Separation method of chlorodifluoromethane and hexafluoropropylene

Abstract

A method for separating R22 and HFP, the method comprising: a mixing step for obtaining a mixture for extraction, the mixture being a mixture of a first mixture containing R22 and HFP and an extraction solvent containing an organic solvent selected from the group consisting of dichloromethane, chloroform, 1, 1, 1-trichloroethane, 1, 1, 2-trichloroethane, 1, 1, 1, 2-tetrachloroethane, 1, 1, 2, 3, 3-tetrachloroethane, 1, 1, 2, 3-tetrachloroethane, 1, 1, 2, 3, 3-tetrachloroethane, 1, 1, 2, 3, 3-tetrachloroethane, 1, 1, 2, 3-tetrachloroethane, 1, 1, 2, 3, 3-tetrachloroethane, 1, 1, 2, 3-tetrachloroethane, 1, 1, at least one chlorine-containing compound selected from the group consisting of 1, 1, 1, 2-tetrachloroethane, pentachloroethane, hexachloroethane, trichloroethylene and tetrachloroethylene; and an extraction distillation step in which the mixture for extraction is distilled to obtain a first distillate having HFP as the main component and a first bottoms product having the extraction solvent as the main component and containing R22, respectively, and an extraction distillation step in which the mixture for extraction is distilled to obtain a first distillate having HFP as the main component and a first bottoms product having R22 as the main component.

Description

Technical Field

[0001] This application relates to a method for separating chlorodifluoromethane and hexafluoropropene. Background Art

[0002] Hexafluoropropene is a compound used as a raw material for fluororesins and the like. For example, it is obtained by the thermal decomposition reaction of chlorodifluoromethane. Hereinafter, hexafluoropropene will also be referred to as "HFP", and chlorodifluoromethane will also be referred to as "R22".

[0003] When attempting to obtain highly pure HFP through the thermal decomposition reaction of R22, separation of unreacted R22 from the generated HFP is sought. As a method for separating a raw material from a reaction product, for example, distillation using a boiling point difference can be cited. However, since R22 and HFP form an azeotropic composition or a quasi-azeotropic composition, it is difficult to separate them by distillation.

[0004] As a method for separating R22 and HFP, Patent Document 1 discloses extractive distillation using a polar organic solvent such as methanol.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Publication No. 39-19624 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, as will be described later, the polar organic solvents disclosed in Patent Document 1 are all compounds with low flash points. Therefore, an effective separation of R22 and HFP without using compounds with low flash points is sought.

[0010] An object of one aspect of this application is to provide a separation method in which an extraction solvent that is a compound with a high flash point or no flash point is used to efficiently separate R22 and HFP from a mixture of R22 and HFP that is difficult to separate due to the formation of an azeotropic composition or a quasi-azeotropic composition.

[0011] Solutions to the Problems

[0012] This application includes the following aspects.

[0013] <1>A method for separating chlorodifluoromethane and hexafluoropropene, comprising:

[0014] A mixing step of obtaining a mixture for extraction, wherein the mixture for extraction is a mixture of a first mixture and an extraction solvent, the first mixture contains chlorodifluoromethane and hexafluoropropene, and the extraction solvent contains at least one chlorine-containing compound selected from the group consisting of dichloromethane, chloroform, 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane, hexachloroethane, trichloroethylene and tetrachloroethylene; and

[0015] An extraction distillation step of distilling the aforementioned mixture for extraction to obtain a first distillate and a first bottom product respectively, wherein the first distillate has hexafluoropropene as the main component, and the first bottom product has the aforementioned extraction solvent as the main component and contains chlorodifluoromethane.

[0016] <2>The method for separating chlorodifluoromethane and hexafluoropropene according to <1>, wherein the aforementioned chlorine-containing compound has a boiling point of 40 to 130 °C.

[0017] <3>The method for separating chlorodifluoromethane and hexafluoropropene according to <1> or <2>, wherein the aforementioned chlorine-containing compound is a compound that makes the relative volatility Rv of chlorodifluoromethane with respect to hexafluoropropene less than 0.9 when adding the aforementioned chlorine-containing compound in an amount three times the total molar amount of chlorodifluoromethane and hexafluoropropene.

[0018] <4>The method for separating chlorodifluoromethane and hexafluoropropene according to any one of <1> to <3>, wherein the aforementioned chlorine-containing compound is a compound that makes the relative volatility Rv of chlorodifluoromethane with respect to hexafluoropropene less than 0.9 when adding the aforementioned chlorine-containing compound in an amount equal to the total molar amount of chlorodifluoromethane and hexafluoropropene.

[0019] <5>The method for separating chlorodifluoromethane and hexafluoropropene according to any one of <1> to <4>, wherein the aforementioned extraction solvent contains at least one chlorine-containing compound selected from the group consisting of 1,1,1-trichloroethane, trichloroethylene, tetrachloroethylene, chloroform and dichloromethane.

