Argonne Premium Coals Research Articles

Activation energies and evolved gas analysis for Argonne premium coals

ABSTRACT A set of eight coals from the premium Argonne coal sample program were studied using thermogravimetric and evolved gas analysis. Gaseous combustion products were analyzed using an FTIR spectrometer and a chemiluminescence analyzer. Additionally, modulated thermogravimetric experiments were carried out to determine activation energies associated with the combustion of each sample. The exhaust from the thermogravimetric analyzer was directed to the gas analyzers for detecting and quantifying CO, CO2, and NO. Evolved gas analysis was conducted at a ramp rate of 5°C for CO, CO2 evolution, and 20°C per minute for nitric oxide evolution, with the furnace temperature varying between 20°C–750°C. Modulated thermogravimetric analysis experiments were carried out in the same temperature range. The temperature was increased at a rate of 2°C per minute for the modulated experiments. Each test had a superposed temperature modulation with amplitude ±5°C and a period of 200 seconds. The experiments provide valuable information on the combustion kinetics and emission characteristics of selected American coals.

Thermal Behavior of Crystalline Minerals in Argonne Premium Coals under Air and Argon Atmospheres: Comparison between Bituminous, Sub-bituminous, and Brown Coals

Thermal Behavior of Crystalline Minerals in Argonne Premium Coals under Air and Argon Atmospheres: Comparison between Bituminous, Sub-bituminous, and Brown Coals

Two dimensional 1H magnetic resonance relaxometry-based analyses of Argonne premium coals

1H magnetic resonance (MR) is a useful technique for determining molecular structure of coals. Most previous MR studies were based on one-dimensional 1H magnetic resonance relaxometry. Two-dimensional (2D) 1H magnetic resonance relaxation correlation methods, T1–T2* and T1ρ–T2*, were used to evaluate Argonne premium coals, including Beulah-Zap (BZ), Wyodak-Anderson (WA), Pittsburgh #8 (PIT), Upper Freeport (UF), and Pochontas #3 (POC) coals as received. Samples were also measured after oxidization at low temperature (110 and 210 °C). From the 2D relaxation correlations, various hydrogen-containing components were distinguished and characterized. The change of hydrogen during low temperature oxidation was analyzed, and the hydrogen content estimated. The technique captured significant differences between low rank coals (BZ and WA) and high rank coals (PIT, UF, and POC). The order of T1/T2* ratios is aliphatic hydrogen > aromatic hydrogen > hydrogen- and oxygen-containing functional groups > moisture in BZ and WA coals. The PIT, UF, and POC coals mainly contain aromatic hydrogens. The T1–T2* and T1ρ–T2* spectra of BZ and WA coals change significantly during low temperature oxidation. Our new MR method provides new insight into coal behaviour.

Structural Characterization of Indian Vitrinite-Rich Bituminous Karharbari Coal.

The detailed investigation of the chemical structure of vitrinite-rich Karharbari coal was performed utilizing advanced analytical techniques. The salient objective of this work is the evaluation of various structural properties of coal, which is necessary for identifying the chemical and physical interactions between coal and various reactants during its utilization. Karharbari coal is a poorly organized coal with high aromatic content. The value of corrected aromaticity (fa’) was found to be 0.82 by 13C NMR spectroscopy and was also confirmed by XRD (aromaticity = 0.84) and FT-IR analysis (aromaticity = 0.82). The average molecular weight of the aromatic cluster was found to be 507 amu by the NMR result, which is closer to the result obtained by HRTEM (MW = 530 amu). The structural and lattice parameters of Karharbari coal were obtained by NMR spectroscopy and then compared with the similar rank Argonne Premium coal. The molecular weight distribution was obtained by LD-TOF-MS and compared with HRTEM fringe model analysis. The presence of different heteroatoms like carbon, oxygen, nitrogen, and sulfur with their functionalities was determined by using the XPS technique. Different carbon/oxygen functionalities present in the Karharbari coal were found to be (C–C) and (C–H) 68.5%, (C–O) 23.4%, (COO–) 1.9%, and (C=O) 6.0%. Nitrogen functionalities such as pyridine, pyrrolic, quaternary, and oxidized nitrogen and their compositions (mol %) were 19.3, 45.6, 31.2, and 3.7%, respectively. Different forms of sulfur were also found to be present, namely, thiophenes, sulfones, sulfuric acid, and sulfates with the molar contents of 16.4, 41.6, 21.3, and 20.5%, respectively. This information will be useful in improvising coal utilization techniques.

