Sequential thermal dissolution and oxidative depolymerisation of Cheji coal

Organic matter in soft coal (SC) and hard coal (HC) from the same mine was extracted by sequential thermal dissolution (TD) followed by oxidative depolymerisation (OD) to obtain soluble components, which were studied using both gas chromatography/mass spectrometry (GC/MS) and Orbitrap-MS to acquire detailed molecular structure information. Toluene (TOL), tetrahydrofuran (THF), and methanol (ME) were the three solvents used in sequential TD. TOL relaxes the macromolecular structure in coals and exhibits a good solubilisation effect on arenes, THF further destroys non-covalent bonds through swelling, and ME weakens hydrogen bonds among macromolecules and attacks the weak -C-O- bridged bonds. With a higher coalification degree, soluble components from HC show more aromatised structure compared to SC. After the OD treatment, aromatic compounds with a higher degree of condensation were detected in the OD products, and HC contains more fused aromatic rings.