Chemical Engineering and Processing 45 (2006) 471–480 Turbulence intensity in an electrochemical cell: Effect on reactor performance A. Bannari a , C. Cirtiu b , F. Kerdouss a , P. Proulx a, ∗ , H. M´ enard b a Department of Chemical Engineering, Universit´ e de Sherbrooke, Sherbrooke, QC, Canada J1K 2R1 b Departement of Chemistry, Universit´ e de Sherbrooke, Sherbrooke, QC, Canada J1K 2R1 Received 8 February 2005; received in revised form 21 November 2005; accepted 21 November 2005 Available online 19 January 2006 Abstract In order to study the improvement in reaction efficiency associated with the improved flow characteristics over static or quasi static cells, a dynamic electrochemical reactor is designed and tested. Experimental results are compared to a computational fluid dynamics (CFD) model of the cell, based only on turbulence characteristics. We intend to identify the optimal geometrical configuration, using CFD to determine how the electrodes, inlet and outlet tubes should be positionned. It is found that the overall reaction efficiency of the cell correlates almost perfectly with the volumetric turbulence intensity. The incidence angle (IA) formed by the inlet and the position of the electrodes governs the overall reaction rate. © 2005 Elsevier B.V. All rights reserved. Keywords: Electrocatalytic hydrogenation (ECH); Computational fluid dynamics (CFD); Porous media; Multiphase flow 1. Introduction An interesting alternative chemical process for the produc- tion of cyclohexanone and cyclohexanol is the electrocatalytic hydrogenation (ECH) of phenol. In this approach we carry out the hydrogenation process using electrocatalysis to generate in situ atomic hydrogen. Room temperature and atmospheric pres- sure operation are important advantages of the ECH process compared to catalytic hydrogenation. It is well established [1,2] that the generation of the atomic (H ads ) and molecular hydro- gen (H 2 ) on the metallic sites can occur by one of the following steps: H 2 O + M + e - ⇋ MH ads + OH - (Volmer reaction) (1) H 2 O + MH ads + e - ⇋ M + H 2 + OH - (Heyrovsky reaction) (2) 2MH ads ⇋ 2M + H 2 (Tafel reaction) (3) ∗ Corresponding author. Tel.: +1 819 821 8000; fax: +1 819 821 7855. E-mail address: pierre.proulx@usherbrooke.ca (P. Proulx). Noble metals are catalytically very active, and many studies have been carried out on their surface, especially platinum, pal- ladium, and rhodium. Noble metals have been used as polycrys- talline metals or monocrystals, metal blacks, metals supported on graphite, microparticles incorporated into redox active poly- mers [3]. The electrode materials play an important role for the kinetics of the ECH. Likewise, the efficiency of the electrocat- alytic hydrogenation is dependent on the adsorption and desorp- tion power of the substrate toward the unsaturated molecules, the current density, the pH, the solvent nature [4]. The key param- eters of the ECH process are both the nature of the metallic nanoaggregates and the nature of the non-conductive material (support). The rate of hydrogen formation is controlled by the current density. The greater the fraction of atomic hydrogen in- volved in Eq. (1), the higher the ECH yield. The mechanism proposed for the electrohydrogenation pro- cess [5] is described by Eqs. (1)–(6). The first step is the forma- tion of the electrosorbed hydrogen (H ads ) on the metallic sites (M) of the catalyst by reduction of water (Eq. (1)). In addi- tion, a non-conductive material (A) is used for the adsorption of the organic molecules (Eq. (4)). As in catalytic hydrogenation, the (C C) bond is hydrogenated by the reaction of the organic molecule with the adsorbed hydrogen (Eq. (5)) who occurs at the adlineation point, where the metal nanoaggregates (M), the 0255-2701/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.cep.2005.11.007