A method and apparatus for online purification of sulfur hexafluoride using inorganic molecular sieve membranes

Abstract

This invention relates to a method for purifying sulfur hexafluoride (SF6) using an inorganic molecular sieve membrane. The method involves first pretreating a SF6-containing mixed gas feedstock into a purification unit and a pretreatment unit, followed by membrane separation. After single-stage or multi-stage membrane separation, a high-purity SF6 product is obtained. The permeate side of the membrane separation yields a product rich in N2, while the residual side yields a product rich in SF6, which can be reused as an insulating gas. The SF6 purification process using membrane separation exhibits excellent stability, is simple to operate, consumes little energy, and is suitable for practical applications in the electrical industry.

Description

Technical Field

[0001] This invention relates to the technical field of gas purification and separation, and particularly to an apparatus for separating and purifying SF6 from an N2 / SF6 mixed gas. Background Technology

[0002] Sulfur hexafluoride (SF6) is widely used in high-voltage electrical appliances due to its excellent dielectric and arc-quenching properties. While N2 / SF6 mixtures are slightly inferior to pure SF6 in performance, they are significantly cheaper and less prone to condensation at low temperatures, thus reducing SF6 leakage and greenhouse gas emissions. Therefore, N2 / SF6 mixtures are increasingly being used as insulation in large-scale high-voltage projects. However, as a greenhouse gas, SF6 is strictly prohibited from direct release into the atmosphere. Consequently, the separation and recovery of SF6 / N2 mixed insulating gases in electrical appliances has become a major challenge that must be addressed.

[0003] Existing technologies for SF6 purification include low-temperature distillation, low-temperature freezing, and adsorption. However, these methods are generally characterized by complex processes and high energy consumption. Membrane separation technology is a rapidly developing new separation technology that has been well applied in gas separation. Organic membrane separation of SF6 has been documented in various journals, but the separation performance of organic membranes for SF6 is poor, and they are not resistant to high pressure or high temperature. Furthermore, organic membrane separation of SF6 often requires multi-stage pretreatment of the gas to be purified, including drying water vapor to prevent its impact on the membrane material's separation performance. Adsorption dehumidification is commonly used, but due to the complex composition of the feed gas, other gaseous components often compete with the adsorbent for adsorption, thus interfering with the dehumidification pretreatment. Compared to organic membranes, inorganic molecular sieve membranes offer better separation performance, are resistant to high temperature and pressure, and are corrosion-resistant, thus having greater application potential. Therefore, there is an urgent need for a simple, efficient, and direct method and apparatus for SF6 purification using inorganic molecular sieve membranes.

[0004] For inorganic molecular sieve membranes, a high-pressure feed environment is essential to meet flux requirements. However, compared to organic membranes, inorganic membranes have a lower yield, making the screening of membrane materials with good separation performance for high-pressure applications a time-consuming and labor-intensive task. Improvements to existing technologies are needed to rapidly screen suitable inorganic membrane materials. Summary of the Invention

[0005] The purpose of this invention is to provide a method for gas separation using inorganic molecular sieve membranes to purify SF6, thereby solving the problems of high equipment investment, complex operation, and high energy consumption associated with traditional adsorption separation methods.

[0006] This invention provides a method for online purification of sulfur hexafluoride using inorganic molecular sieve membranes, comprising the following steps:

[0007] (1) The gas to be purified, which contains particulate matter, water vapor, impurity gas and SF6, is first passed through a purification unit to remove particulate matter;

[0008] (2) After the gas feed pressure for removing particulate matter is controlled within the range of 0.1 to 5 MPa and the feed temperature is controlled within the range of -100 to 500°C, it is fed into the membrane separation device. Sulfur hexafluoride is retained on the permeate side by the membrane layer to obtain the permeate product sulfur hexafluoride. Water vapor and other impurity gases permeate through the membrane layer and are enriched on the permeate side.

