A MIL-101(Cr) series MOF material, its preparation method and application

Abstract

The application discloses a kind of MIL-101 (Cr) series MOFs material and its preparation method and application, it is related to chemical material technical field.The preparation method of the material includes: terephthalic acid or its derivative, chromium salt, modifier and water are mixed, and mixture is obtained;The mixture is heated under closed condition, and MIL-101 (Cr) series MOFs material is obtained.The MIL-101 (Cr) series MOFs material is used for separating hexafluoroethane and hydrogen fluoride hydrocarbon mixed gas, and separation effect is good when separating, it is very stable in air, the time of obtaining pure component is long, reusability is good, it is not necessary to use N, N-dimethylformamide and acetone multiple exchange soaking before column packing, can be applied strongly, raw material is cheap and easy to obtain and can be prepared in large quantities.

Description

Technical Field

[0001] This invention belongs to the field of chemical materials technology, and in particular relates to a MIL-101(Cr) series MOFs material, its preparation method and application. Background Technology

[0002] In recent years, with the rapid advancements in the electronics industry, the purity requirements for electronic gases have gradually increased. Among perfluorinated electronic gases, hexafluoroethane (Hexafluoroethane) accounts for 50% of the usage, demonstrating its indispensable role in the electronics industry. Hexafluoroethane (R116) is non-toxic, odorless, and highly stable. In the semiconductor and microelectronics industries, it is used as a plasma etching gas, a device surface cleaning agent, and also in optical fiber production and cryogenic refrigeration. Due to its minimal edge lateral erosion, high etching rate, and high precision, hexafluoroethane perfectly meets the requirements of small linewidth manufacturing processes, solving the problem of high-precision fine-line etching of deep submicron integrated circuits (0.18–0.25 micrometers) that conventional wet etching methods cannot achieve. High-purity hexafluoroethane is an essential dielectric for very large-scale integrated circuits, playing a crucial role in the development of the semiconductor industry. It can fundamentally change the current energy-intensive situation and meet new demands.

[0003] Electronic-grade purification of hexafluoroethane mainly employs distillation; however, distillation requires low temperature and high pressure, resulting in high energy consumption and demanding equipment requirements. Furthermore, fluorination operations are highly corrosive, placing stringent demands on both operation and equipment. Therefore, developing a reasonable processing method to obtain high-purity hexafluoroethane has become an urgent problem to be solved. Summary of the Invention

[0004] In view of this, the present invention provides a MIL-101(Cr) series MOFs material, its preparation method and application, the main purpose of which is to solve the technical problems of poor separation effect of hexafluoroethane and hydrofluorocarbon mixed gas, high energy consumption and high requirements for operating equipment.

[0005] On one hand, the present invention provides a method for preparing MIL-101(Cr) series MOFs materials, comprising the following steps: mixing terephthalic acid or its derivatives, chromium salt, modifier and water to obtain a mixture; heating the mixture under closed conditions to obtain MIL-101(Cr) series MOFs materials.

[0006] Optionally, the modifier is selected from at least one of HF, HCl, sodium acetate, ethylenediamine, diethylenetriamine, tetramethylammonium hydroxide, and N-(phosphonocarboxymethyl)iminodiacetic acid.

[0007] Optionally, the terephthalic acid derivative is selected from at least one of terephthalic acids modified with -NO2, -NH2, -SO3H, -pyridine, -CH3, -CF3, -OCH3, -CN, -(NO2)2, -(NH2)2 or -(OH2)2, or the terephthalic acid derivative is 1,4-naphthalenedicarboxylic acid.

[0008] Optionally, the molar ratio of the terephthalic acid or its derivative to the chromium salt is 0.9-1:1-1.5.

[0009] Optionally, the molar ratio of the terephthalic acid or its derivative to the chromium salt is selected from 0.9:1, 1:1, 1:1.1, 1:1.2 or 1:1.5.

[0010] Optionally, the ratio of the chromium salt to the modifier is 1:0.05 to 0.40.

[0011] Optionally, the mass ratio of the chromium salt to the modifier is any value from 1:0.0876, 1:0.1752, 1:0.219, 1:0.2628, 1:0.3504, or a range between any two.

[0012] Optionally, the chromium salt is selected from at least one of chromium nitrate nonahydrate, chromium trichloride, and chromium trioxide. The chromium salt of the present invention can be selected from the prior art as appropriate.

[0013] The MIL-101(Cr) series MOFs materials of the present invention can all be prepared by different modifiers or different reaction raw materials in the above preparation methods.

[0014] Optionally, when the modifier is HF, MIL-101(Cr)-F is obtained by hydrothermal reaction of chromium salt, terephthalic acid, deionized water and modifier.

[0015] Optionally, when the modifier is HCl, MIL-101(Cr)-Cl is obtained by hydrothermal reaction of chromium salt, terephthalic acid, deionized water and modifier.

[0016] Optionally, when the modifier is an aqueous solution of sodium acetate, MIL-101(Cr)-OH is obtained by hydrothermal reaction of chromium salt, terephthalic acid, deionized water and modifier.

[0017] The above-mentioned modification of MIL-101(Cr) in this invention is achieved by adding a modifier to the reaction raw materials to obtain the corresponding modified MIL-101(Cr) series MOF materials.

[0018] Optionally, when the modifier is ethylenediamine, after the chromium salt, terephthalic acid and deionized water are subjected to a hydrothermal reaction to obtain the MIL-101(Cr) material, the MIL-101(Cr) reacts with ethylenediamine to obtain MIL-101(Cr)-ED.

[0019] Alternatively, when the modifier is ethylenediamine, MIL-101(Cr) is modified with ethylenediamine to obtain MIL-101(Cr)-ED.

[0020] Optionally, when the modifier is diethylenetriamine, after the chromium salt, terephthalic acid and deionized water are subjected to a hydrothermal reaction to obtain the MIL-101(Cr) material, the MIL-101(Cr) reacts with diethylenetriamine to obtain MIL-101(Cr)-DETA.

