A method for removing 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile

Abstract

The present invention relates to a method for removing 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile, comprising: 1) filling an adsorbent column with an adsorbent, and calcining the adsorbent to constant weight at 250-500 °C under a nitrogen atmosphere, wherein the adsorbent is an aluminophosphate molecular sieve with a structural formula of (El x Al y P z )O2; 2) stopping the nitrogen supply, evacuating the adsorbent column with a vacuum pump to an absolute pressure of 0.01 MPa, and cooling the adsorbent to room temperature for standby; 3) introducing the perfluoroisobutyronitrile raw material to be treated into the adsorbent column, controlling the absolute pressure in the adsorbent column to reach 0.1 MPa and keeping it constant; 4) starting a diaphragm compressor to press the gas in the adsorbent column into a gas cylinder, and stopping when the pressure in the adsorbent column reaches 0.01 MPa. The single-pass adsorption rate of this method for 1,1,1,2,3,3,3-heptafluoropropane can reach 90.4%, and it can be completely removed after secondary adsorption, and the regeneration effect is good. The impurity removal method of the present invention has the advantages of simple operation, mild conditions, high product yield, large adsorption capacity, good regeneration effect, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of gas separation and purification, and particularly relates to a method for removing 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile. Background Art

[0002] Perfluoroisobutyronitrile is a new type of environmentally friendly insulating gas with excellent insulation performance and environmentally friendly performance. It is considered to be an ideal substitute for SF6 at this stage. The new generation of insulating medium developed with it has been successfully applied to gas insulated switchgear (GIS) and gas insulated pipeline (GIL), and has attracted extensive attention from researchers at home and abroad.

[0003] Since there are many synthetic routes for perfluoroisobutyronitrile, the types and contents of various impurities in products from different manufacturers vary greatly. Although the technical routes of each manufacturer are different, the synthesis process of perfluoroisobutyronitrile requires the dehydration reaction of heptafluoroisobutyramide, so the impurity 1,1,1,2,3,3,3-heptafluoropropane is commonly found in commercially available perfluoroisobutyronitrile products, and the product purity range is concentrated between 99.2% and 99.9%.

[0004] Patent CN110526834A discloses a method for preparing high-purity perfluoroisobutyronitrile based on adsorption and cryogenic distillation. The method removes most of the water and a small amount of acidic substances by adsorption, and then uses cryogenic distillation to remove non-condensable gases, halogenated hydrocarbons and fluorocarbon compounds, and finally obtains high-purity perfluoroisobutyronitrile gas with a purity of 99.99%.

[0005] Patent CN112979499A discloses a method for separating a mixed gas of perfluoroisobutyronitrile and carbon dioxide. The method uses a modified adsorbent to remove pentafluoropropionitrile, trifluoroethylene, ethanedinitrile and saturated fluorocarbon compounds produced by the decomposition of perfluoroisobutyronitrile, and then further purifies the perfluoroisobutyronitrile by distillation to finally obtain perfluoroisobutyronitrile gas with a purity higher than 99.3%.

[0006] Although these methods can increase the purity of perfluoroisobutyronitrile to more than 99%, or even 99.99%, they all require the use of a combination of multiple unit operations for purification, such as adsorption and distillation, and low-temperature distillation usually consumes a lot of energy. In addition, the removal effect of the key impurity 1,1,1,2,3,3,3-heptafluoropropane is not described in detail.

[0007] Therefore, how to further improve the quality of perfluoroisobutyronitrile and achieve deep removal of the key impurity 1,1,1,2,3,3,3-heptafluoropropane while simplifying the operating process and reducing energy consumption is a problem that needs to be solved. Summary of the invention

[0008] In order to overcome the problems of the prior art, the present invention proposes a method for removing 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile, which further improves the quality of perfluoroisobutyronitrile, simplifies the operation process and reduces energy consumption.

[0009] In order to achieve the above object, the present invention provides a method for removing 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile in a first aspect, comprising the following steps:

[0010] 1) The adsorption column is filled with an adsorbent, and the adsorbent is calcined at 250-500° C. to a constant weight under a nitrogen atmosphere;

[0011] The adsorbent has a structural formula of (El x Al y P z )O2 aluminum phosphate molecular sieve; wherein x, y, z are all molar fractions, and the value range is: x≥0.001, y≥0.01, z≥0.01, and x+y+z=1.

