Ethylene selective trimerization catalyst system and method for selective ethylene trimerization

Abstract

The present invention provides an ethylene selective trimerization catalyst system comprising a chromium compound, a nitrogen-containing compound containing a pyrrole-pyridine group, an alkyl metal compound, and a halogen-containing promoter; the structure of the nitrogen-containing compound containing a pyrrole-pyridine group is shown in formula (I). The present application also provides a method for the selective trimerization of ethylene. The ethylene selective trimerization catalyst system provided herein has high catalytic activity for the selective trimerization of ethylene, as it contains a nitrogen-containing compound containing a pyrrole-pyridine group, with a catalytic activity of up to 6.78*10 5 The product has a selectivity of 1-hexene exceeding 95% and a solid by-product polyethylene wax content below 0.2 wt%. This reduces the solid content in the reaction system, ensures the safe and stable operation of the continuous ethylene selective trimerization production unit, and provides a reliable basis for the continuous production of highly selective ethylene trimerization.

Description

Technical Field

[0001] The present invention relates to the technical field of ethylene oligomerization, in particular to an ethylene selective trimerization catalyst system and an ethylene selective trimerization method. Background Art

[0002] Advanced linear α-olefins such as 1-hexene and 1-octene are important organic chemical raw materials, widely used in polyolefin comonomers, surfactant synthesis intermediates, synthetic lubricants, and oil additives. The domestic α-olefin industry started late and is still generally in its developmental stages. With breakthroughs in α-olefin production and application technologies and the development of downstream markets, α-olefins have enormous potential for growth. Some ethylene projects are planning to construct 1-hexene plants, and a large number of coal-to-liquids projects have already implemented mixed LAOs to extend the industrial chain and improve efficiency, but have yet to separate and purify the monoolefins. Therefore, the development of the 1-hexene industry presents a growth opportunity for domestic companies.

[0003] The selective trimerization of ethylene to 1-hexene offers higher selectivity than both FT synthesis and ethylene oligomerization, leading numerous R&D institutions to investigate this technology. Currently, Chevron Phillips, Sinopec, and CNPC have mastered this technology, but production capacity and output remain insufficient. The catalytic system for selective trimerization determines the reaction's catalytic activity, product selectivity, and by-product ratio. Therefore, developing a highly active, highly selective, and low-by-product catalytic system is crucial for the commercialization of selective trimerization of ethylene to 1-hexene. Summary of the Invention

[0004] The technical problem solved by the present invention is to provide a high-activity and high-selectivity ethylene selective trimerization catalytic system.

[0005] In view of this, the present application provides an ethylene selective trimerization catalyst system, comprising a chromium compound, a nitrogen-containing compound containing a pyrrole-pyridine group, an alkyl metal compound, and a halogen-containing promoter;

[0006] The structure of the nitrogen-containing compound containing a pyrrole-pyridine group is shown in formula (I):

[0007]

[0008] wherein R1 and R2 are independently selected from hydrogen, C1-C10 alkyl, C1-C10 alkenyl, C6-C10 cycloalkyl or C6-C10 aryl;

[0009] R3 is selected from C1-C10 alkyl, C6-C10 cycloalkyl or C6-C10 aryl;

[0010] R4 is selected from halogen, C1-C10 alkyl, C1-C10 alkenyl or C6-C10 cycloalkyl.

[0011] Preferably, R1 and R2 are independently selected from H, substituted or unsubstituted methyl, substituted or unsubstituted ethyl, substituted or unsubstituted propyl, substituted or unsubstituted isopropyl, substituted or unsubstituted n-butyl, substituted or unsubstituted tert-butyl, substituted or unsubstituted vinyl, substituted or unsubstituted propenyl, substituted or unsubstituted cyclopentyl, substituted or unsubstituted cyclohexyl, substituted or unsubstituted phenyl or substituted or unsubstituted naphthyl;

[0012] R3 is selected from ethyl, n-propyl, n-butyl, n-hexyl, isopropyl, cyclopentyl, cyclohexyl, phenyl, benzyl, 4-halophenyl, 4-aminophenyl, 4-alkylphenyl or 4-methoxyphenyl;

[0013] R4 is selected from halogen, substituted or unsubstituted methyl, substituted or unsubstituted ethyl, substituted or unsubstituted propyl, substituted or unsubstituted isopropyl, substituted or unsubstituted n-butyl, substituted or unsubstituted tert-butyl, substituted or unsubstituted vinyl, substituted or unsubstituted propenyl, substituted or unsubstituted cyclopentyl or substituted or unsubstituted cyclohexyl.

