Influence of imidazolium-based ionic liquids on coal oxidation

In order to find the ionic liquids (ILs) which can significantly suppress coal oxidation, nine imidazolium-based ILs, [EMIm][BF4], [EMIm]Ac, [BMIm][BF4], [BMIm]Ac, [AMIm][BF4], [HOEtMIm][BF4], [HOEtMIm][NTf2], [AOEMIm][BF4] and [EOMIm][BF4], were used to treat lignite sample to reveal the inhibitory effect of ILs on coal oxidation activity. The TGA results showed that the ILs can reduce the mass loss of coal, of which the ILs [HOEtMIm][BF4] and [HOEtMIm][NTf2] showed the strongest reducing effect, while the IL [AMIm][BF4] showed the weakest reducing effect. Differential thermal analysis (DTA) results indicated that the heat release of [HOEtMIm][BF4] and [HOEtMIm][NTf2]-treated coal were very less. At the same time, the oxidation reactions of the two coals were delayed. IR results showed that ILs treatment can effectively destroy the associated hydroxyl in coal and change the content of carbonyl and ether bonds. In the process of coal oxidation, the oxidation activity of hydrogen bonding, ether bonds in [HOEtMIm][BF4] and [HOEtMIm][NTf2]-treated coal were weakened significantly at the initial oxidation process. With the oxidation processing, the content of generated carbonyl was reduced. The micro mechanism of the reduced coal oxidation activity was ascribed to the weaker oxidation activity of the ether bonds and the inhibited formation of the carbonyl groups.