METHOD FOR PRODUCING A CORE-SHELL CATALYST

Abstract

A process for producing an eggshell catalyst, comprising the coating of the outer surface of a geometric shaped support body with a catalytically active multielement oxide or a powder P, wherein the powder P, after being coated, is converted by thermal treatment to a catalytically active multielement oxide, and one or more liquid binders, wherein the coating is conducted in a horizontal mixer and the Froude number during the coating in the horizontal mixer is from 0.0160 to 0.1200.

Claims

1.-15. (canceled)

16. A process for producing an eggshell catalyst, comprising the coating of the outer surface of a geometric shaped support body with a) one or more catalytically active multielement oxides and one or more liquid binders, wherein the binder is removed later, or b) one or more powders P and one or more liquid binders, wherein the powder P, after the coating, is converted by thermal treatment to one or more catalytically active multielement oxides, wherein the coating is conducted in a horizontal mixer and the Froude number during the coating in the horizontal mixer is from 0.0040 to 0.1200.

17. The process according to claim 16, wherein the Froude number during the coating in the horizontal mixer is from 0.0160 to 0.0600.

18. The process according to claim 16, wherein the diameter of the mixing drum on the horizontal mixer is from 0.5 to 2.5 m.

19. The process according to claim 16, wherein the length of the mixing drum of the horizontal mixer is from 0.25 to 1.5 m.

20. The process according to claim 16, wherein hollow cylindrical geometric shaped support bodies having a length of 3 to 8 mm, an external diameter of 4 to 8 mm and a wall thickness of 1 to 2 mm are used as geometric shaped support bodies.

21. The process according to claim 16, wherein the eggshell catalyst, based on the overall composition, has an active composition content of 5% to 50% by weight.

22. The process according to claim 16, wherein from 0.05 to 0.5 kg/kg of the liquid binder is used in the coating, based on the active composition.

23. The process according to claim 16, wherein the duration of coating is from 0.5 to 10 minutes per % by weight of active composition content.

24. The process according to claim 16, wherein the catalytically active multielement oxide or the powder P comprises the elements Mo, V and optionally W or the elements Mo, Bi and optionally Fe.

25. The process according to claim 16, wherein the catalytically active multielement oxide or the powder P comprises the elements Mo, W, V, Cu and optionally Sb, where 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 2.4 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 %.

26. An eggshell catalyst consisting of a geometric shaped support body and one or more catalytically active multielement oxides applied to the outer surface of the geometric shaped support body, obtainable by a process of claim 16, wherein the pore volume and the active composition content meet the following condition:
PV/AM.sup.0.55>0.140, where PV is the pore volume in ml/g and AM is the active composition content in % by weight and the pore volume is determined after the removal of the binder, and the abrasion level is less than 5.5% by weight and the abraded material is determined before the removal of the binder.

27. The eggshell catalyst according to claim 26, wherein the pore volume and active composition content meet the following condition:
PV/AM.sup.0.55>0.155, where PV is the pore volume in ml/g and AM is the active composition content in % by weight, and the abrasion level is less than 2.5% by weight.

28. The eggshell catalyst according to claim 26, wherein hollow cylindrical geometric shaped support bodies having a length of 3 to 8 mm, an external diameter of 4 to 8 mm and a wall thickness of 1 to 2 mm were used.

29. The eggshell catalyst according to claim 25, wherein the eggshell catalyst, based on the overall composition, has an active composition content of 5% to 50% by weight.

30. A process for heterogeneously catalyzed partial gas phase oxidation over a fixed catalyst bed, wherein the fixed catalyst bed comprises an eggshell catalyst according to claim 26.

Description

[0139] FIG. 1 shows an illustrative particle size distribution of the powder P.

[0140] FIG. 2 shows a particle size distribution of finely divided MoO.sub.3.

[0141] The measurements were conducted as described in WO 2011/134932 A1. In each case, the cumulative proportion of the particles in % by volume was plotted against particle size in ?m. The measurements were effected at two different blowing gas pressures (triangle: p=0.2 bar; square: p=1.0 bar).

[0142] FIG. 3 shows an x-ray image of the eggshell catalyst with an active composition content of 25% by weight from example 7 (noninventive).

[0143] FIG. 4 shows an x-ray image of the eggshell catalyst with an active composition content of 25% by weight from example 8 (inventive).

[0144] FIG. 5 shows an x-ray image of the eggshell catalyst with an active composition content of 20% by weight from example 9 (noninventive).

[0145] FIG. 6 shows an x-ray image of the eggshell catalyst with an active composition content of 20% by weight from example 10 (inventive).

[0146] FIG. 7 shows an x-ray image of the eggshell catalyst with an active composition content of 15% by weight from example 11 (noninventive).

[0147] FIG. 8 shows an x-ray image of the eggshell catalyst with an active composition content of 15% by weight from example 12 (inventive).

[0148] Comparison of the x-ray images shows much thicker layers of active composition with the same active composition content, as a result of the more porous structure of the eggshell catalysts of the invention.

