Method for continuous production of ultra-high molecular weight polyethylene by slurry polymerization

Abstract

This invention relates to a method for the continuous production of ultra-high molecular weight polyethylene (UHMWPE) via ethylene slurry polymerization. The method involves using 2-6 ethylene slurry polymerization reactors connected in series under hydrogen-free atmosphere and ethylene slurry polymerization conditions. Deviations in polymerization temperature, polymerization pressure, and gas phase composition between each reactor are controlled within a specific range. Continuous slurry polymerization is performed on raw materials containing ethylene and optional comonomers, enabling the continuous production of UHMWPE with a viscosity-average molecular weight of 1.5-8 million g / mole. This method offers flexible polymerization, a wide range of control, and stable polymer properties. Furthermore, the resulting UHMWPE exhibits low metal content, low ash content, and excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to a method for the continuous production of ultra-high molecular weight polyethylene (UHMWPE) by slurry polymerization, and more specifically, to a method for the continuous production of UHMWPE by connecting multiple polymerization reactors in series under ethylene slurry polymerization conditions. The method involves continuously polymerizing raw materials containing ethylene and optional comonomers in 2-6 series polymerization reactors using alkanes or mixed alkanes as polymerization solvents in the presence of a polyethylene catalytic system to obtain UHMWPE. Prior Technology

[0002] Ultra-high molecular weight polyethylene (UHMWPE) generally refers to linear polyethylene with a relative molecular mass of 1.5 million g / mol or higher. It has advantages that ordinary polyethylene does not have, such as excellent wear resistance, extremely high impact strength, excellent self-lubricating properties, excellent chemical resistance and low temperature resistance, excellent anti-adhesion properties, hygiene, non-toxicity and pollution-free properties, and recyclability. It has been widely used in textiles, papermaking, food, chemical industry, packaging, agriculture, construction, medical, water purification, sports, entertainment, military and other fields.

[0003] The main production methods for ultra-high molecular weight polyethylene (UHMWPE) are ethylene slurry polymerization and ethylene gas-phase polymerization. Among them, ethylene slurry polymerization is one of the main methods for producing polyethylene.

[0004] In the batch process of producing ultra-high molecular weight polyethylene using ethylene slurry, the catalyst, co-catalyst, and polymerization solvent are added to the reactor all at once, and ethylene is continuously added until the polymerization reaction stops. The batch process can fully utilize the polymerization activity of the catalyst and can obtain ultra-high molecular weight polyethylene with a high viscosity-average molecular weight. However, the production process is complicated and there are differences between different batches of products.

[0005] For example, Chinese patent application 201510078777.4 discloses a catalyst for ultra-high molecular weight polyethylene (UHMWPE) and a batch slurry method for preparing UHMWPE using ethylene. The method involves adding alkylaluminum as a co-catalyst to a single stirred-tank slurry reactor; adding the UHMWPE catalyst to the single stirred-tank slurry reactor; opening the ethylene feed valve and introducing ethylene when the temperature of the single stirred-tank slurry reactor reaches 50°C; controlling the reaction temperature at 60°C-70°C and the reaction pressure at 0.5 MPa-0.7 MPa; continuously introducing ethylene and polymerizing for 2 hours to obtain UHMWPE through batch polymerization.

[0006] In the continuous ethylene slurry process for producing ultra-high molecular weight polyethylene (UHMWPE), the catalyst, co-catalyst, polymerization solvent, and ethylene are continuously added to the polymerization reactor. Except during special periods such as start-up and shutdown, the feeding and slurry discharge are continuous during normal continuous production. The continuous process has high production efficiency, simple operation, and relatively uniform polymer quality and performance. However, due to the limitations of the fully mixed flow feeding and discharging method, the slurry discharged reflects the distribution of the catalyst and the polymer obtained from it in the polymerization reactor at different residence times. This distribution is closely related to the reactor configuration, mixing method, feed position, discharge position, and discharge method. A small amount of the main catalyst in the feed may short-circuit out of the reactor, while it may remain in the reactor for a long time. Therefore, it is difficult to obtain UHMWPE with a high viscosity-average molecular weight, and the molecular weight distribution is wider than that of the batch process.

[0007] For example, Chinese patent applications 201610892424.2, 201610892732.5, 201610892836.6, and 201610892837.0 disclose methods for preparing copolymerized ultra-high molecular weight polyethylene, wherein the ultra-high molecular weight polyethylene molecular chain has at least two segments, and is prepared by homopolymerization followed by copolymerization, or by copolymerization followed by homopolymerization.

[0008] Chinese patent CN1781956A discloses a continuous manufacturing method for polyethylene, wherein raw material monomers are polymerized in three reactors arranged in series to produce polyethylene resin. The method is characterized in that at least one reactor, in addition to the necessary raw material monomers, uses a combination of at least (a) a solid catalyst containing titanium, magnesium, and halide components (metallocene compounds and aluminoxanes) and (b) an organoaluminum compound, and simultaneously mixes with other reactors supplying raw material monomers in a multi-stage continuous polymerization process. Finally, polyethylene with a resin composition having an limiting viscosity range of 1.1 to 6.0 and a density range of 0.935 g / cm³ to 0.965 g / cm³ is obtained. The resin composition has a broad bimodal molecular weight distribution, making it particularly suitable for manufacturing high molecular weight polyethylene films or hollow molding materials with excellent environmental stress cracking resistance, impact strength, and excellent rigidity. It is clear from the disclosure that the polyethylene resin involved is not ultra-high molecular weight polyethylene.

[0009] Similarly, Chinese patent CN1781953A discloses a continuous manufacturing method for polyethylene, which involves polymerizing and mixing raw material monomers in four reactors arranged in series to produce polyethylene resin.

[0010] Chinese patent CN1405224A discloses a method for manufacturing a three-stage polymerized polyethylene resin composition, which limits the limiting viscosity of each component in the polymer by generating three polymers with non-ultra-high molecular weight components.

[0011] CN103342842A discloses a high-density polyethylene resin composition for microporous membranes and its preparation method. The method involves continuous series polymerization in two polymerization reactors. The first reactor is used for hydrogenation copolymerization, while the second reactor is used for copolymerization only, thereby directly forming a uniform mixture of ultra-high molecular weight polyethylene components and medium- and low molecular weight polyethylene components.

[0012] The current method for producing ultra-high molecular weight polyethylene mainly uses the ethylene slurry intermittent polymerization method, which has low production efficiency and makes it difficult to control the quality of different batches. On the other hand, the ethylene slurry single-reactor continuous polymerization method has problems such as slurry backmixing, which limits the increase in molecular weight and makes it difficult to produce ultra-high molecular weight polyethylene with high viscosity-average molecular weight. Summary of the Invention

[0013] Based on existing technology, the inventors have conducted in-depth research and discovered that under hydrogen-free atmosphere and ethylene slurry polymerization conditions, by using 2-6 ethylene slurry polymerization reactors connected in series and controlling the deviations in polymerization temperature, polymerization pressure, and gas phase composition between each reactor within a certain range, continuous slurry polymerization of raw materials containing ethylene and optional comonomers can continuously produce ultra-high molecular weight polyethylene with a viscosity-average molecular weight of 1.5-8 million g / mole.

[0014] Furthermore, under the tandem ethylene slurry continuous polymerization method of the present invention, the polymerization activity of the main catalyst can be fully utilized, thereby obtaining ultra-high viscosity-average molecular weight polyethylene with low metal element content and low ash content, which can be applied to fields with high requirements for impurities such as aerospace and medical materials.

[0015] In other words, the method for continuous production of ultra-high viscosity-average molecular weight polyethylene by slurry polymerization of the present invention does not require a harsh ethylene slurry polymerization reactor configuration and polymerization reaction conditions. It can achieve continuous production of ultra-high viscosity-average molecular weight polyethylene with high viscosity-average molecular weight, low metal element content, low ash content and high tensile strength. It is very suitable for industrial-scale production and can be applied to the subsequent preparation of high-strength ultra-high molecular weight polyethylene fibers, artificial medical joints and other high-end materials.

[0016] Specifically, this invention provides a method for the continuous production of ultra-high viscosity-average molecular weight polyethylene (a copolymer of ethylene homopolymer, ethylene, and comonomers) via slurry polymerization. The method employs 2-6 (preferably 3-4, most preferably 3) ethylene slurry polymerization reactors connected in series as reactors. Under a hydrogen-free atmosphere, and with the polymerization temperature, polymerization pressure, and gas phase composition deviations between reactors controlled within a certain range, continuous slurry polymerization is carried out on a raw material containing ethylene and optional comonomers. Specifically, a main catalyst and a co-catalyst, along with the raw material containing ethylene and optional comonomers, are continuously introduced into the first polymerization reactor. In subsequent polymerization reactors… The reaction vessel is supplemented with raw materials containing ethylene and optional comonomers to ensure that the gas phase composition in each polymerization reaction vessel deviates from that in the first polymerization reaction vessel by no more than ±10%, the polymerization pressure in subsequent polymerization reaction vessels deviates from that in the first polymerization reaction vessel by no more than ±20%, and the polymerization temperature deviates from that in the first polymerization reaction vessel by no more than ±8%. The slurry in each polymerization reaction vessel leaves the reaction vessel by overflow or by actively controlling the flow rate and then enters the next reaction vessel or the post-processing system. In this way, ultra-high viscosity-average molecular weight polyethylene with low metal element content, low ash content and high mechanical properties can be obtained.

[0017] The present invention also provides an ultra-high molecular weight polyethylene (a copolymer of ethylene homopolymer, ethylene and comonomers) with a viscosity-average molecular weight of 1.5-8 million g / mole, preferably 3-7 million g / mole, a metal element content of 0-40 ppm, preferably 0-30 ppm, a bulk density of 0.30-0.55 g / cm³, preferably 0.33-0.52 g / cm³, a comonomer mole insertion rate of 0-2.0%, preferably 0-1.0%, a tensile yield strength greater than 21 MPa, preferably greater than 23 MPa, a tensile breaking strength greater than 33 MPa, preferably greater than 35 MPa, and an ash content of less than 200 ppm, preferably less than 150 ppm.

[0018] Technical effect

[0019] The slurry polymerization method for continuous production of ultra-high molecular weight polyethylene of the present invention requires a low amount of co-catalyst, has a stable polymerization process, offers flexible production methods, and provides a wide range of product adjustability. Furthermore, it solves the backmixing problem caused by continuous polymerization methods in the prior art.

[0020] In this invention, ultra-high molecular weight polyethylene is continuously produced through slurry polymerization, which allows the main catalyst to fully exert its polymerization activity and yields ultra-high viscosity-average molecular weight polyethylene with low metal element content and low ash content.

[0021] In the continuous production method of ultra-high molecular weight polyethylene by ethylene slurry polymerization of the present invention, the ethylene slurry polymerization activity is high, and the ultra-high molecular weight polyethylene (ethylene homopolymer and ethylene copolymer) produced thereby has high viscosity-average molecular weight, low metal element and ash content, and excellent mechanical properties.

