High-temperature and short-contact-time oxidative dehydrogenation of ethane in the presence of Pt/Al2O3 and BaMnAl11O19 catalysts

The oxidative dehydrogenation of ethane over a Pt/gamma -Al2O3 catalyst in adiabatic conditions (that is at T= 800-1000 degreesC and few milliseconds contact time) resulted in the production of ethylene with 50% yield. In order to better elucidate the single roles that gasphase reactions and heterogeneous phase reactions might play in the high-temperature activation of ethane, a detailed experimental and theoretical investigation was addressed. The results suggested that the performance of the adiabatic reactor relied on a cooperation between catalytic reactions (responsible for deep and partial oxidation of ethane to COx, H2O, and H-2) and homogeneous reactions (responsible for the formation of olefins). In autothermal conditions, thus, the main function of the Pt-catalyst appeared to be that of accelerating ignition of the radical process, through the initial combustion of ethane which can occur at temperatures as low as 200 degreesC. It was demonstrated that the same function can be equally well accomplished by a Pt-free oxidation catalyst like the BaMnAl11O19 which is active in the deep oxidation of ethane. Even in the presence of the hexa-aluminate material, which has no activity in the selective oxidation of ethane to ethylene, yields to ethylene higher than 50% were observed in the autothermal reactor by preheating the ethane/air feed stream at a proper temperature. (C) 2001 Academic Press.