Comparison of the chemical structure of coal hydrogenation products,athabasca tar sand bitumen and Green River shale oil

Coal hydrogenation products, Athabasca tar sand bitumen, and Green River shale oil produced by retorting were analyzed by the Brown—Ladner method and the Takeya et al. method on the basis of elemental analysis and ¹H-NMR data, by ¹³C-NMR spectroscopy and by FT-IR spectroscopy. Structural characteristics were compared.The results show that the chemical structure of oils from Green River shale oil and Athabasca tar sand bitumen, and the oils produced in the initial stage of hydrogenation of Taiheiyo coal and Clear Creek, Utah, coal is characterized as monomers consisting of units of one aromatic ring substituted highly with C_3–6 aliphatic chains and heteroatom-containing functional groups. The chemical structure of asphaltenes from Green River shale oil and Athabasca tar sand bitumen is characterized by oligomers consisting of units of 1–2 aromatic rings substituted highly with C_3–5 aliphatic chains and heteroatom-containing functional groups. The chemical structure of asphaltenes from coal hydrogenation is characterized by dimers and/or trimers of unit structures of 2 to 5 condensed aromatic rings, substituted moderately with C_2–5 aliphatic chains and heteroatom-containing functional groups.The close agreement between fa(¹H-NMR) and fa(¹³C-NMR) for Green River shale oil derivatives and Athabasca tar sand derivatives indicates that the assumption of 2 for the atomic H/C ratio of aliphatic structures is reasonable. For coal hydrogenation products, a value of 1.6–1.7 for the H/C ratio of aliphatic structures would be more reasonable.     

Characterisation of aliphatic chains in vacuum residues (VRs) of asphaltenes and resins using molecular modelling and FTIR techniques

Asphaltenes are the main components of crude oil, and their chemical structures are very difficult to be analysed and characterised. Fourier Transform Infrared Spectroscopy (FT-IR) is one of the available analytical methods for interpreting the structure of asphaltenes and it has been used to characterise functional groups in these compounds. In the present work, FT-IR spectra of alkyl-benzenes, obtained both experimentally and theoretically (by quantum mechanic modelling), were studied using a semi-empirical software AM1. Based on these spectra, the linear relationship between the intensity ratios at 2927 and 2957 cm^− 1, and the ratios nCH₂ / mCH₃ from carbon chains of alkyl-benzenes, have been analysed to determine the terminal aliphatic chains of asphaltenes. This methodology was satisfactorily evaluated using molecular average structures found in the literature. Also, using both theoretical IR and experimental DRIFTS spectra, with deconvolution, the relationship between methylene and methyl groups, which are part of the aliphatic chains, were calculated for three types of Brazilian vacuum residue asphaltenes.     

Estimation of aliphatic H/C ratios for coal liquefaction products by spin-echo 13C n.m.r.

The direct estimation of aliphatic H/C ratios for coal liquefaction products using a part-coupled spinecho (PCSE) ¹³C n.m.r. method is described. The method, which enables proportions of aliphatic C, CH, CH₂ and CH₃ groups to be deduced, has been applied to a low molecular weight (<200) aromatic fraction of hydrogenated anthracene oil (HAO) and to higher molecular weight (?280) aromatic and asphaltene fractions of supercritical gas (SCG) extracts and a hydrogenation residue (pitch). Aliphatic H/C ratios for these occur in the range 1.9-2.3, the SCG extract fractions having the highest values because they contain significantly more CH₃ and less CH than the HAO and pitch fractions.     

Fate of aliphatic groups in low-rank coals during extraction and pyrolysis processes

Information on the nature of aliphatic groups in some bituminous coals and lignites was obtained by determining their fate during extraction and pyrolysis processes of differing severity. Aromatics (neutral oils) and asphaltenes from supercritical gas and hydrogen-donor solvent extracts and from pyrolysis and hydropyrolysis tars have been characterized by an n.m.r.-based structural analysis method which identifies hydroaromatic, methyl and long alkyl (?C₈) groups. The results indicate that methyl and other alkyls account for about half of the aliphatic carbon, long alkyl chains being the major aliphatic group in the lignites. There is evidence to suggest that some of the long alkyl chains are joined to aromatic structures. Hydroaromatic groups are small consisting of only 1–2 rings and account for less of the aliphatic carbon in bituminous coals than previously thought. Their concentrations and those of long alkyl chains in the aromatics and asphaltenes generally decrease with increasing process severity.     

