Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D201/00—Preparation, separation, purification or stabilisation of unsubstituted lactams
  • C07D201/02—Preparation of lactams
  • C07D201/12—Preparation of lactams by depolymerising polyamides
• • 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
  • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
  • C08J11/14—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with steam or water
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
  • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
  • B09B3/40—Destroying solid waste or transforming solid waste into something useful or harmless involving thermal treatment, e.g. evaporation
• • 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
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D201/00—Preparation, separation, purification or stabilisation of unsubstituted lactams
  • C07D201/16—Separation or purification
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D223/00—Heterocyclic compounds containing seven-membered rings having one nitrogen atom as the only ring hetero atom
  • C07D223/02—Heterocyclic compounds containing seven-membered rings having one nitrogen atom as the only ring hetero atom not condensed with other rings
  • C07D223/06—Heterocyclic compounds containing seven-membered rings having one nitrogen atom as the only ring hetero atom not condensed with other rings with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
  • C07D223/08—Oxygen atoms
  • C07D223/10—Oxygen atoms attached in position 2
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G69/00—Macromolecular compounds obtained by reactions forming a carboxylic amide link in the main chain of the macromolecule
  • C08G69/02—Polyamides derived from amino-carboxylic acids or from polyamines and polycarboxylic acids
  • C08G69/08—Polyamides derived from amino-carboxylic acids or from polyamines and polycarboxylic acids derived from amino-carboxylic acids
  • C08G69/14—Lactams
  • C08G69/16—Preparatory processes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
  • B09B2101/00—Type of solid waste
  • B09B2101/75—Plastic waste
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2077/00—Use of PA, i.e. polyamides, e.g. polyesteramides or derivatives thereof, as moulding material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
  • B29K2105/06—Condition, form or state of moulded material or of the material to be shaped containing reinforcements, fillers or inserts
• • 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
  • C08J2377/00—Characterised by the use of polyamides obtained by reactions forming a carboxylic amide link in the main chain; Derivatives of such polymers
  • C08J2377/02—Polyamides derived from omega-amino carboxylic acids or from lactams thereof
• • 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 is a method for recovering a fibrous filler and ⁇ -caprolactam by depolymerizing a fiber-reinforced polyamide resin composition that achieves both cyclical use of fossil resources and reduction of greenhouse gas emissions.
• the present invention relates to a recycling method for depolymerizing a fiber-reinforced polyamide 6 resin composition using a small amount of water, which has a high heat capacity and heat of vaporization, and recovering a high-purity fibrous filler and ⁇ -caprolactam at a high yield.
• Patent Literature 1 discloses a method of producing hydrocarbons by a process including pyrolysis and steam cracking of waste plastics. Although these methods have the advantage of being able to convert mixed waste plastics into pyrolysis oil, they require cracking at a high temperature of 800°C or higher in order to convert the pyrolysis oil into secondary raw materials such as plastic monomers.
• the ⁇ -caprolactam recovery method disclosed in Patent Document 2 is a high-yield reaction with a depolymerization yield of polyamide 6 of 80% or more, the depolymerization reaction takes a long time. Furthermore, since a large amount of superheated steam, about 10 times that of polyamide 6 fiber, is required, this technology remains a problem in achieving both the recycling of fossil resources and the reduction of greenhouse gas emissions. In addition, since this method uses phosphoric acid as a catalyst, the reaction is susceptible to impurities, such as catalyst deactivation due to additives contained in plastics and adhering impurities in waste plastics.
• Patent Document 2 does not disclose a method for recovering a high-purity fibrous filler with a small amount of adhered organic matter.
• the ⁇ -caprolactam recovery methods disclosed in Patent Documents 3 and 4 use only water for the depolymerization reaction, and do not use a catalyst such as phosphoric acid. There is an advantage that reaction deactivation due to does not occur.
• a large amount of water which has a specific heat capacity of 4.2 kJ/kg K and a heat of vaporization of 2,250 kJ/kg, is about 10 times that of polyamide 6. , a large amount of energy is required for the depolymerization reaction and recovery of ⁇ -caprolactam from a low-concentration ⁇ -caprolactam aqueous solution.
• Patent Documents 3 and 4 do not disclose recovery of a high-purity fibrous filler with a small amount of adhered organic matter.
• At least one of the aqueous solution (B1) is added and contacted to obtain a mixture (C) containing at least a fibrous filler (D), ⁇ -caprolactam, polyamide 6 oligomer and water (B), and then the mixture
• a method for recovering the fibrous filler (D) and ⁇ -caprolactam from (C) characterized by performing the following steps (a) to (c) in this order: fibrous filler and ⁇ -caprolactam collection method.
• a mixture (C) containing at least a fibrous filler (D), ⁇ -caprolactam, a polyamide 6 oligomer, and water (B) is prepared, followed by solid-liquid separation (I).
• the aqueous solution of polyamide 6 oligomer (B1) is an extract obtained in a step of hot water extraction of polyamide 6 oligomer from polyamide 6, which is a product of polyamide 6 production, according to items 1 to 5.
• the polyamide 6 resin composition (A) containing at least the fibrous filler (D) is waste of a resin molding containing at least the polyamide 6 containing the fibrous filler (D). , a method for recovering a fibrous filler and ⁇ -caprolactam according to any one of items 1 to 6.
• a method for producing polyamide 6, comprising obtaining ⁇ -caprolactam by the method according to any one of items 1 to 7, and polymerizing polyamide 6.
• the present invention provides a method for recovering ⁇ -caprolactam and a fibrous filler by depolymerizing a polyamide 6 resin composition containing a fibrous filler, in which even a small amount of water having a high specific heat capacity is used, ⁇ -caprolactam and high It is possible to provide a method for recovering a pure fibrous filler with low energy consumption.
