JP2000053800A - Decomposition treatment of waste plastic and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuously operatable method for carrying out decomposition treatment of a waste plastic, capable of recovering a high-purity monomer, hardly containing an insoluble impurity content of catalyst, etc. SOLUTION: In this waste plastic decomposing treatment method for reacting supercritical water or subcritical water with a waste plastic to hydrolyze the waste plastic and recovering the resultant monomer, a treating fluid after hydrolysis treatment is filtered with a filtering body after hydrolysis treatment under temperature conditions of 200-500 deg.C to remove insoluble impurity and the monomer is recovered and when the difference pressure between the inlet and the outlet of the filtering body becomes definite pressure or above, the filtering body is reversely washed with supercritical water or subcritical water and regenerated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a decomposition method for recovering monomers from waste plastics such as discarded polyethylene terephthalate and an apparatus used therefor.

[0002]

2. Description of the Related Art There are various methods of treating waste plastic, such as a landfill method and a combustion method. As a method of not discharging harmful waste, there is a chemical recycling method in which waste plastic is decomposed into monomers and turned into resources. . The Chemical Recycling Law is a treatment method that is useful for environmental protection, in which raw materials can be collected and no waste is generated.

[0003] Since the Containers and Packaging Recycling Law was enforced in April 1997, polyethylene terephthalate (hereinafter, referred to as "polyethylene terephthalate") has been introduced.
The demand for recycling PET (abbreviated as PET) is increasing.
As a chemical recycling method of PET, a method of decomposing PET by a solvolysis reaction using a solvent such as an alcohol or glycol in the presence of a catalyst to recover a monomer is known. However, the alcohol solvolysis method uses a large amount of a solvent such as alcohol and requires a catalyst, so that the cost is high, and the use of alcohol having a low flash point involves danger.
There is a problem in the method of recovering T.

[0004] In recent years, supercritical water splitting has attracted attention in chemical recycling. Supercritical water splitting is a method of recovering terephthalic acid and ethylene glycol by hydrolyzing PET with supercritical or subcritical water,
This is an excellent method in that monomers can be recovered without using an organic solvent or a catalyst.

[0005]

A number of patents have been filed for a chemical recycling method of PET using supercritical water or subcritical water (for example, Japanese Patent Publication No. Hei 3-16).
No. 328, JP-A-8-3022061, JP-A-5-3
No. 1000, JP-A-9-77905), and a technique for recovering high-purity terephthalic acid that can be reused as a monomer has not been found.

[0006] In order to reuse terephthalic acid recovered from waste PET as a monomer such as polyester, a high-purity terephthalic acid with a small amount of foreign matter (pigment, catalyst) is required. Therefore, in the supercritical water splitting method for recovering terephthalic acid from waste PET, removal of impurities is an important issue.

[0007] In general, an inorganic catalyst such as antimony oxide is used for the polymerization of PET, and these remain in the product PET as they are. For opaque products such as fibers, inorganic pigments such as titanium oxide are usually used. Therefore, when PET is hydrolyzed to terephthalic acid and ethylene glycol with supercritical water or subcritical water, inorganic components such as catalysts and pigments remain in the processing fluid as fine solids. Since these impurities usually have a small primary particle size of 1 μm or less, their removal is extremely difficult, and there is a problem that terephthalic acid is mixed in when the crystals are recovered.

As a general method for removing fine solids in a liquid, a method using a filter such as a ceramic filter is known. When this method is applied to the hydrolysis of PET, the solubility of terephthalic acid in water changes remarkably depending on the temperature. Therefore, it is necessary to perform filtration under a temperature condition at which terephthalic acid is completely dissolved in water.

[0009] Further, since the filter is clogged with time, it is necessary to periodically backwash the filter to remove clogged solids in order to perform continuous treatment. If the temperature is lowered during washing, terephthalic acid precipitates and blocks the filter body, or causes problems such as precipitation in the housing of the filter body or in the piping.

