UCLA Says We Can Hack The Ocean To Store Carbon Dioxide

On January 12, 2021, a research team from UCLA published a paper entitled “Saline Water-Based Mineralization Pathway for Gigaton Scale Carbon Dioxide Management” in the journal of the American Chemical Society. Here is an excerpt from that paper.

“This perspective proposes a potential pathway to diminish atmospheric CO2 accumulations which is distinct from traditional carbon capture and geological sequestration strategies and from existing negative emissions technologies (NETs).

“Unlike conventional sorbent or solvent based CO2 capture processes where substantial energy expenditures are associated with demixing and desorbing CO2, the single step carbon sequestration and storage (sCS2) approach relies on electrolytic carbonate mineral precipitation using renewable energy within a simple and scalable process design. Although numerous approaches have implied electrolysis for carbon management, the sCS2 approach is unique in the following ways:

1. 1. CO2 mineralization for promoting solid carbonate formation: The thermodynamic and kinetic barriers to carbonate precipitation are overcome by direct and in situ electrochemical forcing to stabilize dissolved inorganic carbon and divalent cations [Ca,Mg] to form carbonate minerals.
   2. Flow through membrane-less electrolysis: A flowing electrolyte (seawater) is dissociated while in motion. The process utilizes cost-effective mesh electrodes while also decreasing the number of components and assembly steps and reducing the risk of device failure.
   3. Integrated electrolytic reactor/rotary drum filter: An electroactive thin film mesh cathode (eTFC) is suggested to be integrated within a rotary drum filter configuration, allowing for the filtration of dilute and poly-dispersed mineral precipitates at a low energy cost. These attributes render sCS2 as an approach worthy of more detailed evaluation, development, and scaling for global-scale carbon management.”

Carbon Dioxide & Seawater

Most experts agree that halting climate change — and the global warming, extreme heat events, and stronger storms that come with it — will require the removal of carbon dioxide and other greenhouse gasses from the atmosphere. But with humans pumping out an estimated 37 billion metric tons of carbon dioxide annually, current strategies for capturing it seem likely to fall short, says a UCLA press release.

A proposed pathway that could help extract billions of metric tons of carbon dioxide from the atmosphere each year has been suggested by UCLA researchers. Instead of directly capturing atmospheric carbon dioxide, the technology would extract it from seawater, enabling the seawater to absorb more. Why? Because, per unit volume, seawater holds nearly 150 times more carbon dioxide than air.

“To mitigate climate change, we need to remove carbon dioxide from the atmosphere at a level between 10 billion and 20 billion metric tons per year,” said senior author Gaurav Sant, who is the director of the UCLA Institute for Carbon Management and professor of civil and environmental engineering at the UCLA Samueli School of Engineering. “To fulfill a solution at that scale, we’ve got to draw inspiration from nature.”

Since the atmosphere and the oceans are in a state of equilibrium, if carbon dioxide is extracted from the ocean, carbon dioxide from the atmosphere can then dissolve into seawater. In this scenario, seawater is like a sponge for carbon dioxide that has already absorbed its full capacity. The sCS2 process aims to wring it out, allowing the sponge to absorb more carbon dioxide from the atmosphere.

The proposed technology would incorporate a flow reactor — a system that is continuously fed raw materials and yields products. The seawater would flow through a mesh that allows an electrical charge to pass into the water, rendering it alkaline. This kicks off a set of chemical reactions that ultimately combine dissolved carbon dioxide with calcium and magnesium native to seawater, producing limestone and magnesite by a process similar to how seashells form. The seawater that flows out would then be depleted of dissolved carbon dioxide and ready to take up more. A co-product of the reaction, besides minerals, is hydrogen, which is a clean fuel.

In addition to its potential scale of billions of metric tons of carbon dioxide, the approach suggested by the UCLA team has important advantages over current ideas for addressing the atmospheric accumulation of carbon dioxide.

The name includes “single-step” to differentiate it from other concepts that require carbon dioxide from the atmosphere to undergo a multi-step concentration process before it can be stored. While some plans propose storing captured carbon dioxide in geological formations such as depleted natural oil and gas reservoirs, there is a risk of leaks returning that carbon dioxide into the atmosphere. By contrast, sCS2 is meant to durably store carbon dioxide in the form of solid minerals.

“What’s nice about turning carbon dioxide into a rock is, it’s not going anywhere,” said Sant, who is a member of the California NanoSystems Institute at UCLA. “Durable, safe and permanent storage is the premise of our solution,” added first author Erika Callagon La Plante, a former UCLA assistant project scientist who is currently an assistant professor at the University of Texas at Arlington.

The team carried out detailed analyses of the material and energy inputs and the costs required to realize their concept, as well as what to do with the byproducts. Given the enormous magnitude of the carbon dioxide challenge, it estimates it would take nearly 1,800 sCS2 plants to immobilize 10 billion metric tons of carbon dioxide each year at a cost in the trillions of dollars.

“We should be clear: Managing and mitigating carbon dioxide is foremost an economic challenge,” Sant said. “Many of today’s approaches for carbon management either require more clean energy than we can produce or are unaffordable. As such, we need to create solutions that are accessible and that will not impoverish the world. We have tried to use a lens of pragmatism to consider how we may be able to achieve synthetic interventions at an unprecedented scale, while considering the finite energy and financial resources we have.”

Still, the researchers believe that sCS2, even at smaller scales, represents an advance in carbon capture and storage that should be considered as a potential part of any overall strategy for confronting climate change.

The researchers have been testing a prototype system in the waters off Los Angeles for over a year. A second system will begin operating in Singapore later this year. The research was supported by the U.S. Department of Energy’s Office of Fossil Energy, the Anthony and Jeanne Pritzker Family Foundation, the Grantham Foundation for the Protection of the Environment, the National Science Foundation, the U.S.–China Clean Energy Research Center for Water-Energy Technologies, the University of Texas at Arlington, and the UCLA Institute for Carbon Management.

The Takeaway

One of the byproducts of the UCLA system is green hydrogen — about 37 kilograms for every ton of carbon dioxide removed. That could help offset part of the cost of the system, which in its current form costs about $100 a ton, although that figure should drop as economies of scale kick in.

And who should pay for this? Oil, coal, and gas companies should pay, since they are responsible for putting the carbon dioxide into the atmosphere in the first place. Why not let Adam Smith’s unseen hand work its magic on the companies that have been making obscene profits for generations?

The good news about this concept from UCLA is that it may eliminate the need for more drastic geoengineering strategies that will have unknown and unknowable consequences. This is simplicity itself, a system that takes advantage of the calcium and magnesium that are already present in the oceans to help solve the most pressing climate problem in the history of humanity.