Method for producing polyamide and method for producing regenerated polyamide composition

Abstract

To provide a method which, in recycling of polyamide in which multiple types of polyamides are mixed, such as recycling from articles containing polyamide blends, enables polyamides to be separated by type at a high recovery rate or a polyamide mixture to be obtained at any desired ratio.SOLUTION: Provided is a method for producing a first or second polyamide, comprising: step 1: dissolving a polyamide resin composition containing a first polyamide and a second polyamide having higher solubility in a metal chloride alcohol solution, which contains a metal chloride and an alcohol, than the first polyamide, into the metal chloride alcohol solution, thereby obtaining a polyamide solution; step 2: mixing the polyamide solution with a first poor solvent to precipitate the first polyamide; step 3: separating the first polyamide precipitated in step 2 from a first liquid phase by solid-liquid separation; optionally, step 4: mixing the first liquid phase separated in step 3 with a second poor solvent to precipitate the second polyamide; and optionally, step 5: separating the second polyamide precipitated in step 4 from a second liquid phase by solid-liquid separation.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing a polyamide and a method for producing a polyamide composition. [Background technology]

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

[0003] In recent years, technological developments have been made regarding the recycling of plastics with the aim of saving resources and becoming carbon neutral, and polyamides are no exception. In particular, polyamide 66 (polyhexamethylene adipamide), which is one of the polyamides produced in large quantities, is one of the polyamides that should be given priority for recycling.

[0004] 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 (Patent Documents 1 and 2).

[0005] Polyamides collected from the market for recycling may contain multiple types of polyamides mixed together. For example, polyamide 66 and polyamide 6 have similar properties and similar solubility in solvents. Therefore, polyamides collected from the market contain a mixture of these, and often also contain other resins. Separation of these resins is a challenge in recycling them.

[0006] Non-Patent Document 1 describes a method of treating a blended felt of polyamide 66 and polyamide 6 with a low-concentration methanol solution containing calcium chloride to dissolve the highly soluble polyamide 6, and then performing solid-liquid separation, and then treating the solid residue with a high-concentration methanol solution containing calcium chloride to dissolve the polyamide 66, thereby separating polyamide 66 and polyamide 6. However, when the recovery from such a mixture is scaled up, it has been found that the yield of polyamide 6 decreases because the blended polyamide 6 is difficult to dissolve when treated with a low-concentration methanol solution containing calcium chloride. The cause of this is assumed to be the occurrence of areas between the fibers where the solution cannot efficiently contact due to the swollen polyamide 66, even though it is not dissolved. As a result, not only is the yield of polyamide 6 low, but the residual polyamide 66 has a low purity. In addition, even if it is attempted to recover a regenerated polyamide by mixing polyamide 6 and polyamide 66, the amount of polyamide 6 dissolved changes depending on the degree of mechanical processing, so it is not possible to determine the conditions for obtaining a regenerated polyamide at a desired mixing ratio from the mixing ratio of the raw materials. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2018-172618 A [Patent Document 2] Patent No. 5110704 [Non-patent literature]

[0008] [Non-Patent Document 1] Journal of Chemical Engineering, Vol. 39, No. 3, pp. 238-243, 2013 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a method capable of separating polyamides by type at a high recovery rate in recycling polyamides containing a mixture of multiple types of polyamides, for example, in recycling polyamides from articles containing polyamide blends, and a method for obtaining a regenerated polyamide in which a first polyamide and a second polyamide are mixed in any ratio. [Means for solving the problem]

[0010] As a result of intensive research by the inventors to solve the above-mentioned problems, they have found that in recycling polyamide by dissolution, a polyamide resin composition containing at least two types of polyamides is dissolved in a metal chloride alcohol solution containing a metal chloride and alcohol to obtain a polyamide solution, a poor solvent is mixed with the polyamide solution under relatively weak precipitation conditions to precipitate the polyamide and perform solid-liquid separation, and a poor solvent is mixed with the polyamide solution after solid-liquid separation under relatively strong precipitation conditions to precipitate the polyamide and perform solid-liquid separation, thereby making it possible to precipitate and separate each type of polyamide and to obtain a recycled polyamide in which a first polyamide and a second polyamide are mixed in any ratio, thereby completing the present invention.

[0011] That is, the present invention is as follows. [1] The process is as follows: Step 1: a step of dissolving a polyamide resin composition containing a first polyamide and a second polyamide having a higher solubility in the metal chloride alcohol solution than the first polyamide in a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a polyamide solution; Step 2: mixing the polyamide solution with a first poor solvent to precipitate a first polyamide; and Step 3: A step of subjecting the first polyamide precipitated in step 2 to solid-liquid separation. A method for producing a first polyamide, comprising: [2] The process is as follows: Step 1: a step of dissolving a polyamide resin composition containing a first polyamide and a second polyamide having a higher solubility in the metal chloride alcohol solution than the first polyamide in a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a polyamide solution; step 2: mixing the polyamide solution with a first poor solvent to precipitate a first polyamide; step 3: subjecting the first polyamide precipitated in step 2 to solid-liquid separation from the first liquid phase; Step 4: mixing the first liquid phase obtained by solid-liquid separation in step 3 with a second poor solvent to precipitate a second polyamide; and Step 5: A step of subjecting the second polyamide precipitated in step 4 to solid-liquid separation from the second liquid phase. A method for producing a second polyamide, comprising: [3] The process is as follows: Step 1: a step of dissolving a polyamide resin composition containing a first polyamide and a second polyamide having a higher solubility in the metal chloride alcohol solution than the first polyamide in a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a polyamide solution; Step 2: mixing the polyamide solution with a first poor solvent to partially precipitate the first polyamide, or to precipitate the first polyamide and partially precipitate the second polyamide; Step 3: subjecting the polyamide composition precipitated in step 2 to solid-liquid separation from the first liquid phase; Step 4: mixing the first liquid phase separated by solid-liquid separation in step 3 with a second poor solvent to precipitate a polyamide; and Step 5: subjecting the polyamide precipitated in step 4 to solid-liquid separation from the second liquid phase; 1. A method for producing a regenerated polyamide composition comprising a first polyamide and a second polyamide, comprising: [4] The method according to any one of [1] to [3], wherein the first polyamide is polyamide 66 and the second polyamide is polyamide 6. [5] The method according to any one of [1] to [4], wherein the metal chloride is zinc chloride or calcium chloride. [6] The method according to [5], wherein the metal chloride is calcium chloride. [7] The method according to any one of [1] to [6], wherein the alcohol is methanol. [8] The method according to any one of [1] to [7], wherein the first or second poor solvent is the same as the alcohol contained in the metal chloride alcohol solution used for dissolution. [9] The method according to any one of [1] and [4] to [8], wherein the purity of the first polyamide produced is 98% or more.

