Method and composition for separating chlorodifluoromethane and hexafluoropropylene

Abstract

To provide a separation method that uses an extraction solvent with a low global warming potential to efficiently separate R22 and HFP from a mixture of R22 and HFP, which are difficult to separate due to the formation of an azeotropic composition or azeotropic-like composition.SOLUTION: A separation method for chlorodifluoromethane and hexafluoropropylene includes: a mixing step in which a first mixture containing chlorodifluoromethane and hexafluoropropylene is mixed with an extraction solvent containing hydrofluorocarbon, resulting in a mixture for extraction; and an extraction distillation step in which the mixture for extraction is distilled to yield a first top distillate primarily composed of chlorodifluoromethane and a first bottom distillate primarily composed of the extraction solvent and containing hexafluoropropylene.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for separating chlorodifluoromethane and hexafluoropropylene and to a composition. [Background Art]

[0002] Hexafluoropropylene is a compound used as a raw material for fluororesins and the like, and is obtained, for example, by a thermal decomposition reaction of chlorodifluoromethane. Hereinafter, hexafluoropropylene is also referred to as "HFP", and chlorodifluoromethane is also referred to as "R22". When it is intended to obtain high-purity HFP by thermal decomposition of R22, separation of unreacted R22 from the produced HFP is required. As a method for separating the raw material from the reaction product, for example, distillation utilizing a difference in boiling points can be mentioned. However, since R22 and HFP form an azeotropic composition or an azeotrope-like composition, separation by distillation is difficult.

[0003] As a method for separating R22 and HFP, Patent Document 1 discloses extractive distillation using a perfluoro or halogenated polyfluoro compound having 2 or more carbon atoms that is liquid under distillation conditions. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 51-128901 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] However, the perfluoro or halogenated polyfluoro compound disclosed in Patent Document 1 has a high global warming potential, as described below. Hereinafter, the global warming potential is also referred to as "GWP". Accordingly, efficient separation of R22 and HFP without using a compound having a high GWP is desired. It is also required to obtain high-purity HFP by separating R22 and HFP.

[0006] An aspect of the present disclosure aims to provide a separation method for separating chlorodifluoromethane (R22) and hexafluoropropylene (HFP) with high efficiency from a mixture of R22 and HFP, which are difficult to separate due to the formation of an azeotropic composition or azeotrope-like composition, using an extraction solvent with a low global warming potential. Another object of an aspect of the present disclosure is to provide a composition with high purity of HFP. [Means for Solving the Problem]

[0007] The present disclosure includes the following aspects. <1> A mixing step of obtaining an extraction mixture, which is a mixture of a first mixture containing chlorodifluoromethane and hexafluoropropylene, and an extraction solvent containing a hydrofluorocarbon; An extractive distillation step of distilling the extraction mixture to respectively obtain a first distillate containing chlorodifluoromethane as a main component and a first bottom product containing the extraction solvent as a main component and hexafluoropropylene; A method for separating chlorodifluoromethane and hexafluoropropylene, comprising: <2> The method for separating chlorodifluoromethane and hexafluoropropylene according to <1>, wherein the hydrofluorocarbon has a boiling point of 0°C to 120°C. <3> The method for separating chlorodifluoromethane and hexafluoropropylene according to <1> or <2>, wherein the hydrofluorocarbon is a compound that, when added in an amount of 3 times the total molar amount of chlorodifluoromethane and hexafluoropropylene, makes the relative volatility Rv of chlorodifluoromethane to hexafluoropropylene greater than 1.1. <4> The interaction distance Ra between hexafluoropropylene and the hydrofluorocarbon determined from the value of Hansen solubility parameter HFP is smaller than the interaction distance Ra between chlorodifluoromethane and the hydrofluorocarbon R22 , the method for separating chlorodifluoromethane and hexafluoropropylene according to any one of <1> to <3>. <5> The interaction distance Ra HFP the interaction distance Ra R22 has a ratio of 0.7 or less, the method for separating chlorodifluoromethane and hexafluoropropylene according to <4>. <6> The method for separating chlorodifluoromethane and hexafluoropropylene according to any one of <1> to <5>, wherein the hydrofluorocarbon has 2 to 8 carbon atoms. <7> The method for separating chlorodifluoromethane and hexafluoropropylene according to any one of <1> to <6>, wherein the hydrofluorocarbon comprises at least one selected from the group consisting of a saturated compound represented by the following formula (1) and an unsaturated compound represented by the following formula (2). (1) C x1 H y1 F z1 (2) C x2 H y2 F z2 In the formula (1), x1 is an integer of 2 to 8, y1 is an integer of 1 to (x1)×2+1, and z1 is (x1)×2+2-y1, In the formula (2), x2 is an integer of 2 to 8, y2 is an integer of 1 to (x2)×2-1, and z2 is (x2)×2-y2. <8> The method for separating chlorodifluoromethane and hexafluoropropylene according to any one of <1> to <7>, wherein the hydrofluorocarbon comprises at least one selected from the group consisting of 1,1,1,2,2,3,3,4,4-nonafluorobutane, 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexene, 1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexane, 1,1,1,3,3-pentafluorobutane, 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane, 1,1,1,2,2,3,4,5,5,5-decafluoropentane, 1,1,2,2,3,3,4-heptafluorocyclopentane, and 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane. <9> The molar ratio of the amount of hydrofluorocarbon added in the mixing step is 1 / 1 to 30 / 1 relative to the total molar amount of chlorodifluoromethane and hexafluoropropylene. <1> ~ <8> A method for separating chlorodifluoromethane and hexafluoropropylene as described in any one of the following. <10> The process further comprises a second distillation step of distilling the first bottom product to obtain a second distillate mainly composed of hexafluoropropylene, <1> ~ <9> A method for separating chlorodifluoromethane and hexafluoropropylene as described in any one of the following. <11> The first mixture further comprises chlorotrifluoroethylene, The first canned product further contains chlorotrifluoroethylene. <1> ~ <10> A method for separating chlorodifluoromethane and hexafluoropropylene as described in any one of the following. <12> The first mixture further comprises chlorotrifluoroethylene, The first canned product further contains chlorotrifluoroethylene, The second distillate further comprises chlorotrifluoroethylene. <10> The method for separating chlorodifluoromethane and hexafluoropropylene as described in [reference]. <13> The method further comprises an adsorption step in which the second distillate is brought into contact with an adsorbent to obtain a purified product mainly composed of hexafluoropropylene. <12> The method for separating chlorodifluoromethane and hexafluoropropylene as described in [reference]. <14> The adsorbent includes synthetic zeolite, <13> The method for separating chlorodifluoromethane and hexafluoropropylene as described in [reference]. <15> A composition comprising hexafluoropropylene and chlorodifluoromethane, wherein the content of hexafluoropropylene is 99.5% by mass or more of the total composition. <16> Furthermore, it contains chlorotrifluoroethylene, <15> The composition described above. [Effects of the Invention]

