Application of metal organic framework material in purification of tetrafluoromethane and method for purifying tetrafluoromethane

Abstract

The invention belongs to the technical field of adsorption separation materials, and particularly relates to application of a metal organic framework material in tetrafluoromethane purification, namely a method for purifying tetrafluoromethane. The invention provides application of a metal organic framework material in purification of tetrafluoromethane. The metal organic framework material comprises metal ions and an organic ligand, the metal ions comprise transition metal ions and / or alkaline earth metal ions; the organic ligand has a structure as shown in a formula I. According to the method, the specific metal organic framework material with an electropositive pore channel internal environment is used for preferentially adsorbing the perfluorocarbon and the sulfur hexafluoride which are larger than tetrafluoromethane in molecular size and larger in surface electronegative area, and high-purity tetrafluoromethane can be obtained through separation. Meanwhile, the preparation method of the metal organic framework material is simple and easy to operate and amplify. The metal organic framework material provided by the invention is stable in structure and performance, and the adsorbent provided by the invention is far superior to most solid adsorbents.

Description

Technical Field

[0001] The invention belongs to the technical field of adsorption separation materials, and in particular relates to application of metal organic framework materials in tetrafluoromethane purification and a method for purifying tetrafluoromethane. Background Art

[0002] Tetrafluoromethane (CF4, also known as carbon tetrafluoride, R14) is a perfluorocarbon compound with good stability. It is an important plasma etching gas in the current electronics industry and is widely used in surface etching and cleaning of materials such as silicon, silicon dioxide, silicon nitride and tungsten. With the rapid development of the electronics industry, high-purity tetrafluoromethane is the guarantee for the production of high-precision and high-quality products. The current purity requirement for electronic-grade tetrafluoromethane is ≥99.999%.

[0003] The main synthesis processes of tetrafluoromethane include hydrofluorocarbon fluorination, methane fluorination, chlorofluoromethane fluorination, fluorocarbon method and plasma method. Other perfluorocarbon compounds and sulfur hexafluoride may be produced during the production process. These fluorine-containing gas impurities have similar physical and chemical properties to tetrafluoromethane and are one of the most difficult impurities to remove in tetrafluoromethane.

[0004] At present, the traditional distillation method is mainly used in the industry to separate perfluorocarbons and sulfur hexafluoride in tetrafluoromethane. For example, Chinese patent CN115073261A discloses a method for purifying electronic grade tetrafluoromethane, which first removes hydrogen fluoride and dechlorination by absorption, and then removes light and heavy impurities by the last two stages of distillation to obtain high-purity tetrafluoromethane; however, since the product and the impurities have low boiling points, similar physical and chemical properties, and low impurity content, the process requires high energy consumption and low efficiency.

[0005] In contrast, the physical adsorption separation method based on solid porous materials is one of the ideal alternatives to distillation because it does not require phase change during the process and has lower energy consumption, especially in removing low-concentration gas impurities. However, the performance of the adsorbents currently used is limited, and it is difficult to achieve compatibility with high adsorption capacity and selectivity for low-concentration perfluorocarbons and sulfur hexafluoride. For example, Chinese patent CN101863734A discloses a tetrafluoromethane purification method combining flash evaporation and adsorption, which uses two-stage flash evaporation to remove most impurities, and finally pressurizes the adsorber equipped with molecular sieves to remove trace perfluoro impurities. Although this method can successfully separate and obtain high-purity tetrafluoromethane, due to the low adsorption performance of the adsorbent, most of the perfluoro impurities still need to be removed by pre-flash evaporation, and adsorption needs to be performed under high pressure, which consumes a lot of energy. Summary of the invention

[0006] The purpose of the present invention is to provide an application of a metal organic framework material in the purification of tetrafluoromethane and a method for purifying tetrafluoromethane. The metal organic framework material provided by the present invention is used as an adsorbent with excellent performance, high efficiency and stability, and can selectively and effectively remove low-concentration perfluorocarbon compounds (C2-C10 perfluoroolefins and C2-C10 perfluoroalkanes) and sulfur hexafluoride in tetrafluoromethane; at the same time, no other purification process is required to assist, the purification steps of tetrafluoromethane are simplified, the energy consumption is low, and it is suitable for industrial application.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides an application of a metal organic framework material in the purification of tetrafluoromethane. The metal organic framework material comprises metal ions and organic ligands; the metal ions comprise transition metal ions and / or alkaline earth metal ions; and the organic ligands have a structure shown in Formula I:

[0009]

[0010] In formula I, R1 to R4 are independently selected from hydrogen, hydroxyl, halogen, carboxyl, amino or C1 to C4 alkyl, and L is selected from a single bond, vinylene or C6 to C8 arylene.

