Solution polymerization system and method for producing polyolefin

Abstract

The invention discloses a solution polymerization system for producing polyolefin. The solution polymerization system comprises at least two polymerization reactors and a rectification device, wherein the polymerization reactors are communicated with each other; gas phase outlets are formed in the tops of the polymerization reactors; the inlet of the rectification device is respectively communicated with the gas phase outlet of each polymerization reactor; and a top outlet and a lower outlet of the rectification device are respectively communicated with each polymerization reactor through a heat exchanger and a multi-path flow valve. According to the system, polymerization reaction heat is efficiently removed, pipeline blockage caused by the fact that evaporated oligomers enter external circulating cooling equipment is avoided, meanwhile, the concentration and the temperature gradient between different polymerization reactors in the polymerization process can be accurately regulated and controlled, and then the properties of polyolefin products are effectively regulated and controlled according to different product performance requirements; the device can be suitable for industrial preparation of polyolefin products with different properties, the polyolefin products are stable in property, and the device is low in cost.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer preparation, and particularly relates to a solution polymerization system and method for producing polyolefins. Background Art

[0002] The solution polymerization method is one of the commonly used polyolefin production processes in industry, and generally, metallocene catalysts or Ziegler-Natta catalysts are selected as catalysts. However, in general solution polymerization methods, while increasing the polyolefin yield, the heat release during polymerization increases rapidly, and the heat removal efficiency of the solution polymerization process is limited, making it difficult to remove heat in a timely manner. Moreover, as the mass fraction of polyolefin in the reaction mixture increases, the viscosity of the system becomes larger, and the temperature and concentration gradients of the reaction mixture are difficult to control, resulting in unstable and difficult-to-regulate properties of polyolefin products.

[0003] To address the above problems, in the prior art, part of the solution is evaporated by controlling the pressure in the reactor, and the evaporated gas is cooled and then recycled to the reactor to remove the heat of the polymerization reaction. For example, the CX process of Mitsui Petrochemical Industries, Ltd. in Japan and the Hostalen process of BASELL Company both use this method to remove the heat of the polymerization reaction. Chinese Patent Document CN1597706 also reports the use of the solution evaporation method to remove the heat of the polymerization reaction. However, since most of the evaporated gas is recycled to the polymerization reactor that generates the vapor, it is difficult to effectively control the concentration gradient in the reactor, resulting in unstable and difficult-to-regulate properties of polyolefin products. In addition, the evaporated gas will contain some oligomers, and when cooled and recycled to the reactor, the oligomers will block the circulation pipeline or condenser.

[0004] To address this problem, Chinese Patent Document CN115141301B reports that the material after the reaction in the polymerization reactor first enters a flash tank for gas-liquid separation, and then the light component gas-phase mixture is cooled, and the heat removal and control of the concentration gradient are carried out by controlling the delivery of the cooled light component mixture to different reactors. Although this solution improves the problems of difficult heat removal and difficult control of the concentration gradient existing in the solution polymerization process to a certain extent, the properties of the polyolefin products obtained by this solution are unstable and the regulation effect is not obvious. In addition, the use of solution evaporation to remove the heat of the polymerization reaction in this solution will also bring new problems. The most prominent problem is that the evaporated gas phase will contain some oligomers, which cannot be removed by flash distillation operation. When the oligomers in the evaporated gas-phase mixture are cooled and pass through equipment such as heat exchangers in the external circulation cooling loop, it is easy to cause problems such as pipeline blockage. Summary of the Invention

[0005] In view of this, the present invention provides a solution polymerization system for producing polyolefins. By connecting the top of the polymerization reactor to the rectification device, the components evaporated in the polymerization reactor during the reaction are effectively separated in the rectification device, and the oligomers therein are discharged from the system; the remaining separated light components are respectively recycled to the same or different polymerization reactors as needed after heat exchange. While efficiently removing the heat of polymerization reaction and avoiding the blockage of pipelines caused by the evaporated oligomers entering the external circulation cooling equipment, the concentration and temperature gradients between different polymerization reactors in the polymerization process can be accurately regulated, and then the properties of polyolefin products can be effectively regulated according to different product performance requirements, which can be applied to the industrial preparation of polyolefin products with different properties, and the properties of polyolefin products are stable, while reducing the device cost.

