Coal Jane V. Thomas Wyoming Analytical Laboratories, 605 South Adams, Laramie, Wyoming 82070 Research on coal and products from coal, including products of combustion, is becoming more concerned with environmental applications and with coal products from liquefaction, pyrolysis, and combustion. PROXIMATE AND ULTIMATE ANALYSIS Rapid Methods. Samples (Al)described quick laboratory methods for determinations such as ash, moisture, sulfur, and sodium and also discussed the use of statistics. Rexin (A2) reported on methods for rapid and reliable approximation of ASTM procedures for use in coal quality control in mining; determinations discussed included microwave air-drying, ash, sodium, and calorific values. Moisture. Baumann and co-workers (A3)described a laboratory instrument that determines moisture even in a severe industrial environment. Riley and Burris (A4) evaluated a pulsed NMR method for determining moisture in low-rank coals and presented methods to further improve the method. Litton and Page (As) used proximate analyses of coals from lignite to low-volatile bituminous to develop a parameter called the moist fuel ratio, which they found to be highly correlated to both the spontaneous combustion and dust-producing characteristics. Nitrogen. Keleman and co-workers (A@used XPS to identify and quantify the organically bound nitrogen forms present in fresh Argonne premium coal samples;XPS spectra obtained on a variety of model compounds were used to establish a curve resolution methodology. Mitra-Kirtley and others (A7) determined five different nitrogen structures by X-ray absorption near-edge spectroscopy (XANES) methodology in several coals of different ranks. Hamalainen and co-workers (AS)studied the suitability of an ion-selective electrode for the determination of ammonia in pyrolysis gases of fossil fuels (Finnish energy peat samples and a coal sample). The peroxyacetic acid oxidation products from a series of coals of organic sulfur contents from 0.5 to 9.8 wt k were examined by Palmer and colleagues (AS),and the distributions of organic sulfur and nitrogen compounds were determined by gas chromatography; the number of sulfur compounds detected was small compared with that of organic nitrogen compounds detected, suggesting that the sulfur chemistry of coal is considerably more simple than its nitrogen chemistry. Sulfur. Demir and colleagues (AlO)used optical microscopy and SEM-EDX to study two samples of Illinois coals to evaluate the spatial distribution of organic sulfur withii macerals occurring next to pyrite grains, both in the raw coal and their semicokes. Ailey-Trent et al. (All)developed a reaction scheme for the determination of the forms of sulfur which takes advantage of the selective oxidizing power of perchloric acid. Sulfate, pyritic, and organic sulfur were removed sequentially from a single sample of coal by solutions of HC104 boiling at 120, 155, and 205 "C, respectively, and converted to Sod2- for subsequent turbidimetric measurement; a standard additions technique was applied to alleviate the problem of low sulfur recoveries. In the analysis of coal for sulfate sulfur by ASTM methods, Norton and Peters (A12) found that the calculated sulfate content
was not affected by digestion time of the barium sulfate precipitate, implying that precipitate digestion may not be necessary, even in the presence of alkali and alkaline-earth elements. They noted that errors associated with sampling due to the inhomogeneity of the coal were most likely greater than any increase in accuracy that may result from digestion of the precipitate. Huggins and others (Al3)examined the forms of sulfur in selected coals before and after extraction with perchloroethylene by a combination of sulfur XAFS and Moessbauer spectroscopiesand standard chemical methods; they devised a hybrid scheme for determining pyritic S, elemental S, organic sulfide, thiophene, oxidized organic sulfur forms, and sulfate. Feurstenau and co-workers (A14 presented a simple procedure for the determination of pyritic sulfur content in the products from physical separation processes based on the assumption that the organic sulfur content in the combustible material is constant; the pyritic sulfur can be calculated from the total sulfur and ash content of the coal. Mitchell and colleagues 0115) used a well-swept, fixed-bed reactor in the determination of organic sulfur forms in some coals and kerogens by highpressure temperature-programmed reduction. Elemental Analysis. Laser spark emission spectroscopy (LASS)was used by Ottesen (Ala qualitatively to characterize complex ash deposits prepared by the combustion of pulverized coals in a pilot-scale combustor. Gloudenis and Tyson ( A I 3 constructed a flow injection system incorporating a stopped-flow microwave-heated reactor for the preparation of solutions for subsequent analysis by atomic spectrophotometric techniques. Sluny samples were injected into the manifold and into a glass reactor mounted inside a microwave oven; "03 was flushed into the reactor. The reactor was then sealed and the contents were heated, with the microwave apparatus programmed to hold