Method for preparing chlor-alkali from anion exchange membrane

Abstract

The invention discloses a method for preparing chlor-alkali by using an anion exchange membrane, and belongs to the technical field of chlor-alkali preparation. The electrolytic tank equipment comprises an electrodialysis membrane stack, a feed liquid device and a power supply; the electrodialysis membrane stack comprises an anode plate, an anion exchange membrane and a cathode plate which are connected in sequence; and the anode plate and the anion exchange membrane or the cathode plate and the anion exchange membrane are connected through a sealing soft silica gel sheet. According to the electrolytic tank equipment, the traditional electrodialysis membrane stack structure for industrial preparation of chlor-alkali is changed. The high-purity sodium hydroxide is successfully prepared through the electrolytic tank equipment, the method is simple and efficient, the environmental and economic problems caused by using a perfluorinated cation exchange membrane are avoided, industrial production is expected to be achieved, and a new thought is provided for the chlor-alkali industry.

Description

Technical Field

[0001] The invention relates to the technical field of chlor-alkali preparation, and in particular to a method for preparing chlor-alkali using an anion exchange membrane. Background Art

[0002] The chlor-alkali process plays a leading and irreplaceable role in the chemical industry, as its products are used in more than 50% of all chemical processes, and about 99.5% of the world's caustic soda is produced through the traditional chlor-alkali process. Chlor-alkali chemical products are diverse, with a wide range of applications and high economic extension value. Its products are not only widely used in the chemical industry, but also play a significant role in agriculture, electricity, and food processing.

[0003] Its main product, caustic soda, scientifically known as sodium hydroxide, also known as caustic soda and caustic soda, is a highly corrosive alkali that is easily soluble in water to form an alkaline solution and easily reacts with water vapor and carbon dioxide in the air to deliquesce and deteriorate. Caustic soda has a wide range of uses and can be used in alumina, dyes, pulp, chemical fibers, metal smelting, water treatment, cotton fabric finishing, petroleum refining, purification of coal tar products, and food processing. According to data from the China Chlor-Alkali Industry Association, the production capacity of my country's chlor-alkali industry has fluctuated and increased in recent years.

[0004] Typical chlor-alkali electrolysis includes two half reactions: the hydrogen evolution reaction at the cathode and the chlorine evolution reaction at the anode, accompanied by the generation of sodium hydroxide in the electrolyte. Since the 1880s, three processes have emerged in the chlor-alkali industry: diaphragm electrolyzer, mercury electrolyzer and the current ion membrane electrolyzer. In the diaphragm electrolyzer, a porous asbestos pad is used to separate the anode chlorine evolution reaction and the cathode hydrogen evolution reaction, and NaOH is simultaneously formed in the cathode compartment, but there are problems such as asbestos wool pollution, poor product quality, and complex operation and management. The alkali production process of the mercury electrolyzer is carried out in steps, and the concentration of the resulting alkali solution is close to 50%, which can be sold directly as a commodity, and it is of high purity and contains almost no chloride ions. In addition, it does not require post-treatment operations to evaporate and concentrate the alkali solution. However, the high price of mercury, large investment, mercury toxicity and environmental pollution, and the need to strictly control the content of mercury in the discharged wastewater have limited its development. The operation of the ion membrane electrolyzer is very similar to that of the diaphragm electrolyzer, but the difference is that a polymer ion exchange membrane is used instead of a porous asbestos pad to separate Cl2 and NaOH. Compared with the diaphragm method, the ion membrane method has the advantages of low power consumption, high liquid alkali concentration, high degree of production automation, and less environmental pollution. It is the main development direction of the chlor-alkali industry.