Reactivities of American, Chinese and Estonian oil shale semi-cokes and Argonne premium coal chars under oxy-fuel combustion conditions

Reactivities of American, Chinese and Estonian oil shale semi-cokes and Argonne premium coal chars under oxy-fuel combustion conditions

Direct determination of organic and inorganic oxygen in coals from the Argonne Premium sample program by solid sampling electrothermal vaporization inductively coupled plasma optical emission spectrometry

This paper presents a new analysis method for directly determining organic and inorganic oxygen in coals, varying in rank from lignite to semi-anthracite. By means of Electrothermal Vaporization Inductively Coupled Plasma Optical Emission Spectrometry (ETV-ICP OES) the coals are thermally decomposed in an argon atmosphere up to a temperature of 2400°C and the released oxygen is continuously detected throughout the temperature range. The study presented mainly focuses on assigning the obtained peaks in the transient emission signal to organic or inorganic oxygen, then evaluating the accuracy of this method. To assign the peaks, the raw coals were demineralized and the resulting changes were analyzed using ETV-ICP OES and FTIR spectroscopy. The precision of the analysis was evaluated by comparing the obtained oxygen values with published data for the total set of Argonne Premium Coals. The analysis method described is time- and cost-efficient and well suited to the fast characterization of coal, enabling the rapid recognition even of the critical silicate-rich coals. It can be automated to a large extent and applied in process-accompanying analyses.

Dynamic nature of supercritical CO2 adsorption on coals

Adsorption on non-rigid solids was shown to be a dynamic process. Excess adsorption and desorption isotherms of CO2 on eight Argonne Premium coal samples were measured at 55 °C and pressures up to 14 MPa by manometric method. The excess adsorption isotherms of CO2 on powdered coals showed almost Langmuir-like to rectilinear shape behavior at low pressures up to 9 MPa, and it increased noticeably at pressures higher than 9 MPa. There was a significant hysteresis between the excess adsorption and desorption isotherms for each rank of coals, which was related to the volumetric uncertainties occurring during the adsorption isotherm measurements. The parameters related to the adsorption capacity and micro porous characteristics of the coal were obtained at different pressure ranges by fitting the experimental data to the modified Dubinin-Astakhov (D-A) equation at the increasingly larger pressure ranges, using only the first 4 data points of the excess adsorption isotherm initially, and progressively using additional data points for the subsequent values. It was shown that the curve fit parameters vary with pressure, and therefore, concluded that the adsorption on non-rigid solids such as CO2 on coal is indeed a dynamic process. It was suggested that new adsorption isotherm equations need to be developed considering the dynamic nature of the adsorption on solid adsorbents.

Solid-Sampling Electrothermal Vaporization Inductively Coupled Plasma Optical Emission Spectrometry for Direct Determination of Total Oxygen in Coal.

A new analytical method for direct determination of total oxygen contents in eight coal samples of the Argonne Premium Coal (APC) series and in the NIST SRM 1632d is presented. The development of a suitable calibration procedure, optimization of measurement conditions, and the application of a tailored data processing for handling of plasma effects and high blanks enable the quantification of oxygen simultaneously with other trace, minor, or major elements in whole coal samples by means of electrothermal vaporization inductively coupled plasma optical emission spectrometry (ETV-ICP OES). For comparison, the oxygen contents were determined by a direct oxygen analyzer. The obtained oxygen values of the APC and the reference material NIST SRM 1632d were compared to data in the literature. The precision of the ETV-ICP OES was within ±3.5%, and the recovery better than 92%. With this good accuracy, the developed direct solid sampling method ETV-ICP OES is well suited for the fast determination of oxygen in coals, varying in rank from lignite to semianthracite, in a content range of about 100 ppm up to 27% using 1.5 mg sample weight. This direct analysis method represents an accurate, advantageous alternative to currently used methods for estimation of total oxygen contents in coals.

