KR20220078953A - A preparation methods of Ziegler-Natta catalysts to control molecular weight distribution of ultra-high molecular weight polyethylene - Google Patents

Abstract

The present invention is a method for preparing a catalyst capable of controlling molecular weight distribution according to the organic compound used by preparing a solid catalyst containing titanium tetrachloride, a diether compound and an organic halide compound and then performing a polymerization reaction. A catalyst having excellent, uniform particle size and high apparent density while easily controlling the molecular weight distribution of ultra-high molecular weight polyethylene can be prepared simply and efficiently.

Description

{A preparation methods of Ziegler-Natta catalysts to control molecular weight distribution of ultra-high molecular weight polyethylene}

The present invention relates to a method for preparing a magnesium-supported titanium solid catalyst for preparing ultra-high molecular weight polyethylene. This is a method of preparing a catalyst capable of controlling molecular weight distribution according to the organic compound used by preparing a solid catalyst containing titanium tetrachloride, a diether compound, and an organohalide compound and then performing a polymerization reaction.

Ultra-high molecular weight polyethylene means polyethylene with a weight average molecular weight of 250,000 - 10,000,000 g/mol, and has excellent properties such as rigidity, abrasion resistance, chemical resistance and electrical properties because the molecular weight is very large compared to general-purpose polyethylene. Since ultra-high molecular weight polyethylene has excellent mechanical properties and wear resistance among thermoplastic engineering plastics, it has been used for mechanical parts requiring wear resistance such as gears, bearings, and cams. It is also used as a material for joints.

Ultra-high molecular weight polyethylene has a very high molecular weight and has little flowability in the molten state, so it is produced in powder form. Therefore, the particle size and distribution of the powder and the apparent density are very important. Ultra-high molecular weight polyethylene is processed by dissolving it in an appropriate solvent due to the difficult property of melt processing, but powder with a large particle size may impair its dissolution properties. In addition, when the apparent density is low, there is a problem in powder transport, so the particle size and apparent density of the powder act as important factors affecting productivity during the processing process.

The properties and processability of polyolefin materials are affected by the polydispersity of molecular weight distribution. In general, the smaller the polydispersity, the better the physical and odor properties, but the lower the processability and environmental stress resistance. The wider the polydispersity, the better the processability and environmental stress resistance, but the physical and odor properties are impaired.

In the case of polypropylene, the molecular weight distribution is controlled by controlling the electron donor of the Ziegler-Natta catalyst used. In the case of polyethylene whose electron donor role is unclear, polydispersity is controlled by changing the catalyst to chromium or metallocene instead of Ziegler-Natta catalyst, or polyethylene having a double molecular weight distribution using a multi-stage reactor or a mixture of two or more catalysts methods are mainly used for making

The preparation of a Ziegler-Natta catalyst containing magnesium and titanium compounds and a preparation method of ultra-high molecular weight polyethylene using the same have been reported in several patents. Korean Patent Registration No. 0822616 discloses a method for preparing a catalyst containing magnesium, titanium and a silane compound capable of producing an ultra-high molecular weight polyolefin polymer with high catalytic activity and uniform particle size distribution, but there is room for improvement in terms of apparent density. , U.S. Patent No. 4,962,167 reports a method for preparing an ultra-high molecular weight polyethylene catalyst by reacting a magnesium halide compound, a titanium alkoxide, an aluminum halide and a silicon alkoxide compound, but has relatively low catalytic activity and apparent density. U.S. Patent No. 5,587,440 discloses a method for producing 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, but the polymerization activity of the catalyst is low.

Korean Patent Registration No. 1959694 discloses control of molecular weight distribution and polydispersity by mixing two different catalysts, but it is limited to metallocene single site catalysts. In US Patent No. 9725535, polydispersity is controlled through a Ziegler-Natta catalyst having two or more active metals, but the polydispersity is limited to only 4.5 at a maximum. U.S. Patent No. 8557935 reports a catalyst composition having a polydispersity of 15 or more by mixing a Ziegler-Natta catalyst and a metallocene catalyst, but has a low activity. In addition, this method of combining catalysts is not suitable for application to ultra-high molecular weight polyethylene, which requires uniform particle size and high apparent density of polymerized powder.

Therefore, in the present invention, it is intended to provide a method for preparing a catalyst for ultra-high molecular weight polyethylene that is easy to control molecular weight distribution and polydispersity while satisfying uniform particle size distribution, high apparent density, and high polymerization activity, which are the required characteristics of ultra-high molecular weight polyethylene.

An object of the present invention is to provide a method for simply and efficiently preparing a catalyst having excellent polymerization activity, uniform particle size and high apparent density, and at the same time, the molecular weight distribution of ultra-high molecular weight polyethylene can be easily controlled.

An object is to be solved by a method for preparing a catalyst for preparing ultra-high molecular weight polyethylene, characterized in that it includes the following steps.

