A novel SiO2-supported nickel catalyst and its application in ethylene polymerization

Abstract

This invention relates to the field of olefin polymerization technology, and discloses a novel SiO2-supported nickel catalyst and its application in ethylene polymerization. The catalyst uses a nickel complex containing a pyridine imine structure as the active center, and forms a stable heterogeneous catalytic system through the interaction of anchoring groups with an activated SiO2 support. Compared with traditional homogeneous nickel catalysts, this SiO2-supported nickel catalyst exhibits higher catalytic activity and better thermal stability in ethylene homopolymerization and copolymerization reactions, and can maintain stable polymerization performance over a wide temperature range. At the same time, by designing the catalyst structure and controlling the loading method, the molecular weight, molecular weight distribution, and branching degree of the polymer can be effectively adjusted, thereby achieving controllable adjustment of the structure and properties of polyethylene.

Description

Technical Field

[0001] This invention relates to the field of olefin polymerization technology, specifically a novel SiO2-supported nickel catalyst and its application in ethylene polymerization. Background Technology

[0002] Polyethylene wax is a low molecular weight polyethylene material. With its strong wear resistance, excellent chemical stability, low melt viscosity, and wide or narrow molecular weight distribution, it can be used as a pigment dispersant, lubricant, and hot melt adhesive. It is widely used in inks and coatings, plastic processing and modification, and daily product manufacturing. At present, high-quality polyethylene wax still relies on imports, and it has great potential and broad prospects in the domestic market. High-end polyethylene wax is usually prepared by ethylene synthesis. Nickel catalysts based on pyridine have attracted widespread attention in ethylene oligomerization due to their relatively low cost, strong structural tunability, and certain tolerance to polar functional groups, making them a preferred catalyst for the industrial production of high-end polyethylene waxes. However, most existing nickel-based catalytic systems are still mainly homogeneous catalysts, which are prone to problems such as insufficient catalyst thermal stability, severe wall adhesion of the reaction system, and difficulty in controlling the morphology of the polymerization products during actual polymerization processes, thus limiting their application in high-temperature conditions and industrial continuous polymerization processes. To overcome these shortcomings, constructing heterogeneous catalytic systems by loading homogeneous catalysts onto solid supports has become an important research direction for improving the practical performance of nickel-based catalysts. Among numerous inorganic supports, SiO2 is widely used in the research of supporting polymerization catalysts due to its advantages such as large specific surface area, abundant surface hydroxyl groups, good chemical stability, and ease of surface modification. By immobilizing metal complexes on the SiO2 surface, not only can the thermal stability of the catalyst be improved to a certain extent, but the morphology of the polymer during polymerization can also be improved, reducing the risk of reactor contamination. In recent years, functional anchoring groups such as hydroxyl groups and metal alkoxides have been introduced into the structure of nickel complexes to enhance the interaction between the catalyst and the support, thereby improving the loading efficiency and catalytic stability. However, existing methods still have limitations, such as restrictions on the loading method, difficulty in balancing catalytic activity and stability, and insufficient ability to control the polymer structure. Summary of the Invention

[0003] The purpose of this invention is to provide a novel SiO2-supported nickel catalyst and its application in ethylene polymerization. By rationally designing the pyridineimide ligand structure and loading it onto the surface of an inorganic support, the stability and practical performance of the catalyst are improved, and the efficient preparation of polyethylene wax is achieved.

[0004] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a SiO2 supported nickel catalyst, comprising an active component and a support, wherein the active component is a pyridineimine nickel complex represented by the following general formula (I):

[0005] General Formula (I) In general formula (I), the anchoring group R is selected from one of -OH, -ONa, -SO3H, -SO3Na, -COOH, and -COONa; wherein the pyridineimine nickel complex is loaded onto the surface of the SiO2 support through the anchoring group.

[0006] A further provision of the present invention is that the anchoring group R is selected from one of -OH, -SO3H and -COOH.

[0007] A pyridineimine ligand for synthesizing the pyridineimine nickel catalyst of claim 1, the pyridineimine ligand having the structure shown in general formula (II):

[0008] General Formula (II) Among them, the ligand L-Na is derived from the reaction of ligand L through an equimolar amount of NaH.

