Thermogravimetry−Photoionization Mass Spectrometry of Different Rank Coals

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 spectral 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.