An ionic liquid catalyst, a preparation method and a method for catalyzing polymerization of alpha-olefins

Abstract

The application discloses an ionic liquid catalyst, a preparation method and a method for catalyzing alpha-olefin polymerization reaction. 1~20 alkyl, C 6~40 aryl; Mt is a metal element or a metalloid element in a Lewis acid; Y and X are the same or different and are selected from halogen elements; m is a number ranging from 0.5 to 2.5; n is equal to the valence of Mt; and 0<=k<=m*n. The patent uses a novel ionic liquid with the structure shown in formula I as a catalyst, and the reaction conversion rate reaches more than 90% in 10 minutes. The time-based operation efficiency of an alpha-olefin oligomerization device based on an ionic liquid catalyst in industry is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of α-olefin polymerization reaction, specifically relating to a novel ionic liquid catalyst, its preparation method, and its method for catalyzing α-olefin polymerization reaction. Background Technology

[0002] Polyalphaolefin base oil (PAO) is an alpha olefin (typically C8~C10). 12 PAO is obtained through polymerization, separation, and hydrogenation. Compared with mineral base oils, PAO has advantages such as high viscosity index, low pour point, good oxidation and thermal stability, low volatility, and non-toxicity, making it an important component in the preparation of high-end lubricating oils. In industrial production, BF3 and AlCl3 catalysts are mainly used to catalyze the oligomerization of α-olefins. Catalytic systems composed of BF3 and protonated co-catalysts (such as n-butanol, US4956512A, CN101824354) or aprotic catalysts (such as butyl acetate, CN101883838A, US20110039743A1) are typically used for low viscosity (kinematic viscosity ≤10 mmHg at 100℃). 2 / s) Production of synthetic base oils. A drawback of BF3 is its high toxicity; such catalysts often require expensive methods to remove or recycle it. Catalytic systems composed of AlCl3 and proton donors (such as alcohols or organic acids) are suitable for preparing medium-to-high viscosity PAO (kinematic viscosity at 100℃ can be divided into low viscosity ≥10 mm). 2 However, residual chlorine in AlCl3 catalysts within the α-olefin oligomers can lead to hydrogen chloride production during subsequent vacuum distillation, causing equipment corrosion. Furthermore, the presence of chlorine can poison and deactivate subsequent hydrogenation catalysts. US3997622 addresses this issue by adding metallic aluminum and polyol derivatives to the AlCl3 catalytic system to suppress chlorine residue in the α-olefin oligomers. Additionally, AlCl3-catalyzed α-olefin reactions are homogeneous; the catalyst is deactivated upon quenching, and therefore cannot be recycled.

[0003] Ionic liquids, as heterogeneous catalysts for olefin oligomerization, have the advantage that the catalyst phase and the product obtained from the reaction can be separated into layers through static phase during the post-reaction treatment. The separated ionic liquid catalyst can also be recycled in the oligomerization reaction (Gao Congcong et al. Journal of Shandong University (Engineering Science), 2013, 43(04):93-98.). The separability of heterogeneous catalysts also reduces the amount of alkaline quenching agent used in the post-treatment process and the corresponding amount of water washing.

[0004] In EP0791643A1, an ionic liquid catalyst (7 g) prepared using 1-ethyl-3-methylimidazolium chloride and AlCl3 (molar ratio 1:2) was reacted at -5°C with heptane (213 g) as a diluent. This catalyst catalyzed a mixture of 1-hexene, 1-octene, and 1-decene (total 460 g) for 3 hours. The resulting product had a kinematic viscosity of 19.85 mmHg at 100°C. 2 The viscosity index is 152, and the reaction conversion rate is 88%, which is relatively low.

[0005] Stenzel et al. (Journal of Molecular Catalysis A: Chemical 2003, 192, 217-222) used the ionic liquid catalyst 1-butyl-3-methylimidazolium chloride / AlCl3 / EtAlCl2 to catalyze the reaction of 1-octene at 60 °C for 16 hours, with a total conversion rate of only 4%. By adding TiCl4 to the above catalytic system, the reaction time of 1-octene at 60 °C could be shortened to 4 hours, and the product with a molecular weight of Mn = 890 g / mol was obtained with a reaction yield of 72%.

