Abstract:
The present invention relates to a highly active titanium based supported catalyst suitable for olefin (co)polymerization, preparation and use of the same. The catalyst according to the present invention is obtained by supporting a titanium based catalyst component containing a halide promoter on spherical silica. The resultant catalyst is excellent in its particle morphology and flowability, has highly catalytic activity, has excellent hydrogen response and has superior comonomer incorporation, the polymer prepared by using such a catalyst has its particle morphology further improved.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a highly active titanium based supported catalyst suitable for olefin (co)polymerization, in particular ethylene (co)polymerization by a gas phase process, preparation and use of the same. 
     BACKGROUND OF THE INVENTION 
     It is well known that halocarbons have been applied in vanadium based catalysts for olefin polymerization as activity promoters and there are a number of patents involving them. For example, the vanadium based catalysts developed by Union Carbide Corporation have been successfully utilized for the industrial production of polyethylene by a gas phase process, with the key point being the incorporation of halocarbons as activity promoters, resulting in an improvement in the activity of vanadium based catalysts by a factor of 4 to 10 times. Further, U.S. Pat. No. 4,508,842 and CN 87107589A disclose the use of CFCl 3  and the like as promoters; EP 286001 discloses the use of CH 2 Cl 2  or CF 2 ClCFCl 2  as promoters; and U.S. Pat. No. 4,892,853 discloses the use of hexachloropropane or octachloropropane as promoters. In particular, Chinese Patent Application Publication No. CN 1056107A discloses a vanadium based catalyst obtained by supporting a promoter by a chemical bond, wherein the promoter is chemically bonded with said catalyst by reacting a halogenated alcohol, together with hydroxyl groups on the surface of silica, with an organic aluminium compound, thus promoting the activity of the vanadium center. 
     By investigating the promotion effect of halocarbons on vanadium based catalysts, the researchers from Union Carbide Corporation found out that only CH 2 Cl 2  could promote the activity of the titanium center, and most of halocarbons such as CFCl 3 , CHCl 3 , CCl 4  largely inhibit the titanium center and substantially decrease the catalytic activity[Polymer Material Science and Engineering, pp. 106-107(1991)]. The synthesis for bimodal or broad molecular weight distribution (MWD) polyethylene by using titanium/vanadium bimetallic catalysts is also based on the substantially inhibiting effect of CFCl 3 , CHCl 3  and the like on the titanium center[U.S. Pat. No. 5,442,018]. 
     However, this is not always the case, as demonstrated by the catalysts disclosed in Chinese Patent Application Publication No. CN 1189505A. In said catalyst, halocarbons represented by general formula R a CX (4-a)  (wherein R represents hydrogen, unsubstituted or halogen-substituted alkyl groups having less than 6 carbon atoms, X represents fluorine, chlorine or bromine, and a represents an integer of less than 4) are used. In a suitable molar ratio of the halocarbons to titanium, the catalytic activity of conventional titanium-centered Ziegler-Natta catalysts can be improved by 50 to 100% when used in gas phase polymerization of ethylene. However, since halocarbons are separately added into the polymerization reactor, one obvious disadvantage is the additional step required for adding the halocarbons to the polymerization reactor with its attendant problems of inaccurate feed, mixing problems, contact with the other catalyst components, and the like. After extensive studies made by the present inventors, it has been found out that in the titanium based catalyst with silica as carrier material, the halide promoter according to the present invention becomes a molecularly structural component of the catalyst composition by chemically bonding to silica through chemical reaction between said promoter and hydroxyl groups on the surface of silica, and further, the amounts of the supported promoter can be controlled by regulating the temperature and time for heat-activating the carrier material. Therefore, it is unnecessary to externally add halocarbons into the polymerization reactor, in order to obtain the promotion effect from the halide, and thus the disadvantages associated with the prior arts can be overcome. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a highly active titanium based supported catalyst suitable for ethylene (co)polymerization, which has overcome the disadvantages associated with the prior silica-supported titanium based catalyst and is obtained by supporting a halide promoter onto a carrier material. When the catalyst is used for ethylene polymerization, not only the catalytic activity is largely enhanced, but also the particle morphology of the resulting polymer is further improved and the bulk density is markedly increased. 
     Another object of the present invention is to provide a process for the preparation of the catalyst in accordance with the present invention. 
     Still another object of the present invention is to provide the use of the catalyst in accordance with the present invention for olefin (co)polymerization. 
     In its one aspect, the present invention provides a highly active titanium based supported catalyst suitable for ethylene (co)polymerization, comprising: 
