A process for the preparation of 1-hexene by ethylene oligomerization

Abstract

The application relates to a method for preparing 1-hexene through ethylene oligomerization, wherein ethylene is subjected to oligomerization with a catalyst and a cocatalyst in a solvent under a set reaction temperature and a reaction pressure, the reaction is terminated after the reaction is completed, and 1-hexene is obtained; the catalyst is an isoquinoline diimine type catalyst, and a structural formula is shown as formula C. The method for preparing 1-hexene through ethylene oligomerization can prepare 1-hexene with high catalytic activity and high selectivity, and can effectively inhibit the formation of high-carbon-number oligomerization products and polymers.

Description

Technical Field

[0001] This invention relates to the field of α-olefin preparation technology, and specifically to a method for preparing 1-hexene by ethylene oligomerization. Background Technology

[0002] Linear α-olefins are straight-chain olefins with terminal double bonds, widely used as comonomers for polyethylene and as raw materials for the synthesis of fine chemicals such as high-grade lubricants and surfactants, with continuously growing market demand. Ethylene oligomerization is the main technical route for producing linear α-olefins. Homogeneous nickel catalytic systems, represented by Shell's SHOP process, offer advantages such as mild operating conditions, but catalyst-product separation is cumbersome, requiring reduction and water washing to remove catalyst residues, increasing costs and affecting product purity. To address the separation challenges of homogeneous catalysis, researchers have explored heterogeneous methods, such as loading active nickel components onto silica gel, alumina, or polymer supports. However, these methods generally suffer from low α-olefin selectivity and loss of active components due to support swelling. While molecular sieve-supported heterogeneous catalysts (CN117181311A) and catalysts with special N-coordination structures (CN121314694A) have made progress in separation in recent years, they still cannot fundamentally solve the problem of low selectivity for the target product.

[0003] The current process suffers from unsatisfactory overall selectivity for C6-C8 linear α-olefins, particularly lacking flexibility in selectively controlling products such as C6 1-hexene. Oligomerization easily generates isomerization byproducts like methylcyclopentane and methylenecyclopentane, as well as high-carbon-number oligomers and polymers, leading to low overall selectivity and atom economy for linear α-olefins. Existing improvements primarily focus on support replacement or ligand substituent modification, lacking sufficient understanding of the steric confinement effect of the catalyst framework itself and its influence on the competition between chain growth and β-hydrogen elimination. This makes it difficult to effectively suppress high-carbon-number products and polymers while maintaining high activity and high selectivity for 1-hexene. Therefore, developing a process that leverages the steric confinement effect of the catalyst framework to selectively prepare 1-hexene while reducing the formation of high-carbon-number products and polymers is a crucial technological direction that urgently needs breakthrough. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing 1-hexene by ethylene oligomerization in order to solve the above-mentioned problems.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing 1-hexene by ethylene oligomerization involves carrying out an oligomerization reaction of ethylene with a catalyst and a co-catalyst in a solvent at a set reaction temperature and pressure, and terminating the reaction after the reaction is completed to obtain 1-hexene.

[0007] The catalyst is an isoquinoline diimine type catalyst, and its structural formula is shown in Formula C:

[0008]

[0009] Formula C

[0010] In formula C, R1~R 10 Each group is independently selected from H, C1~C3 alkyl, C1~C3 alkoxy, halogen, and nitro.

[0011] As a preferred technical solution, in formula C, R1~R 10 All are H;

[0012] Alternatively, at least one of R3, R4, R8, and R9 is selected from halogens, and the rest are H;

[0013] Or, R2, R5, R7, R 10 At least one of them is selected from C1-C3 alkyl, and the rest are H;

[0014] Or, R3, R4, R7, R8, R9, R 10 At least one of them is selected from C1~C3 alkoxy groups, and the rest are H.

[0015] In a preferred embodiment, the catalyst is selected from any one of the compounds represented by formula C1 to C4:

[0016]

[0017] Formula C1

[0018]

[0019] Formula C2

[0020]

[0021] Formula C3

[0022]

[0023] Formula C4.

