A hydrate membrane, a method for preparing the same, a membrane module, and a membrane separation method

Abstract

The application provides a hydrate membrane, a preparation method thereof, a membrane assembly and a membrane separation method. The hydrate membrane comprises a porous support layer and a hydrate separation layer located on at least one side surface of the porous support layer; the hydrate separation layer comprises cage-type hydrate crystals formed in situ through phase transition under the condition that the temperature is 0-20 DEG C and the pressure is 0.1-6 MPa by using a hydrate mother liquor containing a thermodynamic promoter, and the average pore size of the hydrate separation layer is 0.35-0.55 nm. The hydrate membrane has high separation selectivity and high permeation flux, and has good rigidity and uniformity of membrane pores, high long-term operation stability, is convenient for in-situ preparation of large-area separation membranes, and can realize efficient recovery and utilization of helium in a hydrocarbon raw gas.

Description

Technical Field

[0001] This invention relates to the field of gas separation membrane technology, specifically to a hydrate membrane, its preparation method, membrane module, and membrane separation method. Background Technology

[0002] Helium is a strategic rare gas with excellent physical and chemical properties such as low density, low boiling point, and extremely strong chemical inertness. It is widely used in high-end fields such as aerospace, low-temperature superconductivity, medical imaging, and the electronics industry. Hydrocarbon feedstock gases are the main source of industrial helium production. Hydrocarbon feedstock gases include natural gas and coalbed methane. The helium volume content in hydrocarbon feedstock gases is usually 0.03% to 2%, which is a low-concentration component. Efficiently enriching and extracting helium from hydrocarbon feedstock gases is of great significance for ensuring a stable supply of helium resources.

[0003] Currently, the mainstream process for helium extraction from hydrocarbon feedstocks in the industrial sector is cryogenic distillation. This process requires cooling the hydrocarbon feedstock to temperatures of ≤-160℃, resulting in high energy consumption, large equipment size, complex systems, and high investment and operating costs. It is only suitable for large-scale centralized processing and is difficult to adapt to the on-site helium extraction needs of small and medium-sized gas fields. In addition, processes such as pressure swing adsorption and cryogenic adsorption have drawbacks such as limited adsorption capacity of adsorbents, high regeneration frequency, and low helium recovery rate, which significantly restrict their large-scale application.

[0004] Membrane separation technology boasts significant advantages such as room-temperature operation, low energy consumption, simple process flow, compact equipment, and no phase change, making it an ideal alternative technology for helium extraction from hydrocarbon feedstocks. However, existing polymeric separation membranes generally suffer from a technical contradiction between selectivity and permeate flux. High-selectivity membranes typically have low permeate flux, requiring ultra-large membrane areas to meet capacity requirements. Conversely, high-flux membranes lack sufficient helium separation selectivity, hindering effective helium purification. This contradiction directly leads to low helium separation efficiency, limiting large-scale industrial applications. Furthermore, conventional polymeric membranes are susceptible to swelling and plasticization due to hydrocarbon components, further exacerbating membrane performance degradation and failing to meet the requirements for long-term stable helium extraction from hydrocarbon feedstocks. Therefore, there is an urgent need for a separation membrane that combines high separation selectivity, high permeate flux, simple membrane preparation, good membrane pore size rigidity and uniformity, and long-term operational stability to achieve efficient recovery and utilization of helium from hydrocarbon feedstocks. Summary of the Invention

[0005] This invention provides a hydrate membrane, its preparation method, membrane module, and membrane separation method. This hydrate membrane combines high separation selectivity, high permeate flux, simple membrane preparation, good pore rigidity and pore size uniformity, and long-term stable operation, enabling efficient recovery and utilization of helium from hydrocarbon feedstock gases.

[0006] The present invention provides a hydrate membrane, comprising: a porous support layer and a hydrate separation layer located on at least one side surface of the porous support layer; the hydrate separation layer comprises cage-like hydrate crystals formed in situ by phase change from a hydrate mother liquor containing a thermodynamic promoter at a temperature of 0°C to 20°C and a pressure of 0.1 MPa to 6 MPa, wherein the average pore size of the hydrate separation layer is 0.35 to 0.55 nm.

[0007] According to one embodiment of the present invention, the thermodynamic accelerator includes a first thermodynamic accelerator, or a combination of a first thermodynamic accelerator and a second thermodynamic accelerator; the first thermodynamic accelerator includes cyclic ether thermodynamic accelerators and / or quaternary ammonium salt thermodynamic accelerators; the second thermodynamic accelerator includes one or more of cycloalkane accelerators, amino acid accelerators, and heterocyclic accelerators; the porous support layer includes a porous support material, which includes one or more of inorganic porous materials, organic porous materials, and metallic porous materials.

[0008] According to one embodiment of the present invention, the cyclic ether thermodynamic promoter includes tetrahydrofuran and / or tetrahydropyran; and / or, the quaternary ammonium salt thermodynamic promoter includes one or more of tetrabutylammonium bromide, tetrabutylammonium chloride, and tetrabutylammonium fluoride.

[0009] According to one embodiment of the present invention, the average pore size of the porous support material is 0.1~20μm; and / or, the inorganic porous material includes ceramics and / or alumina; and / or, the organic porous material includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polypropylene, polyester, and rubber; and / or, the metallic porous material includes one or more of carbon steel, stainless steel, and titanium alloy.

[0010] According to one embodiment of the present invention, the mass percentage of the thermodynamic promoter in the hydrate mother liquor is 3-30%.

[0011] According to one embodiment of the present invention, the thickness of the hydrate membrane is 0.5~15 mm; and / or, the thickness of the hydrate separation layer is 0.5~500 μm.

[0012] The present invention also provides a method for preparing the above-mentioned hydrate membrane, comprising the following steps: S1-1, providing a porous support layer; S1-2, preparing a hydrate mother liquor containing a thermodynamic promoter; S1-3, coating the hydrate mother liquor onto at least one side surface of the porous support layer, and inducing a phase transition in situ to generate cage-like hydrate crystals under conditions of 0℃~20℃ and 0.1MPa~6MPa pressure, thereby forming a hydrate separation layer and obtaining the hydrate membrane.

[0013] The present invention also provides a membrane module comprising the above-described hydrate membrane or the hydrate membrane prepared by the above-described preparation method.

