Argonne Premium Coals Research Articles

Trace mercury concentrations in coals and coal-derived material determined by atomic absorption spectrophotometry

The volatility of mercury can cause large errors during quantification when methods based on acid digestion are applied. In this study, mercury levels in coals have been determined by an atomic-absorption- based instrument hitherto not used with coals or coal-derived materials. The results have been compared with ‘certified’ values of reference materials. The instrument is relatively easy to use: solid and liquid samples may be introduced directly, without pretreatment. The range of samples studied included the Argonne Premium Coal Samples and other coals, coal-derived products, biomass materials, sand and kaolin. The instrument gave correct mercury concentrations for certified reference materials. Samples of silver birch and forest residue contained similar concentrations of mercury as observed in coals; other biomass samples contained far smaller quantities of mercury. Thus, the use of biomass in power generation would not necessarily lead to any great reduction of mercury in emissions from power plant: careful selection appears necessary. Only 3% of the mercury of the original coal was detected in the filter cake (corresponding to undissolved coal and mineral matter) from a coal liquefaction pilot plant. Mercury in the original coal appears to have passed either to (i) gas formed during liquefaction (between 2 and 4% daf) or to (ii) the dissolved coal extract, possibly in the form of organometallic complexes. The presence of 0.15 ppm mercury in a coal tar pitch also suggests the organometallic retention of mercury in this fraction. All solid residue streams from a gasification pilot plant, operating at about 930–960°C, have shown nearly negligible mercury, compared to the original coal, indicating that the bulk of the mercury in the feedstock was released into the product gas.

98/00011 Elucidation of the nature of organic nitrogen in the Argonne premium coals

Diffusive isotopic fractionation factors are important in order to understand natural processes and have practical application in radioactive waste storage and carbon dioxide sequestration. We determined the isotope fractionation factors and the effective diffusion coefficients of chloride and bromide ions during aqueous diffusion in polyacrylamide gel. Diffusion was determined as functions of temperature, time and concentration. The effect of temperature is relatively large on the diffusion coefficient (D) but only small on isotope fractionation. For chlorine, the ratio, D35Cl/D37Cl varied from 1.00128 ± 0.00017 (1σ) at 2 °C to 1.00192 ± 0.00015 at 80 °C. For bromine, D79Br/D81Br varied from 1.00098 ± 0.00009 at 2 °C to 1.0064 ± 0.00013 at 21 °C and 1.00078 ± 0.00018 (1σ) at 80 °C. There were no significant effects on the isotope fractionation due to concentration. The lack of sensitivity of the diffusive isotope fractionation to anything at the most common temperatures (0 to 30 °C) makes it particularly valuable for application to understanding processes in geological environments and an important natural tracer in order to understand fluid transport processes.

98/00790 Analysis of pyrolysis reactions of various coals including argonne premium coals using a new distributed activation energy model

98/00790 Analysis of pyrolysis reactions of various coals including argonne premium coals using a new distributed activation energy model

Analysis of Pyrolysis Reactions of Various Coals Including Argonne Premium Coals Using a New Distributed Activation Energy Model

A simple method presented by the author for estimating both f(E) and k0 in the distributed activation energy model (DAEM) was applied to analyze the pyrolysis reactions of 19 different coals, including 8 Argonne premium coals. First, f(E) and k0 for the changes in total volatiles were estimated using the thermogravimetric curves measured at three different heating rates for all the coals. It was found that f(E) curves were significantly dependent on coal rank, whereas the k0 vs E relationships were found to be little dependent on coal rank. This suggests the similarity of the pyrolysis reactions for all the coals. For the Argonne premium coals, the peak E value of f(E) curves shifted from 215 to 275 kJ/mol in accordance with the coal rank. The validity of the method was clarified by comparing the predicted thermogravimetric curves with the experimental ones. Next, fi(E) and k0i for the changes in the evolution of gas components and tar were also estimated using the formation rates measured and the k0 vs E relationships estimated above.

