In situ study of the decomposition of pyrite in coal during hydropyrolysis

Abstract

The thermal behaviours of pure pyrite, pyrite in coal and in situ formed Fe–S compounds under reductive atmospheres were studied over a wide temperature range (room temperature to 1050 °C), using a thermogravimetric analyser (TGA), temperature-programmed reduction coupled with online mass spectrometry (TPR–MS), X-ray diffraction (XRD) and scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (SEM–EDS). The results suggest that the inherent hydrogen and oxygen in coal can promote the decomposition of pyrite at low temperature, while external H2 plays a principal role in sulfur removal in the hydropyrolysis (HyPy) of coal, where only very little pyrite in demineralized Yanzhou coal (YZ-Dem) is transformed to new organic sulfur forms, and the Fe–S compounds produced in the final products are thermally stable. In contrast, ferric iron can accelerate organic sulfur elimination in complex ways, and complete conversion from in situ formed Fe–S or Fe–C compounds to elemental iron occurs under a H2 atmosphere.