Method for producing polyamide

Abstract

To provide a method for producing polyamide having excellent recovery efficiency of polyamide while energy used in recycling is reduced.SOLUTION: A method for producing polyamide of the present invention includes: step 1: a step of heating and dissolving a polyamide composition being a raw material into a first metal chloride alcohol solution containing metal chloride and alcohol to obtain a polyamide solution; and step 2: a step of cooling the polyamide solution obtained in step 1 to separate into polyamide and a second metal chloride alcohol solution, wherein the temperature of the composition in the heating and dissolving of step 1 is higher than the boiling point of the alcohol by 5°C or more, and the pressure is higher than 0.1 MPa.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing polyamides. [Background technology]

[0002] Polyamides, including nylon 6 and nylon 66, are representative engineering plastics that have excellent heat resistance and mechanical properties. They are widely used in textiles, automobile parts, electrical appliance parts, and more, and are one of the irreplaceable materials in modern society.

[0003] In recent years, technological developments have been made regarding the recycling of plastics with the aim of resource conservation and carbon neutrality, and polyamides are no exception.

[0004] Recycling methods can be broadly divided into material recycling, in which molded products are re-pelletized, and chemical recycling, in which monomers are reused through depolymerization. While material recycling raises concerns about quality instability because the polymer degradation and additives contained in the molded product remain intact in the recycled polymer, it requires fewer resources and energy because it does not involve chemical reactions and requires fewer auxiliary materials, making it the preferred method for recycling with a fixed end use. Furthermore, prior to chemical recycling, when additives and coatings are removed from processed or used polyamide recovered from factories or markets, a process to recover clean polyamide is required, just like material recycling. Therefore, material recycling technology is also useful for chemical recycling. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-172618 Summary of the Invention [Problem to be solved by the invention]

[0006] One possible method for recovering polyamides is to dissolve the polyamide in a solvent, remove insoluble impurities, and then precipitate and recover the polyamide by some method. However, many of the solvents used to dissolve polyamides are unsuitable for industrial use, such as strong acids like formic acid and sulfuric acid, or expensive solvents like HFIP. One example of an industrially usable solvent is the dissolution and recovery method using ethylene glycol (Patent Document 1). However, this method requires a very high-temperature reaction, which raises concerns about glycolysis of the polyamide. In addition, the solvent used must be completely removed from the sherbet-like solid by distillation and drying, which is thought to require a large amount of energy, including heating during the reaction.

[0007] Therefore, an object of the present invention is to provide a method for producing polyamide, which reduces the energy used during recycling and has excellent polyamide recovery efficiency. [Means for solving the problem]

[0008] That is, the present invention is as follows. [1] The following process: Step 1: A step of dissolving a raw material polyamide composition in a first metal chloride alcohol solution containing a metal chloride and an alcohol under heating to obtain a polyamide solution; Step 2: cooling the polyamide solution obtained in step 1 to separate it into a polyamide and a second alcohol solution of a metal chloride; Including, the temperature during the heating and dissolving in step 1 is higher than the boiling point of the alcohol by 5°C or more, and the pressure is higher than 0.1 MPa; A method for producing polyamide, characterized by: [2] The method for producing a polyamide according to [1], wherein the second metal chloride alcohol solution obtained in the step 2 is used as the first metal chloride alcohol solution. [3] The method for producing a polyamide according to [1] or [2], wherein the mass proportion of the metal chloride in 100 mass% of the first metal chloride alcohol solution is 5 to 15 mass%. [4] The method for producing a polyamide according to any one of [1] to [3], wherein the mass ratio (mass%) of the metal chloride in 100 mass% of the second alcoholic solution of metal chloride is 0.9 to 1.1 times the mass ratio (mass%) of the metal chloride in 100 mass% of the first alcoholic solution of metal chloride. [5] the first metal chloride alcoholic solution and the second metal chloride alcoholic solution contain water; The method for producing a polyamide according to any one of [1] to [4], wherein the mass ratio (mass%) of water in 100 mass% of the second alcoholic solution of metal chloride is 0.9 to 1.1 times the mass ratio (mass%) of water in 100 mass% of the first alcoholic solution of metal chloride. [6] the mass ratio of the metal chloride in 100 mass% of the first metal chloride alcohol solution is 10 mass% or less, the molar ratio of water to 1 mole of metal chloride in the first metal chloride alcohol solution is 0.2 to 2.5 moles, the temperature of the heating and dissolving in step 1 is higher than the boiling point of the first metal chloride alcohol solution by 5°C or more and lower than 100°C; The method for producing a polyamide according to any one of [1] to [5]. [7] the mass ratio of the metal chloride in 100 mass% of the first metal chloride alcohol solution is 10 mass% or less, the molar ratio of water to 1 mole of metal chloride in the first metal chloride alcohol solution is 0.2 to 2.5 moles, The temperature of the heating and dissolving in step 1 is 100 to 160°C. The method for producing a polyamide according to any one of [1] to [6]. [Effects of the Invention]

[0009] The present invention can provide a method for producing polyamide, which is excellent in polyamide recovery efficiency while reducing the energy used during recycling. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, the embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following description and can be practiced in various modifications within the scope of the gist thereof.

