Method for producing purified difluoromethane (HFC-32), and composition containing HFC-32

Abstract

The present disclosure provides a method for efficiently purifying difluoromethane (HFC-32).　Specifically, the present disclosure provides a method for producing purified HFC-32, the method comprising an extractive distillation step for bringing a composition containing HFC-32 and a component X into contact with a solvent A to obtain a composition containing a reduced amount of the component X, wherein the component X is at least one selected from the group consisting of pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), and dichlorodifluoromethane (CFC-12), and the solvent A is at least one of an amine or a fluorinated ether.

Description

Method for producing purified difluoromethane (HFC-32) and composition containing HFC-32

[0001] The present disclosure relates to a method for producing purified difluoromethane (HFC-32) and compositions containing HFC-32.

[0002] HFC-32 is useful as a refrigerant or as a raw material for mixed refrigerants in combination with other components (for example, HFC-410A, which is a mixed refrigerant of HFC-32 and HFC-125).

[0003] In relation to the present disclosure, for example, Patent Document 1 discloses a method for separating HFC-32 and HFC-125. In detail, it discloses "a method for separating HFC-32 and HFC-125 from a first mixture by using an extractant comprising methylene chloride, the method comprising the steps of adding the extractant to the first mixture to produce a second mixture, separating HFC-32 and HFC-125 in the second mixture by extractively distilling the second mixture in an extractive distillation zone of a distillation column, and thereby recovering HFC-125 as an overhead product of the column and HFC-32 from the bottom of the column."

[0004] JP 2007-91762 A

[0005] An object of the present disclosure is to provide a method for efficiently purifying HFC-32 and a composition containing HFC-32.

[0006] The present disclosure includes, for example, aspects described in the following items. Item 1. A method for producing purified HFC-32, comprising an extractive distillation step of contacting a composition containing difluoromethane (HFC-32) and component X with a solvent A to obtain a composition in which the content of component X has been reduced from the composition, wherein component X is at least one selected from the group consisting of pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), and dichlorodifluoromethane (CFC-12), and solvent A is at least one of an amine and a fluorinated ether. Item 2. The production method according to item 1 above, further comprising a distillation step of distilling the composition containing component X and solvent A obtained from the bottom of the extractive distillation column after the extractive distillation step to separate component X from solvent A. Item 3. Item 4. The production method according to item 1 or 2, wherein the extractive distillation step using a first distillation column for performing the extractive distillation step is performed under a pressure of 0.05 to 5 MPaG (gauge pressure). Item 5. The production method according to item 1 or 3, wherein the distillation step using a second distillation column for performing the distillation step is performed under a pressure of 0.05 to 3 MPaG (gauge pressure). Item 6. The production method according to any one of items 1 to 4, further comprising a solvent recovery step of recovering the solvent A used in the extractive distillation step and recycling the recovered solvent A to the extractive distillation step. Item 7. The amine is a compound represented by the general formula: NR １ R ２ R ３ [In the formula, R １ , R ２ and R ３ are the same or different and represent hydrogen or a hydrocarbon group having 1 to 3 carbon atoms which may have a substituent. １ , R ２ and R ３Item 7. The method according to any one of items 1 to 6, wherein the amine is at least one selected from the group consisting of monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, mono-n-propylamine, di-n-propylamine, tri-n-propylamine, mono-isopropylamine, and di-isopropylamine. Item 8. The method according to any one of items 1 to 6, wherein the fluorinated ether is represented by the general formula R ４ -O-R ５ [In the formula, R ４ and R ５ are the same or different C ｎ H ｍ F ｌwherein n is an integer of 1 to 20, m+l=2n+1, and m and l are integers of 0 or more. Item 9. The method according to any one of items 1 to 8, wherein the fluorinated ether is at least one selected from the group consisting of 1,1,1,2,2,3,3,4,4-nonafluoro-4-methoxybutane (HFE-7100), 1,1,1,2,2,3,3,4,4-nonafluoro-4-ethoxybutane (HFE-7200), and 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-(trifluoromethyl)pentane (HFE-7300). Item 10. Item 11. A composition containing difluoromethane (HFC-32), component X, and substance A, wherein the total concentration of the three components is 99.5% by mass or more with respect to the entire composition, component X is at least one selected from the group consisting of pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), and dichlorodifluoromethane (CFC-12), and substance A is at least one of an amine and a fluorinated ether, and the content of component X is more than 0% by mass and not more than 0.4% by mass with respect to the entire composition, and the content of substance A is more than 0% by mass and not more than 0.1% by mass with respect to the entire composition. Item 11. A composition containing difluoromethane (HFC-32) and a substance A, wherein the total concentration of the two components is 99.5% by mass or more relative to the total composition, said substance A being at least one of an amine and a fluorinated ether, and the content of said substance A is more than 0% by mass and 0.1% by mass or less relative to the total composition. Item 12. A composition containing difluoromethane (HFC-32) and a component X, wherein the total concentration of the two components is 99.5% by mass or more relative to the total composition, said component X being at least one selected from the group consisting of pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), and dichlorodifluoromethane (CFC-12), and the content of said component X is more than 0% by mass and 0.4% by mass or less relative to the total composition.Item 13. The method comprises an extractive distillation step of contacting a composition containing difluoromethane (HFC-32) and component X with a solvent A to obtain a composition in which the component X has been reduced from the composition, wherein the component X is at least one selected from the group consisting of pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), and dichlorodifluoromethane (CFC-12), and the solvent A is at least one of an amine and a fluorinated ether, wherein the extractive distillation step using a first distillation column for performing the extractive distillation step is performed under a pressure of 0.05 to 5 MPaG (gauge pressure), and wherein the distillation step using a second distillation column for performing the distillation step is performed under a pressure of 0.05 to 3 MPaG (gauge pressure), a method for producing purified HFC-32, wherein the amine is at least one selected from the group consisting of monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, mono-n-propylamine, di-n-propylamine, tri-n-propylamine, mono-isopropylamine, and di-isopropylamine; and the fluorinated ether is at least one selected from the group consisting of 1,1,1,2,2,3,3,4,4-nonafluoro-4-methoxybutane (HFE-7100), 1,1,1,2,2,3,3,4,4-nonafluoro-4-ethoxybutane (HFE-7200), and 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-(trifluoromethyl)pentane (HFE-7300).

