JP2024076897A - Separation method for chlorodifluoromethane and hexafluoropropylene, and composition - Google Patents

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

This disclosure relates to a method and composition for separating chlorodifluoromethane and hexafluoropropylene.

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

As a method for separating R22 and HFP, Patent Document 1 discloses extractive distillation using a perfluorinated or halogenated polyfluorinated compound having two or more carbon atoms that is liquid under distillation conditions.

Japanese Patent Application Laid-Open No. 51-128901

However, the perfluor or halogenated polyfluor compounds disclosed in Patent Document 1 have a high global warming potential, as described below. Hereinafter, global warming potential is also referred to as "GWP." Therefore, there is a need for efficient separation of R22 and HFP without using compounds with high GWP. There is also a need to obtain high-purity HFP by separating R22 and HFP.

One aspect of the present disclosure aims to provide a method for separating R22 and HFP with high efficiency 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.
Another object of one aspect of the present disclosure is to provide a composition having high purity HFP.

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 mixture for extraction to obtain a first distillate mainly composed of chlorodifluoromethane and a first bottom product mainly composed of the extraction solvent and containing hexafluoropropylene;
The method for separating chlorodifluoromethane and hexafluoropropylene comprises the steps of:
<2> The method for separating chlorodifluoromethane and hexafluoropropylene according to <1>, wherein the hydrofluorocarbon has a boiling point of 0 to 120° C.
<3> The method for separating chlorodifluoromethane and hexafluoropropylene according to <1> or <2>, wherein the hydrofluorocarbon is a compound that makes the relative volatility Rv of chlorodifluoromethane to hexafluoropropylene greater than 1.1 when the hydrofluorocarbon is added in an amount three times the total molar amount of chlorodifluoromethane and hexafluoropropylene.
<4> The method for separating chlorodifluoromethane and hexafluoropropylene according to any one of <1> to <3>, wherein an interaction distance Ra ^HFP between hexafluoropropylene and the hydrofluorocarbon calculated from a value of Hansen solubility parameter is smaller than an interaction distance Ra ^R22 between chlorodifluoromethane and the hydrofluorocarbon.
<5> The method for separating chlorodifluoromethane and hexafluoropropylene according to <4>, wherein a ratio of the interaction distance Ra ^HFP to the interaction distance Ra ^R22 is 0.7 or less.
<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 includes 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 hydrofluorocarbon is 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, or 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 method for separating chlorodifluoromethane and hexafluoropropylene according to any one of <1> to <8>, wherein a molar ratio of the amount of the hydrofluorocarbon added in the mixing step is 1/1 to 30/1 relative to a total molar amount of chlorodifluoromethane and hexafluoropropylene.
<10> The method for separating chlorodifluoromethane and hexafluoropropylene according to any one of <1> to <9>, further comprising a second distillation step of distilling the first bottoms to obtain a second distillate containing hexafluoropropylene as a main component.
<11> The first mixture further contains chlorotrifluoroethylene,
The first can further comprises chlorotrifluoroethylene.
<1><2> A method for separating chlorodifluoromethane and hexafluoropropylene according to any one of <1> to <10>.
<12> The first mixture further contains chlorotrifluoroethylene,
The first can further comprises chlorotrifluoroethylene;
The second distillate further comprises chlorotrifluoroethylene.
<10> The method for separating chlorodifluoromethane and hexafluoropropylene according to <10>.
<13> The method for separating chlorodifluoromethane and hexafluoropropylene according to <12>, further comprising an adsorption step of contacting the second distillate with an adsorbent to obtain a purified product mainly composed of hexafluoropropylene.
<14> The method for separating chlorodifluoromethane and hexafluoropropylene according to <13>, wherein the adsorbent contains synthetic zeolite.
<15> A composition comprising hexafluoropropylene and chlorodifluoromethane, the content of hexafluoropropylene being 99.5 mass% or more based on the total mass of the composition.
<16> The composition according to <15>, further comprising chlorotrifluoroethylene.

According to one aspect of the present disclosure, there is provided a method for efficiently separating 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 the present disclosure, a composition having high purity of HFP is provided.