[0011] [Polyamide manufacturing method] The method for producing a polyamide of the present embodiment includes the following steps: Step 1: A step of dissolving a raw material polyamide composition in a first metal chloride alcohol solution containing a metal chloride and an alcohol under heating to obtain a polyamide solution; Step 2: cooling the polyamide solution obtained in step 1 to separate it into a polyamide and a second alcohol solution of a metal chloride; The temperature during the heating and dissolving in step 1 is at least 5°C higher than the boiling point of the alcohol contained in the first metal chloride alcohol solution, and the pressure is higher than 0.1 MPa. The manufacturing method of this embodiment may be a manufacturing method consisting of only steps 1 and 2, or may further include other steps.

[0012] The compounds used in the production method of this embodiment will be described below.

[0013] <Polyamide composition> The polyamide composition may consist of only polyamide, or may contain polyamide and other components. In the method for producing a polyamide according to the present embodiment, components other than polyamide are preferably excluded.

[0014] (polyamide) As the polyamide, a polymer polymerized through an amide bond, such as a polymer obtained by polycondensation of a diamine compound and a dicarboxylic acid compound, or a polymer obtained by ring-opening polymerization of a cyclic lactam, can be used. The diamine compound is not particularly limited, but examples thereof include ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, nonanediamine, methylpentanediamine, and p-phenylenediamine. The dicarboxylic acid compound is not particularly limited, but examples thereof include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, terephthalic acid, and isophthalic acid. The cyclic lactam is not particularly limited, but examples thereof include ε-caprolactam, undecane lactam, and lauryllactam. The combination of the diamine compound, the dicarboxylic acid compound, and the cyclic lactam compound is not particularly limited, and multiple types of each compound may be used in combination. Polyhexamethylene adipamide (for example, polyhexamethylene adipamide composed of hexamethylene diamine and adipic acid) has high solubility and is suitable for the polyamide production method of this embodiment.

[0015] The shape and particle size of the polyamide are not particularly limited. The method for measuring the particle size and particle size distribution of the polyamide is not particularly limited, and examples thereof include laser diffraction, laser scattering, centrifugal sedimentation, particle tracking, and dynamic scattered light methods.

[0016] The polyamide may be, for example, a polyamide to which other resins, metals, etc., as other components, are mixed, attached, or coated. The polyamide composition may contain polyamide coated with a silicone resin and / or a urethane resin (preferably a silicone resin), or may consist solely of polyamide coated with a silicone resin and / or a urethane resin (preferably a silicone resin). The mass proportion of the polyamide relative to 100 mass% of the polyamide composition is preferably 30 to 100 mass%, more preferably 70 mass% or more, even more preferably 80 mass% or more, still more preferably 85 mass% or more, and particularly preferably 100 mass%, from the viewpoint of achieving even better polyamide recovery efficiency relative to the energy used in the production method of this embodiment. When other components other than polyamide are contained, a step of separating the polyamide from the other components may be included. The separation method is not particularly limited, but if the other components are insoluble in the polyamide composition while it is dissolved, they can be separated by methods such as filtration, centrifugation, and sedimentation. If the other components dissolve in the solvent together with the polyamide, possible methods include separation by extraction separation in the dissolved state, membrane separation, electrodialysis, etc., or precipitating the polyamide in the precipitation step described below and then washing the precipitated polyamide.

[0017] <First metal chloride alcohol solution> The first metal chloride alcohol solution contains a metal chloride and a first alcohol. The first metal chloride alcohol solution may be a solution consisting of only the metal chloride and the first alcohol, or may further contain other components. In particular, from the viewpoint of the solubility of polyamide, the ratio of the total mass of the metal chloride and the first alcohol to 100 mass% of the first metal chloride alcohol solution is preferably 80 mass% or more, more preferably 90 mass% or more, and even more preferably 100 mass%.

[0018] Examples of the first alcohol include monoalcohols such as methanol, ethanol, linear or branched propanol, linear or branched butanol, diols such as ethylene glycol, 1,3-propylene diol, butanediol, combinations thereof, etc. Among these, from the viewpoint of the solubility of polyamide, methanol, ethanol, or combinations thereof are preferred, and methanol is more preferred. The first alcohols may be used alone or in combination of two or more.

