A preparation method and system for polyolefin

Abstract

The present invention provides a method and a system for preparing polyolefin. The preparation method includes: subjecting raw materials to a polymerization reaction to obtain a polymer solution; mixing and reacting the polymer solution with a complexing agent and hydrazine hydrate to obtain a mixed solution; separating the mixed solution by passing it through an adsorption column filled with an adsorbent to obtain a metal-removed polymer solution; and subjecting the metal-removed polymer solution to devolatilization and extrusion granulation to obtain polymer particles. The preparation system includes: a polymerization reaction unit, a metal-removing unit, a devolatilization unit, an extrusion granulation unit, etc. The method and system of the present invention can deeply and efficiently remove the residual metals in the polymer, and at the same time have the advantages of short process flow, low production cost, and continuous long-term operation.

Description

Technical Field

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

[0002] Metallocene catalysts have been a research hotspot in organometallic chemistry, catalytic chemistry, polymer chemistry, and materials science in recent decades. By using such catalysts, olefin polymers with a narrow molecular weight distribution and a uniform chemical composition distribution can be obtained. At the same time, the molecular structure and molecular weight of the polymer can be highly controllable by adjusting the structure of the catalyst. The industrial high-performance polymers prepared by using metallocene catalysts mainly include polyolefin elastomers (POE), polyolefin plastomers (POP), cycloolefin copolymers (COC), cycloolefin polymers (COP), etc. Among them, cycloolefin copolymers have excellent heat resistance, chemical corrosion resistance, high toughness, UV-Vis transparency, and extremely low hygroscopicity and extractability, and can be used as optical storage media, medical packaging materials, etc.

[0003] Currently, the industry mostly uses highly efficient metallocene olefin polymerization catalyst systems to produce polyolefin products. Generally, metallocene catalysts contain elements in Groups IVB, VB, and VIB of the periodic table, especially vanadium, titanium, and zirconium. The cocatalysts mainly contain elements such as aluminum. Such catalysts are usually called transition metal catalysts, and they have high olefin polymerization catalytic activity. However, after the polymerization is completed, the metals in the catalyst remain in the polyolefin product, which will have a negative impact on the appearance, dielectric properties, optical properties, medical material properties, etc. of the end product. Therefore, for polyolefin products, especially high-end polyolefin products such as medical grade and optical grade, how to efficiently remove metal residues (abbreviated as demetallization, deashing) is of utmost importance.

[0004] The commonly used polymer deashing methods mainly include pickling, alcohol washing, and adsorption methods. Among them, the adsorption method is the most commonly used deashing method in the polymer industrial production, and has the advantages of simple process, large adsorption capacity, few interference factors, and good stability. Although the application range of the adsorption method is relatively wide, it is usually difficult to reduce the metal content in the polymer solution to below 10 ppm. The main reason is that metal ions are dissolved in the polymer solution in the form of oil-soluble metal organic complexes, and the adsorption process is limited by the diffusion control of the metal organic complexes in the high-viscosity system, and deep removal cannot be achieved. In addition, in the industrial process, supported adsorbent fillers are often used for complexing deashing. Such adsorbents are solid fillers prepared by impregnating and calcining an alumina carrier and a complexing agent material, and the effective loading amount of the complexing agent is relatively low, which is limited in application.

[0005] CN107011485A discloses a three-active-center composite catalyst and a method for preparing cycloolefin copolymer by using the same. The method for preparing the cycloolefin copolymer is carried out in a batch polymerization reactor. Using titanium trichloride of salicylidene-2-mercaptoaniline, rac-vinylbis(indenyl)zirconium dichloride and zirconocene dichloride as the three-active-center composite catalyst (i.e., the main catalyst), and a toluene solution of methylaluminoxane (MAO) as the cocatalyst, with cycloolefin as the comonomer, and adding ethylene by supplementary metering during the polymerization process, controlling the pressure at 0.1 MPa to carry out the polymerization reaction. After the reaction is completed, the reaction solution is poured into ethanol containing 15% (v / v%) hydrochloric acid (composed of 150 mL hydrochloric acid and 1000 mL ethanol) for precipitation and then filtration. The filter cake is washed with ethanol (300 mL) and then dried to a constant weight to obtain the cycloolefin copolymer. However, this preparation method does not involve the removal of metals in the polymer.

[0006] CN108752526A discloses a catalytic system for preparing ethylene and / or α-olefin and cycloolefin copolymer. The catalytic system includes a main catalyst and a cocatalyst. The main catalyst is a metallocene compound, and the cocatalyst is an organoboron compound and an alkylaluminum. The method for preparing ethylene and / or α-olefin and cycloolefin copolymer by using this catalytic system includes the following steps: under the conditions of a temperature of 40-100 °C and a pressure of 1-30 bar, adding an inert organic solvent, ethylene / α-olefin and cycloolefin into the reactor respectively; after ethylene and / or α-olefin are dissolved to saturation in the inert organic solvent, adding a triisobutylaluminum solution, a metallocene catalyst solution and an organoboron compound solution in sequence for polymerization reaction. Using this cocatalyst can polymerize cycloolefin copolymer more efficiently than MAO, MMAO and dMAO, and also reduce the metal content in the polymerization product, greatly reducing the post-treatment cost.

[0007] CN103374089A discloses a method for removing catalysts from an ethylene-α-olefin copolymer solution. The copolymer solution contains an ethylene-α-olefin copolymer, an organic solvent and a catalyst. The catalyst contains an alkylaluminum cocatalyst and a vanadium compound main catalyst. The method includes: (1) contacting water with the copolymer solution to obtain a first mixture; (2) adjusting the pH value of the first mixture obtained in step (1) to 4-9 with a pH regulator to obtain a second mixture; (3) centrifuging to separate and remove the precipitate from the second mixture obtained in step (2), wherein, based on the volume of the copolymer solution, the addition amount of the water is 0.1-20% by volume. This method has a significant effect on removing residual catalysts in the copolymer solution and has a low cost. The pH regulator used in this method is a hydroxide of an alkali metal and / or a hydroxide of an alkaline earth metal, preferably sodium hydroxide. The metal removal rate of this method is not high enough, and the polymer products prepared cannot meet the index requirements of medical-grade and optical-grade polymers.

[0008] US4716207A discloses a method for preparing nodular polymers by preparing copolymer chains and coupling them with a coupling agent. The deashing step in this method mainly includes: feeding the copolymer product from the reactor through a conduit into the deashing section, where the catalyst residue reacts with water to form a hydroxide insoluble in hydrocarbons, and then extracting the hydroxide into dilute acid to remove the residues of vanadium and aluminum compounds. However, the metal removal rate of this method is not high enough, and the polymer products prepared cannot meet the requirements of medical-grade and optical-grade polymer specifications.

[0009] CN110016092A discloses a method for continuously preparing polyolefins, especially for continuously preparing polyolefin elastomers or their mixtures. This method uses a tank reactor for prepolymerization, which has the effect of increasing the viscosity of the reaction system to facilitate the subsequent operation of the screw reactor; and uses a static mixer for static mixing polymerization to continue increasing the system viscosity and extending the reaction residence time; at the same time, uses a reactive screw extruder for extrusion polymerization to achieve the occurrence of polymerization reactions at high conversion rates and high viscosities. This method is suitable for the preparation of various types of polyolefins, especially suitable for the preparation of polyolefin elastomers or their mixtures. However, this method does not involve the process of removing metals from polymers, and the polymer products prepared cannot meet the requirements of medical-grade and optical-grade polymer specifications.

[0010] CN113207283A discloses a system for solution polymerization. The system includes: a reactor system for receiving an antisolvent, a monomer, and a solvent, and reacting the monomer to form a polymer, wherein the antisolvent is not a solvent for the polymer and is used to lower the lower critical solution temperature (LCST) of the system; a plurality of devolatilization vessels located downstream of the reactor system, wherein each devolatilization vessel operates at a lower pressure than the previous devolatilization vessel, and wherein the plurality of devolatilization vessels receive the polymer solution from the reactor system; and a liquid-liquid separator for receiving the polymer solution from the reactor system and promoting the separation between the polymer and the volatiles by reducing the pressure and temperature of the polymer solution in the liquid-liquid separator. However, this system does not involve the process of removing metals from polymers, and the polymer products prepared cannot meet the requirements of medical-grade and optical-grade polymer specifications.

[0011] US20120088893A1 discloses a solution polymerization method. The method comprises the following steps: A) polymerizing one or more monomers in the presence of a solvent comprising a heavy hydrocarbon solvent and a light hydrocarbon solvent to form a polymer solution; B) transferring the polymer solution to a liquid-liquid separator without adding heat to the solution, and actively reducing the pressure of the polymer solution in a controlled manner before or within the liquid-liquid separator, thereby inducing the formation of at least two liquid phases, namely a polymer-rich phase and a solvent-rich phase, and the polymer concentration in the polymer-rich phase is higher than that in the polymer solution transferred to the liquid-liquid separator; C) removing the solvent-rich phase. This solution polymerization process is mainly used to solve the problem of solvent separation in the polymer preparation process and does not involve a demetallization process.

[0012] US4992529A discloses a method for mixed acid demetallization. This method involves the reaction of a monocarboxylic acid with a metal in an organic phase to form a carboxylate that is insoluble in the organic phase. The carboxylate reacts with the inorganic acid in the mixed acid to form an inorganic salt that is soluble in the aqueous phase. The carboxylic acid is reduced and returns to the organic phase, where it reacts with the metal in the polymer solution to form a carboxylate again. This cycle continues until all the metal in the polymer solution is completely transferred to the aqueous phase, thereby achieving the removal of metal residues. Here, the carboxylic acid acts as a phase transfer catalyst. The idea of this method is relatively novel, but the demetallization effect is not ideal. Additionally, a large amount of water is required.

[0013] CN114534694A discloses a complexing adsorption filler and its preparation method and application. The adsorption filler is a molecular sieve filler loaded with a hydroxyquinoline compound, and an organic acid can be loaded on the molecular sieve loaded with the hydroxyquinoline compound. This adsorption filler can effectively remove the residual catalyst in the polyolefin solution, and has the advantages of fast deashing speed, large adsorption capacity, and low pressure drop. It is suitable for catalyst removal in various olefin solution polymerization processes. However, the preparation process of this adsorption filler is complex and cumbersome, and the loading amount of hydroxyquinoline is relatively low, resulting in a low adsorption capacity of the adsorption filler and a high operating cost.

[0014] CN114989331A discloses a method for complexing deashing of polyolefin solutions. The method comprises the following steps: 1) adding diminazene to the polyolefin solution to complex and adsorb metal ions in the solution to form a complex; 2) passing the polyolefin solution containing the complex through an adsorption column filled with a porous metal oxide for adsorption treatment to obtain a purified polyolefin solution. This deashing method can efficiently remove the residual metal in the polyolefin solution, has a simple process, low filler swelling, low system pressure drop, and a long service life of the deashing filler and a long replacement cycle of the adsorption column, which can significantly save the treatment cost. However, due to the general complexing ability of diminazene to metals, the metal removal rate is relatively low, especially the content of metal aluminum in the polymer is relatively high.

[0015] CN102875702A discloses a method for removing metals from polymers. This method involves adding an organic base, such as n-butyllithium, phenyllithium, etc., to the polymer solution, then adding an oxidant, washing with water after the reaction, and finally centrifuging to remove the metal residues in the solution. Although this method has a relatively high efficiency in removing metal residues from polymers, the use of organic bases introduces some metal ions, resulting in high raw material input and the cost of removing residual catalysts. Moreover, the external organic bases require high equipment requirements.

[0016] CN114392724A discloses a special deashing adsorbent for polyolefins, its preparation method and application. This deashing adsorbent is prepared by using pyridine-3-carboxylic acid as a complexing agent and loading it on an oxide support. This deashing adsorbent can efficiently remove residual metals in polyolefin solutions, significantly reduce the metal residues in polyolefin products, and has the advantages of fast deashing rate, large adsorption capacity, low swelling, and low solution pressure drop compared with traditional chelating adsorption methods. However, the preparation process of this deashing adsorbent is complex and cumbersome, and the loading amount of pyridine-3-carboxylic acid is relatively low, resulting in a low adsorption capacity of the adsorbent and high operating costs.

[0017] CN113856637A discloses a method for removing metal residues in the production process of COC and COP using a complexing adsorption filler. Compared with traditional adsorption resins, this adsorption filler has the advantages of fast metal deashing speed and large adsorption capacity, and there is no swelling phenomenon. This adsorption filler is prepared by the following method: reacting silica solid, solvent, and phosphorus tribromide in proportion to prepare brominated silica solid, then reacting with an appropriate amount of diethyl iminodiacetate to obtain a yellow solid, and acidifying with hydrochloric acid to obtain the adsorption filler. The preparation process of this adsorption filler is cumbersome and complex, and the heavy metal removal rate is not high.

[0018] US5073621A discloses a method for demetallization using water as a solubilizer. This method first dissolves a dicarboxylic acid in water and then adds it to the polymer solution, which can better remove the metals in the polymer solution. However, this method is prone to cause emulsion of the solution, which is not conducive to the reaction between the dicarboxylic acid and metal ions, affects the metal removal rate, and the process is difficult to control.

