Olefin polymerization device for producing polyolefin and method for producing polyolefin

Abstract

The invention discloses an olefin polymerization device for producing polyolefin and a method for producing polyolefin. Through flexible combination of fluidized bed reactors and degassing of polyethylene particles discharged from the reactors, a wide molecular weight distribution / multimodal polyethylene or polyethylene block copolymer resin product can be produced. According to the invention, a pipeline for connecting the top of the intermediate tank with the purging gas of the reactor is additionally arranged and is used for conveying polyethylene particles in the intermediate tank to the corresponding polymerization reactor, so that the polymerization environment in the reactor is stabilized, and gas phase components from the previous reactor are effectively removed in the conveying process, for example, 99.9 wt% of hydrogen in the intermediate tank can be removed, and the yield of the polyethylene particles is improved. The production of polyolefin with higher relative molecular mass in the second reactor is ensured, a polyethylene product with target molecular weight and distribution is obtained, the existing production process is simplified, and the energy consumption is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of olefin polymerization, and in particular relates to an olefin polymerization device for producing polyolefin and a method for producing polyolefin. Background Art

[0002] Broad molecular weight distribution / multimodal polyethylene resin can significantly improve the processing performance of polyethylene (PE) without sacrificing the physical properties of PE. It can be used to process products such as films, blow-molded bottles, pipes and profiles to produce products with the same performance as traditional PE, which can significantly reduce the amount of raw materials used. In addition, broad molecular weight distribution / multimodal polyethylene resin has good recyclability and the mechanical properties of the secondary used resin are better than those of the first used unimodal polyethylene resin. The production technology of broad / multimodal polyethylene has developed rapidly, and there are three production methods: (1) melt blending method, that is, production using parallel reactors. This method requires complete uniform mixing of polymers, high cost, and it is difficult to uniform the quality of polyethylene products; (2) one-stage reaction method, that is, using a multi-active center catalyst in one reactor to prepare broad / multimodal polyethylene by taking advantage of the different polymerization behaviors of different active centers. Due to the difficulty of catalyst matching and process control, it has not yet been widely used. (3) segmented reaction method, that is, a polymerization method using two or more reactors in series. This method has good flexibility and a wide adjustment range for the polyethylene resin grades produced. It is currently the mainstream method for producing broad / multimodal polyethylene.

[0003] Among all polyethylene production processes, fluidized bed polyethylene production process occupies half of polyethylene production capacity due to its advantages such as no use of solvents, small equipment investment, energy saving and environmental protection. At present, dual fluidized bed reactors have been commercialized to produce molecular weight distribution / multimodal polyethylene resin products. Its polymerization process technology is to generate a copolymer with a high melt flow rate value (MI) and a low relative molecular weight in the first fluidized bed reactor, and then this copolymer and the catalyst enter the second fluidized bed reactor together to further polymerize into a copolymer product with a low MI value and a high relative molecular weight. There are problems such as the cross-flow of reaction materials between the two fluidized bed reactors in this process, the uneven residence time of polymer particles in the two gas phase reactors, and the limited circulation of polymer particles between reactors with different reaction conditions. Before the low molecular weight polymer polymerized in the first fluidized bed reactor is sent to the second fluidized bed reactor, all raw materials from the first reactor should be removed. The investment in discharge equipment is large, the use efficiency is low, and the operating cost is high.

