Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2001-10-09
2002-07-09
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S531000, C549S532000
Reexamination Certificate
active
06417378
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an epoxidation process using a pre-treated titanium zeolite. The process comprises reacting olefin, hydrogen, and oxygen in the presence of a catalyst comprising a noble metal and a pre-treated titanium zeolite. The zeolite pre-treatment consists of contacting the zeolite with a leaching agent. Surprisingly, the pretreated titanium zeolite shows decreased ring-opening to unwanted glycols and glycol ethers in olefin epoxidation.
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. 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 catalysts that reduce the likelihood of ring-opening of epoxides to glycols or glycol ethers. I have discovered an effective, convenient epoxidation process that reduces unwanted ring-opened products and gives good productivity and selectivity to epoxide.
SUMMARY OF THE INVENTION
The invention is an olefin epoxidation process that comprises reacting olefin, oxygen, and hydrogen in the presence of a catalyst comprising a noble metal and pre-treated titanium zeolite, wherein the pre-treated titanium zeolite is formed by contacting a titanium zeolite with a leaching agent such that greater than 0.1 weight percent of the titanium is removed from the titanium zeolite. I surprisingly found that catalysts produced with the pretreated titanium zeolite give significantly reduced ring-opened by-products compared to untreated titanium zeolite.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention employs a catalyst that comprises a noble metal and pre-treated 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, 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.
Titanium zeolites may also contain impurities of anatase. Although anatase amounts of less than 5 weight percent anatase (compared to the total amount of titanium zeolite) are acceptable, it is preferred that the titanium zeolite is substantially anatase-free.
The pre-treated titanium zeolite is formed by contacting a titanium zeolite with a leaching agent. The leaching agent can be any compound that is capable of removing greater than 0.1 percent of titanium from the titanium zeolite, based on the amount of titanium in the zeolite (i.e., (moles Ti leached)/(moles Ti in zeolite
initial
)>0.1%). Preferred leaching agents include chelating organic compounds such as glycols, carboxylic acid compounds, and hydroxy ketone compounds. Preferred leaching agents also include mineral acids.
Glycols are organic compounds that contain two or more hydroxy functionalities. Suitable glycols include, but are not limited to, glycerol, propylene glycol, ethylene glycol, and the like. Carboxylic acid compounds contain one or more carboxylic acid functionality. Examples of carboxylic acid compounds include, but are not limited to, acetic acid, pyruvic acid, lactic acid, and the like. Hydroxy ketone compounds contain one or more hydroxy functionality and one or more ketone functionality. Examples of hydroxy ketone compounds include, but are not limited to, acetol, 2-hydroxyacetophene, 2′-hydroxyacetophenone, and the like. Suitable mineral acids include sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, and the like. Particularly preferred chelating organic compounds include propylene glycol and lactic acid. The leaching agent may also consist of a combination of hydrogen peroxide and a chelating organic compound.
The titanium zeolite pre-treatment can be performed at room temperature, however elevated temperatures greater than 40° C. ar
Arco Chemical Technology L.P.
Carroll Kevin M.
Trinh Ba K.
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