A system and method for controlling the gas composition within a reactor during the gas phase copolymerization of olefins

Abstract

The present application belongs to the technical field of olefin gas phase polymerization, and discloses a system and method for controlling gas composition in a reactor during olefin gas phase copolymerization, which comprises a gas supply tank, a gas outlet of the gas supply tank being connected with a gas inlet of the reactor through a gas phase discharge pipeline, and a gas outlet of the reactor being connected with the gas supply tank through a circulating gas return pipeline; the gas supply tank is connected with a liquid phase olefin feeding unit and a gas phase olefin feeding unit, the gas supply tank is provided with a temperature control unit and a first pressure control unit, and a circulating compressor is arranged on the gas phase discharge pipeline or the circulating gas return pipeline. The system and method can stabilize the gas composition in the reactor during copolymerization, thereby producing copolymer products with stable composition, and have the characteristics of less equipment, simple process and easy operation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of olefin gas phase polymerization, and particularly relates to a system and method for controlling the composition of gas in a reactor during olefin gas phase copolymerization. BACKGROUND

[0002] Olefin gas phase copolymerization is an important part of the polyolefin process, and is widely used in the production process of linear low density polyethylene, random copolymer polypropylene and impact copolymer polypropylene products. In the process of olefin gas phase copolymerization, the ratio of various olefins in the gas phase in the reactor is different, and the properties of the copolymer obtained by polymerization are also greatly different. In the production of olefin copolymer, only the stable ratio of various olefins in the polymerization reactor is controlled, stable copolymer products can be obtained.

[0003] In the existing continuous polyolefin process, the Spheripol process of Lyondell-Basell Company in the bulk-gas phase process, the Hypol process of Prime Polymer Company, the Borstar process of Borealis and the loop process of ExxonMobil, and the Unipol process of Greace Company in the gas phase process, the Novolen process of CB&I Company, the Innovene process of INEOS Company, the Horizone process of JPP Company, and the Spherizone process and Catalloy process of Lyondell-Basell Company, all of which are designed to have an olefin gas phase copolymerization stage, and the composition control of various gases in the copolymerization reactor is realized through automatic control between the feed flow of each gas raw material and the chromatographic analysis results of online sampling of the gas in the reactor. This method must be equipped with flow meters, regulating valves, online chromatographs and other devices and instruments, which is expensive and complex to control. SUMMARY

[0004] In view of the above problems, the present application provides a system and method for controlling the composition of gas in a reactor during olefin gas phase copolymerization. The system and method of the present application can realize the control of the composition of copolymerization olefin gas in the reactor, and the system contains less equipment, has low cost, simple process and easy operation.

[0005] The first aspect of the present application provides a system for controlling the composition of gas in a reactor during olefin gas phase copolymerization, which comprises a gas supply tank, the gas outlet of the gas supply tank is connected with the gas inlet of the reactor through a gas phase discharge pipeline, and the gas outlet of the reactor is connected with the gas supply tank through a circulating gas return pipeline;

[0006] The gas supply tank is connected with a liquid phase olefin feeding unit and a gas phase olefin feeding unit, and is provided with a temperature control unit and a first pressure control unit; and a circulating compressor is arranged on the gas phase outlet pipeline or the circulating gas return pipeline.

[0007] The second aspect of the present application provides a method for controlling the gas composition in a reactor during an olefin gas phase copolymerization process by using the above system, which comprises the following steps:

[0008] 1) The liquid phase olefin feeding unit introduces liquid phase olefin into the gas supply tank, the gas supply tank is heated, and the liquid phase olefin is partially gasified; the gas phase olefin feeding unit introduces gas phase olefin into the gas supply tank, and the temperature and pressure of the gas supply tank are controlled so that the gasified liquid phase olefin and the gas phase olefin form a mixed olefin gas for copolymerization;

[0009] 2) Olefin gas phase copolymerization stage: the mixed olefin gas in the gas supply tank is introduced into the reactor, and a circulating compressor is used to make the gas circulate between the reactor and the gas supply tank, and the reactor performs copolymerization reaction; along with the copolymerization reaction, the gas phase olefin is continuously introduced into the gas supply tank, and the liquid phase olefin is continuously gasified; the temperature and pressure of the gas supply tank are maintained by the temperature control unit and the first pressure control unit, and are the same as those in step 1);

[0010] 3) After the copolymerization reaction is completed, the gas circulation is stopped, and the unreacted monomers in the reactor are recovered.

