Production of ethanol from dilute glucose solutions - A technical-economic evaluation of various refining alternatives

In order for ethanol to be competitive with gasoline, the production cost of ethanol must be lower than it is today. One economically crucial step in the production of ethanol from lignocellulosics is refining, since hydrolysis yields dilute glucose solutions which, after fermentation, result in a dilute ethanol solution, 2-3 wt-% ethanol. A technical-economic investigation of various energy-saving alternatives to conventional distillation has been performed. The energy-saving techniques investigated were: multi-column distillation, distillation with mechanical vapour recompression, distillation with an absorption heat transformer, phase separation with potassium carbonate and extraction of ethanol from the fermentation broth with Aldol 85. The most economical refining step for the production of ethanol from a dilute glucose solution, around 5 wt-%, was found to be multi-column distillation