Novel (Co-,Ni)- p- tert-Butylcalix[4]arenes as Dispersed Catalysts for Heavy Oil Upgrading: Synthesis, Characterization, and Performance Evaluation

This study investigates the promotional effects of a potentially new class of oil-soluble dispersed catalyst precursors for upgrading of vacuum gas oil (VGO), that is metal-based p-tert-butylcalix[4]arenes (TBC[4]s). Co- and Ni-TBC[4] were synthesized, and the metal-ligand complexation was confirmed by scanning electron microscopy-energy dispersive X-ray, inductively coupled plasma, X-ray diffraction, UV-vis, Fourier transform infrared, and ¹ H NMR. The thermogravimetric and calorimetric behaviors of the synthesized complexes, which are key properties of dispersed hydrocracking catalysts, were also studied. The differential scanning calorimetry profile of Ni-TBC[4] and Co-TBC[4] showed that the organometallic structure has lower thermal stability compared with that of the parent TBC[4]. This apparent drawback can be positively exploited by employing TBC[4] as a carrier of the metal, where the active sites are formed in situ by the destruction of the organometallic complex on reaching the desired reaction conditions. The catalytic performance of the synthesized precursors was evaluated using a batch autoclave reactor with varying concentrations of catalyst precursors at 420-450 °C. The results show that the synthesized metal-based TBC[4] dispersed catalysts evidently enhanced the hydrogenation activity and reduced coke formation. The addition of 500 ppm Co and Ni as standalone dispersed catalysts produced distillate yields of 45.7 and 49.7 wt % and a coke laydown of 2.6 and 2.3 wt %, respectively. Increasing the concentration of catalyst precursors enhanced the conversion of VGO from 86.17% at 100 ppm Ni to 88.28% at 500 ppm Ni. Moreover, as the metal concentration increased from 100 to 500 ppm, the distillate yield increased from 36.87 to 49.66 wt %, while the yield of gases decreased from 20.48 to 17.12 wt % because the hydrogenation reactions were enhanced. In contrast, the yields of distillate and naphtha decreased by 14.12 and 15.36%, respectively, as the temperature increased from 420 to 450 °C.