Nitrogen migration and transformation in gasification chars prepared from torrefied fiberboard

Abstract

Low-temperature thermal conversions can efficiently modify nitrogen configurations in biomass. This study focused on nitrogen migration and transformation during the torrefaction and subsequent gasification of fiberboard (FB), a common bioresource sourced from waste furniture, flooring, etc., which is characterized by high nitrogen content. The results indicated that as torrefaction temperatures reached 230 °C, the nitrogen loss rates in FB gradually decreased with further increased temperatures. This trend was primarily attributed the significant nitrogen loss due to the decomposition of urea formaldehyde (UF) before 230 °C. When the temperature rose to higher levels, the pyrolysis of lignocellulose caused the generation of active oxygen-containing groups, facilitating nitrogen re-fixation in chars. Moreover, amide-N in the FB was converted into more stable forms, pyrrole (N-5) and pyridine (N-6), thereby reducing the conversion of nitrogen into volatile compounds. During the gasification process, as torrefaction temperatures increased, the contents of quaternary nitrogen (N-Q) and nitrogen oxide (N-O) increased in the gasification chars from torrefied FB, while the contents of N-5 and N-6 decreased. This study analyzed the nitrogen migration pathways in torrefaction vs. torrefaction-gasification, exploring potential transformation mechanisms such as deamination reactions, Maillard reactions, and ring condensation reactions. These findings provide a crucial theoretical foundation for optimizing the treatment of waste FB and understanding the nitrogen migration and transformation during torrefaction-gasification integral process.