JP2006241380A - Method for decomposing plastic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for decomposing a plastic that can recover a compound of an organic acid, a polyol and an organic acid in a high yield, that are used as raw materials of a resin, and can again reproduce from the recovered raw materials of a resin a similar plastic without degrading its physical properties. <P>SOLUTION: The method for decomposing a plastic comprises the following processes: an aqueous solution 2 containing a polyol 3, an organic acid 4, and an organic acid compound constituting a crosslinking part 5, that are each a raw material monomer of an unsaturated polyester resin, is obtained by decomposing a plastic 1 containing an unsaturated polyester resin formed from an unsaturated polyester part and a crosslinking part using subcritical water having a temperature lower than the decomposition temperature of the unsaturated polyester resin (process A); and the resulted aqueous solution 2 is filtered after controlling its pH to 4-12 (process B), to separate an organic compound 5 from the aqueous solution 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for decomposing a plastic containing an unsaturated polyester resin particularly suitable for FRP (fiber reinforced plastic).

  Plastics are lightweight, high-strength, strong against rust and corrosion, free to color, excellent in electrical insulation, easy to mold, and capable of mass production. It is used in large quantities as materials for household goods. For this reason, the amount of waste plastic continues to increase.

Conventionally, most of the waste plastic has been disposed of by landfill or incineration. However, when waste plastic is landfilled, the ground after landfill becomes unstable, and it is difficult to secure land for landfill. In addition, when waste plastic is incinerated, harmful gases (for example, CO ₂ ) and bad odors are generated, which not only causes concern about environmental pollution, but also causes a problem that the incinerator is damaged.

  Therefore, the Containers and Packaging Waste Law (Recycling Law) was enacted in 1995, and waste plastics were collected and required to be reused. With the enforcement of this law, the development of technologies for recycling waste plastics is rapidly progressing.

  For example, a method for recovering an oily substance obtained by thermally decomposing waste plastic using supercritical water as a reaction medium is disclosed (see Patent Document 1).

In addition, after crushing the cured unsaturated polyester resin, which is waste plastic, the decomposition product obtained by decomposing with dicarboxylic acid or diamine at a temperature of about 100 ° C. to 300 ° C. is reused as a resin raw material. A method of re-synthesizing is also disclosed (see Patent Document 2).
Japanese Patent Laid-Open No. 10-67991 Japanese Patent Laid-Open No. 9-221565

  However, when the waste plastic is pyrolyzed using the supercritical method described in Patent Document 1 described above, the treatment temperature is too high, so that the main chain and the side chain in the waste plastic are cleaved randomly and the resulting oily oil is obtained. The substance contained many kinds of low molecular weight components. The oily substance obtained by pyrolyzing waste plastic is mainly reused as a liquid fuel. However, in order to ensure the quality of the oily substance after pyrolysis, the oily substance is catalyzed (for example, zeolite) after the pyrolysis. ) Must be reformed and post-processing is required, which has been a factor in increasing processing costs. Further, even when the reforming process is performed, it is difficult to reuse the reformed product oil as a petroleum product (for example, kerosene or light oil) itself.

  Further, in the method described in Patent Document 2, the obtained decomposition product can be reused as an unsaturated polyester resin raw material. However, when the cured unsaturated plastic is decomposed at a high temperature exceeding 280 ° C., the thermal decomposition proceeds. Therefore, there has been a problem that the strength of the thermosetting resin is lowered when re-cured. Furthermore, even when the temperature during decomposition was a low temperature of about 100 ° C. to 180 ° C., the recovery rate of the resin raw material that can be recovered after decomposition was low. For these reasons, the proportion of the recovered raw material resin used as a product after recuring has been low.

  The present invention has been made in order to solve the above-described problems. That is, the plastic decomposition method of the present invention uses a plastic containing an unsaturated polyester resin formed from an unsaturated polyester portion and a crosslinked portion. An aqueous solution containing a polyhydric alcohol and an organic acid, which are raw materials monomers of the unsaturated polyester resin, a cross-linked part and a compound of the organic acid, is decomposed using subcritical water that is lower than the thermal decomposition temperature of the saturated polyester resin. The obtained aqueous solution is adjusted to pH 4 to 12, and then the obtained aqueous solution is filtered to separate an organic compound from the aqueous solution.

