Method for producing fluoromonomer

Abstract

Provided is a method for producing a fluoromonomer with an excellent conversion rate from a fluorine-containing polymer.　This method for producing a fluoromonomer involves heating a fluorine-containing polymer in the presence of at least one of metal and alloy and pyrolyzing the fluorine-containing polymer to obtain a fluoromonomer, the method being characterized in that the heating temperature during the heating is 300-900°C, and the metal and the alloy are in a molten state during the heating.

Description

Fluoromonomer manufacturing method

[0001] The present invention relates to a method for producing a fluoromonomer.

[0002] There has been a demand for recycling fluoropolymers such as polytetrafluoroethylene. Patent Document 1 discloses a method for obtaining fluoroolefins by pyrolyzing a fluoropolymer in the presence of an inert solid and steam using a rotary kiln.

[0003] Patent No. 4010300

[0004] In producing a fluoromonomer from a fluoropolymer, it is desired to further improve the rate at which the fluoropolymer is converted into a fluoromonomer (i.e., conversion rate).The present inventors produced a fluoromonomer from a fluoropolymer by the method described in Patent Document 1, and found that there is room for improvement in the conversion rate of the fluoropolymer.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a fluoromonomer which is excellent in conversion rate to a fluoropolymer.

[0006] As a result of intensive investigations into the above-mentioned problems, the present inventors have found that the conversion rate of a fluoropolymer can be improved by heating the fluoropolymer in the presence of at least one of a metal and an alloy in a molten state at a heating temperature of 300 to 900°C, and have arrived at the present invention.

[0007] That is, the inventors have found that the above problems can be solved by the following configurations. [1] A method for producing a fluoromonomer, comprising heating a fluoropolymer in the presence of at least one of a metal and an alloy to thermally decompose the fluoropolymer to obtain a fluoromonomer, characterized in that the heating temperature during the heating is 300 to 900°C, and the metal and the alloy are in a molten state during the heating. [2] The method for producing a fluoromonomer according to [1], wherein the metal and the alloy contain at least one selected from the group consisting of tin, lead, zinc, bronze, brass, and aluminum. [3] The method for producing a fluoromonomer according to [1] or [2], wherein the fluoropolymer contains at least one selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene-based copolymers, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, vinylidene fluoride-hexafluoropropylene copolymers, and perfluoropolyether rubber. [4] The method for producing a fluoromonomer according to any one of [1] to [3], wherein the amount of the metal and the alloy used is 0.5 to 20 parts by mass per 100 parts by mass of the fluoropolymer used. [5] The method for producing a fluoromonomer according to any one of [1] to [4], wherein the pyrolysis of the fluoropolymer is carried out using a rotary kiln. [6] The method for producing a fluoromonomer according to any one of [1] to [5], wherein the melting points of the metal and the alloy are 100 to 700°C.

[0008] According to the present invention, a method for producing a fluoromonomer with an excellent conversion rate to a fluoropolymer can be provided.

[0009] 1 is a schematic side view showing an example of a thermal decomposition apparatus used in the method for producing a fluoromonomer of the present invention.

[0010] The meanings of terms used in the present invention are as follows. A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. A "unit" is a collective term that includes an atomic group derived from one molecule of the monomer that is formed directly by polymerizing the monomer, and an atomic group obtained by chemically converting a part of the atomic group. A "unit based on a monomer" will hereinafter also be referred to simply as a "unit".

[0011] [Method for producing fluoromonomer] The method for producing a fluoromonomer of the present invention (hereinafter also referred to as "the present production method") is a method for obtaining a fluoromonomer by heating a fluoropolymer in the presence of at least one of a metal and an alloy and pyrolyzing the fluoropolymer, wherein the heating temperature during the heating is 300 to 900°C and the metal and alloy are in a molten state during the heating. The present production method is suitable for recycling fluoropolymers. According to the present production method, the conversion rate of the fluoropolymer is excellent. Although the details of the reason for this are unknown, it is presumed that heating the fluoropolymer in the presence of at least one of a molten metal and an alloy improves the efficiency of heat transfer to the fluoropolymer, and the metal and alloy act as a catalyst to improve the efficiency of pyrolysis of the fluoropolymer, resulting in an improved conversion rate of the fluoropolymer.

[0012] <Fluorine-containing polymer> The fluorine-containing polymer is not particularly limited as long as it is a polymer having fluorine atoms, and may be a resin or rubber. The fluorine-containing polymer may be obtained from waste materials containing a fluorine-containing polymer, etc.

