Membrane separation and pressure swing adsorption coupled sulfur-iodine circulating hydrogen purification method and device

Abstract

The invention discloses a sulfur-iodine circulating hydrogen purification method and device coupled with membrane separation and pressure swing adsorption. The method comprises the following steps: feeding decomposition product gas from a hydroiodic acid decomposition unit into a pretreatment unit for condensation and water removal to realize primary separation; the mixed gas obtained after primary separation enters membrane separation equipment, the membrane separation equipment achieves primary separation between hydrogen and other impurities based on a molecular size exclusion mechanism, hydrogen in the mixed gas enters a permeation side through a membrane material, and hydrogen-rich gas flow obtained after primary purification is formed; the hydrogen-rich gas flow enters a PSA purification device, the PSA purification device adopts a gradient adsorbent bed layer to purify the hydrogen-rich gas flow, and high-purity hydrogen is obtained. According to the invention, the problems of low purity and low yield in sulfur-iodine cycle hydrogen purification are solved, and an efficient purification scheme is provided for thermochemical hydrogen production technologies such as sulfur-iodine cycle and the like.

Description

Technical Field

[0001] This invention relates to thermochemical sulfur-iodine cycle (SI cycle) hydrogen production technology, specifically to a method and apparatus for purifying hydrogen using a sulfur-iodine cycle coupled with membrane separation and pressure swing adsorption, which is used to efficiently remove components such as HI, I2, and H2O, thereby improving hydrogen purity and recovery rate. Background Technology

[0002] Hydrogen energy, as a highly efficient renewable energy source, has garnered widespread attention and research globally due to its high efficiency, cleanliness, environmental friendliness, and sustainability. Currently, hydrogen production primarily originates from natural gas (48%), petroleum (30%), coal (18%), and water electrolysis (4%). Methods for producing hydrogen from fossil fuels mainly include hydrocarbon reforming and pyrolysis. These methods offer advantages such as mature technology, considerable output, and low cost. However, considering the limited reserves of fossil fuels, the need for product purification during hydrogen production, and the unavoidable carbon emissions, this approach struggles to meet future low-carbon development goals and is unsuitable as a primary hydrogen production method in the long term. On the other hand, water electrolysis uses electricity to decompose water, converting electrical energy into chemical energy stored in hydrogen and oxygen. This method not only produces hydrogen with high purity (over 99.8%) but also boasts mature technology and a wide range of applications. However, its high power consumption and low energy conversion efficiency limit its widespread use. Therefore, in order to achieve more sustainable and environmentally friendly hydrogen production, it is particularly important to explore new technologies and methods to reduce energy consumption and improve conversion efficiency.

[0003] Among numerous hydrogen production technologies, thermochemical sulfur-iodine cycle water splitting 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 intermediates at relatively mild reaction temperatures, ultimately producing hydrogen (H2) and oxygen (O2). Compared to direct water splitting, each step in the thermochemical sulfur-iodine cycle requires relatively lower temperatures, making it widely compatible with various heat sources, such as solar and nuclear energy. Notably, the thermochemical sulfur-iodine cycle utilizes 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. Furthermore, because this technology can operate under fully fluidized conditions, it is well-suited for scale-up production and continuous operation. Especially noteworthy is the use of sulfuric acid decomposition as an endothermic process in the high-temperature stage, which allows for excellent integration with high-temperature gas-cooled reactors. Compared to other hydrogen production methods, the sulfur-iodine cycle demonstrates greater feasibility in terms of technology and economics, and is widely recognized as one of the most promising hydrogen production methods in the field of thermochemical water splitting. This method not only improves hydrogen production efficiency but also provides new ideas for sustainable energy solutions. Thermochemical sulfur-iodine cycle water splitting for hydrogen production consists of the following three 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 water splitting for hydrogen production is considered a potential technology for large-scale hydrogen production due to its high efficiency and zero carbon dioxide emissions. The hydroiodic acid decomposition unit is a crucial component ensuring the continuous and stable operation of the entire system. At high temperatures of 400-500℃, hydroiodic acid decomposes into hydrogen and iodine vapor through catalysis; however, due to thermodynamic equilibrium limitations, the decomposition efficiency is typically less than 23%. Therefore, after the catalytic reaction, the system still contains various gaseous components, including hydroiodic acid, iodine, water vapor, and hydrogen. Since the system is a closed-loop design, effective recovery of iodine and hydroiodic acid after the reaction is essential to ensure process stability and material recycling. Therefore, how to efficiently separate and purify these gaseous components becomes a key issue affecting the overall operating efficiency and technical feasibility of the unit.

