Recovery of Ethanol
The method for recovery of ethanol from fermentation broth is shown in this sketch:
Other options have had a great deal of attention in the research laboratory, but
steam stripping
is the mainstay of the industry. One very important advance in the last decade or so has been recycle of the waste aqueous stream from stripping back to the fermenter. This puts back a small amount of ethanol but more importantly reuses nutrients. The fermentation uses almost all of the carbohydrates but only part of the nitrogenous compounds. There is also a significant saving because less liquid goes to waste treatment. Recycle has the restraint of buildup of non-volatile components, however, glycerol reaches concentrations that make its recovery for sale practical.
Continue to discussion of distillation.