FIG. 2 is a diagram showing an example of a material flow in the separation method of the present disclosure. FIG. 2 is a diagram showing another example of the flow of materials in the separation method of the present disclosure.

Embodiments of the present disclosure are described in detail below. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values and their ranges, and do not limit the present disclosure.

In the present disclosure, the term "step" includes not only a step that is independent of other steps, but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.
In the present disclosure, the numerical range indicated using "to" includes the numerical values before and after "to" as the minimum and maximum values, respectively.
In the present disclosure, each component may contain multiple types of the corresponding substance. When multiple substances corresponding to each component are present in the composition, the ratio of each component means the total ratio of the multiple substances present in the composition, unless otherwise specified.
When an embodiment of the present disclosure is described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. In addition, the size of the members in each drawing is conceptual, and the relative relationship between the sizes of the members is not limited to this.

In this disclosure, "distillate" refers to the material that is distilled from the top side of a distillation column, and "bottoms" refers to the material that is distilled from the bottom side of a distillation column.
In the present disclosure, the term "main component" means that the amount of components other than the component in question 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 point of a compound is a value at normal pressure, which is 1.013×10 ⁵ Pa.

[Separation method]
The separation method according to one embodiment of the present disclosure includes 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 a hydrofluorocarbon, and an extractive 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. Hereinafter, hydrofluorocarbon is also referred to as "HFC".

The separation method of the present embodiment may include steps other than the mixing step and the extractive distillation step.
The other step may be, for example, a second distillation step in which the first bottom product is distilled to obtain a second distillate containing HFP as a main component. The separation method of the present embodiment preferably further includes a second distillation step.

In the separation method of the present embodiment, a hydrofluorocarbon (HFC), which is a compound having a lower GWP than the perfluor or halogenated polyfluor compounds disclosed in Patent Document 1, is used as an extraction solvent, thereby achieving highly efficient separation of R22 and HFP.
Table 1 below shows GWP values for some of the HFCs used as the extraction solvent in the separation method of this embodiment. For comparison, Table 1 also shows GWP values for perfluorocarbons (PFCs). The GWP values for HFCs and PFCs shown in Table 1 below are values (100-year values) from the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC). However, among the values shown in Table 1 below, the GWPs of 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 GWP value is listed in the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC), that value (100-year value) is used, and if not, the measured value is applied. The GWP of the extraction solvent, which is a mixture, is a weighted average based on the composition mass.

Each step of the separation method of this embodiment is described below.

<Mixing step>
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.

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

The molar ratio of HFP to R22 contained in the first mixture is not particularly limited. The molar ratio of the HFP content to the R22 content contained 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 contained in the first mixture is also referred to as "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, which is difficult to separate by distillation. However, according to the separation method of this embodiment, R22 and HFP can be separated with high efficiency.

(Extraction Solvent)
The extraction solvent contains at least HFC and may further contain other compounds. Here, HFC is a compound in which part or all of the hydrogen constituting a hydrocarbon compound is replaced with fluorine. Unlike chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), HFC is a compound that does not contain chlorine atoms. Note that HFC includes not only saturated hydrofluorocarbons but also hydrofluorocarbons having a carbon-carbon double bond.
From the viewpoint of separating R22 and HFP with high efficiency, the content of HFC in the entire 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 be 100% by mass.

HFCs contained in the extraction solvent include hydrofluorocarbons with a carbon number of 2 to 8. From the viewpoint of separating R22 and HFP with high efficiency, the carbon number of HFCs is preferably 2 to 8, more preferably 3 to 7, and even more preferably 4 to 6.

The HFC preferably contains at least one selected from the group consisting of a saturated compound represented by formula (1) and an unsaturated compound represented by formula (2).
(1) C _x1 H _y1 F _z1
(2) C _x2 H _y2 F _z2
In formula (1), x1 is an integer from 2 to 8, y1 is an integer from 1 to (x1)×2+1, z1 is (x1)×2+2-y1, and in formula (2), x2 is an integer from 2 to 8, y2 is an integer from 1 to (x2)×2-1, and z2 is (x2)×2-y2.

