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Science Notebook

Researchers convert 100 per cent of CO2 industrial exhaust into ethylene

Print edition : Oct 01, 2022 T+T-

Researchers convert 100 per cent of CO2 industrial exhaust into ethylene

An abstract illustration showing atoms passing through water and an electrified membrane under a shining sun. Meenesh Singh, UIC

An abstract illustration showing atoms passing through water and an electrified membrane under a shining sun. Meenesh Singh, UIC | Photo Credit: Meenesh Singh, UIC

As the UIC system runs on electricity, using renewable energy can make the process carbon negative.

A team of researchers led by Meenesh Singh at the University of Illinois Chicago (UIC) has discovered a way to convert 100 per cent of carbon dioxide (CO 2) captured from industrial exhaust into ethylene, a key building block for plastic products. The findings were published in a recent issue of Cell Reports Physical Science. While researchers have been exploring the possibility of this conversion for more than a decade, the UIC’s method is perhaps the first one to achieve nearly total utilisation of CO 2. Previous attempts relied on reactors that produced ethylene within the source CO 2 emission stream. In these cases, according to the UIC release, typically only about 10 per cent of CO 2 emissions gets converted, and the ethylene must later be separated from the CO 2 in an energy-intensive process often involving fossil fuels.

The UIC’s system uses electrolysis to transform captured CO 2 gas into high purity ethylene, with other carbon-based fuels and oxygen as byproducts. An electric current is passed through a cell divided into two sections separated by a membrane: one half is filled with captured CO 2 and the other with a water-based solution. An electrified catalyst draws charged hydrogen atoms from the water molecules into the other half through the membrane, where they combine with charged carbon atoms from the CO 2 molecules to form ethylene.

Because the system runs on electricity, using renewable energy can make the process carbon negative. According to Meenesh Singh, the method surpasses the net-zero carbon goal of other carbon capture and conversion technologies. “It’s a net negative,” he said. “For every 1 tonne of ethylene produced, you’re taking 6 tonnes of CO 2 from point sources that otherwise would be released to the atmosphere.”

Among manufactured chemicals worldwide, ethylene ranks third for 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 produce the chemicals used in antifreeze, medical sterilisers, and vinyl sidings for houses.

It is usually made in a process called steam cracking that requires enormous amounts of heat. Cracking generates about 1.5 tonnes of carbon emissions per tonne of ethylene created. On average, manufacturers produce around 160 million tonnes of ethylene each year, which results in more than 260 million tonnes of CO 2 emissions worldwide.

With their electrolysis approach, the UIC scientists were able to produce other carbon-rich products useful to industry. They also achieved a very high solar energy conversion efficiency, converting 10 per cent of energy from the solar panels directly to carbon product output. This is well above the state-of-the-art standard of 2 per cent, the UIC release said. For all the ethylene they produced, the solar energy conversion efficiency was around 4 per cent, approximately the same rate as photosynthesis.