Differential current density brine electrolytic bath
By employing a differentiated electrode layout and a series-parallel arrangement of electrolytic cells, the problems of uneven reaction and high energy consumption in electrolytic cells were solved, enabling efficient generation of sodium hypochlorite under low-temperature conditions and reducing the risk of electrode failure and energy consumption.
Patent Information
- Application Number
- CN202511299230.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-12
- Publication Date
- 2025-11-11
AI Technical Summary
The uniform design of the electrode working area in existing electrolytic cells leads to uneven reaction, high overall energy consumption, and severe electrode failure, especially at low temperatures, resulting in low effective chlorine concentration.
By adopting a differentiated electrode layout and series-parallel arrangement, the electrode reaction area gradually decreases from the inlet end to the outlet end, forming a series circuit, and the current density gradually increases. Combined with coatings such as Ru-Ti and Ru-Ir-Ti, the electrode performance is optimized.
It reduces electrode heating, improves current efficiency and effective chlorine concentration at the outlet, reduces salt consumption and energy consumption, and is suitable for low-temperature environments.
Smart Images
Figure CN120925003A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of sodium hypochlorite preparation by electrolysis of brine, specifically a brine electrolyzer with differentiated current density. Background Technology
[0002] Sodium hypochlorite is prepared by electrolyzing brine. The process involves the chemical reaction of electrolyzing brine (mainly sodium chloride solution). The principle is that the prepared brine is injected into an electrolytic cell containing anode and cathode. Under the action of an external electric field, the electrode reaction and the solution reaction occur to generate sodium hypochlorite solution. At the same time, hydrogen gas and other gases are released at the cathode.
[0003] In existing electrolyzers, the electrodes are arranged in a conventional bipolar series-parallel configuration, with each electrode having an equal working area and the same theoretical current density throughout the entire electrolyzer. However, the temperature of the brine at the inlet of the electrolyzer is relatively low, especially in northern winters, often leading to electrode failure due to the excessively low water temperature. At the same time, the effective chlorine concentration at the inlet of the electrolyzer is also very low. As the water flows along the direction of the electrolyzer, the temperature and effective chlorine concentration gradually increase. However, the design of existing electrolyzers causes all electrodes to operate under the same parameters, resulting in an uneven overall reaction and high overall energy consumption. Summary of the Invention
[0004] To address the shortcomings of existing technologies, this invention provides a differentiated current density brine electrolyzer, which solves the problems mentioned in the background section.
[0005] To achieve the above objectives, the present invention provides the following technical solution: a differentiated current density brine electrolyzer, wherein the differentiated current density brine electrolyzer comprises the following steps: S1. Differentiated electrode layout: After determining the number of electrolytic cells, the size of the cell body, and the direction of brine flow, the electrodes are grouped according to the number of cells, and the reaction area of each group of electrodes is arranged in a manner that decreases sequentially from the inlet end to the outlet end. S2, Electrode series-parallel arrangement: The electrodes are assembled in a series-parallel bipolar configuration, with the cathode and anode serving as end electrodes, and intermediate bipolar plates connected alternately to form a series circuit. Since the current is the same, the current density gradually increases with the direction of salt water flow. Therefore, along the direction of electrolyte flow, the electrode area of the first-stage reaction is the largest, the electrode area of subsequent reaction stages is no larger than the electrode area of the previous stage, and the electrode area of the last-stage reaction is the smallest.
[0006] Furthermore, in step S1, the brine flows in from the negative end and out from the positive end, where the negative end is the inlet and the positive end is the outlet.
[0007] Furthermore, in step S1, the number of reaction stages in the electrolytic cell is ≥3 stages; the effective chlorine concentration at the outlet of the electrolytic cell is ≥6g / L.
[0008] Furthermore, in step S1, the anode coating of the electrolytic cell includes, but is not limited to, Ru-Ti and Ru-Ir-Ti coatings.
[0009] Furthermore, in step S1, the cathode of the electrolytic cell is pure titanium, or pure titanium is coated with platinum group metals, and the cathode coating includes, but is not limited to, Ru-Ti, Ru, Pt-Ru, and Ru-Ir coatings.
[0010] Furthermore, in step S2, the electrodes of the same reaction stage in the electrolytic cell have the same size.
[0011] Furthermore, in step S2, the electrode plates of the electrolytic cell are of the same height, and the area difference is achieved only by changing the length.
