Catalytic system for ethylene selective oligomerization and preparation method and application thereof

Abstract

The invention belongs to the technical field of ethylene oligomerization catalysis, and discloses a catalytic system for ethylene selective oligomerization and a preparation method and application thereof, and the catalytic system comprises a carbon bridge bidentate phosphine chromium catalyst, an organic boron auxiliary agent and an aluminum-containing activator in a molar ratio of 1: (1-50): (100-1500). The carbon-chromium catalyst is prepared by the following steps: reacting CrCl3 (THF) 3, a ligand and CH2Cl2 under stirring, filtering, and carrying out post-treatment to obtain the catalyst, the catalyst and the aluminum-containing activating agent are uniformly mixed, and then the organic boron auxiliary agent is added and stirred. The catalyst system constructed by the carbon bridge bidentate phosphine chromium catalyst, the organic boron auxiliary agent and the aluminum-containing activating agent realizes ethylene selective oligomerization. The catalytic system can realize high-efficiency and high-selectivity preparation of 1-hexene and 1-octene under the condition that aluminoxane co-catalysts such as MAO and MMAO are not adopted, the catalytic activity is high, the reaction initiation is rapid, the operation is stable, and the repeatability is good.

Description

Technical Field

[0001] The invention belongs to the technical field of ethylene oligomerization catalysis, and in particular relates to a catalytic system for ethylene selective oligomerization and a preparation method and application thereof. Background Art

[0002] Linear alpha olefin (LAO), that is, a straight-chain monoolefin with a double bond at the end of the molecular chain, generally refers to C4~C40 in industry. Among them, C4 (1-butene), C6 (1-hexene) and C8 (1-octene) are key monomer raw materials for the preparation of copolymer polyethylene, occupying the main application market of linear alpha olefins. The addition of comonomers can change the polymer chain structure and obtain differentiated copolymer polyethylene products, which is an important way to develop high-end polyethylene grades.

[0003] Non-selective ethylene oligomerization is the main preparation route for polymerization-grade 1-octene. The resulting α-olefin composition is complex, the selectivity of high-value 1-hexene and 1-octene is low, the product separation cost is high, and the process economy is low. Therefore, the development of ethylene selective oligomerization technology with high selectivity for 1-octene has become a hot topic in the current industry. The chromium-based catalyst coordinated by the PNP skeleton ligand disclosed in Sasol's patent applications WO2004056478A1 and CN105263890B can catalyze ethylene tetramerization to produce 1-octene with high selectivity, and its content in the product exceeds 60%, but it will produce solid polymers that hinder continuous production and easily cause pipeline blockage.

[0004] Patent application CN101605605A discloses a chromium catalyst coordinated by a novel PCCP framework ligand for ethylene tetramerization, which has high selectivity for 1-octene, and the polymer content is significantly lower than that of a PNP framework catalyst. However, in the catalytic system of the oligomerization method described in the above patent, the co-catalyst aluminoxane (including methylaluminoxane, modified methylaluminoxane, etc.) used is large in amount and expensive, and large-scale production will result in high production costs of the product; and those skilled in the art generally believe that the presence of water and oxygen is not conducive to ethylene oligomerization, and active aluminum-containing reagents need to be used to strictly control the water oxygen content during the production process. This makes the known ethylene oligomerization reaction require a larger co-catalyst, which is unfavorable for the economy of the entire process. Therefore, how to keep the high-value 1-hexene and 1-octene content high enough and low solid polymer content, while reducing the production cost of the polymerization process, thereby improving its economy, is still a challenge for those skilled in the art. Summary of the invention

[0005] In order to solve the high cost problem of ethylene polymerization catalytic systems in the prior art, the purpose of the present invention is to provide a catalytic system, preparation method and application for ethylene selective polymerization. The catalytic system has low cost and avoids a series of problems caused by aluminoxane co-catalysts in the existing ethylene polymerization system, such as high raw material cost, limited source, and harsh storage and use conditions, thereby helping to improve the economic efficiency of industrial production.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A catalytic system for selective polymerization of ethylene comprises a chromium catalyst, an organic boron auxiliary agent and an aluminum-containing activator in a molar ratio of 1:1-50:100-1500.

[0007] Furthermore, the chromium catalyst is prepared by the following process: weighing CrCl3(THF)3 and a ligand in CH2Cl2, reacting under stirring, filtering, and performing post-treatment to obtain a catalyst; The catalyst and the aluminum-containing activator are uniformly mixed, and then an organic boron auxiliary agent is added and stirred to obtain a catalytic system.

[0008] Further, the ligand has any of the following structures:

[0009] Among them, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 are independently selected from hydrogen, halogen, alkyl or aryl.

[0010] Furthermore, the alkyl group has 1 to 8 carbon atoms, and the aryl group has 6 to 15 carbon atoms.

[0011] Furthermore, the alkyl group is one or more of methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, cyclopentyl and cyclohexyl; The aryl group is one or more of phenyl, biphenyl, naphthyl and substituted phenyl.

