CN113087999B - Method for efficiently preparing high-performance polyolefin blend by single-reactor two-stage process - Google Patents
Method for efficiently preparing high-performance polyolefin blend by single-reactor two-stage process Download PDFInfo
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- 230000000694 effects Effects 0.000 claims abstract description 26
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 claims abstract description 8
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- 239000000178 monomer Substances 0.000 claims description 21
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- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 2
- 150000001335 aliphatic alkanes Chemical class 0.000 claims description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 2
- 229910052804 chromium Inorganic materials 0.000 claims description 2
- 239000011651 chromium Substances 0.000 claims description 2
- YNLAOSYQHBDIKW-UHFFFAOYSA-M diethylaluminium chloride Chemical compound CC[Al](Cl)CC YNLAOSYQHBDIKW-UHFFFAOYSA-M 0.000 claims description 2
- UAIZDWNSWGTKFZ-UHFFFAOYSA-L ethylaluminum(2+);dichloride Chemical compound CC[Al](Cl)Cl UAIZDWNSWGTKFZ-UHFFFAOYSA-L 0.000 claims description 2
- AHAREKHAZNPPMI-UHFFFAOYSA-N hexa-1,3-diene Chemical compound CCC=CC=C AHAREKHAZNPPMI-UHFFFAOYSA-N 0.000 claims description 2
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- 229910052760 oxygen Inorganic materials 0.000 claims description 2
- 230000000379 polymerizing effect Effects 0.000 claims description 2
- 125000000383 tetramethylene group Chemical group [H]C([H])([*:1])C([H])([H])C([H])([H])C([H])([H])[*:2] 0.000 claims description 2
- 229910052723 transition metal Inorganic materials 0.000 claims description 2
- 150000003624 transition metals Chemical class 0.000 claims description 2
- SQBBHCOIQXKPHL-UHFFFAOYSA-N tributylalumane Chemical compound CCCC[Al](CCCC)CCCC SQBBHCOIQXKPHL-UHFFFAOYSA-N 0.000 claims description 2
- ORYGRKHDLWYTKX-UHFFFAOYSA-N trihexylalumane Chemical compound CCCCCC[Al](CCCCCC)CCCCCC ORYGRKHDLWYTKX-UHFFFAOYSA-N 0.000 claims description 2
- MCULRUJILOGHCJ-UHFFFAOYSA-N triisobutylaluminium Chemical compound CC(C)C[Al](CC(C)C)CC(C)C MCULRUJILOGHCJ-UHFFFAOYSA-N 0.000 claims description 2
- LFXVBWRMVZPLFK-UHFFFAOYSA-N trioctylalumane Chemical compound CCCCCCCC[Al](CCCCCCCC)CCCCCCCC LFXVBWRMVZPLFK-UHFFFAOYSA-N 0.000 claims description 2
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- VPGLGRNSAYHXPY-UHFFFAOYSA-L zirconium(2+);dichloride Chemical compound Cl[Zr]Cl VPGLGRNSAYHXPY-UHFFFAOYSA-L 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
- C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
- C08L23/04—Homopolymers or copolymers of ethene
- C08L23/08—Copolymers of ethene
- C08L23/0807—Copolymers of ethene with unsaturated hydrocarbons only containing more than three carbon atoms
- C08L23/0815—Copolymers of ethene with aliphatic 1-olefins
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L2205/00—Polymer mixtures characterised by other features
- C08L2205/02—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group
- C08L2205/025—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group containing two or more polymers of the same hierarchy C08L, and differing only in parameters such as density, comonomer content, molecular weight, structure
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- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Polymerisation Methods In General (AREA)
- Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
Abstract
The invention discloses a method for efficiently preparing a high-performance polyolefin blend by a two-stage process in a single reactor. By adopting a single-reactor two-stage method high-efficiency polymerization process, the high-molecular weight high-branching-degree polyolefin component A is produced in the first stage of polymerization, the prepolymerization effect of gradual temperature rise is produced in a reactor by utilizing the difference between the heat release of olefin polymerization and the heat removal capacity of internal/external circulation of a device, the temperature of the reactor can reach the temperature required by the second stage of polymerization after the first stage of reaction is finished, and the second stage of polymerization is carried out to obtain the low-molecular weight low-branching-degree polyolefin component B. And finally, controlling the product discharging flow, and reducing the temperature and pressure in the reactor to the working condition before the polymerization starts, thereby realizing intermittent production or continuous production. The method has the advantages of high production efficiency, simple switching operation, short flow, low equipment investment, low energy consumption and the like, and can efficiently prepare the high-performance polyolefin blend. The process is particularly suitable for polyolefin catalysts with rapid activity release and extremely short activation periods.
Description
Technical Field
The invention relates to a synthesis method of a high-performance polyolefin material, belonging to the technical field of polyolefin in the synthetic resin industry.