[0014] The present invention also provides a membrane separation method for helium in helium-containing hydrocarbon feed gas, comprising the following steps: passing the helium-containing hydrocarbon feed gas into a membrane module for membrane separation to obtain helium-containing permeate gas and residual permeate gas; the membrane module includes the membrane module described above.

[0015] According to one embodiment of the present invention, the membrane module includes a single-stage membrane module or a two-stage membrane module consisting of a first-stage membrane module and a second-stage membrane module connected in series. When a single-stage membrane module is used for membrane separation, the following steps are included: S2-1, a helium-containing hydrocarbon feed gas is introduced into the first-stage membrane module, and the feed-side pressure is controlled to be higher than the permeate-side pressure, so that helium gas preferentially permeates through the membrane module to form helium-containing permeate gas, while large molecular hydrocarbon components in the feed gas are retained to form residual gas. Preferably, the operating conditions for membrane separation using the single-stage membrane module are: temperature 0~20℃, feed-side pressure 0.2~26MPa, and permeate-side pressure 5~50kPa. When a two-stage membrane module is used for membrane separation, the following steps are included: S2-1, a helium-containing hydrocarbon feed gas is introduced into the first-stage membrane module for first-stage membrane separation, and the feed-side pressure is controlled to be higher than the first-stage permeate-side pressure, so that helium gas preferentially permeates through the membrane module to form helium-containing permeate gas, while large molecular hydrocarbon components in the feed gas are retained to form residual gas. First, a primary permeate gas is formed, and large molecular hydrocarbon components are retained to form a primary residual gas; S2-2, the primary permeate gas is passed into a secondary membrane module for secondary membrane separation to further remove residual impurities, resulting in a high-concentration helium-containing secondary permeate gas, with residual large molecular components retained to form a secondary residual gas; S2-3, the secondary residual gas is refluxed to the feed gas inlet of the primary membrane module and mixed with the helium-containing hydrocarbon feed gas for cyclic separation to improve the helium recovery rate; preferably, the operating conditions for membrane separation using the two-stage series membrane module are as follows: in the primary membrane separation, the temperature is 0~20℃, the primary feed side pressure is 0.2~26MPa, and the primary permeate side pressure is 40~60% of the primary feed side pressure; in the secondary membrane separation, the temperature is 0~20℃, the secondary feed side pressure is the same as the primary permeate side pressure, and the secondary permeate side pressure is 5~50kPa.

[0016] This invention provides a hydrate membrane, its preparation method, membrane module, and membrane separation method. The hydrate membrane includes a porous support layer and a hydrate separation layer located on at least one side surface of the porous support layer. The hydrate separation layer comprises cage-like hydrate crystals formed in situ by phase change from a hydrate mother liquor containing a thermodynamic promoter at temperatures of 0°C to 20°C and pressures of 0.1 MPa to 6 MPa. The average pore size of the hydrate separation layer is 0.35 to 0.55 nm. This invention introduces a thermodynamic promoter into the hydrate mother liquor to generate a hydrate separation layer in situ under specific temperature and pressure conditions with a pore size suitable for the molecular dynamics diameter of helium. This achieves efficient and selective helium permeation through molecular sieving effect. Simultaneously, the hydrate membrane is resistant to hydrocarbon swelling, can be regenerated in situ, has simple membrane preparation, good pore rigidity and pore size uniformity, and can be used stably for long-term cycling. The porous support layer further enhances its mechanical strength and adaptability to operating conditions. Therefore, the separation selectivity, permeate flux, and long-term operational stability of the hydrate membrane are improved, thereby achieving efficient recovery and utilization of helium from hydrocarbon feedstock gases. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the hydrate membrane in an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of the process flow for secondary membrane separation of helium-containing hydrocarbon feed gas using a hydrate membrane, as described in an embodiment of the present invention.

[0019] Figure label:

[0020] 1-Porous support layer, 2-Hydrate separation layer. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0022] This invention provides a hydrate membrane, such as Figure 1 As shown, it includes a porous support layer 1 and a hydrate separation layer 2 located on at least one side surface of the porous support layer 1; the hydrate separation layer 2 includes cage-shaped hydrate crystals formed in situ by phase transformation of a hydrate mother liquor containing a thermodynamic promoter under conditions of 0℃~20℃ and 0.1MPa~6MPa, and the average pore size of the hydrate separation layer 2 is 0.35~0.55nm.

[0023] The hydrate membrane of this invention possesses high separation selectivity, high permeation flux, and long-term operational stability, enabling efficient recovery and utilization of helium from hydrocarbon feedstock gases. The specific analysis is as follows: 1) This invention introduces a thermodynamic promoter into the hydrate mother liquor, precisely controlling the phase change conditions to a temperature of 0℃~20℃ and a pressure of 0.1MPa~6MPa, thus promoting the in-situ generation of the hydrate separation layer through the mother liquor phase change. The hydrate separation layer's cavities are constructed from the orderly arrangement of water molecules, with an internal average pore size controlled within the range of 0.35~0.55nm. The membrane exhibits good pore rigidity and pore size uniformity, strictly limiting the dynamic passage size of gas molecules, thus endowing the membrane with excellent molecular sieving performance. Furthermore, the pore size is highly matched to the 0.26nm dynamic diameter of helium molecules. Driven by pressure difference, helium, with its smaller molecular size, preferentially permeates through the hydrate separation layer channels, while large molecular components such as methane and nitrogen are effectively retained, significantly suppressing the non-selective permeation of large molecular components and achieving a synergistic improvement in separation selectivity and permeation flux. 2) This hydrate membrane, with water molecules as its main structure, effectively avoids membrane structure damage caused by the swelling of hydrocarbon components, thus improving the long-term operational stability of the hydrate membrane. Furthermore, the membrane is free from the risk of poisoning and failure, allowing for multiple long-term cycles. During equipment shutdown and maintenance, the hydrate membrane can be regenerated in situ without disassembling the equipment, effectively ensuring continuous and stable operation of the overall process. The porous support layer provides reliable mechanical strength and structural stability for the hydrate separation layer, adapting to different operating pressures and temperatures, thereby significantly improving the mechanical strength and adaptability of the hydrate membrane. Therefore, the hydrate membrane of this invention combines high separation selectivity, in-situ preparation of large-area separation membranes, high permeate flux, simple membrane preparation, good membrane pore rigidity and uniformity, and long-term operational stability, enabling efficient recovery and utilization of helium from hydrocarbon feedstock gases.

