Nitrogen products and reaction pathway of nitrogen compounds during the pyrolysis of various organic wastes

•The nitrogen products from pyrolysis were investigated at 500 °C for 3 organic wastes.•Identification of more than 80 nitrogen products similar for two different wastes.•Light nitriles majority in the gases whereas diversity and heavy in condensables.•14 and 72 N-products respectively identified in gaseous and condensed fractions.•Proposal of a reaction pathway from proteins of organic wastes until N-products.

The nitrogen compounds in tars were investigated at temperature of 500 °C during the pyrolysis of three organic wastes (sewage sludge, food waste, wood) and their mixture, representatives of a common municipal waste. The analyses of both gaseous and condensed tars related the formation of up to respectively 14 and 72 nitrogen compounds, with widely forms of compounds. In gases, light nitriles (acetonitrile, propanenitrile) seemed to be the main products whereas, in condensed tars, several chemical families were represented: long chain nitriles and amides, pyrrolic and pyrrolidinic compounds and diketopiperazines (DKPs). Moreover, several compounds, rarely previously detected, were observed, such as oximes. All those nitrogen compounds probably originated from proteins but also from fatty acids and sugars. The nature of those compounds was found to be only slightly influenced when wastes have similar nitrogen functionalities contents, such as food waste and sewage sludge. That would suggest that reaction pathways for nitrogen compounds are similar for such wastes. For wood, its low nitrogen content hindered the detection of nitrogen products, which could be also due to a different reaction pathway for nitrogen. The mixture of those wastes had only slightly effects on nitrogen products and thus on the reaction pathway. Using nitrogen products, this paper was concluded with a possible reaction pathway for the nitrogen of sewage sludge and food waste during pyrolysis.