Method for preparing mixed metal oxide catalysts containing molybdenum and bismuth

Abstract

The present invention relates to a process for producing mixed oxide catalysts on the basis of molybdenum and bismuth oxides in which the precursor compounds of the components of mixed oxide catalysts provided in the form of a solution and/or suspension are subjected to a spray-drying with a specific temperature regime and the spray particles obtained in this way are then calcined to yield a catalytic active mass, and to the mixed oxide catalysts obtainable by this process and to the use of these catalysts in the partial oxidation of olefins, in particular in the partial gas phase oxidation of propene to acrolein and acrylic acid. The spray drying of the precursor compounds containing solution or suspension is performed in concurrent with a gas stream having a specific entrance temperature. Alternatively, when the main gas stream has a higher entrance temperature, an additional colder gas stream can be fed in downstream. The thus obtained mixed oxide catalysts give lower a maximum temperature in the hot spot of catalyst fixed bed when they are used in the partial gas phase oxidation of olefins.

Claims

1. A process for producing a mixed oxide catalyst, the process comprising a) providing a solution and/or suspension of precursor compounds of components of mixed oxide catalyst, wherein the solution and/or suspension contains a precursor compound of bismuth and a precursor compound of molybdenum or a precursor compound of bismuth and molybdenum, and wherein, when the suspension is subjected to spray-drying, a concentration of solids in the suspension is 10 to 50% by weight, b) spray-drying the solution and/or suspension provided in a) in cocurrent together with a gas stream having an entrance temperature into a spray dryer of 160+/−10° C. to 200+/−10° C. and an exit temperature from the spray dryer of 90+/−10° C. to 105+/−10° C., wherein the gas stream has a mean flow velocity in the spray dryer of 2.0+/−0.3 cm/s to 4.5+/−0.3 cm/s, or b′) spray-drying the solution and/or suspension provided in a) essentially in cocurrent together with a main gas stream having an entrance temperature into the spray dryer of 260+/−10° C. to 300+/−10° C. and an exit temperature from the spiny dryer of 115+/−10° C. to 130+/−10° C., wherein the main gas stream has a mean flow velocity in the spray dryer of 2.0+/−0.3 cm/s to 4.5+/−0.3 cm/s, with feeding of an additional gas stream having an entrance temperature of less than 100° C. and not more than 30° C. into the spray dryer between entrance and exit points of the main gas stream into the spray dryer and from the spray dryer, wherein the additional gas stream has a mean flow velocity of less than 2.0 cm/s, and c) calcining spray particles obtained from b) or b′) to yield a catalytic active mass.

2. The process according to claim 1, wherein the process comprises b′) in which the additional gas stream is fed in at an angle of 90+/−5° to 0° relative to a wall of the spray dryer upward in an axial direction of the spray dryer.

3. The process according to claim 1, wherein the process comprises b′) in which the additional gas stream is fed into the spray dryer at a point between one third and three quarters of a distance between the entrance and exit points for the main gas stream in the spray dryer.

4. The process according to claim 1, wherein a throughput of the solution and/or suspension sprayed into the spray dryer is 1 to 6 kg/h.

5. The process according to claim 1, wherein the solution and/or suspension provided in a) comprises precursor compounds of all components of the mixed oxide catalyst.

6. The process according to claim 1, wherein the solution and/or suspension in a) also contains at least one precursor compound of elements selected from the group consisting of iron, tungsten, phosphorous, cobalt, nickel, alkali metal, alkaline earth metal, cerium, manganese, chromium, vanadium, niobium, selenium, tellurium, gadolinium, lanthanum, yttrium, palladium, platinum, ruthenium, silver, gold, samarium, silicon, aluminum, titanium, and zirconium.

7. The process according to claim 1, wherein solutions and/or suspensions comprising precursor compounds each of different components of the mixed oxide catalyst are used in step a) and steps a) and b) or a) and b′) are repeated more than once.

8. The process according to claim 7, further comprising d) mixing the catalytic active masses obtained from c) then solutions and/or suspensions of precursor compounds each of different components of the mixed oxide catalyst are used in b) or b′), to yield a catalytic active mass comprising all the components of the mixed oxide catalyst.

9. The process according to claim 8, further comprising e) adding a shaping agent and/or binder to the catalytic active mass obtained from c) or d), f) shaping the catalytic active mass obtained from e) to obtain a shaped body comprising the mixed oxide catalyst, and g) drying and/or calcining and/or heat-treating the shaped catalyst body obtained from f).