[10] The method according to any one of [2] and [4] to [8], wherein the purity of the second polyamide produced is 98% or more. Effect of the Invention

[0012] According to the present invention, in recycling polyamides containing a mixture of multiple types of polyamides, for example, in recycling polyamides from articles containing polyamide blends, it is possible to provide a method capable of separating each type of polyamide at a high recovery rate and with high purity, and a method for obtaining a regenerated polyamide in which a first polyamide and a second polyamide are mixed in any ratio. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention will be described in detail below.

[0014] (Production method of polyamide) In the present invention, the method for producing a polyamide is a method for producing a first polyamide or a second polyamide by separating it from a polyamide resin composition containing at least two kinds of polyamides (hereinafter referred to as "first polyamide" and "second polyamide"). For example, it can be used for recycling polyamides and purifying polyamides, and in particular, it can be used for recycling polyamides. Specifically, the polyamide resin composition is treated with a metal chloride alcohol solution, which is a solvent for dissolving polyamides, to dissolve both the first polyamide and the second polyamide in the metal chloride alcohol solution, precipitate the first polyamide using a poor solvent capable of precipitating only the first polyamide, recover the first polyamide by solid-liquid separation, and then precipitate the second polyamide from the liquid phase obtained by solid-liquid separation using a poor solvent capable of precipitating the second polyamide, and recover the second polyamide by solid-liquid separation, thereby producing the first polyamide or the second polyamide. By first dissolving both the first polyamide and the second polyamide in a metal chloride alcohol solution, it becomes possible to separate the polyamides by type at a high recovery rate.

[0015] (First method for producing polyamide) In one embodiment, the method for producing a polyamide is a first method for producing a polyamide. The first method for producing a polyamide includes the steps of: Step 1: a step of dissolving a polyamide resin composition containing a first polyamide and a second polyamide having a higher solubility in the metal chloride alcohol solution than the first polyamide in a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a polyamide solution; Step 2: mixing the polyamide solution with a first poor solvent to precipitate a first polyamide; and Step 3: A step of subjecting the first polyamide precipitated in step 2 to solid-liquid separation.

[0016] In addition, the first method for producing a polyamide may further include the following optional steps: Step 4: mixing the first liquid phase obtained by solid-liquid separation in step 3 with a second poor solvent to precipitate a second polyamide; and Step 5: A step of subjecting the second polyamide precipitated in step 4 to solid-liquid separation from the second liquid phase.

[0017] (Second method for producing polyamide) In another embodiment, the method for producing a polyamide is a method for producing a second polyamide. The method for producing a second polyamide comprises the steps of: Step 1: a step of dissolving a polyamide resin composition containing a first polyamide and a second polyamide having a higher solubility in the metal chloride alcohol solution than the first polyamide in a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a polyamide solution; step 2: mixing the polyamide solution with a first poor solvent to precipitate a first polyamide; step 3: subjecting the first polyamide precipitated in step 2 to solid-liquid separation from the first liquid phase; Step 4: mixing the first liquid phase obtained by solid-liquid separation in step 3 with a second poor solvent to precipitate a second polyamide; and Step 5: A step of subjecting the second polyamide precipitated in step 4 to solid-liquid separation from the second liquid phase.

[0018] (Conditions for the production of polyamide) The conditions of the polyamide production method are described below. The conditions described below are common to the first and second polyamide production methods, except where the first and second polyamide production methods are particularly distinguished from each other.

[0019] <Polyamide resin composition> In the method for producing a polyamide composition, the polyamide used as a raw material is called a "polyamide resin composition". When the method for producing a polyamide composition is used for recycling polyamide, the "polyamide resin composition" refers to a polyamide-containing object before recycling, such as a polyamide-containing part, a polyamide-containing member, an object from which a non-polyamide-containing part has been removed, and a crushed product thereof. When the method for producing a polyamide composition is used for purifying polyamide, the "polyamide resin composition" refers to polyamide before purification. The polyamide resin composition contains at least two types of polyamide (a first polyamide and a second polyamide). The form of the polyamide resin composition is not particularly limited, and examples thereof include an article containing a polyamide blended product and an article containing a polyamide mixed resin.

[0020] <Polyamide (first polyamide and second polyamide)> The "first polyamide" and the "second polyamide" refer to two different types of polyamides contained in the polyamide resin composition, which are to be separated in the method for producing the polyamide composition. Of the "first polyamide" and the "second polyamide", the polyamide having a higher solubility in the alcohol solution of a metal chloride described later is called the "second polyamide". The combination of the first polyamide and the second polyamide is not particularly limited, but examples thereof include a combination of the first polyamide being polyamide 66 and the second polyamide being polyamide 6.

[0021] The polyamide production method of the present invention allows the production of a target polyamide with high purity. In the first polyamide production method, the purity of the first polyamide produced is preferably 90% or more, more preferably 98% or more, and even more preferably 99% or more. In the second polyamide production method, the purity of the second polyamide produced is preferably 90% or more, more preferably 98% or more, and even more preferably 99% or more. The purity of the polyamide in the present invention represents the weight of each polyamide relative to the sum of the weights of the first polyamide and the second polyamide, and does not change due to, for example, water or a solvent remaining in the polyamide.

[0022] <Metal chloride alcohol solution> The term "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 solvent for dissolving the polyamide. The metal chloride alcohol solution is required to be able to sufficiently dissolve both the first polyamide and the second polyamide.

