Extraction of Low-Rank Coals Oxidized with Hydrogen Peroxide in Conventionally Used Solvents at Room Temperature

A new method was developed for extracting a great deal of brown coal in several conventionally used solvents at room temperature. The coal was pretreated with hydrogen peroxide in liquid phase at 60 °C for 2 h to break some weak covalent bonds and to introduce oxygen functional groups. The pretreated coal was extracted by binary solvents of a low-molecular-weight alcohol (methanol, ethanol, 1-propanol, or 2-methyl-1-propanol) and an aromatic compound (1-methylnaphthalene, 2-methylnaphthalene, m -xylene, or phenol) of different mixing ratios at room temperature by the conventional method. In the binary solvent of methanol-1-methylnaphthalene consisting of 0.56−0.44 volumetric ratio, surprisingly, 84 wt % of the pretreated coal were extracted. The pretreated coal was extracted by 13 wt % even in a pure methanol, but it was not extracted at all in a pure 1-methylnaphthalene. The extraction mechanism of the oxidized coal in the binary solvent was discussed. Since 1-methylnaphthalene is involved in coal-derived liquids and methanol is one of most popular solvents, the developed method will be useful for utilizing low-rank coals efficiently.