[0009] A method for preparing a SiO2-supported nickel catalyst includes the following steps: (1) Activation treatment of SiO2 The SiO2 support was subjected to heat treatment under vacuum conditions to remove moisture and impurities from the support surface and activate the surface hydroxyl groups; specifically, the SiO2 was placed in a vacuum tube furnace and heated and activated at 300°C for 12 hours, and then cooled for later use. (2) Synthesis of nickel complexes Under anhydrous and oxygen-free conditions, (DME)NiBr2 is subjected to a coordination reaction with a pyridineimine ligand, wherein the pyridineimine ligand includes one of L1-L3; the reaction is carried out in dichloromethane (DCM) solvent, and the nickel precursor and ligand are stirred to fully react and generate a structurally stable nickel complex. (3) Loading of nickel complexes The nickel complex solution obtained in step (2) was mixed with the activated SiO2 support in step (1), and the mixture was stirred at room temperature for about 12 hours to load the nickel complex onto the SiO2 surface. After the reaction was completed, the mixture was filtered, the solid product was collected, and dried at room temperature to obtain the SiO2-supported nickel catalyst. (4) Characterization of catalysts The structure and morphology of the obtained SiO2-supported nickel catalyst were characterized. The structural information of the ligands and nickel complexes was analyzed by nuclear magnetic resonance (NMR). The crystal structure characteristics of the catalyst were analyzed by X-ray diffraction (XRD). The surface morphology and dispersion of the supported catalyst were observed by scanning electron microscopy (SEM) to confirm that the nickel complexes were successfully supported on the SiO2 support surface.

[0010] A further provision of the present invention is that the pyridineimine ligand is converted into its sodium salt form by NaH treatment.

[0011] An application of a SiO2-supported nickel catalyst in ethylene polymerization, the application being used to prepare polyethylene wax, the polymerization reaction being carried out in an organic solvent, with an ethylene pressure of 0.1-50 MPa, a reaction temperature of 0-200℃, and a reaction time of 0.05-8.00 h.

[0012] In summary, the present invention has the following beneficial effects: 1. This SiO2-supported nickel catalyst exhibits higher catalytic activity and better thermal stability in the homopolymerization and copolymerization of ethylene, and can maintain stable polymerization performance over a wide temperature range; 2. By designing the catalyst structure and controlling the loading method, the molecular weight, molecular weight distribution, and branching degree of the polymer can be effectively adjusted, thereby achieving controllable adjustment of the structure and properties of polyethylene. 3. Supported catalysts are beneficial for improving the morphology of polymerization products, reducing the risk of reactor wall adhesion during polymerization, and enhancing the operational stability and industrial applicability of the system, thus showing good application prospects. Attached Figure Description

[0013] Figure 1 The hydrogen NMR spectrum (400MHz, CDCl3) of substrate S1 of this invention. Figure 2 The hydrogen nuclear magnetic spectrum (400MHz, CDCl3) of A1 of this invention; Figure 3 The hydrogen NMR spectrum (400MHz, CDCl3) of the L1 ligand of this invention. Figure 4 The hydrogen NMR spectrum (400MHz, CDCl3) of the L2 ligand of this invention. Figure 5 This is the single-crystal diffraction pattern of Ni2 according to the present invention; Figure 6 This is a diagram illustrating the physical morphology of the polyethylene wax of this invention. Detailed Implementation

[0014] The present invention will be further described below with reference to the accompanying drawings in the embodiments of the present invention. Example

[0015]

