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
2001-10-16
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...
C526S348000, C526S125100, C526S158000, C526S124300, C526S124200, C526S124100, C502S115000, C502S227000, C502S233000, C502S250000
Reexamination Certificate
active
06303716
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high-activity solid catalyst suitable for gas phase polymerization of ethylene, a process for preparing the same and use of the same in ethylene polymerization.
BACKGROUND OF THE INVENTION
Since the successful development of high-activity catalysts for polyethylene in 1970's, there has been rapid progress with respect to the researches into the catalysts for ethylene polymerization and three systems in terms of the composition of the catalysts, i.e. chromium type high-activity catalysts, Ziegler-Natta type high-activity catalysts and metallocene type high-activity catalysts, have been formed. Among them, Ziegler-Natta type high-activity catalysts are very important in the field of catalysts for their excellent performance and the processes for preparing them have been developed from the grinding process as well as the suspending-impregnating process utilized in the early stages to the chemical reaction process utilized at present. Processes for producing polyethylenes are continuously renewed and among them, the gas phase process for synthesizing polyethylenes are being widely utilized for low investment to equipment, low energy consumption, excellent product performance and high economical benefits. Recently, exploitation of various novel catalysts makes the gas phase process develop rapidly, and there are many patents issued with respect to the processes for preparing such catalysts.
For example, U.S. Pat. No. 4,497,904 discloses a catalyst which has a narrow particle size distribution and is very suitable for the gas phase polymerization process, prepared by reacting butyloctyl magnesium as raw material with butyl chloride to form a spherical magnesium chloride as a carrier of the catalyst, and then reacting a halide containing titanium with said carrier. The catalyst is disadvantageous in that dialkyl magnesium as raw material is expensive, which results in high cost. It is described in U.S. Pat. No. 4,438,019 that powdered magnesium, titanium tetrachloride, propyl titanate and butyl chloride are reacted to obtain a catalyst for polymerizing olefins; though said catalyst has high initial activity, it gives rise to the appearance of hot spots during the polymerization and the formation of agglomerates of molten polyethylene, or fragmentation of the catalyst particles; moreover, said catalyst must be oxidized from Ti
3+
to Ti
4+
prior to use. To overcome the disadvantage, U.S. Pat. No. 4,894,424 describes that an appropriate amount of water is added during the preparation of the catalyst to inactivate it, reduce the initial polymerization reaction rate and prevent the appearance of hot spots. However, the preparation of such a catalyst is too complicated and the amount of water to be added should be strictly controlled so as to inactivate the catalyst.
U.S. Pat. Nos. 4,349,648 and 4,302,565 disclose catalysts for gas phase polymerizing ethylene, prepared by reacting anhydrous magnesium chloride with tetrahydrofluran and titanium tetrachloride to form a complex, then impregnating said complex onto silica gel as carrier, followed by drying the resulting product to form a main catalyst component having good flowability and finally activating said component with an alkyl aluminum compound. Such catalysts has very high initial activity, giving rise to the appearance of hot spots and the formation of agglomerates of polyethylene, and the resulting polyethylenes have low and medium densities (from 0.91 to 0.94 g/cm
3
).
In order to overcome the above disadvantages, the present inventors proposed a catalyst in Chinese Patent Application No. 93112345.3, which is prepared by using powdered magnesium as raw material to form a complexed magnesium halide carrier having reducing capability and then supporting active components onto said carrier by impregnating, with more than 80% of titanium being trivalent. Said catalyst is advantageous for a simple preparing procedure, low initial activity of polymerization reaction, smooth and stable reaction, high catalytic activity, good morphology of the resulting polymer particles and lack of fine particles. However, said catalyst must be subjected to prepolymerization so as to be readily fed into the fluidized bed and thus there is a room for improvement.
SUMMARY OF THE INVENTION
In view of the above, the present inventors conducted extensive and intensive research with a view to obtain a novel catalyst for gas phase polymerizing ethylene. As a result, it is found that a novel catalyst for polymerizing ethylene can be prepared by using commercial powdered magnesium as raw material, forming a magnesium halide in the nascent state, then reacting said magnesium halide with a titanium compound and an alkyl aluminum compound in the presence of an electron donor compound to form a complex, supporting said complex onto silica carrier and drying the resulting mixture by heating to form a solid main catalyst component, and finally mixing said main catalyst component with an organometallic compound as cocatalyst. The catalyst according to the present invention is characterized by a simple preparing procedure, smooth and stable reaction, uniform heat liberation and less agglomerates when used for gas phase polymerizing ethylene, high polymerization activity, high sensitivity to the modification by hydrogen and high copolymerization power, and low-, medium-and high-density polyethylene products can be obtained by using the catalyst and the products thus obtained have good particle morphology.
Therefore, an object of the present invention is to provide a high activity solid catalyst suitable for gas phase polymerizing ethylene, which is free of the above disadvantages associated with the prior catalysts and can be readily fed into the fluidized bed without prepolymerization.
Another object of the present invention is to provide a process for preparing the catalyst according to the present invention.
Still another object of the present invention is to provide a process for gas phase polymerizing ethylene.
These and other objects, features and advantages of the present invention will be apparent to those skilled in the art from the following detailed description taken in connection with the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
The present invention in its one aspect provides a high activity solid catalyst for gas phase polymerizing ethylene, comprising A) a solid main catalyst component containing titanium, prepared by reacting commercial powdered magnesium with an alkyl halide in a hydrocarbon solvent to form a magnesium halide in the nascent state, then reacting said magnesium halide with a titanium compound and an alkyl aluminum compound in the presence of an electron donor compound and finally supporting the resulting complex onto silica carrier, wherein said electron donor compound is an organic compound containing at least one atom of oxygen, sulfur, nitrogen, silicon or phosphorus; and B) an organometallic compound as cocatalyst; wherein the ratio of the cocatalyst to the main catalyst component, in terms of the molar ratio of the metal contained in component B) to titanium contained in component A), is (30-300):1.
The present invention in its another aspect provides a process for preparing the catalyst according to the present invention.
The present invention in its third aspect provides a process for gas phase polymerizing ethylene.
The preparation procedure for the catalyst according to the present invention is described as follows.
(1) Treatment of Silica Carrier
Silica carrier used in the present invention is preferably subjected to a treatment in the following manner. Silica is treated by heating in a fluidized bed through which a carrier gas such as air, nitrogen or argon is passed. The conditions for the treatment are such that the temperature is controlled at 500-800° C., preferably 600-700° C. and the treatment time is from 2 to 12 hours, preferably from 3 to 10 hours. The treated silica is then removed for further reaction.
The silica treated as above
Chai Zixiao
Xiao Mingwei
Ye Xiaofeng
China Retrochemical Corp.
Choi Ling-Siu
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wu David W.
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