Aromatic Sheets Research Articles

New indexes for thermal maturity assessment based on asphaltene fraction

The level of crude oil thermal maturity has so far been done using biomarker ratios. Despite valuable geochemical information provided by biomarker ratios, they usually face problems in thermal maturity assessment. This paper aims to introduce new indexes for thermal maturity assessment. For this purpose, three crude oil samples were heated at 100 °C for a while and then sampled. The asphaltene fractions of heated samples were analyzed by XRD and FTIR methods after precipitation. The variations of derived indexes from diffractograms and spectra indicate that aromaticity, the average diameter of aromatic sheets, and branched index increase during the heating process. In contrast, the average height perpendicular to the aromatic sheets and subsequently the average number of aromatic sheets decrease. Since these variations are concerning time and temperature, they can be considered as thermal maturity indicators. These alterations are also consistent with previous researches. In this paper, the thermal maturity of eight Iranian crude oil samples, which biomarker ratios were unable to determine their thermal maturity level, has been assessed using these novel indicators for the first time. These crude oil samples belong to three distinct genetic groups, and thermal maturity has been evaluated in all families. In the first genetic group, the Fahliyan reservoir has more mature crude oil samples than the crude oil sample of the Kazhdumi reservoir. In the second group, the Buwaib sample possesses more maturity level than Khatiah crude oil. Eventually, the Sarvak reservoir contains more mature crude oil than two other Kazhdumi samples. The final results are compatible with the other data, such as reservoir depth and API.

Study on the association driving force of low temperature coal tar asphaltenes

The aggregation of petroleum asphaltenes has been studied for decades by numerous experimental techniques, however, few studies had been performed on the special supramolecular structure of coal tar asphaltenes. In this paper, the methylation, alkylation experiments and molecular dynamics simulation were used to study the π-π interaction and hydrogen bond between coal tar asphaltenes. The results showed that the inter aromatic layer distance (Me) of asphaltenes, methylated and alkylated asphaltenes were 3.74, 2.12 and 1.73 respectively, and the average number of aromatic sheets (dm) was increased compared with asphaltenes. Asphaltenes existed in the form of aggregates in the toluene, as the concentration increased, the particle size also increased significantly, moreover, the particle size and the Me of alkylated asphaltenes are significantly less than asphaltenes, indicating that the π-π interaction was the main driving force for asphaltene association. Meanwhile, molecular simulation results showed the π-π interaction energy of asphaltenes dimers was -165.269 kcal·mol−1, which was much larger than the hydrogen bond energy -5.807 kcal·mol−1. In addition, the asphaltenes dimer layer spacing in quinoline, toluene and ethanol were 3.836 Å, 2.57 Å, and 4.783 Å respectively, which were all larger than the interlayer spacing of asphaltenes dimer 1.99 Å, and the asphaltenes dimer had a better disaggregates effect in quinolone.

Introducing a Novel Approach for Oil‐Oil Correlation based on Asphaltene Structure: X‐ray Diffraction