[0011] The present application provides a mixed gas with stable composition for copolymerization of olefin to the reactor through the gas-liquid two-phase gas supply tank, and a circulating compressor is arranged between the reactor and the gas supply tank to make the gas circulate between the reactor and the gas supply tank, so that the gas composition in the reactor is basically stable, thereby producing a copolymer product with stable composition. Compared with the prior art, the system and method of the present application have the characteristics of less equipment, simple process and easy operation, and realize the stability of the gas composition in the reactor during the copolymerization process.

[0012] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 It is a structural schematic diagram of a system for controlling the gas composition in a reactor during an olefin gas phase copolymerization process.

[0014] Figure 2 It is a structural schematic diagram of another system for controlling the gas composition in a reactor during an olefin gas phase copolymerization process.

[0015] Marked as follows: 1-reaction, 2-gas supply tank, 3-circulating compressor, 4-liquid phase olefin feeding unit, 5-gas phase olefin feeding unit, 6-heat exchanger, 7-pressure reducing valve, 8-back pressure valve. DETAILED DESCRIPTION

[0016] The specific embodiments of the present application are described in detail below. It should be appreciated that the detailed description and specific examples which are described herein are presented for the purpose of illustrating the application and not for the purpose of limiting the same.

[0017] According to the first aspect of the present application, the present application provides a system for controlling the gas composition in a reactor during the process of gas phase copolymerization of olefins, the system comprising a gas supply tank, a gas outlet of the gas supply tank being connected to a gas inlet of the reactor through a gas phase discharge pipeline, and a gas outlet of the reactor being connected to the gas supply tank through a recycle gas return pipeline.

[0018] The gas supply tank is connected to a liquid phase olefin feeding unit and a gas phase olefin feeding unit, and is provided with a temperature control unit and a first pressure control unit, and a circulating compressor is arranged on the gas phase discharge pipeline or the recycle gas return pipeline.

[0019] In the present application, the gas supply tank provides the reactor with gas raw materials of specific composition required for copolymerization, including copolymerized olefins and a small amount of hydrogen as a molecular weight regulator. The gas supply tank is provided with monitoring instruments for temperature, pressure and liquid level, respectively. The size of the gas supply tank is not strictly required, and is generally 0.1-10 times the volume of the reactor.

[0020] According to the present application, the liquid phase olefin feeding unit intermittently or continuously provides the gas supply tank with liquid olefin raw materials. If the pressure of the source of the liquid olefin raw materials is lower than the working pressure of the gas supply tank, the feeding unit can use a diaphragm pump as a power equipment for conveying; if the pressure of the source of the liquid olefin raw materials is higher than the working pressure of the gas supply tank, the feeding unit can realize raw material conveying by pressure difference without additional power equipment. The liquid olefin feeding unit can select an instrument containing flow control, which is automatically controlled with the liquid level of the gas supply tank to realize continuous feeding of liquid olefins.

[0021] In the present application, the gas phase olefin feeding unit continuously provides the gas supply tank with gas phase olefin raw materials. The pressure of the source of the gas phase olefin raw materials is higher than the working pressure of the gas supply tank.

[0022] According to the present application, the first pressure control unit is a pressure reducing valve or a first regulating valve arranged on the connecting pipeline between the gas phase olefin feeding unit and the gas supply tank, and the first regulating valve is electrically connected to the pressure instrument signal of the gas supply tank to stabilize the pressure of the gas supply tank at a set value.

