Drying IPA with silica gel ? - Page 1
Forum section: electronics / general

author: BravoV
author_rank: Super Contributor
timestamp: October 02, 2018, 06:42:14 am
content: My IPA is said to be 85% purity, say I submerge enough silica gel, will it absorb the water and increase the IPA concentration without any bad side effect ?The IPA will be used for cleaning & wiping electronics related stuffs only.

author: daqq
author_rank: Super Contributor
timestamp: October 02, 2018, 07:06:41 am
content: I don't think so. Silica gel is not selectively absorptive.

author: BradC
author_rank: Super Contributor
timestamp: October 02, 2018, 07:16:47 am
content: I dry most solvents with CaCl, but it doesn't do so well with alcohols (forms complexes). I have some zeolite that works, but again short term only and you'd want a *lot* of zeolite to adsorb 15% water.You could put some dry (and I mean baked dry) salt in there and separate out the brine layer but unless you are willing to tolerate some residue you'd need to distill the result.It'd be *much* easier to find some better quality IPA.

author: Ampera
author_rank: Super Contributor
timestamp: October 02, 2018, 07:57:12 am
content: Quote from: BradC on October 02, 2018, 07:16:47 amYeah, I'd say if you only have an 85% solution of India Pale Ale, you might want to get something a bit higher quality. Would save you the trouble of having to purify it.

author: IanB
author_rank: Super Contributor
timestamp: October 02, 2018, 08:20:32 am
content: The water may help the IPA to clean better. Water can dissolve some things better than alcohol.

author: CJay
author_rank: Super Contributor
timestamp: October 02, 2018, 11:25:04 am
content: This site might be useful, try not to choke when you see the unfortunate banner.http://delloyd.50megs.com/moreinfo/drying.html

author: jpanhalt
author_rank: Super Contributor
timestamp: October 02, 2018, 11:48:41 am
content: Quote from: CJay on October 02, 2018, 11:25:04 amSome "interesting" recommendations there. I have no problem with using things like CaCl2, molecular sieves, and so forth (i.e., non-reactive drying agents) liberally. Using strong reactive agents, such as Pb/Na and LiAlH4, can cause problems. In particular, the recommendation to use Pb/Na alloy for drying chlorinated hydrocarbons (e.g., methylene chloride -- dicloromethane -- and chloroform) can initiate a radical chain reaction with violent results.

author: kosine
author_rank: Regular Contributor
timestamp: October 02, 2018, 12:02:24 pm
content: You could also try sodium polyacrylate, which is cheap and readily available as water gel crystals for gardeners. It's likely to absorb some of the IPA as well, but what's left might be of a higher concentration:https://wat.lewiscollard.com/archive/www.newton.dep.anl.gov/askasci/chem07/chem07132.htmA method that might be more successful would be to get a suitable seeled container and place the IPA in a dish surrounded by the crystals. They'll absorb moisture from the air, and the IPA will (hopefully) evaporate more of its water content as the humidity drops.

author: CJay
author_rank: Super Contributor
timestamp: October 02, 2018, 12:11:35 pm
content: Quote from: jpanhalt on October 02, 2018, 11:48:41 amooh, yes, that one's a fun one, highly not recommended.

author: coppercone2
author_rank: Super Contributor
timestamp: October 02, 2018, 12:55:45 pm
content: you need to find the molecular seive equivilant of the silica, I think its 10-30x distribution.So it might seperate out some kinda long oils or something, selectively, but otherwise it will absorb everything in your IPA mixture.You want like a 3A sieve for IPA to do a good job, in bead form, all other methods will result in shit floating around, so you need to redistill it after drying (distill with minimum turbulence and boiling, preferably under a vacuum for fast evaporation rather then actual boiling). With the quality molecular sieve beads, you can decant it with fairly low solids content, but re distillation is still recommended, but it won't be a complete mess like with a salt.But you would not use sieves until you distil it to the concentration that forms the azeotrope with water or is otherwise unreasonable to distill, using dehydration for cleanup in any concentration prior would just be kinda dumb.Not doing at least one vacuum distillation to try to bust the azeotrope prior to using dehydration is also kinda dumb.https://en.wikipedia.org/wiki/Azeotrope_tables\also shitty cheap molecular seives will cloud the mixture much more then good ones that are sintered properly and stuff.

author: macboy
author_rank: Super Contributor
timestamp: October 02, 2018, 01:43:26 pm
content: Quote from: BravoV on October 02, 2018, 06:42:14 am85% isn't great. Just a little too much water.You should be able to find 91% (by volume, or 87.7% by weight) quite easily, as this is the natural percentage that isopropanol and water will distill at (its azeotrope). The 91% stuff works well as a cleaner and because it is an azeotrope, it should evaporate (more or less) completely leaving no water behind. However, it can't effectively be used to remove water, for that you want >95%, so that it can take up some water and still remain over the magic 91% purity which evaporates completely.