[0009] (3) During membrane separation, a purge gas is passed through the permeate side to remove the separated products in time, or vacuum suction is used to remove the separated products. The separated products are then filled for use or discharged in compliance with standards.

[0010] 4) The sulfur hexafluoride gas on the permeate side is passed into the drying unit for drying, and the dried sulfur hexafluoride is compressed and filled or refilled for use after reaching the required concentration; the membrane in the membrane separation device is an inorganic molecular sieve membrane.

[0011] Preferably, the impurity gas includes one or more of nitrogen and oxygen, the acidic gas includes one or more of carbon dioxide, sulfur dioxide, and nitrogen oxides, and the drying unit is one or more of adsorbent dehumidification, absorbent dehumidification, and condensation dehumidification.

[0012] Preferably, the permeate gas concentration is detected by the detection unit. When the sulfur hexafluoride concentration is lower than a certain value, the permeate gas is purified by micro-SF6 adsorption to obtain high-purity nitrogen or a nitrogen-oxygen mixture. When the sulfur hexafluoride concentration is higher than a certain value, the permeate gas is introduced into the inlet side of the membrane separation device to mix with the gas from which impurities have been removed.

[0013] Preferably, in step (1), the gas mixture to be separated is pretreated by a pretreatment unit; the pretreatment includes one or more of compression, filtration, and heating.

[0014] Preferably, in step (1), the gas product on the permeate side is controlled to be extracted by a back pressure valve; the feed pressure of the gas mixture to be separated is controlled within the range of 0.1 to 5 MPa; and the feed temperature of the gas mixture to be separated is controlled within the range of -100 to 500°C.

[0015] Preferably, the inorganic membrane is a tubular membrane or a hollow fiber membrane. The separation membrane is composed of multiple tubular membranes or hollow fiber membranes, and the separation device is assembled from single-stage or multi-stage separation components; the inorganic membrane is selected from one or more of SSZ-13, DDR, LTA, and MFI; if a purge gas is used, the purge gas is an inert gas.

[0016] Preferably, the gas to be purified originates from sulfur hexafluoride circuit breakers (GIS) or gas-insulated transmission lines (GIL) that use N2 / SF6 as insulating gas.

[0017] Preferably, the method further includes a screening and evaluation step for membrane materials in a membrane separation device. The screening and evaluation step establishes a diffusion coefficient model of the binary mixture on a molecular sieve membrane using the Maxwell-Stefan model and predicts the separation performance of the membrane material under different pressures using low-pressure two-component separation data.

[0018] Preferably, the screening and evaluation steps specifically include:

[0019] (1) Test the single-component N2 flux at one or more points under low pressure, and obtain the self-diffusion coefficient of N2 using the single-point Maxwell-Stefan model; the formula is as follows:

[0020]

[0021]

[0022]

[0023]

[0024] δ(m): Thickness of the molecular sieve membrane, ρ(kg m) -3 ): Density of the molecular sieve membrane. D(m) 2 s -1 ): Gas diffusion coefficient, K (kPa) -1 ): Gas equilibrium constant. -ΔH (kJ mol) -1 ): Gas adsorption enthalpy, K0 (kPa) -1 ): The pre-exponential factor of the adsorption equilibrium constant.

[0025] (2) By The overall diffusion coefficient of nitrogen was obtained, and further derived using the Maxwell-Stefan equation. Derive the N2 permeation flux at higher pressures;

[0026] (3) Test the SF6 flux at two or more points under low pressure. If the SF6 flux at the first point is greater than 1×10⁻⁶ at the lowest pressure, then the SF6 flux at the first point is greater than 1×10⁻⁶ at the lowest pressure. - 4 mol m -2 s -1 If the flux is lower than this value, the membrane does not meet the requirements. If the flux is lower than this value, the next pressure point should be tested, a linear equation should be established, and the equation for the change of viscous flow with pressure should be obtained. Derive the SF6 flux under high pressure;

[0027] (4) Select membranes with suitable performance based on actual usage pressure and selectivity requirements.

