Nitrogen migration of biomass nitrogen-containing model compound (2,5-Diketopiperazine) during pressurized pyrolysis/gasification: Effect of pressure and atmosphere

Pressurized oxy-biomass combustion is regarded as a promising carbon capture technology of negative CO₂ emissions. However, biomass combustion emits NOx, which might be significantly affected by pressure and atmosphere. In this paper, biomass nitrogen-containing model compound (2,5-Diketopiperazine, DKP) was employed to explore the nitrogen migration in pressurized oxy-biomass combustion. The pressurized pyrolysis/gasification of DKP was carried out on a pressurized fixed bed reactor at various temperatures, atmospheres and pressures. The results show that the dominant nitrogen-containing precursors of NOx are NH₃ and HCN, the formation ratios of which can be affected by temperature, atmosphere, and pressure. As temperature increases, NH₃ formation ratios slightly changes, whereas HCN formation ratios significantly increases. When the temperature increases to above 700 °C, the formation ratio of HCN exceeds that of NH₃. As pressure rises, NH₃ formation ratios increases significantly, while HCN formation ratios decreases at temperatures above 800 °C and slightly increases at temperatures below 800 °C. In CO₂ atmosphere, DKP is gasified to produce more nitrogenous precursors compared with that in N₂ atmosphere, and with pressure increasing, less nitrogenous precursors are produced due to its enhanced reduction by CO under gasification conditions. This study provides a deep insight to the nitrogen migration in pressurized oxy-biomass combustion.