[0005] At present, perfluorinated cation exchange membrane is the core of chlor-alkali equipment, but its preparation is complicated and has high technical requirements. For a long time, the production of perfluorinated cation exchange membrane has been mainly concentrated in the United States, Japan, Canada and other countries. The main companies include DuPont, Dow, Gore, Asahi Glass, Asahi Chemical, Ballard, Canada. The ion exchange membranes used in my country's chlor-alkali industry have long been dependent on imports, and the permeability of domestic ion membranes is still not high. Although domestic ion exchange membranes have made breakthroughs in comprehensive performance and cost performance, there is still a certain gap with foreign countries in terms of stability. At the same time, the synthesis of perfluorinated cation exchange membranes will also lead to the production of harmful substances-fluorocarbon compounds. The carbon-fluorine bond is stable and difficult to transform and degrade naturally. If it is recycled or handled improperly, harmful substances will be produced, which will affect the environment and human body. Compared with perfluorinated cation exchange membranes, anion exchange membranes have a simpler preparation process, more research, and lower prices, and have greater advantages in research and development and economy.

[0006] Therefore, researching and developing a new type of chlor-alkali process using anion exchange membrane is of great significance for solving the problems of the above-mentioned 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 by anion exchange membrane. The method successfully prepares high-purity sodium hydroxide, and the preparation process is simple, efficient, economical and environmentally friendly.

[0008] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] The present invention provides an electrolytic cell device, including an electrodialysis membrane stack, a feed liquid device and a power supply;

[0010] The electrodialysis membrane stack comprises 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 via a sealing soft silicone sheet.

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

[0013] Preferably, the feed liquid device of the present invention comprises an anode chamber feed liquid device and a cathode chamber feed liquid device;

[0014] Preferably, the anode chamber feed liquid device is connected to the anode chamber composed of the anode plate and the anion exchange membrane;

[0015] Preferably, the cathode chamber feed liquid device is connected to the cathode chamber composed of the cathode plate and the anion exchange membrane.

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

[0017] Preferably, the number of the anion exchange membrane is ≥1.

[0018] The cathode plate in the above device is connected to the negative pole of the power supply, and the anode plate is connected to the positive pole of the power supply.

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

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

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

[0022] (1) using the above-mentioned electrolytic cell equipment, circulating deionized water into the anode chamber composed of the anode plate and the anion exchange membrane, and circulating sodium chloride solution 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 chamber and the cathode chamber to undergo redox reaction, generating a sodium hydroxide solution in the cathode chamber.

[0024] The preparation method firstly circulates deionized water in the anode chamber and the anode chamber feed liquid device, and circulates sodium chloride solution in the cathode chamber and the cathode chamber feed liquid device, so that the air in the equipment is discharged and the system is stable.

[0025] In some specific embodiments of the present invention, the circulation is driven by a peristaltic pump.

[0026] Then, under the action of the electric field, the anode chamber and the cathode chamber undergo redox reactions.

[0027] The above-mentioned redox reaction specifically comprises a chlorine evolution reaction and an oxygen evolution reaction in the anode chamber, and a hydrogen evolution reaction in the cathode chamber.

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

[0029] This device is different from the traditional device, so the anode chamber will also undergo oxygen evolution reaction while the chlorine evolution reaction occurs.

[0030] The hydroxide ions further combine with the sodium ions in the cathode chamber to obtain 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] In addition, the chloride ions in the sodium chloride solution in the cathode chamber and the hydroxide ions generated by the above hydrogen evolution reaction form a competitive relationship when passing through the anion exchange membrane. The chloride ions with a fast transmembrane rate preferentially pass through the anion exchange membrane to reach the anode, and relatively more hydroxide ions and sodium ions remain in the cathode chamber to further combine to generate sodium hydroxide.

[0033] When the concentration of the sodium hydroxide solution in the cathode chamber no longer increases within a certain period of time or the increase is small (<0.1 mol), the experiment is stopped.

[0034] Preferably, the sodium chloride solution 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 the present 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 supply of the present invention adopts direct current.

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

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

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

[0039] The method of the present invention successfully prepares sodium hydroxide solutions of different concentrations with high purity, all of which are above 96%.