[0023] From the viewpoint of being able to sufficiently dissolve both the first polyamide and the second polyamide, the metal chloride alcohol solution preferably has a total mass ratio of the metal chloride, alcohols, and water relative to 100 mass% of the metal chloride alcohol solution of 80 mass% or more, more preferably 90 mass% or more, and even more preferably 100 mass%.

[0024] <<Alcoholic drinks>> Examples of the alcohols contained in the metal chloride alcohol solution 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, and combinations thereof. Among these, from the viewpoint of being able to sufficiently dissolve both the first polyamide and the second polyamide, methanol, ethanol, or a combination thereof is preferred, and methanol is more preferred.

[0025] <<Metal chlorides>> Examples of the metal chloride contained in the metal chloride alcohol solution include zinc chloride, magnesium chloride, and calcium chloride, with zinc chloride and calcium chloride being preferred, and calcium chloride being most preferred.

[0026] The mass ratio of water in the above-mentioned metal chloride alcohol solution is preferably 30 mass% or less, more preferably 15 mass% or less, and further preferably 10 mass% or less. The mass ratios of water in the metal chloride and alcohol solvent can be changed so that the mass ratio of water falls within the above range.

[0027] <<Metal chloride concentration>> The concentration of the metal chloride in the metal chloride alcohol solution is preferably 10% by mass or more, more preferably 12% by mass or more, and even more preferably 15% by mass or more from the viewpoint of improving the solubility of the polyamide resin composition. On the other hand, 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 become mixed in as an impurity.

[0028] <Poor solvents ("first poor solvent and second poor solvent")> The term "poor solvent" refers to a poor solvent for polyamide. In the method for producing polyamide, two poor solvents (hereinafter referred to as "first poor solvent" and "second poor solvent") are used. The term "first poor solvent" refers to a poor solvent used to precipitate a first polyamide by mixing with a polyamide solution. The term "second poor solvent" refers to a poor solvent used to precipitate a second polyamide by mixing with a polyamide solution after separating and removing the precipitated first polyamide. The first poor solvent and the second poor solvent may be different types of poor solvents or may be the same type of poor solvent. Details of the first poor solvent and the second poor solvent will be described later.

[0029] Hereinafter, the "poor solvent" that can be used as the first poor solvent and the second poor solvent will be described. The poor solvent refers to a poor solvent for each polyamide, and may be, for example, a solvent in which 100 g of a solvent is added to 1 g of a polyamide (e.g., nylon 66) and the amount of polyamide dissolved in the solution after stirring at 20°C for 1 hour is 0.05 g or less. The poor solvent is not particularly limited as long as it is a poor solvent for polyamide and is preferably compatible with the alcohol solution of a metal chloride, and examples of the poor solvent include alcohols, water, and mixtures of alcohols and water. The poor solvent may further contain salts, pH adjusters, etc. in a content sufficient to maintain the function as a poor solvent.

[0030] Examples of the alcohols used as the poor solvent include those exemplified as the alcohols contained in the alcohol solution of a metal chloride.

[0031] Examples of the salts include alkali metal salts, alkaline earth metal salts, transition metal salts, and ammonium salts, and more preferably include sodium salts, potassium salts, lithium salts, calcium salts, magnesium salts, barium salts, strontium salts, copper salts, and ammonium salts. Examples of the anions of the 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.

[0032] 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, and the like.

[0033] Examples of pH adjusters include water-soluble basic salts, acid salts, and buffers (e.g., a mixture of an acid and a salt, or a mixture of a base and a salt), 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., a mixture of acetic acid and sodium acetate), and phosphate buffers (e.g., a mixture of acetic acid and sodium acetate).

[0034] The poor solvent is preferably water or an alcohol, and from the viewpoint of facilitating the reuse of the solvent, it is more preferable that the poor solvent is the same as the alcohol contained in the metal chloride alcohol solution used for dissolution. On the other hand, since water is highly effective as a poor solvent for polyamide, it is also possible to select water from the viewpoints of improving the recovery rate of polyamide and reducing the amount of solvent used.

[0035] (Process 1: Melting process) Step 1 is a step of dissolving both the first polyamide and the second polyamide contained in the polyamide resin composition in a metal chloride alcohol solution to obtain a polyamide solution. The conditions for carrying out step 1 are not particularly limited as long as the conditions are such that both the first polyamide and the second polyamide are almost entirely dissolved. Step 1 may be carried out, for example, by heating and dissolving.

[0036] <Amount of polyamide resin composition used> As the amount of the polyamide resin composition used in step 1, the concentration of the total amount of polyamide in the heated polyamide solution (e.g., the total amount of the first polyamide and the second polyamide) is 5% by mass or more, preferably 7% by mass or more, and 15% by mass or less, preferably 13% by mass or less. If the amount is less than the lower limit, too much solvent is required, and if the amount is more than the upper limit, the viscosity increases, prolonging the dissolution time and deteriorating operability.

[0037] <Conditions for heating and dissolving> When step 1 is carried out by dissolving by heating, the temperature for dissolving by heating 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 70° C. or lower. If the temperature is low, dissolution will be slow, and conversely, if the temperature is too high, exceeding the boiling point, the alcohol will volatilize and disappear, reducing solubility, and is also undesirable from the standpoint of corrosivity and decomposition. During the above step 1, the temperature may be constant or may be changed within the above range.

[0038] The time for heat dissolution is preferably as long as possible from the viewpoint of sufficiently dissolving the polyamide resin composition, for example, 5 minutes or more is preferable, 30 minutes or more is more preferable, and 1 hour or more is even more preferable. On the other hand, the time for heat dissolution is preferably not too long from the viewpoint 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, for example, 100 hours or less is preferable, 50 hours or less is more preferable, and 24 hours or less is even more preferable.

[0039] The dissolution may be carried out in either a batch or continuous manner. In the case of 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. In the case of a continuous system, the solvent may be continuously passed through the solid, or the solution may be circulated. Circulation is preferred because it allows the amount of solvent used to be reduced.

[0040] The shape of the container is not particularly limited, and any shape such as a tank type or a circulation type may be used.