[0021] Alternatively, when the modifier is diethylenetriamine, MIL-101(Cr) is modified with diethylenetriamine to obtain MIL-101(Cr)-DETA.

[0022] Optionally, when the modifier is N-(phosphonocarboxymethyl)iminodiacetic acid, after the chromium salt, the -NH2 modified terephthalic acid and deionized water undergo a hydrothermal reaction to obtain the MIL-101(Cr)-NH2 material, the MIL-101(Cr)-NH2 and N-(phosphonocarboxymethyl)iminodiacetic acid react to obtain MIL-101(Cr)-PMIDA.

[0023] Alternatively, when the modifier is N-(phosphonocarboxymethyl)iminodiacetic acid, MIL-101-NH2 is modified with N-(phosphonocarboxymethyl)iminodiacetic acid to obtain MIL-101(Cr)-PMIDA.

[0024] Optionally, when the modifier is mercaptoacetaldehyde, after the chromium salt, the terephthalic acid modified with -NH2, and the deionized water undergo a hydrothermal reaction to obtain the MIL-101(Cr)-NH2 material, the MIL-101(Cr)-NH2 is modified with mercaptoacetaldehyde to obtain MIL-101(Cr)-SH.

[0025] Alternatively, when the modifier is mercaptoacetaldehyde, MIL-101-NH2 is modified with mercaptoacetaldehyde to obtain MIL-101(Cr)-SH.

[0026] The above-mentioned modification of the present invention can be achieved by adding a modifier to MIL-101(Cr) or MIL-101(Cr)-NH2 after the synthesis of MIL-101(Cr) or MIL-101(Cr)-NH2 to improve MIL-101(Cr) or MIL-101(Cr)-NH2 in order to obtain the corresponding modified MIL-101(Cr) series MOF materials.

[0027] Optionally, terephthalic acid modified with -NO2, -NH2, -SO3H, -pyridine, -CH3, -CF3, -OCH3, -CN, -(NO2)2, -(NH2)2, or -(OH2)2, chromium salt, modifier, and water are subjected to hydrothermal reaction to obtain MIL-101(Cr)-NO2, MIL-101(Cr)-NH2, MIL-101(Cr)-SO3H, MIL-101-Pyridine, MIL-101(Cr)-CH3, MIL-101(Cr)-CF3, MIL-101(Cr)-OCH3, MIL-101(Cr)-CN, MIL-101(Cr)-(NO2)2, MIL-101(Cr)-(NH2)2, and MIL-101(Cr)-(OH2)2 materials, respectively.

[0028] Optionally, the compound containing -Pyridine is selected from 2-(4-pyridyl)terephthalic acid;

[0029] Compounds containing -CF3 are selected from compound 2-(trifluoromethyl)terephthalic acid;

[0030] Compounds containing -OCH3 are selected from compound 2-(methoxy)terephthalic acid;

[0031] Compounds containing -CN are selected from compound 2-(cyano)terephthalic acid;

[0032] The compounds containing -(NH2)2 are selected from compound 2,5-diaminoterephthalic acid;

[0033] The compounds containing -(NO2)2 are selected from compound 2,5-dinitroterephthalic acid.

[0034] Those skilled in the art can also choose other corresponding compounds with the above-mentioned functional groups according to actual needs.

[0035] Optionally, 1,4-naphthalenedicarboxylic acid (1,4-NDC), chromium salt, modifier and water are subjected to a hydrothermal reaction to obtain MIL-101-NDC material.

[0036] The MIL-101(Cr) of this invention refers to MIL-101(Cr)-F that has not been modified by functional groups.

[0037] The above-mentioned modification of the present invention is mainly achieved by first functionalizing terephthalic acid to form a derivative of terephthalic acid or directly selecting its corresponding derivative, and then reacting the derivative, chromium salt, modifier and water to obtain the modified MIL-101(Cr) series MOF material.

[0038] This invention allows for the modification of materials with different modifiers to obtain different MIL-101(Cr) series MOFs materials, thereby adjusting the pore size and active sites within the cages of the MIL-101(Cr) series MOFs, resulting in stronger / weaker forces on fluorine-containing gases, and thus adjusting the time required to separate pure tetrafluoroethane / pentafluoroethane / hexafluoroethane components.

[0039] Optionally, the heating temperature is 65–250°C, and the heating time is 5–144 hours.

[0040] Optionally, the heating temperature is selected from any value or a range between 65°C, 150°C, 180°C, 200°C, 220°C or 250°C.

[0041] The heating time is selected from any one of 5h, 8h, 12h, 24h, 72h, 144h or any range between two.

[0042] Optionally, heating the mixture under closed conditions specifically includes: the mixture undergoing a constant-temperature hydrothermal reaction in a stainless steel autoclave lined with polytetrafluoroethylene.

[0043] Optionally, the heated product is washed and dried to obtain the MIL-101(Cr) series MOFs material; the washing is performed by reflux in water at 80-90°C and / or solvent at 65-75°C to remove unreacted reactants; the drying is performed by drying the washed product at 110-120°C for 1-24 hours.

[0044] Optionally, the washing is performed by reflux in water at 85°C and / or solvent at 70°C to remove unreacted reactants; the drying is performed by drying the washed product at 110 or 120°C for 24 hours.

[0045] Secondly, the present invention uses the above method to prepare a MIL-101(Cr) series MOF material.

[0046] Optionally, the MIL-101(Cr) series MOFs materials are selected from at least one of MIL-101-F, MIL-101-Cl, MIL-101-NH2, MIL-101-NO2, MIL-101-SO3H, MIL-101-OH, MIL-101-Pyridine, MIL-101-NDC, MIL-101-SH, MIL-101-ED, MIL-101-DETA, MIL-101-PMIDA, MIL-101-CH3, MIL-101-CF3, MIL-101-OCH3, MIL-101-CN, MIL-101-(NH2)2, MIL-101-(NO2)2, and MIL-101-(OH)2.

[0047] Optionally, the molecular structure of the MIL-101(Cr) series MOFs material includes an inner cage with an inner diameter of 15–30 angstroms and an inner cage with an inner diameter of 20–40 angstroms.

