Ethylene oligomerization catalysts and their use

Abstract

The application provides an ethylene oligomerization catalyst and application thereof, and comprises a binuclear chromium catalyst and a cocatalyst, wherein the structure of the binuclear chromium catalyst is as follows: n is 1-3. The binuclear chromium catalyst is used in selective tetramerization of ethylene, 1-octene can be generated with high selectivity, the catalyst has high catalytic activity, and production efficiency is high.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of olefin polymerization, and particularly relates to an ethylene oligomerization catalyst and application thereof. BACKGROUND

[0002] 1-octene is mainly used for producing high-end PE, POE, and used as a raw material for producing plasticizers, alcohol for detergents and lubricating oil additives, and is an important organic raw material and chemical intermediate. At present, ethylene selective oligomerization is one of the main methods for industrially preparing linear 1-octene.

[0003] Patent CN100548946C discloses a catalytic system of PNP ligand, chromium source and methylaluminoxane, and the catalytic system can realize selective tetramerization of ethylene and industrialized production of 1-octene. However, the selectivity of 1-octene in the product is only 70%, and the product generally contains about 20% of by-product hexene and 10% of other various olefins, the raw material utilization rate is low, and the production cost is high.

[0004] How to further improve the selectivity of 1-octene and reduce the production cost of 1-octene is the research focus in the field. SUMMARY

[0005] The present application aims to provide an ethylene oligomerization catalyst, which can efficiently make ethylene to occur tetramerization reaction with high selectivity by using a dinuclear chromium catalyst system, and the catalyst has high activity and good catalytic effect.

[0006] The present application also provides application of the catalyst in the field of ethylene oligomerization.

[0007] In order to achieve the above application purposes, the present application adopts the following technical solutions:

[0008] An ethylene oligomerization catalyst, comprising a dinuclear chromium catalyst and a cocatalyst, wherein the structure of the dinuclear chromium catalyst is:

[0009]

[0010] n is 1-3;

[0011] Preferably, the dinuclear chromium catalyst is prepared by reacting a diphosphine ligand with a chromium source.

[0012] Preferably, the structure of the diphosphine ligand is: n is 1-3.

[0013] Preferably, the chromium source is chromium chloride tetrahydrofuran or chromium chloride.

[0014] Preferably, the reaction is carried out in a solvent, and the solvent is selected from tetrahydrofuran and methyltetrahydrofuran.

[0015] The reaction route is shown below:

[0016]

[0017] Preferably, the molar ratio of the bisphosphine ligand to chromium in the chromium source is 1:1 to 1:1.1;

[0018] Preferably, the reaction temperature is 0–50°C and the reaction pressure is atmospheric pressure.

[0019] Preferably, the selected bisphosphine ligand is prepared by reacting difuranylphosphine chloride of Formula I with dibromoalkane of Formula II under the action of alkyllithium.

[0020] Where n is 1 to 3;

[0021] The reaction route is shown below:

[0022]

[0023] Preferably, the molar ratio of the dibromoalkane shown in Formula II to the difuranylphosphine chloride shown in Formula I is 0.5 to 0.6:1.

[0024] Preferably, the molar ratio of alkyllithium to difuranylphosphine chloride shown in Formula I is 1.05 to 1:1.

[0025] Preferably, the reaction temperature is -78℃ to room temperature, and the reaction pressure is atmospheric pressure.

[0026] Currently, the catalysts used for ethylene oligomerization are mononuclear catalysts, and their reaction mechanism is as follows: ① The catalytically active metal reacts with two molecules of ethylene to form a five-membered ring intermediate; ② The five-membered ring intermediate reacts with one molecule of ethylene to form a seven-membered ring intermediate; ③ The seven-membered ring intermediate continues to react with one molecule of ethylene to form a nine-membered ring intermediate; ④ The nine-membered ring intermediate undergoes an elimination reaction to form 1-octene. For example... Figure 1 As shown:

[0027] During this process, many side reactions occur, such as: ① the seven-membered ring intermediate undergoes an elimination reaction to form 1-hexene; ② the nine-membered ring intermediate continues to react with one molecule of ethylene, undergoing further elimination to form 1-decene, and may even continue to generate alkenes with twelve, fourteen, or even higher carbon numbers. The energy differences between these cyclic intermediates are not significant, making it difficult to avoid these side reactions.