[0006] CN102776023B describes an ionic liquid catalyst prepared using triethylamine hydrochloride / AlCl3 (molar ratio 1:2.5). 1-Decanene (10% wt of 1-decene) was added to this catalyst at 20°C, and the reaction was carried out for 2 hours. After post-treatment and hydrogenation, a kinematic viscosity of 63 mmHg at 100°C was obtained. 2 With PAO having a viscosity index of 163, the reaction conversion rate was 95%. By increasing the reaction temperature to 100°C and increasing the catalyst dosage to 100% wt of 1-decene, the oligomerization reaction time could be shortened to 15 minutes, and the reaction conversion rate was 97%.

[0007] Current technologies suffer from problems such as high reaction temperature, low reaction conversion rate, long reaction time, and / or large catalyst dosage. Summary of the Invention

[0008] The inventors discovered the following problems in the prior art: (1) Polar ionic liquid catalysts form a heterogeneous reaction with non-polar α-olefin monomers, which leads to insufficient contact between the catalyst and the monomer and a relatively long reaction time (usually more than 1 hour), which is not conducive to industrial scale-up production. (2) The reaction time can be reduced by increasing the reaction temperature or the amount of catalyst, but this often requires higher energy consumption and catalyst costs. The above reasons have inhibited the industrial application of ionic liquid catalysts for catalyzing α-olefins.

[0009] To address the aforementioned technical problems, this invention proposes a novel ionic liquid catalyst. This catalyst, at room temperature, significantly reduces the amount of catalyst required and achieves high conversion rates in a short time. For example, the amount of catalyst required is only 3.8% of the molar amount of α-olefin, and oligomer products can be obtained in 10 minutes of reaction, with a conversion rate of up to 91%.

[0010] The ionic liquid provided by this invention has a structure as shown in Formula I:

[0011] Among them, R1, R2, and R3 may be the same or different, and are independently selected from C. 1~20 Alkyl, C 6~40 Aryl; Mt is a metallic or metalloid element in Lewis acids, such as aluminum, boron, tin, iron, copper, titanium, zirconium, antimony, zinc, gallium, lanthanum, potassium, lithium, nickel, cobalt, or manganese. Y and X may be the same or different, and are selected from halogen elements; m is a number between 0.5 and 2.5, for example, m is 1, 1.5 or 2; n is equal to the valence state of Mt, for example, n is 1, 2, 3 or 4; 0≤k≤m×n.

[0012] According to an embodiment of the present invention, R1, R2, and R3 are independently selected from C. 1~10 Alkyl, C 6~20 Aryl; furthermore, R1, R2, and R3 are independently selected from C 1~6 Alkyl (C 1~4 Alkyl), C 6~12 Aryl.

[0013] According to an embodiment of the present invention, R1 and R2 are the same; preferably, R1 and R2 are selected from C. 1~4 Alkyl groups, such as methyl, ethyl, propyl, isopropyl, and butyl.

[0014] According to an embodiment of the present invention, Y and X are independently selected from fluorine, chlorine, bromine, and iodine.

[0015] According to some embodiments of the present invention, k=0.

[0016] According to some embodiments of the present invention, Mt is Al.

[0017] According to some embodiments of the present invention, the ionic liquid is .

[0018] According to an embodiment of the present invention, the ionic liquid is an olefin oligomerization catalyst; Furthermore, the olefin feedstock can be one or more straight-chain or branched C2~C3 structures. 20 Terminal olefins or straight-chain or branched C4~C 20 The internal olefins.