[0048] The series of MOFs materials synthesized in this invention adsorb and separate fluorine-containing gases through the pore structures of 15-30 Å and 20-40 Å in the molecular structures of two specific types of MOFs materials. Because the pores of the MIL-101(Cr) series MOFs materials are rich in O and active sites such as benzene rings and pyridine rings, they have stronger interactions with tetrafluoroethane and pentafluoroethane containing carbon-hydrogen bonds, but weaker interactions with hexafluoroethane. They can selectively adsorb tetrafluoroethane and pentafluoroethane or molecules with smaller particle sizes, but cannot adsorb hexafluoroethane molecules with relatively larger particle sizes.

[0049] In their scientific research, the inventors discovered that in traditional techniques for the adsorption separation of hexafluoroethane (R116) from gases such as chlorofluorocarbons (CFCs), most of these CFC impurities can be removed through adsorption distillation. However, the production process of hexafluoroethane also generates hydrofluorocarbons (HFCs) impurities. Although many of these impurities have different boiling points from hexafluoroethane, they are difficult to separate due to their tendency to form azeotropes and azeotropic-like compounds. For example, hexafluoroethane can form azeotropic-like compounds with tetrafluoroethane (HFC-134a, i.e., CF3CH2F) and pentafluoroethane (HFC-125, i.e., CF3CHF2), making them difficult to separate from R116 through distillation. Traditional methods often achieve separation by multiple distillations or by increasing the number of trays in the distillation column. However, this method requires low temperature and high pressure, resulting in high energy consumption and demanding equipment requirements. Furthermore, the fluorination process is highly corrosive, requiring sophisticated operation and equipment, making it neither economical nor easy to obtain high-purity hexafluoroethane with very low HFC content. In addition, the diameter of hexafluoroethane molecules is similar to that of HFC-134a and HFC-125 molecules, making them difficult to separate using conventional adsorption methods. Traditional molecular sieves are easily poisoned, thus losing their activity and causing the entire equipment to stop working. Furthermore, they have low selectivity for different fluorine-containing gases.

[0050] Therefore, through long-term scientific research, the inventors have innovatively applied MOFs, represented by the MIL-101(Cr) series (MIL-101-F, MIL-101-NH2, MIL-101-NO2, MIL-101-SO3H, etc.), to the separation and purification of hydrofluorocarbons (HFC-134a and HFC-125) from hexafluoroethane. The MIL-101(Cr) series MOFs are composed of metallic chromium ions and terephthalic acid and its derivative ligands. It is a novel porous material with ultra-high specific surface area, large pore size, and good thermal / chemical / water stability. It possesses a three-dimensional pore structure, generally with metal ions as connecting points and organic ligands supporting a 3D spatial extension, and contains unsaturated Lewis acid sites within its structure. Compared to traditional physical adsorbents (zeolites, activated carbon, molecular sieves, etc.), MOFs have a designable and well-defined pore structure, tunable functional groups and metal centers, and incorporate various forces such as hydrogen bonds and van der Waals forces. This material can effectively separate and purify hexafluoroethane from its difficult-to-separate hydrofluorocarbon impurities (HFC-134a and HFC-125), thereby obtaining high-purity hexafluoroethane.

[0051] Thirdly, the present invention provides the application of the above-mentioned MIL-101(Cr) series MOFs materials in the separation of hexafluoroethane and hydrofluorocarbon mixtures.

[0052] Optionally, the hydrofluorocarbon is selected from at least one of pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), monofluoroethane (HFC-161), 1,1-difluoroethane (HFC-152a), and tetrafluoroethane.

[0053] Optionally, the mixed gas is a mixture of hexafluoroethane, pentafluoroethane, and tetrafluoroethane.

[0054] Optionally, under conditions of 298 K, atmospheric pressure, and a mixed gas flow rate of 1–4 mL / min, the hexafluoroethane reaches saturation in the adsorption column after 0.37–0.75 minutes, with an adsorption capacity of 0 L / kg; the pentafluoroethane reaches saturation in the adsorption column after 147–600 minutes, with an adsorption capacity of 6.97–30 L / kg; and the tetrafluoroethane reaches saturation in the adsorption column after 148–601 minutes, with an adsorption capacity of 8.16–35 L / kg.

[0055] Optionally, under conditions of 298 K, atmospheric pressure, and a mixed gas flow rate of 1 mL / min, the hexafluoroethane reaches saturation in the adsorption column after 0.38–0.75 minutes, with an adsorption capacity of 0 L / kg; the pentafluoroethane reaches saturation in the adsorption column after 485.73–569.71 minutes, with an adsorption capacity of 23.12–27.11 L / kg; and the tetrafluoroethane reaches saturation in the adsorption column after 486.12–570.10 minutes, with an adsorption capacity of 25.59–30.30 L / kg.

[0056] Fourthly, the present invention provides a gas chromatography column, wherein the packing material of the gas chromatography column is the above-mentioned MIL-101(Cr) series MOFs material.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] 1) The method for synthesizing MIL-101(Cr) series MOFs materials in this invention is simple and easy to operate.

[0059] 2) The MIL-101(Cr) series MOFs materials synthesized in this invention have good stability and are consistent with existing materials (such as powder X-ray diffraction, infrared spectroscopy, specific surface area, etc.).

[0060] 3) The MIL-101(Cr) series MOFs materials synthesized in this invention have high adsorption capacity and adsorption selectivity for difficult-to-separate hydrofluorocarbon impurities (HFC-134a and HFC-125) generated during the production of hexafluoroethane, thereby achieving the separation of hexafluoroethane and hydrofluorocarbon impurities.

[0061] 4) This invention uses the synthesized MIL-101(Cr) series MOFs material as a packing agent to prepare a gas chromatography column, realizing the separation and purification of hexafluoroethane under different temperatures, ratios and other conditions. Attached Figure Description

[0062] Figure 1 This is a schematic diagram of the three-dimensional structure of the MIL-101(Cr) series MOFs material prepared in the embodiment of the present invention. The structure has two different types of inner cages (including inner cages with an inner diameter of 15 to 30 angstroms and inner cages with an inner diameter of 20 to 40 angstroms).