[0006] To achieve the above object, the present invention provides a solution polymerization system for producing polyolefins, comprising:

[0007] At least two interconnected polymerization reactors, each of the polymerization reactors is provided with a gas phase outlet at the top;

[0008] A rectification device, the inlet of the rectification device is respectively connected to the gas phase outlets of the polymerization reactors; the top outlet and the bottom outlet of the rectification device are respectively connected to the polymerization reactors through heat exchangers and multi-way flow valves; a heavy component discharge port is also provided at the bottom of the rectification device.

[0009] Optionally, in the solution polymerization system for producing polyolefins provided by the present invention, the polymerization reactors are connected in series or in parallel.

[0010] Optionally, in the solution polymerization system for producing polyolefins provided by the present invention, a middle outlet is further provided on the rectification device, and the middle outlet is connected to the tops of the polymerization reactors through heat exchangers and multi-way flow valves.

[0011] Optionally, in the solution polymerization system for producing polyolefins provided by the present invention, product outlets are provided on the side walls of each of the polymerization reactors; products can be taken out from the product outlets of each of the polymerization reactors, and can be specifically adjusted according to actual needs. For example, products can be taken out only from the last polymerization reactor, or products can be taken out from multiple polymerization reactors respectively;

[0012] A catalyst inlet and a polymerization monomer inlet are provided on each of the polymerization reactors, or a catalyst inlet and a polymerization monomer inlet are provided on one of the polymerization reactors.

[0013] Optionally, in the solution polymerization system for producing polyolefins provided by the present invention, a stirrer is provided in each of the polymerization reactors, and the stirrer is composed of an outer slurry and an inner slurry;

[0014] The outer impeller is selected from an anchor impeller or a frame impeller; the inner impeller is selected from at least one of an inclined blade impeller, a straight blade impeller, a turbine impeller, and a propeller impeller. The number of layers of the inner impeller is not specifically limited. For example, the inner impeller can be selected to have 2 - 6 layers, and can be specifically adjusted according to actual conditions, such as 2 layers, 3 layers, 4 layers, 5 layers, or 6 layers.

[0015] Optionally, in the solution polymerization system for producing polyolefins provided by the present invention, the rectifying device is selected from a rectifying column, and the number of trays of the rectifying column is 4 - 30; it can be specifically adjusted according to actual conditions, such as the number of trays being 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 17, 20, 22, 25, 27, 29, etc.

[0016] The number of polymerization reactors is 2 - 8, and can be specifically adjusted according to actual conditions, such as 2, 3, 4, 5, 6, 7, or 8, etc.

[0017] The present invention also provides a solution polymerization method for producing polyolefins, using the above - mentioned solution polymerization system for producing polyolefins, and comprising the following steps:

[0018] The polymerization monomer undergoes solution polymerization in each polymerization reactor under the action of a catalyst. During the polymerization process, the light components (gaseous components) formed by evaporation at the top of each polymerization reactor respectively enter the rectifying device for separation;

[0019] The light components (mainly including low - boiling - point solvents, low - boiling - point olefin monomers, etc.) discharged from the top outlet of the rectifying device are heat - exchanged through a heat exchanger and then transported to at least one polymerization reactor through a multi - way flow valve;

[0020] The heavy components without oligomers (mainly including high - boiling - point solvents or high - boiling - point olefin monomers and without oligomers) discharged from the lower outlet of the rectifying device are heat - exchanged through a heat exchanger and then transported to at least one polymerization reactor through a multi - way flow valve;

[0021] The heavy components (mainly including oligomers) discharged from the heavy - component discharge port of the rectifying device are transported to a separation and recovery unit.

[0022] Optionally, in the solution polymerization method for producing polyolefins provided by the present invention, the intermediate components (mainly including olefin monomers or solvents with boiling points between the heavy components without oligomers and the light components) discharged from the middle outlet of the rectifying device are heat - exchanged through a heat exchanger and then transported to at least one polymerization reactor through a multi - way flow valve. In the above description, high - boiling - point and low - boiling - point are relative to the components in the entire reaction system and are not absolute. If there is no substance with a boiling point between the light components and the heavy components without oligomers, then no substance is discharged from the middle outlet of the rectifying device.

