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

Abstract

The present invention belongs to the technical field of adsorption and separation materials, and specifically relates to the application of metal-organic framework materials in the purification of tetrafluoromethane and a method for purifying tetrafluoromethane. The present invention provides the application of metal-organic framework materials in the purification of tetrafluoromethane, wherein the metal-organic framework materials include metal ions and organic ligands; the metal ions include transition metal ions and / or alkaline earth metal ions; and the organic ligands have the structure shown in Formula I. The present invention utilizes a specific metal-organic framework material with a positively charged pore environment to preferentially adsorb perfluorocarbon compounds and sulfur hexafluoride that are larger in molecular size and have a larger negative surface area than tetrafluoromethane, thereby separating and obtaining high-purity tetrafluoromethane. At the same time, the method for preparing the metal-organic framework material involved in the present invention is simple, 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.

Description

Technical Field

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

[0002] Tetrafluoromethane (CF4, also known as carbon tetrafluoride or R14) is a highly stable perfluorocarbon compound and a key plasma etching gas in the electronics industry. It is widely used for 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 essential for producing high-precision, high-quality products. Currently, the 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] Currently, traditional distillation is the primary method used in industry to separate perfluorocarbons and sulfur hexafluoride from tetrafluoromethane. For example, Chinese patent CN115073261A discloses a method for purifying electronic-grade tetrafluoromethane. This method involves first removing hydrogen fluoride and dechlorinating the product through absorption, followed by a final two-stage distillation process to remove light and heavy impurities, respectively, to obtain high-purity tetrafluoromethane. However, because the product and the impurities have low boiling points, similar physical and chemical properties, and a low impurity content, this process requires high energy consumption and is inefficient.

[0005] In contrast, the physical adsorption separation method based on solid porous materials does not require phase change during the process and has lower energy consumption. It is one of the ideal alternatives to distillation, especially in removing low-concentration gas impurities. However, the performance of the adsorbents currently used is limited, and it is difficult to achieve compatibility of high adsorption capacity and selectivity for low-concentration perfluorocarbons and sulfur hexafluoride. For example, Chinese patent CN101863734A discloses a tetrafluoromethane purification method that combines flash evaporation and adsorption. It uses two-stage flash evaporation to remove most impurities, and finally pressurizes the adsorbent 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 present invention aims 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 serves as an adsorbent with excellent performance, high efficiency and stability, and can selectively and effectively remove low concentrations of perfluorocarbon compounds (C2-C10 perfluoroolefins and C2-C10 perfluoroalkanes) and sulfur hexafluoride from tetrafluoromethane. At the same time, it does not require the assistance of other purification processes, simplifies the purification steps of tetrafluoromethane, has low energy consumption, and 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 the use 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, hydroxy, 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 phenylene.

[0013] Preferably, the metal organic framework material has a one-dimensional straight through 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 salts of metal ions; the molar ratio of the metal salt to the organic ligand having the structure shown in Formula I is (1-3):1;

[0017] The raw materials for the solvothermal reaction further include a deprotonating agent, which 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; 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 a metal-organic framework material as an adsorbent with a gas mixture containing tetrafluoromethane for adsorption; 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:

[0022]

[0023] In formula I, R1 to R4 are independently selected from hydrogen, hydroxy, 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 gas mixture containing tetrafluoromethane comprises tetrafluoromethane and impurity gases, and the impurity gases comprise 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 the use of a metal-organic framework material for 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 the structure represented by Formula I. The present invention utilizes a specific metal-organic framework material with a positively charged internal pore environment to preferentially adsorb perfluorocarbons and sulfur hexafluoride, which are larger than tetrafluoromethane molecules and have a greater negative surface area, to separate and obtain 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; and the organic ligands have a structure as shown in Formula I. The metal organic framework material provided by the present invention has a one-dimensional straight through pore with a pore size range of The accessible surfaces of the pores are primarily positively charged. Due to the differences in size, shape, and molecular surface area between tetrafluoromethane and other impurity molecules, the metal-organic framework material has the weakest effect on tetrafluoromethane. It can then preferentially and efficiently adsorb other perfluorocarbons (C2-C10 perfluoroolefins and C2-C10 perfluoroalkanes) and sulfur hexafluoride with higher molecular weights. This allows for the production of a tetrafluoromethane product with a purity greater than 99.999% in a single step, with perfluorocarbon and sulfur hexafluoride concentrations below 1 ppm.

