SHELL CATALYST FOR PRODUCING ALKENYL CARBOXYLIC ACID ESTERS HAVING AN IMPROVED PD AND AU DISTRIBUTION

Abstract

The present invention relates to a Pd- and Au-containing shell catalyst which is characterised by an improved Pd and Au distribution. The invention also relates to two methods for producing said catalyst and to a method for producing vinyl acetate monomer using said catalyst.

Claims

1. A Pd- and Au-containing shell catalyst wherein it has a concentration profile of the palladium and of the gold within the shell catalyst where the maximum of the palladium concentration and the maximum of the gold concentration are disposed in a range from 0 to 40 micrometers from the geometric macroscopic surface of the catalyst shaped body and the distance between the maximum of the palladium concentration and the maximum of the gold concentration is in the range from 0 to 10 micrometers.

2. The shell catalyst as claimed in claim 1, wherein the maximum of the Pd concentration and the maximum of the Au concentration are in the range from 5 to 40 micrometers, preferably 5 to 35 micrometers, particularly preferably 5 to 30 micrometers, from the surface of the shell catalyst.

3. The shell catalyst as claimed in claim 1, wherein the distance between the maximum of the palladium concentration and the gold concentration is in the range from 0 to 8 micrometers, preferably in the range from 0 to 5 micrometers.

4. The shell catalyst as claimed in claim 1, wherein the maximum of the Pd concentration is closer to the geometric surface than the maximum of the Au concentration.

5. The shell catalyst as claimed in claim 1, wherein the shell comprising Pd and Au has a thickness of 30 to 200 micrometers, preferably 40 to 180 micrometers, particularly preferably 50 to 160 micrometers, most preferably 60 to 140 micrometers.

6. The shell catalyst as claimed in claim 1, further comprising an alkali metal acetate, preferably potassium acetate.

7. The shell catalyst as claimed in claim 1, wherein the proportion of Pd is in the range from 0.2% to 2.0% by weight, preferably in the range from 0.4% to 1.75% by weight and particularly preferably in the range from 0.7% to 1.5% by weight and the proportion of Au is in the range from 0.1% to 1.2% by weight, preferably in the range from 0.2% to 1.0% by weight and most preferably in the range from 0.3% to 0.8% by weight, in each case based on the total weight of the catalyst shaped body after reduction and loss on drying.

8. A process for producing a Pd- and Au-containing shell catalyst as claimed in claim 1, comprising the steps of: (a) subjecting a bed of a catalyst support to a recirculating motion, wherein the bed is heated to a temperature of 60 C. to 120 C. before or after subjection to the recirculating motion, (b) sequential or simultaneous application of a dissolved Pd-containing precursor compound and a dissolved Au-containing precursor compound by spray application onto the bed of the catalyst support subjected to the recirculating motion, wherein in the case of simultaneous application the temperature is 5 C. to 30 C., preferably 7 C. to 25 C., most preferably 10 C. to 20 C., below the temperature established in step (a) and wherein in the case of sequential application the temperature of the first application is 5 C. to 30 C., preferably 7 C. to 25 C., most preferably 10 C. to 20 C., below the temperature established in step (a).

9. The process as claimed in claim 8, wherein step (b) is followed by a step (c) comprising reduction of the metal components of the precursor compounds to the elemental metals by subjecting the catalyst support body obtained in step (b) to a heat treatment in a non-oxidizing atmosphere.

10. The process as claimed in claim 8, wherein the temperature of the application or in the case of sequential application the temperature of the first application in step (b) is in the range from 55 C. to 115 C., preferably in the range from 55 C. to 110 C., more preferably in the range from 60 C. to 100 C., particularly preferably in the range from 65 C. to 90 C.

11. The process as claimed in claim 8, wherein in step (b) in a first step a dissolved Au-containing precursor compound is applied and in a second step a dissolved Pd-containing precursor compound is applied.

12. A process for producing a Pd- and Au-containing shell catalyst as claimed in claim 1, comprising the steps of: (a) subjecting a bed of a catalyst support to recirculating motion and contacting the bed with atomized water by spray application at a temperature in the range from 55 C. to 110 C.; (b) sequential or simultaneous application of a dissolved Pd-containing precursor compound and a dissolved Au-containing precursor compound by spray application onto the bed of the catalyst support subjected to the recirculating motion, wherein in the case of simultaneous application the temperature is the same as in step (a) and wherein in the case of sequential application the temperature of the first application is the same as in step (a).

