Method for adsorbing and separating octafluoropropane in binary mixed gas system of octafluoropropane and nitrogen

Abstract

The invention discloses a method for adsorbing and separating octafluoropropane in a binary mixed gas system of octafluoropropane and nitrogen. Carrying out adsorption separation on mixed gas containing nitrogen and octafluoropropane through an adsorption column filled with a metal-organic framework material; the metal-organic framework material is obtained by dissolving Zn salt, Cr salt powder and an organic ligand pyrazole-4-carboxylic acid in a solvent, reacting at 140-150 DEG C through a solvothermal method to obtain a product, and purifying and activating the product. The molar ratio of the Zn salt to the Cr salt is controlled to be (4-5): 1. The dynamic adsorption capacity of octafluoropropane of the metal organic framework material can reach 1.29 mmol / g, and efficient selective adsorption separation and extraction of low-concentration octafluoropropane in a binary gas mixing system of octafluoropropane and nitrogen can be achieved.

Description

Technical Field

[0001] The present invention relates to the field of gas adsorption and separation, and in particular to a metal organic framework adsorption material for adsorbing and separating octafluoropropane from nitrogen and a preparation method thereof. Background Art

[0002] Octafluoropropane (C3F8) is chemically stable, colorless, odorless, highly electronegative, and insulating. It is widely used as an etching agent in the refrigeration and air-conditioning industries, as well as in the semiconductor industry. C3F8 is the fourth most abundant perfluorinated gas globally. The refrigeration / air-conditioning and semiconductor manufacturing industries are the primary sources of C3F8 emissions. The aluminum smelting industry is also a potential source of C3F8 emissions. According to a United Nations climate assessment report, C3F8 is a typical greenhouse gas with a GWP100 (global warming potential) of 8830. It is stable, has a lifespan of over 2600 years, and is not easily degraded. Due to the extreme stability of perfluorinated compounds (PFCs), their long lifespan and strong infrared absorption, once emitted, these gases permanently alter the atmosphere's radiation absorption capacity. According to some current emission reports, the global baseline mole fraction of C3F8 has increased nearly tenfold over the past 40 years. In addition, there are studies showing that the calculated emissions of perfluorinated compounds (PFCs) are significantly higher than most previous emission estimates, indicating that the actual emissions of PFCs are significantly underestimated. Therefore, the development of efficient C3F8 removal technology is very important for protecting the environment and mitigating the greenhouse effect.

[0003] In order to reduce or eliminate the emission of perfluorinated compounds (PFCs) in industrial processes, four possible methods are as follows: (1) recovery / recycling of PFCs (capture / recycle); (2) conversion of PFCs to non-PFCs (emission reduction / destruction); (3) chemical process optimization using reconfiguration and endpoint detection; and (4) replacement of PFCs with non-PFCs (alternative chemistry). Among them, the common technologies for converting PFCs to non-PFCs (emission reduction / destruction) are mainly destructive technologies such as incineration, thermal oxidation and plasma pyrolysis. However, these technologies bring many negative factors, such as high energy consumption, the generation of secondary pollutant gases after incineration and low economic benefits. The current industry standards for the recovery / recycling (capture / recycle) of PFCs also rely on cryogenic and liquefaction methods, which are both energy-consuming and harmful to the environment. Therefore, it is necessary to develop a more environmentally friendly and economically viable alternative for the recovery / recycling of PFCs.

[0004] The concentration of C3F8 in the air is extremely low, with the global baseline mole fraction of C3F8 being only at the ppt level. Separation at the ppt level is clearly undesirable, so C3F8 removal can focus on exhaust gas removal from related factories, typically below 3000 ppm. For such low-concentration component separation, adsorption separation offers the highest operability due to its low energy consumption, long adsorbent life, no need for long-term maintenance, and simple process. To meet the needs of industries such as semiconductors and electronics, achieve the recycling of expensive resources, and reduce the environmental burden, effective physical adsorption processes have been developed. The separation and recovery of C3F8 from C3F8 / N2 at low concentrations is a very necessary and challenging task. Metal-organic frameworks (MOFs), as new adsorption materials, are being widely used in gas adsorption separation.

