JP2006008984A - Method for decomposing or separating plastic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for decomposing or separating a plastic, by which a dehydration treatment cost can be lowered, and further by which the plastic produced from raw materials including a polyhydric alcohol and an organic acid can be recovered in a quality capable of being again easily utilized as the same plastic. <P>SOLUTION: This method for decomposing or separating the plastic is characterized by having a process for treating the plastic comprising unsaturated polyester portions and their cross-linked portions in semi-critical water of temperature below the thermal decomposition temperature of the plastic to decompose the plastic into the polyhydric alcohol and the organic acid which are raw material monomers for the plastic, and further into a cross-linked portion acid copolymer which is a compound of the organic acid constituting the cross-linked portions and the unsaturated polyester portions, and a process for supplying a hydrophobic solvent and an acid to the aqueous solution containing the polyhydric alcohol, the organic acid and the cross-linked portion acid copolymer obtained in the decomposition process to separate into the solid portions of the cross-linked portion acid copolymer and the liquid phase. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention decomposes a plastic (thermosetting resin) consisting of an unsaturated polyester part and its cross-linked part or a waste containing them, and forms a solid content of the cross-linked part acid copolymer, a polyhydric alcohol and an organic acid. The technology relates to the technology for disassembling and separating plastics.

Conventionally, most plastic waste has been subjected to landfill disposal or incineration, and has not been effectively used as a resource. In addition, landfill disposal has problems such as difficulty in securing landfill site and instability of the ground after landfill, and incineration treatment has problems such as furnace damage, generation of harmful gases and odors, and CO ₂ emission. For this reason, the Containers and Packaging Waste Law was enacted in 1995, and plastics must be collected and reused. Furthermore, with the enforcement of various recycling laws, the flow of collection and recycling of products containing plastics tends to accelerate. In recent years, attempts have been made to recycle plastics in accordance with these circumstances, and as one of them, plastic waste is decomposed into oil by reaction using supercritical water as a reaction medium, and useful oil is obtained. A method for collecting an object has been proposed (see, for example, Patent Document 1).

  In addition, a method has been proposed in which fiber reinforced plastics used for various structural materials, etc. are decomposed using supercritical water or subcritical water to recover plastics such as glass fibers and carbon fibers and reuse them. (For example, refer to Patent Document 2). In these methods, the plastic becomes an oily component having a low molecular weight by decomposition, and is mainly reused as a liquid fuel. In addition, a decomposition method using a hydrolysis reaction with high-temperature steam has been proposed, and the organic polymer component of the thermoplastic plastic and the thermosetting plastic can be temporarily decomposed by this method. In addition, a chemical recycling method has been proposed in which a cured unsaturated polyester resin waste is decomposed using a decomposition component such as dicarboxylic acid or diamine to obtain a resin raw material, and the unsaturated polyester resin is re-synthesized (for example, (See Patent Document 3). However, since the plastic component is decomposed randomly in the supercritical method, it is difficult to maintain a constant quality because the decomposition product becomes a multi-component oily substance. For this reason, post-treatment such as reforming the oil quality using a catalyst typified by zeolite is necessary, resulting in high costs, and the reformed product oil is also made into petroleum products such as kerosene and light oil. This has been difficult and has not been put into practical use. Further, in the method described in Patent Document 3, although the decomposed resin is reused again as the unsaturated polyester resin, the physical properties when re-curing is caused by thermal decomposition because of the high decomposition temperature. However, it is different from the original unsaturated polyester resin (decreases as a thermosetting resin) and the utilization rate of the decomposition resin to be recured is low.

In view of this, the present inventors have proposed a method of decomposing and separating a plastic comprising an unsaturated polyester and its cross-linked portion using subcritical water at a temperature below the thermal decomposition temperature of the plastic and reusing it. (Japanese Patent Application No. 2004-093363). In this method, in addition to a monomer that can be reused as a raw material for the unsaturated polyester resin, a cross-linked acid copolymer (such as a styrene fumarate resin) that is a copolymer of a cross-linked part and an organic acid is generated and recovered. And can be reused.
JP-A-5-31000 Japanese Patent Laid-Open No. 10-87872 Japanese Patent Laid-Open No. 9-221565

  The above-mentioned crosslinked part acid copolymer is recovered in a state dissolved in an aqueous solution, and is deposited by acidifying the aqueous solution due to its properties, but at this time, it contains a large amount of water. Accordingly, when the cross-linked acid copolymer is dehydrated to obtain a solid content, the cross-linked acid copolymer may be simply heated to evaporate water. Because it contains about 9 times the weight of water, a large amount of heat energy is required. Furthermore, dehydration of the carboxyl group and various other reactions are likely to occur due to heating. For example, the molecular weight of the crosslinked acid copolymer after dehydration increases, the viscosity increases, and when it is reused, subsequent molding is possible. There were problems such as difficulty.