[0019] CN1067898A discloses a method for removing residual metal catalysts after polymer hydrogenation. This method adds hydrogen peroxide as an oxidant and sebacic acid as a precipitant to the hydrogenated butadiene-styrene random copolymer solution. Dissolving sebacic acid in a diethylene glycol-butyl ether aqueous solution to make a sebacic acid solution greatly improves the metal removal effect in the solution. However, the positions of the two carboxyl groups of the dicarboxylic acid used in this method are not fixed, and the complexing effect on metals is poor, resulting in a low metal removal rate.

[0020] CN105624405B discloses a method for recovering catalyst metal ions from synthetic diamond wastewater. The method filters the synthetic diamond wastewater to obtain a filtrate, reacts it with hydrazine hydrate under alkaline conditions to obtain a precipitate, filters and washes the precipitate, and dries it under a reducing atmosphere to recover the catalyst metal powder. The metal ion recovery rate of this method reaches over 95%, and among them, the recovery rate of C O 2+ is close to 100%. However, the traditional hydrazine hydrate reduction process needs to be carried out under strong alkaline conditions. Under this condition, metallic aluminum will form a gel-like white precipitate of aluminum hydroxide, and polymers are likely to deposit on its surface to form a coating layer, and then form oil-soluble microparticles, which exist in the polymer solution and prevent the reduction reaction of aluminum ions with hydrazine hydrate, making it impossible to achieve efficient removal of aluminum ions.

[0021] The existing metal removal technologies in the polymer solution polymerization process have deficiencies such as cumbersome adsorbent preparation processes, long metal removal process flows, and low removal efficiency. Therefore, developing a new continuous solution polymerization method and system, especially a new continuous solution polymerization preparation method and system for polyolefins, has become one of the urgent problems to be solved in this field. Summary of the Invention

[0022] To solve the above technical problems, the purpose of the present invention is to provide a method and system for preparing polyolefins. The method and system of the present invention can deeply and efficiently remove the residual metals in the polymer, and at the same time have the advantages of short process flow, low production cost, and continuous long-term operation.

[0023] To achieve the above purpose, the first aspect of the present invention provides a method for preparing polyolefins, which includes the following steps:

[0024] (1) Polymerize the raw materials for the polymerization reaction to obtain a polymer solution;

[0025] (2) After mixing and reacting the polymer solution with a complexing agent and hydrazine hydrate, a mixed solution is obtained; the mixed solution is separated by passing through an adsorption column filled with an adsorbent to obtain a metal-removed polymer solution;

[0026] Among them, the complexing agent includes one or a combination of several of dicarboxylic acids and their derivatives. The dicarboxylic acid contains a carbon-carbon double bond and two carboxyl groups are arranged on the same side of the carbon-carbon double bond, and it has a cis structure in the spatial configuration;

[0027] (3) After devolatilization of the metal-removed polymer solution, a devolatilized polymer and volatile components are obtained;

[0028] (4) After subjecting the polymer after devolatilization to extrusion granulation, polymer particles are obtained.

[0029] In the above preparation method, preferably, in step (1), the raw materials for the polymerization reaction include an olefin monomer, a solvent, and a catalyst system. More preferably, the raw materials for the polymerization reaction further include a scavenger.

[0030] In some specific embodiments of the present invention, the olefin monomer includes one or a combination of several of ethylene, α-olefins, cycloolefins, etc. Preferably, the olefin monomer includes ethylene and a comonomer, and the comonomer includes α-olefins and / or cycloolefins, etc.; more preferably, the comonomer is a cycloolefin. According to the specific embodiments of the present invention, the cycloolefin includes one or a combination of several of norbornene, ethylidene norbornene, cyclopentene, cyclohexene, etc.

[0031] In some specific embodiments of the present invention, the solvent includes one or a combination of several of C6-C12 alkanes, cycloalkanes, aromatics, etc.; preferably, the solvent includes one or a combination of several of cyclohexane, methylcyclohexane, n-hexane, toluene, etc.

[0032] In some specific embodiments of the present invention, the catalyst system includes a metallocene catalyst system, and the metallocene catalyst system includes a metallocene compound as the main catalyst and a cocatalyst. Generally, the metallocene compound includes transition metal elements of Group IVB, VB, and VIB, especially vanadium, titanium, zirconium, etc., coordinated with ligands such as cyclopentadiene or cyclopentadiene derivatives to form complexes, and specifically may include various metallocene compounds conventional in the field of olefin polymerization or disclosed in prior art documents. According to the specific embodiments of the present invention, the cocatalyst includes one or a combination of several of alkylaluminoxanes and / or organoborides, etc. Specifically, the alkylaluminoxane includes one or a combination of several of methylaluminoxane (MAO), modified methylaluminoxane (MMAO), ethylaluminoxane (EAO), and isobutylaluminoxane (i-BAO), etc. The organoboride includes one or a combination of several of tris(pentafluorophenyl)boron, N,N-dimethyl-tetrakis(pentafluorophenyl)boron, and tris(pentafluorophenyl)carbon-tetrakis(pentafluorophenyl)boron, etc.

[0033] In some specific embodiments of the present invention, the scavenger includes alkylaluminum and / or haloalkylaluminum, etc. Specifically, it may include trimethylaluminum, triethylaluminum, tri-n-propylaluminum, triisobutylaluminum, tri-n-butylaluminum, triisopentylaluminum, tri-n-pentylaluminum, tri-n-hexylaluminum, triisohexylaluminum, diethylmethylaluminum, dimethylethylaluminum, monochlorodimethylaluminum, dichloromethylaluminum, monochloro-diethylaluminum, dichloroethylaluminum, monochloro-di-n-propylaluminum, dichloro-n-propylaluminum, monochloro-diisobutylaluminum, dichloro-isobutylaluminum, monochloro-di-n-butylaluminum, dichloro-n-butylaluminum, monochloro-diisopentylaluminum, dichloro-isopentylaluminum, monochloro-di-n-hexylaluminum, dichloro-n-hexylaluminum, monochloro-diisohexylaluminum, and dichloro-isohexylaluminum, etc., or a combination of one or more of them. Preferably, the scavenger includes triisobutylaluminum and / or triethylaluminum, etc.

[0034] According to the specific embodiments of the present invention, the mixing ratio of the olefin monomer, solvent, catalyst system, and scavenger in the raw materials for the polymerization reaction can be conventionally adjusted by those skilled in the art according to different production requirements and different target products. The present invention does not particularly limit this mixing ratio.

[0035] In the above preparation method, preferably, in step (1), the temperature of the polymerization reaction is 70 - 180 °C, more preferably 80 - 145 °C.

[0036] In the above preparation method, preferably, in step (1), the pressure of the polymerization reaction is 0.5 - 1.5 MPa, more preferably 0.6 - 1.2 MPa.

[0037] In the above preparation method, preferably, in step (1), the time of the polymerization reaction is 30 - 120 min, more preferably 45 - 100 min.

[0038] In some specific embodiments of the present invention, in step (1), the polymerization reaction is carried out in a polymerization reactor. The main catalyst, cocatalyst in the metallocene catalyst system, the scavenger, the olefin monomer, and the solvent can enter the polymerization reactor from the bottom of the polymerization reactor for the polymerization reaction. Specifically, the polymerization reactor is provided with a stirrer, such as a paddle stirrer. The polymerization reaction process can adopt a full-pot operation mode, and the polymer solution obtained after the reaction flows out from the top of the polymerization reactor. Moreover, a pressure control valve can be provided on the polymer solution pipeline of the polymerization reactor to control the pressure of the polymerization reaction. At the same time, a high and low temperature oil bath system can be used to control the polymerization reaction temperature through the jacket of the polymerization reactor. In addition, a cooling coil is not provided inside the polymerization reactor to prevent the polymer from sticking to the wall of the cooling coil.

[0039] In the above preparation method, preferably, the weight percentage of the polymer in the polymer solution obtained in step (1) is 15-45%; more preferably, the weight percentage of the polymer in the polymer solution is 25-35%.

[0040] In the above preparation method, preferably, the obtained polymer may include one or a combination of several of cycloolefin copolymer (COC), cycloolefin polymer (COP), polyethylene, polypropylene, polyolefin plastomer (POP), polyolefin elastomer (POE), etc. More preferably, the obtained polymer is cycloolefin copolymer (COC).

[0041] According to the specific embodiments of the present invention, preferably, the above preparation method further includes a raw material preparation step of olefin monomer and solvent before step (1), and the raw material preparation step includes mixing and preheating the olefin monomer and the solvent. More preferably, the raw material preparation step may include: mixing ethylene with the solvent, dissolving ethylene to obtain a mixture of ethylene and the solvent; mixing the comonomer with the solvent, dissolving the comonomer to obtain a mixture of the comonomer and the solvent; and mixing and preheating the mixture of ethylene and the solvent and the mixture of the comonomer and the solvent to obtain a mixture of olefin monomer and the solvent.

[0042] In some specific embodiments of the present invention, the temperature for dissolving ethylene is 20-90°C, and the pressure is 0.1-5.0 MPa; preferably, the temperature for dissolving ethylene is 25-50°C, and the pressure is 0.8-3.0 MPa.

[0043] In some specific embodiments of the present invention, the temperature for mixing the comonomer with the solvent is 25-75°C, and the pressure is 0.05-0.2 MPa; preferably, the temperature for mixing the comonomer with the solvent is 35-55°C, and the pressure is 0.1-0.15 MPa.

[0044] In some specific embodiments of the present invention, the temperature of the mixture of olefin monomer and the solvent obtained after mixing and preheating is 60-160°C, preferably 70-150°C.

[0045] In some specific embodiments of the present invention, the solvent used for mixing with ethylene is the same as the solvent used for mixing with the comonomer.

[0046] In some specific embodiments of the present invention, the raw material preparation steps of the olefin monomer and the solvent may specifically include: storing ethylene in an ethylene buffer tank; then injecting the ethylene in the ethylene buffer tank into an ethylene dissolution tank, mixing it with the solvent in the ethylene dissolution tank, and dissolving the ethylene to obtain a mixture of ethylene and the solvent; mixing the comonomer with the solvent in a comonomer storage tank, dissolving the comonomer to obtain a mixture of the comonomer and the solvent; then, according to the molar ratio of ethylene to the comonomer (routinely designed by those skilled in the art), mixing the mixture of ethylene and the solvent and the mixture of the comonomer and the solvent in a pipeline and preheating them through a preheater to obtain a mixture of the olefin monomer and the solvent. Among them, the ethylene stored in the ethylene buffer tank may include fresh ethylene and / or recycled ethylene. In some specific embodiments of the present invention, the mixture of the olefin monomer and the solvent then enters a polymerization reactor, contacts with a catalyst system and an optional scavenger, and undergoes the polymerization reaction described in step (1).

[0047] In the above preparation method, preferably, the metals in the polymer solution include one or a combination of several of vanadium, titanium, zirconium, etc. and aluminum, etc. More preferably, the metals in the polymer solution include zirconium and aluminum, etc.

[0048] In the above preparation method, preferably, in step (2), the dicarboxylic acid has the structure shown in Formula I as follows:

[0049]

[0050] In Formula I, R1 and R2 are the same or different, and R1 and R2 each independently selected from an H atom, a straight-chain or branched-chain alkyl group having 1 to 10 carbon atoms; preferably, R1 and R2 are the same or different, and R1 and R2 each independently selected from an H atom, a straight-chain or branched-chain alkyl group having 1 to 5 carbon atoms.

[0051] In the above preparation method, preferably, in step (2), the derivatives of the dicarboxylic acid include one or a combination of several of the acid anhydride, acyl halide, amide, ester, and nitrile formed by the dicarboxylic acid. More preferably, the derivatives of the dicarboxylic acid include the acid anhydride of the dicarboxylic acid.

[0052] According to the specific embodiments of the present invention, the acid anhydride of the dicarboxylic acid has the structure shown in Formula II as follows:

[0053]

[0054] In Formula II, R1 and R2 are the same or different, and R1 and R2 each independently selected from an H atom, a straight-chain or branched-chain alkyl group having 1 to 10 carbon atoms; preferably, R1 and R2 are the same or different, and R1 and R2 each independently selected from an H atom, a straight-chain or branched-chain alkyl group having 1 to 5 carbon atoms.

[0055] In some specific embodiments of the present invention, in step (2), the dicarboxylic acid and its derivatives include maleic acid (i.e., cis-butenedioic acid), maleic anhydride, cis-methylbutenedioic acid (i.e., 2-methylmaleic acid), cis-methylbutenedioic anhydride (i.e., 2-methylmaleic anhydride), 2,3-dimethylmaleic acid, and 2,3-dimethylmaleic anhydride, etc., or a combination of one or more of them.

[0056] In some specific embodiments of the present invention, the metal complex formed by the dicarboxylic acid and its derivatives and the metal ion has the structural formula shown in Formula III below:

[0057]

[0058] In Formula III, R1 and R2 are the same or different, and R1 and R2 each independently selected from an H atom, a straight-chain or branched-chain alkyl group having 1 to 10 carbon atoms, and M is a metal ion; preferably, R1 and R2 are the same or different, and R1 and R2 each independently selected from an H atom, a straight-chain or branched-chain alkyl group having 1 to 5 carbon atoms, and M is a metal ion.