[0024] Furthermore, the catalyst is a coordination compound formed by coordinating an isoquinoline diimine-type ligand of formula L with an iron-containing compound:

[0025]

[0026] Formula L

[0027] In formula L, R1~R 10 Each group is independently selected from H, C1~C3 alkyl, C1~C3 alkoxy, halogen, and nitro.

[0028] In a preferred embodiment, the isoquinoline diimine ligand is selected from any one of the compounds shown in formulas L1 to L4:

[0029]

[0030] Formula L1

[0031]

[0032] Formula L2

[0033]

[0034] Formula L3

[0035]

[0036] Formula L4.

[0037] The above-described method for preparing isoquinoline diimine ligands involves reacting a diacetyl isoquinoline derivative with the general structure shown in Formula I with a diamino isoquinoline derivative with the general structure shown in Formula II. The specific reaction formula is as follows:

[0038] .

[0039] As a preferred technical solution, the diacetylisoquinoline derivative is selected from one of 1,3-diacetylisoquinoline, 5-methyl-2,6-diacetylisoquinoline, and 7-methoxy-1,3-diacetylisoquinoline; the diaminoisoquinoline derivative is selected from one of 1,3-diaminoisoquinoline and 6-bromo-1,3-diaminoisoquinoline.

[0040] As a preferred technical solution, the following steps are included: condensing diacetylisoquinoline derivative and diaminoisoquinoline derivative in an organic solvent in the presence of an acidic catalyst, and then performing post-treatment after the reaction to obtain the isoquinoline diimine ligand.

[0041] As a preferred technical solution, the molar ratio of the diacetylisoquinoline derivative to the diaminoisoquinoline derivative is 1:1~5;

[0042] The acidic catalyst is selected from at least one of p-toluenesulfonic acid, methanesulfonic acid, benzenesulfonic acid, sulfuric acid, phosphoric acid, trifluoroacetic acid, and trifluoromethanesulfonic acid;

[0043] The organic solvent is selected from at least one of toluene, xylene, benzene, and chlorobenzene;

[0044] The condensation reaction is carried out under reflux conditions, with a reaction temperature of 100~130℃ and a reaction time of 8~24 hours. During the reaction, the water generated in the reaction is removed by a water separator.

[0045] The post-processing includes the following steps: concentrating the reaction solution, recrystallizing, filtering, washing, and drying.

[0046] In a preferred embodiment, recrystallization is carried out using an organic solvent selected from one or more of dichloromethane, chloroform, ethyl acetate, methanol, and ethanol; the washing solvent is selected from one or more of n-hexane, cyclohexane, and petroleum ether.

[0047] For example, in a preferred embodiment, the preparation method of the isoquinoline diimine ligand is as follows: diacetyl isoquinoline derivative and diamino isoquinoline derivative are added to a reaction vessel, followed by the addition of toluene and p-toluenesulfonic acid. The reaction is carried out at reflux temperature, and water generated during the reaction is removed using a water separator until no more water droplets are precipitated in the water separator. After the reaction is completed, the mixture is recrystallized with dichloromethane, washed with n-hexane, and dried under vacuum to obtain the isoquinoline diimine ligand. The molar ratio of diacetyl isoquinoline derivative to diamino isoquinoline derivative is 1:2.5, the amount of p-toluenesulfonic acid is 5 μmol, the reaction temperature is 100-120 °C, and the reaction time is 8-16 h.

[0048] Preferably, the preparation method of the isoquinoline diimine catalyst is as follows: the isoquinoline diimine ligand is mixed with an iron-containing compound in an anhydrous organic solvent, and a coordination reaction is carried out under the protection of an inert gas. After the reaction is completed, the reaction liquid is separated into solid and liquid components, the solid components are collected, washed and dried to obtain the isoquinoline diimine catalyst.

