A process for the preparation of a nickel-based catalyst for the polymerization of olefins

Abstract

The application discloses a preparation method of a nickel catalyst for olefin polymerization, and comprises the following steps: (1) reacting acenaphthenequinone, a water-removing agent and a substituted aniline in a first solvent under the action of a catalyst; after the reaction is completed, cooling, filtering and concentration crystallization are performed to obtain a diimine ligand; and (2) reacting the diimine ligand and a nickel salt in a second solvent; after the reaction is completed, concentration crystallization, filtering and washing are performed to obtain the nickel catalyst. The application effectively solves the problems of poor selectivity, low yield and complex post-treatment in the preparation process of the nickel catalyst, and has the advantages of a short process flow, high yield and simple post-treatment.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and more specifically to a method for preparing a nickel-based catalyst for olefin polymerization. Background Technology

[0002] With the development of research and application of olefin resin materials, they have gradually become essential materials for people's daily life and industrial and agricultural production, and have also become indispensable materials in cutting-edge technology, national defense construction and other fields. Among them, polyethylene (PE) materials have the characteristics of good chemical resistance, low price, simple preparation, low density and good mechanical properties.

[0003] Currently, polyolefin elastomers are mainly obtained by copolymerizing ethylene and α-olefins using metallocene catalysts. However, metallocene catalysts suffer from drawbacks such as difficult synthesis, low yield, large co-catalyst consumption, and high cost. Nickel-based catalysts, especially nickel diimine complex catalysts, can generate highly branched, high-molecular-weight polyethylene from a single ethylene monomer. Asymmetric nickel diimine complex catalysts, in particular, exhibit high catalytic activity, moderate polymer branching, and adjustable branch ratios of different lengths, making them crucial for polyethylene elastomer preparation. This work is considered a significant milestone in post-transition metal-catalyzed ethylene polymerization research. The resulting polyethylene elastomer products have performance properties comparable to some commercially available POE thermoplastic elastomer products and can replace them in the preparation of encapsulating films for photovoltaic modules, demonstrating significant commercial application value.

[0004] The key to preparing nickel-based olefin polymerization catalysts lies in the synthesis of the diimine ligand, and the synthesis of imines using weak acids as catalysts is the most classic method. Brookhart's research group initially used this method to synthesize N-aryl α-diimine ligands. For structures with relatively small steric hindrance, good yields can be obtained using acid catalysts. For example, in 2011, Yuan Jianchao's research group synthesized chlorinated tetrasubstituted-N-aryl-α-diimine ligands using formic acid as a catalyst, with yields of 88–92% (J. Organomet. Chem. 2011, 696, 3251); in 2013, Yuan Jianchao's research group synthesized highly active o-phenyl-substituted acenaphthene-skeletal α-diimine ligands with yields of 62–67% (J. Mol. Catal. A Chem. 2013, 370, 132); and in 2014, Chen Changle's research group synthesized a class of large conjugated skeleton diimine ligands using acetic acid as a catalyst, with a yield of approximately 70% (Dalton). Trans., 2014, 43, 2900); In 2019, Li Yougui's research group synthesized para-aryl-substituted α-diimine ligands using formic acid as a catalyst, with a yield of about 70% (CN109762027A). For ligands with large steric hindrance, the yields are low. For example, in 2015, Sun Wenhua's research group synthesized a series of asymmetric α-diimine nickel complexes containing bis(4-fluorophenyl)methyl-substituted acenaphthene skeletons, with ligand yields ranging from 35% to 39% (Dalton Trans., 2015, 44, 12282); in 2015, Gao Menglong's research group synthesized symmetric α-diimine ligands using formic acid as a catalyst, but with large steric hindrance, the yields were only 7% to 13% (CN104628596A); in 2022, Sun Wenhua's research group synthesized camphene-substituted α-diimine nickel complexes, with ligand yields ranging from 11% to 38%, and the yields decreased with increasing substituent steric hindrance (Appl Oranomet Chem. 2022, 36, 6606).

