Ethylene oligomerization catalytic system with fluorinated modifiers and its application

Abstract

This invention proposes an ethylene oligomerization catalytic system with a fluorinated modifier and its application, belonging to the field of ethylene oligomerization technology. The fluorinated modifier-based ethylene oligomerization catalytic system includes a main catalyst, a co-catalyst, ligands, and a fluorinated modifier; wherein the main catalyst is at least one of an organochromium compound and a chromium halide; the co-catalyst is an aluminum-containing metal compound; and the ligand is a bidentate or tridentate phosphine, nitrogen, carbon, or silicon ligand. This invention uses a fluorinated modifier to regulate the selective oligomerization process of ethylene, effectively inhibiting polymer formation with a small amount and effectively suppressing active site deactivation at high temperatures. Its application in industrial production can increase the reaction temperature of the ethylene oligomerization system, utilize high temperatures to improve polymer solubility, avoid pipeline blockage and reactor wall adhesion, ensure long-term operation of the equipment, and greatly improve the economics of continuous ethylene oligomerization processes.

Description

Technical Field

[0001] This invention belongs to the field of ethylene oligomerization technology, specifically relating to ethylene oligomerization catalytic systems containing fluorine modifiers and their applications. Background Technology

[0002] In the industrial production of linear α-olefins, ethylene selective oligomerization catalytic systems are prone to generating polymeric byproducts, leading to pipeline blockage and reactor wall adhesion, severely impacting continuous reaction. Increasing the reaction temperature can improve the solubility of these polymers and alleviate pipeline blockage; typically, the temperature is raised to 90-100℃. However, such high temperatures significantly reduce the activity of the chromium catalyst. Therefore, designing and developing an ethylene selective catalytic system that combines high activity and high selectivity at high temperatures is essential. Summary of the Invention

[0003] This invention proposes a homogeneous catalytic system for quaternary ethylene oligomerization with a fluorinated modifier. The addition of the fluorinated modifier can significantly improve the catalytic activity of the ethylene oligomerization system at high temperature, while maintaining the original high selectivity of the system.

[0004] This invention proposes an ethylene oligomerization catalytic system containing a fluorinated modifier, comprising a main catalyst, a co-catalyst, a ligand, and a fluorinated modifier; wherein,

[0005] The main catalyst is at least one of organochromium compounds and chromium halides;

[0006] The co-catalyst is an aluminum-containing metal compound;

[0007] The ligands are phosphine, nitrogen, carbon, or silicon ligands with bidentate or tridentate structures;

[0008] The structural formula of the fluorine-containing modifier is as follows:

[0009] ; ; ; ; ; ; ; ; ; ; ; ; Where n = 1 to 20;

[0010] R1 to R8 are each independently selected from hydrogen, fluorine, unsubstituted alkane group, fluorinated alkane group, fluorinated alkene group, and fluorinated aryl group, and R1 to R8 cannot be independently selected from hydrogen and unsubstituted alkane group at the same time.

[0011] Furthermore, fluorinated alkane groups include monofluorinated alkane groups, polyfluorinated alkane groups, and perfluorinated alkane groups; fluorinated olefin groups include monofluorinated olefin groups, polyfluorinated olefin groups, and perfluorinated olefin groups; and fluorinated aryl groups include monofluorinated aryl groups, polyfluorinated aryl groups, and perfluorinated aryl groups.

[0012] Preferably, the fluorinated modifier is a 1-H perfluoroalkane or a decafluorobiphenyl.

[0013] Furthermore, the ligand is a phosphine ligand with bidentate or tridentate structures.

[0014] Furthermore, the main catalyst is at least one of an organochromium compound and a chromium halide;

[0015] Preferably, the main catalyst is at least one of chromium acetylacetone and chromium trichloride tetrahydrofuran.

[0016] Furthermore, the co-catalyst is at least one selected from methylaluminoxane, modified methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, alkylaluminum, and diethylethoxyaluminum.

[0017] Preferably, the co-catalyst is at least one of methylaluminoxane and modified methylaluminoxane.

[0018] Furthermore, the solvent is at least one of aromatic hydrocarbons, halogenated aromatic hydrocarbons, aliphatic hydrocarbons, and halogenated aliphatic hydrocarbons;

[0019] Preferably, the solvent is at least one selected from cyclohexane, methylcyclohexane, n-heptane, benzene, toluene, xylene, and chlorobenzene.

