JP2004217871A - Method of recovering useful components from dyed polyester fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering useful components of high purity from dyed polyester fiber products efficiently and economically. <P>SOLUTION: In this method for recovering useful components from dyed polyester fiber products, the dyed polyester fiber is treated with a solvent of an alkylene glycol at a temperature higher than the glass transition temperature of the polyester up to 220°C to extract/remove the dye, when useful components are recovered from the dyed polyester fiber products. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for recovering a useful component from a polyester fiber containing a dye.
[0002]
[Prior art]
Polyester, for example, polyethylene terephthalate, is widely used as a fiber, film, resin, etc. due to its excellent properties. However, effective use of polyester waste such as fibrous, film, and resin generated in these manufacturing processes is costly. This is a major issue not only in terms of environmental issues but also in terms of environmental issues.
[0003]
Regarding the treatment method, various proposals have been made by material recycling, thermal recycling, and chemical recycling. In material recycling, polyester resin waste such as PET bottles is collected mainly by local governments and actively reused.However, it is extremely difficult to apply this recycling method to fiber waste. , There is no embodiment.
[0004]
Also, thermal recycling, which converts polyester waste to fuel, has the advantage of reusing the combustion heat of polyester waste, but since the calorific value is relatively low, there is nothing other than burning a large amount of polyester waste, There is a problem of loss of polyester raw material, which is not preferable in terms of resource saving.
[0005]
On the other hand, in the chemical recycling, since the polyester waste is regenerated into the raw material monomer, there is little deterioration in quality due to the regeneration, and it is excellent as closed loop recycling.
[0006]
Most of the chemical recycling targets resin waste and film waste. As a method of recycling polyester fiber waste, for example, after depolymerizing polyester waste with an excess of ethylene glycol (hereinafter sometimes abbreviated as EG), the obtained bis-β-hydroxyethyl terephthalate is directly polycondensed. (Eg, see Patent Document 1). However, in this method, in a depolymerization reaction step, polyester waste and EG are put into a depolymerization reaction system at a time and depolymerized. Therefore, the inputted polyester waste may be agglomerated in the reactor and may not be stirred. Therefore, the depolymerization system becomes non-uniform and the depolymerization time is prolonged. In addition, the amount of EG used is not only economically disadvantageous, but also impurities such as diethylene glycol are produced as by-products, and the resulting polyester However, there are drawbacks in that the physical properties, especially the softening point, are remarkably lowered, and only low-grade polyester can be obtained. As described above, the technology for efficiently treating polyester fiber waste has not been completed in the conventional technology.
[0007]
In addition, when fibers outside the polyester production process are to be collected, mixing of polyester fibers containing dyes may be unavoidable. The dye contained in these dyed polyester fibers decomposes during a series of reactions such as depolymerization at a high temperature in the presence of a catalyst, and is dispersed in the useful components to be recovered, thereby significantly deteriorating the quality. There has been no example of addressing such problems and taking measures.
[0008]
[Patent Document 1]
JP-A-48-61447 (claims)
[0009]
[Patent Document 2]
US Pat. No. 3,806,316 (claim)
[0010]
[Problems to be solved by the invention]
An object of the present invention is to solve the problems of the prior art and to establish a method for recovering high-purity useful components from dyed polyester fiber products. Still other objects and advantages of the present invention will become apparent from the following description.
[0011]
[Means for Solving the Problems]
According to one aspect of the present invention, a dyeing step includes extracting and removing a dye from a dyed polyester fiber with an alkylene glycol extraction solvent at a temperature equal to or higher than the glass transition temperature of the polyester and equal to or lower than 220 ° C. A method for recovering a useful component from a polyester fiber is provided.
