JP2001018224A - Method for grinding discarded polyethylene terephthalate bottle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform the simultaneous grinding and cleaning of polyethylene terephthalate bottles to upgrade their recovery efficiency by using a wet grinder for grinding the bottles and injecting water or water containing detergent into the grinder to carry out the grinding process for the bottles, when the discarded bottles are to be ground. SOLUTION: Polyethylene terephthalate(PET) bottles compressed for volume loss are charged into a grinder, then water or water containing detergent is injected into the grinder to carry out the grinding process, and thereby the PET bottles are turned to flakes. After that, a mixture of flakes and cleaning water discharged from the grinder is separated by specific gravity into the flakes and impurities such as metal and sand. Next, the flakes and the cleaning water are separated from each other and the flakes are rinsed with limpid water to be centrifiugally dehydrated. The grinds obtained as described are processed by cleaning, sorting out impurities and the like into PET flakes, which are, in turn, depolymerized using surplus ethylene glycol and preferably, in the presence of a catalyst to obtain a bis-β-hydroxyethyl terephthalate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for crushing discarded polyethylene terephthalate bottles. More specifically, the present invention relates to a pulverization method in which the polyethylene terephthalate bottle that has been discarded is simultaneously pulverized and the foreign substances adhering to the bottle and the residue in the bottle are washed and removed, thereby improving the collection efficiency of the bottle.

[0002]

2. Description of the Related Art Polyethylene terephthalate bottles,
The consumption of so-called PET bottles (PET bottles) is increasing year by year, and roughly, 260,000 tons were consumed in 1998, and the consumption is expected to reach 300,000 tons in 2000. Consumption is expected to increase year after year, and collection and reuse of used PET bottles, so-called recycling, is an indispensable proposition in terms of resource saving and environmental pollution.

Recently, the separate collection and recycling of used PET bottles are required by law, and the government and the private sector are working together to recycle used PET bottles. However, the recycling rate is as low as 5 to 7%, and the current situation is that it has not yet reached the target value. In order to improve the recycling rate of PET bottles, it is necessary to build an effective collection system and increase the reuse rate of collected PET bottles.

Currently, used PET bottles are collected by municipalities, sorted, reduced in volume and compressed to make PET bottle bale (for example, about 40.times.40.times.60 cm) and handed over to re-commercializing companies. The re-commercialization trader unpacks this and separates foreign substances such as metal and PVC bottles, separates the colored bottles that cannot be recycled after washing, and then separates the labels, aluminum, etc. after crushing. Furthermore, after washing, plastics (polyethylene, polystyrene, etc.) other than polyethylene terephthalate are separated, dehydrated and dried, and then the metal is further separated by magnetic force to obtain flakes or pellets for remanufacturing. The flakes or pellets are sent to a user, who uses the flakes or pellets as a polymer raw material.
Products other than bottles include packaging films, carpets, and short fiber products.

[0005]

However, the above-mentioned recovery and recycling methods have the following problems. Firstly, in the current method, the packaging bale of PET bottles contains a lot of garbage and foreign matter, so the processing efficiency, especially the collection yield, is low in re-commercializing companies, and the problem of foreign matter contamination has not been completely solved. Quality fluctuations due to foreign matter in flakes or pellets used for remanufacturing are increased. This quality fluctuation lowers the product yield during remanufacturing and increases the cost of remanufacturing. In addition, since the types of remanufactured products are limited for hygiene reasons,
There is also a problem that the sales market is small. For this reason,
At present, PET bottles are only slightly recycled.

[0006] Further, the PET bottles currently subject to separate collection and re-commercialization are transparent PET bottles designated for the second kind (for soft drinks, soy sauce, and sake), and other colored bottles are excluded. is there. Also, for example, PET bottles such as edible oil, mayonnaise, and dressing cannot be easily washed, and thus cannot be treated by the current recycling method despite the rapid increase in the amount.

