Purification process of hexafluorobutadiene

Abstract

The invention discloses a purification process of hexafluorobutadiene, and relates to the technical field of fluorine chemical industry, in the purification process of hexafluorobutadiene provided by the invention, key fluorocarbon impurities are adsorbed and separated by introducing raw materials into a separation adsorption tower; according to the method, the key fluorocarbon impurities are adsorbed by the conventional filler respectively, the high-boiling-point fluorocarbon impurities are collected in the separation adsorber kettle, and the fluorocarbon impurities with approximate boiling points are adsorbed by the calcium-magnesium modified molecular sieve, so that deep removal of the key fluorocarbon impurities is facilitated. According to the present invention, with the combination of the first adsorption acid removal, the first adsorption water removal and the later double-tower continuous rectification, the deep removal of the small molecule impurities and the fluorocarbon impurities is completely achieved, when the sodium ion replacement rate in the calcium-magnesium modified molecular sieve is more than 95%, the purity of the obtained hexafluorobutadiene is more than 99.99%, the key fluorocarbon impurity is controlled to be less than 50 ppm, and the purity of the obtained hexafluorobutadiene is more than 99.99%; the high-purity requirement of an electronic-grade material is met, and meanwhile, the yield reaches 90% or above.

Description

Technical Field

[0001] The invention relates to the technical field of fluorine chemical industry, and in particular to a purification process of hexafluorobutadiene. Background Art

[0002] The preparation process of hexafluorobutadiene is diverse. According to the different starting materials, it can be mainly divided into fluorination polymerization preparation method, thermal polymerization preparation method, etc. These preparation methods have significant differences in reaction conditions, intermediate products, yields, etc. For example, the fluorination polymerization preparation method usually involves low-temperature fluorination reaction and dechlorination reaction, with complicated steps and low yields; while the thermal polymerization preparation method can obtain a higher hexafluorobutadiene yield through steps such as dimerization, photochlorination, fluorination and dechlorination. However, various by-products are inevitably produced in the crude hexafluorobutadiene obtained by these preparation methods. The presence of these by-products poses a severe challenge to the high purification of hexafluorobutadiene, especially large molecular fluorocarbon organic impurities. How to achieve deep removal of by-products and control fluorocarbon impurities within 100ppm or even lower is a technical problem faced by this field. Summary of the invention

[0003] The main purpose of the present invention is to propose a purification process for hexafluorobutadiene, which is helpful for deep removal of macromolecular carbon fluorine organic impurities in crude hexafluorobutadiene, and to propose a further solution for effectively improving the purity of hexafluorobutadiene to more than 99.99%, controlling the macromolecular carbon fluorine organic impurities to less than 50 ppm, and achieving a yield of more than 90%.

[0004] The crude hexafluorobutadiene obtained from the preparation of hexafluorobutadiene usually contains the following by-products: N2, O2, CO2, HF, H2O, hexafluoro-2-butyne (boiling point -25°C), hexafluorocyclobutene (boiling point 5°C), heptafluoro-1-butene and isomers (boiling point 8°C), heptafluoro-2-butene and isomers (boiling point 8°C), octafluoro-1-butene (boiling point 4.85°C), and the boiling point of hexafluorobutadiene is 6-7°C. The removal of H2O and HF in the prior art can basically achieve the effect of deep removal. However, the boiling point of most of the macromolecular fluorocarbon organic impurities (hereinafter referred to as fluorocarbon impurities or key fluorocarbon impurities) in the by-products is close to that of hexafluorobutadiene. The removal of fluorocarbon impurities is the key difficulty in the high purification of hexafluorobutadiene.

