A single-step process for the production of carbon fiber precursors.

Abstract

To provide a method for preparing a fiber precursor, the method makes it possible to obtain important advantages in terms of a product quality and a production cost.SOLUTION: There is provided an integrated and improved single-step process for producing a carbon fiber precursor, specifically the process is configured as a production method to start from a comonomer preparation step and to end at a spinning step for obtaining a final precursor fiber.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an integrated and improved single - step process for the production of carbon fiber precursors, specifically a process that starts from comonomers and reaches the spinning step to obtain the final fiber precursor.

[0002] More specifically, the present invention forms part of the field related to the production of fiber precursors that define the preparation of polymers starting from acrylonitrile or copolymers composed mainly of acrylonitrile (95 - 99.5% by weight based on the total weight of the polymer) and one or more other comonomers generally in the range of 0.5 - 5% by weight based on the total weight of the polymer.

[0003] Preferred comonomers are molecules having one or more acid groups such as acrylic acid, itaconic acid, sulfonated styrene and analogs, and optionally neutral vinyl molecules such as methyl acrylate, methyl methacrylate, vinyl acetate, acrylamide and analogs.

[0004] The polymers and copolymers thus prepared are subsequently subjected to spinning to produce fiber precursors in the form of tow that are wound or collected in a box.

[0005] Subsequently, carbon fibers are obtained by appropriate heat treatment of these polyacrylonitrile - based fiber "precursors".

[0006] There are various industrial processes for the production of acrylic fibers, using various polymerization methods and spinning methods.

[0007] The current technology can be classified and systematized as follows.

[0008] A. Batch process (2 steps) In a two-step batch process, for carbon fibers, the polymer is generally produced in an aqueous suspension, isolated, and then dissolved in a suitable solvent for spinning and conversion into fibers or fiber precursors. The solvents most commonly used for preparing the spinning solution are aqueous solutions of dimethylacetamide (DMAc), dimethylformamide (DMF), sodium thiocyanate (NaSCN), and, as recently described in patent EP2894243B1, a mixture of dimethyl sulfoxide (DMSO) and a variable amount of water.

[0009] B. Continuous process (1 step) On the other hand, in continuous processes, polymerization occurs in a solvent, and the resulting solution is used directly for spinning without intermediate separation of the polymer. The most commonly used solvents in these processes are aqueous solutions of dimethylformamide (DMF), dimethyl sulfoxide (DMSO), zinc chloride (ZnCl2), and sodium thiocyanate (NaSCN).

[0010] While batch processes offer advantages in terms of management, single-stage processes are generally preferred for obtaining high-performance carbon fibers, especially in large-scale plants, because the two polymerization and spinning steps are independent.

[0011] Single-step processes can be further classified into continuous polymerization processes and batch polymerization processes.

[0012] In a continuous polymerization process, a solution of comonomers in a solvent and a suitable catalyst are generally supplied continuously to one or a series of connected reactors. After a predetermined residence time, a solution containing the high molecular weight copolymer produced during the reaction, unreacted monomers or comonomers, and non-decomposed catalyst is recovered from a single reactor or from the last of the series of connected reactors.

[0013] Historically, solvents used in this type of process have mainly been aqueous solutions of DMF or sodium thiocyanate. More recently, the preferred solvent is DMSO due to its low environmental impact and extremely low toxicity. The catalysts used in these processes are generally peroxides or azo compounds that initiate radical chain reactions by thermal decomposition.

[0014] These continuous, single-step processes are highly efficient and enable the production of high-quality, high-performance fiber precursors and carbon fibers, but they are not without their problems and constraints.

[0015] In particular, continuous processes are inherently difficult to control at an industrial level. This is because any problem occurring at one point in the process directly and immediately affects other steps in the process, resulting in damage to the entire manufacturing process (for example, a problem in polymerization immediately affects spinning, and vice versa).

