Turning waste into raw material: how sunlight turns plastic into acetic acid
Researchers use sunlight to turn plastic into acetic acid. The process runs at room temperature, requires only water - and could even break down microplastics in bodies of water.
Plastic waste is one of the most persistent environmental problems of our time. Every year, millions of tonnes of plastic end up in soils, rivers and oceans, some of which breaks down into microplastics and now reappears in drinking water and food. A team from the University of Waterloo in Ontario, Canada, has now developed a process that does not simply break down this waste, but transforms it into an industrially valuable substance: Acetic acid.
The basic idea sounds amazingly simple. Sunlight hits a special catalyst, which then triggers chemical reactions that break down plastic chains and convert them into acetic acid. No high-pressure furnace, no combustion, no fossil energy. The reaction takes place at room temperature and under normal pressure. Light is used as the energy source - both artificial and real sunlight in the experiment.
A catalyst modelled on mushrooms
The centrepiece of the system is an unusual iron catalyst. The team developed a bio-inspired cascade photocatalysis with iron atoms embedded in carbon nitride. This works in a similar way to how certain types of fungi break down organic substances with the help of enzymes. This cascade principle means that several reaction steps take place directly one after the other in the same system. The reactor immediately processes intermediate products further and does not remove them.
When sunlight hits the system, highly reactive hydroxyl radicals are initially produced. These attack the long plastic chains and break them down into smaller components. This produces CO₂ intermediates, among other things. In the next step, the same catalyst utilises these intermediates and converts them further. The end result is acetic acid.
Tested with the most common everyday plastics
The process works with a whole range of materials that you encounter in everyday life. The team successfully tested the process with polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP) and polyvinyl chloride (PVC). The yield varied and was best with PVC.
Of particular note: it also works with mixed plastic streams. In practice, waste is rarely mixed. This significantly increases the chances of later use.
Acetic acid: far more than just kitchen vinegar
The end product sounds unspectacular at first, but is actually a sought-after industrial raw material. The food industry uses acetic acid as a preservative, it is a raw material for plastics and solvents and also plays a role in energy systems. Worldwide, the annual production volume is several million tonnes.
To date, the industry has produced acetic acid almost exclusively from fossil raw materials. The process from Waterloo would reverse this cycle: A valuable raw material is created from plastic waste and sunlight without emitting additional CO₂ in the process.
Directly combating microplastics in water
The reaction takes place in the water, which could be a particularly efficient way of combating plastic pollution in bodies of water. Instead of just filtering out microplastics mechanically - which is time-consuming and incomplete - this approach would break down the particles chemically at a molecular level.
Source: University of Waterloo
The stability of the catalyst was also tested. According to the study, the iron atoms remained firmly anchored in the material and did not come loose.
Still a laboratory, but with a clear perspective
Before you imagine a rooftop solar-powered plastic-to-vinegar reactor, the team is still at the laboratory stage, but can imagine that this approach could be adapted for scalable, solar-powered recycling and environmental remediation. The researchers have already shown that targeted improvements to the reactor design and materials can significantly increase the yield.
The process does not yet solve the plastic problem on a global scale - this will require further development, investment and political will. What it does show is that plastic waste does not have to be a dead end. With the right catalyst and light from the sun, it can become a source material for something useful.
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