[0005] To achieve the purpose of the invention, the present invention provides a purification process for hexafluorobutadiene, comprising the following steps:

[0006] S1. The crude hexafluorobutadiene is introduced into an adsorption tower, and then acid and water are removed by adsorption in sequence;

[0007] S2, the crude hexafluorobutadiene after dehydration is introduced into a separation adsorber to separate and adsorb fluorocarbon impurities;

[0008] S3, subjecting the crude hexafluorobutadiene after the adsorption treatment to a double-tower continuous distillation treatment, firstly introducing the distillation tower A to remove heavy component impurities, and then introducing the distillation tower B to remove light component impurities, to obtain the hexafluorobutadiene finished product;

[0009] In step S2, the crude hexafluorobutadiene after dehydration by adsorption is introduced into the bottom of the separation adsorber, the bottom of the separation adsorber is the kettle part, the top of the kettle part is the separation section, and the crude hexafluorobutadiene after adsorbing fluorocarbon impurities is discharged from the top of the separation adsorber through the lower half of the separation section and the upper half of the separation section of the separation adsorber in sequence; the lower half of the separation section is filled with regular fillers, and the upper half of the separation section is filled with calcium-magnesium modified molecular sieves, and the calcium-magnesium modified molecular sieves are prepared by replacing sodium ions with calcium ions and magnesium ions using 5A molecular sieves as the structural basis, and the sodium ion replacement rate is more than 80%.

[0010] The present invention introduces raw materials into a separation adsorption tower to adsorb and separate fluorocarbon impurities. The separation adsorber combines the effects of flash evaporation, separation and adsorption to separate and adsorb fluorocarbon impurities with a large boiling point difference into a regular packing in the lower half of the separation section. The high-boiling point impurities are collected in large quantities in the separation adsorber kettle. The upper half of the separator uses a calcium-magnesium modified molecular sieve to adsorb fluorocarbon impurities with a boiling point close to that of hexafluorobutadiene. The calcium-magnesium modified molecular sieve replaces the sodium ions loaded in the original 5A molecular sieve structure with calcium-magnesium ions in a known manner, so that the heat generated by the reaction when the sodium ions directly contact hexafluorobutadiene containing unsaturated double bonds and then generate more by-products can be effectively reduced, which is helpful for deep removal of key fluorocarbon impurities.

[0011] Since HF has a corrosive effect on various chemical materials and equipment, the present invention chooses to first remove the HF impurity in the crude product to avoid HF from corrosive damage to subsequent process equipment. However, water is difficult to remove during the distillation process, so water is removed after HF is removed to greatly improve the efficiency of the subsequent distillation treatment.

[0012] Preferably, in the calcium-magnesium modified molecular sieve, the sodium ion replacement rate is above 95%, thereby improving the removal effect of fluorocarbon impurities.

[0013] Preferably, the calcium-magnesium modified molecular sieve is composed of a silicon-aluminum skeleton with a silicon-aluminum molar ratio of 2.8-3.2, loaded with calcium-magnesium ions with a calcium-magnesium molar ratio of 1:1 to 1:3, and the pore size of the molecular sieve is controlled to be 0.6 to 0.8 nm by the silicon-aluminum molar ratio and the calcium-magnesium molar ratio.

[0014] Preferably, in step S1, in the acid removal by adsorption step, a magnesium oxide adsorbent is used; in the water removal by adsorption step, a calcium type molecular sieve adsorbent is used.

[0015] The basic oxide properties of magnesium oxide adsorbent are used to combine with HF for removal. It only combines with acidic substances to remove HF. Calcium-type molecular sieves easily adsorb polar water molecules. The above two adsorbents are highly selective, basically do not consume hexafluorobutadiene, and have stable adsorption effects in a wide range of gas flow rates.

[0016] Preferably, in step S1, in the adsorption and acid removal step, magnesium oxide adsorbent is used; in the adsorption and water removal step, calcium type molecular sieve adsorbent is used, the gas flow rate of the crude hexafluorobutadiene is 30-50kg / h, and the adsorption pressure during the adsorption process is 0.07-0.09Mpa.

[0017] The above preferred purification parameters help the raw material C4F6 to pass through the adsorbent in a gaseous state and at a higher adsorption pressure, which helps to deeply remove HF and H2O impurities, greatly improve the subsequent distillation efficiency, and there is basically no raw material loss in the adsorption process. After two-stage adsorption and impurity removal, the yield can reach more than 98%.

[0018] Preferably, a jacket is provided in the separation section of the separation adsorber, and a refrigerant is introduced to cool the jacket to 5-10° C. This helps to improve the adsorption effect of separating and adsorbing fluorocarbon impurities with large boiling point differences in the lower half of the separation section.

