Kinetics of dibenzothiophene hydrodesulfurization reactions using CoMoP/Al2O3 and NiMoP/Al2O3

Over the last decades, the regulatory agencies, aiming to limit vehicle emissions, established more stringent fuel specifications, including ultra-low sulfur contents in diesel and gasoline. In such way, hydrodesulfurization (HDS) is a key process in the oil refining scheme for producing low sulfur fuels. The evaluation of the HDS reaction kinetics of refractory compounds, as dibenzothiophene (DBT), is an important tool in the search for improving the activity of usual industrial catalysts. In this context, the main objective of this work was the estimation of kinetic parameters of DBT HDS reactions using CoMoP/Al2O3 and NiMoP/Al2O3 catalysts at operational conditions which provide a wide range of DBT conversions. The estimation results were evaluated using statistical tests as t-Student and chi-square. Good fits to the evaluated experimental data were provided by two power-law models with different levels of detail: one considering the global DBT conversion only and the other considering a reactional scheme with two parallel routes (direct desulfurization to biphenyl and hydrogenation to cyclohexylbenzene). The apparent activation energies found were of the order of 90 to 100 kJ mo1(-1). Regarding the biphenyl hydrogenation to cyclohexylbenzene, the parameter estimation was hindered because this reaction is expected to be significant at conditions with high DBT conversions only.