[0019] According to an embodiment of the present invention, the ionic liquid is an α-olefin oligomerization catalyst; Furthermore, the α-olefin is C4~C 20 Terminal olefins, including but not limited to straight-chain and branched C4~C 20 Terminal olefins, such as 1 Butene, 1-pentene, 1 Hexene, 1-Heptene, 1 Octene, 1-nonene, 1 decene, 1-undecene, 1 Dodecene, 1-Tridecene, 1 Tetradecene, 1-Pentadecene, 1 Hexadecene, 1-Heptadecanene, 1 One or more of octadecene.

[0020] The present invention also provides a method for preparing the above-mentioned ionic liquid, comprising the following steps: (1) Compound A reacts with compound B to produce compound C; Compound A: Compound B: Compound C: ; (2) MtY with substituted or unsubstituted R3 of compound C n The reaction produces the ionic liquid. R1, R2, R3, Mt, X, Y, and n all have the constraints shown above.

[0021] According to an embodiment of the present invention, MtY n The molar ratio of compound C to compound C is m, where m is a number ranging from 0.5 to 2.5.

[0022] According to an embodiment of the present invention, MtY n It is a Lewis acid, a halometallic salt, selected from one or more of aluminum trichloride, aluminum tribromide, boron trichloride, boron trifluoride, tin chloride, ferric chloride, copper chloride, cuprous chloride, titanium tetrachloride, titanium tetrabromide, zirconium tetrachloride, antimony chloride, zinc chloride, gallium chloride, and various halides of lanthanum, potassium, lithium, nickel, cobalt, manganese and other metals.

[0023] According to an embodiment of the present invention, step (1) is carried out in diethyl ether.

[0024] According to some embodiments of the present invention, the preparation route of the ionic liquid is as follows: .

[0025] The present invention also provides the application of the above-described ionic liquid as a catalyst in olefin oligomerization, preferably α-olefin oligomerization. The present invention also provides a method for olefin oligomerization, preferably α-olefin oligomerization, comprising using the above-described ionic liquid as a catalyst; According to an embodiment of the present invention, the olefin feedstock for olefin oligomerization has the limitations shown above.

[0026] According to an embodiment of the present invention, the α-olefin has the limitations shown above.

[0027] According to an embodiment of the present invention, the α-olefin is C8~C6. 12 When α-olefins are involved, poly-α-olefin base oil (PAO) is prepared.

[0028] According to an embodiment of the present invention, the amount of the ionic liquid is 0.3 to 30% of the molar amount of the olefin raw material or α-olefin, preferably 0.5 to 5%, for example 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 20% or 30%.

[0029] According to an embodiment of the present invention, the temperature of the olefin oligomerization reaction is -10°C to 160°C, for example 0°C to 40°C, preferably room temperature.

[0030] According to an embodiment of the present invention, the olefin oligomerization reaction has a conversion rate of >90% within 10 min.

[0031] Beneficial effects Existing technologies often improve the conversion rate of olefin oligomerization by increasing temperature, catalyst concentration, or extending reaction time. This patent, however, uses a novel ionic liquid with the structure shown in Formula I as a catalyst, achieving a conversion rate of over 90% within a 10-minute reaction time. This significantly improves the time-dependent operating efficiency of industrial α-olefin oligomerization reactors catalyzed by ionic liquid catalysts.

[0032] Terminology Definitions and Explanations The numerical ranges described in this application specification and claims, when the numerical range can only be "integers", should be understood to include the two endpoints of the range and every integer within the range. For example, "1-4" should be understood to include every integer of 1, 2, 3, or 4.

[0033] C 1~20 Alkyl group: understood as a straight or branched saturated monovalent hydrocarbon group having 1 to 20 carbon atoms, preferably C. 1~10Alkyl groups are saturated monovalent hydrocarbon groups that have 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 carbon atoms, either linear or branched. Examples include methyl, ethyl, propyl, butyl, pentyl, hexyl, isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, 2-methylbutyl, 1-methylbutyl, 1-ethylpropyl, 1,2-dimethylpropyl, neopentyl, 1,1-dimethylpropyl, 4-methylpentyl, 3-methylpentyl, 2-methylpentyl, 1-methylpentyl, 2-ethylbutyl, 1-ethylbutyl, 3,3-dimethylbutyl, 2,2-dimethylbutyl, 1,1-dimethylbutyl, 2,3-dimethylbutyl, 1,3-dimethylbutyl, or 1,2-dimethylbutyl, or their isomers.

