Investigation and Characterization of Asphaltenes and Asphaltene Co-Precipitates and Their Role in Emulsion Formation/Stabilization
Ehrmann, Brandie Michelle (author)
Marshall, Alan G. (professor directing dissertation)
Chanton, Jeffrey (university representative)
Dorsey, John G. (committee member)
Rodgers, Ryan P. (committee member)
Stiegman, Albert E. (committee member)
Department of Chemistry and Biochemistry (degree granting department)
Florida State University (degree granting institution)
Asphaltenes are a solubility defined class of crude oil compounds that precipitate from solution upon normal alkane addition. They are experimentally investigated due to their tendencies to cause refinery issues. Their ability to aggregate (even at very low concentrations), flocculate, and precipitate cause refinery pipes to clog, foul, and (in some cases) corrode. Asphaltenes are a heterogeneous mixture of compounds; highly aromatic and rich in heteroatom content. Nearly every aspect of asphaltene science is debated in literature. Varying opinions are presented in terms of asphaltene molecular weight, structure and composition. Molecular weight is highly controversial because of chemical aggregation tendencies. Molecular structure of asphaltenes is disputed in terms of molecular linkage. Whether asphaltenes are highly condensed molecular structures or highly alkylated is an intensely researched subject matter. Chemical composition is questioned in terms of heteroatom content and polarity. What role heteroatoms play in aggregation and molecular structure is also still largely unknown. The aim of this document is to investigate asphaltenes using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) (see chapter two). The ultrahigh resolution, high resolving power capabilities, and high mass accuracy make the instrumentation ideal for probing a complex mixture, such as asphaltenes. Outlined in Chapter Three is an investigation into pre-fractionated asphaltenes by size-exclusion chromatography (SEC). The SEC technique is frequently used to aid in asphaltene molecular weight determination, but often times plagued by the asphaltene molecule's inherent tendency to aggregate. The mass spectral analysis of these fractionated asphaltenes provides insight into asphaltene heteroatom content, aromaticity and alkylation. The observed decrease in alkylation trends point to a size-based separation. Class compositional profiles are provided as function of SEC eluents. Chapter four presents a study that examines asphaltene molecular structure. Model compounds are probed by tandem mass spectral analysis to gain understanding into the fragmentation tendencies of catacondensed and pericondensed molecular structures. The observed patterns are correlated to the fragmentation results from a real asphaltene sample. Results offer new insight into asphaltene molecular structure. Asphaltenes are often blamed for emulsion formation in crude oil because of their surface active characteristic and capabilities. Chapters five and six examine what role asphaltenes play in emulsion formation. A detailed crude oil compositional study is presented in chapter five. Generated results indicate that a sub-set of asphaltenes, known as asphaltene co-precipitates, with unique 'transitional' characteristics may prove most responsible for the role of asphaltenes in emulsion formation. Chapter six studies lab generated emulsions and their respective (isolated) interfacial layer. The isolated interfacial layer was depleted by successive emulsion formation. The implications from the successive depletion study point to distinct heteroatom functionalities that act as 'primary' and 'secondary' stabilizers. In addition, identical heteroatom classes and chemical functionalities are identified with similar "transitional' characteristics, just as those identified in chapter five (and previous studies. Aggregation of asphaltenes causes erroneous molecular weight determination and/or leads to misinterpretations of molecular structure. In addition, aggregation and how it occurs may provide insight into crude oil bio-markers. Molecular polarity behavior of asphaltenes is also paramount because asphaltenes are a solubility defined fraction of crude oil. The data presented in chapter seven monitor asphaltene co-precipitate molecular progression as a function of Soxhlet extraction in normal alkane solvent. Asphaltene co-precipitates indicate that polarity may be a driving factor in asphaltene aggregation and solubility behavior. Lastly, chapter eight details a massive collaborative series of experiments used to examine a real-world emulsion scenario. All efforts were made to provide a comprehensive explanation for why the observed field emulsion existed but the results and the mass spectral analysis showed no promising answer.
July 14, 2010.
A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Includes bibliographical references.
Alan G. Marshall, Professor Directing Dissertation; Jeffrey Chanton, University Representative; John G. Dorsey, Committee Member; Ryan P. Rodgers, Committee Member; Albert E. Stiegman, Committee Member.
Florida State University
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