[0012] Furthermore, the substituted phenyl group specifically includes mono-, di- and tri-substituted phenyl groups of alkyl, halogen, vinyl and alkoxy.

[0013] Further, the organic boron auxiliary agent is triethylborane, triphenylborane, triphenylborane ammonia complex, dodecyl di(methyl)ammonium tetra(pentafluorophenyl)borate, tetradecyl di(methyl)ammonium tetra(pentafluorophenyl)borate, hexadecyl di(methyl)ammonium tetra(pentafluorophenyl)borate, octadecyl di(methyl)ammonium tetra(pentafluorophenyl)borate, eicosyl di(methyl)ammonium tetra(pentafluorophenyl)borate, triisopropyl borate, tri(pentafluorophenyl)borane, trityl One or more of tetrakis(pentafluorophenyl)borate, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, N,N-dihexylanilinium tetrakis(pentafluorophenyl)borate, N,N-dioctylanilinium tetrakis(pentafluorophenyl)borate, N,N-didodecylanilinium tetrakis(pentafluorophenyl)borate, N-methyl-N-dodecylanilinium tetrakis(pentafluorophenyl)borate, and N,N-dioctadecyl (2,4,6-trimethylanilinium) tetrakis(pentafluorophenyl)borate.

[0014] Furthermore, the organic boron auxiliary agent is one or more of trityltetrakis(pentafluorophenyl)borate, N,N-dimethylaniliniumtetrakis(pentafluorophenyl)borate, N,N-dihexylaniliniumtetrakis(pentafluorophenyl)borate and N,N-dioctylaniliniumtetrakis(pentafluorophenyl)borate.

[0015] Further, the aluminum-containing activator includes one or more of trimethylaluminum, diethylaluminum chloride, triethylaluminum, triisobutylaluminum, diethylethoxyaluminum, diethylaluminum monochloride, ethylaluminum dichloride, sesquiethylaluminum chloride, methylaluminoxane, modified methylaluminoxane, ethylaluminoxane, tri-n-propylaluminum, tri-n-butylaluminum, triisopropylaluminum, tri-n-hexylaluminum, tri-n-heptylaluminum and tri-n-octylaluminum.

[0016] Furthermore, the molar ratio of the chromium catalyst, the organic boron auxiliary agent and the aluminum-containing activator in the catalyst system is 1:1~50:100~1500.

[0017] Furthermore, the molar ratio of the chromium catalyst, the organic boron auxiliary agent and the aluminum-containing activator in the catalyst system is 1:1~10:300~500.

[0018] A method for preparing a catalytic system for selective oligomerization of ethylene comprises the following steps: The chromium catalyst is mixed with an aluminum-containing activator for activation, and then an organic boron auxiliary is added, and the mixture is reacted under stirring to obtain a catalyst system.

[0019] A method for selective polymerization of ethylene comprises the following steps: The solvent and the catalyst system prepared by the method are used to carry out ethylene polymerization reaction on ethylene gas.

[0020] Furthermore, the ethylene polymerization reaction temperature is 30-110° C., and the reaction pressure is 1.0-5.5 MPa.

[0021] Furthermore, the ethylene polymerization reaction temperature is 40-80° C., and the reaction pressure is 1.0-4.0 MPa.

[0022] Furthermore, the solvent is one or more of n-butane, isobutane, cyclopentane, methylcyclopentane, n-hexane, cyclohexane, methylcyclohexane, n-heptane, n-octane, benzene, toluene and xylene.

[0023] Furthermore, the solvent is methylcyclohexane.

[0024] Furthermore, the specific process is: under an inert atmosphere, the solvent and the catalyst system are sequentially added into the reactor, and stirred; under heating, ethylene gas is continuously introduced at a constant pressure to react; after the reaction is completed, the introduction of ethylene is stopped, and a quencher is added to terminate the reaction.

[0025] Further, the molar concentration of chromium in the catalyst system is 0.001-0.050 mmol / L, based on the molar amount of chromium atoms; Furthermore, the molar concentration of chromium in the catalyst system is 0.010-0.020 mmol / L based on the molar amount of chromium atoms.

[0026] Compared with the prior art, the catalyst system for selective oligomerization of ethylene according to the present invention has the following beneficial effects: The chromium catalyst in the present invention is a carbon-bridge bidentate phosphine chromium catalyst, and the catalyst system constructed by the chromium catalyst, the organic boron auxiliary agent and the aluminum-containing activator realizes the selective polymerization of ethylene. In addition, the catalyst system can realize the high-efficiency and high-selectivity preparation of 1-hexene and 1-octene without using aluminoxane auxiliary catalysts such as MAO and MMAO, has high catalytic activity, rapid reaction initiation, stable operation and good repeatability.