[0149] Thus, the present invention encompasses especially the following embodiments of the invention: [0150] 1. A process for producing an eggshell catalyst, comprising the coating of an outer surface of a geometric shaped support body with [0151] a) one or more catalytically active multielement oxides and one or more liquid binders, wherein the binder(s) is/are removed later, or [0152] b) one or more powders P and one or more liquid binders, wherein the powder(s) P, after the coating, is/are converted by thermal treatment to one or more catalytic reactive multielement oxides, [0153] wherein the coating is conducted in a horizontal mixer and the Froude number during the coating in the horizontal mixer is from 0.0040 to 0.1200. [0154] 2. The process according to embodiment 1, wherein the Froude number during the coating in the horizontal mixer is from 0.0080 to 0.1000. [0155] 3. The process according to embodiment 1 or 2, wherein the Froude number during the coating in the horizontal mixer is from 0.0120 to 0.0800. [0156] 4. The process according to any of embodiments 1 to 3, wherein the Froude number during the coating in the horizontal mixer is from 0.0160 to 0.0600. [0157] 5. The process according to any of embodiments 1 to 4, wherein the diameter of the mixing drum of the horizontal mixer is from 0.5 to 2.5 m. [0158] 6. The process according to any of embodiments 1 to 5, wherein the length of the mixing drum of the horizontal mixer is from 0.25 to 1.5 m. [0159] 7. The process according to any of embodiments 1 to 6, wherein hollow cylindrical geometric shaped support bodies having a length of 3 to 8 mm, an external diameter of 4 to 8 mm and a wall thickness of 1 to 2 mm are used as geometric shaped support bodies. [0160] 8. The process according to any of embodiments 1 to 7, wherein the eggshell catalyst, based on the overall composition, has an active composition content of 5% to 50% by weight. [0161] 9. The process according to any of embodiments 1 to 8, wherein from 0.05 to 0.5 kg/kg of the liquid binder is used in the coating, based on the active composition. [0162] 10. The process according to any of embodiments 1 to 9, wherein from 0.10 to 0.4 kg/kg of the liquid binder is used in the coating, based on the active composition. [0163] 11. The process according to any of embodiments 1 to 10, wherein from 0.15 to 0.3 kg/kg of the liquid binder is used in the coating, based on the active composition. [0164] 12. The process according to any of embodiments 1 to 11, wherein the liquid binder is water, an organic solvent, a solution of an organic substance in water, a solution of an organic substance in an organic solvent and/or a solution of an organic substance in an aqueous solution of an organic solvent. [0165] 13. The process according to any of embodiments 1 to 12, wherein the liquid binder is a solution consisting of 20 to 90% by weight of water and 10 to 80% by weight of an organic compound. [0166] 14. The process according to any of embodiments 1 to 13, wherein the liquid binder consists of 20 to 90% by weight of water and 10 to 80% by weight of glycerol. [0167] 15. The process according to any of embodiments 1 to 14, wherein the liquid binder consists of 50 to 90% by weight of water and 10 to 50% by weight of glycerol. [0168] 16. The process according to any of embodiments 1 to 15, wherein the liquid binder consists of 70 to 80% by weight of water and 20 to 30% by weight of glycerol. [0169] 17. The process according to any of embodiments 1 to 16, wherein the duration of coating is from 0.5 to 10 minutes per % by weight of active composition content. [0170] 18. The process according to any of embodiments 1 to 17, wherein the duration of coating is from 1.0 to 7 minutes per % by weight of active composition content. [0171] 19. The process according to any of embodiments 1 to 18, wherein the duration of coating is from 1.5 to 4 minutes per % by weight of active composition content. [0172] 20. The process according to any of embodiments 1 to 19, wherein the catalytically active multielement oxide or the powder P comprises the elements Mo, V and optionally W or the elements Mo, Bi and optionally Fe. [0173] 21. The process according to any of embodiments 1 to 20, wherein the catalytically active multielement oxide comprises the elements Mo, W, V, Cu and optionally Sb, where 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 3.0 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 %. [0180] 22. The process according to embodiment 21, wherein the stoichiometric coefficient a of the element W in the general formula (I) is from 0.6 to 3.5. [0181] 23. The process according to embodiment 21 or 22, wherein the stoichiometric coefficient a of the element W in the general formula (I) is from 0.8 to 2.5. [0182] 24. The process according to any of embodiments 21 to 23, wherein the stoichiometric coefficient a of the element W in the general formula (I) is from 1.0 to 2.0. [0183] 25. The process according to any of embodiments 21 to 24, wherein the stoichiometric coefficient b of the element V in the general formula (I) is from 1.5 to 5.5. [0184] 26. The process according to any of embodiments 21 to 25, wherein the stoichiometric coefficient b of the element V in the general formula (I) is from 2.0 to 5.0. [0185] 27. The process according to any of embodiments 21 to 26, wherein the stoichiometric coefficient b of the element V in the general formula (I) is from 2.5 to 4.5. [0186] 28. The process according to any of embodiments 21 to 27, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is from 0.4 to 2.8. [0187] 29. The process according to any of embodiments 21 to 28, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is from 0.6 to 2.6. [0188] 30. The process according to any of embodiments 21 to 29, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is from 0.8 to 2.4. [0189] 31. The process according to any of embodiments 21 to 30, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is from 0.1 to 1.6. [0190] 32. The process according to any of embodiments 21 to 31, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is from 0.2 to 1.2. [0191] 33. The process according to any of embodiments 21 to 32, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is from 0.3 to 0.8. [0192] 34. The process according to any of embodiments 21 to 33, wherein the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 10 to 90 mol %. [0193] 35. The process according to any of embodiments 21 to 34, wherein the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 15 to 85 mol %. [0194] 36. The process according to any of embodiments 21 to 35, wherein the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 20 to 80 mol %. [0195] 37. An eggshell catalyst consisting of a geometric shaped support body and one or more catalytically active multielement oxides applied to the outer surface of the geometric shaped support body, obtainable by a process of embodiments 1 to 36, wherein the pore volume and the active composition content meet the following condition:

