A heterocyclic amine catalyst ligand and a method for preparing high-carbon α-olefins using the same.

Abstract

This invention provides a heterocyclic amine catalyst ligand and a method for preparing high-carbon α-olefins using it. The heterocyclic amine catalyst ligand is used for the catalytic synthesis of high-carbon α-olefins with more than C8 atoms. The structural formula of the catalyst ligand is as follows: where R is an aromatic group or alkyl group, and R1 is hydrogen or methyl. In this scheme, when the catalyst ligand with the above structure is mixed with a chromium source and a co-catalyst and introduced into an ethylene reaction system for in-situ polymerization, the presence of four nitrogen atoms in the ligand structure allows for easier coordination with transition metals, resulting in a rapid reaction. This allows the ligand structure to directly achieve in-situ polymerization of olefins without the need for a synthetic catalyst. Simultaneously, the R group (phenyl or alkyl) in the ligand structure increases the steric hindrance of the ligand, limiting the approach angle and direction of reactant molecules, thus facilitating the selective generation of high-carbon α-olefins with more than C8 atoms.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, and in particular to a heterocyclic amine catalyst ligand and a method for preparing high-carbon α-olefins using the same. Background Technology

[0002] Alpha-olefins, as comonomers, can be used to develop polyethylene products with higher monomer content and superior performance. However, the slow pace of domestic production has become a bottleneck in the development of polyethylene in my country. Alpha-olefins refer to monoolefins with double bonds at the ends of their molecular chains. Generally, C8 and above are considered high-carbon alpha-olefins. Both low-carbon and high-carbon alpha-olefins have indispensable applications. C4-C8 are used as comonomers for polyethylene, C6-C8 are used for POE and low molecular weight fatty acids, and C8-C... 12 Used in PAO, lubricating oils and amine additives, C 12 -C 16 Used in the production of detergents, C 18 + Used in lubricants and drilling fluids.

[0003] Currently, the main production processes for α-olefins are: wax cracking, mixed C4 separation, ethylene oligomerization / polymerization, and vegetable oil methods. Among these, ethylene oligomerization and polymerization are the primary methods for producing α-olefins. Catalysts play a crucial role in the efficient and high-yield production of α-olefins. Chromium catalysts, using a metal cycling mechanism, are now widely accepted for catalyzing the trimerization of ethylene. Chromium-based catalysts have attracted considerable attention due to their high selectivity for linear olefins (especially 1-hexene and 1-octene). Even slight changes in the ligand structure can significantly alter their metal coordination ability and the catalytic activity of the complex. Therefore, by rationally adjusting and modifying the ligand structure, highly active transition metal polyolefin catalysts can be developed. Although a large number of transition metal polyolefin catalysts have been developed, these catalysts currently exhibit high selectivity for C8 α-olefins and are mostly used for synthesizing C8 α-olefins, not for the synthesis of α-olefins with more than C8 olefins.

[0004] Therefore, there is an urgent need to provide a heterocyclic amine catalyst ligand and a method for preparing high-carbon α-olefins using it. Summary of the Invention

[0005] This invention provides a heterocyclic amine catalyst ligand and a method for preparing high-carbon α-olefins using the same, which can solve the problem of low selectivity of traditional catalysts for α-olefins with C8 or more.

[0006] In a first aspect, the present invention provides a heterocyclic amine catalyst ligand for catalytic synthesis of high-carbon α-olefins with more than 8 carbon atoms;

[0007] The structural formula of the catalyst ligand is as follows:

[0008]

[0009] In the formula, R is an aromatic group or an alkyl group, and R1 is a hydrogen group or a methyl group.

[0010] Preferably, the aromatic group is phenyl, and the alkyl group has an even number of carbon atoms between 2 and 8.

[0011] Preferably, the catalyst ligand has the following structural formula:

[0012]

[0013] In a second aspect, the present invention also provides a method for preparing the heterocyclic amine catalyst ligand according to any one of the first aspects above, the method comprising: dissolving an aldehyde reactant and an amine reactant separately in a first organic solvent, and then mixing and reacting the two to obtain the heterocyclic amine catalyst ligand; wherein the aldehyde reactant is pyrrole-2-carboxaldehyde or 3,5-dimethyl-2-pyrrolecarboxaldehyde, and the amine reactant is ethylenediamine, butanediamine, hexamethylenediamine, octanediamine, or p-phenylenediamine.

[0014] Preferably, the first organic solvent is methanol, and the molar ratio of the aldehyde reactant to the amine reactant is (10-11):(0.5-5).

