Hydrogen purification method and device with sulfur-iodine cycle coupling membrane separation and pressure swing adsorption

Abstract

The application discloses a kind of coupling membrane separation and pressure swing adsorption's sulfur-iodine cycle hydrogen purification method and device.The method comprises: the decomposition product gas from hydrogen iodide decomposition unit enters preliminary treatment unit and is condensed to remove water, to realize preliminary separation;After preliminary separation, mixed gas enters membrane separation equipment, and membrane separation equipment is based on molecular size rejection mechanism to realize the preliminary separation between hydrogen and other impurities, and hydrogen in mixed gas enters the permeation side through membrane material, to form the preliminary purification hydrogen-rich gas stream;Hydrogen-rich gas stream enters PSA purification device, and PSA purification device uses gradient adsorbent bed to purify hydrogen-rich gas stream, to obtain high-purity hydrogen.The application solves the problem of low purity and low yield in sulfur-iodine cycle hydrogen purification, and provides an efficient purification scheme for sulfur-iodine cycle and other thermochemical hydrogen production technologies.

Description

TECHNICAL FIELD

[0001] The present application relates to a hydrogen production technology based on the thermochemical sulfur-iodine cycle (SI cycle), and in particular to a hydrogen purification method and device coupling membrane separation and pressure swing adsorption for efficiently removing components such as HI, I2, H2O, etc., to improve hydrogen purity and recovery rate. BACKGROUND

[0002] Hydrogen energy, as a highly efficient renewable energy carrier, has attracted worldwide attention and research due to its high efficiency, environmental friendliness, and sustainability. Currently, the production of hydrogen is mainly derived from natural gas (48%), oil (30%), coal (18%), and the remaining 4% from water electrolysis. The method of producing hydrogen from fossil fuels mainly includes hydrocarbon reforming and pyrolysis, which has the advantages of mature technology, considerable output, and relatively low cost. However, considering the limited reserves of fossil fuels, the need for product purification during hydrogen production, and the inevitable carbon emissions, this method is difficult to meet the future low-carbon development goals and is not suitable as the main production method of hydrogen in the long term. On the other hand, water electrolysis for hydrogen production uses electricity as the driving force to split water, converting electrical energy into chemical energy stored in hydrogen and oxygen. This method not only produces hydrogen with high purity (above 99.8%), but also has mature technology and wide application. However, due to the high energy consumption and low energy conversion efficiency of this process, its widespread application is limited. Therefore, to achieve more sustainable and environmentally friendly hydrogen production, it is particularly important to explore new technologies and methods that can reduce energy consumption and improve conversion efficiency.

[0003] Among the many hydrogen production technologies, the thermochemical sulfur-iodine cycle water splitting for hydrogen production is considered one of the most promising methods for large-scale hydrogen production in the future. This technology involves a series of chemical reactions between water and specific intermediate substances at relatively mild reaction temperatures, ultimately producing hydrogen (H2) and oxygen (O2). Compared to direct water splitting for hydrogen production, the thermochemical sulfur-iodine cycle requires relatively low temperatures for each step, making it compatible with a wide range of heat sources, such as solar and nuclear energy. In particular, the thermochemical sulfur-iodine cycle water splitting for hydrogen production uses three basic thermochemical reactions to complete the water splitting process, successfully reducing the required thermal decomposition temperature to below 900°C, achieving high hydrogen production thermal efficiency. In addition, since this technology can operate under full-flow conditions, it is well suited for large-scale production and continuous operation. In particular, the use of sulfuric acid decomposition as an endothermic process during the high-temperature stage allows for good integration with high-temperature gas cooled reactors. Compared to other hydrogen production methods, the sulfur-iodine cycle shows greater feasibility in terms of technology and economics and is recognized as one of the most promising methods for hydrogen production in the field of thermochemical water splitting. This method not only improves hydrogen production efficiency but also provides a new approach to sustainable energy solutions. The thermochemical sulfur-iodine cycle water splitting for hydrogen production consists of the following 3-step chemical reactions:

[0004] Bunsen reaction: SO2 + I2 + 2H2O → 2HI + H2SO4;

[0005] H2SO4 decomposition reaction: 2H2SO4 → 2H2O + 2SO2 + O2;

[0006] HI decomposition reaction: 2HI → I2 + H2.

[0007] Thermochemical sulfur-iodine cycle is considered as one of the potential technologies for large-scale hydrogen production due to its high efficiency and zero carbon dioxide emission. The hydrogen iodide decomposition unit is the key to ensure the continuous and stable operation of the whole system. Under the high temperature condition of 400-500℃, hydrogen iodide is decomposed into hydrogen and iodine vapor by the action of catalyst, but due to the limitation of thermodynamic equilibrium, the decomposition efficiency is usually less than 23%. Therefore, after the catalytic reaction, there are still many gas components such as hydrogen iodide, iodine, water vapor and hydrogen in the system. Since the system is designed as a closed cycle, in order to ensure the stability of the process and the recycling of materials, the iodine and hydrogen iodide after reaction must be effectively recovered. Therefore, how to efficiently separate and purify these gas components becomes a key problem affecting the operation efficiency and technical feasibility of the whole device.

[0008] CN 114195094 B discloses a thermochemical sulfur-iodine cycle hydrogen production whole process method and device. The high-temperature gas mixture after decomposition in the HI decomposition tower exits from the top of the tower and enters the condensation tower. The iodine-containing liquid in the condensation tower is sprayed from the top and meets the high-temperature gas from the HI decomposition tower. A part of it is recirculated to the top of the tower for spraying, and the rest enters the Bunsen reaction premixing tank. Hydrogen exits from the top of the tower and enters the NaOH washing tank. In this method, the mixed gas produced by the decomposition tower is in contact with the iodine-containing liquid in the condensation tower for a short time, which cannot guarantee that all the hydrogen iodide and iodine are dissolved in the sprayed liquid. At the same time, due to entrainment of mist, the mixed gas flowing out from the top of the condensation tower contains iodine, hydrogen iodide, hydrogen and water. In this method, it is also mentioned that sodium hydroxide solution is used to neutralize hydrogen iodide, and iodine is dissolved in the liquid. However, this method will cause iodine loss and produce sodium iodide by-product, and additional iodine needs to be added to the system, which is not consistent with the original intention of the thermochemical sulfur-iodine cycle hydrogen production, i.e. only water flows into the system, and the products are hydrogen and oxygen.

