CN116284558B

CN116284558B - Preparation method of spinning dope for PAN-based carbon fiber precursor and preparation method of PAN-based carbon fiber precursor

Info

Publication number: CN116284558B
Application number: CN202310565094.6A
Authority: CN
Inventors: 宋德武; 李凯; 刘海亮; 陈浩; 沈怀宇
Original assignee: Jilin Chemical Fiber Group Co ltd; Jilin Carbon Valley Carbon Fiber Ltd By Share Ltd
Current assignee: Jilin Chemical Fiber Group Co ltd; Jilin Carbon Valley Carbon Fiber Ltd By Share Ltd
Priority date: 2023-05-19
Filing date: 2023-05-19
Publication date: 2023-08-04
Anticipated expiration: 2043-05-19
Also published as: CN116284558A

Abstract

The invention discloses a preparation method of a spinning dope for PAN-based carbon fiber precursors and a preparation method of PAN-based carbon fiber precursors, wherein the preparation method of the spinning dope for PAN-based carbon fiber precursors comprises the following steps: (1) Mixing acrylonitrile, itaconic acid, azodiisobutyronitrile and dimethyl sulfoxide to obtain a raw material liquid; (2) filtering the raw material liquid; (3) The filtered raw material liquid is subjected to polymerization reaction in a polymerization kettle to obtain a polymerization liquid; (4) The polymer solution is subjected to single removal, concentration and filtration treatment to obtain the spinning solution. According to the invention, the spinning solution for spinning is obtained by mixing the raw materials and performing one-step polymerization, and the raw material solution is subjected to polymerization reaction after being filtered, so that impurities in the raw materials can be removed, thereby improving the conversion efficiency of the polymerization reaction and the polymerization degree of a polymerization product, avoiding the influence of the impurities on the spinning process of the spinning solution, and being beneficial to improving the quality of the spinning solution obtained by spinning.

Description

Preparation method of spinning dope for PAN-based carbon fiber precursor and preparation method of PAN-based carbon fiber precursor

Technical Field

The invention belongs to the technical field of carbon fiber manufacturing and application, and particularly relates to a preparation method of a spinning solution for PAN-based carbon fiber precursor and a preparation method of PAN-based carbon fiber precursor.

Background

Carbon fiber is a high strength ratio, high specific modulus, reinforced and functional fiber material, which is a high-tech product developed rapidly in the 60 s of the 20 th century. The composite material has low density, heat resistance, chemical corrosion resistance, friction resistance, thermal shock resistance, electric conduction, heat conduction, radiation resistance, good damping, shock absorption, noise reduction and other comprehensive properties, and is widely applied to a plurality of fields such as sports equipment, entertainment and leisure, tourism facilities, automobile components, train parts, aircraft manufacturing, electric power, petroleum, chemical industry, navigation, biomedicine, building, strategic missiles, bulletproof armor and the like.

The main raw material of the high-strength carbon fiber is Polyacrylonitrile (PAN) -based carbon fiber precursor, and the quality of the precursor determines the quality of the carbon fiber to a great extent. In the prior art, a one-step production method of PAN-based carbon fiber precursor is adopted, namely, acrylonitrile and other comonomers are added into a reaction kettle together with a solvent to be mixed, and after a certain time under a certain temperature and atmosphere, the mixture is polymerized to form a spinning solution containing polyacrylonitrile with a certain molecular weight, and the spinning solution can be directly used for preparing the PAN-based carbon fiber precursor by spinning.

However, when the PAN-based carbon fiber precursor is prepared by the method, the polymerization process is difficult to control, the problem of gel easily occurs in the production process, the conversion rate of the polymerization reaction is reduced, and the polymerization degree of the polymerization product is low. Further spinning with the obtained spinning dope may affect the quality of the obtained PAN-based carbon fiber precursor and the carbon fiber produced from the precursor.

Therefore, in order to obtain high quality carbon fibers, improvements in the compounding process are required to improve the quality of the spinning dope and the filaments when preparing PAN-based carbon fiber filaments. The spinning dope and the precursor with higher quality can produce the carbon fiber with higher strength. The obtained high-strength carbon fiber can be used for manufacturing structures such as blades in wind turbines, and has good application prospects.

In view of this, the present invention has been made.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a preparation method of a spinning solution for PAN-based carbon fiber precursor and a preparation method of PAN-based carbon fiber precursor, wherein the preparation process of the spinning solution can avoid the influence of impurities in raw materials, and plays roles of improving the conversion efficiency of polymerization reaction and the polymerization degree of a polymerization product.

In order to solve the technical problems, the invention adopts the basic conception of the technical scheme that:

the first object of the invention is to provide a preparation method of a spinning dope for PAN-based carbon fiber precursor, which comprises the following steps:

(1) Mixing acrylonitrile, itaconic acid, azodiisobutyronitrile and dimethyl sulfoxide to obtain a raw material liquid;

(2) Filtering the raw material liquid;

(3) The filtered raw material liquid is subjected to polymerization reaction in a polymerization kettle to obtain a polymerization liquid;

(4) The polymer solution is subjected to single removal, concentration and filtration treatment to obtain the spinning solution.

In the above scheme, acrylonitrile and itaconic acid are used as comonomers, and the polymerization reaction is carried out in dimethyl sulfoxide (DMSO) as a solvent by initiating with Azodiisobutyronitrile (AIBN) to obtain a polymerization solution containing a polymerization product. The obtained polymer solution is subjected to subsequent treatment of single removal, concentration and filtration, and then the spinning solution which can be directly used for spinning is obtained.

In the preparation process of the spinning solution, the raw material solution formed by mixing various production raw materials is filtered, and then enters a polymerization kettle for polymerization reaction, so that impurities in the raw materials can be removed. In particular, impurities contained in acrylonitrile, such as metallic iron, copper, organic derivatives, etc., which cause chain transfer of the high molecular polymer, decrease in conversion during polymerization, and decrease in polymerization degree of the polymerization product, may also undergo self-polymerization reaction and addition reaction with acrylonitrile, further affecting polymerization reaction.

According to the invention, impurities in raw materials are removed by adding a step of filtering treatment, so that the conversion rate or conversion efficiency of the polymerization reaction in the step (3) is improved, and meanwhile, the polymerization degree of a polymerization product is improved.

Further, in the step (2), the filtering accuracy of the filtering treatment of the raw material liquid is 0.5 to 1.0 μm, and the filtering accuracy is preferably 0.5 μm;

preferably, the raw material liquid is subjected to two-stage filtration treatment;

more preferably, the raw material liquid sequentially passes through a cartridge filter and a disc filter to realize two-stage filtration treatment.

In the scheme, the filtering precision is controlled within a proper range, so that impurities affecting the polymerization reaction can be filtered, the polymerization effect is ensured, and the problem of loss of production raw materials participating in the polymerization reaction in raw material liquid is also reduced.

Further, in the step (3), the temperature in the polymerization kettle is controlled to be 58-60 ℃, and the polymerization reaction is carried out in a micro-positive pressure environment which is 30-50 Pa higher than the external air pressure of the polymerization kettle, wherein the reaction time is 12-23 h, preferably 13-15 h, and more preferably 13.5h;

Preferably, the conversion of the polymerization reaction is 90% to 95%.

The polymerization of acrylonitrile is a free radical addition polymerization, and the polyaddition reaction of small molecular monomers is an exothermic process, so that the reaction temperature is strictly controlled during the reaction. In the invention, each addition polymerization needs to open one pi bond of olefin, two sigma single bonds are generated at the same time, energy is required to be absorbed when the pi bond is opened, energy can be released when the two sigma single bonds are generated, and the heat can be released by about 73.3kJ/mol in the whole reaction process.