[0023] Whether to discharge components from the middle outlet of the rectification device depends on the polymerization reaction system.

[0024] The heat exchanger therein is used to adjust the temperature of the discharged materials at different positions of the rectification device, and the multi-way flow valve is used to control the material flow ratio of the discharged materials at different positions of the rectification device to be transported to different polymerization reactors, thereby precisely regulating the concentration and temperature gradients between different polymerization reactors in the polymerization process.

[0025] Optionally, in the solution polymerization method for producing polyolefins provided by the present invention, the liquid volume in each of the polymerization reactors accounts for 50%-100% of the total volume of each of the polymerization reactors.

[0026] The parameters of the above-mentioned polymerization reactors can be adjusted according to actual situations without specific limitations. The recommended temperature in each of the polymerization reactors of the present invention is 60-280°C;

[0027] The pressure in each of the polymerization reactors is 1.5-10.0 MPa;

[0028] The ratio of the evaporation rate (referring to the flow rate of the gas-phase components evaporated from the polymerization reactor into the rectification device) to the feeding rate (referring to the total feeding flow rate, including the total feeding flow rates of the polymerization monomer, solvent, and catalyst) in each of the polymerization reactors is 0.05-0.60.

[0029] The parameters of the above-mentioned rectification device can be adjusted according to actual situations without specific limitations. The recommended rectification device of the present invention is selected from a rectification tower, and the top pressure of the rectification tower is 0.25-4.0 MPa;

[0030] The top temperature of the rectification tower is 40-160°C, preferably 50-100°C;

[0031] The reflux ratio at the top of the rectification tower is 0.5-4.0, preferably 0.8-3.0.

[0032] Optionally, in the solution polymerization method for producing polyolefins provided by the present invention, the temperature of the light components, the intermediate components, and / or the heavy components without oligomers separated from the rectification device after being cooled by the heat exchanger is 20-60°C, preferably 25-40°C. It can be determined according to actual situations. For example, only the light components and the intermediate components can be selected for heat exchange.

[0033] Optionally, in the solution polymerization method for producing polyolefins provided by the present invention, the polymerization monomer of the polyolefin is selected from one or more of C2-C8 olefins, such as ethylene, propylene, butene, isopentene, 1-hexene, 1-heptene, 1-octene, and so on;

[0034] The solvent used is selected from one or more of C4-C20 alkanes, such as butane, n-pentane, n-hexane, cyclohexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, and so on;

[0035] The catalyst is a conventional Ziegler-Natta catalyst or metallocene catalyst in the industry.

[0036] Compared with the prior art, the present invention has at least the following beneficial effects:

[0037] Beneficial effect 1: The solution polymerization system for producing polyolefins provided by the present invention, by setting at least two interconnected polymerization reactors, connecting the top of the polymerization reactor to a rectification device, and at the same time connecting the top outlet and the lower outlet of the rectification device to each polymerization reactor through a heat exchanger and a multi-way flow valve respectively; and a heavy component discharge port is further provided at the bottom of the rectification device. Using this solution polymerization system for olefin polymerization reaction, by using the rectification device to precisely control the gas-phase mixture formed during the polymerization process and discharging the oligomers out of the system without recycling. On the one hand, it can efficiently remove the heat of the polyolefin reaction and avoid the blockage of pipelines caused by the evaporated oligomers entering the external circulation cooling equipment. On the other hand, it can precisely regulate the concentration and temperature gradients between different polymerization reactors in the polymerization process, meet the requirements of different polyolefin product properties, and at the same time the prepared polyolefin products are stable, which is conducive to large-scale industrial production.

[0038] Beneficial effect 2: Generally, the amount of solvent used in polyolefin products prepared by solution polymerization method is large, and a large amount of energy is required in the subsequent process of separating and removing the solvent; and the metallocene catalyst used in the polymerization process is sensitive to temperature, so it is necessary to strictly control the temperature distribution in the reactor to ensure that the temperature in the reactor is within a reasonable range. The solution polymerization method for producing polyolefins provided by the present invention utilizes the characteristics of the solution polymerization reaction carried out under reflux state, directly separates the components evaporated during the reaction effectively, and after cooling and circulation, returns to each polymerization reactor according to a certain ratio as required. While precisely regulating the concentration and temperature gradients between different polymerization reactors in the polymerization process, it can reduce the amount of solvent used, and at the same time reduce the energy consumption for separating and removing the solvent from the product subsequently, further reducing the cost. Description of the Drawings

[0039] Figure 1 It is a flow chart of a solution polymerization system for producing polyolefins provided by the present invention;

[0040] Figure 2 It is a flow chart of the solution polymerization method for producing polyolefins in the comparative example of the present invention.

