Lignocellulosic biomass is generally composed of cellulose. hemicellulose and lignin (Table 5.2.1). Before ethanol fermentation. biomass has to be pre-treated with acid or alkali. and/or with cellulases to be hydrolyzed into sugar solution.

(a) Concentrated Sulfuric Acid Process

The process of Arkenol Co. Ltd. (USA) was modified and improved in NEDO project between 2001 and 2005. Concentrated sulfuric acid is sprayed on to wood chips (moisture of about 15%) which is then kneaded well at room temperature. During the kneading the structure of cellulose is decrystallized. Concentration of sulfuric acid is then adjusted at 20 to 30% by adding water, and the wood material is kept at around 90oC for 10 to 15 min for hydrolysis. After solid fraction is removed through filtration, sugar components are separated from the acid on ion-exchange chromatography. Sugar solution containing hexoses and pentoses are fermented by yeast or Zymomonas strains genetically modified. Sulfuric acid is concentrated again to reuse.