Electronics > Projects, Designs, and Technical Stuff
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.
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