[0041] Among them, R1 - the first reaction kettle; R2 - the second reaction kettle; R3 - the third reaction kettle; D1 - the distillation column; T1, T2 - the transfer pumps; F1, F2 - the feed pipelines; C1 - the top outlet pipeline; C2 - the middle outlet pipeline; C3 - the lower outlet pipeline; C11, C21, C31 - the branch pipelines of the first reaction kettle; C12, C22, C32 - the branch pipelines of the second reaction kettle; C13, C23, C33 - the branch pipelines of the third reaction kettle; E1 - the first gas-phase outlet pipeline; E2 - the second gas-phase outlet pipeline; E3 - the third gas-phase outlet pipeline; O1 - the heavy component discharge pipeline; P1, P2, P3 - the product pipelines; H1, H2, H3 - the heat exchangers; S1, S2, S3 - the multi-way flow valves. Detailed implementation manners

[0042] The present invention will be specifically described below through embodiments. It is necessary to point out here that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention according to the above content of the present invention.

[0043] For those embodiments in which specific experimental steps or conditions are not indicated, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For those reagents or instruments whose manufacturers are not indicated, they are all conventional reagent products that can be obtained through commercial purchase.

[0044] Embodiment 1

[0045] This embodiment provides a solution polymerization system for producing polyolefins, including:

[0046] At least two interconnected polymerization reactors, each of which is provided with a gas-phase outlet pipeline at the top;

[0047] A distillation device, the inlet pipelines of the distillation device are respectively connected to the gas-phase outlet pipelines of each polymerization reactor; the top outlet pipeline and the lower outlet pipeline of the distillation device are respectively connected to each polymerization reactor through a heat exchanger and a multi-way flow valve; a heavy component discharge port is also provided at the bottom of the distillation device.

[0048] In an optional implementation manner, the polymerization reactors are connected in series or in parallel.

[0049] In an optional implementation manner, a middle outlet pipeline is also provided on the distillation device, and the middle outlet is connected to the top of each polymerization reactor through a heat exchanger and a multi-way flow valve.

[0050] In an optional implementation manner, product outlets are provided on the side walls of each polymerization reactor.

[0051] In an alternative embodiment, each polymerization reactor is provided with a catalyst inlet and a polymerization monomer inlet, or one of the polymerization reactors is provided with a catalyst inlet and a polymerization monomer inlet.

[0052] In an alternative embodiment, each polymerization reactor is provided with a stirrer, and the stirrer is composed of an outer impeller and an inner impeller;

[0053] The outer impeller is selected from an anchor impeller or a frame impeller; the inner impeller is selected from at least one of an inclined blade impeller, a straight blade impeller, a turbine impeller and a propeller impeller, and the number of layers of the inner impeller is not specifically limited. For example, the inner impeller can be selected as 2 - 6 layers, and can be specifically adjusted according to actual conditions, such as 2 layers, 3 layers, 4 layers, 5 layers or 6 layers.

[0054] In an alternative embodiment, the rectification device is selected from a rectification column, and the number of trays of the rectification column is 4 - 30; it can be specifically adjusted according to actual conditions, such as the number of trays being 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 17, 20, 22, 25, 27, 29, etc.

[0055] In an alternative embodiment, the number of polymerization reactors is 2 - 8, and can be specifically adjusted according to actual conditions, such as 2, 3, 4, 5, 6, 7 or 8, etc.

[0056] In an alternative embodiment, each polymerization reactor can be provided with a jacket to pass cooling water for heat removal.

[0057] The solution polymerization system and method for producing polyolefins provided by the present invention are applicable to the copolymerization or homopolymerization of existing olefins. For the convenience of comparison, the copolymerization of ethylene and octene is used for description in the following examples. The solvent used is n - hexane, the catalyst is a metallocene catalyst (constrained geometry catalyst GCG, with a relative molecular mass of 383), and the cocatalyst is triethylaluminum.

