Experimental investigations of inorganic membrane reactors: A distributed feed approach for partial oxidation reactions

An inorganic membrane reactor (MBR) is investigated for the oxidative dehydrogenation of ethane to ethylene. A tube and shell configuration is used where ethane is fed at the top of an annular packed catalyst bed and air permeates radially outward into the reaction zone along the length of the permeable reactor wall (porous alpha-alumina membrane). Using a magnesium oxide catalyst doped with lithium and samarium oxide, the effects of the overall ethane to oxygen feed ratio, temperature, and residence time are evaluated. The results are compared to a tubular reactor (PFR) operated with the same catalyst and conditions. The MBR outperforms the PFR in both ethylene yield and selectivity at low feed ratios. At 873 K, an ethane to oxygen feed ratio of 0.5, and a residence time of 4 s, per pass ethylene yields of 50.5 and 8.1% are produced in the MBR and PFR, respectively. The corresponding ethylene selectivities are 53 and 8.4%. As the feed ratio increases, the performance of the MBR and PFR merges. In addition, periodic counter-propagating blue flames are observed in the tubular reactor for some experiments with feed ratios between 0.25 and 1.0. No flames are observed in the MBR.