[0063] Figure 2 This is a schematic diagram of the coordination environment of the MIL-101(Cr) series MOFs material (taking MIL-101-NO2 as an example) prepared in the embodiments of the present invention;

[0064] Figure 3The image shows the X-ray powder diffraction pattern of the MIL-101(Cr) series MOFs material (taking MIL-101-NO2 as an example) prepared in the embodiments of the present invention, which characterizes the purity of the sample.

[0065] Figure 4 This is the infrared spectrum of the MIL-101(Cr) series MOFs material (taking MIL-101-NO2 as an example) prepared in the embodiments of the present invention, at 1257 cm⁻¹. -1 The nitro functional groups modified with terephthalic acid ligands were characterized.

[0066] Figure 5 This is the N2 adsorption curve of the MIL-101(Cr) series MOFs material (taking MIL-101-NO2 as an example) prepared in the embodiments of the present invention at 77K;

[0067] Figure 6 The adsorption curves of the MIL-101(Cr) series MOFs material (taking MIL-101-NO2 as an example) prepared in the embodiments of the present invention for hexafluoroethane, pentafluoroethane and tetrafluoroethane at 298K;

[0068] Figure 7 This is the GC separation curve of the hexafluoroethane / pentafluoroethane / tetrafluoroethane mixture of MIL-101-NO2 at 298K in Example 2 of the present invention;

[0069] Figure 8 This is the GC separation curve of the cycling performance of the hexafluoroethane / pentafluoroethane / tetrafluoroethane mixture of MIL-101-NO2 at 298K in Example 2 of the present invention. Detailed Implementation

[0070] The present application is further illustrated below with reference to specific embodiments. The following descriptions are merely a few embodiments of the present application and are not intended to limit the present application in any way. Although the present application discloses preferred embodiments as follows, they are not intended to limit the present application. Any modifications or variations made by those skilled in the art without departing from the scope of the technical solution of the present application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

[0071] Unless otherwise specified, the raw materials used in the embodiments of this application are all purchased commercially and used directly without any special treatment.

[0072] This invention provides a method for preparing MIL-101(Cr) series MOFs materials: terephthalic acid or its derivatives, chromium salts, water and modifiers are mixed to obtain a mixture; the mixture is heated under sealed conditions to obtain MIL-101(Cr) series MOFs materials.

[0073] The modifier in the method of the present invention can be modified by participating in the hydrothermal reaction, or by modifying terephthalic acid first and then participating in the hydrothermal reaction, or by modifying the basic chromium-based metal-organic framework material; those skilled in the art can choose different modification methods according to their needs.

[0074] As a preferred embodiment of the above, the derivative of terephthalic acid is a compound of terephthalic acid modified with -NO2, -NH2, -SO3H, -OH, -Pyridine, -CH3, -CF3, -OCH3, -CN, -(NO2)2, -(NH2)2 or -(OH2)2 or at least one of 1,4-naphthalenedicarboxylic acid (1,4-NDC).

[0075] As a preferred embodiment of the above, the derivatives of terephthalic acid are selected as follows:

[0076] -Pyridine is selected from the compound 2-(4-pyridyl)terephthalic acid;

[0077] -CF3 is selected from compound 2-(trifluoromethyl)terephthalic acid;

[0078] -OCH3 is selected from compound 2-(methoxy)terephthalic acid;

[0079] -CN is selected from compound 2-(cyano)terephthalic acid;

[0080] -(NH2)2 is selected from compound 2,5-diaminoterephthalic acid;

[0081] -(NO2)2 is selected from compound 2,5-dinitroterephthalic acid;

[0082] The derivatives of terephthalic acid are selected from 1,4-naphthalenedicarboxylic acid.

[0083] As a preferred embodiment of the above embodiments, the modifier of the present invention is selected from HF, HCl, sodium acetate, ethylenediamine, diethylenetriamine or N-(phosphonocarboxymethyl)iminodiacetic acid.

[0084] Examples 1 to 19 below are examples of preparing MIL-101(Cr) series MOFs materials.

[0085] Example 1 (MIL-101(Cr)-F)

[0086] Chromium nitrate hydrate (4.0 g), terephthalic acid (1.66 g), and hydrofluoric acid (0.4 mL) were added to a container containing 48 mL of water. After stirring for a few minutes, the mixture was transferred to a 100 mL PTFE-lined stainless steel autoclave and heated at 493 K for 8 hours. Unreacted reactants were removed by reflux in hot ethanol (333 K, 300 mL) and hot water (353 K, 300 mL), respectively. Finally, the green solid was dried at 373 K overnight to obtain the MIL-101-F material.

[0087] Example 2 (MIL-101(Cr)-Cl)

[0088] Chromium chloride hexahydrate (266 mg, 1 mmol), terephthalic acid (166 mg, 1 mmol), and concentrated hydrochloric acid (0.1 mL) were added to 9 mL of deionized water and stirred for 30 minutes to dissolve. The mixture was then transferred to a 23 mL polytetrafluoroethylene-lined container, sealed, and placed in an oven at 190 °C for 14 hours. After the solution cooled to room temperature, it was washed three times each with solvents such as N,N-dimethylformamide and ethanol. Finally, it was dried in an oven at 80 °C to obtain a green powder sample, named MIL-101(Cr)-Cl.

[0089] Example 3 (MIL-101(Cr)-OH)

[0090] 2 g of chromium nitrate nonahydrate and 0.82 g of terephthalic acid were added to 25 mL of 0.05 mol / L sodium acetate aqueous solution and stirred for 30 minutes. The mixture was then transferred to a hydrothermal reactor lined with polytetrafluoroethylene, sealed, and transferred to a constant-temperature drying oven heated to 200°C for 12 hours of constant-temperature crystallization. After the reaction was completed, the reactor was allowed to stand until it cooled to room temperature. The sample was then thoroughly filtered, washed with water, and placed in a drying oven at 150°C for 5 hours of constant-temperature drying. The resulting green crystals were MIL-101(Cr)-OH.

