Pea-size pellets on a semi-truck can trap up to 90% of its carbon dioxide

For a diesel truck, Remora says the tailpipe is "a more efficient place to start" for catching carbon dioxide than the air afterward, while the exhaust is still concentrated.

That is the approach of Remora, a startup building carbon capture equipment for semi-trucks and locomotives. Paul Gross, the founder, says the company retrofits vehicles with a box mounted behind the cab that extracts and purifies carbon dioxide from exhaust, and can produce gas pure enough to carbonate drinks.

The workhorse is a cylinder filled with pellets about the size of peas. The company routes hot exhaust from the tailpipe through that cylinder. The pellets are full of microscopic pores, tiny holes sized to grab carbon dioxide molecules. The carbon dioxide gets stuck inside, while the other, cleaner gases keep moving and are released.

Once the pellets on one side of the cylinder fill up, a vacuum pulls the trapped carbon dioxide out for storage, while the other side keeps capturing. On the truck, the gas is held in pressure vessels and later offloaded as a liquid into a larger tank.

The pellets matter because older carbon capture systems relied on liquid solvents, chemicals that absorb carbon dioxide. Gross says those liquids are corrosive and volatile, can break down, and can even add cancer causing compounds to exhaust, a major reason the technology did not spread. Gross says the device "can reduce a vehicle's emissions by at least 80%," and the company says it can remove up to 90% of carbon dioxide from semi-truck exhaust.

The captured gas is then picked up by distributor trucks and sold to buyers that already need carbon dioxide, including food and beverage companies, greenhouses that feed it to plants, and water treatment plants. Exhaust becomes both less pollution and a product that pays the truck operator.