Effect of Swelling by Organic Solvent on Structure, Pyrolysis, and Methanol Extraction Performance of Hefeng Bituminous Coal

[Image: see text] N-methyl-2-pyrrolidone (NMP), pyridine (Py), tetrahydrofuran (THF), and tetralin (THN) were used to swell Hefeng acid-washed bituminous coal (HBC(AC)). The swelling effect on HBC(AC) by each solvent is different, among which NMP presented well swelling performance, with a swelling degree of 2.11. FTIR results showed that acid washing and swelling processes presented a marginal effect on HBC, and there was no damage to the macromolecule structure of the coal. TG–DTG profiles of the swollen coals illustrated that the total weight loss of each sample was lower than that of the acid-washing one, while the temperature of the maximum weight loss rate peak was almost unchanged, around 445 °C. Extract yield by methanol followed the order of HBC(AC) > HBC > HBC(AC–NMP) (swelled by NMP), showing that acid washing promoted the methanol extraction process, with a higher extract yield of 3.21%, which is twice that of HBC (1.66%).