Petroleomics: Applications in the Fingerprinting of the Acidic and Basic Crude Oil Components Detected by Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

• Other Authors: Klein, Geoffrey Christoffersen (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Biochemistry; Biophysics; Molecular biology; Chemistry
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-2822

We have previously demonstrated the ability of electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) to resolve and identify the polar species found in all petroleum distillates. The ultrahigh resolving power and mass accuracy of FT-ICR MS allows for the identification of thousands of compounds in crude oils without prior chromatographic separation. In Chapter 3, we compare positive-ion ESI FT-ICR mass spectra of a South American crude oil with spectra of its SARA-isolated asphaltenes, resins, and aromatics, to determine the effect of the other components on the relative mass spectral abundances of the polar aromatics. Saturates are unobservable by ESI. For the chosen oil, little to no signal was obtained for the asphaltenes and resins due to their mostly acidic nature. The mass distributions, heteroatom class distributions, type (rings plus double bonds) distributions, and carbon number distributions of the aromatic fraction and unfractionated crude oil were highly similar. Thus, the saturates, asphaltenes, and resins do not affect the relative abundances of polar aromatics observed by positive-ion electrospray FT-ICR MS. It is therefore not necessary to isolate the polar aromatic fraction in order to characterize its chemical composition in a petroleum crude oil. The diminishing clean oil reserve is driving the search for new or improved ways to reduce the level of NSO-containing species found in high abundance in heavy crude oils. Hydrotreatment is the currently preferred technique to remove those polar species. Unfortunately, nitrogen compounds are known to cause coke formation on the surface of the hydrotreatment catalyst, leading to partial or complete deactivation. In Chapter 4, we use positive- and negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) to identify those nitrogen compounds that resist hydrotreatment. ESI preferentially ionizes polar (e.g., heteroatom-containing) species: basic molecules are detected as positive ions and acidic/neutral molecules as negative ions. FT-ICR MS resolves thousands of species in a single mass spectrum, allowing for unambiguous determination of elemental composition, CcHhNnOoSs, for identification of compound class (numbers of N, O, S heteroatoms, type (rings plus double bonds), and carbon number (revealing the extent of alkylation). We find that hydrotreatment-resistant compounds typically contain a single nitrogen atom, both pyridinic benzalogs and pyrollic benzalogs. Compounds with more than one heteroatom, such as NxOx, NxSx and Nx, are partially removed. Compound classes with lower double bond equivalents or fewer CH2 groups are preferentially removed. Species that contain an oxygen atom or OxSx are fully removed by hydrotreatment. A suite of ten crude oils that contain a varied of total acid numbers (TAN), corrosive character, and are derived from different source rock material are analyzed by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in Chapter 5. A variety of graphical methods are used to visually display each crude oil and reveal the lack of correlation between the basic and acidic species to TAN and corrosive character. The similarity in class and percent relative abundance of the basic polar species indicates that they play no role in the corrosive character of a crude oil and can not be used as biomarkers for geographical identification. The analysis of the acidic species illustrates the lack of correlation of any one specific class or type of compound to corrosivity or TAN. The vast difference in relative abundance of the carboxylic acids suggests that although these compounds contribute to corrosivity, other species, such as the non-polar sulfur compounds, also play a key role in the corrosive nature of a crude oil. These differences, however, do lend to the use of these carboxylic acids as biomarkers for specific geographical location as well as locaters of specific regions with in a reservoir. Asphaltenes are typically defined by their solubility in benzene and insolubility in pentane or heptane. They are believed to exist in petroleum crude oil as a colloidal suspension, stabilized by surface-adsorbed resins. Their normal equilibrium under reservoir conditions may be disrupted during production by pressure reduction, crude oil chemical composition changes, introduction of miscible gases and liquids, mixing with diluents and other oils, and by acid stimulation, hot oiling, and other oilfield operations. Electrospray ionization preferentially ionizes polar N-, S-, and O-containing compounds and its combination with ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry makes a powerful tool for the compositional analysis of petroleum-derived materials such as asphaltenes. In Chapter 6, we compare the compositional differences between heptane-precipitated asphaltenes and asphaltenes collected by live oil depressurization. We find that the heptane-precipitated asphaltenes contain higher double bond equivalents (number of rings and double bonds) compared to the asphaltenes induced by pressure drop. On the other hand, the pressure drop product exhibits a higher abundance of species containing sulfur. Thus, the solubility criterion for asphaltenes defines a significantly different chemical composition than the (more field-relevant) pressure-drop criterion. Asphaltenes are also known to deposit in both the petroleum recovery and topside refining processes. There normal equilibrium in both live and dead crude oil may be disrupted during production by pressure reduction; crude oil chemical composition changes, mixing with diluents and other oilfield operations. In Chapter 7, we compare a dead crude oil deposit asphaltene with its crude oil counterpart and a live crude oil deposit asphaltene. Negative-ion electrospray is the desired mode because of the acidic nature of asphaltenes. We find that the dead crude oil deposits contain higher aromatic character (more saturated), are enriched in oxygenated species as well as multiple heteroatomic classes compared to their crude oil counterpart. The two deposit asphaltenes, live and dead, are very similar in the types of classes detected. For some of the classes, O4S in particular, the dead oil typically deposits larger (more aromatic, longer alkyl chains) compounds compared to the live oil. This detailed compositional comparison of the dead deposit asphaltenes to its crude oil counterpart will provide information for the development of more cost- effective methods to control the deposition of asphaltenes and to increase the overall efficiency of the processing fields with asphaltene problems. === A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy. === Fall Semester, 2005. === October 12, 2005. === Ion Cyclotron Resonance, FT-ICR, Petroleum, Electrospray, Mass Spectrometry === Includes bibliographical references. === Alan G. Marshall, Professor Directing Dissertation; William M. Landing, Outside Committee Member; William T. Cooper, Committee Member; Michael Blaber, Committee Member; Ryan P. Rodgers, Committee Member.