Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
1999-09-24
2004-11-23
Nguyen, Cam N. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S242000, C502S243000, C502S253000, C502S262000, C502S326000, C502S328000, C502S339000, C502S340000, C502S344000, C502S407000, C502S439000
Reexamination Certificate
active
06821922
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a supported catalyst based on pyrogenically produced mixed oxide, which catalyst is in particular suitable for the production of vinyl acetate monomer (VAM).
BACKGROUND OF THE INVENTION
Pyrogenically produced oxides are distinguished by extreme fineness and a correspondingly elevated specific surface area, very high purity, spherical particle shape and the absence of pores. Due to these properties, there is increasing interest in pyrogenically produced oxides as supports for catalysts (D. Koth, H. Ferch, Chem. Ing. Techn. 52, 628 (1980)). In some cases, pyrogenic oxides are also used as a catalyst.
Since pyrogenically produced oxides are particularly finely divided, shaping them into catalyst supports or catalysts occasions some difficulties.
It is known from DE-B 21 00 778 to use pellets based on pyrogenically produced silicon dioxides as catalyst supports in the production of vinyl acetate monomer.
Further production processes for the production of vinyl acetate monomer are known from the documents DE 16 68 088, U.S. Pat. No. 4,048,096, EP-A 0 519 435, EP-A 0 634 208, EP-A 0 723 810, EP-A 0 634 209, EP-A 0 632 214, EP-A 0 654 301 and EP-A 0 723 810. These documents also describe processes for the production of supported catalysts. Depending upon the embodiment, supported catalysts are obtained which have a homogeneous distribution of noble metal over the support cross-section and have a more or less pronounced shell profile.
EP-A 0 723 810 describes a pretreatment method for catalyst supports for the production of vinyl acetate monomer with elements of groups IA, IIA, IIIA and IVB of the periodic system.
The disadvantage of these prior art processes is that they give rise to catalysts which result in an unfavorable relationship of selectivity and activity in the production of vinyl acetate monomer.
It is known to produce pyrogenic mixed oxides by simultaneously reacting at least two different metals in the form of volatile metal compounds, for example chlorides, in a H
2
/O
2
flame. One example of such an oxide is the SiO
2
/Al
2
O
3
mixed oxide, which is produced by Degussa-Hüls AG, Germany, and sold under the tradename AEROSIL® MOX 170. When producing AEROSIL® MOX 170, a mixture of SiCl
4
and AlCl
3
is directly hydrolyzed in a flame. Corresponding silanes, such as for example methyltrichlorosilane, trichlorosilanes etc. may also be used as a raw material instead of or in addition to the chlorides. (Degussa Technical Bulletin Pigments, No. 11: Basic Characteristics of AEROSIL®, pages 37 and 11-12; AT-A 195 893; DE-A 952 891; DE-A 25 33 925; DE-A 27 02 896).
SUMMARY OF THE INVENTION
The present invention uses novel moldings based on pyrogenically produced mixed oxide having the following physicochemical parameters:
External diameter
0.8-25 mm
BET surface area
5-400 m
2
/g
Pore volume
0.2-1.8 ml/g
Fracture strength
5 to 350 N
Composition
At least two members selected from the group
SiO
2
, Al
2
O
3
, TiO
2
and ZrO
2
in any
desired combination, but with
the exception of SiO
2
/Al
2
O
3
mixed
oxides, in which >75 wt. % of SiO
2
is
present.
Other constituents
<1 wt. %
Bulk density
250-1500 g/l
The moldings according to the invention may be present as extruded moldings, extrudates or tablets. They may assume the form of cylinders, cylinders having rounded end faces, spheres, rings, wagon wheels, miniliths or other shapes conventional for fixed bed catalysts.
The moldings according to the invention based on pyrogenically produced mixed oxide having the following physicochemical parameters:
External diameter
0.8-25 mm
BET surface area
5-400 m
2
/g
Pore volume
0.2-1.8 ml/g
Fracture strength
5-350 N
Composition
At least two members selected from the group
SiO
2
, Al
2
O
3
, TiO
2
and ZrO
2
in any
desired combination, but with the
exception of SiO
2
/Al
2
O
3
mixed oxides,
in which >75 wt. % of SiO
2
is present.
