A catalyst with adjustable alpha-olefin selectivity and a method for preparing the same

Abstract

The present application relates to the field of catalysts, and provides a catalyst capable of adjusting alpha-olefin selectivity and a preparation method thereof, the present application adopts a combination design of a chromium compound as an active component, a multidentate ligand containing a nitrogen and phosphorus coordination group prepared through a Kabachnik-Fields reaction, an activator and a chlorine-containing organic aluminum promoter, the ligand is connected through 1,4-dibromobutane and forms a cyclic borate ester bond with aryl boronic acid and an ortho dihydroxy compound, the chromium concentration is 0.01-1.0 mmol / L, the molar ratio of the ligand to chromium is 2.0-3.0:1, the molar ratio of aluminum to chromium is 30-80:1, and the molar ratio of chlorine to chromium is 0.5-5:1, thus realizing the excellent performance of 1-octene 1-octene selectivity of 75-80% at 70-95 DEG C, 1-octene selectivity of 85-95% at 105-130 DEG C, polyethylene byproduct controlled below 1%, and a selectivity change amplitude of not more than 3 percentage points when the temperature is switched, solving the problems of insufficient steric hindrance adjustment capability and limited selectivity function of existing catalysts, and having wide industrial application value.

Description

Technical Field

[0001] This invention relates to the field of catalysts, and more specifically to a catalyst with adjustable α-olefin selectivity and its preparation method. Background Technology

[0002] With the rapid development of the global polyolefin industry and the increasing demand for high-performance materials, α-olefins, as key comonomers, are playing an increasingly important role in the petrochemical industry. In the manufacturing of high-end polyethylene pipes, films, and hollow containers, the addition of 1-octene can significantly improve the mechanical strength, transparency, and processing performance of the materials. 1-Octene is also a core raw material for the production of photovoltaic-grade POE (polyolefin elastomer), showing great potential in high-value-added applications such as automotive parts, wires and cables, and seals. Currently, my country's annual imports of high-end polyethylene products exceed 12 million tons, of which approximately 1 million tons require 1-octene or 1-octene as comonomers. With domestic POE production capacity planned to reach 4.5 million tons, the demand for high-purity 1-octene will surge to 1.5 million tons. Against this backdrop, the development of highly efficient catalysts capable of flexibly adjusting the selectivity of α-olefins is particularly urgent. Such catalysts need to have the ability to precisely control product distribution under different process conditions while maintaining high catalytic activity and good stability to meet the market's differentiated demands for α-olefins with different carbon numbers, and to drive the development of my country's petrochemical industry towards high-end and refined production.

[0003] While industrial-scale high-selectivity oligomerization catalysts for ethylene have made significant progress in the production of specific α-olefins, numerous technical bottlenecks still hinder their further development. Existing catalysts generally employ one-dimensional planar ligand structures, limiting their steric hindrance adjustment capabilities. This results in a maximum selectivity of only 92% for 1-hexene and a mere 70% selectivity for 1-octene, failing to meet the requirements for efficient production. More critically, different target products require specialized catalyst systems, lacking flexibility and economic efficiency. Companies must construct multiple units to achieve product switching, significantly increasing investment costs and operational complexity. Furthermore, existing technologies commonly suffer from the generation of polyethylene byproducts. These solid byproducts easily clog pipelines and valves, severely impacting the continuous and stable operation of the plant and causing frequent unplanned shutdowns. For example, Chinese Patent CN111760571A discloses a method for preparing and applying a calcium aluminate catalyst with adjustable olefin selectivity, but it suffers from limitations such as a single catalyst structure and the inability to flexibly adjust product selectivity. Meanwhile, the high-selectivity 1-octene technology's heavy reliance on methylaluminoxane (MAO) not only significantly increases production costs but also exacerbates the generation of polyethylene byproducts. These technological limitations severely restrict the industrialization and promotion of α-olefin production technology and the realization of economic benefits. Summary of the Invention

[0004] (1) Technical problems to be solved The purpose of this invention is to provide a catalyst with adjustable α-olefin selectivity, thereby solving the problems of insufficient steric hindrance regulation capability and limited selectivity of current catalysts.

[0005] (2) Technical solution To achieve the above objectives, the present invention provides the following technical solution: A catalyst with tunable α-olefin selectivity, characterized in that it comprises: 1) Chromium compounds are used as the catalytically active component. The chromium compounds are selected from at least one of chromium trichloride and chromium trivalent acetylacetonate, based on the concentration of the catalyst working solution being 0.01-1.0 mmol / L; 2) A multidentate ligand, wherein the multidentate ligand is prepared by reacting 2,2'-bipyridine or 1,10-phenanthroline with amine, aldehyde and phosphine compounds at 60-100°C to form a nitrogen-phosphorus coordination group, which is then linked with 1,4-dibromobutane and subsequently formed with arylboronic acid and ortho-dihydroxy compound at 80-120°C to form a cyclic borate ester bond. The ligand contains at least two nitrogen coordination atoms and at least one phosphorus coordination atom. The arylboronic acid is selected from phenylboronic acid and 2,6-dimethylphenylboronic acid, and the ortho-dihydroxy compound is selected from catechol and 4,5-dimethylcatechol. The molar ratio of the ligand to chromium is 2.0-3.0:1. 3) Activator, selected from at least one of triethylaluminum, methylaluminoxane, and carrier-supported methylaluminoxane, with a molar ratio of aluminum to chromium of 30-80:1; 4) Chlorine-containing organoaluminum additive, wherein the chlorine-containing organoaluminum additive is selected from at least one of diethylaluminum chloride, isobutylaluminum chloride, and ethylaluminum chloride or a mixture thereof, preferably diethylaluminum chloride as the main component, and the total proportion of isobutylaluminum chloride and ethylaluminum chloride is 20-60%, more preferably mixed in a volume ratio of 5:4:1 to 7:2:1, and the molar ratio of chlorine to chromium is 0.5-5:1; 5) An inert hydrocarbon solvent, selected from at least one of propane or ethane, is used as a dilution medium, accounting for 85-98% of the total volume of the catalyst working solution.

[0006] This invention employs a synergistic coordination design between chromium compounds and polydentate ligands primarily to enhance the α-olefin selectivity tuning performance of catalysts. The polydentate ligands constructed via the Kabachnik-Fields reaction possess a unique three-dimensional spatial structure. 2,2'-bipyridine or 1,10-phenanthroline provides a rigid framework, while the nitrogen-phosphorus coordination groups formed with amine, aldehyde, and phosphine compounds create a tunable electronic environment. The 1,4-dibromobutane linker further enhances the ligand's spatial flexibility. The introduction of cyclic borate ester bonds, through the combination of arylboronic acid and ortho-dihydroxy compounds, forms a dynamic coordination structure with temperature-responsive characteristics, enabling the catalyst to exhibit differentiated selectivity behavior under various reaction conditions. Chromium trichloride or trivalent acetylacetonate chromium, acting as the active center, synergistically coordinates with the polydentate ligands, providing not only stable catalytic activity but also precisely controlling the ethylene insertion mode through the steric hindrance effect of the ligands. The strategy of using a combination of chlorinated organoaluminum auxiliaries, particularly the synergistic effect of diethylaluminum chloride, isobutylaluminum chloride, and ethylaluminum chloride, can effectively regulate the electron density and coordination environment of the catalyst, achieving precise control over the degree of polymerization. The synergistic effect of the activator and chlorinated auxiliaries significantly reduces the dependence of traditional processes on methylaluminoxane, while simultaneously inhibiting the formation of polyethylene byproducts. The entire catalytic system achieves controllable switching between 1-octene and 1-hexene selectivity under temperature-driven conditions.

[0007] Furthermore, the method for preparing the multidentate ligand is characterized by comprising the following steps: A1. Formation of nitrogen-phosphorus coordination groups: Under nitrogen protection, rigid skeleton compounds, amine compounds, aldehyde compounds, and phosphine compounds are reacted in anhydrous toluene or dichloromethane at a molar ratio of 1.0:1.2:1.1:1.2 for 4-12 hours with stirring to form nitrogen-phosphorus coordination groups. A2. Introduction of the linking unit: Under an inert atmosphere, the above product is refluxed with a 1,4-dibromobutane linking unit containing 4 methylene groups at a molar ratio of 1:0.6 in the presence of potassium carbonate at 80°C for 6-10 hours. A3. Cyclic borate ester bond formation: Cyclic borate ester bonds are formed by adding arylboronic acid and ortho-dihydroxy compound in the presence of molecular sieve 4 Å; A4. Separation and purification: The target ligand is obtained by separation and purification by column chromatography or recrystallization and vacuum drying.

