Transformation of Nickel Octaethylporphine in Hydrodemetallization Reactions

Abstract

The transformation of nickel (Ni) porphyrins in hydrodemetallization (HDM) was investigated using 2,3,7,8,12,13,17,18-nickel-octaethylporphine (Ni-OEP) as the model compound, which was dissolved in a white oil. The HDM reactions were carried out in a high-pressure trickle-bed reactor over the oxidic and sulfided NiMo/Al2O3 catalyst. The molecular formulas of Ni compounds in the feed and hydrotreated products were characterized by positive-ion electrospray ionization (+ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The hydrotreated products were separated into two subfractions by silica gel chromatography. Molecular structures of Ni-containing intermediates were investigated by ultraviolet–visible (UV–vis) spectrometry, hydrogen nuclear magnetic resonance (1H NMR), and density function theory (DFT) calculations. The major Ni-containing intermediates of Ni-OEP were dihydrogenated (Ni-OEPH2) and tetrahydrogenated (Ni-OEPH4) porphyrins during the hydrotreating. The structure of Ni-OEPH2 was speculated as 1,2-dihydro-Ni-OEPH2, which could be further hydrogenated into Ni-OEPH4. Ni-OEPH4 was first detected in the Ni-OEP hydrotreated products, which should be much more unstable than Ni-OEPH2 and could be easily demetallized. The main pathway of Ni-OEP conversion during the hydrotreating was the hydrodemetallization route, and Ni was removed with the porphyrin ring rapid fragmentation. The results indicate that the catalyst with high hydrogenation and hydrogenolysis activities on hydrocarbons as well as sulfur and nitrogen compounds could have a high activity on the HDM of Ni porphyrins.

Advances and Challenges in the Molecular Characterization of Petroporphyrins

“…Porphyrins were proposed to be converted into hydrogenated species before demetallation; however, direct experimental evidence was not available because the intermediates are not easy to characterize using traditional technologies. Recently, FT-ICR MS was used for the characterization of hydrotreated intermediates of nickel 151 and vanadyl 61 porphyrins with the model compound octaethylporphyrin (OEP). Dihydrogenated and tetrahydrogenated porphyrins were clearly detected in the ESI mass spectra, and their contents were quantified in the products obtained with oxidic and sulfidated NiMo/Al2O3 catalysts, respectively.…”

“…130 One reason for the interest in the metal porphyrins reactivity concerns the demetallization steps achieved through hydrodemetallization or hydrotreating, as reported for nickel porphyrins and vanadyl porphyrins. 149,150 DFT calculations contributed to determining the more likely pathways for the hydrogenation of nickel porphyrins and the detection of the intermediate. 149 The results indicate that best catalysts may display both high hydrogenation and hydrogenolysis activities.…”

“…149,150 DFT calculations contributed to determining the more likely pathways for the hydrogenation of nickel porphyrins and the detection of the intermediate. 149 The results indicate that best catalysts may display both high hydrogenation and hydrogenolysis activities. Moreover, it was recently shown that demetallization can be achieved using microwave irradiation.…”

“…The tetrahydrogenated species is more unstable and could be easily demetallized. 149 The main pathway of Ni/V-OEP conversion during hydrotreating was the hydrodemetallization route, and Ni was removed with the porphyrin ring rapid fragmentation. It was found that VO tetrahydrogenated porphyrins are more unstable than their Ni counterpart, which could decompose at room temperature.…”

“…The structure of Ni-OEPH2 was speculated as 1,2-dihydro-Ni-OEPH2, which could be further hydrogenated into Ni-OEPH4. The tetrahydrogenated species is more unstable and could be easily demetallized . The main pathway of Ni/V-OEP conversion during hydrotreating was the hydrodemetallization route, and Ni was removed with the porphyrin ring rapid fragmentation.…”