Method for separating bis (trifluoromethyl) sulfide and trans-1, 3, 3, 3-tetrafluoropropene

Abstract

The invention belongs to the technical field of organic compound separation, and discloses a method for separating bis (trifluoromethyl) sulfide and trans-1, 3, 3, 3-tetrafluoropropene. According to the method disclosed by the invention, a ketone compound or an ester compound is used as an extracting agent, and the separation of the bis (trifluoromethyl) sulfide and the trans-1, 3, 3, 3-tetrafluoropropene is realized through extractive distillation. According to the method disclosed by the invention, efficient separation of the bis (trifluoromethyl) sulfide and trans-1, 3, 3, 3-tetrafluoropropene azeotropic system can be realized, the operation process is simple, the used extraction agent is a conventional and non-corrosive organic solvent, and the separation process is green and safe.

Description

Technical Field

[0001] The invention relates to the technical field of organic compound separation, and in particular to a method for separating bistrifluoromethyl sulfide and trans-1,3,3,3-tetrafluoropropylene. Background Art

[0002] Bis(trifluoromethyl)sulfide is a fluorinated sulfide with high dielectric strength, low boiling point, and low gross potential (GWP). It exhibits good environmental and safety characteristics, and has good application potential in electrical insulation and arc extinguishing media, and is expected to become a practical SF6 substitute gas. Trans-1,3,3,3-tetrafluoropropene (E-HFO-1234ze) has an ozone depletion potential (ODP) of 0 and a GWP of 6. It has excellent environmental performance and is considered to be an ideal substitute for trans-1,3,3,3-tetrafluoropropene (HFC-134a). Bis(trifluoromethyl)sulfide (boiling point is -22°C) and E-HFO-1234ze (boiling point is -18.9°C) have similar boiling points and are easy to form azeotropes. The vapor components of the azeotropes still maintain a relatively stable ratio, and it is difficult to completely separate the azeotropes by simple conventional separation techniques such as boiling and condensation. Summary of the invention

[0003] The object of the present invention is to overcome the deficiencies of the prior art and provide a method for efficiently separating bistrifluoromethyl sulfide and trans-1,3,3,3-tetrafluoropropylene with a green and safe operation process.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] In a first aspect, the present invention provides a method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropylene, comprising the following steps:

[0006] (1) taking a mixture of bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropylene as a raw material and an extractant;

[0007] The mass ratio of bistrifluoromethyl sulfide to trans-1,3,3,3-tetrafluoropropylene is 55-65:45-35;

[0008] The extractant is a ketone compound and / or an acid anhydride compound;

[0009] (2) feeding the extractant from the top of the extractive distillation tower, feeding the mixed raw material from the bottom of the extractive distillation tower, the top fraction of the extractive distillation tower is the bistrifluoromethyl sulfide product, and the bottom fraction is the trans-1,3,3,3-tetrafluoropropene product and the extractant;

[0010] (3) The bottom fraction of the tower is fed into an extractant recovery tower, the top fraction is the trans-1,3,3,3-tetrafluoropropene product, the bottom fraction is the extractant, and the bottom fraction is recovered and circulated to the extractive distillation tower.

[0011] The method of the present invention utilizes the characteristic that the addition of the selected extractant can significantly change the relative volatility of bistrifluoromethyl sulfide and trans-1,3,3,3-tetrafluoropropene, and uses two devices, an extractive distillation tower and an extractant recovery tower, to separate the trans-1,3,3,3-tetrafluoropropene and bistrifluoromethyl sulfide mixture, and can efficiently separate bistrifluoromethyl sulfide and trans-1,3,3,3-tetrafluoropropene, and the purity of bistrifluoromethyl sulfide and trans-1,3,3,3-tetrafluoropropene is above 99.5%. The entire separation process adopts industrially mature distillation technology, the operation process is simple, and the extractant used is a conventional, non-corrosive organic solvent, and the separation process is green and safe.

[0012] As a preferred embodiment of the method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropene of the present invention, in step (1): the extractant is a ketone compound containing 3 to 6 carbon atoms and / or an anhydride compound containing 5 to 8 carbon atoms.

