Sciencemadness Discussion Board

Is electrolysing brine a viable method of HCL production?

jupiteri35 - 15-9-2019 at 02:19

Just wanted to know if I could make some HCL by electrolysis of NaCl. Sulfuric acid is hard to come by in my area, so I have to resort to this.
1 amp would make 0,038 mol of Cl per hour. The main problem I think is hypochlorous acid, which is made along with HCl when chlorine dissolves in water. Will it screw up reactions or can I leave it in for most purposes? Is it possible to remove it from the solution? Has anybody here tried doing this before?

mackolol - 15-9-2019 at 04:42

Electrolysis of brine oxidises your NaCl to NaOCl and further to NaClO2, NaClO3 and NaClO4 and almost no chlorine, so it's good only for making chlorates.

The best and cheapest way of making chlorine is electrolysis of hydrochloric acid, you can also carry on electrolysis of ZnCl2 solution.
If you want to yield Cl2 from NaCl in water, you must have ion exchange membrane that doesn't allow OH- Ions to connect with Cl- ions, but that's unreachable for amateur chemist I think.

You could also do an electrolysis of NaCl in Ethylene or propylene carbonate, but at first, You must react Your NaCl with AlCl to make NaAlCl4, which is further electrolised. There must not be any water in reaction as well.
And AlCl3 is not that cheap, but apart from that, if you had AlCl3 you could simply electrolise it in water to Cl2.

Here is the link for NaAlCl4 electrolysis:

[Edited on 15-9-2019 by mackolol]

XeonTheMGPony - 15-9-2019 at 04:52

You need Mercury to make a Chloro-Alkali cell, you then need to burn the resulting Chlorine and Hydrogen to make the HCl, this then needs to be bubbled through water to get your solution, or the gas led into your reaction mixture.

[Edited on 15-9-2019 by XeonTheMGPony]

etherealvapour - 15-9-2019 at 09:24

Yes, it works, you don't really need to use Hg, or buy an expensive Nafion membrane. See my post here:
You electrolyze brine (saturated NaCl solution), in a two compartment cell, separated by a diaphragm, which can be anything that prevents the compartments from mixing, but still passes ions through. The result won't be as pure as that made with an ion-exchange membrane, but it's fine, and you can purify the HCl, although purifying the NaOH takes more work (read up on some older patents when industry used to make NaOH, Cl2, HCl this way, pre-1970 was more common).
Key points:
- Use a carbon/graphite anode, industrially they use Pt coated anodes, use that if you have it, as the carbon anode will slowly corrode
- Use 2 compartments, some diaphragm, be it thick paper, porous/sintered glass, or industrially they used to use asbestos.
- Keep temperature under 60C, room temperature is fine, unless you want to increase chlorate production
- one compartment can be brine, the cathode compartment can be water, but having both brine will work fine too
As you do this, the Cl2 will become dissolved in the anode compartment, giving you HCl/HClO. If you let it decompose under UV or sunlight, it will favor decomposition to HCl + O2, without UV, it favors decomposing to Cl2 and H2O.
To avoid wasting Cl2, you should bubble it through another solution and repeat this process.
Industrially they tend to burn the H2 and Cl2 (the other compartment will produce H2), if you can set this up, you can make anhydrous HCl this way, very cheaply (as cheap as it's done industrially), if you don't need that, bubble the hydrogen chloride gas into H2O to make hydrochloric acid. The other compartment will have NaOH mixed with NaCl, you can separate them by fractional crystallization and other separation techniques (look at the patents for some ideas), there may also be a bit of NaOCl in both compartments since you didn't use a membrane, and that's the disadvantage to using a diaphragm - the product is not as pure. Of course the HCl can be distilled and purified further, but for the NaOH the purification is not as easy.
All in all, it works, is not too hard to do, although you do have to deal with H2 and Cl2 gases.

hodges - 15-9-2019 at 15:44

Sulfuric acid is hard to come by in your area - well what about muriatic acid (which is the HCl you are trying to make)? Sold for cleaning bricks and masonry.

If you have a way of distilling, you can make HCl from sodium bisulfate (the active ingredient in some powdered toilet bowl cleaners), and ordinary table salt (sodium chloride).

I wouldn't recommend trying to make HCl from hydrogen and chlorine. It can be done, but it is an extremely violent reaction. Very similar to making water from hydrogen and oxygen.

vmelkon - 15-9-2019 at 20:17

H2SO4 is a common chemical. All cars have it.

Herr Haber - 16-9-2019 at 03:10

Quote: Originally posted by vmelkon  
H2SO4 is a common chemical. All cars have it.

