Comparative assessment of water and organic acid washing pretreatment for nitrogen-rich pyrolysis: Characteristics and distribution of bio-oil and biochar

Nitrogen-containing compounds are important organic compounds that can be produced in large quantities by the nitrogen-rich pyrolysis of biomass. The aim of this study was to investigate the effect of washing pretreatment on the yield and selectivity of nitrogen-containing compounds during corn cob nitrogen-rich pyrolysis in a fixed-bed reactor. Water and organic acids were used for washes. Urea was used as the exogenous nitrogen source in nitrogen-rich pyrolysis at 500 °C. After washing pretreatment, bio-oil derived from nitrogen-rich pyrolysis had the highest yield (44.9%) and lowest water content (26.3%) and acidity. The resulting bio-oil contained a few types of compounds. Water washing improved the selectivity of pyrrole, pyridine, imidazole, and nitrile. Organic acid washing promoted the production of pyridone and imidazolinone in nitrogenous heterocyclic compounds, especially 2(1H)-pyridinone, the content of which reached 7.48%. Biochar derived from nitrogen-rich pyrolysis contained abundant nitrogenous functional groups, and the stability of biochar was optimal after washing pretreatment. Therefore, washing pretreatment could enhance the production of high-value nitrogen-containing chemicals during nitrogen-rich pyrolysis.