David M. Bodily

Structural characterization of coal-hydrogenation products by proton and carbon-13 nuclear magnetic resonance

Heavy oil derived from coal hydrogenation was separated into saturated fractions, neutral aromatic oil, and asphaltene, and these materials were subsequently fractionated according to the magnitude of their respective molecular sizes by gel-permeation chromatography. These GPC subfractions were analysed by proton and carbon-13 n.m.r. spectroscopy and by an additional procedure using gas chromatography for the paraffinic GPC subfractions. 13C-n.m.r. spectra for the GPC subfraction of saturated material showed typical long straight-chain paraffin spectral patterns accompanied by iso-and cycloparaffinic carbon signals. The results from gas-chromatographic measurement for the paraffinic GPC subfractions agree fairly well with the trends of average carbon numbers and contents of straight-chain paraffins obtained by varying the fraction numbers, estimated from 13C-n.m.r. analyses. The ratios of aromatic carbon to total carbon (fa) for aromatic oil and asphaltene GPC subfractions obtained directly from 13C-n.m.r. spectra are slightly lower than the results from the 1H-n.m.r. method assuming x = y = 2 in the Brown—Ladner equation. Peak intensities of the respective carbon species in 13C-n.m.r. spectra were compared with the peak intensities of correspondingly bonded species obtained from 1H-n.m.r. measurement. Some inadequacy was recognized in both measurements. It is assumed that there are two reasons for the discrepancy, one of which is the inaccuracy of 13C-n.m.r. results owing to the long relaxation times and the effect of Nuclear Overhauser Enhancement, and another is the application of unsuitable values of x and y for calculations from the Brown—Ladner equation. New analytical treatments for 13C-n.m.r. results in combination with 1H-n.m.r. analyses are suggested in this study to avoid these uncertainties in structural analyses. From this procedure, it is believed that the actual contents of aromatic and aliphatic carbon and appropriate values of x and y can be derived.

Transpassive Oxidation of Pyrite

The electrochemical behavior of mineral and coal pyrites in basic borate/sulfate solutions was investigated using cyclic voltammetry with both stationary and rotating disk electrode. Emphasis was centered on transpassive oxidation. In the transpassive region, 0.4 to 0.8 V (SCE), aggressive oxidation of pyrite occurred. The reaction products in this region are Fe(III) oxides, sulfate ion, and partially oxidized sulfur intermediates. The formation of sulfur and polysulfides was identified by in situ Raman spectroscopy. Exposure of pyrite to anodic potentials higher than the transpassive region resulted in rapid oxidation of sulfur intermediates to sulfate ion. The effect of electrode rotation speed, electrode precondition time, and upper potential of the scan in the transpassive region was observed to be critical to the formation of sulfur intermediates. Sulfur intermediates, formed in the transpassive region, dramatically affected subsequent oxidation reactions occurring in the lower potential region. The magnitude of two dominant oxidation peaks, a ferrous hydroxide peak and an iron sulfide peak, observed in this region correlated directly with the quantity of sulfur intermediates formed in the transpassive region. This effect was less pronounced for coal pyrites compared to mineral pyrite.

Application of Raman spectroscopy to metal-sulfide surface analysis

The surface products of electrochemically oxidized pyrite (FeS(2)) are investigated as a function of applied potential by using Raman spectroscopy. The parameters necessary for sulfur formation on the pyrite surface were determined. An optical multichannel apparatus, consisting of an argon laser, a triple spectrograph, and a charge-coupled-device detector, was utilized for the Raman measurements. The advantages of this system for surface characterization include high resolution and high sensitivity as well as the capability of identifying compounds and making in-situ measurements.

