Method for producing hydrogen by electrolysis of water based on the synergistic effect of electrodialysis-ultrasound

Abstract

The present application relates to a kind of hydrogen production based on electrolysis of water-electricity dialysis-ultrasonic synergistic effect, belong to the technical field of hydrogen production by electrolysis of water.The process of hydrogen production by electrolysis of alkali-containing electrolyte in electrolytic cell is continuously or intermittently dialysis treatment to part of electrolyte in electrolytic cell, to remove the carbonate in the part of electrolyte, and the alkali liquor obtained by dialysis separation is added to electrolytic cell, and water is supplemented to electrolytic cell to ensure that the concentration of alkali liquor in electrolytic cell is within the required range;At the same time, the electrolyte in electrolytic cell is intermittently treated by ultrasound.The present application introduces dialysis treatment and ultrasonic treatment steps in conventional alkaline water electrolysis hydrogen production process, which can effectively improve the conductivity of electrolyte and reduce the gas content in electrolyte, thereby effectively reducing the energy consumption of alkaline water electrolysis hydrogen production process.

Description

Technical Field

[0001] This invention relates to a method for producing hydrogen from water by electrolysis based on the synergistic effect of electrodialysis and ultrasound, belonging to the field of water electrolysis hydrogen production technology. Background Technology

[0002] Hydrogen energy is an abundant, green, low-carbon, and widely applicable secondary energy source. As an important component of the future energy system, it is gradually becoming a crucial carrier for global energy transition and development, further contributing to achieving carbon peaking and carbon neutrality goals. Hydrogen energy is mainly used in various fields such as automobiles, rockets, generators, and fuel cells. Compared to fossil fuels such as oil and natural gas, hydrogen energy has no carbon emissions and does not pollute the environment, exhibiting better environmental protection performance. Hydrogen production technologies through water electrolysis mainly include alkaline electrolysis, proton exchange membrane (PEM) electrolysis, solid oxide electrolyzers (SOEC), and anion exchange membrane electrolysis. Among these, alkaline water electrolysis is a significant component of the current water electrolysis market. While alkaline water electrolysis has low fixed and operational costs, its electricity costs are high. Therefore, breakthroughs in reducing the energy consumption of alkaline water hydrogen production technologies will play a crucial role in addressing the volatility issues of renewable energy.

[0003] During water electrolysis, the bubbles generated cover the electrode surface, hindering contact between the electrode and the electrolyte and reducing the conductivity of the electrode / electrolyte interface. Secondly, the inability of oxygen in the electrolyte to escape in time directly affects the purity of the hydrogen gas. During water electrolysis, the hydrogen (oxygen) gas is separated into gas and liquid in a separator. When dissolved gases are present, tiny hydrogen (oxygen) bubbles adhere to the surface of water molecules, causing incomplete separation. These entrained oxygen bubbles are returned to the electrolytic cell with the circulating electrolyte, further reducing the conductivity of the electrode / electrolyte interface. The aqueous solution inevitably absorbs CO2 from the air, increasing the carbonate content, which can reach 1%–3% (Na2CO3, K2CO3). Carbonates are non-conductive, and the higher their content, the lower the conductivity of the electrolyte. When the carbonate content is high enough (1 mg / L), it directly affects the performance of water electrolysis, causing the electrolyte conductivity to decrease, the electrolysis current to drop, the unit power consumption to increase, and the electrolysis efficiency to decrease, ultimately leading to the electrolytic cell being repaired or even scrapped. Summary of the Invention

[0004] To address the problems existing in current alkaline water electrolysis hydrogen production processes, this invention provides a water electrolysis hydrogen production method based on the synergistic effect of electrodialysis and ultrasound. This method introduces electrodialysis and ultrasound treatment steps into the conventional alkaline water electrolysis hydrogen production process. Electrodialysis opens the electrolyte by removing carbonates, improving its conductivity and reducing the impact of carbonates on the efficiency of ultrasound treatment. Ultrasound treatment promotes rapid gas escape from the electrolyte, improving the wetting properties of the electrolyte / electrode interface and reducing the gas content in the electrolyte, thereby effectively reducing the energy consumption of the alkaline water electrolysis hydrogen production process.

[0005] The objective of this invention is achieved through the following technical solutions.

