Abstract:

Macondo surrogate, source oil purchased from National Institute of Standards and Technology (NIST), and heavy crude oil (bitumen) underwent photo-oxidation in a solar simulator for 0-10 days. Both were fractionated to yield structurally defined fractions: saturates, 1-ring, 2-ring, 3-ring, 4-ring, and 5+ring aromatics. Those fractions with acceptable yields underwent photo-oxidation as well, to determine each structural class's contribution to the transformation products.

Suggested Citation:

Huan Chen, Ryan P. Rodgers, Phoebe Zito. 2019. Microcosm study: Photochemical oxidation of crude oil. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/n7-w8rh-ev52

Purpose:

Understand the mechanism of photochemical oxidation of crude oil.

Data Parameters and Units:

There are 2 folders named “Photooxidation microcosm NIST 2779” and “Photooxidation microcosm Surroage” and contains the data showing the effects of photo-oxidation on two types of oil - NIST 2779 and Macondo oil (MC252). Each folder has 2 sub-folders - “Oil” and “PSC”. The folder named “Oil” contains the data regarding the amount of oil remaining after the experiment at different time points. Whereas, the folder named "PSC" contains the water-soluble fraction generated by solar irradiation from the water-insoluble “Oil” at different time points. Note - “PSC” is photo-solubilized carbon. The main parameters are as follows: Number of Peaks = Number of Peaks on Full Spectrum with signal magnitude greater than six times the baseline root-mean-square noise % R. A. = Percent Relative Abundance DBE = double bond equivalents - number of aromatic rings plus double bonds to carbon % R. A.(No Hits Discarded) = Percent Relative Abundance with Non-Classified Peaks Removed A. M. W. average = Relative abundance weighted average molecular weight A.W. average C# = relative abundance weighted average carbon number A.W. average DBE = average number of double bond equivalents A.W. average H/C = relative abundance weighted average hydrogen-to-carbon ratio A.W. average O/C = relative abundance weighted average oxygen-to-carbon ratio A.W. average N/C = relative abundance weighted average nitrogen-to-carbon ratio Sum R. A. = Sum of Relative Abundance for all mass spectral peaks RMS Error = Root Mean Square Error PosESI = Positive Electrospray Ionization NegESI = Negative ion electrospray ionization APPI = atmospheric pressure photoionization

Methods:

The initial concentration of crude oil: 385 µL of oil in 50 mL artificial seawater. Microcosms that examined the degradation process were established by dispensing 385 µL of the Macondo crude oil (MC252, NIST 2779) in 50 mL autoclave-sterilized 70% artificial seawater (ASW) (Instant Ocean Aquarium Systems, Inc., Mentor, OH, USA). The amount of oil generated 120µm oil films. Oil was irradiated with simulated sunlight. A set of experiments were done in the dark as control. At each time point (t=24, t=48, t=72, t=96, t=120), water layer of the microcosms was transferred to a sterile container with a sterile glass pipette. Water fractions were then filtered through 0.2 µm membrane filters to remove the microbial population. 20 mL of the samples were acidified to pH 2 with HCl and the water-soluble organics were extracted by the solid-phase extraction described by Dittmar et al., (2008). Acidified samples were loaded on to a Bond Elute PPL (Agilent Technologies) stationary phase cartridge. Each sample was then desalted with pH 2 water and eluted with methanol at a final concentration of 100 ug mL-1 prior to Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) analysis. Extraction blank and solvent blank were included.

Instruments:

The Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer is custom-built with a 9.4 Tesla superconducting magnet.

Provenance and Historical References:

Dittmar, Thorsten, Koch, Boris, Hertkorn, Norbert, Kattner, Gerhard, (2008). A simple and efficient method for the solid‐phase extraction of dissolved organic matter (SPE‐DOM) from seawater, Limnol. Oceanogr. Methods, 6, doi:10.4319/lom.2008.6.230.

Individual Files: