Seeking advice

The appropriate tank temperature varies with the current density, and the optimal tank temperature is generally maintained at 85–90°C. Within this range, an increase in temperature leads to an increase in the pores of the membrane, which helps to improve the membrane’s electrical conductivity and reduce the cell voltage. It also aids in increasing the conductivity of the electrolyte and reducing the voltage drop across the solution. However, the tank temperature must not exceed 90°C; otherwise, the amount of water evaporating increases, leading to an increase in the gas-liquid ratio and a rise in voltage. At the same time, as the electrolyte approaches boiling point, the performance of the membrane deteriorates more rapidly, it becomes difficult for the current efficiency to return to its original level, and this also accelerates the corrosion of the electrodes as well as the passivation of the active coating. At a constant current density, an increase in temperature causes the pores in the ion membrane on the cathode side to enlarge, thereby increasing the mobility of sodium ions and thus improving current efficiency. When the current density decreases, in order to achieve the highest current efficiency, the slot temperature must be reduced accordingly, but not too much. At too low temperatures, —COO– within the membrane binds with Na+, forming —COONa, which reduces the ion exchange capacity. At the same time, the membrane on the cathode side loses water due to the lack of hydrated sodium ions, resulting in irreversible changes to its structure. This reduces the resistance to OH- reverse osmosis, leading to a decrease in current efficiency. Even if the temperature is increased, it is difficult to restore the membrane’s performance; generally, a tank temperature of at least 65°C is required. Furthermore, if the temperature is appropriately increased within the operating range, it can increase the pores in the membrane, which helps to reduce the cell voltage. Under normal conditions, for every 1°C increase in tank temperature, the tank voltage can be reduced by 5–10 mV. However, the tank temperature cannot be too high; if it exceeds 92°C, a large amount of water vapor will be generated, causing the tank voltage to rise. The cell temperature required for DuPont membranes varies depending on the type of electrolyzer; it is generally between 80 and 90 degrees.

Thank you, I’ve learned it. Some people say that a lower slot temperature is beneficial for protecting the electrode coating, and it also extends the service life of the ion membrane, right?

It can’t be too low either; if it is too low, the voltage in the corresponding slot increases, and there is also an optimal operating temperature for the slot.

Why can’t the temperature be below 65°C? What are the consequences? Please give your advice

At too low temperatures, —COO– within the membrane binds with Na+, forming —COONa, which reduces the ion exchange capacity. Reduce current efficiency and increase slot voltage

When the current density decreases, in order to achieve the highest current efficiency, the slot temperature must be reduced accordingly——could this be explained in more detail? Thank you.

The tank temperature is controlled based on the current; a higher current results in a higher tank temperature, but it must not exceed 87 degrees in the NCZ mode.

These are also things I copied from the Internet. I believe this sentence refers to the situation where, as the current density decreases, the slot temperature remains unchanged; for example, if the current drops to 7 KA, the slot temperature is still 85 degrees. This corresponds to the condition that the slot temperature must not exceed 90°C, otherwise the amount of water evaporating increases, leading to an increase in the gas-liquid ratio and thus a rise in voltage. At the same time, as the electrolyte approaches boiling point, the performance of the membrane deteriorates more rapidly, it becomes difficult to restore the current efficiency to its original level, and this also exacerbates the corrosion of the electrodes as well as the passivation of the active coating. ” This is the same as what happens when the slot temperature is too high, right? It’s just my personal understanding; I’m not sure if it’s correct

When the current density is low and the temperature is too high, the moisture content of the ion membrane becomes relatively high, causing the channels to open wider. As a result, the repulsive force exerted by the COO- ions on chloride and hydroxide ions decreases. Coupled with the reduction in electric field force, the diffusion of chloride ions increases. All these factors lead to an increase in the backflow of hydroxide ions (a decrease in current efficiency), as well as an increase in the amount of chloride ions that migrate into the alkaline solution (an increase in salt content in the alkaline solution and a decline in its quality)!