Microchannel reactor, ethylene polymerization process and use

Abstract

This invention discloses a microchannel reactor, an ethylene polymerization method, and an application. The microchannel reactor includes a premixing unit, a mixing and preheating unit, and a reaction unit connected in sequence. Using this microchannel reactor for ethylene polymerization offers advantages such as high-efficiency mass transfer, stable temperature control, and adjustable process, achieving rapid and efficient polymerization by enhancing mass and heat transfer during the reaction process.

Description

Technical Field

[0001] This invention relates to a microchannel reactor, as well as a method and application of ethylene polymerization based on the above-described microchannel reaction. Background Technology

[0002] Alpha-olefins, as important substances used in comonomers, detergents, lubricants, plasticizers, etc., are widely used commercially. Commonly used α-olefins are usually produced through the oligomerization or oligomerization of ethylene. Ethylene oligomerization or oligomerization is carried out in the presence of a catalyst using ethylene as a reactant.

[0003] In ethylene oligomerization or oligomerization processes, ethylene is in a gaseous state and must be dissolved in a solvent to react with the active sites of the catalyst. In traditional batch reactors, ethylene dissolves slowly, requiring strong stirring and high pressure to ensure the reaction proceeds smoothly. At scale-up, this reaction type becomes difficult to control, and the resulting polymers can easily clog the container walls and agitator. Microchannel reactors are flow-channel reaction devices in microchemical technology; however, commonly used ethylene oligomerization catalysts, such as iron-based, chromium-based, and zirconium-based catalysts, have poor solubility, resulting in unsatisfactory reaction performance in microchannel reactions. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, this invention provides a novel microchannel reactor. Using this microchannel reactor for ethylene polymerization offers advantages such as high-efficiency mass transfer, stable temperature control, and adjustable process. By enhancing mass and heat transfer during the reaction process, it achieves the goal of rapid and efficient polymerization.

[0005] The first aspect of the present invention provides a microchannel reactor, comprising a premixing unit, a mixing and preheating unit, and a reaction unit connected in sequence.

[0006] According to some embodiments of the microchannel reactor of the present invention, preferably, the premixing unit is used to mix the premixed solution a of metal salt and organoaluminum with the catalyst ligand and organic solvent to obtain a mixed solution; the mixing and preheating unit is used to mix and preheat the mixed solution with ethylene to obtain a preheated mixture; the reaction unit is used to preheat the mixture to carry out an ethylene polymerization reaction.

[0007] According to some embodiments of the microchannel reactor of the present invention, preferably, the microchannel reactor further includes a post-processing unit after the reaction unit for terminating the reaction.

[0008] According to some embodiments of the microchannel reactor of the present invention, preferably, the microchannel reactor has multiple structural units.

[0009] According to some embodiments of the microchannel reactor of the present invention, preferably, each of the structural units is independently selected from one or more of the following: T-shaped structure, Y-shaped structure, heart-shaped structure, serpentine structure, and bow-shaped structure.

[0010] According to some embodiments of the microchannel reactor of the present invention, preferably, the structural units are used in series or in parallel. For example, but not limited to, one or more of the following structures are used in series or in parallel: T-shaped structure, Y-shaped structure, heart-shaped structure, serpentine structure, or bow-shaped structure. For example, the structure of the microchannel reactor can be selected from a T-shaped structure in the premixing unit, and from a heart-shaped, bow-shaped, or serpentine structure in the reaction unit, etc., made of silicon carbide, but not limited to the above structures and materials.

[0011] According to some embodiments of the microchannel reactor of the present invention, preferably, the length of a single reaction unit of the microchannel reactor is 50-30000m, more preferably 100-10000m. For example, but not limited to, 50-30000m, 50-25000m, 50-20000m, 50-15000m, 50-10000m, 50-5000m, 50-1000m, 50-500m, 50-100m, 100-25000m, 100-20000m, 100-15000m, 100-10000m, 100-5000m, 100-1000m, 100-500m, 500-25000m, 500-20000m, 500-15000m, 500-10000m, 500-5000m, 500-1000m, etc.

[0012] According to some embodiments of the microchannel reactor of the present invention, preferably, the inner diameter of the microchannel reactor is 0.1-5 mm. Examples, but not limited to, are 0.1-5 mm, 0.1-4 mm, 0.1-3 mm, 0.1-2 mm, 0.1-1 mm, 0.1-0.5 mm, 0.5-5 mm, 0.5-4 mm, 0.5-3 mm, 0.5-2 mm, 0.5-1 mm, 1-5 mm, 1-4 mm, 1-3 mm, 1-2 mm, 2-5 mm, 2-4 mm, 2-3 mm, 3-5 mm, 3-4 mm, and 4-5 mm.

