JP2009007416A - Method for degrading plastic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for degrading a plastic by which a fluid in a reaction vessel can efficiently be heated up in degradation of the plastic etc., with a fluid in the supercritical state or the subcritical state and the apparatus efficiency can be improved. <P>SOLUTION: There are provided a step (A) of feeding a plastic molded product 2 and the fluid 3 to the reaction vessel 1 and carrying out a degradation treatment of the plastic molded product 2 in the supercritical state or the subcritical state and a step (B) of newly feeding the plastic molded product 2 to the fluid 3 in which the degradation product of the plastic molded product 2 subjected to the degradation treatment in the step (A) is dissolved and carrying out the degradation treatment of the plastic molded product 2 in the supercritical state or the subcritical state. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for decomposing plastics.

  Conventionally, for example, detoxifying and decomposing harmful substances, decomposing and recycling food waste, etc., or decomposing plastic waste and synthesizing plastic raw materials such as organic acids and alcohols or FRP ( In order to collect and reuse the glass fiber in the glass fiber reinforced plastic), it has been proposed as a configuration of various apparatuses to decompose by a supercritical or subcritical hydrothermal reaction.

  However, for example, in the decomposition of plastics using a fluid in a supercritical state or a subcritical state as in Patent Document 1, a mixture of crushed granular plastic and fluid becomes a slurry of solid-liquid mixing. However, it is not always easy to supply the raw material into the reaction tank and continuously take out the reaction solution from the reaction tank. The reason for this is that, firstly, the pump for feeding the slurry-like mixed liquid at a high temperature and high pressure is expensive, and problems such as wear of parts due to solid matter are likely to occur, and secondly, This is because it is difficult to discharge the entire amount of unreacted solids remaining in the reaction tank while ensuring the reactivity. In particular, when the plastic is FRP, inorganic components such as glass fiber having a high specific gravity and calcium carbonate remain unreacted, and it is difficult to discharge the reaction solution with these components having high sedimentation properties.

  In such a case, a batch reactor as shown in FIG. 7 is employed. The batch method is a batch process, and the input raw material (FRP) is extracted as it is after the reaction of one batch. When the reaction product is taken out from the reaction vessel 1, the reaction vessel 1 is in a supercritical state or a subcritical state, and thus is in a high temperature / high pressure state. It needs to be cooled. Moreover, in order to take out a decomposition product, it is necessary to depressurize the inside of the reaction tank 1 to a normal pressure. In the next batch, it is necessary to reheat the fluid 3 in the normal temperature state to the supercritical state or the subcritical state. Therefore, in the processing including the series of operations as described above, the processing time is generally long, and a large amount of heat is used for heating the fluid, so that there are significant problems in terms of productivity and cost.

Therefore, it is conceivable to adjust the supply amounts of the plastic and the fluid so that the plastic concentration in the fluid becomes as high as possible in the reaction tank and supply the plastic and the fluid to the reaction tank. However, the plastic concentration naturally has an upper limit, and if the treatment is performed in the vicinity of the upper limit, there arises a new problem that solids adhere to the inner wall surface of the high-temperature reaction tank. Furthermore, batch processing is still performed, and there is a limit to improving the efficiency of the apparatus, such as shortening the heating time of the fluid and reducing the required heat amount, only by adjusting the supply amount of the plastic and fluid to the reaction tank.
JP 2006-232942 A

  The present invention has been made in view of the circumstances as described above, and can efficiently raise the temperature of the fluid in the reaction tank in the decomposition of the plastic or the like in the fluid in the supercritical state or the subcritical state, thereby improving the efficiency of the apparatus. It is an object of the present invention to provide a plastic decomposition method that can be improved.

  The present invention is characterized by the following in order to solve the above problems.

  First, in the method for decomposing a plastic according to the present invention, a process (A) in which a plastic molded article and a fluid are supplied to a reaction vessel, and the plastic molded article is decomposed in a supercritical or subcritical state, and the process (A) And a step (B) of newly supplying the plastic molded product to the fluid in which the decomposition product of the plastic molded product decomposed in step 1 is dissolved, and decomposing the plastic molded product in a supercritical or subcritical state.

  Second, in the first invention, the step of taking out the contents from the reaction vessel between the step (A) and the step (B), solid-liquid separating it, and supplying the separated liquid to the reaction vessel. The method for decomposing a plastic according to claim 1, comprising:

  Third, in the first invention, after the step (A), the fluid in the lower part of the reaction tank containing the undecomposed component of the plastic molded product settled on the bottom of the reaction tank is taken out from the reaction tank, and in the step (B), A fluid of the same degree as the taken-out fluid is newly supplied to the reaction tank together with the plastic molded product.

