Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Utility Patent
1999-03-08
2001-01-02
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S470000, C568S471000, C568S475000, C502S304000, C502S305000, C502S439000, C502S523000
Utility Patent
active
06169214
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the preparation of a catalyst which consists of a carrier and a catalytically active oxide material applied to the surface of the carrier, in which the carrier is first moistened with an adhesive liquid (a liquid binder), a layer (coat) of active oxide material is then bound (applied) to the surface of the moistened carrier by bringing it into contact with dry, finely divided, active oxide material, and the adhesive liquid is then removed from the moistened carrier coated with active oxide material.
The present invention furthermore relates to catalysts which consist of a carrier and a catalytically active oxide material applied to the surface of the carrier and which are defined as coated catalysts, and to the use of such coated catalysts.
BACKGROUND OF THE INVENTION
It is generally known that oxidative chemical reactions can often advantageously be carried out in the gas phase over catalytically active oxides. Thus, DE-A 23 51 151 relates to the catalytic oxidation, ammoxidation and oxidative dehydrogenation of olefins of 3 to 5 carbon atoms over a catalytically active oxide material in the gas phase. Embodiments are, for example, the conversion of butadiene to maleic anhydride, of propene to acrolein, of acrolein to acrylic acid, of propene to acrylonitrile and of 2-butene to butadiene. DE-A 16 42 921 and DE-A 21 06 796 describe the catalytic gas phase oxidation of aromatic and unsatured hydrocarbons, naphthalene, o-xylene, benzene or n-butene to carboxylic acids or anhydrides thereof. Embodiments are, for example, the conversion of o-xylene to phthalic anhydride and of butadiene to maleic anhydride. DE-A 25 26 238 discloses that acrylic acid or methacrylic acid can be produced by catalytic gas-phase oxidation of acrolein or methacrolein over catalytically active oxide materials. DE-A 20 25 430 relates to the catalytic gas-phase oxidation of indanes to, for example, anthraquinone. In addition to oxygen, the catalytically active oxide material may contain only one other element or more than one other element (multielement oxide materials).
Catalytically active oxide materials which comprise more than one metallic element, in particular more than one transition metal, are particularly frequently used. In this case, the term multimetal oxide materials is used. Usually, multi-element oxide materials are not simple physical mixtures of oxides of the elemental constituents but heterogeneous mixtures of complex polycompounds of these elements.
As a rule, such catalytic gas-phase oxidations are carried out on a large industrial scale in fixed-bed reactors, ie. the reaction gas mixture flows through a fixed catalyst bed and the oxidative chemical reaction takes place during the residence time therein.
Most catalytic gas-phase oxidations are highly exothermic and are therefore advantageously carried out in practice in multiple contact tube fixed-bed reactors. The contact tube length is usually a few meters and the internal diameter of the contact tube is usually a few centimeters. Heat exchange media flowing around the contact tubes remove the process heat (cf. for example DE-A 44 31 957 and DE-A 44 31 949).
Fixed beds comprising finely divided, pulverulent, catalytically active oxide material are not very suitable for carrying out catalytic gas-phase oxidations since they are not usually capable of withstanding industrial loading with starting reaction gas mixture without hydraulic transport.
This means that the catalytically active oxide material is usually converted into moldings whose length is tailored to the internal diameter of the contact tube and is as a rule a few millimeters.
U.S. Pat. No. 4,366,093 generally recommends hollow cylinders (rings) as the preferred geometry of such moldings. The height and external diameter should be from 3 to 6 mm and the wall thickness from 1 to 1.5 mm. The only shaping methods considered by U.S. Pat. No. 4,366,093 are pelletizing or extrusion to give unsupported catalysts (the total hollow cylinder consists of catalytically active material which may be diluted with finely divided, inert material) or impregnation of carrier rings to give support catalysts. The disadvantage of annular unsupported catalysts having a wall thickness of ≦1.5 mm is that the mechanical stability during introduction into the contact tube is not completely satisfactory. The disadvantage of supported catalysts is that they are limited to those oxidic active materials which can be formed from solutions. In addition, a single impregnation results only in slight absorption of active materials.
U.S. Pat. No. 4,438,217 and U.S. Pat. No. 4,522,671 recommend unsupported catalyst rings which have an external diameter of from 3 to 10 mm, an internal diameter which is from 0.1 to 0.7 times the external diameter and a height which is from 0.5 to 2 times the external diameter and are based on multimetal oxides containing molybdenum as the main component, for the preparation of acrolein or methacrolein by gas-phase catalytic oxidation. With a view to the required mechanical stability, 1 mm is considered to be just possible as a lower limit of the wall thickness. However, the disadvantage of larger wall thicknesses is that they are associated with an increase in the diffusion distance out of the reaction zone, which promotes undesirable secondary reactions and hence reduces the selectivity with respect to the desired product.
U.S. Pat. No. 4,537,874 likewise recommends catalyst beds comprising unsupported catalyst rings based on multimetal oxides containing molybdenum as the main component for the preparation of &agr;,&bgr;-monoethylenically unsaturated aldehydes by gas-phase catalytic oxidation. The wall thickness of the hollow cylinders is 2 mm in all examples.
Annular coated catalysts help to resolve the contradiction which exists in the case of unsupported catalyst rings between required mechanical stability (increasing wall thickness) on the one hand and limitation of the diffusion distance out of the reaction zone (decreasing wall thickness) on the other hand, while maintaining the otherwise particularly advantageous ring geometry. The mechanical stability is ensured by the annular carrier, and the catalytically active oxide material can be applied in the desired layer thickness to the ring surface.
However, a very general problem in the case of coated catalysts is their production on an industrial scale, ie. they are to be prepared on an industrial scale in such a way that
they have the layer thickness required with regard to the catalyst activity,
the catalytically active coat adheres satisfactorily in the required thickness to the surface of the carrier,
the coat thickness shows very slight fluctuations over the surface of a carrier,
the coat thickness shows very slight fluctuations over the surface of different carriers,
the size of the specific, catalytically active surface area based on the mass unit of the active material is satisfactory and
the output of the production process is satisfactory.
This applies in particular in the case of hollow cylindrical carriers whose rolling behavior, in contrast to carrier spheres, has a preferred direction and is responsible for the prior art processes for the preparation of coated catalysts having catalytically active oxide materials being essentially limited to spherical coated catalysts.
DE-A 20 25 430 discloses that coated catalysts based on catalytically active oxide materials can be prepared by applying the catalytically active material to the carrier by the plasma spray or flame spray method. The disadvantage with regard to the suitability of this method is that at least one main component must be fusible at the working temperature of the flame spray or plasma burner. Another disadvantage of this method is that the size of the specific catalytically active surface area is as a rule unsatisfactory. All embodiments of DE-A 20 25 430 are spherical coated catalysts. As a comparative example, DE-A 20 25 430 includes a process for the preparation of spherica
Linden Gerd
Tenten Andreas
Weidlich Peter
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Padmanabhan Sreeni
LandOfFree
Catalyst consisting of a hollow cylindrical carrier having a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Catalyst consisting of a hollow cylindrical carrier having a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Catalyst consisting of a hollow cylindrical carrier having a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2532276