A clean, sustainable fuel made ‘out of thin air’ and plastic waste
(Nanowerk News) Researchers have demonstrated how carbon dioxide can be captured from industrial processes – or even directly from the air – and turned into a clean, sustainable fuel using only energy from the Sun.
Researchers from the University of Cambridge developed a solar-powered reactor that converts captured CO22 and plastic waste into sustainable fuels and other valuable chemical products. In tests, CO2 is converted to syngas, the main building block for sustainable liquid fuels, and plastic bottles are converted to glycolic acid, which is widely used in the cosmetic industry.
Unlike previous tests of their solar fuel technology, the team took CO22 from real-world sources – such as industrial exhaust or the air itself. The researchers were able to capture and concentrate CO2 and turn it into a sustainable fuel.
Although improvements are needed before this technology can be used on an industrial scale, the results are reported in the journal Joules (“Integrated Capture and Utilization of Solar-Based CO22 of Exhaust Gas and Air”), represents another important step towards producing clean fuels to power the economy, without the need for environmentally damaging oil and gas extraction.
For several years, Professor Erwin Reisner’s research group, based in Yusuf Hamied’s Department of Chemistry, has been developing a sustainable, net zero carbon fuel inspired by photosynthesis – the process by which plants convert sunlight into food – using artificial leaves. This artificial leaf converts CO2 and water becomes fuel only by using solar energy.
Until now, their solar-based experiments have used concentrated, pure CO2 of a cylinder, but for the technology to have practical use it needs to be able to actively capture CO22 from industrial processes, or directly from the air. However, since CO2 is just one of many types of molecules in the air we breathe, making this technology selective enough to convert very dilute CO22 is a huge technical challenge.
“We are not only interested in decarbonization, but also defossilization – we need to completely eliminate fossil fuels to create a truly circular economy,” said Reisner. “In the medium term, these technologies can help reduce carbon emissions by capturing them from industry and turning them into something useful, but ultimately, we need to completely eliminate fossil fuels and capture CO2.2 from the air.”
The researchers took inspiration from carbon capture and storage (CCS), in which CO2 captured and then pumped and stored underground.
“CCS is a popular technology within the fossil fuel industry as a way to reduce carbon emissions while continuing oil and gas exploration,” said Reisner. “But if instead of carbon capture and storage, we have carbon capture and utilization, we can make something useful out of CO2 instead of burying it underground, with unknown long-term consequences, and eliminating the use of fossil fuels.”
The researchers adapted their solar-powered technology so that it works with exhaust gases or directly from the air, converting CO2 and plastic into fuels and chemicals using only solar power.
By bubbling air through a system containing an alkaline solution, CO2 is selectively trapped, and other gases present in the air, such as nitrogen and oxygen, escape from the bubbles which are harmless. This bubbling process allows researchers to concentrate CO22 of the air in the solution, making it easier to work with.
The integrated system contains a photocathode and anode. The system has two compartments: CO2 is captured on one side2 solution to be converted into syngas, a simple fuel. On the other hand, plastic is converted into useful chemicals using only sunlight.
“The plastic component is an important trick for this system,” said co-first author Dr Motiar Rahaman. “Capture and use CO2 from the air makes chemistry more difficult. But, if we add plastic waste to the system, the plastic donates electrons to CO2. Plastic decomposes into glycolic acid, which is widely used in the cosmetic industry, and CO22 converted into syngas, which is a simple fuel.”
“This solar-powered system takes two harmful waste products – plastic and carbon emissions – and turns them into something that is actually useful,” said first co-author Dr Sayan Kar.
“Instead of storing CO2 underground, like in CCS, we can capture it from the air and make clean fuel out of it,” said Rahaman. “In this way, we can remove the fossil fuel industry from the fuel production process, which hopefully will help us avoid climate damage.”
“The fact that we can effectively take CO2 out of the air and making something useful out of it is special,” says Kar. “It’s satisfying to see that we can actually do it using just sunlight.”
Scientists are currently working on a bench-top demonstrator device with increased efficiency and practicality to highlight the benefits of combining direct air capture with CO2.2 utilization as a pathway to a zero-carbon future.