[0012] 2) Stop the nitrogen flow, use a vacuum pump to evacuate the adsorption column to an absolute pressure of 0.01 MPa, and cool the adsorbent to room temperature for use;

[0013] 3) passing the perfluoroisobutyronitrile raw material to be treated into an adsorption column, and controlling the absolute pressure in the adsorption column to reach 0.1 MPa and keep it constant;

[0014] 4) Turn on the diaphragm compressor to press the gas in the adsorption column into the gas cylinder. Stop when the pressure in the adsorption column reaches 0.01 MPa. Use a gas chromatograph to analyze the content of 1,1,1,2,3,3,3-heptafluoropropane in the cylinder gas;

[0015] 5) Repeat step 4) until the level of 1,1,1,2,3,3,3-heptafluoropropane is undetectable.

[0016] Further, in step 1), the pore size of the aluminum phosphate molecular sieve is 0.3-1.2 nm, and the preferred pore size is 0.7-0.9 nm. More preferred aluminum phosphate molecular sieves are: AlPO-5, AlPO-8 and VPI-5, all of which are three-dimensional pore structures formed by aluminum oxide tetrahedrons and phosphorus oxide tetrahedrons, belonging to the hexagonal crystal system, and the pore systems are 12, 14 and 18 respectively.

[0017] Furthermore, in step 2), the vacuuming process needs to be carried out at a calcination temperature of 250-500°C.

[0018] Furthermore, in step 3), the content of 1,1,1,2,3,3,3-heptafluoropropane in the perfluoroisobutyronitrile raw material to be treated is at least 552.5 ppm.

[0019] Furthermore, in step 4), the filling factor of perfluoroisobutyronitrile in the gas cylinder is 0.5-1.5.

[0020] Furthermore, in step 5, a hydrogen flame ionization detector is used to detect the content of 1,1,1,2,3,3,3-heptafluoropropane.

[0021] The second aspect of the present invention provides the use of aluminum phosphate molecular sieve in the removal of 1,1,1,2,3,3,3-heptafluoropropane in perfluoroisobutyronitrile, wherein the structural formula of the aluminum phosphate molecular sieve is (El x Al y P z )O2.

[0022] Further, the pore size of the aluminum phosphate molecular sieve is 0.3-1.2 nm, and the preferred pore size is 0.7-0.9 nm. More preferred aluminum phosphate molecular sieves are: AlPO-5, AlPO-8 and VPI-5, all of which are three-dimensional pore structures formed by aluminum oxide tetrahedrons and phosphorus oxide tetrahedrons, belonging to the hexagonal crystal system, and the pore systems are 12, 14 and 18 respectively.

[0023] The advantages and beneficial effects of the present invention compared to the prior art are:

[0024] 1. In the method of the present invention, aluminum phosphate molecular sieve is used as an adsorbent, which has excellent adsorption effect and large adsorption capacity for 1,1,1,2,3,3,3-heptafluoropropane, can achieve deep removal of 1,1,1,2,3,3,3-heptafluoropropane in perfluoroisobutyronitrile, and also has a certain adsorption effect on other organic and inorganic impurities in perfluoroisobutyronitrile; after the perfluoroisobutyronitrile is adsorbed, 1,1,1,2,3,3,3-heptafluoropropane can reach an undetectable level, which helps to further improve the quality of perfluoroisobutyronitrile;

[0025] 2. The method for removing 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile of the present invention has simple operation, mild conditions and high product yield;

[0026] 3. The present invention is the first to apply aluminum phosphate molecular sieve to remove 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile. The aluminum phosphate molecular sieve has good regeneration performance. After heating and calcination, heptafluoropropane will be desorbed from the adsorbent, and then the adsorbent can be replaced with nitrogen to complete regeneration and recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0028] Figure 1It is a schematic diagram of the structure of the device for removing 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile in various embodiments and comparative examples of the present invention;

[0029] Figure 2 is a gas chromatography result diagram of the perfluoroisobutyronitrile raw material to be treated;

[0030] Figure 3 This is a gas chromatography result chart after removing 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile by the method described in Example 1. DETAILED DESCRIPTION

[0031] In the following examples, unless otherwise specified, all experimental instruments and raw materials involved are commercially available.