  According to the method for decomposing a plastic according to the present invention, a compound of an organic acid, a polyhydric alcohol, and an organic acid that can be reused as a resin raw material can be recovered in high yield, and physical properties are almost deteriorated from the recovered resin raw material. The same plastic can be regenerated again without any problems. As a result, waste plastic can be recycled and effectively used.

  Hereinafter, a plastic disassembling method according to an embodiment of the present invention will be described with reference to the accompanying drawings.

  A plastic disassembling method according to an embodiment of the present invention will be described with reference to FIG.

  First, as shown in FIG. 1, a plastic 1 containing an unsaturated polyester resin formed from an unsaturated polyester portion and a crosslinked portion is hydrolyzed using subcritical water whose temperature is lower than the thermal decomposition temperature of the unsaturated polyester resin. (Step A). When decomposed, an aqueous solution 2 is obtained. In the aqueous solution 2, a polyhydric alcohol 3 (for example, glycol) and an organic acid 4 (for example, fumaric acid), which are raw materials for the unsaturated polyester resin, and an unsaturated polyester resin are used. And a compound 5 of the organic acid (for example, styrene fumarate: a copolymer of styrene and fumaric acid).

  Next, after adjusting the pH of the obtained aqueous solution 2 within the range of 4 to 12, the aqueous solution after pH adjustment is filtered (step B). After filtration, the filtrate is dried and separated as a solid of organic acid compound 5 (eg, styrene fumarate).

  Then, the polyhydric alcohol which isolate | separated the compound 5 of the organic acid and the aqueous solution containing the organic acid 4 are distilled (process C), and the polyhydric alcohol 3 and the organic acid 4 are obtained.

  In general, when hydrolyzing plastics made from raw materials containing polyhydric alcohols and organic acids, thermosetting plastics cannot be decomposed at low temperatures (about 100 ° C), and thermoplastic plastics cannot be decomposed. In order to do so, a processing time of several tens of hours is required, and the reaction takes a long time. On the other hand, when plastics are hydrolyzed under high temperature (about 360 ° C) and high pressure (about 20MPa), as in the case of using critical water (critical temperature of critical point 374.4 ℃, critical pressure 22.1MPa), decomposition products There is a concern that the secondary decomposition of the material will occur and that the apparatus will be corroded. For this reason, it was difficult to decompose the raw material monomer in a high yield by decomposing in units of the raw material monomer of the resin. According to the method for decomposing a plastic according to the embodiment of the present invention, by decomposing using a subcritical water (below 280 ° C., 7 MPa or less) that is less than the thermal decomposition temperature of the unsaturated polyester resin, The raw material monomer unit of the saturated polyester resin can be separated and recovered. Furthermore, after adjusting the pH of the aqueous solution after decomposition with subcritical water, the organic acid compound can be separated and recovered in a high yield by filtration.

  In the plastic decomposition method, when adjusting the pH of the aqueous solution obtained after the decomposition, hydrochloric acid, sulfuric acid, nitric acid or the like is added to the aqueous solution to adjust the pH.

  Although the pH is defined as 4 or more, when the pH is less than 4, the organic acid compound 5 (styrene fumarate) swells like an agar, making it difficult to recover the organic acid compound 5, glycol and fumaric acid. Because. Moreover, when pH exceeds 12, the intensity | strength of the filter agent generally used for filtration will fall, and it will become difficult to filter the compound 5 of an organic acid efficiently.

  When the pH of the aqueous solution is adjusted to 4 to 7, the aqueous solution can be filtered using a hollow fiber, a microfiltration membrane (MF), an ultrafiltration membrane (UF) or a reverse osmosis membrane (RO). Filtration using a hollow fiber or a microfiltration membrane (MF) is preferable because filtration is possible at a low processing pressure, so that the equipment is simplified. In addition, when the pH of the aqueous solution is adjusted to 7 to 12, it can be filtered using a microfiltration membrane, an ultrafiltration membrane or a reverse osmosis membrane. The ratio at which 5 can be separated and recovered is preferable.

