Efficient co-production of glucose and carboxylated cellulose nanocrystals from cellulose-rich biomass waste residues via low enzymatic pre-hydrolysis and persulfate oxidation

Carboxylated cellulose nanocrystals (cCNCs) can be prepared directly from biomass in a one-step ammonium persulfate (APS) oxidation. However, the cellulose in the biomass is not fully utilized because APS oxidation degrades the cellulose amorphous regions. In this paper, to improve cellulose utilization rate, a two-step method (enzymatic pre-hydrolysis and APS oxidation) was developed to co-produce fermentable sugar and cCNCs from xylooligosaccharides manufacturing waste residue (XOR) of corncob. Enzymatic pre-hydrolysis produced 26.1 g of glucose per 100 g of XOR with a cellulase loading of 5 FPU/g cellulose in 24 h. Subsequent oxidation produced 22.9 g cCNCs with 0.5 MAPS in 8 h. In contrast, the one-step APS method only produced 28.3 g cCNCs per 100 g of XOR. The total cellulose utilization rate by the two-step method increased by 73 % compared to the one-step APS method. Structural characteristics of cCNCs prepared by the two-step method were slightly different from those of the one-step method, but good properties were maintained. Therefore, the co-production method could prepare glucose and cCNCs with stable properties from XOR with a greatly improved cellulose utilization rate.