Unrecyclable Plastic Waste Transformed Into Useful Chemicals: A Critical Step Towards a Net-Zero Society

Oak Ridge National Laboratory (ORNL) scientists developed a technology using a special chemical catalyst to convert unrecyclable plastic waste into valuable chemicals. This innovation addresses plastic pollution and brings us closer to recycling while reducing carbon emissions.

Using Organocatalyst to Convert Plastic Waste Into Valuable Chemicals

A significant portion of plastic waste, around 80%, usually ends up in landfills or the environment. ORNL researchers reported having devised a technology capable of transforming traditionally unrecyclable plastic waste mixtures into valuable chemicals, introducing an innovative approach to address the global plastic waste crisis.

Their research, titled "Selective deconstruction of mixed plastics by a tailored organocatalyst" published in the journal Materials Horizons, introduces a novel organocatalyst.

Led by ORNL's Tomonori Saito and former postdoctoral researcher Md Arifuzzaman, the team explains that this organocatalyst is capable of breaking down various condensation polymers, the first of its kind to convert a blend of consumer plastics into top-tier monomers. Arifuzzaman, now affiliated with Re-Du, currently serves as an Innovation Crossroads fellow.

The shift towards employing organocatalysis instead of metal-based catalysis is driven by the ability to conduct these processes in gentler and more environmentally friendly conditions. Organocatalysts are also characterized by increased stability against air and moisture and lower toxicity, enhancing their overall manageability.

That means utilizing this technology to transform plastic waste into chemicals is both energy-efficient and emits fewer greenhouse gases than conventional petroleum-based methods.

This represents a significant stride towards realizing a net-zero society by enabling efficient and low-carbon plastic recycling, promoting the development of a closed-loop circular plastic economy, as emphasized by the study's corresponding author, Saito.

ORNL's Organocatalyst Explained

ORNL's organocatalyst consists of two components: trifluoracetic acid (TFA) and triazabicyclododecane (TBD). This catalyst employs a dual-activation mechanism, with ethylene glycol serving as a nucleophile in the deconstruction of condensation polymers. The TFA component contributes to high conjugate basicity, enhancing the nucleophile's reactivity in breaking down the polymer.

Meanwhile, the protonated TBD component (TBDH+) coordinates with a carbonyl group in the polymer chain, increasing reactivity and weakening the bonds that need to be broken. This means that the organocatalyst can sequentially break down various polymer mixtures, utilizing a gradual increase in reaction temperature to facilitate the separation of resulting monomers.

The research team effectively applied their organocatalyst to mixed consumer plastics, swiftly converting all condensation polymers into monomers. Notably, this process left other plastics like polyolefin and cellulose untouched, simplifying their separation.

In a comprehensive life cycle assessment, the recycling approach showed substantial environmental advantages. Crafting polymers such as polyethylene terephthalate, polycarbonate, polyurethane, and polyamide from these deconstructed monomers resulted in significantly reduced greenhouse gas emissions (up to 95% less) and a markedly lower energy requirement (up to 94% less) compared to conventional production methods. This eco-friendly methodology represents a promising solution for addressing plastic waste challenges.

As similar solvolysis chemical recycling processes are already in use by various companies, the team aims to scale up their process. However, it is essential to consider additional factors when scaling up, incorporating them into life cycle and economic analysis models to ensure that the process is not only financially viable but also more environmentally friendly than alternatives in a linear plastic economy.