Seawater treatment system and seawater treatment method

Abstract

A seawater treatment system and a seawater treatment method, which are used to solve the technical problem of a low degree of resource utilization of seawater in the prior art. The seawater treatment system comprises: a filtration device, which is used for removing solid particle impurities from seawater and outputting filtered water; a nanofiltration device, which is used for separating and filtering out monovalent ions and multivalent ions from the filtered water and outputting a nanofiltration permeate and a nanofiltration concentrate; a softening device, which is used for removing multivalent ions from the nanofiltration concentrate and outputting softened water; an electrolytic hydrogen production device, which is used for decomposing organic matter in the nanofiltration permeate, producing hydrogen and outputting electrolyzed water; and a desalting device, which is used for separating salt from fresh water in the electrolyzed water, wherein an anode (12) and a cathode (13) of the electrolytic hydrogen production device are staggered, the cathode (13) is of a hollow structure having a shell layer (131) and a hollow layer (132), the hollow structure has an opening (133), an exhaust structure is arranged on the shell of an electrolytic cell, and the opening (133) outputs hydrogen via the exhaust structure.

Description

Seawater treatment system and seawater treatment method Technical Field

[0001] The present invention relates to the technical field of seawater treatment, and in particular to a seawater treatment system and a seawater treatment method. Background Art

[0002] Desalination technology has become an important means of addressing global water shortages, enjoying widespread use worldwide and promising prospects. Currently, desalination primarily utilizes technologies such as reverse osmosis (RO), multi-stage flash evaporation (MSF), and multiple-effect evaporation (MED). RO membrane separation technology is widely used due to its advantages, including no phase change, room-temperature operation, ease of operation, low energy consumption, high effluent quality, and high automation. However, due to the presence of high concentrations of impurities in seawater, such as low-solubility substances like calcium sulfate, fine clay components, and high-molecular-weight organic matter (biopolymers) produced by biological metabolism, these impurities adhere to the surface of the RO membrane, easily causing scaling and clogging, resulting in a continuous decrease in the membrane's permeability. Therefore, current desalination processes generally limit the recovery rate of RO membrane systems to between 30% and 50%. Even with evaporative desalination technology, continued scaling can significantly increase energy consumption and reduce evaporative desalination efficiency.

[0003] Pretreatment is performed before RO membrane separation to remove contaminants in seawater that tend to adhere to the RO membrane and reduce permeability, thereby reducing the risk of RO membrane scaling and clogging. Currently, the most widely used pretreatment process involves coagulation and solid-liquid separation using a ferric chloride solution. This method not only requires a large amount of reagents, but also contains a large number of impurities in the coagulated solids, which is not conducive to the recovery and utilization of valuable resources such as calcium and magnesium.

[0004] As global energy consumption grows, fossil fuels and other energy sources will become increasingly depleted, with serious negative impacts on the environment. The development and utilization of hydrogen energy will usher in an era of sustainable development for humanity, and large-scale, affordable hydrogen production is a crucial prerequisite for its development and utilization. Among the many hydrogen production methods, water electrolysis offers low cost, pollution-free products, and significant technological advantages. Seawater reserves are abundant on Earth, so combining desalination with water electrolysis to produce hydrogen can significantly increase the resource utilization of seawater.

[0005] In order to obtain the highest possible current density and the smallest hydrogen evolution overpotential at a certain electrical energy, the electrode material needs to have characteristics such as high surface area, high conductivity, good catalytic activity, long-term mechanical and chemical stability, low cost and safety. Generally, precious metals such as Pt, Pd, and Au are considered to be electrode materials with excellent and efficient electrocatalytic hydrogen evolution performance. However, seawater is alkaline, and the electrolysis of hydrogen in alkaline water involves multi-process water dissociation. The electrolysis reaction rate of hydrogen production is far lower than that in acidic systems. Even if precious metal electrodes are used, the improvement in the hydrogen production efficiency of seawater electrolysis is very limited. In addition, the sources of precious metals are scarce and expensive, making large-scale industrial production impossible. Therefore, it is necessary to develop highly active and stable non-precious metal catalysts suitable for the electrolysis of seawater in an alkaline environment.

[0006] To this end, researchers have devoted considerable effort to the selection and design of cathode materials. Nanocrystalline materials, rare earth alloys, and amorphous materials all offer promising performance. Nickel alloys are among the most extensively studied cathode materials due to their simple preparation methods, diverse selection, and excellent catalytic properties. However, current nickel alloys suffer from high overpotentials, poor voltage stability, low strength, and poor corrosion resistance, making them unsuitable for alkaline seawater environments. Summary of the Invention

[0007] One object of the present invention is to provide a cathode material for hydrogen electrolysis, its preparation method, and its application to address the technical problems of nickel alloy materials in the prior art, such as high overpotential, poor voltage stability, low strength, and poor corrosion resistance. Another object of the present invention is to provide a seawater treatment system and method to address the technical problem of low seawater resource utilization in the prior art.

[0008] In order to achieve the above-mentioned purpose, according to the first aspect of the present invention, a cathode material for hydrogen production by electrolysis is provided, and the technical solution is as follows: The cathode material for hydrogen production by electrolysis includes a main phase and a doped phase, wherein the main phase is a Ni-Cr-Fe intermetallic compound, and the doped phase includes any of Mo element, intermetallic compounds of Mo and Cr and / or Fe, and Cr-Ni intermetallic compounds.

[0009] As a further improvement of the cathode material for hydrogen production by electrolysis: the main phase is Ni 2.9 Cr 0.7 Fe 0.36 ; The doped phase includes any of Mo element, FeMo, Fe3Mo, Fe2Mo, FeCrMo, CrMo, CrNi, and Cr3Ni2.