[0005] Starting from ketones and amines, imine compounds can be synthesized through condensation reactions and the removal of one water molecule. This reaction is reversible, which is the main reason for the low yield of diimine ligands, especially those containing highly sterically hindered substituents. Amines with highly sterically hindered substituents have significant steric hindrance, hindering the forward reaction. Simultaneously, diimines with highly sterically hindered substituents are unstable, and the generated water reacts with the diimine in the reverse reaction, leading to low yields. Furthermore, existing techniques suffer from numerous process steps and low post-processing efficiency.

[0006] For example, IR106828B discloses a process for preparing homogeneous α-diimine nickel catalysts with different ligands for ethylene polymerization. This invention proposes a novel method for synthesizing symmetrical α-diimine nickel catalysts with acenaphthene and 2,6-diisopropylaniline structural frameworks, as well as a highly active and acceptable ethylene polymerization process. The asymmetric complex is prepared using a novel method, with a structural framework of acenaphthenequinone, one side being 2,6-diisopropyl and the other side being 2,4,6-trimethylaniline groups.

[0007] For example, CN112538098A discloses an α-sulfonic acid-β-diimine nickel complex, its preparation method, and its application in catalytic olefin polymerization. The preparation method of the α-sulfonic acid-β-diimine nickel complex includes the following steps: (1) reacting substituted aniline and acetylacetone to obtain a β-diimine compound; (2) sulfonating the β-diimine compound with SO3.NMe3 to obtain an α-sulfonic acid-β-diimine lithium salt compound; (3) reacting the α-sulfonic acid-β-diimine lithium salt compound with a nickel salt to obtain the α-sulfonic acid-β-diimine nickel complex.

[0008] For example, CN108912009A discloses an asymmetric diimine nickel catalyst, its ligands, preparation method, and applications. The preparation method for the asymmetric diimine nickel catalyst is as follows: a diketone compound is reacted with two amine compounds of different structures and zinc halide in an organic acid solvent at 60-120℃ for 0.5-6 h to form an intermediate compound; then, at room temperature, the intermediate compound is reacted with an aqueous solution of a weak acid salt in an organic polar solvent for 0.2-5 h to form a ligand compound; finally, in an organic solvent at ambient temperature, the ligand compound is reacted with a nickel precursor compound of formula DMENiX2 to obtain the asymmetric diimine nickel catalyst, where DME represents ethylene glycol dimethyl ether. Summary of the Invention

[0009] To address the problems of existing technologies, such as the reversible reaction of amines with acenaphthoquinone to form imines, insufficient driving force for the forward reaction, low reaction yield, and cumbersome process, this invention provides a method for preparing a nickel-based catalyst for olefin polymerization with mild reaction conditions, simple post-processing, and high yield.

[0010] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: a method for preparing a nickel-based catalyst for olefin polymerization, comprising the following steps:

[0011] (1) Under the action of a catalyst, acenaphthene, dehydrating agent and substituted aniline are reacted in the first solvent. After the reaction is completed, the mixture is cooled, filtered, concentrated and crystallized to obtain the diimine ligand.

[0012] (2) The above-mentioned diimine ligand was reacted with nickel salt in a second solvent. After the reaction was completed, the mixture was concentrated and crystallized, filtered, and washed to obtain a nickel-based catalyst.

[0013] In a preferred embodiment of the present invention, the substituted aniline has the following general formula:

[0014]

[0015] Among them, R1, R2, R3, R4, and R5 can be the same or different, and each can be independently selected from H, F, Cl, Br, I, NO2, alkyl or alkoxy groups with 1-6 carbon atoms, benzyl, and diphenylmethyl.

[0016] In a preferred embodiment of the present invention, the substituted aniline is at least one of 2-di(p-chlorophenyl)methyl-4,6-dimethylaniline, 3,4,5-trimethylaniline, and 2-naphthylamine.

[0017] In a preferred embodiment of the present invention, the dehydrating agent is at least one of molecular sieve, trimethyl orthoacetate, acetal, and ketal.

[0018] In a preferred embodiment of the present invention, the catalyst is at least one of formic acid, acetic acid, p-toluenesulfonic acid, and zinc chloride.