[0016] A Schlenk flask containing 4-methoxyphenylboronic acid (11.40 g, 75.0 mmol), 2-acetyl-6-bromopyridine (10.00 g, 50.0 mmol), and K₂CO₃ (13.82 g, 100.0 mmol) was evacuated to negative pressure using a double-row tube and brought into a glove box. Pd(PPh₃)₄ (1.0 mmol) was added to the mixture. The Schlenk flask was then connected to the double-row tube, and under continuous N₂ bubbling, Tol (160 mL), ethanol (40 mL), and distilled water (40 mL) were added. The mixture was stirred at room temperature for 1 h, then heated to 95 °C and stirred for 24 h. Samples were taken using a long needle, and the reaction was observed by thin-layer chromatography (TLC). After the mixture cooled to room temperature, it was analyzed using DCM (100... Extracted three times with 1 mL of solvent, the organic layer was washed with saturated NaCl solution and dried with anhydrous MgSO4 for 2 h; the solvent was removed under reduced pressure to obtain the crude product, which was purified by column chromatography (EA / PE=1 / 10); dried at 35 °C for 5 h to obtain substrate S1 as a white solid.

[0017] 1 H NMR (400 MHz, CDCl3): δ 8.13-8.01 (m, 2H), 7.93-9.87 (m, 1H), 7.86-7.79 (m, 2H), 7.08-6.96 (m, 2H), 3.88 (s, 3H), 2.81 (s, 3H).

[0018]

[0019] The main raw materials are Al and S1, which yield a white solid L1.

[0020] 1 H NMR (400 MHz, CDCl3): δ 8.06-7.99 (m, 3H), 7.81-7.74 (m, 2H), 7.27-7.11 (m, 20H), 7.06-6.92 (m , 15H), 6.71 (s, 2H), 5.36 (s, 1H), 5.34 (s, 2H), 3.90 (s, 3H), 1.19 (s, 3H).

[0021] Example 2:

[0022] A 500 mL Schlenk flask was connected to a double-row tube. Under continuous N2 bubbling, a 200 mL solution of DCM containing ligand L1 (12.02 g, 15.0 mmol) was added. The mixture was stirred at -10 °C for 10 min. After the temperature stabilized, BBr3 (2.0 mol·L⁻¹) was added using a long needle. -1 DCM (22.5 mL, 45.0 mmol) was slowly added dropwise to a Schlenk flask; stirred at -10 °C for 1 h, then stirred at room temperature for 4 h; the mixture was cooled to -10 °C again, and the BBr3 in the reaction system was slowly quenched with 40 mL of ice H2O, and stirred at room temperature for 12 h; DCM (100 mL) was extracted three times, the organic layer was dried with anhydrous MgSO4 for 2 h, and after removing volatiles under reduced pressure, the crude product was recrystallized from DCM and CH3OH; filtered, and dried in a drying oven at 35 °C for 5 h to obtain ligand L2 as a white solid.

[0023] 1 H NMR (400 MHz, Chloroform-d): δ 8.04-7.67 (m, 5H), 7.24-7.06 (m, 18H), 7.04-6.84 (m, 14H), 6.69 (s, 2H), 5.33 (d, J = 8.1 Hz, 3H), 1.17 (s, 3H).

[0024] Example 3:

[0025] A 500 mL Schlenk flask was connected to a double-row tube. Under continuous N2 bubbling, a THF (100 mL) solution of ligand L2 (3.94 g, 5.0 mmol, 1.2 eq.) was added. NaH (60% dispersionin mineral oil, 0.24 g, 6.0 mmol, 1.0 eq.) was slowly added with a spatula. The mixture was stirred at room temperature for 12 h. After filtration through diatomaceous earth, volatiles were removed under reduced pressure. The mixture was then dried in a drying oven at 35 °C for 5 h. Ligand L3 was a white solid.

[0026] Example 4: Under a nitrogen atmosphere, L1-L3 (1 mmol) and (DME)NiBr2 (1 mmol) were added to a 50 mL Schlenk tube and dissolved in dichloromethane (20 mL). After stirring at room temperature for 12 h, most of the volatiles were evaporated to obtain a concentrated solution, and then excess diethyl ether was added to form a precipitate. The complex was collected by filtration and washed with diethyl ether (30 mL) to obtain the pyridineimine nickel catalyst Ni1-Ni3, with a yield of 86-95%. The single crystal structure of the sterically hindered pyridineimine nickel catalyst Ni2 prepared in this example is as follows: Figure 5 As shown.

