Artificial photosynthesis system may lead to greener plastics

Singapore: Scientists have developed a device that mimics photosynthesis and uses sunlight, water and carbon dioxide to produce ethylene gas - a key chemical used in large quantities for manufacturing plastics, rubber and fibres.

The method, developed by researchers National University of Singapore (NUS), could be scaled up to provide a more eco- friendly and sustainable alternative to the current method of ethylene production.

Ethylene, which is the building block of polyethylene, is an important chemical feedstock produced in large quantities for manufacturing plastics, rubber and fibres.

More than 170 million tonnes of ethylene was produced worldwide in 2015 alone, and the global demand is expected to exceed 220 million tonnes by 2020.

Current industrial production of ethylene employs steam cracking of fossil fuels at between 750 to 950 degrees Celsius, which consumes a large amount of energy and poses a strain on natural fuel resources.

The current method also leaves a significant carbon footprint, emitting about two tonnes of carbon dioxide for every tonne of ethylene produced.

Recognising the need for a more eco-friendly method, researchers tapped into renewable energy to produce ethylene.

The team first designed a copper catalyst that could generate ethylene from readily available water and carbon dioxide when powered by electricity.

This copper catalyst was subsequently introduced into an artificial photosynthesis system to convert carbon dioxide and water into ethylene using only solar energy.

"Carbon capture is a key step in fighting human-driven climate change. There has been a steady increase in the atmospheric concentration of carbon dioxide because the rate of carbon dioxide emissions exceeds that of carbon capture," said Jason Yeo Boon Siang from NUS.

"This has been attributed as a major cause of global warming which leads to undesirable environmental changes," Siang said.

"Our device not only employs a completely renewable energy source but also converts carbon dioxide, a greenhouse gas into something useful. This could potentially close the carbon cycle," he said.

The team also incorporated a battery in the prototype device to attain stable and continuous production of ethylene, a key challenge in artificial photosynthesissystems.

The battery stores excess solar energy collected in the day to power the device at night or under low light, ensuring that operations are not interrupted by varying amount of sunlight throughout the day.

The invention marks a significant milestone in the realisation of a scalable artificial photosynthesis system for clean and sustainable production of important organic molecules like ethylene, researchers said.