[0007]

Accordingly, the present inventors have studied a method for increasing the efficiency of the process of collecting discarded PET bottles into flakes or pellets from the collection of discarded PET bottles. The present inventors have found that the efficiency of collecting PET bottles can be improved by crushing the bottle by using a wet crusher and injecting water or water containing a detergent into the crusher, thereby achieving the present invention. That is, in the present invention, when crushing a discarded polyethylene terephthalate bottle, a wet crusher is used for crushing the bottle, and the bottle is crushed by injecting water or water containing a detergent into the crusher. A method for crushing discarded polyethylene terephthalate bottles, characterized in that:

According to a preferred embodiment of the present invention, the discarded polyethylene terephthalate bottle to be charged into the wet-type pulverizer is a packing bale in which the bottle is reduced in volume or a bottle which is not compressed and reduced in the packing bale. Being, separating polyethylene terephthalate and flakes of dissimilar plastic from crushed bottles,
The flakes of polyethylene terephthalate (which may include colored flakes) include those used for depolymerization to bis-β-hydroxyethyl terephthalate (BHET).

As the discarded polyethylene terephthalate bottle (hereinafter sometimes referred to as a PET bottle) in the present invention, used and discarded or discarded as a defective molded product is used. These PET bottles may be transparent or colored. In addition, the clear PET bottle of the second kind (soft drink, soy sauce,
Or other plastic bottles such as edible oil, mayonnaise, and dressing. The plastic bottle is usually integrated with a label, cap or skirt made of a different kind of plastic, for example, polyethylene, polypropylene, polystyrene, polyvinyl chloride, etc. There is no need to separate. Of course, the smaller the amount of this dissimilar plastic, the better.
% By weight.

[0010] The PET bottle may be in the form of a packing veil whose volume has been reduced or compressed, or may be a bottle which has not been volume reduced and compressed. Conventionally, a side compression method is used for the volume reduction compression, but other methods such as a lantern compression method, an oblique rotation cutting compression method, and a heat cutting compression method can also be used. In the present invention, if the crusher for crushing the discarded PET bottle is a wet crusher, any type of wet crusher, for example, a wet crusher with a cutter knife, a single-shaft or twin-shaft wet crusher, a screw-type wet crusher And a two-stage wet pulverizer.

In the present invention, it is necessary to pulverize the bottle by injecting water or water containing a detergent into the wet pulverizer. The detergent is not particularly limited, but a known detergent such as a household detergent can be used. The flakes obtained by such crushing are crushed under the following conditions:
The size of the sieve mainly varies depending on the size of the sieve, but is usually 8 to 15 mm.

In the present invention, as described above, a PET bottle bale in which a waste PET bottle is reduced in volume and compressed is unpacked without being unpacked, or a PET bottle in which the volume is not reduced and compressed is continuously fed to a crusher. Since it is charged and pulverized by injecting water or water containing a detergent into the pulverizer, the work of unpacking the bale before the pulverization can be omitted, the work of separating different kinds of plastics can be omitted, and the workability is improved. Improvements are made, and it is also effective in health and safety measures. Further, since the cleaning is performed by using the energy of mixing and friction at the time of pulverization, the cleaning effect is extremely high, and the edible oil, the machine oil and the like are easily removed by the cleaning agent. Therefore, a high degree of cleaning effect can be obtained. Furthermore, a part of the pulverized material does not become dust or the like and is scattered, and the pulverization environment can be maintained well.

[0013] The mixture of the flakes of PET bottles and the washing water, which is pulverized by the method of the present invention and discharged from the pulverizer, is then subjected to a specific gravity separation treatment to remove impurities such as metals,
It can be separated into stone, glass, sand, etc. and flakes. The flakes are then separated from the wash water, the flakes are rinsed with clear water and centrifuged. The separated washing water and the rinse water after use can be filtered and reused as the water for the wet grinding. Sewage is subjected to water treatment. In this way, the pre-treatment steps for PET bottle recycling are greatly simplified. Therefore, automation of this pretreatment step can be easily achieved. In addition, since effective pulverization and washing are performed as described above, according to the present invention, there is no problem even if the contents of the plastic bottle remain.

