CN111821818B

CN111821818B - A method and device for inorganic membrane multi-stage gas separation

Info

Publication number: CN111821818B
Application number: CN202010476743.1A
Authority: CN
Inventors: 顾学红; 谢继贤; 王学瑞; 张萍
Original assignee: Nanjing Tech University
Current assignee: Nanjing Tech University
Priority date: 2019-06-27
Filing date: 2020-05-29
Publication date: 2025-02-11
Anticipated expiration: 2040-05-29
Also published as: CN111874881B; CN111874881A; CN111821818A

Abstract

The present invention discloses an inorganic membrane multi-stage gas separation method, the steps are: S1, pre-treating the raw gas in a pre-treatment unit. S2, the pre-treated raw gas enters the multi-stage membrane separation component for separation treatment, the permeate gas enters the lower component, and the retentate gas refluxes to continue separation. S3, collecting gas products on the retentate side of the first-stage component and the permeate side of the last-stage component and recycling them. The device includes a pre-treatment module, a single-stage membrane component, an air pump, a mass flow controller and a back pressure valve. After the raw material is pre-treated, it enters the multi-stage membrane component through the mass flow controller, the back pressure valve controls the pressure on the retentate side of the first-stage component, and multiple components are connected in series through pipelines. The permeate gas of each stage enters the next stage as the raw gas, and the retentate gas of the first stage is connected to the back pressure valve to control the top extraction. The retentate gas of each other stage component is returned to the upper component through the air pump to mix with the feed gas, and the gas product on the permeate side of the last stage component is collected under normal pressure.

Description

Method and device for multistage gas separation by inorganic membrane

Technical Field

The invention relates to a method for separating inorganic membrane multi-stage gas, in particular to separation and purification of binary or multi-component mixed gas with low single-stage membrane separation selectivity.

Background

The gas product is used as an important basic raw material in the modern industry, and has a very wide application range. In addition to common industrial gases in industry, special gases play an important role in industries such as electronic information, aerospace, petrochemical industry, medical treatment, environmental protection and the like. For example, ultra-pure nitrogen can be used as a protector of an ultra-large scale integrated circuit, and neon isotopes can be used in the military industry such as missile guidance. However, the enterprise scale of the special gas in China is smaller, the independent research and development result is smaller, the gas used for producing the submicron integrated circuit can not be produced in large scale in China at present, the research and application of the isotope separation of the special gas are still a starting stage, and the production dependency is imported abroad. The separation method of the mixed gas mainly comprises a low-temperature rectification method, a pressure swing adsorption method and a membrane separation method. The low-temperature rectification method relates to phase-change separation, has the advantages of higher energy consumption, larger device scale, high equipment cost, low recovery rate of the pressure swing adsorption method, continuous vacuumizing and compressing of gas, high equipment cost, complex operation and the like. The special gas separation and purification field also relates to noble metal catalysis method, thermal diffusion method, molecular sieve purification technology and other methods. However, the method has the problems of high cost, high energy consumption, high equipment cost, complex operation and the like.

In the application of membrane method for separating gas, a biogas decarbonization process of coupling two-stage membrane separation and CO ₂ liquefaction is mentioned in the patent with the patent number of CN201310329942.X, but the process needs to be coupled with low-temperature liquefaction, the operation is more complicated, a device for separating gas by a three-section gas separation membrane unit is designed in the patent with the patent number of CN201510045066.7, an additional mixing container is added in the reflux process of the device, and the separation requirement is difficult to reach for a system with lower membrane separation coefficient, and the limitation is larger.

In addition, in a specific membrane separation application area,

Disclosure of Invention

The invention aims to provide a method for separating and purifying gas by using an inorganic membrane multistage gas, which solves the problems of high equipment investment, complex operation and high energy consumption of the traditional methods such as low-temperature rectification, pressure swing adsorption and the like. The series connection of the multi-stage membrane components can effectively improve the separation purity of a mixed system with lower membrane separation selectivity, realize the recovery of target gas, remarkably increase the productivity and improve the economic benefit.

