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.     

The characterization of asphaltenes and preasphaltenes obtained under various coal liquefaction conditions

A CP-MAS ¹³C NMR study of asphaltenes and preasphaltenes obtained under various coal liquefaction conditions is reported. The carbon aromaticity, f_a, of the solid extracts from the reaction products has a close relation with the reaction conditions. By plotting f_a against the atomatic $\text{H}\text{C}$ ratio for these solid products on the characterization chart for model polycyclic aromatic compounds, the molecular structures with relation to the liquefaction pathway from coal to oil can be proposed.     

Chemical structure of asphaltenes and preasphaltenes obtained by coal hydrogenation under high-speed heating conditions

The results of experimental studies on the determination of the chemical structure of asphaltenes and preasphaltenes in the liquid hydrogenates of coal from the Zashulanskoe field in Transbaikalia are reported. These results were obtained under the conditions of high-speed heating (～200 K/min; reaction time, 10 min). It was found that the structural characteristics of asphaltenes and preasphaltenes obtained by high-speed hydrogenation at 425°C and 10 MPa exhibited a number of special features. At similar fractions of aromatic carbon, these products differed from the coal hydrogenates obtained at a slow rate of heating (5 K/min; reaction time, 120 min) in terms of the distribution of hydrogen and oxygen over structural groups. In them, the hydrogen content of CH₂ and CH_ar groups was smaller and that of CH₃ groups was greater. The highest concentration of total oxygen-containing groups was detected in the high-speed process preasphaltenes, whereas it was lower in the asphaltenes.     

Relation of the chemical structure of coal to its hydropyrolysis

The hydropyrolysis of Illinois No. 6 coal has been studied in a batch reactor, in which the reactions were initiated by explosion of $\text{H}{}_2\text{O}{}_2$ mixtures. The ratio of H₂ to O₂ was kept at 8, while the total pressure of the gas mixture was changed to vary the reaction temperature. The heating rate was ≈ 50 000 °C s^?1, and the reaction time was < 50 ms. The conversion of the feed coal increased from 19% at 620 °C to 81%at ? 1500 °C. At conversions < 50%, the gaseous product consisted of mainly CH₄ and CO in almost equal proportions, and at conversions ? 60% the concentration of CO increased. Comparison with results from a large flow reactor revealed that comparable conversions were obtained in the present batch reactor, although product distributions were markedly different from each other. The dissimilar product distribution is attributed to different reacting media: preburning of H₂ and O₂ in the flow reactor versus in situ burning of the mixture in the batch reactor. The H/C ratios of solid residues after the hydropyrolysis decreased linearly as the conversion increased, revealing that the portions of coal having high H/C ratios were preferentially gasified. This observation was substantiated by a high H/C ratio, 1.74 of the first portion of coal gasified, and by a sharp decrease in H/C ratio in subsequent gasified portions. These data indicated that aliphatic side chains (or linkages) and single-ring aromatic clusters in the feed coal were gasified first, followed by larger aromatic clusters. Semi-quantitative determination of the distribution of different aromatic clusters showed good agreement with current structural information on coal. Thus, the effects of reaction variables were explained in terms of the structural features of coal, and the ratelimiting steps in the hydropyrolysis process were identified.     

Effect of coal rank on the composition of organic matter (Short Communication)

It was demonstrated that the ratios between the fractions of carbon and hydrogen in CH₃, CH₂, and CH groups regularly changed in the coal metamorphism series.     