[0008] CN 114195094 B discloses a complete process and apparatus for thermochemical sulfur-iodine cycle hydrogen production. In this process, the high-temperature gas mixture from the decomposition of an HI (hydrogen iodine) column exits from the top of the column and enters a condenser. Iodine-containing liquid is sprayed from the top of the condenser, where it encounters the high-temperature gas from the HI decomposition column. A portion of the gas is recycled back to the top of the column for spraying, while the remainder enters a Bunsen reaction premixing tank. Hydrogen gas exits from the top of the column and enters a NaOH washing tank. In this method, the brief contact between the mixed gas produced in the decomposition column and the iodine-containing liquid in the condenser cannot guarantee that all hydroiodic acid and iodine are dissolved in the sprayed liquid. Furthermore, due to mist entrainment, the mixed gas exiting from the top of the condenser contains four gases: iodine, hydroiodic acid, hydrogen, and water. The method also mentions the subsequent neutralization of hydroiodic acid with sodium hydroxide solution, dissolving the iodine in the liquid. However, this method results in iodine loss and the production of sodium iodide as a byproduct, requiring additional iodine to be added to the system. This contradicts the original intention of thermochemical sulfur-iodine cycle hydrogen production, which is that the only medium flowing into the system is water, and the products are hydrogen and oxygen.

[0009] CN116443814B proposes a method and system for iodine recovery and recycling in thermochemical sulfur-iodine cycle hydrogen production. This method involves sending a mixed gas containing H2, HI, I2, and H2O from an HI decomposition tower to a condenser for washing. A portion of the liquid mixture obtained at the bottom of the tower is sent to the top for spray washing of the mixed gas. The H2-containing gas after condensation is sent to a washing tank, where H2O2 solution is periodically added. H2O2 oxidizes the HI in the gas to I2, and the resulting hydrogen gas leaves the washing tank as the product gas. The material in the washing tank is then transported to a microporous filter, where iodine solids are deposited on the filter plates. The H2O2 solution passes through the filter plates and returns to the washing tank. The liquid mixture from the bottom of the condenser is used to flush and dissolve the iodine solids deposited on the microporous filter plates. The resulting iodine-containing liquid leaves the microporous filter, is oxidized in an oxidation tank, and then sent to the Bunsen reactor. However, in actual operation, hydrogen peroxide decomposes into water and oxygen, producing oxygen in a hydrogen atmosphere, posing an explosion risk and making the method unusable in practical applications. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and apparatus for purifying hydrogen gas by coupling membrane separation and pressure swing adsorption in a sulfur-iodine cycle.

[0011] This invention, from the perspective of synergistic enhancement of molecular sieving and pressure swing adsorption (PSA), optimizes key factors such as membrane material composition and structural design, adsorbent corrosion resistance modification, and process coupling control. It employs a carbon molecular sieve membrane with a zirconium oxide-modified surface to preferentially separate hydrogen, significantly reducing the impurity load of the PSA purification unit. The PSA purification unit uses a gradient adsorbent design (modified activated carbon + molecular sieve) to achieve the staged removal of HI, I2, and H2O, avoiding purity fluctuations caused by the failure of a single adsorbent. This invention solves the problems of low purity and low yield in hydrogen purification using the sulfur-iodine cycle, providing an efficient purification solution for thermochemical hydrogen production technologies such as the sulfur-iodine cycle, and accelerating the implementation of renewable energy hydrogen production. The technical solution of this invention is as follows:

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

[0013] 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.

[0014] 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.

[0015] S3: The hydrogen-rich gas stream 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 stream, which includes a modified activated carbon layer and a molecular sieve layer. The hydrogen-rich gas stream 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.

[0016] According to a preferred embodiment of the present invention, the carbon molecular sieve membrane with a zirconium oxide modified layer on its surface is prepared by the following method:

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

[0018] 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;

[0019] 3) Under an inert atmosphere, heat the polymer layer to the carbonization temperature at a heating rate of 1-5℃ / min; then hold the temperature for 1-2 hours and allow it to cool naturally to room temperature to obtain the carbon molecular sieve membrane material; slow heating is crucial to control thermal stress, prevent membrane cracking and curling, and allow the polymer chains to decompose and reconstruct in an orderly manner.

[0020] 4) Surface activation of carbon molecular sieve membrane material by soaking it in a 10-30wt% dilute nitric acid solution;

[0021] 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 minutes to obtain a carbon molecular sieve membrane with a zirconium oxide modified layer on the surface.

[0022] According to a preferred embodiment of the present invention, the method for preparing the modified activated carbon in the modified activated carbon layer includes:

[0023] Triethylamine solution is added dropwise to dry activated carbon, ensuring complete absorption by the activated carbon. The resulting activated carbon is sealed and left to stand for 12-24 hours for aging. The aged activated carbon is then subjected to programmed temperature drying: first, it is dried at 60-80℃ for 2-3 hours, then the temperature is 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 is cooled to room temperature to obtain modified activated carbon.

[0024] According to a preferred embodiment of the present invention, the molecular sieve layer is selected from 13X molecular sieves, and the bulk density of the molecular sieve layer is 700-800 kg / m³. 3 The filling height is 1.5-2.0m, the particle size is 1.6-2.5mm, and the specific surface area is 500-700m². 2 / g. Adsorption tower diameter 0.3-0.4m. Modified activated carbon layer packing height 0.5-1.0m, adsorbent particle size 2-3mm, packing density 400-550kg / m³. 3 .

