Reports: UR249498-UR2: Elucidation of Sulfur Chemical Forms in Petroleum and Coal Derived Asphaltenes

Sudipa Mitra-Kirtley, PhD , Rose-Hulman Institute of Technology

There are three areas that the principal investigator carried on research with undergraduate students from Rose-Hulman Institute of Technology on this project: off-campus experimentation, on-campus analysis work, and disseminating research results at conferences. The research was performed on characterizing sulfur chemical structures in fossil fuel materials, such as coal oils, coal asphaltenes, petroleum asphaltenes, kerogens, and bitumens.


In April of 2011, the principal investigator, Sudipa Mitra-Kirtley (SMK) was accompanied by two undergraduate students, Amanda Barnett, a senior, and Brian Kodalen, a sophomore, to the synchrotron facility at the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). There the team collected data for three days to investigate carefully the saturation effects on x-ray absorption spectra by studying samples prepared with different sulfur concentrations. Both sulfur models and fossil fuel samples were studied to make comparisons. The second trip was made in August, 2011 to the same facility, by SMK and Kodalen, to study many pristine and demineralized samples of sulfur model compounds and fossil fuel samples, for a three-day duration. The pristine and chemically treated samples were provided by Andrew Pomenrantz's laboratory at Schlumberger Doll Research (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.

On-campus work

In spring quarter of 2011, Barnett took a directed research course under the PI and analyzed the coal asphaltene and coal oil data collected in the previous year, using the software package WinXas. The fitting analysis was first done with various sulfur model spectra, and then on fossil fuels. This was a lengthy project involving correct positions of arctangents, and the positions and widths of the signature peaks. At the term end Barnett submitted a mini-thesis; this work was not funded, and it was part of a degree requirement.

In summer 2011, the principal investigator and two undergraduate students, Chad Wine and Kodalen analyzed a multitude of x-ray absorption spectra at Rose-Hulman Institute of Technology for 6 weeks. A new software analysis package was written to cater to particular analysis needs, and this was a remarkable improvement over the previous package. Analysis results were compared using this new technique, and two older techniques. Fossil fuel sulfur results using various possible model compounds were found and compared to determine the best model structures to use. Concurrent literature search was also done regularly to support the theories. Conference calls were made once every week with Dr. Pomerantz to discuss the results, and how to proceed with future analysis.

The basic outline of the analysis procedure was:

1.     Each model spectrum was background corrected and normalized.

2.     Each fossil fuel sample spectrum was then fitted with combinations of model spectra. This process was different from the previous one; the need to include arc-tangent steps was eliminated and the problem of fitting spectra with multiple arc-tangent steps was excluded.

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 analysis the spectra. She also used WinXAS to fit all the data, both the sulfur model set and the fossil fuel set, and compared the results with Kodalen's and previous results. Many older sulfur model and fossil-fuel files were tried to obtain reproducibility.

A more exhaustive sulfur model data base was used for the analysis. Different forms of pyrrhotite, pyrite, elemental sulfur, organic sulfide, thiophene, sulfoxide, sulfone, isethionic acid, and sulfate forms of sulfur were investigated in all the fossil fuel samples.

The overall results were obtained this year:

1.     There are no big differences between oil and asphaltenes derived from coal and petroleum. This is despite the fact that there are some chemical differences between the two sets, including molecular sizes.

2.     Saturation effects of sulfur need to be considered carefully while collecting x-ray absorption data of sulfur models and fossil fuels.

3.     Samples were freeze-dried in liquid nitrogen and ground extensively to ensure that there are no issues with particle sizes. This novel way of preparing samples and has proved to be very successful.

4.     Demineralization of both sulfur model samples and fossil fuel samples is necessary to obtain accurate spectra, but this process does not change the sulfur structures in the samples.

Conference presentations

Wine and Sean Gorsky (from previous year) presented the results from coal oil and coal asphaltene analysis at the Butler Undergraduate conference, held on April 15, 2011. The co-authors from RHIT were Barnett and SMK.

A poster presentation was made by Gorsky on these results at the annual Physics and Optical Engineering Advisory meeting in February, 2011, at RHIT.

A poster presentation was made by SMK at the Petrophase Conference at Imperial College, London, on the coal results.

All of these 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.      Study kerogens and asphaltenes to investigate saturation and demineralization effects,

b.     Investigate coal fractions (extracted oils and asphaltenes) as a function of coal rank, and

c.      Aim towards various degrees of thermal maturation and oxidation treatments of different kerogen samples.

This work will be the first of its kind, and will contribute greatly in understanding fossil fuel formation.

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