[0032] Experimental instruments, see Table 1.

[0033] Table 1

[0034] instrument model source Gas Chromatograph GC9560 Shanghai Huaai Chromatography Analysis Technology Co., Ltd. Adsorption column Φ3cm*60cm self made Vacuum Pump 2XZ-4 Shanghai Keneng Pump Industry Diaphragm compressor N145AN.18 KF Technologies (Shanghai) Co., Ltd. Gas cylinders 250mL Swagelok (Shanghai) Fluid System Technology Co., Ltd.

[0035] See Table 2 for raw materials.

[0036] Table 2

[0037] raw material source 5A molecular sieve Henan Shengwei Desiccant Co., Ltd. 10X molecular sieve Henan Shengwei Desiccant Co., Ltd. NaY molecular sieve Henan Shengwei Desiccant Co., Ltd. ZSM-5 molecular sieve Henan Shengwei Desiccant Co., Ltd. AlPO-5 molecular sieve Zhuoran Environmental Technology (Dalian) Co., Ltd. AlPO-8 molecular sieve Zhuoran Environmental Technology (Dalian) Co., Ltd. VPI-5 molecular sieve Zhuoran Environmental Technology (Dalian) Co., Ltd. Activated carbon Henan Shengwei Desiccant Co., Ltd. Heptafluoroisobutyronitrile crude product Beijing Yuji Technology Development Co., Ltd.

[0038] In the following examples, the test methods involved are shown in Table 3:

[0039] Table 3

[0040]

[0041] In the following examples and comparative examples, the perfluoroisobutyronitrile raw materials to be treated are crude heptafluoroisobutyronitrile purchased from Beijing Yuji Technology Development Co., Ltd., wherein the content of 1,1,1,2,3,3,3-heptafluoropropane is 552.5 ppm.

[0042] Comparative Example 1

[0043] Use Figure 1 The device shown in the figure is used to remove 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile, comprising the following steps:

[0044] The adsorption column is filled with 1L of 5A molecular sieve adsorbent, and the adsorbent is calcined at 350°C to constant weight under a nitrogen atmosphere. Stop the nitrogen flow, and use a vacuum pump to evacuate the adsorption column to 0.01MPa (absolute pressure), and cool to room temperature. The perfluoroisobutyronitrile raw material to be treated is passed into the adsorption column at 200mL / min. After the pressure in the adsorption column reaches 0.1MPa (absolute pressure) and remains constant, the perfluoroisobutyronitrile feed valve is closed. Turn on the diaphragm compressor to press the gas in the adsorption column into the cylinder. The pressure in the adsorption column stops when it reaches 0.01MPa (absolute pressure), and the content of 1,1,1,2,3,3,3-heptafluoropropane in the cylinder gas is analyzed by gas chromatograph.

[0045] Comparative Example 2

[0046] The adsorption column is filled with 1L of 10X molecular sieve adsorbent, and the adsorbent is calcined at 350°C to constant weight under a nitrogen atmosphere. Stop the nitrogen flow, and use a vacuum pump to evacuate the adsorption column to 0.01MPa (absolute pressure), and cool to room temperature. The perfluoroisobutyronitrile raw material to be treated is passed into the adsorption column at 200mL / min. After the pressure in the adsorption column reaches 0.1MPa (absolute pressure) and remains constant, the perfluoroisobutyronitrile feed valve is closed. Turn on the diaphragm compressor to press the gas in the adsorption column into the cylinder. The pressure in the adsorption column stops when it reaches 0.01MPa (absolute pressure), and the content of 1,1,1,2,3,3,3-heptafluoropropane in the cylinder gas is analyzed by gas chromatograph.

