Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B17/00—Recovery of plastics or other constituents of waste material containing plastics
  • B29B17/02—Separating plastics from other materials
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J11/00—Recovery or working-up of waste materials
  • C08J11/04—Recovery or working-up of waste materials of polymers
  • C08J11/06—Recovery or working-up of waste materials of polymers without chemical reactions
  • C08J11/08—Recovery or working-up of waste materials of polymers without chemical reactions using selective solvents for polymer components
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/02—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques
  • C08J3/09—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques in organic liquids
  • C08J3/11—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques in organic liquids from solid polymers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/62—Plastics recycling; Rubber recycling

Definitions

• the present invention relates to a method for producing polyamide, a method for producing a polyamide solution, and a polyamide solution.
• Polyamides including polyamide 6 and polyamide 66, are representative engineering plastics that have excellent heat resistance and mechanical properties and are widely used in textiles, automobile parts, electrical appliance parts, and more, making them one of the irreplaceable materials in modern society.
• polyamide 66 polyhexamethylene adipamide
• polyamide 66 polyhexamethylene adipamide
• One possible method for recycling polyamide is to dissolve the polyamide in a solvent, remove impurities as insoluble matter, and then precipitate and recover the polyamide by some method, for example, adjusting the polyamide concentration by concentration or dilution, or adjusting the polyamide solubility by addition of a poor solvent or cooling (Patent Documents 1 and 2).
• many of the solvents that dissolve polyamides are not suitable for industrial use, such as strong acids such as formic acid and sulfuric acid, and expensive solvents such as HFIP.
• An example of the use of a solvent that is easy to use industrially is a dissolution and recovery method using ethylene glycol (Patent Document 1).
• Patent Document 2 describes a method in which a silicone-coated polyamide cloth is treated with a methanol solution of calcium chloride to dissolve the polyamide, and the polyamide is diluted with a large amount of water or methanol to obtain the desired polyamide as a powder.
• Patent Document 2 When recycling polyamide by dissolving in such an alcohol solution of metal chlorides, it is preferable to reuse the solution since it is undesirable to discard the solution after polyamide precipitation as it places an environmental burden and increases the amount of raw materials used, and Patent Document 2 also describes a method of reusing the solution. This method involves drying and recovering the metal chlorides, and then adding alcohol again to dissolve them, but because metal chlorides strongly interact with the solvent, drying requires a large amount of energy, which is fatal for a recycling process aimed at reducing the environmental burden.
• the object of the present invention is to provide a method for producing polyamide that requires less energy and produces less waste when recycling polyamide by dissolving it in an alcoholic solution of a metal chloride.
• the steps include: heating and dissolving a polyamide composition in a first metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a heated polyamide solution; mixing the heated polyamide solution obtained in the above step with a poor solvent to precipitate polyamide; performing solid-liquid separation of the mixture of the precipitated polyamide and the solution in the above step into polyamide and solution to recover polyamide; and using the solid-liquid separated solution in the above step as a raw material to obtain a second metal chloride alcohol solution in which the solubility of polyamide is within a predetermined range.
• Step 1 A step of heating and dissolving a polyamide composition in a first metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a heated polyamide solution
• Step 2 mixing the heated polyamide solution obtained in step 1 with a poor solvent to precipitate a polyamide
• Step 3 A step of recovering the polyamide by subjecting the mixture of the precipitated polyamide and the solution in step 2 to solid-liquid separation into the polyamide and the solution
• step 4 using the solution obtained by solid-liquid separation in step 3 as a raw material, obtaining a second metal chloride alcohol solution in which the solubility of polyamide is 90% or more of the solubility of polyamide in the first metal chloride alcohol solution.
• the poor solvent is the alcohol, 2.
• the second alcohol solution of metal chloride is obtained by concentrating the solution obtained by solid-liquid separation in step 3 and/or by adding a metal chloride to the solution obtained by solid-liquid separation.
• step 4 comprises a step of reducing the alcohol content by removing an alcohol component from a solution using the solution obtained by solid-liquid separation in step 3 as a raw material, thereby obtaining a second alcohol solution of a metal chloride.
• Step 1 A step of heating and dissolving a polyamide composition in a first metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a heated polyamide solution
• Step 2 mixing the heated polyamide solution obtained in step 1 with a poor solvent to precipitate a polyamide
• Step 3 A step of recovering the polyamide by subjecting the mixture of the precipitated polyamide and the solution in step 2 to solid-liquid separation into the polyamide and the solution
• step 4 using the solution obtained by solid-liquid separation in step 3 as a raw material, obtaining a polyamide solution as a second metal chloride alcohol solution in which the solubility of polyamide is 90% or more of the solubility of polyamide in the first metal chloride alcohol solution.
• a polyamide solution comprising a metal chloride, an alcohol, and a compound having an amide bond with a molecular weight of 1,000 or less, wherein the concentration of the compound having an amide bond with a molecular weight of 1,000 or less is 0.1% by mass or more and 5% by mass or less.
• the present invention provides a method for recycling polyamide by dissolution that can reduce the energy required for recovering polyamide while maintaining sufficient solubility of the polyamide solution reused from the residual solution.
• the method for producing polyamide according to the present embodiment is a method for producing a product polyamide (usually a powdery polyamide precipitated by crystallization) from a raw polyamide (hereinafter referred to as a "polyamide composition").
• the method can be used for recycling polyamide and purifying polyamide, and can be particularly used for recycling polyamide.
• the polyamide composition is dissolved in a metal chloride alcohol solution, which is a polyamide dissolving solution, and the polyamide is precipitated using a poor solvent, and the polyamide is recovered by solid-liquid separation, thereby producing polyamide.
• a polyamide dissolving solution which is a solvent capable of sufficiently dissolving polyamide, can also be obtained from the residual solution after polyamide recovery. This makes it possible to sufficiently maintain the solubility of the polyamide dissolving solution reused from the residual solution while reducing the waste rate of the residual solution after polyamide recovery.
• the method for producing a polyamide of the present invention comprises the following steps: Step 1: A step of heating and dissolving a polyamide composition in a first metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a heated polyamide solution; Step 2: mixing the heated polyamide solution obtained in step 1 with a poor solvent to precipitate a polyamide; Step 3: A step of recovering the polyamide by subjecting the mixture of the precipitated polyamide and the solution in step 2 to solid-liquid separation into the polyamide and the solution; Step 4: A step of obtaining a second metal chloride alcohol solution in which the solubility of polyamide is 90% or more of the solubility of polyamide in the first metal chloride alcohol solution, using as a raw material the solution obtained by solid-liquid separation in step 3.