[0049] Preferably, the molar ratio of the isoquinoline diimine ligand to the iron-containing compound is 1:1~2;

[0050] The iron-containing compound is selected from one or more of ferrous chloride, ferrous bromide, ferrous iodide, ferrous sulfate, ferrous acetate, and ferrous acetylacetone.

[0051] The anhydrous organic solvent is an anhydrous ether solvent, selected from one or more of tetrahydrofuran, diethyl ether, 1,4-dioxane, and ethylene glycol dimethyl ether;

[0052] The inert gas is nitrogen or argon;

[0053] During the coordination reaction, the reaction temperature is 20~40℃ and the reaction time is 6~24 hours;

[0054] Washing includes washing with anhydrous cold tetrahydrofuran and washing with anhydrous diethyl ether;

[0055] The drying process is vacuum drying, and the drying time is 3 to 6 hours.

[0056] In a preferred embodiment, the preparation method of the isoquinoline diimine catalyst includes the following steps: adding the isoquinoline diimine ligand and anhydrous ferrous chloride to anhydrous tetrahydrofuran at a molar ratio of 1:1.2, stirring and reacting under nitrogen protection for 12 hours, filtering after the reaction, washing the obtained solid repeatedly with anhydrous cold tetrahydrofuran and anhydrous diethyl ether, and finally drying under vacuum to obtain the isoquinoline diimine catalyst.

[0057] As a preferred embodiment of the present invention, the co-catalyst is an alkylaluminoxane, including methylaluminoxane (MAO), modified methylaluminoxane (MMAO), ethylaluminoxane (EAO), and isobutylaluminoxane (IBAO), and the molar ratio of the co-catalyst to the isoquinoline diimide catalyst is 50~500:1.

[0058] As a preferred embodiment of the present invention, the solvent is a hydrocarbon solvent, including C5~C64 solvents. 10 Alkanes, cycloalkanes, and aromatic hydrocarbons.

[0059] As a preferred embodiment of the present invention, the concentration of the catalyst in the solvent, calculated as metal, is 0.01~0.1 mmol / mL.

[0060] As a preferred embodiment of the present invention, the reaction temperature is 40~120℃ and the reaction pressure is 1~10 MPa. More preferably, the reaction temperature is 40~60℃ and the reaction pressure is 1~4 MPa.

[0061] As a preferred technical solution of the present invention, the reaction is terminated with a terminator after the reaction is completed, wherein the terminator includes acidified ethanol with a mass fraction of 5-20%.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] This invention provides a method for the selective oligomerization of ethylene to prepare 1-hexene, which can produce 1-hexene with high catalytic activity and selectivity, and effectively inhibit the formation of high-carbon-number oligomers and polymers. The isoquinoline diimine catalyst used in this invention has a unique ten-membered ring chelate structure. This rigid framework has a significant steric constraint effect on the ethylene chain growth process, which is beneficial for competition in the β-hydrogen elimination reaction, thereby generating hexene with high selectivity and inhibiting the formation of high-carbon-number oligomers and polymers. Simultaneously, the substituent groups on the isoquinoline core can synergistically regulate the electron cloud state of the metal active center through electronic effects and steric hindrance, achieving effective regulation of catalytic activity and product distribution. Detailed Implementation

[0064] The following description is provided to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples and are not intended to limit the scope of the invention; other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0065] Unless otherwise specified, the instruments or reagents used in the embodiments of this invention are all conventional commercial instruments or reagents, and the purity specifications used are analytical grade or chemically pure.

[0066] The main reagent information in the examples is as follows:

[0067] 1,3-Dichloroisoquinoline (CAS: 7742-73-6 Sigma-Aldrich)

[0068] Triphenylphosphine (CAS: 603-35-0 Sigma-Aldrich)

[0069] Diphenylphosphine palladium dichloride (CAS: 13965-03-2 Sigma-Aldrich)

[0070] Triethylamine (CAS: 121-44-8, Guoyao Reagent)

[0071] Vinyl ethyl ether (CAS: 109-92-2 Sigma-Aldrich)

[0072] 6-Bromo-1,3-Dichloroisoquinoline (CAS: 552331-05-2, Anaiji Chemical)