[0016] Furthermore, changing the operating conditions requires a long transition time to reach a steady state, resulting in the generation of non-specification material.

[0017] Another constraint of continuous processes relates to long residence times and the potential for stagnation areas throughout the apparatus, which tend to form gels within the reactor or in succession within the reactor. These gels hinder efficient heat exchange and therefore prevent the removal of necessary reaction heat. The formation of these gels necessitates frequent plant shutdowns to mechanically remove the gels themselves, incurring associated operating costs and production losses.

[0018] The above limitations of continuous processes are overcome by using a batch-mode polymerization process, as described, for example, JP2018084002A, in which a solvent, preferably DMSO, comonomer, and catalyst are supplied to a stirred reactor equipped with a cooling system at the start of the reaction and kept stirred at a controlled temperature for a predetermined time. At the end of the reaction, the contents of the reactor, i.e., the polymer in solution, unreacted comonomer, and undecomposed catalyst, are discharged and subsequently supplied to the next step of the process, while the reactor is prepared for a new cycle. In this way, the contents of the reactor are renewed in each cycle without creating stagnation regions of polymer solution that tend to form gels over time.

[0019] Furthermore, operating in batch mode simplifies plant management, allowing reactor contents to be diverted to a waste treatment section in the event of a malfunction or operational error, for example, without involving downstream spinning plants in the problem. In fact, these spinning plants can continue to receive a supply of dope (i.e., a homogeneous solution of fiber precursors) stored in intermediate tanks, or they can remain idle without producing out-of-specification fibers.

[0020] However, when considering the fiber preparation process as a whole, it has various weaknesses that can be improved in terms of both optimizing the performance of the resulting product and reducing manufacturing costs.

[0021] The first disadvantage of processes described according to the latest technology is the difficulty in adding ammonia, primary amines, or secondary amines, which stems from both the aggressive nature of reactants such as gaseous ammonia and the difficulty in obtaining homogeneous dispersions in highly viscous media. These additives are known to greatly contribute to the production of precursors and the improvement of spinning processes for obtaining high-performance carbon fibers. In fact, as described in EP3783132A1 and the references contained therein, it is known that converting the acid-end groups of possible comonomers (e.g., acrylic acid or itaconic acid) to ammonium salts facilitates the solidification stage of spinning and the oxidation stage in subsequent processing for carbon fiber production. The prior art attempts to solve this problem by treating the dope or DMSO solvent with gaseous ammonia added to the dope at a stage before supplying the ammonia-containing dope to the spinning machine, as described in JP2017186682, for example.

[0022] To avoid the use of gaseous ammonia and to obtain polymers with higher hydrophilicity in any case, the use of ammonium itaconate as a comonomer has been claimed (CN105624819A).

[0023] As taught in CN104558397A, CN104558395A, and CN106589223A, it is also claimed that the salt may be used in aqueous solution, considering its low solubility in common organic solvents. In this case, the ammonium salt of itaconic acid is supplied to the polymerization reactor in aqueous solution at the highest possible concentration to keep the amount of water in the system as low as possible (<0.5% by weight).

[0024] For similar reasons, acrylonitrile is also distilled before use to remove the water it contains (generally about 0.5%).

[0025] Therefore, the presence of water in the mixture of reactants is a technical disadvantage in obtaining a water-free spinning solution at the end of the process.

[0026] Surprisingly, the applicant has found that even when a certain amount of water (1 to 5% by weight based on the weight of the reaction mixture) is present, it does not have an adverse effect on the polymerization reaction. Furthermore, as taught in EP2,894,243 (CN104,775,174B), a DMSO dope containing such an amount of water can be advantageously spun to produce a fiber precursor with excellent results.

