STUDY OF HYDRODESULFURIZATION BY THE USE OF S-35 LABELED DIBENZOTHIOPHENE .1. HYDRODESULFURIZATION MECHANISM ON SULFIDED MO/AL2O3

To estimate the behavior of sulfur on a hydrodesulfurization catalyst, S-35-labeled dibenzothiophene ([S-35]DBT) was hydrodesulfurized on a sulfided Mo/Al2O3 in a fixed-bed pressurized flow reactor. After the hydrodesulfurization of [S-32]DBT reached the steady state, the reactant solution of [S-35]DBT was substituted for that of [S-32]DBT at the same concentration of DBT. In this period, the radioactivities of unreacted [S-35]DBT and formed [S-35]H2S was monitored. The radioactivity of unreacted [S-35]DBT reached the steady state immediately, while more time was needed for that of formed [S-35]H2S to reach the steady state. This shows that the sulfur in dibenzothiophene was not directly released:as hydrogen sulfide but initially accommodated on the catalyst. After the-radioactivity of formed [S-35]H2S reached the steady state, the reactant solution of [S-32]DBT was substituted for that of [S-35]DBT at the same concentration of DBT again. The behavior of sulfur on the catalyst was determined from the rates of an increase and decrease of formed [S-35]H2S. It was found that the amount of labile sulfur, which could be calculated from the maximum amount of S-35 accommodated on the catalyst, increased with increasing the reaction temperature and DBT concentration. In addition, it was suggested that the total sulfur on the catalyst sulfided under practical HDS reaction conditions existed as MoS1.92.