JP2006232934A - Method for decomposing/recovering plastic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for decomposing/recovering plastics in such a form that decomposed plastics can be utilized again as similar plastics. <P>SOLUTION: The method comprises decomposing a thermosetting resin composed of an unsaturated polyester portion and a crosslinked portion thereof using subcritical water with a temperature below the thermal decomposition temperature to produce an aqueous solution containing a polyhydric alcohol, an organic acid, and a compound of an organic acid composing the crosslinking portion and the unsaturated polyester portion, separating the aqueous solution by using a membrane separation method to a solid component of the compound of the organic acid and an aqueous solution containing the polyhydric alcohol and the organic acid, and removing water in the aqueous solution containing the polyhydric alcohol and the organic acid to recover the polyhydric alcohol and the organic acid. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a plastic decomposition and recovery method for recovering valuable materials from plastics, particularly waste plastics.

Conventionally, most plastic waste has been subjected to landfill disposal or incineration, and has not been effectively utilized as a resource. In addition, landfill disposal causes problems such as difficulty in securing landfill site and unstable land after landfill, and incineration treatment causes problems such as furnace damage, generation of harmful gases and odors, and CO ₂ emissions. Arise. For this reason, the Containers and Packaging Waste Law was enacted in 1995, requiring plastics to be collected and reused. In addition, with the recent enforcement of various recycling laws, the flow of collection and reuse of products containing plastics tends to accelerate.

Against this background, in recent years, many studies have been made on the recycling of plastic waste, and one of them is useful for decomposing oil from plastic waste by a reaction using supercritical water as a reaction medium. A method for recovering the oil has been proposed. In addition, for fiber reinforced plastics used in various structural materials, a method has been proposed in which plastic components are decomposed using supercritical water or subcritical water, and fibers such as glass fibers and carbon fibers are recovered and reused. Yes. In these methods, the plastic waste becomes an oily component having a low molecular weight by the decomposition treatment, and is mainly reused as a liquid fuel. In addition, a chemical recycling method is proposed in which a cured unsaturated polyester resin waste is decomposed by using a decomposition component such as dicarboxylic acid or diamine to recover a resin raw material, and an unsaturated polyester resin is re-synthesized (for example, (See Patent Document 1).
Japanese Patent Laid-Open No. 9-221565

  However, when plastics are decomposed and recovered using supercritical water, the plastic components are randomly decomposed, so that the decomposition product becomes a multi-component oily substance, and it is difficult to maintain a constant quality. For this reason, post-treatment such as reforming the oil quality using a catalyst typified by zeolite is required, resulting in an increase in cost. Moreover, since it is difficult to make the modified oil quality into petroleum components such as kerosene and light oil, it has not been put into practical use. On the other hand, when plastics are decomposed and recovered using the chemical recycling method, the decomposed resin is reused again as an unsaturated polyester resin, but thermal decomposition occurs due to the high decomposition temperature, and the resin is recycled. The physical properties when cured are different from those of the original unsaturated polyester resin (decreases as a thermosetting resin). Moreover, the utilization factor of the decomposition resin which occupies for a recured product becomes low.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for decomposing and recovering plastic that can be decomposed and recovered in such a manner that the plastic can be used again as a similar plastic.

  In order to solve the above-mentioned problems, the method for decomposing and recovering plastic according to the present invention includes decomposing a thermosetting resin comprising an unsaturated polyester portion and a cross-linked portion thereof with subcritical water at a temperature lower than the thermal decomposition temperature. To produce an aqueous solution containing a polyhydric alcohol, an organic acid, and an organic acid compound that constitutes the crosslinked portion and the unsaturated polyester portion, and the aqueous solution is separated from the solid content of the organic acid compound and the polyhydric alcohol using a membrane separation method. And the aqueous solution containing the organic acid, and the water in the aqueous solution containing the polyhydric alcohol and organic acid is removed to recover the polyhydric alcohol and organic acid.

