Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By addition of entire unsaturated molecules – e.g.,...
Reexamination Certificate
2001-05-07
2004-02-10
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By addition of entire unsaturated molecules, e.g.,...
C585S514000, C585S520000, C585S529000
Reexamination Certificate
active
06689927
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the production of octene isomers by the oligomerization of butene. Specifically, the invention relates to the oligomerization of butene to high selectivities of octene isomers and, specifically, to 2,4,4-trimethylpentene.
BACKGROUND OF THE INVENTION
Processes for the oligomerization of lighter olefins to produce C
8
oligomers are known. Oligomerization processes have been long employed to produce good quality motor fuel from butene. Such oligomerization processes are also referred to as catalytic condensation and polymerization with the resulting motor fuel often referred to as polymer gasoline. Methods have always been sought to improve the octane number of the gasoline boiling range oligomerization products. In addition, the oligomerization process is also susceptible to catalyst fouling from the condensation of heavy oligomers into coke that covers the catalyst.
Another process that has met the continuing demand for the conversion of light hydrocarbons into high octane motor fuels was the alkylation of isobutane with propylene, butenes and amylenes using a hydrofluoric acid (HF) catalyst, commonly referred to as HF alkylation. The HF process has provided a highly successful method for the production of high octane motor fuels.
A number of arrangements are known for using oligomerization in combination with other processes such as saturation and dehydrogenation as substitutes for acid catalyzed isomerization alkylation. Patents disclosing the dehydrogenation of light paraffin stream with oligomerization of the dehydrogenation effluent include U.S. Pat. No. 4,393,259 B1, U.S. Pat. No. 5,049,360 B1, U.S. Pat. No. 4,749,820 B1, U.S. Pat. No. 4,304,948 B1 and U.S. Pat. No. 2,526,966 B1.
Trimethylpentenes are the preferred product in the production of gasoline. High selectivities to trimethylpentenes, and specifically to 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene, are desired because they can be hydrogenated to 2,2,4-trimethylpentane which has a very high research and motor octane numbers.
TABLE 1
Research
Motor
C
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Isomer
Octane Number
Octane Number
2,2,4-trimethylpentane
100
100
2,3,4-trimethylpentane
102.7
95.9
2,2,3-trimethylpentane
109.6
99.9
2,3,3-trimethylpentane
106.1
99.4
Isomers of 2,4,4-trimethylpentene typically include 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene but will hereinafter be collectively referred to as 2,4,4-2-trimethylpentene. Among the trimethylpentanes, 2,2,4-trimethylpentane is desired when a high vapor pressure gasoline blending stock is desired because it has a relatively low boiling point and a relatively high vapor pressure.
TABLE 2
Boiling Point
C
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Isomer
at 1 atm (° C.)
2,2,4-trimethylpentane
99.2
2,3,4-trimethylpentane
113.5
2,2,3-trimethylpentane
109.8
2,3,3-trimethylpentane
114.8
U.S. Pat. No. 5,877,372 B1 endeavors to oligomerize to diisobutene by dimerization of pure isobutene. Diisobutene is typically 2,4,4-trimethylpentene, but it tends to isomerize to 2,3,4-trimethylpentene. Affordable feedstocks for butene oligomerization processes are typically provided by one of the effluent streams from a fluidized catalytic cracking unit which usually includes a mixture of isobutene, n-butene and butane. Hence, dimerization of pure isobutene is not typically feasible.
Efforts in the prior art to increase the selectivity to 2,4,4-trimethylpentene from butene mixtures typically involve attempting to encourage the dimerization of isobutene and suppress both the dimerization of n-butene and the co-dimerization of isobutene and n-butene. U.S. Pat. No. 4,469,911 B1 discloses oligomerizing isobutene and n-butene together over a resin catalyst at lower temperatures. The lower temperatures are reported to favor selective dimerization of isobutene with itself to produce isobutene dimer or diisobutene rather than the codimerization of isobutene with n-butene to produce codimers or subsequent oligomerization to produce trimers. Although this process is reported to produce a selectivity to 2,4,4-trimethylpentene as high as 86.2 liquid volume percent, the attendant selectivity to dodecene was as high as 12.2 liquid volume percent. Dodecene in the product lowers octane numbers and lowers vapor pressure.
