Pyrolysis of mixtures of methane and ethane: activation of methane with the aid of radicals generated from ethane

Abstract

Direct chemical conversion of methane (CH₄) has been actively researched in order to use natural gas as a chemical resource. However, the high stability of CH₄ molecules hinders the chemical conversion of CH₄. In this study, we investigated pyrolysis of mixtures of CH₄ and ethane (C₂H₆) at 973–1073 K. Even though CH₄ alone did not react in the temperature range, mixtures of CH₄/C₂H₆ and of Ar/C₂H₆ showed different pyrolysis behaviours; the co-existence of CH₄ significantly increased yields of propylene (C₃H₆), propane (C₃H₈) and toluene. Mass spectrometry analysis using ¹³C-labeled CH₄ revealed that carbon contained in CH₄ was incorporated into the pyrolysis products. The results suggested that CH₄ was activated with the aid of C₂H₆. We assumed that CH₄ was attacked by radical species generated from pyrolysis of C₂H₆ and was converted into methyl radicals. The CH₄-derived methyl radicals were incorporated into pyrolysis products via radical reactions. This study clarified that CH₄ can be activated by radicals generated from co-existing molecules without the help of catalysts or extremely high temperature.