Patent Publication Number: US-2021187491-A1

Title: Preparation Method Of Catalyst For Ethylene Polymerization

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit and priority of Korean Patent Application No. 10-2019-0174006 filed Dec. 24, 2019. The entire disclosure of the above application is incorporated herein by reference. 
     FIELD 
     The present disclosure relates to a magnesium-supported titanium solid catalyst and a preparation method of ultra-high molecular weight polyethylene using the same. The present disclosure relates to a method for preparing ultra-high molecular weight polyethylene with uniform particle sizes and high apparent density by preparing a solid catalyst containing titanium tetrachloride and a phthalate compound and then performing polymerization using the same. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     The ultra-high molecular weight polyethylene (UHMEP) means polyethylene with a weight average molecular weight of 250,000 to 10,000,000 g/mol. Because the molecular weight thereof is very large compared to that of general-purpose polyethylene, the ultra-high molecular weight polyethylene has excellent properties such as stiffness, abrasion resistance, chemical resistance and electrical properties. Because the ultra-high molecular weight polyethylene among thermoplastic engineering plastics has excellent mechanical properties and wear resistance, not only has the UHMEP been used for mechanical parts that require wear resistance, such as gears, bearings, and cams, the UHMEP has been also used as a material for artificial joints, especially because of excellent wear resistance, impact strength and biocompatibility thereof. 
     The UHMEP has a very high molecular weight and thus has little flow in a molten state and thus is produced in a powder form. Therefore, particle sizes and distribution of powders and apparent density thereof are very important. The ultra-high molecular weight polyethylene may not be subjected to a melting process and thus may be dissolved in an appropriate solvent. Powders with large particle sizes may impair dissolution properties. Further, when the apparent density is low, powder transport may be difficult. Thus, the particle size and the apparent density of the powders act as important factors affecting productivity in a production process. 
     Preparation of catalyst containing magnesium and titanium compound and preparation method of ultra-high molecular weight polyethylene using the same have been reported in several patents. Korean Patent No. 0822616 discloses a method for preparing a catalyst containing magnesium, titanium and silane compound which is capable of being used for preparing an ultra-high molecular weight polyolefin polymer having a uniform particle size distribution at a high catalyst activity. However, the polymer should be improved in terms of the apparent density. U.S. Pat. No. 4,962,167 discloses a method for preparing a catalyst for production of ultra-high molecular weight polyethylene, the method including reacting a magnesium halide compound, a titanium alkoxide, an aluminum halide and a silicon alkoxide compound; however, the catalyst is characterized by relatively low catalyst activity and the resulting polymer has low apparent density. U.S. Pat. No. 5,587,440 discloses a method for preparing ultra-high molecular weight polyethylene having a uniform particle size distribution and high apparent density using a catalyst obtained by reacting a titanium compound with organoaluminum. However, there is a disadvantage that the polymerization activity of the catalyst is low. Therefore, a purpose of the present disclosure is to provide a preparation method of a catalyst for producing ultra-high molecular weight polyethylene (UHMEP), in which the catalyst has high polymerization activity while the resulting UHMEP has uniform particle size distribution and high apparent density as required characteristics thereof. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     The present disclosure has been made in an effort to provide a preparation method of a catalyst for producing ultra-high molecular weight polyethylene (UHMEP), in which the catalyst has high polymerization activity while the resulting UHMEP has uniform particle size and high apparent density. 
     The method of preparing the catalyst capable of achieving the purpose is characterized by including: 
     (1) reacting magnesium dichloride (MgCl 2 ) with alcohol to prepare a magnesium compound solution; 
     (2) reacting titanium tetrachloride with the magnesium compound solution prepared in the step (1) to prepare a precursor; and 
     (3) reacting the precursor with titanium tetrachloride and at least one phthalate compound represented by a following general formula (I) to prepare the catalyst: 
       R 1 OOC(C 6 H 4 )COOR 2    (I)
 