[0005] Chinese invention patent CN114471468B discloses a method for separating octafluoropropane from sulfur hexafluoride by adsorption using metal-organic framework materials. This technology separates a mixed gas containing octafluoropropane and sulfur hexafluoride through an adsorption column filled with metal-organic framework materials, and controls the adsorption separation temperature to be between 15°C and 60°C. This technology synthesizes a series of metal-organic framework materials with microporous and ultra-microporous structures for the adsorption of octafluoropropane; the metal ion is Zr 4+ 、Cu 2+ 、Zn 2+ 、Co 2+ 、Mn 2+ or Ni 2+ The organic ligand is one or more of terephthalic acid, trimesic acid, and dimethylimidazole. Under the condition of a volume ratio of SF6 to C3F8 of 1500:1, the adsorption capacity of TEA-Zr-MOF for octafluoropropane reached 2.89mmol / g. This technology mainly utilizes the weak interaction between SF6 and the adsorbent, which will flow out of the adsorption column first and C3F8 later, thereby achieving mixed gas separation. However, since the molecular dynamic diameter of nitrogen is much smaller than the pore size of the adsorbent and C3F8, nitrogen molecules are easily adsorbed in the pores of the adsorbent, causing some nitrogen to lag in outflow. Therefore, the adsorbent of this technology is not suitable for the adsorption separation of binary mixed gas systems of octafluoropropane and nitrogen. Summary of the Invention

[0006] To address existing technical issues, the present invention proposes a method for the adsorption separation of octafluoropropane from a binary gas mixture of octafluoropropane and nitrogen. Under the conditions of 298K, 170kPa, and a C3F8 / N2 volume ratio of 1:400, the method achieves a dynamic adsorption capacity of 0.85mmol / g for C3F8 and an octafluoropropane removal rate of 99.95%. The method is easy to operate and effectively achieves C3F8 / N2 separation.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0008] A method for adsorbing and separating octafluoropropane from a binary gas mixture of octafluoropropane and nitrogen comprises: passing a mixed gas containing nitrogen and octafluoropropane through an adsorption column filled with a metal-organic framework material for adsorption separation; the metal-organic framework material is prepared by dissolving Zn salt, Cr salt powder, and an organic ligand pyrazole-4-carboxylic acid in a solvent, reacting the resulting product at 140-150° C. through a solvothermal method, and then purifying and activating the resulting product; and the molar ratio of the Zn salt to the Cr salt is controlled to be 4-5:1.

[0009] To further achieve the purpose of the present invention, preferably, the adsorption column is a vertical container filled with adsorbent and opened at the top and bottom.

[0010] Preferably, the adsorption column is 10-25 cm long and the fixed bed is 5-15 cm in diameter.

[0011] Preferably, the volume ratio of the binary gas mixture of octafluoropropane and nitrogen is 1:400-1:500, and the concentration of octafluoropropane is 2000-2500 ppm.

[0012] Preferably, the adsorption temperature of the adsorption column is 25° C. to 35° C., the pressure in the adsorption column is 1.5 bar to 1.7 bar, and the flow rate of the binary mixed gas of octafluoropropane and nitrogen is 0.8 to 1.5 L / min.

[0013] Preferably, the solvent dissolved in the solvent is one or more mixed solutions of deionized water, methanol, ethanol and N-dimethylformamide solution.

[0014] Preferably, the Zn salt and Cr salt are both selected from one or more of chlorides, nitrates, sulfates, carbonates and acetates of Zn and Cr.

[0015] Preferably, the metal-organic framework material is synthesized by the following steps:

[0016] (1) dissolving Zn salt, Cr salt powder and organic ligand pyrazole-4-carboxylic acid in a solvent, and stirring the mixture thoroughly at room temperature until it is completely dissolved; controlling the molar ratio of Zn salt to Cr salt to be 4 to 5:1;

[0017] (2) transferring the solution obtained in step (1) into a reaction kettle, and synthesizing a metal-organic framework material by a solvothermal method at 140-150° C.;

[0018] (3) After the mixture in the reactor of step (2) is cooled to room temperature, the mixture is filtered or centrifuged, washed thoroughly, and then dried;

[0019] (4) activating the product obtained in step (3);

[0020] Preferably, in step (1), the stirring is magnetic stirring, and the stirring speed is 400-500 rpm;

[0021] In step (2), the solvent thermal method is carried out for 12 to 15 hours in an oven; the reaction kettle is a stainless steel autoclave lined with polytetrafluoroethylene;

[0022] Preferably, in step (3), the washing is performed by using DMF, anhydrous ethanol, and deionized water in sequence for 2-3 times and then centrifuged; the drying is performed by placing the mixture in an oven at 90-100° C. for 12-18 hours;

[0023] In step (4), the activation is to place the product in a vacuum drying oven and reduce the pressure to a vacuum degree of 1 to 10 - 2 mbar, and heated to 110-130℃ for activation for 20-24h to further remove the solvent molecules in the pore structure of the adsorbent.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. The metal organic framework material of the present invention has a strong adsorption affinity for octafluoropropane, with an adsorption selectivity of up to 195, which indicates its excellent separation ability, that is, it can meet the separation requirements under conditions of extremely low C3F8 concentrations.