[0023] According to the present application, the temperature control unit maintains the temperature of the materials in the gas supply tank near the set value of the gas supply tank. The temperature control unit can include a jacket water system arranged on the outer surface of the gas supply tank and / or a heat exchanger arranged on the recycle gas return pipeline.

[0024] The jacket water system is a conventional temperature control system, which comprises instruments for controlling the temperature and flow rate of the jacket water, so that the temperature of the gas supply tank can be maintained within a certain range of the set temperature value. The heat exchange medium of the heat exchanger is circulating water. If the temperature control unit only comprises the heat exchanger, the heat exchanger needs to comprise instruments for controlling the flow rate and temperature of the heat exchange medium, and the circulating gas pipeline needs to comprise a cross-line design connecting the gas inlet and outlet of the reactor, so that the circulating gas can only circulate between the gas supply tank, the compressor and the heat exchanger. These are all achievable according to the prior art.

[0025] In the present application, the circulating compressor is a power source for realizing the circulation of the reaction gas between the reactor and the gas supply tank, and a centrifugal compressor can be generally selected.

[0026] According to one specific embodiment of the present application, the pressure of the reactor is higher than that of the gas supply tank, the circulating compressor is arranged on the gas phase discharge pipeline, a second pressure control unit is arranged on the circulating gas return pipeline, the second pressure control unit is a second regulating valve or a back pressure valve (such as a self-operated back pressure valve), and the second regulating valve is electrically connected with the pressure instrument signal of the reactor.

[0027] According to another specific embodiment of the present application, the pressure of the reactor is lower than that of the gas supply tank, the circulating compressor is arranged on the circulating gas return pipeline, a third pressure control unit is arranged on the gas phase discharge pipeline, the third pressure control unit is a third regulating valve or a pressure reducing valve (such as a self-operated pressure reducing valve), and the third regulating valve is electrically connected with the pressure instrument signal of the reactor.

[0028] According to the second aspect of the present application, the present application provides a method for controlling the gas composition in the reactor during the gas phase copolymerization of olefins by using the above-mentioned system, which comprises the following steps:

[0029] 1) The liquid phase olefin feeding unit introduces liquid phase olefins into the gas supply tank, the gas supply tank is heated, and the liquid phase olefins are partially gasified; the gas phase olefin feeding unit introduces gas phase olefins into the gas supply tank, and the temperature and pressure of the gas supply tank are controlled, so that the gasified liquid phase olefins and the gas phase olefins form a mixed olefin gas for copolymerization;

[0030] 2) The olefin gas phase copolymerization stage: the mixed olefin gas in the gas supply tank is introduced into the reactor, and the circulating compressor is used to circulate the gas between the reactor and the gas supply tank, the reactor performs the copolymerization reaction, and along with the progress of the copolymerization reaction, the gas phase olefins are continuously introduced into the gas supply tank, the liquid phase olefins are continuously gasified, and the temperature and pressure of the gas supply tank are maintained by the temperature control unit and the first pressure control unit of the gas supply tank, and are the same as those in step 1);

[0031] 3) After the copolymerization reaction is completed, the gas circulation is stopped, and the unreacted monomers in the reactor are recovered.

[0032] In the present application, the liquid phase olefin and the gas phase olefin can be selected from at least one of ethylene, propylene and alpha-olefin containing 4-10 carbon atoms, and the molecular weight of the liquid phase olefin is greater than that of the gas phase olefin.

[0033] According to the present application, the feeding of the liquid phase olefin into the gas tank can be introduced only once before the copolymerization, not introduced during the copolymerization; can be introduced intermittently for several times during the continuation of the copolymerization; or continuously introduced during the whole process through the automatic control of the flow regulating instrument and the liquid level of the gas tank.

[0034] In the present application, the temperature, pressure and volume of the liquid phase olefin of the gas tank can be determined according to the needs, as long as the mixed olefin gas for copolymerization can be continuously provided, for example, the liquid volume in the gas tank accounts for 10%-90% of the volume of the gas tank, the temperature of the gas tank is 0-100℃, and the pressure of the gas tank is 0.1-10.0 MPa.