[0004] The Dow Chemical Company of the United States has developed a chain shuttling technology based on a reversible chain transfer reaction. The obtained high-density polyethylene-low-density polyethylene-based multi-block polymers (OBCs) have the advantages of superior processing performance, high-temperature elasticity, good wear resistance and excellent compression deformation characteristics, and can be used in a variety of application fields. Patent CN 200480030566.3 proposes a multi-zone circulation reactor and method for producing polyolefins with a bimodal molecular weight distribution. 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 problem with this patent is that there is cross-flow of the reaction gas, and the descending section in the moving bed state cannot be applied to the production of polyethylene with a large heat release. Patent CN 102060943A discloses a method for preparing bimodal polyethylene and a gas phase reactor comprising at least four fluidized beds. In this method, the 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. This 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. Patent CN107405593B discloses an olefin polymerization device and an olefin polymerization method. The device or method provided by the invention can realize the condensation of the gas material discharged from the polymerization reactor, and 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 passed into the polymerization reactor to realize the 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 relatively high energy consumption in order to condense and separate the gas discharged from the polymerization reactor. Setting up one polymerization reactor cannot achieve continuous switching between olefin homopolymerization and copolymerization reactions.

[0005] Although the preparation of broad molecular weight distribution / multimodal polyethylene resins is mature and many methods for removing all gas phase components from the first reactor are known and have been described, there is still a need to develop an olefin polymerization apparatus for producing polyolefins and a discharge system for an olefin polymerization apparatus and a method of using the same. Summary of the invention

[0006] In view of the above technical problems, the object of the present invention is to provide an olefin polymerization device for producing polyolefin and a method for producing polyolefin.

[0007] The present invention provides an olefin polymerization device for producing polyolefins, comprising:

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

[0009] A first intermediate tank, wherein the feed port of the first intermediate tank is connected to the discharge port of the first fluidized bed reactor via a first discharge pipeline b, the first discharge pipeline is provided 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, the first gas phase balance pipeline c is provided with a control valve;

[0010] a second fluidized bed reactor, wherein the feed port of the second fluidized bed reactor is connected to the discharge port of the first intermediate tank via a feed pipeline f, and a control valve is provided on the feed pipeline f; a second circulating gas pipeline g is provided between the top and the bottom of the second fluidized bed reactor, and a first purge gas pipeline e 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, and a purge gas compressor is provided on the first purge gas pipeline;

[0011] A second intermediate tank, wherein the feed port of the second intermediate tank is connected with the discharge port of the second fluidized bed reactor via a second discharge pipeline h, the second discharge pipeline h is provided with a control discharge valve, the top of the second intermediate tank is connected with the top of the second fluidized bed reactor via a second gas phase balance pipeline i, the second gas phase balance pipeline i is provided with a control valve; the top of the second intermediate tank is provided with a second purge pipeline k connected with the top of the first fluidized bed reactor for purging the second intermediate tank, the second purge pipeline is provided with a purge gas compressor, and the discharge port of the second intermediate tank is connected with the first fluidized bed reactor;

[0012] A polymer devolatilizer, wherein the feed port of the polymer devolatilizer is connected with the discharge port of the first intermediate tank and the discharge port of the second intermediate tank;

[0013] A condensate storage tank, wherein a feed port of the condensate storage tank is connected with the top of the first intermediate tank, the top of the second intermediate tank and the top of the polymer devolatilization tank through a pressure relief pipeline, and a heat exchanger is provided upstream of the feed port of the condensate storage tank.

[0014] In the olefin polymerization device for producing polyolefins described in the present invention, both the first circulating gas pipeline and the second circulating gas pipeline are provided with a compressor and a heat exchanger.

[0015] In the olefin polymerization device for producing polyolefins described in the present invention, the discharge port of the second intermediate tank is connected to the first fluidized bed reactor for conveying the material in the second intermediate tank to the first fluidized bed reactor.

[0016] In the olefin polymerization device for producing polyolefins described in the present invention, the first fluidized bed reactor and the second fluidized bed reactor both include a straight section and an expanded section, and are both provided with a gas distribution plate.

[0017] In the olefin polymerization device for producing polyolefins of the present invention, a jacket is arranged outside the polymer devolatilization tank for controlling the temperature of the polymer devolatilization tank; and a stirring device is arranged inside the polymer devolatilization tank.

