Process for continuously producing multifunctional modified film material polyethylene

Abstract

The invention discloses a process for continuously producing multifunctional modified film material polyethylene, which belongs to the technical field of chemical production and comprises a first reaction system, a second reaction system, a third reaction system and a slurry mixing tank, the first reaction system, the second reaction system and the third reaction system are connected in parallel through pipelines and then are connected with the slurry mixing tank through pipelines, and raw materials of the first reaction system comprise a main catalyst I, a catalyst promoter I, a solvent, a chain terminator and an ethylene monomer; the raw materials comprise a main catalyst II, a cocatalyst II, a solvent, a chain terminator, a comonomer and an ethylene monomer, and the third reaction system comprises a main catalyst III, a cocatalyst III, a solvent, a chain terminator, a comonomer and an ethylene monomer.

Description

Technical Field

[0001] The invention relates to the technical field of chemical production, in particular to a process for continuously producing multifunctional modified film material polyethylene. Background Art

[0002] Polyethylene (PE) is a general-purpose thermoplastic resin made from the polymerization of ethylene monomer. It exhibits excellent chemical stability, electrical insulation, and processing properties, making it widely used in film products such as packaging films, agricultural greenhouse films, and composite flexible packaging. In industrial applications, PE often also includes copolymers of ethylene with small amounts of α-olefins (such as 1-butene, 1-hexene, and 1-octene) to tailor its density, crystallinity, and mechanical properties to meet the needs of different applications.

[0003] 1. Limitations of traditional polyethylene film modification process

[0004] Currently, the modification of polyethylene film materials mainly relies on the mechanical blending method of pellets, that is, physically mixing polyethylene pellets with different properties. However, this method has the following key problems:

[0005] 1. Poor mixing uniformity affects film quality

[0006] Due to the differences in particle size, density and melting properties of different polyethylene pellets, mechanical blending is difficult to achieve uniform dispersion at the molecular level, resulting in defects such as "fish eyes" (unmelted particles), crystal points or film breaks during the film blowing process, which seriously affect the optical properties and mechanical strength of the film.

[0007] Functional additives (such as nanofillers and antistatic agents) are prone to agglomeration due to insufficient compatibility, further exacerbating the problem of uneven dispersion.

[0008] 2. Melt shearing causes molecular chain degradation and loss of mechanical properties

[0009] During the high-temperature and high-shear melt blending process, polyethylene molecular chains are prone to chain scission reactions, especially in the blending system of high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE), whose tensile strength and impact toughness generally decrease by 10% to 15%, affecting the durability of the film.

[0010] In addition, secondary granulation will aggravate the narrowing of molecular weight distribution and further deteriorate the processing rheological properties.

[0011] 3. Low precision in controlling functional components and poor product consistency

[0012] Traditional mechanical blending has limited control over the proportion of functional components (typically >±5%), making it difficult to achieve high-precision formulation control, leading to batch-to-batch performance fluctuations. For example, variations in the anti-blocking agent content can cause film blocking or excessive surface haze.

[0013] For high-end film materials that require the synergistic effect of multiple components (such as high barrier and high puncture resistance films), physical blending methods are difficult to achieve the optimal distribution of each component.

[0014] The existing process is insufficient in molecular structure design. Although modern polymerization technology (such as multi-reactor series process and bimodal catalyst) can produce polyethylene products with bimodal or multimodal molecular weight distribution, it is still difficult to meet the requirements of ultra-low density (<0.910g / cm 3 ), high rigidity (flexural modulus > 800 MPa) and ultra-wide molecular weight distribution (MWD > 20) still face bottlenecks in the synergistic demand:

[0015] Density and rigidity contradiction: Ultra-low density polyethylene (ULDPE) usually requires the introduction of a large amount of α-olefin to reduce crystallinity, but excessive copolymerization will sacrifice the rigidity of the material;

[0016] Limited control over molecular weight distribution: A wide distribution design can improve processing performance, but traditional catalysts make it difficult to precisely control both the degree of long-chain branching and the distribution of short chains simultaneously, resulting in insufficient melt strength or increased necking during film blowing.

