Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – From nonhydrocarbon feed
Reexamination Certificate
2000-10-19
2003-02-11
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
From nonhydrocarbon feed
C585S640000
Reexamination Certificate
active
06518474
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Disclosed is a process for producing isobutylene by the dehydration of tertiary butyl alcohol, and more particularly to a process for producing substantially pure isobutylene containing no or relatively small amounts of higher oligomer byproducts. In one particular embodiment, disclosed is a process for producing substantially pure isobutylene by dehydration of tertiary butyl alcohol in the presence of a Y-zeolite catalyst having a silica to alumina ratio of less than or equal to about ten.
2. Description of the Related Art
Isobutane may be reacted with oxygen to form a peroxidation reaction product containing tertiary butyl hydroperoxide and tertiary butyl alcohol, along with minor amounts of acetone, methanol, various esters and acids. One typical use of tertiary butyl hydroperoxide manufactured in this manner is to produce epoxides. For example, the process for the manufacture of substituted epoxides from alpha-olefins such as propylene is discussed in U.S. Pat. No. 3,351,635. In this process, an organic hydroperoxide such as tertiary butyl hydroperoxide may be reacted with an olefinically unsaturated compound such as propylene in the presence of a soluble molybdenum catalyst. Products of this reaction include propylene oxide and tertiary butyl alcohol.
In one conventional vapor phase process, tertiary butyl alcohol may be used to produce isobutylene by way of a vapor phase reaction at very high temperatures, i.e., from about 350 to about 450° C. Such conventional vapor phase processes typically are accompanied by a large consumption of energy and require expensive heating equipment and other costly hardware.
In one conventional liquid phase process for the dehydration of tertiary butyl alcohol, azeotroping agents, such as benzene or xylene, are used to remove water from the liquid phase reaction product. However, azeotroping agents are typically expensive and may cause production of relatively heavy molecular weight products that must be purged from the process system. Examples of such conventional liquid phase products are described in, for example, U.S. Pat. Nos. 4,165,343 and 4,155,945.
Other conventional processes for the dehydration of tertiary butyl alcohol include those processes employing ion exchange resins. One example of such a process for the dehydration of X tertiary butyl alcohol is described in U.S. Pat. No. 3,256,250. This process employs sulfonated and nitrated styrene divinyl benzene resin which may be utilized to produce isobutylene. U.S. Pat. No. 3,510,538 describes a process in which tertiary butyl alcohol is continuously dehydrated over a cation exchange resin with water formed during the process being continuously removed to increase dehydration rates. However, cation exchange resins are expensive, and typically cannot be operated at temperatures greater than about 110° C. to about 120° C. Furthermore, to obtain useful rates of dehydration and relatively high conversion percentages, water must be continuously removed from the system.
Other conventional process for the dehydration of tertiary butyl alcohol are employed to produce higher molecular weight conversion products. For example, U.S. Pat. No 5,157,192 describes a process for the conversion of tertiary butyl alcohols to C-8 olefins over certain zeolite catalysts, such as certain beta-zeolites. In this process, tertiary butyl alcohol may be converted to 2,2,4-trimethylpentane(diisobutylene). A two-step partial oxidation-dimerization process to yield C-8 olefins is described.
SUMMARY OF THE INVENTION
Disclosed herein is a process for producing isobutylene from tertiary butyl alcohol in the presence of Y-zeolites. Using the disclosed process, tertiary butyl alcohol may be dehydrated at relatively low temperatures and pressures to produce isobutylene in substantially quantitative yield with little or substantially no diisobutylene formed. Surprisingly, these results may be achieved using zeolites having a silica to aluminum ratio of less than about 10, and in the presence of water in the process. Advantageously, the disclosed method obtains good conversion of tertiary butyl alcohol with relatively low silica to alumina ratio. Low silica to alumina ratio zeolite catalysts typically cost less and are more readily available than zeolite catalysts having higher silica to alumina ratios.
Using the disclosed process, substantially high yields of isobutylene may be produced in the substantial absence of dimer byproducts, such as diisobutylene. Such substantially high yield isobutylene products may be advantageously produced for use, for example, in plants where it is desirable to reduce isobutylene to isobutane and recycle it. For example, isobutane may be recycled to a peroxidation reactor to make more tert-butylhydroperoxide. The tert-butylhydroperoxide may be used (with propylene) in the presence of a molybdenum catalyst to produce more propylene oxide and tert-butylalcohol. The tert-butylalcohol may then be recycled to the above process. Other end uses for which substantially high purity isobutylene product of the disclosed process may be employed include, but are not limited to, for the production of substantially high purity isobutylene for sale to polymer markets, and where it is desirable to produce a mixture of isobutylene and isobutane for alkylation.
Whether a tertiary butyl alcohol-containing feed stream contains a relatively large amount of other components or is substantially pure tertiary butyl alcohol, relatively high conversion of tertiary butyl alcohol and relatively high selectivity to isobutylene may be advantageously achieved using the disclosed method. One or more other advantages of embodiments of the disclosed method include, but are not limited to, no need for large consumption of energy and/or expensive heating equipment as required with high temperature conventional processes, no need for expensive azeotroping agents or purge of relatively heavy molecular weight azeotrope products that must be purged from the process system, no requirement for continuous removal of water from the system, etc.
In one respect, disclosed is a method of producing isobutylene, including: contacting tertiary butyl alcohol with a Y-zeolite catalyst to produce isobutylene; wherein the Y-zeolite catalyst may have a silica to alumina ratio of less than about 10. The contacting may occur as part of a batch process (e.g., in a kettle or any other batch process reaction vessel suitable for producing isobutylene from tertiary butyl alcohol using Y-zeolite catalysts as described herein), or as part of a continuous flow process employing a feed stream that includes tertiary butyl alcohol (e.g., in any continuous flow process reaction vessel suitable for producing isobutylene from tertiary butyl alcohol using Y-zeolite catalysts as described herein). In one embodiment, water may also be present with tertiary butyl alcohol in a batch process reaction vessel or continuous flow feed stream. In another embodiment, a feed stream may include from about 70% to about 100% by weight tertiary butyl alcohol by total weight of the feed stream. In m another embodiment, the feed stream may include from about 70% to less than about 100% by weight tertiary butyl alcohol by total weight of the feed stream, and from greater than about 0% to about 30% by weight water by total weight of the feed stream. In another embodiment, conversion of tertiary butyl alcohol may be from about 80% to about 100%, and selectivity to isobutylene may be from about 85% to about 100%.
In another respect, disclosed is a method of producing isobutylene, including: contacting a feed stream including tertiary butyl alcohol and water with a Y-zeolite catalyst to produce isobutylene; wherein the Y-zeolite catalyst may have a silica to alumina ratio of less than or equal to about 10; wherein the contacting occurs within a reaction vessel at a temperature of greater than or equal to about 140° C., a pressure of from about 50 psig to 1000 psig, and a liquid hourly space velocity (“LHSV”) of from about 0.1
Mueller Mark A.
Sanderson John R.
Griffin Walter D.
Huntsman International LLC
O'Keefe Egan & Peterman, LLP
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