Coal solubilization accelerated by reductive methylation under ultrasonic irradiation and its coal rank dependence

In reductive methylation reaction of coals using molten potassium under ultrasonic irradiation, the relation between irradiation time in anionization and solubilization has been studied. Two kinds of coals of the different rank were allowed to react in various irradiation times (15 similar to 180 min). In ultrasonic irradiation method in comparison with conventional method, it was observed that the number of introduced methyl groups and the total yield of soluble products increased remarkably at shorter reaction time. These results are due to that the scission of C-O-C bonds in coals, reductive methylation, and methylation of aromatic compounds or OH groups mere accelerated at the initial stage of the reaction, and also that lamination layer by aromatic stacking and entangled structure by long chain alkyl groups in higher rank coal (Kairan), entangled structure by long chain alkyl groups and bridged structure by OH groups in low rank coal (Kitadein) mere relaxed, respectively, by ultrasonic irradiation. Accordingly, the effect of ultrasonic irradiation on reductive methylation reaction was influenced by the structure of original coals.