Researchers at EPFL have patented a new concept that could cut trucks’ CO₂ emissions by almost 90%. The EPFL system captures CO₂ directly in the trucks’ exhaust system and liquefies it in a box on the vehicle’s roof. The liquid CO₂ would then be delivered to a service station and where it will be turned back into fuel using renewable energy.

The project is being coordinated by the Industrial Process and Energy Systems Engineering group, led by François Maréchal, at EPFL’s School of Engineering. The patented concept is the subject of an open-access paper published in Frontiers in Energy Research. In their study, the scientists used the example of a delivery truck.

First, the vehicle’s flue gases in the exhaust pipe are cooled down and the water is separated from the gases. CO₂ is isolated from the other gases (nitrogen and oxygen) with a temperature swing adsorption (TSA) system, using metal-organic frameworks (MOFs) adsorbent, which are specially designed to absorb CO₂. Those materials are being developed by the Energypolis team at EPFL Valais Wallis, led by Wendy Queen.

Once the material is saturated with CO₂, it is heated so that pure CO₂ can be extracted from it. High speed turbocompressors developed by Jürg Schiffmann’s laboratory at EPFL’s Neuchâtel campus use heat from the vehicle’s engine to compress the extracted CO₂ and turn it into a liquid. That liquid is stored in a tank and can then be converted back into conventional fuel at the service stations using renewable electricity.

Simple heat and mass flows for CO₂ capture from diesel engine exhaust: exhaust cooling, TSA cycle, product CO₂ compression, and liquefaction. Sharma and Maréchal

The whole process takes place within a capsule measuring 2 m x 0.9 m x 1.2 m, placed above the driver’s cabin.

The weight of the capsule and the tank is only 7% of the vehicle’s payload. The process itself uses little energy, because all of its stages have been optimized.

—François Maréchal

The researchers’ calculations show that a truck using 1 kg of conventional fuel could produce 3kg of liquid CO₂, and that the conversion does not involve any energy penalty.

Only 10% of the CO₂ emissions cannot be recycled, and the researchers propose to offset that using biomass.

The system could theoretically work with all trucks, buses and even boats, and with any type of fuel. The advantage of this system is that, unlike electric or hydrogen-based ones, it can be retrofitted to existing trucks in order to neutralize their impact in terms of carbon emissions.

Resources

• Sharma Shivom, Maréchal François (2019) “Carbon Dioxide Capture From Internal Combustion Engine Exhaust Using Temperature Swing Adsorption” Frontiers in Energy Research doi: 10.3389/fenrg.2019.00143