[0034] C 6~40 Aryl: understood as an aryl group having 6 to 40 carbon atoms, such as phenyl, naphthyl, anthracene, phenanthryl, pyrene, pentabenzophenanthryl, diphenylpyrene or their isomers.

[0035] C2~C of straight or branched chain structure 20 Terminal olefins: understood as α-olefins with 2 to 20 carbon atoms having a straight or branched chain structure, including straight or branched C2, C3, C4, C5, C6, C7, C8, C9, C6, C7, C8, C9, C9, C16, C16, C17, C18, C19, C16, C18, C19 ... 10 C 11 C 12 C 13 C 14 C 15 C 16 C 17 C 18 C 19 C 20 Terminal olefins. Examples include ethylene, propylene, 1-butene, isobutene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 2-ethyl-1-butene, 2,3-dimethyl-1-butene, 1-heptene, 2-methyl-1-hexene, 2,3-dimethyl-1-pentene, 2,3,3-trimethyl-1-butene, 1-octene, 2-methyl-1-heptene, 2,3-dimethyl-1-hexene, 2,3,3-trimethyl-1-pentene, 1-nonene, 1-decene, 2,4,4,6-tetramethyl-1-heptene, etc.

[0036] C4~C of straight or branched chain structure 20 Internal alkenes: understood as internal alkenes with 4 to 20 carbon atoms having a straight-chain or branched structure, including straight-chain or branched C4, C5, C6, C7, C8, C9, and C6 atoms. 10 C 11 C 12 C13 C 14 C 15 C 16 C 17 C 18 C 19 C 20 Inner alkenes. For example, 2-butene, 2-pentene, 2-methyl-2-butene, 2-hexene, 3-hexene, 2-methyl-2-pentene, 3-methyl-2-pentene, 2,3-dimethyl-2-butene, 2-heptene, 3-heptene, 2-methyl-2-hexene, 3-methyl-3-hexene, 2,3-dimethyl-2-pentene, 2-octene, 2,3-dimethyl-2-hexene, 2,3,4-trimethyl-2-pentene, etc. Detailed Implementation

[0037] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0038] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0039] Example 1 Preparation of N,N-dimethylmethyleneammonium chloroaluminate ionic liquid: Under nitrogen protection, N,N,N',N,'-tetramethylmethylenediamine (5.12 g, 50.11 mmol) and 10 mL of diethyl ether solvent were added to a 100 mL reaction tube containing a magnetic rotor. The reaction tube was placed in a cold trap at 0 °C. Acetyl chloride (4.75 g, 60.51 mmol) was premixed with 10 mL of diethyl ether and then added dropwise to the reaction tube. After stirring for 30 min, the temperature of the reaction tube was raised to room temperature, and stirring was continued for 160 min. The resulting product was washed with diethyl ether solution and then dried under vacuum to obtain 4.45 g of N,N-dimethylmethylene ammonium chloride, with a yield of 95%. The N,N-dimethylmethylene ammonium chloride... 1 H NMR (500 MHz, DMSO-d6) d 8.18 (s, 2H), 3.67 (s, 6H).

[0040] Under nitrogen protection and at room temperature, N,N-dimethylmethylene ammonium chloride (4.31 g, 46.01 mmol) was added to a 100 mL reaction tube containing a magnetic rotor. Then, AlCl3 (12.58 g, 94.35 mmol) solid powder was added part by part. After stirring for 5 h, liquid N,N-dimethylmethylene ammonium chloroaluminate ionic liquid was obtained, the structure of which is shown in the figure below: .