[0019] In a preferred embodiment of the present invention, the first solvent and the second solvent are both at least one of dichloromethane, dichloroethane, methanol, ethanol, and diethylene glycol dimethyl ether.

[0020] In a preferred embodiment of the present invention, the nickel salt is at least one of nickel bromide, nickel chloride, nickel bromide of ethylene glycol dimethyl ether, nickel chloride of diethanol dimethyl ether, and nickel bromide of diethylene glycol dimethyl ether.

[0021] In a preferred embodiment of the present invention, the molar ratio of acenaphthoquinone, substituted aniline, and catalyst is 1:1.5-2.5:0.1-10, the mass ratio of acenaphthoquinone to dehydrating agent is 1:0.5-2.0, and the amount of the first solvent is 5-70 times the mass of acenaphthoquinone.

[0022] In a preferred embodiment of the present invention, the molar ratio of the diimine ligand to the nickel salt is 1:0.9 to 1.3, and the amount of the second solvent is 5 to 40 times the mass of the diimine ligand.

[0023] In a preferred embodiment of the present invention, the reaction temperature in step (1) is 20-150°C and the reaction time is 5-20h; the reaction temperature in step (2) is 20-60°C and the reaction time is 4-24h.

[0024] This invention removes water generated during the reaction by adding a dehydrating agent to the system and optimizing the synthesis process, thus promoting the reaction to proceed in the forward direction to generate the target diimine ligand. The diimine ligand then reacts with nickel salt to generate a nickel-based catalyst. By timely removing water generated in the synthesis reaction, the equilibrium can be effectively pushed towards the forward reaction, improving the reaction conversion rate and yield.

[0025] The dehydrating agent in this invention can be a chemical dehydrating agent, a physical dehydrating agent, or a mixture thereof. The chemical dehydrating agent can be an orthoester, acetal, ketal, etc. Specifically, the orthoester includes trimethyl orthoformate, triethyl orthoformate, trimethyl orthoacetate, triethyl orthoacetate, etc., preferably trimethyl orthoacetate or triethyl orthoacetate, more preferably trimethyl orthoacetate; the acetal includes methyl acetal, acetal, diethoxymethane, 1,3-dioxane, etc., preferably methyl acetal; the ketal includes acetone dimethyl acetal, acetone diethanol, butanone dimethyl acetal, etc.; the physical dehydrating agent includes molecular sieves, anhydrous sodium sulfate, anhydrous magnesium sulfate, silica gel, color-changing silica gel, calcium chloride, etc., preferably molecular sieves. The chemical dehydrating agent selected in this invention differs from conventional dehydrating agents such as acetic anhydride and thionyl chloride. Conventional dehydrating agents such as acetic anhydride and thionyl chloride are unsuitable for this reaction because they easily replace aniline in the reaction. The advantages of the chemical dehydrating agent used in this invention are that the dehydration process is irreversible, the reaction is complete, and the products of the chemical dehydrating agent's reaction with water, such as alcohols, ketones, aldehydes, and esters, have low boiling points and can be easily separated from the products.

[0026] In this invention, the first solvent and the second solvent can be alkanes, alkylbenzenes, ethers, esters, alcohols, haloalkanes, nitriles, etc., with 5-10 carbon atoms, specifically pentane, hexane, cyclohexane, heptane, octane, dichloromethane, chloroform, dichloroethane, trichloroethane, benzene, toluene, xylene, diethyl ether, methyl tert-butyl ether, tetrahydrofuran, methyltetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, methanol, ethanol, propanol, butanol, cyclohexanol, ethyl acetate, butyl acetate, acetonitrile, propionitrile, benzonitrile, etc. The first solvent and the second solvent are preferably at least one selected from dichloromethane, dichloroethane, methanol, ethanol, and diethylene glycol dimethyl ether.

