JP2003181835A - Method for separating polyethylene terephthalate from pulverized substance of used pet bottle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently separate polyethylene terephthalate from the pulverized substance of used PET bottles. <P>SOLUTION: Used PET bottles containing polyolefins and OPS are pulverized, and the obtained pulverized substance is placed in ethylene glycol of a temperature of 12 to 30°C, and a gravity separation treatment is applied. Thus, polyethylene terephthalate is separated by the specific gravity from the polyolefins and OPS. Therefore, this method for efficiently separating polyethylene terephthalate from the pulverized substance of used PET bottles can be provided. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for separating polyethylene terephthalate from ground PET bottles. More specifically, the present invention relates to a method for removing polyethylene terephthalate by removing the resin constituting the cap, the label, etc., particularly the polyolefin and the OPS, from the crushed PET bottles (flakes) mixed with the cap, the label, etc.

[0002]

2. Description of the Related Art Polyethylene terephthalate bottles,
The consumption of so-called PET bottles is increasing year by year, and improving the collection rate and recycling rate of used PET bottles has become an essential issue on a global scale. Currently, the law requires separate collection and recycling of used PET bottles, and the government and the private sector are working together to collect and recycle used PET bottles. At that time, local governments instruct consumers to remove caps and labels from used PET bottles, wash them with water, and then dispose of them as resource waste. There are overwhelmingly many cases. Many labels have perforations for easy removal, but some do not have perforations,
Not uniform.

Conventionally, a label and a cap are removed from a collected PET bottle manually, or,
A method has been employed in which after dry pulverization is performed as it is, the remaining polyolefins are removed by performing wind force selection, washing with water, and then performing specific gravity separation in water, or after passing through a label removing device, the bottle is pulverized.

However, since such means requires manpower, the workability thereof may be deteriorated due to scattering of the residual contents and a rotten odor. Further, there are cases where complete removal is difficult and a special label removing device is required, which is a problem. Furthermore, it is difficult to remove the stopper ring or the handle of the cap, and it may remain in the flakes obtained by crushing. Although they can be separated by wind power sorting or specific gravity sorting in water, it is difficult to separate the specific gravity of a substance having a specific gravity larger than that of water from polyethylene terephthalate, and its solution is awaited.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to efficiently separate polyethylene terephthalate from a crushed product of a used PET bottle including a cap, a label, etc. by removing various polymers by the cap, the label, etc. is there.

Another object of the present invention is to promote the recycling of caps, labels, etc. by separating the resin constituting the caps, labels, etc., particularly polyolefins, from used PET bottles and OPS.

Further objects and advantages of the present invention will be apparent from the following description.

[0008]

According to the present invention, a pulverized product of a used PET bottle containing polyolefins and OPS is subjected to a specific gravity separation treatment in ethylene glycol at a temperature of -12 to 30 ° C to obtain polyethylene terephthalate. It is achieved by a method for separating polyethylene terephthalate from ground PET bottles, which is characterized in that it is separated from PEGs and OPS.

Regarding labels for PET bottles (polyethylene terephthalate bottles), voluntary design guidelines are set from the viewpoint of facilitating recycling and improving efficiency. Labels include polyethylene stretch labels, shrink labels, OPP roll labels, paper labels, and the like. Among these, shrink labels include those made of polyolefin, OPS (stretched polystyrene), and polyethylene terephthalate. . Since those made of polyethylene or polyolefin have a smaller specific gravity than water, they can be easily separated from polyethylene terephthalate by specific gravity selection. Also,
The label made of polyethylene terephthalate is the same material as the flakes of polyethylene terephthalate forming the bottle body. Further, the paper label is disintegrated by crushing and wet washing, and is removed together with water by flowing out. On the other hand, OPS composed of polystyrene, a copolymer of methacrylic acid ester and acrylic acid ester, and styrene-butadiene rubber is used in a large amount, but since the specific gravity is about 1.05, which is larger than that of water, the specific gravity separation in water is Have difficulty.