[0009] CN116443814B proposes a method and system for iodine recovery cycle in thermochemical sulfur-iodine cycle hydrogen production. The method sends the mixed gas containing H2, HI, I2 and H2O discharged from the HI decomposition tower to the condensation tower for washing. The liquid mixture obtained at the bottom of the tower is partially sent to the top of the tower to spray wash the mixed gas. The gas containing H2 after condensation tower washing is sent to the washing tank, and H2O2 solution is supplemented in the washing tank at regular intervals. H2O2 is used to oxidize HI in the gas to I2, and the obtained hydrogen gas is used as product gas to leave the washing tank. The material in the washing tank is transported to the microporous filter, and the iodine solid is deposited on the filter plate of the microporous filter. The H2O2 solution permeates the filter plate and returns to the washing tank. The iodine-containing liquid obtained by flushing and dissolving the iodine solid deposited on the filter plate of the microporous filter is sent to the Bunsen reaction tower after oxidation in the oxidation tank. However, in actual operation, hydrogen peroxide will decompose into water and oxygen, and oxygen will be produced in a hydrogen atmosphere, which poses an explosion risk to the device, and the method cannot be used in actual operation. SUMMARY

[0010] The purpose of the present application is to overcome the shortcomings of the prior art and provide a sulfur-iodine cycle hydrogen purification method and device coupled with membrane separation and pressure swing adsorption.

[0011] From the perspective of synergistic effect of molecular sieve separation and pressure swing adsorption, by optimizing key factors such as membrane material composition and structure design, corrosion-resistant modification of adsorbent, and process coupling regulation, carbon molecular sieve membrane with a zirconium oxide modification layer on the surface is used to preferentially separate hydrogen, greatly reducing the impurity load of the PSA (pressure swing adsorption) purification device. The PSA purification device uses a gradient adsorbent design (modified activated carbon + molecular sieve) to achieve the graded removal of HI, I2 and H2O, avoiding the purity fluctuations caused by the failure of a single adsorbent. The present application solves the problems of low purity and low yield in sulfur-iodine cycle hydrogen purification, provides an efficient purification scheme for sulfur-iodine cycle and other thermochemical hydrogen production technologies, and accelerates the landing of renewable energy hydrogen production. The technical scheme of the present application is as follows:

[0012] On the one hand, the present application provides a sulfur-iodine cycle hydrogen purification method coupled with membrane separation and pressure swing adsorption, which includes the following steps:

[0013] S1: The decomposition product gas from the hydriodic acid decomposition unit enters the pretreatment unit, which condenses the gas, with water vapor condensed into liquid water, and higher solubility hydriodic acid and iodine vapor brought into the liquid phase;

[0014] S2: the pretreated mixed gas enters a membrane separation device, the membrane separation device uses a carbon molecular sieve membrane with a zirconium oxide modification layer on the surface as a separation material; when the mixed gas flows through the membrane separation device, hydrogen gas penetrates the membrane material to enter the permeation side, forming a preliminarily purified hydrogen-rich gas stream, and other gases that do not penetrate the membrane remain on the shell side of the membrane reactor and are discharged from the outlet;

[0015] S3: the hydrogen-rich gas stream from the membrane separation device enters a PSA purification device, the PSA purification device uses a gradient adsorbent bed to purify the hydrogen-rich gas stream, wherein the gradient adsorbent bed includes a modified activated carbon layer and a molecular sieve layer; the hydrogen-rich gas stream sequentially passes through the modified activated carbon layer and the molecular sieve layer, and HI and I2 are adsorbed by the gradient adsorbent bed to obtain high-purity hydrogen gas.

[0016] According to a preferred scheme of the present application, the carbon molecular sieve membrane with a zirconium oxide modification layer on the surface is prepared by the following method:

[0017] 1) Dissolve polyimide powder in a solvent to prepare a 10-20 wt% casting solution;

[0018] 2) immerse the porous alumina carrier in the casting solution, and form a polymer layer with a thickness of <1 μm on the porous alumina carrier by a pulling and dipping method;

[0019] 3) heat the polymer layer to a carbonization temperature at a heating rate of 1-5 ℃ / min in an inert atmosphere; then, after constant temperature for 1-2 hours, naturally cool to room temperature to obtain a carbon molecular sieve membrane material; slow heating is crucial, which can control thermal stress, avoid membrane cracking and curling, and allow ordered decomposition and reconstruction of polymer chains.

[0020] 4) soak the carbon molecular sieve membrane material in a 10-30 wt% dilute nitric acid solution for surface activation;

[0021] 5) dissolve a zirconium source in a solvent to form a stable sol; immerse the activated molecular sieve membrane material in the sol, and coat it by a pulling method; then, evaporate the solvent at room temperature, and the sol is converted into a gel on the membrane surface; perform heat treatment in an inert gas at 300-400 ℃ for 10-30 min to obtain a carbon molecular sieve membrane with a zirconium oxide modification layer on the surface.

[0022] According to a preferred scheme of the present application, the preparation method of the modified activated carbon in the modified activated carbon layer includes:

[0023] The triethylamine solution is dropped onto dry activated carbon, ensuring that the triethylamine solution is completely absorbed by the activated carbon; the obtained activated carbon is sealed and aged for 12-24 hours; the aged activated carbon is subjected to programmed temperature drying: first dried at 60-80°C for 2-3 hours, then heated to 100-120°C for 3-4 hours, so as to promote the combination of triethylamine and surface functional groups; finally, the activated carbon after programmed temperature drying is cooled to room temperature to obtain the modified activated carbon.

[0024] According to a preferred scheme of the present application, the molecular sieve layer is selected from 13X molecular sieve, the bulk density of the molecular sieve layer is 700-800 kg / m 3 , the filling height is 1.5-2.0 m, the particle size is 1.6-2.5 mm, and the specific surface area is 500-700 m 2 / g. The adsorption tower has a diameter of 0.3-0.4 m. The modified activated carbon layer has a filling height of 0.5-1.0 m, an adsorbent particle size of 2-3 mm, and a filling density of 400-550 kg / m 3 .

[0025] According to a preferred scheme of the present application, multiple PSA purification devices are used in S3 for adsorption-desorption alternately; wherein the adsorption process is carried out at an operating pressure of 1 MPa to 3 MPa, and the modified activated carbon layer removes iodine and most of the hydroiodic acid through chemical adsorption; the molecular sieve layer captures water and hydroiodic acid by using the surface polar active sites and the surface area thereof, and high-purity hydrogen gas is collected at the product gas outlet of the PSA purification device; when the impurity front approaches the bottom end of the gradient adsorbent bed, the gas inlet is stopped, and the desorption stage is switched to, so as to prevent the impurities from penetrating and polluting the product gas;

[0026] The desorption stage includes the following steps:

[0027] 1) Forward pressure reduction: after stopping the gas inlet, the PSA purification device is gradually reduced in pressure along the gas inlet direction, so that the gas in the device flows out along the gas inlet direction; the effluent of this step is mainly residual high-purity hydrogen gas; the gas is introduced into other PSA purification devices that have completed regeneration for pressure equalization and pressure increase;

[0028] 2) Reverse pressure reduction: the pressure in the PSA purification device is reduced to near atmospheric pressure, and the adsorbed impurities are desorbed; the flow direction of the desorbed gas is opposite to the adsorption direction, so as to avoid the pollution of the desorbed impurities to the high-purity adsorbent layer at the bottom of the tower; the high-concentration impurity gas is transported to the HI decomposition section for recycling;

[0029] 3) Flushing: high-purity product hydrogen gas is introduced from other PSA purification devices to flush the gradient adsorbent bed in a reverse flow; the flushing gas reduces the partial pressure of the impurities, and the residual impurities are completely removed by displacement and purging, so that the adsorbent bed is regenerated;

[0030] 4) Pressure boosting: receiving hydrogen gas discharged from other PSA purification devices in a forward pressure-reducing manner, and performing rapid energy-saving pressure equalization and pressure boosting to recover to the adsorption pressure and enter the adsorption stage; if the target adsorption pressure is not reached through pressure equalization and pressure boosting, the product gas or raw material gas is injected to smoothly rise to the adsorption pressure.