Specifically, in the present invention, the polymer isIntroducing nitrogen into a polymerization kettle to form a micro-positive pressure environment with pressure 30-50 Pa higher than external pressure in the polymerization kettle, and strictly controlling the temperature of the polymerization kettle within 58-60 ℃ through a hot water circulation temperature control system so as to control the reaction process in the polymerization kettle to control the polymerization product, namely the relative molecular weight of the generated polymer to be 0.8x10 ⁵ ～2.5×10 ⁵ 。

It is found that if the raw material liquid is directly subjected to polymerization reaction without filtration, the exothermic rate of the polymerization kettle reaction is affected, the kettle temperature is easy to be unstable, and the conversion rate of the polymerization reaction is not easy to be controlled. In the invention, the filtered raw material liquid is adopted to carry out the polymerization reaction, and meanwhile, the technological parameters are controlled in the polymerization reaction process, so that the polymerization reaction process can be completed within 12-23 hours, and the conversion rate can reach about 95%. Compared with the scheme that the reaction time of the traditional process generally needs about 35 hours, the production efficiency of the spinning solution is obviously improved.

Further, in the step (3), the dynamic viscosity range of the obtained polymer solution is controlled to be 40-60 pa.s, and then the step (4) is continued, and the polymer solution is subjected to the processes of desingulation, concentration and filtration to prepare a spinning stock solution.

Because of the correlation between the molecular weight and the viscosity of the polymer, when the dynamic viscosity of the polymer solution obtained by the polymerization reaction is 40-60 pa.s, the polymerization reaction is fully carried out, and the dynamic viscosity is further increased after the subsequent processes of removing monomers, concentrating and filtering, so as to obtain the spinning stock solution with the dynamic viscosity of 65-70 pa.s. The spinning dope with the viscosity range can be fed into a spinning dope storage tank for spinning to prepare PAN-based carbon fiber precursor. If the viscosity is outside the above range, the polymerization reaction is insufficient, and the obtained dope may affect the quality of the filaments to be produced later.

Further, in the step (4), the polymer solution is subjected to the processes of desingulation, concentration and filtration to prepare a spinning solution, which comprises the following steps:

carrying out single removal treatment on the polymerization solution under the reduced pressure condition of-65 to-101 kPa to remove unreacted monomers;

filtering the polymerization solution subjected to the single removal treatment with the filtering precision of 0.5-0.8 mu m, and concentrating the polymerization solution under the pressure of-88 to-101 kPa;

After concentration treatment, the polymer solution is subjected to primary filtration with the filtration precision of 0.5-0.8 mu m, and then is subjected to secondary filtration with the filtration precision of 0.2-0.3 mu m to obtain spinning stock solution;

preferably, the concentrated polymer solution is subjected to primary filtration by a plate-and-frame filter having a filtration accuracy of 0.5 μm, and then to secondary filtration by a disc filter having a filtration accuracy of 0.3. Mu.m.

Specifically, the process of removing monomers refers to removing residual monomers in the polymerization solution by vacuum. In the invention, the polymerization liquid led out from the polymerization kettle enters a single removal tower, and unreacted monomers are removed under the condition of reduced pressure of-65 to-101 kPa, so that the residual quantity is reduced to below 0.1 percent by mass. The polymerized liquid after the single removal treatment is filtered once, is fed from the top of a concentration tower, is uniformly mixed by a filler, is concentrated and defoamed on tower internals which are shaped like humps, and then is sequentially filtered by a plate frame filter and a disc filter, and can be collected in a spinning solution storage tank to wait to be sent to a spinning unit for spinning.

Further, in the step (1), itaconic acid and dimethyl sulfoxide are mixed to obtain a monomer solution, azodiisobutyronitrile and dimethyl sulfoxide are mixed to obtain an initiator solution, and then the monomer solution and the initiator solution are mixed with acrylonitrile and dimethyl sulfoxide to obtain a raw material liquid;

Preferably, the mass ratio of itaconic acid to dimethyl sulfoxide is 1:3.0 to 1:5.0 to obtain the monomer solution, preferably according to a mass ratio of 1:3.8 to 1:4.2, mixing to obtain the monomer solution;

the mass ratio of the azodiisobutyronitrile to the dimethyl sulfoxide is 1:13.0 to 1:14.5 mixing to obtain the initiator solution, preferably according to a mass ratio of 1:13.5 to 1:14.2 mixing to obtain the initiator solution.

In the scheme, itaconic acid and AIBN in the production raw materials are solid raw materials, and are respectively mixed with DMSO as a solvent to form a liquid form, and then are fed into a polymerization kettle, so that the method is more suitable for an industrial production process, and uniform mixing of the production raw materials is ensured.

Specifically, AIBN and DMSO are added into an AIBN preparation tank according to a proportion, stirred and dissolved to prepare an initiator solution, and then fed into a polymerization kettle.

Further, in the step (1), the mixture ratio of the prepared raw material liquid is as follows:

1200-1400 parts by weight of acrylonitrile;

110-130 parts by weight of monomer solution;

110-130 parts of dimethyl sulfoxide;

0.5 to 1.5 weight portions of initiator solution;

preferably, the ratio is:

1300 parts by weight of acrylonitrile;

125 parts by weight of a monomer solution;

125 parts by weight of dimethyl sulfoxide;

1 part by weight of an initiator solution.

Further, in the step (1), acrylonitrile as a raw material is obtained by mixing acrylonitrile from an acrylonitrile tank with recovered acrylonitrile from an acrylonitrile recovery tank, and a mass ratio of the acrylonitrile from the acrylonitrile tank to the recovered acrylonitrile is 8:1 to 10:1, preferably 10:1.

specifically, acrylonitrile from an acrylonitrile storage tank and recovered acrylonitrile from an acrylonitrile recovery tank are respectively sent to a mixer to be mixed, and then are sent to an acrylonitrile metering tank, and the acrylonitrile metering tank is used for feeding materials into a polymerization kettle according to the raw material proportion.

Preferably, the recovered acrylonitrile is obtained by rectification in the process of the polymerization liquid for the dealkylation treatment.

Specifically, the polymerization solution led out from the polymerization kettle enters a single removal tower for single removal treatment, unreacted acrylonitrile can be removed from the polymerization solution by the single removal tower, and recovered acrylonitrile with purity meeting the requirement is obtained after rectification treatment.

Further, in the step (1), DMSO as a raw material is obtained by mixing DMSO having a purity of 99% from a DMSO tank and the recovered DMSO having a purity of 99%.

Specifically, the spinning dope prepared in the invention is sent to a spinning unit for spinning so as to obtain PAN-based carbon fiber precursors. In the spinning unit, the PAN-based carbon fiber precursor is obtained after the spinning solution is subjected to the process steps of spinning, solidification forming, water washing, drafting and the like. In the process steps, particularly in the processes of solidification molding and water washing, the separated solution containing DMSO is sent to a recovery unit, and the solution is purified to 99% purity after multistage dehydration and rectification, so that the recovery and the utilization of DMSO can be realized.

In the preparation method, the preparation and polymerization of the raw material liquid in the steps (1) to (3) are batch processes, and the processes of the removal, concentration and filtration in the step (4) are continuous processes.

Specifically, in the invention, each production raw material is sent into different metering containers from respective storage devices, then is fed into a raw material liquid preparation kettle from each metering container according to the raw material proportion, and is stirred and mixed uniformly in the raw material liquid preparation kettle to obtain the raw material liquid. The feeding process is a batch process, namely, the feeding is stopped after the feeding amount reaches a certain amount.

The raw material liquid evenly mixed in the raw material liquid preparation kettle is conveyed by a raw material liquid conveying pump, and is filtered in a raw material liquid filtering device, wherein the raw material liquid filtering device comprises a cartridge filter and a disc filter for realizing two-stage filtering treatment, and is conveyed into a raw material liquid storage tank after being filtered. The constant amount of the raw material liquid in the raw material liquid storage tank is pumped into a batch polymerization kettle for polymerization reaction, and after the polymerization reaction is completed, the obtained polymerization liquid is sent into a polymerization liquid buffer tank for collection.

The polymerization solution in the polymerization solution buffer tank can be continuously conveyed to a single-removing tower for single-removing treatment, and then continuous concentration and filtration treatment are continuously carried out, so that the spinning solution is finally obtained.

