CN1621423A - Process for preparing linear low density polyethylene - Google Patents

Abstract

A catalyst system for preparing linear low-density polyethylene by in-situ copolymerization. The catalyst system uses a homogeneous or supported novel α-bisimine pyridine iron complex as an oligomerization catalyst, and a homogeneous or supported metallocene The complex is composed of co-polymerization catalysts, with ethylene as the only raw material and alkylaluminoxane as the only co-catalyst, which first generates α-olefin in situ, and then completes the in-situ copolymerization reaction with ethylene to prepare linear low-density polyethylene. The resulting linear low-density polyethylene has the characteristics of low melting point, low density, and high comonomer insertion rate.

Description

A kind of preparation method of linear low density polyethylene

technical field

The present invention relates to a process for the preparation of linear low density polyethylene (LLDPE).

Background technique

The preparation of LLDPE by the copolymerization of ethylene and α-olefins with metallocene catalysts or constrained geometry catalysts is a research hotspot in recent years. The required ones are usually produced by ethylene oligomerization, and then undergo rectification to obtain hexene, octene, and decane. ene etc. If an in-situ copolymerization catalyst system can be used, that is, an oligomerization catalyst is used in the reaction system to first oligomerize ethylene into α-olefin, then add a copolymerization catalyst, and then in-situ copolymerize with ethylene to form LLDPE. This will simplify the production process, and at the same time solve the problem that domestic α-olefins are mainly dependent on imports, and greatly reduce production costs.

When the traditional Ziegler-Natta catalyst is applied to the copolymerization of ethylene and α-olefin, LLDPE with high insertion rate cannot be obtained, and the copolymerization performance of high carbon number α-olefin is even worse. And the methylaluminoxane (MAO) that Kaminsky found in the eighties can improve the cocatalyst of catalytic activity and polymerization thereof (Angew.Chem.Int.Ed.Engl.19,396(1980)) . At present, the preparation of copolymers of ethylene, propylene, and high-carbon alpha-olefins by metallocene catalysts is a research hotspot of polyolefin materials. In recent years, the emerging constrained geometry catalysts are currently the most ideal ethylene copolymerization catalysts. Bazan [J.Am.Chem.Soc.120,7143(1998)] designed and synthesized (C ₆ H ₅ B-OEt) ₂ ZrCl ₂ can catalyze ethylene oligomerization under the effect of MAO to obtain ethylene oligomer, and then LLDPE was successfully obtained by in-situ copolymerization of ethylene with constrained geometry catalyst. However, its biggest disadvantage is that the ethylene oligomerization catalyst it adopts is unstable and the α-olefin selectivity of the catalyst is poor, the selectivity is 40-90%, and its oligomerization products are 1-alkenes, 2-alkyl-1- Alkenes and 2-alkenes, wherein 2-alkyl-1-alkenes and 2-alkenes cannot form copolymerization products with ethylene.

In addition, Bazan [Macromolecules, 34 (2001) 2411] studied a new type of α-bisimine pyridine iron complex as an oligomerization catalyst and ethyl indenyl zirconium dichloride as a copolymerization catalyst to prepare LLDPE in series. The carbon number distribution of the oligomer obtained by the oligomerization catalyst is relatively wide, and it is easy to leave high carbon number oligomers in the polymer.

Contents of the invention

Based on the above technical background, the present invention adopts a novel α-bisimine pyridine iron complex with high activity and high selectivity as an oligomerization catalyst (α-olefin selectivity > 95%, carbon number distribution of C ₄ -C ₃₀ , mainly C ₄ ～C ₁₀ (>80%)), using metallocene catalysts as copolymerization catalysts, ethylene as the only monomer, and alkylaluminoxane as the only co-catalyst, LLDPE was prepared by in-situ polymerization of ethylene, solving Insufficiency in the above research focuses on solving the problem of high carbon number α-olefin residues.

