Method for producing chlor-alkali by anion exchange membrane

Abstract

This invention discloses a method for preparing chlor-alkali using anion exchange membranes, belonging to the technical field of chlor-alkali preparation. The electrolytic cell equipment includes an electrodialysis membrane stack, a feed solution device, and a power source. The electrodialysis membrane stack comprises an anode plate, an anion exchange membrane, and a cathode plate connected in sequence. The anode plate and the anion exchange membrane, or the cathode plate and the anion exchange membrane, are connected by a sealing soft silicone sheet. This electrolytic cell equipment changes the traditional electrodialysis membrane stack structure used in industrial chlor-alkali preparation. This invention successfully prepares high-purity sodium hydroxide using the described electrolytic cell equipment. The method is simple and efficient, avoiding the environmental and economic problems associated with using perfluorinated cation exchange membranes, and holds promise for industrial-scale production, providing a new approach for the chlor-alkali industry.

Description

Technical Field

[0001] This invention relates to the technical field of chlor-alkali preparation, and more particularly to a method for preparing chlor-alkali using anion exchange membranes. Background Technology

[0002] The chlor-alkali process plays a dominant and irreplaceable role in the chemical industry, as its products account for over 50% of all chemical processes, and approximately 99.5% of caustic soda globally is produced through the traditional chlor-alkali process. Chlor-alkali chemicals are diverse, with wide applications and high economic value. Their products are not only widely used in the chemical industry but also play a significant role in agriculture, power generation, and food processing.

[0003] Its main product, caustic soda, scientifically known as sodium hydroxide, also called caustic soda or lye, is a highly corrosive alkali. It readily dissolves in water to form an alkaline solution and readily reacts with water vapor and carbon dioxide in the air, causing deliquescence and deterioration. Caustic soda has a wide range of applications, including alumina, dyes, pulp, chemical fibers, metal smelting, water treatment, cotton textile finishing, petroleum refining, coal tar product purification, and food processing. According to data from the China Chlor-Alkali Industry Association, my country's chlor-alkali industry capacity has shown a fluctuating upward trend in recent years.

[0004] Typical chlor-alkali electrolysis involves two half-reactions: hydrogen evolution at the cathode and chlorine evolution at the anode, accompanied by the formation of sodium hydroxide in the electrolyte. Since the 1880s, three processes have emerged in the chlor-alkali industry: diaphragm electrolyzers, mercury electrolyzers, and the current ion-exchange membrane electrolyzers. In diaphragm electrolyzers, porous asbestos pads are used to separate the chlorine evolution reaction at the anode and the hydrogen evolution reaction at the cathode, and NaOH is simultaneously formed in the cathode compartment. However, this process suffers from problems such as asbestos contamination, poor product quality, and complex operation and management. Mercury electrolyzers produce alkali in a stepwise manner, yielding an alkali solution with a concentration close to 50%, which can be sold directly as a commodity. This solution is highly pure and almost chloride-free. Furthermore, it eliminates the need for post-treatment operations involving evaporation and concentration of the alkali solution. However, the high price of mercury, the large investment required, and the environmental pollution caused by mercury toxicity necessitate strict control over the mercury content in wastewater discharge, all of which limit its development. The operation of an ion-exchange membrane electrolyzer is very similar to that of a diaphragm electrolyzer, but the difference lies in the use of a polymer ion-exchange membrane instead of a porous asbestos pad, which allows Cl2 and NaOH to separate. Compared with the diaphragm method, the ion-exchange membrane method has advantages such as low power consumption, high liquid alkali concentration, high degree of automation, and less environmental pollution, and is the main development direction of the chlor-alkali industry.

[0005] Currently, perfluorinated cation exchange membranes are the core component of chlor-alkali plants, but their preparation is complex and requires advanced technology. For a long time, the production of perfluorinated cation exchange membranes has been mainly concentrated in countries such as the United States, Japan, and Canada, with major companies including DuPont, Dow, and Gore in the US; Asahi Glass and Asahi Kasei in Japan; and Ballard Chemicals in Canada. my country's chlor-alkali industry has long relied on imports for ion exchange membranes, and the penetration rate of domestically produced ion exchange membranes remains low. Although domestically produced ion exchange membranes have made breakthroughs in overall performance and cost-effectiveness, they still lag behind foreign products in terms of stability. Furthermore, the synthesis of perfluorinated cation exchange membranes can lead to the generation of harmful substances—fluorocarbons. Carbon-fluorine bonds are stable and difficult to degrade naturally; improper recycling or treatment can produce harmful substances that impact the environment and human health. In contrast, anion exchange membranes have a simpler preparation process, have been more extensively studied, and are less expensive, giving them a significant advantage in terms of research and development and economics.