[0027] Under the above catalyst system, conventional industrial unsubstituted hydrocarbon solvents can be used for the reaction. The reaction process does not require special harsh conditions, the raw materials are widely available, the cost is lower, and the production safety is high, which is more suitable for industrial continuity and scale. DETAILED DESCRIPTION

[0028] In order to facilitate understanding of the present invention, the present invention is described more fully below. The present invention can be implemented in a variety of different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0029] The following is a detailed description with reference to the embodiments. These embodiments are only for illustration and are not intended to limit the application scope of the present invention and do not constitute a limitation to the present invention.

[0030] The present invention provides a catalytic system for selective ethylene oligomerization, comprising three components: a chromium catalyst A, an organic boron auxiliary agent B, and an aluminum-containing activator C. The catalytic system can achieve high-efficiency and high-selectivity preparation of 1-hexene and 1-octene without using aluminoxane auxiliary catalysts such as MAO (methylaluminoxane) and MMAO (modified methylaluminoxane), thereby avoiding a series of problems such as high raw material cost, limited sources, and harsh storage and use conditions caused by aluminoxane auxiliary catalysts in existing ethylene oligomerization systems, and is helpful to improve the economic efficiency of industrial production.

[0031] The chromium catalyst A was prepared by the following process: 20 μmol of CrCl3(THF)3 and 20 μmol of ligand were weighed into 10 mL of CH2Cl2 solution, and the mixture was continuously stirred at room temperature for 18 h and then filtered. The solvent was evaporated in vacuo, 15 mL of n-hexane was added to complete precipitation and filtered, and the filter cake was washed with n-hexane and then vacuum dried to obtain the catalyst; The obtained catalyst and the aluminum-containing activator are mixed and stirred evenly to obtain a mixed solution, and the organic boron auxiliary agent is weighed and added to the mixed solution and continued to stir for 1 hour to prepare a catalytic system solution.

[0032] The ligand in the chromium catalyst A has any of the following structures:

[0033] Among them, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , R 10 are independently selected from hydrogen, halogen, alkyl or aryl.

[0034] Preferably, halogen is fluorine, chlorine, bromine or iodine.

[0035] Preferably, the alkyl group has 1 to 8 carbon atoms, and is preferably one or more of methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, cyclopentyl and cyclohexyl; Preferably, the aryl group has 6 to 15 carbon atoms, and is preferably one or more of phenyl, biphenyl, naphthyl and substituted phenyl.

[0036] The substituted phenyl group specifically includes mono-, di- and tri-substituted phenyl groups such as the above-mentioned alkyl groups, halogen groups, vinyl groups and alkoxy groups.

[0037] Preferably, the organic boron auxiliary agent B is triethylborane, triphenylborane, triphenylborane ammonia complex, dodecyl di(methyl)ammonium tetra(pentafluorophenyl)borate, tetradecyl di(methyl)ammonium tetra(pentafluorophenyl)borate, hexadecyl di(methyl)ammonium tetra(pentafluorophenyl)borate, octadecyl di(methyl)ammonium tetra(pentafluorophenyl)borate, eicosyl di(methyl)ammonium tetra(pentafluorophenyl)borate, triisopropyl borate, tri(pentafluorophenyl)borane, trityl One or more of tetrakis(pentafluorophenyl)borate, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, N,N-dihexylanilinium tetrakis(pentafluorophenyl)borate, N,N-dioctylanilinium tetrakis(pentafluorophenyl)borate, N,N-di(dodecyl)anilinium tetrakis(pentafluorophenyl)borate, N-methyl-N-dodecylanilinium tetrakis(pentafluorophenyl)borate, and N,N-dioctadecyl (2,4,6-trimethylanilinium) tetrakis(pentafluorophenyl)borate. Preferably, one or more of trityl tetrakis(pentafluorophenyl)borate, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, N,N-dihexylanilinium tetrakis(pentafluorophenyl)borate, and N,N-dioctylanilinium tetrakis(pentafluorophenyl)borate.

[0038] Preferably, the aluminum-containing activator C includes one or more of trimethylaluminum, diethylaluminum chloride, triethylaluminum, triisobutylaluminum, diethylethoxyaluminum, diethylaluminum monochloride, ethylaluminum dichloride, sesquiethylaluminum chloride, methylaluminoxane, modified methylaluminoxane (CAS No. 206451-54-9), ethylaluminoxane, tri-n-propylaluminum, tri-n-butylaluminum, triisopropylaluminum, tri-n-hexylaluminum, tri-n-heptylaluminum and tri-n-octylaluminum.

[0039] Preferably, the molar ratio of the chromium catalyst A, the organic boron additive B and the aluminum-containing activator C in the catalyst system is 1:1~50:100~1500.

[0040] More preferably, the molar ratio of the chromium catalyst A, the organic boron additive B and the aluminum-containing activator C in the catalyst system is 1:1-10:300-500.

[0041] Preferably, the preparation method of the catalytic system is as follows: the chromium catalyst A is first mixed and activated with the aluminum-containing activator C, stirred at room temperature for 15 to 120 minutes, and then the organic boron auxiliary agent B is added, mixed and stirred for 20 to 60 minutes to obtain the catalyst system.

