JP2008137929A - Method for recovering caprolactam from nylon 6 fiber containing dye - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering caprolactam, with which a nylon 6 fiber containing a dye is heat-treated with an aqueous alkali solution to remove only a dye component and the nylon 6 fiber from which the dye component is removed is depolymerized. <P>SOLUTION: The method for recovering caprolactam from a nylon 6 fiber containing a dye comprises a process (process a) for heat-treating a nylon 6 fiber containing a dye in an aqueous alkali solution and eluting the dye component in the aqueous alkali solution, a process (process b) for taking out the nylon 6 fiber in the aqueous alkali solution and a process (process c) for depolymerizing the nylon 6 fiber from which the dye component is removed to recover caprolactam. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for removing dye from nylon 6 fibers containing dye, such as fabric, clothing, airbags, etc., and relates to a chemical recycling method using this method. The present invention relates to a chemical recycling method for recovering high-grade caprolactam by depolymerizing nylon 6 fiber from which a dye component is removed from nylon 6 fiber.

  Nylon fibers represented by nylon 6 fibers are widely used as clothing and industrial materials, and are known as fibers that can be easily recycled. As a method of recycling nylon 6 fiber, thermal recycling method that incinerates and recovers it as thermal energy, material recycling that is remolded and reused after being melted, chemically depolymerized and returned to the raw material of nylon, There is chemical recycling that is reused for nylon production.

  Among these, chemical recycling decomposes nylon into raw materials and can be used for a wide range of applications including reuse as nylon raw materials. Therefore, it can be said that this is an industrially useful recycling method. However, nylon 6 fibers are often dyed and used in a state containing a dye, and the dye or a decomposition product of the dye has been one of the causes for lowering the quality of the nylon raw material obtained by depolymerization.

  As a method for chemically recycling nylon 6 fibers, for example, Patent Document 1 discloses a method of depolymerizing a nylon clothing product in which the material of cloth and clothing accessories is substantially unified with nylon 6 in the presence of a phosphoric acid catalyst. A method for recovering ε-caprolactam has been proposed. Although this method is certainly a method suitable for chemical recycling, it is a method performed in advance by limiting the materials to be used, and it is necessary to prevent mixing of nylon fibers produced by other methods. In addition, although there are descriptions of inorganic pigments for the dyes used, there is no description of organic pigments that are widely used for dyeing nylon fibers, and when the method described in this document is applied to dyed nylon fibers, depolymerization Sometimes pigment components and pigment-derived impurities could not be removed from the caprolactam, and the recovered caprolactam quality was not satisfactory.

  Non-Patent Document 1 describes the elution desorption method and the chemical decomposition decolorization method as general decolorization methods, but this is a general decolorization method for fibers, and it is a high quality from nylon 6 fibers containing dyes. No specific means is disclosed about what operation should be performed at what stage in order to obtain caprolactam.

  Patent Document 2 proposes a method for obtaining a high-purity lactam by subjecting a crude lactam aqueous solution obtained by phosphoric acid catalyzed depolymerization of nylon 6 to an alkali treatment and activated carbon treatment, followed by distillation purification. There is no description about dyes, and it is the present invention that pigment components and pigment-derived impurities cannot be sufficiently removed from caprolactam even when applied directly to nylon 6 fibers containing dyes, and a satisfactory recovery rate cannot be obtained. It became clear by examination of the person.

Patent Document 3 proposes a method of extracting a dye from a polyester fiber containing the dye with an alkylene glycol which is a constituent component of the polyester. In polyester, it was possible to extract a dye with alkylene glycol, which is one of the monomer components of the copolymer, but caprolactam, which is a monomer of nylon 6, was unable to extract the dye from nylon 6 fiber. found.
Japanese Unexamined Patent Publication No. 07-310204 (paragraph [0030]) Japanese Patent Publication No. 48-31116 (Detailed Description of the Invention) JP 2004-217871 A (Means for Solving the Problem and Examples) Okawara Shin et al., “Dye Handbook”, Kodansha, March 1986, pp. 53-54

  Therefore, in the present invention, when recovering caprolactam by depolymerizing a nylon 6 fiber containing a dye, a simple operation can be performed without any problem of caprolactam purity degradation or degradation of caprolactam recovery due to decomposition of the dye component. The objective is to recover caprolactam with high purity and high yield.