  Fourthly, in any one of the first to third inventions, in step (B), the plastic is pressurized to a pressure at least equal to the internal pressure of the reaction tank that is decomposed in a supercritical or subcritical state. A plastic molded product is supplied to the reaction tank from the supply unit.

  Fifth, in any one of the first to fourth inventions, after the step (B) is repeated a predetermined number of times, the contents are taken out from the reaction tank and solid-liquid separated to obtain a decomposed plastic molded product. The step of removing the dissolved component of the plastic molded product decomposition product from the separated solution containing the dissolved component and supplying the remaining separated solution to the reaction vessel.

  Sixth, in any one of the first to fourth inventions, after repeating step (B) a predetermined number of times, a fluid is supplied to the reaction tank to reduce the concentration of the plastic molded product decomposition product, and then the reaction tank The contents of are discharged.

  Seventh, in any one of the first to sixth inventions, the plastic molded article is a plastic containing an unsaturated polyester resin.

  Eighth, in any one of the first to seventh inventions, when the reaction liquid is water and the liquid temperature of the fluid in the reaction tank is lowered within the range of 80 to 100 ° C. in the step (B). Insert plastic moldings.

  According to the first aspect of the present invention, the plastic molded product is newly supplied to the reaction tank and decomposed with the fluid without discharging the fluid in which the decomposition product of the plastic molded product is dissolved in the reaction tank. Compared to the conventional method where the fluid is discharged from the reaction tank and a new fluid is supplied to the reaction tank to raise the temperature, the heating time can be shortened, and the heat consumption and fluid usage can be reduced. The apparatus efficiency can be improved.

  Further, according to the second aspect, since the solid content in the contents of the reaction vessel is removed, the amount of plastic molded product input in the next step can be the same as the initial amount. Therefore, the apparatus efficiency can be further improved.

  According to the third invention, since the fluid having a high concentration of undecomposed components of the plastic molded product in the reaction tank is removed, the concentration of the undecomposed components and decomposed products of the fluid in the reaction tank is suppressed. The Therefore, solid content can be prevented from sticking to the inner wall surface of the high-temperature reaction tank and the stirring ability of the fluid in the reaction tank can be prevented from being degraded in the decomposition treatment of the reaction tank.

  According to the fourth aspect of the present invention, by supplying a plastic molded product to the reaction tank from the plastic supply section pressurized to at least the pressure equal to the internal pressure of the reaction tank, the decomposition treatment is performed without lowering the temperature of the reaction tank. Can be started. Therefore, the cooling time of the reaction vessel can be reduced, the amount of heat consumed for heating can be reduced, and the apparatus efficiency can be further improved.

  According to the fifth aspect, since the dissolved component of the plastic molded product decomposition product is removed from the fluid in the reaction tank and the fluid is reused, it is not necessary to use a new fluid. Therefore, the total amount of fluid used can be reduced.

  According to the sixth aspect of the invention, it is possible to lower the concentration of the decomposed product of the plastic molded product of the fluid in the reaction tank and discharge the contents in the reaction tank. If the plastic product decomposition product is discharged without lowering the concentration, problems such as blockage may occur in the discharge pipe connected to the reaction tank, which may hinder subsequent operations and reduce the efficiency of the apparatus.

  According to the seventh and eighth aspects of the present invention, the above-described effect can be realized in a more concrete and reliable manner by setting the plastic molded product to be disassembled and the fluid to be used to a predetermined one. be able to.

<Embodiment 1>
FIG. 1 is a schematic view of a disassembling apparatus for explaining an embodiment of the plastic disassembling method of the first invention.

  First, a decomposition apparatus used in the decomposition method of the present invention will be described.

  The decomposition apparatus includes a plastic supply pipe 4 that supplies the plastic molded product 2 to a reaction tank 1 that decomposes the plastic molded product 2 with a fluid 3 in a supercritical or subcritical state, and a fluid supply pipe 5 that supplies the fluid 3. And are connected. A discharge pipe 6 for discharging the contents decomposed in the reaction tank 1 is connected to the bottom of the reaction tank 1, and a discharge opening / closing valve 7 is provided in the discharge pipe 6. By opening and closing the discharge opening / closing valve 7, the contents in the reaction tank 1 can be discharged through the discharge pipe 6. The reaction tank 1 is made of, for example, a stainless steel cylindrical tank and is made pressure-resistant, and a heater is provided on the outer periphery (not shown). Further, the reaction tank 1 is provided with a stirring means 8 for mixing the plastic molded product 2 and the fluid 3 introduced into the reaction tank 1 by rotation of a stirring blade by a stirring motor. There are provided a pressure detector formed by a pressure gauge or the like for measuring the pressure of the gas, a temperature sensor formed by a temperature sensor for measuring the temperature in the reaction tank 1 or the like.

