JP2010144131A - Method for decomposing plastic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve decomposition efficiency together with an increase of processing amount of plastics to be decomposed in decomposition of plastics containing an inorganic filler. <P>SOLUTION: The plastics containing an inorganic filler is hydrothermally decomposed in a subcritical state with a process liquid in which a dispersant that disperses the inorganic filler is coexisted. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for decomposing plastics.

  Until now, most plastic waste has been landfilled or disposed of, and has not been effectively used as a resource. However, with the implementation of various recycling laws over the past few years, the flow of plastic recycling has tended to accelerate. Among them, a method of decomposing a thermosetting resin obtained by cross-linking a copolymer of polyhydric alcohol and acid with a cross-linking material using subcritical water at a temperature lower than or equal to the thermal decomposition temperature of the thermosetting resin has been studied. Regarding this decomposition method, various measures have been taken to obtain a copolymer of a crosslinked part and an acid (styrene fumaric acid copolymer: hereinafter referred to as SFC) together with a monomer that can be reused as a raw material for the thermosetting resin. It has been proposed together with improvement measures (for example, Patent Documents 1 and 2).

  However, in this method, when the thermosetting resin is decomposed by subcritical water decomposition, water as a solvent is several times (by 2 to 4) by weight with respect to a thermosetting substance such as FRP as a decomposition target. Required), and the amount of solvent affects the degree of stirring during decomposition. The amount of solvent is considered to be a major factor affecting efficiency, throughput, and decomposition rate. For this reason, when considering the efficiency of the decomposition reaction, an increase in the amount of solvent can be expected to improve the decomposition rate, but on the other hand, the amount of thermosetting resin that can be decomposed relative to the capacity of the reaction layer decreases There is.

  On the other hand, if the amount of solvent is decreased in order to increase the processing amount, sufficient stirring cannot be obtained, and the subcritical water decomposition product is not sufficiently decomposed, or the decomposition takes a long time. After all, it does not lead to efficient reaction.

  In addition, in order to improve the treatment amount, studies have been made to remove in advance inorganic fillers contained in thermosetting resins that are not subject to subcritical water decomposition.

This is a method in which an acid is reacted with an inorganic filler to change it into a water-soluble substance and solid-liquid separation is performed. However, since the combination of an inorganic filler and an acid is limited, it is not a general-purpose method. In addition, since new products and salts are generated after the reaction with the acid, there is a concern that treatment such as neutralization is required when the solvent is reused or discarded.
JP 2007-169524 A JP 2006-247476 A

  The present invention eliminates the above-mentioned adverse effects when decomposing a plastic that recovers a styrene organic acid copolymer by decomposing a thermosetting resin comprising a polyester part and a crosslinked part containing an inorganic filler with subcritical water. It is an object of the present invention to provide a method for improving the decomposition efficiency, that is, a method for decomposing a plastic that makes it possible to satisfy both conflicting factors of an increase in throughput and an improvement in decomposition efficiency.

  The plastic decomposition method of the present invention is characterized by the following.

  First: An inorganic filler-containing plastic is hydrothermally decomposed in a subcritical state with a treatment liquid in which a dispersant for dispersing the inorganic filler coexists.

  Second: The dispersant is an anionic surfactant.

  Third: The inorganic filler-containing plastic is hydrothermally decomposed by further coexisting alkali in the treatment liquid.

  According to the first aspect of the invention, when recycling a resin contained in an inorganic filler-containing plastic such as FRP, it is possible to improve the decomposition rate universally regardless of the type of the inorganic filler and increase the processing amount. It becomes. In addition, the decomposition time can be shortened. By adding the dispersant, the viscosity of the treatment solution containing the inorganic filler decreases, and the energy required for stirring also decreases.