[0013] According to some embodiments of the microchannel reactor of the present invention, preferably, the microchannel reactor is used for ethylene polymerization reaction.

[0014] A second aspect of the present invention provides a method for ethylene polymerization based on the above-described microchannel reactor, comprising the following steps:

[0015] Step a: Premix the metal salt and organoaluminum to obtain premix solution a;

[0016] Step b: The premixed solution a is mixed with the catalyst ligand and solvent in the premixing unit of the microchannel reactor to obtain a mixed solution;

[0017] Step c: Using the mixture as a catalyst and ethylene as a starting material, the mixture is mixed and preheated in the mixing and preheating unit of a microchannel reactor to obtain a preheated mixture;

[0018] Step d: The preheated mixture is subjected to ethylene polymerization in the reaction unit of a microchannel reactor.

[0019] According to some embodiments of the method of the present invention, preferably, the metal salt is a chromium-containing compound, preferably one or more of chromium chloride, chromium isooctanoate and chromium acetylacetonate.

[0020] According to some embodiments of the method described in this invention, preferably, the organoaluminum is selected from one or more of alkylaluminum compounds, alkoxyaluminum compounds, and alkylaluminum chloride compounds, and more preferably from one or more of methylaluminoxane, trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, diethylaluminum chloride, diethylaluminum chloride, ethylaluminoxane, and modified methylaluminoxane.

[0021] In some embodiments of the method according to the present invention, preferably, the catalyst ligand is selected from one or more of pyrrole-type ethylene trimerizing catalyst ligands, bisphosphine-type ethylene tetramerizing catalyst ligands, and diimine-type ethylene oligomerizing catalyst ligands. More preferably, the bisphosphine-type ethylene tetramerizing catalyst ligand is selected from PNP-type tetramerizing catalyst ligands and / or PCCP-type tetramerizing catalyst ligands; in the present invention, the catalyst ligand can be prepared in-house or commercially available. For example, PNP-type tetramerizing catalyst ligands can be prepared with reference to J. Am. Chem. Soc. 2004, 126(45), 14712.

[0022] According to some embodiments of the method of the present invention, preferably, the solvent is selected from alkanes or aromatic compounds, more preferably from one or more of straight-chain alkanes, branched-chain alkanes, cycloalkanes, aromatics and substituted aromatics, and more preferably from one or more of pentane, heptane, hexane, cyclohexane, methylcyclohexane, benzene, toluene, xylene and monochlorobenzene.

[0023] According to some embodiments of the method described in this invention, preferably, the molar ratio of metal salt, catalyst ligand, and organoaluminum is 1:0.2-5:20-2000. For example, but not limited to, 1:0.2:20, 1:0.5:50, 1:1:1000, 1:1.5:800, 1:2:1000, 1:3:1500, 1:5:1200, and 1:5:2000.

[0024] According to some embodiments of the method of the present invention, preferably, the concentration of the catalyst, based on the metal element in the metal salt, is 0.1-50 μmol / L. Examples, but not limited to, are 0.1-50 μmol / L, 0.5-50 μmol / L, 1-50 μmol / L, 5-50 μmol / L, 10-50 μmol / L, 15-50 μmol / L, 20-50 μmol / L, 25-50 μmol / L, 30-50 μmol / L, 35-50 μmol / L, 40-50 μmol / L, 45-50 μmol / L, 0.1-40 μmol / L, 0.5-40 μmol / L, 1-40 μmol / L, etc. l / L, 5-40μmol / L, 10-40μmol / L, 15-40μmol / L, 20-40μmol / L, 25-40μmol / L, 30-40μmol / L, 35-40μmol / L, 0.1- 30μmol / L, 0.5-30μmol / L, 1-30μmol / L, 5-30μmol / L, 10-30μmol / L, 15-30μmol / L, 20-30μmol / L, 25-30μmol / L.

[0025] In some embodiments of the method according to the present invention, preferably, the amount of ethylene used is 3-30% by weight of the solvent.

[0026] According to some embodiments of the method described in this invention, preferably, the premixing temperature in step a is -20 to 0°C, and the mixing time is 1 to 10 minutes.

