ETHANOL, THE ULTIMATE FEEDSTOCK - A TECHNOECONOMIC EVALUATION OF ETHANOL MANUFACTURE IN FLUIDIZED-BED BIOREACTORS OPERATING WITH IMMOBILIZED CELLS

Ethanol appears to be a key factor in the "biomass alternative" to fossil feedstocks for producing fuels and chemicals. If produced at a low enough price relative to crude oil, it and its derivates could account for 159 billion pounds, or 50%, of the US production of synthetic organic chemicals, presently valued at $113 billion. This use would consume 4.2 billion bushels, or about 54%, of the corn crop. This study evaluated the potential savings in ethanol manufacture to be gained by applying advanced process engineering or genetic engineering of improved organisms, centering on the use of fluidized bed bioreactors operating at high cell densities with immobilized cells of either the Saccharomyces yeast or the bacterium: Zymomonas mobilis. A new continuous plant could produce at about $1.82/gal based on Zymomonas or $1.97/gal based on the Saccharomyces yeast. The bacterium has a competitive edge as a result of its lower sensitivity to product inhibition. There appears to be no inherent design limitation to effect the engineering improvements required for the advanced process. In a longer-term, more difficult research effort, it might be possible to reduce or, eliminate product inhibition to reduce cost even further.