[0008] According to one aspect of this disclosure, a separation method is provided for highly efficient separation of R22 and HFP from a mixture of R22 and HFP that is difficult to separate due to the formation of an azeotrope or azeotrope-like composition, using an extraction solvent with a low global warming potential. Furthermore, according to one aspect of this disclosure, a composition with high purity of HFP is provided. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example of the flow of substances in the separation method disclosed herein. [Figure 2] This figure shows another example of the material flow in the separation method of this disclosure. [Modes for carrying out the invention]

[0010] The embodiments of this disclosure are described in detail below. However, this disclosure is not limited to the embodiments described below. In the embodiments described below, the components (including elemental steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit this disclosure.

[0011] In this disclosure, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes, provided that the purpose of such process is achieved. In this disclosure, the numerical range indicated using "~" includes the numbers before and after "~" as the minimum and maximum values, respectively. In this disclosure, each component may contain multiple types of the corresponding substance. If multiple types of the substance corresponding to each component are present in the composition, the proportion of each component means the total proportion of the multiple types of substances present in the composition unless otherwise specified. When embodiments are described in this disclosure with reference to the drawings, the configuration of such embodiments is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each figure are conceptual, and the relative relationships between the components are not limited thereto.

[0012] In this disclosure, "distillate" means the substance distilled from the top of a distillation column, and "bottom product" means the substance distilled from the bottom of a distillation column. In this disclosure, "main component" means that the amount of other components is relatively small. The amount of the "main component" is preferably 50 mol% or more of the total, more preferably 60 mol% or more, even more preferably 70 mol% or more, and most preferably 80 mol% or more. In this disclosure, unless otherwise specified, the boiling points of compounds are given at atmospheric pressure, which is 1.013 × 10⁻⁶. 5 It is Pa.

[0013] [Separation method] A separation method in one embodiment of the present disclosure comprises a mixing step of obtaining an extraction mixture which is a mixture of a first mixture containing chlorodifluoromethane (R22) and hexafluoropropylene (HFP) and an extraction solvent containing hydrofluorocarbons, and an extraction distillation step of distilling the extraction mixture to obtain a first distillate mainly composed of R22 and a first bottom product mainly composed of the extraction solvent and containing HFP, respectively. Hereinafter, hydrofluorocarbons will also be referred to as "HFCs".

[0014] The separation method of this embodiment may include other steps besides the mixing step and the extraction distillation step. Other steps include, for example, a second distillation step in which the first bottom product is distilled to obtain a second distillate mainly composed of HFP. The separation method of this embodiment preferably further includes a second distillation step.

[0015] In the separation method of this embodiment, among compounds with lower GWP compared to the perfluor or halogenated polyfluor compounds disclosed in Patent Document 1, a highly efficient separation of R22 and HFP was achieved by using hydrofluorocarbons (HFCs) as the extraction solvent. Table 1 below shows the GWP values ​​for some of the HFCs used as extraction solvents in the separation method of this embodiment. For comparison, the GWP values ​​for perfluorocarbons (PFCs) are also shown in Table 1 below. The GWP values ​​for HFCs and PFCs shown in Table 1 below are the values ​​(100-year values) from the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5). However, among the values ​​shown in Table 1 below, the GWP values ​​for 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane and 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane are measured values. The GWP value of the extraction solvent used in the separation method of this embodiment is preferably 5000 or less, more preferably 4000 or less, and even more preferably 3000 or less. If the above GWP value is listed in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5), that value (100-year value) shall be used; otherwise, the measured value shall be applied. The GWP of the extraction solvent, which is a mixture, shall be a weighted average based on the compositional mass.

[0016] [Table 1]

[0017] The following describes each step of the separation method of this embodiment.

[0018] <Mixing process> In the mixing step, an extraction mixture is obtained, which is a mixture of a first mixture containing R22 and HFP, and an extraction solvent containing HFC.

[0019] (First mixture) The first mixture contains at least R22 and HFP, and may also contain other compounds. Examples of other compounds in the first mixture include compounds produced by the thermal decomposition reaction of R22, specifically chlorotrifluoroethylene, tetrafluoroethylene, trifluoroethylene, perfluorocyclobutane, 1,1,1,2,3,3,3-heptafluoropropane, 1,1,1,2-tetrafluoroethane, 1,1,1,2,2-pentafluoroethane, dichlorodifluoromethane, etc. Hereinafter, chlorotrifluoroethylene will also be referred to as "CTFE" and tetrafluoroethylene as "TFE". If the first mixture contains other compounds, the other compounds in the first mixture may be one type or two or more types. The total content of R22 and HFP in the first mixture can be, for example, 50 mol% or more, and may be 80 mol or more, 90 mol or more, 99 mol or more, or 100 mol. If the first mixture contains CTFE among the other compounds, the CTFE content relative to the entire first mixture may be less than 10 mol%, and may be between 0.01 mol% and 5 mol%, or between 0.01 mol% and 2 mol%.

