Reports: UR255809-UR2: Research on Geochemistry of Shale Oil and its Derivatives by Sulfur Speciation
Sudipa Mitra-Kirtley, PhD, Rose-Hulman Institute of Technology
A significant amount of XANES data has been collected and analyzed, and some of the results have been presented and published in conference proceedings. Two undergraduate students were involved in part of the analysis of the data. The Principal Investigator has again submitted a proposal for more synchrotron radiation beam time so that continuation of the present project can be possible. The experiments that were done and will be continued in the future are on X-ray Absorption Near-Edge Spectroscopy (XANES), as described below. The uniqueness of this particular project (and more of future projects) is that the photon beam was of micron dimensions, thus making it possible to study the solid samples at this spatial resolution. The PI conducted a series of XANES experiments at beamline 10.3.2 at Lawrence Berkeley Laboratory along with Dr. Sirine Fakra, a beamline scientist at LBL. Different shale rock samples, after being ground to very fine particles, were studied. Sulfur K-edge XANES experiments were performed on different batches of the same sample as well as on different samples. There were 13 samples in total, 12 oil shale samples and one petroleum asphaltene samples. All the oil shale samples were obtained from U. S. Geological Survey at Colorado. The results were significantly different among the different batches of the same sample, which was very surprising, pointing to the inhomogeneity of the samples at the micron level. Another sample, a petroleum asphaltene, was also studied. This sample was part of a very large project organized by the international Petrophase group, whereby each research group performed different studies on the same sample that was prepared the same way in the same laboratory in Colombia. Data Acquisition: During April 2017, the PI used part of her beamtime grant Lawrence Berkeley Laboratory Advanced Light Source (ALS). With the three days of beamtime she collected data of XAS, XRD, and XRF all in the micro-range of beam size. This was done at beam line 10.3.2 at the synchrotron radiation facility of ALS. Dr. Sirine Fakra from ALS collaborated with the PI. The energy of the photons was around the 2372 eV which is at the sulfur K-edge. 12 oil shale samples and a petroleum asphaltene sample were studied extensively. Si (111) crystals were used in the double crystal configuration. An Amptek silicon drift fluorescence detector 1-element (XR-100SDD) was used to do the XRF mapping, chemical mapping and record the S K-edge quick Quick X-ray Absorption Near-Edge Spectroscopy (QXANES) spectra. The in-depth analysis of the samples at the micron level gave insights into the sulfur chemical forms of the different shale samples. The photon beam size was about 30 microns, and at that level, parts of the same sample showed significant differences for some samples. This shows that the shales have clusters of different sulfur chemical structures dispersed at different sites of the same sample. This finding is significant, and will probably lead to new ways of thinking of the homogeneity, or the lack thereof, of shale samples. The asphaltene sample, on the other hand, showed typical sulfur structures (thiophenic being the dominant form, with little oxygen and saturated structures) that are usually seen in most asphaltene samples. The next set of experiments will involve whole shale samples, which will be studied with similar methods, and extensive imaging of the samples are expected to reveal more insights about the dispersion of certain sulfur chemical structures. On-campus work During the summer of 2017 the PI worked on XANES data analysis. Undergraduate students from Rose-Hulman, Brandon Keltz and Zihang Xu worked on the data analysis. The PI, along with the students, did extensive work on the analysis procedures. Different new computer software programs were constructed and results were compared between the different methods of analysis, as well as with results from a previous experiment from a different scientific group on similar data. A manuscript is being documented based on the analysis, and the next set of experiments will provide the much needed information to complete the manuscript. The students gathered extensive experience not only in the data analysis but also in understanding the physics behind XANES, and in the importance of studying heteroatoms, such as sulfur, in fossil-fuel materials. Presentations The PI presented an oral and two poster presentations on the XANES, and XRF results at the Annual Petrophase Conference in Le Havre, France. The presentations were very well received, and several future project ideas with scientists from other research groups have opened up. Two publications: 1. Micro x-ray fluorescence and micro x-ray absorption near-edge structure studies on Petrophase asphaltene, Annual Petrophase conference, Le Havre, France, June, 2017. 2. An in-depth study of sulfur using imaging XANES with synchrotron radiation, Annual Petrophase conference, Le Havre, France, June, 2017. 3. Asphaltene aggregation in Petrophase 2017 samples, Annual Petrophase conference, Le Havre, France, June, 2017. The next step of the project will be to 1. Collect more data at APS during a future beam time. The PI has submitted another proposal to ALS for additional beamtime. 2. Collect more micro-XAS, XRF, and XRD data at ALS on sections of the whole shale samples using the unique micron sized photon beam. 3. Analyze all the data for new results and trends.