Scientists have developed a prototype device that mimics natural photosynthesis to produce ethylene gas using only sunlight, water and carbon dioxide.
The advance from the National University of Singapore (NUS) produces ethylene at room temperature and pressure using benign chemicals, and could be scaled-up to provide an alternative to current ethylene production.
The development led by assistant Professor Jason Yeo Boon Siang from the Department of Chemistry at NUS Faculty of Science and the Solar Energy Research Institute of Singapore (SERIS) was first published in ACS Sustainable Chemistry & Engineering.
Ethylene is an important chemical feedstock produced in large quantities for manufacturing plastics, rubber and fibres. Over 170 million tonnes of ethylene was produced worldwide in 2015, 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°C to 950°C. The current method also emits about two tonnes of carbon dioxide for every tonne of ethylene produced.
Recognising the need for a more eco-friendly method, Asst Prof Yeo and his team began investigating renewable energy to produce ethylene. The team first designed a copper catalyst in 2015 that could generate ethylene from 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. The prototype device designed to carry out the reaction is said to have achieved a 30 per cent Faradaic efficiency of ethylene based on the amount of electrons generated from solar energy. According to NUS, the overall energy efficiency of solar-to-ethylene is also comparable to the level of energy efficiency of natural photosynthesis by plants.
“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. This has been attributed as a major cause of global warming which leads to undesirable environmental changes,” said Prof Yeo. “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.”
The team also incorporated a battery in the prototype device to attain stable and continuous production of ethylene, a key challenge in artificial photosynthesis systems. The battery stores excess solar energy collected in the day to power the device at night or under low light.
The team said it will continue to work on its device to scale up the production of ethylene as well as employ similar systems to produce liquid fuels such as ethanol and propanol.