  Compound 5 of organic acid (styrene fumarate) is a divalent acid. When pH is 9 or higher, both divalent ions are ionized and compatible with water, and when pH is 4-7, only monovalent ions are ionized. When it is in a suspended state and has a pH of less than 4, both divalent ions are not ionized and the water solubility is lowered and the agar-like swelling occurs. Therefore, in the case of pH 9 or higher in a dissolved state, if a microfiltration membrane finer than the hollow fiber or a membrane smaller than that is used, it can be surely filtered, and about pH 4-7 which is in a suspended state Since the particles are relatively large, it is possible to reliably filter even with hollow fibers. In addition, in the case of pH 7-9, the state in the case of pH 4-7 and the state in the case of pH 9 or more coexist, and similarly to the case of pH 9 or more, the fine filtration membrane finer than the hollow fiber or smaller than that Use of a membrane makes it possible to reliably filter.

  Further, a method for decomposing FRP (fiber reinforced plastic) using the method for decomposing plastic according to the embodiment of the present invention will be described in detail with reference to FIG.

  First, 480 g of FRP (comprising 34 wt% of propylene glycol-maleic anhydride-styrene copolymer, glass fiber and 66 wt% of calcium carbonate as a filler) pulverized under 1.7 mm is prepared.

  Next, as shown in FIG. 2 (a), pulverized FRPa 480g, potassium hydroxide b (Nacalai Tesque) in a stainless steel cylindrical pressure vessel 10 (inner diameter 150mm, depth 350mm, pressure 7MPa) (Manufactured) 53 g and pure water c1800 g are added, and then the lid 11 of the heat-resistant container 10 is closed.

  Thereafter, as shown in FIG. 2B, the FRP is decomposed by subcritical water by heating at 230 ° C. for 120 minutes. After cooling to room temperature, solid-liquid separation is performed using a glass filter (GC-25, manufactured by Advantech Toyo Co., Ltd.). As shown in FIG. 2 (c), the separated solid is an inorganic substance d of glass fiber and calcium carbonate, and is recovered and reused as an inorganic filler. The aqueous solution e from which the inorganic substance d has been removed contains decomposed glycol, fumaric acid, and styrene fumarate (styrene / fumaric acid copolymer). The aqueous solution e1710 ml is used as test water for a filtration test described later.

  Next, as shown in FIG. 2 (d), 1N HClf is added to the aqueous solution e from which the inorganic substance d has been removed to adjust the pH to 4-12. Thereafter, the obtained aqueous solution e ′ is filtered by a filtration device using a microfiltration membrane (MF). A filtering device 20 using a microfiltration membrane is shown in FIG. In the filtering device 20, a microfiltration membrane 22 is disposed inside the container 21 below the center of the height of the container 21. A nitrogen gas cylinder 24 is connected to the upper side of the container 21 via a nitrogen supply pipe 23 for supplying nitrogen gas h, and a pressure regulator 25 is installed in the nitrogen supply pipe 23. The amount of nitrogen gas introduced into the container 21 is adjusted, and the pressure in the container 21 is adjusted. Below the container 21, a cylinder 26 for storing the filtrate g that has passed through the microfiltration membrane 22 is connected via a filtrate pipe 27. The microfiltration membrane 22 used here is a test flat membrane having a nominal diameter of 0.1 μm, and is a polytetrafluoroethylene membrane.

  Styrene fumarate i recovered by filtration has the molecular structure shown in FIG. 3 and is reused as a resin raw material. On the other hand, the filtrate g from which the styrene fumarate has been removed is distilled to recover glycol m and fumaric acid n.