[0027] According to some embodiments of the method described in this invention, preferably, the mixing temperature in step b is 20-40°C and the time is 1-10 minutes.

[0028] According to some embodiments of the method described in this invention, preferably, the mixing preheating temperature in step c is 30-150°C, more preferably 40-100°C.

[0029] According to some embodiments of the method described in this invention, preferably, the temperature of the ethylene polymerization reaction in step d is 30-150°C, more preferably 40-100°C, the pressure is 0.1-10 MPa, and the residence time of the preheated mixture in the reaction unit of the microchannel reactor is 10-1500 seconds.

[0030] According to some embodiments of the method described in this invention, preferably, the flow velocity of the preheated mixture in the reaction unit of the microchannel reactor is 1-20 m / s. Examples, but not limited to, are 1-20 m / s, 1-15 m / s, 1-10 m / s, 1-5 m / s, 2-20 m / s, 2-15 m / s, 2-10 m / s, 2-5 m / s, 3-20 m / s, 3-15 m / s, 3-10 m / s, 3-5 m / s, 5-20 m / s, 5-10 m / s, 10-20 m / s, and 10-15 m / s.

[0031] According to some embodiments of the method of the present invention, preferably, the method includes performing an ethylene oligomerization reaction in a microchannel reactor to obtain a straight-chain α-olefin, or a mixture of straight-chain and branched α-olefins, or performing an ethylene tetramerization reaction to obtain 1-octene, etc., or performing an ethylene trimerization reaction to obtain 1-hexene, etc.

[0032] According to some embodiments of the method described in this invention, the method can be operated intermittently or continuously, using ethylene as the main raw material, and synthesizing α-olefins in a microchannel reactor under the action of a catalyst.

[0033] In one embodiment, the polymerization catalyst used in this invention can be a conventional catalyst system for catalyzing ethylene polymerization, preferably a chromium-based catalyst system. This chromium-based catalyst system may, for example, include a chromium-containing main catalyst composed of a chromium-containing compound and a phosphine-containing ligand, and an organoaluminum co-catalyst that is an alkylaluminum compound or an alkoxyaluminum compound.

[0034] The method of this invention can be carried out in a short time, for example, the polymerization time can be 1-10 minutes, and it has high reaction efficiency. After the reaction stops, the product α-olefin can be obtained through conventional separation and purification steps.

[0035] The third aspect of the present invention provides the application of the above-described microchannel reactor or the above-described ethylene polymerization method in ethylene oligomerization, preferably in ethylene tetramerization or ethylene trimerization.

[0036] The beneficial effects of this invention are:

[0037] (1) The apparatus and method of the present invention have the characteristics of continuous reaction in microchannels, and have advantages such as efficient mass transfer, stable temperature control and adjustable process. They improve the dispersibility of ethylene in solvent and achieve the purpose of rapid and efficient polymerization reaction by strengthening the mass and heat transfer of the reaction process.

[0038] (2) The apparatus and method of the present invention can reduce the valence state of the metal by first premixing the metal salt with organoaluminum at low temperature, and then combining it with the catalyst ligand to form a completely soluble chelate catalyst. Furthermore, the chelate catalyst is applicable to microchannel reactors. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the microchannel reactor provided in Embodiment 1 of the present invention. Detailed Implementation

[0040] To make the present invention easier to understand, the present invention will be described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not limited to the scope of application of the present invention.

[0041]

Preparation Example 1

[0042] References J.Am.Chem.Soc.2004, 126(45), 14712 Preparation of PNP-type tetrameric catalyst ligands.

[0043]

Example 1

[0044] A microchannel reactor, such as Figure 1 As shown, the microchannel reactor comprises a premixing unit, a mixing and preheating unit, and a reaction unit connected in sequence. The premixing unit is used to mix a premixed solution of metal salt and organoaluminum with a catalyst ligand and an organic solvent to obtain a mixed solution. The mixing and preheating unit is used to mix and preheat the mixed solution with ethylene to obtain a preheated mixture. The reaction unit is used to carry out the ethylene polymerization reaction in the preheated mixture. Following the reaction unit, the microchannel reactor also includes a post-treatment unit for terminating the reaction. The microchannel reactor has multiple units connected in series; the premixing and mixing and preheating units have a T-shaped structure, while the reaction unit has a serpentine structure. The length of a single reaction unit in the microchannel reactor is 300 m, and the inner diameter of the microchannel reactor is 1 mm.