[0041] (Step 2: First Polyamide Precipitation Step) Step 2 is a step of mixing a polyamide solution in which the first polyamide and the second polyamide are dissolved with a first poor solvent to precipitate the first polyamide while suppressing precipitation of the second polyamide. The conditions for carrying out step 2 are not particularly limited as long as the conditions are such that the first polyamide is precipitated and precipitation of the second polyamide is suppressed.

[0042] In the method for producing the first polyamide, from the viewpoint of prioritizing the purity of the precipitated first polyamide over the yield, it is preferable that the precipitation conditions be as weak as possible within the range in which the first polyamide can be precipitated.

[0043] In the case of the method for producing the second polyamide, from the viewpoint of precipitating and removing as much of the first polyamide as an impurity in step 2 as possible and suppressing the amount of precipitation of the second polyamide as the target product in step 2, it is preferable to use relatively weak precipitation conditions within a range in which precipitation of the second polyamide is suppressed.

[0044] <Amount of first poor solvent used> In the first method for producing a polyamide, from the viewpoint of setting the weakest possible precipitation conditions, the mass of the first poor solvent used in step 2 is preferably 0.5 times or more, more preferably 0.7 times or more, and even more preferably 0.9 times or more, relative to the mass of the polyamide solution in step 1, and is preferably 10 times or less, more preferably 5 times or less, and even more preferably 3 times or less.

[0045] In the case of the second method for producing a polyamide, from the viewpoint of setting relatively weak precipitation conditions, the mass of the first poor solvent used in step 2 is preferably 0.5 times or more, more preferably 0.7 times or more, and even more preferably 1 time or more, relative to the mass of the polyamide solution in step 1, and is preferably 10 times or less, more preferably 5 times or less, and even more preferably 3 times or less. The appropriate amount of poor solvent can be calculated by measuring the solubility of each polyamide in a solvent obtained by mixing the poor solvent and the dissolving solution. Since the amount of poor solvent varies depending on the type of poor solvent, it cannot be uniquely defined, but it is preferable that the amount of poor solvent is such that metal chloride does not precipitate.

[0046] -First method for producing polyamide- <Metal chloride concentration after addition of first poor solvent> In the first method for producing a polyamide, from the viewpoint of setting the weakest possible precipitation conditions, the metal chloride concentration in the components excluding the polyamide in the polyamide solution after mixing with the first poor solvent in step 2 is preferably 6 mass% or more, more preferably 7 mass% or more, and even more preferably 8 mass% or more, and is preferably 15 mass% or less, more preferably 12 mass% or less, and even more preferably 10 mass% or less. <Water content after addition of first poor solvent> In the case of the first polyamide production method, from the viewpoint of setting the weakest possible precipitation conditions, the molar amount [mol] of water in the polyamide solution after mixing with the first poor solvent in step 2 is preferably not more than the value calculated by the general formula (1) shown below per mol of calcium chloride in the solution, and more preferably not more than the value calculated by the general formula (2) shown below. General formula (1): 0.5[L]×metal chloride concentration[mol / L]-2[mol] General formula (2): 0.5[L]×metal chloride concentration[mol / L]-3[mol]

[0047] -Second method for producing polyamide- <Metal chloride concentration after addition of first poor solvent> In the case of the second method for producing a polyamide, from the viewpoint of setting relatively weak precipitation conditions, the metal chloride concentration in the components excluding the polyamide in the polyamide solution after mixing with the first poor solvent in step 2 is preferably 2 mass% or more, more preferably 3 mass% or more, and even more preferably 4 mass% or more, and is preferably 10 mass% or less, more preferably 8 mass% or less, and even more preferably 7 mass% or less. <Water content after addition of first poor solvent> In the case of the second method for producing a polyamide, from the viewpoint of setting the precipitation conditions as weak as possible, the molar amount of water in the polyamide solution after mixing with the first poor solvent in step 2 is preferably equal to or greater than the value calculated by general formula (2) per mole of calcium chloride in the solution, and more preferably equal to or greater than the value calculated by general formula (1).

[0048] <Temperature> The temperature at which step 2 is carried out is, for example, preferably 10°C or higher, more preferably 15°C or higher, even more preferably 20°C or higher, and preferably 60°C or lower, more preferably 40°C or lower, and even more preferably 30°C or lower.

[0049] (Step 3: First Polyamide Separation Step) Step 3 is a step of performing solid-liquid separation of the first polyamide precipitated in step 2 from the polyamide solution remaining after the precipitation of the first polyamide (hereinafter referred to as the "first liquid phase"). Examples of the method of solid-liquid separation include filtration, decantation, centrifugation, and sedimentation. In the method for producing the first polyamide, the precipitated first polyamide can be used as the first polyamide, which is the product.

[0050] (Step 4: Second polyamide precipitation step) Step 4 is a step of precipitating a second polyamide by mixing the first liquid phase obtained by solid-liquid separation in step 3 (i.e., the precipitated first polyamide has been removed) with a second poor solvent. The conditions for carrying out step 4 are not particularly limited as long as the second polyamide is sufficiently precipitated, and relatively strong precipitation conditions are preferable.

[0051] <Amount of first poor solvent used> In the case of the first polyamide production method and the second polyamide production method, from the viewpoint of providing relatively strong precipitation conditions, the mass of the second poor solvent used in step 4 is preferably 0.5 times or more, more preferably 0.7 times or more, and even more preferably 0.9 times or more, relative to the mass of the polyamide solution in step 1, and is preferably 10 times or less, more preferably 5 times or less, and even more preferably 3 times or less.

[0052] <Metal chloride concentration after addition of second poor solvent> In the first polyamide production method and the second polyamide production method, from the viewpoint of setting relatively strong precipitation conditions, the metal chloride concentration in the polyamide solution after mixing with the second poor solvent in step 4 is preferably 10 mass % or less, more preferably 7 mass % or less, and even more preferably 5 mass % or less.

[0053] <Temperature> The temperature at which step 4 is carried out is, for example, preferably 10°C or higher, more preferably 15°C or higher, even more preferably 20°C or higher, and preferably 60°C or lower, more preferably 40°C or lower, and even more preferably 30°C or lower.

