Solar-powered reactor adds circularity to plastic waste and greenhouse gases

Developed by researchers from Cambridge University, the system converts two waste streams into two chemical products simultaneously, marking the first time this has been achieved in a solar-powered reactor.

The reactor converts carbon dioxide (CO2) and plastics into different products that are useful in a range of industries. In tests, CO2 was converted into syngas, a key building block for sustainable liquid fuels, and plastic bottles were converted into glycolic acid, which is widely used in the cosmetics industry. According to the University, the system can be tuned to produce different products by changing the type of catalyst used in the reactor.

Converting plastics and greenhouse gases into useful and valuable products using solar energy is an important step in the transition to a more sustainable, circular economy. The results are reported in Nature Synthesis.

“Converting waste into something useful using solar energy is a major goal of our research,” Professor Erwin Reisner from the Yusuf Hamied Department of Chemistry, the paper’s senior author, said in a statement. “Plastic pollution is a huge problem worldwide, and often, many of the plastics we throw into recycling bins are incinerated or end up in landfill.”

Other solar-powered ‘recycling’ technologies hold promise for addressing plastic pollution and for reducing the amount of greenhouse gases in the atmosphere, but to date, they have not been combined in a single process.

“A solar-driven technology that could help to address plastic pollution and greenhouse gases at the same time could be a game-changer in the development of a circular economy,” said Subhajit Bhattacharjee, the paper’s co-first author.

“We also need something that’s tuneable, so that you can easily make changes depending on the final product you want,” said co-first author Dr Motiar Rahaman.

The researchers developed an integrated reactor – whose light absorber is based on perovskite - with compartments for plastic and greenhouse gases.

The team designed different catalysts, which were integrated into the light absorber. By changing the catalyst, the researchers could then change the end product. Tests of the reactor under normal temperature and pressure conditions showed that the reactor could convert PET plastic bottles and CO2 into different carbon-based fuels such as CO, syngas or formate, in addition to glycolic acid. The Cambridge-developed reactor produced these products at a rate that is claimed to be higher than conventional photocatalytic CO2 reduction processes.

“Generally, CO2 conversion requires a lot of energy, but with our system, basically you just shine a light at it, and it starts converting harmful products into something useful and sustainable,” said Rahaman. “Prior to this system, we didn’t have anything that could make high-value products selectively and efficiently.”

“What’s so special about this system is the versatility and tuneability – we’re making fairly simple carbon-based molecules right now, but in future, we could be able to tune the system to make far more complex products, just by changing the catalyst,” said Bhattacharjee.

Over the next five years, the team hope to further develop the reactor to produce more complex molecules. The researchers said that similar techniques could in the future be used to develop an entirely solar-powered recycling plant.

The research was supported in part by the European Union, the European Research Council, the Cambridge Trust, Hermann and Marianne Straniak Stiftung, and EPSRC.