TY - JOUR
T1 - High-Pressure Electrochemical Reduction of CO2 to Formic Acid/Formate
T2 - Effect of pH on the Downstream Separation Process and Economics
AU - Ramdin, Mahinder
AU - Morrison, Andrew R.T.
AU - De Groen, Mariette
AU - Van Haperen, Rien
AU - De Kler, Robert
AU - Irtem, Erdem
AU - Laitinen, Antero T.
AU - Van Den Broeke, Leo J.P.
AU - Breugelmans, Tom
AU - Trusler, J. P.Martin
AU - Jong, Wiebren De
AU - Vlugt, Thijs J.H.
PY - 2019
Y1 - 2019
N2 - We use a high-pressure semicontinuous batch electrochemical reactor with a tin-based cathode to demonstrate that it is possible to efficiently convert CO2 to formic acid (FA) in low-pH (i.e., pH < pKa) electrolyte solutions. The effects of CO2 pressure (up to 50 bar), bipolar membranes, and electrolyte (K2SO4) concentration on the current density (CD) and the Faraday efficiency (FE) of formic acid were investigated. The highest FE (?80%) of FA was achieved at a pressure of around 50 bar at a cell potential of 3.5 V and a CD of ?30 mA/cm2. To suppress the hydrogen evolution reaction (HER), the electrochemical reduction of CO2 in aqueous media is typically performed at alkaline conditions. The consequence of this is that products like formic acid, which has a pKa of 3.75, will almost completely dissociate into the formate form. The pH of the electrolyte solution has a strong influence not only on the electrochemical reduction process of CO2 but also on the downstream separation of (dilute) acid products like formic acid. The selection of separation processes depends on the dissociation state of the acids. A review of separation technologies for formic acid/formate removal from aqueous dilute streams is provided. By applying common separation heuristics, we have selected liquid-liquid extraction and electrodialysis for formic acid and formate separation, respectively. An economic evaluation of both separation processes shows that the formic acid route is more attractive than the formate one. These results urge for a better design of (1) CO2 electrocatalysts that can operate at low pH without affecting the selectivity of the desired products and (2) technologies for efficient separation of dilute products from (photo)electrochemical reactors.
AB - We use a high-pressure semicontinuous batch electrochemical reactor with a tin-based cathode to demonstrate that it is possible to efficiently convert CO2 to formic acid (FA) in low-pH (i.e., pH < pKa) electrolyte solutions. The effects of CO2 pressure (up to 50 bar), bipolar membranes, and electrolyte (K2SO4) concentration on the current density (CD) and the Faraday efficiency (FE) of formic acid were investigated. The highest FE (?80%) of FA was achieved at a pressure of around 50 bar at a cell potential of 3.5 V and a CD of ?30 mA/cm2. To suppress the hydrogen evolution reaction (HER), the electrochemical reduction of CO2 in aqueous media is typically performed at alkaline conditions. The consequence of this is that products like formic acid, which has a pKa of 3.75, will almost completely dissociate into the formate form. The pH of the electrolyte solution has a strong influence not only on the electrochemical reduction process of CO2 but also on the downstream separation of (dilute) acid products like formic acid. The selection of separation processes depends on the dissociation state of the acids. A review of separation technologies for formic acid/formate removal from aqueous dilute streams is provided. By applying common separation heuristics, we have selected liquid-liquid extraction and electrodialysis for formic acid and formate separation, respectively. An economic evaluation of both separation processes shows that the formic acid route is more attractive than the formate one. These results urge for a better design of (1) CO2 electrocatalysts that can operate at low pH without affecting the selectivity of the desired products and (2) technologies for efficient separation of dilute products from (photo)electrochemical reactors.
UR - http://www.scopus.com/inward/record.url?scp=85076788563&partnerID=8YFLogxK
U2 - 10.1021/acs.iecr.9b03970
DO - 10.1021/acs.iecr.9b03970
M3 - Article
AN - SCOPUS:85076788563
SN - 0888-5885
VL - 58
SP - 22718
EP - 22740
JO - Industrial and Engineering Chemistry Research
JF - Industrial and Engineering Chemistry Research
IS - 51
ER -