Sciencemadness Discussion Board

Separating cloudy suspension of Benzyl Alcohol on water

Junk_Enginerd - 9-5-2021 at 04:40

I made a working lava lamp from scratch and I'm so fucking pleased with myself. However, somewhere in the process I accidentally muddied it up. The liquids are Benzyl Alcohol to act as lava, and plain water that I've added table salt to until the S.G. was right.

Is there a process I could perform to separate them? It doesn't seem like it's going to happen on its own. Also, is there something I could add to it to make the mixture more resistant to this happening?

I could of course just pour out the water and replace it, but I'd lose a lot of the Benzyl Alcohol doing this, and all I have is in the lamp...

unionised - 9-5-2021 at 05:01

Adding a lot of salt will make the water phase denser and that should help separate the liquids.

clearly_not_atara - 9-5-2021 at 13:04

Shouldn't you want more strongly immiscible liquids? Anisole/water seems like a better choice than BnOH. Anisole has an SG of 0.995 so might not be quite dense enough... or it might work with very pure water. Maybe a dye would be enough to bring up the density of the np phase in that system.

Alternatively, you could replace the NaCl with K2SO4 according to the:
http://en.wikipedia.org/wiki/Hofmeister_series
and see if that doesn't salt BnOH a bit stronger

Junk_Enginerd - 10-5-2021 at 09:03

Quote: Originally posted by unionised  
Adding a lot of salt will make the water phase denser and that should help separate the liquids.


I'll give that a shot, thanks. In an attempt to be a little non-invasive, I tried chilling it. That also helped a bit, I assume by the same mechanism.
Quote: Originally posted by clearly_not_atara  
Shouldn't you want more strongly immiscible liquids? Anisole/water seems like a better choice than BnOH. Anisole has an SG of 0.995 so might not be quite dense enough... or it might work with very pure water. Maybe a dye would be enough to bring up the density of the np phase in that system.

Alternatively, you could replace the NaCl with K2SO4 according to the:
http://en.wikipedia.org/wiki/Hofmeister_series
and see if that doesn't salt BnOH a bit stronger


I would indeed have preferred something less miscible. I'm not sure about any way of making it work if it's not denser than water though, since water can easily be made denser with any salt to match the densities, but the other way around is more difficult. The venn diagram of something that's:



results in a pretty damn small selection. Benzyl alcohol was the best compromise I could find, it's also nice that it's not overly toxic and practically non volatile.

Dioxane or chloroform might have ticked those boxes as well, but the whole thing would have had to be thoroughly sealed, and under considerable pressure since the basic mechanism of the lamp involves heating.

DraconicAcid - 10-5-2021 at 09:40

I think dioxane is miscible with water, isn't it? Just like THF?

If you had something like anisole, you could add a small amount of chloroform to increase the density. Alternatively, you could halogenate something aromatic to increase the density of that compound without increasing its water solubility.