[0091] Example 4 (MIL-101(Cr)-NH2)

[0092] Organic ligands (1.3 mmol; molar ratio of terephthalic acid to 2-aminoterephthalic acid 9:1) and tetramethylammonium hydroxide (63 μL) were added to distilled water (20 mL) and stirred vigorously at 25 °C for 20 min. Subsequently, chromium nitrate nonahydrate (1.3 mmol) was added to the above solution, and the solution was stirred further at 25 °C for 30 min. The resulting mixture was transferred to a polytetrafluoroethylene-lined autoclave and heated at 180 °C for 24 h. The resulting particles were separated by centrifugation and washed with distilled water and methanol. Finally, the sample was vacuum dried at 110 °C for 5 h to obtain the MIL-101(Cr)-NH2 material.

[0093] Example 5 (MIL-101(Cr)-NO2)

[0094] 1.63 g (4.1 mmol) of chromium(III) nitrate nonahydrate, 0.89 g (4.2 mmol) of 2-nitroterephthalic acid, and 0.16 g (4 mmol) of hydrofluoric acid (47-51%) were placed in a 40 mL polytetrafluoroethylene (PTFE) liner containing 20 g of distilled water. The PTFE liner was sealed in a stainless steel autoclave and heated at a rate of 20 K / min to 493 K in an oven under static conditions for 8 hours, then cooled to room temperature. The green product was filtered off, washed in boiling ethanol for 24 hours, and finally dried overnight at 343 K to obtain the MIL-101(Cr)-NO2 material.

[0095] Example 6 (MIL-101(Cr)-SO3H)

[0096] In a 100 mL PTFE-lined stainless steel autoclave containing 50 mL of water, chromium trioxide (CrO3, 1.25 g), sodium 2-sulfoterephthalate (H2BDC-SO3Na, 3.35 g), and concentrated hydrochloric acid (0.772 mL) were added. After stirring for 15 minutes, the container was sealed and reacted at 453 K for 6 days. The resulting mixture was filtered off, and the resulting solid was refluxed in hot methanol (333 K, 250 mL) and hot water (353 K, 400 mL), respectively. Finally, the green solid was dried at 373 K for 12 hours to obtain MIL-101(Cr)-SO3H.

[0097] Example 7 (MIL-101(Cr)-pyridine)

[0098] 2-(4-pyridyl)terephthalic acid (2.43 g) and hydrofluoric acid (0.4 mL) were added to a container with 20 mL of water and stirred for 10 minutes. Then, chromium nitrate hydrate (4.00 g) was added to the container and stirring was continued for 20 minutes. The mixture was transferred to a 100 mL PTFE-lined stainless steel autoclave and heated at 493 K for 8 hours. The resulting mixture was filtered off, and the resulting solid was refluxed in hot water (353 K, 300 mL) and hot methanol or ethanol (343 K, 300 mL) to remove unreacted reactants. Finally, the green solid was dried at 383 K overnight to obtain MIL-101(Cr)-pyridine.

[0099] Example 8 (MIL-101(Cr)-CF3)

[0100] 2-(trifluoromethyl)terephthalic acid (2.34 g) and hydrofluoric acid (0.4 mL) were added to a container with 40 mL of water and stirred for 10 minutes. Then, chromium nitrate hydrate (4.00 g) was added to the container and stirring was continued for 20 minutes. The mixture was transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and heated at 433 K for 12 hours. The resulting mixture was filtered off, and the resulting solid was refluxed in hot water (353 K, 300 mL) and hot methanol or ethanol (343 K, 300 mL) to remove unreacted reactants. Finally, the green solid was dried at 393 K overnight to obtain MIL-101(Cr)-CF3.

[0101] Example 9 (MIL-101(Cr)-OCH3)

[0102] 1.96 g of 2-(methoxy)terephthalic acid and 0.6 mL of hydrofluoric acid were added to a container with 48 mL of water and stirred for 10 minutes. Then, 4.40 g of chromium nitrate hydrate was added to the container and stirring was continued for 20 minutes. The mixture was transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and heated at 453 K for 24 hours. The resulting mixture was filtered off, and the resulting solid was refluxed in hot water (353 K, 300 mL) and hot methanol or ethanol (343 K, 300 mL) to remove unreacted reactants. Finally, the green solid was dried overnight at 393 K to obtain MIL-101(Cr)-OCH3.

[0103] Example 10 (MIL-101(Cr)-CN)

[0104] 1.91 g of 2-(cyano)terephthalic acid and 0.2 mL of hydrofluoric acid were added to a container of 48 mL of water and stirred for 10 minutes. Then, 5.80 g of chromium nitrate hydrate was added to the container and stirring was continued for 20 minutes. The mixture was transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and heated at 433 K for 48 hours. The resulting mixture was filtered off, and the resulting solid was refluxed in hot water (353 K, 300 mL) and hot methanol or ethanol (343 K, 300 mL) to remove unreacted reactants. Finally, the green solid was dried overnight at 393 K to obtain MIL-101(Cr)-CN.

[0105] Example 11 (MIL-101(Cr)-(NH2)2)

[0106] 1.3 mmol of 2,5-diaminoterephthalic acid was added to terephthalic acid (1:9) and tetramethylammonium hydroxide (65 μL) in distilled water (20 mL), and the mixture was stirred vigorously at 25 °C for 20 min. Subsequently, 5.20 g of chromium nitrate nonahydrate was added to the above solution, and the solution was stirred further at 25 °C for 30 min. The resulting mixture was transferred to a polytetrafluoroethylene-lined autoclave and heated at 180 °C for 24 h. The resulting particles were separated by centrifugation and washed with distilled water and methanol. Finally, the sample was vacuum dried at 110 °C for 5 h to obtain (MIL-101(Cr)-(NH2)2) material.