[0019] The mass ratio of the metal chloride relative to 100% by mass of the first metal chloride alcohol solution is preferably 3 to 50% by mass, more preferably 4 to 25% by mass, even more preferably 5 to 15% by mass, and particularly preferably 5 to 10% by mass, from the viewpoint of achieving a higher polyamide recovery efficiency relative to the energy used in the production method of the present embodiment. The mass ratio of the metal chloride relative to 100% by mass of the first metal chloride alcohol solution may be 10% by mass or less. A mass ratio of 3% by mass or more ensures excellent polyamide solubility, while a mass ratio of 5% by mass or more reduces the amount of undissolved polyamide, resulting in a uniform polyamide. Furthermore, a mass ratio of 50% by mass or less eliminates undissolved metal chloride and reduces impurities.

[0020] Examples of the metal chloride include zinc chloride, magnesium chloride, and calcium chloride, with zinc chloride and calcium chloride being preferred, and calcium chloride being most preferred. The metal chloride is preferably anhydrous because the solubility of polyamide decreases when water is mixed in. However, a hydrate (for example, calcium chloride dihydrate) may be mixed in as long as the solubility is within an acceptable range. The mass proportion of water in the metal chloride is preferably 30 mass % or less, more preferably 1 mass % or less, and even more preferably 0.1 mass % or less, and it is particularly preferable that the metal chloride contains no water. In the first metal chloride alcohol solution, the metal chloride is preferably calcium chloride, and the first alcohol is preferably methanol.

[0021] The first metal chloride alcohol solution may contain water, which refers to water contained in the metal chloride, water contained in the alcohol and other components other than the metal chloride, in addition to the water added as a raw material. The molar ratio of water to 1 mole of metal chloride in the first metal chloride alcohol solution is preferably 0.2 to 2.5 moles, more preferably 0.2 to 2.0 moles, and even more preferably 0.2 to 1.5 moles, from the viewpoint of the solubility of polyamide.

[0022] The boiling point of the first metal chloride alcohol solution is preferably 50 to 250°C, more preferably 55 to 230°C, and even more preferably 60 to 220°C. The boiling point of the first metal chloride alcohol solution is preferably higher than the boiling point of the first alcohol.

[0023] Each step in the manufacturing method of this embodiment will be described.

[0024] <Process 1> In the step 1, the polyamide composition is dissolved in the first metal chloride alcohol solution with heating to obtain a polyamide solution. In the step 1, it is preferable to use only the polyamide composition and the first metal chloride alcohol solution.

[0025] The mass ratio of the polyamide composition to 100 mass% of the first metal chloride alcohol solution used in step 1 is preferably 1 to 15 mass%, more preferably 3 to 13 mass%. If it is less than 1 mass%, too much solvent is required, while if it exceeds 15 mass%, the viscosity increases, prolonging the dissolution time and deteriorating operability. Furthermore, for the same reasons as above, the mass proportion of polyamide in 100 mass% of the above-mentioned heated polyamide solution is preferably 1 to 15 mass%, more preferably 3 to 13 mass%.

[0026] In the above step 1, the temperature during heating and dissolving is preferably at least 5°C higher than the boiling point of the first alcohol, from the viewpoint of completely dissolving the polyamide. Complete dissolution of the polyamide refers to a state in which the molecular chains are completely solvated. Although this cannot be confirmed visually, it is not possible to obtain polyamide with the desired properties with high reproducibility without going through this completely dissolved state. Furthermore, from the viewpoint of suppressing the decomposition reaction of the polyamide by the solvent, the temperature during heating and dissolving is preferably not more than 110°C higher than the boiling point of the first alcohol, more preferably not more than 95°C higher than the boiling point of the first alcohol, and even more preferably not more than 80°C higher than the boiling point of the first alcohol. The temperature may vary within the above range during heating and dissolving, but is preferably kept constant.

[0027] The pressure during the heating and dissolving is preferably higher than 0.1 MPa, more preferably 0.2 MPa or higher, and even more preferably 0.5 MPa or higher, from the viewpoint of completely dissolving the polyamide. Furthermore, the pressure during heating and dissolving is preferably 5 MPa or less, more preferably 3 MPa or less, or 1.5 MPa or less, from the viewpoint of the durability of the required equipment. The pressure may vary within the above range during heating and dissolving, but is preferably constant.

[0028] The above-mentioned heating and dissolution is preferably carried out in a sealed container from the viewpoint of preventing the loss of components in the polyamide composition and the first metal chloride alcohol solution during heating and dissolution, so that the second metal chloride alcohol solution obtained after heating and dissolution can be used repeatedly. The shape of the container used for the heating and dissolving is not particularly limited, and any shape such as a tank type or a circulation type may be used.

