A new device developed by engineers at the University of Illinois Chicago (UIC) combines a carbon capture system with an ethylene conversion system.
“This is the first demonstration of a net-negative, all-electric integrated system to capture carbon from pollutants and create a highly valuable resource,” says Meenesh Singh, UIC assistant professor in the department of chemical engineering.
Previously, the same group demonstrated the CO2-ethylene conversion unit (see, “Captured Carbon Serves as Ethylene Feedstock”).
For this work, Singh’s group modified a standard artificial leaf system with inexpensive materials to include a water gradient — a dry side and a wet side — across an electrically charged membrane (Figure 1).
On the dry side, an organic solvent attaches to available CO2 to produce a concentration of bicarbonate, or baking soda, on the membrane. As bicarbonate builds, these negatively charged ions are pulled across the membrane toward a positively charged electrode in a water-based solution on the membrane’s wet side. The liquid solution dissolves the bicarbonate back into CO2, so it can be released and harnessed for CO2 conversion.
Run 24/7, the system remained stable and captured CO2 at a rate of 24 g/day while producing ethylene at a rate of 0.2 g/day.
“From the reaction stoichiometry, we need about 3 g of CO2 to make 1 g of ethylene. So, we can make much more ethylene — up to 8 g/day — with a 24-g/day CO2 capture rate. However, for concept validation we demonstrated production of only about 0.2 g/day,” Singh notes.
The group’s next step is to scale the integrated system to produce ethylene at higher rates — 1 kg/day — and capture carbon at a rate higher than kgs/day.
However, while the electrodialysis unit has an expandable stack that can accommodate up to 5 m2 of membrane, the electrolysis unit needs to be scaled gradually from 1 cm2 to 10 cm2 and then to 100 cm2 and 1 m2.
Next step is to scale the integrated system to produce ethylene at higher rates.
“We are currently working to establish up to 100 cm2 of electrolyzer which can produce up to 100 g/day of ethylene, with an aim to design an electrolyzer that can make 10 kg/day of ethylene,” Singh explains.
He adds that the modular, stackable design will vary with scale, too. For example, a generation-1 modular design can accommodate electrode areas from 10–100 cm2. Generation-2 is being designed to accommodate electrode areas from 100–2,000 cm2, while a production scale module will range from 0.2–3 m2. “Every module design for each scale range is different,” he says.
