Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By addition of extraneous agent – e.g. – solvent – etc.
Reexamination Certificate
1999-05-11
2003-04-08
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By addition of extraneous agent, e.g., solvent, etc.
C585S865000, C585S833000, C585S807000
Reexamination Certificate
active
06545192
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, 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
20
, 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 conduct a separation operation between saturated hydrocarbons and olefins.
SUMMARY OF THE INVENTION
This invention relates to a process for separating and optionally isolating olefins from saturated hydrocarbons, and in particular, to a process for separating and optionally isolating olefins from saturated hydrocarbons in an FT stream. There is provided a process for separating olefins from saturated hydrocarbons in a feedstock, comprising:
a) contacting a feedstock comprising olefins and saturated hydrocarbons with a linear polyaromatic compound under conditions effective to form a reaction mixture comprising linear polyaromatic compound-olefin adducts and saturated hydrocarbons;
b) separating the linear polyaromatic compound-olefin adducts from the saturated hydrocarbons in the reaction mixture to form a saturated hydrocarbon stream and an adducted olefin stream;
c) dissociating the linear polyaromatic compound-olefin adducts in the adducted olefin stream to form linear polyaromatic compounds and an olefin composition; and optionally
d) separating the linear polyaromatic compound formed in step c) from the olefin composition;
whereby the olefin composition is enriched in the concentration of olefins over the concentration of olefins in the feedstock.
DETAILED DESCRIPTION OF THE INVENTION
As used throughout this specification and in the claims, the term “comprising” means “at least,” such that other unmentioned elements, ingredients, or species are not excluded from the scope of invention.
The feed stream to be treated comprises at least olefins and saturated hydrocarbons. The class of saturated hydrocarbons as used herein includes at least a paraffin. The class of saturated hydrocarbons may also include other molecules such as cycloparaffins.
An olefin means any compound containing at least one carbon—carbon double bond. The olefins may be linear, branched, conjugated, contain multiple double bonds anywhere along the chain, substituted, unsubstituted, contain aryl or alicyclic groups, or contain heteroatoms.
The olefins may contain aryl moieties along with an aliphatic or cycloaliphatic moiety within the same compound, or may consist solely of an aliphatic, cycloaliphatic, or cycloaliphatic with aliphatic moieties on the compound. Preferably, the olefin is an aliphatic compound.
The olefin may be branched or linear. Examples of branching include alkyl, aryl, or alicyclic branches. The number of unsaturation points along the chain is also not limited. The olefin may be a mono-, di-, tri-, etc. unsaturated olefin, optionally conjugated. The olefin may also contain acetylenic unsaturation.
An alpha olefin is an olefin whose double bond is located on both of &agr; and &bgr; carbon atoms. An a carbon atom is any terminal carbon atom, regardless of how long the chain is relative to other chain lengths in a molecule. The alpha olefin may be linear or branched. Branches or functional groups may be located on double bond carbon atoms, on carbon atoms adjacent to the double bond carbon atoms, or anywhere else along the carbon backbone. The alpha olefin may also be a poly-ene, wherein two or more points of unsaturation may be located anywhere along the molecule, so long as at least on double bond is in the alpha position.
An internal olefin(s) is an olefin whose double bond is located anywhere along the carbon chain except at any terminal carbon atom. The internal olefin may be linear or branched. The location of a branch or substitution on the internal olefin is not limited. Branches or functional groups may be located on the double bond carbon atoms, on carbon atoms adjacent to the double bond carbon atoms, or anywhere else along the carbon backbone.
The olefin may also be substituted with chemically reactive functional groups. Examples of chemically reactive functional groups are carboxyl, aldehyde, keto, thio, ether, hydroxyl, and amine. The number of functional groups on a molecule is not limited. The functional gro
Fenouil Laurent Alain
Fong Howard Lam-Ho
Slaugh Lynn Henry
Dang Thuan D.
Shell Oil Company
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