[0010] In order to achieve the above-mentioned purpose, according to the second aspect of the present invention, a method for preparing a cathode material for electrolytic hydrogen production is provided, and the technical scheme is as follows: The method for preparing a cathode material for electrolytic hydrogen production comprises the following steps: ball-milling and mixing Ni powder, Cr powder, Fe powder and Mo powder to obtain a mixed powder; adding a forming aid to the mixed powder, and then granulating and sieving to obtain formed particles; pressing the formed particles into a green body; performing a high-temperature sintering treatment on the green body, and cooling it in the furnace to obtain the cathode material for electrolytic hydrogen production.

[0011] As a further improvement of the above preparation method: Ni powder, Cr powder and Fe powder are ball-milled and mixed to obtain a first mixed powder; Mo powder is added to the first mixed powder and ball-milled to obtain a second mixed powder; a forming aid is added to the second mixed powder, followed by granulation and sieving to obtain formed particles.

[0012] As a further improvement to the above preparation method: the particle size of Ni powder, Cr powder and Fe powder is 3 to 10 μm; the mass ratio of Ni powder, Cr powder and Fe powder is 7:2:1; the mass fraction of Mo powder in the second mixed powder is 1 to 13%; the forming aid is stearic acid, and the amount of the forming aid is 2 to 5% of the mass of the second mixed powder; 40 to 80 mesh sieve is used for screening; and pressing and forming is performed under a pressure of 50 to 300 MPa.

[0013] As a further improvement to the above preparation method: the mass fraction of Mo powder in the second mixed powder is 7-9%.

[0014] As a further improvement of the above preparation method: high-temperature sintering treatment is: starting from room temperature to the sintering temperature, the sintering temperature is 800°C, heating from 450-550°C to the sintering temperature, keeping the temperature for 50-70 minutes after each 50-100°C increase, and keeping the temperature for 50-100 minutes after reaching the sintering temperature. Cooling in the furnace will obtain the cathode material for electrolytic hydrogen production.

[0015] As a further improvement of the above preparation method: the high-temperature sintering process is: the first stage: heating from room temperature to 500℃ and keeping warm for 60 minutes; the second stage: continuing to heat up to 580℃ and keeping warm for 60 minutes; the third stage: continuing to heat up to 650℃ and keeping warm for 60 minutes; the fourth stage: continuing to heat up to 720℃ and keeping warm for 60 minutes; the fifth stage: continuing to heat up to 800℃ and keeping warm for 80 minutes.

[0016] In order to achieve the above-mentioned purpose, according to the third aspect of the present invention, an electrolytic hydrogen production device is provided, and the technical solution is as follows: the electrolytic hydrogen production device has a cathode, and the cathode adopts the cathode material for electrolytic hydrogen production described in the first aspect above, or the cathode material for electrolytic hydrogen production prepared by the preparation method described in the second aspect above.

[0017] In order to achieve the above-mentioned purpose, according to the fourth aspect of the present invention, a method for producing hydrogen by electrolysis is provided, and the technical solution is as follows: the method for producing hydrogen by electrolysis comprises the steps of: electrolyzing seawater using the electrolysis hydrogen production device described in the third aspect above.

[0018] In order to achieve the above-mentioned purpose, according to the fifth aspect of the present invention, a seawater treatment system is provided, and the technical solution is as follows: the seawater treatment system comprises: a filtering device for removing solid particulate impurities in seawater and outputting filtered water; a nanofiltration device for separating monovalent ions and polyvalent ions in filtered water and outputting nanofiltration water and nanofiltration concentrated water; a softening device for removing polyvalent ions in nanofiltration concentrated water and outputting softened water; an electrolytic hydrogen production device for decomposing organic matter in nanofiltration water and generating hydrogen, and outputting electrolytic water; a desalination device for separating salt and fresh water in electrolytic water; wherein the electrolytic hydrogen production device comprises an electrolytic cell shell, an anode and a cathode; the anode and cathode are staggered; the anode is installed in the electrolytic cell shell and is used to decompose organic matter in the electrolyte by an anodic electrochemical reaction; the cathode is installed in the electrolytic cell shell and is used to generate hydrogen by a cathode electrochemical reaction; The cathode is a hollow structure having a shell layer and a hollow layer. The hollow structure has an opening. An exhaust structure is provided on the electrolytic cell shell. The opening outputs hydrogen through the exhaust structure.

[0019] As a further improvement of the above-mentioned seawater treatment system: the softened produced water flows back into the filtering device; and the filtering device processes the mixture of seawater and softened produced water.

[0020] As a further improvement to the above-mentioned seawater treatment system: the filtering device includes a fine filtration device and an ultrafiltration device connected in sequence.

[0021] As a further improvement of the above-mentioned seawater treatment system: the softening device includes a flocculation sedimentation tank and a filter press equipment connected in sequence.

[0022] As a further improvement of the above-mentioned seawater treatment system: the desalination device is a reverse osmosis membrane assembly or an evaporation concentration assembly.

[0023] As a further improvement to the above-mentioned seawater treatment system: the shell layer includes a cathode layer and a diaphragm layer manufactured as one body and arranged from the inside out; the cathode layer is a porous body densely covered with three-dimensional interconnected pores; the diaphragm layer is made of a diaphragm material attached to the outer surface of the cathode layer.

[0024] As a further improvement of the above-mentioned seawater treatment system: the material of the cathode layer includes a main phase and a doped phase, the main phase is a Ni-Cr-Fe intermetallic compound, and the doped phase includes any of Mo element, an intermetallic compound of Mo and Cr and / or Fe, and a Cr-Ni intermetallic compound.

[0025] In order to achieve the above-mentioned purpose, according to the sixth aspect of the present invention, a seawater treatment method is provided, and the technical solution is as follows: the seawater treatment method uses the seawater treatment system described in the fifth aspect to treat seawater.