The oligomerization catalyst involved in the present invention is a homogeneous or supported novel α-bisimine pyridine iron complex, and its molecular structural formula is as follows:

R ₁ =-H,-CH ₃

_R2 = -F, -Cl, -Br, -I

R ₃ =—CH ₃ ,—CH ₂ CH ₃ ,—CH(CH ₃ ) ₂ ,—OCH ₃ ,—Br,—Cl,—F

_R4 = -F, -H

X = -Br, -Cl

The co-polymerization catalyst involved in the present invention is a cyclocene-based compound with Ti, Zr or Hf as the central atom or a supported catalyst thereof. The metallocene compound can be single-bridged, double-bridged or non-bridged, and the metallocene with the bridged Zr as the central atom is the best. These compounds are Et(Ind) ₂ ZrCl ₂ , Me ₂ Si(Ind) ₂ ZrCl _2. Et(Ind) ₂ ZrMe ₂ , Me ₂ Si(Ind) ₂ ZrMe ₂ , Cp*SiMe ₂ NBu ^t ZrCl ₂ , Cp*SiMe ₂ NBu ^t TiCl ₂ , or IndSiMe ₂ NBu ^t ZrCl ₂ , etc.

The raw material carrier of the supported oligomerization and copolymerization catalyst involved in the present invention is an organic carrier or an inorganic carrier, generally a porous carrier. Non-limiting examples include: SiO ₂ , MgCl ₂ , Al ₂ O ₃ , talc, zeolite, montmorillonite, polyethylene, or polystyrene. The particle size of the carrier is 0.1-1000 μm, the specific surface area is 60-500 m ² /g, the pore volume is 0.1-7.0 cc/g, and the pore diameter is 30-700 Å.

The cocatalyst involved in the present invention is an alkylaluminoxane, such as methylaluminoxane (MAO), ethylaluminoxane (EAO), or isobutylaluminoxane (iBAO).

The present invention adopts the preparation method that bifunctional catalyst system directly synthesizes LLDPE by ethylene to carry out according to the following steps:

1. Replace the reaction vessel equipped with a stirrer with nitrogen and ethylene respectively, then feed ethylene, add toluene that has been dehydrated and deoxygenated by metal sodium reflux, and the amount added is half of the volume of the vessel. The vessel temperature is 0-100°C. The ideal temperature is 30-70°C,

2. Add alkylaluminoxane cocatalyst and homogeneous or supported oligomerization catalyst in sequence under stirring, and react for 0-30 minutes;

3. Adding homogeneous or supported co-catalysts;

4. Add 10% (volume ratio) hydrochloric acid ethanol solution to terminate the reaction, wash with ethanol, and dry in vacuum to obtain LLDPE product.

A kind of in-situ copolymerization catalyst system for preparing linear low density polyethylene (LLDPE) according to the present invention has the following characteristics:

1. The oligomerization catalyst adopted in the present invention is a homogeneous or loaded α-bisimine pyridine iron complex, and its chemical molecular structural formula is as follows:

R ₁ =-H,-CH ₃

_R2 = -F, -Cl, -Br, -I

R ₃ =—CH ₃ ,—CH ₂ CH ₃ ,—CH(CH ₃ ) ₂ ,—OCH ₃ ,—Br,—Cl,—F

_R4 = -F, -H

X = -Br, -Cl

2. The copolymerization catalyst adopted in the present invention is a homogeneous or supported metallocene catalyst: Ti, Zr, or Hf is a center atom of a cene-based compound. The metallocene compound can be single-bridged, double-bridged or non-bridged, and the metallocene with the bridged Zr as the central atom is the best. These compounds are Et(Ind) ₂ ZrCl ₂ , Me ₂ Si(Ind) ₂ ZrCl _2. Et(Ind) ₂ ZrMe ₂ , Me ₂ Si(Ind) ₂ ZrMe ₂ , Cp*SiMe ₂ NBu ^t ZrCl ₂ , Cp*SiMe ₂ NBu ^t TiCl ₂ , or IndSiMe ₂ NBu ^t ZrCl ₂ , etc.

3. The molar ratio of the oligomerization catalyst used in the present invention to the copolymerization catalyst is 1: 20 ~ 10: 1, the best is 1: 10 ~ 2: 1.