[0035] According to the present application, during the copolymerization reaction process, the fluctuation of the temperature of the material in the gas tank relative to the set temperature of the gas tank is less than 10℃, preferably less than 5℃, and more preferably less than 2℃. The temperature of the material in the gas tank is the actual temperature displayed on the temperature monitoring instrument.

[0036] In the present application, the components, components and parameters not limited can be selected according to the prior art, which belongs to the conventional technical means in the art.

[0037] The present application will be further described below in conjunction with examples, but is not limited by these examples.

[0038] Example 1

[0039] The process flow is shown as Figure 1 The reactor 1 is a 5.0 liter stirred stainless steel kettle with jacketed hot water temperature control; the gas tank 2 is a 2.5 liter stainless steel tank with constant temperature water bath temperature control, and the temperature control range is 5-90℃; the circulating compressor 3 is an air driven piston type gas booster with a flow rate of 63 NL / min; a circulating water jacket heat exchanger 6 is installed on the pipeline for returning the circulating gas to the gas tank, and the circulating water temperature is controllable at 5-40℃, and the circulating water flow rate is 4.0 L / min.

[0040] Gas phase copolymerization raw material preparation: at room temperature, the liquid phase olefin feeding unit 4 pressurizes 1.5 liters of room temperature liquid phase propylene into the gas tank, the constant temperature water bath of the gas tank is started, and the temperature is set to 30℃ for heating; when the temperature in the gas tank is stabilized at 30℃, the pressure of the gas tank is about 1.25 MPa; 0.05 g of hydrogen is added to the gas tank; finally, the pressure of the ethylene feeding pressure reducing valve is set to 1.7 MPa, and the gas phase olefin feeding unit 5 adds ethylene gas into the gas tank, and the final pressure of the gas tank is 1.7 MPa.

[0041] Liquid phase homopolymerization of propylene: 12.9 mg of DQ catalyst, 1.5 mmol of triethylaluminum, 0.2 mmol of methylcyclohexyldimethoxysilane were added into the reactor at room temperature, then 0.1 g of hydrogen was added; the stirring was started, 2.0 L of liquid propylene was added into the reactor through the metering tank, then the reactor temperature control system was started to rapidly increase the reactor temperature to 70°C, and the liquid phase bulk homopolymerization of propylene was carried out for 0.5 h.

[0042] Gas phase copolymerization of propylene and ethylene: after the homopolymerization of propylene was completed, the unreacted monomers were discharged, the valve on the gas supply tank to the reactor pipeline was opened, and mixed gas was introduced into the reactor, and the reactor temperature was set to 70°C; then the valve on the reactor gas outlet to the circulating compressor was opened, the circulating compressor was started, finally the valve on the circulating compressor outlet to the gas supply tank was opened, and the heat exchanger inlet and outlet circulating water valve on the circulating gas return pipeline was opened, and the circulating water temperature was 6°C; as the copolymerization reaction proceeded, the gas phase olefins were continuously introduced into the gas supply tank, and the liquid phase olefins were continuously gasified, and the temperature of the gas supply tank was maintained at 30°C and the gauge pressure was 1.7 MPa, and the actual temperature of the gas supply tank fluctuated less than 2°C relative to the set temperature during the polymerization process. The pressure of the reactor was stabilized at 1.0 MPa by adjusting the pressure reducing valve 7 on the gas supply tank to the reactor gas phase outlet pipeline, and after the reactor pressure was stabilized, the gas sample R-1 was taken from the reactor, and the gas sample R-2 was taken from the reactor after 60 min, then the circulating compressor was stopped, the valves on the reactor gas inlet and outlet pipelines were closed, and the unreacted monomers in the reactor were discharged to obtain 420 g of impact copolymer polypropylene. The polymer was analyzed and tested, and the ethylene mass content was 7.35%, and the rubber phase mass content was 17.25%. The related experimental results are shown in Table 1.

