Ethylene Production Using Solar Energy

Researchers in Singapore have developed an artificial photosynthesis device for greener ethylene production. A team of researchers from the National University of Singapore (NUS) has developed a prototype device that mimics natural photosynthesis to produce ethylene gas using just only sunlight, water, and carbon dioxide.

They published their discoveries in ACS Sustainable Chemistry and Engineering. Ethylene, which is the building block of polyethylene, is an important feedstock produced in large amounts for manufacturing plastics, rubber and fibers. In 2015 worldwide, the production of ethylene was more than 170 million tons and by 2020 the demand is expected to exceed 220 million tons.

Current industrial production of ethylene utilizes steam cracking of fossil fuels at between 750°C to 950°C, which consumes a lot of energy and represents a strain on natural fuel resources. The steam cracking method also leaves a significant carbon footprint, emitting about two tons of carbon dioxide for each ton of ethylene produced.

Accordingly, there is a developing demand for a cleaner and more sustainable way of delivering ethylene. Recognizing the requirement for a more eco- friendly method, a group of scientists led by Assistant Professor Jason Yeo Boon Siang from the Department of Chemistry at the NUS Faculty of Science and the Solar Energy Research Institute of Singapore tapped advantage of renewable energy to produce ethylene.

Initially, in 2015 to produce ethylene from readily available water and carbon dioxide when powered by the power the group composed a copper catalyst. This copper catalyst was subsequently introduced into an artificial photosynthesis system to change over carbon dioxide and water into ethylene using just solar energy.

The prototype device designed to complete the reaction achieved a 30 percent faradaic proficiency of ethylene, which refers to the efficiency of electron transfer in a system facilitating an electrochemical reaction. The overall energy efficiency of solar-to-ethylene is also comparable to the level of energy efficiency of natural photosynthesis by plants.

Yeo said, “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 prompts undesirable environmental change.”

“Our device uses a totally renewable energy source, as well as converts carbon dioxide, a greenhouse gas into something helpful. This could potentially close the carbon cycle.” The group additionally 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 around evening time or under low light, ensuring that operations are not interrupted by varying measure of sunlight for the duration of the day.

For the clean and sustainable production of important organic molecules like ethylene, the invention marks a milestone in the realization of a scalable artificial photosynthesis system. Moving forward, the group will keep on working on their device to scale up the production of ethylene and additionally employ similar systems to produce liquid fuels, for example, ethanol and propanol.

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