[0028] The binuclear catalyst of this invention has the following reaction mechanism: ① Each metal forms a five-membered ring intermediate with two molecules of ethylene; ② The two five-membered rings connect with each other to form a macrocycle; ③ Elimination forms 1-octene. Through the combined action of the two active metal centers in the catalyst, the selectivity for 1-octene is improved. A schematic diagram of the reaction principle is shown below. Figure 2 As shown:

[0029] In this invention, by designing ligands with specific structures, the catalyst can easily form the desired binuclear structure; and the ligands contain multiple coordination sites, which, after coordination with chromium metal, interact with the co-catalyst, which also helps to improve the activity of the catalyst.

[0030] In this invention, the co-catalyst is an alkylaluminoxane or a modified alkylaluminoxane, selected from one or more of methylaluminoxane and modified methylaluminoxane.

[0031] In this invention, the molar ratio of Al to Cr in the co-catalyst is 100:1:-1000:1.

[0032] The present invention also provides the application of the catalyst in the selective oligomerization reaction of ethylene.

[0033] Furthermore, the polymerization can be carried out in a stainless steel reactor. Under an inert gas atmosphere, a dehydrating and deoxygenating reaction solvent and a co-catalyst are added, stirred, and after the temperature stabilizes, the binuclear chromium catalyst described in this invention is added. Hydrogen gas is introduced to 0.1-0.8 MPa, and then ethylene is continuously introduced to maintain the reactor pressure at 2-5 MPa. The reaction is carried out at 40-70°C for 10-30 minutes. Then, the ethylene inlet valve is closed, the temperature is lowered, the pressure is released, and the reactor is discharged to obtain the ethylene tetramer.

[0034] Before the selective oligomerization of ethylene, the reactor is heated to 110-130°C and evacuated, with nitrogen purging during the process. After the temperature is cooled to room temperature, the reaction solvent and co-catalyst are added.

[0035] In this invention, the initial concentration of the binuclear chromium catalyst in the reaction system is 0.1–0.11 mmol / L.

[0036] Furthermore, the oligomerization solvent is one or more of cyclopentane, methylcyclopentane, n-hexane, cyclohexane, methylcyclohexane, and n-heptane.

[0037] This invention provides a novel selective oligomerization catalyst for ethylene with a binuclear structure. This catalyst has a simple structure and a catalytic activity ≥10×10⁻⁶. 6 g product / (molCr·h), 1-octene selectivity can be greater than 85%, which is highly selective and has promising prospects for industrial application. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the current ethylene oligomerization mononuclear catalysis principle.

[0039] Figure 2 This is a schematic diagram illustrating the catalytic principle of the binuclear chromium catalyst of the present invention. Detailed Implementation

[0040] The method of the present application is further illustrated by the following specific examples, but the present application is not limited to the listed examples, and any other known modifications within the scope of the claims of the present application should also be included.

[0041] Gas chromatography (GC): Agilent WAX:1701.42249; carrier gas: high purity nitrogen; injection mode: automatic sampler; nitrogen flow: 64.5ml / min; vaporization chamber temperature: 280℃; split injection, split ratio: 1:40; injection volume: 0.2μl; column flow rate: 1.5ml / min; column temperature: first order temperature programming, initial temperature 50℃, hold for 2min, then increase to 200℃ at a rate of 10℃ / min, hold for 15min; detector temperature: 300℃; external standard method was used for quantitative analysis of 1-octene, 1-hexene and other oligomerization short-chain products.