[0040] Compared with the prior art, the electrolytic cell equipment provided by the present invention includes an electrodialysis membrane stack, a feed liquid 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, or the cathode plate and the anion exchange membrane are connected by a sealing soft silicone sheet. The electrolytic cell equipment has changed the structure of the electrodialysis membrane stack for the traditional industrial preparation of chlor-alkali. The present invention successfully prepared sodium hydroxide with high purity through the electrolytic cell equipment. The method is simple and efficient, avoiding the environmental and economic problems caused by the use of perfluorocation exchange membranes, and is expected to achieve large-scale industrial production, providing a new idea for the chlor-alkali industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A schematic diagram of a device for preparing chlor-alkali by an anion exchange membrane of the present invention;

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

[0043] Figure 3 Schematic diagram of chloride ion concentration in the anode chamber of Examples 1 to 5;

[0044] Figure 4 Schematic diagram of the hydroxide ion concentration in the cathode chamber of Examples 1 to 5;

[0045] Figure 5 Schematic diagram of the purity and conversion rate of alkali produced at different sodium chloride concentrations in Examples 1 to 5. DETAILED DESCRIPTION

[0046] In order to further illustrate the present invention, the method for preparing chlor-alkali with anion exchange membrane provided by the present invention is described in detail below with reference to the examples.

[0047] The present invention provides a method for preparing chlor-alkali by using anion exchange membrane, wherein the reaction device used comprises an electrodialysis membrane stack, a power supply and a liquid storage tank (liquid storage device), such as Figure 1 shown.

[0048] The electrodialysis membrane stack includes an anode plate, an anion exchange membrane and a cathode plate arranged in sequence, wherein 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 connected by a sealing soft silicone sheet. Figure 2 The anode plate is connected to the positive pole of the power supply, the cathode plate is connected to the negative pole of the power supply, the anode plate and the adjacent anion exchange membrane constitute the anode chamber, and the cathode plate and the adjacent anion exchange membrane constitute the cathode chamber.

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

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

[0051] The method for preparing chlor-alkali by anion exchange membrane using the above device comprises 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 feed solution is circulated for 10-30 minutes by a peristaltic pump to discharge bubbles in the membrane stack.

[0053] The anode plate and cathode plate of the reaction device are connected to an external power supply, and a constant current is applied. The flow rate of the liquid in all chambers is controlled at the same rate. Under the action of the electric field, the cathode and the anode undergo redox reactions, and the cathode undergoes a hydrogen evolution reaction to produce hydroxide and hydrogen in the cathode chamber. The chloride ions in the sodium chloride liquid introduced into the cathode chamber and the hydroxide generated by the oxygen evolution reaction at the cathode compete with each other when passing through the anion exchange membrane. The chloride ions with a faster transmembrane rate preferentially reach the anode to undergo a chlorine evolution reaction, and the remaining hydroxide combines with the sodium ions in the cathode chamber to produce sodium hydroxide. Therefore, sodium hydroxide solution and hydrogen can be obtained in the cathode chamber, and chlorine water can be obtained in the anode chamber.

[0054] The above experiment is run until the concentration of the alkali solution stops increasing within a certain period of time or the increase is very small (<0.1 mol), and the alkali production (sodium hydroxide) experiment is stopped.

[0055] Example 1

[0056] This embodiment adopts Figure 1 and Figure 2 The steps of preparing sodium hydroxide using the above-mentioned reaction device are as follows:

[0057] 500 mL of deionized water in the deionized water storage tank was passed into the anode chamber, and 500 mL of 1 mol / L sodium chloride solution in the sodium chloride solution storage tank was passed into the cathode chamber. The chamber liquid was circulated for 30 minutes by a peristaltic pump, and the constant current operation was performed with a current density of 100 mA / cm 2 The flow rate of the slurry in the anode chamber and the cathode chamber was set to 400 mL / min, the current was set to 18.9 A, and the voltage upper limit was set to 101 V.