[0017] 2. Industry Demands and Technical Challenges

[0018] With the growing demand for high-performance films (such as ultra-thin, high-strength cling film and puncture-resistant heavy-duty packaging films) in the packaging industry, the development of a new modification technology that can in-situ control the polyethylene chain structure and avoid mechanical blending defects has become a current research focus. The ideal solution must take into account:

[0019] Uniform dispersion at the molecular level: precise embedding of functional components is achieved through in-situ polymerization or reactive extrusion;

[0020] Customizable structure: simultaneous optimization of density, molecular weight distribution and branching degree in a single polymerization system;

[0021] Green and efficient process: reduces energy consumption and material degradation in melt blending, improving sustainability;

[0022] Traditional polyethylene film material modification processes use mechanical blending of pellets, which can lead to problems such as uneven mixing and poor processing stability. Although existing processes can produce products with bimodal and multimodal molecular weight distributions, they cannot simultaneously meet the synergistic requirements of ultra-low density, high rigidity, and a wide molecular weight distribution, leading to the following problems:

[0023] 1. The difference in pellet size leads to poor mixing uniformity, resulting in fisheye and film breakage defects during film blowing;

[0024] 2. Melt blending causes molecular chain breakage and a 10%-15% decrease in mechanical properties;

[0025] 3. The ratio of functional components cannot be precisely controlled (error > ±5%). Summary of the Invention

[0026] In order to solve the technical problems mentioned in the above background technology, the present invention provides a process for continuously producing multifunctional modified polyethylene film material, and the technical solution adopted is as follows:

[0027] The invention comprises a first reaction system, a second reaction system, a third reaction system and a slurry mixing tank. The first reaction system, the second reaction system and the third reaction system are connected in parallel through pipelines and then connected to the slurry mixing tank through pipelines. The raw materials of the first reaction system include a main catalyst 1, a co-catalyst 1, a solvent, a chain terminator and an ethylene monomer. The raw materials of the second reaction system include a main catalyst 2, a co-catalyst 2, a solvent, a chain terminator, a comonomer and an ethylene monomer. The raw materials of the third reaction system include a main catalyst 3, a co-catalyst 3, a solvent, a chain terminator, a comonomer and an ethylene monomer, wherein the solvent is one of hexane, heptane or octane.

[0028] Furthermore, the first reaction system includes a first reactor, which is a vertical stirred reactor, and produces ultra-low density polyethylene (density ≤ 0.890 g / cm 3 ). Key parameters:

[0029] Temperature 20-40°C, pressure 8.5-12 barg;

[0030] Hydrogen terminator 0.5-1.5kg / t ethylene;

[0031] No comonomer, catalyst activity ≥5×10 6 g PE / mol Ni;

[0032] The first reactor is connected to a first slurry pump through a pipeline. The concentration of the main catalyst is 5-10 mmol / L, the feed flow rate of the main catalyst is 5-10 mol / h, the molar ratio of the co-catalyst to the main catalyst is 0-5:1, hydrogen is used as the chain terminator, the flow rate is 0.5-1.5 kg hydrogen / t ethylene monomer, the solvent is one of hexane, heptane or octane, the liquid level of the first reactor is 70-90%, the pressure of the first reactor is 8.5-12 barg, and the temperature of the first reactor is 20-40°C; the solid-liquid ratio of the first reactor is 1 ton of polyethylene: (4-6) cubic solvent, and the polyethylene produced in the first reactor is transported to the slurry mixing tank via the first slurry pump.

[0033] Furthermore, the second reaction system includes a second reactor, which is a vertical stirred reactor, and uses a titanium-based Ziegler-Natta catalyst (main catalyst 2) to produce a high-density segment (density ≥ 0.945 g / cm 3 ), the parameters are as follows:

[0034] Gradient temperature control (75℃→85℃);

[0035] The amount of comonomer (1-hexene) introduced is 3-6 kg / t ethylene;

[0036] Hydrogen / ethylene molar ratio 0.05-0.8;

[0037] The second reactor is connected to a second slurry pump through a pipeline. The concentration of the main catalyst II is 10-30 mmol / L, the feed flow rate of the main catalyst II is 1.5-3.5 mol / h, the molar ratio of the co-catalyst II to the main catalyst II is 5-20:1, hydrogen is used as the chain terminator, and the flow rate is 3-6 kg hydrogen / t ethylene. The liquid level of the second reactor is 70-90%, the pressure of the second reactor is 6.0-1.0 barg, the temperature of the second reactor is 75-85 ° C, the solid-liquid ratio of the second reactor is 1 ton of polyethylene: (4-6) cubic solvent, the comonomer flow rate is 2.5-6 kg / t ethylene monomer, and the polyethylene produced in the second reactor is sent to the slurry mixing tank through the second slurry pump.

[0038] Furthermore, both the first reactor and the second reactor are provided with a stirrer, and the first reactor and the second reactor are stirred by the stirrer to promote the reaction.