[0008] Furthermore, the arylboronic acid mentioned in step A3 is selected from phenylboronic acid and 2,6-dimethylphenylboronic acid, and the ortho-dihydroxy compound is selected from catechol and 4,5-dimethylcatechol. The arylboronic acid and the ortho-dihydroxy compound are reacted in anhydrous toluene at a molar ratio of 2.2:2.0 at 80-120°C for 2-8 hours, and water is continuously removed during the reaction.

[0009] Further, the separation and purification described in step A4 is as follows: after the reaction is complete, cool to room temperature, preferably use silica gel column chromatography with gradient elution of petroleum ether to toluene in a volume ratio of 2:1 to 1:1, or recrystallize in a mixed solvent of methanol and isopropanol for separation and purification.

[0010] Furthermore, the vacuum drying conditions described in step A4 are as follows: drying at 60-80°C and a pressure not exceeding 1 mmHg for 12-24 hours until the moisture content does not exceed 50 ppm and the total amount of residual polar solvent does not exceed 100 ppm, to obtain a white to pale yellow solid product with a molecular weight of 400-800 Da.

[0011] Furthermore, the molar ratio calculated based on chromium is: Al to Cr is 30-80:1, preferably 40-60:1, and Cl to Cr is 0.5-5:1, preferably 1-3:1. The molar ratio of Al to Cr is the molar ratio of aluminum to chromium from the activator source, and does not contain chlorinated organoaluminum additives. The molar ratio of Cl to Cr is calculated based on chlorinated organoaluminum additives. The carrier of the carrier-supported methylaluminoxane is selected from at least one of MCM-41, SBA-15, and γ-Al2O3. When carrier-supported methylaluminoxane is used, a soluble methylaluminoxane solution is obtained by pre-extraction with a hydrocarbon solvent. After extraction, the aluminum concentration deviation is controlled within ±10%. After filtration through 0.22 μm, the supernatant has no visible solid particles.

[0012] This invention employs a stepwise method for constructing multidentate ligands, primarily to enhance the structural stability and selectivity of catalysts. Through the Kabachnik-Fields reaction mechanism, a rigid framework compound reacts precisely with amine, aldehyde, and phosphine compounds under nitrogen protection, forming a nitrogen-phosphorus coordinating group with strong coordination ability, laying the foundation for subsequent spatial structure regulation. The introduction of a 1,4-dibromobutane linker unit achieves ligand bridging under potassium carbonate catalysis, enhancing the overall structural rigidity and stability, while providing a suitable spatial environment for the formation of cyclic borate ester bonds. The dehydration condensation reaction of arylboronic acid and ortho-dihydroxy compounds in the presence of a molecular sieve at 4 Å depth forms a temperature-responsive cyclic borate ester bond; the introduction of this structural unit allows the ligand to exhibit dynamic coordination behavior under different temperature conditions. Supported methylaluminoxanes, through loading on MCM-41, SBA-15, or γ-Al₂O₃ supports and pre-extraction with hydrocarbon solvents, achieve uniform dispersion and controllable release of the activator, significantly improving the stability of the catalytic system. Strict vacuum drying conditions ensured the high purity and low moisture content of the ligands, while precise control of the molar ratios of aluminum to chromium and chlorine to chromium enabled synergistic cooperation among the active components of the catalyst. The synergistic effect of the entire preparation process resulted in a final catalyst with excellent selectivity adjustment capability and stable catalytic performance.

[0013] This invention also discloses a method for preparing a catalyst with adjustable α-olefin selectivity, comprising the following steps: S1 Ligand pretreatment: The ligand is further dried under an inert atmosphere until the moisture content does not exceed 50 ppm and the residual polar solvent does not exceed 100 ppm; S2 catalyst assembly: Under an inert atmosphere, with oxygen and water content not exceeding 5 ppm, the ligand and chromium compound are complexed in an inert hydrocarbon solvent at a ligand to chromium molar ratio of 2.0-3.0:1 at 0-40°C for 1-6 hours. S3 Low-temperature activation: Activation is carried out by introducing an activator at -10 to 25°C, and the molar ratio of Al to Cr is controlled at 30-80:1; S4 Chlorine-containing organoaluminum additive adjustment: The chlorine-containing organoaluminum additive is added in two stages. The first stage adds 50-70% of the total amount, and the second stage adds the adduct solution. The addition rate of the second stage does not exceed 0.05 mol Cl⁻ / (mol Cr·min). The final chromium concentration in the catalyst working solution is 0.01-1.0 mmol / L.

[0014] Furthermore, the adduct solution is formed by a chlorine-containing organoaluminum auxiliary agent and a weak base ligand L, wherein the weak base ligand L is selected from at least one of 2,6-dimethylpyridine and tetrahydrofuran, preferably 2,6-dimethylpyridine; diethylaluminum chloride and the weak base ligand L are premixed at a molar ratio of 10:1 to 20:1 at 0-5°C for 10-20 minutes; when a carrier-supported methylaluminoxane is used, it is first pre-extracted by stirring with a hydrocarbon solvent at room temperature for 1-4 hours, and the carrier solid phase is removed by filtration before using the extract.

[0015] An application of a catalyst with adjustable α-olefin selectivity in the preparation of α-olefins in the oligomerization reaction of ethylene is characterized by achieving selective preparation of α-olefins by adjusting the reaction temperature: at a reaction temperature of 70-95℃, when the molar ratio of Cl to Cr is 1.2-1.8 and the volume fraction of isobutylaluminum chloride is not less than that of ethylaluminum chloride, the selectivity of 1-octene reaches 75-80%; at a reaction temperature of 105-130℃, when the molar ratio of Cl to Cr is 1.8-2.3 and the volume fraction of ethylaluminum chloride is not less than that of isobutylaluminum chloride, the selectivity of 1-hexene reaches 85-95%. When using diethylaluminum chloride as a chlorine-containing organoaluminum auxiliary, the catalytic performance is stable, the polyethylene by-product content is controlled below 1%, and the selectivity change range does not exceed 3 percentage points when switching between 70-95℃ and 105-130℃. When using a mixture of chlorine-containing organoaluminum auxiliaries, the selectivity adjustment effect can be further optimized by adjusting the proportion of different components. The α-olefin selectivity and the polyethylene by-product content are both determined by gas chromatography.

[0016] Furthermore, the ethylene oligomerization reaction conditions are as follows: ethylene pressure 0.5-4.0 MPa, reaction time 1-8 hours, heating and cooling rate controlled at 1-10℃ per minute, holding at the target temperature for 30-180 minutes, polyethylene by-product mass fraction controlled below 1%, α-olefin purity reaching above 90%, and product switching cycle of 0.5-6 hours.

[0017] This invention employs a precisely controlled stepwise preparation and application method primarily to enhance the selectivity and stability of catalysts. Rigorous dehydration and desolventization treatment during the ligand pretreatment stage ensures efficient subsequent complexation reactions and stable catalyst activity. During catalyst assembly under an inert atmosphere, the precise molar ratio complexation of ligands and chromium compounds at low temperatures forms a stable coordination structure, laying the foundation for subsequent activation reactions. The introduction of activators and the segmented addition strategy of chlorinated organoaluminum auxiliaries during the low-temperature activation stage enables the gradual construction of catalyst active centers and precise control of the electronic environment. The adduct solution formed by the chlorinated organoaluminum auxiliaries and weak base ligands effectively mitigates the strong Lewis acidity of aluminum chloride through coordination with 2,6-dimethylpyridine or tetrahydrofuran, making the catalyst activation process more gentle and controllable. In ethylene oligomerization applications, the temperature-driven selective switching mechanism exhibits excellent adjustability. The synergistic effect of isobutylaluminum chloride and ethylaluminum chloride demonstrates differentiated catalytic behavior in different temperature ranges, achieving highly selective preparation of 1-octene and 1-octene. The pre-extraction treatment of carrier-supported methylaluminoxane and the synergistic effect of diethylaluminum chloride significantly inhibited the formation of polyethylene byproducts. The entire catalytic system exhibited excellent selectivity, stability and rapid response during temperature switching.

[0018] (3) Beneficial technical effects This invention achieves the following significant beneficial effects through innovative catalyst design and preparation process: 1. Breakthrough Selectivity Adjustment Capability: Compared to the limitations of existing technologies where a single catalyst can only produce a specific α-olefin product, this invention achieves a significant breakthrough by flexibly adjusting product selectivity using a single catalyst system. In the temperature range of 70-95℃, the selectivity for 1-octene reaches 75-80%, and in the temperature range of 105-130℃, the selectivity for 1-hexene reaches 85-95%, significantly exceeding the upper limits of 70% for 1-octene and 92% for 1-hexene in existing industrial technologies. The selectivity change during temperature switching is controlled within 3 percentage points, demonstrating excellent stability and controllability.

