An olefin polymerization apparatus for producing a polyolefin and a method of producing a polyolefin

Abstract

This invention discloses an olefin polymerization apparatus and method for producing polyolefins. Through flexible combination of fluidized bed reactors and degassing of polyethylene particles discharged from the reactors, it is possible to produce polyethylene or polyethylene block copolymer resin products with a wide molecular weight distribution / multimodal structure. This invention adds a pipeline connecting the top of the intermediate tank to the reactor purge gas, used to transport polyethylene particles from the intermediate tank to the corresponding polymerization reactor. This stabilizes the polymerization environment within the reactor and effectively removes gaseous components from the previous reactor during this transport process; for example, it can remove 99.9 wt% of hydrogen from the intermediate tank, ensuring the formation of polyolefins with a higher relative molecular mass in the second reactor, obtaining polyethylene products with the target molecular weight and distribution, simplifying existing production processes and reducing energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of olefin polymerization technology, specifically relating to an olefin polymerization apparatus and a method for producing polyolefins. Background Technology

[0002] Wide molecular weight distribution / multimodal polyethylene resin can significantly improve the processing performance of polyethylene (PE) without significantly compromising its physical properties. Using it to process films, blow-molded bottles, pipes, and profiles, products with the same performance as traditional PE can be manufactured, significantly reducing raw material consumption. Furthermore, wide molecular weight distribution / multimodal polyethylene resin is highly recyclable, and the mechanical properties of recycled resin are superior to those of single-peak polyethylene resin used for the first time. The production technology of wide / multimodal polyethylene is developing rapidly, with three production methods: (1) Melt blending method, which uses parallel reactors. This method requires complete and uniform polymer mixing, is costly, and makes it difficult to achieve uniform polyethylene product quality; (2) Single-stage reaction method, which uses a multi-active-center catalyst in a single reactor, utilizing the different polymerization behaviors of different active centers to prepare wide / multimodal polyethylene. Due to the difficulty in catalyst matching and process control, it is not yet widely used; (3) Segmented reaction method, which uses two or more reactors connected in series for polymerization. This method offers better flexibility, allows for a wide range of polyethylene resin grades, and is currently the mainstream method for producing wide / multimodal polyethylene.

[0003] Among all polyethylene production processes, fluidized bed polyethylene production accounts for half of the polyethylene production capacity due to its advantages such as solvent-free operation, low equipment investment, energy saving, and environmental friendliness. Currently, dual fluidized bed reactors are commercially available for producing multi-molecular-weight polyethylene resin products. The polymerization technology involves generating a copolymer with a high melt flow rate (MI) and low relative molecular mass in the first fluidized bed reactor. This copolymer, along with catalysts, then enters the second fluidized bed reactor for further polymerization into a copolymer product with a low MI and high relative molecular mass. This process suffers from problems such as cross-flow of reactants between the two fluidized bed reactors, uneven residence time of polymer particles in the two gas-phase reactors, and limited circulation of polymer particles between reactors with different reaction conditions. Before feeding the low-molecular-weight polymer polymerized in the first fluidized bed reactor into the second fluidized bed reactor, all raw materials from the first reactor must be removed. This process also suffers from disadvantages such as high investment in discharge equipment, low efficiency, and high operating costs.

[0004] Dow Chemical Company developed chain shuttle technology based on reversible chain transfer reactions, resulting in high-density polyethylene-low-density polyethylene-based multiblock polymers (OBCs) with superior processing performance, high-temperature elasticity, good abrasion resistance, and excellent compression set characteristics, making them suitable for various applications. Patent CN 200480030566.3 discloses a multi-zone circulating reactor and method for producing polyolefins with a bimodal molecular weight distribution. This reactor is characterized by an interconnected rising section in a rapidly fluidized state and a descending section in a moving bed state. A problem with this patent is the existence of reactant gas cross-flow, and the descending section in the moving bed state cannot be applied to the production of polyethylene, which has high exothermic properties. Patent CN 102060943A discloses a method for preparing bimodal polyethylene and a gas-phase reactor comprising at least four fluidized beds. In this method, polymer particles are bubbling fluidized in a first or third reactor. Fine powder from the polymer particles is entrained and blown into a second or fourth reactor, which is in a rapidly fluidized state, due to a sifting effect. The fine polymer powder enters a cyclone separator from the outlet of the second or fourth reactor for gas-solid separation. The circulating gas returns to the reactor under the same reaction conditions via a loop; the solid polymer particles enter another bubbling bed with different reaction conditions. This method suffers from complex operation and limitations on the amount of fine powder entrained, restricting the circulation of polymer particles between reactors with different reaction conditions. Patent CN107405593B discloses an olefin polymerization apparatus and an olefin polymerization method. The apparatus or method provided by this invention enables the condensation of gaseous material discharged from the polymerization reactor. After gas-liquid separation, part of the generated gas is recycled back to the reactor to form a loop. The condensate can be selectively introduced into the polymerization reactor to achieve free switching between homopolymerization and copolymerization reactions or between different copolymerization reactions. Simultaneously, the condensate can absorb the heat generated by the reaction. However, the apparatus and method provided by this invention require high energy consumption to enable the gas discharged from the polymerization reactor to pass through condensation and gas-liquid separation. Setting up a polymerization reactor cannot achieve the switching between continuous olefin homopolymerization and copolymerization reactions.