  According to the method for decomposing / recovering plastic according to the present invention, the thermosetting resin is decomposed with subcritical water at a temperature lower than the pyrolysis temperature. It decomposes into an acid compound that constitutes the saturated polyester portion, and prevents the decomposition product from becoming an oily substance composed of various components, whereby a decomposition product of a certain quality can be obtained. Therefore, the decomposition product can be reused again as a raw material for the same thermosetting resin.

  Further, according to the method for decomposing and recovering plastic according to the present invention, since the aqueous solution is separated into a solid content of an organic acid compound and an aqueous solution containing a polyhydric alcohol and an organic acid using a membrane separation method, the processing cost is reduced. The solid content of the organic acid compound can be efficiently recovered while keeping the value low.

  Hereinafter, a method for decomposing and recovering plastic according to an embodiment of the present invention will be described.

  In the present invention, the plastic to be decomposed is a thermosetting resin composed of an unsaturated polyester portion and a cross-linked portion thereof. In this specification, the unsaturated polyester part is a part derived from a polyhydric alcohol and an unsaturated polybasic acid that is an organic acid, and is produced by polycondensation of the polyhydric alcohol and the unsaturated polybasic acid. The unsaturated alkyd resin portion. Moreover, a crosslinked part is a part originating in the crosslinking agent which bridge | crosslinks unsaturated alkyd resin. Therefore, “a thermosetting resin comprising an unsaturated polyester portion and a crosslinked portion thereof” means a reticulated thermosetting resin (a reticulated resin) obtained by crosslinking an unsaturated alkyd resin comprising a polyhydric alcohol and an unsaturated polybasic acid with a crosslinking agent. (Unsaturated polyester 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 polybasic acids such as maleic anhydride, maleic acid, fumaric acid, and phthalic acid. 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 fumaric anhydride as an organic acid may be used in combination with the unsaturated polybasic acid.

  In the present invention, water is added to the thermosetting resin, the temperature and pressure are increased, and the water is heated to a subcritical state below the critical point (critical temperature 374.4 ° C., critical pressure 22.1 MPa or less). By decomposing the curable resin, the monomer derived from the unsaturated polyester (polyhydric alcohol and unsaturated polybasic acid) is recovered from the unsaturated polyester, and the cross-linked product and unsaturated are formed from the portion constituting the cross-linked portion and the unsaturated polyester portion. The organic acid compound constituting the polyester portion is recovered. That is, the organic acid compound constituting the crosslinked part and the unsaturated polyester part is a compound (reactant) of the crosslinking agent and the unsaturated polybasic acid of the unsaturated polyester part.

  In addition, in this invention, although the mixture ratio of a thermosetting resin and water is not restrict | limited in particular, The addition amount of water shall be the range of 100-500 mass parts with respect to 100 mass parts of thermosetting resins. It is desirable. The temperature of the decomposition reaction (subcritical water) is a temperature below the temperature at which the thermosetting resin is hydrolyzed, but below the temperature at which the crosslinked portion and the unsaturated polyester portion are thermally decomposed. It is desirable that the temperature be set in a temperature range of 180 to 270 [° C.]. If the temperature during the decomposition reaction is less than 180 [° C.], the decomposition process takes a lot of time and the processing cost may increase. Conversely, the temperature during the decomposition reaction exceeds 270 [° C.]. Then, the influence of thermal decomposition becomes large, the unsaturated polyester part and its crosslinked part are decomposed, and it may be difficult to recover the acid compound constituting the crosslinked part and the unsaturated polyester part. 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, a shorter reaction time is preferable because the processing cost is reduced. . Further, the pressure of the decomposition reaction is not particularly limited, but is preferably in the range of about 2 to 15 [MPa].

  In general, the plastic decomposition treatment with subcritical water occurs by a thermal decomposition reaction and a hydrolysis reaction. The same applies to a thermosetting resin produced from a raw material containing a polyhydric alcohol and an organic acid. In the case of processing in contact with critical water, the hydrolysis reaction becomes dominant, and the hydrolysis reaction occurs selectively, resulting in a polyhydric alcohol and organic acid (salt) monomer or an oligomer in which a plurality of these are combined. It is to be decomposed. Therefore, also in the present invention, by treating the thermosetting resin in contact with subcritical water, the polyhydric alcohol, the unsaturated polybasic acid, and the organic acid compound constituting the crosslinked portion and the unsaturated polyester portion are obtained. The monomer or oligomer obtained by the decomposition treatment can be recovered and reused as a raw material for producing plastics.

