Electrochemical regeneration of caustic absorbent for the capture of CO2

Electrochemistry has a potential role in the removal of CO 2 from the atmosphere in the process of “electrochemically mediated carbon capture”. The future viability of that technology rests in part on the invention and development of specialized electrochemical reactors. This paper reports tests undertaken with a novel bench-scale electrochemical reactor intended for the potential regeneration of caustic absorbent in the direct air capture of CO 2 . The reactor design was based on capillary effects in micro-porous separators, with a single electrolyte stream and no ion-exchange membranes or gas diffusion electrodes. In batch-recycle mode the reactor converted 1 to 4 molar solutions of M 2 CO 3 (M ≡ Na or K) to MOH + M 2 CO 3 plus separate gas co-products H 2 and (O 2 + CO 2 ). Integral current efficiency for OH − and CO 2 fell from ca. 90% to 10% as the product [OH − ]/[CO 3 = ] ratio climbed from 0 to 3. The current density, full cell voltage, pressure, temperature and electrochemical specific energy ranged respectively from 1–6 kA m −2 , 3–10 V, 105–120 kPa(a), 25–70 ℃ and 4–200 kWh kg CO 2 −1 . Operating time was limited to about 20 h as reactor components deteriorated rapidly with the strong alkali and high oxidation potential around the anode. In some circumstances and with further development such an electrochemical system could potentially replace the thermochemical regeneration of alkaline absorbent for carbon capture.