[0041] Example 2 N,N-dimethylmethyleneammonium chloroaluminate ionic liquid-catalyzed oligomerization of 1-decene: Under nitrogen protection and at room temperature, 29.62 g (211.16 mmol) of 1-decene was added to a 100 mL reaction tube containing a magnetic rotor. Then, the N,N-dimethylmethyleneammonium chloroaluminate ionic liquid catalyst (2.86 g, 7.94 mmol, approximately 3.8% of the molar amount of 1-decene) prepared in Example 1 was added dropwise to the reaction tube, and the mixture was stirred (350 rpm). At 10, 30, and 60 min of reaction time, 5 mL of the reaction liquid was taken, quenched with a 10% NaOH aqueous solution, washed with water, centrifuged, and the resulting organic product was dried over anhydrous Na₂SO₄. The product was analyzed by gel permeation chromatography (GPC) to obtain the polymerization conversion rate, molecular weight of the polymerized product, and molecular weight distribution (data shown in Table 1).

[0042] To compare the performance of the patented ionic liquid catalyst in catalyzing the polymerization of 1-decene with that of conventional ionic liquid catalysts under the same experimental conditions, the corresponding conventional catalysts, including trimethylammonium chloroaluminate ionic liquid and triethylammonium chloroaluminate ionic liquid, were synthesized in Comparative Examples 1 and 2, respectively.

[0043] Comparative Example 1 (1) Preparation of trimethylammonium chloroaluminate ionic liquid: Under nitrogen protection and at room temperature, trimethylamine hydrochloride (17.91 g, 187.40 mmol) and AlCl3 (50.10 g, 375.73 mmol) were added alternately and sequentially to a 100 mL reaction tube containing a magnetic rotor. After stirring for 5 h, a liquid trimethylammonium chloroaluminate ionic liquid was obtained, the structure of which is shown in the figure below: .

[0044] (2) Trimethylammonium chloroaluminate ionic liquid-catalyzed oligomerization of 1-decene: Under nitrogen protection and at room temperature, 29.60 g (211.02 mmol) of 1-decene was added to a 100 mL reaction tube containing a magnetic rotor. Then, 2.98 g (8.22 mmol, approximately 3.9% of the molar amount of 1-decene) of trimethylammonium chloroaluminate ionic liquid catalyst was added dropwise to the reaction tube, and the mixture was stirred (350 rpm). At 10, 30, and 60 min of reaction time, 5 mL of the reaction liquid was taken, quenched with a 10% NaOH aqueous solution, washed with water, centrifuged, and the resulting organic product was dried over anhydrous Na₂SO₄. The product was analyzed by gel permeation chromatography (GPC) to obtain the polymerization conversion rate, molecular weight of the polymerized product, and molecular weight distribution (data shown in Table 1).

[0045] Comparative Example 2 (1) Preparation of triethylammonium chloroaluminate ionic liquid: Under nitrogen protection and at room temperature, triethylamine hydrochloride (10.32 g, 74.97 mmol) and AlCl3 (20.13 g, 150.97 mmol) were added alternately and sequentially to a 100 mL reaction tube containing a magnetic rotor. After stirring for 5 h, a liquid triethylammonium chloroaluminate ionic liquid was obtained, the structure of which is shown in the figure below: .

[0046] (2) Triethylammonium chloroaluminate ionic liquid-catalyzed oligomerization of 1-decene: Under nitrogen protection and at room temperature, 29.60 g (211.02 mmol) of 1-decene was added to a 100 mL reaction tube containing a magnetic rotor. Then, 2.98 g (8.22 mmol, 3.9% of the molar amount of 1-decene) of triethylammonium chloroaluminate ionic liquid catalyst was added dropwise to the reaction tube, and the mixture was stirred (350 rpm). At 10, 30, and 60 min of reaction time, 5 mL of the reaction liquid was taken, quenched with a 10% NaOH aqueous solution, washed with water, centrifuged, and the resulting organic product was dried over anhydrous Na₂SO₄. The product was analyzed by gel permeation chromatography (GPC) to obtain the polymerization conversion rate, molecular weight of the polymerized product, and molecular weight distribution (data shown in Table 1).

