Sudipa Mitra-Kirtley, PhD, Rose-Hulman Institute of Technology
There are three principal areas that the principal investigator carried on research with undergraduate students from Rose-Hulman Institute of Technology on this project: on-campus data analysis work, off-campus experimentation, and presenting of research results at conferences. The project was based on characterizing sulfur chemical structures in fossil fuel materials, such as demineralized and pristine kerogens, bitumens, different sulfur standards of varied dilutions and preparation methods, and petroleum asphaltenes from different depths and formations.
During summer of 2012 Paige Martin, an undergraduate Chemical Engineering sophomore at Rose-Hulman, worked on X-ray Near-Edge Absorption Spectra (XANES) data analysis of several petroleum asphaltenes, resins, kerogens, bitumens, and sulfur model compounds diluted to different concentrations. Paige used a new computer program, which had resulted from a previous project from this grant, and which had been adjusted to make the analysis more efficient and robust. The fitting analysis was first done with various sulfur model spectra of different dilutions, and then on the fossil fuels. New results were compared with previous results for both the standards and the fossil fuels at the beginning to ensure the best analysis method. The PI was working alongside with Paige on the same project, refining the processes along the way, and offering constant guidance. Concurrent literature search was also done regularly. Dr. Andrew Pomerantz of Schlumberger Doll Research (SDR) was consulted periodically on several issues.
At the end of six weeks, Paige submitted a complete report on the results.
The basic outline of the analysis procedure was:
1. Each model spectrum was analyzed for different concentrations to completely eliminate any saturation effects. A database possible was created with the best data for standards.
2. Each fossil fuel sample spectrum was then fitted with the standard database using the new program. This process was direct, and did not involve deconvolution of each spectrum.
3. This same procedure was repeated using the third derivative fitting of the fossil fuel spectra.
4. Percentages of the different sulfur forms were extracted directly using the fitting routines, and various comparisons were made to optimize the routine.
The PI oversaw the entire analysis procedure, including the testing of the new program, as well as independently analyzing the spectra.
The sulfur standard database consisted of different forms of pyrrhotite, pyrite, elemental sulfur, organic sulfide, thiophene, sulfoxide, sulfone, isethionic acid, and sulfate forms of sulfur.
The overall results that were obtained from this part of the project were:
1. There are marked differences between kerogens and bitumens. Bitumen, the organic part of the shale that is soluble in organic solvents, showed large percentages of the polar sulfoxide structures. Kerogens, the insoluble organic parts of shales, showed more elemental and thiophenic sulfur forms.
2. Acid demineralization of the samples did not alter the XANES results for the sulfur standards, the kerogens and the bitumens.
3. There are no big differences between the different petroleum asphaltenes. This is despite the fact that there are some chemical differences between the two sets, including molecular sizes.
4. A novel way to prepare diluted samples with small particle sizes produced excellent XANES results.
In August of 2012, the PI was accompanied by, Brian Kodalen, a Physics and Mathematics junior undergraduate student, to the synchrotron facility at the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). Three collaborators from SDR joined the group from Rose-Hulman. At APS, team collected XANES data from different fossil fuel and more different kinds of sulfur standard samples. The first set of fossil fuel samples belonged to a series of pyrolyzed Green River oil shales, consisting of different kerogens (insoluble organics) and bitumens (soluble organics). The idea was to investigate the effect of high temperatures on these samples. The team also looked at some asphaltenes taken from different depths in the same reservoir and from different kinds of formations (biodegraded, precipitated, etc.). Finally data was collected on bitumens extracted in different solvents, to test the theory that if the bitumens studied before were polar since they were extracted using a polar solvent. Some of the fossil fuel samples were provided by Western Research Institute, Colorado School of Mines, and the Wyoming Research Institute. All the treated samples were provided by Andrew Pomenrantz's laboratory at SDR.
The bending magnet beamline 9-BM at APS, which spans an energy range of 2.1-6 KeV, was used. Si (111) crystal is used in the double crystal configuration. This beamline has a torroidal mirror to focus in the horizontal and vertical directions, and another mirror in the 9-BM enclosure is used to reject higher harmonics. A Lytle detector was used for fluorescence measurements, and an electron yield detector was occasionally used to study surface effects. Sun UNIX was used to change beamline parameters, and to collect the XANES data. The samples were mounted on Teflon sample holder. The liquid samples were dissolved in appropriate solvents and mounted in sample holders sealed by aluminized Mylar films.
∙ Brian Kodalen presented a poster on the results from coal oil and coal asphaltene analysis from the previous year at the annual Physics and Optical Engineering advisory meeting at Rose-Hulman in April, 2012.
∙ A poster presentation was made by SMK at the Petrophase Conference in Florida, in August, 2012, on the previous year's results on asphaltenes and resins.
∙ A manuscript was prepared and submitted to the Journal of American Chemical Society on the results from kerogens and bitumens.
The presentations were well received; new research contacts were made both by the students and the PI.
The next step of the project will be to
a. Analyze the new sulfur standard data collected with better dilution and particle size.
b. Analyze the latest Green River Shale data.
c. Investigate the latest asphaltene data from different treatments, depths, and locations.