  In the present invention, it is desirable that the subcritical water contains an alkali metal hydroxide, whereby the hydrolysis reaction of the thermosetting resin is promoted by the alkali metal hydroxide and the treatment time is increased. The processing cost can be reduced. Furthermore, in a high temperature range close to the supercritical state, polyhydric alcohol produced by treating the thermosetting resin with subcritical water is an organic product produced by treating the thermosetting resin with subcritical water. Although there is a risk of secondary decomposition due to the acid catalytic effect of the acid, the organic acid can be neutralized with an alkali metal hydroxide base, and the polyhydric alcohol is secondary decomposed due to the acid catalytic effect of the organic acid. Can be suppressed. Here, the blending amount of the alkali metal hydroxide is not particularly limited, but the concentration of the alkali metal hydroxide in the subcritical water is preferably 0.2 [mol / liter] or more. . Further, when the concentration of the alkali metal hydroxide is less than 0.2 [mol / liter], the alkali metal hydroxide may make it difficult to obtain the above effect. The upper limit value of the alkali metal hydroxide concentration is not particularly limited, but is preferably 1.0 [mol / liter] or less from the viewpoint of cost.

  Examples of the alkali metal hydroxide include potassium hydroxide (KOH) and sodium hydroxide (NaOH), but are not limited thereto. In addition, a poorly water-soluble base can be added to the subcritical water instead of the alkali metal hydroxide or in combination with the alkali metal hydroxide. Examples of the poorly water-soluble base include calcium carbonate, but are not limited thereto.

  In the method for decomposing and recovering plastic according to the present invention, first, a thermosetting resin to be decomposed and an additive such as water and an alkali metal hydroxide are mixed and heated and pressurized. The thermosetting resin is decomposed with subcritical water. Next, after cooling the subcritical water after the decomposition treatment, the solid and liquid are separated by a method such as filtration. Here, an inorganic filler such as glass fiber or calcium carbonate contained in the thermosetting resin is obtained as a solid, and water and a water-soluble component dissolved therein are obtained as a liquid component.

  Next, the aqueous solution is separated into a compound of an organic acid constituting a cross-linked part and an unsaturated part using a membrane separation method. When the membrane separation method is used, it is desirable to use a UF membrane (UltraFiltration) membrane capable of separating molecules having a molecular weight of 5000 or more. The organic acid compound (for example, styrene fumarate copolymer) has a large number of hydroxyl groups at the terminals, and thus is dispersed in water and is difficult to separate by ordinary filtration. However, even such a dispersed material can be separated into the organic acid compound and the solvent in the case of membrane separation.

  In addition, since the organic acid compound has many molecular weights of about several tens of thousands, the use of a UF membrane that can separate molecules having a molecular weight of 5000 or more makes it possible to separate more reliably and increase the yield. It becomes possible. In addition, when the UF membrane is a negatively charged polysulfone-based spiral membrane, the styrene fumarate copolymer exists as carboxyl ions in the aqueous solution, which is effective in terms of separation performance, separation speed, and maintenance. Styrene fumarate copolymer can be recovered.

The styrene fumarate copolymer has a composition (m, n> 0) represented by the following chemical formula 1. In addition, when the subcritical water is an alkaline solution, the aqueous solution is neutralized by supplying an acid before the step of separating the aqueous solution into the organic acid compound that constitutes the crosslinked portion and the unsaturated portion. It is desirable to remove the produced salt using an ion exchange resin such as a styrene / divinylbenzene copolymer.

  The obtained organic acid compound can be reused as a low shrinkage agent by being used for resin remolding or added to other resins. Moreover, by distilling the aqueous phase obtained above, water, polyhydric alcohols such as glycol, and organic acid can be separately collected. In addition, the water obtained by distillation can be utilized again as water for producing subcritical water. Moreover, it is desirable to remove moisture by using a polyamide-based or polyvinyl alcohol-based reverse osmosis membrane or by absorbing the moisture in a water-absorbing polymer. In these methods, since water can be separated without heating, thermal alteration of the separated organic acid compound can be prevented. The weight of the water-absorbing polymer is desirably a weight that can absorb 80% or more of the water in the aqueous solution. Further, as the water-absorbing polymer, a crosslinked polyacrylate-based or isobutylene maleate-based one may be used.

