A simple question about absorption
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I’m stuck on this issue for the moment; could everyone help me figure it out? If I use solutions of (NH4)2SO4 and a small amount of NH4HSO4 to absorb SO2, is it because the absorbing solution is weakly acidic that its absorption efficiency is lower than that of neutral water? In fact, it should have a much better absorption effect than water, but I just can’t understand why an acidic solution is more effective at absorbing acidic gases than water. It seems to be a stupid question. . .
Method of absorbing sulfur dioxide gas with ammonia water: SO2 + H2O = H2SO3 (sulfurous acid); NH3 + H2O = NH4OH (ammonia water); 2NH4OH + H2SO3 = (NH4)2SO3 (ammonium sulfite) + 2H2O; (NH4)2SO3 + 2H2SO3 = 2NH4HSO3 (ammonium bisulfate) + H2O
The response from upstairs is to avoid using a process involving forced oxidation
It’s been a long time since I graduated; I can’t remember well. I think it’s just a simple dissolution in water; this mainly depends on the solubility of the gas in water (under equal conditions). However, in (NH4)2SO4 and NH4HSO4 (in small amounts), it is primarily the NH4+ ions that play a role. I can’t explain it in detail.
Because sulfur dioxide first reacts with hydrogen ions to form sulfite ions (weak acids undergo reactions in stages), and only then does it combine with ammonium ions. In acidic solutions, the concentration of hydrogen ions is higher than that in water, which facilitates the forward reaction; thus, it is easier to absorb sulfur dioxide. Last edited by davy on 2009-2-4 16:50.]
It is possible that an absorption solution system of (NH4)2SO4-NH4HSO4-H2O has been formed, which enhances the adsorption capacity for SO2. The original poster might want to take a look at the method of treating SO2 exhaust gases using the ammonia process; it might be useful.
It’s simple: the pH of the system described by the original poster is acidic, as both sulfuric acid and ammonium bisulfate are acidic substances. Moreover, SO2 becomes acidic after being absorbed by water; therefore, an alkaline absorbent such as NH3 or NaOH should be used.
One is chemical absorption combined with physical absorption, and the other is pure physical absorption; which one is more effective?
There is some truth to that; the reason is the presence of NH4+ ions, which speeds up the reaction significantly. Many processes for absorbing ammonia also rely on this principle
I wonder if it can be understood in two points: 1. The buffering capacity of the solution – when water absorbs sulfur dioxide, the pH value changes significantly, whereas the pH value of this solution changes little. 2 Similar solubilization
It shouldn’t be considered solely in terms of acidity and alkalinity; rather, it’s the strong adsorption effect of NH4+ ions on sulfur dioxide that matters
Based on Davy’s views, the entry of SO2 into the solution is indeed the controlling step, which is understandable. However, there are also issues related to (NH4)2SO4 and NH4HSO4 that need to be taken into account, as well as the ion balance between NH4 and water. Therefore, replacing NH4 with Na yields less effective results, although this has been proven in wet flue gas desulfurization processes. Thus, there are three controlling steps for this issue: 1. The concentration of hydrogen ions upon entry into the solution; 2. The alkaline environment in the solution after entry; 3. The stability of the hydrogen ion content in the solution within the system. The (NH4)2SO4-NH4HSO4-H2O system is clearly superior to the system using pure water. I hope this is useful!!
Primarily, (NH4)2SO4 and NH4HSO4 solutions can promote the ionization of H2O to produce OH- ions and H+ ions+