In formula (1) and formula (2), x1 and x2 are integers of 2 to 8, and from the viewpoint of separating R22 and HFP with high efficiency, an integer of 3 to 7 is preferable, and an integer of 4 to 6 is more preferable.
In formula (1), y1 is an integer of 1 to (x1)×2+1, and from the viewpoint of separating R22 and HFP with high efficiency, an integer of 1 to (x1)+1 is preferable, and an integer of 1 to 2 is more preferable. From the viewpoint of separating R22 and HFP with high efficiency, the ratio of y1 to the total 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).
In formula (2), y2 is an integer of 1 to (x2)×2−1, and from the viewpoint of separating R22 and HFP with high efficiency, an integer of 1 to (X2) is preferable, and an integer of 1 to (2/3)×(X2) is more preferable. The ratio of y2 to the total 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 separating R22 and HFP with high efficiency.

The HFC may be linear, branched, or contain a cyclic structure. From the viewpoint of separating R22 and HFP with high efficiency, the HFC preferably contains at least one selected from the group consisting of linear saturated compounds and linear unsaturated compounds, and more preferably contains a linear saturated compound.

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 of the fluoroalkyl groups 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.
An example of a commercially available product of 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane is AC-2000 manufactured by AGC Inc. An example of a commercially available product of 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane is AC-6000 manufactured by AGC Inc.

Among the HFCs, from the viewpoint of separating R22 and HFP with high efficiency, 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, It is preferable that the fluorocarbon ether 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 1,1,1,2,2,3,3,4,4-nonafluorobuffer is preferably used. ethane, 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. and more preferably 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 HFC or may contain two or more HFCs.

From the viewpoint of separating R22 and HFP with high efficiency, HFC preferably has a boiling point of 0 to 120°C, more preferably 25 to 120°C, and even more preferably 50 to 120°C. By having the boiling point of HFC equal to or higher than the lower limit, the difference between the boiling point of HFC and that of R22 and that of HFP becomes large, making it easier to separate R22 and HFP with high efficiency and also easier to separate HFP and HFC in the second distillation step described below. In addition, by having the boiling point of HFC equal to or lower than the upper limit, distillation at a low temperature is possible in the extractive distillation step and the second distillation step.

From the viewpoint of separating R22 and HFP with high efficiency, the HFC is preferably a compound that makes the relative volatility Rv of R22 to HFP greater than 1.1 when three times the total molar amount of R22 and HFP is added.
That is, the value of relative volatility Rv when three times the amount of HFC is added relative to the total molar amount of R22 and HFP is preferably greater than 1.1. From the viewpoint of separating R22 and HFP with high efficiency, the value of 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 more, more preferably 1.5 or more, and even more preferably 1.6 or more, and the larger the value, the more preferable.
Moreover, from the viewpoint of separating R22 and HFP with high efficiency, it is particularly preferable that the HFC is a compound that makes the relative volatility Rv of R22 to HFP greater than 1.1 even when 1 to 7 times the total molar amount of R22 and HFP is added.

For example, a mixture of R22 and HFP with a molar ratio (HFP/R22) of about 10/90 forms an azeotropic composition, so that the relative volatility Rv is close to 1, making separation by normal distillation difficult. On the other hand, by adding HFC to the mixture of R22 and HFP, the relative volatility Rv becomes a value farther away from 1, making separation easier. This is presumably because the boiling point of HFC is higher than the boiling points 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 makes it difficult to hinder the volatilization of R22.
Therefore, in the mixing step, from the viewpoint of separating R22 and HFP with high efficiency, it is preferable to select the type of HFC and adjust the amount of HFC added so that the relative volatility Rv in the mixture for extraction is greater than 1.1. In the mixing step, it is more preferable to select the type of HFC and adjust the amount of HFC added so that the relative volatility Rv is 1.3 or more, it is even more preferable to select the type of HFC and adjust the amount of HFC added so that the relative volatility Rv is 1.5 or more, and it is particularly preferable to select the type of HFC and adjust the amount of HFC added so that the relative volatility Rv is 1.6 or more.

