Characteristics and mechanisms of nitrogen transformation during chicken manure gasification in supercritical water

Supercritical water gasification (SCWG) is a clean and efficient method for the energy utilization of biomass waste. Studying the behavior of nitrogen in feedstock during the SCWG process is essential because of its sig-nificant potential impact on the environment. In this study, the characteristics and mechanisms of nitrogen transformation during chicken manure gasification in supercritical water were investigated in autoclave reactors. The results revealed that temperature plays an important role in raw material conversion and product distri-bution, especially for nitrogenous components. In particular, the carbon gasification efficiency was 92.66 % at 700 C, 10 wt%, and K2CO3 as catalysts, implying that the chicken manure was nearly completely converted. NOx was not identified in the gaseous products. As the temperature increased, nitrogen in the raw material was mainly transferred to the liquid. This process is accompanied by the conversion of organic nitrogen to inorganic nitrogen, which is mainly present as NH3-N in liquids. Finally, the migration pathways of nitrogenous in-termediates were investigated. The hydrolysis of proteins and amino acids in the initial phases creates conditions for the Maillard reaction, forming nitrogenous heterocyclic compounds (NHCs). Most NHCs gradually ring -opened and eventually converted to CO2, H2, NH3, and other gases. Only a small number of NHCs undergo a series of polymerization reactions at lower temperatures to form nitrogenous carbon precursors that are chal-lenging to gasify. This study provides a theoretical foundation for the targeted removal of nitrogen components during the SCWG of high-nitrogenous biomass.

Automated summary

This study investigates the behavior of nitrogen during chicken manure gasification in supercritical water, and reveals that temperature plays a crucial role in nitrogen transformation and distribution. The carbon gasification efficiency reaches 92.66%, and no NOx is detected in the gaseous products. As temperature increases, nitrogen is mainly transferred to the liquid phase, accompanied by the conversion of organic nitrogen to inorganic nitrogen. The study also uncovers the migration pathways of nitrogenous intermediates, providing a theoretical foundation for targeted removal of nitrogen components during the supercritical water gasification of high-nitrogenous biomass.