[0026] 2. Under the conditions of 298K, 170kPa, and a volume ratio of C3F8 to N2 of 1:400 (the volume concentration of octafluoropropane is 2500ppm), the metal organic framework material of the present invention has a dynamic adsorption capacity of 0.85mmol / g for C3F8, indicating that the material has a high adsorption capacity for octafluoropropane, which is significantly better than existing adsorbent materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the powder X-ray diffraction pattern of the metal organic framework adsorption material prepared in Example 1 of the present invention.

[0028] Figure 2 This is a scanning electron microscope image of the metal organic framework adsorption material prepared in Example 1 of the present invention.

[0029] Figure 3 This is the adsorption and penetration curve of the metal organic framework adsorption material prepared in Example 1 of the present invention for C3F8 / N2.

[0030] Figure 4 The single-component adsorption isotherms of the metal organic framework adsorption material prepared in Example 1 of the present invention for C3F8 and N2 at different temperatures.

[0031] Figure 5 This is a graph showing the adsorption selectivity of the metal organic framework adsorption material prepared in Example 1 of the present invention for C3F8 / N2. DETAILED DESCRIPTION

[0032] For a better understanding of the present invention, the present invention is further described below with reference to the accompanying drawings and specific embodiments, but the embodiments of the present invention are not limited thereto. The embodiments described are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] At present, there are few studies on the adsorption separation of binary gas mixtures of octafluoropropane and nitrogen, and the differentiated adsorption behavior and identification separation mechanism of the adsorbent have not yet been established. Moreover, in the binary gas mixture system of octafluoropropane and nitrogen at low concentrations (the volume ratio of nitrogen to octafluoropropane is above 400:1), octafluoropropane is difficult to be separated efficiently. Based on the research on the molecular structure and properties of octafluoropropane, the present invention found that the metal-organic framework material has pore channels that match the diameter of octafluoropropane molecules, has high selectivity for octafluoropropane, has high adsorption affinity, and has high adsorption capacity. The metal-organic framework material is a metal-organic framework material with microporous and ultra-microporous structures formed by coordination between metal ions and organic ligands. The metal ion is Zn in a specific range of proportions. 2+ and Cr 3+ , the organic ligand is pyrazole-4-carboxylic acid.

[0034] Specifically, the Cambridge Crystallographic Data Center shows that the cross-sectional area of the pores of the metal-organic framework material synthesized by coordination of Zn and pyrazole-4-carboxylic acid is Slightly larger than the kinetic diameter of octafluoropropane Much larger than the molecular size of nitrogen Oxafluoropropane possesses a strong electron-withdrawing capacity due to the strong electron-attracting ability of the fluorine atoms. By varying the ratios of Zn and Cr metal ions, the positive potential distribution on the adsorbent surface is altered, enhancing the intermolecular interaction between the adsorbent and octafluoropropane. This allows the octafluoropropane to remain as much as possible within the pore structure of the adsorbent surface during mass transfer and exchange on the adsorbent surface, thereby improving its adsorption capacity for octafluoropropane in a binary gas mixture of octafluoropropane and nitrogen. To this end, the present invention provides a method for adsorbing and separating octafluoropropane from a binary gas mixture of octafluoropropane and nitrogen: a gas mixture containing nitrogen and octafluoropropane is passed through an adsorption column loaded with a metal-organic framework material for adsorption separation; the metal-organic framework material is obtained by dissolving Zn salt, Cr salt powder, and an organic ligand pyrazole-4-carboxylic acid in a solvent, reacting the resulting product at 140-150°C via a solvothermal method, and then purifying and activating the resulting product; the molar ratio of Zn salt to Cr salt is controlled to be 4-5:1.

[0035] In the above technical measures of the present invention, the metal-organic framework material is specifically synthesized by the following steps:

[0036] (1) dissolving Zn salt, Cr salt powder and organic ligand pyrazole-4-carboxylic acid in a solvent, and stirring the mixture thoroughly at room temperature until it is completely dissolved; controlling the molar ratio of Zn salt to Cr salt to be 4 to 5:1;

[0037] (2) transferring the solution obtained in step (1) into a reaction kettle, and synthesizing a metal-organic framework material by a solvothermal method at 140-150° C.;

[0038] (3) After the mixture in the reactor of step (2) is cooled to room temperature, the mixture is filtered or centrifuged, washed thoroughly, and then dried;

[0039] (4) activating the product obtained in step (3);