[0027] A further drawback of the conventional process is that it is difficult to remove unreacted volatile monomers or comonomers from the dope before feeding the dope to subsequent filtration and spinning steps. In existing processes, for example, most of the unreacted acrylonitrile is effectively removed using a thin film evaporator (TFE) or a stripping column. However, complete removal can only be achieved by distilling a significant amount of the solvent. There are practical problems in producing a good spinning dope with a residual acrylonitrile content of less than 1,000 ppm (0.1%). Considering the carcinogenicity of acrylonitrile, special precautions are required during subsequent processing steps for acrylonitrile contents exceeding this limit.

[0028] Therefore, the object of the present invention relates to a method for preparing a fiber precursor that overcomes the above-mentioned limitations and drawbacks in the known art and enables obtaining important advantages from the viewpoints of product quality and manufacturing cost.

Embodiments for Carrying Out the Invention

[0029] The present invention is a method for producing a carbon fiber precursor, comprising: i) a step of preparing an acid comonomer solution selected from itaconic acid and acrylic acid in water containing at least a stoichiometric amount of ammonia with respect to the acid groups present, wherein the concentration of the acid comonomer in the water is variable within the range of 3 to 50% by weight, and the total amount of water supplied to the reactor is in the range of 1 to 5% by weight with respect to the total weight of the substances (the mass) charged into the reactor in step ii), the preparation step; ii) Acrylonitrile or a mixture of acrylonitrile and a neutral vinyl comonomer [where the two comonomers, acrylonitrile / neutral vinyl comonomer, are present in a weight ratio in the range of 95:5 to 99.5:0.5], an aqueous solution of the ammonium salt of the acid comonomer prepared in step i), DMSO, 2,2'-azobisisobutyronitrile AIBN, and dodecyl mercaptan or octyl mercaptan are fed into the reactor; iii) The step of maintaining the mixture thus obtained at a temperature in the range of 50 to 80 °C for a time in the range of 10 to 20 hours, preferably 12 to 15 hours, with stirring; iv) The step of discharging the contents of the reactor into a tank maintained at a temperature in the range of 35 to 40 °C to slow down or interrupt the reaction; v) The step of feeding the mixture thus obtained into a thin film evaporation system (TFE) operating at a temperature in the range of 40 to 80 °C and a pressure in the range of 5 to 30 mbar abs; vi) A recovery step of recovering a mixture of acrylonitrile, water, and DMSO from the top of the TFE, where the mixture is reused for the preparation of a new reaction batch; vii) A recovery step of recovering a polymer solution in DMSO from the bottom of the TFE, where the solution is diluted with fresh DMSO to reach a concentration in the range of 15 to 25 wt%, preferably 18 to 22 wt%, based on the total weight of the solution; and, viii) The step of feeding the homogeneous spinning solution obtained at the end of step vii) into a spinning step or a storage tank, relates to a manufacturing method comprising the above steps.

[0030] In particular, the presence of more water during the polymerization stage simplifies the process and can reduce manufacturing costs for various reasons compared to known techniques: - Initial distillation of virgin acrylonitrile to remove trace amounts of water can be avoided; - The use of gaseous ammonia is omitted; -Instead of using more expensive ammonium salts, common itaconic acid or acrylic acid can be used; -However, the presence of itaconic acid or acrylic acid in the form of a hydrochloride salt with ammonia improves the hydrophilicity of the polymer, resulting in a homogeneous and reproducible dope; - Unreacted acrylonitrile can be removed in the form of a mixture with water and DMSO, making this removal effective and allowing all products recovered in the polymerization reactor to be reused.

[0031] The spinning step is carried out using a wet spinning process or a dry jet wet spinning process. After a solidification stage in a solidification bath consisting of a mixture of water and solvent, the resulting bundle of filaments is continuously stretched and washed to a length of approximately 10 times its original length, and then subjected to a final washing step with water to remove any remaining trace amounts of solvent.

[0032] Dodecyl mercaptan or octyl mercaptan functions as a molecular weight modifier.