4. The carrier used in the supported oligomerization catalyst and copolymerization catalyst used in the present invention is an organic carrier or an inorganic carrier, such as SiO ₂ , MgCl ₂ , Al ₂ O ₃ , talc, zeolite, montmorillonite, polyethylene, or poly Styrene, etc., preferably SiO ₂ .

5. the cocatalyst that the present invention adopts is alkyl aluminoxane, as methyl aluminoxane (MAO), ethyl aluminoxane (EAO), or isobutyl aluminoxane (iBAO) etc., wherein with MAO as optimal. Keep the molar ratio of Al/(Fe+Zr or Ti)=500:1~5000:1, preferably 1000:1~3000:1.

6. The polymerization system of the present invention has higher catalytic activity, and the product has a lower melting point and lower crystallinity. The melting point range is 97.8-124.9°C, the crystallinity range is 16.7-65.8%, and the density range is 0.910- 0.940g/cm ³ .

Detailed ways

Example 1

1) All operations are performed under anhydrous and oxygen-free conditions, and all solvents require dehydration and deoxidation treatment.

2) A: Oligomerization catalyst

B: Copolymerization catalyst Et(Ind) ₂ ZrCl ₂

C: co-catalyst MAO

3) Replace a 250mL three-neck flask equipped with a stirrer with nitrogen and ethylene respectively, then pass through ethylene, add 100mL toluene, heat up to 50°C, add MAO under stirring [Al/(Fe+Zr)=2000:1 (molar ratio)], after stirring for 2 minutes, add oligomerization catalyst A, react 2 minutes;

4) Add cocatalyst B, the oligomerization catalyst/cocatalyst molar ratio is 1:20, under the condition of keeping the ethylene pressure in the bottle at 770mmHg, polymerize for 0.5 hours;

5) adding 10% (volume ratio) hydrochloric acid ethanol solution to terminate the reaction, washing with ethanol and vacuum drying to obtain LLDPE product. Its operating conditions and polymer properties are listed in Table 1.

Example 2

1) All operations are performed under anhydrous and oxygen-free conditions, and all solvents require dehydration and deoxidation treatment.

2) A: Oligomerization catalyst

B: Copolymerization catalyst, SiO ₂ supported Et(Ind) ₂ ZrCl ₂

C: co-catalyst MAO

3) Replace a 250mL three-neck flask equipped with a stirrer with nitrogen and ethylene respectively, then pass through ethylene, add 100mL toluene, heat up to 100°C, add MAO under stirring [Al/(Fe+Zr)=1000:1 (molar ratio)], after stirring for 2 minutes, add oligomerization catalyst A, react 10 minutes;

4) Add cocatalyst B (Zr content 0.0050gZr/g supported catalyst), oligomerization catalyst/cocatalyst molar ratio 10:1, under the condition of keeping the ethylene pressure in the bottle at 770mmHg, polymerize for 0.5 hours;

5) adding 10% (volume ratio) hydrochloric acid ethanol solution to terminate the reaction, washing with ethanol and vacuum drying to obtain LLDPE product. Its operating conditions and polymer properties are listed in Table 1.

Example 3

1) All operations are performed under anhydrous and oxygen-free conditions, and all solvents require dehydration and deoxidation treatment.

2) A: Oligomerization catalyst

B: Copolymerization catalyst Et(Ind) ₂ ZrCl ₂

C: co-catalyst MAO

3) Replace a 250mL three-neck flask equipped with a stirrer with nitrogen and ethylene respectively, then pass through ethylene, add 100mL toluene, heat up to 0°C, add MAO under stirring [Al/(Fe+Zr)=2000:1 (molar ratio)], after stirring for 2 minutes, add oligomerization catalyst A;

4) Add co-catalyst B immediately, the oligomerization catalyst/co-catalyst molar ratio is 1: 1, under the condition that the ethylene pressure in the bottle is kept at 770mmHg, polymerize for 1 hour;

5) adding 10% (volume ratio) hydrochloric acid ethanol solution to terminate the reaction, washing with ethanol and vacuum drying to obtain LLDPE product. Its operating conditions and polymer properties are listed in Table 1.