[0019] Preferably, in step S3, the crude hexafluorobutadiene from which the fluorocarbon impurities have been removed by adsorption is introduced into the middle and lower part of the distillation tower A, the distillation equilibrium is controlled, and the heavy component impurities in the gas phase are extracted from the bottom liquid phase of the distillation tower A through gas-liquid phase exchange;

[0020] The crude hexafluorobutadiene from which the heavy impurities are separated enters the distillation tower B from the upper middle part of the distillation tower A, the distillation balance is controlled, the light impurities in the gas phase are collected at the top of the distillation tower B, and the hexafluorobutadiene product from which the light impurities are separated is taken out from the liquid phase in the bottom of the distillation tower B.

[0021] Under the action of the condensate falling from the top of distillation tower A and the rising steam from the bottom of the tower, the gas-liquid two phases are in reverse phase contact step by step, and the mass and heat exchange is carried out. The heavy component impurities in the gas phase are continuously transferred to the liquid phase and fall to the bottom of the tower, so that the large molecular impurities are separated and enriched in the liquid phase of the bottom of distillation tower A; under the action of the top reflux of distillation tower B and the rising gas phase in the bottom of the tower, the gas-liquid two phases are in reverse phase contact step by step, and the mass and heat exchange is carried out. The light component impurities in the liquid phase are continuously transferred to the gas phase and rise to the top of the tower, so that the small molecules are removed from the top of the tower. The continuous distillation process of removing heavy components first and then removing light components is adopted, which is relatively simple to operate and has relatively stable product quality.

[0022] Preferably, in step S3, when the liquid level of the distillation tower A reaches 80%, the temperature of the distillation tower A is controlled to be 30-38°C, the pressure is 0.15-0.25Mpa, and the reflux rate is 500kg / h;

[0023] When the tower liquid level of distillation tower B reaches 80%, the temperature of distillation tower B is controlled to be 18-25°C, the pressure is 0.05-0.15Mpa, and the reflux rate is 350kg / h.

[0024] The temperature and pressure of the distillation tower are controlled by the reboiler heating system of the distillation tower and the condensation tower system of the distillation tower. Under the above purification parameters, macromolecular impurities and small molecular impurities are removed in depth, and the heavy components are concentrated in the tower kettle. Combined with the sodium ion replacement rate increased to 95%, the purity of the obtained hexafluorobutadiene reaches more than 99.99%, which meets the high purity requirements of electronic grade materials and helps to increase the yield to more than 90%. If the temperature range or pressure range in the distillation tower A is adjusted, the heavy components cannot be separated; if the temperature range or pressure range in the distillation tower B is adjusted, the yield will be significantly reduced.

[0025] Specifically, in step S3, the flow rate of crude hexafluorobutadiene entering distillation tower A is controlled to be 30-50 kg / h, and the bottom liquid phase of the distillation tower A extracts heavy component impurities at a flow rate of 2-4 kg / h and enters the heavy component storage tank; the flow rate of crude hexafluorobutadiene entering distillation tower B is controlled to be 28-46 kg / h, and the top of the distillation tower B extracts light component impurities at a flow rate of 2-4 kg / h; the bottom liquid phase of the distillation tower B extracts finished hexafluorobutadiene at a flow rate of 26-42 kg / h and fills it.

[0026] Beneficial effects:

[0027] Compared with the prior art, the method introduces the raw materials into the separation adsorption tower to adsorb and separate the key fluorocarbon impurities, uses conventional fillers to adsorb the fluorocarbon impurities with large boiling point differences, collects the high boiling point fluorocarbon impurities in the separation adsorber kettle, and uses calcium-magnesium modified molecular sieves to adsorb the fluorocarbon impurities with similar boiling points, which helps to deeply remove the key fluorocarbon impurities. Combined with the previous adsorption acid removal and adsorption water removal, and the subsequent double-tower continuous distillation, the overall deep removal of small molecular impurities and fluorocarbon impurities is achieved. When the sodium ion replacement rate in the calcium-magnesium modified molecular sieve reaches more than 95%, the purity of the obtained hexafluorobutadiene reaches more than 99.99%, and the key fluorocarbon impurities are controlled to be less than 50ppm, meeting the high purity requirements of electronic grade materials, and the yield reaches more than 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 It is a schematic diagram of a separation adsorption tower;

[0030] In the attached drawings: 1-separation adsorber; 11-kettle portion; 12-separation section; 121-lower half of the separation section; 122-upper half of the separation section; 13-jacket.

