Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in two or more physically distinct zones
Reexamination Certificate
1998-07-02
2001-01-16
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymerizing in two or more physically distinct zones
C526S129000, C526S210000, C526S158000, C526S348000, C502S103000
Reexamination Certificate
active
06174969
ABSTRACT:
The present invention relates to a process for polymerizing C
2
-C
8
-alk-1-enes by means of a Ziegler-Natta catalyst system in a reactor cascade comprising at least two reactors, a homo- or copolymer of C
2
-C
8
-alk-1-enes being prepared in one reactor R
A
, upstream of which one or more further reactors may be connected, the reaction mixture from R
A
being discharged and being transferred to a subsequent reactor R
B
and the polymerization in R
B
and in the reactors which may be connected to R
B
being carried out in the presence of a liquid or dissolved regulator for regulating the catalyst activity.
The present invention furthermore relates to an apparatus for polymerizing C
2
-C
8
-alk-1-enes by means of the novel process.
Polymers of C
2
-C
8
-alk-1-enes may be prepared both by liquid-phase polymerization and by polymerization of a suspension or by gas-phase polymerization. Since the resulting solid polymer can be readily separated from the gaseous reaction mixture, gas-phase polymerization is increasingly being carried out. The polymerization is carried out with the aid of a Ziegler-Natta catalyst system which usually consists of a titanium-containing solid component, an organic aluminum compound and an organic silane compound (EP-B 45 977, EP-A 171 200, U.S. Pat. No. 4,857,613, U.S. Pat. No. 5,288,824).
The polymers of C
2
-C
8
-alk-1-enes include the corresponding homopolymers, copolymers and block or impact copolymers. The latter are generally mixtures of different homo- or copolymers of C
2
-C
8
-alk-1-enes which in particular have good impact strength. They are usually prepared in reactor cascades comprising at least two reactors connected in series and often in a process involving two or more stages, the polymer obtained in a first reactor being transferred, in the presence of still active Ziegler-Natta catalyst components, to a second reactor in which further monomers are polymerized onto said polymer.
In the preparation of some polymers of C
2
-C
8
-alk-1-enes in reactor cascades, in particular in the polymerization of polypropylene block copolymers with more than 20% by weight of a propylene/ethylene copolymer containing from 15 to 80% by weight of ethylene, the occurrence of lumps or agglomerates of the polymer particles and the formation of coatings and build-ups on the reactor walls and reactor baffles are frequently observed in the reactor. This formation of coatings complicates the temperature and reaction control during the copolymerization. The result is that the times on stream of the reactors have to be shortened in order to be able to ensure a controlled reaction in every case. Shorter times on stream of reactors in turn result in an increase in the setup times and hence in the production costs, so that coating adversely affects the cost-efficiency of the preparation of such copolymers.
U.S. Pat. No. 4,739,015, DE-A 41 19 345 and DE-A 44 32 798 disclose processes for the preparation of propylene/ethylene copolymers in which the formation of coatings is substantially reduced by the use of a compound, such as an alkanol, which regulates the catalyst activity. In U.S. Pat. No. 4,739,015, the regulators present in the liquid state are added to the reaction system of the second polymerization stage either directly or diluted with a solvent or, preferably, diluted with a gas. In DE-A 41 19 345 and DE-A 44 32 798, the alkanol is added directly to the reaction mixture of the second polymerization stage. In these processes, however, it is still not possible completely to avoid the formation of coatings.
It is an object of the present invention to remedy the disadvantages described and to provide a process which further reduces or completely suppresses the tendency to agglomeration of the polymer particles and to the formation of coatings.
We have found that this object is achieved by a process for polymerizing C
2
-C
8
-alk-1-enes by means of a Ziegler-Natta catalyst system in a reactor cascade comprising at least two reactors, a homo- or copolymer of C
2
-C
8
-alk-1-enes being prepared in a reactor R
A
, upstream of which one or more further reactors may be connected, the reaction mixture from R
A
being discharged and being transferred to a subsequent reactor R
B
and the polymerization in R
B
and in the reactors which may be connected to R
B
being carried out in the presence of a liquid or dissolved regulator for regulating the catalyst activity, wherein the regulator is added to the reaction mixture after discharge from R
A
and before entry into R
B
.
C
2
-C
8
-Alk-1-enes which in particular may be used in the novel process are ethylene, propylene, but-1-ene, pent-1-ene, hex-1-ene, hept-1-ene or oct-1-ene, ethylene, propylene or but-1-ene being preferably used. The process is suitable for preparing homopolymers of the C
2
-C
8
-alk-1-enes or copolymers of C
2
-C
8
-alk-1-enes, preferably with up to 30% by weight of other alk-1-enes of up to 8 carbon atoms polymerized herein. Copolymers are to be understood here as meaning both random copolymers and block or impact copolymers.
As a rule, the novel process is used in a polymerization involving two or more stages, i.e. the polymerization conditions define the stages to such an extent that polymers having different properties are produced. For the homopolymers or random copolymers, this may be, for example, the molar mass, i.e. polymers having different molar masses are prepared in the stages for broadening the molar mass distribution. Preferably, different monomers or monomer compositions are polymerized in the stages. This usually leads to block or impact copolymers.
The novel process is particularly suitable for preparing homopolymers of propylene or copolymers of propylene with up to 30% by weight of other alk-1-enes of up to 8 carbon atoms as polymerized units. Here, the copolymers of propylene are random copolymers or block or impact copolymers. If the copolymers of propylene have a random structure, they generally contain up to 15, preferably up to 6,% by weight of other alk-1-enes of up to 8 carbon atoms, in particular ethylene, but-1-ene or a mixture of ethylene and but-1-ene.
The block or impact copolymers of propylene are polymers in which a propylene homopolymer or a random copolymer of propylene with up to 15, preferably up to 6,% by weight of other alk-1-enes of up to 8 carbon atoms is prepared in the first stage and then a propylene/ethylene copolymer containing from 15 to 80% by weight of ethylene is polymerized onto said homopolymer or copolymer in the second stage, it being possible for the propylene/ethylene copolymer additionally to contain further C
4
-C
8
-alk-1-enes. As a rule, the propylene/ethylene copolymer is polymerized on in an amount such that the copolymer produced in the second stage accounts for from 3 to 60% by weight in the end product. The novel process is particularly preferred when the amount of the propylene/ethylene copolymer prepared in the second stage is from 20 to 60% by weight.
The polymerization is carried out, according to the invention, by means of a Ziegler-Natta catalyst system. The catalyst systems used are in particular those which, in addition to a titanium-containing solid component a), also contain cocatalysts in the form of organic aluminum compounds b) and electron donor compounds c).
However, Ziegler-Natta catalyst systems based on metallocene compounds may also be used in the novel process.
For the preparation of the titanium-containing solid component a), the titanium compounds generally used are the halides or alcoholates of trivalent or tetravalent titanium, alkoxytitanium halide compounds or mixtures of different titanium compounds also being suitable. Titanium compounds which contain chlorine as halogen are preferably used. The titanium halides which, apart from titanium, contain only halogen are likewise preferred, especially the titanium chlorides and in particular titanium tetrachloride.
The titanium-containing solid component a) preferably contains at least one halogen-containing magnesium compound. Halogens are understood here as chlorin
Kersting Meinolf
Langhauser Franz
Lutz Gerald
BASF - Aktiengesellschaft
Choi Ling-Siu
Keil & Weinkauf
Wu David W.
LandOfFree
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