Coal Asphaltenes Research Articles

Liquefaction of Hongliulin coal asphaltenes and conversion of oxygenic structure

Based on the multistage liquefaction process, asphaltene was prepared from Hongliulin coal and deeply liquefied with Ni-Co-Mo, Co-Mo, and Fe2O3 catalysts. The yields of each component were obtained. Ultimate analysis, FT-IR and XPS was used to investigate the conversion of oxygenic structure. The results showed that the ability to catalyze asphaltene conversion was ranked as Ni-Co-Mo > Co-Mo > Fe2O3 in the range of 440–480 °C. The highest oil yield was 44.31% at 470 °C with Ni-Co-Mo catalyst. Ni-Co-Mo catalyst could effectively increase the H/C ratio and reduce the oxygen content of asphaltene, which had a strong correlation with the trend of oil yield. The main forms organic oxygen in remaining asphaltene after liquefaction were C = O, C-O and COO and the contents decreased sequentially. Ni-Co-Mo could catalyze the cleavage of C = O significantly to form a large amount of C-O and improve the oil yield after 460 °C. The C-O content was about 34% in remaining asphaltene, which was mainly a relatively stable aromatic ether structure and was not susceptible to hydrocracking reactions.

Application of the Y-Rule and Theoretical Study to Understand the Topological and Electronic Structures of Polycyclic Aromatic Hydrocarbons from Atomic Force Microscopy Images of Soot, Coal Asphaltenes, and Petroleum Asphaltenes

Application of the Y-Rule and Theoretical Study to Understand the Topological and Electronic Structures of Polycyclic Aromatic Hydrocarbons from Atomic Force Microscopy Images of Soot, Coal Asphaltenes, and Petroleum Asphaltenes

The effects of solvent extraction on nanoporosity of marine-continental coal and mudstone

Coal and organic-rich mudstone develop massive nanopores, which control the storage of adsorbed and free gas, as well as fluid flows. Generation and retention of bitumen and hydrocarbons of oil window reservoirs add more uncertainty to the nanoporosity. Solvent extraction is a traditional way to regain unobstructed pore networks but may cause additional effects due to interactions with rocks, such as solvent adsorbing on clay surfaces or absorbing in kerogens. Selected marine-continental coal and mudstone in Eastern Ordos Basin were studied to investigate how pore structures are affected by these in-situ-sorptive compounds (namely residual bitumen and hydrocarbons) and altered by solvent extractions. Solvent extraction was performed to obtain bitumen-free subsamples. Organic petrology, bulk geochemical analyses and gas chromatography were used to characterize the samples and the extracts. Low-pressure argon and carbon dioxide adsorptions were utilized to characterize the nanopore structures of the samples before and after extraction. The samples, both coal and mudstone, are in oil windows, with vitrinite reflectance ranging from 0.807 to 1.135%. The coals are strongly affected by marine organic input, except for the sample C-4; the mudstones are sourced by either marine or terrestrial organic input, or their mixture. As for the coals affected by marine organic input, residual bitumen and hydrocarbons occupying or blocking pores <10 nm becomes weak with thermal maturation. Bitumen derived from terrestrial organic matter mainly affects small pores, since coal asphaltene molecules are much smaller than petroleum asphaltene molecules. The mudstone M-2 with high extract production showed an increase of nanopores after extraction, due to the exposure of the filled or blocked pores. However, most transitional mudstones saw decreases of the pores because pore shrinkage caused by solvents adsorbing on and swelling clay minerals (mainly kaolinite and illite/smectite mixed layers) counteracts the released pore spaces. Solvent extractions on the coals significantly increased the micropores <0.6 nm, since the heat of sorption of alkanes reaches the peak in the pores within 0.4–0.5 nm. By contrast, solvent extractions on the mudstones decreased the micropores ∼0.35 nm, which is perhaps caused by evaporative drying of solvent displacing residual water in clay.