[0020] <6>The method for separating chlorodifluoromethane and hexafluoropropene according to any one of <1> to <5>, wherein the molar ratio of the addition amount of the aforementioned chlorine-containing compound in the aforementioned mixing step with respect to the total molar amount of chlorodifluoromethane and hexafluoropropene is 1 / 1 to 30 / 1.

[0021] <7>The method for separating chlorodifluoromethane and hexafluoropropene according to any one of <1> to <6> further includes: a second distillation step of distilling the aforementioned first bottom product to obtain a second distillate having the aforementioned chlorodifluoromethane as the main component.

[0022] <8>The method for separating chlorodifluoromethane and hexafluoropropene according to any one of <1> to <7>, wherein the first mixture further contains chlorotrifluoroethylene,

[0023] The first bottom product further contains chlorotrifluoroethylene.

[0024] <9>The method for separating chlorodifluoromethane and hexafluoropropene according to <7>, wherein the first mixture further contains chlorotrifluoroethylene,

[0025] The first bottom product further contains chlorotrifluoroethylene,

[0026] The second distillate further contains chlorotrifluoroethylene.

[0027] Effects of the Invention

[0028] According to one aspect of the present application, there is provided a separation method in which an extraction solvent that is a compound having a high flash point or no flash point is used to efficiently separate R22 and HFP from a mixture of R22 and HFP that is difficult to separate due to the formation of an azeotropic composition or a pseudo-azeotropic composition. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a diagram showing an example of the flow path of substances in the separation method of the present application. DETAILED DESCRIPTION

[0030] Hereinafter, embodiments of the present application will be described in detail. However, the present application is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values and their ranges, and the present application is not limited.

[0031] In the present application, the term "process" includes a process that is independent of other processes, and even in a case where it cannot be clearly distinguished from other processes, as long as the purpose of the process can be achieved, the process is also included.

[0032] In the present application, the numerical ranges indicated by "~" respectively include the numerical values described before and after "~" as the minimum value and the maximum value.

[0033] In the present application, each component may contain multiple substances that meet the requirements. When there are multiple substances that meet each component in the composition, the proportion of each component means the total proportion of the multiple substances present in the composition unless otherwise specified.

[0034] In this application, when describing the embodiments with reference to the accompanying drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. In addition, the dimensions of the components in each figure are conceptual dimensions, and the relative relationships of the dimensions between the components are not limited thereto.

[0035] In this application, "distillate" refers to the substance distilled from the top side of the distillation column, and "bottom product" refers to the substance distilled from the bottom side of the distillation column.

[0036] In this application, "main component" means that the amount of components other than this component is relatively small. The amount of the "main component" is preferably 50 mol% or more of the whole, more preferably 60 mol% or more, further preferably 70 mol% or more, and most preferably 80 mol% or more.

[0037] In this application, unless otherwise specified, the boiling point of the compound is the value under normal pressure, and the normal pressure is 1.013×10 5 Pa.

[0038] [Separation method]

[0039] The separation method in one embodiment of this application has: a mixing step of obtaining an extraction mixture, which is a mixture of a first mixture and an extraction solvent, the first mixture contains chlorodifluoromethane (R22) and hexafluoropropene (HFP), and the extraction solvent contains at least 1 chlorine-containing compound selected from the group consisting of dichloromethane, chloroform, 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane, hexachloroethane, trichloroethylene and tetrachloroethylene; and an extraction distillation step of distilling the aforementioned extraction mixture to obtain a first distillate and a first bottom product respectively, the first distillate has HFP as the main component, and the first bottom product has the aforementioned extraction solvent as the main component and contains R22. Hereinafter, at least 1 chlorine-containing compound selected from the group consisting of dichloromethane, chloroform, 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane, hexachloroethane, trichloroethylene and tetrachloroethylene is also referred to as "CL compound".

[0040] The separation method of this embodiment may have other steps in addition to the mixing step and the extraction distillation step.

[0041] As other steps, for example, a second distillation step of distilling the first bottom product to obtain a second distillate having R22 as the main component can be cited. The separation method of this embodiment preferably also has a second distillation step.

[0042] In the separation method of this embodiment, among compounds with a high flash point or no flash point, by using a CL compound as an extraction solvent, efficient separation of R22 and HFP is achieved.

[0043] In the separation method of this embodiment, for a part of the CL compound used as the extraction solvent, the flash point values are shown in Table 1 below. Additionally, for comparison, the flash point values of an example of a compound with a low flash point, namely methanol, dimethylformamide, and acetone, are also shown in Table 1 below. It should be noted that the flash point values shown in Table 1 below are values obtained by the measurement method based on JIS K2265 (2007).

[0044] In the separation method of this embodiment, the CL compound used as the extraction solvent is preferably a compound with no flash point or a flash point of 250 °C or higher, more preferably a compound with no flash point or a flash point of 300 °C or higher, further preferably a compound with no flash point or a flash point of 350 °C or higher, particularly preferably a compound with no flash point or a flash point of 400 °C or higher, and most preferably a compound with no flash point.

[0045] [Table 1]

[0046]

[0047] Hereinafter, each process of the separation method of this embodiment will be described.

[0048] <Mixing process>

[0049] In the mixing process, an extraction mixture is obtained, which is a mixture of a first mixture and an extraction solvent. The first mixture contains R22 and HFP, and the extraction solvent contains a CL compound.

[0050] (First mixture)

[0051] The first mixture contains at least R22 and HFP and may also contain other compounds. As other compounds contained in the first mixture, compounds generated by the thermal decomposition reaction of R22, etc. can be cited. Specifically, as other compounds contained in the first mixture, trifluorochloroethylene, tetrafluoroethylene, trifluoroethylene, perfluorocyclobutane, 1,1,1,2,3,3,3-heptafluoropropane, 1,1,1,2-tetrafluoroethane, 1,1,1,2,2-pentafluoroethane, dichlorodifluoromethane, etc. can be cited. Hereinafter, trifluorochloroethylene will also be referred to as "CTFE", and tetrafluoroethylene will also be referred to as "TFE".

[0052] When the first mixture contains other compounds, the other compounds contained in the first mixture can be only one kind or two or more kinds.

[0053] As the total content rate of R22 and HFP relative to the entire first mixture, for example, it can be 50 mol% or more, it can be 80 mol% or more, it can be 90 mol% or more, it can be 99 mol% or more, and it can be 100 mol%.

[0054] When the first mixture contains CTFE among other compounds, the content rate of CTFE relative to the entire first mixture can be less than 10 mol%, it can be 0.01 mol% to 5 mol%, and it can be 0.01 mol% to 2 mol%.

[0055] The molar ratio of HFP to R22 contained in the first mixture is not particularly limited. The molar ratio of the content of HFP contained in the first mixture to the content of R22 can be 1 / 99 to 50 / 50, it can be 3 / 97 to 40 / 60, and it can be 5 / 95 to 30 / 70. Hereinafter, the molar ratio of the content of HFP contained in the first mixture to the content of R22 will also be referred to as "molar ratio (HFP / R22)".

[0056] In particular, a mixture of HFP and R22 with a molar ratio (HFP / R22) of 10 / 90 will become an azeotropic composition and is difficult to separate by distillation. However, according to the separation method of the present embodiment, R22 and HFP can be separated with high efficiency.

[0057] (Extraction solvent)

[0058] The extraction solvent contains at least a CL compound and may also contain other compounds.

[0059] From the viewpoint of separating R22 and HFP with high efficiency, the content rate of the CL compound relative to the entire extraction solvent is preferably 90 mass% or more, more preferably 95 mass% or more, further preferably 99 mass% or more, and can be 100 mass%.

[0060] As the CL compound contained in the extraction solvent, from the viewpoint of having a preferable boiling point, a CL compound having 1 to 2 carbon atoms is preferred, and from the viewpoint of low toxicity, a CL compound having 1 carbon atom is more preferred.

[0061] As the number of chlorine atoms contained in 1 molecule of the CL compound contained in the extraction solvent, 1 to 6 can be cited. From the viewpoint of low toxicity, 1 to 4 is preferred, and 1 to 3 is more preferred.

[0062] When the number of carbon atoms is 2 or more, the CL compound contained in the extraction solvent can be a saturated compound or an unsaturated compound.

[0063] As specific examples of the CL compound, dichloromethane, chloroform, 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane, hexachloroethane, trichloroethylene, and tetrachloroethylene can be cited.

[0064] Among the CL compounds, from the viewpoint of separating R22 and HFP with high efficiency, it is preferable to contain at least one selected from the group consisting of 1,1,1-trichloroethane, trichloroethylene, tetrachloroethylene, chloroform, and dichloromethane, more preferably to contain at least one selected from the group consisting of chloroform and dichloromethane, and further preferably to contain chloroform.

[0065] The extraction solvent may contain only one kind of CL compound or may contain two or more kinds.

[0066] From the viewpoint of separating R22 and HFP with high efficiency, the CL compound preferably has a boiling point of 40 to 130°C, more preferably has a boiling point of 40 to 80°C, and further preferably has a boiling point of 40 to 65°C. By making the boiling point of the CL compound equal to or higher than the aforementioned lower limit value, the difference in boiling point between it and R22 and the difference in boiling point between it and HFP become larger, and it is easy to separate R22 and HFP with high efficiency. Also, in the second distillation step and the like described later, it is easy to separate R22 and the CL compound. In addition, by making the boiling point of the CL compound equal to or lower than the aforementioned upper limit value, distillation at a low temperature can be carried out in the extraction distillation step and the second distillation step.

