Analytical curie-point pyrolysis-gas chromatography as a tool to characterize key parameters relevant to coal reactivity

Abstract

Six coal samples, intended to be representative of the entire range of coal ranks and including two thermoplastic coals, were analyzed by Curie-point pyrolysis-gas chromatography to characterize parameters related to coal reactivity such as coal rank, thermoplasticity, and the addition of a catalyst to the coal. It is shown that the number and nature of the pyrolysis products, particularly the degree of oxygen functionality of the one-ring aromatic compounds formed, are characteristics of the rank of a coal sample. The presence of a series of long-chain n-alkanes, which are believed to be part of the so-called mobile phase of bituminous coals, is indicative of a thermoplastic coal. Low-temperature pre-oxidation is an effective method of destroying the thermoplastic properties of bituminous coals. The oxidative treatment affects the volatilization of the aliphatic moieties of the thermoplastic coals and significantly reduces the number and yield of pyrolysis products. The evolution of long-chain n-alkanes is almost completely eliminated upon pre-oxidation. Addition of potassium carbonate, which acts as a catalyst in coal gasification and combustion, results in an interaction of the alkali-metal ion with the carboxyl and hydroxyl groups in the coal. Because of this interaction the yield of phenolic compounds upon Curie-point pyrolysis is reduced. On the other hand, the formation of phenolic compounds, originating from ether linkages in the coal matrix, is not influenced by the addition of potassium carbonate.