[0029] The above-mentioned heating and dissolving may be carried out by either a batch method or a continuous method. In the case of a batch method, stirring is not particularly limited, but stirring is preferred, as stirring improves the dissolution rate of the polyamide. In the case of a continuous system, the solvent may be continuously passed through the solid, or the solution may be circulated. Circulation is preferred because it reduces the amount of solvent used. For example, the solution may be added while heating and dissolving, so that the mass ratios of the polyamide, metal chloride, and alcohol at the completion of heating and dissolution are within the above ranges.

[0030] The above heating and dissolving is preferably carried out with stirring in order to make the conditions in the reaction vessel uniform.

[0031] The time for carrying out the above heating reaction may be 0.1 to 100 hours, and from the viewpoint of energy consumption and suppression of decomposition reactions, 0.5 to 10 hours is preferred.

[0032] By the above step 1, a polyamide solution can be obtained. The polyamide solution obtained in step 1 is preferably used continuously in step 2. The polyamide solution obtained in step 1 preferably has all of the contained polyamide dissolved therein. It is preferable to maintain the polyamide in a dissolved state until it is used in Step 2 described below, for example by maintaining the temperature of the polyamide solution within ±15°C of the temperature during heating and dissolution (preferably within ±10°C of the temperature, more preferably within ±5°C of the temperature).

[0033] <Process 2> In the step 2, the polyamide solution obtained in the step 1 is cooled to separate it into the polyamide and the second alcohol solution of the metal chloride.

[0034] In the above step 2, it is preferable that no other components are added to the polyamide solution. When other components are added in the step 2, the other components to be added include the alcohol contained in the first metal chloride alcohol, water, a combination thereof, and the like.

[0035] In the step 2, the cooling is preferably performed to room temperature. The cooling method is not particularly limited, and examples thereof include air-cooling the container in which the mixture was heated and melted in the step 1, and flowing a refrigerant inside and outside the container.

[0036] After the cooling, the pressure is preferably atmospheric pressure.

[0037] The cooling is preferably carried out in a sealed container to prevent loss of components in the polyamide solution during cooling. After cooling, the sealed solution may be opened.

[0038] After cooling, a slurry containing the polyamide and the second metal chloride alcohol solution is obtained.

[0039] When the polyamide precipitates as a solid in the slurry, the polyamide and the second metal chloride alcohol solution can be separated by solid-liquid separation. The method of solid-liquid separation is not particularly limited, but examples include filtration, centrifugation, sedimentation, etc. Either method may be a batch method or a continuous method.

[0040] The solid obtained by solid-liquid separation is preferably washed with a solvent. The washing solvent is not particularly limited, but it is preferable to use a solution having the same composition as the liquid portion at the time of precipitation, a good solvent, or a solvent capable of dissolving metal chlorides. Alcohols such as methanol and ethanol, and water are preferred, and combinations of these may also be used.

[0041] The washing method is not particularly limited, and examples thereof include a batch washing method, a continuous washing method in which a washing solvent is passed through a solid-liquid separator such as a filter or a centrifugal separator, and a combination thereof.

[0042] After washing, the polyamide can be dried and solidified by distilling off the washing solvent by heating and / or reducing the pressure, thereby obtaining a powdery polyamide.

[0043] From the viewpoint of enabling repeated use of the metal chloride alcohol solution, it is preferable that the second metal chloride alcohol solution obtained by the manufacturing method of this embodiment is a solution having approximately the same composition as the first metal chloride alcohol solution. The mass proportion (mass %) of the metal chloride in 100 mass % of the second metal chloride alcohol solution is preferably 0.9 to 1.1 times, and more preferably 0.95 to 1.05 times, the mass proportion (mass %) of the metal chloride in 100 mass % of the first metal chloride alcohol solution. The first metal chloride alcohol solution and the second metal chloride alcohol solution may both contain water. The mass ratio (mass %) of water in 100 mass % of the second metal chloride alcohol solution is preferably 0.9 to 1.1 times, and more preferably 0.95 to 1.05 times, the mass ratio (mass %) of water in 100 mass % of the first metal chloride alcohol solution. The above mass ratio of the metal chloride and / or water in the first metal chloride alcohol solution and the second metal chloride alcohol solution can be adjusted, for example, by not diluting the polyamide solution after heating and dissolution with alcohol.

[0044] The manufacturing method of this embodiment can be repeated because the second metal chloride alcohol solution obtained has almost the same composition as the first metal chloride alcohol solution. For example, in a manufacturing method in which the above steps 1 and 2 are repeatedly performed, the separated second metal chloride alcohol solution can be used as the first metal chloride alcohol solution when heating and dissolving a polyamide composition, which is another raw material, thereby significantly reducing the amount of energy used.

