Polymerization device and ethylene polymerization method

Abstract

The invention relates to the technical field of olefin polymerization, and discloses a polymerization device and an ethylene polymerization method. The polymerization device comprises a stirring reaction kettle (1), a reducing pipeline (2), an axial flow circulating pump (3), a loop reactor (4) and a separator (5) which are connected in sequence, wherein the inner diameter of the outlet end pipeline of the reducing pipeline (2) is 60-90% of the inner diameter of the inlet end pipeline. According to the polymerization device provided by the invention, the reducing pipeline is arranged between the stirring reaction kettle and the axial flow circulating pump, so that the separation energy consumption and difficulty of a diluent, a polymerization product and an oligomer in a reaction liquid can be remarkably reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of olefin polymerization, and particularly relates to a polymerization device and an ethylene polymerization method. Background Art

[0002] The slurry polyethylene production process is a low-temperature and low-pressure catalytic process. Supported catalysts are used to catalyze the polymerization reaction of ethylene or ethylene and comonomers in a suitable diluent. The catalyst and its components are usually insoluble in the diluent. During polymerization, the formed polymer particles are suspended in the diluent.

[0003] When using a loop slurry polymerization process to prepare copolymers of ethylene and higher α-olefins such as 1-hexene and / or 1-octene, since the formed ethylene polymer has low solubility in lower alkanes (such as isobutane) and there is no oligomer removal section, the oligomer content in the polymer is relatively high. In the slurry fluid in the loop slurry polymerization system, the flow is in a plug flow state, and the concentration of ethylene and other monomers gradually changes along the flow direction, resulting in poor structural uniformity of the ethylene polymer.

[0004] WO2007084274 discloses a method for polymerizing ethylene with C5-C10 α-olefins in two slurry reaction zones in the presence of a single-site catalyst system to prepare an ethylene polymer. However, WO2007084274 only discloses an example of polymerizing ethylene and 1-octene in n-hexane by a stirred tank slurry polymerization process.

[0005] CN101674880A discloses equipment for the liquid-phase polymerization of one or more α-olefins, comprising: a first reactor selected from a loop reactor and a continuous stirred tank reactor; at least a downstream loop reactor; a connection line for transferring the slurry from the first reactor to the downstream loop reactor, the connection line comprising: one or more adjacent pipes arranged at increasing heights, each pipe forming an angle α greater than the static angle of the resulting polymer with the horizontal direction (x); a switching valve flush with the wall of the downstream loop reactor. Since this invention uses hexane as a solvent, hexane easily forms an azeotrope with the comonomer 1-hexene, and the material concentration in the reactor cannot be accurately measured, and the density of the polymerization product cannot be controlled.

[0006] CN107108991B discloses a method for forming a "first composition comprising a first ethylene / α-olefin interpolymer and a second ethylene / α-olefin interpolymer", the method comprising polymerizing a first mixture comprising ethylene, an α-olefin and optionally a polyene in a stirred tank reactor to form a first ethylene / α-olefin interpolymer, and transferring at least some of the first ethylene / α-olefin interpolymer to a loop reactor, and polymerizing a second mixture comprising ethylene, an α-olefin and optionally a polyene therein in the presence of the first ethylene / α-olefin interpolymer to form a "first composition comprising a first ethylene / α-olefin interpolymer and a second ethylene / α-olefin interpolymer". The invention also provides a polymerization reactor configuration comprising at least the following: a stirred tank reactor followed by a loop reactor. The invention is mainly used for ethylene solution polymerization, where the catalyst and the polymerization monomers form a homogeneous solution, with high requirements for the catalyst, reactor and equipment, and difficult separation of the polymerization products. Summary of the Invention

[0007] The object of the present invention is to solve one of the many problems existing in the existing batch slurry polymerization process devices, such as difficult separation when copolymerizing ethylene with higher α-olefins such as 1-hexene and / or 1-octene, a relatively high content of oligomers in the polymer, poor structural homogeneity of the polymer, and poor impact performance and environmental stress cracking resistance. A polymerization device and an ethylene polymerization method are provided.