[0014] Preferably, the chromium compound is selected from one or more of chromium carboxylates, chromium naphthenates, chromium halides, pyridine-based chromium-containing compounds and chromium diketonates.

[0015] Preferably, the chromium compound is selected from one or more of chromium 2-ethylhexanoate, chromium 2,2,6,6-tetramethylheptanedione, chromium naphthenate, chromium chloride, chromium bromide, chromium fluoride, chromium acetylacetonate, chromium acetate, chromium butyrate, chromium pivalate, chromium laurate and chromium stearate.

[0016] Preferably, the alkyl metal compound is selected from one or more of alkyl aluminum compounds, alkyl boron compounds, alkyl magnesium compounds, alkyl zinc compounds and alkyl aluminum compounds.

[0017] Preferably, the halogen-containing accelerator is selected from one or more of 1,1,2,2-tetrachloroethane, hexachloroethane, 2,4,6-trichlorotoluene, 2,6-dichlorotrichloromethylbenzene, tetrachloromethane, diethylaluminum chloride and 1,2-dibromoethane.

[0018] Preferably, the molar ratio of the chromium compound, the nitrogen-containing compound containing pyrrole-pyridine groups, the alkyl metal compound and the halogen-containing promoter is 1: (0.5-500): (50-500): (1-50).

[0019] Preferably, the preparation method of the nitrogen-containing compound containing pyrrole-pyridine groups comprises the following steps:

[0020] a) reacting 2-formaldehyde pyrrole of formula (i) and a primary amine of formula (ii) in a solvent to obtain an intermediate of formula (iii);

[0021] b) reacting the intermediate of formula (iii) with pyridine of formula (iv) to obtain a nitrogen-containing compound of formula (I);

[0022]

[0023] The present application also provides a method for selective trimerization of ethylene, comprising the following steps:

[0024] mixing a chromium compound, a nitrogen-containing compound containing a pyrrole-pyridine group, and an accelerator in an organic solvent to obtain a premix;

[0025] The premixture and the solution of the halogen-containing promoter are mixed, and ethylene is introduced into the mixture to react.

[0026] Preferably, the reaction temperature is 50-150° C., the pressure is 0-10 MPa, and the reaction time is 0.2-2 h.

[0027] The present application provides an ethylene selective trimerization catalyst system, comprising a chromium compound, a nitrogen-containing compound containing a pyrrole-pyridine group, an alkyl metal compound, and a halogen-containing promoter. The ethylene selective trimerization catalyst system provided by the present application comprises a chromium compound, a nitrogen-containing compound containing a pyrrole-pyridine group, and a chromium metal complex in the chromium compound, which is more firmly complexed and more stable, thereby improving the activity and selectivity of the catalyst system. Experimental results show that the catalytic activity of the catalyst system is as high as 6.78*10 5 g / (g·Cr·h), the selectivity of 1-hexene in the product can reach more than 95%, and the content of solid by-product polyethylene wax is less than 0.2wt%. This reduces the solid content in the reaction system, ensures the safe and stable operation of the continuous production device for ethylene selective trimerization, and provides a reliable basis for the continuous production of high-selectivity ethylene trimerization reaction. DETAILED DESCRIPTION

[0028] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0029] In view of the performance requirements of the catalytic system for high activity, high selectivity and low by-products in the prior art for the selective trimerization of ethylene, the present invention provides a catalytic system for the selective trimerization of ethylene. Since the nitrogen-containing compound in the trimerization system is a pyrrole-pyridine structure, it is more firmly complexed with chromium metal and has high stability. Therefore, the catalytic system has high catalytic activity, high selectivity for 1-hexene in the product, and low content of solid by-product polyethylene wax, which reduces the solid content in the reaction system, ensures the safe and stable operation of the continuous production device for the selective trimerization of ethylene, and provides a reliable basis for the continuous production of high-selectivity ethylene trimerization reactions. Specifically, the present invention provides a catalytic system for the selective trimerization of ethylene, including an ethylene selective trimerization catalyst system, including a chromium compound, a nitrogen-containing compound containing a pyrrole-pyridine group, an alkyl metal compound, and a halogen-containing promoter;

[0030] The structure of the nitrogen-containing compound containing pyrrole-pyridine groups is shown in formula (I):

[0031]

[0032] wherein R1 and R2 are independently selected from hydrogen, C1-C10 alkyl, C1-C10 alkenyl, C6-C10 cycloalkyl or C6-C10 aryl;

[0033] R3 is selected from C1-C10 alkyl, C6-C10 cycloalkyl or C6-C10 aryl;

[0034] R4 is selected from halogen, C1-C10 alkyl, C1-C10 alkenyl or C6-C10 cycloalkyl.