[0025] According to a preferred embodiment of the present invention, in S3, multiple PSA purification devices are used alternately for adsorption-desorption; wherein, 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, and high-purity hydrogen is collected at the product gas outlet of the PSA purification device. 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;

[0026] The desorption phase includes the following steps:

[0027] 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 product in this step is mainly residual high-purity hydrogen; this gas is led to other PSA purification units that have completed regeneration for pressure equalization and boosting.

[0028] 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.

[0029] 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;

[0030] 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.

[0031] On the other hand, the present invention provides a sulfur-iodine cycle hydrogen purification apparatus for implementing the aforementioned method, comprising:

[0032] 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.

[0033] 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.

[0034] 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.

[0035] Compared with the prior art, the beneficial effects of the present invention include:

[0036] (1) After pretreatment and condensation to remove water, the mixed gas generated in the hydroiodic acid decomposition unit enters the membrane separation stage for preliminary purification. This stage uses a zirconium oxide-modified carbon molecular sieve (CMS) membrane. Based on the molecular size exclusion effect, H2 molecules (kinetic diameter 0.29 nm) preferentially permeate through the membrane pores, while HI molecules (kinetic diameter approximately 0.36 nm) and I2 molecules (kinetic diameter approximately 0.55 nm), due to their size being close to or larger than the membrane pore size, are effectively retained on the feed side, thus achieving preliminary separation between hydrogen and other impurity gases. A ZrO2 (zirconia) modification layer is introduced onto the membrane surface. This modification layer has strong Lewis acidity and can interact with I⁻ in HI molecules through Lewis acid-base interactions, forming local adsorption sites and enhancing the selective adsorption and blocking effect on HI. This synergistic physical and chemical mechanism significantly improves the separation efficiency of the membrane material for polar molecules such as HI, making the membrane separation process not only dependent on size sieving but also possessing a certain degree of chemical selectivity, thus improving the overall purification performance.

[0037] (2) The PSA purification device utilizes the differences in adsorption capacity of various components in a gas mixture under different pressures by a gradient adsorbent bed. By periodically changing the system pressure, the target gas can be separated and purified. The PSA purification device of this invention adopts a gradient adsorbent bed design, giving full play to the advantages of different adsorbent materials. The upper layer of the adsorbent bed is filled with modified activated carbon material, whose rich π-electron system can efficiently adsorb iodine molecules (I2) through π–π interactions, achieving selective capture of iodine vapor. The nitrogen atoms on the tertiary amine have lone pairs of electrons, which, as excellent electron donors, can instantly and strongly interact with iodine molecules (I2) as electron acceptors to form stable charge-transfer complexes. The lower layer is filled with molecular sieves, which mainly utilize the hydrogen bonding forces between their polar surfaces and HI molecules to efficiently remove residual hydroiodic acid molecules. Through the synergistic effect of multiple adsorbent layers, high-purity hydrogen with a purity higher than 99.99% can be obtained, meeting the application requirements of ultrapure hydrogen in high-end industrial fields. Attached Figure Description

[0038] Figure 1 This is a schematic flowchart of the sulfur-iodine cycle hydrogen purification method of the present invention, which combines membrane separation and pressure swing adsorption.

[0039] Figure 2 This is a schematic diagram of a thermochemical sulfur-iodine cycle hydrogen production system incorporating the hydrogen purification method of the present invention.

[0040] Figure 3 This is a SEM image of the interface of the zirconium oxide-modified carbon molecular sieve membrane of the present invention.

[0041] Figure 4 This is a schematic diagram of a zirconium oxide-modified carbon molecular sieve membrane.

[0042] Figure 5 This is a schematic diagram of a membrane reactor.

[0043] Figure 6 This is a schematic diagram of a PSA adsorption device.

[0044] Among them, 1-Bunsent reaction tower; 2-Separated tower; 3-Hydroiodic acid phase storage tank; 4-Distillation tower; 5-Heat exchanger; 6-Hydroiodic acid decomposition tower; 7-Cryogenic equipment; 8-Membrane separation equipment; 9-PSA purification unit; 10-Make-up 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 tower; 20-Heat exchanger; 22-Reboiler; 23-Condenser; 24-Heat pump; 25-Reheater; 26-Cooling water tank. Detailed Implementation

[0045] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0046] This invention primarily provides a method and apparatus for purifying hydrogen using a sulfur-iodine cycle coupled with membrane separation and pressure swing adsorption. While numerous studies have reported on thermochemical sulfur-iodine cycle water decomposition for hydrogen production, the technical solution provided in this invention pertains to a specific step within the overall process of thermochemical sulfur-iodine cycle water decomposition for hydrogen production. More precisely, it pertains to the hydrogen separation and purification process. This invention does not limit the scope of other steps in the thermochemical sulfur-iodine cycle water decomposition for hydrogen production (e.g., the Bunsen reaction and two-phase separation, the purification and concentration of the H2SO4 phase, the HI decomposition process, etc.).

