Investigations into Asphaltene Deposition, Stability, and Structure.

Petroleum;Small-angle Scattering;Deposition;Asphaltenes;Chemical Engineering;Engineering;Science;Chemical Engineering

Hoepfner, Michael PaulSolomon, Michael J. ;

University of Michigan

关键词: Petroleum;    Small-angle Scattering;    Deposition;    Asphaltenes;    Chemical Engineering;    Engineering;    Science;    Chemical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/100081/mhoepfne_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Asphaltenes are known to cause a number of petroleum production, transportation and processing concerns. The overarching goal of this body of work was to elucidate the fundamental structure and behavior of asphaltenes for ultimate application in a number of different fields. In this dissertation, asphaltenes were studied over length scales ranging from the macro to the micro scale. The dissertation begins by reporting the results of a study on the destabilization and deposition of asphaltenes using a capillary flow apparatus. Asphaltenes were destabilized by adding a precipitant to crude oil, and deposition was detected by an increase in the differential pressure across a capillary. These experiments revealed that the asphaltene deposition rate decreases continuously with decreasing precipitant concentration and no critical onset concentrations were observed. In addition, it was observed that sub-micrometer sized asphaltenes dominate the deposition process and the deposition rate is proportional to the concentration of insoluble asphaltenes. The destabilization of asphaltenes from crude oil after precipitant addition was also studied using small-angle neutron scattering (SANS) to detect precipitation at the incipient stages. No critical stability conditions were observed and at least a small quantity of insoluble asphaltenes were detected with any amount precipitant added, which was in agreement with the capillary deposition results. In addition, these experiments revealed that the fractal dimension of asphaltene clusters changes from approximately 1.7 to 2.1 when transitioning from soluble (not precipitating) to insoluble (precipitating) asphaltenes. In the last phase of this investigation, the structure of asphaltenes was further studied using both small-angle X-ray and neutron scattering (SAXS/SANS). For the first time, the relative fraction of asphaltenes in the aggregated vs. molecular state was estimated and fit to a thermodynamic aggregation model. The model results reveal moderate aggregation numbers (3-5) and free energies of association of approximately -31 kJ/mol. In addition, novel solvent background corrected wide-angle X-ray scattering results (WAXS) of asphaltenes in a liquid environment are presented which reveal the local molecular ordering in asphaltene nanoaggregates.