Liquefaction reaction of coal: 1. Depolymerization of coal by cleavages of ether and methylene bridges

The roles of ether and methylene bridges in the depolymerization of coal have been re-evaluated on the basis of the results of a mild liquefaction reaction (400 °C, 30 min) and the distributions of oxygen and carbon atoms obtained by cross-polarization, magic angle spinning (CP/MAS) ¹³C n.m.r. spectrometry. Coals ranging from 66.2 to 87.4 wt% C (dmmf) were used as sample coals. The content of etheric oxygen was < 3.7 per 100 carbon atoms and the cleavage of ether bridges contributed to the formation of preasphaltene. The conversion to hexane solubles in the mild liquefaction reaction correlated well with CH₂ carbon content of coal, though the conversion to pyridine solubles did not. These results suggest that the formation of oil from preasphaltene is caused by the scission of CH₂ bridges and some naphthenic CH₂ bonds. The phenolic OH oxygen-rich portions in coal tended to remain as a residue formed by the condensation reaction of phenolic OH groups.     

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.     

Characterization of organic material in coal by proton-decoupled 13C nuclear magnetic resonance with magic-angle spinning

¹³C n.m.r. spectra have been obtained on ten solid coal samples of various types and on three coal-derived materials, using high-power proton decoupling, cross polarization and magic-angle spinning, and provide valuable information on the carbon distribution between aromatic and non-aromatic structures in the sample. Apparent carbon aromaticities, f_a′, have been determined and have been correlated with H/C ratios and as one factor in fuel values. Both solvent refining and reverse combustion (see introduction) are found to increase the aromatic fraction. These techniques should be very useful in characterizing and optimizing coal-conversion processes.     

An h.p.l.e. and m.s. analysis of distillate fractions of neutral oil from hydrogenated Akabira coal to elucidate chemical structures

Akabira coal-derived neutral oil was separated into 25 narrow boiling range fractions covering 183–423 °C, and subsequently separated into compound class fractions : alkanes, monoaromatics, naphthalene-type diaromatics, fluorene-type diaromatics and tri- and/or tetraaromatics, by high performance liquid chromatography (h.p.l.c.). The compound type analyses of the distillate/h.p.l.c. fractions were performed using electron impact mass spectroscopy (e.i.m.s.) or field ionization mass spectroscopy (f.i.m.s.). Aromatic/hydroaromatic compound types and the alkyl side-chain carbon distribution of the distillate/h.p.l.c. fractions were clarified, based on the separation behaviour of h.p.l.c. and the type analyses according to Z value by m.s. By the distillation/h.p.l.c./m.s. method, coal-derived oil was characterized in terms of the distribution of the numbers of aromatic rings, naphthenic rings and carbons of alkyl groups attached to these rings. The variations in chemical structure in a compound class with distillation temperature are discussed in terms of these chemical structural factors.     

Review of the kinetics of pyrolysis and hydropyrolysis in relation to the chemical constitution of coal

Kinetic data show that the pyrolysis reactions of hard coal may be interpreted in terms of parallel first order reactions, relating to the coal functional groups which can be considered as predecessors of the pyrolysis products. This relation is confirmed by C-, H- and O-balances of pyrolysis products and those of the corresponding predecessor structural groups of the coal. The activation energies measured are of the same order of magnitude as the bonding energies of bridge CC bonds between the aromatic ring-systems in the coal molecule. These observations suggest a mechanism of coal pyrolysis, consisting of the following steps: rupture of CC bridges; formation of radical groups; and recombination of radicals to stable molecules part of which, i.e., those of low molecular weight, diffuse out of the solid matter whereas the rest (whose diffusion in the pore system of the solid is prevented due to their higher molecular weight) react with each other at higher temperatures to give coke, releasing elementary hydrogen. In the presence of hydrogen > 500 °C, additional reactions of partial hydrogenation of polynuclear aromatics with subsequent hydrocracking will occur, leading to increased formation of highly aromatic tar, BTX, CH₄ and H₂O.     