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

[0019] S1, adding polymerization monomers and catalysts to the first fluidized bed reactor to carry out polymerization reaction, after 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 in the first intermediate tank and the first fluidized bed reactor is balanced, continuing to open the pressure relief pipeline between the first intermediate tank and the condensate storage tank, and closing the pressure relief pipeline after the pressure in the first intermediate tank and the first gas phase balance pipeline is vented;

[0020] 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 for polymerization reaction, after the material level in the second fluidized bed reactor reaches the set height, connecting the second discharge pipeline to transport the polymerization product in the second fluidized bed reactor to the second intermediate tank, 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 in the second intermediate tank and the second fluidized bed reactor is balanced, continuing to open the pressure relief pipeline between the second intermediate tank and the condensate storage tank, and closing the pressure relief pipeline after the pressure in the second intermediate tank and the second gas phase balance pipeline is vented;

[0021] 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 for polymerization reaction, after the material level in the first fluidized bed reactor reaches the set height, transporting the polymerization product to the polymer devolatilization tank for devolatilization treatment, and directly transporting part of the polymerization product in the second intermediate tank 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, and the gas generated by devolatilization is transported to the condensate storage tank via the pressure relief pipeline.

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

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

[0024] In the method for producing polyolefins of the present invention, the first fluidized bed reactor performs homopolymerization or copolymerization, and the second fluidized bed reactor performs copolymerization.

[0025] Beneficial effects of the present invention:

[0026] The present invention discloses an ethylene polymerization process, which can realize the production of wide molecular weight distribution / multimodal polyethylene or polyethylene block copolymer resin products through flexible combination between fluidized bed reactors and degassing of polyethylene particles discharged from the reactors. The present invention adds a pipeline connecting the top of the intermediate tank and the reactor purge gas, which is used to transport the polyethylene particles in the intermediate tank to the corresponding polymerization reactor, stabilize the polymerization environment in the reactor, and effectively remove the gas phase components from the previous reactor during this transportation process. For example, 99.9wt% of hydrogen in the intermediate tank can be removed to ensure the generation of polyolefins with higher relative molecular weight in the second reactor, obtain polyethylene products with target molecular weight and distribution, simplify the existing production process, and reduce energy consumption. At the same time, by controlling the sequence and switching time of the control valve group switch 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 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 method, discharge setting and discharge count, making the entire discharge program operation flexible and easy to control. 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 equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic structural diagram of an olefin polymerization device for producing polyolefins according to the present invention.

[0028] Wherein, the reference numerals are:

[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 Enlarged segment

[0033] 2.8 straight section

[0034] 3.9 Gas distribution plate

[0035] 4, 10, 13, 14 compressors

[0036] 5, 11, 15 heat exchanger

[0037] 6.12 Material introduction point

[0038] 16 Condensate storage tank

[0039] 17 Polymer Devolatilizer

[0040] 18 First intermediate tank

[0041] 19 Second intermediate tank

[0042] a The first circulating gas pipeline

[0043] b. The first discharge pipeline

[0044] c The first gas phase balance pipeline

[0045] d, j, n branch pressure relief pipeline

[0046] eFirst purge gas line

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

[0048] g Second circulating gas line

[0049] h Second discharge pipeline

[0050] i Second gas phase balance pipeline

[0051] k Second purge line

[0052] o Pressure relief line DETAILED DESCRIPTION

[0053] The present invention is described in detail below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art in this field can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0054] An olefin polymerization device for producing polyolefins comprises 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, comprising a straight section 2 and an expanded section 1, with a gas distribution plate 3 provided inside, and a material introduction point 6 provided on the side wall of the straight section 2, through which the raw materials required for the reaction are transported to the reactor for reaction; a first circulating gas pipeline a is provided between the top and the bottom of the first fluidized bed reactor R-1, and a compressor 4 and a heat exchanger 5 are provided on the first circulating gas pipeline a, and the gas raw materials that have not reacted during the polymerization process can be circulated through the first circulator pipeline a for reaction.