In the scheme, the preparation of the raw material liquid and the polymerization reaction are carried out in an intermittent mode, and in the actual production process, the performance of the polymerization liquid obtained from each batch can be detected, so that the staged detection in the production process is realized, and the technological parameters are flexibly adjusted according to the detection result and the production requirement. If a continuous production mode is adopted, the production line is stopped to perform detection or process adjustment, so that the production efficiency is seriously affected.

In the preparation method of the invention, the process adjustment which may need to be carried out generally occurs before the polymerization reaction is finished, so that the continuous treatment mode can be adopted for the subsequent processes of removing the sheet, concentrating and filtering, thereby achieving higher production efficiency.

A second object of the present invention is to provide a spinning dope for polyacrylonitrile-based carbon fiber precursors, which has a kinetic viscosity of 60 to 75pa.s, preferably 65 to 70pa.s;

preferably, the spinning solution is prepared by the preparation method of the spinning solution for PAN-based carbon fiber precursor.

The third object of the present invention is to provide a method for preparing PAN-based carbon fiber precursors, comprising the steps of:

A. controlling the temperature of the spinning solution to be 25-35 ℃, filtering and then conveying to a spinning component;

B. spinning the spinning solution in air by a spinning component;

C. the sprayed tows enter a coagulating bath, and are coagulated to form nascent fibers;

D. the primary fiber is subjected to washing drafting, oiling, drying and steam drafting to obtain PAN-based carbon fiber precursor;

the spinning solution in the step A is prepared by the preparation method of the spinning solution for PAN-based carbon fiber precursor.

In the scheme, the PAN-based carbon fiber precursor is prepared from the spinning solution by adopting a dry-jet wet spinning method. As the filtering step of the raw material liquid obtained by mixing production raw materials is added in the preparation process of the spinning raw material liquid, the polymer in the spinning raw material liquid is more uniformly distributed, so that the yarn breakage rate and the yarn breakage rate in the spinning process can be reduced, and the PAN-based carbon fiber precursor with better mechanical property can be obtained.

In the step B, the height of an air layer of spinning in the air is 1-5 mm, the humidity of the air layer is 20-60%, and the temperature of the air layer is 25-35 ℃; in the step C, the coagulating liquid in the coagulating bath is DMSO water solution, the concentration is 20-40%, and the temperature is 2-10 ℃;

Preferably, in the step B, the height of an air layer of spinning in air is 2-4 mm, the humidity of the air layer is 40-50%, and the temperature of the air layer is 25-30 ℃; in the step C, the concentration of the DMSO aqueous solution in the coagulating bath is 25-32%, and the temperature is 3-5 ℃.

Further, in the step D, the nascent fiber is subjected to multi-channel washing drafting, wherein the washing temperature is 30-40 ℃, and the total drafting multiple of the washing drafting is 1.5-3.0 times;

and/or, the fibers after water washing enter an oil feeding groove for oiling, the oiling agent temperature is 20-30 ℃, and the draft multiple in the oil feeding groove is 1.5-3.0 times;

and/or, drying the fibers after oiling at the temperature of 120-160 ℃, wherein the draft multiple in the drying process is 1.0-1.5 times;

and/or, the dried fiber is drafted again in a high-pressure steam draft box at a draft multiple of 2-5 times in saturated steam of 0.5-1.6 MPa.

In the scheme, the filtering step of raw material liquid obtained by mixing production raw materials is added in the preparation process of the spinning raw material liquid, and the hole structure in the fiber can be reduced in the spinning process, so that high-power drafting can be applied in the spinning process, and broken filaments or broken filaments are not easy to occur. However, if unfiltered raw material liquid is directly polymerized to prepare spinning raw material liquid, tests show that if high-power drafting is applied in the spinning process, phenomena of yarn breakage and broken yarn easily occur, and the quality and yield of the raw yarn are affected. Meanwhile, the unfiltered raw material liquid is directly polymerized to prepare spinning raw material liquid, and the spinning raw material liquid cannot adapt to low-multiple drafting, and the spinning raw material liquid is solidified during spinning, so that nascent fibers cannot be formed.

Tests also show that when PAN-based carbon fiber precursors are prepared by adopting spinning solutions prepared from unfiltered raw material solutions, and the obtained precursors are further prepared into carbon fibers, the carbonization temperature cannot be increased in the carbonization process. The method is characterized in that under the condition that raw material liquid is not filtered, a large amount of impurity elements exist in the prepared spinning raw material liquid, defect holes exist in fibers due to the fact that the impurity elements exist in the raw material liquid in the spinning process, and the defect holes are further amplified due to cracking reaction in the high-temperature carbonization process, so that a yarn breakage phenomenon is generated. Therefore, when carbonizing a fiber with excessive impurities in the precursor, the carbonization temperature cannot reach a higher level in a high temperature region, and the strength and modulus of the carbon fiber are affected, so that the high-strength carbon fiber cannot be obtained.

A fourth object of the present invention is to provide a PAN-based carbon fiber precursor having a strength of 6.0 to 13.5CN/dtex, preferably 11.0 to 12.0CN/dtex;

preferably, the PAN-based carbon fiber precursor is prepared by the preparation method of the PAN-based carbon fiber precursor.

By adopting the technical scheme, compared with the prior art, the invention has the following beneficial effects.

1. In the invention, after the raw materials are mixed to obtain the raw material liquid, the raw material liquid is filtered and then is sent into a polymerization kettle for polymerization reaction, so that impurities in the raw materials can be removed before polymerization, and the influence of the impurities on the polymerization effect is avoided. The impurity in the raw materials is removed through advanced filtration, so that the polymerization degree and conversion rate can be improved, and further the influence of the impurity on the precursor or carbon fiber prepared from the obtained spinning dope is eliminated.

2. In the invention, the raw material liquid formed by mixing the production raw materials is intermittently polymerized to obtain the polymerized liquid, and the obtained polymerized liquid is collected and then subjected to subsequent treatment of single removal, concentration and filtration in a continuous mode, so that flexible process adjustment is conveniently carried out on the steps before the polymerized liquid is obtained in the production process, and meanwhile, the production efficiency is ensured to the greatest extent.

3. The PAN-based carbon fiber precursor prepared by the method has the advantages of light specific gravity and low density, has high strength and high modulus, is thin and soft, can be used for preparing high-performance carbon fibers, has excellent mechanical properties and wide application, and can be used for preparing high-strength carbon fibers, and particularly can be used for preparing blades in wind motors or other structures requiring high strength.

The following describes the embodiments of the present invention in further detail with reference to the accompanying drawings.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. It is evident that the drawings in the following description are only examples, from which other drawings can be obtained by a person skilled in the art without the inventive effort. In the drawings:

FIG. 1 is a schematic flow chart of the preparation of the spinning dope in the present invention;

FIG. 2 is a process flow diagram of a spinning unit in accordance with the present invention;

FIG. 3 is a schematic diagram of a recovery unit in the present invention;

fig. 4 is a schematic diagram of the invention employing condensate as the power source for a liquid jet vacuum system.

In the figure: 1. removing a single tower; 2. a condenser; 3. a condensate storage tank; 4. a jet liquid storage tank; 5. recovering a monomer storage tank; 6. a condensate pump; 7. a vacuum circulation pump; 8. a vacuum ejector; 9. a liquid jet vacuum system.

It should be noted that these drawings and the written description are not intended to limit the scope of the inventive concept in any way, but to illustrate the inventive concept to those skilled in the art by referring to the specific embodiments.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions in the following examples will be clearly and completely described, and the following examples are provided for illustrating the present invention but are not intended to limit the scope of the present invention.

The invention provides a preparation method of a spinning dope for PAN-based carbon fiber precursor, which takes azodiisobutyronitrile as an initiator to initiate acrylonitrile and itaconic acid to carry out intermittent polymerization in dimethyl sulfoxide solution to prepare the spinning dope. Because a plurality of polymerization kettles are not required to be connected in series, the reaction time can be greatly shortened, the number of the polymerization kettles is reduced, and the investment cost is saved.