[0028] The present invention also provides an apparatus for online purification of sulfur hexafluoride using an inorganic membrane, characterized in that the apparatus comprises a pretreatment unit, a mass flow controller and a membrane separation device connected in sequence, wherein the pretreatment unit is provided with an inlet for the gas to be purified, the membrane separation device is provided with a sulfur hexafluoride product gas outlet on the permeate side and an impurity nitrogen outlet on the permeate side.

[0029] Preferably, the impurity nitrogen outlet is connected to a detection unit, one path of which is connected to the trace SF6 adsorption unit and the other path is connected to the feed side of the membrane separation unit; the purification unit includes one or more of a solid filter and a micron filter.

[0030] Beneficial effects

[0031] First, this invention is simple to operate, requiring only a single or multi-stage membrane separation unit connected in series to purify sulfur hexafluoride gas. Furthermore, this invention uses hydrophobic molecular sieve membranes as the separation membrane material, requiring only the removal of particulate matter from the mixed gas, eliminating the need for pre-membrane dehumidification and focusing solely on post-membrane dehumidification and drying, thus reducing the impact of complex components on dehumidification and drying. Simultaneously, the process employed in this invention requires low investment, features compact equipment, and can achieve sulfur hexafluoride separation at room temperature, resulting in energy conservation, environmental protection, and significant economic benefits.

[0032] Secondly, this invention successfully predicts the relationship between feed pressure and separation selectivity in the N2 / SF6 binary component of small-pore molecular sieve membranes by establishing a semi-empirical formula that couples the total diffusion coefficient of the mixture with the adsorption amount through the Maxwell-Stefan model. This allows for rapid screening of membrane materials under low-pressure conditions, saving time and effort. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a single-stage nitrogen / sulfur hexafluoride membrane separation device, wherein: 1. Pretreatment unit; 2. Mass flow controller; 3. First membrane separation unit; 4. Back pressure valve; 5. Air pump; 6. Second membrane separation unit;

[0034] Figure 2 This is a schematic diagram of a single membrane separation unit;

[0035] Figure 3 A schematic diagram illustrating the application of membrane separation in the purification of insulating gases;

[0036] Figure 4 Figure 1. N2 / SF6 separation performance of SSZ-13 membrane with CO2 / CH4 selectivity of 160 as a function of pressure;

[0037] Figure 5 Figure 1. Change of N2 / SF6 separation performance of SSZ-13 membrane with CO2 / CH4 selectivity of 160 as a function of temperature;

[0038] Figure 6 The graph shows the N2 / SF6 separation performance of the SSZ-13 membrane with a CO2 / CH4 selectivity of 400 as a function of pressure.

[0039] Figure 7 The graph shows the N2 / SF6 separation performance of the SSZ-13 membrane with a CO2 / CH4 selectivity of 400 as a function of temperature.

[0040] Figure 8 The diffusion coefficient of N2 in a small-pore molecular sieve membrane as a function of pressure is given by the single- or dual-component diffusion coefficient.

[0041] Figure 9 Experimental and calculated values ​​vary with pressure. Detailed Implementation

[0042] Example 1

[0043] like Figure 1 As shown, the device in this embodiment 1 includes a pretreatment unit 1, a mass flow controller 2, a first membrane separation device 3, a back pressure valve 4, a gas pump 5, and a second membrane separation unit 6 connected in sequence. The pretreatment unit has an inlet for the gas to be purified, the membrane separation device has a sulfur hexafluoride product gas outlet on the permeate side, and the membrane separation device has an impurity nitrogen gas outlet on the permeate side.

