Method for producing tetrafluoroethylene and octafluorocyclobutane

Abstract

This method for producing tetrafluoroethylene and octafluorocyclobutane comprises converting 1,1,1,2,2-pentafluoroethane into tetrafluoroethylene and octafluorocyclobutane in a gas phase in the presence of a silicon oxide, wherein the conversion is carried out at 750°C or lower.

Description

Methods 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 reduce the amount of impurities generated other than tetrafluoroethylene and octafluorocyclobutane. 【0006】 Therefore, the objective of one embodiment of this disclosure is to provide a novel manufacturing method that can reduce the amount of impurities generated other than tetrafluoroethylene and octafluorocyclobutane. 【0007】This disclosure includes the following aspects: <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 oxide, and carrying out the conversion at 750°C or below. <2> The method for producing tetrafluoroethylene and octafluorocyclobutane according to <1>, wherein the conversion is carried out in the presence of a metal element. <3> The method for producing tetrafluoroethylene and octafluorocyclobutane according to <2>, wherein the metal element is an alkali metal element. <4> The method for producing tetrafluoroethylene and octafluorocyclobutane according to <2> or <3>, wherein the metal element is used as an alkali metal salt. <5> The method for producing tetrafluoroethylene and octafluorocyclobutane according to any one of <2> to <4>, wherein the metal element is used as a fluorine-containing alkali metal salt. <6> The method for producing tetrafluoroethylene and octafluorocyclobutane according to any one of <1> to <5>, wherein the conversion reaction is carried out in a fluidized bed reactor. <7> The method for producing tetrafluoroethylene and octafluorocyclobutane according to <6>, 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. <8> The method for producing tetrafluoroethylene and octafluorocyclobutane according to any one of <1> to <7>, wherein silicon tetrafluoride is produced. <9> The method for producing tetrafluoroethylene and octafluorocyclobutane according to any one of <1> to <8>, 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 dioxide. 【0008】 This disclosure provides a novel manufacturing method that can reduce the amount of impurities generated other than tetrafluoroethylene and octafluorocyclobutane. 【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, wherein, 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 the conversion is carried out at a temperature of 750°C or lower. Experiments have shown that the manufacturing method of the present disclosure makes it possible to reduce the amount of impurities generated other than FO-1114 and C318. 【0011】 (Raw materials, etc.) The manufacturing 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 dioxide. 【0012】 In the manufacturing method of this disclosure, the raw material gas may contain HFC-125, or it may contain components other than HFC-125. The raw material gas may consist only of HFC-125, or it may contain isomers, disproportionation products, impurities, etc., obtained when producing HFC-125. From the viewpoint of suppressing side reactions, the HFC-125 content is preferably 10 mol% or more, more preferably 30 mol% or more, and even more preferably 50 mol% or more, based on the total amount of the raw material gas. The HFC-125 content may be 100 mol% of the total amount of the raw material gas. 【0013】Silicon oxide may be in a crystalline or amorphous (non-crystalline) state. Examples of silicon oxide particles include silica sand, quartz, diatomaceous earth, colloidal silica, precipitated silica, silica gel, fumed silica, and rice husks, with silica sand being preferred from the viewpoint of purity and cost. 【0014】 The shape of silicon dioxide particles is not particularly limited and may be irregular in shape, such as natural products or pulverized materials, or may be cullet-like, flaky, or spherical. They may also be molded into pellets, hollow shapes, cylindrical shapes, etc. Furthermore, silicon dioxide particles may have a porous structure (e.g., porous). These shapes may be combined as appropriate, for example, a porous cylindrical molded product. 【0015】 It is preferable that the silicon dioxide particles have a low impurity content. From the viewpoint of suppressing the generation of unwanted by-products, the silicon dioxide content in the silicon dioxide particles should be low, preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. 【0016】 From the viewpoint of suppressing clogging in the reactor, the average particle size of silicon dioxide particles when introduced into the reactor is preferably 20 μm or more, and more preferably 50 μm or more. From the viewpoint of ensuring sufficient surface area for reaction sites, the average particle size of silicon dioxide particles when introduced into the reactor is preferably 10 mm or less, more preferably 5 mm or less, and even more preferably 1 mm or less. 