Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-10-04
2002-03-26
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S532000, C549S536000, C549S537000
Reexamination Certificate
active
06362349
ABSTRACT:
This invention pertains to a process for the direct oxidation of olefins, such as ethylene and propylene, by oxygen to olefin oxides, such as ethylene oxide and propylene oxide.
Olefin oxides, such as propylene oxide, are used to alkoxylate alcohols to form polyether polyols, such as polypropylene polyether polyols, which find significant utility in the manufacture of polyurethanes and synthetic elastomers. Olefin oxides are also important intermediates in the manufacture of alkylene glycols, such as propylene glycol and dipropylene glycol, and alkanolamines, such as isopropanolamine, which are useful as solvents and surfactants.
Propylene oxide is produced commercially via the well-known chlorohydrin process wherein propylene is reacted with an aqueous solution of chlorine to produce a mixture of propylene chlorohydrins. The chlorohydrins are dehydrochlorinated with an excess of alkali to produce propylene oxide. This process suffers from the production of a low concentration salt stream. (See K. Weissermel and H. J. Arpe,
Industrial Organic Chemistry,
2
nd
ed., VCH Publishers, Inc., New York, N.Y., 1993, pp. 141-146 and 264-265.)
Another commercial route to propylene oxide relies on the transfer of an oxygen atom from an organic hydroperoxide or peroxycarboxylic acid to an olefin. In the first step of this process, a peroxide generator, such as isobutane or acetaldehyde, is autoxidized with oxygen to form a peroxy compound, such as t-butyl hydroperoxide or peracetic acid. This compound is used to epoxidize propylene, typically in the presence of a transition metal catalyst, including titanium, vanadium, molybdenum, or other heavy metal compounds or complexes. Along with the olefin oxide produced, this process disadvantageously produces equimolar amounts of a coproduct, for example an alcohol, such as t-butanol, or an acid, such as acetic acid, whose value must be captured in the market place. (See
Industrial Organic Chemistry
, ibid., pp. 265-269.)
It is known to oxidize olefins directly with oxygen in the presence of a metal oxide, such as a transition metal oxide or a lanthanide rare earth metal oxide, supported on a zeolite carrier. Representative references include U.S. Pat. No. 3,641,066, U.S. Pat. No. 3,957,690, and U.S. Pat. No. 3,963,645. Disadvantageously, these catalysts exhibit low activities and low selectivities to the olefin oxide. Large quantities of partial combustion products, such as acetic acid, and complete combustion products, such as carbon dioxide, are produced.
It is also known to oxidize ethylene directly with oxygen in the presence of a supported silver catalyst containing a transition metal oxide and/or a lanthanide rare earth metal oxide. Zeolites are disclosed as suitable supports. Representative art includes U.S. Pat. No. 5,447,897. While this process may be suitable for producing ethylene oxide selectively, the process fails to produce propylene oxide or higher alkylene oxides in high selectivity.
It is known further to oxidize olefins, including propylene, directly with oxygen in the presence of hydrogen and a catalyst to the corresponding olefin oxide. One catalyst disclosed for this process is a titanosilicate or vanadosilicate containing a platinum group metal or a lanthanide metal. Representative art includes WO-A 96/02323 and WO-A 97/25143. This process also fails to produce propylene oxide in high productivity.
The art also discloses a process of oxidizing C
3
and higher olefins directly with oxygen to the olefin oxide, the process being conducted in the presence of hydrogen and a catalyst comprising gold, a titanium-containing support, such as a titanosilicate or titanium dioxide or titanium dispersed on silica, and optionally, at least one promoter element, such as a Group 1, Group 2, a lanthanide, or actinide element. Representative art includes WO-A 98/00413, WO-A 98/00414, and WO-A 98/00415.
In view of the above, a need continues to exist for an efficient direct route to olefin oxides, particularly propylene oxide and higher olefin oxides, from the reaction of oxygen with C
2
and higher olefins. The discovery of such a process which simultaneously achieves high selectivity to the olefin oxide at an economically advantageous conversion of the olefin would represent a significant achievement over the prior art. For commercial viability such a process would also require that the catalyst be easily regenerated.
This invention is a novel process of preparing an olefin oxide directly from an olefin and oxygen. The process comprises contacting an olefin with oxygen in the presence of a reducing agent and a catalyst under process conditions sufficient to produce the corresponding olefin oxide. The catalyst employed in the unique process of this invention comprises a metal component dispersed on a metal ion-exchanged metallosilicate.
The novel process of this invention is useful for producing an olefin oxide directly from an olefin and oxygen and a reducing agent. Unexpectedly, the process of this invention produces the olefin oxide in a high selectivity. Partial and complete combustion products, such as acetic acid and carbon dioxide, which are found in large amounts in many prior art processes, are produced in lesser amounts in the process of this invention. Significantly, the process of this invention can be operated at a high temperature, specifically greater than 120° C., while maintaining a high selectivity to olefin oxide. Operation at higher temperatures advantageously provides steam credits from the heat produced. Accordingly, the process of this invention can be integrated into a total plant design wherein the heat derived from the steam is used to drive additional processes, for example, the separation of the olefin oxide from water. Most advantageously, the catalyst can be prepared inexpensively and regenerated easily. Accordingly, the process of this invention is highly desirable for oxidizing olefins directly to olefin oxides.
The novel process of this invention comprises contacting an olefin with oxygen in the presence of a reducing agent and an epoxidation catalyst under process conditions sufficient to prepare the corresponding olefin oxide. In one preferred embodiment, a diluent is employed with one or more of the reactants, as described in detail hereinafter. The relative molar quantities of olefin, oxygen, reducing agent, and optional diluent can be any which are sufficient to prepare the desired olefin oxide. The catalyst, which is described in detail hereinafter, comprises a metal component dispersed on a metal ion-exchanged metallosilicate. In a preferred embodiment of this invention, the olefin employed is a C
2-12
olefin, and it is converted to the corresponding C
2-12
olefin oxide. In a more preferred embodiment, the olefin is a C
3-8
olefin, and it is converted to the corresponding C
3-8
olefin oxide. In a most preferred embodiment, the olefin is propylene, and the olefin oxide is propylene oxide.
Any olefin can be employed in the process of this invention. Monoolefins are preferred, but compounds containing two or more olefins, such as dienes, can also be employed. The olefin can be a simple hydrocarbon containing only carbon and hydrogen atoms. Alternatively, the olefin can be substituted at any of the carbon atoms with an inert substituent. The term “inert”, as used herein, requires the substituent to be substantially non-reactive in the process of this invention. Suitable inert substituents include, but are not limited to, halide, ether, ester, alcohol, and aromatic moieties, preferably, chloro, C
1-12
ether, ester, and alcohol moieties, and C
6-12
aromatic moieties. Non-limiting examples of olefins which are suitable for the process of this invention include ethylene, propylene, 1-butene, 2-butene, 2-methylpropene, 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, 1-hexene, 2-hexene, 3-hexene, and analogously, the various isomers of methylpentene, ethylbutene, heptene, methylhexene, ethylpentene, propylbutene, the octenes, including preferably 1-octene, and other higher analogues of thes
Bowman Robert G.
Clark Howard W.
Hartwell George E.
Kuperman Alex
The Dow Chemical Company
Trinh Ba K.
Zuckerman Marie F.
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