  As a result of intensive studies to solve the above-mentioned problems, the inventor removed the dye-containing nylon 6 fiber after removing the dye by heat treatment with an alkaline aqueous solution and removing the dye, Subsequently, it was found that efficient chemical recycling can be achieved by recovering caprolactam by depolymerization, and the present invention was completed.

  That is, the present invention includes a step of heat-treating a nylon 6 fiber containing a dye in an alkaline aqueous solution to elute the dye component in the alkaline aqueous solution (step a), and a step of taking out the nylon 6 fiber in the alkaline aqueous solution ( Caprolactam is recovered from the dye-containing nylon 6 fiber, which includes a step (c step) of depolymerizing the nylon 6 fiber from which the dye component obtained in step b is removed and recovering caprolactam. This is a method for recovering higher-grade caprolactam by allowing a reducing agent to coexist in step a. The dye component contained in the nylon 6 fiber is decomposed under depolymerization conditions to cause a decrease in caprolactam purity and lowers the caprolactam recovery rate. Therefore, the method of the present invention is applied to the nylon 6 fiber containing the dye. It was found to be particularly effective.

  According to the present invention, the dye can be removed from the nylon 6 fiber containing the dye by a simple method. In addition, by using the above method in chemical recycling of nylon 6 fiber containing a dye, caprolactam can be recovered with a high yield and the amount of residue can be reduced. Moreover, since a high-purity caprolactam with a smaller amount of impurities can be recovered, the quality required as, for example, a nylon raw material can be obtained industrially advantageously without complicated purification.

  The present invention is a method in which a nylon 6 fiber containing a dye is heat-treated in an alkaline aqueous solution, the dye component is eluted in the alkaline aqueous solution, and the nylon 6 fiber in the alkaline aqueous solution is taken out. A method for chemically recycling a nylon 6 fiber containing a dye, characterized in that caprolactam is recovered by depolymerizing the nylon 6 fiber from which components have been removed.

<Nylon 6 fiber>
In the present invention, the nylon 6 fiber to be used is not particularly limited, but it is preferably a single composition, that is, a homopolymer, but not to impair the effects of the present invention, for example, all monomers As long as it is 50 mol% or less, preferably 10 mol% or less, more preferably 5 mol% or less, other copolymerization components may be copolymerized. When depolymerization is performed using an acidic catalyst such as phosphoric acid as the depolymerization catalyst, the catalyst may be deactivated by the diamine component of the copolymerization component, but a catalyst corresponding to the catalyst amount deactivated by the diamine component is added. By doing so, the depolymerization reaction can be performed without problems. These nylon 6 fibers may be added with a polymerization degree adjusting agent, a terminal group adjusting agent and the like. Examples of copolymer components include diamine components such as hexanemethylenediamine, 1,4-diaminobutane, p-phenylenediamine, and p-xylylenediamine, and dicarboxylic acids such as adipic acid, sebacic acid, succinic acid, terephthalic acid, and isophthalic acid. An amino acid component, such as an acid component or laurolactam, etc. can be mentioned. Examples of the polymerization degree adjusting agent and the end group adjusting agent include acetic acid and benzoic acid.

<Nylon 6 fiber containing dye>
The dye contained in the nylon 6 fiber referred to in the present invention is generally an acid dye, but other dyes are not particularly limited as long as they are removed by an alkaline aqueous solution described later.

