Analysis of Ignition-Extinction Type Phenomena in Electrically Heated Reactors with Endothermic Reactions

Joule-heated reactors, in which an electric current flowing through the catalyst or support provides the thermal energy needed to carry out an endothermic reaction, are rapidly emerging as alternatives to the conventional reactors that burn fossil fuels to supply the heat. Recent experimental data show that these reactors can display jumps in the conversion of the limiting reactant versus applied voltage, similar to the ignition behavior observed in traditional reactors with exothermic reactions. In this work, we provide a possible explanation for such a jump- or ignition-type phenomenon. Specifically, we show that when the electrical conductivity of the catalytic layer is an exponentially increasing function of the temperature, a discontinuous jump or drop in conversion or temperature could occur. We use the simplest mathematical model to provide a qualitative explanation of the observed jump phenomenon and show that the observed behavior is mainly due to the electrical properties of the catalyst layer, regardless of the kinetics of the endothermic reaction. The impact of the electrical properties of the catalyst layer and operating variables on the computed bifurcation diagrams of limiting reactant conversion versus applied voltage is also discussed.