• the method for producing a polyamide may further include steps (referred to as "other steps") other than steps 1 to 4. In the method for producing a polyamide, steps 1 to 4 and optionally other steps may be repeated.
• the polyamide used as the raw material is called the "polyamide composition”.
• the "polyamide composition” refers to a polyamide-containing object before recycling, such as a polyamide-containing part, a polyamide-containing member, an object from which non-polyamide-containing parts have been removed, and crushed products thereof.
• the polyamide manufacturing method is used for purifying polyamide
• the "polyamide composition” refers to the polyamide before purification.
• the polyamide composition may consist of polyamide alone, or may further contain other components. Examples of other components include heat stabilizers.
• the polyamide composition may also be in the form of a composite of polyamide and various other polymers (e.g., coating, laminate, blend, polymer alloy, etc.).
• the other polymers preferably have resistance to dissolution in metal chloride alcohols, and examples of such other polymers include polyolefins, nitriles, polyesters, polyimides, and silicones.
• a polymer polymerized through an amide bond such as a polycondensation product of a diamine compound and a dicarboxylic acid compound, or a ring-opening polymerization product of a cyclic lactam
• the diamine compound is not particularly limited, but examples thereof include ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, nonanediamine, methylpentanediamine, and p-phenylenediamine.
• polyamide examples include polycaproamide (nylon 6), polyhexamethylene adipamide (nylon 66), polytetramethylene adipamide (nylon 46), polytetramethylene sebacamide (nylon 410), polypentamethylene adipamide (nylon 56), polypentamethylene sebacamide (nylon 510), polyhexamethylene sebacamide (nylon 610), polyhexamethylene dodecamide (nylon 612), polydecamethylene adipamide (nylon 106), polydecamethylene sebacamide (nylon 1010), poly Lidecamethylene dodecamide (nylon 1012), polyundecaneamide (nylon 11), polydodecanamide (nylon 12), polycaproamide/polyhexamethylene adipamide copolymer (nylon 6/66), polycaproamide/polyhexamethylene terephthalamide copolymer (nylon 6/6T), polyhexamethylene adipamide/polyhexamethylene terephthalamide
• polyamide 66 itself is a polyamide resin already generally known, and is usually produced by polycondensation of hexamethylenediamine and adipic acid.
• polyamide 66 may be a copolymer containing at least one monomer unit selected from the group consisting of lactam, aminocarboxylic acid, and combinations of other diamines and dicarboxylic acids in an amount of less than 30% by mass based on the total mass of all monomer units.
• polyamides may be commercially available or may be produced by known methods. There are no particular limitations on the specific method for producing polyamides, but examples include a method of ring-opening polymerization of lactams, a method of self-condensation of ⁇ -aminocarboxylic acids, and a method of condensing diamines and dicarboxylic acids.
• the product polyamide may be a simple "polyamide” or may be produced as a "polyamide composition" containing polyamide, solvent, and additives.
• the “polyamide” produced refers to the polyamide after recycling.
• the “polyamide” refers to the polyamide after purification.
• Metal chloride alcohol solution refers to a solution containing a metal chloride and an alcohol.
• the metal chloride alcohol solution may further contain components other than the metal chloride and the alcohol.
• the metal chloride alcohol solution functions as a dissolving liquid for dissolving polyamide, that is, a good solvent for polyamide.
• the metal chloride alcohol solution used as a solvent for dissolving the polyamide composition by heating is called the “first metal chloride alcohol solution”
• the metal chloride alcohol solution obtained as a polyamide dissolving liquid from the solution after polyamide recovery is called the “second metal chloride alcohol solution”.
• the "second metal chloride alcohol solution” must be capable of sufficiently dissolving polyamide.
• the second metal chloride alcohol solution can be used as a solvent for dissolving another polyamide, for example, as the first metal chloride alcohol solution in the method for producing polyamide. This makes it possible to sufficiently maintain the concentration of the obtained polyamide solution while reducing the waste rate of the remaining solution after polyamide recovery.
• the total mass ratio of the metal chloride and alcohols relative to 100% by mass of the metal chloride alcohol solution is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, from the viewpoint of the solubility of the polyamide.
• Alcohols contained in the first and second metal chloride alcohol solutions include monoalcohols such as methanol, ethanol, linear or branched propanol, linear or branched butanol, diols such as ethylene glycol, propylene diol (e.g., propylene glycol), butanediol, diethylene glycol, trihydric alcohols such as glycerin, other polyhydric alcohols, combinations of these, etc.
• monoalcohols such as methanol, ethanol, linear or branched propanol, linear or branched butanol
• diols such as ethylene glycol, propylene diol (e.g., propylene glycol), butanediol, diethylene glycol
• trihydric alcohols such as glycerin, other polyhydric alcohols, combinations of these, etc.
• methanol, ethanol, or combinations of these are preferred from the viewpoint of the solubility of polyamide, and methanol is
• Metal chlorides contained in the first and second metal chloride alcohol solutions include zinc chloride, magnesium chloride, calcium chloride, etc., with zinc chloride and calcium chloride being preferred, and calcium chloride being most preferred.
• the mass proportion of water in the metal chloride is not particularly limited, and may be adjusted so that the water content in the alcoholic solution of the metal chloride is the desired amount, and the metal chloride may be anhydrous, hydrated, or a mixture thereof.
• the concentration of the metal chloride in the metal chloride alcohol solution is preferably 15% by mass or more, more preferably 18% by mass or more, and even more preferably 20% by mass or more, from the viewpoint of improving the solubility of the polyamide composition.
• the concentration of the metal chloride in the metal chloride alcohol solution is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less, from the viewpoint that if the concentration is too high, the metal chloride is likely to remain undissolved and is likely to be mixed in as an impurity.
• Other preferable properties of the "second metal chloride alcohol solution” will be described in "Step 4" below.
• the water concentration in the metal chloride alcohol solution is preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less from the viewpoint of improving the solubility of the polyamide composition, while the water concentration is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more from the viewpoint of improving the solubility of calcium chloride in methanol.
• the term "poor solvent” refers to a poor solvent for polyamide, and is used to precipitate polyamide by mixing with a heated polyamide solution.
• the poor solvent is a poor solvent for polyamide, preferably a solvent compatible with the metal chloride alcohol solution, and is not particularly limited as long as it dissolves metal chloride.
