Study of thermal decomposition reactions in coals by pyrolysis-gas chromatography-mass spectrometry

Abstract

The thermal decomposition of heteroatom-containing segments occurring in coals has been studied by pyrolysing a series of synthetic polymers. The polymers contained aryl ether segments in various molecular surroundings, aryl sulphide and heteroaromatic with oxygen or sulphur atoms. The scission of aryl ether bonds results mainly in phenols at 500–800°C, and the temperature at which phenol production takes place depends on the nature of the bonds attaching the aryl ether segment to the macromolecular matrix. Almost no phenol formation from heteroaromatic segments was observed. The production of phenols from low-rank coals is similar to that from a polymer in which aryl ether segments are bonded through keto and methylene groups to the neighbouring segments. The scission of aryl sulphides results in the formation of hydrogen sulphide. Hydrogen sulphide is also produced from dibenzothiophene segments, although at a considerably higher pyrolysis temperature. The formation of hydrogen sulphide is similar from aryl sulphides and low-rank coals. The amount of hydrogen sulphide produced by pyrolysis proved to be directly proportional to the organic sulphur content of Hungarian low-rank coals.