Olefin polymerization system, application thereof and olefin polymerization method

Abstract

The invention discloses an olefin polymerization system, application thereof and an olefin polymerization method. The olefin polymerization system comprises a first fluidized bed reactor, a second fluidized bed reactor, an intermediate tank arranged between the first fluidized bed reactor and the second fluidized bed reactor, and a buffer tank, the top of the intermediate tank is connected with an outlet in the middle of the first fluidized bed reactor through a discharging pipeline, and the bottom of the intermediate tank is connected with a feeding hole in the middle of the second fluidized bed reactor through a feeding pipeline; the top of the first fluidized bed reactor is connected with the top of the intermediate tank through a gas phase balance pipeline; a branch pipeline connected with the buffer tank is arranged on the gas phase balance pipeline; and control valves are arranged on the discharging pipeline, the gas phase balance pipeline, the branch pipeline and the feeding pipeline. According to the invention, 99.9 wt% of hydrogen in the gas phase component from the first reactor can be effectively removed.

Description

Technical Field

[0001] The present invention relates to the technical field of olefin polymerization, and in particular to an olefin polymerization system for producing polyolefin and application thereof, as well as an olefin polymerization method. Background Art

[0002] The tandem reactor method is the main method that has been industrialized at present. It uses two reactors in series to produce bimodal polyolefin products, especially polyethylene products. Products with different molecular weights are generated by the first and second reactors. By controlling the different polymerization conditions of the two reactors, such as different hydrogen partial pressures, polymerization temperatures and times, and changing the proportion of comonomers, polyethylene with a bimodal molecular weight distribution is obtained. The core of the bimodal polyethylene production technology is to produce a polymer product with a lower relative molecular weight through hydrogen adjustment in the first reactor, and then the polymer is transported to the second reactor for hydrogen fine-tuning or without hydrogenation to produce a polymer with a higher relative molecular weight. At present, many companies at home and abroad use this method to produce bimodal polyethylene, such as the slurry tandem reactor production process developed by Phillips, Mitsui Petrochemical, Solvay, Hoechst and other companies, the UnipolⅡ developed by UCC and the Borstar bimodal polyethylene production process developed by Borealis.

[0003] The gas phase fluidized bed olefin polymerization process has the advantages of low equipment investment, short process flow, high operational flexibility, no waste gas emissions and no solvent recovery, and has gradually become the mainstream process for producing polyethylene. This process uses a high-efficiency catalyst combined with a gas phase fluidized bed to produce full-density polyethylene products from linear low-density polyethylene (LLDPE) to high-density polyethylene (HDPE).

[0004] With the development of polyolefin fluidized bed process technology research and catalyst technology research, gas phase fluidized bed reactor can be used to produce a variety of polyolefin products, while reducing production costs, and is favored by many industrial enterprises. Among the hot technologies in the past decade, the technical research and development of dual fluidized bed polymerization reactors has become a hot direction. Excessive hydrogen is used in the reactor to produce low molecular weight parts and control the molecular weight of the polymer suitable for providing good processability of the final polymer. The high molecular weight part that affects the physical properties is produced under polymerization conditions of low hydrogen concentration. It is well known in the art that low molecular weight polymers are preferably produced in the first reactor. In order to obtain a multimodal polymer with good physical properties, before the polymerized polymer is sent to the second reactor where the high molecular weight polymer production occurs, all gas phase components from the first reactor should be removed, wherein the gas phase components are ethylene, α-olefins and hydrogen carried by the discharge of the first reactor, especially all hydrogen from the first reactor should be removed.

[0005] Patents US 7786254B2 and US 7582723B2 describe a method for producing wide / bimodal polyethylene in series by connecting two conventional gas phase reactors. In this method, a cyclone separator and a gas-solid separation element are added between the first reactor and the second reactor. However, this method has problems such as the cross-flow of reactants between the two gas phase reactors and the uneven residence time of polymer particles in the two gas phase reactors. Patent CN102060943A discloses a method for preparing bimodal polyethylene and a gas phase reactor comprising at least four fluidized beds. In this method, polymer particles enter a cyclone separator from the outlet of the second reactor or the fourth reactor for gas-solid separation, and the circulating gas returns to the reactor under the same reaction conditions through a circulation loop; this method has the problem of complex operation method and the amount of fine powder entrainment limiting the circulation amount of polymer particles between reactors with different reaction conditions. Patent CN105617952B provides a discharging system and method for a fluidized bed reactor. This method adds an injection device to the original discharging system, and uses the injection device to suck the balance gas in the sedimentation container to form a negative pressure, so that the multi-temperature zone fluidized bed reactor can achieve upper discharging, reduce the liquid content of the discharged material, and reduce energy consumption. However, this discharging system is only suitable for improving the discharging efficiency of the fluidized bed pressure vessel in the condensing state process.

[0006] Although the fluidized bed process technology for preparing bimodal polyethylene is mature and many methods for removing all hydrogen from the first reactor are known and have been described, there is still a need to develop an olefin polymerization unit for producing polyolefins and a discharge system for an olefin polymerization unit and a method of using the same.

[0007] Patent CN 200480030566.3 proposes a multi-zone circulation reactor and method for producing polyolefins with bimodal molecular weight distribution. However, the reactor is characterized by an ascending section in a fast fluidized state and a descending section in a moving bed state connected to each other. The problems of these two patents are that there is cross-flow of reaction gas, and the descending section in the moving bed state cannot be applied to the production of polyethylene with a large heat release.

[0008] Patent CN 102060943A discloses a method for preparing bimodal polyethylene and a gas phase reactor comprising at least four fluidized beds. In the method, polymer particles are bubbling fluidized in the first reactor or the third reactor, and the fine powder in the polymer particles is entrained and blown to the second reactor or the fourth reactor in a fast fluidized state due to elutriation. The polymer fine powder enters the cyclone separator from the outlet of the second reactor or the fourth reactor for gas-solid separation, and the circulating gas returns to the reactor with the same reaction conditions through a circulation loop; the solid polymer particles enter another bubbling bed with different reaction conditions. However, the method has the problem that the operation method is complicated and the amount of fine powder entrainment limits the circulation amount of polymer particles between reactors with different reaction conditions.

