Method for producing hydrogen in situ from seawater

Abstract

The application belongs to the technical field of electrolytic hydrogen production and specifically relates to a seawater in-situ hydrogen production method. The method comprises a phase change mass transfer tank, which comprises a seawater area (1), a phase change mass transfer layer (2) and an electrolyte area (3); seawater is discharged from a seawater tank, sequentially passes through a pre-filter, a primary heat exchanger and a secondary heat exchanger, and enters the seawater area (1) to perform phase change mass transfer; electrolyte enters the electrolyte area (3) from an electrolyte mixing tank; phase change mass transfer is performed at the phase change mass transfer layer (2), and the phase change mass transfer layer (2) is an IPN film; the electrolyte area (3) is discharged to an electrolysis tank to perform electrolysis to produce hydrogen. In the application, the IPN film is prepared from polyvinyl alcohol and polyimide, and a series of modification measures such as fluorination are adopted to ensure that the IPN film has high hydrophobicity and good water vapor permeability, so as to improve the efficiency of electrolytic hydrogen production; in addition, the IPN film is simple to prepare and has a high yield.

Description

Technical Field

[0001] This invention belongs to the field of electrolytic hydrogen production technology, specifically relating to an in-situ hydrogen production method from seawater. Background Technology

[0002] Green hydrogen refers to hydrogen produced by generating electricity from renewable energy sources such as solar and wind power, and then producing hydrogen through water electrolysis. Compared to gray or blue hydrogen, green hydrogen achieves zero carbon emissions throughout the entire process from production to use, making it a truly clean energy source. However, the vast majority of Earth's water resources are seawater, and other usable freshwater resources such as rivers, lakes, or groundwater are insufficient to meet humanity's future demand for hydrogen energy. To further promote the production and application of green hydrogen, seawater electrolysis hydrogen production technology is receiving increasing attention from the scientific and industrial communities. However, because seawater contains a large amount of chloride ions and microorganisms, these impurities can cause side reactions such as chlorine evolution at the electrodes during electrolysis, which accelerates the corrosion of electrode materials and equipment. To address this issue, current seawater electrolysis hydrogen production technologies mainly include two types: seawater desalination followed by electrolysis and in-situ seawater electrolysis. In-situ seawater electrolysis eliminates the seawater desalination step, offering advantages such as lower energy consumption and higher production efficiency. The technical principle involves installing a hydrophobic and permeable membrane in a phase change mass transfer device. Seawater and potassium hydroxide electrolyte are located on opposite sides of the membrane. The difference in saturated vapor pressure between the seawater and electrolyte sides due to the different ion concentrations allows water vapor to evaporate and transfer from the seawater side to the electrolyte side, thus transferring water molecules from the seawater to the potassium hydroxide electrolyte. Finally, water is electrolyzed in an electrolysis device to produce hydrogen. A key aspect of this technology is ensuring that the hydrophobic and permeable membrane has sufficient hydrophobicity to block seawater and prevent Cl- from entering the electrolyte. - The problem is that impurities and ions can seep into the electrolyte and cause pollution. Secondly, it is necessary to ensure the migration efficiency of water molecules in the gas phase. In addition, it is also required to have a certain degree of corrosion resistance and mechanical strength.

[0003] Chinese patent CN114481164A discloses a device, system, and method for hydrogen production by electrolysis of a non-pure aqueous solution based on liquid-phase hygroscopicity. The device includes an electrolyte layer, a water vapor mass transfer layer and an oxygen evolution catalyst layer attached to both sides of the electrolyte layer, and a hydrogen evolution catalyst layer and an ion exchange membrane located between the oxygen evolution catalyst layer and the hydrogen evolution catalyst layer. The oxygen evolution catalyst layer is provided with an anode electrode, and the hydrogen evolution catalyst layer is provided with a cathode electrode. The water vapor mass transfer layer is one of a TPU membrane, PDMS membrane, or PTFE membrane with a pore size of 0.1–100 µm, or a porous water vapor mass transfer layer prepared from graphene, PVDF particles, or PTFE particles through spraying, screen printing, or electrostatic adsorption. In this patent, the hydrogen evolution catalyst layer, ion exchange membrane, and oxygen evolution catalyst layer function similarly to an electrolytic cell, while the water vapor mass transfer layer functions as a phase change mass transfer layer.