The multistage inorganic membrane gas separation method can meet the separation requirement only by a membrane separation process, does not need to be coupled with other processes, can directly reflux the residual gas of each stage to the upper stage, can realize the separation of a gas system with lower single-stage membrane separation selectivity by multistage membrane separation, greatly improves the separation efficiency and reduces the operation cost. The technology has great application potential in the fields of enrichment of oxygen, nitrogen and rare gas in air, preparation of high-purity electronic gas, separation and purification of isotope gas, recovery and separation of natural gas nitrogen removal and hydrocarbon components in petrochemical industry and the like.

In one application field, the invention also realizes the online recycling technology of xenon in the closed-circuit medical xenon anesthesia process by adopting the DD3R molecular sieve membrane, and can selectively separate CO ₂/Xe. The single component carbon dioxide permeability was 1.5X10 ^- ⁷mol·m^-2·s^-1·Pa^-1 and the separation selectivity of carbon dioxide to xenon was 570. The permeation flux is higher than that of the traditional membrane material by an order of magnitude, and the DD3R molecular sieve has certain hydrophobicity due to the full silicon characteristic, so that the blocking of water vapor to the pore canal of the molecular sieve can be effectively weakened.

In a first aspect of the invention, there is provided:

A method for inorganic membrane multistage gas separation comprising the steps of:

Step 1, sending a gas mixture to be separated into gas separation equipment for separation;

The gas separation equipment is formed by connecting a plurality of membrane components in series, and materials obtained from the permeation side of the upper stage are sent to the permeation side of the lower stage for continuous separation;

And 2, obtaining a first gas component on the permeation side of the final stage, and extracting a second gas component on the permeation side of the first stage.

In one embodiment, in step 1, the gas mixture to be separated is subjected to pretreatment of the mixed gas by a pretreatment unit.

In one embodiment, the pretreatment comprises compression, drying, filtration, or heating.

In one embodiment, in step 1, the gaseous product on the retentate side of the first stage is withdrawn under controlled pressure by a backpressure valve.

In one embodiment, in step 1, the resulting material from the retentate side of the next stage is returned to the retentate side of the previous stage or stages.

In one embodiment, in step 1, the gas mixture to be separated is fed to the membrane module having a gas composition closest to the gas composition of the gas mixture to be separated on the retentate side.

In one embodiment, in step 1, the pressure range of the gas mixture to be separated is controlled to be 0.1-5 mpa.

In one embodiment, a reflux ratio is required for a membrane module containing reflux retentate, where the reflux ratio refers to the amount of gas refluxed on the retentate side of the stage membrane module and the amount of gas to be separated entering the gas separation device.

In one embodiment, the operating temperature of each stage of membrane module is 28K-973K.

In one embodiment, the material used in the gas separation membrane installed in the membrane module may be one or more of inorganic membrane materials such as molecular sieve membrane, ceramic membrane, carbon membrane, etc., and the carrier of the gas separation membrane may be in the form of tube or hollow fiber, etc.

In one embodiment, the gas mixture to be separated contains one or more of N ₂、CO₂、H₂、O2、Kr、Xe、CH₄ and He.

In one embodiment, the composition of the gas mixture to be separated is a mixture of 5% CO ₂,30％N₂ and 65% Xe and further contains H ₂O,H₂ O at a partial pressure of 2.3kPa, and the gas separation membrane employed is a DD3R molecular sieve membrane.

In a second aspect of the invention, there is provided:

an inorganic membrane multi-stage gas separation apparatus comprising:

a pretreatment unit for pretreating a gas mixture to be separated;

the gas separation device is connected with the pretreatment unit and is used for separating gas components in the gas mixture to be separated;

the gas separation equipment comprises a plurality of membrane assemblies which are connected in series, wherein a permeate side gas outlet of a membrane assembly of the upper stage is connected with a permeate side gas inlet of a membrane assembly of the lower stage;

The permeate side air outlet of the membrane assembly of the last stage is connected with a first gas component receiving pipeline, and the retentate side air outlet of the membrane assembly of the first stage is connected with a second gas component receiving pipeline.

In one embodiment, the membrane assembly comprises a shell and a gas separation membrane arranged in the shell, wherein the permeation side inlet and the permeation side outlet are connected with the shell, and the permeation side of the gas separation membrane is connected with the permeation side outlet.