• Examples of the poor solvent include a water-containing solution and an alcohol-containing solution. From the viewpoint of reducing the amount of accumulated moisture, which is a dissolution inhibitor in the metal chloride alcohol solution after reuse, an alcohol-containing solution that does not contain water is preferred.
• the solubility of the metal chloride alcohol solution can be restored by distilling off a part of the solvent from the solution after precipitating the polyamide.
• the alcohol component removed in step 4 from the solution using the solution obtained by solid-liquid separation in step 3 as the raw material may be used as the poor solvent for step 2 from the next time onwards.
• the solvent may be such that, when 100 g of the solvent is added to 1 g of polyamide (eg, nylon 66) and the mixture is stirred at 20° C. for 1 hour, the amount of polyamide dissolved in the solution is 0.05 g or less.
• the water-containing solution is a liquid containing water or water and a component other than water, such as alcohols (e.g., those exemplified as alcohols contained in the metal chloride alcohol solution), salts, pH adjusters, etc.
• salts include alkali metal salts, alkaline earth metal salts, transition metal salts, and ammonium salts, and more preferably sodium salts, potassium salts, lithium salts, calcium salts, magnesium salts, barium salts, strontium salts, copper salts, and ammonium salts.
• anions of salts include chloride ions, fluoride ions, bromide ions, iodide ions, sulfate ions, sulfite ions, phosphate ions, nitrate ions, nitrite ions, methanesulfonate ions, benzenesulfonate ions, toluenesulfonate ions, citrate ions, oxalate ions, malate ions, tartrate ions, maleate ions, fumarate ions, and acetate ions.
• Preferred salts include sodium chloride, potassium chloride, lithium chloride, calcium chloride, magnesium chloride, sodium bromide, potassium bromide, calcium bromide, magnesium bromide, sodium sulfate, potassium sulfate, sodium nitrate, potassium nitrate, calcium nitrate, magnesium nitrate, etc.
• pH adjusters include water-soluble basic salts, acid salts, and buffers (e.g., mixtures of acids and salts, mixtures of bases and salts), such as sodium acetate, potassium acetate, sodium phosphate, disodium monohydrogen phosphate, monosodium dihydrogen phosphate, potassium phosphate, dipotassium monohydrogen phosphate, monopotassium dihydrogen phosphate, acetate buffers (e.g., mixtures of acetic acid and sodium acetate), and phosphate buffers (e.g., mixtures of acetic acid and sodium acetate).
• buffers e.g., mixtures of acids and salts, mixtures of bases and salts
• the water-containing solution is a liquid containing alcohols or alcohols and components other than alcohols.
• alcohols include those exemplified as alcohols contained in the metal chloride alcohol solution.
• components other than alcohols include salts.
• salts include those exemplified as salts that may be contained in the water-containing solution.
• the concentration of the metal chloride in the alcohol-containing solution is preferably as low as possible, preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less.
• the water-free alcohol-containing solution refers to an alcohol-containing solution that does not intentionally use water as a raw material, and may contain a small amount of water. For example, the water content of the alcohol-containing solution may be 0.5% by mass or less.
• Step 1 is a step of heating and dissolving a polyamide composition in a first metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a heated polyamide solution.
• the polyamide contained in the polyamide composition is sufficiently dissolved in the metal chloride alcohol solution, which is a solvent.
• the preferable conditions for step 1 are described below.
• the concentration of the polyamide in the heated polyamide solution is preferably 5% by mass or more, more preferably 7% by mass or more, and preferably 15% by mass or less, and more preferably 13% by mass or less.
• the temperature for heating and dissolving is not particularly limited, but is preferably 30° C. or higher, more preferably 40° C. or higher, and preferably 90° C. or lower, and more preferably 75° C. or lower.
• the temperature at 30° C. or higher dissolution does not take too long, while setting the temperature at 90° C. or lower not only prevents the alcohol from volatilizing, maintains solubility, but also contributes to suppressing corrosion of the equipment and solvolysis of the polyamide (e.g., alcoholysis and hydrolysis).
• the temperature may be constant or may be changed within the above range.
• the time for heating and dissolving is preferably as long as possible from the viewpoint of sufficiently dissolving the polyamide composition, and is, for example, preferably 5 minutes or more, more preferably 30 minutes or more, and even more preferably 1 hour or more.
• the time for heating and dissolving is preferably not too long from the viewpoints of preventing deterioration of the polyamide due to heating, loss of alcohols in the metal chloride alcohol solution due to volatilization, and suppressing production costs, and is, for example, preferably 100 hours or less, more preferably 50 hours or less, and even more preferably 24 hours or less.
• the dissolution may be carried out in either a batch or continuous manner.
• a batch method there is no particular limitation as to whether or not stirring is performed, but stirring is preferred, as stirring increases the dissolution rate of the polyamide solid.
• the solvent may be continuously passed through the solid, or the solution may be circulated. Circulation is preferred because it allows the amount of solvent used to be reduced.
• the shape of the container is not particularly limited, and any shape such as a tank type or a circulation type may be used.
• the shape of the container used when the polyamide resin composition and the alcohol solution of the metal chloride are heated and dissolved is not particularly limited, and any shape such as a tank type or a circulation type may be used.
• the materials of the containers and piping are also not particularly limited, and examples thereof include SUS316, SUS316L, SUS329J4L, and SUS444.
• the surfaces of these materials may be lined or coated, and examples of such treatment include glass, fluorine-based resin, rubber, and epoxy, and from the viewpoint of corrosion resistance, glass and fluorine resin are preferred.
• the materials of the container and piping themselves can be selected without considering the corrosiveness.
• Step 2 is a step of mixing the heated polyamide solution obtained in step 1 with a poor solvent to precipitate the polyamide.
• the heated polyamide solution is placed in a poor solvent-containing environment from a good solvent environment of a metal chloride alcohol solution, and the solubility of the polyamide decreases, causing it to precipitate. Preferred conditions for step 2 are described below.
• the manner in which the heated polyamide solution and the poor solvent are mixed in step 2 is not particularly limited, and examples thereof include a manner in which the heated polyamide solution is added to the poor solvent, a manner in which the poor solvent is added to the heated polyamide solution, a manner in which the heated polyamide solution and the poor solvent are added to a container, etc.
• the manner of addition is not particularly limited, and examples thereof include dripping, continuous injection from above the liquid, spraying, etc. During mixing, the solution may be left to stand without stirring, or may be stirred.
• the mass of the poor solvent used in step 2 is preferably 1 time or more, more preferably 2 times or more, and even more preferably 3 times or more, relative to the mass of the heated polyamide solution.
