Methane / hydrogen quality separation method and system

Abstract

The invention provides a methane / hydrogen quality separation method and system.The method comprises the following specific steps that methane / hydrogen mixed raw material gas is pressurized, cooled and desulfurized and then mixed with a hydrate accelerant solution to react, and methane hydrate and a gas-phase product are obtained through separation; decomposing the methane hydrate, and separating to obtain methane; and after a gas-phase product is dried, a solid hydrogen storage alloy is utilized for adsorption, and separation of hydrogen and residual methane is achieved. Compared with hydrogen, methane is easier for water molecules to form hydrates, and hydrogen can be selectively combined with the hydrogen storage alloy to generate hydrides, so that efficient separation of methane and hydrogen can be realized through a multi-step process flow and equipment configuration based on selective host-guest interaction.

Description

Technical Field

[0001] The present invention relates to the technical field of methane / hydrogen separation, and in particular to a methane / hydrogen separation method and system based on hydrate pre-separation and hydrogen storage alloy refining. Background Art

[0002] Hydrogen / methane separation technology has been widely used in fields such as associated hydrogen extraction from natural gas, by-product hydrogen in chemical industry, and transportation of hydrogen-enriched natural gas. However, conventional separation methods (such as pressure swing adsorption, cryogenic distillation, membrane separation, etc.) have the following technical bottlenecks when dealing with low-concentration hydrogen (5 - 30% vol) and light hydrocarbon mixed systems: (1) Low separation efficiency due to similar physical properties: The kinetic diameter difference between hydrogen (molecular diameter 0.289nm) and methane (molecular diameter 0.38nm) is small, and conventional molecular sieve adsorbents are difficult to achieve highly selective separation. Especially under high-pressure conditions, the separation factor is generally lower than 50; (2) Insufficient energy consumption economy: Cryogenic distillation requires cooling the mixed gas to below -160°C, and the energy consumption intensity is as high as 3.5kWh / Nm 3 H2~4.2kWh / Nm 3 H2; (3) Although polymer membrane separation is simple to operate, it is restricted by the Robeson upper limit, and its hydrogen permeability and selectivity are negatively correlated. In recent years, separation technologies based on host-guest interactions have shown unique advantages. Natural gas hydrate method: By regulating the hydrate nucleation conditions (pressure 2MPa - 10MPa, temperature 2°C - 10°C), selective capture is achieved using the guest molecule size effect. In addition, the theoretical hydrogen storage density of solid hydrogen storage alloys reaches more than 2.5wt%, and they show chemical inertness to C1 - C3 hydrocarbons. Therefore, hydrogen and natural gas separation can also be achieved using the reversible hydrogen absorption and desorption characteristics. However, the hydrogen purity in the residual gas phase of the hydrate method usually only reaches 90% - 92%; although the hydrogen storage alloy can obtain high-purity hydrogen of more than 99%, hydrocarbon impurities in the raw material gas easily cause surface passivation of the alloy, resulting in capacity attenuation. Summary of the Invention

[0003] To solve the problems existing in the prior art, the present invention provides a methane / hydrogen separation method and system. Since methane is more likely to form hydrates with water molecules than hydrogen, and hydrogen can selectively combine with the hydrogen storage alloy to form hydrides, based on the above selective host-guest interactions, through multi-step process flows and equipment configurations, efficient separation of methane and hydrogen can be achieved.

[0004] To achieve the above object, the present invention provides the following technical solution: A methane / hydrogen separation method, the specific steps are as follows:

[0005] Pressurize, cool, and desulfurize the methane / hydrogen mixed raw material gas, then mix it with the hydrate promoter solution for reaction, and separate to obtain methane hydrate and a gas-phase product;

[0006] Decompose and separate methane hydrate to obtain methane;

[0007] After drying the gas-phase product, adsorb it using a solid hydrogen storage alloy to separate hydrogen from the remaining methane.

[0008] Furthermore, in the step of pressurizing, cooling, and desulfurizing the methane / hydrogen mixed feed gas, the pressure of the methane / hydrogen mixed feed gas after pressurization is 5 MPa to 8 MPa, the temperature of the methane / hydrogen mixed feed gas after cooling is 0 to 5 °C, ZnO-TiO2 composite adsorbent is used for desulfurization, and the H2S concentration in the methane / hydrogen mixed feed gas after desulfurization is less than 0.1 ppm.

[0009] Furthermore, the concentration of the hydrate promoter solution is 0.001 mol / L to 0.1 mol / L; the hydrate promoter is one or two of sodium dodecyl sulfate, sodium alkylbenzene sulfonate, tetrahydrofuran, polyvinyl alcohol, acetic acid, and ethylene glycol.

