A process for the selective trimerization of ethylene to produce 1-hexene

Abstract

This invention belongs to the field of petrochemical catalysis technology and relates to a method for the selective trimerization of ethylene to 1-hexene. The key feature is that the selective trimerization of ethylene to 1-hexene is catalyzed by a quaternary system of chromium compounds, pyrrole ligands, trialkylaluminum, and chloride auxiliaries, and the reaction is carried out in a cyclohexane solvent. This invention provides a high-boiling-point cyclohexane inert organic solvent for the catalytic system. Compared with known solvents in the catalytic system, using cyclohexane as a solvent not only helps reduce the generation of volatile organic compounds during 1-hexene production but also simplifies the separation process of 1-hexene and other α-olefins, reducing separation energy consumption and thus lowering the production cost of 1-hexene and other α-olefins. Furthermore, using cyclohexane as a solvent in the selective trimerization of ethylene is expected to reduce solvent costs, as cyclohexane can be produced in large quantities using benzene hydrogenation alkylation.

Description

Technical Field

[0001] This invention belongs to the field of petrochemical catalysis technology and relates to a method for selective trimerization of ethylene to produce 1-hexene. Background Technology

[0002] 1-Hexene is a high-quality comonomer for producing high-grade polyolefin resins. LLDPE and HDPE resins produced using 1-hexene as a comonomer have better tensile strength, rheological properties, resistance to rapid and slow cracking, and impact resistance than 1-butene copolymer resins, making them particularly suitable for producing packaging films and agricultural covering films.

[0003] Selective trimerization of ethylene is the preferred process for producing 1-hexene. The following are the main patents related to selective trimerization of ethylene, but the inventions primarily concern the catalyst system.

[0004] European invention patent EP0608447 A1 (filed in 1993) discloses a process for preparing a catalyst for the selective trimerization of ethylene. Its key feature is that the catalytic system consists of a chromium source-pyrrole or 2,5-dimethylpyrrole-triethylaluminum-halogen promoter. Example 1 provides results of the selective trimerization of ethylene (80°C, 3.75 MPa, 30 min) in cyclohexane solvent using a chromium compound-pyrrole-triethylaluminum-diethylaluminum chloride. The chromium compound is chromium isooctanoate, chromium pyrrole, chromium acetylacetone, chromium naphthenate, and chromium chloride. The reactivity is in the range of 1.2-2.6 × 10⁻⁶. 4 The product concentration was between g / gCr.h; the liquid product accounted for 98% and the solid product accounted for 2%; the liquid product contained 92-97% trimer, <1% dimer, and the remainder were tetramers and larger polymers. Example 8 provided the results of selective trimerization of ethylene in cyclohexane solvent using a chromium isooctanoate-2,5-dimethylpyrrole-triethylaluminum-halide quaternary catalytic system (under the same conditions as above). The halide was n-butane bromide, trimethylbromosilane, and germanium chloride (GeCl4). When n-butane bromide was used as a promoter, the catalytic activity of the quaternary system was 2.5-2.7 × 10⁻⁶. 4 g liquid product / g Cr.h. Liquid products account for >99% of the total product; the selectivity of trimers is 93-94%; the selectivity of dimers is <1%; the remainder are tetramers and higher polymers. When trimethylbromosilane is used as an auxiliary, the catalytic activity of the quaternary system is 1.4 × 10⁻⁶. 4 g liquid product / g Cr.h. Liquid product accounts for >99% of total product; the selectivity of trimer is 90%; the selectivity of dimer is <1%; the remainder are tetramers and higher polymers. When germanium tetrachloride is used as an auxiliary agent, the reactivity of the quaternary system is 5.5-6.6 × 10⁻⁶. 4g liquid product / g Cr.h. The liquid product accounts for >99% of the total product, the selectivity of the trimer is 96-98%, the selectivity of the dimer is <1%, and the remainder are tetramers and higher polymers. This invention patent also illustrates, from the opposite perspective, the importance of adding a halide promoter for the selective trimerization of ethylene in the above catalytic system through an example (Example 2): under the same reaction conditions (80℃, 3.75 MPa, 30 min), the ethylene oligomerization activity of the chromium isooctanoate-pyrrole-triethylaluminum ternary system is 4×10⁻⁶. 3 With g / gCr.h, the proportion of liquid products decreased to 74%, while the proportion of solid products increased to 26%. The proportion of ethylene trimer decreased to 55%, while the proportions of dimer, tetramer, and pentamer all increased to 9%, and the proportion of hexamer reached 5%.

[0005] US Patent 5910619 (filed in 1995) discloses a process for producing α-olefins. Its key feature is the use of a quaternary catalytic system composed of chromium compounds, pyrrole compounds and their derivatives, alkylaluminum, and halides. The chromium compounds include chromium alkoxides, chromium carboxylates, chromium β-diketones, salts formed by chromium and β-ketoester anions, chromium β-ketocarboxylates, chromium amide complexes, chromium carbonyl complexes, chromium carbapenene complexes, chromium cyclopentadienyl complexes, and more than twenty other types. The pyrrole compounds and their derivatives include pyrrole and 2,5-dimethylpyrrole. The alkylaluminum refers to trialkylaluminum. The halides include carbon tetrachloride, chloroform, dichloroethane, trichloroethane, tetrachloroethane, pentachloroethane, hexachloroethane, titanium tetrachloride, and germanium tetrachloride. Example 1 provides the results of selective trimerization of ethylene in a quaternary system of chromium isooctanoate-2,5-dimethylpyrrole-triethylaluminum-carbon tetrachloride in cyclohexane solvent (80°C, 3.5 MPa, 30 min): trimer selectivity 93.7%, C 10-20 Total content 5.90%, dimer and tetramer 0.01% and 0.3% respectively, solids 0.02%, no C 20-30 product.

[0006] Chinese invention patent CN1256968A (application date 1998) discloses a novel selective trimerization catalyst for ethylene. Its technical feature is that the catalyst consists of four components: a chromium compound, a pyrrole derivative, a trialkylaluminum compound, and a promoter, which carry out the selective trimerization of ethylene in a heptane solvent. The promoter is a halogenated aromatic compound. Example 1 provides the results of the selective trimerization of ethylene (100℃, 5.0 MPa, 1 h) in a quaternary system of chromium isooctanoate-2,5-dimethylpyrrole-triethylaluminum-2-fluoro-6-chloro-trichloromethylbenzene in a heptane solvent: activity 321269.20 g / gCrh, trimer selectivity 89.43%, pentamer selectivity 5.74%, C12 + Liquid products accounted for 4.13%, while dimers, tetramers, and solid products were all much less than 1.0%.

[0007] Chinese invention patent CN1294109A (application date 2000) discloses a catalyst for the oligomerization of ethylene to 1-hexene and its application method. Its technical feature is that the catalyst is a quaternary system composed of a chromium compound, a pyrrole derivative, an alkylaluminum compound, and a modifier. The ethylene oligomerization reaction is carried out in an alkane solvent. The modifier is a halogenated compound, including 1,2,3,4,5,6-hexachlorocyclohexane γ-form, 1,4-(di)trichloromethyl-2,3,5,6-tetrachlorobenzene, and 1,3,5-(tri)trichloromethyl-2,4,6-trichlorobenzene. The alkane solvent is selected from one or a mixture of n-heptane, isoheptane, n-octane, isooctane, n-decane, n-dodecane, cyclohexane, methylcyclohexane, and cyclopentane. Example 1 provides the results of ethylene oligomerization in n-heptane solvent using a quaternary system composed of chromium isooctanoate-2,5-dimethylpyrrole-triethylaluminum-1,2,3,4,5,6-hexachlorocyclohexane γ-molecule (110 °C, 5.0 MPa, 1.2 h): the reactivity was 3.5 × 10⁻⁶. 5 g / gCr.h, trimer selectivity 90.01%, pentamer selectivity 9.00%, solid product 0.10%, dimer and tetramer 0.24% and 0.43%, respectively.

[0008] Chinese invention patent CN1490291A (filed in 2003) discloses a method for preparing 1-hexene. Its technical feature is the use of a chromium compound-pyrrole derivative-alkylaluminum-modifier quaternary catalytic system to carry out ethylene oligomerization in an alkane or cycloalkane solvent. First, a portion of the raw material ethylene is mixed with the solvent in a premixer, and then mixed with the components of the quaternary catalytic system. The alkane or cycloalkane solvent includes n-heptane, isoheptane, n-octane, n-decane, n-dodecane, cyclohexane, methylcyclohexane, and cyclopentane.

[0009] Chinese invention patent CN1872416A (application date 2006) discloses a selective trimerization catalyst for ethylene and its application method. Its technical feature is the use of a quaternary catalyst system of chromium compound-PNP ligand-alkyl aluminum-promoter to carry out the selective trimerization reaction of ethylene in an organic solvent. The chromium compound is chromium acetylacetone, chromium chloride tetrahydrofuran, and / or chromium isooctanoate; the N atom of the PNP ligand may have isopropyl, butyl, cyclopropyl, cyclopentyl, or cyclohexyl groups, and the P atom may have phenyl, benzyl, fluorenyl, or naphthyl groups; the alkyl aluminum includes trimethylaluminum, triethylaluminum, tripropylaluminum, tributylaluminum, or / and triisobutylaluminum; the organic solvent includes benzene, toluene, xylene, cumene, n-heptane, n-hexane, methylcyclohexane, cyclohexane, 1-hexene, 1-octene, and ionic liquids. Example 1 provides the results of selective trimerization of ethylene in toluene solvent using a chromium isooctanoate-(diphenyl)phosphine-(cyclopropyl)phosphine-triethylaluminum-1,1,2,2-tetrachloroethane quaternary system (80°C, 5.0 MPa, 30 min): reaction activity 5.68 × 10⁻⁶. 7 g / mol Cr.h (1.09×10) 6 (g / g Cr.h), 1-hexene selectivity 95.03%, 1-octene selectivity 1.02%, 1-butene selectivity 0.32%, polymer selectivity 0.2%.