[0031] In another aspect, the present application provides a sulfur-iodine cycle hydrogen purification device for implementing the foregoing method, comprising:

[0032] a pretreatment unit receiving the decomposition product gas from the hydrogen iodide decomposition unit, condensing the gas to obtain an iodine-containing liquid and a preliminarily pretreated mixed gas;

[0033] a membrane separation device separated into a shell side and a tube side by a carbon molecular sieve membrane with a zirconium oxide modification layer on the surface, the shell side receiving the preliminarily pretreated mixed gas, wherein the hydrogen gas permeates the membrane material to enter the permeation side to form a preliminarily purified hydrogen-rich gas stream, and other gases that do not permeate the membrane remain on the shell side and are discharged from the outlet;

[0034] a PSA purification device having at least one gas phase inlet, one gas phase outlet, and one purge gas inlet; the gas phase inlet receives the hydrogen-rich gas stream from the tube side of the membrane separation device, and the HI and I2 therein are adsorbed; the PSA purification device uses a gradient adsorbent bed layer composed of a modified activated carbon layer and a molecular sieve layer to purify the hydrogen-rich gas stream, and the purified product gas is discharged from the gas phase outlet; the purge gas inlet is used for flushing and regeneration of the adsorbent in the desorption stage; there are multiple PSA purification devices, which are alternately used in the adsorption-desorption stages through mutual switching.

[0035] Compared with the prior art, the present application has the following beneficial effects:

[0036] (1) After the mixed gas generated in the hydrogen iodide decomposition unit is pretreated and condensed to remove water, it enters the membrane separation stage for preliminary purification. In this stage, a zirconium oxide modified carbon molecular sieve (CMS) membrane is used. Based on the molecular size exclusion effect, H2 molecules (kinetic diameter of 0.29 nm) can preferentially pass through the membrane pores to realize rapid permeation, while HI molecules (kinetic diameter of about 0.36 nm) and I2 molecules (kinetic diameter of about 0.55 nm) are effectively retained on the raw material side due to their size close to or larger than the membrane pore size, thereby realizing the preliminary separation between hydrogen and other impurity gases. A ZrO2 (zirconium oxide) modification layer is introduced on the surface of the membrane. This modification layer has strong Lewis acidity and can interact with I⁻ in the HI molecule to form local adsorption sites, enhancing the selective adsorption and barrier effect of HI. This physical and chemical synergistic mechanism significantly improves the separation efficiency of the membrane material for HI and other polar molecules, making the membrane separation process not only rely on size sieving, but also have certain chemical selectivity, improving the overall purification performance.

[0037] (2) The PSA purification device utilizes the difference in adsorption capacity of the gradient adsorbent bed at different pressures for each component in the gas mixture, and realizes the separation and purification of the target gas by periodically changing the system pressure. The PSA purification device of the present application adopts a gradient adsorbent bed design, which fully utilizes the characteristics of different adsorbent materials. The upper layer of the adsorption bed is filled with modified activated carbon material, which has a rich π electron system that can efficiently adsorb iodine molecules (I2) through π-π interaction to achieve selective capture of iodine vapor. The nitrogen atom on the tertiary amine has a lone pair of electrons, which can form a stable charge transfer complex with iodine molecules (I2) as an excellent electron donor and an electron acceptor; the lower layer is filled with molecular sieve, which mainly utilizes the hydrogen bond force between its polar surface and HI molecules to efficiently remove residual hydrogen iodide molecules. Through the synergistic effect of multiple layers of adsorbents, high-purity hydrogen gas with a purity of more than 99.99% can be obtained, meeting the application requirements of high-end industrial fields for ultra-pure hydrogen. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The flowchart of the sulfur-iodine cycle hydrogen purification method coupled with membrane separation and pressure swing adsorption of the present application.

[0039] Figure 2 The schematic diagram of the thermochemical sulfur-iodine cycle hydrogen production system containing the hydrogen purification method of the present application.

[0040] Figure 3 The SEM image of the zirconia-modified carbon molecular sieve membrane interface of the present application.

[0041] Figure 4 The schematic diagram of the zirconia-modified carbon molecular sieve membrane of the present application.

[0042] Figure 5 The schematic diagram of the membrane reactor equipment.

[0043] Figure 6 The schematic diagram of the PSA adsorption device equipment.

[0044] 1-Bunsent reaction column; 2-layered column; 3-hydrogen iodide phase storage tank; 4-distillation column; 5-heat exchanger; 6-hydrogen iodide decomposition column; 7-cryogenic equipment; 8-membrane separation equipment; 9-PSA purification device; 10-supplement water tank; 11-sulfuric acid phase buffer tank; 12-sulfuric acid purifier; 13-sulfuric acid storage tank; 14-multi-effect evaporator; 18-concentrated sulfuric acid storage tank; 19-bayonet type sulfuric acid decomposition column; 20-heat exchanger; 22-reboiler; 23-condenser; 24-heat pump; 25-supplement heater; 26-cooling water tank. DETAILED DESCRIPTION

[0045] Preferred embodiments of the present application will be described in more detail below. Although the following describes preferred embodiments of the present application, it is to be understood that the present application can be carried out in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this application will be thorough and complete, and fully convey the scope of the present application to those skilled in the art.

[0046] The present application mainly provides a hydrogen purification method and device coupled with membrane separation and pressure swing adsorption. There are many documents reporting the thermal chemical sulfur-iodine cycle for hydrogen production by water splitting. The technical solution provided by the present application is one part of the whole process of the thermal chemical sulfur-iodine cycle for hydrogen production by water splitting, and specifically belongs to the hydrogen separation and purification process. The present application does not limit other parts of the thermal chemical sulfur-iodine cycle for hydrogen production by water splitting (such as the Bunsen reaction and two-phase separation, the purification and concentration process of H2SO4 phase, and the HI decomposition process).

[0047] The technical solution of the present application can be combined into any existing thermal chemical sulfur-iodine cycle for hydrogen production by water splitting to replace the hydrogen separation and purification process (from the HI decomposition tower) in the existing process. For easy comparison, the purification process of the present application is shown in Figure 1 .

