(692b) Shallow-Bed Reactor Design and Analysis for the Autothermal Oxidative Dehydrogenation of Ethane over Movtenbox Catalysts

The oxidative dehydrogenation of ethane (ODHE) has gained increasing attention as an alternative method for producing ethylene from ethane. Despite various reactor designs that have been proposed in the literature for implementing ODHE, the impact of external and internal transport effects using large catalyst particles at an industrial scale have not been discussed thus far. Due to the high adiabatic temperature rise values associated with this system, ignition can occur at the particle level for larger catalyst particles (≥1 mm size) rather than merely at the bed level in the pseudo-homogeneous limit. In this work, we use a cell model with finite-size eggshell type catalyst particles (Figure 1b) to present a comprehensive ignition-extinction analysis of the oxidative dehydrogenation of ethane (ODHE) in an adiabatic shallow-bed reactor.

Our results reveal that external mass transfer can increase the ratio of ethane to oxygen on the catalyst surface (Figure 1c), thereby improving ethylene selectivity but decreasing ethane conversion (at a fixed space time). We show that diffusion limitations in the catalyst reduce ethylene selectivity and shrink the region of multiplicity, highlighting the need for eggshell particles containing a thin active layer. We also examine the impact of ethane to oxygen ratio, feed dilution, space time, catalyst particle size, operating pressure, and active layer thickness on ignition and extinction behavior. A multi-layered bed with eggshell catalyst particles (Figure 1a) is proposed for near complete conversion of oxygen, enhanced ethane conversion and ethylene selectivity. Our results indicate the possibility of autothermal operation of the ODHE process with 20%+ per pass conversion of ethane (without dilution) and 90%+ selectivity to ethylene.