[0056] The feed port of the first intermediate tank 18 is connected with the discharge port of the first fluidized bed reactor R-1 through the first discharge pipeline b, and a control valve KV-101 is provided on the first discharge pipeline. The top of the first intermediate tank 18 is connected with the top of the first fluidized bed reactor R-1 through the first gas phase balance pipeline c, and a control valve KV-102 is provided on the first gas phase balance pipeline c; the first intermediate tank 18 is used to store the polymerization product prepared in 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, and under the action of the pressure difference, the polymerization product in the first fluidized bed reactor R-1 is discharged to 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 components in the first intermediate tank 18 return to the first fluidized bed reactor R-1 under the action of the pressure difference until the gas phase mixing reaches equilibrium, that is, the gas phase pressures are equal. The first gas phase equilibrium line c is also provided with a branch pressure relief pipeline d connected to the condensate storage tank 16, and the branch pressure relief pipeline d is provided with a control valve KV-103. When the control valve KV-103 is opened, the first intermediate tank 18 is depressurized for the second time, and the removed gas is heat exchanged by the heat exchanger 15, and the condensate enters the condensate storage tank 16. The discharge pipeline of the condensate storage tank 16 is provided with a control valve KV-114, and the uncondensed gas enters the membrane separation and deep-cold recovery system.

[0057] The feed port of the second fluidized bed reactor R-2 is connected to the discharge port of the first intermediate tank 18 through a feed pipeline f, and a control valve KV-105 is provided on the feed pipeline f; a second circulating gas pipeline g is provided between the top and the bottom of the second fluidized bed reactor R-2, and a compressor 10 and a heat exchanger 11 are provided on the second circulating gas pipeline g, and the gas raw materials that have not reacted during the polymerization process can be circulated through the second circulator pipeline g. A first purge gas pipeline e connected to the top of the first intermediate tank 18 is also provided at the top of the second fluidized bed reactor R-2 for purging the first intermediate tank 18, and a purge gas compressor 13 is provided on the first purge gas pipeline e. The polymerization product obtained in the first fluidized bed reactor R-1 is further polymerized in the second fluidized bed reactor R-2.

[0058] The second fluidized bed reactor R-2 is a conventional device in the art, comprising a straight section 9 and an expanded section 7, with a gas distribution plate 9 provided inside. A material introduction point 12 is provided on the side wall of the straight section 9, and the raw materials required in the reaction process are transported to the reactor through the material introduction point for reaction.

[0059] The feed port of the second intermediate tank 19 is connected to the discharge port of the second fluidized bed reactor R-2 through a second discharge pipeline h, and a control discharge valve KV-106 is provided on the second discharge pipeline h. The top of the second intermediate tank 19 is connected to the top of the second fluidized bed reactor R-2 through a second gas phase balance pipeline i, and a control valve KV-107 is provided on the second gas phase balance pipeline i; the top of the second intermediate tank 19 is provided with a second purge pipeline k connected to the top of the first fluidized bed reactor R-1 for purging the second intermediate tank 19, and the second purge pipeline k is provided with a purge gas compressor 14 The discharge port 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 in 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 to the second intermediate tank 19 under the action of the pressure difference. After the discharge process is completed, the control valve KV-107 is opened. At this time, part of the gas phase components in the second intermediate tank 19 are returned to the second fluidized bed reactor under the action of the pressure difference until the gas phase mixing reaches equilibrium, that is, the gas phase pressures are equal.

[0060] The second gas phase equilibrium line i is also provided with a branch pressure relief pipeline j connected to the condensate storage tank 16. The branch pressure relief pipeline j is provided with a control valve KV-108. When the control KV-108 is opened, the second intermediate tank 19 is depressurized for the second time. After the removed gas is heat exchanged by the heat exchanger 15, the condensate enters the condensate storage tank 16, and the uncondensed gas enters the membrane separation and deep-cold recovery system.