[0031] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0033] The technical scheme of the present invention is further described in detail below in conjunction with specific embodiments or comparative examples. In the following embodiments and comparative examples, raw materials, reagents, etc. not otherwise specified are all commercially available, and the same batch of raw materials or reagents are used in the embodiments and comparative examples; the preparation methods without special conditions are all prepared by conventional, well-known preparation methods.

[0034] Each example and comparative example uses the same batch of crude hexafluorobutadiene as raw material, and the impurity content in the raw material is as follows:

[0035] Serial number Impurities Content (ppm) 1 HF 10 2 <![CDATA[H2O]]> 100 3 Key Fluorocarbon Impurities 2500-3500 The purity of crude hexafluorobutadiene is 99.5％

[0036] N2, O2 and CO2 in the raw materials are relatively easy to separate and are not listed separately as key points in the specific implementation method. The analysis methods for the content of key impurities in the raw materials and purified products are all conventional national standard analysis methods in the gas industry.

[0037] A specific purification process of hexafluorobutadiene is provided as a reference for the preparation of specific examples or comparative examples:

[0038] Preparation process item (1)

[0039] S1. The crude hexafluorobutadiene is introduced into an adsorption tower, and is successively subjected to acid removal and water removal by adsorption. After acid removal by adsorption, the HF content is detected, and after water removal by adsorption, the H2O content is detected.

[0040] S2, the crude hexafluorobutadiene after dehydration is introduced into a separation adsorber to separate and adsorb fluorocarbon impurities;

[0041] S3. The crude hexafluorobutadiene from which the fluorocarbon impurities have been removed by adsorption is introduced into the middle and lower part of the distillation tower A by pressurization, the distillation equilibrium is controlled, and the heavy component impurities in the gas phase are extracted from the bottom liquid phase of the distillation tower A by gas-liquid phase exchange; the content of large molecular impurities, i.e., key fluorocarbon impurities, is detected by online analysis of the gas phase at the top of tower A using a GC-2014C chromatograph.

[0042] The crude hexafluorobutadiene from which the heavy impurities are separated enters the distillation tower B from the middle and upper part of the distillation tower A, the distillation balance is controlled, the light impurities in the gas phase are collected at the top of the distillation tower B, and the hexafluorobutadiene product from which the light impurities are separated is taken out from the liquid phase in the bottom of the distillation tower B;

[0043] Specifically, in step S2, the crude hexafluorobutadiene product after dehydration by adsorption is decompressed and enters the bottom of the separation adsorber, such as Figure 1 As shown, the bottom of the separation adsorber (1) is a kettle part (11), and the upper part of the kettle part (11) is a separation section (12). The separation section lower section (121) and the separation section upper section (122) of the separation adsorber (1) are sequentially passed through. A jacket (13) is provided in the separation section (12), and cooling water is introduced to cool to 5-10° C., and the crude hexafluorobutadiene product with adsorbed fluorocarbon impurities is discharged from the top of the separation adsorber (1);

[0044] Specifically, the lower half (121) of the separation section is filled with a regular filler cy700 wire mesh filler, and the upper half (122) of the separation section is filled with a calcium-magnesium modified molecular sieve, which is prepared by replacing sodium ions with calcium and magnesium ions using 5A molecular sieve as the structural basis;

[0045] Specifically, the calcium-magnesium modified molecular sieve is composed of a silicon-aluminum skeleton with a silicon-aluminum molar ratio of 2.8-3.2, and is loaded with calcium-magnesium ions with a calcium-magnesium molar ratio of 1:1 to 1:3. The pore size of the molecular sieve is controlled to be 0.7nm by the silicon-aluminum molar ratio and the calcium-magnesium molar ratio.

