Spectroscopic Analysis of Crude Oil Asphaltenes at Molecular Level (original) (raw)
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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
Structural Study of Asphaltenes from Iranian Heavy Crude Oil
Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles, 2013
-Étude structurale d'asphaltènes de pétrole brut lourd iranien-Dans la présente étude, la précipitation d'asphaltènes du pétrole brut lourd iranien (au large du golfe Persique) a été effectuée au moyen de n-pentane (n-C 5) et de n-heptane (n-C 7) comme alcanes légers précipitants. Plusieurs techniques analytiques, chacune utilisant différents principes, ont ensuite été utilisées pour caractériser la structure des asphaltènes précipités. Le rendement en asphaltènes obtenu par l'utilisation du précipitant n-pentane était plus élevé que pour les asphaltènes précipités à l'aide du n-heptane. L'extraction des asphaltènes a affecté les fractions de maltènes n-C 5 et n-C 7 à des températures inférieures à 204 °C, comme l'indiquent les données obtenues par la technique de distillation simulée. La viscosité du pétrole lourd est influencée par la teneur et le comportement des asphaltènes. La dépendance de la viscosité du pétrole lourd testé avec le taux de cisaillement appliqué a été déterminée et l'écoulement était faible à γ. supérieur à 25 s-1. Les échantillons de pétrole lourd reconstitués ont été préparés en ajoutant différentes quantités d'asphaltènes aux maltènes (pétrole lourd désasphalté) et les effets des asphaltènes ont été plus prononcés à la basse température de 25 °C, comparés à ceux obtenus à des températures plus élevées. Selon le modèle de loi de puissance utilisé dans cette étude, la fluidité du pétrole lourd testé a révélé un caractère pseudoplastique. Les résultats structuraux obtenus à partir de la spectroscopie InfraRouge à Transformée de Fourier (IRTF) ont montré la présence de différents groupes fonctionnels dans les asphaltènes précipités. Par exemple, la présence de différents hydrocarbures (aliphatique, aromatique et alicyclique), basée sur leurs caractéristiques dans le spectre IRTF, a été confirmée. Les résines sont des dispersants efficaces et le retrait de cette fraction du pétrole brut perturbe la nature colloïdale du pétrole lourd, la floculation et la précipitation des asphaltènes finissant par se produire. L'apparition de pores sur les images SEM (Scanning Electron Microscopy) a été utilisée comme indicateur du détachement de la résine. A l'aide de la spectroscopie de Résonance Magnétique Nucléaire (RMN) 1 H et 13 C, deux paramètres structuraux importants des asphaltènes ont été déterminés. A savoir, l'aromaticité (f a) et le nombre moyen d'atomes de carbone par chaîne alkyle latérale (n carbone), où f a pour les asphaltènes n-C 5 était plus faible (0,39) que celui obtenu avec le solvant n-C 7 (0,49). En outre, les valeurs du paramètre n carbone étaient respectivement de 7,7 et 5,7 pour les asphaltènes n-C 5 et n-C 7. L'identification structurale des composés du pétrole représente un prérequis pour les différentes techniques utilisables pour la transformation du pétrole lourd.
Fuel, 2007
Asphaltenes derived from Algerian oil wells were characterized by Raman spectrometry to investigate their molecular structures in solid-state. The aromatic sheet diameter (L a ) was estimated using the integrated intensities of the G and the D1 mode, along with the Tuinstra equation [Tuinstra F, Koenig JL. J Chem Phys 1970;53:1126]. The values obtained for three Algerian Hassi-Messaoud asphaltene samples are on the same order as the literature values and also consistent with the X-ray diffraction results. The Raman spectra corresponding to the G and the D bands can be fitted with Gaussian, Lorentzian, and Gaussian/Lorentzian hybrid functions in a self-consistent manner. A three peak fitting procedure found that the Gaussian/Lorentzian hybrid function with G being Gaussian and D Lorentzian is the best combination. Incorporation of the X-ray data on the height of the crystallite, L c , gives rise to an estimate of eight asphaltene molecules in each asphaltene aggregate.
