Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2001-10-19
2002-08-27
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S532000
Reexamination Certificate
active
06441204
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 to palladium on a niobium-containing support.
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 on a titanium zeolite support. 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.
Mixed catalyst systems for olefin epoxidation with hydrogen and oxygen have also been disclosed. For example, JP 4-352771 at Example describes the use of a mixture of titanosilicate and Pd/C for propylene epoxidation. U.S. Pat. No. 6,008,388 also describes a catalyst in which palladium is typically added to a titanium zeolite to form a catalyst system, but additionally teaches that the palladium can be incorporated into a support before mixing with the zeolite. However, the only supports that are disclosed include silica, alumina, and activated carbon. In addition, copending Appl. Ser. No. 09/624,942 discloses a mixed catalyst system that is useful in olefin epoxidation comprising a titanium zeolite and a gold-containing supported catalyst.
One disadvantage of the described direct epoxidation catalysts is that they all show either less than optimal selectivity or productivity. An additional disadvantage is that they are prone to ring-open under standard reaction conditions to form less desirable ring-opened products such as glycols or glycol ethers. As with any chemical process, it is desirable to develop new direct epoxidation methods and catalysts.
In sum, new processes for the direct epoxidatioh of olefins are needed. Especially desirable are new catalyst systems that are useful in the process. 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 catalyst comprising palladium on a niobium-containing support. The new catalyst mixture is useful in the epoxidation of olefins with hydrogen and oxygen.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention employs a catalyst mixture that comprises a titanium zeolite and a supported catalyst comprising palladium and a support, wherein the support is a niobium-containing inorganic oxide. 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, ZSM48, 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. The supported catalyst comprises palladium and a support, wherein the support is a niobium-containing inorganic oxide. Suitable niobium-containing inorganic oxide supports include niobium oxides and niobium mixed oxides. Niobium oxides include oxides of niobium wherein the valency of niobium is 2 to 5. Suitable niobium oxides include such oxides as NbO, Nb
2
O
3
, NbO
2
, and Nb
2
O
5
. Niobium mixed oxides such as niobium oxide-silica, niobium oxide-alumina, and niobium oxide-titania may also be used. The amount of niobium present in the support is preferably in the range of from about 0.1 to about 86 weight percent. Preferred niobium-containing inorganic oxide supports include Nb
2
O
5
and niobium oxide-silica.
The catalyst employed in the process of the invention also contains palladium. The typical amount of palladium 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. The manner in which the palladium is incorporated into the catalyst is not considered to be particularly critical. For example, the palladium (for example, Pd tetraamine bromide) may be supported on the niobium-containing inorganic oxide support by impregna
Arco Chemical Technology L.P.
Carroll Kevin M.
Trinh Ba K.
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