[0033] In step i) preparing the acid comonomer solution, the concentration of the acid comonomer in the water is preferably variable within the range of 3 to 50% by weight, more preferably within the range of 5 to 30% by weight, and the total amount of water supplied to the reactor is in the range of 1 to 5% by weight relative to the total weight of the substance (the mass) introduced into the reactor in step ii) of the method according to the present invention.

[0034] In practice, the total mass of the substance (the mass) introduced into the reactor refers to the total mass of the components supplied to the reactor in step ii) of the method according to the present invention.

[0035] In step i), the neutral vinyl comonomer may be selected from methyl acrylate or vinyl acetate.

[0036] In step ii), supplying to the reactor, 90 to 150 parts by weight, more preferably 100 parts by weight, of acrylonitrile or a mixture of acrylonitrile and a neutral vinyl comonomer [wherein the weight ratio of the two comonomers, acrylonitrile / neutral vinyl comonomer, is in the range of 95:5 to 99.5:0.5]; 2 to 15 parts by weight, more preferably 10 parts by weight, of an aqueous solution of the ammonium salt of the acid comonomer prepared in step i); 300 to 500 parts by weight, more preferably 400 parts by weight, of DMSO; 0.2 to 0.5 parts by weight, more preferably 0.3 parts by weight, of 2,2'-azobisisobutyronitrile AIBN; and 0.05 to 0.15 parts by weight, more preferably 0.1 parts by weight, of dodecyl mercaptan or octyl mercaptan are supplied.

[0037] In step iii), the mixture obtained in step ii) is maintained under stirring, the temperature is preferably variable between 65 and 75°C, and the duration is in the range of 10 to 20 hours, preferably 12 to 15 hours.

[0038] The present invention makes it possible to obtain a gel-free, insoluble aggregate-free solution of acrylonitrile copolymer, thereby increasing the advantages associated with solution polymerization, while eliminating the dangerous and expensive steps of doping with gaseous ammonia or treating the solvent, which are necessary to obtain a polymer solution with improved spinnability and improved performance in subsequent oxidation and carbonization steps.

[0039] Furthermore, steps vi) and vii) do not jeopardize the polymerization reagent recovery and reuse process because water is present in the polymer solution and unreacted comonomers. It is also possible to reach low levels of residual comonomers (especially acrylonitrile), down to the order of 200-300 ppm, thereby improving the safety of environmental conditions in subsequent processing steps.

[0040] A further advantage of the method according to the present invention is determined by the specific amount of water contained in the spinning solution or doping solution subsequently supplied to the spinning step: the proportion of water remaining in the homogeneous solution for the production of acrylic fibers obtained by the method according to the present invention is, in fact, perfectly compatible with acrylic fiber spinning techniques that follow either dry spinning or wet spinning techniques, and DJWS (dry jet wet spinning or air gap) techniques: therefore, it is not necessary to completely remove water from the spinning solution.

[0041] Furthermore, as claimed in US3,932,577, the presence of a low percentage of water in the acrylic fiber spinning solution facilitates the compatibility of the solution itself with the coagulation bath, resulting in fibers free of vacuoles and cracks.

[0042] Another advantage of the presence of water in the polymerization process is that both fresh acrylonitrile, which generally contains a small amount of water (about 0.5 wt%) and does not require further purification, and acrylonitrile recovered from the demonomerization process, which also contains a small amount of water, can be used. The presence of small but variable amounts of water in the main comonomer does not pose a problem. This is because the total amount of water in the reaction system can be adjusted to the desired value and accurately reproduced in various batches by adding an aqueous solution of the acid comonomer chlorided with ammonia in an amount that always ensures the same water content in the system.

[0043] In this specification, the term polymer means a copolymer obtained starting from acrylonitrile and one or more other comonomers (in amounts ranging from 95 to 99.5% by weight of acrylonitrile and generally in amounts ranging from 0.5 to 5% by weight of one or more other comonomer monomers based on the total weight of the polymer).

