Slurry-phase hydrocracking of heavy oil over Mo precursors: Effect of triphenylphosphine ligands

Abstract A practical approach to enhancing the performance of dispersed catalysts during slurry-phase hydrocracking is the modification of the ligand structure of the catalyst precursor. An oil-soluble Mo precursor with triphenylphosphine ligands (Mo-TPP) was prepared and further applied to the slurry-phase hydrocracking of vacuum residue (VR). For comparison, a commercial precursor termed Mo-octoate was also used. In a dispersibility test, Mo-TPP was completely dissolved at 200 °C and then finely dispersed in the VR. Thermogravimetric analysis revealed that Mo-TPP decomposed rapidly in the range 220–270 °C to produce zerovalent Mo. During the decomposition process, direct conversion of Mo-TPP to MoS2 was favored via reaction with H2S gas generated from the VR at 250 °C. The sulfidation behavior of Mo-TPP reduced the average size and stacking number of the resulting unsupported MoS2 catalyst, which led to greater exposure of the rim sites (Morim) on the catalyst surface than when Mo-octoate was used. The Mo-TPP precursor resulted in better catalytic performance than the Mo-octoate precursor in a semibatch reactor at 410 °C and under 110 bar H2. In particular, the use of Mo-TPP enhanced the radical scavenging and hydrodesulfurization activities, owing to excellent hydrogenation ability originating from the initial number of Morim sites. The phosphate compound, derived from the TPP ligands, promoted the conversion of asphaltenes via demetallization of the intrinsic V species in the VR. These results demonstrated that Mo-TPP is an efficient precursor for achieving coke suppression that also improves product quality.