Structure Of Asphaltenes Research Articles

Sub- and supercritical water in the processes of conversion of Domanik rock organic matter

Studies on the conversion of organic matter of high-carbon Domanik (siliceous-clay carbonate) rock of the Romashkinskoye deposit with a mineral content Corg of 7.07% in sub- and supercritical water have been carried out. It was shown that subcritical water at a temperature of 320°С and 17.0 MPa leads to a partial decomposition of the kerogenic structure, increasing the yield of bitumen from 3.12 to 3.98%, and a more complete recovery of asphaltenes and heavy C22-C30 n-alkanes from the rock sample. Supercritical water at temperatures of 374 and 420°C and pressures above 24.4 MPa leads to intensive formation of hydrocarbon and inorganic gases in the processes of kerogen decomposition, destruction of aliphatic substituents from condensed heteroatomic structures of resins and asphaltenes, and the carbonate component of Domanik rock. Degradation of the organic matter of the Domanik rock is also accompanied by the formation of saturated hydrocarbons with an increased content of light C12-C21 n-alkanes, and carbonaceous substances, such as carbene-carboids. Changes in the structure of asphaltenes and their paramagnetic properties were determined by the EPR method. The influence of sub- and supercritical water on phase changes in the composition of rock minerals, as well as on the yield and composition of formed gases, was revealed.

Study of the molecular structure of hexane-insoluble asphaltenes in coal tar pitch

A comprehensive study of the functional-group composition and structure of hexane-insoluble asphaltenes of coal tar pitch was carried out by methods of chemical elemental analysis, nuclear magnetic resonance (NMR), IR spectroscopy, scanning electron microscopy, X-ray diffraction (XRD), thermal analysis in combination with chromatography-mass spectrometry. It is shown that a hypothetical macromolecule of asphaltenes can be considered as a set of condensed aromatic nuclei of the peri-condensed type of 7 rings, which have alkyl substituents and connecting bridges consisting on average of 2 carbon atoms. The ratio of various structural units in the asphaltene powder is as follows: for one S-containing structure there are 4-5 N-and 1.3-1.7 O-containing structures. Sulfur atoms are contained in thiophene-like, thermally stable fragments of the structure and pass into the coke residue without decomposition. Oxygen is contained in thermally unstable carboxyl and phenolic groups, which decompose with the release of CO2, as well as in the composition of aromatic ethers that pass into the coke residue. The crystallographic characteristics of ordered structures formed by macromolecules of asphaltenes are studied. The average diameter of the packets is La of about 0.66 nm, with a thickness of Lc ≈ 1.30 nm, the distance between individual layers is d002 ≈ 0.34 nm, the average number of layers in the packages is n ≈ 5-7 pieces. In this case, the crystallinity of asphaltene powders does not exceed 30%. The data obtained by different methods are in good agreement and more fully characterize the structure of macromolecules of asphaltenes of coal tar pitch.

Investigation of the electronic and supramolecular structure of petroleum asphaltenes

Investigation of the electronic and supramolecular structure of petroleum asphaltenes

Computational and infrared spectroscopic investigations of N-substituted carbazoles.

The carbazole moiety is a commonly identified structural motif in the high-molecular-weight components of petroleum, known as asphaltenes. Detailed characterization of carbazoles is important for understanding the structure of asphaltenes and addressing challenges in the areas of heavy oil recovery, transportation, upgrading, and oil spills, arising from asphaltene properties and composition. In this work we study carbazole and the four N-substituted carbazoles 9-methylcarbazole, 9-ethylcarbazole, 9-vinylcarbazole and 9-phenylcarbazole. Experimental far- and mid-infrared spectra of these five carbazoles are measured using transmission and photoacoustic techniques. The molecular structures of the monomers and the respective dimers, optimized at the ωB97X-D/6-311++G(d,p) level of the density functional theory (DFT), are subjected to harmonic vibrational frequency calculations. The effect of changing substituents on the N-H bond, π-π stacking distances, and angles between monomers within the dimers, in addition to intermolecular interactions, is investigated. Noncovalent interaction analysis is employed to highlight the areas of attractive and repulsive interactions in the dimers. Thermochemistry calculations show that the formation of dimers of all carbazoles is spontaneous at 298 K. Comparison of the calculated vibrational spectra of these compounds with experimental spectra indicates that the existence of both monomers and dimers must be invoked to account for the observed bands in the infrared spectra. Excellent correlations between the experimentally-determined and calculated harmonic vibrational energies are obtained, with an experimental-to-calculated scaling factor of 0.95-0.96. These findings highlight the coupled computational-experimental approach for the interpretation of vibrational spectra and are essential for improving the spectroscopic characterization of N-substituted carbazoles.