[0047] Table 1 shows the molecular weight, molecular weight distribution, and mass content of the products obtained by catalyzing the oligomerization of 1-decene under the same reaction conditions using various ionic liquid catalysts at 10, 30, and 60 min, as determined by GPC analysis.

[0048] Table 1

[0049] As shown in Table 1, under the same reaction conditions, the content (also equal to the polymerization conversion rate) of the polymerized product obtained by the N,N-dimethylmethyleneammonium chloroaluminate ionic liquid used in Example 2 at 10, 30, and 60 min was greater than that of the traditional ionic liquid catalysts trimethylammonium chloroaluminate ionic liquid (Comparative Example 1) and triethylammonium chloroaluminate ionic liquid (Comparative Example 2). Furthermore, for the polymerization reaction of 1-decene catalyzed by N,N-dimethylmethyleneammonium chloroaluminate ionic liquid (Example 2), the polymerization conversion rate reached 91.4% after 10 min of reaction. In addition, the molecular weight of the polymerized product of 1-decene catalyzed by N,N-dimethylmethyleneammonium chloroaluminate ionic liquid was lower than that of the other two ionic liquids. This phenomenon may be due to its rapid polymerization reaction, which generates a large amount of heat during the reaction, causing the temperature of the reaction system to rise. The increased temperature inhibits the chain growth process in the polymerization reaction, so it can be observed that the molecular weight of the polymerized product obtained by N,N-dimethylmethyleneammonium chloroaluminate ionic liquid is lower than that of the corresponding trimethylammonium chloroaluminate and triethylammonium chloroaluminate ionic liquids. The molecular weight of the polymerized product can be controlled by controlling the reaction temperature.

[0050] Furthermore, the N,N-dimethylmethylene ammonium chloroaluminate ionic liquid catalyst exhibits good polymerization conversion rates for various α-olefin monomers, as shown in Examples 2, 3, 4 and Table 2. Under the same reaction conditions, using 1-decene, 1-hexene, and 1-tetradecene as monomers, the polymerization conversion rates after 10 min of reaction with the N,N-dimethylmethylene ammonium chloroaluminate ionic liquid catalyst were all greater than 90%, demonstrating the broad applicability of the N,N-dimethylmethylene ammonium chloroaluminate ionic liquid to the polymerization reactions of various olefin feedstocks.

[0051] Example 3 N,N-dimethylmethyleneammonium chloroaluminate ionic liquid-catalyzed oligomerization of 1-hexene: Under nitrogen protection and at room temperature, 17.78 g (211.26 mmol) of 1-hexene was added to a 100 mL reaction tube containing a magnetic rotor. Then, 2.97 g (8.24 mmol, approximately 3.9% of the molar amount of 1-hexene) of N,N-dimethylmethylene ammonium chloroaluminate ionic liquid catalyst prepared in Example 1 was added dropwise to the reaction tube, and the mixture was stirred (350 rpm). At 10, 30, and 60 min of reaction time, 5 mL of the reaction liquid was taken, quenched with a 10% NaOH aqueous solution, washed with water, centrifuged, and the resulting organic product was dried over anhydrous Na₂SO₄. The product was analyzed by gel permeation chromatography (GPC) to obtain the polymerization conversion rate, molecular weight of the polymerized product, and molecular weight distribution (data shown in Table 2).