Structural Characterization of Asphaltenes of Different Origins
Energy & Fuels, 1995
Asphaltenes from Maya crude and its hydroprocessed oils at different reaction conditions were precipitated and studied by scanning and transmission electron microscopy (SEM and TEM). In order to better understand the changes occured in asphaltene structure during hydroprocessing the crude oil fractionation procedure with solvents was used to separate asphaltenes based on their solubility properties. Different asphaltene morphologies were observed depending on the mixture of solvents used for fractionating asphaltenes and reaction conditions at which crude oil was hydroprocessed. A comparison between asphaltenes from hydroprocessed and pure Maya crude oil was carried out on the way to distinguish morphological changes at microscopic level. It was observed that removal of alkyl chains during hydroprocessing makes asphaltenes suffer a rearrangement in solid state favoring stacking of aromatic cores as determined by TEM. SEM microscopy allowed different fractions of asphaltenes for seeing that they are constituted by agglomerate particles, porous structures, and smooth surfaces.
Energy & Fuels, 2000
Viscosimetry, tensiometry, and X-ray diffraction have been employed to determine physicochemical and structural properties of an Algerian asphaltene in solution. A new viscosity analysis scheme was adopted to extract information about the shape of the asphaltene aggregates, the solvation, and the inter-aggregate interactions. The average molecular weight (MW) was deduced by combining the surface tension and viscosity studies. The average MW of this asphaltene appears to be small in comparison with those measured by vapor pressure osmometry (VPO) but comparable with the recent results from mass spectroscopy, atomic force microscopy, and fluorescent spectroscopy. X-ray measurements show that asphaltene molecules aggregate, even in the neat phase, and an average aggregate is composed of 4-5 aromatic sheets. The viscosity study suggests that asphaltenes in toluene solutions behave in accordance with a spherical micellar model containing aggregated asphaltene molecules with a substantial amount of solvation.
Asphaltenes in heavy crude oil: Designation, precipitation, solutions, and effects on viscosity
Journal of Petroleum Science and Engineering, 2016
The results of the evaluation of asphaltene content in heavy crude oil depend on the solvent chosen; and the products obtained at this evaluation have varying effects on oil viscosity. In the experiments performed to separate compounds that might be assigned conditionally to the group of asphaltenes, not only standard solvents such as pentane and hexane but also diethyl and diisopropyl ethers as well as hexamethyldisiloxane were employed. The chemical composition of asphaltenes (as estimated using the IR method) depends on the precipitant used. The quantity of precipitated asphaltenes is directly correlated with the energy of the intermolecular interaction of the solvent. In this study, the effects of different "asphaltenes" on oil properties were evaluated by measuring the rheology of the solutions in tetralin at a wide range of temperatures. These solutions demonstrate very different properties (from Newtonian fluid to gel) depending on the concentration. Viscosity depends on the nature of the solvent used to precipitate asphaltenes. Using diethyl ether yields the smallest quantity of asphaltenes but they creates the most viscous solutions. The removal of asphaltenes leads to a significant decrease in heavy oil viscosity. Heavy oil viscosity can be decreased by 2-3 orders. The intensity of the effect is determined by the solvent's solubility parameter.
Review on aggregation of asphaltene vis-a-vis spectroscopic studies
Fuel, 2016
Both petroleum and coal derived asphaltene finds important place on the present research areas of hydrocarbon based liquid and solid fuels. It has earned a name of 'unwanted' fame for its deleterious impacts arising mainly due to its self aggregational phenomenon. Over the period of time the asphaltene aggregation has been seriously investigated worldwide even at the molecular scale. Besides several methods, the spectroscopic findings (UV Vis and Fluorescence), in this regard, contribute to substantial meaningful data. The major spectroscopic researches on the aggregation of asphaltene over the last ten years have been reviewed in this present study. A brief discussion on the asphaltene molecular structure and molecular weight also comes as a prelude. Asphaltenes derived from both petroleum and coal have been considered.