[0044] Preferred comonomers are molecules having one or more acid groups, such as acrylic acid, itaconic acid, sulfonated styrene, and analogs, and optionally, neutral vinyl molecules, such as methyl acrylate, methyl methyl acrylate, vinyl acetate, acrylamide, and analogs.

[0045] In particular, the polymers are high molecular weight polymers in the range of 100,000 to 300,000 Da.

[0046] Dimethyl sulfoxide (DMSO) solvent is chosen because of its low environmental impact and low toxicity.

[0047] The spinning solution or doping solution obtained at the end of step vii) can be used immediately for supply to a suitable spinning line, or it can be stored in a heated tank.

[0048] The solution is sent to a filter press battery equipped with a 40 μm to 5 μm selective cloth to remove all particles, and then to the spinning line.

[0049] The spinning line used may be a wet spinning type in which a spinneret is placed in a coagulation bath consisting of a mixture of water and a solvent. After coagulation, the filament bundles are continuously drawn and washed according to known techniques to produce tows, which are collected on spools or boxes and subsequently sent to a carbonization line for the production of carbon fibers.

[0050] Alternatively, the spinning line used may be a dry-jet wet spinning type (air-gap spinning) with a spinneret held in the air at a short distance from the surface of a coagulation bath consisting of a mixture of water and a solvent. After coagulation, the filament bundles are continuously drawn and washed according to known techniques to produce tows, which are collected on spools or boxes and subsequently sent to a carbonization line for the production of carbon fibers.

[0051] example Some examples of methods according to the present invention are presented below, without limiting them to the present invention.

[0052] Example 1 A 15 kg aqueous solution containing 99 kg of acrylonitrile, 400 kg of DMSO, 0.1 kg of n-octyl mercaptan, and 1 kg of itaconic acid, 0.25 kg of ammonia, and 13.75 kg of water was introduced at room temperature into a stainless steel reactor equipped with a stirrer and a cooling jacket. The resulting solution was then heated to 65°C, and 0.3 kg of 2,2'-azobisisobutyronitrile (AIBN) was added. The heat of reaction was removed by circulating cold water through the reactor's cooling jacket, and the solution was maintained at 65°C for 7 hours with stirring; then the temperature was raised to 72°C, and the system was maintained with stirring for a further 7 hours. Under the indicated conditions, a conversion equal to 90.4% of the supplied acrylonitrile was obtained.

[0053] At the end of the above stage, the contents of the reactor were discharged into a tank maintained at 35°C and subsequently supplied to a thin-film evaporator (TFE) maintained at 80°C and a residual pressure of 25 mbar.

[0054] A mixture containing acrylonitrile, water, and DMSO was recovered from the top of the TFE and incorporated into the feed mixture for the reactor.

[0055] A homogeneous solution of copolymer was recovered from the bottom of the TFE, having a viscosity of 450 poise at 60°C and containing 0.03% by weight of residual acrylonitrile.

[0056] The dope thus prepared was supplied to a wet spinning line containing a 24,000-hole spinneret in a coagulation bath maintained at 55°C with 60% DMSO and 40% water. The resulting filament bundles were continuously drawn to 10 times their original length and then washed. At the end of the drawing and washing sections, the tow was collected on a spool at a speed of 70 m / min and exhibited the following characteristics: ·Titer: 1.22dtex; • Tenacity: 59.5 cN / tex: • Elongation: 14.5% A 24k precursor yarn winding, suitable for the production of carbon fiber, was obtained.

[0057] Example 2 A 15 kg aqueous solution containing 97 kg of acrylonitrile, 2 kg of methyl acrylate, 400 kg of DMSO, 0.1 kg of dodecyl mercaptan, and 1 kg of itaconic acid, 0.250 kg of ammonia, and 13.75 kg of water was introduced at room temperature into a stainless steel reactor equipped with a stirrer and a cooling jacket. The resulting solution was then heated to 65°C, and 0.3 kg of 2,2'-azobisisobutyronitrile (AIBN) was added. The heat of reaction was removed by circulating cold water through the reactor's cooling jacket, and the solution was maintained at 65°C for 10 hours with stirring; then the temperature was raised to 70°C, and the system was maintained for a further 10 hours with stirring. Under the indicated conditions, a conversion equal to 91.8% of the supplied acrylonitrile was obtained.

