Method for producing fluoroolefin

Abstract

The purpose of the present invention is to provide a method for producing a fluoroolefin, which has high reaction conversion rate and target product selectivity, can obtain a target product at a high yield, has a low by-product ratio, and does not produce waste liquid, and which can solve the problems of the prior art. A method for producing a fluoroolefin, which is characterized by subjecting a fluorinated alkane to a dehydrofluorination reaction in the presence of activated carbon containing a metal salt.

Description

Technical Field

[0001] The present invention relates to a method for producing fluoroolefins. Background Art

[0002] Hydrofluoroolefins (HFOs) are known as ideal substitutes for HCFCs due to their lower ODP (ozone depletion potential) and GWP (global warming potential) values. HFOs are known to be useful compounds as coolants, heat transfer fluids, fire extinguishing agents, propellants, foaming agents, expansion agents, gas guides, polymerization media or monomers.

[0003] Patent document 1 describes a method for producing pentafluoropropylene, wherein hexafluoropropane is contacted with a catalyst containing magnesium, zinc, aluminum, etc. at a temperature of about 200°C to 500°C, optionally in the presence of an inert gas. Patent document 2 describes a method for producing 1,1,1,3,3-pentafluoropropene, characterized in that 1,1,1,3,3,3-hexafluoropropane is contacted with activated carbon in a gaseous state to perform dehydrofluoric acid removal. Patent document 3 describes a method for producing hydrofluoropropylene, which comprises the following steps: (a) adding a precipitate containing a precipitate of the formula: C3F x Cl y H 8-x-y (a) introducing a supply stream of an alkali metal hydroxide into a reactor for producing a halogenated propane as shown in (wherein x is 5 or 6, y is 0 or 1, and x+y≤6); (b) reacting the halogenated propane with an aqueous base in a liquid phase to produce the formula: C3F z-1 H 7-z (where z is x-1); (c) removing at least a portion of the halogenated propene from the reactor in the form of a vapor stream, wherein (a), (b) and (c) are at least partially performed simultaneously. Patent document 4 states that 1,1,3,3,3-pentafluoropropene (CF3CH=CF2, HFC-1225zc) can be produced by thermally decomposing 1,1,1,3,3,3-hexafluoropropane (CF3CH2CF3, HFC-236fa) in a hollow tubular reactor whose inner surface is made of a material resistant to hydrogen fluoride at a temperature of about 700°C to about 1000°C and a total pressure of almost atmospheric pressure in the absence of a dehydrofluorination catalyst.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Publication No. 2001-509803

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 9-67281

[0008] Patent Document 3: U.S. Patent Publication No. 2011 / 0269999

[0009] Patent Document 4: Japanese Patent Application No. 2008-518938 Summary of the invention

[0010] Problem that the invention aims to solve

[0011] However, regarding Patent Documents 1 and 2, in the method using a catalyst containing magnesium, zinc, aluminum, etc. or coconut shell activated carbon, there is a problem of low reaction conversion rate. In addition, regarding Patent Document 3, in the reaction using an aqueous base, the reaction method such as continuously introducing an aqueous base and a related transfer catalyst and returning the unreacted raw material to the reactor according to the reflux conditions becomes complicated, and under large-scale production conditions, there is a problem of generating a large amount of waste liquid. In addition, regarding Patent Document 4, in the thermal decomposition reaction under high temperature conditions, there is a problem that impurities with similar physical properties and difficult to separate in distillation refining are synthesized in multiple types and at a high generation ratio.

[0012] Therefore, the object of the present invention is to provide a method for producing fluoroolefins that can solve the problems of the prior art, wherein the method has high reaction conversion rate and selectivity of the target product, can obtain the target product in high yield, has a low ratio of by-products, and does not generate waste liquid.

[0013] Solutions for solving problems

[0014] The present invention provides the following method.

[0015] [1] A method for producing a fluoroolefin, comprising subjecting a fluorinated alkane to a dehydrofluorination reaction in the presence of activated carbon containing a metal salt.

[0016] [2] The method according to [1], wherein the fluoroolefin is represented by the following general formula (1).

[0017] CxHyFz(1)

[0018] (Wherein, x=3-5, y≥1, z≥1, y+z≤2x.)

[0019] [3] The method according to [2], wherein the fluorinated alkane is represented by the following general formula (2).

[0020] CxHmFn(2)

[0021] (Wherein, x=3-5, m≥2, n≥2, m+n=2x+2.)