[0005] Although methods for preparing broad molecular weight distribution / multimodal polyethylene resins are well-established and many methods for removing all gaseous components from the first reactor are known and described, there is still a need to develop an olefin polymerization apparatus for producing polyolefins and a discharge system for the olefin polymerization apparatus, as well as methods for its use. Summary of the Invention

[0006] To address the above-mentioned technical problems, the present invention aims to provide an olefin polymerization apparatus for producing polyolefins and a method for producing polyolefins.

[0007] This invention provides an olefin polymerization apparatus for producing polyolefins, comprising:

[0008] A first fluidized bed reactor, wherein a first circulating gas pipeline a is provided between the top and bottom of the first fluidized bed reactor;

[0009] The first intermediate tank has its inlet connected to the outlet of the first fluidized bed reactor via a first discharge pipeline b, which is equipped with a control valve. The top of the first intermediate tank is connected to the top of the first fluidized bed reactor via a first gas phase balance pipeline c, which is equipped with a control valve.

[0010] The second fluidized bed reactor has its inlet connected to the outlet of the first intermediate tank via a feed line f, which is equipped with a control valve. A second circulating gas line g is provided between the top and bottom of the second fluidized bed reactor. A first purge gas line e, which is connected to the top of the first intermediate tank, is provided at the top of the second fluidized bed reactor for purging the first intermediate tank. A purge gas compressor is provided on the first purge gas line.

[0011] The second intermediate tank has its inlet connected to the outlet of the second fluidized bed reactor via a second discharge pipeline h, which is equipped with a control discharge valve. The top of the second intermediate tank is connected to the top of the second fluidized bed reactor via a second gas phase balance pipeline i, which is equipped with a control valve. The top of the second intermediate tank is connected to the top of the first fluidized bed reactor via a second purge pipeline k, which is used to purge the second intermediate tank. The purge pipeline is equipped with a purge gas compressor. The outlet of the second intermediate tank is connected to the first fluidized bed reactor.

[0012] A polymer devolatilization tank, wherein the inlet of the polymer devolatilization tank is connected to the outlet of the first intermediate tank and the outlet of the second intermediate tank;

[0013] A condensate storage tank is provided, with its inlet connected to the top of the first intermediate tank, the top of the second intermediate tank, and the top of the polymer devolatilization tank via a pressure relief pipeline. A heat exchanger is located upstream of the condensate storage tank's inlet.

[0014] The olefin polymerization apparatus for producing polyolefins according to the present invention has a compressor and a heat exchanger on both the first and second circulating gas pipelines.

[0015] The olefin polymerization apparatus for producing polyolefins according to the present invention has a second intermediate tank outlet connected to the first fluidized bed reactor for conveying the material in the second intermediate tank to the first fluidized bed reactor.

[0016] The olefin polymerization apparatus for producing polyolefins according to the present invention includes a first fluidized bed reactor and a second fluidized bed reactor, both of which include a straight section and an enlarged section, and both are equipped with gas distribution plates inside.

[0017] The olefin polymerization apparatus for producing polyolefins according to the present invention includes a jacket on the outside of the polymer devolatilization tank for controlling the temperature of the polymer devolatilization tank; and a stirring device inside the polymer devolatilization tank.

[0018] The present invention also provides a method for producing polyolefins using the apparatus described above, comprising the following steps:

[0019] S1, add polymerization monomers and catalyst to the first fluidized bed reactor to carry out polymerization reaction. After the material level in the first fluidized bed reactor reaches the predetermined height, connect the first discharge pipeline to transport the polymerization product in the first fluidized bed reactor to the first intermediate tank. After the discharge is completed, close the first discharge pipeline and connect the first gas phase balance pipeline to transport the gas phase component in the first intermediate tank to the first fluidized bed reactor. After the gas phase in the first intermediate tank and the first fluidized bed reactor is balanced, disconnect the first gas phase balance pipeline and continue to open the pressure relief pipeline between the first intermediate tank and the condensate storage tank to release the pressure in the first intermediate tank and the first gas phase balance pipeline and then close the pressure relief pipeline.

[0020] S2, connect the first purge gas pipeline between the second fluidized bed reactor and the first intermediate tank to transport the polymerization product in the first intermediate tank to the second fluidized bed reactor for polymerization reaction. After the material level in the second fluidized bed reactor reaches the set height, connect the second discharge pipeline to transport the polymerization product in the second fluidized bed reactor to the second intermediate tank. After the discharge is completed, close the second discharge pipeline and connect the second gas phase balance pipeline to transport the gas phase component in the second intermediate tank to the second fluidized bed reactor. After the gas phase in the second intermediate tank and the second fluidized bed reactor is balanced, disconnect the second gas phase balance pipeline and continue to open the pressure relief pipeline between the second intermediate tank and the condensate storage tank to release the pressure in the second intermediate tank and the second gas phase balance pipeline and then close the pressure relief pipeline.

