Catalytic self-sustaining combustion of the alkanes with Pt/ZSM-5 packed bed in a microscale tube

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Experimental studies on the combustion of methane, propane and n-octane with Pt/ZSM-5 packed bed were performed in a tube with a diameter of 4mm in order to acquire several performance indicators, including the self-sustaining combustion limit, conversion efficiency, and heat output among others. The increase of equivalence ratio (Φ) extended the velocity limits (v) of self-sustaining combustion in varying degrees for the three fuels under study. Methane presented a relatively narrow self-sustaining combustion region, low conversion (≤25%), high CO selectivity (5–11%) and low tube wall temperature (<250°C) at Φ=1.0 and v=0.8–1.4m/s. The catalytic reactivity for methane oxidization over Pt/ZSM-5 was highly activated at temperatures over 455°C, this being responsible for the methane combustion performance. In the case of propane combustion processes, a homogenous reaction occurred downstream the catalyst section and led to high conversion. Under Φ=1.0 and v=0.8–1.4m/s conditions, propane conversion was higher than 45% while the CO2 selectivity remained over 96%. n-Octane showed similar combustion performance than propane, with a little backward gap detected. The released heat by fuel combustion increased in the order: methane, n-octane, and propane, with the maximum heat values being 12, 19, and 32W, respectively. Propane was suitable for micro combustion with the catalyst, as a result of the low catalytic ignition temperature (124°C) and high catalytic reactivity.