Method for decomposing halogen atom-containing polymers

Abstract

To provide a method for decomposing a halogen atom-containing polymer which can be realized under relatively mild conditions without incineration or landfilling. [Solution] The present invention provides a method for decomposing a halogen-atom-containing polymer, comprising a step of subjecting a mixture containing a halogen-atom-containing polymer and a solid metal hydroxide to mechanochemical treatment. By subjecting the mixture of the halogen-atom-containing polymer and the solid metal hydroxide to mechanochemical treatment, the halogen atoms contained in the halogen-atom-containing polymer are converted into ions and inorganicized, and the carbon atoms contained therein are converted into compounds such as oxalic acid, thereby decomposing the halogen-atom-containing polymer.

Description

[Technical Field]

[0001] This invention relates to a method for decomposing a halogen atom-containing polymer. [Background technology]

[0002] Polymers containing halogen atoms, such as fluorine and chlorine atoms, are valued for their high chemical stability and heat resistance, and are applied in a wide range of fields, from scientific and medical equipment and various flame retardants to everyday products. On the other hand, these polymers often present waste disposal problems as a consequence of their high chemical stability and heat resistance. For example, if a polymer containing fluorine atoms is to be incinerated, the presence of the carbon-fluorine bond, the strongest covalent bond, requires high-temperature treatment for decomposition, and the hydrogen fluoride gas generated by incineration will degrade the incinerator material. Therefore, landfill disposal is necessary to dispose of these polymers, but this is also problematic given the current shortage of final disposal sites for waste. Consequently, a new waste disposal method for halogen atom-containing polymers that is neither incineration nor landfill is needed.

[0003] Against this backdrop, for example, Non-Patent Document 1 proposes a treatment method in which a fluorine atom-containing polymer is decomposed into carbon dioxide and fluoride ions by contacting the polymer with subcritical water in the presence of hydrogen peroxide. With such a treatment method, not only can the fluorine atom-containing polymer be mineralized under relatively mild conditions, but the fluoride ions produced in the treatment can be reacted with calcium ions to obtain calcium fluoride, which can be used as a raw material for all fluorine-containing compounds, and this method is also excellent in terms of resource recycling.

[0004] Furthermore, Patent Document 1 describes the decomposition of a fluorine atom-containing polymer by contacting it with subcritical water at 200°C or higher in the presence of a permanganate, and Patent Document 2 describes the decomposition of a fluorine atom-containing polymer by contacting it with subcritical water at 200°C or higher in the presence of a basic compound such as an alkali metal hydroxide or an alkaline earth metal hydroxide. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-104578 [Patent Document 2] Japanese Patent Publication No. 2021-155478 [Non-patent literature]

[0006] [Non-Patent Document 1] Hisao Hori et al., Ind. Eng. Chem. Res., 2015, 54, pp8650-8658 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] This invention has been made in view of the above circumstances, and aims to provide a method for decomposing halogen atom-containing polymers that can be achieved under relatively mild conditions, without incineration or landfill. [Means for solving the problem]

[0008] As a result of intensive studies to solve the above problems, the present inventors have found that by subjecting a mixture of a halogen atom-containing polymer to be treated and a solid metal hydroxide to mechanochemical treatment, the halogen atoms contained in the halogen atom-containing polymer are ionized and mineralized, and the carbon atoms contained therein are converted into compounds such as oxalic acid, whereby the halogen atom-containing polymer is decomposed. The present invention has been completed based on such findings and provides the following.

[0009] (1) The present invention comprises a step of subjecting a mixture containing Polychlorotrifluoroethylene to be treated and a solid Potassium hydroxide to mechanochemical treatment, and in this step, the amount of the above solid Potassium hydroxide used is 15 to Polychlorotrifluoroethylene times the mass of the above 20 , and is characterized in being a method for decomposing Polychlorotrifluoroethylene .

[0011] ( 2 ) Further, the present invention is a method for decomposing Section (1) as described in Polychlorotrifluoroethylene , wherein the mechanochemical treatment is mechanical stirring using a ball mill.

Advantages of the Invention

[0014] According to the present invention, a method for decomposing a halogen atom-containing polymer that can be realized under relatively mild conditions, neither by incineration nor by landfill, is provided.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, an embodiment of the method for decomposing a halogen atom-containing polymer of the present invention will be described. Note that the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the present invention.