[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 larger molecular weight perfluorinated impurities (such as hexafluoroethane, etc.) in the tetrafluoromethane feed gas, with high adsorption capacity and high adsorption selectivity, to 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. The adsorbent provided by the present invention is far superior to the vast majority of solid adsorbents. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the PXRD pattern of the stability study of the metal organic framework material prepared in Example 1;

[0034] Figure 2 The PXRD pattern of the metal organic framework material prepared in Example 2 was used to investigate its stability.

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

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

[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 the use 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, hydroxy, 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, more preferably zinc ions or nickel ions.

[0043] In the present invention, in Formula I, R1-R4 are independently selected from hydrogen or a C1-C4 alkyl group. L is selected from a single bond or a phenylene group. The C1-C4 alkyl group is preferably a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, or a tert-butyl group. 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 through 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 surface accessible to guest molecules in the pores is primarily positively charged. In some embodiments, the pores also contain metal sites accessible to guest molecules. Due to the differences 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 preferentially and efficiently adsorbing other perfluorocarbons and sulfur hexafluoride with larger molecular weights. This allows for the production of a tetrafluoromethane product with a purity greater than 99.999% in a single step, with perfluorocarbon and sulfur hexafluoride concentrations below 1 ppm.

[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 a transition metal salt and / or an alkaline earth metal salt. The metal salt preferably includes one or more of chlorides, nitrates, acetates, carbonates, sulfates, perchlorates and acetylacetonates of the metal ion, more preferably acetates of the metal ion. In a specific embodiment of the present invention, the metal salt is preferably one or more of chlorides, nitrates, acetates, carbonates, sulfates, perchlorates and acetylacetonates of zinc ions, or the metal salt is preferably one or more of chlorides, nitrates, acetates, carbonates, sulfates, perchlorates and acetylacetonates of nickel ions, or the metal salt is preferably one or more of chlorides, nitrates, acetates, carbonates, sulfates, perchlorates and acetylacetonates of copper ions; or the metal salt is preferably one or more of chlorides, nitrates, acetates, carbonates, sulfates, perchlorates and acetylacetonates of cobalt ions. 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 represented by Formula I is preferably (1-3):1, more preferably 1:1.

[0049] In the present invention, the raw materials for the solvothermal reaction preferably further include a deprotonating agent. The mixing step 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 comprises one or more of an organic amine, a metal hydroxide, and a metal alkoxide, more preferably triethylamine or sodium methoxide, and most preferably sodium methoxide. The present invention has no particular requirement for the amount of the deprotonating agent used, as long as the solvothermal reaction proceeds smoothly to produce 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 methanol, acetonitrile, or N,N-dimethylformamide, and most preferably methanol. The present invention has no particular requirements for the amount of the polar solvent used; it only requires ensuring that the raw materials are evenly mixed and the solvothermal reaction proceeds smoothly.

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

[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 the obtained solid product is washed and / or soaked to obtain the solvothermal reaction solid phase product. The solid-liquid separation is preferably filtered. 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 produces a solid-phase product. The present invention preferably further comprises activating the solid-phase product under vacuum conditions to produce the metal-organic framework material. In the present invention, the activation temperature is 25-200°C, more preferably 120-200°C, and specifically 150°C in the embodiment. The activation time is preferably 12-24 hours. In the present invention, the activation serves to remove residual solvent and gas molecules within the pore structure of the metal-organic framework material.

[0055] The present invention provides a method for purifying tetrafluoromethane, comprising the following steps: contacting a metal-organic framework material as an adsorbent with a gas mixture containing tetrafluoromethane for adsorption; 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:

[0056]

[0057] In formula I, R1 to R4 are independently selected from hydrogen, hydroxy, 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 gas mixture containing tetrafluoromethane preferably includes tetrafluoromethane and impurity gases, and the impurity gases preferably include 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 gas mixture containing tetrafluoromethane is the largest. The volume percentage of tetrafluoromethane in the gas mixture containing tetrafluoromethane is preferably ≥97%. Among the impurity gases, hexafluoroethane has the closest physical and chemical properties to tetrafluoromethane and is one of the impurities that is most difficult to separate.