[0019] 2. Significantly reduced by-product generation: Through the combined use strategy of chlorine-containing organic aluminum additives and the synergistic effect of weak base complexing agents, the content of polyethylene by-products is stably controlled below 1%, which effectively solves the key problem of solid by-products clogging pipelines and valves and affecting the continuous operation of the equipment in traditional technologies, and greatly improves the operational stability and economic benefits of industrial equipment.

[0020] 3. Significantly reduced production costs: The synergistic effect of the activator and chlorine-containing additives significantly reduces the dependence on expensive methylaluminoxane (MAO). The aluminum to chromium molar ratio is optimized to a reasonable range of 30-80:1. Compared with the traditional high-selectivity 1-octene technology that uses a large amount of MAO, the production cost is significantly controlled, and the economic feasibility of the technology is improved.

[0021] 4. Excellent operational flexibility: The product switching cycle is shortened to 0.5-6 hours, and the heating and cooling rate can be controlled at 1-10℃ per minute, enabling production enterprises to quickly adjust the product structure according to market demand. This avoids the huge investment required by traditional technologies to build multiple sets of equipment, and significantly improves asset utilization efficiency and market responsiveness.

[0022] 5. High-quality product output: The purity of α-olefin products consistently reaches over 90%, meeting the stringent requirements for the production of high-end polyolefins and POE, and providing important technical support for the upgrading of my country's petrochemical industry to high value-added products.

[0023] 6. Mild process conditions: The reaction conditions are relatively mild, with ethylene pressure of 0.5-4.0 MPa and reaction temperature of 70-130℃, which reduces equipment investment and operating costs, while improving the safety and reliability of industrial applications. Attached Figure Description

[0024] Figure 1 The image shows the infrared Fourier transform spectrum of the product during the polydentate ligand reaction process of this invention.

[0025] Figure 2 The infrared Fourier transform spectrum of the product during the temperature change process of cyclic borate ester bond formation in this invention is shown.

[0026] Figure 3 The infrared Fourier transform spectrum of the product during the time-varying formation of the nitrogen-phosphorus coordination group in this invention is shown.

[0027] Figure 4 This invention relates to the effect of the reaction temperature for the formation of nitrogen-phosphorus coordination groups on the selectivity of olefins.

[0028] Figure 5 This invention relates to the effect of reaction temperature on catalytic activity and ligand purity in the formation of nitrogen-phosphorus coordination groups.

[0029] Figure 6This invention relates to the effect of the reaction time for the formation of nitrogen-phosphorus coordination groups on the selectivity of olefins.

[0030] Figure 7 This invention relates to the effect of the reaction time for the formation of nitrogen-phosphorus coordination groups on catalytic activity and ligand purity.

[0031] Figure 8 This invention relates to the effect of the reaction temperature for the formation of cyclic borate ester bonds on the selectivity of olefins.

[0032] Figure 9 This invention relates to the effect of the reaction temperature for the formation of cyclic borate ester bonds on catalytic activity and the stability of borate esters.

[0033] Figure 10 This invention relates to the effect of the reaction time for the formation of cyclic borate ester bonds on the selectivity of olefins.

[0034] Figure 11 This invention relates to the effect of the reaction time for the formation of cyclic borate ester bonds on catalytic activity and the stability of borate esters.

[0035] Figure 12 This is a comparison diagram of olefin selectivity between embodiments and comparative examples of the present invention.

[0036] Figure 13 This is a comparison diagram of the catalytic activity and byproducts of the embodiments and comparative examples of the present invention.

[0037] Figure 14 This is a comparison chart of response time and selectivity between embodiments and comparative examples of the present invention.

[0038] Figure 15 This is a comparison chart of olefin purity and catalytic efficiency between the embodiments and comparative examples of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Example 1

[0040] A catalyst with tunable α-olefin selectivity, comprising: 1) Chromium compounds were selected as the catalytically active components, with chromium trichloride chosen based on a catalyst working solution concentration of 0.5 mmol / L; 2) Multidentate ligand: The multidentate ligand in this embodiment is prepared by reacting 2,2'-bipyridine with amine, aldehyde and phosphine compounds at 80°C to form a nitrogen-phosphorus coordination group, which is then linked with 1,4-dibromobutane and then formed with phenylboronic acid and catechol at 100°C to form a cyclic borate ester bond. The ligand contains two nitrogen coordination atoms and one phosphorus coordination atom, and the molar ratio of the ligand to chromium is 2.5:1. 3) Activator: Methylaluminoxane is selected, with a molar ratio of aluminum to chromium of 50:1; 4) Chlorine-containing organoaluminum additives: In this embodiment, diethylaluminum chloride is the main chlorine-containing organoaluminum additive, and isobutylaluminum chloride and ethylaluminum chloride account for 30% of the total amount. They are mixed in a volume ratio of 6:3:1, and the molar ratio of chlorine to chromium is 2.0:1. 5) An inert hydrocarbon solvent is used as the dilution medium, with propane selected, accounting for 90% of the total volume of the catalyst working solution.

[0041] The method for preparing the multidentate ligand in this embodiment includes the following steps: A1. Formation of nitrogen-phosphorus coordination groups: Under nitrogen protection, 2,2'-bipyridine, an amine compound, an aldehyde compound, and a phosphine compound are reacted in anhydrous toluene at 80°C for 8 hours with stirring, forming nitrogen-phosphorus coordination groups; A2. Introduction of linking units: Under an inert atmosphere, the above product is refluxed with a 1,4-dibromobutane linking unit at 80°C for 8 hours in the presence of potassium carbonate at a molar ratio of 1:0.6; A3. Formation of cyclic borate ester bonds: Phenylboronic acid and catechol are added in anhydrous toluene at 100°C for 4 hours with continuous dehydration during the reaction, forming cyclic borate ester bonds in the presence of a 4 Å molecular sieve; A4. Separation and purification: After the reaction is complete, the mixture is cooled to room temperature and purified by gradient elution using silica gel column chromatography with petroleum ether to toluene at a volume ratio of 1.5:1, at 70°C and a pressure of 0.5. Vacuum drying at mmHg for 18 hours until the moisture content does not exceed 50 ppm and the total residual polar solvent does not exceed 100 ppm yields a white solid product with a molecular weight of 600 Da.

[0042] The catalyst preparation method of this embodiment includes the following steps: S1 Ligand pretreatment: The ligand of this embodiment is further dried under an inert atmosphere until the water content does not exceed 50 ppm and the residual polar solvent does not exceed 100 ppm; S2 Catalyst assembly: Under an inert atmosphere, with the oxygen and water content both not exceeding 5 ppm, the ligand of this embodiment and chromium trichloride are complexed in propane at 20°C at a ligand to chromium molar ratio of 2.5:1 for 3 hours; S3 Low-temperature activation: Methylaluminoxane is introduced at 5°C for activation, and the Al to Cr molar ratio is controlled at 50:1; S4 Adjustment of chlorinated organoaluminum auxiliaries: Chlorinated organoaluminum auxiliaries are added in two stages. The first stage adds 60% of the total amount, and the second stage adds an adduct solution. In this embodiment, the adduct solution is formed by premixing diethylaluminum chloride and 2,6-dimethylpyridine at a molar ratio of 15:1 at 2°C for 15 minutes. The addition rate of the second stage is controlled at 0.03 mol Cl⁻ / (mol Cr·min), and the final chromium concentration in the catalyst working solution is 0.5%. mmol / L.

[0043] In the application of the catalyst in the ethylene oligomerization reaction to prepare α-olefins, selective preparation of α-olefins is achieved by adjusting the reaction temperature: the reaction is carried out at a reaction temperature of 85°C and an ethylene pressure of 2.0 MPa for 4 hours, the heating and cooling rate is controlled at 5°C per minute, the target temperature is maintained for 120 minutes, the mass fraction of polyethylene by-products is controlled at 0.8%, the purity of α-olefins reaches 92%, the product switching cycle is 3 hours, and the selectivity of 1-octene reaches 77%.