  Next, specific examples 1 to 3 of the above-described plastic decomposition and recovery method will be described.

[Specific Example 1]
First, with reference to FIG. 1, the specific example 1 of the said decomposition | disassembly and collection | recovery method of a plastic is demonstrated.

  In this specific example 1, 600 is obtained by pulverizing FRP resin under 1.7 [mm] in a stainless steel cylindrical pressure resistant container having an inner diameter of 150 [mm], a depth of 350 [mm], and a pressure resistance of 7 [MPa]. [G], pure water 1800 [g], and potassium hydroxide (Nacalai Tesque) 100 [g] are added, and the FRP resin is decomposed by heating at 230 [° C.] for 120 [minutes] with the lid covered. To process. Here, the composition of the FRP resin is 34 [wt%] propylene glycol-maleic anhydride-styrene copolymer (unsaturated polyester resin), 66 [wt%] glass fiber and calcium carbonate as a filler. .

  And after a decomposition process, after cooling a cylindrical heat-resistant container to room temperature, the solid substance containing the inorganic substance of glass fiber and a calcium carbonate is removed from a solution by carrying out solid-liquid separation of the solution with a glass filter (Advantech GC-25). Then, the solid matter of the styrene fumarate copolymer is recovered from the solution using a membrane separation method, and the pH value of the filtrate is adjusted (neutralized) to 6 to 9 using a 1N-HCl solution. The filtrate was passed through a spiral membrane made of a polysulfone-based material, and the concentrate (styrene fumarate copolymer) and permeate (glycol, fumaric acid, KCl) were recovered. In this specific example, the outer shape of the spiral membrane was 2 [inch], and the water flow pressure and water flow rate were 1.5 [MPa] and 1 [l / min]. In addition, a film that can separate molecules having a molecular weight of 5000 or more was used as the spiral film.

The concentrations of glycol and fumaric acid are analyzed by a gas chromatograph analyzer and an ion chromatograph analyzer, respectively, and the concentration of glycol and fumaric acid is multiplied by the amount of sample, whereby the recovery rate of glycol and fumaric acid is expressed by the following formula 1. , 2 was used for calculation. In this embodiment, the blending ratio of glycol and fumaric acid in the unsaturated polyester resin is 23 [wt%].

As a result, the recovered amounts and recoveries of glycol and fumaric acid are as shown in Table 1 below. Moreover, after adjusting the pH value of the concentrate and the permeate to 2, the residue was dried at 100 [° C.] and 120 [min] in a dryer, and the weight was measured. From the measured weight, glycol and fumaric acid As a result of calculating the recovered amount of the styrene fumarate copolymer by subtracting the recovered amount, the recovered amount of the styrene fumarate copolymer was as shown in Table 1 below. In addition, the weight of the solid content of the styrene fumarate copolymer obtained at this time was 140 [g].

[Specific Example 2]
Next, specific example 2 of the above-described plastic decomposition / recovery method will be described.

In this specific example 2, in order to remove inorganic substances, a solution obtained by decomposing FRP resin with subcritical water is filtered, and then the pH value of the filtrate is adjusted (neutralized) to 6 to 9 using a 1N-HCl solution. . The FRP resin was decomposed under the same conditions as in the above specific example 1. Then, after the adjustment of the pH value is completed, the filtrate is passed through a spiral membrane similar to that of Specific Example 1, and the concentrated solution and the permeate are collected. Next, salt (KCL) in the permeated liquid was removed by passing the permeated liquid at a flow rate of 0.5 [l / min] through a column packed with an ion exchange resin of a styrene / divinylbenzene copolymer. Thereafter, the permeate was collected. As a result, the recovered amounts and recovery rates of glycol and fumaric acid were as shown in Table 2 below. Moreover, in order to confirm the removal of the salt (KCL) produced | generated by the neutralization process, as a result of measuring the evaporation residue amount of a collection | recovery liquid, the evaporation residue amount became like Table 2 shown below.