[0020] The molar ratio of HFP to R22 in the first mixture is not particularly limited. The molar ratio of the HFP content to the R22 content in the first mixture may be 1 / 99 to 50 / 50, 3 / 97 to 40 / 60, or 5 / 95 to 30 / 70. Hereinafter, the molar ratio of the HFP content to the R22 content in the first mixture will also be referred to as the "molar ratio (HFP / R22)". In particular, a mixture of HFP and R22 with a molar ratio (HFP / R22) of 10 / 90 forms an azeotropic composition, making separation by distillation difficult. However, according to the separation method of this embodiment, R22 and HFP can be separated with high efficiency.

[0021] (Extraction solvent) The extraction solvent contains at least HFCs and may also contain other compounds. Here, HFCs are compounds in which some or all of the hydrogen atoms constituting a hydrocarbon compound are replaced with fluorine. Unlike chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), HFCs are compounds that do not contain chlorine atoms. In addition to saturated hydrofluorocarbons, HFCs also include hydrofluorocarbons that have a carbon-carbon double bond. From the viewpoint of efficiently separating R22 and HFP, the HFC content in the total extraction solvent is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and may also be 100% by mass.

[0022] Examples of HFCs included in the extraction solvent include hydrofluorocarbons having 2 to 8 carbon atoms. From the viewpoint of efficiently separating R22 and HFP, the carbon number of HFCs is preferably 2 to 8, more preferably 3 to 7, and even more preferably 4 to 6.

[0023] The HFC preferably contains at least one selected from the group consisting of saturated compounds represented by formula (1) and unsaturated compounds represented by formula (2). (1) C x1 H y1 F z1 (2) C x2 H y2 F z2 In equation (1), x1 is an integer between 2 and 8, y1 is an integer between 1 and (x1) × 2 + 1, and z1 is (x1) × 2 + 2 - y1. In equation (2), x2 is an integer between 2 and 8, y2 is an integer between 1 and (x2) × 2 - 1, and z2 is (x2) × 2 - y2.

[0024] In equations (1) and (2), x1 and x2 are integers between 2 and 8. From the viewpoint of efficiently separating R22 and HFP, integers between 3 and 7 are preferred, and integers between 4 and 6 are more preferred. In equation (1), y1 is an integer between 1 and (x1) × 2 + 1, and from the viewpoint of efficiently separating R22 and HFP, an integer between 1 and (x1) + 1 is preferred, and an integer between 1 and 2 is more preferred. The ratio of y1 to the sum of y1 and z1, y1 / (y1 + z1), is preferably 1 / (2 × (x1) + 2) to 1 / 2, and more preferably 1 / (2 × (x1) + 2) to 2 / (2 × (x1) + 2), from the viewpoint of efficiently separating R22 and HFP. In equation (2), y2 is an integer between 1 and (x2) × 2 - 1, and from the viewpoint of efficiently separating R22 and HFP, an integer between 1 and (x2) is preferred, and an integer between 1 and (2 / 3) × (x2) is more preferred. The ratio of y2 to the sum of y2 and z2, y2 / (y2 + z2), is preferably 1 / (2 × (x2)) to 1 / 2, and more preferably 1 / (2 × (x2)) to 1 / 3, from the viewpoint of efficiently separating R22 and HFP.

[0025] HFCs may be linear, branched, or include a cyclic structure. From the viewpoint of efficiently separating R22 and HFP, it is preferable that the HFCs include at least one selected from the group consisting of linear saturated compounds and linear unsaturated compounds, and more preferably a linear saturated compound.

[0026] Specific examples of HFCs include 1,1,1,2,2,3,3,4,4-nonafluorobutane, 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexene, 1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexane, 1,1,1,3,3-pentafluorobutane, 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane, 1,1,1,2,2,3,4,5,5,5-decafluoropentane, 1,1,2,2,3,3,4-heptafluorocyclopentane, 1,1, Examples include 1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane, 3,3,4,4,4-pentafluoro-1-butene, 1,1,1,2,2,3-hexafluoropropane, 1,1,1,2,3,3-hexafluoropropane, 1,1,2,2,3-pentafluoropropane, 1,1,2,3,3-pentafluoropropane, 1,1,1,2,3-pentafluoropropane, 1,1,1,3,3-pentafluoropropane, 1,1,1-trifluoropropane, and 2,2-difluoropropane. For example, AC-2000, manufactured by AGC Inc., is a commercially available product of 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane. For example, AC-6000, also manufactured by AGC Inc., is a commercially available product of 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane.

[0027] Among HFCs, 1,1,1,2,2,3,3,4,4-nonafluorobutane, 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexene, 1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexane, 1,1,1,3,3-pentafluorobutane, 1,1,1,2,2,3,3,4,4,5,5, Preferably, it contains at least one selected from the group consisting of 6,6-tridecafluorooctane, 1,1,1,2,2,3,4,5,5,5-decafluoropentane, 1,1,2,2,3,3,4-heptafluorocyclopentane, and 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane, and preferably 1,1,1,2,2,3,3,4,4-nonafluoro Tan, 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexene, 1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexane, 1,1,1,3,3-pentafluorobutane, 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane, and 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane It is more preferable to include at least one selected from the group consisting of 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane, 1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexane, and 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexene. The extraction solvent may contain only one type of HFC, or it may contain two or more types.

