Electrodialysis with Bipolar Membranes for the Sustainable Production of Chemicals from Seawater Brines at Pilot Plant Scale

Abstract

Environmental concerns regarding the disposal of seawater reverse osmosis brines require the development of new valorization strategies. Electrodialysis with bipolar membrane (EDBM) technology enables the production of acid and base from a salty waste stream. In this study, an EDBM pilot plant with a membrane area of 19.2 m2 was tested. This total membrane area results much larger (i.e., more than 16 times larger) than those reported in the literature so far for the production of HCl and NaOH aqueous solutions, starting from NaCl brines. The pilot unit was tested both in continuous and discontinuous operation modes, at different current densities (200–500 A m–2). Particularly, three different process configurations were evaluated, namely, closed-loop, feed and bleed, and fed-batch. At lower applied current density (200 A m–2), the closed-loop had a lower specific energy consumption (SEC) (1.4 kWh kg–1) and a higher current efficiency (CE) (80%). When the current density was increased (300–500 A m–2), the feed and bleed mode was more appropriate due to its low values of SEC (1.9–2.6 kWh kg–1) as well as high values of specific production (SP) (0.82–1.3 ton year–1 m–2) and current efficiency (63–67%). These results showed the effect of various process configurations on the performance of the EDBM, thereby guiding the selection of the most suitable process configuration when varying the operating conditions and representing a first important step toward the implementation of this technology at industrial scale.

Analysis of Operational Parameters in Acid and Base Production Using an Electrodialysis with Bipolar Membranes Pilot Plant

“…The three main line of process (acid, base and salt) were equipped with 2 tanks (IBC) of 1 m 3 each. These tanks together with a complex system of piping allow the operation of the pilot plant in different process configuration (batch, continuous, and feed and bleed mode) [ 29 ]. In addition, a cylindrical tank of 0.125 m 3 is used for the electrode rinse solution (ERS), which is continuously recirculated.…”

“…Very recently, the authors have presented the production of HCl and NaOH from NaCl brines by means of EDBM in a novel pilot plant [ 29 ]. This EDBM unit is configured with a total membrane area of 19.2 m 2 , more than 16 times larger than that reported in the literature for the same application.…”

Origin of Limiting and Overlimiting Currents in Bipolar Membranes

“…Such capability is of foreseeable importance as emerging BPM applications have been applied to a wide variety of source water compositions and salinities. For example, a BPM-integrated electrosorption process was suggested for boron removal from low salinity first pass seawater reverse osmosis permeate, while on the other end of the spectrum, bipolar membrane electrodialysis has been applied for valorization of hypersaline reverse osmosis brines . Future iterations of the presented framework should thus focus on ensuring the accuracy of BPM performance over a wide salinity range, with particular emphasis on improving prediction capability in the low salinity regime, where the external solution and the associated boundary layers become important to consider, and where our current model shows the largest discrepancy from experimental data.…”

Electrodeionization for the Bio-Succinic Acid Production Process

“…Electrodialysis is an electrochemical separation method that combines dialysis and electrolysis in which the ion-exchange membranes are arranged in a direct current field. Electrodialysis is an environmentally friendly process . However, its main disadvantages, such as the high susceptibility of membranes to fouling, low perm selectivity, and excessive system resistance, create problems with scaling and hinder the application of this technique in practice.…”

“…Electrodialysis is an environmentally friendly process. 6 However, its main disadvantages, such as the high susceptibility of membranes to fouling, low perm selectivity, and excessive system resistance, create problems with scaling and hinder the application of this technique in practice. Ion exchange is a widely known and widely used separation technique that is inexpensive and relatively easy to scale.…”