【0017】 The average particle size of silicon dioxide particles is determined as the particle size (D50) at which the cumulative particle size distribution curve, obtained by measurement using a Coulter counter, reaches 50%. The aperture diameter is set appropriately according to the particle size range of the object being measured. 【0018】It is preferable to include a metal element along with silicon dioxide during the conversion reaction. The presence of a metal element in the conversion reaction promotes the dehydrofluoride reaction from HFC-125. The silicon dioxide and metal element may be an integrated compound or composite containing both, or separate substances containing silicon dioxide and the metal element separately may be used, or two or more of these may be used in combination. Examples include glass containing silicon dioxide and an oxide of a metal element, sodium silicate, sodium silicate cullet, composites in which a metal-containing compound is supported on silicon dioxide particles, and combinations of silicon dioxide particles and metal-containing compounds. 【0019】 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 high-purity 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." 【0020】 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. 【0021】 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 _K２ CO ３ Examples include CO and the like. The alkali metal-containing compound is preferably an alkali metal salt. For example, LiF, NaF, Na ２ SiF ６ , KF, K ２ CO ３ , K ２ SiF ６ , CsF, and the like. 【0022】 Among the alkali metal-containing compounds, fluorine-containing alkali metal salts are preferred. Since fluorine-containing alkali metal salts originally contain fluorine elements, even if they are fluorinated by the generated hydrogen fluoride, the quality change is suppressed, and fluctuations in reaction conditions can be suppressed. For example, when carried out in a fluidized bed reactor, the fluid state can be maintained. 【0023】 The fluorine-containing alkali metal salt preferably contains at least one selected from the group consisting of LiF, NaF, Na ２ SiF ６ , KF, K ２ SiF ６ , and CsF. From the viewpoint of maintaining the performance as a reactant at the heating temperature in the conversion reaction and being less reactive or non-reactive with respect to silicon tetrafluoride, it is more preferable to contain at least one selected from the group consisting of NaF, KF, and K ２ SiF ６ . 【0024】 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, still more preferably 300°C or higher, particularly preferably 350°C or higher, and extremely preferably 400°C or higher. The upper limit value of the thermal decomposition temperature of the fluorine-containing alkali metal salt is not particularly limited and may be 1000°C or lower. The thermal decomposition temperature of the fluorine-containing alkali metal salt is measured by thermogravimetric analysis. 【0025】When the fluorine-containing alkali metal salt reacts with silicon tetrafluoride generated by the conversion reaction to form a reactant, at least a part of the reactant may return to the fluorine-containing alkali metal salt by thermal decomposition. To confirm whether the reactant has thermally decomposed and returned to the original fluorine-containing alkali metal salt, micro-Raman spectroscopy is used. As the micro-Raman spectroscopy apparatus, for example, LabRAM HR Evolution manufactured by Horiba, Ltd. can be used. As the measurement conditions, the excitation wavelength is 532 nm, the objective lens is ×100_VIS_LWD, the confocal aperture is 100 μm, the 200 μm pinhole, the grating is 300, and the center wave number is 1800 cm －１ is carried out. 【0026】 From the viewpoint of maintaining the powdery state of the reactant better over time during the reaction, the water content in 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 water content in the reactant is measured by a Karl Fischer moisture meter or the like. The water content in the reactant is the value in the state immediately before the start of the reaction. 【0027】 The silicon content in the reactant may be 1 atm% or more, 5 atm% or more, or 10 atm% or more. Also, the silicon content in the reactant may be 90 atm% or less, 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 be 90 atm% or less, 80 atm% or less. The content of the metal element in the reactant may be 1 atm% or more, 5 atm% or more, or 8 atm% or more. The content of the metal element in the reactant may be 90 atm% or less, 50 atm% or less. 【0028】 The content of each element in the reactant is determined by scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX analysis). 【0029】In the reactant, the silicon content (atm%) is preferably higher than the content (atm%) of the metal element, more preferably higher than the total content of the alkaline earth metal and the Group 13 element of the periodic table, and preferably the element with the highest content (atm%) among the elements excluding oxygen is silicon. 【0030】 (Diluent) In the production method of the present disclosure, a diluent may or may not be used in the conversion reaction. 