Method for producing tetrafluoroethylene and octafluorocyclobutane

Abstract

In this method for producing tetrafluoroethylene and octafluorocyclobutane, 1,1,1,2,2-pentafluoroethane is converted into tetrafluoroethylene and octafluorocyclobutane in a gas phase in the presence of silicon oxide. In this conversion, no diluent is used, or 60 vol% or less of a diluent is used relative to the total amount of 1,1,1,2,2-pentafluoroethane and the diluent.

Description

Method for producing tetrafluoroethylene and octafluorocyclobutane 【0001】 This disclosure relates to methods for producing tetrafluoroethylene and octafluorocyclobutane. 【0002】 In recent years, halogenated alkenes such as fluoroolefins have attracted attention as compounds with low global warming potential. For example, Patent Document 1 describes a method for producing hydrofluoroolefins in which hydrofluorocarbons are converted to hydrofluoroolefins in the presence of a fluorine-containing compound having a standard boiling point higher than that of the target hydrofluoroolefin. This production method includes a step of contacting the hydrofluorocarbon with a catalyst. Specifically, alumina (Al) is used as the catalyst. ２ O ３ ) is used. 【0003】 Among the halide alkenes, tetrafluoroethylene is useful as a raw material for polytetrafluoroethylene. Polytetrafluoroethylene has excellent physical properties such as electrical insulation, water and oil repellency, chemical resistance, and heat resistance, and is therefore widely used in fields such as water repellents, oil repellents, resists, adhesives, electrical insulating layers, lubricants, inks, and paints. Octafluorocyclobutane is also useful because tetrafluoroethylene can be obtained by thermal decomposition. 【0004】 International Publication No. 2017 / 104829 【0005】 In the production of useful tetrafluoroethylene and octafluorocyclobutane, it is desirable to increase the total amount of tetrafluoroethylene and octafluorocyclobutane produced. 【0006】 Therefore, the objective of one embodiment of this disclosure is to provide a novel manufacturing method that can increase the total amount of tetrafluoroethylene and octafluorocyclobutane produced. 【0007】This disclosure includes the following aspects: <1> A method for producing tetrafluoroethylene and octafluorocyclobutane, wherein, in the presence of silicon dioxide, 1,1,1,2,2-pentafluoroethane is converted to tetrafluoroethylene and octafluorocyclobutane in the gas phase, and in the conversion, no diluent is used, or a diluent is used in an amount of 60% by volume or less relative to the total amount of 1,1,1,2,2-pentafluoroethane and diluent. <2> The method for producing tetrafluoroethylene and octafluorocyclobutane according to <1>, wherein the diluent comprises at least one selected from the group consisting of nitrogen, carbon dioxide, helium, and water. <3> The method for producing tetrafluoroethylene and octafluorocyclobutane according to <1> or <2>, wherein the diluent is used in an amount of 20 to 60% by volume relative to the total amount of 1,1,1,2,2-pentafluoroethane and diluent. <4> A method for producing tetrafluoroethylene and octafluorocyclobutane according to any one of <1> to <3>, wherein the diluent is not used, or the diluent is used in an amount of 30% by volume or less relative to the total amount of 1,1,1,2,2-pentafluoroethane and the diluent. <5> A method for producing tetrafluoroethylene and octafluorocyclobutane according to any one of <1> to <4>, wherein the conversion is carried out in the presence of a metal element. <6> A method for producing tetrafluoroethylene and octafluorocyclobutane according to <5>, wherein the metal element is an alkali metal element. <7> A method for producing tetrafluoroethylene and octafluorocyclobutane according to <5> or <6>, wherein the metal element is used as a fluorine-containing alkali metal salt. <8> A method for producing tetrafluoroethylene and octafluorocyclobutane according to any one of <1> to <7>, wherein the conversion is carried out at a temperature of 400 to 1000°C. <9> A method for producing tetrafluoroethylene and octafluorocyclobutane according to any one of <1> to <8>, wherein the conversion reaction is carried out in a fluidized bed reactor. <10> A method for producing tetrafluoroethylene and octafluorocyclobutane according to <9>, wherein the average particle size of the silicon dioxide when it is introduced into the fluidized bed reactor is 20 μm to 10 mm or less.<11> A method for producing tetrafluoroethylene and octafluorocyclobutane according to any one of <1> to <10>, wherein silicon tetrafluoride is produced. <12> A method for producing tetrafluoroethylene and octafluorocyclobutane according to any one of <1> to <11>, comprising: producing tetrafluoroethylene, octafluorocyclobutane and hydrogen fluoride by a dehydrofluorination reaction of 1,1,1,2,2-pentafluoroethane in the gas phase; and producing silicon tetrafluoride by a reaction between the produced hydrogen fluoride and silicon oxide. 【0008】 This disclosure provides a novel manufacturing method that can increase the total amount of tetrafluoroethylene and octafluorocyclobutane produced. 【0009】 In this disclosure, numerical ranges indicated using "~" mean a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Also, in numerical ranges described in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In this disclosure, the amount of each component means the total amount of multiple substances if there are multiple substances corresponding to each component, unless otherwise specified. 【0010】 [Manufacturing Method] The manufacturing method of the present disclosure is a method for producing FO-1114 and C318 in which, in the presence of silicon dioxide, 1,1,1,2,2-pentafluoroethane (hereinafter also referred to as HFC-125) is converted in the gas phase to tetrafluoroethylene (hereinafter also referred to as FO-1114) and octafluorocyclobutane (hereinafter also referred to as C318), and in the said conversion, no diluent is used, or a diluent is used in an amount of 60% by volume or less relative to the total amount of HFC-125 and the diluent. 【0011】According to the manufacturing method of the present disclosure, it is possible to increase the total production amount of FO-1114 and C318. The reason for the above effect is not clear, but it is speculated as follows. 