The greater part of macromolecule aromatic structure unit of low-rank coal contains mainly 1—2 rings. In order to understand the mechanism of methane formation during coal pyrolysis

the thermodynamics and kinetics calculation were conducted for toluene pyrolysis using DFT method. The results showed that the rate-control step is the dehydrogenization or demethylation process for all routes of methane formation. The energy barrier of toluene demethylation can be significantly reduced by the participation of hydrogen free radical. When temperature is lower than 675 K

the formation of methane is mainly through the following steps: firstly

breaking of the C—H bond in methyl of toluene; secondly

the hydrogen free radical formed adds to the toluene in ipso position and then demethylation; finally

formation of methane is from the formed methyl that captures a hydrogen atom in side chain of toluene. When temperature is higher than 975 K

methane is mainly from toluene demethylation first and then the formed methyl captures a hydrogen atom in side chain of toluene. When the temperature is between 675 K and 975 K

formation of methane is a competitive result of the two routes mentioned above.