Problems with waste acid regeneration reactions
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I’m just starting to learn about the regeneration of spent acid, and I have two questions I’d like to ask the experts here. First, once dilute sulfuric acid enters the incinerator, how is sulfur in its +6 valence state reduced to sulfur dioxide in its +4 valence state? Why cannot sulfur dioxide be oxidized to sulfur trioxide in a high-temperature, peroxide-rich environment, and why is a catalyst required?
This is due to the reaction mechanism; you can understand it by looking at their chemical reaction equations
The conversion of sulfur dioxide to sulfur trioxide requires a catalyst
Thank you, yes, I wonder why? Carbon monoxide can be burned to form carbon dioxide as long as there is sufficient temperature and oxygen; then why doesn’t it work the same way with S?
Hehe, this is from high school chemistry. The conversion of sulfur dioxide to sulfur trioxide is a reversible reaction.
Didn’t learn high school chemistry well :'( The reaction 2 SO2 + O2 → 2SO3 is a reversible reaction. In the catalytic oxidation of sulfur dioxide to form sulfur trioxide, there is a contradiction between reaction thermodynamics and reaction kinetics: to achieve a high conversion rate, it is desirable for the reaction to take place at lower temperatures. To accelerate the reaction rate, it is desirable to carry out the reaction at higher temperatures. In actual production, in order to take into account resource utilization, environmental protection, and the company’s production capacity, the reaction is often carried out in stages. First, take advantage of the high initial SO2 concentration and the large mass transfer driving force. At lower temperatures, the reaction conversion rate is rapidly increased to 70%-75%, after which the temperature is quickly raised to a higher value; taking advantage of the kinetic properties of the reaction, the conversion rate is then rapidly increased to 85%-90%. Upon entering the third stage, the reaction proceeds at a lower temperature; by taking advantage of the thermodynamic advantages of the reaction, the conversion rate is increased once again to 97%-98%. Since the increase is not significant, it won’t take much time either. This arrangement of the reaction sequence takes into account both the reaction conversion rate and the reaction rate. However, if a high conversion rate is desired (such as 99.5%), the reaction must be carried out at lower temperatures, which takes longer and significantly affects the company’s production capacity; in such cases, the “two reactions and two extractions” process described in this textbook must be employed