Ethylene glycol pretreatment of softwood coupled with fast pyrolysis for sugar production: Solvent recycling and regeneration

Abstract

Organosolv pretreatment of biomass with high-boiling solvents like ethylene glycol (EG) can overcome biomass recalcitrance for improving its fast pyrolysis performance. However, solvent recovery and recycling are challenging, hindering the economic feasibility of this technology. This study proposes a novel process combining sulfuric acid-assisted EG pretreatment of pine with fast pyrolysis, investigating the effects of EG recovery and regeneration on pyrolytic product distribution. The results showed that both initial and recovered EG solution effectively deconstructed pine into hemicellulosic monosaccharides, cellulose-rich fraction, and high-purity organosolv lignin, facilitating subsequent pyrolytic saccharification into levoglucosan. After five pretreatment cycles, the EG recovery rate decreased to 86.4 wt%, and the pretreatment effect declined linearly. However, during the sixth pretreatment, adding sulfuric acid to restore the initial pH kept the EG recovery rate above 85.0 wt% and maintained its initial deconstruction effectiveness, yielding 16.89 wt% hemicellulosic monosaccharides and 44.53 wt% levoglucosan. Pretreatment of pine with recycled and regenerated EG solution facilitates the targeted breakage of cellulose glycosidic bonds to form levoglucosan at lower activation energy (136.66 kJ·mol−1) than the raw feedstock (177.71 kJ·mol−1). This study provides an efficient method for recycling and regenerating high-boiling solvents for the pretreatment of recalcitrant softwood and efficient pyrolytic sugar production.