• the present invention provides a polyamide 6 resin composition (A) containing at least a fibrous filler (D), water (B) heated to 290 ° C. or higher and 350 ° C. or lower, or heated to 290 ° C. or higher and 350 ° C. or lower At least one of the polyamide 6 oligomer aqueous solution (B1) is added and contacted to obtain a mixture (C) containing at least a fibrous filler (D), ⁇ -caprolactam, polyamide 6 oligomer and water, and then the A method for recovering a fibrous filler (D) and ⁇ -caprolactam from a mixture (C), characterized by performing the following steps (a) to (c) in this order.
• Polyamide 6 resin composition is a polyamide resin mainly composed of 6-aminocaproic acid and/or ⁇ -caprolactam. Other monomers may be copolymerized to the extent that the object of the present invention is not impaired.
• main raw material means that a total of 50 mol% or more of 6-aminocaproic acid-derived units or ⁇ -caprolactam-derived units is contained in a total of 100 mol% of the monomer units constituting the polyamide resin. means It is more preferable to contain 6-aminocaproic acid-derived units or ⁇ -caprolactam-derived units in an amount of 70 mol% or more, more preferably 90 mol% or more.
• Other monomers to be copolymerized include, for example, amino acids such as 11-aminoundecanoic acid, 12-aminododecanoic acid and para-aminomethylbenzoic acid, lactams such as ⁇ -laurolactam, tetramethylenediamine, pentamethylenediamine, Hexamethylenediamine, 2-methylpentamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4-/2,4,4-trimethylhexamethylenediamine, 5-methylnona Aliphatic diamines such as methylenediamine, aromatic diamines such as metaxylylenediamine and paraxylylenediamine, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 1-amino-3 -aminomethyl-3,5,5-trimethylcyclohexane,
• polyamides 6 may be added with polymerization degree modifiers, terminal group modifiers, and the like.
• polymerization degree modifiers and terminal group modifiers include acetic acid and benzoic acid.
• the degree of polymerization of the polyamide 6 of the present invention is not particularly limited, but the relative viscosity measured at 25 ° C. in a 98% concentrated sulfuric acid solution with a resin concentration of 0.01 g / mL is in the range of 1.5 to 5.0 Preferably.
• the relative viscosity is in such a preferable range, the reaction efficiency with a small amount of water tends to be high, so it can be exemplified preferably.
• the polyamide 6 resin composition (A) of the present invention contains a fibrous filler (D).
• the fibrous filler (D) here specifically includes glass fiber, glass flat fiber, modified cross-section glass fiber, glass cut fiber, flat glass fiber, carbon fiber, etc., and two or more of these may be used. may be used together. Among these, glass fiber is preferred.
• the content of the fibrous filler (D) in the resin composition (A) is preferably 1 to 200 parts by mass with respect to 100 parts by mass of the resin composition (A).
• the resin composition (A) of the present invention may further contain fillers, thermoplastic resins other than polyamide 6, various additives, and the like within a range that does not impair the purpose of the present invention.
• the filler may be either an organic filler or an inorganic filler, and examples include non-fibrous fillers, and two or more of these may be blended.
• non-fibrous fillers include talc, wollastonite, zeolite, sericite, mica, kaolin, clay, pyrophyllite, bentonite, asbestos, alumina silicate, non-swelling silicates such as calcium silicate, Li-type fluorine Swellable layered silicates such as teniolite, Na-type fluoroteniolite, Na-type tetrasilicon fluoromica, swelling mica of Li-type tetrasilicon fluoromica, silicon oxide, magnesium oxide, alumina, silica, diatomaceous earth, zirconium oxide, titanium oxide, Metal oxides such as iron oxide, zinc oxide, calcium oxide, tin oxide and antimony oxide, metal carbonates such as calcium carbonate, magnesium carbonate, zinc carbonate, barium carbonate, dolomite and hydrotalcite
• Organic onium ions include, for example, ammonium ions, phosphonium ions, and sulfonium ions.
• additives include N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamide), tetrakis[methylene-3-(3',5'-di- Phenolic compounds such as t-butyl-4'-hydroxyphenyl)propionate]methane, phosphorus compounds, mercaptobenzimidazole compounds, dithiocarbamic acid compounds, sulfur compounds such as organic thioacid compounds, N,N'- Thermal stabilizers such as amine compounds such as di-2-naphthyl-p-phenylenediamine and 4,4'-bis( ⁇ , ⁇ -dimethylbenzyl)diphenylamine, isocyanate compounds, organic silane compounds, organic titanate compounds , organic borane compounds, coupling agents such as epoxy compounds, polyalkylene oxide oligomer compounds, thioether compounds, ester compounds, plasticizers such as organic phosphorus compounds, crystal nuclei such as
• thermoplastic resins other than polyamide 6 contained in the polyamide 6 resin composition (A) include polyamide resins other than polyamide 6, polyester resins, polyolefin resins, modified polyphenylene ether resins, polysulfone resins, polyketone resins, and polyethers. Examples include imide resins, polyarylate resins, polyethersulfone resins, polyetherketone resins, polythioetherketone resins, polyetheretherketone resins, polyimide resins, polyamideimide resins, and tetrafluoropolyethylene resins. You may mix
• the amount of the thermoplastic resin other than polyamide 6 is preferably 30 parts by mass or less per 100 parts by mass of polyamide 6 in the polyamide 6 resin composition (A) of the present invention.
• the polyamide 6 resin composition (A) containing at least the fibrous filler (D) of the present invention may be waste of a resin molding containing at least the polyamide 6 having the fibrous filler (D).
• the waste of resin moldings includes polyamide 6 products, industrial waste generated in the process of manufacturing polyamide 6 products, and waste after use of polyamide 6 products.
