Sciencemadness Discussion Board - Purifying NaOH from drain opener

Purifying NaOH from drain opener

Melkor333 - 16-8-2022 at 07:47

Here in Canada, it’s quite difficult to find crystal drain cleaners that are pure NaOH (or even have NaOH). The ones that do contain it are mixed in with other stuff like NaCl and carbonates. I recently bought Drano Kitchen Granules Clog Remover, the sds states it’s 60-100% NaOH and 10-30% NaCl. I did a crude titration and it’s definitely not pure NaOH, I think it’s around 80% purity. So is there any way to purify the NaOH from the NaCl, and some way that doesn’t require too much equipment or other chemicals?

B(a)P - 16-8-2022 at 13:08

Assuming the product is cheap, you could try recrystallisation. I a say cheap because you are going to loose a fair bit of your sodium hydroxide. Sodium chloride has a pretty flat solubility curve, sodium hydroxide has a nice steep one. Assuming you have 80% sodium hydroxide and 20% mostly sodium chloride you could take a portion of your mixed chloride hydroxide product and add enough water to dissolve the chloride portion. Take the temperature up to what ever is needed to dissolve everything, then put it in the fridge. The crystals that form will be somewhat pure sodium hydroxide. You could repeat the process if purity is particularly important.
Don't use your best glass for this as hot concentrated sodium hydroxide will not be kind to it. It is also very unkind to human skin and eyes, so make sure you take appropriate precautions.

Tsjerk - 16-8-2022 at 13:23

Quote: Originally posted by B(a)P

The crystals that form will be somewhat pure sodium hydroxide. You could repeat the process if purity is particularly important.

You can make solutions with more than a gram of NaOH per milliliter.

Maybe you can extract the NaOH with water, but then you will be left with wet hydroxide which isn't easy to dry. Except by heating to close to the melting point of NaOH.

Extraction with methanol or ethanol would be easier, which would be easier to get rid of. But still not fun to work with.

[Edited on 16-8-2022 by Tsjerk]

DraconicAcid - 16-8-2022 at 14:11

I don't know about sodium chloride, but if you want carbonate-free sodium hydroxide solution, make a saturated solution of sodium hydroxide in a sealed plastic bottle and let it sit overnight. Na2CO3 is far less soluble, especially at high concentrations of sodium.

If you want solid sodium hydroxide, good luck. I don't think it crystallizes well.

B(a)P - 16-8-2022 at 14:33

Quote: Originally posted by Tsjerk

Quote: Originally posted by B(a)P

The crystals that form will be somewhat pure sodium hydroxide. You could repeat the process if purity is particularly important.

I have tired the process myself and it is not as hard as you make out.
At 0 C sodium hydroxide is soluble to 40 g/100 mL of water. The sodium hydroxide forms nice crystals and the water can easily be decanted off. Once the crystals have been blotted dry on paper towel an hour in the oven at a touch over 100 C will dry them nicely.

Tsjerk - 17-8-2022 at 01:19

Okay, I didn't expect that. But how much NaOH do you get out of solution? Because this paper says you can dissolve around 1 mol of NaCl in a liter of 10 molar NaOH. Which corresponds with a 40 g/100 ml NaOH solution.
You would need a molar ratio smaller than 1:10 to get NaOH to crystalize out of the mix. 20/80% NaCl/NaOH is larger with approximately 1:7.

B(a)P - 17-8-2022 at 01:42

Quote: Originally posted by Tsjerk

Okay, I didn't expect that. But how much NaOH do you get out of solution? Because this paper says you can dissolve around 1 mol of NaCl in a liter of 10 molar NaOH. Which corresponds with a 40 g/100 ml NaOH solution.
You would need a molar ratio smaller than 1:10 to get NaOH to crystalize out of the mix. 20/80% NaCl/NaOH is larger with approximately 1:7.

Ah you make an excellent point! I did not think about the common ion effect.
That being the case, what I proposed will not work.

Amos - 17-8-2022 at 12:23

I can't think of a particularly large number of reactions where some salt will cause issues. I would just keep this product and use it as is (in a higher amount to account for the mass percentage of NaOH) unless you are absolutely positive no sodium chloride can be present.

Anyone here who is telling you that you can obtain the bulk of your solid NaOH again after dissolving it in water is lying or hasn't ever tried and can't think critically about the process. It's not going to happen. If you want to crystallize out the salt and then use NaOH as a solution within the next couple of days, that's an option, but you'd probably want to repeat this laborious process every single time you wanted NaOH solution, as it will react fairly quickly with atmospheric CO2.

[Edited on 8-17-2022 by Amos]

Sulaiman - 17-8-2022 at 16:56

If NaOH drain unblocker is legally purchasable at your location then "pure" NaOH and KOH are also probably legal.
Check out online shopping sites, especially soap making suppliers.

I can't get "pure" NaOH or KOH,
Commercially "pure" is (here) c99%
Atmospheric CO2 and especially H2O react visibly quickly.
If there is a choice between 'flake' and 'prill' I would choose 'prill' as there is less dust,
and reaction with the atmosphere is slower due to lower surface area per gramme.