[0028] From the viewpoint of efficiently separating R22 and HFP, HFCs preferably have a boiling point of 0 to 120°C, more preferably 25 to 120°C, and even more preferably 50 to 120°C. When the boiling point of HFCs is above the lower limit, the difference between the boiling point of R22 and the boiling point of HFP becomes large, making it easier to efficiently separate R22 and HFP, and also making it easier to separate HFP and HFC in the second distillation process described later. Furthermore, when the boiling point of HFCs is below the upper limit, distillation at a lower temperature becomes possible in the extraction distillation process and the second distillation process.

[0029] From the viewpoint of efficiently separating R22 and HFP, the HFC is preferably a compound that, when three times the amount of HFC is added relative to the total molar amount of R22 and HFP, causes the specific volatility Rv of R22 relative to HFP to be greater than 1.1. In other words, when three times the amount of HFC is added relative to the total molar amount of R22 and HFP, the value of the relative volatility Rv is preferably greater than 1.1. From the viewpoint of efficiently separating R22 and HFP, the value of the relative volatility Rv when three times the amount of HFC is added relative to the total molar amount of R22 and HFP is preferably 1.3 or higher, more preferably 1.5 or higher, even more preferably 1.6 or higher, and the higher the value, the better. Furthermore, from the viewpoint of efficiently separating R22 and HFP, it is particularly preferable that the HFC is a compound that increases the relative volatility Rv of R22 relative to HFP to more than 1.1, even when 1 to 7 times the amount of HFC is added relative to the total molar amount of R22 and HFP.

[0030] For example, a mixture of R22 and HFP with a molar ratio (HFP / R22) of around 10 / 90 forms an azeotropic composition, resulting in a specific volatility Rv close to 1, making separation by normal distillation difficult. On the other hand, adding HFC to the above mixture of R22 and HFP causes the specific volatility Rv to deviate from 1, making separation easier. This is presumed to be because the boiling point of HFC is higher than that of R22 and HFP, and the high affinity between HFC and HFP makes it difficult for HFP to volatilize, while the low affinity between HFC and R22 does not hinder the volatilization of R22. Therefore, in the mixing process, from the viewpoint of efficiently separating R22 and HFP, it is preferable to select the type of HFC and adjust the amount of HFC added so that the specific volatility Rv in the extraction mixture is greater than 1.1. In the mixing process, it is more preferable to select the type of HFC and adjust the amount of HFC added so that the specific volatility Rv is 1.3 or higher, even more preferable to select the type of HFC and adjust the amount of HFC added so that the specific volatility Rv is 1.5 or higher, and particularly preferable to select the type of HFC and adjust the amount of HFC added so that the specific volatility Rv is 1.6 or higher.

[0031] The relative volatility Rv of R22 with respect to HFP is expressed by the following formula (3). Equation (3): Rv = (Mole fraction of R22 in the gas phase / Mole fraction of R22 in the liquid phase) / (Mole fraction of HFP in the gas phase / Mole fraction of HFP in the liquid phase) Furthermore, the relative volatility Rv of R22 with respect to HFP is measured as follows. Specifically, a mixture of HFP and R22 with a molar ratio (HFP / R22) of 10 / 90, along with an extraction solvent as needed, is poured into a 1L autoclave equipped with a pressure gauge. The temperature is adjusted to a gauge pressure of 0.19 MPaG and maintained for one day to stabilize the composition inside the autoclave. When measuring the specific volatility Rv value when three times the amount of HFC is added to the total molar amount of R22 and HFP, three times the amount of HFC is added as the extraction solvent as needed. Next, measurement samples are taken from the gas phase and liquid phase, respectively, and after complete gasification, they are analyzed by gas chromatography to calculate the relative volatility of R22 relative to HFP, Rv. In other words, the specific volatility Rv when three times the amount of HFC is added means the value when the molar ratio (HFP / R22) is at least 10 / 90 and the gauge pressure is 0.19 MPaG when three times the amount of HFC is added to the mixture of HFP and R22.

[0032] From the perspective of efficiently separating R22 and HFP, HFCs use the interaction distance Ra, which is determined from the Hansen solubility parameter. HFP However, the interaction distance Ra between R22 and HFC R22 It is preferable that the compound is smaller than the interaction distance Ra. HFP Interaction distance Ra R22 Ratio to (Ra HFP / Ra R22 From the viewpoint of efficiently separating R22 and HFP, the ratio is preferably 0.7 or less, more preferably 0.5 or less, and even more preferably 0.3 or less.

[0033] Here, the interaction distance Ra HFP and interaction distance Ra R22 These are represented by the following equations (4) and (5). Equation (4): Ra HFP =[4×(δD HFP -δD HFC ) 2 +( δP HFP -δP HFC ) 2 +(δH HFP -δH HFC ) 2 ] 0.5 Equation (5): Ra R22 =[4×(δD R22 -δD HFC ) 2 +( δP R22 -δP HFC ) 2 +(δH R22 -δH HFC ) 2 ]0.5 In equations (4) and (5), δD HFP δP HFP , and δH HFP These terms represent the dispersion term, polar term, and hydrogen bonding term in the Hansen solubility parameter of HFP, respectively, and δD HFC δP HFC , and δH HFC These terms represent the dispersion term, polar term, and hydrogen bonding term in the Hansen solubility parameter of HFCs, respectively, and δD R22 δP R22 , and δH R22 These terms represent the dispersion, polarity, and hydrogen bonding terms in the Hansen solubility parameters for R22, respectively, and are all in units of (MPa). 1 / 2 That is the case. The dispersion, polarity, and hydrogen bonding terms in the Hansen solubility parameters for each of the above compounds are estimated from literature values ​​or the chemical structure of the compounds using computer software (Hansen Solubility Parameters in Practice (HSPiP) version 4). The Hansen solubility parameter for a mixture containing two or more compounds is calculated as a vector sum of the values ​​obtained by multiplying the Hansen solubility parameter of each compound by the volume ratio of each compound to the total volume of the mixture.