Further, the present invention also provides a method for spinning with the prepared spinning dope to produce PAN-based carbon fiber precursors. In order to realize the process of obtaining the spinning dope from the production raw material and then obtaining the PAN-based carbon fiber precursor from the spinning dope, the production system adopted in the embodiment of the invention at least comprises a raw material liquid preparation unit, a polymerization unit and a spinning unit. The production raw materials are mixed in the raw material liquid preparation unit to obtain raw material liquid, and then enter the polymerization unit to realize polymerization reaction, and finally the spinning raw material liquid is formed. The spinning dope is transported to a spinning unit to produce PAN-based carbon fiber precursors.

The preparation method of the spinning dope for PAN-based carbon fiber precursor provided by the invention specifically comprises the following steps:

(2) Filtering the raw material liquid;

Wherein steps (1) and (2) are carried out in the raw material liquid preparation unit, steps (3) and (4) are carried out in the polymerization unit, and finally obtained spinning solution is pumped to a spinning unit for producing PAN-based carbon fiber precursors.

As shown in fig. 1, in the embodiment of the present invention, the raw material liquid preparing unit includes a raw material liquid preparing tank, a raw material liquid filtering device, and a raw material liquid storage tank. And adding the acrylonitrile, the itaconic acid, the azodiisobutyronitrile and the dimethyl sulfoxide serving as production raw materials into the raw material liquid preparation kettle according to the proportion, and stirring and mixing uniformly to obtain the raw material liquid. The raw material liquid filtering device is communicated with the raw material liquid preparation kettle, and the uniformly mixed raw material liquid is sent into the raw material liquid filtering device through the raw material liquid conveying pump to be filtered so as to remove impurities in the raw material liquid, and then enters the raw material liquid storage tank to be stored. The filtered raw material liquid in the raw material liquid storage tank can be sent to a polymerization unit for polymerization.

Specifically, acrylonitrile as a production raw material in the present invention includes fresh acrylonitrile (i.e., acrylonitrile purchased or produced directly) and also includes recovered acrylonitrile. Wherein, the recovered acrylonitrile is stored in an acrylonitrile recovery tank; fresh acrylonitrile is stored in an acrylonitrile storage tank, the temperature of the acrylonitrile storage tank is controlled to be 0-25 ℃, the acrylonitrile storage tank is sealed by nitrogen, the pressure in the tank is controlled to be 0-400 Pa, and the acrylonitrile storage tank is provided with a polymerization inhibition system.

In step (1), fresh acrylonitrile and recovered acrylonitrile are processed according to 8:1 to 10:1 into a mixer, mixing in the mixer, feeding into an acrylonitrile metering tank, controlling the feeding amount by the acrylonitrile metering tank, and adding acrylonitrile into a raw material liquid preparation kettle.

AIBN with 99% purity with DMSO according to 1:3.0 to 1:5.0, adding the mixture into an AIBN preparation tank, stirring and dissolving the mixture to form an initiator solution, then conveying the initiator solution into an initiator metering tank, controlling the feeding amount by the initiator metering tank, and adding the initiator solution into a raw material liquid preparation kettle.

Itaconic acid with 99% purity and DMSO were mixed according to 1:13.0 to 1:14.5, respectively conveying the materials into an itaconic acid metering tank, mixing itaconic acid and DMSO to obtain monomer solution, filtering the monomer solution, and adding the monomer solution into a raw material liquid preparation kettle.

In addition, the DMSO to be supplemented is independently added into a raw material liquid preparation kettle. Specifically, DMSO with purity of 99% purchased or produced directly is stored in a DMSO storage tank, and the DMSO purified to 99% after recovery treatment is transferred to another mixer, mixed, and then introduced into a DMSO metering tank. And adding a proper amount of solvent DMSO into the raw material liquid preparation kettle through the DMSO metering tank control.

In the step (1), the ratio of the production raw materials comprises: 1200 to 1400 parts by weight of acrylonitrile, 110 to 130 parts by weight of monomer solution, 110 to 130 parts by weight of DMSO, and 0.5 to 1.5 parts by weight of initiator solution.

Further, in the step (2) of the embodiment of the present invention, the raw material liquid is filtered by the raw material liquid filtering device to achieve a filtering accuracy of 0.5 to 1.0 μm.

Specifically, in the embodiment of the invention, a raw material liquid filtering device with the filtering precision of 0.5 μm is adopted to filter the raw material liquid, the raw material liquid filtering device comprises a cylinder filter and a disc filter, and the raw material liquid sequentially passes through the cylinder filter and the disc filter to realize two-stage filtering treatment.

In a further scheme, the polymerization unit comprises a polymerization kettle, and the filtered raw material liquid prepared in the raw material preparation unit is added into the polymerization kettle in a constant quantity through a raw material liquid feeding pump for polymerization reaction. The polymerization kettle is 45m ³ And a batch polymerization kettle adopts a DMSO one-step method to obtain a polymerization solution.

In the polymerization process, namely in the step (3) of the preparation method, nitrogen is introduced into a polymerization kettle to ensure the polymerization condition, AIBN is used for initiating the polymerization reaction, and the temperature in the polymerization kettle is controlled to be 58-60 ℃ through a hot water circulation temperature control system. The polymerization reaction is carried out for about 13.5 hours under the micro-positive pressure environment with the pressure of 30-50 Pa higher than the external pressure of the polymerization kettle, and the conversion rate can reach 95%.

Further, the dynamic viscosity range of the polymer solution obtained in the polymerization kettle is controlled to be 40-60 pa.s, then the step (4) is continuously carried out, the polymer solution is subjected to the processes of single removal, concentration and filtration to prepare spinning stock solution, the defoaming effect of the polymer solution can be realized while the concentration treatment is carried out, and the dynamic viscosity control range of the obtained spinning stock solution is 60-75 pa.s.

Further, the polymerization unit also comprises a polymerization liquid buffer tank, and the polymerization liquid obtained by the polymerization reaction in the polymerization kettle is sent into the polymerization liquid buffer tank to be collected.

In the embodiment of the invention, the preparation process and the polymerization process of the raw material liquid are both intermittent processes, so that the process parameters can be flexibly adjusted in the actual production process.

In a further scheme of the embodiment of the invention, in order to realize the single removal treatment of the polymerization liquid in the step (4), the polymerization unit further comprises a single removal tower, and the single removal tower is connected with a vacuum system, so that the polymerization liquid enters the single removal tower, and unreacted monomers are removed under the condition of reduced pressure of-65 to-101 kPa, so that the residual quantity is reduced to below 0.1 percent by mass.

In a further scheme, after the polymerization solution is subjected to filtration treatment with the filtration precision of 0.5-0.8 mu m, feeding is carried out from the top of a concentration tower, and after the polymerization solution is uniformly mixed by a filler, concentration and defoaming treatment are carried out on a hump-shaped tower inner member. Then, the polymer solution is subjected to primary filtration by a plate-frame filter with the filtration precision of 0.5 mu m, and then is subjected to secondary filtration by a disc-type filter with the filtration precision of 0.3 mu m, so that the spinning solution is obtained, and the spinning solution can be sent into a spinning solution storage tank for storage. The spinning dope stored in the spinning dope storage tank can be directly conveyed to the spinning unit, and is used for spinning in the spinning unit.

Further, the single removing tower and the concentration tower are connected with a vacuum system for realizing an internal negative pressure environment. Specifically, the vacuum system is a liquid jet type vacuum system, liquid is adopted as a power source, and the liquid is ejected from a nozzle at a high speed to generate vacuum at a suction inlet, so that the vacuumizing effect is realized.

In detail, condensate generated after the gas discharged from the top of the tower is condensed by a condenser is used as a power source of the liquid jet type vacuum system in the working process of the single removing tower and the concentration tower. The mode for realizing vacuum is suitable for a large-batch system with large vacuumizing volume, and the embodiment utilizes the mode to realize the optimization of the whole vacuum system and can reduce energy consumption.

