Method for separating 1, 1, 1, 3, 3-pentafluoropropane from hydrogen fluoride

Abstract

The invention provides a method for separating 1, 1, 1, 3, 3-pentafluoropropane and hydrogen fluoride, which adopts ionic liquid as an extracting agent to separate 1, 1, 1, 3, 3-pentafluoropropane and hydrogen fluoride from a mixture of 1, 1, 1, 3, 3-pentafluoropropane and hydrogen fluoride through extractive distillation, the ionic liquid is ionic liquid containing bis (trifluoromethanesulfonyl) imine anions. According to the separation method, when the extraction agent is recycled, the operation temperature in the kettle of the flash evaporator is low; according to the invention, high-efficiency separation of 1, 1, 1, 3, 3-pentafluoropropane and hydrogen fluoride can be realized, the use amount of the extraction agent is reduced, and the production cost is reduced. The solubility of hydrogen fluoride in the ionic liquid can be improved, so that the escape difficulty of HFC-245fa is lower under the same condition, and the purpose of remarkably improving the relative volatility of a hydrogen fluoride and HFC-245fa azeotropic system is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, relates to polyfluoroolefins, and specifically relates to a method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride. Background Art

[0002] 1,1,1,3,3-pentafluoropropane (HFC-245fa) is the raw material for synthesizing 1,3,3,3-tetrafluoropropylene (HFO-1234ze). HFO-1234ze has zero ozone depletion potential and a greenhouse effect potential of 6. It has excellent environmental performance and is considered to be an ideal substitute for 1,1,1,2-tetrafluoroethane (HFC-134a).

[0003] HFC-245fa can be synthesized by liquid phase fluorination of hydrogen fluoride and 1,1,1,3,3-pentachloropropane (HCC-240fa) as raw materials. Due to the catalyst activity and the reaction characteristics, the reactor outlet is generally a mixture of HFC-245fa and hydrogen fluoride, and the typical product composition is 40-50% HFC-245fa by mass. HFC-245fa (boiling point is 15.3℃) and hydrogen fluoride (boiling point is 19.5℃) have similar boiling points, and conventional separation technology is difficult to separate the two.

[0004] The Chinese patent with the authorization announcement number CN101952229B reports a method of enriching HFC-245fa in the bottom of the tower by adding 1,3,3,3-tetrafluoropropylene (HFO-1234ze) to a mixture of HFC-245fa and hydrogen fluoride to form a ternary azeotrope, and then performing two or three distillations on the top of the tower to separate relatively pure hydrogen fluoride. Since this method obtains a ternary azeotrope of HFO-1234ze, HFC-245fa and hydrogen fluoride at the top of the tower, the top of the secondary distillation tower is relatively pure HFO-1234ze, and the azeotrope of HFC-245fa and hydrogen fluoride flows out from the bottom of the tower. The azeotrope is subjected to three distillations to obtain hydrogen fluoride with higher purity, which has high operating costs, large equipment investment, and a large amount of extractant.

[0005] The Chinese patent application publication number CN107074541A reports a method for extracting hydrogen fluoride from a mixture of HFC-245fa and hydrogen fluoride using an ionic liquid containing halogen anions as an extractant, wherein the main approach is to separate and purify HF by forming a homogeneous system with the extractant and HF. Since this method retains a certain amount of HFC-245fa in the absorption phase, multiple cycles are required, and the amount of extractant used is large, which is not easy to recover and has a high separation cost. Summary of the invention

[0006] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride, so as to solve the technical problem that the operating temperature in the kettle of the flash evaporator needs to be further reduced when an ionic liquid extractant is used for separation in the prior art.

[0007] Another object of the present invention is to provide a method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride, so as to solve the technical problem of large amount of extractant required when using ionic liquid extractant for separation in the prior art.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions to achieve the above problems:

[0009] A method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride, wherein the method uses an ionic liquid as an extractant and separates 1,1,1,3,3-pentafluoropropane and hydrogen fluoride from a mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride through extractive distillation.