[0073] 7-Methoxy-1,3-Dichloro-isoquinoline (CAS: 24623-40-3, Leyan Reagent)

[0074] 1,3-Diaminoisoquinoline (CAS: 1955-65-3, Debye Technology)

[0075] 6-Bromo-1,3-Diaminoisoquinoline (CAS: 2097504-84-0, Leyan Reagent)

[0076] 1,3-Dichloro-5-methylisoquinoline (CAS: 21902-40-9, Anaiji Chemical)

[0077] 2,6-Diacetylpyridine (CAS: 1129-30-2 Sigma-Aldrich)

[0078] Ferric chloride (CAS: 7705-08-0, Guoyao Reagent)

[0079] Toluene (CAS: 108-88-3 Sigma-Aldrich)

[0080] Dichloromethane (CAS: 75-09-2 Sigma-Aldrich)

[0081] Tetrahydrofuran (CAS: 109-99-9 Sigma-Aldrich)

[0082] 1,4-Dioxane (CAS: 123-91-1, China National Pharmaceutical Reagent)

[0083] Ethyl acetate (CAS: 141-78-6, Guoyao Reagent)

[0084] Sodium chloride (CAS: 7647-14-5, Guoyao Reagent)

[0085] Anhydrous sodium sulfate (CAS: 7757-82-6, Guoyao Reagent)

[0086] Unless otherwise specified, all reagents involved must be anhydrous.

[0087] Preliminary Example 1

[0088] The synthesis route for ligand L1 is as follows:

[0089]

[0090]

[0091] 1,3-Dichloroisoquinoline (1 mmol, 198 mg), triphenylphosphine (6 mol%, 15.7 mg), and palladium dichloride catalyst (5 mol%, 35 mg) were added to a three-necked flask and purged with nitrogen. Then, 1,4-dioxane (50 ml) was added using a syringe to dissolve the flask, followed by the addition of triethylamine (4 mmol, 404 mg) and vinyl ethyl ether (3.5 mmol, 350 mg). The mixture was heated and stirred until completely dissolved, and then reacted at 110 °C for 16 hours.

[0092] After the reaction was complete, the mixture was cooled to room temperature. A 2 mol / L HCl solution was slowly added dropwise under nitrogen protection. The solution was then heated to 50°C and hydrolysis continued for 2 hours. After hydrolysis, the mixture was diluted with a large amount of water and extracted with ethyl acetate. The organic phase was washed twice with saturated sodium chloride and dried over anhydrous sodium sulfate for 30 min. Finally, the solvent was evaporated by rotary evaporation, and the mixture was purified by column chromatography (EA:HEX = 1:5) to give 1,3-diacetylisoquinoline in 80% yield. 1 H-NMR CDCl3 400MHz δ=8.85-7.71,s,5-Ar-H; δ=2.11,s,6-CH3).

[0093] 1,3-Diacetylisoquinoline (1 mmol, 213.1 mg) and 1,3-diaminoisoquinoline (2.5 mmol, 397.5 mg) were added to a three-necked flask, followed by 50 mL of toluene and p-toluenesulfonic acid (5 μmol, 700 μL). The mixture was refluxed at 110 °C for 12 h, with water separation performed under reflux until no more water droplets precipitated. After the reaction, the mixture was recrystallized from dichloromethane, washed with n-hexane, and dried under vacuum to obtain ligand L1 in 90% yield. 1 H-NMR CDCl3 400MHz δ=7.99-7.50,s,10-Ar-H; δ=2.86,s,6-CH3).

[0094] Catalyst C1 Synthesis Route:

[0095]

[0096] Ligand L1 (1 mmol, 336.1 mg) and anhydrous FeCl2 (1.2 mmol, 194.4 mg) were added to 25 mL of anhydrous tetrahydrofuran and stirred under nitrogen for 12 hours. After the reaction was completed, the mixture was filtered. The solid was washed twice with anhydrous cold tetrahydrofuran, then three times with anhydrous diethyl ether, and finally dried under vacuum for 4 hours. The yield was 85%.

