The problem of chlorine reacting with water
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Our company currently handles exhaust gases containing hydrogen chloride and chlorine. Hydrogen chloride is first absorbed using two stages of water absorption, while chlorine is treated with two stages of alkaline absorption. During the initial water absorption stage, does much reaction take place between water and chlorine? Is the hydrochloric acid obtained through the absorption of secondary water produced by the reaction of chlorine gas and water? What concentration of hydrochloric acid can be obtained when water reacts with chlorine?
In the process you described, the reaction between chlorine and water is usually minimal, but some reaction does occur inevitably. When chlorine dissolves in water, it forms dilute hydrochloric acid and hypochlorous acid (HOCl); the reaction is as follows: Therefore, during the two-stage water absorption process, it is indeed possible for a small amount of hydrochloric acid (HCl) to be generated. However, the extent of this reaction depends on factors such as the pH value of water, temperature, chlorine concentration, and contact time. Typically, in this type of industrial application, it is advisable to maintain the pH of the water at neutral or slightly alkaline levels in order to optimize the absorption of hydrogen chloride, thereby preventing the formation of excessive hydrochloric acid. In practical applications, as water absorbs hydrogen chloride and releases negative charges, the solution becomes slightly acidic; under these conditions, some of the chlorine gas may react with water to form hydrochloric acid at a lower concentration. As for the concentration of hydrochloric acid obtained by absorbing chlorine gas in water, it is usually relatively low, because chlorine gas tends to form the metastable hypochlorous acid with water rather than directly converting into a large amount of hydrochloric acid. If high-concentration hydrochloric acid is to be produced through water absorption, it needs to be carried out under more controlled conditions, such as by increasing the initial concentration of chlorine gas and/or adjusting the pH value of the solution. In summary, in your process, the hydrochloric acid obtained through secondary water absorption may be produced by the reaction of some chlorine gas with water, but its concentration is usually not very high. The main source of hydrochloric acid remains direct absorption of hydrogen chloride. .
Not much; the solubility of hydrogen chloride is much greater than that of chlorine gas. Chlorine dissolves in water to form hydrogen chloride and hypochlorous acid. Since a large amount of hydrogen chloride is already dissolved in your water, the dissolution reaction shifts to the left, resulting in an even lower solubility.
First of all, is your process for synthesizing hydrochloric acid one in which an excess of chlorine is used? If so, controlling it in this way puts your process on the verge of danger. The process for synthesizing hydrochloric acid should involve an excess of hydrogen gas. Second, you have water absorption, followed by alkali absorption; there are two components in the product: hydrochloric acid and sodium hypochlorite. This indicates that your main product is hydrochloric acid; in accordance with environmental protection design requirements, the subsequent alkali absorption serves as a safety measure. A colleague mentioned that when hydrogen chloride gas is combined with chlorine gas, the solubility of hydrogen chloride is much higher than that of chlorine. According to Raoult’s law, the solubility of chlorine decreases after it dissolves; therefore, the reaction between water and chlorine can only be a hydrolysis reaction. The concentration can be ignored.