Composition of the isopropanol-soluble portion and fast pyrolysis product distribution of the insoluble part from Pakistani lignite

Pakistani lignite (PLC) was thermally dissolved at 300 °C using isopropanol (IPA) to obtain a soluble portion (SP) and insoluble portion (ISP). Proximate analysis, ultimate analysis, Fourier transform infrared spectrometry (FTIR), thermogravimetric analysis (TG-DTG) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) results were compared to explore the influence of the thermal dissolution process on the pyrolysis for PLC and ISP. Results showed that the thermal dissolution process mainly dissolved some light components of low-rank coal, and more phenols, aldehydes, esters and ethers were found in the SP, indicating that low-carbon alcohols can break the ether bridge bond in coal and generate oxygen-containing organic compounds (OCOCs). Compared with PLC, ISP had better thermal stability, low activation energy and pre-exponential factor. Furthermore, thermal dissolution dissolves small molecular compounds in coal channels, enlarges the pore structure and mass transfer rate, and enables the compounds produced in the pyrolysis process to diffuse to the surface of coal faster. On the other hand, IPA could be used as a hydrogen supply solvent to weaken the oxygen bridge bond in the macromolecular structure of coal, so that it is easier to break during pyrolysis. Thus, it was demonstrated that the low molecular weight compounds have a significant effect on the low temperature pyrolysis characteristics of PLC, and these two processes could potentially improve the added value of coal.