Process for production of a zeolite-containing molding

Details Process for production of a zeolite-containing molding Process for production of a zeolite-containing molding

1999-12-06

2002-12-10

Fiorilla, Christopher A. (Department: 1625)

Plastic and nonmetallic article shaping or treating: processes

Outside of mold sintering or vitrifying of shaped inorganic...

Producing microporous article

C264S638000, C264S656000

Reexamination Certificate

active

06491861

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a molding containing at least one porous oxidic material, a process for its production, and its use for the reaction of organic compounds, in particular for the epoxidation of organic compounds having at least one C—C double bond. The molding described herein has high abrasion resistance and excellent mechanical properties.
2. Description of the Background
Abrasion-resistant moldings comprising catalytically active materials are employed in many chemical processes, in particular in processes using a fixed bed. Accordingly, there is a huge wealth of literature on this subject. There is significantly less literature on the use of catalysts based on porous oxidic materials, for example zeolites, and especially relating to the molding of such materials.
For the production of solids, a binder, an organic viscosity-enhancing compound and a liquid for converting the material into a paste are generally added to the catalytically active material, ie. the porous oxidic material, and the mixture is compacted in a mixing or kneading apparatus or an extruder. The resulting plastic material is then molded, in particular using an extrusion press or an extruder, and the resulting moldings are dried and calcined.
A number of inorganic compounds are used as binders.
For example, according to US-A 5,430,000, titanium dioxide or hydrated titanium dioxide is used as the binder. Examples of further prior art binders are:
hydrated alumina or other aluminum-containing binders (WO 94/29408);
mixtures of silicon and aluminum compounds (WO 94/13584);
silicon compounds (EP-A 0 592 050);
clay minerals (JP-A 03 037 156);
alkoxysilanes (EP-B 0 102 544).
The organic viscosity-enhancing substances used are generally hydrophilic polymers, eg. cellulose or polyacrylates.
The Applicant itself, in DE-A 196 23 611.8, furthermore describes an oxidation catalyst having a zeolite structure and molded by compacting shaping processes, and its use in the preparation of epoxides from olefins and hydrogen epoxide, and, in DE-A 196 23 609.6, an oxidation catalyst which is based on titanium or vanadium silicalites having the zeolite structure and which has likewise been molded by compacting shaping processes and contains from 0.01 to 30% by weight of one or more noble metals as defined therein.
In all publications according to the prior art cited above, water is used in the preparation of the moldings described there, as a liquid for converting the material into a paste (pasting agent).
However, the moldings described above and based on a porous oxidic material, for example zeolites and in particular titanium silicalites, have several disadvantages. Thus many of the moldings described in the above literature have insufficient mechanical strength for use as a catalyst in a fixed bed.
This is particularly important when secondary reactions of certain binders are undesirable and for this reason whole classes of binders which can impart sufficient strength to such a molding cannot be used, for example because of other adverse properties. For example, aluminum-containing binders cannot be used in the preparation of titanium silicalite which is used as a catalyst for the epoxidation of, for example, propylene with hydrogen peroxide, since the acidity induced by the aluminum-containing binder results in a greater degree of ring cleavage and formation of by-products. Moreover, titanium-containing binders can lead to high decomposition rates of the hydrogen peroxide used if these titanium-containing binders result in detectable titanium dioxide contents in the molding.
It is also undesirable to use binders which contain >100 ppm of alkali metals or alkaline earth metals. By using such binders, the catalytic activity of, for example, titanium silicalite can be severely adversely affected since the catalytically active Ti centers are inactivated by the alkali metal or alkaline earth metal ions.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide a molding which contains at least one porous oxidic material and has sufficient mechanical stability to be used as a catalyst in a fixed bed. When it is used for catalytic reactions, the activity or selectivity losses due to secondary reactions of the added binder should be avoided in comparison with the prior art catalysts. A process for its production is also provided.
We have found surprisingly, that this object is achieved and, a molding which contains at least one porous oxidic material and exhibits virtually no activity and selectivity losses, or none at all, when used as a catalyst can be obtained if a mixture containing at least one alcohol and water is used as a pasting agent in its production.
Further improved moldings of the type under discussion here are obtained if a metal acid ester or a mixture of two or more thereof is used as the binder in addition to the pasting agent defined above.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, the present invention relates to a molding containing at least one porous oxidic material and obtainable by a process which comprises the following stages:
(I) addition of a mixture containing at least one alcohol and water to a mixture containing a porous oxidic material or a mixture of two or more thereof and
(II) kneading, molding, drying and calcination of the mixture according to stage (I) after addition, and
a process for the production of a molding containing at least one porous oxidic material, which comprises the following stages:
(I) addition of a mixture containing at least one alcohol and water to a mixture containing a porous oxidic material or a mixture of two or more thereof, and
(II) kneading, molding, drying and calcination of the mixture according to stage (I) after addition.
The novel preparation of the moldings described above starting from a porous oxidic material in powder form comprises the formation of a plastic material which contains at least one porous oxidic material, a binder, a mixture containing at least one alcohol and water, if required one or more organic viscosity-enhancing substances and further prior art additives.
The plastic material obtained by thorough mixing, in particular kneading, of the above components is preferably molded by means of extrusion pressing or extruding and the resulting molding is then dried and finally calcined.
There are no particular restrictions with regard to the porous oxidic materials which may be used for the production of the novel molding, as long as it is possible to prepare a molding as described herein starting from these materials.
The porous oxidic material is preferably a zeolite, particularly preferably a titanium-, zirconium-, chromium-, niobium-, iron- or vanadium-containing zeolite, in particular a titanium silicalite.
Zeolites are known to be crystalline aluminosilicates having ordered channel and cage structures which have micropores. The term micropores as used in the present invention corresponds to the definition in Pure Appl. Chem. 45 (1976), p. 71 et seq., in particular p. 79, and denotes pores having a diameter of less than 2 nm. The network of such zeolites is composed of SiO
4
and AlO
4
tetrahedra which are linked via common oxygen bridges. An overview of the known structures is given, for example, by W. M. Meier and D. H. Olson in the Atlas of Zeolite Structure Types, Elsevier, 4th Edition, London 1996.
There are also zeolites which contain no aluminum and in which some of the Si(IV) has been replaced by titanium as Ti(IV) in the silicate lattice. The titanium zeolites, in particular those having a crystal structure of the MFI type, and possibilities for their preparation are described, for example in EP-A 0 311 983 or EP-A 0 405 978. Apart from silicone and titanium, such materials can also contain additional elements, such as aluminum, zirconium, tin, iron, cobalt, nickel, gallium, boron or small amounts of fluorine.
In the zeolites described, some or all of the titanium itself therein may be replaced by vanadium, zirconium, chromium,

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