[0020] Furthermore, the molar ratio of aluminum in the fluorinated modifier to the co-catalyst is 0.001-10:1;

[0021] Preferably, the molar ratio of the fluorinated modifier to aluminum in the co-catalyst is 0.01-1:1.

[0022] Furthermore, the concentration of chromium in the main catalyst in the reaction system is 1×10⁻⁶. -7 -1×10 -4 mol / L;

[0023] The molar ratio of aluminum in the co-catalyst to chromium in the main catalyst is 20-3000:1;

[0024] The molar ratio of ligand to chromium in the main catalyst is 0.5:1-10:1;

[0025] An embodiment of the present invention also proposes the application of the ethylene oligomerization catalytic system containing fluorine modifiers described in any of the above claims in the ethylene oligomerization reaction.

[0026] Furthermore, the reaction temperature is 0-150 ℃;

[0027] The reaction pressure is 0.1-10 MPa;

[0028] The reaction time is 1-300 min.

[0029] This invention has the following advantages:

[0030] This invention employs a fluorinated modifier to regulate the selective oligomerization process of ethylene. With a small dosage, it effectively inhibits polymer formation and suppresses deactivation of active sites at high temperatures. Its application in industrial production increases the reaction temperature of the ethylene oligomerization system, enhancing polymer solubility and preventing pipeline blockage and reactor wall adhesion, thus ensuring long-term operation of the equipment and significantly improving the economics of continuous ethylene oligomerization. Furthermore, the fluorinated modifier maintains high selectivity for 1-hexene and 1-octene, guaranteeing the yield of high-value target products and improving economic efficiency. Moreover, this invention only adds a small amount of fluorinated modifier to the existing ethylene oligomerization ternary system; the original process scheme requires minimal modification, making it simple, feasible, easy to implement, and highly economical. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. In the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0032] In existing technologies, because the donor of bidentate or tripentate phosphine ligands is the phosphorus atom, their coordination ability is relatively weak. At higher temperatures, the complex may dissociate, generating byproduct polymer-forming active centers. Therefore, at excessively high temperatures, oligomerization active centers may partially transform into polymer-forming active centers, leading to a decrease in oligomerization activity and an increase in polymer formation. Furthermore, the polymer and other solid byproducts generated at high temperatures can easily clog pipes.

[0033] Achieving high catalytic activity and selectivity in high-temperature ethylene oligomerization catalytic systems solely through ligand structure design is limited by long design cycles and significant control difficulties. The inventors of this application have discovered that directly introducing other modifiers to enhance the high-temperature activity of the system can significantly reduce the difficulty of process optimization. Traditional ethylene oligomerization catalytic systems are ternary systems, including a main catalyst, a co-catalyst, and a ligand. This invention innovatively adds a fourth component, a fluorinated modifier, to improve the high-temperature stability of the catalytic system and inhibit polymer formation. This results in a high-temperature selective ethylene catalytic system that exhibits both high activity and high selectivity, and effectively solves the problem of polymer clogging the pipeline during ethylene oligomerization.

[0034] One embodiment of the present invention provides an ethylene oligomerization catalytic system containing a fluorinated modifier, comprising a main catalyst, a co-catalyst, a ligand, and a fluorinated modifier;

[0035] The main catalyst is at least one of organochromium compounds and chromium halides;

[0036] The co-catalyst is an aluminum-containing metal compound;

[0037] The ligands are phosphine, nitrogen, carbon, or silicon ligands with bidentate or tridentate structures;

[0038] The structural formula of the fluorine-containing modifier is as follows:

[0039] ; ; ; ; ; ; ; ; ; ; ; ; Where n = 1 to 20;

[0040] R1 to R8 are each independently selected from hydrogen, fluorine, unsubstituted alkane group, fluorinated alkane group, fluorinated alkene group, and fluorinated aryl group, and R1 to R8 cannot be independently selected from hydrogen and unsubstituted alkane group at the same time.