[0040] Based on the purpose of the present invention and conventional operations in the field, in the above steps, the stirring involved in step (1) is preferably magnetic stirring, and the stirring speed is preferably 400-500 rpm; in step (2), the solvent thermal treatment time is preferably 12-15 hours, and the solvent thermal method is preferably carried out in an oven; the reactor is preferably a stainless steel autoclave lined with polytetrafluoroethylene; in step (3), washing is preferably performed with DMF, anhydrous ethanol, and deionized water in order for 2-3 times and centrifugation; drying is preferably performed in an oven at 90-100°C for 12-18 hours; in step (4), activation is preferably performed by placing the product in a vacuum drying oven and reducing the pressure to a vacuum degree of 1-10 -2 mbar, heated to 110-130℃ for activation for 20-24h, the purpose is to remove the solvent molecules in the pore structure of the adsorbent.

[0041] The adsorption column is preferably a vertical container filled with adsorbent and open at the top and bottom. The adsorption column length is preferably 10-25 cm, and the fixed bed diameter is preferably 5-15 cm. The adsorption column length and fixed bed diameter can be adjusted appropriately based on actual conditions.

[0042] The volume ratio of the binary gas mixture of octafluoropropane and nitrogen in the present invention is preferably 1:400-1:500, the concentration of octafluoropropane is 2000-2500 ppm. The adsorption temperature of the adsorption column is preferably 25°C to 35°C, the pressure in the adsorption column is preferably 1.5 bar to 1.7 bar, and the flow rate of the binary gas mixture of octafluoropropane and nitrogen is preferably 0.8 to 1.5 L / min.

[0043] In the technical measures of the present invention, the solvent dissolved in the solvent is a mixed solution of deionized water, methanol, ethanol and N-dimethylformamide solution. The Zn salt and the Cr salt are both selected from one or more of chlorides, nitrates, sulfates, carbonates and acetates of Zn and Cr.

[0044] The breakthrough time (Breakthrough Time) and saturation time (Saturation Time) involved in the embodiments of the present invention are key parameters that describe the dynamic behavior of the adsorption column. The breakthrough time indicates the time required when the target component in the adsorption column feed is first detected at the outlet (reaching 0% to 5% of the inlet concentration), indicating that the adsorbent begins to "break through" and the adsorption capacity is gradually exhausted. The saturation time indicates the time required for the adsorption column to be fully saturated (outlet concentration ≈ inlet concentration), at which time the adsorbent no longer has adsorption capacity. After adsorption, the metal-organic framework material is desorbed by vacuum drying or nitrogen purging fixed bed method. The adsorption breakthrough time of the present invention is preferably 60-70min, and the adsorption saturation time is preferably 120-140min. After adsorption, the metal-organic framework material is desorbed by vacuum drying or nitrogen purging fixed bed method.

[0045] 1. Preparation of Metal-Organic Framework Adsorption Materials for Adsorption and Separation of Octafluoropropane from Nitrogen

[0046] Example 1

[0047] (1) 48 parts by weight of zinc nitrate hexahydrate, 12 parts of chromium nitrate nonahydrate, and 60 parts of pyrazole-4-carboxylic acid were weighed and dissolved in 3600 parts of N-N-dimethylformamide solution. The mixture was placed in a magnetic stirrer and stirred at a speed of 450 r / min for 10 minutes until it was completely dissolved.

[0048] (2) The solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and reacted in an oven at 140 °C for 12 h.

[0049] (3) After the reaction is complete and the product has cooled to room temperature, it is filtered and washed twice with DMF, anhydrous ethanol, and deionized water in that order to remove residual reactants and residual solvent molecules. Finally, the sample is dried in an oven at 100°C for 12 hours to further remove residual solvent molecules.

[0050] (4) Place the sample in a vacuum drying oven and reduce the pressure until the vacuum degree reaches 1-10 -2 mbar, and heated to 120 ° C for activation for 20 h to further remove the solvent molecules in the pore structure of the adsorbent, thereby obtaining a metal organic framework adsorption material for adsorption and separation of octafluoropropane in nitrogen.

[0051] Example 2

[0052] (1) 50 parts by weight of zinc nitrate hexahydrate, 10 parts of chromium nitrate nonahydrate, and 60 parts of pyrazole-4-carboxylic acid were weighed and dissolved in 3600 parts of N-N-dimethylformamide solution. The mixture was placed in a magnetic stirrer and stirred at a speed of 450 r / min for 10 minutes until it was completely dissolved.

[0053] (2) The solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and reacted in an oven at 140 °C for 12 h.

[0054] (3) After the reaction is complete and fully cooled to room temperature, the product is filtered and washed three times with DMF, anhydrous ethanol, and deionized water in order to remove residual reactants and residual solvent molecules. Finally, the sample is dried in an oven at 100°C for 12 hours to further remove residual solvent molecules and activate the adsorbent sample.

