Chemistry of inorganic compounds – Zeolite – Organic compound used to form zeolite
Reexamination Certificate
2002-02-20
2004-10-19
Sample, David (Department: 1755)
Chemistry of inorganic compounds
Zeolite
Organic compound used to form zeolite
C423S716000, C423S717000, C502S060000, C502S242000
Reexamination Certificate
active
06805851
ABSTRACT:
The present invention relates to an improved process for the preparation of a crystalline solid, comprising at least one zeolitic material, the reaction discharge from the crystallization being fed, directly and without removal of any components, to a continuous drying, the solid per se prepared in this manner and its use as a catalyst, as support material for catalysts, as a sorbent, as a pigment or as a filler for plastics, in particular for the preparation of epoxides from olefins, and in turn the preparation of propylene oxide starting from propene with the use of a hydroperoxide, in particular H2O2.
Zeolites are known to be crystalline aluminosilicates having ordered channel and cage structures whose pore openings are in the range of micropores smaller than 0.9 nm. The network of such zeolites is composed of SiO4- and AlO4-tetrahedra which are linked via common oxygen bridges. An overview of the known structures is to be found, for example, in M. W. Meier, D. H. Olson, Ch. Baerlocher, “Atlas of Zeolite Structure Types”, 4th Edition, Elsevier, London 1996, pages 9 to 229.
Exchangeable cations are present in zeolites in order to compensate the negative electrovalency produced by the incorporation of Al(III) into the Si(IV) silicate lattice; in particular, said cations may be cations of sodium, of potassium, of lithium or of cesium, depending on the preparation process. If these cations are exchanged for protons, for example by an ion exchange, the correspondingly acidic solids having a zeolite structure, i.e. the H-form, are obtained.
Zeolites which contain no aluminum and in which some of the Si(IV) has been replaced by titanium as Ti(IV) in the silicate lattice are also known. These 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 405 978. In addition to silicon and titanium, such materials may also contain additional elements, such as, for example, aluminum, zirconium, tin, iron, cobalt, nickel, gallium, boron or small amounts of fluorine. In the zeolite catalysts used in the novel process, some or all of the titanium of the zeolite may be replaced by vanadium, zirconium, chromium or niobium or a mixture of two or more thereof. The molar ratio of titanium and/or vanadium, zirconium, chromium or niobium to the sum of silicon and titanium and/or vanadium and/or zirconium and/or chromium and/or niobium is as a rule from 0.01:1 to 0.1:1.
It is known that titanium zeolites can be identified from a specific pattern in the determination of the X-ray diffraction diagrams and additionally from a skeletal vibration band in the infrared range at about 960 cm−1 and can thus be distinguished from alkali metal titanates or crystalline or amorphous TiO2 phases.
It is known that titanium zeolites having the MFI structure are suitable as catalysts for oxidation reactions. Thus, for example, EP-A 0 100 118 and EP-A 0 100 119 disclose a process in which propene can be epoxidized in the aqueous phase with hydrogen peroxide over titanium zeolites to give propylene oxide. The preparation of cyclohexanone oxime from cyclohexanone by reaction with ammonia and hydrogen peroxide is described in EP-A 0 208 311. Further reactions used in such catalysts, such as the hydroxylation of aromatics and the oxidation of saturated C2- to C18-hydrocarbons with H2O2 are disclosed in GB-A 2 116 974 and EP-A 0 376 453, respectively.
Typically, the abovementioned titanium zeolites are prepared by reacting an aqueous mixture of an SiO2 source, a titanium oxide and a nitrogen-containing organic base, such as, for example, tetrapropylammonium hydroxide, in the presence or absence of an alkali solution in a pressure-resistant container at elevated temperatures for several hours or a few days, a crystalline product being obtained. This is as a rule filtered off, washed and dried and calcined at elevated temperatures to remove the nitrogen-containing organic phase. In the powder thus obtained, at least some of the titanium is present within the zeolite framework in varying proportions with four-, five- or six-fold coordination (Behrens et al., J. Chem. Soc., Chem. Commun. (1991) 678-680). In order to improve the catalytic behavior, this may be followed by repeated treatment by washing with a solution of hydrogen peroxide in sulfuric acid, after which the titanium zeolite powder has to be dried and calcined again, as described, for example, in EP-A 0 276 362. The titanium zeolite powder thus obtained must finally be processed with addition of suitable binders in a shaping step in order to make it available as a catalyst in a form capable of being handled. One method for this purpose is described in EP-A 0 200 260.
The above-described crystallization of the titanium zeolite from suitable starting materials by hydrothermal reaction is generally carried out at from 50 to 250° C. over a sufficiently long period, an autogenous pressure being established as a function of the temperature.
After the crystallization, there is the problem of separating the desired crystalline solid, having particle sizes of, as a rule, substantially less than 1 &mgr;m, from the strongly alkaline mother liquor still containing organic template. For this purpose, EP-A 0 893 158 describes, in the examples, either the separation by conventional centrifuging and subsequent washing of the solid or the addition of flocculants with subsequent centrifuging. According to this publication, the subsequent drying is carried out by spray-drying or drying by means of fluidized-bed spray granulation. Both the separation of the zeolite from the suspension obtained in the crystallization and the addition of flocculants constitute an additional process step which is time-consuming and expensive.
It is an object of the present invention to provide a process for the preparation of a crystalline solid comprising at least one zeolitic material, which process does not have the abovementioned disadvantages and in particular manages without additional intermediate steps between crystallization and drying.
We have found that this object is achieved by a process for the preparation of a crystalline solid comprising at least one zeolitic material, in which the solid is crystallized from at least one precursor compound and the reaction discharge of the crystallization is fed directly to a drying stage. Here, the term “directly” means that no removal of any components is effected between crystallization and drying, and preferably the product of the crystallization is fed to the drying stage without a further intermediate stage.
The novel drying is preferably effected by means of spray-drying or drying by means of fluidized-bed spray granulation, each of which may be carried out continuously or batchwise. The drying is dried while maintaining a temperature in the range of from 100 to 350° C., preferably from 100 to 250° C., while maintaining the safety conditions necessary in the process, until the free-flowing powder is obtained. The drying is preferably carried out in an atmosphere which comprises oxygen and at least one inert gas. This atmosphere is preferably circulated as a carrier gas stream. Conventional inert gases, such as, for example, nitrogen, carbon monoxide, carbon dioxide, helium and argon or mixtures of two or more thereof, may be used as the inert gas. The oxygen content of the atmosphere is preferably less than 10, more preferably less than 5, % by volume. Furthermore, a stack gas mixture having a COx content which ensures that there are no explosion problems may be used as inert gas, it being possible to obtain such a stack gas mixture by combustion of natural gas for stack gas production and it being possible simultaneously to generate energy for the energy-intensive stages of the process.
In the drying according to the invention, it is essential that the atmosphere be adjusted, in particular with respect to the oxygen content, so that the procedure is carried out safely outside the explosion limits.
If the crystallization d
Hill Friedrich
Möller Ulrich
Rieber Norbert
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sample David
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