Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By addition of entire unsaturated molecules – e.g.,...
Reexamination Certificate
1999-12-20
2001-09-04
Yildirim, Bekir L. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By addition of entire unsaturated molecules, e.g.,...
C585S510000
Reexamination Certificate
active
06284938
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the production of oligomers from light olefins.
BACKGROUND OF THE INVENTION
PRIOR ART
Processes for the oligomerization of light olefins to produce C
7
and higher carbon number oligomers are well known. Oligomerization processes have been long employed to produce good quality motor fuel components from propylene and butylene. 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. Despite a long history of safe operation, recent concerns over the possibility of a catastrophic release of HF acid from HF alkylation units has prompted the investigation of modification or alternatives to the HF alkylation process for the production of motor fuels. One existing alternative is a similar alkylation process that uses sulfuric acid as the catalyst. While the use of sulfuric acid may decrease the degree of the hazard that some associate with the use of HF acid, the sulfuric acid process is still perceived as possibly presenting the same hazard and is not as economically advantageous as the HF alkylation process. Therefore, processing methods have been sought to improve the operation of oligomerization processes as substitutes for acid catalyzed alkylation.
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, U.S. Pat. No. 5,049,360, U.S. Pat. No. 4,749,820, U.S. Pat. No. 4,304,948, and U.S. Pat. No. 2,526,966.
It also known to hydrotreat the olefinic hydrocarbon streams produced by oligomerization to saturate olefins. Patent GB 2186287 discloses dehydrogenation of and oligomerization of a C
4
fraction to produce a jet aircraft fuel that is optionally hydrogenated into premium gasoline. The hydrotreatment of jet fuels, diesel fuels and lubes produced by dehydrogenation and oligomerization of light paraffins is disclosed in U.S. Pat. No. 4,678,645. However, hydrotreating is not always beneficial for gasoline fractions produced by oligomerization and can lower octane ratings, but is known to be particularly beneficial when saturating isooctenes to isooctanes.
Some prior art process that use highly acidic halide type catalysts for polymerization have suggested the recycle of paraffins to the polymerization zone for purposes of cooling. Such references include U.S. Pat. No. 4,200,714 and U.S. Pat. No. 4,254,294. However, heavier paraffin streams in these references are disclosed exclusively for the purposes of controlling reaction zone temperature.
It is a further object of this invention to increase the octane number of the saturated oligomerization products.
It is a yet further object of this invention to reduce the impact of catalyst fouling by coke accumulation in oligomerization processes.
BRIEF SUMMARY OF THE INVENTION
It has been surprisingly found that the introduction of heavy paraffins into an oligomerization zone for the oligomerization of olefins will have the benefit of reducing catalyst fouling and significantly improving the operation of the oligomerization zone. The process introduces a stream of heavy paraffins that have a carbon number of at least 8 into the oligomerization zone. The heavy paraffins keep the surface of the catalyst flushed of heavy isomers that can condense and foul the surface of the catalyst. In addition to the inhibition of fouling the recycling of the heavy paraffins to the oligomerization zone maintains the activity of the catalyst that promotes the selectivity of the oligomerization zone to desired olefins.
While not wishing to be bound to any theory it is believed that the flushing action of the heavy paraffins may be responsible for the improved selectivity of the oligomerization products. Flushing of the catalyst with the heavy paraffin stream maintains a liquid phase flow across the catalyst. The liquid phase flow may be responsible for rapidly removing the initial products from the surface of the catalyst before further reaction can take place to form heavies and cracked products. The oligomerization reaction is highly exothermic so it is believed that the presence of the heavy liquid paraffin also moderates any temperature rise in the reaction zone at large and locally within the catalyst.
A number of specific operational steps can separately or collectively provide the oligomerization improvements of this invention. The flushing benefits of this invention are facilitated by the use of liquid phase conditions and heavier hydrocarbons. Passing heavier hydrocarbons, such as octanes and higher, enhances the improvements of this invention to the oligomerization zone. Furthermore the invention has been proven to raise octane number of gasoline streams substantially when used in conjunction with a mild acid catalyst in the oligomerization zone. Substantial liquid phase conditions in conjunction with the heavy paraffin addition of this invention will offer substantial improvements to the catalyst life, and the catalyst life may be further improved as oligomerization zone approaches 100% liquid phase conditions.
Accordingly, in one embodiment, this invention is an oligomerization process for the production of C
8
and higher carbon number olefins. The process passes an oligomerization zone feed comprising C
3
or higher olefins to an oligomerization zone and contacts the oligomerization zone feed at oligomerization conditions with an oligomerization catalyst. A heavy saturate stream comprising paraffins having a carbon number of at least 8 passes into contact with the feed and the catalyst. The process recovers an oligomerization effluent stream comprising the paraffins and C
8
or heavier olefin products. Preferably the oligomerization effluent stream is passed to a separator and separated into a product stream comprising C
8
or higher carbon number olefins and said heavy saturate stream, a portion of said heavy saturate stream is recycled to the oligomerization zone, a portion of the heavy saturate stream is rejected from the process and a heavy paraffin stream is combined with the olefins of the feed stream or the effluent stream to provide make up paraffins for said heavy saturate stream.
In a more specific embodiment, this invention is an oligomerization process for the production of C
9
and higher carbon number oligomers. The process passes an oligomerization zone feed comprising C
3
and/or C
4
olefins to an oligomerization zone and contacts the oligomerization zone feed at oligomerization conditions. A heavy saturate stream comprising C
6
and higher carbon number paraffins passes into contact with the feed and the catalyst to the oligomerization zone to maintain at least a portion of the combined heavy saturate stream and feed in liquid phase conditions in the oligomerization zone. The process recovers an oligomerization effluent stream comprising the paraffins and product oligomers comprising C
9
and higher olefin products. Separation of the oligomerization effluent stream provides an oligomerization product stream comprising product oligomers and provides the heavy saturate stream comprising the paraffins wherein the highest carbon number of the sat
Frame Robert R.
Gimre Steven C.
Muldoon Brian S.
Stine Laurence O.
Paschall James C.
Tolomei John G.
UOP LLC
Yildirim Bekir L.
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