Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-05-31
2003-08-05
Dunn, Tom (Department: 1725)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S531000, C549S523000, C502S064000, C502S071000, C502S072000
Reexamination Certificate
active
06603027
ABSTRACT:
The invention relates to a novel zeolite-based supported catalyst. It also relates to a process for the manufacture of such a catalyst and to its use in liquid-phase chemical reactions, such as the epoxidation reaction of olefins under the action of hydrogen peroxide.
It is known to use a zeolite as catalyst in olefin epoxidation reactions. Thus, Patent Application EP 100,119 discloses a process for the epoxidation of olefins by means of hydrogen peroxide in the presence of a synthetic zeolite comprising titanium atoms. This synthetic zeolite comprising titanium atoms is known under the name of titanium silicalite and is abbreviated to TS-1.
It is also known that zeolites become deactivated with use and that, consequently, it is necessary regularly to carry out regeneration treatments, generally by washing with solvents or by heating, in order to restore the activity thereof. It is important for the zeolite not to degrade under the regeneration conditions.
It is also known that zeolites, in particular TS-1 obtained according to the process disclosed in the abovementioned patent application, can be composed of very fine particles which it is difficult to separate from the reaction mixture in order to carry out the regeneration thereof. Furthermore, when zeolites, in particular TS-1, are composed of coarse grains, a significant decrease in the catalytic activity of this catalyst, on the one hand, and a poor resistance to attrition of the particles, on the other hand, are observed.
The aim of the invention is to overcome these disadvantages by providing a novel catalyst which has a shape such that it is easy to separate from the reaction mixture, in order to carry out the regeneration thereof, and which exhibits good mechanical properties and a high activity.
The subject-matter of the invention is a catalyst comprising a zeolite deposited on a honeycomb-shaped support. “Honeycomb-shaped” is understood to denote a shape composed of components with a cellular structure, whatever the shape of the cells. The catalyst according to the invention has a level of catalytic activity similar to that of a fine powder and can be regenerated without significant loss of zeolite or of the catalytic activity. More particularly, it has been found that the deposition of a zeolite on a honeycomb-shaped support makes it possible to achieve a very high level of activity, comparable with the level of activity of the fine powder, without, however, having the disadvantages thereof.
The honeycomb-shaped support is advantageously composed of an inert material which withstands the regeneration conditions and on which it is possible to make the zeolite adhere by means of a binder. Silicas are highly suitable as support. It can relate, for example, to silicas combined with other magnesium or aluminium oxides and their mixtures. The support is preferably cordierite or mullite. A particular preference is shown for cordierite because it results in better adhesion of the zeolite to the support. When the catalyst is subsequently regenerated in the presence of an oxidizing agent, such as hydrogen peroxide, a preference is shown for mullite because it exhibits better resistance to such regeneration conditions, which result in acidification of the medium. However, cordierite can also be regenerated in the presence of an oxidizing agent, provided that the pH is maintained during the regeneration at a value of 3 to 4 approximately.
The honeycomb-shaped support is generally provided in the form of a cartridge comprising from 10 to 1200 cells per inch
2
(cpi
2
). The number of cells is preferably from 50 to 450 cpi
2
, for example from 70 to 400 cpi
2
.
Zeolite is understood to denote a solid comprising silica which exhibits a microporous crystalline structure. The zeolite is advantageously devoid of aluminium. The zeolite can comprise titanium. The zeolite according to the invention is preferably a zeolite in which several silicon atoms have been replaced by titanium atoms.
Good results have been obtained with zeolites of titanium silicalite type. The latter advantageously exhibit a crystalline structure of ZSM-5, ZSM-11 or MCM-41 type or of beta type. They preferably exhibit an infrared absorption band at approximately 950-960 cm
−1
.
Those corresponding to the formula xTiO
2
(1-x)SiO
2
in which x is from 0.0001 to 0.5, preferably from 0.001 to 0.05, are highly effective. Materials of this type, known under the name of TS-1, exhibit a microporous crystalline zeolite structure analogous to that of the zeolite ZSM-5. The properties and the main applications of these compounds are known (B. Notari, Structure-Activity and Selectivity Relationship in Heterogeneous Catalysis, R. K. Grasselli and A. W. Sleight Editors, Elsevier, 1991, p. 243-256). Their synthesis has been studied in particular by A. Van der Poel and J. Van Hooff (Applied Catalysis A, 1992, Volume 92, pages 93-111) and by Thangaraj et al. (Zeolites, 12 (1992), 943-950).
The zeolite content in the catalyst according to the invention, expressed as percentage by weight of zeolite in the catalyst, is generally greater than or equal to 1% and less than or equal to 60%. The zeolite content is preferably greater than or equal to 5% and less than or equal to 40%.
The catalyst according to the invention withstands, during phases of conditioning the catalyst or of regeneration, dry heating operations (at 500° C., for example) or heating operations in the presence of solvent, without significant loss of active elements. In addition, hydrogen peroxide, used as oxidizing reactant during the synthesis or as regeneration agent, does not cause significant damage to the catalyst either.
The invention also relates to a process for the manufacture of the above-described catalyst. According to this process, the zeolite is, in a first stage, dispersed in a binder and, in a second stage, the dispersion thus obtained is deposited by impregnation on a honeycomb-shaped support.
The binder employed is generally a silicon-based compound. Mention may be made, by way of examples, of colloidal silicas, silica sols, silicates (for example, tetraalkyl silicates) and silicone resins. Colloidal silicas are preferred. Several grades of colloidal silica may be suitable. They are characterized in particular by the size of the particles, by their specific surface, by their pH and by the nature of the counterion.
The size of the colloidal silica particles is generally between 1 and 30 &mgr;m. The size of the particles is preferably between 5 and 25 &mgr;m. There is a marked preference for particles with a size of between 7 and 20 &mgr;m.
Excessively fine zeolite particles result in a troublesome thixotropy. Excessively coarse particles result in a sedimentation which is too fast for efficient use. The size of the particles is generally greater than or equal to 0.1 &mgr;m and less than or equal to 10 &mgr;m. The size of the particles is advantageously greater than or equal to 1 &mgr;m and less than or equal to 5 &mgr;m.
The colloidal silicas can exhibit an acidic or basic pH. When the pH is acidic, the counterion is advantageously a chloride anion and/or the silica particles can be covered at the surface with a layer of alumina. When the pH is alkaline, the counterion is advantageously a sodium cation or an ammonium cation and/or surface silicon atoms can be replaced by aluminium atoms.
In the first stage of the process according to the invention, a dispersion of the zeolite in a binder is prepared, optionally with stirring. The ratio by weight of the amount of zeolite charged to the amount of binder can vary within a very wide proportion. This ratio is generally less than or equal to 20 and greater than or equal to 0.1. This ratio is preferably less than or equal to 15 and greater than or equal to 0.5. A ratio in the region of 10 makes it possible to limit the amount of material to be deposited on the honeycomb-shaped support while fixing the desired amount of zeolite, without, however, blocking the channels of the support.
It can be advantageous to add water thereto. The amount of water i
Catinat Jean-Pierre
Strebelle Michel
Dunn Tom
Ildebrando Christina
Larson & Taylor PLC
Solvay SA
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