Muhammad Rabnawaz, an associate professor in Michigan State University’s top-ranked School of Packaging and recent inductee into the National Academy of Inventors, has always believed that the most brilliant solution is also the simplest.
That belief is reflected in his team’s new publication in the journal Advanced Sustainable Systems.
Rabnawaz and his colleagues showed that sodium chloride — table salt — can outperform much more expensive materials being explored to help recycle plastics.
“This is really exciting,” Rabnawaz said. “We need simple, low-cost solutions to take on a big problem like plastics recycling.”
Although plastics have historically been marketed as recyclable, the reality is that nearly 90% of plastic waste in the United States ends up in landfills, in incinerators or as pollution in the environment.
One of the reasons plastics have become so disposable is that the materials recovered from recycling aren’t valuable enough to spend the money and resources required to get them.
According to the team’s projections, table salt could flip the economics and drastically reduce costs when it comes to a recycling process known as pyrolysis, which works through a combination of heat and chemistry.
Although Rabnawaz expected salt to have an impact because of how well it conducts heat, he was still surprised by how well it worked. It outperformed expensive catalysts — chemicals designed to spur reactions along — and he believes his team has just started tapping into its potential.
Furthermore, the work is already getting attention from big names in industry, he said.
In fact, the research was partially supported by Conagra Brands, a consumer packaged goods company.
A catalyst worth its salt
Pyrolysis is a process that breaks down the plastics into a mixture of simpler, carbon-based compounds, which come out in three forms: gas, liquid oil and solid wax.
That wax component is often undesirable, Rabnawaz said, yet it can account for more than half of products, by weight, of current pyrolysis methods. That’s even when using catalysts, which are helpful, but they often can be toxic or prohibitively expensive to be applied in managing waste plastics.
Platinum, for example, has very attractive catalytic properties, which is why it’s used in catalytic converters to reduce harmful emissions from cars. But it’s also very pricey, which is why thieves steal catalytic converters.
Although bandits are unlikely to rob platinum-based materials from a sweltering pyrolysis reactor, attempting to recycle plastics with those catalysts would still require a hefty investment — millions, if not hundreds of millions, of dollars, Rabnawaz said. And current catalysts aren’t efficient enough to justify that cost.
“No company in the world has that kind of cash to burn,” Rabnawaz said.