Investigation on the structure of low-temperature coal tar asphaltene precipitated with different n-alkane solvents

ABSTRACTTo study the effects of deasphalting solvents on asphaltene, n-pentane asphaltene (As-5), n-heptane asphaltene (As-7), and soluble in n-heptane but insoluble in n-pentane asphaltene (As-(5–7)) were precipitated from low-temperature coal tar. Gel Permeation Chromatography (GPC), nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) are used to analyze their structure. The results show that As-(5–7) is composed of the aromatic layer periphery of As-5, so the aromatic degree of As-(5–7) is lower and the content of alkyl and naphthenic base groups is larger. What is more, the aromatic ring consistency and condensation degree of As-(5–7), As-5, and As-7 increase gradually, so their coking potential and hydrogenating difficulty increase.

Laser-Based Mass Spectrometric Determination of Aggregation Numbers for Petroleum- and Coal-Derived Asphaltenes

Petroleum- and coal-derived asphaltenes have been studied with three laser-based mass spectrometric techniques: laser desorption ionization–mass spectrometry (LDI–MS), in which a single laser desorbs and ionizes solid analytes; surface-assisted laser desorption ionization–mass spectrometry (SALDI–MS), in which a single laser desorbs and ionizes solid analytes from an activated surface; and laser desorption laser ionization mass spectrometry (L2MS), in which desorption and ionization are separated spatially and temporally with independent pulsed laser sources. We find that asphaltene nanoaggregates can be detected in LDI–MS and SALDI–MS under mild conditions of relatively low laser power, whereas L2MS avoids aggregation and fragmentation, detecting asphaltenes as monomeric molecules. A comparison of the L2MS and SALDI–MS results yields an estimate of the distribution of aggregation numbers (number of molecules comprising the nanoaggregate). The most probable aggregation number observed for nanoaggregates of petroleum asphaltenes is approximately 6–8 molecules, consistent with the Yen–Mullins model of asphaltenes and predictions from the island geometry for asphaltene molecules. Additionally, the nanoaggregates are found to be relatively monodisperse, because most aggregates observed have aggregation numbers within one molecule of the most probable. In contrast, the nanoaggregates of coal asphaltenes are found to be smaller and more polydisperse, with aggregation numbers ranging from 3 to 6 molecules. Under higher powers, SALDI–MS measurements show that nanoaggregates decompose to form small multimers and monomers, suggesting that the aggregates are bound noncovalently. Coal asphaltene nanoaggregates decompose at lower laser powers than petroleum asphaltene nanoaggregates, indicating that the coal asphaltene nanoaggregates are bound less strongly than petroleum asphaltene nanoaggregates.

Simulation of the destructive hydrogenation of coal asphaltene (Short Communication)

Data of the computer simulation of the destructive hydrogenation of coal asphaltene are reported. These data were obtained by quantum-chemical methods for refining the geometric configurations of the asphaltene molecule and its radical fragments (UPM3) and the directions of the unimolecular thermal degradation and hydrogenation of a radical fragment (UHF/6-311 + G(d,p)).

Comparison of the Structures of Molecules in Coal and Petroleum Asphaltenes by Using Mass Spectrometry

Asphaltenes are a complex mixture of aromatic compounds that are present in petroleum and liquefied coal and have unknown molecular structures. Determination of the molecular structures of asphaltenes is greatly hindered by the extreme complexity of the mixtures. The average molecular weight of coal asphaltenes is known to be roughly half that of petroleum asphaltenes. In this study, tandem mass spectrometry experiments were used to compare the fragmentation patterns of molecular ions of the same mass-to-charge (m/z) value derived from coal and petroleum asphaltenes. The fragmentation pathways of the asphaltene ions were used to determine structural differences between the two types of asphaltenes. This type of analysis is new to the field of asphaltenes research and has not yet been utilized to compare coal and petroleum asphaltenes. Thus, this study was performed to both confirm its viability as well as further corroborate previous data gathered using different techniques. The results reported here demonstrate that the molecules in coal asphaltenes have shorter alkyl chains and larger aromatic cores than their petroleum-derived counterparts with the same molecular weight (MW). Furthermore, they have a higher aromatic-to-alkane carbon ratio, independent of the MW. However, the typical petroleum and coal asphaltenes (when considering the most abundant molecules in each) have a similarly sized aromatic core (∼8 rings), but very different total lengths of the alkyl side chains (∼4 for coal asphaltenes, ∼22 for petroleum asphaltenes).