[0015] Preferably, the mixing reaction is carried out at a temperature of 20-35°C for 12-24 hours.

[0016] Thirdly, the present invention also provides a method for preparing high-carbon α-olefins from heterocyclic amine catalyst ligands according to any one of the first aspects, the method comprising:

[0017] Heterocyclic amine catalyst ligand, chromium source, co-catalyst, and second organic solvent are introduced into an ethylene gas reaction system for in-situ polymerization to obtain the high carbon α-olefin; wherein the high carbon α-olefin is an α-olefin with more than 8 carbons.

[0018] Preferably, the chromium source is chromium 2-ethylhexanoate, the second organic solvent is cyclohexane, n-hexane or methylcyclohexane, and the co-catalyst is a composite system of diethylaluminum monochloro and triethylaluminum.

[0019] Preferably, the content of the heterocyclic amine catalyst ligand is 2-5 μmol, the content of the chromium source is 2-5 μmol, the content of the second organic solvent is 15-25 mL, and the molar ratio of the co-catalyst to the chromium source is (100-800):1.

[0020] Preferably, the reaction temperature is 50-70℃, the time is 30-60 min, and the pressure is 1.0-3.0 MPa.

[0021] Fourthly, the present invention also provides a heterocyclic amine metal catalyst, which is obtained by reacting the heterocyclic amine catalyst ligand described in any one of the first aspects with a trivalent chromium salt.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] This invention provides a five-membered heterocyclic amine catalyst ligand structure. This catalyst ligand structure exhibits high selectivity for high-carbon α-olefins with C8 or more atoms, and can effectively catalyze the synthesis of high-carbon α-olefins with C8 or more atoms with a chromium source. Specifically, when this catalyst ligand is mixed with a chromium source, a co-catalyst, etc., and introduced into an ethylene reaction system for in-situ polymerization, the presence of four nitrogen atoms in the ligand structure allows for easier coordination with transition metals, resulting in a rapid reaction. This allows the ligand structure to directly achieve in-situ polymerization of olefins without the need for a synthesis catalyst. At the same time, the R group (phenyl or alkyl) in the ligand structure increases the steric hindrance of the ligand, limiting the approach angle and direction of reactant molecules, thereby facilitating the selective generation of high-carbon α-olefins with C8 or more atoms. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 These are the infrared spectra of the catalyst ligands prepared in Examples 1 to 3 of this invention;

[0026] Figure 2 This is the 1H NMR spectrum of the catalyst ligand prepared in Example 1 of this invention;

[0027] Figure 3 This is the 1H NMR spectrum of the catalyst ligand prepared in Example 2 of this invention;

[0028] Figure 4 This is the 1H NMR spectrum of the catalyst ligand prepared in Example 3 of this invention. Detailed Implementation

[0029] 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. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] This invention provides a heterocyclic amine catalyst ligand for catalytic synthesis of high-carbon α-olefins with 8 or more carbon atoms.

[0031] The structural formula of the catalyst ligand is as follows:

[0032]

[0033] In the formula, R is an aromatic group or an alkyl group, and R1 is a hydrogen group or a methyl group.

[0034] In this embodiment of the invention, a five-membered heterocyclic amine catalyst ligand with the above-described structure is provided. This catalyst ligand exhibits high selectivity for high-carbon α-olefins with C8 or more, and can effectively catalyze the synthesis of high-carbon α-olefins with C8 or more with a chromium source. Specifically, when this catalyst ligand is mixed with a chromium source, a co-catalyst, etc., and introduced into an ethylene reaction system, it can be seen from the above formula that the ligand structure has four nitrogen atoms, which makes it easier to coordinate with transition metals and the reaction is rapid. Thus, this ligand structure can directly achieve in-situ polymerization of olefins without the need for a synthesis catalyst. At the same time, the R group (phenyl or alkyl) in the ligand structure can increase the steric hindrance of the ligand, restricting the approach angle and direction of reactant molecules, thereby facilitating the selective generation of high-carbon α-olefins with C8 or more.

[0035] According to some preferred embodiments, the aromatic group is phenyl, and the alkyl group has an even number of carbon atoms from 2 to 8 (e.g., 2, 4, 6 or 8).

