Simultaneous Sodium Hydroxide Production by Membrane Electrolysis and Carbon Dioxide Capture

Abstract

The simultaneous process of NaOH production via electrolysis of NaCl and CO2 capture was investigated due to the expectation of reduction in capital cost. It was found that seawater concentration of NaCl solution was adaptable to be used as both anolyte and catholyte and that 90 °C was the most proper temperature for NaOH production among the test conditions in this work. Under these electrolyte and temperature conditions, the simultaneous NaOH production and CO2 capture processes were conducted and more than 98.83 % of OH− was reacted with CO2 to yield aqueous carbonate solutions. Additional electrochemical CO2 capture tests were carried out depending on the different CO2 concentration of mixed gases.

Electrochemical carbon dioxide capture to close the carbon cycle

“…Electrolysis can enable the pH-swing in the vicinity of (two) electrodes as shown in Figure (6). (Membrane) electrolysis for CO 2 capture is used for alkali absorbent (re)generation [38,[69][70][71][72][73] or simultaneous H 2 production [36,[74][75][76]. H 2 production can (partially) offset the cost of CO 2 capture and is possible when water electrolysis takes place.…”

“…Alternative to water electrolysis, salt electrolysis, such as NaCl [69] and KCl [38] can also be used for CO 2 capture. If so, only an alkaline pH (at the cathode) is enabled, because at the anode e.g., the reaction 2Cl -→ Cl 2 (g) + 2etakes place instead of the oxygen evolution reaction (OER) [70].…”

“…Furthermore, CaCO 3 is easier to transport and store compared to CO 2 (g). NaCl electrolysis for alkaline absorbent (re)generation follows reaction (8) [69]:…”

“…Using salt electrolysis for CO 2 capture is especially interesting due to salt availability in the seawater, leveraging possible substitution of the electrolyte with abundant seawater [69]. The produced (toxic) Cl 2 (g) at the anode can be treated by the produced NaOH solution using a scrubber, or can alternatively be utilized as a feedstock for the synthesis of HCl, Cl containing polymers and bleaching agents [69].…”

“…Using salt electrolysis for CO 2 capture is especially interesting due to salt availability in the seawater, leveraging possible substitution of the electrolyte with abundant seawater [69]. The produced (toxic) Cl 2 (g) at the anode can be treated by the produced NaOH solution using a scrubber, or can alternatively be utilized as a feedstock for the synthesis of HCl, Cl containing polymers and bleaching agents [69]. Alternatively, using water electrolysis and by inserting two ion exchange membranes (IEMs) between the electrodes (Figure (9)), produces H 2 simultaneous acidifies seawater to recover CO 2 (g) [36,80,81].…”