Recycling of plastics to close the carbon cycle

24 Feb. () –

A new method presented in ‘science’ to convert plastic waste into fuel and raw materials promises to help close the carbon loop at low temperature and high performance.

Used masks, shopping bags and food wrappers contain many potentially useful raw materialsbut it has turned out to be much cheaper to continue making more of these single-use plastics than to recover and recycle them.

Now an international research team led by the PNNL (Pacific Northwest National Laboratory) has cracked the code that blocked previous attempts to break down these persistent plastics.

Normally, to recycle plastics you have to “break” the strong and stable bonds that make them so persistent in the environment. This process requires high temperatures, which is why it is expensive and consumes a lot of energy.

The novelty consists in combining cracking with a second reaction phase that immediately completes the conversion into a gasoline-like liquid fuel with no unwanted by-products.

The second reaction phase uses what are known as alkylation catalysts. These catalysts provide a chemical reaction currently used by the oil industry to improve the octane number of gasoline.

In the current study, the alkylation reaction occurs immediately after the cracking step in a single reaction vessel, at room temperature (70 ºC).

“Cracking just to break links results in links forming uncontrollably, and that’s a problem in other approaches,” he explains. it’s a statement Oliver Y. Gutiérrez, study author and PNNL chemist–. The secret formula here is that when one link is broken in our system, another one is immediately formed in a directed way, giving us the final product we want. That is also the secret that enables this low-temperature conversion,” he adds.

In their study, the team of researchers, co-led by scientists from the Technical University of Munich (Germany), pointed to other recent advances in the oil industry to commercialize the second part of the process described here for the treatment of crude oil.

Johannes Lercher, lead author of the study, director of the Institute for Integrated Catalysis at PNNL and Professor of Chemistry at the Technical University of Munich, notes that “the fact that industry has successfully used these emerging alkylation catalysts demonstrates its stable and robust nature.”

As he points out, “this study points to a new practical solution to close the carbon cycle of plastic waste that is closer to being implemented than many others that are being proposed.”

In their study, the researchers point out a limitation in their results. The process works with low-density polyethylene (LDPE, plastic resin code no. 4) products, such as plastic films and squeezable bottles, and with polypropylene (PP, plastic resin code no. 5) products that are not typically picked up in bins. curbside recycling programs in the United States. High-density polyethylene (HPDE, plastic resin code no. 2) would require pre-treatment to allow the catalyst access to the bonds it needs to break.

Petroleum-derived plastic waste is an untapped resource that can serve as a feedstock for useful durable materials and fuels. More than half of the 360 ​​million tons of plastics that are produced each year in the world are the plastics that are the subject of this study.

But looking at a mountain of plastic and seeing its value requires the mindset of an innovator, the ingenuity of a chemist, and a realistic understanding of economics. These scientists try to change the dynamics by applying their knowledge to effectively break chemical bonds.

“To solve the problem of persistent plastic waste, we have to get to a critical point where it makes more sense to collect it and reuse it than to treat it as disposable,” Lercher says. “We’ve shown here that we can do that conversion quickly, in mild conditions, which is one of the incentives to move towards that tipping point.”