The pyrolysis behaviour of solvent extracted metaplast material from heated coal using LDI-TOF mass spectroscopy measurements

•Metaplastic material was extracted from heat treated coal with a solvent.•This material was re-heated to evaluate its molecular changes.•Analysis by LDI-TOF-MS revealed significant differences between 400 °C and 425 °C samples.•Identified molecular changes occurred in the 500–1000 Da range.•These molecular structures were removed to produce both volatile tars and heavier species.

The majority of the world’s iron is manufactured in a blast furnace using coke as the reductant; yet some fundamental aspects of coke making remain poorly understood. This study is based on understanding the molecular changes that occur in the metaplast as it ages, by re-pyrolysing solvent extracted material to the same temperature at which it was initially created in the semi-coke. Semi-cokes were produced at 400 °C and 425 °C and the tetrahydrofuran-soluble (THF) component extracted. The extracts were characterised using laser desorption/ionisation time of flight mass spectrometry (LDI-TOF-MS) before and after pyrolysis. Both the THF extracted samples had a molecular range of 200–3000 Da with a peak occurring at 422 Da. On reheating, the extracts produced significantly different molecular behaviour, with the 400 °C extracts producing larger molecular structures concentrating at ∼1500 Da and the 425 °C extracts producing material concentrating a ∼750 Da. Volatile tars from the coal were lower in molecular weight (peak MW 259 Da) than those produced from pyrolysing the extracts (peak MW 333–347 Da) and common species were identified in all volatile samples. The results were discussed in relation to the existence of oligomeric structures previously found in petroleum pitches.