[0097] Preliminary Example 2

[0098] The synthesis route for ligand L2 is as follows:

[0099]

[0100] 1,3-Diacetylisoquinoline (1 mmol, 213.1 mg) and 6-bromo-1,3-diaminoisoquinoline (2.5 mmol, 592.3 mg) were added to a three-necked flask, followed by 50 mL of toluene and p-toluenesulfonic acid (5 μmol, 700 μL). The mixture was refluxed at 120 °C for 15 hours, with water separation performed under reflux until no more water droplets were precipitated. After the reaction, the mixture was recrystallized from dichloromethane, washed with n-hexane, and dried under vacuum to obtain ligand L2 in a yield of 46%. 1 H-NMR CDCl3 400MHz δ=7.85-7.52,s,9-Ar-H; δ=2.82,s,6-CH3).

[0101] C2 synthesis route for catalysts:

[0102]

[0103] Ligand L2 (1 mmol, 416.1 mg) and anhydrous FeCl2 (1.2 mmol, 194.4 mg) were added to 25 mL of anhydrous tetrahydrofuran and stirred under nitrogen for 12 hours. After the reaction was completed, the mixture was filtered. The solid was washed twice with anhydrous cold tetrahydrofuran, then three times with anhydrous diethyl ether, and finally dried under vacuum for 4 hours. The yield was 61%.

[0104] Preliminary Example 3

[0105] The synthesis route for ligand L3 is as follows:

[0106]

[0107]

[0108] 1,3-Dichloro-5-methylisoquinoline (1 mmol, 211.0 mg), triphenylphosphine (6 mol%, 15.7 mg), and palladium dichloride catalyst (5 mol%, 35 mg) were added to a three-necked flask and purged with nitrogen. Then, 1,4-dioxane (50 mL) was added using a syringe to dissolve the flask, followed by the addition of triethylamine (4 mmol, 404 mg) and vinyl ethyl ether (3.5 mmol, 350 mg). The mixture was heated and stirred until completely dissolved, and then reacted at 110 °C for 15 hours.

[0109] After the reaction was complete, the mixture was cooled to room temperature. Under nitrogen protection, 2M HCl solution was slowly added dropwise. The solution was then heated to 50°C and hydrolysis continued for 2 hours. After hydrolysis, the mixture was diluted with a large amount of water and extracted with ethyl acetate. The organic phase was washed twice with saturated sodium chloride and dried over anhydrous sodium sulfate for 30 min. Finally, the solvent was evaporated by rotary evaporation, and the mixture was purified by column chromatography (EA:HEX = 1:5) to give 5-methyl-2,6-diacetylisoquinoline in 83% yield. 1 H-NMR CDCl3 400MHz δ=8.72-7.47,s,4-Ar-H; δ=2.23,s,3-CH3; δ=2.15,s,3-CH3).

[0110] 5-Methyl-2,6-diacetylisoquinoline (1 mmol, 227.1 mg) and 1,3-diaminoisoquinoline (2.5 mmol, 397.5 mg) were added to a three-necked flask. Then, 50 mL of toluene and p-toluenesulfonic acid (5 μmol, 700 μL) were added. The mixture was refluxed at 110 °C for 12 hours, with water separation performed under reflux until no more water droplets precipitated. After the reaction, the mixture was recrystallized from dichloromethane, washed with n-hexane, and dried under vacuum to obtain ligand L3 in 74% yield. 1H-NMR CDCl3 400MHz δ=7.99-7.51,s,10-Ar-H; δ=2.87,s,6-CH3).

[0111] C3 synthesis route using catalysts:

[0112]

[0113] Ligand L3 (1 mmol, 336.1 mg) and anhydrous FeCl2 (1.2 mmol, 194.4 mg) were added to 25 mL of anhydrous tetrahydrofuran and stirred under nitrogen for 12 hours. After the reaction was completed, the mixture was filtered, washed twice with anhydrous cold tetrahydrofuran, then three times with anhydrous diethyl ether, and finally dried under vacuum for 4 hours, with a yield of 86%.