[0022] This invention employs a multi-stage (2-6 reactors) continuous method to produce ultra-high molecular weight polyethylene (UHMWPE). Simultaneously, the polymerization temperature, polymerization pressure, and polymerization gas phase composition of each reactor after the first reactor are within a certain range (preferably substantially the same between reactors). As a result, the UHMWPE obtained by the method of this invention has a single narrow peak distribution, which exhibits superior mechanical properties compared to UHMWPE with broad or multi-peak distributions in the prior art. Simple Explanation of the Diagram

[0023] none Implementation

[0024] The specific embodiments of the present invention will be described in detail below. However, it should be noted that the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the scope of the patent application in the appendix.

[0025] In the context of this invention, unless otherwise explicitly defined or the meaning is beyond the understanding of those skilled in the art, hydrocarbon or hydrocarbon derivative groups with three or more carbon atoms (such as propyl, propoxy, butyl, butane, butene, butenyl, hexane, etc.) have the same meaning when not prefixed with "n-" as when prefixed with "n-". For example, propyl is generally understood as n-propyl, and butyl is generally understood as n-butyl, unless otherwise explicitly stated.

[0026] In order to avoid complexity, this specification does not explicitly state whether the valence of each substituent or group in the compound is monovalent, divalent, trivalent, or tetravalent. Those skilled in the art can make specific judgments based on the position or substitution of these substituents or groups (such as groups G, D, B, A, and F as described or defined in this specification) in the structural formula of the corresponding compound, and select the appropriate definition for the valence at that position or substitution from the definitions given for these substituents or groups in this specification.

[0027] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meaning conventionally understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0028] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to refer to materials, substances, methods, steps, apparatus, or components, the objects referred to by such prefixes cover those conventionally used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0029] In the context of this specification, except where expressly stated, any matters or issues not mentioned herein shall apply directly to those known in the art without any modification. Furthermore, any embodiments described herein may be freely combined with one or more other embodiments described herein, and any resulting technical solutions or concepts shall be considered part of the original disclosure or original record of this invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider such combination to be clearly unreasonable.

[0030] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this specification are based on weight, unless being based on weight would not conform to conventional understanding of those skilled in the art.

[0031] The specific embodiments of the present invention will be described in detail below. However, it should be noted that the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the scope of the patent application in the appendix.

[0032] In the context of this invention, unless otherwise specified, the physical properties of substances (such as boiling point) are measured at room temperature (25°C) and normal pressure (101325 Pa).

[0033] Through in-depth research, the inventors of this invention have discovered that in the polymerization method of this invention, by using an alkane solvent with a boiling point of 0-90°C or a mixed alkane solvent with a saturated vapor pressure of 4-200 KPa at 20°C as the polymerization solvent (preferably an alkane solvent with a boiling point of 25-82°C or a mixed alkane solvent with a saturated vapor pressure of 30-160 KPa at 20°C), compared with conventional polymerization solvents, the specific polymerization solvent of this invention and the boiling point differences between ethylene and optional copolyolefins used as reactants are significant. This allows for convenient and efficient post-processing of the obtained ultra-high molecular weight polyethylene. Furthermore, the obtained ultra-high molecular weight polyethylene powder has a low solvent residue content, which is beneficial for shortening the drying time of the polyethylene powder and saving post-processing costs.

[0034] Furthermore, the polymerization method of the present invention employs a multi-stage (2-6 reactors) continuous process to produce ultra-high molecular weight polyethylene (UHMWPE) with variations in polymerization pressure and temperature within a certain range (preferably substantially the same between reactors). This allows for the production of UHMWPE at high polymerization temperatures, maximizing the polymerization activity of the main catalyst. Moreover, existing technologies using single-stage (1-reactor) polymerization reactors, 1-2 stage loop reactors, or 3 or more stage loop cascades are only suitable for homopolymerization. In contrast, the polymerization method of the present invention is applicable to slurry polymerization of both homopolymerization and copolymerization, and can achieve a higher coolefin insertion rate.

[0035] The polymerization method of this invention, after preparing ultra-high molecular weight polyethylene powder, eliminates the need for complex post-purification treatments (such as washing with high-purity solvents, washing with high-purity water, high-temperature cooking, and filtration after polymer melting). Only the reaction solvent needs to be removed (through filtration, decantation, rapid boiling, and evaporation) to obtain high-purity ultra-high molecular weight polyethylene with low metal content, low ash content, and excellent mechanical properties.

[0036] In this invention, a multi-stage (2-6 reactors) continuous method is used to produce ultra-high molecular weight polyethylene (UHMWPE) with the polymerization pressure and temperature deviation of each reactor within a certain range (preferably substantially the same between reactors). This effectively solves the backmixing problem in the continuous polymerization method for producing polyethylene in the prior art, and ensures complete release of catalyst activity, thereby further improving the degree of polymerization of ethylene or ethylene and other comonomers. In addition, the substantially identical reaction conditions between reactors further ensure the stable chain elongation of polyethylene. The resulting UHMWPE homopolymer and ethylene copolymer have high viscosity-average molecular weight and low metal element and ash content.

[0037] The ultra-high molecular weight polyethylene (UHMWPE) produced by the multi-stage (2-6 reactors) continuous method of the present invention exhibits excellent mechanical properties. Without being limited by any theory, the inventors of the present invention believe that in the polymerization method of the present invention, a main catalyst and a co-catalyst, along with raw materials containing ethylene and optional comonomers, are continuously added to the first polymerization reactor, while ethylene and optional comonomers are continuously added to subsequent reactors in series. This ensures that the gas phase composition in each subsequent reactor deviates from that in the first reactor within a certain range (preferably substantially the same between reactors). Thus, under substantially the same gas phase composition, the polymerization activity of the main catalyst is fully utilized, and the polymerization temperature and pressure in each reactor deviate from those in the first reactor within a certain range (preferably substantially the same between reactors). Consequently, the UHMWPE obtained by the method of the present invention exhibits a single narrow peak distribution, which, compared to the broad peak or multi-peak distribution of UHMWPE in the prior art, results in superior mechanical properties.

[0038] The polyethylene of this invention includes homopolymers obtained by homopolymerization of ethylene and copolymers obtained by copolymerization of ethylene and comonomers. In this invention, polyethylene is sometimes also referred to as an ethylene polymer.

[0039] The method for continuous production of ultra-high viscosity-average molecular weight polyethylene via slurry polymerization according to the present invention uses polyethylene as the main catalyst, which is not particularly limited herein. It can be any catalyst commonly used in the art for catalyzing ethylene polymerization, or a complex, compound, or composition having catalytic activity for homopolymerization of ethylene monomers or copolymerization of ethylene and comonomers. Specifically, it can be a composite catalyst selected from one or more of metallocene catalysts, non-metallocene catalysts, Ziegler-Vita catalysts, and Ziegler catalysts. Preferably, it includes supported or carrier-supported supported single-center metal catalysts, supported multi-center metal catalysts, Ziegler-Vita catalysts, supported Ziegler-Vita and metallocene composite catalysts, supported bis or polymetallocene catalysts, supported Ziegler-Vita and non-metallocene composite catalysts, supported bis or poly non-metallocene catalysts, supported metallocene and non-metallocene composite catalysts, supported post-transition metal catalysts, and carrier-supported Ziegler-Vita catalysts, etc.

[0040] Specifically, the main catalyst for polyethylene can be selected from supported non-metallocene catalysts, such as those specified in invention patents CN200310106156.X, CN200310106157.4, CN200410066068.6, CN200510119401.X, CN200610107651.6, CN200710162677.5, CN 200710162667.1, CN200710162672.2, CN 200710162675.6, CN200710162676.0, CN200710162666.7, CN200910180100.6, CN... 200910180607.1, CN200910180601.4, CN200910180606.7, CN200910180602.9, CN200910180605.2, CN20091018 0603.3, CN200910180604.8, CN200910210988.3, ​​CN200910210984.5, CN200910210989.8, CN200910210986.4, C N200910210985. 86012.7, CN201010284870.8, CN201010285982.5, CN201010284856.8, CN201010285970.2, CN201010285956.2, CN201010285969.X, CN201010285958.1, CN201010285967.0, CN201010285994.8, CN201110259336.6, CN201110 259219.X, CN201110259330.9, CN201110259327.7, CN201110259367.1, CN201110259289.5, CN201110259359.7 , CN201110259282.3, CN201110259318.8, CN201110259258.X, CN201110259300.8, CN201110259254.1, CN00111 0259299.9, CN201110259245.2, CN201110259296.5, CN201110259338.5, CN201110259370.3, CN201110259339.X、CN201110259293.1、CN201110259356.3、CN201210063756.1、CN201210063777.3、CN20121006 3788.1, CN201210063818.9, CN201210063824.4, CN201210063843.7, CN201210063854.5, CN2012 10063876.1, CN201210063878.0, CN201210063891.6, CN201210063894.X, CN201210063907.3, CN 201210063909.2, CN201210063935.5, CN201210063941.0, CN201210063945.9, CN201310189677. X、CN201310227368.7、CN201310227370.4、CN201310227830.3、CN201310227393.5、CN20131045 2714.1, CN201710814678.7, CN201710814595.8, CN201710814594.3, CN201710814593.9, CN2017 Supported non-metallocene catalysts as described in CN201710814591.X, CN201811144599.0, CN201811144768.0, CN201811139936.7, CN201811140811.6, CN201811139946.0, CN201811139741.2, and CN201310091208.4.

[0041] As the main catalyst for polyethylene, it can be selected from supported metallocene catalysts, such as those specified in invention patents CN201110247347.2, CN201110080343.X, CN201010518904.5, CN201010519660.2, CN201210289014.0, CN200910078596.6, CN201310090758.4, CN201310090736.8, 201310521768.9, CN201410589467.4, CN201410590067.5, CN201610835700.1, and 201610944191.6. CN201710959423.X, CN201110247349.1, CN201110080294.X, CN201110080395.7, CN201210289017.4, CN201210289031.4, CN201310091192.7, CN20 1310540973.X, CN201510724626.1, CN200410086283.2, CN200610137777 .8, CN201610944182.7, CN201710312720.5, CN201110080422.0, CN201110 080422.0, CN201110080394.2, CN201010519406.2, CN201010519715.X, C N201010519174.0, CN201010519429.3, CN201210289004.7, CN2013100908 47.9, CN201310091209.9, CN201310540975.9, CN201410554709.6, CN201410513506.2, CN00130388.0, CN200710176589.0, CN201610944083.9, CN2 01110246705.8, CN201110247085.X, CN2011102914899, CN201010521674 .8, CN201310090752.7, CN201310090848.3, CN2013100908483, CN2015106 24502.6, CN201710166709.2, CN20171031225.2, CN201110246710.9, CN20 1110080374.5, CN201010519797.8, CN201210289012.1, CN201210418645.8. Supported metallocene catalysts as described in CN201310090998.4, CN201410252254.2, CN201610393399.3, CN201610956141.X, CN201710958837.0, etc.

