•EMIA shows high performance on the dissolution of lignites.•Extraction temperature and lignite type significantly affect extraction behaviors.•Extraction yield increases with the increase of carboxyl content of lignites.The extraction behaviors of three lignites with ionic liquid (IL)-1-ethyl-3-methylimidazolium acetate (EMIA) were studied in this work. The effects of extraction temperature and lignite type on extract yield and product compositions were primarily investigated. Also the relationship between the extract yield of lignites and the quantities of oxygen-containing functional groups in lignites was investigated. It was found that EMIA is a more efficient solvent for the dissolution of lignites compared to the performance of 1-butyl-3-methyl-imidazolium chloride (BMIC). Extraction temperature and lignite type significantly affect extraction behaviors of lignite with EMIA. The extract yield of lignites with EMIA increases with the quantity of carboxylic groups in lignite increases. Only a small amount of aliphatic alkyl structure components are extracted at low temperature. More aromatic structure components are extracted by EMIA at high extraction temperature.

The depolymerization behaviors of Xianfeng lignite (XL) in ionic liquid 1-butyl-3-methyl-imidazolium trifluoromethanesulfonate ([Bmim]OTf) was studied in this paper. Also, the thermal extracts and residues obtained from thermal depolymerization of XL at different extraction conditions were analyzed. It was found that [Bmim]OTf had good performance in the depolymerization of XL when the extraction was carried out at 280°C for 4 h with [Bmim]OTf/XL at 3.5. The extraction yield of XL with [Bmim]OTf defined as tetrahydrofuran solubles (THFS) reached to 20.1%. The depolymerization of XL with [Bmim]OTf was promoted markedly with the addition of tetralin (THN), H2 and ZnCl2 catalyst, and the yield of THFS reached to 30.0%, 36.9% and 46.8%, respectively. The results showed that the amount of hydrogen bonds in thermal extracts increased significantly with the addition of THN. The contents of aromatics and aliphatic hydrocarbon were enhanced greatly under the existence of H2 and ZnCl2.