[0047] The technical solution of this invention can be integrated into any existing thermochemical sulfur-iodine cycle water decomposition hydrogen production process to replace the existing hydrogen (from the HI decomposition tower) separation and purification process. For comparison, the purification process of this invention is as follows: Figure 1 As shown.

[0048] This embodiment provides a sulfur-iodine cycle hydrogen purification method using coupled membrane separation and pressure swing adsorption, which can be implemented according to the following steps:

[0049] (1) The four mixed gases of hydrogen, iodine, hydroiodic acid and water generated by the hydroiodic acid decomposition tower are introduced into the cryogenic equipment. At (-20℃~-5℃) and normal pressure, the water changes from gaseous state to liquid state. At the same time, the hydroiodic acid and iodine in the mixed gas are adsorbed into the liquid phase, so as to achieve the effect of crude purification of hydrogen.

[0050] (2) The crudely purified hydrogen gas is introduced into the membrane separation device. The gaseous gas flows into the device from the shell side and comes into contact with the carbon molecular sieve membrane with a zirconium oxide modified layer. Based on the molecular size exclusion effect, H2 molecules (kinetic diameter of 0.29 nm) can preferentially pass through the membrane pores and achieve rapid permeation, while HI molecules (kinetic diameter of about 0.36 nm) and I2 molecules (kinetic diameter of about 0.55 nm), which are larger than the membrane pore size, are effectively retained on the feed side, thereby achieving preliminary separation between hydrogen gas and other impurity gases. A ZrO2 (zirconia) modification layer is introduced on the membrane surface. This modification layer has strong Lewis acidity and can interact with I⁻ in HI molecules to form local adsorption sites, enhancing the selective adsorption and blocking effect of HI. This physical and chemical synergistic mechanism significantly improves the separation efficiency of the membrane material for polar molecules such as HI, making the membrane separation process not only dependent on size sieving but also possessing a certain degree of chemical selectivity, thus improving the overall purification performance. Therefore, hydrogen can pass through the membrane pores in the membrane separation unit, while macromolecules such as hydroiodic acid, iodine, and water cannot pass through the membrane pores and flow out from the other side of the shell side, returning to the hydroiodic acid decomposition tower for further decomposition; while hydrogen, after passing through the membrane, flows out under the inert atmosphere in the tube layer and enters the PSA purification unit.

[0051] (3) The hydrogen component after membrane separation and purification flows into the PSA purification unit filled with a gradient adsorbent bed (composed of a modified activated carbon layer and a molecular sieve layer). The hydrogen-rich gas flows through the modified activated carbon layer and the molecular sieve layer from top to bottom, and removes the residual hydroiodic acid and iodine in a directional manner. When the impurity front approaches the bottom of the gradient adsorbent bed, the gas intake is stopped, and desorption and regeneration are carried out. The hydroiodic acid and iodine desorbed by PSA are returned to the Bunsen reaction unit to participate in the cycle, achieving near-zero loss of raw materials and improving the overall hydrogen production efficiency.

[0052] This invention utilizes a membrane-PSA synergistic pressure matching design. The membrane separation stage employs medium-high pressure (2-4 MPa), using a zirconium oxide-modified carbon molecular sieve membrane to preferentially separate hydrogen, significantly reducing the impurity load on the PSA unit. The permeate directly enters the PSA purification unit, where a gradient adsorbent design (modified activated carbon + molecular sieve) achieves the staged removal of HI, I2, and H2O, avoiding purity fluctuations caused by the failure of a single adsorbent. This staged, highly efficient purification process achieves ultra-high purity hydrogen.

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

[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) Construction of ZrO2 modified layer: The zirconium source (such as zirconium oxychloride ZrOCl2·8H2O or zirconium oxynitrate ZrO(NO3)2) was dissolved in a methanol / water (volume ratio 2-4:1) mixed solvent. A small amount of nitric acid was added to inhibit hydrolysis and form a stable sol. The pretreated carbon molecular sieve membrane was immersed in the above sol for 5-10 min and then coated by dip coating. Subsequently, the solvent was allowed to evaporate slowly at room temperature for 12-24 h, and the sol was transformed into a gel on the membrane surface. Heat treatment was carried out in an inert gas at 300-400℃ for 10-30 min to transform the ZrO2 gel into a stable zirconium oxide layer.

[0064] After preliminary purification via membrane separation, the hydrogen gas enters a pressure swing adsorption (PSA) purification unit. The PSA system employs a gradient adsorbent bed design, fully leveraging the unique advantages of different adsorbent materials. The upper layer of the adsorption bed is filled with modified activated carbon, whose abundant π-electron system can efficiently adsorb iodine molecules (I2) through π–π interactions, achieving selective capture of iodine vapor. The lower layer is filled with molecular sieves, which primarily utilize the hydrogen bonding forces between their polar surfaces and HI molecules to efficiently remove residual hydroiodic acid molecules. Through the synergistic effect of multiple adsorbent layers, high-purity hydrogen gas with a purity exceeding 99.99% can be obtained, meeting the application requirements of ultrapure hydrogen in high-end industrial fields.

