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