[0042] The present invention also provides a method for selective polymerization of ethylene, comprising: under a certain temperature and pressure, using unsubstituted hydrocarbons as solvent, catalyzing ethylene under the above-mentioned catalytic system, causing ethylene selective polymerization reaction to occur, and generating high carbon α-olefins such as 1-hexene and 1-octene.

[0043] Preferably, the ethylene polymerization reaction temperature is 30-110° C., and the reaction pressure is 1.0-5.5 MPa.

[0044] More preferably, the ethylene polymerization reaction temperature is 40-80° C., and the reaction pressure is 1.0-4.0 MPa.

[0045] Preferably, the unsubstituted hydrocarbon solvent is one or more of n-butane, isobutane, cyclopentane, methylcyclopentane, n-hexane, cyclohexane, methylcyclohexane, n-heptane, n-octane, benzene, toluene and xylene.

[0046] More preferably, the unsubstituted hydrocarbon solvent is methylcyclohexane.

[0047] Preferably, the ethylene selective oligomerization reaction process is as follows: in an inert atmosphere, a solvent and a catalyst system are sequentially added into a well-sealed reactor, and stirred, and when a certain temperature is reached, ethylene gas is continuously introduced at a constant pressure to react. After the reaction is completed, the introduction of ethylene is stopped, and a quencher is added to terminate the reaction.

[0048] Preferably, the molar concentration of chromium in the catalyst system is 0.001 to 0.050 mmol / L, measured in terms of the molar amount of chromium atoms; More preferably, the molar concentration of chromium in the catalyst system is 0.010-0.020 mmol / L.

[0049] In the embodiments of the present invention, the carbon-bridged diphosphorus ligand used is prepared by reacting a substituted alkyne with a substituted chlorophosphine.

[0050] Since the ethylene polymerization process is extremely sensitive to impurities such as water and oxygen, the solvent used in continuous production needs to be stripped by high-purity nitrogen to remove oxygen and molecular sieve to remove water to avoid catalyst deactivation. Various reagents and raw materials used in the present invention are commercially available or can be obtained by public preparation methods.

[0051] The catalyst activity of the polymerization reaction was qualitatively and quantitatively analyzed by each component in the reaction solution. The conditions of the GC analysis instrument used were as follows: Instrument model: Shimadzu GC2010 Chromatographic column: DB-5 (30m, 0.25mm, 0.25μm); Column temperature: 40°C for 3min, heated to 160°C at 10°C / min, held for 5min, then heated to 300°C at 30°C / min, held for 15min. Inlet temperature: 280°C. FID temperature: 300°C. N2 flow rate: 40mL / min. H2 flow rate: 400mL / min, septum purge (N2) flow rate: 3.0mL / min. Carrier gas (N2) flow rate: 1.0mL / min. Injection volume: 1.0μL.

[0052] Example 1 (1) Preparation of catalyst: Weigh 20 μmol of CrCl3(THF)3 and 20 μmol of ligand 1 in 10 mL of CH2Cl2 solution, stir continuously at room temperature for 18 h, filter, evaporate the solvent in vacuo, add 15 mL of n-hexane to complete precipitation and filter, wash the filter cake with n-hexane and dry in vacuo to obtain catalyst A1; the structural formula of catalyst ligand 1 is as follows:

[0053] (2) Preparation of catalyst system solution: 1.5 μmol of catalyst A1 and 750 μmol of trimethylaluminum were mixed and stirred for 120 min to obtain a mixed solution. 30 μmol of triphenylborane amine complex was weighed and added to the mixed solution and stirred for 35 min to prepare a catalyst system solution. The solution was stored in a glove box under a nitrogen atmosphere.

[0054] (3) Intermittent polymerization: A 500mL stainless steel polymerization autoclave was used, and the autoclave was heated to 150°C. After evacuation, it was replaced with nitrogen several times, and then filled with ethylene for replacement three times, and then cooled to the set temperature. Then, 200mL of cyclopentane was added at 40°C, and 2.5mL of the above-prepared catalyst system solution was added at the same time. Then, hydrogen was pressurized to 0.1MPa, and the reaction pressure was controlled to 2.0MPa. Ethylene was introduced, and ethylene polymerization was carried out at 30°C. After half an hour, the reaction was completed, and the system was cooled to room temperature. After depressurization, the liquid phase product was collected in a conical flask, and 2mL of isooctyl alcohol was added as a terminator to terminate the reaction. The product analysis data results are shown in Table 1.