[0047] Comparative Example 3

[0048] The adsorption column is filled with 1L of NaY molecular sieve adsorbent, and the adsorbent is calcined at 350°C to constant weight under a nitrogen atmosphere. Stop the nitrogen flow, and use a vacuum pump to evacuate the adsorption column to 0.01MPa (absolute pressure), and cool to room temperature. The perfluoroisobutyronitrile raw material to be treated is passed into the adsorption column at 200mL / min. After the pressure in the adsorption column reaches 0.1MPa (absolute pressure) and remains constant, the perfluoroisobutyronitrile feed valve is closed. Turn on the diaphragm compressor to press the gas in the adsorption column into the cylinder. The pressure in the adsorption column stops when it reaches 0.01MPa (absolute pressure), and the content of 1,1,1,2,3,3,3-heptafluoropropane in the cylinder gas is analyzed by gas chromatograph.

[0049] Comparative Example 4

[0050] The adsorption column is filled with 1L of ZSM-5 molecular sieve adsorbent, and the adsorbent is calcined at 350°C to constant weight under a nitrogen atmosphere. Stop the nitrogen flow, and use a vacuum pump to evacuate the adsorption column to 0.01MPa (absolute pressure), and cool to room temperature. The perfluoroisobutyronitrile raw material to be treated is passed into the adsorption column at 200mL / min. After the pressure in the adsorption column reaches 0.1MPa (absolute pressure) and remains constant, the perfluoroisobutyronitrile feed valve is closed. Turn on the diaphragm compressor to press the gas in the adsorption column into the cylinder. The pressure in the adsorption column stops when it reaches 0.01MPa (absolute pressure), and the content of 1,1,1,2,3,3,3-heptafluoropropane in the cylinder gas is analyzed by gas chromatograph.

[0051] Comparative Example 5

[0052] The adsorption column is filled with 1L of activated carbon adsorbent. Under nitrogen atmosphere, the adsorbent is calcined at 250°C to constant weight. Stop the nitrogen flow, evacuate the adsorption column to 0.01MPa (absolute pressure) with a vacuum pump, and cool to room temperature. The perfluoroisobutyronitrile raw material to be treated is passed into the adsorption column at 200mL / min. After the pressure in the adsorption column reaches 0.1MPa (absolute pressure) and remains constant, the perfluoroisobutyronitrile feed valve is closed. Turn on the diaphragm compressor to press the gas in the adsorption column into the cylinder. Stop when the pressure in the adsorption column reaches 0.01MPa (absolute pressure), and use a gas chromatograph to analyze the content of 1,1,1,2,3,3,3-heptafluoropropane in the cylinder gas.

[0053] Comparative Example 6 (10X molecular sieve adsorption twice)

[0054] Adsorption was carried out twice continuously according to the conditions of Comparative Example 2, and the content of 1,1,1,2,3,3,3-heptafluoropropane in the cylinder gas was analyzed by gas chromatograph.

[0055] Example 1

[0056] The adsorption column is filled with 1L of AlPO-5 molecular sieve adsorbent, and the adsorbent is calcined at 350°C to constant weight under a nitrogen atmosphere. Stop the nitrogen flow, and use a vacuum pump to evacuate the adsorption column to 0.01MPa (absolute pressure), and cool to room temperature. The perfluoroisobutyronitrile raw material to be treated is passed into the adsorption column at 200mL / min. After the pressure in the adsorption column reaches 0.1MPa (absolute pressure) and remains constant, the perfluoroisobutyronitrile feed valve is closed. Turn on the diaphragm compressor to press the gas in the adsorption column into the cylinder. The pressure in the adsorption column stops when it reaches 0.01MPa (absolute pressure), and the content of 1,1,1,2,3,3,3-heptafluoropropane in the cylinder gas is analyzed by gas chromatograph.

[0057] Figure 2 , Figure 3 The gas chromatograph results are before and after removal treatment.

[0058] Example 2

[0059] The adsorption column is filled with 1L of AlPO-8 molecular sieve adsorbent, and the adsorbent is calcined at 350°C to constant weight under a nitrogen atmosphere. Stop the nitrogen flow, and use a vacuum pump to evacuate the adsorption column to 0.01MPa (absolute pressure), and cool to room temperature. The perfluoroisobutyronitrile raw material to be treated is passed into the adsorption column at 200mL / min. After the pressure in the adsorption column reaches 0.1MPa (absolute pressure) and remains constant, the perfluoroisobutyronitrile feed valve is closed. Turn on the diaphragm compressor to press the gas in the adsorption column into the cylinder. The pressure in the adsorption column stops when it reaches 0.01MPa (absolute pressure), and the content of 1,1,1,2,3,3,3-heptafluoropropane in the cylinder gas is analyzed by gas chromatograph.

