Sulfite Pretreatment Enhances Tobacco Stalk Deconstruction for Cellulose Saccharification and Lignin Pyrolysis

Sulfite-catalyzed acid pretreatment to overcome the inherent recalcitrance of biomass offers a significant advantage in terms of obtaining high glucose conversion. However, the residual lignin after enzymatic hydrolysis has not been fully exploited. Herein, this study introduced a joint approach using sulfite-catalyzed acid pretreatment (SPROL) and pyrolysis to upgrade tobacco stalk to produce fermentable sugar, and the resulting lignin is used to produce bio-oil and bio-char. The results suggest that SPROL pretreated tobacco stalk yields a high cellulose-based glucose selectivity of 75.9% with 15 FPU/g substrate enzyme dosage at 50 °C after 72 h of enzymolysis. Lignin characterization reveals that sulfonation occurred during SPROL pretreatment, and as the dosage of sulfonating agent increased, the thermal stability of the residue lignin decreased. After sample pyrolysis at 600 °C for 30 min, approximately 22%, 33%, and 45% of the lignin undergoes conversion into bio-oil, bio-char, and gas products, respectively. The bio-oil analysis results demonstrated that acetic acid is the most abundant identified GC-MS component at around 69.91% at the optimal condition, which implied that it could be of high value when utilized for pyroligneous acid. This research provides a synthetic approach using the SPORL technique to process tobacco stalk into fermentable sugar, bio-oil, and bio-char, which is significant for the commercial utilization of agricultural waste into value-added products.