[0044] In this embodiment, the raw gas undergoes pretreatment by pretreatment unit 1 to ensure that parameters such as moisture content, pressure, and temperature meet requirements. The pretreatment unit 1 used in this invention is not particularly limited and can include a compression device, a filtration device, or a heating device. It pretreats the raw gas before it enters the series membrane separation assembly to achieve the corresponding gas state requirements. The treated raw gas is then sequentially fed into the first gas separation membrane assembly 3 and the second membrane separation unit 6 at appropriate feed positions via mass flow controller 2.

[0045] In this embodiment, when the membrane modules are connected in series, the upstream module is the first stage, the permeate gas is used as the feed gas for the downstream second stage, and the (downstream) permeate side is the final product outlet.

[0046] The single membrane module used in this invention Figure 2 The membrane module consists of a housing and an internal sulfur hexafluoride purification membrane. The housing is made of stainless steel or nylon. The housing and the gas separation membrane divide the internal space of the module into a permeate side and a effluent side. Figure 2Taking a hollow fiber gas separation membrane as an example, its configuration is tubular, with the selective separation layer located outside the hollow fiber membrane. The shell has an inlet and an outlet, and both ends are sealed with threaded caps. One end has a permeate-side outlet, and the other end has a purge gas inlet. The permeate-side outlet yields a gas product rich in ultra-low sulfur hexafluoride. The residual gas outlet, after single-stage or multi-stage separation, yields a pure sulfur hexafluoride product.

[0047] When using the above structure, a major improvement is that a membrane separation device is used to directly separate the sulfur hexafluoride mixture. The residual gas is not limited to the return to the gas tank as a reflux method. The residual gas can be adjusted to enter the next stage gas separation component for further separation of the residual side products according to the purity requirements.

[0048] During the feeding process of the above-mentioned single-stage membrane module raw materials, the pressure range is controlled between 0.1 and 5 MPa.

[0049] The operating temperature range of the sulfur hexafluoride purification process of the above membrane separation unit is -100 to 500℃.

[0050] When using the multi-stage purification process described above, during the residual gas reflux process of each module, the gas reflux ratio (reflux ratio refers to the ratio of (the amount of gas refluxed from the residual side of the membrane module in that stage - the amount of gas permeated from the membrane module in that stage) to the amount of gas to be separated entering the gas separation equipment) is controlled to be <10. For example, in a series device containing 10 membrane modules, the mixed gas feed position is at the 5th stage membrane module. For the 4th stage membrane module, it simultaneously receives gas refluxed from the residual side of the 5th stage and gas obtained from the permeate side of the 3rd stage. Therefore, the reflux ratio is: the amount of gas refluxed from the residual side of the 4th stage (the amount of gas from the permeate side of the 3rd stage + the amount of gas refluxed from the residual side of the 5th stage - the amount of gas permeated from the 4th stage) / the amount of gas to be separated entering the gas separation equipment.

[0051] The length of the SSZ-13 molecular sieve membrane used in the above separation device is in the range of 10-200 cm.

[0052] The effective area of ​​the SSZ-13 molecular sieve membrane used in the above separation device is 0-20000 m². 2 Within the range.

[0053] Example 2

[0054] A gas containing 48% N2, 50% SF6, 2% water vapor, and trace amounts of dust, with a flow rate of 100 mL / min, is introduced into a pretreatment unit to remove solid particles from the mixed gas, bringing the temperature of the treated gas to 25°C. The pretreated feed gas is then fed into the separation unit at a controlled feed rate through the first-stage inlet via a mass flow controller. The permeate side outlet of the first-stage component is connected to a back pressure valve to maintain the permeate side pressure at 0–5 bar (gauge pressure). A 5 cm long SSZ-13 molecular sieve membrane with a CO2 / CH4 bicomponent selectivity of 160 at a pressure drop of 0.1 MPa is selected, while the N2 / SF6 selectivity for a single-stage membrane process can reach 800. The SF6 concentration on the permeate side as a function of pressure is shown in Table 1, and the permeability as a function of pressure is shown in Table 2. Figure 4 .

[0055] Table 1. SF6 concentration on the permeate side of the membrane separation unit as a function of pressure.

