The Role of NO and NO2 in Partial Oxidation of Methane

  • Miss Yii Leng Chan, Centre for Petroleum, Fuels and Energy, The University of Western Australia, Australia
  • Dr John Bromly, Centre for Advanced Energy Science and Engineering, Curtin University of Technology, Australia
  • Dr Gia Hung Pham, Centre for Advanced Energy Science and Engineering, Curtin University of Technology, Australia
  • Prof Dongke Zhang, The University of Western Australia, Australia

    • NOx is well known as a promoter in the oxidation of hydrocarbons. The role of NO and NO2 depends on the reaction conditions (specifically, low/high pressure, fuel-lean/rich, and low/high temperature). The present work aims to identify the individual effect of small amounts (1000 ppm) of NO and NO2 on the partial oxidation of methane in a laminar flow reactor under elevated pressure (1 MPa).

    In this study, it was found that the addition of NOx reduced the initiation temperature by approximately 15oC. The promoting effect of NOx, which was considerably less at elevated pressure than was observed in previous atmospheric pressure experiments, is proposed to result from a cycling process of interconversion between NO and NO2. In the fuel-rich condition used in the present work, NO2 serves as a reaction initiator (CH4 + NO2 => CH3• + HNO2), while NO acts to transform relatively unreactive species (such as CH3O2•, HO2•) into their reactive counterparts (CH3O•, OH•), thus speeding up the entire process. It may be noted this contrasts with certain low pressure oxidising conditions, where NO has a much greater accelerating effect than NO2. The oxidation of NO to NO2 is extremely fast under the high pressure conditions and in the presence of O2 as used in this work. Hence, under the conditions of this study, cofeeding NOx either as NO or NO2 produced a similar accelerating effect.