[0024] For example, the in-situ temperature of the phase change can be 0°C, 5°C, 10°C, 15°C, or 20°C, etc.

[0025] For example, the pressure in situ for phase change can be 0.1 MPa, 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa, 5.5 MPa or 6 MPa, etc.

[0026] For example, the average pore size of the hydrate separation layer can be 0.35 nm, 0.37 nm, 0.39 nm, 0.40 nm, 0.43 nm, 0.47 nm, 0.50 nm, 0.52 nm, or 0.55 nm, etc.

[0027] In this embodiment of the invention, a thermodynamic promoter is used to adjust the phase equilibrium conditions of the hydrate mother liquor, enabling cage-like hydrates to be generated in situ under relatively mild conditions of 0°C to 20°C and 0.1 MPa to 6 MPa, thereby reducing the film-forming driving force and improving the controllability of film formation.

[0028] In this embodiment of the invention, the average pore size of the hydrate separation layer can be measured by scanning electron microscopy or transmission electron microscopy.

[0029] In some embodiments, the thermodynamic promoter includes a first thermodynamic promoter, or a combination of a first thermodynamic promoter and a second thermodynamic promoter; the first thermodynamic promoter includes cyclic ether thermodynamic promoters and / or quaternary ammonium salt thermodynamic promoters; the second thermodynamic promoter includes one or more of cycloalkane promoters, amino acid promoters, heterocyclic promoters, and ketone-aldehyde promoters. When the first thermodynamic promoter is a cyclic ether and / or quaternary ammonium salt component, it can preferentially stabilize the target cage-like hydrate lattice, shorten the nucleation induction period, promote continuous and dense crystal packing, and further improve the separation selectivity and permeation flux of the hydrate membrane. When the first thermodynamic promoter is further compounded with the second thermodynamic promoter, the solution structure, interfacial tension, and mass transfer rate can be synergistically controlled by cycloalkane, amino acid, heterocyclic, or ketone-aldehyde components, thereby improving the crystal size distribution and pore size uniformity, which is more conducive to obtaining a hydrate separation layer with an average pore size of 0.35 nm to 0.55 nm.

[0030] In some embodiments, the cyclic ether thermodynamic promoters include tetrahydrofuran and / or tetrahydropyran. Tetrahydrofuran has a strong hydrate-inducing ability, which can reduce the equilibrium pressure required for hydrate formation and participate in the formation and stabilization of cage-like structures during in-situ phase transitions, promoting the formation of a dense and uniform crystal network of the hydrate separation layer under conditions of 0℃~20℃ and 0.1MPa~6MPa. Simultaneously, the generated hydrate crystal pore structure can be tuned to be highly compatible with the molecular dynamics of helium, widening the molecular sieving difference between helium and impurity gases such as methane, significantly improving the helium permeation efficiency and enrichment effect.

[0031] In some embodiments, the quaternary ammonium salt thermodynamic promoter includes one or more of tetrabutylammonium bromide, tetrabutylammonium chloride, and tetrabutylammonium fluoride. Its cations have large volume and stable ionic structure, which can promote the formation of cage hydrates under relatively mild operating conditions and improve the thermal and mechanical stability of the crystal skeleton. This, in turn, endows the hydrate membrane with high separation selectivity, high permeation flux and excellent long-term operating stability, thereby achieving efficient separation and recovery of helium from hydrocarbon feedstock gas.

[0032] In some embodiments, the hydrate separation layer also includes a porous filter cloth. As a component of the hydrate separation layer, the porous filter cloth can adsorb and evenly spread the hydrate mother liquor, preventing the mother liquor from flowing and accumulating, making the hydrate phase transformation more uniform. At the same time, it limits the growth space by its own number of layers and the thickness of a single layer, and precisely control the overall thickness of the separation layer. On the other hand, it can serve as a mechanical skeleton to improve the overall strength of the separation layer, resist the pressure difference and airflow erosion, and prevent the membrane layer from cracking, pulverizing and falling off. This makes the separation layer, filter cloth and support layer form an integrated structure, which is conducive to the long-term stable operation of the hydrate membrane.

[0033] In some embodiments, the porous filter cloth includes one or more of polytetrafluoroethylene porous filter cloth, polyester porous filter cloth, polypropylene porous filter cloth, and nylon porous filter cloth.

[0034] In some implementations, the porosity of the porous filter cloth is 50% to 85%.

[0035] For example, the porosity of the porous filter cloth can be 50%, 60%, 70%, 75%, 80% or 85%, etc.

[0036] In some embodiments, the average pore size of the porous filter cloth is 0.5~200μm.

[0037] For example, the average pore size of the porous filter cloth can be 0.5μm, 1μm, 5μm, 10μm, 20μm, 40μm, 60μm, 80μm, 100μm, 120μm, 140μm, 160μm, 180μm or 200μm, etc.

[0038] In some embodiments, the average pore size of the porous support material is 0.1~20μm. This pore size range enables the construction of continuous mass transfer channels for the feed gas within the support layer, effectively reducing the operating pressure drop of the membrane module and ensuring smooth gas transport; at the same time, it can provide a stable substrate constraint for the surface hydrate separation layer, preventing the hydrate phase from penetrating into the pores of the support layer, and completely preserving and maintaining the structural integrity and sieving separation performance of the hydrate separation layer.

[0039] For example, the average pore size of the porous support material can be 0.1 μm, 1 μm, 5 μm, 10 μm, 15 μm or 20 μm, etc.

[0040] In this embodiment of the invention, the average pore size of the porous support material can be measured by scanning electron microscopy or transmission electron microscopy.

[0041] In this embodiment of the invention, by adjusting the porosity of the porous support material and the hydrate separation layer, it is possible to ensure that the support layer has sufficient gas flow channels, effectively shares the load, and stabilizes the membrane structure, while allowing the separation layer to maintain a regular pore structure and excellent molecular sieving ability, further balancing gas permeation flux and helium separation selectivity. In some embodiments, the porosity of the porous support material is 10%~40%, and the porosity of the hydrate separation layer is 5%~32%.

[0042] For example, the porosity of the porous support material can be 10%, 15%, 20%, 25%, 30%, 35%, or 40%, etc.

[0043] For example, the porosity of the hydrate separation layer can be 5%, 10%, 15%, 20%, 25%, 30%, or 32%, etc.

