Synthesis method of high-strength polyacrylonitrile

Abstract

The invention provides a high-strength polyacrylonitrile synthesis method. According to the method, acrylonitrile is used as a first monomer and is mixed with a second monomer and a third monomer according to a certain proportion, azodiisobutyronitrile is used as an initiator, and high-strength polyacrylonitrile is produced by adopting a unique mode and a water-phase suspension continuous polymerization method. The method has the advantages of high efficiency, low energy consumption, small safety risk, environmental friendliness, few product residual impurities and the like, can be used for producing polyacrylonitrile products with high relative molecular weight, good heat resistance and high strength, and is suitable for producing polyacrylonitrile products in different application fields.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyacrylonitrile, and relates to a method for synthesizing high-strength polyacrylonitrile. Background Art

[0002] Carbon fiber is a material with excellent physical properties, capable of withstanding high temperatures without losing strength. Carbon fiber is "soft on the outside and rigid on the inside", with a small density, very light material, lighter than aluminum metal, but having far higher strength than steel, and having advantages such as corrosion resistance and high toughness. It is essential in the fields of national defense, military, and civilian use, and plays an important role in supporting the transformation and upgrading of China's manufacturing industry and ensuring national defense security.

[0003] Although domestic carbon fiber technology and industry have made great progress, high-strength carbon fiber still cannot meet domestic demand. As the matrix of carbon fiber, polyacrylonitrile precursor is the key to determining the performance of carbon fiber. Only high-performance polyacrylonitrile precursor can produce high-performance carbon fiber. Among the many reasons restricting the development of carbon fiber in China, the backward level of polyacrylonitrile precursor is the biggest bottleneck.

[0004] The production processes of polyacrylonitrile mainly include homogeneous solution polymerization and aqueous precipitation polymerization. Homogeneous solution polymerization is one of the most commonly used methods in the production of polyacrylonitrile-based carbon fiber precursor. Its advantages are simple production process and fewer defects in polyacrylonitrile molecules, but there are problems such as small output, high cost, and high safety risks. The aqueous precipitation polymerization process has advantages such as large output, high efficiency, and low safety risks, but the strength of polyacrylonitrile is not high, and it is difficult to remove residual impurities in polyacrylonitrile, which affects the quality of carbon fiber. In addition, CN10126017B and CN101475665A respectively used azobisisobutyronitrile and azobisisoheptonitrile as initiators to prepare ultra-high molecular weight polyacrylonitrile by aqueous suspension polymerization method, but both are in batch mode, affecting production efficiency and making it difficult to achieve large-scale industrial production. Summary of the Invention

[0005] The technical problem to be solved by the present invention is, aiming at the current situation that the strength of polyacrylonitrile synthesized by aqueous precipitation polymerization method is not high, by using the research results of the unit in the synthesis of polyacrylonitrile polymer materials, to provide a method for synthesizing high-strength polyacrylonitrile with large output, high efficiency, and low safety risks, so as to promote the development of the carbon fiber industry.

[0006] The polyacrylonitrile production process adopted by the present invention is aqueous suspension continuous polymerization method. Compared with the conventional homogeneous solution polymerization method and aqueous precipitation polymerization method, this method takes the advantages of both, eliminates their disadvantages, reasonably formulates the process flow, reaction formula, and process parameters, produces high-strength polyacrylonitrile products that meet the requirements of the carbon fiber industry, and is applicable to the production of polyacrylonitrile products in different application fields.

[0007] The technical solution of the present invention is as follows:

[0008] A method for synthesizing high-strength polyacrylonitrile, comprising the following steps:

[0009] The first step: feeding acrylonitrile raw material, comonomer vinyl acetate, and comonomer methyl acrylate into a raw material mixing tank according to the required ratio, fully mixing under the action of a stirrer, and then delivering them to the bottom inlet of the reactor by a delivery pump, and at the same time, delivering the initiator azobisisobutyronitrile and the reaction medium pure water to the bottom inlet of the reactor according to the specified dosage by a delivery pump;

[0010] The reactor is a fully mixed kettle reactor with stirring. The outside of the reactor is a jacket structure, and refrigerant cooling water is introduced into the jacket to exchange heat in the reactor. The polymerization monomer, initiator and reaction medium are fully mixed and rapidly polymerized under the action of the reactor stirring paddle. In order to take away the reaction heat in time and maintain the temperature and pressure required for the reaction, promote the increase of polymer molecular weight and improve the conversion rate of monomer raw materials, it is necessary to control the reaction temperature in the reactor by adjusting the flow rate of refrigerant cooling water.

