This study deals with the promotional effects of dispersed cocatalysts on hydrocracking of vacuum gas oil (VGO). The influence of oil-soluble molybdenum-, iron-, and cobalt-based materials is investigated with and without the presence of a commercial first-stage W–Ni/Al2O3–SiO2 hydrocracking catalyst. The experiments are conducted in a batch autoclave reactor (at 8.5 MPa and 420 °C). The dispersed metal catalysts enhanced the hydrogenation activity and reduced coke formation. Cobalt- and molybdenum-based cocatalysts show lower coke formation than the Fe cocatalyst. An addition of 500 ppm of Co or Mo cocatalyst decreased the amount of coke to 0.9 wt % from 2.5 wt % observed during the thermal cracking. The dispersed catalyst together with the supported catalyst shows similar decrease in coke formation and enhanced the yield of naphtha. A 5-lump kinetic model is developed based on the experimental data using dispersed and supported catalysts. The model incorporates coke formation and conversion of VGO to distillate, naphtha, and C1–C5 hydrocarbons. The VGO hydrocracking to distillate requires least activation energy (1.5 kcal/mol) as compared to the other competing reactions. On the basis of kinetic model results, it is concluded that VGO is most likely cracked to form distillate, followed by cracking of distillate, then distillate is cracked to form naphtha, and finally naphtha is cracked to gases.
A series of CoMo/γ‐Al2O3 catalysts were prepared with an addition of 0.0, 0.5, 1.0, or 1.5 % phosphorus pentaoxide to investigate the influence of phosphorus addition on the simultaneous hydrodesulphurization (HDS) of refractory sulphur compounds. Two sets of HDS experiments were carried out using sulphur bearing model compounds: (i) DBT (dibenzothiophene) with 4‐MDBT (4‐methyl dibenzothiophene) and (ii) DBT (dibenzothiophene) with 4,6‐DMDBT (4,6‐dimethyl dibenzothiophene). The Langmuir‐Hinshelwood mechanism based kinetics model was developed from the experimental conversion and product distribution data for simultaneous HDS of the two sulphur compounds via direct desulphurization (DDS) and hydrogenation (HYD) routes. The kinetic model fits the experimental data quite adequately for all the species. The HDS rate for DBT was found to be approximately 2 and 7 times higher than that estimated for 4‐MDBT and 4,6‐DMDBT, respectively. Enhancement of HDS rate by P addition was observed up to 0.01 g/g (1.0 wt%) P2O5 while a higher amount of P is not advantageous. A marginal preference towards HYD pathway was observed for the HDS of 4,6‐DMDBT while the DDS route was predominant during the HDS of DBT and 4‐MDBT.The trends in values of the rate constants estimated by the Langmuir‐Hinshelwood kinetic model compared well with pseudo‐first rate constants.
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