A closed-loop polygeneration strategy via K2CO3-driven staged thermal conversion of rice husk

A staged K 2 CO 3 -mediated polygeneration process for rice husk was developed. • Catalytic torrefaction achieved deoxygenation and in-situ acid fixation. • Fractional condensation yielded monocyclic phenols with 85.53% relative purity. • In-situ K 2 Si 4 O 9 templating created 3D honeycomb porous carbon structure. • A closed-loop strategy achieved over 74% potassium recovery rate. To address high bio-oil acidity, complex compositions, and catalyst recovery difficulties during high-ash biomass pyrolysis, this study proposes a K 2 CO 3 -mediated staged catalytic thermal conversion process for rice husk. The regulatory mechanism on multiphase products and potassium migration fate was systematically investigated. During catalytic torrefaction (240–270 °C), K 2 CO 3 induced significant biomass pre-deoxygenation, releasing abundant oxygen as CO and CO 2 . This stage achieved targeted extraction of primary phenolic compounds (56.34%, predominantly guaiacol and its derivatives) while converting organic acids into solid potassium salts. This pretreatment effectively stripped acidic precursors, blocking secondary tar condensation during the main pyrolysis (550 °C) and yielding a highly deacidified bio-oil. Coupled with fractional condensation, monocyclic phenol purity in the 60 °C fraction reached 85.53% (versus 23.96% in direct pyrolysis), while the methane content in the syngas increased to 60.9%. The migration fate and occurrence forms of potassium were systematically tracked, revealing that over 74% of potassium remained in a water-soluble state post-pyrolysis. Regarding solid-phase evolution, active potassium etched the silica skeleton at elevated temperatures to form a K 2 Si 4 O 9 template. Its subsequent removal via mild water washing created a 3D honeycomb porous biochar, concurrently achieving a > 74% water-soluble potassium recovery rate. Based on these findings, a comprehensive strategy integrating heat integration potential, soluble silicate valorization, and catalyst recycling is proposed. Download: Download high-res image (335KB) Download: Download full-size image