[0022] [4] The method according to any one of [1] to [3], wherein the dehydrofluorination reaction is carried out in a gas phase.

[0023] [5] The method according to [4], wherein the dehydrofluorination reaction is carried out at a temperature of 250 to 650°C.

[0024] [6] The method according to any one of [1] to [3], wherein the metal of the metal salt is an alkali metal and / or an alkaline earth metal.

[0025] Effects of the Invention

[0026] According to the present invention, a method for producing fluoroolefins that solves the problems of the prior art is provided. The method has high reaction conversion rate and selectivity of the target product, can obtain the target product at a high yield, has a low ratio of by-products, and does not generate waste liquid. According to the present invention, by using activated carbon containing a metal salt catalyst, a high conversion rate can be achieved even if the reaction temperature is lowered. By lowering the reaction temperature, the generation of impurities that are difficult to separate in distillation refining due to similar physical properties is suppressed. Even if the temperature in the reactor is about 500°C, the conversion rate is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of an example of an apparatus for carrying out the dehydrofluorination reaction of the present invention. DETAILED DESCRIPTION

[0028] [Supply of raw materials and products]

[0029] The feedstock of the present invention is a fluorinated alkane composed of fluorine atoms, hydrogen atoms and carbon atoms. In the present invention, since a fluoroolefin is produced by a dehydrofluorination reaction, it is necessary to have at least one hydrogen atom.

[0030] The product fluoroolefin is preferably represented by the following general formula (1).

[0031] CxHyFz(1)

[0032] (Wherein, x=3-5, y≥1, z≥1, y+z≤2x.)

[0033] In this case, the fluorinated alkane as the feed material is preferably represented by the following general formula (2).

[0034] CxHmFn(2)

[0035] (Wherein, x=3-5, m≥2, n≥2, m+n=2x+2.)

[0036] Examples of the fluorinated alkanes as the raw materials include 1,1,1,3,3,3-hexafluoropropane (HFC-236fa), 1,1,2,3,3,3-hexafluoropropane (HFC-236ea), 1,1,1,2,4,4,4-heptafluorobutane, 1,1,1,2,3,3,3-heptafluoro-2-methylbutane, 1,1,1,3,3,3-heptafluoro-2-(monofluoromethyl)butane, 1,1,1,2,5,5,5-heptafluoropentane, 1,1,1,3,5,5,5-heptafluoropentane, and 1,1,1,4,4,4-hexafluorobutane. These may be used alone or as a mixture of two or more thereof.

[0037] Examples of the fluoroolefins of the product include 1,1,3,3,3-pentafluoropropylene (HFO-1225zc), (E)-1,2,3,3,3-pentafluoropropylene ((E)-HFO-1225ye), (Z)-1,2,3,3,3-pentafluoropropylene ((Z)-HFO-1225ye), 1,1,1,4,4,4-hexafluoro-2-butene, 3,3,3-trifluoro-2-trifluoromethyl-1-propylene, 1,1,1,5,5,5-hexafluoro-2-pentene, and 1,1,4,4,4-pentafluoro-1-butene.

[0038] [Reaction catalyst]

[0039] In the present invention, activated carbon containing a metal salt is used as a reaction catalyst. Examples of the metal salt include halides (particularly chlorides, fluorides, bromides, iodides, etc.), hydroxides, carbonates, bicarbonates, nitrates, sulfites, sulfates, acetates, etc., of alkali metals and alkaline earth metals. More specific examples of the metal salt include alkali metal salts such as lithium chloride, sodium chloride, potassium chloride, lithium fluoride, sodium fluoride, potassium fluoride, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, lithium sulfate, sodium sulfate, potassium sulfate, lithium acetate, sodium acetate, and potassium acetate; and alkaline earth metal salts such as barium chloride, magnesium chloride, calcium chloride, barium fluoride, magnesium fluoride, calcium fluoride, barium hydroxide, magnesium hydroxide, calcium hydroxide, barium carbonate, magnesium carbonate, calcium carbonate, barium bicarbonate, barium bicarbonate, calcium bicarbonate, barium sulfate, magnesium sulfate, calcium sulfate, barium acetate, magnesium acetate, and calcium acetate. These may be used alone or as a mixture of two or more thereof.

