JPH11302443A - Recycling of pet bottle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process to prepare again polyester articles of high purity by converting spent PET bottles recovered from the city into dimethyl terephthalate and ethylene glycol as main raw materials for the preparation of polyester articles. SOLUTION: A highly pure polyester polymer is obtained from PET bottle wastes by a process comprising steps; a monomer preparing step wherein recovered PET bottles subjected to necessary pretreatments such as sorting out foreign matters, crushing, washing and the like to give polyester flakes or polyester pellets, which purified ethylene glycol is added, flowed by depolymerization to give crude polyester monomers, to which subsequently purified methanol is added to effect transesterification followed by separation by crystallization, melting and purification by distillation to give purified dimethyl terephthalate and purified ethylene glycol, which are reacted together to give highly pure polyester monomers, and a polymer formation step wherein a highly pure polyester polymer is obtained by melt polymerization of the obtained highly pure polyester monomers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recycling used PET bottles.

[0002]

2. Description of the Related Art Polyethylene terephthalate bottles,
The consumption of so-called PET bottles is increasing year by year, and roughly 200,000 tons in 1997 and 26 in 1998.
It consumes 10,000 tons and is expected to reach 300,000 tons in 2000. Since then, consumption is expected to increase year by year, and improving the collection and recycling rates of used PET bottles has become an essential proposition on a global scale.

Recently, separate collection and recycling of used PET bottles have become mandatory by law, and the government and the private sector have been working together to collect and recycle used PET bottles. Is about 5-7%, which is low compared to other countries, and has not yet reached the target value. To improve the collection rate, it is necessary for the government and the private sector to cooperate to establish an effective collection system.On the other hand, increasing the recycling rate of collected PET bottles is also a resource-saving and energy-saving perspective. Has become a major challenge.

Conventionally, collected PET bottles are sorted, reduced in volume and compressed by municipalities, and bale of PET bottles (for example,
0x40x60cm) and handed over to re-commercialization companies. The re-commercialization company unpacks it and separates foreign substances such as metal and PVC bottles, and after washing, separates the colored bottles and then pulverizes them to separate labels, aluminum and the like.
Furthermore, after washing, plastics other than polyester (polyethylene, polystyrene, etc.) are separated, dehydrated and dried, and then metal is further separated by magnetic force.
Flakes or pellets.

[0005] The flakes or pellets are sent to a user, who uses the flakes or pellets as raw materials to produce products other than PET bottles, such as carpets, packaging films for eggs and the like, and short fibers.

[0006]

However, the above-mentioned conventional collection and recycling method has the following problems. First, under the current recycling law, there is a lot of garbage and foreign matter mixed in, so the recovery yield of re-commercialization companies is low,
Moreover, since the problem of foreign material contamination has not been completely solved,
The quality fluctuation is large due to the amount of the foreign matter mixed in the flakes or pellets. In addition, since the types of products that can be regenerated from flakes or pellets are limited for sanitary reasons or the like, there is a problem that the sales market is small. For this reason, at present, PET bottles are only slightly recycled.

[0007] As described above, all of the currently produced and marketed PET bottles are generally used after being used unless the PET bottles can be recycled.
It is industrial waste, and some that are currently collected and recycled are destined to become general and industrial waste. This is the same for other polyester products. This kind of general / industrial waste requires final disposal such as incineration or landfill. However, these treatments involve the problem of environmental pollution, and it is difficult to continue as is. Further, such a processing method has a large problem from the viewpoint of resource saving and energy saving.

[0008] Therefore, the present invention uses a used PET bottle recovered from the city as dimethyl terephthalate (DMT) and ethylene glycol (EG), which are main raw materials for producing a polyester product, to produce a high-purity polyester product again. The task is to be able to do so.

[0009]

Means for Solving the Problems In order to solve the above-mentioned problems, as a result of diligent studies on a method for obtaining high-purity raw materials and products from starting raw materials containing impurities and foreign substances such as PET bottle wastes, the present invention has been completed. The invention employs the following configuration. That is, the plastic bottle recycling method according to the present invention is capable of separating foreign materials into used plastic bottle waste,
A pretreatment step of subjecting the polyester flakes or polyester pellets to necessary pretreatment such as grinding and washing, and a depolymerization step of adding purified ethylene glycol to the obtained polyester flakes or polyester pellets and depolymerizing to obtain a crude polyester monomer. And a transesterification step of adding purified methyl alcohol to the obtained crude polyester monomer to obtain crude dimethyl terephthalate, a crude purification step of crystallizing and separating the obtained crude dimethyl terephthalate, and melting the obtained crude dimethyl terephthalate. A purified step of reacting the obtained purified dimethyl terephthalate with purified ethylene glycol to obtain a high-purity polyester monomer; and a melt-polymerizing the obtained high-purity polyester monomer to obtain a high-purity polyester. Is characterized in that the PET bottles waste obtaining high purity polyester polymer through a polymer product to obtain a polymer.

