Direct epoxidation process using carbonate modifiers

Details Direct epoxidation process using carbonate modifiers Direct epoxidation process using carbonate modifiers

2001-11-15

2002-06-04

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

06399794

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an epoxidation process using a carbonate-containing modifier. The process comprises reacting olefin, hydrogen, and oxygen in the presence of a modifier and a catalyst comprising a noble metal and a titanium zeolite. The modifier is (a) calcium carbonate in the presence of carbon dioxide or (b) ammonium bicarbonate. Surprisingly, the process results in higher activity and selectivity to epoxide, as well as increased catalyst life.
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 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. U.S. Pat. No. 5,859,265 discloses a catalyst in which a platinum metal, selected from Ru, Rh, Pd, Os, Ir and Pt, is supported on a titanium or vanadium silicalite. Additionally, it is disclosed that the catalyst may also contain additional elements, including Fe, Co, Ni, Re, Ag, or Au.
One disadvantage of the described direct epoxidation catalysts is that they are prone to ring-open the epoxide product under standard reaction conditions to form less desirable ring-opened by-products such as glycols or glycol ethers. U.S. Pat. No. 6,008,388 describes a direct olefin epoxidation process in which the selectivity for the reaction of olefin, oxygen, and hydrogen in the presence of a noble metal-modified titanium zeolite is greatly enhanced by the addition of a nitrogen compound to the reaction mixture. Also, increasing the catalyst activity as well as maximizing the catalyst life are important objectives in order to achieve an economical process. As with any chemical process, it is desirable to develop new direct epoxidation methods and catalysts.
In sum, new processes for the direct epoxidation of olefins are needed. Especially desirable are processes that increase activity, selectivity to the epoxide, as well as improving catalyst life. I have discovered an effective, convenient epoxidation process that reduces unwanted ring-opened products, increases catalyst activity, and improves catalyst life.
SUMMARY OF THE INVENTION
The invention is an olefin epoxidation process that comprises reacting olefin, oxygen, and hydrogen in the presence of a modifier and a catalyst comprising a noble metal and titanium zeolite. The modifier is either (a) calcium carbonate in the presence of carbon dioxide or (b) ammonium bicarbonate. This process surprisingly gives significantly reduced ring-opened by-products, and increased catalyst activity and life compared to processes that do not use the modifier.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention employs a catalyst that comprises a noble metal and titanium zeolite. 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 employed in the process of the invention also contains a noble metal. While any of the noble metals can be utilized (i.e., gold, silver, platinum, palladium, iridium, ruthenium, osmium), either alone or in combination, palladium is particularly desirable. Typically, the amount of noble metal present in the catalyst will be in the range of from 0.01 to 20 weight percent, preferably 0.05 to 10 weight percent.
The manner in which the noble metal is incorporated into the catalyst is not considered to be particularly critical. For example, the noble metal may be supported on the titanium zeolite by impregnation, adsorption, ion-exchange, precipitation. Alternatively, the noble metal may be first supported on another support such as an inorganic oxide, inorganic chloride, carbon, or organic polymer resins, or the like, and then physically mixed with the titanium zeolite. Preferred inorganic oxides include oxides of Group 2, 3, 4, 5, 6, 13, or 14 elements. Particularly preferred inorganic oxide supports include silica, alumina, titania, zirconia, niobium oxides, tantalum oxides, molybdenum oxides, tungsten oxides, amorphous titania-silica, amorphous zirconia-silica, amorphous niobia-silica, and the like. Preferred organic polymer resins include polystyrene, styrene-divinylbenzene copolymers, crosslinked polyethyleneimines, and polybenzimidizole. Suitable supports also include organic polymer resins grafted onto inorganic oxide supports, such as polyethylenimine-silica. Preferred supports also include c

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