[0055] (4) Place the sample in a vacuum drying oven and reduce the pressure until the vacuum degree reaches 1-10 -2 mbar, and heated to 120 ° C for activation for 20 h to further remove the solvent molecules in the pore structure of the adsorbent, thereby obtaining a metal organic framework adsorption material for adsorption and separation of octafluoropropane in nitrogen.

[0056] Example 3

[0057] (1) 45 parts by weight of zinc nitrate hexahydrate, 15 parts of chromium nitrate nonahydrate, and 60 parts of pyrazole-4-carboxylic acid were weighed and dissolved in 3600 parts of N-N-dimethylformamide solution. The mixture was placed in a magnetic stirrer and stirred at a speed of 450 r / min for 10 minutes until it was completely dissolved.

[0058] (2) The solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and reacted in an oven at 140 °C for 12 h.

[0059] (3) After the reaction is complete and the product has cooled to room temperature, it is filtered and washed four times with DMF, anhydrous ethanol, and deionized water in order to remove residual reactants and residual solvent molecules. Finally, the sample is dried in an oven at 100°C for 12 hours to further remove residual solvent molecules and activate the adsorbent sample.

[0060] (4) Place the sample in a vacuum drying oven and reduce the pressure until the vacuum degree reaches 1-10 -2 mbar, and heated to 120 ° C for activation for 24 h to further remove the solvent molecules in the pore structure of the adsorbent to obtain a metal organic framework adsorption material for adsorption and separation of octafluoropropane in nitrogen.

[0061] Comparative Example 1 (excluding Cr)

[0062] (1) 60 parts by weight of zinc nitrate hexahydrate and 60 parts of pyrazole-4-carboxylic acid were weighed and dissolved in 3600 parts of N-N-dimethylformamide solution. The mixture was placed in a magnetic stirrer and stirred at a speed of 450 r / min for 10 minutes until it was completely dissolved.

[0063] (2) The solution was transferred to a 500 ml polytetrafluoroethylene-lined stainless steel autoclave and reacted in an oven at 140°C for 12 h.

[0064] (3) After the reaction is complete and the product has cooled to room temperature, filter it and wash it 2-3 times with DMF, anhydrous ethanol, and deionized water in order to remove residual reactants and residual solvent molecules. Finally, dry the sample in an oven at 100°C for 12 hours to further remove residual solvent and activate the adsorbent sample.

[0065] (4) Place the sample in a vacuum drying oven and reduce the pressure until the vacuum degree reaches 1-10 -2 mbar was heated to 120 °C for activation for 24 h to further remove the solvent molecules in the pore structure of the adsorbent.

[0066] Comparative Example 2 (excluding Zn)

[0067] (1) 60 parts by weight of chromium nitrate nonahydrate and 60 parts of pyrazole-4-carboxylic acid were weighed and dissolved in 3600 parts of N-N-dimethylformamide solution. The mixture was placed in a magnetic stirrer and stirred at a speed of 450 r / min for 10 minutes until it was completely dissolved.

[0068] (2) The solution was transferred to a 500 ml polytetrafluoroethylene-lined stainless steel autoclave and reacted in an oven at 140°C for 12 h.

[0069] (3) After the reaction is complete and the product has cooled to room temperature, filter it and wash it 2-3 times with DMF, anhydrous ethanol, and deionized water in order to remove residual reactants and residual solvent molecules. Finally, dry the sample in an oven at 100°C for 12 hours to further remove residual solvent and activate the adsorbent sample.

[0070] (4) Place the sample in a vacuum drying oven and reduce the pressure until the vacuum degree reaches 1-10 -2 mbar, and heated to 120 °C for activation for 20 h to further remove the solvent molecules in the pore structure of the adsorbent.

[0071] 2. Powder X-ray Diffraction and Scanning Electron Microscopy Tests of Metal-Organic Framework Adsorbents for Adsorption and Separation of Octafluoropropane from Nitrogen

[0072] (1) The phase purity and crystallinity of the materials were characterized using a Smart Lab SE XRD instrument from Rigaku, Japan. The structure and crystallinity of the adsorbent samples were characterized using Cu target Kα radiation, a scanning step of 2° / min, and a scanning range of 2θ = 5° to 60°.

[0073] (2) A Sigma 360 scanning electron microscope (SEM) from the German ZEISS company was used to characterize the micromorphology, size, and elemental distribution of the adsorbent samples. After being fully ground, the samples were smeared on a conductive adhesive and sprayed with gold to increase the conductivity of the samples, which helped enhance the imaging effect of the samples in the SEM.