[0046] Specifically, in step S3, when the liquid level of the distillation tower A reaches 80%, the temperature of the distillation tower A is controlled to be 30-38°C, the pressure is 0.15-0.25Mpa, and the reflux rate is 500kg / h;

[0047] When the tower liquid level of distillation tower B reaches 80%, the temperature of distillation tower B is controlled to be 18-25°C, the pressure is 0.05-0.15Mpa, and the reflux rate is 350kg / h.

[0048] Specifically, in step S3, the flow rate of crude hexafluorobutadiene entering distillation tower A is controlled to be 30-50 kg / h, and the bottom liquid phase of distillation tower A extracts heavy component impurities at a flow rate of 2-4 kg / h and enters the heavy component storage tank; the flow rate of crude hexafluorobutadiene entering distillation tower B is controlled to be 28-46 kg / h, and the top of distillation tower B extracts light component impurities at a flow rate of 2-4 kg / h; the bottom liquid phase of distillation tower B extracts finished hexafluorobutadiene at a flow rate of 26-42 kg / h and fills. The purity of the finished hexafluorobutadiene is tested, and the yield is calculated by the mass ratio of the input and output raw materials.

[0049] Example 1

[0050] The raw material is purified according to the preparation process item (1), wherein:

[0051] In step S1, in the adsorption and acid removal step, magnesium oxide adsorbent is used; in the adsorption and water removal step, calcium type molecular sieve adsorbent 5A molecular sieve is used; the adsorption pressure during the adsorption process is 0.08Mpa, and the gas flow rate of the crude hexafluorobutadiene product is 40kg / h;

[0052] In step S1, the calcium ion replacement rate in the calcium-magnesium modified molecular sieve is 100%.

[0053] Example 2

[0054] The process steps are similar to those of Example 1, except that the gas flow rate parameters in step S1 are:

[0055] In step S1, the gas flow rate of crude hexafluorobutadiene is 30 kg / h;

[0056] Example 3

[0057] The process steps are similar to those of Example 1, except that the gas flow rate parameters in step S1 are:

[0058] In step S1, the gas flow rate of the crude hexafluorobutadiene is 50 kg / h;

[0059] Example 4

[0060] The process steps are similar to those of Example 1, except that the calcium ion replacement rate of the calcium-magnesium modified molecular sieve is 80%.

[0061] Example 5

[0062] The process steps are the same as those of Example 1, except that the separation section (12) is not cooled in step S2.

[0063] Comparative Example 1

[0064] The process steps are similar to those of Example 1, except that in step 2, 5A molecular sieve is used instead of the calcium-magnesium modified molecular sieve.

[0065] Comparative Example 2

[0066] The process steps are similar to those of Example 1, except that the calcium ion replacement rate of the calcium-magnesium modified molecular sieve is 40%.

[0067] Comparative Example 3

[0068] The process steps are similar to those of Example 1, except that the calcium ion replacement rate of the calcium-magnesium modified molecular sieve is 20%.

[0069]

[0070] It can be seen from the data in the above table that the conventional 5A molecular sieve is used as an adsorbent in Comparative Example 1, except that the sodium ions of the 5A molecular sieve are not replaced. The calcium-magnesium modified molecular sieves in Example 1, Example 4, and Comparative Examples 2 to 3 replace the sodium ions in the 5A molecular sieve structure with calcium-magnesium ions. The difference is that the sodium ion replacement rate is reduced from 100% to 80%, 40%, and 20%. It can be seen that with the reduction of the sodium ion replacement rate, the content of key fluorocarbon impurities is increasing, but it is lower than the case where the sodium ions are not replaced in Comparative Example 1. It can be seen that the use of Calcium ions and magnesium ions replace sodium ions in 5A molecular sieve. As the sodium ion replacement rate increases, the content of key fluorocarbon impurities gradually decreases. When the sodium ion replacement rate reaches more than 80%, the purity of hexafluorobutadiene reaches more than 99.99%, the key fluorocarbon impurities are within 60ppm, and the yield reaches more than 86%. Through similar experiments, it was found that when the sodium ion replacement rate of the calcium-magnesium modified molecular sieve reaches more than 95%, the key fluorocarbon impurities can be controlled to less than 50ppm, and the yield reaches more than 90%.

