Effects of organic solvent treatment on the chemical structure and pyrolysis reactivity of brown coal

Dewatering and upgrading of Yunnan brown coal in non-polar solvent (tetrahydronaphthalene, THN) were carried out at mild conditions with bench-scale apparatus, and the resultant samples were separated from the slurry and analyzed with Fourier transform infrared spectroscopy (FTIR), 13C nuclear magnetic resonance (13C NMR) and thermo-gravimetric analyzer coupled with mass spectroscopy (TG-MS) to explore the structure changes and variance of pyrolysis reactivity that introduced in the treatment. The results show that the solvent treatment is effective in dewatering and upgrading of Yunnan brown coal. Carboxyl groups and CO bonds in ethers, esters, alcohols start decomposing at 150 and 200 °C, respectively, while the aliphatic, aromatic structures as well as phenolic groups remain relatively stable below 300 °C. The coal structure becomes more associated and compact after the solvent treatment, and the pyrolysis reactivity of the treated sample is slightly lower than that of the raw coal.