The pulverized product obtained by the method of the present invention is
Perform processing such as washing and foreign matter separation into pet flakes,
The pet flakes are depolymerized with excess ethylene glycol, preferably in the presence of a catalyst, to give bis-β
-Hydroxyethyl terephthalate (BHET). Depolymerized product, ie, BH
The mixed solution containing ET and ethylene glycol removes different plastics such as polyethylene, polystyrene, polypropylene and vinyl chloride other than pets, and further adds water to the mixed solution of BHET and ethylene glycol to obtain crude BHET, ethylene glycol. A mixture of three types of glycol and water is obtained, and the resulting mixture of three types is subjected to hot filtration, ion exchange, and adsorption treatment to remove foreign plastics, solid foreign substances, precipitates, dissolved ions, and colored substances to remove foreign substances. The mixed solution obtained by the treatment is cooled to 20 ° C. or lower, and BHET is crystallized and solid-liquid separated, or the mixed solution is subjected to distillation and evaporation to obtain BHET.
And the obtained molten BHET is heated to a temperature exceeding 190 ° C. and 25
The step of obtaining purified bis-β-hydroxyethyl terephthalate by vacuum evaporation at a temperature of 0 ° C. or less and a residence time of the molten BHET in the evaporator of 10 minutes or less, further purification BHET obtained This can be subjected to a melt polycondensation reaction using at least a part of the raw material to obtain a high-purity polyester polymer.

According to the above method, the pet flakes are melted in a water-rich state to the extent of centrifugal dehydration and simultaneously hydrolyzed into a polyester having a low polymerization degree, and the polyester melt is depolymerized with purified ethylene glycol. Is effective. BHET obtained by depolymerization
About 10% of linear oligomers having a degree of polymerization of about 2 to 4 are present in the mixture. When water is added to the mixed solution of BHET and ethylene glycol and the temperature is maintained at 80 to 120 ° C, the linear oligomers are obtained. It is preferable to improve the yield because the equilibrium between and BHET shifts to the BHET side and the amount of linear oligomer decreases.

The above three kinds of mixed solutions are 80 to 120.
After the equilibrium between the oligomer having a polymerization degree of 2 or more and BHET coexisting in BHET and BHET is shifted to the BHET side while maintaining the temperature at 10 ° C. for 10 minutes or more, more preferably for 30 minutes or more, the triple mixed solution is subjected to hot filtration. To remove solid foreign matter and sediment,
After performing ion exchange by cooling to an upper limit temperature at which ion exchange and adsorption treatment is possible, and then performing an adsorption operation such as decolorization with an adsorbent, the triple mixed solution is reduced to 0 ° C or lower, more preferably to -5 ° C or lower. After cooling, BHET is crystallized and separated into solid and liquid, or the mixed solution of three kinds is distilled and evaporated to separate BHET to obtain a crude BHET melt, which is then evaporated in vacuo to obtain purified bis-β- Hydroxyethyl terephthalate (BHET) is preferred.

In the BHET separation, crude BHE
The filtrate obtained by crystallization and solid-liquid separation of T is subjected to a dialysis membrane treatment to increase the ethylene glycol concentration in the filtrate, and thereafter, the ethylene glycol contained in the filtrate is purified by a known operation such as distillation. After the recovery, the water is recycled to the depolymerization step again, and the water obtained in the dialysis membrane treatment and the water separated when the ethylene glycol is purified and recovered are also recycled to the water addition step again, or the BHET separation is performed. In the process, the ethylene glycol separated when performing the distillation / evaporation operation on the triple mixed solution is directly recycled to the depolymerization step again, and the separated water is also directly recycled to the water addition step again. It is economical.

In the removal of the above-mentioned different kinds of plastics, different kinds of plastics such as polyethylene, polystyrene, polypropylene, and vinyl chloride mixed in a waste PET bottle are compatible with each other, easily form a eutectic mixture, and furthermore, BHET after completion of the depolymerization reaction. And ethylene glycol are insoluble in a two-component mixed solution, and have a lower specific gravity than the two-component mixed solution, so that they are separated into layers as a eutectic mixed floating layer of different kinds of plastics. If the layer is extracted from the depolymerization tank, different kinds of plastics can be effectively removed.