In one embodiment, the gas separation membrane is tubular or hollow fiber.

In one embodiment, the material of the gas separation membrane is a molecular sieve membrane, a ceramic membrane or a carbon membrane.

In one embodiment, the retentate outlet of the membrane module of the next stage is connected to the retentate outlet of the membrane module of the previous stage or stages.

In one embodiment, the air outlet on the retentate side of the membrane module of the next stage is connected with the membrane module of the upper stage through a micro air pump.

In one embodiment, the pretreatment unit is connected to the gas separation device via a mass flow controller.

In one embodiment, the pretreatment unit is coupled to a membrane module of any stage.

In one embodiment, the retentate side air outlet of the first stage membrane module is connected with a back pressure valve.

In a third aspect of the invention, there is provided:

the device for separating the multi-stage gas of the inorganic membrane is applied to separating the multi-component gas.

Advantageous effects

The invention has simple operation, and can realize the separation and concentration of the gas only by connecting the multi-stage membrane separation components in series. The device investment is low, the gas separation can be realized at normal temperature, the energy is saved, the environment is protected, and the economic benefit is obvious. For a mixed gas system with low single-stage membrane separation selectivity and low purity of separation products, the multi-stage membrane separation can obviously improve the purity of gas separation, and particularly, the multi-stage membrane separation can generate huge economic benefits for the separation and concentration of some special gases.

Drawings

FIG. 1 is a schematic diagram of a separation process of a multistage series membrane separation device.

FIG. 2 is a schematic diagram of several typical retentate (except for the first stage) reflux modes.

FIG. 3 shows the effect of Xe molar composition on the CO ₂/Xe gas mixture separation performance (feed pressure: 3 bar).

FIG. 4 shows DD3R molecular sieve membrane separation performance.

FIG. 5 shows the separation performance of DD3R molecular sieve membranes for CO ₂ and Xe.

Wherein, 1, a pretreatment unit; 2, a mass flow controller, 3, a membrane component, 4, a shell, 5, a gas separation membrane, 6, a retentate side air inlet, 7, a retentate side air outlet, 8, a seal head, 9, a permeate side air outlet, 10, a pipeline, 11, a micro air pump, 12 and a back pressure valve.

Detailed Description

Fig. 1 shows that the raw material gas is pretreated by the pretreatment unit 1, so that the parameters of moisture content, pressure, temperature and the like of the raw material gas meet the requirements. The pretreatment unit 1 used in the present invention is not particularly limited, and may include a compression device, a drying device, a filtration device, or a heating device, and the raw material is pretreated before entering the series membrane separation module to meet the corresponding gas state requirements. The treated feed gas enters the multistage membrane separation module at a suitable feed location via mass flow controller 2.

In the invention, when the membrane modules are connected in series, the module at the most upstream is the 1 st stage, and the retentate is the nth stage discharged as the final product (the most downstream).

The single membrane module used in the present invention is shown in fig. 1, wherein the membrane module 3 comprises a housing 4 and an inner gas separation membrane 5, the housing 4 is made of stainless steel or nylon, the housing 4 and the gas separation membrane 5 divide the space in the module into a permeation measurement side and a permeation residual side, the tubular gas separation membrane 5 is taken as an example, the configuration of the tubular gas separation membrane 5 is tubular, and the separation layer is selected to be positioned outside the tubular membrane. There are air inlet 6 and gas outlet 7 on the casing, and the casing both ends adopt threaded head 8, and one end has permeate side gas outlet 9, and the other end is the dead end. The single-stage membrane modules 3 are connected in series by a pipeline 10, the permeate side air outlet 9 of the upper stage is connected with the air inlet 6 of the shell of the lower stage to complete the series operation of the device, and the permeate residual air outlet 7 of the lower stage is connected with the air inlet 6 of the shell of the upper stage to complete the reflux operation.

