Weathered crude oil

Brunnock et al. [67] have also determined beach pollutants. They showed that weathered crude oil, crude oil sludge, and fuel oil can be differentiated by the n-paraffin profile as shown by gas chromatography, wax content, wax melting point, and asphaltene content. The effects of weathering at sea on crude oil were studied parameters unaffected by evaporation and exposure are the contents of vanadium, nickel, and n-paraffins. The scheme developed for the identification of certain weathered crude oils includes the determination of these constituents, together with the sulfur content of the sample. 

Mansuy et al. [97] investigated the use of GC-C-IRMS as a complimentary correlation technique to GC and GC-MS, particularly for spilled crude oils and hydrocarbon samples that have undergone extensive weathering. In their study, a variety of oils and refined hydrocarbon products, weathered both artificially and naturally, were analyzed by GC, GC-MS, and GC-C-IRMS. The authors reported that in case of samples which have lost their more volatile n-alkanes as a result of weathering, the isotopic compositions of the individual compounds were not found to be extensively affected. Hence, GC-C-IRMS was shown to be useful for correlation of refined products dominated by n-alkanes in the C10-C20 region and containing none of the biomarkers more commonly used for source correlation purposes. For extensively weathered crude oils which have lost all of their n-alkanes,it has been demonstrated that isolation and pyrolysis of the asphaltenes followed by GC-C-IRMS of the individual pyrolysis products can be used for correlation purposes with their unaltered counterparts [97]. 

Weathered crude oil crude oil which, due to natural causes during storage and handling, has lost an appreciable quantity of its more volatile components also indicates uptake of oxygen. 

BioPetro is a bacterial product formulated to provide facultative bacteria selected for in situ bioremediation of refined and crude hydrocarbons, such as fresh and weathered crude oils, heavy... 

Photo 63 A rope skimmer is shown recovering a weathered crude oil. (Environment Canada)... 

Photo 67 An elevating skimmer recovers weathered crude oil. (Oil Spill Response Limited)... 

Table X. Mass Spectrometric Analyses of Weathered Crude Oils (Wt %) °...

Weathered crude oil is not acutely toxic to invertebrates. Essentially all of the toxic/volatile components are rapidly dissipated to the atmosphere upon weathering, whereas the water-soluble fraction is transported to the water column where it is susceptible to various ameliorating processes. Lee et aL (1980) exposed zooplankton from the Gulf of Mexico to crude oil from the 1979 Ixtoc blowout. The oil was collected 2 months after the blowout from the Gulf of Mexico and was not toxic at concentrations of up to 14 mg L the highest concentration tested. Similarly Wong etaL (1981) showed that survival of the cladoceran Daphnia pulex exposed to 24-hour weathered... 

Incardona, J.P. Carls, M.G. Teraoka, H. Sloan, C.A. Collier, T.K. Scholz, N.L. 2005. Aryl hydrocarbon receptor-independent toxicity of weathered crude oil during fish development. Environmental Elealth Perspective, v. 113, p. 1755-1762. 

Vinyls Vinyl chloride co-polymer resins were developed in the USA in the late 1930s. They have better weather and slightly more chemical resistance than chlorinated rubber paints. They are generally resistant to crude oil but application is more critical. For example, they are particularly sensitive to moisture present on a surface during painting and this can lead to adhesion failure. They are also more prone to solvent entrapment than chlorinated rubber paints. 

Figure 1 Plot of weathering ratio (C3-dibenzothiophenes C3-chrysenes) versus source ratio (C3-dibenzothio-phenes C3-phenanthrenes) for fresh and degraded oil samples from three different crude oil spills (Reprinted with permission from Environ. Sci. Technol, 30, 2332. 1996 American Chemical Society)...

In contrast to infrared spectrometry there is no decrease in relative sensitivity in the lower energy region of the spectrum, and since no solvent is required, no part of the spectrum contains solvent absorptions. Oil samples contaminated with sand, sediment, and other solid substances have been analysed directly, after being placed between 0.5 mm 23-reflection crystals. Crude oils, which were relatively uncontaminated and needed less sensitivity, were smeared on a 2 mm 5-reflection crystal. The technique has been used to differentiate between crude oils from natural marine seepage, and accidental leaks from a drilling platform. The technique overcomes some of the faults of infrared spectroscopy, but is still affected by weathering and contamination of samples by other organic matter. The absorption bands shown in Table 9.1 are important in petroleum product identification. 