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

From the viewpoint of separating R22 and HFP with high efficiency, the HFC is preferably a compound in which the interaction distance Ra ^HFP between HFP and HFC calculated from the value of the Hansen solubility parameter is smaller than the interaction distance Ra ^R22 between R22 and HFC. From the viewpoint of separating R22 and HFP with high efficiency, the ratio of the interaction distance Ra ^HFP to the interaction distance Ra ^R22 (Ra ^HFP /Ra ^R22 ) is preferably 0.7 or less, more preferably 0.5 or less, and even more preferably 0.3 or less.

Here, the interaction distances Ra ^HFP and Ra ^R22 are expressed by the following formulas (4) and (5), respectively.
Equation (4): Ra ^HFP = [4 × (δD ^HFP - δD ^HFC ) ² + (δP ^HFP - δP ^HFC ) ² + (δH ^HFP - δH ^HFC ) ² ] ^0.5
Formula (5): Ra ^R22 = [4 × (δD ^R22 - δD ^HFC ) ² + (δP ^R22 - δP ^HFC ) ² + (δH ^R22 - δH ^HFC ) ² ] ^0.5
In formulas (4) and (5), δD ^HFP , δP ^HFP , and δH ^HFP represent the dispersion term, polar term, and hydrogen bond term in the Hansen solubility parameter of HFP, respectively, δD ^HFC , δP ^HFC , and δH ^HFC represent the dispersion term, polar term, and hydrogen bond term in the Hansen solubility parameter of HFC, respectively, and δD ^R22 , δP ^R22 , and δH ^R22 represent the dispersion term, polar term, and hydrogen bond term in the Hansen solubility parameter of R22, respectively, all in units of (MPa) ^1/2 .
The dispersion term, polarity term, and hydrogen bond term in the Hansen solubility parameters of each compound are values estimated from literature values or the chemical structure of the compound using computer software (Hansen Solubility Parameters in Practice (HSPiP) version 4). The Hansen solubility parameter of a mixture containing two or more compounds is calculated as the vector sum of the Hansen solubility parameters of each compound multiplied by the volume ratio of each compound to the entire mixture.

From the viewpoint of separating R22 and HFP with high efficiency, the molar ratio of the amount of HFC added in the mixing step 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. Hereinafter, the molar ratio of the amount of HFC added relative to the total molar amount of R22 and HFP in the mixing step is also referred to as "molar ratio (HFC/(R22+HFP))".
For example, as described below, when a first mixture containing R22 and HFP is supplied to the extractive distillation column, and an extraction solvent containing an HFC is further supplied to the extractive distillation column, the "molar ratio (HFC/(R22+HFP))" represents the molar ratio of the amount of HFC supplied to the extractive distillation column to the total amount of R22 and HFP supplied to the extractive distillation column.

The timing of adding the extractive solvent to the first mixture in the mixing step is not particularly important as long as it is before the extractive distillation step. From the viewpoint of efficiency of the distillation operation, it is preferable to carry out the extractive distillation step simultaneously with the mixing step in which the first mixture is supplied to the extractive distillation column and the extractive solvent is further supplied to the extractive distillation column to prepare the mixture for extraction in the column.
In the mixing step, for example, an extraction solvent is added to the first mixture to obtain a mixture of the first mixture and the extraction solvent, but an operation of mixing the first mixture with the extraction solvent may be performed separately.

<Extractive distillation process>
In the extractive distillation step, the mixture for extraction obtained in the mixing step is distilled to obtain a first distillate mainly composed of R22 and a first bottoms product mainly composed of the extraction solvent and containing HFP.

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

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 products. In order to perform the distillation operation economically, taking into account the temperatures of the condensers and reheaters 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. Extractive distillation can be performed in a batch or continuous manner, and in some cases in a semi-continuous manner in which the distillate and bottom products are intermittently withdrawn or intermittently charged, but it is preferable to continuously supply the extraction solvent to the distillation apparatus.