13. The process as claimed in claim 12, wherein step (b) is followed by a step (c) comprising reduction of the metal components of the precursor compounds to the elemental metals by subjecting the catalyst support body obtained in step (b) to a heat treatment in a non-oxidizing atmosphere.

14. The process as claimed in claim 12, wherein in step (b) in a first step a dissolved Au-containing precursor compound and in a second step a dissolved Pd-containing precursor compound is applied.

15. A process for producing alkenyl carboxylic esters, in particular VAM or allyl acetate monomer, with the shell catalyst as claimed in claim 1.

Description

[0085] The invention shall now be more particularly elucidated with reference to a plurality of working examples though these shall not be considered limiting.

[0086] FIG. 1 shows by way of example for catalyst 1 a plot of the experimental data points of the Pd concentrations and the sigmoid function determined by means of the same measurement for determining the start of the geometric surface after determination of x.sub.surface.

[0087] FIG. 2 shows a plot of the experimental data points of the Pd concentrations and the curve of catalyst 1 obtained using the appropriate fit function.

[0088] FIG. 3 shows a plot of the experimental data points of the Au concentrations and the curve of catalyst 1 obtained using the appropriate fit function.

[0089] FIG. 4 shows a plot of the curves of the Pd concentrations and the Au concentrations of catalyst 1 obtained using the appropriate fit functions.

[0090] FIG. 5 shows a plot of the curves of the Pd concentrations and the Au concentrations of catalyst 2 obtained using the appropriate fit functions.

[0091] FIG. 6 shows a plot of the curves of the Pd concentrations and the Au concentrations of catalyst 3 obtained using the appropriate fit functions.

[0092] FIG. 7 shows a plot of the selectivities at different space-time yields of the catalysts 1 and 2 and their associated trend lines in the reaction of acetic acid, ethylene and oxygen to afford vinyl acetate monomer.

WORKING EXAMPLES

Methods of Measurement

Pore Volume

[0093] Pore volume was measured by the mercury porosimetry method according to DIN 66133 in a pressure range from 1 to 2000 bar.

BET Surface Area

[0094] BET surface areas were determined according to DIN 66135. To determine micropore volume and micropore surface area the adsorption isotherms of nitrogen at the temperature of liquid nitrogen (77 K) was determined with a Micromeritics ASAP 2020 M instrument.

Element Distribution in Support Material

[0095] The distribution of the Pd and Au in the catalyst shaped body was determined by making a section of the spherical catalyst shaped body by halving the support. This made it possible to determine the spatial distribution of the metal using EDX spectroscopy (energy dispersive X-ray diffraction), also known as EDX spectroscopy (Energy Dispersive X-ray), with the electron microscope. A measuring head which is sensitive to Pd and Au was passed across the sample, thus making it possible to determine the respective distributions thereof along a line from the outer surface towards the middle of the catalyst shaped body.

[0096] Measurement was carried out using a LEO 1530 electron microscope coupled to a Quantax EDX unit with a a Bruker XFlash 4010 detector. Measurement conditions were as follows: [0097] Acceleration voltage (EHT): 20 KV [0098] Aperture: 120 m [0099] Working distance: about 16 mm (Optimum for SEM-EDX geometry) [0100] SEM Detector: SE2 [0101] Magnification: Low (e.g. 55) [0102] Measurement duration: about 10-15 min.

[0103] The starting point of the measurement was set at least 80 m from the outer edge of the sample and the measurement was performed from there over the sample toward the center of the sphere. The line of measurement had a length of 1600 m.

[0104] The measurement for various catalyst geometries is generally carried out such that the starting point of the measurement is set at least 80 m from the original geometric surface of the sample, the sample head is moved from there vertically in the direction of the original geometric surface of the sample and also further over the sample.

[0105] This made it possible to determine the shell thickness of the Pd and the shell thickness of the Au. The inner end of the shell thickness was defined as the point at which the intensity first has a value less than the sum of the braking radiation and three times the standard deviation thereof.

