Dense phase epoxidation

Details Dense phase epoxidation Dense phase epoxidation

2001-10-16

2004-03-23

Morris, Patricia L. (Department: 1625)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

Reexamination Certificate

active

06710192

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the epoxidation of an olefin such as propylene by reaction with hydrogen and oxygen using a solid catalyst such as Pd on TS-1, the improvement being that the reaction is carried out in carbon dioxide solvent under dense reaction mixture phase conditions.
BACKGROUND OF THE INVENTION
Epoxides constitute an important class of chemical intermediates useful for the preparation of polyether polyols, glycols, glycol ethers, surfactants, functional fluids, fuel additives and the like. Many different methods for synthesizing epoxides from the corresponding olefins have been described in the literature. A Japanese patent application assigned to the Tosoh Corporation and published in 1992 (Kokai No. 4-352771) proposed making propylene oxide by reacting propylene, hydrogen and oxygen using a catalyst comprising a Group VIII metal and a crystalline titanosilicate.
As with any chemical process, it would be desirable to attain further improvements in epoxidation methods of this type.
Dense phase reaction mixture conditions have been employed in various reaction systems, most notably in the production of tertiary butyl hydroperoxide by direct oxidation of isobutene. See, for example, U.S. Pat. Nos. 4,408,081 and 4,408,082.
SUMMARY OF THE INVENTION
In accordance with the present invention, the epoxidation is carried out by reacting olefin, hydrogen and oxygen using a noble metal on titanium or vanadium zeolite catalyst, the improvement being that the reaction is carried out using CO
2
as the essential solvent at dense phase reaction conditions.
DETAILED DESCRIPTION
There are a number of significant advantages which are achieved through practice of the present invention. CO
2
is the essential solvent used for the reaction and accordingly solvolysis of the oxirane product is suppressed due to the absence of any nucleophile species except for water of reaction. Leaching of noble metal from the solid catalyst is minimal due to insolubility in CO
2
. Because the olefin, hydrogen and oxygen are totally miscible in the dense phase system, better control of the reagent concentrations can be achieved and the dead space in the reactor can be substantially eliminated.
In general, reagents and catalysts previously taught for this reaction can be used. In this regard, reference is made to prior teachings such as Kokai No. 4-352771 above referred to as well as U.S. Pat. Nos. 6,005,123 and 6,008,388, the disclosure's of which are incorporated herein by reference.
The catalysts to be used in the present process are comprised of a titanium or vanadium zeolite and a noble metal (preferably an element of Group VIII of the Periodic Table). Suitable zeolites are those crystalline materials having a porous molecular sieve structure with titanium or vanadium atoms substituted in the framework. The choice of 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 or vanadium 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 or vanadium 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.
The titanium-containing zeolites useful as catalysts in the epoxidation step of the process 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-containing 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). Also suitable for use are the titanium-containing molecular sieves having framework structures isomorphous to zeolite beta, mordenite, ZSM-48, ZSM-12, and MCM41. The titanium-containing zeolite preferably contains no elements other than titanium, silicon and oxygen in the lattice framework, although minor amounts of boron, iron, aluminum, and the like may be present. Other metals such as tin or vanadium may also be present in the lattice framework of the zeolite in addition to the titanium, as described in U.S. Pat. Nos. 5,780,654 and 5,744,619.
Preferred titanium-containing zeolite catalysts suitable for use in the process of this invention will generally have a composition corresponding to the following empirical formula xTiO
2
(1−x)Sio
2
where x is between 0.0001 and 0.500. 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.
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 0.1 to 5 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 zeolite by impregnation means or the like or first supported on another substance such as silica, alumina, activated carbon or the like and then physically mixed with the zeolite. Alternatively, the noble metal can be incorporated into the zeolite by ion-exchange with, for example, Pd tetraamine chloride with or without added ammonium hydroxide. The catalyst is recovered by filtration and washing and is substantially free (<0.1 wt. %) of halide. There are no particular restrictions regarding the choice of noble metal compound or complex used as the source of the noble metal. For example, suitable compounds for such purpose include the nitrates, sulfates, halides (e.g., chlorides, bromides), carboxylates (e.g., acetate), and amine complexes of noble metals. Similarly, the oxidation state of the noble metal is not considered critical. In the case of palladium for instance, the palladium may be in an oxidation state anywhere from 0 to +4 or any combination of such oxidation states. To achieve the desired oxidation state or combination of oxidation states, the noble metal compound after being introduced into the catalyst may be fully or partially pre-reduced. Satisfactory catalytic performance can, however, be attained without any pre-reduction whatsoever. To achieve the active state of palladium, the catalyst may undergo pretreatment such as thermal treatment in nitrogen, vacuum, hydrogen or air.
The catalyst may additionally comprise a binder or the like and may be molded, stray dried, shaped or extruded into any desired form prior to use in epoxidation. In addition to the noble metal, the catalyst may be modified with additional elements such as, for example, lanthanide metals (e.g., europium) iron, cobalt, nickel, boron, aluminum, phosphorus, calcium, vanadium, chromium, manganese, copper, zinc, and gallium.
The olefin to be used can be any organic compound containing at least one site of ethylenic unsaturation (i.e., at least one carbon-carbon double bond). The olefin can be aliphatic, aromatic or cycloaliphatic in character and may have either a linear or branched structure, with the site(s) of theylenic unsaturation being terminal and/or internal. The olefin preferably contains 2-30 carbon atoms; the process of the invention is particularly suitable for expoxidizing C
2
-C
6
mono-olefins. More than one double bond may be present, as in a d

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