[0035] In the nitrogen-containing compounds containing pyrrole-pyridine groups provided herein, specifically, R1 and R2 are independently selected from H, substituted or unsubstituted methyl, substituted or unsubstituted ethyl, substituted or unsubstituted propyl, substituted or unsubstituted isopropyl, substituted or unsubstituted n-butyl, substituted or unsubstituted tert-butyl, substituted or unsubstituted vinyl, substituted or unsubstituted propenyl, substituted or unsubstituted cyclopentyl, substituted or unsubstituted cyclohexyl, substituted or unsubstituted phenyl or substituted or unsubstituted naphthyl; R3 is a substituent on a primary amine, selected from One of ethyl, n-propyl, n-butyl, n-hexyl, isopropyl, cyclopentyl, cyclohexyl, phenyl, benzyl, 4-halophenyl, 4-aminophenyl, 4-alkylphenyl and 4-methoxyphenyl; R4 is selected from halogen atom, substituted or unsubstituted methyl, substituted or unsubstituted ethyl, substituted or unsubstituted propyl, substituted or unsubstituted isopropyl, substituted or unsubstituted n-butyl, substituted or unsubstituted tert-butyl, substituted or unsubstituted vinyl, substituted or unsubstituted propenyl, substituted or unsubstituted cyclopentyl or substituted or unsubstituted cyclohexyl.

[0036] In the present invention, the pyrrole-pyridine nitrogen-containing compound is preferably one of the following structural compounds of formula (L1) to formula (L4):

[0037]

[0038] The preparation method of the pyrrole-pyridine nitrogen-containing compound described in the present application comprises the following steps:

[0039] a) reacting 2-formaldehyde pyrrole of formula (i) and a primary amine of formula (ii) in a solvent to obtain an intermediate of formula (iii);

[0040] b) reacting the intermediate of formula (iii) with a para-substituted pyridine of formula (iv) in the presence of triethylamine to obtain a nitrogen-containing compound of formula (I);

[0041]

[0042] In the preparation of nitrogen-containing compounds containing pyrrole-pyridine groups, 2-formaldehyde pyrrole of formula (i) and a primary amine of formula (ii) are first reacted in a solvent. The molar ratio of 2-formaldehyde pyrrole of formula (i) to the primary amine of formula (ii) is preferably 1:(1-1.5), more preferably 1:1.2. The solvent is preferably a mixture of methanol and toluene, with a volume ratio of methanol to toluene of preferably (1-3):1, more preferably 2:1. The reaction is preferably carried out under reflux, and the reaction time is preferably 5-12 hours. After the reaction, the resulting reaction product is post-processed and purified to obtain an intermediate of formula (iii).

[0043] In the preparation method provided by the present invention, after obtaining the intermediate (iii), triethylamine is added to anhydrous ether as a solvent, stirred and then cooled, and a para-substituted pyridine of the structure of formula (iv) is added dropwise. After the addition is complete, the reaction is stirred at low temperature and then stirred at room temperature. The molar ratio of the intermediate and the para-substituted pyridine of the structure of formula (iv) is preferably 1: (1 to 1.5), specifically 1:1, 1:1.05, 1:1.1, 1:1.14, 1:1.2, 1:1.29, 1:1.3, 1:1.36, 1:1.4, 1:1.45 or 1:1.5; the molar ratio of triethylamine to the intermediate of the structure of formula (iii) is preferably (1 to 3): 1, more preferably (1-2): 1, specifically 1:1, 1.1:1, 1.16:1, 1.2:1, 1.3:1, 1.38:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.76:1, 1.8:1, 1.9:1 or 2:1; the temperature of the dropwise addition reaction is preferably -5 to 5°C, more preferably 0°C; the stirring reaction time at room temperature is preferably 8 to 24 hours. After the reaction is completed, the obtained reaction product is post-treated (purified) to obtain a light yellow solid powder of the organic ligand having the structure of formula (I).

[0044] In the ethylene selective trimerization catalytic system provided in the present application, the chromium compound serves as component a, the nitrogen-containing compound containing pyrrole-pyridine groups serves as component b, the alkyl metal compound serves as component c, and the halogen-containing promoter serves as component d, that is, the ethylene selective trimerization catalytic system consists of component a, component b, component c and component d.

[0045] Wherein, the nitrogen-containing compound containing pyrrole-pyridine groups is the nitrogen-containing compound described in the above technical solution or the nitrogen-containing compound prepared by the method described in the above technical solution, which will not be described in detail here.

