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Cambridge researchers use sunlight to convert plastic waste and CO2 into hydrogen and chemical feedstocks

July 2, 2023

CO2 can be captured from dilute sources, such as air, and converted into synthesis gas using sunlight, reveals a new study. The process can simultaneously upcycle PET plastic to glycolic acid with the aim of creating a net-zero carbon future, according to the study authors.

The technology produces value-added fuels and chemicals directly from industrially relevant CO2 streams and plastic waste, powered solely by sunlight at ambient temperature and pressure, and is “an important step toward a circular economy.”

“We have shown that we can take atmospheric excess CO2 and discarded PET plastics and make fuels (synthesis gas) and value-added products (glycolic acid, a cosmetic skin care product ingredient) from them using only sunlight,” Sayan Kar, Marie Curie postdoctoral research associate at the University of Cambridge, UK, tells Packaging Insights.

“Our research provides a way for the upcycling of discarded packaging material. In this study, we specifically use PET plastic waste, but prior research from our group has shown how other packaging materials such as paper and wood can be used for fuel production using sunlight.”

Packaging made to be upcycled
The method the researchers use captures CO2 from flue gas or air and its direct conversion into syngas using solar irradiation without any externally applied voltage. The overall process uses flue gas or air as a carbon source, discarded plastic waste as an electron donor and sunlight as the sole energy input. This strategy opens new avenues for future carbon-neutral or negative solar fuel and waste upcycling technologies.

“Packaging materials can be developed and synthesized based on their ease of upcycling. For example, in our system, plastics such as PET and [polylactic acid] PLA are easier to upcycle than LDPE and HDPE,” explains Kar.

“Packaging materials must be produced keeping in mind their intended use and upcyclability at the end of use. Once upcycled, the obtained products can reenter the economy as skin care pharmaceutics, material precursors or any other intended use depending on the upcycled material.”

The scientists use an integrated photoelectrochemical system that captures CO2 from exhaust stream concentrations and ambient air and directly converts it into synthesis gas (CO + H2, a precursor of industrial liquid fuel production).

“To achieve this, we bubble air through a solution where the atmospheric CO2 gets trapped and concentrated. We then use sunlight to convert this trapped CO2 into fuels. The fuel production is enhanced by pretreated waste PET plastics in the system,” says Kar.

“PET is converted to glycolic acid, which has broad applications in the cosmetics industry. We use an in-house modified solar absorber that takes the solar energy from sunlight and facilitates the whole process.”

Scaling the solution
The researchers explain their motivation is to reduce emissions and plastic waste, saying it is “likely that a net carbon-zero future will rely on the recycling of atmospheric CO2 to produce sustainable fuels and chemicals.” Additionally, the scientists say recycling waste plastics is critical to protect our environment from irreversible damage.

Current processes for CO2 utilization use concentrated CO2 streams and are not integrated with the capture of dilute CO2 sources. Direct conversion of chemically captured CO2 remains challenging due to its thermodynamic stability. Most prior processes relied on concentrated streams of carbon dioxide.

“The technology is still in the lab-scale proof-of-concept stage. The system’s efficiency, durability and stability need to be looked at in more detail before any scale-up, and would at least require a decade,” explains Kar.

“However, once matured, this technology would provide an integrated solution to many global challenges such as increasing CO2 levels, sustainable fuel production, and waste recycling in a unified process driven solely by sunlight.”

The research was published in Joule.

By Sabine Waldeck


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