[0039] Furthermore, the third reaction system includes a third reactor, which is connected to a third slurry pump through a pipeline. The third reactor is a horizontal four-zone reactor, and the hydrogen concentration in each zone decreases gradually (12 kg / t in zone 1 → 0 kg / t in zone 4). A metallocene catalyst (main catalyst three) (such as CGC type) is used to generate a wide molecular weight distribution product (MWD = 30-40), and the latent heat of solvent evaporation is used to remove the reaction heat. The concentration of the main catalyst three is 10-30 mmol / L, the feed flow rate of the main catalyst three is 1.5-3.5 mol / h, and the co-catalyst three and the main catalyst are separated. The molar ratio of the third agent is 5-20:1, hydrogen is used as the chain terminator, the chain terminator is only fed into one zone, the flow rate is 3-12 kg hydrogen / t ethylene, the liquid level of the third reactor is 40-60%, the pressure of the third reactor is 6.0-1.0 barg, the temperature of the third reactor is 75-85°C, the solid-liquid ratio of the third reactor is 1 ton of polyethylene: (4-6) cubic solvent, the comonomer feed ratio of each zone is 1 zone: 2 zone: 3 zone: 4 zone = 0: (2-4): (6-10): (16-24), and the polyethylene produced in the third reactor is pumped into the slurry mixing tank through the third slurry pump.

[0040] Furthermore, the first reactor, the second reactor and the third reactor are respectively connected to the first heat exchanger, the second heat exchanger and the third heat exchanger through pipelines, and the heat generated by polymerization in each reactor is taken away by each heat exchanger to stably control the temperature of the reactor.

[0041] Furthermore, the slurry mixing tank is provided with a multi-stage high-efficiency agitator. The multi-stage high-efficiency agitator refers to an agitator having multiple layers of agitating blades from top to bottom on the agitator rod, which can stir the entire slurry in the slurry mixing tank and fully mix the polyethylene produced in the first reactor, the second reactor and the third reactor.

[0042] Furthermore, the slurry mixing tank is connected to a fourth slurry pump, a powder separator and a powder dryer through pipelines. The mixed polyethylene produced in the slurry mixing tank is sent to the powder separator through the fourth slurry pump for polyethylene powder separation, and then sent to the powder dryer for drying.

[0043] The present invention has the following advantages: compared with conventional film material modification processes, this process performs sufficient mixing at the polyethylene powder stage, that is, the first reaction system, the second reaction system and the third reaction system react independently and then enter the slurry mixing tank together for mixing, thereby realizing raw material mixing modification, greatly improving mixing uniformity, and improving the quality of film material modified products; in addition, this process adopts three reactors in parallel, and can produce polyethylene film material modified products with different functions in any proportion (the first reactor, the second reactor, and the third reactor enter the slurry mixing tank in different proportions) according to the requirements of film material modification. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a process flow chart of the present invention.

[0045] Figures: 1. Slurry mixing tank, 2. First reactor, 3. First slurry pump, 4. Second reactor, 5. Second slurry pump, 6. Third reactor, 7. Third slurry pump, 8. First heat exchanger, 9. Second heat exchanger, 10. Third heat exchanger, 11. Fourth slurry pump, 12. Powder separator, 13. Powder dryer. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0047] Please refer to Figure 1The polyethylene powder stage refers to the stage after the first reactor, the second reactor, and the third reactor each produce polyethylene powder with different properties through polymerization reaction and then enter the slurry mixing tank. The polyethylene powder in this stage is mixed in the slurry and is in a slurry state.

[0048] The first reactor 2 uses a new nickel-based catalyst, which does not require a comonomer. Only ethylene monomer is needed to produce ultra-low density polyethylene at low temperature and low pressure, which is used to significantly improve the toughness of film products.

[0049] The second reactor 4 uses one of titanium-based and metallocene catalysts, and the comonomer is an α-olefin with 3-10 carbon atoms, and the comonomer is one or more of propylene, 1-butene, 1-hexene, 1-octene, etc., to produce high-density polyethylene with high tensile strength, good gloss and excellent processing performance.

[0050] The third reactor 6 uses one of titanium-based and metallocene catalysts, and the comonomer is an α-olefin with 3-10 carbon atoms. It uses a multi-zone reactor, and the hydrogen solubility in each zone decreases successively to produce polyethylene with a wide molecular weight distribution, which is used to improve the various mechanical properties of film products.