[0010] Furthermore, in the step of pressurizing, cooling, and desulfurizing the methane / hydrogen mixed feed gas, then mixing and reacting it with the hydrate promoter solution, and separating to obtain methane hydrate and gas-phase product, the reaction conditions for generating methane hydrate are a reaction temperature of 2 °C to 7 °C, a pressure of 5 MPa to 6 MPa, and a reaction residence time of 30 min to 60 min;

[0011] The hydrogen concentration in the obtained gas-phase product is 92% to 96%.

[0012] Furthermore, in the step of decomposing and separating methane hydrate to obtain methane and liquid products, the decomposition temperature of the methane hydrate is 20 °C to 30 °C, and the pressure is 1.5 MPa to 2.5 MPa.

[0013] Furthermore, in the step of drying the gas-phase product and then adsorbing it using a solid hydrogen storage alloy to separate hydrogen from the remaining methane, the solid hydrogen storage alloy is one of TiFe, TiMn, LaNi, and TiV-based alloys.

[0014] The present invention also provides a methane / hydrogen separation system, including:

[0015] A methane / hydrogen mixed feed gas pretreatment part, which is used for pressurizing, cooling, and desulfurizing the methane / hydrogen mixed feed gas, and introducing the pretreated mixed feed gas into the methane hydrate part;

[0016] A methane hydrate part, which is used for mixing and reacting the mixed feed with the hydrate promoter solution to separate methane hydrate and gas-phase product;

[0017] A hydrate decomposition section for receiving the methane hydrate generated by the methane hydrate section, and decomposing and separating the methane hydrate to obtain methane and a liquid product;

[0018] A hydrogen adsorption section for receiving the gas-phase product obtained by the methane hydrate section, drying the gas-phase product, and adsorbing it using a solid-state hydrogen storage alloy to separate hydrogen from the remaining methane.

[0019] Further, the methane / hydrogen mixed raw gas pretreatment section includes a compression device, a first heat exchange device, and a desulfurization device. The inlet of the compression device is connected to the methane / hydrogen mixed raw gas source, and is used to pressurize the methane / hydrogen mixed raw gas to 5 MPa to 8 MPa. The outlet of the compression device is connected to the inlet of the first heat exchange device, and is used to cool the pressurized methane / hydrogen mixed raw gas to 0 to 5 °C. The outlet of the first heat exchange device is connected to the inlet of the desulfurization device, and is used to reduce the H2S concentration in the pressurized and cooled methane / hydrogen mixed raw gas to less than 0.1 ppm. The outlet of the desulfurization device is connected to the methane hydrate section;

[0020] The methane hydrate section includes a reaction mixing device and a separation device. The raw material inlet of the reaction mixing device is connected to the outlet of the methane / hydrogen mixed raw gas pretreatment section, and is used to obtain the pressurized, cooled, and desulfurized methane / hydrogen mixed raw gas. The promoter inlet of the reaction mixing device is connected to the liquid outlet of the hydrate decomposition section. The outlet of the reaction mixing device is connected to the inlet of the separation device. The liquid outlet of the separation device is connected to the inlet of the hydrate decomposition section. The gas outlet of the separation device is connected to the hydrogen adsorption section;

[0021] The hydrate decomposition section includes a decomposition chamber and a second heat exchanger. The liquid outlet of the methane hydrate section is connected to the inlet of the decomposition chamber. The pressure in the decomposition chamber is 1.5 MPa to 2.5 MPa. The second heat exchanger heats the methane hydrate in the decomposition chamber to 20 °C to 30 °C, and the methane hydrate decomposes into methane and a hydrate promoter solution. The liquid outlet of the decomposition chamber is connected to the promoter inlet of the reaction mixing device through a liquid storage tank. The gas outlet of the decomposition chamber is connected to the inlet of the methane storage device;

[0022] The hydrogen adsorption section includes a drying device and a plurality of hydrogen storage alloy adsorption beds. The gas inlet of the drying device is connected to the gas outlet of the hydrate decomposition section. The inlets of the plurality of hydrogen storage alloy adsorption beds are all connected to the gas outlet of the drying device. The first outlet of the plurality of hydrogen storage alloy adsorption beds is connected to the inlet of the methane storage device. The second outlet of the plurality of hydrogen storage alloy adsorption beds is connected to the metal hydride storage device.