[0004] Chinese patent CN113088986A discloses a device, system, and method for in-situ hydrogen production from seawater based on polyelectrolyte gel. The waterproof and breathable layer used is a PTFE, TPU, or PDMS waterproof and breathable membrane with a pore size of 0.1–100 µm. Alternatively, it can be a porous waterproof and breathable layer prepared from hydrophobic materials through spraying, screen printing, or electrostatic adsorption. In this patent, the waterproof and breathable layer functions as a phase change mass transfer layer.

[0005] The aforementioned patent has the following drawbacks: The membrane material used in the phase change mass transfer layer must possess both high hydrophobicity to prevent seawater from spreading on the membrane surface and to prevent impurities such as chloride ions from penetrating into the electrolyte, thereby corroding the equipment and reducing electrode lifespan; and a certain degree of hydrophilicity, meaning that water vapor microdroplets can form good contact with the membrane surface through hydrogen bonding and other interactions to ensure good water vapor permeability and improve the efficiency of hydrogen production by electrolysis. Therefore, the microstructure of the selected membrane material should have a suitable porosity, pore size, and a balance between hydrophilicity and hydrophobicity. However, single-material materials such as TPU membranes, PDMS, or PTFE membranes, before modification, are difficult to balance hydrophilicity and hydrophobicity. In addition, the preparation of porous water vapor mass transfer layers by spraying, screen printing, or electrostatic adsorption methods requires high precision equipment and skilled operators, resulting in higher costs.

[0006] Therefore, based on the technical requirements of phase change mass transfer, the key to whether the in-situ seawater hydrogen production technology can be fully promoted is whether a low-cost and high-yield method can be found to prepare membrane materials that have both high hydrophobicity and good water vapor permeability. In addition, the membrane material also needs to have certain corrosion resistance, chemical stability and mechanical strength. Summary of the Invention

[0007] The purpose of this invention is to provide a method for in-situ hydrogen production from seawater, using an IPN membrane as a phase change mass transfer layer to ensure that the phase change mass transfer layer has both high hydrophobicity and good water vapor permeability, thereby further improving the efficiency of in-situ hydrogen production from seawater electrolysis. In addition, the IPN membrane preparation method is simple to operate, the required equipment is readily available, the cost is controllable, and the yield is high.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] The in-situ hydrogen production method from seawater according to the present invention includes a phase change mass transfer tank, which comprises a seawater zone, a phase change mass transfer layer, and an electrolyte zone. The phase change mass transfer layer is located between the seawater zone and the electrolyte zone. Seawater is discharged from the seawater tank and sequentially passes through a pre-filter, a primary heat exchanger, and a secondary heat exchanger before entering the seawater zone of the phase change mass transfer tank for phase change mass transfer. Electrolyte is introduced into the electrolyte zone of the phase change mass transfer tank from an electrolyte mixing tank. Phase change mass transfer takes place at the phase change mass transfer layer, which is selected as an IPN membrane. The discharge from the electrolyte zone enters an electrolyzer for in-situ hydrogen production from seawater.

[0010] in:

[0011] The preparation process of the IPN membrane includes the following steps: preparing cross-linked polyvinyl alcohol; adding diisocyanate, tetracarboxylic acid dianhydride and water to a polar solvent for prepolymerization reaction, followed by adding a fluorinating agent for modification to obtain a hydrophobic polyamic acid precursor; mixing the hydrophobic polyamic acid precursor, cross-linked polyvinyl alcohol and polar solvent for swelling, then adding a dehydration catalyst and cross-linking agent B for dehydration cyclization reaction, and finally obtaining the IPN membrane through film formation treatment.

[0012] The preparation of the cross-linked polyvinyl alcohol includes the following steps: dissolving polyvinyl alcohol in water to obtain a polyvinyl alcohol aqueous solution; and adding an initiator and cross-linking agent A to perform cross-linking to obtain cross-linked polyvinyl alcohol. The concentration of the polyvinyl alcohol aqueous solution is 15~30wt%.

[0013] The crosslinking temperature is 55-65℃, the crosslinking time is 20-35min, the initiator is benzoyl peroxide, the crosslinking agent A is 1,3-dimethylurea, and the mass ratio of the added initiator, crosslinking agent A and polyvinyl alcohol is (0.03-0.06):(0.1-0.15):1.