Variable-Temperature High-Resolution Proton NMR Study of Laboratory-Frame and Rotating-Frame Spin−Lattice Relaxation in Coals

We have carried out the first systematic in situ variable-temperature (25-180 °C) high-resolution proton NMR study of laboratory-frame and rotating-frame proton spin-lattice relaxation of coal samples, based on the CRAMPS technique. For coal samples that have been exposed to air, we confirmed the fact that paramagnetic oxygen is the main source of laboratory-frame proton spin-lattice relaxation (T 1 ). We demonstrate that paramagnetic oxygen trapped in coal can be used as a sensitive probe for monitoring structural and dynamical changes in coal as the temperature is varied. High-temperature spin-lattice relaxation experiments help to reveal the structural heterogeneity of coal because of reduced proton and electron spin-diffusion rates at high temperature. Large domains, on the order of 200-800 A, with distinctively different paramagnetic oxygen concentrations, were found in all three coal samples studied, consisting of one low-volatile and two high-volatile bituminous coals from the Argonne Premium Coal bank. In particular, we found that aliphatic-rich domains with a length-scale larger than 500 A exist in Premium Coal 601. The observed dependences of the rotating-frame 1 H spin-lattice relaxation time T 1p on the strength of the spin-lock field and temperature support the view that the main relaxation mechanism is time-dependent 1 H- 1 H dipolar interactions in coals. From these dependences, we estimate that the correlation time of molecular motion responsible for rotating-frame proton spin-lattice relaxation in coals is on the order of 5 μs, which is in agreement with conclusions drawn from previous proton dipolar-dephasing studies. Two T 1p values were identified for each of the three coal samples studied, indicating the existence of structural heterogeneity in coal on a spatial scale of at least 50 A. The sizes of heterogeneous domains in coal are estimated on the basis of measured spin-lattice relaxation times and the analysis of proton spin-diffusion processes.

In Situ Variable-Temperature High-Resolution 1H NMR Studies of Molecular Dynamics and Structure in Coal

We have carried out the first systematic in situ variable-temperature high-resolution 1H NMR study of coal samples between 25 and 230 °C based on the CRAMPS (combined rotation and multiple-pulse spectroscopy) technique. The coal samples studied include two high-volatile and one low-volatile bituminous coals from the Argonne premium coal bank. We found unexpectedly that there are no dramatic changes of 1H CRAMPS resolution over this temperature range. Slight deterioration of resolution at high temperature suggests interference of thermally promoted molecular motion with coherent averaging by the multiple-pulse sequence. Based on a “time-suspension” experiment using the CMG-48 pulse sequence and proton dipolar-dephasing experiments, we estimated the correlation time of the thermally promoted molecular motion as being about 10 μs, which is several orders of magnitude slower than the molecular motion induced with pyridine saturation of coal at room temperature. This result suggests that thermal treatment alone up to 230 °C is not enough to break either the covalent bonds or the noncovalent associative bonds that connect the macromolecular network of coal. With improved dipolar-dephasing experiments based on BR-24 1H CRAMPS detection, we were able to analyze quantitatively the proton dipolar-dephasing behaviors of aliphatic and aromatic protons in coal. We found that the dipolar-dephasing curve of a coal at high temperature can be described as two Gaussian dephasing components, which indicate a coexistence of molecules with two distinctly different mobilities. The promotion of molecular mobility in coal at higher temperature is attributed to an increase of the fraction of molecules in relatively mobile states. This 1H CRAMPS study provides detailed correlations of molecular dynamics with molecular structure for coals at temperatures between 25 and 250 °C.

15N CPMAS NMR of the Argonne Premium Coals

15N NMR data are reported for the Argonne Premium Coals. Arguments are presented to explain discrepancies between observations and conclusions obtained from NMR experiments and those obtained by XPS and XANES techniques. Detectability of different types of nitrogens is discussed in terms of cross-polarization dynamics together with the effects of the large chemical shift anisotropy that is found in different types of nitrogen functional groups. Data on acid-treated coals confirm the presence of pyridinic type nitrogens that were not observed in a previous 15N NMR study of coals.