[0054] (Step 5: Second polyamide separation step) Step 5 is a step of performing solid-liquid separation of the second polyamide precipitated in step 4 from the polyamide solution remaining after the precipitation of the second polyamide (hereinafter referred to as "second liquid phase"). Examples of the method of solid-liquid separation include filtration, decantation, centrifugation, and sedimentation. In the method for producing the second polyamide, the precipitated second polyamide can be used as the second polyamide product.

[0055] (Method of producing recycled polyamide composition) The present invention further provides a method for producing a recycled polyamide composition. The method for producing a recycled polyamide composition is a method for producing a recycled polyamide composition containing a first polyamide and a second polyamide having a desired composition from a polyamide resin composition containing a first polyamide and a second polyamide, and can be used, for example, for recycling polyamides and purifying polyamides, and can be used in particular for recycling polyamides. The method for producing a recycled polyamide composition is a method carried out by the same steps as the above-mentioned method for producing polyamides, and it is possible to produce a recycled polyamide composition having a desired composition by adjusting the amount of precipitation of the first polyamide in step 2 (first polyamide precipitation step) or by partially precipitating the second polyamide.

[0056] The method for producing the recycled polyamide composition includes the following steps: Step 1: a step of dissolving a polyamide resin composition containing a first polyamide and a second polyamide having a higher solubility in the metal chloride alcohol solution than the first polyamide in a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a polyamide solution; Step 2: mixing the polyamide solution with a first poor solvent to partially precipitate the first polyamide, or to precipitate the first polyamide and partially precipitate the second polyamide; Step 3: subjecting the polyamide composition precipitated in step 2 to solid-liquid separation from the first liquid phase; Step 4: mixing the first liquid phase separated by solid-liquid separation in step 3 with a second poor solvent to precipitate a polyamide; and Step 5: subjecting the polyamide precipitated in step 4 to solid-liquid separation from the second liquid phase; The present invention relates to a method for producing a recycled polyamide composition comprising a first polyamide and a second polyamide, the method comprising the steps of:

[0057] (Conditions for the manufacturing method of the recycled polyamide composition) The conditions for the method for producing the recycled polyamide composition are described below. Note that the conditions other than those described below are the same as those in the method for producing the polyamide described above.

[0058] (Process 1: Melting process) The conditions for step 1 are the same as those for step 1 in the above-mentioned method for producing a polyamide.

[0059] (Step 2: Partial Precipitation of First Polyamide) Step 2 is a step of mixing a polyamide solution in which the first polyamide and the second polyamide are dissolved with a first poor solvent to partially precipitate the first polyamide while suppressing precipitation of the second polyamide. The conditions for performing step 2 can be appropriately selected as weak precipitation conditions (e.g., weaker precipitation conditions than step 2 of the method for producing the first polyamide) under which only a part of the first polyamide precipitates and precipitation of the second polyamide is suppressed, or strong precipitation conditions (stronger than step 2 of the method for producing the first polyamide and weaker than step 4) under which the second polyamide precipitates together with the first polyamide. By adjusting the degree of precipitation of the first and second polyamides in step 2 and precipitating the first polyamide and the second polyamide with a desired composition in step 4, it becomes possible to produce a recycled polyamide composition having a desired composition in step 3 or step 5.

[0060] <Amount of first poor solvent used> The mass of the first poor solvent used in step 2 is preferably 0.1 times or more, more preferably 0.3 times or more, and even more preferably 0.5 times or more, relative to the mass of the polyamide solution in step 1, and is preferably 10 times or less, more preferably 5 times or less, and even more preferably 3 times or less.

[0061] <Metal chloride concentration after addition of first poor solvent> As a condition for partially precipitating the first polyamide in step 2, the metal chloride concentration in the components excluding the polyamide in the polyamide solution after mixing with the first poor solvent is preferably 6% by mass or more, more preferably 7% by mass or more, and even more preferably 8% by mass or more. On the other hand, as a condition for partially precipitating the second polyamide as well, the metal chloride concentration in the components excluding the polyamide in the polyamide solution after mixing with the first poor solvent is preferably 8% by mass or more, more preferably 7% by mass or more, and even more preferably 6% by mass or more.

[0062] <Water content after addition of first poor solvent> As conditions for partially precipitating the first polyamide, the molar amount [mol] of water in the polyamide solution after mixing with the first poor solvent in step 2 is preferably equal to or less than the value calculated by the following general formula (1) per mol of calcium chloride in the solution, and more preferably equal to or less than the value calculated by the following general formula (2). On the other hand, as conditions for partially precipitating the second polyamide, it is preferably equal to or more than the value calculated by the following general formula (2), and more preferably equal to or more than the value calculated by the following general formula (1). General formula (1): 0.5[L]×metal chloride concentration[mol / L]-2[mol] General formula (2): 0.5[L]×metal chloride concentration[mol / L]-3[mol]

[0063] <Temperature> The temperature at which step 2 is carried out is, for example, preferably 10°C or higher, more preferably 15°C or higher, even more preferably 20°C or higher, and preferably 60°C or lower, more preferably 40°C or lower, and even more preferably 30°C or lower.

[0064] (Step 3: Polyamide separation step) The conditions for step 3 are the same as those for step 3 in the above-mentioned method for producing a polyamide.

[0065] (Step 4: Polyamide Precipitation Step) Step 4 is a step of mixing the first liquid phase obtained by solid-liquid separation in step 3 (i.e., the partially precipitated first polyamide or the mixture of the first polyamide and the partially precipitated second polyamide has been removed) with a second poor solvent to precipitate a polyamide with a desired composition. The conditions for carrying out step 4 are not particularly limited as long as the second polyamide is sufficiently precipitated, and relatively strong precipitation conditions are preferable.

[0066] <Amount of second poor solvent used> From the viewpoint of achieving relatively strong precipitation conditions, the mass of the first poor solvent used in step 4 is preferably 0.5 times or more, more preferably 1 time or more, and even more preferably 1.2 times or more, relative to the mass of the polyamide solution in step 1, and is preferably 30 times or less, more preferably 20 times or less, and even more preferably 10 times or less.

