Page 117 - Biofuels Refining and Performance

100 Chapter Three

Aldehydes

Product alcohol
Stripper
Feed from fermentor
column
(Mash) Rectifying
column

Fusel oil

Stillage
Steam
Wastewater Steam
Figure 3.10 Two-column system for distillation of ethanol.

from the head vapor, condensed, and partly used as reflux. Fusel oil is
taken out from several plates of the rectifying section [9, 47, 82].
With efficient distillation, the stillage should contain less than 0.1%
ethanol since the presence of ethanol significantly increases the chem-
ical oxygen demand (COD) of wastewater. For each 1% ethanol left in
the stillage, the COD of the stillage is incremented by more than 20 g/L.
Due to the potential impact of residual ethanol content, therefore, proper
control over distillation can greatly affect the COD of stillage [82].

3.15 Alternative Processes for Ethanol
Recovery and Purification
Since distillation is a highly energy-consuming process, several
processes have been developed for purification of ethanol from fer-
mentation broth: for example, solvent extraction, CO extraction, vapor
2
recompression systems, and low-temperature blending with gasoline
[9]. However, these processes are not established in the industrial pro-
duction of ethanol.