[0042] Raw material sources:

[0043] PCl2(NEt2) (CAS 1069-08-5) Shanghai Jizisheng Chemical Technology Co., Ltd.

[0044] CrCl3(THF)3 (10170-68-0) Shanghai Jizisheng Chemical Technology Co., Ltd.

[0045] Catalyst preparation

[0046] Preparation of bis(2-furyl)chlorophosphine: under nitrogen protection, furan (0.5mol) was dissolved in 300mL of diethyl ether, and cooled to -78℃. Butyllithium solution (0.4mol) was slowly added dropwise, and the dropwise addition was completed in 2h. After the dropwise addition, the reaction was continued at room temperature for 2h. The obtained reaction solution was cooled to 0℃, and PCl2(NEt2) (0.2mol) was slowly added. After the addition was completed, the reaction was continued at 0℃ for 14h. HCl solution (0.44mol) was added to the reaction solution, and after the addition was completed, the reaction was continued for 3h. The reaction solution was filtered, and the filtrate was removed from the light fraction to obtain a red oil crude product. The crude product was distilled under reduced pressure to obtain a colorless oil product, with a yield of 51%. 1 H-NMR (400MHz, 25℃, CD2Cl2): δ = 7.80ppm (dd, 2H, 3 J HH = 2.0Hz, 4 J HH = 0.8Hz), 7.07-7.06 (m, 2H), 6.54-6.52 (m, 2H). 31 P{ 1 H}-NMR (162MHz, 25℃, CD2Cl2): δ = 17.84ppm (s).

[0047] Preparation of Ligand 1:

[0048]

[0049] Under nitrogen protection, bis(2-furyl)phosphine chloride (0.1 mol) was dissolved in 100 mL THF, and cooled to -78 °C. Butyllithium solution (0.11 mol) was added dropwise, and after the addition was completed, the reaction was carried out at -78 °C for 2 h. After the reaction was completed, 1,3-dibromopropane in tetrahydrofuran (0.06 mol) was added dropwise, and after the addition was completed, the reaction was carried out at room temperature for 2 h. After the reaction was completed, the solvent was removed to obtain a crude product. The crude product was extracted with dichloromethane, and the extract was concentrated and purified by crystallization to obtain Ligand 1 as a white solid with a yield of 85%. 1 H-NMR (400 MHz, 25 °C, CD2Cl2): δ = 7.75 ppm (dd, 4H, 3 J HH = 2.0 Hz, 4 J HH = 0.8 Hz), 7.06-7.02 (m, 4H), 6.54-6.52 (m, 4H), 1.42-1.39 (m, 6H). 31 P{ 1 H}-NMR (162 MHz, 25 °C, CD2Cl2): δ = 25.28 ppm (s).

[0050] Preparation of Ligand 2: According to the preparation method of Ligand 1, 1,3-dibromopropane was replaced by 1,4-dibromobutane to obtain Ligand 2 with a yield of 87%. 1 H-NMR (400 MHz, 25 °C, CD2Cl2): δ = 7.75 ppm (dd, 4H, 3 J HH = 2.0 Hz, 4 J HH = 0.8 Hz), 7.06-7.02 (m, 4H), 6.54-6.52 (m, 4H), 1.42-1.38 (m, 8H). 31 P{ 1 H}-NMR (162 MHz, 25 °C, CD2Cl2): δ = 25.15 ppm (s).

[0051] Preparation of Ligand 3: According to the preparation method of Ligand 1, 1,3-dibromopropane was replaced by 1,5-dibromopentane to obtain Ligand 3 with a yield of 88%. 1 H-NMR (400 MHz, 25 °C, CD2Cl2): δ = 7.75 ppm (dd, 4H, 3 J HH = 2.0 Hz, 4 JHH = 0.8 Hz), 7.06-7.02 (m, 4H), 6.54-6.52 (m, 4H), 1.42-1.38 (m, 8H), 1.29-1.28 (m, 2H). 31 P{ 1 H}-NMR (162 MHz, 25 °C, CD2Cl2): δ = 25.11 ppm (s).