[0010] The problem to be solved by the present invention is PET.
When recovering monomers by decomposing waste plastics such as by using supercritical water or subcritical water, monomers do not precipitate on the filter installed to recover high-purity monomers with a low content of insoluble impurities such as catalysts An object of the present invention is to provide a waste plastic decomposition treatment method and a device capable of continuous operation including such a backwashing means.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a method of recovering a monomer produced by reacting supercritical water or subcritical water with waste plastic to hydrolyze the waste plastic and recovering a monomer produced. In the decomposition treatment method, the treatment fluid after the hydrolysis treatment is filtered through a filter under a condition in which the monomer is dissolved, specifically, at a temperature of 200 to 500 ° C. to remove the insoluble impurities to remove the monomer. When the pressure difference between the inlet and the outlet of the filter body is higher than a certain pressure, for example, the differential pressure is 0.1 to 5.0 MPa,
Preferably, a method for decomposing waste plastics, characterized in that the filter is backwashed with supercritical water or subcritical water to regenerate the filter at a pressure of 0.2 to 1.0 MPa. It is.

Another aspect of the present invention for solving the above problems is to provide a reactor, a supply system for supplying an object to be treated containing waste plastic and supercritical water or subcritical water to the reactor, 200-500 ° C.
A separation system for removing insoluble impurities by filtration through a filter under the temperature conditions of the above, wherein the backwash means using supercritical water or subcritical water as a backwash medium in the filter. The present invention relates to an apparatus for decomposing waste plastics, characterized in that:

Here, supercritical water refers to water having a temperature of 374 ° C. or higher and a pressure of 22 MPa or higher.
Shows liquid water at ３７374 ° C. In the present invention, a reactor for hydrolyzing waste plastic using supercritical water or subcritical water may be a pipe type or a vessel type. The hydrolysis conditions in the supercritical state of water in the present invention are such that the reaction temperature is 374 ° C. or higher and the pressure is 22-50 MPa.
Hydrolysis conditions in a subcritical state of water include a reaction temperature of 200 to 374 ° C. and a pressure of 1.6 to 50.
It may be performed in MPa.

Examples of the waste plastic to be treated in the present invention include plastics such as PET, 6-nylon, 6-6 nylon, 6-10 nylon and polycarbonate.

Taking PET as an example, when PET is treated in supercritical water or subcritical water, a hydrolysis reaction proceeds, and the PET is decomposed into terephthalic acid and ethylene glycol, which are the raw material monomers for PET.

Since the polyester such as PET contains a catalyst for polymerizing the monomer and insoluble impurities such as inorganic pigments, the processing fluid after the hydrolysis treatment contains the monomer, supercritical water or subcritical water. It consists of water and impurities insoluble in these fluids. Therefore, it is necessary to remove the insoluble impurities by filtering the fluid after hydrolysis with a filter.

The filter is not particularly limited as long as it can filter a high-temperature fluid. However, a filter made of ceramic such as alumina, a laminated metal mesh filter, a metal nonwoven fabric filter, or a sintered metal filter made of stainless steel or the like may be used. Good.

Monomers such as terephthalic acid which are solid at normal temperature are also in solution at high temperature and high pressure. Therefore, by filtration under high temperature and high pressure, only insoluble impurities such as catalyst in the hydrolyzed fluid can be captured on the filter body by filtration, and do not contain insoluble impurities from the liquid after filtration. High-purity terephthalic acid can be recovered. However, during continuous filtration, the filter is clogged by the trapped insoluble impurities, the differential pressure of the filter increases, and continuous processing becomes difficult.

Therefore, when the filter is clogged and the pressure difference between the inlet and the outlet becomes equal to or higher than a predetermined pressure, the filter is backwashed. The differential pressure at which backwashing is performed varies depending on the type of the filter, the type of insoluble impurities to be removed, the particle size, and the like, but is usually preferably in the range of 0.1 to 1.0 MPa. Supercritical water or subcritical water at 200 to 500 ° C. is used as a medium for the backwashing treatment. If the temperature of the backwashing treatment medium is lower than 200 ° C., clogging of the filter body due to precipitation of terephthalic acid or the like occurs, and if it exceeds 500 ° C., side reactions such as decarboxylation of terephthalic acid or condensation of ethylene glycol occur to produce The yield decreases. By using supercritical water or subcritical water as a medium for the backwash treatment, solidification of a monomer such as terephthalic acid which is solid at room temperature can be prevented, so that the filtration surface and piping are not blocked.

When the filter is backwashed, terephthalic acid in the housing housing the filter is extruded with supercritical water or subcritical water at a low flow rate and then with supercritical water or subcritical water. By performing the backwashing treatment, the recovery rate of terephthalic acid can be increased, and the amount of terephthalic acid in the backwash wastewater can be reduced.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a flow chart showing an outline of a waste plastic decomposition treatment apparatus according to a fourth aspect for waste PET.