[0010] Chinese invention patent CN102558107A (filed in 2010) discloses a method for preparing a chromium source and its application in an olefin oligomerization catalyst. The chromium source is tris(tetrahydrofuran)trihalomethane, and its application in olefin oligomerization is achieved by forming a quaternary catalyst system of tris(tetrahydrofuran)trihalomethane-pyrrole derivative-alkylaluminum-modifier, which carries out the olefin oligomerization reaction in an organic solvent. The organic solvent includes n-hexane, cyclohexane, n-heptane, isoheptane, n-octane, isooctane, n-decane, n-dodecane, methylcyclohexane, benzene, toluene, o-xylene, 1-hexene, and 1-octene, preferably n-heptane or toluene. Example 7 provides the results of selective trimerization of ethylene in a quaternary system consisting of tris(tetrahydrofuran)trihalomethylene, dimethylpyrrole, triethylaluminum, and tetrachloroethane in n-heptane solvent (80°C, 5 MPa, 30 min): reaction activity 185 kg / gCr·h, trimer selectivity 88.2%, pentamer selectivity 5.66%, C 12 + The total polymer content was 4.21%, with dimers, tetramers, and solid polymers all less than 1%.

[0011] Chinese invention patent CN103102237A (application date 2011) discloses a method for improving the performance of a catalyst for selective trimerization of ethylene. Its technical feature is that the catalyst is a quaternary system of chromium compound-pyrrole derivative-alkylaluminum compound-modifier, and three of the four catalyst components must be dispersed in an organic solvent and subjected to microwave irradiation. The organic solvent is n-heptane or toluene. Example 2 provides the results of ethylene trimerization (120°C, 5 MPa, 30 min) of the quaternary system of chromium isooctanoate-2,5-dimethylpyrrole-triethylaluminum-hexachloroethane in n-heptane solvent: reaction activity 320.2 kg / gCr.h, trimer selectivity 96.3%, tetramer selectivity 0.53%, C 10 The above polymers comprise 3.10%, and the solid products comprise 0.06%.

[0012] Chinese invention patent CN107597191A (application date 2017) discloses a catalyst for the selective trimerization of ethylene to prepare 1-hexene. The catalyst consists of a chromium compound, a phosphorus-containing compound, and an activator. Its key feature is that the phosphorus-containing compound has a biphenyl or binatidine ring structure and is substituented with phosphorus-containing substituents and alkyl or / and alkoxy substituents. The chromium compound includes chromium acetylacetonate, chromium tetrahydrofuran trichloride, and chromium isooctanoate. The activator is one or two of methylaluminoxane, dealkylated aluminum methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, trimethylaluminum, triethylaluminum, triisobutylaluminum, diethylaluminum chloride, and diethylaluminum chloride. A mixture of methylaluminoxane and triethylaluminum is preferred. The selective trimerization of ethylene with the catalyst is carried out in an inert solvent. The inert solvent includes cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, heptane, toluene, xylene, and benzene.

[0013] Chinese invention patent CN114225968A (application date 2022) discloses a selective trimerization catalyst composition for ethylene. Its technical feature is that the catalyst composition consists of four components: a chromium compound, a cyclopentadiene derivative, triethylaluminum, and tetrachloroethane. The chromium compound is chromium isooctanoate, chromium acetylacetone, or / and chromium chloride tetrahydrofuran. The cyclopentadiene derivative is pentaphenylcyclopentadiene. Examples provide results of the ethylene trimerization reaction of the catalyst system in cyclohexane solvent. Example 1 shows the results of the ethylene trimerization reaction (30℃, 0.1 MPa, 0.1 h) of the chromium acetylacetone-pentaphenylcyclopentadiene-triethylaluminum-tetrachloroethane quaternary system: reaction activity 1.89 × 10⁻⁶. 5 g / gCr. h, 1-hexene selectivity 92.7%, C 10 +The selectivity was 4.86%, with 0.29% for the solid polymer, and less than 1.0% for the dimer, tetramer, and pentamer. Example 4 presents the results of the ethylene trimerization reaction (100°C, 5.0 MPa, 0.6 h) of the chromium isooctanoate-pentaphenylcyclopentadiene-triethylaluminum-tetrachloroethane quaternary system: reactivity 2.82 × 10⁻⁶. 5 g / gCr. h, 1-hexene selectivity 93.7%, C 10 + The selectivity was 4.15%, with the solid polymer having a selectivity of 0.11%, and the selectivity of dimers, tetramers, and pentamers all being less than 1.0%.

[0014] In addition to the aforementioned invention patents, the following published documents also report research on the selective trimerization of ethylene to prepare 1-hexene. Similarly, these mainly involve research on catalyst systems.

[0015] The published literature "Du Xiangdong. Study on the Catalytic System and Reaction Mechanism of Selective Trimerization of Ethylene to 1-Hexene [M]. Beijing University of Chemical Technology, 2002" reported the study of ethylene oligomerization reaction in a ternary catalytic system of chromium isooctanoate-pyrrole-triethylaluminum and a quaternary system of chromium isooctanoate-pyrrole-triethylaluminum-tetrachloroethane, with n-heptane as the solvent.

[0016] In the study of the chromium isooctanoate-pyrrole-triethylaluminum ternary catalytic system, the authors investigated the effects of pyrrole ligand dosage (expressed as N / Cr molar ratio), main catalyst dosage (expressed as Cr concentration), and ethylene oligomerization reaction temperature, pressure, and time. The results showed that under the conditions of a reaction temperature and pressure of 80℃ and 3.5 MPa, a catalyst dosage of 0.4 mmol / L, a co-catalyst dosage (TEA / Cr(EH)3) of 15, and a reaction time of 1 h, when the ligand dosage varied between 2 and 9, the activity of the ethylene oligomerization reaction first increased and then decreased with increasing ligand dosage, reaching a maximum value of 9747 g / gCr·h at a ligand dosage of 3. Variations in ligand dosage have some impact on the carbon number distribution of α-olefins, but the products generally maintain a pattern of ethylene trimer being the most abundant (approximately 46-61%), followed by dimer (approximately 26-40%), and ethylene tetramers and higher polymers being generated in relatively small amounts (approximately 12-15%). When the main catalyst dosage varies between 0.1-0.8 mmol / L (with a fixed ligand dosage of 3), the activity of the ethylene oligomerization reaction first increases and then decreases with increasing main catalyst dosage, reaching a maximum of 9747 g / gCr·h at a main catalyst dosage of 0.4 mmol / L. Variations in the main catalyst dosage within the range of 0.1-0.8 mmol / L have a significant impact on the carbon number distribution of α-olefins. When the main catalyst dosage is low (e.g., 0.1), the products are mainly ethylene dimers (up to nearly 90%). With increasing main catalyst dosage, the proportion of ethylene dimers decreases significantly, the proportion of trimers increases significantly, and the generation of ethylene tetramers and higher polymers also increases. When the amount of main catalyst is 0.6-0.8, the proportion of ethylene trimer reaches its maximum, approximately 55%. At this point, the proportion of ethylene dimer decreases to about 32%. The remainder consists of ethylene tetramers and higher polymers. When the amounts of ligand and main catalyst remain constant (3 and 0.4 mmol / L, respectively), and the reaction temperature, pressure, and time vary between 60-100℃, 2.5 MPa-6.0 MPa, and 1-4 h, respectively, these variations only significantly affect the activity of ethylene oligomerization, without fundamentally affecting the carbon number distribution of α-olefins. For example, with increasing reaction temperature, the reaction activity first increases and then decreases, reaching a maximum of 14816 g / gCr·h at 90℃. However, when the reaction temperature reaches 100℃, the reaction activity drops sharply to 6046 g / gCr·h; with increasing reaction pressure, the reaction activity generally shows a monotonic increasing trend. However, the reaction pressure reaches its maximum value at 5-6 MPa and fluctuates around 17,000-18,000 g / gCr.h. Within this range of conditions, the proportion of ethylene trimer fluctuates between 40-60%, and the proportion of dimer fluctuates between 30-40%. The remainder consists of ethylene tetramers and higher polymers.

[0017] In the study of the quaternary system of chromium isooctanoate-pyrrole-triethylaluminum-tetrachloroethane, the authors investigated the effects of the amount of main catalyst and the electronic auxiliary tetrachloroethane. The results showed that in the quaternary system with tetrachloroethane as the electronic auxiliary, two main changes occurred in the ethylene oligomerization reaction: firstly, the reactivity was significantly improved; and secondly, the selectivity of the ethylene trimer was significantly improved. For example, at reaction temperatures of 90 °C, pressures of 4.5 MPa, and times of 1 h, and ligand and main catalyst amounts of 3 and 0.0625 mmol / L, respectively, the reactivity of the ethylene oligomerization reaction first increased and then decreased as the amount of tetrachloroethane (TCE) (expressed as the TCE / Cr molar ratio) gradually increased in the range of 0:1–20:1, reaching a maximum value of 321,123 g / gCr·h at a ratio of 3:1. It exhibited a relatively high value (between 260,000 and 320,000) in the range of 3:1–5:1. It is worth noting that when the amount of TCE is too high (e.g., 10:1-20:1), the reactivity drops sharply to the range of 91,000-130,000. In contrast to the change in reactivity, as the amount of tetrachloroethane (TCE) (expressed as the TCE / Cr molar ratio) gradually increases within the range of 0:1-20:1, the proportion of ethylene trimer generally shows a gradual increasing trend, while the proportion of ethylene dimer generally shows a decreasing trend. Specifically, when the TCE dosage increased from 1:1 to 2:1, both the reactivity and the selectivity of the ethylene trimer increased dramatically: from 35692 g / gCr.h to 185769 g / gCr.h and from 46.6% to 79.2%, respectively (the ethylene dimer decreased from 39.4% to 3.4%). When the TCE dosage reached the range of 3:1-5:1, the ethylene oligomerization reaction exhibited high reactivity and selective trimerization characteristics (reactivity between 260000 and 320000, and ethylene trimer selectivity at the level of 83-84%). When the TCE dosage continued to increase to the range of 10:1-20:1, although the reactivity had decreased significantly, the selectivity of the ethylene trimer further increased to the level of 88-89%.

[0018] This shows that chloride promoters in the quaternary catalytic system are key components for regulating the activity of ethylene oligomerization and the selectivity of trimers.

