Converting Plastic to Hydrogen Fuel

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Plastic waste is a massive problem, there is no doubt about that, but ever since Blue Planet 2 aired on the BBC last year, attention has been firmly focused on what can be done to reduce the volume of single-use items and other plastic waste that is slowly amassing across the planet.

Fundamental Uses and Disadvantages of Plastics

Despite receiving much criticism, it would be difficult to live in a completely plastic-free world. Plastics have many beneficial properties and are easy to mass-produce; they are used in single-use drinks bottles, food storage containers, children’s toys and millions of other everyday items we take for granted. However, they are also a massive problem: knowing how to manage, dispose of and recycle them is becoming progressively more challenging.

Furthermore, they have a hugely negative effect on the environment. It is predicted that more than 300 million tonnes of plastic are produced globally every year, with a mere 10% of that being recycled - the rest makes its way into landfill, or is found on the streets or in the ocean. It’s clear that recycling isn’t enough, we need to think of novel ways to reduce our plastic consumption, and where possible reuse and recycle it.

Converting Plastics into Useful Fuel

A team of scientists from Swansea University and the University of Cambridge have been thinking outside the box and have developed a means of converting plastic to hydrogen fuel that could be employed to power cars in the future.

A lot of energy goes into making plastic, and when this plastic is discarded, the energy is lost. The researchers’ simple, low-energy sunlight driven process – which operates under ambient temperature and pressure - could recover some of this missing energy. The method – known as photoreforming – uses semiconductor nanoparticles in the form of cadmium sulfide quantum dots as a photocatalyst to degrade the plastic.

Method

Firstly, the plastic is cut into small pieces and its surface scrubbed to roughen it up. Quantum dots are added to the plastic which is then immersed in an alkaline solution. Irradiation with sunlight - or a solar simulator lamp which mimics sunlight – is used to drive two simultaneous chemical reactions. The first sees hydrogen produced from the water in the alkaline solution while in the second, plastic polymers are oxidized to small organic molecules which can be recycled.

The process produces hydrogen gas. You can see bubbles coming off the surface. You can use it, for example, to fuel a hydrogen car.

Moritz Kuehnel, Department of Chemistry, Swansea University

Results

The method has so far been tested on three common polymers – polylactic acid, polyethylene terphthalate and polyurethane – and results have been comparable to those achieved with state-of-the-art hydrogen evolution photocatalyst systems employing expensive sacrificial agents. The team have demonstrated proof-of-concept by converting a PET bottle into hydrogen in a first-of-its-kind, visible light-driven, noble-metal free photoreforming process.

Photoreforming in this way represents a cheaper alternative to recycling as the plastic doesn’t have to be pure and clean – in other words not contaminated with food or oils, which can in fact, improve the reaction. “The beauty of this process is that it’s not very picky. It can degrade all sorts of waste,” Kuehnel told the BBC. "Even if there is food or a bit of grease from a margarine tub, it doesn't stop the reaction, it makes it better.”

Conclusion

The process now needs to be scaled up to an industrial level – which make take several years – but it’s clear that the process has a great environmental and economic value in the real world. It has substantial potential in converting massive amounts of plastic waste which might otherwise end up in landfill into valuable chemicals and fuel.

References and Further Reading

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