JP4065658B2 - Method for recovering active ingredients from polyethylene terephthalate fiber waste - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In the present invention, polyethylene terephthalate fiber waste containing impurities is subjected to a pretreatment such as discrimination, pulverization, granulation, etc. by a discriminator, and then subjected to a chemical reaction treatment to produce high-purity bis (β-hydroxyethyl as an active ingredient) ) A method for easily and efficiently recovering terephthalate or terephthalic acid component and ethylene glycol.
[0002]
[Prior art]
Polyester, such as polyethylene terephthalate, is widely used as a fiber, film, resin, etc. due to its excellent properties, but effective utilization of polyester waste such as fiber, film, resin, etc. generated in these manufacturing processes is costly. It has become a major problem including environmental problems as well as from the surface, and various proposals have been made by material recycling, thermal recycling, and chemical recycling as treatment methods.
[0003]
Of these, polyester resin waste such as PET bottles is collected and actively reused mainly by local governments in material recycling, but it is extremely difficult to adopt this recycling method for fiber waste. There are no examples.
[0004]
Thermal recycling, which converts polyester waste into fuel, has the advantage of reusing the heat of combustion of polyester waste, but it has a relatively low calorific value, and is nothing but burning a large amount of polyester waste. There is a problem of loss, which is not preferable in terms of resource saving.
[0005]
On the other hand, in chemical recycling, polyester waste is regenerated as a raw material monomer, so that there is little deterioration in quality due to regeneration, and it is suitable for closed loop recycling. Most of the chemical recycling targets resin waste and film waste. As a method for recycling polyester fiber waste, for example, in JP-A-48-61447, polyester waste is depolymerized with an excess of ethylene glycol (hereinafter sometimes abbreviated as EG) and then obtained bis- A method of directly polycondensing β-hydroxyterephthalate (hereinafter sometimes abbreviated as “BHET”) to obtain a regenerated polyester has been proposed. This method is a depolymerization reaction system in which polyester waste and EG are depolymerized in a depolymerization step. Since the depolymerization is performed by batch charging into the reactor, the charged polyester waste is solidified inside the reactor and cannot be stirred.
[0006]
Therefore, the depolymerization system becomes non-uniform and the depolymerization time becomes long, and the amount of EG used is not only economically disadvantageous, but also impurities such as diethylene glycol are by-produced in the reaction product. The physical properties of the resulting polyester, particularly the softening point, are markedly lowered, and there are disadvantages such that only low-quality polyester can be obtained. In such a conventional technique, a technique for efficiently treating polyester fiber waste has not been completed.
[0007]
In addition, when fibers outside the polyester manufacturing process are targeted for collection, it may be unavoidable to mix different fibers with polyesters such as polyethylene, polypropylene, nylon, and cotton. Furthermore, even if the material is polyester, those containing a dye are decomposed during a series of reactions such as depolymerization and dispersed in the recovered monomer, and the quality is remarkably deteriorated. There has never been any example that mentions the quality of recovered monomer when these impurities are mixed.
[0008]
[Problems to be solved by the invention]
The object of the present invention is to solve the problems of the prior art, improve the handling in the subsequent reaction process in the pretreatment process, and provide the facility for removing impurities in the reaction process. The object is to establish an efficient and economical method for recovering an active ingredient capable of obtaining a high-purity recovered monomer from contained fiber waste.
[0009]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors, in the pretreatment process, after removing fibers other than the active ingredient polyethylene terephthalate by an appropriate discriminating apparatus, the fibers that passed the discrimination test in order to advance the reaction efficiently. Recover the active ingredients to efficiently obtain high-purity recovered monomer by incorporating the reaction process with the reaction conditions that do not decompose the impurities after the pretreatment process, after crushing the scraps to an appropriate size, then granulating and solidifying The method has been found and the present invention has been completed.