[0012]
After the dye extraction step, a solid-liquid separation step of separating into a dye-extracted polyester fiber and an extraction solvent containing a dye, the dye-extracted polyester fiber is subjected to a depolymerization reaction with alkylene glycol in the presence of a depolymerization catalyst, A depolymerization reaction step of obtaining a depolymerization solution containing bis-β-hydroxyalkyl terephthalate (BHAT), a transesterification reaction step of subjecting the depolymerization solution to transesterification with a transesterification catalyst and methanol, and a transesterification reaction step And a useful component recovery step of separating and recovering dimethyl terephthalate and alkylene glycol from the transesterification reaction mixture obtained in the above. By combining these steps, it is possible to easily recover high-purity useful components from the dyed polyester fiber product.
[0013]
A solids removal step of removing solids during or after the reaction of the depolymerization reaction step, and a depolymerization solution concentration step of distilling and evaporating at least a part of the alkylene glycol from the depolymerization solution to concentrate the depolymerization solution. It is also preferable to include at least one of a step of dissolving and removing the polyamide and a step of dissolving and removing the polyamide.
[0014]
It is preferable that the polyester fiber is a fiber made of polyethylene terephthalate.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described using examples and the like. It should be noted that these examples and the like and the description illustrate the present invention, and do not limit the scope of the present invention. It goes without saying that other embodiments can also belong to the category of the present invention as long as they conform to the gist of the present invention. For example, in the present invention, the term “step” does not mean only a step that can be recognized and distinguished from the other, but includes a step combined with other operations, a step dispersed in a plurality of practical steps, A process in which another process element is included in the process, or a process in which a plurality of processes can be performed in one process can also be included in the scope of the present invention as long as they meet the gist of the present invention.
[0016]
As the polyester fiber targeted in the useful component recovery method of the present invention, typically, a fiber made of polyethylene terephthalate or a fiber made of another polyalkylene terephthalate can be exemplified.Other materials such as nylon and cotton can be used. It may be contained in the form of a blend or the like, or may contain other plastic components used for the purpose of surface modification or the like.
[0017]
In the useful component recovery method of the present invention, first, a dye is extracted and removed from a dyed polyester fiber in a dye extraction step. Various disperse dyes and the like are used in the dyed polyester, and many of the molecules contain a component such as a diazo group or a halogen (Cl or Br) that reduces the grade of a useful component to be recovered.
[0018]
When the dyed polyester containing these components is subjected to a depolymerization reaction with an alkylene glycol in the presence of a catalyst, the diazo group cleavage reaction and the elution of halogen atoms occur simultaneously, and the quality of the useful components to be recovered is reduced. It decreases remarkably.
[0019]
On the other hand, the disperse dye and the like are bonded to the polyester fiber by an intermolecular force, and the dye can be extracted and removed from the fiber by solvent extraction. A method of removing a dye or a surface finishing agent from polyester fiber with methylene chloride can be exemplified (for example, see Patent Document 2). However, if methylene chloride is mixed in the depolymerization reaction step, there is a high possibility that the Cl component contained in the solvent itself will be mixed into the useful recovery component, and it is not suitable as an extraction solvent. In order to avoid mixing with useful components, it is necessary to provide a drying step for removing the extraction solvent. However, since drying requires a large amount of equipment and energy, it is very disadvantageous in terms of cost.
[0020]
These problems can be solved by using an alkylene glycol extraction solvent as the extraction solvent. Here, the alkylene glycol extraction solvent is a solvent mainly composed of alkylene glycol. If a component other than the alkylene glycol is contained, the subsequent recovery step becomes complicated. Therefore, it is generally advantageous to use a large amount of the alkylene glycol, but the actual purity of the component is not so high. Can be arbitrarily determined according to
[0021]
The alkylene glycol used in the dye extraction step is preferably a glycol capable of forming a skeleton structure of a polyester fiber from which a useful component is to be recovered. Further, the alkylene glycol used in the dye extraction step and the alkylene glycol used in the depolymerization reaction step are preferably the same type of alkylene glycol. In any case, it is easy to obtain useful components of good quality, it is easy to recover useful components, particularly alkylene glycol, and it is possible to use them in a dye extraction step, a depolymerization reaction step, etc. This is because an advantage is obtained.