     A. a supported catalyst component which is a titanium-containing active component supported on an inert carrier material, comprising at least one titanium compound, at least one magnesium compound, at least one halide promoter, at least one electron donor compound and at least one porous inert carrier material; and 
     B. an alkyl aluminium cocatalyst. 
     In its second aspect, the present invention provides a process for preparing the supported catalyst component in accordance with the present invention, comprising dissolving the titanium compound and the magnesium compound mentioned above into an electron donor compound, thereby obtaining a mother liquor, and then supporting said compounds onto an inert carrier material by impregnation. 
     In its third aspect, the present invention relates to the use of the catalyst in accordance with the present invention for olefin (co)polymerization. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In the catalyst component A as mentioned above, the magnesium compound, the electron donor compound, the titanium compound and the porous inert carrier material have been described in U.S. Pat. No. 4,302,565, which is incorporated herein by reference. 
     In the catalyst component A as mentioned above, the halide promoter is a class of compounds represented by general formula F-R 1 [R 2   b X (3-b) ], wherein; 
     F represents an oxygen-containing functional group which is reactive with the organoaluminium compound, the titanium compound or hydroxyl groups, such as aldehyde groups, acyl groups, hydroxyl groups and the like; R 1  represents a divalent C 1 -C 6  aliphatic or aromatic group which is attached to oxygen atom in the functional group F; R 2  represents hydrogen, unsubstituted or halogen-substituted C 1 -C 6  alkyl, C 3 -C 6  cycloalkyl or C 6 -C 10  aromatic groups, b is 0, 1 or 2, and X is F, Cl or Br. 
     When F represents hydroxyl groups, said promoter is a class of halogenated alcohols, specific compounds being 2,2,2-trichloroethanol, 2,2-dichloroethanol, 2-chloroethanol, 1,1,-dimethyl-2,2,2-trichloroethanol, 4-chlorobutanol, para-chloro-phenol, iso-chlorophenol, ortho-chlorophenol, 2-chlorocyclohexanol and the like, with 2,2,2-trichloroethanol, 2,2-dichloroethanol, 2-chloroethanol and 1,1-dimethyl-2,2,2-trichloroethanol being preferred. 
     When F represents acyl groups, said promoter is a class of halogenated acyl halide, suitable examples of such compounds being trichloroacetyl chloride, dichloroacetyl chloride, chloroacetyl chloride, o-chlorobenzoyl chloride and 2-chlorocyclohexyl carbonyl chloride, with trichloroacetyl chloride, dichloroacetyl chloride and chloroacetyl chloride being preferred. 
     In the catalyst component A as mentioned above, preferable titanium compounds are those represented by general formula Ti(OR) 4-n X n , wherein R represents C 1 -C 14  aliphatic hydrocarbon groups, X represents a group selected form the group consisting of F, Cl, Br and mixtures thereof and n is 0, 1 or 2. Suitable examples are selected from the group consisting of titanium tetrachloride, titanium trichloride, titanium tetrabromide, titanium tetraiodide, titanium tetrabutoxide, titanium tetraethoxide, triethoxy titanium chloride, diethoxy titanium dichloride, methoxy titanium trichloride, ethoxy titanium trichloride and mixtures thereof, with titanium tetrachloride, ethoxy titanium trichloride and the like being preferred. 
     The magnesium compound which can be used is preferably those represented by general formula MgX 2 , wherein X represents a group selected from Cl, Br, I or mixtures thereof. Specific examples can be magnesium dichloride, magnesium dibromide, magnesium diiodide, with magnesium dichloride being perferred. 
     The electron donor (ED) compound which can be used is preferably selected from the group consisting of alkyl esters of aliphatic or aromatic carboxylic acids, aliphatic ethers, cyclic ethers and aliphatic ketones. Among them, alkyl esters of C 1 -C 4  saturated aliphatic carboxylic acids, alkyl esters of C 7 -C 8  aromatic carboxylic acids, C 2 -C 6  aliphatic ethers, C 3 -C 4  cyclic ethers, C 3 -C 6  saturated aliphatic ketones are preferred. Most preferably are methyl formate, ethyl acetate, butyl acetate, diethyl ether, dihexyl ether, tetrahydrofuran (THF), acetone and methyl isobutyl ketone. These electron donor compounds can be used alone or in a mixture of two or more of them. 
     The carrier material is a solid, particulate porous material, which contains an amount of hydroxyl groups on its surface, with dehydrated silica being preferred. A suitable carrier material is particulate silica, characterized by an average particle diameter of 20-80 μm, a pore volume of 1.5-5 ml/g, a specific surface area of 230-350 m 2 /g and an average pore diameter of 18-40 nm; most preferred silica is characterized by an average particle diameter of 50 μm, a pore volume of 1.6 ml/g and a specific surface area of 300 m 2 /g. 
     In the titanium-containing catalyst component A in accordance with the present invention the magnesium compound, the electron donor compound and the halide promoter are used in amounts of 0.5 to 50 moles, preferably 1.5 to 5 moles; 0.5 to 50 moles, preferably 1 to 10 moles; and 0.1 to 50 moles, preferably 0.5 to 10 moles, per mole of the titanium compound, respectively. 