[0011] Step 2: The materials in the reactor all flow in from the bottom and out from the top. The mixed materials after the reaction are discharged from the upper discharge port of the reactor and enter the monomer removal distillation kettle. Steam is introduced from the bottom of the kettle for heating. The unreacted monomers and a part of the water are vaporized and enter the condenser from the gas phase outlet at the top of the distillation kettle. After being cooled, they are converted into liquid phase and enter the separator. The oil and water phases are separated in the separator, and the oil phase composed of the unreacted monomers is discharged from the upper part of the separator for reuse, and the condensed water is discharged from the bottom of the separator.

[0012] The third step: the polymer material from which unreacted monomers have been removed is taken out from the discharge port at the bottom of the distillation kettle and enters the vacuum drum filter. Under the action of vacuum filtration, the water in the polymer material passes through the filter screen, and the polymer particles are retained on the surface of the filter screen to form a wet filter cake, which is then washed by spraying the wet filter cake with washing water. The washing water is vacuum-sucked, passes through the wet filter cake and the filter screen, and merges with the water sucked from the polymer material to form a filtrate. The washed wet filter cake is scraped off the drum surface by a scraper and enters the drying unit.

[0013] Step 4: The wet filter cake first falls onto the distributor of the dryer and is evenly distributed on the drying net. Then hot air is introduced from under the drying net. The hot air slowly passes through the polymer bed on the drying net from the mesh holes, taking away the moisture in the polymer. The dried polymer is taken out from the discharge port at the rear of the dryer to obtain polyacrylonitrile.

[0014] Reaction raw material ratio:

[0015] Acrylonitrile raw material content: 80~99% (wt)

[0016] Comonomer vinyl acetate content: 0~10% (wt)

[0017] Content of comonomer methyl acrylate: 0 - 10% (wt)

[0018] Content of initiator azobisisobutyronitrile: 0.01 - 3.0%

[0019] Reaction medium pure water: reaction raw materials = 1 - 3:1

[0020] The production process conditions are as follows:

[0021] Reactor temperature: 50 - 70 °C

[0022] Reactor pressure: 100 - 300 Kpa

[0023] Temperature of monomer removal kettle: 80 - 110 °C

[0024] Pressure of monomer removal kettle: 0 - 100 Kpa

[0025] Vacuum filtration temperature: 40 - 90 °C

[0026] Pressure of vacuum filter: 0 - 50 Kpa

[0027] Drier temperature: 70 - 160 °C

[0028] The quality requirements of raw materials are as follows:

[0029] Purity of acrylonitrile raw material: ≥99.9%

[0030] Purity of comonomer vinyl acetate: ≥98.5%

[0031] Purity of comonomer methyl acrylate: ≥98.5%

[0032] Purity of initiator azobisisobutyronitrile: ≥99.0%

[0033] The beneficial effects of the present invention are as follows:

[0034] 1. Low material and energy consumption: The technology of the present invention is advanced, the process is reasonable, the reaction conversion rate of raw materials is high, the raw materials are fully utilized, and the material consumption is reduced.

[0035] 2. High efficiency and large production capacity; The specific heat capacity of water is large, which can quickly absorb and transfer the heat released by the polymerization reaction, improve the heat exchange speed, can greatly improve the production capacity of the reaction kettle, and has high production efficiency.

[0036] 3. High product quality: (1) Water is used as the polymerization reaction medium, and there is no chain transfer reaction to the solvent, which reduces the probability of defects such as molecular branching, and is conducive to the preparation of high relative molecular weight polyacrylonitrile products. (2) Vinyl acetate and acrylate are used to modify acrylonitrile polymers to reduce the brittleness of acrylonitrile polymers, improve elasticity and toughness, and help improve the strength of polyacrylonitrile precursors. (3) This synthesis method uses azobisisobutyronitrile as an initiator, and uses a self-designed polymerization reaction system and monomer removal system to reduce impurity residues in the polymer, which is conducive to the preparation of high-strength carbon fibers.