[0061] The feed port of the polymer devolatilization tank 17 is connected with the discharge port of the first intermediate tank R-1 through a feed pipeline m, and a control valve KV-111 is provided on the feed pipeline m for conveying the material in the first intermediate tank 18 to the polymer devolatilization tank 17; the feed port of the polymer devolatilization tank 17 is also connected with the discharge port of the second intermediate tank 19 through a feed pipeline p, and a control valve KV-110 is provided on the feed pipeline p for conveying the material in the second intermediate tank 19 to the polymer devolatilization tank 17; the top of the polymer devolatilization tank 17 is connected with the condensate storage tank 16 through a pressure relief pipeline n, and a control valve KV-113 is provided on the pressure relief pipeline n. After the removed gas is heat exchanged by the heat exchanger 15, the condensate enters the condensate storage tank 16, and the uncondensed gas enters the membrane separation and deep cold recovery system. The polymer devolatilization tank 17 is a conventional device in the art. In the present invention, a jacket is provided on the outside of the polymer devolatilization tank 17 to control the temperature of the polymer devolatilization tank. A stirring device is provided inside the polymer devolatilization tank 17 to facilitate gas-solid separation. A control valve KV-115 is provided on the discharge pipeline of the polymer devolatilization tank 17 to feed the degassed solid material into the granulation system.

[0062] In another embodiment of the present invention, the discharge port of the second intermediate tank 19 is connected to the first fluidized bed reactor R-1 through a feed pipeline 1 for transporting the material in the second intermediate tank 19 to the first fluidized bed reactor R-1. A control valve KV-112 is provided on the feed pipeline 1, and the product obtained by polymerization in the second fluidized bed reactor R-2 can be selectively transported to the first fluidized bed reactor R-1 for further polymerization reaction.

[0063] The device of the present invention can obtain a wide molecular weight distribution / multimodal polyethylene resin or a block polyethylene resin by adding different comonomers to two or more series fluidized bed reactors to generate ethylene copolymerization. In order to realize the synthesis of the above-mentioned polyethylene resin product, it can be realized by selecting reaction conditions different from those of the first fluidized bed reactor in the second fluidized bed reactor or the subsequent reactor, such as changing the catalyst injection amount, the type of comonomer, the polymerization reaction time, the ratio of the chain transfer agent to the catalyst, the polymerization reaction temperature and pressure and other parameters. The polymer obtained from the first gas phase reactor is transferred to the second gas phase reactor, and the catalyst component carried by the polymer particles will continue to exert its catalytic activity. The polymerization reaction continues to be carried out under different reaction conditions in the second gas phase reactor. Therefore, by maintaining different gas phase mixed components in each gas phase reactor, even different polymer fragments can grow on the same particles.

[0064] In the embodiment of preparing different wide molecular weight distribution / multimodal polyethylene resins or polyethylene block copolymer resins by gas phase polymerization of ethylene using this process, by maintaining different concentrations of chain terminator concentrations in each reactor, the synthesis of the above copolymer can be obtained by changing the type and content of the comonomer. In the ethylene polymerization process of the present invention, it is provided that the polymer generated from the first fluidized bed reactor is degassed and then transferred to the second fluidized bed reactor for continued polymerization to form different wide molecular weight distribution / multimodal polyethylene resins. After the polymer generated in the second fluidized bed reactor is degassed, it is transferred to the first fluidized bed reactor again for continued 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 when the second fluidized bed reactor is transferred to the first fluidized bed reactor, the gas phase components of the reactor should be effectively removed to avoid affecting the polymerization conditions in other reactors. Therefore, the discharging system provided by the ethylene polymerization process can meet the requirements and realize the production of wide molecular weight distribution / multimodal polyethylene resin or block polyethylene resin.