【0031】 Generally, in the production method of halogenated alkenes, from the viewpoint of suppressing the disproportionation reaction caused by the concentration increase of the produced halogenated alkenes and the concern of explosion due to the concentration increase depending on the type of halogenated alkenes, a diluent gas is used. In particular, in the production method using the alumina catalyst described in Patent Document 1, since the conversion rate decreases when the amount of the diluent is reduced, the use of a diluent gas such as nitrogen or carbon dioxide is essential. However, diluent gases such as nitrogen gas and carbon dioxide have a lower boiling point or a boiling point range close to that of the reaction product, the halogenated alkene, so energy is required to separate and purify the diluent gas from the reaction product. 【0032】 In the production method of the present disclosure, since silicon oxide is used, silicon tetrafluoride (SiF ４ ) with a boiling point of -95 °C is generated and released as a gas outside the reaction system. Therefore, the generation of retained by-products and the deterioration of the catalyst can be easily suppressed, and the reactivity can be easily controlled by the residence time, reaction temperature, etc. Therefore, since the concentration in the outlet gas of FO-1114 and C318 can be controlled by these controls, HFC-125, which is a raw material, can be included in the outlet gas to a certain extent or more. The HFC-125 in the outlet gas also functions as a diluent. Therefore, in the production method of the present disclosure, it is also possible to use it while suppressing the amount of the diluent gas used. The production method of the present disclosure also includes an embodiment in which no diluent gas is used. 【0033】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, difluoromethane (R32), trifluoromethane, and tetrafluoromethane. From the viewpoint of low flammability and availability, the diluent preferably contains at least one selected from the group consisting of nitrogen, argon, R32, carbon dioxide, helium, and water, more preferably contains at least one selected from the group consisting of nitrogen, R32, helium, and argon, and even more preferably contains at least one selected from the group consisting of nitrogen and R32. 【0034】 When R32 is used as a diluent in the manufacturing method of the present disclosure, the following advantages are available. In a mixture of the raw materials HFC-125 (boiling point: -48.5°C) and R32 (boiling point: -51.7°C), the boiling points are close, making it difficult to separate R32. However, when HFC-125 is converted to FO-1114 and C318 by the dehydrofluoridation reaction, the boiling point of FO-1114 is -76.3°C and the boiling point of C318 is -5.8°C, thus improving the separability from R32. Therefore, according to the manufacturing method of the present disclosure, it becomes easier to separate and recover R32 contained in the raw material gas. Accordingly, when R32 is used as a diluent in the manufacturing method of the present disclosure, it may further include a separation step to separate at least a portion of R32 (difluoromethane) from the product. 【0035】 The raw materials may be a mixed refrigerant R410A consisting of HFC-125 and R32, or a mixture containing R410A. Although R410A is used as a refrigerant for household air conditioners, in recent years, R32 has sometimes been used alone due to its global warming potential. Due to the aforementioned reason that their boiling points are close, it is extremely difficult to extract R32 from R410A by distillation and purification, but the method disclosed herein makes it possible to extract R32 from R410A. 【0036】From the above perspective, the raw material may contain HFC-125 and R32, with a mass ratio of HFC-125 to R32 (HFC-125:R32) of 40:60 to 60:40, and the total amount of HFC-125 and R32 in the raw material may be 90% by mass or more. Such a raw material has a composition that is prone to azeotropic formation, making it difficult to extract R32 by distillation purification. However, by adjusting, for example, the reaction temperature, reaction time, and the composition of the reactants, conditions can be set to completely convert HFC-125. As HFC-125 is consumed by the conversion reaction, the ratio of R32 to HFC-125 increases. As a result, even if the mixture containing HFC-125 and R32 has an azeotropic composition or an azeotropic-like composition, it becomes possible to separate and extract the excess R32 as a high-purity compound. The mass ratio of HFC-125 to R32 in the raw material (HFC-125:R32) may be 45:55 to 55:45. Furthermore, the total amount of HFC-125 and R32 in the raw material may be 95% by mass or more, or 98% by mass or more. In addition, the raw material may be used refrigerant. For example, refrigerant remaining after use of R410A, which consists of HFC-125 and R32, may be used as the raw material for this disclosure. 【0037】 From the viewpoint of increasing the amount of FO-1114 and C318 generated in the outlet gas, it is preferable to use the diluent in an amount of 20 to 60% by volume relative to the total amount of HFC-125 and diluent. Furthermore, from the viewpoint of suppressing the amount of C318 generated, it is preferable to use the diluent in an amount of 30% by volume or less relative to the total amount of HFC-125 and diluent. 