Coal macerals density

Determinations of the density of various coal macerals have also been reported (Table 6.2), and although the variations are not great, the general order of density for macerals (having the same approximate carbon content) is... 

Due to the variation in chemical make up of coal macerals, their densities are different and this property has been exploited to produce maceral concentrates. Early studies in this area have been reviewed by Golouskin (44). Typically the... 

Variations in Properties of Coal Macerals Elucidated by Density Gradient Separation... 

The observed changes in density are related in a complex way to the chemical structure of the coal or maceral (3). In order to better understand the chemical variations occurring in coal macerals we have examined the ultimate analysis of selected density fractions separated from the same coal. 

Figure 1. Procedure for density gradient centrifugation separation of coal macerals.

Figure 2. Maceral density distribution of a high volatile bituminous coal, PS0C-106. All densities are aqueous densities at 25 °C. Magnification of photographs is 1250x.

We wish to report data on a series of whole coals and coal macerals using conventional CP/MAS, dipolar dephasing, and 2-D dipolar dephasing techniques. These data provide a wealth of new structural information and demonstrate that multiple pulse and 2-D spectroscopic techniques can be utilized on complex carbonaceous materials. We also report data obtained on maceral samples separated by the density gradient centrifugation method which separates coal maceral groups according to density. 

Figure 2. CP/MAS spectra of PSOC-2 and PSOC-858 whole coals and the maceral groups separated from the coal by density gradient centrifugation. The density ranges represent the range of densities employed as indicated in Figure 1. The corresponding fa values are given for each sample.

Electron spin resonance determinations of g-values, linewidths, radical densities and saturation properties have been performed on carbon radicals in samples of coal macerals isolated by density gradient centrifugation techniques. These data are compared with elemental analyses and density measurements. Each maceral type exhibits a different ESR signature" which can be understood in terms of the nature of the starting organic and the extent of coalification. 

There have been a large number of electron spin resonance (ESR) studies of coal and coal products,(1J but a microscopic interpretation of the resulting data has been hampered by the chemical heterogeneity of the coal samples examined. While several surveys of specially selected macerals have appeared, 3), the recent evolution of maceral separation techniques - now allows detailed ESR observations to be made on coals systematically fractionated in which coal rank, maceral type, and maceral density are simultaneously distinguished. The present report surveys the behavior of a variety of ESR properties of carbon radicals in exinite, vitrinite, and inertinite macerals in a variety of coals of different rank. These data... 

Petrographic analysis of the separated macerals, density determinations, and elemental analyses were performed at Argonne National Laboratories. The ash content of these samples is less than 1%. The oxygen levels reported here are obtained by difference. Computer correlations of the resulting parameters were done using the Statistical Analysis System on the VS/CMS system at the ER E-Linden site. Linear-regression analyses are also performed with that system. In the correlation plots which follow, samples will be identified by coal rank and maceral group. 

The ability to examine individual coal macerals provides an opportunity for a detailed study of the roles of the chemistry of the starting organic material and the effect of coalification on the final materials. The different macerals exhibit distinct g-value, linewidth and radical density signatures which are related to their chemistry. The present overview will be extended to a qualitative analysis of the ESR properties and the behavior of these macerals under reaction conditions. 

Successfully applying the method used by Fenton to prepare his concentrates depends upon two factors. First, there must be adequate density differences between the macerals in the sample, and second, there must be an initially high concentration of the required maceral. In attempting to separate either resinite or cutinite from sporinite of the same coal, neither of these conditions can be fulfilled, at least when the coal is of bituminous rank or higher. If, however, samples on a semi microscale are acceptable, it is possible to prepare concentrates of resinites of satisfactory purity from bituminous coals by simple mechanical means. The method has been described by Murchison and Jones (17) and mainly involves picking with fine probes on differently prepared surfaces of coal under a stereoscopic microscope. Resinites from lignites pose less of a problem because their occurrence in fairly substantial lumps is quite common these and fossil resins such as kauri gum and amber usually can be prepared to a purity of almost 100% with ease. 

The preparation of maceral concentrates for study has been achieved by one of two approaches, either by hand picking or by a variety of techniques which exploit the variation in density between the various maceral groups. The first level of hand picking is the judicious sampling of lithotypes. This term is used to identify the various layers found in a coal seam. For humic coals there are four main designations of lithotypes vitrain, clarain, durain, and fusain (42). Vitrain bands are sources of fairly pure vitrinite group macerals while fusinite and semi-fusinite can be obtained from fusain. These are the... 

Free Radicals in Macerals. Electron spin resonance (ESR) has been used to study carbon free radicals in coals, and to some extent, separated macerals. The technique provides information on radical density and the environment of the radicals. The resonance position, termed the g-value, is dependent on the structure of the molecule which contains the free electron. The line width is also sensitive to the environment of the unpaired electron. In an early study, Kroger (71) reported that the spin concentration varied between maceral groups with liptinite < vitrinite inertinite. For this limited set of samples the spin concentration increases with rank for liptinites and vitrinites and decreases for the micrinite samples. On the other hand, van Krevelen (72) found the same general results except... 

Product characterization from liquefaction has not been extensive. Phi 1p and Russell (95) have examined products by Py-GCMS from metal halide catalyzed hydrogenation of a vitrinite, alginite, and inertinite, each from a different source. They were able to correlate Py-GCMS results with reaction temperature. King, et al. (96) examined the short contact time liquefaction of macerals separated by DGC from a single hvB bituminous coal. They found correlations between density and reactivity and composition of the products. 

Substantial variation in the chemical composition of macerals has been shown for a number of coals. Density gradient... 

The maceral groups from these coals were separated by the density gradient centrifugation (DGC) technique described by Dyrkacz... 

Table I. Elemental Analysis and Maceral Composition of Coal PSOC-2 and PSOC-858 Separated by Density Gradient Centrifugation Techniques...

Some 37 samples from 16 coals of the Pennsylvania State University coal data base (PSOC) were examined. Separate density fractions were obtained by isopycnic density gradient centrifugation of small ( 3iim) coal particles in an aqueous CsCl density gradient. (4J The individual samples are listed by PSOC numbers, coal description, ASTM designation of coal-rank maceral type, and density in Table I. After separation, the samples... 

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