METHOD FOR PRODUCING CATALYSTS CONTAINING CHROME, FOR THE OXIDATIVE DEHYDROGENATION OF N-BUTENES TO FORM BUTADIENE WHILE AVOIDING CR(VI) INTERMEDIATES

Abstract

Process for producing a multimetal oxide catalyst comprising molybdenum, chromium and at least one further metal by mixing of a pulverulent multimetal oxide comprising molybdenum and at least one further metal but no chromium with pulverulent chromium(III) oxide and thermal treatment of the resulting pulverulent mixture in the presence of oxygen at a temperature in the range from 350 C. to 650 C.

Claims

1.-4. (canceled)

5. A process for producing a multimetal oxide catalyst comprising molybdenum, chromium and at least one further metal by mixing of a pulverulent multimetal oxide comprising molybdenum and the at least one further metal but no chromium with pulverulent chromium(III) oxide and thermally treating the resulting pulverulent mixture in the presence of oxygen at a temperature in the range from 350 C. to 650 C., wherein the multimetal oxide comprising molybdenum and the at least one further metal but no chromium has the general formula (I)
Mo.sub.12Bi.sub.aFe.sub.bCo.sub.cNi.sub.dX.sup.1.sub.fX.sup.2.sub.gO.sub.x(I) wherein: X.sup.1=W, Sn, Mn, La, Ce, Ge, Ti, Zr, Hf, Nb, P, Si, Sb, Al, Cd and/or Mg; X.sup.2=Li, Na, K, Cs and/or Rb, a=0.1 to 7; b=0 to 10; c=0 to 10; d=0 to 10; f=0 to 50; g=0 to 2; and x=a number determined by the valence and abundance of the elements other than oxygen in (I), and the multimetal oxide catalyst comprising molybdenum, chromium and at least one further metal has the general formula (II)
Mo.sub.12Bi.sub.aFe.sub.bCo.sub.cNi.sub.dCr.sub.eX.sup.1.sub.fX.sup.2.sub.gO.sub.y(II) where the variables have the following meanings: X.sup.1=W, Sn, Mn, La, Ce, Ge, Ti, Zr, Hf, Nb, P, Si, Sb, Al, Cd and/or Mg; X.sup.2=Li, Na, K, Cs and/or Rb, a=0.1 to 7; b=0 to 10; c=0 to 10; d=0 to 10; e=>0 to 5; f=0 to 50; g=0 to 2; and y=a number determined by the valence and abundance of the elements other than oxygen in (II).

6. The process according to claim 5, wherein the production of the pulverulent multimetal oxide which comprises molybdenum and at least one further metal but no chromium comprises the steps (i) to (iv): (i) producing a multimetal oxide precursor composition comprising molybdenum and at least one further metal but no chromium, (ii) shaping of shaped bodies from the multimetal oxide precursor composition, (iii) calcining the shaped bodies, (iv) milling of the shaped bodies to give a pulverulent multimetal oxide.

7. The process according to claim 6, wherein the process comprises the steps (v) to (viii): (v) mixing of the pulverulent multimetal oxide comprising molybdenum and at least one further metal but no chromium with pulverulent chromium(III) oxide, (vi) thermally treating the pulverulent mixture in the presence of oxygen at a temperature of from 350 to 650 C. to give a pulverulent multimetal oxide catalyst comprising molybdenum, chromium and at least one further metal, (vii) coating of a support body with the pulverulent multimetal oxide catalyst, (viii) thermally treating the coated support body.

8. The process according to claim 5, wherein the multimetal oxide catalyst which comprises molybdenum, chromium and at least one further metal and has the general formula (IIa)
Mo.sub.12Bi.sub.aFe.sub.bCo.sub.cNi.sub.dCr.sub.eX.sup.1.sub.fX.sup.2.sub.gO.sub.y(IIa), where the variables have the following meanings: X.sup.1=W, Sn, Mn, La, Ce, Ge, Ti, Zr, Hf, Nb, P, Si, Sb, Al, Cd and/or Mg; X.sup.2=Li, Na, K, Cs and/or Rb, a=0.1 to 7; b=0 to 5; c=0 to 10; d=0 to 10; e=0.01 to 5; f=0 to 50; g=0 to 2; and y=a number determined by the valence and abundance of the elements other than oxygen in (II).