[0074] 3. Fixed-bed adsorption permeation test of metal-organic framework adsorbents for the adsorption and separation of octafluoropropane from nitrogen

[0075] (1) Before conducting the fixed bed adsorption permeation test, the granular adsorbent is first subjected to pretreatment such as calcination activation and vacuum drying to remove other impurity gases adsorbed in the pores, and the adsorption column device is preheated in advance to reach the temperature conditions required for the test. Then, the activated adsorbent sample is quickly filled into a stainless steel filling column with an inner diameter of 10 mm and a length of 300 mm and the filling mass is recorded. A small amount of cotton and a copper mesh are used to block both ends to prevent the adsorbent sample from being blown out. A C3F8 / N2 (1:400) binary mixture gas is passed into the adsorption column at a flow rate of 1 L / min. The outlet of the adsorption column is connected to a gas chromatograph and a portable sulfur hexafluoride helium ion detector is used to detect the outlet gas composition, and finally the adsorption permeation curve is obtained. The permeation time in the present invention is the time corresponding to when the C3F8 concentration at the outlet of the adsorption column reaches 5-10% of the initial concentration, and the saturation time is the time when the C3F8 concentration at the outlet of the adsorption column reaches 95-100% of the initial concentration.

[0076] (2) The inlet C3F8 concentration (ppm volume concentration) measured by the fixed bed adsorption permeation test was converted into mass concentration using the following calculation formula:

[0077]

[0078] Among them, c m is the mass concentration of C3F8 gas, unit: mg / m 3 ; M is the relative molecular weight of C3F8 gas, unit: g / mol; N A is Avogadro's constant; V is the gas volume concentration at the adsorption column inlet, unit: ppm; T is the test temperature, unit: K; P is the mixed gas pressure, unit: kPa.

[0079] The dynamic adsorption capacity of the gas can be calculated through the gas adsorption permeation curve. The calculation formula is as follows:

[0080]

[0081] Where Q is the dynamic adsorption capacity of the gas, unit: mmol / g; F is the flow rate of C3F8 gas, unit: mL / min; m is the mass of the adsorbent, unit: g; C0 is the gas mass concentration at the adsorption column inlet, unit: mg / L; t s is the adsorption saturation time, unit: min; C x is the gas concentration at the outlet of the adsorption column at any time, unit: mg / L.

[0082] 4. Single-component static isothermal adsorption test and adsorption selectivity analysis of metal-organic framework adsorbent materials for adsorption and separation of octafluoropropane from nitrogen

[0083] (1) The adsorption isotherms of the materials for C3F8 and N2 were measured using a Beijing Bester BSD-660C A6C gas adsorption and microporous analyzer at 298K, 303K, and 308K, respectively. The test pressure range was 0-170kPa. Before the test, a certain amount of adsorbent material was placed in a sample tube dedicated to the instrument and pretreated by vacuum desorption. The vacuum desorption temperature and desorption time were different for different adsorbent materials. The purity of the single-component gases C3F8 and N2 during the test was 99.99%.

[0084] (2) Since the adsorbent surface is not always homogeneous, this study selected a model that considers the heterogeneity of the material surface—the two-site Langmuir-Freundlich model (DSLF). The adsorption isotherms of the material for two pure components were fitted at 298 K. The fitting parameters were substituted into the IAST selectivity calculation equation to calculate the selectivity of the material for the binary gas mixture of C3F8 and N2 (1:400, v / v). The DSLF equation is as follows:

[0085]

[0086] Where q e (mmol / g) is the saturated adsorption capacity of the adsorbent; q1, q2 are the adsorption capacities of site 1 and site 2 on the adsorbent surface: mmol / g; b1, b2 are the affinity constants of site 1 and site 2, which are usually related to the adsorption energy; m, n represent the surface heterogeneity of site 1 and site 2, that is, the difference from the ideal homogeneous surface.

[0087] IAST can predict adsorption equilibrium of mixtures based on the adsorption isotherms of pure components and is suitable for analyzing competitive adsorption of multiple components. The core assumptions of IAST include setting the adsorption phase to an ideal solution state, the mutual independence of different components within the adsorption phase, thermodynamic equilibrium between the adsorption phase and the gas phase, and uniform energy distribution on the adsorbent surface with no preferential adsorption sites. The adsorption selectivity calculation equation is as follows:

[0088]

[0089] Where x1 is the mole fraction of component 1 in the adsorbed phase; x2 is the mole fraction of component 2 in the adsorbed phase; y1 is the mole fraction of component 1 in the gas phase; y2 is the mole fraction of component 2 in the gas phase. 1 / 2 is a parameter describing the adsorption selectivity of component 1 and component 2.

