A single-site catalyst system, method of preparation and use

Abstract

The application discloses a preparation method of a single-center catalyst system and application thereof, and the preparation method comprises the following steps: (1) performing vacuum distillation on a modified methylaluminoxane solution, separating out a solvent and aluminum alkyl to obtain a solid product; (2) dissolving the solid product obtained in step (1) with a pentane solution to obtain a homogeneous solution with different aluminum contents; and (3) combining the homogeneous solution obtained in step (2) with a single-active-center catalyst to form a catalyst system. When the single-active-center catalyst system is used for preparing polyethylene wax, different solvents can be avoided from being introduced into a polymerization system, a process flow of the polyethylene wax is simplified, and energy consumption for solvent separation is reduced; reduction of active aluminum helps to improve polymerization activity, the obtained polyethylene wax has lower metal content and narrower molecular weight distribution, the devolatilization efficiency of the polyethylene wax is improved, and the obtained polymer has a VOCs content lower than 20 ppm.

Description

Technical Field

[0001] This invention relates to the field of catalysis technology, specifically to a single-center catalytic system, its preparation method, and its application. Background Technology

[0002] Polyethylene wax refers to polyethylene with a weight-average molecular weight of 500-10000 g / mol, and is a representative synthetic wax produced from ethylene. Polyethylene wax has good chemical stability, is colorless, odorless, and non-toxic. Its chemical composition, saponification value, electrical properties, and density are similar to paraffin wax. It is completely insoluble in water and all aqueous solutions, and is widely used in ink manufacturing as polishing wax, high-grade floor paint, high-end car polishing wax, rubber release agent and anti-aging agent; textile softener and lubricant; gloss lubricant and release agent for polyvinyl chloride products; and as a cable filler, diesel flow modifier, cable masterbatch additive, cardboard coating, glass bottle coating, hot melt adhesive, and special craft candles, etc.

[0003] The molecular weight of polyethylene wax determines its application, while its molecular weight distribution affects its performance. Taking its application in color masterbatches as an example, molecular weight distribution has a significant impact on the performance of polyethylene wax. When using waxes with similar molecular weights but different molecular weight distributions as dispersants in carbon black masterbatches, to achieve the same tinting strength, the dosage of 400P wax (MWD = 2.74) is 3%, while that of F4 wax (MWD = 15.97) requires more than 10%. This indicates that waxes with a narrower molecular weight distribution have a higher dispersion rate compared to waxes with a wider molecular weight distribution.

[0004] Polyethylene wax can be obtained through three methods: first, as a byproduct of slurry polyethylene production; second, as a product of polyethylene pyrolysis or degradation; and third, as a low molecular weight polyethylene obtained by ethylene polymerization.

[0005] Polyethylene wax production via polymerization generally employs single-center metallocene or non-metallocene catalysts, and the properties of the product vary depending on the polymerization process. CN200780043554.8 discloses a method for preparing polyethylene wax by ethylene polymerization in the presence of a Ziegler-Natta catalyst system composed of titanium tetrachloride and dialkyl aluminum halides. The polymerization is carried out under essentially solvent-free conditions, and is used to prepare synthetic polyethylene wax with high crystallinity and low viscosity. EP0367597A1 discloses a metallocene gas-phase polymerization method supported on silica gel for preparing polyethylene wax with a narrow molecular weight distribution (less than 5). WO / 2013 / 027958 discloses a method for preparing polyethylene wax using a metallocene catalyst and a dual-loop reactor. According to the invention, a highly active polyethylene wax with a uniform and narrow molecular weight distribution can be polymerized. WO / 2018 / 083290 relates to a method for preparing polyethylene wax, the method comprising the steps of providing a catalyst solution, wherein the catalyst solution comprises at least one activating compound, an alkylaluminoxane, and a methyl metallocene complex, wherein the molar ratio of the activating compound to aluminum contained in the alkylaluminoxane is from 0.0005 to 0.20; and polymerizing ethylene by contacting the ethylene and the catalyst solution.

[0006] Modified methylaluminoxane (MMAO) is a co-catalyst for metallocene and other catalysts in the polyolefin industry, playing a crucial role in the development of core catalyst technologies, the improvement of polyolefin performance, the production of α-olefins, and even the development of high-end lubricating materials.

