Analysis of Coal Extracts

Analysis of coal extract with the ion-trap detector. Finnigan MAT Application Data Sheet ADS 12. 

The test methods of interest for the analysis of coal extracts include tests that measure chemical composition. The preeminent test methods are those that are applied to measurement of the asphaltene content. The issue with coal extracts is that the presence of asphaltene constituents in the extracts is solvent dependent. But assuming that a test is necessary to determine that whether asphaltene constituents are or are not present, several test are methods available. 

There are methods for the direct determination of organic sulfur in coal (3.4), but details regarding individual molecular structures are much harder to obtain. Much of the research designed to obtain this information has concentrated on the analysis of coal extracts (5.6) and pyrolysis products (7.8). Unfortunately the sulfur species from pyrolysis processes may be highly modified and usually account for only a very small percentage of the total sulfur in the coal. 

In Curie-point Py-LVMS studies of maceral concentrates (22). vitrinitic moieties were shown to be the main source of the hydroxy aromatic components. Thus, the hydroxy aromatic signals observed in Figure 2d appear to be primarily derived from vitrinite-like components by means of pyrolytic processes. Presumably, therefore, the "nonmobile phase", rather than the "mobile phase , is the main source of the phenols observed in TG/MS and Py-MS studies of Pittsburgh 8 coal (9,16). Further support for this conjecture comes from the observation that phenolic products are also observed in Py-MS analysis of pyridine extracts of Pittsburgh 8 coal known to contain colloidal matter whereas the corresponding tetrahydrofuran extracts, free of colloidal material, produced no phenols (21). 

CHARACTERIZATION of the PYRIDINE-EXTRACT. Pyridine is known to cling to coals. The extract was therefore stirred with a methanol/water/HCl mixture for two days as suggested by Buchanan.(lS) Elemental analysis of the extract revealed 1.85% N. The original coal contained 1.92% N (daf) so it is apparent that the methanol/water/HCl treatment followed by drying successfully removed pyridine from the extract. The FTIR spectrum of the extract did not reveal the presence of pyridine. 

Trace element analysis of coal and extract ashes... 

A test method for the batch extraction of treated or untreated solid waste or sludge, or solidified waste, to provide an indication of the leaching potential (ASTM D-5233) is also available. The goal of this test method is to provide an extract for measurement of the concentration of various analytes and therefore may be applied to a study of the smaller molecules that reside within the coal matrix. This test method, as written, is intended to provide an extract suitable for measurement of the concentration of analytes that will not volatilize under the conditions of the test method and may appear to offer limitations on the use of coal, but the test method does describe a procedure for performing a batch extraction of a solid. Again, the sampling and handling requirements that may be associated with the analysis of coal should also be applied to the method. 

The objective of this communication is to report structural information on a bituminous coal from a thorough characterization of its extracts. The characterization was carried out according to a scheme devised on the basis of our current understanding of coal chemistry. The scheme consists of considerations in preparation, fractionation, and analysis of coal-derived liquids (CDL) to obtain molecular-level information on the CDL per se as well as on the parent coal. The information obtained relates mostly to the structure of component clusters. 

High-resolution NMR spectrometry was used first by Brown and Ladner for structural characterization of coal pyrolysis products (3). Other workers have extended this type of analysis to coal extracts (4) and coal hydrogenation products (5,6,7), A recently published com-... 

Figure 4. Analysis of water extracts from coal. Pvunp Micro Feeder. Column SC-01, 50 cm X 0.22 mm i.d. Mobile phase acetonitrile-water, gradient profile as Indicated. Flow-rate 1.04 yl/min. Sample 2.5 ml of distilled water in contact with powdered coal. Precoliatm Develosil ODS-15/30, 10 X 0.2 mm i.d. Wavelength of UV detection 225 nm. Reproduced with the permission from Ref.7 Copyright 1983, Huethig.

Wroblewski, A. E., Lensink, C., Markuszewski, R., and Verkade, J. G., P NMR spectroscopic analysis of coal pyrolysis condensates and extracts for heteroatom functionalities possessing labile hydrogen, Ener. Fuels 2, 765 (1988). 

Kotz etal. (1972, Decomposition of biological materials for the determination of extremely low contents of trace elements in limited amounts with nitric acid under pressure in a Teflon tube) Hartstein et al. (1973, Novel wet-digestion procedure for trace-metal analysis of coal by atomic absorption) Jackson etal. (1978), Automated digestion and extraction apparatus for use in the determination of trace metals in foodstuffs) Campos etal. (1990, Combustion and volatilization of solid samples for direct atomic absorption spectrometry using silica or nickel tube furnace atomizers) Erber et al. (1994, The Wickbold combustion method for the determination of mercury under statistical aspects) and Woit-tiez and Sloof (1994, Sampling and sample preparation). 