[0048] The hydrogen purification method coupled with membrane separation and pressure swing adsorption provided in the present embodiment can be implemented in the following steps:

[0049] (1) Hydrogen, iodine, hydrogen iodide, and water mixed gas generated by the hydrogen iodide decomposition tower is introduced into a cryogenic device, and under the condition of (-20℃~-5℃) and normal pressure, the water changes from gas to liquid, and at the same time, the hydrogen iodide and iodine in the mixed gas are adsorbed into the liquid phase, achieving the effect of crude hydrogen purification;

[0050] (2) The crude hydrogen is introduced into the membrane separation device, and the gaseous hydrogen flows into the device from the shell side. After contacting the carbon molecular sieve membrane with a zirconia modification layer on the surface, based on the molecular size exclusion effect, H2 molecules (kinetic diameter of 0.29 nm) can preferentially pass through the membrane pore to realize rapid permeation, while HI molecules (kinetic diameter of about 0.36 nm) and I2 molecules (kinetic diameter of about 0.55 nm) are effectively trapped on the raw material side due to their size being larger than the membrane pore size, thereby realizing the preliminary separation between hydrogen and other impurity gases. A ZrO2 (zirconia) modification layer is introduced on the surface of the membrane. The modification layer has strong Lewis acidity and can interact with I- in HI molecules to form local adsorption sites, thereby enhancing the selective adsorption and barrier effect of HI. The physical and chemical synergistic mechanism significantly improves the separation efficiency of the membrane material for polar molecules such as HI, so that the membrane separation process not only relies on size sieving but also has certain chemical selectivity, thereby improving the overall purification performance. Therefore, hydrogen can permeate through the membrane pores, while hydrogen iodide, iodine, and water molecules cannot pass through the membrane pores and flow out from the other side of the shell side, returning to the hydrogen iodide decomposition tower for further decomposition; and the hydrogen that has permeated through the membrane flows out under the driving of the inert gas in the tube layer and enters the PSA purification device.

[0051] (3) The hydrogen component separated by the membrane separation is introduced into the PSA purification device filled with a gradient adsorbent bed (composed of a modified activated carbon layer and a molecular sieve layer). The hydrogen-rich gas stream sequentially passes through the modified activated carbon layer and the molecular sieve layer from top to bottom to remove residual hydrogen iodide and iodine. When the impurity front approaches the bottom end of the gradient adsorbent bed, the gas supply is stopped, and desorption and regeneration are performed. The hydrogen iodide and iodine desorbed (desorbed) by the PSA return to the Bunsen reaction unit for recycling, thereby achieving near-zero loss of raw materials and improving the overall hydrogen production efficiency.

[0052] The process of the present application is designed by matching the membrane-PSA pressure. In the membrane separation stage, the zirconia-modified carbon molecular sieve membrane preferentially separates hydrogen at a medium-high pressure (2-4 MPa), significantly reducing the impurity load of the PSA unit. The permeated gas directly enters the PSA purification device, and the gradient adsorbent design (modified activated carbon + molecular sieve) realizes the graded removal of HI, I2, and H2O, thereby avoiding the purity fluctuation caused by the failure of a single adsorbent. The process realizes efficient purification in stages and achieves ultra-high purity hydrogen.

[0053] The sulfur-iodine cycle hydrogen purification device coupled with membrane separation and pressure swing adsorption provided in the embodiment mainly includes a cryogenic device, a membrane separation device, and a PSA purification device.

[0054] The cryogenic equipment serves as a pretreatment unit, and it has at least one gas phase inlet, one liquid phase outlet, and one gas phase outlet. The gas phase inlet is used to receive the mixed gas generated by the hydroiodic acid decomposition unit upstream of the thermochemical sulfur-iodine cycle. The components of the mixed gas are mainly hydrogen, iodine vapor, water vapor, and hydroiodic acid gas. The liquid phase outlet is used to discharge the iodine-containing liquid after cryogenic separation. The gas phase outlet is used to discharge the mixed gas after preliminary pretreatment.

[0055] Membrane separation equipment, such as Figure 5 As shown, it is divided into a shell side and a tube side by a membrane material. The shell side has at least one gas inlet and one gas outlet; the tube side has at least one gas outlet. The gas inlet in the shell side is used to receive the mixed gas generated by the cryogenic equipment, and the gas outlet is used to discharge the gas that has not permeated the membrane after membrane separation. The gas outlet in the tube side discharges purified hydrogen through the pipeline pressure difference.

[0056] PSA purification equipment, such as Figure 6 As shown, it has at least one gas phase inlet, one gas phase outlet, and one purge gas inlet. The gas phase inlet is used to receive purified hydrogen produced by the membrane separation device, the gas phase outlet is used to discharge high-purity hydrogen after pressure swing adsorption, and the purge gas inlet is used to purge impurities.

[0057] In the complete process system of the present invention, the gas outlet of the cryogenic equipment is connected to the membrane separation equipment, and the membrane separation equipment is connected to the PSA purification device.

[0058] In a specific embodiment of the present invention, the membrane material in S2 is a carbon molecular sieve membrane with a zirconium oxide modified layer on its surface, and its preparation method is as follows:

[0059] (1) Preparation of precursor polymer solution: Polyimide powder was dissolved in a solvent to prepare a uniform, bubble-free casting solution with a concentration of 10-20 wt%. The solution was filtered to remove impurity particles;

[0060] (2) Film formation: The diluted casting solution is dipped and impregnated to form an extremely thin (<1μm) polymer layer on the porous alumina carrier;

[0061] (3) Carbonization: Under an inert atmosphere, slowly heat to the carbonization temperature (500-800℃) at a low heating rate (1-5℃ / min). Slow heating is crucial to control thermal stress, prevent film cracking and curling, and allow the polymer chains to decompose and reconstruct in an orderly manner. After holding at the temperature for 1-2 hours, allow to cool naturally to room temperature.

[0062] (4) Surface pretreatment (activation): Soak the carbon molecular sieve membrane material in a 10-30 wt% dilute nitric acid solution for 30-60 min;

[0063] (5) ZrO2modification layer construction: zirconium source (such as zirconium oxychloride ZrOCl2·8H2O or zirconyl nitrate ZrO(NO3)2) is dissolved in a mixture of methanol / water (volume ratio 2-4:1). A small amount of nitric acid is added to inhibit hydrolysis and form a stable sol. The pretreated carbon molecular sieve membrane is immersed in the above sol for 5-10 min, and then coated by pulling method. Subsequently, the solvent is slowly evaporated at room temperature for 12-24 h, and the sol is converted to a gel on the membrane surface. Heat treatment is carried out at 300-400°C in an inert gas for 10-30 min to convert the ZrO2gel to a stable zirconia layer.

[0064] The hydrogen gas preliminarily purified by membrane separation enters a pressure swing adsorption (PSA) purification device. The PSA system adopts a gradient adsorbent bed design, fully utilizing the characteristics of different adsorbents. The upper layer of the adsorbent bed is filled with modified activated carbon, which has a rich π-electron system and can effectively adsorb iodine molecules (I2) through π-π interaction, realizing selective capture of iodine vapor. The lower layer is filled with molecular sieve, which mainly utilizes the hydrogen bond force between its polar surface and HI molecules to effectively remove residual hydroiodic acid molecules. Through the synergistic effect of multiple layers of adsorbents, high-purity hydrogen gas with a purity higher than 99.99% can be obtained, meeting the application requirements of high-end industrial fields for ultra-pure hydrogen.