【0012】 In the reaction to obtain FO-1114 and C318 from HFC-125, hydrogen fluoride is generated. The generated hydrogen fluoride reacts with alumina (Al ２ O ３ ), for example, when used as a catalyst, to generate AlF ３ , and reacts with calcium carbonate (CaCO ３ ) to generate CaF ２ when used as a catalyst. Here, since the boiling point of AlF ３ is 1260°C and the boiling point of CaF ２ is 2533°C, these are solids in the reaction system. Therefore, the generated AlF ３ and CaF ２ remain in the reaction system and cover the reaction sites existing on the surface of the catalyst. When the reaction sites of the catalyst are covered, the activity of the catalyst decreases rapidly. When using reactants other than alumina (Al ２ O ３ ) and calcium carbonate (CaCO ３ ), these reactants tend to react with the generated hydrogen fluoride and become fluorinated and altered. 【0013】 In contrast, in the manufacturing method of the present disclosure, FO-1114 and C318 are obtained by the dehydrofluorination reaction of HFC-125 in the presence of silicon oxide. At this time, the generated hydrogen fluoride reacts with the silicon oxide particles, or the HFC-125 and the silicon oxide particles react directly. In either case of the reaction scheme, silicon tetrafluoride (SiF ４ ) is generated. Since the boiling point of silicon tetrafluoride is -95°C, it is a gas in the reaction system and is released outside the reaction system. Therefore, in the manufacturing method of the present disclosure, it is considered that the problems caused by the remaining by-products in the system are suppressed, and the decrease in the reaction production amount is suppressed. 【0014】In the production method of the present disclosure, attention is paid to the amount of diluent used in the reaction of converting HFC-125 to FO-1114 and C318 in the presence of silicon oxide. Specifically, it has been found that when no diluent is used or the diluent is 60% by volume or less based on the total amount of HFC-125 and the diluent, the total production amount of FO-1114 and C318 increases. 【0015】 (Raw materials, etc.) The production method of the present disclosure uses HFC-125 as a raw material. The conversion of HFC-125 to FO-1114 and C318 is carried out in the presence of silicon oxide. 【0016】 In the production method of the present disclosure, the raw material gas only needs to contain HFC-125, and may also contain components other than HFC-125. The raw material gas may consist only of HFC-125, or may contain isomers, disproportionation products, impurities, etc. obtained when producing HFC-125. From the viewpoint of suppressing side reactions, the content of HFC-125 is preferably 10 mol% or more, more preferably 30 mol% or more, and still more preferably 50 mol% or more based on the total amount of the raw material gas. The content of HFC-125 may be 100 mol% based on the total amount of the raw material gas. 【0017】 Silicon oxide may be in a crystalline state or an amorphous state. Examples of the silicon oxide particles include silica sand, quartz, diatomaceous earth, colloidal silica, precipitated silica, silica gel, fumed silica, rice husks, etc. Silica sand is preferred from the viewpoints of purity and price. 【0018】 The shape of the silicon oxide particles is not particularly limited and may be any of irregular shapes such as natural products and crushed products, pellet shapes, flake shapes, spherical shapes, etc. Further, it may be formed into a pellet shape, a hollow shape, a cylindrical shape, etc. The silicon oxide particles may have a pore structure (such as porous). These shapes may be appropriately combined, for example, a porous cylindrical molded product, etc. 【0019】The silicon oxide particles preferably have a low impurity content. From the viewpoint of suppressing the generation of unnecessary by-products, the silicon oxide content in the silicon oxide particles preferably has a low impurity content, preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more. 【0020】 From the viewpoint of suppressing clogging in the reactor, the average particle diameter of the silicon oxide particles at the time of charging into the reactor is preferably 20 μm or more, more preferably 50 μm or more. From the viewpoint of ensuring the surface area serving as the reaction point, the average particle diameter of the silicon oxide particles at the time of charging into the reactor is preferably 10 mm or less, more preferably 5 mm or less, and still more preferably 1 mm or less. 【0021】 The average particle diameter of the silicon oxide particles is determined as the particle diameter (D50) at which the cumulative value becomes 50% in the volume-based cumulative particle size distribution curve obtained by measurement using a Coulter counter. The aperture diameter is appropriately set according to the particle diameter range of the measurement target. 【0022】 In the conversion reaction, it is preferable to have a metal element present together with the silicon oxide. When the conversion reaction is carried out in the presence of a metal element, the dehydrofluorination reaction from HFC-125 is promoted. The silicon oxide and the metal element may be an integrated compound or composite containing both, or separate substances containing the silicon oxide and the metal element separately may be used, or two or more of these may be used in combination. Examples include glass containing silicon oxide and a metal element oxide, sodium silicate, silica callet, etc., a composite in which a metal-containing compound is supported on silicon oxide particles, and a combination of silicon oxide particles and a metal-containing compound. 【0023】When silicon dioxide and metal elements are integrated, their uneven distribution within the reaction system is easily suppressed. When silicon dioxide and metal elements are used as separate substances, it is easier to prepare highly pure versions of each, and the generation of unwanted by-products during the reaction is easily suppressed. When used as separate substances, it is sufficient for the silicon dioxide particles and metal elements to be separate raw materials, and the metal elements may subsequently adhere to the silicon dioxide particles to form a single unit. Hereinafter, compounds and composites containing both silicon dioxide and metal elements, as well as substances containing silicon dioxide and metal elements separately, will be collectively referred to as "reactants." 【0024】 From the viewpoint of promoting the dehydrofluoride reaction from HFC-125, alkali metal elements are preferred as the metal element. Preferably, the alkali metal element is at least one selected from the group consisting of Li, Na, K, Rb, and Cs, more preferably at least one selected from the group consisting of Na, K, and Cs from the viewpoint of activity, selectivity, or availability, and even more preferably at least one selected from the group consisting of Na and K. 