Microwave-Assisted Conversion of Low Rank Coal under Methane Environment

Addition of methane during microwave coal pyrolysis could greatly affect the product distribution to valuable products including the formation of char. In this work, low rank coal was exposed to microwave energy in the presence of different methane concentrations (0, 25, 50, and 90%) at 980 °C for 2 h. Increasing methane concentration was found to increase both the char and tar yields mainly due to carbon deposition during methane decomposition and hydrogenation of trapped carbon into tars. Analysis of the gas composition suggested that some of the methane was activated in the presence of the coal minerals, which could act as a catalyst, forming light hydrocarbons C2–C7 which account for up to 5% of the gaseous products at a methane concentration of 90%; they accounted for less than 0.5% in the absence of methane. Methyl groups may also have been substituted into aromatic compounds as observed in the tar analysis where the number of methyl substitutions in the detected parent phenol and naphthalene increa...