[0065] The preparation method of the modified activated carbon in the modified activated carbon layer includes: (1) drying the coconut shell activated carbon in a drying box at 80-110°C for 2-4 hours to completely remove the internal adsorbed water and air; (2) slowly and uniformly dropping an equal volume of triethylamine solution onto the pretreated activated carbon in a fume hood under continuous stirring to ensure that the liquid is completely absorbed without visible liquid residue; (3) transferring the impregnated wet carbon into a sealed container and standing at room temperature for 12-24 hours; (4) transferring the aged activated carbon to a drying tray and placing it in a drying box. Programmed temperature drying is used, drying at 60-80°C for 2-3 hours, which mainly removes possible solvents and part of the physically adsorbed triethylamine; then slowly heating to 100-120°C and maintaining at this temperature for 3-4 hours. The purpose of this process is to promote the weak bond interaction between triethylamine and the functional groups such as hydroxyl groups on the surface of activated carbon, thereby significantly reducing its volatility and improving the stability of the product, preventing loss in subsequent use. (5) After drying, turn off the heating and cool the drying box to room temperature. Immediately pack the product into a sealed bag or sealed barrel to prevent adsorption of water and other impurities from the air.

[0066] For the molecular sieve layer, the present application can select 13X molecular sieve. The packing density of the molecular sieve layer is 700-800 kg / m 3 , the packing height is 1.5-2.0 m, the particle size is 1.6-2.5 mm, and the specific surface area is 500-700 m2 / g. The adsorption tower has a diameter of 0.3-0.4 m.

[0067] In the embodiment of the present application, multiple PSA purification devices (absorption towers filled with gradient adsorbent beds) are used for the alternate use of adsorption and desorption, i.e., the PSA purification devices are regenerated by desorption after being saturated by adsorption; and when part of the PSA purification devices are used for adsorption, the other part of the PSA purification devices are used for desorption; the desorption regeneration is realized by rapid pressure reduction and other processes, so that the adsorbent is regenerated efficiently. The desorption gas can be recycled, so that the material closed-circuit circulation and resource efficient recovery are realized.

[0068] In a specific embodiment of the present application, the adsorption process is carried out at an operating pressure of 1 MPa to 3 MPa, the modified activated carbon layer removes iodine and most of the hydroiodic acid by chemical adsorption; the molecular sieve layer captures water and hydroiodic acid by using the surface polarity active sites and its surface area, and high-purity hydrogen gas is collected at the product gas outlet of the PSA purification device; when the impurity front approaches the bottom end of the gradient adsorbent bed, the gas inlet is stopped, and the desorption stage is switched to prevent the impurities from penetrating and polluting the product gas;

[0069] The desorption stage of the present application includes the following steps:

[0070] 1) Forward pressure reduction: after stopping the gas inlet, the PSA purification device is gradually reduced in pressure along the gas inlet direction (adsorption direction), so that the gas in the device flows out along the gas inlet direction; the effluent of this step is mainly residual high-purity hydrogen gas; the gas is introduced into other PSA purification devices that have been regenerated for pressure equalization;

[0071] 2) Reverse pressure reduction: the pressure in the PSA purification device is reduced to near atmospheric pressure, and a large amount of adsorbed impurities are desorbed; the desorption gas flows in the opposite direction to the adsorption direction, so as to avoid the desorbed impurities from polluting the high-purity adsorbent layer at the bottom of the tower; the high-concentration impurity gas is transported to the HI decomposition section for recycling;

[0072] 3) Flushing: high-purity product hydrogen gas is introduced from other PSA purification devices to flush the gradient adsorbent bed in a reverse flow (from the bottom in and the top out); the flushing gas reduces the partial pressure of the impurities, and the residual impurities are completely removed by displacement and purging, so that the adsorbent bed is regenerated;

[0073] 4) Pressure increase: the hydrogen gas discharged from other PSA purification devices by forward pressure reduction is received, and rapid energy-saving pressure equalization is carried out to restore the adsorption pressure and enter the adsorption stage; if the target adsorption pressure is not reached by pressure equalization, the adsorption pressure is smoothly increased by injecting product gas or raw material gas.

[0074] In the control of the pressure change rate, the pressure change rate of the forward decompression step is 10-40 kPa / s, the pressure change rate of the reverse decompression step is 5-20 kPa / s, the pressure change rate of the pressure equalization and pressure increase step is 5-25 kPa / s, and the pressure change rate of the smooth pressure increase step is 2-10 kPa / s.

[0075] The technical solution of the present application can be combined into any existing thermochemical sulfur-iodine cycle water decomposition hydrogen production whole process to replace the existing hydrogen gas (from the HI decomposition tower) separation and purification process. A thermochemical sulfur-iodine cycle hydrogen production whole process using the method of the present application is introduced below, which is a typical application case of the present application, as shown in Figure 2 The specific process is as follows:

[0076] Sulfur dioxide, iodine and water in the Bunsen reaction tower 1 react to generate hydroiodic acid and sulfuric acid. The generated two mixed acid solutions are layered in the layering tower 2, the lower layer hydroiodic acid phase solution is passed into the hydroiodic acid phase storage tank 3, and the upper layer sulfuric acid solution is passed into the sulfuric acid phase buffer tank 11. The operating temperature of the Bunsen reaction tower 1 is 80-130℃, and the pressure is 0-5atm. The temperature in the layering tower 2 is 80-130℃, and the pressure is 0-5atm.

[0077] The pressure in the sulfuric acid purifier 12 is adjusted to 0-5 atm by falling film evaporation, and the reverse reaction 2HI + H2SO4 = SO2 + I2 + 2H2O occurs to remove the HI impurities in the sulfuric acid phase. The generated sulfur dioxide and iodine vapor is discharged from the top of the sulfuric acid purifier 12 and mixed with water vapor in the multi-effect evaporator 14 and introduced into the Bunsen reaction tower 1. The purified sulfuric acid is concentrated from 50%-55% to 75%-85% by the multi-effect evaporator, and the liquid sulfuric acid is transported to the bayonet type sulfuric acid decomposition tower 19 by a pump. High temperature helium gas at 4 MPa-4.5 MPa and 900 ℃-950 ℃ is used as a heat source to heat the bayonet type sulfuric acid reactor. The full fluorinated ether rubber ring is used at the tube plate of the bayonet type sulfuric acid decomposition tower 19, and the tube plate material is PTFE material. Since the top of the bayonet type sulfuric acid reactor is high temperature helium gas, the heat is transferred downward along the silicon carbide tube. Among the current corrosion resistant materials, the full fluorinated ether rubber and PTFE tube plate cannot be used stably above 200 ℃ for a long time, and the metal material cannot resist sulfuric acid corrosion, and there is a risk of leakage during long-term use. Therefore, a sulfuric acid circulation system is added at the tube plate to cool the sulfuric acid and maintain its temperature below 180 ℃. The reaction H2SO4 = SO3 + H2O occurs in the tube of the bayonet type sulfuric acid reactor, and the generated sulfur trioxide and water vapor rise in the tube layer, and then settle in the gap between the silicon carbide tubes filled with sulfur trioxide decomposition catalyst at the top of the reactor, and the reaction 2SO3 = 2SO2 + O2 occurs. The generated sulfur dioxide and oxygen flow downward along the tube gap to heat the continuously evaporated and decomposed sulfuric acid in the tube from bottom to top, and then the sulfur dioxide and oxygen flow out of the bayonet type sulfuric acid reactor, are heated and returned to the Bunsen reaction tower 1 to participate in the circulating reaction, and the oxygen is discharged from the top of the sulfuric acid phase buffer tank 11.