Effect of coal rank on hydrocracking reactivities of primary coal extracts prepared in a flowing-solvent reactor: The Argonne premium coal sample set

Catalytic hydrocracking experiments were performed using ‘primary’ coal extracts, to establish correlations between coal rank and extract reactivities, in isolation from secondary effects associated with the coal dissolution step. A strong correlation was obtained between liquefaction conversion and carbon content of the original coals: R 2 = 0.96. Strong correlations were also found between hydrocracking conversions of material boiling > 450°C in the extracts and carbon content: for 30 and 60 min hydrocracking reaction times, R 2 = 0.92 and 0.93 respectively. The data indicate that the 450°C b.p. material taken into solution during profiles of liquefaction extracts and their corresponding hydrocracked (30 min) products, including the apparent disappearance of most material appearing under the excluded peaks. The extension of reaction time from 30 to 60 min gave rise to much less significant changes. U.v. fluorescence (u.v.-f.) spectra also showed that the first 30 min of hydrocracking gave rise to more significant structural changes than subsequent reaction did. The use of reaction times < 30 min might allow more detailed information to be gleaned about the relative rates of coal extract hydrocracking as a function of coal rank. Matrix-assisted laser desorption ionization mass spectrometry (MALDI-m.s.) was used to confirm (1) the presence of very large molecular mass materials in the extracts and (2) the very significant reduction in molecular masses achieved by the hydrocracking process. The results clearly show that in two-stage liquefaction processes, the overall yield of distillates (b.p. < 450°C) is strongly influenced by coal rank.

Effect of heating rate on normal and catalytic fixed-bed hydropyrolysis of coals

Fixed-bed hydropyrolysis tests have been conducted on a UK bituminous coal (Gedling), the Wyodak Argonne Premium coal sample and the high-sulfur Mequinenza lignite at a pressure of 15 MPa with heating rates of 5 and 300 K min −1. The tar yields and overall conversions increased markedly by ∼5–20 wt% daf coal as the heating rate was decreased from 300 to 5 K min −1 for final temperatures of 520 and 600°C, both with and without a sulfided molybdenum catalyst. Conversions of > 90 wt% were achieved with slow heating in catalytic hydropyrolysis for all three coals. The small increases in gas yield indicated that tar-forming as opposed to hydrogasification reactions are promoted by slow heating. These results demonstrate the value of slow heating for analytical applications of hydropyrolysis, which include the determination of organic sulfur forms and the covalently bound biomarker hydrocarbons in coals and petroleum source rocks.

Fossil fuel characterization using laser desorption mass spectrometry: Applications and limitations

traditional gas-phase methods. The application and limitations of these techniques to model compounds and fossil-derived materials is discussed in this study. LD and MALDI mass spectrometry are increasingly used to detect intact molecular species, such as proteins with masses from 1000 to 100,000 amu and beyond.' MALDI is also being used for a few high molecular weight polymers.2 A good example, related to coal-type systems, is the report on lignin mass spectrometry by MALDI.3 Here the mass spectrum shows a wide molecular distribution of several hundred to larger than 16000, with the center of gravity of the distribution around 2600. The results are interpreted in terms of oligomeric lignin molecules. Thus, if there are indeed large molecular species in a polymeric content in fossil fuel extracts, MALDI is an attractive technique. We have previously reported laser desorption of coal extracts that show only low molecular weight ions (<ZOO0 amu).4-6 We compare LD with fast atom bombardment and desorption chemical ionization mass spectrometry, two other soft ionization techniques. All of these techniques produce similar data that differ only in minor details. We have used our two TOF mass spectrometers for coal analysis by MALDI, have carefully analyzed our data and the instrumental conditions and conclude that the bulk of coal material produces only low molecular weight ions (up to 2000 amu). In agreement with these reports, Hanky showed LD and MALDI data of pyridine extracts which produced a distribution of ions between 150 and 1500.7 In addition, field ionization mass spectrometry has found similar pattern in the low mass region.8 Recently, Herod et. aI9-'* have interpreted their LD and MALDI data in terms of high mass species being desorbed. We have presented alternate interpretations for these results.6 In our hands, LD or MALDI of coals and extracts do not show any reproducible ion intensity over mass 2000. The conditions whereby large molecular ions can be desorbed intact are very specialized. This paper will describe the scope and limitations of laser desorption and matrix-assisted laser desorption in time-of-flight mass spectrometers as applied to high molecular weight molecules, such as proteins and polymer systems. EXPERIMENTAL The coals used in this study are the Argonne Premium Coal Samples. The procedures for the pyridine extract of the Argonne Premium Coals have been reported previousl~.~ The laser desorption mass spectra and matrix-assisted laser desorption mass spectra were recorded on a linear time-of-flight mass spectrometer constructed at Argonne and a Kratos Kompact MALDI 111 linear/reflectron time-of-flight mass spectrometer. The spectra were produced by exposing the samples distributed as thin layer on a stainless steel sample holder to laser pulses from either a Nd:YAG or a