[0056]

[0057] Example 3

[0058] A gas containing 48% N2, 50% SF6, 2% water vapor, and trace dust, with a flow rate of 100 mL / min, is introduced into a pretreatment unit to remove solid particles, bringing the treated gas temperature to 25°C. The pretreated gas is then fed into the separation unit at a controlled feed rate through the first-stage inlet via a mass flow controller. A back pressure valve is connected to the permeate side outlet of the first-stage module to maintain the permeate side pressure at 1 Bar (gauge pressure), and the membrane module temperature is controlled between 25-200°C. A 5 cm long SSZ-13 molecular sieve membrane with a CO2 / CH4 bicomponent selectivity of 160 at a pressure drop of 0.1 MPa is selected, while the N2 / SF6 selectivity for a single-stage membrane process can reach 800. The SF6 concentration on the permeate side as a function of temperature is shown in Table 2, and the permeability as a function of temperature is shown in Table 3. Figure 5 .

[0059] Table 2. SF6 concentration on the permeate side of the membrane separation unit as a function of temperature.

[0060]

[0061] Example 4

[0062] A gas containing 48% N2, 50% SF6, 2% water vapor, and trace dust, with a flow rate of 150 mL / min, was introduced into a pretreatment unit to remove solid particles, bringing the treated gas temperature to 25°C. The pretreated gas was then fed into the separation unit at a controlled feed rate through the first-stage inlet via a mass flow controller. A back pressure valve was connected to the permeate side outlet of the first-stage module to maintain the permeate side pressure at 1-5 Bar (gauge pressure), and the membrane module temperature was controlled at 25-200°C. A 20 cm long SSZ-13 molecular sieve membrane with a CO2 / CH4 bicomponent selectivity of 400 at a pressure drop of 0.1 MPa was selected. The SF6 concentration on the permeate side as a function of temperature is shown in Table 3, as is its variation with pressure in Table 4, and the permeability as a function of pressure is shown in Table 5. Figure 6 See changes with temperature Figure 7 .

[0063] Table 3. SF6 concentration on the permeate side of the membrane separation unit as a function of temperature.

[0064]

[0065]

[0066] Table 4. SF6 concentration on the permeate side of the membrane separation unit as a function of pressure.

[0067]

[0068] Example 5

[0069] A diffusion coefficient model for binary mixtures on a molecular sieve membrane was established based on the Maxwell-Stefan model. A single-point Langmuir model was used to represent the gas adsorption amount in the molecular sieve, and the gas permeation flux through the molecular sieve membrane (N) was also used. i ,molm -2 s -1 It can be obtained from the Maxwell-Stefan equation.

[0070]

[0071]

[0072]

[0073]

[0074] δ(m): Thickness of the molecular sieve membrane, ρ(kg m) -3 ): Density of the molecular sieve membrane. D(m) 2 s -1 ): Gas diffusion coefficient, K (kPa) -1 ): Gas equilibrium constant. -ΔH (kJ mol)-1 ): Gas adsorption enthalpy, K0 (kPa) -1 ): The pre-exponential factor of the adsorption equilibrium constant. The diffusion coefficient of N2 as a function of pressure is derived. Figure 9 The graph shows that the diffusion coefficient increases with increasing pressure.

[0075] In the MS model, the diffusion coefficient of gas molecules is independent of the amount adsorbed within the membrane. However, the diffusion rate of adsorbed molecules in molecular sieves generally depends on their loading. This is especially true for small-pore 8-membered ring molecular sieves such as SSZ-13 and DDR, where the loading dependence of the N2 diffusion rate is very strong. This strong loading dependence makes accurate modeling of permeation behavior in molecular sieve membranes extremely complex. Therefore, a key assumption in establishing this model is to decompose the total diffusion coefficient of the N2 component into two terms: the diffusion coefficient used to describe the adsorption dependence and the self-diffusion coefficient of N2. The specific calculations are as follows:

[0076]

[0077]

[0078]

[0079] This refers to the diffusion coefficient of N2 in a binary component. This patent argues that the diffusion coefficient in a multi-component system is primarily influenced by two factors: one is the change in diffusion coefficient due to variations in the adsorption capacity itself, i.e., the loading dependence; the other is the change in diffusion coefficient caused by collisions between the binary components. Assuming that gas molecules can only undergo inter-adsorption site transitions in the molecular sieve membrane when the second adsorption site is vacant, then... This is used to represent this load dependency. θ total This indicates the total adsorption occupancy rate of the gas in the binary component. The N2 diffusion coefficient, which is only affected by the adsorption amount, is derived from the adsorption amount and diffusion coefficient of single-component N2 under different pressures. In the molecular sieve membrane, the N2 diffusion coefficient decreases with increasing adsorption amount; when the N2 adsorption amount is 0, ... Approaching infinity, at this point This represents the diffusion coefficient of N2 at vacant sites. In summary, as pressure increases, the adsorption capacity increases. The N2 flux decreases because the adsorbent coverage on the surface does not increase linearly with increasing partial pressure. The N2 permeation flux decreases linearly, which can be used to predict the N2 permeation flux at higher pressures.

[0080] For SF6, its kinetic diameter is 0.56 nm, much larger than the pore size of an eight-membered ring molecular sieve. Therefore, the permeation and diffusion of SF6 rely on non-selective defects. The permeability caused by Knudsen diffusion remains unchanged with varying feed pressure, while viscous flow increases linearly with pressure differential. The permeability of N2 through non-molecular sieve pores is then calculated using the following formula;

[0081] Calculation of viscous flow in non-molecular sieve channels:

[0082]

[0083] Among them, P Vis，i η represents the permeability of component i due to viscous flow; η is the kinetic viscosity of component i; Knudsen diffusion calculation for non-molecular sieve pores:

[0084]

[0085] Among them, P Kn，i The permeability of component i due to Knudsen diffusion was calculated; the permeability of N2 through intergranular defects accounted for 1.3% of the overall permeability, having almost no effect on separation performance. However, according to equations (8) and (9), the effect of non-molecular sieve viscous flow on the permeability of SF6 increases linearly with increasing pressure. Therefore, all the above calculations suggest that at higher pressures, the separation performance of membranes with effective pore sizes between N2 and SF6 is related to pressure (e.g., ...). Figure 8 (as shown), and Figure 9 The experimental and calculated values ​​for pressure variation show consistency, thus confirming the reliability of the model. Based on the predicted separation performance of the membrane material under high pressure, combined with the required separation performance of the membrane material in practical applications, it is possible to quickly determine whether the membrane material meets the requirements, thereby completing the membrane material selection process.

