Analysis of Volatile Organic Pyrolysis Products of Bituminous and Anthracite Coals with Single-Photon Ionization Time-of-Flight Mass Spectrometry and Gas Chromatography/Mass Spectrometry

The volatile organic compound (VOC) emissions from the pyrolysis of anthracite and bituminous coals are studied using both online single-photon ionization time-of-flight mass spectrometry (SPI-TOFMS) and offline gas chromatography/mass spectrometry (GC/MS) techniques. It is found that the combination of the online and offline techniques is effective in the VOC analysis. It reveals that the dominant pyrolysis products of both anthracite and bituminous coals are comprised of a mixture of non-aromatic hydrocarbons, mainly alkanes and light alkenes, aromatic compounds, and their corresponding isomers. Rank variation of coal samples has important impacts on the release of pyrolysis products. High-volatile bituminous coal releases more VOCs than low-volatile anthracite coal under the same temperature. The relative contents of the pyrolysis products of the two coals also differ. SH coal releases more short-chain aliphatic and oxygen-containing compounds, while XT coal releases more aromatic and sulfur-containing compounds. The temperature has an important influence on the release of VOCs from coal pyrolysis. The relative signal intensities of most products increase as the temperature increases. According to the time-evolved spectra, the higher the temperature, the earlier and faster the release of VOCs, regardless of the coal type. For both coals, the release of most VOCs is favored at higher temperatures. For bituminous coal, at a fixed temperature, almost all alkenes and dienes started to release at approximately the same time, except propylene, which has two peaks, indicating that there may be two steps in the release of this compound. The aromatics were released a little delayed, especially at low temperatures.