Impact of pretreatment with photocatalysis sequential coupling Fenton oxidation on physicochemical properties, pyrolysis behaviors, and product distribution of walnut shell

Naturally occurring alkali and alkaline earth metals (AAEMs) in biomass can adversely affect its pyrolysis behavior and product distribution and contribute to ash deposition in boilers. To address these challenges, we proposed a new idea of photocatalysis sequential coupling Fenton oxidation for biomass pretreatment. Our findings revealed that sequential pretreatment has the optimal moderating effects on biomass relative to individual photocatalysis and Fenton oxidation. The lignin and AAEMs in biomass were effectively reduced via sequential pretreatment, which was accompanied by cellulose content increased by 80.78% relative to untreated. Also, the slagging/fouling inclinations of biomass were successfully alleviated, and the pyrolysis performance was effectively improved. The kinetic parameters obtained based on the Coats-Redfern method can characterize the pyrolysis behavior well. During fast pyrolysis, sequential pretreatment caused the productivity of bio-oil was increased by 30.14% relative to untreated. In particular, the productivity of levoglucosan in bio-oil was increased by 364.71%. This study presented a novel and effective pretreatment strategy to improve the pyrolysis behavior and product distribution of biomass and alleviate ash deposition problems in boilers.