[0052] Catalyst 1 preparation: under nitrogen protection, the chromium trichloride tetrahydrofuran complex (10 mmol) was added into THF, stirred and suspended, and cooled to 0 °C. The ligand 1 (10 mmol) THF solution was added dropwise, and after the dropwise addition was completed, the reaction was continued at 0 °C for 2 h. The temperature was restored to room temperature, and the reaction was continued for 2 h. The temperature was raised to 50 °C, and the reaction was continued for 2 h. After the reaction was completed, the reaction liquid was concentrated to obtain the crude catalyst product. The crude product was recrystallized in tetrahydrofuran / hexane to obtain the catalyst 1.

[0053] Catalyst 2 preparation: according to the preparation method of catalyst 1, the ligand 1 was replaced by ligand 2 to obtain catalyst 2.

[0054] Catalyst 3 preparation: according to the preparation method of catalyst 1, the ligand 1 was replaced by ligand 3 to obtain catalyst 3.

[0055] Example 1

[0056] A 2L reaction kettle was heated to 110-130 °C, vacuumized for 2-4 h, and replaced with nitrogen for three times during the period. After the temperature was cooled to room temperature, 1L of dehydrated and deoxygenated methylcyclohexane, a certain amount of modified methylaluminoxane, were added, stirred, and after the temperature was constant, a certain amount of catalyst 1 was added, hydrogen was introduced to 0.5 MPa, then ethylene was continuously introduced, the pressure of the reaction kettle was maintained at 5 MPaG, and the reaction was carried out at 40 °C for 20 min. Then, the ethylene inlet valve was closed, a low-temperature circulating water bath was used for rapid cooling, slow pressure relief, and the kettle was unloaded to obtain the ethylene oligomerization product. The addition amount of catalyst and modified methylaluminoxane is shown in Table 1.

[0057] Examples 2-9

[0058] According to Example 1, the oligomerization reaction was carried out under different conditions, and the reaction conditions are shown in Table 1.

[0059] Comparative Example 1

[0060] Without pre-preparing the catalyst, the bis(2-furyl)chlorophosphine and the chromium trichloride tetrahydrofuran complex were directly added into the oligomerization reaction.

[0061] A 2-L reactor was heated to 110-130°C, vacuumed for 2-4 h, and replaced with nitrogen three times during the process. When the temperature cooled to room temperature, dehydrated and deoxygenated methylcyclohexane, and a certain amount of modified methylaluminoxane were added. After the temperature was constant, a certain amount of ligand 1 and chromium trichloride tetrahydrofuran complex were added. Hydrogen was introduced to 0.5 MPa, and then ethylene was continuously introduced. The pressure in the reactor was maintained at 5 MPa, and the reaction was carried out at 40°C for 20 min. Then, the ethylene inlet valve was closed, and the reactor was rapidly cooled with a low-temperature circulating water bath, slowly depressurized, and discharged to obtain the ethylene oligomerization product. The amounts of ligand 1 and chromium trichloride tetrahydrofuran complex added are shown in Table 1.

[0062] Comparative Example 2

[0063] The ligand 4 has the structure The ligand 4 and the chromium trichloride tetrahydrofuran complex were directly added to the oligomerization reaction.

[0064] Ethylene oligomerization: Before the reaction, the reactor was heated to 110-130°C, vacuumed for 2-4 h, and replaced with nitrogen three times during the process. When the temperature cooled to room temperature, dehydrated and deoxygenated methylcyclohexane and a certain amount of modified methylaluminoxane were added. After the temperature was constant, a certain amount of ligand 4 and chromium trichloride tetrahydrofuran complex were added. Hydrogen was introduced to 0.5 MPa, and then ethylene was continuously introduced. The pressure in the reactor was maintained at 5 MPa, and the reaction was carried out at 40°C for 20 min. Then, the ethylene inlet valve was closed, and the reactor was rapidly cooled with a low-temperature circulating water bath, slowly depressurized, and discharged to obtain the ethylene oligomerization product. The amounts of ligand 4 and chromium trichloride tetrahydrofuran complex added are shown in Table 1.