【0025】 Alkali metal elements may also be used as alkali metal-containing compounds, such as alkali metal fluorides, halides such as chlorides, hydroxides, and carbonates. Examples of alkali metal chlorides include NaCl, examples of alkali metal hydroxides include NaOH and KOH, and examples of alkali metal carbonates include Na ２ CO ３ _K ２ CO ３ Examples include alkali metal-containing compounds, preferably alkali metal salts, such as LiF, NaF, and Na ２ SiF ６ ,KF,K ２ CO ３ _K ２ SiF ６ Examples include CsF. 【0026】Among alkali metal-containing compounds, fluorine-containing alkali metal salts are preferred. Because fluorine-containing alkali metal salts inherently contain the element fluorine, even if they are fluorinated by the generated hydrogen fluoride, the alteration is suppressed, and fluctuations in reaction conditions are minimized. For example, when carried out in a fluidized bed reactor, the fluid state can be maintained. 【0027】 Fluorine-containing alkali metal salts include LiF, NaF, and Na ２ SiF ６ ,KF,K ２ SiF ６ Preferably, it contains at least one selected from the group consisting of , and CsF, and is less reactive or non-reactive to silicon tetrafluoride while maintaining its performance as a reactant at the heating temperature in the inversion reaction, such as NaF, KF and K ２ SiF ６ It is more preferable to include at least one selected from the group consisting of the following: 【0028】 From the viewpoint of maintaining the performance as a reactant at the heating temperature in the conversion reaction, the thermal decomposition temperature of the fluorine-containing alkali metal salt is preferably 100°C or higher, more preferably 150°C or higher, even more preferably 300°C or higher, particularly preferably 350°C or higher, and extremely preferably 400°C or higher. There is no particular upper limit to the thermal decomposition temperature of the fluorine-containing alkali metal salt, and it may be 1000°C or lower. The thermal decomposition temperature of the fluorine-containing alkali metal salt is measured by thermogravimetric analysis. 【0029】 Fluorine-containing alkali metal salts may react with silicon tetrafluoride produced by a conversion reaction to form reactants, and at least a portion of these reactants may revert back to the fluorine-containing alkali metal salt through thermal decomposition. Confirmation of whether the reactants have reverted to the original fluorine-containing alkali metal salt through thermal decomposition is performed by micro-Raman spectroscopy. As a micro-Raman spectroscopy instrument, for example, the LabRAM HR Evolution manufactured by Horiba, Ltd. can be used, and the measurement conditions are: excitation wavelength 532 nm, objective lens ×100_VIS_LWD, confocal aperture 100 μm, 200 μm pinhole, grating 300, and center wavenumber 1800 cm. －１ It will be implemented there. 【0030】 From the viewpoint of maintaining the powder state of the reactant in the best possible condition throughout the reaction, the moisture content of the reactant is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. The moisture content of the reactant is measured using a Karl Fischer moisture meter or the like. Note that the moisture content of the reactant is the value immediately before the start of the reaction. 【0031】 The silicon content in the reactant may be 1 atm% or more, 5 atm% or more, or 10 atm% or more. The silicon content in the reactant may also be 90 atm% or less, or 80 atm% or less. The oxygen content in the reactant may be 1 atm% or more, 5 atm% or more, or 10 atm% or more. The oxygen content in the reactant may also be 90 atm% or less, or 80 atm% or less. The metal element content in the reactant may be 1 atm% or more, 5 atm% or more, or 8 atm% or more. The metal element content in the reactant may also be 90 atm% or less, or 50 atm% or less. 【0032】 The content of each element in the reactant is determined by scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX analysis). 【0033】 In the reactant, the silicon content (atm%) is preferably greater than the metal element content (atm%), and is preferably greater than the total content of alkaline earth metals and Group 13 elements of the periodic table. Furthermore, silicon is preferably the element with the highest content (atm%) among the elements excluding oxygen. 【0034】 (Diluent) In the manufacturing method of the present disclosure, no diluent is used in the inversion reaction, or a diluent is used in an amount of 60% by volume or less relative to the total amount of HFC-125 and the diluent. 【0035】In general, in methods for producing alkene halides, diluent gases are used to suppress disproportionation reactions caused by high concentrations of the resulting alkene halides, and also because high concentrations of certain types of alkene halides pose a risk of explosion. In particular, in the production method using an alumina catalyst described in Patent Document 1, reducing the amount of diluent lowers the conversion rate, making the use of diluent gases such as nitrogen and carbon dioxide essential. However, since diluent gases such as nitrogen and carbon dioxide have lower boiling points than or are close to the boiling points of the alkene halides that are the reaction products, energy is required to separate and purify the diluent gas from the reaction products. 【0036】 In the manufacturing method disclosed herein, silicon dioxide is used, and silicon tetrafluoride (SiF) has a boiling point of -95°C. ４ This generates FO-1114 and C318, which are released as a gas outside the reaction system. Therefore, the generation of retained by-products and the deterioration of the catalyst are easily suppressed, and the reactivity can be easily controlled by residence time, reaction temperature, etc. Thus, the concentrations of FO-1114 and C318 in the outlet gas can be controlled by these controls, so that the outlet gas can contain a certain amount or more of the raw material HFC-125. The HFC-125 in the outlet gas also functions as a diluent. Therefore, in the manufacturing method of this disclosure, it is also possible to use a reduced amount of diluent gas. The manufacturing method of this disclosure also includes embodiments in which no diluent gas is used. 【0037】 Furthermore, in the manufacturing method disclosed herein, it is possible to increase the total amount of FO-1114 and C318 produced even if the raw material gas is used as part or all of the diluent. 