[0041] In this invention, the inventors innovatively propose adding a fluorinated modifier to the catalytic system. Firstly, the fluorinated modifier can stabilize the active center of the main catalyst. Secondly, it can replace the methyl groups on the co-catalyst (such as MAO or MMAO), increasing the volume of the alkylaluminoxane, increasing the steric hindrance of the ligand structure, preventing small impurity molecules and long-chain molecules from attacking the active center, and inhibiting deactivation reactions. Thirdly, the fluorinated modifier also reacts with residual trimethylaluminum and other alkylaluminum groups on the co-catalyst (such as MAO or MMAO), preventing further substitution of chromium centers by trimethylaluminum to generate side reactive sites, thus avoiding the formation of polymers. The reduced polymer content avoids reactor wall adhesion and pipeline blockage that are prone to occur in subsequent industrial applications, reducing the difficulty of industrial application. Fourthly, after adding the fluorinated modifier to improve the high-temperature stability of the catalytic system, increasing the polymer solubility by raising the temperature also helps avoid reactor wall adhesion and pipeline blockage caused by polymers, which is beneficial for the continuous ethylene oligomerization process and ensures the long-term operation of the catalytic system.

[0042] In this embodiment of the invention, the fluorinated modifier is at least one of fluorinated hydrocarbons and other fluorinated compounds. Specifically, as shown in the formula above, the fluorinated modifier can be perfluorobenzene, mono- or polyfluoro-substituted benzene, mono- or polyfluoro-substituted biphenyl, mono- or polyfluoro-substituted naphthalene, perfluoroalkanes, mono- or polyfluoro-substituted alkanes, perfluoroamines, mono- or polyfluoro-substituted amines, perfluoroethers, mono- or polyfluoro-substituted ethers, perfluorosulfides, mono- or polyfluoro-substituted sulfides, perfluoroolefins, mono- or polyfluoro-substituted olefins, perfluoroalkynes, mono- or polyfluoro-substituted alkynes, perfluorosilanes, mono- or polyfluoro-substituted silanes, perfluoroboranes, mono- or polyfluoro-substituted boranes, perfluorophosphine, mono- or polyfluoro-substituted phosphine, etc.

[0043] In a preferred embodiment of the present invention, the fluorinated alkane groups include monofluorinated alkane groups, polyfluorinated alkane groups, and perfluorinated alkane groups; the fluorinated olefin groups include monofluorinated olefin groups, polyfluorinated olefin groups, and perfluorinated olefin groups; and the fluorinated aryl groups include monofluorinated aryl groups, polyfluorinated aryl groups, and perfluorinated aryl groups.

[0044] Preferably, the fluorinated modifier can be 1-H perfluoroalkane or decafluorobiphenyl. More preferably, the fluorinated modifier can be 1-H perfluorohexane. The addition of 1-H perfluorohexane to the system can increase the solubility of the complex formed by the ligand and the active chromium center in the solvent, which is beneficial to the ethylene oligomerization reaction. Furthermore, the active hydrogen contained in 1-H-perfluorohexane more readily reacts with the residual trimethylaluminum in the co-catalyst, preventing further substitution of the chromium center by trimethylaluminum and the generation of side reactive sites, thus avoiding the formation of polymers.

[0045] In this embodiment of the invention, the ligand is a bidentate or tridentate phosphine ligand, a bidentate or tridentate nitrogen ligand, a bidentate or tridentate carbon ligand, or a bidentate or tridentate silicon ligand. Preferably, the ligand is a bidentate or tridentate phosphine ligand.

[0046] Those skilled in the art will understand that ligand structure has a significant impact on the activity and selectivity of selective oligomerization of ethylene. Since the donor of phosphine ligands with bidentate or tridentate structures is the phosphorus atom, their coordination ability is relatively weak. At higher temperatures, the complex may dissociate, generating byproduct polymers and active centers, leading to decreased oligomerization activity and increased polymer formation. Therefore, this invention focuses on improving the defects of bidentate or tridentate phosphine, nitrogen, carbon, and silicon ligands under high-temperature reactions.

[0047] In one embodiment of the present invention, the main catalyst is at least one of an organochromium compound and a chromium halide. Preferably, the main catalyst is at least one of chromium acetylacetone and chromium trichloride tetrahydrofuran.

[0048] In one embodiment of the present invention, the co-catalyst is at least one selected from methylaluminoxane (MAO), modified methylaluminoxane (MMAO), ethylaluminoxane, isobutylaluminoxane, alkylaluminum, and diethylethoxyaluminum. Preferably, the co-catalyst is at least one selected from methylaluminoxane and modified methylaluminoxane.