9. The process according to claim 5, wherein in formula (I): a=0.3 to 1.5; b=2 to 4; c=3 to 10; d=0; f=0.1 to 10; and g=0.01 to 1; and wherein in formula (II): a=0.3 to 1.5; b=2 to 4; c=3 to 10; d=0; e=0.1 to 2; f=0.1 to 10; and g=0.01 to 1.

Description

EXAMPLES

[0208] Catalyst Production

Example 1

[0209] Two starting materials A and B are used.

[0210] Starting material A: 1 kg of milled chromium-free catalyst corresponding to example B (page 28) of DE 10 2007 004 961 A1. The catalyst has the stoichiometry Mo.sub.12Co.sub.7Fe.sub.3Bi.sub.0.6K.sub.0.08Si.sub.1.6O.sub.x. The catalyst was milled by means of an opposed jet mill.

[0211] Starting material B: 14 g of Bayoxide C GN-M from Lanxess (Cr.sub.2O.sub.3)

[0212] The two starting materials are mixed at 190 rpm in an Amixon mixer for 15 minutes. The mixed powders are heated to 510 C. over a period of 3 hours 53 minutes using a linear ramp in a Nabertherm muffle furnace and then maintained at this temperature for 7 hours 47 minutes in a normal atmosphere using an inflow of 1000 standard l/h of air. After the calcination, an active composition having the calculated stoichiometry Mo.sub.12Co.sub.7Fe.sub.3Bi.sub.0.6K.sub.0.08Cr.sub.0.6Si.sub.1.6O.sub.x is obtained.

[0213] Support bodies (steatite rings having the dimensions 532 mm (external diameterinternal diameterlength) were coated with the precursor composition. Coating was carried out in a HiCoater LHC 25/36 (from Ldige, D-33102 Paderborn). This HiCoater was modified in order to allow continuous introduction of powder. This consisted of a funnel-shaped powder reservoir which was connected via a Tygon tube (internal diameter: 8 mm, external diameter 11.1 mm; from Saint-Gobain Performance, 89120 Charny, France) to the drum of the HiCoater. The drum radius was 18 cm. The depth of the drum was 20 cm. The axis about which the drum rotated was aligned horizontally. For the coating operation, 710 g of the catalytic active oxide composition powder were placed in the powder reservoir. Powder metering was carried out by continuous pressure metering. The pulse time valve was set to 30 ms and the pressure set was 0.6 bar above ambient pressure (1 atm). The powder in the funnel-shaped powder reservoir was continuously stirred during the coating operation in order to ensure uniform metering (running time of stirrer: 4 s, pause time of stirrer 1 s, modified V-shaped anchor stirrer, constructed in-house by BASF SE). The binder was an aqueous solution composed of 75% by weight of water and 25% by weight of glycerol. This was sprayed separately by means of a liquid metering device into the drum. The liquid was pumped by means of an HPLC pump from Watson-Marlow (model 323) into the metering arm located in the drum (spray pressure 3 bar, forming pressure 2 bar, mass flow: 1.8 g of glycerol/water solution (1:3)/min). The powder metering device and the liquid metering device were arranged parallel to one another. The nozzle from Schlick (DE) model 570/0 S75 installed on the metering arm and also the exit opening of the solids metering device which was likewise fastened underneath on the metering arm were aligned parallel at a spacing of 6 cm and by means of an angle measuring instrument at an angle of 40 to the horizontal. Powder metering was carried out outside the spray cone of the nozzle. The nozzle opening and exit opening of the solids metering device pointed in the direction of rotation of the drum. The drum rotated clockwise at 15 rpm during coating. Coating was carried out at 25 C. over a period of 30 minutes. The coated support materials were then dried at an air inlet temperature of 130 C. and an air outlet temperature of 81 C. for 27 minutes. They were then cooled in the static drum to 25 C. over a period of 30 minutes. During the coating operation, the powder fed in was mostly taken up on the surface of the support. The material which was not taken up was collected in a filter downstream of the drum. No formation of twins occurred and agglomeration of the finely divided oxidic composition was not observed.