Specifically, fig. 4 shows a schematic flow diagram of the single removal tower 1 connected to a liquid jet vacuum system 9, using condensate of the overhead gas as a vacuum power source. Wherein, the polymerization liquid from the polymerization liquid buffer tank enters the single removing tower 1 to realize single removing treatment, the top outlet of the single removing tower 1 is connected with the condenser 2, the gas discharged from the top of the single removing tower can enter the condenser 2, and the condensate liquid generated by the condenser 2 enters the jet liquid storage tank 4 through the vacuum ejector 8 under the action of the vacuum circulating pump 7. The liquid jet type vacuum system 9 comprises a vacuum ejector 8, an ejection liquid storage tank 4 and a vacuum circulating pump 7 which are sequentially connected, and the three components form a circulating passage. The vacuum circulation pump 7 is operated to drive the liquid in the jet liquid storage tank 4 to continuously circulate through the vacuum ejector 8, so that a negative pressure is formed at the top of the single-stripping tower 1 by utilizing the Venturi effect.

Further, the condenser 2 is also connected with a condensate storage tank 3, and the condensate storage tank 3 is connected with a recovered monomer storage tank 5 through a condensate pump 6. The vacuum circulation pump 7 can also pump the liquid in the jet liquid storage tank 4 into the condensate storage tank 3. In the embodiment of the present invention, the working procedure of the liquid jet vacuum system 9 is specifically as follows.

Before the whole production system is started, pure DMSO liquid with the total volume of 50% of the liquid level is injected into the injection liquid storage tank 4, and the liquid is driven to circulate through the vacuum ejector 8 by the vacuum circulating pump 7, so that the venturi effect occurs to enable the top of the single stripping tower 1 to form negative pressure. After the operation, the polymerization liquid is decompressed and evaporated in the single removal tower 1, the gas discharged from the tower top passes through the condenser 2 to generate condensate, one part of the condensate enters the condensate storage tank 3, and the other part of the condensate enters the injection liquid storage tank 4 through the vacuum ejector 8 under the suction action of the vacuum circulating pump 7. As the condensate passes through the vacuum ejector 8, a venturi effect likewise occurs, causing a negative pressure to form inside the condenser 2, and also at the top of the stripping column 1. When the liquid level in the jet liquid storage tank 4 exceeds 75% of the total capacity, the liquid therein is pumped into the condensate storage tank 3 by the vacuum circulation pump 7, and when the liquid level in the condensate storage tank 3 exceeds 75% of the total capacity thereof, the liquid in the condensate storage tank 3 is pumped to the recovered monomer storage tank 5 by the condensate pump 6.

The main components of the liquid collected by the recovered monomer storage tank 5 are acrylonitrile and DMSO, and the liquid can be recycled in a polymerization kettle. Specifically, in the stable production process, the process steps of the removal and concentration treatment are stably controlled, and the acrylonitrile concentration in the liquid collected in the recovered monomer tank 5 can be kept substantially stable. When the liquid in the monomer storage tank 5 is needed to be recycled, the concentration of the acrylonitrile in the liquid is detected, and then the recycling amount in the polymerization kettle is determined according to the detected concentration and the raw material ratio of the polymerization reaction.

The above describes the process of creating a negative pressure at the top of the stripper column 1 using the liquid jet vacuum system 9 and using condensate as the power source. The purpose of forming negative pressure at the top of the concentration tower by using the liquid jet type vacuum system 9 and adopting condensate as a power source can be achieved by replacing the single removing tower 1 in fig. 4 with the concentration tower.

In the embodiment of the invention, the process of removing the sheets, concentrating and filtering in the preparation method is a continuous process, namely, the polymerization liquid in the polymerization liquid buffer tank is continuously conveyed to a removing column for removing the sheets, and then continuous concentrating and filtering are continuously carried out, so that the spinning dope is finally obtained. The use of a continuous process is advantageous for achieving higher production efficiency.

Further, the dynamic viscosity of the polymerization solution obtained in the polymerization kettle after the process of removing monomers and concentrating is normally 60-75 pa. However, if the viscosity is outside the above range, the effect of the resulting dope for spinning is impaired. The production system of this embodiment further comprises a dope buffer tank, and if the concentrated polymer hydrodynamic viscosity discharged from the concentration tower exceeds the above-mentioned range of 60 to 75pa.s, the polymer hydrodynamic viscosity is fed into the dope buffer tank and then is fed into the mixer by means of a transfer pump.

The polymerization solution obtained by polymerization reaction in the polymerization solution buffer tank also passes through the mixer when being conveyed to the single-removal tower. And mixing the concentrated polymer solution with the kinetic viscosity which does not meet the standard with normal polymer solution (namely, polymer solution with the kinetic viscosity of 40-60 pa.s obtained through polymerization reaction) in the mixer in proportion, feeding the mixture into a single removing tower and a concentrating tower again for single removing and concentrating, and sending the mixture into a spinning solution storage tank for spinning after the mixture is subjected to detection index qualification (namely, the kinetic viscosity is qualified).

In detail, if special conditions such as power failure, water cut-off and gas cut-off are met, the situation that the dynamic viscosity of the concentrated polymerization solution discharged from the concentration tower exceeds 60-75 pa.s can occur, and the concentrated polymerization solution is sent into a spinning solution buffer tank. And after water and air supply are restored, the concentrated polymerization liquid with unqualified viscosity in the spinning solution buffer tank is conveyed to a mixer by a conveying pump. In the mixer, the concentrated polymerization liquid with unqualified viscosity and the normal polymerization liquid are mixed according to the ratio of not higher than 1:18 (i.e., the mass of the concentrated polymer solution having an unacceptable viscosity is 1/18 or less of the mass of the normal polymer solution), preferably according to 1: mixing the components according to the mass ratio of 18-30, and sending the components into a single removing tower together, so that the concentrated polymer liquid with unqualified viscosity can be subjected to single removing and concentration treatment again.

In the above-mentioned scheme, if the viscosity of the polymer solution after the concentration treatment is not qualified, the polymer solution is collected in a spinning solution buffer tank, and is conveyed by a conveying pump to be mixed with the polymer solution conveyed to the single removal tower for the first time and then is conveyed to the single removal tower together. Therefore, the concentrated polymer liquid with unqualified viscosity can be sent back to the single-removing tower and the concentration tower for single-removing and concentration, and the process of single-removing treatment by conveying the polymer liquid in the polymer liquid buffer tank to the single-removing tower is not influenced, so that the continuous carrying out of single-removing, concentration and defoaming and filtering treatment in the whole process flow is ensured.

The mixing ratio was controlled at 1:18 to 30, and more preferably controlled to 1:18 to 22, and the optimal value is 1:20, the concentrated polymer liquid with unqualified viscosity in the spinning solution buffer tank can be consumed as soon as possible under the condition that the conveying speed of the polymer liquid in the polymer solution buffer tank to the single removing tower is not influenced. If the ratio of the viscosity-unqualified polymer solution is higher than the above range, gel particles are generated to affect the quality of the obtained spinning solution, and the problem of blocking the spinning holes during spinning can occur to cause yarn breakage.

In a further scheme of the embodiment of the invention, the prepared spinning solution is pumped to a spinning unit, the spinning unit adopts dry-jet wet spinning to realize high-speed and continuous spinning at multiple spinning positions, and the high-orientation, uniform, fine denier and few-defect filaments are ensured to be obtained through the processes of water washing drafting, steam drafting and the like.

The preparation method of the PAN-based carbon fiber precursor provided by the embodiment of the invention specifically comprises the following steps:

A. controlling the temperature of the spinning solution to be 25-35 ℃, and conveying the spinning solution to a spinning component after filtering;

B. spinning the spinning solution in air by a spinning component;

D. and (3) washing and drafting the nascent fiber, oiling, drying and steam drafting to obtain the PAN-based carbon fiber precursor.

