Characterization Of Nickel And Vanadium Compounds In Petroleum

Nickel and vanadium generally are incorporated into organic compounds in petroleum.About 20%~50% nickel and vanadium compounds are in the form of porphyrin,others are called non-porphyrin which does not have characteristic absorption peaks in ultraviolet and visible spectrophotometer(UV-vis).The molecular composition of non-porphyrins is unclear so far.The progresses of high resolution mass spectrometry enable the resolving of molecular composition of nickel and vanadium compounds in petroleum.However,nickel porphyrins as well as vanadium containing non-porphyrins are hard to be ionized in normal ionization sources,therefore they cannot be detected by mass spectrometers.This thesis will introduce the development and application of analysis method for petroleum porphyrins based on electrospray(ESI)Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS).A novel ionization method was developed for ESI analysis by adding ammonium formate into analytes as an ionization promoter.The selectivity and sensitivity were largely improved and enabled the direct analysis of nickel porphyrins in petroleum.The method could ionize aromatics and those heteroatoms with weak polarity function groups which cannot be ionized in normal ESI analysis which was found to be a capable for the molecular characterization of weak-and non-polar compounds in petroleum as well as other complex mixtures.The applicability of this method is better than that of atmosphere pressure photoionization(APPI),which is generally considered as the most appropriate ionization technique for non-polar compounds analysis.In addition,it was found that nickel porphyrins could generate molecular ions and protonated ions simultaneously in ESI.Nickel and vanadium compounds were enriched by precipitation,extraction,and column chromatography.The separated fractions and their demetalization products were characterized by position ion ESI with ammonium formate.Many porphyrins were identified by mass spectrometry from the non-porphyrin fractions.The result provides a vital evidence for the assumption that non-porphyrins have identical core skeletons as porphyrins.The UV-vis spectra of various porphyrin model compounds were investigated in different solvent environment.It was found that the molar absorption coefficient for Soret characteristic peaks of each model compound in complex matrix are much lower than that detected separately.The results indicate the UV-vis analysis should underestimate the content of porphyrins in petroleum.In other words,the concept of non-porphyrin should be redefined.This thesis provides novel analysis method for the understanding of the existence form of nickel and vanadium in petroleum.The evidence obtained by mass spectrometry and UV-vis challenge the concept of petroleum non-porphyrin and lay the methodological and theoretical foundation for the investigation of existence forms of nickel and vanadium compounds in petroleum.