[0046] In the above-mentioned ethylene selective trimerization catalytic system, the chromium compound is selected from one or more of chromium 2-ethylhexanoate, chromium 2,2,6,6-tetramethylheptanedionate, chromium cyclohexaneate, chromium chloride, chromium bromide, chromium fluoride, chromium acetylacetonate, chromium acetate, chromium butyrate, chromium pivalate, chromium laurate, chromium stearate and pyrrole-based chromium-containing compounds; in a specific embodiment, the chromium compound is selected from chromium 2-ethylhexanoate, chromium butyrate or chromium pivalate.

[0047] In the above-mentioned ethylene selective trimerization catalytic system, the alkyl metal compound is an unhydrolyzed alkyl metal, selected from one or more of alkyl aluminum compounds, alkyl boron compounds, alkyl magnesium compounds, alkyl zinc compounds and alkyl aluminum compounds. Specifically, the alkyl metal compound is an alkyl aluminum compound, and more specifically, the alkyl metal compound is triethyl aluminum.

[0048] In the above-mentioned ethylene selective trimerization catalytic system, the halogen-containing promoter is selected from one or more of 1,1,2,2-tetrachloroethane, hexachloroethane, 1,3,5-trichlorotoluene, carbon tetrachloride, 2,6-dichlorotrichloromethylbenzene, tetrachloromethane, diethylaluminum chloride and 1,2-dibromoethane. Specifically, the halogen-containing promoter is selected from hexachloroethane, 1,1,2,2-tetrachloroethane, 1,3,5-trichlorotoluene or carbon tetrachloride.

[0049] According to the present invention, the molar ratio of components a, b, c, and d in the ethylene selective trimerization catalytic system is 1:(0.5-500):(50-500):(1-50), preferably 1:(2-6):(50-200):(1-30).

[0050] The preparation method of the ethylene selective trimerization catalytic system described in the present application comprises the following steps: pre-mixing a chromium compound (a), a nitrogen-containing compound containing a pyrrole-pyridine group (b), and a halogen-containing promoter (d); then introducing the mixture into an organic solution containing an alkyl aluminum (c) under ethylene trimerization reaction conditions to allow the mixture to mix and contact.

[0051] The present invention also provides a method for preparing 1-hexene by selective trimerization of ethylene, which uses any of the above catalyst systems and introduces ethylene into the solvent of the catalyst system to carry out ethylene trimerization reaction.

[0052] In the process of preparing 1-hexene by selective trimerization of ethylene, the reaction temperature is 70-150° C., the reaction pressure is 0-9 MPa, and the reaction time is 0.2-2 h.

[0053] The present invention provides a catalytic system for selective ethylene trimerization, comprising a nitrogen-containing compound containing pyrrole-pyridine groups having a structure of formula (I), a chromium compound, an alkyl metal compound, and a halogen-containing promoter. Experimental results show that the catalytic system for selective ethylene trimerization using the nitrogen-containing compound containing pyrrole-pyridine groups of the present invention has a catalytic activity of up to 6.78*10 5 g / (gCr.h), the selectivity of 1-hexene in the product can reach more than 95%, and the content of solid by-product polyethylene wax is less than 0.2wt%, which reduces the solid content in the reaction system, ensures the safe and stable operation of the continuous production device for ethylene selective trimerization, and provides a reliable basis for the continuous production of high-selectivity ethylene trimerization reaction.

[0054] In order to further understand the present invention, the ethylene selective trimerization catalyst system and the ethylene selective trimerization method provided by the present invention are described in detail below with reference to the examples. The protection scope of the present invention is not limited by the following examples.

[0055] Example 1

[0056] A) Synthesis of nitrogen-containing compound L1 containing pyrrole-pyridine group:

[0057] 1) 3,4-Dimethyl-2-formylpyrrole (0.1 mol) and isopropylamine (0.12 mol) were added to a solution of 100 mL of methanol and toluene (v / v = 2:1), heated under reflux overnight, then cooled to room temperature. The reaction solution was distilled under reduced pressure to remove the solvent to obtain a yellow oil. The yellow oil was dissolved in 20 mL of THF, dried over anhydrous magnesium sulfate, filtered, and the filtrate was distilled under reduced pressure. 15 mL of ether was added to precipitate a solid. The yield was 93%;