• the upper limit is preferably 10 times or less, more preferably 5 times or less, and even more preferably 3 times or less.
• the temperature of the solution during mixing is preferably a temperature at which the solution does not freeze, and is, for example, preferably 10° C. or higher, more preferably 15° C. or higher, even more preferably 20° C. or higher, and preferably 90° C. or lower, more preferably 75° C. or lower.
• the temperature of the solution may be constant throughout the process, or may be changed from the temperature at the time of mixing. For example, it is possible to add a poor solvent at 90° C. and lower the temperature to 10° C. Heating and cooling may be repeated to change the state of the precipitated particles.
• the time taken for precipitation is not particularly limited. By changing the time for adding the solution and/or poor solvent, the desired precipitation rate, precipitation temperature range, etc. can be achieved, and the shape and properties of the particles can be changed. In addition, by providing a mixing time after the addition, it is possible to stabilize the yield and control the state of the particle surface modification, secondary particle generation, particle crushing, etc.
• Step 3 is a step of recovering polyamide by separating the mixture of the precipitated polyamide and the solution in step 2 into polyamide and the solution.
• the recovery method by solid-liquid separation may be a commonly used solid-liquid separation method.
• the recovery method by solid-liquid separation may be appropriately selected depending on the shape of the polyamide, and examples thereof include filtration, centrifugation (when the polyamide is a powder, particle, or solid object having a size that can be handled manually), scooping up using a mesh or perforated tool (when the polyamide is a particle or solid object having a size that can be handled manually), and pulling up using a rod-shaped tool (when the polyamide is a solid object having a size that can be handled manually).
• the polyamide recovered by solid-liquid separation may be washed with a solvent.
• Metal chlorides and other impurities can be removed from the recovered polyamide by washing. Washing may be performed once or multiple times.
• the solvent used for washing is preferably a solvent capable of dissolving metal chlorides.
• solvents examples include monoalcohols such as methanol, ethanol, linear or branched propanol, linear or branched butanol, diols such as ethylene glycol, propylene diol (e.g., propylene glycol), butanediol, and diethylene glycol, trihydric alcohols such as glycerin, other polyhydric alcohols, combinations of these alcohols, water, etc., and from the viewpoint of reusing the solvent after washing, it is preferable to use the same alcohol as in step 1.
• water is preferable as the solvent used for washing. For example, by using the same alcohol as in step 1 for the first washing and using water for the second washing and thereafter, recovery of metal chlorides and washing efficiency can be achieved at the same time.
• Step 4 is a step of obtaining a second metal chloride alcohol solution having a polyamide solubility within the above-mentioned predetermined range from the solution obtained by solid-liquid separation in step 3 (hereinafter, sometimes referred to as "residual solution").
• residual solution the solution obtained by solid-liquid separation in step 3
• the washing liquid may be mixed with the solution obtained by solid-liquid separation.
• the second metal chloride alcohol solution can be used as a polyamide dissolving solution because the polyamide solubility is within the above-mentioned predetermined range.
• the second metal chloride alcohol solution (i.e., polyamide dissolving solution) obtained in step 4 can be used as a solvent for further dissolving another polyamide.
• the second metal chloride alcohol solution obtained in step 4 can be used as the first metal chloride alcohol solution used in the next step 1. This makes it possible to reduce the amount of the solution after polyamide recovery that is discarded as waste liquid and to reduce the loss of metal chlorides and alcohols, which are components of the metal chloride alcohol solution used as a polyamide dissolving solution.
• the solubility of polyamide In order for the second metal chloride alcohol solution obtained in step 4 to be a solution capable of sufficiently dissolving polyamide, the solubility of polyamide must be 90% or more of the solubility of polyamide in the first metal chloride alcohol solution, preferably 95% or more, and more preferably 98% or more.
• the solubility of polyamide in the second metal chloride alcohol solution obtained in each step 4 is preferably 90% or more of the solubility of polyamide in the first metal chloride alcohol solution used in the initial step 1, more preferably 95% or more, and even more preferably 98% or more.
• the solubility of polyamide can be measured, for example, by the method described in the Examples.
• the concentration of the metal chloride contained in the second metal chloride alcohol solution is preferably 80 to 120% of the concentration of the metal chloride contained in the first metal chloride alcohol solution, more preferably 90 to 110%, and even more preferably 95 to 105% or less. If the difference with the concentration of the first metal chloride alcohol solution is large, the liquid properties such as density and viscosity will change, making it necessary to change the process conditions. Therefore, in order to avoid changing the process conditions, it is preferable that the concentration of the metal chloride contained in the second metal chloride alcohol solution relative to the concentration of the metal chloride contained in the first metal chloride alcohol solution is within the above range.
• the second metal chloride alcohol solution obtained in step 4 preferably has a concentration of compounds having an amide bond with a molecular weight of 1000 or less, which causes a decrease in the dissolution rate, as low as possible.
• concentration of compounds having an amide bond with a molecular weight of 1000 or less contained in the second metal chloride alcohol solution obtained in step 4 is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 0.5% by mass or less.
• the concentration of compounds having an amide bond with a molecular weight of 1000 or less contained in the second metal chloride alcohol solution is preferably 200% or less, more preferably 150% or less, and even more preferably 100% or less of the concentration of compounds having an amide bond with a molecular weight of 1000 or less contained in the first metal chloride alcohol solution.
• the second metal chloride alcohol solution obtained in step 4 preferably has a water concentration that causes a decrease in the dissolution rate of polyamide as low as possible.
• the water concentration contained in the second metal chloride alcohol solution obtained in step 4 is preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less.
• the water concentration is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more.
• the water content in the second metal chloride alcohol solution is as small as possible relative to the water content of the first metal chloride alcohol solution.
• the difference obtained by subtracting the water concentration in the first metal chloride alcohol solution from the water concentration in the second metal chloride alcohol solution obtained in step 4 is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less.
• step 4 may include a step (restoration step) of restoring the solution made from the solution (residual solution) separated in step 3 so that the solubility of the polyamide is within the above-mentioned predetermined range to obtain a second metal chloride alcohol solution.
• the restoration step may be performed by removing the alcohol component from the solution made from the solution (residual solution) separated in step 3 to reduce the alcohol content and obtain a second metal chloride alcohol solution (i.e., obtaining the residual solution with a reduced alcohol content as the second metal chloride alcohol solution).
• the alcohol component may be removed, for example, by distilling off the alcohol component by heating and/or reducing pressure, membrane separation, etc.