[0037] 4. Safe and environmentally friendly; water replaces organic solvents to improve the safety of polymerization reactions and reduce environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the process flow of the present invention;

[0039] Wherein: 1-acrylonitrile raw material, 2-comonomer vinyl acetate, 3-comonomer methyl acrylate, 4-initiator azobisisobutyronitrile, 5-reaction medium pure water, 6-raw material mixing tank, 7-reactor, 8-cooling water, 9 distillation kettle, 10, condenser, 11-liquid separation tank, 12-unreacted monomer, 13-condensed water, 14-water vapor, 15-vacuum drum filter, 16-washing water, 17-filtrate, 18-dryer, 19-hot air, 20-polyacrylonitrile. DETAILED DESCRIPTION

[0040] The process scheme of the present invention is mainly divided into four parts: polymerization unit, monomer removal and recovery unit, filtration and washing unit and drying unit. Figure 1 Process flow diagram, illustrating the best implementation of the present invention:

[0041] A method for synthesizing high-strength polyacrylonitrile, comprising the following steps:

[0042] The first step: feeding acrylonitrile raw material 1, comonomer vinyl acetate 2, and comonomer methyl acrylate 3 into a raw material mixing tank 6 according to the required ratio, fully mixing under the action of a stirrer, and then delivering them to the bottom inlet of a reactor 7 by a delivery pump, and at the same time, delivering an initiator azobisisobutyronitrile 4 and a reaction medium pure water 5 to the bottom inlet of the reactor according to the specified dosage by a delivery pump;

[0043] The described reactor 7 is in the form of a fully mixed tank reactor with stirring. The outside of the reactor 7 has a jacket structure, and refrigerant cooling water 8 is introduced into the jacket for heat exchange of the reactor; the polymerization monomers, initiator, and reaction medium are fully mixed under the action of the reactor stirring paddle and rapidly undergo a polymerization reaction. In order to timely remove the reaction heat and maintain the temperature and pressure required for the reaction, promote the increase of the polymer molecular weight and improve the conversion rate of the monomer raw materials, it is necessary to control the reaction temperature in the reactor by adjusting the flow rate of the refrigerant cooling water 8.

[0044] Second step: The material flow direction in the reactor 7 is all from bottom to top. The reacted mixed material is discharged from the upper discharge port of the reactor 7 and enters the monomer removal distillation kettle 9. Steam 14 is introduced from the bottom of the kettle for heating. The unreacted monomer and a part of the water are vaporized and enter the condenser 10 from the top gas outlet of the distillation kettle. After being cooled, it is transformed into a liquid phase and enters the separation tank 11; in the separation tank 11, oil and water are separated. The oil phase composed of the unreacted monomer 12 is discharged from the upper part of the separation tank 11 for reuse, and the condensed water 13 is discharged from the bottom of the separation tank 11.

[0045] Third step: The polymer material from which the unreacted monomer 12 has been removed is taken out from the bottom discharge port of the distillation kettle and enters the vacuum drum filter 15. Under the action of vacuum filtration, the water in the polymer material passes through the filter screen, and the polymer particles are retained on the surface of the filter screen to form a wet filter cake. Then, the wet filter cake is washed by spraying washing water 16. The washing water 16 is vacuum suctioned, passes through the wet filter cake and the filter screen, and is collected together with the water suctioned out from the polymer material to form a filtrate 17; the washed wet filter cake is scraped off from the surface of the drum by a scraper and enters the drying unit.

[0046] Fourth step: The wet filter cake first falls onto the distributor of the dryer 18 and is evenly distributed on the drying net. Then, hot air 19 is introduced from below the drying net. The hot air slowly passes through the polymer bed layer on the drying net from the mesh holes, taking away the moisture in the polymer. The dried polymer is taken out from the discharge port at the tail of the dryer to obtain polyacrylonitrile 20.

[0047] Example 1:

[0048] Reaction raw material ratio:

[0049] Acrylonitrile content: 97% (wt)

[0050] Vinyl acetate content: 1.5% (wt)

[0051] Methyl acrylate content: 1.5% (wt)

[0052] Content of initiator azobisisobutyronitrile: 0.8% (wt)

[0053] Pure water (kg) of reaction medium: reaction raw materials (kg) = 1.5:1

[0054] The main production process conditions are as follows:

[0055] Reactor temperature: 60°C

[0056] Reactor pressure: 100 - 150 Kpa

[0057] Temperature of monomer removal kettle: 85 - 105°C, Pressure of monomer removal kettle: 20 - 60 Kpa

[0058] Vacuum filtration temperature: 60 - 80°C, Vacuum filtration pressure: 10 - 40 Kpa.