Background
Polyolefin plastics, namely polymers of olefins, are one of general plastics, mainly comprise Polyethylene (PE), polypropylene (PP), thermoplastic elastomer (POE), ethylene-vinyl acetate copolymer (EVA) and the like, and are high-molecular materials with large yield and wide application range. Polyolefin materials are widely produced, processed, manufactured and used in various forms in daily life, and are widely applied to the fields of urban gas pipelines, water pipelines, filling films, building materials and the like. At present, high-end polyethylene products have good market prospects at home and abroad, particularly, the requirements in the industries of plates, pipes, films, cables and the like are very vigorous, and although the supply of the high-end polyethylene products is increased year by year, the high-end polyethylene products still meet the demand. The production process of the polyolefin products at home and abroad can adopt a double/multiple polymerization reaction kettle series connection process, a double/multiple polymerization reaction kettle parallel connection process or a single polymerization reaction kettle process.
In the prior art, patent application CN201180009019.7 discloses a process for producing a bimodal polyethylene blend for blow moulding applications in at least two slurry loop reactors in series, wherein one reactor produces high molecular weight polyethylene and the other reactor produces low molecular weight polyethylene; wherein the density of the high molecular weight polyethylene is 0.925 to 0.942 g/cc, the density of the low molecular weight polyethylene is 0.960 to 0.975 g/cc, and the density of the bimodal polyethylene product is 0.935 to 0.960 g/cc. Patent application CN201280021440.4 discloses a process for separately preparing two molecular weight polyethylene resins in a loop reactor using a ziegler-natta catalyst, followed by physically blending the prepared polyethylene resins to obtain a multimodal polyethylene blend. Patent application CN201310311017.4 discloses a method for preparing wide/bimodal polyethylene in a single reactor, which adopts a series coordination metal catalyst system composed of zirconium dichloride as a first catalyst and a metallocene catalyst as a second catalyst to prepare wide/bimodal polyethylene in a single polymerization reactor. It can be seen that the production of high performance polyolefin blends is mostly done by a dual/multiple reactor series/parallel process or by a dual/multiple active site hybrid combination catalyst. For example, in the processes disclosed in patent applications CN201180009019.7 and CN201280021440.4, the two polymerization reactors connected in series are used, and the reaction materials need to pass through the two polymerization reactors connected in series to produce the polyethylene blend, so the processes have the significant problems of large equipment size, large engineering investment, high operation cost, complex operation process, and the like. Although patent applications CN201010515067.0 and CN201310311017.4 adopt a single polymerization kettle process with simple process flow to prepare bimodal polyethylene products, the problems of complex catalytic system, harsh catalyst preparation conditions, difficult operation of polymerization process, and poor thermal stability in the operation process exist.
In view of the above problems, the inventors of the present invention have conducted research to solve the problems exposed in the prior art of the related art, and desire to provide a method for achieving two-stage sequential polymerization of high-performance polyolefin blends in a single reactor by using the temperature-rising thermal effect of prepolymerization in the single reactor, so as to shorten the production process, which has the significant advantages of simple process, low equipment investment cost, simple modification, wide applicability to catalysts, and the like, and the polyolefin blend product has the characteristics of significantly enhanced impact resistance, environmental stress cracking resistance, flexibility, tensile strength, tensile modulus, and the like. In particular, the present invention is particularly suitable for polyolefin catalysts with rapid activity release and extremely short activation period. The invention is also characterized in that no molecular weight regulator is added in the prepolymerization stage and the molecular weight regulator is added in the second stage in the polymerization process, namely the post-hydrogenation production technology. The post-hydrogenation production process can reduce the equipment investment of a molecular weight regulator separation and recovery device, improve the once-through conversion rate of ethylene and further reduce the production cost and the equipment investment.
Disclosure of Invention
In view of the above deficiencies of the prior art, it is an object of the present invention to provide a process for efficiently producing high performance polyolefin blends in a single reactor. The preparation method can solve the problems of long process flow, large equipment investment and high operation cost in the existing polyolefin blend preparation process. The single-reactor polymerization process has the advantages of high production efficiency, simple switching operation, short flow, low equipment investment, low energy consumption and the like, and can efficiently prepare the polyolefin blend with high performance. The polyolefin blends can be processed by adopting the processing technologies such as conventional twin-screw extrusion, injection molding or blow molding, and the processed products have obvious improvement in the aspects of strength/rigidity/toughness, such as obviously enhanced impact property, environmental stress cracking resistance, flexibility, tensile strength, tensile modulus and the like.