[0019] The published paper "Ning Yingnan. The Role of Co-catalysts in Ethylene Trimerization Catalysis System [M]. Daqing Petroleum Institute, 2009" reports the author's research on the role of five co-catalysts in the selective trimerization of ethylene in a quaternary catalytic system of chromium isooctanoate-2,5-dimethylpyrrole-co-tetrachloroethane using cyclohexane as solvent. The five co-catalysts are triethylaluminum, trimethylaluminum, tri-n-hexylaluminum, triisobutylaluminum, and methylaluminoxane. The results show that all five co-catalysts have good co-catalytic activity in the quaternary catalytic system. Under the same reaction conditions, the highest activity of ethylene oligomerization with triethylaluminum as co-catalyst occurs when the co-catalyst dosage (expressed as Al / Cr molar ratio) is 15, reaching a value of 1.38 × 10⁻⁶. 6 g / molCr·h. At this point, the selectivity of ethylene trimer reached its maximum value of 92.36%, the selectivity of ethylene dimer was 0.47%, and the remainder were tetramers and higher polymers. With increasing triethylaluminum dosage, both the reactivity and the selectivity of ethylene trimer decreased, while the selectivity of dimers and pentamers and higher polymers increased. When trimethylaluminum was used as a co-catalyst, the highest activity of the ethylene oligomerization reaction occurred in the co-catalyst dosage range (expressed as Al / Cr molar ratio) of 60-80, with a value of approximately 4.7 × 10⁻⁶. 5 The maximum selectivity of ethylene trimers was observed when the amount of co-catalyst (expressed as Al / Cr molar ratio) was 10, reaching 94.02%. At this point, the selectivity of ethylene dimers was 0.23%, with the remainder being tetramers and higher polymers. The reactivity increased with increasing trimethylaluminum content, while the selectivity of ethylene trimers decreased. The selectivity trends of dimers and pentamers and higher polymers were opposite to those of trimers. Both ethylene oligomerization activity and trimer selectivity were poor when tri-n-hexylaluminum and triisobutylaluminum were used as co-catalysts, while the worst ethylene oligomerization activity and trimer selectivity were observed when methylaluminoxane was used as a co-catalyst.

[0020] The publicly available paper, "Yan Xiaowei. Study on the Kinetics of High Selectivity Trimerization of Ethylene to 1-Hexene in M-System Catalysis [M]. East China University of Science and Technology, 2012," reports the author's research on the selective trimerization of ethylene in a quaternary catalytic system of organometallic compound M-ligand N-alkylmetal compound co-catalyst B-halide A (M, N, B, and A systems were encrypted by the author). The solvent used was n-heptane. The halogenated co-catalysts used in the paper also included dichloromethane, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, hexachloroethane, 1,1,2,2-tetrabromoethane, and carbon tetrachloride. The optimized reaction conditions were as follows: main catalyst concentration (M concentration) of 0.0242 mmol / L, co-catalyst B concentration (expressed as the molar ratio of B to chromium) of 140, ligand concentration (expressed as the molar ratio of ligand N to M) of 5, halide promoter concentration (expressed as the molar ratio of promoter to M) of 15, reaction temperature of 95 °C, and reaction pressure of 2.5 MPa. The results show that among the halide promoters studied by the authors, the use of halide A and carbon tetrachloride enables the quaternary catalytic system to exhibit both high reactivity and high ethylene trimer selectivity. When halide A was used as an auxiliary agent, the reactivity was 11134 g / mmol M.h, the selectivity of ethylene trimer was 90.6%, the selectivity of dimer was 1.08%, and the remainder were tetramers and above. When carbon tetrachloride was used as an auxiliary agent, the reactivity was 14442 g / mmol M.h, the selectivity of ethylene trimer was 89.4%, the selectivity of dimer was 0.974%, and the remainder were tetramers and above.

[0021] The publicly available literature Appl. Catal. A: Gen. 193(2000)29-38 reported the effect of chloride promoters on the selective trimerization of ethylene in a chromium isooctanoate-2,5-dimethylpyrrole-triethylaluminum-chloride quaternary catalytic system. The authors conducted relevant experimental studies using n-heptane as a solvent. The results showed that the ethylene trimerization reaction exhibited the best activity and selectivity under the following conditions: reaction temperature, pressure, and time of 90℃, 3.5MPa, and 30 min, and the ratio of chromium source, ligand, co-catalyst, and chloride (tetrachloroethane) of 0.01:0.03:0.3:0.03-0.06. The ethylene conversion reached 23-27%, the 1-hexene selectivity was 93-95%, the 1-decene selectivity was 4-6%, and the polymer content was low (<0.17‰). Within the investigated chloride dosage range (Cr / TCE ratio of 0.01:0 to 0.01:0.30), the selectivity of ethylene trimer increased with increasing TCE dosage. Correspondingly, the selectivity of ethylene pentamer decreased with increasing TCE dosage. However, on the other hand, the activity of the ethylene trimer reaction showed a trend of first increasing and then decreasing with increasing TCE dosage. When the TCE dosage was too high (e.g., Cr / TCE = 0.01:0.12-0.01:0.30), the ethylene conversion rate plummeted to 2-6%, while the amount of ethylene polymer formed increased dramatically to 1.65%-9.66%. These results indicate that the primary role of TCE in the quaternary system is to improve the selectivity of the ethylene trimer reaction. At appropriate dosages, TCE can also significantly increase the activity of the ethylene trimer reaction. The authors also investigated the auxiliary effects of 1,2-dichloroethane and monochloroheptane. The results showed that 1,2-dichloroethane and chloroheptane also improved the selectivity of ethylene trimer, but the quaternary catalytic system composed of these two chlorides had low catalytic activity and a relatively large amount of ethylene polymer was generated.

[0022] The published literature J. Mole. Catal. A: Chem. 221 (2004) 9-17 also studied the role of halides in the chromium isooctanoate-2,5-dimethylpyrrole-triethylaluminum-halide quaternary catalytic system. In this study, the authors also used n-heptane as the solvent for the ethylene oligomerization reaction. The halide promoters investigated included 1-fluorononane, 1-chlorobutane, 1-bromobutane, 2,2-dichloropropane, 1,1,2,2-tetrachloroethane, hexachloroethane, α,α,α-trifluorotoluene, α,α,α-trichlorotoluene, tetrachloromethane, and tetrachlorogermanium. The results showed that, under the conditions of reaction temperature, pressure, and time of 100℃, 5.0 MPa, and 1 h, and a molar ratio of chromium isooctanoate, 2,5-dimethylpyrrole, triethylaluminum, and halides of 1:5:100:10, the quaternary catalytic system composed of tetrachloroethane and hexachloroethane exhibited both high activity and high trimer selectivity for the oligomerization of ethylene. Specifically, when tetrachloroethane was used as the fourth component, the reaction activity reached 186.7 kg 1-hexene / g Cr·h, the trimer selectivity reached 91.0%, the dimer selectivity was 0.5%, and the remainder was tetramers and higher polymers. When hexachloroethane was used as the fourth component, the reaction activity reached 161.5 kg 1-hexene / g Cr·h, the trimer selectivity reached 95.0%, the dimer selectivity was 0.4%, and the remainder was tetramers and higher polymers. The authors also investigated the effect of hexachloroethane dosage (HCE / Cr = 0, 2, 4, 6, 8, 10, 30) on the ethylene oligomerization reaction. The results showed that with increasing hexachloroethane dosage, both the activity of the ethylene oligomerization reaction and the selectivity of the trimer exhibited a trend of first increasing and then decreasing. The maximum reactivity occurred when the hexachloroethane dosage was 6, with a value of 230.9 kg 1-hexene / g Cr.h. The maximum trimer selectivity occurred when the hexachloroethane dosage was 10, with a value of 95.0%. This also shows that the primary role of hexachloroethane in the quaternary system is to improve the selectivity of ethylene trimerization. At appropriate dosages, it can also significantly improve the reactivity. Notably, the authors' results also indicated that in the ternary system with 0 hexachloroethane dosage, the selectivity of the ethylene trimer was only 48.5%. At this point, the proportion of dimers in the polymer was as high as 20.5%, and the proportion of pentamers was as high as 24.2%. The proportion of tetramers was 3%, and C... 12 + It accounts for 3.8%.

[0023] The article "Synthetic Resins and Plastics", published in 2005, 22(2): 19, reported the effects of halides such as carbon tetrachloride, germanium tetrachloride, tin tetrachloride, and o-trichloromethylchlorobenzene on the trimerization of ethylene to 1-hexene in the chromium isooctanoate-pyrrole-alkylaluminum-chloride quaternary catalytic system. The authors used n-heptane as a solvent in this study.

[0024] The published paper ISSN 09655441, Petroleum Chemistry, 2011, Vol. 51, No. 6, pp.442–447, reports the kinetics of ethylene oligomerization in a quaternary system of chromium isooctanoate-2,5-dimethylpyrrole-triethylaluminum-carbon tetrachloride. The authors used n-heptane as a solvent in this study.

[0025] The published paper *Chin. J. Chem.* 2011, 29, 1149–1153 reported the effects of trimethylaluminum, triethylaluminum, tri-n-hexylaluminum, triisobutylaluminum, and methylaluminoxane on the trimerization of ethylene in the chromium isooctanoate-2,4-dimethylpyrrole-alkylaluminum-tetrachloroethane quaternary system. Cyclohexane was used as the solvent in this study. The ethylene trimerization conditions were: reaction temperature 80 °C, reaction pressure 2.0 MPa, reaction time 30 min, and a chromium source to ligand molar ratio of 1:3. The results showed that the quaternary system with triethylaluminum as a co-catalyst yielded the best selective trimerization results for ethylene. When the amount of co-catalyst (based on the Al / Cr molar ratio) was 15, the reaction activity reached 1.38 × 10⁻⁶. 6 g / mol Cr.h (equivalent to 2.65 × 10⁻⁶) 4 (g / g Cr.h), the selectivity of 1-hexene reached 92.36%, the selectivity of 1-butene and 1-octene was about 0.40%, the selectivity of 1-decene was 0.72%, the liquid products above decene were 5.99%, and the polymers were 0.05%.

[0026] The publicly available literature, Guangzhou Chemical Industry, 2013, 41(12): 117-119, reports the influencing factors of the selective trimerization of ethylene in a tetrahydrofuran-chromium-pyrrole-triethylaluminum-tetrachloroethane quaternary system, using n-heptane as the solvent. The results show that the above-mentioned quaternary catalytic system composed of tetrahydrofuran-chromium also has high catalytic activity and selectivity for the trimerization of ethylene, comparable to that of the chromium isooctanoate catalytic system.