[0058] Example 2

[0059] This example provides a solution polymerization method for producing polyolefins, using the Figure 1 solution polymerization system for producing polyolefins shown, and includes the following steps:

[0060] A mixed solution of ethylene, octene and n - hexane is transported through feed pipeline F1 by transfer pump T1 to the first reaction kettle R1. A mixture of n - hexane and catalyst is transported through feed pipeline F2 by transfer pump T2 into the first reaction kettle R1. Ethylene and octene carry out a copolymerization reaction in n - hexane under the action of the catalyst. Among them, the flow rate of ethylene is 110 kg / h, the flow rate of octene is 110 kg / h, the flow rate of the catalyst is 0.0014 kg / h, and the total flow rate of n - hexane is 640 kg / h. Ethylene, octene, n - hexane and the catalyst are all input into the first reaction kettle R1, and then are successively input into the second reaction kettle R2 and the third reaction kettle R3 (the three reaction kettles are connected in series), and the polymerization reaction pressure in each reaction kettle is controlled to be 4 MPa.

[0061] Adjust the evaporation gas flow rate in the first reaction kettle R1, the second reaction kettle R2 and the third reaction kettle R3 to be 55 kg / h. The evaporated gases in each reaction kettle are respectively transported through the first gas - phase outlet pipeline E1, the second gas - phase outlet pipeline E2 and the third gas - phase outlet pipeline E3 to the distillation column for distillation D1. Control the material flow rate discharged from the top outlet pipeline C1 of the distillation column D1 to be 30 kg / h, the material flow rate discharged from the middle outlet pipeline C2 to be 80 kg / h, the material flow rate discharged from the lower outlet pipeline C3 to be 50 kg / h, and the material (mainly oligomers) flow rate discharged from the bottom heavy - component discharge pipeline O1 to be 5 kg / h (discharged into the subsequent separation and recovery unit). And control the reflux ratio at the top of the distillation column D1 to be 1.3, the operating pressure at the top of the distillation column to be 2000 kPa, the top - tower temperature to be 50 °C, and the bottom - tower temperature to be 220 °C;

[0062] The material (mainly ethylene) discharged from the top outlet pipeline C1 is heated to 40 °C through heat exchanger H3, and then is adjusted by multi - way flow valve S2 and respectively enters the first reaction kettle R1, the second reaction kettle R2 and the third reaction kettle R3 through the branch pipeline C11 of the first reaction kettle, the branch pipeline C12 of the second reaction kettle and the branch pipeline C13 of the third reaction kettle.

[0063] The material (mainly n - hexane) discharged from the middle outlet pipeline C2 is heated to 40 °C through heat exchanger H1, and then is adjusted by multi - way flow valve S1 and respectively enters the first reaction kettle R1, the second reaction kettle R2 and the third reaction kettle R3 through the branch pipeline C21 of the first reaction kettle, the branch pipeline C22 of the second reaction kettle and the branch pipeline C23 of the third reaction kettle.

[0064] The material (mainly octene) discharged from the lower outlet pipeline C3 is heated to 40 °C through heat exchanger H2, and then is adjusted by multi - way flow valve S3 and respectively enters the first reaction kettle R1, the second reaction kettle R2 and the third reaction kettle R3 through the branch pipeline C31 of the first reaction kettle, the branch pipeline C32 of the second reaction kettle and the branch pipeline C33 of the third reaction kettle.

[0065] Meanwhile, the product is withdrawn from the product pipeline P3 on the side wall of the third reactor R3 (in this embodiment, the product pipelines P2 and P1 corresponding to the first reactor R1 and the second reactor R2 do not withdraw products). Among them, the stirrers in the first reactor R1, the second reactor R2, and the third reactor R3 are all composed of an outer paddle and an inner paddle. The outer paddle is an anchor paddle, and the inner paddle is composed of three layers of 45-degree inclined blades, with each layer of inclined blades consisting of four blades. All three reactors are made of 500L stainless steel. The trays of the distillation column adopt sieve trays, and the number of trays is 12. The entire polymerization process operates continuously.