The extraction solvent has affinity for HFP. Therefore, by extractively distilling the mixture for extraction containing R22, HFP and the extraction solvent, a first distillate containing R22 as the main component is obtained from the top side of the extractive distillation tower. The composition of this first distillate is not limited as long as it contains R22 as the main component, but the molar fraction of R22 in the first distillate is preferably 90 mol% or more, more preferably 99 mol% or more. In addition, the molar fraction of HFP in the first distillate is preferably 1/10 or less of the molar fraction of HFP in the first mixture, more preferably 1/100 or less. The molar fraction of HFP in the first distillate is preferably 10 mol% or less, more preferably 1 mol% or less.
The first distillate containing high concentrations of R22 may be reused as a feedstock for producing HFP.

A first bottom product containing HFP, which is mainly composed of the extractive solvent and has affinity for the extractive solvent, is obtained from the bottom side of the extractive distillation column. The molar fraction of HFP relative to the total of R22 and HFP contained in the first bottom product is preferably 90 mol% or more, more preferably 99 mol% or more. The molar fraction of R22 relative to the total of R22 and HFP contained in the first bottom product is preferably 1/10 or less, more preferably 1/100 or less, of the molar fraction of R22 in the first mixture. The molar fraction of R22 relative to the total of R22 and HFP contained in the first bottom product is preferably 10 mol% or less, more preferably 1 mol% or less.
In addition, when the first mixture contains CTFE, the first bottoms product contains CTFE.
The first bottom product preferably further undergoes a second distillation step described below.

<Second distillation step>
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 the boiling point difference between the extraction solvent contained in the first bottom product and HFP, which is an affinity component thereof, is large, the second distillation step can be easily carried out by a normal distillation separation operation. The second distillation step can be carried out using a distillation apparatus similar to that of the above-mentioned extractive distillation step. Various conditions of the second distillation step, such as the operating temperature, operating pressure, reflux ratio, total number of stages of the distillation column, position of the charging stage, etc., are not particularly limited and can be appropriately selected to achieve the desired separation.

The second distillation step separates the extracting solvent and HFP, and a second distillate containing HFP and having a molar fraction of HFP relative to the total of R22 and HFP increased from the molar fraction of HFP relative to the total of R22 and HFP in the first mixture, i.e., HFP is concentrated compared to the first mixture, is obtained from the top side of the distillation column. The molar 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.
In addition, when the first mixture contains CTFE, the second distillate also contains CTFE. When the second distillate contains CTFE, it is preferable that the second distillate further undergoes an adsorption step described later.

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

<Adsorption process>
As described above, when the second distillate contains CTFE, the separation method of this embodiment may further include an adsorption step of contacting the second distillate with an adsorbent to obtain a purified product mainly composed of HFP.

Examples of the adsorbent include synthetic zeolite, activated carbon, activated alumina, metal organic frameworks, porous coordination polymers, covalent organic frameworks, etc. The adsorbent may be used alone or in combination of two or more kinds.
From the viewpoint of efficient separation of HFP and CTFE, it is preferable to use synthetic zeolite as the adsorbent, that is, the adsorbent preferably contains synthetic zeolite.
Examples of synthetic zeolite include A-type zeolite, X-type zeolite, beta-type zeolite, ferrierite-type zeolite, modelnite-type zeolite, L-type zeolite, and Y-type zeolite, and among them, from the viewpoint of efficiently separating HFP and CTFE, A-type zeolite is preferred, and 5A-type zeolite is more preferred.Furthermore, examples of synthetic zeolite include improved synthetic zeolite with acid resistance.
Examples of ion species coordinated in the molecular framework of synthetic zeolite include potassium ions, sodium ions, calcium ions, etc. From the viewpoint of obtaining a pore size suitable for adsorption of CTFE, the synthetic zeolite preferably contains calcium ions.
The pore size of the synthetic zeolite is preferably 0.42±0.03 nm.

In the adsorption step, for example, the second distillate is passed through a packed tower filled with an adsorbent, so that CTFE is adsorbed on the adsorbent, and high-purity HFP with less CTFE, that is, the refined product mainly composed of HFP is obtained.The mole fraction of HFP in the refined 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 refined product is preferably 1.00 mol% or less, more preferably 0.50 mol% or less, and even more preferably 0.10 mol% or less.
When the second distillate contains compounds other than HFP and CTFE, the separation method of the present embodiment may further include a removal step of removing the other compounds, if necessary.