[0114] Preliminary Example 4

[0115] The synthesis route for ligand L4 is as follows:

[0116]

[0117]

[0118] 7-Methoxy-1,3-dichloroisoquinoline (1 mmol, 226.9 mg), triphenylphosphine (6 mol%, 15.7 mg), and palladium dichloride catalyst (5 mol%, 35 mg) were added to a three-necked flask and purged with nitrogen. Then, 1,4-dioxane (50 mL) was added using a syringe to dissolve the flask, followed by the addition of triethylamine (4 mmol, 404 mg) and vinyl ethyl ether (3.5 mmol, 350 mg). The mixture was heated and stirred until completely dissolved, and then reacted at 110 °C for 12 hours.

[0119] After the reaction was complete, the mixture was cooled to room temperature. Under nitrogen protection, 2M HCl solution was slowly added dropwise. The solution was then heated to 50°C and hydrolysis continued for 2 hours. After hydrolysis, the mixture was diluted with a large amount of water and extracted with ethyl acetate. The organic phase was washed twice with saturated sodium chloride and dried over anhydrous sodium sulfate for 30 min. Finally, the solvent was evaporated by rotary evaporation, and the mixture was purified by column chromatography (EA:HEX = 1:5) to give 7-methoxy-1,3-diacetylisoquinoline in 76% yield. 1 H-NMR CDCl3 400MHz δ=7.98-7.54,s,4 -Ar-H; δ=3.83,s,3 -OCH3; δ=2.17,s,6 -CH3).

[0120] 7-Methoxy-1,3-diacetylisoquinoline (1 mmol, 243.1 mg) and 1,3-diaminoisoquinoline (2.5 mmol, 397.5 mg) were added to a three-necked flask. Then, 50 mL of toluene and p-toluenesulfonic acid (5 μmol, 700 μL) were added. The mixture was refluxed at 110 °C for 12 hours, with water separation performed under reflux until no more water droplets precipitated. After the reaction, the mixture was recrystallized from dichloromethane, washed with n-hexane, and dried under vacuum to give ligand L4 in 77% yield. 1 H-NMR CDCl3 400MHz δ=7.98-7.34,s,9 -Ar-H; δ=3.75,s,3 -OCH3; δ=2.84,s,6 -CH3).

[0121] C4 catalyst synthesis route:

[0122]

[0123] Ligand L4 (1 mmol, 366.1 mg) and anhydrous FeCl2 (1.2 mmol, 194.4 mg) were added to 25 mL of anhydrous tetrahydrofuran and stirred under nitrogen for 12 hours. After the reaction was completed, the mixture was filtered, washed twice with anhydrous cold tetrahydrofuran, then three times with anhydrous diethyl ether, and finally dried under vacuum for 4 hours, with a yield of 75%.

[0124] Example 1

[0125] Ethylene oligomerization was carried out in a 500 mL high-pressure reactor. The reactor was heated to 120 °C and evacuated for 3 hours. After several nitrogen purgings, ethylene was introduced and the reactor temperature was lowered to the reaction temperature. Then, 200 mL of dehydrated toluene was added, along with 10 mmol of catalyst C1 (based on metal content) and 1 mol of methylaluminoxane (based on Al molar ratio) as co-catalysts. The oligomerization reaction was carried out at 55 °C and 2 MPa. After 60 min of reaction, the temperature was lowered and the pressure was released. The reaction was terminated with 10% acidified ethanol.

[0126] Example 2

[0127] Ethylene oligomerization was carried out in a 500 mL high-pressure reactor. The reactor was heated to 120 °C and evacuated for 3 hours. After several nitrogen purgings, ethylene was introduced and the reactor temperature was lowered to the reaction temperature. Then, 200 mL of dehydrated toluene, 10 mmol of catalyst C2 (based on metal content) and 1 mol of methylaluminoxane (based on Al molar ratio) were added as co-catalysts. The oligomerization reaction was carried out at 50 °C and 2.5 MPa. After 60 min of reaction, the temperature was lowered and the pressure was released. The reaction was terminated with 10% acidified ethanol.