[0071] In Example 5, the separation section of the separation adsorber was not cooled, which slightly reduced the deep adsorption effect of fluorocarbon impurities and the yield of hexafluorobutadiene.

[0072] Examples 1 to 3 have basically no effect on the adsorption removal of HF and H2O. It can be seen that when magnesium oxide adsorbent is used as the adsorbent in the adsorption removal of acid step, calcium type adsorbent is used as the adsorbent in the adsorption removal of water step, and the adsorption pressure is 0.7-0.9Mpa, the adsorption effect is stable in a wide range of gas flow rates, and the effects of deep acid removal and water removal are achieved. When 5A molecular sieve is used as an adsorbent for water removal, due to its strong selectivity for polar molecules, water is preferentially removed. Therefore, C4F6 raw material is basically not adsorbed in this step, and the effect on fluorocarbon impurities is minimal.

[0073] It also provides a comparison of the adsorbent effects of acid removal and water removal by adsorption.

[0074] (1) Replace different adsorbents to remove HF, introduce raw materials under the following conditions, and record the test results after adsorption and acid removal, as follows:

[0075]

[0076] As shown in the above table, when sodium lime is used as an adsorbent, the adsorption pressure is 0.08Mpa, the gas flow rate is 5.0L / min, and the online detection result is HF content 0.1≤HF≤0.5ppm; when the gas flow rate is 10.0L / min, the online detection result is HF content 0.5≤HF≤1.0ppm, and heat is generated. This shows that using sodium lime as an adsorbent can remove most of the HF in the raw material at low flow rates, but the adsorption effect deteriorates at high flow rates and heat is generated. When NaF is used as an adsorbent, the adsorption pressure is 0.08Mpa, the gas flow rate is 5.0L / min, and the online detection result is HF content 5.0≤HF≤10.0ppm; when the gas flow rate is 10.0L / min, the online detection result is HF content 8.0≤HF≤12.0ppm, indicating that the NaF adsorbent is poor. When magnesium oxide is used as an adsorbent, the online detection result is HF≤0.2ppm when the adsorption pressure is 0.08Mpa and the gas flow rate is 5.0L / min; when the gas flow rate is 10.0L / min, the online detection result is HF≤0.2ppm, which shows that the magnesium oxide adsorbent has very excellent HF adsorption performance and stable adsorption effect.

[0077] (2) Replace different adsorbents to remove H2O, introduce raw materials under the following conditions, and record the test results after adsorption and water removal, as shown in the following table:

[0078]

[0079]

[0080] As shown in the above table, molecular sieves 3A, 4A, 10A and 13X were used as dehydration adsorbents at an adsorption pressure of 0.08Mpa and a gas flow rate of 5.0L / min. The experimental results showed that the adsorbents heated up severely, so the experiment was stopped and the adsorber was purged with nitrogen to prevent the temperature from continuing to rise. Therefore, molecular sieves 3A, 4A, 10A and 13X are not suitable as dehydration adsorbents for C4F6 raw materials. 5A molecular sieve was used as an adsorbent at an adsorption pressure of 0.08Mpa and a gas flow rate of 5.0L / min. The online detection result was H2O≤2.0ppm; when the gas flow rate was 10.0L / min, the online detection result was H2O≤2.0ppm. This shows that 5A molecular sieve is relatively stable and can be used as a dehydrating agent for C4F6. The moisture detection meets the standard. When XH-11 molecular sieve is used as dehydration adsorbent, the adsorbent is slightly heated at an adsorption pressure of 0.08Mpa and a gas flow rate of 5.0L / min, and H2O≤2.0ppm; when the gas flow rate is 10.0L / min, the adsorbent is moderately heated, and the experiment is terminated to prevent the temperature from continuing to rise. XH-11 is also not suitable as a dehydration adsorbent for C4F6 raw materials.