[0067] <Metal chloride concentration after addition of first poor solvent> In the case of the first polyamide production method, from the viewpoint of setting relatively strong precipitation conditions, the metal chloride concentration in the polyamide solution after mixing with the first poor solvent in step 2 is preferably 1 mass % or more, preferably 10 mass % or less, more preferably 8 mass % or less, and even more preferably 6 mass % or less.

[0068] <Temperature> The temperature at which step 4 is carried out is, for example, preferably 10°C or higher, more preferably 15°C or higher, even more preferably 20°C or higher, and preferably 60°C or lower, more preferably 40°C or lower, and even more preferably 30°C or lower.

[0069] (Step 5: First and second polyamide separation step) Step 5 is a step of performing solid-liquid separation of the first polyamide and the second polyamide having the desired composition precipitated in step 4 from the second liquid phase. Examples of the solid-liquid separation method include filtration, decantation, centrifugation, and sedimentation. The precipitated first polyamide and second polyamide can be made into a regenerated polyamide composition containing the first polyamide and the second polyamide, which are the products. EXAMPLES

[0070] The present invention will be described in detail below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples. The measurement and evaluation methods applied in the examples and comparative examples are shown below.

[0071] [Polyamide solubility] The solubility of the polyamide can be measured, for example, by the following method. Weigh out 100 g of polyamide dissolving solvent into a 250 mL glass bottle with a stir bar. Add 10 g of polyamide, put the lid on, and stir while heating to 50°C in a water bath. After stirring for 24 hours, return to 25°C. If no precipitation occurs, add more polyamide and repeat the same procedure. If precipitation occurs, filter and recover the supernatant, and add water in an amount 10 times the amount of the recovered liquid to precipitate polyamide. Filter and recover the precipitated polyamide, wash thoroughly with water, and vacuum dry at 60°C. Then measure the weight of the recovered polyamide and calculate the solubility from the ratio of the dissolved amount to the recovered liquid amount.

[0072] [Polyamide Purity] The purity of the polyamide can be determined, for example, by the following method. Weigh out 6 mL of 5.56 mol / L HCl solution and 150 mg of polyamide into a microwave heating vial that already has a stirrer in it. Seal the container and heat it in a microwave heating device at 170°C for 30 minutes. Transfer the resulting solution to a 25 mL round-bottom flask, and add the liquid that was used to wash the microwave-heated container with 5 mL of water. Remove the solvent using a rotary evaporator, and dry the resulting solid in a vacuum dryer at 50°C. Add 2 mL of heavy water to the dried solution to dissolve it, and determine the concentration from the integral ratio of the peaks of the hydrolyzate of each polyamide using 1H-NMR. The polyamides used in the examples were polyamide 66 and polyamide 6, and their solubilities in a 22 wt % calcium chloride methanol solution at 25° C. were 15.0% and 17.0%, respectively.

[0073] [Example 1] 300g of polyamide 66-polyamide 6 blended fabric (weight ratio 1:1) and 3kg of 22wt% calcium chloride methanol solution (no water added) were added to a 5L glass bottle containing a stirrer, and the bottle was placed in a water bath at 60°C and dissolved while stirring with a magnetic stirrer for 12 hours to obtain a polyamide solution. The recovered polyamide solution was transferred to a 10L beaker containing a stirrer, and 5.9kg of methanol was added while stirring to obtain a precipitate. The resulting solid precipitate was filtered and collected using a 10μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and then heated and dried in a vacuum dryer at 80°C to obtain 146.5g (yield: 98.0%) of powdered polyamide. As a result of composition analysis, the purity of polyamide 66 (first polyamide) was 98.2%. The filtrate separated by filtration was placed in a 20 L stainless steel jacketed reactor equipped with an agitator, and 8.6 kg of water was added while stirring. After the addition, a cooling liquid was run through the jacket to cool the inside temperature to 5°C, and stirring was continued for 3 hours. The obtained solid precipitate was filtered and collected using a 10 μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and heated and dried in a vacuum dryer at 80°C, obtaining 126.7 g (84.0%) of powdered polyamide. As a result of composition analysis, the purity of polyamide 6 (second polyamide) was 98.0%.

[0074] [Example 2] In a 5L glass bottle containing a stirrer, 300g of polyamide 66-polyamide 6 blended fabric (weight ratio 1:1) and 3kg of 26.4wt% calcium chloride methanol solution (containing 257.9g of water) were added, placed in a water bath at 60°C, and dissolved while stirring with a magnetic stirrer for 12 hours to obtain a polyamide solution. The recovered polyamide solution was transferred to a 10L beaker containing a stirrer, and 5.3kg of methanol was added while stirring to obtain a precipitate. The resulting solid precipitate was filtered and recovered with a 10μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and then heated and dried in a vacuum dryer at 80°C to obtain 151.8g of powdered polyamide (yield: 101.0%). As a result of composition analysis, the purity of polyamide 66 (first polyamide) was 99.0%. The filtrate separated by filtration was placed in a 20 L stainless steel jacketed reactor equipped with an agitator, and 8.0 kg of water was added while stirring. After the addition, a cooling liquid was run through the jacket to cool the inside temperature to 10°C, and stirring was continued for 3 hours. The obtained solid precipitate was filtered and collected using a 10 μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and heated and dried in a vacuum dryer at 80°C, obtaining 145.5 g (97.0%) of powdered polyamide. As a result of composition analysis, the purity of polyamide 6 (second polyamide) was 98.0%.

[0075] [Example 3] 300g of polyamide 66-polyamide 6 blended fabric (weight ratio 1:1) and 3kg of 30.0wt% calcium chloride methanol solution (containing 146.0g of water) were added to a 5L glass bottle containing a stirrer, and the bottle was placed in a water bath at 60°C and dissolved while stirring with a magnetic stirrer for 12 hours to obtain a polyamide solution. The recovered polyamide solution was transferred to a 10L beaker containing a stirrer, and 9.0kg of methanol was added while stirring to obtain a precipitate. The resulting solid precipitate was filtered and recovered with a 10μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and then heated and dried in a vacuum dryer at 80°C to obtain 146.0g of powdered polyamide (yield: 97.0%). As a result of composition analysis, the purity of polyamide 66 (first polyamide) was 98.0%. The filtrate separated by filtration was placed in a 20 L stainless steel jacketed reactor equipped with an agitator, and 12.2 kg of water was added while stirring. After the addition, a cooling liquid was run through the jacket to cool the inside temperature to 10°C, and stirring was continued for 3 hours. The obtained solid precipitate was filtered and collected using a 10 μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and dried by heating in a vacuum dryer at 80°C, obtaining 140.8 g (94.0%) of powdered polyamide. As a result of composition analysis, the purity of polyamide 6 (second polyamide) was 97.0%.