[0060] Example 3

[0061] The adsorption column is filled with 1L of VPI-5 molecular sieve adsorbent, and the adsorbent is calcined at 350°C to constant weight under a nitrogen atmosphere. Stop the nitrogen flow, and use a vacuum pump to evacuate the adsorption column to 0.01MPa (absolute pressure), and cool to room temperature. The perfluoroisobutyronitrile raw material to be treated is passed into the adsorption column at 200mL / min. After the pressure in the adsorption column reaches 0.1MPa (absolute pressure) and remains constant, the perfluoroisobutyronitrile feed valve is closed. Turn on the diaphragm compressor to press the gas in the adsorption column into the cylinder. The pressure in the adsorption column stops when it reaches 0.01MPa (absolute pressure), and the content of 1,1,1,2,3,3,3-heptafluoropropane in the cylinder gas is analyzed by gas chromatograph.

[0062] Example 4 (AlPO-5 molecular sieve adsorption twice)

[0063] This embodiment is a preferred solution based on the embodiment 1. Two consecutive adsorptions are performed according to the conditions of the embodiment 1, and the content of 1,1,1,2,3,3,3-heptafluoropropane in the cylinder gas is analyzed by gas chromatograph.

[0064] Example 5 (Regeneration effect of AlPO-5 molecular sieve)

[0065] Nitrogen is introduced into the adsorption column, and the saturated AlPO-5 molecular sieve adsorbent (i.e., AlPO-5 saturated with 1,1,1,2,3,3,3-heptafluoropropane) is calcined at 350°C. After 12 hours, the introduction of nitrogen is stopped, and the adsorption column is evacuated to 0.01MPa (absolute pressure) with a vacuum pump, and cooled to room temperature. The perfluoroisobutyronitrile raw material to be treated is introduced into the adsorption column at 200mL / min. After the pressure in the adsorption column reaches 0.1MPa (absolute pressure) and remains constant, the perfluoroisobutyronitrile feed valve is closed. The diaphragm compressor is turned on to press the gas in the adsorption column into the cylinder. The pressure in the adsorption column stops when it reaches 0.01MPa (absolute pressure), and the above conditions are repeated for adsorption again. After two adsorptions, the content of 1,1,1,2,3,3,3-heptafluoropropane in the cylinder gas is analyzed by gas chromatograph.

[0066] Test Example 1

[0067] In order to compare the effects of different adsorbents on the removal of 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile, this test example compared the content of 1,1,1,2,3,3,3-heptafluoropropane before and after the reaction of Comparative Examples 1 to 5 and Example 1. The results are shown in Table 4.

[0068] Table 4 Comparison of the effects of different adsorbents

[0069]

[0070] The data in Table 4 show that each molecular sieve has a certain degree of adsorption effect on 1,1,1,2,3,3,3-heptafluoropropane, among which the adsorption effect of aluminum phosphate molecular sieve AlPO-5 is the most significant, and the single-pass adsorption rate of 1,1,1,2,3,3,3-heptafluoropropane reaches 90.4%, which is much higher than other types of molecular sieves. This may be due to the regular pore structure and large specific surface area of ​​aluminum phosphate molecular sieve, which are more conducive to the adsorption of 1,1,1,2,3,3,3-heptafluoropropane.

[0071] Test Example 2

[0072] In order to compare the effects of different aluminum phosphate molecular sieves on the removal of 1,1,1,2,3,3,3-heptafluoropropane in perfluoroisobutyronitrile, this test example compared the content of 1,1,1,2,3,3,3-heptafluoropropane before and after the reaction of Examples 1 to 3. The results are shown in Table 5.

[0073] Table 5 Comparison of adsorption effects of different aluminum phosphate molecular sieves

[0074]

[0075] The data in Table 5 show that different aluminum phosphate molecular sieves have good adsorption effects on 1,1,1,2,3,3,3-heptafluoropropane, and the single-pass adsorption rate reaches more than 85%. The pore size of ALPO-8 is 7.9*8.7A, the pore size of VPI-5 is 12.7*12.7A, and the pore size of ALPO-5 is 7.3*7.3A. In comparison, the AlPO-5 molecular sieve with a pore size of about 7.3*7.3A has the best adsorption effect. This may be because the adsorbent pore size is too large, which will cause the adsorption of part of perfluoroisobutyronitrile, affect the adsorption capacity, and reduce the adsorption rate of heptafluoropropane.