[0059] In the above preparation method, preferably, in step (2), the mixing ratio of the polymer solution to the complexing agent is 1 g of polymer: 10 -5 -10 -3 mol of complexing agent (i.e., a combination of one or more of the dicarboxylic acid and its derivatives).

[0060] In the above preparation method, preferably, in step (2), the complexing agent is added to the polymer solution in the form of a solution, and the concentration of the combination of one or more of the dicarboxylic acid and its derivatives in the complexing agent solution is 0.1 - 10 mol / L, more preferably 0.1 - 5 mol / L. In some specific embodiments of the present invention, the solvent in the complexing agent solution includes one or more combinations of water, alcohols, ketones, and hydrocarbons, etc., preferably including one or more combinations of water, ethanol, and acetone, etc.

[0061] In the above preparation method, preferably, in step (2), the mixing ratio of the polymer solution to the hydrazine hydrate is 1 g of polymer: 10 -5 -10 -3 mol of hydrazine hydrate.

[0062] In the above preparation method, preferably, in step (2), the hydrazine hydrate is added to the polymer solution in the form of a solution, and the mass fraction of hydrazine hydrate in the hydrazine hydrate solution is 20%-80%, more preferably 40%-80%. In some specific embodiments of the present invention, the solvent in the hydrazine hydrate solution includes water and / or alcohol, etc.

[0063] In the above preparation method, preferably, in step (2), the process of mixing and reacting the polymer solution with the complexing agent and hydrazine hydrate is carried out under stirring conditions, and the stirring speed can be adjusted by those skilled in the art according to the production scale, and vigorous stirring is preferably adopted.

[0064] In the above preparation method, preferably, in step (2), the temperature for mixing and reacting the polymer solution with the complexing agent and hydrazine hydrate is 60-150°C, more preferably 80-130°C.

[0065] In the above preparation method, preferably, in step (2), the reaction time of the polymer solution with the complexing agent and hydrazine hydrate is 2-100 minutes, more preferably 5-60 minutes.

[0066] In the above preparation method, preferably, in step (2), the adsorbent includes an oxide adsorbent; more preferably, the adsorbent includes one or a combination of several of aluminum oxide, zinc oxide, silica, etc.

[0067] In the above preparation method, preferably, in step (2), the shape of the adsorbent includes one or a combination of several of powder, sphere, strip, etc. Among them, the strip can include shapes such as clover, four-leaf clover, cylinder, etc. The size of the adsorbent can be conventionally adjusted by those skilled in the art, and the present invention does not make special limitations on it.

[0068] In the above preparation method, preferably, in step (2), the bulk density of the adsorbent is 0.35-0.8 g / mL, more preferably 0.4-0.6 g / mL.

[0069] In the above preparation method, preferably, in step (2), the specific surface area of the adsorbent is 200-350 m 2 / g, and the pore volume is 0.4-0.8 mL / g.

[0070] In the above preparation method, preferably, in step (2), the separation temperature is 30-120°C, more preferably 50-100°C.

[0071] In the above preparation method, preferably, in step (2), the separation pressure is 0.1-5.0 MPa, more preferably 0.2-3.0 MPa.

[0072] In the above preparation method, preferably, in step (2), the volumetric space velocity of the liquid for the separation is 0.1 - 10 h -1 , more preferably 0.5 - 8 h -1 .

[0073] In the polyolefin preparation method of the present invention, a dicarboxylic acid and its derivatives having a cis structure in the spatial configuration are used as a metal complexing reagent. After the dicarboxylic acid and its derivatives having a cis structure react with metal ions in the polymer solution, metal complexes are formed. In particular, a complexation reaction occurs with aluminum ions in the polymer solution to generate a water-soluble aluminum ion complex. Then, using hydrazine hydrate as a strong reducing reagent, metal ions such as zirconium and aluminum in the polymer solution are reduced to metal atoms to form a precipitate. Then, through an adsorption column filled with an oxide adsorbent, the precipitate is separated, and thus the filtration and removal of metal atoms are completed, and the filtrate obtained is a polymer solution after demetallization. In the absence of a complexing agent, aluminum ions will form a gel-like aluminum hydroxide precipitate under the alkaline conditions during the reduction by hydrazine hydrate. This precipitate will be further coated with the polymer to form oil-soluble fine particles and exist in the polymer solution, preventing the aluminum ions from reacting with hydrazine hydrate in the reduction reaction, resulting in the difficulty of filtering or adsorbing and removing aluminum ions in the subsequent process, and thus leading to a low removal rate of aluminum ions. However, in the method of the present invention, by introducing an efficient complexing reagent, that is, a dicarboxylic acid and its derivatives having a cis structure in the spatial configuration, compared with the traditional complexing reagent, the complexing agent of the present invention can quickly form a stable metal ion complex with aluminum ions, avoiding the formation of a gel-like white precipitate of aluminum hydroxide by metal aluminum ions under alkaline conditions, and significantly improving the removal efficiency of metal ions.

[0074] In the above preparation method, preferably, step (2) specifically includes: mixing and reacting the polymer solution with a complexing agent solution and a hydrazine hydrate solution to obtain a mixture; subjecting the mixture to oil-water separation, and separating the obtained oil phase through an adsorption column filled with an adsorbent to obtain a polymer solution after demetallization. According to the specific embodiments of the present invention, the formed precipitate can be separated out along with the aqueous phase during the oil-water separation process.

[0075] More specifically, step (2) may include: after the polymer solution (from the polymerization reactor) is heat-exchanged and depressurized, it enters the termination reaction and complex reduction of metal equipment, and the complexing agent solution and hydrazine hydrate solution are injected into the termination reaction and complex reduction of metal equipment. While terminating the polymerization reaction, the complexing agent reacts with metal ions in the polymer solution to form metal complexes, and hydrazine hydrate reduces metal ions (mainly zirconium, aluminum, etc.) in the polymer solution into metal atoms to obtain a mixed solution; the mixed solution is subjected to oil-water separation, and the obtained oil phase is heat-exchanged and pressurized, and then separated through an adsorption column filled with an adsorbent to obtain a polymer solution after metal removal.

[0076] In some specific embodiments of the present invention, the termination reaction and complex reduction of metal equipment may be a conventional kettle-type equipment with a stirrer, and the present invention does not particularly limit its structure.

[0077] According to the specific embodiments of the present invention, after the polymerization reaction, the solvents in the complexing agent solution and hydrazine hydrate solution can be used as terminators to deactivate the active centers in the polymer solution, efficiently terminate the polymerization reaction, and prevent the problems of continued polymerization or explosion polymerization in the subsequent treatment process. Therefore, the complexing agent solution and hydrazine hydrate solution adopted in the present invention serve both as metal removal reagents for the complex reduction method and as terminators, enabling the processes of terminating the polymerization reaction and complex reduction of metal removal to proceed continuously in a coordinated manner, thereby improving the process efficiency.

[0078] In some specific embodiments of the present invention, the temperature of the polymer solution after heat exchange is 60 - 150 °C, preferably 80 - 130 °C. To prevent the polymer solution from vaporizing after depressurization, the polymer solution flowing out of the polymerization reactor is processed by first cooling and then depressurizing. A heat exchanger can be used to heat-exchange and cool the polymer solution.

[0079] In some specific embodiments of the present invention, the pressure of the polymer solution after depressurization is 0.03 - 0.1 MPa, preferably 0.03 - 0.08 MPa. A pressure control valve can be used to depressurize the polymer solution.

[0080] In some specific embodiments of the present invention, the temperature of the oil phase obtained by oil-water separation after heat exchange is 30 - 120 °C, preferably 50 - 100 °C. A heat exchanger can be used to heat-exchange the oil phase obtained by oil-water separation.

[0081] In some specific embodiments of the present invention, the pressure of the oil phase obtained by oil-water separation after pressurization is 0.1 - 5.0 MPa, preferably 0.2 - 3.0 MPa. A booster pump can be used to pressurize the oil phase obtained by oil-water separation. Specifically, the booster pump is interlocked with the liquid level of the termination reaction and complex reduction metal equipment to maintain a coherent and stable outflow rate of the mixed liquid. Pressurizing the oil phase obtained by oil-water separation with a booster pump can effectively address the problem of difficult fluid transportation caused by excessive pressure drop in the adsorption column, thereby improving the efficiency of fluid separation through the adsorption column.

[0082] In some specific embodiments of the present invention, the number of the adsorption columns is two, one in use and one in reserve, and they can be switched alternately. Specifically, the online switching can be carried out through the pressure drop interlock of the three-way regulating valve with the adsorption column.

[0083] In the above preparation method, preferably, the metal content in the de-metallized polymer solution obtained in step (2) is less than 1 ppm.

[0084] In the above preparation method, preferably, in step (3), the pressure for devolatilization of the de-metallized polymer solution is 10 - 50 bar, and the temperature is 210 - 280 °C.

[0085] In some specific embodiments of the present invention, the equipment used for devolatilization of the de-metallized polymer solution may include a flash tank.

[0086] In some specific embodiments of the present invention, step (3) may specifically include: after the de-metallized polymer solution is heat-exchanged, it enters the flash tank, and the de-metallized polymer solution is flash-separated to obtain the devolatilized polymer and volatiles. The devolatilized polymer flows out from the bottom of the flash tank, and the volatiles flow out from the top of the flash tank.

[0087] In some specific embodiments of the present invention, the temperature of the de-metallized polymer solution after heat exchange is 210 - 360 °C, preferably 220 - 300 °C. A heat exchanger can be used to heat up the de-metallized polymer solution.

[0088] In the above preparation method, preferably, the volatile content in the devolatilized polymer obtained in step (3) is 5% or less (by weight percentage).

[0089] In some specific embodiments of the present invention, two or more flash tanks connected in series can be used to remove volatile components from the de-metallized polymer solution, so as to remove as much residual volatile components in the polymer solution as possible, and make the content of volatile components in the polymer after devolatilization less than 5%. Each flash tank can be equipped with a heat exchanger to provide the heat required for the devolatilization process. At the same time, a gear pump or a screw pump suitable for transporting high-viscosity fluids can be installed at the bottom of each flash tank to send the devolatilized polymer to downstream equipment.

[0090] In some specific embodiments of the present invention, the volatile components obtained after devolatilizing the de-metallized polymer solution include one or a combination of ethylene, unreacted comonomers, solvents, etc. Preferably, the weight percentage of the unreacted comonomers in the volatile components obtained in step (3) is 20-55%, more preferably 30-45%.

[0091] In the above preparation method, preferably, in step (4), the equipment used for extrusion granulation of the devolatilized polymer includes an extrusion granulator. The extrusion end of the extrusion granulator is provided with a degassing port. After extrusion, the volatile components in the devolatilized polymer are further removed, and then granulated at the granulation end of the extrusion granulator to obtain polymer particles. More preferably, the extrusion end of the extrusion granulator is provided with a vacuum degassing device, and the vacuum degassing device is connected to the degassing port. The vacuum degassing device includes, but is not limited to, a vacuum pump.

[0092] In some specific embodiments of the present invention, the devolatilized polymer enters the extrusion granulator through a gear pump or a screw pump provided at the bottom of the flash tank.

[0093] In some specific embodiments of the present invention, the extrusion granulator includes a twin-screw extrusion granulator. Preferably, the length-diameter ratio of the extrusion screw of the twin-screw extrusion granulator is 40-80:1, more preferably 45-65:1.

[0094] In some specific embodiments of the present invention, the number and position of the degassing ports at the extrusion end of the extrusion granulator can be adjusted by those skilled in the art according to actual situations. Preferably, degassing ports are respectively provided in the middle section and the end section of the extrusion end of the extrusion granulator, and a vacuum degassing device connected to the degassing port. According to the specific embodiments of the present invention, if the number of degassing ports of the extrusion granulator is too small, the volatile components that have separated from the polymer solution cannot be removed from the extrusion granulator in time, resulting in the re-dissolution of the volatile components into the polymer solution and affecting the devolatilization efficiency; if the number of degassing ports is too large, although the volatile components can be removed in time, it will greatly reduce the heat exchange area of the barrel of the extrusion granulator, reduce the heat exchange capacity of the barrel, and thus reduce the devolatilization ability of the extrusion granulator.

[0095] In some specific embodiments of the present invention, a stripping port may be further provided at the extrusion end of the extrusion granulator, for continuously injecting steam through the stripping port, so that the steam and the volatile components form an azeotrope, reducing the partial pressure of the gas phase, increasing the interfacial area, and facilitating the replacement of the volatile components from the polymer solution.

[0096] In the above preparation method, preferably, the VOC content in the polymer particles obtained in step (4) is less than 50 ppm.

[0097] According to the specific embodiments of the present invention, preferably, the above preparation method further includes step (5): rectifying the volatile components obtained in step (3). More preferably, step (5) further includes: rectifying the volatile components removed by the extrusion granulator. In some specific embodiments of the present invention, ethylene, unreacted comonomer, and solvent can be obtained respectively after rectification.

[0098] In some specific embodiments of the present invention, the rectification can be carried out using a rectification column. Preferably, the operating conditions of the rectification column are: the bottom temperature is 130 - 150 °C, the bottom pressure is 10 - 30 Torr, the highest top temperature is 90 - 110 °C, and the reflux ratio is 1 - 25 (preferably 5 - 20).