10. The process according to claim 1, further comprising h) providing a washcoat suspension comprising the catalytic active mass obtained from c), i) applying the washcoat suspension from h) to a support material, and j) drying and/or calcining and heat-treating the support material obtained from to yield a supported mixed oxide catalyst.

11. A method for preparing an unsaturated aldehyde and/or acid, the method comprising: partially oxidizing at least one olefin in the presence of a mixed oxide catalyst obtained by the process according to claim 1.

12. The method according to claim 11, wherein the olefin is a C.sub.1-C.sub.4 olefin.

Description

EXAMPLES

(1) I. Production of Mixed Oxide Catalysts

(2) 1.1 Provision of Suspensions for Catalyst Production

Example 1

(3) A first solution (referred to hereinafter as solution I) was prepared by first dissolving the nitrates of iron, cobalt, nickel, manganese and potassium in the mass fractions of 23.2:47.26:29.28:0.0646:0.2067 in 3.5 litres of water, heating the mixture obtained to 50° C. while stirring and then adding a nitric acid solution of 0.1 mol Sm.sup.3+ and 2 mol of HNO.sub.3.

(4) A separate second solution (referred to hereinafter as solution II) was prepared by dissolving 2118.6 g of ammonium heptamolybdate in 2.7 litres of water and then adding a solution of 4.4 g of phosphoric acid in 1 litre of water.

(5) A further separate solution (referred to hereinafter as solution III) was prepared from 1280 g of bismuth nitrate and 0.72 mol of HNO.sub.3.

(6) Solution II was provided, and solution III was added gradually thereto, while stirring. Solution I was added to the mixture thus obtained to yield a suspension.

(7) 1.2 Production of Active Masses for the Catalysts

(8) All the active masses for the catalysts were produced by spray-drying in a rotary disc tower of the Mobile Minor™ type (http://www.niro.com/niro/cmsdoc.nsf/WebDoc/ndkk5j9c7h) from GEA-Niro (GEA Germany, GEA Group Aktiengesellschaft, Peter-Müller-Str. 12, 40468 Dusseldorf, Germany). This spray dryer has a cylindrical section having a diameter of 0.8 m and a height of 0.62 m, in which the spray-drying is effected, and an inverted conical section that adjoins the lower end thereof and has a length of 0.72 m, which serves to collect the spray particles generated.

(9) According to the invention, the specific particle size distribution is determined in wet dispersion by means of laser scattering according to the International Standard ISO 13320. In the context of the present invention, the particle size distribution was determined with a Particle Size Analyzer of the LS™ 13320 series and a Universal Liquid Module, both from Beckmann Coulter (Brea, Calif.), using PIDS (Polarization Intensity Differential Scattering) data. The spray particles were dispersed in ethanol and subjected to the determination of particle size distribution without ultrasound bath treatment at a relative pumping rate of about 31%. The optical model for particle size determination is the Fraunhofer model. The measurement time for the particle size determination is about 82 seconds.

(10) The particle diameters d.sub.x reported as the measurement result are defined such that X % of the total particle volume consists of particles having a smaller diameter. This means that (100-X) % of the total particle volume consists of particles having a diameter≥d.sub.x.

Example 2a (Inventive)

(11) The suspension obtained in Example 1 was dried in a GEA-Niro Mobile Minor™ rotary disc spray dryer: The suspension was sprayed into the spray dryer, from the top downward in cocurrent with the incoming air, at a metering rate of 2+/−0.1 l/h together with 51+/−2.5 Nm.sup.3/h of air (corresponding to a mean flow rate in the spray dryer of about 2.8+/−0.3 cm/s) that had an entrance temperature into the spray dryer of 200° C. through a rotary disc having a rotation rate of 45 000 min.sup.−1. The exit temperature of the air from the spray dryer was 105° C. The spray-dried particles obtained had a residual moisture content of 14.5%. The particle size distribution of the spray powders obtained was d.sub.5=11.22 μm, d.sub.10=13.86 μm, d.sub.50=26.33 μm, d.sub.90=46.39 μm and d.sub.95=56.90 μm. The mean of the particle size distribution was 29.39 μm and the median 26.33 μm. The maximum of the particle size distribution was 28.70 μm.

