High resolution Chromatographic characterization of depolymerized coals of different rank: aliphatic and aromatic hydrocarbons

Volatile matter evolved during pyrolysis of 20 different rank coals was studied by thermogravimetry-photoionization mass spectrometry (TG-PI-MS). The composition of the TGA effluent revealed several significant trends with coal rank. First, the relative intensities of peaks due to compounds containing oxygen such as C n H 2n O (n ) 2, 3, or 4), phenols, and dihydroxybenzenes decreased with increasing coal rank. Also, the relative intensities of peaks due to aromatic compounds such as naphthalenes, phenanthrenes, and pyrenes increased with increasing coal rank. Mass signals due to sulfur compounds evolved from coal showed qualitative correlations between CS 2 (%TIC) and pyritic sulfur content and between CH 3 SH (%TIC) and aliphatic sulfur content. Several of the coals were extracted with a solvent to remove the soluble portion of the coal. TG-PI-MS analysis of the raw coal, extracted material and coal residue remaining after solvent extraction produced very similar mass spectra. These results suggest that the majority of the compounds observed by TG-PI-MS are products of thermal cleavage of bonds within the coal structure. This conclusion is further supported by 337 nm laser desorption mass spectrometry of the solvent extracts. The results from these analyses suggest that volatile matter, like coal itself, consists of compounds with a range of molecular weights but with similar molecular structures.

Section: Methodssupporting

confidence: 63%

Section: Methodsmentioning

confidence: 99%

Thermogravimetry−Photoionization Mass Spectrometry of Different Rank Coals

and¹,

Johnston²,

Tomić³

et al. 1999

“…Some experimental approaches provided average results that were unsuitable for the definition of the number and kind of different aromatic structures, and other approaches provided hopelessly complex arrays of data that could not be successfully partitioned. This feature is well illustrated by the chromatographic results for the liquefaction products of the Pocahontas coal . The chromatograms typically exhibit numerous sharp signals atop an intense and very broad background of other signals throughout the interval when aromatic compounds with three to eight aromatic rings emerge.…”

Section: Introductionmentioning

confidence: 71%

“…The chromatograms typically exhibit numerous sharp signals atop an intense and very broad background of other signals throughout the interval when aromatic compounds with three to eight aromatic rings emerge. Aromatic compounds with four or more rings and their methylated derivatives are clearly present. , But the composition of these mixtures cannot be readily defined because of the very large number of isomeric compounds. Chrysene, for example, provides six monomethyl compounds, but there are more than 30 dimethylchrysenes.…”

Section: Introductionmentioning

confidence: 99%

Oxidation and Decarboxylation. A Reaction Sequence for the Study of Aromatic Structural Elements in Pocahontas No. 3 Coal

Stock

Obeng

1997

Oxygen in basic solution has been used to oxidize Pocahontas No. 3 coal to a mixture of aromatic carboxylic acids, and copper(I) oxide in N-methylpyrrolidinone-quinoline has been used to decarboxylate the acids to provide a mixture of hydrocarbons. Most pendant alkyl groups have been removed in this sequence and the product distribution is much less complex than the product distributions that are obtained in direct oxidation reactions or in the analysis of coal liquids and extracts. Approximately 25% of the aromatic carbon atoms are retained in the products. The structures of these compounds have been investigated by gas chromatography-mass spectrometry and by high-resolution and laser desorption mass spectrometry. Approximately 150 compounds were detected in the GCMS experiments including a broad array of bi-, ter-, and quateraryls, fluorene and fluoranthene derivatives, polycyclic aromatic hydrocarbons with four, five, and six rings, dibenzo-and dinaphthofurans, and dibenzo-and dinaphthothiophenes. High-resolution mass spectrometry provided additional evidence concerning the principal products and extended the mass range to approximately 400 Da. Laser desorption work revealed that even larger molecules were present in the reaction products with distinct signals at 550 Da and definite intensity extending to 1200 Da. These results are compatible with many other results that have been obtained in the past decade and strongly infer that the relatively high-ranking Pocahontas No. 3 coal has many large, condensed, aromatic clusters that are methylated and connected through biaryl and heterocyclic linkages.

“…Soxhlet solvent extraction and chemical class fractionation procedures were used to isolate the C 15+ hydrocarbon components. , The supercritical fluid and solvent-extracted analytes were analyzed by gas chromatography/mass spectrometry using a Hewlett-Packard 5890 gas chromatograph and a Hewlett-Packard 5970 mass-selective detector. The extract compound quantitation, identification, and carbon-preference index (CPI) analysis were performed using the procedures described in detail previously. − …”

Section: Methodsmentioning

confidence: 99%

Geochemical Significance of n-Alkane Compositional-Trait Variations in Coals

Nelson

Lazar

et al. 1998

Self Cite

The compositional traits of C 9-34 n-alkanes were measured in supercritical CO 2 extracts from 14 U.S. coals of varied geologic ages and wide thermal maturity range (lignite through lowvolatile bituminous). The analysis data exhibit no unique component depletion pattern signatures diagnostic of known types of postgeneration physical, chemical, or microbiological degradation processes that commonly affect crude oil in sedimentary rocks. The C 9-34 n-alkanes in Paleocene and Upper Cretaceous age coals exhibit bimodal carbon-number distribution profiles that strongly resemble those of the biogenic n-alkanoic acids present in brown coals. The compositional trait similarities between these n-alkanes and n-alkanoic acids and the covariance of the bulk coal organic matter atomic oxygen-to-carbon (O/C) ratios and carbon-preference index (CPI) values offer tangible evidence for the existence of a genetic linkage between these two series of compounds. Our analysis results indicate that the C 2-5 alkanes and C 6+ hydrocarbons in coals attain their maximum abundances over the thermal maturity interval from 0.50 to 0.72% R 0 , which, in turn, strongly suggests that these two groups of compounds are formed concurrently by similar overall reaction processes during coal maturation. The compositional traits of the C 4-5 alkanes and C 9-34 n-alkanes in coals appear to uniquely mimic those of the alkane products formed by mineral-catalyzed defunctionalization and cracking of n-alkanoic acids, which suggests that mineral catalysis rather than temperature-controlled thermolysis may be a critical variable controlling the formation and compositional traits of natural gas and C 9+ n-alkanes during coal maturation. These mechanistic insights should be useful to those seeking to formulate improved geochemical models for predicting hydrocarbon evolution during coal maturation.