Evolution of heavy components in bio-oil during oxidative pyrolysis of cellulose, hemicellulose, and lignin

Biomass oxidative pyrolysis introduces restricted oxygen into the reaction zone, realizing autothermal pyrolysis to address the heat supply challenges inherent in large-scale applications. However, heavy components (＞200 Da) in bio-oil are critical precursors that lead to coke formation upon heating, which hinders the utilization of bio-oil. In this study, the conventional and oxidative pyrolysis experiments of cellulose, hemicellulose, and lignin in a fix-bed reactor were conducted at temperatures ranging from 300 °C to 800 °C, aiming to investigate the evolution of heavy components in bio-oil during biomass oxidative pyrolysis. The results showed that the addition of oxygen promoted the generation of bio-oil. Compared to conventional pyrolysis, the addition of oxygen mostly increased the yields of cellulose-oil, hemicellulose-oil, and lignin-oil by 28.21 %, 10.94 %, and 16.84 %, respectively. Further comprehensive analysis revealed that oxygen promoted the depolymerization of three components at a lower temperature range (＜ 500 °C). With increasing temperatures, oxygen enhanced the polymerization of volatiles from cellulose and lignin, where oxygen, acting as a binder, promoted the generation of phenolic compounds of heavy components in lignin-oil. Conversely, as the temperature increased, oxygen enhanced the oxidative decomposition of volatiles from hemicellulose, inhibiting the generation of heavy components in hemicellulose-oil. To sum up, this study presented a global evolution route of heavy components in bio-oil during oxidative pyrolysis of three components.