Example 2b (Inventive)

(12) The suspension obtained in Example 1 was dried in a GEA-Niro Mobile Minor™ rotary disc spray dryer: The suspension was sprayed into the spray dryer, from the top downward in cocurrent with the incoming air, at a metering rate of 2+/−0.1 l/h together with 51+/−2.5 Nm.sup.3/h of air (corresponding to a mean flow rate in the spray dryer of about 2.8+/−0.3 cm/s) that had an entrance temperature into the spray dryer of 180° C. through a rotary disc having a rotation rate of 45 000 min.sup.−1. The exit temperature of the air from the spray dryer was 92+/−5° C. The spray-dried particles obtained had a residual moisture content of 16.4%. The particle size distribution of the spray powders obtained was d.sub.5=10.74 μm, d.sub.10=16.20 μm, d.sub.50=33.00 μm, d.sub.90=60.74 μm and d.sub.95=91.39 μm. The mean of the particle size distribution was 37.99 μm and the median 33.00 μm. The maximum of the particle size distribution was 34.59 μm.

Example 2c (Inventive)

(13) The suspension obtained in Example 1 was dried in a GEA-Niro Mobile Minor™ rotary disc spray dryer: The suspension was sprayed into the spray dryer, from the top downward in cocurrent with the incoming air, at a metering rate of 2+/−0.1 l/h together with 71+/−2.5 Nm.sup.3/h of air (corresponding to a mean flow rate in the spray dryer of about 4.0+/−0.3 cm/s) that had an entrance temperature into the spray dryer of 180° C. through a rotary disc having a rotation rate of 45 000 min.sup.−1. The exit temperature of the air from the spray dryer was 99+/−5° C. The spray-dried particles obtained had a residual moisture content of 14%. The particle size distribution of the spray powders obtained was d.sub.5=13.20 μm, d.sub.10=16.16 μm, d.sub.50=30.25 μm, d.sub.90=51.33 μm and d.sub.95=63.76 μm. The mean of the particle size distribution was 33.71 μm and the median 30.25 μm. The maximum of the particle size distribution was 31.51 μm.

Example 3a (Comparative Example)

(14) The suspension of Example 1 was dried in a GEA-Niro Mobile Minor™ rotary disc spray dryer: The suspension was sprayed into the spray dryer, from the top downward in cocurrent with the incoming air, at a metering rate of 2+/−0.1 l/h together with 51+/−2.5 Nm.sup.3/h of air (corresponding to a mean flow rate in the spray dryer of about 2.8+/−0.3 cm/s) that had an entrance temperature into the spray dryer of 300° C. through a rotary disc having a rotation rate of 45 000 min.sup.−1. The exit temperature of the air from the spray dryer was 180+/−5° C. The spray-dried particles obtained had a residual moisture content of 2.2%. The particle size distribution of the spray powders obtained was d.sub.5=0.503 μm, d.sub.10=6.970 μm, d.sub.50=19.87 μm, d.sub.90=37.10 μm and d.sub.95=41.86 μm. The mean was 21.31 μm and the median 19.87 μm. The maximum of the particle size distribution was 19.76 μm.

Example 3b (Comparative Example)

(15) The suspension of Example 1 was dried in a GEA-Niro Mobile Minor™ rotary disc spray dryer: The suspension was sprayed into the spray dryer, from the top downward in cocurrent with the incoming air, at a metering rate of 2+/−0.1 l/h together with 51+/−2.5 Nm.sup.3/h of air (corresponding to a mean flow rate in the spray dryer of about 2.8+/−0.3 cm/s) that had an entrance temperature into the spray dryer of 212° C. through a rotary disc having a rotation rate of 45 000 min.sup.−1. The exit temperature of the air from the spray dryer was 120° C. The spray-dried particles obtained had a residual moisture content of 6.4%. The particle size distribution of the spray powders obtained was d.sub.5=3.25 μm, d.sub.10=10.54 μm, d.sub.50=24.90 μm, d.sub.90=45.86 μm and d.sub.95=59.07 μm. The mean was 27.81 μm and the median 24.90 μm. The maximum of the particle size distribution was 28.70 μm.

