Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-07-13
2002-01-15
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S065000, C526S124300, C526S216000, C526S903000, C502S104000, C502S107000, C502S127000
Reexamination Certificate
active
06339136
ABSTRACT:
The invention relates to a process for making propylene polymers or copolymers in propylene medium.
BACKGROUND OF THE INVENTION
Several processes for polymerizing alpha-olefins, for example propylene, are known. Such processes where Ziegler-Natta catalysts are employed, are for example slurry polymerization carried out in a solvent such as n-hexane, bulk or slurry polymerization carried out in a liquefied alpha-olefin monomer such as propylene and gas phase polymerization carried out in a gaseous monomer such as gaseous propylene. Further, combinations of these processes are also known such as slurry polymerization followed by gas polymerization.
Gas phase processes are advantageous in that recovery and reuse of inert hydrocarbon or monomer is more simple than in slurry processes. The cost for equipment for monomer recovery and reuse is small compared to slurry processes. One disadvantage of the gas phase processes is that the monomer inside the reactor is in vapor phase and therefor the monomer concentration is relatively low compared that of slurry processes. This results in a lower reaction rate. In order to increase the polymer yield per unit weight of catalyst, it is necessary to extend the residence time in the reactor by increasing the volume of the reactor.
In a book Y. V. Kissin, Kinetics of Polyolefin Polymerization with Heterogenous Ziegler-Natta Catalyst (1981), p. 10,11,70,71,125 the influence of temperature in propylene polymerization with TiCl
3
-based Z-N catalysts has been discussed. The active centers of catalysts have been shown to be stable up to 80° C. In a polymerization process carried out at relatively high temperatures, eg. 70-80° C. and high monomer concentration, the stage at which the rate of chain initiation and chain termination are equal, is reached early.
The overall polymer yield of such catalysts is in general low and very costly ash removal is necessary in the process.
According to EP0417995 a special catalyst for propylene polymerization at very high temperatures of 150-300° C. is disclosed. The catalyst has a typical structure which is possible with a claimed organoaluminium component and a silicon compound. However this process is not practical because the proposed polymerization temperatures are higher than the melting temperature of polypropylene.
Sergeev et al. (Macromol. Chem., 185, (1984), 2377-2385) have observed with TiCl
4
/EB-AlEt
3
/EB catalysts a slight increase of isotactic index when passing from 20° C. to 60° C. and a rapid decline above 70° C. Further Spitz and Guoyt (Macromol. Chem., 190 (1989), 707-716) reported for MgCl
2
/TiCl
4
catalyst that the number of active centers remains constant within the range of 50-70° C. Above 80° C. the activity decreases and the catalyst is deactivated.
In many patent applications it is mentioned that higher temperatures, such as up to 100° C., could be used. However in such publications, for example EP0438068 and EP0412750, only lower temperatures of 70-80° C. are presented in the examples. Therefore, according to prior art only lower temperatures of up to 80° C. has been used.
From U.S. Pat. No. 5,093,415 it is known a high temperature (over 100° C.) process employing a special catalyst containing magnesium, titanium, halide and carboxylic acid ester containing two coplanar ester groups attached to adjacent carbon atoms. However this is a gas phase process and comparative examples at lower temperatures show activity decrease above 80° C.
Finnish patent application 954814 concerns a process for polymerizing propylene in at least one slurry reactor, where the temperature and the pressure are above the supercritical temperature and pressure of the reaction mixture. One of the main advantages of operating under supercritical conditions is that great amounts of hydrogen can be freely added to the slurry reactor because hydrogen readily dissolves into the supercritical fluid.
SUMMARY OF THE INVENTION
The present invention concerns a multistage process for homo or copolymerizing propylene, wherein propylene is polymerized in the presence of a catalyst system comprising a procatalyst component and a cocatalyst component, said procatalyst component comprising magnesium, titanium and at least one internal donor compound, at an elevated temperature in a reaction medium, in which a major part is formed by propylene. The present invention is characterized in that the polymerization is carried in at least one slurry reactor in the presence of liquid propylene at a polymerization temperature between 80-91° C. and by using a catalyst system where said internal donor compound is slightly soluble, the amount of said slightly soluble donor compound in the catalyst system being at least 1 w-%. This kind of catalyst system produces within said temperature range a high productivity and essentially constant isotacticity within wide melt index range.
According to another embodiment of the invention the catalyst system can include at least two internal donor compounds, of which one is slightly soluble internal donor compound and another internal one donor compound is easily soluble, and the amount of said slightly soluble donor compound in the procatalyst is at least 1 w-%.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention it has been found that by using in propylene polymerization a catalyst system having at least one internal donor compound which is slightly soluble in eluting agents and by using this donor compound in a certain amount a highly stereospecific catalyst system is obtained which give certain performance between temperature range of 80-91° C. First, the catalyst system gives a high productivity and secondly, the catalyst system gives relatively high isotacticity index, which remains essentially constant although polymers have varying melt index. With ordinary Ziegler-Natta catalysts the isotacticity index is at a lower level and drops when the melt index increases.
Examples of the catalyst systems, which are usable according to the invention, among others, are generally disclosed for example in Finnish patents FI86866, FI96615, FI88047, FI88048 and Finnish patent application FI963707. These catalysts have been presented for use only in relatively low temperatures.
According to this invention a suitable catalyst system comprises a procatalyst composition prepared from magnesium dichloride, titanium compound and at least one internal donor compound having a slight solubility in hydrocarbons or compounds used as cocatalyst, and a conventional cocatalyst compound. According to one embodiment of the invention the procatalyst composition is obtained by applying transesterification method, which is generally disclosed for example in Finnish patent 88048. The transesterification reaction is carried out at an elevated temperature between a lower alcohol and a phthalic acid ester, whereby the ester groups from lower alcohol and phthalic acid change their place.
MgCl
2
can be used as such or it can be combined with silica, e.g. by absorbing the silica with a solution or slurry containing MgCl
2
. The lower alcohol used can be preferably methanol or ethanol, particularly ethanol.
The titanium compound used in the preparation of the procatalyst is preferably an organic or inorganic titanium compound, which is at the oxidation state of 3 or 4. Also other transition metal compounds, such as vanadium, zirconium, chromium, molybdenum and tungsten compounds can be mixed with the titanium compound. The titanium compound usually is halide or oxyhalide, an organic metal halide, or a purely metal organic compound, in which only organic ligands have been attached to the transition metal. Particularly preferable are the titanium halides, especially TiCl
4
. Preferably the titanation is carried out in at least two steps.
The transesterification can be carried out e.g. by selecting a phthalic acid ester—a lower alcohol pair, which spontaneously or by the aid of a catalyst, which does not damage the procatalyst composition, transesterifies the catalyst at an elevated temperatures. It is preferable to carry
Bergmann Fred
Garoff Thomas
Harlin Ali
Huikku Sirpa Ala
Leinonen Timo
Borealis A/S
Choi Ling-Siu
Wu David W.
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