[0013] From the viewpoint of achieving superior effects of the present invention, the fluoropolymer preferably contains at least one selected from the group consisting of polytetrafluoroethylene (hereinafter also referred to as "PTFE"), tetrafluoroethylene copolymer, polychlorotrifluoroethylene (hereinafter also referred to as "PCTFE"), polyvinylidene fluoride (hereinafter also referred to as "PVdF"), polyvinyl fluoride (hereinafter also referred to as "PVF"), vinylidene fluoride-hexafluoropropylene copolymer (hereinafter also referred to as "FKM"), and perfluoropolyether rubber. One type of fluoropolymer may be used alone, or two or more types may be used in combination.

[0014] Specific examples of tetrafluoroethylene copolymers include tetrafluoroethylene-ethylene copolymer (hereinafter also referred to as "ETFE"), tetrafluoroethylene-hexafluoropropylene copolymer (hereinafter also referred to as "FEP"), tetrafluoroethylene-propylene copolymer (hereinafter also referred to as "FEPM"), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer.

[0015] Preferred tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers are copolymers (hereinafter also referred to as "PFA") in which the ratio of PAVE units to the total of tetrafluoroethylene units (hereinafter also referred to as "TFE units") and perfluoroalkyl vinyl ether units (hereinafter also referred to as "PAVE units") is 0.1 mol% or more but less than 20 mol%, and copolymers (hereinafter also referred to as "FFKM") in which the ratio of PAVE units is 20 to 70 mol%. PFA may be a copolymer consisting only of TFE units and PAVE units, or may contain one or more units based on other monomers other than these. Specific examples of other monomers include other fluorine-containing monomers (e.g., hexafluoropropylene) and monomers having oxygen-containing polar groups (e.g., 5-norbornene-2,3-dicarboxylic anhydride). FFKM may be a copolymer consisting only of TFE units and PAVE units, or may contain one or more units based on other monomers other than these. Specific examples of the other monomers include a unit based on a monomer having a fluorine atom and a nitrile group, and a unit based on a monomer having a fluorine atom and a plurality of vinyl groups.

[0016] The form of the fluoropolymer is not particularly limited, but a sheet or granular form is preferred from the viewpoint of further improving the pyrolysis efficiency. In this case, the size of the fluoropolymer is preferably 1 to 10 mm, more preferably 2 to 5 mm, from the viewpoint of more excellent effects of the present invention. Here, the size of the fluoropolymer means the thickness when the fluoropolymer is in sheet form, and means the average particle size on the sieve standard when the fluoropolymer is in granular form. The thickness can be measured with a thickness gauge or the like, and the particle size can be measured with a sieve having various openings. The fluoropolymer may be previously subjected to a pulverization treatment, cutting treatment, etc. so as to achieve the above-mentioned size.

[0017] <Metals and Alloys> Metals and alloys are in a molten state during heating in the present production method. That is, the melting points of metals and alloys are equal to or lower than the heating temperature during thermal decomposition of the fluorine-containing polymer, and the boiling points of metals and alloys are higher than the heating temperature during thermal decomposition of the fluorine-containing polymer.

[0018] Examples of metals include tin, lead, zinc, aluminum, and magnesium. The alloy preferably contains at least one selected from the group consisting of tin, lead, zinc, and aluminum. Examples of alloys include bronze, brass, and tin-lead solder. In terms of achieving better effects of the present invention, the metal and alloy preferably contain at least one selected from the group consisting of tin, lead, zinc, bronze, brass, and aluminum, more preferably contain at least one selected from the group consisting of tin, lead, zinc, and aluminum, and even more preferably contain tin. The metal and alloy may be used alone or in combination of two or more types.

[0019] The melting point of the metal or alloy is 900°C or lower, and is preferably 100 to 700°C, more preferably 150 to 500°C, and even more preferably 150 to 300°C, in order to obtain better effects of the present invention. The boiling point of the metal or alloy is higher than 300°C, and is preferably higher than 700°C, more preferably higher than 900°C, in order to suppress volatilization during heating. The upper limit of the boiling point is not particularly limited, but is often 4000°C or lower.

[0020] The form of the metals and alloys before heating is not particularly limited, but a sheet or granular form is preferred from the viewpoint of providing better effects of the present invention. The size of the metals and alloys before heating is preferably 1 to 10 mm, more preferably 2 to 5 mm, from the viewpoint of providing better effects of the present invention. Here, the size of the metals and alloys before heating refers to the thickness when the metals and alloys before heating are in sheet form, and refers to the average particle size based on a sieve when the metals and alloys before heating are in granular form. The thickness can be measured using a thickness gauge or the like, and the particle size can be measured using a sieve with various openings. The metals and alloys may be previously subjected to a crushing process, cutting process, or the like to obtain the above sizes.