     The component B which can be used is an alkyl aluminium represented by formula AlR 3 , wherein R can be same or different and represents C 1-8  alkyl groups, and one or two of the alkyl groups can be substituted with chlorine. Preferable examples are selected from the group consisted of AlEt 3 , Al(i-Bu) 3 , Al(n-C 6 H 13 ) 3 , Al(n-C 8 H 17 ) 3 , and AlEt 2 Cl. The alkyl aluminium mentioned above can be used alone or in combination. 
     The catalyst component in accordance with the present invention is preferably prepared by a process comprising the steps of: 
     (1) activating a carrier material in a conventional manner, preferably dehydrating at a temperature of 600° C. for 4 hours; 
     (2) adding the. heat-activated carrier material into a lower alkane solvent, followed by addition of an alkyl aluminium compound, and then reacting the mixture for a period of time, followed by evaporating the solvent and drying, thereby obtaining a solid powder; 
     (3) dissolving a titanium compound and a magnesium compound in an electron donor compound to prepare a mother liquor, wherein the titanium compound is added into the electron donor compound before or after the addition of the magnesium compound, or both the titanium compound and the magnesium compound are added simultaneously; 
     (4) adding the carrier material activated in step (2) into the mother liquor from step (3) and reacting them for a period of time, followed by drying to remove excess solvent, i.e. the electron donor compound, thereby obtaining a solid material; 
     (5) suspending the solid material from step (4) in a lower alkane solvent and then reducing with one or more alkyl aluminium compounds, followed by drying, thereby obtaining the final catalyst component; 
     wherein said halide promoter is incorporated into the catalyst component A by i) adding during the treatment of the carrier material in said step (2), ii) adding during supporting the catalyst complex from said step (3) onto the carrier material and iii) adding during the reduction of the catalyst in said step (5). 
     The lower alkane solvents used in step (2) and step (5) can be C 3 -C 9  alkanes, preferably C 5  and C 6  alkanes, such as isopentane, pentane, hexane and the like. 
     The alkyl aluminium compounds which can be used in step (2) and step (5) are preferably those represented by general formula AlR′ m X 3-m , wherein R′ can be same or different and represents C 1 -C 8  alkyl groups, X represents a halogen, m is an integer of 1 to 3. Preferable alkyl aluminium compounds are AlEt 3 , Al(n-C 6 H 13 ) 3 , AlEt 2 Cl, and the like. 
     It should be particularly noted that the halide promoter in accordance with the present invention can be incorporated into the catalyst component A by any effective manner. For example, an excellent promotion effect can be achieved by adopting one of the following methods: i) adding during the treatment of the carrier material in said step (2), ii) adding during supporting the catalyst complex from said step (3) onto the carrier material and iii) adding during the reduction of the catalyst in said step (5). 
     The catalyst according to the present invention is suitable for ethylene homopolymerization and copolymerization of ethylene and α-olefins, with the α-olefins being olefins having 3-10 carbon atoms, such propylene, butene-1, hexane-1, 4-methylpentene-1, octane-1, and the like. The polymerization reaction can be carried out in an inert solvent by a slurry process or a gas phase process. The polymerization temperature can be ranged from 50° C. to 100° C. Since in the catalyst according to the present invention, the halide promoter is supported onto the catalyst carrier, the resulting catalyst are more suitable for gas phase polymerization of ethylene and can exhibit excellent properties. 
     In comparison with the prior art catalysts, the catalyst system for gas phase polymerization of ethylene according to the present invention is obtained by chemically bonding a halide promoter and is suitable for all titanium-centered Ziegler-Natta catalysts. In addition, the promoter can be incorporated into the catalyst component A by any effective manner. For example, an excellent promotion effect can be achieved by adopting one of the following methods: i) adding the promoter during the treatment of the carrier material in said step (2), ii) adding the promoter during supporting the catalyst complex from said step (3) onto the carrier material and iii) adding the promoter during the reduction of the catalyst in said step (5). More particularly, when 2,2,2-trichloroethanol or trichloroacetyl chloride is used as the promoter, excellent promotion effect can be achieved in a very small amount, for example, in a ratio of 2,2,2-trichloroethanol (or trichloroacetyl chloride)/Ti of 0.1-3. Therefore, the catalyst system according to the present invention is industrially valuable. Moreover, the catalyst system according to the present invention is particularly suitable for gas phase polymerization of ethylene, with a smooth polymerization kinetic curve, without blocking or adhering to the wall of the polymerization reactor. The polymers prepared by using the catalyst system according to the present invention have a density and a melt index which can be easily regulated. Finally, the catalyst system according to the present invention is excellent in comonomer incorporation and is particularly suitable for preparing LLDPE (linear low-density polyethylene). 
    