[0049] In one embodiment of the present invention, the solvent is at least one selected from aromatic hydrocarbons, halogenated aromatic hydrocarbons, aliphatic hydrocarbons, and halogenated aliphatic hydrocarbons. Preferably, the solvent is at least one selected from cyclohexane, methylcyclohexane, n-heptane, benzene, toluene, xylene, and chlorobenzene.

[0050] In one embodiment of the present invention, the molar ratio of the fluorinated modifier to aluminum in the co-catalyst is 0.001-10:1. Preferably, the molar ratio of the fluorinated modifier to aluminum in the co-catalyst is 0.01-1:1.

[0051] In one embodiment of the present invention, the concentration of chromium in the main catalyst in the reaction system is 1×10⁻⁶. -7 -1×10 -4 mol / L. Preferably, the concentration of chromium in the main catalyst in the reaction system is 1×10⁻⁶ mol / L. -6 -1×10 -5 mol / L.

[0052] In one embodiment of the present invention, the molar ratio of aluminum in the co-catalyst to chromium in the main catalyst is 20-3000:1. Preferably, the molar ratio of aluminum in the co-catalyst to chromium in the main catalyst is 500-1500:1.

[0053] In one embodiment of the present invention, the molar ratio of the ligand to the central chromium metal in the main catalyst is 0.5:1-10:1. Preferably, the molar ratio of the ligand to the central chromium metal in the main catalyst is 1:1.05.

[0054] An embodiment of the present invention also proposes the application of the above-mentioned fluorinated modifier catalytic system in the ethylene oligomerization reaction.

[0055] In this embodiment of the invention, the catalytic system of the above-mentioned fluorine-containing modifier is applied to the ethylene oligomerization reaction, and the resulting oligomerization product mainly consists of C4-C4O4O4. 10+ The system consists of linear α-olefins, small amounts of cycloalkanes, and polymers, with C6 and C8 selectivity >85%. Preferably, when the fluorinated modifier 1-H perfluorohexane is added, the ethylene oligomerization activity at 90°C is 6 times that of the system without the fluorinated modifier at the same temperature. Therefore, the addition of the fluorinated modifier in this invention achieves both high activity and high selectivity in the ethylene oligomerization catalytic system at high temperatures.

[0056] In one embodiment of the present invention, the reaction temperature is 0-150 °C; preferably, the reaction temperature is 40-120 °C; more preferably, the reaction temperature is 80-110 °C.

[0057] In one embodiment of the present invention, the reaction pressure is 0.1-10 MPa; preferably, the reaction pressure is 1-5 MPa.

[0058] In one embodiment of the present invention, the reaction time is 1-300 min; preferably, the reaction time is 30-60 min.

[0059] In one embodiment of the present invention, the reactor used for the ethylene oligomerization reaction is a continuous stirred reactor or a plug flow reactor.

[0060] The present invention will now be described in detail with reference to the embodiments.

[0061] Example 1 Methods for ethylene oligomerization using fluorine-containing modifier-based ethylene oligomerization catalytic systems include:

[0062] A heptane solution containing 7 wt% Al was used, with a molar ratio of symmetrical isopropyl PNP [Ph2PN(isopropyl)PPh2] to chromium acetylacetone (Cr(acac)3) of 1:1.05 and methylaluminoxane (MMAO) as the co-catalyst, resulting in a molar concentration of approximately 2.4 mol / L.

[0063] The fluorinated modifier is 1H-perfluorohexane. Specifically, the structural formula of 1H-perfluorohexane is:

[0064] ;

[0065] The 120 mL oligomerization reactor was removed from an oven at 105 °C and evacuated for 30 min, during which time it was purged multiple times with high-purity nitrogen and ethylene. The reactor temperature was then raised to the reaction temperature of 90 °C using an oil bath, and 20 mL of methylcyclohexane was added as the reaction solvent. The concentration of the chromium-based catalyst in the reaction medium was set to 6 × 10⁻⁶. -5 Add MMAO (a co-catalyst) at a molar ratio of Al:Cr = 1000, and add 1H-perfluorohexane at a molar ratio of modifier:Al of 0.1, stirring the reaction mixture. Open the ethylene pressure regulating valve, introduce ethylene, and maintain the reaction pressure at 1 MPa. The oligomerization reaction time is 30 min.