[0007] According to the present disclosure, it is possible to efficiently purify HFC-32.

[0008] 1 is a diagram showing an outline of the process for producing purified HFC-32 according to the present disclosure, in which HFC-125, HFC-143a, and CFC-12 constituting component X mean that at least one of these three components is contained.

[0009] As a result of intensive research, the present inventors have found that HFC-32 can be efficiently purified by a production method including an extractive distillation step of contacting a composition containing HFC-32 and at least one member (component X) selected from the group consisting of pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), and dichlorodifluoromethane (CFC-12) with a specific solvent to obtain a composition in which the content of component X has been reduced from the composition.

[0010] The present disclosure was completed as a result of further research based on this finding.

[0011] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits (i.e., "greater than or equal to, less than or equal to").

[0012] In this specification, an azeotropic composition means a composition that behaves as if it were a single substance, with no difference in composition between the liquid phase and the vapor phase under a constant pressure.

[0013] As used herein, an azeotrope-like composition refers to a composition that can form an azeotropic composition, has a composition that is close to the azeotropic composition, and exhibits behavior similar to that of an azeotropic composition. An azeotrope-like composition can be distilled and / or refluxed with little change in composition. Therefore, an azeotrope-like composition can be handled almost equivalently to an azeotropic composition. One characteristic of an azeotrope-like composition is that the difference in pressure between the boiling point curve and the dew point curve on a pressure-composition diagram is within 5%.

[0014] In this specification, the normal boiling point means the boiling point at a standard atmospheric pressure of 1013.25 hPa.

[0015] In this specification, gauge pressure refers to a relative pressure based on atmospheric pressure, and means the pressure difference obtained by subtracting atmospheric pressure from absolute pressure. In this specification, gauge pressure is expressed with the letter "G" added, for example, MPaG. On the other hand, when "G" is not added, it means absolute pressure.

[0016] In this specification, the "purity" of a refrigerant refers to the component ratio (mol % or mass %) determined by quantitative analysis using gas chromatography.

[0017] In this specification, the term "main component" means a component that is contained in an amount of preferably 85 mol% to 99.9 mol%, more preferably 90 mol% to 99.9 mol%, even more preferably 95 mol% to 99.9 mol%, and particularly preferably 99 mol% to 99.9 mol%.

[0018] In this specification, extractive distillation refers to a distillation operation in which an extracting solvent is added to a mixture of two or three components that have very close standard boiling points and are difficult to separate by conventional distillation, and whose relative volatility (relative volatility) is close to 1, or to a mixture of a combination that has an azeotropic composition, to prepare a mixture for extraction, thereby making the relative volatility of the original two or three components farther from 1, thereby facilitating separation. Note that if the relative volatility is 1, separation by distillation is impossible.

[0019] In this specification, the relative volatility (α) is the ratio of the molar fraction of liquid phase component A to the molar fraction of liquid phase component B when the composition containing at least component A and component B is in a vapor-liquid equilibrium state. Ａ , the mole fraction of the liquid phase component B is x Ｂ The mole fraction of gas phase component A in equilibrium with the liquid phase is y Ａ , the mole fraction of gas phase component B is y Ｂ In this case, the relative volatility of component A to component B is α Ａ→Ｂ = (y Ａ / x Ａ ) / (y Ｂ / x Ｂ ) is defined as:

[0020] In this specification, when component A is HFC-32 and component B is HFC-125, the relative volatility of component A relative to component B, that is, the "relative volatility of HFC-32 relative to HFC-125", is expressed as α 32→125 It is written as follows.