[0027] The published literature Applied Catalysis A: General 481 (2014) 39–48 reports a kinetic study of the trimerization of ethylene in a chromium isooctanoate-2,5-dimethylpyrrole-alkylaluminum-halide quaternary system, with n-heptane as the reaction solvent. The authors compared the co-catalyst effects of dichloromethane, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, and 1,1,2,2-tetrachloroethylene, tetrachloromethane, hexachloroethane, and 1,1,2,2-tetrabromoethane. They also compared the co-catalyst effects of triethylaluminum, triisobutylaluminum, ethyl sesquialuminum chloride, and diethylzinc. The results showed that, except for the catalytic system involving ethyl sesquialuminate chloride and diethylzinc which lacked ethylene oligomerization catalysis, the other quaternary systems involving halides and alkylaluminum exhibited significant catalytic activity and selectivity for ethylene trimerization, with similar product distribution patterns. Among these, the quaternary systems involving triethylaluminum and tetrachloroethane, and triethylaluminum and tetrachloromethane, showed the best activity and selectivity for ethylene trimerization. Under the conditions of reaction temperature, pressure, and time of 95℃, 2.5 MPa, and 60 min, respectively, a main catalyst concentration of 0.0242 mmol / L, and a molar ratio of chromium source, ligand, co-catalyst, and halide of 1:5:140:15, the reaction activities were 214 kg / gCr·h and 278 kg / gCr·h, respectively, with trimer selectivity of 90.6% and 89.4%, respectively. Furthermore, the authors also investigated the effect of reaction pressure in a Cr / DMP / TCE / TEA system of 1:5:15:140. The results showed that as the reactor pressure increased (1.0 → 1.5 → 2.0 → 3.0 MPa), the reactivity increased, the trimer selectivity decreased, and the proportions of tetramers and pentamers increased.

[0028] We note that in the ethylene trimerization process, although the four-component catalyst system of chromium compound-ligand-alkylaluminum-halide promoter is crucial for the selectivity and efficiency of 1-hexene synthesis (the mass of product produced per unit mass of catalyst (calculated as Cr) per unit time (h)), the ethylene trimerization reaction needs to be carried out in an inert organic solvent with a large solvent volume, and the optimization of organic solvent selection has long been neglected. While existing patents mention the use of various inert organic solvents, including saturated hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane, n-hexane, methylcyclohexane, n-heptane, isoheptane, n-octane, isooctane, n-decane, and n-dodecane, as well as unsaturated hydrocarbons such as benzene, toluene, xylene, and cumene, only n-heptane and cyclohexane are frequently used solvents in the examples. Summary of the Invention

[0029] To address the above problems, this invention provides a method for the selective trimerization of ethylene to prepare 1-hexene.

[0030] The main technical feature of this invention is that the selective trimerization of ethylene to prepare 1-hexene catalyzed by a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-chloride auxiliary is carried out in a dicyclohexane solvent.

[0031] Cyclohexane is a high-boiling-point (227℃) inert organic solvent belonging to the cycloalkanes. Using cyclohexane as a solvent in the selective trimerization of ethylene not only helps reduce the generation of volatile organic compounds (VOCs) during 1-hexene production, but also simplifies the separation process of 1-hexene and other α-olefins, reducing separation energy consumption and thus lowering the production cost of 1-hexene and other α-olefins. Furthermore, using cyclohexane as a solvent in the selective trimerization of ethylene is expected to reduce solvent costs, as cyclohexane can be produced in large quantities using the benzene hydrogenation alkylation method.

[0032] As mentioned earlier, in existing methods for the selective trimerization of ethylene to produce 1-hexene, n-heptane (boiling point 98.5℃) and cyclohexane (boiling point 80.7℃) are two of the most commonly used inert organic solvents. However, compared with bicyclohexane, they have the following disadvantages: First, both have low boiling points. During the production of 1-hexene, low-boiling-point solvents are easily volatilized and become environmental pollutants (VOCs). Second, their boiling points overlap with the boiling ranges of the products of the selective trimerization of ethylene (in addition to 1-hexene, there are also 1-octene and 1-decene and their various isomers), which is not conducive to the separation of products and solvents, leading to a more complex separation process. Third, a large amount of low-boiling-point solvent needs to be vaporized and taken out from the top of the separation tower when separating from the reaction products, resulting in excessive energy consumption. In addition, there are limitations on the amount and cost of n-heptane solvent. This is because, industrially, n-heptane is mainly obtained by separating it from the C7 alkane fraction (boiling point range 90-100℃) during petroleum processing. Since there are numerous isomers of the C7 alkane fraction, extracting the relatively low-content n-heptane from it is energy-intensive and yields low output.

[0033] Other inert alkane solvents mentioned in existing related invention patents, such as cyclopentane (boiling point 49.2℃), methylcyclopentane (boiling point 72.82℃), n-hexane (boiling point 69℃), isoheptane (boiling point 90℃), methylcyclohexane (boiling point 101℃), n-octane (boiling point 125-127℃), isooctane (boiling point 98-99℃), n-decane (boiling point 174℃), and n-dodecane (boiling point 216.3℃), also suffer from limitations in usage and cost, and / or the volatilization of low-boiling-point solvents and separation from products. This is because, among these alkane solvents, except for methylcyclohexane which can be produced in large quantities through toluene hydrogenation, the others, like n-heptane, are mainly obtained through fine separation from the corresponding fractions of petroleum processing. Furthermore, cyclopentane, methylcyclopentane, and n-hexane, due to their even lower boiling points, exhibit more pronounced volatility issues and separation problems from product mixtures during use.

[0034] Although aromatic unsaturated solvents such as benzene, toluene, xylene, and cumene are listed as usable solvents in existing related invention patents, it is difficult to find examples in invention patents involving the quaternary system that use these solvents to carry out ethylene selective trimerization and obtain relatively high reactivity and 1-hexene selectivity. Conversely, according to the published literature ACS Catal. 2019, 9, 1197-1210, when ethylene trimerization is carried out in the quaternary system of chromium isooctanoate-2,5-dimethylpyrrole-triethylaluminum-diethylaluminum chloride, if the reaction is carried out in cyclohexane solvent (90 °C, 5.0 MPa, 30 min), the ethylene trimer 1-hexene can be synthesized efficiently (1-hexene yield 63.03 g, TOF = 29960 mol / mol Cr.h, solid product percentage approximately 0.1%). In contrast, if the reaction is carried out in toluene solvent (under the same conditions), the synthesis efficiency of ethylene trimer 1-hexene is very low (1-hexene yield 3.95 g, TOF = 1876 mol / mol Cr.h, solid product percentage approximately 0.6%). The authors' research shows that in cyclohexane solvent, metallic chromium ions can form a complex structure with 2,5-dimethylpyrrole ligands. However, in toluene solvent, there is a competitive relationship between toluene molecules and 2,5-dimethylpyrrole ligands, leading to the large-scale formation of the di(tolyl)chromium complex. The large-scale formation of the di(tolyl)chromium complex is presumed to be the fundamental reason for the deactivation of the chromium isooctanoate-2,5-dimethylpyrrole-triethylaluminum-diethylaluminum chloride quaternary system during the ethylene trimerization reaction in toluene solvent.

[0035] In fact, early researchers in this field had already discovered the solvent problem in the selective trimerization of ethylene to prepare 1-hexene. During our literature review, we found that in Chinese invention patent CN1128745A (application date 1995), the inventor provided a method for manufacturing 1-hexene, characterized by using 1-hexene (boiling point 62.8℃) as a solvent and employing a quaternary system of metallic chromium compound (A) - trialkylaluminum (B) - pyrrole or its derivative (C) - halogenated auxiliaries (D) to catalyze the selective trimerization of ethylene. The metallic chromium compound (A) includes trichlorotri(ethylenediamine)chromium, pyridine compounds of chromium, and isooctanoic acid compounds of chromium, etc.; the trialkylaluminum includes trimethylaluminum and triethylaluminum, etc.; the pyrrole or its derivative (C) includes pyrrole, 2,5-dimethylpyrrole, and 2,5-diethylpyrrole, etc.; the halogenated auxiliaries include diethylaluminum chloride, ethyl sesquichloride aluminum, n-butyl bromide, germanium tetrachloride, tin tetrachloride, and trimethylchlorosilane, etc. Example 1 presents the results of selective trimerization of ethylene in a quaternary system of trichlorotris(4-dimethylaminopyridine)chromium-triethylaluminum-2,5-dimethylpyrrole-germanium tetrachloride in 1-hexene solvent (100°C, 4 MPa, 2 h): reaction activity 29220 g / gCr.h, trimer selectivity 79.8%, pentamer selectivity 17.3%, and the proportions of dimer, tetramer, and polymer are 0.1%, 0.4%, and <0.1%, respectively. Example 2 uses trichlorotris(ethylenediamine)chromium instead of the chromium source in Example 1; Example 3 uses chromium isooctanoate instead of the chromium source in Example 1; Example 4 uses ethyl sesquichloride aluminum instead of germanium tetrachloride used in Example 1. The ethylene trimerization activities in Examples 2-4 were 27836, 28961, and 30883 g / gCr.h, respectively, with trimer selectivity of 74.8%, 70.9%, and 76.4%, and pentamer selectivity of 20.9%, 22.4%, and 19.4%, respectively. The proportions of dimers, tetramers, and polymers were all less than 1.0%. In this invention, the inventors used the target product (1-hexene) of the selective trimerization of ethylene as the reaction solvent to simplify the process of separating 1-hexene in the selective trimerization of ethylene and reduce separation energy consumption. However, a drawback of this invention is that 1-hexene itself is not an inert organic compound and may participate in the oligomerization reaction of ethylene, reducing the activity and selectivity of the catalytic system. In addition, since the selective trimer of ethylene has low selectivity (only 70-76%), and the generated species contain a large number of α-olefins with other carbon numbers, the large amount of 1-hexene used as a solvent must undergo repeated distillation when separating the 1-hexene product, which inevitably increases energy consumption and undermines the invention's effectiveness.

[0036] Besides Chinese invention patent CN1128745A (application date 1995), Chinese invention patents CN1872416A (application date 2006) and CN102558107A (application date 2010) also mention using 1-hexene and 1-octene (boiling point 122-123℃), products of ethylene oligomerization, as solvents for the selective trimerization of ethylene. Undoubtedly, the purpose and shortcomings of using 1-octene as a solvent for the selective trimerization of ethylene are similar to those of using 1-hexene.

[0037] Unlike existing methods that use 1-hexene and 1-octene as solvents for the selective trimerization of ethylene, the present invention uses bicyclohexane as a solvent that is not only inert but also a high-boiling-point solvent, with a boiling point (227°C) much higher than that of the main products of the selective trimerization of ethylene, 1-hexene (boiling point 62.8°C) and 1-decene (boiling point 169°C). Therefore, when preparing 1-hexene through the selective trimerization of ethylene in bicyclohexane solvent, the separation of the main products 1-hexene and 1-decene, along with their minor isomers, from the solvent can be accomplished using a distillation column with a low theoretical plate number and low reflux ratio. A large amount of solvent does not need to be vaporized; it can be collected from the bottom of the distillation column, and after simple adsorption, depurification, and drying, it can be recycled. Clearly, the use of bicyclohexane as a solvent for the selective trimerization of ethylene in this invention is more conducive to simplifying the separation process and saving separation energy consumption.

