JP2005171066A - Method for decomposing plastic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for decomposing plastics by which a plastic can be easily decomposed at low temperatures, and can be reused as a raw material of similar plastics again. <P>SOLUTION: The method for decomposing a plastic produced from a polyhydric alcohol and an organic acid comprises decomposing the plastic in a weakly alkaline solution containing a hydroxy acid, wherein, in the weakly alkaline solution containing the hydroxy acid, the plastic decomposes quickly and easily, thereby secondary decomposition of the resulted decomposition product can be prevented. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a technique for decomposing and recovering plastics and waste containing plastics so that they can be reused.

Conventionally, most plastic waste has been subjected to landfill disposal or incineration, and has not been effectively used as a resource. In landfill disposal, there are problems such as difficulty in securing a landfill site and instability of the ground after landfilling, and incineration treatment causes 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 decompose and recycle plastics in accordance with these situations. For example, as one of them, a method has been proposed in which plastic waste is decomposed into oil by a reaction using supercritical water as a reaction medium to recover a useful oil (see, for example, Patent Document 1). In addition, for fiber reinforced plastics used in various structural materials, etc., there is a method of decomposing plastic components using supercritical water or subcritical water, and collecting and reusing fibers such as glass fibers and carbon fibers. It has been proposed (see, for example, Patent Document 2). In these methods, plastic becomes an oily component whose molecular weight has been reduced by decomposition, and can be reused mainly as a liquid fuel.

In addition, a plastic decomposition method using a hydrolysis reaction by high-temperature steam has been proposed, and the organic polymer component of the thermoplastic plastic and the thermosetting plastic can be decomposed temporarily by this method. Furthermore, the cured unsaturated polyester resin waste is decomposed using decomposition components such as dicarboxylic acids and diamines, and the resin raw material obtained by the decomposition is re-synthesized and chemically recycled. A method has also been proposed (see, for example, Patent Document 3).
JP-A-5-31000 Japanese Patent Laid-Open No. 10-87872 Japanese Patent Laid-Open No. 9-221565

  However, when the plastic is decomposed by the supercritical method as in Patent Document 1 and Patent Document 2, the plastic component is decomposed randomly, so that the decomposition product becomes an oily substance composed of various components, and it is difficult to maintain a constant quality. It is. For this reason, post-treatment such as reforming the oil quality using a catalyst typified by zeolite is necessary, and the cost is high, and the petroleum product itself such as kerosene and light oil is also used in the reformed product oil. It is difficult to achieve this, and it has not yet been put into practical use.

  Further, in the method of Patent Document 3, the resin component obtained by decomposition is reused as an unsaturated polyester resin again, but the resin component obtained because decomposition is performed at a high decomposition temperature. Has undergone thermal decomposition, and the physical properties of the cured product obtained by re-curing are different from those of the original unsaturated polyester resin. For this reason, there was a problem that the utilization rate of the decomposition resin component used when obtaining a recured product had to be lowered.

  The present invention has been made in view of the above points, and provides a method for decomposing a plastic that can be easily decomposed at a low temperature and can be reused as a raw material for the same plastic again. It is intended.

  A method for decomposing a plastic according to claim 1 of the present invention is a method for decomposing a plastic produced from a polyhydric alcohol and an organic acid, wherein the plastic is decomposed in a weakly alkaline solution containing an oxyacid. It is characterized by.

  The invention of claim 2 is characterized in that, in claim 1, the pH of the solution is 7-11.

  According to a third aspect of the present invention, in the first or second aspect, the solution contains a salt having at least one of a carbonate group and a phosphate group.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the temperature of the solution is equal to or lower than a thermal decomposition temperature of the plastic.

  The invention of claim 5 is characterized in that in any one of claims 1 to 4, the decomposition product is further hydrolyzed after the plastic is decomposed in the solution.

  According to the present invention, the plastic can be decomposed at a low temperature equal to or lower than the thermal decomposition temperature of the plastic, and can be reused as the same plastic raw material as before the decomposition.

  Further, according to the invention of claim 2, the plastic can be decomposed without fear of corroding the apparatus as in the case of a strong alkali having a large pH value.

  According to the invention of claim 3, the plastic can be efficiently decomposed while maintaining the pH within a target range.

  According to the invention of claim 4, the plastic can be decomposed at a temperature equal to or lower than the thermal decomposition temperature of the plastic, and can be reused as a raw material of the same plastic as before the decomposition. is there.

  According to the invention of claim 5, the low molecular weight component obtained by decomposing the plastic can be further decomposed into a monomer and oxyacid, and the monomer can be reused as a raw material for the plastic and the oxyacid can be reused for the decomposition of the plastic. It will be.