<Other contents>
The nylon 6 fiber containing the dye used in the present invention may contain other inclusions, and the raw material / material constituents other than nylon 6 may be any organic or inorganic substance. Nylon 6 fiber may contain other fibers, polymers, coating agents, oil agents, fillers, and the like. For example, cellulosic fibers such as cotton, hemp and rayon, protein fibers such as wool and silk, acrylic fibers, polyurethane, polyacrylate, polyethylene terephthalate, nylon 66, resin additives, oils for fibers, chemical processing agents for fibers Further, glass fiber, carbon fiber, titanium oxide, silica and the like may be included. The content of raw materials and raw materials other than nylon 6 containing these dyes is desirably 50% by mass or less, and more preferably 20% by mass or less.

<Process a>
In the present invention, first, a step (a step) is carried out in which the nylon 6 fiber containing the dye is heated with an alkaline aqueous solution to elute the dye. In step a, a nylon 6 fiber containing a dye and an aqueous alkaline solution are mixed and stirred while heating.

(Alkaline aqueous solution)
Examples of the base in the alkaline aqueous solution used in the step a of the present invention include alkali metal hydroxide, alkaline earth metal hydroxide, alkali metal carbonate, alkaline earth metal carbonate, alkali metal bicarbonate, alkaline earth metal At least one selected from bicarbonate is used. Preferably, lithium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide are used. More preferred are sodium hydroxide and potassium hydroxide.

  In this case, the amount of the base in the alkaline aqueous solution used is preferably in the range of 0.1 to 10 mol, particularly preferably in the range of 0.1 to 1 mol, with respect to 1 mol of caprolactam units constituting the nylon 6 to be depolymerized. . If it is this range, sufficient decoloring effect will be acquired, and it is too much, decomposition | disassembly of nylon does not advance too much, and it is excellent in the recovery amount of caprolactam. In the above, it is usually difficult to strictly grasp the nylon 6 content of the recycled fiber. If the exact content of nylon 6 is known, it may be calculated based on that amount, but if the exact content is unknown, the nylon 6 to be depolymerized is constructed as follows. The amount of caprolactam units will be estimated. That is, when it is considered that components other than the dye are substantially composed only of nylon 6, a value obtained by dividing the total weight of the nylon 6 fiber by the molecular weight of caprolactam can be used for convenience. In addition, when a considerable amount of other different components are contained in the nylon 6 fiber, such as in the case of blended spinning, the amount considered to be substantially composed of nylon 6 is taken into consideration as the amount of nylon 6 The value obtained by dividing by the molecular weight of caprolactam is used.

(Reducing agent)
In the present invention, a reducing agent can coexist in the alkaline aqueous solution in the step a. The reducing agent chemically reduces and solubilizes organic pigments to enhance the decoloring effect, and specific examples include hydrosulfite sodium, zinc powder, acidic sodium sulfite and the like. Preferably, hydrosulfite sodium is mentioned. When the reducing agent is used, the amount of the reducing agent used is preferably in the range of 0.01 to 0.1 mol with respect to 1 mol of caprolactam units constituting the nylon 6 to be depolymerized. When the amount is less than 0.01 mol, a sufficient decoloring effect cannot be obtained. The amount of caprolactam unit in the above is also estimated by the same method as described above.

(Nylon form)
Nylon 6 fiber containing dye used in this process can be used in any form, but when recycling collected clothing, buttons and chucks made of different types of resin from metal fittings and nylon 6 fiber in advance, etc. From the viewpoint of improving workability, it is preferable that other materials such as cellulose fibers insoluble in the solution of caprolactam as a raw material are removed.

  The size of the nylon 6 fiber containing the dye that is put into the alkaline aqueous solution is not particularly specified, but if it is too large to efficiently remove the dye component, stirring is difficult and the contact efficiency with the alkaline aqueous solution is poor. Even if it is too small, the separation operation of taking out the nylon 6 fiber in the subsequent process becomes complicated, and therefore it is preferable that the nylon 6 fiber is cut into an appropriate size according to the equipment.