Quantitative multi-element analysis of Argonne Premium Coal samples by ETV-ICP OES – A highly efficient direct analytical technique for inorganics in coal

A new and highly efficient solid sampling method was developed for fast direct multi-element analysis in coals using electrothermal vaporization as sample introduction system for inductively coupled plasma optical emission spectrometry (ETV-ICP OES). With ETV coupled to ICP OES it is possible to analyze trace and major elements simultaneously in whole coal samples with a minimum effort of sample preparation and short analyzing times. The quantitative determination of Al, Ba, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Si, Ti, V and Zn by ETV-ICP OES in all eight Argonne Premium Coals, covering the rank range from lignite to semi-anthracite, is presented. The results are comparable with the reported element contents in literature. It is shown, that the fast direct solid sampling multi-element spectroscopic method, based on electrothermal vaporization of powdered samples, is proved to be a suitable alternative to labor intensive traditional methods.

Direct determination of sulfur species in coals from the Argonne premium sample program by solid sampling electrothermal vaporization inductively coupled plasma optical emission spectrometry.

A new direct solid sampling method for speciation of sulfur in coals by electrothermal vaporization inductively coupled plasma optical emission spectrometry (ETV-ICP OES) is presented. On the basis of the controlled thermal decomposition of coal in an argon atmosphere, it is possible to determine the different sulfur species in addition to elemental sulfur in coals. For the assignment of the obtained peaks from the sulfur transient emission signal, several analytical techniques (reflected light microscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction) were used. The developed direct solid sampling method enables a good accuracy (relative standard deviation ≤ 6%), precision and was applied to determine the sulfur forms in the Argonne premium coals, varying in rank. The generated method is time- and cost-effective and well suited for the fast characterization of sulfur species in coal. It can be automated to a large extent and is applicable for process-accompanying analyses.

S-XANES analysis of thermal iron sulfide transformations in a suite of Argonne Premium Coals: A study of particle size effects during pyrolysis

A suite of four bituminous Argonne Premium Coal Samples, namely Pittsburgh#8 (P8), Blind Canyon (BC), Upper Freeport (UF), and Illinois #6 (IL6), were pyrolyzed according to the Easy Ro kinetic model (Burnham and Sweeney, 1989) to Ro=4.3 and iron sulfide thermal transformations were tracked by the use of S-XANES (Sulfur X-ray Absorption Near Edge Structure.) It was shown that the pyrite transformed first to pyrrhotite by Ro=1.5, and then started to transform to troilite by Ro=2.4. Some Argonne Coals displayed evidence of structural instability. In addition, particle size effects were examined. Pyrolysis was performed on not-ground (large-particled) coal samples, which were subsequently ground to micron-size particles before data collection. S-XANES was also collected for the not-ground post-pyrolysis IL6 coal to show the effect of the extent of reaction on the surface of the particles as opposed to the bulk. It was found that the pyrite-to-pyrrhotite transformation in large particles of IL6 coal proceeded from the surface of the particle and progress inward, consistent with the shrinking core model. A scheme for determining particle size based on organic sulfur content was also developed for a coal model consisting of a 50/50mol% mixture of pyrite and Maya petroleum vacuum resid asphaltene for a range of known particle sizes. Lastly, the behavior of both marcasite (a polymorph of pyrite) and pyrite in a coal model was investigated for large (~100μm) and small (~5μm) particles. The marcasite proved to be less structurally stable than pyrite for the large particles, with an abrupt transformation to a mixture of pyrrhotite and troilite, and an abrupt drop in aliphatic sulfur content, indicating consequent H2S generation at Ro=2.4. This transformation is much less pronounced for pyrite at the same point in pyrolysis.