[0107] Example 12 (MIL-101(Cr)-(NO2)2)

[0108] 1.63 g (4.1 mmol) of chromium(III) nitrate nonahydrate, 0.89 g (4.2 mmol) of 2,5-dinitroberaphthalic acid, and 0.16 g (4 mmol) of hydrofluoric acid (47-51%) were placed in a 40 mL polytetrafluoroethylene (PTFE) liner containing 20 g of distilled water. The PTFE liner was sealed in a stainless steel autoclave and heated at a rate of 20 K / min to 493 K in an oven under static conditions for 8 hours, then cooled to room temperature. The green product was filtered off, washed in boiling ethanol for 24 hours, and finally dried overnight at 343 K to obtain the MIL-101(Cr)-NO2 material.

[0109] Example 13 (MIL-101(Cr)-NDC)

[0110] 1,4-Naphthalenedicarboxylic acid (2.20 g) and hydrofluoric acid (0.6 mL) were added to a container with 96 mL of water and stirred for 10 minutes. Then, chromium nitrate hydrate (4.00 g) was added to the container and stirring was continued for 20 minutes. The mixture was transferred to a 200 mL PTFE-lined stainless steel autoclave and heated at 493 K for 12 hours. The resulting mixture was filtered off, and the resulting solid was refluxed in hot water (353 K, 300 mL) and hot methanol or ethanol (343 K, 300 mL) to remove unreacted reactants. Finally, the green solid was dried at 393 K overnight to obtain MIL-101(Cr)-NDC.

[0111] Examples 14-15 (modification with two functional groups)

[0112] Terephthalic acid (1.80 g, 1.98 g) and hydrofluoric acid (0.5 ml, 0.2 ml) modified with -CH3 or -(OH)2 functional groups were added to a container with 40 ml of water. After stirring for 10 minutes, chromium nitrate hydrate (4.00 g) was added to the container and stirring was continued for 20 minutes. The mixture was transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and heated at 463 K for 48 h. Unreacted reactants were removed by reflux in hot water (353 K, 300 mL) and hot ethanol (343 K, 300 mL), respectively. Finally, the green solid was dried at 383 K overnight. MIL-101(Cr)-CH3 material and MIL-101(Cr)-(OH2)2 material were obtained sequentially.

[0113] Example 16 (MIL-101(Cr)-ED)

[0114] The MIL-101(Cr)-F synthesized in Example 1 was treated in vacuum at 423 K for 12 hours to remove water residues from the sample; 500 mg of dehydrated MIL-101(Cr)-F was suspended in 50 mL of anhydrous toluene in a three-necked round-bottom flask; then, an appropriate amount of ethylenediamine (1.0 mL) was added to the suspension, and the mixture was refluxed and stirred at 383 K for 8 hours; the product was recovered by filtration and washed with toluene and ethanol, and then dried at 353 K for 12 hours to obtain the MIL-101(Cr)-ED material.

[0115] Example 17 (MIL-101(Cr)-DETA)

[0116] The MIL-101(Cr)-F synthesized in Example 1 was treated in vacuum at 423 K for 12 hours to remove water residues from the sample; 500 mg of dehydrated MIL-101(Cr)-F was suspended in 50 mL of anhydrous toluene in a three-necked round-bottom flask; then, an appropriate amount of diethylenetriamine (1.0 mL) was added to the suspension, and the mixture was refluxed and stirred at 383 K for 8 hours; the product was recovered by filtration and washed with toluene and ethanol, and then dried at 353 K for 12 hours to obtain the MIL-101(Cr)-DETA material.

[0117] Example 18 (MIL-101(Cr)-SH)

[0118] The MIL-101(Cr)-NH2 synthesized in Example 4 was mixed with mercaptoacetaldehyde (molar ratio (1-5):(1-5)) in methanol, heated at 65°C in an oil bath, refluxed, and reacted under magnetic stirring for 24 hours. After the reaction was completed, the mixture was centrifuged and washed several times with methanol to obtain the mercapto-functionalized metal-organic framework MIL-101(Cr)-SH.

[0119] Example 19 (MIL-101(Cr)-PMIDA)

[0120] After activating the MIL-101-NH2 synthesized in Example 4 at 353 K for 12 hours, a mixture of MIL-101(Cr)-NH2 / PMIDA / DCC with a molar ratio of 1:1.5:2 was prepared in 80 mL of DMF in a round-bottom flask; DCC was used as a catalyst for the reaction between the NH2 grafted in MIL-101 and the glyphosate group; the reaction mixture was stirred under reflux at 150 °C for 48 hours; the product was filtered, washed with toluene and methanol, and dried at 373 K for 12 hours to obtain MIL-101(Cr)-PMIDA material; wherein, PMIDA: polymethyl methacrylate, DCC: N,N'-dicyclohexylcarbodiimide.

[0121] Analysis of the 19 modified MIL-101(Cr) series MOFs materials synthesized in Examples 1-19 above: Figure 1 This is a schematic diagram of the three-dimensional structure of the MIL-101(Cr) series MOFs material, which has two different types of inner cages (29 angstroms and 34 angstroms).

[0122] Figure 2 This is a schematic diagram of the coordination environment of MIL-101(Cr) series MOFs materials (taking MIL-101-NO2 as an example).

[0123] Figure 3 Powder X-ray diffraction analysis was performed on MIL-101(Cr) series MOFs materials (taking MIL-101-NO2 as an example) to characterize the purity of the samples.

[0124] Depend on Figure 3 It can be seen that the structure of the MIL-101(Cr)MOFs material prepared in the embodiments of the present invention is consistent with the structure of the standard MIL-101(Cr)MOFs material, and it still has the corresponding structure after column breakthrough separation test. The structure of the MIL-101(Cr)MOFs material prepared in the embodiments of the present invention is consistent with the structure of the standard MIL-101(Cr)MOFs material, and it does not undergo phase change after adsorption and column breakthrough separation test, maintaining the main framework structure. This indicates that the present invention not only prepared a material with the MIL-101(Cr)MOFs structure, but also has good stability. After being used for adsorption and separation, the sample purity is still maintained and its structure remains stable.