Example 4a (Inventive)

(16) The suspension from Example 1 was dried in a GEA-Niro Mobile Minor™ rotary disc spray dryer: The suspension was sprayed into the spray dryer, from the top downward in cocurrent with the incoming air, at a metering rate of 2+/−0.1 l/h together with 51+/−2.5 Nm.sup.3/h of air (corresponding to a mean flow rate in the spray dryer of about 2.8+/−0.3 cm/s) that had an entrance temperature into the spray dryer of 275° C. through a rotary disc having a rotation rate of 45 000 min.sup.−1. Via a perpendicular feed at half the height of the drying space of the spray dryer, 20 Nm.sup.3/h of additional air (corresponding to a mean flow rate in the spray dryer of about 1.0+/−0.3 cm/s) that had an entrance temperature into the spray dryer of 20° C. were sprayed into the spray dryer at an angle of 90° to the dryer wall. The exit temperature of the air from the spray dryer was 125° C., irrespective of whether it entered the spray dryer from the top downward or from the side. The spray-dried particles obtained had a residual moisture content of 11.2%. The particle size distribution of the spray powders obtained was d.sub.5=9.646 μm, d.sub.10=12.30 μm, d.sub.50=23.00 μm, d.sub.90=38.93 μm and d.sub.95=44.58 μm. The mean was 24.94 μm and the median 23.00 μm. The maximum of the particle size distribution was 23.82 μm.

Example 4b (Inventive)

(17) The suspension from Example 1 was dried in a GEA-Niro Mobile Minor™ rotary disc spray dryer: The suspension was sprayed into the spray dryer, from the top downward in cocurrent with the incoming air, at a metering rate of 2+/−0.1 l/h together with 51+/−2.5 Nm.sup.3/h of air (corresponding to a mean flow rate in the spray dryer of about 2.8+/−0.3 cm/s) that had an entrance temperature into the spray dryer of 275° C. through a rotary disc having a rotation rate of 45 000 min.sup.−1. Via a perpendicular feed at half the height of the drying space of the spray dryer, 20 Nm.sup.3/h (corresponding to a mean flow rate in the spray dryer of about 1.0+/−0.3 cm/s) of additional air that had an entrance temperature into the spray dryer of 20° C. were sprayed into the spray dryer from the top downward (at an angle of 0° to the dryer wall of the spray dryer in the direction of the main air stream). The exit temperature of the air from the spray dryer was 125° C., irrespective of whether it entered the spray dryer from the top downward or from the side. The spray-dried particles obtained had a residual moisture content of 11.2%. The particle size distribution of the spray powders obtained was d.sub.5=2.046 μm, d.sub.10=8.712 μm, d.sub.50=22.00 μm, d.sub.90=38.66 μm and d.sub.95=44.54 μm. The mean was 23.60 μm and the median 22.00 μm. The maximum of the particle size distribution was 38.82 μm.

(18) 1.3 Production of Catalysts from Spray-Dried Powders

Example 5

(19) The powders produced in examples 2a to 2c, 3a to 3b and 4a to 4b were calcined in an air circulation oven at a temperature of 430+/−5° C. for a period of one hour. The mixed oxides obtained were then sprayed as an aqueous suspension onto a ceramic spherical catalyst support made of SiO.sub.2 and dried at 60° C. in an air stream. The pellets thus obtained were subsequently circulated in a drum for homogenization. To solidify the active mass applied, the material obtained was also subjected to a heat treatment at a temperature of 520° C. for a period of 5 hours. All catalysts produced in this way had the composition (Mo.sub.12Bi.sub.1.5(Co+Ni).sub.6.0Fe.sub.1.8Mn.sub.0.01K.sub.0.06P.sub.0.04Si.sub.0.66Sm.sub.0.1)O.sub.x.

(20) II. Testing of the Mixed Oxide Catalysts

Example 6

(21) The catalysts produced in Example 5 from the active masses of Examples 2a to 2c and 3a to 3b were used in the partial gas phase oxidation of propene. For this purpose, a tubular reactor having an internal tube diameter of 20.5 mm was charged in each case with a catalyst fixed bed having a length of 285 cm. The tubular reactor was surrounded by a bath with which the temperature of the catalyst fixed bed and of the reaction mixture flowing through the catalyst fixed bed was regulated. A feed gas stream composed of propene (about 7% by volume, chemical grade), air and inert substances was introduced into the tubular reactor and the propene was converted over the fixed catalyst bed. The amount of propene supplied was chosen such that the quotient of propene gas rate in litres per hour and the catalyst charge used in litres has a value of 146 h.sup.−1. The propene conversion was adjusted via the choice of bath temperature to a value of 97+/−0.5%. In addition, the air rate for oxidation was adjusted such that, at the propene conversion established, the residual oxygen content in the gas stream after a single pass through the reactor was 6% by volume. For all catalysts, the cumulative yield of acrolein and acrylic acid was always more than 90%, and the yield of acrolein was always at least 84%. In all tests with the catalysts based on the active masses of Examples 2a to 2c and 3a to 3b, the respective maximum temperature in the catalyst fixed bed was determined.

