Hydrodenitrogenation (HDN) is still
a challenging process that
many refineries need to overcome. The influence of catalysts on HDN
efficiency cannot be ignored. In this study, Qilu atmospheric residue
was subjected to a pilot-scale continuous hydrotreater, and liquid
products were obtained from four outlets under two typical catalyst
gradations. Basic nitrogen (BN) and non-basic nitrogen (NBN) compounds
in the feedstock and liquid products were investigated by positive
and negative (±) electrospray ionization (ESI) Fourier transform
ion cyclotron resonance mass spectrometry. It shows that during hydrotreating,
compared to BN, NBN compounds were more refractory. The removal of
multi-heteroatom compounds occurred mainly in BN compounds, and the
conversion of multi-heteroatom compounds and the hydrodearomatization
of N1 class species happened simultaneously in NBN compounds.
By comparing the effects of two typical catalyst gradations on the
products, it was clear that in the removal of N1 class
species, catalyst gradations had subtle differences. The significant
difference in N removal efficiency was reflected in removal and transformation
of N-containing compounds containing multiple heteroatoms in both
BN and NBN compounds during the refining section. This observation
provides a new contribution to understanding the use of different
catalyst gradations in the beds and the effect of each catalyst on
the resulting liquid products.
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