  The present invention has been made in view of the above points, and the solid content of the crosslinked acid copolymer that is easily swollen with a large amount of water can be taken out in a dehydrated state without heating. To provide a method for decomposing / separating plastics, which can reduce processing costs and can recover plastics produced from raw materials containing polyhydric alcohols and organic acids in a form that can be easily reused as similar plastics. It is intended.

  The method for decomposing / separating a plastic according to the present invention comprises treating a plastic comprising an unsaturated polyester part and a cross-linked part thereof with subcritical water at a temperature lower than the thermal decomposition temperature, and then producing a polyhydric alcohol as a raw material monomer of the plastic and an organic acid. And a step of decomposing into a cross-linked part acid copolymer which is a compound of an organic acid constituting the cross-linked part and the unsaturated polyester part, and a polyhydric alcohol, an organic acid and a cross-linked part acid copolymer obtained in the decomposing step And a step of separating the solid content and the liquid phase of the cross-linked part acid copolymer by supplying a hydrophobic solvent and an acid to an aqueous solution containing.

  In this invention, it is preferable to have the process of removing the water of the liquid phase obtained at a isolation | separation process, and collect | recovering a polyhydric alcohol and an organic acid.

  Moreover, in this invention, it is preferable to supply an acid so that pH of the aqueous solution obtained at a decomposition | disassembly process may be 4 or less in a isolation | separation process.

  In the present invention, it is preferable to use a hydrophobic solvent having a solubility in water of 0.1 to 5 wt% at room temperature.

  Moreover, in this invention, it is preferable that the usage-amount of a hydrophobic solvent is 0.5 times or more of solubility.

  In the present invention, the hydrophobic solvent is preferably at least one selected from acetates, ketones, alcohols, and ethers.

  In the present invention, the hydrophobic solvent is preferably at least one selected from isobutyl acetate, methyl isobutyl ketone, alcohols having 5 to 10 carbon atoms, and diisopropyl ether.

  Moreover, in this invention, it is preferable to perform the process of isolate | separating into solid content and a liquid phase of a bridge | crosslinking part acid copolymer by a precipitation separation method.

  In the present invention, a crosslink produced by subcritical water decomposition is provided by supplying a hydrophobic solvent and an acid to an aqueous solution containing a polyhydric alcohol, an organic acid, and a cross-linked acid copolymer obtained in the decomposition step. The partial acid copolymer can be separated and recovered without being swollen with a large amount of water. Therefore, it is possible to take out the solid content of the crosslinked acid copolymer in a dehydrated state without heating, and as a result, heating energy for dehydration is unnecessary and the processing cost for dehydration is eliminated. Produced from raw materials including polyhydric alcohols and organic acids. The plastic can be recovered with the property that it can be easily used as a similar plastic again.

  Hereinafter, the best mode for carrying out the present invention will be described.

  In the present invention, the plastic to be decomposed / separated is a plastic produced from a raw material containing a polyhydric alcohol and an organic acid, and examples of such plastic include polyester resins. Among them, a plastic (thermosetting resin) such as an unsaturated polyester resin can be mentioned.

  Further, in detail, in the present invention, the plastic to be decomposed / separated is a plastic comprising an unsaturated polyester portion and a cross-linked portion thereof. Here, the “unsaturated polyester portion” is a portion derived from a polyhydric alcohol and an unsaturated polybasic acid that is an organic acid, and is an unsaturated alkyd formed by polycondensation of the polyhydric alcohol and the unsaturated polybasic acid. The resin part. The “crosslinking part” is a part derived from a crosslinking agent that crosslinks the unsaturated alkyd resin. Therefore, “plastic consisting of an unsaturated polyester part and its crosslinked part” means a reticulated thermosetting resin (reticulated unsaturated polyester) in which an unsaturated alkyd resin consisting of a polyhydric alcohol and an unsaturated polybasic acid is cross-linked by a cross-linking agent. Resin).