[0036] In this embodiment of the invention, the structural formula of the catalyst ligand can specifically be one of the following:

[0037]

[0038]

[0039] According to some more preferred embodiments, the catalyst ligand has the following structural formula:

[0040]

[0041] In the embodiments of the present invention, the inventors have discovered through extensive experimental verification that, due to the synergistic effect between the five-membered heterocyclic structure and the p-phenylenediamine structure in the catalyst ligand of the above structure, and the fact that the ligand has two methyl electron-donating groups, the catalyst ligand of the above structure, when combined with a chromium source, can achieve the highest catalytic activity for ethylene oligomerization and selectivity for high carbon atoms above C8, thus being more conducive to the catalytic synthesis of high carbon α-olefins above C8.

[0042] This invention also provides a method for preparing the heterocyclic amine catalyst ligand according to any one of the above claims. The method includes: dissolving the aldehyde reactant and the amine reactant separately in a first organic solvent, and then mixing and reacting the two to obtain the heterocyclic amine catalyst ligand.

[0043] The aldehyde reactants are pyrrole-2-carboxaldehyde or 3,5-dimethyl-2-pyrrolecarboxaldehyde, and the amine reactants are ethylenediamine, butanediamine, hexamethylenediamine, octanediamine, or p-phenylenediamine.

[0044] In this embodiment of the invention, a series of heterocyclic amine catalyst ligands with coordination ability are prepared by performing Schiff base reactions with the above-mentioned types of aldehyde reactants and the above-mentioned types of amine reactants under certain conditions.

[0045] According to some preferred embodiments, the first organic solvent is methanol, and the molar ratio of the aldehyde reactant to the amine reactant is (10-11):(0.5-5) (for example, it can be 10:0.5, 10:2, 10:3, 10:4, 10:5, 11:0.5, 11:1, 11:3 or 11:5).

[0046] According to some preferred embodiments, the temperature of the mixing reaction is 20-35°C (e.g., 20°C, 25°C, 30°C or 35°C), and the time is 12-24h (e.g., 12h, 16h, 20h or 24h).

[0047] In this embodiment of the invention, under nitrogen protection, aldehyde and amine reactants are first dissolved in methanol. Then, the dissolved amine reactants are added dropwise to the aldehyde reactant solution. After the addition is complete, the solution is heated to react. By controlling the ratio of raw materials and reaction conditions in the reaction process, heterocyclic amine catalyst ligands with high yield and high purity can be obtained.

[0048] It should be noted that after the reaction is completed, the temperature of the reaction solution should first be lowered to room temperature. Then, the reaction product should be washed and filtered three times with n-hexane. Finally, the reaction product should be dried in a vacuum drying oven at 55°C for 24 hours to obtain the heterocyclic amine catalyst ligand solid powder.

[0049] This invention also provides a method for preparing high-carbon α-olefins using the heterocyclic amine catalyst ligand described in any one of the above claims, the method comprising:

[0050] Heterocyclic amine catalyst ligand, chromium source, co-catalyst, and second organic solvent are introduced into an ethylene gas reaction system for in-situ polymerization to obtain the high carbon α-olefin; wherein the high carbon α-olefin is an α-olefin with more than 8 carbons.

[0051] In this embodiment of the invention, the reaction for synthesizing high-carbon α-olefins using heterocyclic amine catalyst ligands must be carried out under anhydrous and oxygen-free conditions. Specifically, firstly, a stainless steel reactor equipped with a magnetic stirrer, temperature control system, and pressure regulation system is dried and its airtightness is checked. It is then replaced three times with ethylene to ensure the absence of oxygen and water influences, and preheated at a predetermined temperature. Subsequently, in an ethylene gas environment, a certain amount of cyclohexane, a co-catalyst, the prepared heterocyclic amine catalyst ligand, and a chromium source are introduced into the reactor to catalyze the oligomerization reaction of ethylene. During the reaction, the catalyst ligand structure, through its unique dual-coordination, rigid structure, electronic effects, and steric hindrance, effectively catalyzes the synthesis of high-carbon α-olefins with C8 or more carbons in conjunction with the chromium source and co-catalyst.

[0052] After the reaction was completed, the reactor was cooled to room temperature, unreacted ethylene was discharged, and the reaction was quenched with diluted HCl (10%) ethanol solution. The liquid-phase reaction products were separated from the catalyst, and quantitative analysis was performed by gas chromatography. The catalyst activity was calculated based on the reaction products.

[0053] According to some preferred embodiments, the chromium source is chromium 2-ethylhexanoate, the second organic solvent is cyclohexane, n-hexane or methylcyclohexane, and the co-catalyst is a composite system of diethylaluminum monochloro and triethylaluminum.