[0128] Example 3

[0129] Ethylene oligomerization was carried out in a 500 mL high-pressure reactor. The reactor was heated to 120 °C and evacuated for 3 hours. After several nitrogen purgings, ethylene was introduced and the reactor temperature was lowered to the reaction temperature. Then, 200 mL of dehydrated toluene was added, along with 10 mmol of catalyst C3 (based on metal content) and 1 mol of methylaluminoxane (based on Al molar ratio) as co-catalysts. The oligomerization reaction was carried out at 50 °C and 2 MPa. After 60 min of reaction, the temperature was lowered and the pressure was released. The reaction was terminated with 10% acidified ethanol.

[0130] Example 4

[0131] Ethylene oligomerization was carried out in a 500 mL high-pressure reactor. The reactor was heated to 120 °C and evacuated for 3 hours. After several nitrogen purgings, ethylene was introduced and the reactor temperature was lowered to the reaction temperature. Dehydrated toluene (200 mL) was added, along with 10 mmol of catalyst C4 (based on metal content) and 1 mol of methylaluminoxane (based on Al molar ratio) as co-catalysts. The oligomerization reaction was carried out at 60 °C and 2.5 MPa. After 60 min of reaction, the temperature was lowered and the pressure was released. The reaction was terminated with 10% acidified ethanol.

[0132] Comparative Example 1

[0133]

[0134] Synthesis of ligand L1': 2,6-Diacetylpyridine (1 mmol, 163.2 mg) and aniline (2.5 mmol, 232.8 mg) were added to a three-necked flask, followed by the addition of 50 mL of toluene and p-toluenesulfonic acid (5 μmol, 700 μL). The mixture was refluxed at 100 °C for 12 hours to remove water. After the reaction was complete, the mixture was recrystallized from dichloromethane, washed with n-hexane, and dried under vacuum to obtain ligand L1'.

[0135]

[0136] Synthesis of catalyst C1': Ligand L1' (1 mmol, 313.6 mg) and anhydrous FeCl2 (1.2 mmol, 152.1 mg) were added to 25 mL of anhydrous tetrahydrofuran and stirred for 12 hours under nitrogen protection. After the reaction was completed, the mixture was filtered, washed twice with anhydrous cold tetrahydrofuran and three times with anhydrous diethyl ether, and dried under vacuum for 4 hours to obtain catalyst C1'.

[0137] Ethylene oligomerization catalytic activity test: The test was conducted under the following conditions: a 500 mL high-pressure reactor was used, 200 mL of dehydrated toluene was added, the catalyst dosage was 10 mmol (based on metal), 2 mol of methylaluminoxane (based on Al), the reaction temperature was 40 °C, the ethylene pressure was 2.0 MPa, the reaction time was 60 min, and the reaction was terminated with 10% acidified ethanol.

[0138] Comparative Example 2

[0139] A catalyst with the same structure as ligand L1, but with the metal center replaced by CoCl2.

[0140] Synthesis of catalyst C2': Ligand L1 (1 mmol, 336.1 mg) and anhydrous CoCl2 (1.2 mmol, 155.8 mg) were added to 25 mL of anhydrous tetrahydrofuran and stirred for 12 hours under nitrogen protection. After the reaction was completed, the mixture was filtered, washed twice with anhydrous cold tetrahydrofuran and three times with anhydrous diethyl ether, and dried under vacuum for 4 hours to obtain catalyst C2'.

[0141] Ethylene oligomerization catalytic activity test: 200 mL of dehydrated toluene, 10 mmol of catalyst (based on metal content), and 2 mol of methylaluminoxane (based on Al content) were added to a 500 mL high-pressure reactor. The reaction temperature was 55 °C, the ethylene pressure was 2.0 MPa, the reaction time was 60 min, and the reaction was terminated with 10% acidified ethanol.