Less and less true.

draculic acid69 - 16-9-2019 at 04:05

Quote: Originally posted by Herr Haber  
Quote: Originally posted by vmelkon  
H2SO4 is a common chemical. All cars have it.

Less and less true.

How so?all cars have lead acid batteries.except hybrids.but even they'd still have one for the starter motor don't they.

j_sum1 - 16-9-2019 at 04:20

Modern car batteries are sealed. And cracking one of those open is an ecpensive way to get acid.

mackolol - 16-9-2019 at 05:21

Ah yeah... You meant HCl production not Cl2 my bad.

You could synthesise H2SO4, used for production of HCl from sulfur and CuCl2 as shown in one of Nurdrages youtube video.

Just burn sulfur that should be available and cheap in where you live and just bubble resulting SO2 fumes into solution of CuCl2 in water. When all the CuCl2 is converted into insoluble CuCl, you change SO2 to Regular oxygen, could be air till all CuCl is oxidised. After few cycles you filter your salt and concentrate your sulfuric acid by strong heating.

rockyit98 - 16-9-2019 at 06:16

if you can find rock salt and super phosphate fertilizer you can distill HCl.
Ca(H2PO4)2 +2CaCl2 ---(heat)----->Ca3PO4 +4HCl
both are cheap.

jupiteri35 - 17-9-2019 at 10:08

Quote: Originally posted by jupiteri35  
Recently I bought this felt sheet for one of my other projects. Do you reckon multiple sheets of it sown together would make a good ion-exchange membrane? it is 3mm thick

felt_.jpg - 13kB

AJKOER - 8-12-2019 at 08:27

I do NOT recommend electrolysis path as the process is slow and product is dilute and likely impure.

Per an old thread, "Using Oxalic Acid to Make H2SO4,..." at one can prepare many acids starting with H2C2O4, however, safety suggests not attempting to produce very concentrated acids (like H2SO4, see below).

For HCl from CaCl2 and Oxalic acid:

H2C2O4 + CaCl2 --> 2 HCl + CaC2O4 (s)

An extract from the referenced thread including the excellent work done by Formatik, which includes the preparation of HCl cited above:

Quote: Originally posted by Formatik  
Quote: Originally posted by Formatik  
Copper sulfate and oxalic acid could then work to also form H2SO4.

Sulfuric acid from copper sulfate and oxalic acid:

This works! Few minor complications though.

Concentrated stoichiometric aqueous solutions of copper sulfate and oxalic acid dihydrate yields a very fine light green copper oxalate precipitate and eventually a clear slight yellow and when more concentrated pale green solution. This solution was found to contain H2SO4.

Because the copper oxalate was so fine, it passed through filters. So the yellowish solution was let sit a few hours until clear and siphoned in part. The siphoned solution was evaporated for a few days and the solid removed. Then the solution was boiled down until thick fumes formed (H2SO4).

The boiled down liquid had the color brown and gave a further crystallization, which was a white solid that somewhat stuck together. It seems the white solid can be removed by further siphoning. The warm liquid when dripped onto paper tissue ate holes through it under carbonization.

Sulfuric acid from calcium sulfate and oxalic acid:

Calcium sulfate is also reported to work. There was a thread recently on here somewhere mentioning a reference where calcium sulfate was said to work, though I doubt the claim the acid is of good purity.

But we need to consider that copper sulfate is much more soluble than calcium sulfate and the solubility product of calcium oxalate is 2.32E-9, whereas copper oxalate is 4.43E-10. So copper sulfate is better suited for those reasons. It's possible solubility of both oxalates is increased in acid solution.

Sulfuric acid from magnesium sulfate and oxalic acid:

When I mixed stoichiometric concentrated solutions of oxalic acid and magnesium sulfate, there was no precipitation (no magnesium oxalate formed). After standing for several hours there was crystallization (not sure if that was any reaction, but I suspect unreacted crystallization of reagents), and the liquid was always heavily contaminated with solids. Even after several crystallizations, and finally boiling the liquid down left only solids and no acid. If this route does form any sulfuric acid (which isn't entirely clear to me, it would be much more contaminated than the acid from the above copper route.

And further:

Quote: Originally posted by Formatik  
As long as sulfuric acid is present it could be expected to form equilibrium with the magnesium oxalate, forming this soluble acid oxalate. And so hindering isolation. This would explain why I saw no precipitate. I remain skeptical that a route through magnesium sulfate could prove useful. I won't pursue that reaction more. I've also tried some other reactions and described them below. Some success, some failure.

Perchloric acid attempt from oxalic acid (failed):

I've attempted to get perchloric acid through oxalic acid but this didn't work. The literature describes preparation of impure chloric acid from solutions of sodium chlorate and oxalic acid frozen in a freezing mixture (Böttger, Lieb. Ann. 57 [1846] 138). Ammonium oxalate is about as soluble as sodium oxalate, so I've attempted something similar with ammonium perchlorate and oxalic acid. The details are in the attached file below.