【0038】The diluent gas is preferably at least one selected from the group consisting of nitrogen, argon, hydrogen, carbon dioxide, helium, propane, isobutane, n-butane, ethane, propylene, and fluorinated methane. Examples of fluorinated methane include monofluoromethane, trifluoromethane, and tetrafluoromethane. From the viewpoint of low flammability, the diluent preferably contains at least one selected from the group consisting of nitrogen, argon, carbon dioxide, helium, and water, more preferably contains at least one selected from the group consisting of nitrogen, helium, and argon, and even more preferably contains nitrogen. 【0039】 The diluent should be used at a concentration of 60% by volume or less relative to the total amount of HFC-125 and the diluent. From the viewpoint of increasing the amount of FO-1114 and C318 generated in the outlet gas, it is preferable to use the diluent at a concentration of 20 to 60% by volume relative to the total amount of HFC-125 and the diluent. Furthermore, from the viewpoint of suppressing the amount of C318 generated, it is preferable to use the diluent at a concentration of 30% by volume or less relative to the total amount of HFC-125 and the diluent. 【0040】 (Reaction Scheme) In the manufacturing method of the present disclosure, silicon tetrafluoride (SiF ４ ) is generated. In the manufacturing method of the present disclosure, a reaction scheme is conceivable in which, in the gas phase, FO-1114, C318 and hydrogen fluoride are generated by the dehydrofluorination reaction of HFC-125 (first step), and silicon tetrafluoride is generated by the reaction of the generated hydrogen fluoride with silicon oxide (second step). The first step and the second step may proceed continuously without distinction. 【0041】 【0042】 Furthermore, the manufacturing method disclosed herein may be other than the reaction scheme described above. For example, silicon dioxide or a metal compound may react directly with HFC-125 to produce silicon tetrafluoride. In addition, other compounds may be produced in addition to silicon tetrafluoride. 【0043】Since the generated silicon tetrafluoride is a gas, it is released from the reaction system. Therefore, the influence of by-products on silicon oxide is suppressed, and the rapid decrease in the production of FO-1114 and C318 is prevented. 【0044】 In conventional manufacturing methods using alumina, calcium carbonate, etc. as catalysts, the generated hydrogen fluoride reacts with the catalyst as follows. 【0045】 【0046】 The generated aluminum fluoride (AlF ３ ) and calcium fluoride (CaF ２ Since the substance is a solid, it is not released outside the reaction system but remains within it, coating the surfaces of the catalysts, alumina and calcium carbonate. As a result, the active sites on the surface of the catalyst are covered and the catalyst becomes inactive. Therefore, in conventional manufacturing methods, it is necessary to remove the degraded catalyst and replace it with a new one. Consequently, conventional manufacturing methods using alumina, calcium carbonate, etc. as catalysts have unstable productivity and require stopping the reaction each time the catalyst is replaced. In contrast, the manufacturing method disclosed herein has the advantage of reducing the work of removing the degraded catalyst while maintaining productivity. 【0047】 Furthermore, in the manufacturing method disclosed herein, the reaction can be continued by replenishing the consumed silicon dioxide. The amount of consumed silicon dioxide can be calculated from the amount of silicon tetrafluoride released from the reaction system. Specifically, the amount of released silicon tetrafluoride can be measured by passing the released silicon tetrafluoride through water, an alkaline aqueous solution, etc., to obtain hydrogen fluoride, hexafluorosilicic acid, or salts thereof, and then titrating these. On the other hand, in conventional manufacturing methods using alumina or calcium carbonate as a catalyst, AlF is present in the reaction system. ３ or CaF ２ Because the catalyst remains in place, it is difficult to estimate the amount of degraded catalyst. Therefore, it is difficult to accurately estimate the amount of catalyst to be replenished using conventional manufacturing methods. 【0048】 When reacting in a fluidized bed, it is desirable that the fluidity of the catalyst does not change significantly, but in conventional methods, AlF３ or CaF ２ Because of the adhesion of the by-product SiF, the weight and density of the catalyst change, causing fluctuations in fluidity. Therefore, it is difficult to maintain an appropriate flow state. In contrast, the manufacturing method of this disclosure uses SiF as a by-product. ４ Since it is a gas and is released outside the reaction system, there is no significant change in the fluidity of silicon dioxide particles, making it easy to maintain an appropriate flow state. 【0049】 The silicon tetrafluoride produced can be used as a raw material for manufacturing high-performance optical fibers, as a gas for semiconductor manufacturing, etc. Furthermore, the silicon tetrafluoride released outside the reaction system can be recovered as hydrogen fluoride or fluoride salts by reacting with water or alkali. These recovered compounds can be used as etching agents or as raw materials for organofluorine compounds. For example, calcium carbonate (CaCO3) can be used as a catalyst. ３ Calcium fluoride (CaF) generated by conventional methods using ) ２ Converting fluorite into hydrogen fluoride requires the extreme condition of reacting it with sulfuric acid, and also requires the solid CaF ２ Pre-processing, such as crushing, is required. 【0050】 (Reaction Conditions) The manufacturing method of this disclosure is carried out in the gas phase because HFC-125 is a gas at room temperature and pressure. The reactor used to react HFC-125 with the reactant can be any reactor capable of withstanding the temperature and pressure described later, and its shape and structure are not particularly limited. An example of a reactor is a cylindrical vertical reactor. Examples of reactor materials include glass, stainless steel, iron, nickel, chromium, and alloys mainly composed of iron, nickel, or chromium. The inside of the reactor may be coated with platinum or gold. The reactor may also be equipped with heating means such as an electric heater to heat the inside of the reactor. 【0051】 The reactants may be contained in a fixed-bed, fluidized-bed, or mobile-bed reactor. If a fixed-bed reactor is used, it may be either a horizontal or vertical fixed-bed reactor. The reactor may rotate as a whole. The reaction may be a flow-through reactor or a batch reactor. 