Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-04-07
2001-07-03
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S532000, C549S533000, C502S243000, C502S344000
Reexamination Certificate
active
06255499
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention pertains to a process and catalyst for the hydro-oxidation of olefins, such as propylene, by oxygen in the presence of hydrogen to olefin oxides, such as propylene oxide.
Olefin oxides, such as propylene oxide, are used to alkoxylate alcohols to form 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 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. 264-265.)
Another well-known route to olefin oxides relies on the transfer of an oxygen atom from an organic hydroperoxide or peroxycarboxylic acid to an olefin. In the first step of this oxidation route, a peroxide generator, such as isobutane, ethylbenzene, or acetaldehyde, is autoxidized with oxygen to form a peroxy compound, such as t-butyl hydroperoxide, ethylbenzene hydroperoxide, or peracetic acid. The peroxide is used to epoxidize the olefin, typically in the presence of a transition metal catalyst, including titanium, vanadium, molybdenum, and other 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 methylphenylcarbinol, or an acid, such as acetic acid. Coproducts such as t-butanol and acetic acid must be recycled or their value must be captured in the market place. Other coproducts must be further processed into products of commercial value; for example, methylphenylcarbinol must be dehydrated to form styrene. (
Industrial Organic Chemistry
, ibid., pp. 265-269.)
More recently, the direct oxidation of olefins, such as propylene, with oxygen in the presence of hydrogen and a catalyst has been reported to yield olefin oxides, such as propylene oxide, as illustrated in EP-Al -0,709,360. It is taught that the catalyst comprises ultrafine particles of metallic gold deposited on titanium dioxide, preferably, the crystalline anatase phase. This catalyst exhibits a disadvantageously short lifetime. Moreover, when operated at temperatures of greater than about 100° C., the catalyst exhibits low olefin oxide selectivity and high water production.
Other hydro-oxidation processes are known, for example, as described in international patent publications WO 98/00413 and WO 98/00415, wherein an olefin, such as propylene, is reacted with oxygen in the presence of hydrogen and a catalyst comprising gold deposited on a titanosilicate support or gold deposited on a support comprising a disorganized phase of titanium dispersed on silica. International patent publication WO 98/00414 describes a similar process wherein the catalyst comprises gold and a promoter metal, such as a Group 1, Group 2, or lanthanide rare earth metal, deposited on a titanium-containing support. The catalysts of these references achieve better lifetime and better hydrogen efficiency at comparable olefin selectivity when compared with the catalyst of EP-A1-0,709,360. The catalyst of WO 98/00414 also exhibits higher activity than the catalyst of EP-A1-0,709,360. Nevertheless, improvements in activity, lifetime, and hydrogen efficiency are still desirable.
SUMMARY OF THE INVENTION
This invention is a novel hydro-oxidation process of preparing an olefin oxide directly from an olefin and oxygen in the presence of hydrogen. The process comprises contacting an olefin having three or more carbon atoms with oxygen in the presence of hydrogen and in the presence of a catalyst under process conditions sufficient to produce the corresponding olefin oxide. The unique catalyst which is employed in the process of this invention comprises oxidized gold dispersed on a titanium-containing support. The words “oxidized gold” mean that the gold is present as non-metallic gold, that is, gold in one or more positive oxidation state(s) of greater than 0. Any modem analytical method (for example, X-ray photoelectron spectroscopy) or combination of analytical methods that can determine the presence of oxidized gold can be suitably employed.
The novel process of this invention is useful for producing an olefin oxide directly from oxygen and an olefin having three or more carbon atoms. Unexpectedly, the process of this invention produces the olefin oxide at high operating temperatures and over a sustained period of time with high activity and high selectivity. Partial and complete combustion products, such as acrolein and carbon dioxide, are produced in low amounts in the process of this invention. Significantly, the process of this invention can be operated at higher temperatures than prior art processes, specifically, temperatures from greater than about 130° C. up to about 300° C. 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, the latter being produced as a co-product of the hydro-oxidation process. Even more advantageously, in preferred embodiments of the process of this invention, the hydrogen efficiency, as measured by the molar ratio of water to olefin oxide produced, is significantly improved when compared with processes of the prior art. In preferred embodiments, for example, a water to olefin oxide molar ratio of less than about 10:1 can be achieved over sustained periods of time at high operating temperatures. Even more advantageously, in preferred embodiments, the process achieves improved olefin conversion with little deactivation over a period of at least about 100 hours. Most advantageously, the process can be conducted using lower gold loadings than those used in prior art processes.
In another aspect, this invention is a unique catalyst composition comprising oxidized gold dispersed on a titanium-containing support. As noted hereinbefore, the oxidized gold comprises non-metallic gold, that is, gold characterized by one or more oxidation states greater than 0.
The novel composition of this invention can be effectively used in the aforementioned hydro-oxidation process wherein an olefin having three or more carbon atoms is converted to the corresponding olefin oxide. Besides being active and highly selective for the olefin oxide, in preferred embodiments, the novel catalyst of this invention utilizes hydrogen more efficiently and exhibits a significantly longer lifetime, as compared with catalysts of the prior art. Moreover, the catalyst of this invention achieves this high performance level at operating temperatures which are higher than those used in prior art processes. Operation at higher temperatures results in useful steam credits for running associated or downstream processes. As an added advantage, the catalyst of this invention can be operated with lower gold loadings than those used in prior art processes. A lower gold loading provides advantageous economic benefits. Accordingly, this unique catalyst possesses highly desirable properties for the process of oxidizing propylene and higher olefins to their corresponding olefin oxides.
In one preferred embodiment, the catalyst of this invention can be advantageously prepared by an impregnation technique that greatly simplifies commercial preparation, as compared with the prior art preparation method involving deposition-precipitation. The impregnation method advantageously avoids the h
Bowman Robert G.
Clark Howard W.
Hartwell George E.
Kuperman Alex
Meima Garmt R.
The Dow Chemical Company
Trinh Ba K.
Zuckerman Marie F.
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