[0042] As the main catalyst for polyethylene, it can be selected from Ziegler-Vita type catalysts supported on a support, such as those specified in invention patents CN201010522112.5, CN201010240355.X, CN201010502803.9, CN201010511310.1, CN200710121105.2, CN201010502778.4, CN201010502717.8, CN201010240379.5, CN201110148492.5, and CN20111. The Ziegler-Vita type catalysts involved in CN201110148527.5, CN201110148545.3, CN201110306102.2, CN201010240378.0, CN200410086382.0, CN98101108.X, CN200410078280.4, CN200910088546.6, etc., such as the existing CMU catalyst (also known as CM catalyst) of Beijing Aoda Branch of China Petroleum & Chemical Corporation.

[0043] Among them, supported non-metallocene catalysts, supported metallocene catalysts, and Ziegler-Vita catalysts are preferred.

[0044] The polyethylene main catalyst typically contains an active metal, which can be a commonly used active metal in the art, such as those selected from Group IVB elements (e.g., titanium, zirconium, or hafnium); Group VB elements (e.g., vanadium); and Group VIII elements (e.g., iron, cobalt, nickel, palladium). Group IVB metals are preferred, with titanium being the most preferred. It should be noted that, unless otherwise specified, the molar amount of the polyethylene main catalyst in this invention is calculated based on the active metal element in the polyethylene main catalyst.

[0045] According to the present invention, the polyethylene main catalyst can be a supported catalyst, and the support can be selected from at least one of porous silicone support, layered porous support, organic polymer support, magnesium compound support, and oxide support.

[0046] The magnesium compound carrier can be selected from magnesium compounds, such as magnesium halides, magnesium alkoxy halides, magnesium alkoxy compounds, alkyl magnesium compounds, magnesium alkyl halides, and magnesium alkylalkoxy compounds. These magnesium compounds can be used individually or in combination.

[0047] As porous supports, examples include organic or inorganic porous solids that are conventionally used as supports in the manufacture of supported olefin polymerization catalysts.

[0048] Specifically, examples of organic porous solids include olefin homopolymers or copolymers, polyvinyl alcohol or copolymers thereof, cyclodextrin, (co)polyester, (co)polyamide, vinyl chloride homopolymers or copolymers, acrylate homopolymers or copolymers, methacrylate homopolymers or copolymers, and styrene homopolymers or copolymers, as well as partially crosslinked forms of these homopolymers or copolymers, wherein partially crosslinked (e.g., styrene polymers with a crosslinking degree of at least 2% but less than 100%) are preferred.

[0049] According to the present invention, when using an organic porous solid as a carrier, the organic porous solid can also be thermally activated before use. This thermal activation can be carried out in a conventional manner, such as heating the organic porous solid under reduced pressure or an inert atmosphere. The inert atmosphere referred to here means a gas containing only trace amounts or no components that can react with the organic porous solid. Examples of inert atmospheres include nitrogen or rare gas atmospheres, with nitrogen atmosphere being preferred. Since organic porous solids have poor heat resistance, this thermal activation process is conducted without damaging the structure and basic composition of the organic porous solid itself. Generally, the thermal activation temperature is 50-400°C, preferably 100-250°C, and the thermal activation time is 1-24 hours, preferably 2-12 hours. After thermal activation, the organic porous solid needs to be stored under positive pressure in an inert atmosphere for later use.

[0050] Examples of inorganic porous solids include refractory oxides of metals from Groups IIA, IIIA, IVA, or IVB of the periodic table (such as silicon dioxide, aluminum oxide, magnesium oxide, titanium oxide, zirconium oxide, or thorium oxide), or any refractory composite oxide of these metals (such as aluminum silicate, aluminum magnesium oxide, silicon titanium oxide, magnesium titanium oxide, and aluminum titanium oxide), as well as clay, molecular sieves (such as ZSM-5 and MCM-41), mica, montmorillonite, bentonite, and diatomaceous earth. Examples of such inorganic porous solids also include oxides generated by the high-temperature hydrolysis of gaseous metal halides or gaseous silica compounds, such as silica gel obtained by the high-temperature hydrolysis of silicon tetrachloride, or aluminum oxide obtained by the high-temperature hydrolysis of aluminum trichloride. Preferred materials include silicon dioxide, alumina, magnesium oxide, aluminum silicate, aluminum magnesium oxide, titanium dioxide silicate, titanium dioxide, molecular sieves, and montmorillonite, with silicon dioxide being particularly preferred. Suitable silicon dioxide can be manufactured by conventional methods or can be any commercially available product, such as Grace 955, Grace 948, Grace SP9-351, Grace SP9-485, Grace SP9-10046, Grace 2480D, Grace 2212D, Grace 2485, Davsion Syloid 245, and Aerosil 812 from Grace Corporation; ES70, ES70X, ES70Y, ES70W, ES757, EP10X, and EP11 from Ineos Corporation; and CS-2133 and MS-3040 from PQ Corporation.

[0051] According to the present invention, the co-catalyst is one or more of aluminoxane, alkylaluminum, and haloalkylaluminum, preferably one or more of alkylaluminum.

[0052] Examples of aluminum oxanes include linear aluminum oxanes represented by the following general formula (I-1) and cyclic aluminum oxanes represented by the following general formula (I-2).

[0053] (I-1) (I-2)

[0054] In the aforementioned general formula, the groups R are the same or different from each other (preferably the same), each independently selected from C1-C8 alkyl groups, preferably methyl, ethyl, propyl, butyl and isobutyl, most preferably methyl; n is any integer in the range of 1-50, preferably any integer in the range of 10-30.

[0055] As the aluminum oxane, methyl aluminum oxane, ethyl aluminum oxane, isobutyl aluminum oxane and n-butyl aluminum oxane are preferred, methyl aluminum oxane and isobutyl aluminum oxane are further preferred, and methyl aluminum oxane is most preferred.

[0056] These aluminum oxanes can be used alone or in combination in any proportion.

[0057] Examples of alkylaluminum compounds include those represented by the general formula (II):

[0058] Al(R) 3(II)

[0059] Wherein, the groups R are the same or different from each other (preferably the same), and each is independently selected from C1-C8 alkyl groups, preferably methyl, ethyl, propyl, butyl and isobutyl, with methyl being the most preferred.

[0060] Specifically, examples of alkylaluminum include trimethylaluminum (Al(CH3)3), triethylaluminum (Al(CH3CH2)3), tri-n-propylaluminum (Al(C3H7)3), triisopropylaluminum (Al(iC3H7)3), triisobutylaluminum (Al(iC4H9)3), tri-n-butylaluminum (Al(C4H9)3), triisopentylaluminum (Al(iC5H11)3), tri-n-pentylaluminum (Al(C5H11)3), tri-n-hexylaluminum (Al(C6H13)3), triisohexylaluminum (Al(iC6H13)3), diethylmethylaluminum (Al(CH3)(CH3CH2)2), and dimethylethylaluminum (Al(CH3CH2)(CH3)). 2) etc., among which trimethylaluminum, triethylaluminum, tripropylaluminum and triisobutylaluminum are preferred, and triethylaluminum and triisobutylaluminum are most preferred.

[0061] These alkylaluminums can be used alone or in combination in any proportion.

[0062] Examples of such haloalkylaluminum compounds include those represented by the general formula (III):

[0063] Al(R) nX 3-n(III)

[0064] Wherein, the groups R are the same or different from each other (preferably the same), and each is independently selected from C1-C8 alkyl groups, preferably methyl, ethyl, propyl, butyl and isobutyl, with methyl being the most preferred; X represents fluorine, chlorine, bromine, or iodine; n represents 1 or 2.

[0065] Specifically, examples of the haloalkyl aluminum include, for instance, dichlorodimethylaluminum (Al(CH3)2Cl), dichloromethylaluminum (Al(CH3)Cl2), dichlorodiethylaluminum (Al(CH3CH2)2Cl), dichloroethylaluminum (Al(CH3CH2)Cl2), dichlorodipropylaluminum (Al(C3H7)2Cl), dichloropropylaluminum (Al(C3H7)Cl2), dichlorodi-n-butylaluminum (Al(C4H9)2Cl), dichlorodi-n-butylaluminum (Al(C4H9)Cl2), dichlorodiisobutylaluminum (Al(iC4H9)2Cl), dichloroisobutylaluminum (Al(iC4H9)Cl2), dichlorodi-n-pentylaluminum (Al(C5H11)2Cl), and dichlorodi-n-pentylaluminum (Al(C5H11)2Cl). 11) Cl 2), dichlorodiisopentylaluminum (Al(iC 5H 11) 2Cl), dichlorodiisopentylaluminum (Al(iC 5H 11)Cl 2), dichlorodi-n-hexylaluminum (Al(C 6H 13) 2Cl), dichlorodi-n-hexylaluminum (Al(C 6H 13)Cl 2), dichlorodiisohexylaluminum (Al(iC 6H 13) 2Cl), dichloroisohexylaluminum (Al(iC 6H 13)Cl 2), dichloromethylethylaluminum (Al(CH 3)(CH 3CH 2)Cl), dichloromethylpropylaluminum (Al(CH 3)(C 3H 7)Cl), dichloromethyl-n-butylaluminum (Al(CH 3)(C 4H 9)Cl), dichloromethylisobutylaluminum (Al(CH 3)(iC 4H 9)Cl), dichloroethylpropylaluminum (Al(CH 3)(iC 4H 9)Cl), dichloroethylpropylaluminum (Al(CH 3)(iC 4H 9)Cl), dichloroethylpropylaluminum (Al(CH 3)(iC 4H 9)Cl), dichloromethyl-n-butyl ... The preferred materials include diethylaluminum chloride (Al(CH2CH3)(C3H7)Cl), diethylaluminum chloride (AlCH2CH3)(C4H9)Cl), dimethylaluminum chloride (Al(CH2CH3)(C4H9)Cl), diethyl ...

[0066] These alkyl halogenated aluminum halide can be used alone or in combination in any proportion.

[0067] Furthermore, according to the present invention, the co-catalyst can be used alone, or multiple co-catalysts can be used in combination in any proportion as needed, without any particular limitation.

[0068] In this invention, unless otherwise specified, the amount of the co-catalyst is expressed as the content of aluminum (Al) element.

[0069] According to the present invention, the polymerization solvent is selected from alkane solvents with boiling points of 0-90°C or mixed alkane solvents with saturated vapor pressure of 4-200 kPa at 20°C.