[0055] Example 2 (1) Preparation of catalyst: Weigh 20 μmol of CrCl3(THF)3 and 20 μmol of ligand 2 in 10 mL of CH2Cl2 solution, stir continuously at room temperature for 18 h, filter, evaporate the solvent in vacuo, add 15 mL of n-hexane to complete precipitation and filter, wash the filter cake with n-hexane and dry in vacuo to obtain catalyst A2; the structural formula of catalyst ligand 2 is as follows:

[0056] (2) Preparation of catalyst system solution: 1.0 μmol of catalyst A2 was mixed with 600 μmol of triethylaluminum and stirred for 15 min to obtain a mixed solution. 10 μmol of tetradecyldi(methyl)ammoniumtetrakis(pentafluorophenyl)borate was added to the mixed solution and stirred for 50 min to prepare a catalyst system solution. The solution was stored in a glove box under a nitrogen atmosphere.

[0057] (3) Intermittent polymerization: Use a 500mL stainless steel polymerization autoclave, heat the autoclave to 150°C, evacuate and replace with nitrogen several times, then fill with ethylene for replacement three times, and then cool to the set temperature. Then add 200mL of n-octane at 100°C, and add 2.5mL of the above-prepared catalyst system solution at the same time, then pressurize the hydrogen to 0.1MPa, control the reaction pressure to 5.5MPa, pass ethylene, and carry out ethylene polymerization at 90°C. After half an hour, the reaction is completed, the system is cooled to room temperature, and the liquid product is collected in a conical flask after depressurization, and 2mL of isooctyl alcohol is added as a terminator to terminate the reaction. The product analysis data results are shown in Table 1.

[0058] Example 3 (1) Preparation of catalyst: Weigh 20 μmol of CrCl3(THF)3 and 20 μmol of ligand 3 in 10 mL of CH2Cl2 solution, stir continuously at room temperature for 18 h, filter, evaporate the solvent in vacuo, add 15 mL of n-hexane to complete precipitation and filter, wash the filter cake with n-hexane and dry in vacuo to obtain catalyst A3; the structural formula of catalyst ligand 3 is as follows:

[0059] (2) Preparation of catalyst system solution: 1.2 μmol of catalyst A3 and 360 μmol of diethyl ethoxyaluminum were mixed and stirred for 120 min to obtain a mixed solution. 18 μmol of triisopropyl borate was added to the mixed solution and stirred for 40 min to prepare a catalyst system solution. The solution was stored in a glove box under a nitrogen atmosphere.

[0060] (3) Intermittent polymerization: Use a 500mL stainless steel polymerization autoclave, heat the autoclave to 150°C, evacuate and replace with nitrogen several times, then fill with ethylene for replacement three times, and then cool to the set temperature. Then add 200mL of n-heptane at 90°C, and add 2.5mL of the above-prepared catalyst system solution at the same time, then pressurize the hydrogen to 0.1MPa, control the reaction pressure to 4.0MPa, pass ethylene, and carry out ethylene polymerization at 80°C. After half an hour, the reaction is completed, the system is cooled to room temperature, and the liquid product is collected in a conical flask after depressurization, and 2mL of isooctyl alcohol is added as a terminator to terminate the reaction. The product analysis data results are shown in Table 1.

[0061] Example 4 (1) Preparation of catalyst: Weigh 20 μmol of CrCl3(THF)3 and 20 μmol of ligand 4 in 10 mL of CH2Cl2 solution, stir continuously at room temperature for 18 h, filter, evaporate the solvent in vacuo, add 15 mL of n-hexane to complete precipitation and filter, wash the filter cake with n-hexane and dry in vacuo to obtain catalyst A4; the structural formula of catalyst ligand 4 is as follows:

[0062] (2) Preparation of catalyst system solution: 2.5 μmol of catalyst A4 and 1000 μmol of triisobutylaluminum were mixed and stirred for 45 min to obtain a mixed solution. 5 μmol of N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate was added to the mixed solution and stirred for 30 min to prepare a catalyst system solution. The solution was stored in a glove box under a nitrogen atmosphere.

[0063] (3) Intermittent polymerization: Use a 500mL stainless steel polymerization autoclave, heat the autoclave to 150°C, evacuate and replace with nitrogen several times, then fill with ethylene for replacement three times, and then cool to the set temperature. Then add 200mL of methylcyclohexane at 60°C, and add 2.5mL of the above-prepared catalyst system solution at the same time, then pressurize the hydrogen to 0.1MPa, control the reaction pressure to 3MPa, pass ethylene, and carry out ethylene polymerization at 50°C. After half an hour, the reaction is completed, the system is cooled to room temperature, and the liquid product is collected in a conical flask after depressurization, and 2mL of isooctyl alcohol is added as a terminator to terminate the reaction. The product analysis data results are shown in Table 1.

