Comparison of methods for the determination of organic oxygen in coals

doi:10.1016/0016-2361(86)90333-9

Fuel

Volume 65, Issue 11, November 1986, Pages 1563-1570

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Abstract

Coals distributed widely in rank and geographical origin have been analysed for organically-bound oxygen by several conventional and fast neutron activation analysis (FNAA) techniques. Pyrolysis of demineralized coal with measurement of evolved CO₂ by coulometry was found to be the most reliable of the conventional methods. Direct FNAA determinations of organic oxygen by analyses of demineralized coal (DMC) samples yielded data in excellent agreement with pyrolysis, as did values computed using a modified ‘by difference’ calculation. The convergence of data from these totally independent approaches, suggests a measure of true organic oxygen levels has been achieved. A ‘difference method’ based on FNAA determinations of total dry coal oxygen and inorganic oxygen in low temperature ash yielded organic oxygen data that were typically lower than pyrolysis values, possibly due to oxidation of organic sulphur in the ashing process and/or the presence of non-extractable mineral oxygen in the DMC used in the pyrolysis method. A third FNAA ‘difference method’ based on simultaneous determinations of both total oxygen and silicon contents of dry whole coals, followed by estimation of the inorganic oxygen contents based on the silicon contents, was found to be rapid and adaptable to on-stream analysis. However, observed mineralogy-dependent deviations from a simple inorganic oxygen-silicon relationship suggest that the latter technique would be most successful when applied to coals with similar mineralogy.

