Comparison of three methods for extracting Liuhuanggou bituminous coal

Microwave-assisted extraction (MAE), ultrasonic-assisted extraction (UAE), and ultrasonic/microwave-assisted extraction (UMAE) were separately conducted on the extraction of Liuhuanggou bituminous coal (LBC) sequentially using petroleum ether, carbon disulfide (CDS), methanol, and isometric CDS/acetone mixture as solvents to afford extracts 1-4 (E1-E4) from MAE (EM1-EM4), UAE (EU1-EU4), and UMAE (EUM1-EUM4). The highest total extract yield of 10.6 wt% was obtained by UMAE, while MAE is the most effective for extracting highly condensed arenes from LBC. The carbon types in LBC mainly consist of aliphatic (22.2%) and aromatic (73.7%) carbons. Each aromatic cluster of LBC contains 2 or 3 aromatic rings on average. The molecular masses of EU3, EU4, EM3, and EM4 range from 200 to 1500 u, while those in EUM3 and EUM4 distribute from 100 to 900 u. EUM2 is a promising feedstock to produce advanced aromatic polymers and EUM3 could be converted to clean light oil by catalytic hydroconversion after removing heteroatom-containing species (HACSs). MAE and UMAE are ideal tools to obtain value-added chemicals for their high selectivity of extracting HACSs.