According to the recycling method of the present invention, a high-purity polyester product that can be marketed again can be produced from used PET bottles. Purified ethylene glycol can be obtained by distilling and purifying the crude ethylene glycol obtained in the transesterification step of the crude polyester monomer. If this is used in the monomer production step and the depolymerization step, resources can be effectively reused. It is preferable because it can be used. From the same viewpoint, it is also effective to purify the crude methyl alcohol obtained in the monomer production step by distillation and use it in the above-mentioned transesterification step.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to specific examples. FIG. 1 is a flowchart showing the recycling method of the present invention (particularly, a portion surrounded by a chain line), and partially shows an outline of a conventional polyester product manufacturing process. In the present embodiment, a bale obtained by reducing the volume of a used PET bottle and compressing it is used as a raw material. This PET bottle veil is manufactured by a known method currently used by municipalities.

The PET veil is pre-treated by a pre-treatment facility. The contents of this pretreatment are, for example, bale unraveling, washing, crushing, simple separation, etc. (some parts can be omitted in some cases). And so on. Generally, metal products are separated by magnetic force, and PVC bottles are separated by X-ray transmittance. Plastic bottles after sorting
Wash in the same manner as before.

Next, the PET bottle is crushed and flaked into a size of about 5 cm square using a known crusher. Labels, plastic lids,
The aluminum lid peels off. Plastics other than polyester (eg, polyethylene, polystyrene, etc.) are separated from the flakes after the pulverization using, for example, a liquid specific gravity difference. After the separation, the flakes are washed and the metal is separated again using magnetic force. As a result, a coarse polyester flake with a small amount of foreign matter that can be used in the practice of the present invention can be obtained.

[0014] The crude polyester flakes obtained in the pretreatment step are weighed and depolymerized. Specifically, first, purified ethylene glycol (EG) is added to the weighed polyester flakes, and the resulting mixture is charged into a depolymerization facility to be depolymerized into a crude polyester monomer. The above-mentioned crude polyester flakes with less foreign matter are heated and pressurized in the presence of a suitable catalyst to obtain a crude polyester monomer (BHET).
Can be depolymerized. Next, the crude polyester monomer is sent to a transesterification facility, purified methyl alcohol (MeOH) is added, and the mixture is heated and pressurized in the presence of a suitable catalyst to continuously produce crude ethylene glycol by-produced in the transesterification reaction. The monomer is converted to crude dimethyl terephthalate (DMT) while being taken out of the system. The extracted crude ethylene glycol is supplied to EG /
It is sent to a MeOH distillation purification facility to be purified and used as EG required for the depolymerization step and EG required for the monomer production step for obtaining a high-purity polyester monomer.

The crude dimethyl terephthalate (DMT) obtained in the above transesterification step is separated by crystallization and crudely purified.
Get MT.

The crude DMT is melted. The molten partially purified DMT is purified by a distillation column to obtain high-purity DMT.
The obtained high-purity DMT is transferred to a separately-installed high-purity monomer production facility in a molten state, and the EG obtained by transesterification of the crude polyester monomer is purified together with purified EG to obtain a raw material for polyester production. Use as Thereby, a high-purity polyester product group can be reproduced.

The lower left part of FIG. 1 shows a process for producing various polyester products using high-purity DMT and purified EG obtained by the above-mentioned recycling process as in the case of the conventional virgin raw material. A polyester polymer (polymer) obtained from EG as a raw material can be made into a polyester film in a film-forming facility to form various polyester film product groups. Products such as carpets, tire cords, and automobile interior materials can also be used. Further, the above-mentioned polymer can be used as a raw material for a group of engineering plastic products and a group of plastic bottle products by performing necessary treatment in a solid-phase polymerization facility.