[0006] Therefore, researching and developing a novel chlor-alkali process using anion exchange membranes is of great significance for solving the aforementioned problems in the chlor-alkali process. Summary of the Invention

[0007] In view of this, the technical problem to be solved by the present invention is to provide a method for preparing chlor-alkali using anion exchange membranes. The method successfully prepares high-purity sodium hydroxide; the preparation process is simple, efficient, economical, and environmentally friendly.

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

[0009] This invention provides an electrolytic cell device, including an electrodialysis membrane stack, a feed solution device, and a power source;

[0010] The electrodialysis membrane stack includes an anode plate, an anion exchange membrane, and a cathode plate connected in sequence.

[0011] The anode plate and the anion exchange membrane, or the cathode plate and the anion exchange membrane, are connected by a sealing soft silicone sheet.

[0012] The anode plate, anion exchange membrane, and cathode plate are tightly connected by a sealing soft silicone sheet and fixed by studs and nuts.

[0013] Preferably, the feeding device of the present invention includes an anode chamber feeding device and a cathode chamber feeding device;

[0014] Preferably, the anode chamber feed device is connected to the anode chamber formed by the anode plate and the anion exchange membrane;

[0015] Preferably, the cathode chamber feed device is connected to the cathode chamber formed by the cathode plate and the anion exchange membrane.

[0016] Preferably, the anion exchange membrane of the present invention is selected from AHA membrane, AMX membrane or AGU membrane.

[0017] Preferably, in this invention, the anion exchange membrane is ≥1 sheet.

[0018] In the above-mentioned device, the cathode plate is connected to the negative terminal of the power supply, and the anode plate is connected to the positive terminal of the power supply.

[0019] The thickness of the sealing soft silicone sheet in the above-mentioned equipment is 1.2-2mm.

[0020] The present invention also provides the application of the above-mentioned electrolytic cell equipment in the preparation of chlor-alkali.

[0021] This invention also provides a method for preparing chlor-alkali based on anion exchange membranes, comprising the following steps:

[0022] (1) Using the above-mentioned electrolytic cell equipment, deionized water is circulated into the anode chamber composed of the anode plate and the anion exchange membrane, and sodium chloride solution is circulated into the cathode chamber composed of the cathode plate and the anion exchange membrane.

[0023] (2) Turn on the power supply to allow the anode and cathode chambers to undergo an oxidation-reduction reaction, generating a sodium hydroxide solution in the cathode chamber.

[0024] The above preparation method first involves circulating deionized water in the anode chamber and the anode chamber feed solution device, and circulating sodium chloride solution in the cathode chamber and the cathode chamber feed solution device, so that air is discharged from the equipment and the system is stabilized.

[0025] In some specific embodiments of the present invention, the cycle is performed under the drive of a peristaltic pump.

[0026] Then, under the influence of an electric field, the anode and cathode chambers undergo a redox reaction.

[0027] Specifically, the above redox reactions involve chlorine and oxygen evolution in the anode chamber and hydrogen evolution in the cathode chamber.

[0028] The chlorine evolution reaction produces chlorine gas, the oxygen evolution reaction produces hydrogen ions and oxygen gas, and the hydrogen evolution reaction produces hydroxide ions and hydrogen gas.

[0029] This device differs from traditional devices in that oxygen evolution occurs simultaneously with chlorine evolution in the anode chamber.

[0030] The hydroxide ions further combine with sodium ions in the cathode chamber to form a sodium hydroxide solution.

[0031] The raw material sodium chloride solution of the present invention is fed into the cathode chamber and further converted into sodium hydroxide.

[0032] Furthermore, the chloride ions in the sodium chloride solution in the cathode chamber and the hydroxide ions generated by the hydrogen evolution reaction above compete with each other when passing through the anion exchange membrane. The chloride ions with the faster transmembrane rate preferentially pass through the anion exchange membrane to reach the anode, while the remaining relatively large number of hydroxide ions and sodium ions further combine in the cathode chamber to form sodium hydroxide.

[0033] The experiment is stopped when the concentration of sodium hydroxide solution in the cathode chamber no longer increases or increases only slightly (<0.1 mol) within a certain period of time.

[0034] Preferably, the sodium chloride solution of this invention is selected from a saturated sodium chloride solution or a sodium chloride solution with a concentration of 1-5.5 mol / L. In some specific embodiments of this invention, the sodium chloride solution is selected from a saturated sodium chloride solution or a sodium chloride solution with a concentration of 1 mol / L, 2 mol / L, 3 mol / L, or 4 mol / L.

