Microwaving plastic waste can generate clean hydrogen

 Chemists have used microwaves to convert plastic bags, milk bottles, and other supermarket packaging into a clean source of hydrogen.

Plastic waste can already be converted to hydrogen using other methods, and commercial facilities are being developed to rework the plastic. However, a brand new approach holds the promise of being quicker and fewer energy-intensive.

Peter Edwards at the University of Oxford says he and his colleagues wanted to “confront the grim reality” of plastic waste, with the united kingdom alone producing 1.5 million tonnes every year. because the density of hydrogen in plastic bags is about 14 percent by weight, plastic offers a possible new source for countries eyeing cleanly produced hydrogen to tackle temperature change.

Most existing approaches involve first using very high temperatures of quite 750°C to decompose plastic into syngas, a mix of hydrogen and carbon monoxide gas, then employing a second step to filter the hydrogen.

Edwards and his team instead broke the plastic into small pieces with a kitchen blender and mixed it with a catalyst of iron oxide and alumina. When blasted with a microwave generator at 1000 watts, the catalyst created hot spots within the plastic and stripped out the hydrogen – recovering 97 percent of the gas within the plastic within seconds.

The solid material left over was almost exclusively carbon nanotubes. The single-step approach has the advantage of just heating the catalyst, not all of the plastic, leading to less energy use, because the plastic doesn't absorb microwaves.

The results hold out “an attractive potential solution for plastic waste”, says Edwards. Although only done at a little scale, using about 300 grams of plastic for every test, larger experiments are already being planned.