Chemistry of hydrocarbon compounds – Adding hydrogen to unsaturated bond of hydrocarbon – i.e.,... – Using transition metal-containing catalyst
Reexamination Certificate
2001-05-22
2003-04-15
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Adding hydrogen to unsaturated bond of hydrocarbon, i.e.,...
Using transition metal-containing catalyst
C585S276000
Reexamination Certificate
active
06548721
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for saturating an oxygenate containing stream to destroy substantially all oxygenates. Moreover, this invention relates to saturating essentially all olefins in the oxygenate containing stream.
BACKGROUND OF THE INVENTION
Processes for the oligomerization of light olefins to produce heavy olefin oligomers are known. Oligomerization processes have been long employed to produce high quality motor fuel from C
4
olefins. 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 the oligomerization method of the indirect alkylation process set forth in, for example, U.S. Pat. Nos. 6,080,903 B1, 5,990,367 B1 and 5,895,830 B1, light aliphatic olefins such as C
4
olefins are contacted with solid phosphoric acid (SPA) catalyst in the presence of a heavy paraffin diluent such as cyclohexane or isooctane. The presence of the paraffin diluent is believed to promote the oligomerization in the liquid phase to yield predominantly dimerized oligomers such as C
8
olefins. Light paraffinic feed can be dehydrogenated to provide the feed for the indirect alkylation process. Patents disclosing such dehydrogenation include U.S. Pat. Nos. 4,393,259 B1, 5,049,360 B1, 4,749,820 B, 4,304,948 B1 and 2,526,966 B1.
Other oligomerization processes using an ionic exchange resin catalyst to oligomerize light olefins to produce oligomers such as C
8
olefins are also known. These processes often include an oxygenate such as tert-butyl alcohol (TBA) or sec-butyl alcohol (SBA) in the feed for modifying the catalyst to maintain desired selectivity. When water is added to feed containing C
4
olefins, it reacts with C
4
olefins to generate TBA and SBA which moderate the resin catalyst. References disclosing resin catalyzed oligomerization include U.S. Pat. No. 5,877,372 B1 and EP 0994088 A1. A dehydrogenation zone to convert paraffinic feed into olefinic feed can also precede the resin catalyzed oligomerization.
The oligomerization of C
4
olefins across an acidic catalyst such as SPA produces a variety of C
8
olefins. When the feed contains only isobutylene, the predominantly produced olefin is 2,4,4-trimethylpentene which can be saturated to 2,2,4-trimethylpentane. Normal butenes present in the feed oligomerize to produce C
8
olefins such as 2,2,3-trimethylpentene and dimethylhexenes. Secondary reactions can also occur in which 2,4,4-trimethylpentene product isomerizes through a methyl shift to give 2,3,4-trimethylpentene or 2,2,3-trimethylpentene and dimethylhexenes. Additionally, C
4
olefins can also trimerize to produce triisobutane after saturation.
Table 1 gives the octane numbers and boiling points for C
8
isomers and for C
12
.
TABLE 1
Research
Motor
Boiling Point
Isomer
Octane Number
Octane Number
at 1 atm (° C.)
2,2,4-trimethylpentane
100
100
99.2
2,3,4-trimethylpentane
102.7
95.9
113.5
2,2,3-trimethylpentane
109.6
99.9
109.8
2,3,3-trimethylpentane
106.1
99.4
114.8
2,2-dimethlyhexane
72.5
73
106.7
2,3-dimethylhexane
91.1
88.5
115.6
Triisobutane
95
90
216
Product oligomers with higher octane numbers and lower boiling points are the most preferred. Accordingly, 2,2,4-trimethylpentane is the most preferred C
8
isomer; whereas, 2,3,4-trimethylpentane and 2,3,3-trimethylpentane are the least preferred C
8
isomers because of their high boiling point temperature. The dimethylhexanes are undesirable because of their low octane numbers and relatively high boiling points and triisobutane is undesirable because of its very high boiling point temperature.
