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Reverse electrodialysis (RE) is a promising technology for electric power generation from controlled mixing of two differently concentrated salt solutions, where ion-exchange membranes are adopted for the generation of ionic currents within the system. Channel geometry strongly influences fluid flow and thus crucial phenomena such as pressure drop and concentration polarization. Profiled membranes are an alternative to the more commonly adopted net spacers and offer a number of advantages: avoiding the use of non-conductive and relatively expensive materials, reducing hydraulic losses and increasing the active membrane area. In this work, Computational Fluid Dynamic simulations were performed to predict the fluid flow and mass transfer behaviour in channels with profiled membranes for RE applications. In particular, channels equipped with pillars were simulated. The influence of channel geometry on fluid flow and concentration polarization was assessed by means of a parametric analysis for different profile geometries. The unit cell approach along with periodic boundary conditions was adopted to simulate fully developed boundary conditions. Transport equations, valid also for concentrated solutions, were obtained from the rigorous Stefan–Maxwell equation along with the assumptions of binary electrolyte and local electroneutrality. Simulation results show that, in the geometries investigated here, the pumping power consumption is much lower than in a conventional net spacer and very close to that of the empty channel, while calm zones are generated by the profiles, which may accentuate polarization phenomena. [ABSTRACT FROM PUBLISHER]

Abstract: Reverse electrodialysis (RED) is a process that can be used to generate energy from salinity gradients. Since its application in practice requires the use of natural seawater and river water, the presence of multivalent ions is inevitable, but this currently limits RED performance. Membranes with selectivity for monovalent ions may overcome this limitation. Standard ion exchange membranes have low monovalent-ion selectivity. We used a relatively fast method to coat a standard commercial anion exchange membrane to improve its monovalent-ion selectivity. The coating layer was formed by copolymerization of 2-acryloylamido-2-methylpropanesulfonic acid (AMPS) as the active polymer and N,N-methylenebis(acrylamide) (MBA) as the crosslinker, using UV irradiation. The monovalent ion selectivity of the resulting membranes was comparable to that of commercial monovalent-selective membranes. Furthermore, the modified membranes with their negatively charged coating showed increased hydrophilicity and exhibited sufficient antifouling potential against organic foulants. When they were tested in an RED stack, their performance was found to depend especially on the proportion of the divalent ions (sulfate) in the river water stream. However, the use of the currently available monovalent selective membranes was not found to be very effective for obtaining higher gross power densities in RED. [Copyright &y& Elsevier]

Technologies for the exploitation of renewable energies have been dramatically increasing in number, complexity and type of source adopted. Among the others, the use of saline gradient power is one of the latest emerging possibilities, related to the use of the osmotic/chemical potential energy of concentrated saline solutions. Nowadays, the fate of this renewable energy source is intrinsically linked to the development of the pressure retarded osmosis and reverse electrodialysis technologies. In the latter, the different concentrations of two saline solutions is used as a driving force for the direct production of electricity within a stack very similar to the conventional electrodialysis ones. In the present work, carried out in the EU-FP7 funded REAPower project, a multi-scale mathematical model for the Salinity Gradient Power Reverse Electrodialysis (SGP-RE) process with seawater and concentrated brines has been developed. The model is based on mass balance and constitutive equations collected from relevant scientific literature for the simulation of the process under extreme conditions of solutions concentration. A multi-scale structure allows the simulation of the single cell pair and the entire SGP-RE stack. The first can be seen as the elementary repeating unit constituted by cationic and anionic membrane and the relevant two channels where dilute and concentrate streams flow. The reverse electro-dialysis stack is constituted by a number of cell pairs, the electrode compartments and the feed streams distribution system. The model has been implemented using gPROMS®, a powerful dynamic modelling process simulator. Experimental information, collected from the FUJIFILM laboratories in Tilburg (the Netherlands), has been used to perform the tuning of model formulation and eventually to validate model predictions under different operating conditions. Finally, the model has been used to simulate different possible scenarios and perform a preliminary analysis of the influence of some process operating conditions on the final stack performance. [ABSTRACT FROM AUTHOR]