[0021] S3, connect the second purge gas pipeline between the first fluidized bed reactor and the second intermediate tank to transport part of the polymerization product in the second intermediate tank to the first fluidized bed reactor for polymerization reaction. After the material level in the first fluidized bed reactor reaches the set height, the polymerization product is transported to the polymer devolatilization tank for devolatilization treatment. Part of the polymerization product in the second intermediate tank is directly transported to the polymer devolatilization tank for devolatilization treatment. After the devolatilization treatment is completed, the polymer product is transported to the granulation system for granulation. The gas generated by devolatilization is transported to the condensate storage tank through the pressure relief pipeline.

[0022] In the method for producing polyolefins according to the present invention, the mass ratio of the capacity of the first fluidized bed reactor and the second fluidized bed reactor is 0.5:5, preferably 1:3.

[0023] In the method for producing polyolefins described in this invention, the polyethylene produced in the second fluidized bed reactor is returned to the first fluidized bed reactor for polymerization at a mass ratio of 1:(1-10), preferably 1:4, and more preferably 1:3.

[0024] The method for producing polyolefins according to the present invention includes a first fluidized bed reactor for homopolymerization or copolymerization, and a second fluidized bed reactor for copolymerization.

[0025] Beneficial effects of this invention:

[0026] This invention discloses an ethylene polymerization process that, through the flexible combination of fluidized bed reactors and the degassing of polyethylene particles discharged from the reactors, can produce polyethylene or polyethylene block copolymer resin products with a wide molecular weight distribution / multi-peak structure. This invention adds a pipeline connecting the top of the intermediate tank to the reactor purge gas, used to transport polyethylene particles from the intermediate tank to the corresponding polymerization reactor. This stabilizes the polymerization environment within the reactor and effectively removes gaseous components from the previous reactor during this transport process; for example, it can remove 99.9 wt% of hydrogen from the intermediate tank, ensuring the formation of higher relative molecular mass polyolefins in the second reactor, resulting in polyethylene products with the target molecular weight and distribution. This simplifies existing production processes and reduces energy consumption. Simultaneously, by controlling the sequence and timing of the opening and closing of the control valve group in the discharge system, the pressure difference between the two fluidized bed pressure vessels and the intermediate tank can be effectively adjusted, thereby controlling the discharge rate and achieving stable discharge. This also avoids problems such as cross-flow of reactants between the two fluidized bed reactors and uneven residence time of polymer particles in the two fluidized bed reactors. The DCS (Distributed Control System) allows for the setting of sequential control status, programmatic discharge, discharge mode, discharge settings, and discharge counting, making the entire discharge process flexible and easy to control. With limited equipment investment, it achieves maximum efficiency gains, energy conservation and consumption reduction, lower production costs, improved safety, and reduced environmental pollution, providing crucial technical support for polyolefin production plants. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the olefin polymerization apparatus for producing polyolefins according to the present invention.

[0028] In the attached figures, the following labels are used:

[0029] R-1 First Fluidized Bed Reactor

[0030] R-2 Second Fluidized Bed Reactor

[0031] KV-101, KV-102, KV-103, KV-104, KV-105, KV-106, KV-107, KV-108, KV-109, KV-110, KV-111, KV-112, KV-113, KV-114, KV-115 control valve

[0032] 1.7 Expanded Section

[0033] 2, 8 straight sections

[0034] 3, 9 Gas distribution plate

[0035] Compressors 4, 10, 13, and 14

[0036] Heat exchangers 5, 11, and 15

[0037] 6, 12 Material Inlet Points

[0038] 16 Condensate Storage Tank

[0039] 17 Polymer devolatilization tank

[0040] 18 First Intermediate Tank

[0041] 19 Second Intermediate Tank

[0042] a First circulating gas pipeline

[0043] b First discharge pipeline

[0044] c First gas phase balance pipeline

[0045] pressure relief pipelines of branches d, j, and n

[0046] e First purge gas line

[0047] f, l, m, p feed lines

[0048] g Second circulating gas pipeline

[0049] h Second discharge pipeline

[0050] i Second gas phase balance pipeline

[0051] k Second purge pipeline

[0052] o Pressure relief pipeline Detailed Implementation

[0053] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0054] An olefin polymerization apparatus for producing polyolefins includes a first fluidized bed reactor R-1, a first intermediate tank 18, a second fluidized bed reactor R-2, a second intermediate tank 19, a polymer devolatilization tank 17, and a condensate storage tank 16.

[0055] The first fluidized bed reactor R-1 is a conventional device in the art, including a straight section 2 and an enlarged section 1. It is equipped with a gas distribution plate 3 inside. The side wall of the straight section 2 is equipped with a material inlet point 6. The raw materials required for the reaction process are transported into the reactor through the material inlet point 6 for reaction. A first circulating gas pipeline a is provided between the top and bottom of the first fluidized bed reactor R-1. The first circulating gas pipeline a is equipped with a compressor 4 and a heat exchanger 5. The gaseous raw materials that have not been reacted during the polymerization process can be circulated through the first circulating pipeline a for reaction.