[0008] To achieve the above object, a first aspect of the present invention provides a polymerization device, wherein the polymerization device comprises a stirred reaction kettle 1, a reduced-diameter pipeline 2, an axial flow circulation pump 3, a loop reactor 4 and a separator 5 connected in sequence; wherein the inner diameter of the pipeline at the outlet end of the reduced-diameter pipeline 2 is 60-90% of the inner diameter of the pipeline at the inlet end.

[0009] A second aspect of the present invention provides a method for ethylene polymerization, wherein the method is carried out in the device of the first aspect of the present invention and comprises the following steps:

[0010] (1) Introduce raw material I comprising ethylene, a diluent, a catalyst, an optional cocatalyst, an optional hydrogen and an optional comonomer into the stirred reaction kettle for slurry full-kettle polymerization to obtain a reaction slurry;

[0011] (2) The reaction slurry enters the axial flow circulation pump through the reduced-diameter pipeline and is transported by the axial flow circulation pump to the loop reactor, where it contacts raw material II comprising ethylene, a diluent, a catalyst, an optional cocatalyst, an optional hydrogen and an optional comonomer for slurry polymerization to obtain a reaction liquid;

[0012] (3) Separate the reaction liquid to obtain a polymerization product.

[0013] Through the above technical solution, the beneficial technical effects achieved by the present invention are as follows:

[0014] 1) The polymerization device in the present invention includes a stirring reactor and a loop reactor. On the one hand, it can avoid the fragmentation of catalyst particles in the loop reactor, reduce the fine powder content, and improve the operation stability of the reaction system; on the other hand, the polymer produced in the stirring reactor further grows in the loop reactor, so that the performance of the polymerization product can be further enhanced.

[0015] 2) The polymerization device in the present invention is applicable to metallocene zirconium catalysts, can realize the production of bimodal / multimodal polyethylene, reduce the reaction process, lower the energy consumption of the device, improve the reaction efficiency, and significantly improve the impact performance and environmental stress cracking resistance of the prepared polymerization product.

[0016] 3) In the polymerization device of the present invention, by setting a reduced-diameter pipeline, the energy required for separating the diluent from the polymerization product can be reduced, effectively solving the separation problem faced in the preparation of ethylene-1-hexene copolymer by the stirred tank slurry polymerization process, facilitating the steady-state regulation of the polymerization device, and ensuring the stable operation of the device.

[0017] 4) The method for ethylene polymerization in the present invention has a simple and compact process flow. The boiling point of the diluent used is significantly different from that of the comonomer, no azeotrope will be formed, and the residual content of the diluent in the polymerization product is lower than that of the loop slurry process, which is more advantageous in the production of ethylene-1-hexene copolymer. Description of the Drawings

[0018] Figure 1 is a schematic structural diagram of the polymerization device provided in the present invention.

[0019] Description of the Reference Numerals in the Drawings

[0020] 1, stirring reactor; 2, reduced-diameter pipeline; 3, axial flow circulation pump

[0021] 4, loop reactor; 5, separator; 6, buffer tank

[0022] 51, solid-liquid separator; 52, distillation column

[0023] A, detection point; B, detection point Detailed Embodiments

[0024] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0025] The first aspect of the present invention provides a polymerization device, wherein the polymerization device includes a stirring reactor 1, a reduced-diameter pipeline 2, an axial-flow circulation pump 3, a loop reactor 4 and a separator 5 connected in sequence; wherein, the inner diameter of the pipeline at the outlet end of the reduced-diameter pipeline 2 is 60-90% of the inner diameter of the pipeline at the inlet end.

[0026] Wherein, in the present invention, the inventors have found through research that by arranging a reduced-diameter pipeline between the stirring reactor and the axial-flow circulation pump, on the one hand, the separation energy consumption and difficulty of diluents, polymerization products and oligomers in the reaction liquid can be significantly reduced, and on the other hand, it is beneficial to the steady-state regulation of the polymerization device and can ensure the stable operation of the device.

[0027] In a preferred embodiment of the present invention, the stirring reactor 1 is a stirring reactor capable of full-kettle operation. Wherein, the stirring reactor of the present invention is not particularly limited, and any reaction kettle capable of full-kettle operation and equipped with stirring can be used in the present invention.