[0038] It should be noted that the cyclohexane solvent used in this invention belongs to the C1294109A solvent family. Existing related invention patents CN1294109A (application date 2000), CN1490291A (application date 2003), and CN102558107A (application date 2010) all mention using n-dodecane (boiling point 216.3℃) as a solvent for the selective trimerization of ethylene. Essentially, using n-dodecane as a solvent for the ethylene trimerization reaction possesses the advantages of the cyclohexane solvent used in this invention. However, n-dodecane is mainly obtained through fine separation from relevant fractions in petroleum processing, which is resource-limited, costly, and unsuitable for large-scale industrial applications. In the past, cyclohexane was also a rare chemical. However, we have recently developed a technology for the hydrogenation alkylation of benzene to produce phenylcyclohexane (CN118847190A (application date 2024)). Complete hydrogenation of phenylcyclohexane allows for the convenient large-scale production of bicyclohexane solvent. Therefore, bicyclohexane solvent will be a cheap and readily available high-boiling-point inert organic solvent in the future.

[0039] The technical solution of the present invention is as follows: A method for the selective trimerization of ethylene to 1-hexene involves selective trimerization of ethylene in a dicyclohexane solvent to prepare 1-hexene, and the specific steps are as follows: The first step is to purify the dicyclohexane solvent. The purpose of refining cyclohexane solvent is mainly to remove dissolved oxygen and moisture.

[0040] The purpose and requirements for refining bicyclohexane solvent in this invention are no different from those for refining solvents used in various ethylene oligomerization reactions (e.g., n-heptane, cyclohexane, and toluene) reported in existing patents and publications. This is because the complex catalyst systems of various ethylene oligomerization reactions all exhibit similar sensitivities to oxygen and moisture. Furthermore, this invention does not limit the methods and conditions for refining bicyclohexane solvent. Engineers skilled in the art can refine bicyclohexane solvent based on their experience or by referring to the refining methods for various solvents used in ethylene oligomerization reactions (e.g., n-heptane, cyclohexane, and toluene) reported in existing patents and publications.

[0041] For example, engineers skilled in the art can refer to the solvent purification methods provided in the following published literature to purify the bicyclohexane solvent used in this invention: Zhang Wei, Optimization and Influence Law of Co-catalysts for Iron-Based Ethylene Oligomerization, 2018, Zhejiang University; Yan Xiaowei, Study on the Kinetics of High Selectivity Trimerization of Ethylene to 1-Hexene in M-Based Catalytic Systems, 2012; Bahri-Laleh, et al. Polym. Bull. 75, 3555–3565 (2018). The present invention provides a method for purifying bicyclohexane solvent in the laboratory as follows: First, bicyclohexane is pre-dehydrated by soaking in activated 4A molecular sieves at room temperature for 12 hours. Then, the pre-dehydrated bicyclohexane solvent is refluxed in the presence of sodium wire at a temperature above 220°C for at least 2 hours. During reflux, metallic sodium reacts with trace amounts of water in the solvent to generate sodium hydroxide and hydrogen gas, and reacts with trace amounts of oxygen in the solvent to generate sodium oxide. After reflux, the purification temperature is lowered to 180°C and held at this temperature for at least 2 hours. Then, a small amount of benzophenone is added to the solvent, and the color change of the solvent is observed. If the solvent exhibits a persistent and stable blue color, it indicates that the bicyclohexane solvent has reached an anhydrous and oxygen-free state. The purified bicyclohexane solvent is stored in an environment isolated from air and moisture, with a small amount of sodium wire added to the container.

[0042] The second step involves the selective trimerization of ethylene with cyclohexane as a solvent to produce 1-hexene. The selective trimerization of ethylene to 1-hexene is carried out in a quaternary catalytic system consisting of a chromium compound, a pyrrole ligand, a trialkylaluminum compound, and a chloride promoter, using bicyclohexane as the solvent. The chromium compound is one or a mixture of two or more of chromium isooctanoate, chromium acetylacetonate, and chromium tetrahydrofuran chloride, preferably chromium isooctanoate; The pyrrole ligand is one or a mixture of two of pyrrole and 2,5-dimethylpyrrole, preferably 2,5-dimethylpyrrole; The trialkylaluminum is one or a mixture of two or more of trimethylaluminum, triethylaluminum, tripropylaluminum, tri-n-butylaluminum, and triisobutylaluminum, preferably triethylaluminum; The chloride auxiliary is one or a mixture of two or more of tetrachloroethane, hexachloroethane, trichloromethylbenzene, titanium tetrachloride, and germanium tetrachloride, preferably one or a mixture of two or more of tetrachloroethane, hexachloroethane, and trichloromethylbenzene.

[0043] In the quaternary catalytic system, the suitable range of the molar ratio of chromium compound, pyrrole ligand, trialkylaluminum and chloride promoter is 1:0.5~20:30~200:2~20, and the preferred range is 1:1~10:30~100:3~10.

[0044] The amount of bicyclohexane solvent used, expressed as the molar concentration of chromium (Cr), is suitable in the range of 0.05~0.4 μmol / L, preferably in the range of 0.06~0.3 μmol / L, and more preferably in the range of 0.09~0.2 μmol / L.

[0045] The suitable range of reaction conditions is: reaction temperature 60~110℃, reaction pressure 1~5 MPa, and reaction time 30~120 min; The preferred range of reaction conditions is: reaction temperature of 70~90℃, reaction pressure of 1.5~4.5 MPa, and reaction time of 45~100 min.

[0046] Under the aforementioned conditions, the specific method for selective trimerization of ethylene using bicyclohexane as a solvent in a quaternary catalytic system composed of chromium compounds, pyrrole ligands, trialkylaluminum, and chloride promoters is not fundamentally different from the specific method for selective trimerization of ethylene using other known solvents (such as n-heptane and cyclohexane) in similar catalytic systems described in existing patents and publications. Therefore, engineers skilled in the art can, based on their experience or by referring to the specific methods for selective trimerization of ethylene using other known solvents (such as n-heptane and cyclohexane) in similar catalytic systems described in existing patents and publications, use the bicyclohexane solvent provided in this invention to carry out the selective trimerization of ethylene.

[0047] The specific procedure for selective trimerization of ethylene in the laboratory using a chromium compound-pyrrole ligand-trialkylaluminum-chloride catalytic system with commercially available bicyclohexane (Aladdin, ≥99%) as solvent in a 0.5 L stainless steel high-pressure reactor is as follows: Before the reaction, the reactor and auxiliary feed system were first purified. Specifically, the reactor was continuously evacuated at 110°C for 1 hour to remove air and moisture from the reactor and auxiliary system. Then, the reactor and auxiliary feed system were purged with nitrogen three times. Evacuation was performed after each nitrogen purging to meet the reaction's requirement for an anhydrous and oxygen-free environment. After the final nitrogen purging-evacuation operation, ethylene feedstock was used to purge the reactor, and the pressure was increased to 0.3-0.4 MPa. The reactor temperature was then lowered from 110°C to a constant range of 50-55°C. Next, 40 ml of purified bicyclohexane solvent was added to a clean Shrek bottle in a glove box. Then, 1.0 ml of a pre-prepared 10 mmol / L bicyclohexane chromium compound solution was added to the Shrek bottle and mixed well. Finally, 60 μmol of pyrrole ligand liquid was added to the Shrek bottle and mixed well. The resulting solution is the main catalyst solution, sealed and stored for later use. Separately, take 40 ml of purified bicyclohexane solvent and place it in another clean Shrek bottle. Then, add 0.5 ml of a 1 mol / L trialkylaluminum toluene solution and 0.06 mmol of chloride auxiliary agent sequentially, and shake well. The resulting solution is the co-catalyst solution, sealed and stored for later use.

[0048] When constructing the catalyst system in situ in the reactor, the purified reactor is first evacuated to -0.1 to -0.2 MPa. The co-catalyst solution is then injected into the feed buffer tank, and the pressure difference is used to draw it into the reactor, with stirring initiated. The main catalyst solution is injected into the reactor in the same manner. The feed system is then flushed with 20 ml of purified dicyclohexane solvent, and the flushing liquid is also drawn into the reactor. Finally, ethylene is slowly introduced into the reactor to raise the reactor pressure to the reaction pressure (2 MPa). The reaction temperature is then controlled at 80°C to initiate the selective trimerization of ethylene. Ethylene is continuously added during the reaction to maintain a constant system pressure.

[0049] After the reaction was complete, the reactor was carefully opened, and approximately 3 mL of acidified ethanol was added to terminate the reaction. The reaction product was then subjected to solid-liquid separation. A small amount of the liquid product was centrifuged and analyzed by gas chromatography. The solid product (ethylene wax) was washed with methanol, dried overnight in an oven at 80 °C, and weighed. The activity and selectivity of the selective tetramerization of ethylene were calculated using the above reaction data.

[0050] The beneficial effects of this invention are: The quaternary system of chromium compound-pyrrole ligand-triethylaluminum-halide auxiliary is an important catalytic system for the selective trimerization of ethylene to prepare 1-hexene. This invention provides a high-boiling-point (227°C) bicyclohexane inert organic solvent for this catalytic system. Compared with known solvents for this catalytic system, using bicyclohexane as a solvent not only helps reduce the generation of volatile organic compounds (VOCs) during 1-hexene production, but also simplifies the separation process of 1-hexene and other α-olefins, reduces separation energy consumption, and thus lowers the production cost of 1-hexene and other α-olefins. Furthermore, using bicyclohexane as a solvent in the selective trimerization of ethylene is expected to reduce solvent costs, as bicyclohexane can be produced in large quantities using benzene hydrogenation alkylation. Detailed Implementation

[0051] The specific embodiments of the present invention will be further described below in conjunction with the technical solution.

[0052] The liquid-phase product α-olefins from the oligomerization of ethylene can be analyzed using a Shimadzu GC2014C gas chromatograph. The chromatograph uses an FID detector and a PONA column (50 m × 0.2 mm × 0.2 μm). The detector temperature is 330 °C, the injection port temperature is 330 °C, and the column oven temperature is 50 °C. The temperature programming method is as follows: after injection, the column oven is held at 50 °C for 5 min, then increased to 320 °C at a rate of 10 °C / min, held for 10 min, and then cooled to 50 °C until the next injection.