Quantitative Estimation of Major and Trace Elements in Coals of the Benue Trough, Nigeria

The concentrations of major and trace elements in ash residues of coals of the Benue Trough, Nigeria have been determined by electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry, respectively. Major and trace element determination in rocks by fusion on an iridium strip heater followed by electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry is extended here to coal ash, and the accuracy of the method is evaluated by including an Argonne Premium Coal reference sample in each analysis program. Si and Al are the major elements detected in the coal ashes. An assessment using worldwide concentration ranges of trace elements in coal ashes indicates that the Benue Trough coal ash residues are enriched in some hazardous trace elements, including Be, V, Co, and Cr. The estimated concentrations of most of the elements in the raw coals are higher than the world averages for coal. The results obtained for the Argonne Premium Coal show very good correlations with the literature and certified values, indicating that the technique described in this study can be routinely used to determine element concentrations in coals.

Determination of the Average Aromatic Cluster Size of Fossil Fuels by Solid-State NMR at High Magnetic Field

We show that the average aromatic cluster size in complex carbonaceous materials can be accurately determined using fast magic-angle spinning (MAS) NMR at a high magnetic field. To accurately quantify the nonprotonated aromatic carbon, we edited the 13C spectra using the recently reported MAS-synchronized spin–echo, which alleviated the problem of rotational recoupling of 1H-13C dipolar interactions associated with traditional dipolar dephasing experiments. The dependability of this approach was demonstrated on selected Argonne Premium coal standards, for which full sets of basic structural parameters were determined with high accuracy.

Evolution of Hydrogen Chloride and Change in the Chlorine Functionality during Pyrolysis of Argonne Premium Coal Samples

In order to understand chlorine chemistry in coal pyrolysis, the dynamics of HCl evolution and changes in chlorine functional forms during temperature-programmed pyrolysis of eight Argonne premium coal samples have been examined with an online HCl-monitoring technique and by the Cl 2p X-ray photoelectron spectroscopy (XPS) method. The rate profiles of HCl evolved show at least three distinct peaks at 390, 520, and 600 °C, and the presence of these peaks depends strongly on the type of coal. The HCl peak at 390 °C appears with four coals alone and becomes considerably small by water washing, whereas the high-temperature peaks above 450 °C observed with almost all of the coals do not change significantly after washing. Yields of HCl up to 1000 °C are in the range of 50–90% in many cases, and the yield tends to decrease with increasing atomic Ca/Cl ratio in coal. The chlorine XPS analyses show that the chlorine in each coal is enriched at the surface and composed of inorganic and organic functional forms. The extent of the enrichment and proportion of organic chloride species increase after pyrolysis at 450 °C, whereas they decrease at high temperatures of 800 and 1000 °C. Some model experiments followed by the chlorine XPS measurements show that the reaction of HCl with carbon active sites proceeds readily at 500 °C to produce organic C–Cl forms, which release HCl again above 500 °C upon reheating in an inert gas. On the basis of the above-mentioned results, it is possible that HCl evolved below 450 °C in coal pyrolysis comes predominantly from water-soluble chlorine functional groups in coal, whereas HCl formation above 450 °C originates mainly from organic chlorides, which could be present inherently in coal and/or may be formed by secondary reactions of HCl evolved at a lower temperature with carbon active sites in the nascent char.

Solid-State NMR Studies of Fossil Fuels using One- and Two-Dimensional Methods at High Magnetic Field

We examine the opportunities offered by advancements in solid-state NMR (SSNMR) methods, which increasingly rely on the use of high magnetic fields and fast magic angle spinning (MAS), in the studies of coals and other carbonaceous materials. The sensitivity of one- and two-dimensional experiments tested on several Argonne Premium coal samples is only slightly lower than that of traditional experiments performed at low magnetic fields in large MAS rotors, since higher receptivity per spin and the use of 1H detection of low-gamma nuclei can make up for most of the signal loss due to the small rotor size. The advantages of modern SSNMR methodology in these studies include improved resolution, simplicity of pulse sequences, and the possibility of using J-coupling during mixing.