[0012] This invention provides a differentiated current density brine electrolyzer, which has the following beneficial effects: 1. This differentiated current density brine electrolyzer, which uses differentiated electrodes, can reduce the heat generated in the electrolyzer and lower the requirements for electrodes at low temperatures. Moreover, by increasing the current density at the outlet, the current efficiency at the outlet is significantly improved. Thus, under the same conditions, the effective chlorine concentration at the outlet is increased, and the salt consumption and energy consumption of the electrolyzer are reduced. Attached Figure Description
[0013] Figure 1 This is a schematic diagram of the process flow of a differentiated current density brine electrolyzer according to the present invention; Figure 2 This is a schematic table comparing the parameters of a differentiated current density brine electrolyzer of the present invention with those of a conventional electrolyzer. Detailed Implementation
[0014] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.
[0015] like Figures 1-2 As shown, the present invention provides a technical solution: a differentiated current density brine electrolyzer, which includes the following steps: S1. Differentiated electrode layout: After determining the number of electrolytic cells, the size of the cell body, and the direction of brine flow, the electrodes are grouped according to the number of cells, and the reaction area of each group of electrodes is arranged in a manner that decreases sequentially from the inlet end to the outlet end. The brine flows from the negative end to the positive end, with the negative end being the inlet and the positive end being the outlet. The electrolytic cell has a reaction stage of ≥3 stages; the effective chlorine concentration at the outlet of the electrolytic cell is ≥6g / L; The anode coating of the electrolytic cell includes, but is not limited to, Ru-Ti and Ru-Ir-Ti coatings, in order to improve the current efficiency of chlorine evolution at the anode and significantly reduce the cell voltage; The cathode of the electrolytic cell is pure titanium, or pure titanium coated with platinum group metals. The cathode coating includes, but is not limited to, Ru-Ti, Ru, Pt-Ru, and Ru-Ir coatings to reduce the overpotential of hydrogen evolution, thereby saving energy. S2, Electrode series-parallel arrangement: The electrodes are assembled in a series-parallel bipolar configuration, with the cathode and anode serving as end electrodes, and intermediate bipolar plates connected alternately to form a series circuit. Since the current is the same, the current density gradually increases with the direction of salt water flow. Therefore, along the direction of electrolyte flow, the electrode area of the first-stage reaction is the largest, the electrode area of subsequent reaction stages is no larger than the electrode area of the previous stage, and the electrode area of the last-stage reaction is the smallest. In this electrolytic cell, the electrodes of the same reaction stage have the same size, and the electrode plates of the electrolytic cell have the same height. The difference in area is achieved only by changing the length, which facilitates processing and installation. Example: The brine flows in from the negative end and out from the positive end, where the negative end is the inlet and the positive end is the outlet. The electrolytic cell has four stages. The length × diameter of the tank is 80cm × 16cm, and the total volume is 16L. The electrolyte flows along the length of the tank. The coating length is the reaction area, and the width of each electrode is uniformly 8cm. Stage 1, i.e., the inlet end, cathode side: Coating length 22cm, working area = 22cm × 8cm × 20 = 3520cm² 2 ; Level 2 and Level 3, i.e., intermediate bipolar plates: coating length 16cm, single-level working area = 16cm × 8cm × 20 = 2560cm² 2 ; Stage 4, i.e., the outlet end, anode side: Coating length 10cm, working area = 10cm × 8cm × 20 = 1600cm² 2 ; In the formula for calculating the working area of each electrode, 20 represents the number of electrode plates.
[0016] The anode side is coated with a Ru-Ir-Ti coating with a thickness of 10 micrometers; the cathode side is coated with a Ru-Ti coating with a thickness of 3 μm. The current in the series circuit is 300A, which is conducted through bipolar plates in series. The brine concentration was 3% NaCl solution, the inlet temperature was 17℃, and the outlet temperature rose to 33℃ due to electrolysis heating. The electrolysis time lasted for 2 hours. The parameters recorded during the electrolysis process are as follows: The outlet available chlorine concentration is 8.6 g / L, the inlet brine temperature is 17℃, the energy consumption per unit available chlorine is 4.56 kWh / kg, and the salt consumption is 3.35 kg NaCl / kg available chlorine. Traditional electrolytic cells use a uniform electrode coating length of 16cm, and their single-stage working area is 2560cm². 2 The current density of each electrode is 1172 A / m. 2 The rest of the setup is the same as that of an electrolytic cell using differentiated electrodes; The parameters recorded during the electrolysis process in a traditional electrolytic cell are as follows: The outlet available chlorine concentration is 7.67 g / L, the inlet brine temperature is 17℃, the outlet temperature rises to 40℃, the energy consumption per unit available chlorine is 5.12 kWh / kg, and the salt consumption is 3.93 kg NaCl / kg available chlorine. Based on the parameters recorded in the above electrolysis test, the electrodes of the traditional electrolytic cell operate under a uniform current density. Due to the low temperature and high resistance at the inlet end, the high current density not only greatly increases the risk of electrode failure, but also leads to more severe heat generation. However, under low available chlorine concentration conditions, current density has little effect on current efficiency (efficiency of generating available chlorine); Therefore, the electrolyzer with differentiated electrodes (hereinafter referred to as differentiated electrolyzer) of this invention can reduce the heat generation of the electrolyzer, reduce the requirements for electrodes at low temperatures, and increase the current density at the outlet end, which greatly improves the current efficiency at the outlet end. Thus, under the same conditions, the effective chlorine concentration at the outlet is increased, and the salt consumption and energy consumption of the electrolyzer are reduced.