[0027]

[0028] Example 5: Synthesis of SiO2-supported pyridineimine nickel catalyst (1) Activation of silica support: Silica was placed in a crucible and inserted into a vacuum tube furnace. Under dynamic vacuum conditions, the temperature was raised to 300°C at a heating rate of 2°C / min and held at this temperature for 12 hours to complete activation. Subsequently, the activated silica was allowed to cool naturally to room temperature in the vacuum furnace. The material was then immediately transferred to an argon-filled glove box for storage.

[0029] (2) Preparation of silica-supported nickel catalyst: In an argon-filled glove box, a mixture of composite Ni2 or Ni3 with an activated SiO2 support was dissolved in anhydrous dichloromethane (DCM); the resulting suspension was stirred at room temperature for 12 hours; subsequently, the solid catalyst was separated by filtration, washed with anhydrous DCM, and dried at room temperature for 2 hours; the heterogeneous catalysts obtained in this process were labeled as Ni2@SiO2 and Ni3@SiO2, respectively.

[0030] Application Example 1: This example provides a method for efficiently preparing pyridineimine nickel catalyst and polyethylene wax. The specific steps are as follows: A 350 mL thick-walled pressure glass reactor was connected to a high-pressure gas pipeline and dried under vacuum at 90°C for 1 hour. The reactor was then adjusted to the desired polymerization temperature. 20 mL of toluene was added to the 350 mL glass reactor, and a magnetic stir bar was placed in a glove box. A specified amount of diethylaluminum chloride was then added. The reactor was then connected to the high-pressure pipeline, and the solution was degassed. The reactor was heated to the target temperature using an oil bath and held at this temperature for 5 minutes. Next, a sterically hindered pyridine imine nickel catalyst dissolved in 2 mL of dichloromethane was injected into the polymerization system using a syringe. After rapid stirring, ethylene was introduced into the reactor and the pressure was maintained at 8 atm. After 10 minutes of reaction, 40 mL of acidified ethanol was added, and stirring continued for 30 minutes. The resulting polymer was thoroughly washed with ethanol and then dried under vacuum at 55°C for 8 hours to obtain polyethylene wax.

[0031] The performance of polyethylene wax obtained by catalyzing ethylene polymerization at different temperatures using the pyridineimine nickel catalyst Ni1-Ni3 obtained in Example 4 is shown in Table 1: Table 1: Study on the ethylene polymerization catalyzed by nickel pyridineimine catalyst a

[0032] a Polymerization conditions: sterically hindered pyridine fluorinated imine nickel catalyst = 5 μmol, 2 mL CH2Cl2, 500 equivalent diethylaluminum chloride, toluene = 20 mL; ethylene = 8.0 atm, 10 min.

[0033] b The yield is the average of at least two runs; the activity unit is 10. 6 g · mol -1 · h -1 .

[0034] c Determination in trichlorobenzene by gel permeation chromatography (GPC), units: 10 3 g · mol -1 .

[0035] d Branching degree is given per 1000 carbon atoms.

[0036] Number of branches per 1000C = (CH3 / 3) / [(CH+CH2+CH3) / 2]*1000.

[0037] e The melting point was determined by differential scanning calorimetry (DSC).

[0038] The experimental conditions for ethylene polymerization were: a molar ratio of Et2AlCl to Ni of 500, a polymerization time of 10 minutes, and ethylene pressure maintained at a high purity of 8 atm. The catalytic performance was evaluated using a temperature gradient system from 0 to 120 °C (Table 1). Within the 0-120 °C temperature range, catalysts Ni1-Ni3 exhibited the best polymerization activity at 60 °C; for example, the homogeneous catalyst Ni1 showed an activity of 2.86 × 10⁻⁶ at 0 °C. 6 g·mol⁻¹·h⁻¹, while the activity increased to 4.32 × 10⁻¹ at 60℃. 6 g·mol⁻¹·h⁻¹; however, at 120℃, the catalytic activity is almost negligible (Table 1, entries 1, 3, 5); the system exhibits good thermal stability in the range of 0-90℃, but the catalytic performance decreases sharply at high temperatures; as the polymerization temperature increases, the melting point of the resulting polyethylene ( T m The degree of branching decreased; the degree of branching increased from 61 to 91 / 1000 carbon atoms (Table 1, entries 1 and 4); these trends can be attributed to the enhancement of chain transfer reactions at high temperatures, including β-elimination and catalyst decomposition.

