Lets look at boiling and estimate costs - work with me here, this may not be correct!
Latent heat of vapourisation and densities (at 25C except for water, 4C)
Water - 2257 kJ/kg (1 kg/l)
Methanol - 1100 kJ/kg (0.7865 kg/l)
Acetone - 518 kJ/kg (0.7846 kg/l)
Sources:
http://www.engineeringtoolbox.com/fluids-evaporation-latent-heat-d_147.htmlhttp://www.engineeringtoolbox.com/liquids-densities-d_743.html1 Joule = 1 Watt second so 1kWh = 3600 kJ.
So approximately we're talking, to boil off one litre of each + cost at 15p/kWh:
Water => 9.4 pence
Methanol => 3.6 pence
Acetone => 1.7 pence
So in a 100l batch the phase change cost of recovering, say, 7.5l Meth is 27 pence
If we have 25l Acetone cosolvent phase change cost would also be 42.5 pence
The way to look at it is that we're used to recovering several litres of Methanol from batches and the latent heat of vapourisation for Acetone is half that of Methanol. Recovering 1l of Methanol is approximately the same cost as recovering 2l Acetone.
So that's the phase change cost, what about heating the Acetone to it's boiling point before that can take place?
The Specific Heat Capacity of Acetone is 2.15 kJ/kg.K.
25l weighs 19.6 kg. To heat from 20C to its boil point (56C) would take (56-20)*19.6*2.15 = 1517 kJ. Or approximately 6p (leccy again at 15p per kWh).
So for our 100l batch example, the total of heating + phase change part of Acetone recovery by boiling increases the batch cost by 48.5p, or just under 0.5ppl (plus any heat losses and elevated vapour pressure because it's in a mix rather than pure).
Personally I think that makes it viable to recover the Acetone by boiling at atmospheric pressure, but only because it takes very little energy, relatively, to vapourise Acetone.