AbstractAsphaltenes have always been an attractive subject for researchers. However, the application of this fraction of the geochemical field has only been studied in a limited way. In other words, despite many studies on asphaltene structure, the application of asphaltene structures in organic geochemistry has not so far been assessed. Oil‐oil correlation is a well‐known concept in geochemical studies and plays a vital role in basin modeling and the reconstruction of the burial history of basin sediments, as well as accurate characterization of the relevant petroleum system. This study aims to propose the X‐ray diffraction (XRD) technique as a novel method for oil‐oil correlation and investigate its reliability and accuracy for different crude oils. To this end, 13 crude oil samples from the Iranian sector of the Persian Gulf region, which had previously been correlated by traditional geochemical tools such as biomarker ratios and isotope values, in four distinct genetic groups, were selected and their asphaltene fractions analyzed by two prevalent methods of XRD and Fourier‐transform infrared spectroscopy (FTIR). For oil‐oil correlation assessment, various cross‐plots, as well as principal component analysis (PCA), were conducted, based on the structural parameters of the studied asphaltenes. The results indicate that asphaltene structural parameters can also be used for oil‐oil correlation purposes, their results being completely in accord with the previous classifications. The average values of distance between saturated portions (dr) and the distance between two aromatic layers (dm) of asphaltene molecules belonging to the studied oil samples are 4.69Å and 3.54Å, respectively. Furthermore, the average diameter of the aromatic sheets (La), the height of the clusters (Lc), the number of carbons per aromatic unit (Cau), the number of aromatic rings per layer (Ra), the number of sheets in the cluster (Me) and aromaticity (fa) values of these asphaltene samples are 10.09Å, 34.04Å, 17.42Å, 3.78Å, 10.61Å and 0.26Å, respectively. The results of XRD parameters indicate that plots of dr vs. dm, dr vs. Me, dr vs. fa, dm vs. Lc, Lc vs. La, and fa vs. La perform appropriately for distinguishing genetic groups. A comparison between XRD and FTIR results indicated that the XRD method is more accurate for this purpose. In addition, decision tree classification, one of the most efficacious approaches of machine learning, was employed for the geochemical groups of this study for the first time. This tree, which was constructed using XRD data, can distinguish genetic groups accurately and can also determine the characteristics of each geochemical group. In conclusion, the obtaining of structural parameters for asphaltene by the XRD technique is a novel, precise and inexpensive method, which can be deployed as a new approach for oil‐oil correlation goals. The findings of this study can help in the prompt determination of genetic groups as a screening method and can also be useful for assessing oil samples affected by secondary processes.

Influence of asphaltene structural parameters on solubility

This paper investigates the influence of asphaltene’s structural parameters on its solubility, including aromatic sheet diameter and aromaticity. Aromatic sheet diameter (La) was determined by integrating the D1 and G bands of Raman spectra. Aromaticity was determined by the ratio of the integrated Fourier Infrared peaks of aliphatic carbon relative to aromatic carbon. Asphaltenes were extracted from five dead crude oils. Two types of solubility tests were conducted, with asphaltenes dissolved in both nonpolar (aromatic hydrocarbons) and polar (cyclic ethers and aromatic amines) solvents and re-precipitated using pentane; in addition to a scenario where asphaltenes were dissolved in toluene and re-precipitated using nonpolar (alkanes) and polar titrants (esters). The largest La was estimated to be 7.34 nm, while the other asphaltenes have a La within the range of 1.52–2.35 nm. La increases monotonically with aromaticity, which was inversely proportional to the hydrogen bonding capability. In terms of dispersant polarity, π-π interactions dominated, evidenced by a better asphaltene stability, which increased with aromatic core size. A reverse trend was recorded with nonpolar precipitants due to hydrogen bonding. This study argues that to inhibit the aggregation of asphaltene with large La, polar inhibitors should be used.

The effect of composition change and allocation in raw material on the carbonaceous structural evolution during calcination process

To investigate the effect of calcination process on the characteristics of different carbonaceous structures, decant oil (DO) and low-temperature coal tar (LCT) were selected as materials to refine and blend to prepare the green cokes with different microstructures, and the influence of calcination on the structural evolution of green cokes with different orientation and planarity was studied. It is concluded that the nitrogen content of calcined needle coke decreased to a relatively low value at the calcination temperature of 1300℃ and the removal of QI decreased the sulfur content in calcined cokes. Calcination process would further promote the accumulation of aromatic lamellae on the original basis. The abundant QI in LCT led to the formation of mosaic structures in green coke stage and calcination aggravated the poor planarity of aromatic sheets of mosaic texture. The refining process and blend of raw materials significantly enhanced the proportion of key components and calcination improved the extendability and planarity of graphitic aromatic sheets with the increase of Tri-Ar and Tetra-Ar. In addition, calcination further optimized the aromatic lamellae of acicular domain texture with good planarity and structural orientation, and DO-CNC obtained the highest stacking parameters (Lc = 3.55 nm; N = 11.30; d002 = 3.445 Å).