Another attempt of sulfuric acid from oxalic acid and CuSO4 (beware!):

I made another attempt with the copper sulfate and oxalic acid. But this time used larger amounts. This time I only filtered and siphoned the filtrate, and did not evaporate and collect more solids. But this time I just boiled down the filtrate. Something very bad happened on boiling near the end, all of the sulfuric acid and contents in the 600mL beaker ejected entierly! I think the sulfuric acid reacted violently with residual oxalate (another crystallization would have been good) and the heating might have been too high.

The purity of acid made this way should be alright for some purposes. CuSO4 has a solubility of 0.19g in 100g of 92.70% H2SO4 at 25 C (Solubilities of inorganic and organic compounds, 2nd ed. (1919) by A. Seidell). CuSO4 should be the end-product copper salt and the white solid that was seen earlier in the brown acid.

On another similar note, aqueous copper sulfate yields no precipitate or any reaction of note when added slowly into an excess of aqueous citric acid. The reactivity of citrates might be the reason why there is no reaction. Oxalic acid can be boiled with nitric acid and is able to partially resist the attack.

Hydrochloric acid from calcium chloride and oxalic acid:

Aqueous solutions of CaCl2 and oxalic acid yield an immediate fine white precipitate of calcium oxalate when mixed. The liquid part of the solution of this eventually attacked and disintegrated aluminium foil evolving H2, whereas aqueous oxalic acid was unreactive. The calcium oxalate could be filtered with filter paper.

Nitric acid from copper nitrate and oxalic acid:

Aqueous copper nitrate and oxalic acid when mixed immediately gave a light green-blue precipitate (same one as by copper sulfate). This is one way to recover nitric acid from copper nitrate. Calcium nitrate should also work instead of copper nitrate. So, oxalic acid is yet another acid that will liberate nitric acid from some nitrates.

Both hydrochloric and nitric acids unlike sulfuric acid are very easy to purify by distillation.

[Edited on 11-5-2012 by Formatik]

I believe H2C2O4 is now under restrictions in many jurisdictions, so OTC products containing Oxalic acid may now be the only source.

[Edited on 8-12-2019 by AJKOER]

garphield - 12-12-2019 at 16:41

You don't need sulfuric acid to make HCl, it can be generated from sodium bisulfate (easily bought as a ph lowering chemical for pools, at least where i live) and table salt. NurdRage has a video on it that I remember watching. Sodium bisulfate might be restricted too but I doubt it as it's much less dangerous than sulfuric acid.

symboom - 13-12-2019 at 00:34

Eventually battery acid will be very hard to come by as a source of sulfuric acid batteries are increasingly becoming the gel acid type and the glass mat type sealed batteries Which will also mean the battery acid refill that one can currently get for the older capped refillable batteries will soon be phased out also sulfuric acid drain cleaner is also being raised out even in the US which is know for having a good supply of otc chemicals it seems like the diy fix it yourself way of doing things is fading.
Copper sulfate might be the last to be around to make sulfuric acid. Just my observations

Amos - 13-12-2019 at 07:57

If you combine any reasonably strong non-volatile acid (think phosphoric, or even sodium bisulfate) with sodium sulfite, bisulfite, or metabisulfite, you get off-gassing of sulfur dioxide, which can be bubbled into any strength of hydrogen peroxide to yield sulfuric acid, which can be concentrated by boiling. I suspect this route will be viable for decades to come in most jurisdictions.

WGTR - 13-12-2019 at 08:56

I have made a tiny amount of hydrochloric acid via electrolysis, if anyone is interested. The electrodes were made from activated carbon, and the whole setup worked like a giant capacitor. The sodium and chlorine ions would attach to the surface of their respective electrodes at low voltage potentials. After the “capacitor” was fully charged, the chloride electrode material could be taken out and rinsed free of excess salt. This electrode could then have a reverse potential applied between it and a low surface area counter electrode, and free acid would appear in the solution over a period of days.

My challenge was to produce the pure acid directly without distillation or using/wasting other reagents. If you can purify the acid of excess salts by distillation, then washing the chloride electrode is not necessary. In fact, the extra salt speeds up the creation of the acid by improving solution conductivity.

garphield - 13-12-2019 at 15:27

It also might be possible to make sulfuric acid from sodium bisulfate by heating it, which forms sodium pyrosulfate which then reacts with water to form sodium sulfate and sulfuric acid, but I can’t find much about it online other than that it exists so it might require too high temperature to be practical or the sodium sulfate + sulfuric acid might just reform sodium bisulfate.