The effect of saltwater concentration on ion-exchange membrane soda production

1. An excessively low salt concentration will lead to the dissociation of water, with H ions migrating from within the membrane in place of sodium ions. 2. An excessively low saltwater concentration will increase the migration of water molecules, thereby increasing the amount of chloride ions that migrate to the cathode chamber and leading to an increase in salt content in the alkali. 3. An excessively low saltwater concentration will cause the membrane to delaminate and bubble due to increased water migration inside the membrane and water electrolysis.

The saltwater concentration has a significant impact on current efficiency, cell voltage, and the amount of alkali required for salt removal. A too low saltwater concentration is not only unfavorable for improving current efficiency and reducing salt content in the alkali. It also becomes the main cause of bubbling in the ion exchange membrane. Although slight bubbling has little impact, excessive bubbling in the ion exchange membrane leads to an increase in cell voltage and a decrease in current efficiency. When the concentration of the anolyte is below 50 g/l, delamination of the membrane occurs, resulting in permanent damage to the ion exchange membrane. Therefore, it is usually necessary to maintain the anode solution concentration at 190–210 g/l, with a minimum level of not less than 170 g/l.

Well, yes :) What about when the salt concentration is too high? From what I know regarding the impact of salt concentration levels on ion-exchange membrane cells, there seems to be more discussion on low salt concentrations. I’d really like to learn more about the specific effects of high salt concentrations on these cells. Thank you, and I hope everyone will participate more~!:handshake

The concentration of the brine fed into the cell is generally maintained between 300 and 315 g/l; both too high and too low concentrations affect the current efficiency.

:) Are there any other effects besides the increased NaCl content, which reduces the water permeability of the membrane and leads to an increase in osmotic concentration, thereby causing separation between the perfluorocarboxylic acid and perfluorosulfonic acid layers and the formation of bubbles?:handshake

In electrolysis, the current efficiency increases as the sodium chloride content rises, but it reaches a maximum value. In ion-exchange membrane cells, when the sodium chloride content exceeds a certain maximum value, the current efficiency decreases. This is because as the sodium chloride content rises, the moisture content of the membrane drops, causing the membrane to shrink; as a result, the channels through which ions pass become narrower, which hinders the passage of Na+ ions and leads to a decrease in current efficiency. Therefore, the sodium chloride concentration is generally controlled at 300–310 g/l, while the concentration at the anode solution outlet is controlled at 210 g/l.

Effects of excessively high sodium chloride concentration: 1. Excessively high concentrations reduce the conductivity of the solution, leading to an increase in cell voltage. 2. Excessively high concentrations can cause sodium chloride to crystallize out in the anode chamber due to temperature changes, thereby damaging the membrane and the electrolyzer and affecting its operation. 3. Excessively high concentrations cause the ion membrane to contract, increasing membrane resistance and voltage. Note: The effect of saltwater concentration on ion-exchange membrane soda production that we are discussing refers to the concentration of the anode solution; the concentration of the saltwater fed into the process generally doesn’t matter, though this can vary depending on the specific process used.

The concentration of brine entering the tank will directly affect the concentration of the anode solution.

In my opinion. The concentration of the brine leaving the tank is very important. The circulation rate inside the electrolytic cell is very high. It is greater than the flow rate into the tank. It helps to keep the saltwater concentration inside the electrolyzer as uniform as possible. In other words, the concentration at the outlet is closer to that of the brine inside the cell.

The concentration of the brine exiting the cell represents the concentration of the anolyte inside the electrode chamber, and its control is achieved by adjusting the flow rate of the concentrated brine entering the cell. In other words, to maintain a certain concentration of brine exiting the cell, sodium chloride must be continuously added to the electrolyzer for the electrolytic production of chlorine and caustic soda. Sodium chloride is added to the electrolyzer in solution form; of course, it is necessary to maintain a certain concentration. Depending on the required concentration of the brine exiting the electrolyzer, if the concentration of the concentrated brine used as input is high, the flow rate of this brine into the electrolyzer should be lower, while if the concentration is low, the flow rate should be higher. As the brine fed into the cell in the natural circulation process of ion-exchange membrane electrolysis, it also serves to circulate the electrolyte.