Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-04-27
2001-02-27
Aulakh, Charanjit S. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C502S066000, C502S262000, C549S531000, C549S523000
Reexamination Certificate
active
06194591
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an epoxidation process using a modified titanium zeolite catalyst and hydrogen peroxide in water solvent. Surprisingly, the modified catalyst shows improved activity in aqueous olefin epoxidation compared to the unmodified catalyst.
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, 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. Another commercially practiced technology is the direct epoxidation of ethylene to ethylene oxide by reaction with oxygen over a silver catalyst.
Much current research is conducted in the direct epoxidation of olefins with oxygen and hydrogen. For example, JP 4-352771 discloses the formation of propylene oxide from propylene, oxygen, and hydrogen using a catalyst containing a Group VIII metal such as palladium on a crystalline titanosilicate. The Group VIII metal is believed to promote the reaction of oxygen and hydrogen to form an in situ oxidizing agent. 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. Other direct epoxidation catalyst examples include gold supported on titanosilicates, see for example PCT Intl. Appl. WO 98/00413.
Besides oxygen and alkyl hydroperoxides, another oxidizing agent useful for the preparation of epoxides is hydrogen peroxide. U.S. Pat. No. 4,833,260, for example, discloses olefin epoxidation using hydrogen peroxide and a titanium silicate zeolite. The preferred solvent for this reaction is water due to the cost and availability of aqueous hydrogen peroxide. However, the reaction in water proceeds at low rates and a co-solvent is necessary to give sufficient productivity to epoxide. Clerici, et al.,
J. Catal
. (1991) 129, 159, for example, teach that a water concentration above 50 weight percent considerably decreases the rate of reaction in propylene epoxidation. The Clerici article also teaches that methanol is considered the best solvent for the epoxidation of propylene. Thus, one distinct disadvantage of olefin epoxidation with hydrogen peroxide by titanium zeolites is the need for expensive co-solvents. This requirement results in additional expense for olefin epoxidation processes using hydrogen peroxide.
In sum, new processes that would allow the aqueous epoxidation of olefins using hydrogen peroxide are needed. Particularly valuable processes would result in increased productivity to epoxide.
SUMMARY OF THE INVENTION
The invention is an olefin epoxidation process that comprises reacting an olefin with hydrogen peroxide in water solvent in the presence of a modified titanium zeolite catalyst. The modified catalyst comprises a titanium zeolite chemically treated with the addition of palladium, platinum, or copper compounds. We surprisingly found that the modified catalysts give significantly higher activity in the aqueous epoxidation of olefins compared to unmodified catalysts.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention employs a catalyst that comprises a titanium zeolite chemically treated with a platinum, palladium, or copper modifier. 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 titanium zeolite catalyst is chemically modified by treatment with a palladium, platinum, or copper compound, or mixtures thereof. We surprisingly found that modification of the titanium zeolite is crucial for improving the activity of titanium zeolite catalysts in olefin epoxidation reactions with hydrogen peroxide in water.
There are no particular restrictions regarding the choice of palladium, platinum or copper compounds used as the modifier. For example, suitable compounds include the nitrates, sulfates, halides (e.g., chlorides, bromides), carboxylates (e.g., acetate), and amine complexes of palladium; the halides, acetylacetonates, and amine complexes of platinum; and the nitrates, sulfates, halides, hydroxides, carboxylates, acetylacetonates, and amine complexes of copper. Also, cationic copper and palladium compounds stabilized with an anion such as BF
4
−
or PF
6
−
are useful as modifiers. Particularly preferred modifiers include CuCl
2
, PdBr
2
, PdCl
2
, Pt(NH
3
)
4
Cl
2
, Pd(NH
3
)
4
Br
2
, Pd(NH
3
)
4
Cl
2
, Pd(NH
3
)
4
(NO
3
)
2
, (CH
3
CN)
2
PdCl
2
, and (CH
3
CN)
2
Pd(BF
4
)
2
. If palladium halides such as PdBr
2
or PdCl
2
are used, NH
4
OH is typically added to solubilize the compounds before impregnation or exchange.
The modifier is added to the titanium zeolite in an amount preferably in the range of about from about 0.01 to 10 weight percent of Pd, Pt, or Cu, more preferably from about 0.01 to 5 weight percent of the modifier metal (Pd, Pt, or Cu), and most preferably from about 0.01 to 2 weight percent of the modifier metal. The manner in which the modifier is incorporated into the catalyst is not considered to be particularly critical. For example, the modifier can be incorporated into the zeolite by ion-exchange. Alternatively, the modifier may be supported on the zeolite by impregnation or the like.
After modifier incorporation, the catalyst may be recovered prior to use in olefin epoxidation or may be used directly in olefin epoxidation without recovering a solid catalyst. Suitable catalyst recovery methods include filtration and washing, rotary evaporation and the like. The catalyst is typically dried at a temperature greater than 40° C. prior to use in epoxidation. The catalyst may additionally comprise a binder or the like and may be molded, spray dr
Grey Roger A.
Pitchai Rangasamy
Arco Chemical Technology L.P.
Aulakh Charanjit S.
Carroll Kevin M.
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