Remove flux from IPA (need more but only have used stuff)

[Psi]

So i need more IPA for PCB cleaning but it can't be bought for love nor money due to covid19.  Well.. unless you want to pay 10x price.

However I do have 10 liters of used IPA that's full of dissolved flux, i think it's mostly rosin.

Any ideas how to remove the flux?

Can i distill the IPA off with a heat source and a condensing column leaving the flux behind?
(yes i'm aware of the flammability safety issues trying to do this)

[Ian.M]

If you've got the laboratory glassware to set up to do that, it should work well enough, but odds are the used IPA has adsorbed a significant quantity of moisture from the atmosphere, so expect to only get 91% purity even if you use a fractionating column.  If you need better than that, you'll either need to separate the water by salting out then discard the aqueous phase, or add a strong desiccant like anhydrous calcium oxide, prior to distillation.

Lastly, the lower explosive limit for isopropanol vapour is only 2.2%, so for %DEITY%'s sake make sure you've got intrinsically safe forced ventilation, no naked flames, and that any electric heating devices  have intrinsically safe controllers.

[Psi]

Thanks.

Yes, safety is definitely a concern.

I'm not out of IPA just yet, stocks of IPA might recover before i need more, but it's good to know there are options.

[T3sl4co1l]

That.

In the mean time, perhaps you can settle for acetone, MEK, denatured ethanol (unless it's been wiped out too?..) or others.  Usually not too aggressive, but spot-check as always.

Incidentally, vapor condensation is about the only way to responsibly work with chlorinated solvents (1,1,1-TCE most importantly).  Terrifically good for cleaning to begin with, you're basically putting the work inside a Soxhlet extractor.

Tim

[jogri]

so expect to only get 91% purity even if you use a fractionating column.

It will be worse than 91%, you can only manage a maximal purity of 87.7% as IPA forms an azeotrope with water... But that is the best case, expect maybe 60-75% purity with a DIY setup and not much experience with distillations. If you want to remove the remaining water i would advise you to use either molecular sieves (3A) and/or magnesium sulfate. Don't bother with CaO, that stuff is just too nasty. Distill it, then add enough MgSO4 until that stuff doesn't form white fluidy blobs (you'll see) and stays as a fine powder. Decant it, then add the molecular sieves (after you've put them in an oven at 200°C for some time [let them cool down before adding them]).

If you want another solvent that is still available go to a hardware store and grab some Acetone and denatured alcohol (paint supplies).

And please work with small portions (500ml-1l max), just set it up, let it run through and NEVER open it when it is still hot. If you need help with it just PM me, i've done quite a few distillations over the years.

[tom66]

For PCB cleaning - it's modestly expensive but I've found "FLUXCLENE" by Electrolube to work rather well. It contains IPA but also works to break down flux rather than just loosen it from the surface, my boards have never looked cleaner.  I don't know if it's in stock in Aus, but there may be an equivalent there. And, if it is stocked, it's far more likely to still be in stock than IPA.

[jogri]

For PCB cleaning - it's modestly expensive but I've found "FLUXCLENE" by Electrolube to work rather well. It contains IPA but also works to break down flux rather than just loosen it from the surface, my boards have never looked cleaner.  I don't know if it's in stock in Aus, but there may be an equivalent there. And, if it is stocked, it's far more likely to still be in stock than IPA.

Looks like it's just a rather expensive mixture of different solvents... Mainly Cyclohexane, iPA and PGME. If you absolutely need something like that i recommend buying the solvents in bulk and just mixing them (another option would be to mix gasoline, iPA and diethyl ether (can be synthesized at home), that should make a rather similar flux remover)

[Ian.M]

so expect to only get 91% purity even if you use a fractionating column.

It will be worse than 91%, you can only manage a maximal purity of 87.7% as IPA forms an azeotrope with water... But that is the best case, expect maybe 60-75% purity with a DIY setup and not much experience with distillations.

Sorry, I grabbed bad data for the isopropanol water azeotrope.

[jpanhalt]

I have done preliminary experiments with adding a "Cellosolve" to IPA or ethanol.  Cellosolve has become generic for ether alcohols with this structure: ROR'OH.  Most commonly the alcohol is erhylene glycol, and they are named as derivaives of ethanol, e.g., butoxyethanol, ethoxyethanol (https://en.wikipedia.org/wiki/2-Butoxyethanol).  They are relatively non-toxic.   Even non-mineral brake fluid contains them.

The former is used widely as an industrial solvent in paints and floor finish strippers. The latter has a lower boiling point.  Both are miscible in water.  I tried the former with 50% water and it worked, but a bit more slowly than with lower concentrations of water.  I have been trying the latter in various mixtures with denatured ethanol and IPA.  You can rinse with water or just blow off with air.  Cellosolves are easy to make but the cost of chemicals is artificially inflated. 

I would go ahead and distill the IPA to get rid of non-volatiles.  If that doesn't work, you can add a little acetone to it but not sure that will help.  You can get ethoxyethanol from a lot of sources.   I would try your neat distilled IPA  plus 10% cellosolve.  I paid about $20 USD for 500 ml.  The company was based in India, but shipped from the US.  Nicely packaged too.

[KL27x]

...denatured ethanol (unless it's been wiped out too?..) or others.

I bought a gallon of denatured at the first hardware store I tried. I went to the paint section and asked for alcohol. First response was "we're all out." After specifying the "stuff for cleaning paint," the lightbulb went off, and they had plenty of it.

Over here, they seem to add Bitrex. The main problem is for cleaning glass, it leaves visible streaks. But this buffs/wipes off with a dry cloth after the glass is completely dried a few seconds, later.

In hindsight, I contemplating buying a bottle of lighter fluid at a preceeding stop at the pharmacy, just in case.

[Psi]

The main problem is for cleaning glass, it leaves visible streaks.

Yes, the white streaks are why i don't just use methylated spirits instead.