Characterisation of the neutral oil from a low-temperature coal tar

Tar resulting from fluidised-bed, low-temperature carbonisation of coal was treated to yield a neutral oil from which a series of six other samples was extracted. These were examined by proton magnetic resonance (p.m.r.) spectroscopy, low-ionising-voltage (11 eV) mass spectroscopy (m.s.), gel chromatography followed by fluorescent indicator analysis, and cryoscopy. Aliphatic fractions separated chromatographically were also examined by infra-red spectroscopy. Distributions of hydrogen between chemical types were found for the several fractions from 60 MHz p.m.r. spectra and presented in terms of average structural parameters. M.s. analysis indicated negligible cracking of paraffin components, and the average molecular weight of 197 agreed well with cryoscopic determinations. For the carbon ratio, f_a, between aromatic and total, agreement between m.s. and p.m.r. depends on the p.m.r. structural analysis scheme adopted. P.m.r. and m.s. structural analyses of the aromatics emphasise the predominance of di- and tri-nuclears, with about 40% of available sites substituted, and the importance of acenes in lowtemperature carbonisation material. Gas and gel chromatography showed urea-adductable paraffins to be largely straight-chain C₁₀-C₂₆, much as for tars from carbonisation at higher temperature.     

Characterization of vitrinite concentrates. 2. Magic-angle 13C nuclear magnetic resonance studies

The fraction aromaticity determined by ¹³C n.m.r. with cross-polarization and magic-angle spinning of 19 vitrinite concentrates obtained from the Lower Kittaning seam shows a range of values from ≈ 0.65 for the samples of lowest rank (83 wt% C (dmmf) to about 0.83 for those of highest rank (91 wt%C (dmmf)). It was determined that the wt% aromatic carbon correlates to the wt% fixed carbon and is in good agreement with the results reported by other authors. The combination of the ¹³C n.m.r. results with FTIR measurements allows a number of coal parameters to be estimated. The atomic ratios of aliphatic hydrogen to carbon were demonstrated to vary from 1.8–2.0 to between 2.4–2.6 and previous assumptions that a single value can be used in calculating structural parameters for coal of any rank are not strictly valid. The calculation of the aromatic $\text{H}\text{C}$ ratio indicates that in mean structural units there is approximately one aromatic hydrogen atom for every six carbons in vitrinites of carbon content 83 wt%C (dmmf) and that this ratio changes progressively with rank to a value of about one aromatic hydrogen for every four carbons for vitrinites of carbon content 91 wt%C (dmmf).     

Study of the preasphaltenes of coal liquefaction and its hydro-conversion kinetics catalyzed by SO4/ZrO2

The investigation of hydro-conversion behavior of the heavy intermediate products derived from coal direct liquefaction is advantageous to optimize the technological conditions of direct coal liquefaction and improve the oil yield. In this paper, the hydro-conversion of preasphaltenes catalyzed by SO₄²⁻/ZrO₂ solid acid was investigated based on the structural characterization of preasphaltenes and its hydro-conversion products, and the determination of products distribution and the kinetics of preasphaltenes hydro-conversion. The results indicated that the content of condensed aromatic rings increased, and the contents of hydrogen, oxygen and aliphatic side chains of preasphaltenes decreased with the increase of coal liquefaction temperature. The preasphaltenes showed higher hydro-conversion reactivity while SO₄²⁻/ZrO₂ solid acid was used as catalyst. Higher temperature and longer time were in favor of increasing the conversion and the oil + gas yield. The conversion of preasphaltenes hydro-conversion under 425 °C, for 40 min reached 81.3% with 51.2% oil + gas yield. SO₄²⁻/ZrO₂ solid acid was in favor of the catalytic cracking rather than the catalytic hydrogenation in the hydro-conversion of preasphaltenes. The activation energy of preasphaltenes conversion into asphaltenes was 72 kJ/mol. The regressive reactions were only observed at a higher temperature.     