[0021] The present disclosure includes the following embodiments.

[0022] The production method disclosed herein is a method for producing purified HFC-32, comprising an extractive distillation step of contacting a composition containing difluoromethane (HFC-32) and component X with a solvent A to obtain a composition in which the content of component X has been reduced from the composition, wherein component X is at least one selected from the group consisting of pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), and dichlorodifluoromethane (CFC-12), and solvent A is at least one of an amine and a fluorinated ether.

[0023] In the extractive distillation step, it is preferable to apply the production method of the present disclosure, particularly when the composition containing HFC-32 and component X (also referred to as the "composition for extractive distillation" or the "feedstock composition") is an azeotropic composition or an azeotrope-like composition. Here, component X, i.e., HFC-125, HFC-143a, and CFC-12, can all form an azeotropic composition or an azeotrope-like composition when mixed with HFC-32. In recent years, the recovery of used refrigerants (particularly mixed refrigerants) and the recycling of specific components have been promoted, and therefore, in the present disclosure, for example, used HFC-410A (a mixed refrigerant of HFC-32 and HFC-125) can be used as the composition for extractive distillation (feedstock composition).

[0024] (Extractive Distillation Step) The extractive distillation step in the production method of the present disclosure is a step of contacting a composition (composition for extractive distillation) containing component X (at least one selected from the group consisting of HFC-125, HFC-143a, and CFC-12) and HFC-32 with solvent A (at least one of an amine and a fluorinated ether) to obtain a composition in which component X has been reduced from the composition. In other words, the extractive distillation step is a step of subjecting a composition (composition for extractive distillation) containing component X and HFC-32 to extractive distillation in the presence of solvent A to obtain a composition in which component X has been reduced from the composition. In the present disclosure, "reduction" in the extractive distillation step means reducing the content of a specific compound (component X) in the composition for extractive distillation.

[0025] The composition for extractive distillation contains component X and HFC-32 in a total concentration of preferably 99.5% by mass or more, more preferably 99.7% by mass or more, even more preferably 99.8% by mass or more, and even more preferably 99.9% by mass or more. For example, when component X is primarily HFC-125, the composition for extractive distillation can be prepared by recovering used HFC-410A, optionally removing easily separable by-products through a prior separation step (such as an optional distillation step), and then obtaining a composition (particularly an azeotropic composition or azeotrope-like composition) containing HFC-125 and HFC-32 preferably in the total concentration described above.

[0026] Similarly, ・HFC-407A (HFC-32+HFC-125+HFC-134a) ・HFC-407B (HFC-32+HFC-125+HFC-134a) ・HFC-407C (HFC-32+HFC-125+HFC-134a)・HFC-407D (HFC-32+HFC-125+HFC-134a) ・HFC-407E (HFC-32+HFC-125+HFC-134a) ・HFC-407F (HFC-32+HFC-125+HFC-134a) ・HFC-407H (HFC-32+HFC-125+HFC-134a) ・HFC-407I (HFC-32+HFC-125+HFC-134a) ・HFC-410B (HFC-32+HFC-125)・HFC-425A (HFC-32+HFC-134a+HFC-227ea) ・HFC-427A (HFC-32+HFC-125+HFC-134a+HFC-143a)・R-438A (HFC-32+HFC-125+HFC-134a+R-600+R601a) ・R-439A (HFC-32+HFC-125+R600a) ・R-442A (HFC-32+HFC-125+HFC-134a+HFC-152a+HFC-227ea)・R-444A (HFC-32+HFC-152a+HFO-1234ze(E)) ・R-448A(HFC-32+HFC-125+HFC-134a+HFO-1234ze(E)+HFO-1234yf)・R-449A (HFC-32+HFC-125+HFC-134a+HFO-1234yf) ・R-452A (HFC-32+HFC-125+HFO-1234yf) ・HFC-458A (HFC-32+HFC-125+HFC-134a+HFC-227ea+HFC-236fa)・R-463A (R-744+HFC-32+HFC-125+HFO-1234yf+HFC-134a) ・R-466A (HFC-32+HFC-125+CF ３ I) A composition for extractive distillation can be obtained by subjecting a used recovered refrigerant mixture containing one or more components X, such as R-504 (HFC-32+HCFC-115), and HFC-32 as constituent components to an optional distillation process.

[0027] The composition for extractive distillation preferably consists only of HFC-32 and component X, but it is acceptable for the composition for extractive distillation to contain inevitable impurities depending on the conditions of the preparation process of the composition for extractive distillation. The above-mentioned phrase "the composition for extractive distillation contains component X and HFC-32 in a total concentration of preferably 99.5% by mass or more" means that the composition for extractive distillation consists essentially of HFC-32 and component X, or, even if it contains other components, they are only inevitable impurities.