  The plastic molded product 2 to be decomposed in the present invention may be any one of a thermosetting resin and a thermoplastic resin. Examples of the thermosetting resin include unsaturated polyester resins, acrylic resins, and epoxy resins. Examples of the thermoplastic resin such as resin include polyvinyl chloride resin, polyethylene resin, and polystyrene resin. Moreover, the plastic molded product 2 may contain inorganic substances such as glass fiber and calcium carbonate.

  Examples of the fluid 3 used in the present invention include water, monohydric alcohol, polyhydric alcohol, and the like, and mixtures thereof. In order to further promote the decomposition of the plastic molded product 2, potassium hydroxide, sodium hydroxide, etc. An aqueous solution of an alkali metal hydroxide can also be used as the fluid 3.

  In this embodiment, the plastic molded product 2 and the fluid 3 are separately supplied to the reaction tank 1, but the granular material obtained by pulverizing the plastic molded product 2 and the fluid 3 such as water are stirred in the pretreatment tank. After the slurry is formed, the slurry of the plastic molded product 2 and the fluid 3 may be supplied into the reaction tank 1 through a supply pipe by a liquid feed pump, for example. Further, it is possible to prevent the plastic molded product 2 supplied together with the fluid 3 in the reaction tank 1 from sinking to the lower part of the reaction tank 1 and making it difficult to undergo a decomposition reaction. The maximum particle size of the plastic molded product 2 is 30 mm or less in order to improve the mixing efficiency of the plastic molded product 2 with respect to the fluid 3 and to improve the reaction efficiency with the fluid 3 such as preventing sticking to the inner wall surface. It is preferable to use after pulverization. It is desirable that the maximum particle size of the plastic molded product 2 is smaller.

  Next, a method for decomposing plastic will be described.

  First, in the step (A), the plastic molded product 2 and the fluid 3 are supplied to the reaction tank 1 from the plastic supply pipe 4 and the fluid supply pipe 5, respectively. After the plastic molded product 2 and the fluid 3 are thus supplied to the reaction tank 1, the reaction tank 1 is sealed, and the plastic molded product 2 and the fluid 3 are heated with a heater while being stirred by the stirring means 8. And it heats, detecting the temperature in reaction tank 1 with a temperature detector, and the pressure in reaction tank 1 with a pressure detector, respectively, and controls heating according to the detected temperature and pressure. As a result, the temperature and pressure at which the fluid 3 in the reaction tank 1 becomes supercritical or subcritical is maintained, and the plastic molded article 2 is decomposed using the supercritical or subcritical fluid 3 as a reaction catalyst.

  For example, when an unsaturated polyester resin is used as the plastic molded product 2 and water is used as the fluid 3, the plastic concentration is supplied to the reaction vessel 1 so that the plastic concentration becomes 10 to 50 wt%. By adjusting the temperature and pressure to 0.0 to 4.0 MPa and maintaining the water in a supercritical state or subcritical state and reacting for 30 minutes to 4 hours, the unsaturated polyester resin is transesterified to obtain a decomposition product. It can be hydrolyzed to monomers such as styrene maleic acid copolymer and polyhydric alcohol. As a result of hydrolysis, 80% or more of the plastic molded product is dissolved in the fluid 3 and is in a state of drastically decreasing from the plastic concentration at the initial supply.

  After the predetermined decomposition treatment time has elapsed, the fluid 3 is naturally cooled or reduced in pressure by a pressure reducing valve provided in the reaction tank 1 (not shown), vaporized and cooled, and then the operation of the step (B) is performed when the pressure becomes normal pressure or lower. Do. This step (B) is repeated.

  In the step (B), a new plastic molded product 2 is supplied from the plastic supply pipe 4 to the reaction tank 1 without discharging the fluid 3 in the reaction tank 1. When an alkali metal hydroxide aqueous solution is used as the fluid 3 in the step (A), the alkali metal hydroxide consumed together with the plastic molded product 2 may be added.