[0081] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A purification process for hexafluorobutadiene, characterized in that: The steps include: S1. The crude hexafluorobutadiene is introduced into an adsorption tower, and then acid and water are removed by adsorption in sequence; S2, the crude hexafluorobutadiene after dehydration is introduced into a separation adsorber (1) to separate and adsorb fluorocarbon impurities; S3, subjecting the crude hexafluorobutadiene after the adsorption treatment to a double-tower continuous distillation treatment, firstly introducing the distillation tower A to remove heavy component impurities, and then introducing the distillation tower B to remove light component impurities, to obtain the hexafluorobutadiene finished product; In step S2, the crude hexafluorobutadiene product after dehydration by adsorption is introduced into the bottom of the separation adsorber (1), the bottom of the separation adsorber (1) is a kettle part (11), the upper part of the kettle part (11) is a separation section (12), and passes through the lower half section (121) and the upper half section (122) of the separation adsorber (1) in sequence, and the crude hexafluorobutadiene product after adsorbing fluorocarbon impurities is discharged from the top of the separation adsorber (1); the lower half section (121) of the separation section is filled with regular filler, and the upper half section (122) of the separation section is filled with calcium-magnesium modified molecular sieve, and the calcium-magnesium modified molecular sieve is prepared by replacing sodium ions with calcium ions and magnesium ions using 5A molecular sieve as the structural basis, and the sodium ion replacement rate is more than 80%.

2. The purification process of hexafluorobutadiene as claimed in claim 1, characterized in that: In the calcium-magnesium modified molecular sieve, the sodium ion replacement rate is above 95%.

3. The purification process of hexafluorobutadiene as claimed in claim 2, characterized in that: The calcium-magnesium modified molecular sieve is composed of a silicon-aluminum skeleton with a silicon-aluminum molar ratio of 2.8-3.2, and is loaded with calcium-magnesium ions with a calcium-magnesium molar ratio of 1:1 to 1:

3.

4. The purification process of hexafluorobutadiene as claimed in claim 2, characterized in that: In step S1, in the adsorption and acid removal step, magnesium oxide adsorbent is used; in the adsorption and water removal step, calcium type molecular sieve is used.

5. The purification process of hexafluorobutadiene as claimed in claim 4, characterized in that: In step S1, the gas flow rate of the crude hexafluorobutadiene is 30-50 kg / h, and the adsorption pressure during the adsorption process is 0.07-0.09 MPa.

6. The purification process of hexafluorobutadiene as claimed in claim 5, characterized in that: A jacket (13) is provided in the separation section (12) of the separation adsorber (1), and a refrigerant is introduced to cool the separation section (12) to 5-10°C.

7. The process for purifying hexafluorobutadiene according to claim 2, 3, 4, 5 or 6, characterized in that: In step S3, the crude hexafluorobutadiene from which the fluorocarbon impurities have been removed by adsorption is introduced into the middle and lower part of the distillation tower A, the distillation equilibrium is controlled, and the heavy component impurities in the gas phase are extracted from the bottom liquid phase of the distillation tower A through gas-liquid phase exchange; The crude hexafluorobutadiene from which the heavy impurities are separated enters the distillation tower B from the upper middle part of the distillation tower A, the distillation balance is controlled, the light impurities in the gas phase are collected at the top of the distillation tower B, and the hexafluorobutadiene product from which the light impurities are separated is taken out from the liquid phase in the bottom of the distillation tower B.

8. The process for purifying hexafluorobutadiene as claimed in claim 7, characterized in that: In step S3, when the liquid level of distillation tower A reaches 80%, the temperature of distillation tower A is controlled to be 30-38°C, the pressure is 0.15-0.25Mpa, and the reflux rate is 500kg / h; When the tower liquid level of distillation tower B reaches 80%, the temperature of distillation tower B is controlled to be 18-25°C, the pressure is 0.05-0.15Mpa, and the reflux rate is 350kg / h.

9. The process for purifying hexafluorobutadiene as claimed in claim 8, characterized in that: In step S3, the flow rate of crude hexafluorobutadiene entering distillation tower A is controlled to be 30-50 kg / h, and the bottom liquid phase of the distillation tower A extracts heavy component impurities at a flow rate of 2-4 kg / h and enters the heavy component storage tank; the flow rate of crude hexafluorobutadiene entering distillation tower B is controlled to be 28-46 kg / h, and the top of the distillation tower B extracts light component impurities at a flow rate of 2-4 kg / h; the bottom liquid phase of the distillation tower B extracts finished hexafluorobutadiene at a flow rate of 26-42 kg / h and fills it.

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