[0028] In a preferred embodiment of the present invention, the height-to-diameter ratio of the stirring reactor 1 is 1-3:1, preferably 1.5-2.5:1.

[0029] In a preferred embodiment of the present invention, a feed inlet and a stirring motor are provided at the bottom of the stirring reactor 1. Wherein, in the present invention, when ethylene polymerization is carried out using the polymerization device of the present invention, ethylene, diluent, catalyst, optional cocatalyst, optional hydrogen and optional comonomer can enter the stirring reactor from the feed inlet.

[0030] In a preferred embodiment of the present invention, the ratio of the inner diameter of the stirring reactor 1 to the inner diameter of the pipeline at the inlet end of the reduced-diameter pipeline 2 is 5-18:1, preferably 9.6-12:1; the ratio of the inner diameter of the stirring reactor 1 to the inner diameter of the pipeline at the outlet end of the reduced-diameter pipeline 2 is 8-20:1, preferably 12-15:1.

[0031] Wherein, in the present invention, by controlling the ratio of the inner diameter of the stirring reactor to the inner diameter of the pipeline at the inlet end and the outlet end of the reduced-diameter pipeline, the outlet pressure and outlet flow rate of the reduced-diameter pipeline can be increased by 20-30% respectively.

[0032] In a preferred embodiment of the present invention, the inner diameter of the pipeline at the outlet end of the reduced-diameter pipeline 2 is 75-85% of the inner diameter of the pipeline at the inlet end. Wherein, in the present invention, when the inner diameter of the pipeline at the outlet end of the reduced-diameter pipeline is 75-85% of the inner diameter of the pipeline at the inlet end, the outlet pressure and flow rate of the reduced-diameter pipeline have better improvement effects, the separation energy consumption of diluents, polymerization products and oligomers in the reaction liquid is the lowest, and it is easy to carry out steady-state regulation.

[0033] In a preferred embodiment of the present invention, the length-diameter ratio of the reduced-diameter pipe 2 is 1.5 - 3:1, preferably 2 - 2.5:1.

[0034] Wherein, in the present invention, the length-diameter ratio of the reduced-diameter pipe refers to the ratio of the total length of the reduced-diameter pipe to the inner diameter of the pipe at the inlet end of the reduced-diameter pipe. If the length-diameter ratio of the reduced-diameter pipe is too large, the transfer resistance of the reaction slurry from the stirring reactor to the loop reactor will increase, resulting in an increase in overall energy consumption; if the length-diameter ratio of the reduced-diameter pipe is too small, the equipment layout and connection space will be limited. When the length-diameter ratio of the reduced-diameter pipe is within the range defined in the present invention, the effect is the best.

[0035] In a preferred embodiment of the present invention, the axial flow circulation pump 3 is used to generate an axial driving force, so that the liquid in the loop reactor flows uniformly along the axis. Among them, the axial flow circulation pump can make the flow rate of the liquid in the loop reactor be 2 - 8 m / s, preferably 4 - 5 m / s.

[0036] In a preferred embodiment of the present invention, a jacket is provided outside the loop reactor 4. Among them, the jacket is used to heat the loop reactor 4.

[0037] In a preferred embodiment of the present invention, the inner diameter of the loop reactor 4 is the same as the inner diameter of the pipe at the outlet end of the reduced-diameter pipe 2.

[0038] In a preferred embodiment of the present invention, the separator 5 includes a solid-liquid separator 51 and a distillation column 52; the solid-liquid separator 51 is connected to the loop reactor 4, one end of the distillation column 52 is connected to the solid-liquid separator 5, and the other end is connected to the stirring reactor 1 and / or the loop reactor 4.

[0039] Wherein, in the present invention, the reaction liquid from the loop reactor is subjected to solid-liquid separation in the solid-liquid separator to obtain a liquid phase component and a solid phase component. The solid phase component is dried to obtain a polymerization product. The liquid phase component is distilled to remove oligomers and then returned to the stirring reactor and / or the loop reactor as a diluent.

