How should the salt content in the caustic soda produced by ion-exchange membrane cells be controlled after they have been in operation for over three years?
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Our company’s ion membrane electrolysis units have been in operation for three years, and the condition of the ion membranes in the cells is still good overall. However, recent monitoring has shown an increase in the salt content in the produced caustic soda (as the operating current has been relatively low recently). Besides increasing the current density, what other methods are there to reduce the salt content in the alkali without decreasing the current density?
Factors affecting the high chloride content in caustic soda: 1. Low current density. Solution: Increase the current density. 2. High cell temperature. Lower the temperature within the controlled range
There’s no good solution other than replacing the membrane.
Simply increasing the current density is not a good approach
There isn’t a very good solution; increasing the alkali concentration slightly within the specified range might help a bit, and reducing the tank temperature could also be effective. However, both of these methods carry risks – if the changes are too significant, it can lead to a decrease in current efficiency and damage to the membrane’s carboxylic acid layer, which cannot be repaired. In such cases, the salt content in the alkali will increase further. It seems better to increase the electrical density within the specified range.
The high salt content in the alkali is mainly due to the prolonged operation of the ion exchange membrane, which results in a decrease in its resistance to permeation; chloride ions migrate to the cathode side where they form salt. A temporary solution is to lower the temperature of the solution and increase the alkali concentration. Calculate the costs to see whether it’s more cost-effective for xw to continue running, or to replace the membrane.
1. Operating near the limit current density causes deterioration of the carboxylate layer in the ion exchange membrane.
Due to power restrictions, the electrolyzers can be used in rotation, so that those with better performance are shut down while the remaining electrolyzers are operated at full capacity. The ion membrane takes about 36 months to develop, so there’s no need to be too concerned about it.
Personally, I don’t think the performance of a membrane will deteriorate drastically after three years of operation. The original poster should reduce the tank temperature; high temperatures under low load conditions can lead to an increase in sodium chloride migration, as well as an increase in auxiliary reactions at the anode