Sciencemadness Discussion Board

Super simple sulfuric acid from bisulfate->pyrosulfate->hydrolysis?

Junk_Enginerd - 9-7-2020 at 06:12

I've read some discussions here about trying convert sodium bisulfate to sulfuric acid and from what I gather it's regarded as difficult and discussion usually seems to end up with SO3.

But in the wiki I see that sodium bisulfate is quite easily pyrolyzed to sodium pyrosulfate, which according to the wiki hydrolyzes to sulfuric acid. This seems excessively simple.

Just make pyrosulfate and add it to water. Presumably heat would drive the reaction to completion, and also drive off excess water for concentrated sulfuric acid.

Though I just realized I forgot the sodium. What does the sodium end up forming? Is it an inseparable contaminant or easily dealt with?

woelen - 9-7-2020 at 06:28

Adding sodium pyrosulfate to water simply leads to formation of sodium bisulfate:

Na2S2O7 + H2O --> 2 NaHSO4

The reaction is slightly more complicated, because the Na2S2O7 dissolves:

Na2S2O7 --> 2 Na(+) + S2O7(2-)

S2O7(2-) in turns reacts with water: S2O7(2-) + H2O --> 2 HSO4(-)

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This method hence is not suitable for making H2SO4. If you really want to make H2SO4, then you need to heat NaHSO4 to well over 1000 C. At 300 C or so you get Na2S2O7 and you drive off water from the NaHSO4 (the reverse of the reaction, I give at the start of my post). This reaction can be done with moderate equipment. In order to get sulfuric acid, you need to drive off SO3 from the Na2S2O7 and that requires heating to 1000 C or 1100 C. That is very hot and is not easily done. Besides that, handling the super hot and super corrosive SO3 vapor is another issue.

Junk_Enginerd - 9-7-2020 at 07:56

Quote: Originally posted by woelen  
Adding sodium pyrosulfate to water simply leads to formation of sodium bisulfate:

Na2S2O7 + H2O --> 2 NaHSO4

The reaction is slightly more complicated, because the Na2S2O7 dissolves:

Na2S2O7 --> 2 Na(+) + S2O7(2-)

S2O7(2-) in turns reacts with water: S2O7(2-) + H2O --> 2 HSO4(-)

------------------------------------------------------------------------------------

This method hence is not suitable for making H2SO4. If you really want to make H2SO4, then you need to heat NaHSO4 to well over 1000 C. At 300 C or so you get Na2S2O7 and you drive off water from the NaHSO4 (the reverse of the reaction, I give at the start of my post). This reaction can be done with moderate equipment. In order to get sulfuric acid, you need to drive off SO3 from the Na2S2O7 and that requires heating to 1000 C or 1100 C. That is very hot and is not easily done. Besides that, handling the super hot and super corrosive SO3 vapor is another issue.


This makes sense, but the wiki on sodium pyrosulfate does not agree. Is the wiki wrong then?

The wiki also states that SO3 is liberated starting at 400°C. Is this also wrong, or do you say 1000-1100°C because it is required to get a decent rate in the reaction?

Heat I have no problems generating... Amongst my other hobbies is glassworking, metal casting and pottery. Should it ever be needed, I should be able to get a solid 1300°c any time. But what on earth would be the reactor vessel for something like that? Steel would be eaten alive, no?

plastics - 9-7-2020 at 12:18

941 Celsius - reaction complete

0781DDF2-B9B5-4365-A24F-7D9CFB04AD5B.jpeg - 1.4MB

draculic acid69 - 9-7-2020 at 16:55

Quote: Originally posted by Junk_Enginerd  
I've read some discussions here about trying convert sodium bisulfate to sulfuric acid and from what I gather it's regarded as difficult and discussion usually seems to end up with SO3.

But in the wiki I see that sodium bisulfate is quite easily pyrolyzed to sodium pyrosulfate, which according to the wiki hydrolyzes to sulfuric acid. This seems excessively simple.

Just make pyrosulfate and add it to water. Presumably heat would drive the reaction to completion, and also drive off excess water for concentrated sulfuric acid.

Though I just realized I forgot the sodium. What does the sodium end up forming? Is it an inseparable contaminant or easily dealt with?


Any sodium present would obviously just reattach to any sulfuric acid formed.woelen is right

draculic acid69 - 9-7-2020 at 17:01

Quote: Originally posted by plastics  
941 Celsius - reaction complete



What exactly are we looking at? Tube furnace? Reaction?

woelen - 9-7-2020 at 23:30

Wikipedia is notalways right when it comes to specific properties of chemicals. I have corrected quite a few pages (e.g. wrong colors mentioned in the text, wrong properties about being hygroscopic or not, and several other things). Websites are parroting each other. One website says something wrong and after a while many other websites say the same wrong thing :-(

Junk_Enginerd - 10-7-2020 at 03:18

Quote: Originally posted by plastics  
941 Celsius - reaction complete



Is the reactor borosilicate or something exotic like fused silica?
Quote: Originally posted by draculic acid69  


Any sodium present would obviously just reattach to any sulfuric acid formed.woelen is right


Makes sense. So perhaps saying it hydrolyzes to sulfuric acid is correct then, but it leaves out the fact that it also immediately forms bisulfate after...
Quote: Originally posted by woelen  
Wikipedia is notalways right when it comes to specific properties of chemicals. I have corrected quite a few pages (e.g. wrong colors mentioned in the text, wrong properties about being hygroscopic or not, and several other things). Websites are parroting each other. One website says something wrong and after a while many other websites say the same wrong thing :-(


Of course, but I didn't mean wikipedia, I meant the sciencemadness wiki. I'd correct it myself, but I'm not confident enough that I'm correct...

Tsjerk - 10-7-2020 at 03:22

The sciencemadness wiki is wrong even more often, because it is checked by way fewer people.

I don't see a reason to assume the hydrolyzation of pyrosulfate goes via H2SO4.

[Edited on 10-7-2020 by Tsjerk]