Coal-derived liquid asphaltenes diffusion and adsorption in supported hydrotreating catalysts

Hindered diffusion and adsorption phenomena of coal asphaltenes inside the porous network of hydrotreating catalysts are discussed in this paper. After solvent extraction from a coal-derived liquid and solubilization in THF, asphaltenes were contacted with a series of mesoporous hydrotreating catalysts and adsorption–diffusion phenomena recorded by UV–Vis spectroscopy measurements. The effect of the porosity of various NiMo(P) catalysts supported on monomodal mesoporous or bimodal (meso–macro) alumina carrier was investigated. The parameters estimations have been performed, discussed and those obtained with the bimodal (meso–macro) alumina catalyst have been compared to petroleum asphaltenes data [31]. The range of studied concentrations corresponds to cluster formation domain. The results evidence that coal asphaltenes aggregates are smaller, have lower molecular weight and exhibit a much higher diffusion coefficient than petroleum asphaltene aggregates. These results bring important insights for the interpretation of the performance of the catalysts during coal-derived liquid upgrading. Concerning adsorption phenomena, the adsorption constants of coal asphaltenes and petroleum asphaltenes have been found equivalent. The adsorption saturation concentration of coal asphaltenes is higher than that of petroleum asphaltenes. The effective diffusion coefficients obtained at ambient temperature were correlated to the catalytic performances observed during coal-derived liquid hydrotreatment. It points out that the conversion of coal-derived liquid into the porous network of our catalyst is a hindered phenomenon, and that pore size distribution of the support has a great influence on the hydroliquefaction efficiency.

The thermal evolution of asphaltene-bound biomarkers from coals of different rank: A potential information resource during coal biodegradation

Asphaltenes from coals of different rank were oxidised using ruthenium tetroxide with the aim of investigating the changes in bound biomarker distributions as a function of increasing maturity. There is preliminary evidence for epimerization of bound hopanoid biomarkers from the biological configuration into the more stable geological configuration. The 22R↔22S epimerization in the bound 17α(H),21β(H) homohopanoids lags behind the corresponding isomerization in the maltenes between mean vitrinite reflectance (Ro) values of ca. 0.5% to 0.7%. In general, the asphaltenes evolve towards a more thermally stable structure with decreasing amounts of aliphatic moieties and increasing amounts of lower molecular weight side chains relative to the higher molecular weight ones. Bound biomarkers in coal asphaltenes could be important sources of information particularly where free hydrocarbon biomarkers have been altered or completely lost to biodegradation which occurs during the generation of microbial gas.

No.1 アスファルテン分子サイズの拡散係数に基づく評価(構造,重質油,その他)

No.1 アスファルテン分子サイズの拡散係数に基づく評価(構造,重質油,その他)

Molecular-Weight Distributions of Coal and Petroleum Asphaltenes from Laser Desorption/Ionization Experiments

Molecular-weight distributions (MWDs) of asphaltenes extracted from coal and petroleum have been measured in laser desorption/ionization (LDI) mass spectrometric experiments. The dried-droplet and solvent-free sample preparation methods are compared. The coal asphaltenes have a relatively narrow MWD (full width ≈ 150 amu) with an average molecular weight of ≈340 amu. The petroleum asphaltenes display a broader MWD (full width ≈ 300 amu) and are heavier on average (≈680 amu). The LDI spectra also provide evidence for the formation of noncovalent clusters of the two types of asphaltenes during the desorption process. Petroleum and coal asphaltenes exhibit aggregation as do large model polycyclic aromatic hydrocarbons (PAHs) with five or more fused rings also included in the study. Smaller PAHs (pyrene) exhibit less aggregation, especially when alkane-chain substituents are incorporated to the molecular structure. This indicates that asphaltenes possess large PAHs and, according to the relatively small molec...