[0040] The present invention is characterized in that activated carbon containing the above-mentioned metal salt is used. As an activated carbon catalyst, for example, coconut shell charcoal for gas purification and catalyst / catalyst carrier (granular egret GX, SX, CX, XRC manufactured by Takeda Pharmaceutical Industry, PCB manufactured by Toyo Calgon Co., Ltd., YASHIKOR manufactured by Taihei Chemical Industry Co., Ltd., Kuraray Carbon GG, GC) etc. can be listed, which can be used alone or in combination with two or more. The loading amount of the metal salt in the activated carbon is preferably 0.01 to 10% by weight relative to the total weight of the loaded catalyst, more preferably 0.1 to 5% by weight, and further more preferably 0.5 to 1.5% by weight. Activated carbon that has not been subjected to pickling treatment, etc. contains metal salts derived from nature. In this case, the loading amount (i.e., content) of the metal salt can be determined, for example, by SEM-EDX, etc. When the loading amount is determined by SEM-EDX, SEM-EDX is used to measure several points on the surface of the sample and is determined based on the average value of these measured values. Preferred properties of activated carbon include pH and acetone adsorption capacity. The preferred range of pH is 8 to 12, and the more preferred range is 9 to 11. The acetone adsorption capacity is preferably 29% by weight or more, and more preferably 35% by weight or more. The shape of activated carbon is not particularly limited, and any shape such as granular, powdery, granular, spherical, cylindrical, honeycomb, sheet, and fibrous can be used. The type of activated carbon is not particularly limited, and any of steam charcoal, crushed charcoal, and granulated charcoal derived from coconut shell charcoal, coal, and charcoal can be used. As activated carbon, coconut shell charcoal is most preferred.

[0041] [Reaction conditions]

[0042] The reaction temperature is preferably 250° C. to 650° C., more preferably 400° C. to 625° C., further more preferably 500° C. to 600° C., and particularly preferably 500° C. to 550° C. The contact time between the reaction substrate and the catalyst (activated carbon loaded with a metal salt) is preferably 0.1 to 300 seconds, more preferably 5 to 120 seconds, and further more preferably 10 to 60 seconds.

[0043] [Carrier gas]

[0044] When implementing the present invention, a carrier gas is used for dilution of raw material gas, drying of reactor, etc. In particular, raw materials, reaction products and other substances can be moved in the reaction device while adjusting the concentration by circulating carrier gas. The carrier gas is selected to be a gas that does not react with these substances. For example, nitrogen, rare gases (helium, neon, argon, etc.) and the like can be listed. When a carrier gas is used, the carrier gas is mixed and used in a ratio of usually 0 to 99%, more preferably 0 to 75%, and most preferably 0 to 50% relative to the total flow rate of raw materials, reaction products and other substances.

[0045] [Reaction device]

[0046] Examples of the material of the reaction device include corrosion-resistant metals such as stainless steel, Inconel, monel, Hastelloy, and nickel. Among them, nickel is preferred from the viewpoint of corrosion resistance.

[0047] As an apparatus for carrying out the dehydrofluorination reaction of the present invention, for example, an apparatus constructed in the following manner can be cited: a catalyst of various shapes is filled in a cylindrical tube equipped with a heater for adjusting the reaction temperature, and the raw gas is made to flow from one end of the tube to the other end. When the cylindrical tube filled with the catalyst is extended in the vertical direction, the flow direction of the raw gas flows evenly little by little from top to bottom, and this method of using gravity to make the raw gas flow little by little is preferred. When the cylindrical tube is extended in the vertical direction and the raw gas flows from bottom to top, from the viewpoint of reaction efficiency, it is preferred to arrange a granular catalyst with a large particle size at the lower part of the cylindrical tube, and a powdered catalyst with a small particle size at the upper part of the cylindrical tube.

[0048] In the following, a specific example of the apparatus for carrying out the dehydrofluorination reaction of the present invention is schematically described. Figure 1 The device is composed of the following parts: a raw material storage tank 1 for containing raw materials (reaction substrates), a gas storage tank ( Figure 1 In the figure, there is a nitrogen gas storage tank 2, a cylindrical catalyst tower 3 connected to the raw material storage tank through a pipeline and vertically erected, an evaporator 4 arranged just in front of the catalyst tower, and a collecting tank 5 located downstream of the catalyst tower. When the raw material is liquid at room temperature, it is directly injected into the evaporator 4 heated to a temperature above the boiling point in a liquid state through an injection pump (not shown in the figure), and is vaporized in the evaporator 4. The raw gas is mixed with a carrier gas (nitrogen) in the evaporator 4, and the mixed gas contacts the catalyst in the process of moving from the top to the bottom of the catalyst tower, promoting the dehydrofluorination reaction. The reaction gas after passing through the bottom of the catalyst tower, in the process of passing through the collecting tank filled with water inside, the reaction products and unreacted raw materials and hydrogen fluoride will be collected in the collecting tank, and only the carrier gas will be discharged outside the reaction device.