[0023] Further, the compression device is a piston compressor, a centrifugal compressor, a screw compressor, or a membrane compressor;

[0024] The first heat exchange device is a liquid ammonia refrigeration unit;

[0025] The desulfurization device uses a ZnO-TiO2 composite adsorbent;

[0026] The reaction mixing device is a vertical stirring kettle, which is equipped with a coil heat exchanger and a microbubble generator. The reaction temperature in the vertical stirring kettle is 2°C to 7°C, the pressure is 5 MPa to 6 MPa, and the reaction residence time is 30 min to 60 min;

[0027] The separation device is a hydrocyclone separator, and the product enters the hydrocyclone separator at a flow rate of 12 m / s to 15 m / s;

[0028] The alloy used in the hydrogen storage alloy adsorption bed is one of the TiFe, TiMn, LaNi, and TiV series alloys;

[0029] Before use, the hydrogen storage alloy adsorption bed is subjected to pickling and hydrogen plasma activation treatment. Among them, the pickling treatment uses nitric acid with a concentration of 1% to 20%, and the treatment time is 1 min to 30 min; the temperature of the hydrogen plasma treatment is 150°C to 450°C, the hydrogen pressure is 0.1 MPa to 1.0 MPa, and the time is 0.5 h to 10 h.

[0030] Furthermore, the second heat exchanger exchanges heat with multiple hydrogen storage alloy adsorption beds through demineralized water.

[0031] Compared with the prior art, the present invention has at least the following beneficial effects:

[0032] A methane / hydrogen separation method provided by the present invention realizes the efficient separation of methane and hydrogen through a multi-step process combining methane hydrate formation and hydrogen storage alloy adsorption. The methane recovery rate of this method can reach more than 98%, and the hydrogen purity can reach more than 99%, which is significantly better than traditional separation technologies and meets the industrial requirements of high-purity gas products.

[0033] In the process, the methane / hydrogen mixed feed gas is pressurized, cooled, and desulfurized, and various parameters are precisely controlled. For example, the pressure after pressurization is 5 MPa to 8 MPa, the temperature after cooling is 0 to 5 °C, and ZnO-TiO2 composite adsorbent is used for desulfurization to make the H2S concentration less than 0.1 ppm, avoiding the influence of H2S on the hydrate formation rate or poisoning the hydrogen storage alloy. When mixing and reacting with the hydrate promoter solution, the reaction conditions are strictly controlled, and the reaction is carried out at 2 °C to 7 °C and 5 MPa to 6 MPa for 30 min to 60 min. The hydrogen concentration in the obtained gas-phase product can reach 92% to 96%. The decomposition conditions of methane hydrate are set at 20 °C to 30 °C and 1.5 MPa to 2.5 MPa to ensure efficient decomposition. The solid hydrogen storage alloy is used to adsorb hydrogen in the gas-phase product to realize the separation of hydrogen from the remaining methane. At the same time, by optimizing the reaction conditions, such as precisely controlling the temperature and pressure, and recycling the liquid-phase product, the energy consumption is greatly reduced, and the economy and market competitiveness are improved. In addition, cheap hydrogen storage alloy materials are used, and the liquid-phase product generated in the process can be recycled, reducing resource waste and pollution, highly meeting the requirements of green chemistry and sustainable development.

[0034] The present invention provides a methane / hydrogen separate quality system, which is composed of a methane / hydrogen mixed feed gas pretreatment part, a methane hydrate part, a hydrate decomposition part, and a hydrogen adsorption part. Each part works together to achieve the efficient separation of methane and hydrogen. The whole system realizes an efficient separation effect with a methane recovery rate of more than 98% and a hydrogen purity of more than 99% by optimizing the equipment configuration and process flow, which is superior to the traditional technology and meets the industrial requirements.

[0035] Specifically, the pretreatment section of the methane / hydrogen mixed feed gas is equipped with a compression device, a first heat exchange device, and a desulfurization device. The compression device can pressurize the feed gas to 5 MPa to 8 MPa, and the temperature after cooling is 0 to 5 °C. The ZnO-TiO2 composite adsorbent is used for desulfurization to make the H2S concentration less than 0.1 ppm, providing high-quality feed gas for subsequent reactions and avoiding the influence of H2S on the formation rate of hydrates or poisoning the hydrogen storage alloy. The methane hydrate section forms methane hydrates and separates the gas-phase products under precisely controlled conditions through a reaction mixing device and a separation device. The reaction mixing device is a vertical stirring kettle equipped with a coil heat exchanger and a microbubble generator, and the reaction conditions are stable. The hydrate decomposition section uses a decomposition chamber and a second heat exchanger to decompose methane hydrates at 1.5 MPa to 2.5 MPa and heat them to 20 °C to 30 °C. The decomposed liquid-phase products can be recycled. The hydrogen adsorption section separates hydrogen from the remaining methane by using a drying device and multiple hydrogen storage alloy adsorption beds, and the hydrogen storage alloy adsorption bed uses one of the alloys of TiFe, TiMn, LaNi, and TiV systems. At the same time, the system reduces energy consumption and improves economy by recycling liquid-phase products and optimizing reaction conditions. Moreover, the use of inexpensive hydrogen storage alloy materials and the recycling of liquid-phase products reduce resource waste and pollution, which conforms to the concepts of green chemistry and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a schematic flow chart of the method for separating methane and hydrogen of the present invention;

[0037] Figure 2 is a schematic structural diagram of the methane / hydrogen separation system of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0039] The present invention provides a method for separating methane and hydrogen, and the specific process is as Figure 1 shown:

[0040] Step 1: The H2 and CH4 mixed gas is pressurized under the action of the compression device 1 to reach the pressure conditions required for forming methane hydrates.

