High-pressure electrochemical reduction of CO2 to formic acid/formate: effect of pH on the downstream separation process and economics
File(s)
Published version
Author(s)
Type
Journal Article
Abstract
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.
Date Issued
2019-12-26
Date Acceptance
2019-11-22
Citation
Industrial & Engineering Chemistry Research, 2019, 58 (51), pp.22718-22740
ISSN
0888-5885
Publisher
American Chemical Society (ACS)
Start Page
22718
End Page
22740
Journal / Book Title
Industrial & Engineering Chemistry Research
Volume
58
Issue
51
Copyright Statement
© 2019 American Chemical Society. This is an open access article published under a Creative Commons Non-Commercial No
Derivative Works (CC-BY-NC-ND) (http://pubs.acs.org/page/policy/authorchoice_ccbyncnd_termsofuse.html) Attribution License, which permits copying and
redistribution of the article, and creation of adaptations, all for non-commercial purposes.
Derivative Works (CC-BY-NC-ND) (http://pubs.acs.org/page/policy/authorchoice_ccbyncnd_termsofuse.html) Attribution License, which permits copying and
redistribution of the article, and creation of adaptations, all for non-commercial purposes.
Identifier
https://pubs.acs.org/doi/10.1021/acs.iecr.9b03970
Subjects
Science & Technology
Technology
Engineering, Chemical
Engineering
LIQUID-LIQUID EQUILIBRIA
GAS-DIFFUSION ELECTRODES
CARBON-DIOXIDE REDUCTION
TIE-LINE DATA
CARBOXYLIC-ACIDS
TERNARY-SYSTEMS
REACTIVE EXTRACTION
PHASE-EQUILIBRIA
BIPOLAR MEMBRANES
AQUEOUS-SOLUTIONS
03 Chemical Sciences
09 Engineering
Chemical Engineering
Publication Status
Published
Date Publish Online
2019-11-22