[0054] In this embodiment of the invention, chromium 2-ethylhexanoate is used as the chromium source, which has good solubility in organic solvents. Using it for in-situ polymerization exhibits higher activity and better selectivity for higher carbon atoms, thus being more conducive to the catalytic synthesis of higher carbon α-olefins. Furthermore, this embodiment of the invention found that, compared to a single type of cocatalyst, using a cocatalyst formed by a mixture of diethylaluminum monochloro and triethylaluminum in conjunction with the chromium source and heterocyclic amine catalyst ligands for ethylene oligomerization not only enhances the catalytic activity of the heterocyclic amine catalyst ligands but also improves the C8 polymerization rate. + To increase the yield of high-carbon olefin products, the co-catalyst in the embodiments of the present invention is preferably a mixture of diethylaluminum monochloro and triethylaluminum in a 1:1 molar ratio.

[0055] Meanwhile, compared to n-hexane and methylcyclohexane, ethylene has higher solubility in cyclohexane, allowing the co-catalyst, heterocyclic amine catalyst ligand, chromium source, and ethylene to dissolve sufficiently. This facilitates more effective collisions between ethylene and the active center, thereby increasing the chain growth rate and enabling the oligomerization of C8 cyclohexane as the solvent. + The selectivity is high, therefore, the second organic solvent in the embodiments of the present invention is preferably cyclohexane.

[0056] According to some preferred embodiments, the content of the heterocyclic amine catalyst ligand is 2-5 μmol (e.g., 2 μmol, 3 μmol, 4 μmol or 5 μmol), the content of the chromium source is 2-5 μmol (e.g., 2 μmol, 3 μmol, 4 μmol or 5 μmol), the content of the second organic solvent is 15-25 mL (e.g., 15 mL, 18 mL, 20 mL, 23 mL or 25 mL), and the molar ratio of the co-catalyst to the chromium source is (100-800):1 (e.g., 100:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1 or 800:1).

[0057] Experiments of this invention have confirmed that appropriate amounts of heterocyclic amine catalyst ligands, co-catalysts, and chromium sources are beneficial for promoting the polymerization of ethylene to form high-carbon α-olefins with more than C8 carbons. For example, if the content of heterocyclic amine catalyst ligands is too low, some chromium sources will fail to effectively complex with the ligands, resulting in fewer effective active centers. This not only leads to low catalytic activity, but also causes non-effective active centers to initiate side reactions such as isomerization and ethylene dimerization at higher temperatures, which can easily lead to bimolecular deactivation reactions: the chain transfer occurs after the collision of the two-molecule chain growth reaction active intermediates, forming high-carbon-number olefin products, which also reduces decene selectivity. Although increasing the content of heterocyclic amine catalyst ligands can improve the initial activity of the catalyst to a certain extent, too many ligands can lead to interactions or aggregation between active centers, which may reduce the overall catalytic efficiency. Meanwhile, in the embodiments of the present invention, it was found that as the molar ratio of the co-catalyst and the chromium source increases, the overall catalytic activity shows an upward trend. However, the distribution of high carbon α-olefin products above C8 shows a trend of first increasing and then decreasing. Therefore, in the embodiments of the present invention, the molar ratio of the co-catalyst and the chromium source is (100-800):1.

[0058] According to some preferred embodiments, the reaction temperature is 50-70°C (e.g., 50°C, 55°C, 60°C, 65°C, or 70°C), the time is 25-50 min (e.g., 25 min, 30 min, 35 min, 40 min, or 50 min), and the pressure is 1.0-2 MPa (e.g., 1 MPa, 1.2 MPa, 1.5 MPa, 1.8 MPa, or 2 MPa).

[0059] In this embodiment of the invention, a high reaction pressure, i.e., an increased ethylene concentration in the system, is beneficial to increasing the probability of collision between ethylene and the active center, thereby increasing catalytic activity. However, when the pressure is increased further after reaching a certain level, the solubility reaches saturation, the ethylene insertion process is hindered, chain growth becomes difficult, the chain termination reaction is accelerated, and ultimately the selectivity of high carbon olefins in the oligomerization product decreases. Therefore, based on the catalytic activity of ethylene oligomerization, the selectivity of high carbon α-olefins with C8 or more, and economic considerations, the pressure conditions within the above range are adopted in this embodiment of the invention.

[0060] This invention also provides a heterocyclic amine metal catalyst, which is obtained by reacting the heterocyclic amine catalyst ligand described in any one of the above embodiments with a trivalent chromium salt.

