JP2010163620A - Decomposition-separation process for plastic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a decomposition-separation process for plastic, by which the treatment cost for dehydration can be kept low and plastic produced from raw materials containing polyhydric alcohol and organic acid can be recovered as user-friendly plastic again. <P>SOLUTION: The process comprises a step of treating plastic comprising an unsaturated polyester part and its crosslinking part with subcritical water at a temperature less than decomposition temperature in the presence of alkali, so as to decompose the plastic into polyhydric alcohol that is a raw material monomer of plastic, an organic acid salt that is a raw material monomer of plastic, and a crosslinking part-acid copolymer salt that is an organic acid compound composed of a crosslinking part and an unsaturated polyester part and a step of supplying a solvent with a dissolution parameter of 9 or more and acid to an aqueous solution containing the polyhydric alcohol, the organic acid salt, and the crosslinking part-acid copolymer salt obtained in the previous decomposition step, so as to separate the solution into a solid content of the crosslinking part-acid copolymer and an liquid phase. <P>COPYRIGHT: (C)2010,JPO&INPIT

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 situations, and one of them is the use of useful oils by decomposing plastic wastes into oils by reaction using supercritical water as a reaction medium. 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.

  Accordingly, the present inventors have proposed a method of decomposing and recovering a plastic composed of an unsaturated polyester and its cross-linked portion using subcritical water below the thermal decomposition temperature of the plastic and reusing it in a reusable form. (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 portion and a cross-linked portion thereof with subcritical water at a temperature lower than the thermal decomposition temperature in the presence of an alkali to produce a raw material monomer for plastic. Decomposing into a monohydric alcohol, a salt of an organic acid that is a raw material monomer of the plastic, and a cross-linked part acid copolymer salt that is a compound of an organic acid constituting the cross-linked part and the unsaturated polyester part, By supplying a solvent having a solubility parameter of 9 or more and an acid to an aqueous solution containing the resulting polyhydric alcohol, an organic acid salt and a crosslinked acid copolymer salt, the solid content of the crosslinked acid copolymer A solvent having a solubility parameter of 9 or more, and using a cyclic compound having an oxygen atom or a sulfur atom in the ring, Dehydrating the solid bridge portion acid copolymer, bridge acid copolymer is a styrene - is characterized in that a fumaric acid resin.

  In the present invention, it is preferable to have a step of recovering polyhydric alcohol and organic acid by removing liquid phase water and solvent obtained in the separation step.

  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, the solvent is preferably compatible with water.

  In the present invention, the solvent is preferably at least one selected from tetrahydrofuran and 1,4 dioxane.

  In the present invention, the solvent is preferably thiophene.

  In the present invention, by supplying a solvent having a solubility parameter of 9 or more 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 product is generated by subcritical water decomposition. The cross-linked acid copolymer thus obtained 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.

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

  Hereinafter, modes 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, the above-mentioned plastic is treated with subcritical water at a temperature lower than the thermal decomposition temperature, and a polyhydric alcohol and an organic acid that are raw material monomers for the plastic, and a compound of an organic acid that constitutes a crosslinked portion and an unsaturated polyester portion It is a process of decomposing | disassembling into the bridge | crosslinking part acid copolymer which is. 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 fumarate which is a compound of an organic acid. It decomposes into a cross-linked acid copolymer of 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 the present invention, in order to accelerate subcritical decomposition and shorten the time, a metal hydroxide such as potassium hydroxide or sodium hydroxide or a metal chloride such as potassium chloride (KCl) is blended in 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, a solution having a solubility parameter of 9 or more and an acid are supplied to an aqueous solution containing the polyhydric alcohol obtained in the decomposition step, an organic acid, and a cross-linked acid copolymer. This is a step of separating the solid content of the partial acid copolymer into a liquid phase (water and solvent).

  Here, when the solubility parameter of the solvent is less than 9, it cannot be efficiently dehydrated from the crosslinked acid copolymer, and the object of the present invention cannot be achieved. As such a solvent, a cyclic compound having an oxygen atom or a sulfur atom in the ring is used. It is also preferred that the solvent is compatible with water. Specifically, tetrahydrofuran, 1,4 dioxane, thiophene, or the like can be used alone or in combination.

  Moreover, the compounding quantity of the said solvent is not specifically limited, Although the smaller one is preferable, For example, it is preferable to set it as 50-300 mass parts with respect to 100 mass parts of aqueous solution obtained at a decomposition | disassembly process.

  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 solvent and the acid are added to the aqueous solution obtained in the decomposition step and supplied. At this time, the acid is an aqueous solution (liquid phase solution) obtained in the decomposition step. It is preferable to blend so that the pH of the aqueous phase portion 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.

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

[Recovery process]
After separating into a solid part and a liquid phase of the cross-linked part acid copolymer as described above, the solid part is collected by filtration, and the solid part is washed with water or ether, thereby cross-linking part acid copolymer. (Light brown solid) can be obtained.