[0010]
That is, the object of the present invention is to
Not transported to the next step by eliminating the fiber waste when it is determined that the different fibers are polyethylene terephthalate was analyzed by discriminating device polyethylene terephthalate textile waste, said about what is determined that polyethylene terephthalate The fiber waste is put into a pulverizer in the form of a lump and the fiber waste is first pulverized to 30 to 150 mm, and then the pulverized product is further pulverized to 2 to 50 mm. Pre-treatment of solidifying into a cylindrical solid material having a length of 20 mm and a length of 2 to 60 mm to a bulk density of 0.10 to 1.0 g / cm ^3, and then transporting the solid material to a reaction step described later by pneumatic transportation A method for recovering a high-purity active ingredient from polyethylene terephthalate fiber waste by combining the steps and the following reaction steps (a) to (f).
(A) Crude polyethylene terephthalate obtained through the pretreatment step was put into ethylene glycol containing a depolymerization catalyst, and depolymerized at a temperature of 120 to 190 ° C. to obtain bis (β-hydroxyethyl) terephthalate (BHET Depolymerization reaction step to obtain
(B) the depolymerization reaction step in the reaction or polyethylene other than the polyethylene terephthalate after the reaction, polystyrene, polypropylene, foreign matter removing step of removing the foreign plastics such polyvinyl chloride le;
(C) a filtration and sorting step of filtering and sorting undissolved components after the depolymerization reaction;
(D) A BHET concentration step in which concentrated BHET is obtained by subjecting a mixture of BHET and ethylene glycol obtained through the filtration and sorting step to distillation / evaporation to distill / evaporate ethylene glycol;
(E) a transesterification reaction step in which transesterification is performed by adding and introducing a transesterification catalyst and methanol into a mixed solution of crude BHET and crude ethylene glycol obtained in the BHET concentration step;
(F) a purification step of separating and recovering purified dimethyl terephthalate and purified ethylene glycol from a mixture of crude dimethyl terephthalate , crude methanol and crude ethylene glycol obtained in the transesterification step;
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the active ingredient recovery method of the present invention, fibers different from polyethylene terephthalate , such as nylon, polyethylene, polypropylene, cotton, and the like cannot be active ingredients, and therefore fiber waste mixed with a large amount thereof is eliminated at the stage of acceptance. That is, when the fiber waste is analyzed by a discriminating device such as a near-infrared spectrometer and this shows an absorption pattern different from that of polyethylene terephthalate , it is not transported to the next process and eliminated at that stage. Only the fiber waste that has passed the inspection by the near-infrared analysis is transported to the next process.
[0012]
It is desirable that the fiber waste that has passed the inspection by the near infrared analysis is granulated and solidified from the viewpoint of handling property in the reaction step after the pretreatment step or the air transportability after the pretreatment step. However, it is extremely difficult to directly feed yarn waste having a continuous structure into a granulator, and it is necessary to first grind the fiber waste to an appropriate size. The size of the pulverized product is preferably 2 to 50 mm. If the pulverized diameter is large, there is a problem that solidification is insufficient in the next granulation step. As an embodiment of pulverization, it is preferable to use a two-stage pulverizer in order to improve the pulverization capacity. That is, the polyethylene terephthalate fiber waste is roughly pulverized to 30 to 150 mm by a primary pulverizer, and then pulverized to 2 to 50 mm by a secondary pulverizer. When the size of the pulverized product is specified to be 2 to 50 mm directly in the primary pulverizer, the load applied to the pulverizer becomes excessive and warps and becomes inefficient.
[0013]
Next, the pulverized product is put into a granulator to solidify the pulverized product into a cylindrical solid. The size of the diameter is preferably 2 to 20 mm, more preferably 4 to 6 mm. The length is preferably 2 to 60 mm. The granulation method is a method in which the pulverized material is pushed into a hole having a specified size, and a part of the surface is melted by frictional heat generated on the surface of the polyethylene terephthalate and solidified as a binder. If it is large, the surface of the solidified product will not be sufficiently solidified due to the effect of the frictional heat becoming minute.