The characterization of coal macerals by diffuse reflectance infrared spectroscopy

Diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy was applied to study the structure of vitrinites, liptinites and fusinites isolated from different rank coals (77.0-91.5%C) using a centrifugal float-sink procedure. Among the macerals separated from a given coal, liptinites are characterized by the highest proportion of aliphatic CH groups, occurring principally as CH₂, and fusinites by the most aromatic structure. Macerals separated from the low rank coals show comparable content of hydroxyl groups that occur as free OH or form similar types of hydrogen bonds. Carbonyl groups appear not only as conjugated ketones and quinones in vitrinites, but also as carboxylic groups in liptinites and low rank fusinites. CH_ar/CH_al ratio does not vary with carbon content in liptinites, but increases in vitrinites and fusinites. In the case of liptinites and vitrinites, a linear relationship between CH_ar/CH_al and reflectance is observed up to vitrinite R₀ value of 1.80%. For all macerals, the ratio CH_ar/CC increases with reflectance, but at different rates. Structural parameters CH_ar/CH_al and CH_ar/CC calculated from DRIFT spectra are very helpful in monitoring the differences among macerals of given coal and following structural rearrangement occurring with rank.     

Depolymerization of Turkish lignites. 2. Effect of phenol concentration in a closed system

A lignite (C, 66.9 wt%) was depolymerized, using sulphuric acid as a catalyst, in a closed system in which the phenol/coal ratio was varied from 1.5 to 10. The products were separated by solvent extraction and silica gel chromatography. The i.r. and n.m.r. spectra, and the molecular weight of the products were measured. In the experiments with a phenol/coal ration of 10, complete depolymerization of the coal was seen provided the temperature of depolymerization was at least 210 °C. The products generally contained disubstituted aromatic structures connected by methylene bridges, it was found that as the phenol/coal ratio was increased there was a decrease in the number of methylene bridges connecting the aromatic structures. The molecular weights of the straight-chain pentane and benzene-soluble material were lower than the molecular weights of similar fractions in depolymerization experiments carried out in open systems. A method for the structural analysis of straight-chain pentane and benzene-soluble material based on i.r., ¹H n.m.r. and molecular weight measurements is suggested.     

Chemical structure of heavy oil from coal hydrogenation 1. Hydrogenation with zinc chloride catalyst

Oil product from the hydrogenolysis of a high-volatile bituminous coal was separated by solubility, fractionated by gel permeation chromotography and characterized by structural analysis. The average structural unit in the hexane-soluble, aromatic oil fraction consists of 1–3 aromatic rings with 0.3-0.5 of the ring carbons substituted by alkyl groups and oxygen containing groups. Molecular weights vary from 200 to 500. The larger molecular weight fractions have longer alkyl chains and lower carbon aromaticities. The molecules are mainly of single unit structures. The average structural units in asphaltene fractions contain from 2.5-4 aromatic rings, are of higher carbon aromaticities and contain shorter alkyl groups. The asphaltene molecules consist of two or more structural units, crosslinked together, and have molecular weights of 300–1400. The oxygen content of the fractions decreases with decreasing molecular weight. Increasing the amount of ZnCl₂ catalyst during hydrogenolysis resylts in an increased yield of lower-molecular-weight material, but no change in the structural properties of the product. This is interpreted to mean that ZnCl₂ is active in the scission of covalent bonds between structural units during liquefaction and that the hydrogenolysis reaction is mostly cleavage of crosslinks between structural units with minimal reaction of the units themselves.     

Hydrogen incorporation during coal liquefaction

Coal hydrogenation reactions have been investigated using a deuterium tracer method which makes it possible to determine which structural positions in the coal react with hydrogen gas or donor solvent during liquefaction. ²H₂ and/or tetralin-d₁₂ were reacted with a Pittsburgh Seam coal at 13.8 to 22.1 MPa and 360 to 425 °C for 0.25 to 1.0 h. Hydrogenation and exchange indices were formulated to indicate the relative contribution of each type of reaction to the total H incorporation. In the coal-deuterium gas system, deuterium incorporation in the solvent-separated products increases in the order oil < asphaltene < preasphaltene < residue. However, in the coal-tetralin-d₁₂-deuterium gas system, deuterium incorporation is similar in each of these four fractions. In both systems, ²H incorporation varies with structural position, with the α-aliphatic positions exhibiting the greatest extent of incorporation. The α-tetralyl radical appears to be an important intermediate in hydrogen transfer to and exchange with the coal. The results indicate that in the donor system the abstraction of hydrogen from the solvent by coal-derived radicals is involved in the rate-determining step of the formation of the soluble products. Evidence indicates that considerable direct interaction of the gas-phase hydrogen with the coal also occurs in the donor solvent system.     

