A team at the Massachusetts Institute of Technology (MIT) has justified the benefits of extracting carbon dioxide from seawater, rather than from the atmosphere. These studies are presented in a paper in the journal Energy & Environmental Science. A practical demonstration of the proposed technology will take place over the next two years. If everything works out, a new type of business will appear in the world – the extraction of CO2 from the seas and oceans on a commercial basis and without subsidies.
Image Source: MIT
According to 2022 IEA (International Energy Agency) data, the most efficient technologies for capturing carbon dioxide from the atmosphere require about 6.6 GJ of energy, or 1.83 MWh per tonne of CO2 captured. A significant part of the energy spent on this goes to maintain the operating temperatures of the absorbents or to operate compressors that compress air to effective pressure values.
According to some estimates, by 2030 the cost of capturing a ton of CO2 will be in the range of $300 to $1000. Today, the highest carbon tax is levied on industrialists in Uruguay: $137 per ton. This amount does not and will not cover the cost of extracting CO2 from the atmosphere for a long time, but with sea water, things can be different, MIT is sure.
Carbon dioxide is more profitable to extract from sea water, if only because its concentration there is 100 times greater than in air. Oceans and seas are natural absorbents of CO2. Marine waters are said to absorb 30-40% of humanity’s annual carbon emissions. Previously, methods have been proposed to extract carbon dioxide from water, but they require either expensive filtration membranes or a constant supply of chemicals.
In the system proposed by MIT scientists, seawater passes through two chambers. In the first chamber, the current passed through the electrodes saturates the liquid with protons and acidifies it, turning dissolved inorganic bicarbonates into carbon dioxide. In the vacuum chamber, the liquid is degassed and carbon dioxide is extracted. In the second chamber, the reversed polarity on the electrodes causes protons to deposit on electrical contacts and this alkalizes the water, after which it is dumped into the ocean.
As the electrodes in the first chamber are depleted and saturated with protons in the second, the polarity of the applied voltage in the chambers changes and water can be pumped in the reverse order with the same result – taken in by the second chamber and thrown out of the first – with the same effect of extracting CO2. The process is then repeated in reverse order. This eventually leads to contamination of the electrodes with sedimentary minerals, but this is a solvable problem.
Finally, the proposed process makes it possible to return water with an alkaline balance to the ocean, which will be good for the environment. The ocean is acidifying – this has already led, for example, to the death of coral reefs and a number of marine life.
Scientists do not hide the fact that a lot of work will still have to be done to implement the project. There is no ready-made project according to the proposal, but these are all solvable tasks and there is nothing to be afraid of. Ultimately, the scientists hope to bring the cost of extracting carbon dioxide from seawater down to $56 per tonne or so. This will be the impetus for the commercialization of this area.
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