[0011] Preferably, the metal ions include one or more of zinc ions, nickel ions, cobalt ions and copper ions;

[0012] In formula I, R1 to R4 are independently selected from hydrogen or C1 to C4 alkyl, and L is selected from a single bond or a phenylene group.

[0013] Preferably, the metal organic framework material has a one-dimensional straight channel; the channel shape is square, diamond or triangle; the pore size range is

[0014] Preferably, the method for preparing the metal organic framework material comprises the following steps:

[0015] The metal salt, the organic ligand with the structure shown in formula I and a polar solvent are mixed to carry out a solvothermal reaction to obtain the metal organic framework material.

[0016] Preferably, the metal salt comprises one or more of chloride, nitrate, acetate, carbonate, sulfate, perchlorate and acetylacetonate metal salt of metal ions; the molar ratio of the metal salt to the organic ligand of the structure shown in formula I is (1-3):1;

[0017] The raw materials of the solvothermal reaction also include a deprotonating agent, and the deprotonating agent includes one or more of an organic amine, a metal hydroxide, and a metal alkoxide; the polar solvent includes one or more of water, acetonitrile, methanol, ethanol, acetone, N,N-dimethylformamide, N,N-diethylformamide, and N,N-dimethylacetamide;

[0018] The temperature of the solvent thermal reaction is 0 to 220° C., and the time is 0.1 to 96 hours.

[0019] Preferably, the solvothermal reaction directly obtains a solvothermal reaction solid phase product; and further comprising: activating the solvothermal reaction solid phase product under vacuum conditions to obtain the metal organic framework material;

[0020] The activation temperature is 25-200°C.

[0021] The present invention provides a method for purifying tetrafluoromethane, comprising the following steps: contacting and adsorbing a metal organic framework material as an adsorbent with a gas mixture containing tetrafluoromethane; the metal organic framework material comprises metal ions and organic ligands; the metal ions comprise transition metal ions and / or alkaline earth metal ions; the organic ligands have a structure shown in Formula I:

[0022]

[0023] In formula I, R1 to R4 are independently selected from hydrogen, hydroxyl, halogen, carboxyl, amino or C1 to C4 alkyl, and L is selected from a single bond, vinylene or C6 to C8 arylene.

[0024] Preferably, the tetrafluoromethane-containing gas mixture comprises tetrafluoromethane and impurity gas, and the impurity gas comprises one or more of C2-C10 perfluoroolefins, C2-C10 perfluoroalkanes and sulfur hexafluoride;

[0025] The tetrafluoromethane-containing gas mixture is obtained from a crude tetrafluoromethane product by pre-separation and purification, wherein the pre-separation and purification is to remove one or more of HF, F2, N2, O2, H2O, carbon oxides and hydrofluorocarbons from the crude tetrafluoromethane product;

[0026] Preferably, the contact adsorption method includes any one or more of fixed bed adsorption, fluidized bed adsorption and moving bed adsorption; the contact adsorption process includes a combination of one or more of a single-tower or multi-tower pressure swing adsorption process, a temperature swing adsorption process and a vacuum desorption adsorption process;

[0027] The metal organic framework material selectively adsorbs C2-C10 perfluoroolefins, C2-C10 perfluoroalkanes and sulfur hexafluoride in the gas mixture containing tetrafluoromethane, and separates and obtains weakly adsorbed tetrafluoromethane.

[0028] Preferably, the temperature of the contact adsorption is -10 to 50°C, and the pressure of the contact adsorption is ≤10 bar;

[0029] The desorption regeneration temperature of the metal organic framework material after contact adsorption is 25-150° C., and the desorption regeneration pressure is ≤1 bar.

[0030] The present invention provides an application of a metal organic framework material in the purification of tetrafluoromethane, wherein the metal organic framework material comprises metal ions and organic ligands; the metal ions comprise transition metal ions and / or alkaline earth metal ions; and the organic ligands have a structure shown in Formula I. The present invention utilizes a specific metal organic framework material having a positively charged pore internal environment to preferentially adsorb perfluorocarbon compounds and sulfur hexafluoride having a larger molecular size than tetrafluoromethane and a larger negatively charged surface area, thereby separating and obtaining high-purity tetrafluoromethane.

[0031] The present invention provides a method for purifying tetrafluoromethane, comprising the following steps: contacting and adsorbing a metal organic framework material as an adsorbent with a gas mixture containing tetrafluoromethane; the metal organic framework material comprises metal ions and organic ligands; the metal ions comprise transition metal ions and / or alkaline earth metal ions; the organic ligands have a structure shown in Formula I. The metal organic framework material provided by the present invention has a one-dimensional straight through channel with a pore size range of The accessible surface of the guest molecules in the pores is mainly positively charged. Due to the difference in size, shape and molecular surface area between tetrafluoromethane and other impurity molecules, the metal organic framework material has the weakest effect on tetrafluoromethane, while it can preferentially and efficiently adsorb other perfluorocarbons (C2-C10 perfluoroolefins and C2-C10 perfluoroalkanes) and sulfur hexafluoride with larger molecular weights, thereby obtaining a tetrafluoromethane product with a purity greater than 99.999% in one step, and the concentrations of perfluorocarbons and sulfur hexafluoride are less than 1ppm.