[0026] The present invention has the following advantages: (1) By alloying Ni with transition metal elements Cr, Fe, and Mo, the present invention obtains more substantial intrinsic catalytic activity, as shown in the following: The Ni-Mo bond is strong, and driven by thermodynamic laws, the alloying of Ni and Mo leads to favorable positioning of hydrogen atoms. Mo doping promotes electron transfer between elements, increases the electron density difference between intermetallic compounds, reduces the impedance of the cathode material, accelerates the electron transfer rate in the HER, and improves the intrinsic catalytic activity of the cathode material. Mo doping leads to the formation of new phases, changes the surface morphology, increases the surface roughness, and significantly increases the electrochemically active surface area.

[0027] Fe and Ni are both transition metals and belong to the VIII B group elements and have the same electronic layer structure. Adjusting the natural electronic structure of the catalytic surface can easily produce a synergistic effect, thereby reducing the overpotential of the cathode material and improving the hydrogen evolution catalytic activity.

[0028] Cr is in the same group as Mo in the periodic table. Its outer layer contains unpaired d electrons, which can produce a very obvious electrocatalytic synergistic effect on the hydrogen evolution reaction. In addition, the Cr element can significantly improve its corrosion resistance in alkaline solution.

[0029] (2) Compared with disordered solid solution alloys, the metal elements in the cathode material for electrolytic hydrogen production of the present invention mainly exist in the form of intermetallic compounds. The intermetallic compounds are composed of metal elements and non-metal elements in a specific ratio. Due to the mixed bond form of metallic bonds and covalent bonds, the electronic structure of the material can be further optimized. On the one hand, it has significantly better strength and corrosion resistance. On the other hand, it can promote the adsorption and release of ions in the process of electrolytic hydrogen production, reduce the dissociation energy barrier of water in the electrolyte system, improve the hydrogen production efficiency in the electrolyte system, and show good catalytic activity and stability. Preferably, when the cathode material for electrolytic hydrogen production of the present invention contains an appropriate amount of Mo element, it can improve the catalytic activity together with other phases. The unreacted Mo, the newly formed Mo-containing phase, and the phase formed between NiCrFe all have a certain degree of catalytic effect on the hydrogen evolution activity. When they are in a good and stable ratio with each other, they can simultaneously exert the maximum catalytic hydrogen evolution effect.

[0030] (3) The cathode material for hydrogen electrolysis, prepared by the element powder reaction synthesis method of the present invention, has micron-scale pores, which can greatly increase the specific surface area of ​​the material and provide sufficient active sites. At the same time, the micron-scale pores provide channels for hydrogen to escape, preventing hydrogen from accumulating on the electrode surface and covering the catalytic active sites.

[0031] (4) The present invention adopts a special sintering process. First, it ensures that the phases formed by sufficient sintering are as much as possible intermetallic compounds, and reduces the content of other impurities such as solid solution alloys, carbon elements, carbides, and carbon oxides, so that the structure is single, the composition is uniform, and the distribution of various constituent elements is uniform without segregation. Second, it ensures that the material does not deform, shrinks or expands in proportion, and does not undergo local melting, bending, etc. Third, it ensures that a large number of pores are generated in the material to increase the specific surface area, thereby improving the reaction efficiency. Fourth, it improves the sintering efficiency. Preferably, the metal element powder of the present invention can fully mix Ni powder, Cr powder and Fe powder when mixed in a step-by-step manner. On the basis of ensuring that the three elements of Ni-Cr-Fe as the base metal are in the best ratio, it can clearly explore the catalytic hydrogen evolution effect of different Mo powder contents on its doping, thereby obtaining the most suitable Mo powder ratio for mixing and adjusting the best hydrogen evolution activity ratio.

[0032] (5) The present invention uses a filtration device, a nanofiltration device, a softening device and an electrolytic hydrogen production device to pre-treat seawater, which can effectively remove impurities in seawater such as low-solubility substances such as calcium sulfate, fine clay components, and high-molecular organic matter (biopolymers) produced by biological metabolism. When RO membrane separation technology is used for desalination, these impurities can be effectively prevented from causing scaling and clogging of the RO membrane, and the evaporation efficiency can be improved when evaporation desalination is used.

[0033] (6) The present invention first removes solid particulate impurities through a filtration device, and then uses a nanofiltration device to enrich the multivalent ions. This not only reduces the softening treatment volume and the amount of flocculation and sedimentation agents used, but also improves the purity of the flocculation precipitation, facilitates further recycling of valuable resources such as calcium and magnesium, and can also improve the electrolysis efficiency.

[0034] (7) The present invention processes nanofiltration water by using an electrolytic hydrogen production device. Chloride ions in the nanofiltration water lose electrons at the anode and become chlorine gas. Chlorine gas is hydrolyzed into chloride ions and hypochlorous acid. Hypochlorous acid generates hydroxyl radicals ·OH that can deeply oxidize and remove organic matter. At the same time, the cathode electrochemical reaction of the electrolytic hydrogen production device generates clean energy hydrogen, which can generate more economic benefits. The use of green electricity can fully meet the demand, with low electricity costs and significant overall economic benefits. Therefore, the present invention utilizes the anode electrochemical reaction of the electrolytic hydrogen production device to generate highly active free radicals to decompose organic matter in water and utilizes the cathode electrochemical reaction to generate clean energy hydrogen. While obtaining hydrogen energy, the organic matter is deeply removed, thereby significantly improving the subsequent desalination efficiency and achieving efficient and deep utilization of seawater resources.

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Additional aspects and advantages of the present invention will be partially given in the following description, partially become apparent from the following description, or be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings that constitute a part of the present invention are used to assist in understanding the present invention. The contents provided in the drawings and their related descriptions in the present invention can be used to explain the present invention, but do not constitute improper limitations on the present invention.