[0007] CN115124560A discloses a method for continuously preparing modified methylaluminoxanes through multi-step hydrolysis using a combination of microreactors. This method can achieve effective micro-dispersion of water in an inert solvent, thereby realizing the mixed hydrolysis of various alkylaluminoxanes. The entire reaction process is efficient, safe, and controllable, with high product yield and high activity.

[0008] CN 118126074 A provides a method for preparing methylaluminoxane and modified methylaluminoxane, comprising the following steps: Step 1, reacting aluminum carboxylate with trimethylaluminum in a solvent at a certain temperature to prepare a methylaluminoxane precursor; Step 2, pyrolyzing the methylaluminoxane precursor obtained in Step 1 at a certain temperature to obtain methylaluminoxane; Step 3, mixing the methylaluminoxane obtained in Step 2 with long-chain alkylaluminum, heating, and then diluting with a solvent to a certain concentration to obtain a methylcyclohexane and n-heptane solution of modified methylaluminoxane.

[0009] In summary, existing catalyst systems still suffer from low polymerization activity, high metal content, high VOC content in the prepared polyethylene wax, and off-odors during processing. Furthermore, the MMAO solutions disclosed in existing patents use toluene, methylcyclohexane, or n-heptane solutions as solvents. When used as co-catalysts in the production of polyethylene wax, this increases the difficulty of separating and recycling the polymerization solvent, thereby increasing production costs. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention provides a method for preparing a single-center catalytic system and its application.

[0011] The technical solution adopted in this invention is:

[0012] This invention provides a method for preparing a single-center catalytic system, comprising the following steps:

[0013] (1) The modified methylaluminoxane solution was subjected to vacuum distillation to separate the solvent and alkylaluminum, and a solid product was obtained.

[0014] (2) Dissolve the solid product obtained in step (1) with pentane solution to obtain homogeneous solutions with different aluminum contents;

[0015] (3) The homogeneous solution obtained in step (2) is combined with a single active site catalyst to form a catalyst system.

[0016] Solvents in commercially available MMAO methylcyclohexane or heptane solutions are separated by vacuum distillation. The content of free alkyl aluminum in MMAO is controlled by adjusting the vacuum level and distillation temperature, thereby controlling the total aluminum content of MMAO. Pentane is then added to prepare a pentane solution of MMAO. This avoids introducing different solvents into the polymerization system, which would increase the separation energy consumption and waste liquid volume of the solvent recovery unit and increase the residual amount of high-carbon alkanes in the polymer. Furthermore, this method can reduce the active aluminum in the MMAO solution, which helps to improve the polymerization activity, resulting in polyethylene wax with lower metal content and a narrower molecular weight distribution.

[0017] In preferred step (1), the pressure of vacuum distillation is 0.1-50 kPa and the distillation temperature is 50-150 °C.

[0018] In preferred step (1), the modified methylaluminoxane is at least one of methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, and n-butylaluminoxane.

[0019] In preferred step (2), the total aluminum content of the homogeneous solution is 3-10% wt, the active aluminum content is 0-20% of the total aluminum content, and the solution density of the homogeneous solution is 0.60-0.70 g / cm³. 3More preferably, the total aluminum content of the homogeneous solution is 4-8% wt, the active aluminum accounts for 0-10% of the total aluminum content, and the solution density of the homogeneous solution is 0.62-0.66 g / cm³. 3 .

[0020] In preferred step (2), the pentane solution is at least one of n-pentane, isopentane, neopentane or cyclopentane.

[0021] In preferred step (3), the single active site catalyst is a non-metallocene catalyst or / and a metallocene catalyst.

[0022] This invention provides a catalyst system obtained using the above preparation method.

[0023] This invention provides a method for using the above-mentioned catalyst system in the preparation of polyethylene wax. The method uses a single active site catalyst as the main catalyst, the homogeneous solution obtained in step (2) as the co-catalyst, and an alkane solvent with a boiling point of 0-90℃ or a pentane solvent with a saturated vapor pressure of 4-200KPa at 20℃ as the polymerization solvent. Under polymerization conditions of polymerization temperature of 40-150℃ and polymerization pressure of 1.0-4.0MPa, ethylene and comonomers are subjected to slurry polymerization reaction in a reactor to obtain polyethylene wax.

[0024] The preferred polymerization solvent is at least one of n-pentane, isopentane, neopentane, or cyclopentane.

[0025] Using the above method, polyethylene waxes with narrower molecular weight distribution and adjustable true density, melting point, and crystallinity can be prepared.