【0038】 (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. 【0039】 【0040】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. 【0041】 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. 【0042】 In conventional manufacturing methods using alumina, calcium carbonate, etc. as catalysts, the generated hydrogen fluoride reacts with the catalyst as follows. 【0043】 【0044】 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. 【0045】 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 ２Because 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. 【0046】 When reacting in a fluidized bed, it is desirable that the fluidity of the catalyst does not change significantly, but in conventional methods, AlF ３ 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. 【0047】 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. 【0048】 (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. 【0049】 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. 【0050】 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. 【0051】 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. 【0052】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. 【0053】 In the manufacturing method of this disclosure, from the viewpoint of reducing the amount of impurities generated other than FO-1114 and C318, it is preferable to carry out the conversion from HFC-125 at 750°C or below, preferably at 730°C or below, more preferably at 720°C or below, even more preferably at 710°C or below, and particularly preferably at 700°C or below. When the conversion is carried out in this temperature range, 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. 【0054】 Furthermore, from the viewpoint of increasing the ratio of FO-1114 / C318 produced, it is preferable to carry out the conversion at 660°C or below, more preferably at 650°C or below, even more preferably at 630°C or below, particularly preferably at 610°C or below, and extremely preferably at 600°C or below. On the other hand, from the viewpoint of increasing the amount of FO-1114 produced, it is preferable to carry out the conversion at 640°C or above, more preferably at 650°C or above, even more preferably at 670°C or above, particularly preferably at 690°C or above, and extremely preferably at 700°C or above. 【0055】 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. 【0056】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. 【0057】 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. 【0058】 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. 【0059】 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. 【0060】 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. 【0061】 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. ３The 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. 【0062】 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. 【0063】 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. 【0064】 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. 【0065】 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. 【0066】 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. 【0067】 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. 【0068】 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. 【0069】 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. 【0070】 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. 【0071】 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. 【0072】 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. 【0073】 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 raw materials (and diluents if diluents are included) contained in the reactor outlet gas (however, compounds derived from the carbon atoms of the raw material HFC-125, excluding compounds such as silicon tetrafluoride that do not have carbon atoms derived from the raw material). A selectivity of 100% is preferred because it eliminates the need for a post-reaction purification step, but side reactions may occur in the reaction temperature range necessary to obtain a desirable conversion rate. A higher selectivity is preferred because it reduces the amount of waste, lowers the energy load of the post-reaction purification step, 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. 【0074】 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. 【0075】 The manufacturing method of this disclosure makes it possible to reduce the amount of impurities generated other than FO-1114 and C318. The amount generated is confirmed by analyzing the reactor outlet gas by gas chromatography and using the area ratio (GCAare%) corresponding to FO-1114 and C318. The amount of impurities generated other than FO-1114 and C318, calculated from the area ratio (GCAare%) of the reactor outlet gas, is preferably 30% or less, more preferably 20% or less, and even more preferably 10% or less. 【0076】 In the manufacturing method of the present disclosure, the ratio of FO-1114 / C318 produced can be set according to the purpose, and may be, for example, 3 or more, 10 or more, or 50 or more. 【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 39 are examples, and Examples 1 and 40 are comparative examples. 