Submitted to: Biotechnology and Bioengineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 1, 1995
Publication Date: N/A
Full Text Available
Interpretive Summary: With the fuel ethanol industry now easily exceeding one billion dollars in annual sales, there is renewed incentive to improve the ethanol production process. Current processes require large, expensive fermentors because yeast, the microorganisms used for this technology, are only productive when the ethanol produced in the fermentation brew remains at low concentration. Low ethanol yield also requires the use of large, energy consuming distillation equipment to recover the biofuel. One alternative is to strip ethanol from the fermenting brew as it is produced, by recycling the fermentor contents through a stripping column. The stripping column is structured so that the ethanol can evaporate into warm carbon dioxide gas which passes through the column and then to a cooling unit where the ethanol is liquefied and recovered. The cold carbon dioxide gas is reheated and returned to the column. One potential problem with this process is the clogging of the column with yeast cells that grow on its interior surfaces. This paper describes this phenomenon and a method to overcome it. Successful application of this process in industry might reduce the cost of producing ethanol and potentially provide significant economic benefits not only to ethanol producers, but to corn growers, biofuel consumers and taxpayers.
By recycling the contents of a 14-L fermentor through a stripping column to continuously remove ethanol and reduce product inhibition, continuous complete conversion of nutrient feed containing 600 g/L glucose was achieved in a small pilot plant. Ethanol was recovered from the carbon dioxide stripping gas in a refrigerated condenser and the gas was reheated with steam and recycled by a blower. Fouling of the column packing by attached growth of the yeast limited operation. Weekly washing of the column packing in situ was required to prevent fouling and loss of performance. Productivity of ethanol in the fermentor as high as 15.8 g/L/hr and condensate production of up to 10 L/day of almost 50% ethanol (by volume) were maintained for up to 60 days of continuous operation.