Oxygen feed membranes in autothermal steam-reformers – A robust temperature control

In conventional autothermal steam-reformers, the spatial temperature distribution leads to hot-spot problems. Here we demonstrate a solution approach for this problem using ceramic membranes with highly interconnected open pores and a permeability that varies over the length of the reformer. Due to this spatially non-constant characteristic, these membranes function as oxygen feed distributors. Predictions based on a theoretical optimization showed that almost isothermal characteristics should be possible in small-scale applications. For experimental validation, membranes were produced via the HAPES processing route, which leads to open porosities between 71 and 78% and permeability constants varying from 3.8 × 10−12 to 3.9 × 10−13 m2. The experimental results show that a membrane with staged permeabilities can reduce a typical temperature peak for 94% down to a value below 5 K deviation from the isothermal behavior without any losses in conversion rate or hydrogen and CO-selectivities. Additionally, it could be confirmed that a premix of 6.5% oxygen to the feed gases is necessary to obtain optimal results.