[0014]
If solidification is insufficient in this way, in the subsequent pneumatic transportation process, the solid matter will collapse due to collision with the piping, and it will be easy to build a bridge in the storage tank at the transport destination, and it will be extremely difficult to discharge from the storage tank. Become. In the granulation method, it is necessary to operate at a temperature not lower than the glass transition point and not higher than the melting point of polyethylene terephthalate . That is, as a granulation method, there is a method in which the fiber waste is heated to a melting point of polyethylene terephthalate or higher and completely melted, and then cooled and solidified. However, in the granulation method, impurities such as nylon are decomposed. The quality of the recovered monomer is deteriorated.
[0015]
In addition, if the solids are completely solidified in the granulation method, there is an adverse effect that the reaction rate is greatly reduced as the contact efficiency between the solvent and the granulated solids deteriorates in the reaction step. Therefore, the present invention employs a granulation method in which only a part of the surface of the fiber waste is melted and solidified at an operating temperature not lower than the glass transition point and not higher than the melting point of polyethylene terephthalate . With this granulation method, it became possible to improve handling while suppressing decomposition of impurities and a decrease in reaction rate.
[0016]
Further, when granulation / solidification is not performed, the pulverized product has a bulk density of about 0.10 g / cm ³ , and in this case, the bulk density becomes very bulky when charged into the reactor in the subsequent reaction step, and The pulverized product absorbs ethylene glycol so that stirring in the reaction vessel becomes very difficult. Bulk specific gravity with the granulating or solids are in terms of smoothly advancing increases but the final bulk density reaction 0.10~1.0g / cm ^3, and preferably is increased to 0.40 g / cm ³ or more It is necessary to improve handling properties. From the above viewpoint, granulation and solidification after pulverization play a very important role in the present invention.
[0017]
The solid matter after granulation and solidification is transported to the reaction step by pneumatic transportation. In addition, a series of pretreatment steps can be performed automatically by saving labor, including putting the polyethylene terephthalate waste into a pulverizer. Hereinafter, each process of the reaction process will be described.
[0018]
In step (a), the polyethylene terephthalate fiber solid material that has passed through the pretreatment step is subjected to a depolymerization reaction in excess ethylene glycol at a known depolymerization catalyst, at a temperature of 120 to 190 ° C. at a known catalyst concentration. Here, when the temperature of the ethylene glycol is less than 120 ° C., the depolymerization time becomes very long and it is not efficient. On the other hand, when the temperature exceeds 210 ° C., thermal decomposition of the oil agent contained in the fiber waste becomes remarkable, and nitrogen compounds generated by decomposition are dispersed in the recovered monomer, making it difficult to separate in the subsequent purification step. The temperature is preferably 140 to 190 ° C. Existing chemical recycling technology requires high-temperature operation, making it difficult to cope with oil contamination.
[0019]
In addition, when the polyethylene terephthalate fiber waste handled in the present invention is colored with a dye, the dye may be decomposed in the reaction step to have a low molecular weight and be dispersed in the recovered monomer to significantly reduce the quality. Therefore, when handling the colored fiber waste, it is effective to incorporate a step of discharging the dye before the step (a). In this step, the granulated solid containing the dye is put into a solvent such as water, alkylene glycol, dimethylformamide, para-xylene, 2-heptanone, and heated at 100 to 190 ° C. while being pressurized, and the dye is extracted. To do. The discharging method may be a batch method or a continuous extraction method such as a countercurrent multistage extraction method. The solidified product after the dye extraction is washed with alkylene glycol and then transported to the step (b) in the same manner as the fiber waste not containing the dye.
[0020]
Further, when nylon that could not be excluded at the stage of acceptance is mixed, the nylon is decomposed in the reaction process, and it is mixed as a nitrogen compound such as ε-caprolactam in the recovered monomer, making separation difficult. Therefore, it is effective to incorporate a step of dissolving and removing nylon into the solidified product containing nylon before the step (a). In this step, a solidified material containing nylon is introduced into a solvent such as alkylene glycol and heated to 100 to 190 ° C. to dissolve and remove nylon. In addition, this process may be performed in the above-described discharging process.
