High solubility of Victorian brown coal in 'distillable' ionic liquid DIMCARB

Ionic liquids formed by association of carbon dioxide (CO2) with low molecular weight secondary amines to form carbamate salts (e.g. N,N-dimethylammonium N′,N′-dimethylcarbamates, or DIMCARB) as solvents have been identified as 'distillable' as they reform their volatile precursor components upon heating at relatively low temperature and, thus, can be recovered by condensation. DIMCARB was selected for the solubilisation of a number of Victorian brown coals including Loy Yang coal, a dark, a medium light and a light lithotype and a Yallourn woody coal. The coal was mixed with DIMCARB at a mass ratio of 1:20 for 24 h at room temperature. The soluble product was recovered by centrifugation followed by acid washing to remove residual DIMCARB. The solubilisation yields achieved were between 10% and 63% in the order of woody coal < dark lithotype < medium light lithotype < Loy Yang < light lithotype. The soluble and non-soluble products were characterised by FTIR, NMR and pyrolysis GC-MS. Results revealed a positive correlation between the solubility and aliphatic content in the coals. Polycyclic aliphatic and aromatic compounds, specifically the triterpenoid group, were selectively dissolved by DIMCARB.