Other constituents
<1 wt. %
Bulk density
250-1500 g/l,
may be produced by homogenizing pyrogenically produced mixed oxide as desired with one or more compounds selected from the group methylcellulose, methylhydroxyethylcellulose, wax, magnesium stearate, aluminium stearate and polyethylene glycol with addition of water, drying the product at a temperature of 70°-150° C., optionally comminuting it to yield a powder, compressing the powder to yield moldings and performing heat treatment for a period of 0.5 to 10 hours at a temperature of 400° to 1200° C.
The moldings according to the invention may be produced in stamping presses, eccentric presses, isostatic presses, extrusion presses, rotary presses or compactors.
Before pressing, one particular embodiment of the invention may exhibit the following composition:
mixed oxide
50-90 wt. %
methylhydroxyethylcellulose
0.1-20 wt. %, preferably
5-15 wt. %
wax
0.1-15%, preferably 5-12 wt. %
polyethylene glycol
0.1-15%, preferably
5-10 wt. %
Fracture strength, specific total surface area and pore volume may be adjusted to a certain extent by varying the quantities of starting materials and the compression pressure.
Alternatively, the moldings according to the invention based on pyrogenically produced mixed oxide having the following physicochemical parameters:
External diameter
0.8-25 mm
BET surface area
5-400 m
2
/g
Pore volume
0.2-1.8 ml/g
Fraction strength
5-350 N
Composition
At least two members selected from the group
SiO
2
, Al
2
O
3
, TiO
2
and ZrO
2
in any
desired combination but with the
exception of SiO
2
/Al
2
O
3
mixed oxides,
in which >75 wt. % of SiO
2
is
present.
Other constituents
<1 wt. %
Bulk density
250-1500 g/l,
may be produced by homogenizing pyrogenically produced mixed oxide as desired with one or more compounds from the group methylcellulose, methylhydroxyethylcellulose, wax, magnesium stearate, aluminium stearate and/or polyethylene glycol with addition of water, subjecting the product to a kneading and shaping process, extruding it, optionally chopping the extrudates to the desired length by means of a chopping device, drying the product at a temperature of 70°-150° C. and performing heat treatment for a period of 0.5 to 10 hours at a temperature of 400° to 1200° C.
Any mixers or mills which permit good homogenization, such as for example blade mixers, fluidized bed mixers, centrifugal mixers or air-swept mixers, are suitable for performing the process according to the invention. Particularly suitable mixers are those with which the material being mixed may additionally be compacted, such as for example plough bar mixers, pan mills or ball mills. Mixing and kneading may, however, also proceed directly in an extruder. The extrudates may also be produced in single or twin-screw extruders, extrusion presses as well as in compactors.
After homogenization, the product may be largely dried at 70°-150° C., such that, after an optional comminution operation, a pourable powder is obtained.
The moldings according to the invention may be used either directly as a catalyst or as a catalyst support.
One object of the present invention is to provide a supported catalyst which, with identical or improved selectivity, exhibits greater activity than known catalysts.
The present invention accordingly provides a supported catalyst which contains palladium and/or the compounds and alkali metal compounds thereof, as well as additionally gold and/or the compounds thereof (Pd/alkali metal/Au system) or cadmium and/or the compounds thereof (Pd/alkali metal/Cd system) or barium and/or the compounds thereof (Pd/alkali metal/Ba system) or palladium, alkali metal compounds and mixtures of gold and/or cadmium and/or barium as the catalytically active components on a support or molding, characterized in that the support is based on pyrogenically produced mixed oxide having the following physicochemical parameters:
External diameter
0.8-25 mm
BET surface area
5-400 m
2
/g
Pore volume
0.2-1.8 ml/g
Fracture strength
5-350 N
Composition
At least two members selected from the group
SiO
2
, Al
2
O
3
, TiO
2
and ZrO
2
in
any desired combination
but with the except
Daly Francis
Krause Helmfried
Lansink Rotgerink Hermanus G. J.
Mangold Helmut
Reisinger Martin
Degussa - HULS AG
Nguyen Cam N.
Smith , Gambrell & Russell, LLP
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