[0099] Specifically, step (5) may include: feeding the volatile components obtained in step (3) and the volatile components removed by the extrusion granulator into a rectification column for rectification. After the ethylene flowing out from the top of the rectification column enters the reflux drum, is vented, and undergoes gas-liquid separation, ethylene is obtained. At the same time, the unreacted comonomer flowing out from the side wall of the rectification column and the solvent flowing out from the bottom of the rectification column are obtained. The liquid phase obtained after gas-liquid separation in the reflux drum is returned to the rectification column for re-rectification.

[0100] According to the specific embodiments of the present invention, preferably, the above preparation method further includes step (6): recycling one or several of the ethylene, unreacted comonomer, and solvent obtained in step (5). Specifically, step (6) may include: compressing the ethylene obtained after gas-liquid separation in the reflux drum, and then returning it to step (1) as one of the raw materials for the polymerization reaction; and / or, returning the unreacted comonomer and / or solvent obtained after rectification to step (1) as one of the raw materials for the polymerization reaction.

[0101] In some specific embodiments of the present invention, the ethylene obtained after gas-liquid separation in the reflux drum can be compressed by a compressor and then returned to the ethylene buffer tank as one of the raw materials for the polymerization reaction for recycling. In the present invention, the recycled ethylene is called recycled ethylene.

[0102] In some specific embodiments of the present invention, the unreacted comonomer flowing out from the side wall of the rectification column can be returned to the comonomer storage tank, and the solvent flowing out from the bottom of the rectification column can be returned to the ethylene dissolution tank and / or the comonomer storage tank as one of the raw materials for the polymerization reaction for recycling.

[0103] The second aspect of the present invention provides a polyolefin preparation system for implementing the above polyolefin preparation method. The system at least includes: a polymerization reaction unit, a de-metallization unit, a devolatilization unit, and an extrusion granulation unit.

[0104] Among them, the polymerization reaction unit at least includes a polymerization reactor; the polymerization reactor is at least provided with a polymerization reaction raw material inlet and a polymer solution outlet.

[0105] The de-metallization unit at least includes a termination reaction and complex reduction metal equipment, and an adsorption column; the termination reaction and complex reduction metal equipment is at least provided with a polymer solution inlet, a complexing agent inlet, a reducing agent inlet, and a mixed liquid outlet; the adsorption column has an inlet and an outlet.

[0106] The devolatilization unit at least includes a flash tank; the flash tank is at least provided with a material inlet, a devolatilized polymer outlet, and a volatile component outlet.

[0107] The extrusion granulation unit at least includes an extrusion granulator.

[0108] The polymer solution outlet of the polymerization reactor is connected to the polymer solution inlet of the termination reaction and complex reduction metal equipment through a pipeline. The mixed liquid outlet of the termination reaction and complex reduction metal equipment is communicated with the inlet of the adsorption column through a pipeline. The outlet of the adsorption column is connected to the material inlet of the flash tank through a pipeline. The devolatilized polymer outlet of the flash tank is connected to the extrusion granulator through a pipeline.

[0109] In the above-mentioned preparation system, preferably, the polymerization reaction raw material inlet of the polymerization reactor is arranged at the bottom of the polymerization reactor, and the polymer solution outlet is arranged at the top of the polymerization reactor. In some specific embodiments of the present invention, the polymerization reaction raw material inlet of the polymerization reactor includes an olefin monomer and solvent inlet, as well as a catalyst system and scavenger inlet. Specifically, the main catalyst and cocatalyst in the metallocene catalyst system, and the scavenger are respectively transported through the material conveying branch pipelines. After the three material conveying branch pipelines converge into a material conveying main pipeline, it is connected to the catalyst system and scavenger inlet of the polymerization reactor. Preferably, after the three material conveying branch pipelines converge into a material conveying main pipeline, it is connected to the catalyst system and scavenger inlet of the polymerization reactor through a loop reactor, and the loop reactor is used for strengthening the mixing and activation of the main catalyst, cocatalyst in the metallocene catalyst system and the scavenger.

[0110] In the above-mentioned preparation system, preferably, the polymerization reactor is provided with a stirrer, such as a paddle stirrer.

[0111] In the above-mentioned preparation system, preferably, the polymerization reactor is provided with an external jacket, and a high and low temperature oil bath system can be used to control the polymerization reaction temperature through the external jacket of the polymerization reactor.

[0112] In the above-mentioned preparation system, preferably, no cooling coil is arranged in the polymerization reactor to prevent the polymer from sticking to the wall of the cooling coil.

[0113] In the above-mentioned preparation system, preferably, a heat exchanger and a pressure control valve are arranged on the pipeline connecting the polymer solution outlet of the polymerization reactor and the polymer solution inlet of the termination reaction and complex reduction metal equipment.

[0114] According to the specific embodiments of the present invention, preferably, the above-mentioned preparation system further includes: a raw material preparation unit, and the raw material preparation unit at least includes an ethylene buffer tank, an ethylene dissolution tank and a comonomer storage tank; the ethylene buffer tank can be provided with a fresh ethylene inlet, an optional circulating ethylene inlet, and an ethylene outlet; the ethylene dissolution tank can be provided with a solvent inlet, an ethylene inlet, and an ethylene and solvent mixture outlet; the comonomer storage tank can be provided with a solvent inlet, a comonomer inlet, and a comonomer and solvent mixture outlet; the ethylene outlet of the ethylene buffer tank is connected to the ethylene inlet of the ethylene dissolution tank through a pipeline, and material conveying branch pipelines are respectively arranged at the ethylene and solvent mixture outlet of the ethylene dissolution tank and the comonomer and solvent mixture outlet of the comonomer storage tank. After the two material conveying branch pipelines converge into a material conveying main pipeline, it is connected to the olefin monomer and solvent inlet of the polymerization reactor. More preferably, a preheater is arranged on the material conveying main pipeline.

[0115] In some specific embodiments of the present invention, the reaction termination and complex reduction metal equipment may be a conventional kettle-type equipment with a stirrer, and the present invention does not particularly limit its structure.

[0116] In the above preparation system, preferably, the polymer solution inlet of the reaction termination and complex reduction metal equipment is arranged at the bottom of the reaction termination and complex reduction metal equipment, the complexing agent inlet and the reducing agent inlet are both arranged at the bottom of the reaction termination and complex reduction metal equipment, and the mixed liquid outlet is arranged at the top of the reaction termination and complex reduction metal equipment.

[0117] In the above preparation system, preferably, the de-metallization unit further includes: a centrifugal separator; the centrifugal separator may be provided with an inlet and an outlet; the inlet of the centrifugal separator is connected to the mixed liquid outlet of the reaction termination and complex reduction metal equipment through a pipeline, and the outlet of the second centrifugal separator is connected to the inlet of the adsorption column through a pipeline.

[0118] In the above preparation system, preferably, the de-metallization unit further includes: a complexing agent storage tank and a reducing agent storage tank; the complexing agent storage tank is connected to the complexing agent inlet of the reaction termination and complex reduction metal equipment through a pipeline, and the reducing agent storage tank is connected to the reducing agent inlet of the reaction termination and complex reduction metal equipment through a pipeline.

[0119] In the above preparation system, preferably, a heat exchanger and a booster pump are arranged on the pipeline connecting the outlet of the centrifugal separator and the inlet of the adsorption column. More preferably, the booster pump is interlocked with the liquid level of the reaction termination and complex reduction metal equipment to maintain a continuous and stable outflow rate of the mixed liquid.

[0120] In the above preparation system, preferably, the number of adsorption columns is two, which are used for one in operation and one in standby, and are switched alternately. Specifically, the online switching can be carried out through the pressure drop interlock of the three-way regulating valve and the adsorption column.

[0121] In the above preparation system, preferably, the material inlet of the flash tank is arranged on the side wall of the flash tank, the polymer outlet after devolatilization is arranged at the bottom of the flash tank, and the volatiles outlet is arranged at the top of the flash tank.

[0122] In the above-mentioned preparation system, preferably, the number of the flash tanks is one or more than two. When more than two flash tanks are used, the more than two flash tanks are arranged in series. More preferably, each flash tank is equipped with a heat exchanger, and the heat exchanger is arranged on the pipeline connected to the material inlet of the flash tank for providing the heat required for the devolatilization process. Moreover, a transfer pump is arranged on the pipeline connected to the polymer outlet after devolatilization of each flash tank for transferring the polymer after devolatilization. Specifically, the transfer pump may include a gear pump, a screw pump or the like.

[0123] In the above-mentioned preparation system, preferably, a degassing port is arranged at the extrusion end of the extrusion granulator. More preferably, the number of the degassing ports is two, which are respectively arranged in the middle section and the end section of the extrusion end of the extrusion granulator. Further preferably, a vacuum degassing device is arranged at the extrusion end of the extrusion granulator, and the vacuum degassing device is connected to the degassing port. The vacuum degassing device includes, but is not limited to, a vacuum pump.

[0124] In the above-mentioned preparation system, preferably, the extrusion granulator includes a twin-screw extrusion granulator. More preferably, the ratio of the length to the diameter of the extrusion screw of the twin-screw extrusion granulator is 40-80:1, and further preferably 45-65:1.

[0125] In the above-mentioned preparation system, preferably, a stripping port is further arranged at the extrusion end of the extrusion granulator for continuously injecting steam through the stripping port to form an azeotrope with the volatile components, reduce the partial pressure of the gas phase, increase the interfacial area, and facilitate the replacement of the volatile components from the polymer solution.

[0126] According to the specific embodiments of the present invention, preferably, the above-mentioned preparation system further includes: a rectification unit, and the rectification unit at least includes a rectification column and a reflux drum; the rectification column may be provided with a volatile component inlet, an ethylene outlet, an unreacted comonomer outlet, and a solvent outlet; the volatile component inlet of the rectification column is connected to the volatile component outlet of the flash tank through a pipeline; the ethylene outlet of the rectification column is communicated with the reflux drum; the reflux drum is provided with a reflux pipeline, and the reflux pipeline is connected to the rectification column for returning the liquid phase obtained after gas-liquid separation in the reflux drum to the rectification column for rectification again. Specifically, the volatile component inlet of the rectification column may be arranged on the side wall of the rectification column, the ethylene outlet may be arranged at the top of the rectification column, the unreacted comonomer outlet may be arranged on the side wall of the rectification column, and the solvent outlet may be arranged at the bottom of the rectification column.

[0127] In the above preparation system, preferably, the degassing port at the extrusion end of the extrusion granulator is communicated with the volatile matter inlet of the rectification column through a pipeline. Specifically, the degassing port at the extrusion end of the extrusion granulator is communicated with the volatile matter inlet of the rectification column through a pipeline and the vacuum degassing device.

[0128] According to a specific embodiment of the present invention, preferably, the above preparation system further includes: a circulation unit, the circulation unit at least includes a compressor, the inlet of the compressor is connected to the reflux tank through a pipeline, and the outlet of the compressor is connected to the circulating ethylene inlet of the ethylene buffer tank through a pipeline.

[0129] In the above preparation system, preferably, the circulation unit further includes a comonomer circulation pipeline, and the comonomer circulation pipeline is used to connect the unreacted comonomer outlet of the rectification column and the comonomer inlet of the comonomer storage tank.

[0130] In the above preparation system, preferably, the circulation unit further includes a solvent circulation pipeline, and the solvent circulation pipeline is used to connect the solvent outlet of the rectification column and the solvent inlet of the ethylene dissolution tank and / or the solvent inlet of the comonomer storage tank.

[0131] In the art, in the process of preparing polyolefins, especially cycloolefin copolymers, by using a metallocene catalyst system and a solution polymerization method, the residual content of catalyst metal in the polymer solution obtained after the polymerization reaction is usually relatively high. The metal residue in the polymer will cause many problems such as excessive metal in the product, decreased light transmittance, color change, and deteriorated properties such as heat resistance and aging resistance. This limits the application of cycloolefin copolymers in the fields of optics, medicine, etc.

[0132] The polyolefin preparation method and system provided by the present invention are a method and system for continuously preparing polyolefins (especially cycloolefin copolymers) with ultra-low metal content by solution polymerization, which can deeply and efficiently remove the residual metal in the polymer and realize the continuous preparation of polyolefins (especially cycloolefin copolymers) with ultra-low metal content.

[0133] In terms of demetallization, the technical solution of the present invention uses a dicarboxylic acid and its derivatives with a cis structure in the spatial configuration as a metal complexing reagent. After reacting with metal ions in the polymer solution, metal complexes are formed, especially by complexing with aluminum ions in the polymer solution to form water-soluble aluminum ion complexes. Then, hydrazine hydrate is used as a reducing demetallization reagent to reduce metal ions such as zirconium and aluminum remaining in the polymer solution to metal atoms, forming precipitates. Most of the precipitates can be removed by oil-water separation, and then the precipitates are further filtered and separated through an adsorption column filled with an oxide adsorbent, thereby completing the removal of metal atoms and obtaining a demetallized polymer solution. The technical solution of the present invention uses a complexing reduction-filtration technology to achieve deep removal of metal residues in the polymer solution. Compared with traditional polymer demetallization technologies such as pickling, water washing, and alcohol washing, the technical solution of the present invention has the advantages of high demetallization efficiency, fast speed, simple process, low cost, and continuous long-cycle operation. It can be widely applied to the field of polymer metal removal, has universality and high efficiency, and has broad industrialization prospects.

