Evaluation of Diluted and Undiluted Trickle-Bed Hydrotreating Reactor with Different Catalyst Volume

In this work, a comparative study on the combined effects of hydrodynamics and kinetics on the hydrodesulfurization (HDS) of a straight-run gas oil (SRGO) using a trickle-bed reactor with and without diluent (SiC) and different catalyst volume (0.1, 0.07, and 0.050 × 10^-3 m³, respectively) was carried out. The tests were conducted in a pilot plant under conditions close to those used in industrial-scale units (5492 kPa, 445.4 m³(STP)/m³ H₂/oil ratio, 623-643K, 0.9 and 2.5 h^-1 LHSV values). The catalyst used was a commercial CoMoP/Al₂O₃ formulation shaped as tri-lobed extrudates (1/20 in, nominal size) or as crushed particles (d_p = 1.2 × 10^-3 m). Contrarily to that usually claimed, the undiluted systems showed better performance than those comprising small diluent (SiC) particles (d_p ~ 5 × 10^-5 m). Calculations to evaluate hydrodynamic variables (plug-flow behavior, wall effects, wetting, and back-mixing) were carried out in order to explain the observed facts. The possible influences of the size of the diluent particles used are discussed.