Crystallization during the production of sodium hypochlorite
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When producing sodium hypochlorite, chlorine reacts with liquid caustic; the concentration of the liquid caustic is around 20-22%. Why does crystallization occur, leading to blockages in the pipes during the reaction? Could some expert please analyze this? Is it due to the high reaction temperature?
What is the temperature for controlling the reaction? It’s not sodium hypochlorite crystals that block the pipes; rather, it’s sodium chloride, which is a by-product of the reaction, that causes the pipes to get blocked.
The reaction temperature is approaching 59°C. The temperature is too high; originally the effective chlorine level could have been 18 mg/L, but now it’s only 10 mg/L – the loss is severe. Should we still proceed? Are these salts the reason for the high temperature?
The reaction temperature must be controlled; crystallization primarily involves the production of large amounts of sodium chloride, so it is essential to ensure the salt content in the raw materials~~~~
Are you saying that the salt content in our raw material, liquid caustic soda, is high?
This post was last edited by qugd on 2016-11-8 at 13:29. In the production process of sodium hypochlorite, the raw materials are liquid caustic soda and chlorine gas. During the reaction, one molecule of chlorine produces one molecule of sodium hypochlorite and one molecule of sodium chloride. Sodium chloride has a relatively low solubility in water; if the conditions are not properly controlled, the produced sodium hypochlorite will decompose to form oxygen and sodium chloride. This leads to supersaturation of sodium chloride, resulting in the precipitation of solid particles that can cause blockages in pipes and valves. Control the reaction conditions: the temperature should not be too high to prevent the decomposition of sodium hypochlorite. This ensures an appropriate concentration of available chlorine while also reducing the likelihood of sodium chloride precipitating out. This is a matter of optimizing process conditions; only by strictly controlling the reaction conditions can chlorine be utilized to the best extent.
Thank you for your reply; I understand now
This post was last edited by swl on 2017-4-14 at 12:55. Hello, original poster! Regarding the question raised by the original poster, I believe it is necessary to consider three main aspects: 1. The ratio of the alkaline solution: If the ratio of alkali to water is not properly controlled, resulting in an excessively high concentration of the alkaline solution, this will lead to a high level of NaCl in the final product, causing turbidity; in severe cases, it may even result in crystallization ； 2. Temperature control of the reaction mixture: During the chlorination process using an alkaline solution, if the reaction temperature is too high, side reactions will increase, resulting in an excessive amount of NaCl in the final product and thus crystallization ； 3. Gas (liquid) contact efficiency in the reactor: Although the production processes for sodium hypochlorite are generally similar across different manufacturers, the chlorine gas distributors (key points in the production process) vary from one company to another. If the chlorine distributor is not properly configured, it can result in uneven contact between chlorine and the alkaline solution, leading to localized excess of chlorine (and thus excessively high local reaction temperatures). The overall temperature may not necessarily reflect this situation, and as a result, the final product may contain too much NaCl, which can cause crystallization ； These reasons can exist independently, or several of them may coexist. For reference!