[0045] In the production method of this embodiment, the properties and shape of the resulting polyamide can be adjusted by setting the conditions in step 1 above within specific ranges. When the mass ratio of metal chloride in 100 mass% of the first metal chloride alcohol solution is 10 mass% or less, the molar ratio of water per mole of metal chloride in the first metal chloride alcohol solution is 0.2 to 2.5 moles, and the temperature of the heat dissolution in step 1 is at least 5°C higher than the boiling point of the first metal chloride alcohol solution and lower than 100°C, a powder polyamide with many pores (for example, a powder polyamide having pores of 5 mL / g or more (preferably 7 mL / g or more)) can be obtained. When the mass ratio of the metal chloride in 100 mass% of the first metal chloride alcohol solution is 10 mass% or less, the molar ratio of water per mole of metal chloride in the first metal chloride alcohol solution is 0.2 to 2.5 moles, and the temperature of the heat dissolution in step 1 is 100 to 160°C, a powder polyamide with low porosity (for example, a powder polyamide having pores of 4 mL / g or less (preferably 3 mL / g or less)) can be obtained.

[0046] In the conventional method for regenerating polyamide, polyamide is dissolved in a high-concentration alcohol solution of metal chloride, and then diluted and crystallized with alcohol. In this method, in order to reuse the solvent after polyamide production, it is necessary to concentrate it, which requires a great deal of energy. In other words, when polyamide production is repeated, the conventional method requires a very high amount of energy relative to the amount of recovered polyamide. The inventors of the present invention have conducted further research and have noticed that metal chlorides are temperature-independent and do not precipitate even at low temperatures, while polyamides are highly temperature-dependent and tend to precipitate at low temperatures. They have then discovered that polyamides can be dissolved by heating even when the metal chloride concentration in a metal chloride alcohol solution is low. Based on these findings, they have discovered that a method for regenerating polyamides by combining metal chlorides and polyamides involves heating and dissolving polyamide in a dilute metal chloride alcohol solution, and then lowering the temperature to precipitate the polyamide, thereby obtaining a metal chloride alcohol solution that can be reused as is, and that the amount of energy required per recovered polyamide can be reduced compared to the energy consumed in concentrating the solvent to reuse it.

[0047] In the production method of this embodiment, a solid polyamide is preferably obtained, and a powdered polyamide is more preferably obtained.

[0048] The weight average molecular weight of the polyamide obtained by the production method of this embodiment is preferably 10,000 to 100,000. The weight average molecular weight can be measured by the method described in the Examples below.

[0049] The polyamide obtained by the production method of this embodiment can be used, for example, as a raw material for fibers, fabrics, airbags, etc. [Example]

[0050] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0051] The evaluation and analysis methods used in the examples and comparative examples are as follows.

[0052] (Weight average molecular weight) 10 mg of polyamide was dissolved in 10 mL of the following eluent, and GPC measurement was carried out under the following conditions. The molecular weight distribution was calculated from the molecular weight calibration curve of the standard substance, and the weight average molecular weight was determined. Measuring equipment: HLC-8320GPC (TOSOH) Column: TSKgel GMHHR-H(S) x 3 (4.6 mm I.D. x 15 cm) (TOSOH) Eluent: HFIP (Na trifluoroacetate - 5 mmol / L) Flow rate: 0.175mL / min Column temperature: 40℃ Detector: Differential refractive index analysis (built into analytical equipment) Standard material: PMMA

[0053] Examples and comparative examples were carried out in the following manner. The polyamide resin compositions used were as follows: <Polyamide resin composition> PA66 pellets: Polyamide 66 pellets (Leona (trademark) 1300 grade, manufactured by Asahi Kasei Corporation), the weight average molecular weight of which was previously analyzed by GPC was 47,000.

[0054] [Example 1] A 300 mL pressure-resistant stainless steel reactor equipped with a Teflon® inner tube and a stirrer was charged with 10.0 g of polyamide 66 pellets and 200 g of calcium chloride methanol solution (20 g calcium chloride, 180.0 g methanol). The reactor was placed in a 140 °C oil bath and stirred with a magnetic stirrer for 8 hours to dissolve the mixture, yielding a polyamide solution. The maximum pressure during stirring was 1.0 MPa. The reactor was then removed from the oil bath and air-cooled to room temperature. The reactor was opened, and the slurry inside was poured into a filter equipped with a 10 μm membrane filter. A solid precipitate (39.5 g) and a filtrate (169 g) were separated and recovered. The recovered solid precipitate was thoroughly washed with water and dried to obtain 9.9 g of polyamide 66 powder (99.0% yield). Based on the weight ratio to the wet state, the resulting polyamide 66 powder particles were calculated to have 2.99 mL / g of pores. The weight average molecular weight as determined by GPC analysis was 47,000. Using 169 g of the obtained filtrate and 8.5 g of polyamide 66 pellets, the same procedure as above (second polyamide production) was carried out, yielding 8.4 g of polyamide powder (yield 99.4%).

