Sciencemadness Discussion Board

Cleaning volatile solvents

mycotheologist - 6-12-2012 at 12:47

Lets use hardware store hydrocarbon distillates like naphtha as an example. If you do an evaporation test and see that there is no visible residue left behind, you can conclude that it doesn't contain a large amount of solid impurities but I suppose there could be trace amounts of heavy metals and stuff that you won't be able to see. Would activated charcoal take care of that?

Mailinmypocket - 6-12-2012 at 13:11

Quote: Originally posted by mycotheologist  
Lets use hardware store hydrocarbon distillates like naphtha as an example. If you do an evaporation test and see that there is no visible residue left behind, you can conclude that it doesn't contain a large amount of solid impurities but I suppose there could be trace amounts of heavy metals and stuff that you won't be able to see. Would activated charcoal take care of that?


Distillation!

mycotheologist - 7-12-2012 at 15:52

I meant without distillation. Distillation is a lot of hassle, especially for higher BP solvents.

kristofvagyok - 7-12-2012 at 17:44

Vacuum distillation?

There is no other such efficient method for cleaning solvents like distillation, or distillation from something (e.g.: THF, dioxane should be distilled from benzophenone and potassium).

And remember that absorbents like molecular shieves, charcoal ect. won't get out a lot thing from the solvent what you use in it.

[Edited on 8-12-2012 by kristofvagyok]

mycotheologist - 8-12-2012 at 05:41

Can you elaborate on what you said about distilling from benzophenone and potassium? I've never distilled any ethers before so maybe it doesn't apply to anything I've done but I'm interested.

smaerd - 8-12-2012 at 06:17

Sometimes a solvent can be cleaned by doing water rinses, or salt water rinses. Or by addition of pH neutral rinsed with DI water and, dried activated carbon and letting it sit(not ideal for solvents like acetone due to condensation reactions on the A.C. surface). Ideally though like everyone else has said, distillation.

I haven't really heard about heavy metal contaminants in non-polar solvents. I guess with some of them it would be possible? Activated carbon can remove heavy metals from aq. solutions though.

unionised - 8-12-2012 at 06:22

Most heavy metal impurities are solids. If you evaporate some of the solvent down on a clean class watch glass and don't see any residue there's probably not much metallic contamination.
The exception would be organometallics which can be volatile.

If the boiling point of the impurity is similar to that of the solvent then simple distillation won't help.

If you need to remove trace metals from aliphatic hydrocarbons you can reflux them with aqueous acid for a while then separate then, dry them and re distil.

Do you have any particular solvents and impurities in mind?

mycotheologist - 8-12-2012 at 07:40

Quote: Originally posted by smaerd  
Sometimes a solvent can be cleaned by doing water rinses, or salt water rinses. Or by addition of pH neutral rinsed with DI water and, dried activated carbon and letting it sit(not ideal for solvents like acetone due to condensation reactions on the A.C. surface). Ideally though like everyone else has said, distillation.

I haven't really heard about heavy metal contaminants in non-polar solvents. I guess with some of them it would be possible? Activated carbon can remove heavy metals from aq. solutions though.


Good idea, I didn't think of washing with water. It wouldn't work with acetone either way since its miscible with water. I know you can't beat distillation but its a lot of trouble setting up the apparatus, heating the sandbath (I never use oil anymore because its too messy) then cleaning up afterwards. Can't wait until I have the equipment for vacuum distillations, heating is the biggest hassle for me so being able to reduce the pressure will simplify things a lot.

I have no idea what non-polar solvents might be contaminated with, I just said heavy metals as an example. For low density NP solvents like hydrocarbon distillates you could probably remove metals and other insolubles by adding water then letting the insolubles settle at the bottom (in the water layer) then separating the layers.


Quote: Originally posted by unionised  

If you need to remove trace metals from aliphatic hydrocarbons you can reflux them with aqueous acid for a while then separate then, dry them and re distil.

Do you have any particular solvents and impurities in mind?

No particular impurities in mind but the solvents I have in mind are petroleum distillates, toluene and xylene. There are other things I have in mind though such as hardware store HCl and household ammonia. I usually make my own HCl and NH3 solutions but I don't have very big flasks so its hard for me to get the concentration up, would be much easier to start with drain cleaner but what I like about gas bubbling is I end up with a 100% pure solution (or at least as pure as the water I bubble it into).

I don't mind volatile impurities as much because they won't be present in my product (if my product is a solid that is).

[Edited on 8-12-2012 by mycotheologist]

m1tanker78 - 8-12-2012 at 10:12

I extract toluene from a fuel line cleaner. It's actually a mixture of acetone, 2-butoxyethanol, IPA, MeOH, MEK, and toluene (the major component). All components except toluene are miscible in water so I do several washes and separations then dry and distill. The distillation may be unnecessary but I do it anyway. I store it with a few pieces of sodium but this may also be unnecessary. Fractional distillation as is left me with contaminated toluene because the BPs are so close and fractional distillation is rather slow.

I suppose it's better to say that I extract everything from the toluene with water..

Tank

mycotheologist - 12-12-2012 at 04:18

Why do you store it with sodium, to keep it dry?