When a resin other than polyethylene terephthalate is mixed in recycled polyethylene terephthalate, the original physical properties of polyethylene terephthalate are generally impaired, and, for example, coloring or discoloration occurs, which hinders remanufacturing. In addition, problems such as clogging of filters and piping systems in the recycling process, pollution, and increased load of decolorization equipment occur, and partial dissolution in the depolymerization reaction of polyethylene terephthalate and formation of compounds by side reactions, etc. When OPS is mixed with polyethylene terephthalate, methacrylic acid ester and acrylic acid ester will coexist in addition to the terephthalic acid ester produced by the glycolysis of polyethylene tarephthalate, and therefore the purity of the target terephthalic acid ester will be high. There is also the problem of deterioration.

In order to construct a PET bottle recycling system by efficiently removing the components other than polyethylene terephthalate that accompany the collected PET bottles, the present inventor uses components such as OPS having a greater specific gravity than water. The present invention has been completed as an alternative method to the conventional specific gravity separation in water, considering that it is necessary to perform appropriate separation from polyethylene terephthalate.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to specific examples. In the present embodiment, a used PET bottle is collected and the volume-compressed veil is used as a raw material. This PET bottle veil is manufactured by a known method currently adopted by the municipalities.

As described in Japanese Patent Laid-Open No. 2000-53802, it is preferable that the PET bottle veil is continuously put into a crusher as a veil without being unpacked, and water is injected to crush it in water. . The size of the crushed product is 5
-50 mm, more preferably 7-30 mm. By crushing the PET bottle bale without unpacking, workability can be improved and effective safety and hygiene measures can be taken.

O from ground polyethylene terephthalate
In order to remove the resin other than PS-containing polyethylene terephthalate, the pulverized product may be subjected to a specific gravity separation treatment using ethylene glycol held at a predetermined temperature. Further, in order to recycle the caps and labels, respectively, a two-stage separation system is effective in which the polyolefins are first subjected to specific gravity separation using water, and then the OPS is subjected to specific gravity separation using ethylene glycol.

The specific gravity of ethylene glycol has a large temperature dependency, and in one example, 1.135,0 at -12 ° C.
1.127 at 20 ° C, 1.116 at 20 ° C and 1.107 at 30 ° C. The specific gravity of OPS is about 1.05, and the larger the specific gravity difference between OPS and ethylene glycol, the easier the separation. Therefore, in consideration of the above relationship and the melting point (-13 ° C) of ethylene glycol, it is preferable to perform the specific gravity separation of OPS using ethylene glycol at a temperature of -12 ° C to 30 ° C. Furthermore, the viscosity of ethylene glycol has a large temperature dependency, and in one example, it is 5.7 × 10 ^-2 Pa · s at 0 ° C and 2.1 × 10 ^-2 Pa · s at 20 ° C. When the temperature is low, the viscosity becomes high, so that the liquid running out of ethylene glycol from the OPS to be removed tends to become worse. Therefore, it is more preferable to perform the specific gravity separation at a temperature of ethylene glycol of 10 to 25 ° C. By using ethylene glycol in such a temperature range, polyolefins having a specific gravity of less than 1 and OPS having a specific gravity of about 1.05 are used.
Floats in an ethylene glycol solution, whereas polyethylene terephthalate, which has a specific gravity of about 1.34, sinks in the solution, so that OPS and polyolefins can be easily removed from the polyethylene terephthalate. The quantitative relationship between the pulverized product that is separated from the specific gravity and ethylene glycol is
The weight ratio is 1: 4 to 1:20, more preferably 1: 5 to 5.
1:20 is good.

The ethylene glycol attached to the separated OPS and polyolefins can be removed by heating to reduce the viscosity and then centrifuging or rinsing with water. When rinsed with water, ethylene glycol can be recovered by further distilling the resulting ethylene glycol aqueous solution.