[0067] Regarding a part of the CL compound used as the extraction solvent in the separation method of the present embodiment, the boiling point values are shown in Table 2 below.

[0068] [Table 2]

[0069] Compound Name Boiling Point (°C) Dichloromethane 40 Chloroform 61 1,1,1-Trichloroethane 74 Trichloroethylene 87 Tetrachloroethylene 121

[0070] From the viewpoint of separating R22 and HFP with high efficiency, the CL compound is preferably a compound in which the relative volatility Rv of R22 with respect to HFP is less than 0.9 when adding a CL compound in an amount three times the total molar amount of R22 and HFP.

[0071] In other words, the value of the relative volatility Rv when adding a CL compound in an amount three times the total molar amount of R22 and HFP is preferably less than 0.9. From the viewpoint of separating R22 and HFP with high efficiency, the value of the relative volatility Rv when adding a CL compound in an amount three times the total molar amount of R22 and HFP is preferably 0.8 or less, more preferably 0.7 or less, further preferably 0.6 or less, and particularly preferably 0.5 or less.

[0072] From the viewpoint of separating R22 and HFP with higher efficiency, the CL compound is preferably a compound in which the relative volatility Rv of R22 with respect to HFP is less than 0.9 when adding a 1-fold amount of the CL compound relative to the total molar amount of R22 and HFP.

[0073] In other words, even when adding a 1-fold amount of the CL compound relative to the total molar amount of R22 and HFP, the value of the relative volatility Rv is preferably less than 0.9. From the viewpoint of separating R22 and HFP with higher efficiency, the value of the relative volatility Rv when adding a 1-fold amount of the CL compound relative to the total molar amount of R22 and HFP is preferably 0.8 or less, more preferably 0.7 or less, further preferably 0.6 or less, and particularly preferably 0.5 or less.

[0074] For example, a mixture composed of R22 and HFP with a molar ratio (HFP / R22) of about 10 / 90 forms an azeotropic composition, and thus, the relative volatility Rv is close to 1, making it difficult to separate by ordinary distillation. On the other hand, by adding a CL compound to the above mixture of R22 and HFP, the relative volatility Rv becomes a value deviated from 1, making it easy to separate. It is presumed that the reason is that the boiling point of the CL compound is higher than the boiling points of R22 and HFP, and the CL compound has a high affinity for R22. Therefore, it is difficult to volatilize R22, and since the CL compound has a low affinity for HFP, it does not easily hinder the volatilization of HFP.

[0075] Therefore, in the mixing process, from the viewpoint of separating R22 and HFP with high efficiency, it is preferable to select the type of CL compound and adjust the addition amount of the CL compound in such a way that the relative volatility Rv of the extraction mixture is less than 0.9. In the mixing process, it is more preferable to select the type of CL compound and adjust the addition amount of the CL compound in such a way that the relative volatility Rv becomes 0.8 or less, further preferably in such a way that the relative volatility Rv becomes 0.7 or less, particularly preferably in such a way that the relative volatility Rv becomes 0.6 or less, extremely preferably in such a way that the relative volatility Rv becomes 0.5 or less, and most preferably in such a way that the relative volatility Rv becomes 0.4 or less.

[0076] The relative volatility Rv of R22 with respect to HFP is represented by the following formula (3).

[0077] 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)

[0078] In addition, the relative volatility Rv of R22 with respect to HFP is measured as follows.

[0079] Specifically, a mixture of HFP and R22 with a molar ratio (HFP / R22) of 10 / 90, and, if necessary, an extraction solvent are injected into a 1-L autoclave equipped with a manometer. The temperature is adjusted so that the gauge pressure becomes 0.19 MPaG, and the temperature is maintained for 1 day to stabilize the composition inside the autoclave. It should be noted that when measuring the value of the relative volatility Rv when adding a CL compound in an amount three times the total molar amount of R22 and HFP, a CL compound in an amount three times the total molar amount of R22 and HFP is added as the extraction solvent injected as needed.

[0080] Next, measurement samples are taken from the gas phase and the liquid phase, completely vaporized, and then analyzed by gas chromatography to calculate the relative volatility Rv of R22 with respect to HFP.

[0081] In other words, the above relative volatility Rv refers to the value when the molar ratio (HFP / R22) is 10 / 90 and the gauge pressure is 0.19 MPaG.

[0082] From the viewpoint of separating R22 and HFP with high efficiency, the molar ratio of the addition amount of the CL compound in the mixing step with respect to the total molar amount of R22 and HFP is preferably 1 / 1 to 30 / 1, more preferably 1 / 1 to 15 / 1, and still more preferably 3 / 1 to 10 / 1. Hereinafter, the molar ratio of the addition amount of the CL compound in the mixing step with respect to the total molar amount of R22 and HFP will also be referred to as "molar ratio (CL / (R22 + HFP))".