[0056] The inlet of the first intermediate tank 18 is connected to the outlet of the first fluidized bed reactor R-1 through the first discharge pipeline b. The first discharge pipeline is equipped with a control valve KV-101. The top of the first intermediate tank 18 is connected to the top of the first fluidized bed reactor R-1 through the first gas phase balance pipeline c. The first gas phase balance pipeline c is equipped with a control valve KV-102. The first intermediate tank 18 is used to store the polymerization product prepared by the first fluidized bed reactor R-1. When the material level in the first fluidized bed reactor R-1 reaches the discharge height, the control valve KV-101 is opened. Under the action of pressure difference, the polymerization product in the first fluidized bed reactor R-1 is discharged into the first intermediate tank 18. After the discharge process is completed, the control valve KV-102 is opened. At this time, part of the gas phase component in the first intermediate tank 18 returns to the first fluidized bed reactor R-1 under the action of pressure difference until the gas phase mixing reaches equilibrium, that is, the gas phase pressure is equal. The first gas phase equilibrium line c is also equipped with a branch pressure relief line d connected to the condensate storage tank 16. The branch pressure relief line d is equipped with a control valve KV-103. When the control valve KV-103 is opened, the first intermediate tank 18 is subjected to secondary pressure reduction. After the removed gas is heated by the heat exchanger 15, the condensate enters the condensate storage tank 16. The discharge line of the condensate storage tank 16 is equipped with a control valve KV-114. The uncondensed gas enters the membrane separation and cryogenic recovery system.

[0057] The feed inlet of the second fluidized bed reactor R-2 is connected to the outlet of the first intermediate tank 18 via a feed line f, which is equipped with a control valve KV-105. A second circulating gas line g is located between the top and bottom of the second fluidized bed reactor R-2. The second circulating gas line g is equipped with a compressor 10 and a heat exchanger 11. Unreacted gaseous raw materials during polymerization can be circulated through the second circulating gas line g. The top of the second fluidized bed reactor R-2 is also equipped with a first purge gas line e, which is connected to the top of the first intermediate tank 18 for purging the first intermediate tank 18. The first purge gas line e is equipped with a purge gas compressor 13. The polymerization product obtained in the first fluidized bed reactor R-1 undergoes further polymerization in the second fluidized bed reactor R-2.

[0058] The second fluidized bed reactor R-2 is a conventional device in the field, including a straight section 9 and an enlarged section 7. It is equipped with a gas distribution plate 9 inside and a material inlet point 12 on the side wall of the straight section 9. The raw materials required for the reaction process are transported to the inside of the reactor through the material inlet point for reaction.

[0059] The inlet of the second intermediate tank 19 is connected to the outlet of the second fluidized bed reactor R-2 via a second discharge pipeline h, which is equipped with a control discharge valve KV-106. The top of the second intermediate tank 19 is connected to the top of the second fluidized bed reactor R-2 via a second gas phase balance pipeline i, which is equipped with a control valve KV-107. The top of the second intermediate tank 19 is connected to the top of the first fluidized bed reactor R-1 via a second purge pipeline k for purging the second intermediate tank 19, and the second purge pipeline k is equipped with a purge gas compressor 14. The outlet of the second intermediate tank 19 is connected to the first fluidized bed reactor R-1. The second intermediate tank 19 is used to store the polymerization product prepared by the second fluidized bed reactor R-2. When the material level in the second fluidized bed reactor R-2 reaches the discharge height, the control valve KV-106 is opened, and the material is discharged into the second intermediate tank 19 under the action of pressure difference. After the discharge process is completed, the control valve KV-107 is opened. At this time, part of the gas phase component in the second intermediate tank 19 returns to the second fluidized bed reactor under the action of pressure difference until the gas phase mixing reaches equilibrium, that is, the gas phase pressure is equal.

[0060] The second gas phase balance line i is also equipped with a branch pressure relief line j connected to the condensate storage tank 16. The branch pressure relief line j is equipped with a control valve KV-108. When the control valve KV-108 is opened, the second intermediate tank 19 is subjected to secondary pressure reduction. After the removed gas is heated by the heat exchanger 15, the condensate enters the condensate storage tank 16, and the uncondensed gas enters the membrane separation and cryogenic recovery system.

[0061] The inlet of the polymer devolatilization tank 17 is connected to the outlet of the first intermediate tank R-1 via a feed line m. A control valve KV-111 is installed on the feed line m to transport the material in the first intermediate tank 18 to the polymer devolatilization tank 17. The inlet of the polymer devolatilization tank 17 is also connected to the outlet of the second intermediate tank 19 via a feed line p. A control valve KV-110 is installed on the feed line p to transport the material in the second intermediate tank 19 to the polymer devolatilization tank 17. The top of the polymer devolatilization tank 17 is connected to the condensate storage tank 16 via a pressure relief line n. A control valve KV-113 is installed on the pressure relief line n. After the desorbed gas is heated by the heat exchanger 15, the condensate enters the condensate storage tank 16, and the uncondensed gas enters the membrane separation and cryogenic recovery system. The polymer devolatilization tank 17 is a conventional device in the art. In this invention, the polymer devolatilization tank 17 is provided with a jacket on the outside to control the temperature of the polymer devolatilization tank. The polymer devolatilization tank 17 is provided with a stirring device to help gas-solid separation. The discharge pipeline of the polymer devolatilization tank 17 is provided with a control valve KV-115 to send the degassed solid material into the granulation system.