[0013] As a further preferred embodiment of the method for separating bistrifluoromethyl sulfide and trans-1,3,3,3-tetrafluoropropene described in the present invention, the extractant is at least one of acetone, n-pentanone, 2-hexanone, cyclohexanone, monomethyl adipate, dimethyl adipate, dimethyl 2-methylglutarate, and dimethyl glutarate.

[0014] As a further preferred embodiment of the method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropene of the present invention, the extractant is n-pentanone and dimethyl 2-methylglutarate in a mass ratio of 1:1.

[0015] As a further preferred embodiment of the method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropene of the present invention, the extractant is 2-hexanone and dimethyl glutarate in a mass ratio of 3:1.

[0016] As a further preferred embodiment of the method for separating bistrifluoromethyl sulfide and trans-1,3,3,3-tetrafluoropropene of the present invention, the mass ratio of 2-hexanone, dimethyl adipate and dimethyl 2-methylglutarate is 1:1:1.

[0017] As a further preferred embodiment of the method for separating bistrifluoromethyl sulfide and trans-1,3,3,3-tetrafluoropropene of the present invention, the mass ratio of 2-hexanone, dimethyl adipate, dimethyl 2-methylglutarate and dimethyl glutarate is 1:2:1:2.

[0018] As a preferred embodiment of the method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropene of the present invention, in step (2): the mass ratio of the extractant to the mixture raw material is 13 to 15:1.

[0019] As a preferred embodiment of the method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropene according to the present invention, in step (2): the operating conditions of the extractive distillation tower are: the tower operating pressure is 170 kPa to 180 kPa, the tower top temperature is -9.1°C to -7.2°C, the tower bottom temperature is 115.6°C to 216.2°C, and the reflux ratio is 1.5 to 2.5.

[0020] As a preferred embodiment of the method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropene according to the present invention, in step (3): the operating conditions of the recovery tower are: the operating pressure in the tower is 160 kPa to 170 kPa, the tower top temperature is -7.4°C to -5.9°C, the tower bottom temperature is 132.5°C to 253.8°C, and the reflux ratio is 0.5 to 4.3.

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

[0022] The method of the present invention uses ketone compounds or ester compounds as extractants, and the addition of the selected extractants can significantly change the relative volatility of bistrifluoromethyl sulfide and trans-1,3,3,3-tetrafluoropropylene. The two devices of the extractive distillation tower and the extractant recovery tower are used to separate the trans-1,3,3,3-tetrafluoropropylene and bistrifluoromethyl sulfide mixture, so as to achieve the efficient separation of the azeotropic system of bistrifluoromethyl sulfide and trans-1,3,3,3-tetrafluoropropylene, and the purity of bistrifluoromethyl sulfide and trans-1,3,3,3-tetrafluoropropylene is above 99.5%. The whole separation process adopts the industrially mature distillation technology, the operation process is simple, and the extractant used is a conventional, non-corrosive organic solvent. The separation process is green and safe, and the amount of the extractant is low, and the production cost is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is a process flow chart for separation of bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropylene;

[0024] Figure 1The meanings of the numbers are as follows: T1—extractive distillation tower; T2—extractant recovery tower; feed—mixture of trans-1,3,3,3-tetrafluoropropene and bis(trifluoromethyl sulfide); bis(trifluoromethyl sulfide)—overhead distillate of the extractive distillation tower; extractant containing trans-1,3,3,3-tetrafluoropropene—bottom effluent of the extractive distillation tower; trans-1,3,3,3-tetrafluoropropene—overhead distillate of the extractant recovery tower; extractant—bottom effluent of the extractant recovery tower. DETAILED DESCRIPTION

[0025] The invention uses ketone compounds or ester compounds with a boiling point in the range of 50°C-250°C as extractants, and purifies bistrifluoromethyl sulfide and trans-1,3,3,3-tetrafluoropropylene from a mixture of bistrifluoromethyl sulfide and trans-1,3,3,3-tetrafluoropropylene by extractive distillation.

[0026] The extractant is a ketone compound containing 3-6 carbon atoms, specifically acetone, n-pentanone, 2-hexanone or cyclohexanone; and / or an anhydride compound containing 5-8 carbon atoms, specifically monomethyl adipate, dimethyl adipate, 2-methyl dimethyl glutarate or dimethyl glutarate.

