Improving physicochemical properties of upgraded Indonesian lignite through microwave irradiation with char adsorbent

To upgrade Indonesian lignite by significantly reducing volatile matter content, char adsorbent was employed to accelerate lignite pyrolysis through microwave irradiation. Physicochemical properties of pyrolyzed lignite were determined with the assistance of char adsorbent on Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray spectroscopy, N2 adsorption porosimetry, and contact angle analysis. Under the same microwave power of 800 W and irradiation time of 12.5 min, the lignite temperature remarkably increased from 150 °C to 656 °C with the aid of 10 g char adsorbent. Its apparent aromaticity increased from 0.50 to 0.97. The relative content of superficial carbon functional groups attributed to π-π∗ transitions increased from 1.18% to 6.71%. The volatile matter content (dried basis) markedly decreased from 48.94% to 6.47% due to the release of volatile compounds in the lignite.