According to the recycling method of the present invention, after returning used polyester products to the raw materials of the polyester product group, it is possible to produce a commercially available polyester product group again. This eliminates the need for incineration, landfill, and other final disposal of used polyester products in the future as general and industrial waste. For this reason, resource and energy savings, which are the final objectives, can be achieved.

The pretreatment equipment, polyester depolymerization equipment, transesterification equipment, crude DMT crude purification equipment, crude DMT purification equipment, monomer production equipment, polymer production equipment, EG / MeOH distillation purification equipment used in the present invention are as follows: Although the individual facilities have already been established, the feature of the present invention is to combine these existing technologies to construct a closed recycling system for used polyester products, and to recycle used polyester products again. The point is to return to a group of products that can be marketed. In the present invention, since a used polyester product is once converted into a high-purity raw material and then polymerized again as a monomer to produce a product, various commercial products similar to the case of using a virgin raw material are produced. You can do it.

[0020]

EXAMPLE A high-purity polyester flake was obtained by subjecting the PET bottle bale sorted and collected and collected by municipalities to pretreatment such as the above-described foreign matter separation, crushing, and washing. 100 kg of this flake is put into a depolymerization facility, and 65 kg of E
After adding G, the internal temperature is 205 ° C. and the internal pressure is 2.5 kg / cm ²
A depolymerization reaction was performed for 3 hours under the conditions of G to obtain 125 kg of a crude monomer (BHET). 55 kg of methyl alcohol (MeOH) is added to the crude monomer, and the internal temperature is adjusted to 12%.
86 kg of crude dimethyl terephthalate (DMT) was obtained by conducting a transesterification reaction for 3 hours while taking out only the crude EG distilled off by the reaction at 0 ° C. and an internal pressure of 6.5 kg / cm ² G while taking it out of the system. .

The obtained crude dimethyl terephthalate was cooled, crystallized and separated to obtain a crude purified DMT. This crude purification D
MT is melted and purified in a distillation column to obtain high-purity DMT83.
kg. The quality of the obtained high-purity DMT was as shown in Table 1, and was sufficiently usable as a raw material for producing a group of polyester products.

[0022]

[Table 1]

[0023]

As described above, the method for recycling PET bottles according to the present invention is to recycle a used PET bottle into high purity DMT and EG, and then use these as raw materials to produce a polyester product group again. As a result, it is possible to recycle used polyester products in a closed recycling system, eliminating the need for incineration and landfill as general and industrial waste, and achieving the desired resource and energy savings Becomes In addition, the recycling system according to the present method includes waste of polyester materials other than PET bottles, such as polyester fiber waste, polyester-based automotive interior material waste, polyester-based engineering plastic waste represented by polybutylene terephthalate, and polyester-based waste. Basically, it can respond to recycling of film waste and the like.

[Brief description of the drawings]

FIG. 1 is a process chart showing a recycling system of the present invention.

Claims (4)

[Claims] 1. A pretreatment step of subjecting used PET bottle waste to pretreatment such as separation of foreign matter, crushing, and washing into polyester flakes or polyester pellets;
Depolymerization step of adding ethylene glycol to the obtained polyester flakes or polyester pellets to depolymerize to obtain a crude polyester monomer, and transesterification step of adding purified methyl alcohol to the obtained crude polyester monomer to obtain crude dimethyl terephthalate, A crude purification step of crystallizing and separating the obtained crude dimethyl terephthalate, a purification step of melting and distilling and purifying the obtained crude dimethyl terephthalate, and reacting the resulting purified dimethyl terephthalate with purified ethylene glycol to obtain a high-purity polyester. A high-purity polyester polymer is obtained from PET bottle waste through a monomer generation step of obtaining a monomer and a polymer generation step of melt-polymerizing the obtained high-purity polyester monomer to obtain a high-purity polyester polymer. Method of recycling that PET bottles. 2. The PET bottle recycling method according to claim 1, wherein the transesterification reaction is performed while continuously removing crude ethylene glycol by-produced in the transesterification step of the crude polyester monomer outside the system. 3. The PET bottle according to claim 1, wherein purified ethylene glycol obtained by distilling and purifying the crude ethylene glycol obtained in the transesterification step of the crude polyester monomer is used in the monomer production step and the depolymerization step. Recycling method. 4. The PET bottle recycling method according to claim 1, wherein the crude methyl alcohol obtained in the monomer production step is purified by distillation and used in the transesterification step.