Experimental evaluation of thermal maturity of crude oil samples by asphaltene fraction: Raman spectroscopy and X-ray diffraction

Thermal maturity level of crude oil samples is commonly investigated using popular biomarkers such as steranes and hopanes. Although crude oil's thermal maturity is an important goal for petroleum engineers and geochemists, fewer researches have been published about crude oil maturity than kerogen, source rock, and coal samples. This paper aims to assess the crude oil thermal maturity by asphaltene fraction analyzed by Raman spectroscopy and X-ray diffraction (XRD) methods for the first time. For this goal, the thermal maturity levels of three crude oil samples were investigated by geochemical parameters. In the next step, the asphaltene fractions of studied samples were precipitated and analyzed by two known Raman spectroscopy and X-ray diffraction methods to assess the applications of asphaltene fraction in determining the level of thermal maturity. Raman spectra indicated that during the maturation of organic matters, the amounts of disordered structures of asphaltenes diminish, and the position of the D1 band, as well as its area and intensity, are considered as maturity indicators. The Raman band separation (RBS) between two D1 and G bands, ratios of intensity and area of D1/G, and G's width are influenced by maturity. In this study, the RBS values increase from 210 cm−1 to 237 cm−1 by maturity increment. The results of XRD showed that the average distance between aromatic sheets (dm), the average height of the cluster perpendicular to the plain of sheets (Lc), aromaticity, and the ratio of intensities of two prominent detected bands of 002 and γ (I002/Iγ) are dependent on the maturity variations. Maturity increment resulted in increasing aromaticity (from 23% to 40%), I002/Iγ (from 0.24 to 0.34), and dm as well as decreasing Lc (from 33.84 °A to 29 °A) values. Since there is a good positive correlation between maturity and aromaticity and I002/Iγ, the cross plot of aromaticity versus I002/Iγ can be applied as a novel and proper tool for assessing the maturity of crude oil samples by the XRD patterns of their asphaltene fractions. Eventually, the results of this paper represent that RBS, intensity and area ratios of D1/G bands, G's width, aromaticity, Lc, and I002/Iγ parameters can be implemented for crude oil maturity assessment. The findings of this study can help for a better understanding of crude oil maturity level by the asphaltene fraction through a simple and inexpensive procedure.

Asphaltenes behavior during petroleum reservoirs acidizing (a molecular-scale onset study)

In the present study, we report our findings on asphaltenic sludge formation onset during petroleum reservoir acidizing treatment. To achieve this goal, we perform a series of molecular dynamics (MD) simulations at high temperature and pressure (550 K, 200 bar) on asphaltenic-oil (containing different molecular structures of asphaltenes) /hydrochloric acid (HCl) systems. Our simulation results indicate formation of asphaltenic sludge onset due to reservoir acidizing. Accumulation of the ionized asphaltenes at the oil/aqueous interface is the cause of sludge formation onset. Presence of ionized asphaltenes at the oil/water interface is attributed to the strong ion-ion interaction between ionized asphaltenes and acid ions (H+ and Cl-). Sludge formation onset is further stabilized via hydrogen bonding forces between ionized asphaltenes and interfacial water.