[0070] Among them, the preferred alkane solvents, with boiling points between 0-90℃, are those with boiling points between 25-82℃. Examples include 2,2-dimethylpropane (also known as neopentane, boiling point 9.5℃, saturated vapor pressure 146.63 kPa at 20℃), 2-methylbutane (also known as isopentane, boiling point 27.83℃, saturated vapor pressure 76.7 kPa at 20℃), n-pentane (boiling point 36.1℃, saturated vapor pressure 56.5 kPa at 20℃), and cyclopentane (boiling point 49.26℃, saturated vapor pressure 34.6 kPa at 20℃). KPa), n-hexane (boiling point 68.73℃), cyclohexane (boiling point 80.7℃), 2-methylpentane (also known as isohexane, boiling point 60.3℃), 3-methylpentane (boiling point 64.0℃), 2,3-dimethylbutane (boiling point 58.7℃), 2,2-dimethylbutane (boiling point 58.7℃), preferably n-pentane, isopentane, cyclopentane, n-hexane, and cyclohexane.

[0071] As the mixed alkane solvent with a saturated vapor pressure of 4-200 KPa at 20°C, it is preferred to have a mixed alkane solvent with a saturated vapor pressure of 30-160 KPa at 20°C. It can be a mixed solvent formed by mixing different alkane solvents in proportion, such as a mixed solvent formed by solvents of hexane and its isomers, or solvents of pentane and its isomers. It can also be a mixture of alkane extracted from a solvent distillation unit according to the distillation range. Specifically, combinations such as n-pentane and isopentane, isopentane and neopentane, n-pentane and cyclopentane, n-pentane and neopentane, isopentane and cyclopentane, neopentane and cyclopentane, n-hexane and cyclopentane, n-hexane and n-pentane, n-hexane and 3-methylpentane, n-hexane and 2,2-dimethylbutane, n-hexane and 2,3-dimethylbutane, n-hexane and cyclohexane, n-hexane and isohexane, isohexane and cyclohexane, n-pentane, isopentane and cyclopentane, n-hexane, isohexane and cyclohexane, etc., are possible, but are not limited to these. In this invention, when using mixed alkanes as the reaction solvent, the amount of each alkane solvent can be arbitrarily adjusted, as long as the saturated vapor pressure of the resulting mixed solvent at 20°C is 4-200 kPa (preferably 30-160 kPa).

[0072] In one embodiment of the present invention, the mixed alkane having a saturated vapor pressure of 4-200 kPa (preferably 30-160 kPa) at 20°C is preferably a mixed alkane having a saturated vapor pressure of 4-200 kPa (preferably 30-160 kPa) at 20°C, formed by mixing two or more alkanes selected from n-pentane, isopentane, neopentane, and cyclopentane. More preferably, it is a combination of n-pentane and isopentane, a combination of isopentane and neopentane, a combination of n-pentane and cyclopentane, a combination of isopentane and cyclopentane, a combination of n-pentane, isopentane, and n-pentane, etc. Regarding the proportions of each alkane in the mixed alkane, for example, when two alkane solvents are mixed, the molar ratio can be 0.01-100:1, preferably 0.1-10:1; when three alkane solvents are mixed, the molar ratio can be 0.01-100:0.01-100:1, preferably 0.1-10:0.1-10:1, as long as the resulting mixed solvent has a saturated vapor pressure of 4-200 kPa (preferably 30-160 kPa) at 20°C. In one embodiment of the present invention, only alkane solvents with boiling points of 0-90°C or mixed alkane solvents with a saturated vapor pressure of 4-200 kPa at 20°C are used as polymerization solvents.

[0073] Using alkane solvents with boiling points of 0-90℃ or mixed alkane solvents with saturated vapor pressures of 4-200 KPa at 20℃ as polymerization solvents provides a feasible option for preparing ultra-high viscosity-average molecular weight polyethylene with different viscosity-average molecular weights and other properties through ethylene slurry polymerization. For example, using alkane solvents with lower boiling points (such as n-pentane, isopentane, or cyclopentane) or mixed alkane solvents with higher saturated vapor pressure at 20°C (such as combinations of n-pentane and neopentane, or isopentane and neopentane) facilitates heat removal from the ethylene slurry polymerization reaction, allowing it to proceed at higher polymerization pressures and lower polymerization temperatures. Furthermore, the polymer dries easily, and the solvent is readily recoverable and reusable. Conversely, using alkane solvents with higher boiling points (such as n-hexane, cyclohexane, or 3-methylpentane) or mixed alkane solvents with lower saturated vapor pressure at 20°C (such as combinations of n-hexane and cyclohexane, n-hexane and 3-methylpentane, or cyclohexane and 2-methylpentane) reduces solvent recovery losses. To effectively remove heat from the polymerization reaction, it can proceed at lower polymerization pressures and higher polymerization temperatures.

[0074] According to the present invention, in the continuous production of ultra-high molecular weight polyethylene by ethylene slurry polymerization, the polymerization temperature of each reactor in series is 40-100°C, preferably 50-90°C. In this invention, the polymerization temperature of each reactor after the first reactor deviates from the polymerization temperature of the first reactor by no more than ±8%, and preferably the polymerization temperature of each reactor after the first reactor is substantially the same as the polymerization temperature of the first reactor. In this invention, "substantially the same temperature" means a deviation from a reference value of no more than ±5%, preferably no more than ±2%. Wherein, when ethylene slurry polymerization is carried out at a higher polymerization temperature, a solvent with a higher boiling point can be selected; conversely, when ethylene slurry polymerization is carried out at a lower polymerization temperature, a solvent with a lower boiling point can be selected. It is known that under ethylene slurry polymerization conditions, under similar and comparable conditions such as polymerization pressure, main catalyst, co-catalyst, and solvent, within the polymerization temperature range described in this invention, the viscosity-average molecular weight of the resulting ultra-high viscosity-average molecular weight polyethylene first increases and then decreases with increasing polymerization temperature. Therefore, according to the present invention, the viscosity-average molecular weight of ultra-high viscosity-average molecular weight polyethylene obtained by ethylene slurry polymerization can be adjusted and controlled by the polymerization temperature.

[0075] According to the present invention, in the continuous production of ultra-high molecular weight polyethylene by ethylene slurry polymerization, the polymerization pressure of each reactor in series is 0.2-4.0 MPa, preferably 1.0-3.0 MPa, and more preferably 2.0-3.0 MPa. In the present invention, the deviation of the polymerization pressure of each reactor after the first reactor from the polymerization pressure of the first reactor does not exceed ±20%, preferably not more than ±10%, and more preferably the polymerization pressure of each reactor after the first reactor is substantially the same as the polymerization pressure of the first reactor. In the present invention, "substantially the same pressure" means a deviation from a reference value not exceeding ±5%, preferably not more than ±2%. In one embodiment of the present invention, the pressure of each reactor is the same. Wherein, if ethylene slurry polymerization is carried out at a higher polymerization temperature, a lower polymerization pressure can be selected; conversely, if ethylene slurry polymerization is carried out at a lower polymerization temperature, a higher polymerization pressure can be selected. It is known in the art that, in the process of ethylene polymerization (homogeneous polymerization or copolymerization with other monomers), the reaction pressure in the reactor can be controlled by the ethylene as a polymerization raw material and optional comonomers. Under ethylene slurry polymerization conditions, and under similar and comparable conditions such as polymerization temperature, main catalyst, co-catalyst, and solvent, within the polymerization pressure range described in this invention, as the polymerization pressure increases, the viscosity-average molecular weight of the resulting ultra-high viscosity-average molecular weight polyethylene also first increases and then decreases. Therefore, according to this invention, the viscosity-average molecular weight of ultra-high viscosity-average molecular weight polyethylene obtained by ethylene slurry polymerization can also be adjusted and controlled by polymerization pressure.

[0076] According to the present invention, in the method for continuous production of ultra-high molecular weight polyethylene by ethylene slurry polymerization, hydrogen is not used, that is, the polymerization reaction is carried out in a hydrogen-free atmosphere.

[0077] According to the present invention, when ethylene slurry polymerization is used to continuously produce ultra-high molecular weight polyethylene, the comonomer is not necessary. It is mainly required when producing ultra-high molecular weight ethylene copolymer. Therefore, in the slurry polymerization of the present invention, when the comonomer is in the memory of each polymerization reactor, the volume concentration of the comonomer can be 0.01-5%, 0.02-5%, or 0.05-3%.

[0078] Generally, under comparable conditions, the molecular weight of polymers obtained by copolymerization will be lower than that obtained by homopolymerization. Different polyethylene main catalysts have different copolymerization performance in producing ultra-high molecular weight ethylene copolymers. For main catalysts with good copolymerization performance, a lower volume concentration of comonomers can be used, but the viscosity-average molecular weight of the final polymer needs to be taken into account.

[0079] According to the present invention, the comonomer used in the preparation of ultra-high molecular weight ethylene copolymers by ethylene slurry polymerization can be selected from at least one of α-olefins, dienes, cyclic olefins, and other olefinically unsaturated compounds. The α-olefin can be a C3-C10 α-olefin, such as propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 4-methyl-1-pentene, 4-methyl-1-hexene, 1-octene, 1-decene, 1-undecene, 1-dodecene, and styrene. The cyclic olefin can be such as 1-cyclopentene, ethylene-imide norbornene, and norbornene. The dienes can be such as 1,4-butadiene, 2,5-pentadiene, 1,6-heptadiene, vinyl norbornene, norbornene, and 1,7-octadiene. The other olefinically unsaturated compounds can be such as vinyl acetate and (meth)acrylate. The comonomer is preferably an α-olefin of C3-C10, more preferably selected from at least one of 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene, and even more preferably selected from at least one of 1-butene, 1-hexene, and 1-octene.

[0080] This invention employs 2-6 ethylene slurry polymerization reactors connected in series, preferably 3-4, and most preferably 3. The main catalyst and co-catalyst are continuously added from the first polymerization reactor. The concentration of the main catalyst in the first polymerization reactor is 0.001-0.100 mmol / L polymerization solvent, preferably 0.005-0.050 mmol / L polymerization solvent; the molar ratio of the co-catalyst to the main catalyst is 20-200:1, preferably 30-100:1.

[0081] According to the present invention, no main catalyst or co-catalyst is added to the reactors other than the first polymerization reactor. Additionally, polymerization solvent may be introduced into the reactors other than the first polymerization reactor as needed to adjust the slurry concentration in each reactor. According to the present invention, when continuous production is carried out in series, the slurry in the reactors leaves the reactors by overflow or by actively controlled flow extraction and enters the next reactor or the post-processing system; preferably, the slurry leaves the reactors by overflow and enters the next reactor or the post-processing system.