[0043] Example 2

[0044] The process flow is shown in Figure 2 The reactor 1 is a 5.0 L stirred stainless steel kettle with jacketed hot water temperature control; the gas supply tank 2 is a 2.5 L stainless steel tank with constant temperature water bath temperature control, and the temperature control range is 4-90°C; the circulating compressor 3 is an air-driven piston type gas booster with a maximum flow rate of 63 NL / min; the pipeline for returning the circulating gas to the gas supply tank is provided with a circulating water jacket heat exchanger 6, and the circulating water temperature is controllable at 5-40°C, and the circulating water flow rate is 4.0 L / min.

[0045] Preparation of gas phase copolymerization raw materials: at room temperature, the liquid phase olefin feeding unit 4 pressurized the normal temperature liquid phase butene into the gas supply tank at 1.5 L, the gas supply tank constant temperature water bath was started, and the temperature was set to 40°C to start heating; when the temperature in the gas supply tank was stabilized at 40°C, the pressure in the gas supply tank was about 0.35 MPa, the ethylene feeding pressure reducing valve was set to 0.55 MPa, and the gas phase olefin feeding unit 5 added ethylene gas into the gas supply tank, and finally the gauge pressure of the gas supply tank was 0.55 MPa.

[0046] Propylene liquid phase homopolymerization: 19.8 mg of DQ catalyst, 1.5 mmol of triethylaluminum, 0.2 mmol of methylcyclohexyldimethoxysilane were added into the reactor at room temperature, then 0.1 g of hydrogen was added; the stirring was started, 2.0 L of liquid propylene was added into the reactor through a metering tank, then the temperature control system of the reactor was started to rapidly increase the temperature of the reactor to 70°C, and the liquid phase bulk polymerization of propylene was carried out for 0.5 h.

[0047] Ethylene, butene gas phase copolymerization: after the propylene homopolymerization, the unreacted monomers were discharged, the valve on the gas supply tank-circulating compressor-reactor pipeline was opened, and the circulating compressor was started to introduce the mixed gas into the reactor, and the temperature of the reactor was set to 70°C; then the valve from the reactor outlet to the gas supply tank was opened, and the heat exchanger inlet and outlet circulating water valves on the circulating gas return pipeline were opened, and the circulating water temperature was 15°C; as the copolymerization reaction proceeded, the gas phase olefins were continuously introduced into the gas supply tank, and the liquid phase olefins were continuously gasified, and the temperature of the gas supply tank was maintained at 40°C and the gauge pressure was 0.55 MPa, and the actual temperature of the gas supply tank during the polymerization fluctuated less than 2°C relative to the set temperature. The back pressure valve 8 on the circulating gas return pipeline was adjusted to stabilize the reactor pressure at 0.8 MPa, and after the reactor pressure was stabilized, the gas sample R-1 was taken from the reactor, and the gas sample R-2 was taken from the reactor after 60 min, then the circulating compressor was stopped, the valves on the gas inlet and outlet pipelines of the reactor were closed, the unreacted monomers in the reactor were discharged, and 679 g of impact copolymer polypropylene was obtained. The polymer was analyzed and tested, and the ethylene molar content was 11.39% and the butene molar content was 1.06%. The related experimental results are shown in Table 1.

[0048] Example 3

[0049] The difference from Example 1 is that the gas supply tank pressure is controlled to be 2.25 MPa, the copolymerization pressure is 1.4 MPa, the copolymerization time is 30 min, and the actual temperature of the gas supply tank during the copolymerization fluctuates by a maximum of 3.2°C relative to the set temperature. A total of 479 g of polymer is obtained in the experiment, and the ethylene mass content is 8.68% and the rubber phase mass content is 16.04% when the polymer is analyzed and tested. The rest is the same as Example 1. The related experimental results are shown in Table 1.