The pet flakes obtained in the pretreatment step are preferably depolymerized. In this case, the pet flakes are melted in a water-rich state to the extent of centrifugal dehydration and simultaneously hydrolyzed to reduce the degree of polymerization. It is effective to react the pet melt with purified ethylene glycol in the presence of a known catalyst to perform depolymerization. In particular, according to the present invention, a crystallization-treated and whitened portion can be used without any problem in order to increase the strength and dimensional stability of a PET bottle, and the crystallization treatment and depolymerization of the whitened portion can be used. This method is effective for

The BHET obtained in the depolymerization contains about 1 to 4% by weight of a cyclic oligomer in addition to the linear oligomer. This cyclic oligomer has a melting point much higher than that of polyethylene terephthalate, 325 to 32.
7 ° C., which has an adverse effect on, for example, products during and after molding of PET bottles. According to the above-mentioned method, a purified bis-β-hydroxyethyl terephthalate containing no cyclic oligomer can be obtained, so that a very high quality polyester resin can be obtained.

After the completion of the depolymerization reaction, water is added to the mixed solution of BHET and ethylene glycol, and the resulting mixed solution is maintained at a temperature of 80 to 120 ° C. to maintain the equilibrium between the linear oligomer and BHET. After the transfer to the BHET side, the triple-mixed solution is hot-filtered at a temperature of 100 ° C. or less, and unreacted linear and cyclic oligomers as a high-melting precipitate,
By removing solid foreign substances such as solidified solids and metals from the remaining different plastics, and then performing ion exchange and adsorption treatment to remove dissolved ions and coloring matters, all harmful foreign substances contained in BHET can be removed.

By the above-mentioned ion exchange, salts accompanying the raw materials, catalyst ions during the polymerization of polyester, ions of added stabilizers, ions mixed in from other steps, and the like are removed.
The adsorbent is then used to remove the coloring agent of the pet and coloring due to thermal deterioration of the organic matter, thereby producing scale on the heat transfer surface and BHE in the vacuum evaporation step of BHET.
Acceleration of the decomposition and polymerization of T can be prevented, and the process can be stabilized and the purity of purified BHET can be maintained.

As described above, since effective foreign matter removal is performed, mixing of different types of plastics into the crushed PET bottle is allowed, and according to the present invention, waste PET bottles that can be reused can be used. The types are expanded to all types of PET bottles, not just the second type designated containers, and the recycling rate of PET bottles can be greatly improved. In addition, regarding the plastic bottle waste volume reduction method currently being implemented by municipalities, only the side compression method is currently adopted due to restrictions from the plastic bottle waste recycling process. ADVANTAGE OF THE INVENTION According to this invention, various volume reduction compression methods, such as a lantern compression method, an oblique rotation cutting compression method, and a heat cutting compression method, are attained, and the transportation freight cost of PET bottle waste at the time of re-commercialization is reduced significantly. Therefore, the economic effect is very large.

In the above-mentioned vacuum distillation purification, since BHET is very unstable thermally,
It is preferable to evaporate quickly under the condition of 0.3 to 0.5 mmHg. At the time of vacuum evaporation, impurities mixed in the catalyst, stabilizer, and waste bottle at the time of PET polymerization may concentrate on the heat transfer surface of the evaporator and cause various troubles. Impurities scatter,
It is entrained and mixed into purified BHET, enters the bottom of the evaporator and inhibits polymerization, generates ethylene glycol by decomposition of BHET, etc., causing a decrease in vacuum system capacity, an increase in evaporation temperature, This can lead to thermal decomposition of BHET, causing not only a vicious cycle, but also clogging the bottom of the evaporator. In the above method, the ion exchange treatment and the adsorption treatment are performed to remove dissolved ions and coloring matter, so that the life of the vacuum evaporator can be improved.

In the above-mentioned vacuum evaporation, it is desirable to reduce the temperature and the residence time as much as possible. However, as a practical condition for maintaining a stable degree of vacuum in the vacuum evaporation, 0.3 to 0.5 is preferable.
It is appropriate to be about mmHg. In addition, the residence time is preferably as short as possible, but there is a physical limit,
Depending on the processing capacity of the vacuum evaporator, latent heat of evaporation, etc., it is appropriate to set the time within 10 minutes. When high-purity purified BHET is obtained as described above, this purified BHET can be subjected to a melt polycondensation reaction to obtain a high-purity polyester polymer.

[0026]

The present invention will be described in more detail with reference to the following examples.