[0058] At the end of the above stage, the contents of the reactor were discharged into a tank maintained at 35°C and subsequently supplied to a thin-film evaporator (TFE) maintained at 80°C and a residual pressure of 25 mbar.

[0059] A mixture containing acrylonitrile, water, and DMSO was recovered from the top of the TFE and sent to the reactor.

[0060] A homogeneous solution of the copolymer was recovered from the bottom of the TFE, having a viscosity of 420 poise at 60°C and containing 0.03% by weight of residual acrylonitrile.

[0061] The dope thus prepared was fed into a wet spinning line containing a 48,000-hole spinneret in a coagulation bath maintained at 55°C with 60% DMSO and 40% water. The resulting filament bundles were continuously drawn to 10 times their original length and then washed. At the end of the drawing and washing sections, the tow was collected at a speed of 60 m / min using a suitable cross-wrapper and exhibited the following characteristics: ·Titer: 1.25dtex; • Tenacity: 56.2 cN / tex: • Elongation: 13.6% A 48K precursor box suitable for the production of carbon fiber was obtained.

[0062] Example 3 A spinning solution in DMSO was prepared according to the procedure described in Example 1.

[0063] The dope thus prepared was supplied to a dry-jet wet spinning line in which a spinneret with 3,000 pores was positioned 4 mm from the surface of a solidification bath at 5°C containing 35% DMSO and 65% water. After solidification, the resulting filament bundles were stretched in water, then stretched in steam to nine times their original length (steam stretching), and finally washed to remove any remaining solvent. At the end of the stretching and washing sections, a 12K precursor spool was obtained by stacking four 3K tows from a single spinneret. The resulting fibers were collected on the spool at a speed of 240 m / min, had a perfectly round cross-section, were compact, crack-free, and possessed the following characteristics: ·Titer: 1.0dtex; • Tenacity: 65.3 cN / tex: • Elongation: 14.1% This indicates that it is suitable for the manufacture of carbon fiber. [Note] The present invention also includes the following embodiments [1] to [9]. [1] A method for producing a carbon fiber precursor: i) A preparation step comprising preparing an acid comonomer solution selected from itaconic acid and acrylic acid in water containing at least a stoichiometric amount of ammonia relative to the present acid groups, wherein the concentration of the acid comonomer in the water is variable in the range of 3 to 50% by weight, and the total amount of water supplied to the reactor is in the range of 1 to 5% by weight relative to the total weight of the substance (the mass) introduced into the reactor in step ii); ii) A step of supplying acrylonitrile or a mixture of acrylonitrile and a neutral vinyl comonomer [wherein the weight ratio of the two comonomers, acrylonitrile / neutral vinyl comonomer, is in the range of 95:5 to 99.5:0.5], an aqueous solution of the ammonium salt of the acid comonomer prepared in step i), DMSO, 2,2'-azobisisobutyronitrile AIBN, and dodecyl mercaptan or octyl mercaptan to the reactor; iii) Maintain the mixture thus obtained at a temperature in the range of 50 to 80°C for 10 to 20 hours, preferably in the range of 12 to 15 hours, under stirring; iv) Discharging the contents of the reactor into a tank maintained at a temperature in the range of 35-40°C to slow down or interrupt the reaction; v) A step of supplying the thus obtained mixture to a thin-film evaporation system (TFE) operating at a temperature in the range of 40 to 80°C and a pressure in the range of 5 to 30 mbar abs; vi) A recovery step of recovering a mixture of acrylonitrile, water, and DMSO from the top of the TFE, wherein the mixture is reused for preparing a new reaction batch; vii) A recovery step of recovering the polymer solution in DMSO from the bottom of the TFE, wherein the solution is diluted with fresh DMSO to a concentration of 15-25% by weight, preferably 18-22% by weight, relative to the total weight of the solution; and viii) A step of supplying the homogeneous spinning solution obtained at the end of step vii) to a spinning step or storage tank. A manufacturing method that includes this. [2] The method according to [1], wherein the spinning step is carried out by a wet spinning process or a dry jet wet spinning process. [3] The method according to [1] or [2], wherein the homogeneous spinning solution obtained in