Mass-transfer studies in an electrochemical reactor with a small interelectrode gap

Electrodialysis membrane desalination with diagonal membrane spacers: a review

Electrodialysis desalination uses ion exchange membranes, membrane spacers, and conductors to remove salt from water. Membrane spacers, made of polymeric strands, reduce concentration polarization. These spacers have properties such as porosity and filament shape that affect their performance. One important property is the spacer-bulk attack angle. This study systematically reviews the characteristics of a 45° attack angle of spacers and its effects on concentration polarization and fluid dynamics. Membrane spacers in a channel create distinct flow fields and concentration profiles. When set at a 45° attack angle, spacers provide greater turbulence and mass-heat transfer than traditional spacers. This is because both the transverse and longitudinal filaments become diagonal in relation to the bulk flow direction. A lower attack angle (<45°) results in a lower pressure drop coupled with a decline in wakes and stream disruption because when the filaments are more parallel to the primary fluid direction, the poorer their affect. This research concludes that membrane spacers with a 45° spacer-bulk attack angle function optimally compared to other angles.

Scaling Organic Electrosynthesis: The Crucial Interplay between Mechanism and Mass Transport

Organic electrosynthesis opens new avenues of reactivity and promises more sustainable practices in the preparation of fine chemicals and pharmaceuticals. The full value of this approach will be realized by taking these processes to the production scale; however, achieving this goal will require a better understanding of the influence of mass transport on reaction behavior and the interactions between reactive species and electrodes inherent to organic electrosynthesis. The limited options for cell geometries used on small scale limit elucidation of these features. Here, we show how advanced cell geometries allow us to control the interplay between reaction mechanism and mass transport, leading to improved performance of three modern organic electrosynthetic reactions. Each reaction shows a unique relationship with mass transport, highlighting the importance of understanding this relationship further to maximize the utility of organic electrosynthesis at scale.

Electrodialysis desalination: The impact of solution flowrate (or Reynolds number) on fluid dynamics throughout membrane spacers

The incorporation of a spacer among membranes has a major influence on fluid dynamics and performance metrics. Spacers create feed channels and operate as turbulence promoters to increase mixing and reduce concentration/temperature polarization effects. However, spacer geometry remains unoptimized, and studies continue to investigate a wide range of commercial and custom-made spacer designs. The in-depth discussion of the present systematic review seeks to discover the influence of Reynolds number or solution flowrate on flow hydrodynamics throughout a spacer-filled channel. A fast-flowing solution sweeping one membrane's surface first, then the neighboring membrane's surface produces good mixing action, which does not happen commonly at laminar solution flowrates. A sufficient flowrate can suppress the polarization layer, which may normally require the utilization of a simple feed channel rather than complex spacer configurations. When a recirculation eddy occurs, it disrupts the continuous flow and effectively curves the linear fluid courses. The higher the flowrate, the better the membrane performance, the higher the critical flux (or recovery rate), and the lower the inherent limitations of spacer design, spacer shadow effect, poor channel hydrodynamics, and high concentration polarization. In fact, critical flow achieves an acceptable balance between improving flow dynamics and reducing the related trade-offs, such as pressure losses and the occurrence of concentration polarization throughout the cell. If the necessary technical flowrate is not used, the real concentration potential for transport is relatively limited at low velocities than would be predicted based on bulk concentrations. Electrodialysis stack therefore may suffer from the dissociation of water molecules. Next studies should consider that applying a higher flowrate results in greater process efficiency, increased mass transfer potential at the membrane interface, and reduced stack thermal and electrical resistance, where pressure drop should always be indicated as a consequence of the spacer and circumstances used, rather than a problem.

Steps, hops and turns: examining the effects of channel shapes on mass transfer in continuous electrochemical reactors

Solution moving through an electrode, hence hopping from one electrode to another, has the greatest effect on an electrochemical reaction when compared to simple turns within a flow channel.

Modeling and Hydraulic Characterization of a Filter-Press-Type Electrochemical Reactor by Using Residence Time Distribution Analysis and Hydraulic Indices

Modeling and hydraulic characterization of a filter-press-type electrochemical reactor was studied by means of residence time distribution and hydraulic indices. For these purposes, a theoretical and approximation of residence time distribution experimental curves with axial dispersion model and Danckwerts’ boundary conditions, the Morrill dispersion index, the short-circuiting index, the Morrill volumetric efficiency index, and useful volume percent were used in order to establish deviation from plug-flow ideal, as well as dead volume, and the hydraulic efficiency. The hydraulic efficiency measure of the filter-press-type electrochemical reactor confirms uniformity of flow and a highly effective useful volume percent (91 %-98 % for all liquid flow rates tested). The axial dispersion coefficients computed (0.0005–0.0021 m2/s) indicates a small deviation of plug-flow ideal. Hence, the plug-flow reactor model is reliable for purpose modeling of the filter-press-type electrochemical reactor used in this research. Furthermore, hydrodynamic characterization of the tested filter-press-type electrochemical reactor by using hydraulic indices demonstrated its suitability for several electrochemical applications.