[0026] The beneficial effects of this invention are:

[0027] This invention uses a pentane solution of MMAO as a co-catalyst, which avoids introducing different solvents into the polymerization system, thereby preventing increased separation energy consumption and waste volume in the solvent recovery unit and increasing the residual amount of high-carbon alkanes in the polymer. The reduction in active aluminum helps improve polymerization activity, resulting in polyethylene wax with lower metal content and a narrower molecular weight distribution. This is significant for simplifying the polyethylene wax process, reducing solvent separation energy consumption, and improving product quality. Furthermore, it can improve the devolatilization efficiency of polyethylene wax, resulting in a polymer with VOC content below 20 ppm. Detailed Implementation

[0028] 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.

[0029] 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.

[0030] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this specification are based on weight, unless being based on weight would not be in accordance with the common 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 claims 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] In this invention, ethylene copolymer wax is also called copolymer polyethylene wax or polyethylene wax.

[0034] This invention provides a method for preparing a modified methylaluminoxane (MMAO) solution. The method involves separating the solvent from a commercially available MMAO solution in methylcyclohexane or heptane by vacuum distillation. The content of free alkyl aluminum in the MMAO is controlled by adjusting the vacuum level and distillation temperature, thereby controlling the total aluminum content of the MMAO. Pentane is then added to prepare a pentane solution of the MMAO. The total aluminum content in the MMAO solution is 6-8% wt, with active aluminum accounting for 0-5% of the total aluminum content. The density of the MMAO solution is 0.62-0.66 g / cm³. 3 .

[0035] The present invention also provides a method for preparing polyethylene wax with a narrow molecular weight distribution, using a homogeneous non-metallocene catalyst and / or a metallocene catalyst as the main catalyst, a pentane solution of the above-mentioned MMAO as the co-catalyst, and an alkane solvent with a boiling point of 0-90℃ or an alkane solvent with a saturated vapor pressure of 4-200 kPa at 20℃ as the polymerization solvent, preferably 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℃ as the polymerization solvent. The polymerization reaction is carried out at a polymerization temperature of 40-150℃, preferably 60-150℃, more preferably 100-140℃, and a polymerization pressure of 1.0-4.0 MPa under ethylene solution polymerization conditions to obtain polyethylene wax.

[0036] According to the present invention, the homogeneous non-metallocene catalyst used as the main catalyst can be prepared by the following method.

[0037] According to the present invention, the term "non-metallocene complex" is a single-center olefin polymerization catalyst, as opposed to a metallocene catalyst, which does not contain cyclopentadienyl groups or their derivatives such as cyclopentadienyl, fluorene, or indene rings in its structure, and is an organometallic compound that can exhibit olefin polymerization catalytic activity when combined with a co-catalyst (such as those described below). (Therefore, the non-metallocene complex is sometimes also referred to as a non-metallocene olefin polymerization complex.) The compound comprises a central metal atom and at least one polydentate ligand (preferably a tripentate or more dental ligands) coordinated to the central metal atom, and the term "non-metallocene ligand" refers to the aforementioned polydentate ligand.

[0038] According to the present invention, the non-metallocene complex is selected from compounds having the following chemical structural formula:

[0039] The non-metallocene complex is a compound represented by formula (I):

[0040]

[0041] In formula (I), groups R1, R2, R3, and R4 are each independently selected from hydrogen and C1-6 straight-chain or branched hydrocarbon groups, preferably each independently selected from hydrogen and C1-6 straight-chain or branched alkyl groups, and more preferably each independently selected from hydrogen, methyl, ethyl, propyl, butyl, isobutyl, sec-butyl, and tert-butyl.

[0042] R6, R7, R8, and R9 are each independently selected from hydrogen and C1-6 straight-chain or branched hydrocarbon groups, preferably each independently selected from hydrogen and C1-6 straight-chain or branched alkyl groups, and more preferably each independently selected from hydrogen, methyl, ethyl, propyl, butyl, isobutyl, sec-butyl, and tert-butyl.

[0043] R5 represents hydrogen or a C1-12 straight-chain or branched hydrocarbon group, preferably hydrogen, C1-6 straight-chain or branched alkyl or C6-10 aryl, more preferably hydrogen, C1-3 straight-chain or branched alkyl or phenyl, and even more preferably hydrogen, methyl, ethyl, n-propyl or isopropyl.