Aromatic products of 340 °C supercritical-toluene extraction of two Turkish lignites: an n.m.r. study

Fractions of Elbistan and Seyitomer (Turkish) lignites, extracted with supercritical toluene at 340 °C and 8 MPa, have been separated by solvent extraction and silica-gel chromatography. Analyses by n.m.r. and i.r. spectroscopies and other methods have been combined in structural-analysis schemes to yield information about the average molecule in aromatic extracts. Carbon aromaticities, f_a, derived from 22.63 MHz ¹H-decoupled pulse Fourier-transform (PFT) ¹³C-n.m.r. are more widely spread for Elbistan (0.34–0.56) than for Seyitomer (0.40–0.43), and are lower than for supercritical-gas (SCG) products from bituminous coals. ¹³C-n.m.r. also reveals the presence of aromatic ether-O in polar fractions. Narrow aromatic signals in 100 MHz ¹H-n.m.r. spectra suggest the presence of single-aromatic-ring average structures. In the hexane-soluble aromatics, 27% (Elbistan) and 29% (Seyitomer) of the available sites are substituted by alkyI groups, some of which are at least eight carbon atoms long; the hexane-soluble polar and asphaltene/asphaltol fractions contain fewer such groups.     

Hydrotreating catalyst deactivation by coke from SRC-II oil

Samples of a CoMo/Al₂O₃ catalyst were partially deactivated with SRC-II feed in an autoclave reactor to give coked samples of 5 to 18 %C. The coked catalysts were analyzed for surface area, pore volume, coronene adsorption and diffusivity, and their catalytic activity determined for hydrodesulfurization (HDS), hydrodeoxygenation (HDO) and C-N hydrogenolysis (CNH) using model compounds. All of the above measurements decreased with increase in coke content. Property data indicate that some pores are blocked by coke and diffusivity results show narrowing of pore mouths with increasing coke content. Catalyst deactivation versus coke level was identical for HDS and HDO, but less for CNH. A simple model of coke deactivation was developed to relate activity to coke content. Coke is envisioned as forming wedge-like deposits in the catalyst pores.     

Characterization of coal liquids by 13C n.m.r. and FT-i.r. spectroscopy — fractions of oils of SRC-I and asphaltenes and preasphaltenes of SRC-I and SRC-II

Coal-derived products of SRC-I liquefaction of Blacksville coal and vacuum tower bottoms (VTB) of SRC-II liquefaction of Powhatan mine coal (both bituminous and from the Pittsburgh Seam) were separated into fractions by solvent extraction. The SRC-I was first extracted with ethylacetate, and solubles were subsequently separated into oils and a mixture of asphaltenes and preasphaltenes (APA). The VTB was Soxhlet extracted with pentane to remove any residual oils, followed by tetrahydrofuran to recover APA. The APA portions were then separated by sequential elution solvent chromatography (SESC) into fractions differing in chemical functionality, and then examined by ¹³C n.m.r. and FT-i.r. spectroscopic techniques. APA are intermediates and end products of coal liquefaction. SRC-II APA are of higher molecular weight than the APA of SRC-I. The lower numbered fractions of APA of SRC-I in SESC separation have the same functional groups as the corresponding fractions of middle and heavy distillates. However, the higher numbered fractions are rich in oxygen, which is mainly in carbonyl groups. Part of the carbonyl groups are in esters which cross-link aromatic clusters. Therefore, APA and the coal itself are ‘oligomeric’ in structure, with aromatic clusters linked by carbon bridges with different functional groups. The nature of carbonyl groups in APA has been analysed in detail.     

Dependence of coal liquefaction behaviour on coal characteristics. 7. Structural differences between coals of different rank and the asphaltenes derived from them

Aslphaltenes are difficult to characterize by any procedure that involves chromatography. In an attempt to obtain useful information on unfractionated asphaltenes and their structural relations to their parent coals, asphaltenes from a set of eight coals of hvA rank and different coalification history have been studied by ¹ H n.m.r. In addition, structural features in the coals and their asphaltenes were compared by g.c.-m.s. analysis of the products of oxidation by pertrif luoroacetic acid. Protons α to a benzene ring are the most abundant in the asphaltenes, and their relative concentration changes little with the rank of the parent coal. Protons in the β-position are abundant, however, and may be associated with aliphatic junctions linking two or more aromatic ring systems. Whereas malonic and ethane-trioic acids are the major aliphatic di-and tri-acids from oxidation of the coals, succinic and propane-or butane-tricarboxylic acids are the corresponding products that dominate the distributions from the asphaltenes. These and other differences help to define the structural changes caused by liquefaction. In addition, the results indicate the nature of structural changes with increasing rank, which are manifest in the oxidation products from the asphaltenes as well as from the coals.     