• Examples of polyamide 6 products having a fibrous filler (D) include molded parts for housing building materials, electrical and electronic molded parts, aircraft parts, industrial machine parts, extrusion moldings, on-site polymerization moldings, RIM moldings, and the like. . Furthermore, product scraps, pellet scraps, lump-like scraps, and cutting scraps generated during the cutting process are also subject to waste.
• the polyamide 6 oligomer in the present invention is a polyamide 6 oligomer mainly composed of 6-aminocaproic acid and/or ⁇ -caprolactam.
• the polyamide 6 oligomer may contain other monomers as long as the object of the present invention is not impaired.
• "mainly constituting” means that the unit derived from 6-aminocaproic acid or the unit derived from ⁇ -caprolactam in the total 100 mol% of the monomer units constituting the polyamide 6 oligomer is 50 mol% or more in total. means to contain It is more preferable to contain 6-aminocaproic acid-derived units or ⁇ -caprolactam-derived units in an amount of 70 mol% or more, more preferably 90 mol% or more.
• polyamide 6 oligomer examples include, for example, amino acids such as 11-aminoundecanoic acid, 12-aminododecanoic acid, and para-aminomethylbenzoic acid, lactams such as ⁇ -laurolactam, tetramethylenediamine, and pentamethylene.
• Diamine Diamine, hexamethylenediamine, 2-methylpentamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4-/2,4,4-trimethylhexamethylenediamine, 5- Aliphatic diamines such as methylnonamethylenediamine, aromatic diamines such as metaxylylenediamine and paraxylylenediamine, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 1-amino -3-aminomethyl-3,5,5-trimethylcyclohexane, bis(4-aminocyclohexyl)methane, bis(3-methyl-4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, Alicyclic diamines such as 1,4-bis(3-aminopropyl
• the number average molecular weight of the polyamide 6 oligomer of the present invention is not particularly limited, but the number average molecular weight is preferably in the range of 100 to 5000, more preferably in the range of 200 to 3000, and in the range of 200 to 2000. One is particularly preferable and can be exemplified. When the molecular weight of the polyamide 6 oligomer is within such a preferable range, the solubility in water tends to be high, and the polyamide 6 oligomer aqueous solution (B1) used in the present invention tends to be easily prepared.
• the number average molecular weight here was calculated by GPC analysis using 1,1,1,3,3,3-hexafluoro-2-propanol as a solvent. Showa Denko GPC-HFIP805 was used as the column, and PMMA was used as the standard substance.
• polyamide 6 and polyamide 6 oligomer when the total mass ratio of water (B) and polyamide 6, or water, polyamide 6 and polyamide 6 oligomer is X: 1, and the reaction time is Y ° C., the product of X and Y is 2,000 or less.
• the mixture (C) is prepared under the conditions of
• the water (B) used here is not particularly limited, but any water such as tap water, ion-exchanged water, distilled water, and well water may be used. From the viewpoint of , ion-exchanged water and distilled water are preferably used.
• water heated to 290°C or higher and 350°C or lower and water in the polyamide 6 oligomer aqueous solution (B1) heated to 290°C or higher and 350°C or lower are reaction substrates.
• water is raised to a pressure of 22.1 MPa and a temperature of 374.2° C., it becomes neither liquid nor gas. This point is called the critical point of water, and hot water at a temperature and pressure lower than the critical point is called subcritical water.
• the water (B) or the polyamide 6 oligomer aqueous solution (B1) used in the present invention has a temperature of 290° C. or more and 350° C. or less and corresponds to subcritical water.
• the temperature of the water (B) or the aqueous polyamide 6 oligomer solution (B1) of the present invention is preferably 300° C. or higher and 340° C. or lower, more preferably 320° C. or higher and 340° C. or lower. By being in such a preferable range, there is a tendency that corrosion of equipment during the reaction can be suppressed.
• the pressure of water (B) or the aqueous polyamide 6 oligomer solution (B1) is preferably higher than the saturated vapor pressure.
• Water may be in a liquid state, in a gaseous state such as water vapor, or both.
• the pressure of the 6-oligomer aqueous solution (B1) is preferably higher than the saturated vapor pressure.
• the upper limit of the pressure of water (B) or the aqueous polyamide 6 oligomer solution (B1) is not particularly limited, but can be exemplified by 20 MPa or less. Such a pressure range tends to increase the ionic product of water, which is preferable.
• a method of pressurizing and sealing the inside of a pressure vessel is used to bring the water into such a pressure range.
• a gas may be sealed in addition to water (B) or the aqueous polyamide 6 oligomer solution (B1).
• gases include air, argon, and nitrogen. From the viewpoint of suppressing side reactions such as oxidation reactions, it is preferable to use nitrogen or argon.
• the degree of gas pressurization is not particularly limited because it is set to a target pressure, but 0.3 MPa or more can be mentioned.
• the present invention relates to the mass ratio of water (B) and polyamide 6 when preparing the mixture (C), the sum of water (B) and water in the aqueous polyamide 6 oligomer aqueous solution (B1), and the ratio of polyamide 6 and polyamide 6 oligomer
• the total mass ratio or the total mass ratio of water, polyamide 6 and polyamide 6 oligomer in the aqueous polyamide 6 oligomer aqueous solution (B1) is X: 1, and the reaction temperature is Y ° C.
• the product of X and Y is 2, 000 or less.
• the product of X and Y is preferably 1,600 or less, more preferably 1,300 or less, and particularly preferably 1,200 or less.
• the lower limit of the product of X and Y is not particularly limited.
• the present invention is an energy-saving ⁇ -caprolactam and a high-purity fibrous filler from a polyamide 6 resin composition having a fibrous filler for the purpose of achieving both the cyclical use of fossil resources and the reduction of greenhouse gas emissions. It relates to the collection method.
