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What's The Principle Of Ion-exchange Membrane Caustic Soda Electrolysis?

Jun 02, 2020

1. Introduction to Caustic Soda

The main product of ionic membrane electrolysis for the production of caustic soda is caustic soda. The chemical name is sodium hydroxide, also known as caustic soda, caustic soda and caustic soda. It should be called caustic soda. Its by-products include chlorine and hydrogen. The molecular formula of sodium hydroxide is NaOH. At room temperature, pure anhydrous sodium hydroxide is a white translucent crystalline, shiny or slightly colored solid. It is highly corrosive, soluble in water, and emits a lot of heat when dissolved And as the water temperature rises, its solubility increases significantly. Solid caustic soda is easy to deliquesce when exposed to air. It can be used as a desiccant, but it cannot dry gases such as sulfur dioxide, carbon dioxide, and hydrogen chloride.

The chlor-alkali industry belongs to the basic organic chemical raw material industry. The basic chemical raw materials usually refer to "three acids and two bases", that is, hydrochloric acid, sulfuric acid, nitric acid, caustic soda and soda ash. And hydrogen can further produce many chemical products, so the chlor-alkali industry and its related products involve many fields of the national economy and people's lives. In addition to the application of the chemical industry, it is also used in light industry, textile, petrochemical, metallurgy, and public utilities. There are many uses. Thousands of products consume caustic soda and chlorine.

caustic soda flakes 

2. Introduction to Ion Membrane Electrolysis

Compared with membrane electrolysis alkali production technology, ion membrane electrolysis alkali production has been recognized by the world as more advanced and economical sodium hydroxide production method, which is the development direction of current electrolysis alkali production technology. Therefore, ion membrane electrolysis alkali production Its technology has developed rapidly at home and abroad. This method has the characteristics of energy saving, high product quality, no environmental pollution, low operating costs, and significant economic benefits, and is widely used by caustic soda manufacturers around the world.

Ion membrane method caustic soda production tasks can be divided into: ① primary brine purification equipment; ② secondary brine purification; ③ refined brine electrolysis; ④ chlorine and hydrogen treatment:


Among them, the electrolysis of refined brine is the core position of the entire process production process, and the preparation of brine is the key to ensure the smooth progress of electrolytic brine production. It has also been called "refined brine is the blood of the electrolytic cell" by chlor-alkali production technicians.


3. The process of ionic membrane electrolysis

The ion exchange membrane used in the chlor-alkali industry is a cation exchange membrane that is resistant to chlor-alkali corrosion. The inside of the membrane has a very complicated chemical structure. There are membranes with fixed ions and exchangeable counter ions in the membrane, which have the ability to repel a certain ion in the external solution. There are active groups in the membrane body of the cation exchange membrane used in the electrolytic salt solution.

Due to the hydrophilic properties of the sulfonic acid group, the membrane swells in solution and the membrane structure becomes loose, resulting in many finely curved channels, so that the counter ion Na + in the active group can be the same charge in the aqueous solution Na + to exchange. At the same time, the fixed ions in the active groups in the membrane have the ability to repel Cl- and OH-, see Figure 3, so as to obtain a high-purity sodium hydroxide solution.

The cathode chamber and anode chamber of the electrolytic cell are separated by a cation exchange membrane, refined brine enters the anode chamber, and pure water is added to the cathode chamber. When energized, H2O generates electricity on the surface of the cathode to generate hydrogen. Na + migrates from the anode chamber to the cathode chamber through the ion membrane and combines with OH- to form NaOH; Cl- discharges on the anode surface to produce chlorine. After electrolysis, NaCl is consumed, and the concentration of the brine is reduced to light brine, which leaves the anode chamber with chlorine gas and is discharged. The schematic diagram of ion exchange membrane electrolysis to produce sodium hydroxide and chlorine is shown in below figures. The concentration of sodium hydroxide can be adjusted by the amount of pure water entering the cathode chamber of the electrolysis cell.

Below are principle diagram of ion exchange membrane electrolysis to produce sodium hydroxide and chlorine:


            principle of caustic soda electrolysis

Below are caustic soda ion-exchange membrance electrolyzer:



Green Power provides the key equiment of DC power supply for the electrolyzer to make the electrolysis process happen. 


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