In this work, innovative use of Salinity Gradient Power (SGP) as renewable energy source for indirect production of hydrogen is addressed. A lab-scale reverse electrodialysis (RED) unit, fed with different NaCl solutions mimicking highly concentrated brine (5 M), Reverse Osmosis retentate (1 M), seawater (0.5 M) and brackish water (0.1 M), was coupled to an alkaline polymer electrolyte (APE) water electrolysis cell. SGP-RED unit, equipped with 27 cell-pairs, reached at best an Open Circuit Voltage (OCV) of 3.7 V and maximum gross power density of 3.2 W m −2 MP (membrane pair) when feeding the low concentration compartment (LCC) with 0.1 M NaCl and the High Concentration Compartment (HCC) with 5 M NaCl. The single-cell APE water electrolysis unit, operated at 1.8 V, attained a current density of 120 mA cm −2 under the following configuration: 10% w/w KOH electrolyte, highly conductive anion selective membrane composed of inert low-density polyethylene, finely milled anion selective particles and water-soluble poly (ethylene glycol-ran-propylene glycol), non-Platinum catalysts (NiCo 2 O 4 and NiFe 2 O 4 ) loading of 10 mg cm −2 and 15%w/w polymer binder at both cathode and anode, and operational temperature of 65 °C. The integrated system resulted in a maximum hydrogen production rate of 44 cm 3 h −1 per cm 2 of electrode surface area. [ABSTRACT FROM AUTHOR]

With a total capacity of 70 million cubic meters per day, seawater desalination industry represents the most affordable source of drinking water for many people living in arid areas of the world. Seawater Reverse Osmosis (SWRO) technology, driven by the impressive development in membrane materials, modules and process design, currently shows an overall energy consumption of 3–4 kW h per m 3 of desalted water, substantially lower than thermal systems; however, the theoretical energy demand to produce 1 m 3 of potable water from 2 m 3 of seawater (50% recovery factor) is 1.1 kW h. In order to move towards this goal, the possibility to recover the energy content of discharged concentrates assumes a strategic relevance. In this work, an innovative approach combining Direct Contact Membrane Distillation (DCMD) and Reverse Electrodialysis (RE) is tested for simultaneous water and energy production from SWRO brine, thus implementing the concept of low energy and Near-Zero Liquid Discharge in seawater desalination. DCMD operated on 1 M NaCl RO retentate fed at 40–50 °C resulted in a Volume Reduction Factor (VRF) up to 83.6% with transmembrane flux in the range of 1.2–2.4 kg/m 2 h. The performance of RE stack fed with DCMD brine (4–5.4 M) and seawater (0.5 M) was investigated at different temperatures (10–45 °C) and flow velocities (0.7–1.1 cm/s). Experimental data show the possibility to obtain an Open Circuit Voltage (OCV) in the range of 1.5–2.3 V and a gross power density of 0.9–2.4 W / m MP 2 (membrane pair). In general, optimization is required to find best operating conditions for the proposed system. [ABSTRACT FROM AUTHOR]

Abstract: This study deals with the membrane and interface electrical properties investigation by electrochemical impedance spectroscopy (EIS). The EIS is a powerful technique for characterizing electrical behavior of systems in which coupled electrical processes occur at different rates. A systematic study on the effect of solution concentration, temperature and velocity, on the electrical resistance of anion- and cation-exchange membranes (AEMs and CEMs) and their interfaces (electrical double layer and diffusion boundary layer), was carried out. At the best of our knowledge, for the first time electrolyte concentrations up to 4M were used for the study of membranes and interface by EIS. Moreover, Pulsed Gradient Spin Echo Nuclear Magnetic Resonance (PGSE-NMR) technique was used to measure the water self-diffusion coefficients in swelled membrane as a function of the solution concentration and temperature. These measurements gave additional important insights about the effect of the electrolyte solution and fixed charges concentration in membrane, on membrane microstructure and its transport and electrical properties. [Copyright &y& Elsevier]

Reverse electrodialysis (RED) is a membrane-based renewable energy technology that can harvest energy from salinity gradients. The anticipated feed streams are natural river and seawater, both of which contain not only monovalent ions but also divalent ions. However, RED using feed streams containing divalent ions experiences lower power densities because of both uphill transport and increased membrane resistance. In this study, we investigate the effects of divalent cations (Mg 2+ and Ca 2+ ) on RED and demonstrate the mitigation of those effects using both novel and existing commercial cation exchange membranes (CEMs). Monovalent-selective Neosepta CMS is known to block divalent cations transport and can therefore mitigate reductions in stack voltage. The new multivalent-permeable Fuji T1 is able to transport divalent cations without a major increase in resistance. Both strategies significantly improve power densities compared to standard-grade CEMs when performing RED using streams containing divalent cations.