Characterization of Petroporphyrins Using Ultraviolet−Visible Spectroscopy and Laser Desorption Ionization Time-of-Flight Mass Spectrometry

Abstract

Petroporphyrins were extracted from two typical Chinese heavy crude oils, Tahe and Du84, and then purified by silica gel chromatography, followed by demetallization by methyl sulfonic acid. The extraction and purification were monitored using ultraviolet−visible spectroscopy, and the final petroporphyrins were analyzed using laser desorption ionization time-of-flight mass spectrometry. The soft ionization mass spectrometric technique proved to be effective for the characterization of petroporphyrins. The results show that, in Tahe crude oil, vanadium is more abundant than nickel and 75% of the vanadyl porphyrins are of the etioporphyrin (ETIO) type, with remaining fractions attributed to deoxophylloerythroetioporphyrin (DPEP) and benzo types. The ∑DPEP/∑ETIO ratio was found to be 0.18. In contrast, the Du84 heavy crude oil contains more abundant nickel than vanadium, with its nickel porphyrins comprising mainly DPEP and ETIO types, with each occupying 45%, and the tetrahydrobenzo-DPEP and benzo types attributed to the remaining 10%. The ∑DPEP/∑ETIO ratio is ∼1.1. These results suggest that the Tahe crude oil has higher thermal maturity than the Du84 crude oil, and the former is in its mature stage, whereas the latter is in its evolution stage.