Can waste plastic become a useful fuel source in the future?

Worldwide, more than 400 million tonnes of plastic is produced every year – roughly the same weight as all of humanity. Today, around 85% ends up in landfill or is lost to the environment where it will stay for hundreds, perhaps thousands, of years.

Now the race is on to find the best way to break those chemical bonds and reclaim the Earth’s precious resources locked into plastic.

Mechanical recycling, where waste plastic is washed, shredded, melted and reformed, degrades plastic over time and can result in inconsistent quality products.

The plastics industry is keen on chemical recycling, where additives are used to alter the chemical structure of waste plastic, turning it back into substances that can be used as raw materials, perhaps for making fuel like petrol and diesel.

But that approach is currently costly and inefficient and has been criticised by environmental groups.

Prof Reisner and his team have developed a process that can convert not one, but two waste streams – plastic and CO2 – into two chemical products at the same time – all powered by sunlight.

The technology transforms CO2 and plastic into syngas – the key component of sustainable fuels such as hydrogen. It also produces glycolic acid, which is widely used in the cosmetics industry.

The system works by integrating catalysts, chemical compounds which accelerate a chemical reaction, into a light absorber.

Other solar-powered technologies hold promise for tackling plastic pollution and CO2 conversion, but this is the first time they have been combined in a single process.

In addition, Prof Reiner says his system can handle otherwise unrecyclable plastic waste.

Researchers around the world are looking for ways to turn unwanted plastic into something useful.

When broken down, the elements of plastic can be re-made into a myriad of new products including detergents, lubricants, paints and solvents, and biodegradable compounds for use in biomedical applications.

Nature has found ways of breaking down polymers – substances made up of very large molecules – and plastic is a synthetic polymer.

Victoria Bemmer from the University of Portsmouth is developing enzymes that can break down plastic.

Using machine learning, Dr Bemmer and her team have developed variants of enzymes adapted to deconstruct all varieties of polyethylene terephthalate (PET), a type of polyester.

Where chemical recycling uses chemicals, the Portsmouth University team are able to use water. And the highest temperature they need is 70C, meaning energy consumption can be kept low compared to other processes.

Dr Bemmer and her team are developing their enzymes further and hope that their work will help them create a sustainable circular economy for plastic-based clothing too.

Polyester made from PET is the most widely used clothing fibre in the world.

However, recycling synthetic fabrics using enzymes is not easy. The addition of dyes and other chemical treatments make it difficult for them to be degraded in a natural process.

The team hopes their enzymes will reduce the PET in waste textiles to a soup of simple building blocks, ready to be made back into new polyesters.

Worldwide production of plastic continues to increase and is expected to triple by 2060. For many, recycling remains the focus in addressing the issue, but some argue this will never be enough.

Back in Cambridge, Prof Reisner’s team is taking “baby steps in the direction” of commercialisation. They plan to develop the system over the next five years to produce more complex products and hope that one day the technique could be used to develop an entirely solar-powered recycling plant.

Around 600 million tonnes of syngas is already produced every year, says Prof Reisner, but it’s largely from fossil fuels.

Tags: Fossil Fuels, Plastic Waste, Sunlight, Syngas