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

  In the present invention, the plastic to be decomposed is manufactured using polyhydric alcohol and organic acid as raw materials. Typical examples of such plastics include saturated or unsaturated polyester resins. In the present invention, this plastic is decomposed in a weakly alkaline solution containing an oxyacid.

  Here, the oxyacid is a hydroxycarboxylic acid having at least one hydroxyl group and carboxyl group in one molecule of the organic substance, and glycolic acid, lactic acid, hydroacrylic acid, α-oxyacetic acid, glyceric acid, tartronic acid, malic acid. And aliphatic oxyacids such as tartaric acid and citric acid, and aromatic oxyacids such as salicylic acid, m-oxybenzoic acid, p-oxybenzoic acid, mandelic acid and trovic acid. The molecular weight of the oxyacid is preferably 1000 or less, more preferably 500 or less from the viewpoint of reactivity and fluidity, but is not particularly limited.

  Various oxyacids can be used as described above, and are not particularly limited, but it is also preferable to use a dibasic acid and a glycol. Examples of such oxyacids include maleic anhydride and propylene glycol esters and terephthalic acid and ethylene glycol esters. Thus, an oxyacid having at least one ester bond in the molecule has a structure similar to that of a plastic made from a polyhydric alcohol and an organic acid, which are targets of decomposition, and has better compatibility and improved reactivity. It is. In addition, when water is used as a solvent as described later, the compatibility with water is high, which is also preferable in this respect.

  In addition, when using a compound having at least one unsaturated group in the molecule such as maleic anhydride, an unsaturated group is present in the molecule of the low molecular weight component (other than the monomer) obtained by decomposing the plastic. It is possible to introduce a reactive site by having an unsaturated group, and it is easy to reuse as a raw material for plastics. The unsaturated group is usually 1 to 2 in one molecule, but is not particularly limited.

  In the oxyacid consisting of dibasic acid and glycol, in addition to the above, glycol in which H is not attached to β position of OH group (glycol in which H is not bonded to carbon bonded to carbon to which OH group is bonded) ) Is also preferred. The glycol in which H is not attached to the β position of the OH group is not particularly limited, but is preferably neopentyl glycol, and includes neopentyl glycol and dibasic acid as shown in [Chemical Formula 1]. It is preferable to use an oxyacid.

  Then, a weakly alkaline solution having an oxyacid can be obtained by adding and dissolving the above oxyacid and weak alkali compound in a solvent. The amount of oxyacid added is not particularly limited and can be set as necessary, but is preferably equal to or greater than the weight of the plastic to be decomposed. Moreover, as a weak alkali, the salt which has either a carbonate radical and a phosphate radical can be used. Examples of the salt having a carbonate group include sodium bicarbonate and sodium carbonate, and examples of the salt having a phosphate group include sodium phosphate, but are not limited thereto. Thus, by using a salt having either carbonate or phosphate as a weak alkali, the pH can be maintained within a target range and the plastic can be efficiently decomposed.

  Furthermore, it is preferable that the weak alkaline solution containing oxyacid contains a salt having Ca root. Although it does not specifically limit as a salt which has Ca root, A calcium carbonate, a calcium phosphate, etc. can be mentioned. Thus, by containing the salt which has Ca root, it can suppress that the organic acid and polyhydric alcohol produced | generated when a plastic is decomposed | disassembled are secondary-decomposed. The compounding quantity of the salt which has Ca root is not specifically limited, Although it can set arbitrarily, it is desirable that it is more than the weight of the plastic made into decomposition | disassembly object. Of course, as described later, the pH of the solution is set so as not to deviate from the range of 7 to 11.

  Moreover, as a solvent which dissolves oxyacid and weak alkali, water, alcohol, or the like can be used, and water is particularly preferable. Since water is highly compatible with oxyacids and has good compatibility with components generated by decomposition, it can efficiently decompose plastics. Water is advantageous as a solvent because it is inexpensive and readily available, and waste liquid treatment is relatively easy.

  And the weakly alkaline solution having an oxyacid preferably has a pH in the range of 7 to 11, and by adjusting the addition amount of a weakly alkaline compound such as a salt having any of the above carbonate groups and phosphate groups, The pH can be set to be weakly alkaline in the range of 7-11. If the pH is smaller than 7 (close to neutrality), the efficiency of plastic decomposition becomes low, and a large amount of decomposition time is required. On the other hand, if the pH is higher than 11, there is a possibility that problems such as strong alkalinity and corrosion of the device may occur.

  Thus, when a plastic produced from a raw material containing a polyhydric alcohol and an organic acid is decomposed, a solvent, an oxyacid, and an alkali are added to the plastic, and the temperature is increased. A plastic decomposition reaction is allowed to proceed in a weakly alkaline solution containing an acid to decompose into a low molecular weight component, monomer, or oligomer, which can be recovered and reused.