• Water has a specific heat capacity of 4.3 kJ/kg K and a heat of vaporization of 2,250 kJ/kg, which are extremely high compared to other organic solvents. By setting the product of these conditions within these conditions, it is possible to achieve both the production efficiency of ⁇ -caprolactam and energy saving. Further, when the residence time at the reaction temperature Y° C.
• the condition that the product of X, Y and Z is 60,000 or less can be preferably exemplified. More preferably, the condition is 40,000 or less, more preferably 30,000 or less, and particularly preferably 20,000 or less.
• the lower limit of the product of X, Y and Z is not particularly limited, but the condition of 5,000 or more is preferable, the condition of 8,000 or more is more preferable, and the condition of 9,000 or more is particularly preferable. can.
• the mixture (C) is a polyamide 6 resin composition (A) containing at least a fibrous filler (D), in addition to water (B) heated to 290 ° C. or higher and 350 ° C. or lower, 290 ° C. or higher and 350 ° C.
• the polyamide 6 oligomer aqueous solution (B1) heated to 0° C. or lower is further added and brought into contact with each other.
• the structure of the polyamide 6 oligomer in the polyamide 6 oligomer aqueous solution (B1) is the same as described in (2) above.
• the composition of the polyamide 6 oligomer in the aqueous polyamide 6 oligomer aqueous solution (B1) is not particularly limited, but a preferred example is that the content of the linear polyamide oligomer of 2 to 12-mer is 90% by mass or more. More preferably, the amount of the linear 2-12-mer oligomer is 93% by mass or more, and particularly preferably 95% by mass or more.
• the solubility in water is increased, and further the polyamide 6 oligomer terminal carboxylic acid Since the concentration is high, the reaction between polyamide 6 and water is accelerated, and the efficiency of producing ⁇ -caprolactam tends to be high.
• the amount of linear 2- to 12-mer oligomers in the polyamide 6 oligomer was quantitatively analyzed by high-performance liquid chromatography using an aqueous formic acid solution and an acetonitrile formic acid solution as eluents.
• a polyamide 6 oligomer contained in the resin or a polyamide 6 oligomer prepared by the same method as that for synthesizing an ordinary fatty acid-based polyamide 6 resin may be used.
• a polyamide 6 oligomer obtained as a by-product may be used.
• a resin composition (A) containing at least polyamide 6 and water (B) heated to 290° C. or higher and 350° C. or lower, or 290° C. or higher It is preferable to use a polyamide 6 oligomer recovered as a by-product when adding at least one of the polyamide 6 oligomer aqueous solution (B1) heated to 350° C. or less to produce ⁇ -caprolactam.
• the polyamide 6 oligomer aqueous solution (B1) is prepared by heating and mixing the polyamide 6 oligomer and water.
• the water used here is not particularly limited, and tap water, ion-exchanged water, distilled water, well water, etc. can be used. Water is preferably used.
• the concentration of the polyamide 6 oligomer in the polyamide 6 oligomer aqueous solution (B1) may be any concentration as long as the polyamide 6 oligomer is dissolved in water when heated to 290 ° C. or higher and 350 ° C. or lower, but preferably 20. It can be exemplified to be 15% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less.
• the solubility in water when preparing the aqueous polyamide 6 oligomer aqueous solution (B1) is increased, and the aqueous polyamide 6 oligomer aqueous solution can be prepared at a lower temperature.
• (B1) can be prepared.
• an extract containing a polyamide 6 oligomer obtained in a step of hot-water extracting a polyamide 6 oligomer from polyamide 6, which is a product of polyamide 6 production can be used as the polyamide 6 oligomer aqueous solution (B1).
• a polyamide 6 resin obtained by polymerizing ⁇ -caprolactam contains, as impurities, unreacted monomers produced in the polymerization equilibrium reaction and polyamide 6 oligomers. Therefore, in order to remove these, pellets after polymerization are supplied to a hot water extraction tower, and unreacted monomers and polyamide 6 oligomers are extracted and removed by hot water extraction.
• aqueous polyamide 6 oligomer aqueous solution (B1) of the present invention is also a preferable form from the viewpoint of reducing industrial waste. I can give an example.
• reaction methods such as a batch method and a continuous method can be adopted.
• it is a continuous type, it is an extruder equipped with a heating function, a tubular reactor, a tubular reactor equipped with a mixing mechanism such as a baffle, a line mixer, a vertical or horizontal reactor, and a vertical reactor equipped with a stirrer.
• the atmosphere in the production is desirably a non-oxidizing atmosphere, preferably an inert atmosphere such as nitrogen, helium, or argon, and a nitrogen atmosphere is preferable from the viewpoints of economy and ease of handling.
• Solid-liquid separation (I) step The method for recovering the fibrous filler (D) and ⁇ -caprolactam of the present invention contains at least the fibrous filler (D), ⁇ -caprolactam, polyamide 6 oligomer, and water.
• the mixture (C) is characterized by subjecting the mixture (C) to solid-liquid separation (I) in a temperature range below the boiling point of water at the operating pressure.
• solid-liquid separation (I) of the mixture (C) in a temperature range below the boiling point of water at the operating pressure, ⁇ -caprolactam and polyamide 6 oligomer are separated into a liquid phase and the fibrous filler (D) into a solid phase. do.
• Solid-liquid separation (I) can be performed at any temperature within the temperature range below the boiling point of water at the operating pressure, and the mixture (C) of the present invention is prepared at a temperature of 290° C. or higher and 350° C. or lower. Solid-liquid separation (I) is preferably carried out at a temperature not higher than the preparation temperature of the mixture (C). Solid-liquid separation (I) of the mixture (C) containing at least the fibrous filler (D), ⁇ -caprolactam, polyamide 6 oligomer, and water is more preferably performed at 95 ° C. or less, and can be performed at 90 ° C. or less. It can be exemplified more preferably.