  The supply amount of the plastic molded product 2 in this step (B) is considered to be supplied so that the plastic concentration is 10 to 50 wt%, as described above. Since the fluid 3 in the reaction tank 1 is in a state where the plastic concentration is drastically reduced, in practice, the supply amount of the plastic molded product 2 is the same as the supply amount of the plastic molded product 2 initially supplied in the step (A). A similar amount can be supplied. When the plastic molded product 2 is supplied to the reaction tank 1, the plastic molded product 2 can be supplied if the liquid temperature of the fluid 3 is lower than the boiling point, so there is no need to wait for the temperature to drop to room temperature. For example, when the fluid 3 is water, a new plastic molded product is obtained when the liquid temperature in the reaction vessel 1 drops below the boiling point of water (100 ° C.), that is, about 80 to 100 ° C. under normal pressure. 2 can be supplied. And after supply of the plastic molded product 2, since it heats with a heater from the temperature until a fluid will be in a supercritical state or a subcritical state, temperature rising time can be shortened and heat consumption can be reduced. In addition, since the fluid 3 is not newly supplied, the amount of fluid 3 used can be reduced. Such an effect can be made more remarkable by repeatedly performing the operation of the step (B).

When an unsaturated polyester resin is used as the plastic molded article 2, the concentration of the styrene maleic acid copolymer produced by hydrolysis in the fluid 3 is increased by repeating the above step (B). As a result, the viscosity of the fluid 3 increases, causing problems in operability such as discharge, or the dissolved decomposition product precipitates when the saturation solubility is exceeded. Therefore, depending on the concentration and viscosity of the fluid 3, the process (B) The number of repetitions can be defined. Moreover, when the molded article which uses inorganic substances, such as glass fiber, as the plastic molded article 2, the density | concentration in the fluid 3 of the inorganic substance produced | generated by hydrolysis raises by the repetition operation of the said process (B). Along with this, the agitation of the fluid 3 is lowered and a problem occurs in operability such as discharge, so that the number of repetitions of the step (B) can be defined. The number of repetitions of the step (B) may be defined empirically. For example, the concentration of the styrene maleic acid copolymer or the like is directly measured, or the viscosity of the fluid 3 in the reaction tank 1 is measured by a viscometer. By measuring, it is possible to determine the end of the repetitive operation of the step (B) and to control the discharge of the contents in the reaction tank 1.
<Embodiment 2>
FIG. 2 is a schematic view of a disassembling apparatus for explaining an embodiment of the plastic disassembling method of the second invention.

  In this embodiment, it has the process of taking out the content from the reaction tank 1 between a process (A) and a process (B), carrying out solid-liquid separation of this, and supplying a separated liquid to the reaction tank 1. . That is, after the decomposition treatment is completed in the step (A), when the decomposition product of the plastic molded product 2 cannot be completely dissolved in the fluid 3, or when the undecomposed component of the plastic molded product 2 remains. The contents inside are opened from the discharge open / close valve 7 and discharged to the outside through the discharge pipe 6, and the solid content separating means 9 such as a filter press capable of squeezing filtration is used to separate the undecomposed components which are solid contents. Only the separated liquid is returned again into the reaction tank 1 through the fluid supply pipe 5. For example, when the plastic molded product 2 is FRP that is a composite material of an unsaturated polyester resin and an inorganic material such as glass fiber or calcium carbonate, undecomposed unsaturated polyester resin or inorganic material is separated.

Since the solid content is separated from the contents in the reaction tank 1 by the above operation, the amount of the plastic molded product 2 supplied in the next step (B) is the plastic molding initially supplied in the step (A). An amount equivalent to the supply amount of the product 2 can be supplied from the plastic supply pipe 4.
<Embodiment 3>
FIG. 3 is a schematic view of a disassembling apparatus for explaining an embodiment of the plastic disassembling method of the third invention.

  In this embodiment, after the decomposition process is completed in the step (A), the sample is allowed to stand for a predetermined time, and the undecomposed component of the plastic molded product 2 or the decomposed product of the plastic molded product 2 cannot be completely dissolved in the fluid 3. The dissolved components are allowed to settle at the bottom of the reaction vessel 1. The fluid 3 at the lower part of the reaction tank 1 containing the undecomposed components of the plastic molded product 2 is discharged to the outside from the discharge pipe 6 connected to the bottom of the reaction tank 1, thereby undecomposed components from the contents in the reaction tank 1. Isolate etc. At this time, since the fluid 3 is also discharged together with undecomposed components, in the step (B), the fluid 3 having the same degree as the extracted fluid 3 is newly supplied to the reaction tank 1 together with the plastic molded product 2. Yes.