[0134] The preparation method and system of polyolefins of the present invention at least have the following beneficial technical effects:

[0135] 1. In the absence of a complexing agent, aluminum ions will form flocculent aluminum hydroxide precipitates under the alkaline conditions during the reduction by hydrazine hydrate. This precipitate will be further coated by the polymer to form oil-soluble microparticles and exist in the polymer solution, preventing the reduction reaction between aluminum ions and hydrazine hydrate, resulting in a low removal rate of aluminum ions and unable to achieve deep removal of metal ions. The present invention uses a dicarboxylic acid and its derivatives with a cis structure in the spatial configuration as a complexing reagent. Compared with traditional complexing reagents, the dicarboxylic acid and its derivatives with a cis structure in space can quickly form stable metal ion complexes with aluminum ions, avoiding the formation of gel-like white precipitate aluminum hydroxide of metal aluminum ions under alkaline conditions, and significantly improving the removal efficiency of metal ions.

[0136] 2. The present invention uses hydrazine hydrate as a reducing demetallization reagent. Hydrazine hydrate has strong reducibility and can quickly and efficiently react with metal ions in the polymer to generate metal atoms, forming precipitates. The by-products are discharged from the system in the form of amines and nitrogen. The by-products are easily separated and have no impact on the performance of the polymer. The operation is simple and easy.

[0137] 3. Since the present invention uses hydrazine hydrate as a reducing demetallization reagent, the main function of the adsorbent is to filter the precipitates formed by metal atoms, and there is basically no need to adsorb metal ions, avoiding the problem that the service life of the adsorbent is affected due to adsorption saturation. It can greatly extend the service life of the adsorbent and can operate stably for a long cycle without replacing the adsorbent.

[0138] 4. The present invention uses an oxide as an adsorbent to remove metal atoms. The preparation process of the adsorbent is simple, has a high adsorption capacity, is not prone to swelling, has a small pressure drop in the adsorbent bed, has good long-term operation stability, and has low operating costs.

[0139] 5. The complexing agent solution and hydrazine hydrate solution used in the present invention can simultaneously serve as polymerization terminators, enabling the processes of terminating the polymerization reaction and complexing and reducing metals to proceed synergistically and continuously, which is beneficial for adjusting the polymer molecular weight and molecular weight distribution and improving process efficiency.

[0140] In summary, the polyolefin preparation method and system provided by the present invention can deeply and efficiently remove the metal residues in the catalyst in the polymer, and prepare polyolefin products with high transparency, ultra-low metal content, low VOC content, heat resistance, aging resistance, and high dielectric properties, especially high-purity cycloolefin copolymer products. The polyolefin products prepared by the method and system of the present invention can meet the requirements of medical-grade and optical-grade polymer materials. In addition, the method and system of the present invention have the advantages of a short process flow, low production costs, no need for water washing, and can operate continuously for a long period. BRIEF DESCRIPTION OF THE DRAWINGS

[0141] Figure 1 It is a schematic structural diagram of the polyolefin preparation system provided for the specific embodiments of the present invention.

[0142] Description of the reference numerals in the drawings:

[0143] 1 - Ethylene buffer tank; 2 - Ethylene dissolution tank; 3 - Comonomer storage tank; 4 - Polymerization reactor; 5 - Equipment for terminating the reaction and complexing and reducing metals; 6 - Complexing agent storage tank; 7 - Reducing agent storage tank; 8 - Centrifugal separator; 9 - First adsorption column; 10 - Second adsorption column; 11 - Flash tank; 12 - Distillation column; 13 - Reflux tank; 14 - Gear pump; 15 - Extrusion granulator; 16 - Compressor; 17 - Preheater; 18 - First heat exchanger; 19 - Pressure control valve; 20 - Second heat exchanger; 21 - Booster pump; 22 - Third heat exchanger; 23 - Loop reactor;

[0144] 151 - Degassing port; 152 - Vacuum degassing device. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0145] In order to have a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention will be described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0146] Example 1

[0147] This example provides a polyolefin preparation system, as Figure 1As shown, the preparation system includes: a raw material preparation unit, a polymerization reaction unit, a demetallization unit, a devolatilization unit, an extrusion granulation unit, a rectification unit, and a circulation unit;

[0148] Among them, the raw material preparation unit at least includes an ethylene buffer tank 1, an ethylene dissolution tank 2, and a comonomer storage tank 3; the ethylene buffer tank 1 is provided with a fresh ethylene inlet, a recycled ethylene inlet, and an ethylene outlet; the ethylene dissolution tank 2 is provided with a solvent inlet, an ethylene inlet, and an ethylene and solvent mixture outlet; the comonomer storage tank 3 is provided with a solvent inlet, a comonomer inlet, and a comonomer and solvent mixture outlet;

[0149] The polymerization reaction unit at least includes a polymerization reactor 4; the polymerization reactor 4 is provided with an olefin monomer and solvent inlet, a catalyst system and scavenger inlet, and a polymer solution outlet;

[0150] The demetallization unit at least includes a termination reaction and complex reduction metal device 5, a complexing agent storage tank 6, a reducing agent storage tank 7, a centrifuge separator 8, a first adsorption column 9, and a second adsorption column 10; the termination reaction and complex reduction metal device 5 is provided with a polymer solution inlet, a complexing agent inlet, a reducing agent inlet, and a mixture outlet; the centrifuge separator 8 is provided with an inlet and an outlet; both the first adsorption column 9 and the second adsorption column 10 have an inlet and an outlet;

[0151] The devolatilization unit at least includes a flash tank 11; the flash tank 11 is provided with a material inlet, a devolatilized polymer outlet, and a volatile component outlet;

[0152] The extrusion granulation unit at least includes an extrusion granulator 15;

[0153] The rectification unit at least includes a rectification column 12 and a reflux drum 13; the rectification column 12 is provided with a volatile component inlet, an ethylene outlet, an unreacted comonomer outlet, and a solvent outlet;

[0154] The circulation unit at least includes a compressor 16, a comonomer circulation pipeline ( Figure 1 not shown in the figure), and a solvent circulation pipeline ( Figure 1 not shown in the figure).

[0155] The ethylene outlet of the ethylene buffer tank 1 is connected to the ethylene inlet of the ethylene dissolution tank 2 through a pipeline. The ethylene and solvent mixture outlet of the ethylene dissolution tank 2 and the comonomer and solvent mixture outlet of the comonomer storage tank 3 are respectively provided with a material conveying branch pipeline. After the two material conveying branch pipelines converge into a material conveying main pipeline, it is connected to the olefin monomer and solvent inlet of the polymerization reactor 4. And, metering pumps are respectively arranged on the two material conveying branch pipelines ( Figure 1(not shown in the figure), a preheater 17 is provided on the main material conveying pipeline.

[0156] The main catalyst, cocatalyst, and scavenger in the metallocene catalyst system are respectively conveyed through the material conveying branch pipelines. After the three material conveying branch pipelines converge into the main material conveying pipeline, they are connected to the catalyst system and scavenger inlets of the polymerization reactor 4 through the loop reactor 23. And injection pumps are respectively provided on the three material conveying branch pipelines ( Figure 1 not shown in the figure). The loop reactor 23 is used for intensively mixing and activating the main catalyst, cocatalyst, and scavenger in the metallocene catalyst system.

[0157] The polymer solution outlet of the polymerization reactor 4 is connected to the polymer solution inlet of the termination reaction and complex reduction of metal 5 through a pipeline, and a first heat exchanger 18 and a pressure control valve 19 are provided on this pipeline.

[0158] The polymerization reactor 4 is provided with a stirrer, such as a paddle stirrer. The polymerization reactor 4 is provided with an external jacket, and a high and low temperature oil bath system can be used to control the polymerization reaction temperature through the external jacket of the polymerization reactor 4. No cooling coil is provided inside the polymerization reactor 4 to prevent the polymer from sticking to the wall of the cooling coil.

[0159] The termination reaction and complex reduction of metal 5 can be a conventional kettle-type device with a stirrer.

[0160] The complexing agent storage tank 6 is connected to the complexing agent inlet of the termination reaction and complex reduction of metal equipment 5 through a pipeline; the reducing agent storage tank 7 is connected to the reducing agent inlet of the termination reaction and complex reduction of metal equipment 5 through a pipeline.

[0161] The inlet of the centrifuge separator 8 is connected to the mixed liquid outlet of the termination reaction and complex reduction of metal equipment 5 through a pipeline; the outlet of the centrifuge separator 8 is connected to the inlet of the first adsorption column 9 or the second adsorption column 10 through a pipeline, and a second heat exchanger 20 and a booster pump 21 are provided on this pipeline. The booster pump 21 is interlocked with the termination reaction and complex reduction of metal equipment 5 in terms of liquid level to maintain a continuous and stable outflow rate of the mixed liquid.

[0162] In this embodiment, two adsorption columns in parallel are adopted, one in use and one in reserve, and they are switched alternately. Online switching can be carried out through the pressure drop interlock of the three-way regulating valve with the first adsorption column 9 and the second adsorption column 10.

[0163] The outlet of the first adsorption column 9 or the second adsorption column 10 is connected to the material inlet of the flash tank 11 through a pipeline, and a third heat exchanger 22 is provided on this pipeline.

[0164] The polymer outlet of the flash tank 11 after devolatilization is connected to the extrusion granulator 15 through a pipeline and a gear pump 14.

[0165] An outgassing port 151 is provided at the extrusion end of the extrusion granulator 15. The number of the outgassing ports 151 is two, which are respectively arranged in the middle section and the end section of the extrusion end of the extrusion granulator 15. A vacuum outgassing device 152 is further provided at the extrusion end of the extrusion granulator 15, and the vacuum outgassing device 152 is connected to the outgassing port 151. The vacuum outgassing device 152 includes, but is not limited to, a vacuum pump.

[0166] In this embodiment, the extrusion granulator 15 is a twin-screw extrusion granulator. The length-diameter ratio of the extrusion screw of the twin-screw extrusion granulator is 45-65:1.

[0167] The volatile matter outlet of the flash tank 11 is connected to the volatile matter inlet of the rectification column 12 through a pipeline.

[0168] The outgassing port 151 at the extrusion end of the extrusion granulator 15 is communicated with the volatile matter inlet of the rectification column 12 through a pipeline and the vacuum outgassing device 152.

[0169] The ethylene outlet of the rectification column 12 is communicated with the reflux tank 13; the reflux tank 13 is provided with a reflux pipeline, and the reflux pipeline is connected to the rectification column 12 for returning the liquid phase obtained after gas-liquid separation in the reflux tank 13 to the rectification column 12 for rectification again.

[0170] The inlet of the compressor 16 is connected to the reflux tank 13 through a pipeline, and the outlet of the compressor 16 is connected to the circulating ethylene inlet of the ethylene buffer tank 1 through a pipeline.

[0171] The comonomer circulation pipeline is used to connect the unreacted comonomer outlet of the rectification column 12 and the comonomer inlet of the comonomer storage tank 3.

[0172] The solvent circulation pipeline is used to connect the solvent outlet of the rectification column 12 and the solvent inlets of the ethylene dissolving tank 2 and the comonomer storage tank 3.

[0173] Examples 2-7

[0174] Examples 2-7 respectively provide a method for preparing a polyolefin, and all adopt the polyolefin preparation system provided in Example 1.