[0065] The preparation method of modified activated carbon in the modified activated carbon layer includes: (1) drying coconut shell activated carbon in a drying oven at 80-110℃ for 2-4 hours to completely remove the adsorbed moisture and air inside; (2) in a fume hood and under continuous stirring, slowly and evenly dripping triethylamine solution onto the pretreated activated carbon using an equal volume impregnation method to ensure that the liquid is completely absorbed and there is no visible liquid residue; (3) transferring the impregnated wet carbon into a sealed container and letting it stand at room temperature for 12-24 hours; (4) transferring the aged activated carbon to a drying tray and placing it in a drying oven. The temperature is increased by programmed drying at 60-80℃ for 2-3 hours. This stage mainly removes possible solvents and some physically adsorbed triethylamine; then, the temperature is slowly increased to 100-120℃ and maintained at this temperature for 3-4 hours. The purpose of this process is to induce triethylamine to form weak bonds with functional groups such as hydroxyl groups on the surface of activated carbon, thereby significantly reducing its volatility, improving product stability, and preventing loss during subsequent use. (5) After drying, turn off the heating and cool to room temperature in the drying oven. Immediately pack the product into a sealed bag or sealed container to prevent the adsorption of moisture and other impurities from the air.

[0066] For the molecular sieve layer, 13X molecular sieve can be used in this invention. The bulk density of the molecular sieve layer is 700-800 kg / m³. 3 The filling height is 1.5-2.0m, the particle size is 1.6-2.5mm, and the specific surface area is 500-700m².2 / g. Adsorption tower diameter 0.3-0.4m.

[0067] In this embodiment of the invention, multiple PSA purification units (absorption towers filled with gradient adsorbent beds) are used in an alternating adsorption-desorption process. Specifically, the PSA purification units undergo desorption and regeneration after adsorption saturation; and while some PSA purification units are performing adsorption, others are performing desorption. Desorption and regeneration are achieved through processes such as rapid depressurization, resulting in efficient adsorbent regeneration. The desorbed gas can be recycled, achieving closed-loop material circulation and efficient resource recovery.

[0068] In one specific embodiment of the present invention, 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.

[0069] The desorption stage of this invention includes the following steps:

[0070] 1) Forward depressurization: After the gas intake is stopped, the PSA purification unit gradually depressurizes along the gas intake direction (adsorption direction) so that the gas in the unit flows out along the gas intake direction; the outflow product in this step is mainly residual high-purity hydrogen; this gas is introduced to other PSA purification units that have completed regeneration for pressure equalization and boosting.

[0071] 2) Reverse depressurization: The pressure inside the PSA purification unit is reduced to near atmospheric pressure, and a large number of 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.

[0072] 3) Flushing: High-purity product hydrogen is introduced from other PSA purification units and purged in a countercurrent manner (from the bottom of the tower to the top of the tower) to 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;

[0073] 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.

[0074] Regarding the control of the pressure change rate, the pressure change rate of the forward depressurization step is 10 ~ 40 kPa / s, the pressure change rate of the reverse depressurization step is 5 ~ 20 kPa / s, the pressure change rate of the equalization and pressure increase step is 5 ~ 25 kPa / s, and the pressure change rate of the steady pressure increase step is 2 ~ 10 kPa / s.

[0075] The technical solution of this invention can be integrated into any existing thermochemical sulfur-iodine cycle water decomposition hydrogen production process to replace the existing hydrogen (from the HI decomposition tower) separation and purification process. The following describes a thermochemical sulfur-iodine cycle hydrogen production process using the method of this invention, as a typical application example, such as... Figure 2 As shown, the specific process is as follows:

[0076] In Bunsen reactor 1, sulfur dioxide, iodine, and water react to produce hydroiodic acid and sulfuric acid. The resulting mixed acid solutions are allowed to separate into two phases in a separator 2. The lower hydroiodic acid phase is fed into a hydroiodic acid phase storage tank 3, while the upper sulfuric acid phase is fed into a sulfuric acid phase buffer tank 11. The operating temperature of Bunsen reactor 1 is 80-130°C, and the pressure is 0-5 atm. The temperature and pressure in separator 2 are also 80-130°C and 0-5 atm.

