Experimental investigation on using ionic liquid to control spontaneous combustion of lignite

Abstract

Coal spontaneous combustion (CSC) has become a safety topic and has been widely debated. This study investigated the inhibiting effect on CSC by using a series of novel ionic liquids (ILs) as chemical inhibitors. The microstructure and thermokinetic characters were observed and evaluated by Fourier transform infrared spectroscopy and synchronous thermal analyser. The results indicated that ILs could destroy reactive groups on relatively active coal surfaces, such as OH, aliphatic CH, and O-containing groups. However, as aromatic CH is the main chain of coal molecule, damaging it is difficult. Different anions and cations found in ILs exhibited different abilities for destroying the groups on the surface of coal molecules. The damage was caused by the properties of anions and cations by affecting the chain length, number of chains of the anion and cations, and electronegativity strength. The changes in microstructure increased the physical adsorption capacity of inhibitive coal samples during low-temperature oxidation, which changed the characteristic temperature points. In stages of water evaporation and desorption mass loss (stage 2) and the thermal decomposition (stage 3), the apparent activation energy of coal samples increased. The kinetic characteristics of the obstructed coal sample were predicted using the Flynn–Wall–Ozawa method. The development ability was delayed and the risk level was reduced of CSC in stages 2 and 3. Therefore, ILs should be utilised at relatively low-temperatures (<230.0 °C) to control CSC.