[0049] Example

[0050] [Preparation of Catalyst]

[0051] The catalyst used in the examples was prepared by immersing coconut shell-based activated carbon and granular Egret C2X (grade name: C2x4 / 6-2) provided by Osaka Gas Chemical Co., Ltd. in an aqueous solution containing a metal salt as described in Table 1. The loading amount of the catalyst was determined by using SEM-EDX to confirm the concentration distribution of the surface elements of the measured object. The loading amount was determined by measuring three points on the surface of the sample and the average value of these measured values.

[0052] [Examples 1 to 13]

[0053] The activated carbon containing the metal salt described in Table 1 is filled into a cylindrical reactor made of nickel (size: 2 inches in diameter, 1000 mm in length) and heated and dried. Then, the raw material 1,1,1,3,3,3-hexafluoropropane (HFC-236fa) is ventilated from the upper end to the lower end of the cylindrical reactor without using a carrier gas, and the reaction is carried out at the temperature, linear velocity and residence time described in Table 1. In the rear section of the reactor, a water collector for removing the generated HF, a molecular sieve (MS-3A) packed tower for the purpose of dehydration of the crude product gas, and a filter for removing particulates are passed to obtain a crude product gas. The composition of the crude product gas is confirmed by GC analysis. The results are shown in Table 1.

[0054] [Comparative Examples 1 to 3]

[0055] The reaction was carried out in the same manner as in Example 1 using activated carbon without a metal salt as a catalyst or without using a catalyst. The results are shown in Table 1.

[0056] [Table 1]

[0057]

[0058] In Table 1, the impurity generation ratio is the GC area ratio (equivalent to the molar ratio) of each impurity when the GC area of ​​the entire crude product injected into the gas chromatograph (GC) is set to 100%. The conversion rate (%) is 100%-[(after reaction: the number of moles of HFC-236fa in the crude gas) / (before reaction: the number of moles of HFC-236fa introduced)]×100%. The selectivity (%) is [(after reaction: the number of moles of HFO-1225zc in the crude gas / the number of moles of HFC-236fa converted)]×100%. In addition, the impurities are shown as follows.

[0059] 1225yeZ: Z isomer of CF3-CF=CHF

[0060] 1225yeE: CF3-CF=E isomer of CHF

[0061] 1234zeE: E isomer of CF3-CH=CHF

[0062] As can be seen from Table 1, when the dehydrofluorination reaction of 1,1,1,3,3,3-hexafluoropropane (HFC-236fa) is carried out at a temperature of 500-550°C in the presence of activated carbon containing 0.5-5% by weight of an alkali metal hydroxide, alkali metal bicarbonate, alkali metal carbonate, alkali metal acetate, or alkaline earth metal chloride, the product 1,1,3,3,3-pentafluoropropene (HFO-1225zc) is obtained at a conversion rate of more than 60% and a selectivity of more than 80% when an alkali metal salt is used (Examples 1-9), and the product 1,1,3,3,3-pentafluoropropene (HFO-1225zc) is obtained at a conversion rate of more than 56% and a selectivity of more than 86% when an alkaline earth metal salt is used (Examples 10-13). From the viewpoint of obtaining high-purity HFO-1225zc with impurities removed, a purified yield of 60% or more can be achieved in Examples 1 to 9, and a purified yield of 50% or more can be achieved in Examples 10 to 13. When an alkaline earth metal salt is used as the metal salt, the conversion rate is lower than that of an alkali metal salt, but the selectivity is equivalent to that of an alkali metal salt. On the other hand, in Comparative Example 1 using activated carbon without a metal salt as a catalyst and Comparative Example 2 using no catalyst, the conversion rates were 38.5% and 37.2%, respectively. In addition, when no catalyst was used but the reaction temperature was as high as 775°C, although a conversion rate of 73% was obtained, impurities (1225yeZ, 1225yeE, 1234zeE) that were difficult to separate from the product HFO-1225zc were generated, and the amount of impurities generated was all above 0.1%. The production conditions that generate these impurities at a concentration of 0.1% or more cannot be adopted because the impurities cannot be removed by distillation purification.

Claims

1. A method for producing fluoroolefins, characterized in that: The fluorinated alkane is subjected to a dehydrofluorination reaction in the presence of activated carbon containing a metal salt.

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