[0066] Examples 3 - 6

[0067] Examples 3 - 6 are similar to Example 2, except that some process parameters are different, as shown in Table 1 specifically.

[0068] Comparative Example 1

[0069] This comparative example is similar to Example 2, except that the distillation column and related circulation circuits are omitted in this comparative example. The flowchart of the specific solution polymerization method for producing polyolefin in this comparative example is as Figure 2 shown, and the specific steps are as follows:

[0070] A mixed solution of ethylene, octene, and n - hexane is transported through the feed pipeline F1 to the first reactor R1 by the transfer pump T1, and a mixture of n - hexane and catalyst is transported through the feed pipeline F2 to the inside of the first reactor R1 by the transfer pump T2. Ethylene and octene carry out a copolymerization reaction in n - hexane under the action of the catalyst. Among them, the flow rate of ethylene is 110 kg / h, the flow rate of octene is 110 kg / h, the total flow rate of n - hexane is 640 kg / h, and the flow rate of the catalyst is 0.0014 kg / h. Ethylene, octene, n - hexane, and the catalyst are all input into the first reactor R1, and then sequentially input into the second reactor R2 and the third reactor R3 (the three reactors are connected in series).

[0071] The evaporation gas flow rates in the first reactor R1, the second reactor R2, and the third reactor R3 are all 55 kg / h. The evaporated gases in each reactor are respectively transported through the first gas phase outlet pipeline E1, the second gas phase outlet pipeline E2, and the third gas phase outlet pipeline E3 to the heat exchangers H1, H2, and H3, cooled to 40 °C, and then respectively recycled to the first reactor R1, the second reactor R2, and the third reactor R3. That is to say, these three reactors all remove the reaction heat through solution evaporation. The evaporated gas is cooled in the external circulation circuit and then recycled back to the original reactor. The evaporated gas only plays the role of removing the polymerization reaction heat and cannot change the temperature and concentration gradients of different reactors.

[0072] All polyolefin products are taken out through the product pipeline P3 on the side wall of the third reactor R3 ((in this comparative example, the product pipelines P2 and P3 corresponding to the first reactor R1 and the second reactor R2 do not take out products)).

[0073] Among them, the stirrers in the first reactor R1, the second reactor R2, and the third reactor R3 are all composed of an outer paddle and an inner paddle. The outer paddle is an anchor paddle, and the inner paddle is composed of three layers of 45-degree inclined blades, with four blades in each layer of inclined blades. All three reactors are made of 500L stainless steel. The entire polymerization process runs continuously.

[0074] Comparative Example 2

[0075] Comparative Example 2 is similar to Comparative Example 1, with the only difference being the reactor temperature, as shown in Table 1 specifically.

[0076] Comparative Example 3

[0077] Comparative Example 3 is similar to Comparative Example 1, with the only difference being the reactor temperature, as shown in Table 1 specifically.

[0078] The products obtained in each example and comparative example were respectively tested for the mass fraction of polyolefin in solution, the mass fraction of octene in polyolefin, the weight-average molecular weight of polyolefin, and the dispersity index of polyolefin. The specific test results are shown in Table 1 below.

[0079] Table 1

[0080]

[0081]

[0082] From the data in the above table, it can be seen that the ranges of the mass fraction of polyolefin in the reaction mixture, the mass fraction of the comonomer octene in polyolefin, the weight-average molecular weight of polyolefin, and the dispersity index (PDI) of polyolefin in Examples 2-6 are 17.1%-23.3%, 20.2%-35.7%, 141023-252937, and 2.0-3.9 respectively. It shows that by using the solution polymerization method provided by the present invention in the solution polymerization system, the precise control of the properties of polyolefin products can be achieved by adjusting process parameters, and the entire polymerization process has very high operation flexibility.

