Nitrogen-rich pyrolysis to nitrogen-containing compounds in CO2/N2 atmosphere: Nitrogen configuration and transformation path

The product distribution of cellulose pyrolysis at varying nitrogen carrier and temperature was studied in a tube furnace, elucidating the reaction mechanism of cellulose and urea (chitosan) in CO2 pyrolysis. The nitrogen-rich pyrolysis in CO2 atmosphere improves the nitrogen compound content in bio-oil. CO2, serving as a mild oxidizing agent, enhances the production and release of biochar volatiles and the creation of additional pores. This leads to an improved development of porosity across the micropore, mesopore, and macropore ranges. When the mixing ratio of urea is 60% at 550 'C, the highest nitrogen compound content is 45.03%, which is 1.7 times higher than that in N2 atmosphere. When the mass mixture ratio of chitosan is less than 60%, its content reaches its maximum at 500 'C, reaching 13.32%, which is 1.2 times the content under N2 atmosphere. The formation paths of oxygen compounds (aldehydes, ketones and alcohols) and main nitrogen compounds (pyridine, pyrrole, imidazole and pyrazine) in bio-oils under CO2 atmosphere are discussed. The coupling relationship between biochar N functional groups and the generation of bio-oil N heterocyclic substances was proposed.