[0053] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0054] Example 1: This example illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in a bicyclohexane solvent, the catalytic system also exhibits high activity and high selectivity in the bicyclohexane solvent.

[0055] The first step is to purify the dicyclohexane solvent. The purification of commercially available cyclohexane solvent (Aladdin, ≥99%) is carried out in two steps. First, 150 ml of cyclohexane solvent is added to a Shrek flask that is protected from air and moisture. A suitable amount of pre-activated 4A molecular sieve is added, and the flask is sealed. The solvent is then thoroughly soaked and pre-dehydrated at room temperature for 12 hours. Next, the pre-dehydrated cyclohexane solvent is further dehydrated and deoxygenated using sodium wire at reflux temperature (220-230℃) for 4 hours. During reflux, metallic sodium reacts with trace amounts of water in the solvent to produce sodium hydroxide and hydrogen gas, and reacts with trace amounts of oxygen to produce sodium oxide. After reflux, the purification temperature is lowered to 180℃ and held at this temperature for 2 hours. Then, a small amount of benzophenone is added to the solvent, and the color change is observed. Once the solvent turns a stable, persistent blue color, it indicates that the cyclohexane solvent has reached an anhydrous and oxygen-free state. The purification process is then stopped. The refined cyclohexane solvent was sealed in a Shrek bottle and stored in a glove box that was isolated from air and moisture. A small amount of sodium wire was added to the Shrek bottle.

[0056] The second step involves the selective trimerization of ethylene with cyclohexane as a solvent to produce 1-hexene. The reaction was carried out in a 0.5 L stainless steel high-pressure reactor. The catalyst system used was a quaternary system of chromium isooctanoate-2,5-dimethylpyrrole-triethylaluminum-tetrachloroethane. The operating steps are as follows: (1) Purify the reactor and auxiliary feeding system to remove air and moisture. Specific operations include: first, continuously evacuating the reactor at 110°C for 1 hour. Then, purging the reactor and auxiliary feeding system with nitrogen gas three times. Evacuation is performed after each nitrogen purging. After the final nitrogen purging-evacuation operation, ethylene feedstock is used to purge the reactor, and the pressure is increased to 0.4 MPa. The temperature of the reactor is then reduced from 110°C to a constant range of 50-55°C. (2) Prepare the main catalyst solution and the co-catalyst solution in a glove box. The specific steps include: First, add 40 ml of purified bicyclohexane solvent to a clean Shrek bottle. Then, take 1.0 ml of a pre-prepared 10 mmol / L bicyclohexane isooctanoate chromium solution and add it to the Shrek bottle, shaking well. Next, add 60 μmol of 2,5-dimethylpyrrole ligand liquid to the Shrek bottle and shake well. The resulting solution is the main catalyst solution, sealed and ready for use. Separately, take another 40 ml of purified bicyclohexane solvent and place it in another clean Shrek bottle. Then, add 0.5 ml of a 1 mol / L triethylaluminum (co-catalyst) toluene solution and 0.06 mmol of tetrachloroethane (auxiliary agent) sequentially, shaking well. The resulting solution is the co-catalyst solution, sealed and ready for use.

[0057] (3) Constructing the catalyst system in situ in the reactor. Specific operations include: First, evacuating the purified reactor to -0.1 ~ -0.2 MPa. Then, injecting the co-catalyst solution into the feed buffer tank and using the pressure difference to draw it into the reactor, and starting the stirrer. Injecting the main catalyst solution into the reactor in the same manner. Next, flushing the feed system with 20 ml of purified dicyclohexane solvent, and drawing the flushing liquid into the reactor. Finally, slowly introducing ethylene into the reactor to raise the reactor pressure to the reaction pressure (2 MPa). Then, controlling the reaction temperature at 80°C, initiating the selective trimerization reaction of ethylene, with a reaction duration of 40 min. Continuously replenishing ethylene during the reaction to maintain a constant system pressure.

[0058] Based on the above feeding data, the following can be calculated: Cyclohexane dosage (expressed as Cr concentration in the main catalyst): 0.099 μmol / L Chromium isooctanoate / 2,5-dimethylpyrrole / triethylaluminum / tetrachloroethane = 1:6:50:6 (4) After the reaction is complete, carefully open the reactor and add about 3 mL of acidified ethanol to terminate the reaction. Then, separate the reaction products into solid and liquid components. Take a small amount of the liquid product and centrifuge it for gas chromatography analysis. The solid product (ethylene wax) is washed with methanol, dried overnight in an oven at 80 °C, and weighed. Calculate the activity and selectivity of the selective tetramerization of ethylene using the above reaction data.

[0059] The results show that, under given conditions, the catalytic system exhibits a catalytic activity of 2.41 × 10⁻⁶ ppm using cyclohexane as the solvent. 4 kg / gCr.h, the selectivity for 1-hexene reached 98.64%, the selectivity for 1-butene and 1-octene was 0.36%, the selectivity for 1-decene was 0.63%, the selectivity for liquid products above decene was 0.37%, and the selectivity for polymers was 0.001%.

[0060] Comparative Example 1: This example is used for comparison and illustration. When 1-hexene is prepared by the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in a bicyclohexane solvent, the catalytic system also exhibits high activity and high selectivity in the bicyclohexane solvent.

[0061] Example 1 was repeated, but the catalytic system was modified to use cyclohexane solvent for the selective trimerization of ethylene. Therefore, in the first step of purifying the cyclohexane solvent, when further dehydrating and deoxygenating the pre-dehydrated cyclohexane solvent with sodium wire, a small amount of benzophenone was directly added to the cyclohexane solvent simultaneously with the sodium wire. The reflux temperature was approximately 80°C, and the total reflux time was 6 hours. Other operations remained unchanged. The results showed that, under given conditions, the catalytic system using cyclohexane as the solvent exhibited a catalytic activity of 3.28 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene was 98.61%, the selectivity for 1-butene and 1-octene was 0.18%, the selectivity for 1-decene was 0.64%, the liquid products above decene were 0.27%, and the polymers were 0.3%.

[0062] Comparing these reaction results with those in Example 1 shows that when 1-hexene is prepared using the selective trimerization method of ethylene provided by this invention, i.e., when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium isooctanoate-2,5-dimethylpyrrole-triethylaluminum-tetrachloroethane in a bicyclohexane solvent, the catalytic system also exhibits high activity and high selectivity in a bicyclohexane solvent.

[0063] Comparative Example 2: This example is used for further comparison and illustration. When 1-hexene is prepared by the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in a bicyclohexane solvent, the catalytic system also exhibits high activity and high selectivity in the bicyclohexane solvent.

[0064] Example 1 was repeated, but the catalytic system was modified to use n-heptane solvent for the selective trimerization of ethylene. Therefore, in the first step of purifying the n-heptane solvent, when further dehydrating and deoxygenating the pre-dehydrated n-heptane solvent with sodium wire, a small amount of benzophenone was directly added to the cyclohexane solvent simultaneously with the sodium wire. The reflux temperature was approximately 100°C, and the total reflux time was 6 hours. Other operations remained unchanged. The results showed that, under given conditions, the catalytic system using n-heptane as the solvent exhibited a catalytic activity of 3.41 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene was 98.01%, the selectivity for 1-butene and 1-octene was 0.32%, the selectivity for 1-decene was 0.79%, the selectivity for liquid products above decene was 0.53%, and the selectivity for polymers was 0.35%.

[0065] Comparing these reaction results with those in Example 1 also shows that when 1-hexene is prepared using the selective trimerization method of ethylene provided by this invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium isooctanoate-2,5-dimethylpyrrole-triethylaluminum-tetrachloroethane in a bicyclohexane solvent, the catalytic system also exhibits high activity and high selectivity in a bicyclohexane solvent.

[0066] Example 2: This example illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in a bicyclohexane solvent, the amount of bicyclohexane solvent is allowed to vary within a certain range without changing the catalytic characteristics of the catalytic system for the selective trimerization of ethylene.

[0067] Repeat Example 1, but change the amount of bicyclohexane used (expressed as the Cr concentration of the main catalyst) to 0.2 μmol / L. That is, when preparing the main catalyst solution and the co-catalyst solution, the amount of bicyclohexane solvent used is changed to 20 ml each. After adding the co-catalyst solution and the main catalyst solution to the reactor, flush the feed system with 9 ml of bicyclohexane solvent instead. All other operations remain unchanged.

[0068] The results show that, under given conditions, the catalytic system exhibits minimal catalytic performance changes when the amount of bicyclohexane solvent is reduced, resulting in a Cr concentration of 0.2 μmol / L for the main catalyst: the catalytic activity reaches 1.87 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 93.61%, the selectivity for 1-butene and 1-octene was 1.48%, the selectivity for 1-decene was 2.49%, the liquid products above decene were 2.42%, and the polymers were 0.002%.

[0069] Example 3: This example further illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in bicyclohexane solvent, the amount of bicyclohexane solvent is allowed to vary within a certain range without changing the catalytic characteristics of the catalytic system for the selective trimerization of ethylene.

[0070] Repeat Example 1, but change the amount of bicyclohexane used (expressed as the Cr concentration of the main catalyst) to 0.3 μmol / L. That is, when preparing the main catalyst solution and the co-catalyst solution, the amount of bicyclohexane solvent used is changed to 10 ml each. After adding the co-catalyst solution and the main catalyst solution to the reactor, flush the feed system with 13.3 ml of bicyclohexane solvent instead. All other operations remain unchanged.

[0071] The results show that under given conditions, the catalytic system exhibits minimal catalytic performance changes when the amount of bicyclohexane solvent is reduced, resulting in a Cr concentration of 0.3 μmol / L for the main catalyst: the catalytic activity reaches 1.64 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 97.29%, the selectivity for 1-butene and 1-octene was 0.6%, the selectivity for 1-decene was 1.25%, the liquid products above decene were 0.86%, and the polymers were 0.001%.

[0072] Example 4: This example further illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in a bicyclohexane solvent, the amount of bicyclohexane solvent is allowed to vary within a certain range without changing the catalytic characteristics of the catalytic system for the selective trimerization of ethylene.

