jm112583

Op-Temp = Operational Temp We have an oil jacketed boiling tank with a 1500 Watt heater. We control the op-temp. If I set the op-temp to 130 degrees the controller will maintain 130 degrees. Nomally, in a non-vacuum, simple distiller, we would run an op-temp of 130*C to efficiently recover Ethanol. In this Vacuum distillation version.... for some reason we still need an op-temp of 130*C to recover ethanol efficiently even though we've dropped the boiling point by 50*C. We tried an op-temp of 90*C yesterday and it took 5 hours to recover 3.3 Liters of ethanol (Less than one gallon). Through experience we should have recovered all 5 gallons over the 5 hour period, probably even within 4 hours. At the 130*C op-temp we were able to recover all 5 gallons in 6 hours. This is no different than if we were running the same cycle without vacuum. We should run a bit more quickly and at a much lower op-temp, about 80*C-90*C, but for some reason we cannot and we do not understand why. I hope I'm not being too confusing. We are using virgin ethanol as well. 96%!! So water is not the issue.

We're in the process of getting our solvent recycler to work with the vacuum distillation of ethanol. The purpose would be to be able to boil the ethanol off at a lower temperature to preserve the quality of the contaminant. The boiling point of ethanol is 79*C and under vacuum (28 inHg) it drops to around 34*C. We typically use a rule of an additional op-temp of 50 degrees Celsius above the boiling point of the solvent is enough to boil the solvent and maintain that boil. In the case of Ethanol, we would use an op-temp of 130*C. Under vacuum we can assume that we would need an op-temp of around 85*C. What we have found is that we still need to give the ethanol an op-temp of around 130*C to get it to boil under vacuum and it is a slower boil than without vacuum. Does anyone know why the ethanol requires so much heat to boil under vacuum?? This goes against everything that we know and have proven to work for vacuum distillation and we're at a roadblock. Any and all insight will be greatly appreciated. Thanks in advance!