[0009] Patent CN 107405593B provides an olefin polymerization device and an olefin polymerization method. The device or method provided by the invention can realize the condensation of gas materials discharged from the polymerization reactor. After gas-liquid separation, the generated gas part is circulated back to the reactor to form a circulation loop, and the condensate can be selectively introduced into the polymerization reactor to realize free switching between homopolymerization and copolymerization or between different copolymerization reactions, and the condensate can absorb the heat generated by the reaction. However, the device and method provided by the invention require high energy consumption to enable the gas discharged from the polymerization reactor to pass through condensation and gas-liquid separation, and setting up a polymerization reactor cannot realize continuous switching between olefin homopolymerization and copolymerization reactions. Summary of the invention

[0010] In order to solve the technical problem that the discharge of the first reactor in the prior art olefin polymerization reaction carries a large amount of hydrogen, the present invention provides an olefin polymerization system and its application, and an olefin polymerization method. The present invention can realize the smooth progress of olefin homopolymerization and copolymerization, or the switching between different copolymerization reactions, and is particularly suitable for the production of bimodal polyethylene.

[0011] To achieve the above-mentioned purpose, the present invention provides an olefin polymerization system, which comprises: a first fluidized bed reactor, a second fluidized bed reactor, an intermediate tank disposed between the first fluidized bed reactor and the second fluidized bed reactor, and a buffer tank; the top of the intermediate tank is connected to the middle outlet of the first fluidized bed reactor via a discharge pipeline, and the bottom of the intermediate tank is connected to the middle feed port of the second fluidized bed reactor via a feed pipeline; the top of the first fluidized bed reactor is connected to the top of the intermediate tank via a gas phase balance pipeline; a branch pipeline connected to the buffer tank is disposed on the gas phase balance pipeline; the discharge pipeline, the gas phase balance pipeline, the branch pipeline, and the feed pipeline are all provided with control valves;

[0012] The discharge pipeline is provided with a first control valve. When the first control valve is opened, the product of the first fluidized bed reactor is discharged to the intermediate tank through the discharge pipeline under the action of pressure difference; the intermediate tank is used to stabilize the polymerization environment in the second fluidized bed reactor and remove the gas phase components from the first fluidized bed reactor;

[0013] The second fluidized bed reactor is provided with a gas distribution plate, and the inlet height of the feed pipeline is above the gas distribution plate, and the height is 0.1-1 m.

[0014] In one embodiment, the discharge pipeline has a horizontal angle greater than 20° and less than 45°, and the length of the pipeline is no more than 2m.

[0015] In one embodiment, the second fluidized bed reactor adopts a double valve group, wherein a second control valve is provided on the side of the feed pipeline close to the second fluidized bed reactor, and a seventh control valve is provided on the side close to the intermediate tank. When the second control valve and the seventh control valve are opened, the material in the intermediate tank is transported to the second fluidized bed reactor by the purge gas. After the material transportation is completed, the second control valve and the seventh control valve are closed, and the control valve on the branch pipeline is opened to release the pressure of the intermediate tank and the pipeline to carry out the next discharge procedure.

[0016] In one embodiment, a third control valve is provided on the gas phase balance pipeline. After the first control valve is opened for a period of time, the third control valve is opened; after the first control valve is closed, the gas phases in the intermediate tank and the first fluidized bed reactor are mixed and balanced. When the gas phase pressures in the intermediate tank and the first fluidized bed reactor are equal, the third control valve is closed; a certain time difference is set between the switching actions of the first control valve and the third control valve to make it easier to input the product in the first fluidized bed reactor into the intermediate tank, and after the product input is completed, the gas phase pressures in the intermediate tank and the first fluidized bed reactor are balanced.

[0017] In one embodiment, a fourth control valve is provided on the branch pipeline. When the fourth control valve is opened, the intermediate tank is depressurized for a second time, and the gas removed from the intermediate tank enters the buffer tank and undergoes membrane separation and deep-cold recovery therein.

[0018] In one embodiment, the pipeline between the first control valve and the first fluidized bed reactor is connected to an external circulating gas connecting pipeline and to a circulating gas compressor, and a fifth control valve is provided on the circulating gas connecting pipeline; when the first fluidized bed reactor reaches the discharge material level height, the circulating gas is backflushed and the first control valve is closed; after the first control valve is closed, the fifth control valve always remains in an open state until the next discharge procedure begins.

[0019] In one embodiment, a purge gas connecting pipeline is provided on the top of the intermediate tank and is connected to a purge gas compressor. A sixth control valve is provided on the purge gas connecting pipeline. The purge gas is used to transport the material in the intermediate tank to the second fluidized bed reactor, while also protecting the pressure balance and polymerization environment of the second fluidized bed reactor.

[0020] In one embodiment, a gas sampling port is provided at the bottom of the intermediate tank, and a ball valve is provided on the pipeline connected to the gas sampling port.

[0021] In one embodiment, ethylene homopolymerization or copolymerization is carried out in the first fluidized bed reactor, and copolymerization is carried out in the second fluidized bed reactor.

[0022] In one embodiment, the reactant of the homopolymerization reaction is one of ethylene, propylene and butene; the reactant of the copolymerization reaction is α-olefin, and the α-olefin is preferably an α-olefin with less than 18 carbon atoms, and more preferably at least one of butene, 4-methyl-1-pentene, hexene and octene.

[0023] In one embodiment, the catalyst used in the homopolymerization reaction or copolymerization reaction is selected from one of a Ziegler-Natta catalyst, a chromium catalyst, a metallocene catalyst and a late transition metal catalyst, and the catalyst used in the second fluidized bed reactor is preferably a metallocene catalyst or a composite thereof.

[0024] In one embodiment, the co-catalyst used in the homopolymerization or copolymerization reaction is an aluminum compound such as an alkyl aluminum or an alkoxy aluminum, preferably at least one of trimethyl aluminum, triethyl aluminum, diethyl aluminum monochloride, tri-n-hexylaluminum and a modified alkyl aluminum compound, more preferably triethyl aluminum.

[0025] In one embodiment, the reaction pressure of the first fluidized bed reactor is 0.5-5 MPa, preferably 2-3 MPa; the reaction temperature is 80-110°C, preferably 85-100°C.

[0026] In one embodiment, a molecular weight regulator, preferably hydrogen, is used in the reaction in the first fluidized bed reactor and the second fluidized bed reactor.

[0027] In one embodiment, the discharging program of the olefin polymerization system is controlled by a DCS distributed control system, and the discharging program setting includes the setting of sequential control state, program discharging, discharging mode, discharging setting and discharging count.

[0028] In one embodiment, the top of the first fluidized bed reactor and / or the second fluidized bed reactor is an expansion section.

