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Solvent recovery
OK, first off, sorry if this is in the wrong place or has been asked before. The search didn't find it.
Is it reasonable to use a rotary evaporator to recover solvent from waste for use in non-critical applications like washing glassware?
(I realise a still would be better and so on but that's not the question here. If you did it would it work and would it be safe?)
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crazyboy
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What waste are you talking about? Do you mean rotovaping reactions and saving the solvent to wash glassware? It could certainly work, but it might get
a but messy if you got a nonpolar solvent, say xylene mixed in with your DCM or whatever.
The main problem I have with my rotovap is solvent recovery. The condenser (or perhaps the vapor duct) is designed poorly such that the solvent vapors
exit the vapor duct right under the vacuum inlet so they hardly pass through condenser coils. To protect my vacuum I am forced to pass the solvent
vapors over an ice trap followed by a NaOH trap in the hope of condensing solvents and trapping air. In evaporating 100ml+ solvent I will be lucky to
catch five drops in the solvent catch.
Ideally I would have a dry ice/acetone trap but I can't go out and buy dry ice every time I want to evaporate something, I only wish there I had an
electronic solution like a cold coil or a cryocooler.
If I could collect waste solvents I would use them to wash glass but I just buy a gallon of acetone for $9 and it lasts me a long time.
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peach
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That isn't really a clear enough question, recover solvent from waste. You mean, you have a big mix of solvent waste and want to get the individual
solvents back, it's mixed with oils and greases or you're removing it from a reaction?
Rotovaps are designed to remove solvent from a reaction as rapidly as possible, for bulk or high throughput work. Almost universally, they're used for
concentrating a liquid or drying to a solid by removing the solvent (I stress, removing - they're not purifying it as it goes, just concentrating the
thing in the flask).
People routinely have problems with it not condensing properly because the vacuum is too deep or the trap not cold enough (even with dry ice).
They are not designed for purity and you can't fractionate with them, not accurately anyway. They remove the solvent WAY over the 10 drops per minute
recommendation for a pure result. It's not at all hard to do something very similar using normal glass, a stir bar and a vacuum. I can easily get
solvent pouring through to the receiver as a constant stream using normal still setups.
You only really need a rotovap if you're working in a lab and doing tons of solvent removal or need it done immediately. The difference in the time it
takes between a normal still and a rotovap isn't really important at home. A rotovap is a normal glass still with the stir bar replaced by a rotating
flask and not much else. They also don't usually have thermometers, which are fairly important for purifying something via a phase transition.
As an example, if your solvent is contaminated with something that happens to boil around the same temperature, roughly, it'll end up in the receiving
flask of the rotovap due to the lack of fine temperature control and the massive vapour flow rate.
If you want to recycle your solvents, you'd be better off using a flask with a vigreux stuck in it. This is how the high end labs dry and clean up
their solvents as they work (solvent stills). You also have the option of fractionating mixtures.
I bought 25l of acetone not long ago for decorating. More on that later. But I save an empty 5l container and then dump the dirty acetone into that to
use it for washing mucky tools and things.
A lot of these solvents will happily boil at very low temperatures. For example, DCM boils not a lot over room temperature. I have wondered about
making a still to clean up the really dirty stuff by just whacking some form of tubing on the top of the 5l metal cans it comes in and then warming it
up a little.
{acetone / decorating}
Acetone is the cheat code for uber decorating skillZ. Cleans glass brilliantly, also cleans white PVC window / door frames with one wipe back to new
looking. One of my favourites is to not bother masking anything that's PVC, metal, glass etc and then emulsion blast an entire room. You can get razor
sharp lines (better than taped) very easily afterwards because the acetone will wipe the emulsion off in no time, but not off the walls (unless you
rub at them). I constantly have containers of it beside me as I'm working.
[Edited on 1-11-2010 by peach]
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unionised
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The only significant volatile impurity would be water and that would settle out. They are extracts from soil, looking for pesticides. These are the
ones where I didn't find any pesticides.
BTW, I know (as I said) that a still would be better.
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peach
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If these are just liquids, with no solids, and water is the main impurity, the only thing you have to then look at is how water behaves around the
specific solvents in question.
If it was immiscible, I'd guess you'd use a sep funnel instead.
So I'm assuming they're mixed. Leaving the next thing to consider being their boiling point and the possibility of azeotropes.
Alternatively, depending on how much water you're talking about, how about drying agents? If you don't need the absolute maximum amount of water out,
there are many possible options.
For washing glassware, water often isn't even an issue, provided there's a lot of the volatile present. I never bother drying my glassware much
between water and acetone rinses. I run it under the tap until it's too hot to touch, immediately empty it and then flick the remaining water out.
Whilst it's still hot, I gave it a squirt with the acetone then flick that out as well. The warmth of the glass usually gets it drip free a minute or
two after I put it down.
The next step up from that is vacuum flame drying, which is only really necessary for anhydrous work.
It depends which stage of washing and such you're talking about. For removing bulk gunk, fairly impure solvent will do. For polishing it to a clean
standard, it needs a few ml's of distilled solvent squirting in.
The question is still a bit vague, as there's no mention of the specific solvents. Most of the things it's extracted from the soil will be heavy
organics, which shouldn't distill over too rapidly if the solvent is a highly volatile one. Leaving just the water to consider.
[Edited on 1-11-2010 by peach]
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unionised
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The stuff is an extract in DCM from soil.
There's some stuff dissolved in it from the soil. That stuff will be mainly involatile.
The liquid is mainly slightly damp DCM with involatile dross in it.
The lab doesn't have a solvent still so knowing how much better it would be isn't helpful. We do have a couple of rotovaps and I have plenty of
experience in using them.
We also produce some gunged up glassware.
We could use high purity solvents to clean it but it makes more sense to me to run the soil extracts through a rotovap and use that solvent for a
preliminary clean up. Obviously this wouldn't be the final clean up so trace contamination shouldn't matter.
What I'm hoping to find out are
Does anyone know if this is possible- in particular, has anyone done something similar?
Also is there any particular risk from doing so?
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gutter_ca
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Yes, we use this method in our lab.
Whenever we're rotovaping solely MeCL2, we save it seperately for glassware rinsing.
Environmental lab, sounds like same as you.
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unionised
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Thanks for the reply. I doubt this will carry much weight with my boss, but it's worth a try.
Anyone else?
(Incidentally, sorry, should have mentioned dichloromethane earlier. I would have done so, but I'm an idiot)
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gutter_ca
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Write it into the glassware cleaning SOP, prove you don't get any contamination, and you should be golden.
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