[0078] The hydrogen iodide phase solution at the bottom of the layered column 2 is fed into the hydrogen iodide phase storage tank 3, and then the separation of hydrogen iodide, iodine and water is carried out at 80-160°C and 0-5 atm in the rectification column 4, and the saturated hydrogen iodide solution dissolving iodine is refluxed to the Bunsen reaction column 1 at the bottom of the rectification column 4. Pure hydrogen iodide gas is obtained at the top of the column, and then the temperature of the gas is heated to 450-550°C in the heat exchanger 5 at a pressure of 0-3 atm. The preheated hydrogen iodide gas is decomposed into hydrogen and iodine vapor in the hydrogen iodide decomposition column 6, and the hydrogen, iodine vapor and unreacted hydrogen iodide are condensed in the cryogenic device 7 to remove excess water, and are subjected to crude purification. The iodine-containing hydrogen iodide solution obtained by condensation is refluxed to the Bunsen reaction column 1, and the purified hydrogen is fed into the membrane separation device 8. The shell side pressure in the membrane separation device is 2-4 MPa, and the tube side pressure is 1-1.5 MPa. The hydrogen gas flows into the tube side of the zirconia-modified carbon molecular sieve membrane from the shell side, and the molecules with a larger diameter cannot pass through the membrane material and flow out from the other side of the shell side. The hydrogen gas in the tube side of the membrane separation device flows into the PSA purification device 9, and the modified activated carbon and molecular sieve preloaded therein selectively adsorb specific gases by adjusting different pressures. The modified activated carbon first adsorbs iodine vapor in the mixed gas, and the molecular sieve adsorbs the remaining hydrogen iodide into the multi-stage pore structure to achieve the purpose of purifying hydrogen. The purified hydrogen gas flows out of the PSA purification device 9, and the adsorbed iodine vapor and hydrogen iodide gas are desorbed after desorption and then refluxed to the Bunsen reaction column 1.

[0079] Example 1

[0080] The initial temperature in the Bunsen reaction column 1 is 115°C, and the pressure is 1 atm. The amount of feed in the column is 2.6 mol of SO2, 13.5 mol of I2, 3.6 mol of HI and 25.2 mol of water. The Bunsen reaction occurs, and SO2+I2+2H2O=2HI+H2SO4, and sulfuric acid and hydrogen iodide are generated. The obtained mixed acid solution is fed into the layered column 2. After the mixed acid solution is left to stand for 15 min, the upper sulfuric acid phase solution and the lower hydrogen iodide phase solution containing a large amount of iodine are obtained. The sulfuric acid phase solution is discharged from the top of the layered column by a pump and fed into the sulfuric acid phase buffer tank 11, and the hydrogen iodide phase is fed into the hydrogen iodide phase storage tank 3.

[0081] After the two-phase separation, the sulfuric acid phase contains a small amount of hydroiodic acid and iodine impurities. The composition of the H2SO4 phase is H2SO4 1.82 mol, HI 0.21 mol, I2 0.04 mol, and H2O 10.01 mol. The H2SO4 phase enters the sulfuric acid purifier 12, and the pressure is adjusted to 0.1 atm by a vacuum pump. The HI impurities in the H2SO4 phase are removed by the reverse reaction 2HI + H2SO4 = SO2 + I2 + 2H2O through evaporation under reduced pressure. The generated SO2 and I2 vapor is discharged from the top of the sulfuric acid purifier 12 and mixed with water vapor in the multi-effect evaporator 14, and then introduced into the Bunsen reaction tower 1. The purified H2SO4 is concentrated from 55% to 80% by the multi-effect evaporator. The liquid H2SO4 is transported to the bayonet-type sulfuric acid decomposition tower 19 by a pump. The bayonet-type sulfuric acid reactor is heated using high-temperature helium gas at 4 MPa and 950°C. The tube sheet of the bayonet-type sulfuric acid reactor is made of PTFE material and is sealed with a perfluoroether rubber ring. Since the top of the bayonet-type sulfuric acid reactor is high-temperature helium gas, the heat is transferred downward along the silicon carbide tube. However, the perfluoroether rubber and PTFE tube sheet cannot be used stably above 200°C, and metal materials cannot resist sulfuric acid corrosion, which may leak over a long period of time. Therefore, a sulfuric acid circulation system is added at the tube sheet to cool the sulfuric acid and maintain its temperature below 180°C. The H2SO4 = SO3 + H2O reaction occurs in the tube of the bayonet-type sulfuric acid reactor. The generated SO3 and H2O vapor rise in the tube and then settle into the gap between the silicon carbide tubes filled with SO3 decomposition catalyst at the top of the reactor. The 2SO3 = 2SO2 + O2 reaction occurs in the gap between the tubes, and the generated SO2 and O2 flow downward along the gap to heat the continuously evaporated and decomposed H2SO4 in the tube from bottom to top. Then, the SO2 and O2 flow out of the bayonet-type sulfuric acid reactor, are heated, and return to the 1-Bunsen tower to participate in the cyclic reaction. The O2 is discharged from the top of the H2SO4 buffer tank 11.

[0082] The HI phase solution at the bottom of the separation tower 2 enters the HI phase storage tank 3, and then the HI, I2, and H2O are separated in the rectification tower 4 at 120°C and 1 atm. The saturated HI solution containing dissolved I2 is refluxed to the Bunsen tower at the bottom of the rectification tower. Pure HI gas is obtained at the top of the tower, and then the temperature of the gas is heated to 450°C in the heat exchanger 5 at 1 atm. The preheated HI gas is decomposed into H2 and I2 vapor in the HI decomposition tower 6. The H2, I2 vapor, and unreacted HI are condensed in the cryogenic equipment 7 to remove excess water, and then the resulting HI solution containing I2 is refluxed to the Bunsen reaction tower 1. The purified H2 enters the membrane separation equipment 8, and the shell side pressure in the membrane separation equipment is 3 MPa, and the tube side pressure is 1.3 MPa.

