Drying IPA with silica gel ? Will this work ?

[BravoV]

As IPA is hygroscopic, even it was highly concentrated at the beginning like 97%, when used often like opening the bottle lid, it will gradually getting wetter as water vapor is absorbed through time.

Still have few unused big bags of silica gel from my camera hobby, its used for lens/cameras dry box.

I've been thinking of to dry it using a fresh coffee filter as sieve/filter, and then loaded with fresh silica gel in the filter, and then pour or sort of rinse the IPA over it, and repeat if needed, until the blue dyed silica gel turned pink colored as water is absorbed.

Realistically I'm not ambitious to achieve 99.99% purity using this method, its just if this work up to certain extent, its not too troublesome and cheap in maintaining/improving the dryness of the IPA.

Scope of the IPA used is just for electronics only, like ordinary cleaning off soldering flux or PCB, nothing else.

Random image from Google on blue dyed silica gel turning into pink once water is absorbed.

[rikkitikkitavi]

What is the problem with some moisture in the IPA, if used for cleaning?

Provided you screw back the cap there is only so much water that can be present in the free space of the bottle. Leave it open all kinds of contaminants might be present (even TOC in the form of bugs as IPA is highly toxic to insects) and the slow evaporation of IPA increases the concentration. Slowly...

Some CO2 will dissolve in the water, but since IPA is miscible with water due to high polarity you can probably expect some CO2 be present in IPA aswell to begin with but the low protonization doesnt cause any significant corrosion before all gases evaporates with the cleaning agent.

So provided you use sufficiently clean IPA to begin with, some extra pure water and dissolved gases shouldnt be a problem when cleaning electronics. This is the most important factor.
Ash residue and high volatiles residue,  fex dissolved ionic compounds or high volatiles compromize the cleanliness of the PCB.
An "Acid specification" expressed as acetic acid content is also good, that means that very little acidic compounds are present. The alcohol will hoever oxidize over time to isopropylic acid by air oxygen but this is volatile but to a lesser degree and I expect very little problem from this, but a 20 year old bottle I might consider twice before using.

Filtering , ie direct contact between silica gel and IPA might however dissolve any solubles that end up in your IPA, or even disperese fine particles of silica gel that will end up on your PCB, absorbing humidity now and forever on the surface.

So my point is, why bother if only used for cleaning  and second by filtering it through silica you might end up contaminating your IPA far worse. 
My proposal is to leave it be.
If possible obtain pharma grade IPA instead of the technical 99% typically used for cleaning. It is far superior , to the extreme in purity.

BR Rickard

EDIT: if you need to be sure, put your IPA can /bottle in a tightly sealed clear plastic container (fex one with a snap on lid) and put some silica gel next to it. The plastic container has so low diffusion permeability to water vapour so that as long as the lid is sealed tight the humidity is keept low.

Notethat  I have not googled if silica gel has a higher absorbant factor than silica gel to water, if that is the case, then the IPA will of course dry out the silica instead...

[IanB]

I once accidentally left the cap off a small bottle of IPA. When I came back to the bottle it was empty and dry. So I think perhaps IPA evaporates faster than it absorbs water. As long as you replace the cap on the bottle after use, I don't think there will be any problem with it getting wet.

As far as the particular question about silica gel, it may not be selective for water only. It is possible it will also absorb IPA, in which case it will be ineffective as a drying agent.

[rikkitikkitavi]

To remove water to obtain absolute alcohol typically filtering through molecule sieves is the way, they are solid ceramic materials that doesnt release particles and have a strong affinity only towards water due to the size of molecules.

 

[ChristofferB]

Silica gel is typically not used for liquid drying. Molecular sieves are the way to go, but for cleaning it is way overkill. All miscible solvents evaporates as azeotropes, so most of the water in the IPA will likely evaporate along with it.

If the surface of the pcb or components has cavities or sites that accept water (microscopically) these will likely already be populated from the moisture in the air, and will then be dehydrated by the IPA.

[Shock]

I've been thinking of to dry it using a fresh coffee filter as sieve/filter, and then loaded with fresh silica gel in the filter, and then pour or sort of rinse the IPA over it, and repeat if needed, until the blue dyed silica gel turned pink colored as water is absorbed.

Not tried it, but the problem I see is the silica gel could absorb the IPA as well, or break it down into a gummy mess. Silca gel could also contaminate the remaining IPA.

Aside from the molecular sieve you can also use fractional distillation. But you might as well just go an buy pure IPA and save your distilling efforts for ethanol. Which sounds more productive to me.

The main problem with handling pure IPA is it absorbs moisture after opening the container. For that reason if you have it in bulk you pour off into smaller containers and then top up your squirt bottle or dispenser.

I did a quick calculation and air with 50% humidity trapped in a 50% filled 1L bottle of pure IPA at 25C would take about 90 openings to reduce the purity by 0.1%.

