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

Abstract

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 1H 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.

Recent Advances in Heavy Oil Upgrading Using Dispersed Catalysts

“…Different compounds are used to obtain oil-soluble precursors that have the ability to disperse in the hydrocarbon environment such as metal salts of organic amines, organic acids (acetic, naphthenic, octoic, oxalic, etc. ), metal-containing quaternary ammonium compounds, etc. , The oil-soluble dispersed catalyst has a unique trait that is its capability to disperse well in the heavy oil with a greater surface-area-to-volume ratio. The metal sulfide, which is the active species for the reaction, is formed in situ from the oil-soluble precursors during the reaction.…”

“…The active sites would be formed in situ by the destruction of the organometallic complex upon reaching the desired reaction conditions. The first attempt to utilize metallocalixarenes as oil-soluble dispersed catalyst precursors for heavy-oil upgrading was made by evaluating the catalytic performance of cobalt- and nickel-based p-tert -butylcalix­[4]­arenes (TBC[4]­s) for the hydrocracking of heavy vacuum gas oil (HVGO) . The catalyst precursors were successfully synthesized and characterized by different characterization techniques.…”

“…Proposed in situ sulfidation mechanism of dispersed catalyst derived from the metal-based calixarene precursor. [Reprinted with permission from ref . Copyright 2019, American Chemical Society, Washington, DC.…”

“…), metal-containing quaternary ammonium compounds, etc. 9,57 The oil-soluble dispersed catalyst has a unique trait that is its capability to disperse well in the heavy oil with a greater surface-area-tovolume ratio. The metal sulfide, which is the active species for the reaction, is formed in situ from the oil-soluble precursors during the reaction.…”

“…The first attempt to utilize metallocalixarenes as oil-soluble dispersed catalyst precursors for heavy-oil upgrading was made by evaluating the catalytic performance of cobalt-and nickel-based p-tert-butylcalix [4]arenes (TBC [4]s) for the hydrocracking of heavy vacuum gas oil (HVGO). 57 The catalyst precursors were successfully synthesized and characterized by different characterization techniques. Figure 18 shows a possible mechanism of thermal decomposition, followed by in situ sulfidation of Ni-and Cobased TBC [4]s catalyst precursors.…”