“…It is believed that the free radical mechanism is important in the liquefaction of many low-ranking coals, such as Xiaolongtan lignite [13], Shengli lignite [74,75,81], Kansk-Achinsk lignite [78], Elbistan lignite [79], Mengen lignite [85], Beypazari lignite [86], Longkou [66], and Catalan lignite [72,95]. The initial free-radical intermediates formed during this mechanism are stabilized to form oil, AS, and PA by catalytic processes involving gaseous hydrogen and a hydrogen donor solvent (Fig.…”