     where each of R 1  and R 2  represents an alkyl group of 1 to 10 carbon atoms. 
     The magnesium compound solution used in the present disclosure may be prepared by reacting the magnesium dichloride with the alcohol in presence of a hydrocarbon solvent. Types of the hydrocarbon solvent that may be used may include aliphatic hydrocarbons such as pentane, hexane, heptane, octane, decane, and kerosene, alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane, and methylcyclohexane, aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, cumene, and cymene, and halogenated hydrocarbons such as dichloropropane, dichloroethylene, trichloroethylene, carbon tetrachloride, and chlorobenzene. 
     The alcohol used to prepare the magnesium compound solution in the step (1) is not particularly limited and may include alcohol having 4 to 20 carbons. 
     The polymerization reaction of the present disclosure is carried out using a magnesium-supported titanium catalyst prepared by the method and an organometallic compound of Groups II and III of the periodic table. 
     In the present disclosure, a beneficial organometallic compound used as a co-catalyst in the polyethylene polymerization may be represented by a general formula of MR n , where M is a periodic table group II or IIIA metal component such as magnesium, calcium, zinc, boron, aluminum, and gallium, R represents an alkyl group having 1 to 20 carbons such as methyl, ethyl, butyl, hexyl, octyl and decyl, and n represents a valence of the metal component. A more preferable organometallic compound may include trialkyl aluminum having an alkyl group having 1 to 6 carbons such as triethyl aluminum and triisobutyl aluminum, and a mixture thereof. In some cases, the organoaluminum compound may include ethyl aluminum dichloride, diethyl aluminum chloride, ethyl aluminum sesquichloride, and diisobutyl aluminum hydride. 
     The polymerization reaction may include gas phase or bulk polymerization in absence of an organic solvent or liquid slurry polymerization in presence of an organic solvent. These polymerizations are performed in absence of oxygen, water, and other compounds that may act as catalytic poisons. 
     Examples of the solvent may include alkanes or cycloalkanes such as pentane, hexane, heptane, n-octane, isooctane, cyclohexane, and methylcyclohexane; alkylaromatics such as toluene, xylene, ethylbenzene, isopropylbenzene, ethyltoluene, n-propylbenzene, diethylbenzene; halogenated aromatics such as chlorobenzene, chloronaphthalene and ortho-dichlorobenzene; and mixtures thereof. The examples of the solvent may be useful for removing polymerization heat and obtaining high catalyst activity. 
     The present disclosure provides a simple and efficient method of preparing a catalyst capable of being used for producing the ultra-high molecular weight polyethylene having the uniform particle size and high apparent density at the excellent polymerization activity. 
     Further aspects and areas of applicability will become apparent from the description provided herein. It should be understood that various aspects of this disclosure may be implemented individually or in combination with one or more other aspects. It should also be understood that the description and specific examples herein are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     DETAILED DESCRIPTION 
     The present disclosure will be described in more detail based on following Examples. However, these Examples are for illustrative purposes only, and the present disclosure is not limited to these Examples. 
     EXAMPLES 
     Example 1 
     [Preparation of Solid Catalyst for Preparation of Ultra-High Molecular Weight Polyethylene] 
     Step (1): Preparation of magnesium halide alcohol adduct solution 
     After replacing an atmosphere of a 1 L reactor equipped with a mechanical stirrer with a nitrogen atmosphere, 20 g of solid magnesium dichloride (MgCl 2 ), 120 ml of toluene, and 60 ml of normal butanol were added to the reactor and stirred at 350 rpm. After raising a temperature to 65° C. for 1 hour, the reactor was maintained for 2 hours to obtain a uniform magnesium halide alcohol adduct solution that was well dissolved in a solvent. 
     Step (2): Preparation of magnesium halide carrier 
     After cooling the temperature of the solution prepared in step (1) to 20° C., 20 ml of TiCl 4  was slowly injected to thereto for 40 minutes (0.5 ml/min). Then, 62.5 ml of TiCl 4  was injected thereto more rapidly for 100 minutes (0.625 ml/min). At this time, the temperature was maintained so that the temperature of the reactor did not rise 25° C. or higher carefully. When the injection was completed, the temperature of the reactor was raised to 60° C. for 1 hour and was maintained for 1 hour additionally. When all processes were completed, the reactor was allowed to stand and a solid component was completely settled and then a supernatant was removed, and then the solid component in the reactor was washed and precipitated once with 300 ml of toluene to completely remove liquid impurities to obtain a carrier. 
     Step (3): Preparation of catalyst carrying titanium and diisobutyl phthalate 
     200 ml of toluene was added to the carrier, and the mixture was maintained 25° C. while stirring the mixture at 250 rpm. Then, 27 ml of TiCl 4  was injected thereto at a time and the mixture was maintained for 1 hour to perform a first reaction. After injecting 36.2 mmol of diisobutyl phthalate thereto, the reactor temperature was raised to 60° C. and the reactor was maintained for 1 hour to perform a second reaction between TiCl 4  and the carrier. When all processes were completed, the reactor was allowed to stand to completely settle the solid component and then a supernatant was removed. The prepared solid catalyst was washed and precipitated six times with 200 ml of hexane to remove impurities. 
     [Ultra-High Molecular Weight Polyethylene Polymerization] 