[0058] 2) The solid precipitate (0.11 mol) was dissolved in 80 mL of diethyl ether, triethylamine (0.15 mol) was added and stirred for 20 min. The mixture was cooled to 0°C, and 3-methylpyridine (0.12 mol) was added dropwise to the reaction solution. After the addition was complete, stirring was continued for 30 min, and then stirred at room temperature for 12 h. The reaction solution was filtered, and the filtrate was distilled under reduced pressure and allowed to stand at -30°C for 24 h. It was filtered and washed with cold diethyl ether to obtain a yellow solid. The yellow solid was dried in vacuo at 50°C to obtain a light yellow solid powder, which is the nitrogen-containing compound L1. The structural formula is shown below:

[0059]

[0060] The prepared ligand L1 was subjected to nuclear magnetic resonance spectroscopy analysis, and the results were: 1 HNMR (400MHz, d6-DMSO): 1.05~1.15(d, 6H), 2.04~2.16(m, 6H), 2.29~2.32(s, 3H), 2.89~2.97(m, 1H), 4.36~ 4.39(s, 2H), 5.36~5.44(s, 1H), 5.81~5.84(s, 1H), 6.61~6.66(d, 1H), 7.35~7.40(d, 1H), 8.03~8.11(s, 1H).

[0061] B) Preparation of catalyst system

[0062] In a glove box, a certain mass of chromium 2-ethylhexanoate, L1, and hexachloroethane are weighed, a certain amount of n-heptane is added to dissolve, stirred evenly, and set aside; triethylaluminum is first added to the solvent during the selective trimerization of ethylene, and then a mixture of L1, chromium 2-ethylhexanoate, and hexachloroethane is added, and ethylene is introduced to carry out the trimerization reaction.

[0063] C) Ethylene trimerization experiment

[0064] A 500 mL autoclave and a quartz liner were heated at 100-130°C for more than 1 h and set aside. The autoclave was evacuated and replaced with nitrogen several times and kept warm to a reaction temperature of 120°C. 200 mL of dehydrated and deoxygenated n-heptane was added as a solvent. 1.2 mL of triethylaluminum was accurately added using a catalyst storage tank. 1 mL of the above-mentioned catalyst containing L1 was added. The molar ratio of chromium 2-ethylhexanoate, L1, triethylaluminum, and hexachloroethane was 1:3:200:5. The reaction temperature was set to 120°C for the polymerization experiment. Ethylene was introduced, the reaction pressure was adjusted to 5 MPa, and the reaction time was 0.5 h. After the reaction was completed, the temperature was lowered to room temperature with cooling water, the pressure was released, and the product was tested and analyzed. The results are shown in Table 1.

[0065] Example 2

[0066] A) Synthesis of nitrogen-containing compound L2:

[0067] 1) 2-Formylpyrrole (0.1 mol) and cyclopentylamine (0.12 mol) were added to a solution of 100 mL of methanol and toluene (v / v = 2:1), heated under reflux overnight, then cooled to room temperature. The reaction solution was distilled under reduced pressure to remove the solvent to obtain a yellow oil. The yellow oil was dissolved in 20 mL of THF, dried over anhydrous magnesium sulfate, filtered, and the filtrate was distilled under reduced pressure. 15 mL of ether was added to precipitate a solid. The yield was 89%;

[0068] 2) The solid precipitate (0.11 mol) was dissolved in 80 mL of diethyl ether, triethylamine (0.15 mol) was added and stirred for 20 min. The mixture was cooled to 0°C, and 3-chloromethylpyridine (0.12 mol) was added dropwise to the reaction solution. After the addition was complete, stirring was continued for 30 min, and then stirred at room temperature for 12 h. The reaction solution was filtered, and the filtrate was distilled under reduced pressure and allowed to stand at -30°C for 24 h. It was filtered and washed with cold diethyl ether to obtain a yellow solid. The yellow solid was dried in vacuo at 50°C to obtain a light yellow solid powder, which is the nitrogen-containing compound L2. The structure is shown below:

[0069]

[0070] The prepared ligand L2 was subjected to nuclear magnetic resonance spectroscopy analysis, and the results were: 1HNMR (400MHz, d6-DMSO): 1.48~1.56(m, 4H), 1.73~1.81(m, 4H), 2.64~2.68(m, 1H), 4.35~4.62(s, 2H), 4.64~4.69(s, 2H), 5.36~ 5.44(s, 1H), 5.71~5.75(d, 1H), 5.89~5.94(d, 1H), 6.34~6.38(s, 1H), 6.60~6.66(d, 1H), 7.38~7.42(d, 1H), 8.07~8.11(s, 1H).

[0071] B) Preparation of catalyst system:

[0072] In a glove box, a certain mass of chromium 2-ethylhexanoate, L2, and 1,1,2,2-tetrachloroethane were weighed, a certain amount of cyclohexane was added to dissolve, stirred evenly, and set aside; triethylaluminum was first added to the solvent during the selective trimerization of ethylene, and then a mixture of L1, chromium 2-ethylhexanoate, and 1,1,2,2-tetrachloroethane was added, and ethylene was introduced to carry out the trimerization reaction.