[0058] Figure 1A schematic diagram of a device for preparing chlor-alkali by an anion exchange membrane of the present invention;

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

[0060] Example 2

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

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

[0063] Example 3

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

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

[0066] Example 4

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

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

[0069] Example 5

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

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

[0072] Figure 3 It is a schematic diagram of the change of chloride ion concentration in the anode chamber of the above-mentioned Examples 1-5, indicating that the chloride ion concentration in the solution gradually decreases as the anode chlorine evolution reaction proceeds.

[0073] Figure 4 Schematic diagram of the change in hydroxide ion concentration in the cathode chamber of the above-mentioned Examples 1-5, wherein the hydroxide ion concentration is shown in Table 1.

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

[0075] The experiment was stopped when the hydroxide concentration increased by less than 0.1 mol within a certain period of time, and the following experimental results were obtained, as shown in Table 1.

[0076] Table 1 Sodium hydroxide results prepared by Examples 1-5

[0077]

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

[0079] The results of Examples 1-5 show that the concentration of sodium hydroxide produced by replacing the perfluorocation exchange membrane with an anion exchange membrane is higher than the concentration of the sodium chloride solution in the initial cathode chamber. This is mainly because in the alkali production process, under the action of the electric field, chloride ions and hydroxide ions are transported from the cathode chamber to the anode chamber across the anion exchange membrane in the form of hydrated ions, taking away part of the water in the cathode chamber. As a result, the volume of the aqueous solution in the anode chamber increases, the volume of the aqueous solution in the cathode chamber decreases, and the sodium ions in the cathode chamber cannot pass through the anion exchange membrane, so the sodium ion concentration in the cathode chamber increases, and the sodium hydroxide concentration increases.

[0080] By comparing the results of Examples 1-5, it is shown that as the concentration of sodium chloride solution is increased, the amount of substance added with sodium ions increases, and the concentration of final sodium hydroxide is also gradually improved. Moreover, the concentration of chloride ions in the final anode compartment is close to 0, which is substantially converted into chlorine, and the purity of final sodium hydroxide is more than 96%. In addition, as shown in Comparative Examples 1-5, as the concentration of sodium chloride increases, its conversion rate does not change significantly, and is maintained at about 90%, which is mainly because its conversion rate is mainly related to the amount of sodium ion substance, and under the action of electric field, the sodium ions in the anion compartment cannot reach the anode compartment through the anion exchange membrane, so the conversion rate of sodium hydroxide is maintained at a certain level.

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

[0082] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. An electrolytic cell device, characterized in that: It includes an electrodialysis membrane stack, a feed and liquid device and a power supply; 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 via a sealing soft silicone sheet.

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

3. The device according to claim 1, characterized in that The anion exchange membrane is selected from AHA membrane, AMX membrane or AGU membrane.

4. The electrolytic cell device according to any one of claims 1 to 3, characterized in that: The anion exchange membrane is ≥1.

5. Use of the electrolytic cell equipment according to any one of claims 1 to 4 in the preparation of chlor-alkali.

6. A method for preparing chlor-alkali based on anion exchange membrane, characterized in that: The following steps are involved: (1) Using the electrolytic cell device according to any one of claims 1 to 4, circulate deionized water into the anode chamber composed of the anode plate and the anion exchange membrane, and circulate sodium chloride solution into the cathode chamber composed of the cathode plate and the anion exchange membrane; (2) Turn on the power supply to allow the anode chamber and the cathode chamber to undergo redox reaction, generating a sodium hydroxide solution in the cathode chamber.

7. The method according to claim 6, characterized in that The sodium chloride solution is selected from a saturated sodium chloride solution or a sodium chloride solution with a concentration of 1-5.5 mol / L.

8. The method according to claim 6, characterized in that The power supply adopts direct current.

9. The method according to claim 8, characterized in that The current of the direct current is 1.89-50.5A; The current density of the direct current is 10-120 mA / cm 2 .

10. The method according to claim 6, characterized in that The flow rates of the deionized water and the sodium chloride solution are independently 200-500 mL / min.

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