[0044] In this embodiment of the invention, the porosity of the porous support material and the porosity of the hydrate separation layer can be measured by the low-temperature nitrogen adsorption method (BET method).

[0045] In some embodiments, the inorganic porous material includes ceramics and / or alumina. Ceramic materials typically possess high temperature resistance, pressure resistance, and chemical inertness, making them suitable as a stable support matrix for hydrate membranes; alumina, on the other hand, exhibits good mechanical strength and surface stability, reducing the adverse effects of gaseous and aqueous environments on the support layer. By selecting ceramics and / or alumina as porous support materials, the porous support layer can maintain its pore structure without collapse over a wide temperature and pressure range and provide a smooth and stable adhesion interface for the hydrate separation layer, thereby improving the long-term operational reliability of the hydrate membrane.

[0046] In some embodiments, the organic porous material includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polypropylene, polyester, and rubber. Organic porous materials typically possess properties such as corrosion resistance, ease of processing, and easy adhesion of hydrate membranes, making them suitable as stable support substrates for hydrate membranes; they provide a smooth and stable adhesion interface for the hydrate separation layer, thereby improving the long-term operational reliability of the hydrate membrane.

[0047] In some embodiments, the porous metallic material includes one or more of carbon steel, stainless steel, and titanium alloys. Carbon steel and stainless steel porous matrices are easy to process and shape, and possess high compressive strength, making them suitable for withstanding pressure fluctuations in on-site helium extraction systems. Titanium alloy porous matrices combine excellent corrosion resistance and structural strength, making them more suitable for long-term contact with complex natural gas and coalbed methane components. This type of porous support material provides a low-flow-resistance, high-mechanical-strength framework, ensuring the stable in-situ formation of the hydrate separation layer and maintaining the regularity of the microporous structure, thereby improving the efficient and selective separation of helium.

[0048] In some embodiments, the thermodynamic promoter in the hydrate mother liquor comprises 3-30% by mass. The concentration of the thermodynamic promoter directly affects the hydrate phase transition temperature and the average pore size distribution of the hydrate separation membrane. This concentration range, through intermolecular and ionic interactions, ensures the regular arrangement of hydrate crystals, forming pores adapted to the size of helium molecules. This facilitates further improvement in the separation selectivity, permeation flux, and long-term operational stability of the hydrate membrane, achieving efficient separation and recovery of helium from hydrocarbon feedstock gases.

[0049] For example, the mass percentage of thermodynamic promoter in the hydrate mother liquor can be 3%, 5%, 8%, 11%, 14%, 18%, 19%, 20%, 21%, 22%, 25%, or 30%, etc.

[0050] In some embodiments, when the thermodynamic promoter includes a first thermodynamic promoter and a second thermodynamic promoter, the mass ratio of the first thermodynamic promoter to the second thermodynamic promoter is (1 ~ 5000):1. This better improves the crystal size distribution and pore size uniformity, which is beneficial for obtaining a hydrate separation layer with an average pore size of 0.35 nm to 0.55 nm.

[0051] For example, the mass ratio of the first thermodynamic accelerator to the second thermodynamic accelerator can be 1:1, 10:1, 20:1, 30:1, 50:1, 100:1, 500:1, 1000:1, 1500:1, 2000:1, 2500:1, 3000:1, 3500:1, 4000:1, 4500:1, or 5000:1, etc.

[0052] In some embodiments, the thickness of the hydrate membrane is 0.5–15 mm. This thickness range provides the membrane with sufficient mechanical strength, pressure differential resistance, and field installation adaptability, while effectively reducing gas mass transfer resistance, accelerating helium permeation rate, and stably retaining large molecular components such as methane. This further enhances the separation selectivity and permeation flux of the hydrate membrane.

[0053] For example, the thickness of the hydrate film can be 0.5 mm, 1 mm, 1.5 mm, 2 mm, 5 mm, 7 mm, 9 mm, 11 mm, 13 mm or 15 mm, etc.

[0054] In this embodiment of the invention, the thickness of the hydrate film can be measured by transmission electron microscopy or atomic force microscopy.

[0055] In some embodiments, the thickness of the hydrate separation layer is 0.5~500 μm. This thickness range allows for a continuous and complete separation layer structure with regular crystal arrangement, creating stable and effective sieving channels; at the same time, it controls the length of the gas diffusion path, maintains a suitable operating pressure drop, and facilitates the efficient separation of low-concentration helium.

[0056] For example, the thickness of the hydrate separation layer can be 0.5μm, 1μm, 5μm, 10μm, 15μm, 30μm, 50μm, 70μm, 90μm, 120μm, 150μm, 200μm, 300μm, 400μm or 500μm, etc.

[0057] In this embodiment of the invention, the thickness of the hydrate separation layer can be measured by transmission electron microscopy or atomic force microscopy.

[0058] This invention also provides a method for preparing the above-mentioned hydrate membrane, comprising the following steps: S1-1, providing a porous support layer; S1-2, preparing a hydrate mother liquor containing a thermodynamic promoter; S1-3, coating the hydrate mother liquor onto at least one surface of the porous support layer, and inducing a phase change in situ under conditions of 0℃~20℃ and 0.1MPa~6MPa to form cage-like hydrate crystals, thereby forming a hydrate separation layer and obtaining a hydrate membrane. By first providing a porous support layer, a stable framework is provided for the subsequent adhesion and pressure resistance of the hydrate separation layer; and then preparing a hydrate mother liquor containing a thermodynamic promoter, the hydrate formation conditions can be reduced and the controllability of film formation can be improved. After coating the mother liquor onto at least one surface of the support layer, inducing a phase change in situ under conditions of 0℃~20℃ and 0.1MPa~6MPa to form cage-like hydrate crystals makes the interface between the separation layer and the support layer more tightly bonded, thereby reducing the shedding of the separation layer and the generation of defects. Therefore, a continuous, dense hydrate membrane with screening capabilities can be obtained under relatively mild operating conditions, which is more conducive to the stable enrichment and recovery of low-concentration helium in hydrocarbon feedstock gas, while taking into account the energy consumption control, structural compactness and applicability required for continuous on-site operation.

