Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-07-25
2001-10-23
Keys, Rosalynd (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S523000, C549S524000
Reexamination Certificate
active
06307073
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a liquid-phase epoxidation process using a mixed catalyst system to produce epoxides from hydrogen, oxygen, and olefins. The mixed catalyst system contains a titanium zeolite and a gold-containing supported catalyst. Surprisingly, this reaction is performed in the absence of palladium, which has typically been required in previous liquid-phase direct oxidation processes.
BACKGROUND OF THE INVENTION
Many different methods for the preparation of epoxides have been developed. Generally, epoxides are formed by the reaction of an olefin with an oxidizing agent in the presence of a catalyst. The production of propylene oxide from propylene and an organic hydroperoxide oxidizing agent, such as ethyl benzene hydroperoxide or tert-butyl hydroperoxide, is commercially practiced technology. This process is performed in the presence of a solubilized molybdenum catalyst, see U.S. Pat. No. 3,351,635, or a heterogeneous titania on silica catalyst, see U.S. Pat. No. 4,367,342. Hydrogen peroxide is another oxidizing agent useful for the preparation of epoxides. Olefin epoxidation using hydrogen peroxide and a titanium silicate zeolite is demonstrated in U.S. Pat. No. 4,833,260. One disadvantage of both of these processes is the need to pre-form the oxidizing agent prior to reaction with olefin.
Another commercially practiced technology is the direct epoxidation of ethylene to ethylene oxide by reaction with oxygen over a silver catalyst. Unfortunately, the silver catalyst has not proved very useful in epoxidation of higher olefins. Therefore, much current research has focused on the direct epoxidation of higher olefins with oxygen and hydrogen in the presence of a catalyst. In this process, it is believed that oxygen and hydrogen react in situ to form an oxidizing agent. Thus, development of an efficient process (and catalyst) promises less expensive technology compared to the commercial technologies that employ pre-formed oxidizing agents.
Many different catalysts have been proposed for use in the direct epoxidation of higher olefins. For liquid-phase reactions, the catalysts typically contain palladium which promotes the formation of the in situ oxidizing agent. For example, JP 4-352771 discloses the epoxidation of propylene oxide from the reaction of propylene, oxygen, and hydrogen using a catalyst containing a Group VIII metal such as palladium on a crystalline titanosilicate. The vapor-phase oxidation of olefins has been shown to produce epoxides over gold supported on titanium oxide (Au/TiO
2
or Au/TiO
2
-SiO
2
), see for example U.S. Pat. No. 5,623,090, and gold supported on titanosilicates, see for example PCT Intl. Appl. WO 98/00413. U.S. Pat. No. 5,623,090 also demonstrates that the Au/TiO
2
-SiO
2
catalyst is useful for the epoxidation of olefins in hydrocarbon solvents such as benzene (see Example 7).
One disadvantage of the described direct epoxidation catalysts is that they all show either less than optimal selectivity or productivity. As with any chemical process, it is desirable to develop new direct epoxidation methods and catalysts.
I have discovered an effective, convenient epoxidation process using a mixed catalyst system that gives good productivity and selectivity to epoxide.
SUMMARY OF THE INVENTION
The invention is an olefin epoxidation process that comprises reacting an olefin, oxygen, and hydrogen in an oxygenated solvent in the presence of a catalyst mixture comprising a titanium zeolite and a supported gold-containing catalyst. Although neither of the catalysts alone produce epoxide, it is surprisingly found that the catalyst mixture produces epoxide with high selectivity and productivity.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention employs a catalyst mixture that comprises a titanium zeolite and a supported catalyst comprising gold and a support. Suitable titanium zeolites are those crystalline materials having a porous molecular sieve structure with titanium atoms substituted in the framework. The choice of titanium zeolite employed will depend upon a number of factors, including the size and shape of the olefin to be epoxidized. For example, it is preferred to use a relatively small pore titanium zeolite such as a titanium silicalite if the olefin is a lower aliphatic olefin such as ethylene, propylene, or 1-butene. Where the olefin is propylene, the use of a TS-1 titanium silicalite is especially advantageous. For a bulky olefin such as cyclohexene, a larger pore titanium zeolite such as a titanium zeolite having a structure isomorphous with zeolite beta may be preferred.
Titanium zeolites comprise the class of zeolitic substances wherein titanium atoms are substituted for a portion of the silicon atoms in the lattice framework of a molecular sieve. Such substances are well known in the art.
Particularly preferred titanium zeolites include the class of molecular sieves commonly referred to as titanium silicalites, particularly “TS-1” (having an MFI topology analogous to that of the ZSM-5 aluminosilicate zeolites), “TS-2” (having an MEL topology analogous to that of the ZSM-11 aluminosilicate zeolites), and “TS-3” (as described in Belgian Pat. No. 1,001,038). Titanium-containing molecular sieves having framework structures isomorphous to zeolite beta, mordenite, ZSM-48, ZSM-12, and MCM-41 are also suitable for use. The titanium zeolites preferably contain no elements other than titanium, silicon, and oxygen in the lattice framework, although minor amounts of boron, iron, aluminum, sodium, potassium, copper and the like may be present.
Preferred titanium zeolites will generally have a composition corresponding to the following empirical formula xTiO
2
(1−x)SiO
2
where x is between 0.0001 and 0.5000. More preferably, the value of x is from 0.01 to 0.125. The molar ratio of Si:Ti in the lattice framework of the zeolite is advantageously from 9.5:1 to 99:1 (most preferably from 9.5:1 to 60:1). The use of relatively titanium-rich zeolites may also be desirable.
The catalyst mixture employed in the process of the invention also contains a supported catalyst comprising gold and a support. The support is an inorganic oxide that contains titanium or zirconium. The amount of titanium or zirconium present in the support is preferably in the range of from about 0.1 to about 75 weight percent. Preferred supports include titania, zirconia, amorphous titania-silica, Ti/MCM-41, Ti-MCM-48, Ti/SBA-15, and ETS-10.
The supported catalyst useful in the process of the invention also contains gold. The typical amount of gold present in the catalyst will be in the range of from about 0.01 to 20 weight percent, preferably 0.01 to 10 weight percent, and most preferably 0.01 to 5 weight percent. While various methods known to those skilled in the art may be used, preferably the gold may be supported by a deposition-precipitation method in which a gold compound is deposited and precipitated on the surface of the support by controlling the pH and temperature of the aqueous gold solution (as described in U.S. Pat. No. 5,623,090).
There are no particular restrictions regarding the choice of gold compound used in the preparation of the supported catalyst. For example, suitable compounds include gold halides (e.g., chlorides, bromides, iodides), cyanides, and sulfides. Chloroauric acid is particularly useful.
The titanium zeolite and the supported catalyst may be used in the epoxidation process as a mixture of powders or as a mixture of pellets. In addition, the titanium zeolite and supported catalyst may also be pelletized or extruded together prior to use in epoxidation. If pelletized or extruded together, the catalyst mixture may additionally comprise a binder or the like and may be molded, spray dried, shaped or extruded into any desired form prior to use in epoxidation. The weight ratio of titanium zeolite:supported catalyst is not particularly critical. However, a titanium zeolite:supported catalyst ratio of 0.01-100 (grams of titanium zeolite per gram of supported catalyst) is preferred.
The process of the
Arco Chemical Technology L.P.
Carroll Kevin M.
Keys Rosalynd
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