[0077] Inside the sulfuric acid purifier 12, the pressure is adjusted to 0-5 atm via falling film evaporation, resulting in the reverse reaction 2HI + H2SO4 = SO2 + I2 + 2H2O to remove HI impurities from the sulfuric acid phase. The generated sulfur dioxide and iodine vapors are discharged from the top of the sulfuric acid purifier 12 and mixed with water vapor in the multi-effect evaporator 14 before being introduced into the Bunsen reaction tower 1. The purified sulfuric acid is then processed by a multi-effect evaporator to increase its concentration from 50%-55% to 75%-85%. Liquid sulfuric acid is then pumped into a bayonet-type sulfuric acid decomposition tower 19. 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 tube sheet of the bayonet-type sulfuric acid decomposition tower 19 uses perfluoroether rubber rings, and the tube sheet material is PTFE. Since the top of the bayonet-type sulfuric acid reactor is filled with high-temperature helium, heat is transferred downwards along the silicon carbide tubes. Currently, among corrosion-resistant materials, perfluoroether rubber and PTFE tube sheets cannot be used stably for extended periods above 200℃, and metal materials cannot withstand sulfuric acid corrosion, posing a risk of leakage with long-term use. Therefore, a sulfuric acid circulation system is added to the tube sheet to cool the sulfuric acid, maintaining its temperature below 180℃. In the bayonet-type sulfuric acid reactor, the reaction H2SO4 = SO3 + H2O occurs within the tubes. The generated sulfur trioxide and water vapor rise within the tube layer and then settle at the top of the reactor into the gap between the silicon carbide tubes filled with sulfur trioxide decomposition catalyst. There, the reaction 2SO3 = 2SO2 + O2 occurs, and the generated sulfur dioxide and oxygen flow downwards along the gap between the tubes, heating the sulfuric acid that is continuously evaporated and decomposed from bottom to top within the tubes. Subsequently, the sulfur dioxide and oxygen flow out of the bayonet-type sulfuric acid reactor, are heat-exchanged, and return to the Bunsen reaction tower 1 to participate in the recycling reaction. Oxygen is discharged from the top of the sulfuric acid phase buffer tank 11.

[0078] The hydroiodic acid phase solution at the bottom of the layered column 2 enters the hydroiodic acid phase storage tank 3, and then undergoes separation of hydroiodic acid, iodine, and water in the distillation column 4 at 80-160°C and 0-5 atm. The saturated hydroiodic acid solution containing dissolved iodine is refluxed at the bottom of the distillation column 4 to the Bunsen reaction column 1. Pure hydroiodic acid gas is obtained at the top of the column, and then the gas temperature is heated to 450-550°C and the pressure is 0-3 atm in the heat exchanger 5. The preheated hydroiodic acid gas decomposes into hydrogen and iodine vapor in the hydroiodic acid decomposition tower 6. The hydrogen, iodine vapor, and unreacted hydroiodic acid are condensed in the cryogenic device 7 to remove excess water and undergo crude purification. The iodine-containing hydroiodic acid solution obtained from the condensation is refluxed to the Bunsen reactor 1. The purified hydrogen enters the membrane separation device 8. The shell-side pressure of the membrane separation device is 2-4 MPa, and the tube-side pressure is 1-1.5 MPa. Hydrogen flows into the tube side of the membrane separation device from the zirconia-modified carbon molecular sieve membrane. Larger molecules cannot pass through the membrane material and flow out from the other side of the shell side, mixing with the feed material of the distillation column, and then flowing into the distillation column 4. Subsequently, the reaction 2HI = H2 + I2 occurs in the hydroiodic acid decomposition tower 6. Hydrogen gas in the membrane separation tube flows into the PSA purification unit 9. By adjusting the pressure of pre-filled modified activated carbon and molecular sieve, specific gases are selectively adsorbed. The modified activated carbon first adsorbs iodine vapor in the mixed gas, and the molecular sieve adsorbs the remaining hydroiodic acid into the multi-level pore structure, thereby purifying the hydrogen gas. The purified hydrogen gas flows out of the PSA purification unit 9. After desorption, the adsorbed iodine vapor and hydroiodic acid gas are desorbed and returned to the Bunsen reaction tower 1.

[0079] Example 1

[0080] The initial temperature inside Bunsen reaction tower 1 is 115℃, the pressure is 1 atm, and the feed amounts are 2.6 mol SO2, 13.5 mol I2, 3.6 mol HI, and 25.2 mol water. The Bunsen reaction occurs: SO2 + I2 + 2H2O = 2HI + H2SO4, producing sulfuric acid and hydroiodic acid. The resulting mixed acid solution is passed into layered tower 2. After standing for 15 minutes, an upper sulfuric acid phase solution and a lower hydroiodic acid phase solution containing a large amount of iodine are obtained. The sulfuric acid phase solution is pumped from the top of the layered tower to a sulfuric acid buffer tank 11, and the hydroiodic acid phase flows to a hydroiodic acid storage tank 3.