[0073] Repeat Example 1, but change the amount of bicyclohexane used (expressed as the Cr concentration of the main catalyst) to 0.4 μmol / L. That is, when preparing the main catalyst solution and the co-catalyst solution, the amount of bicyclohexane solvent used is changed to 10 ml each. After adding the co-catalyst solution and the main catalyst solution to the reactor, flush the feed system with 5 ml of bicyclohexane solvent instead. All other operations remain unchanged.

[0074] The results show that, under given conditions, the catalytic system exhibits minimal catalytic performance changes when the amount of bicyclohexane solvent is reduced, resulting in a Cr concentration of 0.4 μmol / L for the main catalyst: the catalytic activity reaches 1.21 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 98.81%, the selectivity for 1-butene and 1-octene was 0.18%, the selectivity for 1-decene was 0.77%, the selectivity for liquid products above decene was 0.24%, and the selectivity for polymers was 0.001%.

[0075] Example 5: This example further illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in a bicyclohexane solvent, the amount of bicyclohexane solvent is allowed to vary within a certain range without changing the catalytic characteristics of the catalytic system for the selective trimerization of ethylene.

[0076] Repeat Example 1, but change the amount of bicyclohexane used (expressed as the Cr concentration of the main catalyst) to 0.06 μmol / L. That is, when preparing the main catalyst solution and the co-catalyst solution, the amount of bicyclohexane solvent used is changed to 50 ml each. After adding the co-catalyst solution and the main catalyst solution to the reactor, flush the feed system with 66.7 ml of bicyclohexane solvent instead. All other operations remain unchanged.

[0077] The results show that, under given conditions, the catalytic system exhibits minimal catalytic performance in the selective trimerization of ethylene when the amount of bicyclohexane solvent is reduced, resulting in a Cr concentration of 0.06 μmol / L for the main catalyst: the catalytic activity reaches 7.21 × 10⁻⁶. 3 g / gCr.h, the selectivity for 1-hexene reached 98.31%, the selectivity for 1-butene and 1-octene was 0.45%, the selectivity for 1-decene was 0.70%, the liquid products above decene were 0.53%, and the polymers were 0.001%.

[0078] Example 6: This example further illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in bicyclohexane solvent, the amount of bicyclohexane solvent is allowed to vary within a certain range without changing the catalytic characteristics of the catalytic system for the selective trimerization of ethylene.

[0079] Repeat Example 1, but change the amount of bicyclohexane used (expressed as the Cr concentration of the main catalyst) to 0.05 μmol / L. That is, when preparing the main catalyst solution and the co-catalyst solution, the amount of bicyclohexane solvent used is changed to 80 ml each. After adding the co-catalyst solution and the main catalyst solution to the reactor, flush the feed system with 40 ml of bicyclohexane solvent instead. All other operations remain unchanged.

[0080] The results show that, under given conditions, the catalytic system exhibits minimal catalytic performance changes when the amount of bicyclohexane solvent is reduced, resulting in a Cr concentration of 0.05 μmol / L for the main catalyst: the catalytic activity reaches 1.19 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 98.64%, the selectivity for 1-butene and 1-octene was 0.36%, the selectivity for 1-decene was 0.63%, the selectivity for liquid products above decene was 0.38%, and the selectivity for polymers was 0.001%.

[0081] Example 7: This example illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in bicyclohexane solvent, different chromium compounds can be used when constructing the catalyst system without changing the applicability of bicyclohexane solvent to the selective trimerization of ethylene.

[0082] Repeat Example 1, but in the second step of preparing the main catalyst solution, replace the chromium compounds used with chromium acetylacetone and chromium chloride tetrahydrofuran in sequence. All other operations remain unchanged.

[0083] The results show that when the chromium compound of the main catalyst is chromium acetylacetone, the catalytic activity of the catalytic system can reach 1.86 × 10⁻⁶ under given conditions using bicyclohexane as a solvent. 4 The selectivity for 1-hexene reaches 93.57% at g / gCr·h. When the chromium compound of the main catalyst is tetrahydrofuran chromium chloride, the catalytic activity of the catalytic system can reach 1.79 × 10⁻⁶ g / gCr·h under given conditions using bicyclohexane as solvent. 4 g / gCr.h, the selectivity for 1-hexene reached 93.21%.

[0084] Example 8: This example illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in bicyclohexane solvent, different pyrrole ligands can be used when constructing the catalyst system without changing the applicability of bicyclohexane solvent to the selective trimerization of ethylene.

[0085] Repeat Example 1, but in the second step of preparing the main catalyst solution, replace the pyrrole ligand used with pyrrole. All other operations remain unchanged.

[0086] The results show that when the ligand of the main catalyst is pyrrole, the catalytic activity of the catalytic system can reach 6.46 × 10⁻⁶ under given conditions using bicyclohexane as the solvent. 3 g / gCr.h, the selectivity for 1-hexene reached 85.36%.

[0087] Example 9: This example illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide promoter in bicyclohexane solvent, different trialkylaluminum can be used as co-catalysts when constructing the catalyst system without changing the applicability of bicyclohexane solvent to the selective trimerization of ethylene.

[0088] Repeat Example 1, but in the second step of preparing the cocatalyst solution, replace the trialkylaluminum cocatalyst with trimethylaluminum, tripropylaluminum, tri-n-butylaluminum, and triisobutylaluminum in sequence. All other operations remain unchanged.

[0089] The results showed that when the co-catalyst was trimethylaluminum, the catalytic activity of the catalytic system under given conditions using bicyclohexane as the solvent could reach 8.78 × 10⁻⁶. 3 g / gCr.h, the selectivity for 1-hexene reached 86.4%.

[0090] When the co-catalyst is tripropylaluminum, the catalytic activity of the catalytic system can reach 1.43 × 10⁻⁶ under given conditions using bicyclohexane as the solvent. 3 g / gCr.h, the selectivity for 1-hexene reached 62.43%.

[0091] When the co-catalyst is tri-n-butylaluminum, the catalytic activity of the catalytic system can reach 5.87 × 10⁻⁶ under given conditions using bicyclohexane as the solvent. 3 g / gCr.h, the selectivity for 1-hexene reached 72.57%.

[0092] When the co-catalyst is triisobutylaluminum, the catalytic activity of the catalytic system can reach 1.87 × 10⁻⁶ under given conditions using bicyclohexane as the solvent. 3 g / gCr.h, the selectivity for 1-hexene reached 92.61%.

[0093] Example 10: This example illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in bicyclohexane solvent, different chloride auxiliaries can be used when constructing the catalyst system without changing the applicability of bicyclohexane solvent to the selective trimerization of ethylene.

[0094] Repeat Example 1, but in the second step of preparing the co-catalyst solution, replace the chloride promoter with hexachloroethane and trichloromethylbenzene in sequence. All other operations remain unchanged.

[0095] The results showed that when the chloride promoter was hexachloroethane, the catalytic activity of the catalytic system under given conditions, using bicyclohexane as the solvent, could reach 2.48 × 10⁻⁶. 4 The selectivity for 1-hexene reaches 98.42% (g / gCr·h). When the chloride promoter is trichloromethylbenzene, the catalytic activity of the catalytic system under given conditions using bicyclohexane as solvent can reach 3.25 × 10⁻⁶ g / gCr·h. 4 g / gCr.h, the selectivity for 1-hexene reached 98.26%.

[0096] Example 11: This example further illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in bicyclohexane solvent, different chloride auxiliaries are allowed to be used when constructing the catalyst system without changing the applicability of bicyclohexane solvent to the selective trimerization of ethylene.

[0097] Repeat Example 1, but in the second step of preparing the co-catalyst solution, replace the chloride promoter with titanium tetrachloride and germanium tetrachloride in sequence. All other operations remain unchanged.

[0098] The results showed that when titanium tetrachloride was used as the chloride promoter, the catalytic activity of the catalytic system under given conditions using bicyclohexane as the solvent could reach 7.22 × 10⁻⁶. 3 g / gCr.h, the selectivity for 1-hexene reached 81.31%.

[0099] When the chloride promoter is germanium tetrachloride, the catalytic activity of the catalytic system can reach 8.48 × 10⁻⁶ under given conditions using cyclohexane as the solvent. 3 g / gCr.h, the selectivity for 1-hexene reached 84.65%.

[0100] Example 12: This example illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by this invention, i.e., when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary agent in a bicyclohexane solvent, the ratio between chromium compound / pyrrole ligand / trialkylaluminum / halide auxiliary agent can be changed within a certain range when constructing the catalyst system without changing the applicability of bicyclohexane solvent to the selective trimerization of ethylene.

[0101] Repeat Example 1, but in the second step of preparing the main catalyst solution, change the ratio of chromium compound to pyrrole ligand to 1:10 and 1:20 respectively. That is, change the amount of 2,5-dimethylpyrrole ligand used to 100 μmol and 200 μmol respectively when preparing the main catalyst solution, while keeping other operations unchanged.

[0102] The results showed that when the ratio of chromium compound to pyrrole ligand was 1:10, the catalytic activity of the catalytic system under given conditions, using bicyclohexane as solvent, could reach 1.86 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 94.82%.

[0103] When the ratio of chromium compound to pyrrole ligand is 1:20, the catalytic system exhibits a catalytic activity of 1.13 × 10⁻⁶ under given conditions using bicyclohexane as the solvent. 4g / gCr.h, the selectivity for 1-hexene reached 85.63%.

[0104] Example 13: This example further illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary agent in bicyclohexane solvent, the ratio between chromium compound / pyrrole ligand / trialkylaluminum / halide auxiliary agent can be changed within a certain range when constructing the catalyst system without changing the applicability of bicyclohexane solvent to the selective trimerization of ethylene.

[0105] Repeat Example 1, but in the second step of preparing the main catalyst solution, change the ratio of chromium compound to pyrrole ligand to 1:1 and 1:0.5 respectively. That is, change the amount of 2,5-dimethylpyrrole ligand used to 10 μmol and 5 μmol respectively when preparing the main catalyst solution, while keeping other operations unchanged.

[0106] The results showed that when the ratio of chromium compound to pyrrole ligand was 1:1, the catalytic system exhibited a catalytic activity of 2.03 × 10⁻⁶ under given conditions using bicyclohexane as the solvent. 4 g / gCr.h, the selectivity for 1-hexene reached 90.93%.

[0107] When the ratio of chromium compound to pyrrole ligand is 1:0.5, the catalytic system, under given conditions using bicyclohexane as solvent, exhibits a catalytic activity of 4.85 × 10⁻⁶. 3 g / gCr.h, the selectivity for 1-hexene reached 86.27%.