[0059] Drier temperature: 85 - 140°C, Main quality indicators of polyacrylonitrile products:

[0060] Moisture content: ≤1.5%

[0061] Viscosity-average molecular weight: 1.2×10 6

[0062] DSC exothermic temperature Tp: 320°C

[0063] TG weight loss temperature Tf: 440°C, Tensile strength: 7.8 cN / dtex

[0064] Example 2:

[0065] Reaction raw material ratio:

[0066] Acrylonitrile content: 96% (wt)

[0067] Vinyl acetate content: 0% (wt)

[0068] Methyl acrylate content: 4.0% (wt)

[0069] Content of initiator azobisisobutyronitrile: 0.7% (wt)

[0070] Reaction medium pure water (kg): Reaction raw materials (kg) = 1.5:1, The main production process conditions are as follows:

[0071] Reactor temperature: 60°C

[0072] Reactor pressure: 100 - 150 Kpa

[0073] Temperature of monomer removal kettle: 85 - 105°C, Pressure of monomer removal kettle: 20 - 60 Kpa

[0074] Vacuum filtration temperature: 60 - 80°C, Vacuum filtration pressure: 10 - 40 Kpa.

[0075] Drier temperature: 85 - 140°C, Main quality indicators of polyacrylonitrile products:

[0076] Water content: ≤1.5%

[0077] Viscosity-average molecular weight: 1.3×10 6 DSC exothermic temperature Tp: 328 °C

[0078] TG weight loss temperature Tf: 450 °C Tensile strength: 8.6 cN / dtex

[0079] Example 3:

[0080] Acrylonitrile content: 80% (wt)

[0081] Vinyl acetate content: 10% (wt)

[0082] Methyl acrylate content: 10% (wt)

[0083] Content of initiator azobisisobutyronitrile: 3.0% (wt) Reaction medium pure water (kg): Reaction raw materials (kg) = 1:1 The main production process conditions are as follows:

[0084] Reactor temperature: 50 °C.

[0085] Reactor pressure: 100 - 150 Kpa.

[0086] Temperature of monomer removal kettle: 80 - 110 °C.

[0087] Pressure of monomer removal kettle: 40 - 100 Kpa.

[0088] Vacuum filtration temperature: 60 - 90 °C.

[0089] Pressure of vacuum filter: 0 - 50 Kpa.

[0090] Drier temperature: 70 - 160 °C.

[0091] Raw material quality requirements are as follows:

[0092] Acrylonitrile purity: ≥99.9%

[0093] Vinyl acetate purity: ≥98.5%

[0094] Methyl acrylate purity: ≥98.5%

[0095] Azobisisobutyronitrile purity: ≥99.0%

[0096] Main quality indicators of polyacrylonitrile products:

[0097] Water content: ≤1.5%

[0098] Viscosity-average molecular weight: 1.5×10 6 DSC exothermic temperature Tp: 325 °C

[0099] TG weight loss temperature Tf: 446 °C Tensile strength: 8.8 cN / dtex

[0100] Example 4:

[0101] Reaction raw material ratio:

[0102] Acrylonitrile content: 99% (wt)

[0103] Vinyl acetate content: 1% (wt)

[0104] Methyl acrylate content: 0% (wt)

[0105] Content of initiator azobisisobutyronitrile: 0.01% (wt) Reaction medium pure water (kg): Reaction raw materials (kg) = 3:1 The main production process conditions are as follows:

[0106] Reactor temperature: 70 °C.

[0107] Reactor pressure: 150 - 300 Kpa.

[0108] Monomer removal kettle temperature: 80 - 100 °C.

[0109] Monomer removal kettle pressure: 0 - 80 Kpa.

[0110] Vacuum filtration temperature: 40 - 80 °C.

[0111] Vacuum filter pressure: 0 - 50 Kpa.

[0112] Dryer temperature: 70 - 160 °C.

[0113] Raw material quality requirements are as follows:

[0114] Acrylonitrile purity: ≥ 99.9%

[0115] Vinyl acetate purity: ≥ 98.5%

[0116] Methyl acrylate purity: ≥ 98.5%

[0117] Azobisisobutyronitrile purity: ≥ 99.0%

[0118] Main quality indicators of polyacrylonitrile products:

[0119] Moisture content: ≤ 1.5%

[0120] Viscosity-average molecular weight: 1.8×10 6

[0121] DSC exothermic temperature Tp: 330 °C

[0122] TG weight loss temperature Tf: 452 °C

[0123] Tensile strength: 9.2 cN / dtex

[0124] In summary, the technical route implemented by the present invention has the advantages of high efficiency, low energy consumption, small environmental pollution and high product quality. It can produce polyacrylonitrile products with high relative molecular weight and good thermal properties, and is a relatively advanced polyacrylonitrile synthesis method suitable for multi-target products at present.