[0027] In this invention, the catalyst can be a protic acid, a Lewis acid, or an acid salt. Specifically, the protic acid can be sulfuric acid, hydrogen chloride, hydrogen bromide, formic acid, acetic acid, trifluoroacetic acid, difluoroacetic acid, oxalic acid, benzenesulfonic acid, or p-toluenesulfonic acid; the acid salt can be potassium hydrogen sulfate or sodium hydrogen sulfate; and the Lewis acid can be ferric chloride, zinc chloride, titanium tetrachloride, aluminum trichloride, boron trifluoride, etc. The catalyst is preferably at least one selected from formic acid, acetic acid, p-toluenesulfonic acid, and zinc chloride.

[0028] In this invention, if the mass ratio of the dehydrating agent to acenaphthoquinone is too small, dehydration will be incomplete, resulting in reduced reaction selectivity and low yield. If the mass ratio is too large, the reaction will be complete, leading to a high yield, but it will be uneconomical. If the molar ratio of substituted aniline to acenaphthoquinone is too small, the acenaphthoquinone reaction will be incomplete, resulting in low conversion. If the molar ratio is too large, the acenaphthoquinone reaction will be complete, leading to a high yield, but when using two substituted anilines with different structures, i.e., in the preparation of asymmetric diimine, a large molar ratio of substituted anilines will lead to an increase in symmetric diimine byproducts and a decrease in the selectivity of the target product. When the catalyst is a weak acid such as acetic acid or oxalic acid, the amount of catalyst can be appropriately increased. In summary, the preferred molar ratio of acenaphthoquinone, substituted aniline, and catalyst is 1:1.5–2.5:0.1–10, and the preferred mass ratio of acenaphthoquinone to the dehydrating agent is 1:0.5–2.0. A large amount of the first solvent results in good raw material solubility and a fast reaction rate, but excessive use is uneconomical. The preferred amount of the first solvent is 5 to 70 times the mass of acenaphthoquinone, and more preferably 20 to 55 times the mass of acenaphthoquinone.

[0029] In this invention, the higher the temperature at which the diimine ligand is synthesized, the faster the reaction rate. However, excessively high temperatures can lead to an increase in side reactions and a decrease in reaction selectivity. Aniline with a lower molecular weight also requires a lower reaction temperature. Therefore, the reaction temperature in step (1) is preferably 20–150°C, and the reaction time is preferably 5–20 h.

[0030] In this invention, the nickel salt can be nickel bromide, nickel chloride, or their alcohol or ether complexes, specifically nickel bromide with ethylene glycol dimethyl ether, nickel chloride with diethanol dimethyl ether, nickel bromide with diethylene glycol dimethyl ether, nickel chloride with diethylene glycol dimethyl ether, nickel bromide with diethylene glycol, etc. The nickel salt is preferably at least one selected from nickel bromide, nickel chloride, nickel bromide with ethylene glycol dimethyl ether, nickel chloride with diethanol dimethyl ether, and nickel bromide with diethylene glycol dimethyl ether. The molar ratio of the diimine ligand to the nickel salt is preferably 1:0.9 to 1.3, and the amount of the second solvent is preferably 5 to 40 times the mass of the diimine ligand.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. High reaction yield: This invention removes water generated during the reaction by adding a specific dehydrating agent to the reaction system and optimizing the synthesis process, thereby generating the target product diimine. This can effectively drive the equilibrium towards the forward reaction, improve reaction selectivity, reduce symmetric diimine byproducts, and increase reaction yield. It is especially suitable for the synthesis of sterically hindered asymmetric diimines, with asymmetric diimine ligand yield of over 60%.

[0033] 2. Simple operation: By adding a specific dehydrating agent to the reaction system and optimizing the synthesis process, the present invention can synthesize diimine ligands in one step in the same reactor, which significantly shortens the synthesis steps of diimine ligands and simplifies the operation.