  Here, in a weakly alkaline solution containing an oxyacid, the plastic is quickly and easily hydrolyzed, and high-temperature and high-pressure reaction conditions are unnecessary. Therefore, it is possible to prevent the decomposition products from secondary decomposition as in the case of decomposing plastics under high temperature and high pressure conditions. It can be reused as a raw material for similar plastics. The reaction temperature (that is, the temperature of the weak alkaline solution containing the oxyacid) is set to a temperature lower than the thermal decomposition temperature of the plastic to be decomposed. If the plastic to be decomposed is a thermosetting unsaturated polyester, thermal decomposition will occur. Since the temperature is generally around 300 ° C., it is preferably set in the range of about 150 to 300 ° C., and the plastic can be efficiently decomposed into low molecular weight components, monomers and oligomers. When the reaction temperature is 150 ° C. or lower, a great deal of time is required for decomposition, resulting in an increase in processing cost. In particular, when the reaction time is as low as about 100 ° C., it takes a long time of several tens of hours or more to decompose the thermoplastic. Further, when the temperature is raised to a temperature exceeding 300 ° C., the influence of thermal decomposition increases, and finally the production rate of low molecular weight components, monomers and oligomers to be collected decreases, and the recovery rate decreases. The pressure is not particularly limited, and when heating to a temperature higher than the boiling point of the solvent of the weakly alkaline solution containing oxyacid, heating is performed with the saturated vapor pressure of the solvent obtained by sealing and heating the reactor. Decomposition can be carried out under pressure.

  Moreover, after decomposing | disassembling a plastic in the weakly alkaline solution which has an oxy acid as mentioned above, you may have the process of hydrolyzing this decomposition product further. By further hydrolyzing the decomposition product in this way, low molecular weight components other than the monomer obtained by decomposing the plastic can be monomerized, and the recovered monomer can be easily reused as a plastic raw material. In addition, the oxyacid reacting with the low molecular weight component can be decomposed and recovered, and the oxyacid can be used again for the decomposition of the plastic.

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

(Example 1)
To a product obtained by polycondensation of maleic anhydride and propylene glycol in equimolar amounts, a styrene monomer is added in a molar ratio of styrene monomer 3 to this product 7, and an unsaturated polyester resin is obtained. Obtained. To 10 g of this unsaturated polyester resin, 5 g of styrene monomer, 0.15 g of methyl ethyl ketone peroxide (manufactured by NOF Corporation, trade name “Permec N”) as a polymerization initiator, and 0.15 g of cobalt naphthenate as an accelerator are added, After curing at room temperature for 1 hr, the product was cured at 100 ° C. for 2 hr to obtain a cured product. The thermal decomposition temperature of this cured product was about 320 ° C.

  Then, 2 g of this unsaturated polyester resin cured product, 2 g of glycolic acid, 10 g of pure water, 0.5 g of sodium bicarbonate were charged into the reaction tube 1 and sealed. Here, the pH of the solution in the reaction tube 1 was 9.2. Next, the reaction tube 1 was immersed in a constant temperature bath 2 (with a stirrer 4) at 230 ° C. and left for 4 hours. Thereafter, the reaction tube 1 was taken out of the thermostat 2 and put into the cooling bath 3 to be rapidly cooled and returned to room temperature (see FIG. 1).

  Thereafter, the reaction tube 1 is taken out from the cooling bath 3 and opened, and the components inside the reaction tube 1 are collected using pure water and a solvent (a nonpolar solvent such as chloroform) and filtered using a glass filter. Thus, unreacted unreacted plastic was separated, and the decomposition reaction rate of the plastic was determined from its mass. The recovered water component and solvent component were analyzed with a gas chromatograph mass spectrometer and ion chromatography, and the glycol monomer component and organic acid component were quantitatively analyzed to determine the recovery rate. These results are shown in Table 1.

(Example 2)
In Example 1, oxyacid synthesized from maleic anhydride and neopentyl glycol was used in place of glycolic acid. The chemical structure of the oxyacid was analyzed by GC-MS and confirmed to be [Chemical Formula 2]. The pH of the solution in the reaction tube was 8.9. Otherwise, the plastic was decomposed in the same manner as in Example 1. In the same manner as in Example 1, the decomposition reaction rate of the plastic was determined, and the recovery rate was determined by quantitative analysis of the glycol monomer component and the organic acid component. These results are shown in Table 1.

(Example 3)
In Example 1, oxyacid synthesized from maleic anhydride and propylene glycol was used instead of glycolic acid. The chemical structure of the oxyacid was analyzed by GC-MS and confirmed to be [Chemical Formula 3]. The pH of the solution in the reaction tube was 9.0. Otherwise, the plastic was decomposed in the same manner as in Example 1. In the same manner as in Example 1, the decomposition reaction rate of the plastic was determined, and the recovery rate was determined by quantitative analysis of the glycol monomer component and the organic acid component. These results are shown in Table 1.