[0029] In one embodiment, the first control valve, the second control valve, the third control valve, the fourth control valve, the fifth control valve, the sixth control valve, and the seventh control valve are pneumatic control valves.

[0030] In one embodiment, the reaction product of the first fluidized bed reactor is a low molecular weight polyolefin; and the reaction product of the second fluidized bed reactor is a high molecular weight polyolefin.

[0031] The present invention also provides an olefin polymerization method, which adopts an olefin polymerization system and comprises the following steps:

[0032] (1) When the first fluidized bed reactor reaches the set material level, close the fifth control valve on the circulating gas connecting pipeline;

[0033] (2) opening a first control valve on the discharge pipeline, and under the action of the pressure difference, the product of the first fluidized bed reactor is discharged from the discharge pipeline to the intermediate tank;

[0034] (3) After a certain period of time of discharging, the first control valve on the discharging pipeline is closed, and the fifth control valve on the circulating gas connecting pipeline is opened. The closing and opening actions of the first control valve and the fifth control valve are performed simultaneously, and the fifth control valve is always kept open until the next discharging procedure starts;

[0035] (4) After the discharge is completed, the third control valve on the gas phase balance pipeline is opened, and the gas phase components in the intermediate tank are partially returned to the first fluidized bed reactor due to the pressure difference, until the gas phases in the intermediate tank and the first fluidized bed reactor are mixed and balanced, and the gas phase pressures are equal, and then the third control valve is closed;

[0036] (5) After the third control valve is closed, there is still a certain pressure in the intermediate tank. The fourth control valve on the branch pipeline is opened to discharge the gas components in the intermediate tank to the buffer tank for membrane separation and cryogenic recovery of the exhaust gas, thereby further reducing the pressure of the intermediate tank and removing 99.9wt% of the hydrogen in the intermediate tank;

[0037] (6) Open the sixth control valve on the purge gas connecting pipeline and the second control valve on the feed pipeline at the same time to transport the material in the intermediate tank to the second fluidized bed reactor. After the reaction is completed, close the second control valve and the sixth control valve, open the fourth control valve on the branch pipeline, release the pressure of the intermediate tank and the pipeline, and proceed to the next discharge procedure.

[0038] The present invention further provides an application of an olefin polymerization system in olefin binary copolymerization, ternary copolymerization or tetra- or higher-level copolymerization.

[0039] The present invention increases the difference in the molar ratio of hydrogen to ethylene in the two reactors by an order of magnitude, so that one reactor produces a resin with a lower relative molecular mass, and the other reactor produces a resin with a higher relative molecular mass. The products of the two reactors are repeatedly blended in situ in the second reactor to obtain a polyethylene product with a target molecular weight distribution. The entire process is highly flexible and easy to control the molecular weight and molecular weight distribution of polyethylene. This technology uses ZN-type catalysts, chromium-based catalysts or single-site metal catalysts to produce full-density bimodal polyethylene products from linear low-density polyethylene (LLDPE) to high-density polyethylene (HDPE), with a density range of 0.918 to 0.970 g / m 3 , melt index 0.02~1.00g / 10min.

[0040] According to the sequence of the control valve group switches set in the discharge program of the present invention and the adjustment of the control valve switch time, a simple and effective degassing effect can be achieved, and the problems of reactant cross-flow between the two fluidized bed reactors and the uneven residence time of polymer particles in the two fluidized bed reactors can be effectively solved. The removed gas passes through the membrane and deep cold recovery system of the later stage, and the various hydrocarbons in the exhaust gas are efficiently recovered. Compared with the existing bimodal polyolefin production technology, the present invention reduces equipment investment, saves production costs and saves manpower and material resources, and also meets safety and environmental protection requirements.

[0041] The present invention significantly improves the discharge efficiency of the fluidized bed pressure vessel in the preparation process of bimodal polyolefins by the dual fluidized bed method by optimizing the discharge system of the olefin polymerization process. The present invention removes the nitrogen purge conveying process in the traditional discharge system, and newly sets up a purge gas connecting pipeline between the top of the intermediate tank and the second fluidized bed reactor, which is used to transport the polyolefins in the intermediate tank to the second fluidized bed reactor, stabilizes the polymerization environment in the second fluidized bed reactor, effectively removes the gas phase components from the first fluidized bed reactor, can remove 99.9wt% of hydrogen in the intermediate tank, ensures the generation of polyolefins with higher relative molecular weight in the second fluidized bed reactor, obtains polyolefin products with target molecular weight and distribution, and reduces energy consumption. At the same time, the order and switching time of the control valve group switch set in the discharge system can effectively adjust the pressure difference between the two fluidized bed pressure vessels and the intermediate tank, thereby controlling the discharge rate and realizing stable discharge. It also avoids the problems of reactants flowing through each other between the two fluidized bed reactors and the uneven residence time of polymer particles in the two fluidized bed reactors. The DCS distributed control system can be used to set the sequential control state, program discharge, discharge mode, discharge setting and discharge count, so that the entire discharge program operation becomes flexible and easy to control. The fluidized bed olefin polymerization device and the discharge system for the olefin polymerization device of the present invention and the use method thereof can be used for bimodal polyolefin pilot and industrial devices. With limited equipment investment, the maximum efficiency improvement can be achieved, and energy saving and consumption reduction, production cost reduction, safety improvement and environmental pollution reduction can be achieved, which also provides important technical support for polyolefin production devices.

[0042] In addition, a gas distribution plate is provided in the second fluidized bed reactor of the present invention, and the inlet height of the feed pipeline is 0.1 to 1 m above the gas distribution plate, which can make the reaction more complete.

[0043] The present invention has a more guiding significance for the catalyst feeding system of the polyolefin pilot and small-scale test devices. The present invention can provide strong technical support for the polyolefin continuous production device and improve the stable production efficiency of the polyolefin production device. It also has important guiding significance for the polyolefin polymerization process and the production technology service of the development of new polyolefin products to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 FIG. 1 is a schematic diagram of an olefin polymerization system according to an embodiment of the present invention.