In this embodiment, the R22 and HFP contained in the first mixture are efficiently separated in the manner described above. As a result, R22 is obtained in high concentration as the main component of the first distillate in the extractive distillation process, and HFP, which is more concentrated than the first mixture, is obtained as the second distillate in the second distillation process. Then, by passing through an adsorption process or the like as necessary, HFP of even higher purity can be obtained.

Next, the flow of materials in the separation method of this embodiment will be described with reference to FIG.
As shown in FIG. 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 extractive distillation column 2 operated under pressure, for example. The extractive distillation column 2 has 1 to 100 stages, and the first mixture 1 is supplied to the extractive distillation column 2. An extractive solvent 3 containing HFC at a molar fraction 1 to 30 times the total molar fraction of R22 and HFP contained in the first mixture 1 is supplied to a stage above the stage to which the first mixture 1 is supplied to the extractive distillation column 2. Distillation is thus performed, and a first distillate 4 containing R22, which is a component that does not have affinity for the extractive solvent 3, as a main component is extracted from the top side of the extractive distillation column 2. In the obtained first distillate 4, the molar fraction of R22 relative to the total of R22 and HFP is increased compared to a similar molar fraction in the first mixture 1. In this way, the first distillate 4 is obtained which has an increased molar fraction of R22 compared to the first mixture 1, i.e., a mixture having a concentrated molar concentration of R22.

Also, a mixture containing HFP and mainly containing the extractive solvent is withdrawn as a first bottom product 5 from the bottom side of the extractive distillation column 2. The first bottom product 5 is then fed to a solvent recovery column 6, which is another distillation column operated under pressure, for example, and a second distillate 7 substantially free of the extractive solvent is obtained from the top side of the column. In the obtained second distillate 7, the molar fraction of HFP relative to the total of R22 and HFP is increased compared to the similar molar fraction in the first mixture 1. Thus, a mixture having an increased molar fraction of HFP compared to the first mixture 1, i.e., a mixture having a concentrated molar concentration of HFP, is obtained as the second distillate 7.
In this specification, the term "substantially free of A" means that the content of A is 0.1 mol % or less.

A second bottom product 8 containing the extraction solvent 3 as a main component is obtained from the bottom side of the solvent recovery column 6. The extraction solvent 3 is thus recovered, and the recovered extraction solvent 3 is reused. The reused extraction solvent 3 is heated or cooled by a heat exchanger 9 as necessary, and then supplied to the extractive distillation column 2.
In FIG. 1, reference numeral 10 denotes a condenser, and reference numeral 11 denotes a heater.

In the extractive 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 be supplied to the same stage at which the reflux is supplied. In some cases, the extraction solvent 3 may be supplied to the same stage as the first mixture 1. Furthermore, the first mixture 1 may be mixed with the extraction solvent 3 in advance before being supplied to the extractive distillation column 2 and then supplied.
By using the above-mentioned apparatus and operations, R22 and HFP can be separated from the first mixture 1 containing R22 and HFP, and HFP substantially free of R22 can be obtained.

Next, the flow of materials when the first mixture contains CTFE will be described with reference to FIG.
2, a first mixture 21 containing R22, HFP, and CTFE is supplied to a stage below the center of extractive distillation column 2, and an extraction solvent 3 containing HFC is supplied to a stage of extractive distillation column 2 above the supply stage of first mixture 21, and distillation is performed. Then, a first distillate 4 containing R22 as a main component is withdrawn from the top side of extractive distillation column 2, and a mixture containing HFP and CTFE and containing the extraction solvent as a main component is withdrawn as first bottoms 25 from the bottom side of extractive distillation column 2.
Next, the first bottoms 25 is supplied to the solvent recovery column 6 and distilled, and a second distillate 27 substantially free of the extractive solvent and containing HFP and CTFE is obtained from the top side of the solvent recovery column 6, and a second bottoms 8 mainly containing the extractive solvent 3 is obtained from the bottom side of the solvent recovery column 6. The extractive solvent 3 recovered as the second bottoms 8 is supplied to the extractive distillation column 2 for reuse.