[0044] R10 represents hydrogen or a C1-6 straight-chain or branched hydrocarbon group, preferably hydrogen or a C1-6 straight-chain or branched alkyl group, more preferably hydrogen, methyl and ethyl, and even more preferably hydrogen;

[0045] Group Y is O or S, preferably O; group A is S or O, preferably S; M is selected from Group IVB metal elements, preferably titanium, zirconium and hafnium, more preferably titanium; group X is selected from fluorine, chlorine, bromine and iodine, preferably chlorine or bromine; Indicates a single or double bond; ------ represents a coordinate bond; n represents the valence state of atom M, such as 1, 2, 3, 4, or 5.

[0046] Wherein, the non-metallocene complex shown in formula (I) is selected from at least one of 3-tert-butylsalicylene-2-methylthioaniline titanium trichloride, salicylene-2-methylthioaniline titanium trichloride, salicylene-2-phenylthioaniline titanium trichloride, 3,5-di-tert-butylsalicylene-2-propylthioaniline titanium trichloride, 3-tert-butylsalicylene-2-propylthioaniline titanium trichloride, 3,5-di-tert-butylsalicylene-2-mercaptoaniline titanium trichloride, salicylene-2-mercaptoaniline titanium trichloride, salicylene-2-methylthioaniline titanium trichloride, salicylene-2-propylthioaniline titanium trichloride, 3,5-di-tert-butylsalicylene-2-methylthioaniline titanium trichloride, 3,5-di-tert-butylsalicylene-2-methylthioaniline titanium trichloride, and 3,5-di-tert-butylsalicylene-2-propylthioaniline titanium trichloride.

[0047] In this invention, the metallocene compound is a compound represented by formula (II) or formula (III).

[0048]

[0049] In formula (II), R1 is a C1-C8 straight-chain or branched alkyl, C13-C21 diarylalkyl, C1-C8 alkylsilyl, or diarylsilyl, preferably a C1-C4 straight-chain or branched alkyl, C13-C17 diarylalkyl, C1-C4 alkylsilyl, or C12-C16 diarylsilyl, more preferably methyl, ethyl, isopropyl, diphenylmethyl, dimethylsilyl, or diphenylsilyl; cyclopentadiene-R2 and cyclopentadiene-R3 are each independently selected from unsubstituted or substituted cyclopentadienyl, fluorenyl, or indenyl.

[0050]

[0051] In formula (III), cyclopentadiene-R4 and cyclopentadiene-R5 are each independently selected from cyclopentadienyl, fluorenyl or indene, and R6 and R7 are each independently selected from hydrogen, C1-C8 straight-chain or branched alkyl, preferably hydrogen, C1-C4 straight-chain or branched alkyl.

[0052] It is known to those skilled in the art that all the foregoing method steps are preferably carried out under substantially anhydrous and oxygen-free conditions. "Substantially anhydrous and oxygen-free" here means that the water and oxygen content in the system is consistently less than 100 ppm. Furthermore, the metallocene catalyst of the present invention typically needs to be stored under sealed conditions in the presence of a slightly positive pressure inert gas (such as nitrogen, argon, helium, etc.) for later use.

[0053] According to the present invention, MMAO pentane solution is used as a cocatalyst, and the modified methylaluminoxane is at least one selected from methylaluminoxane, ethylaluminoxane, isobutylaluminoxane and n-butylaluminoxane; methylaluminoxane and isobutylaluminoxane are further preferred, and methylaluminoxane is most preferred.

[0054] Examples of aluminum oxanes include linear aluminum oxanes represented by the following general formula (IV-1) and cyclic aluminum oxanes represented by the following general formula (IV-2).

[0055]

[0056] In formulas (IV-1) and (Ⅳ-2), the groups R are the same or different from each other, preferably the same, and are each independently selected from C1-C8 alkyl groups, preferably methyl, ethyl and isobutyl, with methyl being the most preferred; n is any integer in the range of 1-50, preferably any integer in the range of 10-30.

[0057] These aluminum oxanes can be used alone or in combination in any proportion.

[0058] According to the present invention, in the solution polymerization preparation method of polyethylene wax with narrow molecular weight distribution, the polymerization solvent is selected from alkane solvents with boiling points of 0-90℃ or mixed alkane solvents with saturated vapor pressure of 4-200KPa at 20℃.