[0059] This invention also provides a membrane module, comprising the aforementioned hydrate membrane or a hydrate membrane prepared by the aforementioned method. This membrane module assembles the hydrate membrane between a housing, a seal, and inlet / outlet gas channels to form a continuously operating separation unit. The porous support layer of the membrane provides mechanical strength, while the hydrate separation layer provides a size-screening channel for helium. Thus, even under conditions of continuous natural gas or coalbed methane intake, pressure fluctuations, and complex composition, it can still effectively enrich helium using cage-like hydrate crystals with an average pore size of 0.35 to 0.55 nm. This results in a module that combines good separation efficiency with structural stability, thereby reducing energy consumption and equipment footprint during on-site helium extraction. Therefore, this membrane module is more suitable for site-constrained applications such as gas field gathering and transportation stations, and is beneficial for improving the continuity, economy, and engineering applicability of low-concentration helium recovery.

[0060] This invention also provides a membrane separation method for helium in helium-containing hydrocarbon feedstock gas, comprising the following steps: passing the helium-containing hydrocarbon feedstock gas into the aforementioned membrane module for membrane separation to obtain helium-containing permeate gas and residual gas. After the feedstock gas enters the membrane module, helium preferentially permeates through the hydrate separation layer of the membrane module due to the specific pore size of the cage-like hydrate crystals, while the permeation of larger kinetic-size components such as methane is restricted. This results in a helium-enriched gas flow on the permeate side and a relatively helium-poor gas flow on the residual side. Since the hydrate separation layer in this membrane module can form and maintain its separation function under relatively mild conditions of 0°C to 20°C and 0.1 MPa to 6 MPa, the dependence of the helium extraction process on cryogenic systems and high-energy-consuming units is reduced, thereby improving the separation efficiency and continuous operation stability of low-concentration helium recovery. Therefore, it is more suitable for compact on-site deployment and long-term operation in natural gas fields, coalbed methane fields, and their gathering and processing stations.

[0061] In some embodiments, the helium-containing hydrocarbon feed gas undergoes pretreatment before being introduced into the membrane module for membrane separation. This pretreatment includes the following steps: sequentially passing the helium-containing hydrocarbon feed gas through a dust removal filter; controlling the temperature of the pretreated helium-containing hydrocarbon feed gas to 0~20℃, the pressure to 0.2~26MPa, and ensuring that the solid impurity content in the helium-containing hydrocarbon feed gas is less than 0.01g / m³. 3 By controlling the content of solid impurities to an extremely low level, we can prevent solid particles from scratching or clogging the hydrate membrane pores, thus preventing damage to the membrane structure and degradation of sieving performance. At the same time, we can regulate the temperature and pressure of the feed gas to the optimal operating range of the hydrate membrane, matching the stable operation of the membrane with suitable phase change conditions for molecular sieving. This ensures long-term stability of the hydrate membrane's separation selectivity and permeate flux, extends the service life of the membrane module, and ensures continuous, efficient, and stable operation of the helium extraction process from helium-containing hydrocarbon feed gas.

[0062] In this embodiment of the invention, the pretreated helium-containing hydrocarbon feed gas is fed into the membrane module using a feed gas-side feeding method. Under single-stage separation conditions, the permeate-side pressure is controlled at 5–50 kPa. When using two-stage separation, the first-stage permeate-side pressure is controlled at approximately half the first-stage feed-side pressure. Helium preferentially permeates through the in-situ hydrate membrane, forming helium-enriched permeate gas. Large molecular components such as methane, ethane, and nitrogen are retained by the membrane layer, forming first-stage residual permeate gas. Depending on the operating pressure difference across the membrane, the helium concentration in the permeate-enriched gas can be increased to 2–16 times the helium concentration of the feed gas. If it is necessary to further increase the helium concentration in the helium-enriched product and improve the helium recovery rate, a two-stage membrane purification method can be used. This involves passing the first-stage permeate helium-enriched gas into the second-stage membrane module for secondary separation, further removing residual methane and nitrogen impurities. A helium-enriched product with a helium purity ≥20% is obtained on the second-stage permeate side. The second-stage residual permeate gas can be recycled back to the feed end of the first-stage membrane module, improving the overall helium recovery rate.

[0063] In some embodiments, the membrane module includes a single-stage membrane module or a two-stage tandem membrane module consisting of a primary membrane module and a secondary membrane module connected in series.

[0064] When using a single-stage membrane module for membrane separation, the following steps are included:

[0065] S2-1. Helium-containing hydrocarbon feed gas is introduced into the first-stage membrane module, and the feed-side pressure is controlled to be higher than the permeate-side pressure, so that helium gas preferentially permeates through the membrane module to form helium-containing permeate gas, while the large molecular hydrocarbon components in the feed gas are retained to form residual permeate gas; the operating conditions for single-stage membrane separation are: temperature 0~20℃, feed-side pressure 0.2~26MPa, and permeate-side pressure 5~50kPa.

[0066] When using a two-stage tandem membrane module for membrane separation, the following steps are included:

[0067] S2-1. Helium-containing hydrocarbon feed gas is introduced into the primary membrane module for primary membrane separation. The feed side pressure is controlled to be higher than the permeate side pressure. Helium gas preferentially permeates to form primary permeate gas, while large molecular hydrocarbon components are retained to form primary residual gas.

[0068] S2-2. The primary permeate gas is introduced into the secondary membrane module for secondary membrane separation to further remove residual impurities and obtain a high-concentration helium-containing secondary permeate gas. The residual macromolecular components are retained to form secondary permeate gas.

[0069] S2-3. The secondary permeate gas is returned to the feed gas inlet of the primary membrane module and mixed with the helium-containing hydrocarbon feed gas for circulation and separation to improve the helium recovery rate.

[0070] The primary and secondary membrane modules are connected in series. The operating conditions for primary membrane separation are: temperature 0~20℃, primary feed side pressure 0.2~26MPa, and primary permeate side pressure 40~60% of the primary feed side pressure. The operating conditions for secondary membrane separation are: temperature 0~20℃, secondary feed side pressure equal to the primary permeate side pressure, and secondary permeate side pressure 5~50kPa. By connecting the primary and secondary membrane modules in series, the feed gas is initially enriched, and then the primary permeate gas is further purified, thereby increasing the helium concentration step by step. In primary membrane separation, the pressure difference between the primary feed side and the primary permeate side drives helium to permeate preferentially, while larger molecular components are retained on the permeate side, enabling effective separation of impurities such as methane at the upstream stage. After the secondary permeate gas is refluxed to the feed gas inlet, the helium that has not permeated can be recovered again, thereby reducing helium loss and improving the overall recovery rate.