Iron Species in Argonne Premium Coal Samples: An Investigation Using X-ray Absorption Spectroscopy

Iron K-edge X-ray absorption spectroscopy (XAS) has been used to examine the iron species that are present within the Argonne Premium Coal Samples. This technique was applied to both native coal samples and ones which had been extracted with concentrated hydrochloric acid. The near-edge absorption spectra (XANES) were analyzed using a deconvolution procedure to determine the relative amounts of oxo-ferrous, oxo-ferric, and pyritic environments in the coals. Three coals, Beulah-Zap, Wyodak-Anderson, and Lewiston-Stockton, apparently contain significant amounts of ferric species. Extended X-ray absorption fine structure (EXAFS) spectra were used to confirm the pyritic contents that were deduced from the near-edge spectra.

96/01196 Properties of second order transitions in Argonne Premium coals

96/01196 Properties of second order transitions in Argonne Premium coals

96/02266 Quantification of organic oxygen species on the surface of fresh and reacted Argonne Premium coal

96/02266 Quantification of organic oxygen species on the surface of fresh and reacted Argonne Premium coal

Properties of second order transitions in Argonne Premium coals

Differential scanning calorimetry (DSC) has been used to investigate the thermal transitions occurring for a series of eight Argonne Premium coals. Each of the coals was subjected to different heating/cooling profiles in order to determine the effect of cooling at varying rates on the second order process and to determine the effect of temperature of exposure on the second order process. The variable cooling rate scans showed that the position of the transition increased with decreasing cooling rate of the previous scan. The sequential heating scans demonstrated that the rank of coal had a direct influence on the resistance of the second order process to exposure to heat. Low rank coals showed a greater degree of resistance and this was assumed to be related to the density of non-covalent bonds within the structure.

Surface Tension of Coal Extracts in Organic Solvents

In this study, two Argonne premium coals were extracted with CS 2 -N-methyl -2-pyrrolidinone mixed solvent and the surface tensions of coal extract solution were measured

Distribution of Pendant Alkyl Groups in the Argonne Premium Coals

The ruthenium(VIII) oxidation reaction has been employed to determine the distribution of alkyl groups that are bonded to aromatic structural elements in lignin and the Argonne Premium Coals. The lignin, as expected, has few aromatic methyl groups, 0.02 per 100 carbon atoms. The results for the coals, Beulah-Zap 0.86, Wyodak 1.16, Illinois No. 6 1.76, Blind Canyon 2.45, Pittsburgh No. 8 2.05, Lewiston-Stockton 2.39, Upper Freeport 2.09, and Pocahontas No. 3 7.28 methyl groups per 100 carbon atoms, exhibit a steeply stepped discontinuous rank dependence. The abundances of the other small alkyl groups, which are least prevalent in the lignin and the low-rank coals, range from about 0.2 ethyl and 0.05 propyl groups to about 0.01 butyl groups per 100 carbon atoms in the bituminous coals. The curious rank dependence for the methyl group abundances may be the consequence of major structural changes that accompany the transformation of a medium-volatile bituminous coal into a low-volatile bituminous coal. The chemical origins of the methane that is formed during the pyrolytic decomposition of these fossil materials are discussed. The analysis suggests that methane, the major portion of which is obtained at high temperature after ethane and the other simple hydrocarbons have formed and the paraffinic and hydroaromatic fragments have decomposed, is not produced predominantly from the structural elements that exist in the unreacted coal through conventional processes such as β scission and ipso substitution. The methane that is formed at higher temperatures is accompanied by even greater molecular quantities of dihydrogen. The observations suggest that methane is produced by three reaction sequences involving oxidative condensation, hydrogen atom addition reactions that produce reactive hydroaromatic compounds, and carbene chemistry that provides a pathway to convert simple aromatic structures into methylated cyclopentane derivatives.