[0006] The method for producing hydrogen from water by electrolysis based on the synergistic effect of electrodialysis and ultrasound includes the following steps:

[0007] In the process of producing hydrogen by electrolysis of an electrolyte containing alkali (the alkali refers to a substance whose anions are all hydroxide ions when ionized in an aqueous solution), a portion of the electrolyte in the electrolytic cell is subjected to continuous or intermittent electrodialysis to remove carbonates (carbonates formed by the electrolyte absorbing CO2 from the air) from this portion of the electrolyte. The alkali solution obtained by electrodialysis is added to the electrolytic cell, and water is added to the electrolytic cell to ensure that the concentration of alkali solution in the electrolytic cell is within the required range. At the same time, the electrolyte in the electrolytic cell is subjected to intermittent ultrasonic treatment.

[0008] Furthermore, the volume of electrolyte used in each electrodialysis treatment is 10 to 20% of the total volume of electrolyte in the electrolytic cell.

[0009] Furthermore, the concentration of the alkaline solution in the electrolytic cell is maintained in the range of 2–3 mol / L.

[0010] Furthermore, the alkali solution is KOH, and the corresponding carbonate is K2CO3; or, the alkali solution is NaOH, and the corresponding carbonate is Na2CO3.

[0011] Furthermore, the ultrasound frequency is 40–50 kHz, the duration of each ultrasound session is 5–8 minutes, and the ultrasound cycle is once every 1–2 hours.

[0012] Furthermore, the concentration of the alkaline solution in the electrolytic cell is maintained in the range of 2-3 mol / L, the frequency of the ultrasound is 40-50 kHz, the duration of each ultrasound is 5-8 min, the ultrasound cycle is once every 1-2 hours, and the volume content of gas in the electrolyte is reduced by 20-30%.

[0013] Beneficial effects:

[0014] (1) In the process of producing hydrogen by electrolysis of water, the present invention can open the circuit of carbonate in the electrolyte by electrodialysis treatment of part of the electrolyte, quickly remove carbonate in the electrolyte, improve the conductivity of the electrolyte, reduce the influence of carbonate on the efficiency of ultrasonic treatment of electrolyte, and ensure that the alkali in the electrolyte is maintained within a certain concentration range, thereby reducing the problem of poor stability of the hydrogen production system caused by the fluctuation of alkali concentration.

[0015] (2) In the process of producing hydrogen by electrolysis of water, the present invention can promote the rapid overflow of gas from the electrolyte by intermittently ultrasonically treating the electrolyte in the electrolyzer, solve the problem of low desorption capacity of bubbles at the electrode interface, thereby improving the wetting performance of the electrolyte / electrode interface and reducing the gas content in the electrolyte; in addition, ultrasonic treatment can also solve the problem of slow diffusion caused by excessively high alkaline concentration in the electrolyte.

[0016] (3) This invention utilizes the synergistic effect of electrodialysis and ultrasound to regulate the gas content and carbonate concentration in the electrolyte, and maintains the alkali concentration in the electrolyte within a certain range, effectively reducing the gas content in the electrolyte and improving the conductivity of the electrolyte, thereby effectively reducing the energy consumption in the process of producing hydrogen by electrolysis of water. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments. Unless otherwise specified, the methods described are conventional methods, and the raw materials described are obtainable from publicly available commercial sources.

[0018] Example 1

[0019] When producing hydrogen using alkaline water electrolysis, the initial electrolyte in the electrolyzer contains a KOH concentration of 2 mol / L, a K₂CO₃ mass fraction of 3%, and a current density of 4.60 mA / mm². 2 The electrolyte temperature is 65-75℃, and the electrode is made of Ni material. Based on the electrode area S entering the electrolyte and the current density formula J = current / S, the average current is determined to be 226A and the average voltage is 44.49V.

[0020] In this embodiment, during the electrolytic hydrogen production process, a portion of the electrolyte in the electrolytic cell is subjected to electrodialysis treatment every 20 minutes. The volume of electrolyte subjected to electrodialysis treatment each time is 10% of the total volume of electrolyte in the electrolytic cell. K2CO3 and KOH are separated using an electrodialysis selective membrane. The K2CO3 separated from this portion of electrolyte is removed, and the KOH obtained from the electrodialysis separation is added back to the electrolytic cell. Water is also added to the electrolytic cell to ensure that the concentration of alkali in the electrolytic cell is ~2.5 mol / L. At the same time, the electrolyte in the electrolytic cell is subjected to intermittent ultrasonic treatment at a frequency of 45 kHz for 5 minutes each time, with the ultrasonic cycle being once every 1 hour.