[0083] For example, as will be described later, when a first mixture containing R22 and HFP is supplied to an extractive distillation column, and further, an extraction solvent containing a CL compound is supplied to the extractive distillation column, "molar ratio (CL / (R22 + HFP))" represents the molar ratio of the supply amount of the CL compound supplied to the extractive distillation column with respect to the total supply amount of R22 and HFP supplied to the extractive distillation column.

[0084] Regarding the addition of the extraction solvent to the first mixture in the mixing step, as long as it is before the extractive distillation step, the timing is not particularly limited. It should be noted that from the perspective of distillation operation efficiency, it is preferable to perform the extractive distillation step simultaneously with the mixing step. In the mixing step, after supplying the first mixture to the extractive distillation column, the extraction solvent is further supplied to the extractive distillation column to prepare an extraction mixture in the column.

[0085] It should be noted that in the mixing step, for example, by adding the extraction solvent to the first mixture, a mixture of the first mixture and the extraction solvent is obtained, but the operation of mixing the first mixture and the extraction solvent can be carried out separately.

[0086] <Extractive distillation step>

[0087] In the extractive distillation step, the extraction mixture obtained through the mixing step is distilled to obtain a first distillate and a first bottom product respectively. The first distillate has HFP as the main component, and the first bottom product has the extraction solvent as the main component and contains R22.

[0088] The extractive distillation step can be implemented by using commonly used distillation apparatuses, such as distillation columns like plate columns, packed columns, etc. Various conditions of the extractive distillation step, such as operating temperature, operating pressure, reflux ratio, total number of plates of the distillation column, position of the feed plate, position of the extraction solvent supply plate, etc., are not particularly limited and can be appropriately selected to achieve the target separation. When using a plate column as the distillation column in the extractive distillation step, as the number of plates of the distillation column, for example, 1 to 100 can be cited. From the perspective of obtaining high-purity HFP, it is preferably 30 or more, and more preferably 50 or more. Since both R22 and HFP have low boiling points, it is preferable to perform extractive distillation under pressure. For example, it is preferably set to a pressure of 0 to 5 MPaG (gauge pressure).

[0089] Furthermore, the temperatures at the top and bottom of the distillation column are determined according to the operating pressure and the compositions of the distillate and the bottom product. Considering the temperatures of the condensers and reboilers provided at the top and bottom of the column, in order to perform the distillation operation economically, the temperature at the top of the column is preferably set to -60 to 100 °C, and the temperature at the bottom of the column is preferably set to 20 to 300 °C. The extractive distillation can be batchwise or continuous, and depending on the situation, it can also be implemented by a semi-continuous method of intermittently extracting the distillate and the bottom product or intermittently feeding the raw materials. Regarding the extraction solvent, it is preferable to continuously supply it to the distillation apparatus.

[0090] The extraction solvent has an affinity for R22. Therefore, by subjecting the extraction mixture containing R22, HFP, and the extraction solvent to extractive distillation, a first distillate mainly composed of HFP is obtained from the top side of the extractive distillation column. As long as the first distillate mainly contains HFP, its composition is not limited. The molar fraction of HFP in the first distillate is preferably 90 mol% or more, more preferably 99 mol% or more, still more preferably 99.9 mol% or more, and may be 100 mol%. In addition, the molar fraction of R22 in the first distillate is preferably 1 / 100 or less of the molar fraction of R22 in the first mixture, more preferably 1 / 500 or less, and may be 0. The molar fraction of R22 in the first distillate is preferably 10 mol% or less, more preferably 1 mol% or less, still more preferably 0.1 mol% or less, and may be 0 mol%.

[0091] When the first distillate contains other compounds in addition to HFP and CTFE described below, the separation method of the present embodiment may further have a first removal step of removing the aforementioned other compounds from the first distillate as needed.

[0092] A first bottom product mainly composed of the extraction solvent and containing R22 having an affinity for the extraction solvent is obtained from the bottom side of the extractive distillation column. The molar fraction of R22 contained in the first bottom product relative to the total of R22 and HFP is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly preferably 98 mol% or more, and may be 100 mol%. In addition, the molar fraction of HFP contained in the first bottom product relative to the total of R22 and HFP is preferably 1 / 4 or less of the molar fraction of HFP in the first mixture, more preferably 1 / 10 or less, still more preferably 1 / 20 or less, and may be 0. The molar fraction of HFP contained in the first bottom product relative to the total of R22 and HFP is preferably 30 mol% or less, more preferably 20 mol% or less, still more preferably 10 mol% or less, particularly preferably 2 mol% or less, and may be 0 mol%.

[0093] It should be noted that when the first mixture contains CTFE, the first bottom product contains CTFE.

[0094] The first bottom product preferably further undergoes a second distillation step described below.

