In-situ characterization of volatiles from pyrolysis of Fengfeng coal by a double ionization time-of-flight mass spectrometer

Coal from Fengfeng (FF) colliery, Hebei, China, was pyrolyzed in a self-developed pyrolysis reactor coupled with double ionization sources (viz., electron impact ionization (EI) and photoionization (PI)) and time-of-flight mass spectrometer (Py-EI/PI-TOFMS), to characterize in-situ the primary products from pyrolysis (heteroatom-containing compounds in particular). The relative contents of various pyrolysis products were obtained by semi-quantitative analysis and the temperature-evolved profile of each product was obtained by scanning the signal of the distinguished peak with the lapse of time; in addition, the evolution of five small molecule gaseous products (viz., H₂O, CO, CO₂, H₂ and CH₄) was analyzed by EI-TOFMS. The results indicate that the Py-PI-TOFMS system is able to detect and characterize the primary products in-situ during coal pyrolysis. In the pyrolysis products with a mass-to-charge ratio (m/z) less than 240, which account for about 70% of detected volatiles, hydrocarbons consist of mainly aromatics of 1–3 rings, whereas the phenolic compounds are dominated by phenols containing 1–3 benzene rings (especially the 3-ring phenols). The peak temperature with maximum evolution of phenols containing the same alkyl substituents shifts to lower temperature with the increase of the number of aromatic rings. In addition, the relative contents of nitrogen/sulfur-containing compounds are all less than 1.0%, where the content of sulfur-containing heterocyclic compounds is higher than that of nitrogen-containing heterocyclic compounds.