[0052] Example 4 The oligomerization of 1-tetradecene catalyzed by N,N-dimethylmethyleneammonium chloroaluminate ionic liquid: Under nitrogen protection and at room temperature, 41.25 g (210.06 mmol) of 1-tetradecene was added to a 100 mL reaction tube containing a magnetic rotor. Then, 2.96 g (8.22 mmol, approximately 3.9% of the molar amount of 1-tetradecene) of the N,N-dimethylmethylene ammonium chloroaluminate ionic liquid catalyst prepared in Example 1 was added dropwise to the reaction tube, and the mixture was stirred (350 rpm). At 10, 30, and 60 min of reaction time, 5 mL of the reaction liquid was taken, quenched with a 10% NaOH aqueous solution, washed with water, centrifuged, and the resulting organic product was dried over anhydrous Na₂SO₄. The product was analyzed by gel permeation chromatography (GPC) to obtain the polymerization conversion rate, molecular weight of the polymerized product, and molecular weight distribution (data shown in Table 2).

[0053] Table 2 shows the molecular weight, molecular weight distribution, and mass content of the products obtained by catalyzing the oligomerization of 1-decene, 1-hexene, and 1-tetradecene with N,N-dimethylmethyleneammonium chloroaluminate ionic liquid at 10, 30, and 60 min, respectively, under the same reaction conditions.

[0054] Table 2

[0055] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An ionic liquid, characterized in that, The ionic liquid has a structure as shown in Formula I: Formula I Among them, R1, R2, and R3 may be the same or different, and are independently selected from C. 1~20 Alkyl, C 6~40 Aryl; Mt is a metallic element and / or metalloid element in Lewis acids, selected from one or more of aluminum, boron, tin, iron, copper, titanium, zirconium, antimony, zinc, gallium, lanthanum, potassium, lithium, nickel, cobalt and manganese; Y and X may be the same or different, and are selected from halogen elements; m is a number between 0.5 and 2.5; n equals the valence state of Mt; 0≤k≤m×n.

2. The ionic liquid according to claim 1, characterized in that, n is a number selected from 1 to 4.

3. The ionic liquid according to claim 1, characterized in that, R1, R2, and R3 are independently selected from C 1~10 Alkyl, C 6~20 Aryl; preferably, R1, R2, and R3 are independently selected from C 1~6 Alkyl (C 1~4 Alkyl), C 6~12 Aryl.

4. The ionic liquid according to claim 1, characterized in that, R1 and R2 are the same, and R1 and R2 are selected from C. 1~4 alkyl.

5. The ionic liquid according to claim 1, characterized in that, k=0, and / or, Mt is Al.

6. The ionic liquid according to claim 1, characterized in that, The ionic liquid is .

7. The method for preparing the ionic liquid according to any one of claims 1 to 6, characterized in that, The preparation method includes the following steps: (1) Compound A reacts with compound B to produce compound C; Compound A: Compound B: Compound C: ; (2) MtY with substituted or unsubstituted R3 of compound C n The reaction produces the ionic liquid. Preferably, MtY n It is a Lewis acid, a halometallic salt, selected from one or more of aluminum trichloride, aluminum tribromide, boron trichloride, boron trifluoride, tin chloride, ferric chloride, copper chloride, cuprous chloride, titanium tetrachloride, titanium tetrabromide, zirconium tetrachloride, antimony chloride, zinc chloride, gallium chloride, and various halides of lanthanum, potassium, lithium, nickel, cobalt, manganese and other metals.

8. An olefin oligomerization catalyst, characterized in that, The catalyst comprises the ionic liquid according to any one of claims 1 to 7; Preferably, the olefin feedstock is selected from C2-C66 chains with straight or branched structures. 20 Terminal olefins or straight-chain or branched C4~C 20 Internal olefins.

9. A method for olefin oligomerization, characterized in that, The olefin oligomerization catalyst used comprises the ionic liquid according to any one of claims 1 to 7; Preferably, the olefin feedstock is selected from C2-C66 chains with straight or branched structures. 20 Terminal olefins or straight-chain or branched C4~C 20 Internal olefins, preferably straight-chain or branched C2~C... 20 Terminal olefins.

10. The olefin oligomerization method according to claim 9, characterized in that, The amount of the ionic liquid used accounts for 0.3% to 30% of the molar amount of the olefin feedstock; And / or, the temperature for olefin oligomerization is -10℃ to 160℃.

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