In order to promote the recycling of the cap and the label by separating the polyolefins and the OPS as well, first, the pulverized product is subjected to specific gravity separation in water to remove the polyolefins. This allows the polyolefins to be separated from the OPS and polyethylene terephthalate. The quantitative relationship between the pulverized product and the water separated by specific gravity is 1: 4 to 1:20 by weight ratio, and more preferably 1: 5 to 1:10. The temperature of the water used for the specific gravity separation is not particularly limited, and it can be performed at room temperature, for example.
Next, by taking out a component having a large specific gravity that is sunk in water and adding it to ethylene glycol in the above temperature range, OPS and polyethylene terephthalate can be separated from each other by specific gravity.

The separated crude polyethylene terephthalate is then treated with ethylene glycol to give crude bis (2-
It can be subjected to a step of being depolymerized to hydroxyethyl) terephthalate. At that time, if a large amount of water is present in the system, the activity of the depolymerization catalyst decreases, and it becomes difficult to smoothly perform depolymerization. In the present invention, since the specific gravity separation is performed in ethylene glycol in the step immediately before depolymerization, there is no possibility of introducing a large amount of water into the depolymerization step, and therefore the above problems can be avoided.

[0019]

EXAMPLES In order to explain the present invention in more concrete modes, specific examples will be given below. Needless to say, the present invention is not limited to this.

Example 1 Using a PET bottle with a cap and a label, which was separately collected and collected by the municipality, 200 kg of a PET bottle veil produced by compressing the volume of the PET bottle was put into a wet crusher with a cutter knife, After crushing into 8 mm x 8 mm flakes and centrifugal dehydration, the crushed product was screwed into a stirring specific gravity separation tank with an upflow circulation draft tube containing ethylene glycol maintained at a temperature of 15 ° C at a speed of 100 kg. / Hour.
Air flow is periodically fed into and discharged from the specific gravity separation tank to generate a vertically pulsating water flow, and the pulverized product is repeatedly expanded and contracted by the pulsating water flow, so that the pulverized product has a low specific gravity. The cap and label were lifted while the high density polyethylene terephthalate was precipitated. The cap and label grits were separated and removed from the polyethylene terephthalate flakes and ethylene glycol by casting the floating cap and label grits with overflowing ethylene glycol into a 2 mm x 2 mm eye basket.

The remaining pulverized material precipitated at the bottom of the specific gravity separator was extracted with a screw conveyor and dehydrated to obtain polyethylene terephthalate flakes separated from the label and the cap material. The polyethylene terephthalate flakes sufficiently satisfied the recycling standard.

Example 2 In the same manner as in Example 1, the flakes obtained by crushing PET bottle veils were first put into a specific gravity separation tank containing water to remove the cap, the polyolefin label and the like. Next, after the remaining pulverized material settled on the bottom of the specific gravity separator was extracted by a screw conveyor and dehydrated,
The mixture was placed in a specific gravity separation tank containing ethylene glycol maintained at a temperature of ° C. After removing the floating OPS label, the remaining pulverized product precipitated at the bottom of the specific gravity separator was extracted with a screw conveyor and deethyleneized to obtain polyethylene terephthalate flakes separated from the label and the cap material. The polyethylene terephthalate flakes sufficiently satisfied the recycling standard.

[0023]

As described above, according to the method of separating polyethylene terephthalate from the pulverized product of the used PET bottle according to the present invention, the cap, the label, etc. can be removed from the pulverized product of the PET bottle mixed with the cap, the label, etc. Since the polyethylene terephthalate can be separated by removing it, it is not necessary to force the consumer to remove the cap, the label and the like, and the recycling of the PET bottle can be facilitated. Further, since the polyolefins constituting the cap and the label can be separated from the OPS, the cap and the label can be recycled.

Claims (2)

[Claims] 1. A pulverized product of a used PET bottle containing polyolefins and OPS is subjected to a specific gravity separation treatment in ethylene glycol at a temperature of −12 to 30 ° C. to separate polyethylene terephthalate from the polyolefins and OPS. A method for separating polyethylene terephthalate from crushed used PET bottles. 2. The method according to claim 1, further comprising a step of separating the pulverized product in water by specific gravity separation to separate polyolefins before the specific gravity separation in ethylene glycol.