[0010] The ionic liquid is an ionic liquid containing bis(trifluoromethanesulfonyl)imide anion.

[0011] The present invention also has the following technical features:

[0012] Preferably, the extractant is recovered by a flash evaporator, and the operating conditions of the flash evaporator are: the operating pressure in the kettle is 1-5 kPa, and the operating temperature in the kettle is 305-329°C.

[0013] Preferably, the mass ratio of the bis(trifluoromethanesulfonyl)imide ionic liquid to the mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is (0.8-1.4):1.

[0014] Preferably, the ionic liquid increases the relative volatility α of 1,1,1,3,3-pentafluoropropane to hydrogen fluoride to 27.62-27.95; the boiling point of the ionic liquid is in the range of 10°C-250°C.

[0015] Preferably, the boiling point of the ionic liquid is in the range of 113.5°C to 131.7°C.

[0016] Preferably, the bis(trifluoromethanesulfonyl)imide ionic liquid is 1,3-dimethylimidazole bis(trifluoromethanesulfonyl)imide ([C 1 mim][Tf 2 N]), 1-methylpyridine bis(trifluoromethanesulfonyl)imide ([C 1 Py][Tf 2 N]), tributyl(ethyl)phosphonium bis(trifluoromethanesulfonyl)imide ([P 4442 ][Tf2 N]) or triethyl(methyl)ammonium bis(trifluoromethanesulfonyl)imide ([N 2111 ][Tf 2 N]).

[0017] Preferably, the mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is composed of the following raw materials in parts by weight: 40% to 50% of 1,1,1,3,3-pentafluoropropane and 50% to 60% of hydrogen fluoride, and the sum of the parts by weight of the raw materials is 100%.

[0018] Preferably, the extractive distillation adopts an extractive distillation tower; the bis(trifluoromethanesulfonyl)imide ionic liquid extractant is fed from the upper part of the extractive distillation tower, and the mixture of raw materials 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is fed from the bottom of the extractive distillation tower; the top fraction of the extractive distillation tower is 1,1,1,3,3-pentafluoropropane product, and the bottom fraction of the extractive distillation tower is hydrogen fluoride and the extractant.

[0019] Further preferably, the operating conditions of the extractive distillation tower are: tower operating pressure is 90-110 kPa, tower top temperature is 15-20°C, tower bottom temperature is 186-272°C, and reflux ratio is 0.0005-0.06.

[0020] Further preferably, the bottom fraction of the flash evaporator is the extractant, and the extractant is circulated to the extractive distillation tower.

[0021] Compared with the prior art, the present invention has the following technical effects:

[0022] (I) The separation method of the present invention has a low operating temperature in the kettle of the flash evaporator when recovering the extractant; it can achieve efficient separation of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride, reduce the amount of extractant used, and reduce production costs.

[0023] (II) The present invention has been verified by quantum chemical calculation and gas-liquid equilibrium experiment, and found that in the ionic liquid of the present invention, there is a strong hydrogen bonding interaction between the bis(trifluoromethanesulfonyl)imide anion containing ionic sites and hydrogen fluoride, and the precise regulation of the intermolecular interaction by cations such as imidazole, pyridine, quaternary phosphonium, and quaternary ammonium can improve the solubility of hydrogen fluoride in the ionic liquid of the present invention, so that under the same conditions, the escape difficulty of HFC-245fa is lower, so as to achieve the purpose of significantly improving the relative volatility of the azeotropic system of hydrogen fluoride and HFC-245fa.

[0024] (III) The present invention utilizes the characteristic that the addition of the selected extractant can significantly change the relative volatility of HFC-245fa and hydrogen fluoride, and uses two devices, an extractive distillation tower and an extractant recovery flash evaporator, to separate the HFC-245fa mixture, which can efficiently separate HFC-245fa and hydrogen fluoride. The entire purification process adopts industrially mature distillation technology, and the operation process is simple and easy to implement. At the same time, the extractant used is a conventional, non-highly corrosive organic solvent, and the purification process is green and safe. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The figure is a schematic flow diagram of a method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride.

