Hydrolysis of biomass tends to produce dilute sugar solutions that lead to dilute fermentation broth. For
example:
hydrolysis of 5% slurry of biomass ® 2% sugar solution
fermentation of 2% sugar solution ® 1% solution of product
uneconomical to distill very dilute ethanol solution. There must be a concentration step somewhere in process.
Alternatives to ethanol may have less expensive and easier recovery of product.