Impact of Temperature, Membrane Type, and Process Parameters in Seawater Acidification Using Bipolar Membrane Electrodialysis

The study investigated a key process of CO2 extraction from seawater using bipolar membrane electrolysis (BP-ED): seawater acidification. This research examined the effects of temperature, membrane type, and process parameters on the seawater acidification process. Three seawater temperatures (12, 23, and 33 °C) were selected to represent various geographical scenarios. This study compared homogeneous and heterogeneous bipolar membranes (BPMs) and ion-exchange membranes (IEMs) with different characteristics. Process performance was evaluated through specific energy consumption (SEC), acidification kinetics, and current density. Regardless of the membrane type, higher temperatures led to significant increases in current density and faster seawater acidification kinetics. BPMs demonstrated a dominant effect on current density versus SEC profiles over the IEMs, where the membrane resistance values of the former were 20- to 57-fold higher than the latter. Nevertheless, IEMs of lower resistance and higher IE capacity had a lower but positive impact on the process. Targeting pH 5 instead of 4 during seawater acidification (i.e.,∼91% and 99% of dissolved organic carbon in the CO2 form, respectively) resulted in 9.1–4.2% faster acidification kinetics and slightly lower SEC values (1.2–3.4%). The research aims to provide insight into the future design of membranes and optimization of the BP-ED process for the extraction of CO2 from seawater.