Effects of lipids on the conversion of nitrogen during protein pyrolysis: A model study

Biomass pyrolysis yields fuels and industrial feedstocks but generates large amounts of NO x precursors and is therefore of limited practical use. Herein, we use glutamic acid, histidine, and tyrosine as protein models and palmitic acid as a lipid model to explore the influence of lipids on the emission of NO x precursors during the pyrolysis of protein-rich biomass at various temperatures. The nitrogen-containing components of solid (coke), liquid (tar), and gaseous pyrolysis products were characterized by X-ray photoelectron spectroscopy, gas chromatography-mass spectrometry, and mass spectrometry, respectively, showing that lipids strongly influence the composition of liquid and gaseous products but not that of solid products. The main nitrogenated tar constituents produced in the absence of palmitic acid were identified as heterocycles and amines, whereas amides and nitriles were additionally generated in its presence. The palmitic acid had the most apparent effect on glutamic acid, generating about 34.16% of amides, followed by histidine, which yielded 9.17% amides and only 4.25% of tyrosine. Thus, our results indicate that the pyrolytic generation of NO x precursors from lipid-rich biomass such as sludge can be reduced by optimizing pyrolysis temperature and providing guidance for developing biomass pyrolysis technologies. • Effects of lipids on the conversion of nitrogen during protein pyrolysis are analyzed • Palmitic acid is used as a lipid model • Glutamic acid, histidine, and tyrosine are used as protein models • Compositions of solid, liquid, and gaseous products (NO x precursors) are probed • Guidelines for the optimization of the pyrolysis of lipid-rich biomass are provided