    
     EXAMPLES 
     The catalyst according to the present invention is described in more details by the following examples, but the catalyst system according to the present invention is not limited to them. 
     Example 1 
     Preparation of Catalyst Component (a): 
     (1) 11 g of SYLOPOL 948# spherical silica (available from Grace Corporation, USA) is weighed and then activated at a temperature of 600° C. for 4 hours. 
     (2) Under nitrogen, to a flask equipped with a stirrer and containing hexane(100 ml) as solvent are added the heat-activated silica from step (1) and 5 ml of a solution of AlEt 3  in hexane(1 mmol/ml) . The mixture is reacted at a temperature of  60° C. for half an hour, followed by slow drop-wise addition of  1.2 ml trichloroacetyl chloride. After the completion of addition, the mixture is reacted for half an hour and then is dried by sweeping with highly pure nitrogen, thereby obtaining flowable powders. 
     (3) To another flask equipped with a stirrer are added 11 g MgCl 2 , 0.4 ml TiCl 4  and 100 ml tetrahydrofuran. The mixture is heated under stirring to reflux for 3 hours, thereby obtaining a catalyst mother liquor. 
     (4) The silica treated in step (2) is mixed with the catalyst mother liquor from step (3). The mixture is stirred under refluxing for 1.5 hours, followed by drying by sweeping with highly pure nitrogen, thereby obtaining flowable, pale yellow solid powders. 
     (5) The product from step (4) is prereduced in 100 ml hexane at a temperature of 60° C. by first drop adding 3.3 ml of a solution of AlEt 2 Cl in hexane (2.2 mmol), after the completion of addition, the mixture is reacted for half an hour, followed by drop adding 14 ml of a solution of AlEt 3  in hexane (1 mmol), after the completion of addition, the mixture is reacted for half an hour and then dried by sweeping with highly pure nitrogen, thereby obtaining powdery catalyst component. Ti, 0.74%. 
     Evaluation of the Catatlyst: 
     Slurry homopolymerization of ethylene: The slurry polymerization is carried out in a 2 liter stainless steel autoclave. The conditions are as follows, the catalyst component, 1.2 mg (in terms of Ti); H 2 /C 2 H 4 =0.25/0.48 MPa; 1 ml of a solution of AlEt 3  in hexane (1 mmol/ml); hexane, 1 liter; 80° C.; 2 hours. 
     Results: smooth catalytic activity; activity, 1.61×10 5  gPE/gTi (1191.4 gPE/gcat); and bulk density of the polymer powders, 0.35 g/ml. 
     Example 2 
     The catalyst component (a) is prepared in a same manner as that in Example 1. 
     Evaluation of the Catalyst: 
     Gas phase homopolymerization of ethylene: Polymerization is carried out in a φ150 mm fluid bed for gas phase polymerization of ethylene, in the presence of 0.15 g catalyst, 35 mmol AlEt 3  and 600 g polyethylene powders as dispersant, under the following polymerization conditions: total pressure, 1.2 MPa; H 2 /C − 2=0.20, temperature, 88° C., 4 hours, productivity, 4500 gPE/gcat, bulk density, 0.36 g/cm 3 , density of the polymer, 0,960 g/cm 3 . 
     Example 3 
     The catalyst component (a) is prepared in a same manner as that in Example 1. 