[0032] In summary, the present invention uses a specific metal organic framework material to achieve the purification of tetrafluoromethane, and can efficiently and preferentially adsorb perfluorinated impurities (such as hexafluoroethane, etc.) with a larger molecular weight in tetrafluoromethane raw gas, with a high adsorption capacity and high adsorption selectivity, and can obtain a high-purity tetrafluoromethane product. The method for preparing the metal organic framework material involved in the present invention is simple, the synthesis conditions are mild, the purification steps are simple, and it is easy to operate and scale up. The metal organic framework material involved in the present invention has a stable structure and stable performance, and the adsorbent provided by the present invention is far superior to most solid adsorbents. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The PXRD pattern of the metal organic framework material prepared in Example 1 for stability investigation;

[0034] Figure 2 The PXRD pattern of the metal organic framework material prepared in Example 2 for stability investigation;

[0035] Figure 3 The adsorption isotherms of tetrafluoromethane and hexafluoroethane at three temperatures for the metal organic framework material prepared in Example 1;

[0036] Figure 4 The adsorption isotherms of tetrafluoromethane and hexafluoroethane at three temperatures for the metal organic framework material prepared in Example 2;

[0037] Figure 5 This is the fixed bed breakthrough curve of the metal organic framework material prepared in Example 1 used in Example 8 for a mixed gas of hexafluoroethane and tetrafluoromethane. DETAILED DESCRIPTION

[0038] The present invention provides an application of a metal organic framework material in the purification of tetrafluoromethane. The metal organic framework material comprises metal ions and organic ligands; the metal ions comprise transition metal ions and / or alkaline earth metal ions; and the organic ligands have a structure shown in Formula I:

[0039]

[0040] In formula I, R1 to R4 are independently selected from hydrogen, hydroxyl, halogen, carboxyl, amino or C1 to C4 alkyl, and L is selected from a single bond, vinylene or C6 to C8 arylene.

[0041] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0042] In the present invention, the metal ions preferably include one or more of zinc ions, nickel ions, cobalt ions and copper ions, and more preferably zinc ions or nickel ions.

[0043] In the present invention, in Formula I, R1 to R4 are independently selected from hydrogen or C1 to C4 alkyl. L is selected from a single bond or a phenylene group. The C1 to C4 alkyl is preferably methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl. In a specific embodiment of the present invention, the organic ligand is specifically 1H,1H'-4,4'-bipyrazole, 3,3'-dimethyl-1H,1H'-4,4'-bipyrazole or 1,4-di(pyrazol-4-yl)benzene.

[0044] In the present invention, the metal organic framework material has a one-dimensional straight channel; the channel shape is square, diamond or triangle; the pore size range is The present invention utilizes a specific metal organic framework material with a positively charged pore environment to preferentially adsorb perfluorocarbon compounds and sulfur hexafluoride, which are larger in molecular size and have a larger negatively charged surface area than tetrafluoromethane, thereby separating and obtaining high-purity tetrafluoromethane.

[0045] In the present invention, the metal organic framework material has a one-dimensional straight through channel with a pore size range of The accessible surface of the pores for guest molecules is mainly positively charged. In some embodiments, the pores also have metal sites accessible to guest molecules. Due to the difference in size, shape and molecular surface area between tetrafluoromethane and other impurity molecules, the metal organic framework material has the weakest effect on tetrafluoromethane, while it can preferentially and efficiently adsorb other perfluorocarbons and sulfur hexafluoride with larger molecular weights, thereby obtaining a tetrafluoromethane product with a purity greater than 99.999% in one step, and the concentrations of perfluorocarbons and sulfur hexafluoride are less than 1ppm.

[0046] In the present invention, the method for preparing the metal organic framework material preferably comprises the following steps:

[0047] The metal salt, the organic ligand with the structure shown in formula I and a polar solvent are mixed to carry out a solvothermal reaction to obtain the metal organic framework material.