[0021] The amount of metal or alloy used is preferably 0.5 to 20 parts by mass, more preferably 0.5 to 15 parts by mass, and even more preferably 1 to 15 parts by mass, per 100 parts by mass of the fluoropolymer used. When the amount of metal or alloy used is 0.5 part by mass or more per 100 parts by mass of the fluoropolymer used, the effects of the present invention are more excellent. When the amount of metal or alloy used is 15 parts by mass or less per 100 parts by mass of the fluoropolymer used, the efficiency of thermal decomposition of the fluoropolymer is more excellent.

[0022] <Steps> In the present production method, a fluoropolymer is heated in the presence of at least one of a metal and an alloy to thermally decompose the fluoropolymer.

[0023] The heating temperature of the fluoropolymer is 300 to 900° C. The heating temperature of the fluoropolymer is preferably 350° C. or higher, more preferably 400° C. or higher, from the viewpoint of improving the thermal decomposition efficiency of the fluoropolymer. The heating temperature of the fluoropolymer is preferably lower from the viewpoint of the design temperature of the equipment, and is preferably 800° C. or lower, more preferably 700° C. or lower, and even more preferably 600° C. or lower.

[0024] The thermal decomposition of the fluoropolymer can be carried out using a known heating device, but is preferably carried out using a rotary kiln in order to obtain better effects of the present invention. A rotary kiln is a rotary furnace, and in this production method, for example, the device described in Japanese Patent No. 4010300 or the device described in Japanese Patent No. 4357999 can be used.

[0025] 1 is a schematic side view showing an example of a pyrolysis apparatus that can be used in this production method, showing part of its internal structure. The pyrolysis apparatus 1 has a hopper 10 capable of storing raw materials (fluoropolymers, metals, alloys, etc.), a cylindrical rotary kiln 20 into which the raw materials are supplied, and a recovery container 30 connected to the rotary kiln 20 for recovering pyrolysis products of the raw materials (fluoromonomers, etc.), residues, etc.

[0026] The rotary kiln 20 has a rotating means (not shown) for rotating the rotary kiln 20 and a heating means (not shown) for heating the raw materials supplied inside the rotary kiln 20. A stirring means for improving the efficiency of thermal decomposition of the raw materials may also be provided inside the rotary kiln 20. The material constituting the inner wall surface of the rotary kiln 20 is not particularly limited, but preferably contains at least one material selected from the group consisting of stainless steel, nickel, and chromium, and may also be an alloy of these materials.

[0027] The raw materials supplied and temporarily stored in the hopper 10 are transported by a conveyor 12 provided adjacent to the hopper 10 and supplied to the rotary kiln 20 via a feed chute 14 connected to the rotary kiln 20. Here, in addition to the raw materials, steam (preferably superheated steam) may be supplied to the feed chute 14 via a steam supply pipe 16. The steam supplied to the feed chute is blown into the rotary kiln 20 via the feed chute. While FIG. 1 illustrates an example in which the steam supply pipe 16 is connected to the feed chute 14, this is not limiting, and the steam supply pipe 16 may be directly connected to the rotary kiln 20. The raw materials supplied to the rotary kiln 20 are heated by a heating means and agitated by the rotation of the rotary kiln 20. As a result, the raw materials are pyrolyzed inside the rotary kiln 20, and the pyrolyzed material is sent to a collection container 30. The gas components of the pyrolyzed products of the raw material are recovered via a gas recovery pipe 32 , and the solids, metals, and alloys of the pyrolyzed products of the raw material are recovered from inside a recovery container 30 .

[0028] The metals and alloys sent to the recovery container 30 may be recovered and reused as raw materials. In order to remove impurities, it is also preferable that the metals and alloys sent to the recovery container 30 be subjected to a purification process such as filtration before being reused as raw materials.

[0029] A solid material containing a fluoropolymer (e.g., pellets, particles, sheets, etc.) and a solid material containing at least one of a metal and an alloy may be separately charged into the hopper 10, or a solid material containing both a fluoropolymer and at least one of a metal and an alloy may be charged.

[0030] <Fluoromonomer> Specific examples of fluoromonomers obtainable by the present production method include tetrafluoroethylene (hereinafter also referred to as "TFE"), hexafluoropropylene (hereinafter also referred to as "HFP"), octafluorocyclobutane (hereinafter also referred to as "c-318"), vinylidene fluoride, vinyl fluoride, chlorotrifluoroethylene, perfluoroalkyl vinyl ether, and mixtures of two or more of these.

[0031] The present invention will be described in detail below with reference to examples. Examples 1 to 5 are working examples, and Example 6 is a comparative example. However, the present invention is not limited to these examples.

[0032] [Raw Materials] Details of the raw materials used in each example are shown below. PTFE (polytetrafluoroethylene): A PTFE sheet (manufactured by AS ONE Corporation, thickness 1 mm) was cut into 5 mm squares and used. PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer): A PFA sheet (manufactured by AS ONE Corporation, thickness 1 mm) was cut into 5 mm squares and used. Tin (Kanto Chemical Co., Ltd., tin (granular)) Lead: A lead plate (manufactured by AS ONE Corporation, thickness 1 mm) was cut into 5 mm squares and used.