PV/AM.sup.0.55>0.140, [0196] where PV is the pore volume in ml/g and AM is the active composition content in % by weight and the pore volume is determined after the removal of the binder, and the abrasion level is less than 5.5% by weight and the abraded material is determined before the removal of the binder. [0197] 38. The eggshell catalyst according to embodiment 37, wherein the pore volume and active composition content meet the following condition:

PV/AM.sup.0.55>0.145, [0198] where PV is the pore volume in ml/g and AM is the active composition content in % by weight. [0199] 39. The eggshell catalyst according to claim 37 or 38, wherein the pore volume and active composition content satisfy the following condition:

PV/AM.sup.0.55>0.150, [0200] where PV is the pore volume in ml/g and AM is the active composition content in % by weight. [0201] 40. The eggshell catalyst according to any of embodiments 37 to 39, wherein the pore volume and active composition content meet the following condition:

PV/AM.sup.0.55>0.145, [0202] where PV is the pore volume in ml/g and AM is the active composition content in % by weight. [0203] 41. The eggshell catalyst according to any of embodiments 37 to 40, wherein the abrasion level is less than 4.5% by weight. [0204] 42. The eggshell catalyst according to any of embodiments 37 to 41, wherein the abrasion level is less than 3.5% by weight. [0205] 43. The eggshell catalyst according to any of embodiments 37 to 42, wherein the abrasion 50 level is less than 2.5% by weight. [0206] 44. The eggshell catalyst according to any of embodiments 37 to 43, wherein hollow cylindrical geometric shaped support bodies having a length of 3 to 8 mm, an external diameter of 4 to 8 mm and a wall thickness of 1 to 2 mm were used. [0207] 45. The eggshell catalyst according to any of embodiments 37 to 44, wherein the eggshell catalyst, based on the overall composition, has an active composition content of 5% to 50% by weight. [0208] 46. The eggshell catalyst according to any of embodiments 37 to 45, wherein the catalytically active multielement oxide or the powder P comprises the elements Mo, V and optionally W or the elements Mo, Bi and optionally Fe. [0209] 47. The eggshell catalyst according to any of embodiments 37 to 46, wherein the catalytically active multielement oxide comprises the elements Mo, W, V, Cu and optionally Sb, where the ratio of the elements conforms to the general formula (I)

Mo.sub.12W.sub.aV.sub.bCu.sub.cSb.sub.d(I) [0210] where [0211] a=0.4 to 5.0, [0212] b=1.0 to 6.0, [0213] c=0.2 to 3.0 and [0214] d=0.0 to 2.0, [0215] and the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 5 to 95 mol %. [0216] 48. The eggshell catalyst according to embodiment 47, wherein the stoichiometric coefficient a of the element Win the general formula (I) is from 0.6 to 3.5. [0217] 49. The eggshell catalyst according to embodiment 47 or 48, wherein the stoichiometric coefficient a of the element Win the general formula (I) is from 0.8 to 2.5. [0218] 50. The eggshell catalyst according to any of embodiments 47 to 49, wherein the stoichiometric coefficient a of the element W in the general formula (I) is from 1.0 to 2.0. [0219] 51. The eggshell catalyst according to any of embodiments 47 to 50, wherein the stoichiometric coefficient b of the element V in the general formula (I) is from 1.5 to 5.5. [0220] 52. The eggshell catalyst according to any of embodiments 47 to 51, wherein the stoichiometric coefficient b of the element V in the general formula (I) is from 2.0 to 5.0. [0221] 53. The eggshell catalyst according to any of embodiments 47 to 52, wherein the stoichiometric coefficient b of the element V in the general formula (I) is from 2.5 to 4.5. [0222] 54. The eggshell catalyst according to any of embodiments 47 to 53, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is from 0.4 to 2.8. [0223] 55. The eggshell catalyst according to any of embodiments 47 to 54, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is from 0.6 to 2.6. [0224] 56. The eggshell catalyst according to any of embodiments 47 to 55, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is from 0.8 to 2.4. [0225] 57. The eggshell catalyst according to any of embodiments 47 to 56, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is from 0.1 to 1.6. [0226] 58. The eggshell catalyst according to any of embodiments 47 to 57, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is from 0.2 to 1.2. [0227] 59. The eggshell catalyst according to any of embodiments 47 to 58, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is from 0.3 to 0.8. [0228] 60. The eggshell catalyst according to any of embodiments 47 to 59, wherein the catalytically active multielement oxide additionally 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. [0229] 61. The eggshell catalyst according to any of embodiments 47 to 60, wherein the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 10 to 90 mol %. [0230] 62. The eggshell catalyst according to any of embodiments 47 to 61, wherein the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 15 to 85 mol %. [0231] 63. The eggshell catalyst according to any of embodiments 47 to 62, wherein the molar proportion of the element Mo in the total amount of all non-oxygen elements is from 20 to 80 mol %. [0232] 64. The eggshell catalyst according to any of embodiments 47 to 63, wherein the specific BET surface area of the catalytically active multielement oxides is from 10 to 35 m.sup.2/g. [0233] 65. The eggshell catalyst according to any of embodiments 47 to 64, wherein the specific BET surface area of the catalytically active multielement oxides is from 13 to 32 m.sup.2/g. [0234] 66. The eggshell catalyst according to any of embodiments 47 to 65, wherein the specific BET surface area of the catalytically active multielement oxides is from 16 to 29 m.sup.2/g. [0235] 67. The eggshell catalyst according to any of embodiments 47 to 66, wherein the specific BET surface area of the catalytically active multielement oxides is from 19 to 26 m.sup.2/g. [0236] 68. A process for heterogeneously catalyzed partial gas phase oxidation over a fixed catalyst bed, wherein the fixed catalyst bed comprises an eggshell catalyst according to any of embodiments 47 to 67. [0237] 69. A process for heterogeneously catalyzed partial gas phase oxidation of acrolein to acrylic acid over a fixed catalyst bed, wherein the fixed catalyst bed comprises an eggshell catalyst according to any of embodiments 47 to 67. [0238] 70. The use of an eggshell catalyst according to any of embodiments 47 to 67 as catalysts for heterogeneously catalyzed partial gas phase oxidation. [0239] 71. The use of an eggshell catalyst according to any of embodiments 47 to 67 as catalysts for the heterogeneously catalyzed partial gas phase oxidation of acrolein to acrylic acid.

EXAMPLES

Example 1 (Comparative Example)

[0240] Annular Eggshell Catalyst C1 with the Catalytically Active Oxide Composition Mo.sub.12V.sub.3W.sub.1.2Cu.sub.2.4O.sub.x and MoO.sub.3

[0241] Production of the Eggshell Catalyst:

[0242] A first solution was produced in a 1.75 m.sup.3 jacketed stainless steel vessel with a beam stirrer. For this purpose, an initial charge of 274 l of water at 25? C. was stirred at 70 rpm. At a metering rate of 50 kg/h, 16.4 kg of copper(II) acetate hydrate (content: 32.0% by weight of Cu) was added. The first solution was stirred for a further 30 minutes.

[0243] Spatially separately therefrom, a second solution was produced in a 1.75 m.sup.3 jacketed stainless steel vessel with a beam stirrer. An initial charge of 614 l of water was heated to 40? C. at 70 rpm. At a metering rate of 300 kg/h, 73 kg of ammonium heptamolybdate tetrahydrate (81.5% by weight of MoO.sub.3) was stirred in at 40? C. Then the contents were heated to 90? C. within 30 min. Ata metering rate of 150 kg/h, 12.1 kg of ammonium metavanadate (77.6% by weight of V.sub.2O.sub.5) was stirred in at 90? C. The contents were stirred for a further 40 minutes. Subsequently, at a metering rate of 50 kg/h, 10.7 kg of ammonium paratungstate heptahydrate (89.6% by weight of WO.sub.3) was stirred in at 90? C. The contents were stirred for a further 30 minutes.

[0244] The second solution was cooled down to 80? C., and then the first solution was stirred into the second solution. 133 l of a 25% by weight aqueous NH.sub.3 solution at a temperature of 25? C. was added to the resultant mixture. Stirring gave rise to a clear solution, which briefly had a temperature of 65? C. and a pH of 8.5. The contents of the stainless steel vessel were transferred to a further 1.75 m.sup.3 jacketed stainless steel vessel with a beam stirrer. The contents were stirred at 40 rpm and heated to 80? C. The pH was kept at 8.5 by automatic metered addition of a 25% by weight aqueous NH.sub.3 solution.

[0245] The resultant solution was introduced into an FS 15 spray tower (GEA Niro, Soeborg, Denmark) by means of a rotary atomizer at 15 000 rpm. The drying was conducted in a hot air stream at an inlet temperature of 350? C.?5? C. The pressure in the spray tower was 1 mbar, and the gas volume flow rate of combustion air was 2300 m.sup.3 (STP)/h. The solution was metered in such that the exit temperature was 110?5? C. The particle size distribution of the resultant spray powder is shown in FIG. 3 of DE 10 2007 010 422 A1.

[0246] 75 kg of the resultant spray powder was metered into a VM 160 kneader with sigma paddles (Aachener Misch- and Knetmaschinen Fabrik Peter K?pper GmbH & Co. KG, W?rselen, Germany) and kneaded with addition of 6.5 l of acetic acid (about 100% strength by weight, glacial acetic acid) and 5.2 l of water (screw speed: 15 rpm). After a kneading time of 4 to 5 minutes, a further 6.5 l of water was added and the kneading process was continued until 30 minutes had elapsed (kneading temperature about 40 to 50? C.). During the kneading, the power consumption of the kneader was monitored. In the event of a rise in power consumption above 25%, 1 l of water was added if required.