[0040] In a preferred embodiment of the present invention, the polymerization device further includes a buffer tank 6, wherein the buffer tank 6 is arranged between the loop reactor 4 and the separator 5.

[0041] Wherein, the reaction liquid from the loop reactor is first stored in the buffer tank, and the solid content of the slurry in the buffer tank is tested. When the solid content of the slurry is 20 - 30 wt%, the slurry in the buffer tank can be transported to the separator for separation.

[0042] In a preferred embodiment of the present invention, detection points are provided on the reduced-diameter pipeline and the loop reactor. Among them, detection point A is used to detect the content of each component in the reaction slurry from the stirred reactor, and detection point B is used to detect the content of each component in the loop reactor. The present invention does not make special limitations on the detection method of the detection points, and the detection can be carried out by using the detection methods well-known in the art. According to the detection results, the feed of the loop reactor is dynamically adjusted.

[0043] The second aspect of the present invention provides a method for ethylene polymerization, wherein the method is carried out in the device described in the first aspect of the present invention, and includes the following steps:

[0044] (1) Introduce raw material I containing ethylene, diluent, catalyst, optional cocatalyst, optional hydrogen, and optional comonomer into the stirred reactor for slurry full-pot polymerization to obtain a reaction slurry;

[0045] (2) The reaction slurry enters the axial flow circulation pump through the reduced-diameter pipeline and is transported by the axial flow circulation pump to the loop reactor, where it contacts raw material II containing ethylene, diluent, catalyst, optional cocatalyst, optional hydrogen, and optional comonomer for slurry polymerization to obtain a reaction liquid;

[0046] (3) Separate the reaction liquid to obtain a polymerization product.

[0047] In step (1):

[0048] In a preferred embodiment of the present invention, before introducing raw material I into the stirred reactor, that is, before starting the reaction, the diluent is first filled into the polymerization device. Among them, in the present invention, the diluent can be divided into three parts. One part is added to the polymerization device in advance before the reaction to fill the stirred reactor and the loop reactor, one part is added to raw material I, and one part is added to raw material II.

[0049] In a preferred embodiment of the present invention, the diluent is selected from one or more of n-butane, isobutane, n-pentane, isopentane, n-hexane, cyclohexane, n-heptane, n-octane, n-nonane, and n-decane, preferably one or more of n-pentane, isopentane, and n-hexane, and more preferably n-pentane.

[0050] In a preferred embodiment of the present invention, the catalyst and the cocatalyst are well-known in the art, and the present invention does not make special limitations on them. For example, the catalyst can be a high-comonomer single-site catalyst, preferably a high-comonomer single-site zirconocene catalyst. The cocatalyst can be one or more of triethylaluminum, triisobutylaluminum, and monochlorodiethylaluminum.

[0051] In a preferred embodiment of the present invention, the comonomer is selected from one or more of 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene and 1-decene, preferably 1-hexene and / or 1-octene, and more preferably 1-hexene.

[0052] In a preferred embodiment of the present invention, the amounts of ethylene, hydrogen and comonomer in raw material I are not particularly limited and can be appropriately selected according to the specific application of the target polymer so that the polymer can meet the specific use requirements. The contents of the diluent, catalyst and cocatalyst in the present invention are also not particularly limited and can be added according to the conventional addition amounts in the art.

[0053] In a preferred embodiment of the present invention, raw material I comprises ethylene, diluent, catalyst, hydrogen and optionally cocatalyst, and does not include comonomer.

[0054] Among them, in the present invention, only ethylene and hydrogen are added to the feed of the stirred reactor, and no comonomer is added. The homopolymerization reaction mainly occurs in the stirred reactor, which helps to generate a relatively uniform ethylene polymerization chain in the stirred reactor.

[0055] In a preferred embodiment of the present invention, the reaction temperature of the stirred reactor is 70-95 °C, preferably 80-90 °C; the reaction pressure of the stirred reactor is 0.4-2 MPa, preferably 0.8-1.2 MPa. Among them, in the present invention, unless otherwise specified, the pressure refers to the gauge pressure.

[0056] In step (2),

[0057] In a preferred embodiment of the present invention, the reaction temperature of the loop reactor is 65-90 °C, preferably 80-85 °C, and the reaction pressure of the loop reactor is 0.5-2.5 MPa, preferably 0.8-1.4 MPa.