[0034] 3. The post-processing is simple. The present invention can be purified by conventional crystallization and other methods in the field. The process is short, the post-processing is simple, and the product quality is good. Attached Figure Description

[0035] Figure 1 The NMR spectrum of the symmetrical diimine prepared in Example 1;

[0036] Figure 2 The NMR spectrum of the asymmetric diimine prepared in Example 2;

[0037] Figure 3 The NMR spectrum of the nickel diimine bromide complex prepared in Example 2;

[0038] Figure 4 The NMR spectrum of the asymmetric diimine prepared in Example 4 is shown. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0040] Example 1

[0041] (1) In a 250 ml four-necked flask equipped with a condenser, 7.1 g (22 mmol) of 2-di(p-chlorophenyl)methyl-4,6-dimethylaniline, 1.8 g (10 mmol) of acenaphthene, 0.36 g (2 mmol) of p-toluenesulfonic acid, 1.7 g of methyl acetal, and 100 g of dichloromethane were added. The mixture was stirred at 60 °C and 200 rpm for 8 h. After cooling, the mixture was filtered, dissolved, and 200 g of methanol was added. The mixture was then crystallized, filtered, and the filter cake was dried to obtain 7.2 g of a symmetrical diimine solid formed by the condensation of two molecules of 2-di(p-chlorophenyl)methyl-4,6-dimethylaniline with acenaphthene, with a yield of 84%.

[0042] (2) In a 250 ml four-necked flask, add the symmetrical diimine solid synthesized in step (1) (4.3 g, 5 mmol), 90 g of dichloroethane, 15 g of methanol, and 1.55 g of nickel bromide in ethylene glycol dimethyl ether (1.55 g, 5 mmol). Stir at 20 °C and 200 rpm for 20 h, concentrate under reduced pressure, add 100 g of diethyl ether, stir to crystallize, filter, wash the filter cake with diethyl ether, and obtain 4.9 g of nickel bromide diimine complex, with a yield of 91%.

[0043] Example 2

[0044] (1) In a 500ml four-necked flask equipped with a condenser, add acenaphthoquinone (3.6g, 20mmol), trimethyl orthoacetate (2.4g), p-toluenesulfonic acid (3.8g, 22mmol), 2-di(p-chlorophenyl)methyl-4,6-dimethylaniline (6.5g, 20mmol), and 100g methanol. Stir at 85℃ and 230rpm for 4h, concentrate to dryness, and add 100g diethylene glycol dimethyl ether and trimethyl orthoacetate (2.4g, 22mmol) to the residue. 4 g (20 mmol), 3,4,5-trimethylaniline (2.8 g, 21 mmol), and acetic acid (6 g, 100 mmol) were stirred at 150 °C and 230 rpm for 6 h, then cooled to room temperature, filtered, concentrated the filtrate, cooled, and crystallized to give 7.9 g of an asymmetric diimine solid formed by the condensation of one molecule of 2-di(p-chlorophenyl)methyl-4,6-dimethylaniline and one molecule of 3,4,5-trimethylaniline with acenaphthoquinone, with a yield of 62%.

[0045] (2) In a 250 ml four-necked flask, add the asymmetric diimine solid synthesized in step (1) (3.2 g, 5 mmol), 90 g of dichloroethane, 15 g of methanol, and 1.61 g of nickel bromide in ethylene glycol dimethyl ether (5.2 mmol). Stir at 28 °C and 230 rpm for 12 h, concentrate under reduced pressure, add 80 g of diethyl ether, stir to crystallize, filter, wash the filter cake with diethyl ether, and obtain 4.1 g of nickel bromide diimine complex, with a yield of 95%.

[0046] Example 3

[0047] (1) In a 250 ml four-necked flask equipped with a condenser, acenaphthoquinone (3.6 g, 20 mmol), molecular sieve (6.2 g), methanol (85 g), 3,4,5-trimethylaniline (6.8 g, 50 mmol), and formic acid (1.38 g, 30 mmol) were added. The mixture was stirred at 25 °C and 270 rpm for 6 h, filtered, concentrated, cooled, and crystallized to obtain 5.0 g of symmetrical diimine solid formed by the condensation of two molecules of 3,4,5-trimethylaniline with acenaphthoquinone, with a yield of 60%.