[0022]
For example, when the alkylene glycol used in the dye extraction step, the glycol capable of forming the skeleton structure of the polyester fiber from which the useful component is to be recovered, and the alkylene glycol used in the depolymerization reaction step are the same kind of alkylene glycol. However, even if the alkylene glycol remains in the dye-extracted polyester fiber after the dye extraction, a high-purity useful component can be recovered without adversely affecting the subsequent process for recovering the useful component. As a result, the process can be simplified, which is very economically advantageous.
[0023]
Examples of the alkylene glycol include EG, diethylene glycol, 1,3-propanediol, 1,4-butanediol and the like. These may be used alone or as a mixture of two or more.
[0024]
Examples of the glycol capable of forming a skeleton structure include EG when the polyester fiber is made of polyethylene terephthalate, and 1,4-butanediol when the polyester fiber is made of polybutylene terephthalate. In the case of a polymer having an ethylene terephthalate structure and a butylene terephthalate structure, any of EG, 1,4-butanediol, and a mixture of EG and 1,4-butanediol may be used.
[0025]
If the dye extraction temperature is too high, the dye will be decomposed. If the extraction temperature is too low, the rate at which the extraction solvent diffuses into the polyester fibers will be insufficient, and the extraction will not be efficient. The extraction temperature is not lower than the glass transition point of the polyester forming the polyester fiber and not higher than 220 ° C, preferably from 150 ° C to 210 ° C. For example, when EG is used as an alkylene glycol and it is desired to perform the dye extraction at 210 ° C., the operation can be performed under pressure to perform the dye extraction without any problem. In addition, when there are a plurality of polyesters forming the polyester fiber, generally, the higher glass transition point may be employed, but when the amount of the polyester having a lower glass transition point is larger, the lower the glass transition point, the lower the glass transition point. In some cases, the other glass transition point may be adopted. That is, depending on the situation, it may be higher than the glass transition point of any of the polyesters.
[0026]
As a method of dye extraction, any of a batch type and a countercurrent type may be adopted. In order to further reduce the total amount of the extraction solvent used to obtain a desired degree of decolorization (degree of extraction), it is preferable to employ a countercurrent method.
[0027]
After completion of the dye extraction, the useful component may be recovered by any method including a known method. An example is shown below.
[0028]
After the dye extraction is completed, the dye-containing extraction solvent and the dye-extracted polyester fiber can be separated in the solid-liquid separation step. It is possible to prevent the occurrence of difficulties such as disturbing the solids and impeding stirring, to reduce the amount of alkylene glycol used in the depolymerization reaction step, and to shorten the depolymerization reaction time, which is economically advantageous. This is because not only does it contribute, but it can also contribute to improving the quality of useful components finally recovered.
[0029]
As a solid-liquid separation method, a known solid-liquid separation method such as a pressure filter, pressure filtration using nitrogen gas, vacuum suction filtration, and centrifugation can be applied. If the desired degree of decolorization cannot be obtained in the batch operation, it is effective to repeat the dye extraction operation again with the alkylene glycol extraction solvent.
[0030]
In the extraction solvent recovery step, the extraction solvent containing the dye after dye extraction can be used to recover the alkylene glycol by distillation and be used again as the alkylene glycol extraction solvent, which is economically effective. Specifically, it is preferably performed after the solid-liquid separation step. The distillation of the extraction solvent containing the dye and the distillation of another alkylene glycol or the like may be performed in combination. This is because the distillation column can be simplified, which is more economically advantageous.
[0031]
The dye-extracted polyester fiber can be reacted with an alkylene glycol in the presence of a depolymerization catalyst in a depolymerization reaction step to obtain a depolymerization solution containing BHAT. Oligomers may be mixed. As described above, it is preferable to use the dye-extracted polyester fiber obtained through the solid-liquid separation step.
