Deriving green plastics from carbon dioxide

A group of researchers based at Osaka University and Tohoku University may have found a way to derive "green plastics" from carbon dioxide by synthesising a ceric oxide catalyst with atmospheric CO2.

The project, which was originally published in the Green Chemistry journal, has been delivered in collaboration with Nippon Steel and involves the creation of plastics without the use of a dehydration agent and does not rely on toxic feedstock, therefore not releasing carbon monoxide as a by-product, thus limiting the amount of pollution emitted during production.

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Both plastic waste and carbon dioxide emissions are a heated issue, particularly regarding the constant struggle against climate change, and different debates rage regarding what should be done with carbon dioxide - whether through sequestration and storage it or turning it into a useful compound.

While many methods exist for turning carbon dioxide into usable plastics, they often require toxic catalysts for the processes, making them unviable in the drive for sustainability. Others result in unusable end-products.

Polycarbonate represents a particularly versatile type of thermoplastic, with a wide variety of uses, such in plastic bottles, CDs or greenhouses and other types of shelters.

Other processes that use readily available substrates have arisen in recent years, with water as the only by-product, but high volumes of end water can prevent the resultant plastics from becoming usable.

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"Most processes use a dehydrating agent to keep water levels low to overcome an equilibrium," said Masazumi Tamura of the Osaka City University, a researcher on the paper. "Some of the issues to address are the high pressure of carbon dioxide needed, the recovery and regeneration of the dehydrating agent, and contamination of by-products generated by its use."

As a result, the researchers opted to create a process that does not use a dehydrating agent and instead opted to focus on the different boiling points between the compounds and "blowing in carbon dioxide at atmospheric pressure" to create a high yield end-product.

Keiichi Tomishige, a researcher from Tohoku University, who helped author the paper, said: "It became clear that among the metal oxide catalysts we used that CeO₂ showed the highest activity.

"This reaction made it the first ever to successfully synthesize polycarbonate diols from carbon dioxide and diols at atmospheric pressure.

"This process, without the need of dehydrating agents, can chemically convert carbon dioxide using any substrate with a boiling point sufficiently higher than water," concluded Kenji Nakao of Nippon Steel Corporation, "and can be applied to the synthesis of carbonates, carbamates, and ureas, which are useful additives for lithium-ion batteries and/or raw materials for polymer synthesis."

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While very few pollutants may be released during the production of the polycarbonates, there is currently no information on how they could be properly disposed of. This may test its viability as a green plastic.

It is likely this is pending further research once a commercial end-product is created from the plastics.

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