According to this embodiment, the concentration of undecomposed components and undissolved components in the plastic of the fluid 3 in the lower part of the reaction tank 1 is increased by sedimentation of undecomposed components and undissolved components of the plastic molded product 2. Since it removes, the increase in the density | concentration of the undecomposed component and undissolved component of the plastic of the fluid 3 of the reaction tank 1 is suppressed. Therefore, in the decomposition treatment of the reaction tank 1, it is possible to prevent solid matter from sticking to the inner wall surface of the high-temperature reaction tank 1 and to prevent the stirring property of the fluid 3 in the reaction tank 1 from being lowered.
<Embodiment 4>
FIG. 4 is a schematic view of a disassembling apparatus for explaining an embodiment of the plastic disassembling method of the fourth invention.

  In this embodiment, a plastic supply unit 10 containing a plastic molded product 2 is connected to a plastic supply pipe 4, and the plastic molded product 2 is sent from the plastic supply unit 10 into the reaction tank 1 by opening and closing the plastic supply opening / closing valve 11. It is. The plastic supply unit 10 is supplied with air pressurized by a compressor or the like, and the inside thereof is pressurized.

A specific operation will be described. For example, after the decomposition treatment in the step (A), the plastic supply unit 10 is at least equal to the internal pressure of the reaction tank 1, specifically, the pressure relative to the internal pressure of the reaction tank 1. The pressure is increased to about 0.9 to 1.1, preferably a pressure slightly higher than the internal pressure, for example, to a pressure of about 1.3 in the pressure ratio. The plastic molded product 2 is supplied to the open reaction tank 1. For example, when the fluid 3 is water, the internal pressure of the plastic supply unit 10 is set to 0.27 MPa or more at the time when the temperature in the reaction tank 1 is 130 ° C. (0.27 MPa) after the decomposition treatment in the step (A). Next, the plastic supply opening / closing valve 11 is opened, and the plastic molded product 2 is supplied to the reaction vessel 1. At the end of the decomposition of the plastic molded product 2 in the step (A), the reaction tank 1 is in a supercritical state or a subcritical state, and in this state, the plastic molded product 2 is supplied from the plastic supply unit 10 pressurized in the step (B). It is possible to start the decomposition process without lowering the temperature of the reaction tank 1 by supplying. Therefore, the cooling time of the reaction tank 1 can be reduced, the amount of heat consumed for heating and the heating time can be reduced, and the processing time can be greatly shortened.
<Embodiment 5>
FIG. 5 is a schematic view of a disassembling apparatus for explaining an embodiment of the plastic disassembling method of the fifth invention.

  In this embodiment, after repeating the step (B) a predetermined number of times, the contents are removed from the reaction vessel 1 by opening the discharge on-off valve 7 and taking out the entire amount from the discharge pipe 6, which is a solid as described in the second embodiment. The solid content is separated by the fraction separating means 9 to obtain a separated liquid. The decomposition product of the plastic molded product 2 is dissolved in the separated liquid, and after the dissolved component of the decomposition product is removed by the dissolved component removing means 12, the remaining decomposed solution is again passed through the fluid supply pipe 5 in the reaction tank 1. The decomposition process in step (B) is resumed again.

  For example, when the plastic molded article 2 is an unsaturated polyester resin, the decomposition product is a styrene maleic acid copolymer and dissolves in the fluid 3, but precipitates when the fluid 3 is in an acidic state. Therefore, as the dissolved component removing means 12, acid is added to the separated liquid obtained by taking out the contents from the reaction tank 1 to precipitate the styrene maleic acid copolymer, which is solid-liquid separated by the solid content separating means 9. Thus, the dissolved component of the decomposition product of the plastic molded product 2 can be removed from the separated liquid. The remaining separation liquid is adjusted to pH by adding an alkali, and then returned to the reaction tank 1 again for treatment.

By such an operation, the fluid 3 used in the step (A) can be reused, and it is not necessary to use a new fluid 3. Therefore, the total usage amount of the fluid 3 can be greatly reduced.
<Embodiment 6>
FIG. 6 is a schematic view of a disassembling apparatus for explaining an embodiment of the plastic disassembling method of the sixth invention.