[0039] Under the same conditions, the catalytic performance was in the following order: Ni3(-ONa) > Ni2(-OH) > Ni1(-OMe); at 60℃, the activities of Ni1, Ni2, and Ni3 were 4.32 × 10⁻⁶. 6 g·mol⁻¹ ·h⁻¹、4.96 × 10 6 g·mol⁻¹·h⁻¹ and 5.94 × 10 6 g·mol⁻¹·h⁻¹ (Entries 3, 5, 8); Notably, Ni₃ retains measurable activity at 120 °C (2.93 × 10⁻¹). 6 Ni3 exhibits excellent thermal stability (g·mol⁻¹ ·h⁻¹).

[0040] Application Example 2: This example provides a method for efficiently preparing polyethylene wax using a SiO2-supported heterogeneous catalyst. The specific steps are as follows: Table 2: Study on the catalytic polymerization of ethylene using SiO2-supported pyridineimine nickel heterogeneous catalyst a

[0041] a Polymerization conditions: pyridineimine nickel catalyst = 5 μmol, 20 mg SiO2 supported, 2 mL CH2Cl2, 500 equivalent diethylaluminum chloride, 20 mL toluene; ethylene = 8.0 atm, 10 min.

[0042] b The yield is the average of at least two runs; the activity unit is 10. 6 g · mol -1 · h -1 .

[0043] c Determination in trichlorobenzene by gel permeation chromatography (GPC), units: 10 3 g · mol -1 .

[0044] d Branching degree is given per 1000 carbon atoms.

[0045] Number of branches per 1000C = (CH3 / 3) / [(CH+CH2+CH3) / 2]*1000.

[0046] e The melting point was determined by differential scanning calorimetry (DSC).

[0047] As shown in Table 2, the heterogeneous ethylene polymerization catalyst supported by SiO2 exhibits significantly better performance than the homogeneous catalyst (Table 2 items 1-10 vs. Table 1 items 6-15). This supported system demonstrates higher catalytic activity, increased polyethylene molecular weight, and improved thermal stability.

[0048] The heterogeneous polymerization catalyst Ni3@SiO2 with -ONa anchoring groups exhibits significantly better catalytic performance than the heterogeneous catalyst Ni2@SiO2 with -OH anchoring groups; at 60℃ and 120℃, Ni3@SiO2 shows catalytic performance of 6.38 × 10⁻⁶ ppm. 6 g mol⁻¹ h⁻¹ and 3.71 × 10⁻¹ 6 The catalytic activity of Ni2@SiO2 decreased by 41.8% from g mol⁻¹ h⁻¹ to g mol⁻¹. In contrast, the activity of Ni2@SiO2 decreased from 5.92 × 10⁻¹ g mol⁻¹ h⁻¹. 6 g mol⁻¹ h⁻¹ at 60℃ decreasing to 3.06 × 10⁻¹ at 120℃ 6 The activity decreased by 48.3% with gmol⁻¹ h⁻¹ (items 8 and 10 in Table 2 compared with items 3 and 5); these results indicate that the -ONa-functionalized supported catalyst has higher catalytic efficiency in the heterogeneous polymerization of ethylene.

[0049] Furthermore, the catalytic performance of heterogeneous catalysts is significantly better than that of their homogeneous counterparts; for example, the homogeneous catalyst Ni2 exhibits negligible activity at 120 °C, while its supported analog Ni2@SiO2 shows 3.06 × 10⁻⁶ activity under the same conditions. 6 The catalytic activity was measured in g·mol⁻¹·h⁻¹ (compare item 10 in Table 1 with item 5 in Table 2); similarly, the catalytic activity of Ni₃ at 120℃ was 2.93 × 10⁻¹. 6 g·mol⁻¹·h⁻¹, while Ni₃@SiO₂ reaches 3.71 × 10⁻¹. 6 g·mol⁻¹·h⁻¹, an increase of 21.0% (Item 15 in Table 1 compared with Item 10 in Table 2).