  Examples of the polyhydric alcohol include glycols such as ethylene glycol, propylene glycol, diethylene glycol and dipropylene glycol, but are not limited thereto. Examples of the unsaturated polybasic acid include, but are not limited to, aliphatic unsaturated dibasic acids such as maleic anhydride, maleic acid, fumaric acid, and phthalic acid. Furthermore, examples of the crosslinking agent include polymerizable vinyl monomers such as styrene and methyl methacrylate, but are not limited thereto. In producing the unsaturated alkyd resin, a saturated polybasic acid such as phthalic anhydride may be used in combination with the unsaturated polybasic acid as the organic acid.

  In the present invention, the following decomposition step, separation step, and recovery step are sequentially performed on plastics such as unsaturated polyester resin (mainly plastic waste of thermosetting plastic) as described above (see FIG. 1). .

[Disassembly process]
In the decomposition step of the present invention, the plastic is treated with subcritical water having a temperature lower than the thermal decomposition temperature, and the polyhydric alcohol, the organic acid, and the organic acid constituting the crosslinked portion and the unsaturated polyester portion are raw material monomers for the plastic. It is the process of decomposing | disassembling into the bridge | crosslinking part acid copolymer which is this compound. In other words, by adding water to the plastic and raising the temperature and pressure to bring the water to a subcritical state below the critical point (critical temperature 374.4 ° C., critical pressure 22.1 MPa), the plastic is decomposed, so that The saturated polyester part is decomposed into a polyhydric alcohol and an organic acid (unsaturated polybasic acid) which are raw material monomers derived from the saturated polyester part, and the part constituting the crosslinked part and the unsaturated polyester part is a styrene fuma which is a compound of an organic acid. It decomposes into a cross-linked acid copolymer such as a rate (styrene-fumaric acid resin). That is, the “organic acid compound constituting the crosslinked part and unsaturated polyester part” is a compound (reactant) of the crosslinking agent and the unsaturated polybasic acid of the unsaturated polyester part.

  In subcritical decomposition of such plastics, water is maintained at a temperature and pressure at which the subcritical state is maintained, and the plastics are hydrolyzed by bringing the subcritical water into contact with the plastics and transesterifying the plastics. Can be done.

  In general, when plastics produced from raw materials containing polyhydric alcohols and organic acids are processed by hydrolysis reaction, a thermoplastic resin becomes a long reaction of several tens of hours at a low temperature around 100 ° C. It cannot be decomposed in the plastic. Further, in the reaction under high temperature and high pressure, corrosion of the apparatus, thermal decomposition, and secondary decomposition of the decomposition products occur, and it is difficult to decompose and separate the resin raw material with a high recovery rate. Accordingly, the temperature at which the thermosetting resin plastic is decomposed using the subcritical water in the present invention is preferably less than 280 ° C., and the pressure in the subcritical state is preferably 7 MPa or less.

  Furthermore, in the present invention, the temperature of the decomposition reaction (subcritical water temperature) is less than the temperature at which the plastic is hydrolyzed but thermally decomposed, and less than the temperature at which the crosslinked portion and the unsaturated polyester portion are thermally decomposed. It is preferable that it is set to the range of 180-250 degreeC. If the temperature during the decomposition reaction is less than 180 ° C., the decomposition process takes a long time and the processing cost may be increased. If the temperature during the decomposition reaction exceeds 250 ° C., the effect of thermal decomposition may occur. There is a possibility that the unsaturated polyester part and the cross-linked part thereof are decomposed and it becomes difficult to recover the acid compound constituting the cross-linked part and the unsaturated polyester part. When styrene is used as the crosslinking agent, subcritical decomposition is preferably performed at a temperature of about 230 ° C. or less in order to prevent thermal decomposition of styrene. The decomposition reaction time varies depending on conditions such as the reaction temperature, and is preferably about 1 to 4 hours below the temperature at which the influence of thermal decomposition does not occur. However, the shorter the reaction time, the lower the processing cost. preferable. Further, the pressure of the decomposition reaction (during treatment with subcritical water) is not particularly limited, but a range of 1.0 to 4.0 MPa is more preferable.