[0066] After liquid-solid separation, the liquid product was analyzed by gas chromatography (the gas chromatography temperature program was as follows: initial temperature 35 ℃, held at this temperature for 10 min, then increased to 280 ℃ at a rate of 10 ℃ / min, held for 15 min). The solid product, polyethylene, was dried and weighed, yielding 0.016 g; the polyethylene content was 0.08 wt%. The reaction activity was calculated based on the product mass, and the oligomerization activity was 56.65 × 10⁻⁶.5 g / mol cat·h.

[0067] Example 2

[0068] Same as Example 1, except that 1H-perfluorohexane was added to the mixture with a modifier:Al molar ratio of 0.3 and the mixture was stirred to react.

[0069] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.016 g; the polyethylene content was 0.09 wt%. The oligomerization activity was 30.52 × 10⁻⁶. 5 g / mol cat·h.

[0070] Example 3

[0071] Same as Example 1, except that the reaction temperature is 110 °C;

[0072] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.006 g; the polyethylene content was 0.04 wt%. The oligomerization activity was 10.23 × 10⁻⁶ g. 5 g / mol cat·h.

[0073] Example 4

[0074] Same as Example 1, except that perfluorohexane was added as a modifier with a molar ratio of 0.1 of modifier to Al and the mixture was stirred to react. The structural formula of perfluorohexane is:

[0075] ;

[0076] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.011 g; the polyethylene content was 0.07 wt%. The oligomerization activity was 16.29 × 10⁻⁶. 5 g / mol cat·h.

[0077] Example 5

[0078] Same as Example 4, except that perfluorohexane was added as a modifier with a molar ratio of modifier to Al of 0.3 and the mixture was stirred to react.

[0079] The reaction product was subjected to liquid-solid separation, and the liquid phase product was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.010 g; the polyethylene content was 0.06 wt%. The oligomerization activity was 17.09 × 10⁻⁶.5 g / mol cat·h.

[0080] Example 6

[0081] Same as Example 4, except that perfluorohexane was added as a modifier with a molar ratio of modifier to Al of 0.5 and the mixture was stirred to react.

[0082] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.012 g; the polyethylene content was 0.07 wt%. The oligomerization activity was 18.15 × 10⁻⁶. 5 g / mol cat·h.

[0083] Example 7

[0084] Same as Example 1, except that perfluorooctane was added as a modifier with a molar ratio of modifier to Al of 1 and the mixture was stirred to react. The structural formula of perfluorooctane is:

[0085] ;

[0086] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.030 g; the polyethylene content was 0.18 wt%. The oligomerization activity was 10.17 × 10⁻⁶. 5 g / mol cat·h.

[0087] Example 8

[0088] Same as Example 1, except that perfluoro-1,3-dimethylcyclohexane was added to the mixture with a modifier:Al molar ratio of 0.3 and the mixture was stirred to react. The structural formula of perfluoro-1,3-dimethylcyclohexane is:

[0089] ;

[0090] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.006 g; the polyethylene content was 0.04 wt%. The oligomerization activity was 11.16 × 10⁻⁶ g / g. 5 g / mol cat·h.

[0091] Example 9

[0092] Same as Example 8, except that perfluoro-1,3-dimethylcyclohexane was added to the mixture with a modifier:Al molar ratio of 0.5 and the mixture was stirred to react.

[0093] The reaction product was subjected to liquid-solid separation, and the liquid phase product was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.008 g; the polyethylene content was 0.05 wt%. The oligomerization activity was 13.27 × 10⁻⁶. 5 g / mol cat·h.

[0094] Example 10

[0095] Same as Example 1, except that perfluoronaphthalene was added to the mixture with a modifier:Al molar ratio of 0.1 and the mixture was stirred to react. The structural formula of perfluoronaphthalene is:

[0096] ;

[0097] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.009 g; the polyethylene content was 0.05 wt%. The oligomerization activity was 12.92 × 10⁻⁶. 5 g / mol cat·h.

[0098] Example 11

[0099] Same as Example 10, except that perfluoronaphthalene was added to the mixture with a modifier:Al molar ratio of 0.3 and the mixture was stirred to react.

[0100] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.004 g; the polyethylene content was 0.02 wt%. The oligomerization activity was 16.53 × 10⁻⁶. 5 g / mol cat·h.

