Coupling of exothermic and endothermic reactions in oxidative conversion of ethane to ethylene over alkaline earth promoted La2O3 catalysts in presence of limited O2

Oxidative conversion of ethane to ethylene over alkaline earth metal (viz. Mg, Ca, Sr and Ba) promoted La2O3 (alkaline earth/La=0.1) in presence of steam (steam/C2H6=1.0) and limited O2 has been studied at different temperatures (700–850°C), C2H6/O2 ratios (4.0–8.0) in the feed, and gas hourly space velocities (5×104 –20×104 cm3 g−1 h−1). Among these catalysts, the Sr promoted La2O3 (Sr/La=0.1) catalyst showed best performance in the process. High selectivity (>80%) for C2+ olefins at 50–70% conversion of ethane could be obtained at 800–850°C and very short contact times (<10 ms) without coke deposition on the catalyst. When the reaction temperature and/or C2H6/O2 ratio were increased, the heat produced in the process decreased markedly because of the occurrence of thermal cracking of ethane (which is endothermic), simultaneously with the exothermic oxidative ethane conversion, thus making the process nearly thermoneutral or mildly exothermic/endothermic, depending upon the process conditions (viz. temperature and C2H6/O2 feed ratio).