[0059] Among them, the preferred alkane solvent with a boiling point of 25-82°C is alkane solvent with a boiling point of 0-90°C, such as 2,2-dimethylpropane (also known as neopentane, boiling point 9.5°C), 2-methylbutane (also known as isopentane, boiling point 27.83°C), n-pentane (boiling point 36.1°C), and cyclopentane (boiling point 49.26°C).

[0060] In the preparation method of polyethylene wax of the present invention, ethylene is polymerized at a polymerization temperature of 80-150°C, preferably 90-150°C, and more preferably 100-140°C, under ethylene solution polymerization conditions. Specifically, if ethylene solution polymerization is carried out at a higher polymerization temperature, a solvent with a higher boiling point and a lower polymerization pressure can be selected; conversely, if ethylene solution polymerization is carried out at a lower polymerization temperature, a solvent with a lower boiling point and a higher polymerization pressure can be selected. It is known that, under ethylene solution polymerization conditions, with similar and comparable conditions such as polymerization pressure, main catalyst, co-catalyst, and solvent, within the polymerization temperature range described in the present invention, as the polymerization temperature and hydrogen-ethylene ratio increase, the weight-average molecular weight of the resulting polyethylene wax decreases accordingly. Therefore, according to the present invention, the weight-average molecular weight of polyethylene wax can be controlled by the polymerization temperature of ethylene solution polymerization and different hydrogen-ethylene ratios.

[0061] 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, as provided by this invention, provides opportunities and choices for preparing polyethylene waxes with different weight-average molecular weights via ethylene solution 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 pressures at 20℃ (such as n-pentane and neopentane, isopentane and neopentane) facilitates heat removal from the ethylene solution polymerization reaction, allowing it to be carried out at higher polymerization pressures and lower polymerization temperatures. Conversely, using alkane solvents with higher boiling points (such as n-hexane, cyclohexane, or 3-methylpentane) or mixed alkane solvents with lower saturated vapor pressures at 20℃ (such as n-hexane and cyclohexane, n-hexane and 3-methylpentane, cyclohexane and 2-methylpentane) allows for effective heat removal from the polymerization reaction, enabling it to be carried out at lower polymerization pressures and higher polymerization temperatures.

[0062] In the polyethylene wax polymerization preparation method of this invention, the ethylene solution polymerization reactor is not limited to any type, as long as it can achieve mutual contact between ethylene and the main catalyst and co-catalyst in the solvent within the polymerization pressure and temperature range described in this invention, and can effectively avoid material adhesion and aggregation. The reactor is a batch-type ethylene slurry stirred tank reactor, and its stirring rate is not particularly limited, as long as it can ensure that the solution 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.

[0063] In the polymerization preparation method of polyethylene wax of the present invention, there is no particular limitation on the polymerization reaction time. Within a certain polymerization time, as long as the catalytic activity of ethylene solution polymerization is higher than 10,000 g ethylene wax / g main catalyst, based on the active metal content in the main catalyst as described in the present invention, the polymerization activity is higher than 10,000 g ethylene wax / g main catalyst. According to the present invention, the homogeneous single-center catalyst as the main catalyst and the aluminoxane as the co-catalyst can be added to the polymerization reaction system in the following ways: first the main catalyst and then the co-catalyst, or first the co-catalyst and then the main catalyst, or the two can be mixed together and then added together, or they can be added separately and simultaneously. When the main catalyst and the co-catalyst are added separately, they can be added sequentially in the same feeding pipeline or sequentially in multiple feeding pipelines. When the two are added separately and simultaneously, multiple feeding pipelines should be selected.

[0064] Examples 1-6

[0065] (1) Add 1L of commercially available MMAO solution (AkzoNobel MMAO-7A) to a flask in a glove box, set different temperatures and negative pressures, and separate the solvent and alkyl aluminum by vacuum distillation to obtain a solid product;

[0066] (2) Add pentane solution to dissolve the obtained solid to obtain a homogeneous solution; that is, MMAO pentane solution.

[0067] (3) Take a portion and test the total aluminum content and effective aluminum content according to the following method. The test results are shown in Table 1.