[rikkitikkitavi]

99,9% IPA is still considered very pure.

[Shock]

They sell 5L 100% pure IPA here for $20 US, when I brought my last lot it was about $15. Deionized water $7 for 5L.

[MyHeadHz]

1.  What you showed pictures of is compressed silica powder, and not silica gel.  Silica gel, which is crystalline, is generally exclusively sold in bead form.  The colors come from the different states of Cobalt Chloride as it gains water- they are not dyed.  Both Silica gel and Cobalt Chloride can be quite dangerous to health if not dealt with carefully (see their respective MSDS's).  It is worth noting that the Cobalt Chloride concentration varies wildly between brands, and the highest quality brands have both the lowest concentration of Cobalt Chloride and most consistent color.  You must check the MSDS of that exact product from that exact manufacturer.  It is MUCH more difficult to deal with compressed silica powder, especially that which is mixed with cobalt chloride dust.  Stay away from that stuff!  It was used a long time ago widely, including in kitty litter, but has been phased out due to health concerns.  You can still find similar products, but with blue dyed chunks (that don't change color) in lieu of any actual cobalt chloride.  The Silica powder by itself is still quite nasty, so never mess with that stuff.  If you must ever use it, stick to professional companies that specialize in it, and follow all safety protocols and use PPE.

2.  Even if it did work (which I do not think it would), it would be expensive, and there are better ways to purify it.  It is much better and cheaper to just buy the pure stuff directly.

3.  What are you going to do with pure IPA anyway?  There are not many use cases for pure IPA.  In general, the most effective solvents for general electronics use are IPA/H2O mixtures (such as 70% IPA and 30% H2O).  Water is the 'universal solvent," but there are some things that IPA works for that H2O won't.  If you use pure IPA, you might end up with a lot of residue/gel/other stuff left over that the IPA cannot dissolve.  The same goes for any other solvent.  Just because something is more pure, does not mean it is "better" for all use cases.  IPA and water are used together because they happen to be stable together, mix together, and also happen to dissolve a wide range of stuff between the two of them-- and they are both quite cheap.  Most of the time, you only need a simple mix of the two and no other solvents.  I've seen several threads lately focusing on pure IPA and it seems rather silly to me, other than for thought experiments or pure curiosity.

[BravoV]

Ok, I guess I have to drop this idea.

Reason why I want to try this is, I have probably +20 liters left of 97% IPA from a 30 liters container, bought from an industrial surplus material shop many years ago, maybe its near a decade.

I've been using it all this time for years, transferred to smaller bottles or containers, most to bigger glass bottles as buffer stock rather than have to pour from that big heavy container, and most frequent used is in my plastic squeeze bottle for cleaning flux or washing/spraying pcb. I've emphasized this at 1st post, its not for human consumption or anything else, only for electronics. 

I remembered that when it was new, when accidentally spilled over my glass table, it evaporated quite fast like dried almost instantly and without any wet residue, nowadays, the spill dried much slowly, and pretty sure, it left some wet residues which I assumed its water, it will dry eventually exactly like water, but took sometimes.

At some cases, when washing my PCBs, I had to use hair dryer to dry it completely, which was not needed in the past when the IPA was fresh.

I can afford to buy new batch of 30 liters of IPA, its just don't like the idea to dispose that +20 liters, and have been thinking if there is an "easy & cheap" way to improve it's dryness, thats all.

Please don't suggest those unsual or maybe expensive "molecular sieve" and etc .. its not my intention.

Btw, my silica is in bead form, not powder form, exactly like this below, and I live in tropical high humidity area, exposed silica gel like below in open air, will turned into pink in just few hours.

Random image from Google


Thanks for replying.

[Ian.M]

Unless you can set up to distil it, there's really no good options.  Even if you can distil it, distillation with a good fractionating column will only get you as far as its azeotrope with water, 87.7 % IPA by weight.  Refining above that concentration is a multi-step process.  One possible approach would be to start by salting out  the bulk of the water in the original solution with ordinary salt, then decant and chemically dry the solvent fraction with anhydrous calcium oxide (quicklime) followed by filtering and distillation into a sealed receiving vessel with a drying tube (desiccant) protecting its vent, to remove suspended calcium hydroxide nanoparticles.   

However distilling 20 litres of IPA would be a significant fire and explosion hazard, and quicklime is extremely caustic and its reaction with water is significantly exothermic so you'd better have good apparatus and PPE and enough organic chemistry experience (or caustics and moonshining experience) to do it reasonably safely.

[Mechatrommer]

dont waste your time on this. this is purity phobic. how much purity reduced after couple of opening the cap? -10%? -20% i have several chemical here.. thinner, spirit, ipa acetone chloroform FeCl etc that laying around for months/years. they dont seem to get any diluted a bit, the thinner can still scorch my skin the same when i bought it year ago. same as spirit and ipa etc. my only concern will be getting a good supplier that supplies pure ingredient in the first place. and as a tip, we usually buy chemical in big bottle, keep that a bit far away where its safe, sealed and seldomly opened, prepare one or few small glass bottle and fill the chemical in it for daily use good for few weeks or month of usage, so our purity phobic will be greatly reduced.