(22) TABLE-US-00001 TABLE 1 Overview of the temperatures in the reactions of Example 6. Catalyst GHSV Propylene T.sub.bath,reactor T.sub.max,reactor (from Example) [h.sup.−1] [% by vol.] [° C.] [° C.] 2a 2057 7.09 348 422 (inventive) 2b 2051 7.12 347 422 (inventive) 2c 2046 7.15 355 419 (inventive) 3a 2036 7.16 352 437 (comparative example) 3b 2025 7.21 360 435 (comparative example)

Example 7

(23) The catalysts produced in Example 5 from the active masses of Examples 2a to 2c and 3a to 3b were used in the partial gas phase oxidation of propene. For this purpose, a tubular reactor having an internal tube diameter of 20.5 mm was charged in each case with a catalyst fixed bed having a length of 285 cm. The tubular reactor was surrounded by a bath with which the temperature of the fixed catalyst bed and of the reaction mixture flowing through the catalyst fixed bed was regulated. A feed gas stream composed of propene (about 7% by volume, chemical grade), air and inert substances was introduced into the tubular reactor and the propene was converted over the fixed catalyst bed. The amount of propene supplied was chosen such that the quotient of propene gas rate in litres per hour and the catalyst charge used in litres has a value of 153 h.sup.−1. The propene conversion was adjusted via the choice of bath temperature to a value of 97+/−0.5%. In addition, the air rate for oxidation was adjusted such that, at the propene conversion established, the residual oxygen content in the gas stream after a single pass through the reactor was 6% by volume. For all catalysts, the cumulative yield of acrolein and acrylic acid was always at least 91%, and the yield of acrolein was always at least 84%. In all tests with the catalysts based on the active masses of Examples 2a to 2c and 3a to 3b, the respective maximum temperature in the catalyst fixed bed was determined.

(24) TABLE-US-00002 TABLE 2 Overview of the temperatures in the reactions of Example 7. Catalyst GHSV Propylene T.sub.bath,reactor T.sub.max,reactor (from Example) [h.sup.−1] [% by vol.] [° C.] [° C.] 2a 2129 7.16 345 422 (inventive) 2b 2157 7.08 350 422 (inventive) 2c 2136 7.16 355 419 (inventive) 3a 2120 7.21 B 360* 437 (comparative example) 3b 2121 7.19 >360 435 (comparative example)

Example 8

(25) The catalysts produced in Example 5 from the active masses of Examples 3a to 3b and 4a to 4b were used in the partial gas phase oxidation of propene. For this purpose, a tubular reactor having an internal tube diameter of 20.5 mm was charged in each case with a catalyst fixed bed having a length of 285 cm. The tubular reactor was surrounded by a bath with which the temperature of the catalyst fixed bed and of the reaction mixture flowing through the catalyst fixed bed was regulated. A feed gas stream composed of propene (about 7% by volume, chemical grade), air and inert substances was introduced into the tubular reactor and the propene was converted over the fixed catalyst bed. The amount of propene supplied was chosen such that the quotient of propene gas rate in litres per hour and the catalyst charge used in litres has a value of 146 h.sup.−1. The propene conversion was adjusted via the choice of bath temperature to a value of 97+/−0.5%. In addition, the air rate for oxidation was adjusted such that, at the propene conversion established, the residual oxygen content in the gas stream after a single pass through the reactor was 6% by volume. For all catalysts, the cumulative yield of acrolein and acrylic acid was always at least 90%, and the yield of acrolein was always at least 84%. In all tests with the catalysts based on the active masses of Examples 4a to 4b and 3a to 3b, the respective maximum temperature in the catalyst fixed bed was determined.

(26) TABLE-US-00003 TABLE 3 Overview of the temperatures in the reactions of Example 8. Catalyst GHSV Propylene T.sub.bath,reactor T.sub.max,reactor (from Example) h.sup.−1 = 50 [% by vol.] [° C.] [° C.] 4a 2057 7.09 354 423 (inventive) 4b 2067 7.06 357 425 (inventive) 3a 2036 7.16 352 437 (comparative example) 3b 2025 7.21 360 435 (comparative example)