Engineers at the University of Illinois Chicago (UIC) have developed a device that can efficiently convert captured carbon dioxide into ethylene, a plastic precursor material. When run using renewable energy, the technique could make for net negative emissions in plastic production.
As much as the world relies on plastic, the versatile material inflicts a terrible toll on the environment, starting with the huge amounts of CO2 emitted during its production. For years scientists have been experimenting with ways to counter this by converting captured CO2 into useful materials such as ethylene, one of the major precursors of plastic, using things like graphene quantum dots or sulfur-eating bacteria.
For the new study, the UIC team designed an electrochemical cell that can make the conversion more efficiently. Half of the chamber is filled with a water-based solution, while the other half contains gaseous carbon dioxide. These are separated by a 3D copper mesh, through which an electrical current is run.
This process draws charged hydrogen atoms out of the water molecules into the other chamber, where they then combine with charged carbon atoms in the CO2, forming C2H4 – ethylene. The team says almost 100% of the carbon dioxide is converted into ethylene, which is much higher than other methods. By-products of the process include oxygen and other carbon-based fuels.
Normally, ethylene production is an energy-intensive process that releases as much as 1.5 tons of CO2 for each ton of ethylene produced. But the team says that if renewable energy sources are used to run the new system, it could make for plastic production that consumes more CO2 than it releases.
“It’s a net negative,” said Meenesh Singh, lead researcher on the study. “For every 1 ton of ethylene produced, you’re taking 6 tons of CO2 from point sources that otherwise would be released to the atmosphere.”
In terms of energy efficiency, the process converts about 10% of the solar energy into carbon products, and about 4% into ethylene. That might not sound like much, but the team says the former is five times higher than the current state-of-the-art, while the second figure is around the same as natural photosynthesis.
The research was published in the journal Cell Reports Physical Science.
Source: University of Illinois Chicago
A carbon atom weighs 12 moles, a hydrogen atom, 1 mole, and an oxygen atom, 16 moles. Since ethylene is C2H4 this process is exchanging two hydrogen atoms for two oxygen atoms on each carbon atom (2CO2+2H2=>C2H4+O4).
My understanding is 44 tons of CO2 is 12 tons of carbon and 32 tons of oxygen. Take out the oxygen and replace it with two tons of hydrogen (ethylene), and the 44 tons of CO2 become 14 tons of C2H4. Or 1 ton of ethylene replaces 3.1428 tons of carbon dioxide, not 1:6.
But then, this is coming from the same school that gave us the Laffer Curve.
If you use the devised method with solar derived electricity - you do produce 1 ton of ethylene without releasing 6 tons of CO2. And for each ton of product, (at 28 amu) you will need much less than a ton of H2 and over 3 tons of CO2 since you aren't using hydrocarbons as your building blocks.