A Carbon‐Based Solid Acid Catalyst Prepared through a One‐Step Hydrothermal Carbonization: Efficient Catalysts for Liquid‐Phase Nitrification

AbstractCarbon‐based solid acid catalysts were successfully prepared by hydrothermal carbonization method and one‐pot method using naphthalene crosslinked by formaldehyde and sulfonated by H2SO4 (98 %). The characterization results showed that the catalysts prepared by hydrothermal carbonization method had more amorphous carbon composed of aromatic carbon sheets with functional groups (−SO3H, −COOH and −OH) than the catalyst prepared by one‐pot method. The preparation conditions of hydrothermal carbonization method were optimized. The F−N−SO3H‐h‐2.49 (1 : 11) prepared under optimal conditions showed high conversion of cyclohexane (48.2 %) and selectivity to nitrocyclohexan (98.2 %) at 125 °C for liquid‐phase nitrification, attributed to high acid site density (3.08 mmol/g) and amorphous carbon structure with hydrophilic functional groups. The F−N−SO3H‐h‐2.49 (1 : 11) also showed excellent thermal stability until 460 °C. The thermal stability of the catalyst is due to mutual electron‐withdrawal of aromatic carbon sheets.

Determination of asphaltene structural parameters by Raman spectroscopy

AbstractThe objective of this study is to determine the aromatic sheet diameter (La) and the number of aromatic sheets per stack (n) for asphaltene molecules from Raman spectra by investigating and optimizing empirical equations proposed in the literature for both crystalline and amorphous carbon materials. The results clearly indicated that the best empirical equation for determining the aromatic sheet diameter for asphaltene was the equation proposed by Tuinstra and Koenig, but only when the graphitization indicator ID/IG would have been determined from the peak integrated ratio, rather than from the peak intensity ratio. The best results of La were obtained when the Raman spectra were deconvoluted and fitted with three peaks using Gaussian function. The number of aromatic sheets per stack for asphaltene was also determined by examining various empirical equations proposed for crystalline carbon materials. The results indicated that these equations could be applied on asphaltene if the first‐order region of Raman spectrum were to be fitted with two peaks, representing the G and D bands. Fitting the spectra with more peaks could result in splitting the G band into two bands (i.e., G and D2 bands), which would shift the G‐band position to a wavenumber below 1581.6 cm−1, and, subsequently, prevent the utilization of these empirical equations.

Comparison of the composition and structure for coal-derived and petroleum heavy subfraction by an improved separation method

The property of coal-derived asphaltene and resin shows remarkable differences from petroleum one, such as the molecular aggregation and thermal cracking characteristics. It is significant to make deep-level analysis of their composition and structure to provide detailed molecule information for coal tar deep processing. In this paper, an improved separation method, which innovatively developed two-stage asphaltene extraction and two-stage silica gel separation coupling process, was built to obtain the purified asphaltene and resin components derived from coal tar (C-asp and C-res) and petroleum (P-asp and P-res). All samples were analyzed comparatively through Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), solid state cross polarization/magic angle spinning nuclear magnetic resonance spectroscopy (13C-CP/MAS-NMR), thermogravimetric analysis (TG) and scanning electron microscopy (SEM). It is found that C-asp and C-res contain more OH groups resulting in stronger aggregate effect and OH-OH and OH-ether O are the main hydrogen bond. C-asp and C-res have more C-O of phenols and C = O of COOH group. C-asp and C-res have fewer and shorter alkyl side chains. The aromatic ring substitutive degree (σ) of C-asp and C-res is higher while the alkyl branching degree of P-asp and P-res is higher. Besides, asphaltene has higher σ, alkyl substituents number (n), average stack height of aromatic sheet (Lc), average number of aromatic sheets associated in per stacked cluster (M) and shorter average substituted alkyl chain length (L) compared with resin. Finally, the average molecular structure models of C-asp, P-asp, C-res and P-res are obtained.

Characterization of Nanostructure Evolution in Coal Molecules of Different Ranks.