[0028] HFC-125 (standard boiling point: -48.1°C), which is one type of component X, and HFC-32 (standard boiling point: -51.7°C) are azeotropic or azeotrope-like, and the azeotropic or azeotrope-like composition of HFC-125 and HFC-32 has a boiling point that is lower than the boiling points of both HFC-125 and HFC-32 (the azeotropic composition at 0.1013 MPa is HFC-32 / HFC-125=87.8 / 12.2 (mol %), and the temperature is -51.8°C). Furthermore, HFC-143a (standard boiling point: -47.3°C), which is one type of component X, and HFC-32 (standard boiling point: -51.7°C) exhibit an azeotrope or azeotrope-like reaction, and the azeotropic composition or azeotrope-like composition of HFC-143a and HFC-32 has a boiling point that is lower than the boiling points of both HFC-143a and HFC-32 (the azeotropic composition at 0.1013 MPa is HFC-32 / HFC-143a=77.8 / 22.2 (mol %), and the temperature is -52.5°C). Furthermore, CFC-12 (normal boiling point: -29.8°C), which is one type of component X, and HFC-32 (normal boiling point: -51.7°C) exhibit an azeotrope or azeotrope-like reaction, and the azeotropic or azeotrope-like composition of CFC-12 and HFC-32 has a boiling point lower than the boiling points of both CFC-12 and HFC-32 (the azeotropic composition at 0.1013 MPa is HFC-32 / CFC-12=96.5 / 3.5 (mol%), and the temperature is -51.7°C). The composition for extractive distillation supplied to the extractive distillation step preferably has a molar ratio of HFC-32 of 50.0% or more and 99.999% or less, more preferably 70.0% or more and 99.999% or less. The composition containing HFC-32 as a main component obtained by extractive distillation preferably has a molar ratio of HFC-32 of 99.500% or more, more preferably 99.900% or more, and even more preferably 99.999% or more.

[0029] The extractive distillation step is preferably a step in which the composition for extractive distillation is contacted with a solvent A and subjected to extractive distillation to obtain a composition containing HFC-32 and substantially free of component X.

[0030] As used herein, "substantially free of component X" means that the content of component X in the composition obtained in the extractive distillation step (when two or more of HFC-125, HFC-143a, and CFC-12 are contained, the total amount thereof) is preferably less than 1 mass%, more preferably less than 0.5 mass%, and particularly preferably less than 0.1 mass%.

[0031] In the extractive distillation step, solvent A, which is at least one of an amine and a fluorinated ether, is used as the extractive solvent. The extractive solvent in the present disclosure preferably consists of at least one of an amine and a fluorinated ether, but it is acceptable for the solvent to contain unavoidable impurities to the extent that they do not affect the extractive distillation step. Hereinafter, solvent A will also be referred to simply as the extractive solvent in the present disclosure.

[0032] The amine may be a liquid amine that can be used as an extraction solvent, but may also be a liquid amine of the general formula: NR １ R ２ R ３ [In the formula, R １ , R ２ and R ３ are the same or different and represent hydrogen or a hydrocarbon group having 1 to 3 carbon atoms which may have a substituent. １ , R ２ and R ３ and the case where all of the amines are hydrogen is excluded.]

[0033] The amine preferably has a normal boiling point of -10 to 160°C.

[0034] The amine is preferably at least one selected from the group consisting of monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, mono-n-propylamine, di-n-propylamine, tri-n-propylamine, mono-isopropylamine, and di-isopropylamine. Among these amines, at least one of diethylamine and triethylamine is more preferred, as the operating conditions of the distillation column can be easily adjusted to pressure and temperature that facilitate operation. The Cas No. and normal boiling points of these amines are shown in Table 1 below.

[0035]

[0036] These amines may be used alone or in combination of two or more.

[0037] The fluorinated ether may be any fluorinated ether as long as it can be used as an extracting solvent. ４ -O-R ５ [In the formula, R ４ and R ５ are the same or different C ｎ H ｍ F ｌ where n is an integer of 1 to 20, m+l=2n+1, and m and l are integers of 0 or more.

[0038] The fluorinated ether is preferably at least one selected from the group consisting of 1,1,1,2,2,3,3,4,4-nonafluoro-4-methoxybutane (HFE-7100), 1,1,1,2,2,3,3,4,4-nonafluoro-4-ethoxybutane (HFE-7200), and 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-(trifluoromethyl)pentane (HFE-7300). Among these fluorinated ethers, at least one selected from the group consisting of HFE-7100, HFE-7200, and HFE-7300 is particularly preferred from the viewpoints of handleability, operating temperature, and the like. The Cas No. and normal boiling points of these fluorinated ethers are shown in Table 2 below.

[0039]

[0040] (However, since HFE-7100 and HFE-7200 are both two-component mixtures, the Cas Nos. of the constituent components are listed together.) These fluorinated ethers can be used alone or in combination of two or more.