Diffusivity of coal and petroleum asphaltene monomers by fluorescence correlation spectroscopy

Abstract Using fluorescence correlation spectroscopy (FCS) we measure the translational diffusion coefficient of Iino coal asphaltenes and UG8 petroleum asphaltenes dispersed in toluene at extremely low concentrations (0.03–3.0 mg/L). Using a simple scaling argument we compare them with several molecules of known size and molecular weight. We find that Iino coal asphaltene molecules – which have a comparatively small alkane fraction – have a diffusion constant of 1.5 × 10−5 cm2/s and corresponding hydrodynamic radius close to 0.25 nm: making them significantly smaller than petroleum asphaltenes.

Molecular size and weight of asphaltene and asphaltene solubility fractions from coals, crude oils and bitumen

The molecular weight of asphaltenes has been a controversy for several decades. In recent years, several techniques have converged on the size of the fused ring system; indicating that chromophores in virgin crude oil asphaltenes typically have 4–10 fused rings. Consequently, the molecular weight debate is equivalent to determining whether asphaltenes are monomeric (one fused-ring system per molecule) or whether they are polymeric. Time-resolved fluorescence depolarization (FD) is employed here to interrogate the absolute size of asphaltene molecules and to determine the relation of the size of the fused ring system to that of the corresponding molecule. Coal, petroleum and bitumen asphaltenes are compared. Molecular size of coal asphaltenes obtained here by FD-determined rotational diffusion match closely with Taylor-dispersion-derived translational diffusion measurements with UV absorption [1]. Coal asphaltenes are smaller than petroleum asphaltenes. N-methyl pyrrolidinone (NMP) soluble and insoluble fractions are examined. NMP soluble and insoluble fractions of asphaltenes are monomeric. It is suggested that the ‘giant’ asphaltene molecules reported from SEC studies using NMP as the eluting solvent may actually be the expected flocs of asphaltene which are not soluble in NMP. Data is presented that intramolecular electronic relaxation in asphaltenes does not perturb FD results.

Size and shape of a coal asphaltene studied by viscosity and diffusion coefficient measurements

Hydrodynamic properties, such as intrinsic viscosity and diffusivity, were measured to investigate the solution state characteristics of coal-derived materials in three organic solvents: toluene, pyridine, and N-methyl-2-pyrolidinone. A coal-derived asphaltene was prepared using coal liquefaction residue and was used as the solute. The translational diffusion coefficient of the coal-derived asphaltene was determined using the Taylor dispersion technique. The sphere equivalent hydrodynamic radius of the coal asphaltene was estimated to be 0.6–0.8 nm, depending on the solvent. The combined intrinsic viscosity and diffusion coefficient data suggest that the shape of coal asphaltene can be modeled as a prolate ellipsoid.

MOLECULAR SIZE AND STRUCTURE OF ASPHALTENES

Fluorescence depolarization measurements are used to determine the size of asphaltene molecules and of model compounds for comparison. Mean molecular weights of 750 amu have been found for petroleum asphaltenes. A strong correlation is established between the size of fused rings in asphaltene molecules and the overall size of these molecules, showing that asphaltenes have one or perhaps two fused ring systems per molecule. Coal asphaltene molecules are found to be much smaller than petroleum asphaltenes.