[0071] like Figure 2As shown, the feed gas enters the primary membrane module and undergoes preliminary separation by the hydrate membrane to obtain primary permeate gas and primary residual gas. The primary residual gas is directly discharged from the system, while the primary permeate gas, either directly or after being pressurized by a booster pump, is sent to the secondary hydrate separator for secondary separation, ultimately yielding secondary permeate gas containing helium (i.e., product gas containing a high concentration of helium). The primary membrane module includes a primary gas guide plate, a primary end cap, and a primary hydrate membrane; the secondary membrane module includes a secondary gas guide plate, a secondary end cap, and a secondary hydrate membrane. The primary and secondary gas guide plates are used to uniformly distribute the feed gas flow, ensuring a stable flow field and preventing flow deviation from eroding the membrane layer. The primary and secondary end caps are sealing caps at both ends of the membrane module, separating the chambers on the feed gas side and the permeate side to ensure pressure resistance and sealing. The core functional components of the primary and secondary hydrate membranes, namely the in-situ generated hydrate membrane layer, achieve molecular sieving separation of helium from other components.

[0072] In this embodiment of the invention, the primary permeate is directly transported out or reused as fuel gas. The entire separation process is operated at near ambient temperature without low-temperature phase change, and the energy consumption is 10% to 30% of that of the traditional low-temperature distillation helium extraction process.

[0073] In this embodiment of the invention, by adjusting the operating conditions of the primary and secondary membrane separation stages, it is beneficial to adapt to continuous on-site gas intake and pressure fluctuation conditions of hydrocarbon feedstock gas, balancing separation efficiency, operational stability, and on-site applicability. In some embodiments, the operating conditions for membrane separation of the two-stage series membrane modules are as follows: in the primary membrane separation stage, the temperature is 0~20℃ (e.g., 0℃, 5℃, 10℃, 15℃, or 20℃, etc.), the primary feed-side pressure is 0.2~26MPa (e.g., 0.2MPa, 2MPa, 5MPa, 10MPa, 20MPa, 23MPa, or 26MPa, etc.), and the primary permeate-side pressure is 40~60% of the primary feed-side pressure (e.g., 40%, 45%, 50%, 55%, or 60%, etc.). In secondary membrane separation, the temperature is 0~20℃ (e.g., 0℃, 5℃, 10℃, 15℃ or 20℃, etc.), the secondary feed side pressure is 0.2~26MPa (e.g., 2MPa, 5MPa, 10MPa, 20MPa, 23MPa or 26MPa, etc.), and the secondary permeate side pressure is 5~50kPa (e.g., 5kPa, 10kPa, 15kPa, 20kPa, 30kPa, 40kPa or 50kPa, etc.).

[0074] In this embodiment of the invention, the membrane module adopts a sleeve-type or tubular structure, mainly composed of a feed gas inlet pipe, a gas distribution guide plate, a hydrate mother liquor inlet pipe, a hydrate membrane separation pipe, a permeate gas outlet pipe, a shell sealing assembly, and a permeate gas outlet pipe. The membrane module has a separation membrane area of ​​no less than 10 m² per unit volume and a pressure resistance rating no less than the pressure required for on-site separation. Simultaneously, the module shell is equipped with functional interfaces such as a temperature monitoring port, a pressure monitoring port, and a condensate discharge port to meet the requirements for operational monitoring and condensate drainage.

[0075] The present invention will be further described in detail below through specific embodiments.

[0076] In the following embodiments, the porous filter cloth plays an auxiliary role and is not specifically limited. It can uniformly carry and spread the hydrate mother liquor, avoid the mother liquor from flowing and accumulating, and ensure the uniformity of film formation. At the same time, the film thickness of the subsequent hydrate separation layer can be precisely controlled by adjusting the number of porous filter cloth layers.

[0077] Example 1

[0078] 1. Preparation of hydrate membranes:

[0079] Water and tetrahydrofuran were mixed to prepare a hydrate mother liquor with a tetrahydrofuran content of 19% by mass. A porous stainless steel support layer was selected, and its outer wall was wrapped with a porous filter cloth. The porous filter cloth was a conventional polytetrafluoroethylene porous filter cloth (single layer thickness of 100 μm), with 3 layers, an average pore size of 50 μm, and a porosity of 60%. The hydrate mother liquor was uniformly sprayed onto the surface of the porous filter cloth on the outer wall of the porous stainless steel support layer. The internal temperature of the tubular hydrate separation device was maintained at 5°C using a constant temperature control system. Using the mixed gas to be separated as the medium, the pressure inside the tubular hydrate separation device was maintained at atmospheric pressure (101.325 kPa, absolute pressure). Under constant temperature and pressure conditions, the mixed gas to be separated was continuously introduced and allowed to stand for 4 hours. The hydrate mother liquor underwent a phase change and formed a hydrate separation layer in situ on the filter cloth, thus obtaining a hydrate membrane.

[0080] The hydrate separation layer has a thickness of 300 μm, an average pore size of 0.42 nm, and a porosity of 6%. The porous support material has an average pore size of 3 μm, a porosity of 25%, and a hydrate membrane thickness of 2.3 mm.

[0081] 2. Membrane module separation process operation:

[0082] The membrane module includes a primary membrane module and a secondary membrane module connected in series. Both the primary and secondary membrane modules contain hydrate membranes prepared according to step 1 above. The permeate outlet of the primary membrane module is connected to the feed inlet of the secondary membrane module, forming a continuous staged purification system to ensure the gradual enrichment of helium.

[0083] 2-1. The raw material gas is a helium-methane binary mixture with a helium volume content of 0.03%.

[0084] 2-2 Feed Parameter Control: Strictly control the feed process parameters, including keeping the feed temperature constant at 5℃ and maintaining the feed side pressure at 3.0MPa.

[0085] 2-3. The helium-methane binary mixture described above is introduced into the first-stage membrane module. The permeate-side pressure of the first-stage membrane module is 1.50 MPa, which is 50% of the first-stage feed-side pressure. Driven by the pressure difference, helium in the binary mixture preferentially permeates through the first-stage membrane module, achieving initial enrichment. After separation by the first-stage membrane, the helium concentration in the permeate gas increases to 4.3%. Subsequently, the helium-enriched permeate gas obtained from the first-stage membrane separation is directly introduced into the second-stage membrane module. The permeate-side pressure of the second-stage membrane module is set to 10 kPa for deep purification. Helium further permeates through the second-stage membrane module, while the remaining large molecular component, methane, is effectively retained. After purification by the second-stage membrane, the final helium purity in the secondary permeate gas is 25.2%, and the total helium recovery rate is 82%. The secondary residual gas retained by the second-stage membrane module is recycled to the feed gas inlet of the first-stage membrane module, mixed with the helium-methane binary mixture, and then circulated for separation.

