JP2002011301A - Waste plastic recycling method and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a solvent from remaining in plastic materials after recycling even in the case that waste foamed polystyrol is treated with the solvent for volume reduction, prevent evaporation of the solvent and secondary generation of harmful substances, and prevent deterioration of the quality of the secondary products, in relation to a method and an apparatus for plasticizing waste plastics using a solvent and recycling the waste plastics. SOLUTION: After waste plastics are plasticized with a solvent, the resulting waste plastics are brought into contact with a supercritical fluid or a subcritical fluid to remove the solvent remaining in the waste plastics by extraction and recycle the resulting plastics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for plasticizing and recycling waste plastics using a solvent.

[0002]

2. Description of the Related Art In recent years, an enormous amount of waste plastic products have been discharged, and how to dispose of such waste products is an important social issue.

[0003] In particular, styrene foam, which is widely used because of its excellent properties of cushioning and heat insulation, has a low bulk density, and the recovery cost per weight becomes extremely large.

[0004] For this reason, disposal of the expanded polystyrene is particularly demanded, and as a processing technique, techniques of high-temperature melting, heat compression, thermal decomposition, and volume reduction by using a solvent or the like have been conventionally developed (Polymer Digest 1996). May issue
58-64).

[0005]

However, the heat treatment methods such as high-temperature melting, heat compression, and thermal decomposition require that styrene monomers, dimers, trimers, and substances that adversely affect the human body, such as formaldehyde and acetaldehyde, be secondary. There is a problem that occurs.

Therefore, in order to solve such a problem,
A method for plasticizing waste plastic using a solvent without burning has been developed, and such an apparatus is shown in FIG.

[0007] As shown in FIG.
A plastic waste material is first plasticized by a melting device 21 and then dried by a drying device 22 to remove the solvent.

However, even when the treatment is performed at a low temperature using a solvent or the like, even if the outflow of the exhaust gas itself can be prevented, there is a possibility that the solvent itself volatilizes and flows out of the system.

[0009] Further, there is a possibility that a solvent may remain in the recycled plastic product, and there is a problem that it becomes an obstacle when processing the secondary product.

In order to evaporate the solvent from the product,
The problem of secondary generation of malignant substances due to high heat, such as heating to 200 ° C. or higher, cannot be solved.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. Even if a method of reducing the volume of waste plastics, especially waste styrofoam using a solvent, is used, the recycled plastics can be used. Provided is a method and an apparatus for recycling waste plastic, in which no solvent remains in the material, no volatilization of the solvent, and no secondary generation of malignant substances occurs, and furthermore, deterioration of the quality of the secondary product can be prevented. The task is to

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention has been made as a method and an apparatus for recycling waste plastic. After plasticizing with a solvent, a supercritical fluid or a subcritical fluid is brought into contact with the waste plastic to extract and remove the solvent remaining in the waste plastic for regeneration.

Another feature of the waste plastic recycling method is that plasticizing the waste plastic using a solvent, molding, and then contacting the waste plastic with a supercritical fluid or a subcritical fluid, The purpose is to extract and remove the solvent remaining in the waste plastic to regenerate it.

[0014] It is also possible to recover a used solvent obtained by plasticizing waste plastic and to bring it into contact with a supercritical fluid or a subcritical fluid for regeneration.

A feature of the waste plastic regenerating apparatus is that the extraction apparatus 3 for bringing a supercritical fluid or a subcritical fluid into contact with the waste plastic plasticized by the solvent to extract and remove the solvent remaining in the waste plastic is provided. To have.

Further, another characteristic of the waste plastic recycling device is that a molding device 2 for molding waste plastic plasticized by a solvent, and a supercritical fluid or subcritical fluid is added to the waste plastic molded by the molding device 2. An extraction device 3 for contacting a fluid to extract and remove a solvent remaining in the waste plastic.

It is also possible to provide a regenerating device 4 for recovering the used solvent obtained by plasticizing the waste plastic and regenerating it by contacting a supercritical fluid or a subcritical fluid.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic block diagram of a waste plastic recycling apparatus as one embodiment.