[0058] In a preferred embodiment of the present invention, the molar contents of ethylene, diluent, catalyst and optionally cocatalyst in the loop reactor are the same as those of ethylene, diluent, catalyst and optionally cocatalyst in the stirred reactor.

[0059] Among them, in the present invention, the contents of ethylene, diluent, catalyst and optionally cocatalyst in the loop reactor and the stirred reactor can be monitored in real time by known methods, and by adjusting the feed of raw material II, the molar contents of ethylene, diluent, catalyst and optionally cocatalyst in the loop reactor can be kept the same as those of ethylene, diluent, catalyst and optionally cocatalyst in the stirred reactor.

[0060] In a preferred embodiment of the present invention, the raw material I comprises hydrogen and a comonomer, the raw material II comprises hydrogen and a comonomer, and the hydrogen / ethylene (mol / mol) and comonomer / ethylene (mol / mol) in the loop reactor are the same as those in the stirred reactor.

[0061] In a preferred embodiment of the present invention, the raw material II comprises ethylene, a diluent, a catalyst, a comonomer and an optional cocatalyst, and does not contain hydrogen.

[0062] Wherein, in the present invention, a comonomer is added to the loop reactor and hydrogen is not added, and copolymerization reaction mainly occurs in the loop reactor. The inventors of the present invention have found through research that when the raw material I contains hydrogen and does not contain a comonomer, and the raw material II contains a comonomer and does not contain hydrogen, such a feeding method can further improve the bulk density, impact performance and environmental stress cracking resistance of the polymerization product.

[0063] In step (3):

[0064] In a preferred embodiment of the present invention, the separation includes first feeding the reaction liquid into a solid-liquid separator for solid-liquid separation to obtain a liquid phase component and a solid phase component; then drying the solid phase component to obtain the polymerization product; distilling the liquid phase component to remove oligomers to obtain a circulating liquid; and returning the circulating liquid to the stirred reactor and / or the loop reactor for use as a diluent.

[0065] Wherein, in the present invention, when performing solid-liquid separation, since the amount of the residual catalyst in the solid phase component is relatively small and can be ignored, the solid phase component can be directly dried to obtain a high-purity polymerization product.

[0066] In a preferred embodiment of the present invention, the content of the diluent in the polymerization product is ≤ 0.35 wt%, preferably 0.2 - 0.32 wt%.

[0067] In a preferred embodiment of the present invention, the polymerization product and an antioxidant are mixed and then granulated to obtain pellets; wherein, the mass of the antioxidant is 0.1 - 0.6% of the mass of the polymerization product, preferably 2.5 - 3.5%; the antioxidant is selected from one or more of antioxidant B225, B215, B561, B900, and preferably antioxidant B225.

[0068] In a preferred embodiment of the present invention, the melt mass flow rate of the pellets, measured according to the method specified in GB / T 3682 at a temperature of 190 °C under a load of 2.16 kg, is 0.01 - 5 g / 10 min, preferably 0.05 - 3 g / 10 min, and more preferably 0.2 - 1 g / 10 min. Among them, in the present invention, the melt flow rate of the polymer can be made as expected by controlling the amount of hydrogen used as a molecular weight regulator in the art.

[0069] In a preferred embodiment of the present invention, the density of the pellets is 0.93 - 0.97 g / cm 3 , preferably 0.94 - 0.96 g / cm 3 ; the bulk density is 0.28 - 0.5 g / cm 3 , preferably 0.3 - 0.45 g / cm 3 ; the Izod impact strength of the pellets is 10 - 60 kJ / m 2 , preferably 15 - 50 kJ / m 2 .