[0076] Test Example 3

[0077] In order to compare the effects of multiple adsorption treatments with different adsorbents on the removal of 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile, this test example compared the contents of 1,1,1,2,3,3,3-heptafluoropropane before and after the reaction in Examples 1 and 4 and Comparative Examples 2 and 6. The results are shown in Table 6.

[0078] Table 6 Comparison of multiple adsorption effects of AlPO-5 molecular sieve and 10X molecular sieve

[0079]

[0080] From the data in Table 6, it can be seen that using AlPO-5 molecular sieve as adsorbent, 1,1,1,2,3,3,3-heptafluoropropane can be completely removed after two adsorptions, while the adsorption rate of 1,1,1,2,3,3,3-heptafluoropropane for faujasite 10X molecular sieve with similar pore size is only 81.2% after two adsorptions.

[0081] Test Example 4

[0082] In order to study the regeneration adsorption effect of the AlPO-5 molecular sieve with the best adsorption effect, this test example compared the content of 1,1,1,2,3,3,3-heptafluoropropane before and after the reaction of Examples 1 and 4 and Comparative Examples 2 and 6. The results are shown in Table 7.

[0083] Table 7 Comparison of regeneration adsorption effect of AlPO-5 molecular sieve

[0084]

[0085] From the data in Table 7, it can be seen that the single-pass adsorption rate of the regenerated AlPO-5 molecular sieve is 88.8%, which is slightly lower than the 90.4% of the fresh AlPO-5 molecular sieve. After the secondary adsorption, 1,1,1,2,3,3,3-heptafluoropropane can also reach undetectable level, which is basically equivalent to the effect of fresh adsorbent.

[0086] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred arrangement scheme, a person skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for removing 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile, characterized in that: The method comprises the following steps: 1) The adsorption column is filled with an adsorbent, and the adsorbent is calcined at 250-500° C. to a constant weight under a nitrogen atmosphere; The adsorbent is one of AlPO-5 molecular sieve adsorbent, AlPO-8 molecular sieve adsorbent and VPI-5 molecular sieve adsorbent; 2) Stop the nitrogen flow, use a vacuum pump to evacuate the adsorption column to an absolute pressure of 0.01 MPa, and cool the adsorbent to room temperature for use; 3) passing the perfluoroisobutyronitrile raw material to be treated into an adsorption column, and controlling the absolute pressure in the adsorption column to reach 0.1 MPa and keep it constant; 4) Turn on the diaphragm compressor to press the gas in the adsorption column into the gas cylinder. Stop when the pressure in the adsorption column reaches 0.01 MPa. Use a gas chromatograph to analyze the content of 1,1,1,2,3,3,3-heptafluoropropane in the cylinder gas; 5) Repeat step 4) until the level of 1,1,1,2,3,3,3-heptafluoropropane is undetectable.

2. The method for removing 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile according to claim 1, characterized in that: In step 2), the vacuuming process needs to be carried out at a calcination temperature of 250-500°C.

3. The method for removing 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile according to claim 1, characterized in that: In step 3), the content of 1,1,1,2,3,3,3-heptafluoropropane in the perfluoroisobutyronitrile raw material to be treated is at least 552.5 ppm.

4. The method for removing 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile according to claim 1, characterized in that: In step 4), the filling factor of perfluoroisobutyronitrile in the gas cylinder is 0.5 to 1.

5.

5. The method for removing 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile according to claim 1, characterized in that: In step 5), the content of 1,1,1,2,3,3,3-heptafluoropropane is detected by a hydrogen flame ionization detector.

6. Application of aluminum phosphate molecular sieve in removing 1,1,1,2,3,3,3-heptafluoropropane from perfluoroisobutyronitrile, characterized in that: The aluminum phosphate molecular sieve is one of AlPO-5 molecular sieve adsorbent, AlPO-8 molecular sieve adsorbent and VPI-5 molecular sieve adsorbent.

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