• the present inventors investigated the dissolution behavior and precipitation behavior of the polyamide 6 oligomer in water in the present invention described in the above item (2).
• the temperature at which the polyamide 6 oligomer dissolves in water is 100 ° C. or higher.
• the temperature at which polyamide 6 oligomer once dissolved in water precipitates is less than 100°C.
• the difference between the temperature at which the polyamide 6 oligomer dissolves in water and the precipitation temperature is due to the fact that the polyamide 6 oligomer is in a supercooled state in a temperature range of less than 100 ° C. and higher than the temperature at which the polyamide 6 oligomer precipitates. is.
• the crystal nucleus of the polyamide 6 oligomer is generated, and the generated crystal nucleus grows to a size sufficient for precipitation to precipitate the polyamide 6 oligomer. pass. Therefore, when the aqueous polyamide 6 oligomer solution dissolved in water is cooled, crystal nuclei of the polyamide 6 oligomer are generated at the stage of cooling to less than 100 ° C., which is the temperature at which the polyamide 6 oligomer dissolves in water, and then in the cooling process. It is believed that the generated crystal nuclei grow and the polyamide 6 oligomer precipitates.
• solid-liquid separation (I) of the mixture (C) containing at least fibrous filler, ⁇ -caprolactam, polyamide 6 oligomer, and water is preferably performed in a temperature range below the boiling point at normal pressure. , It is more preferable to perform the solid-liquid separation (I) at 95°C or lower, and it is even more preferable to perform the solid-liquid separation (I) at 90°C or lower. Further, in the solid-liquid separation (I), the polyamide 6 oligomer is recovered as a liquid phase component by solid-liquid separation, so the lower limit temperature for performing the solid-liquid separation (I) may include the temperature at which the polyamide 6 oligomer is in a supercooled state. Specifically, the temperature is preferably 50° C.
• solid-liquid separation (I) in such a preferable temperature range, at least 97% or more, preferably 98% or more, more preferably 99% or more of ⁇ -caprolactam and polyamide 6 oligomer can be recovered as liquid phase components. This tends to reduce recovery loss of ⁇ -caprolactam and polyamide 6 oligomer due to solid-liquid separation (I).
• the solid-liquid separation (I) of the mixture (C) containing at least the fibrous filler (D), ⁇ -caprolactam, polyamide 6 oligomer, and water of the present invention is performed by separating the separately prepared mixture (C) from the polyamide 6 A method of reheating to a temperature at which the oligomer dissolves, cooling to the solid-liquid separation (I) temperature and performing solid-liquid separation (I), a polyamide 6 resin composition containing at least a fibrous filler (D) (A ) and water (B) heated to 290° C. or higher and 350° C.
• the mixture (C) is subsequently cooled from the preparation temperature to the solid-liquid separation (I) temperature to perform the solid-liquid separation (I).
• a method of cooling the mixture (C) to a temperature at which solid-liquid separation (I) is performed after preparation and performing solid-liquid separation (I) can be mentioned.
• the method for performing solid-liquid separation (I) is not particularly limited, and known methods can be employed. Sedimentation separation, a method combining these methods, and the like can be employed. A decanter separation method in which sedimentation is separated before the filtration operation is also a preferred method.
• the filter used for the filtration operation should be stable under the conditions for solid-liquid separation (I), and for example, a filter sieve or a sintered plate can be suitably used.
• the mesh diameter or pore diameter of this filter is determined by the viscosity, pressure, and temperature of the mixture (C) subjected to the filtration operation, the size of the fibrous filler (D), the purity of the resulting filtrate (content of solids), etc. can be adjusted over a wide range. In particular, it is effective to select the mesh diameter or pore diameter according to the size in the mixture (C) of the fibrous filler (D) recovered as the solid phase component by the solid-liquid separation (I).
• the fibrous filler (D) in the mixture (C) can be separated as filtered matter, preferably the fibrous filler contained in the mixture (C) 95% by mass or more, more preferably 97% by mass or more, and still more preferably 99% by mass or more of the filler (D) can be recovered as a solid content.
• the filtered product separated by solid-liquid separation (I) contains water containing ⁇ -caprolactam and polyamide 6 oligomer
• the filtered product can be washed with fresh water to obtain ⁇ - It is possible to reduce the amounts of caprolactam and polyamide 6 oligomers remaining in the filtered product (step (c)).
• the washing of the filtrate with fresh water is carried out in a temperature range below the boiling point under normal pressure, preferably in a temperature range of 95°C or below, more preferably 90°C or below.
• a complicated process is not required. , it can be said to be a preferable method from the viewpoint of process cost or environmental load.
• the filtrate containing the fibrous filler (D) obtained in the solid-liquid separation (I) is washed with water having a boiling point of water at normal pressure or lower.
• the fibrous filler (D) is recovered.
• a high-purity fibrous filler (D) with a small residual amount of organic matter can be recovered.
• the temperature of the water required for washing is not particularly limited as long as it is below the boiling point of water under normal pressure.
• the recovered fibrous filler (D) is a high-purity fibrous filler (D) such as ⁇ -caprolactam and polyamide 6 oligomer, which has a small residual amount of organic substances.
• the weight loss is preferably 3.0% by mass or less, and can be exemplified as 2.0% by mass or less. It can be exemplified more preferably.
• the fact that the mass reduction of the recovered fibrous filler (D) during the heat treatment is within such a preferable range means that the amount of organic matter adhering to the fibrous filler (D) is small, that is, the mixture (C) It is preferable because it means less recovery loss of ⁇ -caprolactam and polyamide 6 oligomer in the solid-liquid separation (I) and water washing steps.