Mechanism of high-pressure hydrogenolysis of Hokkaido coals (Japan) 3. Chemical structure changes in coal asphaltenes during hydrogenolysis

Abstract Asphaltenes produced by hydrogenolysis of coal were further hydrogenated in a batch autoclave at 400°C and 22 MPa hydrogen pressure. Red-mud was used as a catalyst and sulfur as promoter. The hydrogen content of the residual asphaltene increases and the fraction of aromatic carbon and the fraction of protons bound to aromatic carbons decrease as the reaction proceeds, indicating that hydrogenation of aromatic rings occurs. Aromatic ring systems of more than 2 rings are relatively easily hydrogenated to 2 rings. However, 2 ring systems are not easily hydrogenated. The heteroatoms-to-carbon ratios are similar for both the oil and the residual asphaltene, but less than that of the original asphaltene. The main differences in the chemical structure between the oil and the residual asphaltene are the hydrogen-to-carbon ratio, the fraction of aromatic carbon, the molecular weights and the average degrees of crosslinking. The residual asphaltene is composed of trimers and/or oligomers of unit structures of two or more condensed aromatic rings bound together by crosslinks. The size and composition of the condensed ring systems varies about the average properties measured in these experiments. Cleavage of the crosslinks by hydrogenation and heteroatom removal produces oil, composed for the most part of monomers of unit structures of two condensed aromatic rings. Coals of different rank show similar behavior although the magnitude of the changes depends on rank.

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

Abstract 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 1 H-NMR data, by 13 C-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 ( 1 H-NMR) and fa ( 13 C-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.

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.

Formation and chemical structure of preasphaltenes in short residence time coal hydrogenolysis

Abstract The formation and chemical structure of preasphaltenes in short residence time coal hydrogenolysis were investigated. In short residence time coal hydrogenolysis, preasphaltenes are the major product. The maximum yield for this parametric study was obtained under reaction conditions of 500 °C and 21 s. The formation of preasphaltenes reached the maximum value in the initial stage of the liquefaction reaction. As the liquefaction reaction continued, the deoxygenation of preasphaltenes proceeded. However, the decrease in aromatic atoms bound to the hydroxy, methoxy and oxygen atoms of the diphenyl ether group (Arz.sbnd;O) is small, and the ArO functionality still remains abundant in preasphaltenes. Preasphaltene-I is characterized by carbon aromaticity (fa) of 0.6–0.7, aromatic rings of from 1 to 3–5 per condensed aromatic ring system, 55–70% substitution of aromatic ring carbons and C2–3 aliphatic substituents. The molecular weight ranges from 500 to 650, and is not much different from that of the asphaltenes. The fa values based on the Brown-Ladner method and on solid state CP/MAS 13C n.m.r. spectra data agree closely.

Kinetics of the transpassive oxidation of pyrite. Technical progress report, July 1, 1992--October 20, 1992

In the transpassive region, about 0.4 to 0.8 V (SCE), aggressive oxidation of pyrite occurred. The reaction products in this region were Fe(III) oxide, sulfate ion and partially oxidized sulfur intermediates. The growth kinetics of the reaction of pyrite were studied using chronoamperometry measurement with both stationary and rotating disk electrodes. The effect of electrode rotation speed, solution pH and temperature were examined. Potentiostatic measurements were well correlated by a paralinear rate equation, suggesting the formation of an intermediate passive film, associated with the simultaneous dissolution of the outer layer of the film. Activation energies of 66.17 kJ/mole (15.83 kcal/mole) and 38.67 kJ/mole (9.25 kcal/mole) were obtained for associated parabolic and linear rate constants respectively, at an applied potential of 0.6 V.

Distribution of zinc chloride catalyst in products from short residence time liquefaction of clear creek, Utah coal

Abstract The total recovery of zinc chloride decreases from 94.4 wt% to 75.4 wt%, on the basis of ZnCl 2 catalyst added, with the progress of the liquefaction reaction. Over 90 wt% of zinc and chlorine found in the liquid and solid products is present in the toluene insolubles. The contents of zinc and chlorine in the other products are below 1 wt% and 5 wt%, respectively, of the ZnCl 2 added.