  In order to accelerate subcritical decomposition and shorten the time, it is preferable to mix a metal hydroxide such as potassium hydroxide or sodium hydroxide or a metal chloride such as potassium chloride (KCl) into water as an alkali. . In this case, the blending amount of the alkali is preferably 10 to 100 parts by mass with respect to 100 parts by mass of the plastic that undergoes subcritical decomposition. If the blending amount of the alkali is less than the above, it becomes difficult to promote the decomposition of the plastic, and there is a possibility that the subcritical decomposition cannot be shortened, and the blending amount of the alkali becomes larger than the above. However, the effect of promoting the decomposition of the plastic cannot be greatly improved, and only the cost is increased.

And, when the plastic is subcritically decomposed in this way, a cross-linked acid copolymer salt such as styrene fumarate salt (styrene-fumaric acid resin salt), a polyhydric alcohol such as glycols that are raw material monomers of the plastic, Similarly, an aqueous solution containing a salt of an organic acid such as maleic acid or fumaric acid, which is a raw material monomer for plastics, can be obtained. The crosslinked acid copolymer salt has a styrene skeleton and a fumaric acid skeleton, and is a potassium salt or sodium salt in a state in which an alkali metal such as potassium or sodium is bonded to a carboxyl group (COO ^- K ⁺ or COO ^- Na ⁺ ). It is an alkali metal salt such as water-soluble. Further, salts of organic acids such as maleic acid and fumaric acid are also alkali metal salts such as potassium salt and sodium salt. The alkali metal of these alkali metal salts is derived from the alkali metal salt blended for promoting the subcritical decomposition, the alkali metal salt originally contained in the plastic to be decomposed, or the like.

[Separation process]
In the separation step of the present invention, by supplying a hydrophobic solvent and an acid to an aqueous solution containing the polyhydric alcohol, the organic acid, and the crosslinking acid copolymer obtained in the decomposition step, This is a step of separating the solid content of the coalescence and the liquid phase (water and solvent).

  Here, as the hydrophobic solvent, one kind selected from acetates, ketones, alcohols, and ethers may be used alone, or a plurality may be used in combination.

  As the acetate ester, at least one selected from isobutyl acetate, n-propyl acetate, isopropyl acetate, n-pentyl acetate, and the like can be used. Among them, isobutyl acetate is particularly high in dehydrating performance and industrially. Is also widely used and is preferred.

  As the ketones, at least one selected from methyl isobutyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, methyl n-amyl ketone, ethyl n-butyl ketone, di n-propyl ketone, and the like can be used. Among these, methyl isobutyl ketone is particularly preferable because it has high dehydration performance and is widely used industrially.

  Further, as the alcohol, at least one selected from n-hexanol, cyclohexanol, 2-ethylhexanol, 4-methyl-2-pentanol, isopentyl alcohol, 3,5,5-trimethylhexanol and the like is used. Among these, n-hexanol, 2-ethylhexanol, and 3,5,5-trimethylhexanol, which are alcohols having 5 to 10 carbon atoms (C5 to C10), have high dehydration performance and are inexpensive. preferable.

  As the ethers, at least one selected from diisopropyl ether, diethyl ether, and the like can be used. Among these, diisopropyl ether is particularly preferable because it has a high dehydrating performance and is widely used industrially.

  Furthermore, the hydrophobic solvent used in the present invention preferably has a solubility in water of 0.1 to 5 wt% at normal temperature and pressure. When a solvent having a solubility of less than 0.1 wt% is used, dehydration of the crosslinked acid copolymer is difficult to occur, and the separation operation becomes impossible as in the case where no solvent is added. Further, when a solvent of 5 wt% or more is used, there is a possibility that it is difficult to separate the cross-linked acid copolymer because there is almost no dehydrating ability at a use amount of about solubility.

  Examples of the acid include, but are not limited to, inorganic strong acids such as hydrochloric acid and sulfuric acid. When neutralization is necessary in the subsequent step, a material that can be easily treated with a salt that is a by-product due to neutralization may be selected.