Next, the obtained second distillate 27 is supplied from the lower part of the packed tower 12, the inside of which is filled with an adsorbent containing, for example, 5A type zeolite, while adjusting the pressure, and is caused to flow through the inside of the packed tower 12. The CTFE contained in the second distillate 27 is adsorbed by the adsorbent filled inside the packed tower 12, and a refined product 13 containing HFP as a main component is obtained from an outlet at the top of the packed tower 12. In the refined product 13, the molar fraction of HFP relative to the total of HFP and CTFE is increased compared to the molar fraction of HFP relative to the total of HFP and CTFE in the second distillate 27.
By using the above-mentioned apparatus and operations, R22, CTFE, and HFP can be separated from the first mixture 21 containing R22, CTFE, and HFP, and HFP substantially free of R22 and CTFE can be obtained.

[Composition]
The composition according to one embodiment of the present disclosure includes HFP and R22, and the content of HFP is 99.5% by mass or more relative to the entire composition. The content of HFP relative to the entire 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 according to this embodiment is obtained, for example, by separating a first mixture containing R22 and HFP by the above-mentioned separation method.

The composition of the present embodiment may contain other compounds in addition to HFP and R22. Examples of other compounds contained in the composition include the same as the specific examples of other compounds that may be contained in the first mixture described above.
The composition of the present embodiment may contain CTFE as another compound. The composition containing HFP, R22 and CTFE, and having an HFP content of 99.5 mass% or more relative to the entire composition, can be obtained, for example, by separating a first mixture containing R22, HFP and CTFE by the above-mentioned separation method.

The following provides a detailed explanation of the embodiments of the present disclosure using examples, but the embodiments of the present disclosure are not limited to these.

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

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

(Example A1)
A mixture of R22 and HFP having a molar ratio (HFP/R22) of 1/3 was continuously supplied at 1 kmol per hour from the 50th plate from the top of a 60-plate distillation column, and distillation was performed, and a first distillate was continuously withdrawn from the top side at 0.61 kmol per hour, and a first bottom product was continuously withdrawn from the bottom side at 0.39 kmol per hour. During this time, the pressure in 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 in the first distillate as a whole was 93 mol % for R22 and 7 mol % for HFP, while the content of each component in the first bottoms as a whole was 46 mol % for R22 and 54 mol % for HFP.

(Example A2)
A mixture of R22 and HFP having a molar ratio (HFP/R22) of 1/3 was continuously fed at 1 kmol per hour from the 50th plate from the top of a 60-plate extractive distillation column, and 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane was continuously fed at a rate of 3 kmol per hour from the 10th plate from the top of the column. Hereinafter, 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane is also referred to as "HFC-52-13p".
Then, extractive distillation was continuously performed with the pressure in the extractive distillation column set to 0.5 MPaG (gauge pressure), the column top temperature set to 6.19° C., and the column bottom temperature set to 103.11° C. A first distillate was distilled from the top side of the extractive distillation column at a rate of 0.76 kmol per hour, and a first bottom product was discharged from the bottom side of the column at a rate of 3.24 kmol per hour.

In the first distillate that was withdrawn, no HFC-52-13p was detected, the content of R22 in the entire first distillate was 98.7 mol%, and the remaining component was HFP. On the other hand, the content of each component in the entire first bottoms product was 19 mol ppm for R22, 7.4 mol% for HFP, and the remainder was the extraction solvent, HFC-52-13p.

Next, the first bottom product was continuously supplied at 1 kmol per hour from the 20th plate from the top of a 30-plate solvent recovery tower, and distillation was continuously performed at a pressure of 0.4 MPaG (gauge pressure) in the solvent recovery tower, a top temperature of 15.21° C., and a bottom temperature of 128.27° C. The second distillate was distilled from the top side of the solvent recovery tower at a rate of 0.24 kmol per hour, and the second bottom product was withdrawn from the bottom side at a rate of 3 kmol per hour.
The compositions of the withdrawn second distillate and second bottoms product were analyzed, and the contents of the respective components relative to the entire second distillate were 99.97 mol % for HFP, 0.026 mol % for R22, and the remainder being the extraction solvent. On the other hand, the contents of the respective components relative to the entire second bottoms product were 99.99 mol % or more for HFC-52-13p.

