Ethanol production from enzymatic hydrolyzates of cellulosic fines and hemicellulose-rich liquors derived from aqueous/steam fractionation of forages

This study was aimed at evaluating perennial forages (timothy grass, alfalfa, and reed canary grass) as substrates for ethanol production. Two fractions, derived from the aqueous/steam fractionation of these plants, were used as carbon sources for ethanol production: (i) a solution containing water-soluble hemicelluloses and (ii) cellulosic fines recovered after a delignification step. Both fractions were enzymatically hydrolyzed. The hemicellulose-rich fraction was easily saccharified with 90% of theoretical yield. Cellulosic fines were saccharified at 60-70% of theoretical yield. Increasing the delignification of cellulosic fines by alkaline peroxide treatment resulted in higher sugar yields. The glucose-rich hydrolyzate from cellulosic fines was easily fermented to 80-90% of theoretical ethanol yield with Saccharomyces cerevisiae or Pachysolen tannophilus. The pentose-rich hydrolyzate from water-soluble hemicelluloses was fermented to only 20% of theoretical ethanol yield with Pachysolen tannophilus. A Lime treatment of the hemicellulose-rich liquors improved cell growth but did not improve ethanol production.