[0051] The co-catalyst 1, the co-catalyst 2 and the co-catalyst 3 are any one of triethylaluminum, trimethylaluminum, dimethylaluminum monochloride, dimethylaluminum dichloride, diethylaluminum monochloride, ethylaluminum dichloride and the like.

[0052] The first reactor 2 uses nickel catalyst to generate a density of ≤0.900g / cm at 20-40℃ 3 The second reactor 4 generates branched polyethylene with a density of ≥0.940 g / cm by Ziegler-Natta catalyst at 75-85 ° C. 3 The third reactor 6 adopts four-zone hydrogen gradient control to generate a broad distribution component with MWD>30, and the three slurries are directly granulated after multi-stage mixing.

[0053] Example 1

[0054] Production of high-impact automotive film materials

[0055] First reaction kettle 2: 10% ethylene monomer feed, 80 ℃ to produce 15% carbon 8 branched polyethylene elastomer (density 0.885g / cm 3 ), add main catalyst 1, co-catalyst 1, solvent, and chain terminator to produce low-density, high-toughness polyethylene.

[0056] Second reactor 4: 35% ethylene monomer is fed, and main catalyst 2, co-catalyst 2, solvent, chain terminator and comonomer are introduced to generate high rigidity segment polyethylene with MI=0.5g / 10min.

[0057] The third reverse reactor was fed with 6:55% ethylene monomer, and the hydrogen ratio in the four zones was 10:5:2:0. Main catalyst three, co-catalyst three, solvent, chain terminator, and comonomer were introduced to obtain a broad distribution component with a molecular weight distribution of MWD=33, and produce multimodal polyethylene resin. The tensile strength of the product was significantly improved after mixing.

[0058] The first reactor 2, the second reactor 4 and the third reactor 6 are respectively sent to the slurry mixing tank 1 for stirring through the first slurry pump 3, the second slurry pump 5 and the third slurry pump 7 to produce polyethylene with the above-mentioned comprehensive characteristics, and then sent to the powder separator 12 through the fourth slurry pump 11 for separation of powder and solvent, and then sent to the powder dryer 13 for drying.

[0059] Comparison between Example 1 and existing products:

[0060] Table 1

[0061]

[0062]

[0063] As shown in Table 1, the tensile strength, flexural modulus and notched impact strength of the product of Example 1 of the present invention are significantly improved compared with the conventional products on the market.

[0064] Example 2

[0065] Food packaging barrier film production

[0066] The first reaction system: 50% ethylene monomer feed, 80 ° C to produce a polyethylene elastomer containing 15% carbon 8 branches (density 0.885g / cm 3 ), add main catalyst 1, co-catalyst 1, solvent, chain terminator, and ultra-low density matrix.

[0067] The second reaction system: 30% ethylene monomer is fed, and the second main catalyst, the second co-catalyst, the solvent, the chain terminator, and the comonomer are introduced to generate high crystalline barrier layer polyethylene.

[0068] The third reaction system: 20% ethylene monomer feed, introduction of main catalyst 3, co-catalyst 3, solvent, chain terminator, comonomer, to produce polyethylene with a self-adhesive layer (heat sealing strength> 3N / 15mm).

[0069] The first reactor 2, the second reactor 4 and the third reactor 6 are respectively sent to the slurry mixing tank 1 for stirring through the first slurry pump 3, the second slurry pump 5 and the third slurry pump 7 to produce polyethylene with the above-mentioned comprehensive characteristics, and then sent to the powder separator 12 through the fourth slurry pump 11 for separation of powder and solvent, and then sent to the powder dryer 13 for drying.

[0070] Example 2 is compared with existing products:

[0071] Table 2

[0072]

[0073]

[0074] As shown in Table 2, compared with conventional products on the market, the oxygen transmission rate and water vapor transmission rate of the product of Example 2 of the present invention are significantly reduced, achieving the purpose of high oxygen and moisture barrier.

[0075] The performance of this polyethylene product

[0076] 1. In-situ mixing enables the functional components to be dispersed at nanoscale;

[0077] 2. The product melt index has a wide adjustable range;

[0078] 3. The product density can be adjusted in a wide range;

[0079] 4. Reduce energy consumption compared to traditional blending process (save energy consumption of secondary melting).

