The distribution of vanadium (V) compounds in the petroleum vacuum residuum (VR) and their transformations in hydrodemetallization (HDM) were investigated. V compounds in the VR and its hydrotreated products were extracted by different solvents in sequence to obtain methanol, dimethylformamide (DMF), and toluene extract fractions. The extracts were further separated into several subfractions using silica gel chromatography with various polar solvents. Positive-ion electrospray ionization (ESI) Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses was used to characterize V compounds before and after HDM. The contents of V compounds in the methanol, DMF, and toluene extracts were 9.04, 22.19, and 62.58%, respectively. The V compounds in the methanol extract were mainly porphyrin with a molecular formula of C n H m N 4 V 1 O 1 , which were found undergoing side-chain cracking and could be removed through hydrotreating. C n H m N 5 V 1 O 2 species were found in the DMF extracts, which can be easily converted or removed under severe reaction conditions. The V compounds in the toluene extracts were most resistant for hydrotreating, which were speculated as vanadyl porphyrins with complex substituent groups attached to the core porphyrin structures. The results indicated that a highly active HDM catalyst should possess a highly active hydrogenesis property and macropore size distribution for the different V compounds removed.

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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.