[0061] The heterocyclic amine catalyst ligands prepared in the embodiments of the present invention can be reacted with trivalent chromium salts to prepare chromium metal catalysts. Specifically, 5 mol of the heterocyclic amine catalyst ligands can be first dissolved ultrasonically in 50 mL of tetrahydrofuran. Then, under nitrogen conditions, 10 mol of tetrahydrofuran solution of CrCl(THF)3 is added dropwise to the dissolved heterocyclic amine catalyst ligand solution. After the addition is completed, the temperature is raised and the reaction is stirred. The product is filtered, washed three times with tetrahydrofuran, and vacuum dried at 55°C for 48 hours to finally obtain a heterocyclic amine metal catalyst with the following structure:

[0062]

[0063] Where R is an aromatic group or an alkyl group, and R1 and R2 are the same, both being hydrogen or methyl.

[0064] It should be noted that the heterocyclic amine metal catalysts prepared in the embodiments of the present invention also have excellent catalytic activity and selectivity for high carbon α-olefins with C8 or more. When using them to catalyze the synthesis of high carbon α-olefins, the above-mentioned method for preparing high carbon α-olefins using heterocyclic amine catalyst ligands can be adopted, and the above conditions can be adapted to achieve high-efficiency catalytic synthesis of high carbon α-olefins with C8 or more.

[0065] To more clearly illustrate the technical solution and advantages of the present invention, the following examples provide a detailed description of a heterocyclic amine catalyst ligand and a method for preparing high-carbon α-olefins using the same.

[0066] Example 1:

[0067] Under nitrogen protection, 10.0 mmol of an aldehyde compound (pyrrole-2-carboxaldehyde) was dissolved in 7.5 mL of the first organic solvent (methanol) in a 100 mL three-necked flask with a round bottom, and 5.0 mmol of an amine compound (p-phenylenediamine) was dissolved in 7.5 mL of the first organic solvent (methanol).

[0068] At room temperature (25°C), the dissolved amine compound was added dropwise to the aldehyde compound solution. After the addition was complete, the solution was heated to 27°C and reacted for 24 hours. After the reaction was completed, the temperature of the reaction solution was lowered to room temperature, the product was filtered, and washed three times with n-hexane. The obtained product was dried in a vacuum drying oven at 55°C for 24 hours to obtain a pale yellow solid powder compound, which is the heterocyclic amine catalyst ligand (referred to as compound (Ⅰ)), with a yield of 66.66%.

[0069] The structure of compound (Ⅰ) obtained in Example 1 was characterized in this invention, and the results are as follows: Figure 1 and Figure 2 As shown; from Figure 1 It can be seen that at a wavenumber of 1610 cm⁻¹ -1 and 1645cm -1 Strong characteristic absorption peaks appeared around the left and right edges, which are attributed to the characteristic peaks of C=N, indicating the formation of a Schiff base, thus yielding compound (Ⅰ). From Figure 2 It can be seen that the chemical shift at 8.39 ppm corresponds to the hydrogen proton peak in -CH=N-, around 7.20 ppm corresponds to the hydrogen proton peak on the benzene ring, around 7.10 ppm corresponds to the hydrogen proton peak on the pyrrole ring connected to the nitrogen atom, and around 6.30 ppm and 6.80 ppm correspond to the hydrogen proton peaks on the pyrrole ring connected to the carbon atom. This further indicates the formation of the Schiff base, indicating that compound (Ⅰ) was successfully obtained.

[0070] Example 2:

[0071] Under nitrogen protection, 5.0 mmol of an amine compound (hexamethylenediamine) was dissolved in 7.5 mL of the first organic solvent (methanol) in a 100 mL three-necked flask with a round bottom, and 10.0 mmol of an aldehyde compound (pyrrole-2-carboxaldehyde) was dissolved in 7.5 mL of the first organic solvent (methanol).

[0072] At room temperature (25℃), the dissolved aldehyde compound was added dropwise to the amine compound solution. After the addition was complete, the solution was heated to 27℃ and reacted for 24 hours. After the reaction was completed, the temperature of the reaction solution was lowered to room temperature, the product was filtered, and washed three times with n-hexane. The obtained product was dried in a vacuum drying oven at 55℃ for 24 hours to obtain a white solid powder compound, which is the heterocyclic amine catalyst ligand (referred to as compound (II)), with a yield of 65.32%.