[0026] The meanings of the various numbers in the figure are: T1-extractive distillation tower, F1-flash evaporator,

[0027] The specific contents of the present invention are further explained in detail below in conjunction with embodiments. DETAILED DESCRIPTION

[0028] It should be noted that all raw materials and reagents in the present invention, unless otherwise specified, are all raw materials and reagents known in the prior art and can be obtained from commercial channels. All experimental methods in the present invention, unless otherwise specified, are conventional methods.

[0029] In the present invention, the principle of extractive distillation is to change the relative volatility of HFC-245fa and hydrogen fluoride by adding an ionic liquid extractant containing bis(trifluoromethanesulfonyl)imide anion, so that the relative volatility of HFC-245fa relative to hydrogen fluoride is greater than 1, thereby separating the two. Here, the relative volatility (α) of HFC-245fa relative to hydrogen fluoride is defined as follows:

[0030]

[0031] To determine the relative volatility α of HFC-245fa relative to hydrogen fluoride after the extractant is added. The present invention uses a 300ml stainless steel reactor with gas and liquid sampling valves. Add 50g of extractant and 32g of HFC-245fa / hydrogen fluoride mixture (wherein the HFC-245fa content is 45wt.%) to the reactor. Immerse the reactor in a 15°C constant temperature oil bath, and stir the materials magnetically to fully mix the materials. When the materials in the reactor reach gas-liquid equilibrium, take gas and liquid samples, and determine the composition content of each phase by gas chromatography. According to the above relative volatility definition formula, the relative volatility α value of each experiment is calculated, and the relevant experimental results are shown in Table 1.

[0032] Table 1 α value after adding extractant

[0033]

[0034] As can be seen from Table 1, the addition of imidazole, pyridine, quaternary phosphonium and quaternary ammonium ionic liquids with boiling points in the range of 113.5°C to 131.7°C changes the relative volatility of HFC-245fa relative to hydrogen fluoride, and α changes from less than 1 when no extractant is added to significantly greater than 1, making the relatively non-volatile HFC-245fa more volatile, that is, the HFC-245fa product can be obtained from the top of the tower through extractive distillation.

[0035] From the extractants tested in Table 1, it can be seen that the preferred extractant in the present invention is 1,3-dimethylimidazole bis (trifluoromethanesulfonyl) imide ([C 1 mim][Tf 2 N]).

[0036] The present invention verifies through quantum chemical calculation and gas-liquid equilibrium experiment that in the above-mentioned ionic liquid, there is a strong hydrogen bond between the bis(trifluoromethanesulfonyl)imide anion containing an ionic site and hydrogen fluoride, and the precise regulation of the intermolecular interaction by cations such as imidazole, pyridine, quaternary phosphonium and quaternary ammonium can improve the solubility of hydrogen fluoride in the above-mentioned ionic liquid, so that under the same conditions, the escape difficulty of HFC-245fa is lower, so as to achieve the purpose of significantly improving the relative volatility of the azeotropic system of hydrogen fluoride and HFC-245fa.

[0037] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0038] Embodiment 1:

[0039] This embodiment provides a method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride. The method uses an ionic liquid as an extractant to separate 1,1,1,3,3-pentafluoropropane and hydrogen fluoride from a mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride by extractive distillation.

[0040] The ionic liquid is 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ([C 1 mim][Tf 2 N]).

[0041] The mass ratio of the ionic liquid to the mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is 1.4:1.

[0042] The extractive distillation adopts an extractive distillation tower; the extractant is recovered by a flash evaporator.

[0043] The operation process of this method:

[0044] The extractive distillation tower T1 is a packed tower with a diameter of Φ25 mm and is filled with Φ3*3θ ring stainless steel packing. The packing layer height is 0.8 m. The distillation material feed is the crude product of synthetic HFC-245fa, in which the mass percentage of HFC-245fa is 40% and the mass percentage of HF is 60%.