[0021] Under the electrolysis conditions described in this embodiment, the gas volume content in the electrolyte is reduced by approximately 22% compared to the process without electrodialysis and ultrasonic treatment; and under these electrolysis conditions, after 24 hours of electrolysis, a hydrogen flow rate of 2.6 m³ / h is obtained. 3 / h, the power consumption per kilogram of hydrogen is 43.8 kWh.

[0022] Comparative Example 1

[0023] When producing hydrogen using alkaline water electrolysis, the initial electrolyte in the electrolyzer contains a KOH concentration of 2 mol / L, a K₂CO₃ mass fraction of 3%, and a current density of 4.60 mA / mm². 2 The electrolyte temperature is 65-75℃, and the electrode is made of Ni material. Based on the electrode area S entering the electrolyte and the current density formula J = current / S, the average current is determined to be 226A and the average voltage is 44.49V.

[0024] Electrolysis was carried out directly under the electrolysis conditions described in this comparative example. During the electrolysis process, water was added to the electrolytic cell to ensure that the concentration of the alkali solution in the electrolytic cell was ~2.5 mol / L. After electrolysis for 24 hours under these conditions, a hydrogen flow rate of 1.91 m³ / L was obtained. 3 / h, the electricity consumption per kilogram of hydrogen is 48.5 kW·h.

[0025] Comparative Example 2

[0026] When producing hydrogen using alkaline water electrolysis, the initial electrolyte in the electrolyzer contains a KOH concentration of 2 mol / L, a K₂CO₃ mass fraction of 3%, and a current density of 4.60 mA / mm². 2 The electrolyte temperature is 65-75℃, and the electrode is made of Ni material. Based on the electrode area S entering the electrolyte and the current density formula J=I / S, the average current is determined to be 226A and the average voltage is 44.49V.

[0027] In this comparative example, during the electrolytic hydrogen production process, the electrolyte in the electrolyzer was subjected to intermittent ultrasonic treatment at a frequency of 45 kHz, with each ultrasonic treatment lasting 20 minutes and the ultrasonic cycle being once every 1 hour. Water was also added to the electrolyzer to ensure that the concentration of alkaline solution in the electrolyzer was ~2.5 mol / L.

[0028] Electrolysis under the conditions described in this comparative example for 24 hours yielded a hydrogen flow rate of 1.14 m³ / h. 3 / h, the electricity consumption per kilogram of hydrogen is 52.54 kW·h.

[0029] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing hydrogen from water by electrolysis based on the synergistic effect of electrodialysis and ultrasound, characterized in that: Includes the following steps, In the process of producing hydrogen by electrolysis of an alkaline electrolyte in an electrolytic cell, a portion of the electrolyte in the electrolytic cell is subjected to continuous or intermittent electrodialysis to remove carbonates from that portion of the electrolyte. The alkaline solution obtained by electrodialysis is added to the electrolytic cell, and water is added to the electrolytic cell to ensure that the concentration of the alkaline solution in the electrolytic cell is within the required range. At the same time, the electrolyte in the electrolytic cell is subjected to intermittent ultrasonic treatment.

2. The method for producing hydrogen from water by electrolysis based on the synergistic effect of electrodialysis and ultrasound according to claim 1, characterized in that: The volume of electrolyte used in each electrodialysis treatment is 10-20% of the total volume of electrolyte in the electrolytic cell.

3. The method for producing hydrogen from water by electrolysis based on the synergistic effect of electrodialysis and ultrasound according to claim 1, characterized in that: The concentration of the alkaline solution in the electrolytic cell is maintained in the range of 2 to 3 mol / L.

4. The method for producing hydrogen from water by electrolysis based on the synergistic effect of electrodialysis and ultrasound according to claim 1 or 3, characterized in that: The alkali solution is KOH, and the corresponding carbonate is K2CO3; or, the alkali solution is NaOH, and the corresponding carbonate is Na2CO3.

5. The method for producing hydrogen from water by electrolysis based on the synergistic effect of electrodialysis and ultrasound according to any one of claims 1 to 3, characterized in that: The ultrasound frequency is 40-50 kHz, the duration of each ultrasound session is 5-8 minutes, and the ultrasound cycle is once every 1-2 hours.