[0048] (2) In a 250 ml four-necked flask, add the symmetrical diimine solid synthesized in step (1) (2.1 g, 5 mmol), 50 g of dichloroethane, 5 g of methanol, and 1.71 g of nickel bromide in ethylene glycol dimethyl ether (1.71 g, 5.5 mmol). Stir at 40 °C and 270 rpm for 8 h, concentrate under reduced pressure, add 50 g of diethyl ether, stir to crystallize, filter, wash the filter cake with diethyl ether, and obtain 2.9 g of nickel bromide diimine complex, with a yield of 90%.

[0049] Example 4

[0050] (1) In a 250 ml four-necked flask equipped with a condenser, acenaphthene (3.6 g, 20 mmol), methanol 100 g, p-toluenesulfonic acid (3.8 g, 22 mmol), trimethyl orthoacetate 5.3 g, 2-di(p-chlorophenyl)methyl-4,6-dimethylaniline (6.5 g, 20 mmol), and ethanol 80 g were added. After stirring under reflux at 85 °C and 300 rpm for 4 h, 2-naphthylamine (2.9 g, 20 mmol) and zinc chloride (2.7 g, 20 mmol) were added. After stirring under reflux at 300 rpm for 12 h, the mixture was cooled to room temperature, filtered, concentrated, cooled, and crystallized to obtain 9.0 g of asymmetric diimine solid formed by the condensation of one molecule of 2-di(p-chlorophenyl)methyl-4,6-dimethylaniline and one molecule of 2-naphthylamine with acenaphthene, with a yield of 70%.

[0051] (2) In a 250 ml four-necked flask, add the asymmetric diimine solid synthesized in step (1) (3.2 g, 5 mmol), 80 g of dichloroethane, 10 g of methanol, and 1.86 g of nickel bromide in ethylene glycol dimethyl ether (6 mmol). Stir at 35 °C and 300 rpm for 15 h, concentrate under reduced pressure, add 80 g of diethyl ether, stir to crystallize, filter, wash the filter cake with diethyl ether, and obtain 4.1 g of nickel bromide diimine complex, with a yield of 95%.

Claims

1. A method for preparing a nickel-based catalyst for olefin polymerization, characterized in that, Includes the following steps: (1) Under the action of a catalyst, acenaphthoquinone, a dehydrating agent, and a substituted aniline are reacted in a first solvent. The dehydrating agent is at least one of molecular sieve, trimethyl orthoacetate, and acetal. The substituted aniline is at least one of 2-di(p-chlorophenyl)methyl-4,6-dimethylaniline, 3,4,5-trimethylaniline, and 2-naphthylamine. The molar ratio of acenaphthoquinone, substituted aniline, and catalyst is 1:1.5~2.5:0.1~10. The mass ratio of acenaphthoquinone to dehydrating agent is 1:0.5~2.

0. The amount of the first solvent is 5~70 times the mass of acenaphthoquinone. The reaction temperature is 20~150℃ and the reaction time is 5~20h. After the reaction is completed, the mixture is cooled, filtered, concentrated, and crystallized to obtain a diimine ligand. (2) The above-mentioned diimine ligand is reacted with nickel salt in a second solvent. The molar ratio of the diimine ligand to the nickel salt is 1:0.9~1.

3. The amount of the second solvent is 5~40 times the mass of the diimine ligand. The reaction temperature is 20~60℃ and the reaction time is 4~24h. After the reaction is completed, the solution is concentrated and crystallized, filtered, and washed to obtain the nickel catalyst.

2. The method for preparing the nickel-based catalyst for olefin polymerization according to claim 1, characterized in that, The catalyst is at least one of formic acid, acetic acid, p-toluenesulfonic acid, and zinc chloride.

3. The method for preparing the nickel-based catalyst for olefin polymerization according to claim 1, characterized in that, The first solvent and the second solvent are both at least one of dichloromethane, dichloroethane, methanol, ethanol, and diethylene glycol dimethyl ether.

4. The method for preparing the nickel-based catalyst for olefin polymerization according to claim 1, characterized in that, The nickel salt is at least one of nickel bromide, nickel chloride, nickel bromide with ethylene glycol dimethyl ether, nickel chloride with diethanol dimethyl ether, and nickel bromide with diethylene glycol dimethyl ether.

Images