[0062] In another embodiment of the present invention, the outlet of the second intermediate tank 19 is connected to the first fluidized bed reactor R-1 through the feed pipeline l for conveying the material in the second intermediate tank 19 to the first fluidized bed reactor R-1. The feed pipeline l is equipped with a control valve KV-112, which can selectively convey the product obtained by polymerization in the second fluidized bed reactor R-2 to the first fluidized bed reactor R-1 for further polymerization reaction.

[0063] The apparatus of this invention, by adding different comonomers to two or more fluidized bed reactors in series, induces ethylene copolymerization, thereby obtaining polyethylene resin with a wide molecular weight distribution / multimodal structure or block polyethylene resin. To achieve the synthesis of the aforementioned polyethylene resin products, reaction conditions different from those in the first fluidized bed reactor can be selected in the second fluidized bed reactor or subsequent reaction vessel. These conditions can be varied by changing parameters such as the catalyst injection amount, comonomer type, polymerization time, chain transfer agent to catalyst ratio, polymerization temperature, and pressure. The polymer obtained from the first gas-phase reaction vessel is transferred to the second gas-phase reaction vessel, where the catalyst components carried by the polymer particles continue to exert their catalytic activity. Polymerization continues under different reaction conditions in the second gas-phase reaction vessel. Therefore, by maintaining different gas-phase mixtures in each gas-phase reaction vessel, even different polymer fragments can grow on the same particles.

[0064] In the embodiments of preparing polyethylene resins or polyethylene block copolymer resins with different wide molecular weight distributions / multimodalities using the gas-phase polymerization of ethylene using this process, the synthesis of the above copolymers can be obtained by maintaining different concentrations of chain terminators in each reactor and changing the type and content of comonomers. In the ethylene polymerization process of the present invention, the polymer generated from the first fluidized bed reactor is degassed and then transferred to the second fluidized bed reactor for further polymerization to form polyethylene resins with different wide molecular weight distributions / multimodalities. The polymer generated from the second fluidized bed reactor is degassed and then transferred back to the first fluidized bed reactor for further polymerization to form polyethylene block copolymer resins. When the polymer is directly transferred from the first fluidized bed reactor to the second fluidized bed reactor, or from the second fluidized bed reactor to the first fluidized bed reactor, it is necessary to effectively remove the gaseous components from the other reactors to avoid affecting the polymerization conditions in other reactors. Therefore, the discharge system provided by this ethylene polymerization process can meet the requirements and realize the production of polyethylene resins with wide molecular weight distributions / multimodalities or block polyethylene resins.

[0065] The present invention also provides a method for producing polyolefins, comprising the following steps:

[0066] S1, add polymerization monomers and catalyst to the first fluidized bed reactor R-1 to carry out polymerization reaction. After the material level in the first fluidized bed reactor R-1 reaches the predetermined height, connect the first discharge pipeline b to transport the polymerization product in the first fluidized bed reactor R-1 to the first intermediate tank 18. After the discharge is completed, close the first discharge pipeline b and connect the first gas phase balance pipeline c to transport the gas phase component in the first intermediate tank 18 to the first fluidized bed reactor R-1. After the gas phase in the first intermediate tank 18 and the first fluidized bed reactor R-1 is balanced, disconnect the first gas phase balance pipeline c and continue to open the branch pressure relief pipeline d between the first intermediate tank 18 and the condensate storage tank 16 to release the pressure in the first intermediate tank 18 and the first gas phase balance pipeline c, and then close the branch pressure relief pipeline d.

[0067] S2, connect the first purge gas pipeline e between the second fluidized bed reactor R-2 and the first intermediate tank 18 to transport the polymerization product in the first intermediate tank 18 to the second fluidized bed reactor R-2 for polymerization reaction. After the material level in the second fluidized bed reactor R-2 reaches the set height, connect the second discharge pipeline h to transport the polymerization product in the second fluidized bed reactor R-2 to the second intermediate tank 19. After the discharge is completed, close the second discharge pipeline h and connect the second gas phase balance pipeline i to transport the gas phase component in the second intermediate tank 19 to the second fluidized bed reactor R-2. After the gas phase in the second intermediate tank 19 and the second fluidized bed reactor R-2 is balanced, disconnect the second gas phase balance pipeline i and continue to open the branch pressure relief pipeline j between the second intermediate tank 19 and the condensate storage tank 16 to release the pressure in the second intermediate tank 19 and the second gas phase balance pipeline i, and then close the branch pressure relief pipeline j.

[0068] S3, connect the second purge gas pipeline k between the first fluidized bed reactor R-1 and the second intermediate tank 19 to transport part of the polymerization product in the second intermediate tank 19 to the first fluidized bed reactor R-1 for polymerization reaction. After the material level in the first fluidized bed reactor R-1 reaches the set height, the polymerization product is transported to the polymer devolatilization tank 17 for devolatilization treatment. Part of the polymerization product in the second intermediate tank 19 is directly transported to the polymer devolatilization tank 17 for devolatilization treatment. After the devolatilization treatment is completed, the polymer product is transported to the granulation system for granulation. The gas generated by devolatilization is transported to the condensate storage tank through the pressure relief pipeline.