[0065] The reaction results of the examples and comparative examples are shown in Table 2.

[0066] Table 1 Reaction conditions of examples 1-9 and comparative examples 1-2

[0067]

[0068] Table 2 Reaction results of examples 1-9 and comparative examples 1-3

[0069]

[0070]

[0071] 1-C6 represents 1-hexene, Other C6 represents an alkane / alkene having 6 carbon atoms other than 1-C6, 1-C8 represents 1-octene, C4+C10+ represents an alkane / alkene having 4 and 10 or more carbon atoms, and PE represents a polymer.

[0072] Any modification or equivalent replacement within the technical scheme of the present application without departing from the scope of the technical scheme of the present application shall be covered in the protection scope of the present application.

Claims

1. An ethylene oligomerization catalyst characterized in that, The catalyst comprises a binuclear chromium catalyst and a cocatalyst, the structure of the binuclear chromium catalyst is n is 1-3.

2. The catalyst according to claim 1, characterized in that, The binuclear chromium catalyst is prepared by reacting a biphosphine ligand with a chromium source. The structure of the bisphosphine ligand is: n is 1 to 3.

3. The catalyst of claim 2, wherein The chromium source is chromium chloride tetrahydrofuran or chromium chloride.

4. The catalyst of claim 2, wherein The reaction is carried out in a solvent selected from one or both of tetrahydrofuran and methyl tetrahydrofuran.

5. The catalyst of claim 2, wherein The biphosphine ligand is prepared by reacting a difuryl chlorophosphine shown in formula I with a dibromoalkane shown in formula II under the action of an alkyl lithium. The difuryl chlorophosphine shown in formula I has the structural formula The dibromoalkane shown in formula II has the structural formula n is 1 to 3.

6. The catalyst of claim 5, wherein The molar ratio of the dibromoalkane shown in formula II to the difuryl chlorophosphine shown in formula I is 0.5-0.6:1, and the molar ratio of the alkyl lithium to the difuryl chlorophosphine shown in formula I is 1.05-1:

1.

7. The catalyst of claim 2, wherein The molar ratio of the biphosphine ligand to the chromium in the chromium source is 1:1-1:1.

1.

8. The catalyst of claim 2, wherein The reaction temperature when the biphosphine ligand reacts with the chromium source is 0-50℃, and the reaction pressure is normal pressure.

9. The catalyst of claim 1, wherein The cocatalyst is an alkyl aluminoxane or a modified alkyl aluminoxane.

10. The catalyst of claim 9, wherein The cocatalyst is one or more selected from methyl aluminoxane and modified methyl aluminoxane.

11. The catalyst of claim 1, wherein The molar ratio of Al to Cr in the cocatalyst is 100:1-1000:

1.

12. Use of the catalyst of any one of claims 1-11 in an ethylene selective oligomerization reaction.

13. Use according to claim 12, characterized in that, The preparation method of the ethylene selective oligomerization reaction is: adding a dehydrated and deoxygenated reaction solvent and a cocatalyst under an inert gas atmosphere, stirring, and after the temperature is constant, adding the binuclear chromium catalyst of any one of claims 1-10, passing in hydrogen to 0.1-0.8 MPa, then continuously passing in ethylene, maintaining the pressure of the reaction kettle at 2-5 MPa, and reacting at 40-70℃ for 10 min-30 min.

14. The use according to claim 12, characterized in that, The initial concentration of the binuclear chromium catalyst in the reaction system is 0.1-0.11 mmol / L.

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