Four coals samples at different ranks were analyzed by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and solid-state 13C nuclear magnetic resonance (NMR). The calculated coal molecular model was constructed according to the experimental data. The mode of evolution of four coal molecules with different metamorphic degrees was explored. The results indicate that the nanostructures of these four coal molecules mainly consist of aromatic structures, aliphatic structures and oxygen-containing functional groups. The coal metamorphic degree is the most important factor affecting the evolution of the coal molecular nanostructure. By increasing the coal rank, the aromatic carbon content and aromatic system increase, while the aliphatic carbon content and aliphatic system decrease, and the species and content of oxygen containing functional groups are also reduced. During the evolution of the molecular microcrystalline structure, the degree of vertical order of the aromatic structural unit, the flatness of the aromatic structural unit (La), the average crystallite stacking height (Lc), and the average number of crystallites in a stack (n) increase, while the interlayer distance between aromatic sheets (d002) decreases; the short-range ordering of the coal structure is mainly caused by changes in the orientational arrangement from intramolecular aromatic layers to intermolecular aromatic layers when low-rank coal molecules evolve to high rank coal molecules. The structural evolution mechanism of coal molecules of different ranks has been revealed through the analysis of the mode of evolution of the molecular structure the coal. This study enables us to better understand the nanostructure evolution mechanism of coal molecules at different ranks.

Synthesis and Characterization of Pine-cone Derived Carbon-based Solid Acid: a Green and Recoverable Catalyst for the Synthesis of Pyrano_ pyrazole, Amino-benzochromene, Amidoalkyl Naphthol and Thiazolidinedione Derivatives

In this report, SO<sub>3</sub>H-functionalized Carbon nanoparticles (Pine-SO<sub>3</sub>H) with high acid density have been synthesized by the thermal treatment of sulfuric acid with Pine-Cone as carbon-based at 180°C in a sealed autoclave in a one-step procedure. The resulted Nanocatalyst was characterized by FT-IR, TGA, XRD, FE-SEM and elemental analysis (EA). The result of characterization was shown that the carbon-based acid is amorphous with polycyclic aromatic carbon sheets attached plentiful -OH, -COOH, and -SO<sub>3</sub>H groups. The catalytic activities of Pine-SO<sub>3</sub>H was investigated in the highly efficient synthesis of pyrano[2,3-c] pyrazole, amino-benzochromenes, amidoalkyl naphthol and 5-arylidene-2,4-thiazolidinedione derivatives. The application of Pine-SO<sub>3</sub>H in the synthesis offers several advantages such as simple procedure with an easy work-up, recoverable catalyst, mild condition, eco-friendliness, excellent yields, short reaction times and use of an inexpensive catalyst.

Chemical and structural characterisation of nC<SUB align="right">7 asphaltenes extracted from atmospheric tower bottom and low waxy crude oil from Indian reservoir

Detailed studies on asphaltenes from Indian sources are scarce. In this study, nC7 asphaltenes were extracted from an atmospheric tower bottom and a low waxy crude oil using IP143-based method and characterised using elemental analysis, nuclear magnetic resonance, Fourier-transform infrared spectroscopy, matrix-assisted laser desorption-time of flight mass spectroscopy, X-ray diffraction, and scanning electron microscopy. Results show that both asphaltenes differ widely in structures and molecular weights. It was deduced that both asphaltenes might have formed from kerogen degradation process resulting in higher oxygen content. Lower molecular weight and structural parameters (NMR) of atmospheric tower bottom asphaltene could be due to degradation of aliphatic part during preheating before atmospheric distillation process. Although dispersed, the XRD derived aromaticity of petroleum asphaltenes seems to vary inversely with stacking height and average diameter of the aromatic sheets, possibly due to compact structure of the cluster resulting from decreased stack height. [Received: September 29, 2019; Accepted: November 9, 2019]

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.

Mechanistic Approach to Thermal Production of New Materials from Asphaltenes of Castilla Crude Oil

Asphaltenes are compounds present in crude oils that influence their rheology, raising problems related to the extraction, transport, and refining. This work centered on the chemical and structural changes of the asphaltenes from the heavy Colombian Castilla crude oil during pyrolysis between 330 and 450 °C. Also, the development of new strategies to apply these macromolecules, and the possible use of the cracking products as a source of new materials were analyzed. The obtained products (coke, liquid, and gas) were collected and evaluated through the techniques of proton and carbon-13 nuclear magnetic resonance (1H and 13C NMR), elemental composition, Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), saturates, aromatics, resins, and asphaltenes (SARA) analysis, and gas chromatography–mass spectrometry (GC-MS). A comparison of the applied methods showed that the asphaltene molecules increased the average size of their aromatic sheets, lost their aliphatic chains, condensed their aromatic groups, and increased their degree of unsaturation during pyrolysis. In the liquid products were identified alkylbenzenes, n-alkanes C9–C30, and n-alkenes. Moreover, the gaseous products included methane, ethane, propane, and pentane. An approach of the structural chain reaction was used to define the possible asphaltenes chemical structures before and after pyrolysis. In conclusion, this type of thermal process can be used as an easy route to attain new materials associated with specific structural units from the asphaltenes.

