Producing one ton of ethylene generates an equal amount of carbon dioxide. With global ethylene production exceeding 300 million tons annually, the industry has a significant carbon footprint that researchers aim to reduce or eliminate. A new device from Ted Sargent’s lab at Northwestern University offers a step toward achieving that goal.
The device, an electrolyzer, incorporates three key innovations: it converts syngas—a waste gas from plastic—into ethylene using electricity, employs a novel material to catalyze the reaction, and operates efficiently to lower the overall energy requirement.
Published Feb. 17 in Nature Energy, the findings could be combined with renewable energy to support a greener ethylene supply chain.
“Our goal is to decarbonize chemicals,” said Ted Sargent. “This work is an important step toward that aim.”
Sargent holds the Lynn Hopton Davis and Greg Davis Professorship in Chemistry at Northwestern University’s Weinberg College of Arts and Sciences and is also a professor of electrical and computer engineering at the McCormick School of Engineering.
“We aim to establish a circular system that produces chemical building blocks from waste without relying on fossil fuels,” said Ke Xie, a chemistry research faculty member at Weinberg. “This device is a key part of a new atom- and energy-efficient supply chain.”
Generating Power from Waste
Today, most ethylene is produced via steam cracking, a process that uses high-temperature steam to convert crude oil into chemicals. Researchers are exploring alternative methods that rely on renewable electricity instead.
One approach is to convert carbon dioxide into ethylene, but the process demands too much energy. Sargent and his team therefore focused on syngas—a mixture of carbon monoxide and hydrogen obtained by gasifying plastic waste—which requires far less electricity to transform into ethylene.
“A lot of syngas is already converted into chemicals, so finding a method to turn it into ethylene that is both highly selective and energy-efficient is of strong industrial interest,” Sargent explained.
To achieve efficient conversion, his team needed a new type of electrolyzer—a device that uses energy to drive chemical reactions. Most electrolyzers rely on a liquid water-based electrolyte containing salts with both cations and anions. The team explored the idea of a fully gas-fed system: the cathode supplied with carbon monoxide from syngas and the anode with hydrogen.
“In our initial attempts at a gas-gas electrolyzer, it simply didn’t work,” Sargent said. “We realized it wasn’t just the water we needed—it was the salt too.”
Innovative System Compatible With Renewable Energy
Salt supplies the positive ions (cations) that the electrolyzer’s copper catalyst needs to stabilize crucial reaction intermediates. Bosi Peng, a postdoctoral researcher and first author of the study, searched for a material that could hold these ions while keeping them mobile enough to participate in the reaction.
“We needed a material in just the right ‘Goldilocks’ zone to make the electrolyzer work,” Sargent said. “Bosi discovered a new solution to this challenging problem, which was very exciting.”
The chosen material, sodium polyacrylate (PANa), creates a microenvironment that mimics a liquid salt bath while keeping the system free of liquid water. This approach achieves over 60% higher efficiency than the most energy-efficient previous electrified methods for converting carbon dioxide into ethylene.
“Bosi greatly lowered the electricity required by reducing the voltage needed across the device,” Sargent said. The electrolyzer also performs well with the variable output of renewable energy sources.
“Solar and wind are inexpensive, but their availability fluctuates,” he explained. “We needed a system that could handle intermittent energy, and this device does. A crucial factor was removing liquid water and using a high-concentration salt electrolyte.”
The team’s next steps include further reducing the device’s energy consumption to match that of steam cracking. They are also applying artificial intelligence and machine-learning techniques to identify catalysts that could boost efficiency even more.
Ultimately, the goal is to scale the device for industrial use and continue lowering the carbon footprint of ethylene production.
Read the original article on: Tech Xplore
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