Radical Reactions and Two-Step Kinetics of Sub-Bituminous Coal Liquefaction in Various Solvents

To understand the role of hydrogen donation from solvents to the coal-generated free-radical fragments (coal radicals) in direct coal liquefaction (DCL), a coal with 72.4 wt % carbon was reacted at 440 °C for 10 and 30 min in fast-heating microreactors under a nitrogen atmosphere without or with a solvent, including the non-hydrogen donor solvents naphthalene, 1-methylnaphthalene, and cetane, as well as the hydrogen donor solvents (HDSs) 9,10-dihydrophenanthrene (DHP) and tetrahydronaphthalene (THN). The coal conversion (XC), the yields of oil (YO), asphalt (YA), and gas (YG), as well as the amounts of electron spin resonance (ESR)-measured stable radicals (NR-ESR) and active free radicals acquired hydrogen radicals (NRH) from DHP and THN were studied. A two-step free-radical kinetics for the DCL in DHP and THN was established. The nature of kinetics parameters and their variation with DHP and THN were discussed. It is found that the coal generated a large amount of coal radicals, more than 2.0 × 10–2 mol...