Microwave-assisted pyrolysis of eucalyptus wood with MoO3 and different nitrogen sources for coproducing nitrogen-rich bio-oil and char

The conversion of biomass into valuable nitrogen-containing compounds (NCCs) to co-produce nitrogen-rich bio-oil and char provides a green and economic-friendly approach. The evolution of NCCs in liquid, char, and gas products during the microwave-assisted pyrolysis (MAP) of eucalyptus wood with different ratios of MoO3 and representative nitrogen sources (food waste digestate, soybean straw, and ammonium chloride) were studied at the temperature of 550 °C. The addition of MoO3 increased the content of NCCs in solid and liquid products, and EW/MoO3 = 2/1 had the highest liquid product yield (41.66 wt%). Based on sample/MoO3 = 2/1, adding 40 % soybean straw had the highest content of NCCs (24.05 %) in bio-oil by promoting the formation of nitrile-N (6.16 %) and heterocyclic-N (12.47 %). Besides, the char contained amine-N/pyridine-N (40.71 %), pyrrole-N (5.35 %), protein-N (35.34 %), and graphitic-N (18.60 %). However, the high ash content of 40% food waste digestate might hinder the decomposition of unstable pyrrole-N and nitro-N in solid/liquid products. The content of NCCs in the gas product of adding 40 % ammonium chloride was low, resulting in the nitrogen of char increasing by 4.05 wt%. Lastly, the possible transfer mechanism of nitrogen in eucalyptus wood with different types of nitrogen sources during pyrolysis was obtained by using the species of NCCs.