When the structure is adopted, a main improvement point is that the reflux treatment of the upper stage of the residual gas is adopted, when the gas to be separated contains A, B components, when the separation is carried out by adopting a single-stage membrane assembly, the component B is supposed to enter the permeation side, the residual gas (supposed to be A) cannot reach enough purity, so that the residual gas cannot be effectively reused, when the residual gas is continuously separated by the reflux of the upper stage, the gas containing A which is obtained to be enriched can be further concentrated again, and after the B gas is continuously fed to the serial assembly of the next stage, the material mainly containing the B gas is further separated, finally, the first stage is enabled to obtain purer A, and the last stage is enabled to obtain purer B.

Fig. 1 shows that the raw material gas is separated in the multistage series membrane modules, the permeate gas of each stage of module enters the next stage of module to be separated continuously, and the permeate residual gas returns to the previous stage through the air pump 11 to be mixed with the feed gas.

Figure 1 shows that the permeate outlet 4 of the final stage module collects the separated permeate product. The gas outlet 7 on the retentate side of the first-stage component is connected with a back pressure valve 12 to control the gas outlet amount of retentate gas, and the retentate product is obtained through the back pressure valve 12.

The reflux of the retentate includes, but is not limited to, returning to the upper stage assembly, and the inlet of other membrane assemblies before the retentate flows back to the present stage assembly can be adjusted to mix with the feed gas as required. As for the reflux of the gas on the retentate side, as shown in fig. 2, the gas may be all refluxed to the previous stage in sequence, the gas may be refluxed to the previous stages, or the plurality of membrane modules may be refluxed to the same stage.

In addition, besides the first stage of residual gas outlet, when the system to be separated contains impurities and the impurities are enriched to high concentration after a certain number of stages of separation, branch extraction can be increased at the position of the residual gas outlet of a proper number of stages, so that the influence of high-concentration gas on the membrane separation of a target system is reduced.

In the raw material feeding process of the first-stage membrane component, the pressure range is controlled to be 0.1-5 MPa.

The operating temperature range of the gas separation process of each stage of components is 28K-973K.

In the process of the residual gas flowing back of each stage of the component, the range of the gas flowing back ratio (the flowing back ratio refers to the ratio of the amount of the gas flowing back at the residual side of the stage of the membrane component to the amount of the gas flowing through the stage of the membrane component) and the amount of the gas to be separated entering the gas separation equipment is controlled to be less than 10. For example, a series installation contains 10 membrane modules, the mixed gas feed position is at the 5 th membrane module, then for the 4 th membrane module, the mixed gas feed position also contains gas which flows back from the 5 th permeate side and gas which is obtained from the 3 rd permeate side, and the flow back ratio is the 4 th permeate side backflow gas quantity (3 rd permeate side gas quantity+5 th permeate side backflow quantity-4 th permeate side gas quantity)/the gas quantity to be separated which enters the gas separation equipment.

The pore diameter of the inorganic membrane material adopted in the separation device is in the range of 2-200 nm.

The inorganic membrane used in the membrane separation device can be one or more of ceramic membrane, molecular sieve membrane and carbon membrane. The support may be in the form of a tube or hollow fiber, etc.

Example 1

And (3) introducing the mixed gas of 80% N ₂ and 20% O ₂ into a pretreatment device to remove moisture and other solid particles in the mixed gas, so that the temperature of the treated gas reaches 25 ℃, and the pressure is increased to 1.5MPa. And (3) feeding the pretreated raw gas into a separation device through a first-stage air inlet by a mass flow controller according to a certain feeding amount, wherein an air outlet on the retentate side of the first-stage assembly is connected with a back pressure valve, and the pressure of the retentate side is controlled to be stabilized at 3.5-4 bar (gauge pressure). The residual gas of each level of component is returned to the previous level of component through the air pump, and the reflux ratio is 0.8. The membrane material in each stage of membrane separation component is TiO ₂ coated alumina hollow fiber membrane, the pore diameter of the membrane is 100nm, and the membrane has high mechanical strength and excellent oxidation resistance.

Under the condition, the last-stage permeation gas is extracted under normal pressure, and is subjected to 45-stage membrane separation, wherein the concentration of N ₂ in the last-stage permeation gas is more than 99%. The permeate gas exiting the first stage assembly through the back pressure valve may be directly vented to the atmosphere.