The waste plastic recycling apparatus according to the present embodiment comprises:
As shown in FIG. 1, a mixing device 1 for mixing a waste plastic and a solvent in order to dissolve and plasticize a waste material of the plastic, that is, a part of the waste plastic, and a waste plastic plasticized by the mixing device 1 A molding apparatus 2 for molding a plastic, an extraction apparatus 3 for bringing a supercritical fluid into contact with the molded plastic to extract and remove a solvent, and a used solvent obtained by plasticizing waste plastic with the mixing apparatus 1. And a regenerating device 4 for recovering by contacting with a supercritical fluid or a subcritical fluid.

Although not shown, the mixing apparatus 1 is provided with a stirrer for plasticizing waste plastic with a solvent.

The molding apparatus 2 is configured to be able to extrude plasticized waste plastic into a desired shape, and has a function of extruding and drying. In the present embodiment, waste polystyrene is used as the waste plastic.

Since the supercritical fluid is supplied, the extraction device 3 is made of pressure-resistant stainless steel.

The regenerating device 4 is also made of pressure-resistant stainless steel because the supercritical fluid is supplied.

The waste plastic recycling apparatus of this embodiment is
Further, a solvent pump 5, a fluid pump 6, a fluid recovery device 7, and reduced pressure separation devices 8, 9 are provided.

The solvent pump is a pump for supplying a solvent to the mixing device 1. In the present embodiment, the solvent pump contains dimethyl glutarate, dimethyl adipate, and dimethyl succinate (trade name: Stylo). Solve:
Stylo Japan Co., Ltd.) is used.

The fluid pump 6 is for supplying a fluid used as a supercritical fluid to the extraction device 3, and in this embodiment, carbon dioxide is used as the fluid.

On the other hand, the reduced pressure separation device 8 separates the solvent and the supercritical fluid extracted by the extraction device 3 under reduced pressure.

The other pressure-reduction device 9 separates the solvent and the supercritical fluid recovered by the regenerating device 4 under reduced pressure.

As the decompression / separation device 9, a device having a back pressure valve is used.

The back pressure valve is configured to open at a pressure equal to or higher than a set pressure, and has a function of keeping the pressure constant.

In addition, the waste plastic recycling apparatus of the present embodiment is provided with a piping section (shown in a diagram) and the like.

The waste plastic recycling apparatus of the present embodiment has the above-described configuration. Next, an embodiment of a recycling method for recycling waste styrene as an example of waste plastic using the waste plastic recycling apparatus will be described. I do.

First, waste polystyrene foam is supplied to the mixing device 1.

A solvent is supplied to the mixing device 1 by a solvent pump 5.

By supplying the solvent as described above,
The waste plastic in the mixing device 1 will be plasticized.

Next, the waste plastic plasticized in this way is supplied to a molding device 2 and extruded into a desired shape by the molding device 2.

In the molding apparatus 2, the waste plastic is extruded and dried at the same time.

Next, the molded waste plastic is supplied to the extraction device 3, to which carbon dioxide is supplied from the fluid pump 6. After that, the temperature and pressure are adjusted to obtain a supercritical fluid state.

When the supercritical carbon dioxide comes into contact with the waste plastic, the solvent in the waste plastic is extracted and removed.

The solvent extracted and removed is separated from the solvent by a vacuum separator 8.
And supplied to the regenerating device 4 to be collected.

The carbon dioxide separated by the decompression device 8 is recovered by the fluid recovery device 7 and returned to the fluid pump 6 for reuse.

The used solvent obtained by plasticizing the waste plastic in the mixing device 1 is supplied to the regenerating device 4 and collected.

Carbon dioxide is supplied from the fluid pump 6 to the regenerating device 4 and comes into contact with the used solvent.
Thus, the used solvent and the like collected by the regenerating device 4 are purified and regenerated.

The solvent thus regenerated by the regenerating device 4 is returned to the solvent pump 5 and reused.

