Chemgineer
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Sodium Chlorate Electrolysis
I've successfully synthesised Sodium Chlorate by electrolysing Sodium Chloride with a titanium anode for around 2 weeks.
I the boiled it down to about 50% volume and filtered the remaining liquid from any precipitated solids.
This solution I then put in the freezer and precipitated my product.
Is there a better way? Particularly when trying to isolate a more hygroscopic product than the starting reactant?
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fredsci93
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"titanium ANODE", is this a typo? Titanium is destroyed as an anode in a chlorate cell. anyway, to answer your question, the general procedure is to
boil until the solution begins to precipitate then cool and filter for product, the hygroscopicity is quite annoying but there’s no way around it
sadly.
alternatively, you could boil to dryness and extract with ethanol but this is far more tedious and expensive.
[Edited on 22-9-2021 by fredsci93]
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Chemgineer
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Quote: Originally posted by fredsci93  | "titanium ANODE", is this a typo? Titanium is destroyed as an anode in a chlorate cell. anyway, to answer your question, the general procedure is to
boil until the solution begins to precipitate then cool and filter for product, the hygroscopicity is quite annoying but there’s no way around it
sadly.
alternatively, you could boil to dryness and extract with ethanol but this is far more tedious and expensive.
[Edited on 22-9-2021 by fredsci93] |
Sorry i'm using a platinum titanium substrate electrode. Thanks for confirming, just making sure i'm not being inefficient.
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fredsci93
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All good 
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mysteriusbhoice
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| Quote: Originally posted by Chemgineer | I've successfully synthesised Sodium Chlorate by electrolysing Sodium Chloride with a titanium anode for around 2 weeks.
I the boiled it down to about 50% volume and filtered the remaining liquid from any precipitated solids.
This solution I then put in the freezer and precipitated my product.
Is there a better way? Particularly when trying to isolate a more hygroscopic product than the starting reactant? |
chlorate is soluble in ethanol so you can do a leeching process to extract it all.
or just keep the chloride dissolved in there by boiling it down just until the 1st sign of precipitate then cooling down to precipitate only the
chlorate as the solubility of chloride is constant at a wide range of temperature.
The rest can be leeched in ethanol or methanol which wont carry the chloride.
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Chemgineer
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Thanks, I think ethanol would produce higher purity as it will only dissolve 0.65g/100ml of chloride but then only 14.6g/100ml of chlorate, maybe 96%
purity but i'd need lots of ethanol.
Methanol dissolves 14g/100ml of chloride and 56g/100ml of chlorate, maybe 80% purity?
I guess if the solvent is added and then filtered before everything has gone into solution then the more soluble chlorate should have dissolved more
rapidly due to higher solubility leaving mostly chloride particles in the filter.
I'll probably just stick to boiling it down but I don't need to boil lots of solid out and take the volume to 50%, you have helped me understand how
the solubility curves will work as the temperature is reduced. Thanks!
I think looking at the solubilities from 100 deg C to 0 deg C you would precipitate ~4g/100ml of chloride and 124g/100ml of chlorate so around 97%
purity?
[Edited on 22-9-2021 by Chemgineer]
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Fantasma4500
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fractional recrystallization, reference NaCl vs NaClO3's solubility curve at solubility table
you may wanna add some chromium hydroxide to the electrolyte to prevent chlorate breaking down during electrolysis so you can remove more chloride
most effortless is to just douse the electrolysis chamber in NaCl and have the NaClO3 ppt out as large crystals while the NaCl is continously absorbed
and transformed
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yobbo II
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"most effortless is to just douse the electrolysis chamber in NaCl and have the NaClO3 ppt out as large crystals while the NaCl is continously
absorbed and transformed"
This (alas) will not work. The solubility of NaCl is too low at the concentrations that you (may) get Na Chlorate to come out of the cell liquid
(unless perhaps you have a very low temperature, say below 20C in the cell) and therefor you will fry the anode.
The concentration of the NaCl goes below 60 (approx) grams per litre as you approach a high enough concentration of Chlorate to get it to come out of
the cell liquid.
You have to stop cell freeze and go again.
You can do the above when making Na Perk. as the solubility of the Chlorate is high enough (not to fry the anode and give sensible current effeciency)
when you start to get Perk. depositing on the cell bottom. This has nothing to do with the present question.
Yob
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mysteriusbhoice
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| Quote: Originally posted by yobbo II | "most effortless is to just douse the electrolysis chamber in NaCl and have the NaClO3 ppt out as large crystals while the NaCl is continously
absorbed and transformed"
This (alas) will not work. The solubility of NaCl is too low at the concentrations that you (may) get Na Chlorate to come out of the cell liquid
(unless perhaps you have a very low temperature, say below 20C in the cell) and therefor you will fry the anode.
The concentration of the NaCl goes below 60 (approx) grams per litre as you approach a high enough concentration of Chlorate to get it to come out of
the cell liquid.
You have to stop cell freeze and go again.
You can do the above when making Na Perk. as the solubility of the Chlorate is high enough (not to fry the anode and give sensible current effeciency)
when you start to get Perk. depositing on the cell bottom. This has nothing to do with the present question.
