Unlocking biofuel potential: Synergistic production of biofuel precursors from acid-loaded corncobs via staged pyrolysis

Abstract

Biomass, a renewable resource, presents inherent challenges for selective conversion into high-value chemicals based on the compositional structure of biomass via conventional pyrolysis. This study introduced an innovative two-stage pyrolysis, combining acid-catalyzed low-temperature pyrolysis with catalytic upgrading over ZSM-5, for the targeted valorization of H₃PO₄-loaded corncobs. This approach notably outperformed conventional non-catalytic/catalytic and two-stage non-catalytic pyrolysis, achieving higher yields of levoglucosenone, furfural, and cumulative target products. Mechanistic analyses revealed that H₃PO₄ loading enhanced selective conversion of cellulose and hemicellulose to levoglucosenone and furfural at reduced temperatures by passivating metals and enhancing dehydration reactions. Notably, the maximum furfural yield remained stable across a broad range of acid loadings, ensuring that fluctuations in the actual H₃PO₄ loading did not significantly impact maximum levoglucosenone yield within practical limits. Furthermore, lignin-rich char residue was effectively converted to light aromatics in the catalytic upgrading stage with high selectivity, albeit at a lower overall yield. Optimal conditions were achieved with 5.5 wt% H₃PO₄ at 325 °C for the first stage, followed by catalytic upgrading at 550 °C, producing a maximum total yield of 62.6 mg/g of target products. Peak yields of levoglucosenone and furfural reached 23.5 and 34.5 mg/g, respectively, while light aromatics reached 4.6 mg/g with over 98 % selectivity. This study underscores the potential of coupling acid-catalyzed pyrolysis with catalytic upgrading to achieve targeted co-production of valuable chemicals, providing new insights into biomass valorization.