[0073] C) Ethylene trimerization experiment:

[0074] A 500 mL autoclave and a quartz liner were heated at 100-130°C for more than 1 h and set aside; the autoclave was evacuated and replaced with nitrogen several times, and kept warm to a reaction temperature of 110°C. 200 mL of dehydrated and deoxygenated cyclohexane was added as a solvent, 1.2 mL of triethylaluminum was accurately added using a catalyst storage tank, and 1.2 mL of the above-mentioned catalyst containing L2 was added. The molar ratio of chromium 2-ethylhexanoate, L2, triethylaluminum, and 1,1,2,2-tetrachloroethane was 1:3:150:8. The reaction temperature was set to 110°C for the polymerization experiment, ethylene was introduced, the reaction pressure was adjusted to 5.5 MPa, and the reaction time was 0.75 h. After the reaction was completed, the temperature was lowered to room temperature with cooling water, the pressure was released, and the product was tested and analyzed. The results are shown in Table 1.

[0075] Example 3

[0076] A) Synthesis of nitrogen-containing compound L3:

[0077] 1) 2-Formyl-3-propyl-4-chloromethylpyrrole (0.1 mol) and n-propylamine (0.13 mol) were added to a solution of 100 mL of methanol and toluene (v / v = 2:1), heated under reflux overnight, then cooled to room temperature, and the reaction solution was distilled under reduced pressure to remove the solvent to obtain a yellow oil. The yellow oil was dissolved in 20 mL of THF, dried over anhydrous magnesium sulfate, filtered, and the filtrate was distilled under reduced pressure. 15 mL of ether was added to precipitate a solid. The yield was 88%;

[0078] 2) The solid precipitate (0.11 mol) was dissolved in 80 mL of ether, triethylamine (0.15 mol) was added and stirred for 20 min. The mixture was cooled to 0°C, and 3-fluoropyridine (0.12 mol) was added dropwise to the reaction solution. After the addition was complete, stirring was continued for 30 min, and then stirred at room temperature for 12 h. The reaction solution was filtered, and the filtrate was distilled under reduced pressure and allowed to stand at -30°C for 24 h. It was filtered and washed with cold ether to obtain a yellow solid. The yellow solid was dried in vacuo at 50°C to obtain a light yellow solid powder, which is the nitrogen-containing compound L3, with the structural formula shown below:

[0079]

[0080] The prepared ligand L3 was subjected to nuclear magnetic resonance spectroscopy analysis, and the results were: 1 HNMR (400MHz, d6-DMSO): 1.08~1.12(m, 6H), 1.56~1.62(m, 4H), 2.43~2.49(m, 2H), 3.06~3.11(m, 2H), 4.34~4.41(s, 2 H), 4.52~4.58(s, 2H), 5.25~5.32(s, 1H), 5.89~5.94(s, 1H), 6.64~6.68(d, 1H), 7.13~7.16(d, 1H), 7.80~7.84(s, 1H).

[0081] B) Preparation of catalyst system:

[0082] In a glove box, a certain mass of L3, chromium butyrate, and 1,3,5-trichlorotoluene were weighed, a certain amount of cyclohexane was added to dissolve, stirred evenly, and set aside; during the selective trimerization of ethylene, triethylaluminum was first added to the solvent, and then a mixture of L3, chromium butyrate, and 1,3,5-trichlorotoluene was added, and ethylene was introduced to carry out the trimerization reaction.

[0083] C) Ethylene trimerization experiment:

[0084] A 500 mL autoclave and a quartz liner were heated at 100-130°C for more than 1 h and set aside. The autoclave was evacuated and replaced with nitrogen several times and kept warm to a reaction temperature of 130°C. 200 mL of dehydrated and deoxygenated cyclohexane was added as a solvent. 1.2 mL of triethylaluminum was accurately added from a catalyst storage tank. 0.9 mL of the above-mentioned catalyst containing L3 was added. The molar ratio of chromium butyrate, L3, triethylaluminum, and 1,3,5-trichlorotoluene was 1:4:160:10. The reaction temperature was set to 130°C for the polymerization experiment. Ethylene was introduced, the reaction pressure was adjusted to 5 MPa, and the reaction time was 1 h. After the reaction, the temperature was cooled to room temperature with cooling water, the pressure was released, and the product was tested and analyzed. The results are shown in Table 1.

