i (SO _k ) .l (H ₂ O) (I),
With
M ¹ = Na, K, Rb, Cs and / or NH ₄ ^⊕ ,
M ² = Cu and / or Ag,
M ³ = P
M ⁴ = Mo and / or W,
M ⁵ = Nb, V and / or Ta,
a = 2.7 to 3.3,
b = 0 to 2,
c = 0 to 2,
e = 0 to 0.6,
g = 0 to 3,
i = 0 to 0.1,
l = 0 to 30 and
h, d, f, k = numbers determined by the valency and frequency of the elements in I other than oxygen. 14. Multimetal oxide materials according to claim 13, wherein M ^{1 is} Cs and / or NH ₄ ^⊕ . 15. Multimetal oxide materials according to claim 13 or 14, wherein M ² = Cu. 16. Multimetal oxide materials according to one of claims 13 to 15, where M ⁴ = Mo. 17. Multimetal oxide compositions according to one of claims 13 to 16, where M ⁵ = V. 18. multimetal oxide compositions according to any one of claims 13 to 17, where at a = 2.95 to 3.05. 19. A method for producing a multimetal oxide mass according to Claim 13, characterized in that from sources of elementary constituents produces a dry mix and this calcined at temperatures of 150 to 450 ° C.