  In the separation step of the present invention, the hydrophobic solvent and acid are added to the aqueous solution obtained in the decomposition step and supplied. At this time, the acid is an aqueous solution obtained in the decomposition step ( It is preferable to blend so that the pH of the aqueous phase of the liquid phase is 4 or less. When the pH of the aqueous solution exceeds 4, the solid content of the crosslinked acid copolymer may not be completely precipitated, which may make separation difficult. In the present invention, the lower the pH of the aqueous phase of the aqueous solution, the more easily the solid content of the crosslinked acid copolymer is precipitated.

  Moreover, it is preferable that the usage-amount (supply amount) of the hydrophobic solvent in a isolation | separation process is 0.5 times or more of the solubility of each solvent. The dehydrating ability of the solvent used in the present invention depends on the amount of the cross-linked acid copolymer dissolved in the aqueous solution obtained in the decomposition step. The amount of the cross-linked acid copolymer is determined by the solid content concentration and the decomposition rate at the time of decomposition, but when the decomposition rate is approximately 100 wt%, it depends on the solid content concentration and is usually dissolved in an aqueous solution. The amount of the cross-linked acid copolymer is about 1 to 10 wt%. In this region, the dehydrating ability with a hydrophobic solvent is most effective near the solubility of the solvent. Accordingly, when the amount of the hydrophobic solvent added is small, the dehydration ability may be reduced. Conversely, when the amount of the hydrophobic solvent used is large, the crosslinked acid copolymer is in the form of a highly viscous gum. Operation may be difficult when recovering as a substance.

  When the separation step as described above is performed, depending on the type of the hydrophobic solvent used, the solid content of the crosslinked acid copolymer precipitates or a solid phase is formed between the solvent phase and the aqueous phase. The solid content and the liquid phase of the cross-linked acid copolymer can be separated.

  Here, in the present invention, it is preferable that the step of separating the cross-linked acid copolymer into a solid content and a liquid phase is performed by a precipitation separation method (a method in which the solid content in the liquid is settled by its own weight). Compared with the method of separating by filtration using a filtration membrane, the cross-linked acid copolymer can be easily recovered without the risk of clogging the filter medium and making it impossible to filter or separating from the filter medium. Can do.

[Recovery process]
After the solid content and the liquid phase of the cross-linked part acid copolymer are separated as described above, the solid content is washed with water or ether to obtain a cross-linked part acid copolymer (light brown solid). be able to.

  Further, after removing water from the aqueous solution (aqueous phase) separated from the hydrophobic solvent, an alcohol such as methanol or ethanol is added to the residue, so that a polyhydric alcohol such as glycols dissolved in the alcohol and fumaric acid are added. And the like, and solid alkali metal salts (such as the above-mentioned metal hydroxides and metal chlorides) can be separated, whereby the polyhydric alcohol and the organic acid can be recovered.

  The resin component obtained by decomposing unsaturated polyester resin such as FRP resin with subcritical water as in the present invention is a copolymer of cross-linked acid copolymer (styrene-fumaric acid resin) as shown in [Chemical Formula 1]. It is.

  Although there are no particular upper limits for m and n, for example, m = 3 and n = 300.

  In the crosslinked part acid copolymer, an unsaturated polyester and a plastic composed of the crosslinked part can be precipitated by adding an acid to the aqueous solution after the decomposition step using subcritical water. The polymer is obtained in a state where water is swollen. This is presumably because the fumaric acid skeleton has two carboxyl groups, so that water molecules are easily held around it.

  Therefore, in the present invention, a hydrophobic solvent and an acid are supplied to the aqueous solution after the decomposition step in which the cross-linked acid copolymer is dissolved in order to precipitate the cross-linked acid copolymer in a state where water is not swollen. As a result, an intermediate phase between the phase of the hydrophobic solvent and the aqueous phase or the precipitate can be precipitated to precipitate the crosslinked acid copolymer as a solid content. The crosslinked part acid copolymer can be obtained by washing with a small amount of water or ether and dehydrating without heating by natural drying.

  In addition, the cross-linking part acid copolymer may contain glycols as impurities, and when dehydrated by heating, the carboxyl group of the cross-linking part acid copolymer reacts with the hydroxyl group of the glycol. ], Or the carboxyl groups of different molecular chains are dehydrated and cross-linked three-dimensionally, making it a material that does not have a softening point or melting point, making it difficult to mold and using as a molding material However, in the present invention, since dehydration is performed using a hydrophobic solvent without heating, most of the glycols that are very soluble in water and ether can be removed from the solids. Thus, it is possible to obtain a crosslinked part acid copolymer which is hardly contained, and therefore, it is possible to obtain a crosslinked part acid copolymer which can be easily used as a molding material.