[0068] Methods for testing Al content:

[0069] The total aluminum content in the products of TMA and TIBA hydrolysis was determined by EDTA back titration. The specific procedure is as follows: A certain amount of product solution was accurately weighed and transferred to a Schlenk flask under a nitrogen atmosphere. Water was then slowly added dropwise to ensure complete hydrolysis. Simultaneously, the volume of methane produced was measured using a gas volume flow integrator connected to the Schlenk flask outlet or by water displacement, and the molar number of methane was calculated using the ideal gas law. After the reaction, the solid was dissolved in a 10% v / v sulfuric acid solution and brought to volume in a volumetric flask. A certain volume of the solution was transferred, and its acidity was adjusted to pH 3.0. A certain amount of EDTA was added, and the solution was refluxed for 3 minutes. Subsequently, hexamethylenetetramine buffer solution (approximately 2 mg) was added to adjust the pH to 6. Finally, using xylenol orange as an indicator, the mixture was titrated with a 0.02M ZnSO4 aqueous solution. At the titration endpoint, the color changed from yellow to red. The Al content was calculated based on the amount of zinc consumed.

[0070] (4) Using the above-mentioned MMAO pentane solution as a cocatalyst, and 3,5-di-tert-butylsalicyl-2-mercaptoaniline titanium trichloride or diphenylmethylene (cyclopentadienyl) (9-fluorenyl)zirconium dichloride as the main catalyst, and n-pentane or neopentane as the polymerization solvent, under polymerization conditions of 40-150℃ and 1.0-4.0MPa, the following method was used to carry out solution polymerization of ethylene and comonomer to prepare polyethylene wax PEW1-6. The reaction conditions are shown in Table 1.

[0071] A. High-pressure reactor polymerization

[0072] After raising the stainless steel stirred polymerization reactors of 1L, 2L, 300L, 5L, and 10L to the set temperature, they were replaced three times with ethylene or propylene respectively. Solvent, co-catalyst, comonomer, and main catalyst were added in sequence, the temperature was raised, ethylene was introduced, and the total pressure was kept constant. After polymerization for a period of time, the polymer solution was released, dried, and the resulting product was weighed after drying.

[0073] B. Continuous solution polymerization

[0074] Solvent, main catalyst solution, cocatalyst solution, and comonomer solution are fed into the polymerization reactor from the bottom using metering pumps. Here, they contact ethylene and propylene to undergo polymerization. The materials in the polymerization reactor flow out from the top. A discharge control system is used to control the discharge to ensure continuous discharge and stable reaction in the polymerization reactor. The discharged material goes directly into a receiving tank. The entire process requires a closed system and nitrogen protection, and the purity of the raw materials is also relatively high.

[0075] (5) The number-average molecular weight, weight-average molecular weight, molecular weight distribution, metal content, VOCs content, film transmittance and pigment dispersion of polyethylene wax PEW1-6 were detected by the following methods. The results are shown in Table 2.

[0076] The copolymer content of polyethylene wax was determined using nuclear magnetic resonance (NMR). Specifically, the degree of branching of the sample was determined using a Bruker Avance 600M NMR spectrometer at 120°C. The copolymer sample was dissolved in deuterated o-dichlorobenzene to prepare a solution of approximately 20 wt%, and the solution was scanned 6000 times at 120°C to obtain the sample's... 13 C10 NMR spectrum.

[0077] The molecular weight and molecular weight distribution of polyethylene wax were determined according to GB / T 21864-2005 standard using a Polymer Laboratories PL-220 gel permeation chromatograph. 1,2,4-trichlorobenzene was used as the mobile phase, polystyrene was used as the standard, a differential detector was used, the flow rate was 1.0 mL / min, the measurement temperature was 150 ℃, and the sample concentration was 2.0 mg / mL.

[0078] Color Masterbatch Color Evaluation

[0079] HDPE5000S was used as the carrier resin, with 20% phthalocyanine blue pigment by mass, and 3% dispersant by mass in each phthalocyanine blue pigment masterbatch. The raw materials were formulated according to the recipe and then co-extruded using a twin-screw extruder to obtain blue masterbatch. The prepared blue masterbatch was then added to PE and injection molded to prepare samples and films. The pigment content in the samples and films was 0.4%.

[0080] Evaluation method for tinting strength of phthalocyanine blue pigment: Use a colorimeter to test the tinting strength and color performance of the color sample across the entire wavelength range, and record the transmittance.

[0081] Evaluation of the dispersibility of phthalocyanine blue pigment: The dispersion of the pigment in the matrix was studied using polarized light microscopy.