[0045] Wherein, the reference numerals are:

[0046] The first fluidized bed reactor R1

[0047] The second fluidized bed reactor R2

[0048] Tundish V-110

[0049] Buffer tank V-160

[0050] First control valve KV-201

[0051] Second control valve KV-501

[0052] The third control valve KV-301

[0053] Fourth control valve KV-701

[0054] Fifth control valve KV-101

[0055] Sixth control valve KV-601

[0056] Seventh control valve KV-401

[0057] Control valve KV-401

[0058] Circulating air compressor C-1A

[0059] Purge air compressor C-2A

[0060] Discharge pipeline

[0061] Gas phase balance pipeline b

[0062] Branch pipeline c

[0063] Feed line

[0064] Purge gas connection line d

[0065] Circulating gas connecting pipeline DETAILED DESCRIPTION

[0066] The detailed description and technical contents of the present invention are provided in conjunction with the attached Figure 1 The following is a description: Figure 1 The present invention is further described with reference to the following examples: The following examples are only used to more clearly illustrate the technical solutions of the present invention, and are not intended to limit the protection scope of the present invention.

[0067] Figure 1This is a schematic diagram of an embodiment of an olefin polymerization system of the present invention. The present invention performs gas-solid separation by adding an intermediate tank V-110 between dual fluidized bed reactors. The hydrogen, unreacted ethylene and α-olefin gases in the intermediate tank V-110 are removed through the sequential control action of each control valve and the valve switching time in the discharge program. The polyolefin in the intermediate tank V-110 is transported to the second fluidized bed reactor R2 through a pipeline connecting the top of the intermediate tank V-110 with the purge gas of the second fluidized bed reactor R2, and finally a polyolefin product with a target molecular weight and distribution is obtained. The discharge program is controlled by a DCS distributed control system.

[0068] The olefin polymerization system of the present invention comprises a first fluidized bed reactor R1, a second fluidized bed reactor R2, an intermediate tank V-110 disposed between the first fluidized bed reactor R1 and the second fluidized bed reactor R2, and a buffer tank V-160; the top of the intermediate tank V-110 is connected to the middle outlet of the first fluidized bed reactor R1 via a discharge pipeline a, and the bottom of the intermediate tank V-110 is connected to the middle feed port of the second fluidized bed reactor R2 via a feed pipeline e; the first fluidized bed reactor The top of R1 is connected to the top of the intermediate tank V-110 through a gas phase balance pipeline b; a branch pipeline c connected to the buffer tank V-160 is provided on the gas phase balance pipeline b; control valves are provided on the discharge pipeline a, the gas phase balance pipeline b, the branch pipeline c, and the feed pipeline e; the discharge pipeline a is provided with a first control valve KV-201. When the first control valve KV-201 is opened, the product of the first fluidized bed reactor R1 is discharged to the intermediate tank V-110 through the discharge pipeline a under the action of the pressure difference;

[0069] The intermediate tank V-110 is used to stabilize the polymerization environment in the second fluidized bed reactor R2 and remove gas phase components from the first fluidized bed reactor R1.

[0070] In one embodiment, the discharge pipeline a has a horizontal angle greater than 20° and less than 45°, and the length of the pipeline is no more than 2 m, so as to avoid material accumulation and clogging the pipeline, thereby affecting the discharge process.

[0071] In one embodiment, the second fluidized bed reactor R2 adopts a double valve group, and a second control valve KV-501 is provided on the side of the feed pipeline e close to the second fluidized bed reactor R2, and a seventh control valve KV-401 is provided on the side close to the intermediate tank V-110. When the second control valve KV-501 and the seventh control valve KV-401 are opened, the material in the intermediate tank V-110 is transported to the second fluidized bed reactor R2 by the purge gas. After the material transportation is completed, the second control valve KV-501 and the seventh control valve KV-401 are closed, and the control valve on the branch pipeline c is opened to release the pressure of the intermediate tank V-110 and the pipeline to carry out the next discharging procedure.

[0072] In one embodiment, a gas distribution plate is provided in the second fluidized bed reactor R2, and the inlet height of the feed pipeline e is above the gas distribution plate, preferably at a height of 0.1 to 1 m.

[0073] In one embodiment, a third control valve KV-301 is provided on the gas phase balance pipeline b. After the first control valve KV-201 is opened for a period of time, the third control valve KV-301 is opened; when the first control valve KV-201 is closed, the gas phase in the intermediate tank V-110 and the first fluidized bed reactor R1 are mixed to reach equilibrium. When the gas phase pressure in the intermediate tank V-110 is equal to that in the first fluidized bed reactor R1, the third control valve KV-301 is closed; a certain time difference is set between the switching actions of the first control valve KV-201 and the third control valve KV-301 to make it easier to input the product in the first fluidized bed reactor R1 into the intermediate tank V-110, and after the product input is completed, the gas phase pressure in the intermediate tank V-110 and the first fluidized bed reactor R1 reaches equilibrium.

[0074] In one embodiment, a fourth control valve KV-701 is provided on the branch pipeline c. When the fourth control valve KV-701 is opened, the intermediate tank V-110 is depressurized for the second time, and the gas removed from the intermediate tank V-110 enters the buffer tank V-160 and undergoes membrane separation and deep-cold recovery therein.

[0075] In one embodiment, an external circulating gas connecting pipeline f is connected to the pipeline between the first control valve KV-201 and the first fluidized bed reactor R1 and is connected to the circulating gas compressor C-1A, and a fifth control valve KV-101 is provided on the circulating gas connecting pipeline f; when the first fluidized bed reactor R1 reaches the material level height for discharge, the circulating gas is backflushed and the first control valve KV-201 is closed; when the first control valve KV-201 is closed, the fifth control valve KV-101 always remains in an open state until the next discharge procedure starts.

[0076] In one embodiment, a purge gas connecting pipeline d is provided on the top of the intermediate tank V-110 and is connected to the purge gas compressor C-2A. A sixth control valve KV-601 is provided on the purge gas connecting pipeline d. The purge gas is used to transport the material in the intermediate tank V-110 to the second fluidized bed reactor R2, while also protecting the pressure balance and polymerization environment of the second fluidized bed reactor R2.

[0077] In one embodiment, a gas sampling port is provided at the bottom of the intermediate tank V-110, and a ball valve is provided on the pipeline connected to the gas sampling port, so that the gas in the intermediate tank can be sampled and analyzed to determine the gas component content.

[0078] In one embodiment, ethylene homopolymerization or copolymerization is carried out in the first fluidized bed reactor R1, and copolymerization is carried out in the second fluidized bed reactor R2.

[0079] In one embodiment, the reactant of the homopolymerization reaction is one of ethylene, propylene and butene; the reactant of the copolymerization reaction is α-olefin, and the α-olefin is preferably an α-olefin with less than 18 carbon atoms, and more preferably at least one of butene, 4-methyl-1-pentene, hexene and octene.