Example 4
In Example 2, the plastic was decomposed in the same manner as in Example 2 except that 2 g of calcium carbonate was added when the reaction tube was sealed. In the same manner as in Example 1, the decomposition reaction rate of the plastic was determined, and the recovery rate was determined by quantitative analysis of the glycol monomer component and the organic acid component. These results are shown in Table 1.

(Example 5)
In Example 2, the plastic was decomposed in the same manner as in Example 2 except that 10 g of methanol was used instead of 10 g of pure water. Further, the contents of the reaction tube were recovered in the same procedure except that methanol was used instead of pure water. In the same manner as in Example 1, the decomposition reaction rate of the plastic was determined, and the recovery rate was determined by quantitative analysis of the glycol monomer component and the organic acid component. These results are shown in Table 1.

(Example 6)
In Example 2, the plastic was decomposed in the same manner as in Example 2 except that 0.2 g of potassium phosphate was used instead of 0.5 g of sodium hydrogen carbonate. In the same manner as in Example 1, the decomposition reaction rate of the plastic was determined, and the recovery rate was determined by quantitative analysis of the glycol monomer component and the organic acid component. These results are shown in Table 1.

(Example 7)
In Example 2, the plastic was decomposed in the same manner as in Example 2 except that the immersion time in a thermostatic bath at 230 ° C. was changed to 6 hours. Next, after opening the reaction tube, 10 g of pure water was added, the reaction tube was sealed again, immersed in a thermostat at 100 ° C. for 2 hours, and then rapidly cooled in a cooling bath to return to room temperature. Thereafter, the components inside the reaction tube were recovered using pure water and a solvent (a nonpolar solvent such as chloroform). In the same manner as in Example 1, the decomposition reaction rate of the plastic was determined, and the recovery rate was determined by quantitative analysis of the glycol monomer component, the organic acid component, and the oxyacid synthesized from maleic anhydride and neopentyl glycol. These results are shown in Table 1.

(Comparative Example 1)
The plastic was decomposed in the same manner as in Example 2 except that sodium bicarbonate was not blended. At this time, the pH of the solution in the reaction tube was 3.4. In the same manner as in Example 1, the decomposition reaction rate of the plastic was determined, and the recovery rate was determined by quantitative analysis of the glycol monomer component and the organic acid component. These results are shown in Table 1.

(Comparative Example 2)
In Example 1, the plastic was decomposed in the same manner as in Example 1 except that glycolic acid was not added. In the same manner as in Example 1, the decomposition reaction rate of the plastic was determined, and the recovery rate was determined by quantitative analysis of the glycol monomer component and the organic acid component. These results are shown in Table 1.

(Comparative Example 3)
In Example 2, the plastic was decomposed in the same manner as in Example 2 except that 0.5 g of sodium hydroxide was used instead of 0.5 g of sodium hydrogen carbonate. At this time, the pH of the solution in the reaction tube was 12.6. In the same manner as in Example 1, the decomposition reaction rate of the plastic was determined, and the recovery rate was determined by quantitative analysis of the glycol monomer component and the organic acid component. These results are shown in Table 1.

  In Table 1, each recovery rate was calculated by the recovery amount / the content in the cured product. Moreover, the maleic acid which is a raw material of the cured plastic is recovered as fumaric acid, and the recovery rate of fumaric acid was calculated based on the amount of maleic anhydride in the cured product. Further, in Table 1, (A) was calculated by adding the recovered amount after hydrolysis at 100 ° C. for 2 hours.

  As seen in Table 1, it can be seen that the raw material monomers of glycol and fumaric acid can be recovered at a high recovery rate by decomposing the plastic by the method of the present invention. Moreover, since the oligomer component which consists of a dimer, a trimer ester oligomer component, and styrene can also be collect | recovered qualitatively, it turns out that most resin components can be decomposed | disassembled in the form which can be utilized again as a plastic.

It is the schematic of the apparatus used by an Example and a comparative example.

Explanation of symbols

1 Reaction tube 2 Thermostatic bath 3 Cooling bath

Claims (5)

  A method for decomposing a plastic produced from a polyhydric alcohol and an organic acid, comprising decomposing the plastic in a weakly alkaline solution containing an oxyacid.   The method for decomposing a plastic according to claim 1, wherein the pH of the solution is 7-11.   The method for decomposing a plastic according to claim 1 or 2, wherein the solution contains a salt having at least one of a carbonate group and a phosphate group.   The method for decomposing a plastic according to any one of claims 1 to 3, wherein the temperature of the solution is equal to or lower than a thermal decomposition temperature of the plastic.   5. The method for decomposing a plastic according to claim 1, further comprising hydrolyzing the decomposed product after decomposing the plastic in the solution.

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