Specifically, the process flow of spinning by the spinning unit is shown in fig. 2. And (3) conveying the spinning solution from the polymerization unit to the spinning unit, cooling to 25-35 ℃ through a spinning heat exchanger in the step A, metering by a spinning metering pump, filtering through a disc filter, and conveying to a spinning assembly.

Further, the spinning dope is spun in air by a spinning assembly and then enters a coagulation bath for coagulation to form a nascent fiber. Wherein in the step B, the height of an air layer of spinning in the air is 1-5 mm, the humidity of the air layer is 20-60%, and the temperature of the air layer is 25-35 ℃. In the step C, the coagulating liquid in the coagulating bath is DMSO water solution, the concentration is 20-40%, and the temperature is 2-10 ℃.

In the step D, the primary fiber solidified and formed in the coagulating bath is led out from the yarn by a yarn guiding machine, enters a plurality of washing machines for washing, and applies two drafting forces at the later stage of the washing process, so that the orientation degree of the fiber can be improved, and the residual solvent on the surface of the precursor yarn can be washed off. Specifically, the nascent fiber enters a multi-channel washing machine for washing after being driven, and is washed by 12 groups of spraying and immersing devices in the multi-channel washing machine.

Specifically, in a multi-channel washing machine, fibers are subjected to nine-channel washing and then subjected to two-channel drafting, wherein the drafting multiple of each channel is 1.0-3 times, and the total multiple is 2-3.5 times.

And (3) feeding the drawn fibers into an oil feeding groove for oiling, wherein the temperature of the oil feeding groove is 20-30 ℃ so as to improve the bundling property of the prepared precursor in the subsequent treatment process.

The fibers after oiling are dried by a dryer, the dryer is heated from 120 ℃ to 160 ℃ in a gradient way, the drying treatment of the fibers is realized, and the draft multiple is 1.0-1.5 times, so that the compactness of the fibers is improved.

The dried fiber enters a high-pressure steam drafting box and is secondarily stretched in saturated steam with the pressure of 0.5-1.6 MPa and the drafting multiple of 2-5 times, so that the orientation degree of the fiber is further improved, the performance of the fiber is greatly improved, and the spinning speed is also improved.

Finally, winding the fiber subjected to high-pressure steam drafting into ingots on a winding machine to obtain the PAN-based carbon fiber precursor.

In embodiments of the invention, solvent DMSO may also be recovered. Specifically, the production system also comprises a recovery unit, and the DMSO aqueous solution in the coagulating bath and the DMSO-containing solution separated in the washing process can be sent to the recovery unit for recycling after multistage dehydration and rectification.

In detail, the recovery unit for recovering solvent DMSO in this example is shown in fig. 3. In the water washing step of the spinning process, the water after washing the fibers contains solvent DMSO, which is collected and then sent to a recovery unit. The aqueous DMSO solution in the coagulation bath may also be fed to a recovery unit to recover DMSO therein.

The recovery unit comprises a rectifying tower, a first-stage dehydrating tower, a second-stage dehydrating tower, a third-stage dehydrating tower and a refining tower which are sequentially communicated. The recovered DMSO solution firstly enters a rectifying tower for rectification, waste acrylonitrile is distilled out from the top of the rectifying tower, and the bottom solution is sent to a dehydrating tower for decompression dehydration.

Specifically, the bottom solution of the rectifying tower reaches a dehydration rate of 55% in the primary dehydration tower, then reaches a dehydration rate of 35% in the secondary dehydration tower, and finally reaches a dehydration rate of 9.5% in the tertiary dehydration tower.

The tower bottom solution of each level of dehydration tower is sent to a refining tower, the tower top product of the refining tower is qualified DMSO with the purity of 99 percent, and the DMSO can be pumped to a DMSO storage tank by a DMSO recovery pump after condensation. The bottom solution of the refining tower is sent to a waste liquid storage tank and is sent to sewage treatment by a pump for treatment.

In the recovery process, the emptying gas of each working section sequentially passes through the primary washing tower and the secondary washing tower to be washed and then is emptied. Wherein, acrylonitrile is removed in the first-stage washing tower, DMSO is removed in the second-stage washing tower, the components of the washing liquid are mainly water, and the washing liquid is recovered into a water tank and can be used for coagulation bath or water washing working procedures of a spinning unit.

Example 1

By adopting the production system, the preparation of the spinning solution is carried out according to the following steps:

(1) 1300 parts by weight of acrylonitrile, 125 parts by weight of monomer solution, 1 part by weight of initiator solution and 125 parts by weight of DMSO are mixed to obtain raw material liquid; wherein, the mass ratio of the acrylonitrile from the acrylonitrile storage tank to the acrylonitrile from the acrylonitrile recovery tank is 10:1, mixing and using; the monomer solution is prepared from itaconic acid and DMSO according to a mass ratio of 1:4.0, mixing the AIBN and DMSO to obtain an initiator solution, wherein the mass ratio of AIBN to DMSO is 1:13.8, mixing to obtain;

(2) The raw material liquid enters a raw material liquid filtering device with the filtering precision of 0.5 mu m for filtering treatment;

(3) The filtered raw material liquid is sent to 45m ³ In an intermittent polymerization kettle, controlling the temperature in the polymerization kettle to be 65 ℃, and carrying out polymerization reaction in a micro-positive pressure environment which is 30Pa higher than the external air pressure of the polymerization kettle, wherein the reaction time is 13.5h to obtain a polymerization solution, and the dynamic viscosity of the polymerization solution is 55pa.s;

(4) The polymerization solution enters a single removing tower, unreacted monomers are removed under the condition of reduced pressure of-80 kPa, the residual quantity of the polymerization solution is reduced to be less than 0.1 percent by mass, and then the polymerization solution is subjected to filtration treatment with the filtration precision of 0.5 mu m; then feeding from the top of the concentration tower, uniformly mixing the materials, and concentrating and defoaming on a hump-shaped tower internal part; finally, the spinning solution is subjected to primary filtration by a plate-frame filter with the filtration precision of 0.5 mu m, and then is subjected to secondary filtration by a disc-type filter with the filtration precision of 0.3 mu m, so that the spinning solution with the kinetic viscosity of 70pa.s is obtained and is sent into a spinning solution storage tank for storage.

The preparation of PAN-based carbon fiber precursors was performed as follows:

A. the spinning solution from the polymerization unit is cooled to 30 ℃ by a spinning heat exchanger, then is metered by a spinning metering pump, is filtered by a disc filter with the filtering precision of 0.3 mu m, and is conveyed to a spinning component;

B. Spinning the spinning solution in air by a spinning component; wherein the total number of spinneret holes on the spinneret plate is 12000 holes, the aperture is 0.05mm, and the hole length is 0.1mm; the height of the air layer is 4mm, the humidity of the air layer is 50%, and the temperature of the air layer is 25 ℃;

C. coagulating the spinning of the spinning component in a coagulating bath to obtain nascent fibers, wherein the coagulating liquid is a DMSO aqueous solution with the concentration of 25%, and the temperature of the coagulating liquid is 3 ℃;

d1, the nascent fiber enters a multi-channel washing machine, is subjected to two-channel drafting after nine washing procedures, and is washed by 12 groups of spraying and soaking devices in the multi-channel washing machine; wherein the first water washing temperature is 35 ℃, the temperatures of the second water washing and the eighth water washing are 38 ℃, the ninth water washing temperature is 40 ℃, the water temperature in the two drafting grooves is 60 ℃, and the total drafting multiple of the two drafting is 3 times;

d2, feeding the fibers subjected to the water washing process into an oil feeding groove for oiling, wherein the temperature of the oiling agent in the oil feeding groove is 25 ℃, and the drafting multiple in the oil feeding groove is 0.9 times;

d3, drying the oiled fiber by a dryer, wherein the dryer is gradually heated to 160 ℃ from 120 ℃ to realize the drying treatment of the fiber, and the draft multiple in the drying process is 1.5 times;

d4, the dried fiber enters a high-pressure steam drafting box, and is drafted in saturated steam of 0.5MPa at a draft multiple of 4.3 times;

And D5, winding the fiber subjected to high-pressure steam drafting into an ingot on a winding machine to obtain the PAN-based carbon fiber precursor.