On the other hand, the waste plastic from which the solvent has been extracted and removed expands when the pressure is reduced through the decompression / separation device 8 after the extraction and removal of the solvent by contact with the supercritical carbon dioxide in the extraction device 3. The same effect as foaming can be obtained.

Therefore, when the supercritical carbon dioxide comes into contact with the waste plastic, the solvent in the molded waste plastic is extracted and removed, and at the same time, the regenerated foam molded into a desired shape by swelling like a pseudo foam. Used as plastic products.

As described above, in the present embodiment, the solvent contained in the waste plastic could be almost removed when the waste material of the styrene foam was dissolved, molded, and regenerated.

The solvent and the supercritical carbon dioxide can be reused repeatedly.

(Embodiment 2) This embodiment is another embodiment of the method for recycling waste plastic.

The waste plastic recycling apparatus according to the present embodiment
As shown in FIG. 2, a mixing device 1, an extraction device 3, a recovery device 4, a solvent pump 5, a fluid pump 6, a fluid recovery device 7, and reduced pressure separation devices 8, 9 are provided. Common to 1.

However, the present embodiment does not include the molding device 2 as shown in FIG.
Is different from

That is, in this embodiment, the solvent is extracted and removed with the supercritical fluid as it is, without being formed into the waste plastic dissolved by the solvent, and the plastic is separated under reduced pressure to produce a product.

In this embodiment, the waste plastic is first plasticized by the mixing device 1 and then supplied to the extraction device 3 where the solvent is extracted by the carbon dioxide supplied from the fluid pump 6. Done.

The extracted solvent is separated from the supercritical carbon dioxide under reduced pressure by the reduced pressure separation device 8, and the solvent is recovered by the regeneration device 4.
The operation of recovering carbon dioxide by the fluid recovery device 7 and the like are performed in the same manner as in the first embodiment.

The present embodiment is different from the first embodiment in that waste plastic that has not been extruded is solvent-extracted with supercritical carbon dioxide and commercialized.

Also in this embodiment, the solvent contained in the waste plastic can be almost removed, the waste plastic can be regenerated, and the solvent and carbon dioxide can be reused repeatedly.

(Other Embodiments) In the above embodiment, a case was described in which styrofoam waste was used as waste plastic. However, the type of waste plastic is not limited to this. It is also possible to use waste materials.

Further, the present invention is not limited to the foamable synthetic resin, and it is also possible to use, for example, polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate and the like.

The type of fluid used for the extraction is not limited to the carbon dioxide of the above embodiment, but may be, for example, nitrous oxide.

However, carbon dioxide is mainly used because it has the property of suitably plasticizing the synthetic resin.

The present invention is mainly directed to using a supercritical fluid, but uses a subcritical fluid at a temperature slightly lower than the temperature in the supercritical state or a pressure slightly lower than the pressure in the supercritical state. It is also possible.

That is, even if a subcritical fluid such as subcritical carbon dioxide is brought into contact with the waste plastic, the solvent in the waste plastic can be extracted and removed.

Incidentally, fluids such as carbon dioxide and nitrous oxide
Preferably, it is used at a temperature of 25-100 ° C. and a pressure of 50-500 atm.

At a temperature of 25 ° C. or less or a pressure of 50 atm or less,
This is because carbon dioxide and nitrous oxide are unlikely to be in a subcritical state.

At a temperature of 100 ° C. or higher, gas may be generated depending on the type of waste plastic, or may be inadvertently decomposed into monomers and the like.

Further, if the pressure is 500 atm or more, there is a possibility that the operation of the apparatus including the fluid pump or the like may be hindered.

By the way, carbon dioxide has a critical temperature of 31.1.
° C, the critical pressure is 73.0 atm, and nitrous oxide has a critical temperature of 36.5 ° C and a critical pressure of 71.7 atm.

Further, in the above embodiment, as the solvent,
Although those containing dimethyl glutarate, dimethyl adipate, and dimethyl succinate (trade name: Stylosolve: Stylo Japan) were used, those containing one or two of these components may also be used. Is possible,
Further, d-limonene (manufactured by Yashara Chemical) can be used.