(1) reacting magnesium dichloride (MgCl ₂ ) with tetrahydrofuran and alcohol to prepare a magnesium compound solution;

(2) preparing a precursor by adding titanium tetrachloride to the magnesium compound solution prepared in step (1) and reacting;

(3) preparing a catalyst by first reacting the precursor with titanium tetrachloride, and then performing a secondary reaction by adding a mixture of a diether compound and an organohalide compound represented by the following general formula (I) to the reactant.

R ¹ OR ² -OR ³ … … (I)

(The above R ¹ , R ² and R ³ each independently represent a substituted or unsubstituted linear, branched, cyclic or aromatic hydrocarbon having 1 to 10 carbon atoms)

The organohalide compound refers to an alkane, alkene, cycloalkane or arene compound containing one or two or more of the halogen elements F, Cl, Br, and I.

In step (1), the alcohol is a primary alcohol having 2 to 8 carbon atoms.

In the mixture of the diether compound and the organohalide compound in step (3), the molar ratio is 0.05:1 to 50:1 (diether compound:organohalide compound).

The polymerization reaction of the present invention is carried out using a Ziegler-Natta solid catalyst and an organometallic compound of Group II or IIIA of the Periodic Table as a magnesium-supported titanium catalyst prepared by the above method.

The organometallic compound useful as a cocatalyst in polymerization of polyethylene in the present invention can be represented by the general formula of MR _n , where M is group II or IIIA of the periodic table such as magnesium, calcium, zinc, boron, aluminum, and gallium. It is a group metal component, R represents an alkyl group having 1 to 20 carbon atoms such as methyl, ethyl, butyl, hexyl, octyl, and decyl, and n represents the valence of the metal component.

More preferred organometallic compounds include trialkylaluminum having an alkyl group having 1 to 6 carbon atoms, such as triethylaluminum and triisobutylaluminum; Alternatively, the mixture of trialkylaluminum is beneficial for activating the catalyst and removing impurities in the polymerization reactor. In some cases, organoaluminum compounds such as ethylaluminum dichloride, diethylaluminum chloride, ethylaluminum sesquichloride, and diisobutylaluminum hydride may be used.

The polymerization reaction can be carried out by gas phase or bulk polymerization in the absence of an organic solvent or liquid slurry polymerization in the presence of an organic solvent. These polymerizations are carried out in the absence of oxygen, water, and other compounds that can act as catalyst poisons. Examples of the organic solvent 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, and diethylbenzene; halogenated aromatics such as chlorobenzene, chloronaphthalene, ortho-dichlorobenzene; or a mixture thereof is beneficial in removing the heat of polymerization and obtaining high catalytic activity.

The present invention provides a method for simply and efficiently preparing a catalyst having excellent polymerization activity, uniform particle size and high apparent density, and at the same time, the molecular weight distribution of ultra-high molecular weight polyethylene can be easily controlled.

Hereinafter, the present invention will be described in more detail through the following examples. However, these examples are for illustrative purposes only.The invention is not limited to these examples.

Example

Example 1

[Preparation of solid catalyst for production of ultra-high molecular weight polyethylene]

(1) Step: Preparation of magnesium halide alcohol adduct solution

After replacing the 1L reactor with a mechanical stirrer with a nitrogen atmosphere, 20 g of solid magnesium dichloride (MgCl ₂ ), 120 ml of toluene, 60 ml of n-butanol, and 30 ml of tetrahydrofuran were added and stirred at 350 rpm. After raising the temperature to 80 °C for 1 hour, it was maintained for 2 hours to obtain a uniform magnesium halide alcohol adduct solution dissolved in a solvent as a magnesium compound.

(2) Step: Preparation of Magnesium Halide Carrier

After cooling the temperature of the solution prepared in step (1) to 30 °C, 67 ml of TiCl ₄ was slowly injected into the solution for 120 minutes. At this time, the temperature was maintained taking care not to increase the temperature of the reactor above 25 °C. When the injection was completed, the temperature of the reactor was raised to 60 °C for 1 hour and maintained for an additional 1 hour. When all processes are complete, the reactor is left standing to completely sink the solid component to remove the supernatant, and then the solid component in the reactor is washed once with 300 ml of toluene and precipitated to completely remove impurities in the liquid phase to form a clean magnesium chloride carrier as a solid. obtained with

(3) step: titanium tetrachloride, diether and chlorocyclohexane supported catalyst preparation

200 ml of toluene was added to the magnesium chloride carrier and stirred at 250 rpm while maintaining 25 ^o C. After that, 34 ml of TiCl ₄ was injected into the carrier at a time and maintained for 1 hour for a first reaction. Then, after injecting 1 ml of chlorocyclohexane and 3 ml of 2-isobutyl-2-isopropyl-1,3-dimethoxypropane as diether, the temperature of the reactor was increased. After raising the temperature to 60 degrees and maintaining it for 1 hour, TiCl ₄ and the carrier were subjected to a secondary reaction. When all processes were completed, the reactor was left still to completely sink the solid component, and then the supernatant was removed. A Ziegler-Natta solid catalyst for polyethylene production was prepared by washing and precipitating the prepared sunken solid component once with 200 ml of toluene and 6 times with 200 ml of hexane to remove impurities.