A review on novel applications of asphaltenes: A valuable waste

Asphaltene is the most complex component of crude oil, consisting of various molecular structures, e.g., different molecular weights and number of rings per fused-ring system (or aromatic moiety). Asphaltene has been reported to cause complicated problems during production and transportation. Asphaltene is also asociated with severe detrimental effects to the environment. Because of its problematic nature, asphaltene has been treated as a waste material for many years. Recently, advanced analytical techniques have been applied to elucidate the chemo-physical structure of asphaltene. Progress in research has facilitated the application of asphaltene in various fields. Herein, we provide a comprehensive review of advanced applications of asphaltene in different industries. It is shown that asphaltene has been successfully used in various fields (e.g., polymer industry, nanomaterial synthesis and surface modification, electronics, emulsions, and interfaces). The novel applications in each field is also discussed. This work provides insight to create value-added products from asphaltene and helps researchers to further contribute to these efforts and bring to new markets this precious waste material.

Elucidating the formation pathway of photo-generated asphaltenes from light Louisiana sweet crude oil after exposure to natural sunlight in the Gulf of Mexico

Photooxidation was an important weathering process for spilled oil at the water surface following the Deepwater Horizon oil spill, leading to the rapid formation of polar or oxygenated hydrocarbons, or photo-generated asphaltenes. While the great extent and rapid time scale of this process have been well documented, little is known about the formation pathways and chemical structures of photo-generated asphaltenes. To address this knowledge gap, we conducted a 44-day natural sunlight exposure experiment using Louisiana light sweet crude oil amended in seawater. The saturate, aromatic, resin and asphaltene fractions were separated and quantified by adsorption chromatography. Molecular details were obtained by thermal slicing ramped pyrolysis-gas chromatography–mass spectrometry, while bulk structural changes were quantified by 13C solid-state nuclear magnetic resonance. These analyses illustrate that, in comparison to the “native” petrogenic asphaltenes in crude oil, photo-generated asphaltenes had larger bridged-island structures with smaller aromatic cores and longer alkyl tails in each island. Our results also demonstrated that the large aliphatic fraction of the photo-generated asphaltene was sourced from the alkyl moieties of the aromatic fraction rather than the saturate fraction. A group of intact hydrocarbons, predominantly n-alkanes (C16–C28), was occluded in both native and photo-generated asphaltene matrices. Overall, these results provide insight into the formation mechanisms and structural details of photo-generated asphaltenes in oils after exposure to natural sunlight in Gulf of Mexico waters. This knowledge is valuable for developing remediation strategies for oil spills, in particular those under strong solar irradiance.

Composition of High-Molecular-Weight Heteroatomic Components of Oil Shale Organic Matter

The composition of sulfur-bound compounds of asphaltic–resinous substances of bitumen from oil shale sampled from the Dmitrievskoe deposit (Kuzbass) has been studied using the technique of selective chemical destruction. It has been shown that the structure of asphaltenes and resins contains moieties represented by alkanes, phenylalkanes, phenanthrenes, fluoranthenes, pyrenes, and methyl esters of aliphatic acids that are linked to each other or to the polycondensed core of their molecules through alkyl sulfide bridges. A distinctive feature of asphaltene molecules is the presence of S-bound phenyl- and naphthene-substituted aromatic hydrocarbons and aromatic oxygen-containing compounds in their composition.

Modeling of the Reactivity of Asphaltenes in Electrophilic Substitution Reactions

Quantum-chemical modeling of the spatial and electronic structure of asphaltenes containing different numbers of electron-withdrawing substituents used the DFT/B3LYP-6-31G(d,p) method to predict the reactivity of petroleum asphaltenes upon their chemical modification. The change of torsion angle of the polycondensed aromatic asphaltene structure depending on the type of substituent was studied. The electronic structure and electron-density charge distribution over the aromatic carbon atoms were analyzed to determine the predominant direction of electrophilic substitution of the studied asphaltene model structures. A high degree of polycondensation of the asphaltenes and the presence of electron-donating aromatic heterocyclic fragments were shown not to affect significantly the direction of attack of an electrophilic reagent. Introduction of electron-withdrawing substituents decreased the rate of electrophilic substitution.