In this example, the obtained PAN-based carbon fiber precursor had a single fiber fineness of 1.15dtex, a filament strength of 12CN/dtex, an elongation of 12%, a linear density of 1.38g/cm, and a fiber bundle cross section in a regular circular arrangement.

The PAN-based carbon fiber precursor obtained in the embodiment enters an oxidation furnace at 275 ℃ through a filament-releasing creel to carry out oxidation cyclization, then low-temperature carbonization is completed at 1000 ℃ under the protection of inert gas, finally high-temperature carbonization is carried out by heating to 1500 ℃, and other elements except for the element C in the fiber are removed to form the carbon fiber. The strength of the carbon fiber obtained by final carbonization in this example was 4.95GPa.

Example 2

A dope and a PAN-based carbon fiber precursor were produced by using the same production system and method as in example 1, except that the draft ratio of the steam draft was increased to 4.5 times in step D4 of the PAN-based carbon fiber precursor production process in example 1.

In this example, the obtained PAN-based carbon fiber precursor had a single fiber fineness of 1.15dtex, a filament strength of 12.4CN/dtex, an elongation of 11.6%, a linear density of 1.38g/cm, and a fiber bundle having a regular circular arrangement in cross section.

The PAN-based carbon fiber precursor obtained in the embodiment is put into an oxidation furnace at 280 ℃ through a yarn-placing creel to carry out oxidation cyclization, then low-temperature carbonization is completed at 1050 ℃ under the protection of inert gas, finally high-temperature carbonization is carried out by heating to 1550 ℃, and the strength of the obtained carbon fiber is 4.99Gpa.

Example 3

A dope and a PAN-based carbon fiber precursor were produced by using the same production system and method as in example 1, except that the draft ratio of steam draft was increased to 5.0 times in step D4 of the PAN-based carbon fiber precursor production process in example 1.

In this example, the obtained PAN-based carbon fiber precursor had a single fiber fineness of 1.15dtex, a single filament strength of 13.1CN/dtex, an elongation of 11.2%, a linear density of 1.38g/cm, and a fiber bundle having a regular circular arrangement in cross section, but slight hairiness was present.

The PAN-based carbon fiber precursor obtained in the embodiment enters an oxidation furnace at 275 ℃ through a yarn feeding creel to carry out oxidation cyclization, then low-temperature carbonization is completed at 1000 ℃ under the protection of inert gas, finally high-temperature carbonization is carried out by heating to 1500 ℃, and the strength of the obtained carbon fiber is 4.92Gpa, and compared with the strength of the embodiment 1, the strength of the obtained carbon fiber is slightly reduced.

Example 4

A dope and a PAN-based carbon fiber precursor were produced by using the same production system and method as in example 1, except that the draft ratio of the steam draft was reduced to 2.5 times in step D4 of the PAN-based carbon fiber precursor production process in example 1.

In this example, the obtained PAN-based carbon fiber precursor had a single fiber fineness of 1.15dtex, a single filament strength of 7.7CN/dtex, an elongation of 13.5%, a linear density of 1.38g/cm, and a fiber bundle having a regular circular arrangement in cross section.

The PAN-based carbon fiber precursor obtained in the embodiment is put into an oxidation furnace at 275 ℃ through a yarn-placing creel to carry out oxidation cyclization, then low-temperature carbonization is completed at 1000 ℃ under the protection of inert gas, finally high-temperature carbonization is carried out by heating to 1500 ℃, and the strength of the obtained carbon fiber is 4.72Gpa.

Comparative example 1

This comparative example differs from example 1 described above only in that: in the preparation process of the spinning solution, the filtering treatment in the step (2) is not carried out, and after the raw materials are uniformly mixed to obtain the solution, the solution is directly sent into a batch polymerization kettle for polymerization. The other steps and process parameters were the same as in example 1.

In this comparative example, it was found that the spun yarn was increased by 50% compared with the prior art, the strength was reduced to 5.86CN/dtex, and the cross section was irregularly round. As can be demonstrated by comparing with the precursor obtained in example 1, the invention greatly reduces the rate of the precursor of the PAN-based carbon fiber and remarkably improves the strength by adding the filtering step of the raw material liquid.

The obtained precursor is put into an oxidation furnace at 260 ℃ through a yarn placing creel to carry out oxidation cyclization, then low-temperature carbonization is completed at 900 ℃ under the protection of inert gas, and finally the precursor is heated to 1350 ℃ to carry out high-temperature carbonization to obtain the carbon fiber with the strength of 4.75Gpa. The high-temperature carbonization temperature was lowered and the strength of the carbon fiber was lowered as compared with the carbon fiber obtained in example 1. Illustrating that the PAN-based carbon fiber precursor prepared in example 1 can be carbonized at a higher temperature, resulting in a significant increase in the strength of the carbon fiber.

Comparative example 2

This comparative example differs from example 4 described above only in that: in the preparation process of the spinning solution, the filtering treatment in the step (2) is not carried out, and after the raw materials are uniformly mixed to obtain the solution, the solution is directly sent into a batch polymerization kettle for polymerization. The other steps and process parameters were the same as in example 4 to prepare a spinning dope.

In this comparative example, the obtained dope was fed to a spinning unit for spinning, and the obtained PAN-based carbon fiber precursor had a single fiber fineness of 1.15dtex, a single fiber strength of 6.5CN/dtex, an elongation of 14.1% and a linear density of 1.38g/cm.

As can be seen from the results of this comparative example, since the raw material liquid was directly polymerized without filtration, the impurity content was high, and although the filament breakage was small at a low steam draft multiple, the filament strength was low, and the obtained PAN-based carbon fiber precursor was formed into carbon fiber with a strength of 4.63GPa by the same carbonization process as in example 4.

Therefore, when the spinning dope is used for spinning, the dope can be obtained under a wider drafting multiple range by adding the filtering step of the dope, so that the dope can be used for producing high-strength carbon fibers, and further various production requirements can be met.

Comparative example 3

This comparative example differs from example 3 described above only in that: in the preparation process of the spinning solution, the filtering treatment in the step (2) is not carried out, and after the raw materials are uniformly mixed to obtain the solution, the solution is directly sent into a batch polymerization kettle for polymerization. The other steps and process parameters were the same as in example 3.

In this comparative example, the single fiber of the PAN-based carbon fiber precursor obtained by spinning had a fineness of 1.15dtex, a filament strength of 12.5CN/dtex, an elongation of 11.1% and a linear density of 1.38g/cm. However, in step D4 of the PAN-based carbon fiber precursor preparation process, the fibers produced a large amount of broken filaments during high-temperature steam drawing, and it was found that the raw material liquid was not filtered to prepare a spinning dope, and the broken filament rate was significantly increased at a high drawing multiple due to the large amount of impurities, and the broken filament rate was also significantly increased, resulting in a 30% reduction in the final filament yield as compared with example 3.

Further, the PAN-based carbon fiber precursor obtained in this comparative example was prepared into a carbon fiber by the same carbonization process as in example 3, and the strength of the obtained carbon fiber was 4.70Gpa, which was significantly reduced as compared with example 3.

Comparative example 4

A dope and PAN-based carbon fiber precursor were produced by using the same production system and method as in example 1, except that the reaction time was reduced to 11 hours in step (3) of the dope production process in example 1.

In this comparative example, the resulting spun yarn had a hydrodynamic viscosity of 80pa.s, an increased viscosity, a single fiber fineness of 1.15dtex, a single fiber strength of 10CN/dtex, an elongation of 12.3%, a linear density of 1.38g/cm, and a spun yarn increased in pressure and a strength of 4.70GPa, as compared with example 1, by using the same carbonization process as in example 1.