[0080] In one embodiment, the catalyst used in the homopolymerization reaction or copolymerization reaction is selected from one of a Ziegler-Natta catalyst, a chromium catalyst, a metallocene catalyst and a late transition metal catalyst, and the catalyst used in the second fluidized bed reactor R2 is preferably a metallocene catalyst or a composite thereof.

[0081] In one embodiment, the co-catalyst used in the homopolymerization or copolymerization reaction is an aluminum compound such as an alkyl aluminum or an alkoxy aluminum, preferably at least one of trimethyl aluminum, triethyl aluminum, diethyl aluminum monochloride, tri-n-hexylaluminum and a modified alkyl aluminum compound, and more preferably triethyl aluminum.

[0082] In one embodiment, the reaction pressure of the first fluidized bed reactor R1 is 0.5-5 MPa, preferably 2-3 MPa; the reaction temperature is 80-110°C, preferably 85-100°C.

[0083] In one embodiment, a molecular weight regulator, preferably hydrogen, is used in the reaction in the first fluidized bed reactor R1 and the second fluidized bed reactor R2.

[0084] In one embodiment, the discharge program of the olefin polymerization system is controlled by a DCS distributed control system, and the discharge program setting includes sequential control state, program discharge, discharge mode, discharge setting and discharge count setting.

[0085] In one embodiment, the top of the first fluidized bed reactor R1 and / or the second fluidized bed reactor R2 is an expansion section.

[0086] In one embodiment, the first control valve KV-201, the second control valve KV-501, the third control valve KV-301, the fourth control valve KV-701, the fifth control valve KV-101, the sixth control valve KV-601, and the seventh control valve KV-401 are pneumatic control valves.

[0087] In one embodiment, the reaction product of the first fluidized bed reactor R1 is a low molecular weight polyolefin; and the reaction product of the second fluidized bed reactor R2 is a high molecular weight polyolefin.

[0088] The present invention also provides an olefin polymerization method, which adopts an olefin polymerization system and comprises the following steps:

[0089] (1) When the first fluidized bed reactor R1 reaches the set material level, close the fifth control valve KV-101 on the circulating gas connecting pipeline f;

[0090] (2) Open the first control valve KV-201 on the discharge pipeline a. Under the action of the pressure difference, the product of the first fluidized bed reactor R1 is discharged from the discharge pipeline a to the intermediate tank V-110;

[0091] (3) After a certain period of discharge, the first control valve KV-201 on the discharge pipeline a is closed, and the fifth control valve KV-101 on the circulating gas connecting pipeline f is opened. The closing and opening actions of the first control valve KV-201 and the fifth control valve KV-101 are performed simultaneously, and the fifth control valve KV-101 is always kept open until the next discharge procedure starts;

[0092] (4) After the discharge is completed, the third control valve KV-301 on the gas phase balance pipeline b is opened, and the gas phase components in the intermediate tank V-110 are partially returned to the first fluidized bed reactor R1 due to the pressure difference, until the gas phases in the intermediate tank V-110 and the first fluidized bed reactor R1 are mixed and balanced. After the gas phase pressures are equal, the third control valve KV-301 is closed;

[0093] (5) After the third control valve KV-301 is closed, there is still a certain pressure in the intermediate tank V-110. The fourth control valve KV-701 on the branch pipeline c is opened to discharge the gas components in the intermediate tank V-110 to the buffer tank V-160 for membrane separation and deep cold recovery of the exhaust gas, thereby further decompressing the intermediate tank V-110 and removing 99.9wt% of the hydrogen in the intermediate tank V-110;

[0094] (6) Simultaneously open the sixth control valve KV-601 on the purge gas connecting pipeline d and the second control valve KV-501 on the feed pipeline e to transport the material in the intermediate tank V-110 to the second fluidized bed reactor R2. After the reaction is completed, close the second control valve KV-501 and the sixth control valve KV-601, open the fourth control valve KV-701 on the branch pipeline c, release the pressure of the intermediate tank V-110 and the pipeline, and proceed to the next discharging procedure.

[0095] The present invention further provides an application of an olefin polymerization system in olefin binary copolymerization, ternary copolymerization or tetra- or higher-level copolymerization.

[0096] The present invention will be further described below in conjunction with the embodiments.

[0097] Example 1

[0098] use Figure 1The olefin polymerization system shown in the figure sets the material level discharge height of the first fluidized bed reactor R1, and then starts the reactor program discharge system on the DCS control system to feed the second fluidized bed reactor R2; wherein, the first fluidized bed reactor R1 uses a supported metallocene as the main catalyst, hydrogen as the molecular weight regulator, the polymerization temperature is 85°C, the pressure is 2.0 MPa, the ethylene feed rate is 100 Kg / h, the hydrogen / ethylene (mol / mol) is 1.5±0.05, the butene-1 / ethylene (mol / mol) is 0.19±0.1, the circulation gas velocity is 0.60±0.05 m / s, the catalyst addition amount is 3-4 g / h, and the polyethylene product density obtained is 0.920±0.002 g / cm 3 , a polyethylene copolymer product with a melt index MFR of 13.0±0.2g / 10min (2.16Kg). During the polymerization reaction, the feed amount of butene-1 and hydrogen can be adjusted according to the chromatographic concentration. The second fluidized bed reactor R2 uses Ziegler-Natta as the main catalyst, triethylaluminum as the cocatalyst, hexene-1 as the comonomer, hydrogen as the molecular weight regulator, the polymerization temperature is 85°C, the pressure is 2.0MPa, the ethylene feed amount is 100Kg / h, hydrogen / ethylene (mol / mol) is 0.009±0.05, hexene-1 / ethylene (mol / mol) is 0.005±0.1, the circulation gas velocity is 0.60±0.05m / s, the catalyst addition amount is 3-4g / h, and the density is 0.940±0.002g / cm 3 , linear low-density polyethylene products with melt index MFR1.0±0.2g / 10min(2.16Kg).