[0090] Figure 1 This is the powder X-ray diffraction pattern of the metal-organic framework material prepared in Example 1 of the present invention. As shown in the figure, the material exhibits distinct peaks at 2θ = 9.4, 16.5, 22.6, and 36.7, indicating good crystallinity. These peaks are characteristic of the Zn-MOF framework structure and match well with the peak patterns reported in existing literature, demonstrating the successful synthesis of the metal-organic framework material.

[0091] Figure 2 This is a scanning electron microscope image of the metal organic framework material prepared in Example 2 of the present invention. Figure 2 As shown, the metal organic framework material prepared by the present invention is composed of many tiny block crystals of about 500nm, which are combined into spherical particles of about 10μm. There are many gaps between the crystals, and these gaps fill the surface of the spherical particles.

[0092] Figure 3This is the adsorption penetration curve of the metal organic framework adsorption material prepared in Example 1 of the present invention for C3F8 / N2. The test was carried out under the conditions of a mixed gas flow rate of 1 L / min (V(C3F8:N2)=1:400), a temperature of 298K, and a pressure of 1.7 bar. Breakthrough time (Breakthrough Time) and saturation time (Saturation Time) are key parameters that describe the dynamic behavior of the adsorption column. The breakthrough time indicates the time required when the target component in the adsorption column feed is first detected at the outlet (reaching 0% to 5% of the inlet concentration), indicating that the adsorbent begins to "penetrate" and the adsorption capacity is gradually exhausted. The saturation time indicates the time required for the adsorption column to be fully saturated (outlet concentration ≈ inlet concentration), at which time the adsorbent no longer has adsorption capacity. As Figure 3 The metal organic framework material has a penetration time of 72.5 min and a saturation time of 123.1 min. The longer penetration time and saturation time indicate that the material has a strong adsorption capacity for C3F8. The dynamic saturated adsorption capacity is a key parameter for designing industrial adsorption equipment (such as fixed bed, fluidized bed), which directly reflects the processing capacity or bed life of the adsorbent. Through the penetration time, saturation time and dynamic saturated adsorption capacity calculated for Examples 1-3 and Comparative Examples 1-2, Table 1 is a summary table of the dynamic adsorption capacity of gases calculated by the adsorption penetration curves of gases for Examples 1-3, Comparative Examples 1-2, MS-10A and γ-Al2O3 of the present invention. The test results in Table 1 show that Example 3, the worst case among Examples 1-3 of the present invention, has a higher dynamic saturated adsorption capacity, reaching 0.853 mmol / g (243.39 mg / g), which is much higher than 0.0394 mmol / g and 0.0259 mmol / g of Comparative Examples 1 and 2. The results show that when the molar ratio of Zn to Cr is 4 to 5:1 (Examples 1-3), the adsorption capacity of octafluoropropane by the metal-organic framework material is significantly higher than that of the pure metal MOF (Comparative Examples 1 and 2).

[0093] Table 1

[0094]

[0095] Figure 4The single-component adsorption isotherms of the metal-organic framework adsorption material prepared in Example 1 of the present invention for C3F8 and N2 at different temperatures are shown. As shown in the figure, the metal-organic framework adsorption material prepared in Example 1 of the present invention exhibits a high C3F8 adsorption capacity, with adsorption capacities of 1.83, 1.56, and 1.34 mmol / g at 298K, 303K, and 308K, respectively. Correspondingly, the adsorption capacity of the material for N2 is 0.15, 0.14, and 0.11 mmol / g at the three temperatures. Moreover, within the measured temperature range, the adsorption capacity of the material for C3F8 and N2 decreases with increasing temperature, indicating that the adsorption of C3F8 and N2 by the surface material is a typical physical adsorption process. In addition, at the same temperature, the adsorption capacity of the material for C3F8 is significantly higher than that for N2, and the slope of the C3F8 curve in the low-pressure region is higher than that of the N2 curve. These results indicate that the adsorption material framework can produce a stronger interaction force with C3F8, which indicates that it has excellent separation potential.

