Characterization and classification of Rocky Mountain coals by Curie-point pyrolysis mass spectrometry

Abstract

A set of 102 coal samples from the Rocky Mountain coal province, selected from the Penn State Coal Sample Bank, was analysed by Curie-point pyrolysis mass spectrometry in combination with computerized pattern recognition techniques. The spectra obtained were shown to be quite representative for the coal seams with characteristic differences often present between different seams, fields or regions within the Rocky Mountain Coal province. In general, the spectra were found to be dominated by homologous ion series, e.g., representing dihydroxybenzenes, phenols, naphthalenes, benzenes, alkenes, dienes, alkyl fragments and sulphur compounds with varying degrees of alkyl substitution. The relative abundances of dihydroxybenzenes and naphthalenes were shown to correlate closely with differences in rank, whereas those of phenols, aliphatic hydrocarbons and sulphur compounds appeared to correlate more closely with differences in depositional environment. Different spectra -dominated by aliphatic compound series -were obtained from several samples of a boghead coal (Cannel King seam). Moreover, spectra of two of these boghead coal samples, known to be severely weathered, showed markedly increased CO 2 + and C 6H 6 + signals, indicating the presence of benzenecarboxylic acids. Factor analysis of pyrolysis m.s. data revealed the two main underlying chemical tendencies to be a shift from heteroatomic compounds to hydrocarbon series with increasing rank and a difference in degree of aromaticity corresponding primarily to differences in depositional environment. The dominant rank-related factor exhibited a clear coalification break between the ASTM hvC bituminous and hvB bituminous ranks and appears to represent a significant shift in coalification mechanisms. It was demonstrated that rank-dependent differences in the pyrolysis mass spectra enable correct classification of the spectra into four ASTM rank classes (subbituminous, hvC, hvB and hvA bituminous) in 90% of all cases. Moreover, the discovery of a marked aliphaticity/aromaticity factor in the data could be useful for the direct measurement of aromaticity ( f a ) from pyrolysis mass spectra of whole coals.