[0050] Polyethylene prepared by heterogeneous polymerization through a supported system exhibits higher melting point and molecular weight compared to homogeneous catalytic products, but lower branching degree. For example, polyethylene synthesized from Ni3@SiO2 at 60℃ has a melting point of 122.84℃, while polyethylene prepared using Ni3 under homogeneous conditions has a melting point of 117.93℃, a difference of 4.91℃. Furthermore, the molecular weight increases from 4.4 × 10³ g·mol⁻¹ under homogeneous conditions to 8.3 × 10³ g·mol⁻¹ under heterogeneous conditions, while the branching degree decreases from 62 / 1000℃ to 58 / 1000℃ (Item 8 in Table 2 compared to Item 13 in Table 1).

[0051] This trend highlights the crucial role of electron donor anchoring groups in enhancing catalytic efficiency; the introduction of -OH groups stabilizes the nickel center through electron donation, thereby improving activity; further introduction of -ONa groups significantly increases both activity and polyethylene molecular weight, indicating that -ONa has a stronger electron donor effect than -OH; this enhanced electron density may promote ethylene insertion and inhibit chain transfer, thus optimizing polymerization kinetics; the physical state of the polyethylene product also changes significantly before and after catalyst immobilization: the product changes from a viscous flocculent state to a free-flowing powder state; this morphological transformation has advantages in practical applications because it can reduce the adhesion of the polymer to the reactor wall during polymerization.

[0052] The above description is only a preferred embodiment of the present invention. Therefore, all equivalent changes or modifications made to the structure, features and principles described in the claims of this patent application are included in the scope of this patent application.

Claims

1. A SiO2 supported nickel catalyst, characterized by: It consists of an active component and a support, wherein the active component is a pyridineimine nickel complex represented by the following general formula (I): General Formula (I) In general formula (I), the anchoring group R is selected from one of -OH, -ONa, -SO3H, -SO3Na, -COOH, and -COONa; wherein the pyridineimine nickel complex is loaded onto the surface of the SiO2 support through the anchoring group.

2. The SiO2-supported nickel catalyst according to claim 1, characterized in that: The anchoring group R is selected from one of -OH, -SO3H and -COOH.

3. A pyridylimine ligand for use in the synthesis of a pyridylimine nickel catalyst, characterized in that: The pyridineimine ligand has the structure shown in general formula (II): General Formula (II) Among them, the ligand L-Na is derived from the reaction of ligand L through an equimolar amount of NaH.

4. A method for preparing a SiO2 supported nickel catalyst, characterized by: Includes the following steps: S1: SiO2 support was activated by heating at 300℃ for 12 hours under vacuum to obtain activated SiO2; S2: Under anhydrous and oxygen-free conditions, (DME)NiBr2 and pyridineimine ligands undergo a coordination reaction in dichloromethane solvent to generate a pyridineimine nickel complex. S3: Mix the nickel complex solution obtained in step S2 with the activated SiO2 obtained in step S1, and stir the mixture at room temperature for 5-12 hours to load the nickel complex onto the SiO2 surface. S4: Filter and dry the solid product to obtain the SiO2-supported nickel catalyst.

5. The method for preparing the SiO2-supported nickel catalyst according to claim 4, characterized in that: The pyridineimine ligand contains an anchoring group R, and R is selected from one of -OH, -ONa, -SO3H, -SO3Na, -COOH, and -COONa.

6. The method for preparing the SiO2-supported nickel catalyst according to claim 5, characterized in that: The pyridineimine ligand is converted to its sodium salt form by NaH treatment.

7. The application of a SiO2-supported nickel catalyst in ethylene polymerization, characterized in that: The application is used to prepare polyethylene wax, wherein the polymerization reaction is carried out in an organic solvent, the ethylene pressure is 0.1-50 MPa, the reaction temperature is 0-200℃, and the reaction time is 0.05-8.00 h.

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