[0073] The structure of compound (II) obtained in Example 2 was characterized in this invention, and the results are as follows: Figure 1 and Figure 3 As shown; from Figure 1 It can be seen that at a wavenumber of 1610 cm⁻¹ -1 Strong C=N characteristic absorption peaks appeared on both sides; from Figure 3 It can be seen that the hydrogen proton peak at a chemical shift of approximately 8.40 ppm corresponds to the hydrogen proton peak in -CH=N-, and the hydrogen proton peaks at approximately 4.80, 6.65, and 7.00 ppm correspond to the hydrogen proton peaks on the pyrrole ring bonded to the carbon atom. The hydrogen proton peak at approximately 6.20 ppm corresponds to the hydrogen proton peak on the pyrrole ring bonded to the nitrogen atom. This further indicates the formation of the Schiff base and shows that compound (II) was successfully obtained.

[0074] Example 3:

[0075] Under nitrogen protection, 0.5 mmol of an amine compound (p-phenylenediamine) was dissolved in 3 mL of the first organic solvent (methanol) in a 100 mL three-necked flask with a round bottom, and 10.0 mmol of an aldehyde compound (3,5-dimethyl-2-pyrrolecarboxaldehyde) was dissolved in 3 mL of the first organic solvent (methanol).

[0076] At room temperature (25℃), the dissolved aldehyde compound was added dropwise to the amine compound solution. After the addition was complete, the solution was heated to 27℃ and reacted for 24 hours. After the reaction was completed, the temperature of the reaction solution was lowered to room temperature, the product was filtered, and washed three times with n-hexane. The obtained product was dried in a vacuum drying oven at 55℃ for 24 hours to obtain a pale yellow solid powder compound, which is the heterocyclic amine catalyst ligand (referred to as compound (III)), with a yield of 82.32%.

[0077] The structure of compound (Ⅲ) obtained in Example 3 was characterized in this invention, and the results are as follows: Figure 1 and Figure 4 As shown; from Figure 1 It can be seen that at a wavenumber of 1615 cm⁻¹ -1 1618cm -1 1645cm -1 1605cm -1A strong characteristic absorption peak appeared, attributed to the characteristic peak of C=N, indicating the formation of a Schiff base, thus yielding compound (III). From Figure 4 It can be seen that the chemical shift at 8.39 ppm corresponds to the hydrogen proton peak in -CH=N-, the hydrogen proton peak around 7.08-7.28 ppm corresponds to the hydrogen proton peak on the benzene ring, the hydrogen proton peak around 5.90 ppm corresponds to the hydrogen proton peak on the pyrrole ring connected to the nitrogen atom, the hydrogen proton peak around 4.80 ppm corresponds to the hydrogen proton peak on the pyrrole ring connected to the carbon atom, and the hydrogen proton peak around 2.20 ppm corresponds to the hydrogen proton peak on -CH3. This further indicates the formation of the Schiff base and shows that compound (Ⅲ) was successfully obtained.

[0078] Example 4:

[0079] Under anhydrous and oxygen-free conditions, a 100mL stainless steel reactor equipped with a magnetic stirrer, temperature control system, and pressure regulation system will be dried and its airtightness will be checked. Ethylene will be used to replace the reactor three times to ensure that there is no influence from oxygen and water. The reactor will be preheated at a predetermined temperature (60℃).

[0080] In an ethylene gas environment, 20 mL of a second organic solvent (cyclohexane), 5 μmol of chromium source (chromium 2-ethylhexanoate), 5 μmol of heterocyclic amine catalyst ligand (compound (III)), and a co-catalyst (diethylaluminum chloride and triethylaluminum in a molar ratio of 1:1) were introduced into a reactor to carry out an ethylene oligomerization reaction. The autoclave was filled with ethylene, and after reaching the required pressure (1.5 MPa), the reaction was carried out at 60 °C for 30 min. Afterward, the reactor was cooled to room temperature (25 °C), and unreacted ethylene was discharged. The reaction was quenched with diluted HCl (10%) ethanol solution. The liquid phase was separated from the catalyst, and the distribution of the catalyst active product was calculated by gas chromatography using the area normalization method, and the catalyst activity was calculated based on the product. The molar ratio of the co-catalyst to the chromium source was 600.

[0081] In this embodiment of the invention, C is obtained through calculation. 8+ The selectivity for high-carbon α-olefins reached 42.06%, and the catalytic activity reached 4.04 × 10⁻⁶. 5 g / (mol Cr·h).