[0083] The zirconia-modified carbon molecular sieve membrane is prepared by the following method: polyimide powder is dissolved in a solvent to prepare a casting solution with uniformity, no bubbles and a concentration of 15 wt%. The solution is filtered to remove impurity particles; the diluted casting solution is formed into an extremely thin (0.5 μm) polymer layer on a porous alumina carrier by a pulling and dipping method; and the temperature is slowly increased to 600°C at a rate of 2°C / min under an inert atmosphere. After constant temperature for 2 hours, the temperature is naturally cooled to room temperature; the carbon molecular sieve membrane material is soaked in a 20 wt% dilute nitric acid solution for 60 min; and zirconium nitrate oxide is dissolved in a mixed solvent of methanol / water (volume ratio 2:1). A small amount of nitric acid is added to inhibit hydrolysis, and a stable sol is formed. The pretreated carbon molecular sieve membrane is immersed in the above sol for 10 min, and then coated by a pulling method. Subsequently, the solvent is slowly evaporated at room temperature for 12 h, and the sol is converted into a gel on the membrane surface. Heat treatment is performed at 300°C for 30 min in an inert gas to convert the ZrO2 gel into a stable zirconia layer. Figure 3 SEM image of the interface of the obtained zirconia-modified carbon molecular sieve membrane, Figure 4 Structure schematic diagram of the zirconia-modified carbon molecular sieve membrane.

[0084] Hydrogen flows into the membrane separation device tube from the zirconia-modified carbon molecular sieve membrane, and molecules with a larger diameter cannot permeate the membrane material and flow out from the other side of the shell passage. The hydrogen is mixed with the material at the feed inlet of the rectifying tower 4, and then flows into the rectifying tower 4. Subsequently, the 2HI = H2 + I2 reaction occurs in the hydrogen iodide decomposition tower 6. The hydrogen in the membrane separation tube flows into the PSA purification device 9, and specific gases are selectively adsorbed by the pre-packed modified activated carbon and molecular sieve under different pressure conditions. The modified activated carbon layer has a height of 0.5 meters, the adsorbent particle size is 2.5 mm, and the packing density is 450 kg / m 3 . The 13X molecular sieve has a bulk density of 700 kg / m 3 , a packing height of 1.5 meters, a particle size of 2.5 mm, and a specific surface area of 700 m 2 / g. The adsorption tower has a diameter of 0.4 m.

[0085] The modified activated carbon is prepared by the following method: the coconut shell activated carbon is dried in a drying box at 110°C for 4 hours; an equal volume of triethylamine solution is slowly and uniformly added to the pretreated activated carbon by an equal volume immersion method; the immersed wet carbon is transferred into a sealed container and left to stand at room temperature for 24 hours; and the aged activated carbon is placed in a drying box and dried at 80°C for 3 hours. Subsequently, the temperature is slowly increased to 120°C, and the temperature is maintained at 120°C for 4 hours. The activated carbon is cooled to room temperature in the drying box.

[0086] The modified activated carbon first adsorbs iodine vapor and hydroiodic acid in the mixed gas, and the molecular sieve adsorbs the remaining hydroiodic acid into the multi-stage pore structure to achieve the purpose of purifying hydrogen. The purified hydrogen flows out of the PSA purification device under the conditions of forward pressure reduction of 20 kPa / s, reverse pressure reduction of 12 kPa / s, uniform pressure increase of 15 kPa / s, and pressure increase of 6 kPa / s. After the adsorbed iodine vapor and hydroiodic acid gas are desorbed, they flow back to the 1-Bunsen tower. The purity of the separated hydrogen reaches 99.99%, and the yield is 95.64%.

[0087] Example 2

[0088] The same process as Example 1 is used, except that the carbon molecular sieve membrane carbonization temperature is 500°C, and the zirconium-containing gel after pulling and impregnation is calcined at 350°C. The purity of the separated hydrogen reaches 99.99%, and the yield is 93.25%.

[0089] Example 3

[0090] The same process as Example 1 is used, except that the carbon molecular sieve membrane carbonization rate is 5°C / min. The purity of the separated hydrogen reaches 99.99%, and the yield is 93.17%.

[0091] Comparative Example 1

[0092] The same process as Example 1 is used, except that in the preparation process of the carbon molecular sieve membrane, the zirconium-containing gel after pulling and impregnation is calcined at 700°C (much higher than the carbonization temperature of 600°C of the carbon molecular sieve membrane), which causes the compactness of the carbon molecular sieve membrane to be destroyed, with some cracking. The purity of the separated hydrogen reaches 45.32%, and the yield is 26.35%.

[0093] Comparative Example 2

[0094] The same process as Example 1 is used, except that the activated carbon layer in the PSA purification device uses unmodified coconut shell activated carbon (coconut shell activated carbon layer + molecular sieve layer in Example 1, coconut shell activated carbon layer loading height is 0.5 meters, adsorbent particle size is 2.5mm, loading density is 450kg / m 3 ), the purity of the separated hydrogen reaches 85.32%, and the yield is 80.26%.

[0095] Comparative Example 3

[0096] The same process as Example 1 is used, except that the carbon molecular sieve membrane is not modified with zirconia (the preparation of the precursor polymer solution of the carbon molecular sieve membrane in Comparative Example 3, film formation, carbonization, and surface pretreatment steps are the same as in Example 1, but there is no zirconia modification step), the purity of the separated hydrogen reaches 87.32%, and the yield is 82.26%.

[0097] Comparative Example 4

[0098] The same process as Example 1 was adopted, except that the temperature rising rate was 10℃ / min when carbonizing the carbon molecular sieve membrane, the purity of hydrogen after separation reached 62.32%, and the yield was 65.25%.

[0099] Comparative Example 5

[0100] The same process as Example 1 was adopted, except that the PSA device was only filled with a modified activated carbon layer (the total height of the modified activated carbon layer was 2 meters, the adsorbent particle size was 2.5mm, and the filling density was 450kg / m 3 ), the purity of hydrogen after separation reached 72.32%, and the yield was 67.75%.

[0101] Comparative Example 6

[0102] The same process as Example 1 was adopted, except that the PSA device was only filled with a molecular sieve layer (the molecular sieve layer used 13X molecular sieve, the bulk density of the 13X molecular sieve was 700kg / m 3 , the total height of the filling was 2 meters, the particle size was 2.5mm, and the specific surface area was 700m 2 / g), the purity of hydrogen after separation reached 75.32%, and the yield was 63.93%.

[0103] From the above results, it can be seen that, by coupling the deep cooling pretreatment, the membrane separation and the pressure swing adsorption, the carbon molecular sieve membrane with a zirconium oxide modified layer on the surface is used as the separation material in the membrane separation setting, and the gradient adsorbent design (modified activated carbon layer + molecular sieve layer) is used in the pressure swing adsorption purification device, so that the problems of low purity and low yield in the sulfur-iodine cycle hydrogen purification are solved, and an efficient purification scheme is provided for the sulfur-iodine cycle and other thermochemical hydrogen production technologies.