(Bath ratio of step a)
The usage-amount of the alkaline aqueous solution which elutes a dye component in a process of this invention is 10-100 mass parts with respect to 1 mass part of nylon 6 fiber components. Preferably, it is 10-50 mass parts, More preferably, it is 10-20 mass parts. When the amount of the alkaline aqueous solution used is small, the removal rate of the resin component is slow, and when it is large, the cost is high and it is economically disadvantageous.

(Heating temperature in step a)
Moreover, the heating temperature in a process is 60-100 degreeC normally, Preferably it is 80-100 degreeC, Most preferably, it is 90-100 degreeC. Within this range, it is easy to elute the dye component into the alkaline aqueous solution from the nylon 6 fiber containing the dye, the nylon 6 fiber is not decomposed, and the decomposition of the dye component eluted into the alkaline aqueous solution is suppressed. The workability is also good. Further, the elution step of the dye may be any of reduced pressure, normal pressure, and increased pressure.

(Elution time of step a)
The stirring time for eluting the dye component varies depending on the type of dye, the size of nylon 6 fiber, equipment, etc., but considering production efficiency, it is usually 0.1 to 20 hours, preferably 0.1 to 10 hours, more preferably 0.1 to 5 hours.

<Process b>
The nylon 6 fiber from which the dye component has been removed in step a is taken out from the alkaline aqueous solution in step b. The method of taking out may be taken out by pulling up the nylon 6 fiber from the alkaline aqueous solution into which the nylon 6 fiber is introduced, or the nylon 6 fiber may be taken out by removing the alkaline aqueous solution from the system in which the nylon 6 fiber is introduced. Although it does not matter, filtration operation and centrifugal drainage operation can be adopted from the simplicity of operation.

  Here, it is preferable that the amount of the dye component remaining on the nylon 6 fiber after elution is small, but there is no problem if the amount of the dye component substantially adhering to the nylon 6 fiber is small. When the amount of the eluted dye component is large, it may be rinsed again using an alkaline aqueous solution or rinsed with water or other solvent, but it is preferable to rinse with water. The amount of water used is usually 0.1 to 200 parts by mass with respect to 1 part by mass of nylon fiber, although it depends on the amount of the alkaline aqueous solution from which the dye component is eluted. Preferably, it is 0.5-50 mass parts, More preferably, it is 1-10 mass parts.

<Process c>
The nylon 6 fiber from which the dye component thus removed has been removed is subjected to step c and depolymerized to recover caprolactam. These nylon 6 fibers from which the dye component has been removed in step b may be depolymerized by themselves, or may be depolymerized together with other nylon 6 fiber scraps, etc. It can also be depolymerized together with caprolactam oligomers and the like contained in the water extracted by polymerization.

(Depolymerization)
The depolymerization method performed in the present invention may be any method. Normally, nylon 6 fiber is depolymerized by heating, and a catalyst may be used, and it may be in the absence of water (dry type) or in the presence (wet type).

  The depolymerization pressure may be any of reduced pressure, normal pressure, and increased pressure. The depolymerization temperature is usually 100 to 400 ° C, preferably 200 to 350 ° C, more preferably 220 to 300 ° C. When the temperature is low, the nylon 6 fiber does not melt and the depolymerization rate becomes slow. High temperatures cause unnecessary nylon 6 fiber degradation, leading to a reduction in the purity of the recovered caprolactam.

  When a catalyst is used, an acid or base catalyst is usually used. Examples of the acid catalyst include phosphoric acid, boric acid, sulfuric acid, organic acid, organic sulfonic acid, solid acid, and salts thereof, and examples of the base catalyst include alkali hydroxide, alkali salt, alkaline earth hydroxide, alkali Examples include earth salts, organic bases, solid bases and the like. Preferably, phosphoric acid, boric acid, organic acid, alkali hydroxide, alkali salt, etc. are mentioned. More preferably, phosphoric acid, sodium phosphate, potassium phosphate, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate and the like can be mentioned.