• alcohol which is the solvent of the first metal chloride alcohol solution
• the amount of alcohol to be distilled off may be set to a level where the solubility of the polyamide is 90% or more of the solubility of the polyamide in the first metal chloride alcohol solution.
• the amount of heat required for regeneration of the solution can be reduced, which is preferable from the viewpoint of saving resources and energy.
• the amount of heat required is 2.0 to 3.2 kJ/g.
• the amount of heat required is 1.1 to 2.1 kJ/g.
• the amount of heat required is 1.1 kJ/g or less.
• the amount of heat required is indicated as a value obtained by dividing the amount of heat calculated from the amount of solvent distilled off and the latent heat by the amount of dilution solvent.
• the restoration step may be performed by adding a metal chloride component or an alcohol solution in which a metal chloride component is dissolved to the residual solution to increase the metal chloride content, and obtaining the residual solution with an increased metal chloride content as the second metal chloride alcohol solution.
• the metal chloride may be added to the remaining solution, or the metal chloride concentration may be increased by partially distilling off the solvent and/or membrane separation, as in the restoration step described above.
• the solubility of the polyamide may be restored to 90% or more of the first metal chloride alcohol solution by the restoration step alone, or it may be stopped at less than 90% and restored to 90% or more by adding the metal chloride component or an alcohol solution in which the metal chloride component is dissolved.
• step 4 may include a step (confirmation step) of confirming that the solubility of the polyamide in the second metal chloride alcohol solution is within the above-mentioned specified range.
• the measurement of the solubility of the polyamide in the confirmation step can be performed, for example, by the method described in the Examples.
• the solubility of the polyamide can also be calculated by clarifying the correlation between the solution composition, such as the metal chloride concentration, water content, low molecular weight components, and alcohol content, and the solubility of the polyamide.
• step 4 may include a step of discarding a part of the solution (residual solution) obtained by solid-liquid separation in step 3 (partial discarding step) and a step of replenishing the residual solution with alcohol and/or metal chloride (replenishing step).
• the method for producing polyamide may further include a step of removing impurities other than polyamide from the heated polyamide solution after step 1 (hereinafter, sometimes referred to as an "impurity removing step").
• the impurity removing step is not particularly limited, but may be performed by, for example, removing impurities as insoluble components by filtration, centrifugation, etc.
• impurities such as water and low molecular weight polyamide (partly as insoluble matter) will accumulate in the solution by repeating the process.
• the solution to be repeatedly used is controlled so that the concentration of water and/or low molecular weight polyamide does not exceed a certain value, and when the concentration of water and/or low molecular weight polyamide exceeds the control value as a result of repeated use, it is preferred to operate the solution so that the concentration of water and/or low molecular weight polyamide falls below the control value by, for example, discarding a part or all of the solution.
• the same raw material is used regularly, for example, the accumulated amount of impurities such as water and low molecular weight polyamide is constant or the fluctuation is small
• the amount and number of times of disposal can be determined in advance so that the amount does not exceed a certain value regularly. For example, if it is estimated that the amount exceeds a certain value after 10 repeated uses, a method of discarding 10% of the solution each time or discarding 20% every other time can be used.
• the method for producing polyamide may further include, after step 3, a step of washing the polyamide with a washing solution (hereinafter, sometimes referred to as the "washing step") and a step of removing the attached solution from the polyamide (hereinafter, sometimes referred to as the "attached solution removing step”).
• a washing solution hereinafter, sometimes referred to as the "washing step”
• a step of removing the attached solution from the polyamide hereinafter, sometimes referred to as the "attached solution removing step”
• the washing solution used in the washing step include the liquids exemplified as the alcohol solution and the water-containing solution.
• Examples of the alcohol include monoalcohols such as methanol, ethanol, linear or branched propanol, linear or branched butanol, etc.; diols such as ethylene glycol, propylene diol (e.g., propylene glycol), butanediol, diethylene glycol, etc.; trihydric alcohols such as glycerin; other polyhydric alcohols; and combinations of these, etc., but it is preferable to use the alcohol used in the metal chloride alcohol solution.
• multiple washing solutions may be selected, and from the viewpoint of cleaning properties, it is preferable to wash with a water-containing solution after washing with an alcohol solution.
• methods for performing the attached solution removing step include drying (e.g., heat drying, reduced pressure drying, air drying, etc.), centrifugation, squeezing, etc.
• the same method as described above as the "production method of polyamide” can also be used as the "production method of polyamide solution”. That is, the production method of polyamide solution of the present invention produces a product polyamide from a raw material polyamide (hereinafter referred to as a "polyamide composition"), and can obtain a polyamide solution capable of sufficiently dissolving polyamide from the remaining solution after polyamide recovery.
• This method makes it possible to reduce the amount of the remaining solution after polyamide recovery that is discarded as waste liquid, and to reduce the loss of metal chlorides and alcohols, which are components of the metal chloride alcohol solution used as the polyamide solution.
• the method for producing a polyamide solution of the present invention includes the following steps: Step 1: A step of heating and dissolving a polyamide composition in a first metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a heated polyamide solution; Step 2: mixing the heated polyamide solution obtained in step 1 with a poor solvent to precipitate a polyamide; Step 3: A step of recovering the polyamide by subjecting the mixture of the precipitated polyamide and the solution in step 2 to solid-liquid separation into the polyamide and the solution; Step 4: A step of obtaining a polyamide solution as a second metal chloride alcohol solution, using the solution obtained by solid-liquid separation in step 3 as a raw material, in which the solubility of polyamide is 90% or more of the solubility of polyamide in the first metal chloride alcohol solution.
• the polyamide composition, the polyamide produced, the metal chloride alcohol solution, and the poor solvent in the method for producing a polyamide solution are the same as those explained in the method for producing a polyamide.
• Steps 1 to 3 in the method for producing a polyamide solution are the same as those explained in the method for producing a polyamide.
• Step 4 in the method for producing a polyamide solution can be carried out under the same conditions as those explained in the method for producing a polyamide.
• the polyamide solution contains a metal chloride, an alcohol, and a compound having an amide bond with a molecular weight of 1000 or less, and the concentration of the compound having an amide bond with a molecular weight of 1000 or less is 0.1% by mass or more and 5% by mass or less.
• a polyamide solution having such a composition can sufficiently dissolve polyamide.
• the polyamide solution can be obtained by the above-mentioned "method for producing polyamide” or "method for producing polyamide solution”.
• the precipitated polyamide is generally in a powder form, it is preferable to mold it into a polyamide solid from the viewpoint of workability in the subsequent process.