• Recovery method of ⁇ -caprolactam There is no particular limitation on the recovery method of ⁇ -caprolactam from the filtrate in the solid-liquid separation (I) of the present invention, and any method can be employed. For example, by subjecting the aqueous ⁇ -caprolactam solution obtained by solid-liquid separation (I) to a distillation operation, ⁇ -caprolactam with high purity can be recovered by separating it from water and polyamide 6 oligomer. Further, if the water-insoluble component is precipitated by cooling the ⁇ -caprolactam aqueous solution recovered by the solid-liquid separation (I), it can be separated in advance by a known method such as solid-liquid separation and subjected to distillation separation. .
• Methods for obtaining ⁇ -caprolactam of even higher purity include a method of precision distillation of recovered ⁇ -caprolactam, a method of vacuum distillation with the addition of a trace amount of sodium hydroxide, a method of activated carbon treatment, an ion exchange treatment method, and a recycling method. It can be combined with a purification method such as a method of crystallization. These methods can efficiently remove impurities that are difficult to separate by distillation.
• Polyamide 6 and Molded Articles Thereof According to the method for recovering ⁇ -caprolactam described in the present invention, ⁇ -caprolactam with high purity can be obtained, so that it can be used as a raw material for polymerization of polyamide 6.
• Polyamide 6 can be produced by a generally known method of thermally melt-polymerizing ⁇ -caprolactam in the presence of a small amount of water. Further, the polyamide 6 obtained in this way is melt-kneaded with a fibrous filler (D) and various additives as necessary to produce a polyamide 6 resin composition, and injection molding, extrusion molding, etc.
• Various molded articles such as sheets and films can be obtained by a generally known method.
• the polyamide 6 of the present invention and its molded articles can be used for various purposes such as electric/electronic parts, building materials, various containers, daily necessities, household goods and sanitary goods, taking advantage of their excellent properties.
• it is preferably used for aircraft parts and electric/electronic parts that require toughness and rigidity.
• aircraft-related parts such as landing gear pods, winglets, spoilers, edges, rudders, elevators, failings, and ribs
• electrical and electronic parts such as generators, motors, transformers, and current transformers.
• the above solution viscosity ⁇ r was measured at 25° C. using a 0.01 g/mL solution of 98% concentrated sulfuric acid.
• the melting point is measured using a differential scanning calorimeter, in a nitrogen gas atmosphere, the polyamide is cooled from the molten state to 30 ° C.
• the amount of the above cyclic dimer to tetramer oligomer is obtained by pulverizing polyamide 6, passing through a JIS standard sieve of 24 mesh, collecting polyamide 6 powder that is impermeable to 124 mesh, and adding 20 g of the polyamide 6 powder to 200 mL of methanol.
• High-performance liquid chromatography analysis of the obtained polyamide 6 oligomer revealed that the linear 2- to 12-mer oligomer content was 95.8% by mass.
• the pellets were extracted with 20 times the amount of hot water at 98° C. to recover an extract containing unreacted caprolactam and polyamide 6 oligomer.
• the total amount of unreacted caprolactam and polyamide 6 oligomer in the extract was 0.5% by mass, and polyamide 6 oligomer was 0.1% by mass.
• Example 1 28.6 g of PA6-B prepared in Reference Example 1 and 60.0 g of deionized water were charged into a SUS316L autoclave equipped with a stirrer, a bottom plug valve, and a glass filter (average opening 10 ⁇ m) at the bottom.
• the mass ratio (X:1) of water to polyamide 6 is 3:1.
• the reaction vessel was purged with nitrogen, sealed under a nitrogen pressure of 0.5 MPa, and then reacted at 320° C. for 15 minutes while stirring at 200 rpm. The ultimate pressure during the reaction was 10.4 MPa. Since the reaction temperature Y ° C.
• the inside temperature was cooled to 90°C, and the bottom plug valve was opened while maintaining the temperature at 90°C to perform solid-liquid separation (I).
• solid-liquid separation (I) was performed while introducing nitrogen into the autoclave at 0.3 MPa. Furthermore, about 3 times the amount (mass) of deionized water is introduced into the autoclave and the filtrate is rinsed and washed at 90°C three times, and the filtrate and the wet filtrate are collected. bottom.
• the filtrate obtained by solid-liquid separation (I) was measured by high-performance liquid chromatography, and the amount of ⁇ -caprolactam contained in the filtrate was 14.0 g. 0%. Further, the obtained wet filter cake was subjected to vacuum drying at 50° C. for 12 hours to recover 8.6 g of glass fibers. 1.0 g of the collected glass fiber was weighed into a crucible and treated in an electric furnace heated to 600° C. for 3 hours in an air atmosphere. As a result of evaluating the amount of organic substances adhering to the recovered glass fibers based on the mass reduction, the mass loss was 1.4% by mass, indicating that the recovered glass fibers were high-purity glass fibers with a small amount of organic substances adhering.
• the collected filtrate is heated to 55°C under reduced pressure of 30 mmHg to distill and separate water to obtain a concentrated ⁇ -caprolactam aqueous solution, which is further distilled under reduced pressure of 5 mmHg at a heating temperature of 150 to 170°C.
• ⁇ -caprolactam was recovered.
• the concentration and distillation yield was 95.8%.
• the HPLC impurity content of the distillate ⁇ -caprolactam was 0.48%, and the quality was such that it could be used as a raw material for polymerization of polyamide 6. From the above, it can be seen that the present invention is a low environmental load process capable of recovering high-purity glass fibers and ⁇ -caprolactam without using a large amount of organic solvent.