[0069] The first fluidized bed reactor R-1 and the second fluidized bed reactor R-2 operate under conditions that produce substantially the same fractions.

[0070] In the method for producing polyolefins according to the present invention, the mass ratio of the capacity of the first fluidized bed reactor R-1 and the second fluidized bed reactor R-2 is 0.5:5, preferably 1:3.

[0071] In the method for producing polyolefins according to the present invention, the polyethylene produced in the second fluidized bed reactor R-2 is returned to the first fluidized bed reactor R-1 for polymerization reaction at a mass ratio of 1:(1-10), preferably 1:4, and more preferably 1:3.

[0072] The method for producing polyolefins according to the present invention involves homopolymerization or copolymerization in the first fluidized bed reactor R-1 and copolymerization in the second fluidized bed reactor R-2.

[0073] In this invention, the polymerization reactions in the first fluidized bed reactor R-1 and the second fluidized bed reactor R-2 can be carried out over a wide temperature range. In some embodiments, the polymerization steps in the first fluidized bed reactor R-1 and / or the second fluidized bed reactor R-2 can be carried out at temperatures ranging from 20°C to 125°C, preferably from 55°C to 105°C, more preferably from 60°C to 100°C, and most preferably from 65°C to 98°C. Preferably, the temperatures in the first fluidized bed reactor R-1 and / or the second fluidized bed reactor R-2 can be within the range of 65°C to 100°C and most preferably from 70°C to 98°C.

[0074] The polymerization pressure in the first fluidized bed reactor R-1 and / or the second fluidized bed reactor R-2 can be 1 MPa-3 MPa, preferably 1.5 MPa-2.5 MPa, and more preferably 2.0 MPa-2.2 MPa.

[0075] In some embodiments, the first fluidized bed reactor R-1 performs ethylene homopolymerization or copolymerization, feeding ethylene monomer, a catalyst, optional hydrogen, and optional one or more olefin comonomers into the first fluidized bed reactor for polymerization to produce a first polyethylene fraction. The second fluidized bed reactor performs only copolymerization, where the olefin in the homopolymerization reaction is one of ethylene, propylene, or butene, and the α-olefin in the copolymerization reaction, and the comonomer may include, but is not limited to, C3-C4. 20 The α-olefins include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene, preferably α-olefins with 18 or fewer carbon atoms, more preferably one or more of butene-1, 4-methyl-1-pentene, hexene-1, and octene-1;

[0076] In some embodiments, the comonomer is one of butene-1, hexene-1, or octene-1, which is atomized and sprayed into the reactor through a nozzle at the material inlet point. The material inlet point is located on the distribution plate and the straight section, and the number of such inlet points is one, two, or more.

[0077] In some embodiments, the catalyst used in the homopolymerization or copolymerization reaction is selected from Ziegler-Natta catalysts, chromium-based catalysts, metallocene catalysts, and post-transition metal catalysts, and the second fluidized bed reactor is preferably a metallocene catalyst or a combination thereof.

[0078] In some embodiments, a co-catalyst is also used during the polymerization process. The selected co-catalyst is an aluminum compound such as alkylaluminum or alkoxyaluminum, preferably trimethylaluminum, triethylaluminum, diethylaluminum chloride, tri-n-hexylaluminum or modified alkylaluminum compound, more preferably triethylaluminum.

[0079] In some embodiments, a molecular weight regulator is added during the polymerization process. The molecular weight regulator is hydrogen or oxygen, preferably hydrogen.

[0080] In some embodiments, 10%-30% by weight of the product in the polymer devolatilization tank is prepared in the first fluidized bed reactor, and most preferably at least 25% by weight, for example at least 30% by weight of the product is prepared in the first fluidized bed reactor;

[0081] In some embodiments, 35%-70% by weight of the product in the polymer devolatilization tank is prepared in the first fluidized bed reactor, preferably, at least 60% by weight of the product is prepared in the first fluidized bed reactor.

[0082] In some embodiments, up to 60% by weight of the product in the polymer devolatilization tank is prepared in a second fluidized bed reactor, for example, up to 50%, for example, up to 45% of the polyethylene product is prepared in the second reactor.

[0083] In some embodiments, the MI (melt index) ratio of polyethylene in the first reactor to that in the second reactor is 50-1;

[0084] In some embodiments, the entire discharge process is controlled by a DCS distributed control system, and the discharge process settings include sequential control status, program discharge, discharge mode, discharge settings, and discharge count settings.

[0085] The present invention will be further described below with reference to the embodiments.

[0086] Example

[0087] The following examples illustrate the methods for characterizing the structure and properties of olefin polymers:

[0088] Melt flow index: The melt flow rate is determined according to the conditions of GB / T-3682-2000 (190℃, 2.16kg load), and is usually denoted as MI2.16.

[0089] Density: determined according to GB / 1033-1986 method.