[Ultra-high molecular weight polyethylene polymerization]

A nitrogen atmosphere was created in the 2 liter batch reactor by alternating nitrogen and vacuum three times. After 1000 ml of hexane was injected into the reactor, 1 mmol of triethylaluminum and 0.005 mmol of the obtained solid catalyst were injected based on titanium atoms. After injecting 9 psi of hydrogen, the temperature of the reactor was raised to 80° C. while stirring at 700 rpm, the ethylene pressure was adjusted to 120 psig, and slurry polymerization was carried out for 90 minutes. After polymerization, the temperature of the reactor was lowered to room temperature, and the hexane slurry containing the polymer was filtered and dried to obtain a white powdery polymer.

Polymerization activity (kg-PE/g-catalyst) was calculated as the weight ratio of the polymer produced per amount of catalyst used.

The particle size distribution of the polymer was measured using a laser particle analyzer (Mastersizer X, Malvern Instruments), and the result was that the average particle size was D(v,0.5) and the particle size distribution was (D(v,0.9)-D( v,0.1))/D(v,0.5). Here, D(v,0.5) represents the median size of particles included in the sample, and D(v,0.9) and D(v,0.1) represent particle sizes located at 90% and 10% of the size distribution standard, respectively. it means. The smaller the number of particle size distribution, the narrower the particle size distribution.

M _w (weight average molecular weight), Mn (number average molecular weight) and molecular weight distribution (Polydispersity Index, PDI, M _w /M _n ) of the polymer were measured and analyzed by gel permeation chromatography.

The polymerization results are shown in Table 1 together with the apparent density (g/ml) of the polymer.

Example 2

Example 1 was carried out in the same manner as in Example 1, except that the amount of chlorocyclohexane was adjusted to 0.5 ml.

Example 3

Example 1 was carried out in the same manner as in Example 1, except that the amount of chlorocyclohexane was adjusted to 0.1 ml.

Example 4

Example 1 was carried out in the same manner as in Example 1, except that the amount of chlorocyclohexane was adjusted to 2.0 ml.

Example 5

Example 1 was carried out in the same manner as in Example 1, except that chlorocyclohexane was adjusted with chloroform.

Comparative Example 1

Example 1 was carried out in the same manner as in Example 1, except that chlorocyclohexane was not used.

Comparative Example 2

Example except that chlorocyclohexane and 2-isobutyl-2-isopropyl-1,3-dimethoxypropane were not used in Example 1 1 was carried out in the same manner.

As shown in Table 1 above, in the case of the catalyst prepared by the method of Examples 1 to 5 in which the precursor magnesium chloride carrier was first reacted with titanium tetrachloride, followed by a secondary reaction with a combination of a diether compound and an organohalide compound, Comparative Example It can be seen that the catalyst has a uniform particle size distribution and high apparent density compared to the catalyst prepared by methods 1 and 2. Also, comparing Examples 1 to 4, a high molecular weight distribution and an apparent density value can be obtained only when an appropriate amount of organic halide is injected. In addition, the molecular weight distribution can be selectively controlled according to the amount and type of the organohalide used.

Claims (3)

In the method for producing a Ziegler-Natta solid catalyst for producing polyethylene,
(1) reacting magnesium dichloride (MgCl ₂ ) with tetrahydrofuran and alcohol to prepare a magnesium compound solution;
(2) preparing a precursor by reacting the magnesium compound solution prepared in step (1) with titanium tetrachloride; and
(3) After the first reaction of the precursor with titanium tetrachloride, a second reaction between the product in the first reaction and a mixture of a diether compound and an organohalide compound represented by the following general formula (I) to prepare a solid catalyst comprising steps;
R ¹ - OR ² - OR ³ . … (I)
(The above R ¹ _, R ² _, and R ³ are each independently a substituted or unsubstituted linear, branched, cyclic or aromatic hydrocarbon having 1 to 10 carbon atoms.)
The organohalide compound is an alkane, alkene, cycloalkane, or arene compound containing one or more of the halogen elements F, Cl, Br, and I. Preparation of a Ziegler-Natta solid catalyst for polyethylene production Way. The method according to claim 1, wherein the alcohol is a primary alcohol having 2 to 8 carbon atoms. The method of claim 1, wherein the mixture of the diether compound and the organohalide compound in step (3) has a molar ratio of 0.05:1 to 50:1.