[0034] In the mixing process, the molar ratio of the amount of HFC added is preferably 1 / 1 to 30 / 1, more preferably 1 / 1 to 15 / 1, and even more preferably 3 / 1 to 10 / 1, relative to the total molar amount of R22 and HFP, from the viewpoint of efficiently separating R22 and HFP. Hereinafter, the molar ratio of the amount of HFC added to the total molar amount of R22 and HFP in the mixing process will also be referred to as the "molar ratio (HFC / (R22+HFP))". For example, as will be described later, when a first mixture containing R22 and HFP is supplied to an extraction distillation column, and an extraction solvent containing HFC is further supplied to the extraction distillation column, the "molar ratio (HFC / (R22+HFP))" represents the molar ratio of the amount of HFC supplied to the extraction distillation column to the total amount of R22 and HFP supplied to the extraction distillation column.

[0035] The timing of adding the extraction solvent to the first mixture in the mixing step does not matter as long as it is before the extraction distillation step. However, from the viewpoint of distillation efficiency, it is preferable to perform the extraction distillation step simultaneously with the mixing step, in which the first mixture is supplied to the extraction distillation column, and then the extraction solvent is supplied to the extraction distillation column to prepare the extraction mixture in the column. In the mixing process, for example, by adding the extraction solvent to the first mixture, a mixture of the first mixture and the extraction solvent is obtained. However, the operation of mixing the first mixture and the extraction solvent may be performed separately.

[0036] <Extraction and distillation process> In the extraction distillation process, the extraction mixture obtained in the mixing process is distilled to obtain a first distillate mainly composed of R22 and a first bottom product mainly composed of the extraction solvent and containing HFP.

[0037] The extraction distillation process can be carried out using commonly used distillation apparatus, such as a tray column or packed column. Various conditions for the extraction distillation process, such as operating temperature, operating pressure, reflux ratio, total number of stages in the distillation column, position of the charging stage, and position of the extraction solvent supply stage, are not particularly limited and can be appropriately selected to achieve the desired separation. When a tray column is used in the extraction distillation process, the number of stages in the distillation column can range from 1 to 100, with 30 or more being preferable and 50 or more being more preferable from the viewpoint of obtaining high-purity HFP. Since both R22 and HFP have low boiling points, extraction distillation is preferably carried out under pressure, for example, a pressure of 0 to 5 MPaG (gauge pressure) is preferred.

[0038] Furthermore, the temperatures at the top and bottom of the distillation column are determined according to the operating pressure and the composition of the distillate and bottom product. Considering the temperatures of the condenser and reheater installed at the top and bottom of the column, it is preferable to set the temperature at the top of the column to -60 to 100°C and the temperature at the bottom of the column to 20 to 300°C in order to perform the distillation operation economically. Extractive distillation may be carried out in batch or continuous order, and in some cases, it can also be carried out in a semi-continuous order in which the distillate and bottom product are intermittently withdrawn or intermittently charged, but it is preferable to continuously supply the extraction solvent to the distillation apparatus.

[0039] The extraction solvent has affinity for HFP. Therefore, by extractive distillation of an extraction mixture containing R22, HFP, and the extraction solvent, a first distillate mainly composed of R22 is obtained from the top of the extraction distillation column. The composition of this first distillate is not limited as long as it mainly contains R22, but the mole fraction of R22 in the first distillate is preferably 90 mol% or more, and more preferably 99 mol% or more. Furthermore, the mole fraction of HFP in the first distillate is preferably 1 / 10 or less, and more preferably 1 / 100 or less, of the mole fraction of HFP in the first mixture. The mole fraction of HFP in the first distillate is preferably 10 mol% or less, and more preferably 1 mol% or less. The first distillate containing a high concentration of R22 may be reused as a raw material for producing HFP.

[0040] A first bottom product is obtained from the bottom of the extraction distillation column, mainly composed of the extraction solvent and containing HFP having affinity for this extraction solvent. The mole fraction of HFP relative to the total of R22 and HFP in the first bottom product is preferably 90 mol% or more, and more preferably 99 mol% or more. Furthermore, the mole fraction of R22 relative to the total of R22 and HFP in the first bottom product is preferably 1 / 10 or less, and more preferably 1 / 100 or less, of the mole fraction of R22 in the first mixture. The mole fraction of R22 relative to the total of R22 and HFP in the first bottom product is preferably 10 mol% or less, and more preferably 1 mol% or less. Furthermore, if the first mixture contains CTFE, the first canned product will also contain CTFE. The first canned product preferably undergoes a second distillation process, which will be described later.

[0041] <Second distillation process> In the second distillation step, the first bottom product is distilled to obtain a second distillate mainly composed of HFP. At this time, a second bottom product mainly composed of the extraction solvent is obtained. Since there is a large difference in boiling points between the extraction solvent contained in the first bottom product and its affinity component, HFP, the second distillation step can be easily carried out by a normal distillation separation operation. The second distillation step can be carried out using the same distillation apparatus as the extraction distillation step described above. Various conditions in the second distillation step, such as operating temperature, operating pressure, reflux ratio, total number of stages in the distillation column, and position of the charging stage, are not particularly limited and can be appropriately selected to achieve the desired separation.

[0042] In the second distillation step, the extraction solvent and HFP are separated, and a second distillate containing HFP, in which the mole fraction of HFP relative to the sum of R22 and HFP is increased compared to the mole fraction of HFP relative to the sum of R22 and HFP in the first mixture, i.e., HFP is more concentrated compared to the first mixture, is obtained from the top of the distillation column. The mole fraction of HFP in the second distillate is preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 98 mol% or more. Furthermore, if the first mixture contains CTFE, the second distillate also contains CTFE. If the second distillate contains CTFE, it is preferable that the second distillate further undergoes an adsorption step described later.