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

[0066] S1, adding polymerization monomers and catalysts 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 a predetermined height, connecting the first discharge pipeline b to transport the polymerization product in the first fluidized bed reactor R-1 to the first intermediate tank 18, closing the first discharge pipeline b after the discharge is completed, connecting the first gas phase balance pipeline c to transport the gas phase components in the first intermediate tank 18 to the first fluidized bed reactor R-1, disconnecting the first gas phase balance pipeline c after the gas phases in the first intermediate tank 18 and the first fluidized bed reactor R-1 are balanced, continuing to open the branch pressure relief pipeline d between the first intermediate tank 18 and the condensate storage tank 16, and closing the branch pressure relief pipeline d after the pressure in the first intermediate tank 18 and the first gas phase balance pipeline c is vented;

[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, close the second discharge pipeline h after the discharge is completed, connect the second gas phase balance pipeline i to transport the gas phase components in the second intermediate tank 19 to the second fluidized bed reactor R-2, disconnect the second gas phase balance pipeline i after the gas phase in the second intermediate tank 19 and the second fluidized bed reactor R-2 is balanced, continue to open the branch pressure relief pipeline j between the second intermediate tank 19 and the condensate storage tank 16, and close the branch pressure relief pipeline j after the pressure in the second intermediate tank 19 and the second gas phase balance pipeline i is vented;

[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, transport the polymerization product 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, and the gas generated by devolatilization is transported to the condensate storage tank via the pressure relief pipeline.

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

[0070] In the method for producing polyolefins of the present invention, the capacity-to-mass ratio 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 of 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, more preferably 1:3.

[0072] In the method for producing polyolefins of the present invention, the first fluidized bed reactor R-1 performs homopolymerization or copolymerization, and the second fluidized bed reactor R-2 performs copolymerization.

[0073] The polymerization reaction in the first fluidized bed reactor R-1 and the second fluidized bed reactor R-2 of the present invention can be carried out in a wide temperature range. In certain embodiments, the polymerization step in the first fluidized bed reactor R-1 and / or the second fluidized bed reactor R-2 can be carried out at a temperature of 20°C-125°C, preferably 55°C-105°C, more preferably 60°C-100°C and most preferably 65°C-98°C. Preferably, the temperature in the first fluidized bed reactor R-1 and / or the second fluidized bed reactor R-2 range can be in the range of 65°C-100°C and most preferably 70°C-98°C.

[0074] The polymerization pressure in the first fluidized bed reactor R-1 and / or the second fluidized bed reactor R-2 may be carried out at a pressure of 1 MPa-3 MPa, preferably 1.5 MPa-2.5 MPa, more preferably 2.0 MPa-2.2 MPa;

[0075] In some embodiments, the first fluidized bed reactor R-1 performs ethylene homopolymerization or copolymerization, wherein ethylene monomer, a catalyst, optional hydrogen, and optional one or more olefin comonomers are fed into the first fluidized bed reactor for polymerization to produce a first polyethylene fraction, and the second fluidized bed reactor performs only copolymerization, wherein 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-C 20 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 carbon atoms or less, more preferably one or more selected from 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 through a nozzle and sprayed into the reactor at the material introduction point. The material introduction point is on the distribution plate and the straight barrel section, and the number is one, two or more.

[0077] In some embodiments, the catalyst used in the homopolymerization 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 second fluidized bed reactor is preferably a metallocene catalyst or a composite thereof.

[0078] In some embodiments, a co-catalyst is also used in the polymerization process. The selected co-catalyst is an aluminum compound such as an alkyl aluminum or an alkoxy aluminum, preferably trimethyl aluminum, triethyl aluminum, diethyl aluminum monochloride, tri-n-hexylaluminum or a modified alkyl aluminum compound, more preferably triethyl aluminum.

[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 devolatilizer is prepared in the first fluidized bed reactor, and most preferably at least 25% by weight, such as 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 devolatilizer is prepared in the first fluidized bed reactor, and 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 devolatilizer is produced in the second fluidized bed reactor, such as up to 50%, such as up to 45%, of the polyethylene product is produced in the second reactor.