[0142] [Performance Testing]

[0143] The obtained products were tested and analyzed:

[0144] 1. Catalyst activity test: Calculated based on product yield, the formula is: Catalyst activity = m / (nM × t), unit is g·mol⁻¹ -1 ·h -1 , where m is the total mass of the oligomer (g), nM is the amount of substance of the metal active center (mol), and t is the reaction time (h).

[0145] 2. Product component analysis: Gas chromatography was used to characterize the selectivity of the main products.

[0146] For detailed results, please refer to Table 1.

[0147] Table 1

[0148]

[0149] As shown in Table 1, the method for preparing 1-hexene by ethylene oligomerization provided in the embodiments of the present invention has high catalyst activity, high C6 selectivity (above 90%), low polymer by-product content (below 2.5%), and high 1-hexene selectivity, especially Example 4, which has the best overall performance. Comparative Example 1 (using pyridinediimide ligand) and Comparative Example 2 (using Co as the metal center) show significantly reduced C6 selectivity and catalytic activity, and significantly increased polymer by-product content.

[0150] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing 1-hexene by ethylene oligomerization, characterized in that, At a set reaction temperature and pressure, ethylene was subjected to oligomerization with a catalyst and a co-catalyst in a solvent. The reaction was terminated after the reaction was completed to obtain 1-hexene. The catalyst is an isoquinoline diimine type catalyst, and its structural formula is shown in Formula C: Formula C In formula C, R1~R 10 Each group is independently selected from H, C1~C3 alkyl, C1~C3 alkoxy, halogen, and nitro.

2. The method for preparing 1-hexene by ethylene oligomerization according to claim 1, characterized in that, In formula C, R1~R 10 All are H; Alternatively, at least one of R3, R4, R8, and R9 is selected from halogens, and the rest are H; Or, R2, R5, R7, R 10 At least one of them is selected from C1-C3 alkyl, and the rest are H; Or, R3, R4, R7, R8, R9, R 10 At least one of them is selected from C1~C3 alkoxy groups, and the rest are H.

3. The method for preparing 1-hexene by ethylene oligomerization according to claim 1, characterized in that, The catalyst is selected from any one of the compounds represented by formula C1 to C4: Formula C1 Formula C2 Formula C3 Formula C4.

4. The method for preparing 1-hexene by ethylene oligomerization according to claim 1, characterized in that, The catalyst is a coordination compound formed by coordinating an isoquinoline diimine ligand of formula L with an iron-containing compound: Formula L In formula L, R1~R 10 Each group is independently selected from H, C1~C3 alkyl, C1~C3 alkoxy, halogen, and nitro.

5. The method for preparing 1-hexene by ethylene oligomerization according to claim 1, characterized in that, The cocatalyst is an alkylaluminoxane, including methylaluminoxane, modified methylaluminoxane, ethylaluminoxane, and isobutylaluminoxane. The molar ratio of the cocatalyst to the isoquinoline diimide catalyst is 50~500:

1.

6. The method for preparing 1-hexene by ethylene oligomerization according to claim 1, characterized in that, The solvent is a hydrocarbon solvent, including C5~C64. 10 Alkanes, cycloalkanes, and aromatic hydrocarbons.

7. The method for preparing 1-hexene by ethylene oligomerization according to claim 1, characterized in that, The concentration of the catalyst in the solvent, calculated as metal, is 0.01~0.1 mmol / mL.

8. The method for preparing 1-hexene by ethylene oligomerization according to claim 1, characterized in that, The reaction temperature is 40~120 ℃ and the reaction pressure is 1~10 MPa.

9. The method for preparing 1-hexene by ethylene oligomerization according to claim 8, characterized in that, The reaction temperature is 40~60 ℃ and the reaction pressure is 1~4 MPa.

10. The method for preparing 1-hexene by ethylene oligomerization according to claim 1, characterized in that, The reaction is terminated with a terminator, which includes acidified ethanol with a mass fraction of 5-20%.

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