【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】[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 800°C by flowing HFC-125 at a flow rate of 800 mL / min. 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. 【0081】 [Examples 2-37] The conversion reactions of Examples 2-18 were carried out in the same manner as in Example 1, except that at least one of the following was changed as shown in Tables 1-4: reaction temperature, type of reactant, amount of reactant used, type of flow gas, and flow rate of flow gas. In Examples 19-37, the reaction tube was changed to carry out the conversion reaction. Specifically, in Examples 19-37, the reaction tube was changed to one with an inner diameter of 4.094 cm and a length of 80 cm, and a vibrator was attached to the bottom of the reaction tube. In addition, the total mass of the reactant was changed from 140 g to 840 g, and the total flow rate of the reaction gas was changed from 400 mL / min to 2400 mL / min to carry out the conversion reaction. In Examples 2-37, the oxygen content in the reaction atmosphere was 10,000 ppm by mass or less in all cases. The glass beads (GB) used in Example 35 contain silicon dioxide, sodium, calcium, etc., and have an average particle size of 108 μm. 【0082】 Tables 1-4 show the reaction conditions for Examples 1-37 and the area ratio (GCAare%) of the reactor outlet gas at 0.5 hours from the start of the reaction. Tables 1-4 also show the FO-1114 / C318 ratio calculated from the area ratio (GCAare%). 【0083】 【0084】 【0085】 【0086】 【0087】 As shown in Tables 1 to 4, it can be seen that in Examples 2 to 37, where the conversion reaction temperature is 750°C or lower, the amount of other impurities is significantly lower compared to Example 1, where the reaction temperature is above 750°C. 【0088】 [Example 38] The conversion reaction was carried out in the same manner as in Example 1, except that silica sand and KF were replaced with glass beads (GB), the reaction temperature was changed to 700°C, and nitrogen was replaced with difluoromethane (R32) and used at the flow rates shown in Table 1. The glass beads (GB) contained silicon dioxide, sodium, calcium, etc., and the average particle size was 108 μm. The oxygen content in the reaction atmosphere was 10,000 ppm by mass or less. 【0089】 【0090】 In Example 38, where the conversion reaction temperature is 750°C or lower, the amount of other impurities is significantly lower compared to Example 1, where the reaction temperature is above 750°C. 【0091】 [Example 39] A reaction tube made of Inconel 600 with an inner diameter of 4.094 cm and a length of 80 cm was filled with silica sand and potassium fluoride mixed in a mass ratio of 65 / 35 (546 g / 294 g) and placed in a tubular electric furnace. The conversion reaction was carried out by flowing R410A (a mixed gas of R32 / HFC-125 = 50 mass% / 50 mass%) at the flow rate shown in Table 6 at the temperature shown in Table 3. Table 6 shows the reactor outlet gas data 30 minutes after the start of the reaction. 【0092】 [Example 40] The conversion reaction was carried out under the same conditions as in Example 39, except that the gases flowing through it were changed to R32 and nitrogen, as shown in Table 6. Table 6 shows the reactor outlet gas data 30 minutes after the start of the reaction. 【0093】 【0094】 In Example 39, where the conversion reaction temperature is 750°C or lower, the amount of other impurities is significantly lower compared to Example 1, which is above 750°C. Furthermore, as shown in Example 40, it was confirmed that R32 did not react. On the other hand, as shown in Example 39, FO-1114 was produced in R410A (a mixed gas of R32 and HFC-125), suggesting that HFC-125 reacted selectively. 【0095】The disclosure of Japanese Patent Application No. 2024-218148 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, and carrying out the conversion at a temperature of 750°C or lower.

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

3. The method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 2, wherein the metal element is an alkali metal element.

4. The method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 2, wherein the metal element is used as an alkali metal salt.

5. The method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 2, wherein the metal element is used as a fluorine-containing alkali metal salt.

6. 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.

7. The method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 6, 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.

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

9. 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 of the generated hydrogen fluoride with silicon oxide.

10. The method for producing tetrafluoroethylene and octafluorocyclobutane according to claim 1 or 2, wherein the raw materials for the conversion include 1,1,1,2,2-pentafluoroethane and difluoromethane, the mass ratio of 1,1,1,2,2-pentafluoroethane to difluoromethane is 40:60 to 60:40, and the total amount of 1,1,1,2,2-pentafluoroethane and difluoromethane in the raw materials is 90% by mass or more.

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