[0082] In the method of this invention, when the deviations in polymerization pressure and temperature of each reactor are within a certain range (preferably, the polymerization pressure and temperature of each reactor are substantially the same), the gas phase composition and content in each reactor are kept substantially the same. That is, regardless of whether the material in the previous reactor is extracted by overflow or by actively controlled flow extraction, the raw materials of ethylene and optional comonomers from the previous reactor may enter the current reactor by being sandwiched in the slurry. According to this invention, it is necessary to independently add (supplement) the raw materials of ethylene and optional comonomers to each reactor to maintain the deviations in polymerization pressure and gas phase composition of each reactor within a certain range. In one embodiment of this invention, after purging the gas phase components in the previous reactor, only the slurry is transferred to the next reactor by overflow or by actively controlled flow extraction, and then the next reactor is fed with the same gas phase components as the feed to the previous reactor. In one embodiment of this invention, when homopolymerizing ethylene, since the only gas phase raw material participating in the reaction is ethylene, the transfer of gas phase components (ethylene) accompanying the transfer of the slurry will not affect the gas phase composition of the next reactor.

[0083] When the slurry is transferred between two polymerization reactors, the transfer time and method must be considered. Since the polymerization raw materials, main catalyst, and co-catalyst are present in the slurry, the reaction continues during the transfer process. If the gas and liquid phase composition conditions change significantly during this process, the polymerization product obtained will affect the overall performance of the final ultra-high molecular weight polyethylene. According to the present invention, to reduce or avoid the impact of the polymer generated during this transfer process on the final product, the slurry transfer between the two polymerization reactors should be as fast as possible. A preferred continuous production method is for the slurry to overflow from the overflow port of the previous polymerization reactor and directly enter the next polymerization reactor. Most preferably, to ensure smooth overflow of the slurry to the next polymerization reactor, gravity is used to achieve overflow by installing gas phase pressure balancing pipes on the two cascaded reactors. In a preferred embodiment, before the slurry enters the post-processing system from the last polymerization reactor, it is buffered in an insulated intermediate slurry tank. This intermediate slurry tank can be a storage tank, a stirred tank, or a tank with a relatively small length-to-diameter ratio (e.g., 0.5-5, preferably 1-3), preferably a jacketed heated stirred tank. It is also preferred that the slurry temperature be maintained substantially the same as that of the previous polymerization reactor. The retention time in the intermediate tank is 0.1-4.0 h, preferably 0.5-2.0 h. When the last reactor and the intermediate slurry tank are connected by a pipeline, the pipeline is preferably insulated and has a relatively large diameter (e.g., when the volume of the last polymerization reactor is 1-5 m³, the overflow pipe diameter is 50-400 mm, preferably 100-250 mm; when the volume of the last polymerization reactor is 5-10 m³, the overflow pipe diameter is 100-500 mm, preferably 150-250 mm, and so on). Preferably, the insulation temperature of this pipeline is basically the same as that of the previous polymerization reactor.

[0084] According to the present invention, preferably, the polymerization pressure and polymerization temperature of each cascaded polymerization reactor are substantially the same. According to the present invention, preferably, if a comonomer participates in the reaction, the volume concentration of the comonomer in each cascaded polymerization reactor is substantially the same. According to the present invention, the composition of the reaction raw materials (polymerization gas phase components) in each cascaded polymerization reactor deviates from the gas phase composition of the first reactor by no more than ±10%, preferably the gas phase composition of each reactor after the first reactor is substantially the same as the gas phase composition of the first reactor. In the present invention, "substantially the same gas phase composition" means a deviation from a reference value of no more than ±5%, preferably no more than ±2%. In one embodiment of the present invention, the gas phase components of each reactor are the same. In the present invention, the deviation of the gas phase composition refers to the deviation of each gas phase component relative to all gas phase components. For example, when the volume concentration of the comonomer is 3% (reference value), a deviation of no more than ±10% relative to the reference value means a deviation within the range of 3% × (1 ± 0.1).

[0085] According to the present invention, the residence time of each series polymerization reactor in the continuous production of ultra-high molecular weight polyethylene is 0.1-6 h, preferably 0.5-4 h. The total residence time in each series polymerization reactor is not particularly limited, as long as the ultra-high molecular weight polyethylene described in this invention can be obtained. It is related to the ethylene slurry polymerization reaction. When the catalyst concentration in the polymerization reactor is high, the polymerization pressure is high, and the polymerization temperature is high, the total residence time can be reduced accordingly, generally 1-20 h, preferably 2-12 h, and most preferably 4-8 h. The residence time of each series polymerization reactor can be the same or different. The volume of each series polymerization reactor can be different or the same. According to the present invention, considering the smoothness and matching of continuous production, the full utilization of catalyst activity, and the production capacity of the effective volume of each series polymerization reactor, the preferred residence time and polymerization reactor volume configuration is as follows: when the effective volume of the polymerization reactor is the same, the same polymerization residence time is used; for different polymerization reactors, the polymerization residence time is configured proportionally to the effective volume, that is, if the effective volume of the polymerization reactor is doubled, the residence time is also doubled accordingly. Ideally, each polymerization reactor in a cascaded series should have the same effective volume and the same polymerization residence time, but this is not a limitation. The residence time in each polymerization reactor is also related to the residual catalyst activity in each reactor. In this invention, the effective volume of the polymerization reactor refers to the actual volume under overflow conditions, or the volume of slurry stably remaining in the polymerization reactor under actively controlled slurry exit.

[0086] Unlike the batch polymerization process of ethylene slurry polymerization, where the polymerization residence time is the same as the polymerization reaction time, in this invention, when ethylene slurry polymerization is carried out continuously in series, the polymerization residence time is the average reaction residence time in the continuous process. That is, under continuous and stable production conditions, the total volume of slurry in the polymerization reactor divided by the volume of slurry leaving the polymerization reactor per unit hour. According to this invention, increasing or decreasing the continuous amount of polymerization solvent supplied to each polymerization reactor will directly decrease or increase the polymerization residence time. Simultaneously, increasing or decreasing the concentration of the main catalyst and improving or decreasing the polymerization reactivity will also decrease or increase the polymerization residence time.

[0087] According to the present invention, in each cascaded ethylene slurry polymerization reactor, the slurry concentration is 50-500 g polymer / L polymerization solvent, preferably 100-400 g polymer / L polymerization solvent. The slurry concentration in each cascaded polymerization reactor can be adjusted by regulating the volume of polymerization solvent continuously added to each cascaded polymerization reactor, adjusting the slurry concentration in the preceding polymerization reactor, and adjusting the polymerization residence time. Since the polymerization performance of the main catalyst varies, the activity of catalyzing ethylene homopolymerization or copolymerization of ethylene and comonomers may differ at different polymerization time periods. Therefore, according to the method provided by the present invention, the slurry concentration in each cascaded polymerization reactor can be comprehensively adjusted by regulating the polymerization residence time and / or adding polymerization solvent, taking into account the actual consumption rate of raw materials such as ethylene and comonomers.

[0088] According to the present invention, under a preferred condition, for example, when three polymerization reactors are selected in series, the residence time of each polymerization reactor is configured in a ratio of 1:0.2-1:0.1-1, preferably 1:0.4-0.8:0.2-0.6; or, for example, when four polymerization reactors are selected in series, the residence time of each polymerization reactor is configured in a ratio of 1:0.2-1:0.1-1:0.1-1, preferably 1:0.4-0.8:0.2-0.6:0.1-0.4, and so on.

[0089] According to the present invention, the main catalyst and the co-catalyst are continuously added to the first polymerization reactor. The addition method can be as follows: they can be continuously added to the first polymerization reactor along with the polymerization solvent according to a specified ratio. The main catalyst can be continuously added in the form of a solid powder, or the solid powder catalyst can be added to the same solvent as the polymerization solvent to form a catalyst slurry in a catalyst preparation vessel, which is then continuously pumped into the first polymerization reactor. Alternatively, a pre-prepared catalyst slurry can be directly used and continuously pumped into the first polymerization reactor. Preferably, the solid powder catalyst is added to the same solvent as the polymerization solvent to form a catalyst slurry in a catalyst preparation vessel, which is then continuously pumped into the first polymerization reactor, or a pre-prepared catalyst slurry can be directly used and continuously pumped into the first polymerization reactor. The concentration of the prepared main catalyst is not particularly limited; it only needs to be noted that its concentration in the first polymerization reactor is within the range of 0.001-0.100 mmol / L polymerization solvent, preferably 0.005-0.050 mmol / L polymerization solvent, as defined in this invention. In practice, considering the flexibility and ease of control of the continuous ethylene slurry production process, it is preferable to use a high-concentration main catalyst slurry while continuously adding polymerization solvent at another inlet of the first polymerization reactor, ensuring that the ratio of main catalyst to polymerization solvent in the reactor meets the requirements of this invention. The polymerization solvent mentioned here includes both freshly added polymerization solvent and polymerization solvent recovered from the post-processing system.

[0090] According to the present invention, the co-catalyst can be added to the reactor in liquid form. It can be one or more of pure aluminoxane, alkylaluminum, and haloalkylaluminum, or a solution prepared with an alkane solvent (such as those described in the polymerization solvent), and its concentration is not strictly limited. Preferably, the same solvent as the polymerization solvent is used, generally 0.1-10 mol / L, preferably 0.5-2.0 mol / L, to prepare the co-catalyst stock solution, which is then continuously fed into the first polymerization reactor, such that the ratio of the main catalyst to the co-catalyst is 20-200:1, preferably 30-100:1. As the solvent for the cocatalyst stock solution, the same solvent as the polymerization solvent can be used, or other solvents can be used. Specifically, the solvent can be selected from C5-C10 alkane solvents, such as n-pentane, isopentane, neopentane, cyclopentane, n-hexane, isohexane, cyclohexane, n-heptane, isoheptane, n-decane, etc., or mixed alkane solvents of C5-C10 alkanes in different proportions, such as pentane, hexane, heptane, mixtures of two or more of n-pentane and n-hexane, mixtures of cyclopentane and n-hexane, or mixed alkane solvents cut by distillation and rectification. Preferably, the polymerization solvent described in this invention is the polymerization solvent actually used.

[0091] Based on this invention, the main catalyst, co-catalyst, and polymerization solvent are continuously added to the first polymerization reactor, maintaining the limits set by this invention regarding the concentration of the main catalyst and the amount of co-catalyst. Then, ethylene or ethylene and a comonomer are introduced, and under stable polymerization pressure and temperature conditions, slurry polymerization (homogeneity) of ethylene or slurry polymerization (copolymerization) of ethylene and a comonomer is carried out, while ensuring that the slurry concentration meets the limits set by this invention. Furthermore, it is known in the art that, in order to control the polymerization pressure, an inert gas (e.g., nitrogen) that does not participate in the reaction can be introduced into the polymerization reactor.

[0092] Subsequently, after the first polymerization reactor, the slurry from the preceding reactor is continuously fed into subsequent cascaded polymerization reactors via overflow or actively controlled flow extraction. The feed to these subsequent cascaded reactors includes ethylene and optional comonomers, ensuring that the gas phase composition of each reactor deviates from that of the first reactor by no more than ±10%, and that the polymerization pressure of each reactor deviates from that of the first reactor by no more than ±20%. Furthermore, depending on the polymerization reaction, a polymerization solvent may be introduced into subsequent reactors as needed to adjust the slurry concentration in these reactors, preventing the cascaded reaction from causing the slurry concentration in each reactor to exceed the limits specified in this invention.