[0048] In the present invention, the metal salt includes transition metal salt and / or alkaline earth metal salt. The metal salt preferably includes one or more of chloride, nitrate, acetate, carbonate, sulfate, perchlorate and acetylacetonate metal salt of metal ion, more preferably acetate of metal ion. In a specific embodiment of the present invention, the metal salt is preferably one or more of chloride, nitrate, acetate, carbonate, sulfate, perchlorate and acetylacetonate metal salt of zinc ion, or the metal salt is preferably one or more of chloride, nitrate, acetate, carbonate, sulfate, perchlorate and acetylacetonate metal salt of nickel ion, or the metal salt is preferably one or more of chloride, nitrate, acetate, carbonate, sulfate, perchlorate and acetylacetonate metal salt of copper ion; or the metal salt is preferably one or more of chloride, nitrate, acetate, carbonate, sulfate, perchlorate and acetylacetonate metal salt of cobalt ion. In a specific embodiment of the present invention, the metal salt is specifically zinc acetate (zinc acetate dihydrate), nickel acetate (nickel acetate tetrahydrate), cobalt acetate (cobalt acetate tetrahydrate) or copper acetate. In the present invention, the molar ratio of the metal salt to the organic ligand of the structure shown in formula I is preferably (1 to 3): 1, more preferably 1: 1.

[0049] In the present invention, the raw materials of the solvothermal reaction preferably also include a deprotonating agent. The mixing is replaced by: mixing the metal salt, the organic ligand having the structure shown in Formula I, the deprotonating agent and the polar solvent.

[0050] In the present invention, the deprotonating agent preferably includes one or more of an organic amine, a metal hydroxide and a metal alkoxide, more preferably includes triethylamine or sodium methoxide, and most preferably is sodium methoxide. The present invention has no special requirements on the amount of the deprotonating agent, as long as the solvothermal reaction is carried out smoothly to obtain the metal organic framework material.

[0051] In the present invention, the polar solvent preferably includes one or more of water, acetonitrile, methanol, ethanol, acetone, N,N-dimethylformamide, N,N-diethylformamide and N,N-dimethylacetamide, more preferably includes methanol, acetonitrile or N,N-dimethylformamide, and most preferably is methanol. The present invention has no special requirements for the amount of the polar solvent, as long as the above raw materials are mixed evenly and the solvent thermal reaction proceeds smoothly.

[0052] In the present invention, the mixing is carried out under stirring. The mixing preferably comprises the following steps: dissolving the organic ligand in a polar solution, and then adding the deprotonating agent for premixing. Finally, the metal salt is added. The temperature of the solvothermal reaction is preferably 0 to 220°C, more preferably 40 to 60°C, specifically room temperature, 60°C or 120°C in the embodiment, and the time is preferably 0.1 to 96h, more preferably 6 to 24h, specifically 24h or 8h in the embodiment.

[0053] In the present invention, after the solvothermal reaction is completed, a solvothermal reaction liquid is obtained. The present invention preferably separates the solvothermal reaction liquid into solid and liquid, and washes and / or soaks the obtained solid product to obtain the solvothermal reaction solid phase product. The solid-liquid separation is preferably filtration. The reagent used for the washing or soaking is preferably a low-boiling point organic solvent, specifically one or more of methanol, acetonitrile and dichloromethane in the embodiment. The soaking time is preferably 3 days, and the low-boiling point organic solvent is replaced once a day during the soaking process.

[0054] In the present invention, the solvothermal reaction directly obtains a solvothermal reaction solid phase product; the present invention preferably further comprises: activating the solvothermal reaction solid phase product under vacuum conditions to obtain the metal organic framework material. In the present invention, the activation temperature is 25 to 200°C, more preferably 120 to 200°C, and specifically 150°C in the embodiment. The activation time is preferably 12 to 24 hours. In the present invention, the role of the activation is to remove the residual solvent molecules and gas molecules in the pore structure of the metal organic framework material.

[0055] The present invention provides a method for purifying tetrafluoromethane, comprising the following steps: contacting and adsorbing a metal organic framework material as an adsorbent with a gas mixture containing tetrafluoromethane; the metal organic framework material comprises metal ions and organic ligands; the metal ions comprise transition metal ions and / or alkaline earth metal ions; the organic ligands have a structure shown in Formula I:

[0056]

[0057] In formula I, R1 to R4 are independently selected from hydrogen, hydroxyl, halogen, carboxyl, amino or C1 to C4 alkyl, and L is selected from a single bond, vinylene or C6 to C8 arylene.

[0058] In the present invention, the tetrafluoromethane-containing gas mixture preferably includes tetrafluoromethane and impurity gas, and the impurity gas preferably includes one or more of C2-C10 perfluoroolefins, C2-C10 perfluoroalkanes and sulfur hexafluoride. In a specific embodiment of the present invention, the C2-C10 perfluoroolefin is specifically hexafluoropropylene. The C2-C10 perfluoroalkanes are specifically hexafluoroethane and / or octafluoropropane. In the present invention, the volume percentage of tetrafluoromethane in the tetrafluoromethane-containing gas mixture is the largest. The volume percentage of tetrafluoromethane in the tetrafluoromethane-containing gas mixture is preferably ≥97%. Among the impurity gases, hexafluoroethane is closest to tetrafluoromethane in physical and chemical properties and is one of the impurities that is most difficult to separate.