The method for preparing the high-performance polyolefin blend by the two-stage process in the single reactor is different from the method for preparing the high-performance polyolefin blend by the two-stage process in the prior production process, combines the characteristics of production process parameters, utilizes the characteristics of short reaction time of the first stage, large polymerization heat release and quick release, can obviously improve the temperature of a material system in the reactor, does not add any molecular weight regulator in the first stage of polymerization reaction, has quick catalyst activity release rate, can prepare the polyolefin component A with higher molecular weight, higher branched chain content and wide regulation, and the system temperature can be raised to the temperature near the temperature required by the second stage polymerization reaction in a short time, and a proper amount of molecular weight regulator is added, can prepare the polyolefin component B with lower molecular weight, lower branched chain content and good processing performance, and the polyolefin component A and the polyolefin component B jointly form a high-performance polyolefin blending product. Meanwhile, as the production process of the polyolefin component A is a heating process, the branched chains are more prone to be distributed on a high molecular weight part prepared under a low-temperature condition at the initial stage of a polymerization reaction, so that the branched chain distribution is concentrated to the high molecular weight polyolefin part, the concentration of the comonomer is remarkably reduced along with the progress of the polymerization reaction, the branched chain distribution of a low molecular weight polyolefin part is gradually reduced along with the progress of the polymerization reaction, the polyolefin product with the unevenly distributed branched chains (which is gathered to the high molecular weight part) has stronger mechanical property, environmental stress cracking resistance ESCR and temperature resistance, and the PE100, PE112 and PE125 high-performance polyethylene pipe materials with more excellent performance can be developed. The invention is also characterized in that no molecular weight regulator is added in the prepolymerization stage and the molecular weight regulator is added in the second stage in the polymerization process, namely the post-hydrogenation production technology. The post-hydrogenation production process can reduce the equipment investment of a molecular weight regulator separation and recovery device, improve the once-through conversion rate of ethylene and further reduce the production cost and the equipment investment.
The method for preparing the high-performance polyolefin blend by the two-stage process in the single reactor is particularly suitable for the polyolefin catalyst with quick and stable activity release and extremely short activation period. In the conventional double/multiple reactor series production process, due to the characteristics of different active centers of the catalyst (short polymerization time, high activity, and long polymerization time for producing low molecular weight active centers), the low molecular weight polyethylene component is often produced at a higher temperature in the first reactor, and the high molecular weight polyethylene component is often produced at a lower temperature in the second reactor. The rapid switching of the system in the reactor from the high temperature condition to the low temperature condition can be realized by the strong heat removal of the reactor, but the rapid temperature rise of the system in the reactor is difficult to realize (limited by the slow temperature rise of the external circulation of the reactor, which can not be realized under the existing industrial conditions). In the case of a polyolefin catalyst having a rapid and stable activity release and an extremely short activation period, a large amount of polymerization heat is generated at the initial stage of polymerization, and the heat removal capability of a reactor (particularly, a tank reactor) is limited. Therefore, the invention realizes seamless switching continuous operation of two polymerization conditions of low temperature and high temperature by the rapid temperature rise of polymerization heat effect (namely prepolymerization heat effect) in a single reactor. Meanwhile, due to the discharging treatment at the final stage of the polymerization reaction, a large amount of reaction heat can be quickly removed, and the quick switching from high temperature to low temperature is met, so that the next polymerization (i.e. the next prepolymerization) can be carried out, and the continuous production of the two-stage process in a single reactor is realized. Therefore, the two-stage process in the single reactor can be suitable for batch production and also suitable for continuous production.
According to one aspect of the invention, the invention provides a method for efficiently preparing a high-performance polyolefin blend by a two-stage process in a single reactor, which utilizes a prepolymerization heating effect efficient preparation production technology in the single reactor, and specifically comprises the following steps and characteristics:
1) adding a solvent, a comonomer and a cocatalyst component into a single reactor at a preset temperature T1 and a preset pressure P1 (preset condition R1), introducing a main catalyst and an olefin monomer when the temperature and the pressure of a system in the reactor reach a preset temperature T2 and a preset pressure P2 (preset condition R2), starting prepolymerization, gradually reaching a preset temperature T3 and a preset pressure P3 (preset condition R3) through a period of time T1 under the combined action of polymerization heat and internal/external circulation heat removal of the reactor, namely the prepolymerization heat effect, and polymerizing to form a polyolefin component A within a polymerization time T1;
2) after the prepolymerization heat effect is finished, introducing polymerization components into the reactor again, wherein the polymerization components at least comprise ethylene monomers and molecular weight regulators (comonomers and other components can be added according to needs), the polymerization temperature and the polymerization pressure are increased to a preset temperature T4 and a pressure P4 (a preset condition R4), the polymerization temperature is slowly reduced or kept unchanged after T4 is reached, the polymerization temperature is slowly reduced or kept unchanged from T2 to a preset temperature T5 after the polymerization time is T2, the system pressure is kept unchanged (a preset condition R5), the polyolefin component B is polymerized to be generated in the polymerization time T2, after the polymerization time is T1+ T2, discharging products in the reactor to obtain a high-performance polyolefin blend with adjustable A/B ratio of the two components, and the temperature and the pressure of the reactor are reduced along with discharging to reach a preset temperature T6 and a pressure P6 (a preset condition R6);
in the present invention, the system pressure P2 is slightly increased due to the decrease in system temperature T2 due to the addition of cold material, as compared to the predetermined condition R1. The system temperature T4 is slightly increased compared to the predetermined condition R3, and the polymerization pressure P4 is kept constant or slightly increased. Compared to the predetermined condition R4, the system temperature T5 is slowly decreased or kept constant, and the system pressure P5 is kept constant. Compared with the predetermined condition R5, the system temperature T6 is significantly reduced because of the discharge, and the system pressure P6 is also reduced to a little higher than normal pressure.