[0050] Example 4

[0051] The difference from Example 1 is that the gas supply tank pressure is controlled to be 1.90 MPa, the copolymerization pressure is 1.4 MPa, the copolymerization time is 30 min, and the actual temperature of the gas supply tank during the copolymerization fluctuates by a maximum of 4.5°C relative to the set temperature. A total of 536 g of polymer is obtained in the experiment, and the ethylene mass content is 6.52% and the rubber phase mass content is 14.30% when the polymer is analyzed and tested. The rest is the same as Example 1. The related experimental results are shown in Table 1.

[0052] Example 5

[0053] The difference from Example 1 is that the supply tank pressure is controlled at 1.75 MPa, the copolymerization pressure is 1.4 MPa, the copolymerization time is 30 min, the heat exchanger inlet and outlet circulating water valve is not opened during the copolymerization process, and the actual temperature of the supply tank fluctuates by a maximum of 6.3°C relative to the set temperature. The experiment obtains a total of 476 grams of polymer, and the polymer is analyzed and tested, with an ethylene mass content of 5.53% and a rubber phase mass content of 12.89%. The rest is the same as Example 1. The relevant experimental results are shown in Table 1.

[0054] Comparative Example 1

[0055] The difference from Example 1 is that the circulating compressor and the valve for returning the reactor gas outlet to the supply tank are not opened during the copolymerization process, and the experiment obtains a total of 404 grams of polymer, which is analyzed and tested, with an ethylene mass content of 5.74% and a rubber phase mass content of 14.76%. The rest is the same as Example 1. The relevant experimental results are shown in Table 1.

[0056] Comparative Example 2

[0057] The difference from Example 2 is that the supply tank pressure is controlled at 0.80 MPa, the circulating compressor and the valve for returning the reactor gas outlet to the supply tank are not opened during the copolymerization process, and the copolymerization pressure is 0.7 MPa. The experiment obtains a total of 359 grams of polymer, which is analyzed and tested, with an ethylene molar content of 12.07% and a butene molar content of 0.62%. The rest is the same as Example 1. The relevant experimental results are shown in Table 1.

[0058] Table 1

[0059]

[0060]

[0061] Note: “E / P” is the volume ratio of ethylene to propylene in the gas sample chromatographic analysis, and “E / B” is the volume ratio of ethylene to butene in the gas sample chromatographic analysis.

[0062] As shown in Table 1, the system and method for controlling the gas composition in the reactor during the process of olefin gas phase copolymerization can make the E / P or E / B fluctuation range less than 15%, and can effectively control the gas composition in the reactor during the copolymerization process, thereby producing copolymer products with stable composition. Moreover, when the gas supply tank temperature fluctuation is less than 5°C and a circulating gas compressor is used during the copolymerization process, the gas phase copolymerization process, the gas phase composition in the reactor at the beginning and end of the copolymerization fluctuation range is less than 10%; more preferably (such as Example 1 of the ethylene-propylene copolymer), when the gas supply tank temperature fluctuation is less than 2°C, the gas phase copolymerization process, the gas phase composition in the reactor at the beginning and end of the copolymerization fluctuation range is less than 5%. On the contrary, as shown in the comparative examples, when there is no gas circulation between the gas supply tank and the reactor during the copolymerization process, whether it is ethylene-propylene gas phase copolymerization or ethylene-butylene gas phase copolymerization, the gas phase composition in the reactor at the beginning and end of the copolymerization fluctuation range is more than 40%, in which case the structure of the copolymer obtained by polymerization is very uneven, and the product quality and stability will be greatly affected.

