Economic evaluation of preconcentration in production of ethanol from dilute sugar solutions

The economic feasibility of preconcentrating dilute sugar solutions prior to fermentation is investigated. Two methods, evaporation and reverse osmosis, are compared. A computer program to determine the optimal preconcentration conditions for glucose solutions of 1.5-16 wt% has been developed. It was used to compute the fractional cost for labor and maintenance, preconcentration, fermentation, and distillation. Preconcentration with evaporation resulted in a higher total cost, compared with no preconcentration, for all cases studied, although a six-effect unit was used. Reverse osmosis was found to be economically feasible for preconcentration to about 5-10 wt % depending on the concentration of the feed.