[0045]

Example 2

[0046] Ethylene polymerization based on the microchannel reactor of Example 1:

[0047] Step a: Chromium acetylacetone and modified methylaluminoxane are premixed at -20°C for 5 minutes.

[0048] Step b: The mixture from step a is mixed with the PNP-type tetrameric catalyst ligand (prepared in Preparation Example 1) and methylcyclohexane in a microchannel premixing unit at room temperature.

[0049] Step c: Using the mixture obtained in step b as a catalyst and ethylene as a starting material, the mixture is preheated to 50°C in the mixing and preheating unit of the microchannel reactor to obtain a preheated mixture;

[0050] Step d: The obtained preheated mixture was subjected to ethylene polymerization in the reaction unit of a microchannel reactor. The molar ratio of chromium acetylacetone, catalyst ligand, and organoaluminum was 1:1.5:800. The concentration of the catalyst was 2 μmol / L, calculated as chromium. The ethylene feed pressure in Step c was constant at 2 MPa. The residence time of the catalyst in the microchannel reactor was 300 seconds. The flow rate of the preheated mixture in the reaction unit of the microchannel reactor was 1 m / s. The reaction solution was discharged from the outlet of the microchannel reactor. 5 mL of sample was taken in the post-processing unit, and 1 mL of ethanol was added as a terminator to terminate the reaction. Gas chromatography analysis was performed. The organic phase was analyzed by gas chromatography to calculate the catalyst activity and product composition. Experimental results: The reaction activity was 2.0 × 10⁻⁶. 8 g·mol(Cr) -1 ·h -1 The total selectivity for C6 and C8 olefins was 92% by weight.

[0051]

Example 3

[0052] Based on the microchannel reactor of Example 1, the ethylene polymerization conditions of Example 2 differ in that the length of a single reaction unit in the microchannel reactor is 1000m and the inner diameter of the microchannel reactor is 0.5mm.

[0053] Following the ethylene polymerization conditions of Example 2, the final experimental results showed a reactivity of 2.3 × 10⁻⁶. 8 g·mol(Cr) -1 ·h -1 The overall selectivity for C6 and C8 olefins was 93% by weight.

[0054]

Example 4

[0055] The microchannel reactor based on Example 1 differs in that: step a: chromium acetylacetone and modified methylaluminoxane are premixed at 0°C for 10 minutes.

[0056] Final test results: Reactivity was 1.8 × 10⁻⁶ 8 g·mol(Cr) -1 ·h -1 The total selectivity for C6 and C8 olefins was 90% by weight.

[0057]

Example 5

[0058] The microchannel reactor based on Example 1 differs in that: step a: chromium acetylacetone and modified methylaluminoxane are premixed at 10°C for 10 minutes at low temperature.

[0059] Final test results: The reactivity was 1.7 × 10⁻⁶. 8 g·mol(Cr) -1 ·h -1 The total selectivity for C6 and C8 olefins was 89% by weight.

[0060]

Example 6

[0061] The microchannel reactor based on Example 1 differs in that the molar ratio of chromium acetylacetone, catalyst ligand, and organoaluminum is 1:5:1200.

[0062] Final test results: The reactivity was 2.1 × 10⁻⁶. 8 g·mol(Cr) -1 ·h -1 The overall selectivity for C6 and C8 olefins was 93% by weight.

[0063]

Example 7

[0064] The microchannel reactor based on Example 1 differs in that the flow rate of the preheated mixture in the reaction unit of the microchannel reactor is 2 m / s.

[0065] Final test results: The reactivity was 1.7 × 10⁻⁶. 8 g·mol(Cr) -1 ·h -1 The total selectivity for C6 and C8 olefins was 88% by weight.

[0066] Comparative Example 1

[0067] A conventional stirred tank reactor with a volume of 300 mL was used. After evacuation, the reactor was purged with nitrogen, followed by purging with ethylene. Methylcyclohexane was then added as solvent, and simultaneously, chromium acetylacetone, phosphine ligand, and modified methylaluminoxane were added in a molar ratio of 1:2:800 and mixed thoroughly. The total volume of the mixture was 200 mL, with 1 μmol of chromium acetylacetone. The agitator was started, the ethylene inlet valve was opened, and the pressure was increased to 2 MPa, while the reaction temperature was controlled at 50°C. After 30 minutes, the temperature inside the autoclave was lowered to room temperature. The reaction was discharged, and 5 mL of sample was taken. 1 mL of ethanol was added as a terminator to terminate the reaction. Gas chromatography analysis of the organic phase was performed to calculate the catalyst activity and product composition. The experimental results showed that the reaction activity was 0.5 × 10⁻⁶. 8 g·mol(Cr) -1 ·h -1The total selectivity for C6 and C8 olefins was 85% by weight.