[0027] The principle of extractive distillation is: by adding an extractant, the relative volatility of bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropene is changed, so that the relative volatility of bis(trifluoromethyl) sulfide relative to trans-1,3,3,3-tetrafluoropropene is greater than 1, thereby separating the two. Here, the relative volatility (α) of bis(trifluoromethyl) sulfide relative to trans-1,3,3,3-tetrafluoropropene is defined as follows:

[0028]

[0029] The relative volatility α of bis(trifluoromethyl)sulfide relative to trans-1,3,3,3-tetrafluoropropene after the addition of the extractant was determined, specifically: a 300mL stainless steel reactor was used, and the reactor was equipped with gas and liquid sampling valves. 50g of extractant and 50g of trans-1,3,3,3-tetrafluoropropene / bis(trifluoromethyl)sulfide mixture (wherein the content of trans-1,3,3,3-tetrafluoropropene was 40wt%) were added to the reactor. The reactor was immersed in a -30°C constant temperature oil bath, and the materials were stirred magnetically to fully mix the materials. When the materials in the reactor reached gas-liquid equilibrium, gas phase samples and liquid phase samples were taken, and the composition content of each phase was determined by gas chromatography. According to the definition formula of relative volatility, the relative volatility α value of each experiment was calculated, and the relevant experimental results are shown in Table 1.

[0030] Table 1 α value after adding extractant

[0031] Solvents Boiling point / ℃ α none - 0.86 acetone 56.5 1.71 n-Amylketone 101.5 1.89 2-Hexanone 127 2.01 Cyclohexanone 155 1.86 Monomethyl adipate 162 1.64 Dimethyl adipate 228.7 2.37 Dimethyl 2-methylglutarate 104 2.23 Dimethyl glutarate 103 1.96 The mass ratio of n-pentanone and dimethyl 2-methylglutarate is 1:1 - 2.53 2-Hexanone and dimethyl glutarate in a mass ratio of 3:1 - 2.65 2-Hexanone, dimethyl adipate and dimethyl 2-methylglutarate in a mass ratio of 1:1:1 - 2.77 2-Hexanone, dimethyl adipate, dimethyl 2-methylglutarate and dimethyl glutarate in a mass ratio of 1:2:1:2 - 2.82

[0032] As can be seen from Table 1, after adding ketone compounds or ester compounds with a boiling point in the range of 50°C-250°C, the relative volatility of bis(trifluoromethyl) sulfide to trans-1,3,3,3-tetrafluoropropene is changed, and α changes from less than 1 when no extractant is added to significantly greater than 1, making the relatively non-volatile bis(trifluoromethyl) sulfide more volatile, that is, the bis(trifluoromethyl) sulfide product can be obtained from the top of the tower through extractive distillation.

[0033] From the extractants tested in Table 1, it can be seen that the preferred extractant is dimethyl adipate. In addition, the above extractants can be used alone or in combination of two or more, such as n-pentanone and dimethyl 2-methylglutarate in a mass ratio of 1:1, and 2-hexanone and dimethyl glutarate in a mass ratio of 3:1.

[0034] The invention is verified by quantum chemical calculation and gas-liquid equilibrium experiment, and it is found that in the extractant, there is a strong hydrogen bond between the carbonyl structure and bistrifluoromethyl sulfide, which can improve the solubility of bistrifluoromethyl sulfide in the extractant, so that under the same conditions, the escape difficulty of bistrifluoromethyl sulfide is lower, so as to achieve the purpose of significantly improving the relative volatility of the azeotropic system of trans-1,3,3,3-tetrafluoropropylene and bistrifluoromethyl sulfide.

[0035] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be understood by those skilled in the art that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0036] Unless otherwise specified, the experimental methods used in the examples are all conventional methods; the materials, reagents, etc. used, unless otherwise specified, can be obtained from commercial channels.

