Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2001-11-30
2003-03-18
Dunn, Tom (Department: 1725)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S532000, C549S524000, C423S584000, C502S064000, C502S066000, C502S071000, C502S074000, C502S077000
Reexamination Certificate
active
06534661
ABSTRACT:
FIELD OF THE INVENTION
This invention provides an integrated process using a dual-functional catalyst for producing epoxides of olefins. In particular, it relates to the production of propylene oxide from propylene wherein the hydrogen peroxide intermediate oxidizing or epoxidizing agent is produced in-situ for the concomitant epoxidation of propylene.
BACKGROUND OF INVENTION
Improved methods of producing propylene oxide or epoxide (PO) have long been sought. The current conventional technologies for PO production are based on the catalytic epoxidation of propylene using organic hydroperoxides such as tertiary-butyl hydroperoxide (TBHP) or ethyl benzene hydroperoxide (EBHP). The TBHP and EBHP are generated by the non-catalytic autooxidation of organic substrates (isobutane or ethyl benzene) with oxygen. However, these existing processes have important drawbacks, which involve multiple reaction steps with intervening distillation separations, resulting in high equipment counts and high capital investment costs. The hydrocarbon substrate feed is first oxidized in a first reactor to generate the hydroperoxide intermediate, which is generally then distilled to recover a portion of the unreacted feed and increase the concentration of the hydroperoxide. The concentrated hydroperoxide is then contacted with propylene feed in a second reactor over a suitable catalyst to generate propylene oxide. A series of separation steps must then be conducted, typically by distillation, to recover the propylene oxide product in purified form.
The complexity of the current process is increased by the fact that for every molecule of propylene oxide primary product generated, at least one molecule of a secondary product is generated. In the case of TBHP intermediate, the secondary product is tertiary-butyl alcohol (TBA), while the use of EBHP leads to the formation of acetophenone. In and of themselves these products are not typically desirable as they require further processing with at least two additional reactors and further distillation to generate more desirable products. TBA is generally converted to methyl tertiary-butyl ether (MTBE) in a two-stage process, first by dehydration to form isobutylene, and then reaction with methanol to form MTBE. Acetophenone is first hydrogenated to form methyl benzyl alcohol, which is then dehydrated to form styrene. These additional steps add undesirable capital and operating costs to the conventional propylene oxide process.
In addition to the added cost and complexity, the production of these secondary products adds further difficulty, because on a weight basis these secondary products are produced in greater amount than the desired propylene oxide product. Commercial markets must be found for the secondary products, and the profitability of the propylene oxide plant is highly influenced by the profitability of the markets for MTBE and styrene. The MTBE market, dominated by use in reformulated gasoline, is currently under severe strain because of environmental and health concerns related to its use. The styrene market is highly cyclical, and is too large to be effectively influenced by propylene oxide producers who produce styrene only as a by-product. As a consequence of these various problems with existing propylene oxide processes, considerable research has been directed towards developing alternate processes for propylene oxide production. Generally, this work has sought to develop processes that eliminate the formation of any secondary product along with the desirable propylene oxide.
Another category of propylene oxide processes is based on direct oxidation of propylene with oxygen. For example, U.S. Pat. Nos. 5,698,719; 5,686,380, 5,864,047; 5,625,084; 5,861,519; and 5,763,630 disclose catalysts based on silver for the direct oxidation of propylene to propylene oxide. U.S. Pat. No. 5,703,254 discloses combining silver and gold as catalyst. U.S. Pat. No. 5,760,254 discloses a nitrogen oxide catalyst. U.S. Pat. No. 5,670,674 discloses a platinum-based catalyst. However, none of these patented processes have yet reached a status suitable for commercialization. Generally, the overoxidation of propylene to form carbon oxides such as CO2 is a major problem. A suitable combination of catalyst activity, selectivity, and catalyst life has yet to be achieved, and is likely to present a continuing challenge due to the tendency of molecular oxygen to cause complete oxidation reactions to form CO2.
An alternate approach to a new propylene oxide process is the use of hydrogen peroxide as the oxidizing agent. Unlike organic hydroperoxides such as TBHP and EBHP that form organic by-products during the epoxidation of propylene, the by-product of reacting propylene with hydrogen peroxide is water, an innocuous compound. U.S. Pat. No. 4,701,428 discloses a titanium silicalite catalyst (TS-1), which can be used for the epoxidation of olefins using hydrogen peroxide; this patent is incorporated herein by reference with respect to the titanium silicalite portion of the disclosure. In the epoxidation of propylene to form propylene oxide, selectivity as high as 93% is obtained, based on hydrogen peroxide consumed. Other similar patents are U.S. Pat. Nos. 4,859,785 and 4,954,653. U.S. Pat. Nos. 4,937,216 and 4,824,976 also disclose processes based on TS-1 catalyst for the epoxidation of various olefins, including propylene, and they report selectivities of epoxide formation as high as 98%.
U.S. Pat. Nos. 5,166,372; 5,214,168; 5,262,550; 5,384,418; 5,646,314; 5,693,834; 5,523,426; 5,912,367; 6,066,750 all disclose various versions of an olefin epoxidation process (especially a propylene epoxidation process) where a titanium silicalite is used as the epoxidation catalyst and hydrogen peroxide is used as the epoxidizing agent. Generally, in these patents, hydrogen peroxide is generated in a separate reactor by the autooxidation of a secondary alcohol such as isopropanol. U.S. Pat. Nos. 5,679,749; 6,042,807; and 5,977,009 disclose variations on titanium-based zeolitic catalysts containing other components such as tellurium, boron, germanium, niobium, which are claimed to increase the activity or selectivity of the catalyst for the epoxidation of olefins such as propylene. Also, U.S. Pat. Nos. 5,374,747; 5,412,122; 5,527,520; 5,554,356; 5,621,122; 5,684,170; and 5,695,736 disclose catalysts containing Si and Ti which are isomorphous in structure with the zeolite beta structure. These catalysts are claimed to be useful for the selective epoxidation of olefins such as propylene using hydrogen peroxide as an oxidant.
However, there are significant shortcomings for these prior art processes in the hydrogen peroxide-based epoxidation of propylene that have prevented their commercialization. The cost of hydrogen peroxide produced by current means is generally too high for the peroxide-based route to PO product to be economical. Also, these prior art processes are based on a multi-step approach in which hydrogen peroxide is separately generated using suitable oxidation technology, and then the hydrogen peroxide is used to epoxidize propylene. Normally, there are separation steps provided between these reaction steps. Also, the synthesis of hydrogen peroxide by conventional means normally involves the hydrogenation of a working medium such as anthraquinone or secondary alcohol; this must be oxidized in a third reaction step to regenerate the working medium for re-use in the hydrogen peroxide synthesis.
Another approach is to combine the synthesis of hydrogen peroxide and the epoxidation of propylene into a single step reaction. This requires a dual-functional catalyst, capable of catalyzing the direct reaction of hydrogen and oxygen to form hydrogen peroxide, and simultaneously catalyzing the reaction of said hydrogen peroxide with propylene to form propylene oxide product. Examples are provided by U.S. Pat. Nos. 5,973,171; 6,005,123; 6,008,388; and 6,063,942, all of which disclose catalysts based on combinations of titanium or vanadium based zeolitic structures with noble metals such as
Rueter Michael
Zhou Bing
Dunn Tom
Hydrocarbon Technologies, Inc.
Ildebrando Christina
Kennedy Daniel M.
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