[0247] Thereafter, the kneading material was emptied into an extruder of the G 103-35 10/07 A-572K type (6 Extruder W Packer; The Bonnot Company, Akron, USA/Ohio) and was shaped by means of the extruder to extrudates (length: 1 to 10 cm; diameter 6 mm). In a three-zone belt drier, the extrudates were dried at a belt speed of 10 cm per minute and for a dwell time of 64 minutes. The gas temperatures were 90 to 95? C. (zone 1), about 115? C. (zone 2) and about 125? C. (zone 3). The dried extrudates formed the precursor composition to be subjected to thermal treatment.

[0248] The thermal treatment was conducted in a rotary furnace apparatus according to FIG. 1 of U.S. Pat. No. 7,589,046 with the dimensions and auxiliary elements according to the illustrative embodiment in the description of that document and under the following conditions: [0249] thermal treatment was effected batchwise with an amount of material of 306 kg; [0250] the angle of inclination of the rotary tube to the horizontal was about 0?; [0251] the rotary tube rotated to the right at 1.5 rpm; [0252] throughout the thermal treatment, a gas stream of 205 m.sup.3 (STP)/h was conducted through the rotary tube, which (after displacement of the air originally present) had the following composition and was supplemented by a further 25 m.sup.3 (STP)/h of barrier gas nitrogen at its outlet from the rotary tube:

[0253] 80 m.sup.3 (STP)/h composed of baseload nitrogen (20) and gases released in the rotary tube, 25 m.sup.3 (STP)/h of barrier gas nitrogen (11), 30 m.sup.3 (STP)/h of air (splitter (21)) and 70 m.sup.3 (STP)/h of recirculated cycle gas (19).

[0254] The barrier gas nitrogen was supplied at a temperature of 25? C. The mixture of the other gas streams, coming from the heater, was guided into the rotary tube in each case at the temperature of the material within the rotary tube: [0255] within 10 hours, the material temperature was heated from 25? C. in an essentially linear manner to 300? C., then the material temperature was heated within 2 hours in an essentially linear manner to 360? C., subsequently the material temperature was lowered in an essentially linear manner to 350? C. within 7 h, then the material temperature was increased in an essentially linear manner to 420? C. within 2 hours, and this material temperature was maintained for 30 minutes; [0256] then the 30 m.sup.3 (STP)/h of air in the gas stream conducted through the rotary tube was replaced by a corresponding increase in the baseload nitrogen (which ended the actual thermal treatment operation), the heating of the rotary tube was switched off, and the material was cooled down to a temperature below 100? C. and ultimately to ambient temperature within 2 hours by switching on the rapid cooling of the rotary tube by suction of ambient air, wherein the gas stream was supplied to the rotary tube at a temperature of 25? C.; [0257] throughout the thermal treatment, the pressure (immediately) beyond the rotary tube exit of the gas stream was 0.2 mbar below the outside pressure.

[0258] The oxygen content of the atmosphere at the exit from the rotary tube furnace in all phases of the thermal treatment was 2.9% by volume.

[0259] The resultant catalytic active composition was ground by means of a biplex crossflow classifying mill of the BQ 500 type (Hosokawa-Alpine AG, Augsburg, Germany) to give a finely divided powder. 24 long blades were installed here in the grinding pathways. The mill speed was 2500 rpm. The ventilator throttle vent was fully opened. The metered addition was adjusted to 2.5 rpm. The volume flow rate of output air was 1300 m.sup.3/h, the pressure differential 10 to 20 mbar. The particle size distribution of the above ground catalytic active composition is shown by FIG. 1 (the measurement was conducted analogously to the example of U.S. Pat. No. 9,238,217).

[0260] The ground catalytic active composition, analogously to example 2 of U.S. Pat. No. 8,318,631, was admixed with 15% by weight of finely divided MoO.sub.3 (Molybdenum Trioxide I, Mo content 66.6% by weight, BET surface area 1 m.sup.2/g; H. C. Starck GmbH, Goslar, Germany), based on the catalytic active composition. The particle size distribution of the finely divided MoO.sub.3 is shown in FIG. 2. Finally, the mixture was mixed homogeneously in a GT 550 multimixer (Rotor Lips AG, Uetendorf, Switzerland) at setting 8 over a period of 1 minute. The resulting finely divided mixture was used to produce an annular eggshell catalyst.

[0261] For the coating operation, 70 kg of annular shaped support bodies (external diameter 7 mm, length 3 mm, internal diameter 4 mm, surface roughness IR, 45 ?m, total pore volume about 1% by volume based on the volume of the support body; cf. DE 21 35 620 A1) of the C220 steatite type (CeramTec GmbH, Plochingen, Germany) was introduced into a horizontal mixer of the Hi-Coater type (Gebr?der L?dige Maschinenbau GmbH, Paderborn, Germany) with a drum diameter of 1000 mm and capacity about 600 l. Subsequently, the horizontal mixer was set in rotation at 16 rpm.

