University of Toronto engineers have designed a most efficient and stable process for recycling carbon dioxide into a key chemical building block for plastics – all powered using renewable electricity. The new technology takes a substantial step towards enabling manufacturers to create plastics out of two key ingredients: sunshine and pollution.

Today, non-renewable fossil fuels not only provide the raw material from which plastics are made, they are also the fuel burned to power the manufacturing process, producing climate-warming carbon dioxide. The International Energy Agency estimates the production of the main precursors for plastics is responsible for 1.4 percent of global CO2 emissions.

Dr. Cao-Thang Dinh, left, and Dr. Md Golam Kibria demonstrate their new catalyst. The team demonstrated most efficient and stable process for converting carbon dioxide into the building blocks for plastics. Image Credit: Laura Pedersen, Engineering Strategic Communications, University of Toronto Faculty of Applied Science & Engineering. Click image for the largest view.

A team led by University of Toronto Professor Ted Sargent is turning this process upside down. They envision capturing CO2 produced by other industrial process and using renewable electricity – such as solar power – to transform it into ethylene. Ethylene is a common industrial chemical that is a precursor to many plastics, such as those used in grocery bags.

The system addresses a key challenge associated with carbon capture. While technology exists to filter and extract CO2 from flue gases, CO2 currently has little economic value that can offset the cost of capturing it, thus it’s a money-losing proposition. By transforming this carbon molecule into a commercially valuable product like ethylene, the team aims to increase the incentives for companies to invest in carbon capture technology.

At the core of the team’s solution are two innovations: using a counterintuitively thin copper-based catalyst and a re-imagined experimental strategy.

Post-doctoral fellow Dr. Cao-Thang Dinh, the first author on the paper published in the journal Science explained, “When we performed the CO2 conversion to ethylene in very basic media, we found that our catalyst improved both the energy efficiency and selectivity of the conversion to the highest levels ever recorded.” In this context, efficiency means that less electricity is required to accomplish the conversion. The authors then used this knowledge to further improve the catalyst and push the reaction to favor the formation of ethylene, as opposed to other substances.

Next, the team addressed stability, which has long been a challenge with this type of copper-based catalyst. Theoretical modeling shows that basic conditions – that is, high pH levels – are ideal for catalyzing CO2 to ethylene. But under these conditions, most catalysts, and their supports, break down after less than 10 hours.

The team overcame this challenge by altering their experimental setup. Essentially, they deposited their catalyst on a porous support layer made of polytetrafluoroethylene (PTFE, better known as Teflon) and sandwiched their catalyst with carbon on the other side. This new setup protects the support and catalyst from degrading due to the basic solution, and enables it to last 15 times longer than previous catalysts. As an added bonus, this setup also improved efficiency and selectivity still further.

Dinh said, “Over the last few decades, we’ve known that operating this reaction under basic conditions would help, but no one knew how to take advantage of that knowledge and transfer it into a practical system. We’ve shown how to overcome that challenge.”

Currently their system is capable of performing the conversion on a laboratory scale, producing several grams of ethylene at a time. The team’s long-term goal is to scale the technology up to the point where they are able to convert the multiple tons of chemicals needed for commercial application.

“We made three simultaneous advances in this work: selectivity, energy-efficiency and stability,” says Sargent. “As a group, we are strongly motivated to develop technologies that help us realize the global challenge of a carbon-neutral future.”

This new process sounds like it might be a breakout technology. There are major issues still to solve. Up to 150 hours is still less than a week. An issue often overlooked is the clean up from a used catalyst before the new one goes in. Then comes the costs versus the payout and capitalization. Its a ways off to building a pilot plant. But if there is money to be made, this could be the breakout tech solving a lot of the CO2 worry.

Another goal worth considering is to be able to select for other molecules. The ethylene choice alone may not be valuable enough.


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