The chemical nature of material released from coal-derived asphaltenes by reprecipitation and cyclohexane extraction

The yields and chemical nature of n-pentane solubles released from three coal-extract asphaltenes by reprecipitation with n-pentane and cyclohexane extraction have been investigated. With increasing concentration of n-pentane solubles in the original coal liquid, the yield of oils obtained by reprecipitation increases, as also does the tendency for their structures to resemble those of the original n-pentane solubles. No alkanes below C₄₀ were released from the asphaltenes by extraction with cyclohexane and therefore the long alkyl chains (10% of the total carbon in the lignite asphaltenes) must be bound to aromatic, carboxyl or heteroatomic groups.     

Biomimetic sequestration of carbon dioxide using an enzyme extracted from oyster shell

Carbon dioxide sequestration activity was compared and evaluated using bovine carbonic anhydrase (BCA), and a water soluble protein extract derived from hemocytes from diseased shell (HDS). Para-nitrophenyl acetate (p-NPA) was used to measure the reaction rate. The k _cat /K _m values obtained from the Lineweaver-Burk and Michaelis-Menten equations were 230.7M⁻1s⁻¹ for BCA and 194.1M⁻s⁻ for HDS. Without a biocatalyst, CaCO₃ production took 15 seconds on average, while it took 5 seconds on average when BCA or HDS were present, indicating an approximately 3-fold enhancement of CaCO₃ production rate by the biocatalysts. The biocatalytic hydration of CO₂ and its precipitation as CaCO₃ in the presence of biocatalysts were investigated.     

Quantitative aspects of solid state 13C n.m.r. of coals and related materials

The quantitative aspects of cross-polarization (CP), which is used in conjunction with dipolar decoupling and magic-angle rotation to obtain high resolution ¹³C n.m.r. spectra of coals, have been studied using a bituminous coal (82 wt% C, dmmf basis) and asphaltenes from an extract of the same coal. The condition for obtaining reliable quantitative data, that rotating frame ¹H relaxation times (T_1p′ these govern the extent of CP) are much longer than the time required to polarize the carbons present (≈1 ms), was met for the asphaltenes. In contrast, about half the protons in the coal have T_1p5 of ≈ ? 1 ms, these times being too short to allow CP of all the carbons. Although the aromaticities obtained for this coal were fairly constant (≈0.75) using (CP) contact times > 0.5 ms, the total peak intensity decreased markedly as the contact time was increased and was much less than that for the asphaltenes. These results indicate that not all the carbons in bituminous coals are observed by CP and, as a consequence, aromaticities reported in the literature for some bituminous coals appear to be low.     

Fullerenic structures derived from oil asphaltenes

The handling and properties of heavy oils are becoming an increasingly important problem. Even though petroleum is the widest used source of fuels and it has been studied for decades, its complex nature is still an enigma in several ways. A reasonable approach to a definition of a crude oil is a colloidal fluid formed by several dispersed phases from gases (light hydrocarbons) to solids (heavy paraffins and asphaltenes). Through all these years of research, applications have been found for almost all classes of components in crude oil except for some of the solid phases such as asphaltenes. Very heavy petroleum is a non-newtonian liquid with a viscosity of ≈10⁶ Poise, and an average molecular weight of 600 amu. The solids that are toluene soluble but heptane insoluble are called asphaltenes and are the most aromatic fraction with the highest molecular weight of unconverted petroleum. In the present work, we applied high resolution transmission electron microscopy (HREM) and energy dispersive spectrometry (EDS) in the study of asphaltenes. It was found that when the asphaltenes are well separated from the resins the sample consists of a carbon structure containing S, V, Si, related to fullerenic carbon. During observation in the microscope it was possible to see the formation of fullerenes such as onions and C₂₄₀ @ C₆₀ structures. The fact that they decomposed under further irradiation suggests that they are metastable structures. Since the heteroatoms are still present they are likely to cause instability to the structure. Not only does our result indicate the possibility of obtaining fullerenes from crude oil but it also suggests the asphaltene molecule, when it is resin free, might be a precursor of fullerenic structures.     