Experimental study and modeling of asphaltene deposition on metal surfaces via electrodeposition process: The role of ultrasonic radiation, asphaltene concentration and structure

Asphaltene deposition in the wellbore is considered as a major operational challenge while producing some crude oils. It has been claimed that, external fields, such as electric field and ultrasonic radiation, could help tackling this issue. Although the effect of electric field on the aggregation size and the aggregation rate of asphaltene particles has been investigated before, its correlation with asphaltene deposition in the presence and absence of ultrasonic radiation is not known. In this study, the asphaltene deposition on metal surfaces was first mimicked using an electrodeposition process, and then the effect of ultrasonic radiation on electrodeposition of asphaltene were measured and analysed. Our observations showed that the electric filed itself does not unstable the dissolved asphaltene, and the asphaltene deposition on electrodes, under the effect of DC electric filed, first requires the formation of asphaltene aggregates. The maximum deposition was generated at 2 kV/cm, the exposure time of 300 s to the electric field, and the weight ratio of toluene to heptane 4.2%. It was also found that the structure and composition of asphaltenes, especially their polarity and aromaticity, affect asphaltenes deposition. Among different adsorption kinetic models, the nth-order kinetics model was selected to estimate the amount of deposited asphaltene. Finally, simultaneous ultrasound radiation during the process of electrodeposition, reduced the deposition rate on the metal blades from an average of 65 wt % of the total asphaltene content to 10 wt%. The findings of this study highlight the role of composition and structural properties of asphaltene on its surface deposition in the wellbore. More importantly, simultaneous radiation of ultrasonic waves during electrodeposition process confirms the effectiveness of ultrasonic radiation, as a quite new asphatene remediation technique.

Conformational Analysis of Nonplanar Archipelago Structures on a Cu (111) Surface by Molecular Imaging

We investigated some specially designed model compounds as proxies for archipelago structures in asphaltenes and heavy oils using noncontact atomic force microscopy (nc-AFM). Various adsorption con...

Precipitant Effects on Aggregates Structure of Asphaltene and Their Implications for Groundwater Remediation

Asphaltenes generally aggregate, then precipitate and deposit on the surfaces of environmental media (soil, sediment, aquifer, and aquitard). Previous studies have recognized the importance of asphaltene aggregates on the wettability of aquifer systems, which has long been regarded as a limiting factor that determines the feasibility and remediation efficiency of sites contaminated by heavy oils. However, the mechanisms/factors associated with precipitant effects on asphaltene aggregates structure, and how the precipitant effects influence the wettability of surfaces remain largely unknown. Here, we observe the particle-by-particle growth of asphaltene aggregates formed at different precipitant concentrations. Our results show that aggregates for all precipitant concentrations are highly polydisperse with self-similar structures. A higher precipitant concentration leads to a more compacted aggregates structure, while precipitant concentration near to onset point results in a less compact structure. The well-known Smoluchowski model is inadequate to describe the structural evolutions of asphaltene aggregates, even for aggregation scenarios induced by a precipitant concentration at the onset point where the Smoluchowski model is expected to explain the aggregate size distribution. It is suggested that aggregates with relative high fractal dimensions observed at high precipitant concentrations can be used to explain the relatively low Stokes settling velocities observed for large asphaltene aggregates. In addition, asphaltene aggregates with high fractal dimensions are likely to have high density of nanoscale roughness which could enhance the hydrophobicity of interfaces when they deposit on the sand surface. Findings obtained from this study advance our current understandings on the fate and transport of heavy oil contaminants in the subsurface environment, which will have important implications for designing and implementing more effective and efficient remediation technologies for contaminated sites.

Probing Interfacial Structure and Dynamics of Model and Natural Asphaltenes at Fluid-Fluid Interfaces.