[0070] The present invention will be described in detail below through examples. Among them, the polymerization device in the examples includes a stirred reaction kettle, a reduced-diameter pipeline, an axial flow circulation pump, a loop reactor, a buffer tank, a solid-liquid separator, and a distillation column; among them, the bottom of the stirred reaction kettle is provided with a feed inlet and a stirring motor, with a volume of 200 L, a height of 1.3 m, and a height-to-diameter ratio of 1.8:1. The ratio of the inner diameter of the stirred reaction kettle to the inner diameter of the inlet end pipeline of the reduced-diameter pipeline is 10:1, and the ratio of the inner diameter of the stirred reaction kettle to the inner diameter of the outlet end pipeline of the reduced-diameter pipeline is 12.5:1; the inner diameter of the outlet end pipeline of the reduced-diameter pipeline is 80% of the inner diameter of the inlet end pipeline, and the length-to-diameter ratio is 2.2:1; a jacket is provided outside the loop reactor, and the inner diameter of the loop reactor is the same as the inner diameter of the outlet end pipeline of the reduced-diameter pipeline.

[0071] Unless otherwise specified, all raw materials used below are commercially available.

[0072] Ethylene: polymerization grade, Daqing Petrochemical Company;

[0073] Comonomer: 1-butene, 1-hexene, 1-octene, polymerization grade, Daqing Petrochemical Company;

[0074] Diluent: n-pentane, analytical pure, J&K Scientific;

[0075] Catalyst: Z-N catalyst, grade PSE-CX2 catalyst, purchased from Petrochemical Research Institute of PetroChina Company Limited.

[0076] The short-bridged zirconocene catalyst, abbreviated as metallocene, with the brand number PME-03, was purchased from the Petrochemical Research Institute of PetroChina Company Limited.

[0077] Hydrogen: Obtained by dehydrating and deoxidizing high-purity hydrogen.

[0078] The detection points A and B were detected by on-line gas chromatography, and the concentrations of the catalyst and cocatalyst were detected by the heat release of the reaction and the pressure fluctuation.

[0079] Example 1

[0080] (1) First, the polymerization device was filled with n-pentane, and then the raw material I containing ethylene, n-pentane, Z-N catalyst, triethylaluminum, hydrogen, and 1-hexene was continuously added to the stirred reaction kettle for slurry full-kettle polymerization to obtain a reaction slurry;

[0081] (2) The above reaction slurry entered the axial flow circulation pump through a reduced-diameter pipeline and was transported by the axial flow circulation pump to the loop reactor, where it contacted the raw material II containing ethylene, n-pentane, Z-N catalyst, hydrogen, and 1-hexene for slurry polymerization to obtain a reaction liquid; among them, according to the detection results of the detection points A and B, the molar content of hydrogen / ethylene (mol / mol), 1-hexene / ethylene (mol / mol), ethylene, and catalyst in the liquid phase of the loop reactor was adjusted to be the same as that of hydrogen / ethylene (mol / mol), 1-hexene / ethylene (mol / mol), ethylene, and catalyst in the stirred reaction kettle;

[0082] (3) First, the above reaction liquid was introduced into a solid-liquid separator for solid-liquid separation to obtain a liquid phase component and a solid phase component; then the solid phase component was dried to obtain a polymerization product; the liquid phase component was distilled to remove oligomers to obtain a circulating liquid; and part of the circulating liquid was returned to the stirred reaction kettle and the loop reactor as a diluent.

[0083] Among them, the raw material ratio and reaction conditions in Example 1 are shown in Table 1.

[0084] Example 2

[0085] (1) First, the polymerization device was filled with n-pentane, and then the raw material I containing ethylene, n-pentane, Z-N catalyst, triethylaluminum, and hydrogen was continuously added to the stirred reaction kettle for slurry full-kettle polymerization to obtain a reaction slurry;

[0086] (2) The above reaction slurry enters the axial flow circulation pump through a reduced-diameter pipeline and is transported by the axial flow circulation pump to the loop reactor, where it contacts Feedstock II containing ethylene, n-pentane, Ziegler-Natta catalyst, and 1-hexene to carry out slurry polymerization to obtain a reaction liquid. Among them, according to the detection results at Detection Point A and Detection Point B, the molar contents of ethylene and catalyst in the loop reactor are adjusted to be the same as those in the stirred reaction kettle.