[0081] After the two phases separate, the sulfuric acid phase contains a small amount of hydroiodic acid and iodine impurities, while the H2SO4 phase consists of 1.82 mol H2SO4, 0.21 mol HI, 0.04 mol I2, and 10.01 mol H2O. The mixture enters the sulfuric acid purifier 12, where the pressure is adjusted to 0.1 atm using a vacuum pump. The reverse reaction 2HI + H2SO4 = SO2 + I2 + 2H2O occurs through reduced pressure evaporation, removing the HI impurities from the sulfuric acid phase. The generated sulfur dioxide and iodine vapors are discharged from the top of the sulfuric acid purifier 12 and mixed with water vapor in the multi-effect evaporator 14 before being introduced into the Bunsen reaction tower 1. The purified sulfuric acid is then purified by a multi-effect evaporator to increase its concentration from 55% to 80%. Liquid sulfuric acid is then pumped into a bayonet-type sulfuric acid decomposition tower 19. High-temperature helium gas at 4 MPa and 950 °C is used as a heat source to heat the bayonet-type sulfuric acid reactor. The tube sheet of the bayonet-type sulfuric acid reactor uses perfluoroether rubber rings, and the tube sheet material is PTFE. Because the top of the bayonet-type sulfuric acid reactor is filled with high-temperature helium gas, heat is transferred downwards along the silicon carbide tubes. Currently, among corrosion-resistant materials, perfluoroether rubber and PTFE tube sheets cannot be used stably for extended periods above 200 °C, and metal materials cannot withstand sulfuric acid corrosion, posing a risk of leakage with long-term use. Therefore, a sulfuric acid circulation system is added to the tube sheet to cool the sulfuric acid, maintaining its temperature below 180 °C. In the bayonet-type sulfuric acid reactor, the reaction H2SO4 = SO3 + H2O occurs within the tubes. The generated sulfur trioxide and water vapor rise within the tube layer and then settle at the top of the reactor into the gap between the silicon carbide tubes filled with sulfur trioxide decomposition catalyst. There, the reaction 2SO3 = 2SO2 + O2 occurs, and the generated sulfur dioxide and oxygen flow downwards along the gap between the tubes, heating the sulfuric acid that is continuously evaporated and decomposed from bottom to top within the tubes. Subsequently, the sulfur dioxide and oxygen flow out of the bayonet-type sulfuric acid reactor, return to the 1-Bunsen tower after heat exchange, and participate in the recycling reaction. Oxygen is discharged from the top of the sulfuric acid phase buffer tank 11.

[0082] The hydroiodic acid phase solution at the bottom of the layered column 2 enters the hydroiodic acid phase storage tank 3, and then undergoes separation of hydroiodic acid, iodine, and water in the distillation column 4 at 120°C and 1 atm. The saturated hydroiodic acid solution containing dissolved iodine is refluxed to the Bunsen column at the bottom of the distillation column. Pure hydroiodic acid gas is obtained at the top of the column, and then the gas temperature is heated to 450°C and the pressure is 1 atm in the heat exchanger 5. The preheated hydroiodic acid gas is decomposed in the hydroiodic acid decomposition column 6 to generate hydrogen and iodine vapor. The hydrogen, iodine vapor, and unreacted hydroiodic acid are condensed in the cryogenic device 7 to remove excess water for crude purification. The iodine-containing hydroiodic acid solution obtained from the condensation is refluxed to the Bunsen reaction column 1. The purified hydrogen enters the membrane separation device 8, where the shell-side pressure is 3 MPa and the tube-side pressure is 1.3 MPa.

[0083] The method for preparing the zirconia-modified carbon molecular sieve membrane in this embodiment is as follows: Polyimide powder is dissolved in a solvent to prepare a uniform, bubble-free casting solution with a concentration of 15 wt%. The solution is filtered to remove impurity particles; the diluted casting solution is dipped onto a porous alumina support to form an extremely thin (0.5 μm) polymer layer; under an inert atmosphere, the temperature is slowly heated to 600°C at a heating rate of 2°C / min. After holding at this temperature for 2 hours, it 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; zirconium oxynitrate is dissolved in a methanol / water (volume ratio 2:1) mixed solvent. 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 10 min and then coated using the dip-coating method. Subsequently, the solvent is allowed to slowly evaporate at room temperature for 12 h, and the sol transforms into a gel on the membrane surface. Heat treatment is performed at 300°C in an inert gas for 30 min to transform the ZrO2 gel into a stable zirconia layer. Figure 3 The image shows a SEM image of the interface of the resulting zirconium oxide-modified carbon molecular sieve membrane. Figure 4 This is a schematic diagram of the structure of a zirconium oxide-modified carbon molecular sieve membrane.

[0084] Hydrogen gas flows into the tubular side of the membrane separation unit from a zirconium oxide-modified carbon molecular sieve membrane. Larger molecules cannot permeate the membrane material and exit from the other side of the shell side, mixing with the feed material at the distillation column inlet. The mixture then flows into distillation column 4, where it subsequently undergoes the reaction 2HI = H₂ + I₂ in the hydroiodic acid decomposition column 6. The hydrogen gas in the membrane separation tubular side flows into the PSA purification unit 9, where it selectively adsorbs specific gases by adjusting the pressure of pre-packed modified activated carbon and molecular sieves. The modified activated carbon layer is 0.5 meters high, the adsorbent particle size is 2.5 mm, and the packing density is 450 kg / m³. 3 The bulk density of 13X molecular sieve is 700 kg / m³. 3 The filling height is 1.5 meters, the particle size is 2.5 mm, and the specific surface area is 700 m². 2 / g. The adsorption tower has a diameter of 0.4m.

[0085] The modified activated carbon preparation method in this embodiment is as follows: Coconut shell activated carbon is dried in a drying oven at 110°C for 4 hours; triethylamine solution is slowly and evenly added to the pretreated activated carbon using an equal-volume impregnation method; the impregnated wet carbon is transferred to a sealed container and allowed to stand at room temperature for 24 hours; the aged activated carbon is then placed in a drying oven and dried at 80°C for 3 hours; subsequently, the temperature is slowly increased to 120°C and maintained at this temperature for 4 hours, followed by cooling to room temperature in the drying oven.