[0125] Figure 4 This is the infrared spectrum of MIL-101(Cr) series MOFs materials (taking MIL-101-NO2 as an example), at 1257 cm⁻¹. -1The nitro functional groups modified with terephthalic acid ligands were characterized.

[0126] The above Figure 4 It can be proven that the improved material of this invention has the functional groups corresponding to its raw material ligands, and that the functional groups of the ligands did not decompose after modification.

[0127] Example 20 below is an example of using MIL-101(Cr) series MOFs to separate a mixture of hexafluoroethane and hydrofluorocarbons.

[0128] Example 20

[0129] (1) Dry any one of the MIL-101(Cr) series materials in Examples 1 to 19 above according to the method of Example 1 (the purpose is to remove the solvent in the material channels), and then activate it under vacuum and 100-150°C for 10 hours to finally obtain the activated crystal material;

[0130] (2) Column breakthrough separation experiment was performed in gas chromatography: 1 g of activated MIL-101(Cr) series material was first packed into a stainless steel column (4 mm (inner diameter) × 180 mm (length)) and the column port was sealed with a certain amount of quartz wool. Then, the column was activated with helium at 100-160℃ for 8-12 hours. During the test, the R116 / HFC125 / HFC134a (hexafluoroethane / pentafluoroethane / tetrafluoroethane) ternary mixed gas was allowed to flow through the column at flow rates of 1, 2 and 4 mL / min, respectively, and detected by a gas chromatograph detector.

[0131] Analysis of the separation effect in Example 20 above:

[0132] Figure 5 This is the N2 adsorption curve of MIL-101(Cr)-NO2 material at 77K.

[0133] Depend on Figure 5 This demonstrates that the MIL-101(Cr)-NO2 material prepared by this invention has a large specific surface area, which is consistent with the specific surface area measured in other literature on the synthesis of MIL-101-NO2, indicating the accuracy of its crystallinity and pore size within the cage.

[0134] Figure 6 These are the adsorption curves of MIL-101(Cr)-NO2 material for hexafluoroethane, pentafluoroethane, and tetrafluoroethane at 298K.

[0135] Figure 6 The adsorption capacity of the hexafluoroethane was shown to be 6.7674 cm⁻¹ under the conditions of 298 K temperature and 0-100 kPa pressure. 3 / g; the adsorption capacity of the pentafluoroethane is 62.0502 cm⁻². 3 / g; the adsorption capacity of tetrafluoroethane is 92.4456 cm⁻¹. 3 / g. From Figure 6 The curves clearly show that the adsorption capacity of hexafluoroethane is very small, while the adsorption capacities of pentafluoroethane and tetrafluoroethane are relatively large, with a significant difference. Furthermore, there is a relatively clear difference between pentafluoroethane and tetrafluoroethane. The adsorption capacity of pentafluoroethane / tetrafluoroethane is approximately 10 to 20 times that of hexafluoroethane. Simultaneously, in the low-pressure region, the slope of the hexafluoroethane adsorption curve is significantly smaller than that of the tetrafluoroethane and pentafluoroethane adsorption curves. This indicates that the effect of MIL-101(Cr)-NO2 on tetrafluoroethane and pentafluoroethane is much greater than that on hexafluoroethane. Based on these characteristics, it is evident that MIL-101(Cr)-NO2 has excellent separation performance.

[0136] Figure 7 This is the GC separation curve of the hexafluoroethane / pentafluoroethane / tetrafluoroethane mixture of MIL-101-NO2 at 298K according to the present invention.

[0137] Depend on Figure 7 The curve shape clearly shows that hexafluoroethane has the highest resolution. Due to the weakest interaction between hexafluoroethane and MIL-101(Cr)-NO2, it cannot be retained in the frame and passes directly through the column. Tetrafluoroethane and pentafluoroethane, on the other hand, are retained in the column until it reaches saturation at 569.7 minutes, at which point subsequent tetrafluoroethane and pentafluoroethane directly permeate the column. The separation curves demonstrate that MIL-101(Cr)-NO2 can directly purify hexafluoroethane from a ternary mixture of hexafluoroethane / pentafluoroethane / tetrafluoroethane, with a purification time of up to 569.7 minutes.

[0138] Separation experiments in this invention embodiment: Under conditions of 298 K, normal pressure, and a mixed gas flow rate of 1–4 mL / min, the hexafluoroethane reached saturation in the adsorption column after 0.37–0.75 minutes, with an adsorption capacity of 0 L / kg; the pentafluoroethane reached saturation in the adsorption column after 147–600 minutes, with an adsorption capacity of 6.97–30 L / kg; and the tetrafluoroethane reached saturation in the adsorption column after 148–601 minutes, with an adsorption capacity of 8.16–35 L / kg.

[0139] Specifically, under the conditions of a temperature of 298 K, atmospheric pressure, and a mixed gas flow rate of 1 mL / min, the hexafluoroethane reached saturation in the adsorption column after 0.37955 minutes, with an adsorption capacity of 0 L / Kg; the pentafluoroethane reached saturation in the adsorption column after 569.70509 minutes, with an adsorption capacity of 27.11 L / Kg; and the tetrafluoroethane reached saturation in the adsorption column after 570.09509 minutes, with an adsorption capacity of 30.30 L / Kg.

[0140] Figure 8 This is the GC separation curve of the cycling performance of the hexafluoroethane / pentafluoroethane / tetrafluoroethane mixture of MIL-101-NO2 at 298K according to the present invention.

[0141] Depend on Figure 8 The curve shape shows that after three adsorption and separation processes, the separation effect of the MOF material on the above mixed gas is still the same as that of the fresh material, indicating that the MOF material has good stability and repeatability.

[0142] As shown in the GC separation curves above, the packed column using the MIL-101(Cr) series materials synthesized in this invention can effectively separate the R116 / HFC125 / HFC134a ternary mixed system.