[0037] FIG1 is a graph showing the constant current polarization stability of the cathode at 9% Mo-800° C. of the present invention.

[0038] Figure 2 is the XRD pattern of 0% Mo-800°C, 1% Mo-800°C, 3% Mo-800°C, 5% Mo-800°C, 7% Mo-800°C, and 9% Mo-800°C of the present invention.

[0039] Figure 3 is an SEM photograph of the present invention, wherein (a) is 0% Mo-800°C, (b) is 1% Mo-800°C, (c) is 3% Mo-800°C, (d) is 5% Mo-800°C, (e) is 7% Mo-800°C, and (f) is 9% Mo-800°C.

[0040] FIG4 is a schematic structural diagram of a first embodiment of an electrolytic hydrogen production device according to the present invention.

[0041] FIG5 is a schematic diagram of the AA section in FIG4 after cutting.

[0042] FIG6 is a schematic diagram of the electrolytic hydrogen production device shown in FIG5 from another angle.

[0043] FIG7 is a schematic diagram of the appearance of the cathode in FIG4 .

[0044] FIG8 is a schematic structural diagram of the material layer of the cathode in FIG4 .

[0045] FIG9 is a schematic structural diagram of the anode and cathode in the second embodiment of the electrolytic hydrogen production device of the present invention.

[0046] FIG10 is a schematic diagram of the structure shown in FIG9 from another angle.

[0047] FIG11 is a schematic structural diagram of an embodiment of a seawater treatment system according to the present invention.

[0048] The relevant marks in the above drawings are: 11-electrolytic cell shell, 12-anode, 13-cathode, 14-aeration device, 15-foam cleaning mechanism, 16-water distributor, 17-gas-liquid separator, 111-electrolysis area, 112-flotation area, 113-cathode installation interface structure, 131-shell layer, 132-hollow layer, 133-opening, 1311-cathode layer, 1312-diaphragm layer. DETAILED DESCRIPTION

[0049] The present invention is described below in detail and in detail with reference to the accompanying drawings. A person skilled in the art will be able to implement the present invention based on this description. Before describing the present invention with reference to the accompanying drawings, it should be noted that the technical solutions and technical features provided in the various parts of the present invention, including the following description, may be combined with each other unless they conflict.

[0050] In addition, the embodiments of the present invention described below are generally only part of the embodiments of the present invention, rather than all of the embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making any creative efforts should fall within the scope of protection of the present invention.

[0051] Regarding the terms and units in the present invention: The terms "include", "have" and any variations thereof in the description and claims of the present invention and the related parts are intended to cover non-exclusive inclusions.

[0052] (1) Example of cathode material for electrolytic hydrogen production and preparation method thereof: The preparation method of cathode material for electrolytic hydrogen production comprises the following steps: (1) mixing Ni powder, Cr powder and Fe powder by ball milling to obtain a first mixed powder; specifically: the particle size of Ni powder, Cr powder and Fe powder is 3 to 10 μm; the mass ratio of Ni powder, Cr powder and Fe powder is 7:2:1.

[0053] (2) adding Mo powder to the first mixed powder and ball milling to obtain a second mixed powder; specifically, the mass fraction of Mo powder in the second mixed powder is 1 to 13%.

[0054] (3) adding a forming aid to the second mixed powder, granulating and sieving to obtain formed particles; specifically, the forming aid is stearic acid, and the amount of the forming aid is 4% of the mass of the second mixed powder; and sieving using a 60-mesh sieve.

[0055] (4) Pressing the formed particles into a green body to obtain a green body; specifically, pressing and forming the green body at a pressure of 200 MPa.

[0056] (5) The green body is subjected to high-temperature sintering treatment, and the cathode material for electrolytic hydrogen production is obtained by cooling in the furnace; the high-temperature sintering treatment is specifically as follows: The first stage: heating from room temperature to 500 ° C, and keeping warm for 60 minutes; The second stage: continuing to heat up to 580 ° C, and keeping warm for 60 minutes; The third stage: continuing to heat up to 650 ° C, and keeping warm for 60 minutes; The fourth stage: continuing to heat up to 720 ° C, and keeping warm for 60 minutes; The fifth stage: continuing to heat up to 800 ° C, and keeping warm for 80 minutes.

[0057] Among them, the mass fraction of Mo powder in the second mixed powder is 1%, 3%, 5%, 7%, 9%, 11%, and 13%, and the corresponding cathode materials are expressed as 1% Mo-800℃, 3% Mo-800℃, 5% Mo-800℃, 7% Mo-800℃, 9% Mo-800℃, 11% Mo-800℃, and 13% Mo-800℃.

[0058] Control group 1: The difference from the embodiment is that the following high-temperature sintering treatment process is adopted: First stage: heating from room temperature to 500°C and keeping warm for 60 minutes; Second stage: continuing to heat up to 560°C and keeping warm for 60 minutes; Third stage: continuing to heat up to 630°C and keeping warm for 60 minutes; Fourth stage: continuing to heat up to 700°C and keeping warm for 60 minutes; Fifth stage: continuing to heat up to 770°C and keeping warm for 60 minutes; Sixth stage: continuing to heat up to 850°C and keeping warm for 80 minutes.

[0059] Among them, the mass fraction of Mo powder in the second mixed powder is 1%, 3%, 5%, 7%, 9%, 11%, and 13%, and the corresponding cathode materials are expressed as 1% Mo-850℃, 3% Mo-850℃, 5% Mo-850℃, 7% Mo-850℃, 9% Mo-850℃, 11% Mo-850℃, and 13% Mo-850℃.

