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

Abstract

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).