[0033] [Pyrolysis Apparatus] The pyrolysis apparatus shown in Fig. 1 was used for the pyrolysis of the fluoropolymer in each example. Details of the rotary kiln included in the pyrolysis apparatus are as follows: Material constituting the inner wall surface of the rotary kiln: nickel alloy Internal size of the rotary kiln: diameter 100 mm, length 500 mm

[0034] [Compositional analysis of fluoromonomers] The composition of the fluoromonomers obtained in each example was analyzed by gas chromatography. The analytical equipment and conditions are as follows: Equipment: Agilent 7890B (Agilent) Column: Poraplot-Q (inner diameter 0.32 mm, length 25 m, film thickness 10 μm) Detector: FID Column temperature: 100°C Injection port temperature: 200°C Detector temperature: 250°C

[0035] [Example 1] The interior of the rotary kiln of the thermal decomposition apparatus was heated to 600°C. Then, tin was supplied to the rotary kiln at 2 g / h, PTFE at 300 g / h, and steam at 1000 g / h, and thermal decomposition of PTFE was carried out. During the thermal decomposition, the temperature inside the rotary kiln was maintained at 600°C so that the supplied tin was in a molten state. The rotation speed of the rotary kiln during the thermal decomposition was 5 rpm. After continuing the operation for 2 hours, the amount of solid matter recovered from the rotary kiln and the recovery container was weighed, and the conversion rate of PTFE was calculated from the input amount. The results are shown in Table 1. Furthermore, when the gas generated during the operation was measured by gas chromatography, TFE, HFP, and c-318 were detected. The selectivity of each component is shown in Table 1.

[0036] [Examples 2 and 3] Pyrolysis of PTFE was carried out in the same manner as in Example 1, except that the amount of tin introduced into the rotary kiln was changed to the value shown in Table 1. The conversion rate of PTFE and the analysis results of the gas generated during the operation are shown in Table 1.

[0037] [Example 4] Except for using tin instead of lead, the pyrolysis of PTFE was carried out in the same manner as in Example 2. The conversion rate of PTFE and the analytical results of the gas evolved during the operation are shown in Table 1.

[0038] Example 5 Except for changing PTFE to PFA, thermal decomposition of PFA was carried out in the same manner as in Example 2. The PFA conversion rate and the analytical results of the gas generated during the operation are shown in Table 1.

[0039] [Example 6] Except for not using tin, the pyrolysis of PTFE was carried out in the same manner as in Example 1. The conversion rate of PTFE and the analytical results of the gas generated during the operation are shown in Table 1.

[0040] In Table 1, "metal / fluoropolymer" means the amount of metal used (total amount supplied to the inside of the rotary kiln) relative to the amount of fluoropolymer used (total amount supplied to the inside of the rotary kiln) (unit: mass %).

[0041]

[0042] As shown in Table 1, when the thermal decomposition of a fluoropolymer was carried out in the presence of at least one of a metal and an alloy in a molten state (Examples 1 to 5), it was shown that the conversion rate of the fluoropolymer was excellent.

[0043] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2023-096187, filed on June 12, 2023, are incorporated herein by reference as part of the disclosure of the present invention.

[0044] REFERENCE SIGNS LIST 1 Pyrolysis device 10 Hopper 12 Conveyor 14 Input chute 16 Steam supply pipe 20 Rotary kiln 30 Recovery container 32 Gas recovery pipe

Claims

1. A method for producing a fluoromonomer, comprising heating a fluoropolymer in the presence of at least one of a metal and an alloy to thermally decompose the fluoropolymer to obtain a fluoromonomer, wherein the heating temperature is 300 to 900°C, and the metal and the alloy are in a molten state during the heating.

2. The method for producing a fluoromonomer according to claim 1, wherein the metal and the alloy include at least one selected from the group consisting of tin, lead, zinc, bronze, brass, and aluminum.

3. The method for producing a fluoromonomer according to claim 1 or 2, wherein the fluorine-containing polymer comprises at least one selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene copolymers, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, vinylidene fluoride-hexafluoropropylene copolymers, and perfluoropolyether rubber.

4. The method for producing a fluoromonomer according to claim 1 or 2, wherein the amount of said metal or said alloy used is 0.5 to 20 parts by mass per 100 parts by mass of the fluoropolymer used.

5. The method for producing a fluoromonomer according to claim 1 or 2, wherein the thermal decomposition of the fluoropolymer is carried out using a rotary kiln.

6. The method for producing a fluoromonomer according to claim 1 or 2, wherein the melting point of the metal or alloy is 100 to 700°C.

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