[0064] Example 5 (1) Preparation of catalyst: Weigh 20 μmol of CrCl3(THF)3 and 20 μmol of ligand 5 in 10 mL of CH2Cl2 solution, stir continuously at room temperature for 18 h, filter, evaporate the solvent in vacuo, add 15 mL of n-hexane to complete precipitation and filter, wash the filter cake with n-hexane and dry in vacuo to obtain catalyst A5; the structural formula of catalyst ligand 5 is as follows:

[0065] (2) Preparation of catalyst system solution: 10 μmol of catalyst A5 and 1000 μmol of tri-n-butylaluminum were mixed and stirred for 50 min to obtain a mixed solution. 10 μmol of N,N-dihexylanilinium tetrakis(pentafluorophenyl)borate was added to the mixed solution and stirred for 60 min to prepare a catalyst system solution. The solution was stored in a glove box under a nitrogen atmosphere.

[0066] (3) Intermittent polymerization: Use a 500mL stainless steel polymerization autoclave, heat the autoclave to 150°C, evacuate and replace with nitrogen several times, then fill with ethylene for replacement three times, and then cool to the set temperature. Then add 200mL toluene at 100°C, and add 2.5mL of the above-prepared catalyst system solution at the same time, then pressurize the hydrogen to 0.1MPa, control the reaction pressure to 2.5MPa, pass ethylene, and carry out ethylene polymerization at 75°C. After half an hour, the reaction is completed, the system is cooled to room temperature, and the liquid product is collected in a conical flask after depressurization, and 2mL of isooctyl alcohol is added as a terminator to terminate the reaction. The product analysis data results are shown in Table 1.

[0067] Example 6 (1) Preparation of catalyst: Weigh 20 μmol of CrCl3(THF)3 and 20 μmol of ligand 6 in 10 mL of CH2Cl2 solution, stir continuously at room temperature for 18 h, filter, evaporate the solvent in vacuo, add 15 mL of n-hexane to complete precipitation and filter, wash the filter cake with n-hexane and dry in vacuo to obtain catalyst A6; the structural formula of catalyst ligand 6 is as follows:

[0068] (2) Preparation of catalyst system solution: 2.5 μmol of catalyst A6 and 1750 μmol of methylaluminoxane were mixed and stirred for 90 min to obtain a mixed solution. 20 μmol of trityltetrakis(pentafluorophenyl)borate was weighed and added to the mixed solution and stirred for 20 min to prepare a catalyst system solution. The solution was stored in a glove box under a nitrogen atmosphere.

[0069] (3) Intermittent polymerization: A 500mL stainless steel polymerization autoclave was used, and the autoclave was heated to 150°C. After evacuation, it was replaced with nitrogen several times, and then filled with ethylene for replacement three times, and then cooled to the set temperature. Then, 200mL of cyclohexane was added at 60°C, and 2.5mL of the above-prepared catalyst system solution was added at the same time. Then, hydrogen was pressurized to 0.1MPa, and the reaction pressure was controlled to 5.0MPa. Ethylene was introduced, and ethylene polymerization was carried out at 45°C. After half an hour, the reaction was completed, and the system was cooled to room temperature. After depressurization, the liquid phase product was collected in a conical flask, and 2mL of isooctyl alcohol was added as a terminator to terminate the reaction. The product analysis data results are shown in Table 1.

[0070] Example 7 (1) Preparation of catalyst: Weigh 20 μmol of CrCl3(THF)3 and 20 μmol of ligand 7 in 10 mL of CH2Cl2 solution, stir continuously at room temperature for 18 h, filter, evaporate the solvent in vacuo, add 15 mL of n-hexane to complete precipitation and filter, wash the filter cake with n-hexane and dry in vacuo to obtain catalyst A7; the structural formula of catalyst ligand 7 is as follows:

[0071] (2) Preparation of catalyst system solution: 0.20 μmol of catalyst A7 and 300 μmol of ethylaluminoxane were mixed and stirred for 90 min to obtain a mixed solution. 10 μmol of dodecyldi(methyl)ammoniumtetrakis(pentafluorophenyl)borate was added to the mixed solution and stirred for 25 min to prepare a catalyst system solution. The solution was stored in a glove box under a nitrogen atmosphere.

[0072] (3) Intermittent polymerization: Use a 500mL stainless steel polymerization autoclave, heat the autoclave to 150°C, evacuate and replace with nitrogen several times, then fill with ethylene for replacement three times, and then cool to the set temperature. Then add 200mL of benzene at 70°C, and add 2.5mL of the above-prepared catalyst system solution at the same time, then pressurize the hydrogen to 0.1MPa, control the reaction pressure to 3.5MPa, pass ethylene, and carry out ethylene polymerization at 60°C. After half an hour, the reaction is completed, the system is cooled to room temperature, and the liquid product is collected in a conical flask after depressurization, and 2mL of isooctyl alcohol is added as a terminator to terminate the reaction. The product analysis data results are shown in Table 1.