[0082] VOCs content was detected by gas chromatography: Based on the set parameters of the gas chromatograph, the solution to be tested was repeatedly drawn with a 10 μl micro-syringe to remove air bubbles, and then 0.1 μl of solution was injected into the gas chromatograph. After the components of the sample were fully presented in the chromatogram, the chromatographic peak areas of the pentane series solutions were recorded respectively, and the peak areas were plotted against the concentrations of the corresponding pentane standard solutions.

[0083] Inductively coupled plasma atomic emission spectrometry (ICP-AES) is used to detect metal content. The polymer sample solution is carried into the nebulization system by a carrier gas and then atomized. It enters the axial channel of the plasma in the form of an aerosol. In the high temperature and inert gas, it is fully evaporated, atomized, ionized and excited. The characteristic spectral lines of the contained elements emitted are sent to the spectrometer by the spectrometer system. The spectrometer performs qualitative and quantitative analysis based on the characteristic spectra of the elements.

[0084] Comparative Examples 1-2

[0085] Polymerization method of comparative example: Commercially available MMAO pentane solution (AkzoNobel MMAO-7A, heptane solution and toluene solution) was used as a cocatalyst, 3,5-di-tert-butylsalicyl-2-mercaptoaniline titanium trichloride or diphenylmethylene (cyclopentadienyl) (9-fluorenyl)zirconia dichloride was used as the main catalyst, and n-pentane or neopentane was used as the polymerization solvent. Polymerization was carried out on slurry polymerization of ethylene and comonomers under polymerization conditions of 40-150℃ and 1.0-4.0 MPa, using the same method as in the example, to prepare polyethylene wax PEW7-8. The reaction conditions are shown in Table 1.

[0086] As can be seen from Table 2, the polyethylene wax prepared by this invention has low metal content, high polymer devolatilization efficiency, VOC content of less than 20 ppm, no odor during processing, and compared with existing patented technologies, this invention can obtain polyethylene wax with a narrower molecular weight distribution, thereby further improving the application effect of polyethylene wax.

[0087] Finally, it should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a single-center catalytic system, characterized in that, Includes the following steps: (1) The modified methylaluminoxane solution was subjected to vacuum distillation to separate the solvent and alkylaluminum, and a solid product was obtained. (2) Dissolve the solid product obtained in step (1) with pentane solution to obtain homogeneous solutions with different aluminum contents; (3) The homogeneous solution obtained in step (2) is combined with a single active site catalyst to form a catalyst system.

2. The method for preparing a single-center catalytic system according to claim 1, characterized in that, In step (1), the pressure of vacuum distillation is 0.1-50 kPa and the distillation temperature is 50-150℃.

3. The method for preparing a single-center catalytic system according to claim 1, characterized in that, In step (1), the modified methylaluminoxane contains at least one of methylaluminoxane, ethylaluminoxane, isobutylaluminoxane and n-butylaluminoxane.

4. The method for preparing a single-center catalytic system according to claim 1, characterized in that, In step (2), the total aluminum content of the homogeneous solution is 3-10% wt, the active aluminum accounts for 0-20% of the total aluminum content, and the solution density of the homogeneous solution is 0.60-0.70 g / cm³. 3 .

5. The method for preparing a single-center catalytic system according to claim 4, characterized in that, The total aluminum content of the homogeneous solution is 4-8% wt, with active aluminum accounting for 0-10% of the total aluminum content. The solution density of the homogeneous solution is 0.62-0.66 g / cm³. 3 .

6. The method for preparing a single-center catalytic system according to claim 1, characterized in that, In step (2), the pentane solution is at least one of n-pentane, isopentane, neopentane or cyclopentane.

7. The method for preparing a single-center catalytic system according to claim 1, characterized in that, In step (3), the single active site catalyst is a non-metallocene catalyst and / or a metallocene catalyst.

8. The single-center catalytic system obtained by the preparation method according to any one of claims 1-7.

9. The application of the single-center catalytic system according to claim 8 in the preparation of polyethylene wax, characterized in that, Using a single-active-center catalyst as the main catalyst, the homogeneous solution obtained in step (2) as the co-catalyst, and alkane solvents with boiling points of 0-90℃ or pentane solvents with saturated vapor pressure of 4-200KPa at 20℃ as the polymerization solvents, ethylene and comonomers were subjected to slurry polymerization in a reactor under polymerization conditions of 40-150℃ and 1.0-4.0MPa to obtain polyethylene wax.

10. The application according to claim 9, characterized in that, Pentane is at least one of n-pentane, isopentane, neopentane, or cyclopentane.

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