[0085] Example 4

[0086] A) Synthesis of nitrogen-containing compound L4:

[0087] 1) 2-Formyl-3-chloromethyl-4-methylpyrrole (0.1 mol) and tert-butylamine (0.125 mol) were added to a solution of 100 mL of methanol and toluene (v / v = 2:1), heated under reflux overnight, then cooled to room temperature. The reaction solution was distilled under reduced pressure to remove the solvent to obtain a yellow oil. The yellow oil was dissolved in 20 mL of THF, dried over anhydrous magnesium sulfate, filtered, and the filtrate was distilled under reduced pressure. 15 mL of ether was added to precipitate a solid. The yield was 89%;

[0088] 2) The solid precipitate (0.11 mol) was dissolved in 80 mL of ether, triethylamine (0.15 mol) was added and stirred for 20 min, the mixture was cooled to 0°C, 3-isopropylpyridine (0.12 mol) was added dropwise to the reaction solution, and stirring was continued for 30 min after the addition was complete, and then stirred at room temperature for 12 h. The reaction solution was filtered, and the filtrate was distilled under reduced pressure and allowed to stand at -30°C for 24 h, filtered, and washed with cold ether to obtain a yellow solid. The yellow solid was dried in vacuo at 50°C to obtain a light yellow solid powder, which is the nitrogen-containing compound L4, with the structural formula shown below:

[0089]

[0090] The prepared ligand L4 was subjected to nuclear magnetic resonance spectroscopy analysis, and the results were: 1 HNMR (400MHz, d6-DMSO): 1.10~1.17(s, 9H), 1.29~1.36(d, 6H), 2.05~2.09(s, 3H), 3.10~3.18(m, 1H), 4.34~4.39(s, 2 H), 4.52~4.57(s, 2H), 5.21~5.28(s, 1H), 5.82~5.85(s, 1H), 6.60~6.64(d, 1H), 7.32~7.36(d, 1H), 8.03~8.07(s, 1H).

[0091] B) Preparation of catalyst system:

[0092] In a glove box, a certain mass of L4, chromium pivalate, and carbon tetrachloride are weighed, a certain amount of cyclohexane is added to dissolve, stirred evenly, and set aside; during the selective trimerization of ethylene, triethylaluminum is first added to the solvent, and then a mixture of L4, chromium pivalate, and carbon tetrachloride is added, and ethylene is introduced to carry out the trimerization reaction.

[0093] C) Ethylene trimerization experiment:

[0094] A 500 mL autoclave and a quartz liner were heated at 100-130°C for more than 1 h and set aside. The autoclave was evacuated and replaced with nitrogen several times and kept warm to a reaction temperature of 120°C. 200 mL of dehydrated and deoxygenated cyclohexane was added as a solvent. 1.2 mL of triethylaluminum was accurately added using a catalyst storage tank. 0.9 mL of the above-mentioned catalyst containing L4 was added. The molar ratio of chromium pivalate, L4, triethylaluminum, and carbon tetrachloride was 1:5:180:9. The reaction temperature was set to 120°C for the polymerization experiment. Ethylene was introduced, the reaction pressure was adjusted to 5 MPa, and the reaction time was 0.5 h. After the reaction was completed, the temperature was lowered to room temperature with cooling water, the pressure was released, and the product was tested and analyzed. The results are shown in Table 1.

[0095] Comparative Example 1

[0096]

[0097] The preparation method is the same as that of Example 1, except that L1 is replaced by L5; the results are shown in Table 1.

[0098] Comparative Example 2

[0099] The preparation method is the same as that in Example 1, except that the amount of triethylaluminum added as the catalyst in the ethylene trimerization experiment is 3.6 mL.

[0100] Comparative Example 3

[0101] The preparation method is the same as that of Example 1, except that component d is not added in the preparation of the main catalyst.

[0102] Comparative Example 4

[0103] The preparation method is the same as that of Example 1, except that component a is not added in the preparation of the main catalyst.

[0104] Comparative Example 5

[0105] The preparation method is the same as that in Example 1, except that the amount of triethylaluminum added as the catalyst in the ethylene trimerization experiment is 0.1 mL.

[0106] Table 1 Composition analysis of trimerization products

[0107]

[0108]

[0109] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0110] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An ethylene selective trimerization catalyst system comprising a chromium compound, a nitrogen-containing compound containing a pyrrole-pyridine group, an alkyl metal compound, and a halogen-containing promoter; The structure of the nitrogen-containing compound containing a pyrrole-pyridine group is shown in formula (I): in, R1 and R2 are independently selected from hydrogen, C1-C10 alkyl, C1-C10 alkenyl, C6-C10 cycloalkyl or C6-C10 aryl; R3 is selected from C1-C10 alkyl, C6-C10 cycloalkyl or C6-C10 aryl; R4 is selected from halogen, C1-C10 alkyl, C1-C10 alkenyl or C6-C10 cycloalkyl.