[0059] In the present invention, the tetrafluoromethane-containing gas mixture is preferably obtained from a crude tetrafluoromethane product by pre-separation and purification, and the pre-separation and purification is preferably to remove one or more of HF, F2, N2, O2, H2O, carbon oxides and hydrofluorocarbons in the crude tetrafluoromethane product.

[0060] In the present invention, the contact adsorption method preferably includes any one or more of fixed bed adsorption, fluidized bed adsorption and moving bed adsorption. The contact adsorption process preferably includes a combination of one or more of a single-tower or multi-tower pressure swing adsorption process, a temperature swing adsorption process and a vacuum desorption adsorption process. The metal organic framework material selectively adsorbs C2-C10 perfluoroolefins, C2-C10 perfluoroalkanes and sulfur hexafluoride in the gas mixture containing tetrafluoromethane to separate weakly adsorbed tetrafluoromethane.

[0061] In the present invention, the contact adsorption temperature is preferably -10 to 50°C, specifically room temperature (25°C) in the embodiment, and the contact adsorption pressure is preferably ≤10 bar. The flow rate of the tetrafluoromethane-containing gas mixture is preferably 1 to 3 mL / min.

[0062] The desorption regeneration temperature of the metal organic framework material after contact adsorption is preferably 25-150°C, specifically 100°C in the embodiment; the desorption regeneration pressure is preferably ≤1 bar. The gas used for the desorption regeneration is preferably an inert gas, specifically helium, and the flow rate of the inert gas is preferably 10-15 mL / min.

[0063] In some embodiments of the present invention, the contact adsorption is carried out in a fixed bed adsorption device.

[0064] In some embodiments of the present invention, the contact adsorption is carried out in a fluidized bed adsorption device.

[0065] In some embodiments of the present invention, the contact adsorption is carried out in a moving bed adsorption device.

[0066] In a specific embodiment of the present invention, the specific implementation method of using a metal organic framework material as an adsorbent to carry out the contact adsorption with a gas mixture containing tetrafluoromethane preferably includes the following steps: filling the metal organic framework material to form an adsorbent bed; pre-purging the adsorbent bed with an inert gas; after the pre-purging, passing the gas mixture containing tetrafluoromethane into the adsorbent bed for contact adsorption, and after the contact adsorption, desorbing and regenerating the adsorbed metal organic framework material in the adsorbent bed. The inert gas used for the pre-purging is preferably helium, the temperature of the pre-purging is preferably 90 to 100°C, and the time is preferably 12 to 24 hours. The flow rate of the gas mixture containing tetrafluoromethane into the adsorbent bed is preferably 1 to 3 mL / min.

[0067] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0068] Example 1

[0069] 0.2 mmol of 4,4'-bipyrazole and 30 mL of methanol were mixed, 0.4 mmol of sodium methoxide was added, and the mixture was stirred at 45°C for 30 min, followed by slow addition of 0.2 mmol of zinc acetate dihydrate, and stirred at room temperature for 24 h. After the reaction was completed, the mixture was filtered and washed with methanol several times to obtain the purified metal organic framework material. The purified adsorbent was vacuum degassed at 150°C for 12 hours to obtain the desolventized adsorbent.

[0070] In order to test the stability of the samples, the samples were exposed to air for 6 months and immersed in water for 1 month, and then the PXRD of the adsorbent under each condition was measured. Figure 1 .from Figure 1From the results, whether exposed to air for 6 months or immersed in water for 1 month, the PXRD of the adsorbent is consistent with that of the newly synthesized one, indicating the excellent stability of the material.

[0071] In order to test the adsorption and separation performance of the synthesized metal organic framework material, the single component adsorption test of tetrafluoromethane, hexafluoroethane, sulfur hexafluoride, hexafluoropropylene and octafluoropropane was carried out using the above adsorbent. The adsorption test temperatures were 0°C, 25°C and 40°C, respectively. The adsorption isotherms of tetrafluoromethane and hexafluoroethane are shown in Figure 3 At 25°C and 100kPa, the adsorption of tetrafluoromethane reached 1.89mmol / g, the adsorption of hexafluoroethane reached 2.90mmol / g, the adsorption of sulfur hexafluoride reached 3.22mmol / g, the adsorption of hexafluoropropylene reached 2.93mmol / g, and the adsorption of octafluoropropane reached 2.81mmol / g.