[0073] Example 8 (1) Preparation of catalyst: Weigh 20 μmol of CrCl3(THF)3 and 20 μmol of ligand 8 in 10 mL of CH2Cl2 solution, stir continuously at room temperature for 18 h, filter, evaporate the solvent in vacuo, add 15 mL of n-hexane to complete precipitation and filter, wash the filter cake with n-hexane and dry in vacuo to obtain catalyst A8; the structural formula of catalyst ligand 8 is as follows:

[0074] (2) Preparation of catalyst system solution: 3.0 μmol of catalyst A8 and 360 μmol of tri-n-octylaluminum were mixed and stirred for 80 min to obtain a mixed solution. 9.0 μmol of N,N-dioctylanilinium tetrakis(pentafluorophenyl)borate was added to the mixed solution and stirred for 35 min to prepare a catalyst system solution. The solution was stored in a glove box under a nitrogen atmosphere.

[0075] (3) Intermittent polymerization: Use a 500mL stainless steel polymerization autoclave, heat the autoclave to 150°C, evacuate and replace with nitrogen several times, then fill with ethylene for replacement three times, and then cool to the set temperature. Then add 200mL of n-hexane at 50°C, and add 2.5mL of the above-prepared catalyst system solution at the same time, then pressurize the hydrogen to 0.1MPa, control the reaction pressure to 4.5MPa, pass ethylene, and carry out ethylene polymerization at 40°C. After half an hour, the reaction is completed, the system is cooled to room temperature, and the liquid product is collected in a conical flask after depressurization, and 2mL of isooctyl alcohol is added as a terminator to terminate the reaction. The product analysis data results are shown in Table 1.

[0076] Example 9 (1) Preparation of catalyst: Weigh 20 μmol of CrCl3(THF)3 and 20 μmol of ligand 9 in 10 mL of CH2Cl2 solution, stir continuously at room temperature for 18 h, filter, evaporate the solvent in vacuo, add 15 mL of n-hexane to complete precipitation and filter, wash the filter cake with n-hexane and dry in vacuo to obtain catalyst A9; the structural formula of catalyst ligand 9 is as follows:

[0077] (2) Preparation of catalyst system solution: 2.0 μmol of catalyst A9 and 1600 μmol of modified methylaluminoxane were mixed and stirred for 100 min to obtain a mixed solution. 10 μmol of N-methyl-N-dodecylanilinium tetrakis(pentafluorophenyl)borate was added to the mixed solution and stirred for 40 min to prepare a catalyst system solution. The solution was stored in a glove box under a nitrogen atmosphere.

[0078] (3) Intermittent polymerization: Use a 500mL stainless steel polymerization autoclave, heat the autoclave to 150°C, evacuate and replace with nitrogen several times, then fill with ethylene for replacement three times, and then cool to the set temperature. Then add 100mL toluene and 100mL xylene at 120°C, and add 2.5mL of the above-prepared catalyst system solution at the same time, then pressurize the hydrogen to 0.1MPa, control the reaction pressure to 1.0MPa, pass ethylene, and carry out ethylene polymerization at 110°C. After half an hour, the reaction is completed, the system is cooled to room temperature, and the liquid product is collected in a conical flask after depressurization, and 2mL of isooctyl alcohol is added as a terminator to terminate the reaction. The product analysis data results are shown in Table 1.

[0079] Comparative Example 1 Same as Example 4, except for the preparation of the catalyst system solution and the reaction addition process: the obtained catalyst A4 was mixed and stirred with triisobutylaluminum for 30 minutes to prepare a mixed solution, which was stored in a glove box with a nitrogen atmosphere. Weigh 40 μmol of N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate and dissolve it in toluene and stir for 1 hour for use. During intermittent polymerization, after adding 200 mL of methylcyclohexane at 50°C, 2.0 mL of the above-prepared mixed solution and 1.0 mL of borate toluene solution were added in sequence. Other conditions were the same as those in Example 4. The product analysis data results are shown in Table 1.

[0080] Comparative Example 2 A 500mL stainless steel polymerization reactor was used. The autoclave was heated to 120°C, evacuated and replaced with nitrogen several times, then filled with ethylene for replacement three times, and then cooled to the set temperature. Then, 200mL of methylcyclohexane was added at 50°C, and a methylcyclohexane solution of catalyst A4 prepared with 2.5μmol ligand 4 and 2.5μmol CrCl3(THF)3 was added at the same time. 1.25mL MMAO (7wt% methylcyclohexane solution) was injected into the reactor with a syringe under a slight positive pressure, and then hydrogen was pressurized to 0.1MPa, the reaction pressure was controlled to 3.0MPa, ethylene was introduced, and ethylene polymerization was carried out at 50°C. After half an hour, the reaction was completed, the system was cooled to room temperature, and the liquid product was collected in a conical flask after depressurization. 2mL of isooctyl alcohol was added as a terminator to terminate the reaction. The liquid product was measured and analyzed by gas chromatography. The product analysis data results are shown in Table 1.

[0081] Comparative Example 3 (1) Ethylene polymerization reaction was carried out using catalyst A6.

[0082] (2) Same as comparative example 2, except that ligand 4 is replaced by ligand 6. The data results are shown in Table 1.