[0214] The coated shaped support bodies were treated in a convection drying oven (from Memmert GmbH+Co. KG, model UM 400; internal volume=53 l; air flow=800 l/h) in order to remove the glycerol still present in the sample. For this purpose, the convection drying oven was heated to 300 C. (inclusive of the air temperature) over a period of 2 hours and then maintained at 300 C. for 2 hours. During drying, the material being dried was located in a layer (layer thickness=2 cm) on a perforated plate positioned centrally in the drying oven (the hole diameter of the through openings distributed uniformly over the perforated plate=0.5 cm; the opening ratio of the perforated plate was 60%; the total cross-sectional area of the perforated plate was 35 cm26 cm=910 cm.sup.2). The convection drying oven was then cooled to 40-50 C. over a period of 2-3 hours and the sample was taken out. The hollow-cylindrical coated catalysts taken from the convection drying oven have, based on their total mass, an oxidic coating proportion of 16% by weight.

Example 2 (Comparison)

[0215] A catalyst is produced as per example B (page 28) of DE 10 2007 004 961 A1. The catalyst has the stoichiometry Mo.sub.12Co.sub.7Fe.sub.3Bi.sub.0.6K.sub.0.08Si.sub.1.6O.sub.x.

[0216] Support bodies (steatite rings having the dimensions 532 mm (external diameterinternal diameterlength) were coated with the precursor composition in a manner analogous to example 1.

[0217] The coated shaped support bodies were treated in a convection drying oven in a manner analogous to example 1. The hollow-cylindrical coated catalysts taken from the convection drying oven have, based on their total mass, an oxidic coating proportion of 15% by weight.

Example 3 (Comparison)

[0218] The catalyst was produced as per the example on page 24 of WO 2014/08695, as follows:

[0219] 2 solutions A and B were produced.

[0220] Solution A: 3200 g of water were placed in a 10 l stainless steel pot. While stirring by means of an anchor stirrer, 5.2 g of a KOH solution (32% by weight of KOH) were added to the initially charged water. The solution was heated to 60 C. 1066 g of an ammonium heptamolybdate solution ((NH.sub.4).sub.6Mo.sub.7O.sub.24*4 H.sub.2O, 54% by weight of Mo) were then added a little at a time over a period of 10 minutes. The resulting suspension was stirred for a further 10 minutes.

[0221] Solution B: 1771 g of a cobalt(II) nitrate solution (12.3% by weight of Co) were placed in a 5 l stainless steel pot and heated to 60 C. while stirring (anchor stirrer). 645 g of an iron(III) nitrate solution (13.7% by weight of Fe) were then added a little at a time over a period of 10 minutes while maintaining the temperature. The solution formed was stirred for a further 10 minutes. 619 g of a bismuth nitrate solution (10.7% by weight of Bi) were then added while maintaining the temperature. After stirring for a further 10 minutes, 109 g of chromium(III) nitrate were added in solid form a little at a time and the resulting dark red solution was stirred for a further 10 minutes.

[0222] While maintaining the 60 C., the solution B was pumped into the solution A by means of a peristaltic pump over a period of 15 minutes. During the addition and afterwards, the mixture was stirred by means of a high-speed mixer (Ultra-Turrax). After the addition was complete, the mixture was stirred for a further 5 minutes. 93.8 g of an SiO.sub.2 suspension (Ludox; SiO.sub.2 about 49%, from Grace) were then added and the mixture was stirred for a further 5 minutes.