【0052】 In fixed-bed reactors, various molded bodies of reactant carriers are packed to reduce pressure loss of the reaction fluid. A moving bed reactor is another method where the reactant is packed in a similar manner to a fixed-bed reactor, moved by gravity, and then extracted from the bottom of the reactor for regeneration. In fluidized-bed reactors, the reaction fluid is used to make the reactant layer behave like a fluid, so the reactant mixes with the reaction fluid and moves within the reactor. Fixed-bed reactors are preferred because they offer a wide range of reactant shape options and suppress reactant wear. Fluidized-bed reactors are preferred because they ensure a uniform internal temperature and make it easier to avoid localized overheating. Preventing localized overheating suppresses runaway reactions such as disproportionation, and because the temperature remains constant, the reaction results tend to be more consistent. The manufacturing method disclosed herein is suitable for reactions in fluidized-bed reactors because it suppresses changes in the reactant's properties over time. 【0053】 Fixed-bed reactors include tubular reactors and tank reactors, with tubular reactors being preferred due to their ease of controlling the reaction temperature. Furthermore, multi-tube heat exchange reactors, in which many small-diameter reaction tubes are arranged in parallel and a heat transfer medium is circulated around the outside, can be employed. When multiple reactors are installed in series, multiple reactant layers will be provided. At least one reactant layer is sufficient, but two or more layers are also acceptable. 【0054】 In a fluidized bed reactor, the raw material gas and diluent gas may be flowed from the bottom vertically, and the generated gas may be extracted from the top vertically. From the viewpoint of further increasing fluidity, agitators may be installed in the fluidized bed reactor. In addition, from the viewpoint of preventing uneven flow of gas within the fluidized bed reactor, gas dispersion plates may be provided in the fluidized bed reactor. The material of the gas dispersion plates is not particularly limited, but it is preferable that it be made of a material with low reactivity with the raw material gas, generated gas, etc. Examples of materials for gas dispersion plates include sintered metal. The size, position, and number of gas dispersion plates may be adjusted as appropriate according to the gas flow. 【0055】In the manufacturing method of this disclosure, it is preferable to convert HFC-125 at a temperature of 400 to 1000°C, more preferably at a temperature of 450 to 900°C, and even more preferably at a temperature of 500 to 800°C. When conversion is carried out at a temperature of 400°C or higher, the reaction proceeds appropriately and the conversion rate of FO-1114 and C318 is improved. On the other hand, when conversion is carried out at a temperature of 1000°C or lower, the decrease in selectivity due to carbon-carbon bond cleavage of HFC-125 and the disproportionation reaction of the reaction product (unsaturated compound) are suppressed. 【0056】 By adjusting the temperature within the above temperature range and maintaining the reaction temperature appropriately, it is possible to suppress the decrease in the conversion rate. To maintain the reaction temperature in the reactant layer at the desired temperature, for example, the reactant layer can be heated externally using a heat transfer medium, an electric furnace, or the like. 【0057】 As described above, in the manufacturing method of this disclosure, the reaction can be continued by replenishing the consumed silicon dioxide, and productivity can be maintained. From the viewpoint of continuing the reaction, it is preferable to continuously supply the consumed silicon dioxide. The supply location of silicon dioxide in the reactor is not particularly limited and may be from the top or bottom of the reactor. 【0058】 In the manufacturing method of this disclosure, the raw material gas containing HFC-125 may be supplied to the reactor at room temperature, or it may be appropriately heated (preheated) before being supplied to the reactor. When preheating is performed, it is preferable to heat the raw material gas to 80°C or higher and below the reaction temperature inside the reactor before supplying it to the reactor. Setting the preheating temperature to 80°C or higher makes it less likely for the internal temperature of the reactor to drop, and makes it easier to achieve the set conversion rate. Furthermore, setting the preheating temperature below the reaction temperature inside the reactor suppresses undesirable reactions and improves the selectivity. 【0059】 The dehydrofluoride reaction in this disclosure is a reaction in which the number of molecules increases, so increasing the pressure is detrimental to the forward reaction. The pressure when reacting HFC-125 with the reactant is not particularly limited, but from the viewpoint of improving the conversion rate, -0.05 to 2 MPa is preferred, -0.01 to 1 MPa is more preferred, and atmospheric pressure to 0.5 MPa is even more preferred. In this disclosure, pressure means gauge pressure. 【0060】The residence time for HFC-125 is preferably 0.5 to 300.0 seconds, more preferably 1.0 to 100.0 seconds, and even more preferably 1.5 to 60.0 seconds. 【0061】 The residence time (seconds) is calculated using the following formula: Residence time (seconds) = [Length of the reactor filled with reagent (cm)] / [Linear velocity (cm / second)] Linear velocity refers to the rate at which HFC-125 passes through the reagent per unit time. 【0062】 Furthermore, the average bulk density of the reactant was 0.05 g / cm³. ３ The above is preferable, and 0.1 g / cm³ ３ The above is more preferable, 0.2 g / cm³ ３ The above is even more preferable. The average bulk density of the reactant is 0.05 g / cm³. ３ The conversion rate improves when the above conditions are met. The average bulk density of the reactant is the average value of the reactant's density when no gas is flowing through the reactor. The average bulk density of the reactant is measured by the container method. In the container method, the reactant is placed in a container of known capacity until it overflows, and the excess reactant overflowing from the rim of the container is removed with a spatula or similar tool, and the mass of the reactant in the container is measured. The bulk density (g / mL) is calculated from this mass of reactant and the capacity (volume) of the container. This measurement is performed three times, and the average value is taken as the average bulk density. 