[0041] The mixing ratio of the amine and the fluorinated ether in the solvent A is not limited either, and the solvent A may contain only the amine, the fluorinated ether, or a mixture of these two in any ratio.

[0042] Regarding the temperature range of the standard boiling point in the extractive distillation step, the temperature difference between the extractive solvent and the compounds to be separated in the extractive distillation step should be sufficient to allow separation by simple distillation, stripping, etc., typically a temperature difference of 20°C or more. However, if the standard boiling point is too high, there is a risk that the extractive solvent itself will decompose. Therefore, from the viewpoint of efficiently performing the extractive distillation, the standard boiling point of the extractive solvent is preferably 30 to 135°C, more preferably 35 to 120°C, even more preferably 40 to 100°C, and particularly preferably 50 to 90°C.

[0043] The amount of the extractive solvent used in the extractive distillation step is preferably from 1 to 30 molar equivalents, and more preferably from 5 to 25 molar equivalents, relative to the composition for extractive distillation supplied to the extractive distillation column.

[0044] The concentration of component X in the composition for extractive distillation in the extractive distillation step is preferably 50 mol % or less, more preferably 30 mol % or less, and even more preferably 10 mol % or less.

[0045] The number of theoretical plates of the extractive distillation column used in the extractive distillation step is preferably 10 or more, more preferably 20 or more. From an economical viewpoint, the number of theoretical plates of the extractive distillation column used in the extractive distillation step is preferably 100 or less, more preferably 70 or less.

[0046] In the extractive distillation step, it is preferable to supply the extractive solvent to the upper stage of the extractive distillation column. The extractive solvent used in the extractive distillation step is preferably the extractive solvent recovered and recycled in the extractive solvent recovery step described below.

[0047] In the extractive distillation step, the pressure at which the extractive distillation is carried out (the pressure in the first distillation column) is preferably 0.05 to 5 MPaG (gauge pressure). The lower limit of the pressure is preferably 0.05 MPaG, more preferably 0.1 MPaG, even more preferably 0.25 MPaG, and particularly preferably 0.5 MPaG. The upper limit of the pressure is preferably 5 MPaG, more preferably 4 MPaG, even more preferably 3 MPaG, and particularly preferably 2 MPaG.

[0048] The extractive distillation step can be carried out as a discontinuous operation or a continuous operation, and from an industrial point of view, it is preferable to carry out the extractive distillation step as a continuous operation. Furthermore, by repeating the extractive distillation, the distillate components can be highly purified.

[0049] In the extractive distillation step, when HFC-32 is distilled from the composition for extractive distillation, it is preferable to use an extractive solvent such that when the extractive solvent is added, the relative volatility (specific volatility) of HFC-32 to component X is 1.70 or more, preferably 2.00 or more. This increases the vapor phase molar fraction of HFC-32, thereby increasing the amount of HFC-32 in the vapor phase, making it possible to separate HFC-32 from the top of the extractive distillation column, and the extractive solvent and component X are obtained from the bottom of the extractive distillation column.

[0050] (Extraction Solvent Recovery Step) The production method of the present disclosure preferably includes an extraction solvent recovery step of recovering the extraction solvent used in the extractive distillation step and recycling the recovered extraction solvent to the extractive distillation step.

[0051] The extractive solvent recovery step includes a distillation step (hereinafter also referred to as the "distillation step") of distilling a composition containing component X and solvent A obtained from the bottom of the extractive distillation column after the extractive distillation step to separate component X from solvent A, and can be carried out by recovering the extractive solvent from the composition containing solvent A and recycling it to the extractive distillation step. Note that the distillation step of separating component X from solvent A is preferably a distillation step of separating into a composition containing component X as a main component and a composition containing the extractive solvent as a main component.

[0052] The number of theoretical plates of the solvent recovery column (second distillation column) used in the distillation step is preferably 5 or more, more preferably 10 or more. From an economical viewpoint, the number of theoretical plates of the solvent recovery column is preferably 40 or less, more preferably 30 or less.

[0053] In the distillation step, the pressure at which the distillation is carried out is preferably 0.05 to 3 MPaG (gauge pressure). The lower limit of the pressure is preferably 0.05 MPaG, more preferably 0.1 MPaG. The upper limit of the pressure is preferably 3 MPaG, more preferably 2.5 MPaG.

[0054] By the above distillation step, a composition containing component X as a main component can be separated from the top of the solvent recovery column, and a composition containing the extraction solvent as a main component can be obtained from the bottom of the solvent recovery column.

[0055] The extractive solvent recovery step can be carried out by recovering the extractive solvent from the composition containing the extractive solvent as a main component obtained from the bottom of the column in the distillation step and recycling it to the extractive distillation step. Note that the extractive solvent recovered from the bottom of the column can also be subjected to an optional separation step such as rectification to remove impurities, if necessary, before being recycled to the extractive distillation step.

