Characterisation of the products of low temperature pyrolysis of Victorian brown coal in a semi-continuous/flow through system

•Low temperature pyrolysis of Victorian brown coal was investigated in a flow-through system.•A light lithotype sample provided higher liquid yields than run-of-mine Loy Yang coal.•Process understanding was achieved using Py-GC–MS for solid and GC–MS for liquid products.•Aromaticity of pyrolysis residues improved markedly above 380 °C. Two Victorian brown coal samples, a run-of-mine Loy Yang coal (LY) and a Loy Yang light lithotype (LL), were subjected to pyrolysis at 420–460 °C and 330–460 °C, respectively, under a continuous nitrogen flow. The process produced condensed products in two phases, oil and aqueous, as well as solid residue and gaseous products. An increase in the condensed product yields with increasing temperature was observed for both coals, with LL achieving higher yield than LY at a given temperature (e.g. 26.3 wt% vs 19.5 wt% at 460 °C). The condensed products were characterized by 1H and 13C NMR as well as GC–MS. Abundant triterpenoid polycyclics and aliphatic hydrocarbons were found in the oils from both coals produced at lower temperatures, whilst the yield of aromatics significantly increased with increasing pyrolysis temperature. Analyses of the solid residues by FTIR, solid state 13C NMR and flash pyrolysis GC–MS (Py-GC–MS) also revealed an increasing aromaticity of the residues at higher temperatures. Py-GC–MS analysis identified compound groups released by flash pyrolysis at 650 °C and the results were found to correspond to those of GC–MS for the oil.