ETHYLENE FORMATION BY OXIDATIVE DEHYDROGENATION OF ETHANE OVER MONOLITHS AT VERY SHORT-CONTACT TIMES

The production of ethylene or CO and H-2 from ethane in the presence of air or O2 at atmospheric pressure has been examined over ceramic foam monoliths coated with Pt, Rh, and Pd at contact times on the order of milliseconds. In a fuel-rich regime (C2H6/O2 > 1.5) on Pt, we observe selectivities to ethylene up to 70% with conversions above 80%. On Rh, CO and H-2 (syngas) production dominates, while on Pd, heavy carbon deposition rapidly occurs. Optimum production of ethylene from ethane on Pt is obtained by reacting ethane with a mixture of air and O2 at a C2H6/O2 ratio of approximately 1. 7 at contact times < 10 ms. Optimum production of syngas is obtained on Rh at a C2H6/O2 ratio of 1.0, with approximately 70% selectivity and > 95% conversion Of C2H6. These high selectivities to specific products are strong evidence that very simple reaction pathways dominate. The formation Of C2H4 and the complete reaction of C2H6 strongly argue that the process is initiated by oxidative dehydrogenation. On Pt, this must be followed by beta-hydrogen elimination from adsorbed ethyl and C2H4 desorption. On Rh and Pd, beta-hydrogen elimination is not preferred, resulting in the complete pyrolysis of the adsorbed hydrocarbon and ultimately syngas production (Rh) or carbon deposition (Pd).