[0223] The suspension obtained was spray dried in a spray dryer from NIRO (spray head No. FOA1, speed of rotation 25 000 rpm) over a period of 1.5 hours. The reservoir temperature was maintained at 60 C. during this time. The gas inlet temperature of the spray dryer was 300 C., and the gas outlet temperature was 110 C. The powder obtained had a particle size (do) of less than 40 m.

[0224] The powder obtained was mixed with 1% by weight of graphite, compacted twice under a pressing pressure of 9 bar and broken up through a sieve having a mesh opening of 0.8 mm. The crushed material was once again mixed with 2% by weight of graphite and the mixture was pressed by means of a Kilian S100 tableting press to give rings having dimensions of 532 mm (external diameterlengthinternal diameter).

[0225] The catalyst precursors obtained were calcined batchwise (500 g) in a convection oven from Heraeus, DE (model K, 750/2 S, internal volume 55 l). The following program was used for this purpose: [0226] heat to 130 C. over 72 minutes, hold for 72 minutes [0227] heat to 190 C. over 36 minutes, hold for 72 minutes [0228] heat to 220 C. over 36 minutes, hold for 72 minutes [0229] heat to 265 C. over 36 minutes, hold for 72 minutes [0230] heat to 380 C. over 93 minutes, hold for 187 minutes [0231] heat to 430 C. over 93 minutes, hold for 187 minutes [0232] heat to 490 C. over 93 minutes, hold for 467 minutes

[0233] After the calcination, the catalyst having the calculated stoichiometry Mo.sub.12Co.sub.7Fe.sub.3Bi.sub.0.6K.sub.0.08Cr.sub.0.5Si.sub.1.6O.sub.x was obtained.

[0234] The calcined pellets were milled to a powder. Support bodies (steatite rings having the dimensions 532 mm (external diameterinternal diameterlength) were coated with the precursor composition in a manner analogous to example 1.

[0235] The coated shaped support bodies were treated in a convection drying oven in a manner analogous to example 1. The hollow-cylindrical coated catalysts taken from the convection drying oven had, based on their total mass, an oxidic coating proportion of 15% by weight.

Example 4

[0236] Dehydrogenation Experiments

[0237] Dehydrogenation experiments were carried out in a screening reactor. The screening reactor was a salt bath reactor having a length of 120 cm and an internal diameter of 14.9 mm and a temperature sensor sheath having an external diameter of 3.17 mm. A multiple temperature sensor having seven measurement points was located in the temperature sensor sheath. The lowermost 4 measurement points had a spacing of 10 cm and the uppermost 4 measuring points had a spacing of 5 cm.

[0238] Raffinate II was metered in liquid form through a coriolis flow meter at about 10 bar and subsequently depressurized and vaporized in a heated vaporizer section. This gas was then mixed with nitrogen and fed into a preheater having a steatite bed. Water was introduced in liquid form and vaporized in a stream of air in a vaporizer coil. The air/water vapor mixture was combined with the N.sub.2/raffinate 11 mixture in the lower region of the preheater. The completely mixed feed gas was then fed to the reactor, with an analysis stream for on-line GC measurement being able to be taken off. An analysis stream is likewise taken off from the product gas leaving the reactor and can be analyzed by on-line GC measurement or by means of an IR analyzer for the proportion by volume of CO and CO.sub.2. A pressure regulating valve which set the pressure level in the reactor was installed downstream of the branch of the analysis line.

[0239] A 6.5 cm long after-bed consisting of 16 g of steatite balls having a diameter of from 3.5 to 4.5 mm was introduced on top of the catalyst grating at the lower end of the screening reactor. 120 g of the respective catalyst were then introduced into the reactor (67.5 cm bed height). The catalyst bed was followed by a 7 cm long pre-bed consisting of 16 g of steatite balls having a diameter of from 3 to 4 mm.