the pressure for 5 min. The X-ray absorption fine structure spectroscopic (XAFS) observations on modes of occurrence of trace elements (Cr, As, Mn, Br) in coal were presented by Huggins and colleagues (AIS), who also proposed a classiiication scheme with precise definitions for modes of occurrence, which includes organic/maceral association and inorganic/mineral association. Huffman and coworkers (Al9)used XAFS with a solid-state multielement germanium detector to provide speciation information on arsenic and chromium at realistic concentration levels of 10-100 ppm. Galbreath and Brekke WO) investigated the feasibility of combined wavelength/energydispersivecomputercontrolled scanning electron microscopy for determining trace metal distribution of seven trace metals (CR, Ni, As, Se, Cd, Hg, Pb) among coal minerals and ash particles; they found that the techniques could be combined to determine the trace metal distribution among the inorganic constituents of coal and ash as a function of particle size. An effective yet simple micro-/semimicroanalytical scheme was described by Godbeer and co-workers (A2l)for analysis of coal and ash when only a very small amount of sample was available; an elemental analyzer was used for the determination of carbon, hydrogen, nitrogen, and sulfur in the coal, and the solution resulting from the semimicrodigestion (50 mg of coal or 10 mg of ash) was analyzed by ICP-AES for 19 elements. Analytical Chemistry, Vol. 67, No. 12, June 75, 1995
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Structure. In a study of coal chemical structure, Botto and Cody (AZ2) used scanning transmission X-ray microscopy to spatially map the chemistry of aromatic and aliphatic carbon functionalities in coal to a resolution of less than 0.1 pm. The microstructures of a fresh coalified wood sample and a fresh subbituminous C coal sample were characterized by Hou and others W 3 ) with a combination of two-dimensional and threedimensional proton NMR imaging (MRQ and reflected light optical microscopic SEM analysis. Forced pulsed ruby laser radiation, coupled with GC/MS analysis, was used by Greenwood and colleagues (A24) for the in situ pyrolysis of individual coal macerals; the potential of this technique for the in situ chemical investigation of individual coal macerals, which may be present in very small amounts within the parent coal, they believe was established. NMR. The low-temperature phase behaviors of pyridine-& and N-methylpyrrolidone-dg swollen Pittsburgh No. 8 coal, Illinois No. 6 coal, and Zap lignite were investigated by Yang and coworkers using 'H and 2H NMR line-shape studies; analyses of the NMR data suggested isolation of the individual components of the coal as a consequence of the swelling process. This same group W6) used 'H NMR relaxation techniques to study the mobility of coals swollen with pyridine-& and N-methyl-2-pyrrolidinone-dg as a function of solvent loading at room temperature. In a report on observations of the interactions between water and coal by proton magnetic resonance, Huai et al. (A27) indicated that powdered coal broadens the spectrum of liquid water and increases its chemical shift; NMR spectra of the liquid phase provided a rapid means of studying the interactions in coal/water slurries. Miknis W8)demonstrated the usefulness of liquid- and solidstate 13C and H NMR for the examination of coal liquefaction materials; these techniques provide data not directly obtainable by other methods tb examine the saturation of aromatic rings and to determine the modes of hydrogen utilization during coal liquefaction. Jurkiewicz and Maciel W 9 ) used a carbonyl-labeled compound as an intensity standard for quantitative 13Ccross-polarization magic angle spinning (CP-MAS) NMR analysis of Argonne premium coal samples. Jurkiewicz, Bronnimann, and Maciel 0130) deconvoluted the spectra from 'H combined rotation and multiple pulse NMR spectroscopy (CRAMPS) of pyridine-saturated samples of the Argonne premium samples to yield relative concentrations for individual peaks. Wilson and others (A34 investigated the distribution of protons bonded to sp2- and sp3hybridized carbons in a number of macerals, including liptinites and inertinites, using cross-polarization magic angle spinning and CRAMPS. O n - h e Analyzers. Nie and others (A32) used on-line coupling of microscale, thermogravimetric-type reactors to mass spectrometry and GC/MS systems to study the chemical processes occurring during the thermal degradation of coal. For o n line density determination of coal slurries containing air bubbles, Baumann's group (A33) developed a technique to compensate for the influence of air bubbles on nucleonic density meters using two nucleonic density meters operating in pipe sections under different pressures. To provide simultaneous multiparameter online analysis, Vourvopoulos (A34 proposed to augment the y-neutron activation analysis (PGNAA) with a pulsed fast-thermal neutron source for the determination of H, C, N, 0, and S, as 318R
