FERMENTATIVE ETHANOL PRODUCTION (ALCOHOL, DISTILLATION, ECONOMICS)

Conventional and experimental methods for fermentative ethanol production and recovery are comprehensively reviewed and evaluated. Eleven different fermentation processes are compared on identical economic bases and using a consistent model for yeast fermentation. Feed preparation, fermentation, alcohol recovery and stillage treatment steps are included. The alcohol recovery is by an efficient vacuum distillation method which is also evaluated in detail.;Fermentation processes in which ethanol is selectively removed from the fermentor as it is produced (as by vacuum flashing, membrane dialysis or solvent extraction) offer potential further savings. End product inhibition is alleviated and concentrated sugar solutions can be rapidly fermented with very high volumetric productivity (up to 70 g/L-hr as compared to 14 g/L-hr in simple continuous fermentation). Excluding the cost of the selective ethanol separation step, a potential cost savings of up to 5 cents/L can be achieved as compared to continuous fermentation with recycle.;Detailed designs are presented for alternative selective ethanol removal schemes based on flashing alcohol from the fermenting broth under vacuum. The cost of vacuum equipment is high, but the best of the vacuum type methods (the frigferm process) is calculated to produce alcohol at 48 cents/L--a marginal savings.;With ethanol inhibition removed, inhibition by secondary products and nonmetabolized feed components becomes limiting. The inhibitory effects of eight by-products and nine feed components are reported. Mechanisms are proposed to explain the toxic effects observed.;With molasses feed at ;Recommendations are made for further research to overcome the limitations of by-product and metabolite inhibition, and to further improve ethanol fermentation and recovery processes.;An addendum is included summarizing models for the vapor-liquid equilibrium and other important properties of ethanol, water and fermentation broth.