     A nitrogen atmosphere was created in a 2 liter batch reactor by alternately injecting nitrogen and vacuum three times into the 2 liter batch reactor. After 1,000 ml of hexane was injected into the reactor, 1 mmol of triethylaluminum and 0.005 mmol of the solid catalyst based on a titanium atom were injected to the reactor. After 9 psi of hydrogen was injected thereto, a temperature of the reactor was raised to 80° C. while stirring the mixture therein at 700 rpm. Then, an ethylene pressure was adjusted to 120 psig, followed by slurry polymerization for 90 minutes. After the polymerization was completed, a temperature of the reactor was lowered to room temperature. Hexane slurry containing a resulting polymer was filtered and dried to obtain a white powdery polymer. 
     The polymerization activity (kg-PE/g-catalyst) was calculated as a weight of the polymer as produced per an amount of the catalyst as used. The particle size distribution of the polymer was measured using a laser particle analyzer (Mastersizer X, Malvern Instruments). As a result, the average particle size thereof was D (v, 0.5), and the particle size distribution thereof was expressed as (D (v, 0.9)−D (v, 0.1))/D (v, 0.5), where D (v, 0.5) represents the particle size exhibited by 50% of a sample, and D (v, 0.9) and D (v, 0.1) indicate the particle size exhibited by 90% and 10% of samples, respectively. The smaller the numerical value of the distribution, the narrower the distribution. The M w  (weight average molecular weight) and the molecular weight distribution (M w /M n ) of the polymer were measured and analyzed using gel permeation chromatography. The polymerization results are shown in Table 1 together with the apparent density (g/ml) of the polymer. 
     Example 2 
     Example 2 was conducted in the same manner as in Example 1, except that 36.2 mmol of dimethyl phthalate was used instead of diisobutyl phthalate in Example 1. 
     Example 3 
     Example 3 was carried out in the same manner as in Example 1, except that 36.2 mmol of diethyl phthalate was used instead of diisobutyl phthalate in Example 1. 
     Comparative Example 1 
     Comparative Example 1 was carried out in the same manner as in Example 1, except that 36.2 mmol of ethyl benzoate was used instead of diisobutyl phthalate in Example 1. 
     Comparative Example 2 
     Comparative Example 2 was carried out in the same manner as in Example 1, except that diisobutyl phthalate was not used in Example 1. 
     Comparative Example 3 
     Step (1): Preparation of magnesium halide alcohol adduct solution 
     After replacing an atmosphere of a 1 L reactor equipped with a mechanical stirrer with a nitrogen atmosphere, 20 g of solid magnesium dichloride (MgCl 2 ), 120 ml of toluene, 20 ml of tetrahydrofuran, and 40 ml of normal butanol were added to the reactor and stirred at 350 rpm. After raising a temperature to 65° C. for 1 hour, the reactor was maintained for 2 hours to obtain a uniform magnesium halide alcohol adduct solution that was well dissolved in a solvent. 
     Step (2): Preparation of magnesium halide carrier 
     After cooling the temperature of the solution prepared in step (1) to 20° C., 20 ml of TiCl 4  was slowly injected to thereto for 40 minutes (0.5 ml/min). Then, 62.5 ml of TiCl 4  was injected thereto more rapidly for 100 minutes (0.625 ml/min). At this time, the temperature was maintained so that the temperature of the reactor did not rise 25° C. or higher carefully. When the injection was completed, the temperature of the reactor was raised to 60° C. for 1 hour and was maintained for 1 hour additionally. When all processes were completed, the reactor was allowed to stand and a solid component was completely settled and then a supernatant is removed, and then the solid component in the reactor was washed and precipitated once with 300 ml of toluene to completely remove liquid impurities to obtain a carrier. 
     Step (3): Preparation of catalyst carrying titanium and diisobutyl phthalate 
     200 ml of toluene was added to the carrier, and the mixture was maintained 25° C. while stirring the mixture at 250 rpm. Then, 27 ml of TiCl 4  was injected thereto at a time and the mixture was maintained for 1 hour to perform a first reaction. After injecting 36.2 mmol of diisobutyl phthalate thereto, the reactor temperature was raised to 60° C. and the reactor was maintained for 1 hour to perform a second reaction between TiCl 4  and the carrier. Then, the reactor was allowed to stand to completely settle the solid component and then a supernatant was removed. The prepared solid catalyst was washed and precipitated six times with 200 ml of hexane to remove impurities. 
     [Ultra-High Molecular Weight Polyethylene Polymerization] 
     A nitrogen atmosphere was created in a 2-liter batch reactor by alternately injecting nitrogen and vacuum three times into the 2-liter batch reactor. After 1,000 ml of hexane was injected into the reactor, 1 mmol of triethylaluminum and 0.005 mmol of the solid catalyst based on a titanium atom were injected to the reactor. After 9 psi of hydrogen was injected thereto, a temperature of the reactor was raised to 80° C. while stirring the mixture therein at 700 rpm. Then, an ethylene pressure was adjusted to 120 psig, followed by slurry polymerization for 90 minutes. After the polymerization was completed, a temperature of the reactor was lowered to room temperature. Hexane slurry containing a resulting polymer was filtered and dried to obtain a white powdery polymer. 
     The polymerization activity (kg-PE/g-catalyst) was calculated as a weight of the polymer as produced per an amount of the catalyst as used. The particle size distribution of the polymer was measured using a laser particle analyzer (Mastersizer X, Malvern Instruments). As a result, the average particle size thereof was D (v, 0.5), and the particle size distribution thereof was expressed as (D (v, 0.9)−D (v, 0.1))/D (v, 0.5), where D (v, 0.5) represents the particle size exhibited by 50% of a sample, and D (v, 0.9) and D (v, 0.1) indicate the particle size exhibited by 90% and 10% of samples, respectively. The smaller the numerical value of the distribution, the narrower the distribution. The M w  (weight average molecular weight) and the molecular weight distribution (M w /M n ) of the polymer were measured and analyzed using gel permeation chromatography. The polymerization results are shown in Table 1 together with the apparent density (g/ml) of the polymer. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Titanium 
                   
