Lignocellulosic biomass consists mainly of lignin and the polysaccharides cellulose and hemicellulose. Compared with the production of ethanol from G1 feedstocks, the use of lignocellulosic biomass is more complicated because the polysaccharides are more stable and the pentose sugars are not readily fermentable by Saccharomyces cerevisiae. In order to convert lignocellulose to biofuels the polysaccharides must first be hydrolyzed, or broken down into simple sugars using either acid or enzymes.

Production process of lignocellulosic biomass to ethanol mainly consists of four steps: pretreatment, saccharification of cellulose to simple sugars, fermentation of simple sugars to ethanol, and product separation/purification to fuel grade ethanol. Schematic flow sheet for the production process of bioethanol from lignocelullosic biomass is shown in Fig. 20.1.