Effects of stepwise nitrogen-enriched pyrolysis strategies on nitrogenous compounds enrichment in cellulose pyrolysis bio-oils and nitrogen migration pathways

Nitrogen-enriched pyrolysis strategies can effectively convert biomass into nitrogenous chemicals. However, the bio-oil fractions obtained from conventional one-step pyrolysis (OSP) are still complex, limiting their further upgrading and refining. Therefore, a stepwise nitrogen-enriched pyrolysis strategy was proposed in this study. The aim was to investigate the role of the stepwise process in regulating the enrichment of bio-oil fractions and the evolution of nitrogen forms in biochar obtained from nitrogen-rich pyrolysis of cellulose. The results indicated that selecting lower pyrolysis temperatures (T1 = 250 °C, 300 °C) in the first step (S1) of the stepwise nitrogen-enriched pyrolysis could effectively convert the furans and carbonyls such as esters derived from the cellulose into nitrogenous compounds. Thereby, the relative enrichment of nitrogen-containing compounds was achieved. Of these, O300–S1 was enriched with 84.13% nitrogenous compounds (mainly pyrroles and pyrazines). Elemental and XPS analyses revealed that stepwise pyrolysis was more favorable for N enrichment in biochar, and that stepwise pyrolysis at 300 °C was favorable for nitrogen atoms to dope in the carbon lattice. Finally, the possible migration pathways of NH 3 –N during pyrolysis were proposed. This study presents new insights into the high-value utilization of nitrogenous compounds obtained from lignocellulosic biomass.