2. The ethylene selective trimerization catalyst system according to claim 1, characterized in that Said R1 and R2 are independently selected from H, substituted or unsubstituted methyl, substituted or unsubstituted ethyl, substituted or unsubstituted propyl, substituted or unsubstituted isopropyl, substituted or unsubstituted n-butyl, substituted or unsubstituted tert-butyl, substituted or unsubstituted vinyl, substituted or unsubstituted propenyl, substituted or unsubstituted cyclopentyl, substituted or unsubstituted cyclohexyl, substituted or unsubstituted phenyl or substituted or unsubstituted naphthyl; R3 is selected from ethyl, n-propyl, n-butyl, n-hexyl, isopropyl, cyclopentyl, cyclohexyl, phenyl, benzyl, 4-halophenyl, 4-aminophenyl, 4-alkylphenyl or 4-methoxyphenyl; R4 is selected from halogen, substituted or unsubstituted methyl, substituted or unsubstituted ethyl, substituted or unsubstituted propyl, substituted or unsubstituted isopropyl, substituted or unsubstituted n-butyl, substituted or unsubstituted tert-butyl, substituted or unsubstituted vinyl, substituted or unsubstituted propenyl, substituted or unsubstituted cyclopentyl or substituted or unsubstituted cyclohexyl.

3. The ethylene selective trimerization catalyst system according to claim 1, characterized in that The chromium compound is selected from one or more of chromium carboxylates, chromium naphthenates, chromium halides, pyridine-based chromium-containing compounds and chromium diketonates.

4. The ethylene selective trimerization catalyst system according to claim 1 or 3, characterized in that: The chromium compound is selected from one or more of chromium 2-ethylhexanoate, chromium 2,2,6,6-tetramethylheptanedionate, chromium naphthenate, chromium chloride, chromium bromide, chromium fluoride, chromium acetylacetonate, chromium acetate, chromium butyrate, chromium pivalate, chromium laurate and chromium stearate.

5. The ethylene selective trimerization catalyst system according to claim 1, characterized in that: The alkyl metal compound is selected from one or more of an alkyl aluminum compound, an alkyl boron compound, an alkyl magnesium compound, an alkyl zinc compound and an alkyl aluminum compound.

6. The ethylene selective trimerization catalyst system according to claim 1, characterized in that The halogen-containing accelerator is selected from one or more of 1,1,2,2-tetrachloroethane, hexachloroethane, 2,4,6-trichlorotoluene, 2,6-dichlorotrichloromethylbenzene, tetrachloromethane, diethylaluminum chloride and 1,2-dibromoethane.

7. The ethylene selective trimerization catalyst system according to claim 1, characterized in that: The molar ratio of the chromium compound, the nitrogen-containing compound containing pyrrole-pyridine groups, the alkyl metal compound and the halogen-containing promoter is 1: (0.5-500): (50-500): (1-50).

8. The ethylene selective trimerization catalyst system according to claim 1, characterized in that: The preparation method of the nitrogen-containing compound containing pyrrole-pyridine groups comprises the following steps: a) reacting 2-formaldehyde pyrrole of formula (i) and a primary amine of formula (ii) in a solvent to obtain an intermediate of formula (iii); b) reacting the intermediate of formula (iii) with pyridine of formula (iv) to obtain a nitrogen-containing compound of formula (I); 9. A method for selective trimerization of ethylene, comprising the following steps: mixing a chromium compound, a nitrogen-containing compound containing a pyrrole-pyridine group, and a halogen-containing promoter in an organic solvent to obtain a premix; mixing the premixture and a solution of an alkyl metal compound, introducing ethylene and reacting the mixture; The structure of the nitrogen-containing compound containing a pyrrole-pyridine group is shown in formula (I): wherein R1 and R2 are independently selected from hydrogen, C1-C10 alkyl, C1-C10 alkenyl, C6-C10 cycloalkyl or C6-C10 aryl; R3 is selected from C1-C10 alkyl, C6-C10 cycloalkyl or C6-C10 aryl; R4 is selected from halogen, C1-C10 alkyl, C1-C10 alkenyl or C6-C10 cycloalkyl.

10. The method according to claim 9, characterized in that The reaction temperature is 50-150° C., the pressure is 0-10 MPa, and the reaction time is 0.2-2 h.

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