The yarn hairiness of the yarn prepared in this comparative example was increased and the yarn strength was decreased as compared with the PAN-based carbon fiber yarn obtained in example 1. It can be seen that in this comparative example, the viscosity of the dope increases due to insufficient polymerization time, so that the quality of the dope is lowered. The strength of the PAN-based carbon fiber precursor obtained in this comparative example was also significantly lower than that of example 1 after further carbonization process, indicating that the viscosity of the spinning dope may affect the precursor quality and further affect the carbon fiber quality.

Comparative example 5

A dope and PAN-based carbon fiber precursor were produced by using the same production system and method as in example 1, except that the pressure reduction condition in the process of removing the dope in step (4) of example 1 was changed to-50 kpa.

In this comparative example, the residual amount of the monomer in the obtained polymer solution was 0.3% by mass, the fineness of the single fiber of the obtained PAN-based carbon fiber precursor was 1.15dtex, the strength of the single fiber was 10.5CN/dtex, the elongation was 12.8%, the linear density was 1.38g/cm, the filament was enlarged as compared with example 1, the color of the precursor was slightly yellow, and the obtained PAN-based carbon fiber precursor was prepared into a carbon fiber having a strength of 4.73GPa by the same carbonization process as in example 1.

The precursor yarn prepared in this comparative example had an increased yarn breakage rate, and a poor color, and decreased filament strength, as compared with the PAN-based carbon fiber precursor yarn obtained in example 1. It can be seen that in this comparative example, the reduction in the quality of the strands was caused by the higher residual amount of monomer in the polymerization solution after the pressure of the pressure reduction conditions was adjusted in the process of removing the monomers. The PAN-based carbon fiber precursor obtained in this comparative example was subjected to a further carbonization process, and the strength of the obtained carbon fiber was also significantly lower than in example 1, indicating that the residual amount of monomer in the polymerization solution, or in the spinning dope, could affect the precursor quality and further affect the carbon fiber quality.

Comparative example 6

A dope and a PAN-based carbon fiber precursor were produced by the same production system and method as in example 1, except that the steam pressure in the high-pressure steam box was reduced to 0.2Mpa in step D4 of the PAN-based carbon fiber precursor production process in example 1.

In this comparative example, the obtained PAN-based carbon fiber precursor had a single fiber fineness of 1.15dtex, a filament strength of 9.86CN/dtex, an elongation of 13.5% and a linear density of 1.38g/cm, and compared with example 1, the precursor had an increased filament size and increased broken filaments, and the obtained PAN-based carbon fiber precursor was formed into a carbon fiber having a strength of 4.68GPa by the same carbonization process as in example 1.

The yarn breakage rate and the yarn breakage rate of the yarn prepared in this comparative example were both increased and the yarn strength was decreased as compared with the PAN-based carbon fiber yarn obtained in example 1. It can be seen that in this comparative example, the quality of the filaments was lowered at the same draft multiple after the steam pressure in the steam draft step was lowered. The PAN-based carbon fiber precursor obtained in this comparative example was subjected to a further carbonization process, and the strength of the obtained carbon fiber was also significantly lower than in example 1, indicating that the vapor pressure of the vapor drawing process affected the precursor quality and further affected the carbon fiber quality.

According to the scheme of the embodiments of the invention, PAN-based carbon fiber precursor with light specific gravity, low density and high strength can be prepared, and the PAN-based carbon fiber precursor can be subjected to a further carbonization process flow to prepare a high-performance carbon fiber product, in particular a high-strength carbon fiber product. The carbon fiber has the characteristic of high strength, is particularly suitable for manufacturing blades in wind turbines or other structures requiring high strength, and has good application prospect.

The foregoing description is only illustrative of the preferred embodiment of the present invention, and is not to be construed as limiting the invention, but is to be construed as limiting the invention to any and all simple modifications, equivalent variations and adaptations of the embodiments described above, which are within the scope of the invention, may be made by those skilled in the art without departing from the scope of the invention.

Claims

1. The preparation method of the spinning dope for the PAN-based carbon fiber precursor is characterized by comprising the following steps:

(2) Filtering the raw material liquid;

(4) The polymer solution is subjected to single removal, concentration and filtration treatment to obtain spinning stock solution;

in the step (2), the filtering precision of the filtering treatment of the raw material liquid is 0.5-1.0 mu m;

in the step (3), the reaction time of the polymerization reaction is 12-23 h;

in the step (4), the polymerization solution is subjected to a process of removing monomers under a reduced pressure of-65 to-101 kPa.

2. The method for producing a spinning dope for PAN-based carbon fiber precursors according to claim 1, wherein the dope is subjected to two-stage filtration treatment.

3. The method for producing a dope for PAN-based carbon fiber precursor according to claim 2, wherein the dope is subjected to a two-stage filtration treatment by passing through a cartridge filter and a disc filter in this order.

4. The method for producing a spinning dope for PAN-based carbon fiber filaments according to any one of claims 1 to 3, wherein in the step (3), the polymerization reaction is carried out in a micro-positive pressure environment of 30 to 50Pa higher than the external air pressure of the polymerization vessel by controlling the temperature in the polymerization vessel to 58 to 75 ℃.

5. The method for producing a spinning dope for PAN-based carbon fiber filaments according to any one of claims 1 to 3, wherein in the step (3), the dynamic viscosity of the obtained polymer solution is controlled to be in the range of 40 to 60pa.s, and the step (4) is continued, and the polymer solution is subjected to the processes of desingulation, concentration and filtration to produce a spinning dope.

6. The method for producing a spinning dope for PAN-based carbon fiber filaments according to any one of claims 1 to 3, wherein in the step (1), itaconic acid and dimethyl sulfoxide are mixed to obtain a monomer solution, azobisisobutyronitrile and dimethyl sulfoxide are mixed to obtain an initiator solution, and the monomer solution and the initiator solution are mixed with acrylonitrile and dimethyl sulfoxide to obtain a dope.

7. The method for producing a spinning dope for PAN-based carbon fiber precursors according to claim 6, wherein the mass ratio of itaconic acid to dimethyl sulfoxide is 1:3.0 to 1:5.0 mixing to obtain the monomer solution; the mass ratio of the azodiisobutyronitrile to the dimethyl sulfoxide is 1:13.0 to 1:14.5 mixing to obtain the initiator solution.

8. A method for producing a spinning dope for PAN-based carbon fiber filaments according to any one of claims 1 to 3, wherein in the step (1), acrylonitrile as a raw material is obtained by mixing acrylonitrile from an acrylonitrile tank with recovered acrylonitrile from an acrylonitrile recovery tank, and a mass ratio of the acrylonitrile from the acrylonitrile tank to the recovered acrylonitrile is 8:1 to 10:1.

9. The method for producing a spinning dope for PAN-based carbon fiber filaments according to any one of claims 1 to 3, wherein in said production method, the preparation and polymerization of the raw material liquids in steps (1) to (3) are performed in a batch process, and the process of the removal, concentration and filtration in step (4) is performed in a continuous process.

10. A method for preparing PAN-based carbon fiber precursors, which is characterized by comprising the following steps:

B. spinning the spinning solution in air by a spinning component;

wherein the spinning dope in the step A is prepared by the preparation method of the spinning dope for PAN-based carbon fiber precursor according to any one of claims 1 to 9;

in the step D, the dried fiber is subjected to steam drafting in saturated steam of 0.5-1.6 MPa.

11. The method for producing PAN-based carbon fiber precursor according to claim 10, wherein in step B, the air layer height of the spun yarn in the air is 1 to 5mm, the air layer humidity is 20 to 60%, and the air layer temperature is 25 to 35 ℃; in the step C, the coagulating liquid in the coagulating bath is DMSO water solution, the concentration is 20-40%, and the temperature is 2-10 ℃.

12. The method for producing PAN-based carbon fiber precursor according to claim 10 or 11, wherein in step D, the nascent fiber is drawn by a plurality of water-washing steps, wherein the water-washing temperature is 30 to 40 ℃, and the total draw ratio of the water-washing drawing is 1.5 to 3.0 times;

and/or, the dried fiber enters a high-pressure steam drafting box and is drafted again at a drafting multiple of 2-5 times.