Under what conditions is acid added to the anode of chlorine engineering ion-exchange membrane cells?

The purpose of adding acid to the electrolytic cell is to neutralize OH-. As time passes, the performance of the ion membrane deteriorates, resulting in a decrease in current efficiency. When hydroxide ions that have migrated back through the ion membrane from the cathode side enter the anode chamber, the pH value at the anode increases, and the corrosion resistance of the anode due to alkalis is **reduced**. On the other hand, it leads to an increase in the levels of chlorate and hypochlorite at the anode, causing corrosion of the anode gaskets. Whether to add acid or not, I think it mainly depends on experience and analysis results.

As long as strict control is exercised in accordance with the parameters specified in the operation manual, acid can be added at currents of 5KA or higher. Of course, as the ion membrane ages, the amount of acid added gradually increases.

As required by Japanese company Asahi Kasei, acid must be added whether it is new tanks and new membranes or old tanks and old membranes, or old tanks and new membranes. To prevent the H-formation of the membrane due to an excessive addition of salt acid, our company generally stops adding acid when shutting down the system and restarting it, as well as when reducing the current during shutdown. Acid is added again only after the system has started operating and the current has stabilized, with no further increase.

This post was last edited by guitarpro0724 on 2015-9-15 at 14:52. I’m not very familiar with chlorine engineering. The Asahi Kasei NCZ cell uses 5KA acid addition. I believe that the addition of acid before 5KA is not necessary, as the influence of OH- diffusion is not significant at this point, given the lower temperature and relatively small electrolytic current. Furthermore, the pH is difficult to control; improper operation can easily lead to the hydrogenation of the membrane, and there are certain delays and human factors in acidity analysis. Besides the reasons mentioned by the original poster, I think there are two more points for adding acid. 1. Convert hypochlorous acid dissolved in the anode inlet main pipe into chlorine, allowing it to flow from valves 21 and 39 to the outlet main pipe; this prevents fluctuations in the anode inlet hose of the electrolyzer and facilitates even distribution of the electrolyte. 2. That is, by keeping the PH within the specified range, the calculation of current efficiency is more accurate. This is just my personal opinion; I hope it can be discussed and corrected

This post was last edited by Du Xiaoping on 2015-9-15 22:22: “1. To convert hypochlorous acid dissolved in the anode inlet main pipe into chlorine, from valves 21 and 39 to the outlet main pipe; this helps to prevent fluctuations in the anode inlet hose of the electrolyzer and promotes even distribution of the electrolyte. ”-----I don’t quite understand this sentence – where does the HCLO in the brine entering the tank come from? The brine coming out of the resin tower must not contain dissociated chlorine; of course, none will be present in it either. “2. That is, by keeping the PH within the specified range, the calculation of current efficiency is more accurate. ”------What is your PH level? What are the actual figures? I hope to get your reply.

I happened to be looking at a document on the operations related to chlorine processing today, and it states that when the current rises to 3 KA, the polarized rectifier automatically shuts off; if the conditions are right, it is then possible to start adding acid to the brackish water. Please note that acid should be added to the lightly saline water, not to the salt water entering the tank. I have no experience with chlorination processes, so I’m not sure who can explain the reason for this approach, or whether there’s an error in the relevant information.

The last edit to this post was made by guitarpro0724 on 2015-9-16 at 10:41. The first point concerns the addition of acid to each cell in the electrolyzer, as well as the centralized circulation of weak saline water; this circulating weak saline water contains some free chlorine (the portion that returns to the electrolyzer cells). The impact might not be very significant. Secondly, Asahi Kasei requires the calculation of current efficiency; the acidity at the anode outlet should be between 0.001–0.005 N, and there are deviations in the results obtained through manual analysis.

I checked http://222.194.183.35/hgcp/anliku/anli3-1.htm, and it also states that acid should be added to the brine coming out of the tank. It is mainly unclear regarding the layout of pipelines and valves in the chlorine plant. It is thought that acid may be added initially to reduce the chlorate concentration in the brackish water returning to the tank.

Acid is added to the brine in the chlorine production cells at 5 KA; this is done because a portion of the brine is fed back into the cell circulation, which helps to stabilize the pH of the brine exiting the cell as well as the cell temperature. This ensures that the pH of the brine entering the dechlorination tower remains around 2, thereby guaranteeing effective vacuum dechlorination in that tower.

This post was last edited by aldd7611 on 2015-9-17 at 10:52. After a brief glance, it seems that most of it is the same as actual production; only a small portion differs from real production.