[0016] The method for decomposing a halogen atom-containing polymer of the present invention is characterized by comprising a step of subjecting a mixture containing the halogen atom-containing polymer to be treated and a solid metal hydroxide to mechanochemical treatment. As long as this step is provided, the effects of the present invention can be obtained and it will be within the scope of the present invention. As other steps, a pretreatment step of finely cutting the halogen atom-containing polymer can be mentioned in order to enhance the efficiency of the decomposition reaction, but such pretreatment is not essential. When performing the pretreatment, it is desirable to reduce the particle size until the halogen atom-containing polymer becomes powdery.

[0017] The halogen atom-containing polymer to be decomposed in the present invention is a polymer containing a halogen atom in the molecule, and if even one atom of halogen atom is included in the molecule, it becomes the object of decomposition of the present invention. Examples of such halogen atoms include fluorine atom, chlorine atom, bromine atom, etc. Halogen atom-containing polymers are evaluated for their high chemical resistance, heat resistance, weather resistance, flame retardancy, etc., and are applied in all scenes including industry, medicine, architecture, etc. On the other hand, these polymers tend to have problems in waste treatment as a reverse side of such high chemical stability and heat durability. The present invention provides a method for chemically decomposing these polymers that have become waste. Such halogen atom-containing polymers may be homopolymers or copolymers, and examples of such include polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), polyvinyl chloride, polychlorotrifluoroethylene, polydichlorodifluoroethylene, polychlorotrifluoroethylene, polybromoethylene, etc. Among these, those in which the halogen atom is a chlorine atom and / or a fluorine atom can be preferably mentioned, and an example of such a polymer is polychlorotrifluoroethylene.

[0018] Examples of metal hydroxides include alkali metal or alkaline earth metal hydroxides. In this invention, such metal hydroxides are used in their solid form. Among these metal hydroxides, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide are preferred, and potassium hydroxide is more preferred. The mass of the metal hydroxide used is preferably about 5 to 100 times the mass of the halogen atom-containing polymer, more preferably about 10 to 50 times, and even more preferably about 15 to 50 times.

[0019] Mechanochemical reactions are chemical reactions that occur when mechanical energy is applied to a substance to be treated. Examples of such mechanical energy include friction, shear stress, shear, impact, and compression. In this invention, the halogen atom-containing polymer to be treated is decomposed by applying mechanical energy to a mixture of the halogen atom-containing polymer and a solid metal hydroxide.

[0020] In this invention, a ball mill reaction using a ball mill can be preferred as such a mechanochemical reaction. A ball mill is a device that grinds a sample by placing hard balls and the sample in a cylindrical container and rotating them. The ball mill reaction is a type of mechanochemical reaction in which chemical bonds are broken by frictional heat and triboelectricity generated during the grinding process. This reaction is considered an environmentally friendly technology with low environmental impact due to its advantages such as easy reaction control, simple equipment, solvent-free and non-heating reaction. When using the ball mill reaction as a mechanochemical reaction, both the halogen atom-containing polymer and the solid metal hydroxide, along with several hard balls, are placed in a cylindrical container, the container is sealed, and the container is rotated. When the hard balls collide with each other during this rotation, the halogen atom-containing polymer and metal hydroxide are subjected to effects such as being sandwiched between the hard balls, and the energy generated causes a chemical reaction, leading to the decomposition of the halogen atom-containing polymer.

[0021] A commercially available planetary ball mill can be preferred as an example of a ball mill. An example of conditions for performing a ball mill reaction using such a ball mill is to place about six zirconia balls with a diameter of 10 mm in a 12 mL zirconia cylindrical container, set the revolution-to-rotation ratio to about 1:-2, the disk rotation speed to about 100-800 rpm, and the pot (container) rotation speed to about 200-1600 rpm, but this is not limited to this. The processing time is preferably about 4 to 10 hours.

[0022] While atmospheric pressure and room temperature are possible, the atmosphere in which mechanochemical reactions are carried out is not particularly limited.

