Sorting plastic waste remains a major obstacle to recycling. A team from UCLA and Ewha Womans University now proposes to transform several mixed plastics directly into hydrogen, without separating them beforehand.
The process involves three very common materials: PET from bottles, polyethylene, and polypropylene. These plastics have different chemical properties, which usually complicates their treatment in the same reactor.
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The researchers used an alkaline thermal treatment, called ATT. The method relies on a reaction between plastic waste, heat, and sodium hydroxide, to release the hydrogen contained in the molecules.
Polyethylene and polypropylene, however, are more resistant to this reaction. The team therefore briefly exposes them to moderate heat in the presence of air, which makes their chemical chains more reactive.
In the lab, the system produced hydrogen with a purity exceeding 90%. It operated at temperatures 300 to 400 degrees Celsius lower than those of conventional gasification.
The process also aims to avoid direct carbon dioxide emissions. The released carbon is captured by sodium hydroxide, then converted into solid sodium carbonate.
Analyses indicate that more than 75% of the initial carbon ends up as stable carbonate or liquid organic residues. The portion released as gas remained below 13%.
This technology still needs to be optimized before any industrial use. In particular, the researchers will have to evaluate its profitability, energy consumption, and the recovery of reactants.