Design and Characterization of a Membrane Dielectric-Barrier Discharge Reactor for Ammonia Synthesis

Abstract

Abstract
Ammonia synthesis via non-thermal plasma presents advantages over the Haber–Bosch process, particularly for small-scale and distributed operations powered by intermittent electricity from renewable energy sources. We designed and characterized a membrane Dielectric-Barrier Discharge (mDBD) reactor for ammonia synthesis from nitrogen and hydrogen. The reactor used a porous alumina membrane as dielectric barrier and as distributor of H2. This arrangement enabled greater residence time for N2 decomposition together with greater H2 availability in the reaction zone, as assessed by a computational thermal-fluid model. We evaluated the reactor’s operation with membranes of 0.1, 1.0, and 2.0 µm pore size and porosities between 25 and 51%, and also in conventional DBD mode using a non-porous dielectric. The experimental characterization of the reactor encompassed electrical, optical, and spectroscopic diagnostics, as well as Fourier-Transform Infrared Spectroscopy to analyze gas products, as function of driving voltage. The results show that both, ammonia production and power consumption vary inversely with the product of membrane pore size and porosity. The highest energy yield of 0.25 g-NH3/kWh was obtained with the membrane with 1.0 µm pore size and 35% porosity, whereas the maximum yield under conventional DBD operation was three-times lower. Our findings demonstrate that the use of a membrane dielectric can enhance the performance of DBD-based ammonia synthesis.