[0099] When the first fluidized bed reactor R1 reaches the set material level height, the fifth control valve KV-101 is closed and the first control valve KV-201 is opened. Under the action of the pressure difference, the polymer product is discharged from the discharge pipeline a to the intermediate tank V-110. The first control valve KV-201 is opened for 10 seconds and then closed, ending the discharge to the intermediate tank. At this time, the fifth control valve KV-101 is opened, and the circulating gas back-flushes the discharge port of the first fluidized bed reactor R1. Then the third control valve KV-301 is opened and opened for 13 seconds and then closed. During this period of time, part of the gas phase components in the intermediate tank V-110 return to the expansion section of the first fluidized bed reactor R1 under the action of the pressure difference until the gas phase is balanced. This process is the first decompression of the intermediate tank V-110. Continue to open The fourth control valve KV-701 on the branch pipeline c is opened for 8 seconds and then closed, and the remaining gas in the intermediate tank V-110 is discharged to the buffer tank V-160 for the second decompression. This operation can remove 99.9wt% of the hydrogen component, and the exhaust gas is subjected to membrane separation and deep cold recovery. After the above decompression operation on the intermediate tank V-110, the sixth control valve KV-601 on the purge gas connecting pipeline d and the second control valve KV-501 on the feed pipeline e are opened to transport the polyolefin in the intermediate tank V-110 to the second fluidized bed reactor R2. The two valves are closed for 10 seconds, and the fourth control valve KV-701 is opened to vent the pressure of the intermediate tank V-110 and each pipeline, and the next discharging procedure is carried out. Each discharging process can fill the intermediate tank V-110 with 80% of the polyolefin material of its container volume.

[0100] By sampling the intermediate tank V-110 for gas content analysis, it was found that the volume proportion of hydrogen in the gas components was about 0.1-0.5%, the volume proportion of ethylene was about 10-20%, and the volume proportion of butene-1 was about 70-80%. Ethylene and butene-1 are unreacted monomers, and have little impact on the polymerization environment in the second fluidized bed reactor R2.

[0101] Example 2

[0102] use Figure 1 The olefin polymerization system shown in the figure sets the material level discharge height of the first fluidized bed reactor R1, and then starts the reactor program discharge system on the DCS control system to feed the second fluidized bed reactor R2; wherein, the first fluidized bed reactor R1 uses an inorganic chromium series as the main catalyst, hydrogen as the molecular weight regulator, the polymerization temperature is 110°C, the pressure is 2.3MPa, the ethylene feed rate is 100Kg / h, the hydrogen / ethylene (mol / mol) is 10±0.05, the butene-1 / ethylene (mol / mol) is 0.35±0.1, the oxygen injection amount is 100ppm, the circulation gas velocity is 0.60±0.05m / s, the catalyst addition amount is 7-8g / h, and the polyethylene product density obtained is 0.935±0.002g / cm3 , a polyethylene copolymer product with a melt index MFR of 22.0±0.2g / 10min (2.16Kg). During the polymerization reaction, the feed amount of butene-1 and hydrogen can be adjusted according to the chromatographic concentration. The second fluidized bed reactor R2 uses a chromium series as the main catalyst, hexene-1 as the comonomer, hydrogen as the molecular weight regulator, the polymerization temperature is 100°C, the pressure is 2.2MPa, the ethylene feed amount is 100Kg / h, the hydrogen / ethylene (mol / mol) is 0.009±0.05, the hexene-1 / ethylene (mol / mol) is 0.005±0.1, the circulation gas velocity is 0.60±0.05m / s, the catalyst addition amount is 3-4g / h, and the density is 0.940±0.002g / cm 3 , linear low-density polyethylene products with melt index MFR5.0±0.2g / 10min(2.16Kg).

[0103] When the first fluidized bed reactor R1 reaches the set material level height, the fifth control valve KV-101 is closed and the first control valve KV-201 is opened. Under the action of the pressure difference, the polymer product is discharged from the discharge pipeline a to the intermediate tank V-110. The first control valve KV-201 is opened for 10 seconds and then closed, ending the discharge to the intermediate tank. At this time, the fifth control valve KV-101 is opened, and the circulating gas back-flushes the discharge port of the first fluidized bed reactor R1. Then the third control valve KV-301 is opened and opened for 13 seconds and then closed. During this period of time, part of the gas phase components in the intermediate tank V-110 return to the expansion section of the first fluidized bed reactor R1 under the action of the pressure difference until the gas phase is balanced. This process is the first decompression of the intermediate tank V-110. Continue to open The fourth control valve KV-701 on the branch pipeline c is opened for 8 seconds and then closed, and the remaining gas in the intermediate tank V-110 is discharged to the buffer tank V-160 for the second decompression. This operation can remove 99.9wt% of the hydrogen component, and the exhaust gas is subjected to membrane separation and deep cold recovery. After the above decompression operation on the intermediate tank V-110, the sixth control valve KV-601 on the purge gas connecting pipeline d and the second control valve KV-501 on the feed pipeline e are opened to transport the polyolefin in the intermediate tank V-110 to the second fluidized bed reactor R2. The two valves are closed for 10 seconds, and the fourth control valve KV-701 is opened to vent the pressure of the intermediate tank V-110 and each pipeline, and the next discharging procedure is carried out. Each discharging process can fill the intermediate tank V-110 with 80% of the polyolefin material of its container volume.

[0104] By sampling the intermediate tank V-110 for gas content analysis, it was found that the volume proportion of hydrogen in the gas components was about 0.001-0.01%, the volume proportion of ethylene was about 5-30%, and the volume proportion of butene-1 was about 60-70%. Ethylene and butene-1 are unreacted monomers, and have little impact on the polymerization environment in the second fluidized bed reactor R2.

[0105] Example 3

[0106] use Figure 1 The olefin polymerization system shown in the figure sets the material level discharge height of the first fluidized bed reactor R1, and then starts the reactor program discharge system on the DCS control system to feed the second fluidized bed reactor R2; wherein, the first fluidized bed reactor R1 uses a titanium-based catalyst as the main catalyst, an alkyl magnesium oxide as the carrier, hydrogen as the molecular weight regulator, the polymerization temperature is 90°C, the pressure is 2.2MPa, the ethylene feed rate is 100Kg / h, the hydrogen / ethylene (mol / mol) is 10±0.05, the butene-1 / ethylene (mol / mol) is 0.055±0.001, the circulation gas velocity is 0.60±0.05m / s, the catalyst addition amount is 5-8g / h, and the polyethylene product density obtained is 0.935±0.002g / cm 3 , a polyethylene copolymer product with a melt index MFR of 22.0±0.2g / 10min (2.16Kg). During the polymerization reaction, the feed amount of butene-1 and hydrogen can be adjusted according to the chromatographic concentration. The second fluidized bed reactor R2 does not add a catalyst, uses hexene-1 as a comonomer, does not add hydrogen and a catalyst, the polymerization temperature is 100°C, the pressure is 2.2MPa, the ethylene feed amount is 100Kg / h, the hexene-1 / ethylene (mol / mol) is 0.1±0.1, the circulation gas velocity is 0.60±0.05m / s, and the density is 0.940±0.002g / cm 3 , linear low-density polyethylene products with melt index MFR5.0±0.2g / 10min(2.16Kg).