[0090] The first fluidized bed reactor used Ziegler-Natta as the main catalyst, triethylaluminum as the co-catalyst, and hydrogen as the molecular weight regulator to carry out homopolymerization of ethylene or copolymerization with butene-1. The melt index (MI) was 33.0 ± 0.2 g / 10 min; the density of the resulting polyethylene product was 0.920 ± 0.002 g / cm³. 3 ,

[0091] The second fluidized bed reactor used the same catalyst and co-catalyst, employing hexene-1 as the comonomer and hydrogen as the molecular weight regulator, to perform ethylene copolymerization. The resulting polyethylene product had a density of 0.965 ± 0.002 g / cm³. 3 MI was 1.0 ± 0.2 g / 10 min;

[0092] To better illustrate this process flow, the production of block polyethylene polymer is used as an example. The first fluidized bed reactor performs copolymerization reactions of ethylene and 1-butene, and the second fluidized bed reactor performs copolymerization reactions of ethylene and 1-hexene. After setting the discharge height of the first fluidized bed reactor, the reactor's discharge program is started on the DCS control system. The first fluidized bed reactor has a polymerization temperature of 85℃, a pressure of 2.0MPa, an ethylene feed rate of 100Kg / h, a hydrogen / ethylene ratio of 1.5±0.05, a butene-1 / ethylene ratio of 0.19±0.1, a circulation gas velocity of 0.60±0.05m / s, and a catalyst addition of 3-4g / h. The second fluidized bed reactor has a polymerization temperature of 85℃, a pressure of 2.0MPa, an ethylene feed rate of 50Kg / h, a hydrogen / ethylene ratio of 0.5±0.05, a 1-hexene / ethylene ratio of 1.5±0.1, a circulation gas velocity of 0.65±0.05m / s, and a catalyst addition of 6-8g / h.

[0093] (1) When the first fluidized bed reactor R1 reaches the set material level, the control valve KV-101 is opened. Under the action of pressure difference, the polymer product is discharged from the first discharge pipeline b to the first intermediate tank 18. The control valve KV-101 is opened for 10 seconds and then closed to end the discharge to the first intermediate tank 18. Then the control valve KV-102 is opened and closed for 5 seconds. During this period, some gas phase components in the first intermediate tank 18 return to the expansion section 1 of the first fluidized bed reactor R1 under the action of pressure difference until the gas phase is balanced. Then the control valve KV-103 is opened to continue to depressurize the first intermediate tank 18 and the first gas phase balance pipeline c. This process is the depressurization process of polyethylene powder.

[0094] (2) Continue to open control valve KV-104 on the first purge gas line e and control valve KV-105 on the feed line f. Use the purge gas from the second fluidized bed reactor R2 to transport the polyethylene powder in the first intermediate tank 18 to the second fluidized bed reactor R2 for polymerization. When the second fluidized bed reactor R2 reaches the set material level, control valve KV-106 opens, remains open for 8 seconds, and then closes. Then, control valve KV-107 opens, remains open for 5 seconds, and then closes. Open control valve KV-108 to continue depressurizing the second intermediate tank 19 and the second gas phase balance line i. Open control valve KV-109 on the second purge line k and control valve KV-112 on the feed line l. Use the purge gas from the first fluidized bed reactor R1 to transport the polyethylene powder in the second intermediate tank 19 to the first fluidized bed reactor R1 for polymerization.

[0095] (3) When the first fluidized bed reactor R1 reaches the set material level, control valve KV-101 is opened to discharge material into the first intermediate tank 18. Then, control valve KV-102 is opened until the gas phase is balanced, at which point KV-102 is closed and control valve KV-111 is opened to feed material into the polymer devolatilization tank 17. After the devolatilization is qualified, the material enters the granulation system for granulation and packaging. The volatile components in the first intermediate tank 18, the second intermediate tank 19, and the polymer devolatilization tank 17 are condensed by heat exchanger 15 and then enter the recovery system for separation and recovery for later use.

[0096] Gas content analysis of samples taken from the intermediate tank revealed that hydrogen accounted for approximately 0.1–0.5% of the gas composition, ethylene for approximately 10–20%, and butene-1 for approximately 70–80%. Ethylene and butene-1 are unreacted monomers and have minimal impact on the polymerization environment within reactor R2. The polymerization process conditions and performance characterization results of the prepared olefin polymer product B are shown in Table 1.

[0097] Table 1

[0098]

[0099]

[0100] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. An olefin polymerization apparatus for producing a polyolefin, characterized by, The device comprises: a first fluidized bed reactor provided with a first circulating gas pipeline a between the top and the bottom of the reactor; a first intermediate tank, the feed inlet of which is communicated with the discharge outlet of the first fluidized bed reactor through a first discharge pipeline b provided with a control valve, and the top of the first intermediate tank is communicated with the top of the first fluidized bed reactor through a first gas phase balance pipeline c provided with a control valve; a second fluidized bed reactor, the feed inlet of which is communicated with the discharge outlet of the first intermediate tank through a feed pipeline f provided with a control valve, and the second fluidized bed reactor is provided with a second circulating gas pipeline g between the top and the bottom of the reactor, and the top of the second fluidized bed reactor is provided with a first purge gas pipeline e communicated with the top of the first intermediate tank for purging the first intermediate tank, and the first purge gas pipeline is provided with a purge gas compressor; a second intermediate tank, the feed inlet of which is communicated with the discharge outlet of the second fluidized bed reactor through a second discharge pipeline h provided with a control discharge valve, and the top of the second intermediate tank is communicated with the top of the second fluidized bed reactor through a second gas phase balance pipeline i provided with a control valve; the top of the second intermediate tank is provided with a second purge pipeline k communicated with the top of the first fluidized bed reactor for purging the second intermediate tank, and the second purge pipeline is provided with a purge gas compressor, and the discharge outlet of the second intermediate tank is communicated with the first fluidized bed reactor; a polymer devolatilization tank, the feed inlet of which is communicated with the discharge outlets of the first intermediate tank and the second intermediate tank; a condensate storage tank, the feed inlet of which is communicated with the tops of the first intermediate tank, the second intermediate tank and the polymer devolatilization tank through a pressure relief pipeline, and a heat exchanger is arranged upstream of the feed inlet of the condensate storage tank.

