Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By addition of extraneous agent – e.g. – solvent – etc.
Reexamination Certificate
1999-08-23
2001-08-07
McAvoy, Ellen M. (Department: 1764)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By addition of extraneous agent, e.g., solvent, etc.
C585S809000, C585S833000, C585S865000
Reexamination Certificate
active
06271434
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for separating olefins from saturated hydrocarbons, and more particularly, to a process for separating olefins from saturated hydrocarbons in a Fisher-Tropsch (FT) stream.
BACKGROUND OF THE INVENTION
Many industrial processes produce olefin/saturated hydrocarbon streams that are mixtures of olefins, saturated hydrocarbons, and oxygenates. Olefins are frequently used in the manufacture of polymers such as polyethylene, as drilling mud additives, or as intermediates for the production of oil additives and detergents. Some industrial processes manufacture olefins streams by oligomerizing ethylene over an alpha olefin catalyst to produce mixtures of alpha and internal olefins having a broad range of carbon numbers. However, these streams rely on the use of ethylene as a feedstock material, which add a significant cost to the manufacture of the olefin. On the other hand, the FT process starts with an inexpensive feedstock, syngas, generally derived from natural gas, coal, coke, and other carbonaceous compounds to make oligomers comprised of olefins, aromatics, saturates, and oxygenates.
The FT process, however, is not very selective to the production of olefins. While reaction conditions and catalysts can be tuned to manufacture a stream rich in the desired species within the FT product stream, a large percentage of the FT stream contains other types of compounds which must be separated from the olefins, which olefins are purified, and then sold into different markets. For example, a typical commercial FT stream will contain a mixture of saturated hydrocarbons, olefins, aromatics, and oxygenates such as organic carboxylic acids, alcohols, ethers, esters, ketones, and aldehydes. All these compounds must be separated from the crude FT stream before a particular composition may be offered commercially. To further complicate the separation operation, the FT stream contains compounds having a wide spectrum of carbon numbers, as well as a wide variety of olefins, ranging from C
2
-C
200
species, internal linear olefins, alpha linear olefins, internal branched olefins, alpha branched olefins, and cyclic olefins, many of which have similar molecular weights. Separating and isolating these species is no easy task. Conventional distillation methods are frequently inadequate to separate species having closely related boiling points.
Various processes have been proposed to efficiently separate the different species in an FT stream with sufficient purity that a particular composition is acceptable in the intended application. These processes for separating out different species in an FT stream include the use of molecular sieves, which are restricted to a feed have an average carbon number range which is more limited than a composition containing a broad spectrum of average carbon numbers ranging from C
5
-C
10
, to the use of exchange resins, to the use of super-fractionaters often operated at high pressure, and the use of oligomerization catalysts or etherification techniques to alter the boiling points of the species in the FT stream. Many reactive methods for separating species in an FT stream do not, however, selectively react with olefins while simultaneously reject paraffins.
It would be desirable to conduct a separation operation on an FT stream in which the activity and life of the separating agent is not diminished by the presence of impurities in the stream, such as oxygenates; which remains active under a wide band of average carbon numbers ranging from C
5
-C
20
, and which distinguishes between olefins and paraffins in an FT stream.
U.S. Pat. No. 4,946,560 described a process for the separation of internal olefins from alpha olefins by contacting a feedstock with an adducting compound such as anthracene to form an olefin adduct, separating the adduct from the feedstock, dissociating the olefin adduct through heat to produce anthracene and an olefin composition enriched in alpha olefin, and separating out the anthracene from the alpha olefin. This reference does not suggest the desirability or the capability of anthracene to separate olefins from saturated hydrocarbons or linear alpha olefins from saturated hydrocarbons.
SUMMARY OF THE INVENTION
This invention relates to a process for separating olefins from saturated hydrocarbons, and thereafter treating the olefins to separate linear alpha olefins from internal olefins. The process of the invention is well suited to treating an FT stream.
In particular, there is provided a process for contacting a linear polyaromatic compound with a feedstock composition comprising linear alpha olefins, internal olefins, and saturated hydrocarbons, separating the olefins from the saturated hydrocarbons in the feedstock composition to form an olefin composition and a saturated hydrocarbon stream, subsequently contacting a linear polyaromatic compound with the olefin composition comprising linear alpha olefins and internal olefins, and separating the linear alpha olefins to form a linear alpha olefin stream from the internal olefins, whereby the concentration of linear alpha olefins in the linear alpha olefin stream is enriched over the concentration of linear alpha olefins in the feedstock and in the olefin composition.
In another embodiment of the invention, there is provided a process for treating a feedstock composition comprising linear alpha olefins, internal olefins, and saturated hydrocarbons, comprising:
a) contacting the feedstock composition with a linear polyaromatic compound in a first reaction zone under conditions effective to form a reaction mixture comprising linear polyaromatic compound-olefin adducts and saturated hydrocarbons;
b) separating the first linear polyaromatic compound-olefin adducts from the saturated hydrocarbons in the reaction mixture to form a first adducted olefin stream and a saturated hydrocarbon stream;
oi) dissociating linear polyaromatic compound-olefin adducts in the first adducted olefin stream to form linear polyaromatic compounds and an olefin composition comprising alpha olefins and internal olefins;
oii) contacting the olefin composition with linear polyaromatic compounds in an AO reaction zone under conditions effective to form a reaction mixture comprising linear polyaromatic compound-linear alpha olefin adducts and an internal olefin composition;
oiii) separating the linear polyaromatic compound-linear alpha olefin adducts from the reaction mixture in the AO reaction zone to form a linear alpha olefin adducted stream and an internal olefin stream; and
oiv) dissociating the linear polyaromatic compound-linear alpha olefin adducts in the linear alpha olefin adducted stream to form linear polyaromatic compounds and a linear alpha olefin composition;
whereby the concentration of linear alpha olefins in the linear alpha olefin composition is enriched over the concentration of linear alpha olefins in the olefin composition, and the concentration of linear alpha olefins in the olefin composition is enriched over the concentration of linear alpha olefins in the feedstock.
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Fenouil Laurent Alain
Fong Howard Lam-Ho
Slaugh Lynn Henry
McAvoy Ellen M.
Shell Oil Company
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