[0035] Preferably, the power source of the present invention is direct current (DC).

[0036] Preferably, the DC current is 1.89-50.5A; more preferably 10-30A; and in some specific embodiments of the present invention, it is preferably 18.9A.

[0037] Preferably, the current density of the direct current is 10-120 mA / cm². 2 More preferably, it is 90-110 mA / cm. 2 In some specific embodiments of the present invention, 100 mA / cm is preferred. 2 .

[0038] Preferably, the flow rates of the deionized water and sodium chloride solution are independently 200-500 mL / min; more preferably, they are 300-400 mL / min. In some specific embodiments of the present invention, the flow rates of both the deionized water and sodium chloride solution are preferably 400 mL / min.

[0039] The method described in this invention successfully prepared sodium hydroxide solutions of different concentrations with high purity, all above 96%.

[0040] Compared with existing technologies, the electrolytic cell equipment provided by this invention includes an electrodialysis membrane stack, a feed solution device, and a power source. The electrodialysis membrane stack comprises an anode plate, an anion exchange membrane, and a cathode plate connected in sequence. The anode plate and the anion exchange membrane, or the cathode plate and the anion exchange membrane, are connected by a sealing soft silicone sheet. This electrolytic cell equipment changes the traditional electrodialysis membrane stack structure used in the industrial production of chlor-alkali. This invention successfully produces high-purity sodium hydroxide using this electrolytic cell equipment. The method is simple and efficient, avoiding the environmental and economic problems associated with using perfluorinated cation exchange membranes, and holds promise for large-scale industrial production, providing a new approach for the chlor-alkali industry. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the apparatus for preparing chlor-alkali using the anion exchange membrane of the present invention;

[0042] Figure 2 This is a schematic diagram of the reaction membrane stack device of the present invention;

[0043] Figure 3 Schematic diagrams of chloride ion concentration in the anode chambers of Examples 1-5;

[0044] Figure 4 Schematic diagrams of hydroxide ion concentrations in the cathode chambers of Examples 1-5;

[0045] Figure 5 The diagram shows the purity and conversion rate of alkali produced by different sodium chloride concentrations in Examples 1-5. Detailed Implementation

[0046] To further illustrate the present invention, the method for preparing chlor-alkali using anion exchange membranes provided by the present invention will be described in detail below with reference to embodiments.

[0047] This invention provides a method for preparing chlor-alkali using anion exchange membranes. The reaction apparatus includes an electrodialysis membrane stack, a power supply, and a feed tank (feed device), such as... Figure 1 As shown.

[0048] An electrodialysis membrane stack comprises an anode plate, an anion exchange membrane, and a cathode plate arranged sequentially. The anode plate and the anion exchange membrane are connected by a sealing soft silicone sheet, and the cathode plate and the anion exchange membrane are also connected by a sealing soft silicone sheet. Figure 2 As shown. The anode plate is connected to the positive terminal of the power supply, the cathode plate is connected to the negative terminal of the power supply, the anode plate and the adjacent anion exchange membrane form the anode chamber, and the cathode plate and the adjacent anion exchange membrane form the cathode chamber.

[0049] The anode and cathode electrodes in the reaction apparatus are made of corrosion-resistant titanium coated with ruthenium. The anion exchange membrane used in the membrane stack is an AHA manufactured by Astom Corporation of Japan, with an effective area of ​​189 cm². 2 (21*9cm2 The thickness of the sealing soft silicone sheet is 2mm.

[0050] According to the present invention, the reaction apparatus includes an anode chamber storage tank and a cathode chamber storage tank. Deionized water is injected into the anode chamber storage tank to connect to the anode chamber, and sodium chloride solution is injected into the cathode chamber storage tank to connect to the cathode chamber. Driven by a peristaltic pump, the feed solutions in the anode chamber, cathode chamber, and the feed solutions in the connected storage tanks form a circulation.

[0051] The method for preparing chlor-alkali using the above-mentioned apparatus via anion exchange membrane includes the following steps:

[0052] The deionized water solution in the deionized water solution storage tank is introduced into the anode chamber, and the sodium chloride solution in the sodium chloride solution storage tank is introduced into the cathode chamber. The chamber liquid is circulated by a peristaltic pump for 10-30 minutes to remove air bubbles from the membrane stack.