[0093] Subsequently, the material is discharged from the final stage reactor to the post-processing system. Preferably, the material from the final stage reactor is buffered in an insulated intermediate slurry tank before entering the post-processing system. Ultimately, the ultra-high molecular weight polyethylene of this invention is obtained. In this invention, the so-called "post-processing system" is a system known in the art for recovering polyethylene from the slurry after the polymerization reaction has completed, such as devices for removing polymerization solvents (e.g., filtration, centrifugation, rapid boiling, etc.) and devices for purifying polyethylene.

[0094] In the method for continuous production of ultra-high molecular weight polyethylene by ethylene slurry polymerization of the present invention, there is no particular limitation on the stirring rate in each polymerization reactor, as long as the slurry in the reactor can be properly dispersed. The stirring speed is related to the reactor volume. Generally speaking, the smaller the reactor volume, the higher the required stirring speed. The stirring speed is 10-1000 rpm, preferably 20-500 rpm.

[0095] The ultra-high molecular weight polyethylene obtained by the method of the present invention has a viscosity-average molecular weight of 1.5-8 million g / mole, preferably 3-7 million g / mole. The bulk density of the ultra-high molecular weight polyethylene of the present invention is 0.30-0.55 g / cm³, preferably 0.33-0.52 g / cm³, more preferably 0.39-0.50 g / cm³. The mole insertion rate of the comonomers in the ultra-high molecular weight polyethylene of the present invention is 0.05-4.0%, preferably 0.10-2.0%.

[0096] The ultra-high molecular weight polyethylene obtained by the method of the present invention has a metal element content of 0-40 ppm, preferably 0-30 ppm. The ash content of the ultra-high molecular weight polyethylene of the present invention is less than 200 ppm, preferably less than 150 ppm, and more preferably less than 80 ppm. The tensile yield strength of the ultra-high molecular weight polyethylene of the present invention is greater than 21 MPa, and the tensile breaking strength is greater than 33 MPa; more preferably, the tensile yield strength is greater than 23 MPa, and the tensile breaking strength is greater than 35 MPa.

[0097] The ultra-high molecular weight polyethylene obtained by the method of the present invention has a titanium content of 0-3 ppm, preferably 0-2 ppm, more preferably 0-1 ppm, a magnesium content of 0-10 ppm, preferably 0-5 ppm, more preferably 0-2 ppm, and an aluminum content of 0-30 ppm, preferably 0-25 ppm, more preferably 0-20 ppm.

[0098] In one embodiment of the present invention, a method for continuous production of ultra-high molecular weight polyethylene (UHMWPE) via ethylene slurry polymerization is provided. The method is characterized by using a polyethylene catalyst as the main catalyst, one or more of aluminoxane, alkylaluminum, and haloalkylaluminum as co-catalysts, and using an alkane solvent with a boiling point of 0-90℃ or a mixed alkane solvent with a saturated vapor pressure of 4-200 KPa at 20℃ as the polymerization solvent. Under the conditions of a polymerization temperature of 40-100℃, a polymerization pressure of 0.2-4.0 MPa, a hydrogen volume concentration of 0-2% in the polymerization reactor, and a comonomer volume concentration of 0-10%, 2-6 cascade ethylene slurry polymerization reactors are used for continuous production. The slurry in each reactor leaves the reactor via overflow or extraction and enters the next reactor or a post-processing system. The main catalyst and co-catalyst are continuously added to the first polymerization reactor, and the concentration of the main catalyst in the reactor is 0.001-0.100%. The concentration of polymer was mmol / L, the molar ratio of co-catalyst to main catalyst was 20-200:1, the residence time of each polymerization reactor was 0.1-6h, and the slurry concentration was 50-500 g polymer / L polymerization solvent.

[0099] In one embodiment of the present invention, in the method for continuous production of ultra-high molecular weight polyethylene by ethylene slurry polymerization, an alkane solvent with a boiling point of 25-82℃ or a mixed alkane solvent with a saturated vapor pressure of 30-160 KPa at 20℃ is used as the polymerization solvent. Under the conditions of polymerization temperature of 50-85℃, polymerization pressure of 0.4-3.0 MPa, hydrogen volume concentration in the polymerization reactor of 0-1%, and comonomer volume concentration of 0-5%, 3-4 cascade ethylene slurry polymerization reactors are connected in series for continuous production. The slurry in the reactor leaves the reactor by overflow and enters the next reactor or the post-treatment system. The concentration of the main catalyst in the reactor is 0.005-0.050 mmol / L, the molar ratio of the co-catalyst to the main catalyst is 30-100:1, the residence time of each polymerization reactor is 0.5-4.0 h, and the slurry concentration is 100-400 g polymer / L polymerization solvent.

[0100] According to the present invention, ultra-high molecular weight polyethylene (UHMWPE) with low metal element content, low ash content, and high mechanical properties can be prepared through continuous production via ethylene slurry polymerization. To reduce the metal element content in the polymer, it is necessary to fully release and utilize the catalytic activity of the catalyst for ethylene polymerization. By employing the continuous production method of UHMWPE via ethylene slurry polymerization described in this invention, under the conditions of the polyethylene catalyst, polymerization pressure, polymerization temperature, and polymerization solvent of this invention, UHMWPE with low metal element content, low ash content, and high mechanical properties can be obtained.

[0101] In addition, the molecular weight of the ultra-high viscosity-average molecular weight polyethylene of the present invention does not have a bimodal or multimodal distribution.

[0102] The method for preparing ultra-high viscosity-average molecular weight polyethylene of the present invention can yield ultra-high viscosity-average molecular weight ethylene homopolymers and copolymers of ethylene and comonomers (also commonly referred to as polyethylene or ethylene polymers in this invention) with low metal element content, low ash content, and high mechanical properties. These ethylene homopolymers and copolymers possess high tensile strength and other mechanical properties. Therefore, the polyethylene of the present invention can be used to prepare high-strength ultra-high molecular weight polyethylene fibers, artificial medical joints, and other high-end materials.

[0103] Example

[0104] The present invention will be further described in detail below with reference to the embodiments, but the present invention is not limited to these embodiments.

[0105] The bulk density of ultra-high molecular weight polyethylene was determined in accordance with standard GB 1636-79.

[0106] The contents of active metal elements in polyethylene catalysts and trace elements in ultra-high viscosity-average molecular weight polyethylene, such as titanium, magnesium, calcium, aluminum, and chlorine, were determined by ICP-AES.

[0107] The ash content in ultra-high molecular weight polyethylene was determined according to the national standard GB / T 9345.1-2008 using the direct calcination method. The polymer was burned in a muffle furnace, and the residue was treated at high temperature until constant weight was achieved. The ash content was obtained by dividing the mass of the residue by the initial polymer mass.

[0108] Polymerization activity is the mass of dried ultra-high molecular weight polyethylene powder obtained per unit time divided by the mass of the main catalyst fed per unit time. The unit is kgPE / gCat, which is the number of kilograms of ultra-high molecular weight polyethylene obtained per gram of main catalyst.

[0109] The viscosity-average molecular weight of ultra-high molecular weight polyethylene is calculated as follows: according to standard ASTM D4020-00, the intrinsic viscosity of the polymer is determined using a high-temperature dilution type Ubbelohde viscometer method (capillary inner diameter is 0.44 mm, constant temperature bath medium is No. 300 silicone oil, dilution solvent is decahydronaphthalene, and the measurement temperature is 135℃), and then the viscosity-average molecular weight Mv of the polymer is calculated according to the following formula.

[0110] Mv = 5.37 x 10⁴ x [η] 1.37

[0111] Where η is the intrinsic viscosity.

[0112] The copolymer insertion rate of ultra-high molecular weight polyethylene was determined by nuclear magnetic resonance (NMR) of copolymers with known content and measured externally using a Bruck 66 / S Fourier transform infrared spectrometer.

[0113] The tensile yield strength and tensile breaking strength of ultra-high molecular weight polyethylene were determined in accordance with the national standard GB / T 1040.2-2006.

[0114] Example 1

[0115] The polyethylene main catalyst is the supported non-metallocene catalyst described in Example 2 of Chinese patent application 200710162677.5, wherein the non-metallocene complex structure is as follows: The support is a composite support composed of ES757 porous silica gel and anhydrous magnesium chloride in a mass ratio of 2:1, with a titanium content of 4.25 wt%. It is prepared as a 100 g / L hexane solution of the main catalyst based on solid dry powder.

[0116] The polymerization solvent was n-hexane with a boiling point of 68℃, and the co-catalyst was triethylaluminum, prepared as a 0.88 mol / L hexane solution.

[0117] Three identical ethylene slurry polymerization reactors connected in series were used, each with a volume of 10.4 m3 and an overflow discharge, each with an effective volume of 7.2 m3. The polymerization temperature of each reactor was 65℃. Only ethylene was introduced into each reactor, and no comonomer was introduced into the reactor, so that the polymerization pressure of each reactor reached 2.2 MPa.

[0118] The main catalyst and co-catalyst are added only to the first polymerization reactor. Based on solid dry powder, the feed rate of the main catalyst is 50 g / h, and the co-catalyst is continuously fed to the main catalyst at a molar ratio of 45:1. The polymerization solvent n-hexane is fed to the first polymerization reactor at a rate of 3.47 m³ / h, and the slurry concentration is controlled at 288 g polymer / L polymerization solvent. The polymerization solvent n-hexane is fed to the second polymerization reactor at a rate of 1.74 m³ / h, and the slurry concentration in the second polymerization reactor is controlled at 315 g polymer / L polymerization solvent. The polymerization solvent n-hexane is fed to the third polymerization reactor at a rate of 0.90 m³ / h, and the slurry concentration in the third polymerization reactor is controlled at 330 g polymer / L polymerization solvent.

[0119] The residence time of each polymerization reactor is set at a ratio of 1:0.5:0.25, and the total polymerization residence time is 6 hours.

[0120] After being continuously discharged from the third polymerization reactor, the slurry enters a 10.4 m³ intermediate tank equipped with heating and stirring. After being held for 0.5 h, it enters the post-processing system. After rapid boiling and degassing, it is filtered, centrifuged, and dried to obtain ultra-high molecular weight polyethylene powder. Its viscosity-average molecular weight is 4.6 million g / mole, its bulk density is 0.44 g / cm³, its polymerization activity is 57 kgPE / gCat, its titanium content is 0.86 ppm, its magnesium content is 1.94 ppm, its aluminum content is 23.7 ppm, its ash content is 65 ppm, its tensile yield strength is 24.2 MPa, and its tensile breaking strength is 38.0 MPa.

[0121] Example 2

[0122] It is basically the same as Example 1, but with the following changes:

[0123] The polymerization solvent was changed to n-pentane with a boiling point of 36℃, and the preparation of both the main catalyst and the co-catalyst was changed to n-pentane solution.