[0023] The halogen atom-containing polymers to be treated are subjected to a mechanochemical reaction with solid metal hydroxides, during which the halogen atoms are converted into ions such as chloride ions, fluoride ions, and bromide ions, and the carbon atoms are converted into low-molecular-weight compounds such as oxalic acid, thus decomposing the polymer. These decomposition products can be recycled by dissolving them in a solvent such as water and then recovering them. For example, the fluoride ions can be reacted with calcium ions to convert them into calcium fluoride, which is a raw material for all fluorine compounds, and can be recovered as a precipitate. [Examples]

[0024] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0025] [Example 1] 0.010 g of polychlorotrifluoroethylene (PCTFE), 0.20 g of solid potassium hydroxide, and 6 zirconia balls with a diameter of 10 mm were placed in a zirconia cylindrical container (capacity 12 mL), and the mixture was ball-milled for 6 hours at room temperature and atmospheric pressure using a planetary ball mill (pulverisettle 7) manufactured by Fritsch. The reaction product after treatment was dissolved in 30 mL of pure water and recovered, and the F contained in it was analyzed. By quantifying - , the yield when the fluorine atoms contained in PCTFE were recovered as F - was determined. As a result, the yield of F - was 84%. For the quantification of F Ion chromatography ,

[0026] [Example 2] PCTFE was ball-milled in the same procedure as in Example 1, except that the amount of potassium hydroxide used was 0.15 g. As a result, the yield of F - was 80%.

[0027] [Example 3] PCTFE was ball-milled in the same procedure as in Example 1, except that the amount of potassium hydroxide used was 0.10 g. As a result, the yield of F - was 43%.

[0028] [Example 4] 0.010 g of polychlorotrifluoroethylene (PCTFE), 0.20 g of solid potassium hydroxide, and 6 zirconia balls with a diameter of 10 mm were placed in a zirconia cylindrical container (capacity 12 mL), and using a planetary ball mill (pulverisettle7) manufactured by Fritsch, ball milling was carried out at room temperature and atmospheric pressure for 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or 9 hours. The reaction product after the treatment was dissolved in 30 mL of pure water and recovered, and by quantifying F - and Cl - contained in the recovered solution, the yields when the fluorine atoms and chlorine atoms contained in PCTFE were recovered as F - and Cl - were determined for each reaction time. The results are shown in Table 1. For the quantification of F - and Cl - , ion chromatography was used.

[0029]

Table 1

[0030] As shown in Table 1, when the processing time by ball milling is about 8 to 9 hours, F - and Cl - The yields for each component approached 100%, indicating that the PCTFE was almost completely decomposed. Also, F - and Cl - Since the yield showed a similar upward trend over time, it can be understood that, according to the decomposition method of the present invention, decomposition proceeds by a similar mechanism regardless of the type of halogen atom.

[0031] [Example 5] 0.010 g of polychlorotrifluoroethylene (PCTFE), 0.20 g of solid potassium hydroxide, and six 10 mm diameter zirconia balls were placed in a zirconia cylindrical container (capacity 12 mL). The mixture was then subjected to a ball milling process using a Fritsch planetary ball mill (pulverisettle 7) at room temperature and atmospheric pressure for 9 hours. The reaction product was dissolved in 30 mL of pure water, recovered, neutralized, and then subjected to a total organic carbon (TOC) measurement. The result showed that the amount of carbon atoms in the solution was 1.48 × 10⁻¹⁶. -4 The amount was calculated as moles. On the other hand, the amount of carbon atoms contained in 0.010g of PCTFE is 1.72 × 10⁻⁶. -4 Since it is measured in moles, the amount of carbon atoms recovered in the solution was calculated to be 86%. In addition, from measurements by ion chromatography, it was found that this solution contains 5.21 × 10¹⁶ oxalic acid. -5 It was found to contain moles. As mentioned above, the amount of carbon atoms contained in PCTFE was 1.48 × 10⁻⁶. -4 Since this is measured in moles, and considering that oxalic acid contains 2 carbon atoms, the yield of oxalic acid was calculated to be 61%, indicating that more than half of the carbon atoms in PCTFE were converted to oxalic acid.

Claims

1. A method for decomposing polychlorotrifluoroethylene, comprising the step of subjecting a mixture containing polychlorotrifluoroethylene and solid potassium hydroxide to a mechanochemical treatment, characterized in that the amount of solid potassium hydroxide used in this step is 15 to 20 times the mass of the polychlorotrifluoroethylene.

2. The method for decomposing polychlorotrifluoroethylene according to claim 1, wherein the mechanochemical treatment is mechanical stirring using a ball mill.

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