Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-04-29
2001-03-13
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S124900, C526S129000, C526S130000, C526S133000, C526S134000, C526S156000, C526S160000, C526S161000, C526S217000, C526S220000
Reexamination Certificate
active
06201076
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for polymerizing olefins in the presence of a single-site catalyst, an optional activator, and a fatty amine additive. The fatty amine reduces reactor fouling and sheeting and simultaneously enhances the activity of the catalyst. Overall efficiency of the polymerization process is increased.
BACKGROUND OF THE INVENTION
Interest in metallocene and non-metallocene single-site catalysts (hereinafter all referred to as single-site catalysts) has continued to grow rapidly in the polyolefin industry. These catalysts are more reactive than conventional Ziegler-Natta catalysts, and they produce polymers with improved physical properties. The improved properties include narrow molecular weight distribution, reduced low molecular weight extractables, and good comonomer incorporation, which allows the production of low-density polymers.
Single-site catalysts are typically soluble in the polymerization reaction medium and are therefore advantageous in solution processes. However, for gas-phase, slurry, and bulk monomer processes, it is useful to immobilize the catalyst on an inert carrier or support. Unfortunately, supported catalysts tend to cause reactor fouling and/or sheeting. Reactor fouling results in many serious problems including poor heat transfer, poor particle morphology, and forced reactor shutdown.
To solve these problems, a number of process and catalyst modifications have been disclosed. For example, U.S. Pat. Nos. 4,792,592 and 4,876,320 disclose electrical methods to control reactor static electricity that leads to fouling and sheeting. EP 811,638 teaches addition of antistatic agents to control static buildup. Other additives have also been used to control reactor fouling. See for example U.S. Pat. Nos. 4,885,370, 4,978,722, 5,026,795, 5,037,905, and PCT Intl. Appl. Nos. WO 96/11960 and WO 96/11961.
In particular, WO 96/11960 and WO 96/11961 disclose catalyst systems formed by combining a metallocene, an activator, and a surface modifier applied to a support. Both references teach that the surface modifier must be added to the support during catalyst preparation. Addition of the surface modifier to the reactor during polymerization leads to fouling and a 65 percent loss in catalyst activity. See Example 6 of WO 96/11961. The preferred modifier amount is less than 3.5 percent of the catalyst weight, and the maximum allowable amount is 10 percent. Failure to observe these limits results in increased fouling and substantial reduction of catalyst activity. For instance, Example 6 of WO 96/11960 teaches a significant loss of activity at a modifier concentration of 5 percent.
EP 811,638 teaches addition of an amine antistatic agent to the polymerization reactor to reduce static buildup that can lead to fouling or sheeting. The antistatic agent is added to the reactor in an amount ranging from 1 to 200 ppm based on polymer produced, preferably from 1 to 100 ppm, and most preferably from 1 to 10 ppm (antistatic agent/polymer produced). Higher amounts lead to losses in catalyst activity. Comparative examples 10 and 11 teach that addition of 200 ppm of an ester or 2000 ppm of an ammonium antistatic agent decreases catalyst activity by 50-80%.
In sum, new ways to prevent reactor fouling in olefin polymerizations with single-site catalysts are needed. Particularly valuable processes would use readily available additives that can be fed directly to the reactor. This would prevent additional catalyst preparation expense. Ideally, the additives would increase or have a negligible effect on catalyst activity.
SUMMARY OF THE INVENTION
The invention is a polymerization process. The process comprises polymerizing an olefin in the presence of a supported single-site catalyst, an optional activator, and a fatty amine. The fatty amine is added directly to the polymerization reactor in an amount from about 10 to about 75 weight percent, based on the amount of supported catalyst.
We surprisingly found that the fatty amine, when added directly to the reactor in the prescribed amount, reduces or eliminates reactor fouling without hurting catalyst activity. In fact, the fatty amine actually helps to increase catalyst activity.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention comprises polymerizing an olefin in the presence of a supported single-site catalyst, optionally an activator, and from about 10 to about 75 weight percent, based on the amount of supported catalyst, of a fatty amine. The fatty amine is added directly to the reactor.
