Insight into the ammonia torrefaction and pyrolysis system of cellulose: Unraveling the evolution of chemical structure and nitrogen migration mechanism

This study aimed to investigate the mechanism of nitrogen doping, migration, and conversion during ammonia torrefaction and also explore the evolution law of the chemical structure of cellulose. The results showed that the ammonia torrefaction pretreatment could significantly optimize the distribution of nitrogen and oxygen elements in cellulose. The carbon skeleton first captured the active nitrogenous radicals to form –NHn-N, and pyridine-N and pyrrole-N originated from the conversion of –NHn-N. The existence of CO played a major role in the immobilization of nitrogen. The nitrogen in bio-oil exists mainly in the form of five- and six-membered heterocycles. The correlation analysis showed that the main precursors for the formation of nitrogenous heterocyclic compounds were five-membered O-heterocyclic compounds. Finally, the product distribution characteristics in the torrefaction-pyrolysis systems were summarized, and the nitrogen doping and conversion mechanisms were proposed. This study expanded the boundaries of cellulose pretreatment and the production of high-value chemicals.