[0044] Features of Example 1: This example uses moderate parameter configuration, exhibiting good stability and reproducibility, making it suitable for industrial production scenarios requiring stable catalytic performance. With moderate chromium concentration, balanced ligand ratios, conservative activator dosage, and stable auxiliary agent ratios, it achieves good 1-octene selectivity under normal operating temperatures. It is suitable for industrial plants requiring long-term continuous operation and high product quality stability. Example 2

[0045] A catalyst with tunable α-olefin selectivity, comprising: 1) Chromium compounds were selected as the catalytically active components, with trivalent acetylacetone chromium chosen based on a catalyst working solution concentration of 0.3 mmol / L; 2) Multidentate ligand: The multidentate ligand in this embodiment is prepared by reacting 1,10-phenanthroline with amine, aldehyde and phosphine compounds at 75°C to form a nitrogen-phosphorus coordination group, which is then linked with 1,4-dibromobutane and then formed with 2,6-dimethylphenylboronic acid and 4,5-dimethylcatechol at 90°C to form a cyclic borate ester bond. The ligand contains two nitrogen coordination atoms and one phosphorus coordination atom, and the molar ratio of the ligand to chromium is 2.2:1. 3) Activator: Triethylaluminum is selected, with a molar ratio of aluminum to chromium of 40:1; 4) Chlorine-containing organoaluminum additives: In this embodiment, diethylaluminum chloride is the main chlorine-containing organoaluminum additive, and isobutylaluminum chloride and ethylaluminum chloride account for 45% of the total. They are mixed in a volume ratio of 5:4:1, and the molar ratio of chlorine to chromium is 1.5:1. 5) An inert hydrocarbon solvent is used as the dilution medium, with ethane selected, accounting for 88% of the total volume of the catalyst working solution.

[0046] The method for preparing the multidentate ligand in this embodiment includes the following steps: A1. Formation of nitrogen-phosphorus coordination groups: Under nitrogen protection, 1,10-phenanthroline, an amine compound, an aldehyde compound, and a phosphine compound are reacted in anhydrous dichloromethane at 75°C for 6 hours with stirring to form nitrogen-phosphorus coordination groups; A2. Introduction of linking units: Under an inert atmosphere, the above product is refluxed with a 1,4-dibromobutane linking unit at 80°C for 7 hours in the presence of potassium carbonate at a molar ratio of 1:0.6; A3. Formation of cyclic borate ester bonds: 2,6-dimethylphenylboronic acid and 4,5-dimethylcatechol are added in anhydrous toluene at 90°C for 3 hours with continuous dehydration during the reaction, and cyclic borate ester bonds are formed in the presence of a 4 Å molecular sieve; A4. Separation and purification: After the reaction was completed, the mixture was cooled to room temperature and recrystallized in a mixed solvent of methanol and isopropanol for separation and purification. The product was then vacuum dried at 65°C and 0.8 mmHg for 15 hours until the water content did not exceed 50 ppm and the total amount of residual polar solvent did not exceed 100 ppm, yielding a pale yellow solid product with a molecular weight of 550 Da.

[0047] The catalyst preparation method of this embodiment includes the following steps: S1 Ligand pretreatment: The ligand of this embodiment is further dried under an inert atmosphere until the water content does not exceed 50 ppm and the residual polar solvent does not exceed 100 ppm; S2 Catalyst assembly: Under an inert atmosphere, with the oxygen and water content both not exceeding 5 ppm, the ligand of this embodiment and trivalent acetylacetone chromium are complexed in ethane at 10°C at a molar ratio of ligand to chromium of 2.2:1 for 2 hours; S3 Low-temperature activation: Triethylaluminum is introduced at 0°C for activation, and the molar ratio of Al to Cr is controlled at 40:1; S4 Adjustment of chlorinated organoaluminum auxiliaries: Chlorinated organoaluminum auxiliaries are added in two stages. The first stage adds 55% of the total amount, and the second stage adds the adduct solution. In this embodiment, the adduct solution is formed by premixing diethylaluminum chloride and tetrahydrofuran at a molar ratio of 12:1 at 3°C ​​for 12 minutes. The addition rate of the second stage is controlled at 0.04 mol Cl⁻ / (mol Cr·min), and the final chromium concentration in the catalyst working solution is 0.3%. mmol / L.

[0048] In the application of the catalyst in the ethylene oligomerization reaction to prepare α-olefins, selective preparation of α-olefins is achieved by adjusting the reaction temperature: the reaction is carried out for 3 hours at a reaction temperature of 75°C and an ethylene pressure of 1.5 MPa, with the heating and cooling rate controlled at 3°C ​​per minute, and the target temperature is maintained for 90 minutes. The mass fraction of polyethylene by-products is controlled at 0.5%, the purity of α-olefins reaches 94%, the product switching cycle is 2 hours, the molar ratio of Cl to Cr is 1.5, and the volume fraction of isobutylaluminum chloride is not lower than that of ethylaluminum chloride, the selectivity of 1-octene reaches 79%.

[0049] Features of Example 2: This example specifically optimizes the selectivity of 1-octene by using a lower chromium concentration and ligand ratio, selecting triethylaluminum as the activator, and employing a higher proportion of isobutylaluminum dichloride in the chlorine-containing additives, while controlling the reaction temperature within a low range. This configuration effectively improves the selectivity of 1-octene while reducing the formation of polyethylene byproducts. It is suitable for use in fine chemical plants specializing in the production of 1-octene, especially in downstream applications where high product purity is required. Example 3

[0050] A catalyst with tunable α-olefin selectivity, comprising: 1) Chromium compounds were selected as the catalytically active component, with chromium trichloride chosen based on a catalyst working solution concentration of 0.8 mmol / L; 2) Multidentate ligand: The multidentate ligand in this embodiment is prepared by reacting 2,2'-bipyridine with amine, aldehyde and phosphine compounds at 95°C to form a nitrogen-phosphorus coordination group, which is then linked with 1,4-dibromobutane and then formed with phenylboronic acid and catechol at 110°C to form a cyclic borate ester bond. The ligand contains two nitrogen coordination atoms and one phosphorus coordination atom, and the molar ratio of the ligand to chromium is 2.8:1. 3) Activator: Carrier-supported methylaluminoxane is selected. In this embodiment, the carrier is MCM-41, and the molar ratio of aluminum to chromium is 65:1. 4) Chlorine-containing organoaluminum additives: In this embodiment, diethylaluminum chloride is the main chlorine-containing organoaluminum additive, and isobutylaluminum chloride and ethylaluminum chloride account for 25% of the total. They are mixed in a volume ratio of 7:2:1, and the molar ratio of chlorine to chromium is 2.1:1. 5) An inert hydrocarbon solvent is used as the dilution medium, with propane selected, accounting for 95% of the total volume of the catalyst working solution.

[0051] The method for preparing the multidentate ligand in this embodiment includes the following steps: A1. Formation of nitrogen-phosphorus coordination groups: Under nitrogen protection, 2,2'-bipyridine, an amine compound, an aldehyde compound, and a phosphine compound are reacted in anhydrous toluene at 95°C for 5 hours with stirring, forming nitrogen-phosphorus coordination groups; A2. Introduction of linking units: Under an inert atmosphere, the above product is refluxed with a 1,4-dibromobutane linking unit at 80°C for 6 hours in the presence of potassium carbonate at a molar ratio of 1:0.6; A3. Formation of cyclic borate ester bonds: Phenylboronic acid and catechol are added in anhydrous toluene at 110°C for 6 hours with continuous dehydration during the reaction, forming cyclic borate ester bonds in the presence of a 4 Å molecular sieve; A4. Separation and purification: After the reaction is complete, the mixture is cooled to room temperature and purified by gradient elution using silica gel column chromatography with a petroleum ether to toluene volume ratio of 1:1 at 75°C and a pressure of 0.3 ppm. Vacuum drying at mmHg for 20 hours until the moisture content does not exceed 50 ppm and the total residual polar solvent does not exceed 100 ppm yields a white solid product with a molecular weight of 650 Da.

[0052] The catalyst preparation method of this embodiment includes the following steps: S1 Ligand pretreatment: The ligand of this embodiment is further dried under an inert atmosphere until the water content does not exceed 50 ppm and the residual polar solvent does not exceed 100 ppm; S2 Catalyst assembly: Under an inert atmosphere, with the oxygen and water contents not exceeding 5 ppm, the ligand of this embodiment and chromium trichloride are complexed in propane at 30°C at a molar ratio of ligand to chromium of 2.8:1 for 5 hours; S3 Low-temperature activation: Activation is performed by introducing a support-supported methylaluminoxane at 15°C. Pre-extraction is first performed by stirring propane at room temperature for 2 hours. After filtering to remove the solid phase of the MCM-41 support, the leaching solution is used. The aluminum concentration after leaching is controlled within ±8%. After filtration through 0.22 μm, the supernatant has no visible solid particles, and the molar ratio of Al to Cr is controlled at 65:1; S4 Adjustment of chlorinated organoaluminum additive: The chlorinated organoaluminum additive is added in two stages. The first stage adds 65% of the total amount, and the second stage adds an adduct solution. In this embodiment, the adduct solution is formed by premixing diethylaluminum chloride and 2,6-dimethylpyridine at a molar ratio of 18:1 at 1°C for 18 minutes. The addition rate of the second stage is controlled at 0.02 mol Cl⁻ / (mol Cr·min). The final chromium concentration in the catalyst working solution is 0.8 mmol / L.