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well as other elements commonly found in coal; preliminary data indicated the feasibility of the technique at a cost comparable to conventional PGNAA. Miscellaneous. Thermogravhetry and in situ ESR spectroscopy of free radicals were used by Ibrahm and Seehra (A33 to investigate the coprocessing of a coal with waste tire rubber and with polystyrene and polyethylene. Minimum explosive concentrations of dusts were measured in the US.Bureau of Mines 2@L chamber and in the Fike 1 m3 chamber using electrically activated chemical igniters; Cashdollar and Chatrathi (A36) measured the minimum explosive concentration values for gilsonite dust and for bituminous coal dust in each chamber at several ignition energies. REVIEWS The chemical forms of sulfur and analytical methods for characterization of sulfur content are discussed by Calkins (A33 in a review with 114 references; topics include the following: inorganic forms of sulfur, determination of total sulfur, determination of total organic sulfur content, representative organic sulfur components (thiophenes, benzothiophenes, dibenzothiophenes, nonaromatic sulfur structures), analytical methods for sulfur determination (spectroscopic, chemical degradation), sulfur removal methods from coal, and geochemistry of sulfur in coal. In a review with 94 references, Davidson (A38) reviewed the quantification of organic sulfur in coal, beginning with an examination of the ASTM standard methods and continuing with newer chemical and instrumental methods. Kispert and co-workers (A39) discussed the porosity of the Argonne premium coal samples in a review with 30 references; they have reviewed the current status of spectroscopic techniques used to study the porous structure of coal, emphasizing the recent application of EPR spin probe method to study the APCS, and indicate that the spin probe method provides valuable insight into the micropore size and shape characteristics during the swelling process. Painter's group M40) discussed band assignments, sampling, curve resolution, accuracy, and the use of phenolic resins in a review of the current status of FT-IR in the analysis of coal structure (17 references). NMR imaging of heterogeneous coal macromolecular networks was the topic discussed in a review with 34 references by Cody and others 0141); specific topics included solvent swelling studies (solvent accessibility, three-dimensional NMR imaging for spatial mapping of mobile proton distribution) and solvent transport studies. Nuclear techniques for in situ evaluation of coal and mineral deposits were reviewed by Borsaru (A42), covering techniques developed mostly in the last decade, and based on work published in North America, Europe, and Australia. Mastalerz and Bustin 0143) reviewed electron microprobe and micro-FT-IR analyses applied to maceral chemistry. Characteristics of coals for combustion using petrographic analysis are reviewed by Cloke and Lester (A44 (76 references). The role of on-line mass spectrometry for studying the structure/ reactivity relationships and conversion processes of coal are discussed by Meuzelaar (A45) in a review with 42 references of the use of pyrolysis mass spectrometry for studies of coal structure and structure/reactivity relationships in coal. On-line analysis of coal is discussed in a review by Cutmore et al. (A46); techniques and applications of on-line use of nuclear, capacitance, microwave, and ultrasonic techniques for the coal industry are summarized. Topics in the review of on-line analysis of coal by Kirchner (A7)
include ash measurement (X-ray backscatter, pray backscatter, dual-energy pray transmission, pair production, natural ) , elemental analysis, moisture measurement, coal slurry ash analyzers, and applications of on-line analyzers. Riepe (A481presents a review of analytical methods for analysis of coal and its products, such as ash, gases, and environmental emissions; he also shows how careful analytical control may diminish the emission of dangerous elements, hydrocarbons, sulfur, and nitrogen oxides. A review by Herold (A49)with 137 references of the uses of thii-layer (that is, planar) chromatography in petroleum and coal analysis and related areas covers primarily the period from January 1987 to December 1992; topics discussed include the basics of TLC, sources of information, sample introduction, chromatographic development, petroleum applications, geochemical and geoscience applications, miscellaneous separations, polyaromatic hydrocarbons, oxygenated compounds, and nitrogen-containing compounds. Jane V. Thorns analytical chemist and President of Wyoming
Anal ical Laboratodes, Inc., has been working with coal analysis since her&t job in the coal laboratory at the Illinois State Geolo ical Survey in 1963. She has a B.S. in chemistry and in biologyfiom durray State University (1962, Murray, KY) and a master's degree in chemistry fiom the University of W oming (1971, Laramie, W . She has been an active participant with 2 S T M Committee D-5 on Coal and Coke since 1974, servin as secretary for subcommittees dealing with trace element analysis and cfairing task groups working toward accreditation standards.
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