[0095] <Second distillation step>

[0096] In the second distillation step, the first bottom product is distilled to obtain a second distillate having R22 as the main component. At this time, a second bottom product having the extraction solvent as the main component is obtained. Since the boiling point difference between the extraction solvent contained in the first bottom product and R22 as its affinity component is large, in the second distillation step, it can be easily carried out by a usual distillation separation operation. The second distillation step can be carried out using the same distillation apparatus as that in the aforementioned extractive distillation step. Various conditions of the second distillation step, such as the operating temperature, operating pressure, reflux ratio, total number of plates in the distillation column, position of the feed plate, etc., are not particularly limited and can be appropriately selected to achieve the target separation.

[0097] By the second distillation step, the extraction solvent and R22 are separated, and a second distillate containing R22 and having a molar fraction of R22 relative to the total of R22 and HFP increased compared to the molar fraction of R22 relative to the total of R22 and HFP in the first mixture, that is, R22 is concentrated compared to the first mixture, is obtained from the top side of the distillation column. The molar fraction of R22 in the second distillate is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 98 mol% or more, and can be 100 mol%. The second distillate containing R22 at a high concentration can be reused as a raw material for manufacturing HFP.

[0098] It should be noted that when the first mixture contains CTFE, the second distillate also contains CTFE. When the second distillate contains CTFE, the second distillate may further have an adsorption step of bringing the second distillate into contact with an adsorbent to obtain a refined product having R22 as the main component. In addition, when the second distillate contains other compounds in addition to R22 and CTFE, the separation method of the present embodiment may further have a second removal step of removing the aforementioned other compounds from the second distillate as needed.

[0099] In the second distillation step, a second bottom product containing the extraction solvent at an extremely high concentration is obtained from the bottom side of the distillation column. The obtained second bottom product can be directly supplied to the extractive distillation step and reused as the extraction solvent again. Alternatively, the second bottom product can be further refined to recover the extraction solvent and reused in the extractive distillation step.

[0100] In the present embodiment, by operating as described above, R22 and HFP contained in the first mixture are efficiently separated. Thus, HFP is obtained at a high concentration as the main component of the first distillate in the extractive distillation step, and R22 concentrated compared to the first mixture is obtained as the second distillate in the second distillation step.

[0101] Next, referring to Figure 1 , the flow path of substances in the separation method of the present embodiment will be described.

[0102] As Figure 1 shown, a first mixture 1 containing R22 and HFP in a specified ratio, for example, a molar ratio of 10 / 90 (HFP / R22), is supplied to an extractive distillation column 2 operating under pressure, for example. As the extractive distillation column 2, an extractive distillation column having 1 to 100 plates is used, and the first mixture 1 is supplied into the extractive distillation column 2. Further, an extraction solvent 3 containing a CL compound in a molar fraction that is 1 to 30 times the total molar fraction of R22 and HFP contained in the first mixture 1 is supplied to a plate located above the supply section of the first mixture 1 in the extractive distillation column 2. By performing distillation in this manner, a first distillate 4 mainly composed of a component having no affinity for the extraction solvent 3, that is, HFP, is extracted from the top side of the extractive distillation column 2. In the obtained first distillate 4, the molar fraction of HFP relative to the total of R22 and HFP is increased compared to the same molar fraction in the first mixture 1. Thus, as the first distillate 4, a mixture in which the molar fraction of HFP is increased compared to the first mixture 1, that is, a mixture in which the molar concentration of HFP is concentrated, is obtained.

[0103] In addition, a mixture mainly composed of the extraction solvent and containing R22 is extracted from the bottom side of the extractive distillation column 2 as a first bottom product 5. Next, the first bottom product 5 is supplied to a solvent recovery column 6, for example, another distillation column operating under pressure, and a second distillate 7 substantially free of the extraction solvent is obtained from the top side. In the obtained second distillate 7, the molar fraction of R22 relative to the total of R22 and HFP is increased compared to the same molar fraction in the first mixture 1. Thus, as the second distillate 7, a mixture in which the molar fraction of R22 is increased compared to the first mixture 1, that is, a mixture in which the molar concentration of R22 is concentrated, is obtained.

[0104] It should be noted that in this specification, the term "substantially free of A" means that the content of A is 0.1 mol% or less.

[0105] A second bottom product 8 mainly composed of the extraction solvent 3 is obtained from the bottom side of the solvent recovery column 6. By operating in this manner, the extraction solvent 3 is recovered and the recovered extraction solvent 3 is reused. The reused extraction solvent 3 is supplied to the extractive distillation column 2 after being heated or cooled using a heat exchanger 9 as needed.

[0106] It should be noted that in Figure 1 , the symbol 10 represents a condenser and the symbol 11 represents a heater.

