KR102487347B1 - 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 whose molecular weight distribution can be adjusted 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, wherein the polymerization activity is A catalyst capable of easily controlling the molecular weight distribution of ultra-high molecular weight polyethylene while having excellent uniform particle size and high apparent density can be prepared simply and efficiently.

Description

A preparation method 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 producing ultrahigh molecular weight polyethylene. This is a method for preparing a catalyst whose molecular weight distribution can be controlled 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.

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

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

The physical 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 properties and odor characteristics are deteriorated.

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

Preparation of a Ziegler-Natta catalyst containing a magnesium and titanium compound and a method for preparing ultra-high molecular weight polyethylene using the catalyst 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 having 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 reported 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 has a disadvantage in that the polymerization activity of the catalyst is low.

Korean Patent Registration No. 1959694 discloses mixing two different catalysts to control molecular weight distribution and polydispersity, but it is limited to metallocene single active site catalysts. In U.S. Patent No. 9725535, the polydispersity was controlled through a Ziegler-Natta catalyst having two or more active metals, but the polydispersity was limited to a maximum of 4.5. US Patent No. 8557935 reported a catalyst composition having a polydispersity of 15 or more by mixing a Ziegler-Natta catalyst and a metallocene catalyst, but has a disadvantage of low activity. In addition, this type of catalyst preparation method is unsuitable for application to ultra-high molecular weight polyethylene, which requires uniform particle size and high apparent density of polymerized powder.

Therefore, the present invention is intended to provide a method for preparing a catalyst for ultra-high molecular weight polyethylene that can easily control molecular weight distribution and polydispersity while satisfying uniform particle size distribution, high apparent density, and high polymerization activity, which are 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 capable of easily controlling the molecular weight distribution of ultrahigh molecular weight polyethylene, while having excellent polymerization activity, uniform particle size and high apparent density.

A method for preparing a catalyst for producing ultra-high molecular weight polyethylene comprising the following steps is intended to solve the problem.

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

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

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

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 organic halide compound refers to an alkane, alkene, cycloalkane, or arene compound containing one or more of halogen elements F, Cl, Br, and I.

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

In the step (3), in the mixture of the diether compound and the organohalide compound, 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 a group II or IIIA organometallic compound of the periodic table as a magnesium-supported titanium catalyst prepared by the above method.

In the present invention, the beneficial organometallic compound used as a cocatalyst for polyethylene polymerization can be represented by the general formula of MR _n , where M is a member of periodic table group II or IIIA 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 preferable organometallic compounds include trialkyl aluminum having an alkyl group having 1 to 6 carbon atoms such as triethyl aluminum and triisobutyl aluminum; or a mixture of the trialkylaluminum is beneficial for activating the catalyst and removing impurities in the polymerizer. In some cases, organic aluminum compounds such as ethyl aluminum dichloride, diethyl aluminum chloride, ethyl aluminum sesquichloride, and diisobutyl aluminum hydride may be used.

The polymerization reaction is possible by gas phase or bulk polymerization in the absence of an organic solvent or liquid phase 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, and ortho-dichlorobenzene; or mixtures thereof are beneficial for removing the heat of polymerization and obtaining high catalytic activity.

The present invention provides a method for simply and efficiently preparing a catalyst capable of easily controlling the molecular weight distribution of ultra-high molecular weight polyethylene, while having excellent polymerization activity, uniform particle size and high bulk density.

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]

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

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

Step (2): Preparation of magnesium halide support

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 of the reactor was carefully maintained so that the temperature of the reactor did not rise 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 completed, the reactor is allowed to stand still to completely sink the solid components to remove the supernatant, and then the solid components in the reactor are washed and precipitated once with 300ml of toluene to completely remove liquid impurities, and a clean magnesium chloride carrier as a precursor is used as a solid got it with

Step (3): Preparation of titanium tetrachloride, diether and chlorocyclohexane-supported catalyst

200 ml of toluene was added to the magnesium chloride carrier and maintained at 25 ^° C. while stirring at 250 rpm. Thereafter, 34 ml of TiCl ₄ was injected into the carrier at once and maintained for 1 hour to perform the 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, the TiCl ₄ and the carrier were subjected to a secondary reaction by maintaining the temperature for 1 hour. When all processes were completed, the reactor was allowed to stand to completely settle the solid components, and then the supernatant was removed. The precipitated solid component was washed once with 200 ml of toluene and 6 times with 200 ml of hexane to remove impurities, thereby preparing a Ziegler-Natta solid catalyst for polyethylene production.

[Ultra high molecular weight polyethylene polymerization]

A 2-liter batch reactor was operated by alternating nitrogen and vacuum three times to create a nitrogen atmosphere in the reactor. After 1000 ml of hexane was injected into the reactor, 1 mmol of triethylaluminum and 0.005 mmol of the obtained solid catalyst based on titanium atoms were injected. After hydrogen was injected at 9 psi, the temperature of the reactor was raised to 80° C. while stirring at 700 rpm, and the ethylene pressure was adjusted to 120 psig, followed by slurry polymerization for 90 minutes. After the polymerization was completed, 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, respectively. it means. The smaller the number of the 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 through 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 performed 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 performed 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 performed 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 performed in the same manner as in Example 1, except that chlorocyclohexane was adjusted to chloroform.

Comparative Example 1

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

Comparative Example 2

Example 1 except that chlorocyclohexane and 2-isobutyl-2-isopropyl-1,3-dimethoxypropane were not used. The same as in 1 was performed.

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

Claims (3)

In the method for producing a Ziegler-Natta solid catalyst for producing polyethylene,
(1) preparing a magnesium compound solution by reacting magnesium dichloride (MgCl ₂ ) with tetrahydrofuran and alcohol;
(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, the product from the first reaction and the following general formula (I)
Preparing a solid catalyst by secondary reaction of a mixture of a diether compound and an organohalide compound;
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 organic halide compound is an alkane, alkene, cycloalkane or arene compound containing one or more of halogen elements F, Cl, Br, and I. Preparation of a Ziegler-Natta solid catalyst for polyethylene production, characterized in that Way. The method of 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.