Other patents disclose oligomerizing a mixture of n-butenes and isobutenes under conditions that encourage isobutene dimerization and discourage n-butene dimerization. In U.S. Pat. No. 4,197,185 B1, U.S. Pat. No. 4,244,806 B1 and U.S. Pat. No. 4,324,646 B1, a cut including isobutene, n-butene and butane is oligomerized over an alumina based catalyst such that the isobutene has at least a 90% conversion and the n-butene has lower than a 16% conversion. This method capitalizes on the slower rate of n-butene reactions. U.S. Pat. No. 3,832,418 B1 also discloses a selective dimerization process in which a mixture of n-butenes and isobutenes oligomerize over a catalyst comprising presulfided nickel fluorine on a silica-alumina support with over 80% conversion of isobutene and less than 5% conversion of n-butene. U.S. Pat. No. 5,994,601 B1 discloses oligomerizing a mixture of n-butenes and isobutenes while endeavoring to separate dimers of the n-butenes from dimers of isobutene.
Contrarily, other patents focus on n-butene dimerization. U.S. Pat. No. 4,225,743 B1 discloses codimerizing isobutene with n-butene to form methylheptenes and dimethylhexenes and suppress the formation of 2,4,4-trimethylpentene by using a specific nickel catalyst solution and an organo-aluminum catalyst. U.S. Pat. No. 4,463,211 B1 discloses that dimerization of n-butenes in the presence of minimal isobutenes over a cation exchange resin yields primarily dimethylhexenes. Pimethylhexene reduces the octane number of gasoline.
The indirect alkylation process described in U.S. Pat. No. 6,080,903 B1, U.S. Pat. No. 5,990,367 B1 and U.S. Pat. No. 5,895,830 B1 dimerizes mixtures of n-butene and isobutene over a solid phosphoric acid (SPA) catalyst in the presence of a higher paraffin diluent such as cyclohexane or octane. The presence of the paraffin diluent is believed to promote the oligomerization in the liquid phase to yield predominantly dimerized butene oligomers such as C
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olefins. The liquid phase washes deactivating components from the catalyst to prolong catalyst life. The higher aliphatic olefins can be saturated to provide high octane fuel. The process gives high butene conversion with octene selectivities as high as 87.2 wt-% and selectivities to trimer products as low as 11.7 wt-%. These patents recommend that operating temperatures in a narrow range of 300° to 400° F. (149° to 204° C.) increase the selectivity of C
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olefins.
Even in the context of indirect alkylation, mechanistic theory predicts that in a reaction mixture of isobutene and n-butene in the presence of a SPA catalyst, the isobutene will dimerize with itself to produce 2,4,4-trimethylpentene and isobutene will co-dimerize with n-butene to produce 2,2,3-trimethylpentene. Moreover, the desired 2,4,4-trimethylpentene also has a tendency to shift to 2,3,4-trimethylpentene.
Hence, it is an object of the present invention to run an oligomerization of butene in the presence of a catalyst so as to obtain a desired selectivity to 2,4,4-trimethylpentene from an oligomerization of butenes. It is a further object of this invention to oligomerize a mixture of n-butene and isobutene to obtain a high selectivity to 2,4,4-trimethylpentene. It is a still further object of the present invention to minimize the production of dodecene.
BRIEF SUMMARY OF THE INVENTION
It has been surprisingly found that very high yields of octenes and, specifically, 2,4,4-trimethylpentene, with attendant low selectivity to dodecene are produced from the dimerization of isobutene and/or mixtures of isobutene and n-butene when diluted with a paraffinic diluent. We have surprisingly found that higher conversion of n-butene with isobutene does not diminish the selectivity to 2,4,4-trimethylpentene. In light of earlier belief, we were surprised to find that high selectivity to octe
Abrevaya Hayim
Frame Robert R.
Stine Laurence O.
Dang Thuan D.
Paschall James C.
Tolomei John G.
UOP LCC
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