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

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

[0085] The present invention will be further described below in conjunction with the embodiments.

[0086] Example

[0087] In the following examples, the characterization method of the structure and properties of olefin polymers is as follows:

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

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

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

[0091] The second fluidized bed reactor uses the same catalyst and co-catalyst, uses hexene-1 as a comonomer, and hydrogen as a molecular weight regulator to carry out ethylene copolymerization. The density of the obtained polyethylene product is 0.965±0.002g / cm 3 , MI is 1.0±0.2g / 10min;

[0092] In order to better illustrate the process flow, the production of block polyethylene polymer is used as an example, the first fluidized bed reactor performs copolymerization of ethylene and 1-butene, and the second fluidized bed reactor performs copolymerization of ethylene and 1-hexene. After setting the material level discharge height of the first fluidized bed reactor, the reactor program discharge system is started on the DCS control system. Wherein, the polymerization temperature of the first fluidized bed reactor is 85°C, the pressure is 2.0MPa, the ethylene feed amount 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, and the catalyst addition amount is 3-4g / h; the polymerization temperature of the second fluidized bed reactor is 85°C, the pressure is 2.0MPa, the ethylene feed amount is 50Kg / h, the hydrogen / ethylene (mol / mol) is 0.5±0.05, the 1-hexene / ethylene (mol / mol) is 1.5±0.1, the circulation gas velocity is 0.65±0.05m / s, and the catalyst addition amount is 6-8g / h.

[0093] (1) When the first fluidized bed reactor R1 reaches the set material level, the control valve KV-101 opens. Under the action of the 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, ending the discharge to the first intermediate tank 18. Subsequently, the control valve KV-102 is opened and opened for 5 seconds and then closed. During this period, part of the 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 the pressure difference until the gas phase is balanced. 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 decompression process of the polyethylene powder.

[0094] (2) Continue to open the control valve KV-104 on the first purge gas pipeline e and the control valve KV-105 on the feed pipeline f, and use the purge gas of 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, the control valve KV-106 is opened, and it is kept open for 8 seconds before closing. Then the control valve KV-107 is opened, and it is kept open for 5 seconds before closing. The control valve KV-108 is opened to continue to depressurize the second intermediate tank 19 and the second gas phase balance pipeline i, and the control valve KV-109 on the second purge pipeline k and the control valve KV-112 on the feed pipeline l are opened. The purge gas of the first fluidized bed reactor R1 is used 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, the control valve KV-101 is opened to discharge the material to the first intermediate tank 18, and then the control valve KV-102 is opened until the gas phase is balanced, and then KV-102 is closed, and the control valve KV-111 is opened to feed 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 the heat exchanger 15 and enter the recovery system for separation and recovery for standby use.

[0096] By sampling the intermediate tank 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 entering the R2 reactor has little impact on the polymerization environment. The polymerization process conditions and the performance characterization results of the prepared olefin polymerization product B are shown in Table 1.

[0097] Table 1

[0098]

[0099]

[0100] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and deformations based on the present invention, but these corresponding changes and deformations should all fall within the scope of protection of the claims of the present invention.