[0104] The above has described various embodiments of the present application, and the above description is exemplary, is not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for purifying hydrogen gas using a sulfur-iodine cycle coupled with membrane separation and pressure swing adsorption, characterized in that, Includes the following steps: S1: The decomposition product gas from the hydroiodic acid decomposition unit enters the pretreatment unit, where the gas is condensed, and water vapor is condensed into liquid water, while hydroiodic acid and iodine vapor with high solubility are introduced into the liquid phase. S2: The pretreated mixed gas enters the membrane separation equipment, which uses a carbon molecular sieve membrane with a zirconium oxide modified layer on its surface as the separation material. When the mixed gas flows through the membrane separation equipment, hydrogen permeates through the membrane material into the permeate side, forming a pre-purified hydrogen-rich gas flow. Other gases that do not permeate through the membrane remain on the shell side of the membrane reactor and are discharged from the outlet. The carbon molecular sieve membrane with a zirconium oxide modified layer on its surface was prepared by the following method: 1) Dissolve polyimide powder in a solvent to prepare a casting solution of 10-20 wt%; 2) The porous alumina carrier is immersed in the casting solution, and a polymer layer with a thickness of <1μm is formed on the porous alumina carrier by the dip-coating method; 3) Under an inert atmosphere, the polymer layer is heated to the carbonization temperature at a heating rate of 1-5℃ / min; then held at the temperature for 1-2 hours and allowed to cool naturally to room temperature to obtain the carbon molecular sieve membrane material. 4) Surface activation of carbon molecular sieve membrane material by soaking it in a 10-30wt% dilute nitric acid solution; 5) Dissolve the zirconium source in a solvent to form a stable sol; immerse the activated molecular sieve membrane material in the sol and coat it using the dip coating method; then allow the solvent to evaporate at room temperature, and the sol transforms into a gel on the membrane surface; heat-treat it in an inert gas at 300-400℃ for 10-30 min to obtain a carbon molecular sieve membrane with a zirconium oxide modified layer on the surface. S3: The hydrogen-rich gas flow from the membrane separation equipment enters the PSA purification unit. The PSA purification unit uses a gradient adsorbent bed to purify the hydrogen-rich gas flow, which includes a modified activated carbon layer and a molecular sieve layer. The hydrogen-rich gas flow passes through the modified activated carbon layer and the molecular sieve layer in sequence. HI and I2 are adsorbed by the gradient adsorbent bed to obtain high-purity hydrogen. The method for preparing the modified activated carbon in the modified activated carbon layer includes: adding a triethylamine solution dropwise onto the dry activated carbon to ensure that the triethylamine solution is completely absorbed by the activated carbon; The obtained activated carbon was sealed and left to stand for 12-24 hours for aging. The aged activated carbon was then subjected to programmed temperature drying: first, it was dried at 60-80℃ for 2-3 hours, then the temperature was increased to 100-120℃ and maintained for 3-4 hours to promote the combination of triethylamine with surface functional groups. Finally, the activated carbon after programmed temperature drying was cooled to room temperature to obtain modified activated carbon.

2. The method according to claim 1, characterized in that, The components of the decomposition product gas in S1 include hydrogen, iodine vapor, incompletely decomposed hydroiodic acid, and water vapor generated during the reaction process; the pretreatment unit is a cryogenic device.

3. The method according to claim 1, characterized in that, The condensation temperature of the pretreatment unit is -20℃ to -5℃.

4. The method according to claim 1, characterized in that, In the S2 membrane separation unit, the membrane material separates the membrane into a shell side and a tube side. The mixed gas enters from the shell side, while the hydrogen-rich gas flows out from the tube side and enters the PSA purification unit.

5. The method according to claim 4, characterized in that, The shell-side pressure of the membrane separation equipment is 2-4 MPa, and the tube-side pressure is 1-1.5 MPa.

6. The method according to claim 1, characterized in that, S3 employs multiple PSA purification devices for alternating adsorption-desorption. The adsorption process is carried out at an operating pressure of 1 MPa to 3 MPa. The modified activated carbon layer removes iodine and most of hydroiodic acid through chemical adsorption. The molecular sieve layer uses its surface polar active sites and surface area to capture water and hydroiodic acid. High-purity hydrogen is collected at the product gas outlet of the PSA purification unit. When the impurity front approaches the bottom of the gradient adsorbent bed, the gas intake is stopped and the process switches to the desorption stage to prevent impurities from penetrating and contaminating the product gas. The desorption stage includes the following steps: Desorption 1) Forward depressurization: After the gas intake is stopped, the PSA purification unit gradually depressurizes along the gas intake direction, so that the gas in the unit flows out along the gas intake direction; the outflow of this step is mainly residual high-purity hydrogen; the desorbed gas is led to other PSA purification units that have completed regeneration for equalization and pressurization. 2) Reverse depressurization: The pressure inside the PSA purification unit is reduced to near atmospheric pressure, and the adsorbed impurities are desorbed; the desorbed gas flows in the opposite direction to the adsorption direction to avoid contamination of the high-purity adsorbent layer at the bottom of the tower by the desorbed impurities; the high-concentration impurity gas is transported to the HI decomposition section for recycling. 3) Flushing: High-purity product hydrogen is introduced from other PSA purification units and used to countercurrently purge the gradient adsorbent bed; the flushing gas reduces the partial pressure of impurities, and the residual impurities are thoroughly removed through displacement and purging, thus regenerating the adsorbent bed; 4) Pressure boosting: Receive hydrogen gas discharged from other PSA purification units in the forward depressurization direction, perform rapid and energy-saving pressure equalization and pressure boosting to restore the adsorption pressure and enter the adsorption stage; if the target adsorption pressure is not reached by pressure equalization and pressure boosting, the adsorption pressure is steadily increased by injecting product gas or raw material gas.

7. The method according to claim 6, characterized in that, The pressure change rate in the forward depressurization step is 10 kPa / s to 40 kPa / s, the pressure change rate in the reverse depressurization step is 5 to 20 kPa / s, the pressure change rate in the equalization and pressure increase step is 5 to 25 kPa / s, and the pressure change rate in the steady pressure increase step is 2 to 10 kPa / s.

8. A sulfur-iodine cycle hydrogen purification apparatus for implementing the method of any one of claims 1-7, characterized in that, include: The pretreatment unit receives the decomposition product gas from the hydroiodic acid decomposition unit, condenses the gas, and obtains an iodine-containing liquid and a pre-treated mixed gas. The membrane separation equipment is divided into a shell side and a tube side by a carbon molecular sieve membrane with a zirconium oxide-modified layer on its surface. The shell side receives the pre-treated mixed gas, in which hydrogen permeates through the membrane material into the permeate side, forming a pre-purified hydrogen-rich gas flow. Other gases that do not permeate through the membrane are retained on the shell side and discharged from the outlet. The PSA purification unit has at least one gas phase inlet, one gas phase outlet, and one purge gas inlet. The gas phase inlet receives the hydrogen-rich gas flow from the tubular side of the membrane separation equipment and adsorbs HI and I2 therein. The PSA purification unit uses a gradient adsorbent bed composed of a modified activated carbon layer and a molecular sieve layer to purify the hydrogen-rich gas flow. The purified product gas is produced from the gas phase outlet. The purge gas inlet is used for rinsing and regenerating the adsorbent during the desorption stage. There are multiple PSA purification units, which are used alternately for adsorption-desorption by switching between them.

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