Further, in the above embodiment, the solvent is extracted and removed from the waste plastic only with the supercritical fluid. However, an entrainer such as a lower alcohol such as methanol, ethanol or propanol (also referred to as an auxiliary solvent or a co-solvent) is used. ) Can be used together with a supercritical fluid to extract and remove the solvent.

Furthermore, in the above embodiment, stainless steel is used as the extracting device 3 and the regenerating device 4, but the material of the extracting device 3 and the regenerating device 4 is not limited to this.

However, from the viewpoint of maintaining the corrosion resistance,
Those made of stainless steel are preferred.

Further, in the above embodiment, the solvent extracted and removed by the extraction device 3 and separated by the reduced pressure separating device 8 from the supercritical fluid under reduced pressure is recovered by the regenerating device 4. Since the solvent is different from the used and mixed with the waste plastic in the mixing device 1 and does not particularly contain impurities, the solvent can be directly returned to the solvent pump 5 without being recovered by the regenerating device 4. It is.

[0074]

Embodiments of the present invention will be described below.

(Example 1) As waste plastic, plasticized with a solvent, dried and molded was used. At this time, the content of the solvent in the waste plastic is about 15% by weight.
%Met.

As a test method, 2.60 g of waste plastic was charged into a high-pressure cell, adjusted to 300 atm and 40 ° C., and then carbon dioxide was passed at a flow rate of 1 mL / min for 5 hours.

As a result, the weight of the waste plastic was 2.27 g.
Decreased to. The weight loss rate was 13%, and the solvent content in the waste plastic at this time was 2.6%.

Example 2 As waste plastic, plasticized with a solvent, dried and molded was used. At this time, the content of the solvent in the waste plastic was about 15% by weight.
%Met.

As a test method, 2.57 g of waste plastic was charged into a high-pressure cell, adjusted to 300 atm and 27 ° C., and then carbon dioxide was passed at a flow rate of 1 mL / min for 5 hours.

As a result, the weight of the waste plastic was 2.36 g.
Decreased to. The weight loss was 8%, and the solvent content in the waste plastic at this time was 7.6%.

(Comparative Example 1) As waste plastic, plasticized with a solvent, dried and molded was used. At this time, the content of the solvent in the waste plastic was about 15% by weight.
%Met.

As a test method, 3.05 g of waste plastic was used.
Was vacuum dried on a rotary evaporator at 60 ° C. for 5 hours.

As a result, the weight of the waste plastic was 2.93 g.
Decreased to. The weight loss rate was 4%, and the solvent content in the waste plastic at this time was 12%.

(Comparative Example 2) 2.85 g of waste plastic
Was vacuum dried on a rotary evaporator at 40 ° C. for 5 hours.

As a result, the weight of the waste plastic was 2.81 g.
Decreased to. The weight loss rate was 1%, and the solvent content in the waste plastic at this time was 14%.

FIG. 3 shows the results of the weight reduction ratios of Examples 1 and 2, and Comparative Examples 1 and 2.

As is clear from FIG. 3, in Examples 1 and 2, the rate of weight loss was higher than in Comparative Examples 1 and 2, and the solvent was more preferably extracted and removed than in Comparative Examples. It was confirmed that it was done.

(Example 3) As waste plastic, plasticized with a solvent was used as it was. At this time, the content of the solvent in the waste plastic was about 67% by weight.

As a test method, 1.71 g of plasticized waste plastic was charged into a high-pressure cell and adjusted to 300 atm and 50 ° C., and then 1 mL / min of carbon dioxide and 0.1 mL / min of methanol as an entrainer were combined. For 5 hours.

As a result, the weight of the waste plastic was 0.61 g.
Decreased to. The weight loss rate was 64%, and the solvent content in the waste plastic at this time was 8%.

In Examples 1 and 2, as the high-pressure cell, a SUS316 10 mL solid material cell was used.