[0056] The distillation step can be carried out as a discontinuous operation or a continuous operation, and from an industrial point of view, it is preferably carried out as a continuous operation.

[0057] The production method of the present disclosure preferably includes an extractive distillation step and an extractive solvent recovery step, and more preferably comprises an optional preliminary distillation step for increasing the purity of the composition for extractive distillation, an extractive distillation step, and an extractive solvent recovery step.

[0058] (Composition Comprising HFC-32, Component X, and Substance A (Refrigerant 1)) The present disclosure encompasses a composition comprising difluoromethane (HFC-32), component X, and substance A (hereinafter also referred to as "refrigerant 1"). Component X is the same as that described in the extractive distillation step above, and is at least one selected from the group consisting of pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), and dichlorodifluoromethane (CFC-12). The type of substance A is the same as that of solvent A described in the extractive distillation step above, and is at least one of an amine and a fluorinated ether.

[0059] Refrigerant 1 is a composition containing HFC-32, component X, and substance A, in which the total concentration of the three components is 99.5 mass% or more relative to the entire composition, the content of component X is more than 0 mass% and not more than 0.4 mass% relative to the entire composition, and the content of substance A is more than 0 mass% and not more than 0.1 mass% relative to the entire composition. Refrigerant 1 is a composition containing purified HFC-32 finally obtained by the production method of the present disclosure, in which trace amounts of component X and extraction solvent (solvent A) remain. The expression "more than 0 mass%" can also be expressed as "0.01 mass% or more."

[0060] The total concentration of the three components in Refrigerant 1 is preferably 99.7% by mass or more, more preferably 99.8% by mass or more, and even more preferably 99.9% by mass or more, based on the total composition.

[0061] It is particularly preferred that Refrigerant 1 consists of only HFC-32, Component X, and Substance A, but it is acceptable for unavoidable impurities to be contained.

[0062] The use of the refrigerant 1 is not limited, but it can be used as an air conditioning refrigerant, a heat transfer medium, a refrigerant for car air conditioners, and the like.

[0063] (Composition containing HFC-32 and component X (refrigerant 2)) The present disclosure encompasses a composition containing difluoromethane (HFC-32) and component X (hereinafter also referred to as "refrigerant 2"). The type of component X is the same as described above.

[0064] Refrigerant 2 is a composition containing HFC-32 and component X, in which the total concentration of the two components is 99.5 mass% or more relative to the entire composition, and the content of component X is more than 0 mass% and not more than 0.4 mass% relative to the entire composition. Refrigerant 2 is a composition containing purified HFC-32 finally obtained by the production method of the present disclosure, in which a trace amount of component X remains. The expression "more than 0 mass%" can also be expressed as "0.01 mass% or more."

[0065] The total concentration of the two components in the refrigerant 2 is preferably 99.7% by mass or more, more preferably 99.8% by mass or more, and even more preferably 99.9% by mass or more, based on the total composition.

[0066] It is particularly preferable that the refrigerant 2 consists of only HFC-32 and component X, but it is acceptable for unavoidable impurities to be contained.

[0067] The use of the refrigerant 2 is not limited, but it can be used as an air conditioning refrigerant, a heat transfer medium, a refrigerant for car air conditioners, and the like.

[0068] (Composition containing purified HFC-32) The present disclosure encompasses, as a composition containing purified HFC-32, a composition containing HFC-32 and substance A (hereinafter also referred to as "composition 1"). The type of substance A is the same as described above.

[0069] Composition 1 is a composition containing HFC-32 and substance A, in which the total concentration of the two components is 99.5 mass% or more relative to the total composition, and the content of substance A is more than 0 mass% and not more than 0.1 mass% relative to the total composition. Note that composition 1 is a composition containing purified HFC-32 finally obtained by the production method of the present disclosure, in which a trace amount of extraction solvent (solvent A) remains. Note that the expression "more than 0 mass%" can also be expressed as "0.01 mass% or more."

[0070] The total concentration of the two components in composition 1 is preferably 99.7% by mass or more, more preferably 99.8% by mass or more, and even more preferably 99.9% by mass or more, based on the total concentration of composition 1.

[0071] It is particularly preferred that Composition 1 consists of only HFC-32 and Substance A, but it is acceptable for unavoidable impurities to be contained.

[0072] The uses of Composition 1 are not limited, but it can be used as a leak detector, stabilizer, tracer, etc. when using refrigerants.

[0073] The present disclosure will be specifically described below with reference to examples, but the present disclosure is not limited to these examples.

[0074] In the examples, the concentrations of each component such as HFC-32 were measured using the following measuring device and under the following measuring conditions.