[0055] [Example 2] A 300 mL pressure-resistant stainless steel reactor equipped with a Teflon inner tube and a stir bar was charged with 10.0 g of polyamide 66 pellets and 200 g of calcium chloride methanol solution (20.0 g calcium chloride dihydrate, 180.0 g methanol). The mixture was then placed in a 140 °C oil bath and stirred with a magnetic stirrer for 8 hours to obtain a polyamide solution. The maximum pressure during stirring was 0.8 MPa. The reactor was then removed from the oil bath and allowed to cool to room temperature. The reactor was then opened, and the slurry inside was transferred to a filter equipped with a 10 μm membrane filter. A solid precipitate (30.0 g) and a filtrate (179.0 g) were separated and collected. The collected solid precipitate was thoroughly washed with water and dried to obtain 9.9 g of polyamide 66 powder (99.0% yield). Based on the weight ratio relative to the wet state, the resulting polyamide 66 powder particles were calculated to have a pore volume of 2.03 mL / g. The weight average molecular weight as determined by GPC analysis was 47,000. The same procedure as above was carried out using 178 g of the obtained filtrate and 8.9 g of polyamide 66 pellets, yielding 8.8 g of polyamide powder (yield 98.9%).

[0056] [Example 3] A 300 mL pressure-resistant stainless steel reactor equipped with a Teflon inner tube and a stir bar was charged with 10.0 g of polyamide 66 pellets and 200 g of calcium chloride methanol solution (8.0 g calcium chloride, 192.0 g methanol). The mixture was then placed in a 140 °C oil bath and stirred with a magnetic stirrer for 8 hours to obtain a polyamide solution. The maximum pressure during stirring was 1.0 MPa. The reactor was then removed from the oil bath and allowed to air-cool to room temperature. The reactor was then opened, and the slurry inside was poured into a filter equipped with a 10 μm membrane filter. The solid precipitate (25.2 g) and filtrate (184.3 g) were separated and recovered. The recovered solid precipitate was thoroughly washed with water and dried. The resulting polyamide 66 was a mixture of powder and unmelted pellets (9.9 g yield, 99.0%). Based on the weight ratio with respect to the wet state, the obtained polyamide 66 powder particles were calculated to have 1.55 mL / g of voids. However, since some of the particles were unmelted polyamide 66 pellets, the powder was not obtained as a uniform powder. The weight-average molecular weight analyzed by GPC was 47,000. The same procedure as above was carried out using 180 g of the obtained filtrate and 9.0 g of polyamide 66 pellets, yielding 8.9 g of polyamide powder (yield 98.9%).

[0057] [Example 4] A 300 mL pressure-resistant stainless steel reactor equipped with a Teflon inner tube and a stir bar was charged with 10.0 g of polyamide 66 pellets and 200 g of calcium chloride methanol solution (36.0 g calcium chloride, 164.0 g methanol). The mixture was then placed in a 140 °C oil bath and stirred with a magnetic stirrer for 8 hours to obtain a polyamide solution. The maximum pressure during stirring was 1.0 MPa. The reactor was then removed from the oil bath and allowed to cool to room temperature. The reactor was then opened, and the slurry inside was poured into a filter equipped with a 10 μm membrane filter. A solid precipitate (32.8 g) and a filtrate (176.5 g) were separated and recovered. The recovered solid precipitate was thoroughly washed with water and dried to obtain 8.2 g of polyamide 66 powder (82.0% yield). Based on the weight ratio relative to the wet state, the resulting polyamide 66 powder particles were calculated to have 3.0 mL / g of voids. The weight average molecular weight as determined by GPC analysis was 48,000. The same procedure as above was carried out using 173 g of the obtained filtrate and 8.7 g of polyamide 66 pellets, yielding 7.1 g of polyamide powder (yield 82.1%).

[0058] [Example 5] A 300 mL pressure-resistant stainless steel reactor equipped with a Teflon inner tube and a stir bar was charged with 10.0 g of polyamide 66 pellets and 200 g of calcium chloride methanol solution (20.0 g calcium chloride dihydrate, 180.0 g methanol). The reactor was placed in a 95°C oil bath and stirred with a magnetic stirrer for 8 hours to dissolve the mixture, yielding a polyamide solution. The maximum pressure during stirring was 0.28 MPa. The reactor was then removed from the oil bath and allowed to air-cool to room temperature. The reactor was then opened, and the slurry inside was poured into a filter equipped with a 10 μm membrane filter. A solid precipitate (90.0 g) and a filtrate (118.5 g) were separated and recovered. The recovered solid precipitate was thoroughly washed with water and dried to obtain 9.9 g of polyamide 66 powder (99.0% yield). Based on the weight ratio relative to the wet state, the resulting polyamide 66 powder particles were calculated to have 8.09 mL / g of voids. The weight average molecular weight as determined by GPC analysis was 47,000. The same procedure as above was carried out using 115 g of the obtained filtrate and 5.8 g of polyamide 66 pellets, yielding 5.7 g of polyamide powder (yield 99.1%).