[0106] The start of the geometric surface of the measured catalyst shaped body was determined by fitting the function to the intensities of the braking radiation inside and outside the catalyst shaped body along the measured line at various points

[00003]$I\left(x\right)=\mathrm{base}+\frac{\max }{1+e^{\frac{x_0-x}{\mathrm{rate}}}}$

x. Rate is a measure for the gradient at the inflection point, base corresponds to the intensity I of the braking radiation outside the catalyst shaped body and max corresponds to the intensity I of the braking radiation inside the catalyst shaped body for the region without noble metal loading, i.e. outside the noble metal shell region. The inflection point x.sub.0 of this sigmoid function defines the outer end of the shell and for the subsequent determination of the concentration distribution of the noble metals along the measured line this value x.sub.0 was subtracted from the measured x-values so that all measurement series begin with the point x.sub.surface=0 m of the outer surface. FIG. 1 shows by way of example for catalyst 1 a graphical representation of the measured intensities and the sigmoid function determined by means of the same measurement for determining the start of the geometric surface after determination of x.sub.surface.

[0107] This ensures that a sufficient number of individual catalyst shaped bodies are measured and have their outer surface determined.

[0108] The concentration distribution of the noble metals along the line was determined by calculating the arithmetic average of the intensities at point x from the individual measurements and, from the measured values resulting therefrom, performing a fitting of the concentration distribution of the noble metals using the following Gaussian function.

[00004]$I\left(x\right)=A{e}^{-\frac{x-x_{\max }}{\max }\left(1+e^{\frac{x_{\max }-x}{\mathrm{rate}}}\right)}$ [0109] x.sub.max=position of the peak maximum [0110] A=determines peak height [0111] max=determines asymmetry of the concentration distribution [0112] rate=determines the asymmetry of the concentration distribution

Determination of Elemental Concentrations

[0113] The concentration of the elements was determined by dokimastic digestion via copper cupellation and subsequent ICP-AES analysis and was calculated based on the catalyst shaped body after drying for 2 h at 120 C.

Determination of Hardness

[0114] The hardness of the catalyst shaped body was determined as an average on 99 catalyst shaped bodies using a Dr. Schleuniger Pharmatron AG 8M tablet hardness tester. The catalyst shaped bodies were dried for 2 h at 130 C. before measurement. The instrument settings were as follows: [0115] Hardness: N [0116] Distance to catalyst shaped body: 5.00 mm [0117] Time delay: 0.80 sec [0118] Feed type: 6 D [0119] Speed: 0.60 mm/s

[0120] The following working examples are for elucidation of the invention.

Example 1: Catalyst 1

[0121] 100 g of the bentonite-containing catalyst support material KA-160 (available from Clariant) were weighed in and impregnated with a mixture of 39.3 g of 2 molar KOAc solution and 18.1 g of deionized water according to the pore filling method (incipient wetness). After static drying in the fluidized bed dryer at 90 C. for 35 min the mixture was cooled to room temperature and transferred to an Innojet IAC 025 coater. A process gas was used to set the KOAc-impregnated support into a fluidized bed motion. 36.8 g of deionized water were then sprayed onto the catalyst support at a spray rate rate of 4 g/min. The process air was temperature-controlled to a temperature of 70 C. Subsequently, 7.0 g of an aqueous caesium aurate solution (4.7% by weight Au) was diluted with deionized water to afford 50 g of coating solution and said coating was applied to the catalyst supports in a first coating step at a spray rate of 4 g/min and a process air temperature of 70 C. in the coater. Subsequently in a second coating step a mixture of 2.7 g of an aqueous cesium aurate solution (4.7% by weight Au) and 38.9 g of a tetraammine palladium dihydroxide solution (3.4% by weight Pd) was diluted with deionized water to afford 80 g of coating solution and applied to the catalyst supports at a spray rate of 4 g/min and a process air temperature of 70 C. The catalyst supports continue to be kept in a fluidized bed. After a further static drying in the fluidized bed dryer (90 C./35 min) the catalyst shaped body was subjected to static reduction in a tubular furnace with forming gas (2% H.sub.2 in N.sub.2) at 100 C. for 45 min.