[0014] The diisocyanate is one of toluene diisocyanate, diphenylmethane diisocyanate, or hexamethylene diisocyanate; the tetracarboxylic dianhydride is pyromellitic dianhydride or 3,3',4,4'-benzophenone tetracarboxylic dianhydride; and the polar solvent is one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, or N-methylpyrrolidone.

[0015] The prepolymerization reaction temperature is 28-40℃, and the prepolymerization reaction time is 90-150 min; the fluorinating agent is one of perfluorooctyltriethoxysilane, perfluoropropyl vinyl ether, or 1H,1H,2H,2H-perfluorooctyl acrylate; the modification temperature is 50-65℃, and the modification time is 12-20 min; the molar ratio of fluorinating agent to diisocyanate is (0.3-0.5):1.

[0016] The swelling time is 25-35 min; the dehydration catalyst is one of triethylamine, N-methyldiethanolamine, triethanolamine or dimethylpyridine; the crosslinking agent B is trimesoyl chloride or aminopropyltriethoxysilane; the dehydration cyclization reaction temperature is 140-200℃; the dehydration cyclization reaction time is 60-150 min; the molar ratio of crosslinking agent B, dehydration catalyst and diisocyanate is (0.08-0.12):(0.02-0.06):1; the mass ratio of polyvinyl alcohol and diisocyanate is (0.55-0.85):1.

[0017] The film formation process includes two steps: pre-coating and spin coating. Both steps utilize a spin coater. During pre-coating, the spin coater speed is set to 180-400 rad / min, and the pre-coating time is 18-25 min. During spin coating, the spin coater speed is set to 1800-2800 rad / min, and the spin coating time is 10-20 min. The resulting IPN thickness is 0.5-1.2 μm. The purpose of pre-coating and spin coating is to form an IPN film with basic uniformity and adhesion on the substrate surface through pre-coating, which is beneficial for the spin coating efficiency and the thickness uniformity and thickness control accuracy of the subsequent spin coating.

[0018] The temperature of the electrolyte in the electrolyte zone is 60-75℃; the electrolyte is a 25-35wt% potassium hydroxide solution; at the phase change mass transfer tank, the temperature of the seawater is higher than that of the electrolyte, and the temperature difference is 8-15℃.

[0019] The pre-filter is equipped with a ceramic ultrafiltration membrane; the ceramic ultrafiltration membrane is made of one of alumina, zirconium oxide, titanium oxide or silicon oxide.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) Since each unit of polyvinyl alcohol contains a hydroxyl group, these hydroxyl groups are densely arranged on one side of the polyvinyl alcohol molecular chain, which easily forms a hydrogen bond network, causing molecular chain entanglement and reducing the degree of freedom of the molecular chain. This makes it difficult for the hydrophobic polyamic acid precursor to penetrate into the gaps between the polyvinyl alcohol molecular chains, which is not conducive to the formation of IPN film. Therefore, by adding a crosslinking agent with high molecular rigidity, such as 1,3-dimethylurea, crosslinked polyvinyl alcohol is prepared. The imino group in 1,3-dimethylurea can react with the hydroxyl group after activation. On the one hand, the hydroxyl group density is reduced, and on the other hand, the crosslinking agent molecule acts as a bridge to connect the originally independent polyvinyl alcohol molecular chains, forming a more stable and regular crosslinked network system. This reduces the entanglement of the polyvinyl alcohol molecular chains and promotes the hydrophobic polyamic acid precursor to be evenly distributed around the polyvinyl alcohol molecular chains.

[0022] (2) Fluorides are not only hydrophobic modifiers for polyamic acid. Since the dehydration cyclization reaction of the hydrophobic polyamic acid precursor is an imidization reaction, it needs to be carried out at a high temperature. However, in a high-temperature environment, polyamic acid may sometimes undergo thermal dissociation, which triggers a free radical chain reaction and causes polyamic acid degradation. The fluorine atoms in the fluoride can combine with free radicals to form more stable fluorinated free radicals. These fluorinated free radicals are not easy to trigger a chain reaction, which helps to improve the thermal stability of the material.

[0023] (3) The present invention uses the sequential generation principle. The polyvinyl alcohol molecular chain contains a large number of hydroxyl groups, which can form hydrogen bonds with water molecules, thus giving polyvinyl alcohol good hydrophilicity. By infiltrating the hydrophobic modified hydrophobic polyamic acid precursor into the gaps between hydrophilic polyvinyl alcohol network molecules, and then under the action of a dehydration catalyst, multiple hydrophobic polyamic acid molecules activated at high temperature, the amide group (-CONH2) at one end of one molecule and the carboxyl group in another molecule dehydrate each other to form an imide bond (-CO-NH-CO-), which then cyclizes on both sides of the polyvinyl alcohol molecular chain to generate hydrophobic polyimide.

