Characteristics and formation of nitrogen-containing products from the pyrolysis of maple wood and maize straw

Abstract

Biomass is widely used in residential and industrial sectors as a renewable and carbon-neutral energy source, however, NOx emissions caused by the heat treatment of biomass are of concern. The nitrogen element in biomass plays an important role in N-containing products generated from pyrolysis, while the migration behaviors of fuel-N are still unknown. Slow pyrolysis experiments of maple wood and maize straw were conducted at 350–650 °C in this study. The TG, XPS and GC/MS technologies were performed to investigate the nitrogen migration pathways during prolysis. Results demonstrated that the fuel-N in the two species mainly exists as protein-N, amide-N and inorganic-N functional groups. Char-N occupied the most of total fuel-N from 350 °C to 450 °C, while the yields of tar-N and NOx precursors-N (NH3-N and HCN-N) increased gradually with the rising temperatures. NH3 was found to be the main NOx precursor for the both species, accounting for 15.01–20.19 wt% and 3.18–5.91 wt% of fuel-N in maple wood and maize straw, respectively. More than 85% of NH3-N was produced between 350 °C and 450 °C, attributing to the conversion of fuel-N and tar-N in the devolatilization stage. Differently, around 50% of HCN-N yields were produced by the secondary decomposition of tar-N and char-N at higher temperatures (≥550 °C). Particularly, char-N showed a greater thermal stability in maize straw, while a much higher conversion ratio of NOx precursors-N was observed from maple wood pyrolysis than that of maize straw. These results could provide some guidances on the control of NOx emissions from biomass energy utilization.