[0086] Example 2

[0087] 1. Preparation of hydrate membranes:

[0088] Water and tetrabutylammonium bromide were mixed to prepare a hydrate mother liquor with a tetrabutylammonium bromide mass percentage of 25%. A porous stainless steel support layer was selected, and its outer wall was wrapped with a porous filter cloth. The porous filter cloth was a conventional polytetrafluoroethylene porous filter cloth (single-layer porous filter cloth thickness of 100μm). The film thickness of the subsequent hydrate separation layer was precisely controlled by adjusting the number of porous filter cloth layers. In this embodiment, the number of porous filter cloth layers was 3, the average pore size of the porous filter cloth was 50μm, and the porosity was 60%. The above-mentioned hydrate mother liquor was uniformly sprayed onto the surface of the porous filter cloth on the outer wall of the porous stainless steel support layer. The internal temperature of the tubular hydrate separation device was kept constant at 6°C by a constant temperature control system. Using the mixed gas to be separated as the medium, the pressure inside the above-mentioned tubular hydrate separation device was kept stable at atmospheric pressure. After standing at constant temperature and pressure for 4 hours, the hydrate mother liquor underwent a phase change and formed a hydrate separation layer in situ on the filter cloth, thus obtaining a hydrate membrane.

[0089] The hydrate separation layer has a thickness of 300 μm, an average pore size of 0.43 nm, and a porosity of 7%. The porous filter cloth has an average pore size of 50 μm and a porosity of 60%. The porous support material has an average pore size of 3 μm, a porosity of 25%, and a hydrate membrane thickness of 2.3 mm.

[0090] 2. Membrane module separation process operation:

[0091] The membrane module includes a primary membrane module and a secondary membrane module connected in series. The primary membrane module includes a first hydrate membrane, and the secondary membrane module includes a second hydrate membrane. The first and second hydrate membranes have the same structure and preparation process, both being hydrate membranes obtained in step 1 above. The permeate outlet of the primary membrane module is connected to the feed inlet of the secondary membrane module, forming a continuous staged purification system to ensure the gradual enrichment of helium.

[0092] 2-1. Raw Material Gas Pretreatment: Natural gas with a helium volume content of 0.04% is used as the hydrocarbon raw material gas. This hydrocarbon raw material gas also includes methane (86.59% by volume), nitrogen (9.01% by volume), carbon dioxide (4.34% by volume), and a small amount of solid dust. The hydrocarbon raw material gas undergoes dust removal and filtration pretreatment to ensure that the solid impurity content in the pretreated hydrocarbon raw material gas is below 0.01 g / m³. 3 .

[0093] 2-2 Feed Parameter Control: Strictly control the feed process parameters, including keeping the feed temperature constant at 10℃ and maintaining the feed side pressure at 3.2MPa.

[0094] 2-3. The pretreated natural gas is fed into the first-stage membrane module. The permeate-side pressure of the first-stage membrane module is set to 1.50 MPa. Driven by the pressure difference, helium in the hydrocarbon feed gas preferentially permeates through the first-stage membrane module, achieving initial enrichment. After separation by the first-stage membrane, the helium concentration in the first-stage permeate gas increases to 4.1%. Subsequently, the helium-enriched permeate gas obtained from the first-stage membrane separation is directly fed into the second-stage membrane module. The permeate-side pressure of the second-stage membrane module is set to 15 kPa for further purification. Helium further permeates through the second-stage membrane module, while other macromolecular components (methane, nitrogen, and carbon dioxide) are effectively retained. After purification by the second-stage membrane, the final helium purity in the second-stage permeate gas reaches 23.9%, and the total helium recovery rate is 80.2%.

[0095] Examples 3 to 5:

[0096] This embodiment is basically the same as Embodiment 1, except that the mass percentage of the first thermodynamic accelerator, the mass percentage of the second thermodynamic accelerator, the average pore size of the porous support material, the average pore size and porosity of the porous filter cloth, the type of the first thermodynamic accelerator, and the type of the second thermodynamic accelerator are different. The specific differences are shown in Tables 1 and 2. The remaining conditions and methods are basically the same as in Embodiment 1.

[0097] Example 6:

[0098] This embodiment is basically the same as Embodiment 1, except that the thickness of the hydrate membrane is 2.5 mm. The preparation method of the hydrate membrane includes the following steps: mixing water and tetrahydrofuran to prepare a hydrate mother liquor with a tetrahydrofuran mass percentage of 19%. A porous stainless steel support layer is selected, and its outer wall is wrapped with a porous filter cloth. The porous filter cloth is a conventional polytetrafluoroethylene porous filter cloth (100 μm thick). The thickness of the subsequent hydrate separation layer is precisely controlled by adjusting the number of porous filter cloth layers. In this embodiment, the number of porous filter cloth layers is 5, the average pore size of the porous filter cloth is 50 μm, and the porosity is 60%. The above-mentioned hydrate mother liquor is uniformly sprayed onto the surface of the porous filter cloth on the outer wall of the porous stainless steel support layer. The internal temperature of the tubular hydrate separation device is maintained at 5°C by a constant temperature control system. The mixed gas to be separated is used as the medium, and the pressure inside the tubular hydrate separation device is maintained at 0.1 MPa. After standing at constant temperature and pressure for 4 hours, the hydrate mother liquor undergoes a phase change and forms a hydrate separation layer in situ on the filter cloth, thus obtaining a hydrate membrane.

[0099] The hydrate separation layer has a thickness of 500 μm, an average pore size of 0.41 nm, and a porosity of 6%. The porous support material has an average pore size of 3 μm, a porosity of 25%, and a hydrate membrane thickness of 2.5 mm.

[0100] Example 7:

[0101] This embodiment is basically the same as embodiment 6, except that the feed gas temperature, secondary permeate gas pressure and other parameters are different. For details, please refer to Table 2. The other conditions and methods are basically the same as those in embodiment 6.