[0075] Measuring device: Gas chromatography (using an FID detector) Method for calculating the concentration of each component: Concentration of HFC-32 = number of moles of HFC-32 / (number of moles of HFC-32 + number of moles of component X) Concentration of component X = number of moles of component X / (number of moles of HFC-32 + number of moles of component X)

[0076] Examples 1 to 5 and Comparative Examples 1 to 14 To a composition containing 70 mol % of HFC-32 and 30 mol % of HFC-125, each solvent was added in an amount 6 times by mole relative to the composition, and the relative volatility α of HFC-32 to HFC-125 at 5°C was measured. ３２→１２５ was measured.

[0077] In Example 1, diethylamine was used as the solvent, and the relative volatility α ３２→１２５ In Example 2, triethylamine was used as the solvent, and the relative volatility α ３２→１２５ In Example 3, HFE-7300 was used as the solvent, and the relative volatility α ３２→１２５ In Example 4, HFE-7200 was used as the solvent, and the relative volatility α ３２→１２５ In Example 5, HFE-7100 was used as the solvent, and the relative volatility α ３２→１２５ In Comparative Example 1, isopropyl alcohol (IPA) was used as the solvent, and the relative volatility α ３２→１２５ In Comparative Example 2, tetrahydrofuran (THF) was used as the solvent, and the relative volatility α ３２→１２５ In Comparative Example 3, ethanol was used as the solvent, and the relative volatility α ３２→１２５ In Comparative Example 4, 2-butanol was used as the solvent, and the relative volatility α ３２→１２５ In Comparative Example 5, methyl ethyl ketone (MEK) was used as the solvent, and the relative volatility α ３２→１２５ In Comparative Example 6, n-propanol was used as the solvent, and the relative volatility α ３２→１２５ In Comparative Example 7, ethyl acetate was used as the solvent, and the relative volatility α ３２→１２５ In Comparative Example 8, isobutanol was used as the solvent, and the relative volatility α ３２→１２５ In Comparative Example 9, methanol was used as the solvent, and the relative volatility α ３２→１２５ In Comparative Example 10, acetone was used as the solvent, and the relative volatility α ３２→１２５ In Comparative Example 11, hexane was used as the solvent, and the relative volatility α ３２→１２５ In Comparative Example 12, 5-fluoropropanol was used as the solvent, and the relative volatility α ３２→１２５ In Comparative Example 13, trifluoroethanol was used as the solvent, and the relative volatility α ３２→１２５ In Comparative Example 14, acetonitrile was used as the solvent, and the relative volatility α ３２→１２５was 0.69.

[0078] The results are summarized in Table 3 below.

[0079]

[0080] From the above results, it was found that amines such as diethylamine and triethylamine, and fluorinated ethers such as HFE-7300, HFE-7200, and HFE-7100 are effective as extraction solvents.

[0081] Each of the solvents used in Examples 1 to 5 had a relative volatility α of HFC-32 to HFC-143a at 5°C. ３２→１４３ａ , and the relative volatility α of HFC-32 to CFC-12 at 5°C ３２→１２ are both 1.70 or more, and it has been found that this method is effective not only for the separation of HFC-32 from HFC-125 by extractive distillation, but also for the separation of HFC-32 from HFC-143a and / or CFC-12 by extractive distillation.

[0082] Example 6 In accordance with the flow diagram shown in Figure 1, purified HFC-32 was produced using a composition for extractive distillation containing HFC-32 and component X (HFC-125) as a raw material and HFE-7100 as an extractive solvent by a process consisting of an extractive distillation step and an extractive solvent recovery step.

[0083] (Extractive distillation step) The extractive distillation composition was supplied to the extractive distillation column having 70 theoretical plates at a flow rate of 956 mol / hr from the 45th plate from the top of the column. The extractive solvent (HFE-7100) was supplied to the extractive distillation column from the 3rd plate at a flow rate of 9650 mol / hr. The operating pressure of the extractive distillation column was 0.5 MPaG, and the column top temperature was -10 ° C.

[0084] (Extraction Solvent Recovery Step) The bottoms withdrawn from the column bottom in the extractive distillation step were fed to the fifth plate from the top of an extraction solvent recovery column (hereinafter referred to as the "solvent recovery column") having 15 theoretical plates, and HFC-125 was recovered from the column top at a purity of 99.99%. The operating pressure of the solvent recovery column was 0.4 MPaG, and the column top temperature was -9°C.

[0085] The bottoms containing HFE-7100 (flow rate of HFE-7100: 144 mol / hr) extracted from the bottom of the recovery column were recycled to the extractive distillation step.