Molecular Size and Structure of Asphaltenes from Various Sources

Fluorescence depolarization measurements are used to determine the size of asphaltene molecules and of model compounds for comparison. Mean molecular weights of roughly 750 amu with a range of roughly 500−1000 amu are found for petroleum asphaltenes. A strong correlation is established between the size of an individual fused ring system in an asphaltene molecule and the overall size of this corresponding molecule, showing that asphaltene molecules have one or perhaps two fused ring systems per molecule. Subtle differences in molecular size are found for different virgin crude oil asphaltenes and for a vacuum resid asphaltene. Coal asphaltene molecules are found to be much smaller than petroleum asphaltenes. The molecular sizes of resins and asphaltenes are found to form a continuous distribution.

99/00013 Characterization of tar, char and gas from pyrolysis of coal asphaltenes

99/00013 Characterization of tar, char and gas from pyrolysis of coal asphaltenes

Characterization of tar, char and gas from pyrolysis of coal asphaltenes

Asphaltenes generated by a multiple precipitation procedure were found to contain n-alkanes from C14 to C31, which show an odd over even preference. This result further indicates that alkyl chains or alkylene bridges appear mostly as substituents in the coal macromolecular network. Comparison of the elemental analysis and surface area of pyrolysis chars shows that the surface areas correlate well with the heteroatom content of chars and that of the original coals as well. However, the gasification reactivity in carbon dioxide of ash-free chars cannot be interpreted in terms of their surface area. During the pyrolysis of asphaltenes, chars were formed via the mesophase route. The polarized light optical microscopy of chars confirmed that fluidity of the carbonization system is a major factor controlling the optical texture of resultant chars. Pyrolysis of asphaltenes showed that most of the gaseous components are formed by the cleavage of weak bonds like aryl-alkyl-ethers and strong bonds, mainly methylene and biarylether bridges between the aromatic moieties and methyl groups on the aromatic rings in asphaltene structure.

Original preasphaltenes and asphaltenes in coals

The preasphaltene (PA) and asphaltene (A) fractions from untreated coal show a direct relationship of PA/A (w/w) to the carbon content of coal. Their thermal stability was investigated by in-situ pyrolysis FTIR, and the results show that PA has higher thermal stability than A. By means of a vacuum FTIR method, five types of hydrogen bonds formed by hydroxyl groups were clearly observed in PA and A, i.e., OH- π, self-associated OH, OH–ether oxygen, cyclic OH groups, and OH–N. The self-associated OH and OH–ether oxygen are the two main hydrogen bonds. The insolubility of PA in benzene and A in hexane is determined by the hydrogen bond strengths of the acid/base fraction but is not strongly related to their structural parameters and molecular weight. The acid/base associated strength of preasphaltenes and asphaltenes is estimated to be within the following ranges, asphaltenes, <5.15 kJ/mol; preasphaltenes, 5.15–30.9 kJ/mol.

DIFFUSION-CONTROLLED ADSORPTIVE UPTAKE OF COAL AND PETROLEUM ASPHALTENES IN A NiMo/Al2O3 HYDROTREATING CATALYST

In this work, hindered diffusion of one coal and two petroleum asphaltenes was studied by adsorptive uptake in THF from a bath surrounding a NiMo/Al2O3 catalyst. A mathematical model for the adsorption-diffusion of asphaltenes was developed. The model parameters were obtained by simulating the experimental data with the model solution. Several asphaltene fractions were defined via SEC (Size Exclusion Chromatography), with the molecular weight of each fraction being determined by its elution characteristics. It was found that both the coal and petroleum asphaltenes have very broad molecular weight distributions; however, the molecular weights of the coal asphaltenes (50-2000) were much smaller than those of the petroleum asphaltenes (200-30000). The uptake rates for asphaltene fractions with different molecular weights varied, depending on their diffusion rates and adsorption constants. Simulation results showed that even though the properties of coal and petroleum asphaltenes were quite different, the values of model parameters for the fractions of the three asphaltenes had the same trend and could be estimated by same numerical expressions; with increasing molecular weight of the fraction, the adsorption constant monotonically increased, and the effective diffusivity decreased. The experimental uptake data for the three asphaltenes as a function of molecular weight were well represented by same mathematical model.