[0101] Example 12

[0102] Same as Example 10, except that perfluoronaphthalene was added to the mixture with a modifier:Al molar ratio of 0.5 and the mixture was stirred to react.

[0103] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.004 g; the polyethylene content was 0.02 wt%. The oligomerization activity was 11.25 × 10⁻⁶. 5 g / mol cat·h.

[0104] Example 13

[0105] Same as Example 1, except that the modifier fluoropropyl vinyl ether was added and stirred to react at a modifier:Al molar ratio of 0.5, wherein the structural formula of the fluoropropyl vinyl ether is:

[0106] ;

[0107] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.013 g; the polyethylene content was 0.08 wt%. The oligomerization activity was 9.53 × 10⁻⁶. 5 g / mol cat·h.

[0108] Example 14

[0109] Same as Example 1, except that the modifier methyl nonafluorobutyl ether was added and stirred to react at a modifier:Al molar ratio of 0.3, wherein the structural formula of methyl nonafluorobutyl ether is:

[0110] ;

[0111] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed, yielding 0.029 g; the polyethylene content was 0.17 wt%. The oligomerization activity was 12.34 × 10⁻⁶. 5 g / mol cat·h.

[0112] Example 15

[0113] Same as Example 14, except that the modifier methyl nonafluorobutyl ether was added and stirred to react at a modifier:Al molar ratio of 0.5;

[0114] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.019 g; the polyethylene content was 0.12 wt%. The oligomerization activity was 10.11 × 10⁻⁶. 5 g / mol cat·h.

[0115] Example 16

[0116] Same as Example 1, except that perfluorotributylamine was added to the mixture with a modifier:Al molar ratio of 0.3 and the mixture was stirred to react. The structural formula of perfluorotributylamine is:

[0117] ;

[0118] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.005 g; the polyethylene content was 0.03 wt%. The oligomerization activity was 13.13 × 10⁻⁶. 5 g / mol cat·h.

[0119] Example 17

[0120] Same as Example 1, except that hexafluorobenzene was added to the mixture with a modifier:Al molar ratio of 0.5 and the mixture was stirred to react. The structural formula of hexafluorobenzene is:

[0121] ;

[0122] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.034 g; the polyethylene content was 0.20 wt%. The oligomerization activity was 9.64 × 10⁻⁶. 5 g / mol cat·h.

[0123] Example 18

[0124] Same as Example 1, except that pentafluorobenzene was added to the mixture with a modifier:Al molar ratio of 0.3 and the mixture was stirred to react. The structural formula of pentafluorobenzene is:

[0125] ;

[0126] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.004 g; the polyethylene content was 0.02 wt%. The oligomerization activity was 9.67 × 10⁻⁶. 5 g / mol cat·h.

[0127] Example 19

[0128] Same as Example 18, except that pentafluorobenzene was added to the mixture with a modifier:Al molar ratio of 0.5 and the mixture was stirred to react.

[0129] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.002 g; the polyethylene content was 0.01 wt%. The oligomerization activity was 9.65 × 10⁻⁶. 5 g.

[0130] Example 20

[0131] Same as Example 1, except that the modifier decafluorobiphenyl was added and stirred to react at a molar ratio of modifier to Al of 0.3. The structural formula of decafluorobiphenyl is:

[0132] ;

[0133] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed, yielding 0.026 g; the polyethylene content was 0.15 wt%. The oligomerization activity was 21.29 × 10⁻⁶. 5 g / mol cat·h.

[0134] Comparative Example 1

[0135] Same as Example 1, except that no modifier is added;

[0136] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed to obtain 0.088 g; the polyethylene content was 0.51 wt%. The oligomerization activity was 9.50 × 10⁻⁶. 5 g / mol cat·h.

[0137] Comparative Example 2

[0138] Same as Example 1, except that no modifier is added and the reaction temperature is 50°C;

[0139] The reaction product was subjected to liquid-solid separation, and the liquid phase was analyzed by gas chromatography. The solid product, polyethylene, was dried and weighed, yielding 0.063 g; the polyethylene content was 0.37 wt%. The oligomerization activity was 20.99 × 10⁻⁶ g. 5 g / mol cat·h.