Claims

1. A method for purifying sulfur hexafluoride on-line by an inorganic molecular sieve membrane, characterized by, The method comprises the following steps: (1) the gas to be purified containing particulate matter, water vapor, impurity gas and sulfur hexafluoride is first passed through a purification unit to remove particulate matter; (2) the gas from which particulate matter is removed is fed into a membrane separation device at a feed pressure ranging from 0.1 to 5 MPa and a feed temperature ranging from -100 to 500 DEG C, wherein water vapor and sulfur hexafluoride are retained on the retentate side of the membrane layer to obtain a retentate side product humid sulfur hexafluoride, and other impurity gases are enriched on the permeate side of the membrane layer; (3) during membrane separation, a sweep gas is passed through the permeate side to remove the separation product in time, or the separation product is removed by vacuum pumping, and the separation product is filled for use or discharged according to standards; (4) the retentate side gas sulfur hexafluoride is passed into a drying unit for drying, and after the dried sulfur hexafluoride reaches the required concentration, it is compressed and filled for use or returned for use; the membrane in the membrane separation device is an inorganic molecular sieve membrane; the method further comprises a membrane material screening and evaluation step, wherein a Maxwell-Stefan model is used to establish a diffusion coefficient model of a binary mixture on a molecular sieve membrane, and low-pressure two-component separation data are used to predict the separation performance of the membrane material under different pressures, so as to screen a membrane material meeting the separation performance requirements; the screening and evaluation step specifically comprises: (1) testing single-component N2 flux at one point or multiple points under low pressure, and obtaining the self-diffusion coefficient of N2 from the single-point Maxwell-Stefan model; the formula is as follows: δ(m): thickness of the molecular sieve membrane, p(kg m -3 ): density of the molecular sieve membrane; D(m 2 s -1 ): gas diffusion coefficient, K(kPa -1 ): gas equilibrium constant; -ΔH(kJ mol -1 ): gas adsorption enthalpy, K0(kPa -1 ): pre-exponential factor of the adsorption equilibrium constant; N i : permeation flux of the gas through the molecular sieve membrane, q i : adsorption amount of the gas component i in the molecular sieve; (2) by The total diffusion coefficient of nitrogen was derived, further from the Maxwell-Stefan equation The N2 permeation flux at higher pressures was derived; denotes the total diffusion coefficient of N2 in the binary mixture, θ total denotes the total adsorbed occupancy of the gas in the binary mixture; denotes the diffusion coefficient of N2 influenced only by the adsorbed amount; (3) Test the SF6 flux of the membrane at two or more points at low pressure. If the first point SF6 flux is the lowest flux at the lowest pressure > 1 x 10 -4 mol m -2 s -1 , then the membrane does not meet the use requirements. If the flux is lower than this value, then test the next pressure point, establish a linear equation, and obtain the equation of viscous flow with pressure Deduce the SF6 flux at high pressure; P Vis,i refers to the permeability of component i caused by viscous flow, η i refers to the dynamic viscosity of component i; (4) according to the actual use pressure and selective requirements, a membrane with appropriate performance is screened.

2. The method of claim 1, wherein, the impurity gas comprises one or more of nitrogen, oxygen, carbon dioxide, sulfur dioxide and nitrogen oxide, and the drying unit is one or more of an adsorbent dehumidifier, an absorbent dehumidifier and a condensation dehumidifier.

3. The method of claim 1, wherein, the permeate side gas is subjected to concentration detection by a detection unit, when the concentration of sulfur hexafluoride is lower than a certain value, the permeate side gas is subjected to trace SF6 adsorption purification and then filled for use or discharged according to standards, and when the concentration of sulfur hexafluoride is higher than a certain value, the permeate side gas is passed into the gas inlet side of the membrane separation device to be mixed with the gas from which particulate matter is removed; the retentate side gas is dried by a drying unit and then compressed and filled for use or returned to GIS / GIL for continuous use; in the step (1), the gas mixture to be separated is pretreated by a pretreatment unit; the pretreatment comprises one or more of compression, filtration or heating; in the step (4), the obtained material on the retentate side is subjected to further purification by one or more membrane separation units in the next stage or the next several stages; the gas to be purified is derived from a sulfur hexafluoride circuit breaker (GIS) or a gas insulated transmission line (GIL) using N2 / SF6 as insulating gas.

4. The method of claim 1, wherein in the step (1), the gas product on the retentate side is controlled by a back pressure valve; the feed pressure of the gas mixture to be separated ranges from 0.1 to 5 MPa; and the feed temperature of the gas mixture to be separated ranges from -100 to 500 DEG C.

5. The method of claim 1, wherein, The inorganic molecular sieve membrane is a tubular membrane or a hollow fiber membrane; the inorganic molecular sieve membrane is composed of a plurality of tubular membranes or hollow fiber membranes in a package, and the separation device is obtained by assembling single-stage or multi-stage separation components; the inorganic molecular sieve membrane is selected from one or more of SSZ-13, DDR, LTA and MFI; if a purge gas is used, the purge gas is an inert gas.

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