Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Removing and recycling removed material from an ongoing...
Reexamination Certificate
1999-02-18
2001-02-06
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Removing and recycling removed material from an ongoing...
C526S065000, C526S067000, C585S850000, C585S851000, C585S852000
Reexamination Certificate
active
06184315
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the area of polymerization and more particularly to the polymerization of unsaturated hydrocarbons. Polymerization generally consists in reacting together compounds that comprise an unsaturation or a reactive function: monomers. The products that are obtained at the end of the reaction are in the form of long chains in which the same pattern is repeated: these are the polymers. Very often, the polymerization effluent also contains monomers that have not reacted; at least a portion of these monomers are generally recycled toward the polymerization zone, and the device is then designated as a “polymerization loop.”
Polymerization can be assisted by comonomers. These comonomers, if they enhance the reactivity of the monomers and the quality of the polymers that are produced, are less reactive than the monomers, however. These are generally expensive compounds; it is therefore advantageous to provide for the recycling of comonomers that have not reacted.
In the process according to the invention, the comonomer that is used is an alpha-olefin. When a comonomer is introduced into the polymerization zone, isomers of this comonomer are also very often introduced; moreover, during polymerization, the comonomer is also unavoidably formed from isomers of the comonomer (internal olefins).
These isomers are not reactive; in general they are inert relative to the polymerization reaction. If no provision is made for purging of the polymerization loop, these isomers accumulate and can then represent a large portion of the fluid that is assumed to contain basically the comonomer that circulates in the polymerization loop. The isomers then play a role of contaminating the polymerization loop.
One skilled in the art knows that it is often very difficult to separate the internal olefins from the alpha-olefins, whereby the internal olefins have in particular boiling points that are close to that of the corresponding alpha-olefin. Consequently, provision is generally made for significant purging. It has the drawback of the loss of comonomers, however.
SUMMARY OF THE INVENTION
One of the objects of this invention is to increase the proportion of alpha-olefins (comonomers) in the recycled fluid; to do this, the polymerization purging is subjected to a metathesis reaction in the presence of ethylene (also called “ethenolysis”), which makes it possible to transform a portion of the internal olefins into lighter olefins that will then be eliminated easily to obtain a comonomer concentrate (alpha-olefin).
The ethenolysis reaction for the production of alpha-olefins from internal olefins is well known to one skilled in the art; it is described by, for example, Bradshaw, Howman and Turner in “Olefin Dismutation: Reactions of Olefins on Cobalt Oxide-Molybdenum Oxide-Alumina” J. Catal., 7(3), 269-76 that was published in 1967.
In addition, descriptions of processes of polymerization and of copolymerization of ethylene in the presence of an alpha-olefin are found in the literature. These are, for example Patents EP 50477 and EP 1167248, in which the ethylene reacts with an addition of alpha-olefins and in which the recycling of the monomers that have not reacted is provided for.
This invention relates to a polymerization process that is carried out in at least one reactor that contains at least one catalyst starting from a monomer and a comonomer, and the comonomer that is used, which is an alpha-olefin, is introduced into the polymerization reactor in the form of an approximately pure compound. “Approximately pure compound” in the context of this description is defined as the flow that contains at least 90% by weight of comonomer, preferably at least 95% by weight of comonomer and, even more preferably, at least 97% by weight of comonomer.
The polymerization effluent is then separated into two fractions: a heavy fraction that contains at least one polymer, and a light fraction that comprises the monomer that has not reacted, the comonomer that has not reacted, as well as isomers of this comonomer. At least a portion of the light fraction is then treated during an ethenolysis stage in the presence of an addition of fresh ethylene. The effluent that is produced in the ethenolysis stage is subjected to at least two separations, at the end of which the fraction that contains the comonomer is separated, on the one hand, from the lighter fraction and, on the other, from the fraction that is heavier than it is, whereby this fraction that contains the comonomer is then recycled to the polymerization zone.
The invention also relates to an installation for the implementation of this process.
According to an embodiment of the invention, a feedstock that contains at least partly, if not mostly, a monomer undergoes polymerization in the presence of a comonomer.
The effluent from this polymerization is then separated into two fractions: a heavy fraction that contains the synthesized polymers, and a light fraction that contains the monomer, the fraction of the comonomer that has not reacted as well as isomers of this comonomer and also sometimes a solvent that is used for the polymerization reaction. It has been possible to introduce isomers of this comonomer with the comonomer, but often the majority of these isomers are formed from the comonomer during the polymerization reaction.
After polymerization and then separation, at least a portion of the light fraction of the effluent is subjected to ethenolysis. Generally, another portion of this light fraction is directly recycled toward the polymerization zone, whereby the remainder of the light fraction is evacuated from the polymerization loop via a purge. The effluent from the ethenolysis reaction then undergoes at least two separations to isolate the fraction that contains the comonomer, whereby said fraction is then recycled toward the polymerization zone.
The comonomer that is used for the polymerization reaction is selected based on its ability to enhance the physical properties of the polymer that it is desired to obtain; generally the polymerization reaction is carried out in the presence of a single comonomer. For example, to obtain polyethylene or polypropylene, the comonomer is generally selected from the group that is formed by 1-butene, 1-hexene, 1-octene, 4-methyl 1-pentene, and 1-pentene, and it is introduced into the polymerization feedstock in an amount such that it represents about 1% to 50% by weight relative to the polymerization feedstock, for example, 1-butene is generally introduced in amounts of about 1% to 10% by weight relative to the feedstock, and 1-octene is generally introduced in amounts of about 1% to 50% by weight relative to the feedstock, and 1-hexene is generally introduced in amounts of about 1% to 20% by weight relative to the polymerization feedstock—whereby this feedstock contains both fresh and recycled compounds.
The monomer that is used in the polymerization reaction can be any polymerizable unsaturated monomer; preferably this monomer is ethylene or propylene. The monomer that is used for the polymerization reaction should be very pure, i.e., the flow contains at least 90% by weight of monomer, preferably at least 95% by weight of monomer, and even more preferably at least 99% by weight of monomer.
The treated effluent can be any polymerization effluent that contains internal olefins and in particular an effluent from the polymerization of ethylene.
Without limiting the scope of this invention, among the ethylene polymerization processes that are best known to one skilled in the art, a distinction is made between gaseous processes, stirred-bed or fluidized-bed processes, and liquid, suspension, or solution processes.
The catalysts that are used in gaseous polymerization in a fixed bed and even in some cases liquid polymerization are catalysts with a chromium base as a substrate, catalysts such as organoaluminium-titanium, or combinations of a catalyst with a titanium base as a substrate or a co-catalyst with a triethylaluminum base. For the gaseous processes in a fluidized bed
Forestiere Alain
Hugues Francois
Cheung William
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Wu David W.
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