[0032]
It is preferable to use a known depolymerization catalyst at a known catalyst concentration and carry out a depolymerization reaction in an excess of alkylene glycol at a temperature of 120 to 210 ° C. When the temperature of the alkylene glycol is lower than 120 ° C., the depolymerization time becomes extremely long, and the efficiency becomes inefficient. On the other hand, when the temperature exceeds 210 ° C., thermal decomposition of oils and the like contained in the fiber waste becomes remarkable, and nitrogen compounds and the like generated by decomposition are dispersed in the recovered useful components. Separation becomes difficult. Preferably, it is 140 to 190 ° C. In this respect, the existing chemical recycling technology requires an operation at a high temperature, and thus it has been difficult to cope with mixing of an oil agent.
[0033]
It is useful to remove solids during or after the depolymerization reaction step. This step is called a solid removal step.
[0034]
In the solid removing step, fibers different from polyester, such as polyethylene and polypropylene, which could not be eliminated in the preceding processing step, can be separated by floating. Since these fibers have a lower specific gravity than alkylene glycol, which is a solvent for the depolymerization reaction, and float on the liquid surface, they are separated into layers as suspended solids, and then a method of extracting and removing them is easy to carry out. Yes, preferred.
[0035]
In the solid removal step, after the depolymerization reaction, different fibers such as cotton may be filtered and sorted. These are components having a higher specific gravity than the alkylene glycol and cannot be separated as a suspended solid mass. As described above, in the solid removing step, general solids are removed, including those having a specific gravity smaller than or higher than the alkylene glycol. As a method for removing the solid in general, known methods other than those described above can also be employed.
[0036]
When polyamide such as nylon, which is greatly different from polyester, is mixed in, it is decomposed in the depolymerization reaction step, and nitrogen compounds such as ε-caprolactam are mixed in useful components to be recovered, which makes separation difficult. . Therefore, it is effective to incorporate a polyamide dissolving / removing step for dissolving / removing a solidified substance containing polyamide such as nylon before the depolymerization reaction step.
[0037]
A specific method for dissolving and removing polyamide may be any known method. For example, a recovery target containing polyamide such as nylon in alkylene glycol is charged and heated to 100 to 190 ° C. to dissolve and remove. be able to. This step may be performed simultaneously with the dye extraction step.
[0038]
The depolymerization solution can be concentrated by distilling and evaporating at least a part of the alkylene glycol from the depolymerization solution from which solids have been removed. This step is called a depolymerization solution concentration step. By performing this step, the equipment and energy burden of the subsequent steps can be reduced, and the recovered alkylene glycol can be effectively used. This concentration can be easily performed because the solids have already been removed.
[0039]
It is preferable to distill off the alkylene glycol until it becomes 0.5 to 2.0 parts by weight with respect to 1 part by weight of the dyed polyester fiber charged as a raw material. The alkylene glycol distilled off at this time can be recycled to the dye extraction step and the depolymerization reaction step again.
[0040]
The depolymerization solution can be transesterified with a transesterification catalyst and methanol. This step is called a transesterification step. By this step, useful components can be converted into dimethyl terephthalate and alkylene glycol. Note that the depolymerization solution in this case may be any of a depolymerization solution without solids removed, a depolymerization solution with solids removed, and a depolymerization solution after concentration, but is preferably a depolymerization solution with solids removed. More preferably, it is a depolymerized solution after concentration.
[0041]
In the transesterification step, transesterification with methanol can be carried out in the presence of a known concentration of a known ester exchange catalyst. Thereafter, solid-liquid separation is preferably performed by a solid-liquid separation means such as centrifugation.
[0042]
From the transesterification reaction mixture obtained in the transesterification step, dimethyl terephthalate and alkylene glycol can be separated and recovered. This step is called a useful component recovery step.
[0043]
That is, in the useful component recovery step, the crude dimethyl terephthalate and the crude alkylene glycol obtained in the transesterification reaction step are purified by a purification method such as distillation to obtain high-purity purified dimethyl terephthalate and purified alkylene glycol. At this time, impurities that have passed through the previous steps are captured at the bottom of the column, and thus the useful components to be recovered do not contain impurities, and high-purity products can be obtained.