[0045] The crude product of synthesized HFC-245fa is fed from the middle of the extractive distillation tower T1 at a flow rate of 100 g / h. The ionic liquid (i.e., circulating extractant, ionic liquid) at the bottom of the F1 extractant recovery flasher is fed from the upper part of the extractive distillation tower T1 at a flow rate of 100 g / h. The top distillate HFC-245fa of the extractive distillation tower T1 is the HFC-245fa product. The extractant containing hydrogen fluoride in the bottom distillate of the T1 tower is HF and extractant, which enters the extractant recovery flasher F1. The top distillate hydrogen fluoride of the flasher F1 extractant recovery flasher is the HF product, and the bottom effluent of the flasher F1 is the extractant, which is returned to the extractive distillation tower T1. The operating conditions of the extractive distillation tower T1 and the flasher F1 are shown in Table 2, and the logistics composition is shown in Table 3.

[0046] Table 2 Tower and flash evaporator operating conditions in Example 1

[0047]

[0048] Table 3 Logistics composition in Example 1

[0049]

[0050] Embodiment 2:

[0051] This embodiment provides a method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride. The method uses an ionic liquid as an extractant to separate 1,1,1,3,3-pentafluoropropane and hydrogen fluoride from a mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride by extractive distillation.

[0052] The ionic liquid is 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ([C 1 mim][Tf 2 N]).

[0053] The mass ratio of the ionic liquid to the mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is 1:1.

[0054] The extractive distillation adopts an extractive distillation tower; the extractant is recovered by a flash evaporator.

[0055] The operation process of this embodiment is basically the same as that of Embodiment 1, except that the operating parameters of the distillation tower T1 and the extractant recovery flash evaporator F1 are different. The operating parameters are shown in Table 4, and the logistics composition of Embodiment 2 is shown in Table 5.

[0056] Table 4 Tower and flash evaporator operating conditions in Example 2

[0057]

[0058]

[0059] Table 5 Logistics composition in Example 2

[0060]

[0061] Embodiment 3:

[0062] This embodiment provides a method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride. The method uses an ionic liquid as an extractant to separate 1,1,1,3,3-pentafluoropropane and hydrogen fluoride from a mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride by extractive distillation.

[0063] The ionic liquid is 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ([C 1 mim][Tf 2 N]).

[0064] The mass ratio of the ionic liquid to the mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is 1.25:1.

[0065] The extractive distillation adopts an extractive distillation tower; the extractant is recovered by a flash evaporator.

[0066] The operation process of this embodiment is basically the same as that of embodiment 1, except that the composition of the feed material is changed to HFC-245fa 50%, HF 50%, the flow rate of the extractant is adjusted to 1000 g / h, the operating parameters are shown in Table 6, and the logistics composition of embodiment 3 is shown in Table 7.

[0067] Table 6 Tower and flash evaporator operating conditions in Example 3

[0068]

[0069] Table 7 Logistics composition in Example 3

[0070]

[0071]

[0072] Embodiment 4:

[0073] This embodiment provides a method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride. The method uses an ionic liquid as an extractant to separate 1,1,1,3,3-pentafluoropropane and hydrogen fluoride from a mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride by extractive distillation.

[0074] The ionic liquid is 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ([C 1 mim][Tf 2 N]).

[0075] The mass ratio of the ionic liquid to the mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is 0.8:1.

[0076] The extractive distillation adopts an extractive distillation tower; the extractant is recovered by a flash evaporator.

[0077] The operation process of this embodiment is basically the same as that of embodiment 2, except that the composition of the feed material is changed to HFC-245fa 60%, HF 40%. The operation parameters are shown in Table 8, and the logistics composition of embodiment 4 is shown in Table 9.

[0078] Table 8 Tower operating conditions in Example 4

[0079]

[0080] Table 9 Logistics composition in Example 4

[0081]

[0082] Comparative Example 1:

[0083] This comparative example provides a method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride. The method uses an ionic liquid as an extractant to separate 1,1,1,3,3-pentafluoropropane and hydrogen fluoride from a mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride by extractive distillation.

[0084] The ionic liquid is 1-ethyl-3-methylimidazolium chloride.

[0085] The mass ratio of the ionic liquid to the mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is the same as that in Example 1.

[0086] The extractive distillation adopts an extractive distillation tower; the extractant is recovered by a flash evaporator.

[0087] The operation process of this embodiment is basically the same as that of Example 1, except that the equipment operating conditions are different. The operating parameters are shown in Table 10, and the logistics composition of Comparative Example 1 is shown in Table 11.

[0088] Table 10 Tower and flash evaporator operating conditions in comparative example 1

[0089]

[0090] Table 11 Logistics composition in comparative example 1

[0091]

[0092] As shown in Example 1 and Comparative Example 1, under the same feeding conditions, the mass fraction of HFC-245fa outlet in Example 1 is 99.999%, which is higher than the mass fraction of HFC-245fa outlet in Comparative Example 1, i.e., 99%; there is no significant difference in the mass fraction of hydrogen fluoride between Example 1 and Comparative Example 1, and in addition, the operating temperature of 450°C in the kettle of the flash evaporator in Comparative Example 1 is much higher than the operating temperature of 329°C in the kettle of the flash evaporator in Example 1.

[0093] Comparative Example 2:

[0094] This comparative example provides a method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride. The method uses an ionic liquid as an extractant to separate 1,1,1,3,3-pentafluoropropane and hydrogen fluoride from a mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride by extractive distillation.

[0095] The ionic liquid is tributyl(ethyl)phosphonium chloride.

[0096] The mass ratio of the ionic liquid to the mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is the same as that in Example 2.

[0097] The extractive distillation adopts an extractive distillation tower; the extractant is recovered by a flash evaporator.

[0098] The operation process of this embodiment is basically the same as that of Example 2, except that the equipment operating conditions are different. The operating parameters are shown in Table 12, and the logistics composition of Comparative Example 2 is shown in Table 13.

[0099] Table 12 Tower and flash evaporator operating conditions in comparative example 2

[0100]

[0101] Table 13 Logistics composition in comparative example 2

[0102]

[0103] As shown in Example 2 and Comparative Example 2, under the same feed conditions, the mass fraction of HFC-245fa outlet in Example 2 is 99.99%, which is higher than the mass fraction of HFC-245fa outlet in Comparative Example 2 of 99.4%; there is no significant difference in the mass fraction of hydrogen fluoride between Example 2 and Comparative Example 2. In addition, the operating temperature of 541°C in the kettle of the flash evaporator in Comparative Example 2 is much higher than the operating temperature of 321°C in the kettle of the flash evaporator in Example 2.

[0104] Comparative Example 3:

[0105] This comparative example provides a method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride. The method uses an ionic liquid as an extractant to separate 1,1,1,3,3-pentafluoropropane and hydrogen fluoride from a mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride by extractive distillation.

[0106] The ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate.

[0107] The mass ratio of the ionic liquid to the mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is the same as that in Example 3.

[0108] The extractive distillation adopts an extractive distillation tower; the extractant is recovered by a flash evaporator.

[0109] The operation process of this example is basically the same as that of Example 3, except that the equipment operating conditions are different. The operating parameters are shown in Table 14, and the logistics composition of Comparative Example 3 is shown in Table 15.

[0110] Table 14 Tower and flash evaporator operating conditions in comparative example 3

[0111]

[0112] Table 15 Logistics composition in comparative example 3

[0113]

[0114] As shown in Example 3 and Comparative Example 3, under the same feed conditions, the mass fraction of HFC-245fa at the outlet in Example 3 is 99.99%, which is higher than the mass fraction of hydrogen fluoride at the outlet in Comparative Example 3, which is 99.4%. There is no significant difference in the mass fraction of HFC-245fa between Example 3 and Comparative Example 3. In addition, the operating temperature of 460°C in the kettle of the flash evaporator in Comparative Example 3 is much higher than the operating temperature of 315°C in the kettle of the flash evaporator in Example 3.

[0115] Comparative Example 4:

[0116] This comparative example provides a method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride. The method uses an ionic liquid as an extractant to separate 1,1,1,3,3-pentafluoropropane and hydrogen fluoride from a mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride by extractive distillation.

