Melgar - 26-3-2017 at 18:02
Somehow I went all these years without realizing that isopropanol has probably the best azeotrope with water of any OTC solvent. That is, the
azeotrope boils at about 80C and is about 15% water. So if you need to remove traces of water formed by a reaction that isopropanol won't interfere
with, you can just add 99% IPA to the mixture regularly, and that'll do a pretty good job of drying it.
But that's 99% IPA, which is slightly harder to get than 90% IPA, at least for me. I have a large bottle of 90% IPA that I use mainly as fuel for
alcohol lamps. Today though, I had to dissolve and then dry a water-soluble mixture that I knew would be incredibly frustrating to dry. It was
slightly soluble in IPA, but not soluble enough to make it worth evaporating that much IPA. So I tried the 90% stuff. It dissolved about half as
much as water would, but as I evaporated the solvent, and the volume got smaller and smaller, there wasn't any ot this popping and splattering that
I've come to expect from water. In fact, it just dried right up, without giving me any trouble at all. The azeotrope boiled away all the water, and
the last few percent was pure IPA, which had no particular affinity for this mixture like water did. I wish I'd have thought to do this sooner.
byko3y - 26-3-2017 at 19:50
I see no problem in getting 99% IPA at all: http://www.sciencemadness.org/talk/viewthread.php?tid=13680
This way drying and azeotrope distillation requires no distillation column.
JJay - 26-3-2017 at 20:02
Heet makes some isopropanol-based dry gas. Some varieties contain additives, but they have one variety that is pure anhydrous isopropanol.
Melgar - 27-3-2017 at 00:44
Actually, I think maybe I didn't explain myself well enough. 99% isopropanol is easy enough for me to get, I just have to go a bit further out of my
way and it's slightly more expensive than 90%. However, in this case, dissolving and evaporating a mixture that was very soluble in water and
slightly soluble in IPA, the 90% IPA performed much better than either water or IPA would by itself. It dissolved much more than pure IPA would have,
but boiled away easily at the azeotrope temperature.
XeonTheMGPony - 27-3-2017 at 05:03
IPA is a very old trick, I used to buy 45gallon drums of 99% it was used for the cleaning of electronics, first it was washed in a normal (Well
special mix) deionised water bath then sprayed with IPA and then air dried, same for cleaning refrigeration systems after a burn out, pumped through
the Hx's.
It has a great affinity to water and accelerates the drying process greatly, but as noted it is expensive less you have a recovery system.
for the refrigeration bulk was liquid phase so simple distillation gave it a long cycle life, the board drying was open but used just a few mills per
pcb
Booze - 28-3-2017 at 16:13
You could get 99% by using 3A molecular sives, or by aezeotropic distillation. But I don't know how to do that with isopropal alcohol.