Flash joule heating for enhanced biomass pyrolysis: investigating transient thermal effects on product distribution and reaction networks

Traditional pyrolysis technologies face challenges due to mismatched energy transfer and reaction kinetics. This study uses flash joule heating (FJH) for rapid pyrolysis of six crop straws - corn (CS), wheat (WS), oilseed rape (OS), rice (RS), soybean (SS), and peanut (PS) - at temperatures from 300 to 800 °C and heating rates of 450 to 1000 °C/min. Various techniques, including XPS, FTIR, elemental analysis, and GC/MS, were used to analyze the effects of rapid thermal pulses on three-phase product evolution. At low temperatures (300–400 °C), decarboxylation of hemicellulose formed acids and esters in bio-oil, and CO2-rich biogas. At intermediate temperatures (500-600 °C), cellulose cleavage promoted syngas and bio-oil production, with secondary cracking reducing yields. High temperatures (700-800 °C) led to lignin aromatization, biochar graphitization, and increased H2/CO ratios in gas, while bio-oil aromatized with high levels of aromatic ethers. The study found that material composition and operating parameters significantly affect product distribution. Cellulose-rich straws (CS/OS) produced over 60% gas via high-temperature gasification, while lignin-rich straws (PS) yielded more than 60% biochar at low temperatures. Intermediate temperatures (500-600 °C) optimized bio-oil and biogas production in wheat straw. This research provides a framework for FJH-driven biomass pyrolysis, enhancing the efficient production of biofuels, carbon materials, and bio-oils.