(166a) Electrochemical Marine Carbon Dioxide Removal from Oceanwater | AIChE

(166a) Electrochemical Marine Carbon Dioxide Removal from Oceanwater

Authors 

Hatton, T. A. - Presenter, Massachusetts Inst of Technology
Kim, S., Massachusetts Institute of Technology
Rufer, S., Massachusetts Institute of Technology
Negative Emissions Technologies (NETs) are crucial to avert catastrophic disruption of global climate patterns caused by the continuing atmospheric accumulation of CO2 due to industrial emissions. The recent surge of interest in NETs in which CO2 (currently at an atmospheric concentration of ~420 ppm) is removed from the ambient environment itself, by, e.g., direct air capture (DAC), has not yet been matched by a similar drive to reduce CO2 in oceans, where increasing acidification has led to destruction of coral reefs, and reduced carbonate ion concentrations harm shellfish and other marine life. The total CO2 accumulation rates by oceans rivals that in the atmosphere, and thus effective means for CO2 removal could augment the other NETs to reduce the environmental burden imposed by this greenhouse gas. The concentrations in water (on a volumetric basis) are much higher at 100 mg/L than that in the ambient air (0.77 mg/L), and thus smaller volumes will need to be treated than in DAC, which could provide a processing advantage.

Current approaches for the removal of CO2 from oceanwaters rely on water splitting via, bipolar membrane catalysis and electrodialysis for pH modulation to release the CO2 as a gas (low pH) or carbonate salt (high pH). We have proposed an alternative approach to marine carbon dioxide removal (mCDR) that does not require expensive membranes or addition of chemicals, is easy to deploy, and does not lead to formation of byproducts or secondary streams. In this approach, the pH is regulated through a chloride-mediated reaction with electrodes in asymmetric electrochemical cells through which the seawater flows. In the acidification cell the DIC speciation shifts from bicarbonate and carbonate to CO2 which can then be removed in a membrane contactor. The now-decarbonized water is introduced to a second electrochemical cell where the reverse reaction is promoted, the electrodes are regenerated, and the pH increases before the water is discharged back to the ocean. The CO2 removal approach has perceived advantages in that it does not require expensive membranes or addition of chemicals, is easy to deploy, and does not lead to formation of byproducts or secondary streams.

We will discuss the overall electrochemical swing process, which can be enhanced through flexible electrode configurations to reduce transport and electrical resistances while enabling treatment of large quantities of water. Novel methods for the recovery of molecular CO2 without the need for high vacuum desorption, and of calcium carbonate precipitates without fouling of the electrodes, will be highlighted.