Yob |
If the anode was an Ir-Ta then this is possible technically but at that temperature the pH control part is not possible even using buffers you will
just gas yourself with Cl2 as it releases it given by a graph of Cl2 consumption and temp in these cells.
more on the reason why Ir-Ta can do it is because its made for O2 evolution and will be happy to run without damage even when all chloride is
converted to chlorate but will not make perchlorates for instance.
but the efficiency of this cell will be so low that its not worth doing or relying on. Instead when som1 has Ir-Ta I usually tell them to run at pH
controlled conditions until no more chlorine smell is given off (100% conversion)
I have also got them to test if Ir-Ta can survive running 100% chlorate electrolyte at 200ma/cm^2, 5.8 volts 40 amps 75 Celsius for about 8 days and
it does so just fine without any sign of issues. some perchlorates did form but its incredibly slow because we let it run 5x that of a PbO2 electrode
and it only managed to convert 10% of the chlorate into perchlorate.
The operating voltage was high due to lack of electrocatalytic properties thus the cell only made oxygen gas and probably did very little conversion
to perchlorate but some was present.
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Fantasma4500
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| Quote: Originally posted by yobbo II | "most effortless is to just douse the electrolysis chamber in NaCl and have the NaClO3 ppt out as large crystals while the NaCl is continously
absorbed and transformed"
This (alas) will not work. The solubility of NaCl is too low at the concentrations that you (may) get Na Chlorate to come out of the cell liquid
(unless perhaps you have a very low temperature, say below 20C in the cell) and therefor you will fry the anode.
The concentration of the NaCl goes below 60 (approx) grams per litre as you approach a high enough concentration of Chlorate to get it to come out of
the cell liquid.
You have to stop cell freeze and go again.
You can do the above when making Na Perk. as the solubility of the Chlorate is high enough (not to fry the anode and give sensible current effeciency)
when you start to get Perk. depositing on the cell bottom. This has nothing to do with the present question.
Yob |
i dont quite understand, im speaking from experience.
https://gyazo.com/1bea1184c5bcf04448eb13b06d46bc94
am i a magician or are you saying its less efficient?
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mysteriusbhoice
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innefficient still means 54% efficient and overall sodium chlorate can crystalize out in a non pH controlled cell since chlorate is generated by the
electrolysis of NaOCl.
If the cell was pH controlled and kept above 60 Celsius then you will wreck the anode once chlorate levels drop too low if its not an Ir-Ta MMO.
The advantage of your cell is that you can run it for a long time and passively collect crystals and just keep adding NaCl but with pH control you run
at 87% efficiency instead and you can just fractional crystalize or convert 100% to chlorate if you have the right anode (tantalum based MMO).
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yobbo II
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Going back to what I said above, that Sodium chlorate would not come out of solution if you simply keep adding sodium chloride and run and run the
cell.
I tried this some time ago.
The cells I ran were at 65C (this one was pH controlled) and a non pH controlled one at about 50C.
I monitored Chloride concentrations (and chlorate occasionally) using titration. The chloride concentration was starting to go below 60 or 70 grams
per litre and still no chlorate was coming out of solution (at the temperatures above, I did not stop the cell and let it cool).
I concluded that you would need to run your cell at somewhere below 50C in order to do this. I don't know how low below 50C.
The power got cut to the non pH controlled cell and the temperature fell to room temperature (around 18C) and pile of Na Chlorate come out of
solution.
The anodes will start to be damaged of you run at tooo low a chloride level. CE will suffer too.
If running a cell at these low temperatures there is hardly any point in pH controlling (especially if you find it hard to obtain/pay for acid) the
cell as you don't get much benefit of higher current efficciency if the cell is not hot.
Also I added the Chloride by hanging a basket (composed of passived (used and useless) mmo) in the cell with the Na Chloride suspended in it. You
don't want the deposited Chlorate (if it were to deposit) coming out on top of the Chloride. I don't know how you would cure that problem.
Thinking that there may not be enough surface area of Chloride to keep the cell fed (keep the concentration of Chloride high) I dumped some Chloride
into the cell where it sat on the bottom (plenty of surface area) but the concentration of Chloride still went too low for the anodes sake.
Looking at a graph that shows the solubility of Na Chloride and Chlorate together you would think that you could run the cell at around 60C and have a
high enough conc. of Chloride with Chlorate coming out of solution but it did not work for me.
The solubility of the chlorate will be low enough (at it's very high concentration) and the solubility of the chloride will be high enough at the
cooler temperature....I woiuld hope.
If you had two chambers, one hot and one cool (a crystallizer as it were) it might work OK.
I could not get it to work at the stated temperatures.
Yob
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mysteriusbhoice
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Ir-Ta should survive O2 evolution as they are primarily used for that so theoretically if you wanted the lazy man's chlorate cell you can use that
anode which wont get destroyed even when chloride levels hit zero.
edit: Though at that point you are better off running it to completion in pH controlled conditions at higher temps if you want to straight up use the
liquor for a perchlorate cell or even run the cell till small signs of perchlorates appear as the Ir-Ta MMO is capable of making perchlorates albeit
at 20% efficiency or less and will survive both O2 and O3 evolution as they are also used in electrolytic ozone generators.
[Edited on 21-10-2021 by mysteriusbhoice]
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