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The purpose of this study is to provide insights on the function of noble metals, namely Pt-Pd catalytic system, on the hydrodesulfurization (HDS) of alkyl-substituted dibenzothiophenes (a-DBTs) by means of kinetic modeling and contribution analyses. A series of Pt-Pd systems (1% wt. nominal loading) supported on γ-Al 2 O 3 (0-100, 20-80, 50-50, 80-20 and 100-0; %mol Pt-%mol Pd) are synthesized and evaluated during the HDS of 4,6dimethyldibenzothiophene (4,6-DMDBT) at operating conditions relevant for industry: 320°C, 500 ppm of S and an H 2 pressure of 5.5 MPa. A summary of their characterization is presented as reference herein. Kinetic model based on a Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism and contribution analysis based on predicted reaction rates give rise to the following findings: the bimetallic catalyst 8Pt-2Pd/γ-Al 2 O 3 (80-20; %mol Pt-%mol Pd) leads to the highest activity; in all Pt-Pd/γ-Al 2 O 3 systems, Pt favors desulfurization reactions, i.e., 4,6-DMDBT to 3,3′-dimethylphenyl (3,3′-DMBP) and 4,6-dimethyltetrahydrodibenzothiophene (4,6-DM-th-DBT) to MCHT, whereas Pd favors hydrogenation of 4,6-DMDBT to 4,6-DM-th-DBT; and 4,6-DMDBT and methylcyclohexyltoluene (MCHT) are the hydrocarbons with the lowest and highest affinity to be adsorbed on the active sites from the studied Pt-Pd/γ-Al 2 O 3 systems, respectively.

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The hydrodesulfurization (HDS) of dibenzothiophene (DBT) is investigated over a commercial NiMoP/γ-Al2O3 catalyst in a micro trickled bed reactor (Micro-TBR) at operating conditions of a reactive distillation (RD) column. An analysis with and without reaction is carried out to have a first understanding on the complex interaction between kinetics and transport phenomena. A set of well-accepted criteria is evaluated to elucidate the presence of heat and mass transport limitations. Residence time distribution (RTD) experiments are performed to evaluate axial dispersion through the estimation of axial dispersion coefficient (Daxial,L) from a convection-dispersion model. Experiments with reaction are carried out using hydrogen and DBT as feedstock at reaction temperatures from 533 to 599 K, pressures from 1.5 to 2.5 MPa and inlet molar flow of DBT from 4 to 12×10–8 mol.s–1. A pseudo heterogeneous model accounting for mass transport limitations is used to describe experiments under reaction conditions. The main findings can be summarized as follows: most of RD operating conditions lead to the presence of interfacial mass transport limitations at both interfaces L-S and G-L; convection-dispersion model is able to describe satisfactorily RTD observations, suggesting that axial dispersion phenomena are negligible; conversion of DBT ranges from ca. 22 to 90% having a selectivity to by-product molecules from 30 to 80%, respectively; and the pseudo heterogeneous reaction model describes observations adequately obtaining activation energies ranging from 49 to 62 kJ mol–1 at pressures from 1.5 to 2.5 MPa, respectively. Estimated activation energies are comparatively lower than the activation energies reported in literature for the conventional HDS process, i.e. 40–160 kJ.mol–1, thereby suggesting an apparent catalytic energy savings by using RD technology.