[0021]
In the step (b), different fibers are float-separated in the depolymerization reaction layer from polyethylene terephthalate such as polyethylene and polypropylene which could not be excluded in the discrimination test in the pretreatment step. The different fibers have a specific gravity smaller than that of ethylene glycol, which is a solvent for the depolymerization reaction, and float on the liquid surface. Therefore, these fibers are separated into layers of eutectic mixed suspended solids of different fibers, and then the eutectic mixing is performed. The suspended layer is extracted from the depolymerization and removed.
[0022]
In the step (c), after the depolymerization reaction, different fibers such as cotton that could not be excluded by the discrimination test in the pretreatment step are filtered and selected. The target of the different fiber to be removed in the step (c) is a component having a specific gravity greater than that of ethylene glycol and cannot be separated by the removing method in the step (b). When passing through the step (c), the polyethylene terephthalate is converted to bis (β-hydroxyethyl) terephthalate (hereinafter sometimes abbreviated as BHET), and the reaction solution is a mixed solution of BHET and ethylene glycol.
[0023]
In step (d), the weight ratio of ethylene glycol and polyethylene terephthalate fiber waste from the mixture of BHET and ethylene glycol that has passed step (c) in order to efficiently proceed with the transesterification reaction in step (e) The ethylene glycol is distilled off until the raw material charge ratio becomes 0.5 to 2.0 times. The ethylene glycol distilled off at this time is recycled again to the step (a).
[0024]
In step (e), a mixture of BHET and ethylene glycol from which ethylene glycol has been distilled off in step (d) is subjected to a transesterification reaction with methanol in the presence of a known transesterification catalyst and a known concentration, and then subjected to centrifugation, etc. Solid-liquid separation is performed by solid-liquid separation means.
[0025]
In the step (f), the crude dimethyl terephthalate and crude ethylene glycol obtained in the step (e) are purified by a purification method such as distillation to obtain highly purified dimethyl terephthalate and purified ethylene glycol. At this time, since the impurities that have passed through the reaction step are captured at the bottom of the column, the recovered monomer does not contain impurities and a high purity is obtained.
[0026]
【Example】
Hereinafter, the content of the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. Note that a spectrophotometer (trade name; plastic scan) manufactured by Opto Giken Co., Ltd. was used as the near-infrared analyzer.
[0027]
[Example 1]
When the absorption spectrum was measured with a near-infrared analyzer for 100 kg of polyethylene terephthalate fiber scraps containing no dye generated from the polyester production process, the absorption pattern was consistent with that of the polyethylene terephthalate resin. The whole amount of the fiber waste is put into the primary pulverizer, the screen diameter of the pulverizer is set to 75 mm to perform primary pulverization, and then the pulverized product is charged into the secondary pulverizer to screen the diameter of the pulverizer. Was set to 20 mm and secondary pulverization was performed. Thereafter, the pulverized product was put into a granulator operating under conditions of a diameter of 4 mm, a length of 45 mm, and a granulator internal temperature of 170 ° C., solidified, and then transported to the reaction step by pneumatic transport. The bulk density of the solidified product transported to the reaction step was 0.40 g / cm ³ .
[0028]
In the reaction step, 100 kg of the solidified product was charged into a mixture of 400 kg of ethylene glycol (hereinafter sometimes abbreviated as EG) and 3 kg of sodium carbonate, which had been heated to 185 ° C., and reacted at normal pressure for 4 hours.
[0029]
After completion of the reaction, a mixed liquid of BHET and EG was sent to a distillation tower, and 300 kg of EG was distilled off under conditions of a tower bottom temperature of 140 to 150 ° C. and a pressure of 13.3 kPa. Subsequently, 3 kg of sodium carbonate and 200 kg of methanol were added to 200 kg of the mixture of BHET and EG after EG was distilled off, and the mixture was reacted at 75 to 80 ° C. for 1 h.
