Fluidized Catalytic Oxidation of Ultralow Concentration Methane: A Pilot-Scale Study

Ventilation air methane from coal mining is characterized by large flux and ultralow concentration, which is the largest source of methane emissions in coal mines. This study proposes a fluidized catalytic oxidation process to treat methane using cost-effective natural ore catalysts. Experiments were conducted in a pilot-scale fluidized bed reactor. The results indicate that the methane conversion rate reached 90% at 543 °C, while further temperature increment showed a minor effect on the conversion rate. Within the tested range, the effects of the bed inventory and catalyst particle size on efficiency were insignificant. In the stability test, methane conversion decreased from 97.4 to 90% in the initial 22 h. It was found that ∼35.6 wt % of the catalysts was blown out of the reactor during the reaction due to the low separation efficiency of the used cyclone, causing the conversion rate to decrease. After the reaction, the active component MnO₂ in the natural ore was partially converted to Mn₂O₃ with less surface oxygen vacancies, which also contributed to the decreased activity since the methane catalytic activity was much lower on Mn₂O₃ than that on MnO₂ (T ₉₀ = 795 vs 505 °C).