New solar reactor creates clean hydrogen from plastic waste and car battery acid
Developed by researchers at the University of Cambridge, a new solar-powered reactor could revolutionise plastic waste recycling, in a process that uses old car battery acid to convert discarded materials into clean hydrogen
Two waste streams could be used to create clean hydrogen and industrial chemicals, helping resolve the question of the millions of tons of plastic produced globally each year.
Researchers at the University of Cambridge have developed a method of solar-powered acid photoreforming, utilising battery acid taken from old car batteries to break down plastic waste that has traditionally been harder to recycle, such as nylon textiles, polyurethane foams and polyethylene terephthalate (PET) plastic bottles.
As reported in Joule, the team first applied the car battery acid to the plastic waste, breaking down the long polymer chains. This created ethylene glycol, which is then converted by the photocatalyst into acetic acid and hydrogen when exposed to sunlight.
The acid-stable photocatalyst was key
“The discovery was almost accidental,” said Professor Erwin Reisner from Cambridge’s Yusuf Hamied Department of Chemistry, who led the research. “We used to think acid was completely off limits in these solar-powered systems, because it would simply dissolve everything. But our catalyst developers didn’t—and suddenly a whole new world of reactions opened up.”
“Acids have long been used to break plastics apart, but we never had a cheap and scalable photocatalyst that could withstand them,” said lead author Kay Kwarteng, a Ph.D. candidate in Reisner’s research group, who developed the photocatalyst. “Once we solved that problem, the advantages of this type of system became obvious.”
The reactor was ran for a continuous 260 hours without any loss in performance and was effective across multiple forms of plastic waste, of which current methodologies are limited.
The process was tested with laboratory-grade acid, as well as the recovered car battery acid. This presents a useful route of recycling car batteries, where the lead components are extracted and repurposed, but the neutralised acid is extra waste.
The acid used in the study’s solar-powered acid photoreforming can also be reused rather than being consumed or wasted.
“It’s an untapped resource,” said Kwarteng. “If we can collect the acid before it’s neutralised, we can use it again and again to break down plastics: it’s a real win-win, avoiding the environmental cost of neutralising the acid, while putting it to work generating clean hydrogen.”
Around 91% of globally produced plastics are not recycled
Global plastic production estimates range between 400 million and 460 million tons, and is expected to triple by 2060.
Only 9% of this plastic is recycled, with the rest incinerated, left in landfill or mismanaged. All of these options negatively impact the environment, with 140 million tons of plastic waste in rivers and oceans.
Establishing a more cost effective circular economy
This process could open up new routes for plastics traditionally considered too difficult or expensive to recycle, with high clean hydrogen yield and reusable battery acid making efforts more cost effective.
“These acids are already handled safely in industry,” Kwarteng continued. “The question now is engineering: how do we build reactors that can run continuously and handle real-world waste?”
“We’re not promising to fix the global plastics problem,” said Reisner. “But this shows how waste can become a resource. The fact we can create value from plastic waste using sunlight and discarded battery acid makes this a really promising process.”