Rasmussen [82] describes a gas chromatographic analysis and a method for data interpretation that he has successfully used to identify crude oil and bunker fuel spills. Samples were analysed using a Dexsil-300 support coated open tube (SCOT) column and a flame ionisation detector. The high-resolution chromatogram was mathematically treated to give GC patterns that were a characteristic of the oil and were relatively unaffected by moderate weathering. He compiled the GC patterns of 20 crude oils. Rasmussen [82] uses metal and sulfur determinations and infrared spectroscopy to complement the capillary gas chromatographic technique. 

The most common method for GC/MS analysis of semivolatile compounds (EPA SW-846 8270) includes 16 polycyclic aromatic compounds, some of which commonly occur in middle distillate to heavy petroleum products. The method also quantifies phenols and cresols, compounds that are not hydrocarbons but may occur in petroleum products. Phenols and cresols are more likely found in crude oils and weathered petroleum products. 

Of particnlar significance in the study of petroleum weathering are the biomarker molecules (e.g., pristane, phytane, the hopanes and steranes). Historically, the biomarkers have been employed as crude oil signatures in prospecting and characterization. More recently, such molecules have also been employed in the environmental field, both for the determination of pollutant source and estimation of the degree of weathering. 

The weathering of a crude oil slick at sea. Source-. From Preston, M. R. (1988). Chemical Oceanography, Vol. 9, Aoademic Press, pp. 53-96. 

The density of crude oil is on the order of 0.85 g/cm, so if the sea surface is calm, an oil spill will initially form a slick. The slick is subject to physical processes, such as advection and turbulence, causing it to move vertically and/or horizontally. Advection tends to lead to dispersal or, if land is nearby, shoreline stranding. Turbulence promotes the formation of emulsions, called chocolate mousse, which can be transformed via weathering into tarballs. The lower-molecular-weight compounds tend to evaporate or dissolve. Some fractions of petroleum have solubilities in seawater on the order of tens of milligrams per liter. Some are also photochemically oxidized. 

Weathered Crude A term applied to crude oil which has lost an appreciable amount of volatile components due to evaporation and other conditions of storage and handling. 

Bitumen describes a black or dark brown masticlike material that is thermoplastic in nature and softens upon heating. The sources of bitumen are petroleum or coal deposits. The natural product is commonly called gilsonite or pitch, a mineral formed by an old weathered petroleum flow at the surface of the earth that has left behind the larger molecules from the petroleum. A principal source in the past has been Lake Trinidad, a 445,000 m2 deposit on the island of Trinidad. Bitumen from petroleum or crude oil is called asphalt (qv). It is the material left behind after all the valuable compounds, eg, gasolines, have been distilled out of the cmde oil. The amount and quality of asphalt is dependent on the source of the crude oil used in the refining process. Some cmde oils have a higher content of asphaltic bitumen left after the distillation process. Bitumen from coal is coal-tar pitch. It remains after the valuable coal oils and tars have been distilled out of the coal tars produced by distractive distillation. Most industrial applications for bitumen products use asphalt or coal-tar pitch because the supply is more uniform and plentiful. 

It can be seen that while this particular crude oil contains over 95t by volume pentanes and heavier, these constituents only contribute about 201 to the vapor pressure. Most of the vapor pressure of this oil is contributed by the propane and butanes, since it contains very little methane and ethane. This oil stream is the product of an extremely selective separation process. Crude oil streams, unless they have "weathered" in an open tank for some period of time,... 

Some special problems arise at sea. When crude oil is spilled on the ocean, a slick is formed which spreads out from the source with a rate that depends on the oil viscosity. With sufficient energy an O/W emulsion may be formed, which helps disperse oil into the water column and away from sensitive shorelines. Otherwise, the oil may pick up water to form a water-in-oil emulsion, or mousse ( chocolate mousse ). These mousse emulsions can have high water contents and have very high viscosities, with weathering they can become semi-solid and considerably more difficult to handle, very much like the rag-layer emulsions referred to above. The presence of mechanically strong films makes it hard to get demulsifiers into these emulsions, so they are hard to break. See Chapter 9. 

M., Studies of the Dissolution and Long Term Weathering of Spilled Crude Oils, Manuscript Report EE-145, Environment Canada Ottawa, ON, 1993, 46 pp. 

Little, D.I. (1987) The physical fate of weathered crude and emulsified fuel oils as a function of intertidal sedimentology. In Fate and Effects of Oil in Marine Ecosystems (Kuiper, J., and van den Brink, W.J., eds.), pp. 3-18, Martinus Nijhoff, Boston, MA. 

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