METHOD FOR PRODUCING A CATALYTICALLY ACTIVE MULTI-ELEMENT OXIDE CONTAINING THE ELEMENTS MO, W, V AND CU

Abstract

A process for producing a catalytically active multielement oxide comprising the elements Mo, W, V and Cu, wherein at least one source of the elemental constituents W of the multielement oxide is used to produce an aqueous solution, the resultant aqueous solution is admixed with sources of the elemental constituents Mo and V of the multielement oxide, drying of the resultant aqueous solution produces a powder P, the resultant powder P is optionally used to produce geometric shaped precursor bodies, and the powder P is or the geometric shaped precursor bodies are subjected to thermal treatment to form the catalytically active composition, wherein the aqueous solution used for drying comprises from 1.6% to 5.0% by weight of W and from 7.2% to 26.0% by weight of Mo, based in each case on the total amount of aqueous solution.

Claims

1.-15. (canceled)

16. A process for producing a catalytically active multielement oxide comprising the elements Mo, W, V, Cu and optionally Sb, wherein the ratio of the elements conforms to the general formula (I)
Mo12WaVbCucSbd   (I) where a=0.4 to 5.0, b=1.0to 6.0, c=0.2 to 1.8 and d=0.0 to 2.0, and the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 5 to 95 mol %, which comprises a) using at least one source of the elemental constituents W of the multielement oxide to produce an aqueous solution or aqueous suspension, b) admixing the aqueous solution or aqueous suspension obtained in a) with sources of the elemental constituents Mo, V and optionally Sb of the multielement oxide, c) admixing the aqueous solution or aqueous suspension obtained in b) with sources of the elemental constituents Cu and optionally Sb of the multielement oxide, d) drying the aqueous solution or aqueous suspension obtained in c) and optionally comminuting to produce a powder P, e) optionally using the powder P obtained in d), optionally with addition of one or more shaping auxiliaries and after homogeneous mixing, to obtain geometric shaped precursor bodies from the resulting mixture, and f) subjecting the powder P obtained in d) or the geometric shaped precursor bodies obtained in e) to thermal treatment to form the catalytically active multielement oxide, wherein the aqueous solution or aqueous suspension used in d) comprises from 1.6% to 5.0% by weight of W and from 7.2% to 26.0% by weight of Mo, based in each case on the total amount of aqueous solution or aqueous suspension.

17. The process according to claim 16, wherein the aqueous solution or aqueous suspension obtained in c) is spray-dried in d).

18. The process according to claim 16, wherein the stoichiometric coefficient a of the element W in the general formula (I) is from 1.0 to 2.0 and/or the stoichiometric coefficient b of the element V in the general formula (I) is from 2.5 to 4.5.

19. The process according to claim 16, wherein the aqueous solution or aqueous suspension used in d) comprises from 2.3% to 3.8% by weight of W and/or comprises from 11.5% to 15.0% by weight of Mo, based in each case on the total amount of aqueous solution or aqueous suspension.

20. The process according to claim 16, wherein water-soluble salts are used as the source of the elemental constituents Mo, V and/or W.

21. The process according to claim 16, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is from 0.8 to 1.2.

22. The process according to claim 16, wherein admixing is effected in b) or in c) with at least one source of the elemental constituents Sb of the multielement oxide.

23. A catalytically active multielement oxide comprising the elements Mo, W, V, Cu and optionally Sb, wherein the ratio of the elements conforms to the general formula (I)
Mo.sub.12W.sub.aV.sub.bCu.sub.cSb.sub.d   (I) where a=0.4 to 5.0, b=1.0 to 6.0, c=0.2 to 1.8 and d=0.0 to 2.0, and the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 5 to 95 mol %, obtained by the process of claim 16, wherein the BET surface area of the catalytically active multielement oxide is from 16 to 35 m.sup.2/g.

24. The catalytically active multielement oxide according to claim 23, wherein the stoichiometric coefficient a of the element W in the general formula (I) is from 1.0 to 2.0 and/or the stoichiometric coefficient b of the element V in the general formula (I) is from 2.5 to 4.5.

25. The catalytically active multielement oxide according to claim 23, wherein the BET surface area of the catalytically active multielement oxide is from 19 to 26 m.sup.2/g.

26. The catalytically active multielement oxide according to claim 23, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is from 0.8 to 1.2.

27. The catalytically active multielement oxide according to claim 23, wherein the catalytically active multielement oxide comprises the element Sb.

28. A process for producing an eggshell catalyst, which comprises applying a catalytically active multielement oxide according to claim 23 and optionally binder to the outer surface of a geometric shaped support body.

29. An eggshell catalyst consisting of a geometric shaped support body and the catalytically active multielement oxide according to claim 23 and optionally binder applied to the outer surface of the geometric shaped support body.

30. A process for preparing acrylic acid by gas phase catalytic oxidation of acrolein over a fixed catalyst bed, wherein the fixed catalyst bed comprises the catalytically active multielement oxide according to claim 23.

Description

[0172] Thus, the present invention encompasses especially the following embodiments of the invention: [0173] 1. A process for producing a catalytically active multielement oxide comprising the elements Mo, W, V, Cu and optionally Sb, wherein the ratio of the elements conforms to the general formula (I)

Mo.sub.12W.sub.aV.sub.bCu.sub.cSb.sub.d   (I) [0174] where [0175] a=0.4 to 5.0, [0176] b=1.0 to 6.0, [0177] c=0.2 to 1.8 and [0178] d=0.0 to 2.0, [0179] and the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 5 to 95 mol %, which comprises [0180] a) using at least one source of the elemental constituents W of the multielement oxide to produce an aqueous solution or aqueous suspension, [0181] b) admixing the aqueous solution or aqueous suspension obtained in a) with sources of the elemental constituents Mo, V and optionally Sb of the multielement oxide, [0182] c) admixing the aqueous solution or aqueous suspension obtained in b) with sources of the elemental constituents Cu and optionally Sb of the multielement oxide, [0183] d) drying the aqueous solution or aqueous suspension obtained in c) and optionally comminuting to produce a powder P, [0184] e) optionally using the powder P obtained in d), optionally with addition of one or more shaping auxiliaries and after homogeneous mixing, to obtain geometric shaped precursor bodies from the resulting mixture, and [0185] f) subjecting the powder P obtained in d) or the geometric shaped precursor bodies obtained in e) to thermal treatment to form the catalytically active multielement oxide, [0186] wherein the aqueous solution or aqueous suspension used in d) comprises from 1.6% to 5.0% by weight of W and from 7.2% to 26.0% by weight of Mo, based in each case on the total amount of aqueous solution or aqueous suspension. [0187] 2. The process according to embodiment 1, wherein the stoichiometric coefficient a of the element W in the general formula (I) is from 0.6 to 3.5. [0188] 3. The process according to embodiment 1 or 2, wherein the stoichiometric coefficient a of the element W in the general formula (I) is from 0.8 to 2.5. [0189] 4. The process according to any of embodiments 1 to 3, wherein the stoichiometric coefficient a of the element W in the general formula (I) is from 1.0 to 2.0. [0190] 5. The process according to any of embodiments 1 to 4, wherein the stoichiometric coefficient b of the element V in the general formula (I) is from 1.5 to 5.5. [0191] 6. The process according to any of embodiments 1 to 5, wherein the stoichiometric coefficient b of the element V in the general formula (I) is from 2.0 to 5.0. [0192] 7. The process according to any of embodiments 1 to 6, wherein the stoichiometric coefficient b of the element V in the general formula (I) is from 2.5 to 4.5. [0193] 8. The process according to any of embodiments 1 to 7, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is from 0.4 to 1.6. [0194] 9. The process according to any of embodiments 1 to 8, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is from 0.6 to 1.4. [0195] 10. The process according to any of embodiments 1 to 9, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is from 0.8 to 1.2. [0196] 11. The process according to any of embodiments 1 to 10, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is from 0.1 to 1.6. [0197] 12. The process according to any of embodiments 1 to 11, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is from 0.2 to 1.2. [0198] 13. The process according to any of embodiments 1 to 12, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is from 0.3 to 0.8. [0199] 14. The process according to any of embodiments 1 to 13, wherein the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 10 to 90 mol %. [0200] 15. The process according to any of embodiments 1 to 14, wherein the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 15 to 85 mol %. [0201] 16. The process according to any of embodiments 1 to 15, wherein the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 20 to 80 mol %. [0202] 17. The process according to any of embodiments 1 to 16, wherein the aqueous solution or aqueous suspension obtained in c) is dried and comminuted in d). [0203] 18. The process according to any of embodiments 1 to 16, wherein the aqueous solution or aqueous suspension obtained in c) is spray-dried in d). [0204] 19. The process according to any of embodiments 1 to 18, wherein the powder P obtained in d) is used to produce geometric shaped precursor bodies in e). [0205] 20. The process according to any of embodiments 1 to 18, wherein the powder P obtained in d), with addition of one or more shaping auxiliaries and after homogeneous mixing, is used in e) to obtain geometric shaped precursor bodies from the resulting mixture. [0206] 21. The process according to any of embodiments 1 to 20, wherein the aqueous solution or aqueous suspension used in d) comprises from 1.9% to 5.2% by weight of W. [0207] 22. The process according to any of embodiments 1 to 21, wherein the aqueous solution or aqueous suspension used in d) comprises from 2.1% to 4.5% by weight of W. [0208] 23. The process according to any of embodiments 1 to 22, wherein the aqueous solution or aqueous suspension used in d) comprises from 2.3% to 3.8% by weight of W. [0209] 24. The process according to any of embodiments 1 to 23, wherein the aqueous solution or aqueous suspension used in d) comprises from 8.7% to 22.0% by weight of Mo. [0210] 25. The process according to any of embodiments 1 to 24, wherein the aqueous solution or aqueous suspension used in d) comprises from 10.1% to 18.0% by weight of Mo. [0211] 26. The process according to any of embodiments 1 to 25, wherein the aqueous solution or aqueous suspension used in d) comprises from 11.5% to 15.0% by weight of Mo. [0212] 27. The process according to any of embodiments 1 to 26, wherein water-soluble salts are used as the source of the elemental constituents Mo, W and V. [0213] 28. The process according to any of embodiments 1 to 27, wherein admixing is effected in b) with at least one source of the elemental component Sb of the multielement oxide. [0214] 29. The process according to any of embodiments 1 to 28, wherein admixing is effected in c) with at least one source of the elemental component Sb of the multielement oxide. [0215] 30. The process according to any of embodiments 1 to 29, wherein admixing is effected in b) with at least one source of the elemental component Ta, Cr, Ce, Ni, Co, Fe, Mn, Zn, Nb, Bi, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Si, Al, Ti or Zr of the multielement oxide. [0216] 31. The process according to any of embodiments 1 to 30, wherein admixing is effected in c) with at least one source of the elemental component Ta, Cr, Ce, Ni, Co, Fe, Mn, Zn, Nb, Bi, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Si, Al, Ti or Zr of the multielement oxide. [0217] 32. The process according to any of embodiments 1 to 31, wherein water-soluble salts are used as the source of the elemental constituents Sb. [0218] 33. The process according to any of embodiments 1 to 32, wherein the source of the elemental constituents Cu of the aqueous solution or aqueous suspension obtained in b) is added in solid form. [0219] 34. The process according to any of embodiments 1 to 33, wherein an aqueous solution is prepared in b). [0220] 35. A catalytically active multielement oxide comprising the elements Mo, W, V, Cu and optionally Sb, wherein the ratio of the elements conforms to the general formula (I)

Mo.sub.12W.sub.aV.sub.bCu.sub.cSb.sub.d   (I) [0221] where [0222] a=0.4 to 5.0, [0223] b=1.0 to 6.0, [0224] c=0.2 to 1.8 and [0225] d=0.0 to 2.0, [0226] and the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 5 to 95 mol %, obtainable by a process of embodiments 1 to 34, wherein the BET surface area of the catalytically active multielement oxide is from 16 to 35 m.sup.2/g. [0227] 36. The catalytically active multielement oxide according to embodiment 35, wherein the stoichiometric coefficient a of the element Win the general formula (I) is from 0.6 to 3.5. [0228] 37. The catalytically active multielement oxide according to embodiment 35 or 36, wherein the stoichiometric coefficient a of the element Win the general formula (I) is from 0.8 to 2.5. [0229] 38. The catalytically active multielement oxide according to any of embodiments 35 to 37, wherein the stoichiometric coefficient a of the element Win the general formula (I) is from 1.0 to 2.0. [0230] 39. The catalytically active multielement oxide according to any of embodiments 35 to 38, wherein the stoichiometric coefficient b of the element V in the general formula (I) is from 1.5 to 5.5. [0231] 40. The catalytically active multielement oxide according to any of embodiments 35 to 39, wherein the stoichiometric coefficient b of the element V in the general formula (I) is from 2.0 to 5.0. [0232] 41. The catalytically active multielement oxide according to any of embodiments 35 to 40, wherein the stoichiometric coefficient b of the element V in the general formula (I) is from 2.5 to 4.5. [0233] 42. The catalytically active multielement oxide according to any of embodiments 35 to 41, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is from 0.4 to 1.6. [0234] 43. The catalytically active multielement oxide according to any of embodiments 35 to 42, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is from [0235] 44. The catalytically active multielement oxide according to any of embodiments 35 to 43, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is from 0.8 to 1.2. [0236] 45. The catalytically active multielement oxide according to any of embodiments 35 to 44, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is from 0.1 to 1.6. [0237] 46. The catalytically active multielement oxide according to any of embodiments 35 to 45, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is from 0.2 to 1.2. [0238] 47. The catalytically active multielement oxide according to any of embodiments 35 to 46, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is from 0.3 to 0.8. [0239] 48. The catalytically active multielement oxide according to any of embodiments 35 to 47, wherein the catalytically active multielement oxide comprises at least one of the elements Ta, Cr, Ce, Ni, Co, Fe, Mn, Zn, Nb, Bi, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Si, Al, Ti or Zr. [0240] 49. The catalytically active multielement oxide according to any of embodiments 35 to 48, wherein the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 10 to 90 mol %. [0241] 50. The catalytically active multielement oxide according to any of embodiments 35 to 49, wherein the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 15 to 85 mol %. [0242] 51. The catalytically active multielement oxide according to any of embodiments 35 to 50, wherein the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 20 to 80 mol %. [0243] 52. The catalytically active multielement oxide according to any of embodiments 35 to 51, wherein the BET surface area of the catalytically active multielement oxide is from 17 to 32 m.sup.2/g. [0244] 53. The catalytically active multielement oxide according to any of embodiments 35 to 52, wherein the BET surface area of the catalytically active multielement oxide is from 18 to 29 m.sup.2/g. [0245] 54. The catalytically active multielement oxide according to any of embodiments 35 to 53, wherein the BET surface area of the catalytically active multielement oxide is from 19 to 26 m.sup.2/g. [0246] 55. The catalytically active multielement oxide according to any of embodiments 35 to 54, wherein the ratio R of the catalytically active multielement oxide is from 1.0 to 2.0. [0247] 56. The catalytically active multielement oxide according to any of embodiments 35 to 55, wherein the ratio R of the catalytically active multielement oxide is from 1.1 to 1.9. [0248] 57. The catalytically active multielement oxide according to any of embodiments 35 to 56, wherein the ratio R of the catalytically active multielement oxide is from 1.2 to 1.8. [0249] 58. A process for preparing acrylic acid by gas phase catalytic oxidation of acrolein over a fixed catalyst bed, wherein the fixed catalyst bed comprises a catalytically active multielement oxide according to any of embodiments 35 to 57. [0250] 59. The use of a catalytically active multielement oxide according to any of embodiments 35 to 57 as catalysts for the heterogeneously catalyzed partial gas phase oxidation of acrolein to acrylic acid. [0251] 60. A process for producing an eggshell catalyst, which comprises applying a catalytically active multielement oxide according to any of embodiments 35 to 57 to the outer surface of a geometric shaped support body. [0252] 61. A process for producing an eggshell catalyst, which comprises applying a catalytically active multielement oxide according to any of embodiments 35 to 57 and binder to the outer surface of a geometric shaped support body. [0253] 62. The use of a multielement oxide according to any of embodiments 35 to 57 for production of eggshell catalysts. [0254] 63. An eggshell catalyst consisting of a geometric shaped support body and a catalytically active multielement oxide according to any of embodiments 35 to 57 applied to the outer surface of the geometric shaped support body. [0255] 64. An eggshell catalyst consisting of a geometric shaped support body and a catalytically active multielement oxide according to any of embodiments 35 to 57 and binder applied to the outer surface of the geometric shaped support body. [0256] 65. A process for preparing acrylic acid by gas phase catalytic oxidation of acrolein over a fixed catalyst bed, wherein the fixed catalyst bed comprises an eggshell catalyst according to embodiment 63 or 64. [0257] 66. The use of an eggshell catalyst according to embodiment 63 or 64 as catalysts for the heterogeneously catalyzed partial gas phase oxidation of acrolein to acrylic acid.

EXAMPLES

Example 1 (Comparative Example)

[0258] Annular eggshell catalyst C1 with the catalytically active oxide composition Mo.sub.12W.sub.12V.sub.3Cu.sub.12O.sub.n

[0259] Production of the eggshell catalyst:

[0260] A first solution was prepared from 102.5 g of copper(II) acetate monohydrate (Cu content=32% by weight) and 3180 g of water at 70° C. and stirring for a half-hour.

[0261] For a second solution, 900 g of ammonium heptamolybdate tetrahydrate (Mo content=55% by weight) was added to 7066 g of water at 90° C. with stirring. While maintaining the temperature, the mixture was stirred for 5 minutes, 156 g of ammonium metavanadate (V content=42% by weight) was added, and the mixture was stirred for a further 40 minutes. Subsequently, 132 g of ammonium paratungstate heptahydrate (W content=72% by weight) was added and the mixture was stirred for a further 30 minutes. An orange solution was obtained.

[0262] Next, the first solution was added to the second solution and the mixture was stirred for 15 minutes. To the resultant solution was added 1530 g of a 25% by weight aqueous NH.sub.3 solution, the temperature of which was 25° C. A clear solution having a temperature of about 70° C. and a pH of 8.5 was obtained.

[0263] The resultant solution was finally introduced into a Mobile Minor 2000 spray tower with FO A1 spray head (GEA Niro, Soeborg, Denmark) by means of a rotary atomizer at 30 000 rpm. The drying was conducted in a hot air stream at an inlet temperature of 350° C. and an exit temperature of 120° C. The powder was introduced into a ZS1-18 kneader (Coperion Werner & Pfleiderer GmbH & Co. KG; Stuttgart, Germany). The powder was kneaded at ambient temperature together with 100 ml of glacial acetic acid and 200 ml of water at 15 rpm for 30 minutes. Subsequently, the material was extruded (length 1 to 10 cm, diameter 6 mm). The extrudates were dried at 110° C. in an air circulation drying cabinet for 16 hours.

[0264] 1000 g of the precursor composition taken from the air circulation drying cabinet was calcined batchwise in a rotary furnace (analogously to U.S. Pat. No. 9,149,799 B2). The calcination was conducted under a gas stream composed of air and nitrogen with an oxygen content of 2.3% by volume. The rotary furnace was heated to 400° C. within one hour and kept at that temperature for a further 2 hours. Subsequently, the heating was switched off and the material was cooled to ambient temperature with further rotation.

[0265] The material taken from the rotary furnace was subsequently comminuted to a fine powder in a ZM 200 mill (Retsch GmbH, Haan, Germany).

[0266] The fine powder was used to coat 1600 g of annular support bodies (external diameter 7 mm, length 3 mm, internal diameter 4 mm, surface roughness Rz 45 μm) of the C 220 steatite type (Ceram Tec GmbH, Plochingen, Germany). The coating was conducted in a Hi-Coater LHC 25/36 mixer (Gebruder Lodige Maschinenbau GmbH, Paderborn, Germany). The mixer was retrofitted for continuous powder dosage. For this purpose, a funnel-shaped vessel was connected via a hose (external diameter 11.1 mm, internal diameter 8 mm) to the drum of the mixer. For coating, 500 g of fine powder was introduced into the funnel-shaped vessel. The dosage was effected by means of 50 ms pressure pulses and a positive pressure of 0.7 bar. During the dosage, the contents of the funnel-shaped vessel were moved by means of an anchor stirrer modified in a V shape (made in-house). Between periods of stirring of 2 s, there were pauses for 1 s.

[0267] The binder used was a 25% by weight aqueous solution of glycerol. The solution was metered into the mixer at 3 g/min by means of a two-phase nozzle of the 570 S75 type (Düsen-Schlick GmbH, Coburg, Germany), parallel to the dosage of powder. The powder dosage was 6 cm below the two-phase nozzle and was inclined downward by 40°. The powder was dosed outside the spray cone of the two-phase nozzle. The mixer drum rotated clockwise at 15 rpm. The coating was conducted at 25° C. within 40 minutes. Subsequently, the speed of rotation was lowered to 2 rpm, and drying was effected in an air stream (220 I (STP)/h) at 130° C. for 30 minutes. This was followed by cooling to 25° C. The powder was taken up by the surface of the support bodies. No formation of paired support bodies or agglomeration was observed.

[0268] Subsequently, the coated support bodies were freed of adhering glycerol in a UM 400 air circulation drying cabinet (Memmert GmbH & Co. KG, Schwabach, Germany). The coated support bodies were distributed homogeneously over perforated sheets with a layer thickness of 2 cm. The perforated sheets had a thickness of 0.5 cm, an opening ratio of 60% and an area of 35 cm×26 cm. The air circulation drying cabinet was heated to 300° C. at 3 K/minute and kept at that temperature for a further 2 hours. This was followed by cooling to 40 to 50° C. within 2 to 3 hours.

[0269] The annular eggshell catalyst C1 had an oxidic active composition content of 20.7% by weight. The BET surface area of the catalytically active multielement oxide was 14 m.sup.2/g.

[0270] Analysis of the Eggshell Catalyst:

[0271] A reaction tube (stainless steel (material 1.4541); external diameter 30 mm; wall thickness 2 mm; internal diameter 26 mm; length 464 cm) was charged from the top downward as follows:

[0272] Section 1: length 80 cm [0273] empty tube;

[0274] Section 2: length 60 cm [0275] preliminary bed of steatite rings of geometry 7 mm×3 mm×4 mm (external diameter×length×internal diameter; C 220 steatite from Ceram Tec GmbH);

[0276] Section 3: length 100 cm [0277] fixed catalyst bed composed of a homogeneous mixture consisting of 20% by weight of steatite rings of geometry 7 mm×3 mm×4 mm (external diameter×length×internal diameter; C 220 steatite from Ceram Tec GmbH) and 80% by weight of the eggshell catalyst;

[0278] Section 4: length 200 cm

[0279] fixed catalyst bed consisting exclusively of the eggshell catalyst as in section 3;

[0280] Section 5: length 10 cm

[0281] downstream bed of the same steatite rings as in section 2;

[0282] Section 6: length 14 cm

[0283] Catalyst base made of stainless steel (material 1.4541) for accommodation of the fixed catalyst bed.

[0284] A reaction gas mixture conducted through the respective reaction tube charged as described above, flowing through the reaction tube from the top downward, had the following contents:

[0285] 4.3% by vol. of acrolein,

[0286] 0.3% by vol. of propene,

[0287] 0.2% by vol. of propane,

[0288] 0.3% by vol. of acrylic acid,

[0289] 5.1% by vol. of oxygen,

[0290] 0.4% by vol. of carbon oxides,

[0291] 7% by vol. of water and

[0292] 82.3% by vol. of nitrogen.

[0293] The feed temperature of the reaction gas mixture (at the inlet into the reaction tube) was 210° C., and the space velocity of acrolein on the fixed catalyst bed (as defined in DE 199 27 624 A) was 80 I (STP)/Ih.

[0294] Over the length of the reaction tube (apart from the last 10 cm of the empty tube in section 1 and the last 3 cm of the tube in section 6), a stirred and externally electrically heated salt bath (mixture of 53% by weight of potassium nitrate, 40% by weight of sodium nitrite and 7% by weight of sodium nitrate; 50 kg of salt melt) flowed around the reaction tube (the flow rate at the tube was 3 m/s). The salt bath temperature TB (with which the salt bath was supplied) was set in all cases so as to result in an acrolein conversion of 99.3 mol % based on a single pass of the reaction gas mixture through the fixed catalyst bed. Along the reaction tube, there was no change in the salt bath temperature owing to additional heating (the salt bath emitted more heat than was released by the reaction tube to the salt bath).

[0295] The selectivity of acrylic acid formation (S.sup.AA (mol %)) in this document is understood to mean:

[00001]$S^{AA}=\frac{\mathrm{number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{acrolein}\mathrm{converted}\mathrm{to}}{\mathrm{number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{acrolein}\mathrm{converted}\mathrm{over}-}\times 100.$

[0296] The selectivity of CO.sub.x formation (total combustion) is calculated analogously.

[0297] An active composition (catalyst) leading to the same conversion at lower temperature under otherwise unchanged reaction conditions has a higher activity.

[0298] The conversion of acrolein (C.sup.AC (mol %)) in this document is understood to mean:

[00002]$C^{AC}=\frac{\mathrm{number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{acrolein}\mathrm{con}-}{\mathrm{number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{acrolein}\mathrm{used}}\times 100\mathrm{mol}\%.$

[0299] Table 1 below shows the results obtained as a function of the eggshell catalyst used after 100 hours of operation.

Example 2 (Comparative Example)

[0300] Annular eggshell catalyst C2 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n

[0301] The procedure was as in example 1. The annular eggshell catalyst C2 had an oxidic active composition content of 15.8% by weight. The BET surface area of the catalytically active multielement oxide was 14.8 m.sup.2/g.

Example 3 (Comparative Example)

[0302] Annular eggshell catalyst C3 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.2.4O.sub.n

[0303] The procedure was as in example 1. 205.0 g of copper(II) acetate monohydrate was used rather than 102.5 g of copper(II) acetate monohydrate, and the annular eggshell catalyst C3 had an oxidic active composition content of 20.0% by weight. The BET surface area of the catalytically active multielement oxide was 13.5 m2/g.

Example 4 (Comparative Example)

[0304] Annular eggshell catalyst C4 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2Sb.sub.0.5O.sub.n

[0305] The procedure was as in example 1. To the second solution was additionally added 56.5 g of antimony acetate (Sb content=46.3% by weight), and the annular eggshell catalyst C4, however, had an oxidic active composition content of 20.7% by weight. The BET surface area of the catalytically active multielement oxide was 14.0 m.sup.2/g. The ratio R was 1.60.

Example 5 (Comparative Example)

[0306] Annular eggshell catalyst C5 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n

[0307] The procedure was as in example 1. No aqueous NH.sub.3 solution was added, and the annular eggshell catalyst C5 had an oxidic active composition content of 20.7% by weight. The BET surface area of the catalytically active multielement oxide was 19.3 m.sup.2/g. The ratio R was 1.75.

Example 6 (Comparative Example)

[0308] Annular eggshell catalyst C6 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n

[0309] The procedure was as in example 1. For preparation of the second solution, ammonium paratungstate heptahydrate was added first, then ammonium heptamolybdate tetrahydrate, and subsequently ammonium metavanadate. No aqueous NH.sub.3 solution was added, and the annular eggshell catalyst C6 had an oxidic active composition content of 21.0% by weight. The BET surface area of the catalytically active multielement oxide was 19.6 m.sup.2/g. The ratio R was 1.49.

Example 7

[0310] Annular eggshell catalyst WE1 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n

[0311] The procedure was as in example 1. For preparation of the second solution, ammonium paratungstate heptahydrate was added first and the mixture was stirred for 5 minutes, then ammonium heptamolybdate tetrahydrate was added and the mixture was stirred for a further 10 minutes, and subsequently ammonium metavanadate was added and the mixture was stirred for a further 5 minutes. In addition, the first solution was prepared using 1017 g rather than 3180 g of water, and the second solution was prepared using 2261 g rather than 7066 g of water, i.e. the concentrations of the solutions were increased by a factor of 3.2. No aqueous NH.sub.3 solution was added, and the annular eggshell catalyst WE1 had an oxidic active composition content of 20.2% by weight. The BET surface area of the catalytically active multielement oxide was 20.5 m.sup.2/g. The ratio R was 1.38.

Example 8

[0312] Annular eggshell catalyst WE2 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n

[0313] The procedure was as in example 7. No first solution was prepared. Copper(II) acetate monohydrate was added in solid form to the second solution, and the annular eggshell catalyst WE2 had an oxidic active composition content of 20.7% by weight. The BET surface area of the catalytically active multielement oxide was 19.6 m.sup.2/g.

Example 9

[0314] Annular eggshell catalyst WE3 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2Sb.sub.0.5O.sub.n

[0315] The procedure was as in example 7. Additionally added to the second solution was 56.5 g of antimony acetate (Sb content=46.3% by weight). No first solution was prepared. Copper(II) acetate monohydrate was added in solid form to the second solution, and the annular eggshell catalyst WE3 had an oxidic active composition content of 20.6% by weight. The BET surface area of the catalytically active multielement oxide was 17 m.sup.2/g. The ratio R was 1.65.

Example 10

[0316] Annular eggshell catalyst WE4 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n

[0317] The procedure was as in example 7. No first solution was prepared. Copper(II) acetate monohydrate was added in solid form to the second solution, and the annular eggshell catalyst WE4 had an oxidic active composition content of 15.0% by weight. The BET surface area of the catalytically active multielement oxide was 21.6 m.sup.2/g. The ratio R was 1.43.

Example 11 (Comparative Example)

[0318] Annular eggshell catalyst C7 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.0.0O.sub.n

[0319] The procedure was as in example 10. No copper(II)acetate monohydrate was used, and the annular eggshell catalyst C7 had an oxidic active composition content of 15.3% by weight. The BET surface area of the catalytically active multielement oxide was 23 m.sup.2/g. The ratio R was 1.01.

Example 12

[0320] Annular eggshell catalyst WE5 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.0.2O.sub.n

[0321] The procedure was as in example 10. However, 17.1 g of copper(II) acetate monohydrate was used rather than 102.5 g of copper(II) acetate monohydrate, and the annular eggshell catalyst WE5 had an oxidic active composition content of 15.8% by weight. The BET surface area of the catalytically active multielement oxide was 26 m.sup.2/g.

Example 13

[0322] Annular eggshell catalyst WE6 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.0.4O.sub.n

[0323] The procedure was as in example 10. However, 34.2 g of copper(II) acetate monohydrate was used rather than 102.5 g of copper(II) acetate monohydrate, and the annular eggshell catalyst WE6 had an oxidic active composition content of 15.5% by weight. The BET surface area of the catalytically active multielement oxide was 23.8 m.sup.2/g.

Example 14

[0324] Annular eggshell catalyst WE7 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.0.8O.sub.n

[0325] The procedure was as in example 10. However, 68.3 g of copper(II) acetate monohydrate was used rather than 102.5 g of copper(II) acetate monohydrate, and the annular eggshell catalyst WE7 had an oxidic active composition content of 15.1% by weight. The BET surface area of the catalytically active multielement oxide was 20.1 m.sup.2/g. The ratio R was 1.26.

Example 15

[0326] Annular eggshell catalyst WE8 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.0O.sub.n

[0327] The procedure was as in example 10. However, 85.4 g of copper(II) acetate monohydrate was used rather than 102.5 g of copper(II) acetate monohydrate, and the annular eggshell catalyst WE8 had an oxidic active composition content of 15.1% by weight. The BET surface area of the catalytically active multielement oxide was 25.9 m.sup.2/g. The ratio R was 1.35.

Example 16

[0328] Annular eggshell catalyst WE9 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.1O.sub.n

[0329] The procedure was as in example 10. However, 94.0 g of copper(II) acetate monohydrate was used rather than 102.5 g of copper(II) acetate monohydrate, and the annular eggshell catalyst WE9 had an oxidic active composition content of 15.3% by weight. The BET surface area of the catalytically active multielement oxide was 21.4 m.sup.2/g. The ratio R was 1.37.

Example 17 (Comparative Example)

[0330] Annular eggshell catalyst C8 with the catalytically active oxide composition Mo.sub.12W.sub.12V.sub.3Cu.sub.2.4O.sub.n

[0331] The procedure was as in example 8. However, 205.0 g of copper(II) acetate monohydrate was used rather than 102.5 g of copper(II) acetate monohydrate, and the annular eggshell catalyst C8 had an oxidic active composition content of 20.0% by weight. The BET surface area of the catalytically active multielement oxide was 12.5 m.sup.2/g. The ratio R was 1.85.

Example 18 (Comparative Example)

[0332] Annular eggshell catalyst C9 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n

[0333] The procedure was as in example 1. The second solution was produced using 2261 g rather than 7066 g of water, i.e. the concentrations of the solutions were increased by a factor of 3.2. None of the salts went completely into solution. The annular eggshell catalyst C9 had an oxidic active composition content of 21.0% by weight. The BET surface area of the catalytically active multielement oxide was 14.8 m.sup.2/g.

Example 19

[0334] Annular eggshell catalyst WE10 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.4O.sub.n

[0335] The procedure was as in example 8. However, 119.6 g of copper(II) acetate monohydrate was used rather than 102.5 g of copper(II) acetate monohydrate, and the annular eggshell catalyst WE10 had an oxidic active composition content of 20.8% by weight. The BET surface area of the catalytically active multielement oxide was 22.8 m2/g.

Example 20

[0336] Annular eggshell catalyst WE11 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.8O.sub.n

[0337] The procedure was as in example 8. However, 153.7 g of copper(II) acetate monohydrate was used rather than 102.5 g of copper(II) acetate monohydrate, and the annular eggshell catalyst WE11 had an oxidic active composition content of 21.5% by weight. The BET surface area of the catalytically active multielement oxide was 17.7 m.sup.2/g.

Example 21 (Comparative Example)

[0338] Annular eggshell catalyst C10 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.2.0O.sub.n

[0339] The procedure was as in example 8. However, 171.0 g of copper(II) acetate monohydrate was used rather than 102.5 g of copper(II) acetate monohydrate, and the annular eggshell catalyst C10 had an oxidic active composition content of 21.2% by weight. The BET surface area of the catalytically active multielement oxide was 12.0 m.sup.2/g.

Example 22 (Comparative Example)

[0340] Annular eggshell catalyst BV1 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n

[0341] A first solution was prepared in a stainless steel vessel having a volume of 920 I and a paddle stirrer. 12.1 kg of copper(II) acetate monohydrate (Cu content=32% by weight) was dissolved in 398 kg of water while stirring at about 25° C. The mixture was stirred for a further hour.

[0342] A second solution was prepared in a stainless steel vessel having a volume of 3200 I and a propeller stirrer. To an initial charge of 921 kg of water at 40° C. was added, while stirring, 108.8 kg of ammonium heptamolybdate tetrahydrate (Mo content=55% by weight). The mixture was stirred for 30 minutes while heating to 90° C. Maintaining the temperature, 18.2 kg of ammonium metavanadate (V content=42% by weight) was added to the mixture, which was stirred for a further 40 minutes. Subsequently, 16.1 kg of ammonium paratungstate heptahydrate (W content=72% by weight) was added and the mixture was stirred for a further 30 minutes. An orange solution was obtained. The resultant solution was cooled down to 80° C. The ratio R was 0.59.

[0343] Next, the first solution was added to the second solution and the mixture was stirred while maintaining the temperature of 80° C. for 15 minutes. To the resultant solution was added 176 kg of a 25% by weight aqueous NH.sub.3 solution, the temperature of which was 25° C. A clear solution having a temperature of about 70° C. and a pH of 8.5 was obtained.

[0344] The resultant solution was transferred to a stainless steel vessel having a capacity of 8000 I and a crossbeam stirrer. The solution was heated to 80° C. and finally introduced into an F 15 spray tower (GEA Niro, Soeborg, Denmark) by means of a rotary atomizer at 16 000 rpm. The drying was conducted in a hot air stream at an inlet temperature of 375° C. and an exit temperature of 92° C. The resultant spray powder had the particle size distribution shown in FIG. 1.

[0345] The subsequent procedure was as in example 1.

[0346] The annular eggshell catalyst BV1 had an oxidic active composition content of 20.1% by weight. The BET surface area of the catalytically active multielement oxide was 15.9 m.sup.2/g.

Example 23

[0347] Annular eggshell catalyst BV2 with the catalytically active oxide composition Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n

[0348] To an initial charge of 1319 kg of water in a stainless steel vessel having a capacity of 3200 I and a propeller stirrer was added 76 kg of ammonium paratungstate heptahydrate (W content=72% by weight) at 90 to 95° C. while stirring. After 20 minutes, while maintaining the temperature, 513.4 kg of ammonium heptamolybdate tetrahydrate (Mo content=55% by weight) was added to the mixture, which was stirred for a further 10 minutes. Thereafter, 85.9 kg of ammonium metavanadate (V content=42% by weight) was added and the mixture was stirred for a further 10 minutes. An orange solution was obtained. Subsequently, 57.1 kg of copper(II) acetate monohydrate (Cu content=32% by weight) was added and the mixture was stirred for a further 15 minutes. The resultant spray powder had the particle size distribution shown in FIG. 2.

[0349] The subsequent procedure was as in example 22.

[0350] The annular eggshell catalyst BV2 had an oxidic active composition content of 20.7% by weight. The BET surface area of the catalytically active multielement oxide was 23.2 m2/g.

TABLE-US-00001 TABLE 1 Experimental results AC c.sub.W c.sub.Mo TB S.sup.COx Ex. Catalyst [% by wt.] [% by wt.] [% by wt.] [° C.] [mol %]    1*)**) Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n 20.7 0.73 3.79 259 2.8    2*)**) Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n 15.8 0.73 3.79 262 2.67    3*)**) Mo.sub.12W.sub.1.2V.sub.3Cu.sub.2.4O.sub.n 20.0 0.72 3.76 259 3.3    4*)**) Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2Sb.sub.0.5O.sub.n 20.7 0.72 3.77 251 2.77    5*)**) Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n 20.7 0.82 4.29 246 3.28   6*) Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n 21.0 0.82 4.29 245 3.24  7 Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n 20.2 2.08 10.84 246 2.66  8 Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n 20.7 2.68 13.94 246 2.61  9 Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2Sb.sub.0.5O.sub.n 20.6 2.63 13.72 246 2.66 10 Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n 15.0 2.68 13.94 253 2.64   11*) Mo.sub.12W.sub.1.2V.sub.3Cu.sub.0.0O.sub.n 15.3 2.76 14.35 259 5.74 12 Mo.sub.12W.sub.1.2V.sub.3Cu.sub.0.2O.sub.n 15.8 2.74 14.28 250 3.63 13 Mo.sub.12W.sub.1.2V.sub.3Cu.sub.0.4O.sub.n 15.5 2.73 14.21 245 4.12 14 Mo.sub.12W.sub.1.2V.sub.3Cu.sub.0.8O.sub.n 15.1 2.70 14.07 246 2.85 15 Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.0O.sub.n 15.1 2.69 14.01 246 2.87 16 Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.1O.sub.n 15.3 2.68 13.97 253 2.65   17*) Mo.sub.12W.sub.1.2V.sub.3Cu.sub.2.4O.sub.n 20.0 2.60 13.55 262 3.3   18*)**) Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n 21.0 2.68 13.94 254 2.95 19 Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.4O.sub.n 20.8 2.66 13.87 244 3.17 20 Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.8O.sub.n 21.5 2.64 13.74 246 3.12   21*) Mo.sub.12W.sub.1.2V.sub.3Cu.sub.2.0O.sub.n 21.2 2.63 13.67 254 3.1   22*)**) Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n 20.1 0.70 3.63 259 2.65 23 Mo.sub.12W.sub.1.2V.sub.3Cu.sub.1.2O.sub.n 20.7 2.73 14.07 246 2.8 *)noninventive **)metering sequence noninventive c.sub.W concentration of element W in the solution c.sub.Mo concentration of element Mo in the solution AC active composition TB salt bath temperature (acrolein conversion of 99.3 mol %) S.sup.COx CO.sub.x selectivity (total combustion)