[0175] The methods for preparing polyolefins provided in Examples 2-7 include the following steps:

[0176] (1) In the raw material preparation unit, ethylene (including fresh ethylene and recycled ethylene) is stored in the ethylene buffer tank 1; then the ethylene in the ethylene buffer tank 1 is gently injected into the ethylene dissolution tank 2, where it is mixed with the solvent to fully dissolve the ethylene. The temperature, pressure, and solvent used for ethylene dissolution are shown in Table 1. The solubility of ethylene under these dissolution temperature and pressure conditions can be calculated to obtain a mixture of ethylene and the solvent; the comonomer is mixed with the solvent in the comonomer storage tank 3 to dissolve the comonomer. The solvent used for mixing with the comonomer is the same as that used for mixing with ethylene. The temperature and pressure of the comonomer storage tank 3 are shown in Table 1 to obtain a mixture of the comonomer and the solvent; then, according to the molar ratio of ethylene to the comonomer, after precise metering by a metering pump, the mixture of ethylene and the solvent, and the mixture of the comonomer and the solvent are mixed in the pipeline and preheated by the preheater 17 to obtain a mixture of olefin monomers and the solvent, the temperature of which is shown in Table 1;

[0177] Among them, the comonomer is a cycloolefin, and the molar ratio of ethylene to the comonomer, the total amount of the solvent, etc. can all be conventionally adjusted by those skilled in the art;

[0178] (2) In the polymerization reaction unit, the mixture of olefin monomers and the solvent obtained in step (1) enters the polymerization reactor 4 from the bottom of the polymerization reactor 4. And the main catalyst, cocatalyst, and scavenger in the metallocene catalyst system are respectively transported through an injection pump and a material conveying branch pipeline, and they are merged and intensively mixed and activated through the loop reactor 23 and then enter the polymerization reactor 4 from the bottom of the polymerization reactor 4. A polymerization reaction is carried out in the polymerization reactor 4. The temperature, pressure, and time of the polymerization reaction (i.e., the residence time in the polymerization reactor 4) are shown in Table 1 to obtain a polymer solution, and the weight percentage of the polymer in the polymer solution is shown in Table 1; The polymerization reaction process adopts a full-pot operation mode. The polymer solution obtained after the reaction flows out from the top of the polymerization reactor 4, and the pressure of the polymerization reaction can be controlled by the pressure control valve 19. At the same time, the temperature of the polymerization reaction can be controlled by using a high and low temperature oil bath system through the jacket of the polymerization reactor 4;

[0179] Among them, the main catalyst is a zirconium-containing metallocene compound, the cocatalyst is an alkylaluminoxane, and the scavenger is triisobutylaluminum and / or triethylaluminum. Their dosages can all be conventionally adjusted by those skilled in the art;

[0180] (3) In the de-metallization unit, after the polymer solution obtained in step (2) is cooled by the first heat exchanger 18, it is depressurized by the pressure control valve 19 and then enters the termination reaction and complex reduction metal equipment 5. The temperature and pressure of the polymer solution after cooling and depressurization are shown in Table 1. The complexing agent solution in the complexing agent storage tank 6 and the hydrazine hydrate solution in the reducing agent storage tank 7 are injected into the termination reaction and complex reduction metal equipment 5 according to the calculated amounts. While terminating the polymerization reaction, the complexing agent reacts with the metal ions in the polymer solution to form metal complexes, especially undergoes a complexing reaction with aluminum ions to generate water-soluble aluminum ion complexes, avoiding the formation of aluminum hydroxide precipitation by aluminum ions under alkaline conditions after adding hydrazine hydrate. Hydrazine hydrate reduces metal ions such as zirconium and aluminum in the polymer solution to metal atoms, obtaining a mixed liquid; the mixed liquid is subjected to oil-water separation by the centrifugal separator 8, and then the obtained oil phase is heated by the second heat exchanger 20, pressurized by the booster pump 21, and then separated by passing through the first adsorption column 9 or the second adsorption column 10 filled with adsorbent. The temperature and pressure of the oil phase after heat exchange and pressurization in the oil-water separation are shown in Table 1, obtaining the de-metallized polymer solution;

[0181] (4) In the devolatilization unit, the de-metallized polymer solution obtained in step (3) is heated by the third heat exchanger 22 and then enters the flash tank 11 for flash separation of the de-metallized polymer solution. The temperature of the de-metallized polymer solution after heat exchange, the flash temperature and pressure are shown in Table 1, obtaining the devolatilized polymer and volatile components. The devolatilized polymer flows out from the bottom of the flash tank 11, and the volatile components flow out from the top of the flash tank 11; the content of volatile components in the devolatilized polymer is 5% or less (weight percentage); the weight percentage of the unreacted comonomer in the volatile components is shown in Table 1;

[0182] (5) In the extrusion granulation unit, the devolatilized polymer obtained in step (4) is injected into the extrusion granulator 15 by the gear pump 14 at the bottom of the flash tank 11. After being extruded from the extrusion end of the extrusion granulator 15, the remaining volatile components in the devolatilized polymer are further removed, and then granulation is carried out at the granulation end of the extrusion granulator 15 to obtain polymer particles; the VOC content in the polymer particles is less than 50 ppm; the extrusion granulator 15 is a twin-screw extrusion granulator, and the length-diameter ratios of the extrusion screws of the twin-screw extrusion granulators used in Examples 2 to 7 are shown in Table 1;

[0183] (6) In the rectification unit, the volatile components flowing out from the top of the flash tank 11 obtained in step (4) and the volatile components removed by the extrusion granulator 15 in step (5) enter the rectification column 12 for rectification. The operating conditions of the rectification column 12 are shown in Table 1. After the ethylene flowing out from the top of the rectification column 12 enters the reflux drum 13 and is vented and separated into gas and liquid, ethylene is obtained. At the same time, the unreacted comonomer flowing out from the side wall of the rectification column 12 and the solvent flowing out from the bottom of the rectification column 12 are obtained. After gas-liquid separation in the reflux drum 13, the obtained liquid phase returns to the rectification column 12 for re-rectification;

[0184] (7) In the recycling unit, the ethylene obtained after gas-liquid separation in the reflux drum 13 is compressed by the compressor 16 and then returned to the ethylene buffer tank 1 as one of the raw materials for the polymerization reaction for recycling; the unreacted comonomer flowing out from the side wall of the rectification column 12 is returned to the comonomer storage tank 3, and the solvent flowing out from the bottom of the rectification column 12 is returned to the ethylene dissolution tank 2 and the comonomer storage tank 3 as one of the raw materials for the polymerization reaction for recycling.

[0185] Table 1

[0186]

[0187]

[0188] The demetallization steps in the polyolefin preparation methods provided in Examples 2 to 7 are specifically as described below.

[0189] Example 2

[0190] In the demetallization unit, after the polymer solution obtained in step (2) is cooled by the first heat exchanger 18, it is depressurized by the pressure control valve 19 and then enters the termination reaction and complex reduction metal equipment 5. Under the condition of vigorous stirring, an aqueous maleic acid solution with a concentration of 0.1 mol / L accounting for 2.5% of the volume of the polymer solution and an aqueous hydrazine hydrate solution with a mass fraction of 40% accounting for 0.03% of the volume of the polymer solution are respectively injected. The residence time is 5 minutes. While terminating the polymerization reaction, the complexing agent reacts with the metal ions in the polymer solution to form metal complexes, especially with aluminum ions to undergo a complexation reaction to generate water-soluble aluminum ion complexes. Hydrazine hydrate reduces metal ions such as zirconium and aluminum in the polymer solution to metal atoms to obtain a mixed liquid; the mixed liquid is subjected to oil-water separation by the centrifugal separator 8, and then the obtained oil phase is heated by the second heat exchanger 20 and then pressurized by the booster pump 21, and then at a temperature and pressure of 50 °C and 0.2 MPa, at 0.5 h -1The volumetric space velocity is separated through the first adsorption column 9 or the second adsorption column 10 filled with powdered aluminum oxide to obtain a de-metallized polymer solution; wherein, the bulk density of the aluminum oxide is 0.4 g / mL, the specific surface area is 220 m 2 / g, and the pore volume is 0.4 mL / g.

[0191] Example 3

[0192] In the de-metallization unit, after the polymer solution obtained in step (2) is cooled by the first heat exchanger 18, it is depressurized by the pressure control valve 19 and then enters the termination reaction and complex reduction metal equipment 5. Under the condition of vigorous stirring, a maleic anhydride ethanol solution with a concentration of 0.5 mol / L and accounting for 3% of the volume of the polymer solution, and a hydrazine hydrate ethanol solution with a mass fraction of 40% and accounting for 0.44% of the volume of the polymer solution are respectively injected. The residence time is 10 minutes. While terminating the polymerization reaction, the complexing agent reacts with the metal ions in the polymer solution to form metal complexes, especially complexing with aluminum ions to generate water-soluble aluminum ion complexes. Hydrazine hydrate reduces metal ions such as zirconium and aluminum in the polymer solution to metal atoms to obtain a mixture; the mixture is subjected to oil-water separation by the centrifugal separator 8, and then the obtained oil phase is heat-exchanged by the second heat exchanger 20 and then pressurized by the booster pump 21, and then at a temperature and pressure of 60 °C and 0.5 MPa, at a volumetric space velocity of 2.0 h -1 The volumetric space velocity is separated through the first adsorption column 9 or the second adsorption column 10 filled with powdered zinc oxide to obtain a de-metallized polymer solution; wherein, the bulk density of the zinc oxide is 0.45 g / mL, the specific surface area is 280 m 2 / g, and the pore volume is 0.5 mL / g.

[0193] Example 4

[0194] In the de-metallization unit, the polymer solution obtained in step (2) is cooled by the first heat exchanger 18, then depressurized by the pressure control valve 19, and then enters the termination reaction and complex reduction metal equipment 5. Under the condition of vigorous stirring, a cis-methyl maleic acid acetone solution with a concentration of 1 mol / L and accounting for 1% of the volume of the polymer solution, and an aqueous hydrazine hydrate solution with a mass fraction of 60% and accounting for 2.1% of the volume of the polymer solution are respectively injected. The residence time is 20 minutes. While terminating the polymerization reaction, the complexing agent reacts with the metal ions in the polymer solution to form metal complexes, especially with aluminum ions to undergo a complexation reaction to generate water-soluble aluminum ion complexes. Hydrazine hydrate reduces metal ions such as zirconium and aluminum in the polymer solution to metal atoms to obtain a mixed solution. The mixed solution is subjected to oil-water separation by the centrifugal separator 8, and then the obtained oil phase is heat-exchanged by the second heat exchanger 20, then pressurized by the booster pump 21, and then at a temperature and pressure of 70 °C and 1.0 MPa, with a volume space velocity of 4.0 h -1 is separated through the first adsorption column 9 or the second adsorption column 10 filled with powdered silica to obtain a de-metallized polymer solution; wherein, the bulk density of the silica is 0.5 g / mL, and the specific surface area is 300 m 2 / g, and the pore volume is 0.6 mL / g.

[0195] Example 5

[0196] In the de-metallization unit, the polymer solution obtained in step (2) is cooled by the first heat exchanger 18, then depressurized by the pressure control valve 19, and then enters the termination reaction and complex reduction metal equipment 5. Under the condition of vigorous stirring, a 2,3-dimethyl maleic anhydride aqueous solution with a concentration of 2 mol / L and accounting for 1.5% of the volume of the polymer solution, and an aqueous hydrazine hydrate solution with a mass fraction of 70% and accounting for 1.1% of the volume of the polymer solution are respectively injected. The residence time is 30 minutes. While terminating the polymerization reaction, the complexing agent reacts with the metal ions in the polymer solution to form metal complexes, especially with aluminum ions to undergo a complexation reaction to generate water-soluble aluminum ion complexes. Hydrazine hydrate reduces metal ions such as zirconium and aluminum in the polymer solution to metal atoms to obtain a mixed solution. The mixed solution is subjected to oil-water separation by the centrifugal separator 8, and then the obtained oil phase is heat-exchanged by the second heat exchanger 20, then pressurized by the booster pump 21, and then at a temperature and pressure of 80 °C and 1.5 MPa, with a volume space velocity of 6.0 h -1 is separated through the first adsorption column 9 or the second adsorption column 10 filled with powdered aluminum oxide to obtain a de-metallized polymer solution; wherein, the bulk density of the aluminum oxide is 0.55 g / mL, and the specific surface area is 320 m 2 / g, and the pore volume is 0.7 mL / g.

[0197] Example 6

[0198] In the de-metallization unit, after the polymer solution obtained in step (2) is cooled by the first heat exchanger 18, it is depressurized by the pressure control valve 19 and then enters the termination reaction and complex reduction metal equipment 5. Under the condition of vigorous stirring, a 2,3-dimethylmaleic anhydride ethanol solution with a concentration of 3 mol / L and accounting for 1% of the volume of the polymer solution, and an aqueous hydrazine hydrate solution with a mass fraction of 80% and accounting for 1.8% of the volume of the polymer solution are respectively injected. The residence time is 40 minutes. While terminating the polymerization reaction, the complexing agent reacts with the metal ions in the polymer solution to form metal complexes, especially with aluminum ions to undergo a complexing reaction to generate water-soluble aluminum ion complexes. Hydrazine hydrate reduces metal ions such as zirconium and aluminum in the polymer solution to metal atoms to obtain a mixed solution; the mixed solution is subjected to oil-water separation by the centrifugal separator 8, and then the obtained oil phase is heated by the second heat exchanger 20 and then pressurized by the booster pump 21, and then at a temperature and pressure of 90 °C and 2.0 MPa, with a volume space velocity of 7.0 h -1 is separated through the first adsorption column 9 or the second adsorption column 10 filled with powdered zinc oxide to obtain a de-metallized polymer solution; wherein, the bulk density of the zinc oxide is 0.6 g / mL, the specific surface area is 350 m 2 / g, and the pore volume is 0.8 mL / g.

[0199] Example 7

[0200] In the de-metallization unit, after the polymer solution obtained in step (2) is cooled by the first heat exchanger 18, it is depressurized by the pressure control valve 19 and then enters the termination reaction and complex reduction metal equipment 5. Under the condition of vigorous stirring, a 2,3-dimethylmaleic anhydride acetone solution with a concentration of 5 mol / L and accounting for 5% of the volume of the polymer solution, and an aqueous hydrazine hydrate solution with a mass fraction of 80% and accounting for 0.44% of the volume of the polymer solution are respectively injected. The residence time is 60 minutes. While terminating the polymerization reaction, the complexing agent reacts with the metal ions in the polymer solution to form metal complexes, especially with aluminum ions to undergo a complexing reaction to generate water-soluble aluminum ion complexes. Hydrazine hydrate reduces metal ions such as zirconium and aluminum in the polymer solution to metal atoms to obtain a mixed solution; the mixed solution is subjected to oil-water separation by the centrifugal separator 8, and then the obtained oil phase is heated by the second heat exchanger 20 and then pressurized by the booster pump 21, and then at a temperature and pressure of 100 °C and 3.0 MPa, with a volume space velocity of 8.0 h -1 is separated through the first adsorption column 9 or the second adsorption column 10 filled with powdered silica to obtain a de-metallized polymer solution; wherein, the bulk density of the silica is 0.45 g / mL, the specific surface area is 280 m 2 / g, and the pore volume is 0.45 mL / g.

[0201] Comparative Example 1

[0202] This comparative example provides a method for preparing polyolefin, which is basically the same as the method for preparing polyolefin provided in Example 4, except for the demetallization step.

[0203] The demetallization step of this comparative example is described as follows:

[0204] In the demetallization unit, after the polymer solution obtained in step (2) is cooled by the first heat exchanger 18, it is depressurized by the pressure control valve 19 and then enters the termination reaction and complex reduction metal equipment 5. Under the condition of vigorous stirring, deionized water is continuously injected into the termination reaction and complex reduction metal equipment 5, and the injection amount is 2.1% of the volume of the polymer solution in the termination reaction and complex reduction metal equipment 5, and the residence time is 20 minutes to obtain a mixed solution; the mixed solution is subjected to oil-water separation by the centrifugal separator 8, and then the obtained oil phase is heat-exchanged by the second heat exchanger 20 and then pressurized by the booster pump 21, and then at a temperature of 70 °C and a pressure of 1.0 MPa, at a volume space velocity of 4.0 h -1 The adsorption separation is carried out through the first adsorption column 9 or the second adsorption column 10 filled with powdered silica to obtain the demetallized polymer solution; wherein, the bulk density of the silica is 0.5 g / mL, the specific surface area is 300 m 2 / g, and the pore volume is 0.6 mL / g.

[0205] Comparative Example 2

[0206] This comparative example provides a method for preparing polyolefin, which is basically the same as the method for preparing polyolefin provided in Example 4, except for the demetallization step.

[0207] The demetallization step of this comparative example is described as follows:

[0208] In the demetallization unit, after the polymer solution obtained in step (2) is cooled by the first heat exchanger 18, it is depressurized by the pressure control valve 19 and then enters the termination reaction and complex reduction metal equipment 5. Under the condition of vigorous stirring, a citric acid aqueous solution with a concentration of 0.1 mol / L and accounting for 2.1% of the volume of the polymer solution is injected, and the residence time is 20 minutes. While terminating the polymerization reaction, the metal ions in the polymer solution form metal complexes to obtain a mixed solution; the mixed solution is subjected to oil-water separation by the centrifugal separator 8, and then the obtained oil phase is heat-exchanged by the second heat exchanger 20 and then pressurized by the booster pump 21, and then at a temperature of 70 °C and a pressure of 1.0 MPa, at a volume space velocity of 4.0 h -1The volumetric space velocity is passed through the first adsorption column 9 or the second adsorption column 10 filled with powdered silica for adsorption separation to obtain a polymer solution after demetallization; wherein, the bulk density of the silica is 0.5 g / mL, the specific surface area is 300 m 2 / g, and the pore volume is 0.6 mL / g.

[0209] Comparative Example 3

[0210] This comparative example provides a method for preparing polyolefin, which is basically the same as the method for preparing polyolefin provided in Example 4, except for the demetallization step. In the demetallization unit of this comparative example, components such as the termination reaction and complex reduction metal equipment 5, complexing agent storage tank 6, reducing agent storage tank 7, and centrifuge separator 8 are not provided. After the polymer solution is cooled and depressurized, it is directly subjected to adsorption separation using an adsorption column filled with an adsorbent.

[0211] The demetallization step of this comparative example is as follows:

[0212] Take 250 mL of powdered aluminum oxide (the same as the powdered aluminum oxide in Example 2), heat it to 100 °C, then add 100 mL of maleic acid aqueous solution with a concentration of 0.005 mol / L, continue to stir for 2 hours, filter, take the filter residue, and dry it at 120 °C for 8 hours to obtain maleic acid-pretreated aluminum oxide powder; the bulk density of this maleic acid-pretreated aluminum oxide powder is 0.41 g / mL, the specific surface area is 212 m 2 / g, and the pore volume is 0.42 mL / g;

[0213] In the demetallization unit, after the polymer solution obtained in step (2) is cooled and depressurized, at a temperature and pressure of 70 °C and 1.0 MPa, at a volumetric space velocity of 4.0 h -1 it is passed through the first adsorption column 9 or the second adsorption column 10 filled with the maleic acid-pretreated aluminum oxide powder for adsorption separation to obtain a polymer solution after demetallization.

[0214] Comparative Example 4

[0215] This comparative example provides a method for preparing polyolefin, which is basically the same as the method for preparing polyolefin provided in Example 4, except for the demetallization step.

[0216] The demetallization step of this comparative example is described as follows: In the demetallization unit, the polymer solution obtained in step (2) is cooled by the first heat exchanger 18, then depressurized by the pressure control valve 19, and then enters the termination reaction and complex reduction metal equipment 5. Under the condition of vigorous stirring, an aqueous EDTA solution with a mass fraction of 8% and accounting for 13.7% of the volume of the polymer solution, and an aqueous ethylenediamine solution with a mass fraction of 72% and accounting for 2.1% of the volume of the polymer solution are respectively injected. The residence time is 20 minutes. While terminating the polymerization reaction, EDTA reacts with the metal ions in the polymer solution to form a complex, and ethylenediamine reduces the metal ions in the polymer solution to metal atoms, obtaining a mixed solution; the mixed solution is subjected to oil-water separation by the centrifugal separator 8, and then the obtained oil phase is heated by the second heat exchanger 20, then pressurized by the booster pump 21, and then at a temperature and pressure of 70 °C and 1.0 MPa, with a volume space velocity of 4.0 h -1 is separated through the first adsorption column 9 or the second adsorption column 10 filled with powdered silica to obtain the demetallized polymer solution; wherein, the bulk density of the silica is 0.5 g / mL, the specific surface area is 300 m 2 / g, and the pore volume is 0.6 mL / g.

[0217] Comparative Example 5

[0218] This comparative example provides a method for preparing polyolefin, which is basically the same as the method for preparing polyolefin provided in Example 4, except for the demetallization step.

[0219] The demetallization step of this comparative example is described as follows: In the demetallization unit, the polymer solution obtained in step (2) is cooled by the first heat exchanger 18, then depressurized by the pressure control valve 19, and then enters the termination reaction and complex reduction metal equipment 5. Under the condition of vigorous stirring, an aqueous EDTA solution with a mass fraction of 8% and accounting for 13.7% of the volume of the polymer solution, and an aqueous hydrazine hydrate solution with a mass fraction of 60% and accounting for 2.1% of the volume of the polymer solution are respectively injected. The residence time is 20 minutes. While terminating the polymerization reaction, EDTA reacts with the metal ions in the polymer solution to form a complex, and hydrazine hydrate reduces the metal ions in the polymer solution to metal atoms, obtaining a mixed solution; the mixed solution is subjected to oil-water separation by the centrifugal separator 8, and then the obtained oil phase is heated by the second heat exchanger 20, then pressurized by the booster pump 21, and then at a temperature and pressure of 70 °C and 1.0 MPa, with a volume space velocity of 4.0 h -1 is separated through the first adsorption column 9 or the second adsorption column 10 filled with powdered silica to obtain the demetallized polymer solution; wherein, the bulk density of the silica is 0.5 g / mL, the specific surface area is 300 m 2 / g, and the pore volume is 0.6 mL / g.

[0220] Test Example 1

[0221] The metal content and VOC content in the polymer particles prepared in the above Examples 2-7 and Comparative Examples 1-5 were detected, and the results are shown in Table 2 below. The polymer solutions obtained in step (2) in the above Examples 2-7 and Comparative Examples 1-5 were not treated through the demetallization unit in step (3), but were directly processed through the subsequent devolatilization unit and extrusion granulation unit to obtain polymer particles, and the metal content therein was detected, and the results are shown in Table 2 below.

[0222] Among them, the metal content in the polymer particles was determined by the ignition method, and the specific steps are conventional technical means in the art. In this test example, the ignition method adopted specifically includes: taking 100 g of polymer particles and placing them in a muffle furnace, heating with a programmed temperature rise, rising to 650 °C in 1 hour, then keeping the temperature constant for 2 hours to ensure that the polymer burns fully, and then cooling to room temperature. The ash residue from ignition was added to 5 mL of hydrochloric acid solution (the mass fraction of this hydrochloric acid solution is 19%), and after the ash was completely digested, the metal content in the solution was analyzed by ICP-MS.

[0223] The VOC content in the polymer particles was determined by the oven method, and the specific steps are conventional technical means in the art. In this test example, the operating conditions of the oven method adopted include: 100 °C, vacuum drying.

[0224] Table 2

[0225]

[0226] As can be seen from Table 2, the preparation method and system of the polyolefin of the present invention can deeply and efficiently remove the metal residues of the catalyst in the polymer, significantly reduce the metal residues in the polymer product, and prepare polyolefin products with high transparency, ultra-low metal content and low VOC content, especially high-purity cycloolefin copolymer products.

Claims

1. A method for preparing polyolefin, which comprises the following steps: (1) Subjecting the raw materials for the polymerization reaction to a polymerization reaction, wherein the raw materials for the polymerization reaction include an olefin monomer, a solvent and a catalyst system, to obtain a polymer solution; (2) After mixing and reacting the polymer solution with a complexing agent and hydrazine hydrate, a mixed solution is obtained; passing the mixed solution through an adsorption column filled with an adsorbent for separation to obtain a polymer solution after demetallization; wherein, the complexing agent includes one or a combination of several of dicarboxylic acids and their derivatives, the dicarboxylic acid contains a carbon-carbon double bond and two carboxyl groups are arranged on the same side of the carbon-carbon double bond, and is in a cis structure in terms of spatial configuration; (3) Subjecting the polymer solution after demetallization to devolatilization to obtain a devolatilized polymer and volatile components; (4) Subjecting the devolatilized polymer to extrusion granulation to obtain polymer particles.

2. The method for preparing a polyolefin according to claim 1, wherein In step (1), the raw materials for the polymerization reaction further include a scavenger.

3. The method for preparing a polyolefin according to claim 1, wherein, In step (1), the olefin monomer includes one or a combination of several of ethylene, α-olefin and cycloolefin.

4. The method for preparing a polyolefin according to claim 3, wherein, In step (1), the olefin monomer includes ethylene and a comonomer, and the comonomer includes α-olefin and / or cycloolefin.

5. The method for preparing a polyolefin according to claim 4, wherein, In step (1), the comonomer is a cycloolefin.

6. The method for preparing a polyolefin according to claim 1, wherein, In step (1), the solvent includes one or a combination of several of alkanes, cycloalkanes and aromatic hydrocarbons having 6 to 12 carbon atoms.

7. The method for preparing a polyolefin according to claim 6, wherein, In step (1), the solvent includes one or a combination of several of cyclohexane, methylcyclohexane, n-hexane and toluene.

8. The method for preparing a polyolefin according to claim 1, wherein, In step (1), the catalyst system includes a metallocene catalyst system, and the metallocene catalyst system includes a metallocene compound as the main catalyst and a cocatalyst.

9. The method for preparing a polyolefin according to claim 8, wherein, In step (1), the cocatalyst includes one or a combination of several of alkylaluminoxane and / or organoboride.

10. The method for preparing a polyolefin according to claim 2, wherein, In step (1), the scavenger includes alkylaluminum and / or haloalkylaluminum.

11. The method for preparing a polyolefin according to claim 1, wherein, In step (1), the temperature of the polymerization reaction is 70 - 180 °C.

12. The method for preparing a polyolefin according to claim 1, wherein, In step (1), the pressure of the polymerization reaction is 0.5 - 1.5 MPa.

13. The method for preparing polyolefin according to claim 1, wherein, In step (1), the time of the polymerization reaction is 30 - 120 min.

14. The method for preparing a polyolefin according to claim 1, wherein, The weight percentage of the polymer in the polymer solution obtained in step (1) is 15 - 45%.

15. The method for preparing a polyolefin according to claim 1, wherein, The polymer in the polymer solution obtained in step (1) includes one or a combination of several of cycloolefin copolymer, cycloolefin polymer, polyethylene, polypropylene, polyolefin plastomer and polyolefin elastomer.

16. The method for preparing a polyolefin according to claim 15, wherein, The polymer in the polymer solution obtained in step (1) is a cycloolefin copolymer.

17. The method for preparing a polyolefin according to claim 1, wherein, Before step (1), the preparation method further includes a raw material preparation step for the olefin monomer and the solvent, and the raw material preparation step includes mixing and preheating the olefin monomer and the solvent.

18. The method for preparing a polyolefin according to claim 17, wherein, The raw material preparation step includes: mixing ethylene with a solvent to dissolve ethylene, obtaining a mixture of ethylene and the solvent; mixing a comonomer with the solvent to dissolve the comonomer, obtaining a mixture of the comonomer and the solvent; mixing the mixture of ethylene and the solvent and the mixture of the comonomer and the solvent, and preheating to obtain a mixture of olefin monomers and the solvent.

19. The method for preparing a polyolefin according to claim 18, wherein, The temperature for ethylene dissolution is 20 - 90 °C, and the pressure is 0.1 - 5.0 MPa.

