Environment Technology

New Road-Ready Diesel Fuel Made from Waste Gas

biofuel production

One of the most serious challenges facing the world today is climate change and since the Paris Agreement came into effect, there has been a rising interest in carbon capture and utilization (CCU). Carbon dioxide (CO2) is the most troublesome greenhouse gas.

Professor Jae Sung Lee of Energy and Chemical Engineering at UNIST is leading a new study to reveal new ways to make biofuel from CO2. Lee’s team presented direct CO2 conversion to liquid transportation fuels in a paper recently published in the journal Applied Catalysis B: Environmental. The conversion is achieved by getting CO2 to react with renewable hydrogen (H2) that is generated by solar water splitting.

On the left is the new delafossite-based catalyst used in the reaction between CO2 and H2 generated by solar water splitting. Shown on the right is diesel, produced by the reaction. Credit: UNIST
On the left is the new delafossite-based catalyst used in the reaction between CO2 and H2 generated by solar water splitting. Shown on the right is diesel, produced by the reaction. Credit: UNIST

Currently, the catalysts used for the reactions of H2 with CO2 are limited to low molecular weight substances such as methanol or methane. The reduction effects of CO2 is however generally low due to the low value of these catalysts. The UNIST research team presented a new delafossite based catalyst, which converts CO2 into liquid hydrocarbon-based fuels (e.g., diesel fuel) in a single step. The fuel samples can be used directly by existing diesel vehicles like cars, buses and trucks.

The new catalyst is made up of of inexpensive, earth-abundant copper and steel, and is used to produce diesel in a reaction between CO2 emissions of industrial plants and H2 generated from solar hydrogen plants.

Proposed carbon capture and utilization (CCU) system build on catalytic CO2 conversion to liquid hydrocarbon fuels with hydrogen supplied from solar water splitting. (Image Credit: Ulsan National Institute of Science and Technology)
Proposed carbon capture and utilization (CCU) system build on catalytic CO2 conversion to liquid hydrocarbon fuels with hydrogen supplied from solar water splitting. (Image Credit: Ulsan National Institute of Science and Technology)

Yo Han Choi, the first author of the research explained that compared to methane and methanol, diesel has longer chains of carbon and hydrogen atoms. Longer carbon chains can be created by using delafossite-CuFeO2 as the catalyst precursor. This allows for the production of diesel.

German car manufacturer Audi uses a CO2 to diesel conversion process that is different from the direct CO2 FT synthesis and uses two steps. The first is a reverse water gas shift (RWGS) reaction to CO, which is then followed by a CO Fisher Tropsch (FT) synthesis.

The benefits of the new process are two-fold. The process not only removes harmful CO2 from the atmosphere, but the diesel can then be used as an alternative fuel to gasoline. The team believes that this development brings us a step closer to eliminating greenhouse gas as it holds the potential to revolutionize the automobile industry. Professor Lee feels that the new catalyst breaks through the restrictions of CO2 based FT synthesis and will open the way for new opportunities to recycle CO2 into valuable chemicals and fuels.

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