[0041] Step 2: The gas is cooled through the first heat exchange device 2 to make the gas lower than the formation temperature of methane hydrates.

[0042] Step 3: The gas enters the desulfurization device 3 to remove the sulfur-containing impurity gas that may exist in the feedstock, avoiding the influence of impurities on the formation of methane hydrates and alloy hydrides.

[0043] Step 4: In the hydrate pre-separation stage, the pretreated gas and the hydrate promoter solution enter the reaction mixing device 4, and methane is efficiently captured to form hydrates.

[0044] Step 5: The hydrate slurry enters the separation device 5, and the hydrogen concentration in the separated gas is further increased, providing a high-purity hydrogen source for the subsequent refined process of hydrogen storage alloy. For the gas-phase product of the separation device 5, the hydrogen-containing gas passes through the hydrogen storage alloy adsorption bed 10 to form metal hydrides, realizing the secondary separation of hydrogen and low-concentration methane:

[0045] Step 6: For the solid / liquid slurry product of the separation device 5, it is introduced into the second heat exchanger 7 for hydrate pyrolysis to release pure methane gas, and the liquid-phase product is introduced into the reaction mixing device 4 again for synthesizing methane hydrates.

[0046] Among them, in Step 1, the type of the compression device 1 is a piston type, centrifugal type, screw type and membrane type compressor, and the pressure of the pressurized mixed gas is 5 MPa to 8 MPa;

[0047] Among them, in Step 2, the first heat exchange device 2 is a liquid ammonia refrigeration unit, and the temperature of the cooled gas is between 0 and 5 °C;

[0048] Among them, in Step 3, ZnO-TiO2 composite adsorbent is used in the desulfurization device 3 to control the H2S concentration below 0.1 ppm;

[0049] Among them, in Step 4, the reaction mixing device 4 is a vertical stirring kettle, a coil heat exchanger and a microbubble generator are arranged in the vertical stirring kettle, the reaction temperature in the vertical stirring kettle is 2 °C to 7 °C, the pressure is maintained at 5 MPa to 6 MPa, and the reaction residence time is 30 min to 60 min;

[0050] Among them, in Step 4, the concentration of the hydrate promoter solution is 0.001 mol / L to 0.1 mol / L, and the hydrate promoter is one or two of sodium dodecyl sulfate, sodium alkylbenzene sulfonate, tetrahydrofuran, polyvinyl alcohol, acetic acid, ethylene glycol;

[0051] Among them, in Step 4, the hydrogen concentration in the remaining gas without forming hydrates is 92% to 96%;

[0052] Among them, in Step 5, the separation device 5 is a solid-liquid cyclone separator, and the flow rate at the product inlet of the cyclone separator is 12 m / s to 15 m / s to ensure both the hydrate stability and the separation efficiency of gas and solid / liquid phases;

[0053] Among them, in Step 5, the alloy in the hydrogen storage alloy adsorption bed 10 is one of TiFe, TiMn, LaNi, TiV series alloys;

[0054] Among them, before use, the hydrogen storage alloy adsorption bed 10 in step 5 needs to be pickled and hydrogen plasma activated successively to improve the adsorption efficiency. The pickling treatment uses nitric acid with a concentration of 1% - 20%, and the treatment time is 1 min - 30 min; the temperature of the hydrogen plasma treatment is 150°C - 450°C, the hydrogen pressure is 0.1 MPa - 1.0 MPa, and the time is 0.5 h - 10 h; after every 50 hydrogen absorption and desorption cycles of the hydrogen storage alloy bed, it needs to be heat-treated at 250°C - 450°C for 1 h - 5 h in a 10% H2 / 90% Ar atmosphere for regeneration to ensure the long-term stable operation of the alloy bed;

[0055] Among them, in step 6, the hydration decomposition temperature in the separation device 5 is 20°C - 30°C, and the pressure is 1.5 MPa - 2.5 MPa;

[0056] Among them, in step 6, heat exchange is carried out between the second heat exchanger 7 and the hydrogen storage alloy adsorption bed 10 through demineralized water, and the heat required for hydrate decomposition is provided by the hydrogen absorption reaction of the hydrogen storage alloy adsorption bed 10.