[0140] Table 1 Summary of results for the Examples and Comparative Examples

[0141]

[0142] a Reaction temperature: 90 ℃; b Reaction temperature: 50 ℃. c Reaction temperature: 110 ℃

[0143] The analytical characterization results of the ethylene oligomers prepared in the above examples and comparative examples show that the activity of the ethylene oligomer systems with added fluorinated modifiers in the examples is higher than that of the comparative ethylene oligomer systems without modifiers, and the content of by-product polymers is reduced, with the lowest being below 0.01 wt%. At a reaction temperature of 90 °C, the ethylene oligomer system using 1-H perfluorohexane fluorinated modifier in Example 1 has an activity of 5.6 × 10⁻⁶. 6 g / mol cat·h, which is nearly 6 times that of Comparative Example 1.

[0144] Experimental data show that 1H-perfluorohexane is more effective as a fluorinated modifier than other fluorinated modifiers. This is because the addition of 1H-perfluorohexane to the system increases the solubility of the complex formed between the ligand and the active chromium center in the solvent, which is beneficial to the ethylene oligomerization reaction. This may be one of the reasons for the better activity of 1H-perfluorohexane. In addition, the active hydrogen contained in 1H-perfluorohexane is more likely to react with the residual trimethylaluminum in the co-catalyst, preventing trimethylaluminum and other substances from further replacing the chromium center and forming side reactive sites, thus avoiding the formation of polymers.

[0145] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An ethylene oligomerization catalytic system with a fluorinated modifier, comprising a main catalyst, a co-catalyst, a ligand, and a fluorinated modifier; wherein, The main catalyst is at least one of organochromium compounds and chromium halides; The co-catalyst is an aluminum-containing metal compound; The ligands are phosphine, nitrogen, carbon, or silicon ligands with bidentate or tridentate structures; The structural formula of the fluorine-containing modifier is as follows: ; ; ; ; ; Where n is 6 or 8; R1 to R8 are each independently selected from fluorine, unsubstituted alkane group, perfluorinated substituted alkane group, perfluorinated substituted olefin group, and perfluorinated substituted aryl group, and R1 to R8 cannot be independently selected from unsubstituted alkane group at the same time.

2. The ethylene oligomerization catalytic system according to claim 1, characterized in that, The fluorinated modifier is a 1-H perfluoroalkane.

3. The ethylene oligomerization catalytic system according to claim 1, characterized in that, The ligand is a phosphine ligand with bidentate or tridentate teeth.

4. The ethylene oligomerization catalytic system according to claim 1, characterized in that, The main catalyst is at least one of chromium acetylacetone and chromium trichloride tetrahydrofuran.

5. The ethylene oligomerization catalytic system according to claim 1, characterized in that, The cocatalyst is at least one of methylaluminoxane, modified methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, alkylaluminum, and diethylethoxyaluminum.

6. The ethylene oligomerization catalytic system according to claim 5, characterized in that, The co-catalyst is at least one of methylaluminoxane or modified methylaluminoxane.

7. The ethylene oligomerization catalytic system according to claim 1, characterized in that, The ethylene oligomerization catalytic system further includes a solvent, which is at least one of aromatic hydrocarbons, halogenated aromatic hydrocarbons, aliphatic hydrocarbons, and halogenated aliphatic hydrocarbons.

8. The ethylene oligomerization catalytic system according to claim 7, characterized in that, The solvent is at least one of cyclohexane, methylcyclohexane, n-heptane, benzene, toluene, xylene, and chlorobenzene.

9. The ethylene oligomerization catalytic system according to claim 1, characterized in that, The molar ratio of aluminum in the fluorinated modifier to the co-catalyst is 0.1-1:

1.

10. The ethylene oligomerization catalytic system according to claim 1, characterized in that, The concentration of chromium in the main catalyst in the reaction system is 1×10⁻⁶. -7 -1×10 -4 mol / L; The molar ratio of aluminum in the co-catalyst to chromium in the main catalyst is 20-3000:1; The molar ratio of ligand to chromium in the main catalyst is 0.5:1-10:

1.

11. The application of the ethylene oligomerization catalytic system with fluorine-containing modifier as described in any one of claims 1 to 10 in the ethylene oligomerization reaction.

12. The application according to claim 11, characterized in that, The reaction temperature is 0-150 ℃; The reaction pressure is 0.1-10 MPa; The reaction time is 1-300 min.

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