Asphaltenes are molecular substances that are found in
crude oil, along with
resins,
aromatic hydrocarbons, and saturated hydrocarbons. See [1],[2] below.Asphaltenes consist primarily of CHNOS with trace V and Ni. The CH ratio is approximately 1:1.2 depending on the asphaltene source. Asphaltenes are defined operationally as the n-heptane insoluble, toluene soluble component of a carbonaceous material such as crude oil, bitumen or coal. Asphaltenes have been shown to have a distribution of molecular weights in the range of 400
u to 1500 u with a maximum around 750 u. All techniques are now roughly in accord including many different mass spectral methods (ESI FT-ICR MS, APPI, APCI FIMS, LDI) and many different diffusion techniques (time-resolved fluorescence depolarization, fluorescence correlation spectroscopy, Taylor dispersion). Aggregation of asphaltenes at very low concentrations (in toluene) led to aggregate weights being misinterpreted as molecular weights with techniques such as VPO or GPC. The chemical structure is difficult to assertain, due to the complex nature of the asphaltenes, but has been studied by all available techniques including X-ray, elemental, and pyrolysis GC-FID-GC-MS. However, it is undisputed that the asphaltenes are composed mainly of polyaromatic carbon i.e. polycondensed aromatic benzene units with
oxygen,
nitrogen, and
sulfur,(NSO-compounds) combined with minor amounts of a series of heavy metals, particularly vanadium and nickel which occur in porphyrin structures. Furthermore, asphaltene rotational diffusion measurements show that small PAH chromophores (blue fluorescing) are in small asphaltene molecules while big PAH chromophores (red fluorescing) are in big molecules. This implies that there is only one fused polycyclic aromatic hydrocarbon (PAH) ring system per molecule. Very recent fragmentation studies by FT ICR-MS strongly support this 'island' molecular architecture refuting the 'archipelago' molecular architecture.
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