[0017] In summary, the principle of this differentiated current density brine electrolyzer is as follows: At low temperatures, chloride ions diffuse slowly, and the chlorine gas generated after oxidation on the anode surface also escapes slowly. When the current density is high, oxygen evolution due to side reactions on the anode surface is inevitable. In order to achieve a high effective chlorine concentration, it is often necessary to electrolyze for a long time at a high current density. The accumulation of heat during the electrolysis process leads to the formation of toxic byproducts such as chlorate and the decomposition of hypochlorite, which limits the effective chlorine concentration that can be achieved. If the electrolyzer can accept a lower initial temperature, it will help to achieve a higher effective chlorine concentration, thereby reducing the salt consumption of the electrolyzer. Therefore, by increasing the area of the first-stage reaction electrode and reducing the current density of the first-stage reaction, the requirement for the inlet temperature is significantly reduced. Moreover, when the brine temperature is low, the resistance is high. By using a lower current density, the heat generated in the first-stage reaction is greatly reduced, thereby further reducing the temperature rise. Furthermore, when the effective chlorine concentration is low, the chlorine evolution efficiency is very high, and the lower current density will not affect the overall current efficiency of the electrolyzer. When brine is electrolyzed at a low current density, the temperature gradually increases and the conductivity is improved. In subsequent reaction stages, the length of the electrode can be appropriately shortened, and the cost can be reduced by decreasing the coating area. When the brine reaches the rear of the electrolytic cell, the effective chlorine concentration is already relatively high (e.g., ≥7 g / L). At this point, the marginal current efficiency of sodium hypochlorite generation is already low under conventional current density (see the above embodiment for details). Therefore, this invention significantly increases the current density by shortening the length of the electrode. At the same time, since the electrolysis at the front end minimizes the temperature rise of the electrolyte, a larger current density can be used at the end without the temperature becoming too high, thereby effectively improving the current efficiency.
[0018] The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.
Claims
1. A differentiated current density brine electrolyzer, characterized in that: The differentiated current density brine electrolyzer includes the following steps: S1. Differentiated electrode layout: After determining the number of electrolytic cells, the size of the cell body, and the direction of brine flow, the electrodes are grouped according to the number of cells, and the reaction area of each group of electrodes is arranged in a manner that decreases sequentially from the inlet end to the outlet end. S2, Electrode series-parallel arrangement: The electrodes are assembled in a series-parallel bipolar configuration, with the cathode and anode serving as end electrodes, and intermediate bipolar plates connected alternately to form a series circuit. Since the current is the same, the current density gradually increases with the direction of salt water flow. Therefore, along the direction of electrolyte flow, the electrode area of the first-stage reaction is the largest, the electrode area of subsequent reaction stages is no larger than the electrode area of the previous stage, and the electrode area of the last-stage reaction is the smallest.
2. The differentiated current density brine electrolyzer according to claim 1, characterized in that: In step S1, the brine flows from the negative end to the positive end, where the negative end is the inlet and the positive end is the outlet.
3. The differentiated current density brine electrolyzer according to claim 1, characterized in that: In step S1, the number of reaction stages in the electrolytic cell is ≥3; the effective chlorine concentration at the outlet of the electrolytic cell is ≥6g / L.
4. The differentiated current density brine electrolyzer according to claim 1, characterized in that: In step S1, the anode coating of the electrolytic cell includes, but is not limited to, Ru-Ti and Ru-Ir-Ti coatings.
5. The differentiated current density brine electrolyzer according to claim 1, characterized in that: In step S1, the cathode of the electrolytic cell is pure titanium, or pure titanium coated with platinum group metals. The cathode coating includes, but is not limited to, Ru-Ti, Ru, Pt-Ru, and Ru-Ir coatings.
6. The differentiated current density brine electrolyzer according to claim 1, characterized in that: In step S2, the electrodes of the same reaction stage in the electrolytic cell have the same size.
7. The differentiated current density brine electrolyzer according to claim 1, characterized in that: In step S2, the electrode plates of the electrolytic cell are of the same height, and the area difference is achieved only by changing the length.