JP2002166420A - Method for recovering useful component from polyester resin waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering a useful component efficiently and economically by which a pretreatment process is covered only by concise facilities to a minimum required extent and a recovered high-purity monomer is obtained, with regard to the method for recovering the useful component from polyester resin tailings including impurities. SOLUTION: The method for recovering a useful component comprises a chemical reaction process including the steps to remove most of the impurities by pretreatment facilities limited to a minimum required extent such as grinding, wind force selection, centrifugal separation and pneumatic conveyance and remove the impurities by physical and chemical techniques. Thus the recovered high-purity monomer can be obtained in a simple and efficient manner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a resin waste mainly composed of polyester, which is subjected to a pretreatment such as pulverization, washing, and removal of foreign matter, and then subjected to a chemical reaction treatment to obtain high-purity bis as an active ingredient. The present invention relates to a method for easily and efficiently recovering hydroxyl terephthalate or a terephthalic acid component and an alkylene glycol.

[0002]

2. Description of the Related Art Polyester resin waste is derived from foods, foreign materials such as labels, shrink films, base cups and caps, different plastics such as polyvinyl chloride and polyolefin resins, aluminum derived from caps, and adhesives. Agents, pigments, dyes, etc. may be mixed.
Therefore, the actual method of separating foreign matter from polyester resin waste is a gravity separation method typified by specific gravity separation, an electromagnetic separation method that separates powder, aluminum, iron, etc. by generating a magnetic field with electrostatic force, electromagnet or eddy current It is common to combine methods and spectroscopic separation methods that separate by color.

[0003] For example, when a polyvinyl chloride bottle is separated from a polyalkylene resin, the bottle is separated as it is using X-rays, the bottle is wet-pulverized into flakes, and then immersed and stirred in an alkaline cleaning solution, A method of separating a polyolefin resin having a lower specific gravity than that of a polyolefin resin is employed. In addition, a separation step or an auxiliary step for separation may be required depending on the part or material of the foreign matter to be separated, and even when the same foreign matter is removed, the separation step is often performed a plurality of times. In material recycling for reuse as a powdery recycled polyester resin, the number of separation steps until a product is obtained may reach 10 to 20 steps.

[0004] Further, in the case of polyester resin waste, there are ones such as PET bottles that are separated and collected, and those in which magnetic powder and polyester resin are complexed such as audio tapes and prepaid cards. is there. In particular, in the latter case, it is often very difficult to completely remove foreign matter.In material recycling, the quality of the material is lower than that of the polyester resin before regeneration because the accumulation of foreign matter and various deterioration of the polyester resin occur each time the regeneration is repeated. Decrease by one rank.

[0005] On the other hand, there is a chemical recycling method in which water, a solvent such as methanol or ethylene glycol is used to decompose the monomer constituting the polyester resin and reuse the monomer. Since chemical recycling regenerates polyester waste into raw material monomers using a chemical purification facility, the quality is not greatly reduced due to regeneration and is suitable as closed-loop recycling. Examples of the chemical recycling include a method of hydrolyzing polyester waste in the presence of an alkali compound described in JP-A-11-21374, and a gas-phase methanolysis in methanol described in US Pat. No. 5,952,520. There is a method of obtaining dimethyl terephthalate and ethylene glycol.

However, all of these require high-temperature reaction conditions of 200 ° C. or higher, so that decomposition starts at 190 ° C., and the decomposed product degrades the quality of the final product. There is a problem that the tolerance for mixing different plastics is very low.
Furthermore, Japanese Patent Application Laid-Open No. 2000-169623 proposes a process in which polyethylene terephthalate waste is decomposed with ethylene glycol, and the recovered BHET is purified by a thin film evaporator, and then BHET is melt-polycondensed to obtain a polyethylene terephthalate polymer. In this case, too, there is a step of imposing a heat history of 200 ° C. or more, and the mixing tolerance of different plastics such as polyvinyl chloride which decomposes thermally is low. In other words, although chemical recycling has a higher tolerance for impurity contamination than material recycling,
It was necessary to remove impurities almost completely in the pretreatment step.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems of the prior art, to keep the pretreatment steps to the minimum necessary and simple equipment, and to reduce the amount of monomer recovered even when impurities are mixed. It is an object of the present invention to establish an efficient and economical method for recovering an active ingredient which can obtain a high-purity product without contaminating the active ingredient.

[0008]

Means for Solving the Problems As a result of diligent studies, the present inventors have found that in the pretreatment step, resin waste is pulverized to an appropriate size in order to allow the reaction in the subsequent reaction step to proceed efficiently. By pre-treatment, the majority of impurities are roughly sorted by centrifugal separation using a decanter that also serves as a wind separator and resin washing, and a reaction step with reaction conditions that does not decompose impurities is incorporated after the pre-treatment step. The present inventors have found a method for recovering an effective component that can efficiently obtain a high-purity recovered monomer while simplifying the equipment, and have completed the present invention.

