Sciencemadness Discussion Board

Electrolysis of Sodium Bisulfate to form Sodium Persulfate

LardmanAttack - 6-4-2024 at 02:14

I've been attempting perchlorates once again, and one of the things needed for electrolysis that I've seen time and time again is some sort of inhibiting agent to prevent the reduction of chlorates on the cathode. I'm most interested in Persulfate as it's the least toxic out of all the options. Persulfate (being either sodium or potassium) is a bit hard to find where I live, and I'd like to try my hand at making it myself to explore the chemistry. It's also just a very useful chemical, and I'd like to have some on hand. I read that it's prepared industrially by electrolysis of sodium bisulfate with a platinum anode.
I have both bisulfate and a platinum anode so it's something that I can and would like to do.

The problem is, I can't find much information online about this synthesis.
I have seen a few posts about it on here, but it seems like none of them have actually attempted the reaction. A few patents and articles i've seen have some information, but not enough to know how the synthesis process fully works.

Has anyone on here ever attempted this synthesis before? Is it very difficult?

mysteriusbhoice - 7-4-2024 at 23:04

you dont need persulfate to make perchlorates and making persulfate is HARDER than perchlorates as it needs 500ma/cm^2 and 0C temps and electrode distance of 0.3cm.
There are alternatives to persulfates and one of them is MgSO4 (best) or H2SO4 basically sulfates.
First you need to ensure less than 5g/l chloride is remaining then you have to drop the pH to 1-4 using H2SO4 then the sulfates will help the generation of OH radicals at low pH and once perchlorate builds up you dont need to change the pH after this point. Make sure your current density is at 200ma/cm^2 for sulfates to work as a catalyst otherwise persulfates are needed. For using MgSO4 you just simply add it to the chlorate solution if its neutral at a conc of 12g/l for heptahydrate and no pH adjustment will be needed and any Mg hydroxide that forms on the cathode will act as a diaphragm to prevent reduction.

[Edited on 8-4-2024 by mysteriusbhoice]

[Edited on 8-4-2024 by mysteriusbhoice]

LardmanAttack - 10-4-2024 at 23:06

Quote: Originally posted by mysteriusbhoice  
you dont need persulfate to make perchlorates and making persulfate is HARDER than perchlorates as it needs 500ma/cm^2 and 0C temps and electrode distance of 0.3cm.
There are alternatives to persulfates and one of them is MgSO4 (best) or H2SO4 basically sulfates.
First you need to ensure less than 5g/l chloride is remaining then you have to drop the pH to 1-4 using H2SO4 then the sulfates will help the generation of OH radicals at low pH and once perchlorate builds up you dont need to change the pH after this point. Make sure your current density is at 200ma/cm^2 for sulfates to work as a catalyst otherwise persulfates are needed. For using MgSO4 you just simply add it to the chlorate solution if its neutral at a conc of 12g/l for heptahydrate and no pH adjustment will be needed and any Mg hydroxide that forms on the cathode will act as a diaphragm to prevent reduction.

[Edited on 8-4-2024 by mysteriusbhoice]

[Edited on 8-4-2024 by mysteriusbhoice]



Thank you mysteriousbhoice. Thats a lot of good advice that I didn't previously know. I was actually watching a few of your videos when researching and you really seem to know your stuff.

So I take it that persulfates are the best option if you have them, and the sulfates are not as good as persulfate, but still better than nothing?
Would adding in just the bisulfate be good as well? Or is MgSO4 better?

mysteriusbhoice - 11-4-2024 at 16:29

MgSO4 is better because it also stops reduction of chlorate by the coating of ion conductive Mg(OH)2 in the cathode dont clean it btw if you see a white deposit on the cathode.
The MgSO4 will drop the pH at the start of perchlorate stage and provide sulfate ions and its these 2 conditions that will push off remaining hypochlorite by pH drop which otherwise will prevent perchlorate formation and the SO4 ions will catalyze OH radical formation by increasing O2 evolution potential of the cell.
persulfate does all of these but MgSO4 is a close second to persulfate if you dont mind cleaning your cathodes after the run by soaking in acid.

Hexabromobenzene - 19-4-2024 at 20:02

mysteriusbhoice, What do you think is needed for electrolysis of the diaphragm gypsum for sulfuric acid? Gypsum forms a dense layer and becomes a diaphragm by itself. Probably a simple rag of fabric to hold a gypsum layer is enough

mysteriusbhoice - 20-4-2024 at 17:11

yea the gypsum itself actually acts like more than just a diaphragm it can actually act as a cation exchange membrane due to the sulfate groups. Yea you can have a rag and a cast gypsum with a metal plate as a cathode and the gypsum cast as a solid electrolyte that slowly converts into H2SO4 and Ca(OH)2.

You may need to mix in some NaOH in the cast gypsum because that acts as a way to transfer out sulfate ions.

[Edited on 21-4-2024 by mysteriusbhoice]