• a polyamide solid rather than a powder form, there is an advantage that the raw material is not bulky when spinning polyamide fibers, and is easy to feed.
• Powdered polyamide may be extruded and melted to be molded into so-called pellets, but from the viewpoint of obtaining a polyamide solid with little thermal history, it is preferable to mold the polyamide powder without melting it. Examples of methods for obtaining such a polyamide solid include compression molding and extrusion granulation.
• the polyamide solid is preferably a compact formed by pressing the polyamide powder without melting it.
• a compact of the polyamide powder can be formed by compression molding or extrusion granulation without heating. From the viewpoint of molding the polyamide solid into a compact, it is preferable that the particles (granulation raw material) precipitated in step 3 are 2 mm or less in the total particles, and it is preferable that the particles of 1 mm or less in the total particles are 90% or more.
• the extrusion granulation method As a manufacturing method using the extrusion granulation method, for example, production using the extrusion granulation method can be mentioned.
• the granulation raw material containing the polyamide recovered in step 3 and other additives that are included as necessary can be fed into an extrusion granulator, and the extrudate can be cut and pelletized to produce a granulated product.
• the other additives mentioned above include water, organic solvents, etc. Compounds with a boiling point lower than the boiling point of water are preferred from the viewpoint of being removable in the drying process of the pellets before the spinning process.
• the temperature at which the polyamide recovered in step 3 is molded (for example, the temperature during extrusion granulation) is below the melting point of the polyamide recovered in step 3, from the viewpoint of suppressing the occurrence of black spots, and is preferably 200°C or lower, more preferably 20 to 150°C. It is acceptable for the temperature to deviate from the above temperature range locally and/or for a short period of time due to frictional heat during the molding process, etc.
• extrusion granulators examples include screw type extrusion granulators, roll type extrusion granulators, disk pelleter type extrusion granulators, pellet mill type extrusion granulators, basket type extrusion granulators, blade type extrusion granulators, oscillating type extrusion granulators, gear type extrusion granulators, ring die type extrusion granulators, etc.
• the size of the polyamide solids can be controlled by adjusting various parameters of the extrusion granulator. For example, in the case of a disk pelletizer type extrusion granulator, it can be controlled by adjusting the disk rotation speed, etc.
• the binder for wet granulation water is preferable from the viewpoint of eliminating the need for explosion-proof equipment.
• the amount of water added is preferably 5% or more, more preferably 7% or more, based on the polyamide.
• the binder is not included when used, and the binder is preferably volatile and added in an amount that is easy to remove after molding.
• the upper limit of the amount added is preferably 25% or less, more preferably 15% or less.
• wet granulation When wet granulation is performed, it is preferable to remove the water and/or organic solvent used in wet granulation after granulation.
• a method for removing the water and/or organic solvent after granulation for example, drying at a temperature of 60 to 100°C at atmospheric pressure or reduced pressure is preferable, and vacuum drying may be used.
• the polyamide solid is preferably prepared by stirring 1 g of the polyamide solid and 30 g of a solvent (e.g., a 20 wt % solution of calcium chloride in methanol) at 60° C.
• a solvent e.g., a 20 wt % solution of calcium chloride in methanol
• a separating material having a pore size of 10 ⁇ m e.g., a PTFE membrane filter having a pore size of 10 ⁇ m
• pressure e.g., filtering under pressure at a pressure of 0.01 MPa
• filtering 30 g of the solvent e.g., a 20 wt % solution of calcium chloride in methanol
• filtering under pressure at a pressure of 0.01 MPa passing 100 g of methanol through the filtering material, and then vacuum drying at 50° C.
• the number of insoluble particles having a major axis of 200 ⁇ m or less remaining on the separating material is preferably 50,000 or less per 1 g of the polyamide solid, and no insoluble particles having a major axis greater than 200 ⁇ m are present.
• the number of the above insoluble particles with a major axis of 200 ⁇ m or less remaining on the separation material is preferably 40,000 or less per gram of polyamide solid, and more preferably 20,000 or less.
• the insoluble matter remaining on the separation material in the above-mentioned measurement method may be insoluble matter that could not be removed in the above-mentioned step 2, or insoluble matter such as black spots that occurred during molding to obtain a polyamide solid.
• polyamide solids 1 g of polyamide solids and 30 g of a solvent (e.g., a 20 wt % solution of calcium chloride in methanol) are stirred at 60°C for 12 hours, and the resulting solution is pressure filtered and separated (e.g., pressure filtration and separation under conditions of 0.01 MPa) using a separation material with a pore size of 10 ⁇ m (e.g., a PTFE membrane filter with a pore size of 10 ⁇ m), and then 30 g of a solvent (e.g., a 20 wt % solution of calcium chloride in methanol) is pressure filtered (e.g., pressure filtration and separation under conditions of 0.01 MPa), and then 100 g of methanol is passed through, and then vacuum dried at 50°C.
• the mass of insoluble matter remaining on the separation material is preferably 0.5 ppm by mass or less, more preferably 0.4 ppm by mass or less, and even more preferably 0.2 pp
• the mass of the insoluble matter remaining on the separation material can be obtained by optically measuring the volume of the insoluble matter remaining on the separation material and calculating the mass of the insoluble matter based on the specific gravity of the polyamide solids.
• the insoluble matter remaining on the separation material in the above-mentioned measurement method may be insoluble matter that could not be removed in the above-mentioned step 2, or insoluble matter such as black spots that occurred during molding to obtain a polyamide solid.
• solubility of polyamide can be measured, for example, by the following method. 100 g of polyamide solution is weighed into a 250 mL glass bottle containing a stirrer. 10 g of polyamide is added, the bottle is closed, and the bottle is stirred while being heated to 50° C. in a water bath. After stirring for 24 hours, the temperature is returned to 25° C., and if no precipitation occurs, the same operation is repeated with additional polyamide. If precipitation occurs, the supernatant is filtered and collected, and water is added in an amount 10 times the amount of the collected liquid to precipitate polyamide. The precipitated polyamide is filtered and collected, thoroughly washed with water, and vacuum dried at 60° C., after which the collected weight is measured, and the solubility is calculated from the ratio of the dissolved amount to the collected liquid amount.
• 10 mg of the water-insoluble components are dissolved in 5 mL of eluent under the following GPC conditions as a sample, and GPC measurement is performed under the following conditions, and the concentration of the components with a molecular weight of 1000 or less in the water-insoluble components is calculated from the ratio of the peak area of the molecular weight of 1000 or less to the peak area of the molecular weight of 1000 or more.