[0043] In the second distillation step, a second bottom product containing the extraction solvent at a very high concentration is obtained from the bottom of the distillation column. The obtained second bottom product can be supplied directly to the extraction distillation step and reused as the extraction solvent. Alternatively, the second bottom product can be further purified to recover the extraction solvent, which can then be reused in the extraction distillation step.

[0044] <Adsorption process> As described above, if the second distillate contains CTFE, the separation method of this embodiment may further include an adsorption step in which the second distillate is brought into contact with an adsorbent to obtain a purified product mainly composed of HFP.

[0045] Examples of adsorbents include synthetic zeolites, activated carbon, activated alumina, metal-organic structures, porous coordination polymers, and covalent organic structures. Adsorbents may be used individually or in combination of two or more types. From the viewpoint of efficiently separating HFP and CTFE, it is preferable to use synthetic zeolite as an adsorbent. In other words, it is preferable that the adsorbent contains synthetic zeolite. Examples of synthetic zeolites include type A zeolite, type X zeolite, type beta zeolite, type ferrielite zeolite, type meridite zeolite, type L zeolite, and type Y zeolite. Among these, type A zeolite is preferred from the viewpoint of efficient separation of HFP and CTFE, and type 5A zeolite is more preferred. In addition, improved synthetic zeolites with acid resistance are also preferred. Examples of ionic species that coordinate within the molecular framework of synthetic zeolite include potassium ions, sodium ions, and calcium ions. From the viewpoint of obtaining a pore size suitable for CTFE adsorption, it is preferable that the synthetic zeolite contains calcium ions. A preferred pore size for the synthetic zeolite is 0.42 ± 0.03 nm.

[0046] In the adsorption process, for example, the second distillate is passed through a packed column filled with an adsorbent, thereby adsorbing CTFE onto the adsorbent and obtaining a high-purity HFP with low CTFE content, i.e., a purified product mainly composed of HFP. The mole fraction of HFP in the purified product is preferably 99.00 mol% or more, more preferably 99.50 mol% or more, and even more preferably 99.90 mol% or more. The mole fraction of CTFE in the purified product is preferably 1.00 mol% or less, more preferably 0.50 mol% or less, and even more preferably 0.10 mol% or less. If the second distillate contains compounds other than HFP and CTFE, the separation method of this embodiment may further include a removal step to remove the other compounds, if necessary.

[0047] In this embodiment, R22 and HFP contained in the first mixture are efficiently separated as described above. As a result, R22 is obtained in high concentration as the main component of the first distillate in the extraction distillation step, and HFP, which is more concentrated than in the first mixture, is obtained as the second distillate in the second distillation step. Furthermore, by going through an adsorption step or the like as needed, even higher purity HFP can be obtained.

[0048] Next, the material flow in the separation method of this embodiment will be described with reference to Figure 1. As shown in Figure 1, a first mixture 1 containing R22 and HFP in a predetermined ratio, for example, a molar ratio (HFP / R22) of 10 / 90, is supplied to an extraction distillation column 2, which is operated under pressure, for example. An extraction distillation column 2 with 1 to 100 stages is used, and the first mixture 1 is supplied to the extraction distillation column 2. Then, an extraction solvent 3 containing HFCs at a mole fraction 1 to 30 times the total mole fraction of R22 and HFP contained in the first mixture 1 is supplied to the stages of the extraction distillation column 2 above the stage to which the first mixture 1 was supplied. Distillation is performed in this manner, and a first distillate 4, mainly composed of R22, which is a component that does not have affinity for the extraction solvent 3, is withdrawn from the top side of the extraction distillation column 2. In the obtained first distillate 4, the mole fraction of R22 relative to the total of R22 and HFP is increased compared to a similar mole fraction in the first mixture 1. Thus, as the first distillate 4, a mixture is obtained in which the mole fraction of R22 is increased compared to the first mixture 1, that is, a mixture in which the molar concentration of R22 is concentrated.

[0049] Furthermore, a mixture mainly composed of the extraction solvent and containing HFP is withdrawn from the bottom of the extraction distillation column 2 as the first bottom product 5. Next, this first bottom product 5 is supplied to another distillation column, the solvent recovery column 6, which is operated under pressure, for example, to obtain a second distillate 7 substantially free of the extraction solvent from the top of the column. In the obtained second distillate 7, the mole fraction of HFP relative to the sum of R22 and HFP is increased compared to a similar mole fraction in the first mixture 1. Thus, as the second distillate 7, a mixture is obtained in which the mole fraction of HFP is increased compared to the first mixture 1, that is, a mixture with a concentrated molar concentration of HFP is obtained. In this specification, the phrase "substantially free of A" means that the content of A is 0.1 mol% or less.

[0050] From the bottom of the solvent recovery column 6, a second bottom product 8, mainly composed of the extraction solvent 3, is obtained. In this way, the extraction solvent 3 is recovered and reused. The reused extraction solvent 3 is heated or cooled by a heat exchanger 9 as needed before being supplied to the extraction distillation column 2. In Figure 1, reference numeral 10 denotes a condenser, and reference numeral 11 denotes a heater.

[0051] In the extraction distillation column 2, the position (stage) at which the extraction solvent 3 is supplied is preferably a stage located above the stage at which the first mixture 1 is supplied, and the extraction solvent 3 may also be supplied at the same stage as the reflux supply stage. In some cases, the extraction solvent 3 may also be supplied at the same stage as the first mixture 1. Furthermore, the first mixture 1 may be mixed with the extraction solvent 3 beforehand before being supplied to the extraction distillation column 2. By using the above apparatus and operation, R22 and HFP can be separated from a first mixture 1 containing R22 and HFP, and substantially R22-free HFP can be obtained.

