Written by: Dan Haves, Department of Chemistry, University of Toronto

What if rail systems around the world could be harnessed to help mitigate climate change and clean our air of CO₂? It’s a question that the founders of a US-based startup, CO₂Rail, have been pondering for a number of years. CO₂Rail recently partnered with U of T researchers to explore the feasibility of adding direct air carbon capture technology to freight and passenger trains.

Direct air capture (“DAC”) is a technology that removes carbon dioxide from the air with special machines and compresses it for utilization or permanent storage. The process, however, can be energy and land intensive and often very expensive.

This is why a team of researchers from Canada, the US, England and Germany have set their sights on designing DAC technology that uses less energy and less land at a viable cost. This multi-disciplinary team includes U of T’s Professor Geoffrey Ozin of the department of chemistry, Professor Alán Aspuru-Guzik of the departments of chemistry and computer science, and Professor Jeffrey MacIntosh of the Faculty of Law. Ozin and Aspuru-Guzik also hold appointments to U of T’s Acceleration Consortium, which brings academia, government, and industry together to tackle AI-driven materials discovery.

They outlined their plan this week in Joule to place DAC equipment within special rail cars on already-running trains to take advantage of the global rail network. They were able to demonstrate that rail-based direct air carbon capture could be a near carbon-neutral system capable of harvesting 2.9 gigatonnes of C02 by 2050.

How does the technology work?

These DAC rail cars work by using large intakes that extend up into the slipstream of the moving train to move ambient air into the large CO₂ collection chamber and eliminate the need for energy-intensive fan systems that stationaryDAC operations require. The air then moves through a chemical process that separates the carbon dioxide from the air and the CO_2-free air then travels out of the back of the car and returns to the atmosphere.

After a sufficient amount has been captured, the chamber is closed and the harvested CO₂ is collected, concentrated, and stored in a liquid reservoir, either to be used as feedstock or to be delivered to nearby geological sequestration sites.

Each of these processes is powered by on-board generated, sustainable energy sources that require no external energy input or off-duty charging cycles.

When a train pumps the brakes, its energy braking system converts the entire train’s forward momentum into electrical energy. Currently, this energy is dissipated in the form of heat and discharged out of the top of the locomotive during every braking maneuver. The energy, suggests E. Bachman of CO₂Rail, should be captured, stored, and used for productive purposes.

“For many decades, this enormous amount of sustainable energy has been completely wasted,” says Bachman. “On average, each complete braking maneuver generates enough energy to power 20 average homes for an entire day, so it is nota trivial amount of energy.”

Besides energy, there are also land issues that surround wide-spread DAC deployment. Most stationary DAC operations at require large areas of land to build their equipment and even more to construct renewable sources of energy to power them. In addition, obtaining the necessary permits, conducting surveys, meeting zoning requirements, and achieving community acceptance takes both time and money.

“It’s a huge problem because most everybody wants to fix the climate crisis, but few are happy to have it done in their proverbial ‘backyard’,” says Ozin.

“Rail DAC does not require special zoning, surveys, or building permits. It would be transient and generally unseen by the public.”

Ozin, an Albert Einstein Medal recipient, has spent the better part of the last two decades harnessing sunlight to turn CO₂ into a chemical feedstock for a wide range of commodity products and fuels, a process known as ‘carbon capture and utilization’.

He believes that rail-based direct air capture becomes an even more attractive climate solution because much of the required infrastructure is already in place and the energy is there, just waiting to be utilized.

The potential impact of this technology is also energized by a growing desire for increased rail systems. Earlier this month, European transport organizations said they are committed to tripling high-speed rail use by 2050 to curb C02-heavy air travel.

The team says that, in the near-term, each direct air capture car will harvest over 6,000 metric tonnes of carbon dioxide from the air per year and much more as the technology develops. In the Joule paper, the authors were also able to demonstrate how this technology could scale down to less than $50 USD per tonne.

“It makes the technology not only commercially feasible but commercially attractive,”Bachman says.

“These kinds of numbers are unheard of in direct air capture,” says Ozin. “At these price points and with its capabilities, Rail DAC is likely to soon become the first megatonne-scale, first gigatonne-scale, and overall largest provider of direct air capture services in the world.”

The nextstep for CO₂Rail is to complete the first prototype and to test it in real-world environments. Ozin believes the first direct air carbon capture railcar will be in production by early 2023.