Ammonia (NH3)/nitrogen (N2) torrefaction pretreatment of waste biomass for the production of renewable nitrogen-containing chemicals via catalytic ammonization pyrolysis: Evolution of fuel-N under a N2/NH3-rich atmosphere

To investigate the nitrogen migration and transformation mechanisms that produce high value-added N-containing chemicals, the NH 3 /N 2 torrefaction pretreatments of waste biomass for the production of renewable N-containing compounds were explored, and the effects of torrefaction temperature (200, 225, 250, 275, 300 °C) on fuel properties, structure, crystallinity, surface functional groups and thermal kinetics were evaluated by element analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier infrared spectroscopy (FTIR) and thermogravimetric analysis (TG-DTG). The effects of subsequent catalytic ammonization pyrolysis upgrading of the torrefied biomass with Co/HZSM-5/HZSM-5 catalysts under an NH 3 /N 2 atmosphere on product yield and N-containing compound selectivity were also evaluated with GC/MS and UV-fluorescence spectrometry. Furthermore, nitrogen fixation and migration mechanisms were also proposed in depth. The results showed that NH 3 torrefaction was more effective in enhancing N fixation and retarding the release of N-containing volatiles in torrefied biochar (0.26%–9.43%) and reducing the oxygen content (43.18%–21.81%) via Maillard reactions compared with N 2 torrefaction. With increasing torrefaction severity, the N-containing compound content, higher heating values (HHV), deoxygenation ratio (DEO) and nitrogen-doping ratio (NDR) increased, which were much higher than those of conventional N 2 torrefaction. Higher temperatures promoted the evolution of graphitic-N and oxidized-N and reduced pyrrolic-N and pyridinic-N group formation in torrefied biochar. The maximum content of N-containing compounds of 88.71% was obtained at a torrefaction temperature of 275 °C under NH 3 pyrolysis coupled with the Co/HZSM-5 catalyst, and was achieved via substrate interaction with the -Co-O-Si- catalyst sites and Maillard reactions. Furthermore, the N 2 atmosphere combined with the HZSM-5 catalyst significantly promoted the conversion of HC compounds (∼56.97% at 225 °C during N 2 torrefaction), while the Co/HZSM-5 catalyst combined with the NH 3 atmosphere significantly improved N-containing compound formation. NH 3 pyrolysis facilitated the formation of pyrroles and pyrazines while reducing the formation of amides by deamination and dehydrogenation reactions. Cellulose was conducive to the transformation of pyrrole in NH 3 pyrolysis, while lignin was conducive to the formation of aniline. These results could offer strategies to regulate nitrogen functional groups to enhance N-containing chemicals. • A novel N-containing chemicals production method was developed with NH 3 torrefaction and pyrolysis. • Nitrogen fixation and migration mechanism in solid-gas-liquid phase was proposed. • Higher torrefaction temperature promoted the formation of N-containing compounds under NH 3 atmosphere. • The maximum yield of N-containing chemicals in bio-oil was 88.71%. • NH 3 pyrolysis coupling with Co/HZSM-5was facilitating to production of pyrroles and pyrazines.