Example 4

1) All operations are performed under anhydrous and oxygen-free conditions, and all solvents require dehydration and deoxidation treatment.

2) A: Oligomerization catalyst

B: Copolymerization catalyst Et(Ind) ₂ ZrCl ₂

C: co-catalyst MAO

3) Replace a 250mL three-neck flask equipped with a stirrer with nitrogen and ethylene respectively, then pass through ethylene, add 100mL toluene, heat up to 50°C, add MAO under stirring [Al/(Fe+Zr)=2000:1 (molar ratio)], after stirring for 2 minutes, add oligomerization catalyst A, react 2 minutes;

4) Add co-catalyst B, the oligomerization catalyst/co-catalyst molar ratio is 1: 10, under the condition of keeping the ethylene pressure in the bottle at 770mmHg, polymerize for 0.5 hours;

5) adding 10% (volume ratio) hydrochloric acid ethanol solution to terminate the reaction, washing with ethanol and vacuum drying to obtain LLDPE product. Its operating conditions and polymer properties are listed in Table 1.

Example 5

1) All operations are performed under anhydrous and oxygen-free conditions, and all solvents require dehydration and deoxidation treatment.

2) A: Oligomerization catalyst

B: Copolymerization catalyst Et(Ind) ₂ ZrCl ₂

C: co-catalyst MAO

3) Replace a 250mL three-neck flask equipped with a stirrer with nitrogen and ethylene respectively, then pass through ethylene, add 100mL toluene, heat up to 50°C, add MAO under stirring [Al/(Fe+Zr)=2000:1 (molar ratio)], after stirring for 2 minutes, add oligomerization catalyst A, react 2 minutes;

4) Add co-catalyst B, the oligomerization catalyst/co-catalyst molar ratio is 5: 1, under the condition that the ethylene pressure in the bottle is kept at 770mmHg, polymerize for 1 hour;

5) adding 10% (volume ratio) hydrochloric acid ethanol solution to terminate the reaction, washing with ethanol and vacuum drying to obtain LLDPE product. Its operating conditions and polymer properties are listed in Table 1.

Example 6

1) All operations are performed under anhydrous and oxygen-free conditions, and all solvents require dehydration and deoxidation treatment.

2) A: Oligomerization catalyst

B: Copolymerization catalyst Et(Ind) ₂ ZrCl ₂

C: co-catalyst MAO

3) Replace a 250mL three-neck flask equipped with a stirrer with nitrogen and ethylene respectively, then pass through ethylene, add 100mL toluene, heat up to 50°C, add MAO under stirring [Al/(Fe+Zr)=3000:1 (molar ratio)], after stirring for 2 minutes, add oligomerization catalyst A, react 10 minutes;

4) Add co-catalyst B, the oligomerization catalyst/co-catalyst molar ratio is 1:10, under the condition that the ethylene pressure in the bottle is kept at 770mmHg, polymerize for 1 hour;

5) adding 10% (volume ratio) hydrochloric acid ethanol solution to terminate the reaction, washing with ethanol and vacuum drying to obtain LLDPE product. Its operating conditions and polymer properties are listed in Table 1.

Example 7

1) All operations are performed under anhydrous and oxygen-free conditions, and all solvents require dehydration and deoxidation treatment.

2) A: Oligomerization catalyst

B: Copolymerization catalyst Me ₂ Si(Ind) ₂ ZrCl ₂

C: co-catalyst MAO

3) Replace a 250mL three-neck flask equipped with a stirrer with nitrogen and ethylene respectively, then pass through ethylene, add 100mL toluene, heat up to 50°C, add MAO under stirring [Al/(Fe+Zr)=2000:1 (molar ratio)], after stirring for 2 minutes, add oligomerization catalyst A, react 5 minutes;

4) Add co-catalyst B, the oligomerization catalyst/co-catalyst molar ratio is 1:10, under the condition that the ethylene pressure in the bottle is kept at 770mmHg, polymerize for 1 hour;

5) adding 10% (volume ratio) hydrochloric acid ethanol solution to terminate the reaction, washing with ethanol and vacuum drying to obtain LLDPE product. Its operating conditions and polymer properties are listed in Table 1.