[0262] A nozzle of the 0.5 mm/90? type (D?sen-Schlick GmbH, Coburg, Germany) was used to spray 4.0 liters of a solution of 75% by weight of water and 25% by weight of glycerol onto the support bodies at a liquid supply pressure of about 1.8 bar within 40 minutes. Simultaneously, within the same period of time, 18.2 kg of the finely divided mixture having a specific surface area of 14 m.sup.2/g was metered in continuously outside the spray cone of the atomizer nozzle by means of an agitated channel. During the coating, the finely divided mixture supplied was taken up completely onto the surface of the support body; no agglomeration of the finely divided mixture or formation of twinned catalyst bodies was observed. After the addition of finely divided mixture and solution had ended, air at 110? C. (about 400 m.sup.3/h) was blown into the horizontal mixer at a speed of rotation of 2 rpm. A sample of about 2 kg of coated support bodies was taken. The glycerol still present in the sample was removed in a UM 400 air circulation drying cabinet (capacity 53 l, air flow rate 800 l/h; Memmert GmbH & Co. KG, Schwabach, Germany). The heat treatment conditions were identical to those of example C1 of U.S. Pat. No. 9,238,217. The annular eggshell catalysts C1 taken from the air circulation drying cabinet, based on the total mass thereof, had an active composition content of 22.0% by weight, a pore volume of 0.046 ml/g (measured by a mercury porosimeter) and an abrasion level of 0.10% by weight.

[0263] Testing of the Eggshell Catalysts:

[0264] 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: [0265] Section 1: length 80 cm [0266] empty tube; [0267] Section 2: length 60 cm [0268] preliminary bed of steatite rings of geometry 7 mm?7 mm?4 mm (external diameter?length?internal diameter; C 220 steatite); [0269] Section 3: length 100 cm [0270] 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) and 80% by weight of the eggshell catalyst; [0271] Section 4: length 200 cm [0272] fixed catalyst bed consisting exclusively of the eggshell catalyst as in section 3; [0273] Section 5: length 10 cm [0274] downstream bed of the same steatite rings as in section 2; [0275] Section 6: length 11.5 cm [0276] Catalyst base made of stainless steel (material 1.4541) for accommodation of the fixed catalyst bed.

[0277] 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:

TABLE-US-00001 4.3% by vol. of acrolein, 0.3% by vol. of propene, 0.2% by vol. of propane, 0.3% by vol. of acrylic acid, 5.1% by vol. of oxygen, 0.4% by vol. of carbon oxides, 7.0% by vol. of water and 82.4% by vol. of nitrogen.

[0278] 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 A1) was 100 l (STP)/h.

[0279] 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).

[0280] The selectivity of acrylic acid formation (SAS (mol %)) in this document is understood to mean:

[00002]$S^{\mathrm{AA}}=\frac{\begin{array}{c}\mathrm{number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{acrolein}\\ \mathrm{converted}\mathrm{to}\mathrm{acrylic}\mathrm{acid}\end{array}}{\mathrm{number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{acrolein}\mathrm{converted}\mathrm{overall}}?100.$

[0281] The selectivity of CO.sub.x formation (total combustion) is calculated analogously, including the stoichiometric factor of 3.

[0282] An active composition (catalyst) leading to the same conversion at lower temperature under otherwise unchanged reaction conditions has a higher activity.

[0283] The conversion of acrolein (C.sup.AC (mol %)) in this document is understood to mean:

[00003]$C^{AC}=\frac{\begin{array}{c}\mathrm{number}\mathrm{of}\mathrm{moles}\mathrm{of}\\ \mathrm{acrolein}\mathrm{converted}\mathrm{overall}\end{array}}{\begin{array}{c}\mathrm{number}\mathrm{of}\mathrm{moles}\mathrm{of}\\ \mathrm{acrolein}\mathrm{converted}\mathrm{overall}\end{array}}?100\mathrm{mol}\%.$

[0284] Table 1 below shows the results obtained as a function of the eggshell catalyst used after 100 hours of operation.

Example 2

[0285] Annular Eggshell Catalyst WE1 with the Catalytically Active Oxide Composition Mo.sub.12V.sub.3W.sub.1.2Cu.sub.2.4O.sub.x and MoO.sub.3

[0286] The procedure was as in example 1. For the coating operation, the horizontal mixer rotated at 10 rpm rather than at 16 rpm.

[0287] The annular eggshell catalysts WE1, based on the total mass thereof, had an active composition content of 22.0% by weight, a pore volume of 0.053 ml/g (measured by a mercury porosimeter) and an abrasion level of 0.17% by weight.

Example 3

[0288] Annular Eggshell Catalyst WE2 with the Catalytically Active Oxide Composition Mo.sub.12V.sub.3W.sub.1.2Cu.sub.2.4O.sub.x and MoO.sub.3

[0289] The procedure was as in example 1. For the coating operation, the horizontal mixer rotated at 7 rpm rather than at 16 rpm.

[0290] The annular eggshell catalysts WE2, based on the total mass thereof, had an active composition content of 22.0% by weight, a pore volume of 0.062 ml/g (measured by mercury porosimeter) and an abrasion level of 1.05% by weight.