[0059] [Example 6] A 300 mL pressure-resistant stainless steel reactor equipped with a Teflon inner tube and a stir bar was charged with 10.0 g of polyamide 66 pellets and 200 g of calcium chloride methanol solution (36.0 g calcium chloride, 164.0 g methanol). The reactor was placed in a 140 °C oil bath and stirred with a magnetic stirrer for 8 hours to dissolve the mixture, yielding a polyamide solution. The maximum pressure during stirring was 1.0 MPa. The reactor was then removed from the oil bath, opened, and the solution was mixed with 150 g of methanol and then air-cooled to room temperature. The resulting slurry was then poured into a filter equipped with a 10 μm membrane filter, and the solid precipitate (45.0 g) and filtrate (310.2 g) were separated and collected. The recovered solid precipitate was thoroughly washed with water and dried to yield 9.9 g of polyamide 66 powder (99.0% yield). Based on the weight ratio with respect to the wet state, it was calculated that the particles of the obtained polyamide 66 powder had 3.55 mL / g of voids. The weight-average molecular weight analyzed by GPC was 47,000. 185 g of the obtained filtrate and 9.3 g of polyamide 66 pellets were used to The same procedure as above (second polyamide production) was carried out, and 9.1 g of polyamide powder was obtained (yield 98.4%).

[0060] [Example 7] A 300 mL pressure-resistant stainless steel reactor equipped with a Teflon inner tube and a stir bar was charged with 10.0 g of polyamide 66 pellets and 230 g of calcium chloride methanol solution (50 g of calcium chloride dihydrate, 180.0 g of methanol). The mixture was then placed in a 140 °C oil bath and stirred with a magnetic stirrer for 8 hours to obtain a polyamide solution. The maximum pressure during stirring was 1.0 MPa. The reactor was then removed from the oil bath and allowed to cool to room temperature. The reactor was then opened, and the slurry inside was transferred to a filter equipped with a 10 μm membrane filter. A solid precipitate (43.0 g) and a filtrate (194.0 g) were separated and collected. The collected solid precipitate was thoroughly washed with water and dried to obtain 7.5 g of polyamide 66 powder (75.0% yield). Based on the weight ratio relative to the wet state, the resulting polyamide 66 powder particles were calculated to have a pore volume of 4.73 mL / g. The weight average molecular weight as determined by GPC analysis was 48,000. Using 180 g of the obtained filtrate and 7.8 g of polyamide 66 pellets, the same procedure as above (second polyamide production) was carried out, yielding 7.6 g of polyamide powder (yield 97.1%).

[0061] [Example 8] A 300 mL pressure-resistant stainless steel reactor equipped with a Teflon inner tube and a stir bar was charged with 10.0 g of polyamide 66 pellets and 230 g of calcium chloride methanol solution (50 g of calcium chloride dihydrate, 180.0 g of methanol). The reactor was placed in a 140 °C oil bath and stirred with a magnetic stirrer for 8 hours to dissolve the mixture, yielding a polyamide solution. The maximum pressure during stirring was 1.0 MPa. The reactor was then removed from the oil bath and allowed to air-cool to room temperature. The reactor was then opened, and the solution was mixed with 45 g of methanol and 5 g of water, then air-cooled to room temperature. The slurry was then poured into a filter equipped with a 10 μm membrane filter, and the solid precipitate (35.0 g) and filtrate (254.1 g) were separated and collected. The recovered solid precipitate was thoroughly washed with water and dried, yielding 9.8 g of polyamide 66 powder (98.0% yield). Based on the weight ratio with respect to the wet state, it was calculated that the particles of the obtained polyamide 66 powder had 2.57 mL / g of voids. The weight-average molecular weight analyzed by GPC was 47,000. Using 220 g of the obtained filtrate and 9.6 g of polyamide 66 pellets, the same procedure as above (second polyamide production) was carried out, yielding 9.5 g of polyamide powder (yield 99.3%).