Example 1 PET bottle bale separated and collected by municipalities (veil size: 18 cm of 40 cm × 40 cm × 60 cm)
Kg veil) into a wet grinder equipped with a cutter knife, 1,000 kg of water and 1 kg of liquid kitchen detergent added to the wet grinder with a pump at a flow rate of 2.3 m ³ / Hr. Grinding is performed while circulating between the crusher and the water receiver under the bottom screen, and the specific gravity separator connected to the crusher precipitates metals, sand, glass, etc. with high specific gravity, and from the upper layer Pour the mixture of water and flakes with detergent through the screen provided on the sump,
I took out the flakes. The flakes were rinsed with pure water and centrifugally dehydrated to obtain recovered flakes.

10 kg of the recovered flakes melted in an undried state, 20 kg of ethylene glycol and 20 g of sodium hydroxide previously heated to 180 ° C.
The reaction was carried out at a temperature of 195 to 200 ° C. for 3 hours under normal pressure in a 0-liter stirring autoclave equipped with a reflux condenser.
After completion of the reaction, pure water at 20 ° C was added to the contents of the reactor at 197 ° C.
5 Kg was added, the temperature inside the reactor was 97 to 98 ° C., and the mixture was stirred for 30 minutes. After that, the mixture was filtered while hot with a 325 mesh stainless steel wire mesh filter to remove suspended matters and precipitates (the weight of the removed matter was 0.38 kg). .

The filtrate after hot filtration was added with 50 kg of pure water and heated to 50 ° C. to confirm that the crude BHET was completely dissolved, and at 48 to 50 ° C., an anion / cation exchange resin mixed bed, It was passed through the activated carbon bed for 30 minutes, and it was confirmed that the passing liquid was not colored. Then, in a stirring tank with a 100-liter jacket through brine at 2 ° C., 4-
After crystallization at 5 ° C., crude BHET crystals were separated by a centrifuge. The coloring of the obtained crude BHET crystal was hardly observed. Transfer the crystals to a stirring tank at 60 ° C, 5
The low-boiling components such as moisture were removed with mmHg abs. The temperature was further raised to 120 ° C. to melt the crude BHET, and the ethylene glycol was removed together. The molten crude BHET is supplied to a thin film vacuum evaporator by a metering pump,
At 37 ° C., 0.5 mmHg abs., The residence time in the thin film evaporator was evaporated in 5 minutes, and the mixture was cooled and condensed to obtain purified BHET. The optical density of the obtained purified BHET is 0.011,
The acid value was 0.07 μeq / g, the ash content was 2.6 ppm, and no iron content was found. The optical density is a method for evaluating the quality of BHET, and is a value considered to be proportional to the content of the coloring matter. Specifically, it is a value obtained by measuring the absorbance of a 10% methanol solution of BHET at a wavelength of 380 nm and a cell length of 1.0 cm.

[0030]

According to the crushing method of the present invention, the discarded PET bottles are crushed by using a wet crusher and by injecting water or water containing a detergent into the crusher. Can be performed simultaneously, and the collection efficiency of the bottle can be increased. Further, since the wet pulverization is performed, dust and the like are not generated, and the pulverization environment can be kept favorable.

Claims (6)

[Claims] When grinding a discarded polyethylene terephthalate bottle, a wet crusher is used for crushing the bottle, and water or a detergent-containing water is poured into the crusher to crush the bottle. A method for crushing discarded polyethylene terephthalate bottles. 2. The pulverization method according to claim 1, wherein the discarded polyethylene terephthalate bottle charged into the wet pulverizer is obtained by reducing the volume of the bottle. 3. The pulverization method according to claim 1, wherein the discarded polyethylene terephthalate bottle charged into the wet pulverizer is a bottle that has not been reduced in volume. 4. The crushing method according to claim 1, wherein flakes of polyethylene terephthalate and flakes of different plastics are mixed in the crushed product of the bottle. 5. The pulverizing method according to claim 4, wherein the flakes of polyethylene terephthalate include colored flakes. 6. The method according to claim 4, wherein the flakes of polyethylene terephthalate are used for depolymerization into bis-β-hydroxyethyl terephthalate.