  The inorganic filler has a content of nearly 50% of the whole for the purpose of increasing the molded body and imparting incombustibility. When reusing the resin, there is a method of subcritical water decomposition of the molded body. At this time, the inorganic filler is not subject to decomposition, and becomes an unnecessary substance in the decomposition step. Moreover, although stirring is performed during decomposition, extra energy is required due to the presence of the inorganic filler. Furthermore, since the inorganic filler sucks in water as a solvent, extra water necessary for decomposition is also required. In order to solve these problems, methods for removing the inorganic filler have been studied in the past, for example, as described above. In the case where the inorganic filler is calcium carbonate, it is a method of treating with hydrochloric acid as a pretreatment, separating the solid and liquid, removing the aqueous calcium chloride solution, and subjecting the residue to subcritical water decomposition. In this case, a significant decrease in the amount of treatment is expected, which can be a means of efficiency, but the types of inorganic filler and acid are limited. Even in the case of calcium carbonate, if hydrochloric acid is excessively present, there is a problem that the aqueous calcium chloride solution exhibits acidity and requires treatment. In the present invention, a dispersant for inorganic filler is added in advance to the pulverized compact as a method that can avoid these problems and can take a wide range of measures.

  As a result, the energy required for stirring is reduced, and free water is increased and stirring is facilitated. In addition, since the water required for decomposition and stirring is reduced, it is possible to increase the amount of the pulverized compact that can be charged into the reaction tank having a predetermined capacity. In this way, the efficiency of the reaction can be improved.

  And according to said 2nd invention, said effect is implement | achieved as a remarkable thing more reliably. In this case, when the dispersing agent is adsorbed on the surface of the powder, the intermolecular force between the particles of the powder is weakened, and at the same time, it is covered with an anion to promote electrostatic repulsion between the particles. In addition, inorganic powders are often charged with cations, and anionic dispersants have a characteristic of binding to powder particles relatively firmly and quickly.

  According to the third invention in which the treatment liquid contains an alkali, the above-described effect is realized more remarkably and the following effect is also exhibited.

  1) Hydrolysis ability is improved in subcritical water decomposition.

  2) The stability of the anionic dispersant is increased in an alkaline solvent, and the dispersion effect is maintained.

  3) Since the terminal of the decomposed styrene organic acid copolymer becomes a carboxylate salt due to the action of alkali and becomes water-soluble and dissolves, the specific surface area of the reaction object (molded product pulverized product) increases and the decomposition reaction is accelerated. .

  4) The styrene organic acid copolymer salt dissolved in the decomposition reaction itself becomes a surfactant, adsorbs on the surface of the inorganic filler, promotes dispersion, and improves the stirring uniformity of the treatment liquid.

  The above chain action can be expected, and a large dispersion effect can be obtained with a small amount of dispersant.

  In the present invention, when decomposing the inorganic filler-containing plastic that decomposes the thermosetting resin composed of the polyester part containing the inorganic filler and the crosslinked part to recover the styrene organic acid copolymer, the solvent is used as the solvent with respect to the weight of the inorganic filler. A predetermined amount of dispersant is added. First, the resin to be decomposed is a thermosetting resin obtained by crosslinking a copolymer of a polyhydric alcohol and an organic acid with a crosslinking material, and contains reinforcing fibers and a filler (inorganic filler) as a gap. Yes.

  As such a thermosetting resin, a polyester resin can be exemplified, and in particular, a thermosetting resin such as an unsaturated polyester resin can be exemplified. Examples of the polyhydric alcohol include glycols such as ethylene glycol, diethylene glycol, propylene glycol, and dipropylene glycol, but are not limited thereto. Examples of the organic acid include maleic anhydride, fumaric acid, and maleic acid, but are not limited thereto. Examples of the reinforcing fiber include glass fiber and carbon fiber, but are not limited thereto.

  In the method of the present invention, water and a dispersant are added to the pulverized product containing an inorganic filler, and the temperature and pressure are increased to bring water to a sub-critical point (critical temperature 374.4 ° C., critical pressure 22.1 MPa) or less. The thermosetting resin is decomposed in a critical state, and monomers (polyhydric alcohol and organic acid) are recovered in an aqueous solution. Moreover, a styrene organic acid copolymer is obtained with glass fiber as a solid with it.

