Nickel and vanadyl porphyrins in Arabian heavy crude oil

Abstract

This study reports the isolation and characterization of nickel and vanadyl porphyrins in the residue (1000??F) and asphaltenes from Arabian Heavy crude oil. The residue was obtained by distillation of crude oil, where as the asphaltenes were precipitated by n-haptene from the crude oil. Several literature-reported methods and modified separation methods were tried to isolate the nickel and vanadyl porphyrins from the residue and the asphaltenes. Metalloporphyrins were first extracted from the residue with methanol. The nickel porphyrins were separated from vanadyl porphyrins by means of adsorption chromatography on silica gel and alumina using solvents of increasing polarity. The metalloporphyrins were first soxhlet extracted from the asphaltenes by different proportions of benzene in acetonitrile. Adsorption chromatography on silica gel and alumina, using solvents of increasing polarity, was used to separate the vanadyl porphyrins. No nickel porphyrins were detected in the asphaltenes. The chromatographic separation process was monitored by ultra violet/visible spectrophtometry. Both of the nickel and vanadyl porphyrins were identified and characterized by ultraviolet/visible spectrophotometry and mass spectrometry. Five types of homologous series of vanadyl porphyrins were identified in the residue and asphaltenes:deoxophylleoerythroetrioporphyrins (DPEP, etioporphyrins (Etio), benzoDPEP, benzoEtio, and tetrahydroDPEP. Only two types of homologous series of nickel porphyrins were found in the residue: Etio and benzoDPEP.