[0143] The material underwent 15 adsorption-separation-regeneration cycles, demonstrating excellent column cyclic stability. Longer-term repeated experiments revealed good separation stability of the packed column; no significant change in separation time was observed after 15 weeks. These experiments indicate that the MIL-101(Cr) series packed columns can be used for the effective separation of mixtures of R116 / HFC125 / HFC134a.

[0144] Comparative Example 1

[0145] Azeotropic distillation was used to separate chlorotrifluoromethane and chlorodifluoromethane from hexafluoroethane. Hexafluoroethane is distilled in the presence of anhydrous hydrochloric acid. Taking advantage of the higher vapor pressure and greater volatility of the hydrochloric acid-hexafluoroethane azeotrope or azeotropic mixture formed by hydrochloric acid and other impurities, the hydrochloric acid-hexafluoroethane azeotrope is extracted from the top of the distillation column. Other impurities and their azeotropes or azeotropes with hydrochloric acid are collected as the bottom effluent. The hydrochloric acid-hexafluoroethane azeotrope is liquefied and cooled at a temperature below -50°C, separating it into layers rich in hydrochloric acid and layers rich in hexafluoroethane. The hexafluoroethane-rich layer enters a second distillation column for further distillation. After deacidification via a resin bed, high-purity hexafluoroethane can be obtained (MILLER RN, DESCHEREMR, MAHLERBA, MUTHU Olagappan. Purification process for hexafluoroethane products: US, 6221830B1 [P]. 2001-04-24.).

[0146] However, this method requires highly corrosion-resistant equipment due to the strong corrosive effect of hydrochloric acid, increasing production costs. Furthermore, residual hydrochloric acid in the product can further corrode the cylinders, posing a safety hazard during storage and transportation.

[0147] Comparative Example 2

[0148] Hiromoto Ohno of Showa Denko KK Corporation disclosed a method for the intermittent adsorption removal of impurities such as pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), monofluoroethane (HFC-161), and 1,1-difluoroethane (HFC-152a) from hexafluoroethane. The adsorbent used is a molecular sieve with a pore size of 3.5–11 Å and a silica-alumina ratio <1.5, or a carbon molecular sieve with a pore size of 4–11 Å. The adsorption temperature is -20°C, and the final product is hexafluoroethane with a purity >99.999% (SHOWA DENKO KK. Method for purifying hexafluoro-ethane: US, 09523966P. 2001-08-14.).

[0149] However, because this method involves intermittent operation, it is not suitable for industrial production.

[0150] The experimental results from Examples 1-20 and Comparative Documents 1-2 show that the raw materials of the MIL-101(Cr) series MOFs materials proposed in this invention are cheaper and more readily available, and can be prepared in large quantities. They are very stable in air, do not require multiple exchange soakings with N,N-dimethylformamide and acetone before column packing, have strong applicability, take a long time to obtain pure components, have good separation effect and good reusability.

[0151] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. Use of a MIL-101(Cr) series MOFs material for separating hexafluoroethane from a mixture of hydrofluorocarbons and hydrogen fluoride, characterized in that The preparation method of the MIL-101(Cr) series MOFs material comprises the following steps: mixing terephthalic acid or its derivative, a chromium salt, a modifier and water to obtain a mixture; The mixture is heated under a closed condition to obtain the MIL-101(Cr) series MOFs material; The molecular structure of the MIL-101(Cr) series MOFs material comprises an inner cage with an inner diameter of 15-30 angstroms and an inner cage with an inner diameter of 20-40 angstroms; The hydrofluorocarbon is selected from at least one of pentafluoroethane, 1,1,1-trifluoroethane, monofluoroethane, 1,1-difluoroethane and tetrafluoroethane; The modifier is selected from at least one of HF, HCl, sodium acetate, ethylenediamine, diethylenetriamine, tetramethylammonium hydroxide and N-(phosphonomethyl)iminodiacetic acid.

2. Use according to claim 1, characterized in that, The derivative of the terephthalic acid is selected from at least one of terephthalic acid modified by -NO2, -NH2, -SO3H, -pyridine, -CH3, -CF3, -OCH3, -CN, -(NO2)2, -(NH2)2 or -(OH2)2, and 1,4-naphthalene dicarboxylic acid; The molar ratio of the terephthalic acid or its derivative to the chromium salt is 0.9-1:1-1.

5.

3. Use according to claim 1, characterized in that, The chromium salt is selected from at least one of chromium nitrate nine hydrate, chromium trichloride and chromium trioxide; The heating of the mixture under a closed condition specifically comprises that the mixture is subjected to constant temperature hydrothermal reaction in a polytetrafluoroethylene-lined stainless steel autoclave; The heating temperature is 65-250 DEG C, and the heating time is 5-144 h; The product after the heating is subjected to washing and drying to obtain the MIL-101(Cr) series MOFs material; the washing is refluxing to remove unreacted reactants in 80-90 DEG C water and / or 65-75 DEG C solvent; and the drying is drying the product after the washing at a temperature of 110-120 DEG C for 1-24 h.

4. Use according to claim 1, characterized in that, The MIL-101(Cr) series MOFs material is selected from at least one of MIL-101-F, MIL-101-Cl, MIL-101-NH2, MIL-101-NO2, MIL-101-SO3H, MIL-101-OH, MIL-101-Pyridine, MIL-101-NDC, MIL-101-SH, MIL-101-ED, MIL-101-DETA, MIL-101-PMIDA, MIL-101-CH3, MIL-101-CF3, MIL-101-OCH3, MIL-101-CN, MIL-101-(NH2)2, MIL-101-(NO2)2 and MIL-101-(OH)2.

5. The use according to claim 1, characterized in that, The hexafluoroethane is saturated in the adsorption column for 0.37-0.75 minutes at a temperature of 298K, normal pressure and a mixed gas flow rate of 1-4 mL / min, and the adsorption capacity is 0 L / Kg; the pentafluoroethane is saturated in the adsorption column for 147-600 minutes, and the adsorption capacity is 6.97-30 L / Kg; the tetrafluoroethane is saturated in the adsorption column for 148-601 minutes, and the adsorption capacity is 8.16-35 L / Kg.

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