[0044]
【Example】
Hereinafter, the contents of the present invention will be described more specifically with reference to examples. In addition, each numerical value in an Example was calculated | required by the following method.
[0045]
(Nitrogen content)
The nitrogen content contained in the polyester fabric and the useful recovery component (EG, dimethyl terephthalate) was measured with a trace total nitrogen analyzer (TN-110 manufactured by Mitsubishi Kasei).
[0046]
[Example 1]
100 g of cut polyethylene terephthalate cloth (nitrogen content in the cloth before dye extraction: 1700 wt ppm), which is a dyed polyester fiber according to the present invention and 1000 g of EG, are separable in 2 L. A dye extraction step of extracting the dye by charging into a flask and heating and stirring at a temperature of 175 ° C. for 30 minutes was performed.
[0047]
After the completion of the extraction, as a solid-liquid separation step, suction filtration was performed using an aspirator to separate the dye-containing EG from the dye-extracted and removed fabric (dye-extracted polyester fiber).
[0048]
Thereafter, the fabric from which the dye was extracted and removed and 1000 g of new EG were charged into a separable flask, and the dye was extracted under the same conditions. After the completion of the extraction, solid-liquid separation was performed again to separate the EG containing the dye from the fabric from which the dye was extracted and removed.
[0049]
Thereafter, as a depolymerization reaction step, 100 g of the dye-extracted cloth was charged into a mixture of 400 g of EG, which had been heated to 185 ° C. in advance, and 3 g of sodium carbonate as a depolymerization catalyst, and reacted at normal pressure for 4 hours to obtain bis- A depolymerization solution containing β-hydroxyethylene terephthalate (BHET) was obtained.
[0050]
After the depolymerization reaction in the depolymerization reaction step, solids were removed by filtration with a wire mesh strainer having openings of 350 μm. In this solid removal step, mainly plastics other than polyester could be removed.
[0051]
The obtained depolymerized solution after filtration is sent to a distillation column, and 300 g of EG is distilled off under the conditions of a tower bottom temperature of 140 to 150 ° C. and a pressure of 13.3 kpa to concentrate the depolymerized solution. Was carried out.
[0052]
Next, 1.7 g of sodium carbonate as a transesterification catalyst and 200 g of methanol were added to 200 g of the filtered and concentrated depolymerization solution, and the transesterification reaction step was carried out at 75 to 80 ° C. for 1 hour at normal pressure. Thus, a transesterification reaction mixture was obtained.
[0053]
After the completion of the reaction, the transesterification reaction mixture was cooled to 40 ° C., and subjected to centrifugal separation to solid-liquid separation into a cake mainly composed of crude dimethyl terephthalate and a filtrate mainly composed of methanol and crude EG.
[0054]
Next, the crude dimethyl terephthalate is purified by distillation under the conditions of a pressure of 6.7 kpa and a tower bottom temperature of 180 to 200 ° C., and the filtrate at a pressure of 13.3 kpa and a tower bottom temperature of 140 to 150 ° C. As a result, dimethyl terephthalate and EG were obtained at a yield of 85% by weight, respectively.
[0055]
The recovered dimethyl terephthalate is comparable to commercial products in terms of appearance, acid value, melting color, and sulfated ash, and the recovered EG is comparable to commercial products in diethylene glycol concentration, water content, and melting color. In addition, the nitrogen content of both recovered dimethyl terephthalate and recovered EG was lower than the lower limit of detection, and high-purity useful components were obtained.
[0056]
[Example 2]
2,000 g of EG as the extraction solvent containing the dye obtained in Example 1 was distilled under the conditions of a tower low temperature of 140 to 150 ° C. and a pressure of 13.3 kpa, and 1800 g was distilled off. The distilled EG did not show any coloration due to the incorporation of a dye in appearance, and the nitrogen content was below the lower limit of detection. Thus, the EG was recovered in a form that can be reused as an extraction solvent or for other purposes, for example, as a raw material for polyester synthesis.
[0057]
[Comparative Example 1]
The same black dyed polyethylene terephthalate fabric as used in Example 1 was cut into 100 g, and dimethyl terephthalate and EG were extracted under the same conditions as in Example 1 except that the dye extraction step and the solid-liquid separation step were not performed. Collected. The recovered dimethyl terephthalate was comparable to commercially available products in appearance, acid value, melting colorimetric, and sulfated ash, but contained 11 wt ppm of nitrogen, and the recovered EG contained diethylene glycol concentration, Inspection items for water content and melting colorimetric value were comparable to those of commercial products, but contained 45 ppm by weight of nitrogen, and deterioration in quality was recognized.
[0058]
[Comparative Example 2]
100 g of a cut polyethylene terephthalate fabric dyed in the same black color as used in Example 1 and 1000 g of EG were put into a 5 L autoclave, and heated at a pressure of 430 kpa (absolute pressure) and a temperature of 240 ° C. for 30 minutes. Dimethyl terephthalate and EG were recovered under the same conditions as in Example 1 except that the dye was extracted by stirring. The recovered dimethyl terephthalate was comparable to commercially available products in terms of appearance, acid value, melting colorimetry, and sulfated ash, and the nitrogen content was less than the detection lower limit. Although EG was comparable to a commercial product in the test items of diethylene glycol concentration, water content, and melting colorimetry, EG contained 15% by weight of nitrogen, and degradation in quality was recognized.
[0059]
【The invention's effect】
According to the present invention, there is provided a method for recovering a high-purity useful component from a dyed polyester fiber product. In addition, an efficient and economical method for recovering useful components can be realized.

Claims (9)

A method for recovering useful components from dyed polyester fibers, comprising a dye extraction step of extracting and removing dyes from dyed polyester fibers with an alkylene glycol extraction solvent at a glass transition temperature of the polyester or higher and 220 ° C. or lower. After the dye extraction step, a solid-liquid separation step of separating into a dye-extracted polyester fiber and an extraction solvent containing the dye,
A depolymerization reaction step of subjecting the dye-extracted polyester fiber to a depolymerization reaction with an alkylene glycol in the presence of a depolymerization catalyst to obtain a depolymerization solution containing bis-β-hydroxyalkyl terephthalate (BHAT);
For the depolymerization solution, a transesterification reaction step of performing transesterification with a transesterification catalyst and methanol,
A useful component recovery step of separating and recovering dimethyl terephthalate and alkylene glycol from the transesterification reaction product mixture obtained in the transesterification reaction step,
The method for recovering a useful component according to claim 1, comprising: A solid removal step of removing solids during or after the reaction of the depolymerization reaction step,
From the depolymerization solution, a depolymerization solution concentration step of concentrating the depolymerization solution by distilling and evaporating at least a part of the alkylene glycol,
A polyamide dissolving and removing step for dissolving and removing the polyamide,
The method for recovering useful components according to claim 2, comprising at least one step of: The useful component recovery method according to any one of claims 1 to 3, further comprising an extraction solvent recovery step of recovering the alkylene glycol from the extraction solvent containing the dye by distillation. The method for recovering a useful component according to any one of claims 1 to 4, wherein the alkylene glycol used in the dye extraction step is a glycol capable of forming a skeleton structure of the polyester fiber. The useful component recovery method according to any one of claims 2 to 5, wherein the alkylene glycol used in the dye extraction step and the alkylene glycol used in the depolymerization reaction step are the same kind of alkylene glycol. The method according to claim 1, wherein the alkylene glycol is at least one glycol selected from the group consisting of ethylene glycol, diethylene glycol, 1,3-propanediol, and 1,4-butanediol, or a mixture thereof. The method for recovering useful components according to the above. The method for recovering useful components according to any one of claims 1 to 7, wherein the dye extraction step is performed in a batch-type or countercurrent-type reaction tank. The method for recovering useful components according to any one of claims 1 to 8, wherein the polyester fiber is a fiber made of polyethylene terephthalate.