Identification of metal porphyrins in Duri crude oil

Abstract

Crude oil comprises several complex hydrocarbon mixtures because of their slow natural formation process, including the toluene-soluble asphaltene component. The comparison result of Soxhlet extraction with and without silica was 55.15% and 86.75%, respectively. The Duri crude oil residue is mixed with silica gel, and Soxhlet extraction was performed with toluene. Further Soxhlet extractions and purifications obtain free porphyrin and two metal porphyrins. The Fourier Transform Infrared (FTIR) spectrum of n-heptane column chromatographic separation indicated the presence of a pyrrole ring at wavenumber 800 cm−1 in the fingerprint region as a porphyrin-formed group. UV-Vis absorption spectra of the n-heptane separation showed free porphyrin spectra at a maximum wavelength of 440 nm and those of metal porphyrins ranging 500−700 nm. The results of qualitative analysis of toluene fraction and n-heptane fraction showed the presence of C, Si, S, Ni, V, Fe, and Al. With this combination of spectroscopic techniques (FTIR, UV-Vis), Liquid Chromatography-Mass Spectrometry (LC-MS), and Energy Dispersive X-Ray Spectroscopy (EDX), nickel porphyrin (C32H36N4Ni, 534 m/z) and etioporphyrinato vanadyl (IV) (C32H36N4VO, 541 m/z) are isolated and identified from the silica gel chromatography fraction of the n-heptane Soxhlet extract of the toluene Soxhlet extract obtained from the Duri crude oil residue.