  The usage-amount of a catalyst is 0.01-50 mass parts normally with respect to 100 mass parts of nylon 6 fiber components. Preferably, it is 0.1-20 mass parts, More preferably, it is 0.5-10 mass parts. When the amount of the catalyst used is small, the reaction rate is slow, and when it is large, the side reaction increases and the cost of the catalyst is increased, which is economically disadvantageous.

  The amount of water used for wet depolymerization is 0.1 to 50 parts by mass with respect to 1 part by mass of the nylon 6 fiber component. Preferably, it is 0.5-20 mass parts, More preferably, it is 1-10 mass parts. When the amount of water used is small, the reaction rate is slow, and when it is large, the concentration of the recovered caprolactam aqueous solution is low, which is disadvantageous in obtaining caprolactam.

(Caprolactam recovery method)
When dry depolymerization is performed, the produced caprolactam is distilled from the reactor by vacuum distillation to obtain recovered caprolactam. After the depolymerization reaction is completed, caprolactam may be taken out by distillation under reduced pressure, or may be taken out continuously as the reaction proceeds.

  When wet depolymerization is performed, the produced caprolactam is distilled from the reactor together with water to obtain a recovered caprolactam aqueous solution. After completion of the depolymerization reaction, the caprolactam aqueous solution may be taken out by distillation, or may be taken out continuously as the reaction proceeds. Preferably, water is continuously supplied to the reactor, and the produced caprolactam aqueous solution is continuously removed from the reactor. More preferably, water vapor is continuously supplied to the reaction apparatus at normal pressure, and the produced caprolactam aqueous solution is continuously removed from the reaction apparatus.

  Nylon 6 fibers from which the dye component has been removed in step a have substantially high nylon purity. Therefore, depolymerization in step c can yield high yield and high-purity caprolactam. The obtained caprolactam aqueous solution can recover sufficiently high-purity caprolactam by separating it from water by distillation. Further, when a high-purity caprolactam is required, it can be subjected to precision distillation according to the purpose or combined with a purification method such as recrystallization.

<How to check caprolactam quality>
The purity analysis of caprolactam obtained by the depolymerization performed in the present invention was performed by capillary gas chromatography and high performance liquid chromatography (HPLC). That is, a liquid chromatography equipped with a reverse phase column (ODS120T 5 μm, 4.6 mm ID, 250 mm) as an HPLC column, and a strong column (TC-FFAP, 60 m, 0.25 mm, 0.25 μm) as a gas chromatography column. The caprolactam purity was expressed as HPLC purity and GC purity in terms of peak area ratio by analysis with attached capillary gas chromatography.

  Further, using a spectrophotometer as a measure of the degree of coloring, the transmittance of ε-caprolactam 50 mass% aqueous solution was measured using a 10 mm long quartz cell based on water at a wavelength of 390 nm, and expressed as a color tone. did. Generally, the higher the color tone (transmittance), the lower the degree of coloring.

  Examples of the present invention are shown below, but are not limited thereto.

Example 1
<Process a>
After cutting 200 g of nylon 6-fiber amber fabric into approximately 10 cm square, 3.0 kg of 31.3 g of 96 wt% sodium hydroxide (when 200 g of the nylon 6-fiber amber fabric is estimated to be composed of caprolactam units) , Equivalent to 0.42 mol of sodium hydroxide per mol of caprolactam unit) and charged in a 5 L separable flask, soaked in a 100 ° C silicone oil bath, set a condenser and stirrer, about every 15 minutes The mixture was stirred for 1 minute and heat-treated for 2 hours.

<Process b>
The nylon 6 fiber fabric was taken out from the separable flask after the heat treatment in step a, dehydrated with a centrifugal dehydrator, and then washed with about 1 kg of water three times. Then, it dried with a 60 degreeC warm air dryer, and obtained 196 g of nylon 6 fiber fabrics. It was observed with the naked eye that the resulting nylon 6 fiber fabric was decolorized.