  Although there are no particular upper limits for m and n, for example, m = 3 and n = 300.

  Hereinafter, the present invention will be described specifically by way of examples.

(Decomposition process of unsaturated polyester resin by subcritical water decomposition, inorganic separation method)
The unsaturated polyester resin was manufactured using propylene glycol as the glycol and maleic anhydride as the organic acid and having a weight average molecular weight of 6000 to 10,000. The varnish was mixed with an approximately equivalent amount of styrene, and calcium carbonate was added as an inorganic filler to be cured.

  3 g of this cured product and 15 g of a KOH aqueous solution having a concentration of 1.0 mol / L were charged into a reaction tube, and the inside was replaced with argon gas. This reaction tube was immersed in a thermostat heated to 230 ° C., and the decomposition reaction was performed for 4 hours. After cooling, the contents in the reaction tube were taken out and separated into an inorganic substance and an aqueous solution by filtration.

[Example 1]
The aqueous solution recovered in the decomposition step: 10 g of isobutyl acetate (solubility at room temperature (20 ° C.): 0.67 wt%): 0.1 g was added and stirred, and then 1N HCl was stirred until pH 2 was reached. Then, after reaching pH 2, the mixture was further stirred for 5 minutes. Thereafter, solid-liquid separation was performed by suction filtration to obtain 0.42 g of a solid content (crosslinked part acid copolymer). Further, the solid content was naturally dried to obtain 0.37 g of a crosslinked part acid copolymer.

[Example 2]
In Example 1, instead of isobutyl acetate, methyl isobutyl ketone (solubility at room temperature: 1.9 wt%): 0.2 g was added, and the same operation was performed. 44 g, 0.35 g of a cross-linked acid copolymer after drying was obtained.

Example 3
In Example 1, instead of isobutyl acetate, 2-ethylhexanol (solubility at room temperature: 0.5 wt%): 0.1 g was added, and the same operation was performed to obtain a solid content (cross-linking part acid copolymer) of 0. .41 g, 0.36 g of a cross-linked acid copolymer after drying was obtained.

Example 4
In Example 1, instead of isobutyl acetate, diisopropyl ether (solubility at room temperature: 1.2 wt%): 0.2 g was added, and the same operation was performed to obtain 0.43 g of a solid content (cross-linking part acid copolymer). Then, 0.34 g of a cross-linked acid copolymer after drying was obtained.

Example 5
Aqueous solution recovered in the decomposition step: Isobutyl acetate (solubility at room temperature: 0.67 wt%): 1.0 g was added to 60 g and stirred, then 1N HCl was added with stirring until pH 2 was reached, pH 2 Then, the mixture was further stirred for 5 minutes. Thereafter, the aqueous solution was transferred to a 100 cc graduated cylinder and allowed to stand to measure the volume of the crosslinked part acid copolymer for each elapsed time. After 1 hour, the water in the graduated cylinder was removed to obtain 9.6 g of a solid content (hydrous crosslinked acid copolymer). Further, the solid content was naturally dried to obtain 2.19 g of a crosslinked part acid copolymer.

[Comparative Example 1]
Aqueous solution recovered in the decomposition step: Without adding a solvent to 10 g, 1N HCl was added with stirring until pH 2 was reached, and after reaching pH 2, the mixture was further stirred for 5 minutes. Thereafter, the aqueous solution was subjected to a centrifugal separation operation, and then the solid and liquid were separated by suction filtration to obtain 4.10 g of a solid content (water-containing crosslinked part acid copolymer). Further, the solid content was naturally dried to obtain 0.42 g of a crosslinked part acid copolymer.

[Comparative Example 2]
1.0 g of ethyl acetate (solubility at room temperature: 7.9 wt%): 1.0 g was added to 10 g of the aqueous solution recovered in the decomposition step and stirred, and then 1N HCl was added with stirring until pH 2 was reached. Then, the mixture was further stirred for 5 minutes. Thereafter, the aqueous solution was subjected to a centrifugal separation operation, and then the solid and liquid were separated by suction filtration to obtain 3.26 g of a solid content (water-containing crosslinked part acid copolymer). Further, the solid content was naturally dried to obtain 0.41 g of a crosslinked part acid copolymer.