[0072] Under different temperature conditions, the adsorbent has significantly better adsorption performance for hexafluoroethane, sulfur hexafluoride, hexafluoropropylene and octafluoropropane than tetrafluoromethane, and can adsorb a large amount of hexafluoroethane, sulfur hexafluoride, hexafluoropropylene and octafluoropropane under low pressure, indicating that the material has a good adsorption and separation effect on sulfur hexafluoride in tetrafluoromethane and perfluorocarbon compounds with larger molecular weight.

[0073] Example 2

[0074] 0.5 mmol of 4,4'-bipyrazole and 10 mL of acetonitrile were mixed, 1 mL of triethylamine was added, and the mixture was stirred at 60°C for 10 min, followed by the addition of 0.5 mmol of nickel acetate tetrahydrate and stirring at 60°C for 8 h. After the reaction was completed, the mixture was filtered and washed with acetonitrile, and then the product was soaked in methanol for 3 days (methanol was changed once a day), and finally filtered to obtain the purified metal organic framework material. The purified adsorbent was vacuum degassed at 150°C for 12 hours to obtain the desolventized adsorbent.

[0075] In order to test the stability of the samples, the samples were exposed to air for 3 months and immersed in water for 1 month, and then the PXRD of the adsorbent under each condition was measured. Figure 2 .from Figure 2 From the results, whether exposed to air for 6 months or immersed in water for 1 month, the PXRD of the adsorbent is consistent with that of the newly synthesized one, indicating the excellent stability of the material.

[0076] In order to test the adsorption and separation performance of the synthesized metal organic framework material, the single component adsorption isotherm test of tetrafluoromethane, hexafluoroethane and sulfur hexafluoride was carried out using the above adsorbent. The adsorption test temperatures were 0℃, 25℃ and 40℃, respectively. The specific isotherms are shown in Figure 4At 25°C and 100kPa, the adsorption of tetrafluoromethane reached 2.03mmol / g, the adsorption of hexafluoroethane reached 2.27mmol / g, the adsorption of sulfur hexafluoride reached 2.19mmol / g, the adsorption of hexafluoropropylene reached 2.72mmol / g, and the adsorption of octafluoropropane reached 2.05mmol / g.

[0077] Example 3

[0078] 0.5 mmol of 4,4'-bipyrazole and 15 mL of N,N-dimethylformamide were mixed, and then 0.5 mmol of cobalt acetate tetrahydrate was added. After stirring for 30 min, the mixture was transferred to a 25 mL hydrothermal reactor and reacted at 120 ° C for 24 h. After the reaction was completed, the metal organic framework material was purified by filtration and washed with dichloromethane. The purified adsorbent was vacuum degassed at 150 ° C for 12 hours to obtain a desolventized adsorbent.

[0079] The single component adsorption isotherms of tetrafluoromethane and hexafluoroethane of the synthesized metal organic framework material were tested at 25° C. Under 100 kPa, the adsorption amount of tetrafluoromethane reached 1.46 mmol / g, and the adsorption amount of hexafluoroethane reached 2.11 mmol / g.

[0080] Example 4

[0081] 0.2 mmol of 4,4'-bipyrazole and 30 mL of acetonitrile were mixed and stirred at 45°C for 15 min, followed by the addition of 0.2 mmol of copper acetate and stirring at room temperature for 24 h. After the reaction was completed, the mixture was filtered and washed with acetonitrile to obtain a purified metal organic framework material. The purified adsorbent was vacuum degassed at 150°C for 12 hours to obtain a desolventized adsorbent.

[0082] The single component adsorption isotherms of tetrafluoromethane and hexafluoroethane of the synthesized metal organic framework material were tested at 25° C. Under 100 kPa, the adsorption amount of tetrafluoromethane reached 0.81 mmol / g, and the adsorption amount of hexafluoroethane reached 0.74 mmol / g.

[0083] Example 5

[0084] 0.2 mmol of 3,3'-dimethyl-4,4'-bipyrazole and 30 mL of methanol were mixed, 0.4 mmol of sodium methoxide was added, and the mixture was stirred at 45°C for 30 min, followed by slow addition of 0.2 mmol of zinc acetate dihydrate and stirring at room temperature for 24 h. After the reaction was completed, the mixture was filtered and washed with methanol several times to obtain the purified metal organic framework material. The purified adsorbent was vacuum degassed at 150°C for 12 hours to obtain the desolventized adsorbent.

[0085] The single component adsorption isotherms of tetrafluoromethane and hexafluoroethane of the synthesized metal organic framework material were tested at 25° C. Under 100 kPa, the adsorption amount of tetrafluoromethane reached 1.35 mmol / g, and the adsorption amount of hexafluoroethane reached 1.88 mmol / g.