[0122] The elemental analysis of the catalyst shaped body showed the following proportions: [0123] Pd: 1.3% by weight [0124] Au: 0.46% by weight

[0125] Determination of the noble metal distribution was carried out using a scanning electron microscope LEO 1530 provided with an energy dispersive spectrometer from Bruker AXS. To measure the noble metal concentration across the shell thickness a catalyst shaped body was dissected, glued to an aluminum sample holder and subsequently subjected to vapor deposition of carbon. The detector employed was a nitrogen-free silicon drift chamber detector (XFlash 410) with an energy resolution of 125 eV for the manganese K-alpha line.

[0126] The following parameters were used for the measurement: [0127] Scan resolution: 500 dots [0128] Spacing of data points: 1.8 m [0129] Magnification: 200 times [0130] Beam voltage 20 kV [0131] Beam current 20 nA [0132] Input pulse rate: 50 000 pulses/s. [0133] Measurement time for line scan: 200 s

[0134] The shell thickness of 10 spheres of the shell catalyst batch produced as described above was measured.

[0135] The maximum of the Pd concentration was at 23 micrometers and the maximum of the Au concentration was 25 micrometers below the geometric surface of the shell catalyst. The shell thickness for Pd was 130 micrometers and for Au was 93 micrometers. The curve of the Pd concentrations based on the measured values as well as the values obtained by the corresponding fit function is shown in FIG. 2 and the curve of the Au concentrations based on the measured values as well as after adjustment by the corresponding fit function is shown in FIG. 3. FIG. 4 shows both curves of the fitted function, wherein for better comparability the values of the Au concentration have been multiplied by a factor of 7.

Example 2: Catalyst 2

[0136] 100 g of the bentonite-containing catalyst support material KA-160 (available from Clariant) were weighed in and impregnated with a mixture of 39.3 g of 2 molar KOAc solution and 18.1 g of deionized water according to the pore filling method (incipient wetness). After static drying in the fluidized bed dryer at 90 C. for 35 min the mixture was cooled to room temperature and transferred to an Innojet IAC 025 coater. A process gas was used to set the KOAc-impregnated support into a fluidized bed motion. The process air was temperature-controlled to a temperature of 90 C. and held for 2 minutes before commencement of spray-application of a cesium aurate solution. To this end 7.0 g of an aqueous cesium aurate solution (4.7% by weight Au) were diluted with deionized water to afford 50 g of coating solution and said solution was applied to the catalyst support in a first coating step at a spray rate of 4 g/min in the coater, the start of the spraying operation reducing the temperature of the process air by 15 C. from 90 C. and the process air further being actively reduced to 70 C. and then maintained at this temperature. Subsequently in a second coating step a mixture of 2.4 g of an aqueous cesium aurate solution (4.7% by weight Au) and 38.9 g of a tetraammine palladium dihydroxide solution (3.4% by weight Pd) was diluted with deionized water to afford 80 g of coating solution and applied to the catalyst supports at a spray rate of 4 g/min and a process air temperature of 70 C. The catalyst supports continue to be kept in a fluidized bed. After a further static drying in the fluidized bed dryer (90 C./35 min) the catalyst shaped body was subjected to static reduction in a tubular furnace with forming gas (2% H in No) at 100 C. for 45 min.

[0137] The elemental analysis of the catalyst shaped body showed the following proportions: [0138] Pd: 1.3% by weight [0139] Au: 0.43% by weight

[0140] Determination of the noble metal distribution was carried out as in example 1. The maximum of the Pd concentration and the maximum of the Au concentration were 30 micrometers below the geometric macroscopic surface of the shell catalyst. The shell thickness for Pd was 129 micrometers and for Au was 75 micrometers. FIG. 5 shows both the curves of the Pd and Au concentrations based on their fitted function, wherein for better comparability the values of the Au concentration have been multiplied by a factor of 5.