[0053] The anode and cathode plates of the reaction apparatus are connected to an external power source, and a constant current is applied, maintaining the same flow rate of the liquid in all chambers. Under the influence of the electric field, redox reactions occur at the cathode and anode. Hydrogen evolution occurs at the cathode, producing hydroxide ions and hydrogen gas. Chloride ions in the sodium chloride solution fed into the cathode chamber compete with the hydroxide ions generated from the oxygen evolution reaction at the cathode as they pass through the anion exchange membrane. The chloride ions, with their faster transmembrane rate, preferentially reach the anode and undergo chloride evolution. The remaining hydroxide ions combine with sodium ions in the cathode chamber to produce sodium hydroxide. Therefore, sodium hydroxide solution and hydrogen gas are obtained in the cathode chamber, and chlorine water is obtained in the anode chamber.

[0054] The above experiment was stopped when the concentration of the alkali solution stopped increasing or the increase was very small (<0.1 mol) within a certain period of time.

[0055] Example 1

[0056] This embodiment uses, as follows: Figure 1 and Figure 2 The reaction apparatus described above is used to prepare sodium hydroxide, and the steps are as follows:

[0057] 500 mL of deionized water solution from the deionized water solution storage tank was introduced into the anode chamber, and 500 mL of 1 mol / L sodium chloride solution from the sodium chloride solution storage tank was introduced into the cathode chamber. The chamber solutions were circulated using a peristaltic pump for 30 minutes under constant current operation at a current density of 100 mA / cm². 2 The flow rate of the feed liquid in the anode and cathode chambers was set to 400 mL / min, the current was set to 18.9 A, and the upper limit of the voltage was set to 101 V.

[0058] Figure 1This is a schematic diagram of the apparatus for preparing chlor-alkali using the anion exchange membrane of the present invention;

[0059] Figure 2 This is a schematic diagram of the reaction membrane stack device of the present invention.

[0060] Example 2

[0061] The reaction apparatus used in this embodiment is the same as that in Embodiment 1.

[0062] 500 mL of deionized water solution from the deionized water solution storage tank was introduced into the anode chamber, and 500 mL of 2 mol / L sodium chloride solution from the sodium chloride solution storage tank was introduced into the cathode chamber. The chamber solutions were circulated using a peristaltic pump for 30 minutes under constant current operation, with the current density set to 100 mA / cm². 2 The flow rate of the feed liquid in the anode and cathode chambers was set to 400 mL / min, the current was set to 18.9 A, and the upper limit of the voltage was set to 101 V.

[0063] Example 3

[0064] The reaction apparatus used in this embodiment is the same as that in Embodiment 1.

[0065] 500 mL of deionized water solution from the deionized water solution storage tank was introduced into the anode chamber, and 500 mL of 3 mol / L sodium chloride solution from the sodium chloride solution storage tank was introduced into the cathode chamber. The chamber solutions were circulated using a peristaltic pump for 30 minutes under constant current operation, with the current density set to 100 mA / cm². 2 The flow rate of the feed liquid in the anode and cathode chambers was set to 400 mL / min, the current was set to 18.9 A, and the upper limit of the voltage was set to 101 V.

[0066] Example 4

[0067] The reaction apparatus used in this embodiment is the same as that in Embodiment 1.

[0068] 500 mL of deionized water solution from the deionized water solution storage tank was introduced into the anode chamber, and 500 mL of 4 mol / L sodium chloride solution from the sodium chloride solution storage tank was introduced into the cathode chamber. The chamber solutions were circulated using a peristaltic pump for 30 minutes under constant current operation, with the current density set to 100 mA / cm². 2 The flow rate of the feed liquid in the anode and cathode chambers was set to 400 mL / min, the current was set to 18.9 A, and the upper limit of the voltage was set to 101 V.

[0069] Example 5

[0070] The reaction apparatus used in this embodiment is the same as that in Embodiment 1.

[0071] 500 mL of deionized water solution from the deionized water solution storage tank was introduced into the anode chamber, and 500 mL of saturated sodium chloride solution from the sodium chloride solution storage tank was introduced into the cathode chamber. The chamber solutions were circulated using a peristaltic pump for 30 minutes under constant current operation, with the current density set to 100 mA / cm². 2 The flow rate of the feed liquid in the anode and cathode chambers was set to 400 mL / min, the current was set to 18.9 A, and the upper limit of the voltage was set to 101 V.

[0072] Figure 3 The diagram shows the changes in chloride ion concentration in the anode chamber of Examples 1-5 above, indicating that the chloride ion concentration in the solution gradually decreases as the chlorine evolution reaction proceeds at the anode.

[0073] Figure 4 This is a schematic diagram of the changes in hydroxide ion concentration in the cathode chamber of Examples 1-5 above, where the hydroxide ion concentration is shown in Table 1.

[0074] Figure 5 This is a schematic diagram showing the purity and conversion rate of alkali produced by different sodium chloride concentrations in Examples 1-5 above.

[0075] The experiment was stopped when the hydroxide concentration increased by less than 0.1 mol within a certain time. The experimental results are shown in Table 1.

[0076] Table 1 Results of sodium hydroxide preparation in Examples 1-5

[0077]

[0078] The results of Examples 1-5 show that sodium hydroxide solution was successfully prepared by replacing the perfluorinated cation exchange membrane with anion exchange membrane. This is because the absolute value of the Gibbs free energy of chloride ions is 340 kJ / mol, which is less than the absolute value of the Gibbs free energy of hydroxide ions (430 kJ / mol). Under the action of an electric field, chloride ions cross the membrane faster than hydroxide ions, resulting in a large amount of hydroxide ions remaining in the cathode chamber combining with sodium ions to produce sodium hydroxide solution.

[0079] The results of Examples 1-5 show that the sodium hydroxide concentration produced by replacing the perfluorinated cation exchange membrane with an anion exchange membrane is higher than the initial sodium chloride solution concentration in the cathode chamber. This is mainly because, during the alkali production process, under the influence of the electric field, chloride and hydroxide ions are transported from the cathode chamber to the anode chamber as hydrated ions across the anion exchange membrane, carrying away some of the water in the cathode chamber. This results in an increase in the volume of the aqueous solution in the anode chamber and a decrease in the volume of the aqueous solution in the cathode chamber. Furthermore, sodium ions in the cathode chamber cannot pass through the anion exchange membrane, thus increasing the sodium ion concentration and the sodium hydroxide concentration in the cathode chamber.

[0080] Comparing the results of Examples 1-5, it is shown that as the concentration of the added sodium chloride solution increases, the amount of added sodium ions increases, and the final concentration of sodium hydroxide gradually increases. Furthermore, the final chloride ion concentration in the anode chamber is close to 0, indicating that almost all ions are converted into chlorine gas, and the final purity of sodium hydroxide is above 96%. In addition, comparing Examples 1-5 shows that the conversion rate does not change significantly with increasing sodium chloride concentration, remaining at around 90%. This is mainly because the conversion rate is primarily related to the amount of sodium ions. Under the influence of the electric field, sodium ions in the anion exchange chamber cannot pass through the anion exchange membrane to reach the anode chamber, thus maintaining the conversion rate of sodium hydroxide at a certain level.

[0081] In summary, the present invention provides a method for preparing chlor-alkali using the anion exchange membrane, which produces sodium hydroxide solutions of different concentrations and high purity. The method is simple, the process design is simplified, the product has high purity, and the cost is low, providing a new approach for the development of chlor-alkali processes.

[0082] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for producing chlor-alkali based on an anion exchange membrane, characterized by, Includes the following steps: (1) An electrolytic cell is used to circulate deionized water into the anode chamber formed by the anode plate and the anion exchange membrane, and to circulate sodium chloride solution into the cathode chamber formed by the cathode plate and the anion exchange membrane. (2) Turn on the power supply to allow the anode and cathode chambers to undergo an oxidation-reduction reaction, generating a sodium hydroxide solution in the cathode chamber; The electrolytic cell equipment includes an electrodialysis membrane stack, a feed solution device, and a power supply; The electrodialysis membrane stack includes an anode plate, an anion exchange membrane, and a cathode plate connected in sequence. The anode plate and the anion exchange membrane, and the cathode plate and the anion exchange membrane are all connected by a sealing soft silicone sheet; The anion exchange membrane is selected from AHA membrane, AMX membrane or AGU membrane.

2. The method according to claim 1, characterized in that, The liquid feeding device includes an anode chamber liquid feeding device and a cathode chamber liquid feeding device; The anode chamber feed device is connected to the anode chamber formed by the anode plate and the anion exchange membrane; The cathode chamber feed device is connected to the cathode chamber formed by the cathode plate and the anion exchange membrane.

3. The method according to claim 1 or 2, characterized in that, The anion exchange membrane is ≥1 sheet.

4. The method according to claim 1, characterized in that, The sodium chloride solution is selected from saturated sodium chloride solution or sodium chloride solution with a concentration of 1-5.5 mol / L.

5. The method according to claim 1, characterized in that, The power supply uses direct current.

6. The method according to claim 5, characterized in that, The DC current is 1.89-50.5 A; The direct current has a current density of 10-120 mA / cm 2 .

7. The method according to claim 1, characterized in that, The flow rates of the deionized water and sodium chloride solution are independently 200-500 mL / min.

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