Example 2

A mixed gas of 80% Kr and 20% Xe was introduced into the pretreatment unit, pressurized to 3MPa and kept at a gas temperature of about 25 ℃. And (3) introducing the pretreated mixed gas into a gas inlet of a 10 th-stage membrane assembly of the serial device, controlling the feeding quantity through a mass flow controller, and controlling the gas outlet quantity of the first-stage residual gas by a regulating and controlling back pressure valve. The residual gas of each level of component returns to the previous level of component through the micro air pump, and the reflux ratio is 1. An inorganic ceramic membrane is adopted as a membrane separation material, the pore diameter of the membrane is 50nm, and the membrane has high mechanical strength and excellent oxidation resistance. The retentate gas exiting the first stage assembly through the back pressure valve is recycled, wherein the concentration of Xe is about 35%. The last-stage permeation gas is taken as a raw material and is extracted under normal pressure, and the number of separation stages required for achieving different theoretical purities is as follows:

Example 3

Natural gas with N ₂ content less than 10% (main component CH ₄ > 90%) is introduced into a pretreatment unit, water and other solid particles in the mixed gas are removed, the mixed gas is pressurized to 0.7MPa, and the temperature of the mixed raw gas is controlled to be about 25 ℃. And (3) introducing the pretreated mixed gas into a gas inlet of a 10 th-stage membrane assembly of the series device, controlling the feeding quantity through a mass flow controller, and controlling the gas outlet quantity of the first-stage residual permeation gas through a first-stage regulating back pressure valve so that the pressure of the first-stage residual permeation gas is stabilized at 3.5-4 bar (gauge pressure). The residual gas of each stage of components returns to the previous stage of components through the air pump, and the reflux ratio is 1.5. And an electrodeless ceramic membrane is used as a separation material, and the pore diameter of the membrane is 100-150 nm.

Under the condition, after 20-level separation, the permeation gas of the last level is extracted under normal pressure, wherein the concentration of CH ₄ is more than 99%, the permeation gas is collected as a product, and the residual permeation gas of the first-level component is discharged through a back pressure valve except for backflow and is recycled.

Example 4

And (3) introducing mixed gas with the composition of 50% He and 50% N ₂ into the treatment unit, pressurizing the mixed gas to 1MPa, and controlling the temperature at room temperature. The pretreated raw material mixer enters a 6-stage series membrane module for separation through a 4-stage module air inlet, and the feeding amount is controlled to be 1.5L/h through a mass flow controller. Controlling the back pressure valve to regulate the first level of permeation the residual side pressure is stabilized at 3-3.5 bar. The residual gas seeped by the first-stage component is directly recovered through a back pressure valve, the reflux ratio of the other components is kept at 0.66, the reflux quantity of each-stage component is ensured to be 1L/h, the reflux direction is returned to the feeding of the upper-stage component, and the seepage quantity of each-stage component and the extraction quantity at the last bottom are maintained at 0.5L/h. The separation membrane material adopts a hollow fiber molecular sieve membrane, the pore diameter of the membrane is 2nm, and the mechanical stability is excellent. The last-stage permeation gas is extracted under normal pressure and collected as a product. Under this condition, each level of parameters is obtained according to the balance as follows:

Example 5

The mixed gas with the composition of 90% H ₂ and 10% CO ₂ is introduced into a pretreatment unit, pressurized to 0.5MPa and kept at a gas temperature of about 25 ℃. And (3) introducing the pretreated mixed gas into a gas inlet of a 5 th-stage membrane assembly of the series device, controlling the feeding quantity through a mass flow controller, and controlling the gas outlet quantity of the first-stage residual permeation gas through a regulating and controlling back pressure valve, so that the pressure of the first-stage residual permeation gas is stabilized at 2-2.4 bar (gauge pressure). The residual gas of each level of component is returned to the previous level of component through the air pump, and the reflux ratio is 0.5. Hollow fiber molecular sieve membrane is used as separating membrane material.