[0060] Control group 2: The difference from the embodiment is that the following high-temperature sintering treatment process is adopted: First stage: heating from room temperature to 500°C and keeping warm for 60 minutes; Second stage: continuing to heat up to 580°C and keeping warm for 60 minutes; Third stage: continuing to heat up to 650°C and keeping warm for 60 minutes; Fourth stage: continuing to heat up to 720°C and keeping warm for 60 minutes; Fifth stage: continuing to heat up to 800°C and keeping warm for 60 minutes; Sixth stage: continuing to heat up to 880°C and keeping warm for 60 minutes; Seventh stage: continuing to heat up to 950°C and keeping warm for 80 minutes.

[0061] Among them, the mass fraction of Mo powder in the second mixed powder is 1%, 3%, 5%, 7%, 9%, 11%, and 13%, and the corresponding cathode materials are expressed as 1% Mo-950℃, 3% Mo-950℃, 5% Mo-950℃, 7% Mo-950℃, 9% Mo-950℃, 11% Mo-950℃, and 13% Mo-950℃.

[0062] Control group 3: The difference from the embodiment is that the following high-temperature sintering treatment process is adopted: First stage: heating from room temperature to 500°C and keeping warm for 60 minutes; Second stage: continuing to heat up to 570°C and keeping warm for 60 minutes; Third stage: continuing to heat up to 630°C and keeping warm for 60 minutes; Fourth stage: continuing to heat up to 690°C and keeping warm for 60 minutes; Fifth stage: continuing to heat up to 750°C and keeping warm for 80 minutes.

[0063] Among them, the mass fraction of Mo powder in the second mixed powder is 1%, 3%, 5%, 7%, 9%, 11%, and 13%, and the corresponding cathode materials are expressed as 1% Mo-750℃, 3% Mo-750℃, 5% Mo-750℃, 7% Mo-750℃, 9% Mo-750℃, 11% Mo-750℃, and 13% Mo-750℃.

[0064] Control group 4: Mo powder was not used, and the corresponding cathode materials were expressed as 0% Mo-750°C, 0% Mo-800°C, 0% Mo-850°C, and 0% Mo-950°C.

[0065] Control group 5: Ni powder, Cr powder, Fe powder and Mo powder were directly ball-milled and mixed in a one-step mixing method. The mass fraction of Mo powder in the mixed powder was 9%. The corresponding cathode materials were expressed as Ni / Cr / Fe / Mo-750℃, Ni / Cr / Fe / Mo-800℃, Ni / Cr / Fe / Mo-850℃, and Ni / Cr / Fe / Mo-950℃.

[0066] Then, the electrochemical performance of the cathode materials of the embodiment and the control example was tested using an electrochemical workstation. The working electrode of the three-electrode system used was the prepared cathode material, the reference electrode was a mercury / mercuric oxide electrode, the reference electrode was aligned with the center of the working electrode test surface through a Lu capillary (salt bridge) and separated by 1-2 mm, and the auxiliary electrode was a platinum sheet (10 mm × 10 mm × 0.2 mm). The test was carried out in simulated seawater (26.5 g / L NaCl, 24.0 g / L MgCl2, 3.3 g / L MgSO4, 1.1 g / L CaCl2, 0.2 g / L NaHCO3, 0.73 g / L KCl, 0.28 g / L NaBr, the same below). Before the electrochemical test, the working electrode was sealed and 0.5 cm of the working electrode surface was exposed. 2 The working area is 100 mm, while the non-working surface is encapsulated with waterproof raw tape and 704 silicone rubber. This ensures that the current value automatically collected by the computer is the required current density. All electrochemical test data are collected in a constant temperature water bath. Before valid data testing, the open circuit potential of the working electrode is measured using the three-electrode test method. The open circuit potential of the cathode material stabilizes at around -0.3V within 120 minutes. After the open circuit potential stabilizes, the electrode is tested for corresponding data. The cathode overpotential test process is as follows: the value at which the open circuit potential stabilizes is selected as the first vertex potential, and the value at which the open circuit potential drops 2V is selected as the second vertex potential. The polarization test range is 2V, the scan rate is 4mV / s, and the electrolytic cell parameters are selected according to the reference electrode parameters for mercury / mercuric oxide. The test is then initiated.

[0067] The cathode constant current polarization stability test process is as follows: select the constant current polarization mode test, set the constant current to -10mA, the polarization time to 12h, test the potential of the sample for a long time, and observe the sample state at the same time.

[0068] The cathode overpotential test results are shown in Table 1.

[0069] Table 1

[0070]

[0071] It can be seen from Table 1 that when the sintering temperature is 800℃ and the mass fraction of Mo powder in the second mixed powder is 1-13%, the cathode material obtained has a -10mA / cm 2 The overpotential is less than 150mV, showing good hydrogen evolution activity. Especially when the mass fraction of Mo powder in the second mixed powder is 9%, -10mA / cm 2The overpotential reached -59 mV, close to that of commercial Pt / C electrodes. Compared to the examples, the overpotential of the Ni / Cr / Fe / Mo series was significantly higher, indicating that the step-by-step mixing of the raw materials can improve the mixing of the four transition metal elements, increase the degree of reactivity during sintering, and further enhance the synergistic effect between the elements, thereby improving hydrogen evolution activity.

[0072] FIG1 is a graph showing the polarization stability of the cathode of 9% Mo-800°C of the present invention. As shown in FIG1, when the fixed current density is 10 mA / cm 2 When the test time is 12h, the voltage fluctuation of 9% Mo-800℃ in simulated seawater does not exceed 295mV, indicating that its hydrogen evolution activity can remain stable when used as a cathode material in simulated seawater.

[0073] In addition, the corrosion resistance and yield strength of 9% Mo at 800°C were tested. Corrosion resistance was measured using the open-circuit potential of the cathode material in simulated seawater; a more positive potential indicates better corrosion resistance. Yield strength was measured according to the Chinese national standard GBT 228.1-2010. The results for 9% Mo at 800°C were -0.551V and 185MPa, demonstrating excellent corrosion resistance and yield strength.