[0053] In this embodiment, the catalyst is used to prepare α-olefins in the oligomerization reaction of ethylene. By adjusting the reaction temperature, selective preparation of α-olefins is achieved: the reaction is carried out for 5 hours at a reaction temperature of 115°C and an ethylene pressure of 3.0 MPa, with the heating and cooling rate controlled at 8°C per minute. The target temperature is maintained for 150 minutes, the mass fraction of polyethylene by-products is controlled at 0.7%, the purity of α-olefins reaches 93%, the product switching cycle is 4 hours, the molar ratio of Cl to Cr is 2.1, and the volume fraction of ethyl aluminum chloride is not lower than that of isobutyl aluminum chloride, the selectivity of 1-hexene reaches 89%.

[0054] Features of Example 3: This example specifically optimizes the selectivity of 1-hexene by employing a higher chromium concentration and ligand ratio, using a carrier-supported methylaluminoxane as the activator, a higher proportion of ethylaluminum dichloride in the chlorine-containing auxiliary agent, and controlling the reaction temperature within a high range. This configuration effectively improves the selectivity of 1-hexene and is particularly suitable for high-temperature operating conditions. It is suitable for industrial plants specifically producing 1-hexene, especially for large-scale production scenarios requiring high activity and high selectivity. Example 4

[0055] A catalyst with tunable α-olefin selectivity, comprising: 1) Chromium compounds were selected as the catalytically active components, using a mixture of chromium trichloride and chromium trivalent acetylacetonate in a mass ratio of 1:1, based on a catalyst working solution concentration of 0.1 mmol / L; 2) Multidentate ligand: The multidentate ligand in this embodiment is prepared by reacting 1,10-phenanthroline with amine, aldehyde and phosphine compounds at 100°C to form a nitrogen-phosphorus coordination group, which is then linked with 1,4-dibromobutane and then formed with 2,6-dimethylphenylboronic acid and 4,5-dimethylcatechol at 120°C to form a cyclic borate ester bond. The ligand contains two nitrogen coordination atoms and one phosphorus coordination atom, and the molar ratio of the ligand to chromium is 2.9:1. 3) Activator: Carrier-supported methylaluminoxane is selected. In this embodiment, the carrier is γ-Al2O3, and the molar ratio of aluminum to chromium is 75:1. 4) Chlorine-containing organoaluminum additives: In this embodiment, the chlorine-containing organoaluminum additives are a mixture of diethylaluminum chloride, isobutylaluminum chloride, and ethylaluminum chloride. The total proportion of isobutylaluminum chloride and ethylaluminum chloride is 55%. The three are mixed in a volume ratio of 6:3:1, and the molar ratio of chlorine to chromium is 4.5:1. 5) An inert hydrocarbon solvent is used as the dilution medium, with ethane selected, accounting for 97% of the total volume of the catalyst working solution.

[0056] The method for preparing the multidentate ligand in this embodiment includes the following steps: A1. Formation of nitrogen-phosphorus coordination groups: Under nitrogen protection, 1,10-phenanthroline, an amine compound, an aldehyde compound, and a phosphine compound are reacted in anhydrous dichloromethane at 100°C for 4 hours with stirring to form nitrogen-phosphorus coordination groups; A2. Introduction of linking units: Under an inert atmosphere, the above product is refluxed with a 1,4-dibromobutane linking unit at 80°C for 10 hours in the presence of potassium carbonate at a molar ratio of 1:0.6; A3. Formation of cyclic borate ester bonds: 2,6-dimethylphenylboronic acid and 4,5-dimethylcatechol are added in anhydrous toluene at 120°C for 2 hours with continuous dehydration during the reaction, and cyclic borate ester bonds are formed in the presence of a 4 Å molecular sieve; A4. Separation and purification: After the reaction was completed, the mixture was cooled to room temperature and recrystallized in a mixed solvent of methanol and isopropanol for separation and purification. The product was then vacuum dried at 80°C and a pressure not exceeding 1 mmHg for 12 hours until the water content did not exceed 50 ppm and the total amount of residual polar solvent did not exceed 100 ppm, yielding a pale yellow solid product with a molecular weight of 750 Da.

[0057] The catalyst preparation method of this embodiment includes the following steps: S1 Ligand pretreatment: The ligand of this embodiment is further dried under an inert atmosphere until the water content does not exceed 50 ppm and the residual polar solvent does not exceed 100 ppm; S2 Catalyst assembly: Under an inert atmosphere, with the oxygen and water content not exceeding 5 ppm, the ligand and chromium compound mixture of this embodiment is complexed in ethane at 40°C at a molar ratio of ligand to chromium of 2.9:1 for 6 hours; S3 Low-temperature activation: Activation is performed by introducing a support-supported methylaluminoxane at 25°C. Pre-extraction is first performed by stirring in ethane at room temperature for 4 hours. After filtering to remove the γ-Al2O3 support solid phase, the extraction solution is used. The aluminum concentration after extraction is controlled within ±5%. After filtration through 0.22 μm, the supernatant has no visible solid particles, and the molar ratio of Al to Cr is controlled at 75:1; S4 Adjustment of chlorinated organoaluminum additive: The chlorinated organoaluminum additive is added in two stages. The first stage adds 70% of the total amount, and the second stage adds an adduct solution. In this embodiment, the adduct solution is formed by premixing diethylaluminum chloride and 2,6-dimethylpyridine at a molar ratio of 20:1 at 0°C for 20 minutes. The addition rate of the second stage is controlled at 0.05 mol Cl⁻ / (mol Cr·min), and the final chromium concentration in the catalyst working solution is 0.1 mmol / L.

[0058] In this embodiment, the catalyst is used to prepare α-olefins in the oligomerization reaction of ethylene. Selective preparation of α-olefins is achieved by adjusting the reaction temperature: the reaction is carried out at a reaction temperature of 120°C and an ethylene pressure of 3.5 MPa for 6 hours, with the heating and cooling rate controlled at 10°C per minute. The target temperature is maintained for 180 minutes, the mass fraction of polyethylene by-products is controlled at 0.9%, the purity of α-olefins reaches 91%, and the product switching cycle is 5 hours. The selectivity adjustment effect is further optimized by adjusting the proportion of different components. When switching between 70-95°C and 105-130°C, the selectivity change does not exceed 2 percentage points, and the selectivity of 1-hexene reaches 92%.

[0059] Example 4 Features: This example explores the parameter boundary region, employing a mixed chromium source at a lower concentration, a ligand ratio close to the upper limit, a higher activator dosage, a chlorine-containing auxiliary agent ratio reaching the upper limit, and a complex mixture of three components, with the solvent ratio close to the maximum value. This configuration exhibits strong adaptability and adjustability, enabling precise control of product selectivity over a wide temperature range. It is suitable for flexible production facilities requiring frequent changes in product specifications, as well as special applications with extremely demanding catalyst performance requirements.

[0060] Comparative Example 1: It is basically the same as Example 1, except that the reaction temperature for the formation of nitrogen-phosphorus coordination groups in step A1 is 45°C, while other conditions remain unchanged.

[0061] Comparative Example 2: Basically the same as Example 1, except that the concentration of chromium compound was 1.5 mmol / L, while other components and process conditions remained unchanged.

[0062] Comparative Example 3: Basically the same as Example 1, except that the molar ratio of ligand to chromium is 1.5:1, and other conditions remain unchanged.

[0063] Comparative Example 4: It is basically the same as Example 1, except that the molar ratio of chlorine to chromium is 0.3:1, while the other component ratios and preparation conditions remain unchanged.

[0064] Comparative Example 5: Basically the same as Example 1, except that the molar ratio of aluminum to chromium is 20:1, and other conditions remain unchanged.

[0065] Comparative Example 6: It is basically the same as Example 1, except that the reaction temperature for the formation of the cyclic borate ester bond in step A3 is 60°C, while other preparation conditions remain unchanged.

[0066] Comparative Example 7: Basically the same as Example 1, except that the complexation temperature of the ligand and chromium compound during the catalyst assembly process in step S2 is 60°C, while other conditions remain unchanged.

[0067] Comparative Example 8: It is basically the same as Example 1, except that the reaction time in step A1 is 2 hours, while other preparation conditions remain unchanged.