  In the method shown in FIG. 2, the styrene fumarate is separated by a filtration device using a microfiltration membrane. However, when the pH of the aqueous solution is adjusted to 4 to 7, the styrene fumarate is obtained by a filtration device using a hollow fiber. Separate rates. A filtration device 30 using hollow fibers is shown in FIG. In the filtration device 30, hollow fibers 32 are arranged in a beaker 31, a mechanism 33 for collecting a filtrate from each hollow fiber 32 is connected, and a filtrate pipe 34 is connected to the mechanism 33. A suction bottle 35 is disposed at the end of the filtrate pipe 34, a beaker 36 for storing the filtrate is installed inside the suction bottle 35, and a compressor 37 is connected to the suction bottle 35. As the hollow fiber 32, a Trebino super series (manufactured by Toray Industries, Inc.), which is a replacement cartridge for a commercially available water purifier, was used.

  Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1
In Example 1, a filtration test was conducted using a filtration apparatus using the hollow fiber shown in FIG. The FRP decomposition method was the same as the procedure shown in FIG. 2, and the aqueous solution e shown in FIG. 2 (c) was used as test water for the filtration test. 1N HCl was added to the aqueous solution e, and the pH of the aqueous solution e ′ shown in FIG. 2 (c) was adjusted to 4.6.

(Example 2)
In Example 2, a filtration test was performed using a filtration apparatus using the microfiltration membrane shown in FIG. The FRP decomposition method was the same as the procedure shown in FIG. 2, and the aqueous solution e shown in FIG. 2 (c) was used as test water for the filtration test. 1N HCl was added to the aqueous solution e, and the pH of the aqueous solution e ′ shown in FIG. 2 (c) was adjusted to 4.6.

(Example 3)
In Example 3, a filtration test was conducted using a filtration apparatus using the hollow fiber shown in FIG. The FRP decomposition method was the same as the procedure shown in FIG. 2, and the aqueous solution e shown in FIG. 2 (c) was used as test water for the filtration test. Since this aqueous solution e showed alkalinity, 1N HCl was added to adjust the pH of the aqueous solution e ′ to 9.4.

Example 4
In Example 4, the filtration test was conducted with the filtration apparatus using the microfiltration membrane shown in FIG. The FRP decomposition method was the same as the procedure shown in FIG. 2, and the aqueous solution e shown in FIG. 2 (c) was used as test water for the filtration test. Since this aqueous solution e also showed alkalinity, 1N HCl was added to adjust the pH of the aqueous solution e ′ to 9.4.

(Comparative example)
In the comparative example, FRP was decomposed by the procedure shown in FIG. 2, and the aqueous solution e shown in FIG. 2 (c) was used as test water for the filtration test. 1N HCl was added to the aqueous solution e to adjust the pH of the aqueous solution e ′ to 3.

  The density | concentration of the styrene fumarate collect | recovered from the Example 1- Example 4 mentioned above and the comparative example was calculated | required using the following method.

  First, 300 ml of the aqueous solution shown in FIG. 2 (c) was put as test water in a centrifuge sample container weighed in advance. Thereafter, 1N HCl was added to adjust the pH to 2, followed by centrifugation. Thereafter, the supernatant was removed, washed with pure water, and then centrifuged again. Further, after removing the supernatant, it was dried at 105 ° C. for 2 hours, and the weight of the whole container was measured. The amount of styrene fumarate contained in the aqueous solution e was determined by subtracting only the weight of the sample container for centrifugation previously measured from the weight of the entire container. Based on the determined amount of styrene fumarate, the concentration of styrene fumarate in the aqueous solution e was calculated, and the concentration of styrene fumarate in the filtrate after the filtration treatment was calculated. The styrene fumarate elution inhibition rate (%) was determined from the styrene fumarate concentration in the aqueous solution and filtrate, and the recovery rate of styrene fumarate was evaluated.

Table 1 shows the results of Example 1 and Example 2, and Table 2 shows the results of Example 3 and Example 4. In the comparative example, styrene fumarate swelled like agar, and styrene fumarate, glycol, and fumaric acid could not be recovered.

