Oxidative dehydrogenation of ethane under a cyclic redox scheme – Process simulations and analysis

Steam cracking of ethane is an energy intensive process (15–25 GJth/tonne ethylene) involving significant coke formation and CO2/NOx emissions. We propose an alternative two-step redox (or chemical looping) oxidative dehydrogenation (CL-ODH) scheme where hydrogen, produced from ethane cracking, is selectively oxidized by lattice oxygen from a redox catalyst, in the first step. Regeneration of the lattice oxygen in a subsequent step heats the redox catalyst, with the sensible heat providing the thermal energy needed for the cracking reaction. The overall process provides minimal parasitic energy loss and significantly reduced CO2/NOx formation, while favoring ethylene formation through the removal of hydrogen. In the current study, the CL-ODH process is simulated with ASPEN Plus® using experimental data on a Mn-based redox catalyst. The CL-ODH is compared with steam cracking for an ethylene production capacity of 1 million tonne/year. Results indicate that the CL-ODH process, with 85% single-pass ethane conversion, provides 82% reduction in overall energy demand and 82% reduction in CO2 emissions. The overall downstream section consumes approximately 23.5% less energy, with 32.1% less compression work. Increase in the ethane conversion further reduces the energy demand downstream. For every tonne of ethylene, the process has 7.35 GJth excess fuel energy whereas cracking requires an external fuel input of 1.42 GJth.