[0082] Example 5:

[0083] Under anhydrous and oxygen-free conditions, a 100mL stainless steel reactor equipped with a magnetic stirrer, temperature control system, and pressure regulation system will be dried and its airtightness will be checked. Ethylene will be used to replace the reactor three times to ensure that there is no influence from oxygen and water. The reactor will be preheated at a predetermined temperature (60℃).

[0084] In an ethylene gas environment, 20 mL of a second organic solvent (cyclohexane), 5 μmol of chromium source (chromium 2-ethylhexanoate), 5 μmol of heterocyclic amine catalyst ligand (compound (II)), and a co-catalyst (diethylaluminum chloride and triethylaluminum in a molar ratio of 1:1) were introduced into a reactor to carry out an ethylene oligomerization reaction. The autoclave was filled with ethylene, and after reaching the required pressure (1.5 MPa), the reaction was carried out at 60 °C for 30 min. Afterward, the reactor was cooled to room temperature (25 °C), unreacted ethylene was discharged, and the reaction was quenched with diluted HCl (10%) ethanol solution. The liquid phase was separated from the catalyst, and the distribution of the catalyst active product was calculated by gas chromatography using the area normalization method, and the catalyst activity was calculated based on the product; the molar ratio of the co-catalyst to the chromium source was 600.

[0085] In this embodiment of the invention, C is obtained through calculation. 8+ The selectivity for high-carbon α-olefins reached 36.78%, and the catalytic activity reached 2.24 × 10⁻⁶. 5 g / (mol Cr·h).

[0086] Example 6:

[0087] Under anhydrous and oxygen-free conditions, a 100mL stainless steel reactor equipped with a magnetic stirrer, temperature control system, and pressure regulation system will be dried and its airtightness will be checked. Ethylene will be used to replace the reactor three times to ensure that there is no influence from oxygen and water. The reactor will be preheated at a predetermined temperature (60℃).

[0088] In an ethylene gas environment, 20 mL of a second organic solvent (cyclohexane), 5 μmol of chromium source (chromium 2-ethylhexanoate), 5 μmol of heterocyclic amine catalyst ligand (compound (I)), and a co-catalyst (diethylaluminum chloride and triethylaluminum in a molar ratio of 1:1) were introduced into a reactor to carry out an ethylene oligomerization reaction. The autoclave was filled with ethylene, and after reaching the required pressure (1.5 MPa), the reaction was carried out at 60 °C for 30 min. Afterward, the reactor was cooled to room temperature (25 °C), and unreacted ethylene was discharged. The reaction was quenched with diluted HCl (10%) ethanol solution. The liquid phase was separated from the catalyst, and the distribution of the catalyst active product was calculated by gas chromatography using the area normalization method, and the catalyst activity was calculated based on the product. The molar ratio of the co-catalyst to the chromium source was 600.

[0089] In this embodiment of the invention, C is obtained through calculation. 8+ The selectivity for high-carbon α-olefins reached 41.02%, and the catalytic activity reached 4.68 × 10⁻⁶. 5 g / (mol Cr·h).

[0090] Example 7:

[0091] Example 7 is basically the same as Example 4, except that the heterocyclic amine catalyst ligand is 8 mol.

[0092] In this embodiment of the invention, C is obtained through calculation. 8+ The selectivity for high-carbon α-olefins was 41.28%, and the catalyst activity for ethylene oligomerization was 4.11 × 10⁻⁶. 5 g / (mol Cr·h).

[0093] Example 8:

[0094] Example 10 is basically the same as Example 4, except that the molar ratio of the co-catalyst and the chromium source is 100:1.

[0095] In this embodiment of the invention, C is obtained through calculation. 8+ The selectivity for high-carbon α-olefins was 21.86%, and the catalyst activity for ethylene oligomerization was 2.09 × 10⁻⁶. 4 g / (mol Cr·h).

[0096] Example 9:

[0097] Example 9 is basically the same as Example 4, except that the molar ratio of the co-catalyst and the chromium source is 800:1.

[0098] In this embodiment of the invention, C is obtained through calculation. 8+ The selectivity for high-carbon α-olefins was 40.64%, and the catalyst activity for ethylene oligomerization was 4.12 × 10⁻⁶. 5 g / (mol Cr·h).

[0099] Example 10:

[0100] Example 10 is basically the same as Example 4, except that the second organic solvent is n-hexane.

[0101] In this embodiment of the invention, C is obtained through calculation. 8+ The selectivity for high-carbon α-olefins was 31.49%, and the catalyst activity for ethylene oligomerization was 3.14 × 10⁻⁶. 5 g / (mol Cr·h).