[0124] The polymerization temperature in each polymerization reactor was changed to 60℃, and the polymerization pressure was changed to 2.5 MPa.

[0125] The resulting ultra-high molecular weight polyethylene powder has a viscosity-average molecular weight of 5.75 million g / mole, a bulk density of 0.41 g / cm³, a polymerization activity of 55 kgPE / gCat, a titanium content of 0.57 ppm, a magnesium content of 1.60 ppm, an aluminum content of 18.4 ppm, an ash content of 47 ppm, a tensile yield strength of 24.5 MPa, and a tensile breaking strength of 38.4 MPa.

[0126] Example 3

[0127] It is basically the same as Example 2, but with the following changes:

[0128] The comonomer used is 1-hexene. Ethylene and 1-hexene are introduced into each polymerization reactor to ensure that the volume concentration of the comonomer in the gas phase in each reactor is stably controlled at 0.5%. The polymerization solvent is isopentane with a boiling point of 27.83℃. The formulation of both the main catalyst and the cocatalyst is changed to isopentane solution.

[0129] The resulting ultra-high molecular weight polyethylene powder has a viscosity-average molecular weight of 5.2 million g / mole, a bulk density of 0.44 g / cm³, a comonomer mole insertion rate of 0.32%, a polymerization activity of 63 kgPE / gCat, a titanium content of 0.43 ppm, a magnesium content of 1.25 ppm, an aluminum content of 15.1 ppm, an ash content of 42 ppm, a tensile yield strength of 22.2 MPa, and a tensile breaking strength of 38.2 MPa.

[0130] Example 4

[0131] It is basically the same as Example 1, but with the following changes:

[0132] Four identical ethylene slurry polymerization reactors, each with a volume of 10.4 m³, were connected in series. The effective volume was 7.2 m³ with overflow discharge. The polymerization temperature in each reactor was changed to 70°C. Ethylene was introduced into each reactor, changing the polymerization pressure to 2.7 MPa. No comonomer was present in the reactors. The polymerization solvent was changed to n-pentane, and the main catalyst and co-catalyst were prepared as n-pentane solutions.

[0133] The residence time of each polymerization reactor is set according to the ratio of 1:0.6:0.4:0.2, and the total polymerization residence time is 8 hours.

[0134] The polymerization solvent n-pentane is fed into the first polymerization reactor at a rate of 2.9 m³ / h, and the slurry concentration is controlled at 290 g polymer / L polymerization solvent. In the second polymerization reactor, the feed rate of n-pentane is 2.1 m³ / h, and the slurry concentration is controlled at 310 g polymer / L polymerization solvent. In the third polymerization reactor, the feed rate of n-pentane is 1.6 m³ / h, and the slurry concentration is controlled at 330 g polymer / L polymerization solvent. In the fourth polymerization reactor, the feed rate of n-pentane is 0.7 m³ / h, and the slurry concentration is controlled at 350 g polymer / L polymerization solvent.

[0135] The resulting ultra-high molecular weight polyethylene powder has a viscosity-average molecular weight of 4.38 million g / mole, a bulk density of 0.46 g / cm³, a polymerization activity of 72 kgPE / gCat, a titanium content of 0.38 ppm, a magnesium content of 1.2 ppm, an aluminum content of 14.4 ppm, an ash content of 42 ppm, a tensile yield strength of 24.7 MPa, and a tensile breaking strength of 40.0 MPa.

[0136] Example 5

[0137] It is basically the same as Example 1, but with the following changes:

[0138] The polyethylene main catalyst is a CMU catalyst, supported by anhydrous magnesium chloride, with a titanium content of 4.20 wt%.

[0139] The co-catalyst and main catalyst were continuously fed at a molar ratio of 60:1. The polymerization temperature in each polymerization reactor was changed to 78℃, and the polymerization pressure was changed to 1.0 MPa.

[0140] The slurry was continuously discharged from the third polymerization reactor, filtered, centrifuged, and dried to obtain ultra-high molecular weight polyethylene powder with a viscosity-average molecular weight of 3.65 million g / mole and a bulk density of 0.40 g / cm³. The polymerization activity was 55 kgPE / gCat, the titanium content was 0.85 ppm, the magnesium content was 2.64 ppm, the aluminum content was 26.6 ppm, the ash content was 79 ppm, the tensile yield strength was 23.0 MPa, and the tensile breaking strength was 36.3 MPa.

[0141] Example 6

[0142] It is basically the same as Example 1, but with the following changes:

[0143] The polyethylene main catalyst used was the BCE-type Ziegler-Vita catalyst described in Example 1 of Chinese patent application ZL201010240378.0, with anhydrous magnesium chloride as the support and a titanium content of 9.5 wt%. The co-catalyst and main catalyst were continuously fed at a molar ratio of 75:1. The polymerization temperature in each polymerization reactor was changed to 72°C, and the polymerization pressure was changed to 2.2 MPa.

[0144] This yielded ultra-high molecular weight polyethylene powder with a viscosity-average molecular weight of 3.24 million g / mole and a bulk density of 0.45 g / cm³. The polymerization activity was 42 kgPE / gCat, the tensile yield strength was 23.3 MPa, and the tensile breaking strength was 35.2 MPa.

[0145] Example 7

[0146] It is basically the same as Example 6, but with the following changes:

[0147] The polymerization temperature in each polymerization reactor was changed to 88℃, thereby obtaining ultra-high molecular weight polyethylene powder with a viscosity-average molecular weight of 1.76 million g / mole and a bulk density of 0.42 g / cm3. The polymerization activity was 39 kgPE / gCat, the tensile yield strength was 23.1 MPa, and the tensile breaking strength was 34.3 MPa.

[0148] Example 8

[0149] It is basically the same as Example 6, but with the following changes:

[0150] The product is produced by polymerization in the presence of the comonomer 1-butene, with a 1-butene volume concentration of 2% in each polymerization reactor.

[0151] This yielded ultra-high molecular weight polyethylene powder with a viscosity-average molecular weight of 1.55 million g / mole and a bulk density of 0.39 g / cm³. The polymerization activity was 44 kgPE / gCat, the comonomer mole insertion rate was 0.68%, the tensile yield strength was 23.2 MPa, and the tensile breaking strength was 35.3 MPa.

[0152] Example 9

[0153] It is basically the same as Example 1, but with the following changes:

[0154] The polyethylene main catalyst is the supported metallocene catalyst described in Example 1 of Chinese Patent 201010521674.8, with a silica support and an active titanium content of 0.62 wt%. The co-catalyst is changed to triisobutylaluminum. The co-catalyst and the main catalyst are continuously fed at a molar ratio of 75:1. The polymerization temperature of each polymerization reactor is changed to 72°C, and the polymerization pressure is changed to 2.4 MPa.

[0155] This yielded ultra-high molecular weight polyethylene powder with a viscosity-average molecular weight of 3.24 million g / mole and a bulk density of 0.43 g / cm³. The polymerization activity was 35 kgPE / gCat, with a titanium content of 1.65 ppm, a magnesium content of 3.28 ppm, an aluminum content of 24 ppm, an ash content of 105 ppm, a tensile yield strength of 24.4 MPa, and a tensile breaking strength of 40.4 MPa.

[0156] Example 10

[0157] It is basically the same as Example 1, but with the following changes:

[0158] The polymerization solvent was changed to a mixed alkane solvent consisting of n-pentane and isopentane in a 1:1 molar ratio, with a saturated vapor pressure of 66.6 kPa at 20°C. The formulations of the main catalyst and co-catalyst were changed to use the same solvents as the polymerization solvent.

[0159] This yielded ultra-high molecular weight polyethylene powder with a viscosity-average molecular weight of 4.85 million g / mole and a bulk density of 0.45 g / cm³. The polymerization activity was 63 kgPE / gCat, with a titanium content of 0.72 ppm, a magnesium content of 1.64 ppm, an aluminum content of 21.5 ppm, an ash content of 61 ppm, a tensile yield strength of 24.5 MPa, and a tensile breaking strength of 38.7 MPa.

[0160] Example 11

[0161] It is basically the same as Example 1, but with the following changes:

[0162] The polymerization solvent was changed to a mixed alkane solvent composed of n-pentane, isopentane, and cyclopentane in a 1:1:1 molar ratio, with a saturated vapor pressure of 55.93 kPa at 20°C. The formulations of the main catalyst and co-catalyst were changed to the same solvents as the polymerization solvent.

[0163] This yielded ultra-high molecular weight polyethylene powder with a viscosity-average molecular weight of 5.05 million g / mole and a bulk density of 0.45 g / cm³. The polymerization activity was 66 kgPE / gCat, with a titanium content of 0.70 ppm, a magnesium content of 1.61 ppm, an aluminum content of 20.6 ppm, an ash content of 52 ppm, a tensile yield strength of 24.7 MPa, and a tensile breaking strength of 38.5 MPa.

[0164] Example 12

[0165] It is basically the same as Example 1, but with the following changes:

[0166] The polymerization solvent was changed to a mixed alkane solvent composed of n-pentane, isopentane, cyclopentane, and neopentane in a molar ratio of 6:3:1:3, with a saturated vapor pressure of 80.27 kPa at 20°C. The formulations of the main catalyst and co-catalyst were changed to the same solvents as the polymerization solvent.

[0167] This yielded ultra-high molecular weight polyethylene powder with a viscosity-average molecular weight of 3.25 million g / mole and a bulk density of 0.42 g / cm³. The polymerization activity was 64 kgPE / gCat, with a titanium content of 0.72 ppm, a magnesium content of 1.85 ppm, an aluminum content of 21.4 ppm, an ash content of 61 ppm, a tensile yield strength of 25.8 MPa, and a tensile breaking strength of 39.2 MPa.

[0168] Comparative Example 1

[0169] It is basically the same as Example 1, but with the following changes:

[0170] Ultra-high molecular weight polyethylene was continuously produced using only the first polymerization reactor, with the slurry concentration controlled at 330 g polymer / L polymerization solvent and the average residence time of polymerization being 6 h.

[0171] This yields ultra-high molecular weight polyethylene powder with a viscosity-average molecular weight of 2.4 million g / mole, a bulk density of 0.33 g / cm³, a polymerization activity of 42 kgPE / gCat, a titanium content of 1.37 ppm, a magnesium content of 5.82 ppm, an aluminum content of 37.4 ppm, an ash content of 212 ppm, a tensile yield strength of 20 MPa, and a tensile breaking strength of 32 MPa.

[0172] Comparative Example 2

[0173] It is basically the same as Example 2, but with the following changes:

[0174] Ultra-high molecular weight polyethylene was continuously produced using only the first polymerization reactor, with the slurry concentration controlled at 330 g polymer / L polymerization solvent and the average residence time of polymerization being 6 h.