Large-Amplitude Conformational Changes in Self-Assembled Multi-Stranded Aromatic Sheets.

The orchestration of ever larger conformational changes is made possible by the development of increasingly complex foldamers. Aromatic sheets, a rare motif in synthetic foldamer structures, have been designed so as to form discrete stacks of intercalated aromatic strands through the self‐assembly of two identical subunits. Ion‐mobility ESI‐MS confirms the formation of compact dimers. X‐ray crystallography reveals the existence of two distinct conformational dimeric states that require large changes to interconvert. Molecular dynamics simulation validates the stability of the two conformations and the possibility of their interconversion.

ORR and OER of Co–N codoped carbon-based electrocatalysts enhanced by boundary layer oxygen molecules transfer

Two-step carbonization method was reported to synthesize Co–N doped coal tar pitch (CTP) carbon-based electrocatalysts with hierarchical pore structure, high local order degree and efficient Co-Nx active structure simultaneously. The synergistic effect of the carbon substrate with highly ordered structure and the Co-Nx active sites realized the “Point discharge effect”. The π-π interactions from the CTP aromatic ring sheets and Co-Nx promoted the adsorption and dissociation of oxygen molecules, respectively. The increased diffusion coefficient (D0) indicated the mass transfer of oxygen molecules in the boundary layer was enhanced during the ORR process. Thanks to excellent structural characteristics, ACTP5@Co,N-800 exhibited better ORR performance than commercial Pt/C catalyst under alkaline conditions, and the OER activity was improved simultaneously. This work demonstrated a simple and practical strategy for the development of advanced carbon-based electrocatalysts, and also provided novel insights from kinetics perspectives for improving electrocatalytic efficiency.

A multi-tool structural change investigation of Indian vitrinite rich bituminous coal due to CS2/NMP interaction

Solvents are important constituent in the coal liquefaction process as they act as hydrogen donors and serve as hydrogen shuttles between hydrogen and coal. A mixture of carbon disulfide (CS2) and N- methyl-2-pyrrolidinone (NMP) (1:1, v/v) was used as a solvent for a study of an Indian coal that was kept for swelling. The study of coal swelling provides valuable information, such as, determining the highest energy bond that can be broken by a particular solvent or by a mixture of solvents. It can be concluded from the results that maximum swelling and extraction yield are achieved by a CS2/NMP mixed solvent. The structure change of coal before and after its interaction with the solvent was also studied using techniques such as Fourier-transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), and X-ray powder diffraction (XRD). FTIR indicated that the mixed solvent caused a decrease in the solvent viscosity, enabling the solvent to penetrate more quickly into the coal structure. XRD structural parameters concluded a decrease in aromaticity and stacking height and an increase in the interplanar spacing of raw coal after the swelling process. This was due to a decrease in the crystalline carbon along with an increase in amorphous carbon. XRD results indicated that the four parallelogram-shaped aromatic sheets were parallelly connected. This was also clearly observed in HRTEM images. This work will be helpful in the understanding and development of coal liquefaction technology.

Synthesis and evaluation of a hyperbranched copolymer as viscosity reducer for offshore heavy oil