• the weight of the components with a molecular weight of 1000 or less is calculated from the weight and concentration of the water-insoluble components, and the concentration in the solution is calculated from the solution weight.
• the amount of heat required for concentration is calculated by dividing the total amount of heat given below by the sum of the amount of poor solvent added and the amount of washing solvent used in the washing solution added to the filtrate, for comparison. -Adding Heat- - Latent heat of vaporization of the distilled alcohol - Latent heat of vaporization of the distilled water - The amount of heat required for the metal chloride to reach the desired hydrate from a stable hydrate For example, calcium chloride exists as a stable hexahydrate, and if the target hydrate is a dihydrate, the amount of heat required to remove water to that point can be calculated from the heat of hydration. The amount of heat required for the above calculation may be determined using information described in known literature.
• Example 1 10 g of polyamide 66 pellets and 100 g of 20 wt % calcium chloride methanol solution (water content 0.5 mass%, solubility of polyamide 66 15.0%) were added as polyamide dissolving solution to a 300 mL glass bottle containing a stirring bar, and the bottle was placed in a water bath at 60 ° C. and stirred with a magnetic stirrer for 12 hours to dissolve polyamide 66, to obtain a polyamide solution. The polyamide solution was transferred to a 500 mL three-neck flask equipped with a stirring blade, and 220 g of methanol was added while stirring to obtain a polyamide (polyamide 66) solid precipitate.
• 20 wt % calcium chloride methanol solution water content 0.5 mass%, solubility of polyamide 66 15.0%
• the resulting solid precipitate was filtered and collected with a 10 ⁇ m membrane filter. The filtrate at this time was 280 g.
• the solid precipitate after filtration was thoroughly washed with water.
• the solid precipitate after washing was heated and dried in a vacuum dryer at 80 ° C. to obtain 9.9 g (yield 99.0%) of powdered polyamide 66.
• the solution recovered after filtration was concentrated by an evaporator, and 192.5g of methanol (GC purity 99.0%) was obtained as a fraction, and 87.5g of calcium chloride methanol solution (containing 17.5g of calcium chloride) was obtained as a residue.
• the heat required at this time was 955.5 J/g.
• the solubility of polyamide 66 in this solution was 15%.
• the moisture content in the calcium chloride methanol solution was 0.7% by mass due to moisture absorption.
• the concentration of the compound having an amide bond with a molecular weight of 1000 or less was 0.2% by mass.
• the obtained solution was used as a polyamide dissolving solution and the same process as above was carried out to obtain powdered polyamide 66. The process could be carried out in the same manner as the first time, and powdered polyamide 66 was obtained in a yield of 98.9%.
• Example 2 10 g of polyamide 66 pellets and 100 g of 20 wt % calcium chloride methanol solution (water content 0.5 mass%, solubility of polyamide 66 15.0%) were added as polyamide dissolving solution to a 300 mL glass bottle containing a stirring bar, and the bottle was placed in a water bath at 60 ° C. and stirred with a magnetic stirrer for 12 hours to dissolve polyamide 66, to obtain a polyamide solution. The polyamide solution was transferred to a 500 mL three-neck flask equipped with a stirring blade, and 220 g of methanol was added while stirring to obtain a polyamide (polyamide 66) solid precipitate.
• 20 wt % calcium chloride methanol solution water content 0.5 mass%, solubility of polyamide 66 15.0%
• the resulting solid precipitate was filtered and collected with a 10 ⁇ m membrane filter. The filtrate at this time was 280 g.
• the solid precipitate after filtration was thoroughly washed with water.
• the solid precipitate after washing was heated and dried in a vacuum dryer at 80 ° C. to obtain 9.9 g (yield 99.0%) of powdered polyamide 66.
• the solution recovered after filtration was concentrated by an evaporator, and 187.3g of methanol (GC purity 99.0%) was obtained as a fraction, and 92.8g of calcium chloride methanol solution (containing 17.5g of calcium chloride) was obtained as a residue.
• the heat required at this time was 929.4 J/g.
• the solubility of polyamide 66 in this solution was 14%.
• the moisture content in the calcium chloride methanol solution was 0.7% by mass due to moisture absorption.
• the concentration of the compound having an amide bond with a molecular weight of 1000 or less was 0.2% by mass.
• the obtained solution was used as a polyamide dissolving solution and the same process as above was carried out to obtain powdered polyamide 66. The process could be carried out in the same manner as the first time, and powdered polyamide 66 was obtained in a yield of 98.7%.
• Example 3 10 g of polyamide 66 pellets and 100 g of 20 wt % calcium chloride methanol solution (water content 0.5 mass%, solubility of polyamide 66 15.0%) were added as polyamide dissolving solution to a 300 mL glass bottle containing a stirring bar, and the bottle was placed in a water bath at 60 ° C. and stirred with a magnetic stirrer for 12 hours to dissolve polyamide 66, to obtain a polyamide solution. The polyamide solution was transferred to a 500 mL three-neck flask equipped with a stirring blade, and 220 g of methanol was added while stirring to obtain a polyamide (polyamide 66) solid precipitate.
• 20 wt % calcium chloride methanol solution water content 0.5 mass%, solubility of polyamide 66 15.0%
• the resulting solid precipitate was filtered and collected with a 10 ⁇ m membrane filter. The filtrate at this time was 280 g.
• the solid precipitate after filtration was thoroughly washed with water.
• the solid precipitate after washing was heated and dried in a vacuum dryer at 80 ° C. to obtain 9.9 g (yield 99.0%) of powdered polyamide 66.
• the solution recovered after filtration was concentrated by an evaporator, and 182.5 g of methanol (GC purity 99.0%) was obtained as a fraction, and 97.5 g of calcium chloride methanol solution (containing 17.5 g of calcium chloride) was obtained as a residue.
• the amount of heat required at this time was 905.9 J/g.
• the solubility of polyamide 66 in this solution was 12%. 2.5 g of calcium chloride was added to this solution and dissolved. The solubility of polyamide 66 in this solution was 15%. At this time, the moisture content in the calcium chloride methanol solution was 0.7% by mass due to moisture absorption. In addition, the concentration of the compound having an amide bond with a molecular weight of 1000 or less was 0.2% by mass.
• the obtained solution was used as a polyamide dissolving solution and the same process as above was carried out to obtain powdered polyamide 66. The process could be carried out in the same manner as the first time, and powdered polyamide 66 was obtained in a yield of 99.0%.