     Gas phase copolymerization of ethylene: Polymerization is carried out in a φ150 mm fluid bed for gas phase polymerization of ethylene, in the presence of 0.15 g catalyst from Example 1, 35 mmol AlEt 3  and 600 g polyethylene powders as dispersant, under the following polymerization conditions: total pressure, 1.2 MPa; butene-1 as a comonomer, C −   4 /C −   2 =0.063, H 2 /C −   2 =0.20, temperature, 88° C., 4 hours, productivity, 8500 gPE/gcat, bulk density, 0.36 g/cm 3  density of the polymer, 0.926 g/cm 3 . 
     Comparative Example 1 
     The catalyst component (a) is prepared in a same manner as that in Example 1 except that trichloroacetyl chloride is not added during the preparation. 
     The catalytic activity is evaluated in a same manner as that in Example 1. 
     Results: Ti, 0.69%; smooth catalytic acitivity; acitivity, 1.12×10 5  gPE/gTi (772.8 gPE/gcat); and bulk density of the polymer powders, 0.30 g/ml. 
     Comparative Example 2 
     The catalyst component (a) is prepared in a same manner as that in Comparative Example 1. 
     The catalytic activity is evaluated in a same manner as that in Example 2. 
     Results, activity, 3500 gPE/gcat; and bulk density, 0.35 g/cm 3 . 
     Comparative Example 3 
     The catalyst component (a) is prepared in a same manner as that in Comparative Example 1. 
     The catalytic activity is evaluated in a same manner as that in Example 3. 
     Results: activity, 7000 gPE/gcat; and bulk density, 0.35 g/cm 3 . 
     Example 4 
     The catalyst component (a) is prepared in a same manner as that in Example 1 except that 1.2 ml trichloroacetyl chloride is added, followed by reacting the resulting mixture for half an hour and then adding 5 ml of a solution of AlEt 3  in hexane (1 mmol/ml). 
     The catalytic activity is evaluated in a same manner as that in Example 1. 
     Results: Ti, 0.93%; smooth catalytic activity; activity, 1.61×10 5  gPE/gTi (1497.3 gPE/gcat); and bulk density of the polymer powders, 0.33 g/ml. 
     Example 5 
     The catalyst component (a) is prepared in a same manner as that in Example 1 except that 1.2 ml trichloroacetyl chloride is added after the reduction reaction, followed by reacting the resulting mixture for half an hour and then drying by sweeping with highly pure nitrogen. 
     Results: Ti, 0.87%; smooth catalytic acitivity; activity, 1.40×10 5  gPE/gTi; and bulk density of the polymer powders, 0.31 g/ml. 
     Example 6 
     The catalyst component (a) is prepared in a same manner as that in Example 1 except that 0.7 ml 2,2,2-trichloroethanol is added, instead of 1.2 ml trichloroacetyl chloride. 
     The catalytic activity is evaluated in a same manner as that in Example 1. 
     Results: Ti, 0.80%; smooth catalytic acitivity; activity, 1.38×10 5  gPE/gTi; and bulk density of the polymer powders, 0.32 g/ml. 
     Example 7-9 
     The catalyst component (a) is prepared in a same manner as that in Example 1 except that 0.7 ml 2,2,2-trichloroethanol is added after the reduction reaction, instead of 1.2 ml trichloroacetyl chloride, followed by reacting the resulting mixture for half an hour and then drying by sweeping with highly pure nitrogen. Ti, 0.93%. 
     Results: when carrying out the polymerization under different partial pressures of hydrogen, a smooth catalytic activity can be achieved and the polymerization results are listed in the following table: 
     