[0074] Figure 2 shows the XRD patterns of the present invention at 0% Mo-800°C, 1% Mo-800°C, 3% Mo-800°C, 5% Mo-800°C, 7% Mo-800°C, and 9% Mo-800°C. As can be seen from Figure 2, when no Mo is added, the 0% Mo-800°C phase consists solely of Ni-Cr-Fe intermetallic compounds. When the Mo doping level is low, the Mo element primarily exists as the intermetallic compounds FeMo and Fe3Mo. As the Mo doping level increases, the Mo-Fe intermetallic compounds gradually decrease, and other intermetallic compound phases such as Fe2Mo, FeCrMo, CrMo, CrNi, and Cr3Ni2 begin to appear. When the Mo doping level reaches 7%, a single Mo phase appears, and the corresponding overpotential decreases significantly. However, when the Mo doping level is too high, the corresponding overpotential gradually increases, indicating that an appropriate amount of single Mo phase helps enhance hydrogen evolution activity.

[0075] Figure 3 shows SEM images of the present invention, where (a) is 0% Mo-800°C, (b) is 1% Mo-800°C, (c) is 3% Mo-800°C, (d) is 5% Mo-800°C, (e) is 7% Mo-800°C, and (f) is 9% Mo-800°C. As can be seen from Figure 3, all cathode materials have a three-dimensional through-pore structure with relatively abundant pores, which helps to improve the efficiency of the hydrogen evolution reaction.

[0076] The porosity of the cathode materials in the embodiments was tested using the Archimedean method and was found to be above 35%.

[0077] (II) Electrolytic Hydrogen Production Device and Electrolytic Hydrogen Production Method FIG4 is a schematic structural diagram of a first embodiment of the electrolytic hydrogen production device of the present invention. FIG5 is a schematic cross-sectional view of the AA section in FIG4 . FIG6 is a schematic diagram of the electrolytic hydrogen production device shown in FIG5 from another angle. FIG7 is a schematic diagram of the appearance of the cathode in FIG4 . FIG8 is a schematic structural diagram of the material layer of the cathode in FIG4 . As shown in FIG4-8 , the electrolytic hydrogen production device includes an electrolytic cell shell 11 , an anode 12 , and a cathode 13 .

[0078] The anode 12 is installed in the electrolytic cell housing 11 and is used to oxidize the electrolyte through an anode electrochemical reaction. The anode 12 here can be the same or similar anode as that of the electrocatalytic oxidation reactor (such as a titanium-based metal oxide coating electrode).

[0079] The cathode 13 is installed in the electrolytic cell housing 11 and is used to generate hydrogen through cathode electrochemical reaction. The cathode 13 is a hollow structure having a shell layer 131 and a hollow layer 132 , and the hollow structure has an opening 133 .

[0080] The main purpose of configuring the cathode 13 as a hollow structure having a shell layer 131 and a hollow layer 132 is to provide a hydrogen output channel through the hollow layer 132. Specifically, the hollow layer 132 provides a hydrogen output channel, and the opening 133 is used to output the hydrogen in the hollow layer 132. The electrolyzer shell 11 is provided with an exhaust structure, and the opening 133 outputs hydrogen through the exhaust structure.

[0081] The shell 131 includes a cathode layer 1311 and a diaphragm layer 1312, which are manufactured integrally and arranged from the inside out. The cathode layer 1311 is a porous body densely covered with three-dimensional interconnected pores. This increases the specific surface area of ​​the cathode layer 1311, improves the efficiency of the cathode electrochemical reaction, and allows hydrogen to enter the hollow layer 132 through the pores. The diaphragm layer 1312 is made of a diaphragm material attached to the outer surface of the cathode layer 1311.

[0082] The porous body is a metal porous material, which can further increase the specific surface area of ​​the cathode layer 1311. Specifically, the metal porous material is the cathode material in the above embodiment.

[0083] Typically, the porous body is used to connect to the negative electrode of a DC power supply, and the anode 12 is used to connect to the positive electrode of a DC power supply.

[0084] Thus, since the cathode 13 is a hollow structure having a shell 131 and a hollow layer 132, the hollow structure has an opening 133, and the shell 131 includes a cathode layer 1311 and a diaphragm layer 1312 manufactured as one piece and arranged from the inside out, the cathode layer 1311 is a porous body with dense pores, which is used to connect to the power supply, and the diaphragm layer 1312 is made of a diaphragm material attached to the outer surface of the cathode layer 1311. The hollow layer 132 provides a hydrogen output channel, and the opening 133 is used to output hydrogen. Thus, the diaphragm and the cathode are integrated. For hydrogen production by electrolysis, the separate recovery of hydrogen can be achieved and it helps to simplify the structure of the hydrogen production device by electrolysis.

[0085] In addition, since the diaphragm layer 1312 is made of a diaphragm material attached to the outer surface of the cathode layer 1311, the diaphragm layer 1312 (i.e., the diaphragm) actually also acts as a filter membrane on the outer surface of the cathode layer 1311, which can prevent particulate matter in the electrolyte from entering the cathode layer 1311 through the diaphragm layer 1312 and causing clogging of the pores of the cathode layer 1311.

[0086] The diaphragm material comprises an inorganic membrane. Generally speaking, inorganic membranes are more easily and stably bonded to porous metal materials. Optionally, the diaphragm material may comprise any one of a ceramic membrane, a polymer-ceramic membrane hybrid membrane, and a nanocomposite membrane. Ceramic membranes, polymer-ceramic membrane hybrid membranes, and nanocomposite membranes are all existing electrolyte diaphragms. The ceramic in these membranes may comprise aluminum oxide ceramics or silicon nitride ceramics.

[0087] Typically, the diaphragm layer 1312 itself and / or the diaphragm layer 1312 and the cathode layer 1311 may also form an asymmetric composite layer structure.