[0009] That is, an object of the present invention is to leave the packing waste in a packed state without unpacking or after unpacking and then put it into a pulverizer to put the resin waste into 30 to 15 pieces.
After crushing to 0 mm, the crushed material was further
Crushed, polyethylene from the crushed material by wind separation,
After removing polyester and different plastics such as polystyrene and polyvinyl chloride, use a decanter that also serves to wash and remove foreign substances on the inner and outer surfaces of the polyester resin and / or contents residues in the polyester resin container with water. After removing the different plastics such as polyethylene and polypropylene having a small size into recovered flakes, the recovered flakes are transported by air to a reactor in a reaction step described below, and the following pretreatment steps (a) to (f) This can be achieved by a method of recovering a high-purity active ingredient from polyethylene terephthalate waste by combining the reaction step. (A) a depolymerization reaction step in which the recovered flakes obtained in the pretreatment step are introduced into an excess of alkylene glycol containing a depolymerization catalyst to obtain bis-β-hydroxyterephthalate (BHET); (b) the depolymerization Foreign matter removing step of removing foreign plastics such as polyethylene, polystyrene, polypropylene, polyvinyl chloride, etc. other than polyester during or after the reaction step; (c) Filtration for filtering out undissolved components after the foreign matter removing step (D) a BHET concentration step of subjecting the mixture of the crude BHET and the crude alkylene glycol having undergone the filtration and separation step to a distillation / evaporation operation to distill / evaporate the alkylene glycol to obtain a concentrated BHET; (e) the BHET concentration In the mixture of BHET and alkylene glycol obtained in the step, the transesterification catalyst and meta (F) purified dimethyl terephthalate and purified alkylene from a mixture of crude dimethyl terephthalate, crude methanol and crude alkylene glycol obtained in the transesterification reaction step; A purification step for separating and recovering glycol;

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for recovering an active ingredient according to the present invention, the polyester resin is used in the pretreatment step in view of the reactivity in the reaction step after the pretreatment step or the air transportability after the pretreatment step. It is preferable to pulverize to 2 to 30 mm square. The crushed diameter is more preferably 5 to 20 mm
It is. By this operation, the depolymerization reactivity is improved, and the processing capacity of the polyester resin waste is improved. This effect is particularly effective for a portion where the thickness of the portion that has been crystallized and whitened is increased for increasing the strength and dimensional stability of the PET bottle. As an embodiment of the pulverization, it is preferable to use a two-stage pulverizer in order to improve the pulverization processing capacity.
That is, the waste is roughly pulverized to 30 to 150 mm by a primary pulverizer, and then pulverized to 2 to 30 mm by a secondary pulverizer. When the size of the pulverized product is directly defined in the primary pulverizer to be 2 to 30 mm, the load applied to the pulverizer becomes excessive and inefficient. Further, if a magnetic separator for removing the metal or the like which is a packing material of the polyester resin after the primary pulverization is provided, it is effective in reducing the load on the cutter of the secondary pulverizer.

In many cases, the pulverized material contains a different plastic from polyester such as polyethylene, polypropylene, polystyrene, polyvinyl chloride or the like, which is a cap or label material contained as an impurity in the polyester resin. In the present invention, reaction conditions are selected so as not to reduce the purity of the recovered monomer by decomposing in a later reaction step with respect to mixing of the different plastics, but the different plastics are supplied to the reactor. Since there is a possibility of unfavorable effects on handling such as sticking, causing filter clogging, etc., removing the different plastics in the pretreatment process and minimizing contamination in the reaction process is a smooth reaction. It is important in proceeding.
However, various steps for completely removing the different plastics as in the case of material recycling are not required, and only a minimum necessary step is required.

In order to remove a thin film (polyethylene, polypropylene, polyvinyl chloride, etc.) used for labels, which is different from polyester, from the pulverized material,
First, the labels are removed by wind sorting. At this time, if the air volume is too large, the polyester resin, which is an active ingredient, will be removed together with the air volume. Therefore, it is necessary to appropriately adjust the air volume. By this wind separation, labels mainly composed of polypropylene, polystyrene and polyvinyl chloride can be almost completely removed. Next, the pulverized material is decanted in order to remove caps that cannot be removed by wind separation, and different plastics such as polypropylene and polyethylene having a lower specific gravity than water are removed by centrifugation to obtain recovered flakes. Since the decanter also functions as a facility for washing impurities (such as soy sauce and soft drinks) derived from food and the like remaining in the polyester resin, there is no problem even if the contents remain in the resin.
The washing water separated by centrifugation is recycled to the decanter again, a part of which is purged and subjected to wastewater treatment.

