OSCILLATIONS IN HOMOGENEOUS OXIDATIVE DEHYDROGENATION OF ETHANE TO ETHENE

The non-catalytic homogeneous dehydrogenation of ethane to ethene under unsteady-state conditions, showing sustained oscillations in the reaction temperature and product composition, has been investigated in a flow reaction system under different process conditions. The oscillations 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 oscillations are found to be dependent on heat transfer and hence are thermokinetic in origin. The unsteady/steady reaction behaviour is most probably a result of the competing free radical reactions involved in both the exothermic oxidative conversion of ethane (which is pronounced at lower temperatures) and the endothermic thermal cracking of ethane, particularly unimolecular cracking of ethyl radicals (which is pronounced at higher temperatures), accompanied by different rates of heat transfer, under different reaction conditions.