Fine Structure Evaluation of the Pair Distribution Function with Molecular Models of the Argonne Premium Coals

The pair distribution function (PDF) is one means of evaluating the atomic spatial arrangements of coals. Analysis of PDF based on X-ray diffraction data provides structural information on turbostratic crystalline parameters that can be utilized to further characterize coal structure. With coalification, expectations are of limited growth in aromatic stacking and a slight growth in the aromatic cluster size over the lignite to medium-volatile bituminous range. The PDF can be also used to construct and validate atomistic representations for carbonaceous materials including coal. Here, the PDF was evaluated with molecular slice models of several Argonne Premium coals (Beulah-Zap, Illinois No. 6, Upper Freeport, Pocahontas No. 3), also a non-Argonne Hon Gai anthracite, and compared to experimental observations. Atomistic representations were generated directly from high-resolution transmission electron microscope (HRTEM) lattice fringe images. The Fringe3D approach populates aromatic moieties matching the distributions of fringe: length, layers per stack, interlayer spacing, and orientations to produce an aromatic slice model of limited depth. Perl scripts incorporated appropriate aliphatic and heteroatom components. This approach creates atomistic representations with greater ease, improved accuracy, and reduced computational expense than other construction approaches. The constructed coal models were partially geometry-optimized to achieve realistic bond lengths but without displacement of coal molecules enabling the distribution of fringe length, stacking, and orientations to be duplicated in 3D modeling space. The resulting coal slice models, devoid of cross-links, captured a distribution of turbostratic crystalline dimensions with an average cluster size of about 1 nm, an average interlayer spacing ranging between 0.37 and 0.39 nm, and an average stacking number of ∼2–3 in accordance with HRTEM and XRD data for Argonne coals. These structural models were used to predict PDFs and to evaluate the fine detail of the frequency spectra via examination of intermolecular and intramolecular contributions. There was good agreement between predicted and experimental observations. Analysis of the simulated intermolecular PDF contribution showed strong intensities with increasing coal rank in agreement with the growth in the stacking number and stack height observed from low- to high-rank coals. The simulated intramolecular PDF contribution showed shorter peak amplitudes for low-rank coals in comparison to high-rank coals in agreement with the increase in stack width as coal rank increases. To further examine these contributions, lattice models composed of pyrene molecules were also constructed via Fringe 3D and manipulated to directly investigate the effect of aromatic orientation distributions and stacking on the simulated PDF. Peak intensities of simulated intermolecular PDFs at the average interlayer spacing increased with the degree of alignment (ϕ) according to g(r)interd002 = 0.0014ϕ2 + 0.0107ϕ + 4.2784. This result was consistent with the slight increase in the stacking number observed from low- to high-rank coals with a more dramatic transition for anthracite.

A molecular model for Illinois No. 6 Argonne Premium coal: Moving toward capturing the continuum structure

A large-scale molecular model for Illinois No. 6 Argonne Premium coal is generated based on an automated construction approach in an effort to move toward capturing the continuum structure. The model contains 50,789atoms within 728 molecules and is the largest, most complex coal representation constructed to-date. The aromatic ring size distribution was based on multiple high-resolution transmission electron microscope (HRTEM) lattice fringe micrographs and was duplicated with automated construction protocols (Fringe3D) in molecular modeling space. Additional structural data was obtained from the abundant literature assessing this Argonne Premium coal. Organic oxygen, nitrogen, and sulfur functionalities were incorporated primarily into the polyaromatic structures according to X-ray photoelectron spectroscopy and X-ray adsorption near-edge structure spectroscopy data. Aliphatic carbons were in the form of cross-links (bridges and loops) and pendant alkyl groups based on the combination of laser desorption ionization mass spectrometry (LDIMS), ruthenium ion catalyzed oxidation, elemental analysis, and NMR data in good agreement with the literature. Bound and bulk water was also included. Construction of the coal molecules was performed by use of Perl scripts developed in Materials Studio to eliminate personal bias and improve the accuracy and the scale of the structure generated. The large-scale model captured a broad and continuous molecular weight distribution in accordance with LDIMS data here ranging from 100 to 2850Da, enabling inclusion of structural diversity to capture a portion of the continuum structure. A theoretical pyridine extraction yield, determined by a group contribution approach, was in agreement with the experimental value. The extract and residue representations were generated from the large-scale Illinois coal model and showed consistency with NMR, elemental analysis and LDIMS trends. The distribution of heteroatomic classes and double bond equivalents was also well-defined experimentally based on electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. These data further constrain the molecular weight of extractable material and was consistent with limited pyridine extractability and model heteroatom classes. Future work will be well served by staying within the limits established by the approach and increasing the structural diversity (sampling frequency through increased scale) to better capture the complex nature of coal structural diversity, i.e., the continuum.

