Recovery of 1,1,2,2 -Tetrabromoethane (TBE) and Di
Methyl Iodide (DMI) from Acetone wash.
When using heavy liquids such as TBE and DMI we always have many litres of
Acetone / Heavy liquid mixture to separate.
This would usually be done in a chemistry laboratory using heat and a rotary
evaporator or by flushing with water (which would involve large losses of acetone to
the drainage system) but in our laboratory we wanted to be able to process this
mixture in the safest possible way and, as acetone vapour can, under the right
circumstances, explode (Lower Explosion Limit 2.5% concentration - Upper
Explosion Limit 12.5% concentration) we would obviously wish to avoid this even as
a remote possibility.
To this end we investigated the possibility of distilling the Acetone out using limited
warmth on one side and a partial vacuum with chilling on the other side in a sealed
system thus:
Here we have the mixture contained in vessel A which is connected to the receiving
vessel B via tube C. The system is evacuated with a mechanical rotary pump via tube
C which has a valve V attached to it. The air is drawn out of the system through line
D and the valve closed. Both vessels are then taken to the fume cupboard and the
vessel containing the mixture is suspended in a heated water bath (at a temperature of
around 40°C) which incorporates an ultrasonic transducer whilst the receiving vessel
is placed in a thermally insulated container which is filled with crushed ice to cool the
receiver.
D
C
Using this set up the Acetone, which has a relatively high vapour of 231mm Hg at
25°C, begins to boil out of the mixture and is condensed in the chilled vessel. As the
Acetone vapour condenses the vacuum remains low and the vapour is effectively
‘pumped’ into the receiving vessel.
This would quite effectively condense the Acetone from the mixture on it’s own but
we have found that if we also activate the ultrasonic transducer that the Acetone
vapour is evolved more quickly.
Watch out for:

Be careful not to over fill the mixture vessel A as the vigorously boiling
mixture can have enough energy to climb right out of A and be pumped along
the connecting tube. Filling this point (and no more) in the image below
should help avoid this scenario.

Always keep the spout of vessel A pointing about 45° upwards when carrying
the system from the pump to the fume cupboard and also clamp vessel A in
the ultrasonic bath at this angle to help avoid the above noted point.
When moving the system try to avoid bumping vessel A as the sudden jolt can
cause the rapid boiling as this can flow over the connecting tube
contaminating the Acetone.
Clamp the receiving vessel into the insulated container by some means (retort
stand/ clamp etc) to avoid the possibility of the receiving vessel floating up out
of the ice bath as the ice melts.


Under these conditions the Acetone will come over into the receiving vessel at a rate
of about 500-1000 ml/hr.