Testing of Electrodialysis with bipolar membrane at semi-industrial scale for in-situ reactant production

Introduction. Electrodialysis with bipolar membranes (EDBM) has been gaining attention for the production of chemicals, such as acids and bases, for direct use in situ within circular and integrated processes, thus avoiding transport and handling of highly concentrated and dangerous reagents. Although this process has been explored in recent years at laboratory scale, few studies aimed at the development of pilot scale units. This work aims to fill this gap by scaling up and testing an EDBM unit at semi-industrial scale. Materials and methods. The pilot unit consists of 50 triplets of 0.32 m2 of active membrane area. The setup includes measurement instruments to monitor flowrates, conductivity, pressure, etc. Tests were performed in batch mode with synthetic solutions at initial concentration of 1.0 mol/L NaCl in the saline channels and 0.05 mol/L HCl and NaOH in the acid and base ones, respectively. The effect of a different initial volumes in the compartments was investigated by comparing performance indicators as current efficiency (CE), specific energy consumption (SEC) and specific productivity (SP). Results and discussion. Results showed that, when doubling the volume of acid, a SEC of 1.05 kWh/kgNaOH and CE of 95% were reached at 0.5 mol/L of OH-. Moreover, OH- concentration above 1.0 mol/L could also be reached (with corresponding SEC and CE of 1.05 kWh/kgNaOH and 76%, respectively). Indeed, lowering the acid concentration (by increasing the acid tank volume) reduced undesired effect of diffusion towards the saline channel and partial neutralization of acid and base. This work demonstrated the scalability of the EDBM process and highlighted some practical operating conditions to optimize the EDBM performance indicators.