step vii) is sent to a solidification step in a solidification bath consisting of a mixture of water and solvent before being supplied to step viiii), the resulting bundle of filaments is continuously stretched and washed to a length of about 10 times its original length, and then subjected to a final washing step with water to remove the solvent. [4] The method according to [3], wherein the resulting bundle of filaments is collected on a spool or in a box. [5] The method according to any one of [1] to [4], wherein in step i) for preparing the acid comonomer solution, the concentration of the acid comonomer in water is variable within the range of 5 to 30% by weight, and the total amount of water supplied to the reactor is within the range of 1 to 5% by weight relative to the total weight of the substance (the mass) introduced into the reactor in step ii) of the method according to the present invention. [6] The method according to any one of [1] to [5], wherein in step i), the neutral vinyl comonomer may be selected from methyl acrylate or vinyl acetate. [7] The method according to any one of [1] to [6], wherein in step ii), 90 to 150 parts by weight of acrylonitrile or a mixture of acrylonitrile and a neutral vinyl comonomer [wherein the weight ratio of the two comonomers, acrylonitrile / neutral vinyl comonomer, is in the range of 95:5 to 99.5:0.5]; 2 to 15 parts by weight of an aqueous solution of the ammonium salt of the acid comonomer prepared in step i); 300 to 500 parts by weight of DMSO; 0.2 to 0.5 parts by weight of 2,2'-azobisisobutyronitrile AIBN; and 0.05 to 0.15 parts by weight of dodecyl mercaptan or octyl mercaptan are supplied. [8] The method according to [7], wherein in step ii), 100 parts by weight of acrylonitrile or a mixture of acrylonitrile and a neutral vinyl comonomer [wherein the weight ratio of the two comonomers, acrylonitrile / neutral vinyl comonomer, is in the range of 95:5 to 99.5:0.5]; 10 parts by weight of an aqueous solution of the ammonium salt of the acid comonomer prepared in step i); 400 parts by weight of DMSO; 0.3 parts by weight of 2,2'-azobisisobutyronitrile AIBN; and 0.1 parts by weight of dodecyl mercaptan or octyl mercaptan are supplied. [9] The method according to any one of [1] to [8], wherein in step iii) the mixture obtained in step ii) is maintained under stirring, the temperature is in the range of 65 to 75°C and the time is in the range of 10 to 20 hours, preferably 12 to 15 hours.

Claims

1. A method for producing a carbon fiber residue: i) A preparation step comprising preparing an acid comonomer solution selected from itaconic acid and acrylic acid in water containing at least a stoichiometric amount of ammonia relative to the present acid groups, wherein the concentration of the acid comonomer in the water is variable in the range of 3 to 50% by weight, and the total amount of water supplied to the reactor is in the range of 1 to 5% by weight relative to the total weight of the substance (the mass) introduced into the reactor in step ii); ii) A step of supplying to the reactor acrylonitrile or a mixture of acrylonitrile and a neutral vinyl comonomer [wherein the weight ratio of the two comonomers, acrylonitrile / neutral vinyl comonomer, is in the range of 95:5 to 99.5:0.5], an aqueous solution of the ammonium salt of the acid comonomer prepared in step i), DMSO, 2,2'-azobisisobutyronitrile AIBN, and dodecyl mercaptan or octyl mercaptan; iii) Maintain the mixture thus obtained at a temperature in the range of 50 to 80°C for a period of 10 to 20 hours under stirring; iv) Discharging the contents of the reactor into a tank maintained at a temperature in the range of 35 to 40°C to slow down or interrupt the reaction; v) A step of supplying the thus obtained mixture to a thin-film evaporation system (TFE) operating at a temperature in the range of 40 to 80°C and a pressure in the range of 5 to 30 mbar abs; vi) A recovery step of recovering a mixture of acrylonitrile, water, and DMSO from the top of the TFE, wherein the mixture is reused for preparing a new reaction batch; vii) A recovery step of recovering a polymer solution in DMSO from the bottom of the TFE, wherein the solution is diluted with fresh DMSO to a concentration in the range of 15 to 25% by weight of the total weight of the solution; and viiii) A step of supplying the homogeneous spinning solution obtained at the end of step vii) to a spinning step or a storage tank, A manufacturing method that includes this.

