This study identifies and quantifies the key parameters in gasoil hydr
odesulfurization at conversion levels above 95% (deep HDS) within the
operating window of once-through trickle-flow units. The HDS reaction
rate is markedly affected by trace amounts of basic organo-nitrogen co
mpounds, viz. ca. 0-30 ppm, in the presence of >10 000 ppm polycyclic
aromatics. We conclude that the dominant role of relatively high conce
ntrations of basic organo-nitrogen compounds in model feeds reported i
n the literature closely resembles the presently identified key role o
f trace amounts in deep HDS of a very complex mixture such as gasoil.
The order with respect to basic organo-nitrogen compounds in the HDS o
f a commercial gasoil is ca. -0.15, The influence of variations in the
concentration of bulky polycyclic aromatics such as naphthalenes, chr
ysenes, and pyrenes is negligible. Furthermore, we employed a model ga
soil to compare the activities of a NiMoP/Al2O3 and a CoMo/Al2O3 catal
yst for the hydrodesulfurization of the refractory substituted dibenzo
thiophene compounds at the relatively low hydrogen-to-hydrogen sulfide
ratio representative for once-through trickle-flow reactory, viz. ca.
15 Nl/Nl. In spite of this low hydrogen-to-hydrogen sulfide ratio, th
e NiMoP catalyst seems to display an unexpected activity advantage ove
r the CoMo catalyst in deep HDS. (C) 1998 Elsevier Science B.V.