[0108] Example 14: This example further illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary agent in bicyclohexane solvent, the ratio between chromium compound / pyrrole ligand / trialkylaluminum / halide auxiliary agent can be changed within a certain range when constructing the catalyst system without changing the applicability of bicyclohexane solvent to the selective trimerization of ethylene.

[0109] Repeat Example 1, but in the second step of preparing the cocatalyst solution, change the ratio of chromium compound to triethylaluminum to 1:100 and 1:200 respectively. That is, change the amount of 1 mol / L triethylaluminum toluene solution used to 1 ml and 2 ml respectively when preparing the cocatalyst solution, while keeping other operations unchanged.

[0110] The results showed that when the ratio of chromium compound to trialkylaluminum was 1:100, the catalytic activity of the catalytic system under given conditions, using bicyclohexane as a solvent, could reach 1.89 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 92.21%.

[0111] When the ratio of chromium compound to trialkylaluminum is 1:200, the catalytic system, under given conditions and with bicyclohexane as the solvent, exhibits a catalytic activity of 1.05 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 71.84%.

[0112] Example 15: This example further illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary agent in bicyclohexane solvent, the ratio between chromium compound / pyrrole ligand / trialkylaluminum / halide auxiliary agent can be changed within a certain range when constructing the catalyst system without changing the applicability of bicyclohexane solvent to the selective trimerization of ethylene.

[0113] Repeat Example 1, but in the second step of preparing the cocatalyst solution, change the ratio of chromium compound to triethylaluminum to 1:30. That is, change the amount of 1 mol / L triethylaluminum toluene solution used in preparing the cocatalyst solution to 0.3 ml, while keeping other operations unchanged.

[0114] The results showed that when the ratio of chromium compound to trialkylaluminum was 1:30, the catalytic activity of the catalytic system under given conditions using bicyclohexane as solvent could reach 1.72 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 99.35%.

[0115] Example 16: This example further illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary agent in bicyclohexane solvent, the ratio between chromium compound / pyrrole ligand / trialkylaluminum / halide auxiliary agent can be changed within a certain range when constructing the catalyst system without changing the applicability of bicyclohexane solvent to the selective trimerization of ethylene.

[0116] Repeat Example 1, but in the second step of preparing the cocatalyst solution, change the ratio of chromium compound to chloride auxiliaries to 1:10 and 1:20 respectively. That is, change the amount of tetrachloroethane used to 0.1 mmol and 0.2 mmol respectively when preparing the cocatalyst solution, while keeping other operations unchanged.

[0117] The results showed that when the ratio of chromium compound to chloride was 1:10, the catalytic activity of the catalytic system under given conditions using bicyclohexane as solvent could reach 1.82 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 99.26%.

[0118] When the ratio of chromium compound to chloride is 1:20, the catalytic system, under given conditions using cyclohexane as solvent, achieves a catalytic activity of 8.51 × 10⁻⁶. 3 g / gCr.h, the selectivity for 1-hexene reached 99.61%.

[0119] Example 17: This example further illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary agent in bicyclohexane solvent, the ratio between chromium compound / pyrrole ligand / trialkylaluminum / halide auxiliary agent can be changed within a certain range when constructing the catalyst system without changing the applicability of bicyclohexane solvent to the selective trimerization of ethylene.

[0120] Repeat Example 1, but in the second step of preparing the cocatalyst solution, change the ratio of chromium compound to chloride auxiliaries to 1:2 and 1:3 respectively. That is, change the amount of tetrachloroethane used to 0.02 mmol and 0.03 mmol respectively when preparing the cocatalyst solution, while keeping other operations unchanged.

[0121] The results showed that when the ratio of chromium compound to chloride was 1:2, the catalytic activity of the catalytic system under given conditions, using bicyclohexane as a solvent, could reach 1.65 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 84.35%.

[0122] When the ratio of chromium compound to chloride is 1:3, the catalytic system, under given conditions using cyclohexane as solvent, exhibits a catalytic activity of 1.88 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 91.32%.

[0123] Example 18: This example further illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in a bicyclohexane solvent, the reaction temperature conditions can be changed within a certain range without changing the applicability of the bicyclohexane solvent to the selective trimerization of ethylene.

[0124] Repeat Example 1, but in the second step of the selective trimerization of ethylene, change the reaction temperature to 60°C, 70°C, 90°C and 110°C in sequence, while keeping other operations unchanged.

[0125] The results showed that the catalytic activity reached 3.85 × 10⁻⁶ at a reaction temperature of 60 °C. 3 g / gCr.h, the selectivity for 1-hexene reached 96.92%.

[0126] When the reaction temperature is 70℃, the catalytic activity can reach 1.85 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 97.84%.

[0127] When the reaction temperature is 90℃, the catalytic activity can reach 2.11 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 91.77%.

[0128] When the reaction temperature is 110℃, the catalytic activity can reach 1.59 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 92.69%.

[0129] Example 19: This example further illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in a bicyclohexane solvent, the reaction pressure conditions can be changed within a certain range without changing the applicability of the bicyclohexane solvent to the selective trimerization of ethylene.

[0130] Repeat Example 1, but in the second step of the selective trimerization of ethylene, change the reaction pressure to 1.5 MPa, 4.5 MPa and 5 MPa in sequence, while keeping other operations unchanged.

[0131] The results showed that when the reaction pressure was 1.5 MPa, the catalytic activity could be replicated in Example 1. However, in the second step of the selective trimerization of ethylene, the reaction pressure was changed to 1.5 MPa, 4.5 MPa and 5 MPa in sequence, while other operations remained unchanged.

[0132] The results showed that the catalytic activity reached 1.30 × 10⁻⁶ when the reaction pressure was 1.5 MPa. 4 g / gCr.h, the selectivity for 1-hexene reached 95.76%.

[0133] At a reaction pressure of 4.5 MPa, the catalytic activity can reach 2.87 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 96.54%.

[0134] At a reaction pressure of 5 MPa, the catalytic activity can reach 3.04 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 91.26%.

[0135] Example 20: This example further illustrates that when 1-hexene is prepared using the selective trimerization method of ethylene provided by the present invention, that is, when 1-hexene is prepared by catalyzing the selective trimerization of ethylene in a quaternary system of chromium compound-pyrrole ligand-trialkylaluminum-halide auxiliary in a bicyclohexane solvent, the reaction time conditions can be changed within a certain range without changing the applicability of the bicyclohexane solvent to the selective trimerization of ethylene.

[0136] Repeat Example 1, but in the second step of the selective trimerization of ethylene, change the reaction time to 30 min, 45 min, 100 min and 120 min respectively, while keeping other operations unchanged.

[0137] The results showed that the catalytic activity reached 1.65 × 10⁻⁶ when the reaction time was 30 min. 4 g / gCr.h, the selectivity for 1-hexene reached 96.14%.

[0138] When the reaction time is 45 min, the catalytic activity can reach 1.92 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 98.78%.

[0139] When the reaction time is 100 min, the catalytic activity can reach 1.27 × 10⁻⁶. 4 g / gCr.h, the selectivity for 1-hexene reached 97.31%.

[0140] When the reaction time is 120 min, the catalytic activity can reach 0.85 × 10⁻⁶. 3 g / gCr.h, the selectivity for 1-hexene reached 96.63%.

Claims

1. A method for the selective trimerization of ethylene to produce 1-hexene, characterized in that, The specific steps are as follows: The first step is to purify the dicyclohexane solvent. The second step involves the selective trimerization of ethylene with cyclohexane as a solvent to produce 1-hexene. The selective trimerization of ethylene to 1-hexene is carried out in a quaternary catalytic system consisting of chromium compounds, pyrrole ligands, trialkylaluminum, and chloride promoters, with bicyclohexane as the solvent.

2. The method for selective trimerization of ethylene to 1-hexene according to claim 1, characterized in that, In the second step, The chromium compound is one or a mixture of two or more of chromium isooctanoate, chromium acetylacetonate, and chromium tetrahydrofuran chloride. The pyrrole ligand is one or a mixture of two of pyrrole and 2,5-dimethylpyrrole; The trialkylaluminum is one or a mixture of two or more of trimethylaluminum, triethylaluminum, tripropylaluminum, tri-n-butylaluminum, and triisobutylaluminum; The chloride auxiliary is one or a mixture of two or more of tetrachloroethane, hexachloroethane, trichloromethylbenzene, titanium tetrachloride, and germanium tetrachloride.

3. The method for selective trimerization of ethylene to 1-hexene according to claim 2, characterized in that, In the second step, The chromium compound is chromium isooctanoate; The pyrrole ligand is 2,5-dimethylpyrrole; The trialkylaluminum is triethylaluminum; The chloride auxiliary is one or a mixture of two or more of tetrachloroethane, hexachloroethane, and trichloromethylbenzene.

4. The method for selective trimerization of ethylene to 1-hexene according to claim 1, characterized in that, In the quaternary catalytic system used in the second step, the molar ratio of chromium compound, pyrrole ligand, trialkylaluminum and chloride promoter ranges from 1:0.5 to 20:30 to 200:2 to 20.

5. The method for selective trimerization of ethylene to 1-hexene according to claim 4, characterized in that, In the quaternary catalytic system used in the second step, the molar ratio of chromium compound, pyrrole ligand, trialkylaluminum and chloride promoter ranges from 1:1 to 10:30 to 100:3 to 10.

6. The method for selective trimerization of ethylene to 1-hexene according to claim 1, characterized in that, In the second step, The amount of bicyclohexane solvent used, expressed as the molar concentration of chromium (Cr), ranges from 0.05 to 0.4 μmol / L.

7. The method for selective trimerization of ethylene to 1-hexene according to claim 6, characterized in that, In the second step, The amount of bicyclohexane solvent used, expressed as the molar concentration of chromium (Cr), ranges from 0.06 to 0.3 μmol / L.

8. The method for selective trimerization of ethylene to 1-hexene according to claim 7, characterized in that, In the second step, The amount of bicyclohexane solvent used, expressed as the molar concentration of chromium (Cr), ranges from 0.09 to 0.2 μmol / L.

9. The method for selective trimerization of ethylene to 1-hexene according to claim 1, characterized in that, In the second step, The reaction conditions are as follows: reaction temperature 60~110℃, reaction pressure 1~5 MPa, and reaction time 30~120 min.

10. The method for selective trimerization of ethylene to 1-hexene according to claim 1, characterized in that, In the second step, The reaction conditions are as follows: reaction temperature 70~90℃, reaction pressure 1.5~4.5 MPa, and reaction time 45~100 min.