Under the condition, through the separation of 9-stage components, the concentration of hydrogen in the permeation gas of the final stage is more than 99.9%, the permeation gas is taken as a raw material and is recovered and utilized under normal pressure, the concentration of CO ₂ in the permeation gas discharged from the first-stage component through a back pressure valve is about 30%, in this embodiment, the 5-stage membrane component is fed, after the separation of the stage, the gas on the permeation side of the 5-stage contains 16.3% of CO ₂ and 84.7% of H ₂, and as can be seen through comparison, the further concentration of the CO ₂ gas is finally realized after the permeation side gas of the stage is returned to the upper stage.

Example 6

In this embodiment, DD3R molecular sieve membrane is used for the on-line recycling technology of xenon in the closed-circuit medical xenon anesthesia process. The single component carbon dioxide permeability was 1.5X10 ^-7mol·m^-2·s^-1·Pa^-1 and the separation selectivity of carbon dioxide to xenon was 570. The permeate flux is an order of magnitude higher than that of conventional membrane materials. The membrane separation performance is mainly determined by the difference in the diffusion coefficients of CO ₂ and Xe molecules in the DD3R molecular sieve. However, the mass transfer rate of CO ₂ is significantly reduced by the presence of Xe, which is very different from the separation results of the previous eight-membered ring molecular sieve membranes in the two-membered components of CO ₂/N₂ and CO ₂/CH₄. The molecular dynamics simulation result shows that the adsorption of Xe molecules on the surface of the molecular sieve membrane forms the surface resistance of CO ₂ adsorption and diffusion. Under medical xenon anesthesia related conditions, i.e. carbon dioxide content below 5% and in the presence of water vapor, the CO ₂ permeability and CO ₂/Xe separation selectivity were 2.0X10 ^-8mol·m^-2·s^-1·Pa^-1 and 67, respectively. Due to the all-silicon characteristic of the DD3R molecular sieve membrane, the permeability of CO ₂ is slightly influenced by water vapor, which is different from the phenomenon that the pore channel of the aluminum-containing molecular sieve membrane is easily blocked due to water adsorption. The high CO ₂ flux and the high CO ₂/Xe selectivity and the long-time stability ensure the good prospect of the on-line recycling of the hollow fiber DD3R molecular sieve membrane in medical anesthesia xenon. The DD3R molecular sieve membrane used in this example can be prepared by referring to the prior art, for example, CN110745839A, an activation process of a defect-free DD3R molecular sieve membrane.

First, a separation test of CO ₂/Xe mixture was performed, and FIG. 3 shows the effect of Xe molar composition on CO ₂/Xe mixture separation performance (feed pressure: 3 bar), with a decrease in CO ₂ permeability more pronounced as Xe composition increases (region c of FIG. 2). Finally, when the CO ₂ content is reduced to 5%, the CO ₂ permeability is 0.24 multiplied by 10 ^-7mol·m^-2·s^-1·Pa^-1, however, the separation selectivity of CO ₂/Xe is always about 43, and the good separation selectivity of CO ₂ at low concentration is shown.

The single component permeability of CO ₂ of the hollow fiber DD3R molecular sieve membrane reported by the application is 1.5X10 ^-7mol·m^-2·s^-1·Pa^-1, which is an order of magnitude higher than the reported result of the current literature (the area a of figure 4). The separation performance of the DD3R molecular sieve membrane for the CO ₂ single component, the CO ₂/H₂ O binary component and the CO ₂/H₂ O/Xe ternary component at different temperatures is shown in the b region of FIG. 4, and the c region of FIG. 4 is the long term stability of the DD3R molecular sieve membrane at 3bara for Xe recovery from a mixture of 0.76% H ₂O、4.96％CO₂、29.77％N₂ and 64.51% Xe. Water vapor is often present in the anesthetic exhaled breath. Due to the existence of water vapor, the single-component permeability of CO ₂ is reduced by 37-45% (the b area of fig. 4), however, under the same condition, the gas permeability of the aluminum-containing 8-membered ring molecular sieve membrane is obviously reduced, and the DD3R molecular sieve membrane has better hydrophobic property, so that the reduction of the permeability of CO ₂ caused by water vapor adsorption can be effectively weakened. The non-ionic template and the ion-free synthesis solution are utilized to prepare the DD3R molecular sieve membrane which is more hydrophobic and is used for separating CO ₂/Xe under the wet environment. The effect of water vapor on CO ₂ permeability and selectivity was further studied, as shown in fig. 3, region b, and fig. 5, region a. The separation selectivity of the membrane is higher than that of the dry gas under the water vapor environment. Si-OH at the grain boundary of the molecular sieve membrane layer can strongly adsorb water molecules, thereby blocking the diffusion of gas molecules at the pore canal. Therefore, the Xe permeability is lower than in dry gas under a wet environment. The permeation of water vapor gradually decreases with increasing temperature, for example, 55% at 100 ℃, 52% at 125 ℃, and 42% at 150 ℃. However, the permeability of CO ₂ molecules, whether in wet and dry gases, is primarily contributed by the DD3R molecular sieve.

During the anesthesia process, the impurities of the expired anesthetic gas, except for CO ₂, release nitrogen during the initial stage of anesthesia. It was used to recover xenon from a mixture of 5% CO ₂,30％N₂ and 65% Xe. When 2.3kP water vapor was introduced, both the CO ₂ and N ₂ permeabilities decreased slightly (fig. 3.) eventually, the carbon dioxide permeabilities stabilized at a 2.0x10 ^-8mol·m^-2·s^-1·Pa^-1, CO₂/Xe selectivity of 67±12 and the N ₂ permeabilities were 2.4x10 ^-9mol·m^-2·s^-1·Pa^-1,N₂/Xe selectivities of 8±2.

The separation experiment for recovering xenon by using the first-stage DD3R separation membrane was performed as described above, and then, deep recovery was performed by using multi-stage separation. When a 3-stage serial separation process is employed, recovered xenon gas containing 99.19% and 99.23% of Xe is obtained in the 2 nd and 3 rd stages in this order according to the same operation conditions, indicating that xenon gas having higher purity can be obtained by multistage serial separation.

Claims

1. An inorganic membrane multi-stage gas separation method, characterized in that the device used in the inorganic membrane multi-stage gas separation method comprises:

A pretreatment unit (1), used for pretreating the gas mixture to be separated;

A gas separation device is connected to a pretreatment unit (1) and is used to separate gas components in a gas mixture to be separated; the gas separation device comprises a plurality of membrane modules (3), the membrane modules (3) being connected in series with each other; the permeate side gas outlet (9) of the upper membrane module (3) is connected to the retentate side gas inlet (6) of the lower membrane module (3); the retentate side gas outlet (7) of the lower membrane module (3) is connected to the retentate side gas inlet (6) of the upper membrane module (3);

The permeate-side gas outlet (9) of the last-stage membrane assembly (3) is connected to a first gas component receiving pipeline; the retentate-side gas outlet (7) of the first-stage membrane assembly (3) is connected to a second gas component receiving pipeline;

The membrane assembly (3) comprises a shell (4) and a gas separation membrane (5) installed in the shell (4); the retentate side air inlet (6) and the retentate side air outlet (7) are connected to the shell (4); the permeate side of the gas separation membrane (5) is connected to the permeate side air outlet (9);

The inorganic membrane multi-stage gas separation method comprises the following steps:

A mixed gas consisting of 90% _H2 and 10% _CO2 is introduced into a pretreatment unit, pressurized to 0.5MPa and the gas temperature is maintained at 25°C. The pretreated mixed gas is introduced into the gas inlet of the 5th membrane component of the series device, the feed amount is controlled by a mass flow controller, and the back pressure valve is adjusted to control the gas outlet of the first-stage retentate gas so that the pressure on the first-stage retentate side is stabilized at a gauge pressure of 2 to 2.4 bar. The retentate gas of each stage of the component is returned to the previous stage component through an air pump, and the reflux ratio is 0.5. A hollow fiber molecular sieve membrane is used as the separation membrane material. After separation of 9 stages of components, the concentration of hydrogen in the last stage of permeate gas is >99.9%. The permeate gas is produced as a raw material under normal pressure, and the retentate gas discharged from the first-stage component through the back pressure valve is recycled, wherein the concentration of _CO2 is 30%.