[0175] This yields ultra-high molecular weight polyethylene powder with a viscosity-average molecular weight of 3.15 million g / mole, a bulk density of 0.34 g / cm³, a polymerization activity of 34 kgPE / gCat, a titanium content of 2.51 ppm, a magnesium content of 7.37 ppm, an aluminum content of 41.7 ppm, an ash content of 245 ppm, a tensile yield strength of 20 MPa, and a tensile breaking strength of 31 MPa.

[0176] Comparative Example 3

[0177] It is basically the same as Example 1, but with the following changes:

[0178] Ethylene is introduced into the first polymerization reactor to achieve a polymerization pressure of 2.2 MPa. A mixture of ethylene and nitrogen is introduced into the second and third polymerization reactors, ensuring that the volume ratio of ethylene in the gas phase of the reactors is 50%. Furthermore, the polymerization temperature in the first polymerization reactor is 65°C, and the temperatures in the second and third polymerization reactors are 75°C.

[0179] Ultra-high molecular weight polyethylene powder was obtained, with a viscosity-average molecular weight of 4.05 million g / mole, a bulk density of 0.39 g / cm3, a polymerization activity of 31 kgPE / gCat, a titanium content of 3.65 ppm, a magnesium content of 9.57 ppm, an aluminum content of 42.7 ppm, an ash content of 283 ppm, a tensile yield strength of 19.5 MPa, and a tensile breaking strength of 33 MPa.

[0180] As can be seen from the implementation data of Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, the continuous production of ultra-high molecular weight polyethylene from ethylene slurry using the tandem cascade polymerization method provided by the present invention has high polymerization activity, bulk density and viscosity-average molecular weight, and low titanium, magnesium, aluminum elements and ash content.

[0181] In addition, since the polymerization reaction was carried out in a single reactor in Comparative Examples 1 and 2, ethylene backmixing occurred, which resulted in some catalyst activity not being released completely and uniformly, and its polymerization activity was lower than that in Examples 1 and 2. The viscosity-average molecular weight and bulk density of the obtained polyethylene were lower than those of the polyethylene obtained in Examples 1 and 2. Furthermore, due to the incomplete reaction, the residual content of metal elements was high, and the ash content of the polyethylene was high.

[0182] While the specific embodiments of the present invention have been described in detail above, it should be noted that the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the scope of the claims in the appendix. Those skilled in the art can make appropriate modifications to these embodiments without departing from the technical concept and spirit of the present invention, and these modified embodiments are obviously also included within the scope of protection of the present invention.

[0183] none

Claims

1. A method for continuous production of ultra-high molecular weight polyethylene via slurry polymerization, characterized in that 2-6 ethylene slurry reactors connected in series are used as reactors, and a raw material containing ethylene and optional comonomers is continuously slurry polymerized under a hydrogen-free atmosphere, wherein... In the first polymerization reactor, a main catalyst and a co-catalyst, along with raw materials containing ethylene and optional comonomers, are continuously introduced. Subsequent polymerization reactors are then supplemented with raw materials containing ethylene and optional comonomers to ensure that the gas phase composition in each reactor deviates from that in the first reactor by no more than ±2%, the polymerization pressure in each reactor deviates from that in the first reactor by no more than ±2%, and the polymerization temperature deviates from that in the first reactor by no more than ±2%. The slurry in each reactor is discharged via overflow or actively controlled flow extraction and then enters the next reactor or a post-processing system. The polyethylene catalyst, used as the main catalyst, is selected from one or more of metallocene catalysts, non-metallocene catalysts, and Ziegler-Vita catalysts. The co-catalyst is selected from one or more of aluminoxanes, alkylaluminums, and haloalkylaluminums. An alkane solvent with a boiling point of 0-90℃ or a mixed alkane solvent with a saturated vapor pressure of 4-200 KPa at 20℃ is used as the polymerization solvent. The polymerization temperature in each reactor is 40-100℃, and the polymerization pressure is 0.2-4.0 kPa. MPa, the volume concentration of comonomer in each polymerization reactor is 0-5%, the slurry concentration in each reactor is 50-500 g polymer / L polymerization solvent, and the residence time in each polymerization reactor is 0.1-6 h.

2. The method for continuous production of ultra-high molecular weight polyethylene by slurry polymerization as described in claim 1, wherein, The polymerization solvent is an alkane solvent with a boiling point of 25-82℃ or a mixed alkane solvent with a saturated vapor pressure of 30-160 KPa at 20℃. The polymerization temperature in each reactor is 50-90℃, the polymerization pressure is 1.0-3.0 MPa, the volume concentration of comonomer in each polymerization reactor is 0-3%, the slurry concentration in each reactor is 100-400 g polymer / L polymerization solvent, and the residence time in each polymerization reactor is 0.5-4.0 h.

3. A method for continuous production of ultra-high molecular weight polyethylene by slurry polymerization as described in claim 1 or 2, wherein, Three reactors connected in series are used as reactors. The polymerization slurry overflows directly from the overflow port of the previous polymerization reactor into the next polymerization reactor. The polymerization slurry then optionally enters the post-treatment system from the last polymerization reactor via an intermediate slurry tank. The residence time ratio of each polymerization reactor is 1:0.2-1:0.1-1. Alternatively, four reactors connected in series are used as reactors. The polymerization slurry overflows directly from the overflow port of the previous polymerization reactor into the next polymerization reactor. The polymerization slurry then optionally enters the post-treatment system from the last polymerization reactor via an intermediate slurry tank. The residence time ratio of each polymerization reactor is 1:0.2-1:0.1-1:0.1-1.

4. The method for continuous production of ultra-high molecular weight polyethylene by slurry polymerization as described in claim 3, wherein, When three reactors connected in series are used as reactors, the residence time ratio is 1:0.4-0.8:0.2-0.6, and the intermediate slurry tank into which the polymerization slurry enters from the last polymerization reactor is a jacketed heated stirred tank. When four reactors connected in series are used as reactors, the residence time ratio is 1:0.4-0.8:0.2-0.6:0.1-0.4, and the intermediate slurry tank into which the polymerization slurry enters from the last polymerization reactor is a jacketed heated stirred tank.

5. A method for continuous production of ultra-high molecular weight polyethylene by slurry polymerization as described in claim 1 or 2, wherein, The polymerization solvent is selected from n-pentane, isopentane, neopentane, cyclopentane, n-hexane, cyclohexane, or a mixture of at least two of them.

6. A method for continuous production of ultra-high molecular weight polyethylene by slurry polymerization as described in claim 1 or 2, wherein, The comonomer is selected from at least one of the C3-C10 α-olefins.

7. A method for continuous production of ultra-high molecular weight polyethylene by slurry polymerization as described in claim 1 or 2, wherein, The polyethylene catalyst used as the main catalyst is selected from one or more of the following: supported metallocene catalysts, non-metallocene catalysts, and Ziegler-Vita catalysts. The support is selected from one or more of the following: silicone support, layered porous support, organic polymer support, magnesium compound support, and oxide support.

8. A method for continuous production of ultra-high molecular weight polyethylene by slurry polymerization as described in claim 1 or 2, wherein, The polyethylene catalyst used as the main catalyst is selected from one of supported non-metallocene catalysts and Ziegler-Vita catalysts, and the support is selected from at least one of porous silica support and magnesium compound support.

9. A method for continuous production of ultra-high molecular weight polyethylene by slurry polymerization as described in claim 1 or 2, wherein, The aluminum oxane in the co-catalyst is selected from one or more of methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, and n-butylaluminoxane; the alkylaluminum in the co-catalyst is selected from one or more of trimethylaluminum, triethylaluminum, tripropylaluminum, triisobutylaluminum, trin-butylaluminum, triisopentylaluminum, trin-pentylaluminum, trihexylaluminum, triisohexylaluminum, diethylmethylaluminum, and dimethylethylaluminum; and the haloalkylaluminum in the co-catalyst is selected from one or more of dichlorodimethylaluminum, dichloromethylaluminum, dichlorodiethylaluminum, dichloroethylaluminum, dichlorodipropylaluminum, dichloropropylaluminum, dichlorodi-n-butylaluminum, dichlorodi-n-butylaluminum, dichlorodiisobutylaluminum, dichlorodi-n-hexylaluminum, dichlorodi-n-hexylaluminum, dichlorodiisohexylaluminum, and dichloroisohexylaluminum.

10. A method for continuous production of ultra-high molecular weight polyethylene by slurry polymerization as described in claim 1 or 2, wherein, The concentration of the main catalyst in the first polymerization reactor is 0.001-0.100 mmol / L of polymerization solvent, and the molar ratio of the co-catalyst to the main catalyst is 20-200:

1.

11. A method for continuous production of ultra-high molecular weight polyethylene by slurry polymerization as described in claim 1 or 2, wherein, The polymerization solvent is an alkane solvent with a boiling point of 25-82℃ or a mixed alkane solvent with a saturated vapor pressure of 30-160 KPa at 20℃. The polymerization temperature in each reactor is 50-90℃, the polymerization pressure is 1.0-3.0 MPa, the volume concentration of comonomer in each polymerization reactor is 0-3%, the slurry concentration in each reactor is 100-400 g polymer / L polymerization solvent, and the residence time in each polymerization reactor is 0.5-4.0 h.

12. A method for continuous production of ultra-high molecular weight polyethylene by slurry polymerization as described in claim 1 or 2, wherein, The polymerization solvent is selected from one of the following: n-pentane, isopentane, neopentane, cyclopentane, a combination of n-pentane and isopentane, a combination of isopentane and neopentane, a combination of n-pentane and cyclopentane, a combination of n-pentane and neopentane, a combination of isopentane and cyclopentane, a combination of neopentane and cyclopentane, a combination of n-hexane and n-pentane, and a combination of n-pentane-isopentane-cyclopentane.

13. A method for continuous production of ultra-high molecular weight polyethylene by slurry polymerization as described in claim 1 or 2, wherein, The comonomer is selected from at least one of propylene, 1-butene, 1-pentene, 1-hexene, and 1-octene; and the concentration of the main catalyst in the first polymerization reactor is 0.005-0.050 mmol / L of polymerization solvent, and the molar ratio of the cocatalyst to the main catalyst is 30-100:

1.

14. A method for continuously producing ultra-high molecular weight polyethylene by slurry polymerization as described in any one of claims 1-13, characterized in that the viscosity-average molecular weight is 1.5-8 million g / mole, the metal element content is 0-40 ppm, the tensile yield strength is greater than 21 MPa, and the tensile breaking strength is greater than 33 MPa.

15. The ultra-high molecular weight polyethylene as claimed in claim 14, wherein, Bulk density 0.30-0.55 g / cm3, comonomer mole insertion rate 0-2.0%, ash content less than 200 ppm.

16. The ultra-high molecular weight polyethylene as claimed in claim 14 or 15, wherein, The titanium content is 0-3 ppm, the magnesium content is 0-10 ppm, and the aluminum content is 0-30 ppm.

17. The ultra-high molecular weight polyethylene as claimed in claim 14, wherein, The comonomer is at least one selected from propylene, 1-butene, 1-pentene, 1-hexene, and 1-octene.