Effects of Changes in Physicochemical Properties Caused by Hydrothermal Treatment on Pyrolysis Performance of Indonesian Lignite

An Indonesian lignite (IN) was hydrothermally treated at 100–250°C for 20 min. The changes in some physicochemical properties caused by hydrothermal treatment (HT) were investigated by Fourier transform infrared spectrometry and N 2 adsorption-desorption methods. The effects of HT on pyrolysis performance were studied using thermogravimetric analysis. The results showed that the oxygen-containing functional groups (OCFGs) gradually decomposed with increasing HT temperature. The pore volume first decreased and then increased with the increase in HT temperature. With increasing HT temperature, the maximum pyrolysis rate and final weight loss both decreased. The pyrolysis activation energy increased with increasing HT temperature. The changes in pyrolysis performance can be attributed to the competition between the increase in pore volume and the removal of OCFGs. In summary, pyrolysis reactivity of IN decreased caused by HT.