Comparative Example 1: Catalyst 3

[0141] 100 g of the bentonite-containing support material KA-160 (available from Clariant) were weighed in and impregnated with a mixture of 39.3 g of 2 molar KOAc solution and 18.1 g deionized water according to the pore filling method (incipient wetness). After static drying in the fluidized bed dryer at 90 C. for 35 min the mixture was cooled to room temperature and transferred to an Innojet IAC 025 coater. By means of a process gas the KOAc-impregnated support was set into a fluidized bed motion and heated to 70 C. and the temperature maintained for 2 minutes before spray-application of a cesium laurate solution was commenced. To this end 7.0 g of an aqueous cesium aurate solution (4.7% by weight Au) were diluted with deionized water to afford 50 g of coating solution and said solution was applied to the catalyst support in a first coating step at a spray rate of 4 g/min in the coater, the temperature of the process air falling by 15 C. This was increased to 71 C. by active temperature control and maintained at this temperature. Subsequently in a second coating step a mixture of 2.4 g of an aqueous cesium aurate solution (4.7% by weight Au) and 38.9 g of a tetraammine palladium dihydroxide solution (3.48 by weight Pd) was diluted with deionized water to afford 80 g of coating solution and applied to the catalyst supports at a spray rate of 4 g/min and a process air temperature of 70 C. The catalyst supports continue to be kept in a fluidized bed. After a further static drying in the fluidized bed dryer (90 C./35 min) the catalyst was subjected to static reduction in a tubular furnace with forming gas (2% H2 in N2) at 100 C. for 45 min.

[0142] The elemental analysis of the catalyst showed the following proportions: [0143] Pd: 1.3% by weight [0144] Au: 0.43% by weight

[0145] Determination of the noble metal distribution was carried out as in example 1. The maximum of the Pd concentration was at 43 micrometers and the maximum of the Au concentration was 31 micrometers below the surface of the shell catalyst. The shell thickness for Pd was 183 micrometers and for Au was 148 micrometers. FIG. 6 shows both the curves of the Pd and Au concentrations based on their fitted functions, wherein for better comparability the values of the Au concentration have been multiplied by a factor of 8.

Example 3: Reactor Test

[0146] Test results of catalysts 1, 2 and 3 having regard to their activity, selectivity and productivity in the synthesis of vinyl acetate monomer:

[0147] For the catalytic tests in each case 2.9 g of catalyst were filled into a reactor having a volume of 5.7 ml and then heated to 138 C. under an inert gas. At this temperature the inert gas stream was replaced by a stream of acetic acid, ethylene and oxygen that was passed through the reactor. At regular intervals, downstream of the reactor, samples of the output streams were withdrawn and analyzed by gas chromatography. After a reaction time of 24 hours at 138 C. the reactor temperature was increased to 140 C. and maintained for a further 12 hours. This was followed by further temperature increases to 142 C., 144 C., 146 C. and finally back to 140 C. The respective reaction times were 12 hours in each case and the pressure 5-6 barg. The concentrations of the employed components were: 45% ethylene, 6% O.sub.2, 0.9% CO.sub.2, 9% methane, 15.5% acetic acid, residual N.sub.2.

[0148] Table 1 and FIG. 7 show the selectivity/the activity of catalysts 1, 2 and 3 as a function of O.sub.2 conversion. It is clearly apparent therefrom that the catalysts 1 and 2 produced according to the invention have a much higher activity, selectivity (at the same activity level) and productivity than the comparative catalyst catalyst 3. This is additionally elucidated in FIG. 7 which shows a plot of selectivity for VAM as a function of space-time yield.

TABLE-US-00001 TABLE 1 Catalytic test data of catalysts 1 to 3 Temperature Example [ C.] 138 140 142 144 146 140 Pressure 6 6 5 5 5 5 [barg] Catalyst 1 Yield 823 874 825 861 894 766 [g/(L .Math. h)] Selectivity 96.7 96.7 96.7 96.5 96.4 97.2 [%] O.sub.2 73.4 76.9 72.4 75.8 79.7 65.1 conversion [%] Catalyst 2 Yield 808 854 808 843 882 738 [g/(L .Math. h)] Selectivity 96.8 96.8 96.8 96.7 96.5 97.3 [%] O.sub.2 71.2 74.6 70.4 73.9 77.2 62.1 conversion [%] Catalyst 3 Yield 734 783 738 772 809 685 [g/(L .Math. h)] Selectivity 96.9 96.9 96.9 96.7 96.6 97.3 [%] O.sub.2 64.8 68.7 64.4 68.3 71.1 57.8 conversion [%]