[0083] Table 1 Comparison of reaction effects of Examples 1-10 and Comparative Examples 1-2

[0084] It can be seen from Table 1 that the activity of the catalytic system prepared by the present invention is as high as 73.7×10 6 g / (molCr·h), 1-C6 selectivity was 44.97 wt%, 1-C8 selectivity was 59.79 wt%, and the solid content was 0.05 PEwt%.

[0085] It can be seen from the catalytic performance test results of the embodiments and comparative examples in Table 1 that the catalytic system of the present invention requires pre-mixing and activating the auxiliary agents and feeding them together, and can achieve the same effect as using a large amount of expensive aluminoxane under the condition of lower aluminum reagent dosage, thereby ensuring higher catalytic activity and adjustable α-olefin selectivity, and the production amount of the reaction by-product polyethylene is lower, which reduces the production cost and has broad prospects for industrial application.

[0086] The above description is only for the best embodiment of the present invention, but it should not be understood as limiting the claims. The present invention is not limited to the above embodiments, and its specific structure is allowed to be changed. However, all changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

[0087] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

Claims

1. A catalytic system for selective oligomerization of ethylene, characterized in that: The invention comprises a carbon-bridge bidentate phosphine-chromium catalyst, an organic boron auxiliary agent and an aluminum-containing activator in a molar ratio of 1:1-50:100-1500.

2. The catalytic system for selective oligomerization of ethylene according to claim 1, characterized in that: The carbon-bridged bidentate phosphine-chromium catalyst is prepared by the following process: weighing CrCl3(THF)3 and a ligand in CH2Cl2, reacting under stirring, filtering, and performing post-treatment to obtain a catalyst; The catalyst and the aluminum-containing activator are uniformly mixed, and then an organic boron auxiliary agent is added and stirred to obtain a catalytic system.

3. The catalytic system for selective oligomerization of ethylene according to claim 2, characterized in that: The ligand has any of the following structures: Among them, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 are independently selected from hydrogen, halogen, alkyl or aryl.

4. The catalytic system for selective oligomerization of ethylene according to claim 3, characterized in that: The alkyl group has 1 to 8 carbon atoms, and the aryl group has 6 to 15 carbon atoms.

5. The catalytic system for selective oligomerization of ethylene according to claim 4, characterized in that: The alkyl group is one or more of methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, cyclopentyl and cyclohexyl; The aryl group is one or more of phenyl, biphenyl, naphthyl and substituted phenyl.

6. The catalytic system for selective oligomerization of ethylene according to claim 1, characterized in that: The organic boron auxiliary agent is triethylborane, triphenylborane, triphenylborane ammonia complex, dodecyl di(methyl)ammonium tetra(pentafluorophenyl)borate, tetradecyl di(methyl)ammonium tetra(pentafluorophenyl)borate, hexadecyl di(methyl)ammonium tetra(pentafluorophenyl)borate, octadecyl di(methyl)ammonium tetra(pentafluorophenyl)borate, eicosyl di(methyl)ammonium tetra(pentafluorophenyl)borate, triisopropyl borate, tri(pentafluorophenyl)borane, trityl tetra(pentafluorophenyl)borate. One or more of N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, N,N-dihexylanilinium tetrakis(pentafluorophenyl)borate, N,N-dioctylanilinium tetrakis(pentafluorophenyl)borate, N,N-didodecylanilinium tetrakis(pentafluorophenyl)borate, N-methyl-N-dodecylanilinium tetrakis(pentafluorophenyl)borate, and N,N-dioctadecyl (2,4,6-trimethylanilinium) tetrakis(pentafluorophenyl)borate.

7. The catalytic system for selective oligomerization of ethylene according to claim 1, characterized in that: The aluminum-containing activator includes one or more of trimethylaluminum, diethylaluminum chloride, triethylaluminum, triisobutylaluminum, diethylethoxyaluminum, diethylaluminum monochloride, ethylaluminum dichloride, sesquiethylaluminum chloride, methylaluminumoxane, modified methylaluminumoxane, ethylaluminumoxane, tri-n-propylaluminum, tri-n-butylaluminum, triisopropylaluminum, tri-n-hexylaluminum, tri-n-heptylaluminum and tri-n-octylaluminum.

8. The catalytic system for selective oligomerization of ethylene according to claim 1, characterized in that: The molar ratio of the carbon-bridge bidentate phosphine-chromium catalyst, the organic boron auxiliary agent and the aluminum-containing activator is 1:1-10:300-500.

9. A method for preparing a catalytic system for selective oligomerization of ethylene according to any one of claims 1 to 8, characterized in that: The following steps are involved: The chromium catalyst is mixed with an aluminum-containing activator for activation, and then an organic boron auxiliary is added, and the mixture is reacted under stirring to obtain a catalyst system.

10. A method for selective oligomerization of ethylene, characterized in that: The following steps are involved: The solvent and the catalyst system prepared by the method according to any one of claims 1 to 8 are used to carry out ethylene polymerization reaction on ethylene gas.

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