Distillation: The product of fermentation contains a large amount of water
and some solids, so the water is removed through distillation. Distillation
purifies ethanol to about 95 to 96% purity. The solids are pumped out and
discarded as a protein-rich stock, which may be used only for animal feed.
Dehydration: The ethanol produced is good enough for car engines in
countries like Brazil, but further purification is needed if it has to be blended
with mineral gasoline for ordinary cars. In this stage, a molecular sieve is
used for dehydration. Small beads with pores large enough for water but
not for ethanol absorb the water.
A large amount of energy is consumed in distillation and other steps in this
process. By one estimate, for the production of 1 liter of purified ethanol, about