• Example 2 A SUS316L autoclave equipped with a stirrer, a bottom plug valve, and a glass filter (average opening 10 ⁇ m) at the bottom. 0 g was charged. The mass ratio (X:1) of water to polyamide 6 is 3:1. The reaction vessel was purged with nitrogen, sealed under a nitrogen pressure of 0.5 MPa, and then reacted at 340° C. for 15 minutes while stirring at 200 rpm. Since the reaction temperature Y ° C. is 340 ° C., the product of X and Y is 1,020, and since the residence time at the reaction temperature of 340 ° C. is 15 minutes, the product of X, Y and Z is 15,300. is.
• the inside temperature was cooled to 80°C, and the bottom plug valve was opened while maintaining the temperature at 80°C to perform solid-liquid separation (I).
• solid-liquid separation (I) was performed while introducing nitrogen into the autoclave at 0.3 MPa. Furthermore, about 3 times the amount (mass) of deionized water was introduced into the autoclave and the filtrate was rinsed at 80°C three times, and the filtrate and the wet filtrate were separated. Recovered.
• the filtrate obtained by solid-liquid separation (I) was measured by high-performance liquid chromatography, and the amount of ⁇ -caprolactam contained in the filtrate was 14.2 g. 9%.
• the obtained wet filter cake was subjected to vacuum drying at 50° C. for 12 hours to recover 8.6 g of glass fibers.
• 1.0 g of the collected glass fiber was weighed into a crucible and treated in an electric furnace heated to 600° C. for 3 hours in an air atmosphere.
• the mass loss was 1.5% by mass, indicating that the recovered glass fibers were high-purity glass fibers with a small amount of organic substances adhering.
• Example 3 25.1 g of PA6-B prepared in Reference Example 1 and 25.5 g of deionized water were weighed into a SUS316L autoclave equipped with a stirrer, a bottom plug valve and a glass filter (average opening 10 ⁇ m) at the bottom, and further 36.9 g of an aqueous polyamide 6 oligomer solution having a concentration of 6.5% by weight was added.
• the polyamide 6 oligomer used here is the polyamide 6 oligomer produced by the method described in Reference Example 3.
• the reaction vessel was purged with nitrogen, sealed under a nitrogen pressure of 0.5 MPa, and then reacted at 320° C. for 15 minutes while stirring at 200 rpm. Since the reaction temperature Y ° C. is 320 ° C., the product of X and Y is 960, and since the residence time at the reaction temperature of 320 ° C. is 15 minutes, the product of X, Y and Z is 14,400. . After completion of the reaction, the inside temperature was cooled to 90°C, and the bottom plug valve was opened while maintaining the temperature at 90°C to perform solid-liquid separation (I). At the stage when the filtration rate decreased, solid-liquid separation (I) was performed while introducing nitrogen into the autoclave at 0.3 MPa.
• deionized water of about 3 times the mass of the filtered product was introduced into the autoclave to rinse and wash the filtered product at 90° C. three times, and the filtrate and the wet filtered product were recovered.
• High-performance liquid chromatography analysis of the resulting filtrate revealed that the amount of ⁇ -caprolactam contained in the filtrate was 14.5 g, and the yield relative to polyamide 6 in PA6-B used as a raw material was 82.5%.
• the obtained wet filter cake was subjected to vacuum drying at 50° C. for 12 hours to recover 7.5 g of glass fiber.
• Example 1 By comparing Example 1 and Comparative Example 1, by performing solid-liquid separation (I) following the reaction of the polyamide 6 resin composition containing a fibrous filler with water, high-purity ⁇ -caprolactam and organic matter It can be seen that this is a low environmental load process that can recover high-purity glass fibers with a small amount of adhesion and can reduce industrial waste.
• Example 4 Polymerization of Polyamide 6 10 g of ⁇ -caprolactam recovered by the method described in Example 1, 2.2 mg of benzoic acid, and 10.0 g of deionized water were weighed into a test tube. After the test tube was placed in the autoclave and the inside of the autoclave was replaced with nitrogen, the jacket temperature was set to 250° C. and heating was started. After the internal pressure reached 1.0 MPa, the internal pressure was maintained at 1.0 MPa for 3 hours. After that, the internal pressure was released to normal pressure over 1.5 hours, and heating was stopped when the internal temperature reached 228°C. After completion of the polymerization, the polymer was recovered from the test tube and crushed. The crushed polymer was treated in hot water at 95° C.
• Example 5 58.0 g of PA6-B prepared in Reference Example 1 and 122.0 g of deionized water were weighed into a SUS316L autoclave equipped with a stirrer, a bottom plug valve and a glass filter (average opening 10 ⁇ m) at the bottom.
• the mass ratio (X:1) of water to polyamide 6 is 3:1.
• the reaction vessel was purged with nitrogen, sealed under a nitrogen pressure of 5.0 MPa, and then reacted at 320° C. for 15 minutes while stirring at 200 rpm. The ultimate pressure during the reaction was 19.7 MPa. Since the reaction temperature Y ° C. is 320 ° C., the product of X and Y is 960, and since the residence time at the reaction temperature of 320 ° C.
• the filtrate obtained by solid-liquid separation (I) was measured by high-performance liquid chromatography, and the amount of ⁇ -caprolactam contained in the filtrate was 32.9 g. was 0%. Further, the obtained wet filter cake was subjected to vacuum drying at 50° C. for 12 hours to recover 17.4 g of glass fibers. 1.0 g of the collected glass fiber was weighed into a crucible and treated in an electric furnace heated to 600° C. for 3 hours in an air atmosphere. As a result of evaluating the amount of organic substances adhering to the recovered glass fibers based on the mass reduction, the mass loss was 1.3% by mass, indicating that the recovered glass fibers were high-purity glass fibers with a small amount of organic substances adhering. From the comparison with Example 1, it can be seen that ⁇ -caprolactam tends to be obtained at a high yield by increasing the pressure during the reaction to a pressure higher than the saturated vapor pressure.
