The ion-exchange membrane plays a crucial role in the quality of electrolysis products and production efficiency, and it is also expensive. Therefore, the electrolysis process conditions should ensure that the ion-exchange membrane is not damaged, and the ion-exchange membrane electrolyzer can operate stably for a long time. (1) Brine quality In the ion-exchange membrane caustic soda production technology, the quality of brine has a significant impact on the lifespan of the ion-exchange membrane, cell voltage, and current efficiency. Since the ion-exchange membrane has the characteristic of selectively allowing cations to pass through, in addition to Na+, Ca2+, Mg2+, etc., can also pass through. When Ca2+, Mg2+, etc., pass through the exchange membrane, they will react with a small amount of OH- migrating from the cathode chamber to form precipitates, blocking the ion-exchange membrane, increasing the membrane resistance, causing the cell voltage to rise, and reducing the voltage efficiency.

  In addition to meeting the NaCl content, the quality of brine should strictly control impurities such as Ca2+, Mg2+, etc., in the brine, and the total amount of Ca2+, Mg2+ should be less than 20 ug/L (or 30 ug/L).

  (2) Concentration of sodium hydroxide in the cathode liquid The relationship between the concentration of sodium hydroxide in the cathode liquid and the current efficiency has a maximum value, that is, as the concentration of sodium hydroxide increases, the water content of the ion-exchange membrane on the cathode side decreases, the repulsion force of anions increases, and the current efficiency increases; if the concentration of sodium hydroxide continues to increase, the concentration of OH- in the membrane increases, and the reverse migration increases. When the concentration of sodium hydroxide exceeds 36%, the current efficiency significantly decreases. In addition, as the concentration of sodium hydroxide increases, the cell voltage also increases. Therefore, the concentration of sodium hydroxide is generally controlled at 30%-35%.

  (3) Concentration of sodium chloride in the anode liquid If the concentration of sodium chloride in the anode liquid is too low, OH- from the cathode chamber is prone to reverse osmosis, leading to a decrease in current efficiency; in addition, Cl in the anode liquid is also prone to migrate to the cathode chamber through diffusion, leading to an increase in the salt content of the alkali solution. If the ion-exchange membrane operates at a low salt concentration for a long time, it will also cause the membrane to swell, and in severe cases, it can lead to blistering, delamination of the membrane, and pinholes, causing permanent damage to the membrane. The salt concentration in the anode liquid should not be too high, otherwise, it will cause the cell voltage to rise. In production, the concentration of sodium chloride in the anode liquid is usually controlled at 200-220 g/L.

  (4) pH value of the anode liquid The anode liquid is generally in an acidic environment. Sometimes, hydrochloric acid is added to the brine entering the cell to neutralize the OH- migrating from the cathode chamber, to reduce the oxygen content in chlorine, prevent OH- from reacting with chlorine dissolved in the brine, and improve the anode current efficiency. However, the pH value of the anode liquid should be strictly controlled not to be lower than 2, to prevent the carboxyl acid layer on the cathode side of the ion-exchange membrane from acidification, destroying its conductivity, causing a sharp rise in voltage and permanent damage to the membrane.

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