Na₂ wo₄ /mn/sio₂ catalyst pellets for upgrading h₂ s-containing biogas via the oxidative coupling of methane

Biogas is a promising renewable energy source; however, it needs to be upgraded to increase its low calorific value. In this study, oxidative coupling of methane (OCM) was selected to convert it to a higher fuel standard. Prior to establishing the scaled-up OCM process, the effect of organic/inorganic binders on catalytic activity was examined. The selection of the binders and composition of the catalyst pellet influenced the pore structure, fracture strength, and catalytic activity of the catalyst pellets. It was also observed that the O₂ supply from the inorganic binder is a key factor in determining catalytic activity, based on which the composition of the catalyst pellets was optimized. The higher heating value increased from 39.9 (CH₄, Wobbe index = 53.5 MJ/Nm³) to 41.0 MJ/Nm³ (OCM product mixture, Wobbe index = 54.2 MJ/Nm³), achieving the fuel standard prescribed in many countries (Wobbe index = 45.5–55.0 MJ/Nm³). The reaction parameters (temperature, gas hourly space velocity, size of the reaction system, and the CH₄ /O₂ ratio) were also optimized, followed by a sensitivity analysis. Furthermore, the catalyst was stable for a long-term (100 h) operation under the optimized conditions.