Continuous Fermentation of Ethanol
The traditional processes for making alcoholic beverages are batch operations
that take days or weeks. Industrial ethanol for solvents and other uses was
made from petroleum for several decades because cost was less than for
fermentation. When the price of petroleum rose sharply in the 1970's, the
economics were better for fermentation ethanol but not for the slow
processes. Various improvements such as more energy efficient distillation or
drying, recycle of medium that still had valuable nutrients, and better
process control apply to either batch or continuous processing. The two
types of continuous processing employ some means of retaining yeast cells in
the bioreactor. The tower fermentor uses a strain of yeast that flocculates
to particles that fall back as the fluid rises to an expanding conical
section above the main region for bioreaction..
An alternative to the tower fermenter shown above is immobilized cells. Immobilized yeast can be
packed into a column; this tends to have extremely high rates but evolution
of carbon dioxide can hinder flow through the column and break the yeast from
the gel or support used for their immobilization
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© 1995 H. Bungay