Example 4

[0291] Annular Eggshell Catalyst WE3 with the Catalytically Active Oxide Composition Mo.sub.12V.sub.3W.sub.1.2Cu.sub.2.4O.sub.x and MoO.sub.3

[0292] The procedure was as in example 1. For the coating operation, the horizontal mixer rotated at 4 rpm rather than at 16 rpm.

[0293] The annular eggshell catalysts WE3, based on the total mass thereof, had an active composition content of 22.0% by weight, a pore volume of 0.065 ml/g (measured by mercury porosimeter) and an abrasion level of 4.75% by weight.

Example 5

[0294] Annular Eggshell Catalyst WE4 with the Catalytically Active Oxide Composition Mo.sub.12V.sub.3W.sub.1.2Cu.sub.2.4O.sub.x and MoO.sub.3

[0295] The procedure was as in example 1. For the coating operation, the horizontal mixer rotated at 3 rpm rather than at 16 rpm.

[0296] The annular eggshell catalysts WE4, based on the total mass thereof, had an active composition content of 22.0% by weight, a pore volume of 0.078 ml/g (measured by mercury porosimeter) and an abrasion level of 4.43% by weight.

Example 6

[0297] Annular Eggshell Catalyst WE5 with the Catalytically Active Oxide Composition Mo.sub.12V.sub.3W.sub.1.2Cu.sub.2.4O.sub.x and MoO.sub.3

[0298] The procedure was as in example 1. For the coating operation, the horizontal mixer rotated at 2 rpm rather than at 16 rpm.

[0299] The annular eggshell catalysts WE5, based on the total mass thereof, had an active composition content of 22.0% by weight, a pore volume of 0.086 ml/g (measured by mercury porosimeter) and an abrasion level of 7.37% by weight.

Example 7 (Comparative Example)

[0300] Annular Eggshell Catalyst C2 with the Catalytically Active Oxide Composition Mo.sub.12V.sub.3W.sub.1.2Cu.sub.1.2O.sub.x

[0301] Analogously to example 1, a multielement oxide composition of stoichiometry Mo.sub.12V.sub.3W.sub.1.2Cu.sub.1.2O.sub.x was produced. The amount of copper(II) acetate hydrate for production of the first solution was reduced from 16.4 kg to 8.2 kg. The particle size distribution of the resultant spray powder is shown in FIG. 2 of WO 2011/134932 A1. No MoO.sub.3 was included. The oxygen content of the atmosphere at the exit from the rotary tube furnace in all phases of the thermal treatment was less than 2.0% by volume rather than 2.9% by volume.

[0302] The hollow cylindrical support bodies used for coating had an external diameter of 6 mm, a length of 6 mm and an internal diameter of 4 mm. For coating of the support bodies, 4.5 liters of a solution of 75% by weight of water and 25% by weight of glycerol and 22.3 kg of the ground finely divided powder were metered in continuously within 50 minutes.

[0303] The annular eggshell catalysts C2, based on the total mass thereof, had an active composition content of 25.0% by weight, a pore volume of 0.061 ml/g (measured by mercury porosimeter) and an abrasion level of 0.29% by weight.

Example 8

[0304] Annular Eggshell Catalyst WE6 with the Catalytically Active Oxide Composition Mo.sub.12V.sub.3W.sub.1.2Cu.sub.1.2O.sub.x

[0305] The procedure was as in example 7. For the coating operation, the horizontal mixer rotated at 7 rpm rather than at 16 rpm.

[0306] The annular eggshell catalysts WE6, based on the total mass thereof, had an active composition content of 25.7% by weight, a pore volume of 0.078 ml/g (measured by mercury porosimeter) and an abrasion level of 2.06% by weight.

Example 9 (Comparative Example)

[0307] Annular Eggshell Catalyst C3 with the Catalytically Active Oxide Composition Mo.sub.12V.sub.3W.sub.1.2Cu.sub.1.2O.sub.x

[0308] Analogously to example 7, a multielement oxide composition of stoichiometry Mo.sub.12V.sub.3W.sub.1.2Cu.sub.1.2O.sub.x was produced.

[0309] For coating of the support bodies, 3.4 liters of a solution of 75% by weight of water and 25% by weight of glycerol and 17.5 kg of the ground finely divided powder were metered in continuously within 40 minutes.

[0310] The annular eggshell catalysts C3, based on the total mass thereof, had an oxidic eggshell content of 19.9% by weight, a pore volume of 0.051 ml/g (measured by a mercury porosimeter) and an abrasion level of 0.24% by weight.

Example 10

[0311] Annular Eggshell Catalyst WE7 with the Catalytically Active Oxide Composition Mo.sub.12V.sub.3W.sub.1.2Cu.sub.1.2O.sub.x

[0312] The procedure was as in example 9. For the coating operation, the horizontal mixer rotated at 7 rpm rather than at 16 rpm.

[0313] The annular eggshell catalysts WE7, based on the total mass thereof, had an active composition content of 20.2% by weight, a pore volume of 0.067 ml/g (measured by mercury porosimeter) and an abrasion level of 1.56% by weight.