【0063】From the viewpoint of controlling the efficiency and selectivity of the reaction, it is preferable that the conversion of HFC-125 be carried out in the gas phase in the presence of water, and that the concentration of water be less than 500 volume ppm relative to the total amount of the raw material gas containing HFC-125. The dehydrofluoride reaction in this disclosure also produces water. Therefore, it can be said that the reaction will proceed without problems even if water is present in the system. Furthermore, when hydrogen fluoride is desorbed from the raw material, or when hydrogen fluoride reacts with silicon dioxide, the presence of water molecules may allow the reaction to proceed more efficiently via a hydrogen bond network. Therefore, it is possible to add a small amount of water in the dehydrofluoride reaction in this disclosure, and it is presumed that this may yield good results. On the other hand, from the viewpoint of preventing blockage of the gas flow path due to the reaction between the generated silicon tetrafluoride and water near the outlet to produce hexafluorosilicic acid, etc., it is preferable that the concentration of water be below the above range. 【0064】 A common method for measuring the moisture content of a gas is to use a commercially available dew point meter. A moisture content of less than 500 volume ppm relative to the total volume of the raw material gas containing HFC-125 results in a high conversion rate and allows for the acquisition of the target product with high selectivity. From the viewpoint of further improving the conversion rate and obtaining the target compound with even higher selectivity, a moisture content of 300 volume ppm or less is preferable, more preferably 100 volume ppm or less, even more preferably 50 volume ppm or less, and particularly preferable 10 volume ppm or less. While a lower moisture content is preferable, from the viewpoint of reducing the cost of dehydration treatment of the raw material gas and diluent gas, and from the viewpoint of facilitating process control, a moisture content of 0.5 volume ppm or more is preferable, and more preferably 1 volume ppm or more. 【0065】 The water concentration mentioned above refers to the water content in the raw material gas when it is brought into contact with the reactant. Alternatively, the water concentration may be replaced with the water content in the raw material gas before it enters the reactor. 【0066】 The manufacturing method of this disclosure may further include a step of drying the reactant before contacting the reactant with the raw material gas containing HFC-125. By drying the reactant, water contained in the reactant may be removed and the water concentration adjusted to the above range. 【0067】 The method for drying the reactant is not particularly limited; it may be dried before filling the reactor, or after filling the reactor. If the reactant is dried after filling the reactor, the reactor can be preheated at the same time as drying the reactant. Specifically, the reactant may be dried by filling the reactor with the reactant and heating the reactor while circulating a diluent gas. 【0068】 When drying the reactant by circulating a diluent gas, the moisture content of the diluent gas after circulation is 3 g / m³. ３ It is preferable to dry it to the following extent: 2 g / m² ３ It is more preferable to dry it to the following extent: 1 g / m ３ It is preferable to dry the gas to the following state. The moisture content of the diluted gas after circulation can be determined from the dew point. 【0069】 From the viewpoint of suppressing polymerization of the generated FO-1114, the conversion of HFC-125 is preferably carried out in an atmosphere with an oxygen content of 10,000 ppm by mass or less, more preferably in an atmosphere with an oxygen content of 5,000 ppm by mass or less, and even more preferably in an atmosphere with an oxygen content of 1,000 ppm by mass or less. 【0070】 Oxygen content refers to the amount of oxygen present in the atmosphere where conversion takes place, encompassing all gases present in the site of conversion, including raw material gases and reaction products. For example, oxygen content is the ratio of the mass of oxygen present in the reactor to the total mass of gases present in the reactor where conversion occurs. 【0071】 The oxygen content is measured using an oxygen concentration meter. Any type of oxygen concentration meter may be used, including, for example, zirconia type, magnetic type, electrochemical type, yellow phosphorus emission type, and laser spectrometer. 【0072】In this disclosure, the conversion rate is the ratio (%) of the molar amount of HFC-125 consumed in the reaction to the molar amount of HFC-125 supplied to the reactor. The molar amount of HFC-125 consumed in the reaction is the difference between the molar amount of HFC-125 supplied to the reactor and the molar amount of HFC-125 contained in the gas effluent from the reactor outlet. 【0073】 Generally, a higher conversion rate is preferable from a productivity standpoint. However, from the viewpoint of suppressing explosions and the disproportionation reaction of HFC-125, it is preferable to select operating conditions that result in a conversion rate of 70% or less. A conversion rate of 50% or less is preferable, and 30% or less is more preferable. If the conversion rate is too low, productivity will decrease and the equipment will become larger, so it is preferable to select operating conditions that result in a conversion rate of 5% or more. A conversion rate of 10% or more is preferable, and 15% or more is more preferable. 【0074】 In this disclosure, selectivity refers to the ratio (mol %) of the molar amount of the target product contained in the reactor outlet gas to the total molar amount of compounds other than the diluent and raw materials contained in the reactor outlet gas (however, compounds derived from the carbon of the raw material HFC-125, excluding compounds such as silicon tetrafluoride that do not have carbon derived from the raw material). A selectivity of 100% is preferred because it eliminates the need for a purification step after the reaction, but side reactions may occur in the reaction temperature range required to obtain a desirable conversion rate. A higher selectivity is preferred because it reduces the amount of waste, lowers the energy load of the purification step after the reaction, and extends the life of the reagent. A selectivity of 90% or higher is preferred, 93% or higher is more preferred, and 95% or higher is even more preferred. 【0075】 Compounds other than the raw material compounds and the target product contained in the reactor outlet gas include, for example, water and silicon tetrafluoride. Other compounds such as carbon monoxide and carbon dioxide may also be produced. 