[0102] Example 11:

[0103] The heterocyclic amine ligand compound (Ⅲ) prepared in Example 3 was taken in a three-necked flask with 5 mmol of the mixture. 50 mL of tetrahydrofuran was added and dissolved by sonication at 25 °C for 5 min. 10.00 mmol of a tetrahydrofuran solution of CrCl(THF)3 was added dropwise at room temperature under nitrogen. After the addition was completed, the temperature was raised to 40 °C and the mixture was stirred for 24 h. After the reaction was completed, the three products were filtered and washed three times with tetrahydrofuran. They were then dried under vacuum at 55 °C for 48 h to finally obtain the heterocyclic amine metal catalyst, abbreviated as L6-Cat.

[0104] The above-mentioned heterocyclic amine metal catalysts are used to catalyze the oligomerization of ethylene:

[0105] Under anhydrous and oxygen-free conditions, a 100mL stainless steel reactor equipped with a magnetic stirrer, temperature control system, and pressure regulation system will be dried and its airtightness will be checked. Ethylene will be used to replace the reactor three times to ensure that there is no influence from oxygen and water. The reactor will be preheated at a predetermined temperature (60℃).

[0106] In an ethylene gas atmosphere, 5 μmol of a heterocyclic amine metal catalyst, L6-Cat, along with 20 mL of a second organic solvent (cyclohexane) and a co-catalyst (diethylaluminum chloride and triethylaluminum in a 1:1 molar ratio), were introduced into a reactor to carry out an ethylene oligomerization reaction. The autoclave was filled with ethylene, and after reaching the required pressure (0.5 MPa), the reaction was carried out at 25°C for 30 min. Afterward, the reactor was cooled to room temperature (25°C), unreacted ethylene was discharged, and the reaction was quenched with diluted HCl (10%) ethanol solution. The liquid phase was separated from the catalyst, and the distribution of the catalyst active product was calculated by gas chromatography using the area normalization method, and the catalyst activity was calculated based on the product. The molar ratio of the co-catalyst to the heterocyclic amine metal catalyst was 400.

[0107] In this embodiment of the invention, C is obtained through calculation. 8+ The selectivity for high-carbon α-olefins reached 37.04%, and the catalyst activity for ethylene oligomerization was 2.62 × 10⁻⁶. 5 g / (mol·Cr·h).

[0108] 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 foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing high-carbon α-olefins based on heterocyclic amine catalyst ligands, characterized in that, The method includes: Heterocyclic amine catalyst ligand, chromium source, co-catalyst, and second organic solvent are introduced into an ethylene gas reaction system for in-situ polymerization to obtain the high-carbon α-olefin; wherein the high-carbon α-olefin is an α-olefin with more than 8 carbon atoms. The chromium source is chromium 2-ethylhexanoate, the second organic solvent is cyclohexane, n-hexane, or methylcyclohexane, and the co-catalyst is a composite system of diethylaluminum monochloro and triethylaluminum; the content of the heterocyclic amine catalyst ligand is 2-5 μmol, the content of the chromium source is 2-5 μmol, the content of the second organic solvent is 15-25 mL, and the molar ratio of the co-catalyst to the chromium source is (100-800):1; The structural formula of the catalyst ligand is as follows: In the formula, R is an aromatic group or an alkyl group, and R1 is a methyl group; the aromatic group is a phenyl group, and the alkyl group has an even number of carbon atoms between 2 and 8.

2. The method according to claim 1, characterized in that, The structural formula of the catalyst ligand is as follows: 。 3. The method according to claim 1, characterized in that, The preparation method of the heterocyclic amine catalyst ligand includes: dissolving the aldehyde reactant and the amine reactant separately in a first organic solvent, and then mixing and reacting the two to obtain the heterocyclic amine catalyst ligand; The aldehyde reactant is 3,5-dimethyl-2-pyrrolecarboxaldehyde, and the amine reactant is ethylenediamine, butanediamine, hexamethylenediamine, octanediamine, or p-phenylenediamine.

4. The method according to claim 3, characterized in that, The first organic solvent is methanol, and the molar ratio of the aldehyde reactant to the amine reactant is (10-11):(0.5-5).

5. The method according to claim 4, characterized in that, The mixing reaction is carried out at a temperature of 20-35℃ for 12-24 hours.

6. The method according to claim 1, characterized in that, The reaction is carried out at a temperature of 50-70℃, for a time of 20-60 min, and at a pressure of 1.0-3.0 MPa.

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