Aufklärung der Molekülstruktur von Rohölinhaltstoffen durch NMR-Spektroskopie. III. Quantitative Analyse von Erdölfraktionen im Siedebereich über 220°C

Elucidation of the Molecular Structure of Petroleum Constituents by N.M.R. Spectroscopy. III. Quantitative Analysis of Crude Oil Fractions in the Boiling Range above 220°C A method is presented which permits a quantitative analysis of crude oil products boiling > 220°C by means of the data of the ¹H n.m.r. spectrum. Besides of the quantitative analysis (aromatics, paraffins/naphthenes), further structural informations for both of these groups are given, concerning the number of carbon atoms in aromatic rings, the degree of substitution of the aromatic rings, and the CH₃-share of paraffins/naphthenes.     

Solid state magnetic resonance spectra of Illinois No. 6 coal and some reductive alkylation products

Illinois No. 6 coal and its reductive methylation and butylation products have been studied by magnetic resonance techniques. Conventional CP-MAS¹³Cn.m.r. spectroscopy indicates that 62% of the carbon atoms in the coal are aromatic and that about 6% of the carbon atoms are carbonyl. Esters are more abundant than carboxylic acids. The resonances of methoxy groups and other novel etheric carbon atoms are apparent in the high field region. Dipolar dephasing experiments suggest that methyl carbon atoms constitute no more than 16% of the carbon, methylene and methine carbon atoms about 14% and quaternary aliphatic carbon atoms about 2%. The dipolar dephasing experiments in conjunction with previous work also permit estimates of the hydrogen atom distribution. The THF-insoluble products obtained in the reductive alkylation reactions with¹³C-enriched alkylating agents contain paramagnetic and ferromagnetic substances that adversely influence the solid state n.m.r. spectra. However, good ¹³C n.m.r. spectra were obtained after these substances were extracted with aqueous hydrochloric acid. The O:C alkylation ratios are 1.2 and 1.0 for methylation and butylation, respectively. Dipolar dephasing experiments establish that the decay constants of functional groups in the whole coal and of C- and O-methyl-¹³C and C- and O-butyl-1 -¹³C nuclei in the labelled coal molecules are very similar to those of reference compounds. These findings suggest that the decay constants measured for the ¹³C nuclei in coals and coal-derived solids provide reliable information about their degree of substitution.     

Distribution of aliphatic and aromatic carbons in H-Coal liquids by quantitative 13C FT-n.m.r. spectroscopy

Three H-Coal liquids, ASO, ASB, and VSO, have been characterized by quantitative FT-n.m.r. spectroscopy. FT-parameters were chosen to allow determination of aromatic:aliphatic carbon ratios to within 1% and 2% error of the theoretical and the absolute number of aromatic and aliphatic carbons in a simulated coal liquid, respectively. The aromaticity, f_a, the C_ar:C_al ratio and, the absolute number of both the aromatic and the aliphatic carbons on a per mol basis, have been derived for each H-Coal liquid using c.m.r. in combination with other physical data. By analysis of the chemical shifts of the c.m.r. spectra, the carbon distributions in the H-Coal liquids have been estimated and compared in terms of six structural types. The molecular parameters thus derived are reasonable correlated with the average molecular structures proposed as working hypothesis for the molecular characterization of the three H-Coal liquids.