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Converting Plastic Waste Into Useful Chemicals With Sunlight

Converting Plastic Waste Into Useful Chemicals With Sunlight

In the bid of protecting the world from further harm and damage, constant efforts are made for finding environmentally friendly alternatives. Scientists from the Nanyang Technological University (NTU) have done just that.

They have a found way to convert plastic waste into chemicals of use, with the help of sunlight.

This is the first established process that can fully break down non-biodegradable plastic, such as polyethylene, with visible light and a catalyst that does not contain heavy metals.

This research was led by Assistant Professor Soo Han Sen from NTU who overlooked the research team from the School of Physical and Mathematical Sciences. The team had formed a catalyst that used sunlight to break down the chemical bonds in plastics within a matter of days.

This is an environmentally friendly method of using photochemical reactions to achieve this. Prof Soo said that most other recycling methods involve the use of incineration which generates greenhouse gases as a by-product.

The team’s method involves a catalysed reaction which can break down non-biodegradable consumer plastics, such as polyethylene, within six days. It converts the plastic into formic acid which exists as a naturally occurring preservative and antibacterial agent which can be used for energy generation by power plants and hydrogen fuel cell vehicles.

The process is such that plastic is dissolved in acetonitrile, an organic solvent, where the mixture is heated to 85 deg C. Following that, the catalyst is added, and the mixture is exposed to artificial sunlight at room temperature.

Prof Soo said that the catalyst has a 100 per cent conversion rate, with all plastic processed is converted into formic acid. Carbon dioxide gas is a by-product of this process.

According to the National Environment Agency (NEA), out of the 949,300 tonnes of plastic waste that was produced in 2018, only 40,700 tonnes were recycled. This figure makes up just 4% of the waste produced.

Most of such plastic waste is burned and thus producing greenhouse gases such as carbon dioxide. The remaining mass-burn ash is deposited at Semakau Landfill. It is estimated that the land space will be fully occupied by 2035.

This projection has pushed Singapore to find zero-waste solutions. NTU Smart Campus has its eyes on formulating a way for converting plastic waste into useful chemicals such as polyethylene, polypropylene and polystyrene. These chemicals make up 80 per cent to 90 per cent of the plastics in the world.

The method formulated by Prof Soo and his team is one of the two known processes that make use of sunlight to convert plastic waste into useful chemicals.

The other method is photoreforming, a method developed by scientists from the University of Cambridge, in 2018. Photoreforming method is used for converting plastic to Hydrogen gas. This method fuses plastic together with water and sunlight to produce hydrogen gas. The gas in return can be used for energy generation using hydrogen fuel cells. The setback with this method is that the catalyst used contains cadmium which is a toxic heavy metal.

The method devised by Prof Soo and his team used vanadium in its catalyst. Vanadium, in contrast, is less toxic and is about 1,000 times more abundant than cadmium. It is more affordable too. It serves as a more environmentally friendly option.

NTU’s research team will work with the Agency for Science, Technology and Research’s Institute of Chemical and Engineering Sciences (Ices) and Institute of Materials Research and Engineering to create a continuous flow system for the process.

This method produces minimal carbon dioxide gas and more hydrogen gas hence making it a carbon-neutral process.

Prof Soo added that there still are improvements that can be made to the catalyst. At the moment, a lot of energy is required to recover the powdered form catalyst, after the completed chemical reaction.

The team is looking into ways of creating a solid catalyst that will not dissolve during the process, allowing it to be more easily reused.

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