[0107] The position (tray) where the extraction solvent 3 is supplied to the extraction distillation column 2 is preferably a tray located above the tray to which the first mixture 1 is supplied. The extraction solvent 3 can be supplied to the same tray as the tray to which the reflux is supplied. Depending on the situation, the extraction solvent 3 can be supplied to the same tray as the first mixture 1. Further, with respect to the first mixture 1, before being supplied to the extraction distillation column 2, it can be supplied after being premixed with the extraction solvent 3.

[0108] Through the above apparatus and operations, R22 and HFP are separated from the first mixture 1 containing R22 and HFP, and HFP substantially free of R22 can be obtained.

[0109] It should be noted that the flow path of the substances when the first mixture contains CTFE is as follows.

[0110] Specifically, the first mixture 1 containing R22, HFP, and CTFE is supplied to a tray located lower than the central part of the extraction distillation column 2, and the extraction solvent 3 containing a CL compound is supplied to a tray located above the supply section of the first mixture 1 in the extraction distillation column 2, and distillation is carried out. Then, the first distillate 4 mainly composed of HFP is extracted from the top side of the extraction distillation column 2, and a mixture mainly composed of the extraction solvent and containing R22 and CTFE is extracted from the bottom side of the extraction distillation column 2 as the first bottom product 5.

[0111] Next, the first bottom product 5 is supplied to the solvent recovery column 6 for distillation. A second distillate 7 substantially free of the extraction solvent and containing R22 and CTFE is obtained from the top side of the solvent recovery column 6, and a second bottom product 8 mainly composed of the extraction solvent 3 is obtained from the bottom side of the solvent recovery column 6. The extraction solvent 3 recovered in the form of the second bottom product 8 is supplied to the extraction distillation column 2 for reuse.

[0112] Through the above apparatus and operations, R22 and CTFE are separated from the first mixture 1 containing R22, CTFE, and HFP, and HFP substantially free of R22 and CTFE can be obtained.

[0113] Examples

[0114] Hereinafter, the embodiments of the present application will be described in detail by way of examples, but the embodiments of the present application are not limited thereto.

[0115] [Measurement of relative volatility Rv]

[0116] By the foregoing method, the value of the relative volatility Rv of R22 with respect to HFP was measured when a CL compound was added to a mixture of R22 and HFP with a molar ratio (HFP / R22) of 10 / 90. The relationship between the molar ratio of the addition amount of the CL compound with respect to the total amount of R22 and HFP (CL / (R22 + HFP)) and the relative volatility Rv after adding the CL compound is shown in Table 3.

[0117] In addition, the boiling points of the CL compounds are also shown in Table 3.

[0118] [Table 3]

[0119]

[0120] [Distillation simulation]

[0121] Using the results recorded in the above table obtained by the measurement of the relative volatility Rv of R22 with respect to HFP, simulations of extractive distillation and solvent recovery distillation shown below were carried out using a known calculation method based on thermodynamic properties (Chemcad) (a chemical engineering process simulator of Chemstations, Inc.). The results are shown in Table 4. In the table, "-" means that no solvent is used or distillation using a solvent recovery column is not carried out.

[0122] (Example 1)

[0123] A mixture of R22 and HFP with a molar ratio (HFP / R22) of 15 / 85 was continuously fed at a rate of 1 kmol per hour from the 50th stage from the top of a distillation column with 60 plates, and distillation was carried out. A first distillate was continuously withdrawn from the top of the column at a rate of 0.55 kmol per hour, and a first bottom product was continuously withdrawn from the bottom of the column at a rate of 0.45 kmol per hour. The pressure inside the distillation column during this period was set to 0.5 MPaG (gauge pressure), the top temperature of the column was set to 6.23 °C, and the bottom temperature of the column was set to 7.03 °C.

[0124] Regarding the content rate of each component with respect to the entire first distillate, R22 was 94.4 mol%, and HFP was 5.6 mol%. On the other hand, regarding the content rate of each component with respect to the entire first bottom product, R22 was 73.6 mol%, and HFP was 26.4 mol%.

[0125] (Example 2)

[0126] A mixture of R22 and HFP with a molar ratio (HFP / R22) of 15 / 85 was continuously fed at a rate of 1 kmol per hour from the 50th stage from the top of an extractive distillation column with 60 plates, and chloroform was continuously fed at a rate of 3 kmol per hour from the 15th stage from the top.

[0127] Then, set the pressure in the extractive distillation column to 0.5 MPaG (gauge pressure), set the top temperature of the column to 22.09 °C, and set the bottom temperature of the column to 57.99 °C, and continuously perform extractive distillation. Distill the first distillate from the top side of the extractive distillation column at a rate of 0.12 kmol per hour, and distill the first bottom product from the bottom side of the column at a rate of 3.88 kmol per hour.

[0128] In the first distillate taken out, chloroform was not detected, and the content rate of HFP relative to the whole of the first distillate was 99.9 mol%, and the remaining component was R22. On the other hand, regarding the content rate of each component relative to the whole of the first bottom product, R22 was 21.9 mol%, HFP was 0.9 mol%, and the balance was occupied by chloroform as the extraction solvent.