[0030]
After completion of the reaction, the reaction solution was cooled to 40 ° C., and was subjected to solid-liquid separation by centrifugation into a cake mainly composed of crude dimethyl terephthalate and a filtrate mainly composed of crude EG. Next, the crude dimethyl terephthalate was 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 crude EG at a pressure of 13.3 kPa and a tower bottom temperature of 140 to 150 ° C. Ethylene glycol was obtained with a yield of 85%. The recovered dimethyl terephthalate is no different from the commercial item in terms of appearance, acid value, melt colorimetric, and sulfated ash inspection items. The recovered monomer with high purity was obtained without any inferiority.
[0031]
[Comparative Example 1]
In Example 1, when the screen size of the primary pulverizer was set to 75 mm, primary pulverization was performed, and the pulverizer was applied without performing secondary pulverization, solidification was insufficient, and air in the next step was used. In the storage tank after transportation, a bridge was not built and discharged, causing an abnormality that the line stopped.
[0032]
【The invention's effect】
In the pretreatment process, handling efficiency in the subsequent reaction process is improved, and in the reaction process, a high-purity recovered monomer can be obtained from fiber waste containing impurities by providing equipment for removing impurities in an efficient and economical manner. It is possible to establish an effective active ingredient recovery method.

Claims (6)

Not transported to the next step by eliminating the fiber waste when it is determined that the different fibers are polyethylene terephthalate was analyzed by discriminating device polyethylene terephthalate textile waste, said about what is determined that polyethylene terephthalate The fiber waste is put into a pulverizer as a lump and the fiber waste is first pulverized to 30 to 150 mm, and then the pulverized product is further pulverized to 2 to 50 mm. Pre-treatment of solidifying into a cylindrical solid material having a length of 20 mm and a length of 2 to 60 mm to a bulk density of 0.10 to 1.0 g / cm ^3, and then transporting the solid material to a reaction step described later by pneumatic transportation A method for recovering a high-purity active ingredient from polyethylene terephthalate fiber waste by combining the steps and the following reaction steps (a) to (f).
(A) Crude polyethylene terephthalate obtained through the pretreatment step was put into ethylene glycol containing a depolymerization catalyst, and depolymerized at a temperature of 120 to 190 ° C. to obtain bis (β-hydroxyethyl) terephthalate (BHET Depolymerization reaction step to obtain
(B) the depolymerization reaction step in the reaction or polyethylene other than the polyethylene terephthalate after the reaction, polystyrene, polypropylene, foreign matter removing step of removing the foreign plastics such polyvinyl chloride le;
(C) a filtration and sorting step of filtering and sorting undissolved components after the depolymerization reaction;
(D) A BHET concentration step in which concentrated BHET is obtained by subjecting a mixture of BHET and ethylene glycol obtained through the filtration and sorting step to distillation / evaporation to distill / evaporate ethylene glycol;
(E) a transesterification reaction step in which transesterification is performed by adding and introducing a transesterification catalyst and methanol into a mixed solution of crude BHET and crude ethylene glycol obtained in the BHET concentration step;
(F) a purification step of separating and recovering purified dimethyl terephthalate and purified ethylene glycol from a mixture of crude dimethyl terephthalate , crude methanol and crude ethylene glycol obtained in the transesterification step;   The active ingredient recovery method according to claim 1, wherein a near-infrared analyzer is used for the discrimination device. 2. The active ingredient recovery method according to claim 1, wherein the granulation method in the pretreatment step uses a granulation method in which a part of the polyethylene terephthalate is melted by operating in a temperature range from the glass transition point of polyethylene terephthalate to the melting point.   2. The active ingredient recovery method according to claim 1, wherein the pretreatment process employs an automatic conveyance device to save labor. When the crude polyethylene terephthalate solid material obtained in the pretreatment step contains a dye, the solid material is charged into a solvent at 100 to 190 ° C., followed by a discharge process for extracting the dye and proceeding to the reaction process. Item 2. The active ingredient recovery method according to Item 1. When the crude polyethylene terephthalate solid obtained in the pretreatment step contains nylon, the solid is introduced into a solvent at 100 to 190 ° C. to dissolve and remove the nylon, and then proceeds to the reaction step. Item 2. The active ingredient recovery method according to Item 1.