The issue of acid concentration in ion exchange membranes
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This post was last edited by sunjl1981 on 2013-1-7 00:25. To adjust the pH level inside the electrolyzer, an acid addition valve is installed at the anode inlet. Are there any regulations or requirements regarding the concentration of the acid to be used? What is the basis? Our factory uses Asahi Kasei electrolyzers~ # hcbbs
The acid concentration should not be too high, as this can easily lead to acidification of the ion membrane; around 17% is sufficient
17%; high concentrations can easily cause localized over-acidification inside the electrolyzer, leading to membrane damage and salt crystal formation. Too low affects the effectiveness of formic acid.
The pH value of the brine entering the tank is between 2 and 2.5; the amount of acid added depends on the efficiency of the membrane, with the amount of chlorate at the anode being a key factor. This post was last edited by yzhms on 2009-4-23 at 11:33
The amount of acid added is determined based on the pH value at the anode solution outlet. If too much acid is added, the carboxylic acid film will be acidified, changing from the sodium form to the hydrogen form. The electrical conductivity of the membrane drops sharply. This post was last edited by yzhms on 2009-4-23 11:33]
The pH value range is determined by the requirements of the membrane; it cannot be too low, as this will cause COO- to turn into COOH, increasing the membrane resistance and causing severe damage to the membrane. Nor can the pH value be too high, as this leads to intense side reactions. Last edited by yzhms on 2009-4-23 11:33.]
The acidity at the anode inlet of the electrolyzer is up to 0.15N, while the acidity at the outlet is controlled within the range of 0.001---0.005N
In other words, the pH value of the saltwater being discharged can be maintained around 2.3 to 2.5. This post was last edited by yzhms on 2009-4-23 at 11:34.]
We add 18% HCl (±1%). Last edited by yzhms on 2009-4-23 11:34.]
Can the output reach 2.5? We are currently adding 250 l/h (17%), and the flow rate of the brine inlet is 32.5 m3/h. The pH of the exported brackish water is 3.8, and the purity of chlorine is also over 99%. Everyone, please tell us how much you add and what the pH at the outlet is. This post was last edited by yzhms on 2009-4-21 at 13:54.]
Replying to the original poster: if you want to add acid, you can do so to the refined salt water; this makes it easier to make adjustments. The pH value should be controlled based on the value of the product at the end of the process – if it’s too high, add more acid. In my factory, the pH value of the product at the end of the process is kept between 2.5 and 3.5, and this gives good results. Everyone might consider adopting this approach. This post was last edited by yzhms on 2009-4-23 at 11:35
There’s one more thing I don’t understand: what is the meaning of adding 18% acid, as people mention? I’m not quite clear on that. If it’s added to the saltwater in the tank, it doesn’t matter what kind of acid is used; could you tell me what your idea is?
I consulted experts in chlorine engineering; using 17% acid instead of 31% helps prevent salt crystallization from blocking the inlet of the acid addition pipeline. Some manufacturers have encountered this problem. In fact, even if salt crystallization is not a concern, there are mixers in the ion exchange membrane brine feed system, and the amount of acid can be controlled – so using 17% acid instead of 31% still allows for proper control. For reference only
Around 17%, and for acid No. 31, a volume ratio of 1:1 with water is sufficient
Our process parameters are 2.5-4. The average is around 3.3
Adding it to refined salt water probably won’t work. The age of each slot varies, and the actual condition of the membranes in each slot also differs. Personally, I think a single slot is still better