Chemistry of hydrocarbon compounds – Plural serial diverse syntheses – To produce unsaturate
Reexamination Certificate
2002-01-23
2004-04-27
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Plural serial diverse syntheses
To produce unsaturate
C585S643000, C585S644000, C585S646000, C585S647000
Reexamination Certificate
active
06727396
ABSTRACT:
This invention relates to the production of linear alpha olefins. More particularly, this invention relates to the production of linear alpha olefins having a higher carbon number from alpha olefins having a lower carbon number. More particularly, this invention relates to the production of ethylene and hexene-1.
Linear alpha olefins currently are produced by the selective oligomerization of ethylene. In general, the oligomerization is conducted in the presence of a catalyst, such as an alkylated metal catalyst. Long residence times are used to produce hydrocarbon chains of varying lengths. The olefin double bond remains at the alpha position as each ethylene molecule is added. Ethylene oligomerization produces a wide spectrum of linear alpha olefin products. Extensive fractionation is required to separate the alpha olefins having different carbon numbers.
In accordance with an aspect of the present invention, a linear alpha-olefin having a first number of carbon atoms is subjected to a metathesis reaction under conditions and in the presence of a catalyst that minimizes or eliminates skeletal and/or double bond isomerization to produce a reaction product that includes ethylene and a linear internal olefin (LIO) that has a number of carbon atoms greater than the first number of carbon atoms. Specifically, the feed linear alpha olefin with carbon number is metathesized to ethylene and linear internal olefin with carbon number 2n−2. The resulting linear internal olefin may then be isomerized to produce a linear alpha olefin.
In accordance with an aspect of the present invention, butene-1 is subjected to a metathesis reaction under conditions and in the presence of a metathesis catalyst that minimizes or eliminates skeletal and double bond isomerization to produce a reaction product that includes ethylene and hexene-3. The hexene-3 is then isomerized to hexene-1.
In the metathesis reaction, the catalyst and reaction conditions are such as to minimize isomerization of the butene-1 starting material.
The catalyst used in this aspect for the metathesis reaction may be a supported or unsupported catalyst and the overall catalyst is one that has a minimized amount of both acidic and basic sites.
A catalyst that has a reduced amount of both acidic and basic sites (preferably essentially no acidic and basic sites) improves the selectivity of the metathesis of the lower carbon number alpha-olefin (1-butene) with itself to form ethylene and a linear internal olefin of higher carbon number (3-hexene) by minimizing isomerization.
Metathesis reactions can be characterized as either fully productive, half productive, or non-productive depending upon the symmetry of the molecule with respect to the double bond. Two dissimilar olefins will react in a “fully productive” manner. An example is the reaction of 1-butene with 2-butene. The double bond is in a different position in the respective molecule and these will react rapidly with one another. Two identical molecules will react in either a half productive or non-productive manner. If for example 1-butene reacts with itself, because the double bond is in the same position within each molecule, it will react at a rate considerably slower than the rate of fully productive reactions. If the feed molecules are identical and symmetric around the double bond (for example 2-butene reacting with itself), then no reaction will occur and the system is defined as non-productive.
In many metathesis reaction systems, isomerization activity is incorporated to increase the rates of reaction. By allowing for a shifting double bond, half or non-productive reactions can be reduced. Typical isomerization catalysts include basic metal oxides or promoted zeolites.
In one preferred embodiment, the catalyst or catalyst mixture contains essentially no magnesium oxide in that magnesium oxide catalyst promotes isomerization. Thus, for example, a preferred catalyst (supported or not supported) is a Group VI B or Group VII B metal oxide such as tungsten oxide, molybdenum oxide, or rhenium oxide, with tungsten oxide being particularly preferred.
If a support is used, such support has a minimized amount of both acidic and basic sites and preferably essentially no acid and essentially no basic sites. Preferred supports are silica or zirconia oxide.
Although the catalyst may include a promoter to reduce acidity; for example, an alkali metal (sodium, potassium or lithium), cesium, a rare earth, etc., in a preferred embodiment, the catalyst does not include a promoter.
Generally reaction conditions that tend to favor the primary reaction and discourage subsequent reactions are preferred. Thus a lower pressure and shorter residence times tend to minimize the isomerization reaction.
In accordance with the present invention, a linear alpha olefin with carbon number n, such as butene-1, is subjected to auto-metathesis with itself (half productive reaction) in the presence of a catalyst and under conditions that minimize isomerization of the linear olefin to produce a reaction product that includes ethylene and a linear alpha olefin of carbon number 2n−2, such as hexene-3. The reaction is:
1-C
4
−
+1-C
4
−
⇄C
2
−
+3-C
6
−
The metathesis reaction, in accordance with the invention may be effected at a temperature from about 50° C. to 600° C., preferably from about 200° C. to 350° C., at a weight hourly space velocity (WHSV) of from about 3 to about 200, preferably from about 6 to about 40, and at a pressure of from about 10 psig to about 600 psig, preferably from about 30 psig to about 100 psig.
The butene-1 starting material may be a pure or impure feed,. The portion of the feed that contains reactive C
4
olefins is preferably at least 90% and more preferably at least 95% butene-1. Non reactive components, for example normal butane, may dilute the olefins in the feedstock. Most preferably, the butene-1 starting material is a pure feed i.e. the butene-1 is present in an amount of at least 99%.
In one embodiment, a mixed butene feed is pretreated to provide a butene-1 feed for the metathesis reaction. For example, the mixed butene feed may contain butene-1, butene-2 and isobutylene. Such a feed may be obtained from a steam cracker In the event that the mixed butene stream includes butadiene such butadiene is removed by hydrogenation or extraction.
In one embodiment, the mixed butenes feed following or in conjunction with butadiene hydrogenation is subjected to hydroisomerization conditions to convert butene-1 to butene-2, with isobutylene being separated from a butene-2 stream by fractionation. The butene-2 stream is then isomerized back to butene-1 in a subsequent step for use as feed to the metathesis portion of the process
The hydroisomerization of butene-1 to butene-2 and separation may be accomplished in separate steps or may be combined into a single step. In one embodiment butene-1 is isomerized to butene-2 and isobutylene is separated from butene-2, in a catalytic distillation tower In another embodiment, the isomerization of the butene-1 to butene-2 can also be accomplished by using a fixed bed isomerization reactor or by adjusting the conditions of the butadiene hydrogenation reactor followed by a fractionation tower to produce a butene-2 stream and an isobutylene product.
The isomerization of 1-butene to 2-butene is favored by low temperatures. This reaction is carried out typically in liquid phase either in a catalytic distillation tower or fixed bed reactor as described above.
The subsequent isomerization of 2-butene to 1-butene is favored by higher temperature and preferably is carried out in a vapor fixed bed phase reactor. Alternately, the conversion of butene-2 to butene-1 and the purification of the butene-1 may be accomplished by catalytic distillation. The production of 1-butene from hydrocarbons fed to a steam cracker is described further in U.S. Pat. No. 5,087,780, the contents of which are incorporated herein by reference.
As a further alternative, a mixed butene stream is reacted with for example methanol to
ABB Lummus Global Inc.
Dang Thuan D.
Lillie Raymond J.
Olstein Elliot M.
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