[0129] Next, continuously supply the first bottom product at a rate of 1 kmol per hour from the 10th stage starting from the top of the solvent recovery column with 30 plates, set the pressure in the solvent recovery column to 0.4 MPaG (gauge pressure), set the top temperature of the column to 1.0 °C, and set the bottom temperature of the column to 120.63 °C, and continuously perform distillation. Distill the second distillate from the top side of the solvent recovery column at a rate of 0.88 kmol per hour, and extract the second bottom product from the bottom side of the column at a rate of 3 kmol per hour.

[0130] If the compositions of the extracted second distillate and second bottom product are analyzed respectively, regarding the content rate of each component relative to the whole of the second distillate, R22 becomes 96.1 mol%, HFP becomes 3.9 mol%, and the balance is the extraction solvent. On the other hand, regarding the content rate of each component relative to the whole of the second bottom product, chloroform is 99.99 mol% or more.

[0131] [Table 4]

[0132]

[0133] In the above example, Example 2 is an example of implementation, and Example 1 is a comparative example. As shown in Table 4, in Example 2, compared with Example 1, R22 and HFP were separated with high efficiency, and high-purity HFP was obtained.

[0134] Industrial applicability

[0135] According to an embodiment of the present application, R22 and HFP can be efficiently separated from a mixture containing R22 and HFP. In addition, according to an embodiment of the present application, for example, HFP useful as a raw material for manufacturing fluororesins and the like can be obtained at a high concentration, and the economic advantages are great.

[0136] The entire disclosure of Japanese Patent Application No. 2022-188720 filed on November 25, 2022 is incorporated herein by reference. In addition, all documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard had been specifically and separately incorporated by reference.

[0137] Description of Reference Numerals

[0138] 1 First mixture

[0139] 2 Extractive distillation column

[0140] 3 Extractive solvent

[0141] 4 First distillate

[0142] 5 First bottoms product

[0143] 6 Solvent recovery column

[0144] 7 Second distillate

[0145] 8 Second bottoms product

[0146] 9 Heat exchanger

[0147] 10 Condenser

[0148] 11 Heater

Claims

1. A method for separating chlorodifluoromethane and hexafluoropropene, comprising: A mixing step of obtaining a mixture for extraction, which is a mixture of a first mixture and an extraction solvent, the first mixture containing chlorodifluoromethane and hexafluoropropene, and the extraction solvent containing at least one chlorine-containing compound selected from the group consisting of dichloromethane, chloroform, 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane, hexachloroethane, trichloroethylene, and tetrachloroethylene; and An extraction distillation step of distilling the mixture for extraction to obtain a first distillate and a first bottom product respectively, the first distillate having hexafluoropropene as the main component, and the first bottom product having the extraction solvent as the main component and containing chlorodifluoromethane.

2. The separation method of chlorodifluoromethane and hexafluoropropene according to claim 1, wherein, The chlorine-containing compound has a boiling point of 40 to 130 °C.

3. The method for separating chlorodifluoromethane and hexafluoropropene according to claim 1, wherein The chlorine-containing compound is a compound that makes the relative volatility Rv of chlorodifluoromethane with respect to hexafluoropropene less than 0.9 when adding the chlorine-containing compound in an amount three times the total molar amount of chlorodifluoromethane and hexafluoropropene.

4. The method for separating chlorodifluoromethane and hexafluoropropene according to claim 1, wherein, The chlorine-containing compound is a compound that makes the relative volatility Rv of chlorodifluoromethane with respect to hexafluoropropene less than 0.9 when adding the chlorine-containing compound in an amount one time the total molar amount of chlorodifluoromethane and hexafluoropropene.

5. The method for separating chlorodifluoromethane and hexafluoropropene according to claim 1, wherein The extraction solvent contains at least one chlorine-containing compound selected from the group consisting of 1,1,1-trichloroethane, trichloroethylene, tetrachloroethylene, chloroform, and dichloromethane.

6. The method for separating chlorodifluoromethane and hexafluoropropene according to claim 1, wherein, The molar ratio of the addition amount of the chlorine-containing compound in the mixing step with respect to the total molar amount of chlorodifluoromethane and hexafluoropropene is 1 / 1 to 30 / 1.

7. The method for separating chlorodifluoromethane and hexafluoropropene 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 having chlorodifluoromethane as the main component.

8. The method for separating chlorodifluoromethane and hexafluoropropene according to claim 1, wherein, The first mixture further contains trifluorochloroethylene, The first bottom product further contains trifluorochloroethylene.

9. The method for separating chlorodifluoromethane from hexafluoropropene according to claim 7, wherein, The first mixture further contains trifluorochloroethylene, The first bottom product further contains trifluorochloroethylene, The second distillate further contains trifluorochloroethylene.

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