[0087] (3) First, the above reaction liquid is introduced into a solid-liquid separator for solid-liquid separation to obtain a liquid-phase component and a solid-phase component. Then, the solid-phase component is dried to obtain a polymerization product. The liquid-phase component is distilled to remove oligomers to obtain a circulating liquid, and the circulating liquid is returned to the stirred reaction kettle and the loop reactor as a diluent.

[0088] Among them, the raw material ratios and reaction conditions in Example 2 are shown in Table 1.

[0089] Example 3

[0090] Same as Example 1, except that a short-bridged metallocene zirconium catalyst is used instead of the Ziegler-Natta catalyst. The raw material ratios and reaction conditions in Example 3 are shown in Table 1.

[0091] Example 4

[0092] Same as Example 2, except that a short-bridged metallocene zirconium catalyst is used instead of the Ziegler-Natta catalyst. The raw material ratios and reaction conditions in Example 4 are shown in Table 1.

[0093] Example 5

[0094] Same as Example 3, except that neither Feedstock I nor Feedstock II contains 1-hexene. The raw material ratios and reaction conditions in Example 5 are shown in Table 1.

[0095] Example 6

[0096] Same as Example 4, except that 1-butene is used as the comonomer instead of 1-hexene. The raw material ratios and reaction conditions in Example 6 are shown in Table 1.

[0097] Example 7

[0098] Same as Example 6, except that 1-octene is used as the comonomer instead of 1-butene. The raw material ratios and reaction conditions in Example 7 are shown in Table 1.

[0099] Table 1

[0100]

[0101]

[0102] Continued Table 1

[0103]

[0104]

[0105] Test Example 1

[0106] The polymer product prepared in the example was mixed with antioxidant B225 and granulated in a twin-screw extruder to obtain pellets. Among them, the mass of antioxidant B225 was 0.3% of the mass of the polymer product.

[0107] The content of the comonomer structural unit, melt mass flow rate, density, bulk density, Izod impact strength, environmental stress cracking resistance (ESCR), and n-hexane content of the obtained pellets were tested. The test results are shown in Table 2.

[0108] Among them, the test method for the content of the comonomer unit: high-temperature nuclear magnetic carbon spectrum test.

[0109] The melt mass flow rate MFR was measured by the method specified in GB / T 3682 at a temperature of 190 °C under a load of 2.16 kg.

[0110] The test method for density: GB / T 1033.2.

[0111] The test method for bulk density: GB / T 23771-2009

[0112] The Izod impact strength was tested according to the method for determining the Izod impact properties of plastics in GB / T 1843. At least 5 parallel samples were tested in each group, and the results were averaged.

[0113] The test method for environmental stress cracking resistance (ESCR): GBT 1842-2008 Test method for environmental stress cracking of polyethylene plastics.

[0114] The content of n-hexane extract was determined by the following method: Weigh 5 g of the sample, place it in a Soxhlet extractor, add 100 n-hexane, and perform extraction for 3 h; evaporate the obtained n-hexane, dry the obtained evaporation residue in a vacuum oven at a temperature of 45 °C (with an absolute pressure of 20 kPa) for 3 h and then weigh it. The content of n-hexane extract was calculated using the following formula: Content of n-hexane extract (%) = (weight of evaporation residue / 5) × 100%.

[0115] Table 2

[0116]

[0117] Among them, in Table 2, HD5502 is the grade of polyethylene resin. By comparing Examples 1-7 with HD5502, it can be seen that the performance of the polymerization products prepared in the present invention is equivalent to or better than that of the typical polyethylene product grades in the market.

[0118] As can be seen from Table 2, the performance of the polymerization products prepared in Example 2 and Example 4 has been greatly improved compared with that in Example 1 and Example 3 respectively. This may be because only ethylene and hydrogen are added to the feed of the stirred reactor without adding comonomers, and homopolymerization mainly occurs, which helps to form a more uniform ethylene polymerization chain in the stirred reactor. Comonomers are added to the loop reactor without adding hydrogen, and copolymerization mainly occurs. The ethylene polymerization chain can further grow in the loop reactor, and the comonomer can be inserted into the molecular chain of the ethylene polymerization chain, thereby significantly reducing the melt mass flow rate of the polymerization product and significantly improving the impact performance and environmental stress cracking resistance of the polymerization product.

