Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By addition of extraneous agent – e.g. – solvent – etc.
Reexamination Certificate
1999-08-23
2001-04-03
Knode, Marian C. (Department: 1764)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By addition of extraneous agent, e.g., solvent, etc.
C585S865000, C585S833000, C585S804000
Reexamination Certificate
active
06211423
ABSTRACT:
1. FIELD OF THE INVENTION
This invention relates to a process for separating olefins from saturated hydrocarbons followed by separating linear alpha olefins and internal olefins from a saturated hydrocarbon stream and from an olefin stream.
2. 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 a FT stream with sufficient purity that a particular composition is acceptable in the intended application. These processes for separating out different species in a 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 a FT stream do not, however, selectively react with olefins while simultaneously reject paraffins.
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 in a first step, or further separate the linear alpha olefins from the saturated hydrocarbons removed in the first step along with separating linear alpha olefins from an olefin stream removed in the first step.
As used throughout the specification and claims, the words, “first, second, third, etc” are meant only to distinguish one feed, composition, compound, or reaction zone, etc., from a different feed, composition, compound, reaction zone, etc., and are not meant to designate a particular sequence. For ease of tracking a particular stream and for convenience sake only, olefin streams have been assigned the letter “o,” alpha olefin streams have been assigned the letters “ao,” internal olefin streams have been assigned the letters “io,” and saturated compound streams have been assigned the letter “s.” Their presence does not imply a particular order, sequence, or ascribe a meaning to the description and claim language, nor does a letter's absence in a claim or embodiment imply that a process step or composition not expressly mentioned is required or implicit in the embodiment or claim. Where no spelled number or assigned letter is present, its use is not deemed necessary since other compounds, composition, steps, or reaction zones are not identically expressed in the embodiment or claim. Their absence or presence do not modify or ascribe a particular meaning, other than to differentiate from other identically expressed compounds, compositions, steps, reaction zones, etc in the embodiment or claim.
3. SUMMARY OF THE INVENTION
This invention relates to a process for separating and isolating species in a FT stream. There is provided a process for treating a feedstock comprising saturated hydrocarbons, internal olefins, and alpha olefins, comprising:
a) contacting the feedstock with a linear polyaromatic compound in a first reaction zone under conditions effective to form a reaction mixture comprising first linear polyaromatic compound-olefin adducts and saturated hydrocarbons;
b) separating said olefin adducts from the saturated hydrocarbons in the reaction mixture to form a first olefin adduct stream and a first saturated hydrocarbon stream;
si) contacting at least a portion of the first saturated hydrocarbon stream with a linear polyaromatic compound in a second reaction zone under conditions effective to form a reaction mixture comprising a second linear polyaromatic compound-olefin adduct and saturated hydrocarbons;
sii) separating said second olefin adduct from the reaction mixture in the second reaction zone to form a second olefin adduct stream and a second saturated hydrocarbon stream, wherein the concentration of the saturated hydrocarbons in the second saturated hydrocarbon stream is enriched over the concentration of saturated hydrocarbons in the first saturated hydrocarbon stream, and the concentration of the saturated hydrocarbons in the first saturated hydrocarbon stream is enriched over the concentration of saturated hydrocarbons in the feedstock; and
oi) dissociating said first olefin adducts to form linear polyaromatic compounds and a first olefin composition comprising alpha olefins and internal olefins;
oai) contacting the olefin composition with a linear polyaromatic compound in a third reaction zone under conditions effective to form a reaction mixture comprising linear polyaromatic compound-alpha olefin adducts and an internal olefin composition;
oaii) separating said alpha olefin adducts, and optionally unreacted linear polyaromatic compounds as well, from the reaction mixture in the third reaction zone to form an alpha olefin adduct stream and an internal olefin stream;
oaiii) dissociating the alpha olefin adducts to form linear polyaromatic compounds and an alpha olefin composition;
whereby the concentration of alpha olefins in the alpha olefin composition is enriched over the concentration of alpha olefins in the first olefin composition, and the concentration of alpha olefins in the first olefin composition is enriched over the concentration of alpha olefins in the feedstock.
REFERENCES:
patent: 2775633 (1956-12-01), Fenske et al.
patent: 2953611 (1960-09-01), Spengler
patent: 3306946 (1967-02-01), Snyder et al.
patent: 3444261 (1969-05-01), Caprioli et al.
patent: 3534116 (1970
Fenouil Laurent Alain
Fong Howard Lam-Ho
Slaugh Lynn Henry
Dang Thuan D.
Knode Marian C.
Shell Oil Company
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