Mechanism Study on Nitrogen Migration and Catalytic Denitrification during the Pyrolysis of Lysine and Tryptophan

Catalytic fast pyrolysis can effectively solve the pollution and treatment problems of sewage sludge to realize the green recycling of biomass waste energy. The study on the mechanism of nitrogen migration is a crucial part of the conversion of sewage sludge. Herein, two amino acids of lysine with linear amines and tryptophan with aromatic nitrogen-containing heterocycles were used as typical model compounds to investigate the pyrolysis mechanism and nitrogen migration behavior. The results revealed that lysine mainly underwent two routes: one was to cyclize itself to lactam and cleavage twice with the gradual dehydrogenation to form stable nitrogen-containing heterocycles; the second was first decarboxylation and then cleavage with gradual dehydrogenation to form nitriles. The first route was easier to proceed at low temperatures, while the second route took up more proportions at high temperatures. Tryptophan was converted gradually to stable indoles after decarboxylation, deamination, dehydrogenation, and denitrification. Based on the full understanding of the nitrogen migration mechanism of lysine and tryptophan, the catalytic denitrification mechanism over dolomite, limonite, and HZSM-5 modified with Ni loading catalysts was also explored.