Physical and Chemical Characterizations of Corn Stover from Leading Pretreatment Methods and Effects on Enzymatic Hydrolysis

Lignocellulosic biomass is difficult for hydrolysis due to its recalcitrance on chemical compositions and physical properties. The 3D microstructure of corn stover by X-ray tomography showed the visualized inner pore and fiber structure, indicating closed spaces and density distribution. Dilute sulfuric acid pretreatment on corn stover stems resulted in high lignin content, which led to slow hydrolysis at the beginning stage of enzymatic hydrolysis. The low crystallinity and high porosity of steam explosion pretreated stems exhibited enzymatic hydrolysis faster at the initial stage, while lower final glucan conversion was observed after steam explosion pretreatment due to the lack of lignin removal compared with sulfuric acid pretreatment. The removal of most lignin and increased porosity in the inner biomass by aqueous ammonia pretreatment led to the fastest hydrolysis and highest glucan conversion. Leaves and husks pretreated by sulfuric acid exhibited a higher cellulose digestibility and sugar release rate than the stems due to their lower lignin content. The results suggested that lignin composition played a more important role than porosity and crystallinity during the hydrolysis of lignocellulose.