[0080] Compared with the conventional mechanical blending process of pellets, the present invention has the following effects:

[0081] Serial number Advantages index 1 Functional component dispersion scale <100nm 2 The product melt index has a wide adjustable range 0.1-50g / 10min 3 Wide adjustable range of product density <![CDATA[0.860-0.960g / cm 3 ]]> 4 Processing energy consumption 28% lower than traditional process

[0082] The present invention is simple to operate, easy to use, and suitable for comprehensive promotion and application. Although the embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for continuously producing multifunctional modified polyethylene film material, characterized in that: The invention comprises a first reaction system, a second reaction system, a third reaction system and a slurry mixing tank (1), wherein the first reaction system, the second reaction system and the third reaction system are connected in parallel through pipelines and then connected to the slurry mixing tank (1) through pipelines; The first reaction system, the raw materials include a main catalyst, a co-catalyst, a solvent, a chain terminator and an ethylene monomer; The second reaction system, the raw materials include the second main catalyst, the second co-catalyst, the solvent, the chain terminator, the comonomer and the ethylene monomer; The third reaction system, the raw materials include main catalyst three, co-catalyst three, solvent, chain terminator, comonomer and ethylene monomer.

2. A process for continuously producing multifunctional modified polyethylene film material according to claim 1, characterized in that: The first reaction system comprises a first reactor (2), the first reactor (2) being connected to a first slurry pump (3) via a pipeline, the main catalyst 1 having a concentration of 5-10 mmol / L, the main catalyst feed flow rate of 5-10 mol / h, the co-catalyst 1 to main catalyst 1 having a molar ratio of 0-5:1, hydrogen being used as a chain terminator, the flow rate of which is 0.5-1.5 kg hydrogen / t ethylene monomer, the solvent being one of hexane, heptane or octane, the liquid level of the first reactor being 70-90%, the pressure of the first reactor (2) being 8.5-12 barg, and the temperature of the first reactor (2) being 20-40°C; and the solid-liquid ratio of the first reactor (2) being 1 ton polyethylene: (4-6) cubic solvent.

3. A process for continuously producing multifunctional modified polyethylene film material according to claim 2, characterized in that: The second reaction system includes a second reactor (4), which is connected to a second slurry pump (5) through a pipeline. The concentration of the main catalyst II is 10-30 mmol / L, the feed flow rate of the main catalyst II is 1.5-3.5 mol / h, the molar ratio of the co-catalyst II to the main catalyst II is 5-20:1, hydrogen is used as a chain terminator, and the flow rate is 3-6 kg hydrogen / t ethylene. The liquid level of the second reactor (4) is 70-90%, the pressure of the second reactor (4) is 6.0-1.0 barg, the temperature of the second reactor (4) is 75-85°C, the solid-liquid ratio of the second reactor (4) is 1 ton of polyethylene: (4-6) cubic solvents, and the comonomer flow rate is 2.5-6 kg / t ethylene monomer.

4. A process for continuously producing multifunctional modified polyethylene film material according to claim 3, characterized in that: Both the first reaction kettle (2) and the second reaction kettle (4) are provided with a stirrer.

5. The process for continuously producing multifunctional modified polyethylene film material according to claim 1, characterized in that: The third reaction system includes a third reactor (6), which is connected to a third slurry pump (7) through a pipeline. The third reactor (6) is a horizontal four-zone reactor, and the reaction heat is removed by using the latent heat of solvent evaporation. The concentration of the main catalyst III is 10-30 mmol / L, the feed flow rate of the main catalyst III is 1.5-3.5 mol / h, the molar ratio of the co-catalyst III to the main catalyst III is 5-20:1, hydrogen is used as a chain terminator, and the chain terminator is only fed into one zone at a flow rate of 3-12 kg hydrogen / t ethylene. The liquid level of the third reactor (6) is 40-60%, the pressure of the third reactor (6) is 6.0-1.0 barg, the temperature of the third reactor (6) is 75-85°C, the solid-liquid ratio of the third reactor (6) is 1 ton of polyethylene: (4-6) cubic solvent, and the comonomer feed ratio of each zone is zone 1: zone 2: zone 3: zone 4 = 0: (2-4): (6-10): (16-24).

6. A process for continuously producing multifunctional modified polyethylene film material according to claim 2, 3 or 5, characterized in that: The first reaction kettle (2), the second reaction kettle (4) and the third reaction kettle (6) are respectively connected to a first heat exchanger (8), a second heat exchanger (9) and a third heat exchanger (10) through pipelines.

7. The process for continuously producing multifunctional modified polyethylene film material according to claim 1, characterized in that: The slurry mixing tank (1) is provided with a multi-stage high-efficiency agitator.

8. The process for continuously producing multifunctional modified polyethylene film material according to claim 1, characterized in that: The slurry mixing tank (1) is connected to a fourth slurry pump (11), a powder separator (12) and a powder dryer (13) through pipelines.

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