Example 11 (Comparative Example)

[0314] Annular Eggshell Catalyst C4 with the Catalytically Active Oxide Composition Mo.sub.12V.sub.3W.sub.1.2Cu.sub.1.2O.sub.x

[0315] Analogously to example 7, a multielement oxide composition of stoichiometry Mo.sub.12V.sub.3W.sub.1.2Cu.sub.1.2O.sub.x was produced.

[0316] For coating of the support bodies, 2.4 liters of a solution of 75% by weight of water and 25% by weight of glycerol and 12.4 kg of the ground finely divided powder were metered in continuously within 30 minutes.

[0317] The annular eggshell catalysts C4, based on the total mass thereof, had an active composition content of 15.3% by weight, a pore volume of 0.046 ml/g (measured by mercury porosimeter) and an abrasion level of 0.19% by weight.

Example 12

[0318] Annular Eggshell Catalyst WE8 with the Catalytically Active Oxide Composition Mo.sub.12V.sub.3W.sub.1.2Cu.sub.1.2O.sub.x

[0319] The procedure was as in example 11. For the coating operation, the horizontal mixer rotated at 7 rpm rather than at 16 rpm.

[0320] The annular eggshell catalysts WE8, based on the total mass thereof, had an active composition content of 15.4% by weight, a pore volume of 0.054 ml/g (measured by mercury porosimeter) and an abrasion level of 1.66% by weight.

Example 13 (Comparative Example)

[0321] Annular Eggshell Catalyst C5 with the Catalytically Active Oxide Composition Mo.sub.12V.sub.3W.sub.1.2Cu.sub.1.2O.sub.x

[0322] Analogously to example 7, a multielement oxide composition of stoichiometry Mo.sub.12V.sub.3W.sub.1.2Cu.sub.1.2O.sub.x was produced.

[0323] For coating of the support bodies, 1.6 liters of a solution of 75% by weight of water and 25% by weight of glycerol and 7.8 kg of the ground finely divided powder were metered in continuously within 20 minutes.

[0324] The annular eggshell catalysts C5, based on the total mass thereof, had an active composition content of 10.4% by weight, a pore volume of 0.038 ml/g (measured by mercury porosimeter) and an abrasion level of 0.50% by weight.

Example 14

[0325] Annular Eggshell Catalyst WE9 with the Catalytically Active Oxide Composition Mo.sub.12V.sub.3W.sub.1.2Cu.sub.1.2O.sub.x

[0326] The procedure was as in example 13. For the coating operation, the horizontal mixer rotated at 7 rpm rather than at 16 rpm.

[0327] The annular eggshell catalysts WE9, based on the total mass thereof, had an active composition content of 10.2% by weight, a pore volume of 0.041 ml/g (measured by mercury porosimeter) and an abrasion level of 1.60% by weight.

TABLE-US-00002 TABLE 1 Experimental results with Mo.sub.12V.sub.3W.sub.1.2Cu.sub.2.4O.sub.x and MoO.sub.3 on support bodies (external diameter 7 mm, length 3 mm, internal diameter 4 mm) Abrasion Speed Froude TB S.sup.COx PV level Ex. Cat. [rpm] number [? C.] [mol %] [ml/g] [% by wt.] PV/AM.sup.0.55 1*) C1 16 0.1429 258 3.9 0.046 0.10 0.106 2 WE1 10 0.0558 254 3.8 0.053 0.17 0.122 3 WE2 7 0.0274 253 3.6 0.062 1.05 0.143 4 WE3 4 0.0089 254 3.5 0.065 4.75 0.149 5 WE4 3 0.0050 254 3.5 0.078 4.43 0.179 6*) WE5 2 0.0022 254 3.6 0.086 7.37 0.198 *)comparative example TB salt bath temperature (acrolein conversion of 99.3 mol %) S.sup.COx CO.sub.x selectivity (total combustion) PV pore volume

TABLE-US-00003 TABLE 2 Experimental results with Mo.sub.12V.sub.3W.sub.1.2Cu.sub.1.2O.sub.x on support bodies (external diameter 6 mm, length 6 mm, internal diameter 4 mm) AC Abrasion Speed Froude [% by TB S.sup.COx PV level Ex. Cat. [rpm] number wt.] [? C.] [mol %] [ml/g] [% by wt.] PV/AM.sup.0.55 7*) C2 16 0.1429 25.0 247 3.5 0.061 0.29 0.131 8 WE6 7 0.0558 25.7 247 3.2 0.078 2.06 0.167 9*) C3 16 0.1429 19.9 256 3.1 0.051 0.24 0.124 10 WE7 7 0.0558 20.2 251 2.7 0.067 1.56 0.162 11*) C4 16 0.1429 15.3 259 2.8 0.046 0.19 0.131 12 WE8 7 0.0558 15.4 258 2.5 0.054 1.66 0.153 13*) C5 16 0.1429 10.4 270 2.3 0.038 0.5 0.135 14 WE9 7 0.0558 10.2 271 2.0 0.041 1.6 0.145 *)comparative example AC active composition TB salt bath temperature (acrolein conversion of 99.3 mol %) S.sup.COx CO.sub.x selectivity (total combustion) PV pore volume