Alkali pretreatment is a process in which alkaline solutions like NaOH or KOH are used to remove and solubilize lignin component of lignocellulosic biomass and efficiently increase the accessibility of enzyme to the cellulose component. Using alkali to treat lignocellulosic biomass has been known for years to improve cellulose digestibility. For example, lime has been used to pretreat poplar wood (150°C for 6 hours with 14-atm oxygen; Chang et al. 2001), switchgrass (100°C for 2 hours; Chang et al. 1997), wheat straw (85°C for 3 hours; Chang et al. 1998), corn stover (100°C for 13 hours; Karr and Holtzapple 1998, 2000), and sugarcane bagasse (ambient conditions up to 192 hours; Playne 1984). During dilute NaOH pretreatment of lignocellulosic biomass, the mechanisms of reaction are by solvation and saponification (Hendriks and Zeeman 2009). The intermolecular ester bonds cross—inking

xylan hemicellulose, other hemicellulose, and lignin (Figure 3.2a) are saponified. During solvation and saponification reactions, the lignocellulosic material is swollen, leading to an increase in surface area, decrease in crystallinity of material, disruption of lignin structure, and separation of structural linkages between lignin and carbohydrates (Fan et al. 1987; Sun and Cheng 2002) . Alkaline pretreatment of chopped rice straw with 2% NaOH and 20% solid loading at 85°C for 1 hour decreased the lignin by 36% and substantially increased enzymatic cellulose hydrolysis (Zhang and Cai 2008).