The recovered flakes discharged from the decanter are transported to the reactor in the reaction step by air transport.
The size after grinding in the previous grinding step is 30-150m
When it is specified to be relatively large as m, problems such as deterioration of transport efficiency in this pneumatic transport step and blockage of a rotary valve occur, so that it is effective to pulverize to about 2 to 30 mm as in the present invention. is there. In the recovered flakes before the pneumatic transportation, about 0.5% of the water used in the centrifugation by the decanter remains based on the weight of the recovered flakes. These moistures may have an adverse effect on the reaction rate in the depolymerization step, but are eventually dried during pneumatic transportation, so that the water content is ultimately 0.1% based on the weight of the recovered flakes.
Since the water content is reduced to 1% or less, there is no problem in the progress of the reaction.

Although it is possible to remove most of the components other than the polyester in the above pretreatment step, the pretreatment step is completed in much less steps than when material recycling is performed. This is because even if impurities remain, the impurities can be separated by a physical and chemical separation method in the next reaction step.
In the material recycling, the colored bottle becomes an impurity and must be removed by a sorter. However, in the method of the present invention, the pigment contained in the colored bottle can be removed in a subsequent reaction step. Is unnecessary and can be used as an effective resource. In addition, a series of pretreatment steps can be performed automatically, including saving the manpower including inputting the polyester waste into a pulverizer.

[0015] The recovered flakes that have completed the pretreatment step are transported to the reaction step. Hereinafter, each of the reaction steps will be described.

In the step (a), the recovered flakes that have passed through the pretreatment step are subjected to a depolymerization reaction in a known depolymerization catalyst at a known catalyst concentration of 120 to 210 ° C. in an excess of alkylene glycol. Here, 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 200 ° C., the thermal decomposition of the polyvinyl chloride remaining in the recovered flakes becomes remarkable, and the chlorine compound generated by the decomposition is dispersed in the recovered monomer, making it difficult to separate in the subsequent step. The temperature is preferably between 140 and 190C. The existing chemical recycling technology requires operation at a high temperature of 200 ° C or higher, making it difficult to cope with the contamination of polyvinyl chloride. There was no other way but to remove
In the method of the present invention, reaction conditions are selected so that even if polyvinyl chloride is mixed during the reaction, there is no problem in the quality of the recovered monomer.

In the step (b), different plastics such as polyethylene, polypropylene and polystyrene which could not be removed in the pretreatment step are separated by floating in the depolymerization reaction layer. The different plastic has a lower specific gravity than the alkylene glycol which is a solvent for the depolymerization reaction, and floats on the liquid surface. Therefore, these are separated into layers as a eutectic mixed floating mass of the different plastic, and then the eutectic mixing is performed. The suspended matter layer is removed from the depolymerization and removed.

In the step (c), undissolved components are filtered and separated after the depolymerization reaction. At the time of passing through the step (c), the polyester is bis-β-hydroxyterephthalate (hereinafter, referred to as “bis-β-hydroxyterephthalate”).
BHET), and the reaction solution is B
It is a mixture of HET and alkylene glycol.

In the step (d), the mixture of the alkylene glycol and the polyester resin waste is converted from the mixture of the BHET and the alkylene glycol passed through the step (c) in order to efficiently advance the transesterification reaction in the step (e). The alkylene glycol is distilled off until the weight ratio becomes 0.5 to 2.0 times based on the raw material charge ratio. The alkylene glycol distilled off at this time is recycled to the step (a) again.

In step (e), the mixture of BHET and alkylene glycol from which alkylene glycol has been distilled off in step (d) is subjected to a transesterification reaction with methanol in the presence of a known ester exchange catalyst and a known concentration.
Solid-liquid separation is performed by a solid-liquid separation means such as centrifugation.

In step (f), the crude dimethyl terephthalate and crude alkylene glycol obtained in step (e) are purified by a purification method such as distillation to obtain high-purity purified dimethyl terephthalate and purified alkylene glycol.
At this time, the impurities that have passed through the reaction step are captured at the bottom of the column, and thus the recovered monomers contain no impurities and have high purity.

[0022]

EXAMPLES Hereinafter, the content of the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[Example 1] PET bottle bale which is separately collected and collected by municipalities (bale size: 900 mm)
After unpacking a 120 kg bale of × 1000 mm × 550 mm), put it into the primary crusher, set the screen diameter of the crusher to 75 mm, perform primary crushing, and then transfer the crushed material to the secondary crusher. It was charged and the screen diameter of the pulverizer was set to 10 mm to perform secondary pulverization. After that, the pulverized material was subjected to a wind separator, polyethylene, polystyrene, after removing the label attached to the bottle containing polypropylene as a main component, centrifuged by a decanter, while washing and removing the contents of the bottle, polypropylene, The cap mainly composed of polyethylene and the label not removed by the wind separation were removed to obtain a recovered flake. 100 kg of the recovered flakes was transported to the reaction step by air transport.