[Specific Example 3]
Finally, specific example 3 of the above-described plastic decomposition and recovery method will be described.

In this specific example 3, in order to remove inorganic substances, a solution obtained by decomposing FRP resin with subcritical water is filtered, and then the pH value of the filtrate is adjusted to 6 to 9 using a 1N-HCl solution. The FRP resin was decomposed under the same conditions as in the above specific example 1. Then, after the adjustment of the pH value is completed, the filtrate is passed through a spiral membrane similar to the specific example 3 to collect the concentrated solution and the permeate. Next, salt (KCl) is recovered from the permeate using an ion exchange resin such as a styrene / divinylbenzene copolymer to obtain a recovered liquid. At this time, the weight of the recovered liquid was 2250 [g]. Next, the recovered liquid is transferred to a container containing 3.8 [g] of the water-absorbing polymer, and left for 10 minutes with stirring, so that the water-absorbing polymer absorbs water in the recovered liquid. Thereafter, a concentrated recovery liquid was obtained using Saran mesh (150 [μm]). As a result, the recovered amounts and recovery rates of glycol and fumaric acid are as shown in Table 3. Further, as a result of measuring the recovery amount of the styrene fumarate copolymer, the recovery rate of the resin component composed of glycol, fumaric acid, and styrene fumarate copolymer was as shown in Table 3.

  As mentioned above, although the embodiment to which the invention made by the present inventors was applied has been described, the present invention is not limited by the description and the drawings that form part of the disclosure of the present invention according to this embodiment. That is, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above embodiments are all included in the scope of the present invention.

It is a flowchart which shows the flow of the decomposition | disassembly and collection | recovery process of the plastics used as embodiment of this invention.

Claims (8)

A polyhydric alcohol, an organic acid, and a crosslinked part and an unsaturated polyester part are constituted by decomposing the thermosetting resin composed of the unsaturated polyester part and the crosslinked part with subcritical water having a temperature lower than the thermal decomposition temperature. Producing an aqueous solution containing an organic acid compound;
Separating the aqueous solution into a solid content of the organic acid compound and an aqueous solution containing a polyhydric alcohol and an organic acid using a membrane separation method;
Removing the water in the aqueous solution containing the polyhydric alcohol and the organic acid, and collecting the polyhydric alcohol and the organic acid. The method for disassembling and recovering plastic according to claim 1,
A method for decomposing and recovering plastic, wherein the membrane used in the membrane separation method is a UF membrane capable of separating molecules having a molecular weight of 5000 or more. The method for disassembling and collecting plastic according to claim 2,
The method for decomposing and recovering plastic, wherein the membrane is a polysulfone-based membrane. In the plastics decomposition / recovery method according to any one of claims 1 to 3,
The subcritical water is an alkaline solution, and before the step of removing water in the aqueous solution containing the polyhydric alcohol and organic acid to recover the polyhydric alcohol and organic acid, an acid is supplied to the aqueous solution. A method for decomposing and recovering plastic, comprising a step of neutralizing and removing a salt produced by the neutralization. The method for disassembling and collecting plastic according to claim 4.
A method for decomposing and recovering plastic, wherein the salt is removed using an ionization exchange resin. The method for disassembling and collecting plastic according to any one of claims 1 to 5,
A method for decomposing and recovering plastic, wherein water in an aqueous solution containing the polyhydric alcohol and organic acid is removed by using a reverse osmosis membrane. The method for disassembling and collecting plastic according to any one of claims 1 to 6,
A method for decomposing and recovering plastic, wherein water in the aqueous solution containing the polyhydric alcohol and organic acid is removed by bringing the water-absorbing polymer into contact with the aqueous solution and allowing the water-absorbing polymer to absorb water. The method for disassembling and collecting plastic according to claim 7.
The method for decomposing and recovering a plastic, wherein the water-absorbing polymer is a crosslinked polyacrylate or isobutylene maleate.

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