[0063] The above has described various embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for controlling the gas composition within a reactor during olefin gas-phase copolymerization, characterized in that, The system used in this method includes a gas supply tank, the outlet of which is connected to the inlet of the reactor via a gas phase discharge pipeline, and the outlet of the reactor is connected to the gas supply tank via a recirculating gas return pipeline; the gas supply tank is connected to a liquid phase olefin feed unit and a gas phase olefin feed unit, and is equipped with a temperature control unit and a first pressure control unit; a recirculating compressor is installed on the gas phase discharge pipeline or the recirculating gas return pipeline; the method includes: 1) The liquid phase olefin feeding unit introduces liquid phase olefins into the gas supply tank, the gas supply tank is heated, and the liquid phase olefins are partially vaporized; the gas phase olefin feeding unit introduces gas phase olefins into the gas supply tank, controls the temperature and pressure of the gas supply tank, so that the vaporized liquid phase olefins and gas phase olefins form a mixed olefin gas that copolymerizes. 2) Olefin gas-phase copolymerization stage: The mixed olefin gas in the gas supply tank is introduced into the reactor, and the gas is circulated between the reactor and the gas supply tank by the circulating compressor. The reactor carries out the copolymerization reaction. As the copolymerization reaction proceeds, gaseous olefins are continuously introduced into the gas supply tank, and liquid olefins are continuously vaporized. The temperature and pressure of the gas supply tank are maintained at the same level as in step 1) by the temperature control unit and the first pressure control unit of the gas supply tank. 3) After the copolymerization reaction is completed, stop the gas circulation and recover the unreacted monomers in the reactor.

2. The method for controlling the gas composition in a reactor during olefin gas-phase copolymerization according to claim 1, wherein, The gas supply tank is equipped with monitoring instruments for temperature, pressure, and liquid level.

3. The method for controlling the gas composition in the reactor during the olefin gas-phase copolymerization process according to claim 1, wherein, The temperature control unit includes a jacketed water system located on the outer surface of the gas supply tank and / or a heat exchanger located on the circulating gas return pipeline.

4. The method for controlling the gas composition in a reactor during olefin gas-phase copolymerization according to claim 1, wherein, The first pressure control unit includes a pressure reducing valve or a first regulating valve located on the pipeline connecting the gas phase olefin feed unit and the gas supply tank. The first regulating valve is electrically connected to the pressure gauge signal of the gas supply tank.

5. The method for controlling the gas composition in a reactor during olefin gas-phase copolymerization according to claim 1, wherein, The circulating compressor is located on the gas phase discharge pipeline, and a second pressure control unit is provided on the circulating gas return pipeline. The second pressure control unit is a second regulating valve or a back pressure valve, and the second regulating valve is electrically connected to the pressure gauge signal of the reactor.

6. The method for controlling the gas composition in a reactor during olefin gas-phase copolymerization according to claim 1, wherein, The circulating compressor is located on the circulating gas return pipeline, and a third pressure control unit is provided on the gas phase discharge pipeline. The third pressure control unit is a third regulating valve or a pressure reducing valve, and the third regulating valve is electrically connected to the pressure gauge signal of the reactor.

7. The method for controlling the gas composition in a reactor during olefin gas-phase copolymerization according to claim 1, wherein, The liquid-phase olefin and the gaseous olefin are selected from at least one of ethylene, propylene, and α-olefins containing 4 to 10 carbon atoms, and the molecular weight of the liquid-phase olefin is greater than that of the gaseous olefin.

8. The method for controlling the gas composition in a reactor during olefin gas-phase copolymerization according to claim 1, wherein, The liquid volume in the gas supply tank accounts for 10% to 90% of the gas supply tank volume, the temperature of the gas supply tank is 0 to 100℃, and the pressure of the gas supply tank is 0.1 to 10.0 MPa.

9. The method for controlling the gas composition in a reactor during olefin gas-phase copolymerization according to claim 1, wherein, During the copolymerization reaction, the temperature fluctuation of the material in the gas supply tank relative to the set temperature of the gas supply tank is less than 10℃.

10. The method for controlling the gas composition in a reactor during olefin gas-phase copolymerization according to claim 9, wherein, During the copolymerization reaction, the temperature fluctuation of the material in the gas supply tank relative to the set temperature of the gas supply tank is less than 5℃.

11. The method for controlling the gas composition in a reactor during olefin gas-phase copolymerization according to claim 10, wherein, During the copolymerization reaction, the temperature fluctuation of the material in the gas supply tank relative to the set temperature of the gas supply tank is less than 2℃.

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