【0076】 The manufacturing method of this disclosure makes it possible to increase the total amount of FO-1114 and C318 produced. The amount produced is confirmed by analyzing the reactor outlet gas by gas chromatography and determining the area ratio (GCAare%) corresponding to FO-1114 and C318. 【0077】 FO-1114 obtained by the manufacturing method of this disclosure can be used as a raw material for polytetrafluoroethylene. Polytetrafluoroethylene is widely used in water repellents, oil repellents, resists, adhesives, electrical insulating layers, lubricants, inks, paints, and the like. FO-1114 can be obtained by thermal decomposition of C318 obtained by the manufacturing method of this disclosure. Furthermore, C318 can also be used as an etching gas for semiconductor manufacturing. 【0078】 The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to the following examples unless it exceeds the spirit of the disclosure. Examples 2 to 11 are examples, and Example 1 is a comparative example. 【0079】 (Outlet Gas Composition) One hour after the start of the reaction, the product gas (hereinafter also referred to as "reactor outlet gas") was taken out from the outlet of the reactor and analyzed by gas chromatography. Specifically, the analysis was performed using a gas chromatograph (product name "GC6850", manufactured by Agilent) with a column (product name "DB-1", manufactured by Agilent, length 60 m, inner diameter 0.25 mm, film thickness 1 μm). The table shows the area ratio (GCAare%) of the reactor outlet gas. 【0080】 Furthermore, the obtained area ratio (GCAare%) was converted based on the relative sensitivity of gas chromatography, and the molar composition was determined so that the sum of the components listed in the table equaled 100 mol%. Note that the area ratio (GCAare%) values ​​listed in the table have been rounded to the nearest significant figure, so the sum of each component converted from the area ratio (GCAare%) before rounding may not equal 100 mol%. 【0081】 (Outlet gas composition including diluent) The outlet gas composition (mol%) including the diluent was calculated using the following formula. In the following formula, the diluent concentration is the ratio (volume %) of the diluent gas to the total amount of the raw material gas (HFC-125) and diluent. Outlet gas composition (mol%) including diluent = Molar composition of the outlet gas obtained above (mol%) × (1 - Diluent concentration (volume %) / 100) 【0082】[Example 1] A reaction tube made of Inconel 600 with an inner diameter of 2.04 cm and a length of 30 cm was filled with silica sand and potassium fluoride (KF) mixed in a mass ratio of 1 / 1 (70 g / 70 g) and placed in a tubular electric furnace. The conversion reaction to FO-1114 and C318 was carried out at 700°C by flowing a nitrogen / HFC-125 mixed gas at the flow rate shown in Table 1. The particle size of the silica sand was 75 to 180 μm. The oxygen content in the reaction atmosphere was 10,000 ppm by mass or less. Note that the diluent concentration (volume %) in Table 1 is the ratio (volume %) of the diluent gas to the total amount of raw material gas (HFC-125) and diluent. 【0083】 [Examples 2-4] The conversion reaction was carried out in the same manner as in Example 1, except that the concentration of the nitrogen / HFC-125 mixed gas was changed. The oxygen content in the reaction atmosphere was 10,000 ppm by mass or less. 【0084】 [Examples 5 and 6] The conversion reaction was carried out in the same manner as in Example 4, except that the flow rate of HFC-125 was changed. The oxygen content in the reaction atmosphere was 10,000 ppm by mass or less. 【0085】 [Example 7] The conversion reaction was carried out in the same manner as in Example 2, except that potassium fluoride was replaced with sodium fluoride (NaF). The oxygen content in the reaction atmosphere was 10,000 ppm by mass or less. 【0086】 [Example 8] In Example 2, potassium fluoride is replaced with potassium carbonate (K ２ CO ３ The inversion reaction was carried out in the same manner except for the change to ). The oxygen content in the reaction atmosphere was 10,000 ppm by mass or less. 【0087】 [Example 9] In Example 2, potassium fluoride is mixed with NaF in a mass ratio of 1 / 1 (35 g / 35 g) and potassium hexafluorosilicate (K ２ SiF ６ The inversion reaction was carried out in the same manner, except that the mixture was changed to ). The oxygen content in the reaction atmosphere was 10,000 ppm by mass or less. 【0088】[Example 10] The inversion reaction was carried out in the same manner as in Example 2, except that potassium fluoride was replaced with a mixture of KF and cesium fluoride (CsF) (KF / CsF) in a mass ratio of 3 / 4 (31 g / 39 g). The oxygen content in the reaction atmosphere was 10,000 ppm by mass or less. 【0089】 [Example 11] The conversion reaction was carried out in the same manner as in Example 2, except that silica sand was replaced with silica gel (AGC SI-TEC Co., Ltd., M.S.GEL-100). The oxygen content in the reaction atmosphere was 10,000 ppm by mass or less. 【0090】 Tables 1 and 2 show the reaction conditions for Examples 1 to 12, the area ratio (GCA area%) of the reactor outlet gas at 0.5 hours from the start of the reaction, the molar composition (mol%), and the outlet gas composition (mol%) including the diluent. 【0091】 【0092】 【0093】 As shown in Tables 1 and 2, in Examples 2 to 11, where no diluent was used during conversion, or where the diluent was used at 60% by volume or less relative to the total amount of HFC-125 and diluent, the total amount of FO-1114 and C318 produced was increased compared to Example 1, where the diluent was used at more than 60% by volume relative to the total amount of HFC-125 and diluent. Furthermore, a comparison of Example 1 with Examples 2 and 3 shows that using the diluent at 20% to 60% by volume or less relative to the total amount of HFC-125 and diluent can increase the amount of FO-1114 produced in the outlet gas. In addition, a comparison of Example 2 with Example 3 shows that using the diluent at 30% by volume or less relative to the total amount of HFC-125 and diluent suppresses the amount of C318 produced. 【0094】 The disclosure of Japanese Patent Application No. 2024-218149 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. A method for producing tetrafluoroethylene and octafluorocyclobutane, comprising converting 1,1,1,2,2-pentafluoroethane to tetrafluoroethylene and octafluorocyclobutane in the gas phase in the presence of silicon dioxide, wherein no diluent is used in the conversion, or a diluent is used in an amount of 60% by volume or less relative to the total amount of 1,1,1,2,2-pentafluoroethane and diluent.