[0107] When the first fluidized bed reactor R1 reaches the set material level height, the fifth control valve KV-101 is closed and the first control valve KV-201 is opened. Under the action of the pressure difference, the polymer product is discharged from the discharge pipeline a to the intermediate tank V-110. The first control valve KV-201 is opened for 10 seconds and then closed, ending the discharge to the intermediate tank. At this time, the fifth control valve KV-101 is opened, and the circulating gas back-flushes the discharge port of the first fluidized bed reactor R1. Then the third control valve KV-301 is opened and opened for 13 seconds and then closed. During this period of time, part of the gas phase components in the intermediate tank V-110 return to the expansion section of the first fluidized bed reactor R1 under the action of the pressure difference until the gas phase is balanced. This process is the first decompression of the intermediate tank V-110. Continue to open The fourth control valve KV-701 on the branch pipeline c is opened for 8 seconds and then closed, and the remaining gas in the intermediate tank V-110 is discharged to the buffer tank V-160 for the second decompression. This operation can remove 99.9wt% of the hydrogen component, and the exhaust gas is subjected to membrane separation and deep cold recovery. After the above decompression operation on the intermediate tank V-110, the sixth control valve KV-601 on the purge gas connecting pipeline d and the second control valve KV-501 on the feed pipeline e are opened to transport the polyolefin in the intermediate tank V-110 to the second fluidized bed reactor R2. The two valves are closed for 10 seconds, and the fourth control valve KV-701 is opened to vent the pressure of the intermediate tank V-110 and each pipeline, and the next discharging procedure is carried out. Each discharging process can fill the intermediate tank V-110 with 80% of the polyolefin material of its container volume.

[0108] By sampling the gas content in the intermediate tank V-110 for analysis, the volume proportion of ethylene is about 10-30%, and the volume proportion of butene-1 is about 20-70%. Ethylene and butene-1 are unreacted monomers, and have little impact on the polymerization environment in the second fluidized bed reactor R2.

[0109] Comparative Example 1

[0110] The difference from Example 1 is that no intermediate tank is arranged between the first fluidized bed reactor and the second fluidized bed reactor, the first fluidized bed reactor and the second fluidized bed reactor are directly connected through the discharge pipeline a, the branch pipeline c is directly connected to the discharge pipeline a, and the rest is the same as Example 1.

[0111] After setting the discharge height of the first fluidized bed reactor R1, the reactor program discharge system is started on the DCS control system to feed the second fluidized bed reactor R2; wherein, the first fluidized bed reactor R1 uses a supported metallocene as the main catalyst, hydrogen as the molecular weight regulator, the polymerization temperature is 85°C, the pressure is 2.0MPa, the ethylene feed rate is 100Kg / h, the hydrogen / ethylene (mol / mol) is 1.5±0.05, the butene-1 / ethylene (mol / mol) is 0.19±0.1, the circulation gas velocity is 0.60±0.05m / s, the catalyst addition amount is 3-4g / h, and the polyethylene product density obtained is 0.920±0.002g / cm 3 , a polyethylene homopolymer product with a melt index MFR of 13.0±0.2g / 10min (2.16Kg). During the polymerization reaction, the feed amount of butene-1 and hydrogen can be adjusted according to the chromatographic concentration. The second fluidized bed reactor R2 uses Ziegler-Natta as the main catalyst, triethylaluminum as the cocatalyst, hexene-1 as the comonomer, hydrogen as the molecular weight regulator, the polymerization temperature is 85°C, the pressure is 2.0MPa, the ethylene feed amount is 100Kg / h, hydrogen / ethylene (mol / mol) is 0.009±0.05, hexene-1 / ethylene (mol / mol) is 0.005±0.1, the circulation gas velocity is 0.60±0.05m / s, the catalyst addition amount is 3-4g / h, and the density is 0.940±0.002g / cm 3 , linear low-density polyethylene products with melt index MFR1.0±0.2g / 10min(2.16Kg).

[0112] When the first fluidized bed reactor R1 reaches the set material level height, the fifth control valve KV-101 is closed and the first control valve KV-201 is opened. Under the action of the pressure difference, the polymer product is discharged from the discharge pipeline a to the second fluidized bed reactor R2. The first control valve KV-201 is opened for 10 seconds and then closed, ending the discharge to the second fluidized bed reactor R2. At this time, the fifth control valve KV-101 is opened, and the circulating gas back-flushes the discharge port of the first fluidized bed reactor R1. It is opened for 13 seconds and then closed. The fourth control valve KV-701 on the branch pipeline c is continued to be opened for 8 seconds and then closed. The remaining gas in the first fluidized bed reactor R1 is discharged to the buffer tank V-160 for the second decompression. This operation can remove 50wt% of the hydrogen component, and the exhaust gas is subjected to membrane separation and deep cold recovery sections.

[0113] By analyzing the content of the gas before entering the second fluidized bed reactor R2, it was measured that the volume proportion of hydrogen in the gas components was about 10%, the volume proportion of ethylene was about 30%, and the volume proportion of butene-1 was about 60%.

[0114] It can be seen from the results of Example 1 and Comparative Example 1 that the present invention optimizes the discharging system of the olefin polymerization process, and the newly added intermediate tank between the first fluidized bed reactor and the second fluidized bed reactor stabilizes the polymerization environment in the second fluidized bed reactor, effectively removes the gas phase components from the first fluidized bed reactor, and can remove 99.9wt% of the hydrogen in the intermediate tank, thereby ensuring the production of polyolefins with a higher relative molecular weight in the second fluidized bed reactor, obtaining polyolefin products with target molecular weight and distribution, and reducing energy consumption.

[0115] The above description is only a preferred embodiment of the present invention. It should be noted that for ordinary technicians in this technical field, several improvements can be made without departing from the present invention, and these improvements should also be regarded as the protection scope of the present invention.