[0086] The mass balance for Example 6 using the process of Figure 1 was as follows: F1: 667.1 mol / hr of HFC-32, 289.1 mol / hr of HFC-125, and 9650.6 mol / hr of HFE-7100 (extraction solvent). F2: 6.7 mol / hr of HFC-32, 289.1 mol / hr of HFC-125, and 9650.2 mol / hr of HFE-7100 (extraction solvent). F3: 660.4 mol / hr of HFC-32, 0.0014 mol / hr of HFC-125, and trace amounts (less than 0.1 ppm) of HFE-7100 (extraction solvent). In F4, the amount of HFC-32 was trace (0.1 ppm or less), the amount of HFC-125 was 0.005 mol / hr, and the amount of HFE-7100 (extraction solvent) was 9650.6 mol / hr. In F5, the amounts of HFC-32 were 6.7 mol / hr, HFC-125 was 289.1 mol / hr, and HFE-7100 (extraction solvent) was 0.002 mol / hr. Table 4 below shows the breakdown of the contents of the three components at each of positions F1, F2, F3, F4, and F5 in the process of Example 6 (the total amount of the contents of the three components is 100 mol%).

[0087]

[0088] The amines shown in Examples 1 and 2 and the fluorinated ethers shown in Examples 3 to 5 all have a relative volatility α of HFC-32 relative to component X (HFC-125, HFC-143a, CFC-12). ３２→成分Ｘ is 1.70 or more, which is larger than those of the comparative examples (1.69 or less), and indicates that the separation efficiency is improved compared to those of the comparative examples in that a relatively high concentration of HFC-32 can be secured in the gas phase. Therefore, in the separation of component X and HFC-32, the process of the present disclosure, which uses an amine and at least one extractant (solvent A) selected from fluorinated ethers in the extractive distillation step, is very effective.

[0089] 1. Extractive distillation column 2. Solvent recovery column

Claims

1. A method for producing purified HFC-32, comprising an extractive distillation step of contacting a composition containing difluoromethane (HFC-32) and component X with a solvent A to obtain a composition in which the content of component X has been reduced from the composition, wherein the component X is at least one selected from the group consisting of pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), and dichlorodifluoromethane (CFC-12), and the solvent A is at least one of an amine and a fluorinated ether.

2. The method according to claim 1, further comprising a distillation step of distilling a composition containing said component X and said solvent A obtained from the bottom of the extractive distillation column after said extractive distillation step to separate said component X from said solvent A.

3. The method according to claim 1 or 2, wherein the extractive distillation step using the first distillation column for carrying out the extractive distillation step is carried out under a pressure of 0.05 to 5 MPaG (gauge pressure).

4. The method according to claim 2 or 3, wherein the distillation step using the second distillation column for carrying out the distillation step is carried out under a pressure of 0.05 to 3 MPaG (gauge pressure).

5. The method according to any one of claims 1 to 4, further comprising a solvent recovery step of recovering the solvent A used in the extractive distillation step and recycling the recovered solvent A to the extractive distillation step.

6. The amine has the general formula: NR １ R ２ R ３ [In the formula, R １ , R ２ and R ３ are the same or different and each represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms which may have a substituent. １ , R ２ and R ３ The method according to any one of claims 1 to 5, wherein all of the formulas are hydrogen.

7. The method according to any one of claims 1 to 6, wherein the amine is at least one selected from the group consisting of monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, mono-n-propylamine, di-n-propylamine, tri-n-propylamine, mono-isopropylamine, and di-isopropylamine.

8. The fluorinated ether has the general formula R ４ -O-R ５ [In the formula, R ４ and R ５ are the same or different C ｎ H ｍ F ｌ wherein n is an integer of 1 to 20, m+l is 2n+1, and m and l are integers of 0 or more.

9. The method according to any one of claims 1 to 8, wherein the fluorinated ether is at least one selected from the group consisting of 1,1,1,2,2,3,3,4,4-nonafluoro-4-methoxybutane (HFE-7100), 1,1,1,2,2,3,3,4,4-nonafluoro-4-ethoxybutane (HFE-7200), and 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-(trifluoromethyl)pentane (HFE-7300).

10. A composition containing difluoromethane (HFC-32), component X, and substance A, wherein the total concentration of the three components is 99.5% by mass or more with respect to the entire composition, said component X is at least one selected from the group consisting of pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), and dichlorodifluoromethane (CFC-12), said substance A is at least one of an amine and a fluorinated ether, and the content of said component X is more than 0% by mass and 0.4% by mass or less with respect to the entire composition, and the content of said substance A is more than 0% by mass and 0.1% by mass or less with respect to the entire composition.

11. A composition containing difluoromethane (HFC-32) and substance A, wherein the total concentration of the two components is 99.5 mass% or more relative to the entire composition, said substance A is at least one of an amine and a fluorinated ether, and the content of said substance A is more than 0 mass% and 0.1 mass% or less relative to the entire composition.

12. A composition containing difluoromethane (HFC-32) and component X, wherein the total concentration of the two components is 99.5 mass% or more relative to the entire composition, said component X is at least one selected from the group consisting of pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), and dichlorodifluoromethane (CFC-12), and the content of said component X is more than 0 mass% and 0.4 mass% or less relative to the entire composition.

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