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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
2017, Fuel
Citation Excerpt :
Unfortunately, analytical errors in direct determination and large weight changes in the mineral matter (MM) during high-temperature ashing are reflected in this oxygen value. In consequence, the calculated ODiff is an uncertain value and can sometimes be a negative value using the Standard Method for the Ultimate Analysis of Coal and Coke [7,10]. The complexities of analyzing the organic substances of coals have been discussed in some detail by Given and Yarzab [6].
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.
Determination of organic oxygen in petroleum cokes and coals
2016, Microchemical Journal
Citation Excerpt :
About the analysis of the organic oxygen in coals, different papers have been found where different techniques of quantification have been used. The determination of the total organic oxygen has been carried out by thermogravimetry Fourier transform infrared spectroscopy (TG-FTIR), fast neutron activation analysis (FNAA), or pyrolysis–gas chromatography by different authors [3,14–18]. Others use techniques such as the acetylation–hydrolysis and ion-exchange and titration methods, and solid-state C NMR measurement [19], or XPS [1] to analyse the distribution of oxygen-functional groups in coals.
The accuracy of the oxygen value is important in calculating heat balances for boiler efficiency studies in coke and coal industry, and these data are used for determining the suitability of coals for coking, liquefaction, or gasification processes. Nowadays, organic oxygen is normally estimated by subtracting the determined percentages of all other constituents (carbon, hydrogen, nitrogen, sulphur, and ash content) from 100, so the errors in the determined values are reflected in the estimated organic oxygen value.
This paper describes a rapid and reliable methodology for the analysis of organic oxygen in petroleum cokes and coals using a pyrolysis furnace followed by IR detection, calculating the detection and quantification limits and the uncertainty of the method. The accuracy of the method has been also checked by analyzing reference materials and determining all the constituents (C, H, N, S, and ash content) of the petroleum cokes and coals analysed in this study. The organic oxygen data have been also correlated with the volatile matter as the oxygen-containing compounds constitute part of the total volatile matter and this parameter is important in the selection of coals and in the evaluation of coking of coke which will determine the use of the coke.
The identification of oxygen functional groups in carbonaceous materials by oxygen K-edge XANES
1997, Carbon
The aim of this paper is to assess the potential of oxygen K-edge X-ray absorption near-edge spectroscopy (XANES) for the identification of oxygen functional groups in carbonaceous materials, with a particular view to the identification of functional groups formed during combustion. A suite of aromatic reference compounds was used to provide “fingerprints” for a range of oxygen functional groups. The results indicate that oxygen K-edge XANES is sufficiently sensitive to functional group type for this application. A set of partially gasified chars was prepared from samples of pure acenaphthylene, Wearmouth coal and Cwmbargoed coal. The oxygen K-edge XANES spectra of these chars clearly show that one can follow the simultaneous loss of oxygen species originating in the carbon and formation of new surface complexes during combustion. It is of particular note that anhydrides and lactones can be readily distinguished using this technique. The mechanistic implications of the results for carbon combustion are discussed.
A kinetic investigation of coal liquefaction at short reaction times
1994, Catalysis Today
Coal liquefaction kinetics have been studied at very short reaction times (less than 250 seconds) in order to emphasize the initial underlying physical and chemical processes involved. These studies were made possible by the use of a continuous flow stirred tank reactor (CSTR) which avoids the problems of slow heat up and cool down associated with the massive equipment required for running high-temperature and high-pressure liquefaction reactions. Preliminary physical (NMR and ESR) and chemical analytical results are presented on the coal liquids and reaction residues from Illinois No. 6 hv bituminous and Wyodak Black Thunder subbituminous coals.
ESR results showed that radical concentration in the solid residue changed during coal liquefaction. These changes were accompanied by changes in the NMR-derived aromaticity. The rate of decrease of organic-based radicals was different for Wyodak Black Thunder and Illinois No. 6 coals, perhaps indicating a different mechanism for the quenching of radicals in these bituminous and subbituminous coals. NMR spectra of the liquid products indicated that the initially produced material was relatively aromatic, and that subsequent products had lower aromatic content. This is consistent with secondary hydrogenation of the primary liquefaction products. Finally, the total oxygen contents of the coal residues decreased gradually during the first three minutes of coal liquefaction at 390°C. A corresponding decrease in the hydroxyl content of these residues was also noted.
Development of a reliable coal oxidation (weathering) index - Slurry pH and its applications
1991, Fuel Processing Technology
A simple slurry pH titration method was developed as a means of measuring the degree of mild air oxidation in coal, especially for low rank, non-caking coals. The results show that this pH titration method, with prior rehydration at 150°C, is a practically useful way of determining the degree of air oxidation of a coal sample of known origin but uncertain weathering status. For coals of a lower rank than high volatile bituminous, this method can be simplified to direct measurement of the slurry pH without the rehydration step. Among the variables influencing the rate of mild air oxidation as measured by the slurry pH, temperature is the most important whereas humidity exhibits little or no effect on the initial slurry pH although it has a marked effect on the pH titration profiles. Use of Curie-point pyrolysis-low voltage mass spectrometry on weathered, subbituminous coal samples from a coal storage pile reveals that the main effect of humidity on the composition of the pyrolyzate appears to involve certain sulfur compounds. Application of the initial slurry pH as an oxidation /weathering index yields an activation energy of oxidation/weathering in the 20–150°C range of 50–65 kJ/mol (12–16 kcal/mol) and indicates the existence of several different oxidation mechanisms in the temperature regimes between 60 and 150°C.
<sup>1</sup>H n.m.r. Zeeman relaxation in premium coals and other coals of various rank
1989, Fuel
Proton n.m.r. spin-lattice relaxation measurements are reported of eight available Argonne premium coals and five other coals. Possible relaxation mechanisms are considered, including proton-proton interactions, interactions between the protons and the unpaired electrons present in organic radicals, and interactions between the protons and the unpaired electrons present in paramagnetic oxygen. The effect of possible limitations in proton spin diffusion on relaxation behaviour has also been taken into account. For the two highest rank premium coals an unusually long relaxation time was observed. This was found to be due to the fact that these coals have never been exposed to air. The relaxation rates of the other coals were found to increase strongly with decreasing coal rank. It was concluded that this is due to an increasing amount of paramagnetic oxygen, trapped in the coals even after evacuation. It was also observed that for most coals the relaxation is non-exponential, with a non-exponentiality which increases for decreasing coal rank. This has been attributed to the presence of protons in both a molecular and a macromolecular phase in the coal, with an increasing amount of protons in the molecular phase for decreasing coal rank. The results were found to be consistent with those obtained in other coals of similar rank.

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Comparison of methods for the determination of organic oxygen in coals

Abstract

Geochim. Cosmochim. Acta

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Colloids and Surfaces

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Microchem. J.

Chem. Geol.

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EPRI Journal

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Anal. Chem.