                   
                   
                   
                   
               
               
                   
                 content 
                 Activity 
                   
                 Molec- 
                   
                 Par- 
               
               
                   
                 in  
                 (kg- 
                 Ap- 
                 ular 
                 Average 
                 ticle 
               
               
                   
                 catalyst 
                 PE/g- 
                 parent 
                 weight 
                 particle  
                 size 
               
               
                   
                 (weight 
                 cata- 
                 density 
                 (10 n g/ 
                 size 
                 distri- 
               
               
                 Examples 
                 %) 
                 lyst) 
                 (g/ml) 
                 mol) 
                 (μm) 
                 bution 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Example 1 
                 2.8 
                 28.5 
                 0.45 
                 5.6 
                 131 
                 0.60 
               
               
                 Example 2 
                 2.3 
                 24.3 
                 0.43 
                 5.8 
                 125 
                 0.74 
               
               
                 Example 3 
                 2.6 
                 26.2 
                 0.43 
                 5.6 
                 127 
                 0.76 
               
               
                 Comparative  
                 3.6 
                 15.7 
                 0.39 
                 5.5 
                 112 
                 0.70 
               
               
                 Example 1 
                   
                   
                   
                   
                   
                   
               
               
                 Comparative  
                 7.5 
                 10.8 
                 0.33 
                 5.3 
                 240 
                 1.3 
               
               
                 Example 2 
                   
                   
                   
                   
                   
                   
               
               
                 Comparative  
                 2.9 
                 19.4 
                 0.37 
                 6.2 
                 193 
                 1.1 
               
               
                 Example 3 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, the catalyst prepared by the methods of Examples 1 to 3 may allow production of the ultra-high molecular weight polyethylene with uniform particle size and very high apparent density at excellent polymerization activity. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.