Page 56 - Plastics News January 2020

teChnoLogy

Researchers design an improved pathway to carbon-neutral plastics

esearchers have designed a new and improved system catalyst."One of the c hallenges with this reaction is that
Rfor efficiently converting CO2, water, and renewable while some of the CO2 is converted into ethylene, most
energy into ethylene -- the precursor to a wide range of of it turns into side products, especially carbonate, which
plastic products -- under neutral conditions Researchers dissolves on the liquid side of the electrolyzer," says post-
from U of T Engineering and Caltech have designed a new doctoral fellow Fengwang Li, lead author of the new paper.
and improved system for efficiently converting CO2, water, "This undesired loss increases the cost of ensuing product
separation and purification." In the latest work, Sargent's
team partnered with Caltech chemistry professors Jonas C.
Peters and Theodor Agapie. Their published research on a
class of molecules known as arylpyridiniums suggested that
adding them to the catalyst could favour the production of
ethylene over other side products.Sure enough, adding a
thin layer of this molecule to the copper catalyst surface
significantly increased the selectivity of the reaction for
ethylene. It also led to another benefit: lowering the
working reaction pH from basic to neutral. "The previous
system required the water side of the reaction to be at
high pH, very basic conditions," says Li.
"But the reaction of the CO2 with caustic soda in the
water lowers the pH, so we would've had to continuously
add chemicals to keep the pH up. The new system works
and renewable energy into ethylene -- the precursor to a just as well under neutral conditions, so we can eliminate
wide range of plastic products, from medical devices to that additional cost, as well as loss of CO2 in the form of
synthetic fabrics -- under neutral conditions. The device carbonate." While the prototype is still a long way from
has the potential to offer a carbon-neutral pathway to commercialization, the overall concept offers a promising
a commonly used chemical while enhancing storage of way to address several key challenges in sustainability. It
waste carbon and excess renewable energy."CO2 has low eliminates the need to extract more oil to make plastics
economic value, which reduces the incentive to capture and other consumer goods based on ethylene, and it turns
it before it enters the atmosphere," says Professor Ted waste CO2 into a feedstock, adding a new incentive to
Sargent, the U of T Engineering lead on the project. invest in carbon capture.
"Converting it into ethylene, one of the most widely-used
industrial chemicals in the world, transforms
the economics. Renewable ethylene provides
a route to displacing the fossil fuels that
are currently the primary feedstock for this
chemical."Last year, Sargent and his team
published a paper in Science describing how
they used an electrolyzer -- a device that
uses electricity to drive a chemical reaction
-- to convert CO2 into ethylene with record
efficiency. In this system, the three reactants,
CO2 gas, water and electricity, all come
together on the surface of a copper-based

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