[0059] In the present invention, the gas mixture containing tetrafluoromethane 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, separating and obtaining 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 and conducting 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 is completed, passing the gas mixture containing tetrafluoromethane into the adsorbent bed for contact adsorption; after the contact adsorption is completed, desorbing and regenerating the adsorbed metal-organic framework material in the adsorbent bed. The inert gas used in the pre-purging is preferably helium, the pre-purging temperature is preferably 90-100°C, and the pre-purging time is preferably 12-24 hours. The flow rate of the tetrafluoromethane-containing gas mixture into the adsorbent bed is preferably 1-3 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 the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0068] Example 1

[0069] Mix 0.2 mmol of 4,4'-bipyrazole with 30 mL of methanol, add 0.4 mmol of sodium methoxide, and stir at 45°C for 30 minutes. Then, slowly add 0.2 mmol of zinc acetate dihydrate and stir at room temperature for 24 hours. After the reaction is complete, filter and wash several times with methanol to obtain the purified metal-organic framework. The purified adsorbent is 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 1The results show that the PXRD of the adsorbent is consistent with that of the newly synthesized one, whether exposed to air for 6 months or immersed in water for 1 month, 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 tests of tetrafluoromethane, hexafluoroethane, sulfur hexafluoride, hexafluoropropylene and octafluoropropane were carried out using the above adsorbent. The adsorption test temperatures were 0℃, 25℃ and 40℃, respectively. The adsorption isotherms of tetrafluoromethane and hexafluoroethane are shown in Figure 2. Figure 3 At 25°C and 100kPa, the adsorption capacity of tetrafluoromethane reached 1.89mmol / g, the adsorption capacity of hexafluoroethane reached 2.90mmol / g, the adsorption capacity of sulfur hexafluoride reached 3.22mmol / g, the adsorption capacity of hexafluoropropylene reached 2.93mmol / g, and the adsorption capacity 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 at 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 minutes. Subsequently, 0.5 mmol of nickel acetate tetrahydrate was added and stirred at 60°C for 8 hours. After the reaction was complete, the mixture was filtered and washed with acetonitrile. The product was then soaked in methanol for 3 days (the methanol was changed once a day) and finally filtered to obtain the purified metal-organic framework. 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 The results show that the PXRD of the adsorbent is consistent with that of the newly synthesized one, whether exposed to air for 6 months or immersed in water for 1 month, 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 capacity of tetrafluoromethane reached 2.03mmol / g, the adsorption capacity of hexafluoroethane reached 2.27mmol / g, the adsorption capacity of sulfur hexafluoride reached 2.19mmol / g, the adsorption capacity of hexafluoropropylene reached 2.72mmol / g, and the adsorption capacity 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, followed by the addition of 0.5 mmol of cobalt acetate tetrahydrate. After stirring for 30 minutes, the mixture was transferred to a 25 mL hydrothermal reactor and reacted at 120°C for 24 hours. After completion of the reaction, the metal-organic framework was purified by filtration and washed with dichloromethane. The purified adsorbent was then vacuum-degassed at 150°C for 12 hours to obtain the desolventized adsorbent.

[0079] The single-component adsorption isotherms of tetrafluoromethane and hexafluoroethane on the synthesized metal-organic framework were tested at 25°C. At 100 kPa, the adsorption capacity of tetrafluoromethane reached 1.46 mmol / g, and the adsorption capacity 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 minutes. Subsequently, 0.2 mmol of copper acetate was added and stirred at room temperature for 24 hours. After the reaction was complete, the metal-organic framework was purified by filtration and washed with acetonitrile. The purified adsorbent was then vacuum-degassed at 150°C for 12 hours to obtain the desolventized adsorbent.

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

[0083] Example 5

[0084] Mix 0.2 mmol of 3,3'-dimethyl-4,4'-bipyrazole with 30 mL of methanol, add 0.4 mmol of sodium methoxide, and stir at 45°C for 30 minutes. Then, slowly add 0.2 mmol of zinc acetate dihydrate and stir at room temperature for 24 hours. After the reaction is complete, filter and wash several times with methanol to obtain the purified metal-organic framework. The purified adsorbent is vacuum-degassed at 150°C for 12 hours to obtain the desolventized adsorbent.

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

[0086] Example 6

[0087] 0.5 mmol of 1,4-di(pyrazol-4-yl)benzene was mixed with 10 mL of acetonitrile, and 1 mL of triethylamine was added. The mixture was stirred at 60°C for 10 minutes, followed by the addition of 0.5 mmol of nickel acetate tetrahydrate and stirring at 60°C for 8 hours. After the reaction was complete, the mixture was filtered and washed with acetonitrile. The product was then soaked in methanol for 3 days (the methanol was changed daily) and finally filtered to obtain the purified metal-organic framework. 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 on the synthesized metal-organic framework were tested at 25°C. At 100 kPa, the adsorption capacity of tetrafluoromethane reached 1.02 mmol / g, and the adsorption capacity of hexafluoroethane reached 2.58 mmol / g.