[0052] Next, the material flow when the first mixture contains CTFE will be explained with reference to Figure 2. As shown in Figure 2, a first mixture 21 containing R22, HFP, and CTFE is supplied to the lower stage of the extraction distillation column 2, and an extraction solvent 3 containing HFC is supplied to the upper stage of the extraction distillation column 2, above the supply stage of the first mixture 21, and distillation is performed. Then, the first distillate 4, mainly composed of R22, is withdrawn from the top of the extraction distillation column 2, and the first bottom product 25, a mixture mainly composed of the extraction solvent and containing HFP and CTFE, is withdrawn from the bottom of the extraction distillation column 2. Next, the first bottom product 25 is supplied to the solvent recovery column 6 and distilled to obtain a second distillate 27 from the top of the solvent recovery column 6, which contains HFP and CTFE and is substantially free of the extraction solvent. A second bottom product 8, mainly composed of the extraction solvent 3, is obtained from the bottom of the solvent recovery column 6. The extraction solvent 3 recovered as the second bottom product 8 is supplied to the extraction distillation column 2 for reuse.

[0053] Next, the obtained second distillate 27 is supplied from the bottom of a packed column 12, which is filled with an adsorbent containing, for example, type 5A zeolite, while adjusting the pressure, and circulated through the inside of the packed column 12. The CTFE contained in the second distillate 27 is adsorbed by the adsorbent packed inside the packed column 12, and a purified product 13 mainly composed of HFP is obtained from the outlet at the top of the packed column 12. In the purified product 13, the mole fraction of HFP relative to the sum of HFP and CTFE is increased compared to the mole fraction of HFP relative to the sum of HFP and CTFE in the second distillate 27. By using the above apparatus and procedure, R22 and CTFE can be separated from HFP in a first mixture 21 containing R22, CTFE, and HFP, and HFP can be obtained that is substantially free of R22 and CTFE.

[0054] [Composition] A composition in one embodiment of the present disclosure is a composition comprising HFP and R22, wherein the HFP content is 99.5% by mass or more of the total composition. The HFP content of the total composition is 99.50% by mass or more, preferably 99.70% by mass or more, and more preferably 99.90% by mass or more. The composition of this embodiment can be obtained, for example, by separating a first mixture containing R22 and HFP using the separation method described above.

[0055] The composition of this embodiment may contain other compounds besides HFP and R22. Examples of other compounds included in the composition are the same as those specified above for other compounds that may be included in the first mixture. The composition of this embodiment may also contain CTFE as another compound. A composition containing HFP, R22, and CTFE, in which the HFP content is 99.5% by mass or more of the total composition, can be obtained, for example, by separating a first mixture containing R22, HFP, and CTFE using the separation method described above. [Examples]

[0056] The embodiments of this disclosure will be described in detail below with reference to examples, but the embodiments of this disclosure are not limited to these.

[0057] [Measurement of Specific Volatility (Rv)] Using the method described above, the relative volatility Rv of R22 relative to HFP was measured when HFC was added to a mixture of R22 and HFP with a molar ratio (HFP / R22) of 10 / 90. Table 2 shows the relationship between the molar ratio of the amount of HFC added to the total amount of R22 and HFP (HFC / (R22+HFP)) and the relative volatility Rv after HFC addition. The boiling points of HFCs are also shown in Table 2. Furthermore, the interaction distance Ra between HFP and HFC, which can be determined from the Hansen solubility parameter, is also determined. HFP The interaction distance between R22 and HFC, Ra R22 , and ratio (Ra HFP / Ra R22 The values ​​obtained using the method described above are also shown in Table 2.

[0058] [Table 2]

[0059] [Distillation Simulation] Using the results shown in the table above, obtained by measuring the relative volatility Rv of R22 relative to HFP, simulations of extraction distillation and solvent recovery distillation were performed using a calculation method based on known thermodynamic properties (Chemcad) (Chemstations' chemical engineering process simulator). The results are shown in Table 3. In the table, "-" means that no solvent was used or that distillation using a solvent recovery column was not performed.

[0060] (Example A1) A 60-stage distillation column was subjected to continuous distillation at a rate of 1 kilomol / hour by continuously supplying a mixture of R22 and HFP with a molar ratio (HFP / R22) of 1 / 3 from the 50th stage from the top of the column. The first distillate was continuously withdrawn from the top of the column at a rate of 0.61 kilomol / hour, and the first bottom product was continuously withdrawn from the bottom of the column at a rate of 0.39 kilomol / hour. During this process, the pressure inside the distillation column was 0.5 MPaG (gauge pressure), the top temperature was 6.23°C, and the bottom temperature was 9.19°C. The content of each component relative to the entire first distillate was 93 mol% for R22 and 7 mol% for HFP. On the other hand, the content of each component relative to the entire first canned product was 46 mol% for R22 and 54 mol% for HFP.

[0061] (Example A2) From the 50th stage of a 60-stage extraction distillation column, a mixture of R22 and HFP with a molar ratio (HFP / R22) of 1 / 3 was continuously supplied at a rate of 1 kilomol / hour. Simultaneously, from the 10th stage of the column, 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane was continuously supplied at a rate of 3 kilomol / hour. Hereafter, 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane will also be referred to as "HFC-52-13p". Then, continuous extractive distillation was performed with a pressure of 0.5 MPaG (gauge pressure) in the extractive distillation column, a top temperature of 6.19°C, and a bottom temperature of 103.11°C. The first distillate was distilled from the top of the extractive distillation column at a rate of 0.76 kilomoles per hour, and the first bottom product was bottomed out from the bottom at a rate of 3.24 kilomoles per hour.