[0119] By comparing Example 1 with Example 3, and by comparing Example 2 with Example 4, it can be seen that the catalyst has an important influence on the performance of the polymer. The performance of the polymer prepared with the metallocene zirconium catalyst is better than that of the polymer prepared with the Z-N catalyst. As can be seen from Examples 6 and 7, when 1-butene and 1-octene are used as comonomers respectively, the performance improvement of the prepared polymer is also very large, indicating that the ethylene polymerization device of the present invention has a wide application range.

[0120] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A polymerization device, characterized in that, the polymerization device comprises a stirring reactor (1), a reduced-diameter pipeline (2), an axial flow circulation pump (3), a loop reactor (4) and a separator (5) connected in sequence; wherein, the inner diameter of the pipeline at the outlet end of the reduced-diameter pipeline (2) is 60-90% of the inner diameter of the pipeline at the inlet end.

2. The polymerization device according to claim 1, wherein, the height-diameter ratio of the stirring reactor (1) is 1-3:1; and / or, the ratio of the inner diameter of the stirring reactor (1) to the inner diameter of the pipeline at the inlet end of the reduced-diameter pipeline (2) is 5-18:1; and / or, the ratio of the inner diameter of the stirring reactor (1) to the inner diameter of the pipeline at the outlet end of the reduced-diameter pipeline (2) is 8-20:

1.

3. The polymerization device according to claim 1 or 2, wherein, the inner diameter of the pipeline at the outlet end of the reduced-diameter pipeline (2) is 75-85% of the inner diameter of the pipeline at the inlet end; and / or, the length-diameter ratio of the reduced-diameter pipeline (2) is 1.5-3:

1.

4. The polymerization device according to claim 1, wherein, the inner diameter of the loop reactor (4) is the same as the inner diameter of the pipeline at the outlet end of the reduced-diameter pipeline (2).

5. The polymerization device according to claim 1, wherein, the separator (5) comprises a solid-liquid separator (51) and a distillation column (52); the solid-liquid separator (51) is connected to the loop reactor (4), one end of the distillation column (52) is connected to the solid-liquid separator (5), and the other end is connected to the stirring reactor (1) and / or the loop reactor (4).

6. A method for ethylene polymerization, characterized in that, the method is carried out in the polymerization device according to any one of claims 1-5, and comprises the following steps: (1) Introducing raw material I containing ethylene, diluent, catalyst, optional cocatalyst, optional hydrogen and optional comonomer into the stirring reactor for slurry full-pot polymerization to obtain a reaction slurry; (2) The reaction slurry enters the axial flow circulation pump through the reduced-diameter pipeline, and is transported by the axial flow circulation pump to the loop reactor, and contacts with raw material II containing ethylene, diluent, catalyst, optional cocatalyst, optional hydrogen and optional comonomer for slurry polymerization to obtain a reaction liquid; (3) Separating the reaction liquid to obtain a polymerization product.

7. The method according to claim 6, wherein, the diluent is selected from one or more of n-butane, isobutane, n-pentane, isopentane, n-hexane, cyclohexane, n-heptane, n-octane, n-nonane, n-decane; and / or, the comonomer is selected from one or more of 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene and 1-decene; and / or, the reaction temperature of the stirring reactor is 70-95 °C, and the reaction pressure of the stirring reactor is 0.4-2 MPa.

8. The method according to claim 6 or 7, wherein, the reaction temperature of the loop reactor is 65-90 °C, and the reaction pressure of the loop reactor is 0.5-2.5 MPa.

9. The method according to claim 6 or 7, wherein, The molar contents of ethylene, diluent, catalyst and optional cocatalyst in the loop reactor are the same as those of ethylene, diluent, catalyst and optional cocatalyst in the stirred reactor.

10. The method according to claim 6 or 7, wherein, the separation includes first feeding the reaction liquid into a solid-liquid separator for solid-liquid separation to obtain a liquid phase component and a solid phase component; then drying the solid phase component to obtain the polymerization product; distilling the liquid phase component to remove oligomers to obtain a circulating liquid; and returning the circulating liquid to the stirred reactor and / or the loop reactor for use as a diluent.

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