[0086] Modified activated carbon first adsorbs iodine vapor and hydroiodic acid from the mixed gas. Molecular sieves then adsorb the remaining hydroiodic acid into a multi-level porous structure, thus purifying the hydrogen. The purified hydrogen flows out of the PSA purification unit and, under conditions of forward depressurization of 20 kPa / s, reverse depressurization of 12 kPa / s, equalization and pressure increase of 15 kPa / s, and pressure increase of 6 kPa / s, the adsorbed iodine vapor and hydroiodic acid are desorbed and refluxed to the 1-Bunsen column. The purified hydrogen achieves a purity of 99.99% and a yield of 95.64%.

[0087] Example 2

[0088] The same process as in Example 1 was used, except that the carbon molecular sieve membrane was carbonized at 500°C, and the zirconium-containing gel after dip-coating was calcined at 350°C. The purity of the separated hydrogen reached 99.99%, and the yield was 93.25%.

[0089] Example 3

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

[0091] Comparative Example 1

[0092] The same process as in Example 1 was used, except that in the preparation of the carbon molecular sieve membrane in Comparative Example 1, the zirconium-containing gel after dip-coating was calcined at 700°C (far higher than the carbonization temperature of 600°C for the carbon molecular sieve membrane), which caused the compactness of the carbon molecular sieve membrane to be destroyed, resulting in partial cracking. The purity of the separated hydrogen reached 45.32%, and the yield was 26.35%.

[0093] Comparative Example 2

[0094] The process is the same as in Example 1, 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 from Example 1, with a coconut shell activated carbon layer filling height of 0.5 meters, adsorbent particle size of 2.5 mm, and filling density of 450 kg / m³). 3 The purity of the separated hydrogen reached 85.32%, and the yield was 80.26%.

[0095] Comparative Example 3

[0096] The same process as in Example 1 was used, except that the carbon molecular sieve membrane was not modified with zirconium oxide (the preparation, film formation, carbonization, and surface pretreatment steps of the precursor polymer solution of the carbon molecular sieve membrane in Comparative Example 3 were the same as in Example 1, but without the zirconium oxide modification step). The purity of the separated hydrogen reached 87.32%, and the yield was 82.26%.

[0097] Comparative Example 4

[0098] The same process as in Example 1 was used, except that the heating rate during carbonization of the carbon molecular sieve membrane was 10°C / min, and the purity of the separated hydrogen reached 62.32%, with a yield of 65.25%.

[0099] Comparative Example 5

[0100] The process is the same as in Example 1, except that the PSA device is only filled with a modified activated carbon layer (the total height of the modified activated carbon layer is 2 meters, the adsorbent particle size is 2.5 mm, and the packing density is 450 kg / m³). 3 The purity of the separated hydrogen reached 72.32%, and the yield was 67.75%.

[0101] Comparative Example 6

[0102] The process is the same as in Example 1, except that the PSA device is only filled with a molecular sieve layer (the molecular sieve layer uses 13X molecular sieve, and the bulk density of 13X molecular sieve is 700 kg / m³). 3 The total filling height is 2 meters, the particle size is 2.5 mm, and the specific surface area is 700 m². 2 / g), the purity of the separated hydrogen reached 75.32%, and the yield was 63.93%.

[0103] As can be seen from the above results, this invention solves the problems of low purity and low yield in hydrogen purification in sulfur-iodine cycle by coupling cryogenic pretreatment, membrane separation and pressure swing adsorption. In the membrane separation setting, a carbon molecular sieve membrane with a zirconium oxide modified layer is used as the separation material. In the pressure swing adsorption purification device, a gradient adsorbent design (modified activated carbon layer + molecular sieve layer) is adopted. This provides an efficient purification solution for thermochemical hydrogen production technologies such as sulfur-iodine cycle.

[0104] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent 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. S3: The hydrogen-rich gas stream 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 stream, which includes a modified activated carbon layer and a molecular sieve layer. The hydrogen-rich gas stream 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.

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, 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 minutes to obtain a carbon molecular sieve membrane with a zirconium oxide modified layer on the surface.

7. The method according to claim 1, characterized in that, The preparation method of modified activated carbon in the desorption modified activated carbon layer includes: adding triethylamine solution dropwise onto dry activated carbon to ensure that the triethylamine solution is completely absorbed by the activated carbon; sealing and letting the obtained activated carbon stand for 12-24 hours for aging; subjecting the aged activated carbon to programmed temperature drying: first drying at 60-80℃ for 2-3 hours, then raising the temperature to 100-120℃ and holding for 3-4 hours to promote the combination of triethylamine with surface functional groups; finally cooling the programmed temperature dried activated carbon to room temperature to obtain modified activated carbon.

8. 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.

9. The method according to claim 8, 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.

10. A sulfur-iodine cycle hydrogen purification apparatus for implementing the method of any one of claims 1-9, 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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