[0102] Table 1. Hydrate membrane parameters

[0103]

[0104] The hydrate membranes prepared in the above embodiments were subjected to the following performance tests, and the test results are shown in Table 2.

[0105] Helium permeation flux of the hydrate membrane: Under operating conditions of 5℃ and feed-side pressure of 3.0MPa, the helium permeation flux of the hydrate membrane was measured to be 0.012. The formula for calculating helium permeation flux is as follows: In the formula: J - helium permeation flux, V - Permeate volume, m 3 Effective separation area of ​​A-hydrate membrane, m 2 t - stable infiltration time, h.

[0106] Helium gas integral rate in primary permeate gas and helium gas integral rate in secondary permeate gas: After the membrane separation device has been operating stably, gas samples are collected from the permeate gas outlets of the primary and secondary membrane modules, respectively. Gas chromatographs are used to detect the gas components in each group, and the helium gas integral rate in the primary and secondary permeate gas is determined. Each group of samples is tested in parallel multiple times, and the average value is taken as the final test data.

[0107] Table 2. Hydrate membrane separation effect

[0108]

[0109] As can be seen from the analysis in Table 2, the hydrate membranes in Examples 1-7 have excellent separation selectivity, high permeation flux, and long-term operational stability.

[0110] It should be noted that: for experimental steps or conditions not specified in the examples, the procedures and conditions described in conventional experimental procedures in the literature of this art can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions 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 hydrate membrane, characterized in that, include: A porous support layer and a hydrate separation layer located on at least one side surface of the porous support layer; The hydrate separation layer comprises cage-like hydrate crystals formed in situ by phase transformation of a hydrate mother liquor containing a thermodynamic promoter at a temperature of 0°C to 20°C and a pressure of 0.1 MPa to 6 MPa. The average pore size of the hydrate separation layer is 0.35 to 0.55 nm.

2. The hydrate membrane according to claim 1, characterized in that, The thermodynamic accelerator includes a first thermodynamic accelerator, or a combination of a first thermodynamic accelerator and a second thermodynamic accelerator; The first thermodynamic accelerator includes cyclic ether thermodynamic accelerators and / or quaternary ammonium salt thermodynamic accelerators; The second thermodynamic accelerator includes one or more of cycloalkane accelerators, amino acid accelerators, and heterocyclic accelerators; The porous support layer includes a porous support material, which includes one or more of inorganic porous materials, organic porous materials, and metallic porous materials.

3. The hydrate membrane according to claim 2, characterized in that, The cyclic ether thermodynamic accelerators include tetrahydrofuran and / or tetrahydropyran; And / or, the quaternary ammonium salt thermodynamic promoter includes one or more of tetrabutylammonium bromide, tetrabutylammonium chloride, and tetrabutylammonium fluoride.

4. The hydrate membrane according to claim 2 or 3, characterized in that, The average pore size of the porous support material is 0.1~20μm; And / or, the inorganic porous material includes ceramics and / or alumina; And / or, the organic porous material includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polypropylene, polyester, and rubber; And / or, the porous metal material includes one or more of carbon steel, stainless steel, and titanium alloy.

5. The hydrate membrane according to any one of claims 1 to 4, characterized in that, The mass percentage of the thermodynamic accelerator in the hydrate mother liquor is 3-30%.

6. The hydrate membrane according to any one of claims 1 to 5, characterized in that, The thickness of the hydrate film is 0.5~15mm; And / or, the thickness of the hydrate separation layer is 0.5~500μm.

7. A method for preparing a hydrate membrane according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1-1, Provide a porous support layer; S1-2, Prepare a hydrate mother liquor containing a thermodynamic promoter; S1-3. The hydrate mother liquor is coated on at least one side of the porous support layer, and a phase transition is induced in situ to generate cage-like hydrate crystals under the conditions of temperature 0℃~20℃ and pressure 0.1MPa~6MPa to form a hydrate separation layer, thereby obtaining the hydrate membrane.

8. A membrane module, characterized in that, The hydrate membrane includes the hydrate membrane according to any one of claims 1 to 6 or the hydrate membrane prepared by the preparation method according to claim 7.

9. A membrane separation method for helium in a helium-containing hydrocarbon feed gas, characterized in that, Includes the following steps: A helium-containing hydrocarbon feed gas is passed into a membrane module for membrane separation to obtain helium-containing permeate gas and residual gas; the membrane module includes the membrane module described in claim 8.

10. The membrane separation method according to claim 9, characterized in that, The membrane module includes a single-stage membrane module or a two-stage cascaded membrane module consisting of a first-stage membrane module and a second-stage membrane module connected in series. When using a single-stage membrane module for membrane separation, the following steps are included: S2-1. Helium-containing hydrocarbon feed gas is introduced into the primary membrane module, and the feed side pressure is controlled to be higher than the permeate side pressure, so that helium gas preferentially permeates through the primary membrane module to form helium-containing permeate gas, while large molecular hydrocarbon components are retained to form residual permeate gas. Preferably, the operating conditions for membrane separation using the single-stage membrane module are: temperature 0~20℃, feed-side pressure 0.2~26MPa, and permeate-side pressure 5~50kPa; When using a two-stage tandem membrane module for membrane separation, the following steps are included: S2-1. Helium-containing hydrocarbon feed gas is introduced into the primary membrane module for primary membrane separation. The pressure on the primary feed side is controlled to be higher than that on the primary permeate side. Helium gas preferentially permeates to form primary permeate gas, while large molecular hydrocarbon components are retained to form primary residual permeate gas. S2-2. The primary permeate gas is passed into the secondary membrane module for secondary membrane separation to further remove residual impurities and obtain a high-concentration helium-containing secondary permeate gas. The residual macromolecular hydrocarbon components are retained to form secondary permeate gas. S2-3. The secondary permeate gas is returned to the feed gas inlet of the primary membrane module and mixed with the helium-containing hydrocarbon feed gas for circulation and separation to improve the helium recovery rate. Preferably, the operating conditions for membrane separation using the two-stage tandem membrane module are as follows: in the first-stage membrane separation, the temperature is 0~20℃, the first-stage feed side pressure is 0.2~26MPa, and the first-stage permeate side pressure is 40~60% of the first-stage feed side pressure; in the second-stage membrane separation, the temperature is 0~20℃, the second-stage feed side pressure is equal to the first-stage permeate side pressure, and the second-stage permeate side pressure is 5~50kPa.

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