OSCILLATIONS IN HOMOGENEOUS OXIDATIVE DEHYDROGENATION OF ETHANE TO ETHENE

The non-catalytic homogeneous dehydrogenation of ethane to ethene unde r unsteady-state conditions, showing sustained oscillations in the rea ction temperature and product composition, has been investigated in a flow reaction system under different process conditions. The oscillati ons are observed only over a narrow range of reactor temperature (610- 650 degrees C) and only for a C2H6/O-2 ratio of <8.0. Their period and amplitude are strongly influenced by the temperature, space velocity, C2H6/O-2 ratio and feed dilution by N-2 or water vapour. The oscillat ions are found to be dependent on heat transfer and hence are thermoki netic in origin. The unsteady/steady reaction behaviour is most probab ly a result of the competing free radical reactions involved in both t he exothermic oxidative conversion of ethane (which is pronounced at l ower temperatures) and the endothermic thermal cracking of ethane, par ticularly unimolecular cracking of ethyl radicals (which is pronounced at higher temperatures), accompanied by different rates of heat trans fer, under different reaction conditions.