[0068] Comparative Example 2

[0069] Similar to Comparative Example 1, except that the reaction time was changed from 30 minutes to 5 minutes. Experimental results: The reaction activity was 0.3 × 10⁻⁶. 8 g·mol(Cr) -1 ·h -1 The total selectivity for C6 and C8 olefins was 80% by weight.

[0070] Comparative Example 3

[0071] A microchannel reactor similar to Embodiment 1, except that it lacks a premixing unit, as detailed below:

[0072] This microchannel reactor comprises a mixing and preheating unit and a reaction unit connected in series. The mixing and preheating unit is used to mix and preheat metal salts, organoaluminum compounds, catalyst ligands, organic solvents, and ethylene to obtain a preheated mixture; the reaction unit is used to carry out the ethylene polymerization reaction of the preheated mixture. Following the reaction unit, the microchannel reactor also includes a post-treatment unit for terminating the reaction. The microchannel reactor has multiple units connected in series, with a T-shaped structure in the mixing and preheating unit and a serpentine structure in the reaction unit. The length of a single reaction unit in the microchannel reactor is 300 m, and the inner diameter of the microchannel reactor is 1 mm.

[0073] Ethylene polymerization based on the microchannel reactor described above:

[0074] Step a: Using a mixture of chromium acetylacetone, modified methylaluminoxane, PNP-type tetrameric catalyst ligand (prepared in Preparation Example 1), and methylcyclohexane as a catalyst, and ethylene as a starting material, the mixture was preheated to 50°C in the mixing and preheating unit of a microchannel reactor to obtain a preheated mixture.

[0075] Step b: The obtained preheated mixture was subjected to ethylene polymerization in the reaction unit of a microchannel reactor. The molar ratio of chromium acetylacetone, catalyst ligand, and organoaluminum was 1:1.5:800. The concentration of the catalyst was 2 μmol / L, calculated as chromium. The flow rate of the preheated mixture in the reaction unit of the microchannel reactor was 1 m / s. The ethylene feed pressure in Step a was 2 MPa. The residence time of the catalyst in the microchannel reactor was 300 seconds. The reaction solution was discharged from the outlet of the microchannel reactor. 5 mL of the sample was taken in the post-processing unit, and 1 mL of ethanol was added as a terminator to terminate the reaction. Gas chromatography analysis was performed. The organic phase was analyzed by gas chromatography to calculate the catalyst activity and product composition. Experimental results: The reaction activity was 0.9 × 10⁻⁶. 8 g·mol(Cr) -1 ·h-1 The total selectivity for C6 and C8 olefins was 80% by weight.

[0076] Comparative Example 4

[0077] A microchannel reactor similar to Embodiment 1, except that it lacks a mixing and preheating unit, as detailed below:

[0078] Ethylene polymerization based on the microchannel reactor of Example 1:

[0079] Step a: Chromium acetylacetone and modified methylaluminoxane are premixed at -20°C for 5 minutes.

[0080] Step b: The mixture from step a, the PNP-type tetrameric catalyst ligand (prepared in Preparation Example 1), and methylcyclohexane were used as catalysts, and ethylene was used as the starting material. Ethylene was used in the reaction unit of a microchannel reactor for ethylene polymerization. The molar ratio of chromium acetylacetone, catalyst ligand, and organoaluminum was 1:1.5:800. The concentration of the catalyst was 2 μmol / L, calculated as chromium. The incoming ethylene pressure in step b was constant at 2 MPa. The residence time of the catalyst in the microchannel reactor was 300 seconds. The flow rate of the preheated mixture in the reaction unit of the microchannel reactor was 1 m / s. The reaction solution was discharged from the outlet of the microchannel reactor. 5 mL of the sample was taken in the post-processing unit, and 1 mL of ethanol was added as a terminator to terminate the reaction. Gas chromatography analysis was performed. The organic phase was analyzed by gas chromatography to calculate the catalyst activity and product composition. Experimental results: The reaction activity was 1.2 × 10⁻⁶. 8 g·mol(Cr) -1 ·h -1 The total selectivity for C6 and C8 olefins was 88% by weight.