• Example 4 10 g of polyamide 66 pellets and 100 g of 20 wt % calcium chloride methanol solution (water content 0.5 mass%, solubility of polyamide 66 15.0%) were added as polyamide dissolving solution to a 300 mL glass bottle containing a stirring bar, and the bottle was placed in a water bath at 60 ° C. and stirred with a magnetic stirrer for 12 hours to dissolve polyamide 66, to obtain a polyamide solution. The polyamide solution was transferred to a 500 mL three-neck flask equipped with a stirring blade, and 220 g of methanol was added while stirring to obtain a polyamide (polyamide 66) solid precipitate.
• 20 wt % calcium chloride methanol solution water content 0.5 mass%, solubility of polyamide 66 15.0%
• the resulting solid precipitate was filtered and collected with a 10 ⁇ m membrane filter. The filtrate at this time was 280 g.
• the solid precipitate after filtration was thoroughly washed with water.
• the solid precipitate after washing was heated and dried in a vacuum dryer at 80 ° C. to obtain 9.9 g (yield 99.0%) of powdered polyamide 66.
• 48.1 g of calcium chloride was added to the solution recovered after filtration and dissolved.
• the solubility of polyamide 66 in this solution was 15%.
• the water content in the calcium chloride methanol solution was 0.7% by mass due to moisture absorption.
• the concentration of the compound having an amide bond with a molecular weight of 1000 or less was 0.2% by mass.
• the obtained solution was used as a polyamide dissolving solution and the same process as above was carried out to obtain powdered polyamide 66.
• the process could be carried out in the same manner as the first time, and powdered polyamide 66 was obtained in a yield of 99.0%.
• Example 5 10 g of polyamide 66 pellets and 100 g of 20 wt % calcium chloride methanol solution (water content 0.5 mass%, solubility of polyamide 66 15.0%) were added as a polyamide dissolving solution to a 300 mL glass bottle containing a stirring bar, and the bottle was placed in a water bath at 60° C. and stirred with a magnetic stirrer for 12 hours to dissolve polyamide 66, thereby obtaining a polyamide solution. The polyamide solution was transferred to a 500 mL three-neck flask equipped with a stirring blade, and 220 g of methanol was added while stirring to obtain a polyamide (polyamide 66) solid precipitate.
• 20 wt % calcium chloride methanol solution water content 0.5 mass%, solubility of polyamide 66 15.0%
• the resulting solid precipitate was filtered and collected with a 10 ⁇ m membrane filter.
• the filtrate at this time was 280 g.
• the solid precipitate after filtration was washed with 200 g of methanol on the filter, obtaining 201 g of washing liquid.
• the solid precipitate after washing was thoroughly washed with water.
• the washed solid precipitate was dried by heating in a vacuum dryer at 80° C. to obtain 9.9 g (yield 99.0%) of powdered polyamide 66.
• the solution recovered after filtration was added with washing liquid, and concentrated by evaporator to obtain 390.0g of methanol (GC purity 99.0%) as a fraction and 87.5g of calcium chloride methanol solution (containing 17.5g of calcium chloride) as a residue.
• the heat required at this time was 1014 J/g.
• the solubility of polyamide 66 in this solution was 15%.
• the moisture content in the calcium chloride methanol solution was 0.7% by mass due to moisture absorption.
• the concentration of the compound having an amide bond with a molecular weight of 1000 or less was 0.2% by mass.
• the obtained solution was used as a polyamide dissolving solution and the same process as above was carried out to obtain powdered polyamide 66.
• the process could be carried out in the same manner as the first time, and powdered polyamide 66 was obtained in a yield of 99.0%.
• the resulting solid precipitate was filtered and collected with a 10 ⁇ m membrane filter. The filtrate at this time was 280 g.
• the solid precipitate after filtration was thoroughly washed with water.
• the solid precipitate after washing was heated and dried in a vacuum dryer at 80 ° C. to obtain 9.9 g (yield 99.0%) of powdered polyamide 66.
• the solution recovered after filtration was concentrated with an evaporator, and 70.0 g of methanol (GC purity 95.0%) and 192.5 g of water were recovered as distillates, but calcium chloride could not be restored to anhydrous form. The amount of heat required for this was 2612 J/g.
• the resulting solid precipitate was filtered and collected with a 10 ⁇ m membrane filter. The filtrate at this time was 280 g.
• the solid precipitate after filtration was thoroughly washed with water.
• the solid precipitate after washing was heated and dried in a vacuum dryer at 80 ° C. to obtain 9.8 g (yield 98.0%) of powdered polyamide 66.
• the solution recovered after filtration was concentrated by an evaporator to obtain 70.0 g of methanol (GC purity 98.0%) and 186.0 g of water as a fraction.
• 23.2 g of calcium chloride dihydrate was obtained as a residue.
• the heat required at this time was 2419 J/g.
• the resulting solid precipitate was filtered and collected with a 10 ⁇ m membrane filter.
• the filtrate at this time was 280 g.
• the solid precipitate after filtration was thoroughly washed with water.
• the solid precipitate after washing was heated and dried in a vacuum dryer at 80 ° C. to obtain 9.9 g (yield 99.0%) of powdered polyamide 66.
• the solution recovered after filtration was concentrated by an evaporator to obtain 262.5 g of methanol (GC purity 98.0%) as a fraction.
• 18.6 g of calcium chloride was obtained as a residue.
• the calorific value required at this time was 1599 J/g.
• the resulting solid precipitate was filtered and collected with a 10 ⁇ m membrane filter. The filtrate at this time was 280 g.
• the solid precipitate after filtration was thoroughly washed with water.
• the solid precipitate after washing was heated and dried in a vacuum dryer at 80 ° C. to obtain 9.9 g (yield 99.0%) of powdered polyamide 66.
• the solution recovered after filtration was concentrated by an evaporator, and 182.5g of methanol (GC purity 99.0%) was obtained as a fraction, and 97.5g of calcium chloride methanol solution (containing 17.5g of calcium chloride) was obtained as a residue.
• the heat required at this time was 906 J/g.
• the solubility of polyamide 66 in this solution was 12%.
• the moisture content in the calcium chloride methanol solution was 0.7% by mass due to moisture absorption.
• the concentration of the compound having an amide bond with a molecular weight of 1000 or less was 0.2% by mass.
• the obtained solution was used as a polyamide dissolving solution and the same process as above was carried out to obtain powdered polyamide 66. Some of the solution remained undissolved in the dissolving process, and the dissolving process could not proceed as in the first step.

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