By “single-site catalyst,” we mean all of the metallocene and non-metallocene catalysts now known. Single-site catalysts give polyolefins with characteristically narrow molecular weight distributions and high melt indices compared with polyolefins that are readily accessible with Ziegler-Natta catalysts. The single-site catalyst preferably has the formula:
[L
1
]
a
[L
2
]
b
MX
n
where
M is a Group 3-10 transition metal;
L
1
and L
2
are the same or different polymerization-stable anionic ligands;
a+b=1 or 2;
each X is independently a neutral ligand or a uninegative sigma-bonded ligand; and
a+b+n=the formal oxidation state of M.
The transition metal, M, may be any Group 3 to 10 metal or a metal from the lanthanide or actinide series. (The IUPAC system of numbering groups of elements of the Periodic Table is used throughout this application.) Preferably, the catalyst contains a Group 4 to 6 transition metal; more preferably, the catalyst contains a Group 4 metal such as titanium or zirconium.
Catalysts useful in the process of the invention preferably include polymerization-stable anionic ligands, L
1
and L
2
. Suitable L
1
and L
2
ligands include cyclopentadienyl (substituted or unsubstituted) anions such as those described in U.S. Pat. Nos. 4,791,180 and 4,752,597, the teachings of which are incorporated herein by reference. Suitable L
1
and L
2
ligands also include substituted or unsubstituted boraaryl, pyrrolyl, indolyl, quinolinyl, hydroxypyridinyl, and aminopyridinyl groups as described in U.S. Pat. Nos. 5,554,775, 5,539,124, and 5,637,660, the teachings of which are also incorporated herein by reference. L
1
and L
2
can also be substituted or unsubstituted azaborolinyl ligands, such as those described in PCT Int. Appl. WO 96/34021. Preferably, the catalyst includes, at most, only one substituted or unsubstituted cyclopentadienyl ligand.
The polymerization-stable anionic ligands L
1
and L
2
can be bridged. Groups that can be used to bridge the polymerization-stable anionic ligands include, for example, methylene, ethylene, 1,2-phenylene, dialkylsilyls, and diarylsilyls. Normally, only a single bridge is used in the single-site catalyst, but complexes with two bridging groups are known and can be used. Bridging the ligand changes the geometry around the transition metal and can improve catalyst activity and other properties, such as molecular weight, comonomer incorporation, and thermal stability.
Each X is independently a neutral ligand or a uninegative sigma-bonded ligand. Preferred X ligands include hydride, halide, C
1
-C
20
alkyl, aryl, alkoxy, aryloxy, siloxy, and dialkylamido. More preferably, X is hydride, chloride, bromide, C
1
-C
8
alkoxy, C
3
-C
18
trialkylsiloxy, or C
2
-C
6
dialkylamido. Also particularly preferred are aryl and alkyl groups that do not undergo &bgr;-hydrogen elimination reactions (e.g., olefin formation with loss of M-H); examples are methyl, phenyl, benzyl, neopentyl, and the like.
Two X groups may be joined to form a metallacycle of 4 to 20 atoms, including the metal. Examples include metallacycloalkanes, metallasilacycloalkanes, and metallacyclopentadiene complexes. Butadienyl ligands, which can have a formal &sgr;
2
,&eegr;
2
structure, are also included.
Suitable neutral ligands include, for example, &pgr;-bonded ligands such as &eegr;
2
-ethylene, &eegr;
2
-bis(trimethylsilyl)acetylene, &eegr;
4
-butadiene, &eegr;
2
-benzyne, and the like. Neutral X ligands also include solvating mole
Etherton Bradley P.
Hlatky Gregory G.
Meas, Jr. James H.
Carroll Kevin M.
Equistar Chemicals L.P.
Schuchardt Jonathan L.
Teskin Fred
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