[0088] In the first embodiment shown in Figures 4-8 , the hollow structure is a plate-shaped hollow structure. Thus, cathode 13 is a cathode plate, which facilitates installation and use within the trough-shaped electrolytic cell housing 11. Furthermore, as shown in Figure 7 , the opening 133 is typically provided on the sidewall of the plate-shaped hollow structure that defines the thickness of the plate-shaped hollow structure.

[0089] Figure 9 is a schematic diagram of the anode and cathode structures of the second embodiment of the electrolytic hydrogen production device of the present invention. Figure 10 is a schematic diagram of the structure shown in Figure 9 from another angle. As shown in Figures 9-10, the hollow structure is a tubular hollow structure, with the opening 133 provided at the end of the tubular hollow structure. Furthermore, the anode 12 is cylindrical and is sheathed over the cathode 13.

[0090] The manufacturing method of the cathode 13 may include the steps of: coating a slurry containing a diaphragm material on the outer surface of the cathode material (the shape of which is controlled to be a plate-like hollow structure or a tubular hollow structure during pressing), and then sintering the cathode material coated with the slurry to form a diaphragm layer, which serves as a diaphragm when used.

[0091] In the first embodiment as shown in Figures 4 to 8, the electrolytic cell shell 11 is placed vertically, and the electrolytic cell shell 11 has an electrolysis zone 111 and a flotation zone 112 arranged in sequence from bottom to top; the anode 12 and the cathode 13 are arranged in the electrolysis zone 111, and an air flow floating channel is provided between the anode 12 and the cathode 13, and the air flow floating channel is used to oxidize the gas (such as oxygen) generated when the anode 12 oxidizes the water entering the electrolysis zone 111 through the anode electrochemical reaction and / or the gas in the electrolytic cell shell 11. The gas generated by the aeration device 14 at the lower part of the electrolysis zone 111 is introduced into the flotation zone 112; when the air flow upward channel is used to introduce the gas generated by the aeration device 14 at the lower part of the electrolysis zone 111 in the electrolytic cell shell 11 into the flotation zone 112, the aeration device 14 is provided at the lower part of the electrolysis zone 111 in the electrolytic cell shell 11; the top of the flotation zone 112 is also provided with a foam cleaning mechanism 15, which is used to discharge the foam generated at the top of the flotation zone 112 out of the electrolytic cell shell 11.

[0092] Specifically, a water distributor 16 is provided in the electrolytic cell housing 11 at the lower portion of the electrolysis zone 111. The water distributor 16 is used to introduce water. The water distributor 16 can be a pipe with a plurality of water outlet holes.

[0093] Specifically, the scum cleaning mechanism 15 includes an overflow weir, and the electrolytic cell housing 11 is provided with an overflow port connected to the overflow weir.

[0094] Thus, the electrolytic hydrogen production device also functions as a flotation device, further enhancing the water purification performance of the electrolytic hydrogen production device. Because the diaphragm layer 1312 is made of a membrane material attached to the outer surface of the cathode layer 1311, the cathode layer 1311 is separated from the upward flow channel by the diaphragm. During aeration through the aeration device 14, air does not come into contact with hydrogen, significantly reducing safety risks.

[0095] In addition, a cathode mounting interface structure 113 is provided in the electrolytic cell shell 11 , the input portion of the cathode mounting interface structure 113 is connected to the opening 133 via a sealing connection structure, and the output portion of the cathode mounting interface structure 113 is connected to the exhaust structure.

[0096] The exhaust structure includes a gas-liquid separator 17 arranged on the electrolytic cell shell 11, and the gas-liquid separator 17 has a gas-liquid separation chamber, which is connected to the opening 133 (through the cathode mounting interface structure 113); the gas-liquid separator 17 and the electrolytic cell shell 11 form a connector through the opening 133, and the gas-liquid separation chamber is connected to a reflux pipeline system (not shown in the figure), which is used to return the liquid in the gas-liquid separation chamber to the electrolytic cell shell 11.

[0097] A mechanical stirring and / or heating device may also be provided in the gas-liquid separator 17 to promote the precipitation of hydrogen in the gas-liquid separator 17 and discharge the hydrogen from the gas-liquid separator 17 .

[0098] The embodiment of the electrolytic hydrogen production method of the present invention comprises the following steps: using the electrolytic hydrogen production device of the first embodiment shown in Figures 4-8 to electrolyze simulated seawater. It has been verified that when the current density is 10 mA·cm -2 When the cathode overpotential is 30-90 mV (vs. RHE), the Tafel slope is 80-120 mV·dec -1 (vs. RHE); at a constant 400 mA·cm -2 When electrolysis was continued for 36 to 72 h at a constant current density of 10 mA·cm -2 Electrolysis was continued for 72 to 120 hours at a current density of 1.5, with the potential fluctuation after stabilization being less than 16 mV. This indicates that the cathode material of the present invention has both high catalytic activity in simulated seawater electrolysis and good stability at high current densities, demonstrating excellent hydrogen evolution performance.

[0099] (III) Seawater Treatment System and Seawater Treatment Method FIG11 is a schematic structural diagram of an embodiment of a seawater treatment system of the present invention. As shown in FIG11 , the seawater treatment system includes a filtration device, a nanofiltration device, a softening device, an electrolytic hydrogen production device, and a desalination device.

[0100] The filtering device is used to remove solid particulate impurities from seawater or a mixture of seawater and softened water and output filtered water; the filtering device includes a fine filtration device and an ultrafiltration device connected in sequence; fine filtration is also called microfiltration, commonly known as security filtration, and commonly uses hollow fibers with a filtration accuracy of 5um or 1um; the separation range of ultrafiltration is macromolecular substances and colloidal characteristics with a relative molecular mass of 5 million to 1 million, and the corresponding particle diameter is 0.005 to 0.1μm.

