Oxidative dehydrogenation of ethane at millisecond contact times: Effect of H-2 addition

The oxidative dehydrogenation of ethane using Pt/alpha-Al2O3 and various bi metallic catalysts operating at similar to 1000 degrees C and very short co ntact times is examined with H-2 addition to the feed. When H-2 is added wi th a Pt catalyst, the ethylene selectivity rises from 65 to 72% but ethane conversion drops from 70 to 52%. However, using a Pt-Sn/alpha-Al2O3 catalys t, the C2H4 selectivity increases from 70 to greater than 85%, while the co nversion remains similar to 70%. The process also produces approximately as much H2 as is added to the feed. Effects of other metal promoters, sphere bed and fibermat supports, preheat, pressure, nitrogen dilution, and flow r ate are examined in an effort to further elucidate the mechanism. Deactivat ion of the Pt-Sn catalyst is examined, and a simple method of regenerating the activity on-line is demonstrated. Possible mechanisms to explain high s electivities to ethylene are discussed. Although the process can be regarde d as a simple two-step reaction sequence with the exothermic oxidation of h ydrogen or ethane driving the endothermic dehydrogenation of ethane to ethy lene, the exact contributions of heterogeneous or gas-phase reactions and t heir spatial variations within the catalyst are yet to be determined. (C) 2 000 academic Press.