Carbons prepared from coals for anodes of lithium-ion cells

Carbons were prepared by pyrolysing eight different coals from the Argonne Premium coal sample bank at temperatures near 1000 °C. Electrochemical cells were made to study lithium insertion in these carbons. The electrochemical behavior and physical properties of these pyrolysed coals was compared to that of pyrolysed sugar, PVC and pitch which we have studied carefully before. Using powder X-ray diffraction and small angle X-ray scattering (SAXS), we show that pyrolysed coals which have the smallest fraction of parallel-stacked graphene layers and hence the largest number of nanoscopic pores per unit mass, have the largest capacity for lithium insertion. A reversible capacity of about 450 mAh/g was attained for lithium/carbon cells made from Blind Canyon Seam coal.

One-dimensional description of the average polycyclic aromatic unit in Pocahontas No. 3 coal: an X-ray scattering study

The radial distribution method was used to examine the non-crystalline portion of a low-volatile bituminous coal, Pocahontas No. 3, from Buchanan County, VA, USA. This coal, one of the Argonne Premium Coal Sample Program, was used as received for X-ray absorption/diffraction/scattering experiments. The diffraction due to the crystalline minerals contained in the coal and due to the graphene layering peak was removed from the amorphous scattering component. The latter was fitted to the self-scattering curve constructed from the scattering factor for carbon and the difference was Fourier transformed to obtain the one-dimensional structural details of the average short-range structural unit in this coal. Interpretation of the radial distribution indicates that the average structural unit is ∼ 80% aromatic and consists of polycyclic six-membered rings which are predominantly, if not exclusively, planar. In addition, the average graphene layer has a diameter of ∼ 7.7 Å. The radial distribution function results compare favourably with those obtained by 13C NMR spectroscopy.

E.p.r. HFS spectral characteristics of Mn 2+ impurity ions in Argonne and Alberta coals

A new, more comprehensive study of the 9 and 33 GHz CW e.p.r. Mn 2+ impurity ion spectral characteristics of the eight Argonne premium coals and two Alberta h.v. bituminous coals is reported. These characteristics include the HFS a 1 relative amplitude, linewidth and lineshape as well as a more accurate and reliable determination of the g-value, the HFS parameter A and the c 0 2 and c 0 4 ZFS parameters for powdered coal samples from the ΔM = ±1, Δm = 0 central and weak non-central transitions using the spin Hamiltonian diagonalization spectral simulation method of analysis. The six Mn 2+ Δm = 0 HFS central transitions observed in coal samples do not have two component resonances, unlike those for Mn 2+ in polycrystalline calcite, which is attributed to lineshape broadening. However, the a 1 amplitude and linewidth variation for the six Mn 2+ HFS central transitions observed in each of the coal samples studied is consistent with that observed in polycrystalline calcite. The consistency of the a 1 amplitude and linewidth analysis as well as of the improved values of the e.p.r. spectral parameters for Mn 2+ impurity ions in calcite and coal provides more conclusive confirmation that the e.p.r. spectrum of Mn 2+ originates from the calcite mineral component of coal.

Quantification of Organic Oxygen Species on the Surface of Fresh and Reacted Argonne Premium Coal

X-ray photoelectron spectroscopy (XPS) was used to determine the kinds of organic and inorganic oxygen species present in Argonne Premium coal. In most cases the XPS results for organic oxygen with fresh coal compare favorably with other methods of analysis. The evolution of CO 2 , CO, and H 2 O during pyrolysis at 400 °C was quantified, and their appearance was associated with the loss of hydroxyl and carboxyl groups in fresh coal. Oxidation of fresh coal at 125 °C in air resulted in significant increases in the level of iron and inorganic sulfate on the coal surface. Oxidation of subbituminous and lower rank coal resulted in increases in the level of carboxyl species but decreases in the level of hydroxyl species. The levels of carboxyl, carbonyl, and other species increase upon oxidation of bituminous and higher rank coal. The advantages and limitations of the XPS approach for quantifying organic oxygen functionalities in coal are discussed.