Comparative study of cellulosic sugars production from sugarcane bagasse after dilute nitric acid, dilute sodium hydroxide and sequential nitric acid-sodium hydroxide pretreatment

Abstract

The bioconversion of lignocellulosic biomass to second generation (2G) sugars is crucial for the production of biofuels and commodity chemicals. However, due to its recalcitrant nature, pretreatment is an essential step to increase the accessibility of cellulolytic enzymes to hemicellulose and cellulose to obtain 2G sugars. In this study, sugarcane bagasse (SCB) was pretreated by dilute nitric acid (1% w/v), dilute sodium hydroxide (1% w/v) and sequential nitric acid-sodium hydroxide. The pretreated material was then enzymatically hydrolysed (5 and 10% total solids; TS) by cellulase (Cellic Ctec 2, Novozyme, Curitiba, Brazil). Sequential acid–base pretreated bagasse (cellulosic pulp) led the removal of lignin (70.63%) and hemicellulose (100%) and retained 92.33% cellulose. Enzymatic hydrolysis of sequential acid–base pretreated bagasse (5% TS) showed hydrolysis yield of 75.68% (glucose released), followed by sodium hydroxide pretreated with glucose (68.76%) and xylose (73.26%) and nitric acid pretreated with glucose (31.49%) and xylose (31.49%), respectively. Enzymatic hydrolysis of sequential acid–base pretreated (10% TS) showed hydrolysis yield of 66.20% (glucose), followed by glucose (63.02%) and xylose (60.14%) from sodium hydroxide pretreatment and finally glucose (28.71%) and xylose (23.56%) from dilute nitric acid pretreatment. Therefore, the cellulosic material showed high hydrolysis efficiency after enzymatic saccharification, proving that sequential removal of hemicellulose and lignin from the biomass enables high accessibility of cellulases to the substrate, eventually yielding high amount of 2G sugars.