[0101] The nanofiltration device is used to separate the monovalent ions and polyvalent ions in the filtered water and output the nanofiltration water and nanofiltration concentrated water. Among them, polyvalent ions such as calcium ions, magnesium ions, and sulfate ions are retained in the nanofiltration concentrated water, while monovalent ions such as potassium ions, sodium ions, and chloride ions pass through the nanofiltration membrane and are enriched in the nanofiltration water.

[0102] The softening device is used to remove multivalent ions from the nanofiltration concentrate and output softened product water; the softened product water flows back into the filtration device. The softening device includes a flocculation sedimentation tank and a filter press connected in sequence. The flocculant added to the flocculation sedimentation tank is a ferric chloride solution at a dosage of 0.5 to 1 mg / L.

[0103] The electrolytic hydrogen production device is used to decompose organic matter in nanofiltration water and generate hydrogen and output electrolytic water; the electrolytic hydrogen production device adopts the electrolytic hydrogen production device of the first embodiment shown in Figures 4-8.

[0104] The desalination device is used to separate salt and fresh water in electrolytic water; the desalination device is a reverse osmosis membrane assembly.

[0105] An embodiment of the seawater treatment method of the present invention includes the following steps: using the seawater treatment system shown in Figure 11 to electrolyze natural seawater (obtained from the Institute of Oceanography, Chinese Academy of Sciences, Qingdao), controlling the SS of the filtered water output by the filtration device to be ≤1 mg / L, the nanofiltration water in the nanofiltration device accounts for 40% of the inlet water flow (i.e., the filtered water flow), the electrolytic cell electrode voltage in the electrolysis hydrogen production device is constant at 3.5V, electrolysis is carried out at a constant voltage of 3.5V for 36 hours, the purity of hydrogen in the generated gas is ≥98%, the generated hydrogen flow rate is ≥1005 mL / h, the total organic matter content in the electrolysis water is ≤69 mg / L, and the SDI is ≤2.6, indicating that the inlet water quality of the reverse osmosis membrane assembly is good and the RO membrane is not easily contaminated.

[0106] SS (suspended solids): refers to the suspended matter content, which refers to solid matter suspended in water, including inorganic and organic matter insoluble in water, mud, clay, microorganisms, etc.

[0107] Total organic matter: This includes COD and BOD. COD (Chemical Oxygen Demand) is the chemical oxygen demand, which is a chemical measurement of the amount of reducing substances in a water sample that need to be oxidized. BOD (Biochemical Oxygen Demand) is the biochemical oxygen demand, which refers to the amount of dissolved oxygen consumed by microorganisms to decompose certain oxidizable substances (especially organic matter) in a certain volume of water over a certain period of time.

[0108] SDI (Silting Density Index): It is called silt density index or pollution index value, also known as FI (Fouling Index) value. It is one of the important indicators for measuring reverse osmosis water inlet and is obtained by testing with an SDI pollution index meter.

[0109] The above describes the relevant contents of the present invention. Based on this description, a person skilled in the art will be able to implement the present invention. Based on the above contents of the present invention, all other embodiments obtained by a person skilled in the art without making any creative efforts should fall within the scope of protection of the present invention.

Claims

1. Seawater treatment system, characterized by: include: Filter device, used to remove solid particulate impurities in seawater and output filtered water; Nanofiltration device is used to separate monovalent ions and polyvalent ions in filtered water, and output nanofiltration water and nanofiltration water. Filter concentrated water; Softening device, used to remove polyvalent ions in nanofiltration concentrated water and output softened water; Electrolysis hydrogen production device, used to decompose organic matter in nanofiltration water and produce hydrogen, output electrolysis Water production; desalination device for separating salt and fresh water in electrolytic water; The electrolytic hydrogen production device comprises an electrolytic cell shell (11), an anode (12) and a cathode (13); the anode (12) and the cathode (13) are arranged alternately; the anode (12) is installed in the electrolytic cell shell (11) and is used to decompose organic matter in the electrolyte through an electrochemical reaction of the anode (12); the cathode (13) is installed in the electrolytic cell shell (11) and is used to generate hydrogen through an electrochemical reaction of the cathode (13); The cathode (13) is a hollow structure having a shell layer (131) and a hollow layer (132), the hollow structure having an opening (133), and an exhaust structure is provided on the electrolytic cell shell (11), and the opening (133) outputs hydrogen through the exhaust structure.

2. The seawater treatment system according to claim 1, wherein: The softened produced water flows back into the filtering device; the filtering device processes the mixed liquid of seawater and softened produced water.

3. The seawater treatment system according to claim 1, wherein: The filtering device comprises a fine filtration device and an ultrafiltration device which are connected in sequence.

4. The seawater treatment system according to claim 1, wherein: The softening device comprises a flocculation sedimentation tank and a filter press equipment which are connected in sequence.

5. The seawater treatment system according to claim 1, wherein: The desalination device is a reverse osmosis membrane component or an evaporation concentration component.

6. The seawater treatment system according to claim 1, wherein: The shell layer (131) comprises a cathode (13) layer and a diaphragm layer (1312) which are manufactured as one body and arranged from the inside out; the cathode (13) layer is a porous body with dense three-dimensional interconnected pores; and the diaphragm layer (1312) is made of a diaphragm material attached to the outer surface of the cathode (13) layer.

7. The seawater treatment system according to claim 6, wherein: The material of the cathode (13) layer includes a main phase and a doped phase, wherein the main phase is a Ni-Cr-Fe intermetallic compound, and the doped phase includes any of Mo element, an intermetallic compound of Mo and Cr and / or Fe, and a Cr-Ni intermetallic compound.

8. A method for treating seawater, characterized in that: The seawater treatment system according to any one of claims 1 to 7 is used to treat seawater.

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