[0057] Using the methane / hydrogen fractionation method provided by the present invention, a methane / hydrogen fractionation system is established, and the system structure is as Figure 2 shown, including: a methane / hydrogen mixed raw material gas pretreatment part, which is used to pressurize, cool down, and desulfurize the methane / hydrogen mixed raw material gas, and introduce the pretreated mixed raw material gas into the methane hydrate part;

[0058] The methane / hydrogen mixed raw material gas pretreatment part includes a compression device 1, a first heat exchange device 2, and a desulfurization device 3. The inlet of the compression device 1 is connected to the methane / hydrogen mixed raw material gas source, and is used to pressurize the methane / hydrogen mixed raw material gas to 5 MPa - 8 MPa. The outlet of the compression device 1 is connected to the inlet of the first heat exchange device 2, and is used to cool down the pressurized methane / hydrogen mixed raw material gas to 0 - 5°C. The outlet of the first heat exchange device 2 is connected to the inlet of the desulfurization device 3, and is used to reduce the H2S concentration in the pressurized and cooled methane / hydrogen mixed raw material gas to below 0.1 ppm. The outlet of the desulfurization device 3 is connected to the methane hydrate part;

[0059] The methane hydrate part is used to mix and react the mixed raw material and the hydrate promoter solution to separate methane hydrate and gas-phase products;

[0060] The methane hydrate part includes a reaction mixing device 4 and a separation device 5. The raw material inlet of the reaction mixing device 4 is connected to the outlet of the methane / hydrogen mixed raw material gas pretreatment part, and is used to obtain the pressurized, cooled, and desulfurized methane / hydrogen mixed raw material gas; the promoter inlet of the reaction mixing device 4 is connected to the liquid outlet of the hydration decomposition part. The outlet of the reaction mixing device 4 is connected to the inlet of the separation device 5. The liquid outlet of the separation device 5 is connected to the inlet of the hydration decomposition part. The gas outlet of the separation device 5 is connected to the hydrogen adsorption part;

[0061] A hydration decomposition section for receiving the methane hydrate generated by the methane hydration section, and decomposing and separating the methane hydrate to obtain methane and a liquid product;

[0062] The hydration decomposition section includes a decomposition chamber 6 and a second heat exchanger 7. The liquid outlet of the methane hydration section is communicated with the inlet of the decomposition chamber 6. The pressure in the decomposition chamber 6 is 1.5 MPa to 2.5 MPa. The second heat exchanger 7 heats the methane hydrate in the decomposition chamber 6 to 20 °C to 30 °C, and the methane hydrate decomposes into methane and a hydrate promoter solution. The liquid outlet of the decomposition chamber 6 is communicated with the promoter inlet of the reaction mixing device 4 through a liquid storage tank 8, and the gas outlet of the decomposition chamber 6 is communicated with the inlet of the methane storage device;

[0063] A hydrogen adsorption section for receiving the gas-phase product obtained by the methane hydration section, drying the gas-phase product, and adsorbing it with a solid hydrogen storage alloy to separate hydrogen from the remaining methane.

[0064] The hydrogen adsorption section includes a drying device 9 and a plurality of hydrogen storage alloy adsorption beds 10. The gas inlet of the drying device 9 is connected to the gas outlet of the hydration decomposition section. The inlets of the plurality of hydrogen storage alloy adsorption beds 10 are all connected to the gas outlet of the drying device 9. The first outlet of the plurality of hydrogen storage alloy adsorption beds 10 is communicated with the inlet of the methane storage device, and the second outlet of the plurality of hydrogen storage alloy adsorption beds 10 is communicated with the metal hydride storage device.

[0065] Preferably, the second heat exchanger 7 and the plurality of hydrogen storage alloy adsorption beds 10 exchange heat through demineralized water.

[0066] Example 1:

[0067] (1) Pass the methane / hydrogen mixed raw material gas (H2: 60%, CH4: 40%) into a piston compressor and boost the pressure to 6 MPa; cool the gas temperature to 3 °C through a liquid ammonia refrigeration unit; use a ZnO-TiO2 composite adsorbent to desulfurize and reduce the H2S concentration to below 0.05 ppm;

[0068] (2) Pass the pretreated gas into a vertical stirring kettle equipped with a coil heat exchanger and a microbubble generator. The raw material aqueous solution contains 0.005 mol / L sodium dodecyl sulfate and 0.01 mol / L tetrahydrofuran, and react at 5 MPa and 5 °C for 45 min to form a methane hydrate slurry. Pass the slurry into a hydrocyclone with an inlet flow rate of 13 m / s, and the hydrogen concentration in the separated gas-phase product is increased to 94%;

[0069] (3) Feed the gas-phase product of the cyclone separator into the TiMn₂-based hydrogen storage alloy adsorption bed. Hydrogen reacts with the alloy to form metal hydride, achieving the secondary separation of hydrogen and low-concentration methane. Feed the solid / liquid slurry of the cyclone separator into the heat exchanger, heat it to 25 °C under a pressure of 2 MPa to decompose methane hydrate and release pure methane gas. The liquid-phase product is fed back into the stirring kettle for recycling to form methane hydrate.