  In addition, the solvent can be recovered by separating the liquid phase after collecting the solid content into a solvent such as a yellow liquid and an aqueous solution (aqueous phase) that is a colorless liquid using a separating funnel or the like. it can.

  Furthermore, after removing water from the aqueous solution (aqueous phase) separated from the solvent, an alcohol such as methanol or ethanol is added to the residue, so that polyhydric alcohol such as glycols dissolved in alcohol and organic such as fumaric acid are used. The acid can be separated into a solid alkali metal salt (such as the above-mentioned metal hydroxide or metal chloride), 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 cross-linked acid copolymer as shown in [Chemical Formula 1].

  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, in order to precipitate the crosslinked part acid copolymer in a state where water is not swollen, the solubility parameter is 9 or more in the aqueous solution after the decomposition step in which the crosslinked part acid copolymer is dissolved, and As an intermediate phase (solid phase) between a solvent phase having a solubility parameter of 9 or more and having compatibility with water and an aqueous phase, a solvent having compatibility with water and an acid are supplied. Alternatively, the cross-linked acid copolymer can be precipitated as a solid content by precipitation, and the solid content is collected, washed with a small amount of water or ether, dehydrated and cross-linked without heating by natural drying. A partial acid copolymer can be obtained.

  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 solvent without heating, most of the glycols that are very soluble in water and ether can be removed from the solid content, and the glycols are hardly contained. A cross-linked acid copolymer can be obtained, and therefore, a cross-linked acid copolymer that is easy to use as a molding material with little increase in viscosity due to heating can be obtained.

  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 4000 to 5000. 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]
After adding 20 ml of tetrahydrofuran to 10 g of the aqueous solution recovered in the decomposition step and stirring, 1N HCl was added with stirring until pH 2 was reached, and after reaching pH 2, stirring was further continued for 5 minutes. Thereafter, the solid and liquid were separated by suction filtration to obtain 0.50 g of a solid content (crosslinked part acid copolymer). Further, the solid content was dried (at 105 ° C. for 2 hours, and the following drying was performed under the same conditions) to obtain 0.39 g of a crosslinked part acid copolymer.

[Example 2]
In Example 1, instead of tetrahydrofuran, 1,4 dioxane: 20 ml was added, and the same operation was performed to obtain 0.51 g of a solid content (crosslinked acid copolymer), and a crosslinked acid copolymer after drying. 0.40 g was obtained.

Example 3
In Example 1, 20 ml of thiophene was added instead of tetrahydrofuran, and the same operation was performed to obtain 0.56 g of a solid content (crosslinked part acid copolymer) and 0.42 g of a crosslinked part acid copolymer after drying. Got.

[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, followed by separation of a solid and a liquid by suction filtration to obtain 3.50 g of a solid content (water-containing crosslinked part acid copolymer). Further, the solid content was naturally dried to obtain 0.46 g of a crosslinked part acid copolymer.

[Moisture content and dehydration effect]
About the said Examples 1-3 and the comparative example 1, 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 3 have lower moisture content and higher dehydration effect than Comparative Example 1, and are easily swollen with a large amount of water produced by subcritical water decomposition. The (crosslinked part 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.

  In addition, as a result of measuring the amount of polyhydric alcohol in the solution after separating and taking out the solid content of the cross-linked acid copolymer by gas chromatography, it was the same as the amount before the solid content of the cross-linked acid copolymer was separated. Met.

Claims (6)

  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 in the presence of alkali to produce a polyhydric alcohol as a raw material monomer for plastic and an organic as a raw material monomer for plastic. A step of decomposing the acid salt, and a cross-linked acid copolymer salt that is a compound of an organic acid constituting the cross-linked part and the unsaturated polyester part, and a polyhydric alcohol and an organic acid salt obtained in the decomposing step, A step of separating the solid content and the liquid phase of the cross-linking part acid copolymer by supplying a solvent having a solubility parameter of 9 or more and an acid to the aqueous solution containing the cross-linking part acid copolymer salt. In addition, as a solvent having a solubility parameter of 9 or more, a cyclic compound having an oxygen atom or a sulfur atom in the ring is used, and the solid content of the crosslinked acid copolymer is dehydrated with the solvent, and the crosslinked part Copolymer of styrene - how decomposition and separation of the plastic, which is a fumaric acid resin.   The method for decomposing / separating plastic according to claim 1, further comprising a step of recovering polyhydric alcohol and organic acid by removing water and solvent 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 the solvent is compatible with water.   The method for decomposing / separating plastic according to any one of claims 1 to 4, wherein the solvent is at least one selected from tetrahydrofuran and 1,4 dioxane.   The method for decomposing / separating plastic according to any one of claims 1 to 3, wherein the solvent is thiophene.

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