RogueRose - 28-2-2018 at 16:16
With the success of drying the ethanol using anhydrous CuSO4, I was wondering if it could also be used to dry IPA in the same manner. I've read over
a few threads on this board and the question has been posed a few times but has gone unanswered (using CuSO4). I've tried to find solubility of it in
IPA online and haven't found any answers.
Wiki states that the pentahydrate is slightly soluble in Methanol (~10g/L) and the hydrate is insoluble in ethanol and acetone. So, would anhydrous
CuSO4 be likely to be soluble in IPA in any degree?
I'm also curious about MgSO4 and think that this has been suggested in the past but the problem with this is that it has no color change which is the
nice thing about CuSO4.
I also don't know how to measure the concentration of IPA. I do have a glass hydrometer that measures proof of ethanol, IDK if that can be used in a
similar way just using a different scale than ethanol.
IPA density is .786g/ml
EtOH density is .7893g/ml
Methanol density is .792g/ml
I would think that these being so close that the scale would be pretty similar but I'm not sure if I'm missing something here on how it works.
dpasek - 14-12-2025 at 20:19
I'm resurrecting this old thread BC it has no replies and I am currently interested in the topic.
I also have not found any solubility data for MgSO4 in IPA or in EtOH either.
I have tried MgSO4 in 91 v% IPA azeotrope (87.3 w% IPA).
I prepare MgSO4 as a drying agent by gently heating commercial Epsom Salts at 100 °C until the crystals turn from clear to white, which gives the
trihydrate (by gravimetric estimation) without melting, then raising the temp to 200 °C which gives the monohydrate with the original crystalline
form intact, so it is easy to handle; no crushing needed and there is not much dust. I cannot get to anhydrous with the lab drying oven that I am
using. Supposedly the monohydrate decomposes to anhydrous at 250 °C, but I have not found that yet.
Adding 10g of this MgSo4.1H2O to 50g of 91% IPA gives me 3 distinct phases; a solid phase, an aqueous layer, and an alcohol phase on top. So, some of
the water has salted out of the azeotrope, but I have not yet separated the layers for quantitative determination. A drop of the alcohol layer
evaporated on glass does not leave any visible haze, so the solubility of MgSO4 in IPA cannot be more than trace. I found this reference that probably
applies to my aqueous phase: water 74.5%, IPA 3.%, magnesium sulfate 22.5%, 25 °C.
Another test using 5g of MgSO4.1H2O in 100g of 91% IPA increased the weight of the (very gently dried) salt to 8g suggesting that the salt can go to
the pentahydrate under these conditions, while reducing the water content of the alcohol phase from 12.7% to 10% by weight (by calculation).
I have tried Ammonium Sulfate in 91% IPA but this does not seem to produce any useful results. 2% Ammonium Sulfate in 70% EtOH hand sanitizer gel
works very well for breaking the gel.
More later...
[Edited on 15-12-25 by dpasek]
Fery - 14-12-2025 at 21:19
K₂CO₃. But dehydrate it at high temperature as it is usually sold as sesquihydrate K₂CO₃·1.5H₂O
https://www.jstage.jst.go.jp/article/kakoronbunshu1953/35/9/...
[Edited on 15-12-2025 by Fery]
dpasek - 15-12-2025 at 02:05
Line 16: MgSo4 Upper layer; 48.2% IPA, 51.3% water, does not represent what I obtained for my upper layer, not even close, although it might be my
aqueous (middle) layer.
What I have for the upper IPA layer has much less water than azeotropic. I still need to determine composition to make a proper comparison.
The solid, aqueous, and alcohol layers can be seen in the photos through the translucent plastic bottle that I used.
I will make another attempt to add just enough MgSO4 to make a lower liquid layer to an endpoint that leaves only a trace of solid.
MgSO4 seems cheaper and easier to obtain than K2CO3.
[Edited on 15-12-25 by dpasek]
[Edited on 15-12-25 by dpasek]
UndermineBriarEverglade - 15-12-2025 at 17:09
How dry do you need the IPA? Salting out the water with NaCl is usually used for bulk removal. After that, MgSO4 should work (random source) and it's cheap and reusable. But I'm not sure how far above 91% you'll get.
Simple distillation isn't enough, but industrially IPA is purified by azeotropic distillation.
pesco - 10-1-2026 at 16:18
In histology labs absolute ethanol used for tissue preparation is dewatered using CuSO4 as standard procedure. Works like a charm.
Main reason for its use is change of colour on hydration. Once you see some CuSO4 on the bottom staying white/light blue and not darkening
you know there is no free water left in ethanol.
I see no reason why it wouldn't work with IPA.
It should work with MgSO4, but due to colour indication I would always pick CuSO4 if given a choice.