[0037] Example 1

[0038] like Figure 1As shown, the extractive distillation tower T1 is a packed tower with a tower diameter of Φ25mm, and is filled with Φ3*3θ ring stainless steel packing, and the packing layer height is 0.8m. The distillation material feed is a mixture of trans-1,3,3,3-tetrafluoropropylene and bis(trifluoromethyl)sulfide, wherein the mass percentage of trans-1,3,3,3-tetrafluoropropylene is 40%, the mass percentage of bis(trifluoromethyl)sulfide is 60%, the extractant is dimethyl adipate, and the mass ratio of the extractant to the raw material is 14:1. Material 1 is fed from the middle of the extractive distillation tower T1 at a flow rate of 142g / h, and the extractant of the bottom effluent of the T2 extractant recovery tower is fed from the upper part of the T1 tower at a flow rate of 1742g / h. The top distillate of the T1 tower is a product containing bis(trifluoromethyl)sulfide, and the distillate of the T1 tower bottom is trans-1,3,3,3-tetrafluoropropylene and the extractant, which enters the extractant recovery tower T2. The top distillate of the T2 extractant recovery tower is the trans-1,3,3,3-tetrafluoropropene product, and the bottom outflow of the T2 extractant recovery tower is the extractant, which is returned to T1. The purity of the bistrifluoromethyl sulfide at the top of the T1 tower is 100% by gas chromatography, and the purity of the trans-1,3,3,3-tetrafluoropropene at the top of the T2 tower is 99.8%. The operating conditions are shown in Table 2.

[0039] Table 2 Tower operating conditions in Example 1

[0040]

[0041]

[0042] Example 2

[0043] The operating process of Example 2 is different from that of Example 1 only in that the operating parameters of T1 and T2 are different. The purity of bistrifluoromethyl sulfide in the distillate from the top of T1 tower is 100% by gas chromatography, and the purity of trans-1,3,3,3-tetrafluoropropene in the distillate from the top of T2 tower is 99.9%. The operating parameters are shown in Table 3.

[0044] Table 3 Tower operating conditions in Example 2

[0045] Extractive distillation tower T1 Extractant recovery tower T2 Operating pressure / kPa(A) 170 Operating pressure / kPa(A) 160 Tower top temperature / ℃ -9.1 Tower top temperature / ℃ -7.4 Tower temperature / ℃ 216.2 Tower temperature / ℃ 228.9 Reflux ratio 2.5 Reflux ratio 1.0

[0046] Example 3

[0047] The operating process of Example 3 is different from that of Example 1, except that the compositions of the raw material feed trans-1,3,3,3-tetrafluoropropene and bistrifluoromethyl sulfide are different: the mass percentage of trans-1,3,3,3-tetrafluoropropene is 35%, the mass percentage of bistrifluoromethyl sulfide is 65%, the purity of bistrifluoromethyl sulfide in the T1 tower top distillate determined by gas chromatography is 100%, and the purity of trans-1,3,3,3-tetrafluoropropene in the T2 tower top distillate is 99.9%. The operating parameters are shown in Table 4.

[0048] Table 4 Tower operating conditions in Example 3

[0049] Extractive distillation tower T1 Extractant recovery tower T2 Operating pressure / kPa(A) 180 Operating pressure / kPa(A) 170 Tower top temperature / ℃ -7.2 Tower top temperature / ℃ -5.9 Tower temperature / ℃ 215.2 Tower temperature / ℃ 253.8 Reflux ratio 1.5 Reflux ratio 1.4

[0050] Example 4

[0051] The operating process of Example 4 is different from that of Example 1 only in that the extractant is 2-hexanone, the purity of bistrifluoromethyl sulfide of the T1 tower top distillate is 99.9% by gas chromatography, and the purity of trans-1,3,3,3-tetrafluoropropylene of the T2 tower top distillate is 99.9%. The operating parameters are shown in Table 5.

[0052] Table 5 Tower operating conditions in Example 4

[0053] Extractive distillation tower T1 Extractant recovery tower T2 Operating pressure / kPa(A) 180 Operating pressure / kPa(A) 170 Tower top temperature / ℃ -7.2 Tower top temperature / ℃ -5.9 Tower temperature / ℃ 145.5 Tower temperature / ℃ 152.6 Reflux ratio 1.5 Reflux ratio 4.3

[0054] Example 5

[0055] The operating process of Example 5 is different from that of Example 1, except that the extractant is n-pentanone and dimethyl 2-methylglutarate in a mass ratio of 1:1, the purity of bistrifluoromethyl sulfide of the T1 tower top distillate is 99.9% by gas chromatography, and the purity of trans-1,3,3,3-tetrafluoropropylene of the T2 tower top distillate is 99.9%. The operating parameters are shown in Table 6.

