Nitrogen
flow and fate critically affects the hydrothermal liquefaction
(HTL) of protein-rich feedstock such as livestock manure and algae.
It also impacts the downstream process of HTL aqueous and oil products.
Here, we reveal the migration and transformation pathways of nitrogen
during HTL of typical livestock manures using combined gas chromatography–mass
spectroscopy (GC-MS) and Fourier transform-ion cyclotron resonance
mass spectrometry (FT-ICR MS) analysis. Over 37% of nitrogen in the
manure migrated to the aqueous phase in all HTL experimental trials,
except for beef manure. GC-MS results indicated that the nitrogen
compounds in the biocrude oil were mainly long chain amides, whereas
in the aqueous phase the compounds were mainly small molecules of
pyrazines, pyrroles, and pyridines. FT-ICR MS identified that N1O1, N2, and N2O1 species were dominant in the biocrude oil, while the nitrogen-containing
compounds in the aqueous phase primarily took the form of N2O2 and N2O3. Five reaction pathways
were proposed for the transformation of nitrogen during HTL. This
study first characterized the transformation of nitrogenous compounds
during HTL of livestock manures, which could be greatly beneficial
to biocrude production, oil quality, and aqueous utilization in future
studies.
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