Modeling the electrocatalytic nitrate removal in a rotating cylinder electrode reactor

Abstract

Here, computational fluid dynamics (CFD) simulations have been employed to investigate the transport phenomena occurring in an electrochemical reactor, equipped with an AISI 1018 carbon steel rotating cylinder electrode (RCE), during nitrate electroreduction. A model that resulted from solving the fundamental transport equations that govern the hydrodynamics, mass transport, and current distribution is proposed to assess the behavior of the RCE reactor when addressing the nitrate removal. The results obtained from the simulations offered a wider understanding of the selected electroreduction process. It was determined that the six surrounding Ti|IrO2-based anodes acted as deflectors that promoted the presence of two Taylor vortices, giving rise to three distinct velocity zones inside the reactor. This fact had an impact on mass transport, since the appearance of low-concentration zones was associated with a greater velocity. Furthermore, a slight current distribution (0.990 < jc/jc,AVE < 1.005) was observed along the RCE length due to the two Taylor vortices. The model was validated by performing a series of nitrate electroreduction experiments in an RCE reactor filled with solutions of 400 mL, corroborating that it is sufficiently robust to predict the nitrate concentration decay. At 1000 rpm, operating at 447 A m−2 to ensure mass transport control conditions, 90 % nitrate removal from a 10 mM KNO3 + 500 mM K2SO4 solution was achieved in only 10 min, with a low electrochemical energy consumption of 14.3 Wh g−1.