Taking advantage of its high separation strength, a combination of SEC with MS enhances the capability of MS and makes it possible for the analysis of coal liquids. SEC can be used as a coal liquid sample pretreatment method prior to GC-MS. For SEC, 1-methyl-2-pyrrolidinone (NMP) is often used as eluent. Analytical result for a coal liquefaction extract sample prepared from SEC by GC-MS showed that only the pentane-soluble components could be analyzed [16] the larger aromatic molecules identified by SEC to be present were lost in the GC column. The molecular weight of the aromatics analyzed in the coal liquids were up to 352 with very few aliphatics. 

Natural Deposits. Natural deposits, eg, minerals and fossil fuels, are located by drilling operations. An auger, eg, a screw or worm, is turned in the earth and pulled out, and material is scraped from the auger for analysis. Alternatively, samples can be taken by hoUow core drills which, when withdrawn, enclose a core of the earth that is representative of the strata through which the drill has passed. Such core samples are used in geological surveys for fossil fuels. As the drill drives deeper into the strata, each core is extracted and placed in a shallow box and coded so that a complete cross section of the geological strata can be reconstmcted. From this, the relative thickness of coal and mineral seams can be directly measured. 

A predictive macromolecular network decomposition model for coal conversion based on results of analytical measurements has been developed called the functional group, depolymerization, vaporization, cross-linking (EG-DVC) model (77). Data are obtained on weight loss on heating (thermogravimetry) and analysis of the evolved species by Eourier transform infrared spectrometry. Separate experimental data on solvent sweUing, solvent extraction, and Gieseler plastometry are also used in the model. 

Multidimensional chromatography has also been applied for the analysis of industrial chemicals and related samples. Industrial samples which have been analyzed by multidimensional chromatography include coal tar, antiknock additives in gasoline (3), light hydrocarbons (4, 5), trihaloalkanes and trihaloalkenes in industrial solvents (6-8), soot and particulate extracts, and various industrial chemicals that might be present in gasoline and oil samples. 

The dense fluid that exists above the critical temperature and pressure of a substance is called a supercritical fluid. It may be so dense that, although it is formally a gas, it is as dense as a liquid phase and can act as a solvent for liquids and solids. Supercritical carbon dioxide, for instance, can dissolve organic compounds. It is used to remove caffeine from coffee beans, to separate drugs from biological fluids for later analysis, and to extract perfumes from flowers and phytochemicals from herbs. The use of supercritical carbon dioxide avoids contamination with potentially harmful solvents and allows rapid extraction on account of the high mobility of the molecules through the fluid. Supercritical hydrocarbons are used to dissolve coal and separate it from ash, and they have been proposed for extracting oil from oil-rich tar sands. 

The analysis of geochemical liquids such as crude oils, hydrothermal bitumens, extracts of coals, and host rocks containing dispersed organic matter or pyrolysates... 

Analysis of the results presented in Figures 2 and 4 appears to indicate that hydrogenation of the vitrinite is also accompanied by polymerization (see pyridine extract, Figure 4). If this can be confirmed, it would be worth investigating whether it involves specific fractions in the original vitrinite or has a random character. Solvolysis of different molecular weight fractions of a non-reductively alkylated vitrinite (or coal) may furnish some insight. 

We suggest that the rapid process corresponds to hole-filling and/or adsorption onto surfaces, and that the slow process, which follows first-order behavior, corresponds to swelling of the coal extract. Extrapolation of the linear portion of the curves shown in Figures 10 and 11 to time zero should yield the total uptake of benzene attributed to swelling. The results of this analysis are summarized in Table IV, where the total benzene uptake, M , and the uptake attributed to the hole-filling/adsorption and the swelling processes, and M., are shown. 

In another series of e q>eriments in this laboratory (U), it was found that the particle size of the coal fraction used affected the ash level in the filtered coal extract solution. In these e q>eriments, the coal sample, which is nominally < 200 pm, was divided into different size fractions by sieving, and each fraction digested using the normal procedure. Table 3 shows the results obtained with Point of Ayr and Calverton coals. Note that the Point of Ayr coal was a different batch to that used for the results described previously, with a simil analysis except for ash, which was higher at 19 %. 

Preparation of Coal and Fly Ash for Isotope Dilution Analysis. Separate aliquots of coal and fly ash are weighed out and spiked with 204Pb and 233U, respectively. The chemical treatment and extraction of lead and uranium from coal and fly ash are identical, except coal is ashed at 450 °C before chemical treatment. The samples are dissolved with a mixture of hydrofluoric, nitric, and perchloric acids in Teflon beakers. The lead is separated by dithizone extraction, evaporated to dryness, redissolved in dilute nitric acid, and 10 ng are loaded on filaments with silica gel for mass analysis. 

Table III. Elemental Analysis of Products from Phenanthrene Extraction of Bruceton Coal ...

The elemental analyses of the products from the extraction of Bruceton coal are shown in Table III. The mineral matter was separated from the extract quite efficiently as shown by the ash content of the extracts and the insoluble residue. The elemental composition of all fractions was quite similar to that of the original coal. Only the hydrogen content varied to some extent, increasing with increased solubility. The elemental analysis of the products from the extraction of Ireland Mine coal was incomplete. 

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