Claims

1. A method for synthesizing high-strength polyacrylonitrile, characterized in that: Here are the steps: The first step is to feed acrylonitrile raw material (1), comonomer vinyl acetate (2), and comonomer methyl acrylate (3) into a raw material mixing tank (6) according to a required ratio, and after being fully mixed under the action of a stirrer, the raw materials are delivered to the bottom inlet of a reactor (7) by a delivery pump. At the same time, an initiator azobisisobutyronitrile (4) and a reaction medium pure water (5) are delivered to the bottom inlet of the reactor by a delivery pump according to a specified dosage; Step 2: The materials in the reactor (7) all flow from the bottom to the top. The mixed material after the reaction is discharged from the upper discharge port of the reactor (7) and enters the monomer removal distillation kettle (9). Water vapor (14) is introduced from the bottom of the kettle for heating. The unreacted monomers (12) and a part of the water are vaporized and enter the condenser (10) from the gas phase outlet at the top of the distillation kettle. After being cooled, they are converted into liquid phase and enter the separator (11); oil and water are separated in the separator (11), and the oil phase composed of the unreacted monomers (12) is discharged from the upper part of the separator (11) for reuse, and the condensed water (13) is discharged from the bottom of the separator (11); Step 3: The polymer material from which unreacted monomers (12) are removed is taken out from the discharge port at the bottom of the distillation kettle and enters the vacuum drum filter (15). Under the action of vacuum filtration, water in the polymer material passes through the filter screen, and polymer particles are retained on the surface of the filter screen to form a wet filter cake. The wet filter cake is then sprayed with washing water (16) for washing. The washing water (16) is vacuum-sucked, passes through the wet filter cake and the filter screen, and merges with the water sucked from the polymer material to form a filtrate (17). The washed wet filter cake is scraped off the drum surface by a scraper and enters the drying unit. Step 4: The wet filter cake first falls onto the distributor of the dryer (18) and is evenly distributed on the drying net. Then, hot air (19) is introduced from under the drying net. The hot air slowly passes through the polymer bed on the drying net from the mesh, taking away the moisture in the polymer. The dried polymer is taken out from the discharge port at the rear of the dryer to obtain polyacrylonitrile (20).

2. A method for synthesizing high-strength polyacrylonitrile according to claim 1, characterized in that: The reactor (7) is in the form of a fully mixed kettle reactor with stirring. The outside of the reactor (7) is a jacket structure, and the jacket is passed through the refrigerant cooling water (8) to exchange heat in the reactor. The polymerization monomer, initiator and reaction medium are fully mixed and rapidly polymerized under the action of the reactor stirring paddle. In order to timely remove the reaction heat and maintain the temperature and pressure required for the reaction, promote the increase of polymer molecular weight and improve the monomer raw material conversion rate, it is necessary to control the reaction temperature in the reactor by adjusting the flow rate of the refrigerant cooling water (8).

3. A method for synthesizing high-strength polyacrylonitrile according to claim 1, characterized in that: The acrylonitrile raw material content is 80-99% (wt); the comonomer vinyl acetate content is 0-10% (wt); the comonomer methyl acrylate content is 0-10% (wt); the initiator azobisisobutyronitrile content is 0.01-3.0% (wt); the reaction medium pure water (kg): reaction raw material (kg) = 1-3:

1.

4. A method for synthesizing high-strength polyacrylonitrile according to claim 1, characterized in that: The temperature of the reactor (7) is 50 to 70°C; the pressure of the reactor (7) is 100 to 300 KPa; the temperature of the monomer removal distillation kettle (9) is 80 to 110°C; the pressure of the monomer removal distillation kettle (9) is 0 to 100 KPa; the vacuum filtration temperature is 40 to 90°C; the vacuum filter pressure is 0 to 50 KPa; the temperature of the dryer (18) is 70 to 160°C.

5. A method for synthesizing high-strength polyacrylonitrile according to claim 1, characterized in that: The purity of the acrylonitrile raw material is ≥99.9%; the purity of the comonomer vinyl acetate is ≥98.5%; The purity of the copolymer monomer methyl acrylate is ≥98.5%; the purity of the initiator azobisisobutyronitrile is ≥99.0%.

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