Kinetic rate model interpretation of the SRC-II liquefaction of an Ireland Mine coal

An experimental data base for characterizing the SRC-II liquefaction of an Ireland Mine coal is interpreted using an empirical rate model developed from SRC-II liquefaction data for a Powhatan No. 5 coal exclusively. The model predictions for hydrogen consumption and for the yields of the key components; C₁-C₄ gases, C₅-755 K liquids, and solvent-refined coal (SRC) are compared with the experimental values over a wide range of reactor operating conditions; temperature (703–743 K), pressure (10.2–20.4 MPa), and recycle ash (2.0–10.4 wt%). Model predictions are in good agreement with hydrogen consumption measurements at baseline conditions (728 K and 13.6 MPa) and at more severe conditions (743 K and 20.4 MPa) for a feed slurry containing 30 wt% coal and 10.4 wt% recycle ash (absolute error ± 6.4%). A similar result is obtained forthe C₁-C₄ gases and the C₅-755 K liquids at the baseline conditions; however, the error in the SRC yield prediction is higher (± 12.1%). The model predictions for the key components at the higher severity conditions deviate more than those for the baseline conditions.     

The chemical nature of flash pyrolysis tars. An N.M.R. study

Flash pyrolysis tars from one brown and two bituminous Australian coals were separated into oils, asphaltenes and pre-asphaltenes. The oils were further separated by chromatography while the asphaltenes were separated into basic and acid/neutral fractions. The pre-asphaltenes were silyalated prior to ¹³C- and ¹H-n.m.r. studies. The brown coal tar was less aromatic and contained more long alkyl chains than the tars from the bituminous coals. Aliphatic constituents of the oils, which were relatively abundant, consisted mainly of n-alkanes and straight chain 1-alkenes with an average chain length of ca. C₁₃. The pre-asphaltenes were no more aromatic than the asphaltenes from the same tar but had higher molecular weights.     

Variation of coal extract structure with molecular mass

Asphaltenes and benzene-insolubles, and their methylated counterparts, of high-yield supercritical gas (SCG) and hydrogen donor solvent (HDS) extracts have been separated by size exclusíon chromatography (SEC) on cross-linked polystyrene microspheres so as to investigate the variation in coal extract structure with molecular mass (MM). Narrow SEC fractions have been obtained which have been subjected to elemental, molecular mass (MM), functional group, n.m.r. and voltammetric analyses. The analytical results revealed that the M M range of the solvent fractions was 300 to ≈3000. With increasing MM the following trends were observed: aromaticity decreased, but the degree of condensation of aromatic nuclei did not vary significantly; the size of aliphatic substituents increased; and phenolic hydroxyl content decreased for SCG extract fractions but, in contrast, increased for HDS extract fractions. These variations about averages are considerable and demonstrate that caution is necessary in making use of analytical results for gross fractions. Solubility in benzene of coal extracts results from low MM or from low polarity for higher MM materials.     

Effect of restrictive diffusion on hydrodesulfurization of heavy residue oils over CoMo/Al2O3

The effect of the ratio of reactant molecular diameter to catalyst pore diameter (λ) on the restrictive diffusion under hydrodesulfurization (HDS) reactions of heavy residue oils over CoMo/Al₂O₃ catalysts was investigated. A series of Al₂O₃ with various pore structures were used as supports of CoMo sulfide. The HDS reaction was carried out in a semi-batch Carberry type reactor at 648 K and 10.3 MPa. Two empirical correlations for restrictive diffusion under HDS reaction conditions were developed depending on the value of λ. The results showed that the restrictive diffusion effect under HDS reaction conditions is severe for the lower values of λ. However, this effect seems not prominent for higher values of λ. The order of the magnitude of the effective diffusivity was in the range of 10^?6-10^?7 cm²/s for the sulfur-containing compounds of residue oil in CoMo/Al₂O₃ catalysts at 648 K.     

