Elucidation of the functional sulphur chemical structure in asphaltenes using first principles and deconvolution of mid-infrared vibrational spectra (original) (raw)
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Characterization of sulfur in asphaltenes by sulfur K- and L-edge XANES spectroscopy
Journal of Synchrotron Radiation, 1999
Bitumens exposed to atmospheric conditions undergo various types of weathering including evaporation, biodegrachtion, abiotic oxidation, and water washing. Sulfur present in bitumens is a good marker of oxidation processes as it is very sensitive to oxidation and exhibits a range of oxidation states from-2 to +6. Sulfur K-and Ledge XANES spectroscopy were applied to the asphaltene extracts of a series of recent geological and archeological bitumens from the Middle East. In all the samples, dibenzothiophene is the major sulfur moiety. In the least altered asphaltene, minor species include disulfide, alkyl sulfide and sulfoxide. The proportion of oxidized sulfur (sulfoxide, sulfone, sulfonate and sulfate) increases with the alteration of the samples, whereas the disulfide and alkyl sulfide content decreases. This work illustrates the imerest of XANES spectroscopy as a selective 3nx~be for determining sulfur speciation in natural samples, and the complementarity of S K-and Ledge for identifying the oxidized and reduced forms of sulfur respectively.
Spectroscopic Analysis of Crude Oil Asphaltenes at Molecular Level
Petroleum Chemistry, 2020
In the present study, a scientific challenge of determination of various structural parameters of asphaltenes of medium heavy, heavy, and light crude oils is overcome by different spectroscopy techniques. Fourier Transform Infrared spectroscopy methods revealed indexing information besides clarification of different functional groups of asphaltenes. Analysis of Raman spectra of asphaltenes exhibited a higher average molecular size and more complicated chemical structures for the light crude oil asphaltenes compared to the ones from the heavy and medium heavy oils. Clarification of such chemical structures reveals why asphaltene molecules form aggregates leading to precipitation in particular when the percentage of asphaltenes is closer to and less than 1 wt % as in the case of light crude oils.
Energy & Fuels, 2020
Asphaltenes are a complex mixture of molecular structures with a variety of functionalities, which in turn impacts their physical properties. Discriminating between asphaltenes that are strongly and weakly interfacially active is providing a new direction to mitigate asphaltene-related problems. Whole asphaltenes (WA) were extracted from a South American heavy crude oil, further fractionated into interfacially active asphaltenes (IAA) and remaining asphaltenes (RA), and molecularly characterized by positiveion (+) atmospheric pressure photoionization (APPI) using a 9.4 T Fourier transform ion cyclotron mass spectrometer (FT-ICR MS). The IAA fraction was found to contain a greater abundance of heteroatoms with >50% of IAA containing two or more heteroatoms as compared to ∼30% for RA. The IAA fraction was enriched in oxygen-containing species, more specifically higherorder O x and O x S y groups that were predominantly of low DBE. Gas-phase fragmentation of RA and IAA precursor ions (m/z 650) by infrared multiphoton dissociation (IRMPD) revealed an abundance of multi-core motifs in IAA, while RA was found to be a mixture of single-core and multi-core structures. Analysis of the fragmented ions showed a prevalence of nitrogen-containing species of high DBE (aromatic molecular structures), while oxygen-containing species were most likely associated with aliphatic side chains. Extrography fractionation of RA and IAA verified the abundance of multi-core motifs in IAA, which were highly polar and of low DBE and carbon number. These "atypical" structures of IAA are classified as asphaltenes as a result of their functionality and polarity rather than high aromaticity.
Physicochemical Characterization of Asphaltenes
2016
This work proposes the study on physicochemical characterization of crude oils and their asphaltenes to understand the destabilization mechanism of asphaltenes. Knowledge on the molecular-scale interactions between components of crude oil is vital for the assessment of potential reserves and mitigation efforts of asphaltene-related problems. 11 heavy oil and bitumen samples from various regions of the world were subjected to characterization to attain universal yet simple correlations that are applicable under operating conditions. Comprehensive physicochemical analysis of the samples were performed through density and viscosity measurements of the crude oil, Saturates, Aromatics, Resins, and Asphaltenes (SARA) fractionation, Fourier Transform InfraRed (FTIR) spectroscopy analysis, elemental analysis, solubility profile assessment, and onset asphaltene precipitation (OAP) tests on the crude oil samples. Furthermore, two different types of asphaltenes were examined; n-pentane and n-heptane insolubles. Accordingly, density, zeta potential, and cluster size measurements, as well as high resolution microscopy imaging techniques, were conducted on these asphaltene samples to support the asphaltene stability and onset precipitation test results. The results have revealed that heteroatoms contained within the crude oils and asphaltenes play an important role in defining the physicochemical characteristics of crude oil. In particular, oxygen and metal (mostly V and Ni) functional groups were found to contribute significantly towards asphaltene stability and polarity. Additionally, this study has established that the presence of impurities in the saturates fraction causes it to have a destabilizing power towards vii
The Overriding Chemical Principles that Define Asphaltenes
Energy & Fuels, 2001
Asphaltenes are defined in terms of their solubility classification. This operational definition combined with the previous controversy over asphaltene molecular weight have obscured the governing chemical and structural parameters that define the asphaltene fraction. Here, asphaltenes are investigated by several techniques to elucidate relations between structure and properties. In particular, the asphaltene molecular size is compared to the ratio of aromatic to saturated carbon. The conclusion is obtained that asphaltene molecular structure is governed by the balance between the propensity of fused aromatic ring systems to stack via π-bonding, reducing solubility, vs the steric disruption of stacking due alkane groups, increasing solubility. 10.
Analytical Information on the Asphaltenes from a Few Standard Characterization Techniques
Energy Sources Part A-recovery Utilization and Environmental Effects, 2011
The asphaltene has been obtained from asphalt cement with penetration grade 60, which is extracted from crude Libya petroleum. The elemental composition and some structural properties of the asphaltene samples are determined by various methods, such as SEM, infrared spectroscopy, and X-ray analysis. Some experiments are performed on 1H dynamic nuclear polarization (DNP) in a number of asphaltene suspensions in organic solvents. The frequency dependence of the DNP enhancement under conditions of weak EPR saturation in a low magnetic field is obtained and interpreted as the EPR line shape of some free radicals present in the samples.