[0117] The ionic liquid is triethyl(methyl)ammonium chloride.

[0118] The mass ratio of the ionic liquid to the mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is the same as that in Example 4.

[0119] The extractive distillation adopts an extractive distillation tower; the extractant is recovered by a flash evaporator.

[0120] The operation process of this embodiment is basically the same as that of Example 4, except that the equipment operating conditions are different. The operating parameters are shown in Table 16, and the logistics composition of Comparative Example 4 is shown in Table 17.

[0121] Table 16 Tower and flash evaporator operating conditions in comparative example 4

[0122]

[0123] Table 17 Logistics composition in comparative example 4

[0124]

[0125]

[0126] As shown in Example 4 and Comparative Example 4, under the same feeding conditions, the mass fraction of the hydrogen fluoride outlet in Example 4 is 99.98%, which is higher than the mass fraction of the hydrogen fluoride outlet of Comparative Example 4, which is 99.5%. There is no significant difference in the mass fraction of hydrogen fluoride between Example 4 and Comparative Example 4. In addition, the operating temperature of 388°C in the kettle of the flash evaporator in Comparative Example 4 is much higher than the operating temperature of 305°C in the kettle of the flash evaporator in Example 4.

Claims

1. A method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride, wherein the method uses an ionic liquid as an extractant and separates 1,1,1,3,3-pentafluoropropane and hydrogen fluoride from a mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride by extractive distillation; characterized in that: The ionic liquid is an ionic liquid containing bis(trifluoromethanesulfonyl)imide anion.

2. The method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride according to claim 1, characterized in that: The extractant is recovered by a flash evaporator, and the operating conditions of the flash evaporator are as follows: the operating pressure in the kettle is 1-5 kPa, and the operating temperature in the kettle is 305-329°C.

3. The method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride according to claim 1, characterized in that: The mass ratio of the bis(trifluoromethanesulfonyl)imide ionic liquid to the mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is (0.8-1.4):

1.

4. The method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride according to claim 1, characterized in that: The ionic liquid increases the relative volatility α of 1,1,1,3,3-pentafluoropropane to hydrogen fluoride to 18.39-27.95; the boiling point of the ionic liquid is within the range of 10°C-250°C.

5. The method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride according to claim 4, characterized in that: The boiling point of the ionic liquid is in the range of 110°C to 135°C.

6. The method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride according to claim 1, characterized in that: The bis(trifluoromethanesulfonyl)imide ionic liquid is 1,3-dimethylimidazole bis(trifluoromethanesulfonyl)imide, 1-methylpyridine bis(trifluoromethanesulfonyl)imide, tributyl(ethyl)phosphonium bis(trifluoromethanesulfonyl)imide or triethyl(methyl)ammonium bis(trifluoromethanesulfonyl)imide.

7. The method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride according to claim 1, characterized in that: The mixture of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is composed of the following raw materials in parts by weight: 40% to 50% of 1,1,1,3,3-pentafluoropropane and 50% to 60% of hydrogen fluoride.

8. The method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride according to claim 1, characterized in that: The extractive distillation adopts an extractive distillation tower; the bis(trifluoromethanesulfonyl)imide ionic liquid extractant is fed from the upper part of the extractive distillation tower, and the mixture of raw materials 1,1,1,3,3-pentafluoropropane and hydrogen fluoride is fed from the bottom of the extractive distillation tower; the top fraction of the extractive distillation tower is 1,1,1,3,3-pentafluoropropane product, and the bottom fraction of the extractive distillation tower is hydrogen fluoride and the extractant.

9. The method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride according to claim 8, characterized in that: The operating conditions of the extractive distillation tower are as follows: the tower operating pressure is 90-110 kPa, the tower top temperature is 15-20° C., the tower bottom temperature is 186-272° C., and the reflux ratio is 0.0005-0.

06.

10. The method for separating 1,1,1,3,3-pentafluoropropane and hydrogen fluoride according to claim 8, characterized in that: The bottom fraction of the flash evaporator is the extractant, which is circulated to the extractive distillation tower.

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