Characterization of pyrolysis products of harbolite and Avgamasya asphaltites: comparison with solvent extracts

The products of pyrolysis at 525 and 840 °C of two asphaltites from South-Eastern Turkey have been analysed and compared with the bitumen obtained by solvent extraction. The yield of oil product is reasonably similar for all three treatments, with gas (hydrogen, ethene, C₁C₄ alkanes and hydrogen sulphide) being liberated during pyrolysis. Greater percentages of alkanes with shorter chain lengths (along with some alkenes), and of pentane-soluble aromatic oils with reduced molecular masses, are generated during pyrolysis, at the expense of asphaltenes. The extra alkanes are generated partly by the cracking of aromatic side-chains and also from kerogen. Pyrolysis reduces the number of sulphur linkages in the oil, but nitrogen- and oxygen-containing structures are liberated from kerogen during heating.     

Catalyst’s Sulfur Displacement by Thiophene, as Monitored by Exchange of 35S Radiotracer

The isotopic exchange has been studied between catalyst radiosulfur and H₂S, formed in thiophene hydrodesulfurization (HDS) (named S-displace) on alumina supported molybdena, on CoMoO_x, PdMoO_x, PtMoO_x and on silica–alumina supported NiWO_x. S-displace was compared with radiosulfur exchange data between catalyst radiosulfur and gas phase H₂S (S^exc) determined previously. The extent of S^exc was higher than that of the S-displace for Mo, CoMo in and NiW, whereas the extent of S-displace from PdMoO and PtMoO was significantly higher, than that of S^exc. Thiophene HDS product distribution data are discussed in terms of increased C=C hydrogenation and C–C hydrogenolysis activity, explained by increasing H₂S production with longer circulation time of the thiophene/H₂ mixture, The C₁/C₃<1 ratios among C₄-hydrogenolysis products indicate some coke formation. The decrease of thiophene HDS activity is presumably a consequence of increasing site-blocking with the formation of more H₂S and coke with longer duration of thiophene treatment.     

Liquefaction of coal by SRC-II process: Part I: A new kinetic model

The kinetic experiments were carried out in a continuous stirred tank reactor. Practically important ranges of SRC-II reactor temperature (444–466°C), pressure (10.4–20.8 MPa), nominal slurry residence time (0.54–1.62 h), coal concentration in the feed slurry (25–35 wt%), and inorganic mineral matter concentration (4.75–13.43 wt%) were covered in a total of 43 experimental runs. In each of the experimental runs, the feed slurry was formulated by using vacuum tower bottoms from SRC-II pilot plants using the same feed coal (Powhatan No. 5), to obtain feed compositions similar to those obtained in SRC-II pilot-plant recycle operation. The kinetic model considers the overall conversion to be achieved in two stages. The first stage is the instantaneous dissolution of coal and in the rate controlled second stage all the reactive organic components in the liquid phase are initially assumed to react, each yielding components lighter than itself. The distribution of products in each reaction stage is considered to be independent of the operating conditions. The best rate controlled (second stage) reaction scheme and values of the unknown parameters are obtained by minimizing the overall difference (i.e. for all the components over all the runs) between the measured and model predicted mass fractions of the various components in the reactor. This analysis identifies the reaction of solvent refined coal (pyridine soluble organic matter boiling above 482°C) to be the only significant reaction in the second stage and its rate is determined to be ^-r_SRC = 1.567 × 10⁵ exp (-79.16/RT) · p^0.28 · X_ASH, kg/L h. Overall error in this analysis yielding the reaction scheme, r_SRC and values of product distribution coefficients for both the reaction stages is less than 8% absolute i.e. ±4%.     

The isolation and characterization of lignin of kenaf fiber

In this article, milled wood lignin (MWL) was isolated and purified from retted kenaf fiber, the lignin obtained was characterized by elemental analysis, FTIR, ¹H‐NMR, and ¹³C‐NMR spectroscopy. The C₉ formula is calculated for kenaf fiber MWL as C₉H_9.32O_3.69(OCH₃)_1.30. The spectra of FTIR, ¹H‐NMR, and ¹³C‐NMR show the kenaf fiber lignin to be of the G/S type with high proportion of syringyl (S) unit. The numbers of phenolic and aliphatic hydroxyl groups in the kenaf fiber MWL are estimated to be 0.14 and 1.31, respectively, per C₉ unit. The OH_aliph is 90.3% in total numbers of hydroxyl groups of kenaf fiber MWL, and the OH_ph is 9.7%. It is evident that the β‐O‐4 structures are mainly linkage in the MWL of kenaf fiber, which contain more erythro stereochemistry type in β‐O‐4 units than thero stereochemistry type. In general, the characteristics of lignin of kenaf fiber are similar to that of hardwood. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009