In the reaction step, the flakes are previously heated at 185 ° C.
400 kg of ethylene glycol (hereinafter, may be abbreviated as EG) heated to 3 kg, and sodium carbonate 3
kg of the mixture, and reacted at normal pressure for 4 h. At this time, polyester and other plastics, such as polystyrene, which could not be removed in the pretreatment step, floated on the EG liquid surface, and were removed.

After the completion of the reaction, the mixture of BHET and EG is sent to the distillation column, the temperature at the bottom of the column is 140 to 150 ° C., and the pressure is 13.
300 kg of EG was distilled off under the condition of 3 kPa. Then E
3 kg of sodium carbonate and 200 kg of methanol were added to 200 kg of a mixture of BHET and EG after G was distilled off,
The reaction was carried out at normal pressure at 75 to 80 ° C. for 1 hour.

After completion of the reaction, the reaction solution is cooled to 40 ° C.
By centrifugation, solid-liquid separation was carried out into a cake mainly composed of crude dimethyl terephthalate and a filtrate mainly composed of methanol and crude EG. The crude dimethyl terephthalate is then pressured to 6.
7 kPa, tower bottom temperature 180-200 ° C, crude EG at pressure 1
Purification was performed by distillation under the conditions of 3.3 kPa and a tower bottom temperature of 140 to 150 ° C., and finally dimethyl terephthalate and ethylene glycol were obtained at a yield of 85%. The recovered dimethyl terephthalate is comparable to commercially available products in terms of appearance, acid value, melting color, and sulfated ash, and the recovered ethylene glycol is comparable to commercially available products in diethylene glycol concentration, water content, and melting color. In all cases, recovered monomers of high purity were obtained.

[Comparative Example 1] PET bottle bale separated and collected and collected by municipalities (bale size: 900 mm)
After unpacking a 120 kg bale (× 1000 mm × 550 mm), put it into the primary pulverizer, set the screen diameter of the pulverizer to 75 mm, perform primary pulverization, and perform the next pretreatment step without performing secondary pulverization. Then, after pneumatic transportation, the crushed material clogged the rotary valve, and the line stopped.

[0028]

Efficient and economical active ingredients that can keep the pretreatment process to the minimum necessary and simple equipment and can obtain high-purity products without contaminating the recovered monomer even when impurities are mixed. Recovery methods can be established.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuhiro Sato 77 Kitayoshida-cho, Matsuyama-shi, Ehime Prefecture Teijin Limited Matsuyama Office F-term (reference)

Claims (3)

[Claims] 1. A polyester resin waste packing bale is unpacked without being unpacked, or after being unpacked, put into a pulverizer to first put the resin waste into 30 to 15 pieces.
After crushing to 0 mm, the crushed material was further
Crushed, polyethylene from the crushed material by wind separation,
After removing the resin different from the polyester of the label thin film film composed of polystyrene, polyvinyl chloride, etc., using a decanter which also serves to wash and remove foreign substances on the inner and outer surfaces of the polyester resin and / or the content residue in the polyester resin container with water. A pretreatment step of removing the different plastics such as polyethylene and polypropylene having a lower specific gravity than water to obtain recovered flakes and then transporting the recovered flakes by air to a reactor in a reaction step described below, and the following (a) to A method of recovering a high-purity active ingredient from polyester resin waste by combining with the reaction step (f). (A) a depolymerization reaction step of introducing the recovered flakes obtained in the pretreatment step into an excess of alkylene glycol containing a depolymerization catalyst to obtain bis-β-hydroxyterephthalate (BHET); (b) the depolymerization Foreign matter removing step of removing foreign plastics such as polyethylene, polystyrene, polypropylene, polyvinyl chloride and the like other than polyester during or after the reaction step; (c) Filtration for filtering out undissolved components after the foreign matter removing step (D) a BHET concentration step of subjecting the mixture of the crude BHET and the crude alkylene glycol that has undergone the filtration and separation step to a distillation / evaporation operation to distill and evaporate the alkylene glycol to obtain a concentrated BHET; (e) the BHET concentration In the mixture of BHET and alkylene glycol obtained in the step, transesterification catalyst and meta (F) purified dimethyl terephthalate and purified alkylene glycol from a mixture of crude dimethyl terephthalate and crude methanol and crude alkylene glycol obtained in the transesterification reaction step; A purification step for separating and recovering glycol; 2. The method according to claim 1, wherein the polyester is polyethylene terephthalate. 3. The method for recovering an active ingredient according to claim 1, wherein in the pretreatment step, an automatic transport device is employed to save labor.