Biorefinery process for the simultaneous recovery of lignin, hemicelluloses, cellulose nanocrystals and silica from rice husk and Arundo donax

An integrated biorefinery process based on acidic leaching, alkaline treatment and concentrated sulfuric acid hydrolysis was set up for the simultaneous recovery of lignin, hemicelluloses, silica, and cellulose nanocrystals (CNCs) from Arundo donax and rice husk. These fractions can serve as viable source of bio-chemicals with potential high-value applications. A chromatographic and spectroscopic characterization demonstrated that a combined acidic-alkaline treatment enhanced the degradation of lignin-carbohydrates complexes releasing lignin and hemicelluloses in higher yield and purity than the sole alkaline treatment. The remaining cellulose rich solid was bleached through a totally chlorine free process, and then hydrolyzed for cellulose nanocrystals isolation. A. donax cellulose nanocrystals were extracted and characterized for the first time in literature. Moreover, from rice husk, pure amorphous silica was obtained almost in 90% yield and 99% purity, avoiding incineration. In term of mass balance, it was possible to refine the investigated biomasses for the production of lignin, hemicelluloses, silica and CNCs in almost 40% overall yield.