[0062] In the first distillate extracted, HFC-52-13p was not detected, and the content of R22 in the entire first distillate was 98.7 mol%, with the remaining component being HFP. On the other hand, the content of each component in the entire first canned distillate was 19 mol ppm for R22, 7.4 mol% for HFP, and the remainder was the extraction solvent, HFC-52-13p.

[0063] Next, the first bottom product was continuously supplied at a rate of 1 kilomol / hour from the 20th stage from the top of a 30-stage solvent recovery column, and distillation was carried out continuously with a pressure of 0.4 MPaG (gauge pressure), a top temperature of 15.21°C, and a bottom temperature of 128.27°C inside the solvent recovery column. The second distillate was distilled from the top side of the solvent recovery column at a rate of 0.24 kilomol / hour, and the second bottom product was withdrawn from the bottom side at a rate of 3 kilomol / hour. Compositional analysis of the extracted second distillate and second canned product revealed that the content of each component relative to the entire second distillate was 99.97 mol% for HFP, 0.026 mol% for R22, and the remainder was the extraction solvent. On the other hand, the content of each component relative to the entire second canned product was 99.99 mol% or more for HFC-52-13p.

[0064] [Table 3]

[0065] In the above example, Example A2 is an example, and Example A1 is a comparative example. As shown in Table 3, in Example A2, R22 and HFP are separated with higher efficiency compared to Example A1, and high-purity HFP is obtained.

[0066] [Separation of HFP and CTFE] A cylindrical stainless steel packed column with an inner diameter of 1 inch and an axial length of 50 cm was packed with the adsorbents shown in the table below. The pressure inside the packed column was then adjusted to 0.1 MPaG, and a mixture of HFP 95.587 GC% and CTFE 4.413 GC% was flowed through the bottom of the column. After 1 hour, a sample was taken from the outlet of the packed column and analyzed by gas chromatography. The results are shown in Table 4. In the table below, "MS-4A" refers to Molecular Sieves 4A (manufactured by Union Showa Co., Ltd., metal ion: Na, pore size: 0.35 nm, effective pore size: 0.4 nm), "MS-5A" refers to Molecular Sieves 5A (manufactured by Union Showa Co., Ltd., metal ion: Ca, pore size: 0.42 nm, effective pore size: 0.5 nm), "MS-13X" refers to Molecular Sieves 13X (manufactured by Union Showa Co., Ltd., metal ion: Na, effective pore size: 1.0 nm), and "AW-500" refers to Molecular Sieves AW-500 (manufactured by Union Showa Co., Ltd., acid-resistant molecular sieves).

[0067] [Table 4] [Industrial applicability]

[0068] According to one embodiment of this disclosure, R22 and HFP can be efficiently separated from a mixture containing R22 and HFP. Furthermore, according to one embodiment of this disclosure, HFP useful as a raw material for, for example, fluororesin production can be obtained at a high concentration, offering significant economic advantages. [Explanation of Symbols]

[0069] 1.21 First mixture 2 Extraction distillation column 3. Extraction solvent 4. First distillate 5.25 First batch of canned goods 6. Solvent recovery tower 7.27 Second distillate 8. Second canned item 9 Heat exchanger 10 Condenser 11 Heaters 12 Filling Tower 13 Refined Products

Claims

1. A mixing step to obtain an extraction mixture which is a mixture of a first mixture containing chlorodifluoromethane and hexafluoropropylene, and an extraction solvent containing a hydrofluorocarbon having 6 carbon atoms, An extraction distillation step is performed to distill the extraction mixture to obtain a first distillate mainly composed of chlorodifluoromethane and a first bottom product mainly composed of the extraction solvent and containing hexafluoropropylene, respectively. A method for separating chlorodifluoromethane and hexafluoropropylene, comprising [a specific component / method].

2. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 1, wherein the hydrofluorocarbon has a boiling point of 0 to 120°C.

3. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 1, wherein the hydrofluorocarbon is 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane, 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexene, or 1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexane.

4. The interaction distance Ra between hexafluoropropylene and the hydrofluorocarbon, determined from the Hansen solubility parameter value. ＨＦＰ However, the interaction distance Ra between chlorodifluoromethane and the hydrofluorocarbon Ｒ２２ A method for separating chlorodifluoromethane and hexafluoropropylene according to claim 1, wherein the amount is smaller than the amount specified in claim 1.

5. The interaction distance Ra ＨＦＰ The interaction distance Ra Ｒ２２ The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 4, wherein the ratio to is 0.7 or less.

6. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 1, wherein the molar ratio of the amount of hydrofluorocarbon added in the mixing step is 1 / 1 to 30 / 1 with respect to the total molar amount of chlorodifluoromethane and hexafluoropropylene.

7. A method for separating chlorodifluoromethane and hexafluoropropylene according to any one of claims 1 to 6, further comprising a second distillation step of distilling the first bottom product to obtain a second distillate mainly composed of hexafluoropropylene.

8. The first mixture further comprises chlorotrifluoroethylene, The first canned product further contains chlorotrifluoroethylene. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 1.

9. The first mixture further comprises chlorotrifluoroethylene, The first canned product further contains chlorotrifluoroethylene, The second distillate further comprises chlorotrifluoroethylene. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 7.

10. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 9, further comprising an adsorption step of contacting the second distillate with an adsorbent to obtain a purified product mainly composed of hexafluoropropylene.

11. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 10, wherein the adsorbent includes a synthetic zeolite.

12. A composition comprising hexafluoropropylene, chlorodifluoromethane, and a hydrofluorocarbon having 6 carbon atoms, wherein the content of hexafluoropropylene is 99.5% by mass or more of the total composition.

13. The composition according to claim 12, further comprising chlorotrifluoroethylene.

Images