20. The method for preparing a polyolefin according to claim 18, wherein, The temperature for mixing the comonomer and the solvent is 25 - 75 °C, and the pressure is 0.05 - 0.2 MPa.

21. The method for preparing a polyolefin according to claim 18, wherein, The temperature of the mixture of olefin monomers and the solvent obtained after mixing and preheating is 60 - 160 °C.

22. The method for preparing a polyolefin according to claim 1, wherein In step (2), the dicarboxylic acid has a structure shown in the following formula I: In formula I, R1 and R2 are the same or different, and R1 and R2 each independently selected from an H atom, a linear or branched alkyl group having 1 to 10 carbon atoms.

23. The method for preparing a polyolefin according to claim 22, wherein, In step (2), in formula I, R1 and R2 are the same or different, and R1 and R2 each independently selected from an H atom, a linear or branched alkyl group having 1 to 5 carbon atoms.

24. The method for preparing a polyolefin according to claim 1, wherein, In step (2), the derivatives of the dicarboxylic acid include one or a combination of several of the acid anhydride, acyl halide, amide, ester, and nitrile formed by the dicarboxylic acid.

25. The method for preparing a polyolefin according to claim 1, wherein, In step (2), the mixing ratio of the polymer solution to the complexing agent is 1 g of polymer: 10 -5 -10 -3 mol of complexing agent.

26. The method for preparing a polyolefin according to claim 1, wherein, In step (2), the mixing ratio of the polymer solution to the hydrazine hydrate is 1 g of polymer: 10 -5 - 10 -3 mol of hydrazine hydrate.

27. The method for preparing a polyolefin according to claim 1, wherein In step (2), the temperature for mixing and reacting the polymer solution with the complexing agent and hydrazine hydrate is 60 - 150 °C.

28. The method for preparing a polyolefin according to claim 27, wherein In step (2), the temperature for mixing and reacting the polymer solution with the complexing agent and hydrazine hydrate is 80 - 130 °C.

29. The method for preparing a polyolefin according to claim 1, wherein In step (2), the reaction time of the polymer solution with the complexing agent and hydrazine hydrate is 2 - 100 minutes.

30. The method for preparing a polyolefin according to claim 29, wherein, In step (2), the reaction time of the polymer solution with the complexing agent and hydrazine hydrate is 5 - 60 minutes.

31. The method for preparing a polyolefin according to claim 1, wherein, In step (2), the adsorbent includes an oxide adsorbent.

32. The method for preparing a polyolefin according to claim 31, wherein, In step (2), the adsorbent includes one or a combination of several of aluminum oxide, zinc oxide, and silicon dioxide.

33. The method for preparing a polyolefin according to claim 31, wherein, In step (2), the bulk density of the adsorbent is 0.35 - 0.8 g / mL.

34. The method for preparing a polyolefin according to claim 31, wherein, In step (2), the specific surface area of the adsorbent is 200-350 m 2 / g, and the pore volume is 0.4-0.8 mL / g.

35. The method for preparing a polyolefin according to claim 1, wherein, In step (2), the separation temperature is 30 - 120 °C.

36. The method for preparing a polyolefin according to claim 35, wherein, In step (2), the separation temperature is 50 - 100 °C.

37. The method for preparing a polyolefin according to claim 1, wherein, In step (2), the separation pressure is 0.1 - 5.0 MPa.

38. The method for preparing a polyolefin according to claim 37, wherein, In step (2), the separation pressure is 0.2 - 3.0 MPa.

39. The method for preparing a polyolefin according to claim 1, wherein, In step (2), the volume hourly space velocity of the liquid for the separation is 0.1 - 10 h -1 .

40. The method for preparing a polyolefin according to claim 39, wherein, In step (2), the volumetric space velocity of the liquid for the separation is 0.5 - 8 h -1 .

41. The method for preparing a polyolefin according to claim 1, wherein, Step (2) specifically includes: mixing and reacting the polymer solution with the complexing agent solution and hydrazine hydrate solution to obtain a mixed solution; subjecting the mixed solution to oil-water separation, and passing the obtained oil phase through an adsorption column filled with an adsorbent for separation to obtain a polymer solution after demetallization.

42. The method for preparing a polyolefin according to claim 41, wherein, Step (2) specifically includes: after the polymer solution is heat-exchanged and depressurized, it enters the equipment for termination reaction and complex reduction of metal. The complexing agent solution and hydrazine hydrate solution are injected into the equipment for termination reaction and complex reduction of metal. While terminating the polymerization reaction, the complexing agent reacts with metal ions in the polymer solution to form metal complexes, and hydrazine hydrate reduces the metal ions in the polymer solution to metal atoms, obtaining a mixed liquid; subjecting the mixed liquid to oil-water separation, and after the obtained oil phase is heat-exchanged and pressurized, it is separated through an adsorption column filled with an adsorbent to obtain a metal-removed polymer solution.

43. The method for preparing a polyolefin according to claim 1, wherein The metal content in the metal-removed polymer solution obtained in step (2) is less than 1 ppm.

44. The method for preparing a polyolefin according to claim 1, wherein In step (3), the pressure for devolatilization of the metal-removed polymer solution is 10 - 50 bar, and the temperature is 210 - 280 °C.

45. The method for preparing a polyolefin according to claim 1, wherein Step (3) specifically includes: after the metal-removed polymer solution is heat-exchanged, it enters a flash tank, and the metal-removed polymer solution is flash-separated to obtain a devolatilized polymer and volatiles.

46. The method for preparing a polyolefin according to claim 45, wherein, In step (3), the temperature of the metal-removed polymer solution after heat-exchange is 210 - 360 °C.

47. The method for preparing a polyolefin according to claim 1, wherein, The volatile content in the devolatilized polymer obtained in step (3) is 5% or less.

48. The method for preparing a polyolefin according to claim 1, wherein, The weight percentage content of the unreacted comonomer in the volatiles obtained in step (3) is 20 - 55%.

49. The method for preparing a polyolefin according to claim 1, wherein, In step (4), the equipment used for extrusion granulation of the devolatilized polymer includes an extrusion granulator. The extrusion end of the extrusion granulator is provided with a degassing port. After extrusion, the volatiles in the devolatilized polymer are further removed, and then granulation is carried out at the granulation end of the extrusion granulator to obtain polymer particles.

50. The method for preparing a polyolefin according to claim 49, wherein, In step (4), the extrusion end of the extrusion granulator is provided with a vacuum degassing device, and the vacuum degassing device is connected to the degassing port.

51. The method for preparing a polyolefin according to claim 49, wherein, In step (4), the extrusion granulator includes a twin-screw extrusion granulator; the ratio of the length to the diameter of the extrusion screw of the twin-screw extrusion granulator is 40 - 80:

1.

52. The method for preparing a polyolefin according to claim 1, wherein, The VOC content in the polymer particles obtained in step (4) is less than 50 ppm.

53. The method for preparing a polyolefin according to claim 49, wherein, The preparation method further includes step (5): subjecting the volatiles obtained in step (3) to rectification; and also subjecting the volatiles removed by the extrusion granulator to rectification.

54. The method for preparing a polyolefin according to claim 53, wherein, In step (5), the rectification is carried out using a rectification column. The operating conditions of the rectification column are: the bottom temperature is 130 - 150 °C, the bottom pressure is 10 - 30 Torr, the highest top temperature is 90 - 110 °C, and the reflux ratio is 1 - 25.

55. The method for preparing a polyolefin according to claim 53, wherein, Step (5) specifically includes: subjecting the volatiles obtained in step (3) and the volatiles removed by the extrusion granulator to rectification in a rectification column. The ethylene flowing out from the top of the rectification column enters a reflux tank for venting and gas-liquid separation to obtain ethylene. At the same time, the unreacted comonomer flowing out from the side wall of the rectification column and the solvent flowing out from the bottom of the rectification column are obtained. The liquid phase obtained after gas-liquid separation in the reflux tank returns to the rectification column for re-rectification.

56. The method for preparing a polyolefin according to claim 55, wherein, The preparation method further includes step (6): recycling one or several of ethylene, unreacted comonomer, and solvent obtained in step (5).

57. A polyolefin preparation system for implementing the polyolefin preparation method described in any one of claims 1-56, the system at least comprising: A polymerization reaction unit, a metal removal unit, a devolatilization unit, and an extrusion granulation unit; Wherein, the polymerization reaction unit at least includes a polymerization reactor; the polymerization reactor is at least provided with a polymerization reaction raw material inlet and a polymer solution outlet; The metal removal unit at least includes a termination reaction and complex reduction metal equipment and an adsorption column; the termination reaction and complex reduction metal equipment is at least provided with a polymer solution inlet, a complexing agent inlet, a reducing agent inlet, and a mixed liquid outlet; the adsorption column has an inlet and an outlet; The devolatilization unit at least includes a flash tank; the flash tank is at least provided with a material inlet, a polymer outlet after devolatilization, and a volatile component outlet; The extrusion granulation unit at least includes an extrusion granulator; The polymer solution outlet of the polymerization reactor is connected to the polymer solution inlet of the termination reaction and complex reduction metal equipment through a pipeline, the mixed liquid outlet of the termination reaction and complex reduction metal equipment is communicated with the inlet of the adsorption column through a pipeline, the outlet of the adsorption column is connected to the material inlet of the flash tank through a pipeline, and the polymer outlet after devolatilization of the flash tank is connected to the extrusion granulator through a pipeline.

58. The polyolefin preparation system according to claim 57, wherein, The polymerization reaction raw material inlet of the polymerization reactor is arranged at the bottom of the polymerization reactor, and the polymer solution outlet is arranged at the top of the polymerization reactor.

59. The polyolefin preparation system according to claim 57, wherein, The polymerization reaction raw material inlet of the polymerization reactor includes an olefin monomer and solvent inlet, as well as a catalyst system and scavenger inlet.

60. The polyolefin preparation system according to claim 57, wherein, A heat exchanger and a pressure control valve are arranged on the pipeline connecting the polymer solution outlet of the polymerization reactor and the polymer solution inlet of the termination reaction and complex reduction metal equipment.

61. The polyolefin preparation system according to claim 57, wherein, The polymer solution inlet of the termination reaction and complex reduction metal equipment is arranged at the bottom of the termination reaction and complex reduction metal equipment, the complexing agent inlet and the reducing agent inlet are both arranged at the bottom of the termination reaction and complex reduction metal equipment, and the mixed liquid outlet is arranged at the top of the termination reaction and complex reduction metal equipment.

62. The polyolefin preparation system according to claim 57, wherein, The metal removal unit further includes: a centrifuge separator; the centrifuge separator is provided with an inlet and an outlet; the inlet of the centrifuge separator is connected to the mixed liquid outlet of the termination reaction and complex reduction metal equipment through a pipeline, and the outlet of the centrifuge separator is connected to the inlet of the adsorption column through a pipeline.

63. The polyolefin preparation system according to claim 57, wherein, The metal removal unit further includes: a complexing agent storage tank and a reducing agent storage tank; the complexing agent storage tank is connected to the complexing agent inlet of the termination reaction and complex reduction metal equipment through a pipeline, and the reducing agent storage tank is connected to the reducing agent inlet of the termination reaction and complex reduction metal equipment through a pipeline.

64. The polyolefin preparation system according to claim 62, wherein, A heat exchanger and a booster pump are arranged on the pipeline connecting the outlet of the centrifuge separator and the inlet of the adsorption column.

65. The polyolefin preparation system according to claim 57, wherein The number of the adsorption columns is two, which are used for one open and one standby, and are switched alternately for operation.

66. The polyolefin preparation system according to claim 57, wherein, The material inlet of the flash tank is arranged on the side wall of the flash tank, the polymer outlet after devolatilization is arranged at the bottom of the flash tank, and the volatile component outlet is arranged at the top of the flash tank.

67. The polyolefin preparation system according to claim 57, wherein, The number of the flash tanks is one or more than two. When more than two flash tanks are adopted, the more than two flash tanks are arranged in series.

68. The polyolefin preparation system according to claim 67, wherein, Each flash tank is equipped with a heat exchanger which is arranged on the pipeline connected to the material inlet of the flash tank and used for providing the heat required in the devolatilization process. Moreover, a transfer pump is arranged on the pipeline connected to the polymer outlet after devolatilization of each flash tank and used for transferring the polymer after devolatilization.

69. The polyolefin preparation system according to claim 57, wherein, A degassing port is arranged at the extrusion end of the extrusion granulator.

70. The polyolefin preparation system according to claim 69, wherein, The number of the degassing ports is two, which are respectively arranged at the middle section and the end section of the extrusion end of the extrusion granulator.

71. The polyolefin preparation system according to claim 69, wherein, A vacuum degassing device is arranged at the extrusion end of the extrusion granulator, and the vacuum degassing device is connected with the degassing port.

72. The polyolefin preparation system according to claim 57, wherein, The extrusion granulator comprises a twin-screw extrusion granulator; the ratio of the length to the diameter of the extrusion screw of the twin-screw extrusion granulator is 40-80:

1.

73. The polyolefin preparation system according to claim 57, wherein, A stripping port is further arranged at the extrusion end of the extrusion granulator and used for continuously injecting steam through the stripping port.

Images