[0062] [Example 9] A 300 mL pressure-resistant stainless steel reactor equipped with a Teflon inner tube and a stir bar was charged with 10.0 g of polyamide 66 pellets and 200 g of calcium chloride methanol solution (20 g calcium chloride, 180.0 g methanol). The reactor was placed in a 160 °C oil bath and stirred with a magnetic stirrer for 8 hours to dissolve the mixture, yielding a polyamide solution. The maximum pressure during stirring was 1.0 MPa. The reactor was then removed from the oil bath and allowed to air-cool to room temperature. The reactor was then opened, and the slurry inside was poured into a filter equipped with a 10 μm membrane filter. A solid precipitate (36.0 g) and a filtrate (172 g) were separated and recovered. The recovered solid precipitate was thoroughly washed with water and dried to obtain 9.6 g of polyamide 66 powder (96.0% yield). Based on the weight ratio relative to the wet state, the resulting polyamide 66 powder particles were calculated to have 2.75 mL / g of voids. The weight average molecular weight as determined by GPC analysis was 44,000. Using 169 g of the obtained filtrate and 8.5 g of polyamide 66 pellets, the same procedure as above (second polyamide production) was carried out, yielding 8.1 g of polyamide powder (yield 95.9%).

[0063] [Comparative Example 1] A 300 mL glass bottle containing a stir bar was charged with 10.0 g of polyamide 66 pellets and 200 g of calcium chloride methanol solution (40.0 g calcium chloride, 160 g methanol). The bottle was placed in a 60°C water bath and dissolved with magnetic stirring for 24 hours. Dissolution was carried out at atmospheric pressure. The resulting solution was transferred to a 2 L beaker, and 630 g of methanol was added with a stir bar while stirring. The resulting slurry was poured into a filter equipped with a 10 μm membrane filter, and a solid precipitate (78.4 g) and a filtrate (760.2 g) were separated and collected. The collected solid precipitate was thoroughly washed with water and dried to obtain 9.8 g of polyamide 66 powder (98.0% yield). Based on the weight ratio to the wet state, the resulting polyamide 66 powder particles were calculated to have 7.0 mL / g of voids. GPC analysis revealed a weight-average molecular weight of 47,000. The same procedure as above was carried out using 750.0 g of the obtained filtrate and 37.5 g of polyamide 66 pellets, but the pellets did not dissolve. The filtrate was concentrated using an evaporator, and 640.0 g of methanol was distilled off to obtain a concentrate (110.0 g). The same procedure as above was carried out using 5.5 g of polyamide 66 pellets, yielding 5.4 g of polyamide powder (yield 98.0%).

[0064] [Table 1] [Industrial Applicability]

[0065] The production method of this embodiment can provide a method for producing polyamide that is excellent in polyamide recovery efficiency while reducing the energy used during recycling.

Claims

1. The following process: Step 1: A step of dissolving a raw material polyamide composition in a first metal chloride alcohol solution containing a metal chloride and an alcohol under heating to obtain a polyamide solution; Step 2: cooling the polyamide solution obtained in step 1 to separate it into a polyamide and a second alcohol solution of a metal chloride; Including, the temperature during the heating and dissolving in step 1 is higher than the boiling point of the alcohol by 5°C or more, and the pressure is higher than 0.1 MPa; A method for producing polyamide, characterized by:

2. 2. The method for producing a polyamide according to claim 1, wherein the second metal chloride alcohol solution obtained in step 2 is used as the first metal chloride alcohol solution.

3. 3. The method for producing a polyamide according to claim 1, wherein the mass ratio of the metal chloride in 100 mass% of the first metal chloride alcohol solution is 5 to 15 mass%.

4. 3. The method for producing a polyamide according to claim 1, wherein the mass ratio (mass%) of the metal chloride in 100 mass% of the second alcoholic solution of metal chloride is 0.9 to 1.1 times the mass ratio (mass%) of the metal chloride in 100 mass% of the first alcoholic solution of metal chloride.

5. the first metal chloride alcoholic solution and the second metal chloride alcoholic solution contain water; 3. The method for producing a polyamide according to claim 1, wherein the mass ratio (mass%) of water in 100 mass% of the second alcoholic solution of metal chloride is 0.9 to 1.1 times the mass ratio (mass%) of water in 100 mass% of the first alcoholic solution of metal chloride.

6. the mass ratio of the metal chloride in 100 mass% of the first metal chloride alcohol solution is 10 mass% or less, the molar ratio of water to 1 mole of metal chloride in the first metal chloride alcohol solution is 0.2 to 2.5 moles; the temperature of the heating and dissolving in step 1 is higher than the boiling point of the first metal chloride alcohol solution by 5°C or more and lower than 100°C; A method for producing the polyamide according to claim 1 or 2.

7. the mass ratio of the metal chloride in 100 mass% of the first metal chloride alcohol solution is 10 mass% or less, the molar ratio of water to 1 mole of metal chloride in the first metal chloride alcohol solution is 0.2 to 2.5 moles; The temperature of the heating and dissolving in the step 1 is 100 to 160°C. A method for producing the polyamide according to claim 1 or 2.

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