2. The method according to claim 1, wherein the spinning step is carried out by a wet spinning process or a dry jet wet spinning process.

3. The method according to claim 1, wherein the homogeneous spinning solution obtained in step vii) is sent to a solidification step in a solidification bath consisting of a mixture of water and a solvent before being supplied to step viiii), the resulting bundle of filaments is continuously stretched and washed to 10 times its original length, and then subjected to a final washing step with water to remove the solvent.

4. The method according to claim 3, wherein the obtained filament bundle is collected on a spool or in a box.

5. The method according to claim 1, wherein in step i) preparing the acid comonomer solution, the concentration of the acid comonomer in water is variable within the range of 5 to 30% by weight, and the total amount of water supplied to the reactor is within the range of 1 to 5% by weight relative to the total weight of the substance (the mass) introduced into the reactor in step ii) of the method according to the present invention.

6. The method according to claim 1, wherein in step i), the neutral vinyl comonomer may be selected from methyl acrylate or vinyl acetate.

7. The method according to claim 1, wherein in step ii), 90 to 150 parts by weight of acrylonitrile or a mixture of acrylonitrile and a neutral vinyl comonomer [wherein the weight ratio of the two comonomers, acrylonitrile / neutral vinyl comonomer, is in the range of 95:5 to 99.5:0.5]; 2 to 15 parts by weight of an aqueous solution of the ammonium salt of the acid comonomer prepared in step i); 300 to 500 parts by weight of DMSO; 0.2 to 0.5 parts by weight of 2,2'-azobisisobutyronitrile AIBN; and 0.05 to 0.15 parts by weight of dodecyl mercaptan or octyl mercaptan are supplied.

8. The method according to claim 7, wherein in step ii), 100 parts by weight of acrylonitrile or a mixture of acrylonitrile and a neutral vinyl comonomer [wherein the weight ratio of the two comonomers, acrylonitrile / neutral vinyl comonomer, is in the range of 95:5 to 99.5:0.5]; 10 parts by weight of an aqueous solution of the ammonium salt of the acid comonomer prepared in step i); 400 parts by weight of DMSO; 0.3 parts by weight of 2,2'-azobisisobutyronitrile AIBN; and 0.1 parts by weight of dodecyl mercaptan or octyl mercaptan are supplied.

9. The method according to claim 1, wherein in step iii), the mixture obtained in step ii) is maintained under stirring, the temperature is in the range of 65 to 75°C and the time is in the range of 10 to 20 hours.

10. The method according to claim 1, wherein in step iii), the mixture obtained in step ii) is maintained under stirring at a temperature in the range of 50 to 80°C for a time in the range of 12 to 15 hours.

11. The method according to claim 1, wherein in step vii), the polymer solution in DMSO recovered from the bottom of the TFE is diluted with fresh DMSO to a concentration in the range of 18 to 22% by weight of the total weight of the solution.

12. The method according to claim 9, wherein in step iii), the mixture obtained in step ii) is maintained under stirring at a temperature in the range of 65 to 75°C for a time in the range of 12 to 15 hours.