[0240] The catalysts were activated by being heated overnight at 400 C. in a mixture of oxygen, nitrogen and steam (10/80/10). The reactor was operated using from 100 to 250 standard l/h of a reaction gas having the composition 8% of butene, 2% of butane, 12% of oxygen, 5% of water, 73% of nitrogen at a salt bath temperature of 380 C. for 120 hours. The gas velocity was varied in order to alter the conversion. The salt bath temperature was 380 C. The product gases were analyzed by means of a GC. The conversion and selectivity data are shown in table 1.

[0241] The parameters conversion (X) and selectivity (S) calculated in the examples were determined as follows:

[00002]$X=\frac{\mathrm{mol}\left({\mathrm{butenes}}_{i.Math..Math.n}\right)-\mathrm{mol}\left({\mathrm{butenes}}_{\mathrm{out}}\right)}{\mathrm{mol}\left({\mathrm{butene}}_m\right)}$$S=\frac{\mathrm{mol}\left({\mathrm{butenes}}_{\mathrm{out}}\right)-\mathrm{mol}\left({\mathrm{butenes}}_{i.Math..Math.n}\right)}{\mathrm{mol}\left({\mathrm{butenes}}_{i.Math..Math.n}\right)-\mathrm{mol}\left({\mathrm{butenes}}_{\mathrm{out}}\right)}$

where mol(X.sub.in) is the molar amount of the component X at the reactor inlet, mol (X.sub.out) is the molar amount of the component X at the reactor outlet and butenes is the sum of 1-butene, cis-2-butene, trans-2-butene and isobutene.

[0242] The conversion and selectivity data are shown in table 1 and reproduced in FIG. 1. The selectivities at about 85% conversion are compared. The Cr-comprising catalysts (examples 1 and 3) have, within the scatter of the measured values, the same selectivity for butadiene. The completely Cr-free catalyst of example 2 displays a significantly lower selectivity.

TABLE-US-00001 TABLE 1 Selectivities of the catalysts tested in examples 1 to 3 Catalyst Conversion (n-butene) Selectivity (1,3-butadiene) Example 1 85% 84% Example 2 85% 70% Example 3 85% 86%

[0243] FIG. 1 shows conversion-selectivity curves of the catalysts tested as per examples 1 to 3 (* denotes the value for the first operating stage after the start-up phase, # denotes the values of the first operating stage after the first regeneration phase).

Example 5

[0244] Determination of Cr.sup.6+ in Catalyst Samples

[0245] Sample preparation: about 0.4 to 0.6 g of sample of the oxidic mixture are taken at an average temperature of 265 C. during the thermal treatment. In the case of example 1, sampling is carried out during the linear heating-up phase. In the case of examples 2 and 3, sampling is in each case carried out during the calcination in the course of the fourth heating-up phase in which the material is heated to 265 C. over 36 minutes and held at this temperature for 72 minutes. The samples taken in this way are weighed to within 0.1 mg into a 100 ml volumetric flask and made up to the mark with water. After stirring for 4 hours on a magnetic stirrer, the sample is filtered through a fluted filter (water withdrawal).

[0246] An aliquot of the solution is (depending on content) acidified with phosphoric acid and admixed with an excess over Cr.sup.6+ of 1,5-diphenylcarbazide (about 1 ml). Diphenylcarbazide forms a red-violet complex with dissolved Cr.sup.6+ and the concentration of this complex can be determined photometrically. The blank determination is carried out analogously, only without sample.

[0247] After allowing to stand for 15 minutes, the solutions are measured photometrically and the content is determined taking the blank into account.

[0248] FIG. 2 shows the proportions of hexavalent Cr(VI) formed as an intermediate at 265 C. for the catalysts of examples 1 to 3. In the case of example 1, the proportion of Cr(VI) compounds is below the detection limit of 10 ppm by weight. The catalyst of example 2 does not contain any chromium. In the case of example 3, the proportion of Cr(VI) compounds formed as intermediates is about 6200 ppm by weight (based on Cr(VI)).