Claims

1. An olefin polymerization device for producing polyolefins, characterized in that: include: A first fluidized bed reactor, wherein a first circulating gas pipeline a is provided between the top and the bottom of the first fluidized bed reactor; A first intermediate tank, wherein the feed port of the first intermediate tank is connected to the discharge port of the first fluidized bed reactor via a first discharge pipeline b, the first discharge pipeline is provided 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, the first gas phase balance pipeline c is provided with a control valve; a second fluidized bed reactor, wherein the feed port of the second fluidized bed reactor is connected to the discharge port of the first intermediate tank via a feed pipeline f, and a control valve is provided on the feed pipeline f; a second circulating gas pipeline g is provided between the top and the bottom of the second fluidized bed reactor, and a first purge gas pipeline e 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, and a purge gas compressor is provided on the first purge gas pipeline; A second intermediate tank, wherein the feed port of the second intermediate tank is connected with the discharge port of the second fluidized bed reactor via a second discharge pipeline h, the second discharge pipeline h is provided with a control discharge valve, the top of the second intermediate tank is connected with the top of the second fluidized bed reactor via a second gas phase balance pipeline i, the second gas phase balance pipeline i is provided with a control valve; the top of the second intermediate tank is provided with a second purge pipeline k connected with the top of the first fluidized bed reactor for purging the second intermediate tank, the second purge pipeline is provided with a purge gas compressor, and the discharge port of the second intermediate tank is connected with the first fluidized bed reactor; A polymer devolatilizer, wherein the feed port of the polymer devolatilizer is connected with the discharge port of the first intermediate tank and the discharge port of the second intermediate tank; A condensate storage tank, wherein a feed port of the condensate storage tank is connected with the top of the first intermediate tank, the top of the second intermediate tank and the top of the polymer devolatilization tank through a pressure relief pipeline, and a heat exchanger is provided upstream of the feed port of the condensate storage tank.

2. The olefin polymerization device for producing polyolefin according to claim 1, characterized in that: 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 device for producing polyolefin according to claim 1, characterized in that: The discharge port of the second intermediate tank is connected to the first fluidized bed reactor for conveying the material in the second intermediate tank to the first fluidized bed reactor.

4. The olefin polymerization device for producing polyolefin according to claim 1, characterized in that: The first fluidized bed reactor and the second fluidized bed reactor both include a straight section and an expanded section, and are both provided with a gas distribution plate.

5. The olefin polymerization device for producing polyolefin according to claim 1, characterized in that: A jacket is arranged outside the polymer devolatilization tank for controlling the temperature of the polymer devolatilization tank; and a stirring device is arranged inside the polymer devolatilization tank.

6. A method for producing polyolefins, characterized in that Using the device according to any one of claims 1 to 5, comprising the following steps: S1, adding polymerization monomers and catalysts to the first fluidized bed reactor to carry out polymerization reaction, after 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 in the first intermediate tank and the first fluidized bed reactor is balanced, continuing to open the pressure relief pipeline between the first intermediate tank and the condensate storage tank, and closing the pressure relief pipeline after the pressure in the first intermediate tank and the first gas phase balance pipeline is vented; 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 for polymerization reaction, after the material level in the second fluidized bed reactor reaches the set height, connecting the second discharge pipeline to transport the polymerization product in the second fluidized bed reactor to the second intermediate tank, 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 in the second intermediate tank and the second fluidized bed reactor is balanced, continuing to open the pressure relief pipeline between the second intermediate tank and the condensate storage tank, and closing the pressure relief pipeline after the pressure in the second intermediate tank and the second gas phase balance pipeline is vented; 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 for polymerization reaction, after the material level in the first fluidized bed reactor reaches the set height, transporting the polymerization product to the polymer devolatilization tank for devolatilization treatment, and directly transporting part of the polymerization product in the second intermediate tank 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, and the gas generated by devolatilization is transported to the condensate storage tank via the pressure relief pipeline.

7. The method for producing polyolefin according to claim 6, characterized in that The capacity-to-mass ratio of the first fluidized bed reactor to the second fluidized bed reactor is 0.5:5, preferably 1:

3.

8. The method for producing polyolefin according to claim 6, characterized in that The polyethylene produced in the second fluidized bed reactor is returned to the first fluidized bed reactor for polymerization reaction at a mass ratio of 1:(1-10), preferably 1:4, more preferably 1:

3.

9. The method for producing polyolefin according to claim 6, characterized in that The first fluidized bed reactor performs homopolymerization or copolymerization, and the second fluidized bed reactor performs copolymerization.

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