  The decomposition temperature is preferably below the temperature at which various thermosetting resins are hydrolyzed but the styrene organic acid copolymer is reduced in molecular weight by thermal decomposition and various styrene derivatives are formed. It is preferable to make it. If it is lower than 180 ° C., the decomposition time becomes long, and there is a risk that the yield of the styrene organic acid copolymer may be lowered along with cost problems. On the other hand, if the temperature exceeds 300 ° C., the thermal decomposition of the styrene organic acid copolymer becomes remarkable, the molecular weight is lowered and the styrene derivative is decomposed, and it may be difficult to recover the styrene organic acid copolymer. The decomposition time takes into account the temperature, but is preferably about 1 to 8 hours. Of course, it is not particularly limited to this range.

  The dispersant may be an aqueous dispersant, a non-aqueous dispersant, ionic or nonionic. It is desirable that the molecular chain has a structure close to the structure of the powder particles or a structure close to that of the pigment.

  That is, a phenomenon in which a hydrophilic pigment containing a hydrophilic OH group or carboxylic acid group is easily adsorbed on the powder surface is exemplified, and a dispersant according to the type of inorganic filler of the molded body can be applied.

  As a result, the dispersant adsorbed by adhering to the inorganic filler creates a distance between the particles, weakens the intermolecular force, and simultaneously promotes the dispersion of the secondary aggregated particles.

  The ratio of the pulverized compact and water is not particularly limited, but is preferably 200 to 500 with respect to 100 parts by weight of the compact. The amount of the dispersant is desirably 0.1% to 3.0% with respect to the weight of the pulverized product (thermosetting resin and inorganic filler). If it is less than 0.1%, the dispersion effect is small and the effect is hardly expected. On the other hand, when it exceeds 3.0%, it becomes an excessive amount with respect to a solid substance, and the accumulation of an effect becomes difficult to be anticipated.

  It is more preferable to use an anionic surfactant, but these have a terminal structure such as carboxylic acid, sulfonic acid, phosphoric acid, etc. be able to.

  Although it is effective to contain an alkali in the treatment liquid, the alkali is not particularly limited, but can be used as an aqueous solution of an alkali metal hydroxide. As the alkali metal, potassium hydroxide, sodium hydroxide, or the like can be used. The alkali metal hydroxide is preferably added in the range of 5 to 20 parts by mass with respect to 100 parts by mass of the plastic.

  Therefore, an example will be shown below and will be described in more detail. Of course, the present invention is not limited by the following examples.

First, as a cured product of a thermosetting resin, a varnish in which a polyhydric glycol such as propylene glycol, neopentyl glycol, dipropylene glycol and an unsaturated organic acid, maleic anhydride, are blended with an equivalent amount of glycol. A cured product is prepared by blending 165 parts by weight of calcium carbonate and 90 parts by weight of glass fiber with 100 parts by weight of thermosetting resin in which styrene is blended in an equivalent amount as a crosslinking agent. Further, it is pulverized to about 2 mm in advance so that it can be easily measured. In Examples and Comparative Examples, the glycol recovery rate and SFC (styrene fumaric acid copolymer) recovery rate of the cured product were determined as follows.
[Glycol recovery rate]
The recovery rate of glycol is recovered by solid-liquid separation of water-soluble components after subcritical water decomposition, and the glycol component is quantified from the water-soluble components by gas chromatography analysis (GC analysis). It was.

Glycol recovery rate (%) = quantification result of glycol monomer component / estimated content of glycol monomer in cured product × 100
Estimated content of glycol monomer: Calculated by ratio calculation from raw material blending amount during varnish molding [SFC recovery rate]
The amount of SFC contained in the water-soluble component after subcritical water decomposition is determined as the SFC recovery rate as follows.

  After separating the soluble component after the decomposition treatment by solid-liquid separation, the precipitate formed by adjusting the pH to 2 was dried, and the weight was measured.