[0096] Figure 5 Graph showing the adsorption selectivity of the metal-organic framework adsorbent material for C3F8 / N2 prepared in Example 1 of the present invention. In the field of adsorption separation, IAST (Ideal Adsorbed Solution Theory) is a theoretical model for predicting the competitive adsorption behavior of mixed gas or liquid components on an adsorbent. IAST adsorption selectivity is a key parameter proposed based on this theory, which is used to quantify the preferential adsorption capacity of an adsorbent for different components in a mixture. As shown in the figure, the IAST selectivity of the metal-organic framework adsorbent material prepared in Example 1 of the present invention was calculated under the conditions of a binary gas mixture at 298K and a volume ratio of C3F8 and N2 of 1:400 (volume concentration of octafluoropropane of 2500ppm). As the pressure increased, the selectivity of the material increased from 55 to 195. Under the conditions of 298K and 1.7bar, the adsorption selectivity of the material reached 195, which means that the high selectivity of the metal-organic framework adsorbent material for C3F8 prepared in Example 1 of the present invention indicates that it has excellent separation ability, that is, it can meet the separation requirements under conditions of extremely low C3F8 concentrations.

[0097] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for adsorbing and separating octafluoropropane from a binary gas mixture of octafluoropropane and nitrogen, characterized in that: A mixed gas containing nitrogen and octafluoropropane is adsorbed and separated through an adsorption column filled with a metal-organic framework material; the metal-organic framework material is prepared by dissolving Zn salt, Cr salt powder and an organic ligand pyrazole-4-carboxylic acid in a solvent, reacting the resulting product at 140-150°C through a solvothermal method, and then purifying and activating the resulting product; the molar ratio of the Zn salt to the Cr salt is controlled to be 4-5:

1.

2. The method for adsorbing and separating octafluoropropane in a binary gas mixture system of octafluoropropane and nitrogen according to claim 1, characterized in that: The adsorption column is a vertical container with adsorbent filled inside and openings at the top and bottom.

3. The method for adsorbing and separating octafluoropropane in a binary gas mixture system of octafluoropropane and nitrogen according to claim 1, characterized in that: The adsorption column is 10-25 cm long and the fixed bed is 5-15 cm in diameter.

4. The method for adsorbing and separating octafluoropropane in a binary gas mixture system of octafluoropropane and nitrogen according to claim 1, characterized in that: The volume ratio of the binary gas mixture of octafluoropropane and nitrogen is 1:400-1:500, and the concentration of octafluoropropane is 2000-2500 ppm.

5. The method for adsorbing and separating octafluoropropane in a binary gas mixture system of octafluoropropane and nitrogen according to claim 1, characterized in that: The adsorption temperature of the adsorption column is 25° C. to 35° C., the pressure in the adsorption column is 1.5 bar to 1.7 bar, and the flow rate of the binary mixed gas of octafluoropropane and nitrogen is 0.8 to 1.5 L / min.

6. The method for adsorptive separation of octafluoropropane in a binary gas mixture system of octafluoropropane and nitrogen according to claim 1, characterized in that: The solvent dissolved in the solvent is one or more mixed solutions of deionized water, methanol, ethanol and N-dimethylformamide solution.

7. The method for adsorbing and separating octafluoropropane in a binary gas mixture system of octafluoropropane and nitrogen according to claim 1, characterized in that: The Zn salt and Cr salt are both selected from one or more of chlorides, nitrates, sulfates, carbonates and acetates of Zn and Cr.

8. The method for adsorbing and separating octafluoropropane in a binary gas mixture system of octafluoropropane and nitrogen according to claim 1, characterized in that: The metal-organic framework material is synthesized by the following steps: (1) dissolving Zn salt, Cr salt powder and organic ligand pyrazole-4-carboxylic acid in a solvent, and stirring the mixture thoroughly at room temperature until it is completely dissolved; controlling the molar ratio of Zn salt to Cr salt to be 4 to 5:1; (2) transferring the solution obtained in step (1) into a reaction kettle, and synthesizing a metal-organic framework material by a solvothermal method at 140-150° C.; (3) After the mixture in the reactor of step (2) is cooled to room temperature, the mixture is filtered or centrifuged, washed thoroughly, and then dried; (4) Activating the product obtained in step (3).

9. The method for adsorptive separation of octafluoropropane in a binary gas mixture system of octafluoropropane and nitrogen according to claim 8, characterized in that: In step (1), the stirring is magnetic stirring, and the stirring speed is 400-500 rpm; In step (2), the solvent thermal method is carried out for 12 to 15 hours in an oven; the reaction kettle is a stainless steel autoclave lined with polytetrafluoroethylene.

10. The method for adsorptive separation of octafluoropropane in a binary gas mixture system of octafluoropropane and nitrogen according to claim, characterized in that: In step (3), the washing is carried out by using DMF, anhydrous ethanol, and deionized water in order for 2-3 times and then centrifuging; the drying is carried out by placing the product in an oven at 90-100° C. for 12-18 hours; In step (4), the activation is to place the product in a vacuum drying oven and reduce the pressure to a vacuum degree of 1 to 10 -2 mbar, heat to 110-130℃ and activate for 20-24h.

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