U.S. Pat. Nos. 5,856,604 B1, 5,847,252 B1 and 5,811,608 B1 teach succeeding such oligomerization processes with a saturation reaction zone to convert heavy oligomeric olefins into heavy alkanes that can be blended with gasoline stock. Saturation is known to be particularly beneficial when saturating isooctenes to isooctane gasoline. These patents disclose using a catalyst comprising a metal from a top row of Group VIII of the Periodic Table of the Elements such as nickel and a metal from Group VI-B of the Periodic Table of the Elements such as molybdenum in the saturation reaction zone. However, they indicate no appreciation of the effectiveness of such catalysts with respect to oxygenates and the criticality of properly preparing the catalyst.
One must be careful to avoid catalysts for saturating oligomerized olefins to make gasoline fractions that can lower octane ratings and excessively lower the boiling point down to the range of C
4
hydrocarbons. For instance, saturation catalysts can crack C
8
hydrocarbons down to C
4
hydrocarbons which degrades product quality by lowering the octane rating. On the other hand, cracking of C
12
or heavier hydrocarbons down to lighter hydrocarbons in a saturation unit would be desirable. Saturation catalysts that isomerize C
8
hydrocarbons to a C
8
isomer that has a lower octane number and/or higher boiling point are less desirable.
Saturation processes are typically required to meet certain high level of conversion of olefin to alkane. For example, future gasoline specifications are expected to require a very low level of olefins in the pool. The saturation process must be able to sufficiently convert isooctenes to meet these requirements. Moreover, if unreacted pure isobutene is subjected to saturation for recycling in a process where isobutane is oxidized to obtain tert-butyl hydroperoxide, the recycled isobutane must contain less than 100 ppm isobutylene. In addition, in such a process, the isobutane stream may contain no sulfur and essentially no oxygenates. Hence, high conversion in the saturation process is very important.
U.S. Pat. No. 4,244,806 B1 discloses hydrogenating a stream of isobutene dimers and trimers over a nickle or noble metal catalyst on a non-acidic carrier such as alumina. However, noble metal catalysts are sensitive to the presence of oxygenates and sulfur compounds in the hydrogenation stream. Oxygenates are compounds that contain oxygen such as alcohols, ethers, ketones, aldehydes or water. Notable sulfur compounds include mercaptans and dimethyl disulfides. To avoid diminishing noble metal catalyst activity, a hydrogenation feed may have-to be purified of sulfur through a sulfur unit, thereby increasing the capital cost required to operate with a noble metal catalyst. Furthermore, the hydrogenation feed may have to be purified of oxygenates by running it through at least one oxygenate removal unit (ORU) containing adsorbent to adsorb the oxygenate. Such ORU's must be shut down periodically to regenerate the adsorbent requiring installation of an additional ORU or substantial down time. Additionally, a large volume of regenerant for regenerating the adsorbent must be obtained and disposed of periodically. The elimination or substantial reduction of oxygenates is becoming more important because of recent governmental regulations to decrease or eliminate- the use of methyl tert-butyl ether (MTBE) as a gasoline blending component and heightened environmental concern over the effects of oxygenates. Methods of removing oxygenates will become more useful because oligomerizing C
4
olefins over resin catalyst can produce as much as 5 wt-% C
8
ethers.
Hence, it is an object of the present invention to provide a saturation process that uses a catalyst that can withstand sulfur and oxygenates in the feed. It is a further object of this invention to provide a saturation process that uses a catalyst that essentially saturates all olefins. It is a still further object of the present invention to provide a process that destroys all oxygenates and converts sulfur compounds into easily managed hydrogen sulfide. It is an even further object of the present invention to provide a saturation process that minimally degrades product quality.
SUMMARY OF THE INVENTION
We have discovered a process that utilizes a catal
Abdo Suheil F.
Gordon Jennifer L.
Kokayeff Peter
Mc Culloch Beth
Wei Daniel H.
Dang Thuan D.
Paschall James C.
Tolomei John G.
UOP LLC
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