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Researchers at NTU achieve chemical break through by recycling polyolefins at room temperature

by | Sep 20, 2023

Researchers at the Nanyang Technological University in Singapore have discovered a process which can break down polyolefins, through using chemicals and light emitting diodes (LEDs).

The process involves plastics such as HDPE, LDPE, PVC, PP, PS PVA, EVA being broken down into formic acid and benzoic acid which can then make other chemicals that are used to make fuel cells and liquid organic hydrogen carriers (LOCHs).

The system designed by the researchers at NTU begins with dissolving the plastic within dichloromethane, an organic solvent. Dissolving the plastic causes the polymer chains to spread out, granting the photocatalyst easier access to them. The next step is to combine the solution with the catalyst and then send it through multiple transparent tubes. Whilst in these tubes LED lights will shine on the solution and this combined with the catalyst generates enough energy to break the carbon-to-carbon bonds throughout a two-step process known as tandem carbon–hydrogen bond oxidation or carbon–carbon bond cleavage reaction. This process works through the carbon-hydrogen bonds in the plastics being oxidised, resulting in the bonds becoming less stable and more reactive, consequently the carbon-carbon bonds are broken down.

This whole system works whilst remaining at room temperature and it is not restricted to being a system which only polystyrene, which is what makes it stand apart as a breakthrough from similar systems which have been designed in the past. Whilst other petrochemical technologies are able to chemically recycle plastic at a temperature close to room temperature, this new system will also work on polypropylene polyethylene, polyvinyl chloride, and polyvinyl acetate.

The results from the tests performed by the researchers show that the system has a carbon recovery rate of 77% and there is also a selective formation of valuable, isolable acids that can be used to produce LOHCs. This product is extremely useful as LOHCs are able to store and transport hydrogen gas more safely, meaning they are needed in the clean energy transportation fuel sector. Other products from the process include PVC, HDPE, and LDPE producing formic acid as the main product, with formic and acetic acids being the main product from PP, PVA, and EVA.

Overall, the results show that because the reaction does not require high temperatures, this system is the first step towards recycling plastic waste in the form of polyolefins at room temperature through using chemicals. This is possible because solar-power or LEDs which use renewable electricity can be used to break the carbon bonds. The other benefit of using this method is it avoids producing large amounts of greenhouse gas emissions and it has very low energy costs, making it a realistic approach for a plastic waste free world.

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