Requirements for free chlorine in resin towers
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May I ask what the maximum level of free chlorine allowed in the hydrochloric acid used for resin regeneration in the resin tower is? Is it true that no free chlorine can be present during the next time saltwater is fed into the resin tower? What concentration of free chlorine can resin in a typical resin tower withstand? Thank you
The high-purity acid obtained from the regeneration of resin columns must not contain any free chlorine, and the brine used in this process must also be free of free chlorine; sodium-type chelating resins are not tolerant to free chlorine.
However, for the regenerated 17% hydrochloric acid, some people say that it is sufficient to keep the free chlorine level below 10 ppm; it is not necessary to have it at exactly 0.
This post was last edited by pzhhuagong on 2019-12-30 20:11. Of course, the absence of free chlorine in high-purity acid and primary brine is beneficial for the service life of chelating resins. However, it is unrealistic to have no free chlorine at all in the production process of 31% hydrochloric acid; generally, a level of less than 5 mg/L is required ； During acid regeneration, the flow ratio of pure water to hydrochloric acid is approximately 3.8, and as a result, there is very little free chlorine in the regenerated acid after dilution ； The acid regeneration time is also shorter, so the impact is less. Brine should not contain free chlorine; the flow rate of brine is much higher than that of the regenerated acid. With 24 hours of contact, even trace concentrations in the range of mg/L represent a large amount, which has a significant impact. Under the cyclic action of acids, bases, and saline solutions, chelating resins inevitably suffer some damage; therefore, it is necessary to add resin regularly. If free chlorine is not well controlled, this regular addition will become more frequent; as a result, there is less effective adsorption resin available, which in turn affects the parameters of the saline solution. Therefore, it is best to ensure that hydrochloric acid and saline contain as little free chlorine as possible.
Free chlorine has a significant impact on resins; it is recommended to reduce its level as much as possible. There isn’t a specific ideal level – the less, the better. Higher purity hydrochloric acid can help prevent the formation of free chlorine by containing more hydrogen, and the same goes for once-through brine.