According to some embodiments of the invention, the preset temperature T2 and the preset temperature T3 in step 1) range from 10 to 90 ℃, preferably from 30 to 80 ℃, more preferably from 35 to 78 ℃; the ranges of the preset temperature T4 and the preset temperature T5 in the step 2) are 60-110 ℃, preferably 65-100 ℃, and more preferably 70-90 ℃; the preset temperature T1 is in the range of 15-90 ℃, preferably 25-80 ℃, and more preferably 40-65 ℃; the preset temperature T6 is in the range of 15-90 ℃, preferably 25-80 ℃, and more preferably 40-65 ℃; the temperature difference between the preset temperature T3 and the preset temperature T4 is 5-35 ℃, preferably 7-30 ℃, and more preferably 9-25 ℃; the temperature difference between the preset temperature T2 and the preset temperature T3 is 15-60 deg.C, preferably 20-50 deg.C, more preferably 25-45 deg.C.
According to some embodiments of the invention, the preset pressure P1 and the preset pressure P2 in step 1) range from 1.01 to 2.00bar, preferably from 1.01 to 1.6bar, more preferably from 1.03 to 1.4 bar; the preset pressure P3 is in the range of 3.0-15.0bar, preferably 4-12bar, more preferably 4.5-10 bar; the preset pressure P4 and the preset pressure P5 in the step 2) range from 3 to 18bar, preferably from 4 to 15bar, and more preferably from 4.5 to 12 bar; the preset pressure P6 is in the range of 1.01-3.00bar, preferably 1.05-2.5bar, more preferably 1.1-2.0 bar.
In a preferred embodiment of the present invention, the step 1) and the step 2) are two-stage polymerization production process in a single-group single reactor, and have the characteristic of batch operation. On the basis, the preset conditions R1 are further controlled to be equivalent to R6, so that a plurality of single-group production processes can be used in series, and the two-stage method and the multi-group continuous production process which are combined into a single reactor have the characteristic of continuous method operation. The temperature and pressure changes of the system of the two-stage process of the invention are shown in the temperature and pressure diagram (see fig. 1 and 2) and the ethylene flow dynamics curve diagram in fig. 3.
According to an embodiment of the present invention, the polymerization activity in the polymerization time t2 is significantly lower than that in the polymerization time t1, and the thermal effect in the second stage polymerization is significantly lower than that in the first stage polymerization, and in detail, the ratio of the average polymerization activity per unit time in the polymerization time t2 to the average polymerization activity per unit time in the polymerization time t1 is controlled to be 1:1.5 to 1:15, preferably 1:2 to 1: 10.
According to one embodiment of the invention, the polymerized monomer is ethylene and the comonomer is one or more of propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, butadiene, pentadiene, hexadiene, styrene.
According to one embodiment of the invention, the main catalyst in the step (1) is one or more of metallocene catalyst, chromium-based catalyst, FI catalyst, Ziegler-Natta catalyst and late transition metal catalyst; the cocatalyst is one or more of methylaluminoxane, modified methylaluminoxane, triethylaluminum, triisobutylaluminum, diethylaluminum chloride, dichloroethylaluminum, tributylaluminum, trihexylaluminum, trioctylaluminum and organic boride. Wherein, the molar ratio of the cocatalyst to the main catalyst is in the range of 1-3000, preferably 2-2000, and more preferably 2-1500.
According to one embodiment of the present invention, the polymerization solvent is one or more of linear or isomeric alkanes such as 1-pentane, 1-hexane, 1-heptane, 1-octane, 1-nonane, 2-methylpentane, 3-methylpentane, 2-methylhexane, 3-methylhexane, toluene, etc.
According to an embodiment of the present invention, the ratio of the first polymerization time t1 to the total polymerization time (t1+ t2) is 5% to 30%, preferably 5.5% to 25%, and more preferably 6% to 22%, so as to ensure the rapid release of polymerization heat and rapidly increase the polymerization temperature, thereby forming a positive feedback of polymerization temperature increase and polymerization heat release, and forming a pre-polymerization temperature increase effect.
According to one embodiment of the present invention, the molecular weight regulator added in step 2) is selected from one or more of hydrogen, oxygen, propylene and butylene, and the partial pressure ratio of the molecular weight regulator to the ethylene monomer is in the range of 0.02 to 0.7, preferably 0.05 to 0.5, more preferably 0.08 to 0.45.
According to one embodiment of the present invention, the difference between the molecular weight of the polyolefin component A and the molecular weight of the polyolefin component B is large, the molecular weight of the polyolefin component A is distributed in 10000-10000000g/mol, preferably 4000-8000000g/mol, and the molecular weight of the polyolefin component B is distributed in 1000-500000g/mol, preferably 1200-350000 g/mol. The branched chain contents of the polyolefin component A and the polyolefin component B are also greatly different, and the branched chain content of the polyolefin component A accounts for 50-96%, preferably 60-90% and more preferably 65-88% of the total branched chain content; and benefits from the obvious improvement of the prepolymerization heat effect temperature, the chain transfer rate is obviously improved, the branched chain content of the polyolefin component A can have a wider regulation range according to different catalyst types, the comonomer branched chains are more prone to be distributed on a polyethylene chain segment with high molecular weight, and the polyolefin blend product (A + B) has obviously enhanced impact property, environmental stress cracking resistance, flexibility, tensile strength and tensile modulus.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings briefly described below are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 shows a temperature profile of an exemplary system according to the present invention;
FIG. 2 shows a system pressure curve according to an embodiment of the method of the present invention;
FIG. 3 shows a graph of the change in polymerization activity in one embodiment of the process of the present invention;
FIG. 4 shows the molecular weight distribution and branch distribution of a polyolefin product in one embodiment of the process of the present invention.
Detailed description of the invention
Embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
The method for characterizing the structure and the performance of the polymer comprises the following steps:
(1) melt index: the melt flow rate was determined according to GB/T-3682-2000 conditions (190 ℃ C., load of 2.16 kg), and is generally designated MI 2.16.
(2) Density: determined according to the method of GB/1033-.
(3) Tensile strength, young's modulus and elongation at break: determined according to GB/T1040-.
(4) Impact strength: determined according to GB/T1843-2008.
(5) Weight average molecular weight: measured by high temperature permeation gel chromatography HT-GPC.
(6) Comonomer insertion rate: according to13C-NMR measurement and calculation.
(7) Environmental stress cracking resistance: determined according to GB/T1842-2008.
Example 1
In a single 500L reaction kettle, raising the temperature in the reaction kettle to 41 ℃ by jacket heating/heat removal in the kettle, wherein the pressure in the kettle is 1.08bar, sequentially adding 300L of hexane/pentane/heptane (1:1:1) mixed solvent, 100mL of 1-hexene comonomer and 250mL of 0.8mol/L triethyl aluminum cocatalyst, lowering the temperature in the kettle to 37 ℃ and the pressure to 1.1bar, then adding 1.5g of commercial Ziegler-Natta main catalyst (the molar ratio of the cocatalyst to the main catalyst is 80) and ethylene monomer, starting the first-stage polymerization, controlling the polymerization time to be 30min, rapidly raising the temperature of a material system in the kettle to 78 ℃, raising the ethylene partial pressure to 5.2bar, and preparing 14kg of high-molecular weight polyolefin component A (calculated by a flowmeter) in the first stage; in the later stage of prepolymerization heat effect, 3.0bar of molecular weight regulator hydrogen is introduced into the reaction kettle, then ethylene monomer is immediately charged until the total pressure of the system is 11.8bar, the polymerization temperature is slowly increased to 87 ℃, in this stage, the produced polyolefin component B with low molecular weight and low branching degree reaches 46kg (calculated by a flow meter), the polymerization time is controlled to 230min, the system temperature is reduced to 82 ℃, and the system pressure is kept unchanged at 11.8 bar. And finally, discharging the polyolefin blending product, and reducing the temperature of a material system in the reaction kettle to 57 ℃ and the pressure of the material system to 1.2 bar. The polymerization parameters of the polymerization are detailed in Table 1. The physical properties (molecular weight, branch distribution, branch content, melt index and mechanical properties) of the polyolefin component A, component B and blends are detailed in Table 6. This example was carried out using a batch process.
TABLE 1 Single reactor polymerization parameters
Example 2
In a single 500L reaction kettle, raising the temperature in the reaction kettle to 55 ℃ by jacket heating/heat removal in the kettle, wherein the pressure in the kettle is 1.33bar, sequentially adding 320L of hexane/pentane/heptane (1:2:1) mixed solvent, 85mL of 1-hexene comonomer and 320mL of 0.8mol/L triethyl aluminum cocatalyst, lowering the temperature in the kettle to 43 ℃ and the pressure to 1.28bar, then adding 1.3g of commercial Ziegler-Natta main catalyst (the molar ratio of the cocatalyst to the main catalyst is 140) and ethylene monomer, starting the first-stage polymerization, controlling the polymerization time to be 25min, rapidly raising the temperature of a system in the kettle to 75 ℃, raising the ethylene partial pressure to 6.7bar, and preparing 12kg of high molecular weight polyolefin component A (calculated by a flowmeter) in the first stage; in the later stage of prepolymerization heat effect, 3.2bar of molecular weight regulator hydrogen is introduced into the reaction kettle, then ethylene monomer is immediately charged until the total pressure of the system is 11.3bar, the polymerization temperature is slowly increased to 89 ℃, in this stage, the produced polyolefin component B with low molecular weight and low branching degree reaches 45kg (calculated by a flow meter), the polymerization time is controlled to be 250min, the system temperature is reduced to 84 ℃, and the system pressure is kept unchanged at 11.3 bar. And finally, discharging the polyolefin blending product, and reducing the temperature of a material system in the reaction kettle to 55 ℃ and the pressure of the material system to 1.26 bar. The polymerization parameters of the polymerization are detailed in Table 2. The polyolefin component A, component B and the blend have the physical properties (molecular weight, branch distribution, branch content, melt index and mechanical properties) as detailed in Table 6. This example was carried out using a batch process.
TABLE 2 Single reactor polymerization parameters
Example 3
In a single 500L reaction kettle, raising the temperature in the reaction kettle to 64 ℃ by jacket heating/heat removal in the kettle, wherein the pressure in the kettle is 1.38bar, sequentially adding 320L of hexane/pentane/heptane (1:2:2) mixed solvent, 80mL of 1-hexene comonomer and 330mL of 0.8mol/L triethyl aluminum cocatalyst, lowering the temperature in the kettle to 48 ℃ and the pressure to 1.32bar, then adding 1.35g of improved commercial Ziegler-Natta main catalyst (the molar ratio of the cocatalyst to the main catalyst is 120) and ethylene monomer, starting the first-stage polymerization, controlling the polymerization time to be 35min, rapidly raising the temperature of a system in the kettle to 82 ℃, raising the ethylene partial pressure to 4.5bar, and preparing 15kg of high molecular weight polyolefin component A (calculated by a flowmeter) in the first stage; in the later stage of prepolymerization heat effect, 3.3bar of molecular weight regulator hydrogen is introduced into the reaction kettle, then ethylene monomer is immediately charged until the total system pressure is 11.9bar, the polymerization temperature is slowly raised to 89 ℃, in this stage, the produced low-molecular-weight low-branching-degree polyolefin component B reaches 60kg (calculated by a flowmeter), the polymerization time is controlled to be 280min, the system temperature is reduced to 85 ℃, and the system pressure is kept unchanged at 11.9 bar. Finally, discharging the polyolefin blending product, and reducing the temperature of a material system in the reaction kettle to 61 ℃ and the pressure of the material system to 1.16 bar. The polymerization parameters of the polymerization are specified in Table 3. The physical properties (molecular weight, branch distribution, branch content, melt index and mechanical properties) of the polyolefin component A, component B and blends are detailed in Table 6. This example was carried out using a batch process.
TABLE 3 Single reactor polymerization parameters
Example 4
In a single 500L reaction kettle, raising the temperature in the reaction kettle to 49 ℃ by jacket heating/heat removal in the kettle, wherein the pressure in the kettle is 1.25bar, sequentially adding 300L of hexane/pentane/heptane (1:1:2) mixed solvent, 100mL of 1-hexene comonomer and 230mL of 0.8mol/L triethyl aluminum cocatalyst, lowering the temperature in the kettle to 44 ℃ and the pressure to 1.23bar, then adding 1.38g of commercial Ziegler-Natta main catalyst (the molar ratio of the cocatalyst to the main catalyst is 110) and ethylene monomer, starting the first-stage polymerization, controlling the polymerization time to be 23min, rapidly raising the temperature of a material system in the kettle to 78 ℃, raising the ethylene partial pressure to 5.3bar, and preparing 16kg of high-molecular weight polyolefin component A (calculated by a flowmeter) in the first stage; in the later stage of prepolymerization heat effect, 2.5bar of molecular weight regulator hydrogen is introduced into the reaction kettle, then ethylene monomer is immediately charged until the total pressure of the system is 10.7bar, the polymerization temperature is slowly increased to 85 ℃, and in this stage, the produced polyolefin component B with low molecular weight and low branching degree reaches 57kg (calculated by a flow meter), the polymerization time is controlled to be 260min, the system temperature is reduced to 84 ℃, and the system pressure is kept unchanged at 10.7 bar. Finally, discharging the polyolefin blending product, and reducing the temperature of a material system in the reaction kettle to 52 ℃ and the pressure of the material system to 1.22 bar. The polymerization parameters of the polymerization are detailed in Table 4. The physical properties (molecular weight, branch distribution, branch content, melt index and mechanical properties) of the polyolefin component A, component B and blends are detailed in Table 6. In this example, the continuous process was used for production, and the subsequent temperature, pressure, hydrogen addition, comonomer addition, cocatalyst addition, catalyst addition, and solvent addition were shown in table 4.
TABLE 4 Single reactor polymerization parameters
Example 5
In a single 500L reaction kettle, raising the temperature in the reaction kettle to 53 ℃ by jacket heating/heat removal in the kettle, wherein the pressure in the kettle is 1.12bar, sequentially adding 350L of hexane/pentane/heptane (1:1:1) mixed solvent, 140mL of 1-hexene comonomer, 30mL of 1-octene comonomer and 290mL of 0.8mol/L of triethyl aluminum cocatalyst, lowering the temperature in the kettle to 46 ℃ and the pressure to 1.06bar, then adding 1.55g of commercial Ziegler-Natta main catalyst (the molar ratio of the cocatalyst to the main catalyst is 140) and ethylene monomer, starting the first stage of polymerization, controlling the polymerization time to be 26min, rapidly raising the temperature of a system in the kettle to 76 ℃, raising the ethylene partial pressure to 5.5bar, and preparing 20kg of high molecular weight polyolefin component A (calculated by a flow meter) in this stage; in the later stage of prepolymerization heat effect, 3.6bar of molecular weight regulator hydrogen is introduced into the reaction kettle, then ethylene monomer is immediately charged until the system total pressure is 11.7bar, the polymerization temperature is slowly raised to 88 ℃, in this stage, the produced low molecular weight and low branching degree polyolefin component B reaches 77kg (calculated by a flow meter), the polymerization time is controlled to be 250min, the system temperature is reduced to 85 ℃, and the system pressure is kept unchanged at 11.7 bar. And finally, discharging the polyolefin blending product, and reducing the temperature of a material system in the reaction kettle to 52 ℃ and the pressure of the material system to 1.15 bar. The polymerization parameters of the polymerization are specified in Table 5. The physical properties (molecular weight, branch distribution, branch content, melt index and mechanical properties) of the polyolefin component A, component B and blends are detailed in Table 6. In this example, the continuous process was used for production, and the subsequent temperature, pressure, hydrogen addition, comonomer addition, cocatalyst addition, catalyst addition, and solvent addition were shown in Table 5.
TABLE 5 Single reactor polymerization parameters
Comparative example 1
In this example, a continuous process of dual reactors in series was used to produce polyolefin blends, in a first 500L reactor, 300L of a hexane/pentane/heptane (1:1:1) solvent mixture, 1.5bar of molecular weight regulator hydrogen, 250mL of 0.8mol/L triethylaluminum cocatalyst, 1.1g of a commercial Ziegler-Natta procatalyst (molar ratio of cocatalyst to procatalyst: 120), and ethylene monomer were added sequentially, the system polymerization temperature was 92 deg.C, the system polymerization pressure was 5.1bar, and the polymerization time was controlled to 18min, at which stage a low molecular weight polyolefin component A of 52kg (calculated by a flow meter) was produced, then 98.5% of molecular weight regulator hydrogen was separated from the reaction system by a separation device, and then transferred to a second 600L reactor, and 160mL of 1-hexene comonomer and ethylene monomer were added, the system polymerization temperature was 74 deg.C, the polymerization pressure was 6.5bar and the polymerization time was controlled at 230min, at which stage 78kg (calculated on a flow meter) of the high molecular weight polyolefin component B were prepared and finally the polyolefin blend product was discharged and worked up. The physical properties (molecular weight, branch distribution, branch content, melt index and mechanical properties) of the polyolefin component A, component B and blends are detailed in Table 6. The separation device in the comparative example comprises not only a hydrogen separation device, but also a subsequent ethylene, solvent component, nitrogen and other recycling device.
TABLE 6 index of physical properties of polyolefin blends
Comparing the polymerization processes and polymerization apparatuses in examples 1 to 5 with those in comparative example 1, it can be seen that the process of the present invention, which uses a two-stage process in a single reactor, first produces a polyolefin component a having a high molecular weight and a high branching degree by using the prepolymerization heat effect, and then produces a polyolefin component B having a low molecular weight and a low branching degree in an environment of a high temperature and a molecular weight modifier, can greatly shorten the process flow, reduce the number of separation and recycling apparatuses for various materials such as reactors and separation apparatuses, and reduce the investment in equipment. Meanwhile, the polymerization process has the advantages of short flow, rapid product switching and the like, and is relatively suitable for the production of small-batch high-added-value polyolefin products. In particular, the polymerization process of the present invention is particularly suitable for polyolefin catalysts with rapid and stable activity release and extremely short activation period.
As can be seen from the physical property indexes of the polyolefin blends in Table 6, the single-reactor two-stage process employed in examples 1 to 5, whether it is a batch process (examples 1 to 3) or a continuous process (examples 4 to 5), can produce the polyolefin component A having a high molecular weight and a high branching degree and the polyolefin component B having a low molecular weight and a low branching degree. The final polyolefin blend (A + B) product exhibits high tensile strength, high tensile modulus, high elongation at break and high impact strength. The method is mainly characterized in that the method adopts a single-reactor internal two-stage process, the high-molecular-weight and high-branching-degree polyolefin component A produced by using the prepolymerization heat effect is obtained by polymerization under the conditions of continuously increasing temperature and continuously increasing pressure, the molecular weight of the polyolefin component A is gradually reduced along with the increase of the polymerization temperature, and the concentration of the comonomer is also reduced, namely the comonomer in the polyolefin component A is more prone to be distributed on a polyethylene chain with higher molecular weight. According to the basic knowledge of those skilled in the art, the polyolefin product with such comonomer more concentrated in the high molecular weight polyethylene segment has more tie molecular structure (as shown in fig. 4), and can greatly enhance the mechanical properties of the product, especially the Environmental Stress Cracking Resistance (ESCR). By adopting the polymerization method, PE100, PE112 and PE125 high-performance polyethylene pipe materials with more excellent performance can be developed.
