New method for CO2 extraction from oceans is discovered by MIT researchers.

A novel ocean technology for removing greenhouse gases was discovered by researchers. The method could be used to clean water in ships, offshore drilling rigs, and fish farms used for aquaculture.

The oceans are the primary “sink” for atmospheric carbon dioxide, absorbing 30–40 percent of the gas produced by human activity. A group of MIT researchers claims to have discovered what may be the most effective and cost-effective method for removing carbon dioxide from the oceans. In our fight against climate change, the findings, which were presented in the journal Energy and Environmental Science, may be of assistance.

We require any assistance we can get to reduce emissions of greenhouse gases.

“The carbon dioxide problem is the defining problem of our life, of our existence,” said Kripa Varanasi, one of the researchers on the project. “So clearly, we need all the help we can get.”

The current methods for removing CO2 from saltwater make use of a phenomenon known as water splitting to acidify a feed stream by applying voltage across a stack of membranes. The chemical process by which water is broken down into oxygen and hydrogen is called water splitting. Water, on the other hand, is made up of more than just hydrogen and oxygen in real life. For instance, the bicarbonates that are present in the water are transformed into CO2 molecules, which can be extracted in a vacuum. Chemicals are required to drive the total electrode reactions at either end of the stack, which adds complexity and costs to current methods.

In the new study, the team came up with a method that uses electrochemical cells without membranes to reverse the process. Seawater is introduced to protons by means of reactive electrodes. After that, it reaches the cells, causing carbon dioxide to dissolve. In this recursive procedure, acid is added to the water to dissolve inorganic bicarbonates. The dissolved bicarbonates are then transformed into molecular carbon dioxide and collected as a gas in a vacuum.

The water is then returned to the ocean after passing through a second set of cells with a negative voltage to extract protons and neutralize the acid. The roles of the two cells are periodically switched after one set of electrodes becomes proton-depleted (during acidification) and the other set becomes proton-rich (during alkalinization).

According to Varanasi, taking carbon dioxide out of alkaline water and putting it back in could slowly start to reverse how carbon dioxide is making the oceans more acidic, harming shellfish and coral reefs. In order to prevent an alkalinity rise that could harm local ecosystems, they recommend reinjecting alkaline water through numerous outlets or far offshore.

Once the carbon dioxide has been removed from the water, it still needs to be disposed of somewhere, just like with other methods of removing carbon. It could, for instance, undergo chemical transformation into products like ethanol, which can be utilized as a fuel for transportation or into additional specialized chemicals. Under the ocean floor, it may be buried in deep geologic formations. The idea would be to process seawater by integrating such systems with infrastructure that is already in place or is being developed.

“This system is scalable so that we could integrate it potentially into existing processes that are already processing ocean water or in contact with ocean water,” Varanasi said. “With desalination plants, you’re already pumping all the water, so why not co-locate there? A bunch of capital costs associated with the way you move the water, and the permitting, all that could already be taken care of.”

Carbon dioxide removal could be a simple addition to the processes that are already used to return enormous amounts of water to the ocean, so it would not be necessary to use consumables like chemical additives or membranes there.

The system could also be utilized by ships that would process water as they sailed to lessen the significant contribution that ship traffic makes to overall emissions. Shipping companies may be able to offset some of their emissions and turn their ships into ocean scrubbers with the assistance of international regulations to reduce shipping emissions.

Additionally, aquaculture farms and offshore drilling platforms could make use of the system. It could eventually lead to the worldwide establishment of independent carbon removal facilities. Because seawater has a carbon dioxide concentration that is more than 100 times higher than that of air, researcher T. Alan Hatton claims that the method might be more efficient than air-capture systems. In direct air-capture systems, the gas must first be captured and concentrated before it can be recovered.

“The oceans are large carbon sinks, however, so the capture step has already kind of been done for you,” Hatton said. “There’s no capture step, only release.”

As a result, fewer materials will need to be handled, potentially simplifying the entire procedure and reducing footprint requirements.

The following is the primary goal of the ongoing investigation: figuring out a way to get rid of the separated water and carbon dioxide without using a vacuum. All reported methods face the issue of minerals precipitating, which can clog the electrodes of the alkalinisation cell. To achieve maximum efficiency, this issue must be addressed. Hatton claims that significant effort has been put into resolving these issues, but it is still too early to provide any results. However, the team believes that the system could be ready for a demonstration project within two years. It is possible that that demonstration project will be scaled up and put into use in the real world if it is successful.

 

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