[0089] Example 7

[0090] Mix 0.2 mmol of 1,4-di(pyrazol-4-yl)benzene with 30 mL of methanol, add 0.4 mmol of sodium methoxide, and stir at 45°C for 30 minutes. Then, slowly add 0.2 mmol of zinc acetate dihydrate and stir at room temperature for 24 hours. After the reaction is complete, filter and wash several times with methanol to obtain the purified metal-organic framework. Degas the purified adsorbent in a vacuum at 150°C for 12 hours to obtain the desolventized adsorbent.

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

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

[0093] Table 1 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 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 gas mixture of hexafluoroethane and tetrafluoromethane (3 / 97, v / v) was introduced into the packed column at 25°C at a flow rate of 1 mL / min. The gas concentration at the packed column outlet was determined by gas chromatography using a thermal conductivity 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] 0.20 g of the adsorbent synthesized in Example 2 was 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 hours, a binary gas mixture of hexafluoroethane and tetrafluoromethane (3 / 97, v / v) was introduced into the packed column at 25°C at a flow rate of 1 mL / min. The gas concentration at the packed column outlet was measured using gas chromatography using a thermal conductivity detector (TCD). Tetrafluoromethane penetrated relatively quickly, while the retention time of hexafluoroethane was approximately 182 min / g. High-purity hexafluoroethane (product purity ≥99.999%) was obtained in a single adsorption run. After the breakthrough experiment, the sample packed column was regenerated by purging with helium (100°C, 15 mL / 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 larger molecular weight perfluorinated impurities (such as hexafluoroethane, etc.) in the tetrafluoromethane feed gas, with high adsorption capacity and high adsorption selectivity, to 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. The adsorbent prepared by the present invention is far superior to most solid adsorbents.

[0101] Although the above embodiment provides a detailed description of the present invention, 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 scope of protection 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 includes metal ions and organic ligands; the metal ions are selected from one or more of zinc ions, nickel ions, cobalt ions and copper ions; and the organic ligand has a structure shown in Formula I: Formula I; In Formula I, R1 to R4 are independently selected from hydrogen, hydroxy, halogen, carboxyl, amino or C1 to C4 alkyl, and L is selected from a single bond, vinylene or C6 to C8 arylene; The metal organic framework material has a one-dimensional straight through channel with a pore diameter ranging from 4.5 to 15.0 Å; The gas mixture containing tetrafluoromethane includes tetrafluoromethane and impurity gas, wherein the impurity gas includes one or more of C2-C10 perfluoroolefins, C2-C10 perfluoroalkanes and sulfur hexafluoride.

2. The use according to claim 1, characterized in that 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 phenylene.

3. The use according to claim 1 or 2, characterized in that The pore shape of the metal organic framework material is square, diamond or triangle.

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 comprises one or more of chloride, nitrate, acetate, carbonate, sulfate, perchlorate and acetylacetonate metal salts of metal ions; the molar ratio of the metal salt to the organic ligand having the structure shown in formula I is (1-3):1; The raw materials for the solvothermal reaction further include a deprotonating agent, which 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 0-220° C., and the time is 0.1-96 h.

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 and is contacted with a gas mixture containing tetrafluoromethane for adsorption; the metal organic framework material comprises metal ions and organic ligands; the metal ions are selected from one or more of zinc ions, nickel ions, cobalt ions and copper ions; and the organic ligand has a structure shown in Formula I: Formula I; In Formula I, R1 to R4 are independently selected from hydrogen, hydroxy, halogen, carboxyl, amino or C1 to C4 alkyl, and L is selected from a single bond, vinylene or C6 to C8 arylene; The metal organic framework material has a one-dimensional straight through channel with a pore diameter ranging from 4.5 to 15.0 Å; The gas mixture containing tetrafluoromethane includes tetrafluoromethane and impurity gas, wherein the impurity gas includes one or more of C2-C10 perfluoroolefins, C2-C10 perfluoroalkanes and sulfur hexafluoride.

8. The method according to claim 7, characterized in that The gas mixture containing tetrafluoromethane is obtained from a crude tetrafluoromethane product through 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.

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 single-tower or multi-tower pressure swing adsorption process, a temperature swing adsorption process and a vacuum desorption adsorption process or a combination of one or more; 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 -10~50°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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