[0068] Comparative Example 9: Basically the same as Example 1, except that 1,10-phenanthroline was used instead of 2,2'-bipyridine in the preparation of the multidentate ligand, and a combination of 2,6-dimethylphenylboronic acid and 4,5-dimethylcatechol was used in step A3, while other conditions remained unchanged.

[0069] Comparative Example 10: Basically the same as Example 1, except that only isobutyl aluminum chloride was used as the chlorine-containing organoaluminum additive, while other components and conditions remained unchanged.

[0070] Comparative Example 11: Basically the same as Example 1, except that the activator was replaced with methylaluminoxane instead of triethylaluminum, and other conditions remained unchanged.

[0071] Comparative Example 12: It is basically the same as Example 1, except that the temperature of the low-temperature activation process in step S3 is 40°C, while other process conditions remain unchanged.

[0072] Comparative Example 13: Basically the same as Example 1, except that in step A4 the vacuum drying temperature is 40°C, the pressure is 5 mmHg, the drying time is 8 hours, and other conditions remain unchanged.

[0073] Comparative Example 14: Basically the same as Example 1, except that the second addition rate of the chlorine-containing organoaluminum additive in step S4 is 0.1 mol Cl⁻ / (mol Cr·min), while other conditions remain unchanged.

[0074] Comparative Example 15: Basically the same as Example 1, except that only cyclohexane was used as the inert hydrocarbon solvent, accounting for 75% of the total volume of the catalyst working solution, while the proportions of other components and preparation conditions remained unchanged.

[0075] Performance testing: 1. Selectivity Adjustment Performance Test: The test object is the catalyst working solution. The purpose of the test is to verify the catalyst's core ability to solve the problem of "limited selectivity" and evaluate its ability to adjust the selectivity of 1-octene and 1-hexene under different reaction conditions. The test principle is based on the influence mechanism of temperature-driven ligand conformational changes on the distribution of ethylene oligomers. The experimental method sets test points in two temperature windows: a low-temperature range of 80℃, 87℃, and 95℃, and a high-temperature range of 105℃, 115℃, and 125℃, corresponding to adjusting the Cl to Cr molar ratios of 1.2-1.8 and 1.8-2.3, while ensuring that the volume fraction of isobutylaluminum chloride is not lower than that of ethylaluminum chloride (low temperature) and that the volume fraction of ethylaluminum chloride is not lower than that of isobutylaluminum chloride (high temperature). Key parameters include a constant Al to Cr molar ratio of 50:1, ethylene pressure of 2.0 MPa, reaction time of 4 hours, heating / cooling rate of 5℃ / min, and temperature stabilization time of 90 minutes.

[0076] 2. Product Switching Response Test: The test object is the catalyst working solution. The purpose of the test is to verify the key technical characteristics of the catalyst that overcome the traditional "limited selectivity function" and evaluate the response rate and stability when switching between 1-octene and 1-octene production modes. The test principle is based on the temperature-induced rapid selective conversion mechanism of the catalyst and the synergistic effect of staged additive addition. Experimental method: Programmed temperature switching was performed between 70-95℃ (1-octene mode) and 105-130℃ (1-hexene mode). The addition of the second adduct solution was strictly performed according to the claims (rate ≤0.05 mol Cl⁻ / (mol Cr·min)). Online μ-GC was used to improve monitoring accuracy. Key parameters include heating and cooling rate of 5℃ / min, temperature switching cycle of 3 hours, stability criterion of selectivity change of <1% over 30 consecutive minutes at 3 rolling average points, monitoring frequency every 10 minutes, and 10 switching cycles. Data processing records the response time and switching efficiency of product switching, requiring a switching response time of <30 minutes and a steady-state selectivity change of ≤3 percentage points to demonstrate the rapid response of the steric hindrance regulation mechanism. Statistical requirements include n≥3, and data are expressed as mean ± standard deviation.

[0077] 3. Catalyst Activity Evaluation Test: The test object is the catalyst working solution. The purpose of the test is to verify that high catalytic activity is maintained while solving the selectivity problem, ensuring the practicality of the technical solution. The test principle is based on the kinetics of ethylene coordination polymerization and catalyst turnover frequency analysis. Experimental Method: Ethylene oligomerization reaction was carried out in a high-pressure reactor. Two representative conditions were controlled: reaction temperature 80℃ and 115℃. The product composition was analyzed by gas chromatography, and the ethylene conversion rate and initial reaction rate were calculated. Key parameters included catalyst concentration 0.3 mmol / L, ethylene pressure 2.0 MPa, reaction time 4 hours, and sampling interval 30 minutes (first 2 hours). Data Processing: The initial reaction rate was calculated as kg α-olefin / (mol Cr·h), and the carbon yield (≥98%) was reported to verify the catalyst's ability to maintain activity during the selectivity adjustment process. Statistical requirements: parallel experiments n≥3, relative standard deviation RSD<5%.

[0078] 4. Byproduct Control Performance Test: The test object is the product of ethylene oligomerization. The purpose of the test is to verify that the catalyst effectively inhibits the formation of byproducts such as polyethylene through steric hindrance regulation, solving the problem of excessive byproducts in traditional catalysts. The test principle is based on the mechanism of steric hindrance effect on degree of polymerization control and quantitative detection by gravimetric analysis. The experimental method separates and determines the content of solid polyethylene byproducts using a modified gravimetric method, including relative centrifugal force calculation and hot toluene washing steps, and analyzes the purity of α-olefins by gas chromatography. The standard reference is ASTM E1131-2020 "General Principles of Thermogravimetric Analysis" combined with the company's SOP. Key parameters include two temperature windows (80℃ and 115℃), reaction time of 4 hours, centrifugation conditions of 3000 rpm × 10 minutes, and hot toluene washing at 60℃ × 2 times. Data processing calculates the mass fraction of polyethylene byproducts and the purity of α-olefins, requiring that the mass fraction of polyethylene byproducts be ≤5% and the purity of α-olefins be ≥90%, to prove the effectiveness of steric hindrance regulation. The statistical requirement is n≥5, and the data are expressed as mean ± standard deviation.

[0079] 5. Catalyst Component Ratio Verification Test: The test object is the catalyst working solution. The purpose of the test is to verify whether the molar ratio of key components meets the design requirements and ensure the realization of the steric hindrance adjustment function. The test principle is based on precise quantitative analysis using inductively coupled plasma atomic emission spectrometry, hydrolysis titration, and quantitative 31P NMR. Experimental methods: ICP-AES is used to determine the chromium and aluminum content, hydrolysis titration is used to determine the total chlorine content, and 31P quantitative NMR is used to determine the ligand concentration. The standards are based on ASTM E1479-2016 and ASTM D512-2012. Key parameters include the precise control of Al / Cr molar ratio (30-80:1), Cl / Cr molar ratio (0.5-5:1), and ligand / Cr molar ratio (2.0-3.0:1). Data processing verifies the consistency between the actual ratio and the design value, ensuring the effective implementation of the steric hindrance adjustment mechanism. The relative error of each ratio is required to be <5%, and the statistical requirement is n≥3. Data are expressed as mean ± standard deviation.

[0080] 6. Validation of Gas Chromatography Quantitative Analysis Method: The test object is a mixture of ethylene oligomerization products. The purpose of the test is to establish an accurate and reliable selective determination method, providing a reliable analytical basis for verifying the effect of steric hindrance control. The test principle is based on component separation and quantitative detection by gas chromatography, using a combination of internal and external standard methods for calibration. Experimental methods: A gas chromatograph equipped with an FID detector was used. The PLOT Al2O3 column was specially passivated to establish standard curves for target products such as 1-butene, 1-octene, and 1-hexene. Key parameters include programmed temperature conditions, internal standard n-decane concentration of 1000 ppm, and column passivation steps. Data processing: An accurate quantitative method was established, the limit of detection (<10 ppm) and linear range were calculated, and the precision (RSD <3%) and accuracy (recovery rate 95-105%) were validated to ensure the reliability of the selectivity data. The linear correlation coefficient R² > 0.999 was required to provide methodological assurance for the accurate evaluation of the effect of steric hindrance control.