KOH and NaOH are so hygroscopic that I can't imagine them crystalising from water at any concentration.
But my knowledge is only hobby level.

PS. KOH is supposed to be obtained from wood ash soaked in water,
so after burning quite a lot of wood (to dispose of it) I collected the ashes and added water to make a bucket full of slurry,
that I kept under my outdoor workbench, and gave a stir every day or three.
One day, I found a nice clean EMPTY bucket,
my wife had 'helped' me to tidy up

This experiment is still 'on the list'

[Edited on 18-8-2022 by Sulaiman]

B(a)P - 17-8-2022 at 17:26

Here you go! And only $7 per kg. Also they have similarly priced potassium hydroxide. Excellent suggestion Sulaiman.
https://soapandmore.ca/search?type=product&q=sodium+hydroxide
And as Amos suggests you can save your 80/20 hydroxide chloride mix for reactions where chloride contamination is not an issue.

Junk_Enginerd - 28-8-2022 at 11:15

Quote: Originally posted by Sulaiman

KOH and NaOH are so hygroscopic that I can't imagine them crystalising from water at any concentration.
But my knowledge is only hobby level.

PS. KOH is supposed to be obtained from wood ash soaked in water,
so after burning quite a lot of wood (to dispose of it) I collected the ashes and added water to make a bucket full of slurry,
that I kept under my outdoor workbench, and gave a stir every day or three.
One day, I found a nice clean EMPTY bucket,
my wife had 'helped' me to tidy up

This experiment is still 'on the list'

[Edited on 18-8-2022 by Sulaiman]

Well, I have personally recrystallised plenty of both NaOH and KOH, both intentionally and accidentally. It's no big deal, nothing like ammonium nitrate and calcium chloride which are hygroscopic to the point of being problematic. I've even made some really pretty crystals with NaOH by just leaving it in a jar, which didn't form from cooling down but evaporation in a standard indoor climate, so it's not hygroscopic enough to prevent that at least

I think you won't get much KOH from wood ashes, but certainly a whole bunch of K2CO3 which you could calcine into KOH.

Tsjerk - 28-8-2022 at 12:44

If you leave a solution of hydroxide to evaporate so far it starts crystallizing, it is carbonate crystallizing, not hydroxide. When i leave hydroxide open here, humidity around 40%, it first dissolves in water absorbed, later it crystallizes as the carbonate.

BromicAcid - 28-8-2022 at 13:12

Might be worth investigating but I remember the procedure for making sodium peroxide hydrate where the sodium peroxide crashes out of the solution, but there was a warning that if you attempted to dehydrate it you just made sodium hydroxide. Might be an interesting way to precipitate from solution but I don't remember the details off the top of my head.

OneEyedPyro - 29-8-2022 at 01:05

Quote: Originally posted by Melkor333

Here in Canada, it’s quite difficult to find crystal drain cleaners that are pure NaOH (or even have NaOH). The ones that do contain it are mixed in with other stuff like NaCl and carbonates. I recently bought Drano Kitchen Granules Clog Remover, the sds states it’s 60-100% NaOH and 10-30% NaCl. I did a crude titration and it’s definitely not pure NaOH, I think it’s around 80% purity. So is there any way to purify the NaOH from the NaCl, and some way that doesn’t require too much equipment or other chemicals?

I'd assume you dried it well? Drain cleaner grade NaOH is usually a bit wet but fairly pure otherwise in my experience.

If you do have chloride or other impurities then recrystallization is probably the only practical route.

teodor - 29-8-2022 at 06:14

Buying so impure material put you in a position of a chemist of 19 century. There is an excellent book from 1849 and here you can find the procedure (it is for KOH but NaOH should be similar). It starts with a solution of syrup consistency:
"The greater part of the carbonate separates in solid particles, which swim on the surface ... the solution shaken in a close vessel with 1/3 of its volume of alcohol, and the mixture left to settle. Two strata are formed: the lower stratum is an aqueous solution of chloride, carbonate, and sulphate, together with a portion of KOH, and rests on a precipitate that may contain lime, oxide of iron, and sulfate; the upper stratum is a solution of caustic potash with some chloride in alcohol. This is poured off, freed from the greater part of the spirit, by distillation (in a metal vessel) and boiled down till the hydrate begins to sublime. The resionus matter produced by the decomposition of the alcohol, and found swimming on the surface, is then removed and the hydrate poured out on plates."

I would not evaporate the alcoholic solution too much, in this case, you can use borosilicate glass. Use this product as a solution. If you need NaOH in a crystalline form I think the better alternative is just to buy it in a pure state.

ave369 - 9-10-2022 at 10:39

I would rather look for a drain opener that has two kinds of particles: spherical white globules and small crystals similar to table salt. This means the ingredients were merely crudely mixed together as solids, and it is easy to separate them using, I don't know, gauze cloth? The white globules are NaOH of reasonable purity, and the crystals are NaCl or Na2SO4.

Mateo_swe - 13-10-2022 at 02:07

Maybe it would be easier to ask some friend send you some drain cleaning product with 100% NaOH.
If you know someone living not so far away where its avaliable in the stores.