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Amount of 
                   
                   
                   
                   
                 Activity 
                   Bulk 
               
               
                   
                 catalyst added 
                 H 2   
                 C −   2   
                   
                 Temperature 
                 (10 4  gPE/ 
                 density 
               
               
                 Example 
                 Ti (mg) 
                 (MPa) 
                 (MPa) 
                 C −   6   
                 (° C.) 
                 gTi) 
                 (g/ml) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Ex. 7 
                 1.2 
                 0.25 
                 0.48 
                  0 
                 80 
                  12.0 
                 0.31 
               
               
                 Ex. 8 
                 1.2 
                 0.25 
                 0.48 
                 12 ml 
                 80 
                 18.7 
                 0.33 
               
               
                 Ex. 9 
                 0.6 
                 0.25 
                 0.75 
                  0 
                 80 
                 41.0 
                 0.33 
               
               
                   
               
             
          
         
       
     
     Example 10 
     The catalyst component (a) is prepared in a same manner as that in Example 1 except that 0.7 ml 2,2,2-trichloroethanol is added immediately after the activated silica is mixed with the mother liquor, instead of 1.2 ml trichloroacetyl chloride, followed by reacting the resulting mixture for 1.5 hours and then drying by sweeping with highly pure nitrogen. 
     Results: Ti, 1.10%; smooth catalytic acitivity; activity, 1.56×10 5  gPE/gTi; and bulk density of the polymer powders, 0.31 g/ml. 
     Example 11 
     The catalyst component (a) is prepared in a same manner as that in Example 1 except that 0.7 ml 2,2,2-trichloroethanol is added during the preparation of the mother liquor, instead of 1.2 ml trichloroacetyl chloride. 
     Results: Ti, 1.05%; smooth catalytic acitivity; activity, 1.45×10 5  gPE/gTi; and bulk density of the polymer powders, 0.31 g/ml. 
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE-1 
               
             
             
               
                   
               
               
                 Evaluation for slurry polymerization of catalysts 
               
             
          
           
               
                   
                   
                   
                   
                  Bulk 
                   
                   
                   
               
               
                   
                 Pro- 
                   
                 Activity 
                 Density 
               
               
                 Example 
                 moter 
                 Ti % 
                 (10 4  gPE/gTi) 
                 (g/ml) 
                 MI 
                 FI 
                 MFR 
               
               
                   
               
             
          
           
               
                  Ex. 1 
                 A 
                 0.74 
                 16.1 
                 0.35 
                  0.95 
                 29.6 
                 31.1 
               
               
                 Comp. 
                 None 
                 0.69 
                 11.2 
                 0.30 
               
               
                 Ex. 1 
               
               
                 Ex. 4 
                 A 
                 0.93 
                 16.1 
                 0.33 
               
               
                 Ex. 5 
                 A 
                 0.87 
                 14.0 
                 0.31 
                 0.86 
                 26.6 
                 30.9 
               
               
                 Ex. 6 
                 B 
                 0.80 
                 13.8 
                 0.32 
                 0.52 
                 15.93 
                 30.6 
               
               
                 Ex. 7 
                 B 
                 0.93 
                 12.0 
                 0.31 
                 0.28 
                 6.96 
                 24.9 
               
               
                 Ex. 10 
                 B 
                 1.10 
                 15.6 
                 0.31 
                 0.88 
                 26.2 
                 29.8 
               
               
                 Ex. 11 
                 B 
                 1.05 
                 14.5 
                 0.31 
                 1.12 
                 34.7 
                 31.0 
               
               
                   
               
               
                 Note:  
               
               
                 A, Cl 3 CCOCl;  
               
               
                 B, Cl 3 CCH 2 OH.  
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE-2 
               
             
             
               
                   
               
               
                 Evaluation for gas phase polymerizations 
               
             
          
           
               
                   
                   
                   
                 Activity 
                 Bulk Density 
               
               
                   
                 Example 
                 Promoter 
                 (gPE/gcat) 
                 BD(g/ml) 
               
               
                   
                   
               
               
                   
                 Ex. 2 
                 B 
                 4500 
                 0.36 
               
               
                   
                 Comp. Ex. 2 
                 None 
                 3500 
                 0.35 
               
               
                   
                 Ex. 3 
                 B 
                 8500 
                 0.36 
               
               
                   
                 Comp. Ex. 3 
                 None 
                 7000 
                 0.35 
               
               
                   
                   
               
             
          
         
       
     
     It can be seen from Table-1 that the solid catalyst component (a) prepared by using a promoter can evidently enhance the activity of the catalyst system and/or the bulk density of polyethylene. For example, the activity of the catalyst in Example 1, in which trichloroacetyl chloride is used as the promoter, is markedly improved, with the acitivity being enhanced from about 1.1×10 5  gPE/gTi to about 1.6×10 6  gP/gTi and the bulk density being increased from about 0.30 g/ml to about 0.35 g/ml.