In the above examples, Example A2 is an embodiment and Example A1 is a comparative example. As shown in Table 3, in Example A2, R22 and HFP are separated more efficiently than in Example A1, and HFP with high purity is obtained.

[Separation of HFP and CTFE]
The adsorbents shown in the table below were packed into a cylindrical stainless steel packed tower with an inner diameter of 1 inch and an axial length of 50 cm. Next, the pressure in the packed tower was adjusted to 0.1 MPaG, and a mixture of HFP 95.587 GC% and CTFE 4.413 GC% was passed through the bottom of the packed tower, and after 1 hour, a sample was taken from the outlet of the packed tower and analyzed by gas chromatography. The results are shown in Table 4.
In the following table, "MS-4A" means 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" means 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" means molecular sieves 13X (manufactured by Union Showa Co., Ltd., metal ion: Na, effective pore size: 1.0 nm), and "AW-500" means molecular sieves AW-500 (manufactured by Union Showa Co., Ltd., acid-resistant molecular sieve).

According to one embodiment of the present disclosure, R22 and HFP can be efficiently separated from a mixture containing R22 and HFP. Furthermore, according to one embodiment of the present disclosure, HFP, which is useful as a raw material for, for example, the production of fluororesins, can be obtained in high concentration, which is economically advantageous.

1, 21 First mixture 2 Extractive distillation column 3 Extraction solvent 4 First distillate 5, 25 First bottom product 6 Solvent recovery column 7, 27 Second distillate 8 Second bottom product 9 Heat exchanger 10 Condenser 11 Heater 12 Packed column 13 Purified product

Claims (16)

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 mixture for extraction to obtain a first distillate mainly composed of chlorodifluoromethane and a first bottom product mainly composed of the extraction solvent and containing hexafluoropropylene;
The method for separating chlorodifluoromethane and hexafluoropropylene comprises the steps of: The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 1, wherein the hydrofluorocarbon has a boiling point of 0 to 120°C. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 1, wherein the hydrofluorocarbon is a compound that makes the relative volatility Rv of chlorodifluoromethane to hexafluoropropylene greater than 1.1 when the hydrofluorocarbon is added in an amount three times the total molar amount of chlorodifluoromethane and hexafluoropropylene. 2. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 1, wherein the interaction distance Ra ^HFP between hexafluoropropylene and the hydrofluorocarbon calculated from the value of the Hansen solubility parameter is smaller than the interaction distance Ra ^R22 between chlorodifluoromethane and the hydrofluorocarbon. 5. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 4, wherein the ratio of the interaction distance Ra ^HFP to the interaction distance Ra ^R22 is 0.7 or less. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 1, wherein the hydrofluorocarbon has a carbon number of 2 to 8. 2. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 1, wherein the hydrofluorocarbon comprises at least one selected from the group consisting of saturated compounds represented by the following formula (1) and unsaturated compounds 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. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 1, wherein the hydrofluorocarbon includes 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. 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 relative to the total molar amount of chlorodifluoromethane and hexafluoropropylene. The method for separating chlorodifluoromethane and hexafluoropropylene according to any one of claims 1 to 9, further comprising a second distillation step of distilling the first bottoms to obtain a second distillate containing hexafluoropropylene as a main component. The first mixture further comprises chlorotrifluoroethylene;
The first can further comprises chlorotrifluoroethylene.
2. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 1. The first mixture further comprises chlorotrifluoroethylene;
The first can further comprises chlorotrifluoroethylene;
The second distillate further comprises chlorotrifluoroethylene.
The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 10. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 12, further comprising an adsorption step of contacting the second distillate with an adsorbent to obtain a purified product mainly composed of hexafluoropropylene. The method for separating chlorodifluoromethane and hexafluoropropylene according to claim 13, wherein the adsorbent includes synthetic zeolite. A composition comprising hexafluoropropylene and chlorodifluoromethane, the content of hexafluoropropylene being 99.5% by mass or more relative to the total amount of the composition. The composition of claim 15, further comprising chlorotrifluoroethylene.