2. The method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 1, wherein the diluent comprises at least one selected from the group consisting of nitrogen, carbon dioxide, helium, and water.

3. The method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 1 or 2, wherein the diluent is used in an amount of 20 to 60% by volume relative to the total amount of 1,1,1,2,2-pentafluoroethane and the diluent.

4. A method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 1 or 2, wherein the diluent is not used, or the diluent is used in an amount of 30% by volume or less relative to the total amount of 1,1,1,2,2-pentafluoroethane and the diluent.

5. A method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 1 or 2, wherein the conversion is carried out in the presence of a metal element.

6. The method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 5, wherein the metal element is an alkali metal element.

7. The method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 5, wherein the metal element is used as a fluorine-containing alkali metal salt.

8. A method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 1 or 2, wherein the conversion is carried out at a temperature of 400 to 1000°C.

9. The method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 1 or 2, wherein the conversion reaction is carried out in a fluidized bed reactor.

10. The method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 9, wherein the average particle size of the silicon dioxide when it is introduced into the fluidized bed reactor is 20 μm to 10 mm or less.

11. A method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 1 or 2, wherein silicon tetrafluoride is produced.

12. A method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 1 or 2, comprising: generating tetrafluoroethylene, octafluorocyclobutane, and hydrogen fluoride by a dehydrofluorination reaction of 1,1,1,2,2-pentafluoroethane in the gas phase; and generating silicon tetrafluoride by a reaction between the generated hydrogen fluoride and silicon oxide.

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