[Comparative Example 3]
Aqueous solution recovered in the decomposition step: 1N HCl was added to 60 g with stirring until pH 2 was reached, and after reaching pH 2, the mixture was further stirred for 5 minutes. Thereafter, the aqueous solution was transferred to a 100 cc graduated cylinder and allowed to stand to measure the volume of the crosslinked part acid copolymer for each elapsed time. After 1 hour, the water in the graduated cylinder was removed to obtain 90.2 g of a solid content (hydrous crosslinked acid copolymer). Further, the solid content was naturally dried to obtain 2.44 g of a crosslinked part acid copolymer.

[Moisture content and dehydration effect]
About the said Examples 1-4 and Comparative Examples 1 and 2, the moisture content and the dehydration effect were evaluated.

  The water content was calculated using the following formula.

Moisture content (%) = (A−B) / B
A: Mass of the cross-linking part acid copolymer before drying, B: Mass of the cross-linking part acid copolymer after drying Table 1 shows the results.

  As shown in Table 1, Examples 1 to 4 have lower water content and higher dehydration effect than Comparative Examples 1 and 2, and easily swell with a large amount of water generated by subcritical water decomposition. The polymer (crosslinked acid copolymer) can be dehydrated without heating and the solid content can be taken out. From this result, solid content (crosslinked part) was obtained by dehydrating without heating from a polymer that contains a large amount of water generated by subcritical water decomposition and easily swells, and heating it. Acid copolymer), aqueous solutions containing polyhydric alcohols and organic acids can be easily separated without loss, and plastics made from raw materials containing polyhydric alcohols and organic acids can be reused as similar plastics. Can be disassembled and separated.

[Volume, moisture content, and bulk density over time during sedimentation]
For Example 5 and Comparative Example 3, the volume of the crosslinked acid copolymer was measured for each elapsed time during sedimentation separation, and the water content and bulk density after 60 minutes elapsed were calculated. The results are shown in Table 2.

  As shown in Table 2, the bulk density, which is an important factor in the sedimentation separation, is more than 7 times that of Comparative Example 3 (when no hydrophobic solvent is added), and the water content is also 10 minutes. Since it was 1, sedimentation separation was sufficiently possible.

It is a chart figure which shows an example of embodiment of this invention.

Claims (8)

  A plastic composed of an unsaturated polyester part and its cross-linked part is treated with subcritical water at a temperature lower than the thermal decomposition temperature to form a polyhydric alcohol and an organic acid as raw material monomers for the plastic, and a cross-linked part and an unsaturated polyester part. A step of decomposing into a cross-linked part acid copolymer which is a compound of an organic acid, a hydrophobic solvent in an aqueous solution containing the polyhydric alcohol, organic acid and cross-linking part acid copolymer obtained in the decomposing step; A method for decomposing / separating plastic, comprising a step of separating an acid copolymer from a solid content and a liquid phase of a cross-linked part acid copolymer.   2. The method for decomposing / separating plastic according to claim 1, further comprising a step of recovering polyhydric alcohol and organic acid by removing water in the liquid phase obtained in the separation step.   The method for decomposing / separating plastic according to claim 1 or 2, wherein in the separating step, the acid is supplied so that the pH of the aqueous solution obtained in the decomposing step is 4 or less.   The method for decomposing / separating plastic according to any one of claims 1 to 3, wherein a hydrophobic solvent having a solubility in water of 0.1 to 5 wt% at room temperature is used.   The method for decomposing / separating plastic according to any one of claims 1 to 4, wherein the amount of the hydrophobic solvent used is 0.5 or more times the solubility.   6. The method for decomposing / separating plastic according to claim 1, wherein the hydrophobic solvent is at least one selected from acetates, ketones, alcohols and ethers.   7. The plastic decomposition according to claim 1, wherein the hydrophobic solvent is at least one selected from isobutyl acetate, methyl isobutyl ketone, alcohols having 5 to 10 carbon atoms, and diisopropyl ether. -Separation method.   The method for decomposing / separating a plastic according to any one of claims 1 to 7, wherein the step of separating the cross-linked acid copolymer into a solid content and a liquid phase is performed by precipitation separation.

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