<Process c>
196 g of nylon 6 fiber fabric dried in step b and 7.9 g of 75 wt% aqueous phosphoric acid as a depolymerization catalyst were charged into a depolymerization apparatus and heated to 260 ° C. in a nitrogen atmosphere. Nitrogen was stopped, superheated steam was introduced into the depolymerization apparatus at 250 g / hour to start the reaction, and the caprolactam steam liquid continuously distilled from the depolymerization apparatus was cooled at 260 ° C. for 6 hours, The resulting depolymerization operation was carried out.

  Water was distilled off from the obtained aqueous caprolactam solution at about 70 ° C. under a reduced pressure of 3.3 kPa. The concentrated solution was transferred to a 500 ml Houben flask, 2.3 g of a 40 wt% aqueous sodium hydroxide solution was added, and the mixture was concentrated under reduced pressure at about 100 ° C. and 3.3 kPa. Next, caprolactam was distilled under reduced pressure at about 160 ° C. under a reduced pressure of 0.7 kPa to obtain 172 g of caprolactam having a GC purity of 99.99%, an HPLC purity of 98.48% and a color tone of 87%.

Example 2
In step a, 17.6 g of 85 wt% sodium hydrosulfite in an alkaline aqueous solution (when 200 g of nylon 6 fiber amber colored fabric used as a raw material is estimated to be composed of all caprolactam units, hydrolyzed with respect to 1 mol of caprolactam units. Decolorization, depolymerization, concentration of caprolactam, and distillation were carried out in the same manner as in Example 1 except that sulfite and sodium (corresponding to 0.05 mol) were added. GC purity 99.99%, HPLC purity 99.58%, 172 g of caprolactam having a color tone of 96% was obtained.

Comparative Example 1
Using 200 g of the same nylon 6 fiber amber colored fabric as used in Example 1, except that steps a and b were not performed, depolymerization in step c, concentration of caprolactam, and distillation were performed in the same manner as in Example 1. 173 g of caprolactam having a purity of 99.99%, an HPLC purity of 95.95% and a color tone of 57% was obtained.

  According to the present invention, caprolactam as a raw material can be obtained from nylon 6 fiber containing a dye by an industrially advantageous method.

Claims (7)

A step of heat-treating a nylon 6 fiber containing a dye in an aqueous alkaline solution to elute the dye component into the aqueous alkaline solution (step a), a step of taking out the nylon 6 fiber in the aqueous alkaline solution (step b), b A method for recovering caprolactam from a nylon 6 fiber containing a dye, comprising a step of recovering caprolactam by depolymerizing the nylon 6 fiber from which the dye component obtained in the step has been removed (step c). The method of recovering caprolactam from nylon 6 fiber containing a dye according to claim 1, wherein the step (a) is carried out in the presence of a reducing agent. 3. The nylon 6 fiber containing a dye according to claim 1, wherein the base in the alkaline aqueous solution in the step (a) is a hydroxide of an alkali metal or an alkaline earth metal. A method for recovering caprolactam. The alkali amount used in said (a) process is 0.1-1 mol with respect to 1 mol of caprolactam units which comprise the nylon 6 to depolymerize, The Claim 1 thru | or 3 characterized by the above-mentioned. Of recovering caprolactam from nylon 6 fibers containing The method for recovering caprolactam from nylon 6 fibers containing a dye according to any one of claims 1 to 4, wherein the heat treatment temperature in the step (a) is 80 to 100 ° C. The method for recovering caprolactam from nylon 6 fiber containing a dye according to claim 2, wherein the reducing agent in step (a) is sodium hydrosulfite. Caprolactam from nylon 6 fiber containing dye according to claim 6, wherein the sodium hydrosulfite is 0.01 to 0.1 mol per 1 mol of caprolactam units constituting nylon 6 to be depolymerized. How to recover.