Claims (10)
1. A method for efficiently preparing high-performance polyolefin blend by a two-stage process in a single reactor is characterized by comprising the following steps:
1) adding a solvent, a comonomer and a cocatalyst component into a single reactor at a preset temperature T1 and a preset pressure P1, introducing a main catalyst and an olefin monomer when the temperature and the pressure of a system in the reactor reach the preset temperature T2 and the preset pressure P2, starting prepolymerization reaction, gradually reaching the preset temperature T3 and the preset pressure P3 through a period of time T1 under the combined action of polymerization heat and internal/external circulation heat removal of the reactor, namely the action of prepolymerization heat effect, and polymerizing for a polymerization time T1 to generate a polyolefin component A;
2) after the action of the prepolymerization heat effect is finished, introducing polymerization components into the reactor again, wherein the polymerization components at least comprise ethylene monomers and molecular weight regulators, the polymerization temperature and the polymerization pressure are increased to a preset temperature T4 and a preset pressure P4, the polymerization temperature is slowly reduced or kept unchanged after the polymerization temperature reaches T4, the system pressure is kept unchanged after the polymerization time T2 reaches the preset temperature T5, the polyolefin component B is polymerized and generated in the polymerization time T2, after the polymerization time reaches T1+ T2, the product in the reactor is discharged to obtain a high-performance polyolefin blend with adjustable A/B ratio of the two components, the temperature and the pressure of the reactor are reduced along with the discharge, and the preset temperature T6 and the preset pressure P6 are reached;
the range of the preset temperature T2 and the preset temperature T3 in the step 1) is 10-90 ℃; the range of the preset temperature T4 and the preset temperature T5 in the step 2) is 60-110 ℃; the temperature range of the preset temperature T1 is 15-90 ℃; the temperature range of the preset temperature T6 is 15-90 ℃; the temperature difference between the preset temperature T3 and the preset temperature T4 is 5-35 ℃; the temperature difference between the preset temperature T2 and the preset temperature T3 is 15-60 ℃;
the range of the preset pressure P1 and the preset pressure P2 in the step 1) is 1.01-2.00 bar; the preset pressure P3 is in the range of 3.0-15.0 bar; the preset pressure P4 and the preset pressure P5 in the step 2) range from 3 to 18 bar; the preset pressure P6 is in the range of 1.01-3.00 bar;
the proportion of the first period of polymerization time t1 to the total polymerization time t1+ t2 is 5-30%;
the molecular weight regulator added in the step 2) is one or more selected from hydrogen, oxygen, propylene and butylene, and the partial pressure ratio of the molecular weight regulator to the ethylene monomer is in the range of 0.02-0.7.
2. The method for efficiently preparing the polyolefin blend with high performance according to the two-stage process in the single reactor of claim 1, wherein the ratio of the average polymerization activity per unit time in the polymerization time t2 to the average polymerization activity per unit time in the polymerization time t1 is controlled to be 1:1.5 to 1: 15.
3. The method of claim 1 for efficiently producing high performance polyolefin blends by a single-reactor two-stage process, wherein the olefin monomer is ethylene and the comonomer is one or more of propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, butadiene, pentadiene, hexadiene, and styrene.
4. The method for efficiently preparing the polyolefin blend with high performance by the two-stage process in the single reactor according to claim 1, wherein the main catalyst in the step 1) is one or more of metallocene catalyst, chromium-based catalyst, FI catalyst, Ziegler-Natta catalyst and late transition metal catalyst; the cocatalyst is one or more of methylaluminoxane, modified methylaluminoxane, triethylaluminum, triisobutylaluminum, diethylaluminum chloride, ethylaluminum dichloride, tributylaluminum, trihexylaluminum, trioctylaluminum and organic boride; wherein the molar ratio of the cocatalyst to the main catalyst is 1-3000.
5. The method for preparing polyolefin blends with high performance by the two-stage process in a single reactor according to claim 1, wherein the solvent in step 1) is one or more of linear or isomeric alkanes such as 1-pentane, 1-hexane, 1-heptane, 1-octane, 1-nonane, 2-methylpentane, 3-methylpentane, 2-methylhexane, 3-methylhexane, toluene, etc.
6. The method for preparing polyolefin blends with high performance by the two-stage process in a single reactor according to claim 1, wherein the ratio of the first polymerization time t1 to the total polymerization time t1+ t2 is 5.5% -25%.
7. The method for efficiently preparing high performance polyolefin blends according to the two-stage process in a single reactor according to claim 1, wherein in the step 2), the partial pressure ratio of the molecular weight modifier to the ethylene monomer is in the range of 0.05-0.5.
8. The method for preparing high performance polyolefin blend with high efficiency by the two-stage process in the single reactor as claimed in claim 1, wherein the molecular weight of the polyolefin component A is distributed in 10000-10000000g/mol, and the molecular weight of the polyolefin component B is distributed in 1000-500000 g/mol; the branched content of the polyolefin component A is 50 to 96% of the total branched content.
9. The method for efficiently preparing the high-performance polyolefin blend according to the single-reactor two-stage process technology of claim 1, characterized in that; the range of the preset temperature T2 and the preset temperature T3 in the step 1) is 30-80 ℃; the range of the preset temperature T4 and the preset temperature T5 in the step 2) is 65-100 ℃; the temperature range of the preset temperature T1 is 25-80 ℃; the temperature range of the preset temperature T6 is 25-80 ℃; the temperature difference between the preset temperature T3 and the preset temperature T4 is 7-30 ℃; the temperature difference between the preset temperature T2 and the preset temperature T3 is 20-50 ℃.
10. The method for efficiently preparing the high-performance polyolefin blend according to the single-reactor two-stage process technology of claim 1, characterized in that; the range of the preset pressure P1 and the preset pressure P2 in the step 1) is 1.01-1.6 bar; the preset pressure P3 is in the range of 4-12 bar; the preset pressure P4 and the preset pressure P5 in the step 2) range from 4 to 15 bar; the preset pressure P6 is in the range of 1.05-2.5 bar.
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