[0070] (4) After every 50 absorption and desorption cycles of the hydrogen storage alloy bed, conduct heat treatment at 350 °C for 3 hours in a 10% H₂ / 90% Ar atmosphere to ensure the long-term stable operation of the alloy bed.

[0071] Example 2:

[0072] (1) Feed the methane / hydrogen mixed raw gas (H₂: 50%, CH₄: 50%) into the screw compressor, boost the pressure to 5.5 MPa; cool the gas temperature to 2 °C through a liquid ammonia refrigeration unit; use a ZnO-TiO₂ composite adsorbent for desulfurization to reduce the H₂S concentration to below 0.08 ppm.

[0073] (2) Feed the pretreated gas into the vertical stirring kettle equipped with a coil heat exchanger and a microbubble generator. The raw material aqueous solution contains 0.008 mol / L of polyvinyl alcohol and 0.002 mol / L of acetic acid. React for 50 min under the conditions of 5.2 MPa and 4 °C to form a methane hydrate slurry; feed the slurry into a small cyclone separator with an inlet flow rate of 12 m / s. After separation, the hydrogen concentration in the gas-phase product is increased to 93%.

[0074] (3) Feed the gas-phase product of the cyclone separator into the LaNi₅ hydrogen storage alloy adsorption bed. Hydrogen reacts with the alloy to form metal hydride, achieving the secondary separation of hydrogen and low-concentration methane. Feed the solid / liquid slurry of the cyclone separator into the heat exchanger, heat it to 22 °C under a pressure of 1.8 MPa to decompose methane hydrate and release pure methane gas. The liquid-phase product is fed back into the stirring kettle for recycling to form methane hydrate.

[0075] (4) After every 50 absorption and desorption cycles of the hydrogen storage alloy bed, conduct heat treatment at 300 °C for 4 hours in a 10% H₂ / 90% Ar atmosphere to ensure the long-term stable operation of the alloy bed.

[0076] Example 3:

[0077] (1) Feed the methane / hydrogen mixed raw gas (H₂: 55%, CH₄: 45%) into the centrifugal compressor, boost the pressure to 5.8 MPa; cool the gas temperature to 4 °C through a liquid ammonia refrigeration unit; use a ZnO-TiO₂ composite adsorbent for desulfurization to reduce the H₂S concentration to below 0.06 ppm.

[0078] (2) Feed the pretreated gas into a vertical stirred tank, which is equipped with a coil heat exchanger and a microbubble generator. The raw material aqueous solution contains 0.004 mol / L acetic acid and 0.008 mol / L polyvinyl alcohol. React for 60 minutes at 5.4 MPa and 5 °C to form a methane hydrate slurry; Feed the slurry into a small cyclone separator with an inlet flow rate of 14 m / s. After separation, the hydrogen concentration in the gas-phase product is increased to 93%.

[0079] (3) Feed the gas-phase product of the cyclone separator into a TiFe hydrogen storage alloy adsorption bed. Hydrogen reacts with the alloy to form metal hydrides, realizing the secondary separation of hydrogen and low-concentration methane. Feed the solid / liquid phase slurry of the cyclone separator into a heat exchanger, heat it to 24 °C, and the pressure is 1.9 MPa to decompose the methane hydrate and release pure methane gas. The liquid-phase product is fed back into the stirred tank for recycling to form methane hydrate.

[0080] (4) After every 50 absorption and desorption cycles of the hydrogen storage alloy bed, conduct heat treatment at 340 °C for 3.5 hours in a 10% H2 / 90% Ar atmosphere to ensure the long-term stable operation of the alloy bed.

[0081] Example 4:

[0082] (1) Feed the methane / hydrogen mixed raw material gas (H2: 70%, CH4: 30%) into a screw compressor and boost the pressure to 6.2 MPa; Cool the gas temperature to 2.5 °C through a liquid ammonia refrigeration unit; Use a ZnO-TiO2 composite adsorbent to desulfurize and reduce the H2S concentration to below 0.04 ppm.