author: BravoV
author_rank: Super Contributor
timestamp: October 03, 2018, 02:54:58 am
content: Quote from: CJay on October 02, 2018, 11:25:04 amQuote from: kosine on October 02, 2018, 12:02:24 pmThanks, interesting and I might try it, especially using sodium polyacrylate as I think I've seen it was for sale quite cheaply at local industrial chemical retail shop around here.To all replies, thanks and appreciate the suggestions and notes, I do understand its easier and cheaper to buy new with higher concentration. Its just I have quite plenty here bought or given (forgot which) many2 years ago, prolly > 10 litersand I thought it will be a waste just to throw it away.I was thinking maybe there is a chemical that can just drop in the container and let it suck the water while not reacting with the IPA and let it sink, assuming with minimal residue at the IPA, and of course not thru the trouble of distilling, filtering and etc or like dealing with the mess like using salt.As IPA used widely at electronics especially for cleaning boards when soldering, it will be nice if we have sort chemical that we just dunk inside the IPA storage bottle to absorb "some" of the water, and sink at the bottom. Also our IPA bottle that we used often for soldering job also will suck moisture from the air thru time.

author: coppercone2
author_rank: Super Contributor
timestamp: October 03, 2018, 01:21:40 pm
content: molecular sieves are just that. their made of zeolite and they harmlessly sit on the bottom of most things, but they are sensitive to acids and bases.the main contamination would be from them not being cleaned after sintering or them being poorly sintered. The materials they are made of are practically insoluble in anything (like ceramics). Silica gel is a molecular seive but its size is not well controlled (its between 10-30 angstroms iirc), while molecular seives are controlled to their specifcation number (i.e. 4A molecular sieve corresponds to 4 angstroms).The idea with sieves is that the voids allow for water to 'bond' with the sieve or kinda diffuse into it or however you wanna think about it (i don't know the proper mechanism really), but if you have a mixture of say water and alcohol and there is a big ass sieve like silica it will basically allow for both to enter). But if you have a fine sieve, like 2A, if you have a mixture of water and ethanol, the water can fit into the sieve pores and the alcohol is too big, but since there is a electrotendancy of some kind, you end up with water going into the sieve.They also get warm when they absorb solvents (just like dehydration by other means, i.e. pouring water into sulfuric acid makes it warm up heavily)They are commonly left in anhydrous solvent bottles to maintain anhydrousity when used in excess, but they might physically disintegrate a bit (but into parts that can theoretically be mechanically filtered) and basically not dissolve in the slightest bit.Once saturated they can be heated to remove the absorbed materials and reused, there are procedures for this.The other thing you can do is put it through a HPLC column, which is even more expensive, but traditionally in a modern laboratory, to get anhydrous solvents, you basically push the solvent through a appropriate HPLC column (in a sealed system, kind of like a keg dispenser in a bar), and load in solvent bottles and fresh columns (these are held on a maintenance schedule).Both HPLC columns and molecular sieves are very clean solutions as with residue after use, but there will be slight residue sometimes.The purest of the pure will likely use solvents sourced from drying over things like molecular seives, reactive metals (i.e. sodium) in excess, then continuously boiled in a dean-stark type apparatus. This is obviously very dangerous because you might have a few gallons of boiling solvent in a laboratory that uses it, so unless extreme purity is required people just stick with HPLC or sieves.The idea with the distillation is that if you distill it really nice, any small particles that get left behind after the decanting are filtered out. Also since its boiling hot less water gets into it by diffusion etc.For those confused by reactive purity, using things like Sodium metal to clean up residual water content, the idea is that the shit is already really clean to begin with, cleaned by other means first, think of it as a 'getter' in a vacuum tube system, rather then the vacuum pump. You would obviously not use just a getter to vacuum a tube down because it would blow the fuck up or catch on fire or take forever and drain your wallet dry.Using anything other then vacuum distillation or cheap salt like CaCl2 and then distilling it afterwords is considered at best esoteric and desperate or at worst wasteful.Also you really don't want left over CaCl2 or other salts in electronics grade solvents because they will corrode the fuck out of everything. I would highly recommend careful non vigurous distillation twice before using something dehydrated with corrosive salts (with distillation you get some aerosol forming because of the boiling so some salt particles will transfer over)If you decide to go for molecular sieves you need to look up their retention ability (it's not great, their meant to seal the deal rather then to dehydrate something with 10% water content).

author: georges80
author_rank: Frequent Contributor
timestamp: October 03, 2018, 10:36:16 pm
content: I just use the stuff I get at the local corner electronics storecheers,george.