Petroleomics: chemistry of the underworld

Abstract

Each different molecular elemental composition-e.g., C(c)H(h)N(n)O(o)S(s)-has a different exact mass. With sufficiently high mass resolving power (m/Deltam(50%) approximately 400,000, in which m is molecular mass and Deltam(50%) is the mass spectral peak width at half-maximum peak height) and mass accuracy (<300 ppb) up to approximately 800 Da, now routinely available from high-field (>/=9.4 T) Fourier transform ion cyclotron resonance mass spectrometry, it is possible to resolve and identify uniquely and simultaneously each of the thousands of elemental compositions from the most complex natural organic mixtures, including petroleum crude oil. It is thus possible to separate and sort petroleum components according to their heteroatom class (N(n)O(o)S(s)), double bond equivalents (DBE = number of rings plus double bonds involving carbon, because each ring or double bond results in a loss of two hydrogen atoms), and carbon number. "Petroleomics" is the characterization of petroleum at the molecular level. From sufficiently complete characterization of the organic composition of petroleum and its products, it should be possible to correlate (and ultimately predict) their properties and behavior. Examples include molecular mass distribution, distillation profile, characterization of specific fractions without prior extraction or wet chemical separation from the original bulk material, biodegradation, maturity, water solubility (and oil:water emulsion behavior), deposits in oil wells and refineries, efficiency and specificity of catalytic hydroprocessing, "heavy ends" (asphaltenes) analysis, corrosion, etc.

Fig. 1.

Atomic mass defects for selected isotopes of some common chemical elements. Because no two have the same mass defect, it is possible to determine a unique elemental composition for any molecule from a sufficiently accurate mass measurement.

Fig. 2.

Positive-ion electrospray 9.4-T FT-ICR mass spectrum of a European crude oil, containing ≈8,000 resolved and identified peaks. Several of the mass splits commonly encountered in crude oil are shown in the mass-scale-expanded 300-mDa Inset. Data were provided by A. M. McKenna.

Fig. 3.

Sorting of compounds based on their elemental compositions. (Bottom) Heteroatom class (all species with the same N_nO_oS_s composition). (Middle) Distribution of DBE (double bond equivalents = rings plus double bonds to carbon) distribution for members of the O₂ heteroatom class. (Top) Carbon number distribution for O₂ species with DBE = 2. Graphical combinations of these distributions furnish characteristic images of various petroleum materials.

Fig. 4.

Plots of double bond equivalents (DBE) vs. carbon number for the 375–400°C distillation cut from the negative-ion ESI 9.4 T FT-ICR mass spectrum of Athabasca bitumen (1 mg/ml) in toluene/methanol, spiked with 2% (by volume) ammonium hydroxide. Data were provided by D. F. Smith.

Fig. 5.

van Krevelen plot of H/C ratio vs. S/C ratio for all sulfur-containing ions in an APPI positive-ion 9.4 T FT-ICR mass spectrum of an Asian light crude oil. To avoid overlap between S_x classes, only ions with 300 < m/z < 750 are included. Data were provided by A. M. McKenna.

Fig. 6.

Plot of double bond equivalents vs. carbon number for all monoisotopic C_cH_hS₁ members of the petroleome database, compiled from dozens of positive- and negative-ion ESI and APPI FT-ICR mass spectra. The diagonal line represents the maximum possible DBE for each carbon number. The entries are not abundance-weighted; i.e., each different elemental composition is shown by a single dot. Data were provided by I. Stroe and J. E. Velasquez.