The waste PET to be treated is 270 to 300
Heated to ° C. and melted, and stored in waste PET melting tank 1. The molten waste PET is supplied from a pipe 4 to a pump 5, where it is pressurized and reaches a pipe 6. Water is supplied to a pump 18 via a pipe 17, where the water is pressurized and heated by a heater 7 to become supercritical water or subcritical water at 200 to 500 ° C. and reaches the pipe 3. Both fluids of the pipe 6 and the pipe 3 join at the pipe 8 and are supplied to the reactor 9. The supply system is configured as described above.

The reactor 9 may be a known vertical reactor called a vessel type or a tubular reactor called a pipe type, as shown in FIG. Is a Bessel reactor.

Waste PET introduced (supplied) to the reactor 9
Is mixed with water in a supercritical state or a subcritical state, so that a hydrolysis reaction proceeds and becomes a monomer and is dissolved in the supercritical water or the subcritical water. Processing fluid consisting of monomer, insoluble impurities and supercritical water or subcritical water is supplied to discharge pipe 1
It is discharged via 0.

The flow shown in FIG. 1 is provided with two filtration means for continuous filtration, and the steps of filtration and backwashing will be described with reference to FIG.

First, the valves v1 and v3 are opened (v
2. The valves v4 to v11 are closed), and the processing fluid from the discharge pipe 10 is filtered by the first filter 11. Insoluble impurities in the processing fluid are captured by the first filter 11.

If insoluble impurities accumulate on the filtration surface of the first filter 11 and the differential pressure reaches a certain pressure or higher, v
At the same time as closing the valves 1 and v3, v2 and v
The valve of No. 4 is opened, and the filtration of the processing fluid is continued with the second filter.

Prior to backwashing the first filter 11, it is preferable to perform an extrusion process in order to collect the processing fluid remaining in the first filter 11 and the piping. In order to perform the extrusion process, the valve of v1 is closed, the valves of v3 and v10 are opened, and supercritical water or subcritical water is supplied to the first filter 11 through the backwashing pipe 2, and the first filter 11 And, the processing fluid remaining in the pipe is pushed out and collected. It is preferable to carry out the extrusion treatment until the recovery rate becomes about 90%.

Next, the first filter 11 is backwashed. Close the valves v3 and v10, v5, v7,
Open the v9 valve and use supercritical water or subcritical water.
The first filter 11 is backwashed, and the backwash solution is stored in a backwash solution storage tank 14.
Flash to When the monomer is easily solidified, it is preferable to keep the piping and the valve between the first filter 11 and the backwash liquid storage tank 14 warm.

The insoluble impurities accumulated in the backwashing liquid storage tank 14 can be recovered by means capable of transferring solids such as a Moino pump.

When the pressure difference in the second filter 12 rises above a certain level, a backwashing process is performed as in the case of the first filter 11 described above.

First, the valves v2 and v4 are closed, and at the same time, the valves v1 and v3 are opened, and the first filter 11 continues to filter the processing fluid.

Next, before the backwashing process of the second filter 12 is performed, it is preferable to perform the extrusion process as described above in order to recover the processing fluid remaining in the second filter 12 and the piping. V2 to perform the extrusion process
Is closed, the valves v4 and v11 are opened, supercritical water or subcritical water is supplied to the second filter 12, and the processing fluid remaining in the second filter 12 and the piping is extruded and collected.

Next, the second filter 12 is backwashed. v4 and v11 valves are closed, v6, v8,
Open the v9 valve and use supercritical water or subcritical water.
The second filter 12 is backwashed, and the backwash solution is stored in a backwash solution storage tank 14.
Flash to When the monomer is easily solidified, it is preferable to keep the temperature of the pipes and valves between the second filter 12 and the backwash liquid storage tank 14 as described above.

As shown in FIG. 1, by providing two or more filtration means, when the filter body is clogged and the differential pressure becomes equal to or higher than a predetermined pressure, the other filter body is subjected to a backwashing process while performing a backwashing process. To perform a filtration operation, and can continuously operate the decomposition processing of the waste PET. Unless the waste PET is continuously treated, the filter body is used as one system, and when backwashing is required, the processing fluid from the reactor 9 is stored in a storage tank (not shown) kept warm during the backwashing. You may do so.

The method of recovering the monomer from the filtered processing fluid is not particularly limited, but may be, for example, the processing shown in FIG.

That is, the processing fluid after filtration is supplied to the cooler 1
5, the terephthalic acid solidifies and precipitates from the processing fluid, and ethylene glycol and water remain on the liquid side. Next, a liquid and a solid are separated by a solid-liquid separator 16 such as a centrifugal separator, and the solid is transferred to a terephthalic acid storage tank 19.
The liquid component is transferred to the distillation apparatus 20. The solid is pure terephthalic acid without any insoluble impurities and can be reused as a monomer or the like. On the other hand, by distilling the liquid component, ethylene glycol and water can be separated and recovered.

[0038]

As described above, according to the present invention, a monomer obtained by hydrolyzing waste plastic with supercritical water or subcritical water is filtered through a filter to remove insoluble impurities in the monomer. Supercritical water or subcritical water is used for backwashing the filter used to recover the high-purity raw material monomer, so that the temperature does not decrease and the monomer remains in the filter, its housing, and piping. Since the filter does not precipitate, the filter can be used repeatedly, and the device can be operated continuously for a long period of time.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an embodiment of the apparatus of the present invention.

FIG. 2 is a flow diagram illustrating one embodiment of recovering monomers from a processing fluid after filtration of waste PET.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Waste PET melting tank 2 Backwash pipe 3, 4, 17 pipe 5 Supply pump 6 Pipe 7 Heater 8 Pipe 9 Reactor 10 Discharge pipe 11 First filter 12 Second filter 13 Monomer recovery system 14 Backwash liquid storage tank Reference Signs List 15 cooler 16 solid-liquid separator 18 feed pump 19 terephthalic acid storage tank 20 distillation column v1 to v11 valve

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C10G 1/10 ZAB B09B 3/00 304P B29K 67:00 105: 26 (72) Inventor Akira Suzuki Koto, Tokyo 1-8-2 Shinsuna-ku, Organo Co., Ltd. (72) Inventor Tomoyuki Iwamori 1-8-2 Shinsago, Koto-ku, Tokyo Organo Co., Ltd. (72) Inventor Shinichiro Kawasaki 1-chome, Shinsuna, Koto-ku, Tokyo No.2 No.8 Organo Corporation F-term (reference) 4F074 AA66 AC16 AD04 AD09 EA07 EA23 EA51 EA53 EA64 EA65 EA68 EA72 EA73 4F201 AA24 AA50 AH03 AR02 AR06 BA04 BC01 BC02 BC12 BC25 BN01 BN44 A03 BP19 4B29 A29 BP19 4A29 BA03 CB06A KD02 KD09 KG02 LB10

Claims (6)

[Claims] In a method for decomposing a waste plastic in which supercritical water or subcritical water is reacted with waste plastic to recover a monomer produced by hydrolyzing the waste plastic, a processing fluid after the hydrolysis treatment is used in a method for treating a waste plastic in a water-repellent state. Under a temperature condition of 500 ° C., the monomer is recovered by filtering through a filter to remove insoluble impurities, and when the pressure difference between the inlet and the outlet of the filter becomes a certain pressure or more, the filter is replaced with supercritical water. Alternatively, a method of decomposing waste plastics, comprising backwashing with subcritical water and regenerating the same. 2. The method according to claim 1, wherein the waste plastic is waste polyethylene terephthalate, and the monomer is terephthalic acid. 3. The method according to claim 1, wherein the filter is a ceramic filter or a sintered metal filter. 4. A reactor, a supply system for supplying an object to be treated containing waste plastic and supercritical water or subcritical water to the reactor, and a hydrolyzed processing fluid of 200 to 5 times.
In a waste plastic decomposition treatment apparatus provided with a separation system for removing insoluble impurities by filtering through a filter at a temperature of 00 ° C., a backwashing means using supercritical water or subcritical water as a backwash medium in the filter An apparatus for decomposing waste plastic, comprising: 5. The apparatus according to claim 4, wherein the filter is a ceramic filter or a sintered metal filter. 6. The waste plastic decomposition treatment apparatus according to claim 4, wherein two or more filtration bodies are provided in parallel, so that the backwashing treatment and the filtration treatment can be performed simultaneously. .