Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-11-16
2003-07-22
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...
C526S083000, C526S084000, C526S085000, C526S901000, C525S053000, C525S244000, C525S255000, C525S258000, C525S259000, C525S261000, C525S262000, C525S323000, C422S131000, C422S135000, C422S139000
Reexamination Certificate
active
06596824
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for producing polyolefins, especially propylene block copolymers, and to the production method and a vapor-phase polymerization apparatus for it, in which olefins are polymerized in a mode of vapor-phase polymerization in the presence of an olefin polymerization catalyst, with preventing the polymers produced from depositing in reactors and preventing them from growing into abnormal agglomerates or aggregates, and which therefore ensure long-term continuous and stable production of high-quality polyolefins.
BACKGROUND ART
For the production of polyolefins such as polypropylene and propylene block copolymers, Ziegler-Natta catalysts have been improved to have high activity and high stereospecificity, and the polymer productivity per the unit catalyst used has been greatly increased with the increase in the stereospecificity of the polymers produced. As a result, it has become possible to reduce the metal content such as the catalyst-derived transition metal content of the polymers produced and to reduce the amorphous polypropylene content thereof. Accordingly, for the polymer production method, a mode of vapor-phase polymerization is now increasingly popular in place of conventional solution polymerization, slurry polymerization and bulk polymerization, as it does not require solvent recovery and purification, it facilitates monomer recovery and polymer drying, and it realizes product diversification.
For example, propylene block copolymers are produced in a two-stage process comprising producing a crystalline homopolymer or copolymer of propylene in the former stage polymerization reactor, followed by producing a rubber-like random copolymer of propylene and other &agr;-olefins such as ethylene in the latter stage polymerization reactor. The propylene block copolymer compositions produced have high mechanical strength, good toughness and good heat resistance intrinsic to the crystalline polypropylene, and have good impact resistance, especially good low-temperature impact resistance intrinsic to the rubber-like random copolymer. Therefore, they are widely used for automobile parts including outer members such as bumpers and inner members such as inner panels and doors, and for containers, sheets, etc.
Accordingly, the method of vapor-phase polyolefin production is an extremely excellent process. In the vapor-phase method, however, the polymer produced is separated into a powder phase and a vapor phase in the polymerization reactor of any type having a vapor-phase fluidized bed or an agitation fluidized bed, and therefore, the polymer in the reactor could not be fully fluidized, stirred and unified. Therefore, when compared with that produced in a method of solution polymerization or slurry polymerization, stirring and unifying the polymer produced in the vapor-phase polymerization method is often unsatisfactory. In particular, in the vapor-phase polymerization method of producing propylene block copolymers mentioned above, the rubber-like copolymer produced in the second-stage random copolymerization reactor is sticky, and the polymer and copolymer particles often agglomerate or aggregate and often deposit on the wall of the reactor and on the stirring blades in the reactor.
The polymer deposition interferes with stable, long-term continuous polymerization in the reactor, and, in addition, causes excessive increase in the molecular weight of the polymer produced, and, as the case may be, the polymer is often gelled in the reactor. As a result, the quality of final polymer moldings will be low. Still another problem is that small polymer agglomerates having deposited on the wall of the reactor often clog pipe lines of polymer powder. In addition, they will clog filters in monomer-cooling pipe lines. For these reasons, the quality of final polymer moldings is worsened to the following effect. The polymer having deposited on the wall of a reactor stays in the polymerization line for a long period of time and is gelled to be a non-melting or hardly melting matter. This worsens the appearance of the moldings of the polymer produced in the line, and will be the start point of the fracture of the moldings. After all, the physical properties and the commercial value of the moldings are much lowered.
Accordingly, polymer deposition and agglomeration must be prevented in the process of producing polyolefins, especially propylene block copolymers. For this, Japanese Patent Laid-Open Nos. 151713/1981 and 213012/1983 disclose a method of adding an alkoxyaluminium compound to the polymerization system. In this, however, the alkoxyaluminium compound is not effective if its amount added is not large. Since the aluminium content of the polymer produced therein increases, the method is unfavorable for vapor-phase polymerization.
Japanese Patent Laid-Open No. 69821/1986 discloses a method of using a high-stereospecificity polymerization catalyst, in which from 0.001 to 1 mol, per gram of aluminium of the catalyst, of an active hydrogen compound is fed into the random copolymerization system. However, the method disclosed is for batch polymerization, and not for continuous polymerization. The laid-open specification shows a concrete mode of feeding an active hydrogen compound to the random copolymerization system and says that the bulk density of the polymer produced is high. In this, however, nothing is referred to about the prevention of polymer deposition in reactors. This is natural since the batch polymerization employed therein produces uniform polymers.
On the other hand, Japanese Patent Laid-Open Nos. 225613/1988, 296313/1992, 296314/1992 and 71415/1999 relate to vapor-phase polymerization, and concretely disclose how to feed an alcohol into the monomer-cooling pipe line and into the polymer-transferring pipe line that connects a crystalline polypropylene-producing polymerization reactor and a propylene random copolymer-producing polymerization reactor. In these, however, the olefin polymerization catalyst activity retardant is not directly fed into the polymerization reactors. In the methods disclosed, the catalyst activity retardant is added to the polymerization system by feeding it into the polymer powder pipe line or into the monomer pipe line, to thereby improve the dispersibility of the polymer produced. Anyhow, in these, the catalyst activity retardant is finally added to the polymerization reactors, and the methods will be good.
In Japanese Patent Laid-Open No. 71415/1999, disclosed is an example of metering and feeding a heptane solution of 17 wt. % isopropanol into a pipe line that connects two reactors, former-stage and latter-stage reactors. In this, also disclosed is a comparative example of metering and feeding the same solution directly into the latter-stage reactor. In these example and comparative examples, the systems were driven for 3 weeks, and then compared with each other. They say that the amount of the agglomerates and the aggregates seen in the powder bed in the latter-stage reactor in the method of the example was reduced to 35 to 45% of that in the comparative example; and the amount of the films and the deposits on the reactor wall and on the baffles was reduced to 25 to 35% of that in the comparative example.
To that effect, the conventional improved methods could produce good results in some degree. In Japanese Patent Laid-Open No. 71415/1999, the effect of reducing the polymer agglomeration, aggregation and deposition is quantitatively evaluated. However, even though the method disclosed therein is improved in some degree, it is obvious that its effect of reducing the polymer agglomeration, aggregation and deposition is limited and is not always satisfactory. Therefore, depending on the type of the polymerization reactors used and the polymerization conditions employed, non-negligible polymer agglomerates and aggregates are formed in the method and they deposit on the reactor wall and on the stirring blades, thereby often clogging the polymer take-out pipes. The problem with the method must be solve
Aida Masao
Nambu Tomoo
Toda Masatoshi
Idemitsu Petrochemical Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Teskin Fred
LandOfFree
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