As is well known, resin and asphaltene greatly increase the viscosity of the oil, which causes difficulty for heavy oil to flow and to be displaced. Therefore, reducing the viscosity of heavy oil effectively is the key to enhance oil recovery. A hyperbranched copolymer named as HVR grafted with hydrophilic surfactant monomers, was synthesized and evaluated in this paper as an alternative to reduce the offshore heavy oil viscosity. The synthesis method of HVR through free-radical copolymerizing using the third generation polyamidoamine dendrimer, acrylamide, acrylic acid and surfactant monomers in deionized water was detailed in this paper. Thereupon the characterization of HVR were described by Fourier transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy. The physical properties of HVR solution including apparent viscosity, oil viscosity reducing ability, interfacial tension were comprehensively studied. Otherwise the effect of HVR on sheet structure of asphaltene aggregate and asphaltene aggregation inhibition-dispersion activity were measured by X-ray diffraction and ultraviolet–visible spectrophotometer, respectively. The results indicate that apparent viscosities of HVR solution is relatively not high. For example, after shearing with a Waring blender at 3500 rpm for 20 s, the viscosity of 2500 ppm HVR solution is only 22.7 cP. However, the HVR solution has a relatively high viscosity remaining rate, which is approximately 58%. On the other hand, HVR solution has a good viscosity reducing ability on heavy oil. For the oil viscosities from 350 cP to 500 cP, the viscosity reduction rate of HVR at 2000 ppm is approximately 97% under the oil-water ratio of 3:7. In addition, the oil-water interfacial tension can be reduced by HVR solution at the concentration of 2500 ppm to 1.61 × 10−2 mN m−1. Comparing the asphaltene aggregates after interacting with HPAM and HVR, it illustrates that the layer spacing, interchain distance and diameter of the aromatic sheets are lager if interacting with HVR; meanwhile height of the aromatic clusters and effective number of aromatic sheets are smaller due to the reaction with HVR. In addition, if compared with the asphaltene treated by HPAM, with the increase of HVR concentration, the absorbance of asphaltene in toluene treated by HVR solution decreased significantly. Overall, this new hyperbranched copolymer shows potential for applications in heavy oil viscosity reduction.

Pyrolysis of Asphaltenes Derived from Residual Oils and Their Thermally Treated Pitch.

Thermogravimetric analysis (TGA) was employed to investigate the thermal stability of asphaltenes at different environments (inert and oxidizing atmosphere) and identify their refractory nature. TGA and differential scanning calorimetry were carried out at a temperature range of 50–700 °C, for asphaltene samples obtained from atmospheric residues, vacuum residues (VRs), and aromatic petroleum pitch samples, which were obtained from the cracking of VRs at different temperatures. The TGA results clearly indicate that thermal degradation of asphaltene takes place in a single process that starts around 350 °C and ends at 500 °C, giving ash contents of less than 2%. The derivatives of the TGA for the asphaltene samples suggest that the weight loss of composite material took place in two steps. The first step corresponds to the degradation of aliphatic side chains or easily oxidized hydrocarbons, while the second step corresponds to the degradation of the aromatic sheets or the stacked layers. TGA of asphaltenes in oxidizing atmosphere showed considerable changes in heat flow due to the destructive oxidation of the asphaltene molecular structure. The thermal stability or refractory nature of these asphaltenes have been calculated as heat of energy or enthalpy of the molecule, which corresponds to the π–π interaction between the aromatic ring, hydrogen bonding, and alkyl chain size of the asphaltene molecule.

Molecular Model Construction and Evaluation of Jincheng Anthracite.

Despite its importance, limited representations of the anthracite models have been developed. The first molecular representation of Chinese Jincheng anthracite with the incorporation of diverse molecular structures was constructed based on the available analytical data. Three hundred individual aromatic sheets were first built based on the aromatic fringe distribution obtained from high-resolution transmission electron microscopy. Alkyl chains and nitrogen, sulfur, and oxygen heteroatoms were added in the aromatic skeletons to form diverse anthracite structural units based on 13C NMR, X-ray photoelectron spectroscopy, and ultimate analyses. Fifty-five different anthracite molecules were formed by covalent cross-linking considering the constraint imposed by the molecular weight distribution of the Jincheng anthracite obtained from laser desorption time-of-flight mass spectrometry (LD-TOF MS). These molecules were packed into a three-dimensional cell to form a Jincheng anthracite model (C7730H3916O133N123S25). We showed that the proposed model can provide a reasonable representation of the Jincheng anthracite by comparing the simulated and experimental magnetic resonance spectroscopy, LD-TOF MS, density, and X-ray diffraction data. Because of the large, molecularly diverse structure, many anthracite behavioral processes can be further explored using this model in the future.

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.