Regarding the pH of brine leaving the tank
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This post was last edited by sunjl1981 on 2013-1-6 at 20:57. When we first started using the tank, the pH of the saltwater inside it was around 3.6; after that, acid was added to the saltwater for about half a month to keep the pH at around 2.2. Once the addition of acid stopped, the pH rose to around 4.3. What could be the reason for this? ， ， -
The pH of the anolyte increases as the ion exchange membrane is used for a longer period of time. This is because the membrane ages over time, developing defects such as pinholes, which leads to an increased amount of hydroxide ions migrating in the opposite direction from the cathode chamber. As a result, the pH of the anolyte rises gradually; when it reaches a certain level, it significantly affects the purity of chlorine. At this point, it is necessary to add acid to the anolyte to neutralize the hydroxide ions and thereby improve the purity of chlorine. For now, you can understand this concept in a superficial manner; to grasp the deeper aspects, you need to keep learning and comprehending it through your work.
I understand this principle; it is a process of gradual change. But I think it has nothing to do with aging, as it only takes a short period of half a month
Reply to 3# marongqiang: Hehe, actually the period that causes the most damage to the ion exchange membrane is precisely the unstable phase at the beginning of operation.
Reply 1# marongqiang: It seems there’s a problem with your membrane. Under normal conditions, the pH value of the brine leaving the tank without the addition of acid is around 3. You can go and check the dissolution equilibrium diagram of chlorine in water at different pH levels. Please confirm again whether the pH value you mentioned is shown by an online analyzer or determined through manual analysis; this is very important.
Reply to 5# Chaos and confusion: It was analyzed manually; our pH testing devices are not accurate. The foreigners spent many days trying but still couldn’t get it right
Reply 4# huawei: During performance testing, the foreigners required the PH level to be kept between 2 and 2.2; we didn’t even dare to bring it down to 2, for fear it would have too much of an impact on the membrane
Reply to 7# marongqiang: For safety reasons, the acidity at the outlet of the electrolyzer is checked to be no more than 0.005N when acid is added; the pH value is kept between 2 and 2.5. It can actually be controlled between 2.3 and 2.5. Firstly, this is for safety reasons; secondly, it is to keep the amount of chlorine dissolved in the saline solution as low as possible by adding acid. When considering both factors together, the value should be kept between 2.3 and 2.5. Additionally, when calculating the cathode efficiency using the acid addition value, the acid addition must be such that the acidity at the outlet is above 0.002; otherwise, the calculation results are meaningless.