Asphaltenes are largely responsible for crude oil interfacial behavior. Due to their complex molecular nature, studying connections between interfacial properties and molecular structure is challenging, and these connections remain unclear. Several groups have reported on the interfacial behavior of asphaltenes, but a unified picture of both interfacial dynamics and thermodynamics is still missing. We seek to establish connections between asphaltene interfacial morphology and interfacial dynamics by combining interfacial dilatational deformation with microscopic structural imaging analysis. Understanding the behavior of natural asphaltene samples is made difficult by the inherent molecular variability. Therefore, we have also studied the behavior of an asphaltene model compound to draw fundamental structure-property relationships. This work contains simultaneous interfacial deformation and microscopy in systems of natural and model asphaltenes at air-water and decane-water interfaces. How the dynamics of natural asphaltenes influences the morphological and thermodynamic state of the air-water and decane-water interfaces is discussed based on the deviations observed between isotropic and anisotropic deformations. Areas where model asphaltenes can help us to understand the behavior of natural asphaltenes are identified such as its high surface pressure activity and aggregation character. An aggregation mechanism for model and natural asphaltenes is proposed based on an observed relationship between microscopic and millimetric aggregates.

Effect of asphaltene structure on its aggregation behavior in toluene-normal alkane mixtures

Colloidal behavior of asphaltene in normal alkane-toluene mixture has been under research over the past decades. However, the influence of asphaltene composition and its structure on asphaltene aggregation in such mixtures has not been fully understood yet. In this study, the colloidal behavior of asphaltene in normal alkane-toluene mixture was investigated using image processing approach. Three different types of asphaltenes were extracted from Iranian oil reservoirs. Asphaltenes were characterized by elemental analysis, X-Ray Diffraction (XRD), and Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS). The effects of asphaltene concentration, type of normal alkane, ratio of normal alkane to toluene, and structure of asphaltene on onset of asphaltene flocculation (OAF) and aggregates size were investigated. The onset of asphaltene flocculation decreases with increasing asphaltene concentration. A mathematical model was developed to predict OAF for different normal alkanes and asphaltenes. The proposed mathematical model has an exponential form with two constants, which should be tuned using experimental data. The results indicate that as asphaltene concentration increases, larger aggregates are formed with an average (AS) size between 8 and 15 μm and some aggregates greater than 100 μm may be formed. Moreover, the structure and composition of asphaltene is determinant of aggregates’ size. The lowest aggregates size refers to asphaltene C with the lowest number of fused rings, polarity, and aromaticity, which is the most stable asphaltene with the smallest aggregates size. Asphaltenes A and B have almost the same size as polarity and aromaticity both contribute to the aggregates size. The aggregates formed by n-C7 (AS≈ 7.5 to 8.5 μm) are larger than those of n-C10 (AS≈ 8.5 to 12 μm) and n-C16 (AS≈ 9 to 14 μm). In addition, increasing the ratio of normal alkane to toluene increases the size of asphaltene aggregates up to a maximum value and then gradually decreases.

Experimental and Theoretical Approach To Determine the Average Asphaltene Structure of a Crude Oil from the Golden Lane (Faja de Oro) of Mexico

The structural parameters and average molecular structures of the asphaltenes obtained from the Aguacate oilfield, located in the Golden Lane of Mexico, have been investigated combining experimenta...

Transformation of Organic Matter of Domanik Rock from the Romashkino Oilfield in Sub- and Supercritical Water

The transformation of the organic matter (OM) of low-permeable carbon-rich domanik rock of the Romashkino oilfield in sub- and supercritical water (SCW) at temperatures of 320, 374, and 420°C and pressures of 17, 24.6, and 24.4 MPa in a neutral medium has been studied. The original rock with a TOC content of 7% has a high oil generation potential and a low productivity index. The productivity index increases with an increase in the severity of the thermal treatment of the rock, which is due to intense kerogen degradation resulting in the formation of free hydrocarbons that are easy to recover from the rock. In rock extracts, in comparison with the original rock, the amount of saturated and aromatic hydrocarbons increases by more than two times and that of resin–asphaltene substances decreases. Distinctive features of the yields and compositions of rock extracts depending on the temperature of the experiments have been revealed. The highest yield of the extract was observed in the experiment with subcritical water at 320°C and associated with the degradation of resins and more complete extraction of asphaltenes and high-molecular-weight n-alkanes from the rock. Treatment in SCW at 374 and 420°C leads to intensive degradation of the kerogen structure involving the detachment of aliphatic chains from large fragments of kerogen and asphaltene macromolecules to form lower n-alkanes and carbon-rich substances, such as carbenes and carboids. The structure of asphaltenes becomes more condensed and oxidized in the SCW medium at 420°С, leading to a decrease in their paramagnetic properties. Using the EPR technique, the features of hyperfine splitting of the vanadyl complex line on 14N nitrogen nuclei have been revealed in the spectrum of asphaltenes of the SCW experiment at 420°С, indicating specific changes in their structure.