  In this embodiment, after the step (B) is repeated a predetermined number of times, a predetermined amount of fluid 3 is supplied to the reaction tank 1 from the fluid supply pipe 5. The amount of the fluid 3 to be supplied is not particularly limited because it differs depending on the amount supplied to the reaction tank 1 in the step (A) and the size of the reaction tank 1, but in general, the reaction is performed in the step (A). It can be set to about 10 to 30 vol% of the fluid 3 supplied to the tank 1. By newly adding the fluid 3 to the reaction tank 1, the concentration of the decomposition product of the plastic molded product 2 in the reaction tank 1 is reduced, and then the contents of the reaction tank 1 are opened by opening the discharge on-off valve 7 and the discharge pipe 6 More discharge.

  For example, when an unsaturated polyester resin is used as the plastic molded article 2, the concentration of the styrene-maleic acid copolymer produced by hydrolysis in the fluid 3 is increased by the repeated operation of the step (B). The viscosity of the fluid 3 is increased, causing a problem in operability such as discharge. Moreover, since the decomposition product which melt | dissolved will precipitate if it becomes more than saturation solubility, a problem arises also in operability, such as discharge | emission. Therefore, when the upper limit concentration is reached, the step (B) is stopped, and a new fluid 3 is added for dilution to lower the concentration, thereby preventing operability problems such as discharge. Moreover, the addition of the new fluid 3 is only for the step (A) and the dilution, and the total amount of the fluid 3 can be reduced also in this embodiment.

  After discharging the contents of the reaction tank 1, the decomposition process is restarted from step (A).

It is a schematic diagram of the decomposition | disassembly apparatus for demonstrating one Embodiment of the decomposition | disassembly method of the plastic of 1st invention. It is a schematic diagram of the decomposition | disassembly apparatus for demonstrating one Embodiment of the decomposition | disassembly method of the plastic of 2nd invention. It is a schematic diagram of the decomposition | disassembly apparatus for demonstrating one Embodiment of the decomposition | disassembly method of the plastic of 3rd invention. It is a schematic diagram of the decomposition | disassembly apparatus for demonstrating one Embodiment of the decomposition | disassembly method of the plastic of 4th invention. It is a schematic diagram of the decomposition | disassembly apparatus for demonstrating one Embodiment of the decomposition | disassembly method of the plastic of 5th invention. It is a schematic diagram of the decomposition | disassembly apparatus for demonstrating one Embodiment of the decomposition | disassembly method of the plastic of 6th invention. It is a schematic diagram of the decomposition | disassembly apparatus for demonstrating the conventional plastic decomposition | disassembly method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reaction tank 2 Plastic molded article 3 Fluid 4 Plastic supply pipe 9 Solid content separation means 10 Plastic supply part 12 Dissolved content removal means

Claims (8)

  The plastic molded product and fluid are supplied to the reaction vessel, and the decomposition product of the plastic molded product decomposed in the step (A) is dissolved in the step (A) of decomposing the plastic molded product in a supercritical or subcritical state. And a step (B) of newly supplying a plastic molded product to the fluid and decomposing the plastic molded product in a supercritical or subcritical state.   2. The method according to claim 1, further comprising a step of taking out the contents from the reaction vessel between the step (A) and the step (B), solid-liquid separating the content, and supplying the separated liquid to the reaction vessel. Plastic disassembly method.   After the step (A), the fluid in the lower part of the reaction tank containing undecomposed components of the plastic molded product settled at the bottom of the reaction tank is taken out of the reaction tank. The plastic decomposition method according to claim 1, wherein the plastic is newly supplied to the reaction tank together with the molded product.   In the step (B), a plastic molded product is supplied to the reaction tank from a plastic supply section pressurized to a pressure at least equal to the internal pressure of the reaction tank to be decomposed in a supercritical or subcritical state. The method for decomposing a plastic according to any one of claims 1 to 3.   After repeating the step (B) a predetermined number of times, the content is taken out from the reaction vessel, and the dissolved component of the plastic molded product decomposition product is obtained from the separated solution containing the dissolved component of the plastic molded product decomposition product obtained by solid-liquid separation. 5. The method for decomposing a plastic according to claim 1, further comprising a step of supplying the remaining separated liquid to the reaction vessel.   The process (B) is repeated a predetermined number of times, then a fluid is supplied to the reaction tank to reduce the concentration of the plastic molded product decomposition product, and then the contents of the reaction tank are discharged. The method for decomposing plastic according to claim 1.   The method for decomposing a plastic according to any one of claims 1 to 6, wherein the plastic molded article is a plastic containing an unsaturated polyester resin.   8. The plastic molded product is charged when the reaction liquid is water and the liquid temperature of the fluid in the reaction tank falls within the range of 80 to 100 ° C. in step (B). The method for decomposing plastic according to claim 1.

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