Example 8

1) All operations are performed under anhydrous and oxygen-free conditions, and all solvents require dehydration and deoxidation treatment.

2) A: Oligomerization catalyst

B: Copolymerization catalyst Cp*SiMe ₂ NBu ^t ZrCl ₂

C: co-catalyst MAO

3) Replace a 250mL three-neck flask equipped with a stirrer with nitrogen and ethylene respectively, then pass through ethylene, add 100mL toluene, heat up to 70°C, add MAO under stirring [Al/(Fe+Zr)=2000:1 (molar ratio)], after stirring for 2 minutes, add oligomerization catalyst A, react 10 minutes;

4) Add cocatalyst B, the oligomerization catalyst/cocatalyst molar ratio is 1:20, under the condition of keeping the ethylene pressure in the bottle at 770mmHg, polymerize for 0.5 hours;

5) adding 10% (volume ratio) hydrochloric acid ethanol solution to terminate the reaction, washing with ethanol and vacuum drying to obtain LLDPE product. Its operating conditions and polymer properties are listed in Table 1.

      Table 1. Aggregation conditions and aggregation data in the examples

Oligomerization Copolymerization

Real Catalytic Catalytic Co-catalyst / Catalyst Crystallization Density

Catalyst active melting point

Dosing agent Chemical concentration (g/cm ³

^Sexa (℃)

Example (μmo (μmol (mol/mol) ) (%) )

1) )

1 0.4 0.4 2000 9.94 114.3 29.8 0.923

2 0.4 1 1000 2.85 123. 36.6 0.938

0

3 0.2 0.4 2000 11.1 115. 29.8 0.929

7

4 0.6 0.3 2000 7.62 97.8 16.7 0.914

5 0.8 0.2 2000 3.08 115. 39.8 0.935

                             

6 0.3 0.6 2000 9.88 116. 31.8 0.930

1

7 0.4 0.4 2000 6.53 122. 43.6 0.933

                             

8 0.6 0.3 2000 4.42 116. 38.0 0.932

2

^a Catalyst activity: 10 ⁶ gPE·mol ^-1 (Fe+Zr)·h ^-1 ·atm ^-

Claims (5)

1. a preparation method of linear low density polyethylene, directly synthesize linear low density polyethylene by ethylene under the catalytic system effect that ethylene oligomerization catalyst, copolymerization catalyst and co-catalyst form, main steps are: a) The reaction vessel is replaced with nitrogen and ethylene respectively, then ethylene is introduced, and dehydrated and deoxygenated toluene is added to half the volume of the reaction vessel, and the temperature of the vessel is 0-100°C; b) Add cocatalyst and oligomerization catalyst successively under stirring, oligomerize 0-30min; Cocatalyst is alkyl aluminoxane, and its addition is 500-5000: 1 according to Al/(Fe+Zr or Ti) molar ratio, The oligomerization catalyst is a homogeneous or supported α-bisimine pyridine iron complex, and the molar ratio of the amount added to the copolymerization catalyst in the following steps is 1:20-10:1; c) adding the copolymerization catalyst into the reaction vessel to polymerize for 0.5-1 hour; the copolymerization catalyst is a homogeneous or supported metallocene catalyst; d) adding 10% hydrochloric acid ethanol to the reactant volume to terminate the reaction, washing the polymer with ethanol, and vacuum drying to obtain the target product. 2. The method according to claim 1, characterized in that the temperature of the vessel in step a is 30-70°C. 3. The method of claim 1, wherein the cocatalyst is methylalumoxane, ethylalumoxane or isobutylalumoxane. 4. The method according to claim 1, characterized in that the amount of the co-catalyst added is 1000-3000:1 according to the molar ratio of Al/(Fe+Zr or Ti). 5. The method of claim 1, wherein the molar ratio of the oligomerization catalyst/copolymerization catalyst is 1:10-2:1.