Constitution of Illinois No. 6 Argonne Premium Coal: A Review

A review of the chemical and physical structural features of the Argonne Premium Illinois No. 6 coal is presented. The topics covered include aromatic and aliphatic components, functional groups and heteroatoms, molecular weight distribution, nature of the cross-linked network, porosity, surface area, and density. 13C NMR indicated that Illinois No. 6 high-volatile bituminous coal contains 15 aromatic carbons (three to four fused aromatic rings) and 5 attachments per cluster, and an average cluster molecular weight of 316 Da. Methyl units are the most abundant pendant alkyl groups. XPS data showed that organic oxygen, nitrogen, and sulfur functionalities are primarily ether and phenolic, pyrrolic, and thiophenic groups, respectively. Solvent swelling studies suggested that Illinois coal structure is composed of a covalently bonded network of aromatic clusters that are extensively hydrogen bonded. SANS analyses showed that Illinois coal is mostly microporous and 129Xe NMR indicated that the pore structure ...

Direct Determination of Pyrite Content in Argonne Premium Coals by the Use of Sulfur X-ray Near Edge Absorption Spectroscopy (S-XANES)

Argonne premium coal samples are used by researchers worldwide as standards in coal research. The set consists of a suite of eight samples of varying rank from the United States. The sulfur X-ray near edge absorption spectroscopy (S-XANES) third-derivative analysis method uses a well-defined library of model compounds to curve fit each sample spectrum and enables sulfur speciation to within about 10 mol % for materials such as coals and kerogens. This direct, non-destructive characterization technique, used in conjunction with others, such as X-ray photoelectron spectroscopy, can provide valuable information about chemical and thermal sulfur transformations. The S-XANES third-derivative analysis method provides quantitative results for organic sulfur species in coal but has not been used to quantify inorganic sulfur forms to date. In general, the direct determination of the pyrite content, a metal sulfide, has been problematic. Through wet chemical methods, several of the Argonne premium coal samples are known to exceed 50 mol % pyrite but only show a weak pyrite feature in the S-XANES absorbance and third-derivative spectrum. We show that particle-size effects are responsible for attenuating the pyrite signal for high-pyrite-containing Argonne premium coals. Grinding techniques are discussed that decrease the particle size and produce spectra and results that are in better agreement with those from established wet chemical methods for pyrite determination.

Effect of Moisture on Adsorption Isotherms and Adsorption Capacities of CO2on Coals

The effect of moisture on the adsorption isotherms and adsorption capacities of CO2 on Argonne Premium coals has been investigated. In some experiments a small hysteresis was observed between the adsorption and desorption isotherms. The hysteresis was absent or negligible for high-rank and as-received coals but was discernible for lower rank and dried coals. An equation that accounted for the volumetric changes when an adsorbate alters the structure of an adsorbent was employed to interpret the data. The best-fit solutions indicate that the coal volume decreases upon drying. The microscopic shrinkage estimated using helium expansion was greater than the shrinkage reported using the bed-height technique. The microscopic shrinkage was 5−10% for low-moisture medium and high-rank coals and up to 40% for low-rank coals having higher moisture contents. The CO2 swelling of coals during adsorption isotherm measurements was estimated to be about the same as the shrinkage that occurred during the moisture loss. The...