[0056] Table 6 Tower operating conditions in Example 5

[0057] Extractive distillation tower T1 Extractant recovery tower T2 Operating pressure / kPa(A) 180 Operating pressure / kPa(A) 170 Tower top temperature / ℃ -7.2 Tower top temperature / ℃ -5.9 Tower temperature / ℃ 115.6 Tower temperature / ℃ 132.5 Reflux ratio 2.5 Reflux ratio 1.0

[0058] Example 6

[0059] The operating process of Example 6 is different from that of Example 1, except that the extractant is 2-hexanone and dimethyl glutarate in a mass ratio of 3:1, the purity of bistrifluoromethyl sulfide of the T1 tower top distillate is 99.9% by gas chromatography, and the purity of trans-1,3,3,3-tetrafluoropropylene of the T2 tower top distillate is 99.9%. The operating parameters are shown in Table 7.

[0060] Table 7 Tower operating conditions in Example 6

[0061] Extractive distillation tower T1 Extractant recovery tower T2 Operating pressure / kPa(A) 180 Operating pressure / kPa(A) 170 Tower top temperature / ℃ -7.2 Tower top temperature / ℃ -5.9 Tower temperature / ℃ 128.5 Tower temperature / ℃ 142.1 Reflux ratio 1.5 Reflux ratio 0.5

[0062] Example 7

[0063] The operation process of Example 7 is different from that of Example 1 only in that the extractant is 2-hexanone, dimethyl adipate and dimethyl 2-methylglutarate in a mass ratio of 1:1:1. The purity of bistrifluoromethyl sulfide in the T1 tower top distillate is 100% by gas chromatography, and the purity of trans-1,3,3,3-tetrafluoropropene in the T2 tower top distillate is 99.9%. The operation parameters are shown in Table 8.

[0064] Table 8 Tower operating conditions in Example 7

[0065] Extractive distillation tower T1 Extractant recovery tower T2 Operating pressure / kPa(A) 180 Operating pressure / kPa(A) 170 Tower top temperature / ℃ -7.2 Tower top temperature / ℃ -5.9 Tower temperature / ℃ 168.5 Tower temperature / ℃ 178.1 Reflux ratio 2.0 Reflux ratio 1.0

[0066] Example 8

[0067] The operation process of Example 8 is different from that of Example 1 only in that the extractant is hexanone, dimethyl adipate, dimethyl 2-methylglutarate and dimethyl glutarate in a mass ratio of 1:2:1:2. The purity of bistrifluoromethyl sulfide in the T1 tower top distillate was 99.9% by gas chromatography, and the purity of trans-1,3,3,3-tetrafluoropropylene in the T2 tower top distillate was 100%. The operating parameters are shown in Table 9.

[0068] Table 9 Tower operating conditions in Example 8

[0069] Extractive distillation tower T1 Extractant recovery tower T2 Operating pressure / kPa(A) 180 Operating pressure / kPa(A) 170 Tower top temperature / ℃ -7.2 Tower top temperature / ℃ -5.9 Tower temperature / ℃ 155.1 Tower temperature / ℃ 167.2 Reflux ratio 1.5 Reflux ratio 0.5

[0070] Comparative Example 1

[0071] The operation process of Comparative Example 1 is different from that of Example 1 only in that the extractant is acetone. The purity of bistrifluoromethyl sulfide in the distillate from the top of T1 tower is 96.5% by gas chromatography, and the purity of trans-1,3,3,3-tetrafluoropropene in the distillate from the top of T2 tower is 99.0%.

[0072] Comparative Example 2

[0073] The operation process of Comparative Example 2 is different from that of Example 5 only in that the mass ratio of the extractant is 1:1 between acetone and dimethyl 2-methylglutarate. The purity of bistrifluoromethyl sulfide in the T1 tower top distillate is 95.6% by gas chromatography, and the purity of trans-1,3,3,3-tetrafluoropropylene in the T2 tower top distillate is 98.1%.