[0086] Example 6

[0087] 0.5 mmol of 1,4-di(pyrazol-4-yl)benzene and 10 mL of acetonitrile were mixed, 1 mL of triethylamine was added, and the mixture was stirred at 60 ° C for 10 min, followed by the addition of 0.5 mmol of nickel acetate tetrahydrate and stirring at 60 ° C for 8 h. After the reaction was completed, the mixture was filtered and washed with acetonitrile, and then the product was soaked in methanol for 3 days (methanol was changed once a day), and finally filtered to obtain the purified metal organic framework material. The purified adsorbent was vacuum degassed at 150 ° C for 12 hours to obtain the desolventized adsorbent.

[0088] The single component adsorption isotherms of tetrafluoromethane and hexafluoroethane of the synthesized metal organic framework material were tested at 25° C. Under 100 kPa, the adsorption amount of tetrafluoromethane reached 1.02 mmol / g, and the adsorption amount of hexafluoroethane reached 2.58 mmol / g.

[0089] Example 7

[0090] 0.2 mmol of 1,4-di(pyrazol-4-yl)benzene and 30 mL of methanol were mixed, 0.4 mmol of sodium methoxide was added, and the mixture was stirred at 45°C for 30 min, followed by slow addition of 0.2 mmol of zinc acetate dihydrate and stirring at room temperature for 24 h. After the reaction was completed, the mixture was filtered and washed with methanol several times to obtain a purified metal organic framework material. The purified adsorbent was vacuum degassed at 150°C for 12 hours to obtain a desolventized adsorbent.

[0091] The single component adsorption isotherms of tetrafluoromethane and hexafluoroethane of the synthesized metal organic framework material were tested at 25° C. Under 100 kPa, the adsorption amount of tetrafluoromethane reached 0.83 mmol / g, and the adsorption amount of hexafluoroethane reached 4.09 mmol / g.

[0092] In the present invention, hexafluoroethane is one of the components that is most difficult to separate from tetrafluoromethane. Table 1 summarizes the adsorption performance of tetrafluoromethane and hexafluoroethane of the adsorbent samples synthesized in Examples 1 to 7 at 25°C. It can be seen that the samples prepared in Examples 1 and 2 have a higher hexafluoroethane adsorption capacity under low pressure conditions. Examples 8 and 9 test the actual separation performance of these two samples for tetrafluoromethane / hexafluoroethane mixed gas.

[0093] Table 1 Summary of the adsorption performance of samples for tetrafluoromethane and hexafluoroethane (unit: mmol / g)

[0094] sample Tetrafluoromethane (100kPa) Hexafluoroethane (100kPa) Hexafluoroethane(3kPa) Example 1 1.89 2.90 1.58 Example 2 2.03 2.27 1.44 Example 3 1.46 2.11 0.94 Example 4 0.81 0.74 0.44 Example 5 1.35 1.88 0.80 Example 6 1.02 2.58 0.31 Example 7 0.83 4.09 0.13

[0095] Example 8

[0096] 0.27 g of the adsorbent synthesized in Example 1 was taken and loaded into a packed column with an inner diameter of 4.6 mm and a length of 5 cm. After being purged with helium at 100° C. for 24 h, a binary mixed gas of hexafluoroethane / tetrafluoromethane (3 / 97, v / v) was introduced into the packed column at a flow rate of 1 mL / min at 25° C. The gas concentration at the outlet of the packed column was detected by gas chromatography, and the detector was a thermal conductivity cell detector (TCD). After the breakthrough experiment, the sample packed column was regenerated by purging with helium (100° C., 15 mL / min).

[0097] Figure 5 The fixed bed penetration curve of the adsorbent prepared in Example 1 for the mixed gas of hexafluoroethane and tetrafluoromethane. The solid curve and the hollow curve represent the concentration changes of hexafluoroethane and tetrafluoromethane at the fixed bed outlet, respectively. Figure 5 It can be seen that tetrafluoromethane can penetrate relatively quickly, while the retention time of hexafluoroethane is about 470 min / g. High-purity hexafluoroethane (product purity ≥ 99.999%) can be obtained by a single adsorption, achieving efficient separation of the two components.

[0098] Example 9

[0099] Take 0.20g of the adsorbent synthesized in Example 2, load it into a filling column with an inner diameter of 4.6mm and a length of 5cm, purge it with helium at 100℃ for 24h, then pass a binary mixed gas of hexafluoroethane / tetrafluoromethane (3 / 97, v / v) into the filling column at a flow rate of 1mL / min at 25℃, and use gas chromatography to detect the gas concentration at the outlet of the filling column, and the detector is a thermal conductivity cell detector (TCD). Tetrafluoromethane can penetrate quickly, and the retention time of hexafluoroethane is about 182min / g. High-purity hexafluoroethane (product purity ≥99.999%) can be obtained by a single adsorption. After the penetration experiment, the sample filling column is regenerated by purge with helium (100℃, 15mL / min).

