Electrodialysis with bipolar membranes for HCl and NaOH production: A scale-up analysis from the laboratory to a pilot-plant

Electrodialysis with Bipolar Membranes (EDBM) is an electro-membrane process that produces acidic and alkaline solutions from salty water and electricity. In the available literature, this technology has been explored predominantly at the laboratory scale, with very few investigations at scaled-up levels. This study investigated the effect of scale-up on the performance of the EDBM unit, comparing a laboratory-scale and a semi-industrial-scale unit under “scale-independent” equivalent operating conditions. Moreover, the experiments at both scales allowed the identification of scale-independent parameters governing the EDBM performance and, thus, enabled the assessment of key operational relationships. In this work, we propose a new methodology to find crucial scale-independent parameters and demonstrate the validity of the method through an original experimental campaign. As an application example, the effect of varying the initial solution volume ratios on process performance was systematically analyzed and confirmed across scales. Results indicate that the two units performed comparably, with less than 5 % difference typically observed between lab- and pilot-scale units in key parameters such as current density, voltage, and product concentrations, but also in key performance indicators. Doubling the volume of acid and salt solutions improved the systems performance, in terms of higher sodium hydroxide concentration, enhanced current efficiency, and reduced energy consumption. Indeed, at a OH− concentration target of 0.5 mol L−1, CE and SEC reached values of 86 % and 1.18 kWh kg−1, respectively. A techno-economic analysis estimated a minimum production cost of 278 € ton−1NaOH. This work demonstrates that laboratory-scale experiments can reliably predict the behavior of upscaled systems and provides a solid basis for validating mathematical models, which can then be confidently used to simulate, optimize, and control larger-scale units.