2. The olefin polymerization apparatus for producing a polyolefin according to claim 1, characterized by, The first circulating gas pipeline and the second circulating gas pipeline are both provided with a compressor and a heat exchanger.

3. The olefin polymerization apparatus for producing a polyolefin according to claim 1, characterized by, The discharge outlet of the second intermediate tank is communicated with the first fluidized bed reactor for conveying the material in the second intermediate tank to the first fluidized bed reactor.

4. The olefin polymerization apparatus for producing a polyolefin according to claim 1, characterized by, The first fluidized bed reactor and the second fluidized bed reactor both comprise a straight cylinder section and an enlarged section, and are both provided with a gas distribution plate inside.

5. The olefin polymerization apparatus for producing a polyolefin according to claim 1, characterized by, The polymer devolatilization tank is provided with a jacket outside for controlling the temperature of the polymer devolatilization tank, and is provided with a stirring device inside.

6. A process for producing a polyolefin, characterized by, The device of any one of claims 1-5 is used, comprising the following steps: S1, adding polymerization monomers and catalysts into the first fluidized bed reactor to carry out polymerization, when the material level in the first fluidized bed reactor reaches a predetermined height, connecting the first discharge pipeline to transport the polymerization product in the first fluidized bed reactor to the first intermediate tank, closing the first discharge pipeline after the discharge is completed, connecting the first gas phase balance pipeline to transport the gas phase components in the first intermediate tank to the first fluidized bed reactor, disconnecting the first gas phase balance pipeline after the gas phase balance in the first intermediate tank and the first fluidized bed reactor, and closing the pressure relief pipeline between the first intermediate tank and the condensate storage tank after the pressure in the first intermediate tank and the first gas phase balance pipeline is relieved; S2, connecting the first purge gas pipeline between the second fluidized bed reactor and the first intermediate tank to transport the polymerization product in the first intermediate tank to the second fluidized bed reactor to carry out polymerization, connecting the second discharge pipeline to transport the polymerization product in the second fluidized bed reactor to the second intermediate tank when the material level in the second fluidized bed reactor reaches a predetermined height, closing the second discharge pipeline after the discharge is completed, connecting the second gas phase balance pipeline to transport the gas phase components in the second intermediate tank to the second fluidized bed reactor, disconnecting the second gas phase balance pipeline after the gas phase balance in the second intermediate tank and the second fluidized bed reactor, and closing the pressure relief pipeline between the second intermediate tank and the condensate storage tank after the pressure in the second intermediate tank and the second gas phase balance pipeline is relieved; S3, connecting the second purge gas pipeline between the first fluidized bed reactor and the second intermediate tank to transport part of the polymerization product in the second intermediate tank to the first fluidized bed reactor to carry out polymerization, transporting the polymerization product to the polymer devolatilization tank to carry out devolatilization treatment when the material level in the first fluidized bed reactor reaches a predetermined height, directly transporting part of the polymerization product in the second intermediate tank to the polymer devolatilization tank to carry out devolatilization treatment, and transporting the polymer product to the granulation system to carry out granulation after the devolatilization treatment is completed, and transporting the gas generated by devolatilization to the condensate storage tank through the pressure relief pipeline.

7. The process for producing a polyolefin according to claim 6, characterized in that, The capacity to mass ratio of the first fluidized bed reactor and the second fluidized bed reactor is 0.5:

5.

8. The process for producing polyolefins according to claim 6, characterized in that, The capacity to mass ratio of the first fluidized bed reactor and the second fluidized bed reactor is 1:

3.

9. The process for producing a polyolefin according to claim 6, characterized in that, The polyethylene generated by the second fluidized bed reactor is returned to the first fluidized bed reactor to carry out polymerization at a mass ratio of 1: (1-10).

10. The process for producing a polyolefin according to claim 6, characterized in that, The polyethylene generated by the second fluidized bed reactor is returned to the first fluidized bed reactor to carry out polymerization at a mass ratio of 1:

4.

11. The process for producing polyolefins according to claim 6, characterized in that, The polyethylene generated by the second fluidized bed reactor is returned to the first fluidized bed reactor to carry out polymerization at a mass ratio of 1:

3.

12. The process for producing polyolefins according to claim 6, characterized in that, The first fluidized bed reactor carries out homopolymerization or copolymerization, and the second fluidized bed reactor carries out copolymerization.

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