[0083] Specifically, by comparing the results of Example 2 and Example 3 with the comparative example, it can be found that transporting most of the overhead product of the distillation column to the reactor R1 can significantly increase the mass fraction of polyolefin in the poly solution and the weight-average molecular weight of the polyolefin. By analyzing the differences between the results of Example 4 and Example 5 and the comparative example, it can be found that transporting most of the bottom product of the distillation column to the reactor R1 can effectively increase the mass fraction of the comonomer octene in the polyolefin product. The different results between Example 6 and Comparative Example 1 show that evenly distributing the distillation column product to different reactors can significantly reduce the dispersity index PDI of the polyolefin. By analyzing the result differences among Comparative Example 1, Comparative Example 2, and Comparative Example 3, it is found that in the traditional process, it is difficult to precisely control the product properties by changing process parameters, and the distribution range of the product property indexes in the traditional process is narrow, making it difficult to meet the requirements of different polyolefin grades, while the present invention can achieve precise control of the product properties over a wide range.

[0084] Of course, the present invention may have many other embodiments and their variations. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and variations according to the present invention, but these corresponding changes and variations should all fall within the protection scope of the claims of the present invention.

Claims

1. A solution polymerization system for producing polyolefins, characterized in that, it includes: At least two interconnected polymerization reactors, each of the tops of the polymerization reactors is respectively provided with a gas phase outlet; A rectification device, the inlets of the rectification device are respectively communicated with the gas phase outlets of each of the polymerization reactors; the top outlet and the bottom outlet of the rectification device are respectively communicated with each of the polymerization reactors through a heat exchanger and a multi-way flow valve; a heavy component discharge port is also provided at the bottom of the rectification device.

2. The solution polymerization system for producing polyolefins according to claim 1, characterized in that, A middle outlet is also provided on the rectification device, and the middle outlet is communicated with the tops of each of the polymerization reactors through a heat exchanger and a multi-way flow valve.

3. The solution polymerization system for producing polyolefins according to claim 1, characterized in that, Product outlets are provided on the side walls of each of the polymerization reactors; A catalyst inlet and a polymerization monomer inlet are provided on each of the polymerization reactors, or a catalyst inlet and a polymerization monomer inlet are provided on one of the polymerization reactors.

4. The solution polymerization system for producing polyolefins according to claim 1, characterized in that, Agitators are provided in each of the polymerization reactors, and each agitator is composed of an outer impeller and an inner impeller; The outer impeller is selected from an anchor impeller or a frame impeller; the inner impeller is selected from at least one of an inclined blade impeller, a straight blade impeller, a turbine impeller and a propeller impeller.

5. A solution polymerization method for producing polyolefins, using the solution polymerization system for producing polyolefins according to any one of claims 1-4, characterized in that, it includes the following steps: The polymerization monomer undergoes solution polymerization in each polymerization reactor under the action of a catalyst, and the light components formed by evaporation at the top of each polymerization reactor during the polymerization process respectively enter the rectification device for separation; The light components discharged from the top outlet of the rectification device are heat-exchanged through a heat exchanger and then transported to at least one polymerization reactor through a multi-way flow valve; The heavy components without oligomers discharged from the lower outlet of the rectification device are heat-exchanged through a heat exchanger and then transported to at least one polymerization reactor through a multi-way flow valve; The heavy components discharged from the heavy component discharge port of the rectification device are transported to a separation and recovery unit.

6. The solution polymerization method for producing polyolefins according to claim 5, characterized in that, The intermediate components discharged from the middle outlet of the rectification device are heat-exchanged through a heat exchanger and then transported to at least one polymerization reactor through a multi-way flow valve.

7. The solution polymerization method for producing polyolefins according to claim 5, characterized in that, The liquid volume in each of the polymerization reactors accounts for 50%-100% of the total volume of each of the polymerization reactors.

8. The solution polymerization method for producing polyolefins according to claim 5, characterized in that, The temperature in each of the polymerization reactors is 60-280 °C; and / or The pressure in each of the polymerization reactors is 1.5-10.0 MPa; and / or The ratio of the evaporation rate to the feed rate in each of the polymerization reactors is 0.05-0.

60.

9. The solution polymerization method for producing polyolefins according to claim 5, characterized in that, The rectification device is selected from a rectification column, and the top pressure of the rectification column is 0.25 - 4.0 MPa; and / or the top temperature of the rectification column is 40 - 160 °C; and / or the reflux ratio at the top of the rectification column is 0.5 - 4.

0.

10. The solution polymerization method for producing polyolefin according to claim 6, characterized in that the temperature of the light components, the intermediate components and / or the heavy components without oligomers separated from the rectification device after being cooled by the heat exchanger is 20 - 60 °C.

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