[0083] (2) Feed the pretreated gas into a vertical stirred tank, which is equipped with a coil heat exchanger and a microbubble generator. The raw material aqueous solution contains 0.006 mol / L polyvinyl alcohol and 0.012 mol / L ethylene glycol. React for 40 minutes at 5.5 MPa and 3 °C to form a methane hydrate slurry; Feed the slurry into a small cyclone separator with an inlet flow rate of 14 m / s. After separation, the hydrogen concentration in the gas-phase product is increased to 95.5%.

[0084] (3) Feed the gas-phase product of the cyclone separator into a LaNi5 hydrogen storage alloy adsorption bed. Hydrogen reacts with the alloy to form metal hydrides, realizing the secondary separation of hydrogen and low-concentration methane. Feed the solid / liquid phase slurry of the cyclone separator into a heat exchanger, heat it to 26 °C, and the pressure is 2.1 MPa to decompose the methane hydrate and release pure methane gas. The liquid-phase product is fed back into the stirred tank for recycling to form methane hydrate.

[0085] (4) After every 50 absorption and desorption cycles of the hydrogen storage alloy bed, conduct heat treatment at 360 °C for 2.5 hours in a 10% H2 / 90% Ar atmosphere to ensure the long-term stable operation of the alloy bed.

[0086] Comparative Example 1

[0087] The methane / hydrogen mixed feed gas (H2: 60%, CH4: 40%) was introduced into a centrifugal compressor and pressurized to 6 MPa. The gas temperature was reduced to -50 °C by a liquid ammonia refrigeration unit. Activated carbon adsorbent was used for desulfurization to reduce the H2S concentration to below 0.1 ppm. The pretreated gas was introduced into a low-temperature separation column and separated at -50 °C and 6 MPa. Methane and hydrogen were separated by multi-stage condensation and rectification. The separated hydrogen was introduced into a molecular sieve adsorption bed to further remove trace methane and other impurities.

[0088] Test Results

[0089]

[0090] The above content is a further detailed description of the present invention in combination with specific / preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. Without departing from the concept of the present invention, several alternatives or modifications can be made to these described embodiments, and these alternative or modified forms should be regarded as belonging to the scope of the present invention.

Claims

1. A method for separating methane and hydrogen by fractions, characterized in that, The specific steps are as follows: Pressurize, cool down, and desulfurize the methane / hydrogen mixed feed gas, then mix and react it with the hydrate promoter solution to separate methane hydrate and gas-phase products; Decompose and separate the methane hydrate to obtain methane; After drying the gas-phase products, adsorb them using a solid-state hydrogen storage alloy to separate hydrogen from the remaining methane.

2. The methane / hydrogen separation method according to claim 1, characterized in that, In the step of pressurizing, cooling down, and desulfurizing the methane / hydrogen mixed feed gas, the pressure of the methane / hydrogen mixed feed gas after pressurization is 5 MPa to 8 MPa, the temperature of the methane / hydrogen mixed feed gas after cooling is 0 to 5 °C, and ZnO-TiO2 composite adsorbent is used for desulfurization. The H2S concentration in the methane / hydrogen mixed feed gas after desulfurization is less than 0.1 ppm.

3. A method for separating methane and hydrogen according to the claim, characterized in that The concentration of the hydrate promoter solution is 0.001 mol / L to 0.1 mol / L; the hydrate promoter is one or two of sodium dodecyl sulfate, sodium alkylbenzene sulfonate, tetrahydrofuran, polyvinyl alcohol, acetic acid, and ethylene glycol.

4. The method for separating methane and hydrogen according to the claim is characterized in that, In the step of pressurizing, cooling down, and desulfurizing the methane / hydrogen mixed feed gas, then mixing and reacting it with the hydrate promoter solution to separate methane hydrate and gas-phase products, the reaction conditions for forming methane hydrate are: the reaction temperature is 2 °C to 7 °C, the pressure is 5 MPa to 6 MPa, and the reaction residence time is 30 min to 60 min; The hydrogen concentration in the obtained gas-phase products is 92% to 96%.

5. A method for separating methane and hydrogen by quality according to the claim, characterized in that, In the step of decomposing and separating the methane hydrate to obtain methane and liquid products, the decomposition temperature of the methane hydrate is 20 °C to 30 °C, and the pressure is 1.5 MPa to 2.5 MPa.

6. The method for separating methane and hydrogen according to the claim is characterized in that, In the step of drying the gas-phase products and then adsorbing them using a solid-state hydrogen storage alloy to separate hydrogen from the remaining methane, the solid-state hydrogen storage alloy is one of TiFe, TiMn, LaNi, and TiV-based alloys.