[0024] Because the hydrophobic polyimide surrounds the hydrophilic polyvinyl alcohol molecular chains, seawater cannot spread on the hydrophobic surface, creating a micrometer-sized gap between them. This prevents impurities such as chloride ions in the seawater from entering the electrolyte through the hydrophobic surface. However, water vapor molecules can pass through this micrometer-sized gap and directly contact the hydroxyl groups in the cross-linked polyvinyl alcohol to form hydrogen bonds, thus passing through the hydrophobic surface. It is generally difficult for a single substance to simultaneously possess both hydrophilicity and hydrophobicity, and it is also difficult to adjust the balance between hydrophilicity and hydrophobicity. This invention, however, uses a polymer interpenetrating network (IPN) to composite hydrophilic polyvinyl alcohol and hydrophobic fluorinated modified polyimide into a homogeneous material through forced compatibility. Through repeated experiments, the balance between hydrophilicity and hydrophobicity is adjusted by modifying the ratio of the reactants, resulting in an IPN film that exhibits both hydrophilicity and hydrophobicity. Attached Figure Description

[0025] Figure 1 Flowchart of in-situ hydrogen production from seawater;

[0026] Figure 2 This is a schematic diagram of the phase change mass transfer tank.

[0027] Figure 3 This is a scanning electron microscope image of the IPN film in Example 1;

[0028] In the diagram: 1. Seawater zone; 2. Phase change mass transfer layer; 3. Electrolyte zone. Detailed Implementation

[0029] The present invention will now be described and illustrated in detail with reference to the embodiments.

[0030] Example 1

[0031] Preparation of IPN film:

[0032] Add 120g of polyvinyl alcohol and 500g of deionized water to a three-necked flask, place the flask in a constant temperature water bath, set the water bath temperature to 85℃, and stir until completely dissolved to obtain a polyvinyl alcohol aqueous solution; add 6g of benzoyl peroxide and 18g of 1,3-dimethylurea, set the water bath temperature to 60℃, stir for 25min, centrifuge, and dry under reduced pressure to obtain cross-linked polyvinyl alcohol.

[0033] Prepare a clean and dry three-necked flask. Add 148.03 g of toluene diisocyanate, 203.95 g of pyromellitic dianhydride, 370 g of deionized water, and 900 g of dimethyl sulfoxide to the three-necked flask. Place the three-necked flask in a constant temperature water bath and set the water bath temperature to 35°C. Start stirring and stir for 120 min. Then add 113.07 g of perfluoropropyl vinyl ether for modification and set the water bath temperature to 58°C for modification for 15 min. After that, pass the mixture into a centrifuge and remove impurities by centrifugation to obtain the hydrophobic polyamic acid precursor.

[0034] The hydrophobic polyamic acid precursor was poured into a round-bottom flask. At room temperature, 1000 g of dimethyl sulfoxide and cross-linked polyvinyl alcohol were added, and the mixture was shaken well and allowed to swell for 28 min. Then, 4.05 g of N-methyldiethanolamine and 20.31 g of trimesoyl chloride were added, and the mixture was stirred and passed into a high-temperature reactor. The heating temperature was set to 220 °C, and the mixture was heated and stirred for 120 min to obtain the membrane solution.

[0035] The film solution was added to the substrate of a spin coater for film formation. The spin speed was set to 400 rad / min, and the pre-coating was carried out at 80°C for 18 min. A polyvinyl alcohol aqueous solution was added to the substrate of a spin coater. The spin speed was set to 2800 rad / min, and the high-speed spin coating was carried out at 80°C for 10 min. After drying, rinsing, and re-drying, an IPN film was obtained. The film thickness was measured to be 1.2 μm, and the surface structure was as follows. Figure 3 As shown.

[0036] According to GB / T 1040-2006, the tensile strength and elongation at break of the IPN membrane were tested, requiring a tensile strength ≥125MPa and an elongation at break ≥70%. Based on the differential principle, a laser displacement sensor was used to measure the IPN membrane thickness and thickness uniformity, requiring a thickness deviation of ±0.01μm per square meter of membrane material. Microscopic photography combined with the bubble trapping method was used to measure the liquid phase contact angle on the IPN membrane surface, requiring a contact angle between 118-130°. The calculated yield rate was 94.1%.

[0037] Example 2

[0038] Preparation of IPN film:

[0039] Add 120g of polyvinyl alcohol and 500g of deionized water to a three-necked flask, place the flask in a constant temperature water bath, set the water bath temperature to 85℃, and stir until completely dissolved to obtain a polyvinyl alcohol aqueous solution; add 7.2g of benzoyl peroxide and 16g of 1,3-dimethylurea, set the water bath temperature to 55℃, stir for 35min, centrifuge, and dry under reduced pressure to obtain cross-linked polyvinyl alcohol.

[0040] Prepare another clean and dry three-necked flask. Add 212.72 g of diphenylmethane diisocyanate, 314.98 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 468 g of deionized water, and 1500 g of N-methylpyrrolidone to the three-necked flask. Place the three-necked flask in a constant temperature water bath and set the water bath temperature to 40°C. Start stirring and stir for 90 min. Then add 130.14 g of perfluorooctyltriethoxysilane for modification and set the water bath temperature to 65°C for modification for 12 min. After that, pass the mixture into a centrifuge and remove impurities by centrifugation to obtain the hydrophobic polyamic acid precursor.

[0041] The hydrophobic polyamic acid precursor was poured into a round-bottom flask. At room temperature, 1000 g of dimethyl sulfoxide and cross-linked polyvinyl alcohol were added, and the mixture was shaken and allowed to swell for 25 min. Then, 5.16 g of triethylamine and 15.05 g of aminopropyltriethoxysilane were added, and the mixture was stirred and passed into a high-temperature reactor. The heating temperature was set to 180 °C, and the mixture was heated and stirred for 150 min to obtain the membrane solution.

[0042] The film solution was added to the substrate of the spin coater for film formation. The spin speed was set to 300 rad / min, and the pre-coating was carried out at 80℃ for 21 min. The polyvinyl alcohol aqueous solution was added to the substrate of the spin coater. The spin speed was set to 2300 rad / min, and the high-speed spin coating was carried out at 80℃ for 16 min. After drying, rinsing, and drying again, the IPN film was obtained. The film thickness was measured to be 0.9 μm.

[0043] According to GB / T 1040-2006, the tensile strength and elongation at break of the IPN membrane were tested, requiring a tensile strength ≥125MPa and an elongation at break ≥70%. Based on the differential principle, a laser displacement sensor was used to measure the IPN membrane thickness and thickness uniformity, requiring a thickness deviation of ±0.01μm per square meter of membrane material. Microscopic photography combined with the bubble capture method was used to measure the liquid phase contact angle on the IPN membrane surface, requiring a contact angle between 118-130°. The calculated yield rate was 92.2%.

[0044] Example 3

[0045] Preparation of IPN film:

[0046] Add 120g of polyvinyl alcohol and 500g of deionized water to a three-necked flask, place the flask in a constant temperature water bath, set the water bath temperature to 85℃, and stir until completely dissolved to obtain a polyvinyl alcohol aqueous solution; add 3.6g of benzoyl peroxide and 12g of 1,3-dimethylurea, set the water bath temperature to 65℃, stir for 20min, centrifuge, and dry under reduced pressure to obtain cross-linked polyvinyl alcohol.

[0047] Prepare a clean and dry three-necked flask. Add 142.97 g of hexamethylene diisocyanate, 222.48 g of pyromellitic dianhydride, 330 g of deionized water, and 1000 g of N,N-dimethylformamide to the three-necked flask. Place the three-necked flask in a constant temperature water bath and set the water bath temperature to 28°C. Start stirring and stir for 150 min. Then, add 142.17 g of 1H,1H,2H,2H-perfluorooctyl acrylate for modification. Set the water bath temperature to 50°C and modify for 20 min. After that, pass the mixture into a centrifuge and remove impurities by centrifugation to obtain the hydrophobic polyamic acid precursor.

[0048] The hydrophobic polyamic acid precursor was poured into a round-bottom flask. At room temperature, 1000 g of dimethyl sulfoxide and cross-linked polyvinyl alcohol were added, and the mixture was shaken and allowed to swell for 35 min. Then, 2.54 g of triethanolamine and 22.58 g of aminopropyltriethoxysilane were added, mixed, and then passed into a high-temperature reactor. The heating temperature was set to 250 °C, and the mixture was heated and stirred for 60 min to obtain the membrane solution.

[0049] The film solution was added to the substrate of the spin coater for film formation. The spin speed was set to 180 rad / min, and the pre-coating was carried out at 80℃ for 25 min. The polyvinyl alcohol aqueous solution was added to the substrate of the spin coater. The spin speed was set to 1800 rad / min, and the high-speed spin coating was carried out at 80℃ for 20 min. After drying, rinsing, and drying again, the IPN film was obtained. The film thickness was measured to be 0.5 μm.

[0050] According to GB / T 1040-2006, the tensile strength and elongation at break of the IPN membrane were tested, requiring a tensile strength ≥125MPa and an elongation at break ≥70%. Based on the differential principle, a laser displacement sensor was used to measure the IPN membrane thickness and thickness uniformity, requiring a thickness deviation of ±0.01μm per square meter of membrane material. Microscopic photography combined with the bubble capture method was used to measure the liquid phase contact angle on the IPN membrane surface, requiring a contact angle between 118-130°. The calculated yield rate was 91.5%.

[0051] Example 4

[0052] In-situ electrolysis of seawater to produce hydrogen:

[0053] according to Figure 1 and Figure 2The above describes the construction of an in-situ seawater hydrogen production device. Seawater is discharged from a seawater tank and passes through a pre-filter, a primary heat exchanger, and a secondary heat exchanger in sequence before entering the seawater zone 1 of the phase change mass transfer tank for phase change mass transfer. Electrolyte is introduced from an electrolyte mixing tank into the electrolyte zone 3 of the phase change mass transfer tank. Phase change mass transfer takes place at the phase change mass transfer layer 2. The discharge from the electrolyte zone 3 enters an electrolyzer for in-situ seawater hydrogen production.

[0054] The pre-filter is equipped with a ceramic ultrafiltration membrane; the ceramic ultrafiltration membrane is made of one of the following materials: alumina, zirconium oxide, titanium oxide, or silicon oxide.

[0055] The phase change mass transfer tank consists of a seawater zone 1, an electrolyte zone 3, and a phase change mass transfer layer 2, with the phase change mass transfer layer 2 located between the seawater zone 1 and the electrolyte zone 3. 1500 mL of a 35 wt% potassium hydroxide aqueous solution is introduced into the electrolyte zone 3 at a temperature of 60°C. 1500 mL of pre-filtered seawater is introduced into the seawater zone 1 at a temperature of 70°C. The phase change mass transfer layer 2 is the IPN membrane prepared in Example 1.

[0056] An electric current is applied to the electrolytic cell at 230 mA / cm². 2 Electrolysis was performed for 60 minutes under the specified conditions. The hydrogen gas obtained at the cathode was collected and measured at room temperature. The hydrogen production efficiency was measured to be 432.3 L / h.

[0057] Example 5

[0058] In-situ electrolysis of seawater to produce hydrogen:

[0059] according to Figure 1 and Figure 2 The above describes the construction of an in-situ seawater hydrogen production device. Seawater is discharged from a seawater tank and passes through a pre-filter, a primary heat exchanger, and a secondary heat exchanger in sequence before entering the seawater zone 1 of the phase change mass transfer tank for phase change mass transfer. Electrolyte is introduced from an electrolyte mixing tank into the electrolyte zone 3 of the phase change mass transfer tank. Phase change mass transfer takes place at the phase change mass transfer layer 2. The discharge from the electrolyte zone 3 enters an electrolyzer for in-situ seawater hydrogen production.

[0060] The pre-filter is equipped with a ceramic ultrafiltration membrane; the ceramic ultrafiltration membrane is made of one of the following materials: alumina, zirconium oxide, titanium oxide, or silicon oxide.

[0061] The phase change mass transfer tank consists of a seawater zone 1, an electrolyte zone 3, and a phase change mass transfer layer 2, with the phase change mass transfer layer 2 located between the seawater zone 1 and the electrolyte zone 3. 1500 mL of a 30 wt% potassium hydroxide aqueous solution is introduced into the electrolyte zone 3 at a temperature of 67°C. 1500 mL of pre-filtered seawater is introduced into the seawater zone 1 at a temperature of 75°C. The phase change mass transfer layer 2 is the IPN membrane prepared in Example 2.

[0062] An electric current is applied to the electrolytic cell at 230 mA / cm². 2Electrolysis was performed for 60 minutes under the specified conditions. The hydrogen gas obtained at the cathode was collected and measured at room temperature. The hydrogen production efficiency was measured to be 425.6 L / h.

[0063] Example 6

[0064] In-situ electrolysis of seawater to produce hydrogen:

[0065] according to Figure 1 and Figure 2 The above describes the construction of an in-situ seawater hydrogen production device. Seawater is discharged from a seawater tank and passes through a pre-filter, a primary heat exchanger, and a secondary heat exchanger in sequence before entering the seawater zone 1 of the phase change mass transfer tank for phase change mass transfer. Electrolyte is introduced from an electrolyte mixing tank into the electrolyte zone 3 of the phase change mass transfer tank. Phase change mass transfer takes place at the phase change mass transfer layer 2. The discharge from the electrolyte zone 3 enters an electrolyzer for in-situ seawater hydrogen production.

[0066] The pre-filter is equipped with a ceramic ultrafiltration membrane; the ceramic ultrafiltration membrane is made of one of the following materials: alumina, zirconium oxide, titanium oxide, or silicon oxide.

[0067] The phase change mass transfer tank consists of a seawater zone 1, an electrolyte zone 3, and a phase change mass transfer layer 2, with the phase change mass transfer layer 2 located between the seawater zone 1 and the electrolyte zone 3. 1500 mL of a 25 wt% potassium hydroxide aqueous solution is introduced into the electrolyte zone 3 at a temperature of 60°C. 1500 mL of pre-filtered seawater is introduced into the seawater zone 1 at a temperature of 75°C. The phase change mass transfer layer 2 is the IPN membrane prepared in Example 3.

[0068] An electric current is applied to the electrolytic cell at 230 mA / cm². 2 Electrolysis was performed for 60 minutes under the specified conditions. The hydrogen gas obtained at the cathode was collected and measured at room temperature. The hydrogen production efficiency was measured to be 426.9 L / h.

[0069] Comparative Example 1

[0070] The IPN membrane in Example 4 was replaced with a PTFE membrane, and the remaining steps were the same as in Example 4. The hydrogen production efficiency was measured to be 330.1 L / h.

[0071] Comparative Example 2

[0072] Crosslinked polyvinyl alcohol was prepared and directly subjected to film formation treatment without using a hydrophobic polyamic acid precursor. The remaining steps were the same as in Example 1 to obtain a polyvinyl alcohol film. Hydrogen was produced according to the method described in Example 4, except that the phase change mass transfer layer 2 was replaced with the polyvinyl alcohol film prepared in Comparative Example 2. The hydrogen production efficiency was measured to be 240.5 L / h.

[0073] Comparative Example 3

[0074] The membrane was formed using only a hydrophobic polyamic acid precursor. The precursor was mixed with a polar solvent and swollen. A dehydration catalyst and crosslinking agent B were then added to initiate a dehydration cyclization reaction. After membrane formation, the membrane material was obtained. The remaining steps were the same as in Example 1. Hydrogen was produced according to the method described in Example 4, except that the phase change mass transfer layer 2 was replaced with the hydrophobic polyimide membrane prepared in Comparative Example 3. The measured hydrogen production efficiency was 138.2 L / h.

[0075] Comparative Example 4

[0076] The crosslinking agent A was replaced with a silane coupling agent, γ-(methacryloyloxy)propyltrimethoxysilane, and the remaining steps were the same as in Example 1. Hydrogen was produced according to the method described in Example 4, except that the phase change mass transfer layer 2 was replaced with the IPN membrane prepared in Comparative Example 4. The hydrogen production efficiency was measured to be 315.5 L / h.

[0077] Comparative Example 5

[0078] The fluorinating agent was replaced with a silane coupling agent, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, and the remaining steps were the same as in Example 1. Hydrogen was produced according to the method described in Example 4, except that the phase change mass transfer layer 2 was replaced with the IPN membrane prepared in Comparative Example 5. The hydrogen production efficiency was measured to be 311.7 L / h.

[0079] Although the present invention has been described in detail by way of embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention.

Claims

1. A method for in-situ hydrogen production from seawater, comprising a phase change mass transfer tank, the phase change mass transfer tank comprising a seawater zone (1), a phase change mass transfer layer (2), and an electrolyte zone (3), wherein the phase change mass transfer layer (2) is located between the seawater zone (1) and the electrolyte zone (3), characterized in that, Seawater is discharged from the seawater tank and passes through a pre-filter, a primary heat exchanger, and a secondary heat exchanger in sequence before entering the seawater zone (1) of the phase change mass transfer tank for phase change mass transfer. Electrolyte is discharged from the electrolyte mixing tank and enters the electrolyte zone (3) of the phase change mass transfer tank. Phase change mass transfer is carried out at the phase change mass transfer layer (2), which is an IPN membrane. The discharge from the electrolyte zone (3) enters the electrolyzer for in-situ hydrogen production from seawater. The IPN membrane preparation process includes the following steps: preparing cross-linked polyvinyl alcohol; adding diisocyanate, tetracarboxylic acid dianhydride and water to a polar solvent for prepolymerization reaction, followed by modification with a fluorinating agent to obtain a hydrophobic polyamic acid precursor; mixing the hydrophobic polyamic acid precursor, cross-linked polyvinyl alcohol and polar solvent for swelling, then adding a dehydration catalyst and cross-linking agent B for dehydration cyclization reaction, and finally obtaining an IPN membrane after film formation treatment; The preparation of cross-linked polyvinyl alcohol includes the following steps: dissolving polyvinyl alcohol in water to obtain an aqueous solution of polyvinyl alcohol; adding an initiator and cross-linking agent A to cross-link the polyvinyl alcohol to obtain cross-linked polyvinyl alcohol; cross-linking agent A is 1,3-dimethylurea; the polar solvent is one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone; the fluorinating agent is one of perfluorooctyltriethoxysilane, perfluoropropyl vinyl ether or 1H,1H,2H,2H-perfluorooctyl acrylate.

2. The method for in-situ hydrogen production from seawater according to claim 1, characterized in that, The crosslinking temperature is 55-65℃, the crosslinking time is 20-35min, and the initiator is benzoyl peroxide; the mass ratio of the added initiator, crosslinking agent A and polyvinyl alcohol is (0.03-0.06):(0.1-0.15):

1.

3. The method for in-situ hydrogen production from seawater according to claim 1, characterized in that, The diisocyanate is one of toluene diisocyanate, diphenylmethane diisocyanate, or hexamethylene diisocyanate; the tetracarboxylic dianhydride is pyromellitic dianhydride or 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

4. The method for in-situ hydrogen production from seawater according to claim 1, characterized in that, The prepolymerization reaction temperature is 28-40℃, and the prepolymerization reaction time is 90-150 min; the modification temperature is 50-65℃, and the modification time is 12-20 min; the molar ratio of fluorinating agent to diisocyanate is (0.3-0.5):

1.

5. The method for in-situ hydrogen production from seawater according to claim 1, characterized in that, The swelling time is 25-35 min; the dehydration catalyst is one of triethylamine, N-methyldiethanolamine, triethanolamine or dimethylpyridine; the crosslinking agent B is pyromellitic acid chloride or aminopropyltriethoxysilane; the dehydration cyclization reaction temperature is 180-250℃; the dehydration cyclization reaction time is 60-150 min; the molar ratio of crosslinking agent B, dehydration catalyst and diisocyanate is (0.08-0.12):(0.02-0.06):1; the mass ratio of polyvinyl alcohol and diisocyanate is (0.55-0.85):

1.

6. The method for in-situ hydrogen production from seawater according to claim 1, characterized in that, The film formation process includes two steps: pre-coating and spin coating. Both steps use a spin coater. During pre-coating, the spin coater speed is set to 180-400 rad / min and the pre-coating time is 18-25 min. During spin coating, the spin coater speed is set to 1800-2800 rad / min and the spin coating time is 10-20 min.

7. The method for in-situ hydrogen production from seawater according to claim 1, characterized in that, The temperature of the electrolyte in the electrolyte zone (3) is 60-75℃; the electrolyte is a 25-35wt% potassium hydroxide solution; at the phase change mass transfer tank, the temperature of the seawater is higher than that of the electrolyte, and the temperature difference is 8-15℃.

8. The method for in-situ hydrogen production from seawater according to claim 1, characterized in that, The pre-filter is equipped with a ceramic ultrafiltration membrane; the ceramic ultrafiltration membrane is made of one of the following materials: alumina, zirconium oxide, titanium oxide, or silicon oxide.

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