I can afford to buy new batch of 30 liters of IPA, its just don't like the idea to dispose that +20 liters, and have been thinking if there is an "easy & cheap" way to improve it's dryness, thats all.

right tldr earlier. so dont do that. only buy what you need in couple of years. buy 1 or 2 litre bottle. if you can get 30 litres at cheaper than 1 or 2 litre, then you already make great saving, trying to purify it may cost extra if not a lot of money and time and safety hazard, let the factory do the job. and i will doubt the purity of cheaper 30 litres compared to more decent priced 1 or 2 litre chemicals.

[Shock]

I'd sell it, that way it can get repurposed. If you have problems, fill it up 30% distilled water and sell it as 30L of disinfectant/technical grade and offer free local delivery or meet up with them. Just don't sell it out of the house to avoid attracting the drug lab type of undesirables. Problem sol-vented.

[helius]

While IPA/water mixtures are superior solvents (they are able to dissolve some salts, which alcohol is not very good at), they are definitely not preferred for cleaning sensitive devices like optics or magnetic tape heads. That is why 99.9% IPA is produced. IPA is hygroscopic, so when sitting in an open container it will both evaporate and pull moisture from the air, becoming a lower percent solution over time.
Silica gel can't be used to remove water from alcohols as it has affinity for both (both are polar molecules).

[rikkitikkitavi]

BravoF, if your IPA doesnt leave any residue but slowly evaporating water then it should not be  a problem.

High purity , i e low water content IPA is best used for non polar polutants, and follow up by a rinse with demineralised water will clean up your PCBs nicely.

[Ian.M]

Probably the best idea is to determine how much water it has adsorbed over the years so you know what you are working with, then use it for applications that concentration is suitable for, and also as Mechatrommer suggested, get a smaller quantity of high purity IPA, appropriate to your usage rate, for when you need the 'good stuff'.

To determine the concentration, get the room and solution temperatures as close as you reasonably can to 20 deg C, and either use a hyrometer, or weigh a litre on accurate scales (check against a litre of  water) to determine its specific gravity (density) then look it up in this table: http://www.pharmcoaaper.com/pages/TechLibrary/tech_docs_high_purity_solvents_reagent_chem/specific_gravity_isopropyl_alcohol_water_mix.pdf

[BravoV]

.... doubt the purity of cheaper 30 litres compared to more decent priced 1 or 2 litre chemicals.

Well, the 30 litres I bought is Merck brand made in German, and it came with factory seal, bought them from a surplus from a big chemical surplus shop that sourced from a big chemical factory that was closed. Pretty confident it's quality is much better than those cheap no brand even has the same concentration.

BravoF, if your IPA doesnt leave any residue but slowly evaporating water then it should not be  a problem.

High purity , i e low water content IPA is best used for non polar polutants, and follow up by a rinse with demineralised water will clean up your PCBs nicely.

Mine has almost undetectable dry residues (by eyes) when the IPA and water have evaporated.

As I used it to clean my camera's lenses too, this method is easy to spot on the purity. I did try compare the Merck brand vs other cheap no brand one I bought once, put a droplet each at a very clean glass surface like camera lens, then let it dry in open air. The Merck brand didn't leave any visible residue mark at all, while the no brand one left a very-very faint circle on the dried droplet but noticeable when dried. This method is easier to spot at camera lens or glass lens as they have the faint colored shaded coating at it's reflection.

Probably the best idea is to determine how much water it has adsorbed over the years so you know what you are working with, then use it for applications that concentration is suitable for, and also as Mechatrommer suggested, get a smaller quantity of high purity IPA, appropriate to your usage rate, for when you need the 'good stuff'.

To determine the concentration, get the room and solution temperatures as close as you reasonably can to 20 deg C, and either use a hyrometer, or weigh a litre on accurate scales (check against a litre of  water) to determine its specific gravity (density) then look it up in this table: http://www.pharmcoaaper.com/pages/TechLibrary/tech_docs_high_purity_solvents_reagent_chem/specific_gravity_isopropyl_alcohol_water_mix.pdf

Thanks, noted, but I've decided its not worth the effort as I was just trying to find an easy & cheap to dry it, not interested if its troublesome, guess I have to live with it for now.

[rikkitikkitavi]

Well, leave no trace, that is the purpose of the solvent.

If you need to remove something very greasy, ie non polar fat IPA is not the best to begin with anyhow.

But for cleaning PCbs and electronics is the best.

You keep your IPA.
30 liters will get you far.

And when you don't want it anymore, add some hand washing agent, blue colour and dilute with water and use it as wind screen cleaner