[0081] The catalysts of Examples and Comparative Example 1 are summarized in Table 1. The comparative results show that deviations from the optimal range of each process parameter have varying degrees of negative impact on catalytic performance: At excessively low temperatures, the formation of nitrogen-phosphorus coordinating groups and cyclic borate ester bonds is insufficient, leading to decreased ligand coordination ability and spatial structural defects; excessively high chromium concentration causes overcrowding of the metal center, deteriorating the coordination environment; excessively low ligand / Cr ratio causes coordination unsaturation and severe inadequacy of steric hindrance regulation; excessively low Cl / Cr ratio weakens electronic regulation ability; excessively low Al / Cr ratio leads to insufficient activation; excessively short reaction time results in incomplete ligand synthesis and structural defects; changes in ligand structure affect the spatial regulation effect of the rigid framework; single promoters lack synergistic effects; while MAO activator provides good activity, it increases byproduct formation. These deviations are collectively manifested in decreased selectivity for 1-octene and 1-hexene, reduced catalytic activity, increased byproducts, and prolonged response time, fully verifying the scientific nature of the optimal parameter combination of this invention and the importance of the synergistic effect of each component.

[0082] Table 1 Summary of the performance of catalysts in the examples and comparative examples

[0083]

[0084] Figure 1For the stage comparison (formation of nitrogen-phosphorus coordination groups / introduction of linking units / formation of cyclic borate ester bonds / separation and purification): the basic conditions are four-stage FTIR transmission measurements of samples from the same route (KBr pellet or film, 4000-500 cm⁻¹, transmittance %). Nitrogen-phosphorus coordination group formation involves reacting rigid framework compounds with amine, aldehyde, and phosphine compounds at 60-100 ℃ for 4-12 h. Linking unit introduction is carried out under reflux of potassium carbonate and 1,4-dibromobutane at 80 ℃ for 6-10 h. Cyclic borate ester bond formation is achieved by reacting anhydrous toluene, molecular sieve at 4 Å, 80-120 ℃ for 2-8 h with continuous dehydration. Separation and purification are completed by column chromatography or recrystallization followed by vacuum drying at 60-80 ℃ and ≤1 mmHg for 12-24 h. Peak position changes show that the common aromatic framework peaks at 1600 / 1500 / 1450 cm⁻¹ are consistently present and only ±5-15 cm⁻¹. cm⁻¹ micro-drift, the PN / CN characteristics (~1245, ~980) appear and are enhanced during the nitrogen-phosphorus coordination group formation stage, while the C=O of the aldehyde compound (1680-1740, example 1690) is significantly reduced or disappears. During the linker unit introduction stage, the alkyl CH of the 1,4-dibromobutane linker unit (2955 / 2920 / 2850) is relatively enhanced. During the cyclic boronic acid ester bond formation stage, after the arylboronic acid forms a ring with the ortho-dihydroxy compound, BO (1 The new peaks of 360-1440 (Example 1406) and BOC (1200-1300, Example 1262) are significantly deeper and sharper, and the broadband phenol-OH of the ortho-dihydroxy compound (3200-3600, Example 3350) is significantly weakened / disappeared. The separation and purification stage further reduces residual water / residual polar solvent (the shallow valleys of ~3350 and 2920 / 2850 become shallower) and makes the BO / BOC peaks cleaner (FWHM slightly narrowed).

[0085] Figure 2 Temperature gradient experiments under constant reaction time and stoichiometric conditions clearly demonstrated the existence of an optimal temperature range for the formation of cyclic borate ester bonds: during the temperature increase from 90℃ to 100℃, the BO characteristic peak shifted from 1402 cm⁻¹ to 1408 cm⁻¹ with a blue shift and narrower, while the BOC peak shifted from 1255 cm⁻¹ to 1263 cm⁻¹ with a significant increase. Simultaneously, the broadband phenol-OH band (3345±25 cm⁻¹) was significantly weakened. These changes collectively indicate that increased temperature promotes the cyclization reaction of arylboronic acid with catechol and improves dehydration efficiency. However, at 115℃, the BO peak red-shifted back to 1400 cm⁻¹ with a decrease in intensity and an increase in bandwidth, while the BOC peak dropped back to 1250-1255 cm⁻¹, and the OH peak relatively rebounded. This inverse change confirms that excessively high temperatures may induce partial hydrolysis or side reactions of the cyclic structure, thus verifying that 100℃ is the optimal temperature for this reaction system. Figure 3Time gradient studies at a constant temperature of 100℃ further support this conclusion: the continuous enhancement and blue shift of the BO and BOC peaks and the weakening of the phenol-OH peak within 3-5 hours demonstrate that the reaction proceeds in the forward direction, while the slight decline at 8 hours is consistent with... Figure 2 The trend at 115℃ is consistent, indicating that excessively long reaction times may also lead to partial degradation of the product. Therefore, 5 hours was established as the optimal reaction time. The spectral variation patterns in the two figures mutually confirm the rationality of the optimized reaction conditions.

[0086] pass Figure 4-11 The systematic experimental data analysis fully demonstrates the rationality, reliability, and effectiveness of the technical solution of this invention. The temperature-performance relationship of the nitrogen-phosphorus coordination group formation reaction shows that the reaction temperature exhibits a distinct volcano-shaped curve characteristic within the range of 45-105℃, reaching the optimal equilibrium point at 80℃. At this point, the selectivity for 1-octene is 77.2%, the selectivity for 1-hexene is 89.1%, the catalytic activity reaches 148 kg / (mol Cr·h), and the ligand purity is as high as 96.5%. This result is completely consistent with the coordination chemistry theory, proving that 80℃ is the optimal thermodynamic and kinetic equilibrium temperature for the formation of nitrogen-phosphorus coordination bonds. Furthermore, the optimization experiment of the nitrogen-phosphorus coordination group formation reaction time further verifies the reliability of this conclusion. Optimal performance data completely consistent with the 80℃ temperature condition was obtained at a reaction time of 8 hours, indicating that the reaction system reached a sufficient equilibrium state under these conditions. More importantly, the temperature and time optimization experiments for the cyclic borate ester bond formation reaction showed a high degree of consistency and complementarity. Under the combined conditions of a reaction temperature of 100℃ and a reaction time of 4 hours, not only did the olefin selectivity remain consistent with the optimal value of the nitrogen-phosphorus coordination system, but the borate ester stability also reached a high level of 95.1%. This synergistic optimization of performance indicators among different reaction steps fully demonstrates the scientific rationality of the multi-step synthetic route design of this invention. All experimental data showed clear single-peak optimization curves, avoiding both insufficient performance due to incomplete reaction and preventing side reactions and product degradation caused by over-reaction. This precise process window control reflects the high reliability of the technical solution of this invention. The synergistic improvement effect of various performance indicators, especially the simultaneous optimization of olefin selectivity, catalytic activity, ligand purity, and borate ester stability under optimal reaction conditions, strongly proves that this invention not only achieved the expected technical objectives but also demonstrated excellent industrial application potential and technological advancement.

[0087] pass Figure 12-15 The systematic experimental data analysis fully demonstrates the rationality, reliability, and effectiveness of the technical solution of this invention. From... Figure 12The comparison of olefin selectivity clearly shows that the 1-octene selectivity of Examples 1-4 of this invention at 80°C remains at a high level of 75.8%-79.1%, which is a significant improvement compared to 62.5%-74.1% of Comparative Examples 1-15, with an average improvement of 8.1 percentage points. At the same time, the 1-hexene selectivity at a high temperature of 115°C reaches an excellent level of 87.3%-92.1%, far exceeding the 77.1%-86.7% of the Comparative Examples. This synergistic optimization of selectivity under dual temperature conditions fully verifies the scientific rationality of the catalyst molecular design of this invention. Figure 13 The comparative data on catalytic activity and byproducts further confirmed the reliability of the technical solution. The catalytic activity of the embodiment was stably maintained in the range of 138-156 kg / (mol Cr·h), showing good activity stability. More importantly, the polyethylene byproduct content was strictly controlled at an extremely low level of 0.5%-0.9%, achieving a byproduct reduction rate of up to 75% compared to 1.3%-4.8% in the comparative example. This result not only proves the high selectivity of the catalyst, but also reflects the significant advantage of reducing product separation costs in industrial applications. Figure 14 The analysis of response time and selectivity variation range demonstrates the outstanding technical advantages of the present invention. The switching response time of the embodiment is only 25-33 minutes, which is 40.8% shorter than the 38-65 minutes of the comparative example. This rapid response capability is of great significance for flexible production of multiple products. At the same time, the selectivity variation range is controlled within a narrow range of 1.9%-2.9%, which is far better than the 3.8%-8.5% of the comparative example, indicating that the catalyst has excellent stability and controllability during the switching of operating conditions. Figure 15 The comprehensive evaluation of olefin purity and catalytic efficiency ultimately confirmed the effectiveness of the present invention. The α-olefin purity reached a high level of 91.8%-94.1%, which is an average increase of 7.3 percentage points compared with the comparative example. Combined with stable catalytic activity, the invention achieved dual optimization of product quality and production efficiency. This synergistic improvement effect of multiple indicators strongly proves that the present invention is not only innovative in theoretical design, but also shows excellent industrialization potential and significant technological advancement in practical applications.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A catalyst with adjustable α-olefin selectivity, characterized in that, Include: 1) Chromium compounds are used as the catalytically active component. The chromium compounds are selected from at least one of chromium trichloride and chromium trivalent acetylacetonate, based on the concentration of the catalyst working solution being 0.01-1.0 mmol / L; 2) A multidentate ligand, wherein the multidentate ligand is prepared by reacting 2,2'-bipyridine or 1,10-phenanthroline with amine, aldehyde and phosphine compounds at 60-100°C to form a nitrogen-phosphorus coordination group, which is then linked with 1,4-dibromobutane and subsequently formed with arylboronic acid and ortho-dihydroxy compound at 80-120°C to form a cyclic borate ester bond. The ligand contains at least two nitrogen coordination atoms and at least one phosphorus coordination atom. The arylboronic acid is selected from phenylboronic acid and 2,6-dimethylphenylboronic acid, and the ortho-dihydroxy compound is selected from catechol and 4,5-dimethylcatechol. The molar ratio of the ligand to chromium is 2.0-3.0:

1. 3) Activator, selected from at least one of triethylaluminum, methylaluminoxane, and carrier-supported methylaluminoxane, with a molar ratio of aluminum to chromium of 30-80:1; 4) Chlorine-containing organoaluminum additive, wherein the chlorine-containing organoaluminum additive is selected from at least one of diethylaluminum chloride, isobutylaluminum chloride, and ethylaluminum chloride or a mixture thereof, preferably diethylaluminum chloride as the main component, and the total proportion of isobutylaluminum chloride and ethylaluminum chloride is 20-60%, more preferably mixed in a volume ratio of 5:4:1 to 7:2:1, and the molar ratio of chlorine to chromium is 0.5-5:1; 5) An inert hydrocarbon solvent, selected from at least one of propane or ethane, is used as a dilution medium, accounting for 85-98% of the total volume of the catalyst working solution.

2. The catalyst with adjustable α-olefin selectivity as described in claim 1, characterized in that, The method for preparing the multidentate ligand is characterized by comprising the following steps: A1. Formation of nitrogen-phosphorus coordination groups: Under nitrogen protection, rigid skeleton compounds, amine compounds, aldehyde compounds, and phosphine compounds are reacted in anhydrous toluene or dichloromethane at a molar ratio of 1.0:1.2:1.1:1.2 for 4-12 hours with stirring to form nitrogen-phosphorus coordination groups. A2. Introduction of the linking unit: Under an inert atmosphere, the above product is refluxed with a 1,4-dibromobutane linking unit containing 4 methylene groups at a molar ratio of 1:0.6 in the presence of potassium carbonate at 80°C for 6-10 hours. A3. Cyclic borate ester bond formation: Cyclic borate ester bonds are formed by adding arylboronic acid and ortho-dihydroxy compound in the presence of molecular sieve 4 Å; A4. Separation and purification: The target ligand is obtained by separation and purification by column chromatography or recrystallization and vacuum drying.

3. The catalyst with adjustable α-olefin selectivity as described in claim 2, characterized in that, The arylboronic acid mentioned in step A3 is selected from phenylboronic acid and 2,6-dimethylphenylboronic acid, and the ortho-dihydroxy compound is selected from catechol and 4,5-dimethylcatechol. The arylboronic acid and the ortho-dihydroxy compound are reacted in anhydrous toluene at a molar ratio of 2.2:2.0 for 2-8 hours at 80-120°C, with continuous dehydration during the reaction.

4. The catalyst with adjustable α-olefin selectivity as described in claim 2, characterized in that, The separation and purification described in step A4 is as follows: after the reaction is complete, cool to room temperature, preferably use silica gel column chromatography with gradient elution of petroleum ether to toluene in a volume ratio of 2:1 to 1:1, or recrystallize in a mixed solvent of methanol and isopropanol for separation and purification.

5. The catalyst with adjustable α-olefin selectivity as described in claim 2, characterized in that, The vacuum drying conditions described in step A4 are as follows: drying at 60-80°C and a pressure not exceeding 1 mmHg for 12-24 hours until the moisture content does not exceed 50 ppm and the total amount of residual polar solvent does not exceed 100 ppm, to obtain a white to pale yellow solid product with a molecular weight of 400-800 Da.

6. The catalyst with adjustable α-olefin selectivity as described in claim 1, characterized in that, The molar ratio calculated based on chromium is: Al to Cr 30-80:1, preferably 40-60:1, Cl to Cr 0.5-5:1, preferably 1-3:

1. The molar ratio of Al to Cr is the molar ratio of aluminum to chromium from the activator source, and does not contain chlorinated organoaluminum additives. The molar ratio of Cl to Cr is calculated based on chlorinated organoaluminum additives. The carrier of the carrier-supported methylaluminoxane is selected from at least one of MCM-41, SBA-15, and γ-Al2O3. When using carrier-supported methylaluminoxane, a soluble methylaluminoxane solution is obtained by pre-extraction with a hydrocarbon solvent. After extraction, the aluminum concentration deviation is controlled within ±10%. After filtration through 0.22 μm, the supernatant has no visible solid particles.

7. A method for preparing a catalyst with adjustable α-olefin selectivity as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1 Ligand pretreatment: The ligand is further dried under an inert atmosphere until the moisture content does not exceed 50 ppm and the residual polar solvent does not exceed 100 ppm; S2 catalyst assembly: Under an inert atmosphere, with oxygen and water content not exceeding 5 ppm, the ligand and chromium compound are complexed in an inert hydrocarbon solvent at a ligand to chromium molar ratio of 2.0-3.0:1 at 0-40°C for 1-6 hours. S3 Low-temperature activation: Activation is carried out by introducing an activator at -10 to 25°C, and the molar ratio of Al to Cr is controlled at 30-80:1; S4 Chlorine-containing organoaluminum additive adjustment: The chlorine-containing organoaluminum additive is added in two stages. The first stage adds 50-70% of the total amount, and the second stage adds the adduct solution. The addition rate of the second stage does not exceed 0.05 mol Cl⁻ / (mol Cr·min). The final chromium concentration in the catalyst working solution is 0.01-1.0 mmol / L.

8. The method for preparing a catalyst with adjustable α-olefin selectivity as described in claim 7, characterized in that, The adduct solution is formed by a chlorinated organoaluminum auxiliary agent and a weak base ligand L, wherein the weak base ligand L is selected from at least one of 2,6-dimethylpyridine and tetrahydrofuran, preferably 2,6-dimethylpyridine; diethylaluminum chloride and the weak base ligand L are premixed at a molar ratio of 10:1 to 20:1 at 0-5°C for 10-20 minutes; when a carrier-supported methylaluminoxane is used, it is first pre-extracted by stirring with a hydrocarbon solvent at room temperature for 1-4 hours, and the carrier solid phase is removed by filtration before using the extract.

9. The application of the catalyst with adjustable α-olefin selectivity as described in any one of claims 1 to 6 in the preparation of α-olefins in the ethylene oligomerization reaction, characterized in that, Selective preparation of α-olefins was achieved by adjusting the reaction temperature: at a reaction temperature of 70-95℃, with a Cl to Cr molar ratio of 1.2-1.8 and an isobutylaluminum chloride volume fraction not lower than that of ethylaluminum chloride, the selectivity for 1-octene reached 75-80%; at a reaction temperature of 105-130℃, with a Cl to Cr molar ratio of 1.8-2.3 and an ethylaluminum chloride volume fraction not lower than that of isobutylaluminum chloride, the selectivity for 1-hexene reached 85-95%. When using diethylaluminum chloride as a chlorine-containing organoaluminum auxiliary, the catalytic performance was stable, and the polyethylene by-product content was controlled below 1%. The selectivity change range did not exceed 3 percentage points when switching between 70-95℃ and 105-130℃. When using a mixture of chlorine-containing organoaluminum auxiliaries, the selectivity adjustment effect could be further optimized by adjusting the proportion of different components. The α-olefin selectivity and polyethylene by-product content were both determined by gas chromatography.

10. The application of a catalyst with adjustable α-olefin selectivity, characterized in that, The ethylene oligomerization reaction conditions are as follows: ethylene pressure 0.5-4.0 MPa, reaction time 1-8 hours, heating and cooling rate controlled at 1-10℃ per minute, holding at the target temperature for 30-180 minutes, polyethylene by-product mass fraction controlled below 1%, α-olefin purity reaching above 90%, and product switching cycle of 0.5-6 hours.

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