A year ago, the International Maritime Organization — the United Nations agency that regulates shipping — tightened emissions targets for the shipping industry, bringing it in line with other sectors to achieve net zero emissions by 2050. But low-emission fuels such as methanol, hydrogen and ammonia are not readily available.

Now, chemical oceanographer Jess Adkins of the California Institute of Technology (Caltech) thinks he can help by equipping cargo ships with reactors that can turn carbon dioxide (CO2) emitted from fuel combustion into sea salt, which he says could be preserved for 100,000 years.

The process is similar to what happens naturally in the oceans. “This is a reaction that the planet has been going through for billions of years,” said Adkins, founder of Calcarea, a startup that designs and tests reactors.

“If we can speed up this process, we have a chance of finding a way to store CO2 safely and permanently,” he said.

Natural simulation technology

Seawater naturally absorbs about a third of the CO2 in the atmosphere, making it more acidic and dissolving calcium carbonate, a substance abundant in the ocean. "Calcium carbonate is what makes up coral skeletons, seashells, and all the things that make up most of the sediment on the ocean floor," says Adkins.

The dissolved calcium carbonate then reacts with CO2 in the water to form bicarbonate salts, locking up the CO2. "There are currently 38,000 gigatonnes (38 trillion tonnes) of bicarbonate in the ocean," Adkins added.

Calcarea wants to mimic this natural process by funneling the ship’s exhaust gases into a reactor in the hull, where they mix vigorously with seawater and limestone—a rock made primarily of calcium carbonate and a common ingredient in concrete. The CO2 in the exhaust reacts with the mixture, creating saltwater that locks up the CO2 as bicarbonate salt. With a full-scale reactor, Adkins says, he aims to capture and store about half of the ship’s CO2 emissions.

In the natural world, the reaction takes more than 10,000 years, but in Calcarea's kilns, it takes about a minute, Adkins says, and this is achieved by bringing the CO2 and limestone into close contact.

The brine produced will be discharged into the ocean, where it poses no threat to marine life or the chemical balance of the seawater, Adkins said. He added that the company is also considering adding a pre-filter to the system to remove other contaminants that might be released into the water, such as particles and unburned fuel.

After two years of working on the project, he spun the company out of Caltech in January 2023. He was joined by three co-founders: Caltech undergraduate Melissa Gutierrez, engineer Pierre Forin, and University of Southern California (USC) professor and geochemist Will Berelson.

They have raised $3.5 million in funding and are focused on the shipping industry. “The beauty of it is that the ship is a natural water pump,” Adkins says, noting that the system requires water to be constantly moving around for the reactions between the different elements to occur, something that is naturally provided by the motion of the ship.

The reactors will be tailored to different ship sizes, including “the largest ships available,” the “Newcastlemax” class, which can carry 180,000 tonnes of cargo. “On one of these ships, we’ll be about 4 to 5 per cent of the tonnage and carry about 4,000 tonnes of limestone. But we won’t actually use all of that,” Adkins said.

Carbon capture in the ocean

Before Calcarea is ready to install its first reactor, there are still a number of technical challenges to overcome. For example, how to properly mount the reactor on a ship loaded with limestone and set up a supply chain for transportation.

Current estimates put the cost of the system at around $100 per ton of CO2 captured when released, including the revenue the ship loses by having to make room for the reactor instead of commercial cargo.

Some cargo ships already have similar devices on board, called scrubbers. They are designed to capture and release sulfur gases that are harmful to health and the environment, but not CO2.

Besides Calcarea, there are other companies with carbon capture technology. For example, a British company called Seabound makes a device that captures 25% to 95% of a ship’s CO2 emissions. However, it creates solid carbonate pebbles that have to be unloaded at port.

Adkins believes Calcarea could help decarbonize the industry and transition to greener fuels, and in the more distant future, reactors could even be designed to lock captured CO2 out of the atmosphere, rather than storing it underground.

Ngoc Anh (according to CNN)