Activated carbon and graphite facilitate the upgrading of Indonesian lignite with microwave irradiation for slurryability improvement

To upgrade Indonesian lignite by significantly reducing moisture and volatile matter content for the preparation of quality coal water slurry (CWS) gasification fuel, carbonaceous materials with high dielectric permittivity were employed to accelerate heating rate via microwave irradiation. The physicochemical properties of lignite upgraded through microwave irradiation with the addition of activated carbon and graphite were investigated through Fourier transform-infrared spectroscopy, X-ray photoelectron spectra and N-2 adsorption porosimetry. The oxygen functional groups of the upgraded lignite decreased remarkably, whereas coal rank increased. Furthermore, the atomic ratio of oxygen to carbon and the molar ratio of carbonyl to the aromatic groups of the lignite upgraded with the aid of activated carbon were both lower than those of lignite upgraded with the inclusion of graphite. On the contrary, the aromaticity and aromatic-to-aliphatic ratio of the first type of upgraded lignite were both higher than those of the second type. The hydrophilic functional groups on the surfaces of lignite upgraded with the aid of activated carbon were lower in number than those on the surfaces of lignite upgraded with the inclusion of graphite; the opposite was true given hydrophobic functional groups. The maximum solid concentration of CWS prepared from upgraded lignite with activated carbon assisted microwave irradiation increased markedly from 41.3 wt% to 66.6 wt%. (C) 2015 Elsevier Ltd. All rights reserved.