[0100] From the above examples, it can be seen that the present invention uses a specific metal organic framework material to achieve the purification of tetrafluoromethane, and can efficiently and preferentially adsorb perfluorinated impurities (such as hexafluoroethane, etc.) with a larger molecular weight in tetrafluoromethane raw gas, with a high adsorption capacity and high adsorption selectivity, and a high-purity tetrafluoromethane product can be obtained. The method for preparing the metal organic framework material involved in the present invention is simple, the synthesis conditions are mild, the purification steps are simple, and it is easy to operate and scale up. The metal organic framework material involved in the present invention has a stable structure and stable performance, and the adsorbent prepared by the present invention is far superior to most solid adsorbents.

[0101] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. Application of metal organic framework materials in the purification of tetrafluoromethane, characterized in that: The metal organic framework material comprises metal ions and organic ligands; the metal ions comprise transition metal ions and / or alkaline earth metal ions; the organic ligands have a structure shown in Formula I: In formula I, R1 to R4 are independently selected from hydrogen, hydroxyl, halogen, carboxyl, amino or C1 to C4 alkyl, and L is selected from a single bond, vinylene or C6 to C8 arylene.

2. The use according to claim 1, characterized in that: The metal ions include one or more of zinc ions, nickel ions, cobalt ions and copper ions; In formula I, R1 to R4 are independently selected from hydrogen or C1 to C4 alkyl, and L is selected from a single bond or a phenylene group.

3. The use according to claim 1 or 2, characterized in that: The metal organic framework material has a one-dimensional straight channel; the channel shape is square, diamond or triangle; the pore size range is 4. The use according to claim 1, characterized in that: The preparation method of the metal organic framework material comprises the following steps: The metal salt, the organic ligand with the structure shown in formula I and a polar solvent are mixed to carry out a solvothermal reaction to obtain the metal organic framework material.

5. The use according to claim 4, characterized in that: The metal salt includes one or more of chloride, nitrate, acetate, carbonate, sulfate, perchlorate and acetylacetonate metal salt of metal ions; the molar ratio of the metal salt to the organic ligand of the structure shown in formula I is (1-3):1; The raw materials of the solvothermal reaction also include a deprotonating agent, and the deprotonating agent includes one or more of an organic amine, a metal hydroxide, and a metal alkoxide; the polar solvent includes one or more of water, acetonitrile, methanol, ethanol, acetone, N,N-dimethylformamide, N,N-diethylformamide, and N,N-dimethylacetamide; The temperature of the solvent thermal reaction is 0 to 220° C., and the time is 0.1 to 96 hours.

6. The use according to claim 4 or 5, characterized in that: The solvothermal reaction directly obtains a solvothermal reaction solid phase product; The invention also includes: activating the solid phase product of the solvent thermal reaction under vacuum conditions to obtain the metal organic framework material; The activation temperature is 25-200°C.

7. A method for purifying tetrafluoromethane, characterized in that: The following steps are involved: A metal organic framework material is used as an adsorbent to contact and adsorb a gas mixture containing tetrafluoromethane; the metal organic framework material includes metal ions and organic ligands; the metal ions include transition metal ions and / or alkaline earth metal ions; the organic ligand has a structure shown in Formula I: In formula I, R1 to R4 are independently selected from hydrogen, hydroxyl, halogen, carboxyl, amino or C1 to C4 alkyl, and L is selected from a single bond, vinylene or C6 to C8 arylene.

8. The method according to claim 7, characterized in that The tetrafluoromethane-containing gas mixture includes tetrafluoromethane and impurity gas, and the impurity gas includes one or more of C2-C10 perfluoroolefins, C2-C10 perfluoroalkanes and sulfur hexafluoride; The tetrafluoromethane-containing gas mixture is obtained from a crude tetrafluoromethane product by pre-separation and purification, wherein the pre-separation and purification is to remove one or more of HF, F2, N2, O2, H2O, carbon oxides and hydrofluorocarbons in the crude tetrafluoromethane product.

9. The method according to claim 7 or 8, characterized in that: The contact adsorption method includes any one or more of fixed bed adsorption, fluidized bed adsorption and moving bed adsorption; the contact adsorption process includes a combination of one or more of a single-tower or multi-tower pressure swing adsorption process, a temperature swing adsorption process and a vacuum desorption adsorption process; The metal organic framework material selectively adsorbs C2-C10 perfluoroolefins, C2-C10 perfluoroalkanes and sulfur hexafluoride in the gas mixture containing tetrafluoromethane, and separates and obtains weakly adsorbed tetrafluoromethane.

10. The method according to claim 7 or 8, characterized in that: The contact adsorption temperature is -10 to 50°C, and the contact adsorption pressure is ≤10 bar; The desorption regeneration temperature of the metal organic framework material after contact adsorption is 25-150° C., and the desorption regeneration pressure is ≤1 bar.

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