[0076] [Example 4] 300g of polyamide 66-polyamide 6 blended fabric (weight ratio 1:1) and 3kg of 22.0wt% calcium chloride methanol solution (no water added) were added to a 5L glass bottle containing a stirrer, and the bottle was placed in a water bath at 60°C and dissolved while stirring with a magnetic stirrer for 12 hours to obtain a polyamide solution. The recovered polyamide solution was transferred to a 10L beaker containing a stirrer, and 9.3kg of methanol was added while stirring to obtain a precipitate. The resulting solid precipitate was filtered and recovered with a 10μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and then heated and dried in a vacuum dryer at 80°C to obtain 195.8g of powdered polyamide (yield: 131.0%). As a result of composition analysis, the purity of polyamide 66 (first polyamide) was 77.0%, and a regenerated polyamide with a weight ratio of polyamide 66:polyamide 6=77:23 was obtained. The filtrate separated by filtration was placed in a 20 L stainless steel jacketed reactor equipped with an agitator, and 12.2 kg of water was added while stirring. After the addition, a cooling liquid was run through the jacket to cool the inside temperature to 10°C, and stirring was continued for 3 hours. The obtained solid precipitate was filtered and collected using a 10 μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and heated and dried in a vacuum dryer at 80°C, yielding 91.9 g (61.0%) of powdered polyamide. As a result of composition analysis, the purity of polyamide 6 (second polyamide) was 98.0%.

[0077] [Example 5] In a 5L glass bottle containing a stirrer, 300g of polyamide 66-polyamide 6 blended base fabric (weight ratio 1:1) and 3kg of 26.4wt% calcium chloride methanol solution (containing 257.9g of water) were added, placed in a water bath at 60°C, and dissolved while stirring with a magnetic stirrer for 12 hours to obtain a polyamide solution. The recovered polyamide solution was transferred to a 10L beaker containing a stirrer, and 11.7kg of methanol was added while stirring to obtain a precipitate. The resulting solid precipitate was filtered and recovered with a 10μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and then heated and dried in a vacuum dryer at 80°C to obtain 282.6g of powdered polyamide (yield: 188.0%). As a result of composition analysis, the purity of polyamide 66 (first polyamide) was 53.0%, and a regenerated polyamide with a weight ratio of polyamide 66:polyamide 6 = 53:47 was obtained. The filtrate separated by filtration was placed in a 20 L stainless steel jacketed reactor equipped with an agitator, and 14.8 kg of water was added while stirring. After the addition, a cooling liquid was run through the jacket to cool the inside temperature to 10°C, and stirring was continued for 3 hours. The obtained solid precipitate was filtered and collected using a 10 μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and heated and dried in a vacuum dryer at 80°C, obtaining 15.6 g (10.0%) of powdered polyamide. As a result of composition analysis, the purity of polyamide 6 (second polyamide) was 98.0%.

[0078] [Example 6] 300g of polyamide 66-polyamide 6 blended fabric (weight ratio 1:1) and 3kg of 30.0wt% calcium chloride methanol solution (containing 146.0g of water) were added to a 5L glass bottle containing a stirrer, and the bottle was placed in a water bath at 60°C and dissolved while stirring with a magnetic stirrer for 12 hours to obtain a polyamide solution. The recovered polyamide solution was transferred to a 10L beaker containing a stirrer, and 13.6kg of methanol was added while stirring to obtain a precipitate. The resulting solid precipitate was filtered and recovered using a 10μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and then heated and dried in a vacuum dryer at 80°C to obtain 232.2g of powdered polyamide (yield: 155.0%). As a result of composition analysis, the purity of polyamide 66 (first polyamide) was 64.0%, and a regenerated polyamide with a weight ratio of polyamide 66:polyamide 6=64:36 was obtained. The filtrate separated by filtration was placed in a 20 L stainless steel jacketed reactor equipped with an agitator, and 16.3 kg of water was added while stirring. After the addition, a cooling liquid was run through the jacket to cool the inside temperature to 10°C, and stirring was continued for 3 hours. The obtained solid precipitate was filtered and collected using a 10 μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and heated and dried in a vacuum dryer at 80°C, obtaining 53.2 g (35%) of powdered polyamide. As a result of composition analysis, the purity of polyamide 6 (second polyamide) was 98.0%.

[0079] [Example 7] 300g of polyamide 66-polyamide 6 blended fabric (weight ratio 1:1) and 3kg of 22.0wt% calcium chloride methanol solution (no water added) were added to a 5L glass bottle containing a stirrer, and the bottle was placed in a water bath at 60°C and dissolved while stirring with a magnetic stirrer for 12 hours to obtain a polyamide solution. The recovered polyamide solution was transferred to a 10L beaker containing a stirrer, and 3.9kg of methanol was added while stirring to obtain a precipitate. The resulting solid precipitate was filtered and collected using a 10μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and then heated and dried in a vacuum dryer at 80°C to obtain 114.7g of powdered polyamide (yield: 76.0%). As a result of composition analysis, the purity of polyamide 66 (first polyamide) was 98.2%. The filtrate separated by filtration was placed in a 20L stainless steel jacketed reactor equipped with an agitator, and 6.6 kg of water was added while stirring. After the addition, a cooling liquid was run through the jacket to cool the inside temperature to 10 degrees, and stirring was continued for 3 hours. The obtained solid precipitate was filtered and collected using a 10 μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and heated and dried in a vacuum dryer at 80 ° C, obtaining 172.5 g (115%) of powdered polyamide. As a result of composition analysis, the purity of polyamide 6 (second polyamide) was 87.0%, and a regenerated polyamide with a weight ratio of polyamide 66:polyamide 6 = 13:87 was obtained.

