A breakthrough in converting carbon capture to ethylene production

A team of researchers led by Meenesh Singh at the University of Illinois Chicago has discovered a way to convert 100% of the carbon dioxide captured from industrial exhaust into ethylene, a key building block for plastic products.

Their findings are published in Cell Reports Physical Science.

While researchers have explored the possibility of converting carbon dioxide to ethylene for more than a decade, the UIC team’s approach is the first to achieve nearly 100% use of carbon dioxide to produce hydrocarbons. Their system uses electrolysis to transform captured carbon dioxide gas into high-purity ethylene, with other carbon-based fuels and oxygen as byproducts.

The process can convert up to 6 metric tons of carbon dioxide into 1 metric ton of ethylene, recycling nearly all of the captured carbon dioxide. Because the system runs on electricity, the use of renewable energy can make the process carbon negative.

According to Singh, his team’s approach exceeds the net zero carbon goal of other carbon capture and conversion technologies by actually reducing the industry’s total carbon dioxide output. “It’s a net negative,” he said. “For every 1 ton of ethylene produced, you get 6 tons of CO₂ from point sources that would otherwise be released into the atmosphere”.

Previous efforts to convert carbon dioxide to ethylene have been tied to reactors that produce ethylene within the carbon dioxide emission stream. In these cases, only 10% of CO₂ emissions are usually converted to ethylene. The ethylene must later be separated from the carbon dioxide in an energy-intensive process that often involves fossil fuels.

In the UIC approach, an electric current is passed through a cell, half of which is filled with trapped carbon dioxide, the other half with a water-based solution. An electrified catalyst draws hydrogen atoms charged by water molecules into the other half of the unit separated by a membrane, where they combine with carbon atoms charged by carbon dioxide molecules to form ethylene.

Among chemicals produced worldwide, ethylene ranks third in carbon emissions after ammonia and cement. Ethylene is used not only to create plastic products for the packaging, agricultural, and automotive industries, but also to make chemicals used in antifreeze, medical sterilizers, and vinyl siding for homes.

Ethylene is usually produced in a process called steam cracking that requires large amounts of heat. Cracking generates about 1.5 metric tons of carbon emissions per ton of ethylene generated. On average, manufacturers produce about 160 million tons of ethylene each year, which results in more than 260 million tons of carbon dioxide emissions worldwide.

In addition to ethylene, UIC scientists were able to produce other carbon-rich products useful to industry with their electrolysis approach. They also achieved a very high solar energy conversion efficiency, converting 10% of the energy from the solar panels directly into carbon product production. This is much higher than the latest benchmark of 2%. For all the ethylene they produced, the solar energy conversion efficiency was about 4%, about the same as photosynthesis.