Evaluation of the effect of new-synthesized heterocyclic compounds as inhibitors of ARP deposits

This article is devoted to the studying of the problem of the resin and asphaltene deposits formation in the process of oil production and transportation using the example of high-viscosity oil from the Ashalchinskoe field. The chemical method for the prevention and removal of ARPD, connected with the use of phosphorylated alkylphenols is considered in detail. Extraction of asphaltenes was carried out by selective dilution of the oil sample following by washing in Soxhlet apparatus. Hydrocarbon structure of asphaltenes was studied by the method of IR-spectroscopy on the spectrometer PerkinElmer. Paramagnetic characteristics of asphaltenes were analyzed by EPR method. Rheological properties of oil emulsion were studied by viscosimetry method using rotational viscometer One Touch Lamy Rheology. The graphs that indicate the dependence of the viscosity of oil emulsions on applied shear stress were plotted. The method of the “cold rod” was used to evaluate the inhibitory effect of the new organic compound.

Changes in asphaltene surface topography with thermal treatment

The impact of thermal cracking reaction on asphaltene structure and morphology has been investigated by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The structural and morphological changes at a microscopic level were monitored by comparing the parent asphaltenes from different vacuum residues (VRs) to their corresponding thermally treated asphaltenes, obtained from the by-product pitch after thermal treatment. The SEM analysis indicated that the asphaltene aggregates extracted from atmospheric residues have smooth and rough surfaces with agglomerate particles and bright inclusions. The SEM images of asphaltene aggregates that are extracted from the pitch samples after mild cracking demonstrated cleavage fracture morphology with obvious reduction in inclusions sizes and intensities. The TEM analysis, on the other hand, indicated that the asphaltenes from residual oils have tangled structures, with edges similar to a cauliflower. The tangled structure is mainly credited to the alkyl side-chains that impede the aromatic sheets from stacking. At mild cracking (400 °C), the asphaltene began to exhibit well-ordered layer structures near the edges due to the rupture of the alkyl side-chains. However, the tangled structure has been preserved in the interior of the sample. As the reaction severity increases (415 °C), the stacking of aromatic sheets became more evident even in the sample interior. At the most severe cracking condition (430 °C), an obvious reduction in the cluster diameter has been observed, which mainly resulted from the reduction in the number of aromatic sheets per stack.

Investigation of asphaltene dispersion stability in slurry-phase hydrocracking reaction

Asphaltene precipitation is known as a challenging issue to fully upgrade heavy oils. In this study, asphaltene dispersion stability and sediment formation for a slurry phase hydrocracking reaction of vacuum residue was investigated with changes of temperatures (405–435 °C), LHSV (0.20–0.45 hr-1), pressures (80–180 bar) and superficial gas velocities (0.4–2.2 cm/s) in a bench-scale continuous system. The characteristics of dispersion stability were examined with the solubility parameters at the flocculation point (UV titration), the structure of the asphaltenes (H-NMR), and sediment content in the liquid product (Hot filtration). As results, it was found that the dispersion stability of asphaltene was mainly dependent on the VR conversion. In particular, at about 50% of the VR transition, the solubility was found to be unstable and the amount of deposition increased dramatically. At the same time, microscopic observation directly confirmed asphaltene flocculation. However, when H2 partial pressure was increased, the hydrogenation reaction of asphaltene was promoted so that it could reduce sediment formation and improve both the asphaltene solubility and structure for the stable dispersion. On the other hand, increasing the superficial gas velocity did not give an effect on the asphaltene dispersion stability.