7. A methane / hydrogen separation system, characterized in that, Including: A methane / hydrogen mixed feed gas pretreatment section for pressurizing, cooling down, and desulfurizing the methane / hydrogen mixed feed gas and introducing the pretreated mixed feed gas into the methane hydration section; A methane hydration section for mixing and reacting the mixed feed with the hydrate promoter solution to separate methane hydrate and gas-phase products; A hydration decomposition section for receiving the methane hydrate generated by the methane hydration section and decomposing and separating the methane hydrate to obtain methane and liquid products; A hydrogen adsorption section for receiving the gas-phase products obtained by the methane hydration section, drying the gas-phase products, and adsorbing them using a solid-state hydrogen storage alloy to separate hydrogen from the remaining methane.

8. The methane / hydrogen fractionation system according to claim 7, characterized in that, The pretreatment section of the methane / hydrogen mixed feed gas includes a compression device (1), a first heat exchange device (2), and a desulfurization device (3). The inlet of the compression device (1) is connected to the methane / hydrogen mixed feed gas source, and is used to pressurize the methane / hydrogen mixed feed gas to 5 MPa to 8 MPa. The outlet of the compression device 1 is connected to the inlet of the first heat exchange device (2), and is used to cool the pressurized methane / hydrogen mixed feed gas to 0 to 5 °C. The outlet of the first heat exchange device (2) is connected to the inlet of the desulfurization device (3), and is used to reduce the H2S concentration in the pressurized and cooled methane / hydrogen mixed feed gas to less than 0.1 ppm. The outlet of the desulfurization device (3) is connected to the methane hydrate section; The methane hydrate section includes a reaction mixing device (4) and a separation device (5). The raw material inlet of the reaction mixing device (4) is connected to the outlet of the pretreatment section of the methane / hydrogen mixed feed gas, and is used to obtain the pressurized, cooled, and desulfurized methane / hydrogen mixed feed gas. The promoter inlet of the reaction mixing device (4) is connected to the liquid outlet of the hydration decomposition section. The outlet of the reaction mixing device (4) is connected to the inlet of the separation device (5). The liquid outlet of the separation device (5) is connected to the inlet of the hydration decomposition section. The gas outlet of the separation device 5 is connected to the hydrogen adsorption section; The hydration decomposition section includes a decomposition chamber (6) and a second heat exchanger (7). The liquid outlet of the methane hydrate section is connected to the inlet of the decomposition chamber (6). The pressure in the decomposition chamber (6) is 1.5 MPa to 2.5 MPa. The second heat exchanger (7) heats the methane hydrate in the decomposition chamber (6) to 20 °C to 30 °C, and the methane hydrate decomposes into methane and the hydrate promoter solution. The liquid outlet of the decomposition chamber (6) is connected to the promoter inlet of the reaction mixing device (4) through a liquid storage tank (8). The gas outlet of the decomposition chamber (6) is connected to the inlet of the methane storage device; The hydrogen adsorption section includes a drying device (9) and a plurality of hydrogen storage alloy adsorption beds (10). The gas inlet of the drying device (9) is connected to the gas outlet of the hydration decomposition section. The inlets of the plurality of hydrogen storage alloy adsorption beds (10) are all connected to the gas outlet of the drying device (9). The first outlet of the plurality of hydrogen storage alloy adsorption beds (10) is connected to the inlet of the methane storage device. The second outlet of the plurality of hydrogen storage alloy adsorption beds (10) is connected to the metal hydride storage device.

9. According to the methane / hydrogen fractionation system described in claim 8, wherein The compression device (1) is a piston compressor, a centrifugal compressor, a screw compressor, or a membrane compressor; The first heat exchange device (2) is a liquid ammonia refrigeration unit; The desulfurization device (3) uses a ZnO-TiO2 composite adsorbent; The reaction mixing device (4) is a vertical stirring kettle, and a coil heat exchanger and a microbubble generator are arranged in the vertical stirring kettle. The reaction temperature in the vertical stirring kettle is 2 °C to 7 °C, the pressure is 5 MPa to 6 MPa, and the reaction residence time is 30 min to 60 min; The separation device (5) is a hydrocyclone, and the product enters the hydrocyclone at a flow rate of 12 m / s to 15 m / s; The alloy used in the hydrogen storage alloy adsorption bed (10) is one of the alloys of TiFe, TiMn, LaNi, and TiV series; Before use, the hydrogen storage alloy adsorption bed (10) is subjected to pickling and hydrogen plasma activation treatment. Among them, for pickling treatment, nitric acid with a concentration of 1% - 20% is used, and the treatment time is 1 min - 30 min; for hydrogen plasma treatment, the temperature is 150 °C - 450 °C, the hydrogen pressure is 0.1 MPa - 1.0 MPa, and the time is 0.5 h - 10 h.

10. The methane / hydrogen separation system according to claim 8, characterized in that, The second heat exchanger (7) exchanges heat with multiple hydrogen storage alloy adsorption beds (10) through desalted water.

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