  As shown in Table 1, when the pH of the aqueous solution e after solid-liquid separation is adjusted to 4.6, styrene fumarate should be recovered in high yield regardless of whether hollow fibers or microfiltration membranes are used. I was able to. In addition, as shown in Table 2, when the pH of the aqueous solution e ′ after solid-liquid separation is adjusted to 9.4, styrene fumarate can be recovered in a high yield by using a microfiltration membrane. It was found that the recovery rate of styrene fumarate was slightly reduced when using. From this result, it was found that it is particularly preferable to use a microfiltration membrane when the pH is 7 or more.

  Furthermore, the recovery rate was calculated from the recovered amounts of styrene fumarate, glycol and fumaric acid recovered in Examples 1 to 4. First, the concentration of glycol in the filtrate after filtration was measured with a gas chromatograph analyzer, and the concentration of fumaric acid was measured with an ion chromatograph device. Thereafter, the concentration of the measured glycol and fumaric acid was multiplied by the amount of the sample, and the recovery rate was obtained based on the following formulas 1 and 2.

[Formula 1] Glycol recovery rate (%) = recovered glycol amount (g) / (FRP amount used × glycol blending ratio)
[Formula 2] Recovery rate of fumaric acid (%) = recovered fumaric acid amount (g) / (amount of FRP used x fumaric acid blending ratio)
The amount of FRP used was 480 (g), the proportion of resin in FRP was 34 wt%, and the proportion of glycol and fumaric acid blended in the resin was 23 wt% when the resin part was 100 wt%. . Therefore, FRP amount x glycol blending ratio is 480 (g) x 34 (wt%) x 23 (wt%), FRP amount x fumaric acid blending ratio is 480 (g) x 34 (wt%) x 23 (wt%) ).

These results are shown in Table 3.

  As shown in Table 3, in the comparative example, since the filtration treatment was performed after adjusting the pH of the aqueous solution to 3, styrene fumarate, fumaric acid and glycol could not be recovered. On the other hand, in Examples 1 to 4, it was found that styrene fumarate, fumaric acid and glycol can be recovered in high yield because the aqueous solution was filtered after adjusting the pH of the aqueous solution to 4 to 12. As a result, FRP can be reused as a raw material for FRP again and recovered in high yield, and waste plastic can be recycled and effectively used.

It is a figure explaining the decomposition | disassembly method of the plastic which concerns on embodiment of this invention. It is a figure explaining the decomposition | disassembly method of FRP using the decomposition method of the plastic which concerns on embodiment of this invention. It is a figure which shows the molecular structure of the styrene fumarate collect | recovered from the decomposition | disassembly method of FRP using the decomposition method of the plastic concerning embodiment of this invention. It is a figure which shows the filtration apparatus using the hollow fiber used for the decomposition | disassembly method of FRP using the decomposition method of the plastics concerning embodiment of this invention.

Explanation of symbols

1 ... Plastic containing unsaturated polyester resin,
2 ... aqueous solution (including polyhydric alcohol 3, organic acid 4 and organic acid compound 5),
3 ... polyhydric alcohol,
4 ... Organic acid,
5 ... Organic acid compound,
6 ... aqueous solution (including polyhydric alcohol 3 and organic acid 4),

Claims (3)

A raw material for the unsaturated polyester resin obtained by decomposing a plastic containing an unsaturated polyester resin formed from an unsaturated polyester portion and a crosslinked portion using subcritical water having a temperature lower than the thermal decomposition temperature of the unsaturated polyester resin. An aqueous solution containing a polyhydric alcohol and an organic acid that are monomers, and a compound of the cross-linked portion and the organic acid,
A method for decomposing a plastic, comprising adjusting the obtained aqueous solution to pH 4 to 12, and then filtering the obtained aqueous solution to separate the organic compound from the aqueous solution.   The method for decomposing a plastic according to claim 1, wherein the aqueous solution obtained after decomposition is adjusted to pH 4 to 7, and the obtained aqueous solution is filtered using a hollow fiber or a microfiltration membrane. The method for decomposing a plastic according to claim 1, wherein the aqueous solution obtained after the decomposition is adjusted to pH 7 to 12, and the obtained aqueous solution is filtered through a microfiltration membrane.

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