Will the instability in the acid addition amount affect the cell voltage?

In my opinion, the change in cell voltage actually reflects changes in the concentration of saltwater inside the cell. When the concentration of hydrochloric acid increases, it leads to changes in the amount of water entering the system, and as a result the concentration of saltwater changes, which in turn causes a change in the overall voltage. Therefore, instability in the acid addition amount leads to variations in the cell voltage.

The amount of acid added has a significant impact on the cell voltage of the electrolyzer. We can explain this using an analogy: if the flow rate of the acid decreases, we assume that its flow rate has dropped to zero, meaning no acid is being added. It goes without saying that there will be a substantial change in the cell voltage in such a situation (the cell voltage will increase significantly). It can be seen from this that if the acid addition rate decreases, the cell voltage will increase. Conversely, it will decrease, but it must not exceed the tolerance limit of the ion membrane; if the membrane becomes acidic, that will cause problems.

Thank you all for your advice! There’s one thing I don’t understand: as the acid concentration increases and the amount of acid added decreases, shouldn’t the concentration of OH ions resulting from neutralization remain unchanged? However, after reducing the acid addition rate by nearly 60–70 L/h on several occasions, when the original addition rate was restored, the cell voltage increased slightly. I initially thought it was just a coincidence, but after verifying it several times, it was indeed the case that the cell voltage rose.

Perhaps the quality of the saltwater isn’t very good. When the amount of acid added is reduced, the alkalinity in the anode area increases; hydroxide ions and certain metal ions form precipitates, which adhere to the surface of the ion exchange membrane along with the brine that passes through it. This leads to an increase in the cell voltage. Once the amount of acid added is increased again, the ion exchange membrane remains in an alkaline environment (otherwise, there is a higher likelihood that the membrane will become acidic). Under such alkaline conditions, the precipitates on the membrane surface cannot dissolve or dissolve very slowly. Therefore, every time the amount of acid added is reduced, the tank voltage increases by one unit. 1. It is possible to analyze the quality of saltwater to determine whether there are any values approaching the upper limit. 2. Keep the acid addition rate constant for a period of time to see if the cell voltage decreases. Or increase the amount of acid added while ensuring it does not become too acidic. This post was last edited by limingshuguang on 2007-12-27 09:11]

Based on the above phenomena, it can be concluded that the membrane is in an advanced stage of degradation. The large amount of acid used may have caused further damage to the membrane, possibly as a result of an increased acid concentration that was not adjusted in time. This post was last edited by limingshuguang on 2007-12-27 09:13

I would like to ask everyone: It is well known that too low a concentration of brine can cause the membrane to delaminate and form bubbles, while too high a concentration of brine can affect the cell voltage, causing it to rise and increasing consumption. But what effects does this have on the ion exchange membrane?

Haha,:) I’m the same as you – I want to know the impact of too high a saltwater concentration on ion membranes too!:victory: What a coincidence~!

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 delamination between the perfluorocarboxylic acid and perfluorosulfonic acid layers and the formation of bubbles?

So that means if the concentration of the brackish water is too high, it can also cause the membrane to delaminate and bubble up, right?

A high sodium chloride concentration affects the cell voltage, but if it is too high, operation becomes uneconomical; it should have little impact on the delamination of the membrane.

An excessively high concentration of the catholyte not only reduces current efficiency and increases cell voltage, but also, if the sodium chloride concentration in the anolyte is above or below the specified range, or if the acidity of the anolyte is too high, it can cause delamination and bubbling of the composite membrane. This is because when the NaOH concentration is high, the barrier resin layer (perfluorocarboxylic acid layer) on the catholyte side contracts excessively. If the NaCl concentration in the anolyte is also high, the reduced water permeability leads to an increase in osmotic concentration, causing separation between the perfluorocarboxylic acid layer and the perfluorosulfonic acid layer and the formation of bubbles. During the operation of the electrolyzer, if the circulation of the catholyte suddenly stops, it will also lead to an increase in the concentration of the catholyte. At the same time, this will cause the catholyte to approach boiling point, resulting in membrane contraction and accelerating the deterioration of the membrane. If the anode solution circulation also stops at this point, the sodium chloride content in it will increase, causing the water permeability of the membrane to drop sharply and leading to an increase in osmotic concentration. This will inevitably result in delamination between the perfluorocarboxylic acid layer and the perfluorosulfonic acid layer, forming bubbles.