• Example 6 43.0 g of PA6-B prepared in Reference Example 1 and 60.0 g of deionized water were weighed into a SUS316L autoclave equipped with a stirrer, a bottom plug valve and a glass filter (average opening 10 ⁇ m) at the bottom.
• the weight ratio (X:1) of water to polyamide 6 is 2:1.
• the reaction vessel was purged with nitrogen, sealed under a nitrogen pressure of 0.3 MPa, and then reacted at 320° C. for 15 minutes while stirring at 200 rpm. Since the reaction temperature Y ° C. is 320 ° C., the product of X and Y is 640, and the residence time at the reaction temperature of 320 ° C.
• the filtrate obtained by solid-liquid separation (I) was measured by high-performance liquid chromatography, and the amount of ⁇ -caprolactam contained in the filtrate was 19.2 g. was 9%. Further, the obtained wet filter cake was subjected to vacuum drying at 50° C. for 12 hours to recover 12.9 g of glass fiber. 1.0 g of the collected glass fiber was weighed into a crucible and treated in an electric furnace heated to 600° C. for 3 hours in an air atmosphere. As a result of evaluating the amount of organic substances adhering to the recovered glass fibers based on the mass reduction, the mass loss was 1.4% by mass, indicating that the recovered glass fibers were high-purity glass fibers with a small amount of organic substances adhering.
• Example 7 75.0 g of PA6-B prepared in Reference Example 1 and 150.0 g of deionized water were weighed into an autoclave made of SUS316L equipped with a stirrer, a bottom plug valve and a glass filter (average opening 10 ⁇ m) at the bottom.
• the mass ratio (X:1) between water and polyamide 6 is 2:1.
• the reaction vessel was purged with nitrogen, sealed under a nitrogen pressure of 5.0 MPa, and then reacted at 320° C. for 15 minutes while stirring at 200 rpm. The ultimate pressure during the reaction was 19.8 MPa. Since the reaction temperature Y° C. is 320° C., the product of X and Y is 640, and since the residence time at the reaction temperature of 320° C.
• the filtrate obtained by solid-liquid separation (I) was measured by high-performance liquid chromatography, and the amount of ⁇ -caprolactam contained in the filtrate was 39.3 g. was 9%. From the comparison with Example 6, it can be seen that ⁇ -caprolactam tends to be obtained at a high yield by increasing the pressure during the reaction to a pressure higher than the saturated vapor pressure. Further, the obtained wet filter cake was subjected to vacuum drying at 50° C. for 12 hours to recover 22.5 g of glass fiber. 1.0 g of the collected glass fiber was weighed into a crucible and treated in an electric furnace heated to 600° C. for 3 hours in an air atmosphere.
• the mass loss was 1.4% by mass, indicating that the recovered glass fibers were high-purity glass fibers with a small amount of organic substances adhering.
• Example 8 the hot water extract in the PA6 production process obtained by the method described in Reference Example 4 was concentrated until the concentration of unreacted caprolactam and polyamide 6 oligomer reached 6.5% by mass, and was used as a depolymerization raw material.
• 25.1 g of PA6-B prepared in Reference Example 1 and 25.5 g of deionized water were weighed into a SUS316L autoclave equipped with a stirrer, a bottom plug valve and a glass filter (average opening 10 ⁇ m) at the bottom, and further 36.9 g of the polyamide 6 oligomer aqueous solution having a concentration of 6.5% by weight prepared above was added.
• the reaction vessel was purged with nitrogen, sealed under a nitrogen pressure of 0.5 MPa, and then reacted at 320° C. for 15 minutes while stirring at 200 rpm. Since the reaction temperature Y ° C. is 320 ° C., the product of X and Y is 1,056, and since the residence time at the reaction temperature of 320 ° C. is 15 minutes, the product of X, Y and Z is 15,840. is. After completion of the reaction, the inside temperature was cooled to 90°C, and the bottom plug valve was opened while maintaining the temperature at 90°C to perform solid-liquid separation (I).
• Example 9 the hot water extract in the PA6 production process obtained by the method described in Reference Example 4 was concentrated until the total concentration of unreacted caprolactam and polyamide 6 oligomer was 6.5% by mass, and used as a depolymerization raw material.
• 25.5 g of PA6-B prepared in Reference Example 1 was added to a SUS316L autoclave equipped with a stirrer, a bottom plug valve and a glass filter (average opening 10 ⁇ m) at the bottom, and a concentration of 6.5% by mass prepared above. 60.0 g of an aqueous polyamide 6 oligomer solution was added.
• the reaction vessel was purged with nitrogen, sealed under a nitrogen pressure of 0.5 MPa, and then reacted at 320° C. for 15 minutes while stirring at 200 rpm. Since the reaction temperature Y ° C. is 320 ° C., the product of X and Y is 963, and since the residence time at the reaction temperature of 320 ° C. is 15 minutes, the product of X, Y and Z is 14,454. .
• the inside temperature was cooled to 90°C, and the bottom plug valve was opened while maintaining the temperature at 90°C to perform solid-liquid separation (I). At the stage when the filtration rate decreased, solid-liquid separation (I) was performed while introducing nitrogen into the autoclave at 0.3 MPa.
• deionized water of about 3 times the mass of the filtered product was introduced into the autoclave to rinse and wash the filtered product at 90° C. three times, and the filtrate and the wet filtered product were recovered.
• High-performance liquid chromatography analysis of the obtained filtrate revealed that the amount of ⁇ -caprolactam contained in the filtrate was 14.0 g, and the yield relative to polyamide 6 in PA6-B used as a raw material was 78.4%.
• the obtained wet filter cake was vacuum-dried at 50° C. for 12 hours to recover 7.6 g of glass fibers.

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