Claims

1. An olefin polymerization system, characterized in that: include: A first fluidized bed reactor, a second fluidized bed reactor, an intermediate tank disposed between the first fluidized bed reactor and the second fluidized bed reactor, and a buffer tank; the top of the intermediate tank is connected to the middle outlet of the first fluidized bed reactor via a discharge pipeline, and the bottom of the intermediate tank is connected to the middle feed port of the second fluidized bed reactor via a feed pipeline; the top of the first fluidized bed reactor is connected to the top of the intermediate tank via a gas phase balance pipeline; a branch pipeline connected to the buffer tank is disposed on the gas phase balance pipeline; the discharge pipeline, the gas phase balance pipeline, the branch pipeline, and the feed pipeline are all provided with control valves; The discharge pipeline is provided with a first control valve. When the first control valve is opened, the product of the first fluidized bed reactor is discharged to the intermediate tank through the discharge pipeline under the action of pressure difference. The intermediate tank is used to stabilize the polymerization environment in the second fluidized bed reactor and remove gas phase components from the first fluidized bed reactor; The second fluidized bed reactor is provided with a gas distribution plate, and the inlet height of the feed pipeline is above the gas distribution plate, and the height is 0.1-1 m.

2. The olefin polymerization system according to claim 1, characterized in that: The discharge pipeline has a horizontal angle greater than 20° and less than 45°, and the length of the pipeline is no more than 2m.

3. The olefin polymerization system according to claim 1, characterized in that: The second fluidized bed reactor adopts a double valve group, wherein a second control valve is provided on the side of the feed pipeline close to the second fluidized bed reactor, and a seventh control valve is provided on the side close to the intermediate tank. When the second control valve and the seventh control valve are opened, the material in the intermediate tank is transported to the second fluidized bed reactor by the purge gas. After the material transportation is completed, the second control valve and the seventh control valve are closed, and the control valve on the branch pipeline is opened to release the pressure of the intermediate tank and the pipeline, and the next discharge procedure is carried out; A third control valve is provided on the gas phase balance pipeline. When the first control valve is opened for a period of time, the third control valve is opened again. When the first control valve is closed, the gas phases in the intermediate tank and the first fluidized bed reactor are mixed and balanced. When the gas phase pressures in the intermediate tank and the first fluidized bed reactor are equal, the third control valve is closed. A certain time difference is set between the switching actions of the first control valve and the third control valve, so that the product in the first fluidized bed reactor can be more easily input into the intermediate tank, and after the product input is completed, the gas phase pressures in the intermediate tank and the first fluidized bed reactor are balanced. The branch pipeline is provided with a fourth control valve. When the fourth control valve is opened, the intermediate tank is depressurized for a second time, and the gas removed from the intermediate tank enters the buffer tank and undergoes membrane separation and deep-cold recovery therein.

4. The olefin polymerization system according to claim 1, characterized in that: The pipeline between the first control valve and the first fluidized bed reactor is connected to an external circulating gas connecting pipeline and a circulating gas compressor, and a fifth control valve is arranged on the circulating gas connecting pipeline; when the first fluidized bed reactor reaches the material level of discharge, the circulating gas is backflushed and the first control valve is closed; when the first control valve is closed, the fifth control valve is always kept open until the next discharge procedure starts.

5. The olefin polymerization system according to claim 1, characterized in that: A purge gas connecting pipeline is provided on the top of the intermediate tank and is connected to a purge gas compressor. A sixth control valve is provided on the purge gas connecting pipeline. The purge gas is used to transport the material in the intermediate tank to the second fluidized bed reactor, while also protecting the pressure balance and polymerization environment of the second fluidized bed reactor.

6. The olefin polymerization system according to claim 1, characterized in that: Ethylene homopolymerization or copolymerization is carried out in the first fluidized bed reactor, and copolymerization is carried out in the second fluidized bed reactor. The reaction product of the first fluidized bed reactor is a low relative molecular mass polyolefin; the reaction product of the second fluidized bed reactor is a high relative molecular mass polyolefin.

7. The olefin polymerization system according to claim 6, characterized in that: The reactant of the homopolymerization reaction is one of ethylene, propylene and butene; the reactant of the copolymerization reaction is α-olefin; the catalyst used in the homopolymerization reaction or the copolymerization reaction is selected from one of Ziegler-Natta catalyst, chromium catalyst, metallocene catalyst and late transition metal catalyst, and the catalyst used in the second fluidized bed reactor is a metallocene catalyst or a composite thereof; the co-catalyst used in the homopolymerization reaction or the copolymerization reaction is an alkyl aluminum or alkoxy aluminum compound.

8. The olefin polymerization system according to claim 1, characterized in that: The reaction pressure of the first fluidized bed reactor is 0.5-5 MPa; the reaction temperature is 80-120° C.; a molecular weight regulator is used in the reactions in the first fluidized bed reactor and the second fluidized bed reactor.

9. The olefin polymerization system according to claim 1, characterized in that: The top of the first fluidized bed reactor and / or the second fluidized bed reactor is an expansion section; the first control valve, the second control valve, the third control valve, the fourth control valve, the fifth control valve, the sixth control valve, and the seventh control valve are pneumatic control valves.

10. An olefin polymerization method, characterized in that: The olefin polymerization system according to any one of claims 1 to 9 comprises the following steps: (1) When the first fluidized bed reactor reaches the set material level, close the fifth control valve on the circulating gas connecting pipeline; (2) opening the first control valve on the discharge pipeline, and under the action of the pressure difference, the product of the first fluidized bed reactor is discharged from the discharge pipeline a to the intermediate tank; (3) After a certain period of time of discharging, the first control valve on the discharging pipeline is closed, and the fifth control valve on the circulating gas connecting pipeline is opened. The closing and opening actions of the first control valve and the fifth control valve are performed simultaneously, and the fifth control valve is always kept open until the next discharging procedure starts; (4) After the discharge is completed, the third control valve on the gas phase balance pipeline is opened, and the gas phase components in the intermediate tank are partially returned to the first fluidized bed reactor due to the pressure difference, until the gas phases in the intermediate tank V-110 and the first fluidized bed reactor are mixed and balanced. After the gas phase pressures are equal, the third control valve is closed; (5) After the third control valve is closed, there is still a certain pressure in the intermediate tank. The fourth control valve on the branch pipeline is opened to discharge the gas components in the intermediate tank to the buffer tank for membrane separation and cryogenic recovery of the exhaust gas, thereby further reducing the pressure of the intermediate tank and removing 99.9wt% of the hydrogen in the intermediate tank; (6) Open the sixth control valve on the purge gas connecting pipeline and the second control valve on the feed pipeline at the same time to transport the material in the intermediate tank to the second fluidized bed reactor. After the reaction is completed, close the second control valve and the sixth control valve, open the fourth control valve on the branch pipeline, release the pressure of the intermediate tank and the pipeline, and proceed to the next discharge procedure.

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