[0081] The above description is merely a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, based on the technical teachings provided by the present invention and as common knowledge in the field, other equivalent modifications and improvements can be made, and these should also be considered within the scope of protection of the present invention.

Claims

1. A process for the polymerization of ethylene based on a microchannel reactor, characterized in that, The microchannel reactor comprises a premixing unit, a mixing and preheating unit, and a reaction unit connected in sequence. The method includes the following steps: Step a: Premix the metal salt and organoaluminum to obtain premix solution a; Step b: The premixed solution a is mixed with the catalyst ligand and solvent in the premixing unit of the microchannel reactor to obtain a mixed solution; Step c: Using the mixture as a catalyst and ethylene as a starting material, the mixture is mixed and preheated in the mixing and preheating unit of a microchannel reactor to obtain a preheated mixture; Step d: The preheated mixture is subjected to ethylene polymerization in the reaction unit of a microchannel reactor; The metal salt is a chromium-containing compound; The organoaluminum compound is selected from one or more of alkylaluminum compounds, alkoxyaluminum compounds, and alkylaluminum chloride compounds; The catalyst ligand is selected from one or more of the following: pyrrole-type ethylene trimer catalyst ligand, bisphosphine-type ethylene tetramer catalyst ligand, and diimine-type ethylene oligomer catalyst ligand. The premixing temperature in step a is -20 to 0°C; The mixing temperature in step b is 20-40℃.

2. The method of claim 1, wherein, The metal salt is selected from one or more of chromium chloride, chromium isooctanoate, and chromium acetylacetonate; and / or, The organoaluminum is selected from one or more of methylaluminoxane, trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, diethylaluminum chloride, diethylaluminum chloride, ethylaluminoxane, and modified methylaluminoxane; and / or, The bisphosphine-type ethylene tetramerizing catalyst ligand is selected from PNP-type tetramerizing catalyst ligands and / or PCCP-type tetramerizing catalyst ligands; and / or, The solvent is selected from alkane or aromatic compounds.

3. The method of claim 1, wherein, The solvent is selected from one or more of straight-chain alkanes, branched-chain alkanes, cycloalkanes, aromatics, and substituted aromatics.

4. The method of claim 1, wherein, The solvent is selected from one or more of pentane, heptane, hexane, cyclohexane, methylcyclohexane, benzene, toluene, xylene, and monochlorobenzene.

5. The method according to any one of claims 1-4, characterized in that, The molar ratio of metal salt, catalyst ligand, and organoaluminum is 1:0.2-5:20-2000.

6. The method according to any one of claims 1-4, characterized in that, The concentration of the catalyst is 0.1-50 μmol / L, calculated based on the metal element in the metal salt.

7. The method according to any one of claims 1-4, characterized in that, The premixing time in step a is 1-10 minutes; and / or, The mixing time in step b is 1-10 minutes; and / or, In step c, the mixing preheating temperature is 30-150℃; and / or, In step d, the temperature of the ethylene polymerization reaction is 30-150℃, the pressure is 0.1-10MPa, the residence time of the preheated mixture in the reaction unit of the microchannel reactor is 10-1500 seconds, and the flow velocity of the preheated mixture in the reaction unit of the microchannel reactor is 1-10m / s.

8. The method according to any one of claims 1-4, characterized in that, In step c, the mixing preheating temperature is 40-100℃; and / or, The temperature of the ethylene polymerization reaction in step d is 40-100℃.

9. The method according to any one of claims 1-4, characterized in that, Following the reaction unit, the microchannel reactor also includes a post-processing unit for terminating the reaction.

10. The method of any one of claims 1-4, wherein, The microchannel reactor has multiple structural units.

11. The method of claim 10, wherein, Each of the structural units is independently selected from one or more of the following: T-shaped structure, Y-shaped structure, heart-shaped structure, serpentine structure, and bow-shaped structure. And / or, the structural units are used in series or in parallel.

12. The method according to any one of claims 1-4, characterized in that, The length of a single reaction unit in the microchannel reactor is 50-1000 m; and / or, The inner diameter of the microchannel reactor is 0.1-5 mm.

13. The method according to claim 12, characterized in that, The length of a single reaction unit in the microchannel reactor is 100-300m.

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