Could plastic waste become a useful fuel source?

Those bales of plastic go for recycling – but most of the plastic gets discarded

Plastic waste dumps, says Prof. Erwin Reisner, could be the oil fields of the future.

“Plastic is practically a different form of fossil fuel,” says Prof. Reisner, Professor of Energy and Sustainability at the University of Cambridge. “It’s rich in energy and chemistry that we want to tap into.”

But the chemical bonds that make up plastics are built to last, and of the seven billion tons ever made, less than 10% has been recycled.

Dilyana Mihaylova, Plastics Program Manager at the Ellen MacArthur Foundation, says: “Our extractive, take-make-waste economy [means] Valuable materials worth billions of dollars are lost.”

More than 400 million tons of plastic are produced worldwide every year – roughly as much as all of humanity. Today, around 85% ends up in landfills or is lost to the environment, where it will remain for hundreds, perhaps thousands, of years.

The challenge now is to find the best way to break these chemical bonds and reclaim the planet’s precious resources locked in plastic.

Mechanical recycling, which involves washing, shredding, melting and reshaping plastic waste, degrades plastics over time and can result in inconsistent quality products.

The plastics industry relies heavily on chemical recycling, which uses additives to change the chemical structure of plastic waste and turn it back into substances that can be used as raw materials, perhaps to make fuels like gasoline and diesel.

But this approach is currently costly and inefficient, and has been criticized by environmental groups.

“So,” says Ms. Mihaylova, “just as we can’t move out of the plastic pollution crisis through recycling, neither can we rely on plastic-to-fuel processes to solve the problem.”

Could a new solar-powered system point the way to the future?

Erwin Reisner (left), Subhajit Bhattacharjee (middle) and Motiar Rahaman (right)

Erwin Reisner (left) and his team Subhajit Bhattacharjee (middle) and Motiar Rahaman (right)

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 converts 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 that speed up a chemical reaction, into a light absorber.

“Our process works at room temperature and room pressure,” he says.

“Reactions are automatic when you expose it to sunlight. That’s all you need.”

And, Prof. Reisner assures, the process produces no harmful waste.

“The chemistry is right,” he says.

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

“By combining both, we increase the value of the process,” says Prof. Reisner. “We now have four value streams – plastic waste mitigation, carbon mitigation and the production of two valuable chemicals. We hope this brings us closer to commercialization.”

In addition, Prof. Reiner says his system can process otherwise non-recyclable plastic waste.

“Usually, plastic contaminated with food waste is burned, but this plastic is really good for us. In fact, food is a good substrate – so our process works better.”

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

Once degraded, the plastic elements can be made into a myriad of new products, including cleaning products, lubricants, paints and solvents, as well as biodegradable compounds for use in biomedical applications.

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

Victoria Bemmer

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

“There are already bacteria out there that have enzymes that are designed to break down [polymers] down,” says Dr. Victoria Bemmer, Senior Research Fellow at the University of Portsmouth.

“We can optimize these enzymes by changing their structure very slightly – to make them run faster, make them stronger or more stable.”

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

The enzymes break down the plastic in a similar way to chemical recycling, says Dr. Bemmer, but since they are similar to the enzymes found in nature, the process can be carried out under much “better conditions”.

Where chemical recycling uses chemicals, the Portsmouth University team can use water. And the highest required temperature is 70 °C, so the energy consumption can be kept low compared to other processes.

dr Bemmer and her team are continuing to develop their enzymes and hope their work will help them create a sustainable, circular economy for plastic-based clothing as well.

Polyester made from PET is the world’s most commonly used clothing fiber.

However, recycling synthetic fabrics using enzymes is not easy. The addition of dyes and other chemical treatments make it more difficult to break down in a natural process.

“Polyester is an absolute pain,” says Dr. notice “Furthermore, it is very rarely just pure polyester. You can also find mixed fibers.”

More technology of business:

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

“We are at a very early stage,” says Dr. notice “We don’t yet know whether the dyes and additives in these fabrics inhibit the action of the enzymes on the polyester chain. Hopefully they don’t have an impact and we can just move on, but if they do then we can keep evolving our enzymes.”

Global plastic production continues to increase and is expected to triple by 2060. For many, recycling remains the focus of solving the problem, but some argue it will never be enough.

Back in Cambridge, Prof. Reisner’s team is taking “small steps towards” commercialization. They plan to refine the system over the next five years to make more complex products and hope that one day the technology can be used to develop an all-solar recycling plant.

Around 600 million tons of synthesis gas are already being produced every year, says Prof. Reisner, but mostly from fossil fuels.

“If we can make syngas, we can access almost the entire petrochemical industry and make it sustainable.”

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