Influence of temperature on nitrogen fate during hydrothermal carbonization of food waste

•The nitrogen distribution and evolution in HTC of food waste were investigated.•Nitrogen species and amount in products depended on temperature.•Amines and N-heterocyclic compounds were identified as main bio-oil-N species.•Increasing temperature enhanced incorporation of nitrogen into aromatic heterocycles.

The influence of temperature (180-260 °C) on the fate of nitrogen during hydrothermal carbonization (HTC) of food waste (FW) was assessed. The distribution and evolution of nitrogen in aqueous products and bio-oil, as well as hydrochar, were conducted. Results suggested that elevated temperature enhanced the deamination and the highest ammonium concentration (929.75 mg/L) was acquired at 260 °C. At temperatures above 220 °C, the total N in the hydrochar became stable, whereas the mass percentage of N increased. Amines and heterocyclic-N compounds from protein cracking and Maillard reactions were identified as the main nitrogen-containing compounds in the bio-oil. As to the hydrochar, increasing temperature resulted in condensed nitrogen-containing aromatic heterocycles (e.g. pyridine-N and quaternary-N). In particular, remarkable Maillard reactions at 180 °C and the highest temperature at 260 °C enhanced nitrogen incorporation (i.e. quaternary-N) into hydrochar.

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