Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in two or more physically distinct zones
Reexamination Certificate
1999-07-15
2001-08-07
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
C526S059000, C526S060000, C526S061000, C526S067000, C526S068000, C526S071000
Reexamination Certificate
active
06271318
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for polymerizing olefins such as ethylene and propylene, and more particularly to a method for polymerizing olefins in a multi-stage polymerization apparatus comprising a gas-phase polymerization reactor in which the composition of gas is easily controlled.
2. Background Art
Among a variety of industrial methods for polymerizing olefins such as ethylene and propylene, a gas-phase polymerization method has become of interest. This method utilizes high-activity catalyst and does not require a deashing (removal of catalyst residue) process.
However, in the case of a successive multi-stage gas-phase polymerization method, the composition of gas in a polymerization reactor of a certain stage affects the composition of gas in a polymerization reactor of a subsequent stage. Therefore, adjustment of the composition of gas in the reactor of a subsequent stage may be difficult.
For example, in order to produce a polymer having a broad molecular weight distribution, usually a low molecular weight polymer is produced in a reactor of a certain stage, and in a reactor of a subsequent stage the resultant polymer is further polymerized to yield a higher polymer. In this case, in the preceding polymerization, hydrogen gas of high concentration is used as a chain-transfer agent. However, since hydrogen gas of low concentration is used in the subsequent polymerization, when the polymer is transferred from a preceding reactor to a subsequent reactor there must be removed a large amount of hydrogen gas accompanying a produced polymer.
In addition, when a copolymer such as ethylene-propylene is to be produced, the composition of gas in each polymerization reactor must be adjusted.
Therefore, several methods have been proposed for adjusting the composition of gas in a gas-phase polymerization reactor of a subsequent stage. Japanese Patent Application Laid-Open (kokai) No. 23001/1984 discloses a method in which a purge vessel is provided between two sequential polymerization reactors for adjusting the concentration of hydrogen gas (a chain-transfer agent) contained in an accompanying gas including a polymer fed from a preceding polymerization reactor, wherein the accompanying gas is removed and only the polymer is transferred to a subsequent reactor. Also, Japanese Patent Application Laid-Open (kokai) No. 65703/1982 discloses a method in which an accompanying gas containing a polymer is diluted with inert gas in a purge vessel, to thereby transfer to a subsequent reactor the polymer accompanied by hydrogen gas of low concentration. Furthermore, Japanese Patent Application Laid-Open (kokai) No. 118342/1995 discloses a method in which a purge vessel is formed of a tank for gas and a tank for powder, and an accompanying gas containing a polymer is removed by operation of a valve between the two tanks, and then the polymer in the tank for powder is transferred to a subsequent polymerization reactor by use of pressurized circulating gas from the subsequent reactor. However, these methods still have drawbacks, such as requirement of a purge vessel and complicated valve control operation.
SUMMARY OF THE INVENTION
The present inventors have performed extensive studies in an attempt to solve the above-described drawbacks, and have found that it is possible to adjust the composition of gas and to control temperature, i.e., removal of heat of polymerization, in a gas-phase polymerization reactor by removing gas from a subsequent gas-phase polymerization reactor; pressurizing and cooling the gas to partially liquefy the gas; discharging at least a portion of the gas; and returning the remaining gas and the liquid to the reactor. Based on this finding, the inventors have accomplished the present invention.
Accordingly, an object of the present invention is to provide a method for polymerizing olefins in a multi-stage polymerization apparatus comprising a gas-phase polymerization reactor in a subsequent stage, wherein the composition of gas in the gas-phase reactor is easily adjusted, and whereby a polymer having an intended composition is produced in a continuous process.
In a first aspect of the present invention, there is provided a method for polymerizing olefins in successive, multiple stages by use of a plurality of polymerization reactors disposed in series comprising at least one gas-phase polymerization reactor after a first reactor, wherein a multi-component gas is removed from a gas-phase reactor and pressurized and/or cooled to thereby liquefy a portion of the gas; at least a portion of the removed gas is discharged; and the remaining gas and the liquid are returned to the gas-phase reactor.
In a second aspect of the present invention, there is provided a method for polymerizing olefins in successive multi-stages by use of a plurality of polymerization reactors disposed in series comprising at least one gas-phase polymerization reactor after a first reactor, wherein a multi-component gas is removed from a gas-phase reactor and pressurized and/or cooled to thereby liquefy a portion of the gas; the liquid is returned to the gas-phase reactor; the remaining gas is further pressurized and/or cooled to thereby liquefy a portion of the gas; at least a portion of the gas is discharged; and the remaining gas and the liquid are returned to the gas-phase reactor.
REFERENCES:
patent: 5728353 (1998-03-01), Govoni et al.
Matsuhiro Itaru
Matsuo Youichi
Satou Hideki
Cheung William
Idemitsu Petrochemical Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wu David W.
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