SFC recovery rate (%) = dry weight of precipitate obtained by acid addition to water-soluble matter / estimated SFC content of cured product × 100
Estimated weight of SFC in the cured product: The binding ratio of the structure of carboxylic acid and styrene is obtained by NMR, and the total weight of SFC is estimated by comparison with the amount of styrene blended.
<Comparative Example 1>
In Comparative Example 1, 16 g of pure water is taken with respect to 4 g of the cured product, and these are charged into the reaction tube 1 as shown in FIG. 1 and immersed in a constant temperature bath 2 at 230 ° C. to be subcritical in the reaction tube 1. In this state, the thermosetting resin cured product was decomposed by leaving it immersed for 2 hours. Thereafter, the reaction tube 1 was taken out from the thermostatic bath 2 and immersed in the cooling bath 3, and the reaction tube 1 was rapidly cooled to room temperature.

The content of the reaction tube 1 after the decomposition treatment is a water-soluble component and an inorganic filler (mainly composed of calcium carbonate and glass fiber). By filtering the content, the water-soluble component is separated and reacted. Recovered from tube 1.
<Comparative example 2>
In Comparative Example 2, 0.4 g of NaOH was dissolved in 16 g of pure water as a solvent, and subcritical water decomposition treatment was performed under the same conditions as in Comparative Example 1, and the water-soluble content obtained after decomposition was determined. Similarly, it was recovered by solid-liquid separation.
<Comparative Example 3>
For Comparative Example 3, the total amount was adjusted by increasing the amount of the cured product by 1.5 times in Comparative Example 2 and decreasing the amount of solvent by the amount of increased solid content. The subcritical water decomposition conditions were the same, and the water-soluble component was recovered after decomposition.
<Example 1-5>
For each comparative example, as Example 1-3, 0.4% (0.016 g) of an anionic dispersant (A: polyacrylic acid sodium salt) was added to the solid content, and subcritical water decomposition was performed. The water-soluble component was recovered after decomposition.

Further, as Example 4-5, 0.1% and 3.0% of the same anionic dispersant was added to the solid content to perform subcritical water decomposition, and the water-soluble content was determined after decomposition. It was collected.
<Example 6-7>
In Example 2-3, the anionic dispersant was changed to naphthalenesulfonic acid formalin condensate sodium salt, subcritical water decomposition was performed, and the water-soluble component after decomposition was recovered.

  Table 1 shows the results of determining the glycol recovery rate and the SFC recovery rate for the above comparative examples and examples.

  As shown in Examples 1-2 and 4-6, in comparison with Comparative Examples 1 and 2, by adding a dispersant, a greater dispersion effect can be obtained regardless of the presence or absence of alkali, thereby obtaining a glycol recovery rate. As a result, the main chain was cut, and as a result, the recovery rate of SFC including the cross-linked portion was improved. In Example 1, SFC is recovered not only as a water-soluble substance after decomposition but also as a solid content.

  For Examples 3 and 7, compared with Comparative Example 3, even when the amount of water was small relative to the solid content before decomposition, stirring was sufficiently performed, and the hydrolysis reaction was efficiently performed in subcritical water. It means that it was done.

  That is, it was confirmed that the amount of treatment could be increased 1.5 times (4 g → 6 g) with the same decomposition rate by adding a dispersant.

It is the schematic which showed about the procedure of the decomposition reaction in an Example and a comparative example.

Explanation of symbols

1 Reaction tube 2 Thermostatic bath 3 Cooling bath

Claims (3)

  A method for decomposing a plastic, characterized in that an inorganic filler-containing plastic is hydrothermally decomposed in a subcritical state with a treatment liquid in which a dispersant for dispersing the inorganic filler coexists.   The method for decomposing a plastic according to claim 1, wherein the dispersant is an anionic surfactant.   The method for decomposing a plastic according to claim 1 or 2, wherein an alkali filler is further allowed to coexist in the treatment solution to hydrothermally decompose the plastic containing the inorganic filler.

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