[0074] Comparative Example 3

[0075] The operation process of Comparative Example 3 is different from that of Example 6 only in that the extractant is acetone and dimethyl glutarate in a mass ratio of 3:1. The purity of bistrifluoromethyl sulfide in the T1 tower top distillate is 94.4% by gas chromatography, and the purity of trans-1,3,3,3-tetrafluoropropene in the T2 tower top distillate is 99.1%.

[0076] Comparative Example 4

[0077] The operation process of Comparative Example 4 is different from that of Example 7 only in that the extractant is 2-hexanone, monomethyl adipate and dimethyl 2-methylglutarate in a mass ratio of 2:3:1. The purity of bistrifluoromethyl sulfide in the T1 tower top distillate is 95.6% by gas chromatography, and the purity of trans-1,3,3,3-tetrafluoropropylene in the T2 tower top distillate is 98.4%.

[0078] Comparative Example 5

[0079] The operation process of Comparative Example 5 is different from that of Example 8 only in that the extractant is hexanone, monomethyl adipate, dimethyl 2-methylglutarate and dimethyl glutarate in a mass ratio of 1:1:1:1. The purity of bistrifluoromethyl sulfide in the T1 tower top distillate was 94.6% by gas chromatography, and the purity of trans-1,3,3,3-tetrafluoropropylene in the T2 tower top distillate was 99.0%.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropylene, characterized in that: The following steps are involved: (1) taking a mixture of bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropylene as a raw material and an extractant; The mass ratio of the bistrifluoromethyl sulfide to trans-1,3,3,3-tetrafluoropropylene is 55-65:45-35; The extractant is a ketone compound and / or an acid anhydride compound; (2) feeding the extractant from the top of the extractive distillation tower, feeding the mixed raw material from the bottom of the extractive distillation tower, the top fraction of the extractive distillation tower is the bistrifluoromethyl sulfide product, and the bottom fraction is the trans-1,3,3,3-tetrafluoropropene product and the extractant; (3) The bottom fraction of the tower is fed into an extractant recovery tower, the top fraction is the trans-1,3,3,3-tetrafluoropropene product, the bottom fraction is the extractant, and the bottom fraction is recovered and circulated to the extractive distillation tower.

2. The method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropylene according to claim 1, characterized in that: In step (1): the extractant is a ketone compound containing 3-6 carbon atoms and / or an anhydride compound containing 5-8 carbon atoms.

3. The method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropylene according to claim 2, characterized in that: The extractant is at least one of acetone, n-pentanone, 2-hexanone, cyclohexanone, monomethyl adipate, dimethyl adipate, 2-methyl dimethyl glutarate and dimethyl glutarate.

4. The method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropylene according to claim 3, characterized in that: The extractant is n-pentanone and dimethyl 2-methylglutarate in a mass ratio of 1:

1.

5. The method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropylene according to claim 3, characterized in that: The extractant is 2-hexanone and dimethyl glutarate in a mass ratio of 3:

1.

6. The method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropene according to claim 3, characterized in that: 2-Hexanone, dimethyl adipate and dimethyl 2-methylglutarate in a mass ratio of 1:1:

1.

7. The method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropylene according to claim 3, characterized in that: 2-Hexanone, dimethyl adipate, dimethyl 2-methylglutarate and dimethyl glutarate in a mass ratio of 1:2:1:

2.

8. The method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropylene according to claim 1, characterized in that: In step (2): the mass ratio of the extractant to the mixture raw material is 13 to 15:

1.

9. The method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropylene according to claim 1, characterized in that: In step (2): the operating conditions of the extractive distillation tower are: the tower operating pressure is 170kPa to 180kPa, the tower top temperature is -9.1°C to -7.2°C, the tower bottom temperature is 115.6°C to 216.2°C, and the reflux ratio is 1.5 to 2.

5.

10. The method for separating bis(trifluoromethyl) sulfide and trans-1,3,3,3-tetrafluoropropene according to claim 1, characterized in that: In step (3): the operating conditions of the recovery tower are: the operating pressure in the tower is 160kPa to 170kPa, the top temperature is -7.4°C to -5.9°C, the bottom temperature is 132.5°C to 253.8°C, and the reflux ratio is 0.5 to 4.3.

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