Net-Negative' System ConvertsCO2 Completely to Ethylene

Researchers at the University of Illinoisat Chicago (UIC) have discovered a way to convert 100 percent of the carbondioxide captured in industrial waste gases into ethylene. Ethylene is a keycomponent of plastic products, and when run on renewable energy sources, thetechnology could lead to net negative emissions from plastics production. Arelated paper was published in a recent issue of Cell Reports - PhysicalSciences.

While researchers have been exploring thepossibility of converting carbon dioxide to ethylene for more than a decade,the UIC team achieved the first complete conversion of carbon dioxide tohydrocarbons. Their system converts captured carbon dioxide gas intohigh-purity ethylene through electrolysis, with other carbon-based fuels andoxygen as byproducts.

The process converts 6 tons of CO2 to 1 tonof ethylene, recovering almost all of the captured CO2. Since the system runson electricity, the use of renewable energy sources allows the process to becarbon-negative. The new approach exceeds the net-zero carbon goals of othercarbon capture and conversion technologies by actually reducing totalindustrial carbon dioxide emissions.

Previous attempts to convert CO2 toethylene have relied on reactors that produce ethylene in the CO2 emissionstream, and typically only 10% of CO2 emissions are converted to ethylene,which must then be separated from CO2 in an energy-intensive process thattypically involves fossil fuels.

In the new method, an electric current ispassed through a "cell" that is half filled with captured carbondioxide and the other half with a water-based solution. The charged catalystattracts charged hydrogen atoms from the water molecules to the other half ofthe cell, separated by a membrane, where they combine with charged carbon atomsfrom the carbon dioxide molecules to form ethylene.

Ethylene is the third largest carbonemitter in the global chemical manufacturing process after ammonia and cement.Ethylene is used not only to make plastic products, but also to producechemicals such as antifreeze and medical disinfectants.

Ethylene is typically manufactured using asteam cracking process, which requires a significant amount of heat. Crackingproduces about 1.5 tons of carbon emissions per ton of ethylene produced. Onaverage, manufacturers produce about 160 million tons of ethylene per year,which results in global CO2 emissions of more than 260 million tons.

In addition to ethylene, the team alsoproduced other industrial carbon-rich products through their electrolysismethod while also achieving a very high solar energy conversion efficiency,converting 10 percent of the energy from solar panels directly into carbonproduct output, which is well above the current state-of-the-art standard of 2percent. For all the ethylene produced by the new method, the solar energyconversion efficiency is about 4%, which is roughly the same as the efficiencyof photosynthesis.