As the supercritical fluid, liquefied carbon dioxide gas having a purity of 99.99% manufactured by Liquefied Carbonate Co., Ltd. was used.

[0093]

As described above, in the present invention, a supercritical fluid or a subcritical fluid is brought into contact with waste plastic after plasticization with a solvent, and the ability to penetrate into a solid such as a supercritical fluid is obtained.
By utilizing the extraction ability of the solvent, the solvent remaining in the recycled plastic material can be suitably extracted and removed.

Further, the supercritical fluid does not remain in the recycled plastic, and a step of drying the plastic material after that is not necessary.

Furthermore, the waste plastic from which the solvent has been extracted and removed expands in a pseudo-foaming manner by contacting it with a supercritical fluid or a subcritical fluid. Can be provided.

Further, in the case of molding after plasticizing the waste plastic with a solvent, a supercritical fluid or a subcritical fluid is brought into contact with the molded waste plastic,
There is an advantage that a step of molding a regenerated product after extraction and removal of the solvent is not required.

Further, when a used solvent obtained by plasticizing waste plastic is recovered and regenerated by contacting a supercritical fluid or a subcritical fluid, a new solvent can be used at all times, and the plasticizing treatment of waste material can be performed. Can be performed efficiently.

Further, there is an advantage that the use amount of the solvent is not inadvertently increased.

Further, it is possible to collect and reuse the solvent which has been released outside the system at the time of drying.

Further, when an entrainer such as methanol is used in combination with a supercritical fluid, a larger amount of the solvent contained in the waste plastic can be extracted and removed, and the effect of extracting and removing the solvent is more remarkable. Become.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a waste plastic recycling device according to one embodiment.

FIG. 2 is a schematic block diagram of a waste plastic recycling apparatus according to another embodiment.

FIG. 3 is a graph of an experimental result of an example.

FIG. 4 is a schematic block diagram of a conventional waste plastic recycling apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Mixing device 2 ... Molding device 3 ... Extraction device 4: Regeneration device

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Takashi Moriyoshi 2217-43 Hayashi-cho, Takamatsu-shi, Kagawa Prefecture Inside the High-Temperature-High-Pressure Fluid Research Laboratory (72) Inventor Tsutomu Nakanishi 2217-43 High-Temperature-High-Pressure Fluid Technology Research in Takamatsu-shi, Kagawa Prefecture On-site F term (reference) 4D056 AB17 AB20 AC24 BA16 CA18 CA20 CA21 CA31 CA37 4F301 AA13 AA14 AA15 AA17 AA25 CA03 CA09 CA12 CA35

Claims (6)

[Claims] Claims: 1. A waste plasticized by plasticizing waste plastic with a solvent, and then contacting the waste plastic with a supercritical fluid or a subcritical fluid to extract and remove the solvent remaining in the waste plastic and regenerate the waste plastic. How to recycle plastic. 2. Plasticizing the waste plastic with a solvent, molding, and then contacting the waste plastic with a supercritical fluid or a subcritical fluid to extract and remove the solvent remaining in the waste plastic for regeneration. A method for recycling waste plastics. 3. The method for reclaiming waste plastic according to claim 1, wherein the used solvent obtained by plasticizing the waste plastic is recovered and regenerated by contacting a supercritical fluid or a subcritical fluid. 4. A waste equipment comprising an extraction device (3) for bringing a supercritical fluid or a subcritical fluid into contact with waste plastic plasticized by a solvent to extract and remove a solvent remaining in the waste plastic. Plastic recycling equipment. 5. A molding apparatus (2) for molding waste plastic plasticized by a solvent, and a supercritical fluid or a subcritical fluid is brought into contact with the waste plastic molded by the molding apparatus (2) to form the waste plastic. And an extraction device (3) for extracting and removing the solvent remaining in the waste plastic. 6. The waste apparatus according to claim 4, further comprising a regenerating device for recovering a used solvent obtained by plasticizing the waste plastic and regenerating the used solvent by contacting a supercritical fluid or a subcritical fluid. Plastic recycling equipment.