[0080] [Comparative Example 1] 300g of polyamide 66-polyamide 6 blended fabric (weight ratio 1:1) and 15kg of 22wt% calcium chloride methanol solution (containing 1.1kg of water) were added to a 30L jacketed stainless steel reactor equipped with an agitator, and while running hot water at 30°C, the mixture was stirred for 12 hours to dissolve, and a solution containing a residue was obtained. The resulting solution was passed through a 10μm membrane filter to separate the residue. The filtrate was placed in a 100L jacketed stainless steel reactor equipped with an agitator, hot water at 30°C was run, and stirring was started. 60kg of water was added while stirring to obtain a precipitate. The resulting solid precipitate was filtered and collected with a 10μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and then heated and dried in a vacuum dryer at 80°C to obtain 95g of powdered polyamide (yield 63%). As a result of composition analysis, the purity of polyamide 6 (second polyamide) was 98.2%. The filtrate separated by filtration was placed in a 20 L stainless steel jacketed reactor equipped with an agitator, and 6 kg of water was added while stirring. After the addition, a cooling liquid was run through the jacket to cool the inside temperature to 5°C, and stirring was continued for 3 hours. The resulting solid precipitate was filtered and collected using a 10 μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and heated and dried in a vacuum dryer at 80°C, yielding 195.0 g (yield 130%) of powdered polyamide. As a result of composition analysis, the purity of polyamide 66 (first polyamide) was 0.76.9%. If one attempts to dissolve only polyamide 6, the yield of polyamide 6 will be low and the purity of polyamide 66 will be low.

[0081] [Comparative Example 2] 150g of polyamide 66 pellets, 150g of polyamide 6 pellets, and 15kg of 22wt% calcium chloride methanol solution (containing 1.1kg of water) were added to a 30L jacketed stainless steel reactor equipped with an agitator, and while running hot water at 30°C, the mixture was stirred for 12 hours to dissolve, and a solution containing a residue was obtained. The resulting solution was passed through a 10μm membrane filter to separate the residue. The filtrate was placed in a 100L jacketed stainless steel reactor equipped with an agitator, hot water at 30°C was run, and stirring was started. 60kg of water was added while stirring to obtain a precipitate. The resulting solid precipitate was filtered and collected with a 10μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and then heated and dried in a vacuum dryer at 80°C to obtain 148.2g (yield 98.8%) of powdered polyamide. As a result of composition analysis, the purity of polyamide 6 (second polyamide) was 98.2%. The filtrate separated by filtration was placed in a 20 L stainless steel jacketed reactor equipped with an agitator, and 6 kg of water was added while stirring. After the addition, a cooling liquid was run through the jacket to cool the inside temperature to 5°C, and stirring was continued for 3 hours. The resulting solid precipitate was filtered and collected using a 10 μm membrane filter. The solid precipitate after filtration was thoroughly washed with water and heated and dried in a vacuum dryer at 80°C, yielding 150.0 g (yield 100%) of powdered polyamide. As a result of composition analysis, the purity of polyamide 66 (first polyamide) was .98.0%. If the raw material is not a blend but a mixture of pellets, separation is possible, but it is clear that this method cannot be applied to raw materials with complex mixtures. [Industrial Applicability]

[0082] According to the present invention, it is possible to provide a method for recycling polyamides containing a mixture of multiple types of polyamides, for example, recycling polyamides from articles containing polyamide blends, which enables separation of each type of polyamide with a high recovery rate.

Claims

1. The following steps: Step 1: A step of dissolving a polyamide resin composition containing a first polyamide and a second polyamide having a higher solubility in the metal chloride alcohol solution than the first polyamide in a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a polyamide solution; Step 2: mixing the polyamide solution with a first poor solvent to precipitate a first polyamide; and Step 3: A step of subjecting the first polyamide precipitated in step 2 to solid-liquid separation. A method for producing a first polyamide, comprising:

2. The following steps: Step 1: A step of dissolving a polyamide resin composition containing a first polyamide and a second polyamide having a higher solubility in the metal chloride alcohol solution than the first polyamide in a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a polyamide solution; Step 2: mixing the polyamide solution with a first poor solvent to precipitate a first polyamide; Step 3: subjecting the first polyamide precipitated in step 2 to solid-liquid separation from the first liquid phase; Step 4: mixing the first liquid phase separated by solid-liquid separation in step 3 with a second poor solvent to precipitate a second polyamide; and Step 5: A step of subjecting the second polyamide precipitated in step 4 to solid-liquid separation from the second liquid phase. A method for producing a second polyamide, comprising:

3. The following steps: Step 1: A step of dissolving a polyamide resin composition containing a first polyamide and a second polyamide having a higher solubility in the metal chloride alcohol solution than the first polyamide in a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a polyamide solution; Step 2: mixing the polyamide solution with a first poor solvent to partially precipitate the first polyamide, or to precipitate the first polyamide and partially precipitate the second polyamide; Step 3: subjecting the polyamide composition precipitated in step 2 to solid-liquid separation from the first liquid phase; Step 4: mixing the first liquid phase separated by solid-liquid separation in step 3 with a second poor solvent to precipitate a polyamide; and Step 5: A step of subjecting the polyamide precipitated in step 4 to solid-liquid separation from the second liquid phase; 1. A method for producing a regenerated polyamide composition comprising a first polyamide and a second polyamide, comprising:

4. The process according to any one of claims 1 to 3, wherein the first polyamide is polyamide 66 and the second polyamide is polyamide 6.

5. The method according to any one of claims 1 to 3, wherein the metal chloride is zinc chloride or calcium chloride.

6. 6. The method according to claim 5, wherein the metal chloride is calcium chloride.

7. The process according to any one of claims 1 to 3, wherein the alcohol is methanol.

8. The method according to any one of claims 1 to 3, wherein the first or second poor solvent is the same as the alcohol contained in the alcoholic solution of the metal chloride used for dissolution.

9. 2. The method according to claim 1, wherein the purity of the first polyamide produced is 98% or more.

10. 3. The method according to claim 2, wherein the purity of the second polyamide produced is 98% or more.